Microwave-assisted Synthesis of Coordination and Organometallic Compounds

oxidation of 2,2'-dipyridyldisulfide to sulfate was found to take place, resulting a Cu(I) dimetallic complex [Cu 2 ( μ -Hpyt) 2 (Hpyt) 4 ](SO 4 ) . (Hpyt pyridine-2(1H)-thione), a Cu(I,II) polycationic coordination polymer [Cu(H dimetallic Cu(II) complex [Cu(2-dps)(

derivatives have been used as precursors for obtaining their metal complexes, are shown in Table 1.

Physical principles of microwave irradiation and laboratory equipment
Microwave heating is a physical process where the energy is transferred to the material through electromagnetic waves. Frequencies of microwaves are higher of 500 MHz. It is known that a non-conductive substance can be heated by an electric field, which polarizes its charges without rapid reversion of the electric field. For some given frequencies, the current component, resulting in the phase with electric field, produces a dissipation of the potency within the dielectric material. Due to this effect, a dielectric can be heated through the redistribution of charges under the influence of external electric fields. The potency dissipated within the material depends on the established electric field within the material. This potency is diminished as the electromagnetic field penetrates to the dielectric. The most common microwave application is that of multimode type which accepts broad range thermal charges with problems of microwave uniformity. The application of multimode type is given in a closed metallic box with dimensions of various wave lengths and which supports a large number of resonance modes in a given range of frequencies. A resonance cavity or heater consists on a metallic compartment that contains a microwave signal with polarization of the electromagnetic field; it has many reflections in preferential directions. The superposition of the incident and reflected waves gives place to a combination of stationary waves. If the configuration of the electric field is precisely known, the material to be treated can be put to a position of electric field maximum for an optimal transference of electromagnetic energy. Typical microwave equipment consists of a magnetron tube ( Fig. 1) (Roussy & Pearce, 1995). Just as other vacuum tubes, the anode has a higher potential with respect to the cathode (source of electrons). So, the electrons are accelerated to the anode in the electric field. The cathode is heated till the high temperature expulse electrons. Generally, the anode is close to earth potential and the cathode has a high negative potential. The difference between the magnetron and other vacuum tubes is that the electron flow passes along a spiral; this route is created by external magnetic field B (Fig. 1). The electron cloud produces resonance cavities several times in its trip to the anode. These cavities work as Helmholtz resonators and produce oscillations of fixed frequency, which is determined by the cavity dimensions: small cavities produce higher frequencies, large cavities give smaller frequencies. The antenna in the right zone collects the oscillations. Reactor for batchwise organic synthesis (with permission): 1, reaction vessel; 2, top flange; 3, cold finger; 4, pressure meter; 5, magnetron; 6, forward/reverse power meters; 7, magnetron power supply; 8, magnetic stirrer; 9, computer; 10, optic fiber thermometer; 11, load matching device; 12, waveguide; 13, multimodal cavity (applicator).
The use of a microwave reactor for batchwise organic synthesis (Raner et al, 1995), described in Fig. 2), permits to carry out synthetic works or kinetic studies on the 20-100 mL scale, with upper operating limits of 260ºC and 10 MPa (100 atm). Microwave-assisted organic reactions can be conducted safely and conveniently, for lengthy periods when required, and in volatile organic solvents. The use of water as a solvent is also explored. A typical reactor used for organic and/or organometallic syntheses (Matsumura- Inoue et al, 1994) is presented in Fig. 3, which can be easily implemented using a domestic microwave  oven. Due to some problems occurring during microwave treatment, for example, related with the use of volatile liquids (they need of an external cooling system via copper ports), original solutions to these problems are frequently found in the reported literature. More modern laboratory MW-reactors (Wiesbrock et al, 2004) are shown in Fig. 4. A combination of different techniques can frequently improve yields of final compounds or synthetic conditions. Reunion of microwave and ultrasonic treatment was an aim to construct an original microwave-ultrasound reactor (Chemat et al, 1996) suitable for organic synthesis (pyrolysis and esterification) (Fig. 5). The ultrasound (US) system is a cup horn type; the emission of ultrasound waves is made at the bottom of the reactor. The US probe is not in direct contact with the reactive mixture. It is placed a distance from the electromagnetic field in order to avoid interactions and short circuits. The propagation of the US waves into the reactor is made by means of decalin introduced into the double jacket. This liquid was chosen because of its low viscosity that induces good propagation of US and its inertia towards MW. Some years ago, an alternative method for performing microwave-assisted organic reactions, termed "Enhanced Microwave Synthesis" (EMS), has been examined in an excellent review (Hayes, 2004). By externally cooling the reaction vessel with compressed air, while simultaneously administering microwave irradiation, more energy can be directly applied to the reaction mixture. In "Conventional Microwave Synthesis" (CMS), the initial microwave power is high, increasing the bulk temperature (TB) to the desired set point very quickly. However, upon reaching this temperature, the microwave power decreases or shuts off completely in order to maintain the desired bulk temperature without exceeding it. When microwave irradiation is off, classical thermal chemistry takes over, losing the full advantage of microwave-accelerated synthesis. With CMS, microwave irradiation is predominantly used to reach TB faster. Microwave enhancement of chemical reactions will only take place during application of microwave energy. This source of energy will directly activate the molecules in a chemical reaction. EMS ensures that a high, constant level of microwave energy is applied.
good thermal stability (Nakashima et al, 2008). This complex was expected to be used in functional materials for electronic products. Zirconium acetylacetonate, Zr(acac) 4 , was prepared from its hydrate Zr(acac) 4 . 10H 2 O by microwave dehydration of the latter (Berdonosov et al, 1992). Additionally, a convenient method for 68 Ga-labeling under anhydrous conditions using solid-phase derived gallium-68-acetylacetonate {[ 68 Ga]Ga(acac) 3 } in a microwave-enhanced radiosynthesis was offered (Zoller et al, 2010). 68 Ga was absorbed quantitatively in a cation exchange resin; more than 95% of the generator-eluted 68 Ga was obtained from the cation exchange resin with a 98% acetone/2% acetylacetone mixture providing [ 68 Ga]Ga(acac) 3 as labeling agent for further use in labeling porphyrin derivatives ( 68 Ga-labeled porphyrins may facilitate the medical application for molecular imaging via positron emission tomography). MW-decomposition of metal acetylacetonates is represented much more frequently. Thus, silicalite (Si-MFI) zeolite crystals with incorporated tetravalent metal ions were used to MWsynthesize metallosilicalite (M-MFI; M = Sn, Zr, Sn/Zr, Ti/Zr) zeolites crystals (Hwang et al, 2006). Acetylacetonates were applied as chelating ligands of the metal precursors, to reduce their hydrolysis rates and, therefore, to enhance framework incorporation of each metal in the syntheses of M-MFI zeolites. The resulting zeolite crystals formed showed puck-like morphology and were stacked to form fibers with the degree of self-assembly varied depending on the nature of the tetravalent metal ion used. Chromium-substituted βdiketonate complexes of aluminum were synthesized and employed as precursors for a "soft chemical" process, wherein MWH of a solution of the complex yielded, within minutes, well-crystallized needles of α-(Al 1-x Cr x ) 2 O 3 measuring 20-30 nm in diameter and 50 nm long (Gairola et al, 2009). By varying the microwave irradiation parameters and using a surfactant such as polyvinyl pyrrolidone, the crystallite size and shape can be controlled and their agglomeration prevented. Mg-Al hydrotalcite-like compounds {HT, Mg 6 Al 2 (CO 3 )(OH) 16 •4(H 2 O)} were prepared by the microwave method with ethoxideacetylacetonate or acetylacetonate as precursors . Hydrotalcites prepared with ethoxide-acetylacetonate were found to be better sorbents for 131 Ithan those with acetylacetonate. Also, it was established that organic residues presented in the samples prepared by the microwave method favored the sorption of radioactive anions, in particular 131 Iif compared with nitrate and/or carbonate interlayered hydrotalcites. Ferric acetylacetonate, among other iron salts, was used as a precursor to obtain black magnetic Fe 3 O 4 nanoparticles in polyhydric alcohols in presence of surfactants (polyethylene glycol, cetyltrimethylammonium bromide, sodium dodecyl benzene sulfonate, etc.) and cosolvents (ethylenediamine, formamide, 1,4-butanediamine and/or butanolamine) (Gao et al, 2009). The product can be used in biomedical, mechanic or electronic fields with strong magnetism, controllable size, and good dispersibility. Additionally, as described in a related work (Bilecka et al, 2008),highly crystalline metal oxide nanoparticles such as CoO, ZnO, Fe 3 O 4 , MnO, Mn 3 O 4 , and BaTiO 3 were synthesized in just a few minutes by reacting metal alkoxides, acetates or acetylacetonates with benzyl alcohol under microwave heating. At last, organically dispersible nanoalloys were prepared from mixture of salts and metal acetates/acetylacetonates in oleyamine (OAm) and oleic acid (OA), for instance Pd(acac) 2 -Ni(HCO 2 ) 2 -OAm-OA (nanoalloy PdNi) or Ag(ac)-Cu(ac) 2 -OAm-OAc (AgCu) (Abdelsayed et al, 2009). High activity and thermal stability have been observed for the nanoalloys according to the order CuPd>CuRh>AuPd>AuRh>PtRh>PdRh>AuPt.
www.intechopen.com CVD techniques have been successfully applied to decompose metal complexes, in particular microwave plasma aerosol-assisted chemical vapor deposition (MWAACVD), which was used, among other varieties of AACVD, to prepare Y 2 O 3 stabilized ZrO 2 , Y 2 O 3 doped CeO 2 , Gd 2 O 3 doped CeO 2 and La 0.8 Sr 0.2 MnO 3 thin films on various ceramic substrates starting froml β-diketonate chelates as the source materials (Meng et al, 2004). Amorphous GaF 3 and GaF 3 -BaF 2 thin films were synthesized by electron cyclotron resonance microwave plasma-enhanced CVD (MWPECVD) using metal β-diketonates and a NF 3 gas as starting materials and a fluorinating reagent, respectively (Takahashi et al, 2003). A thin zirconia electrolyte film for a solid oxide fuel cell was prepared on a porous Al 2 O 3 substrate by MPE CVD using two zirconia sources: zirconium acetylacetonate and zirconium tetra-n-butylate (Okamura et al, 2003). As-deposited electrolyte film grown indicated the columnar structure, but this was deformed to a crystal structure with a large crack or pore occurred at grain boundary in film by annealing at 400 o C. Additionally, MWPECVD was shown to be a promising method for the solvent free preparation of catalytic materials (Dittmar & Herein, 2009), such as, for example catalytic active chromia species on zirconia and lanthanum doped zirconia supports. During this process, the adsorption of Cr(acac) 3 probably took place by cleavage of one ligand on both supports. Furthermore, the utilization of the PECVD method can inhibit the formation of large CrO x agglomerates or α-Cr 2 O 3 on both supports and, after upscaling, this method can be used for the preparation of catalysts for fine chemicals in larger scale. In a related work (Dittmar et al, 2004), where cobalt oxide supported on titania, CoO x /TiO 2 , was obtained starting from cobalt(III) acetylacetonate, Co(acac) 3 , (precursor) and TiO 2 (support), the Co(acac) 3 was evaporated and adsorbed on carrier surface in a first step and afterwards decomposed during the microwave-plasma treatment in oxygen atmosphere. Volatile copper(II) acetylacetonate was used for preparation of copper thin films in Ar-H 2 atmosphere at ambient temperature by MWPECVD (Pelletier et al, 1991). The formed pure copper films with a resistance of 2-3 μΩ . cm were deposited on Si substrates. It was noted that oxygen atoms were never detected in the deposited material since Cu-O intramolecular bonds were totally broken by microwave plasma-assistant decomposition of the copper complex. Additionally to the examples described above on the use of β-diketonate-alkoxide mixtures, alkoxides themselves were also reported as precursors for MW-obtaining of inorganic films and structures. Thus, synthesis of TiO 2 and V-doped TiO 2 thin layers was significantly improved and extended under application of microwave energy during the drying and/or calcination step (Zabova et al, 2009). Thin nanoparticulate titania layers were prepared via the sol-gel method using titanium n-butoxide as a precursor. The photocatalytic activities of prepared layers were quantified by the decoloring rate of Rhodamine B. Another type of coordination compounds, molecular adducts of alcohols of the composition VOPO 4 . C n H 2n+1 OH (1-alkanols, n=1-18) and VOPO 4 . C n H 2n (OH) 2 (1,ω-alkanediols, n=2-10) were prepared long ago (Beneš et al, 1997) by the direct reaction of various liquid alcohols with solid and finely ground VOPO 4 . 2H 2 O in a MW field. According to X-ray diffraction data, the structures of all these polycrystalline complexes retained the original layers of (VOPO 4 ) ∞ . Alcohol molecules were placed between the host layers in a bimolecular way, being anchored to them by donor-acceptor bonds between the oxygen atom of an OH group and a vanadium atom as well as by hydrogen bonds. Other adducts, [(n-Bu) 4 N][TlMS 4 ] (M=Mo, W), were also prepared in the conditions of microwave treatment and their nonlinear optical properties were studied (Lang et al, 1996). www.intechopen.com

Carboxylates
MW-synthesized carboxylates are represented mainly by aromatic derivatives possessing multiple carboxylic groups. These complexes are sometimes isolated as adducts with stabilizing ligands as 2,2'-bipy or 1,10-phen, as well as solvent molecules. Thus, by treating Cu(NO 3 ) 2 . 3H 2 O with a V-shaped ligand 4,4'-oxydibenzoic acid (H 2 oba), a dynamic metalcarboxylate framework [Cu 2 (oba) 2 (DMF) 2 ] . 5.25DMF (MCF-23; DMF = N,Ndimethylformamide) was synthesized, which features a wavelike layer with rhombic grids based on the paddle-wheel secondary building units . These layers stack via strong offset π-π stacking of the Ph groups of oba ligands to give 3D porosity. A MWAS solvothermal method was proven to be a faster and greener approach to synthesize phasepure MCF-23 in high yield without impurities, typical for conventional synthesis. In contrast, the product obtained by the conventional solvothermal method was not phasepure. Two isostructural coordination polymers, M 3 (NDC) 3 (DMF) 4 (M = Co, Mn; H 2 NDC = 2,6-naphthalenedicarboxylic acid), crystallizing in the monoclinic system with space group C2/c, were prepared through conventional and MWAS solvothermal methods . These microporous cobalt(II) and manganese(II) coordination polymers underwent reversible structural change upon desolvating, giving stable microporous frameworks containing unsaturated metal sites. Trimesic acid 1 and its analogue, containing four carboxylate units, have been reported in a series of publications related to MWAS of metal complexes. Thus, two isostructural coordination polymers (EMim) 2 [M 3 (TMA) 2 (OAc) 2 ] (M = Ni or Co, EMim = 1-ethyl-3methylimidazolium, H 3 TMA = trimesic acid) with anionic metal-organic frameworks were synthesized under microwave conditions using an ionic liquid EMIm-Br as solvent and template (Lin et al, 2006). In a related report, the microwave solvothermal reaction of nickel nitrate with trimesic acid provided the [Ni 3 (BTC) 2 (H 2 O) 12 ] n (BTC = benzene-1,3,5tricarboxylate anion of trimesic acid), which is a metal coordination polymer composed of 1D zigzag chains (Hsu et al, 2009). In the asymmetric unit, two types of Ni atoms were found: one of the NiO 6 groups was coordinated to only one carboxylate group and thus terminal, the other is bridging, forming the coordination polymer. COOH)} n (crystallized in the monoclinic system and the space group Cc), had a flattened octahedral configuration (Xu & Fan, 2007 btec = 1,2,4,5benzenetetracarboxylic acid, bipy = 2,2'-bipyridine, phen = 1,10-phenanthroline) were synthesized using hydrothermal and microwave methods (Shi et al, 2009). All three complexes were found to be bridged by the ligands to form 3D (first complex) and binuclear (other complexes) structures. Three isostructural 2D metal-organic frameworks, [M(bpydc)(H 2 O) . H 2 O] n (where M = Zn; Co; Ni and bpydc is 2,2'-bipyridine-5,5'-dicarboxylate), were prepared by hydrothermal, ultrasonic and MWAS methods (Huh et al, 2010).The coordination environment of the metal ions was found to be a distorted octahedral geometry. The metal ions were found to be coordinated by two nitrogen atoms from the bipyridyl moiety, two oxygen atoms from one  (Dickhoff et al, 2006). As an example of MW-decomposition of metal carboxylates leading to nanostructures, Ni nanoparticles with average sizes of 43, 71, and 106 nm were obtained by the intramolecular reduction of Ni 2+ ion contained in a formate complex having long-chain amine ligands {oleylamine (=(Z)-9-octadecenylamine), myristylamine (=tetradecylamine), and laurylamine (=dodecylamine)} within an extremely short time under MW conditions (Yamauchi et al, 2009). Formate ion coordinated to Ni 2+ ion acted as a reducing agent for Ni 2+ in this reaction and finally decomposed to hydrogen and carbon dioxide. Also, microwave synthesis of metal oxide nanoparticles, γ-Fe 2 O 3 , NiO, ZnO, CuO and Co-γ-Fe 2 O 3 were carried out by microwave-assisted route through the thermal decomposition of their respective metal oxalate precursors employing polyvinyl alcohol as a fuel (Lagashettya et al, 2007).

Phthalocyanines
Phthalocyanine (Pc) area is industrially important, in a difference with major part of Ncontaining ligands having an academic interest only, since both metal free phthalocyanines and their several metal complexes (Cu, Zn, Ni, Fe, etc.) are produced during several decades in large quantities and used as pigments, in compact disk production, and catalysis, among many other applications. So, novel techniques for their production are permanently in search, as for classic Pcs as for substituted (generally R 4 Pc for symmetrical Pcs; R = alkyl, aryl, Cl, NO 2 , ethers, crowns, etc.). In particular, a variety of metal phthalocyanine complexes has been fabricated via MWH allowing absence of solvents (we note that solvent nature is very important for tetramerization of phthalonitrile and other Pc precursors). Thus, metal substituted octachlorophthalocyanines (M = Fe, Co, Ni, Cu, Zn), hexadecachlorophthalocyanines (M = Fe, Co, Ni, Cu) and tetranitrophthalocyanines (M = Fe, Co, Ni, Cu, Pd) were synthesized by exposure to MW under solvent free and reflux conditions (Safari et al, 2004;Shaabani et al, 2003). The synthesis of various axially substituted Ti phthalocyanines in high yield using MW without solvent was reported (Maree, 2005). The times of reaction, as expected, were short (generally <10 min). Substituted Fe and Co octachloro-, tetranitro-, tetracarboxy-or polyphthalocyanines were easily prepared by MWH of the starting materials under solvent free condition, which reduced reaction time considerably and used as epoxidation catalysts of cyclooctene in homogeneous and heterogeneous conditions by iodosylbenzene as an oxidant (Bahadoran & Dialameh, 2005). Their catalytic activities showed that the electron withdrawing groups on the phthalocyanine ring have a very small effect on stability of the catalyst during the reactions. The tetrasubstituted metal-free phthalocyanine 8 (R = SO 2 NH-p-C 6 H 4 Me) and its nickel and zinc metallophthalocyanines bearing four 14-membered tetraaza macrocycles moieties on peripheral positions were synthesized by cyclotetramerization reaction of phthalonitrile derivative 9 in a multi-step reaction sequence (Biyiklioglu et al., 2007). Additionally, a reaction mixture containing perfluoro-phthalonitrile reacted in a vessel with application of microwave energy for a reaction period sufficient to yield a fluorinated phthalocyanine (Fraunhofer-Gesellschaft et al, 2009), having wide ranging applications, e.g., corrosion-related applications, coating-related applications, catalysis, and the production of optical and electronic materials. Thermal and microwave reactions between [PcSn IV Cl 2 ] and the potassium salts of eight fatty acids led to cis-[(RCO 2 ) 2 Sn IV Pc] compounds {R = (CH 2 ) n Me (n = 4, 6, 8, 10, 12, 14, 16) and (CH) 7 -cis-CH:CH(CH 2 ) 7 Me} in yields ranging from 54 to 90% (Beltran et al, 2005). Some products revealed anticorrosion properties. Triazol-5-one substituted phthalocyanines were prepared quickly by the reactions (1) of 4-nitrophthalonitrile with anhydrous metal (M = Co, Cu, Zn, Ni) salts in DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) and DMAE (dimethylaminoethanol) by MW. Microwave yields were found to be higher than those of the conventional synthesis methods (Kahveci et al, 2006). We note that some metal-free substituted phthalocyanines {2,9(10),16(17),23(24)-tetra(3,5-dimethylphenoxy) phthalocyanine, 2,9(10),16(17), 23(24)-tetra(4-tert-butylphenoxy) phthalocyanine, and 2,9(10),16(17),23(24)-tetra(3,5-di-tert-butyl-4-hydroxyphenyl) phthalocyanine} were also obtained by similar routes with higher yields in comparison with conventional methods (Seven et al, 2009). These Pc-compounds had high thermal stability, which was determined at 520 o C (midpoint), 549 o C, and 400 o C, respectively, as a maximum weight loss temperature. Bisand sub-phthalocyanines, as well as mixed phthalocyanine-porphyrin complexes, were also reported as MW-fabricated. Thus, starting with phthalic and 4-tert-butylphthalic acid derivatives, the bisphthalocyanines of rare earth elements and Hf and Zr were MWprepared (Kogan et al, 2002). Sub-phthalocyanine (SubPc) derivatives with different kind of substituent groups were synthesized from various phthalonitriles using conventional and microwave heating sources ). Compared to the conventional synthesis, it was found that SubPc derivatives were synthesized in a shorter reaction time with a higher synthetic yield by MW. A soluble phthalocyanine-porphyrin complex {Lu(TBPor)Pc} was quickly obtained by MWH; Lu(TBPor)Pc was shown to have better photoelectric conversion properties than porphyrin {Lu(TBPor)OAc}, phthalocyanine {H 2 (TBPc)}, and Lu(TBPor)OAc/H 2 (TBPc) blend . More information on MW-synthesis of phthalocyanines was reported: Ga (Masilela & Nyokong, 2010), and other metals (Co, Ni, Cu, Mg, Al, Pd, Sn, Tb, Lu, Ce, La, Zn) (Hu et al, 2002;Park et al, 2001).

Complexes with N,O-containing ligands
These coordination compounds are widely represented by a series of oximes, amines, imines, Schiff bases, as well as such cyclic N,O-ligands as oxadiazoline. Cluster complexes have been also reported, in particular those that cannot be obtained by standard nonmicrowave techniques. Thus, tetradentate N 2 O 2 ligand [HO(Ar)CH:N-(CH 2 ) 2 -N:CH(Ar)OH] (Ar = o-C 6 H 4 ) and manganese(II), cobalt(II), nickel(II), and zinc(II) diimine complexes ML were synthesized by classical and MW techniques (Pagadala et al., 2009). It was proposed that, probably, the metal is bonded to the ligand through the phenolic oxygen and the imino nitrogen. The reaction of Ni(ClO 4 ) 2 . 6H 2 O with 2-hydroxybenzaldehyde and an aqueous solution of methylamine in acetonitrile/MeOH under MWH and controlled temperature/pressure gave trinuclear cluster [Ni 3 (mimp) 5 -(MeCN)]ClO 4 (mimp = 2methyliminomethylphenolate anion) in only 29 min and also resulted in higher yields in contrast to other synthesis methods ). This complex displayed dominant ferromagnetic interactions through μ 3 -O (oxidophenyl) and μ 2 -O (oxidophenyl) binding modes. Another cluster, unusual for a specific group of complexes, was found for an oxime complex. Thus, the microwave-assisted reaction of Fe(O 2 CMe) 2 with salicylaldoxime (saoH 2 ) in pyridine produced an octametallic cluster [Fe 8 O 4 (sao) 8 (py) 4 ] in crystalline form in 2 min (Gass et al, 2006). The core of the complex contained a cube encapsulated in a tetrahedron while sao 2-exhibited an unique coordination mode η 2 :η 1 :η 1 :μ 3 among the structurally characterized metal complexes containing the sao 2-ligand. The authors noted that [Fe 8 O 4 ] 4+ core is uncommon, observed earlier only in one other complex: [Fe 8 O 4 (pz) 12 Cl 4 ] (pz = pyrazolate anion). The MW-heating had not only led to the isolation of a beautiful and unusual {Fe III 8 } cluster, impossible to produce under ambient reaction conditions, but has also greatly improved the reaction rate and enhanced the yield in comparison to solvothermal methods. Among other oxime complexes, the metal-mediated iminoacylation of ketoximes R 1 R 2 C:NOH (R 1 = R 2 = Me; R 1 = Me, R 2 = Et; R 1 R 2 = C 4 H 8 ; R 1 R 2 = C 5 H 10 ) upon treatment with the platinum(II) complex trans-[PtCl 2 (NCCH 2 CO 2 Me) 2 ] with an organonitrile bearing an acceptor group proceeded under mild conditions in dry CH 2 Cl 2 or in microwave field to give the trans-[PtCl 2 {NH:C(CH 2 CO 2 Me)ON:CR 1 R 2 } 2 ] isomers in moderate yield (Lasri et al, 2006). Nine cobaloximes of the type trans-[Co(dmgH) 2 (B)X], where dmgH -= dimethylglyoximate anion, X -= Cl -, Bror Iand B = pyrazine, Pz (1 to 3), pyrazine carboxylic acid, PzCA (4 to 6), pyrazine carboxamide, PzAM (7 to 9), imidazole (Imi) or histidine (His), were prepared (an example of the complex, N,N'-dihydrogenpiperazonium dichloridobis(dimethylglyoximato-k 2 N,N')cobaltate(III) dihydrate, PpH 2 [Co(dmgH) 2 Cl 2 ] 2 . 2H 2 O, is shown by formula 10) (Martin et al, 2008;Dayalan et al, www.intechopen.com 2009). The free ligands Pz, PzCA and PzAM showed antibacterial activity in the order: Pz > PzCA > PzAM whereas, the free equatorial ligand dmgH 2 was inactive against all the bacteria tested. The cobaltoximes were more active than the corresponding pyrazine and its derivatives as axial ligand in the complexes. It was revealed that the bromo complexes dissociated at higher temperatures compared to the chloro complexes, the iodo cobaloximes being unstable even at low temperature decomposing without any sharp change in mass. Iodocobaloximes were found to be more active than the corresponding chloro-and bromocobaloximes with the antibacterial activity order for the axial halides as I -> Cl -> Brand that of the axial nitrogen heterocycles as histidine > imidazole. Additionally, a 3D coordination polymer, [Cd(μ 3 -HIDC)(bbi) 0.5 ] n {H 3 IDC = 4,5-imidazoledicarboxylic acid, bbi = 1,1'-(1,4butanediyl)bis(imidazole)}, was synthesized under MWH solvothermal conditions . Its crystal structure consisted of 2-D brickwall-like networks of [Cd(μ 3 -HIDC)] n , which are further linked through μ 2 -bbi to generate a 3D structure.  (Bokach et al, 2005). The reaction time can be drastically reduced by focused MW of the reaction mixture. Phenylantimony chloride and Sb chloride complexes with Schiff base ligands having N-S and N-O donor systems were synthesized under MW using a domestic microwave oven from hours to a few seconds with improved yield as compared with conventional heating (Mahajan et al, 2008). The treatment with the ligands and their phenylantimony derivatives at dose levels of 20 mg per rat per day did not cause any significant change in body weight, but a significant reduction in the weights of reproductive organs was observed. Transition metal complexes of Cu(II), Ni(II), Co(II), Mn(II), Zn(II), Hg(II), and Sn(II) were synthesized from the Schiff base (L) derived from 4-aminoantipyrine and 4-fluoro-benzaldehyde using traditional synthetic methodology and microwave-induced organic reaction enhancement (MORE) technique (Ali et al, 2010). Neat reactants were subjected to microwave irradiation giving the required products more quickly and in better yield compared to the classical methodology. As an example of use of Schiff base complexes for catalytic purposes, we note an octahedral titanium binaphthyl-bridged Schiff base complex 11, investigated in respect of catalytic behavior toward epoxidation of allylic alcohols (Soriente et al, 2005). It was established that a mixture of monoterpene alcohol 12, tert-Bu hydroperoxide, the complex 11, and CH 2 Cl 2 , being irradiated with microwave for 15 min, gave 87% terpene epoxy alcohol 13.  (Bhojak et al, 2008). Antibacterial activity of the ligands and complexes were also reported on S. aureus and E. coli. Complexes of Mn(II) with 4 amide group containing ligands (Bhojak et al, 2007) {N, N'-bis-(3-carboxy-1-oxopropanyl)-1,2-ethylenediamine (CPE), N,N'-bis-(3-carboxy-1-oxo-propanyl)-1,2-phenylenediamine (CPP), N,N'-bis-(2-carboxy-1-oxophenelenyl)-1,2-phenylenediamine (CPPP), N,N'-bis-(3carboxy-1-oxoprop-2-enyl)-1,2-phenylenediamine (CPP-2), obtained by MW-heating of amine and carboxylic acid} were MW-synthesized. Typical preparation of these complexes included simple steps: a slurry of ligand (i.e. CPE, CPP, CPPP or CPP-2) was prepared in water or in water-ethanol mixture; in this a solution of Mn(CH 3 COO) 2 . 4H 2 O was added, and the resulting mixture was irradiated in a microwave oven for 2 to 6 minutes at medium power level (600 W) maintaining the occasional shaking. Proposal structures of complexes are shown by formulae 14-17. The antibacterial activity of the ligands and complexes was studied. Additionally, the Chinese-lantern-type Co 2 (O 2 CBut) 4 {2,6-(NH 2 ) 2 C 5 H 3 N} 2 complex reacted with RCN (R = Me or Pr) under microwave irradiation to give the mononuclear amidine complexes Co(O 2 CBut) 2 {H 2 N(C 5 H 3 N)NHC(R):NH} (R = Me or Pr) (Bokach et al, 2006). Al-containing mesoporous silicates (Al-MCM-41 and Al-HMS) supported Mn(salen) catalysts were prepared by three different methods: impregnation of salen ligand and support with dichloromethane and then irradiated by microwave (method A), direct solidstate interaction between salen complex and support under microwave irradiation (method B), as well as the conventional ion exchange (method C) (Yin et al, 2005;Zhang et al, 2003). The effect of catalyst preparation methods on the catalytic activity and selectivity in the styrene epoxidation indicate that the catalyst of Mn(Salen)/Al-HMS-IP prepared by method A showed similar activity to the neat complex and the best selectivity for styrene epoxide. In comparison with the traditional adsorption method, the MW-assisted approach was efficient and environmentally friendly, and improved the loadings of Mn(III)-salen complexes on HMS via a strengthening axial coordination of the surface NH 2 groups of HMS toward the Mn(III)-salen complexes (Fu et al, 2007). The effects of several extrinsic physical fields, such as the magnetic field, the ultrasonic wave and the MW, on the rate and yield of chitosan-Fe(II) complexing reaction were investigated , showing that ultrasound had the greatest effect on the reaction rate and complexing capacity, followed by the magnetic field and the MW. A mechanism for the enhancement of the complexing reaction by the three physical fields was proposed.

Complexes with S-and N,S-containing ligands
According to the available literature, microwave-synthesized complexes of S-containing ligands without other donor heteroatoms are represented by coordination compounds of dithiolene. Thus, dithiolene-transition metal complexes 18 were obtained by a series of steps    (Mondal et al, 2009). BiPh 3 was treated with thiols of varying pKa and functionality (2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptopyrimidine, 2-mercapto-1-methylimidazole and 2-mercaptobenzoic acid) in a 1:3 ratio under a variety of reaction conditions: with toluene or mesitylene under standard reflux conditions and under microwave irradiation, and solvent free with conventional and microwave heating (Andrews et al, 2007). As a result, several reactions yielded the trissubstitution product in good yield and high purity; 2-mercaptobenzoic acid gave the complex Bi 2 L 3 in all reactions carried out in solvent and PhBiL when solvent free, both complexes containing the doubly deprotonated dianion (L = -O 2 C-C 6 H 4 -S-). The authors noted that reactions carried out in the microwave reactor generally gave comparable yields to the conventional methods but in significantly shorter times; however, the solvent free microwave reactions of 2-mercaptobenzoxazole and 2-mercaptopyrimidine caused partial decomposition to give microcrystalline Bi 2 S 3 . MWH of racemic cis-[Ru(bpy) 2 (Cl) 2 ] (bpy = 2,2'-bipyridine) or racemic cis-[Ru(phen) 2 (Cl) 2 ] (phen = phenanthroline) with either (R)-(+)or (S)-(-)-Me p-tolyl sulfoxide yielded the ruthenium bis(diimine) sulfoxide complexes, for example 19 (Pezet et al, 2000). This source of energy improved both yields and reaction rates with a very good diastereoselectivity (73-76%) and represented a significant advance in the asymmetric synthesis of octahedral ruthenium complexes. A lot of complexes of thiosemicarbazone and its derivatives have been MW-obtained. Thus, molybdenum(VI) complexes MoO 2 (L) 2 o f t h e l i g a n d s H L { 3 , 4 , 5trimethoxybenzaldehydethiosemicarbazone (TBTSCZH), 3,4,5trimethoxybenzaldehydesemicarbazone (TBSCZH), 3,4,5trimethoxybenzaldehydebenzothiazoline (TBBZTH) and 3,4,5-trimethoxybenzaldehyde-Swww.intechopen.com benzyldithiocarbazate (TBDTCZH)} were MW-fabricated  by the reactions between dioxobis(2,4-pentanedionato-O,O')molybdenum(VI) and the ligands TBTSCZH, TBSCZH, TBBZTH and TBDTCZH by MW-assisted and conventional thermal methods. All four ligands and their complexes were screened for their biological activity on several pathogenic fungi and bacteria and the data show good activity of these complexes and ligands. The synthesis of some Mn(II), oxovanadium(V) and dioxomolybdenum(VI) complexes with 5chloro-1,3-dihydro-3-[2-(phenyl)ethylidene]-2H-indol-2-one thiosemicarbazone (L 1 H) and 5chloro-1,3-dihydro-3-[2-(phenyl)ethylidene]-2H-indol-2-one semicarbazone (L 2 H) were carried out in unimolar and bimolar ratios in an open vessel under MW using a domestic microwave oven. In the case of the oxovanadium complexes, the metal was found to be in the penta-and hexa-coordinated environments. The ligands and complexes possessed antimicrobial properties. Trigonal bipyramidal and octahedral complexes of Sn(IV) were synthesized by the reaction of dimethyltin(IV) dichloride with 4-nitrobenzanilidethiosemicarbazone (L 1 H), 4chlorobenzanilidethiosemicarbazone (L 2 H), 4-nitrobenzanilidesemicarbazone (L 3 H) and 4chlorobenzanilidesemicarbazone (L 4 H) from dimethyltin(IV) dichloride and monobasic bidentate ligands using MW as the thermal energy source . The antifungal, antibacterial and antifertility activities were examined and the results were indeed very encouraging. A series of mixed ligand ruthenium(II) containing diimines and thiosemicarbazones with general formula [Ru(N-N) 2 (N-S)](PF 6 ) 2 where N-N = bipyridine or 1,10-phenanthroline and N-S = 9-anthraldehyde thiosemicarbazone and the 4-alkyl substituted (R = Me, Et and phenyl) analogs were synthesized using microwave energy (Beckford et al, 2009;Beckford et al, 2010). The compounds quenched the fluorescence of the complex between ethidium bromide and calf-thymus DNA with the Stern-Volmer quenching consisted in the range 1.18-2.71 . 10 4 M -1 . Additionally, the Pd(II) and Pt(II) complexes were synthesized using microwave heating by mixing metal salts in 1:2 molar ratios with heterocyclic ketimines, 3acetyl-2,5-dimethylthiophene thiosemicarbazone (C 9 H 13 N 3 OS 2 ) and 3-acetyl-2,5dimethylthiophene semicarbazone (C 9 H 13 N 3 OS), obtained by reactions of 3-acetyl-2,5dimethylthiophene with thiosemicarbazide and semicarbazide hydrochloride (Sharma et al, 2010). The authors proposed that the ligands coordinate to the metal atom in a monobasic bidentate manner and square planar environment around the metal atoms. The antiamoebic activity of both the ligands and their palladium compounds against the protozoan parasite Entamoeba histolytica was tested. Other data on MW-obtaining thiosemicarbazone complexes were discussed in (Chaudhary et al, 2009;Shen et al, 2008). In case of thiophene derivatives, MW-assisted condensation of salicylaldehyde with 2amino-3-carboxyethyl-4,5-dimethylthiophene in the absence of solvent was efficiently performed to form a potentially tridentate Schiff base, 2-(N-salicylideneamino)-3carboxyethyl-4,5-dimethylthiophene (HSAT), which acted as neutral tridentate with ONO donor sequence towards the lanthanide(III) ions, forming 1:2 metal-ligand complexes of the type [Ln(HSAT) 2 Cl 3 ] where Ln = La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III) and Gd(III) (Kumasi et al, 2009). Additionally, it is known that thiophene can react with elemental iron in the form of metal atoms in cryosynthesis conditions or its carbonyls carrying out the desulfurization of the ligand. In reactions with iron carbonyls, the use of MWH evidently led (Singh et al, 1996) to acceleration of reported reactions of thiophene and its tellurium analogue and its derivatives with [Fe 3 (CO) 12 ]. The following dechalcogenation reactions take place, forming binuclear complexes 20-21 (reactions 2). Among other organometallic compounds, prepared this way, it is necessary to mention chromium, molybdenum, and tungsten carbonyls (Van Atta et al, 2000).

σand π-organometallic compounds
Microwave heating has been applied to obtain a series of metal complexes with classic ligands forming σand π-organometallic compounds: carbonyls, cyclopentadienyls, dienes, and arenes, among others. Generally, as well as for the case of the coordination compounds above, main advantages of MW-application are frequently higher yields and almost always considerably shorter reaction times.

Carbonyls
Among fundamental generalizing publications on MW-fabricated metal carbonyls, we note a review on Group 6 metals, describing, in particular, metal carbonyls synthesis in a conventional MW-oven (Holder, 2005), and a report (Ardon et al, 2004)  ], where dppe = 1,2-bis(diphenylphosphino)ethane, pip = piperidine}. Also, mixed carbonyl-arene complexes are known; thus, the microwaveassisted synthesis of (η 6 -arene)tricarbonylchromium complexes from hexacarbonylchromium and arenes gave high yields of (η 6 -arene)chromium tricarbonyl complexes (Lee et al, 2006). In case of noble metals, by using a gas-loading accessory, microwave-assisted synthesis of Ru 3 (CO) 12 , Ru 3 (CO) 9 (PPh 3 ) 3 , HRu 3 (CO) 9 (C≡CPh) and H 4 Ru 4 (CO) 12 was performed (Leadbeater et al, 2008). Ligand substitution reactions of Ru 3 (CO) 12 with triphenylphosphine were also studied in real time by means of a digital camera interfaced with the microwave unit. Microwave-assisted ligand substitution reactions of Os 3 (CO) 12 in a remarkably short period of time led to the labile complex Os 3 (CO) 11 (NCMe) in high yield without the need for a decarbonylation reagent such as trimethylamine oxide (Jung et al, 2009). Additionally, MWH of Os 3 (CO) 12 in a relatively small amount of acetonitrile was shown to be a useful first step in two-step, one-pot syntheses of the cluster complexes Os 3 (CO) 11 (py) and Os 3 (CO) 11 (PPh 3 ). Microwave-assisted reactions of 3,3,3-tris(3'-substituted pyrazolyl)propanol ligands    (Kunz et al, 2009). These complexes were also prepared directly from [Re(CO) 5 Br] and the corresponding pyrazoles by microwave-assisted synthesis. Beginning with MO 4 -(M = 99m Tc, 186/188 Re), the carbonyl precursor [M(CO) 3 (H 2 O) 3 ] + was synthesized in 3 min in quantitative yield in a microwave reactor (Causey et al, 2008). When di-picolyl ligand (HL = 5-[bis(2-pyridinylmethyl)amino]pentanoic acid) was added to the reaction mixture, the chelate complex [M(CO) 3 (L)] + was formed in high yield in 2 min using MWH at 150 o C. These and further syntheses under MW-heating represented a move away from traditional instant kits toward more versatile platform synthesis and purification technologies that are better suited for producing modern molecular imaging and therapy agents.

Cyclopentadienyls
As metal-Cp complexes, MW-obtained ferrocene derivatives are the most common. Among relatively old and already classic achievements in this area, we emphasize the following condensation reactions. Thus, according to the conventional techniques, Claisen-Schmidt www.intechopen.com template reactions of acetylferrocene 24 and ferrocene carboxaldehyde 26 are usually performed under classical homogeneous conditions in ethanol. Using MWH of the reaction system, it became possible (Villemin et al, 1994) to prepare (reactions 6 and 7) ferrocenylenones 25 and 27 without solvent in presence of solid KOH with higher yields in comparison with those reported earlier. It is noted that the reactions may be accelerated efficiently by microwave irradiation.  (Lu et al, 2003). 1,5-dioxo-3-(pmethylbenzyloxyphenyl)[5]ferrocenophane (28) was MW-prepared (50 W for 30 min with 80°C) in 2-step reaction from 4-hydroxybenzaldehyde in acetone, 4-methylbenzylbromide, CsCO 3 , and further addition of diacetylferrocene in 90% yield (Patti et al, 2009).

Other organometallics
The effect of the microwave irradiation on the reaction of alkynyl alkoxy carbene complexes with urea derivatives was studied (Spinella et al, 2003), showing that in these conditions (CO) 5 W:C(OEt)C≡CPh reacted with ureas, (RNH)C(O)(NHR') (e.g., R , R' = H, Me, allyl, Et), with reduced reaction times to give uracil derivatives 33. It is noteworthy that the use of large amounts of solvents could be drastically reduced or even avoided and, in any case, reaction times were dramatically shortened. The MWAS of two different types of Nheterocyclic carbene-palladium(II) complexes, (NHC)Pd(acac)Cl (NHC = N-heterocyclic carbene; acac = acetylacetonate) and (NHC)PdCl 2 (3-chloropyridine), led to drastic reduction in reaction times (20 to 88 times faster, depending on the complex) (Winkelmann & Navarro, 2010 (Rentzsch et al, 2009). Palladium(II) carbene complexes were also reported in (Scarborough et al, 2009).

Microwave-assisted catalysis using metal complexes
Several reports are dedicated to the use of metal (mainly noble metals, such as Rh, Pd, Os, which in free form are used in catalytic processes) complexes in MWAS or rearrangements of organic compounds. Thus, a highly efficient C-C bond cleavage of unstrained aliphatic ketones bearing β-hydrogens with olefins was achieved using a chelation-assisted catalytic system consisting of (Ph 3 P) 3 RhCl and 2-amino-3-picoline by MW under solvent-free conditions (Ahn et al, 2006). The addition of cyclohexylamine catalyst accelerated the reaction rate dramatically under microwave irradiation compared with the classical heating method. Microwave-assisted Rh-diphosphane-complex-catalyzed dual catalysis, providing [2+2+1] cycloadducts by sequential decarbonylation of aldehyde or formate and carbonylation of enynes within a short period of time, was reported (Lee et al, 2008). Various O-, N-, and C-tethered enynes were transformed into the corresponding products in good yields. The first enantioselective version of this microwave-accelerated cascade cyclization was realized. In the presence of chiral Rh-(S)-bisbenzodioxanPhos complex, the cyclopentenone products were achieved with ee values up to 90%. Osmium complex (μ-H)Os 3 (μ-O:CPh)(CO) 10 was an active catalyst for the allylic rearrangement N-allylacetamide under MW-radiation (Afonin et al, 2008).

SH SH
www.intechopen.com An efficient method for intermolecular hydroarylation of aryl and aliphatic alkenes with indoles using a combination of [(PR 3 )AuCl]/AgOTf as catalyst under thermal and microwave-assisted conditions was developed (Wang ert al, 2008), achieving the gold(I)catalyzed reactions of indoles with aryl alkenes in toluene at 85 o C over a reaction time of 1-3 h w i t h 2 m o l % o f [ ( P R 3 )AuCl]/AgOTf as catalyst (yields 60-95%). Under microwave irradiation, coupling of unactivated aliphatic alkenes with indoles gave the corresponding adducts in up to 90% yield. Additionally, metal acetates were found to be effective catalysts; thus, a rapid and efficient method for the synthesis of β-arylalkenyl nitriles by a one-pot three component coupling reaction of diphenylacetylene, K 4 Fe(CN) 6 , and aryl halides using Pd(OAc) 2 as a catalyst and water as a solvent under MW (Velmathi et al, 2010). The method employed a cyanide source which is safe and inexpensive. Copper-catalyzed cyanation of aryl halides was improved to be more economical and environmentally friendly by using water as the solvent and ligand-free Cu(OAc) 2 . H 2 O as the catalyst under MW (Ren et al, 2009). The suggested methodology was applicable to a wide range of substrates including aryl iodides and activated aryl bromides.

Conclusions
In the coordination and organometallic chemistry, the microwave-assisted synthesis is not developed such sufficiently as for the preparation of inorganic compounds, composites and materials or in the organic synthesis, where microwave heating can be considered as a common preparative tool. However, during the last decade a considerable growth of related reports has been registered. The most number of reports corresponds to MW-reactions of the N-, N,O-, and N,S-containing ligands with sources of metal ions. Some MW-fabricated classic πand σ-organometallic compounds are also presented. Practically in all reports, main attention of researchers is paid to extreme fastness of MWassisted reactions in comparison with classic protocols. The same reactions in the MW-field take place in 10-100 times more rapidly. Moreover, higher or comparable yields are frequently reported. Sometimes, the MW-route leads to products, which it is impossible to get via traditional routes, for instance preparation of several metal cluster complexes. Despite of the development of novel synthesis techniques in chemistry and especially nanotechnology (for example, laser-, sputtering-, CVD-, electron-and ion-beam-, radiation-, or combustion-assisted methods, among many others, the microwave heating remains very attractive for chemists due to its obvious advantages, noted at the beginning of this chapter.

Acknowledgements
The authors are very grateful to Professors Yurii E. Alexeev and Alexander D. Garnovskii (Southern Federal University, Rostov-na-Donu, Russia) for critical revision of the final manuscript.