Metal carbonyls dinuclear compounds

Because of the great strength of iridium-iridium bonds, there is a wealth of information on polynuclear metal-carbonyl cluster compounds of iridium (see Dinuclear Organometallic Cluster Complexes mA Polynuclear Organometallic Cluster Complexes). It4(CO)i2 (45) may be synthesized from... 

Polynuclear Carbonyls. Several stmctures consist of dinuclear metal carbonyls as shown in stmctures (4)—(6). The metal atoms in Mn2(CO) Q, as also for technetium and rhenium, are held together by a metal—metal bond and the compound contains 10 terminal CO ligands, five coordinated to each atom. The CO ligands of Mn2(00) 0 adopt a staggered configuration as illustrated in stmcture... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

The schematic formula given by 62 corresponds to the most frequent mode of localization of the coordination bond (E = O). This mode is present in the majority of metal carbonyls M(CO) (details in Sec. 2.2.5.1) and their derivatives M(CO) mLm. The properties and structures of the compounds mentioned above have been discussed in detail [3,4,21b,98], and do not require special examination. The comparatively rare type of structure given by 63 (E = O) was discovered in the dinuclear complex of fe(diphenylphosphine)methane with Mn2(CO)5. It may be possible in this compound to see the existence of structures with monodentate coordination 62 [3], as well as connections between the metal, bonded to carbon atoms, and the oxygen atoms of any of the one to five carbonyl groups in a simultaneous participation 63 [4],... 

An interesting feature of hydrido transition metal-PF3 complexes is that apart from a few dinuclear systems (Section VI) only mononuclear systems are so far known and there is as yet no corresponding chemistry analogous to that of polynuclear carbonyl hydrido compounds. The trifluorophosphine metal hydrido compounds are usually highly acidic and can readily form metallate ions such as [M(PF3)m]x and [MH(PF3) r. 

For the mononuclear and dinuclear compounds, except V(CO)6, the mnnber of valence electrons per metal atom is 18. The EAN (effective atomic number) of the metal is the number of electrons of the d" configuration added to twice the number of CO groups, one electron being further added in the case of metal-metal bonded dinuclear systems. For trinuclear, tetranuclear, and hexanuclear compoimds (metal-carbonyl clusters), the cluster valence electron counting is 48, 60, and 86, respectively. As the [K(cryptand 2.2.2)] derivative. As the tetraalkylammonium derivative. As the tetrachloroaluminate. 

Uncharged mononuclear and polynnclear metal carbonyls are known for the group 5 to group 10 metals. The EAN rule see Effective Atomic Number Rule) is normally obeyed, so elements with an even atomic number form mononuclear compounds, for example, Cr(CO)6, Fe(CO)5, and Ni(CO)4, while elements with an odd atomic number form dinuclear compounds, for example, Mn2(CO)io and Co2(CO)g, containing metal-metal bonds. 

Metal carbonyls are characterized by IR-active vibrations associated with the carbonyl groups. Especially studied are the carbonyl stretching vibrations around 2000cm". The vibrational spectra give important information about (a) the electronic distribution within the M-CO bond in terminally bonded carbonyl groups (b) the molecular structure associated with the number of bands observed and (c) the type of bonding in dinuclear and polynuclear compounds. 

The same compound reacts differently with dinuclear metal carbonyls, e.g. ... 

Similarly, several other covalent molecules, such as halogens, organometallic compounds, and carbon tetrachloride, take part in such reactions. Susuki and Tsuji reported that addition of carbon tetrachloride to olefins and carbonyla-tion are catalyzed by dinuclear metal carbonyl complexes like [7r-CsHsFe(CO)2]2 and [7r-CsH5Mo(CO)3 ]2 S8-S9>. 

Oxidative cleavage of dinuclear metal carbonyls with tin compounds to form transition metal tin bond has been reported 63>. 

It should be noticed that iron complexes produce mostly monocarbonyl compounds, while nickel complexes give dicarbonyl compounds. The difference between nickel and iron was explained by the structures of the mononuclear iron complex and the dinuclear nickel complex formed by the reactions of the metal carbonyls with phenyl lithium as shown below 92>. 

For mononuclear complexes, reactions at coordinated ligands is a topic of major study, and numerous reviews and even books have been written on this topic. At the time of writing this review, the authors could find no major review articles in this area for dinuclear compounds. The best examples are probably those on the reactions of coordinated molybdenum sulfides discussed earlier. A related observation is the reaction of metal carbonyls with Lewis acids. It has been observed by Shriver and coworkers that carbonyl ligands bridging metal-metal bond atoms show increased tendency to coordinate Lewis acids (equation 96). 

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