Dinuclear metal carbonyls

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... 

There is still controversy over the primary steps in the photolysis of dinuclear metal carbonyls, such as Mn2(CO)10 or [CpFe(CO)2]2, and the field has been recently reviewed (102,103). The controversy has centered on the number of primary photoproducts, their identity, the effects of photolysis wavelength, and the possibility of heterophotolysis (21,103). 

The structures of the dinuclear metal carbonyls (containing two metal atoms) involve either metal-metal bonds or bridging CO groups, or both. For example, the structure of Fe2(CO)9, diiron nonacar-bonyl, contains three CO ligands that form bridges between the iron atoms, and each iron atom also has three other CO groups attached only to that atom. 

A dipole-dipole model reproduces factor group frequencies of i>(CO) in a variety of dinuclear metal carbonyls... 

Examination of the i.r. spectra of trans-[RhX(CO)(PPh3)2] has shown that the frequency of the a,(RhCO) vibration decreases in the order X = F > Cl > Br > I, corresponding to an increase in the jr-acceptor power of the trans ligand. Meanwhile, a theoretical treatment of the CO stretching vibrations of several dinuclear metal carbonyls, including [RhX(CO)2]2 = Cl, Br, or... 

C(OCH3)R] (59) are certainly formed via the initial steps of the above reactions. Isomerization of 59 through pairwise formation of carbene bridges should be a low-energy process. Hence it appears that simple dinuclear metal carbonyls in general have all the prerequisites for yielding bis-/x-methylene complexes in the course of the Fischer procedure for metal carbene synthesis. 

Thus, it is also characteristic of the dinuclear metal carbonyls that only... 

One of the broadest and historically most important areas of dimetal chemistry is that of the simple carbonyl complexes (see Carbonyl Complexes of the Transition Metals). As mentioned above, Co2(CO)s, Fe2(CO)9, and Mn2(CO)io were among the first metal-metal bonded complexes characterized. To this day, these complexes continue to be involved in new chemistry, for example, Co2(CO)g found recent use in a one-pot synthesis of tricyclic 5-lactones .In the case of molybdenum, the zerovalent carbonyl is monomeric however, reduction gives a dinuclear metal carbonyl dianion in which the metal is in the [-1] oxidation state (equation 6). 

The reactions of silanes, particularly R3SiH, with dinuclear metal carbonyls provides a convenient route to a variety of silicon-metal bonds The syntheses follow a two step path ... 

Table l Selected Reactions of Dinuclear Metal Carbonyls with Silicone Hydrides... 

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

As with dinuclear metal carbonyls ( 13.2.4.2.) the prevalent mode of photoreaction of trinuclear metal-carbonyl complexes is cleavage of a metal-metal bond. Subsequent decay of the bond-cleaved intermediate can yield fragmentation or substitution of the complex. These reactions are discussed in 13.3. 

The properties of the PPN cation have also facilitated the crystallization of salts of the dinuclear metal carbonyl anions, [M2(CO)10]2 (M = Cr, Mo, W), and permitted a crystal-structure determination7 of these remarkable complexes. The dinuclear chromium decacarbonyl anion was first prepared by Behrens and Vogl8 by the reaction of Cr(CO)6 with NaBH4 in liquid NH3 at 40°. More recently Hayter9 prepared dinuclear decacarbonyl anions of all three Group VI metals by a photochemical process and isolated them as the tetraethylammonium salts. A convenient synthesis involving isolation of the PPN salts of these anions is described in Sec. D. 

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>. 

Neutral metal carbonyls usually undergo one- or two-electron reductions by several reducing agents. The reduced species normally obey the next inert gas rule and the formulas can be easily predicted accordingly. Dinuclear metal carbonyls on reduction give mononuclear anionic species mononuclear metal carbonyls may become doubly charged with loss of CO or undergo a one-electron reduction with formation of dinuclear anions (equations 36-38). 

The sonoluminesence of mono- and dinuclear metal carbonyls in silicone oil including Fe(CO)s, Cr(CO)6, Mo(CO>6, W(G0)6, Mn2(GO)io, and Go2(GO)s has been investigated by Suslick et Atomic emission was observed from the metals, indicative of the high temperatures produced by cavitation. The presumed mechanism involved pyrolysis of the metal carbonyl compound to generate excited-state metal atoms in the cavity, followed by activation through collision with a third vapor-phase molecule in the system. Individual atomic emission lines were not well resolved. Rather, the peaks were broadened due to the high pressures produced upon cavitation collapse. The intensity of the emission followed the pattern Gr > Mo > Fe > W >> Mn, Co. 

Horvath IT, Bor G, Garland M, Pino P (1986) Cobalt-rhodium heptacarbonyl a coordinatively unsaturated dinuclear metal carbonyl. Organometallics 5(7) 1441-1445... 

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