Cobalt carbonyl derivatives structure

There are a number of amine-catalyzed carbonylation reactions which are catalyzed by cobalt carbonyl and iron carbonyl. It seems to me that these are insertion reactions of metal amides, where carbon monoxide is inserted and then some kind of a reduction or subsequent reaction gives the observed products, urea derivatives or carbamates in alcohols. We do not know the structure of the iron compound it is probably similar to the cobalt species shown. 

Unlike cobalt and rhodium, the chemistry of polynuclear iridium carbonyl derivatives has not been studied in detail (15a). Reduction of Ir4(CO)i2 under carbon monoxide with K2C03 in methanol gives the yellow tetranuclear hydride derivative [Ir4(CO)nH], whereas under nitrogen the brown dianion [Ir8(CO)2o]2- has been isolated as a tetraalkylam-monium salt (97). It has been suggested that the structure of the dianion could result from the linking of two iridium tetrahedra, although its formulation so far is based only on elemental analyses. Clearly such an interesting compound deserves further chemical and structural characterization. 

The structure of the cationic complex [Co2(p,Tj2,772-HC2CH2PEt3)(CO)6]+ has been established by an X-ray diffraction study (Fig. 13).79 The main difference between this type of cationic derivative and the parent propargylium complexes is the absence of any anchimeric assistance from the cobalt to the carbocation center. The cobalt-carbon interaction is replaced by a direct interaction with the heteroatom of the nucleophile. This is reflected in the infrared spectra of the [Co2(/x,r72,T72-HC2CH2nuc)(CO)fi]+ species. The values of the carbonyl stretching bands lie in between those of [Co2(ju.,Tj2,Tj2-HC2CH2OH)(CO)6] and [Co2(m,t, t73-HC2CH2)(CO)6]+. 

An X-ray crystallographic investigation 116) of Co4(CO)io(EtC2Et) has revealed the structure shown in (VI). The structure is derived from that of the parent carbonyl, Co4(CO)i2> by substitution of two bridging carbonyl groups with an alkyne unit coupled with a substantial modification of the C04 skeleton. The structure is different from that first postulated for Co4(CO)io(RC2R ) complexes, where it was assumed that the basic tetrahedron of cobalt atoms remained intact 48, 117). 

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