Cobalt carbonyls structures

The flexible ROC(0)CH2Co(CO)3PR 3 complexes develop a quite peculiar architecture exhibited clearly in the crystalline phase and also in solution [7]. In the absence of (configurational) centres of chirality, the unit cell (Z = 2 or 4) contains always one (or occasionally two) pair(s) of chiral enantiomeric molecules, related by a centre of symmetry. If stereogenic centre(s) is (are) present either in the (ester) alkyl moiety or in the phosphine ligand, individual (non-centrosymmetric) molecules with chiral conformations are formed. A survey of the published alkyl- and acyl-cobalt carbonyl structures [8] showed that this behaviour is quite general in the self-organization of these (and actually also other) transition metal complexes in the crystalline phase. 

Dendrimers containing metal complexes in the branches. In these compounds (Fig. lc), metal complexes may play the role of connectors along the branches of a dendritic structure as in the case of (tpy)Ru(tpy)2+ (tpy=2,2 6, 2"-ter-pyridine) [6], or may be attached to specific sites as in the case of cobalt carbonyls [7]. 

Nickel carbonyl radicals show an even greater tendency than cobalt carbonyls to cluster in a krypton matrix. Three binuclear nickel carbonyls have been detected by EPR spectroscopy in the products of y-irradiated Ni(CO)4 in Kr, yet no mononuclear species has been positively identified (65). 13C hyperfine structure has... 

Fig. 15. The oloso distorted octahedral structure of the cobalt carbonyl acetylene complex Co4(CO)ioC2Et2 (50).

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. 

One of the complexes formed in the reaction of diphenylacetylene and iron dodecacarbonyl is a red, crystalline compound of the composition [Fe2(CO)6(PhC2Ph)], which, on reduction with sodium in liquid ammonia, gives dibenzyl (117). By analogy with the cobalt carbonyl complex, structure (XXXV M = Fe) is proposed, in which the 7r-elcctrons of the triple... 

Co6S(SEt)4(CO)M] respectively (Table 80). In the absence of solvent [Co2(CO)8] and EtSH form [Co5(SEt)5(CO)10]"7 for which a crystal structure is also available.998 In these cobalt-carbonyl-thiolate systems the S atoms doubly or triply bridge metal centres and there appears to be no examples where RS" functions as a monodentate ligand. 

The synthesis of cobalt carbonyl-boimd silanetriol, Coa(CO)9CSi(OH)a (11) was originally reported by Seyferth et al. (34) by careful hydrolysis of Si—Cl bonds present in Coa(CO)9CSiCla (Scheme 8B). The X-ray crystallographic measurement (35) reveals a cage structure for compound 11. The OH groups present in 11 can be used further for the buildup of a number of heterosiloxanes. The cobalt carbonyl-boimd silanetriol 11 exhibits very high catalytic activity in the hydroformylation of 1-hexene in a biphasic vide infra) system (35). 

In solution these carbonyl hydrides act as very weak monobasic acids. The iron and cobalt carbonyl hydrides arc isoelectronic with Ni(CO)4 and have the same tetrahedral structure ... 

An octameric cage structure is found for the cobalt carbonyl cluster anchored silanetriol, Co3(CO)9CSi(OH)3 [25]. 

The catalytic carbonylation of benzylic halides to arylacetic acids has been improved by using two-phase systems under phase-transfer conditions [29]. Usually the reactions were performed with an excess of base in a biphasic system with a metal catalyst in the organic phase. As phase transfer catalysts surfactants are used, which appear to play an important transport function to move the cobalt carbonyl salt from the aqueous phase to the organic droplets (cf. Section 3.2.4). While the structure of the phase transfer co-catalyst was being studied it was observed that benzyltrialkylammonium salts were easily carbonylated. In some cases the yields of arylacetic acids are higher compared with the carbonylation of the corresponding benzyl halides [30]. 

In a very elegant mechanistic study by Ojima et al., involving the amidocarbonylation of three structurally related cyclic amides having methallyl side chains (utilizing cobalt carbonyl catalysis) they have demonstrated [23] that coordination of the amide carbonyl to the cobalt metal is essential for amidocarbonylation, whereas lactame formation is not. A general mechanism of amidocarbonylation, featuring the very unique hydrolysis (alcoholysis) of the acyl-cobalt bond by water (or alcohol) generated in situ, is reproduced in Scheme 1 [23]. 

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