Cobalt, rhodium and nickel

The preparation of organo-a-metal carbonyl complexes is discussed in section A. The occurrence of metal carbonyl alkyls and aryls closely parallels that of the carbonyl hydrides. All the known complexes in this class obey the 18-electron rule and they are rather reactive. 

The crystalline methyl complexes MeM(CO)5, where M = Mn or Re, are stable to oxidation and are thermally stable at room temperature [14,58]. The ethyl and n-propyl analogues of manganese pentacarbonyl are very much less stable [21]. The manganese complex (CO)sMn(CH2)3Mn(CO)s, prepared from Br(CH2)3Br, has an unusual proton magnetic resonance spectrum which suggests that there may be interaction of the hydrogens of the a-carbons with the manganese atom [59]. 

Treatment of MeMn(CO)s with ligands frequently gives substituted acyls, MeCOMn(CO)4L these reactions are discussed on p. 258. 

The volatile methylcobalt tetracarbonyl is thermally very unstable, m.p. —44°, and it decomposes at —35° [60]. It is readily oxidiz. The acylation reactions and the role of alkylcobalt carbonyl complexes in catalytic hydroformylation reactions are discussed on p. 334 and in chapter 9 respectively. 

Treatment of the anion [Co(CO)4] with carbon tetrachloride or bromo-form gives the unusual trinuclear complex Co3(CO)9CR 7.16, where R = Cl or H respectively [61]. The chloride may also be prepared from CCI4 and Co2(CO)s [62]. Analogous complexes where R = CH3 or R CH2 have been prepared from ac lenes and Co2(CO) (see p. 294). 

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Using diolefins and carefully selected Ziegler-type catalysts, it has been possible to obtain the 1,4-c/s-, the 1,4-trans-, and the 1,2-polybutadienes more than 98% pure. In the case of polyisoprene, the 3,4-structure is produced. There are thousands of patents involving every combination of pure or mixed main-group alkyls with transition-element compounds, each claiming advantages. However, compositions containing titanium, vanadium, chromium, and, in special cases, molybdenum, cobalt, rhodium, and nickel are primarily used. 

Cobalt-catalyzed cyclocotrimerization of alkynes and nitriles was pioneered by Wakatsuki, Bonneman, and co-workers [55], Highly selective intramolecular versions of this powerful pyridine-ring annulation were developed further using cobalt, rhodium, and nickel catalysts by Vollhardt, and others [53], These reactions include... 

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