267 the reduced c o l species of these along with

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Unformatted text preview: loximes) as i11ustrated in Fig. 26.7. The reduced c o l species of these, along with vitamin 3 6M. RAVIKANTH T. K. CHANRESHEKAR, and Structure and B onding, 82, 105-88 (1995). 37 R. S . DICKSON, rganometallic Chemistry o Rhodium O f and Iridium, Academic press, New yo&, 1983, 432 pp.; C . WHITE,Organometallic Compounds o Cobalt, Rhodium f and Iridium, Chapman & Hall, London 1985, 296 pp. 1140 Cobalt, Rhodium and Iridium Carbonyls (see p . 926) Because they possess an odd number of valence electrons the elements of this group can only satisfy the 18-electron rule in their carbonyls if M-M bonds are present. In accord with this, mononuclear carbonyls are not formed. Instead [M2(C0)81, [M4(C0)12] and [M6(CO)i61 are the principal binary carbonyls of these elements. But reduction of [Co2(CO),] with, for instance, sodium amalgam in benzene yields the monomeric and tetrahedral, 18-electron ion, [Co(CO)4]-, acidification of which gives the pale yellow hydride, [HCo(C0)4]. Reductions employing Na metal in liquid NH3 yield the “super-reduced’’ [M(CO),]’- (M = Co, Rh, Ir) containing these elements in their lowest formal oxidation state.(38) The importance of cobalt carbonyls lies in their involvement in hydroformylation reactions discussed above. The original, and still widely used, process depends on the use of cobalt salts rather than the newer rhodium catalysts (pp. 1134-5). The mechanism of the cobalt cycle is more difficult to ascertain but it seems clear that the active agent is the hydride, [HCo(C0)41. It is, moreover, plausible that the cycle is basically the same as that outlined in Fig. 26.5 but starting with loss of CO from [HCo(C0)4] rather than loss of phosphine from [Rh(CO)H(PPh3)3],so producing a comparable coordinatively unsaturated inte...
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This note was uploaded on 10/12/2012 for the course CHEMISTRY CHM1040 taught by Professor Jhon during the Spring '12 term at Florida A&M.

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