Studies of chelation. Part 6. Reactions of ditertiary alkylphosphine complexes of Group 6 metal carbonyls with nitrosonium hexafluorophosphate. Preparation and reactions of hydrido-complexes of chromiurn(II) molybdenum(II), and tungsten(II)
Abstract
Substitution of cis-[M(CO)4(L–L)][M = Cr, Mo, or W; L–L = R2P(CH2)2PR2(dcpe, R = C6H11; dmpe, R = Me)] by [NO][PF6] in methyl cyanide produces [M(CO)3(NO)(L–L)][PF6] which probably has the fac configuration. Where M = Cr, the final product of reaction is paramagnetic fac-[Cr(NCMe)3(NO)(L–L)][PF6]2 which undergoes exchange of MeCN for Me2CO in acetone solution. The processes leading to these products have been examined. Where M = W, addition of further [NO][PF6] produces an isomeric complex which is probably dimeric. With cis-[Mo(CO)2(dmpe)2], [NO][PF6] produces [MoH(CO)2(dmpe)2][PF6] in hydrogen-containing solvents, but in liquid SO2 the product is [Mo(CO)2(SO2)(dmpe)2][PF6]2. Oxidation of cis-[Cr(CO)2(dmpe)2] with [NO][PF6] gives both trans-[Cr(CO)2(dmpe)2][PF6] and [CrH(CO)2(dmpe)2][PF6] in methanol, but in methyl cyanide cis-[Cr(NCMe)(CO)2(dmpe)2[PF6]2 is formed. The preparation of [WH(CO)2(dmpe)2]+ is reported. The hydride [MoH(CO)2(dmpe)2][PF6] is reduced by 1,8-bis(dimethylamino)naphthalene to cis-[Mo(CO)2(dmpe)2], but [MoH(CO)2(dmpe)2]I is converted into [MoI(CO)2(dmpe)2] by the same reagent. Reaction with alkyl halide RX (R = prop-2-enyl or benzyl) and with iodine produces [MoX(CO)2(dmpe)2]+. The new complexes are characterised by i.r., n.m.r. (1H and 31P), e.s.r., and visible spectra, and by conductivity and microanalysis. Comparisons are made with reactions of analogous complexes of Ph2P(CH2)2PPh2(dppe) and Ph2PCH2PPh2(dppm), from which it is apparent that the precise nature of the ditertiary phosphine exercises an important influence on the course of both oxidation and substitution reactions in this system.
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