Synthesis, spectroscopic and structural characterisation of chromium(0), molybdenum(0) and tungsten(0) complexes involving primary and secondary phosphines

[M(CO)6] (M=Mo or W) reacts with 4.5 molar equivalents of L (L=PPh2H or PPhH2) in excess ethanolic NaBH4 to yield the fac-trisubstituted species [M(CO)3(L)3] in good yield, with no evidence for species with lower degrees of substitution. IR, 1H-, 13C{1H}-, 31P{1H}- and 95Mo-NMR spectroscopy on these compounds, together with X-ray crystallographic studies on two examples, confirm the fac-tricarbonyl arrangement both in solution and in the solid state. Similar reactions involving PCy2H yield only the cis-disubstituted species [M(CO)4(PCy2H)2]. Reaction of [M′(CO)4(nbd)] (M′=Cr or Mo) or [W(CO)4(TMPA) (TMPA=tetramethylpropylenediamine) with two molar equivalents of L (L=PPh2H, PPhH2 or PCy2H) or with one molar equivalent of L–L (L–L=o-C6H4(PH2)2, PhHPCH2CH2PHPh or PhHPCH2CH2CH2PHPh) in warm toluene solution give [M′(CO)4(L)2], [W(CO)4(L)2], [M′(CO)4(L–L)] or [W(CO)4(L–L)], respectively. Spectroscopic studies indicate that these all exist as cis-disubstituted species in solution and single-crystal X-ray analyses on three examples confirm this assignment in the solid state. The primary and secondary phosphines act as neutral two-electron donors in all cases with retention of the P–H functions. Trends in the spectroscopic and structural data are discussed