Synthesis and reactions involving the phosphine ligands of bis(phosphine)chromium and -molybdenum tetracarbonyl compounds

Synthesis of the compounds M(CO)₄(PPh₂H)(PPh₂R) (M = Cr, Mo; R = CH₂CH CH₂, CH₂C(CH₃) CH₂, CH₂CH CHCH₃, CH₂CH CHPh) is accomplished from the reaction of the appropriate allyl or substituted allyl chloride with [M(CO)₄(PPh₂H)PPh₂]^-. This latter reagent is generated in situ from M(CO)₄(PPh₂H)₂ and one equivalent of BuLi in THF. Addition of 2,2′-azobis(isobutylnitrile) (AIBN), a free radical catalyst, to M(CO)₄(PPh₂H)(PPh₂CH₂CHCH₂) causes the PH unit to add to the allylic double bond, giving M(CO)₄(Ph₂PCH₂CH₂CH₂PPh₂) (M = Mo, Cr). The compounds M(CO)₄(PPh₂H)(PPh₂CH CH₂), not accessible by the route above, can be made by the reaction of [M(CO)₄(PPh₂H)Cl]^- and PPh₂CHCH₂ in the presence of AgNo₃. Addition of base (PhLi) causes the cyclization of the phosphine ligands in these compounds, giving M(CO)₄(Ph₂PCH₂CH₂PPh₂).