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DOI: 10.1039/A703948D (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1997, 3589-3598

Synthesis of acylphosphine complexes by controllable migration of acyl groups from molybdenum to phosphido ligands[hair space]†

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Harry Adams, Neil A. Bailey, Peter Blenkiron and Michael J. Morris

Abstract

The acyl complexes [Mo(COR1)(CO)2(PPh2H)(η-C5H5)] (R1 = Me or Et) have been prepared in high yield by the reaction of [MoR1(CO)3(η-C5H5)] with PPh2H. Deprotonation of the diphenylphosphine ligand with 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu) at –78 °C produced a phosphorus-centred anion which can be alkylated by treatment with R2I (R2 = Me or Et) to give the substituted phosphine acyl complexes [Mo(COR1)(CO)2(PPh2R2)(η-C5H5)], or acylated with R2COCl to produce acylphosphine acyl complexes [Mo(COR1)(CO)2(PPh2COR2)(η-C5H5)]. If the deprotonation is carried out at room temperature, however, migration of the metal acyl group to the phosphorus atom occurs to give the molybdenum-centred anion [Mo(CO)2(PPh2COR1)(η-C5H5)]–, which can in turn be alkylated with R2I to give the acylphosphine alkyl complexes [MoR2(CO)2(PPh2COR1)(η-C5H5)]. The metal-centred anion also undergoes typical reactions with H+ and chlorinated solvents to give [MoX(CO)2(PPh2COR1)(η-C5H5)] (X = H or Cl). Mechanistic studies showed that (i) on deprotonation of the related complex [MoMe(CO)2(PPh2H)(η-C5H5)] the methyl group does not undergo migration to phosphorus, and (ii) the reaction is largely intramolecular but with a measurable intermolecular component. A mechanism is therefore proposed involving nucleophilic attack on the acyl carbon atom by the anionic phosphido ligand. Full spectroscopic data for the new complexes are reported and interpreted, and the crystal structure of [Mo(COMe)(CO)2(PPh2COMe)(η-C5H5)] has been determined.

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