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Herein is reported the structural characterization and scalable preparation of the elusive iron–phosphido complex FpP( t Bu)(F) (2-F, Fp = (Fe(η 5 -C 5 H 5 )(CO) 2 )) and its precursor FpP( t Bu)(Cl) (2-Cl) in 51% and 71% yields, respectively. These phosphide complexes are proposed to be relevant to an organoiron catalytic cycle for phosphinidene transfer to electron-deficient alkenes. Examination of their properties led to the discovery of a more efficient catalytic system involving the simple, commercially available organoiron catalyst Fp 2 . This improved catalysis also enabled the preparation of new phosphiranes with high yields ( t BuPCH 2 CHR; R = CO 2 Me, 41%; R = CN, 83%; R = 4-biphenyl, 73%; R = SO 2 Ph, 71%; R = POPh 2 , 70%; R = 4-pyridyl, 82%; R = 2-pyridyl, 67%; R = PPh 3 + , 64%) and good diastereoselectivity, demonstrating the feasibility of the phosphinidene group-transfer strategy in synthetic chemistry. Experimental and theoretical studies suggest that the original catalysis involves 2-X as the nucleophile, while for the new Fp 2 -catalyzed reaction they implicate a diiron–phosphido complex Fp 2 (P t Bu), 4, as the nucleophile which attacks the electron-deficient olefin in the key first P–C bond-forming step. In both systems, the initial nucleophilic attack may be accompanied by favorable five-membered ring formation involving a carbonyl ligand, a (reversible) pathway competitive with formation of the three-membered ring found in the phosphirane product. A novel radical mechanism is suggested for the new Fp 2 -catalyzed system. 

Acyl(chloro)phosphines RC(O)P(Cl)( t -Bu) have been prepared by formal insertion of tert -butyl phosphinidene ( t -Bu–P) from t -BuP A ( A = C 14 H 10 or anthracene) into the C–Cl bond of acyl chlorides. We show that the under-explored acyl(chloro)phosphine functional group provides an efficient method to prepare bis(acyl)phosphines, which are important precursors to compounds used industrially as radical polymerization initiators. Experimental and computational investigations into the mechanism of formation of acyl(chloro)phosphines by our synthetic method reveal a pathway in which chloride attacks a phosphonium intermediate and leads to the reductive loss of anthracene from the phosphorus center in a P( v ) to P( iii ) process. The synthetic applicability of the acyl(chloro)phosphine functional group has been demonstrated by reduction to an acylphosphide anion, which can in turn be treated with an acyl chloride to furnish dissymmetric bis(acyl)phosphines.