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Novel transient phosphinidene complex Ph−PMo(CO)4PMe3, generated from a 7-phosphanorbornadiene precursor, adds to CC and CC bonds to give Mo(CO)4PMe3-complexed phosphiranes and phosphirenes. The cis-PMe3ligand weakens the interaction between the molybdenum complex and the three-membered ring. Under mild CO pressure the Mo(CO)4PMe3transition metal group detaches from the phosphorus center of the ring structure by selective CO substitution. The resulting byproduct Mo(CO)5PMe3can be reused in the synthesis of the phosphinidene precursor.

A phosphaspiropentene is the plausible kinetic product from the addition of dichlorocarbene to a phosphatriafulvene, which rearranges to a novel P-substituted triafulvene. The calculated barrier of 18.6 kcal mol^-1 for this process is consistent with the temperature of −40 °C at which this reaction proceeds.

Novel terminal rhodium- and cobalt-complexed phosphinidenes, Cp*(PR3)Rh&dbd;PAr (3−5) and Cp(PPh3)Co&dbd;PAr (8), were obtained by dehydrohalogenation of the primary phosphine complexes Cp*RhCl2(PH2Ar) (2) and CpCoI2(PH2Ar) (7) in the presence of a phosphine. X-ray crystal structures are reported for Cp*(PPh3)Rh&dbd;PMes* (3) and Cp(PPh3)Co&dbd;PMes* (8). A comparative reactivity study and a computational survey were performed on the Co-, Rh-, and Ir-containing phosphinidene complexes. All react with organic dihalides to form phosphaalkenes, with the rhodium congener being far more reactive than the iridium and cobalt complexes. Density functional theory calculations give geometrical parameters and ³¹P NMR chemical shifts in good agreement with experimental data. The rhodium congeners exhibit the most pronounced charge separation of the Rh&dbd;P bond, which may explain its higher reactivity. The M−L bond is strong in all Cp(L)M&dbd;PH (M = Co, Rh, Ir) complexes and inhibits reactivity at the metal center. Comparisons with the Zr-containing complex Cp2(PH3)Zr−PH are made.

Stable, crystalline iridium-complexed phosphinidenes, Cp*(L)Ir&dbd;PR, are readily synthesized by (a) the reaction of Cp*(L)IrCl2 (2, L = PPh3) with LiPHMes* and (b) dehydrohalogenation of Cp*(PH2R)IrCl2 (5, R = Mes*, Is, Mes) with in situ capturing of transient Cp*Ir&tbd1;PR (4) with phosphines, phosphites, arsines, isocyanides, and carbon monoxide (L). Cp*Ir&tbd1;PR eluded direct detection. The X-ray crystal structures are reported for Cp*(PPh3)Ir&dbd;PMes* (3) and Cp*(CO)Ir&dbd;PMes* (15). The more congested 3 has an E configuration for its Ir&dbd;P bond, whereas 15 is obtained in its Z form. The ³¹P NMR chemical shifts and ²JPP coupling constants are diagnostic for the E and Z forms. More shielded phosphinidene resonances and larger coupling constants are typical for the E isomers. These iridium-complexed phosphinidenes react with gem-diiodides to form phosphaalkenes, but not with carbonyl groups.