Novel, very stable ruthenium and osmium containing terminal phosphinidene complexes [(eta(6)-Ar)(L)M=Mes*] (Ar=benzene, p-cymene; L=PR(3), CO, and RNC) have been prepared by dehydrohalogenation of novel [(eta(6)-Ar)MX(2)(PH(2)Mes*)] complexes in the presence of a stabilizing ligand. Xray crystal structures are reported for [(eta(6)-C(6)H(6))(PPh(3))Rud=PMes*] (9) and [(eta(6)-pCy)(PPh(3))Os=PMes*] (4). Dehydrohalogenation in the absence of a stabilizing ligand resulted in the new P-spiroannulated Ru(2)P(2)-ring structure 16. Dehydrohalogenation in the presence of but-2-yne gave a novel phosphaallyl complex [(eta(6)-Ar)Ru(eta(3)-R(2)PC(Me)CHMe)] 26, for which an X-ray crystal structure is reported. The mechanism by which 16 and 26 are obtained is presumed to involve the intermediate formation of the 16-electron (eta(6)-benzene)Rud=PMes* phosphinidene complex.

Stable, crystalline iridium-complexed phosphinidenes, Cp*(L)IrdPR, are readily synthesized by (a) the reaction of Cp*(L)IrCl 2 (2, L) PPh 3) with LiPHMes* and (b) dehydrohalogenation of Cp*(PH 2 R)IrCl 2 (5, R) Mes*, Is, Mes) with in situ capturing of transient Cp*Irt PR (4) with phosphines, phosphites, arsines, isocyanides, and carbon monoxide (L). Cp*Irt PR eluded direct detection. The X-ray crystal structures are reported for Cp*(PPh 3)IrdPMes* (3) and Cp*(CO)IrdPMes* (15). The more congested 3 has an E configuration for its IrdP bond, whereas 15 is obtained in its Z form. The 31 P NMR chemical shifts and 2 J PP 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.

Novel terminal rhodium-and cobalt-complexed phosphinidenes, Cp*(PR 3 ) and Cp(PPh 3 )CodPAr (8), were obtained by dehydrohalogenation of the primary phosphine complexes Cp*RhCl 2 (PH 2 Ar) (2) and CpCoI 2 (PH 2 Ar) (7) in the presence of a phosphine. X-ray crystal structures are reported for Cp*(PPh 3 )RhdPMes* (3) and Cp(PPh 3 )CodPMes* (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 31 P NMR chemical shifts in good agreement with experimental data. The rhodium congeners exhibit the most pronounced charge separation of the RhdP bond, which may explain its higher reactivity. The M-L bond is strong in all Cp(L)MdPH (M ) Co, Rh, Ir) complexes and inhibits reactivity at the metal center. Comparisons with the Zr-containing complex Cp 2 (PH 3 )Zr-PH are made.

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Bidentate ligands of the type Mes*PC(R)Py ((E)- 2, R = H; (Z)- 9, R = SiMe3; Mes* = supermesityl = 2,4,6-tri-tert-butylphenyl; Py = 2-pyridyl) were synthesized. Ligand (E)- 2 was synthesized by reacting Mes*P(Li)SiMe2(t-Bu) (4) with 2-pyridinecarboxaldehyde. Ligand (Z)- 9 was synthesized via a PdCl2(dppb)-catalyzed coupling reaction between 2-bromopyridine and Mes*PC(SiMe3)M ((E)- 7, M = ZnCl; (Z)- 8, M = MgBr). Compound (E)- 2 was also characterized by an X-ray crystal structure determination; it has a planar structure with the (E)-configuration. The complexes η1,η1-[Mes*PC(R)Py]PdCl2 (11, R = H; 12, R = SiMe3) were prepared by the reaction of bis(benzonitrile)palladium dichloride with (E)- 2 and (Z)- 9, respectively. The complexes η1,η1-[Mes*PC(R)Py]MePdCl (13, R = H; 14, R = SiMe3) were obtained by a ligand exchange reaction of MePdCl(COD) with (E)- 2 and (Z)- 9, respectively. Complex 13 was alternatively prepared by reaction of 11 with methylmagnesium chloride. Complex 14 was unambiguously identified by an X-ray crystal structure determination. Both 13 and 14 reacted with CO, resulting in the acetyl complexes η1,η1-[Mes*PC(R)Py]AcPdCl (16, R = H; 17, R = SiMe3).