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The synthesis and characterization of cationic platinum complexes of the type [(R(2)PC(2)H(4)PR(2))PtMe(OEt(2))]BAr(F) (R = Cy, Et) are reported. These electrophilic platinum cations are found to react quantitatively with arenes (benzene, toluene) at room temperature by undergoing intermolecular C-H activation with concomitant C-C coupling to generate complexes of the type [[Pt(R(2)PC(2)H(4)PR(2))](2)(mu-eta(3):eta(3)-biaryl)][BAr(F)](2). The dianionic biaryl ligands in these compounds exhibit a rare mu-eta(3):eta(3)-bis-allyl bonding mode and can be removed from the complex with stoichiometric oxidants to generate the free biaryl and [(R(2)PC(2)H(4)PR(2))Pt(mu-X)](2)[BAr(F)](2) (R = Cy, Et; X = Cl, I). The cationic platinum complexes [(R(2)PC(2)H(4)PR(2))PtMe(OEt(2))]BAr(F) (R = Cy, Et) are also quite reactive with water, forming the bridging hydroxide complexes [(R(2)PC(2)H(4)PR(2))Pt(mu-OH)](2)[BAr(F)](2) (R = Cy, Et). A possible mechanism is proposed for the C-C coupling reaction based upon the structures of these bridging biphenyl complexes, which provides a new perspective for the related palladium-catalyzed oxidative coupling of arenes to form biaryls.

Oxidative-addition reactions of Cl2CPN(SiMe3)2 with 1:2 Ni(COD)2/PPh3, Ni(PPh3)4, or (Ph3P)2Ni(C2H4) initially yields the phosphavinyl phosphonium complex Cl(Ph3P)Ni[η2-C(Cl)(PPh3)PN(SiMe3)2] (IIa). Addition of another equivalent of Ni(0) reagent to IIa results in the formation of the novel, dinuclear, phosphavinylidene−phosphorane complex Ni2Cl2(PPh3)2[μ2-η2:η2-C(PPh3)PN(SiMe3)2] (IIIa); the structure of IIIa was established by X-ray diffraction and contains a Ph3PCPR‘ ligand bridged between two four-coordinate, planar nickel atoms in a butterfly arrangement with a Ni−Ni distance that is too long for a significant bonding interaction. The Ph3PCPR‘ ligand, which may be viewed as a phosphavinylidene (CPR) ligand with a phosphine-donor substituent, acts as a six-electron donor to the two nickel atoms. This contrasts with the known diphosphaallene compounds of the types R3PCPR3 and RPCPR that act as two-electron donor ligands. When the reaction of the Ni(0) reagent is performed with Cl2CPMes* (Mes* = 2,4,6-tri-tert-butylphenyl), the mononuclear phosphonio−phosphavinyl complex Cl(Ph3P)Ni[η2-C(H)(PPh3)P(Mes*)] (Va) forms. The structure of Va was established by X-ray diffraction and contains a [C(H)(PR3)P(R‘)] ligand that acts as a three-electron donor to the Ni(PPh3)Cl fragment. This structure also exhibits a puckered, boat-shaped supermesityl ring. Both IIIa and Va exhibit labile PPh3 groups on nickel which are easily substituted with PEt3, but the carbon-bound PPh3 groups could not be substituted with PEt3.

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The oxidative addition reaction of Pt(PEt 3 ) 4 with Cl 2 CdPN(SiMe 3 ) 2 at low temperature (-50 °C) forms the η 1 -phosphavinyl complex cis-Cl(Et 3 P) 2 Pt[C(Cl)dPN(SiMe 3 ) 2 ] (Ia), which isomerizes to the trans-isomer (Ib) upon warming to 0 °C; the structure of Ib was determined by X-ray diffraction studies. Complex Ib reacts with Pt(PEt 3 ) 2 Cl 2 in the presence of 3 equiv of sodium benzophenone to generate the bridging, dinuclear η 1 ,η 2 -cyaphide complex Cl(Et 3 P) 2 -Pt(µ-η 1 ,η 2 -CtP)Pt(PEt 3 ) 2 (II) in good yield, providing a much simpler and higher yield preparation of II, which was synthesized and characterized previously by a more circuitous route. Compound II reacts with 0.5 equiv of [Cl 2 Pt(PEt 3 )] 2 or with 1 equiv of W(CO) 5 (THF) to generate the trinuclear metal-cyaphide complexes Cl(Et 3 P) 2 Pt[µ-η 1 ,η 1 ,η 2 -CtP{Pt(PEt 3 )-(Cl) 2 }]Pt(PEt 3 ) 2 (III) and Cl(Et 3 P) 2 Pt[µ-η 1 ,η 1 ,η 2 -CtP{W(CO) 5 }]Pt(PEt 3 ) 2 (IV), respectively, in which the lone pair of electrons on the CtP phosphorus atom is coordinated to a Pt-(PEt 3 )(Cl) 2 fragment in the former and to a W(CO) 5 fragment in the latter; the structure of IV was determined by X-ray diffraction studies. Compound II also reacts with MeI to form the methyl isocyaphide complex (Cl)(Et 3 P)Pt(µ-CdPMe)Pt(PEt 3 ) 2 (I) (Vc), in which the cyaphide (CtP -) ligand is converted to a methyl isocyaphide (CtPMe) ligand in a semibridging coordination mode. When compound II is reacted with MeOTf, the product is the cationic isocyaphide complex [(Cl)(Et 3 P) 2 Pt(µ-η 1 ,η 2 -CtPMe)Pt(PEt 3 ) 2 ](OTf) (Va), which is likely coordinated in an η 1 ,η 2 -bridging mode. Compound Va reacts with NaI to form Vc, which suggests that Va forms as an intermediate before Vc in the reaction of II with MeI.