Nitrogen- vs Carbon-Coordination of the α-Cyano-Stabilized Phosphorus Ylide Ph3PC(H)CN. X-ray Crystal Structure of {Pd(dmba)[P(OMe)3][N⋮CC(H)PPh3]}(ClO4)

The reaction of the solvated complexes [Pd(CN)(PR'(3))(THF)](ClO(4)) [CN = 2-((dimethylamino)methyl)phenyl-C(1),N or dmba, 2-(1-(R)-(dimethylamino)ethyl)phenyl-C(1),N or (R)-dmphea; PR'(3) = PPh(3), P(OMe)(3)] with a stoichiometric amount of Ph(3)P=C(H)CN (CPPY) (1:1 molar ratio), in THF at low temperature, gives the cationic derivatives {Pd(CN)(PR'(3))[NC-C(H)=PPh(3)]}(ClO(4)), 4-6, in which the ylide ligand is N-coordinated to the Pd(II) center and trans to the ortho-metalated C(6)H(4) group, in an "end-on nitrile" coordination mode that is unprecedented for this ylide. The reaction of [Pd(CN)(NCMe)(2)](ClO(4)) (CN = dmba, (R)-dmphea) with Ph(3)P=C(H)CN (1:2 molar ratio) gives the bis(ylide) complexes [Pd(CN)(Ph(3)PCHCN)(2)](ClO(4)) (7, 8) in which one of the ylides is C-coordinated (trans to the NMe(2) group) and the other one is N-bonded (and trans to the C(6)H(4) group). Either by reaction of [Pd(CN)(NCMe)(2)](ClO(4)) with Ph(3)P=C(H)CN (1:1 molar ratio) or by reaction of the bis(ylide) complexes [Pd(CN)(Ph(3)PCHCN)(2)](ClO(4)) with [Pd(CN)(NCMe)(2)](ClO(4)) (1:1 molar ratio), very insoluble materials of stoichiometry [Pd(CN)(Ph(3)PCHCN)(ClO(4))] (9, 10) are obtained, which appear to be dinuclear derivatives with the ylide acting as a C,N-bridging group, [(CN)Pd(-C,N-Ph(3)PCHCN)(2)Pd(CN)](ClO(4))(2). At the same time, this ylide is shown to be sufficiently nucleophilic to promote the bridge-splitting of the dinuclear [Pd(-Cl)(CN)](2) complexes, giving the mononuclear derivatives [PdCl(CN)(Ph(3)PCHCN)] (11, 12) as a mixture of two isomers; in one of them, the ylide acts as a C-donor while in the other it acts as an N-donor. IR and NMR spectroscopies allow the unambiguous characterization of all of these products, and the X-ray crystal structure of {Pd(dmba)[P(OMe)(3)][NC-C(H)=PPh(3)]}(ClO(4)) (5) is reported. Complex 5 crystallizes in the monoclinic system, space group P2(1)/c, a = 12.5690(10) Å, b = 17.857(2) Å, c = 14.729(2) Å, beta = 92.560(10) degrees, Z = 4, V = 3302.5(6) Å(3), 4881 reflections with I > 2sigma(I) for the refinement of 423 parameters and 30 restraints, R1 = 0.0384, wR2 = 0.0961, and GOF = 1.044.