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)

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Abstract
The reaction of the solvated complexes [Pd(C⌒N)(PR‘3)(THF)](ClO4) [C⌒N = 2-((dimethylamino)methyl)phenyl-C1,N or dmba, 2-(1-(R)-(dimethylamino)ethyl)phenyl-C1,N or (R)-dmphea; PR‘3 = PPh3, P(OMe)3] with a stoichiometric amount of Ph3PC(H)CN (CPPY) (1:1 molar ratio), in THF at low temperature, gives the cationic derivatives {Pd(C⌒N)(PR‘3)[N⋮CC(H)PPh3]}(ClO4), 4−6, in which the ylide ligand is N-coordinated to the PdII center and trans to the ortho-metalated C6H4 group, in an “end-on nitrile” coordination mode that is unprecedented for this ylide. The reaction of [Pd(C⌒N)(NCMe)2](ClO4) (C⌒N = dmba, (R)-dmphea) with Ph3PC(H)CN (1:2 molar ratio) gives the bis(ylide) complexes [Pd(C⌒N)(Ph3PCHCN)2](ClO4) (7, 8) in which one of the ylides is C-coordinated (trans to the NMe2 group) and the other one is N-bonded (and trans to the C6H4 group). Either by reaction of [Pd(C⌒N)(NCMe)2](ClO4) with Ph3PC(H)CN (1:1 molar ratio) or by reaction of the bis(ylide) complexes [Pd(C⌒N)(Ph3PCHCN)2](ClO4) with [Pd(C⌒N)(NCMe)2](ClO4) (1:1 molar ratio), very insoluble materials of stoichiometry [Pd(C⌒N)(Ph3PCHCN)(ClO4)] (9, 10) are obtained, which appear to be dinuclear derivatives with the ylide acting as a C,N-bridging group, [(C⌒N)Pd(μ-C,N-Ph3PCHCN)2Pd(C⌒N)](ClO4)2. At the same time, this ylide is shown to be sufficiently nucleophilic to promote the bridge-splitting of the dinuclear [Pd(μ-Cl)(C⌒N)]2 complexes, giving the mononuclear derivatives [PdCl(C⌒N)(Ph3PCHCN)] (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][N⋮CC(H)PPh3]}(ClO4) (5) is reported. Complex 5 crystallizes in the monoclinic system, space group P21/c, a = 12.5690(10) Å, b = 17.857(2) Å, c = 14.729(2) Å, β = 92.560(10)°, Z = 4, V = 3302.5(6) Å3, 4881 reflections with I > 2σ(I) for the refinement of 423 parameters and 30 restraints, R1 = 0.0384, wR2 = 0.0961, and GOF = 1.044.

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