Stabilized bis-ylides as a source of carbene ligands in palladium(II) and platinum(II) complexes

The reaction of the a-stabilized bis-ylide [Ph3P=C(CO2Me)-C(CO2Me)=PPh3] with M(II) bis-solvato derivatives, cis-[M(C6F5)(2)(OC4H8)(2)] or [M(Cboolean ANDX)(OC4H8)(21)ClO4 (M = Pd, Pt; Cboolean ANDX = orthometalated ligand), yields the ylide-carbene complexes cis-[M(C6F5)(2){C(CO2Me)-C(CO2Me)(PPh3)}(PPh3)](M = Pt 1a, Pd 1b) or [M(Cboolean ANDX){C(CO2Me)-C(CO2Me)(PPh3)}(PPh3)]ClO4 (M = Pt, Cboolean ANDX = o-CH2C6H4P(o-tolyl)(2), 2; M = Pd, Cboolean ANDX = o-CH2C6H4P(o-tolyl)(2), 3; CH2C9H6N-C-8,N, 4; NC5H4-o-C6H4, 5; C13H8N, 6). The reaction appears to proceed with P=C bond cleavage, generating a carbene-ylide ligand [:C(CO2Me)-C(CO2Me)PPh3] and a PPh3 group, both coordinated to the metal center. The reaction of the solvato complexes [M(Cboolean ANDX)(OC4H8)(PPh3)]ClO4 with the bis-ylide results in the selective formation of [M(Cboolean ANDX)-(PPh3)(2)]ClO4 (M = Pt, Cboolean ANDX = o-CH2C6H4P(o-tolyl)(2), 7; M = Pd, Cboolean ANDX = CH2C9H6N-C-8,N, 8), showing that when one vacant position is available, only the PPh3 group binds to the metal center, and the carbene fragment decomposes to O=PPh3 and dimethylfumarate. On the other hand, the reaction of the bis-solvato precursors [Pd(C6F5)(L)(OC4H8)(2)]ClO4 with the bis-ylide yields the corresponding metallacyclopropane [Pd{trans-C(C6F5)(CO2Me)-C(PPh3)(CO2Me)}(L)(PPh3)](ClO4) (L = SC4H8, 9; PPh3, 10), probably through the initial formation of an ylide-carbene complex-similar to 1-6-followed by the migratory insertion of the carbene ligand into the Pd-C(C6F5) bond and coordination of the newly generated ylide function. The crystal structure of complex 1a.CH2Cl2 has been analyzed by X-ray diffraction.