Stabilized Bis-ylides as a Source of Carbene Ligands in Palladium(II) and Platinum(II) Complexes

The reaction of the α-stabilized bis-ylide [Ph3PC(CO2Me)−C(CO2Me)PPh3] with M(II)
bis-solvato derivatives, cis-[M(C6F5)2(OC4H8)2] or [M(C∧X)(OC4H8)2]ClO4 (M = Pd, Pt; C∧X
= orthometalated ligand), yields the ylide-carbene complexes cis-[M(C6F5)2{C(CO2Me)−C(CO2Me)(PPh3)}(PPh3)] (M = Pt 1a, Pd 1b) or [M(C∧X){C(CO2Me)−C(CO2Me)(PPh3)}(PPh3)]ClO4 (M = Pt, C∧X = o-CH2C6H4P(o-tolyl)2, 2; M = Pd, C∧X = o-CH2C6H4P(o-tolyl)2, 3;
CH2C9H6N-C8,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(C∧X)(OC4H8)(PPh3)]ClO4 with the bis-ylide results in the selective formation of [M(C∧X)(PPh3)2]ClO4 (M = Pt, C∧X = o-CH2C6H4P(o-tolyl)2, 7; M = Pd, C∧X = CH2C9H6N-C8,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.