The reaction of the α-stabilized bis-ylide [Ph3PC(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
PC 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 OPPh3 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 complexsimilar to 1−6followed 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.