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

The reaction of the α-stabilized bis-ylide [Ph 3 P C(CO 2 Me)−C(CO 2 Me) PPh 3 ] with M(II) bis-solvato derivatives, cis -[M(C 6 F 5 ) 2 (OC 4 H 8 ) 2 ] or [M(C∧X)(OC 4 H 8 ) 2 ]ClO 4 (M = Pd, Pt; C∧X = orthometalated ligand), yields the ylide-carbene complexes cis -[M(C 6 F 5 ) 2 {C(CO 2 Me)−C(CO 2 Me)(PPh 3 )}(PPh 3 )] (M = Pt 1a, Pd 1b ) or [M(C∧X){C(CO 2 Me)−C(CO 2 Me)(PPh 3 )}(PPh 3 )]ClO 4 (M = Pt, C∧X = o -CH 2 C 6 H 4 P( o -tolyl) 2, 2; M = Pd, C∧X = o -CH 2 C 6 H 4 P( o -tolyl) 2, 3; CH 2 C 9 H 6 N-C 8,N, 4; NC 5 H 4 - o -C 6 H 4, 5; C 13 H 8 N, 6 ). The reaction appears to proceed with P C bond cleavage, generating a carbene-ylide ligand [:C(CO 2 Me)−C(CO 2 Me)PPh 3 ] and a PPh 3 group, both coordinated to the metal center. The reaction of the solvato complexes [M(C∧X)(OC 4 H 8 )(PPh 3 )]ClO 4 with the bis-ylide results in the selective formation of [M(C∧X)(PPh 3 ) 2 ]ClO 4 (M = Pt, C∧X = o -CH 2 C 6 H 4 P( o -tolyl) 2, 7; M = Pd, C∧X = CH 2 C 9 H 6 N-C 8,N, 8 ), showing that when one vacant position is available, only the PPh 3 group binds to the metal center, and the carbene fragment decomposes to O PPh 3 and dimethylfumarate. On the other hand, the reaction of the bis-solvato precursors [Pd(C 6 F 5 )(L)(OC 4 H 8 ) 2 ]ClO 4 with the bis-ylide yields the corresponding metallacyclopropane [Pd{ trans - C (C 6 F 5 )(CO 2 Me)− C (PPh 3 )(CO 2 Me)}(L)(PPh 3 )](ClO 4 ) (L = SC 4 H 8, 9; PPh 3, 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(C 6 F 5 ) bond and coordination of the newly generated ylide function. The crystal structure of complex 1a ·CH 2 Cl 2 has been analyzed by X-ray diffraction.