TRANSITION-METAL STANNYL COMPLEXES .7. PREPARATION OF CARBENE COMPLEXES (PI-ARENE)(CO)2CRCR2 BY THE REACTION OF THE ANIONIC STANNYL COMPLEXES [(PI-ARENE)(CO)2CRSNPH3]- WITH R2CX2 OR [R2CX]Y

Carbene complexes (pi-arene)(CO)2Cr = CR2 are formed in substitution/elimination reactions from the anionic stannyl complexes K[(pi-arene)(CO)2CrSnPh3] [pi-arene = C6H6 (1a), 1,3,5-Me3C6H3 (1b), 1,2,4,5-Me4C6H2 (1c), C6Me6 (1d)] and organic dihalides R2CX2 containing activated C-X bonds or ionic halides [R2CX]Y. Bis(stannyl) complexes (pi-arene)(CO)2Cr(SnPh3)2 (3) and hydrido(stannyl)complexes (pi-arene)(CO)2Cr(H)SnPh3 are formed as byproducts due to the reaction of the eliminated Ph3SnCl with the anionic starting complexes or electron transfer reactions, respectively. The portion and ratio of the byproducts is largely influenced by the steric properties of both the (pi-arene)(CO)2Cr fragment and the organic halide. Pyridinylidene complexes (pi-arene)(CO)2Cr = CHCHCHCHNMe (2) are only obtained from 2-chloro-N-methylpyridinium tetrafluoroborat with 1a-c, but not with 1d. With the sterically less demanding halides [R2N = C(H)CI]CI [NR2 = NMe2, CH2(CH2)(n)N (n = 3, 4)] or 3,3-dichloro-1,2-diphenylcyclopropene the carbene complexes (pi-arene)(CO)2Cr = C(H)NR2 or (pi-arene)(CO)2Cr = C-C(Ph) = CPh are obtained with all employed pi-arene ligands.