Synthesis of Trimethylplatinum(IV) Complexes with N,N- and N,O-Heterocyclic Carbene Ligands and Their Reductive C―C Elimination Reactions

Reactions of the platinum(IV) complexes [PtMe3(OCMe2)3](BF4) (1(BF4)), [(PtMe3I)4] (2), and [PtMe3I(py)2] (3) with the N,N-heterocyclic carbene 1,3-dimethylimidazol-2-ylidene (N,N-hc, 4) resulted in a rapid reductive elimination of ethane, yielding platinum(II) complexes [PtMe(N,N-hc)3]+ (7), trans-[PtMeI(N,N-hc)2] (8), and cis-[PtMe(py)(N,N-hc)2]+ (10), respectively. Subsequent substitution of the iodo ligand in 8 by pyridine resulted in the formation of trans-[PtMe(py)(N,N-hc)2](CF3COO) (9(CF3COO)). 9 and 10 are stereoisomers. In contrast to this, the analogous reaction of [PtMe3(OCMe2)3](BF4) (1(BF4)) with the N,O-heterocyclic carbene 3-methyloxazol-2-ylidene (N,O-hc, 5) was found to yield the tris(carbene)trimethylplatinum(IV) compound [PtMe3(N,O-hc)3](BF4) (12(BF4)), which is thermally stable up to 218 °C in the solid state. Furthermore, reactions of [{PtMe3(acac)}2] (15) with the N,X-heterocyclic carbenes (X = N, O, S; N,S-hc = 3-methylthiazol-2-ylidene, 6) resulted in the formation of monocarbenetr...