Palladium carbene complexes as persistent radicals

A series of palladium(ii) radical carbene complexes, [PC˙(sp(2))P]PdI, [PC˙(sp(2))P]PdBr, and [PC˙(sp(2))P]PdCl (PC(sp(3))H(2)P = bis[2-(di-iso-propylphosphino)-phenyl]methane), is described. Compound [PC˙(sp(2))P]PdI dimerizes to {[PC(sp(2))P]PdI}(2) in the solid state, akin to the formation of Gomberg's dimer. While the bromo and the iodo derivatives could be obtained from the oxidation of [PC(sp(2))P]Pd(PMe(3)) by the respective dihalogens, a halogen transfer reaction from CH(2)Cl(2) was used for the formation of [PC˙(sp(2))P]PdCl. The halogen transfer from CH(2)X(2) (X = Cl, Br, I) could be used to obtain all three radical carbene palladium complexes and also allowed the isolation of [PC(CH(2))P]Pd(PMe(3)), which is the result of methylene group transfer from CH(2)X(2). Compound [PC(CH(2))P]Pd(PMe(3)) was independently synthesized from [PC(CH(3))HP]PdCl(2), which contains a supporting ligand analogous to that of the radical carbene complexes but has one of the hydrogen atoms replaced by a methyl group. All three carbene radical species abstract a hydrogen from 9,10-dihydroanthracene or ( n )Bu(3)SnH.