title: Cyclopropenylidene carbene ligands in palladium catalysed coupling reactions: carbene ligand rotation and application to the Stille reaction.
abstract: Reaction of [Pd(PPh(3))(4)] with 1,1-dichloro-2,3-diarylcyclopropenes gives complexes of the type cis-[PdCl(2)(PPh(3))(C(3)(Ar)(2))] (Ar = Ph 5, Mes 6). Reaction of [Pd(dba)(2)] with 1,1-dichloro-2,3-diarylcyclopropenes in benzene gave the corresponding binuclear palladium complexes trans-[PdCl(2)(C(3)(Ar)(2))](2) (Ar = Ph 7, p-(OMe)C(6)H(4)8, p-(F)C(6)H(4)9). Alternatively, when the reactions were performed in acetonitrile, the complexes trans-[PdCl(2)(NCMe)(C(3)(Ar)(2))] (Ar = Ph 10, p-(OMe)C(6)H(4)11 and p-(F)C(6)H(4)) 12) were isolated. Addition of phosphine ligands to the binuclear palladium complex 7 or acetonitrile adducts 11 and 12 gave complexes of the type cis-[PdCl(2)(PR(3))(C(3)(Ar)(2))] (Ar = Ph, R = Cy 13, Ar = p-(OMe)C(6)H(4), R = Ph 14, Ar = p-(F)C(6)H(4), R = Ph 15). Crystal structures of complexes 6·3.25CHCl(3), 10, 11·H(2)O and 12-15 are reported. DFT calculations of complexes 10-12 indicate the barrier to rotation about the carbene-palladium bond is very low, suggesting limited double bond character in these species. Complexes 5-9 were tested for catalytic activity in C-C coupling (Mizoroki-Heck, Suzuki-Miyaura and, for the first time, Stille reactions) and C-N coupling (Buchwald-Hartwig amination) showing excellent conversion with moderate to high selectivity.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol, UK BS8 1TS.
authors.forename: Ratanon
authors.initials: R
authors.lastname: Chotima
authors.forename: Tim
authors.initials: T
authors.lastname: Dale
authors.forename: Michael
authors.initials: M
authors.lastname: Green
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Hey
authors.forename: Claire L
authors.initials: CL
authors.lastname: McMullin
authors.forename: Adam
authors.initials: A
authors.lastname: Nunns
authors.forename: A Guy
authors.initials: AG
authors.lastname: Orpen
authors.forename: Igor V
authors.initials: IV
authors.lastname: Shishkov
authors.forename: Duncan F
authors.initials: DF
authors.lastname: Wass
authors.forename: Richard L
authors.initials: RL
authors.lastname: Wingad