Nickel(II) and Palladium(II) Complexes of the Small-Bite-Angle P?Stereogenic Diphosphine Ligand MaxPHOS and Its Monosulfide

摘要

Coordination studies of the optically pure diphosphine ligand (t-Bu)_2P(NH)P(t-BuMe) (MaxPHOS) and its monosulfide with several Pd and Ni moieties are described. Treatment of a solution of MaxPHOS·HBF_4 with [M(acac)_2] (M = Ni, Pd) in methanol or dichloromethane cleanly produced [M(MaxPHOS)(acac)]BF_4. Reaction of the same salt with Pd(OAc)_2 in the presence of excess NaBr in methanol produced the corresponding neutral complex [PdBr_2(MaxPHOS)]. The [PdCl_2(MaxPHOS)] complex was prepared by the reaction of free (S)-MaxPHOS with [PdCl_2(cod)]. Reaction of (S)-MaxPHOS·HBF4 with Pd allylic dimers [PdCl(η_3-RC_3H_4)]_2 (R = 2-methyl, 1-phenyl, 1,3-diphenyl) in the presence of excess Na2CO3 and NH4BF4 in dichloromethane produced the cationic complexes [Pd(MaxPHOS)(η_3-R-allyl)]BF_4 in good yields. Reaction of MaxPHOS monosulfide with [Pd(acac)_2] produced the neutral complex [Pd(MaxPHOS·S)_2], where both ligands are anionic. Protonation of this complex generated [Pd(MaxPHOS·S)_2]BF_4, a complex formally bearing an anionic and a neutral ligand. Full characterization, including five crystal structure determinations, for all of the complexes is provided. Preliminary catalytic studies of the performance of the Pd allylic complex [Pd(MaxPHOS)(η~3-2-Me-allyl)]BF4 in allylic substitution reactions are also presented.