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

Coordination studies of the optically pure diphosphine ligand (t-Bu)(2)P(NH)P(t-BuMe) (MaxPHOS) and its monosulfide with several Pd and Ni moieties are described. Treatment of a solution of MaxPHOS center dot HBF4 with [M(acac)(2)] (M = Ni, Pd) in methanol or dichloromethane cleanly produced [M(MaxPHOS)(acac)]BF4. Reaction of the same salt with Pd(OAc)(2) in the presence of excess NaBr in methanol produced the corresponding neutral complex [PdBr2(MaxPHOS)]. The [PdCl2(MaxPHOS)] complex was prepared by the reaction of free (S)-MaxPHOS with [PdCl2(cod)]. Reaction of (S)-MaxPHOS center dot HBF4 with Pd allylic dimers [PdCl(eta(3)-R-C3H4)](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)(eta(3)-R-allyl)]BF4 in good yields. Reaction of MaxPHOS monosulfide with [Pd(acac)(2)] produced the neutral complex [Pd(MaxPHOS center dot S)(2)], where both ligands are anionic. Protonation of this complex generated [Pd(MaxPHOS center dot S)(2)]BF4, 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)(eta(3)-2-Me-allyl)]BF4 in allylic substitution reactions are also presented.