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)2P­(NH)­P­(t-BuMe) (MaxPHOS) and its monosulfide with several Pd and Ni moieties are described. Treatment of a solution of MaxPHOS·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·HBF4 with Pd allylic dimers [PdCl­(η3-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)­(η3-R-allyl)]­BF4 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]­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)­(η3-2-Me-allyl)]­BF4 in allylic substitution reactions are also presented.