Synthesis and Structure of Platinum Bis(phospholane) Complexes Pt(diphos*)(R)(X), Catalyst Precursors for Asymmetric Phosphine Alkylation

Abstract

The complexes Pt((R,R)-Me-DuPhos)(Ph)(Cl) (1) and Pt((R,R)-i-Pr-DuPhos)(Ph)(Cl) (2) have been used as catalyst precursors in Pt-catalyzed asymmetric alkylation of secondary phosphines. To investigate structure–reactivity–selectivity relationships in these reactions, analogous complexes with different bis(phospholane) ligands and/or Pt-hydrocarbyl groups were prepared. Treatment of Pt(COD)(R)(Cl) (R = Me, Ph) with BPE or DuPhos ligands gave Pt((R,R)-Me-BPE)(Me)(Cl) (3), Pt((R,R)-Ph-BPE)(Me)(Cl) (5), Pt((R,R)-Ph-BPE)(Ph)(Cl) (6), and Pt((R,R)-i-Pr-DuPhos)(Me)(Cl) (7). However, treatment of Pt(COD)(Me)(Cl) with (R,R)-Me-FerroLANE gave a mixture of products, which were converted upon heating to Pt((R,R)-Me-FerroLANE)(Me)(Cl) (8). A related mixture formed from Pt(COD)(Ph)(Cl) precipitated trans-[Pt((R,R)-Me-FerroLANE)(Ph)(Cl)]n (9T), which on treatment with AgOTf followed by LiCl gave cis-Pt((R,R)-Me-FerroLANE)(Ph)(Cl) (9) as the major product. The reaction of Pt(COD)(Ph)(Cl) with (R,R)-Me-BPE gave the dinuclear dication [(Pt((R,R)-Me-BPE)(Ph))2(μ-(R,R)-Me-BPE))][Cl]2 (10) instead of the expected Pt((R,R)-Me-BPE)(Ph)(Cl) (4). The iodide Pt((R,R)-Me-BPE)(Ph)(I) (11) was formed from Pt(COD)(Ph)(I) and BPE but decomposed readily. Treatment of Pt(COD)X2 with (R,R)-Me-BPE gave Pt((R,R)-Me-BPE)X2 (X = Cl (12), I (13)). Reaction of Pt(COD)Ph2 with (R,R)-Me-BPE gave Pt((R,R)-Me-BPE)Ph2 (14), which was protonated with HCl to yield 4. Treatment of Pt((R,R)-Me-DuPhos)Cl2 with excess (9-phenanthryl)magnesium bromide gave Pt((R,R)-Me-DuPhos)(9-phenanthryl)(Br) (15), while a similar reaction with excess (6-methoxy-2-naphthyl)magnesium bromide gave Pt((R,R)-Me-DuPhos)Ar2 (16). Complexes 3, 4, 6–10, and 12–14 were structurally characterized by X-ray crystallography. Structure–reactivity–selectivity relationships in this series of Pt catalyst precursors were investigated in the catalytic alkylation of the bis(secondary phosphine) PhHP(CH2)3PHPh with benzyl bromide.