Synthesis, Structure, Dynamics, and Selective Methylation of Platinum and Palladium Diphosphametallacyclobutane Complexes
作者:Timothy W. Chapp、Adam J. Schoenfeld、Matthew D. Sanderson、Cory L. Chang、David S. Glueck、James A. Golen、Curtis E. Moore、Arnold L. Rheingold
DOI:10.1021/om3005367
日期:2012.8.13
Treatment of M(dppe)Cl-2 (M = Pd, Pt) or Pt((R,R)-Me-DuPhos)Cl-2 with IsHPCH(2)PHIs (1; Is = isityl = 2,4,6-(i-Pr)(3)C6H2) and 2 equiv of NaOSiMe3 gave the mononuclear diphosphametallacyclobutane complexes M(dppe)(IsPCH(2)PIs) (M = Pd (2), Pt (3)), or Pt((1,R)-Me-DuPhos)(IsPCH(2)PIs) (4). Dynamic processes involving phosphorus inversion and rotation about the P-C (1s) bonds in 2-4 were characterized by variable-temperature NMR spectroscopy, which suggested that each existed as a single C-2-symmetric diastereomer in solution, consistent with their solid-state structures determined by X-ray crystallography. The MiniPhos derivative IsMePCH(2)PMeIs (5) was prepared as a 5.5/1 rac/meso mixture by sequential arylation and methylation of Cl2PCH2PCl2. Alternatively, the catalyst precursor Pt((1,R)-Me-DuPhos)(Ph)(Cl) mediated alkylation of secondary phosphines in the presence of NaOSiMe3 to yield selectively meso-5 either from PHMe(1s) and CH2I2 or from 1 and MeI. Recrystallization and chromatography yielded diastereomerically enriched rac-5 and meso-5. Treatment of M(dppe)(OTf)(2) (M = Pd, Pt) or Pt((R,R)-Me-DuPhos)(OTf)(2) with meso-5 gave the dications meso-[M(diphos)(IsMePCH(2)PMeIs)][OTf](2) (M(diphos) = Pd(dppe) (6), Pt(dppe) (8), Pt((R,R)-Me-DuPhos) (10)). Similar reactions of rac-5 yielded the dications rac-[M(diphos)(IsMePCH(2)PMeI(5))][OTf](2) (M(diphos) = Pd(dppe) (7), Pt(dppe) (9)) and a 1/1 mixture of the C-2-symmetric diastereomers [Pt((R,R)-Me-DuPhos)(IsMePCH(2)PMeIs)][OTf](2) (11a,b). Treatment of 2 and 3 with 2 equiv of methyl triflate gave the dications 6-9 as ca. 1/1 meso/rac mixtures, and methylation of 4 selectively gave one of the C-2-symmetric diastereomers, 11a. These alkylations proceeded via the observable monomethylated intermediates [M(diphos)(IsMePCH(2)PIs)][OTf] (12-14).