255907-73-4Relevant academic research and scientific papers
Substrate and catalyst screening in platinum-catalyzed asymmetric alkylation of bis(secondary) phosphines. Synthesis of an enantiomerically-pure C2-symmetric diphosphine
Anderson, Brian J.,Glueck, David S.,DiPasquale, Antonio G.,Rheingold, Arnold L.
, p. 4992 - 5001 (2009/03/11)
Platinum-catalyzed asymmetric alkylation of bis(secondary) phosphines was investigated. The modular design of the catalyst precursor Pt(diphos*) (R′)(Cl) and the substrates, a bis(secondary) phosphine HRP-PHR and a benzyl halide, along with an efficient 31P NMR screening method, enabled rapid evaluation of the rate and diastereoselectivity of these reactions. These experiments identified a selective catalyst, Pt(DuPhos)(Ph)(Cl), and showed that the alkylation of PhHP(CH2) 3PHPh (2) was faster and more selective than that of PhHP(CH 2)2PHPh (1), MesHP(CH2)3PHMes (3), or 1,1′-(C5H4PHPh)2Fe (4). Alkylation of 1 with o-CF3C6H4CH2Br using the base NaOSiMe3 and the catalyst precursor Pt((R,R)-i-Pr-DuPhos)(Ph)(Cl), or the analogous Me-DuPhos complex, gave the diphosphine Ph(CH 2o-CF3C6H4)P(CH2) 2P(CH2o-CF3C6H4)Ph (7), which was prepared on a multigram scale and isolated as a borane adduct (6). The rac and meso diastereomers of 6 were separated by recrystallization, and enantiomerically pure 6 was isolated. Both (R,R)- and (S,S)-6, prepared separately in high ee using appropriate catalyst precursors, were characterized by X-ray crystallography, as was meso-7. Separate treatment of (S,S)-1 and meso-7 with Pt(COD)(Ph)(Cl) gave the complexes Pt((S,S)-7)(Ph)(Cl) ((S,S)-8) and Pt(meso-7)(Ph)(Cl) (meso-8). Both diastereomers of 8 were catalyst precursors for synthesis of 7 by alkylation of 1 with o-CF3C6H 4CH2Br, but these reactions were unselective, because ligand 7 was rapidly displaced from its complex, 8.
Chiral Terminal Platinum (II) Phosphido Complexes: Synthesis, Phosphorus Inversion, and Acrylonitrile Insertion
Wicht, Denyce K.,Kovacik, Ivan,Glueck, David S.,Liable-Sands, Louise M.,Incarvito, Christopher D.,Rheingold, Arnold L.
, p. 5141 - 5151 (2008/10/08)
The chiral Pt(II) phosphido complex Pt(dppe)(Me)[P(Mes)(Men)] (dppe = Ph2PCH2CH2-PPh2, Mes = 2,4,6-Me3C6H2, Men = (-)menthyl, 1) was prepared by proton transfer from racemic mesityl(-)menthylphosphine to the methoxide ligand of Pt(dppe)(Me)(OMe). Treatment of Pt(dcpe)[CH(Me)(CN)](Br) with alkali metal phosphides gives Pt(dcpe)[CH(Me)-(CN)](PRR′) (dcpe = Cy2PCH2CH2PCy2, Cy = cyclo-C6H11, R = H, R′ = Mes* - 2,4,6-(t-Bu)3C6H2, 13; R = Me, R′ = Ph, 14). The related series of complexes Pt(diphos*)(Me)-(PRR′) (diphos* = S,S-Chiraphos, R = Ph, R′ = Is = 2,4,6-(i-Pr)3C6H2), 5; R = Me, R′ = Mes*, 6; diphos* = R-Tol-Binap, R = Me, R′ = Mes*, 7) containing chiral diphosphine ligands has been prepared by deprotonation of the cations [Pt(diphos*)(Me)(PHRR′)][BF4] 2, 3, and 4, respectively. The cations, synthesized from Pt(diphos*)(Me)(Cl), AgBF4, and the appropriate secondary phosphine, were isolated as a mixture of diastereomers (2 and 3) or a single isomer (4). Phosphido complexes 1 and 5-7 show only one set of 31P NMR resonances in solution even at low temperature, consistent either with the existence of a single diastereomer or with rapid inversion at phosphorus. However, low-temperature spectra of 13 and 14 reveal the existence of the expected two diastereomers, which interconvert by phosphorus inversion and rotation about the Pt-P bond with barriers of approximately 11.5 and 15.5 kcal/mol, respectively. Treatment of 6 and 7 with HBF4 protonates the phosphido ligand and generates diastereomeric mixtures of the cations 3 and 4, respectively. Acrylonitrile inserts into the Pt-P bond of 1 to give the dialkyl complex Pt(dppe)(Me)[CH(CN)CH2P(Mes)(Men)] (9) as a mixture of four diastereomers; similar product mixtures (10-12) are obtained with 5-7. Complexes 4·3CH2Cl2, 5, and the secondary phosphine PH(Me)(MeS*) (8) were structurally characterized by X-ray crystallography.
