916769-17-0Relevant articles and documents
P-C and C-C bond formation by Michael addition in platinum-catalyzed hydrophosphination and in the stoichiometric reactions of platinum phosphido complexes with activated alkenes
Scriban, Corina,Glueck, David S.,Zakharov, Lev N.,Kassel, W. Scott,DiPasquale, Antonio G.,Golen, James A.,Rheingold, Arnold L.
, p. 5757 - 5767 (2008/10/09)
We recently proposed a new mechanism for platinum-catalyzed hydrophosphination of activated alkenes, in which nucleophilic attack of a phosphido ligand in the intermediate hydride complex Pt(diphos)(PR 2)-(H) (1) on the alkene H2C=CH(X) (X = CN or CO 2R) gave the zwitterion Pt(diphos)(H)(PR2CH 2CHX) (2), containing a cationic Pt center and a phosphine ligand with a pendent stabilized carbanion. Subsequent C-H bond formation involving the Pt-H and the carbanion would yield the product R2PCH 2CH2X (3) and regenerate the catalyst, while attack of the carbanion on another alkene would yield byproducts derived from more than one alkene, such as R2P(CH2CH(X))nCH 2CH2X (7). Several tests of this mechanism and related pathways for product and byproduct formation were investigated. Attempts to trap the proposed carbanion with another electrophile led to the development of a Pt-catalyzed three-component coupling of secondary phosphines, tert-butyl acrylate, and benzaldehyde, yielding the functionalized phosphines R 2PCH2CH(CO2t-Bu)(CHPh(OH)) (R2P = Ph2P (10a); R2P = Me(Is)P (10b, Is = 2,4,6-(i-Pr) 3C6H2)). Reactions of the complexes Pt(diphos)(R′)(PR2) (diphos = (R,R)-Me-Duphos, R′ = Me, PR2 = PPh2 (11), PPh(i-Bu) (12); R′ = Ph, PR 2 = PMeIs (13); diphos = dppe, R' = Me, PR2 = PPh 2 (14), PPh(i-Bu) (15)), models for 1, with tert-butyl acrylate or acrylonitrile gave mixtures of products including Pt-(diphos)(R′)(CH(X) CH2PR2) (A, X = CO2t-Bu or CN), Pt(diphos)(R′)(CH(X)CH2CH(X)CH2PR2) (B), R2PCH2CH2X (3), R2P(CH 2CH(X))n(CH2CH2X) (7), and, in some cases, the dinuclear phosphido-bridged cations [(Pt(diphos)(Me)) 2(μ-PR2)]+ (17). When tert-butanol or water was added to these reactions, more of the phosphines 3 and 7, and less of the intermediates A and B, were formed. Decomposition of A and B gave unidentified platinum dialkyls (C), tentatively formulated as Pt(diphos)(R′)(CH(X) R″). The complex Pt(dppe)(Me)(CH(Me)CO2t-Bu) (21), a model for A, B, and C, was generated either from Pt(dppe)(Cl)-(CH(Me)CO2t-Bu) (20) and ZnMe2 or from Pt(dppe)(Me)(Cl) (19) and ZnBr(CH(Me)CO 2t-Bu)·THF; complexes 20 and 21 did not react with tert-butyl acrylate. These observations are consistent with the proposed nucleophilic mechanism for P-C and C-C bond formation.
