202932-93-2Relevant academic research and scientific papers
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.
Platinum(II) phosphido complexes as metalloligands. Structural and spectroscopic consequences of conversion from terminal to bridging coordination
Scriban, Corina,Wicht, Denyce K.,Glueck, David S.,Zakharov, Lev N.,Golen, James A.,Rheingold, Arnold L.
, p. 3370 - 3378 (2008/10/09)
Treatment of the terminal phosphido complexes Pt(dppe)(Me)(PPh(R)) (R = Ph (1), i-Bu (6)) with Pt(dppe)(Me)(OTf) gave the cationic μ-phosphido complexes [(Pt(dppe)(Me))2(μ-PPh(R))][OTf] (R = Ph (7), i-Bu (8)). Similarly, Pt((R,R)-Me-Duphos)(Me)(PPh(i-Bu)) (10) was converted to [(Pt((R,R)-Me-Duphos)(Me))2(μ-PPh(i-Bu))][OTf] (11). A fluxional process in 8 and 11, presumably involving hindered rotation about the Pt-PPh(i-Bu) bonds, was observed by NMR spectroscopy; it resulted in two diastereomers for 8 and four for 11 at low temperature. Coordination of the metalloligand 10 to the [Pt((R,R)-Me-Duphos)(Me)]+ fragment, yielding 11, resulted in structural changes at the Pt-phosphido group, whose geometry changed from distorted pyramidal to tetrahedral. Decomposition of 6 also gave the cation 8, while oxidation of 6 with H2O2 gave the crystallographically characterized phosphido oxide complex Pt(dppe)(Me)(P(O) Ph(i-Bu)) (12).
Terminal platinum(II) phosphide complexes: Synthesis, structure, and thermochemistry
Wicht, Denyce K.,Paisner, Sara N.,Lew, Belinda M.,Glueck, David S.,Yap, Glenn P. A.,Liable-Sands, Louise M.,Rheingold, Arnold L.,Haar, Christopher M.,Nolan, Steven P.
, p. 652 - 660 (2008/10/08)
A series of terminal Pt(II) phosphide complexes Pt(dppe)(Me)(PRR′) (R = H; R′ = Mes* (1), R′ = Mes (2), R′ = Ph (3), R′ = Cy (4); R = R′ = Mes (5); R = R′ = Ph (6); R = R′ = Cy (7); R = R′ = Et (8); R = Ph, R′ = i-Bu (9)) has been prepared by proton transfer from the appropriate phosphine to the methoxide ligand of Pt(dppe)(Me)(OMe) (10) (dppe = Ph2PCH2-CH2PPh2; Mes* = 2,4,6-(t-Bu)3C6H2; Mes = 2,4,6-Me3C6H2; Cy = cyclo-C6H11). Complexes 1 and 2 were also made by deprotonation of the cations [Pt(dppe)(Me)(PH2Ar)][BF4] (Ar = Mes* (13); Ar = Mes (14)). For comparison to 1, the arylthiolate and aryloxide complexes Pt(dppe)(Me)(EMes*) (E = S (11); E = O (12)) were also prepared from 10. NMR studies of the proton-transfer equilibria between Pt(dppe)(Me)(X), Pt(dppe)(Me)(Y), and the acids HY and HX (see Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw, J. E. J. Am. Chem. Soc. 1987, 109, 1444-1456 and Bryndza, H. E.; Domaille, P. J.; Tam, W.; Fong, L. K.; Paciello, R. A.; Bercaw, J. E. Polyhedron 1988, 7, 1441-1452) provide an approximate partial ranking of Pt-P bond strengths in this series: Pt-PHPh > Pt-PHMes > Pt-PHMes*; Pt-PPh2 > Pt-PMes2. Complementary solution calorimetry investigations probe the role of entropie effects on the equilibria. Both steric and electronic factors appear to be important in controlling relative Pt-P bond strengths. The Pt-S bonds in 11 and Pt(dppe)(Me)(SPh) are stronger than the analogous Pt-P bonds in 1 and 3. Complexes 1 and 5·THF were structurally characterized by X-ray crystallography.
