15630-18-9Relevant academic research and scientific papers
Kinetics of reductive elimination from platinum(IV) as a probe for nonthermal effects in microwave-heated reactions
Lombard, Chloe K.,Myers, Kathryn L.,Platt, Zed H.,Holland, Andrew W.
, p. 3303 - 3306 (2009)
To test the hypothesis that microwaVe heating effects the nonthermal acceleration of reactions proceeding through polarized transition states, the kinetics and product ratios of the strongly medium-dependent thermolyses of (DPPE)Pt(CH3)3/
Energetics and mechanisms of carbon-carbon and carbon-iodide reductive elimination from a Pt(IV) center
Goldberg, Karen I.,Yan, JiYang,Breitung, Eric M.
, p. 6889 - 6896 (1995)
Thermolysis of dppePtMe3I (1, dppe = Ph2PCH2CH2PPh2) in both solid state and solution (acetone-d6) results in competitive methyl iodide and ethane production. The expected Pt(II) products of these reductive elimination reactions, dppePtMe2 (2) and dppePtMeI (3), are also observed. In the presence of added iodide (in acetone-d6), the carbon - carbon bond forming reductive elimination reaction is substantially inhibited, and an equilibrium is established between 1 and the carbon - iodide reductive elimination products, 2/MeI. Thermodynamic and kinetic parameters for the reductive elimination of methyl iodide from 1 were measured under these conditions (ΔH = 66 ± 3 kJ/mol, ΔS = 153 ± 7 J/(mol·K); ΔHre? = 104 ± 1 kJ/mol, ΔSre? = -12 ± 1 J/(mol·K)). Estimates of the enthalpy of the carbon - carbon reductive elimination reaction (ΔH = -105 kJ/mol) and of PtIV-C and PtIV-I bond strengths (132 and 196 kJ/mol, respectively) were made from DSC data. Mechanistic studies of the solution thermolysis support the involvement of a common five-coordinate cationic intermediate (formed by dissociation of iodide), from which both carbon - carbon and carbon - iodide elimination products result. Exclusive production of methyl iodide or ethane can be achieved by the addition or removal of iodide, respectively, from the reaction.
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.
Mechanistic insight into the protonolysis of the Pt-C bond as a model for C-H bond activation by platinum(II) complexes
Romeo, Raffaello,D'Amico, Giuseppina
, p. 3435 - 3446 (2008/10/09)
The kinetic and NMR features of the protonolysis reactions on platinum(II) alkyl complexes of the types cis-[PtMe2L2], [PtMe 2(L-L)], cis-[PtMeClL2], and [PtMeCl(L-L)] (L = PEt 3, P(Pri)3, PCy3, P(4-MePh) 3, L-L = dppm, dppe, dppp, dppb) in methanol suggest a rate-determining proton attack at the Pt - C bond. In contrast, a multistep oxidative-addition - reductive-elimination mechanism characterizes the methane loss on protonation of the corresponding trans-[PtMeClL2] species. Tools that were particularly diagnostic in suggesting different reaction pathways for the two systems were (i) the different results of kinetic deuterium isotope experiments, (ii) the detection or absence of Pt(IV) hydrido alkyl intermediate species by low-temperature 1H NMR experiments, and (iii) the detection or absence of isotope scrambling and incorporation of deuterium into Pt - CH3, combined with the loss of a range of CH nDn-4 isotopomers. For all systems, the rates of protonolysis are retarded by ligand steric congestion, accelerated by ligand electron donation, and almost unaffected by the chain length along the series of chelate complexes. A straight line correlates the rates of protonolysis of cis-dialkyl and cis-monoalkyl complexes, the difference in reactivity between the two systems being almost 5 orders of magnitude (slope of the line = 6 × 104). Factors controlling the dichotomy of behavior between complexes of different geometry have been taken into consideration. Application of the principle of microscopic reversibility suggests the reason why platinum complexes with nitrogen donor ligands appear to be far more efficient than platinum phosphane complexes in activating the C-H bond.
Mechanistic information on the reductive elimination from cationic trimethylplatinum(IV) complexes to form carbon-carbon bonds
Procelewska, Joanna,Zahl, Achim,Liehr, Guenter,Van Eldik, Rudi,Smythe, Nicole A.,Williams, B. Scott,Goldberg, Karen I.
, p. 7732 - 7742 (2008/10/09)
Cationic complexes of the type fac-[(L2)PtIVMe 3(pyr-X)][OTf] (pyr-X = 4-substituted pyridines; L2 = diphosphine, viz., dppe = bis(diphenylphosphino)ethane and dppbz = o-bis(diphenylphosphino)benzene; OTf = trifluoromethane-sulfonate) undergo C-C reductive elimination reactions to form [L2PtIIMe(pyr-X)] [OTf] and ethane. Detailed studies indicate that these reactions proceed by a two-step pathway, viz., initial reversible dissociation of the pyridine ligand from the cationic complex to generate a five-coordinate PtIV intermediate, followed by irreversible concerted C-C bond formation. The reaction is inhibited by pyridine. The highly positive values for ΔS ?obs = +180 ± 30 J K-1 mol -1, ΔH?obs = 160 ± 10 kJ mol-1, and ΔV?obs = +16 ± 1 cm3 mol-1 can be accounted for in terms of significant bond cleavage and/or partial reduction from PtIV to PtII in going from the ground to the transition state. These cationic complexes have provided the first opportunity to carry out detailed studies of C-C reductive elimination from cationic PtIV complexes in a variety of solvents. The absence of a significant solvent effect for this reaction provides strong evidence that the C-C reductive coupling occurs from an unsaturated five-coordinate PtIV intermediate rather than from a six-coordinate PtIV solvento species.
Mechanisms of C-C and C-H alkane reductive eliminations from octahedral Pt(IV): Reaction via five-coordinate intermediates or direct elimination?
Crumpton-Bregel, Dawn M.,Goldberg, Karen I.
, p. 9442 - 9456 (2007/10/03)
The Pt(IV) complexes P2PtMe3R [P2 = dppe (PPh2(CH2)2PPh2), dppbz (o-PPh2(C6H4)PPh2); R = Me, H] undergo reductive elimination reactions to form carbon-carbon or carbon-hydrogen bonds. Mechanistic studies have been carried out for both C-C and C-H coupling reactions and the reductive elimination reactions to form ethane and methane are directly compared. For C-C reductive elimination, the evidence supports a mechanism of initial phosphine chelate opening followed by C-C coupling from the resulting five-coordinate intermediate. In contrast, mechanistic studies on C-H reductive elimination support an unusual pathway at Pt(IV) of direct coupling without preliminary ligand loss. The complexes fac-P2PtMe3R (P2 = dppe, R = Me, H; P2 = dppbz, R = Me) have been characterized crystallographically. The Pt(IV) hydrides, fac-P2PtMe3H (P2 = dppe, dppbz), are rare examples of stable phosphine ligated Pt(IV) alkyl hydride complexes.
Reactions of organotin(IV) compounds with platinum complexes. Part II. Oxidative addition of SnRxCl4-x to [Pt(COD)2] and subsequent reactions with tertiary phosphines
Al-Allaf, Talal A. K.
, p. 25 - 35 (2007/10/03)
Organotin(IV) compounds SnRxCl4-x (R=Me, Ph; x=4-0) add oxidatively to [Pt(COD)2] (COD=cycloocta-1,5-diene) to yield platinum(II) complexes in which Pt has inserted into the Sn-Cl or Sn-R bonds, displacing one COD entity. The new com
