33937-27-8Relevant academic research and scientific papers
Associative reactions of dihydridobis(trimethylphosphine)platinum(II). Molecular structures of (diphenylacetylene)bis(trimethylphosphine)platinum and hydridotris(trimethylphosphine)platinum(II) tetraphenylborate
Packett, Diane L.,Syed, Ashfaquzzaman,Trogler, William C.
, p. 159 - 166 (2008/10/08)
Olefinic and acetylenic ligands such as diphenylacetylene, ethylene, tert-butylethylene, and trans-stilbene displace H2 from PtH2(PMe3)2 to form zerovalent π complexes. The complex Pt(PhC=CPh) (PMe3)2 crystallizes in the orthorhombic space group P212121 with Z = 4, a = 9.508 (2) A?, b = 13.524 (4) A?, c = 16.124 (4) A?, and V = 2073.5 A?3. Refinment of 2040 unique observations >3σ(I) led to R = 0.043 and Rw = 0.056. The complex adopts a nearly square-planar geometry, with Pt-P distances of 2.262 (4) and 2.284 (4) A?, Pt-C distances of 2.06 (1) and 2.04 (1) A?, and a C-C distance of 1.29 (2) A? for the bound acetylenic moiety. The reaction between tert-butylethylene and PtH2(PMe3)2 follows a second-order rate law first order in olefin and platinum complex, with k = (1.95 ± 0.24) × 10-3 M-1 s-1 at 21°C. Hydrogenation of the unsaturated substrate does not occur, which agrees with theoretical predictions for a five-coordinate platinum hydride intermediate. Allyl chloride oxidatively adds to PtH2(PMe3)2 to produce Pt(C3H5) (PMe3)2+, isolated as the BPh4- salt. The family of substrates HMPh3 (M = Si, Ge, and Sn) undergo oxidative addition reactions to yield cis-PtH(SiPh3) (PMe3)2, and cis,trans,cis-PtH2(MPh3)2(PMe3) 2 for M = Ge and Sn. The reaction between methanol and PtH2(PMe3)2 produces [Pt(PM3)2(μ-H)2Pt(PMe3) 2H][OCH3], and on addition of NaBPh4, [PtH(PMe3)3][BPh4] precipitates. The compound [PtH(P(CH3)3)3][B(C6H 5)4] crystallizes in the monoclinic space group P21/n with a = 10.011 (2) A?, b = 12.948 (3) A?, c = 26.699 (4) A?, β = 92.15 (2)°, V = 3458.2 A?3, and Z = 4 at T = 296 (1) K. Refinement of the structure led to Rw = 0.048 for 4325 unique reflections with I > 3μ(I). The PtH[P(CH3)3]3+ species adopts a square-planar geometry. The Pt-P bond trans to hydrogen of 2.324 (1) A is longer than the other two Pt-P bonds by 0.030 A?, demonstrating that hydride ligand has a greater trans influence than trimethylphosphine. The P-Pt-Pt angles of 100.69 (6) and 100.56 (6)° open up from 90° to accommodate the bulk of the phosphine ligands.
Kinetics of cis-trans isomerization and reductive elimination in dihydridobis(trimethylphosphine)platinum(II)
Packett, Diane L.,Trogler, William C.
, p. 1768 - 1775 (2008/10/08)
Solutions of PtH2(PMe3)2 (1) exist as an equilibrium mixture of cis and trans isomers, with the cis isomer dominating in polar solvents. The forward rate constant for trans ? cis isomerization was determined by spin-saturation-transfer studies to be ～0.1 s-1 at -60°C. The isomerization may proceed by an associative mechanism involving a phosphine ligand or solvent molecule, or by dissociation of PMe3 from the cis and trans isomers to form T-shaped intermediates that slowly interconvert. Above -35 °C the phosphine ligands exchange rapidly between the isomers of 1 with rate constants in the range 7-600 s-1. Addition of a trace of free phosphine to solutions of 1 results in the formation of PtH2(PMe3)3 (2), which exchanges phosphine ligands rapidly with trans-1 but not with cis-1. Under a nitrogen atmosphere, 1 decomposes by unimolecular rate-determining reductive elimination of hydrogen with an inverse kinetic isotope effect, kH/kD = 0.45 ± 0.1. This inversion isotope effect supports the theoretical predictions of nearly complete H-H bond formation in the transition state for reductive elimination. In coordinating THF solvent, reductive elimination of H2 occurs slowly, with ΔH? = 9.4 ± 1 kcal mol-1 and ΔS? = -41 ± 3 cal mol-1 deg-1. The large negative entropy of activation reflects solvent reorganization in the transition state. In noncoordinating Me4THF solvent elimination of hydrogen proceeds more rapidly, with ΔH? = 20.0 ± 0.5 kcal mol-1 and ΔS? = -1 ± 2 cal mol-1 deg-1. This value of ΔH?, as well as the large inverse isotope effect, compares favorably with theoretical calculations for hydrogen elimination from 1 and yields an estimate for the Pt-H bond dissociation energy of 62 kcal mol-1.
