A series of diphosphinedichloroplatinum(II) complexes, having bulky phosphine substituents, react with sodium amalgam in THF to yield the corresponding cis dihydride complexes. These dihydride species possess unusual thermal stability and are not highly air sensitive. When diphosphines of intermediate steric bulk are involved it is possible to observe a reversible loss of H2 from these dihydrides. Spectroscopic data are consistent with the presumption that the products of these dehydrogenations are derived from highly reactive bent diphosphine species Pt(diphos). Electron-poor olefins will irreversibly displace H2 from the cis dihydride complexes to yield coordinated olefin complexes. Electron-rich olefins do not exhibit this behavior, but under forcing condition can be catalytically hydrogenated in the presence of the cis dihydride. A proof by induction of the dimeric nature of the product of the reversible dehydrogenation is presented in the form of a crystal structure determination of [Pt(t-Bu)2P(CH2)3P(t-Bu)2]2. The dimeric molecule has crystallographically imposed C2 symmetry. Each Pt atom is three-coordinate, being bound to two P atoms and the other Pt atom. The Pt-Pt separation is 2.765 (1) Å, and the angle between the two P-Pt-P planes is 82°. The molecule as a whole exhibits very severe crowding. The compound crystallizes as a toluene solvate in the monoclinic space group C2h6-C2/c in a cell of dimensions a = 19.101 (6), b = 11.723 (6), c = 23.202 (9) Å, with β = 100.07 (3)°. There are four dimeric molecules and four solvent molecules per unit cell. Based on 5350 unique reflections having Fo2 >3σ(Fo2), the structure was refined by full-matrix least-squares techniques to conventional agreement indices (on F) of R = 0.030 and Rw = 0.040. The nature of the Pt-Pt interaction is discussed and possible explanations for the observed geometry of the dimer are offered.
ASJC Scopus subject areas
- Colloid and Surface Chemistry