Sterically Crowded Diphosphinomethane Ligands: Molecular Structures, UV-Photoelectron Spectroscopy and a Convenient General Synthesis of tBu2PCH2PtBu2 and Related Species
(2003) Sterically Crowded Diphosphinomethane Ligands: Molecular Structures, UV-Photoelectron Spectroscopy and a Convenient General Synthesis of tBu2PCH2PtBu2 and Related Species. New Journal of Chemistry 27(3):pp. 540-550.
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Abstract
A series of highly crowded symmetric and unsymmetrical diphosphinomethanes R2PCH2PR'2, important ligands in transition metal chemistry and catalysis, namely tBu2PCH2PtBu2 (dtbpm, 11), Cy2PCH2PCy2 (dcpm, 2), tBu2PCH2PCy2 (ctbpm, 3), tBu2PCH2PiPr2 (iptbpm, 4) and tBu2PCH2PPh2 (ptbpm, 5), has been prepared in high yields, using a general and convenient route, which is described in detail for 1. Other than 4, which is a colourless liquid, these compounds are crystalline solids at room temperature. Their molecular structures have been determined by single crystal X-ray diffraction, along with that of the higher homologue of 1, tBu2CH2CH2tBu2 (dtbpe, 6). The solid-state structures of the dioxide of 1, tBu2P(O)CH2P(O)tBu2 (7), and of two phosphonium cations derived from 1, protonated [tBu2P(H)CH2PtBu2]+ (8+) and the chlorophosphonium ion [tBu2P(Cl)CH2PtBu2]+ (9+) are also described and show a distinct structural influence of the tetracoordinate P centres. The gas phase UV-photoelectron spectra of the diphosphines 1 – 6 have been measured. Their first two ionisation potentials are found to be nearly degenerate and all in the low energy range from 7.5 to 7.8 eV. Comparison with related mono- and bidentate phosphines demonstrates that 1 – 6 are excellent -donors towards metals, in accord with their known coordination chemistry. Molecular geometries and electronic structures of the diphosphine systems have been studied by quantum chemical calculations and are compared to experiment. Unlike standard semiempirical methods (AM1, PM3, MNDO) which give rather poor minimum structures and seem inadequate for such sterically crowded systems, ab initio calculations (RHF/6-31G**) predict molecular geometries with reasonable accuracy and reflect the observed trends in experimental ionisation potentials.
| Item Type: | Journal Article |
|---|---|
| Status: | Published |
| Keywords: | phosphine ligands |
| Subjects: | 250000 Chemical Sciences > 250200 Inorganic Chemistry > 250202 Main Group Metal Chemistry |
| ID Code: | 9159 |
| Deposited By: | Schultz, Madeleine |
| Deposited On: | 27 August 2007 |
| Alternative Locations: | http://dx.doi.org/10.1039/b210114a |
| Copyright Owner: | Copyright 2003 Royal Society of Chemistry |
| Copyright Statement: | Reproduced by permission of The Royal Society of Chemistry, no further distribution permitted. |