ISSN:
0009-2940
Keywords:
Density-functional theory
;
31P-NMR chemical shift tensor
;
Quasirelativistic pseudopotential
;
Transition-metal phosphane complex
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The 31P chemical shift tensors of the transition-metal phosphane complexes M(CO)5PX3 (M = Cr, Mo, W; X = H, CH3, F, Cl) were studied using a combination of density functional theory and ab initio effective-core potentials. The calculated isotropic shifts agree well with experimental results both for the free ligands and for the complexes, with the largest deviations occuring for the tungsten complexes. A breakdown of the computed phosphorus shielding tensors into contributions from localized molecular orbitals (LMOs) indicates that the positive coordination shift of PH3 and P(CH3)3 is due to increased paramagnetic contributions from the phosphorus lone pair (P-M s̰ bonding) LMO to δ⊥. A similar increase of this contribution is found for PF3 and PCl3. However, for PCl3 complexes these terms are overcompensated by a reduction in the paramagnetic contributions from the P-Cl bonds and by shielding contributions from metal-centered orbitals. This results in a negative overall coordiantion shift. A partial cancellation is found with P(CH3)3 and with PF3. The changes in the 31P-shift tensors of the same phosphane ligands upon protonation are qualitatively and quantitatively very different from the coordination shifts and do not provide good models for the latter.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19961290510
