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Single-Crystal (31)P NMR and X-ray Diffraction Study of a Molybdenum Phosphine Complex:
Klaus Eichele1, Roderick E. Wasylishen, Kalyani Maitra
1Departments of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3, University of Nevada, Reno, Nevada 89557-0020, and McMaster University, Hamilton, Ontario, Canada L8S 4M1.
Abstract:
The molecular structure of (5-methyldibenzophosphole)pentacarbonylmolybdenum(0), 1, has been determined by X-ray crystallography. The crystal is monoclinic C2/c, Z = 8, with unit cell dimensions of: a = 31.113(2) Å, b =7.7917(5) Å, c = 17.9522(12) Å, and beta = 122.135(4) degrees. Least-squares refinement converged to R(F) = 0.0245 for 2407 independent reflections. The molecular structure is typical of phosphine-substituted metal carbonyls. It contains an approximate mirror plane which bisects the dibenzophosphole framework. Phosphorus-31 NMR spectra of powder and single-crystal samples of 1 have been obtained with cross-polarization and (1)H high-power decoupling. The (31)P CP/MAS NMR spectra exhibit exceptionally well-resolved satellites due to spin-spin coupling interactions with (95,97)Mo (I = (5)/(2)). Using first-order perturbation theory, the multiplets have been analyzed to yield (1)J((95,97)Mo,(31)P) = 123(2) Hz and estimates of the molybdenum nuclear quadrupolar coupling constants, chi((95)Mo) = -0.87 MHz and chi((97)Mo) = 10.1 MHz. Phosphorus-31 NMR spectra of a large single crystal of 1 have been investigated as a function of orientation about three orthogonal axes in the applied magnetic field. Analysis of the data yields the three principal components of the phosphorus chemical shift tensor, delta(11) = 112 ppm, delta(22) = -23 ppm, and delta(33) = -40 ppm; delta(22) lies close to the Mo-P bond (8 degrees ), while delta(11) lies in the approximate mirror plane. The phosphorus chemical shift tensor determined for 1 is compared with the limited anisotropic phosphorus shift data available in the literature.