Syntheses and chemistry of Tris(2-pyridyl)phosphine complexes of Group VI transition metals. X-ray structural studies of the molybdenum complexes
Resource
Journal of Organometallic Chemistry 588 (2): 260-267
Journal
Journal of Organometallic Chemistry
Pages
260-267
Date Issued
1999
Date
1999
Author(s)
Abstract
Treatment of P(2-py)3 with Mo(CO)6 or M(CO)3(CH3CN)3 (M=Cr, W) in CH3CN affords compounds of the type P(2-py)3M(CO)3 (1a, M=Cr; 1b, M=Mo; 1c, M=W). Complex P(2-py)3Mo(CO)3·CH2Cl2 was structurally characterized, and its ORTEP drawing shows an almost perfect octahedral arrangement around the Mo center, and the P(2-py)3 ligand occupying the facial position of the octahedron through the coordination of three pyridyl nitrogen atoms. Substitution of CO ligands can take place when treating compounds 1b and 1c with one or two equiv. of NOBF4 in CH3NO2 solvent to afford [P(2-py)3M(CO)3-n(NO)n](BF4) n (2a, M=Mo, n=1; 2b, M=W, n=1; 3a, M=Mo, n=2; 3b, M=W, n=2). These singly and doubly charged cationic species have been characterized by 1H-, 13C-, 31P-, 19F-NMR and IR spectroscopy, as well as elemental analysis. The CO lability of 3a and 3b generated the 16-electron species, [P(2-py)3M(NO)2]2+, which binds to most Lewis basic donor ligands to give complexes of the type, [P(2-py)3M(L)(NO)2](BF4)2 (L=nitriles, aldehydes). A single crystal of [P(2-py)3M(CH3CH2CN)(NO)2](BF 4)2·CH3NO2 was also isolated and structurally characterized. The crystallographic analysis indicated an octahedral arrangement about the Mo metal center. The 1H-NMR downfield shift of the metal-coordinated crotonaldehyde in compounds 4c and 5c is used as a qualitative measurement of relative Lewis acidity, and the acid strength of [P(2-py)3M(NO)2]2+ is comparable to that of TiCl4 when M=Mo and to BF3 and AlCl3 when M=W. The Diels-Alder reactions between cyclohexadienes and methyl vinyl ketone were catalyzed by 0.3 mol% of [P(2-py)3W(CO)(NO)2](BF4)2 (3b) to afford an average 94% conversion and 83% isolated yield. © 1999 Elsevier Science S.A.
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