RUTHENIUM-CATALYZED ARBUZOV REARRANGEMENT OF (ALLYLOXY)PHOSPHINES - ISOLATION AND X-RAY STRUCTURE-ANALYSIS OF AN INTERMEDIATE LEADING TO MECHANISTIC CONCLUSIONS

The [CpRu(CH3CN)3]PF6-catalyzed classical Arbuzov rearrangement of (allyloxy)phosphines Ph(n)P(OC3H5)3-n (n = 0-2) at room temperature in neat (allyloxy)phosphine proceeds to completion in a short time period and gives only the classical Arbuzov rearrangement products, Ph(n)P(O)(C3H5)(OC3H5)2-n (n = 0-2). The reaction mechanism was studied in acetonitrile solution by P-31{H-1} NMR spectroscopy and supported by isolation and characterization of intermediates and final products. In addition to the classical Arbuzov product, with Ph2P(OC3H5), the mono-chelation product [CpRu(CH3CN){eta(3)Ph2P(OC3H5)]PF6 (6) was isolated and characterized; with PhP(OC3H5)2, the bis-chelation products [CpRu{eta(5)-PhP(OC3H5)2}]PF6 (5a,b) were isolated and characterized; with P(OC3H5)3, the intermediate phosphite complex [CpRu{eta(5)-P(OC3H5)3}]PF6 (2), the final product of dealkylation [CpRu{eta(5)-P(O)(OC3H5)2}] (4), the alkylation product [CpRu(eta(3)-C3H5)(CH3CN)2][PF6]2 (1), and the hydrolysis product [CpRu{eta(5)-P(OH)(OC3H5)2}]PF6 (3) have been isolated and characterized by elemental analysis, infrared spectroscopy, and H-1, C-13{H-1}, and P-31{H-1} NMR spectroscopy. The structure of 2 was confirmed by X-ray crystallography. It crystallizes in the monoclinic space group P2(1)/n in a unit cell of dimensions a = 7.603 (5) angstrom, b = 20.507 (3) angstrom, c = 12.054 (2) angstrom, beta = 97.45 (2)-degrees, and rho(calcd) = 1.829 g cm-3 with Z = 4. Refinement converged to R = 0.041 and 1892 independent observed (I/sigma(I) greater-than-or-equal-to 3.0) reflections. The two coordinated alkene moieties are inequivalent having different dihedral angles between the planes of the C5H5 rings and the C-C axes (4.8, 36.10-degrees) and slightly different average Ru-C bond distances of 2.213 (8) and 2.239 (9) angstrom. The P-OH and P = O complexes, 3 and 4, are interconvertible via simple acid-base reactions.