Ruthenium-catalyzed Arbuzov rearrangement of (allyloxy)phosphines: Isolation and X-ray structure analysis of an intermediate leading to mechanistic conclusions

Article abstract of DOI:10.1021/om00040a036

The [CpRu(CH₃CN)₃]PF₆-catalyzed classical Arbuzov rearrangement of (allyloxy)phosphines Ph_nP-(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_nP(O)(C₃H₅)(OC₃H₅) _2-n (n = 0-2). The reaction mechanism was studied in acetonitrile solution by ³¹P{¹H} 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){η³-Ph₂P(OC₃H ₅)]PF₆ (6) was isolated and characterized; with PhP(OC₃H₅)₂, the bis-chelation products [CpRu{η⁵-PhP(OC₃H₅₂}]PF ₆ (5a,b) were isolated and characterized; with P(OC₃H₅)₃, the intermediate phosphite complex [CpRu{η⁵-P(OC₃H₅)₃}]PF ₆ (2), the final product of dealkylation [CpRu{η⁵-P(O)(OC₃H₅)₂}] (4), the alkylation product [CpRu(η³-C₃H₅)(CH₃CN) ₂][PF₆]₂ (1), and the hydrolysis product [CpRu{η⁵-P(OH)(OC₃H₅)₂}]PF ₆ (3) have been isolated and characterized by elemental analysis, infrared spectroscopy, and ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR spectroscopy. The structure of 2 was confirmed by X-ray crystallography. It crystallizes in the monoclinic space group P2₁/n in a unit cell of dimensions a = 7.603 (5) A?, b = 20.507 (3) A?, c = 12.054 (2) A?, β = 97.45 (2)°, and ρ_calcd = 1.829 g cm^-3 with Z = 4. Refinement converged to R = 0.041 and 1892 independent observed (I/σ(I) ≥ 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°) and slightly different average Ru-C bond distances of 2.213 (8) and 2.239 (9) A?. The P-OH and P=O complexes, 3 and 4, are interconvertible via simple acid-base reactions.