Transition metal catalysis in fluorous media: Practical application of a new immobilization principle to rhodium-catalyzed hydroborations of alkenes and alkynes

Addition of a yellow-orange toluene solution of [Rh(C1)(COD)]₂ to a colorless CF₃C₆F₁₁ solution of P(CH₂CH₂R(f6))₃ (R(f6) = (CF₂)₅CF₃)₃) gives a colorless toluene solution of COD and an orange CF₃C₆F₁₁ solution of ClRh[P(CH₂CH₂R(f6))₃]₃ (1). Evaporation of CF₃C₆F₁₁ gives analytically pure 1 (94%), which is insoluble in most organic solvents and stable to 300 °C. Alkenes, catecholborane, and CF₃C₆F₁₁ solutions of 1 (950:950:1 mol ratio for norbomene) are stirred for 1-24 h at 40 °C (heterogeneous conditions). The resulting alkylboranes are extracted with benzene (2x; turnover number (TON) 854 (90%) for norbornene), toluene, or THF, and the catalyst solution is reused (TON 2409 for three cycles). Subsequent reactions with H₂0₂/NaOH give alcohols, which are isolated in 92-77% yields (11 examples). Longer reaction times afford TON values higher than 10000 (2CH₂R(f8))₃]₃ (2), and the nonfluorinated analogue ClRh[P((CH₂)₇CH₃)₃]₃ are similarly prepared. Solubilities and reactivities are compared. Atomic absorption analyses shows rhodium losses of 0.4% (1) and 0.2% (2) per cycle, corresponding to 4.52.2 ppm rhodium/mol of addition product. These data demonstrate the viability and practicality of an exciting new approach to catalyst immobilization.