Syntheses, Structures, Reactivity, and Catalytic Applications of Enantiopure Rhenium-Containing P-Stereogenic Phosphonium Salts, Phosphines, Phosphine Boranes, and Phosphine Oxides

Easily accessed enantiopure (η⁵-C₅H₅)Re(NO)(PPh₃)(CH₃) is treated with Ph₃C⁺ PF₆^– (−78 °C) to generate the methylidene cation [(η⁵-C₅H₅)Re(NO)(PPh₃)(=CH₂)]⁺ and then racemic chiral secondary phosphines PHXX′ (4; X/X′ = a, tBu/Ph; b, Cy/Ph; c, tBu/Cy; d, CH₃/Ph; e, 2-furyl/Ph; f, α-naph/Ph; g, β-naph/Ph) to give the phosphonium salts (S_ReR_P)- and (S_ReS_P)-[(η⁵-C₅H₅)Re(NO)(PPh₃)(CH₂PHXX’)]⁺ PF₆^– (2·H⁺) as mixtures of Re, P-diastereomers that are usually separable (a,b,c,f,g). Treatment of 2a-g·H⁺ with tBuOK generates the phosphines 2a-g, which are variously isolated (2f,g), treated with BH₃·S(CH₃)₂ to give 2a-e·BH₃, or oxidized (O₂ or PhIO) to give 2a-c·O. Oxidations are also effected with 2a,c that has been generated from 2a,c·BH₃ and pyrrolidine. For the diastereomerically pure complexes in the a-c series, configurations have been assigned crystallographically, and the Ph₃P–Re–CH₂–P−X conformations were analyzed in detail. In an unusual but precedented phenomenon, the diastereomers of 2a·H⁺ PF₆^– cocrystallize. 2f,g catalyze highly enantioselective intramolecular Morita–Baylis–Hillman cyclizations of R(CO)CH═CHCH₂CH₂CHO (R═Ph, SiPr), and (S_ReS_P)-2b (2.4 mol %) and [Pd(allyl)Cl]₂ (1.2 mol % based upon “Pd atoms”) give a catalyst for the allylic alkylation of racemic 3-(acetoxy)cyclohexene that furthermore effects a kinetic resolution of the educt (s = 15.0).