Development of Rhenium Catalysts for Amine Borane Dehydrocoupling and Transfer Hydrogenation of Olefins

作者：Jiang Yanfeng; Blacque Olivier; Fox Thomas; Frech Christian M; Berke Heinz^*

来源：Organometallics, 2009, 28(18): 5493-5504.

DOI：10.1021/om900458e

Five-coordinated rhenium(I) hydride complexes of the type [Re(Br)(H)(NO)(PR(3))(2)] (R = Cy 2a, iPr 2b) were prepared from [Re(Br)(2)(NO)(PR(3))(2)(eta(2)-H(2))] (R = Cy 1a, iPr 1b) via deprotonation of the eta(2)-H(2) ligands with various bases. Filling the vacant site of 2a or 2b by various less bulky two-electron donors produced the 18-electron complexes [Re(Br)(H)(NO)(PR(3))(2)(L)] (L = O(2) 3, CH(2)=CH(2) 4, acetylene 5, H(2) 6, CO 7, CH(3)CN 8). The influence of the trans-coordinated ligand oil the Re-H bond was examined. The (1)H NMR chemical shift of the hydride depends oil L in the order O(2) > acetylene > CH(2)=CH(2) > H(2) > CO > CH(3)CN. The reactions of 2a or 2b with the IMes or SIMes ligands afforded the five-coordinatcd complex [Re(Br)(H)(NO)(PR(3))(NHC)] (NHC = IMes 9 (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), SIMes 10 (SIMes = 1,3-bis(2,4,6-trimethylpheiivl)-4,5-dihydroimidazol-2-ylidene)) via replacement of one phosphine. The reaction of 2a or 2b with n-BuLi leads to the formation of the n-butene-coordinated dillydride complexes [Re(H)(2)-(NO)(PR(3))(2)(eta(2) -n-CH(2)=CHC(2)H(5))] (R = Cy 12a, iPr 12b). Species la and 1b reacted also with NaNMe(2) center dot BH(3), affording the tetrahydride complexes [Re(H)(4)(NO)(PR(3))(2)] (R = Cy 14a, iPr 14b) via the intermediacy of 2a and 2b. The molecular structures of complexes 8b, 10a, and 10b were established by single-crystal X-ray diffraction studies. The five-coordinatcd rhenium(l) hydride complexes 2a, 2b, 9a, and 9b catalyzed the dehydrocoupling of Me(2)NH center dot BH(3) and the transfer hydrogenation of olefin using Me(2)NH center dot BH(3) as a hydrogen donor, which showed high activities. Mechanistic studies were carried out indicating that these rhenium(l) hydride catalyses allowed formation of dillydrogen hydride complexes. A plausible catalytic cycle for both dehydrocoupling and transfer hydrogenation was proposed, which implies the ability of rhenium(l) complexes to activate B-H and N-H bonds by the facile redox interplay of Re(l) and Re(Ill) species.

• 出版日期2009-9-28