Reactions of hydroborating reagents with phosphinorhodium hydride complexes:: molecular structures of a Rh2B3 metallaborane cluster, an L2Rh(η2-H2BR2) complex and a mixed valence Rh dimer containing a semi-bridging Bcat (cat=1,2-O2C6H4) group

The formation of products derived from competing reactions in Rh-catalyzed alkene hydroborations prompted us to study in situ interactions of several hydroborating reagents with unsaturated phosphinorhodium complexes. The reaction of [Rh(mu-H)(DiPPE)](2) (1) with borane-dimethylsulfide gave several rhodium-boron containing products including the structurally characterized metallaborane [RhH(DiPPE)](2)B3H7 (2) [DiPPE = 1,2-bis(diisopropylphosphino)ethane]. Addition of thexylborane and 9-H-BBN dimers, containing alkyl groups, to 1 gave the corresponding mononuclear substituted borohydride complexes Rh(eta(2)-H2BRR')(DiPPE) (4: R=H, R' = C(CH3)(2)CH(CH3)(2); 5: R,R'=bicyclo-[3.3.1]-nonane [C8H14]). The analogous monodentate phosphine complex Rh(eta(2)- H2BC8H14)(PPr'(3))(2) (6) was isolated and structurally characterized. Addition of catecholborane (HBcat; cat = 1,2-O2C6H4) to 1 gave the unusual dinuclear species Rh(DiPPE)(mu-H)(2)(mu-Bcat)RhH(DiPPE) (7) containing a semi-bridging Beat group, confirmed by single-crystal X-ray diffraction, and zwitterionic Rh(eta(6) -catBcat)(DiPPE) (8). Implications for rhodium-catalyzed hydroborations are addressed. (C) 2004 Elsevier Ltd. All rights reserved.