55017-05-5Relevant academic research and scientific papers
Homogeneous catalytic dehydrogenation/dehydrocoupling of amine-borane adducts by the Rh(I) Wilkinson's complex analogue RhCl(PHCy2) 3 (Cy ) cyclohexyl)
Sloan, Matthew E.,Clark, Timothy J.,Manners, Ian
, p. 2429 - 2435 (2009)
The Rh(l) complex RhCI(PHCy2)3 (1) (Cy = cyclohexyl, C6H11) has been investigated as a catalyst for the dehydrogenation/dehydrocoupling of dimethylamine-borane adduct Me 2NH·BH3 (3) at 20 °C to afford the cyclic dimer [Me2N-BH2]2 (4). Unlike previously studied neutral and Cationic Rh(l) precatalysts such as [{Rh(μ-CI)(1,5-cod)} 2] and [Rh(1,5-cod)2]OTf (1,5-cod = 1,5-cyclooctadiene, C8H12, OTf = OSO2CF3) with weakly electron-donating ligands at the metal center, which are reduced to catalytically active Rh(0) species, catalytic dehydrogenation of 3 using 1 was found to occur in a homogeneous manner according to nanofiltration experiments, Hg(0) poisoning and kinetic studies. Moreover, the presence of the sterically bulky ligand PHCy2 in complex 1 has been found to significantly increase the rate of reaction previously reported for Wilkinson's catalyst RhCI(PPh3)3. The catalytic activity of 1 toward a range of other amine-borane adducts RR'NH · BH3 (e.g., RR' = 'Pr 2, MeBz, MeH) at 20 °C was also investigated. The third row transition metal analogue of 1, the lr(l) complex lrCI(PHCy2) 3 (2), was also explored as a catalyst for the dehydrocoupling of 3 and was found to exhibit much reduced catalytic activity compared to 1 but proved significantly more active for sterically encumbered substrates. Addition of the strong Lewis acid B(C6F5)3 as a co-catalyst to both 1 and 2 has been found to significantly increase the rate of the dehydrocoupling reactions in all cases. The Rh(l) complex 1 (but not the lr(l) analogue 2) was also found to be active for the catalytic dehydrocoupling of the phosphine-borane adduct Ph2PH·BH3 (14) at 60-90 °C to afford linear dimer Ph2PH-BH2-PPh 2-BH3 (15).
