A simple cobalt-based catalyst system for the controlled dehydropolymerisation of H₃B·NMeH₂ on the gram-scale

Abstract

A simple Co-based catalyst system promotes the efficient and controlled dehydropolymerisation of amine–boranes on scale.

Controlled Synthesis of Well-Defined Polyaminoboranes on Scale Using a Robust and Efficient Catalyst

“…Upon the basis of our detailed mechanistic studies, we propose that this selective, controlled, cascade polymerization results from an ensemble of processes (catalyst speciation, dehydrogenation, propagation, and chain transfer) that are all geared around the concentration of H 3 B•NMeH 2 . We suggest it is likely that similar correlated processes are operating with catalysts that also mediate controlled dehydropolymerization, 25,28,37,41,44 although the precise mechanistic details will likely differ between specific examples.…”

“…Significant progress has been made since this report with regard to the range of transition metal precatalysts that promote dehydropolymerization, 4,21−23 the scope of amine borane substrates, 24−29 and the development of noncatalytic routes. 30−32 In addition to A, notable catalysts for the dehydropolymerization of H 3 B•NRH 2 include those based upon (CpZrCl) 2 (allenediyl); 33 CoH(κ 4 -P(CH 2 CH 2 PPh 2 ) 3 ); 34 ( R PSCSP R )Rh(py)(H)(Cl) [ R PSCSP R = C 6 H 4 -2,6-(SPR 2 )]; 35 Fe(PhNCH 2 CH 2 NPh)(Cy 2 PCH 2 CH 2 PCy 2 ); 36 Cp* 2 TiCl 2 + 2 × n-BuLi; 28,37 ML n ( i Pr 2 PCH 2 CH 2 ) 2 NH) (M = Fe, 27,38,39 Ru, 40 Co; 41 42 DPEphos, 43,44 Xantphos-R (R = Ph, i Pr); 45,46 Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ].…”

“…The breakthrough reports of the metal catalyzed dehydropolymerization of the primary N -alkyl amine-borane H 3 B·NMeH 2 to give soluble, high molecular weight, − (H 2 BNMeH) n came in 2008, using the Ir­(POCOP)­H 2 catalyst [POCOP = κ 3 -(OP t Bu 2 ) 2 C 6 H 3 ] ( A , Scheme B) with H 2 as the only byproduct. Significant progress has been made since this report with regard to the range of transition metal precatalysts that promote dehydropolymerization, ,− the scope of amine borane substrates, − and the development of noncatalytic routes. − In addition to A , notable catalysts for the dehydropolymerization of H 3 B·NRH 2 include those based upon (CpZrCl) 2 (allenediyl); CoH­(κ 4 -P­(CH 2 CH 2 PPh 2 ) 3 ); ( R PSCSP R )­Rh­(py)­(H)­(Cl) [ R PSCSP R = C 6 H 4 -2,6-(SPR 2 )]; Fe­(PhNCH 2 CH 2 NPh)­(Cy 2 PCH 2 CH 2 PCy 2 ); Cp* 2 TiCl 2 + 2 × n -BuLi; , ML n ( i Pr 2 PCH 2 CH 2 ) 2 NH) (M = Fe, ,, Ru, Co; L n = PR 3 /CO/H/Cl); and precatalysts based upon cationic [Rh­(L 2 )]­[BAr F 4 ] [L 2 = Ph 2 PCH 2 CH 2 CH 2 PPh 2 , DPEphos, , Xantphos-R (R = Ph, i Pr); , Ar F = 3,5-(CF 3 ) 2 C 6 H 3 ].…”

“…We were interested to explore whether chain-length control could be extended to potentially more robust ML n ( i Pr 2 PCH 2 CH 2 ) 2 NH)-type systems, that have been shown to operate via ligand cooperative , amine-borane dehydrogenation mechanisms. Inspired by the work of Schneider and Beweries on such group 8 catalyst systems, ,− and our own recent report using Co­(II) precatalysts, we now report the simple, easy to assemble, tolerant-to-air, precatalyst [Rh­{( i Pr 2 PCH 2 CH 2 ) 2 NH}­(NBD)]­Cl, [1]­Cl , for the dehydropolymerization of commercial, as supplied, H 3 B·NMeH 2 in THF solvent, Chart . [1]­Cl promotes the fast (minutes, 298 K), efficient (1–0.01 mol %), and selective production of well-defined (H 2 BNMeH) n in high yield.…”

Cobalt-Catalyzed Ammonia Borane Dehydrogenation: Mechanistic Insight and Isolation of a Cobalt Hydride-Amidoborane Complex

“…First-row examples of Ni, , Ti, − Mn, Cr, , and, increasingly, Fe − complexes for homogeneous amine borane dehydrogenation have been demonstrated; however, for cobalt, there have only been a handful of published examples as depicted in Figure . These include a (PBP)Co pincer complex reported by Peters and Lin, a Cp-based cobalt complex by Waterman and co-workers, tripodal EP 3 (E = N and P) cobalt complexes by Rossin, Shubina, and co-workers, a highly reduced diimine cobaltate complex by Wangelin, Wolf, and co-workers, and most recently a (PNP)Co complex by Weller and co-workers …”