Dehydropolymerisation of methylamine borane using highly active rhodium(iii) bis(thiophosphinite) pincer complexes: catalytic and mechanistic insights

Abstract

The bis(thiophosphinite) pincer complexes [(RPSCSPR)Rh(py)(H)(Cl)] (RPSCSPR = C6H4-2,6-(SPR2)2 with R = iPr, 2a and R = Ph, 2a) are prepared by metalation of the ligand precursor with [Rh(cod)Cl]2 in the...

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

“…We suggest this is as shown in Scheme . Informed by studies of Shubina and Beweries on the reaction of group-9 hydrido halides with H 3 B·NMe 2 H, or H 3 B·NMeH 2 , that results in a close to ergo-neutral chloride/hydride metathesis; the conversion of 2 to 3 by H 3 B·NMeH 2 is proposed to proceed via transition state B to give 3 and H 2 BNMeH/[NMeH 3 ]Cl in the presence of trace NMeH 2 that forms from B–N bond cleavage in H 3 B·NMeH 2 . These two coproducts would likely combine to afford the boronium chloride [H 2 B­(NMeH 2 ) 2 ]­Cl .…”

“…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 ].…”

“…For example, recent work in our laboratories using the cationic [Rh­(DPEphos)­(η-H 2 BNMeCH 2 CH 2 t Bu)]­[BAr F 4 ] catalyst , has revealed an induction process, nonliving chain-growth propagation, partial order in catalyst, and an inverse relationship between catalyst loading and degree of polymerization, with H 2 acting to control chain length. Detailed speciation and mechanistic studies resolve many of these complexities by revealing the true catalyst resting state as a dimeric, neutral , hydride [Rh­(DPEphos)­H 2 ] 2 arising from amine-promoted hydride transfer, ,, that arises from B–N bond cleavage of H 3 B·NMeH 2 . Moreover, a likely coproduct of this hydride transfer, boronium [H 2 B­(NMeH 2 ) 2 ]­[BAr F 4 ], was shown to act as a chain-length control agent, being proposed to protonate the amine-terminus of a growing polymer chain that arises from the low barrier head-to-tail B–N chain-forming events (e.g., Scheme ).…”

Iridium(iii) bis(thiophosphinite) pincer complexes: synthesis, ligand activation and applications in catalysis

“…10 Rh complexes thus obtained are efficient and stable catalysts for the dehydropolymerisation of methylamine borane. 11 With Ni, R PSCSP R complexes were found to show catalytic activity for Kumada coupling that was superior to R POCOP R systems. 12 However, in reactions with stoichiometric amounts of strong bases, ligand activation occurred that led to formation of di- and tetranuclear thiolate bridged complexes.…”