TY - JOUR
T1 - Controlled Synthesis of Well-Defined Polyaminoboranes on Scale Using a Robust and Efficient Catalyst
AU - Brodie, Claire N.
AU - Boyd, Timothy M.
AU - Sotorríos, Lia
AU - Ryan, David E.
AU - Magee, Eimear
AU - Huband, Steven
AU - Town, James S.
AU - Lloyd-Jones, Guy C.
AU - Haddleton, David M.
AU - Macgregor, Stuart A.
AU - Weller, Andrew S.
N1 - Funding Information:
EPSRC (EP/M024210/2; EP/T019867/1), University of Oxford. Drs R. Douthwaite and C. Spicer (York) for help with electrospray experiments. The York Jeol Nanocentre.
Publisher Copyright:
©
PY - 2021/12/15
Y1 - 2021/12/15
N2 - The air tolerant precatalyst, [Rh(L)(NBD)]Cl ([1]Cl) [L = κ3-(iPr2PCH2CH2)2NH, NBD = norbornadiene], mediates the selective synthesis of N-methylpolyaminoborane, (H2BNMeH)n, by dehydropolymerization of H3B·NMeH2. Kinetic, speciation, and DFT studies show an induction period in which the active catalyst, Rh(L)H3 (3), forms, which sits as an outer-sphere adduct 3·H3BNMeH2 as the resting state. At the end of catalysis, dormant Rh(L)H2Cl (2) is formed. Reaction of 2 with H3B·NMeH2 returns 3, alongside the proposed formation of boronium [H2B(NMeH2)2]Cl. Aided by isotopic labeling, Eyring analysis, and DFT calculations, a mechanism is proposed in which the cooperative "PNHP" ligand templates dehydrogenation, releasing H2B═NMeH (ΔG‡calc = 19.6 kcal mol-1). H2B═NMeH is proposed to undergo rapid, low barrier, head-to-tail chain propagation for which 3 is the catalyst/initiator. A high molecular weight polymer is formed that is relatively insensitive to catalyst loading (Mn ∼71 000 g mol-1; Đ, of ∼ 1.6). The molecular weight can be controlled using [H2B(NMe2H)2]Cl as a chain transfer agent, Mn = 37 900-78 100 g mol-1. This polymerization is suggested to arise from an ensemble of processes (catalyst speciation, dehydrogenation, propagation, chain transfer) that are geared around the concentration of H3B·NMeH2. TGA and DSC thermal analysis of polymer produced on scale (10 g, 0.01 mol % [1]Cl) show a processing window that allows for melt extrusion of polyaminoborane strands, as well as hot pressing, drop casting, and electrospray deposition. By variation of conditions in the latter, smooth or porous microstructured films or spherical polyaminoboranes beads (∼100 nm) result.
AB - The air tolerant precatalyst, [Rh(L)(NBD)]Cl ([1]Cl) [L = κ3-(iPr2PCH2CH2)2NH, NBD = norbornadiene], mediates the selective synthesis of N-methylpolyaminoborane, (H2BNMeH)n, by dehydropolymerization of H3B·NMeH2. Kinetic, speciation, and DFT studies show an induction period in which the active catalyst, Rh(L)H3 (3), forms, which sits as an outer-sphere adduct 3·H3BNMeH2 as the resting state. At the end of catalysis, dormant Rh(L)H2Cl (2) is formed. Reaction of 2 with H3B·NMeH2 returns 3, alongside the proposed formation of boronium [H2B(NMeH2)2]Cl. Aided by isotopic labeling, Eyring analysis, and DFT calculations, a mechanism is proposed in which the cooperative "PNHP" ligand templates dehydrogenation, releasing H2B═NMeH (ΔG‡calc = 19.6 kcal mol-1). H2B═NMeH is proposed to undergo rapid, low barrier, head-to-tail chain propagation for which 3 is the catalyst/initiator. A high molecular weight polymer is formed that is relatively insensitive to catalyst loading (Mn ∼71 000 g mol-1; Đ, of ∼ 1.6). The molecular weight can be controlled using [H2B(NMe2H)2]Cl as a chain transfer agent, Mn = 37 900-78 100 g mol-1. This polymerization is suggested to arise from an ensemble of processes (catalyst speciation, dehydrogenation, propagation, chain transfer) that are geared around the concentration of H3B·NMeH2. TGA and DSC thermal analysis of polymer produced on scale (10 g, 0.01 mol % [1]Cl) show a processing window that allows for melt extrusion of polyaminoborane strands, as well as hot pressing, drop casting, and electrospray deposition. By variation of conditions in the latter, smooth or porous microstructured films or spherical polyaminoboranes beads (∼100 nm) result.
UR - http://www.scopus.com/inward/record.url?scp=85120857670&partnerID=8YFLogxK
U2 - 10.1021/jacs.1c10888
DO - 10.1021/jacs.1c10888
M3 - Article
C2 - 34846131
SN - 0002-7863
VL - 143
SP - 21010
EP - 21023
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 49
ER -