The Dehydropolymerization of H3B•NMeH2 to form Polyaminoboranes using [Rh(Xantphos–alkyl)] Catalysts.

Gemma M. Adams, Annie Louise Colebatch, Joseph T. Skornia, Alasdair I. Mckay, Heather C. Johnson, Guy C. Lloyd-jones, Stuart A. Macgregor, Nicholas A. Beattie, Andrew S. Weller

Research output: Contribution to journalArticlepeer-review

Abstract

A systematic study of the catalyst structure and overall charge for the dehydropolymerization of H3B·NMeH2 to form N-methyl polyaminoborane is reported using catalysts based upon neutral and cationic {Rh(Xantphos–R}}
fragments, in which PR2 groups are selected from Et, iPr and tBu. The most efficient systems are based upon {Rh(Xantphos–iPr}}, i.e. [Rh(k3–P,O,P–Xantphos–iPr)(H)2(h1–H3B·NMe3)][BArF4], 6, and Rh(k3–P,O,P–Xantphos–iPr)H,
11. While H2 evolution kinetics show both are fast catalysts (ToF ~ 1500 hr–1), and polymer growth kinetics for dehydropolymerization suggest a classical chain growth process for both, neutral 11 (Mn = 28,000 g mol–1, Ð = 1.9) promotes
significantly higher degrees of polymerization than cationic 6 (Mn = 9,000 g mol–1, Ð = 2.9). For 6 isotopic labelling studies suggest a rate determining NH activation, while speciation studies, coupled with DFT calculations, show the formation of a dimetalloborylene [{Rh(k3–P,O,P–Xantphos–iPr)}2B]+ as the, likely dormant, end product of catalysis. A dual mechanism is proposed for dehydropolymerization, in which neutral hydrides (formed by hydride transfer in cationic 6 to form a boronium co–product) are the active catalysts for dehydrogenation to form aminoborane. Contemporaneous chain–growth polymer propagation occurs on a separate metal center via head-to-tail end chain B–N bond formation of the aminoborane monomer, templated by an aminoborohydride–containing catalyst.
Original languageEnglish
JournalJournal of the American Chemical Society
Early online date29 Dec 2017
DOIs
Publication statusE-pub ahead of print - 29 Dec 2017

Fingerprint

Dive into the research topics of 'The Dehydropolymerization of H3B•NMeH2 to form Polyaminoboranes using [Rh(Xantphos–alkyl)] Catalysts.'. Together they form a unique fingerprint.

Cite this