Group 9 catalysts for the preparation of N-substituted polyaminoboranes Mathew Cross, C. N. Brodie, A. S. Weller The University of York, UK
Polyaminoboranes, (H2BNRH)n, are boron-nitrogen based polymers isoelectronic with polyolefins. The materials properties of polyaminoboranes are essentially unexplored due to the difficulty in reliably synthesising derivatives where the NR group is varied.1 While many catalytic systems have been used to synthesise poly(N- methyl)aminoborane, there are limited options available for different substitutions on the nitrogen.2 Reported herein, the successful dehydropolymerisation of H3B·NRH2 (R = Et, nPr) is mediated by group 9 precatalyst complexes including: Rh{κ3-(R2PCH2CH2)2NH}H2Cl and Co{κ3-(R2PCH2CH2)2NH}Cl2, (R = iPr, Cy).3 Through a combination of kinetic analysis and in situ NMR spectroscopic observation of catalyst speciation, catalyst deactivation routes have been explored including the formation of catalytically inactive Rh{κ3- (iPr2PCH2CH2)2NH}(η1-HBH3)H2. With the dominant deactivation pathway in hand, countermeasures have been developed that allow for the reliable and efficient dehydropolymerisation without catalyst decomposition. This holistic approach of precatalyst modification and catalytic reaction condition optimisation has led to the ability to dehydropolymerise a variety of N-substituted amine-boranes, H3B·NH2R (R = Et, nPr). Characterisation of the polymeric products by gel permeation chromatography (GPC) has shown polymer molecular weight ranges of Mn: 50,000 – 80,000 g mol-1 with narrow dispersities (Đ): 1.5 - 1.8. These results lay the foundations for further customisation of polymer properties including copolymer synthesis and post-synthetic modification such as crosslinking. References 1. A. L. Colebach, A. S. Weller, Chem. Eur. J., 2019, 25, 1379-1390. 2. A. Staubitz, A. P. Soto, I. Manners, Angew. Chem. Int. Ed., 2008, 47, 6212-6215. 3. C. A. De Albuquerque Pinheiro, C. Roiland, P. Jehan, G. Alcaraz, Angew. Chem. Int. Ed., 2018, 57, 1519-1522. 4. E. A. LaPierre, B. O. Patrick, I. Manners, J. Am. Chem. Soc., 2019, 141, 20009-20015. 5. C. N. Brodie, T. M. Boyd, L. Sotorrios, D. E. Ryan, E. Magee, S. Husband, J. S. Town, G. C. Lloyd-Jones, D. M. Haddleton, S. A. Macgregor, A. S. Weller, J. Am. Chem. Soc., 2021.
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