Metal-free dehydropolymerisation of phosphine-boranes using cyclic (alkyl)(amino)carbenes as hydrogen acceptors.

ABSTRACT: The divalent carbene carbon centre in cyclic (alkyl)(amino)carbenes (CAACs) is known to exhibit transition-metal-like insertion into E-H ?-bonds (E?=?H, N, Si, B, P, C, O) with formation of new, strong C-E and C-H bonds. Although subsequent transformations of the products represent an attractive strategy for metal-free synthesis, few examples have been reported. Herein we describe the dehydrogenation of phosphine-boranes, RR'PH·BH₃, using a CAAC, which behaves as a stoichiometric hydrogen acceptor to release monomeric phosphinoboranes, [RR'PBH₂], under mild conditions. The latter species are transient intermediates that either polymerise to the corresponding polyphosphinoboranes, [RR'PBH₂]_n (R?=?Ph; R'?=?H, Ph or Et), or are trapped in the form of CAAC-phosphinoborane adducts, CAAC·H₂BPRR' (R?=?R'?=?tBu; R?=?R'?=?Mes). In contrast to previously established methods such as transition metal-catalysed dehydrocoupling, which only yield P-monosubstituted polymers, [RHPBH₂]_n, the CAAC-mediated route also provides access to P-disubstituted polymers, [RR'PBH₂]_n (R?=?Ph; R'?=?Ph or Et).

SUBMITTER: Oldroyd NL 

PROVIDER: S-EPMC6435733 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature