Ambient Temperature Carbene-Mediated Depolymerization: Stoichiometric and Catalytic Reactions of -Heterocyclic- and Cyclic(Alkyl)Amino Carbenes with Poly(-Methylaminoborane) [MeNH-BH].

The reactions of the -heterocyclic carbenes (NHCs) IDipp and IBu and the cyclic(alkyl)amino carbene (CAAC) CAAC with polyaminoborane [MeNH-BH] were investigated. Stoichiometric quantities of each carbene were found to cause rapid and complete depolymerization, with the major B-N-containing product identified as the NHC-aminoborane adduct, IDipp-BHNMeH (), cyclic borazane [MeNH-BH], or borazine [MeNBH] with IDipp, IBu, and CAAC, respectively. With substoichiometric quantities of IDipp and IBu (down to 10 and 2.5 mol %, respectively), complete loss of high molar mass material was also detected, indicating that the depolymerization is catalytic. The main products of the reaction with substoichiometric IDipp were IDipp-BHNMeH () and [MeNH-BH] and with substoichiometric IBu, [MeNH-BH], and [MeNBH] with product ratios dependent on the quantity of NHC used. Under analogous conditions with CAAC, high molar mass material persisted alongside the formation of [MeNBH]. Further reactivity studies with cyclic borazane [MeNH-BH] and MeNH·BH provided insights into depolymerization pathways. IDipp showed no reactivity toward [MeNH-BH], whereas with 3 equiv of IBu and CAAC, the dehydrogenation product [MeNBH] was formed. With MeNH·BH, 2 equiv of carbene were used as the first acts to accept dihydrogen; the major products with IDipp, IBu, and CAAC were IDipp-BHNMeH (), [MeNBH], and (CAACH)HB═NMeH (), respectively. The double E-H (E = B, N) bond activation product (CAACH)HB═NMe(HCAAC) () was isolated from the reaction between 3 equiv of CAAC and MeNH·BH. A unified mechanism for donor-mediated depolymerization of [MeHN-BH] is proposed.