Ambient Temperature Carbene-Mediated Depolymerization: Stoichiometric and Catalytic Reactions of N -Heterocyclic- and Cyclic(Alkyl)Amino Carbenes with Poly( N -Methylaminoborane) [MeNH-BH 2 ] n .

The reactions of the N -heterocyclic carbenes (NHCs) IDipp and I t Bu and the cyclic(alkyl)amino carbene (CAAC) CAAC Me with polyaminoborane [MeNH-BH 2 ] n 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-BH 2 NMeH ( 1 ), cyclic borazane [MeNH-BH 2 ] 3 , or borazine [MeNBH] 3 with IDipp, I t Bu, and CAAC Me , respectively. With substoichiometric quantities of IDipp and I t Bu (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-BH 2 NMeH ( 1 ) and [MeNH-BH 2 ] 3 and with substoichiometric I t Bu, [MeNH-BH 2 ] 3 , and [MeNBH] 3 with product ratios dependent on the quantity of NHC used. Under analogous conditions with CAAC Me , high molar mass material persisted alongside the formation of [MeNBH] 3 . Further reactivity studies with cyclic borazane [MeNH-BH 2 ] 3 and MeNH 2 ·BH 3 provided insights into depolymerization pathways. IDipp showed no reactivity toward [MeNH-BH 2 ] 3 , whereas with 3 equiv of I t Bu and CAAC Me , the dehydrogenation product [MeNBH] 3, was formed. With MeNH 2 ·BH 3 , 2 equiv of carbene were used as the first acts to accept dihydrogen; the major products with IDipp, I t Bu, and CAAC Me were IDipp-BH 2 NMeH ( 1 ), [MeNBH] 3 , and (CAAC Me H)HB═NMeH ( 2 ), respectively. The double E-H (E = B, N) bond activation product (CAAC Me H)HB═NMe(HCAAC Me ) ( 3 ) was isolated from the reaction between 3 equiv of CAAC Me and MeNH 2 ·BH 3 . A unified mechanism for donor-mediated depolymerization of [MeHN-BH 2 ] n is proposed.