Three- and Five-Membered Anionic Chains of Pnictogenylboranes

An unprecedented family of three- and five-membered substituted anionic derivatives of parent pnictogenylboranes is herein reported. Reacting various combinations of the pnictogenylboranes H2E '-BH2-NMe3 (E '=P, As) with pnictogen-based nucleophiles MER1R2 (E=P, As; R1=H, R2=Bu-t; R1=R2=Ph; M=Na, K) allows for the isolation of the unsymmetrical products [Na(18-crown-6)][H2E '-BH2-(EHBu)-Bu-t] (3: E=E '=P; 4: E=E '=As; 5: E=As, E '=P) and [M(C)][H2E '-BH2-EPh2] (7: E=E '=P, M=Na, C=18-crown-6; 8: E=E '=As; M=K, C=[2.2.2]cryptand; 9: E=P, E '=As, M=Na, C=[2.2.2]cryptand; 10: E=As, E '=P, M=K, C=[2.2.2]cryptand). [Na(18-crown-6)][H2As-BH2-(BuPH)-Bu-t-BH3] (6) is only accessible by a different pathway, using (BuPH2)-Bu-t, BH3 . SMe2 and NaNH2 as starting materials. Additionally, the synthesis of symmetrical diphenyl-substituted compounds [M(18-crown-6)][Ph2E-BH2-EPh2] (11: E=P, M=Na; 12: E=As, M=K) is reported which can be regarded as isostructural inorganic, negatively charged analogs of dppm (1,1-bis(diphenylphosphino)methane) and dpam (1,1-bis(diphenylarsino)methane). Furthermore, an elongation of the pnictogen boron backbone in compounds 3, 7 and 9 ' (similar compound to 9, stabilized however by 18-crown-6), is attainable by reacting them with the pnictogenylboranes H2E '-BH2-NMe3 leading to corresponding five-membered chain-like compounds [Na(18-crown-6)][H2E-BH2-R1R2P-BH2-E ' H-2] (E=E '=P, R1=H, R2=Bu-t (13); E=E '=P, R1=R2=Ph (14); E=E '=As, R1=R2=Ph (15); E=P, E '=As, R1=R2=Ph (16)). Finally, the thermodynamics of the reaction pathways were evaluated by quantum chemical computations.

Automated summary

This article reports an unprecedented family of substituted anionic derivatives of pnictogenylboranes. By reacting various combinations of H2E'-BH2-NMe3 (E'=P, As) with pnictogen-based nucleophiles MER1R2 (E=P, As; R1=H, R2=Bu-t; R1=R2=Ph; M=Na, K), unsymmetrical and symmetrical products were isolated. Furthermore, the thermodynamics of the reaction pathways were evaluated by quantum chemical computations.