Anionic Chains of Parent Pnictogenylboranes.

We report on the synthesis and structural characterization of unprecedented anionic parent compounds of mixed Group 13/15 elements. The reactions of the pnictogenylboranes H2 E-BH2 ⋅NMe3 (1 a=P, 1 b=As) with phosphorus and arsenic centered nucleophiles of the type [EH2 ]- (E=P, As) lead to the formation of compounds of the type [H2 E-BH2 -E'H2 ]- (2: E=E'=P; 3: E=E'=As; 4: E=P, E'=As) containing anionic pnictogen-boron chain-like units. Furthermore, a longer 5-membered chain species [H2 As-BH2 -PH2 -BH2 -AsH2 ]- (5) and a cyclic compound [NHCdipp -H2 B-PH2 -BH2 -NHCdipp ]+ [P5 B5 H19 ]- (6) containing a n-butylcyclohexane-like anion were obtained. All the compounds have been characterized by X-ray structure analysis, multinuclear NMR spectroscopy, IR spectroscopy, and mass spectrometry. DFT calculations elucidate their high thermodynamic stability, the charge distribution, and give insight into the reaction pathway.