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 H2 E'-BH2 -NMe3 (E'=P, As) with pnictogen-based nucleophiles MER1R2 (E=P, As; R1=H, R2=t Bu; R1=R2=Ph; M=Na, K) allows for the isolation of the unsymmetrical products [Na(18-crown-6)][H2 E'-BH2 -EHt Bu] (3: E=E'=P; 4: E=E'=As; 5: E=As, E'=P) and [M(C)][H2 E'-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)][H2 As-BH2 -t BuPH-BH3 ] (6) is only accessible by a different pathway, using t BuPH2 , BH3 ⋅ SMe2 and NaNH2 as starting materials. Additionally, the synthesis of symmetrical diphenyl-substituted compounds [M(18-crown-6)][Ph2 E-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 H2 E'-BH2 -NMe3 leading to corresponding five-membered chain-like compounds [Na(18-crown-6)][H2 E-BH2 -R1R2P-BH2 -E'H2 ] (E=E'=P, R1=H, R2=t Bu (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.

Oxidation of Substituted Phosphanylboranes with Chalcogens.

The elemental chalcogens sulfur, selenium, tellurium and bis(trimethylsilyl)peroxide as an oxygen source are applied for the oxidation of the phosphanylboranes Ph2 P-BH2 ⋅NMe3 (1) and tBuHP-BH2 ⋅NMe3 (2). The corresponding monooxidation products Ph2 P(X)-BH2 ⋅NMe3 (X=O-Te, 3 a-d) and tBuHP(X)-BH2 ⋅NMe3 (X=O-Te, 4 a-d) were obtained in good yields and comprehensively characterized by single crystal X-ray structure analysis, NMR, IR spectroscopy and mass spectrometry. The first oxidation step proceeds very selectively for all chalcogenides. For the tBu derivative, a further oxidation can be realised with O2 , S8 and Se yielding tBu(HX)P(X)-BH2 ⋅NMe3 (X=O, S, Se, 5 a-c). The telluride compounds presented herein are the first examples of neutral Te-substituted phosphanylboranes.

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.