Large-bite diboranes for the mu(1,2) complexation of hydrazine and cyanide

• Published in: Chemical science (Cambridge) Vol. 9; no. 29; pp. 6210 - 6218
• Main Authors: Chen, Chang-Hong, Gabbai, Francois P.
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 07.08.2018; Royal Society of Chemistry
• Subjects: Benzaldehyde; Boranes; Boron; Chelates; Chemical synthesis; Chemistry; Chemistry, Multidisciplinary; Chloroform; Coordination compounds; Cyanides; Diatomic molecules; Diborane; Dilution; Hydrazines; Molecular chains; Organic chemistry; Physical Sciences; Science & Technology; Separation; MOLECULAR RECOGNITION; BIDENTATE LEWIS-ACID; WEAKLY COORDINATING ANIONS; OLEFIN POLYMERIZATION; MEMBRANE-ELECTRODE; ISOBUTENE POLYMERIZATION; CHALCOGEN BONDS; BINDING PROPERTIES; N BOND-CLEAVAGE; C-H
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c8sc01877d

As part of our interest in the chemistry of polydentate Lewis acids as hosts for diatomic molecules, we have investigated the synthesis and coordination chemistry of bidentate boranes that feature a large boron-boron separation. In this paper, we describe the synthesis of a new example of such a diborane, namely 1,8-bis(dimesitylboryl)triptycene (2) and compare its properties to those of the recently reported 1,8-bis(dimesitylboryl) biphenylene (1). These comparative studies reveal that these two diboranes feature some important differences. As indicated by cyclic voltammetry, 1 is more electron deficient than 2; it also adopts a more compact and rigid structure with a boron-boron separation (4.566(5) angstrom) shorter by similar to 1 angstrom than that in 2 (5.559(4) angstrom). These differences appear to dictate the coordination behaviour of these two compounds. While 2 remains inert toward hydrazine, we observed that 1 forms a very stable mu(1,2) hydrazine complex which can also be obtained by phase transfer upon layering a solution of 1 with a dilute aqueous hydrazine solution. The stability of this complex is further reflected by its lack of reaction with benzaldehyde at room temperature. We have also investigated the behaviour of 1 and 2 toward anions. In MeOH/CHCl3 (1/1 vol) both compounds selectively bind cyanide to form the corresponding mu(1,2) chelate complexes with a B-C N-B bridge at their cores. Competition experiments in protic media show that the anionic cyanide complex formed by 1 is the most stable, with no evidence of decomplexation even in the presence of (C6F5)(3)B.