BIS-CATECHOLATE, BIS-DITHIOCATECHOLATE, AND TETRAALKOXY DIBORANE(4) COMPOUNDS - ASPECTS OF SYNTHESIS AND ELECTRONIC-STRUCTURE

The synthesis and characterization of a series of bis-catecholate dibo rane(4) compounds, B-2(1,2-O2C6H4)(2) (3), B-2(1,2-O-2-3-MeC6H3)(2) (6 ), B-2(1,2-O-2-4-MeC6H3)(2) (7), B-2(1,2-O-2-4-(BuC6H3)-C-t)(2) (8), B -2(1,2-O-2-3,5-(Bu2C6H2)-C-t)(2) (9), B-2(1,2-O-2-3-MeOC6H3)(2) (10), bis-ditkiocatecholate diborane(3) compounds, B-2(1,2-S2C6H4)(2) (13), B-2(1,2-S-2-4-MeC6H3)(2) (14), and tetraalkoxy diborane(4) compounds, B-2(OCH2CMe2CH2O)(2) (11) and B-2(OCMe2CMe2O)(2) (12) from B-2(NMe2)(4 ) (1) is described, as are the bis(NHMe2) adducts or 3 and 9, namely [ B-2(1,1-O2C6H4)(2)-(NHMe2)(2)] (1) and [B-2(1,2-O-2-3,5-(Bu2C6H2)-C-t) (2)(NHMe2)(2)] (5). The latter two compounds are intermediates in thr formation of 3 and 9 from 1. Compound 1 is synthesized by reductive co upling of BCl(NMe2)(2), which in turn is prepared from reaction of BCl 3 with B(NMe2)(3) in a 1:2 stoichiometry. We have also tharacterized [ B2Cl4- (NHMe2)(2)] (15) formed from addition of HCl to 1 prior to comp lete reaction with diols, and the salt, [NH2Me2][B(1,2-O2C6H3)(2)] (16 ) which arises from addition of catechol to B(NMe2)(3). Thus, any B(NM e2)(3) impurity present after the preparation of 1 needs to be removed by distillation prior to reaction with alcohols. The dimer, [BCl2-(mu -NMe2)](2) (17) has also been characterized. This is formed from react ion of BCl3 with B(NMe2)(3) if a 2:1 rather than 1:2 stoichiometry is used. Photoelectron spectra of 1, 3, 8, 11, and 12 are reported along with those of the corresponding diols, catechol, 4-Bu-t-catechol, 2,2- dimethyl-1,3-propanediol. and pinacol. The ionization energies of the B-2(OR)(4) compounds follow the series 8 < 3 < 12 < 11. Replacement of O for N in the B2N4 framework increases the IE by ca. 1.65 eV, wherea s the presence of an aromatic ring rather than an aliphatic chain decr eases the IE by ca. 1.50 eV. The presence of electron donating Bu-t-gr oups also decreases the IE.