X-ray structures are described for the bis-catecholate, bis-dithiocatecholate, and tetraalkoxy diborane(4) compounds B2(1,2-O2C6H4)2 (1), B2(1,2-O2-4-ButC6H3)2 (2), B2(1,2-O2-3,5-But 2C6H2)2 (3), B2(1,2-S2C6H4)2 (4), B2(1,2-S2-4-MeC6H3)2 (5), and B2(OCH2CMe2CH2O)2 (6). All the compounds adopt structures in the solid-state in which the B2O4 or B2S4 units are planar or very nearly so. In compounds 2 and 3, the dihedral angles between the two BO2C2 planes are 17.3 and 31.8° respectively whereas in 1, 4 and 5 these angles are exactly 0°. In 6, a 3-fold disorder precluded our obtaining accurate positions for the two boron atoms, yet a dihedral angle of 0° is required by the 3̄ site symmetry. The structure of the bis(Lewis base) adduct of B2Cl4, [B2Cl4(NHMe2)2] (7), is also described and structures of the salt [NH2Me2][B(1,2-O2C6H4)2] (8) and the NMe2-bridged dimer [{BCl2(μ-NMe2)}2] (9) are available in the Supporting Information. Compound 1 crystallized in the monoclinic space group P21/c with a = 4.746(1) Å, b = 16.427(3) Å, c = 7.053(2) Å, β = 98.59(2)°, and Z = 2. Crystals of 2 were monoclinic, space group P21/c with a = 6.847(1) Å, b = 18.871(5) Å, c = 15.270(2) Å, β = 93.16(2)°, and Z = 4. Crystals of 3 were triclinic, space group P1̄ with a = 9.478(4) Å, b = 10.355(4) Å, c = 15.082(7) Å, α = 105.71(3)°, β = 100.31(4)°, γ = 94.58(3)°, and Z = 2. Crystals of 4 were monoclinic, space group P21/c with a = 15.364(3) Å, b = 4.0502(4) Å, c = 21.532(3) Å, β = 99.320(7)°, and Z = 4. Crystals of 5 were monoclinic, space group P21/c with a = 6.0458(9) Å, b = 7.5319(11) Å, c = 16.552(2) Å, β = 96.291(3)° and Z = 2. Compound 6 crystallized in the rhombohedral space group R3̄m with a = 8.876(2) Å, c = 13.821(3) Å and Z = 3. Crystals of 7 were monoclinic, space group P21/c with a = 11.831(3) Å, b = 19.458(5) Å, c = 14.823(5) Å, β = 96.63(4)°, and Z = 12.

The synthesis and characterization of a series of bis-catecholate diborane(4) compounds, B2(1,2-O2C6H4)2 (3), B2(1,2-O2-3-MeC6H3)2 (6), B2(1,2-O2-4-MeC6H3)2 (7), B2(1,2-O2-4-ButC6H3)2 (8), B2(1,2-O2-3,5-But 2C6H2)2 (9), B2(1,2-O2-3-MeOC6H3)2 (10), bis-dithiocatecholate diborane(4) compounds, B2(1,2-S2C6H4)2 (13), B2(1,2-S2-4-MeC6H3)2 (14), and tetraalkoxy diborane(4) compounds, B2(OCH2CMe2CH2O)2 (11) and B2(OCMe2CMe2O)2 (12) from B2(NMe2)4 (1) is described, as are the bis(NHMe2) adducts of 3 and 9, namely [B2(1,2-O2C6H4)2(NHMe2)2] (4) and [B2(1,2-O2-3,5-But 2C6H2)2(NHMe2)2] (5). The latter two compounds are intermediates in the formation of 3 and 9 from 1. Compound 1 is synthesized by reductive coupling of BCl(NMe2)2, which in turn is prepared from reaction of BCl3 with B(NMe2)3 in a 1:2 stoichiometry. We have also characterized [B2Cl4(NHMe2)2] (15) formed from addition of HCl to 1 prior to complete reaction with diols, and the salt, [NH2Me2][B(1,2-O2C6H4)2] (16), which arises from addition of catechol to B(NMe2)3. Thus, any B(NMe2)3 impurity present after the preparation of 1 needs to be removed by distillation prior to reaction with alcohols. The dimer, [BCl2(μ-NMe2)]2 (17) has also been characterized. This is formed from reaction 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-But-catechol, 2,2-dimethyl-1,3-propanediol, and pinacol. The ionization energies of the B2(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, whereas the presence of an aromatic ring rather than an aliphatic chain decreases the IE by ca. 1.50 eV. The presence of electron donating But-groups also decreases the IE.

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