STRUCTURAL STUDIES OF ORGANOBORON COMPOUNDS .59. REACTION OF 2 STERICALLY HINDERED N,N'-DIHYDROXYAMINALS WITH PHENYLBORONIC ACID, AND THE CRYSTAL AND MOLECULAR-STRUCTURES OF THE RESULTING 1,3,5-TRIOXA-6,8-DIAZA-2,4-DIBORACYCLOOCTANES AND ONE OF THE ADDUCTS

The syntheses of the sterically hindered N,N'-dihydroxyaminals; N,N'-bis(1-ethoxycarbonyl-1-methylethyl)-N,N' -dihydroxymethanediamine, 1b, and N,N'-bis(1,1-dimethylethyl)-N,N'-dihydroxymethanediamine, 1c, and their reactions with phenylboronic acid to yield the 1,3,5-trioxa-6,8-diaza-2,4-diboracyclooctanes 3 and 4, respectively, are described. Crystals of 1b are tetragonal, a = 18.413(1), c = 9.867(2) Angstrom, Z = 8, space group I4(1); those of 3 are monoclinic, a = 20.420(4), b = 8.272(4), c = 17.851(5) Angstrom, beta = 117.34(1)degrees, Z = 4, space group C2/c; and those of 4 are monoclinic, a = 9.493(4), b = 16.202(4), c = 14.783(3) Angstrom, beta = 101.90(2)degrees, Z = 4, space group P2(1)/c. The structures were solved by direct methods and were refined by full-matrix least-squares procedures to R = 0.034, 0.039, and 0.040 (R(W) = 0.035, 0.034, and 0.036) for 1550, 1438, and 2187 reflections with I greater than or equal to 3 sigma(F-2), respectively. In the solid state, both 3 and 4 exhibit transannular N... B interactions. In 3 there are two identical (by symmetry) interactions with N...B = 2.433(3) Angstrom that have estimated bond orders of 0.06, while the single transannular interaction in 4 has N-B = 1.953(3) Angstrom and a bond order of about 0.3. The intermediate-strength transannular interaction in 4 is the first to be reported for this type of molecule.