STRUCTURAL STUDIES OF NIDO-(MU-ME(2)B)B5H8, THE UNUSUAL BRIDGING HYDROGENS IN NIDO-2-MEB(6)H(9), AND NIDO-2,3-ME(2)B(6)H(8) AND THE PREDICTED STRUCTURE OF NIDO-2,4-ME(2)B(6)H(8) VIA THE AB-INITIO IGLO NMR METHOD

Gaines' structure of nido-mu(2,3)-(Me(2)B)-B5H8, A, with a doubly electron deficient boron, as well as Shore's structure for nido-2-MeB(6)H(9)-<mu-3,4-H >, Bb, with unsymmetrical bridge hydrogens have been reconfirmed via the ab initiol IGLO/NMR method. The B-11 NMR data of nido-2,3-Me(2)B(6)H(8), C, indicate that the <mu-3,4-H >-, Cb, and <mu-4,5-H >-isomers, Ca-1 are of nearly equivalent stability. nido-2,4-Me(2)B(6)H(8)-<mu-5,6-H >, Da, with symmetrical bridge hydrogens, is predicted to be more stable than the Ca and Cb isomers. These results allow an assessment of some of the factors determining bridge hydrogen placement and substitution patterns in the polyboranes.