Ether carbaboranes. Synthesis and characterization of mono- and di-ether carbaboranes with 1,2- closo-C 2B 10 structures, and their mono- and di-anionic nido-derivatives

Abstract

A series of new closo ether carbaboranes 1-R 1-2-R 2-1,2- closo-C 2B 10H 10 [ 1; R 1 = R 2 = (CH 2)OCH 3: 2; R 1 = (CH 2)OCH 3, R 2 = H: 3; R 1 = (CH 2) 2OCH 3, R 2 = H: 4; R 1 = (CH 2) 3OCH 3, R 2 = H] have been prepared and characterized. Trends in 11B NMR chemical shifts of 1, 2 and 1,2- closo-C 2B 10H 12 are discussed in terms of the electron-withdrawing properties of the CH 2OCH 3 group. A single crystal X-ray diffraction study on 2 reveals dimer formation in the solid state via reciprocal C cageH···O bonding. Partial cage degradation of 1 and 2 affords derivatives of [7,8- nido-C 2B 9H 12] − and of [7,8- nido-C 2B 9H 11] 2− (compounds 5–10). Crystallographic study of one of these, [BTMA][7-(CH 2OCH 3)-7,8- nido-C 2B 9H 11] ( 6), shows that the conformation of the pendant ether group is such that its oxygen atom lies to maximum elevation above the open C 2B 3 polyhedral face, and this conformation is shown to be close to the minimum energy one by the results of molecular orbital calculations at the extended Huckel level.