Control of Stability through Overlap Matching: closo-Carborynes andcloso-Silaborynes

Abstract

The matching of ring and cap orbitals for overlap is used to arrive at the best carborynes among the many possibilities. Accordingly, 1,2-carboranes, 1,2-silaboranes (C2BnHn+2, and Si2BnHn+2, n = 4, 5, 8, and 10), and their dehydrogeno derivatives were studied with use of the Density Functional Theory (B3LYP/6-311+G*). The dehydrogenation of 2,3-C2B5H7 (6a) to 2,3-C2B5H5 (13a) is estimated to be even less endothermic than those of benzene and 1,2- C2B10H12 (1a) to benzyne and 1,2-C2B10H10 (8a) by more than 21 kcal/mol. This is due to the extra stabilization gained through better overlap of the C2B3H3 ring with the 2 BH caps. The relatively larger size of the Si atom leads to overlap requirements in silaboranes that are different from those in carboranes. The lower Si-Si single bond energy and the preference of Si for lower coordination result in unusual structures in dehydrogenosilaboranes. One of the Si atoms moves away from the surface in Si2B10H10 (15), Si2B8H8 (16, 17, and 18), and 1,2-Si2B5H5 (19). One Si atom forms a bridge to a trigonal surface in 2,3-Si2B5H5 (20) and 1,2-Si2B4H4 (21). Estimates of three-dimensional aromaticity with NICS calculations show that the exohedral double bond does not influence three-dimensional aromaticity.

Heteroborane analogs of silicon clusters: Experimental and theoretical studies on Bi2Si5 and Bi2Si5−

“…3. 21,[28][29][30][31] We have shown that structurally the lowest energy isomers of Bi 2 Si 5 resemble those of Bi 2 B 5 H 5 . The four most stable isomers ͑structures 6-9͒ have essentially the same energies within our capacity to calculate them.…”

A photoelectron spectroscopic and computational study of the o-dicarbadodecaborane parent anion

“…Nevertheless, since the hydrogen atoms bonded to o-carborane's two carbon atoms are acidic, the doubly deprotonated di-anion, (C 2 B 10 H 10 ) 2− has been produced by reacting o-carborane with n-butyl-lithium in tetrahydrofuran. [10][11][12] Moreover, the C 2 B 10 H 12 cage itself can accommodate two additional electrons. The (C 2 B 10 H 12 ) 2− dianion has been prepared by reacting o-carborane with the Na/K alloy in tetrahydrofuran, 13 and based on calculations, it is thought to have a nido-structure.…”

Recent advances in transition metal-mediated functionalization of o-carboranes

“…15 Transition metal-promoted reaction of carboryne Carboryne, 1,2-dehydro-o-carborane, is a three-dimensional relative of benzyne (Chart 1). 16 It can react with alkenes, dienes, and alkynes in [2+2], [4+2] cycloaddition and ene-reaction patterns, 17 similar to those of benzyne. 18 Although these reactions show potential for the preparation of functionalized carboranes in a single operation, they are complex and do not proceed in a controlled manner.…”