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• 28347-92-4 5-Cl-closo-2,4-C₂B₅H₆ 

Relevant academic research and scientific papers

Substituent effects on closo-2,4-C2B5H7 derivative rearrangement rates. Comparison of rearrangement pattern and rate constants of a mixed disubstituted carborane, 5-CH3-6-Cl-2,4-C2B5H5, with those of monosubstituted 5-X-2,4-C2B5H6 and disubstituted 5,6-X2 ...

Full title: Substituent effects on closo-2,4-C2B5H7 derivative rearrangement rates. Comparison of rearrangement pattern and rate constants of a mixed disubstituted carborane, 5-CH3-6-Cl-2,4-C2B5H5, with those of monosubstituted 5-X-2,4-C2B5H6 and disubstituted 5,6-X2-2,4-C2B5H5 (X = CH3, Cl): Mechanistic implications and isomer stability correlations. The rearrangement of 5-CH3-6-Cl-closo-2,4-C2B5H5 to an equilibrium mixture of all eight B-CH3-B′-Cl-closo-2,4-C2B5H5 isomers is carried out at 295°C. The first isomer produced is 1-CH3-5-Cl-2,4-C2B5H5 followed by 3-CH3-5-Cl-2,4-C2B5H5. The order of appearance of the other five isomers is as follows: 5-CH3-1-Cl-2,4-C2B5H5, 5-CH3-3-Cl-2,4-C2B5H5, 3-CH3-1-Cl-2,4-C2B5H5, 1-CH3-3-Cl-2,4-C2B5H5, 1-CH3-7-Cl-2,4-C2B5H5. Rearrangement rate comparisons to those of the related mono- and disubstituted compounds 5-X-closo-2,4-C2B5H6 and 5,6-X2-closo-2,4-C2B5H5 (X = CH3, Cl) indicate that (a) the presence of a second substituent accelerates the apparent rearrangement of the first substituent and (b) the effect of Cl in this regard is greater than that of CH3. The rearrangement pattern for 5-CH3-6-Cl-closo-2,4-C2B5H5 rules out a triangle-face-rotation mechanism in which cage-carbon atoms stay in the low-coordination nonadjacent positions and is consistent with a diamond-square-diamond mechanism. The relative stabilities of the eight B-CH3-B′-Cl-closo-2,4-C2B5H5 isomers, after statistical weighting, are 1-CH3-3-Cl- > 3-CH3-5-Cl-> 3-CH3-1-Cl- > 5-CH3-3-Cl- > 1-CH3-5-Cl- > 5-CH3-6-Cl- > 5-CH3-1-Cl- > 1-CH3-7-Cl-C2B5H5. This order of observed isomer stabilities is forecast, with only minor departures, from additive substituent-positional effects.

Reaction of (CH3)3L (L = N, P) with chlorinated compounds of closo -2,4-C2B5H7: Net displacement reactions at boron atoms of closo-carboranes

Unlike the parent pentagonal-pyramidal closo-2,4-C2B5H7, both 3-Cl-closo-2,4-C2B5H6 and 5-Cl-closo-2,4-C2B5H6 readily react with (CH3)3L (L = N, P) to form 1:1 adducts. Removal of Cl- from these two adducts, using BCl3, produces the unique [3-(CH3)3L-closo-2,4-C2B5H 6]+ and [5-(CH3)3L-closo-2,4-C2B5H 6]+ cations, respectively. The reaction of (CH3)3N with 1-Cl-closo-2,4-C2B5H6 proceeds with more difficulty than with the other two B-Cl isomers, but once formed, the 1:1 adduct combines with BCl3 to give the rearrangement product [3-(CH3)3N-closo-2,4-C2B5H 6]+[BCl4]-.