40710-68-7Relevant academic research and scientific papers
Relative reactivities of the small closo carboranes 1,6-C2B4H6 and 2,4-C2B5H7 and of closo-1,10-C2B8H10 toward electrophilic reagents
Nam, Wonwoo,Onak, Thomas
, p. 1581 - 1586 (2008/10/08)
The relative reactivities of the closo carboranes C2BnHn+2 (n = 4, 5, 8), and some of their derivatives, toward electrophilic reagents of the type RX/AlCl3 (RX = CH3Cl, C2H5Cl, Cl2, Br2) are reported from competition studies. Among the three parent carborane compounds, closo-2,4-C2B5H7 is the most reactive toward an electrophilic type of substitution. Alkyl substituents on closo-2,4-C2B5H7 enhance the reactivity of the compound toward an electrophilic substitution, whereas halogen substituents decrease the reactivity. However, in the closo-1,6-C2B4H6 system, the reactivity of the chloro-substituted compound, 2-Cl-1,6-C2B4H5, toward an electrophilic substitution is greater, at the 4-position, than that of the parent carborane. The nature (halogen or alkyl) and cage position of a substituent on closo-2,4-C2B5H7 appear to have little or no influence on the site of electrophilic substitution.
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 ...
Abdou, Zahid J.,Abdou, Gaby,Onak, Thomas,Lee, Sharon
, p. 2678 - 2683 (2008/10/08)
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.
A study on the preparation and rearrangement of the halogenated closo-carboranes ClnC2B4H6-n (n = 1, 2) and ClnC2B5H7-n (n = 1, 2)
Takimoto, Chris,Siwapinyoyos, Gowit,Fuller, Keith,Fung, Alexander P.,Liauw, Ling,Jarvis, Wiley,Millhauser, Glenn,Onak, Thomas
, p. 107 - 110 (2008/10/08)
Dichloro as well as monochloro derivatives of 1,6-C2B4H6 and 2,4-C2B5H7 are prepared, and the effect of the first chlorine substituent on the position of the entering second chlorine substituent is discussed. Both mono- and dichloro derivatives of C2B5H; rearrange at approximately 300°C to a mixture of isomers.
