Cationic Closo Carboranes—Promising Weakly Coordinating Ions

Abstract

ABSTRACT:The unexplored carbon rich cationic closo carboranes, C 3 B n−3 H n +1 (n = 5, 6, 7, 10, 12) are investigated theoretically. The position isomers were calculated at the B3LYP/6-31G * level, and the charge distribution in the cluster is estimated by NBO analysis. The criterion of ring-cap orbital overlap compatibility along with the number of B-C, C-C, and B-B bonds help in explaining the stability order in each category. The most stable isomer is the one with maximum ring-cap orbital overlap and largest number of B-C bonds. The order of relative stability among the trigonal bipyramid is 1c > 1b > 1a , where the stability is proportional to the number of CH caps over the small three-membered ring. The C 3 B 3 H 6 + isomer with the one allyl C3 group (2b) is more favorable than the one with a cyclopropenyl group (2a). Among the C 3 B 4 H 7 + isomers the stability order is 3e > 3d > 3c > 3b > 3a, which mostly depends on the ring-cap orbital overlap. In the bicapped square antiprism (4) where there is large number of isomers, the order follows the rule of ring cap compatibility and the number of B-C bonds. The order of 5e > 5d > 5c > 5b > 5a obtained from the calculations is in perfect agreement with the above sited rules. Equations (1)- (5) devised for estimating the stability of isomers of C 3 B n−3 H n + indicate an increase in stability with cage size. The mono-positive charge of the isomers is distributed throughout the cage, making them suitable candidates as weakly electrophillic cations.

Octacoordinate Carbons Encaged Inside Carborane Clusters: A Density Functional Theory Investigation

“…78,80 This general rule can be understood by the fact that the C-B bond is stronger than the C-C and the B-B bond (the bond energies of C-B, C-C, and B-B bond are 89.0, 82.6, and 70 ( 5 kcal mol -1 , respectively). 80,82 As shown in Table 2, however, the first rule is not able to distinguish the relative stabilities of the isomers which have exactly the same numbers of C-B, C-C, and B-B bonds. Thus, another rule is proposed to predict the relative stabilities of the isomers with the same number of C-B bonds.…”

Rearrangement of dicarboranyl methyl cation to icosahedralC3B9H12+: An ab initio dynamics view

“…We had studied the electronic structure and weakly coordinating nature of potential cationic closo-carboranes (C 3 B nÀ3 H n + ; n = 5, 6, 7, 10, 12) computationally. 22 Among these proposed molecules the 12-vertices closo-tricarbacarborane (1,2,7-C 3 B 9 H 12 + ) closely resembles the closo-anion CB 11 H 12 À in terms of size and the charge distribution. 12,13 As both ions are weakly interacting in nature, one can think of an IL using this pair that may be very inert.…”