Kinetics and mechanism of carborane formation

Abstract

The kinetics of 1,2-dicarba-c/aro-dodecaborane(l2) formation from BioHi2[(CH3)2S]2 and several acetylenes [HC=CCH2Br, HC=CCH20C(=0)CH3, HC=C(CH2)2CH3, HC=C(CH2)sCH3, HC=C(CH2)3C1] have been studied. A mechanism is proposed consistent with the data obtained. AH* and AS* correlate well with the Taft polar substituent constants for the acetylene substituents.A wide variety of substituted 1,2-dicarba-c/oio-dodecaborane(12) derivatives have been synthesized and characterized.2™4 The most common method for their preparation is through the use of diligand derivatives of decaborane, B10H12L2 (L = Lewis base), and acetylenes. Alkyl derivatives are generally prepared in low yields, ca. 30-40%, from the corresponding acetylenes while other derivatives from acetate

Hydroboration reactions with 6-thia-nido-decaborane(11)

“…Kinetic investigations suggest that dissociative loss of L from arad¡rto-6,9-L2BioHi2 to form nido-BioH^L is critical to the formation of C2B10H12. 14 The exact structure of the nido intermediate is not known, but one isolable isomer does not have the chemical reactivity necessary to be this critical intermediate.14-15 There is, however, evidence of hydroboration side products.14 Since «í'í/o-ó-SBgHn is isoelectronic with nido-B,oH i2*L, the hydroboration of acetylenes by 6-SBgHn probably models an intermediate in the insertion of C2H2 into nido-BioHi2-L to ultimately give C2B10H12. In addition to our results and another brief report,14 separate evidence for the intermediacy of a "hydroborated" species is provided by 5-SMe2-9-C6H 11 -w'do-B 1 qH 11 which formed by the reaction of B,0H 2•(8 ß2)2 with cyclohexene.…”

Synthesis and Biological Evaluation of Diaryl‐Substituted Carboranes as Inhibitors of Hypoxia Inducible Factor (HIF)‐1 Transcriptional Activity

“…[45,46] LBs remove H 2 from B 10 H 14 to give a B 10 H 12 (LB) 2 complex. The ortho-carborane scaffold can be generated from the coupling of decaborane (B 10 H 14 ) with alkynes.…”

“…It has been reported that the reaction of acetylenes with decaborane requires the presence of Lewis bases (LBs). [45,46] LBs remove H 2 from B 10 H 14 to give a B 10 H 12 (LB) 2 complex. Dissociation of one mole of LB from this complex affords a reactive intermediate B 10 H 12 (LB), which reacts with acetylenes followed by elimination of LB and H 2 to give carboranes.…”

Molecular Rods Combining o-Carborane and Bicyclo[1.1.1]pentane Cages: An Insertion of the Triple Bond Located Next to a Highly Strained Cage

“…Later, Sneddon and co-workers published a modified method in which alkynes react with decaborane in some ionic liquids, and very recently, a catalytic effect of silver cation was recognized to accelerate the reaction with B 10 H 12 (MeCN) 2 . There are several papers discussing the mechanism of various modifications of the addition reaction. ,, According to computational studies, the decaborane cluster attacks π-orbitals of the alkyne triple bond, and after that, there is only a slight opportunity to develop a charged (or radical) center on either involved carbon atom. There would be, therefore, no reason for rearrangement of the neighboring BCP cage during the course of the reaction.…”