Ring-opening and ring-expansion reactions of carborane-fused borirane

Abstract

Though the reaction chemistry of three-membered ring molecules such as cyclopropanes and their heteroatom-containing analogues has been extensively studied, the chemical properties of their boron analogues, boriranes, are little known...

Boosting Ring Strain and Lewis Acidity of Borirane: Synthesis, Reactivity and Density Functional Theory Studies of an Uncoordinated Arylborirane Fused to o‐Carborane

“…Single‐crystal X‐ray diffraction analysis shows a planar five‐membered ring with a short B1−O1 (1.365(4) Å) single bond(Figure 4 ). [14] It is worth noting that this reaction is accomplished at room temperature within minutes, while a similar reaction of a NHC‐coordinated o‐ carborane‐fused borirane reported by the Xie group [5a] requires 80 °C. This difference should be a result of the combination of ring strain and Lewis acidity achieved in 1 .…”

“…The N1−C3 bond length of 1.297(2) Å is typical for a N=C double bond. It should be noted that the same reaction with Xie's NHC‐coordinated borirane requires 80 °C [5a] . Furthermore, the reaction with an equimolar amount of acetonitrile led to the formation of a new 3‐coordinate boron‐containing species showing a resonance at δ B 42.1.…”

“…One fine point to note is that in literature an NHC‐coordinated borirane was reported to react with PhCHO to give a product similar to 3 . However, the reaction occurs only upon heating, [5a] in contrast to the reaction of 1 under ambient temperature. Because of the additional coordination, the barrier for the carbonyl moiety insertion was calculated to be 21.3 kcal/mol (Figure S33), 11.3 kcal/mol higher than the insertion barrier calculated for the reaction of the tricoordinated borirane 1 Ph , consistent with the experimental observation that thermal condition is needed.…”

Functionalization of o-carboranes via carboryne intermediates

“…Similar to benzyne, 31 o-carboryne can be trapped by transition metals to form a series of metal-carboryne species, 30,[32][33][34][35] or by boron to generate carborane-fused boriranes. [36][37][38][39] It is noted that another type of metal-carboryne complex in which a transition metal is s-bonded to two cage B atoms of m-carborane has also been known. [40][41][42] The structures of the aforementioned metal complexes resemble that of metalbenzyne complexes.…”

Regioselectivity of Pd-catalyzedo-carborane arylation: a theoretical view

“…[31][32][33] The most challenging factor in broadening the applications of carboranes is the ability to perform selective functionalizations at the desired B-H or C-H vertex. 19,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] In order to give a glance of icosahedral carboranes, the number system of dicarba-closo-dodecarboranes (C 2 B 10 H 12 ) has been shown in Scheme 1(a). The electrostatic potential (ESP) surface calculation of o-carborane reveals charge separation character (Scheme 1(b)), wherein the positive charge resides mainly on B-H bonds and the negative charge resides mainly on C-H bonds.…”