C−H Bond Activation of Arenes by [8,8′-μ-I-3,3′-Co(1,2-C₂B₉H₁₀)₂] in the Presence of Sterically Hindered Lewis Bases

Abstract

Reactions of the iodonium derivative of cobalt bis(dicarbollide) anion [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] with Lewis bases in aromatic solvents were studied. The reactions proceed through the iodonium bridge opening, and the structure of the reaction products depends strongly on the nature of the Lewis base and solvent used. The reactions with conventional Lewis bases (L) give the corresponding products of Lewis base addition, [8-L-8′-I-3,3′-Co(1,2-C2B9H10)2], whereas the reactions with sterically hindered Lewis bases (L*) result in activation of the C−H bond of the aromatic solvent with formation of the corresponding aryl derivatives [8-Ar-8′-I-3,3′-Co(1,2-C2B9H10)2]−. Activated arenes, such as toluene, could react with [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] without Lewis bases, whereas strongly deactivated arenes do not give C−H activation products even in the presence of sterically hindered Lewis bases.

Fundamental and Applied Properties of Borocations

“…14, left) À anion is also feasible, and this can be viewed as a masked form of a borinium cation. A related "quasi-borinium" cation, 22, derived from [μ- 8,8 0 -I-3,3 0 -Co(1,2-C 2 B 9 H 10 ) 2 ] has been proposed by Sivaev and co-workers to be the active electrophile in the dehydroboration of arenes [67,68]. Other carborane compounds with "naked boron vertices" have been used by Michl et al to effect the borodesilation of arylsilanes [69].…”

Mild C–H activation of activated aromatics with [8,8′-μ-I-3,3′-Co(1,2-C2B9H10)2]: Just mix them

“…Recently we found that reaction of the iodonium derivative of cobalt bis(dicarbollide) [m-8,8 0 -I-3,3 0 -Co(1,2-C 2 B 9 H 10 ) 2 ] (1) with benzene in the presence of sterically hindered Lewis bases results in the benzene CeH activation with formation of the corresponding phenyl derivative [12]. It was assumed that the reaction proceeds through breakage of the iodonium bridge with formation frustrated Lewis pair [14] between boron-centered quasi-borinium cation (Lewis acid) and sterically hindered Lewis base.…”

“…In the case of activated arenes (containing electron-donating groups) such as toluene, the reaction proceeds even in the absence of Lewis base. At the same time, CeH activation of sterically hindered electron rich arenes, such as mesitylene, needs the presence of sterically hindered Lewis base [12].…”

“…1). The structure of the [8-I-8 0 -(2,5-Me 2 C 6 H 3 )-3,3 0 -Co(1,2-C 2 B 9 H 10 ) 2 ] À anion resembles the structure of the related phenyl derivative [8-I-8 0 -Ph-3,3 0 -Co(1,2-C 2 B 9 H 10 ) 2 ] À [12]. The BeC (1.600(4) Å) and BeI distances (2.203(3) Å) fall within the range of the corresponding distances for known aryl and iodo derivatives of cobalt bis(dicarbollide) anion (1.570e1.652 Å [12,15] and 2.175e2.240 Å [12,16], respectively).…”

“…An alternative metal-free direct borylations of arenes and heteroarenes using strong boron electrophiles were reported as well [7e11]. Recently we reported activation of CeH bond in arenes [12] and CeX bonds in haloalkanes [13] with highly electrophilic quasi-borinium cation generated from the iodonium derivative of cobalt bis(dicarbollide), [m-8,8 0 -I-3,3 0 -Co(1,2-C 2 B 9 H 10 ) 2 ].…”