A fast and simple B–C bond formation in metallacarboranes avoiding halometallacarboranes and transition metal catalysts

Abstract

An electrophilic substitution on metallacarboranes by using a stabilized carbocation that can be made in situ is reported for the first time. This new synthetic methodology provides a new perspective on easy metallacarborane derivatization with organic fragments, which enhances the properties of both fragments and widens their possible applications. † Electronic supplementary information (ESI) available. See

Aromaticity and Extrusion of Benzenoids Linked to [o‐COSAN]−: Clar Has the Answer

“…A second example was reported in 2011 [17] . In 2020, while searching for a synthetic pathway for a similar [ o ‐COSAN] − ‐naphthalene bridge (see Figure 2B), using the activation of the B−H group with the trityl cation on [3,3′‐Co(1,2‐C 2 B 9 H 11 )(8,8′‐C 10 H 7 ‐1′,2′‐C 2 B 9 H 10 )] − , [18] we observed the formation of a B−C(sp 2 ) bond, but it was not the one sought with the naphthyl, 8‐C 10 H 7 − in the anion, but with the aryl group of the trityl. This led us to modify the reaction strategy and AlCl 3 was used as a Lewis acid, mesitylene as a manageable high boiling solvent (165 °C) with sufficient symmetric steric hindrance to prevent electrophilic attack on its structure, and the benzenoid species and [3,3′‐Co(1,2‐C 2 B 9 H 11 ) 2 ] − as reagents (see Supporting Information) [17, 18] .…”

“…In 2020, while searching for a synthetic pathway for a similar [ o ‐COSAN] − ‐naphthalene bridge (see Figure 2B), using the activation of the B−H group with the trityl cation on [3,3′‐Co(1,2‐C 2 B 9 H 11 )(8,8′‐C 10 H 7 ‐1′,2′‐C 2 B 9 H 10 )] − , [18] we observed the formation of a B−C(sp 2 ) bond, but it was not the one sought with the naphthyl, 8‐C 10 H 7 − in the anion, but with the aryl group of the trityl. This led us to modify the reaction strategy and AlCl 3 was used as a Lewis acid, mesitylene as a manageable high boiling solvent (165 °C) with sufficient symmetric steric hindrance to prevent electrophilic attack on its structure, and the benzenoid species and [3,3′‐Co(1,2‐C 2 B 9 H 11 ) 2 ] − as reagents (see Supporting Information) [17, 18] . First attempts were done with naphthalene, but did not lead to the naphthyl‐bridged [3,3′‐Co(1,2‐C 2 B 9 H 11 ) 2 ] − (Figure 2B), but to an unexpected 3‐methylindenyl bridge (Figure 2C), which had been earlier synthesized and structurally characterized [19–21] …”

“…This led us to modify the reaction strategy and AlCl 3 was used as a Lewis acid, mesitylene as a manageable high boiling solvent (165 °C) with sufficient symmetric steric hindrance to prevent electrophilic attack on its structure, and the benzenoid species and [3,3'-Co(1,2-C 2 B 9 H 11 ) 2 ] À as reagents (see Supporting Information). [17,18] First attempts were done with naphthalene, but did not lead to the naphthyl-bridged [3,3'-Co(1,2-C 2 B 9 H 11 ) 2 ] À (Figure 2B), but to an unexpected 3-methylindenyl bridge (Figure 2C), which had been earlier synthesized and structurally characterized. [19][20][21] From these two reactions with arenes, the one leading to a benzene bridge and the one not leading to a naphthalene bridge but to an extrusion (Figure 2), we concluded the following: considering that the standing framework, the metallacarborane, and the dimensions of both connecting cycles are the same, the difference in behavior is not steric but electronic.…”

Aromaticity and Extrusion of Benzenoids Linked to [o‐COSAN]−: Clar Has the Answer

“…This led us to modify the reaction strategy and AlCl 3 was used as a Lewis acid, mesitylene as a manageable high boiling solvent (165 °C) with sufficient symmetric steric hindrance to prevent electrophilic attack on its structure, and the benzenoid species and [3,3'-Co(1,2-C 2 B 9 H 11 ) 2 ] À as reagents (see Supporting Information). [17,18] First attempts were done with naphthalene, but did not lead to the naphthyl-bridged [3,3'-Co(1,2-C 2 B 9 H 11 ) 2 ] À (Figure 2B), but to an unexpected 3-methylindenyl bridge (Figure 2C), which had been earlier synthesized and structurally characterized. [19][20][21] From these two reactions with arenes, the one leading to a benzene bridge and the one not leading to a naphthalene bridge but to an extrusion (Figure 2), we concluded the following: considering that the standing framework, the metallacarborane, and the dimensions of both connecting cycles are the same, the difference in behavior is not steric but electronic.…”