A two-coordinate boron cation featuring C–B+–C bonding

Shoji, Y.; Tanaka, N.; Mikami, K.; Uchiyama, M.; Fukushima, T.  Nat. Chem. 2014, 6, 498-503

Contributed by Steven Bachrach.
Reposted from Computational Organic Chemistry with permission

This paper is a bit afield from the usual material I cover but this is an interesting reaction. Shoji and coworkers have prepared the two-coordinate boron species 1,¹ and confirmed its geometry by an x-ray crystal structure. What I find interesting is its reaction with CO₂, which gives 2 and organoboranes that are not identified, though presumably derived from 3.

M06-2x/6-311+G(d,p) computations support a hypothetical mechanism whereby first a complex between1 and CO₂ is formed (CP1), that is 4.4 kcal mol^-1 above isolated reactants. Then passing through TS1, which is 4.2 kcal mol^-1 above CP1, an intermediate is formed (INT), which is almost 6 kcal mol^-1 below starting materials. A second transition state is then traversed (about 1 kcal mol^-1 below starting materials), to form an exit complex between 2 and 3, which can then separate to the final products with an overall exothermicity of 10.6 kcal mol^-1. The structures of these critical points are shown in Figure 1.

1 (0.0)	CP1 (4.4)
TS1 (8.6)	INT (-5.7)
TS2 (-1.1)	CP2 (-9.0)

Figure 1. M06-2x/6-311+G(d,p) optimized structures. Relative energy in kcal mol^-1.

References

(1) Shoji, Y.; Tanaka, N.; Mikami, K.; Uchiyama, M.; Fukushima, T. "A two-coordinate boron cation featuring C–B⁺–C bonding," Nat. Chem. 2014, 6, 498-503, DOI: 10.1038/nchem.1948.

InChIs

1: InChI=1S/C18H22B/c1-11-7-13(3)17(14(4)8-11)19-18-15(5)9-12(2)10-16(18)6/h7-10H,1-6H3/q+1
InChIKey=WLUJABFTLHAEMI-UHFFFAOYSA-N

2: InChI=1S/C10H11O/c1-7-4-8(2)10(6-11)9(3)5-7/h4-5H,1-3H3/q+1
InChIKey=CUJVTHUIQVMVHD-UHFFFAOYSA-N

3: InChI=1S/C9H11BO/c1-6-4-7(2)9(10-11)8(3)5-6/h4-5H,1-3H3
InChIKey=ZJKBFARYTPYYGV-UHFFFAOYSA-N

This work is licensed under a Creative Commons Attribution-NoDerivs 3.0 Unported License.