The general procedure for the synthesis of 2,2'-oxybis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) and 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane from carbon dioxide and pinacolborane was as follows: a solution of (PhPSiP)Ni(η3-C8H13) (1.0 mg, 0.0014 mmol) and 1 ,3,5-trimethoxybenzene (11.5 mg, 0.068 mmol) were added to a J.YY NMR tube and the solution was frozen. After cooling, a layer of pinacolborane (9.9 μL, 0.068 mmol) was added. On a double Schlenk line, the headspace was evacuated and passed through 1 atm of CO2 at room temperature.After 15 min, almost complete depletion of pinacolborane was observed, along with the appearance of three major products. The products were identified by comparison with those reported by Sabo-Etienne.After 15 min, products a, b, and c were present in a 61:5:34 ratio with unreacted pinacolborane. However, the product c was gradually consumed over time, and after 12 h, all pinacolborane was consumed, leaving only traces of product c in the reaction mixture.The product integrals showed the presence of 13% 2-methoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborole pentacyclic, 85% 2,2'-oxybis(4,4,5,5-tetramethyl-1,3,2-dioxaborole heterocyclopentane) and a small amount of unidentified by-products. In addition, a peak corresponding to formaldehyde at 8.72 ppm was observed.
