A Neutral Borylene and its Conversion to a Radical by Selective Hydrogen Transfer.

A successful selective reduction of XB-Tip (Tip = 1,3,5-Pr-CH, X = I, Br) with KC and Mg metal, respectively, in the presence of a hybrid ligand (CH(PPh)LSi) leads to a stable low-valent five-membered ring as a boryl radical [CH(PPh)LSiBTip][Br] () and neutral borylene [CH(PPh)LSiBTip] (). Compound reacts with 1,4-cyclohexadiene, resulting in hydrogen abstraction to afford the radical [CH(PPh)LSiB(H)Tip] (). Quantum chemical studies reveal that compound is a B-centered radical, and compound is a phosphane and silylene stabilized neutral borylene in a trigonal planar environment, whereas compound is an amidinate-centered radical. Although compounds and are stabilized by hyperconjugation and π-conjugation, they display high H-abstraction energy and basicity, respectively.