Monosubstituted Doublet Sn(I) Radical Featuring Substantial Unquenched Orbital Angular Momentum

Abstract

Due to their intrinsic high reactivity, isolation of heavier analogues of carbynes remains a great challenge. Here, we report the synthesis and characterization of a neutral monosubstituted Sn(I) radical (<b>2</b>) supported by a sterically hindered hydrindacene ligand, which represents the first tin analogue of a free carbyne. Different from all Sn(I/III) species reported thus far, the presence of a sole Sn-C σ bond in <b>2</b> renders the remaining two Sn 5p orbitals energetically almost degenerate, of which one is singly occupied and the other is empty. Consequently, its <i>S</i> = 1/2 ground state possesses two-fold orbital pseudo-degeneracy and substantial unquenched orbital angular momentum, as evidenced by one component of its <i>g</i> matrix (1.957, 1.896, and 1.578) being considerably less than 2. Consistent with this unique electronic structure, <b>2</b> can bind to an <i>N</i>-heterocyclic carbene to afford a neutral two-coordinate Sn(I) radical and initiate a one-electron transfer to benzophenone to furnish a Sn(II)-ketyl radical anion adduct. As a manifestation of its Sn-centered radical nature, <b>2</b> reacts with diphenyl diselenide and <i>p</i>-benzoquinone to form Sn-S and Sn-O bonds, respectively.