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

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 (2) 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 2 renders the remaining two
Sn 5p orbitals energetically almost degenerate, of which one is singly
occupied and the other is empty. Consequently, its S = 1/2 ground state possesses two-fold orbital pseudo-degeneracy
and substantial unquenched orbital angular momentum, as evidenced
by one component of its g matrix (1.957, 1.896, and
1.578) being considerably less than 2. Consistent with this unique
electronic structure, 2 can bind to an N-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, 2 reacts with diphenyl diselenide
and p-benzoquinone to form Sn–S and Sn–O
bonds, respectively.