Synthesis of a Ga-Stabilized As-Centered Radical and a Gallastibene by Tailoring Group 15 Element–Carbon Bond Strengths

Abstract

A convenient synthetic route to Ga-stabilized pnictogen-centered radicals and gallapnictenes by manipulation of pnictogen-carbon bond strengths is presented. Two equivalents of LGa (L = HC[C(Me)N(Dip)]₂, Dip = 2,6-<i>i</i>-Pr₂C₆H₃) react with Cp^ArAsCl₂ (Cp^Ar = C₅(4-<i>t</i>-BuC₆H₄)₅) with formation of the arsenic-centered radical [L(Cl)Ga]₂As·<b>1</b>. In contrast, the analogous reaction with TerSbCl₂ (Ter = 2,6-Mes₂C₆H₃; Mes = 2,4,6-Me₃C₆H₂) yields the gallastibene LGa═SbTer (<b>2</b>) containing a Ga-Sb double bond, whereas reactions of DipSbCl₂ with one and two equivalents of LGa give the monoinsertion and bisinsertion products L(Cl)GaSb(ClDip) (<b>3</b>) and [L(Cl]Ga]₂SbDip (<b>4</b>), respectively. <b>1</b>-<b>4</b> were structurally characterized by single crystal X-ray diffraction. The description of <b>1</b> as an arsenic-centered radical is consistent with results of electron paramagnetic resonance and density functional theory (DFT) studies. The π-bonding in LGa═SbTer (<b>2</b>) is estimated to 10.68 kcal mol^-1 by variable-temperature (VT) NMR spectroscopy, and DFT studies reveal a significant π-bonding interaction between Sb and Ga.