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

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 -Pr 2 C 6 H 3 ) react with Cp Ar AsCl 2 (Cp Ar = C 5 (4- t -BuC 6 H 4 ) 5 ) with formation of the arsenic-centered radical [L(Cl)Ga] 2 As· 1 . In contrast, the analogous reaction with TerSbCl 2 (Ter = 2,6-Mes 2 C 6 H 3; Mes = 2,4,6-Me 3 C 6 H 2 ) yields the gallastibene LGa═SbTer ( 2 ) containing a Ga–Sb double bond, whereas reactions of DipSbCl 2 with one and two equivalents of LGa give the monoinsertion and bisinsertion products L(Cl)GaSb(ClDip) ( 3 ) and [L(Cl]Ga] 2 SbDip ( 4 ), respectively. 1 – 4 were structurally characterized by single crystal X-ray diffraction. The description of 1 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 ( 2 ) 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.