Synthesis and Reactivity of Germyl-Substituted Gallapnictenes

Decarbonylation of the phospha- and arsaketenyl germylenes (L)GeECO (E = P, As; L = CH[C(Me)NAr]₂, Ar = 2,6-<i>i</i>Pr₂C₆H₃) in the presence of the Ga(I) precursor (L)Ga afforded the corresponding germyl-substituted gallaphosphene <b>1</b> and gallaarsene <b>3</b>, respectively. Both <b>1</b> and <b>3</b> are examples of unsaturated chains with heavier group 13/15/14 elements. The germylene center and the polarized Pn = Ga (Pn = P or As) double bond provide multiple sites for small-molecule activation. For example, gallaarsene <b>3</b> reacted with adamantyl azide in a formal [3 + 2]-cyclization to give <b>4</b> containing a GaAsN₃ heterocycle, clearly underlining the analogy between the As = Ga and C-C multiple bonds. By contrast, the reaction of <b>3</b> with Me-I afforded the 1,3-addition product <b>5</b>, which indicates frustrated Lewis pair character in <b>3</b>. DFT calculations indicate that the Ga-P/As bonds are highly polarized toward the pnictogen center. EDA-NOCV calculations further support this description and additionally shed light on ambiguous bonding scenarios in <b>4</b> and <b>5</b>. These calculations prove that orbital interactions are outweighed by electrostatic interactions, resulting in polar bonds with significant ionic character.