Abstract The synthesis of the mono‐coordinate indium(I) compound InC(Ad)═PTer (Ad = 1‐adamantyl, Ter = 2,6‐Dipp 2 ‐C 6 H 3 ; Dipp = 2,6‐diisopropylphenyl) is reported. Key to the formation of this monomeric species is the steric protection offered by the supporting phosphaalkenyl ligand which hinders aggregation. The title compound can be accessed from the reaction of (InTer) 2 with the phosphaalkyne AdC≡P in an unusual redox‐neutral transformation in which the In─C bond of the (InTer) 2 precursor, known to dissociate in solution, adds across the C≡P triple bond of the phosphaalkyne. This insertion reaction is reversible, as shown by the reaction of InC(Ad)═PTer with B(C 6 F 5 ) 3 , which affords TerInB(C 6 F 5 ) 3 accompanied by extrusion of AdC≡P. In contrast, the lighter analogue (GaTer) 2 promotes the dimerization of the AdC≡P fragment resulting in the formation of the cluster (GaTer) 2 (AdCP) 2 . The formal oxidation state of InC(Ad) = PTer was probed by reaction with methyl‐iodide which affords the indium(III) compound In(Me)IC(Ad) = PTer in a formal single‐site oxidative‐addition reaction at indium.
García‐Romero et al. (2026) studied this question.