A Crystalline Mono-Coordinate Indium(I)-Phosphaalkenyl.

The synthesis of the mono-coordinate indium(I) compound In[C(Ad)═PTer] (Ad = 1-adamantyl, Ter = 2,6-Dipp2-C6H3; 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 In[C(Ad)═PTer] with B(C6F5)3, which affords [TerInB(C6F5)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 In[C(Ad) = PTer] was probed by reaction with methyl-iodide which affords the indium(III) compound In(Me)I[C(Ad) = PTer] in a formal single-site oxidative-addition reaction at indium.