# A Crystalline Mono‐Coordinate Indium(I)‐Phosphaalkenyl

## TL;DR

A new mono-coordinate indium(I) compound is synthesized and shown to reversibly bind and release a phosphaalkyne.

## Contribution

The synthesis and reversible reactivity of a mono-coordinate indium(I) complex with a phosphaalkenyl ligand is demonstrated.

## Key findings

- The indium(I) compound In[C(Ad)=PTer] is formed via a redox-neutral carbometallation of a phosphaalkyne.
- The compound reversibly extrudes the phosphaalkyne upon reaction with a Lewis acid.
- The lighter gallium analogue leads to dimerization of the phosphaalkyne fragment.

## Abstract

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.

The redox neutral carbometallation of a phospha‐alkyne using the dimeric indium(I) compound (InTer)2 is reported. This reaction affords a mono‐coordinate indium(I) compound that can reversibly extrude the phospha‐alkyne upon addition of a Lewis acid.