Preparation, Characterization, and Structural Systematics of Diphosphane and Diarsane Complexes of Gallium(III) Halides

The diphosphane <i>o</i>-C<sub>6</sub>H<sub>4</sub>(PMe<sub>2</sub>)<sub>2</sub> reacts with GaX<sub>3</sub> (X = Cl, Br, or I) in a 1:1 molar ratio in dry toluene to give <i>trans</i>-[GaX<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(PMe<sub>2</sub>)<sub>2</sub>}<sub>2</sub>][GaX<sub>4</sub>], the cations of which contain the first examples of six-coordinate gallium in a phosphane complex. The use of a 1:2 ligand/GaCl<sub>3</sub> ratio produced [GaCl<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(PMe<sub>2</sub>)<sub>2</sub>}][GaCl<sub>4</sub>], containing a pseudotetrahedral cation, and similar pseudotetrahedral [GaX<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(PPh<sub>2</sub>)<sub>2</sub>}][GaX<sub>4</sub>] complexes are the only products isolated with the bulkier <i>o</i>-C<sub>6</sub>H<sub>4</sub>(PPh<sub>2</sub>)<sub>2</sub>. On the other hand, Et<sub>2</sub>P(CH<sub>2</sub>)<sub>2</sub>PEt<sub>2</sub>, which has a flexible aliphatic backbone, formed [(X<sub>3</sub>Ga)<sub>2</sub>{μ-Et<sub>2</sub>P(CH<sub>2</sub>)<sub>2</sub>PEt<sub>2</sub>}], in which the ligand bridges two pseudotetrahedral gallium centers. The diarsane, <i>o</i>-C<sub>6</sub>H<sub>4</sub>(AsMe<sub>2</sub>)<sub>2</sub>, formed [GaX<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(AsMe<sub>2</sub>)<sub>2</sub>}][GaX<sub>4</sub>], also containing pseudotetrahedral cations, and in marked contrast to the diphosphane analogue, no six-coordinate complexes form; a very rare example where these two much studied ligands behave differently towards a common metal acceptor. The complexes [(I<sub>3</sub>Ga)<sub>2</sub>{μ-Ph<sub>2</sub>As(CH<sub>2</sub>)<sub>2</sub>AsPh<sub>2</sub>}] and [GaX<sub>3</sub>(AsMe<sub>3</sub>)] are also described. The X-ray structures of <i>trans</i>-[GaX<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(PMe<sub>2</sub>)<sub>2</sub>}<sub>2</sub>][GaX<sub>4</sub>] (X = Cl, Br or I), [GaCl<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(PPh<sub>2</sub>)<sub>2</sub>}][GaCl<sub>4</sub>], [GaX<sub>2</sub>{<i>o</i>-C<sub>6</sub>H<sub>4</sub>(AsMe<sub>2</sub>)<sub>2</sub>}][GaX<sub>4</sub>] (X = Cl or I), [(I<sub>3</sub>Ga)<sub>2</sub>{μ-Ph<sub>2</sub>As(CH<sub>2</sub>)<sub>2</sub>AsPh<sub>2</sub>}], and [GaX<sub>3</sub>(AsMe<sub>3</sub>)] (X = Cl, Br or I) are reported, and the structural trends are discussed. The solution behavior of the complexes has been explored using a combination of <sup>31</sup>P{<sup>1</sup>H} and <sup>71</sup>Ga NMR spectroscopy.