Unexpected Reactivity and Coordination in Gallium(III) and Indium(III) Chloride Complexes With Geometrically Constrained Thio- and Selenoether Ligands

Reaction of GaCl3 with 1 mol equiv of [14]aneS4 in anhydrous CH2Cl2 gives the exocyclic chain polymer [GaCl3([14]aneS4)] (1) whose structure confirms trigonal bipyramidal coordination at Ga with a planar GaCl3 unit. In contrast, using [16]aneS4 and GaCl3 or [16]aneSe4 and MCl3 (M = Ga or In) in either a 1:1 or a 1:2 molar ratio produces the anion–cation complexes [GaCl2([16]aneS4)][GaCl4] (2) and [MCl2([16]aneSe4)][MCl4] (M = Ga, 3 and M = In, 4) containing trans-octahedral cations with endocyclic macrocycle coordination. The ligand-bridged dimer [(GaCl3)2{o-C6H4(SMe)2}] (5) is formed from a 2:1 mol ratio of the constituents and contains distorted tetrahedral Ga(III). This complex is unusually reactive toward CH2Cl2, which is activated toward nucleophilic attack by polarization with GaCl3, producing the bis-sulfonium species [o-C6H4(SMeCH2Cl)2][GaCl4]2 (6), confirmed from a crystal structure. In contrast, the xylyl-based dithioether gives the stable [(GaCl3)2{o-C6H4(CH2SEt)2}] (8). However, replacing GaCl3 with InCl3 with o-C6H4(CH2SEt)2 preferentially forms the 4:3 In:L complex [(InCl3)4{o-C6H4(CH2SEt)2}3] (9) containing discrete tetranuclear moieties in which the central In atom is octahedrally coordinated to six bridging Cl’s, while the three In atoms on the edges have two bridging Cl’s, two terminal Cl’s, and two mutually trans S-donor atoms from different dithioether ligands. GaCl3 also reacts with the cyclic bidentate [8]aneSe2 to form a colorless, extremely air-sensitive adduct formulated as [(GaCl3)2([8]aneSe2)] (10), while InCl3 gives [InCl3([8]aneSe2)] (14). Very surprisingly, 10 reacts rapidly with O2 gas to give initially the red [{[8]aneSe2}2][GaCl4]2 (11) and subsequently the yellow [{[8]aneSe2}Cl][GaCl4] (12). The crystal structure of the former confirms a dimeric [{[8]aneSe2}2]2+ dication, derived from coupling of two mono-oxidized {[8]aneE2}+• cation radicals to form an Se–Se bond linking the rings and weaker transannular 1,5-Se···Se interactions across both rings. The latter (yellow) product corresponds to discrete doubly oxidized {[8]aneSe2}2+ cations (with a primary Se–Se bond across the 1,5-positions of the ring) with a Cl– bonded to one Se. Tetrahedral [GaCl4]− anions provide charge balance in each case. These oxidation reactions are clearly promoted by the Ga(III) since [8]aneSe2 itself does not oxidize in air. The new complexes have been characterized in the solid state by IR and Raman spectroscopy, microanalysis, and X-ray crystallography where possible. Where solubility permits, the solution characteristics have been probed by 1H, 77Se{1H}, and 71Ga NMR spectroscopic studies.