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.

三氯化镓(GaCl₃)与1摩尔当量的1,4,8,11-四硫杂环十四烷([14]­aneS4)在无水二氯甲烷(CH₂Cl₂)中反应，得到配合物[GaCl₃([14]­aneS4)] (1)，其结构证实Ga原子采取三角双锥配位，包含一个平面型GaCl₃单元。

与之相对，当使用1,4,8,12-四硫杂环十六烷([16]­aneS4)与三氯化镓，或1,4,8,12-四硒杂环十六烷([16]­aneSe4)与三氯化金属MCl₃（M=Ga或In），并按1:1或1:2摩尔比反应时，会生成阴阳离子型配合物：[GaCl₂([16]­aneS4)]⁺[GaCl₄]⁻ (2) 与[MCl₂([16]­aneSe4)]⁺[MCl₄]⁻（3：M=Ga；4：M=In），其阳离子中心均采取反式八面体配位，配体为环内配位的大环配体。

将配体替换为邻苯二(甲硫基)醚(o-C₆H₄(SMe)₂)，按2:1摩尔比与三氯化镓反应，得到二聚体配合物[(GaCl₃)₂{o-C₆H₄(SMe)₂}] (5)，其中Ga(III)采取扭曲四面体配位。该配合物对二氯甲烷表现出异常反应活性：三氯化镓的极化作用可活化二氯甲烷，使其发生亲核进攻，最终生成双锍盐配合物[o-C₆H₄(SMeCH₂Cl)₂]⁺[GaCl₄]₂⁻ (6)，其结构经晶体衍射证实。

与之相对，使用基于二甲苯的二乙硫基配体o-C₆H₄(CH₂SEt)₂时，与三氯化镓反应得到稳定配合物[(GaCl₃)₂{o-C₆H₄(CH₂SEt)₂}] (8)；但若将三氯化镓替换为三氯化铟，则优先生成4:3的铟基四聚体配合物[(InCl₃)₄{o-C₆H₄(CH₂SEt)₂}₃] (9)，其结构包含离散四核单元：中心铟原子与六个桥连氯原子采取八面体配位，边缘三个铟原子分别结合两个桥连氯、两个端基氯，以及来自不同配体的两个反式S供体原子。

三氯化镓还可与环状双齿硒醚配体1,5-二硒杂环辛烷([8]­aneSe2)反应，得到无色且对空气极敏感的二聚体配合物[(GaCl₃)₂([8]­aneSe2)] (10)；而三氯化铟与该配体反应则生成单核配合物[InCl₃([8]­aneSe2)] (14)。

极为意外的是，配合物10可与氧气快速反应：首先生成红色产物[{([8]­aneSe2)₂}][GaCl₄]₂ (11)，其晶体结构证实其包含二聚双阳离子[{([8]­aneSe2)}₂]²⁺，由两个单电子氧化的[8]­aneSe2⁺•自由基偶联而成，通过Se-Se键连接两个环，且两环均存在较弱的跨环1,5-Se···Se相互作用；后续反应得到黄色产物[{([8]­aneSe2)Cl}][GaCl₄] (12)，其阳离子为双氧化的{[8]­aneSe2}²⁺，环上1,5位存在Se-Se主键，其中一个Se原子结合一个氯原子，两种产物的电荷均由四面体配位的[GaCl₄]⁻阴离子平衡。

由于纯的[8]­aneSe2在空气中不会发生氧化，可见上述氧化反应均由Ga(III)中心促进。

所有新型配合物均在固态下通过红外光谱、拉曼光谱、元素微量分析以及X射线单晶衍射（若可行）进行表征；在溶解度允许的条件下，还通过¹H核磁共振、⁷⁷Se{¹H}核磁共振以及⁷¹Ga核磁共振光谱对其溶液态性质开展了研究。