2CH3CN⊂(n-Bu4N)2[{Ir(1,5-COD)}6W4O16]·2CH3CN: A Hybrid Inorganic−Organometallic, Flexible Cavity Host, Acetonitrile−Guest Complex Composed of a [W4O4]n+ Tetratungstate Cube and Six Polyoxoanion-Supported (1,5-COD)Ir+ Organometallic Groups

Abstract

The tetratungstate polyoxoanion-supported organometallic compound 2CH3CN⊂(n-Bu4N)2[{Ir(1,5-COD)}6W4O16]·2CH3CN (2CH3CN⊂1·2CH3CN) is reported, a complex which exhibits an unusual “methyl-first” CH3CN inclusion (“⊂”) chemistry. The synthesis of 2CH3CN⊂1·2CH3CN was accomplished by the reaction of 3 equiv of [Ir(1,5-COD)Cl]2 with 4 equiv of (n-Bu4N)2WO4; an X-ray diffraction single-crystal structure shows that the four tungsten atoms in of 2CH3CN⊂1·2CH3CN are located in tetrahedral positions and combine with four bridging oxygens to yield a tungsten-oxygen cubane structure. The cubane core tungsten atoms are capped by six surrounding [Ir(1,5-COD)]+ groups in an octahedral arrangement relative to the cube, with each [Ir(1,5-COD)]+ group coordinated by two terminal oxygen atoms from the tetratungstate unit. Two sets of flexible acetonitrile-binding cavities, formed between each three of the six [Ir(1,5-COD)]+ groups, form a roughly tetrahedral array surrounding the cube. This host-guest complex binds acetonitrile methyl-first, that is, with the methyl group rather than the nitrile group oriented toward a cubane core oxygen atom. The CMe···O nonbonded distances fall in the range 3.10−4.46 Å for CMe···(μ2-O) and 3.08−4.02 Å for CMe···(μ3-O). Acetonitrile-free 1 was also prepared, and its possible acetonitrile and toluene complexation in benzene and methylene chloride solution was studied by NMR. No binding between acetonitrile or toluene and 1 in solution is observed, even when using greater than 300 mol equiv of guest relative to 1. Therefore, the host-guest interaction between 1 and acetonitrile appears to be weak (Keq < 10 M-1), possibly being limited to the solid state.