Dinuclear Molybdenum and Tungsten Complexes with Metal−Metal Triple Bonds Supported by p-tert-Butylcalix[4]arene Ligands

In hydrocarbon solvents the compounds M2(NMe2)6 (M = Mo, W) react with p-tert-butylcalix[4]arene, H4L, to give the complexes (H2NMe2)2[M2(μ,η2,η2-L)2], 1 (M = Mo, W). In the molecular structure of 1·4THF, the calix[4]arene ligands span the Mo⋮Mo bond of distance 2.193(1) A in a μ,η2,η2 manner such that each Mo atom is coordinated by four phenolic oxygen atoms that lie roughly in a plane with Mo−Mo−O angles that range from 92 to 102°. The calix[4]arene bowl encapsulates the H2NMe2 cations tightly as judged by 1H NMR spectroscopy, and heating to 100 °C under a dynamic vacuum in the solid state fails to remove HNMe2. However, upon refluxing in pyridine, compounds 1 are converted to (H2NMe2)2[M2(η4-L)2]·xpy, 2·xpy. The molecule of 2·4py (M = Mo) has a center of symmetry, and the Mo2−calix[4]arene unit has a dumbbell shape (Mo⋮Mo bond distance 2.226(1) A). Each Mo atom has four Mo−O phenoxide bonds, one of which is hydrogen-bonded to a H2NMe2 cation, which in turn is hydrogen-bonded to a pyridine molecule. Eac...