Preparation and characterization of the kinetic and thermodynamic isomers of dinuclear molybdenum and tungsten complexes with metal-metal triple bonds supported by p-tert-butylcalix[4]arene anions

The reaction between M-2(NMe2)(6) and < 2 equiv, of p-tert-butylcalix[4]arene (H4L) in hydrocarbon solvents leads to (H2NMe2)(2)[M-2(mu, eta(2), eta(2)-L)(2)] 1 (M = Mo, W), which isomerizes to the unbridged isomers (H2NMe2)(2)[M-2(eta(4)-L)(2)] 2 upon heating in refluxing pyridine (L = quadruply deprotonated calix[4]arene); related complexes M-2(eta(4)-HL)(2) 3 (M = Mo, W) are prepared from reactions involving M-2(OBut)(6) and H4L, and these react with HNMe2 to give 2 (M = Mo and W) while [NH2Me2][W-2(eta(4)-L)(eta(4)-HL)] 4 can be obtained by the reaction between 2 and 3 (M = W) in 1:1 ratio.