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†

Abstract

The reaction between M₂(NMe₂)₆ and <2 equiv. of p-tert-butylcalix[4]arene (H₄L) in hydrocarbon solvents leads to (H₂NMe₂)₂[M₂(µ,η²,η²-L)₂] 1 (M = Mo, W), which isomerizes to the unbridged isomers (H₂NMe₂)₂[M₂(η⁴-L)₂] 2 upon heating in refluxing pyridine (L = quadruply deprotonated calix[4]arene); related complexes M₂(η⁴-HL)₂ 3 (M = Mo, W) are prepared from reactions involving M₂(OBu^t)₆ and H₄L, and these react with HNMe₂ to give 2 (M = Mo and W) while [NH₂Me₂][W₂(η⁴-L)(η⁴-HL)] 4 can be obtained by the reaction between 2 and 3 (M = W) in a 1:1 ratio.