Synthesis and characterization five-coordinate molybdenum compounds bearing bi- or tridentate substituted pyrrole ligands: molecular structures of {Mo(NC6H3Pri2-2,6)2R[NC4H3(CH2NMe2)-2]} and {Mo(NC6H3Pri2-2,6)2Cl[NC4H2(CH2NMe2)2-2,5]}, where R=Cl, Me, Bu

Reacting [Mo(NC6H3Pri2-2,6)2Cl2(dme)] with 1 equiv. of Li [NC4H3(CH2NMe2)-2] in diethyl ether at −78 °C yields a red crystalline solid of {Mo(NC6H3Pri2-2,6)2Cl[NC4H3(CH2NMe2)-2]} 1 in 86% yield. Alkylation of 1 with RLi in diethyl ether generates {Mo(NC6H3Pri2-2,6)2R[NC4H3(CH2NMe2)-2]} (2a, R=Me; 2b, R=Bu) in high yield. Similarly, reacting [Mo(NC6H3Pri2-2,6)2Cl2(dme)] with 1 equiv. of Li[NC4H2(CH2NMe2)2-2,5] in diethyl ether at −78 °C affords dark red crystals of {Mo(NC6H3Pri2-2,6)2Cl[NC4H2(CH2NMe2)2-2,5]} 3 in 92% yield, in which one NMe2 unit of the pyrrole ligand of 3 coordinates to molybdenum whilst the other one dangles outside the coordination sphere. Variable-temperature 1H NMR study of 3 reveals fluxional behavior of the two NMe2 units of the pyrrole ligand. The activation energy of the fluxionality has been determined as ΔG≠=10.5 kcal mol−1. Compounds 1, 2a, 2b and 3 have been characterized by NMR spectroscopy and X-ray crystallography.