Experimental and Computational Studies of the Molybdenum-Flanking Arene Interaction in Quadruply Bonded Dimolybdenum Complexes with Terphenyl Ligands

To clarify the nature of the Mo-C-arene interaction in terphenyl complexes with quadruple Mo Mo bonds, ether adducts of composition [Mo-2(Ar-xyl)(1)(O2CR)(2)(OEt2)] have been prepared and characterized (Ar'=Ar-2(xyl), R =Me; AC=ArMes(2), R = Me; Ar'=Ar-2(xyl), R=CF3) (Mes= mesityl; Xyl=2,6-Me2C6H3, from now on xyly1) and their reactivity toward different neutral Lewis bases investigated. PMe P(OMe)(3) and PiPr(3) were chosen as P-donors and the reactivity studies complemented with the use of the C-donors CNXyl and CN2C2Me4 (1,3,4,5 -tetramethylimidazol-2-ylidene). New compounds of general formula [Mo-2(Ar')(1)(O2CR)(2)(L)] were obtained, except for the imidazol-2-ylidene ligand that yielded a salt-like compound of composition [Mo-2(Ar-2(xyl))(O2CMe)(2)(CN2C2Me4)(2)]. The Mo Carene interaction in these complexes has been analyzed with the aid of X-ray data and computational studies. This interaction compensates the coordinative and electronic unsaturation of one of the Mo atoms in the above complexes, but it seems to be weak in terms of sharing of electron density between the Mo and Carene atoms and appears to have no appreciable effect in the length of the Mo Mo, Mo X, and Mo L bonds present in these molecules.