A π-Stacked Organometallic Propeller: Experimental and Theoretical Studies on Reactivity and Bonding in the π-Arene-Bridged Nickel Triple-Decker [{(η5-Me4EtC5)Ni}2(μ-η3:η3-decacyclene)

Abstract

Synthesis, structure, reactivity, and theoretical studies of a new type of Ni triple-decker complexes are reported. A prominent feature of its molecular structure is the (η3:η3)-bis(enyl) coordination of two [(η5-Me4EtC5)Ni] fragments to the central arene ring of the polycondensed π-perimeter decacyclene. The central arene ring of decacyclene displays a distinct chair conformation with significant tilt angles of 25.5 and 26.1°. The three naphthalene units are twisted in a propeller-like fashion with torsion angles of 16°, 16.6°, and 19°, which is twice the twisting observed for the free decacyclene ligand. According to Extended Huckel Molecular Orbital (EHMO) calculations, a qualitative measure for arene lability in the title compound and a number of related arene-bridged metal complexes can be attributed to a subsequent filling of metal−arene antibonding orbitals. The experimentally observed reactivities of π-arene exchange in these complexes are reproduced nicely by the EHMO calculations. The title compound offers access to a number of organonickel chalcogenato complexes under mild conditions by cleavage of the S−S, Se−Se, or Te−Te bonds of diorganyl dichalcogenides R−E−E−R. The title compound is also capable of C−H activation of azobenzene and [(dimethylamino)methyl]ferrocene resulting in orthometallated complexes containing five-membered metallacycles. PES and semi-empirical ZINDO/S calculations were used to study the product of the orthometallation of the title compound with azobenzene. These studies reveal that the HOMO of the metallacycle (IE = 6.45 eV) has dominant Ni−Cp and Ni−Caryl π-antibonding character.