A pi-stacked organometallic propeller: Experimental and theoretical studies on reactivity and bonding in the pi-arene-bridged nickel triple-decker [{(eta(5)-Me4EtC5)Ni}(2)(mu-eta(3):eta(3)-decacyclene)]

Synthesis, structure, reactivity, and theoretical studies of a new type of Ni triple-decker complexes are reported. A prominent feature of its molecul ar structure is the (eta (3):eta (3))-bis- (enyl) coordination of two [(eta (5)-Me4EtC5)Ni] fragments to the central arene ring of the polycondensed p i -perimeter decacyclene. The central arene ring of decacyclene displays a distinct chair conformation with significant tilt angles of 25.5 and 26.1 d egrees. The three naphthalene units are twisted in a propeller-like fashion with torsion angles of 16 degrees, 16.6 degrees, and 19 degrees, which is twice the twisting observed for the free decacyclene ligand. According to E xtended Huckel Molecular Orbital (EHMO) calculations, a qualitative measure for arene lability in the title compound and a number of related arene-bri dged metal complexes can be attributed to a subsequent filling of metal-are ne antibonding orbitals. The experimentally observed reactivities of R-aren e exchange in these complexes are reproduced nicely by the EHMO calculation s. The title compound offers access to a number of organonickel chalcogenat o complexes under mild conditions by cleavage of the S-S, Se-Se, or Te-Te b onds of diorganyl dichalcogenides R-E-E-R. The title compound is also capab le of C-sp2-H activation of azobenzene and [ (dimethylamino)methyl] ferroce ne resulting in orthometallated complexes containing five-membered metallac ycles. PES and semi-empirical ZINDO/S calculations were used to study the p roduct of the orthometallation of the title compound with azobenzene. These studies reveal that the HOMO of the metallacycle (IE = 6.45 eV) has domina nt Ni-Cp and Ni-C-aryl pi -antibonding character.