Ruthenium Carbonyl 1,4-Diaza-1,3-butadiene (R-DAB) Complexes. A Theoretical and Experimental Investigation of the Electronic Structure of Ru2(CO)4(R-DAB)(μ-CO) and Ru2(CO)4(R-DAB)(μ-HC≡CH)

The electronic structure of two binuclear ruthenium clusters containing the 8e donor 1,4-diaza-1,3-butadiene (R-DAB) ligand [Ru2(Co)4(R-Dab)(μ-Co) and Ru2(CO)4(R-DAB)(μ-HC≡CH)] is for the first time discussed by using SCF first principle discrete variational (DV) Xα calculations and gas-phase UV photoelectron (PE) spectroscopy. Despite the short metal-metal interatomic distance, the bonding scheme of both molecules is dominated by the absence of any direct metal-metal bond. On the contrary, the importance of a strong multicentered interaction involving the μ-bridged ligands has been emphasized. As far as the R-DAB moiety is concerned, theoretical results indicated a poorer involvement of n+ and n- linear combinations of nitrogen lone pairs than π3* and π2 levels in metals-R-DAB interactions. Looking into the nature of such a π interaction it has been found that the Ru atom of the metallacycle fragment is mostly involved in M →π3* back-bonding while π2→M donation mainly involves the second Ru atom. © 1988, American Chemical Society. All rights reserved.