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)(mu-CO) and Ru2(CO)4(r-dab)(mu-hc=ch)

The electronic structure of two binuclear ruthenium clusters containing the 8e donor 1,4-diaza-l,3-butadiene (R-DAB) ligand [Ru, (CO) , (R-DAB) (p-CO) and Ru,(CO),(R-DAB)(pHC=CH)] is for the first t ime discussed by using SCF first principle discrete variational ( D V ) X a calculations and gas-phase U V photoelectron (PE) spectroscopy. Despite t h e shor t 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 p-bridged ligands has been emphasized. As f a r a s the R -DAB moiety is concerned, theoretical results indicated a poorer involvement of n + and n- linear combinations of nitrogen lone pairs than rj* a n d r2 levels in metals-R-DAB interactions. Looking into t h e na tur e of such a r interaction it has been found t h a t t h e R u a tom of the metallacycle f r agment is mostly involved in M - r3* back-bonding while r2 - M donation mainly involves t h e second R u a tom