Ruthenium-Komplexe mit Diazadienen, IX. Ein neuartiger Chromophor aus zwei Diazadien-Ruthenium-Einheiten — Struktur und Eigenschaften von [(CO)2(DAD)CH3Ru- RuCH3(DAD)(CO)2] (DAD = ipr—N=CH—CH=N —ipr) / Ruthenium Complexes with Diazadienes, IX. A New Chrom

The two-electron reduction of [(DAD)Ru(CO)2I2] (DAD = RN = CH -CH = NR ) gives the reactive ruthenates(O) [(DAD Ru(CO )2I]-, which add organic electrophiles to afford iodoruthenium organic com pounds such as [(DAD)Ru(CO)2(CH3)I] 3. Their electrochemical behaviour depends on the steric requirem ents of the D A D involved. With a small DAD (R = ipr) the oneelectron reduction gives a Ru(I) interm ediate, which finally yields a stable Ru-Ru-bonded dimer 4. With a bulky DAD(R - CH (ipr)2) the reduction proceeds to the organoruthenates [(DAD)Ru(CO)2R]-. The structure of the dimer 4 was determined by a single crystal X-rax diffraction study: C22H38N4O4Ru2 (624.69), space group F2dd, a = 9.944(2), b = 20.414(3), c = 27.644(5) Å , V = 5611,3(3) Å3, Z = 8; final R-value 0.034 from 2011 reflections. The molecule shows two almost planar (DAD )Ru(CO)2 units, which are staggered with respect to the Ru -Ru single bond. The methyl groups occupy the positions trans to this M-M bond. 4 represents a new type of chromophore with only one very intense and rather narrow absorption band near the infrared (λmax = 745 , ε = 30000 cm2 mmol-1), arising from the presence of a high-lying a-orbital, an antibonding combination of occupied d-orbitals and low-lying D A D π*-orbitals of proper symmetry.