78199-26-5Relevant academic research and scientific papers
Influence of α branching of the 1,4-substituents on the coordination of 1,4-diazabutadienes in mono-, bi-, tri-, and tetranuclear ruthenium carbonyl complexes. Crystal structure of [σ-N,σ-N′,η2-C=N,η 2-C=N′-diglyoxal bis(isopropylimine)]octacarbonyltetraruthenium
Staal,Polm,Vrieze,Ploeger,Stam
, p. 3590 - 3597 (2008/10/08)
A series of 1,4-diazabutadienes (DAB) has been reacted with Ru3(CO)12, resulting in the formation of Ru(CO)3(DAB), Ru2(CO)6(DAB), Ru3(CO)8(DAB), and Ru4(CO)8(DAB)2. The actual complex formed depends upon the reaction conditions and the a branching of the substituents attached to the DAB ligand. The crystal structure of Ru4(CO)8[glyoxal bis-(isopropylimine)]2 has been determined. The crystals are monoclinic with space group Pn. The cell constants are a = 9.506 (1) ?, b = 9.952 (3) ?, c = 16.625 (4) ?, β = 94.975°, and Z = 2. A total of 3241 reflections have been used for the refinement, resulting in R = 4.8% for 360 parameters varied. The metal atoms in the cluster were found in a butterfly arrangement with five intermetallic bond distances ranging from 2.838 (2) to 2.994 (2) ?. The two DAB ligands act as 8e donors, donating two pairs of π electrons of the N=C=N skeleton and two lone pairs. The four pairs of π electrons of the two DAB ligands are donated to the same ruthenium atom which does not contain carbonyl groups. The cluster contains a Ru(CO)4 fragment which is not bonded to the DAB ligands. On the bases of electron counting and 1H NMR results, it was concluded that the DAB ligands in the Ru3(CO)8(DAB) complexes are also in the 8e-donor mode. Low-temperature 1H NMR data of the Ru4(CO)8(DAB)2 clusters indicated the occurrence of an intramolecular exchange process of the butterfly core. For Ru4(CO)8[glyoxal bis(cyclohexylimine)]2, one set of resonances is found at room temperature for the two ligand halves. At low temperature two distinct sets are observed, indicating two inequivalent ligand halves. The activation energy for the exchange process depends upon the substituents attached to the imine nitrogen atoms and decreases with increasing bulkiness.
