Ruthenium complexes octahedral

There are more examples of a second type in which the chirality of the metal center is the result of the coordination of polydentate ligands. The easiest case is that of octahedral complexes with at least two achiral bidentate ligands coordinated to the metal ion. The prototype complex with chirality exclusively at the metal site is the octahedral tris-diimine ruthenium complex [Ru(diimine)3 with diimine = bipyridine or phenanthroline. As shown in Fig. 2 such a complex can exist in two enantiomeric forms named A and A [6,7]. The bidentate ligands are achiral and the stereoisomery results from the hehcal chirality of the coordination and the propeller shape of the complex. The absolute configuration is related to the handness of the hehx formed by the hgands when rotated... 

Foyt et al. [137] interpreted the quadrupole-splitting parameters of low-spin ruthenium(II) complexes in terms of a crystal field model in the strong-field approximation with the configuration treated as an equivalent one-electron problem. They have shown that, starting from pure octahedral symmetry with zero quadrupole splitting, A q increases as the ratio of the axial distortion to the spin-orbit coupling increases. 

A dye which shows particular promise for this application is the octahedral ruthenium(n) complex of 2,2 -bipyridyl (234). While this type of system appears to offer considerable potential as a means of solar energy conversion, the efficiency of the technology, at its current state of development, is significantly lower than that of traditional silicon photocells. 

General Structural Features. The general structure of halfsandwich ruthenium(II)-arene complexes is shown in Fig. 12. The structural, stereochemical and electronic features of metal-arene complexes have been discussed (63). A typical piano-stool geometry consists of an rj6-arene occupying three coordination sites of the pseudo-octahedral complex, leaving the three legs X, Y, and Z available for coordination. The sites X and Y can be taken up by two monodentate ligands, but are more commonly... 

Catalysts for ketone hydrogenation continue to be developed but one of the best systems is still the BINAP-DPEN catalyst first reported by Ohkuma et al. in 1995. " In this system ruthenium is combined with both a chiral diphosphine and a chiral diamine, forming an octahedral complex which gives a high degree of enantioselectivity. This stereoselectivity is considered to be a result of the synergistic effect of the chiral diphosphine and diamine ligands. 

It is, thus, important that the ruthenium(II) complexes that are to be used as building blocks of the future machines contain sterically hindering chelates so as to force the coordination sphere of the metal to be distorted from the perfect octahedral geometry. We will discuss the photochemical reactivity of rotaxanes and catenanes of this family as well as non-interlocking systems like scorpionates since the lability of bulky monodentate ligands could also lead to useful photosubstitution reactions. 

Octahedral ruthenium(III) complexes are relatively inert towards ligand substitution. The reduction from ruthenium(III) to ruthenium(II) as an activation process prior to DNA binding was first suggested in the late 1970s by Clarke and coworkers [35, 46-50]. 

Since the copper complexes, [Cu(NN)2]+ and [Cu(NN)(PR3)2]+ (NN = 1,10-phenanthroline, 2,2 -bipyridine, and their derivatives) were applied to stoichiometric and catalytic photoreduction of cobalt(III) complexes [8a,b,e,9a,d], one can expect to perform the asymmetric photoreduction system with the similar copper(l) complexes if the optically active center is introduced into the copper(I) complex. To construct such an asymmetric photoreaction system, we need chiral copper(I) complex. Copper complex, however, takes a four-coordinate structure. This means that the molecular asymmetry around the metal center cannot exist in the copper complex, unlike in six-coordinate octahedral ruthenium(II) complexes. Thus we need to synthesize some chiral ligand in the copper complexes. 

The clusters (18), (19), (20), and [H2Rn8(CO)2i] (21) are all products from reacting Ru3(CO)i2 nnder different conditions. (18), the major product in the synthesis of all of these complexes, has an octahedral core of ruthenium atoms, with an interstitial hydride. The hydride seems to have some stabilizing effect on the octahedral complex, since all products of higher nuclearity are based on this octahedral framework. As seen in Scheme 6, the structure of the octaruthenium dihydride complex (21) resembles an octahedron with an additional Ru2 unit. Another Ru2 unit is added to this complex... 

McDonagh, A.M., Cifuentes, M.P., Whittall, I.R., Humphrey. M.G.. Samoc, M., Luther-Davies, B., Hockless, D.C.R. Organometallic complexes for nonlinear optics. VII. Cubic optical nonlinearities of octahedral trans-bis bis(diphenylphosphino)methane)ruthenium acetylide complexes x-ray crystal structure of rrans-[Ru(C=CPh)(4-C=CCe H4NO2)(dppm)2]. J. Organomet. Chem. 526, 99-103 (1996)... 

Combined experimental and computational studies on the nature of aromatic C—H activation by octahedral ruthenium(II) complexes Evidence for a-bond metathesis from Hammett studies... 

Ruthenium(III) complexes are seen in Tables 8.2 and 8.3 to be kinetically comparable to the corresponding chromium(III) species, despite a larger Dq for Rura, because the LFAE factor is lower for low-spin d5 than for d3. For Ru(H20)63+, AVjx indicates a much more associative mode of activation than for Ru(H20)62+, which seems typical of octahedral transition metal complexes... 

The group RuNO can occur in both anionic and cationic octahedral complexes in which it is remarkably stable, being able to persist through a variety of substitution and oxidation-reduction reactions. Ruthenium solutions or compounds that have at any time been treated with nitric acid can be suspected of containing nitric oxide bound to the metal. The presence of NO may be detected by infrared absorption ca. 1930-1845 cm-1. 

For [(BINAP)Pd(3-picoline)2] +, AG 50 kj mol was determined for restricted rotation about the Pd-N bonds. The barrier in the analogous platinum complexes were higher, AG 58 kJ mol . The general trend is that the barriers for the Pd-N bonds are somewhat lower than those for Pd-C bonds in analogous covalently bonded aryl complexes. This type of phenomena can also be flowed by P NMR. It would appear that one of the anti isomers is generally preferred in systems with a chiral bidentate ligand. Barriers are also observed in octahedral complexes and have been studied in ruthenium complexes. 

---