Ruthenium trans influence

The complexed arene rings in tethered complexes of ruthenium(II) are close to planar, though the ipso-carbon atom is often pulled slightly towards the metal atom. In the phosphine complexes, the Ru-C(arene) distances trans to the P-donor (2.22-2.29 A) are significantly greater than those trans to the Ru-Cl bonds (2.15-2.25 A). This feature is also evident in non-tethered complexes of the type [RuCl2(r 6-arene)(PR3)] and can be attributed to the higher trans-influence of PR3 relative to that of Cl-.88... 

Electropolymerization of 4-Vinylpyridine Complexes. Investigations of Structural and Electronic Influences on Thin Film Formation. The recent discovery of the reductive polymerization of complexes containing vinylpyridyl ligands (lg), such as Ru -(bpy)2(vpy)22+ has led to the preparation of homogeneous thin layers of very stable electroactive polymers. This method has been extended to 4-vinyl-4 -methyl-2,2 -bipyridine (lg, 21a) and 4-vinyl-l,10-phenanthroline (21b) on both ruthenium and iron. In the following section we discuss our results on thin films derived from the polymerizable ligands BPE and the trans-4 -X-stilbazoles, (4 -X-stilb X - Cl, OMe, CN and H). 

Solvents also influence the stereoselectivity of the phenol reduction, however, the solvent effect is also dependent on the catalyst used14-18. In contrast to ruthenium, which shows little dependence on the solvent, hydrogenations over rhodium are much more solvent sensitive. In this case the cis/trans ratio tends to decrease with increasing dielectric constant of the solvent. 

Several water-soluble ruthenium complexes, with P = TPPMS, TPPTS, or PTA ligands (cf. Section 2.2.3.2), catalyze the selective reduction of crotonaldehyde, 3-methyl-2-butenal (prenal), and trans-cinnamaldehyde to the corresponding unsaturated alcohols (Scheme 2) [33—36]. Chemical yields are often close to quantitative in reasonable times and the selectivity toward the aUyhc alcohol is very high (> 95%). The selectivity of the reactions is critically influenced by the pH of the aqueous phase [11] as well as by the H2 pressure [37]. The hydrogenation of propionaldehyde, catalyzed by Ru(II)/TPPTS complexes, was dramatically accelerated by the addition of inorganic salts [38], too. In sharp contrast to the Ru(II)-based catalysts, in hydrogenation of unsaturated aldehydes rhodium(I) complexes preferentially promote the reaction of the C=C double bond, although with incomplete selectivity [33, 39]. 

Once again, the trans cr-bonding alkyl or aryl ligand exerts a powerful influence on the M-N-O bond angle. Studies on transient intermediates during photolysis of Ru-NO nitrosyls have revealed different modes of binding (and dissociation) of coordinated NO at the ruthenium centers. Metastable NO linkage isomers have been observed for MNO (M = Fe, Ru, Os) and for MNO ° complexes of Ni, as well as for FeNO iron nitrosyl porphyrins [208-212]. 

Nelson DJ, Percy JM. Does the rate of competing isomerisation during alkene metathesis depend on pre-catalyst initiation rate Dalton Trans. 2014 43(12) 4674-4679. Zaja M, Connon SJ, Dunne AM, et al. Ruthenium olefin metathesis catalysts with modified styrene ethers influence of steric and electronic effects. Tetrahedron. 2003 59(34) 6545-6558. 

The obtained stereoselectivities are in the same range as those of other ruthenium- or rhodium-based catalysts. As the carbene addition occurs with trans (exo) diastereoselectivity, the more thermodynamically stable trans (exo) isomer is preferentially formed. It was observed that two steric effects have influence on the stereoselectivity the steric bulk of the 4-position of the styrene derivatives and the steric bulk of the diazoacetate used. In both cases the cisitrans ratio decreases with the... 

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