Bidentate diamine ligands

Aqueous biphasic catalysis is also used in homogeneous hydrogenations.117-119 In new examples Ru clusters with the widely used TPPTN [tris(3-sulfonatophenyl) phosphine] ligand120 and Rh complexes with novel carboxylated phosphines121 were applied in alkene hydrogenation, whereas Ru catalysts were used in the hydro-genation of aromatics. Aerobic oxidation of terminal alkenes to methyl ketones was carried out in a biphasic liquid-liquid system by stable, recyclable, water-soluble Pd(II) complexes with sulfonated bidentate diamine ligands.124... 

FIGURE 5.27 Bidentate diamine ligands (a) trimethylenediamine(tm) (b) tetramethylene-diamine(tmd) (c) tra i-l,2-cyclopentanediarnine(cptm) (d) 2,4-pentanediamine(ptm). 

A stopped-flow spectrophotometer was used to obtain the kinetics data for the reaction of a nickel(II) complex NiL2 of a substituted bidentate diamine ligand (L = tetmeen = 2,3-dimethyl-2,3-diaminobutane) with cyanide ion. The reaction is biphasic one diamine ligand is replaced by two cyanide ligands, then the second diamine ligand is replaced ... 

While it can be shown that for strict octahedral symmetry no d6 ion can have a ground state with two unpaired electrons (only 4 or 0), this might be possible in 6-coordinate complexes in which there are significant departures from Oh symmetry in the ligand field. Perhaps the best documented examples are complexes of the type [Fe(LL)2ox] and [Fe(LL)2mal] where LL represents a bidentate diamine ligand such as o-phen or bipy, and ox, mal represent oxal-... 

Diamine ligands act generally as bidentate ligands forming chelating or bridge structures, given respectively by 156 and 157 ... 

The use of monodentate and bidentate polar ligands such as ethers, amines, chelating diethers, and diamines in RLi diene polymerization has been studied by a number of workers (23-28). For example, the effect of... 

Ruthenium catalysts bearing diamine and bidentate phosphine ligands, illustrated in equation (9), exhibit high enantioselectivity and efficiency in the reduction of ketones. Before the apphcation of this catalyst to asyimnetric activation can be illustrated, important mechanistic information will be outlined. 

Many other chiral copper catalysts have been reported, most of them being derived from C2-symmetrical bidentate nitrogen ligands [13, 27]. Some ligands such as the bipyridine derivatives 14 [60, 61, 62], the diamine 15 [63] and the bis(azaferrocene) 16 [64] are capable to induce high ees, but none of them can compete so far with chiral bisoxazolines in terms of high selectivity combined with effectiveness, general applicability and ease of preparation. 

A large amount of work has been devoted to N-binding macrocyclic complexes of Ni, Cu and Fe, which yield imine ligand products. Bidentate amine ligands, mainly ethylene diamine (en), have been used with Ru and Os complexes. The oxidation of coordinated ethylene diamine and related ligands stops at the diimine stage and does not continue to the dinitrile. The a,a -diimine entity -N=C-C = N- formed in the four-electron oxidation is particularly stable (93). 

There is evidence (NMR, IR, X-ray) that TMEDA forms a (reactive) bidentate complex with the osmium tetroxide whereby the diamine ligand increases the electron density on both the osmium center and also the outlying 0x0 ligands this in turn makes them more electron rich and better hydrogen bond acceptors and so leads to the selectivity observed. ... 

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