Ligands neutral bidentate

L = neutral monodentate ligand L-L = neutral bidentate ligand X = halide ligand Ar = aromatic ligand Cp = cyclopentadiene. 

As reaction proceeds, the polymer chain (which is in random coil form) unwinds as the charge on it grows as a result of neutralization and ionization. This contributes to thickening of the cement paste. Cations released become bound to the polymer chain. Countercations can either be bound to a polyanionic chain by general electrostatic forces or be site-bound at specific centres. More than one type of site binding is possible. Complex formation and, if the ligand is bidentate, chelate formation enhance the effect. 

A combination of P- and N- donors is another useful approach to potentially reactive (and cataly-tically active) Ni species. Similar to O- donors, N is a hard donor capable of stabilizing metal ions in higher oxidation states, whereas the soft donor P is best suited to stabilize medium or low oxidation states. A neutral bidentate P,N ligand combining a hard dimethylamino and a soft phosphine donor in /V,/V -dimethyl-2-(diphenylphosphino)aniline (241) affords the neutral trigonal bipyramidal and the... 

A series of adducts of organocadmium halides with neutral bidentate ligands RCdX L (L = dioxane, bipy or phen) have been prepared by electrochemical oxidation of the metal in the presence of L and the alkyl halide. In the additional presence of [N(n-propyl)4]X, salts of the [RCdX2] anion may be isolated.1064... 

Neutral bidentate [N2] supporting ligands, chromium complexes, 5, 359... 

Studies other than preparative-type transformations have so far been limited to B-pyrazolylpyrazaboles. For example, the latter compounds have been found to react with R BX (where X is a readily leaving group) to form polynuclear boron spiro-cations (see Sect. V.A). It has also been shown that the pyrazolylpyrazaboles offer themselves as a class of neutral bidentate chelating ligands For example, the complexes H2B(pz)jB(pz)2ZnCl2 and Cl2Zn(pz)2B(pz)2B(pz)jZnCl2 were readily accessible by combination of the two reactants in an appropriate solvent. Obviously, a more detailed study of this feature is mandated. 

Reactions of [Ml2(CO)j(NCMe)2] with Neutral Bidentate N S Donor Ligands... 

The dirhenium complexes in System 5 exhibit a peculiar dependence on change from bidentate P ligands to bidentate As ligands. In all cases the As ligands seem to stabilize preferentially the highest oxidation state for the two most extreme electron transfer reactions (the second reduction and the second oxidation for the neutral complexes, third reduction and first oxidation for the positively charged ones), whereas the opposite is the case for the two intermediate electron transfers. 

Complexes with Neutral Bidentate Nitrogen Ligands... 

In 163 [133], 2,3 4,5-di-0-isopropylidene-/3-D-fructopyranose acts as a neutral bidentate ligand which is coordinated by the hydroxyl group (01) and the acetal oxygen atom (06) of the pyranose ring (k 0, 0 coordination). The octahedral coordination of the platinum is com-... 

Sulfur-containing SBs such as thiosemicarbazones or selenosemicarbazones may also exhibit in solution a tautomerism between the thione (7a) and the thiol forms (7b) as indicated in Scheme 4. The tautomer (7a) acts as a neutral bidentate ligand, while the loss of the thiol proton of tautomer (7b) yields a single-charged bidentate ligand.29... 

Studies suggest that the mechanism of AHRs is quite similar to the achiral version, which includes the same fundamental steps in the catalytic cycles that we have seen already. The major difference is the presence of chiral bidentate ligands, such as bisphosphines [R2P-Y-PR2], phosphine-phosphites [R2P-Y-P(OR)2], bisphospites [(RO)2P-Y-P(OR)2], aminophosphines [R2N-Y-PR2], or diamines (such as (-)-sparteine), which we encountered earlier in Chapter 12. The bidentate variation of the cationic cycle, shown in Scheme 12.15b, seems to explain most aspects of the mechanism of AHR when X = OTf or I (in the presence of halide scavengers). Throughout the cycle, the ligand remains bidentate, and this factor seems to enhance enantioselectivity. The neutral cycle variant, which ought to be... 

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