Ligands acac

The Cr—C bond exerts a considerable (ca. 0.1 A) solid-state trans elongation (Table I), and the trans effect is implicated in the enhanced substitution lability of the trans aqua ligand. A variety of chelating systems can be used to form [L6CrR]2+ cations, including diamines (63), polyamines, macrocyclic N4 ligands, acac, bipy, and polycarboxylates such as nta, edta (64), and hedtra. 

Tris(acetylacetonato-<9,<9) iridium(III) is a coordinatively saturated, stable species that has been examined spectroscopically1,2 and used in metal vapor deposition studies.3 4 Removal of one acac ligand (acac = acetylacetonato or 2,4-pentanedionate) generates a family of bis-(acac-<9,<9) iridium(III) complexes exhibiting rich coordination chemistry. In 1976, Bennett and Mitchell isolated these (acac-<9,<9)2Ir(III)(R)(L) complexes as intermediates in yielding preparations of the (acac-<9,<9)3Ir(III) complex from the reaction of acetylace-tone with IrCl3.5... 

The principle scheme of oxygenation of ligand (acac) in complex with Ni(ll), initiated with exo ligand 1 . 

This observation reveals that a potential new catalyst could be achieved by analysis of both processes by trying to balance both steps. Therefore, Peiiana and Goddard [4b] carried out a detail mechanistic analysis in order to investigate the generality of this trend. Diffoent metals (Rh, Pd, Os, and Pt) and ligands ([acac] and [Tp(CO) ) were studied. Figure 25.30 shows a correlation between the computed AH of the C—H activation and the alkene insertion step. An inverse relationship between both processes is observed, which complicates the optimization of the catalytic process. 

Figure 9 Emission spectra of Dy-A-T (-), Dy-A-P (—), and Dy-A-H20 (...) xerogels (Dy +-complex-doped xerogels with the same first ligand acac and different second ligands tppo, phen, and H20). (Reproduced from Ref 102 with permission of The Royal Society of Chemistry.)...

Stationary phase Silica gel (DG Riedel, Hannover, FRG). Mobile phase Af, = benzene Mi = chloroform My = 1,2-dichlorobenzene M4 = n-hexane Ms = CCU M = dichloromethane M7 = ethyl acetate M = toluene M = benzene-dichloromethane (I I) M,o = chloroforin-CCL (7 3) M 1 = dichloromethane-toluene (7 3) M j = n-hexane-CCI4 (2,8) M 3 = chloroform-dichloromethane (7 3) M,j = benzene-toluene (1 1) M,s = chloroform-CsHs-dichloromethane, (6 2 2) Mi<, = acetone-water (6 4). Remarks All single component solvent systems were dried before use, development time 7-20 min, with all dry single component solvent systems the complexes are separated on silica gel layer by an adsorption mechanism and the Rf values of complexes investigated increase in the following order of the ligand acac < bzac < dibzac < ttfac < tfac < hfac. 

Crans and coworkers utilized EPR, V NMR, and absorption spectroscopy to observe the solution chemistry of their series of insulin-enhancing complexes based on the acetylacetone ligand (acac) [46]. Solutions of VO(acac)2 were found to be a mixture of three species, labeled A, B, and C. The B species was observed as a weak shoulder on the resonances attributed to the dominant A EPR signals. Over time, the EPR signal of A(-l-B) converted to C, and this conversion was studied by EPR and absorption spectroscopy. NMR was used to quantify any oxidation of the complex to a V(V) derivative. Quantification of the EPR signal showed fliat 90% of the total vanadium was present as A and B, while 10% was EPR silent as a dimer. After 24 days, the solution components had changed to 25% A(+B) and 65% C. This transformation was later shown to be a pH-dependent process. Preparation of VO(acac)2 at a reduced pH produced flie C-type EPR spectrum quantitatively [59]. 

Eigand (acac ) modes were assigned for [OsX4(acac)] , where X = C1, Br or I. All were consistent with O, O -chelation. " The ligand (acac ) modes in cis- and ran -OsXY(acac)2, where X Y = Cl, Br or I, are approximately independent of the nature of X and Y. A normal coordinate analysis confirms that ligand modes are extensively coupled in Os(acac)3. ... 

We have found earlier - that the inclusion of PhOH in complex Ni(acac)2 L (L = N-methylpirrolidone-2), which is the primary model of NFARD, leads to the stabilization of formed triple complex Ni(acac)2 L PhOH. In this case, as we have established, ligand (acac) is not oxygenated with molecular O. Also the stability of triple complexes Ni(acac)2 L PhOH seems to be due to the formation of stable oxidation of supramolecular macrostmctures due to intra- and intermolecular hydrogen bonds. Formation of supramolecular macrostmctures due to intermolecular (phenol-carboxylate) hydrogen bonds and,... 

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