Lead donor groups

EDTA, leading to a postulate that more than one equivalent of Ca2+ can be captured by X (e.g. one Ca2+ sequestered by the three amines and the three carboxylates and another Ca2 + by the remaining half the donor groups), as the Dreiding model suggests. The fact that there was no interaction at neutral pH of X with phosphate or oxalate anions was separately confirmed. Thus, the dissolution of Ca3(P04)2 and Ca(C204) is entirely due to the cation complexation mechanism. 

Bulk electrochemical reduction of the platinum(IV) complex of the tridentate ligand l,l,l-tris(aminomethyl)ethane(tame), [Pt(tame)2]4+, leads to the quantitative formation of [Pt(tame)2]2+ (28), in which one of the amine donor groups in tame remains noncoordinated.141 The X-ray structure of the diprotonated complex [Pt(Htame)2]4+, as its tetrachlorozincate(II) salt, is also reported. 

Molecular rotors have in common that fluorescent excitation leads to an ICT, in the case of DMABN from the nitrogen in the dimethylamino electron donor group to the nitrile electron acceptor group (Fig. 1). The ICT leads to a highly polar... 

As mentioned previously, in many siderophore complexes, a decrease in pH will result in protonation and dissociation of a donor group. This decrease in effective denticity of the chelator will lead to a corresponding decrease in complex stability and the opening of available coordination sites for the formation of ternary complexes, and/or exchange with other chelators. However, in the case of catecholamide donor group siderophores, such... 

The kinetics of iron(III) dissociation from a series of dihydrox-amate siderophores and siderophore mimics, including rhodo-torulic acid (3) and alcalagin, have been investigated (52,127,128, 177,178). ESI-MS studies show that these systems form multiple species as a function of pH and siderophore/iron ratio (128). The lability of these systems and the resultant multiple species leads to several parallel paths to iron(III) dissociation (177). Both the distribution of structures and kinetics of dissociation were shown to be dependent on the length of the spacer chain between the dihydroxamate donor groups (52,127). 

In conclusion, protonation of the donor group of D-A stilbenes leads to a short wavelength shift of both absorption and fluorescence spectra and a decrease of the fluorescence quantum yield while doubly protonated D-D stilbenes exhibit a monodeprotonation in the excited state and emit an additional long-wavelength bond. 

The high electrophilicity of the positively charged element can be modified by intramolecular donation from remote donor substituents. This interaction leads to solvent-free cations with coordination numbers for the positively charged element > 3 and to a considerable electron transfer from the donor group to the element. Frequently used donor substituents utilize heteroatoms with lone pairs (e.g. amino, hydrazino, methoxy, carboxy, phosphino, etc.), in many cases in combination with pincer-type topology of the ligand, for the stabilization of the cationic center. These strongly stabilized cations are beyond the scope of this review and instead we will concentrate on few examples where we have weak donors such as CC multiple bonds, which stabilize the electron-deficient element atom. 

Among the polydentate carbene ligands, particular interest has recently been placed on cyclic polycarbenes. ImidazoUum precursors like 23 [89] or 24 [90, 91], which upon C2 deprotonation would lead to tetradentate or even hexadentate double-pincer NHC ligands, have been prepared. Their interesting coordination chemistry will be discussed in Sect. 4. Finally, Arnold et al. developed and reviewed NHC ligands which are functionalized with additional anionic (alkoxide or amido) donor groups [92]. 

Another drawback of RCM applies in case of certain substitution patterns that lead to preferential complexation of the catalyst by substrate functional groups, thereby rendering it inactive. This may be overcome either by a more active or different catalyst or by precomplexation of the donor groups, e.g. with titanium salts [41]. 

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