Donor groups lead structures

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. 

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). 

It is clear that hydrogen-bond donor groups, such as alcohols or amides have an especially high contribution to cohesion, whereas hydrocarbon and halogenated groups display the lowest cohesivity. This method is essentially valid in a comparative way, but it can lead to serious discrepancies with experimental results, despite the fact that Ec is not very sensitive to structural irregularities. 

Whereas two methyl N-substituents are inefficient in transmitting the chiral information encoded at the rear side of the heterocyclic ligand (Entry 1 in Table 1), the stereoselectivity is improved by the introduction of N-benzyl substituents (Entry 2). The steric repulsion between the ferf-butyl and benzyl groups leads to a C2 symmetric arrangement of the latter with respect to the carbene donor function as is apparent in the molecular structure determined by X-ray diffraction for the silver(I) complex 20 [51]. In this way the chirality in the heterocycle is transmitted towards the reaction center. Introduction of methoxy groups in the meta-position of the phenyl rings of the benzyl substituents slightly increases the selectivity of the catalyst (Entry 3). 

Substitution of one hydrogen of HOH with an aromatic group leads to a phenol molecule. When paired with methanol, phenol acts as the proton donor molecule in a structure very much akin to the water dimer itself At the SCF/6-31G level, the interoxygen distance is 2.89 A. The electronic contribution to the binding energy is computed to be 6.0 kcal/mol, after removal of BSSE, and 7.1 kcal/mol at the MP2 level with the same basis set. Correction of the correlated result by ZPVE yields a of 5.8 kcaPmol, leading to the conclusion that phenol is a more potent proton donor than is water. 

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