Ligand properties 4-electron ligands

The ligand properties of a cyclic dithioether, 1,4-dithiane monosulphoxide (DTMSO), have been studied by physical measurements . The infrared spectra indicate that the metal cation coordinates to the oxygen lone pair electrons of DTMSO. Both infrared and ligand-field spectra show the presence of octahedral ions MfDTMSO) in the compounds M(DTMS0)g(C104) and M(DTMSO)g(BF4) . In the case of M = Cu these ions are distorted from the regular octahedral structure. 

In a continuation of their earlier work,1 Hathaway and co-workers investigated crystal structures, electronic properties, and structural pathways for a series of five-coordinate complexes with two 1,10-phenanthroline (phen) ligands and axial ligands [(phen)2CuCl]Y [Y BF4 -0.51120 (269), PF6-(270), CF3S03--H20 (271) or BPh4 (272)],243 [(phen)2Cu(H20)][Y]2... 

The series of wide-bite-angle, bulky ligands derived from a cyclobutene scaffold gave Pd complexes (117) showing appreciable activity in the cross-coupling of reactive aryl bromides with trimethylsilylacetylene. A considerable shift of electron density to the phosphorus atoms, probably arising from alternative aromatic canonical structures, may account for the ligand properties.422... 

We applied the QM/MM IMOMM method [41] to Rh-diphosphine catalyzed hydroformylation, to provide a quantitative theoretical characterization of the origin of regioselectivity in Rh-diphosphine systems. We focused on the experimentally characterized xantphos ligands, for which variation in electronic properties is minimal. Using the IMOMM method, which only accounts for the steric properties of ligands, was fully justified. 

Redox reactions usually lead, however, to a marked change in the species, as reactions 4-6 indicate. Important reactions involve the oxidation of organic and metalloprotein substrates (reactions 5 and 6) by oxidizing complex ions. Here the substrate often has ligand properties, and the first step in the overall process appears to be complex formation between the metal and substrate species. Redox reactions will often then be phenomenologically associated with substitution. After complex formation, the redox reaction can occur in a variety of ways, of which a direct intramolecular electron transfer within the adduct is the most obvious. 

Following another line of thought, ligands with electron deficient centers may bind anions. Macrobicyclic ammonium salts displaying such properties have already been described (164) other ligands containing, for instance, trivalent boron sites might also be suitable. 

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