Monomeric ligand complexes

Que and coworkers reported on a similar monomeric iron complex, formed with the BPMEN ligand but without acetic acid [128]. This complex was able to epoxidize cyclooctene in reasonably good yield (75%), but at the same time a small amount of the ris-diol (9 %) was formed. This feature observed with this class of complexes has been further studied and more selective catalysts have been prepared. Even though poor levels of conversion are often obtained with the current... 

In the presence of N,N,N, N",N"-pentamethyldiethylenetriamine ( = PMDETA), monomeric lithium complexes of bulky formamidinate ligands can be isolated. The compounds (Scheme 12) comprise a Li(PMDETA) center coordinated by a bulky formamidinate in either the E-syn- or E-anti-isomeric form. Two of the structures display coordination of the pendant amidinate imine, and can therefore be considered the first examples of if. r -C = N,N metal amidinate coordination. ... 

The same, distorted, octahedral geometry is also found in a number of monomeric diorganotin complexes having two bidentate ligands, such as MejSn(0-NMe-C0-Me)2 (379) and Me Sn(S-CS-NMei)2 (380), or one tetradentate group, such as Me2Sn(salen) (381). 

The crystal structures of monomeric ligands such as GH and EPO in complex with their respective receptors show that these hormones are bivalent and one ligand binds simultaneously to two receptor molecules to form a 1 2 (ligand receptor) complex. Receptor dimerization is further stabilized by additional receptor-receptor interactions. 

Figure 1 Monomeric copper complexes of tetradentate ligands.

A monomeric selenolato complex of zinc (65) was synthesized with a chelating oxazoline ligand.587 The complex was characterized by X-ray crystal structure, 1H, 13C, and 77Se NMR. These studies demonstrate that the compound is helically chiral and solution studies appear to show retention of chirality in solution. The zinc complex is tetrahedral with a Zn—Se average bond length of 2.378(1) A. 

The ligand mercaptoethyl pyridine forms a monomeric ZnL2 complex with the chelate ligand binding through the nitrogen and thioether sulfur.125... 

Furthermore, the utilization of preformed films of polypyrrole functionalized by suitable monomeric ruthenium complexes allows the circumvention of problems due to the moderate stability of these complexes to aerial oxidation when free in solution. A similar CO/HCOO-selectivity with regards to the substitution of the V-pyrrole-bpy ligand by an electron-with-drawing group is retained in those composite materials.98 The related osmium-based redox-active polymer [Os°(bpy)(CO)2] was prepared, and is also an excellent electrocatalyst for the reduction of C02 in aqueous media.99 However, the selectivity toward CO vs. HCOO- production is lower. 

Monomeric, dialkylcopper complexes have been prepared and structurally characterized. The reaction of CpCuPPh3 with lithium fluorenyl18 provided the complex [(fluorenyl)2CuPPh3] [Li(THF)4]+ 11. The use of the anionic ligand CH(Me)PEt2NSiMe319 afforded the mononuclear complex 12 in which the ligand acts as a bridge... 

Selenazyl halides NSeX have not been characterized either as monomers or cyclic oligomers. However, the monomeric ligand is stabilized in metal complexes of the type [MCl4(NSeCl)]2 (M=Mo, W)94... 

In the past, several aluminum-alkyl, halide, and alkoxide complexes supported by multidentate ligands were examined for their catalytic lactide polymerization activities. To this end, monomeric aluminum complexes 148a, b (Fig. 21) were synthesized in our laboratory for producing polyesters with thiolate end groups [137]. These complexes initiated polymerizations under reflux condition in toluene and xylene forming PLAs with narrow molecular weight distributions (PDIs 1.15-1.25). 

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