Magnesium chelating ligand

Chelating ligands for magnesium were expected to influence the relative rate of deprotonation and addition [19], TMEDA gave a modest improvement in the reaction affording a 92 8 ratio of 3 61 under the best conditions. N,N -Dimethylimidazolidinone was not as effective in suppressing the formation of 61. No reaction was observed in DME, even on heating to 50°C. 

A variety of new ligand designs and ligand combinations were used in attempts to mimic some properties of the ubiquitous bent metallocene environment at the early metal centers consequently, some of these systems were used in the further development of butadiene zirconium chemistry. The pyridine based chelate zirconium dichloride complex 43 cleanly formed the butadiene complex 44 upon treatment with butadiene-magnesium. Its structure shows that the C4H6 is arranged perpendicular to the chelate ligand plane. Complex 44 inserts one equivalent of an alkene or alkyne to form the metallacyclic 7i-allyl system 4545 (Scheme 13). 

The first example of chiral tetranuclear supramolecular assembly 5.27 was reported by Saalfrank and coworkers in 1988. Thus the complex [(NH3)4n(Mg (22)5] (5.27) was obtained by serendipity upon treatment of the doubly bidentate ligand 22, which is formed in situ from malonic ester and oxalyl chloride, with MeMgl in aqueous ammonium chloride solution (Scheme 5.13). Later an improved one-pot reaction was used to prepare such tetrahedral complexes of magnesium, manganese, cobalt and nickel by treating the bis(chelate) ligand 22, obtained in situ, with MeLi/MCl2 followed... 

A new approach recently was taken to maintain an excess of soluble scavenging metal in a mud and to minimize the adverse effects of the metal ion. The metal ion is bonded loosely with an organic compound (ligand) that is highly water-soluble. These organometallic compounds are commonly called metal chelates. Examples are hemoglobin in blood (iron chelate) and plant chlorophyll (magnesium chelate). 

Similarly, Arnold found that NHCs with tethered nucleophilic chelating ligands (42-44 Figure 31.9) possessed the ability to catalyze the ROP of lactide as a bifunctional catalyst [63]. The juxtaposition of an alkoxy or amino group with a labile NHC-transition metal (metal = yttrium, titanium, magnesium, zinc) complex allowed the labilized NHC to activate the metal-coordinated monomer (Scheme 31.15). Additionally, a metal-free analog (38), in which an alkoxy ligand was tethered to the NHC, was found to promote similar catalytic activity. These catalyst... 

The mechanism of chelation involves the donation of a pair of electrons to a substrate species (such as iron, copper, calcium, or magnesium) and a reconfiguration of the shape of the new molecule to provide a minimum of bond strain. The chelant or ligand bites the substrate at several points, forming a stable, but not necessarily particularly strong, coordinate bond. 

N,N -Chelation is also exhibited by the dianionic P(III)/P(V) ligands (25) in the MejSn complex (31) [39] and in the magnesium complex (32) [40], which is prepared by oxidation of [Mg(thf)2[ BuNP(p-N Bu)2PN Bu] by elemental tellurium [40]. One of the endocychc N Bu groups in (32) is also weakly coordinated to magnesium, thus providing an intramolecular base-stabihzation similar to that observed for complexes of type (8). 

---