Magnesium complexes structure

Ruben M, Walther D, Knake R, Gorls H, Beckert R (2000) Fixation of carbon dioxide by oxalic amidinato magnesium complexes structures and reactions of trimetallic magnesium carbamato and related complexes. Eur J Inorg Chem 1055-1064... 

Figure 10 The structure of the lithium-magnesium complex [Li(tmeda)(/r-Br)2Mg C(SiMe3)2(SiMe2Ph) (THF)] 23. 

Figure 53 The structure of the ethynyl-bridged aluminum-magnesium complex [Me2AI(/i-EtN)2Mg(/j-Cs=CPh)]2 106.

The phthalocyanine [1-4] system is structurally derived from the aza-[18]-annulene series, a macrocyclic hetero system comprising 18 conjugated n-electrons. Two well known derivatives of this parent structure, which is commonly referred to as porphine, are the iron(III)complex of hemoglobin and the magnesium complex of chlorophyll. Both satisfy the Htickel and Sondheimer (4n + 2)- electron rule and thus form planar aromatic systems. 

Structurally very close to the N,N,O-tridentate ketiminate systems, magnesium complexes bearing bis-amido-oxazolinate complexes 44a-e were used in the PLA preparation from L-lactide in the presence of benzyl alcohol. The low reactivity of 44d, e is due to the presence of a pendant functionality engaging the metal center, and the steric bulk of the phenyl group hindering the coordination of benzyl alcohol or of a monomer to the metal center, contributing to a diminution of the propagation [69]. 

Hybrid scorpionate/cyclopentadienyl-Mg (63) and -Zn (64,65) complexes were structurally characterized and reported to catalyze the formation of PLAs with medium molecular weights and narrow polydispersities [85]. Among them, the magnesium complex 63 is much more active than the others, giving a polymerization of L-lactide in toluene at 90 °C with 97% conversion in 2.5 h. However, it takes 30 h for zinc complexes 64 and 65 to reach similar results under the same conditions. Some representative structures of magnesium and zinc complexes are summarized in Table 2 as they display closely related ROP activity of lactide, and often stmcrnrally similar ligand systems are employed to construct these initiators. 

It has been found that magnesium complexes supported with bidentate p-diketiminate are more active in the ROP of l- and rac-lactide than their structurally analogous zinc complexes. Faster rate of polymerization of magnesium complexes were such that an almost complete conversion (97%) occurred in 1 min at 20 °C for a p-diketiminate magnesium complex [(BDI-l)Mg(0 Pr)]2 31 (O Pr = isopropoxide) whereas the zinc analog needed 33 min for a similar conversion at the same temperature [64] (Table 3, entry 1). Similarly a higher... 

Other anionic complexes of beryllium that have been detected are (NH4)2Be(N03)4,141 (NH4)2Be(NCS)4-MeCN and (NH4)2Be(NCS)3-MeCN.142 ESCA studies on beryllium and magnesium complexes of the type [M(NCS)4]2 and [M(CNS)3L] (L = DMF, py, MeCN) are consistent with N-bonding thiocyanate anions being present.142 The structure of K[Be(NH2)3] shows the beryllium to be in a trigonal planar unit.143... 

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). 

Perhaps the most important of magnesium complexes are the chlorophylls that are involved in photosynthesis in plants the structure of one of these is shown in diagram (4-VI). 

The magnesium complexes 53 (72) and 54 (73) are structurally very similar to 6 and 7. Methyl and phenyl groups bridge the two metal atoms. The lithium-magnesium interatomic distances in 53 and 54 (2.62 and 2.94 A, respectively) are less than the sum of the atomic radii for these metals (3.15 A), (74), indicating that some degree of metal-metal interaction may be present. 

Porphyrins and their derivatives play critical roles in many biological functions. Some of the most remarkable examples are protoporphyrin IX and its iron complex that constitutes the heme prosthetic group, and the magnesium complexes of pheophytin a and bacteriopheophytin a that are known as chlorophyll a and bacteriochlorophyll a, respectively. These natural compounds are illustrated in Fig. 1 together with the structure of porphin,... 

Chlorophyll a with a Q -band at Amax = 665nm (95) is the magnesium complex of the dihydroporphyrin derivative 3 already shown in Fig. 3. The chemically quite different structures of compounds 7 and 8 are given in Fig. 9. 

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