Imides bridging ligands

The hydrolysis of p-nitrophenyl acetate and bis(p-nitrophenyl phosphate) are frequently used to probe hydrolytic activity. A problem with some other dinuclear systems is that the Zn units are held together by bridging ligands which can be cleaved on reaction with the substrate.440 This is not the case in a ditopic ligand such as those designed by Lippard and co-workers based on Kemp s triacid imide with a xylyl spacer.441,442 Both zinc dimers and mixed metal dimers were formed and a structure characterized with a bridging phosphodiester (Figure 6). 

Titanium imido complexes supported by amidinate ligands form an interesting and well-investigated class of early transition metal amidinato complexes. Metathetical reactions between the readily accessible titanium imide precursors Ti( = NR)Cl2(py)3 with lithium amidinates according to Scheme 84 afforded either terminal or bridging imido complexes depending on the steiic bulk of the amidinate anion. In solution, the mononuclear bis(pyridine) adducts exist in temperature-dependent, dynamic equilibrium with their mono(pyiidine) homologs and free pyridine. 

Fig. 3. Bridging amidate and imidate ligands used for the cis-diammineplatinum-blues and the related complexes. Arrows for each ligand show the bridging mode observed crystallographically.

Scheme 2.8 Examples of ligands used to model the carboxylate coreofcarboxylate-bridged dinuclearironenzymes (a) R3XDK[for R = CH3 H2XDK = m-xylenediamine bis(Kemp s triacid) imide] [57] (b) differently substituted terphenyl-based ligands (e.g. for R1 = CH3, R2 = H TolArCOOH) [48].

Ligands having P,N,S and P,N,Se acylic and cyclic combinations can be found in a considerable number of their coordination compounds [967]. The phosphorus-sulfide di-imides, forming complexes with bridge 567 or chelate 568 structures, belong to the first type of ligands [967] ... 

Another unusual species is the compound of Mn" and the imidazoyl anion [Mn3(imid-H)5 2imid], made from manganese carbonyl. The colourless crystals are air sensitive, and have a polymeric structure with alternating [MnN ] octrahedra and [MnN4] tetrahedra, bridged by the imidazole ligands. Each octahedral Mn is surrounded by four tetrahedral Mn s and each tetrahedron is surrounded by two other tetrahedra and two octahedra. 

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