Heterocyclic complexes

As was suggested in the preceding discussion, most of the arene complexes isolated by metal-atom techniques are benzene derivatives. However, heterocyclic ligands are also known to act as 5- or 6-electron donors in transition-metal 7r-complexes (79), and it has proved possible to isolate heterocyclic complexes via the metal-atom route. Bis(2,6-di-methylpyridine)Cr(O) was prepared by cocondensation of Cr atoms with the ligand at 77 K (79). The red-brown product was isolated in only 2% yield the stoichiometry was confirmed by mass spectrometry, and the structure determined by X-ray crystal-structure analysis, which supported a sandwich formulation. 

Two independent papers have reported the synthesis of nitrogen-heterocycle complexes of the type [RhCl3(py-X)3] (py-X = 3-Etpy, 3-CNpy, 4-Etpy, or 4-CNpy) and rr(ans-[RhY2L4] (Y = Cl or Br L = several substituted pyridines, isoquinoline, pyrimidine, pyrazole, thiazole, and substituted imidazoles). All the compounds were prepared catalytically by boiling RhCl3.3H20 with ethanolic solutions of L. It is interesting that 2-substituted... 

The first example in Scheme 10.1 shows that vinylphosphine kinetically first gives the three-membered heterocycle (75%), which upon heating transforms into the thermodynamic product, the four-membered heterocyclic complex. From the other examples we see that, ifthe possibility exists, the preferred route is formation ofa fivemembered ring [18]. 

General methods for the preparation of N-heterocyclic complexes have been well summarized previously (2). One of the new synthetic procedures involves the use of triflato complexes, e.g., cis-... 

Heterocyclic complexes of pentaammineosmium(II) have also been reported for pyridinium (85), 2,6-lutidine (85), 2,6-lutidinium (85), pyrrole (179), furan (179), and thiophene (179), in which the organic ligand is dihapto coordinated via a C==C bond (90). These ligands are thought to rearrange upon oxidation to coordinate through the heteroatom. 

The properties of the N-heterocyclic complexes of silver(II) have recently been reviewed and it was found that in most complexes square planar coordination occurs about the central ion although higher coordination numbers are known.496... 

Table 64 Spin Hamiltonian Parameters Obtained from ESR Studies of N-heterocyclic Complexes of Ag 1... 

The magnetic moments for solid silver(II) N-heterocyclic complexes are generally close to 1.8 BM suggesting quenched orbital angular momentum and spin-only paramagnetism (Table... 

It is also pertinent to mention the occurrence of bridging phosphido and arsenido selenide ligands (Scheme 4).32 The phosphido selenide complexes (1 Scheme 4) were found to be very reactive and readily gave the six-membered heterocyclic complexes (3). In contrast the arsenido selenide systems gave both the four-membered ring intermediates (1 M = Mn, Re) and the six-membered heterocycles (3). 

Wilkinson et al. (128) have reported the partial mass spectrum of the heterocyclic complex C4F8Fe(CO)4. Fragmentation occurs by loss of CO,... 

Malina J, Novakova O, Keppler BK, Alessio E, Brabec V (2001) Biophysical analysis of natural, double-helical DNA modified by anticancer heterocyclic complexes of ruthe-nium(III) in cell-free media. J Biol Inorg Chem 6 435 145... 

Kapitza S, Pongratz M, Jakupec MA, Heffeter P, Berger W, Lackinger L, Keppler BK, Marian B (2005) Heterocyclic complexes of ruthenium(III) induce apoptosis in colorectal carcinoma cells. J Cancer Res Clin Oncol 131 101-110... 

Ala. The action of lysyl oxidase to produce allysine allows three of these modified residues to condense with one lysine residue to form the heterocyclic complex amino acid desmosine. which cross-links two or even three chains. A highly cross-linked network results. 

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