Monomeric 6-coordinate complexes

Iodosylbenzene is sufficiendy reactive on its own to epoxidize electron-deficient olefins such as tetracyanoethylene (43). It is possible that coordinated monomeric iodosylbenzene is substantially more reactive than polymeric iodosylbenzene and that complexation of a monomeric form is sufficient to provide the requisite reactivity with normal olefins. 

Four-coordinate, monomeric aluminium amides. Monomeric, four-coordinate aluminium amido derivatives are now quite numerous, yet none had been structurally characterized before 1980. They may be divided into two broad categories those which are Lewis base adducts and those in which four-coordination for aluminium is a result of complexation by a chelating ligand. 

Zr(C6H402)(L)] derivatives, respectively these complexes are monomeric in solution and presumably five-coordinate. 

A V02+ complex with the compartmental ligand (177) was obtained by the dropwise addition of a VOSO4 solution to an aqueous acetone solution containing LiOH and the ligand.903 The complex is monomeric and the coordination involves the four O atoms. With Ni2+ and Cu2+ both mononuclear positional isomers N202 and 0202 may be prepared according to conditions, but with V02+ only the 0202 positional isomer is obtained. 

A striking difference was observed between the trimethylamine oxide complex and the hexamethylphosphoramide complex, although both complexes are monomeric. Polymerization did not occur by the former complex, whereas it proceeded smoothly with the latter one (Table 5). This difference can be explained by the difference in the electron donating power of the electron donor which occupies the fourth coordination site of the aluminum atom. Hexamethylphosphoramide can be replaced by an aliphatic aldehyde, while trimethylamine oxide cannot. 

Stable 1 1 complexes of the type R3PAg(0C103) have been isolated using bulky phosphines such as PBu3, PCy3 (Cy = cyclohexyl) and P(o-MeC6H4)3 as well as with the less bulky triphenylphosphine and para-substituted triarylphosphines.181 On the basis of molecular weight measurements and also their IR spectra, it was concluded that they had linear two-coordinate monomeric structures in which the perchlorate ion was coordinated to the silver in both the solid state and in dichloromethane solution.181... 

The complexes MX2L2 (M = Zn, X = Cl, Br or I M = Cd, X = Cl) and HgX2L (X = Q, Br, SCN, N03 or S04) have been isolated, where L is the sterically hindered ligand 2-imino-4-oxo-1,3-thiazolidine.880 All complexes are formulated as monomeric tetrahedral with Zn, ligand coordination is via the ring N atom, but in the Cd complexes coordination via sulfur is observed. The ligand is bound via both N and S in the Hg complexes. The SCN is unidentate and S-bonded nitrate is unidentate, whereas sulfate is bidentate. 

Other representatives of the N,0,0-chelates are diorganotin-N-aryI idcne-ce-amino acid complexes (418)859,860, including 418a859 and 418b860, for which five-coordinate monomeric structures were established by X-ray studies. The tridentate ligands in these compounds are near-planar. The tin centers have a distorted TBP geometry with the two... 

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