Tropolonato chelates

Tropolonato chelates, 201 (Figure 32) were first reported by Muetterties and Wright (332). All available spectroscopic data (infrared, 1H, and 29Si NMR) suggest a cationic octahedral structure around silicon. Analogous tropolonato chelates seem to have been isolated from plants and compared with the synthetic compounds (323). 

As might be expected for chelating 0,0 donor ligands it is the intermediate trivalent state of osmium which is stabilized by /J-diketonates (as is the case for catechols, p. 597, and tropolonato complexes, p. 597). In the presence of rc-acceptor chelates such as bipy, phen and terpy the II state is favoured, while with halides the IV state is preferred. The apparent absence of an osmyl complex, e.g. 0s02acac2, is surprising. 

Newer agents under investigation include tris(tropolonato) Bi(III) and nitratobis(tropolonato)Bi(in) a host of bis (mercaptoethanol)Bi(III) complexes, which are formed with 0,S-bidentate chelation, with and without deprotonation of the hydroxyl oxygen and usually having an axial fifth ligand and sialic acid derivatives of Bi(III). The interactions of Bi(III) and its compounds with metallothionein, serum albumin and transferrin have been studied by a variety of groups, as have a number of enzymes that may be related to the mechanism(s) of action of bismuth in treating ulcers. 

In the monohydrate SnY(H20), where H4Y = edta, Sn(iv) is bonded to three pairs of 0 atoms of the ligand and to one H2O molecule. There is no simple description of the geometry of the 7-coordination polyhedron, which is very similar to that in Mn HY(H20)-illustrated in Fig. 27.3(d). With the tropolonato (T) ligand, (a), the metal forms chelate complexes SnT3Cl and SnT3(OH) the configuration... 

The structure of the dianion SiF was first confirmed106 by X-ray diffraction in 1935, and has since been re-examined with a variety of counteranions that of Si(-OC6H46)3 was determined107 in 1969. The tris-chelate cations Si(acac)3 108 Si(tropolonato)3 109 and 511,0 have been resolved for use in mechanistic studies. 

It should be noted that the tropolonato ion forms a five-membered chelate ring and that the bite, that is, the O-to-O distance, is smaller than for /J-diketonato ions. This leads in tristropolonato complexes to considerable... 

Eaton, S. S. Eaton, G. R. Holm, R. H. Muetterties, E. L., Intramolecular Rearrangement Reactions of Tris-Chelate Complexes. IV. Piuther Investigation of the Rearrangements of Tris (a-isopropenyl- and a-isopropyl-tropolonato)metal(III,IV) Complexes J. Amer. Chem. Soc. 1973, 95, 1116-1124. 

The 5-bonded complexes [Rh(CO)X(R2SO)2] (R=Me, Pr , or Bu X=C1 or Br) and [Rh(CO)X(R2S)2] (R=Me, Et, or Pr ) have been prepared and the molecular structure of the chelate tropolonato-complex [Rh(CO)(PPh3>-(C7H5O2)] has been elucidated. The Te-bonded complex [RMCOX KTePhala] has also been isolated and some oxidative addition reactions with X2 (X=Br, I, or SCN) studied. 21... 

Rearrangements in tris-a-isopropyl- (44) and tris-a-isopropenyl-tropolonato-complexes of several metal(iii) cations have been probed by n.m.r. spectroscopy. Two intramolecular processes are likely for these tris-chelates of unsymmetrical ligands, A A inversion and cis trans isomerization. Both... 

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