Rearrangement of Tris-chelate Complexes

Intramolecular Rearrangement of Tris-chelate Complexes.—Co and Cr complexes were considered in the two previous sections and will not be discussed further in this section. A review deals with reactions in this category.  

Miscellaneous.—twisting rather than a bond-rupture mechanism has been established by n.m.r. line-broadening studies for the racemization of Ti complexes of the type [Ti(AA)(BB)2] [BB = acac or 3-acetylpentane-2,4-dionate ion AA = MeaC(0-)(CH2) C(0-)Me2, n=0 or 1].  

has also been used to measure the rate of ring inversion in substituted derivatives of 1,2-diaminoethane (e.g. Me4en) when co-ordinated to [Pr( H9-fod)J [ H9-fod = (CD3)3C(0-)CHC0C3F7]. For the complex with Me en, sG = 42.2 kJ mol at 235 K, which is much larger than the normally expected value of ca. 20 kJ moK.  

Nordan and I. Jonas, J. Inorg. Nuclear Chem., 1976, 12, 33. sii Fujiwara and Y. Yamamoto, Inorg. Nuclear Chem. Letters, 1975, 11, 635. 

Intramolecular Rearrangements of Tris-chelate Complexes.— Recently there has been considerable attention paid to the stereochemical non-rigidity of tris-chelate complexes and a number of reviews have dealt with the subject. Studies of NN-disubstituted dithiocarbarmato-complexes of the type [M(R R -dtc)8] (R, R = alkyl or aryl) have been extended and the results for intramolecular metal-centre inversion (probably by the Bailar trigonal-twist mechanism) are summarized for ruthenium(m) complexes in Table 29. The low values of AG and are surprising for ruthenium(m) since previous studies indicated that tris-chelates of this 

Miscellaneous.— Twisting as opposed to bond-rupture modes of activation are favoured for metal-centred rearrangements of several zirconium / -diketonates (dik) of the type [(A -C6H6)Zr(dik)aCl], [(A -C5H6)Zr(dik)al, and a new cationic species [(A -QH5)Zr(dik)2]+. The methyl H n.m.r. line-broadening patterns associated with 

The kinetics of the cw-A-cw-A inversion of ruthenium(n) dimethylphosphino-dithioato-complexes of the type c/j-[Ru(S2PMe2)(PR3)2] (R = Me, Ph, OMe, or OPh) have been measured by n.m.r. lineshape analysis. The proposed mechan- 

The stereochemical non-rigidity of eight-co-ordinate metal complexes has been demonstrated by and C n.m.r. for the systems [M(S2CNEta)4] (M = Ti, Zr, or and [M(CN)8] (M = Mo or W). The dithiocarbamato-complexes were investigated at temperatures down to 133 K in CS2-CD2CI2 solution, and the [Pr 4N]4[M(CN)8] salts at temperatures down to 113 K in CHCIF2-CH2CI2 as 

Electrolytic oxidation and reduction of four diastereoisomers of tris-[ (+)-3-acetylcamphorato ruthenium(in)] to corresponding ruthenium(iv) and ruthenium(u) species has been carried out and the circular dichroism and absorption spectra are reported. The ruthenium diastereoisomers isomerize in solution at 443 K, and the isomer abundances and rates of 12 isomerizations for the four diastereoisomers have been measured using high-pressure liquid chromatography. 

Intramolecular Rearrangements of Tris-chelate Complexes.—The kinetics and mechanisms of such rearrangements of cobalt(m) and of chromium(iii) complexes have already been discussed at appropriate points in the previous two sections. 

One of the simplest bidentate ligands is the oxalate anion. Racemization of its tris-chelates of cobalt(iii) and chromium(m) have already been mentioned racemization of its rhodium(m) tris-chelate has also been studied recently. The similarity of the kinetic parameters for racemization and for inner-oxygen exchange of [Rh(ox)3l suggests a close similarity of mechanism. A common five-co-ordinate intermediate is proposed, whose lifetime is sufficient for inner router oxygen exchange or for racemization to take place. 

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 

An example of a full kinetic study of a related tetrakis-chelate complex is afforded by the intramolecular rearrangement of [Zr(/r -allyl)4], details of which belong in the organometallic section of this Report.  

Miscellaneous.— Isomerization of [Mo02(dipivaloylmethanato)2] is definitely intramolecular, but it is not possible to choose between a purely non-dissociative twist and a mechanism in which one or both of the bidentate ligands imdergoes partial dissociation to become unidentate. The activation energy for this isomerization is 17.0 kcal mol the frequency factor is gi2.6 454 Interconversion of isomers of octahedral molybdenum(v) complexes of the type MoOL LlX is fast.  

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Intramolecular Rearrangement of Tris-chelate Complexes.— Rate data for the dissociation and racemization of [M(phen)3] + ions (M = Cr, Fe, Co, or Ni) are collected in Table 39. Only the nickel(ii) complex racemizes at a rate comparable to the ligand... 

Dynamics of intramolecular metal-centred rearrangement reactions of tris-chelate complexes. L. H. Pignolet, Top. Curr. Chem., 1975,56,93-137 (85). 

Pignolet, L. H. Dynamics of Intramolecular Metal-Centered Rearrangement Reactions of Tris-Chelate Complexes. 56, 91-137 (1975). 

Dynamics of Intramolecular Metal-Centered Rearrangement Reactions of Tris-Chelate Complexes... 

Several reviews have recently appeared which cover the topics of inter-1 6 and intramolecular1, s-n rearrangement reactions of metal complexes. In order to minimize duplication this review will be limited to intramolecular metal-centered rearrangementjeactions of six-coordinate tris-chelate complexes. Both kinetically slow (rates < 10 2 sec"1) and fast (rates % 10" 2 sec"1 )b complexes will be considered mainly from a mechanistic point of view. In addition various structural and electronic parameters of tris-chelate complexes will be scrutinized in order to assess their affect on the rate and mechanism of rearrangement. 

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