Cyclo-octatetraene complexes

Among mixed-ligand cyclo-octatetraene complexes, the U, Th, Pa, Np, and Pu complexes [(r -Cx 11x)An(p-SPr)2]2 were reported, which can be prepared by reacting the thiol with U(COT)(BH4) [399a], Reduction of the bulky 8-annulene thorium complex [Th COT(TBS)2 2] [COT(TBS)2 = CxIIfi(/-BuMc2Si)2-l,4] by potassium... 

There are many complexes of Cu1 with olefins or other unsaturated compounds, and these are in general rather similar19 to those of Ag+ (page 1051). Although they are usually made by direct reaction with Cu1 halides, they may also be prepared from cupric salts by reduction with trialkyl phosphites in ethanolic solution in presence of the alkene.193 The crystalline compounds obtained when using chelating alkenes such as norbornadiene or cyclic polyalkenes usually have polymeric structures, such as that for the cyclo-octatetraene complex (25-H-V), and only one of the double bonds is normally coordinated. 

C which interconvert at higher temperatures over a barrier of 8.3 0.1 kcal mol". Detailed studies of the dynamic behaviour of the cyclo-octatetraene complexes have been reported previously (see ref. 39) and are discussed in the next section (Group VII). 

Cyclic Alkenes.—The cyclo-octatetraene complexes [M(j -C5HbX -C8H8)] (M = Co or Rh) form unstable solutions in concentrated sulphuric acid. However, in trifluoroacetic acid the stable cationic species [Mfiy -CsHsXCsH,)] are produced. When M = Co, two isomeric forms (12) and (13) are formed upon initial protonation but over a period of two days irreversible isomerization of (12) to (13) occurs. Kinetics of the isomerization of (12) to (13) for M = Rh are first order in (12). The activation parameters found for this process are A/f = 2fi l kcalmol and A5+ = 12 3calK- mol- ... 

Mann has applied the Forsen-Hoffman spin saturation method using C n.m.r. spectroscopy to the solution of several problems of molecular dynamics ie.g. see ref. 1). Using this technique, the cyclo-octatetraene complex [Cr(CO)3(tj -cot)] is shown to be fluxional by means of 1,3- and, to a lesser extent, 1,2-shifts. This new evidence clearly disproves the suggestion that random shifts are occurring in this complex but supports Whitesides argument for 1,3-shifts in which a 16-electron intermediate [Cr(CO)3(rj -cot)] may participate (see Vol. 5). In fact careful analysis of variable-temperature n.m.r. lineshapes does support a non-random fluxional process and at 26.5 °C gives rate constants for 1,3- and 1,2-shifts Ati,3=48 s and A i, = 24 s-i. ... 

Ruthenium.—The cyclo-octatetraene complex [Ru(j -C6Me6)(l-4- y -cot)] is highly fluxional and the barrier to intramolecular exchange of bound and unbound halves of the eight-membered ring is < 6 kcal moL in contrast to 8.6 kcal mol" in [Ru-(CO)3(l-4-7 -cot)]. ... 

There is wide-line n.m.r. evidence for fluxional behaviour even in the solid state, as, for example, for the cyclo-octatetraene complex (18) and the di-iron species Fe2(C8H8)(CO)6. ... 

Cyclo-octatetraene complexes of trivalent actinides have also been prepared. The synthesis of anionic neptunium and plutonium complexes is shown below [169] ... 

C=C distances in the cyclo-octatetraene do not appear to be lengthened [78]. The norbomadiene complex CTHt(AgN03)2 is similar to the cyclo-octatetraene complex 1.10, in that it consists of Ag-NOs chains link by the olefin [78u]. In refluxing solutions of silver salts in cyclo-octatetraene the < clo-octatetraene may dimerize forming a number of isomeric olefins... 

Seven-electron ligands, mixed sandwich complexes, related azulene derivatives and cyclo-octatetraene complexes... 

The cyclo-octatetraene complexes are binuclear and it is thought that the olefin has the tub configuration as shown [45, 46]. Other examples of... 

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