The reactions of binuclear complexes

The stereochemistry of the addition of a,y-dihalides to [ (ti -C5H5)Co 2 (p-CO)2] has already been discussed (Section 6). There are relatively few binuclear systems in which the metal centres act as a nucleophile. 

The reaction of [Pt2(p-dppm)3] dppm = bis(diphenylphosphino)meth-ane with Mel in benzene leads to the methylated product as shown in (35). 

Subsequent reaction of the methylated complex with an excess of Mel in dichloromethane yields the dimethylated product as in (36). The binuclear system appears to be more reactive than mononuclear analogues such as [Pt(PPh3)3], and this has been ascribed to anchimeric assistance by the second platinum centre (Azam et ai, 1984). A similar reaction has been described for [Pd2(p-dppm)3] (Balch et ai, 1981). 

As observed in the work on [Pt2(p-dppm)3], oxidative-addition at one metal centre deactivates the other because of electronic factors the metal centre is now formally in a higher oxidation-state which thus attracts charge. In the absence of restraining ligands this leads to metal—metal bond formation [see (35)]. To circumvent these problems and to investigate the reactivity of a binuclear complex containing isolated metal centres the complexes shown in [11] and [12] (M = Rh or Ir) have been prepared (Schenk et al 1985). 

For species [12, X = PPh2] the reactions with Mel and CH3COCI demonstrate the greater electron-richness compared to [12, X = Cl]. The reaction with Mel proceeds according to (37) that of the rhodium complex proceeds only to equilibrium whereas that of the iridium analogue goes to completion. 

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Reactions of binuclear complexes 29 Stereochemical changes at an unsaturated carbon centre 30 Reactions of coordinatively-saturated complexes 30 Reactions of coordinatively-unsaturated complexes 31 Stereochemical changes at the metal 32 The iodide catalysis effect 38 The reactions of binuclear complexes 39 The reactivity of the carbon centre 41 The reactions of a,o>-dihalogenoalkanes 44 Activation parameters 47... 

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