Stereochemical changes at the metal

The reactions of metal nucleophiles containing a coordinatively-saturated reaction centre are relatively trivial, and invariably occurs with little gross stereochemical change to the complex, as for instance in the reactions of [M(dmgH)2L]- (M = Co, L = py M = Rh, L = PPhj) or [MCCO),] (M = Mn or Re). 

In contrast to the studies with [(Ti -C5Hj)Rh(PPh3)(Ti -C2H4)], where predissociation of a ligand is not essential for this species to react with alkyl halides, the reactions of [Pd(PPha)3] involve the 14-electron species [PdlPPhjIaJ. This behaviour is manifest in the kinetics (Stille and Lau, 1977 

Similarly, in the reactions of /rani-[IrCl(CO)(PPh3)2] with aryl iodides, the rate constant for disappearance of Ir(I) species obeys the two term rate-law shown in (26). The second term, exhibiting an inverse dependence on the concentration of PPh3, is attributed to a highly reactive, 14-electron species [lrCl(CO)(PPh3)] (Mureinik et al., 1979). In (26), Kis the equilibrium constant for dissociation of PPh3 from the complex, 2 s the rate constant for nucleophilic attack of [IrCl(CO)(PPh3)] on Arl and refers to the solvent mediated pathway. 

An interesting, if somewhat anomalous, conclusion comes from a kinetic study of the reactions of [RhCI(PPh3)3] with H2, O2, C2H4 and Mel. Although H2, O2 and C2H4 react with the species [RhCl(PPh3)2], Mel reacts not with this species, but rather [RhCl(PPh3)3], and the derived dimer shown in (27). There is no apparent reason for these various reactivities (Ohtani et al., 1977). 

In considering the reactions of coordinatively-unsaturated complexes, the stereochemistry of the addition at the metal can be either cis or trans. Most of the stereochemical studies in this area have been conducted with complexes of the type, t/-fl/ii-[IrX(CO)(PR3)2]. 

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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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