Oxide ligand substitution

Kinetic and mechanistic studies of nucleophilic substitution at metal(IV) centers are fairly rare (263). Platinum(IV) has the substitution-inert low-spin d configuration, and presumably undergoes nucleophilic substitution by an associative mechanism thanks to its high charge and large size. However there are actually very few data, probably thanks to the tendency for platinum(IV) to oxidize ligands. Substitution kinetics at metal(IV) centers may be more conveniently studied for complexes of the type ML2X2, where M — e.g., Sn, Ti, V, or... 

Oxidative addition of XY substrates to [IrL2(/x-pz)]2 [La = (CO)2, cod] and [Ir(CD)(PPh3)(/i,-pz)]2 occurs via a two-center, two-electron route toward the iridium-iridium bond-containing species 131 (960M3785 980M2743). Complex 132, which is prepared by the ligand-substitution reaction from [Ir(CO)2 (/x-pz)]2, adds methyl iodide to give 133. 

The synthesis of a series of chiral organophosphine oxide/sulfide-substituted binaphtholate ligands has recently been reported by Marks and Yu and their corresponding lanthanide complexes characterized. These complexes, generated in situ from Ln[N(TMS)2]3, cleanly catalysed enantioselective intramolecular hydroamination/cyclisation of 1-amino-2,2-dimethyl-4-pentene albeit with a low enantioselectivity of 7% ee (Scheme 10.82). 

The remarkable physical properties exhibited by the divalent macrobicyclic cage complex [Co(sep)]2+ (29) are unparalleled in Co chemistry.219 The complex, characterized structurally, is inert to ligand substitution in its optically pure form and resists racemization in stark contrast to its [Co(en)3]2+ parent. The encapsulating nature of the sep ligand ensures outer sphere electron transfer in all redox reactions. For example, unlike most divalent Co amines, the aerial oxidation of (29) does not involve a peroxo-bound intermediate. 

Figure 17. Steric effects (Es) on the rates (log kRy) for the outersphere oxidation (3) and the rates (log kL) for the ligand substitution ( ) of Fe(phen)s3+ by (3-...

Base catalysis of ligand substitutional processes of metal carbonyl complexes in the presence of oxygen donor bases may be apportioned into two distinct classifications. The first category of reactions involves nucleophilic addition of oxygen bases at the carbon center in metal carbonyls with subsequent oxidation of CO to C02, eqns. 1 and 2 (l, 2). Secondly, there are... 

This structure validates a point made earlier, that ligand access occurs in the indicated position. At the point where this plausible but unproven assertion was first made, the reference was to reactions in which pyridine N-oxides were acting as oxygen donors. It remains pertinent for ligand substitution as well, but also for oxygen transfer reactions where sulfoxides are the oxygen donor atoms. 

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