Reductive elimination of Phi

A study of the catalytic a-acetoxylation reaction of acetophenone by electrospray ionization tandem mass spectrometry (ESI-MS/MS) has confirmed the mechanism shown in Scheme 4.2. In particular, the trivalent iodine species was detected when iodobenzene and mCPBA in acetic acid were mixed, which indicated the facile oxidation of a catalytic amount of Phi to the iodine(III) species by mCPBA. Most importantly, the protonated alkyliodonium intermediate 3 (R = Ph, = H) was observed at m/z 383 from the reaction solution and this ion gave the protonated a-acetoxylation product 1 at m/z 179 in MS/MS by an intramolecular reductive elimination of Phi [17]. 

The first suggestion that ligand loss was important in reductive eliminatimi reactions from Pt(lV) complexes dates back more than 40 years. In 1969, Ettore observed that added iodide inhibited the reductive elimination of Phi from L2PtPh2l2 in methanol and suggested iodide loss to form a six-coordinate solvento intermediate [13]. Several years later, a five-coordinate intermediate was proposed by Puddephatt in studies of C-C reductive eliminations from Pt(IV) complexes (see Sect. 2.1.1) [15]. Since then, the involvement of five-coordinate intermediates has been supported so consistently in both experimental (e.g., [10,13-42]) and computational studies (e.g., [29, 30, 43 8]) of alkyl C-C, C-H, and C-X reductive elimination that it is now accepted as the norm in mechanistic schemes for reductive elimination from Pt(IV). 

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