Metal-bound phenoxide

The reactivities of hydrido(phenoxo) complexes of trons-[MH(OPh)L2] (6 M = Ni 7 M = Pt) (L = phosphine) were examined (Eqs. 6.29, 6.30 Scheme 6-16), and a high nucleophiUdty for the metal-bound phenoxide was suggested [9, 10]. Reaction with methyl iodide produced anisole and trans-[MH(I)L2] for both Ni and Pt complexes. Phenyl isocyanate also provided the insertion products into the metal-phenoxo... 

Such an interpretation is also supported by the 13C-NMR data. An ortho, para electronic shift of this type has recently been proposed to explain the optical spectral differences between free and metal-bound phenoxides in the transferrins (67). In enterobactin, however, this tautomerism is of fundamental conformational importance as it lowers the energy barrier to rotate the amide bond to —47° from the planar trans configuration (Fig. 6), as is required in order to form a mononuclear octahedral complex. Upon reorientation, the amide proton becomes sterically more shielded from interaction with the solvent and this is reflected in its temperature coefficient which (in absolute value) drops from 4.7 X 10-3 ppm/deg in enterobactin to 1.3 X 10-3 ppm/deg in the Ga3+ chelate. Conversely, the driving force to form the mononuclear complex will favor the electronic delocalization implied in the above tautomerism. 

The 4-methylphenoxide complexes / c-[Re(OAr)(CO)3L2] 0 = PMc3, L2 = diars) show much less tendency to insert electrophiles compared to the methoxide analogues. Neither phenoxide reacts with CO2 whereas only the PMe3 derivative will insert CS2. In contrast both methoxides insert both CO2 and CS2. " Again mechanistic data pointed to a direct attack of metal-bound alkoxide(aryloxide) on the electrophilic carbon atom. 

The reaction of 34 with triethylethylidenephosphorane is more complex. According to the multinuclear NMR data, the reaction occurs at the 1 2 ratio of the reactants. The Sn-O bond is cleaved to give phosphonium phenoxide (38) and stannylene (37) in which the tin atom is also bound to the ylide carbon atom of phosphorane (Scheme 17).61 Metallation reactions of this type are well known.61,75... 

By far the commonest bonding mode for aryloxide ligands is a terminal one in which the phenoxide oxygen atom is bound to only one metal atom. In some cases the phenoxide function may also be a part of a chelate ring and this may constrain the M-O-Ar angle (see below). Chelation may occur via donor heteroatoms or via metallated or jr-bound organic substituents (Section 2.1.2). 

There is also an extensive series of Rue raft like clusters that contain ortho-metaUated phenoxides bound with not only the oxygen and ortho-metallated carbon bridging two metal centres but also the phenoxy ring /r-bound to another metal... 

Ruthenium chemistry typically finds aryloxide ligands attached to the metal in low oxidation states. The extensive number of carbonyl aryloxide compounds reported for this metal exemplifies this (Table 6.34). The cluster compound [(H)2Ru6(CO)i6(M2-0-f -C6H4)] and derivatives contain the metallated phenoxide bridging two metal centres as well as -bound to another. 

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