Inhibiting σ → π Isomerization of Aryloxide Ligands in Late Transition-Metal Complexes
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Abstract
The room-temperature reaction of thallium perfluorophenoxide with RuHCl(PPh3)3 (4a) yields RuH(σ-OC6X5)(PPh3)3 (X = F, 5F), the structure of which was confirmed by spectroscopic, microanalytical, and X-ray analysis. The analogous phenoxide complex (X = H, 5H) is known to be unstable toward σ → π isomerization, and reaction of phenoxide ion with 4a affords RuH(η5-C6H5O)(PPh3)2 (6a). We conclude that the driving force for isomerization in 5F is minimized by the electron deficiency of the perfluorophenoxide ring. In contrast, incorporation of the aryloxide entity within a chelating framework proves insufficient to inhibit isomerization. Thus, reaction of 4a or RuCl2(PPh3)3 (4b) with the sodium salt of 2'-(diphenylphosphino)-1,1'-binaphthyl-2-ol (NaO-MOP) yields RuX(O-MOP)(PPh3) (7a, X = H; 7b, X = Cl). Detailed 1- and 2-D NMR analysis of 7b provides unequivocal evidence that the O-MOP ligand is bound to Ru in a σ fashion through phosphorus and in a π fashion via the aryloxide ring. The crystal structure of 5F·THF is reported.
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