C–H versus O–H Bond Activation in Phosphino-alcohol Ligands: Synthesis of the α‑Hydroxy-alkyl Ruthenium(II) Derivatives [RuCl{κ²(<i>P,C</i>)‑Ph₂PC₆H₄C(R)OH}(η⁶‑arene)]

The coordination of the phosphino-alcohol ligands 2-Ph2PC6H4CH­(R)­OH (R = H, Me) onto an arene-ruthenium­(II) fragment gave rise to the formation of complexes of general formula [RuCl2{2-Ph2PC6H4­CH­(R)­OH}­(η6-arene)] (R = H, arene = C6H6 (3a), p-cymene (3b), mesitylene (3c), C6Me6 (3d); R = Me, arene = p-cymene (5b)). In solution, different isomers were observed depending on the solvent polarity. They arise from the different coordination modes adopted by the phosphino-alcohol: (i) the classical κ1-P mode through the selective coordination of the phosphorus atom, (ii) the establishment of both Ru–P and Cl····H–O interactions, and (iii) the P,O-chelate formation. Treatment of these species with NaPF6 led to the selective formation of the corresponding cationic species [RuCl­{κ2-(P,O)-2-Ph2PC6H4­CH­(R)­OH}­(η6-arene)]­[PF6] 6a–d and 7b, respectively. Unexpectedly, under basic conditions these cationic compounds evolved into the neutral α-hydroxy-alkyl derivatives [RuCl­{κ2-(P,C)-Ph2PC6H4­C­(R)­OH}­(η6-arene)] through a formal C–H bond activation process.