Solvent-Dependent Hemilability of (2-Diphenylphosphino)Phenol in a Ru(II) para-Cymene System

The addition of Ph2P(2-C6H4OH) to [(η6-p-cymene)RuCl(μ-Cl)]2led to the formation of three distinct products, depending on the experimental conditions. The previously reported [(η6-p-cymene)RuClκ2P,O-PPh2(2-C6H4O)], 1, was obtained in 90% yield using MeOH as the solvent, in the presence of a base (Et3N). Conversely, [(η6-p-cymene)RuClκ2P,O-PPh2(2-C6H4OH)]Cl, [2]Cl, was afforded (88% yield) in MeOH without using the base. However, [(η6-p-cymene)RuCl2κP-PPh2(2-C6H4OH)], 3, was the major species in chlorinated solvents. Compounds 1, [2]Cl, and 3 were characterized by analytical and spectroscopic (IR, NMR) methods. The X-ray structures of [2]+and 3 were determined, with the latter forming hydrogen bond dimeric units in the solid state. The dissolution of [2]Cl into a series of deuterated solvents, except methanol, led to rapid equilibration between [2]Cl and 3, revealing the hemilabile behavior of the phosphino-phenol ligand. According to Pulsed-Field Gradient Spin Echo (PGSE)-NMR and DFT studies, the dimeric nature of 3 persists in solution; thus, the hydrogen-bonding properties of MeOH are crucial to stabilize [2]Cl with respect to 3, with the latter being 3.4 kcal mol-1more stable than the former in the gas phase. Compound 1 underwent electrophilic additions by HCl, HBF4, and MeCOCl to give, respectively, [2]Cl (the reverse process being viable with Et3N), [2]BF4, and the ester [(η6-p-cymene)RuCl2κP-PPh2(2-C6H4OCOMe)], 5. The reaction of 1 with AgNO3afforded the nitrate complex [(η6-p-cymene)Ru(NO3)κ2P,O-PPh2(2-C6H4O)], 4. Compounds [2]BF4, 4, and 5 were isolated in the solid state in good to high yields and characterized by elemental analysis and IR and NMR spectroscopy.