P–Ru-Complexes with a Chelate-Bridge-Switch: A Comparison of 2-Picolyl and 2-Pyridyloxy Moieties as Bridging Ligands

Starting from [Ru(pyO)(2)(nbd)] 1 and a N,P,N-tridentate ligand (2a: PhP(pic)(2), 2b: PhP(pyO)(2)) (nbd = 2,5-norbornadiene, pic = 2-picolyl = 2-pyridylmethyl, pyO = 2-pyridyloxy = pyridine-2-olate), the compounds [PhP(μ-pic)(2)(μ-pyO)Ru(κ(2)-pyO)] (3a) and [PhP(μ-pyO)(3)Ru(κ(2)-pyO)] (3b), respectively, were prepared. Reaction of compounds 3 with CO and CNtBu afforded the opening of the Ru(κ(2)-pyO) chelate motif with the formation of compounds [PhP(μ-pic)(2)(μ-pyO)Ru(κ-O-pyO)(CO)] (4a), [PhP(μ-pic)(2)(μ-pyO)(2)Ru(CNtBu)] (5a), [PhP(μ-pyO)(4)Ru(CO)] (4b) and [PhP(μ-pyO)(4)Ru(CNtBu)] (5b). In dichloromethane solution, 4a underwent a reaction with the solvent, i.e., substitution of the dangling pyO ligand by chloride with the formation of [PhP(μ-pic)(2)(μ-pyO)Ru(Cl)(CO)] (6a). The new complexes 3a, 4a, 5a, 5b and 6a were characterized by single-crystal X-ray diffraction analyses and multi-nuclear ((1)H, (13)C, (31)P) NMR spectroscopy. The different coordination behaviors of related pairs of molecules (i.e., pairs of 3, 4 and 5), which depend on the nature of the P–Ru-bridging ligand moieties (μ-pic vs. μ-pyO), were also studied via computational analyses using QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) approaches, as well as the NCI (non-covalent interactions descriptor) for weak intramolecular interactions.