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 CN t Bu 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(CN t Bu)] ( 5a ), [PhP(μ-pyO) 4 Ru(CO)] ( 4b ) and [PhP(μ-pyO) 4 Ru(CN t Bu)] ( 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.