[Bis(pyridin-2-ylmethyl) ether]trichloridorhodium(III) dichloromethane monosolvate: unusual hydrolysis of the methylene bridge in (pyrazolylmethyl)pyridine

In the title compound, [RhCl3(C12H12N2O)]·CH2Cl2, the RhIII atom shows a slightly distorted octahedral geometry being coordinated by two N atoms and one O atom from the 2,2′-(oxydimethanediyl)dipyridine ligand and three Cl atoms. Two Cl atoms adopt a trans arrangement to the two pyridyl N atoms, while the third Cl atom and the O atoms occupy the axial site. The Rh—Cl bonds that are trans to the pyridyl N atoms are slightly longer than the Rh—Cl bond distance trans to the O atom.

In the title compound, [RhCl 3 (C 12 H 12 N 2 O)]ÁCH 2 Cl 2 , the Rh III atom shows a slightly distorted octahedral geometry being coordinated by two N atoms and one O atom from the 2,2 0 -(oxydimethanediyl)dipyridine ligand and three Cl atoms. Two Cl atoms adopt a trans arrangement to the two pyridyl N atoms, while the third Cl atom and the O atoms occupy the axial site. The Rh-Cl bonds that are trans to the pyridyl N atoms are slightly longer than the Rh-Cl bond distance trans to the O atom.
As part of our investigation of pyrazolyl-based transition metal complexes as catalysts for various olefin transformations (Ojwach and Darkwa, 2010 and references therein), we are currently exploring the ability of (pyrazolylmethyl)pyridine ruthenium and rhodium complexes to catalyze olefin hydrogenation reactions. On one such attempt to synthesize the rhodium complex of 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine, the title compound was obtained. This transformation points to the possible hydrolysis of the 2-(3,5-dimethylpyrazol-1-ylmethyl)pyridine compound promoted by RhCl 3 .6H 2 O salt to form the (pyridinylmethyl)ether ligand in the title compound.
In the title compound [RhCl 3 (C 12 H 12 N 2 O)].CH 2 Cl 2 the asymmetric unit contains one molecule of the Rh III complex and a dichloromethane molecule of solvation ( Fig. 1). In the structure, the Rh atom center is in an octahedral environment with two nitrogen atoms from 2,2'-(oxydimethanediyl)dipyridine ligand trans to two chlorine atoms in the equatorial position.
The axial positions are occupied by a third chlorine atom and the oxygen atom from 2,2'-(oxydimethanediyl)dipyridine.
2,2'-(oxydimethanediyl)dipyridine acts as an N,O,N' tridentate ligand in which the angles around the the Rh metal center are close to orthogonal (see Table 1). The bond distances for the Cl atoms to the Rh atom are longer for the Cl atoms trans to the pyridyl N atoms of the 2,2'-(oxydimethanediyl)dipyridine ligand (2.3315 (15) and 2.3479 (15) Å) as compared to the distance of the Cl atom trans to the O atom (2.2941 (5) Å). A similar trend is observed in closely related compounds with the same ligand system where metal-ligand bond distance that is trans to the ether ligand was found to be statistically shorter than the distance between the trans ligands to pyridyl N atoms (the trans effect) (Nanty et al., 2000 and references therein). The Rh atom is slightly off the equatorial plane N 2 Cl 2 and is inclined toward the axial Cl atom as the bond angles N-Rh-Cl would suggest (172.82 (13) and 172.89 (14)°). The O-Rh-Cl bond angle is 176.29 (12)° also pointing to a slight inclination of the Rh toward the equatorial Cl atoms.

Experimental
To a solution of RhCl 3 .6H 2 O (0.20 g, 0.60 mmol) in MeOH (10 ml) was added a solution of 2-(3,5-dimethylpyazol-1ylmethyl)pyridine (0.12 g, 0.60 mmol) in MeOH (10 ml) and the resultant orange solution was stirred for 24 h. After the reaction period, the solution was filtered off and solvent removed in vacuo to afford an orange solid. Recrystallization of the crude product from chloroform gave single crystals suitable for X-ray analysis. The crystals were insoluble in most organic solvents. Yield = 0.09 g (40%). H atoms and refined as riding atoms with U iso (H) = 1.5U eq (C). Fig. 1. The asymmetric unit of the title compound with displacement ellipsoids drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.