Interaction between Anions and Cationic Metal Complexes Containing Tridentate Ligands with exo-CH Groups: Complex Stability and Hydrogen Bonding.

[Re(CO)3([9]aneS3)][BAr′4] ( 1), prepared by reaction of ReBr(CO)5, 1,4,7-trithiacyclononane ([9]aneS3) and NaBAr′4, forms stable, soluble supramolecular adducts with chloride ( 2), bromide, methanosulfonate ( 3) and fluoride ( 4) anions. These new species were characterized by IR, NMR spectroscopy and, for 2 and 3, also by X-ray diffraction. The results of the solid state structure determinations indicate the formation of CH⋅⋅⋅X hydrogen bonds between the anion (X) and the exo-CH groups of the [9]aneS3 ligand, in accord with the relatively large shifts found by 1H NMR spectroscopy in dichloromethane solution for those hydrogens. The stability of the chloride adduct contrasts with the lability of the [9]aneS3 ligand in allyldicarbonyl molybdenum complexes recently studied by us. With fluoride, in dichloromethane solution, a second, minor neutral dimeric species 5 is formed in addition to 4. In 4, the deprotonation of a CH group of the [9]aneS3 ligand, accompanied by CS bond cleavage and dimerization, afforded 5, featuring bridging thiolates. Compounds [Mo(η3-methallyl)(CO)2(TpyN)][BAr′4] ( 6) and [Mo(η3-methallyl)(CO)2(TpyCH)][BAr′4] ( 7) were synthesized by the reactions of [MoCl(η3-methallyl)(CO)2(NCMe)2], NaBAr′4 and tris(2-pyridyl)amine (TpyN) or tris(2-pyridyl)methane (TpyCH) respectively, and characterized by IR and 1H and 13C NMR spectroscopy in solution, and by X-ray diffraction in the solid state. Compound 6 undergoes facile substitution of one of the 2-pyridyl groups by chloride, bromide, and methanosulfonate anions. Stable supramolecular adducts were formed between 7 and chloride, bromide, iodide, nitrate, and perrhenate anions. The solid state structures of these adducts ( 12- 16) were determined by X-ray diffraction. Binding constants in dichloromethane were calculated from 1H NMR titration data for all the new supramolecular adducts. The signal of the bridgehead CH group is the one that undergoes a more pronounced downfield shift when tetrabutylammonium chloride was added to 7, whereas smaller shifts were found for the 2-pyridyl C(3)H groups. In agreement, both types of CH groups form hydrogen bonds to the anions in the solid state structures. [ABSTRACT FROM AUTHOR]