Interaction between Anions and Molybdenum Allyl Dicarbonyl Complexes of 1,4,7-Trithiacyclononane

The labile complex [MoCl(eta 3-methallyl)(CO)2(NCMe)2] reacts with the ligand 1,4,7-trithiacyclononane ([9]aneS3) and the salt NaBAr'4 to afford [Mo(eta 3-methallyl)(CO)2([9]aneS3)][BAr'4] (1 center dot BAr'4). An analogous reaction of [MoBr(eta 3-allyl)(CO)2(NCMe)2] yields [Mo(eta 3-allyl)(CO)2([9]aneS3)][BAr'4] (2 center dot BAr'4). The new compounds 1 center dot BAr'4 and 2 center dot BAr'4 were characterized by IR and NMR spectroscopic analysis and X-ray diffraction studies. Both compounds feature the cyclic thioether [9]aneS3 coordinated as a tridentate ligand to the molybdenum center. The allyl ligand in 2 center dot BAr'4 is aligned with the middle of the OC-Mo-CO angle, which is acute. Both of these features are typical of most pseudo-octahedral allyl dicarbonyl molybdenum complexes. In contrast, the allyl group is rotated in 1 center dot BAr'4, which is attributed to steric hindrance between the methyl substituent and the ligated thioether, and the OC-Mo-CO angle is obtuse. Compound 1 center dot BAr'4 undergoes rapid substitution of [9]aneS3 by either chloride and fluoride ions in dichloromethane, and the products include the known species [{Mo(eta 3-methallyl)(CO)2}2(mu-Cl)3]- and a structurally similar new anionic complex with two fluoro and one hydroxo bridging ligands, respectively. Stable supramolecular adducts were formed in the reactions of 1 center dot BAr'4 and 2 center dot BAr4 with bromide, iodide, hydrogensulfate, and methanesulfonate compounds. The binding constants of these adducts in dichloromethane were calculated from 1H NMR spectroscopic titration data, and the solid-state structures of the 1 center dot Br, 1 center dot HSO4, 1 center dot I, and 2 center dot I adducts were determined by X-ray diffraction studies. The surprising slightly higher stability of the iodide adduct relative to that of bromide was investigated theoretically, with the results pointing to an effect of the differential solvation of the halide ions.