Rhenium-mediated coupling of acetonitrile and pyrazoles. New molecular clefts for anion binding

摘要

The reaction of fac-[ReBr(CO)(3)(NCMe)(2)] (1) with either pyrazole (Hpz) or 3,5-dimethylpyrazole (Hdmpz) in a 1:2 Re/pyrazole ratio affords the known complexes fac-[ReBr(CO)(3)(Hpz)(2)] (2) and [ReBr(CO)(3)(Hdmpz)(2)] (3). Using a 1:1 ratio, MeCN as solvent, and longer reaction times led to a mixture in which the major components are the pyrazolylamidino complexes fac-[ReBr(CO)(3)(HN=C(CH3)pz-kappa N-2,N)] (4) and fac-[ReBr(CO)(3)(HN = C(CH3)dmpz-kappa N-2,N)] (5). The complexes fac-[ReBr(CO)(3)(Hpz)(NCMe)] (6) and fac-[ReBr(CO)(3)(Hdmpz)(NCMe)] (7) (along with 2 and 3) were found to be minor components of these reactions. Analogous reactions of fac-[Re(OClO3)(CO)(3)(NCMe)(2)] yielded fac-[Re(NCCH3)(CO)(3)(HN=C(CH3)pz-kappa N-2,N)]ClO4 (8), fac-[Re(NCCH3)(CO)(3)(HN=C(CH3)dmpz-k(2)N,N)]ClO4 (9), fac-[Re(Hpz)(CO)(3)(HN=C(CH3)pz-kappa N-2,N)]ClO4 (10), and fac-[Re(Hdmpz)(CO)(3)(HN=C(CH3)dmpz-kappa N-2,N)]ClO4 (11). The X-ray structure of 11 showed the perchlorate anion to be hydrogen-bonded by the N-H groups of the pyrazole and pyrazolylamidino ligands. The behavior of the compound fac-[Re(Hdmpz)(CO)(3)(HN=C(CH3)dmpz-kappa N-2,N)]BAr'(4) (13) (synthesized by reaction of [ReBr(CO)(3)(Hdmpz)(2)] (3) with (i) AgOTf and (ii) NaBAr'(4)/MeCN) as an anion receptor has been studied in CD3CN solution. In addition, the structure of the supramolecular adduct fac-[Re(CO)(3)(Hdmpz)(HN=C(CH3)dmpz-kappa N-2,N)]center dot Cl (14), featuring chloride binding by the two N-H groups, was determined by X-ray diffraction.