Rhenium-Mediated Coupling of Acetonitrile and Pyrazoles. New Molecular Clefts for Anion Binding^§

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-κ2N,N)] (4) and fac-[ReBr(CO)3(HN=C(CH3)dmpz-κ2N,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-κ2N,N)]ClO4 (8), fac-[Re(NCCH3)(CO)3(HNC(CH3)dmpz-κ2N,N)]ClO4 (9), fac-[Re(Hpz)(CO)3(HNC(CH3)pz-κ2N,N)]ClO4 (10), and fac-[Re(Hdmpz)(CO)3(HNC(CH3)dmpz-κ2N,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-κ2N,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-κ2N,N)]·Cl (14), featuring chloride binding by the two N−H groups, was determined by X-ray diffraction.