Rhenium complexes of di-2-pyridyl ketone, 2-benzoylpyridine and 2-hydroxybenzophenone: A structural and theoretical study

Abstract

The reactions of di-2-pyridyl ketone (dpk), 2-benzoylpyridine (zpy) and 2-hydroxybenzophenone (Hbp) with [Re(CO)5Cl] (A) and trans-[ReOX3(PPh3)2] (B, X=Cl, Br) were studied. The complex fac-[Re(CO)3(dpk·OCH3)] was isolated from the reaction of A with dpk in methanol. The monoanionic tridentate chelate dpk·OCH3 was formed by the nucleophilic attack of methanol at the carbonylic carbon atom of dpk. A similar attack of water on dpk was observed in the compound cis-[ReOBr2(dpk·OH)]·2(dpkH+Br−), which was formed from dpk and [ReOBr3(PPh3)2] in acetone. The reaction of zpy with B in acetonitrile produced the complexes [ReIIIX3(zpy)(PPh3)], but in methanol as solvent the compounds [ReOX2(zpyH)(PPh3)] were isolated, where zpyH coordinates bidentately as the monoanionic ligand [C6H5(HC-O)C5H4N]−. With A as starting material the complex fac-[Re(CO)3(zpy)Cl] was isolated. The complexes cis-[ReOX2(bp)(PPh3)] were the products of the reaction of Hbp with B in acetonitrile; however, in methanol cis-[ReIIIBr2(bp)(PPh3)2] was isolated. All these complexes were characterized by conductance measurements, elemental analyses, UV–Vis, IR and NMR spectroscopy and by single crystal X-ray diffraction. DFT calculations regarding the electronic ground states show single states for all the complexes, except for the rhenium(III) complexes [ReIIIX3(zpy)(PPh3)] and [ReBr2(bp)(PPh3)2], in which the states are triplet. The DFT and experimental results are in agreement in all cases, especially the anisotropy of the Re–N bond length of fac-[Re(CO)3(dpk·OCH3)] and exact O(1)–Re–O(3) angles for [ReOX2(bp)(PPh3)].