Isolation, X-ray structure and properties of an unusual pentacarbonyl(2,2′-pyridyl-quinoxaline) tungsten complex

The first example of a monodentate complexation of 2-(2′-pyridyl)quinoxaline (pq) to a metal centre through N4 is reported. Photochemical exchange of the THF ligand in W(CO)5THF by pq yields W(CO)5(N4-pq) (1), where the potentially bidentate pq ligand coordinates in an unusual monodentate fashion. Complex 1 is isolated as orange crystals and fully characterized on the basis of NMR, IR, UV–Vis and emission spectroscopy. The structure of 1 was determined by X-ray analysis. W(CO)5(N4-pq) (1) crystallizes in space group P21/n, monoclinic crystal system with α = 7.0237(5) Å, b = 10.4618(8) Å, c = 23.7768(18) Å, Z = 4 and V = 1731.9(2) Å3. Complex 1 exhibits intramolecular CH⋯N and intermolecular CH⋯O hydrogen bonds between the CH groups and nitrogen atoms of quinoxaline and CH groups and oxygen atoms of carbonyls, respectively, resulting in a supramolecular architecture in solid state. The preference to N4 as coordination site is discussed in terms of electronic interactions. Solutions of 1 emits dually at 77 K while they are moderately instable at room temperature, as 1 undergoes chelation via a first-order kinetic process to form W(CO)4pq (2). The determined reaction rate of 1 in toluene is 2.3 × 10−5 s−1 (at 298 K) and is compared with literature values for other W(CO)5L (L:diimine) complexes.