The first pyrazole molybdenum(0) complexes: cis-[Mo(CO)4(Hdmpz)2] crystallizes as a NH⋯OC hydrogen-bonded dimer

The reactions of [Mo(CO)4(NBD)] with two equivalents of Hpz (pyrazole) or Hdmpz (3,5-dimethylpyrazole) in hexane lead to the precipitation of cis-[Mo(CO)4(Hpz)2] or cis-[Mo(CO)4(Hdmpz)2], which are the first pyrazole complexes of molybdenum(0). In the solid state structure of cis-[Mo(CO)4(Hdmpz)2], two molecules are self-assembled by intermolecular hydrogen bonds between the N-bound hydrogen of one Hdmpz ligand and a oxygen atom of a carbonyl group. This explains the lack of planarity observed for the nitrogen donor atom of the Hdmpz involved in the intermolecular interaction. The complexes are unstable in solution and as solids.