Synthesis and reactivity of bis(3,5-dimethylpyrazol-1-yl)methanes functionalized by 2-halophenyl groups on the methine carbon

Three new bis(3,5-dimethylpyrazol-1-yl)methanes [(2-XC6H4)CH(3,5-Me2Pz)2, X = F, Cl and Br] functionalized by 2-halophenyl groups on the methine carbon atom have been synthesized. Upon heating (2-XC6H4)CH(3,5-Me2Pz)2 with Mo(CO)6 or W(CO)5THF in THF at reflux, complexes (2-XC6H4)CH(3,5-Me2Pz)2M(CO)4 (X = F or Cl, M = Mo or W) were obtained. While the similar reaction of (2-BrC6H4)CH(3,5-Me2Pz)2 led to the oxidative addition of the C–Br bond to the Mo or W center to give complexes (C6H4)CH(3,5-Me2Pz)2M(CO)3Br (M = Mo or W). In addition, 2-ImC6H4CH(3,5-Me2Pz)2 (Im = imidazol-1-yl) has been obtained by the reaction of (2-BrC6H4)CH(3,5-Me2Pz)2 with imidazole, which subsequently reacted with PhCH2Cl to form 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazium chloride. Treatment of this imidazole salt with Ag2O and succeedingly with W(CO)5THF or Ru3(CO)12 yielded N-heterocylic carbene complexes LW(CO)5 and LRu3(CO)8(μ-H)(μ-Cl) (L = 1-{2-[bis(3,5-dimethylpyrazol-1-yl)methyl]phenyl}-3-benzylimidazol-2-ylidene), respectively. In the former, L acts as a monodentate ligand by the carbene carbon to the tungsten atom, and two pyrazolyl nitrogen atoms do not take part in the coordination to the metal center. While in the latter, L serves as a bridging bidentate ligand by one pyrazolyl nitrogen and the carbene carbon atoms to a Ru–Ru bond, and a hydride along with a chloride ligand bridges this metal–metal bond.