Sandwich Compounds of Cyanotrispyrazolylborates: Complexation-Induced Ligand Isomerization

Reaction of the new cyanoscorpionate ligand, hydrotris(4-cyano-3-phenyl)pyrazolylborate (TpPh,4CN) with Co(II), Mn(II), and Fe(II) unexpectedly results in the isolation only of crystals containing sandwich complexes in which the ligands have been isomerized to produce the heterocyanoscorpionate hydrobis(4-cyano-3-phenylpyrazolyl)(4-cyano-5-phenylpyrazolyl)borate (TpPh,4CN*). The three complexes have been characterized crystallographically and are isostructural, with each ligand acting in a tridentate manner toward the metal. The isomerization of the ligand appears to be more facile than that of the analogous non-cyano ligand, TpPh, with which crystals of the unisomerized sandwich compound have been isolated for Mn(II) and Fe(II).