Tetramethylcyclobutadienecobalt(I) complexes containing pyrazolate or tetrazolate ligands with various coordination modes

Treatment of Cb∗Co(CO)2I (Cb∗ = η4-C4Me4) with one equivalent of potassium 3,5-dimethylpyrazolate (Me2pzK) or potassium 3,5-bis(trifluoromethyl)pyrazolate ((CF3)2pzK) in tetrahydrofuran at 0 °C afforded (η4-C4Me4(Me2pz))Co(CO)2 and Cb∗Co((CF3)2pz)(CO)2 in 90 and 71% yields, respectively. Treatment of Cb∗Co(CO)2I with one equivalent of Me2pzH followed by the addition of one equivalent Me2pzK in tetrahydrofuran afforded Cb∗Co(Me2pzH)(Me2pz)(CO) in 74% yield. The reaction of Cb∗Co(CO)2I with one equivalent of potassium phenyl tetrazolate (PhtetzK) in tetrahydrofuran at 0 °C afforded [Cb∗Co(Phtetz)(CO)]2 in 44% yield. The solid state structure of (η4-C4Me4(Me2pz))Co(CO)2 revealed nucleophilic addition of a pyrazolate nitrogen atom to a Cb∗ ligand carbon atom to afford a novel tetradentate ligand that bonds to the cobalt ion through an η3-π-allyl interaction and one pyrazolyl nitrogen atom. Two carbonyl ligands are also present. An X-ray crystal structure determination of Cb∗Co((CF3)2pz)(CO)2 showed η1-coordination of the (CF3)2pz ligand and η4-coordination of the Cb∗ ligand. The solid state structure of Cb∗Co(Me2pz)(Me2pzH)(CO) is monomeric with one η1-Me2pz, one η1-Me2pzH, two carbonyl, and one η4-Cb∗ ligands. The η1-Me2pz and η1-Me2pzH ligands are linked by a hydrogen bond involving the uncoordinated nitrogen atoms. The X-ray crystal structure determination of [Cb∗Co(Phtetz)(CO)]2 showed a dimeric molecular structure with two μ:η1,η1-Phtetz ligands connected to the cobalt ions through the 2- and 3-nitrogen atoms, one η4-Cb∗ ligand, and one carbonyl ligand per cobalt center. (η4-C4Me4(Me2pz))Co(CO)2 is highly volatile and sublimes at 60 °C/0.03 Torr.