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.