Treatment of Cb ∗Co(CO) 2I (Cb ∗ = η 4-C 4Me 4) with one equivalent of potassium 3,5-dimethylpyrazolate (Me 2pzK) or potassium 3,5-bis(trifluoromethyl)pyrazolate ((CF 3) 2pzK) in tetrahydrofuran at 0 °C afforded (η 4-C 4Me 4(Me 2pz))Co(CO) 2 and Cb ∗Co((CF 3) 2pz)(CO) 2 in 90 and 71% yields, respectively. Treatment of Cb ∗Co(CO) 2I with one equivalent of Me 2pzH followed by the addition of one equivalent Me 2pzK in tetrahydrofuran afforded Cb ∗Co(Me 2pzH)(Me 2pz)(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 (η 4-C 4Me 4(Me 2pz))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 η 3-π-allyl interaction and one pyrazolyl nitrogen atom. Two carbonyl ligands are also present. An X-ray crystal structure determination of Cb ∗Co((CF 3) 2pz)(CO) 2 showed η 1-coordination of the (CF 3) 2pz ligand and η 4-coordination of the Cb ∗ ligand. The solid state structure of Cb ∗Co(Me 2pz)(Me 2pzH)(CO) is monomeric with one η 1-Me 2pz, one η 1-Me 2pzH, two carbonyl, and one η 4-Cb ∗ ligands. The η 1-Me 2pz and η 1-Me 2pzH 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:η 1,η 1-Phtetz ligands connected to the cobalt ions through the 2- and 3-nitrogen atoms, one η 4-Cb ∗ ligand, and one carbonyl ligand per cobalt center. (η 4-C 4Me 4(Me 2pz))Co(CO) 2 is highly volatile and sublimes at 60 °C/0.03 Torr.