Treatment of Cb ∗ Co(CO) 2 I (Cb ∗ = η 4 -C 4 Me 4 ) with one equivalent of potassium 3,5-dimethylpyrazolate (Me 2 pzK) or potassium 3,5-bis(trifluoromethyl)pyrazolate ((CF 3 ) 2 pzK) in tetrahydrofuran at 0 °C afforded (η 4 -C 4 Me 4 (Me 2 pz))Co(CO) 2 and Cb ∗ Co((CF 3 ) 2 pz)(CO) 2 in 90 and 71% yields, respectively. Treatment of Cb ∗ Co(CO) 2 I with one equivalent of Me 2 pzH followed by the addition of one equivalent Me 2 pzK in tetrahydrofuran afforded Cb ∗ Co(Me 2 pzH)(Me 2 pz)(CO) in 74% yield. The reaction of Cb ∗ Co(CO) 2 I 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 4 Me 4 (Me 2 pz))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 ) 2 pz)(CO) 2 showed η 1 -coordination of the (CF 3 ) 2 pz ligand and η 4 -coordination of the Cb ∗ ligand. The solid state structure of Cb ∗ Co(Me 2 pz)(Me 2 pzH)(CO) is monomeric with one η 1 -Me 2 pz, one η 1 -Me 2 pzH, two carbonyl, and one η 4 -Cb ∗ ligands. The η 1 -Me 2 pz and η 1 -Me 2 pzH 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 4 Me 4 (Me 2 pz))Co(CO) 2 is highly volatile and sublimes at 60 °C/0.03 Torr.