Dirhodium carbonyl complex with the 3,5-bis(diphenylphosphinoethyl)pyrazolato ligand (PNNP C2 ), [(μ-κ 2 :κ 2 -PNNP C2 )Rh 2 (CO) 3 ]BF 4 , is prepared and its reactivity is studied as compared with the previously reported 3,5-bis(diphenylphosphinomethyl)pyrazolate (PNNP), [(μ-κ 2 :κ 2 -PNNP){Rh(CO) 2 } 2 ]BF 4 , and 1,4-bis(diphenylphosphinomethyl)phthalazine (PNNP Ph ) derivatives, [(μ-κ 2 :κ 2 -PNNP Ph ){Rh(CO) 2 } 2 ](BF 4 ) 2 . The three quadridentate ligands are different in the size of the central ring and the charge; six-membered ring/neutral (PNNP C2 ) vs. five-membered ring/mono-negative (PNNP) vs. six-membered ring/neutral (PNNP Ph ). The number of the carbonyl ligands (n) in the dirhodium carbonyl complexes, [(μ-PNNP)Rh 2 (CO) n ](BF 4 ) x , is dependent on the dinucleating ligand: n=2 (PNNP Ph ), 3 (PNNP C2 ) and 4 (PNNP Py ). The three dirhodium carbonyl complexes serve as 4e-acceptors, and their reactivities turn out to be very similar as can be seen from formation of the analogous, unique tetranuclear μ 4 -acetylide ([(μ-PNNP) 2 {Rh(CO)} 4 (μ 4 –CC–R)](BF 4 ) x ) and μ 4 -dicarbide complexes ([(μ-PNNP) 2 {Rh(CO)} 4 (μ 4 –C 2 )](BF 4 ) x ).