Homo- and heteropolymetallic 3-(2-pyridyl)pyrazolate manganese and rhenium complexes

Abstract

fac-[MBr(CO)₃(pypzH)] (M = Mn, Re; pypzH = (3-(2-pyridyl)pyrazole) complexes are prepared from fac-[MBr(CO)₃(NCMe)₂] and pypzH. The result of their deprotonation depends on the metallic substrate: the rhenium complex affords cleanly the bimetallic compound [fac-{Re(CO)₃(μ²-pypz)}]₂ (μ²-pypz = μ²-3-(2-pyridyl-κ¹N)pyrazolate-2κ¹N), which was crystallographically characterized, whereas a similar manganese complex was not detected. When two equivalents of pyridylpyrazolate are used, polymetallic species [fac-M(CO)₃(μ²-pypz)(μ³-pypz)M′] (μ³-pypz = μ³-3-(2-pyridyl-κ¹N)pyrazolate-1κ²N,N:2κ¹N:; M = Mn, M′ = Li, Na, K; M = Re, M′ = Na) are obtained. The crystal structures of the manganese carbonylate complexes were determined. The lithium complex is a monomer containing one manganese and one lithium atom, whereas the sodium and potassium complexes are dimers and reveal an unprecedented coordination mode for the bridging 3-(2-pyridyl)pyrazolate ligand, where the nitrogen of the pyridyl fragment and the nitrogen-1 of pyrazolate are chelated to manganese atoms, and each nitrogen-2 of pyrazolate is coordinated to two alkaline atoms. The polymetallic carbonylate complexes are unstable in solution and evolve spontaneously to [fac-{Re(CO)₃(μ²-pypz)}]₂ or to the trimetallic paramagnetic species [Mn^II(μ²-pypz)₂{fac-{Mn^I(CO)₃(μ²-pypz)}₂}]. The related complex cis-[MnCl₂(pypzH)₂] was also synthesized and structurally characterized. The electrochemical behavior of the new homo- and heteropolymetallic 3-(2-pyridyl)pyrazolate complexes has been studied and details of their redox properties are reported.