Synthesis and characterization of a fluxional Re(I) carbonyl complex fac-[Re(CO)3(dpop′)Cl] with the nominally tri-dentate ligand dipyrido(2,3-a:3′,2′-j)phenazine (dpop′)

A new Re(I) carbonyl complex [Re(CO)3(dpop′)Cl] with nominally N-donor tri-dentate heterocyclic ligand dipyrido(2,3-a:3′,2′-j)phenazine (dpop′) was prepared and characterized. The ligand complexes in a bi-dentate mode undergoing fluxional behavior in room temperature solution. VT NMR results show ΔG‡ of 61.1 kJ mol−1 for [Re(CO)3(dpop′)Cl] is smaller than for comparable tpy related complexes. The electronic absorption spectrum shows solvent dependent MLCT energies at 483 and 368 nm in dichloromethane. A single irreversible Re centered oxidation at +1.29 V and a semi-reversible dpop′ centered reduction at −0.71 V are observed by cyclicvoltammetry. Electrolysis of [Re(CO)3(dpop′)Cl] at −1.0 V produces complete loss of dpop′ from the metal.

Graphical abstractThe new [Re(CO)3(dpop′)Cl] complex was prepared and studied. While dpop′ has been shown to undergo tri-dentate N-donor coordination Ru(II) and Os(II), using NMR data this study established that dpop′ undergoes fluxional bi-dentate coordination with Re(I) and ΔG‡ = 61.1 ± 0.4 kJ mol−1 for the fluxion. The absorption spectrum showed solvent dependent MLCT transitions at 483 and 368 nm in DCM. Irreversible Re oxidation occurs at +1.29 V and dpop′ reductions at −0.71 and −1.44 V versus Ag/AgCl.Figure optionsDownload full-size imageDownload as PowerPoint slide