Synthesis and properties of new Mo(II) complexes with N-heterocyclic and ferrocenyl ligands

New Mo(II) complexes with 2,2′-dipyridylamine (L1), [Mo(CH3CN)(η3-C3H5)(CO)2(L1)]OTf (C1a) and [{MoBr(η3-C3H5)(CO)2(L1)}2(4,4′-bipy)](PF6)2 (C1b), with {[bis(2-pyridyl)amino]carbonyl}ferrocene (L2), [MoBr(η3-C3H5)(CO)2(L2)] (C2), and with the new ligand N,N-bis(ferrocenecarbonyl)-2-aminopyridine (L3), [MoBr(η3-C3H5)(CO)2(L3)] (C3), were prepared and characterized by FTIR and 1H and 13C NMR spectroscopy. C1a, C1b, L3, and C2 were also structurally characterized by single crystal X-ray diffraction. The Mo(II) coordination sphere in all complexes features the facial arrangement of allyl and carbonyl ligands, with the axial isomer present in C1a and C2, and the equatorial in the binuclear C1b. In both C1a and C1b complexes, the L1 ligand is bonded to Mo(II) through the nitrogen atoms and the NH group is involved in hydrogen bonds. The X-ray single crystal structure of C2 shows that L2 is coordinated in a κ2-N,N-bidentate chelating fashion. Complex C3 was characterized as [MoBr(η3-C3H5)(CO)2(L3)] with L3 acting as a κ2-N,O-bidentate ligand, based on the spectroscopic data, complemented by DFT calculations.The electrochemical behavior of the monoferrocenyl and diferrocenyl ligands L2 and L3 has been studied together with that of their Mo(II) complexes C2 and C3. As much as possible, the nature of the different redox changes has been confirmed by spectrophotometric measurements. The nature of the frontier orbitals, namely the localization of the HOMO in Mo for both in C2 and C3, was determined by DFT studies.

Mo(II) allyl complexes react with functionalized ferrocenyl ligands to form new bi- and trinuclear mixed Fe–Mo complexes. The ferrocenyl ligands bind molybdenum as 2-N,N- and 2-N,O-bidentate chelates and yield stable cations. The first oxidation of the Mo–Fe complexes occurs in Mo, followed by Fe and ends in decomposition.Figure optionsDownload as PowerPoint slideHighlights
► New bi- and tri- nuclear mixed Fe–Mo complexes were synthesized.
► The ferrocenyl ligands bind molybdenum as κ2-N,N- and κ2-N,O-bidentate chelates.
► The HOMO of the ferrocene complexes is located in Fe.
► Binding ferrocenyl ligands to Mo(II) changes the nature of the HOMO (located in Mo).