Iron-molybdenum charge-transfer hybrids containing organometallic and inorganic fragments bridged by aryldiazenido ligands in a μ- η⁶:η¹ coordination mode: Syntheses, characterization, X-ray structures, electrochemistry, and theoretical investigation

Representative members of a new family of covalently bonded charge-transfer molecular hybrids, of general formula [(η⁵-C₅H ₅)Fe(μ,η⁶:η¹-p-RC₆H ₄NN)Mo(η²-S₂CNEt₂)₃] ⁺PF₆^- (R: H, 5⁺PF₆ ^-; Me, 6⁺PF₆^-; MeO, 7 ⁺PF₆^-) and [(η⁵-C ₅-Me₅)Fe(μ,η⁶:η¹-C ₆H₅NN)Mo(η²-S₂CNEt ₂)₃]⁺PF₆^-, 8 ⁺PF₆^-, have been synthesized by reaction of the corresponding mixed-sandwich organometallic hydrazines [(η⁶- C₅H₅)Fe(η⁶-p-RC₆H ₄NHNH₂)]⁺PF₆^- (R: H, 1⁺PF₆^-; Me, 2⁺PF₆ ^-; MeO, 3⁺PF₆^-) and [(η⁵-C₅Me₅)Fe(η⁶-C ₆H⁵NHNH₂)]⁺PF₆ ^-, 4⁺PF₆^-, with cis- dioxomolybdenum(VI) bis(diethyldithiocarbamato) complex, [MoO₂(S ₂CNEt₂)₂], in the presence of sodium diethyldithiocarbamato trihydrate, NaSC(=S)-NEt₂·3H ₂O, in refluxing methanol. These iron-molybdenum complexes consist of organometallic and inorganic fragments linked each other through a π-conjugated aryldiazenido bridge coordinated in η⁶ and η¹ modes, respectively. These complexes were fully characterized by FT-IR, UV-visible, and ¹H NMR spectroscopies and, in the case of complex 7⁺PF₆^-, by single-crystal X-ray diffraction analysis. Likewise, the electrochemical and solvatochromic properties were studied by cyclic voltammetry and UV-visible spectroscopy, respectively. The electronic spectra of these hybrids show an absorption band in the 462-489 and 447-470 nm regions in CH₂Cl₂ and DMSO, respectively, indicating the existence of a charge-transfer transition from the inorganic donor to the organometallic acceptor fragments through the aryldiazenido spacer. A rationalization of the properties of 5 ⁺PF₆^--8⁺PF₆^- is provided through DFT calculations on a simplified model of 7 ⁺PF₆^-. Besides the heterodinuclear complexes 5⁺PF₆^--8⁺PF₆ ^-, the mononuclear molybdenum diazenido derivatives, [(η¹-p-RC₆H₄NN)Mo(η²-S ₂CNEt₂)₃] (R: H, 9; Me, 10; MeO, 11), resulting from the decoordination of the [(η⁵-C₅H ₅)Fe]⁺ moiety of complexes 5⁺PF ₆^--7⁺PF₆^-, were also isolated. For comparative studies, the crystalline and molecular structure of complex 10·Et₂O was also determined by X-ray diffraction analysis and its electronic structure computed.