Pyridinediimine Iron Complexes with Pendant Redox-Inactive Metals Located in the Secondary Coordination Sphere

A series of pyridinediimine (PDI) iron complexes that contain a pendant 15-crown-5 located in the secondary coordination sphere were synthesized and characterized. The complex Fe­(^15c5PDI)­(CO)₂ (<b>2</b>) was shown in both the solid state and solution to encapsulate redox-inactive metal ions. Modest shifts in the reduction potential of the metal–ligand scaffold were observed upon encapsulation of either Na⁺ or Li⁺

π-Extended and Six-Coordinate Iron(II) Complexes: Structures, Magnetic Properties, and the Electrochemical Synthesis of a Conducting Iron(II) Metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7–9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)2, and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mössbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9)

Ligand-Based Reduction of CO₂ and Release of CO on Iron(II)

A synthetic cycle for the CO₂-to-CO conversion (with subsequent release of CO) based on iron­(II), a redox-active pydridinediimine ligand (PDI), and an O-atom acceptor is reported. This conversion is a passive-type ligand-based reduction, where the electrons for the CO₂ conversion are supplied by the reduced PDI ligand and the ferrous state of the iron is conserved

π-Extended and Six-Coordinate Iron(II) Complexes: Structures, Magnetic Properties, and the Electrochemical Synthesis of a Conducting Iron(II) Metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7–9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)2, and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mössbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9)

π-Extended and Six-Coordinate Iron(II) Complexes: Structures, Magnetic Properties, and the Electrochemical Synthesis of a Conducting Iron(II) Metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7–9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)2, and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mössbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9)

Pyridinediimine Iron Complexes with Pendant Redox-Inactive Metals Located in the Secondary Coordination Sphere

A series of pyridinediimine (PDI) iron complexes that contain a pendant 15-crown-5 located in the secondary coordination sphere were synthesized and characterized. The complex Fe­(^15c5PDI)­(CO)₂ (<b>2</b>) was shown in both the solid state and solution to encapsulate redox-inactive metal ions. Modest shifts in the reduction potential of the metal–ligand scaffold were observed upon encapsulation of either Na⁺ or Li⁺

NO Coupling by Nonclassical Dinuclear Dinitrosyliron Complexes to Form N₂O Dictated by Hemilability

Selective coupling of NO by a nonclassical dinuclear dinitrosyliron complex (D-DNIC) to form N2O is reported. The coupling is facilitated by the pyridinediimine (PDI) ligand scaffold, which enables the necessary denticity changes to produce mixed-valent, electron-deficient tethered DNICs. One-electron oxidation of the [{Fe­(NO)2}]210/10 complex Fe2(PyrrPDI)­(NO)4 (4) results in NO coupling to form N2O via the mixed-valent {[Fe­(NO)2]2}9/10 species, which possesses an electron-deficient four-coordinate {Fe­(NO)2}10 site, crucial in N–N bond formation. The hemilability of the PDI scaffold dictates the selectivity in N–N bond formation because stabilization of the five-coordinate {Fe­(NO)2}9 site in the mixed-valent [{Fe­(NO)2}]29/10 species, [Fe2(Pyr2PDI)­(NO)4]­[PF6] (6), does not result in an electron-deficient, four-coordinate {Fe­(NO)2}10 site, and hence no N–N coupling is observed

π-Extended and Six-Coordinate Iron(II) Complexes: Structures, Magnetic Properties, and the Electrochemical Synthesis of a Conducting Iron(II) Metallopolymer

Herein, we describe the preparation of three new bidentate π-extended derivatives of the ligand N-phenyl-2-pyridinalimine (ppi) containing a 3-thienyl (4) substituent at position 4 of the aniline ring or 2-thienyl (6) or phenyl (2) substituents at each of the 2,5 positions of the aniline rings. Three iron(2+) complexes (7–9) containing these ligands were prepared by combining two equivalents each of 2, 4, or 6 with Fe(NCS)2, and the resulting neutral, six-coordinate complexes were fully characterized, including with single crystal X-ray diffraction experiments in the case of complexes 7 and 9. Variable temperature magnetic susceptibility and Mössbauer experiments confirm the presence of spin-crossover in complexes 7 and 8, and the unusual solid state variable temperature magnetic properties of complex 9 likely result from crystal packing forces. Electropolymerization of the 2,5-dithienyl-substituted complex (9) produces a conducting and electrochromic metallopolymer film (poly-9)

Ligand-Based Reduction of CO₂ and Release of CO on Iron(II)

A synthetic cycle for the CO₂-to-CO conversion (with subsequent release of CO) based on iron­(II), a redox-active pydridinediimine ligand (PDI), and an O-atom acceptor is reported. This conversion is a passive-type ligand-based reduction, where the electrons for the CO₂ conversion are supplied by the reduced PDI ligand and the ferrous state of the iron is conserved

Bimetallic Iron(3+) Spin-Crossover Complexes Containing a 2,2′-Bithienyl Bridging bis-QsalH Ligand

We describe the synthesis of a new 3,3′-diethynyl-2,2′-bithienyl bridging bis-QsalH ligand (5), and the preparation of four bimetallic iron(3+) complexes containing 5 with Cl− (6), SCN− (7), PF6− (8), and ClO4− (9) counteranions. We show with variable temperature magnetic susceptibility, Mössbauer, and electron paramagnetic resonance (EPR) spectroscopy that each complex undergoes a spin-crossover in the solid state. In all four complexes, we observe very gradual and incomplete S = 5/2, 5/2 to S = 1/2, 1/2 spin-crossover processes, with three of the four complexes exhibiting nearly identical magnetic properties. We investigated the electronic properties of the complexes by cyclic and differential pulse voltammetry, and attempted electropolymerization reactions with acetonitrile solutions of the complexes, which were not successful. Each complex features a single iron(3+) reduction wave at approximately −0.7 V (versus ferrocene), and the oxidation of the 2,2′-bithienyl substituent occurs at +1.1 V. These materials represent a new structural paradigm for the study of rare bimetallic iron(3+) spin-crossover complexes