Synthesis, Characterization, and Reactivity of Furan- and Thiophene-Functionalized Bis(N-heterocyclic carbene) Complexes of Iron(II)

The synthesis of iron­(II) complexes bearing new heteroatom-functionalized methylene-bridged bis­(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis­(acetonitrile)-<i>cis</i>-[bis­(<i>o</i>-imidazol-2-ylidenefuran)­methane]­iron­(II) hexafluorophosphate (<b>2a</b>) and tetrakis­(acetonitrile)-<i>cis</i>-[bis­(<i>o</i>-imidazol-2-ylidenethiophene)­methane]­iron­(II) hexafluorophosphate (<b>2b</b>) were obtained by aminolysis of [Fe­{N­(SiMe₃)₂}₂(THF)] with furan- and thiophene-functionalized bis­(imidazolium) salts <b>1a</b> and <b>1b</b> in acetonitrile. The SC-XRD structures of <b>2a</b> and <b>2b</b> show coordination of the bis­(carbene) ligand in a bidentate fashion instead of a possible tetradentate coordination. The four other coordination sites of these distorted octahedral complexes are occupied by acetonitrile ligands. Crystallization of <b>2a</b> in an acetone solution by the slow diffusion of Et₂O led to the formation of <i>cis</i>-diacetonitriledi­[bis­(<i>o</i>-imidazol-2-ylidenefuran)­methane]­iron­(II) hexafluorophosphate (<b>3a</b>) with two bis­(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds <b>2a</b> and <b>2b</b> are the first reported iron­(II) carbene complexes with four coordination sites occupied by solvent molecules, and it was demonstrated that those solvent ligands can undergo ligand-exchange reactions

Synthesis, Characterization, and Reactivity of Furan- and Thiophene-Functionalized Bis(N-heterocyclic carbene) Complexes of Iron(II)

The synthesis of iron­(II) complexes bearing new heteroatom-functionalized methylene-bridged bis­(N-heterocyclic carbene) ligands is reported. All complexes are characterized by single-crystal X-ray diffraction (SC-XRD), nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Tetrakis­(acetonitrile)-<i>cis</i>-[bis­(<i>o</i>-imidazol-2-ylidenefuran)­methane]­iron­(II) hexafluorophosphate (<b>2a</b>) and tetrakis­(acetonitrile)-<i>cis</i>-[bis­(<i>o</i>-imidazol-2-ylidenethiophene)­methane]­iron­(II) hexafluorophosphate (<b>2b</b>) were obtained by aminolysis of [Fe­{N­(SiMe₃)₂}₂(THF)] with furan- and thiophene-functionalized bis­(imidazolium) salts <b>1a</b> and <b>1b</b> in acetonitrile. The SC-XRD structures of <b>2a</b> and <b>2b</b> show coordination of the bis­(carbene) ligand in a bidentate fashion instead of a possible tetradentate coordination. The four other coordination sites of these distorted octahedral complexes are occupied by acetonitrile ligands. Crystallization of <b>2a</b> in an acetone solution by the slow diffusion of Et₂O led to the formation of <i>cis</i>-diacetonitriledi­[bis­(<i>o</i>-imidazol-2-ylidenefuran)­methane]­iron­(II) hexafluorophosphate (<b>3a</b>) with two bis­(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds <b>2a</b> and <b>2b</b> are the first reported iron­(II) carbene complexes with four coordination sites occupied by solvent molecules, and it was demonstrated that those solvent ligands can undergo ligand-exchange reactions

A Series of [Co(Mabiq)Cl_2–<i>n</i>] (<i>n</i> = 0, 1, 2) Compounds and Evidence for the Elusive Bimetallic Form

The synthesis and characterization of a series of cobalt compounds, coordinated by the redox-active macrocyclic biquinazoline ligand, Mabiq [2–4:6–8-bis­(3,3,4,4-tetramethyldihydropyrrolo)-10–15-(2,2′-biquinazolino)-[15]-1,3,5,8,10,14-hexaene-1,3,7,9,11,14-N₆], is presented. The series includes the monometallic Co­(Mabiq)­Cl₂ (<b>1</b>), Co­(Mabiq)Cl (<b>2</b>), and Co­(Mabiq) (<b>4</b>), with formal metal oxidation states of 3+ → 1+. A binuclear cobaltous compound, Co₂(Mabiq)­Cl₃ (<b>3</b>), also was obtained, providing the first evidence for the ability of the Mabiq ligand to coordinate two metal ions. The electronic structures of the paramagnetic <b>2</b> and <b>3</b> were examined by electron paramagnetic resonance spectroscopy and magnetic susceptibility studies. The Co^II ion that resides in the N₄-macrocylic cavity of <b>2</b> and <b>3</b> adopts a low-spin <i>S</i> = ¹/₂ configuration. The bypirimidine functionality in <b>3</b> additionally coordinates a high-spin <i>S</i> = ³/₂ cobaltous ion in a tetrahedral environment. The two metal ions in <b>3</b> are weakly coupled by magnetometry. The square-planar, low-valent <b>4</b> offers one of a limited number of examples of structurally characterized N₄-macrocyclic Co^I compounds. Spectroscopic and density functional theory computational data suggest that a Co^II(Mabiq^•) description may be a reasonable alternative to the Co^I formalism for this compound