Synthesis, characterization and derivatization of hydroxyl-functionalized iron(ii) bis(NHC) complexes.

The syntheses of a novel hydroxyl-functionalized tetradentate NHC/pyridine hybrid ligand and the corresponding Ag(i) and Fe(ii) complexes are presented. Spectroscopic and X-ray diffraction techniques are used for structural investigations and cyclic voltammetry measurements reveal interesting electronic properties. Transmetalation of the trinuclear Ag(i) complex (C1) yields a mononuclear and a dinuclear iron(ii) bis(NHC) complex (C2 and C3), which can be separated by stepwise precipitation. The former is isostructural to iron(ii) bis(NHC) complex A, which is a versatile oxidation catalyst. Furthermore, suitable conditions for esterification reactions of the ligand precursor and iron(ii) bis(NHC) complex (C2) have been established, demonstrating the utility of the hydroxyl functionality for immobilization and derivatization purposes.

A macrocyclic 'Co0' complex: the relevance of ligand non-innocence to reactivity.

We present a formally zero-valent compound, [Co(Mabiq)Na(OEt2)]2 (1). The complex was characterized by crystallographic, spectroscopic and DFT computational methods. The electronic structure is described as a CoII-(ligand-biradical). Compound 1 is reactive toward proton sources; CoI or CoII products result, depending on the source of protons used. The redox non-innocence of the Mabiq ligand, which accepts both protons and electrons, has important ramifications for reactivity.

A Series of [Co(Mabiq)Cl2-n] (n = 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 (1), Co(Mabiq)Cl (2), and Co(Mabiq) (4), with formal metal oxidation states of 3+ → 1+. A binuclear cobaltous compound, Co2(Mabiq)Cl3 (3), 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 2 and 3 were examined by electron paramagnetic resonance spectroscopy and magnetic susceptibility studies. The Co(II) ion that resides in the N4-macrocylic cavity of 2 and 3 adopts a low-spin S = (1)/2 configuration. The bypirimidine functionality in 3 additionally coordinates a high-spin S = (3)/2 cobaltous ion in a tetrahedral environment. The two metal ions in 3 are weakly coupled by magnetometry. The square-planar, low-valent 4 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.

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)-cis-[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (2a) and tetrakis(acetonitrile)-cis-[bis(o-imidazol-2-ylidenethiophene)methane]iron(II) hexafluorophosphate (2b) were obtained by aminolysis of [Fe{N(SiMe3)2}2(THF)] with furan- and thiophene-functionalized bis(imidazolium) salts 1a and 1b in acetonitrile. The SC-XRD structures of 2a and 2b 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 2a in an acetone solution by the slow diffusion of Et2O led to the formation of cis-diacetonitriledi[bis(o-imidazol-2-ylidenefuran)methane]iron(II) hexafluorophosphate (3a) with two bis(carbene) ligands coordinated in a bidentate manner and two cis-positioned acetonitrile molecules. Compounds 2a and 2b 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.