Iron(II), Cobalt(II), and Nickel(II) Complexes of Bis(sulfonamido)benzenes: Redox Properties, Large Zero-Field Splittings, and Single-Ion Magnets.

Metal complexes of 1,2-diamidobenzenes have been long studied because of their intriguing redox properties and electronic structures. We present here a series of such complexes with 1,2-bis(sulfonamido)benzene ligands to probe the utility of these ligands for generating a large zero-field splitting (ZFS, ) in metal complexes that possibly act as single-ion magnets. To this end, we have synthesized a series of homoleptic ate complexes of the form (X)[M{bis(sulfonamido)benzene}] ( equals 4 minus the oxidation state of the metal), where M (Fe/Co/Ni), X [K/(K-18-c-6)/(HNEt), with 18-c-6 = 18-crown ether 6], and the substituents (methyl and tolyl) on the ligand [bmsab = 1,2-bis(methanesulfonamido)benzene; btsab = 1,2-bis(toluenesulfonamido)benzene] were varied to analyze their effect on the ZFS, possible single-ion-magnet properties, and redox behavior of these metal complexes.

Experimental and Theoretical Investigations of the Existence of Cu(II), Cu(III), and Cu(IV) in Copper Corrolato Complexes.

The most common oxidation states of copper in stable complexes are +I and +II. Cu(III) complexes are often considered as intermediates in biological and homogeneous catalysis. More recently, Cu(IV) species have been postulated as possible intermediates in oxidation catalysis.

Reactivity of TCNE and TCNQ derivatives of quinonoid zwitterions with Cu(I).

The reactions of TCNE- and TCNQ-functionalized (TCNE: tetracyanoethylene and TCNQ: 7,7',8,8'-tetracyanoquinodimethane) zwitterionic benzoquinonemonoimines with a Cu(I)-BIAN complex (BIAN = bis(o,o'-bisisopropylphenyl)acenaphthenequinonediimine) have been investigated and found to follow a diversity of interesting patterns. The complexes [Cu(BIAN)(NCMe)(L2)]BF4 (2) and [Cu(BIAN)(L2)2]BF4 (4) were obtained by reacting [Cu(BIAN)(NCMe)2]BF4 (1) with one and two equivalents of L2, respectively. Following similar procedures, the complexes [Cu(BIAN)(NCMe)(L3)]BF4 (6) and [Cu(BIAN)(L3)2]BF4 (7) were obtained by reaction of 1 with L3.

Silver corrole complexes: unusual oxidation states and near-IR-absorbing dyes.

Macrocycles such as porphyrins and corroles have important functions in chemistry and biology, including light absorption for photosynthesis. Generation of near-IR (NIR)-absorbing dyes based on metal complexes of these macrocycles for mimicking natural photosynthesis still remains a challenging task. Herein, the syntheses of four new Ag(III) corrolato complexes with differently substituted corrolato ligands are presented.

Three-way cooperativity in d8 metal complexes with ligands displaying chemical and redox non-innocence.

Reversible proton- and electron-transfer steps are crucial for various chemical transformations. The electron-reservoir behavior of redox non-innocent ligands and the proton-reservoir behavior of chemically non-innocent ligands can be cooperatively utilized for substrate bond activation. Although site-decoupled proton- and electron-transfer steps are often found in enzymatic systems, generating model metal complexes with these properties remains challenging.

Redox-induced spin-state switching and mixed valency in quinonoid-bridged dicobalt complexes.

The complexes [{(tmpa)Co(II) }2 (μ-L(1) )(2-) ](2+) (1(2+) ) and [{(tmpa)Co(II) }2 (μ-L(2) )(2-) ](2+) (2(2+) ), with tmpa=tris(2-pyridylmethyl)amine, H2 L(1) =2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, and H2 L(2) =2,5-di-[2-(trifluoromethyl)-anilino]-1,4-benzoquinone, were synthesized and characterized. Structural analysis of 2(2+) revealed a distorted octahedral coordination around the cobalt centers, and cobalt-ligand bond lengths that match with high-spin Co(II) centers. Superconducting quantum interference device (SQUID) magnetometric studies on 1(2+) and 2(2+) are consistent with the presence of two weakly exchange-coupled high-spin cobalt(II) ions, for which the nature of the coupling appears to depend on the substituents on the bridging ligand, being antiferromagnetic for 1(2+) and ferromagnetic for 2(2+) .

Synthesis, spectral characterization, structures, and oxidation state distributions in [(corrolato)Fe(III)(NO)](n) (n = 0, +1, -1) complexes.

Two novel trans-A2B-corroles and three [(corrolato){FeNO}(6)] complexes have been prepared and characterized by various spectroscopic techniques. In the native state, all these [(corrolato){FeNO}(6)] species are diamagnetic and display "normal" chemical shifts in the (1)H NMR spectra. For two of the structurally characterized [(corrolato){FeNO}(6)] derivatives, the Fe-N-O bond angles are 175.

Electrochemistry, chemical reactivity, and time-resolved infrared spectroscopy of donor-acceptor systems [(Q(x))Pt(pap(y))] (Q = substituted o-quinone or o-iminoquinone; pap = phenylazopyridine).

The donor-acceptor complex [((O,N)Q(2-))Pt(pap(0))] (1; pap = phenylazopyridine, (O,N)Q(0) = 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone), which displays strong π-bonding interactions and shows strong absorption in the near-IR region, has been investigated with respect to its redox-induced reactivity and electrochemical and excited-state properties. The one-electron-oxidized product [((O,N)Q(•-))Pt(pap(0))](BF4) ([1]BF4) was chemically isolated. Single-crystal X-ray diffraction studies establish the iminosemiquinone form of (O,N)Q in [1](+).

Luminescent dirhenium(I)-double-heterostranded helicate and mesocate.

The semirigid ligands 1,4-bis(2-(2-hydroxyphenyl)benzimidazol-1-ylmethyl)benzene (H2-pBC) and 1,3-bis(2-(2-hydroxyphenyl)benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (H2-mBC), containing two hydroxyphenylbenzimidazolyl units as bis-chelating (or bis(bidentate)) N∩OH donor, were synthesized and were used to assemble neutral, luminescent heteroleptic, unsaturated double-hetero-stranded, rhenium(I)-based helicate (1) and mesocate (2) with the flexible bis(monodentate) nitrogen donor (1,4-bis(benzimidazol-1-ylmethyl)benzene/1,3-bis(benzimidazol-1-ylmethyl)benzene), and Re2(CO)10. The photophysical properties of the complexes were studied. Both complexes 1 and 2 exhibit dual emissions in both solution and solid state.

The redox series [Ru(bpy)2(L)]n, n = +3, +2, +1, 0, with L = bipyridine, "click" derived pyridyl-triazole or bis-triazole: a combined structural, electrochemical, spectroelectrochemical and DFT investigation.

The compounds [Ru(bpy)2(L(1))](ClO4)2 (1(ClO4)2), [Ru(bpy)2(L(2))](ClO4)2 (2(ClO4)2), [Ru(bpy)2(L(3))](ClO4)2 (3(ClO4)2), [Ru(bpy)2(L(4))](ClO4)2 (4(ClO4)2), [Ru(bpy)2(L(5))](ClO4)2 (5(ClO4)2), and [Ru(bpy)2(L(6))](ClO4)2 6(ClO4)2 (bpy = 2,2'-bipyridine, L(1) = 1-(4-isopropyl-phenyl)-4-(2-pyridyl)-1,2,3-triazole, L(2) = 1-(4-butoxy-phenyl)-4-(2-pyridyl)-1,2,3-triazole, L(3) = 1-(2-trifluoromethyl-phenyl)-4-(2-pyridyl)-1,2,3-triazole, L(4) = 4,4'-bis-{1-(2,6-diisopropyl-phenyl)}-1,2,3-triazole, L(5) = 4,4'-bis-{(1-phenyl)}-1,2,3-triazole, L(6) = 4,4'-bis-{1-(2-trifluoromethyl-phenyl)}-1,2,3-triazole) were synthesized from [Ru(bpy)2(EtOH)2](ClO4)2 and the corresponding "click"-derived pyridyl-triazole or bis-triazole ligands, and characterized by (1)H-NMR spectroscopy, elemental analysis, mass spectrometry and X-ray crystallography. Structural analysis showed a distorted octahedral coordination environment about the Ru(II) centers, and shorter Ru-N(triazole) bond distances compared to Ru-N(pyridine) distances in complexes of mixed-donor ligands. All the complexes were subjected to cyclic voltammetric studies, and the results were compared to the well-known [Ru(bpy)3](2+) compound.

Straightforward approach to efficient oxidative DNA cleaving agents based on Cu(II) complexes of heterosubstituted cyclens.

The Cu(II) complexes of cyclen and two of its heterosubstituted analogues were shown to be efficient oxidative DNA cleavers. The reactivity strongly depends on the heteroatom inserted into the macrocycle (O > S > N).

Paramagnetic palladacycles with Pd(III) centers are highly active catalysts for asymmetric aza-Claisen rearrangements.

A combination of spectroscopic and electrochemical methods--XANES, EXAFS, X-ray, (1)H NMR, EPR, Mössbauer, and cyclic voltammetry--demonstrate that the most efficient Pd catalysts for the asymmetric rearrangement of allylic trifluoroacetimidates unexpectedly possess in the activated oxidized form a Pd(III) center bound to a ferrocene core which remains unchanged (Fe(II)) during the oxidative activation. These are the first recognized Pd(III) complexes acting as enantioselective catalysts.

Donor-acceptor systems of Pt(II) and redox-induced reactivity towards small molecules.

Oxidation at a redox-active ligand is shown to enhance reactivity at the metal center and makes it susceptible to chemical reactions which also include H(2) activation.

Isomeric separation in donor-acceptor systems of Pd(II) and Pt(II) and a combined structural, electrochemical and spectroelectrochemical study.

Compounds of the form [(pap)M(Q(2-))] (pap = phenylazopyridine; Q = 3,5-di-tert-butyl-benzoquinone, M = Pd, 1a and 1b, M = Pt, 2a and 2b; Q = 4-tert-butyl-benzoquinone, M = Pd, 3a and 3b; M = Pt, 4a and 4b) were synthesized in a one-pot reaction. The geometrical isomers, which are possible because of the built in asymmetry of these ligands, have been separated by using different temperatures and variable solubility. Structural characterization of 1b shows that the metal centers are in a square planar environment, the pap ligand is in the unreduced neutral state and the quinones are in the doubly reduced, Q(2-) catecholate form.

'Double redox-activity' in azobenzene-quinonoid palladium(II) complexes: a combined structural, electrochemical and spectroscopic study.

Reactions of [(az(-H))Pd(μ-Cl)(2)Pd(az(-H))] (az = azobenzene) with the zwitterionic, p-benzoquinonemonoimine-type ligands 4-(n-butylamino)-6(n-butylimino)-3-oxocyclohexa-1,4-dien-1-olate (Q(1)) or 4-(isopropylamino)-6(isopropylimino)-3-oxocyclohexa-1,4-dien-1-olate) (Q(2)) in the presence of a base leads to the formation of the mononuclear complexes [(az(-H))Pd(Q(1)(-H))] (1) and [(az(-H))Pd(Q(2)(-H))] (2) respectively. Structural characterization of 2 shows an almost square planar coordination geometry around the Pd(II) centre, a short Pd-C bond, a slight elongation of the N=N double bond of the az(-H) ligand and localization of the double bonds within the Q(2)(-H) ligand. Additionally, intermolecular N-H-O interactions exist between the uncoordinated N-H and O groups of two different molecules.