Multiple mixed-valence behavior in trans,trans-[(tpy)(Cl)2Os(III)(mu-1,3-N3)Os(III)(Cl)2(tpy)]+. An azido bridge from the reaction between trans-[Os(VI)(tpy)(Cl)2(N)]+ and NH3

Reaction between the Os(VI)-nitrido complex, trans-[OsVI(tpy)(Cl)2(N)]PF6 (tpy = 2,2':6',2' '-terpyridine), and ammonia (NH3) under N2 in dry CH3CN gives the mu-1,3-azido bridged [OsII-N3-OsII]- dimer, trans,trans-NH4[(tpy)(Cl)2OsII(N3)OsII(Cl)2(tpy)]. It undergoes air oxidation to give the [OsIII-N3-OsIII]+ analogue, trans,trans-[(tpy)(Cl)2OsIII(N3)OsIII(Cl)2(tpy)]PF6 ([OsIII-N3-OsIII]PF6), which has been isolated and characterized. The structural formulation as a mu-1,3-N3 bridged complex has been established by infrared and 15N NMR measurements on the 15N-labeled forms, [OsIII-14N=15N=14N-OsIII]+, [OsIII-15N=14N=15N-OsIII]+, and [OsIII-15N=15N=15N-OsIII]+. Cyclic voltammetric measurements in 0.2 M Bu4NPF6/CH3CN reveal the existence of five chemically reversible waves from 1.40 to -0.12 V for couples ranging from OsV-OsIV/OsIV-OsIV to OsIII-OsII/OsII-OsII. DeltaE1/2 values for couples adjacent to the three mixed-valence forms are 0.19 V for OsIII-OsII, 0.52 V for OsIV-OsIII, and >0.71 V for OsV-OsIV. In CH3CN at 60 degrees C, [OsIII-N3-OsIII]+ undergoes a [2 + 3] cycloaddition with CH3CN at the mu-N3- bridge followed by a solvolysis to give trans-[OsIII(tpy)(Cl)2(5-MeCN4)] and trans-[OsIII(tpy)(Cl)2(NCCH3)]PF6.     

High-valent nonheme iron. Two distinct iron(IV) species derived from a common iron(II) precursor

The reaction of [Fe(II)(beta-BPMCN)(OTf)2] (1, BPMCN = N,N'-bis(2-pyridylmethyl)-N,N'-dimethyl-trans-1,2-diaminocyclohexane) with tBuOOH at low-temperature yields alkylperoxoiron(III) intermediates 2 in CH2Cl2 and 2-NCMe in CH3CN. At -45 degrees C and above, 2-NCMe converts to a pale green species 3 (lambda(max) = 753 nm, epsilon = 280 M(-1) cm(-1)) in 90% yield, identified as [Fe(IV)(O)(BPMCN)(NCCH3)]2+ by comparison to other nonheme [Fe(IV)(O)(L)]2+ complexes. Below -55 degrees C in CH2Cl2, 2 decays instead to form deep turquoise 4 (lambda(max) = 656, 845 nm; epsilon = 4000, 3600 M(-1) cm(-1)), formulated to be an unprecedented alkylperoxoiron(IV) complex [Fe(IV)(BPMCN)(OH)(OOtBu)]2+ on the basis of M?ssbauer, EXAFS, resonance Raman, NMR, and mass spectral evidence. The reactivity of 1 with tBuOOH in the two solvents reveals an unexpectedly rich iron(IV) chemistry that can be supported by the BPMCN ligand.     

Photocatalytic generation of a non-heme oxoiron(IV) complex with water as an oxygen source

The photocatalytic formation of a non-heme oxoiron(IV) complex, [(N4Py)Fe(IV)(O)](2+) [N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine], efficiently proceeds via electron transfer from the excited state of a ruthenium complex, [Ru(II)(bpy)(3)](2+)* (bpy = 2,2'-bipyridine) to [Co(III)(NH(3))(5)Cl](2+) and stepwise electron-transfer oxidation of [(N4Py)Fe(II)](2+) with 2 equiv of [Ru(III)(bpy)(3)](3+) and H(2)O as an oxygen source. The oxoiron(IV) complex was independently generated by both chemical oxidation of [(N4Py)Fe(II)](2+) with [Ru(III)(bpy)(3)](3+) and electrochemical oxidation of [(N4Py)Fe(II)](2+).     

基于非血红素铁模型配合物[FeⅣ(O)(N4Py)]2+的新型N杂环卡宾配合物的理论设计

基于四价非血红素铁模型配合物[FeⅣ(O)(N4Py)]2+, 通过理论计算设计出一种新型N杂环卡宾配合物[FeⅣ(O)(N4Py)]2+. 采用密度泛函理论B3LYP方法, 计算了[FeⅣ(O)(N4Py)]2+的几何结构和电子结构, 并研究了[FeⅣ(O)(N4Py)]2+使环己烷C-H键羟基化的反应机理. 结果表明, [FeⅣ(O)(N4Py)]2+的五重态能量比基态三重态能量高约5.7 kJ/mol, 故五重态几乎不能参与反应. 赤道方向的配位基N杂环卡宾(NHC)对FeO单元的σ-贡献要大于N4Py的贡献, 而它的空间位阻效应也大于N4Py, 因此2+的稳定性强于[FeⅣ(O)(N4Py)]2+. [FeⅣ(O)(N4Py)]2+的三重态的反应能垒比[FeⅣ(O)(N4Py)]2+的三重态反应能垒高2.0 kJ/mol, 且为单态反应, 所以[FeⅣ(O)(N4Py)]2+的反应活性要高于[FeⅣ(O)(N4Py)]2+.     

Iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin

The iron complexes of 5,10,15,20-tetraphenyl-21-oxaporphyrin (OTPP)H have been investigated. Insertion of iron(II) followed by one-electron oxidation yielded a high-spin, six-coordinate (OTPP)Fe(III)Cl(2) complex. The reduction of (OTPP)Fe(III)Cl(2) has been accomplished by means of moderate reducing reagents producing high-spin five-coordinate (OTPP)Fe(II)Cl. The molecular structure of (OTPP)Fe(III)Cl(2) has been determined by X-ray diffraction. The iron(III) 21-oxaporphyrin skeleton is essentially planar. The furan ring coordinates in the eta(1) fashion through the oxygen atom, which acquires trigonal geometry. The iron(III) apically coordinates two chloride ligands. Addition of potassium cyanide to a solution of (OTPP)Fe(III)Cl(2) in methanol-d(4) results in its conversion to a six-coordinate, low-spin complex [OTPP)Fe(III)(CN)(2)] which is spontaneously reduced to [OTPP)Fe(II)(CN)(2)](-) by excess cyanide. The spectroscopic features of [OTPP)Fe(III)(CN)(2)] correspond to the common low-spin iron(III) porphyrin (d(xy))(2)(d(xz)d(yz))(3) electronic configuration. Titration of (OTPP)Fe(III)Cl(2) or (OTPP)Fe(II)Cl with n-BuLi (toluene-d(8), 205 K) resulted in the formation of (OTPP)Fe(II)(CH(2)CH(2)CH(2)CH(3)). (OTPP)Fe(II)(n-Bu) decomposes via homolytic cleavage of the iron-carbon bond to produce (OTPP)Fe(I). The EPR spectrum (toluene-d(8), 77 K) is consistent with a (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z)(2)(1)(d[(x)(2)-(y)(2)])(0) ground electronic state of iron(I) oxaporphyrin (g(1) = 2.234, g(2) = 2.032, g(3) = 1.990). The (1)H NMR spectra of (OTPP)Fe(III)Cl(2), (OTPP)Fe(III)(CN)(2), ([(OTPP)Fe(III))](2)O)(2+), and (OTPP)Fe(II)Cl have been analyzed. There are considerable similarities in (1)H NMR properties within each iron(n) oxaporphyrin-iron(n) regular porphyrin or N-methylporphyrin pair (n = 2, 3). Contrary to this observation, the pattern of downfield positions of pyrrole resonances at 156.2, 126.5, 76.3 ppm and furan resonance at 161.4 ppm (273 K) detected for the two-electron reduction product of (OTPP)Fe(III)Cl(2) is unprecedented in the group of iron(I) porphyrins.     

Reaction of an osmium(VI) nitrido complex with cyanide: formation and reactivity of an osmium(III) hydrogen cyanamide complex

Reaction of [Os(VI)(N)(L(1))(Cl)(OH(2))] (1) with CN(-) under various conditions affords (PPh(4))[Os(VI)(N)(L(1))(CN)(Cl)] (2), (PPh(4))(2)[Os(VI)(N)(L(2))(CN)(2)] (3), and a novel hydrogen cyanamido complex, (PPh(4))(2)[Os(III){N(H)CN}(L(3))(CN)(3)] (4). Compound 4 reacts readily with both electrophiles and nucleophiles. Protonation and methylation of 4 produce (PPh(4))[Os(III)(NCNH(2))(L(3))(CN)(3)] (5) and (PPh(4))[Os(III)(NCNMe(2))(L(3))(CN)(3)] (6), respectively. Nucleophilic addition of NH(3), ethylamine, and diethylamine readily occur at the C atom of the hydrogen cyanamide ligand of 4 to produce osmium guanidine complexes with the general formula [Os(III){N(H)C(NH(2))NR(1)R(2)}(L(3))(CN)(3)](-) , which have been isolated as PPh(4) salts (R(1) = R(2) = H (7); R(1) = H, R(2) = CH(2)CH(3) (8); R(1) = R(2) = CH(2)CH(3) (9)). The molecular structures of 1-5 and 7 and 8 have been determined by X-ray crystallography.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.     

The remarkable reactivity of high oxidation state ruthenium and osmium polypyridyl complexes

There is a remarkable redox chemistry of higher oxidation state M(IV)-M(VI) polypyridyl complexes of Ru and Os. They are accessible by proton loss and formation of oxo or nitrido ligands, examples being cis-[RuIV(bpy)2(py)(O)]2+ (RuIV=O2+, bpy=2,2'-bipyridine, and py=pyridine) and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy=2,2':6',2' '-terpyridine). Metal-oxo or metal-nitrido multiple bonding stabilizes the higher oxidation states and greatly influences reactivity. O-atom transfer, hydride transfer, epoxidation, C-H insertion, and proton-coupled electron-transfer mechanisms have been identified in the oxidation of organics by RuIV=O2+. The Ru-O multiple bond inhibits electron transfer and promotes complex mechanisms. Both O atoms can be used for O-atom transfer by trans-[RuVI(tpy)(O)2(S)]2+ (S=CH3CN or H2O). Four-electron, four-proton oxidation of cis,cis-[(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+ occurs to give cis,cis-[(bpy)2(O)RuV-O-RuV(O)(bpy)2]4+ which rapidly evolves O2. Oxidation of NH3 in trans-[OsII(tpy)(Cl)2(NH3)] gives trans-[OsVI(tpy)(Cl)2(N)]+ through a series of one-electron intermediates. It and related nitrido complexes undergo formal N- transfer analogous to O-atom transfer by RuIV=O2+. With secondary amines, the products are the hydrazido complexes, cis- and trans-[OsV(L3)(Cl)2(NNR2)]+ (L3=tpy or tpm and NR2-=morpholide, piperidide, or diethylamide). Reactions with aryl thiols and secondary phosphines give the analogous adducts cis- and trans-[OsIV(tpy)(Cl)2(NS(H)(C6H4Me))]+ and fac-[OsIV(Tp)(Cl)2(NP(H)(Et2))]. In dry CH3CN, all have an extensive multiple oxidation state chemistry based on couples from Os(VI/V) to Os(III/II). In acidic solution, the OsIV adducts are protonated, e.g., trans-[OsIV(tpy)(Cl)2(N(H)N(CH2)4O)]+, and undergo proton-coupled electron transfer to quinone to give OsV, e.g., trans-[OsV(tpy)(Cl)2(NN(CH2)4O)]+ and hydroquinone. These reactions occur with giant H/D kinetic isotope effects of up to 421 based on O-H, N-H, S-H, or P-H bonds. Reaction with azide ion has provided the first example of the terminal N4(2-) ligand in mer-[OsIV(bpy)(Cl)3(NalphaNbetaNgammaNdelta)]-. With CN-, the adduct mer-[OsIV(bpy)(Cl)3(NCN)]- has an extensive, reversible redox chemistry and undergoes NCN(2-) transfer to PPh3 and olefins. Coordination to Os also promotes ligand-based reactivity. The sulfoximido complex trans-[OsIV(tpy)(Cl)2(NS(O)-p-C6H4Me)] undergoes loss of O2 with added acid and O-atom transfer to trans-stilbene and PPh3. There is a reversible two-electron/two-proton, ligand-based acetonitrilo/imino couple in cis-[OsIV(tpy)(NCCH3)(Cl)(p-NSC6H4Me)]+. It undergoes reversible reactions with aldehydes and ketones to give the corresponding alcohols.     

Tuning of spin crossover behaviour in iron(III) complexes involving pentadentate Schiff bases and pseudohalides

Investigations on a series of eight novel mononuclear iron(III) Schiff base complexes with the general formula [Fe(L(5))(L(1))]·S (where H(2)L(5) = pentadentate Schiff-base ligand, L(1) = a pseudohalido ligand, and S is a solvent molecule) are reported. Several different aromatic 2-hydroxyaldehyde derivatives were used in combination with a non-symmetrical triamine 1,6-diamino-4-azahexane to synthesize the H(2)L(5) Schiff base ligands. The consecutive reaction with iron(III) chloride resulted in the preparation of the [Fe(L(5))Cl] precursor complexes which were left to react with a wide range of the L(1) pseudohalido ligands. The low-spin compounds were prepared using the cyanido ligand: [Fe(3m-salpet)(CN)]·CH(3)OH (1a), [Fe(3e-salpet)(CN)]·H(2)O (1b), while the high-spin compounds were obtained by the reaction of the pseudohalido (other than cyanido) ligands with the [Fe(L(5))Cl] complex arising from salicylaldehyde derivatives: [Fe(3Bu5Me-salpet)(NCS)] (2a), [Fe(3m-salpet)(NCO)]·CH(3)OH (2b) and [Fe(3m-salpet)(N(3))] (2c). The compounds exhibiting spin-crossover phenomena were prepared only when L(5) arose from 2-hydroxy-1-naphthaldehyde (H(2)L(5) = H(2)napet): [Fe(napet)(NCS)]·CH(3)CN (3a, T(1/2) = 151 K), [Fe(napet)(NCSe)]·CH(3)CN (3b, T(1/2) = 170 K), [Fe(napet)(NCO)] (3c, T(1/2) = 155 K) and [Fe(napet)(N(3))], which, moreover, exhibits thermal hysteresis (3d, T(1/2)↑ = 122 K, T(1/2)↓ = 117 K). These compounds are the first examples of octahedral iron(III) spin-crossover compounds with the coordinated pseudohalides. We report the structure and magnetic properties of these complexes. The magnetic data of all the compounds were analysed using the spin Hamiltonian formalism including the ZFS term and in the case of spin-crossover, the Ising-like model was also applied.     

Proton-promoted oxygen atom transfer vs proton-coupled electron transfer of a non-heme iron(IV)-oxo complex

Sulfoxidation of thioanisoles by a non-heme iron(IV)-oxo complex, [(N4Py)Fe(IV)(O)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), was remarkably enhanced by perchloric acid (70% HClO(4)). The observed second-order rate constant (k(obs)) of sulfoxidation of thioaniosoles by [(N4Py)Fe(IV)(O)](2+) increases linearly with increasing concentration of HClO(4) (70%) in acetonitrile (MeCN)at 298 K. In contrast to sulfoxidation of thioanisoles by [(N4Py)Fe(IV)(O)](2+), the observed second-order rate constant (k(et)) of electron transfer from one-electron reductants such as [Fe(II)(Me(2)bpy)(3)](2+) (Me(2)bpy = 4,4-dimehtyl-2,2'-bipyridine) to [(N4Py)Fe(IV)(O)](2+) increases with increasing concentration of HClO(4), exhibiting second-order dependence on HClO(4) concentration. This indicates that the proton-coupled electron transfer (PCET) involves two protons associated with electron transfer from [Fe(II)(Me(2)bpy)(3)](2+) to [(N4Py)Fe(IV)(O)](2+) to yield [Fe(III)(Me(2)bpy)(3)](3+) and [(N4Py)Fe(III)(OH(2))](3+). The one-electron reduction potential (E(red)) of [(N4Py)Fe(IV)(O)](2+) in the presence of 10 mM HClO(4) (70%) in MeCN is determined to be 1.43 V vs SCE. A plot of E(red) vs log[HClO(4)] also indicates involvement of two protons in the PCET reduction of [(N4Py)Fe(IV)(O)](2+). The PCET driving force dependence of log k(et) is fitted in light of the Marcus theory of outer-sphere electron transfer to afford the reorganization of PCET (λ = 2.74 eV). The comparison of the k(obs) values of acid-promoted sulfoxidation of thioanisoles by [(N4Py)Fe(IV)(O)](2+) with the k(et) values of PCET from one-electron reductants to [(N4Py)Fe(IV)(O)](2+) at the same PCET driving force reveals that the acid-promoted sulfoxidation proceeds by one-step oxygen atom transfer from [(N4Py)Fe(IV)(O)](2+) to thioanisoles rather than outer-sphere PCET.     

Synthesis and characterization of pentachlorophenyl-metal derivatives with d0 and d10 electron configurations

By reaction of [TiCl(3)(thf)(3)] with LiC(6)Cl(5), the homoleptic organotitanium(III) derivative [Li(thf)(4)][Ti(III)(C(6)Cl(5))(4)] (1) has been prepared as a paramagnetic (d(1), S = 1/2, g(av) = 1.959(2)), extremely air-sensitive compound. Oxidation of 1 with [N(C(6)H(4)Br-4)(3)][SbCl(6)] gives the diamagnetic (d(0)) organotitanium(IV) species [Ti(IV)(C(6)Cl(5))(4)] (2). Compounds 1 and 2 are also electrochemically related (E(1/2) = 0.05 V). The homoleptic, diamagnetic (d(10)) compounds [N(PPh(3))(2)][Tl(C(6)Cl(5))(4)] (3) and [Sn(C(6)Cl(5))(4)] (4) have also been prepared. Nearly tetrahedral environments have been found for the d(0), d(10), and d(1) metal centers in the molecular structures of compounds 2-4 as well as in that of [Li(thf)(2)(OEt(2))(2)][Ti(III)(C(6)Cl(5))(4)].CH(2)Cl(2) (1') (X-ray diffraction). The reaction of the heavier Group 4 metal halides, MCl(4) (M = Zr, Hf) with LiC(6)Cl(5) in the presence of [NBu(4)]Br gives, in turn, the heteroleptic species [NBu(4)][M(C(6)Cl(5))(3)Cl(2)] (M = Zr (5), Hf (6)). Compounds 5 and 6 are isomorphous and isostructural, with the metal center in a trigonal-bipyramidal (TBPY-5) environment defined by two axial Cl ligands and three equatorial C(6)Cl(5) groups (X-ray diffraction). No redox features are observed for compounds 3-6 in CH(2)Cl(2) solution between -1.6 and +1.6 V.     

Iminic N-bound iminophosphorano versus nitrilic n-bound iminophosphorano Os(IV) complexes: a new double derivatization of the nitrido ligand

The reactions between trans-[Os(IV)(tpy)(Cl)(2)(NCN)] (1) and PPh(3) and between trans-[Os(IV)(tpy)(Cl)(2)(NPPh(3))](+) (2) and CN(-) provide new examples of double derivatization of the nitrido ligand in an Os(VI)-nitrido complex (Os(VI)N). The nitrilic N-bound product from the first reaction, trans-[Os(II)(tpy)(Cl)(2)(NCNPPh(3))] (3), is the coordination isomer of the first iminic N-bound product from the second reaction, trans-[Os(II)(tpy)(Cl)(2)(N(CN)(PPh(3)))] (4). In CH(3)CN at 45 degrees C, 4 undergoes isomerrization to 3 followed by solvolysis and release of (N-cyano)iminophosphorane, NCNPPh(3). These reactions demonstrate new double derivatization reactions of the nitrido ligand in Os(VI)N with its implied synthetic utility.     

Cyanido-bridged Fe(III)-Mn(III) heterobimetallic materials built from Mn(III) Schiff base complexes and di- or tri-cyanido Fe(III) precursors

The reaction of [Fe(III)L(CN)(3)](-) (L being bpca = bis(2-pyridylcarbonyl)amidate, pcq = 8-(pyridine-2-carboxamido)quinoline) or [Fe(III)(bpb)(CN)(2)](-) (bpb = 1,2-bis(pyridine-2-carboxamido)benzenate) ferric complexes with Mn(III) salen type complexes afforded seven new bimetallic cyanido-bridged Mn(III)-Fe(III) systems: [Fe(pcq)(CN)(3)Mn(saltmen)(CH(3)OH)]·CH(3)OH (1), [Fe(bpca)(CN)(3)Mn(3-MeO-salen)(OH(2))]·CH(3)OH·H(2)O (2), [Fe(bpca)(CN)(3)Mn(salpen)] (3), [Fe(bpca)(CN)(3)Mn(saltmen)] (4), [Fe(bpca)(CN)(3)Mn(5-Me-saltmen)]·2CHCl(3) (5), [Fe(pcq)(CN)(3)Mn(5-Me-saltmen)]·2CH(3)OH·0.75H(2)O (6), and [Fe(bpb)(CN)(2)Mn(saltmen)]·2CH(3)OH (7) (with saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion, salpen(2-) = N,N'-propylenebis(salicylideneiminato) dianion, salen(2-) = N,N'-ethylenebis(salicylideneiminato) dianion). Single crystal X-ray diffraction studies were carried out for all these compounds indicating that compounds 1 and 2 are discrete dinuclear [Fe(III)-CN-Mn(III)] complexes while systems 3-7 are heterometallic chains with {-NC-Fe(III)-CN-Mn(III)} repeating units. These chains are connected through π-π and short contact interactions to form extended supramolecular networks. Investigation of the magnetic properties revealed the occurrence of antiferromagnetic Mn(III)···Fe(III) interactions in 1-4 while ferromagnetic Mn(III)···Fe(III) interactions were detected in 5-7. The nature of these Mn(III)···Fe(III) magnetic interactions mediated by a CN bridge appeared to be dependent on the Schiff base substituent. The packing is also strongly affected by the nature of the substituent and the presence of solvent molecules, resulting in additional antiferromagnetic interdinuclear/interchain interactions. Thus the crystal packing and the supramolecular interactions induce different magnetic properties for these systems. The dinuclear complexes 1 and 2, which possess a paramagnetic S(T) = 3/2 ground state, interact antiferromagnetically in their crystal packing. At high temperature, the complexes 3-7 exhibit a one-dimensional magnetic behavior, but at low temperature their magnetic properties are modulated by the supramolecular arrangement: a three-dimensional antiferromagnetic order with a metamagnetic behavior is observed for 3, 4, and 7, and Single-Chain Magnet properties are detected for 5 and 6.     

Mononuclear Ni(III) complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1- (L = thiolate, selenolate, CH2CN, Cl, PPh3): relevance to the nickel site of [NiFe] hydrogenases

The stable mononuclear Ni(III)-thiolate complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- (L = SePh (2), Cl (3), SEt (4), 2-S-C4H3S (5), CH2CN (7)) were isolated and characterized by UV-vis, EPR, IR, SQUID, CV, 1H NMR, and single-crystal X-ray diffraction. The increased basicity (electronic density) of the nickel center of complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- modulated by the monodentate ligand L and the substituted groups of the phenylthiolate rings promotes the stability and reactivity. In contrast to the irreversible reduction at -1.17 V (vs Cp2Fe/Cp2Fe+) for complex 3, the cyclic voltammograms of complexes [NiIII(SePh)(P(o-C6H4S)3)]-, 2, 4, and 7 display reversible NiIII/II redox processes with E(1/2) = -1.20, -1.26, -1.32, and -1.34 V (vs Cp2Fe/Cp2Fe+), respectively. Compared to complex 2 containing a phenylselenolate-coordinated ligand, complex 4 with a stronger electron-donating ethylthiolate coordinated to the Ni(III) promotes dechlorination of CH2Cl2 to yield complex 3 (kobs = (6.01 +/- 0.03) x 10-4 s-1 for conversion of complex 4 into 3 vs kobs = (4.78 +/- 0.02) x 10-5 s-1 for conversion of complex 2 into 3). Interestingly, addition of CH3CN into complex 3 in the presence of sodium hydride yielded the stable Ni(III)-cyanomethanide complex 7 with a NiIII-CH2CN bond distance of 2.037(3) A. The NiIII-SEt bond length of 2.273(1) A in complex 4 is at the upper end of the 2.12-2.28 A range for the NiIII-S bond lengths of the oxidized-form [NiFe] hydrogenases. In contrast to the inertness of complexes 3 and 7 under CO atmosphere, carbon monoxide triggers the reductive elimination of the monodentate chalcogenolate ligand of complexes 2, 4, and 5 to produce the trigonal bipyramidal complex [NiII(CO)(P(C6H3-3-SiMe3-2-S)3]- (6).     

Formation and reactivity of the Os(IV)-azidoimido complex, PPN[Os(IV)(bpy)(Cl)(3)(N(4))

Reactions between the Os(VI)-nitrido complexes, [OsVI(L2)(Cl)3(N)] (L2 = 2,2'-bipyridine (bpy) ([1]), 4,4'-dimethyl-2,2'-bipyridine (Me2bpy), 1,10-phenanthroline (phen), and 4,7-diphenyl-1,10-phenanthroline (Ph2phen)), and bis-(triphenylphosphoranylidene)ammonium azide (PPNN3) in dry CH3CN at 60 degrees C under N2 give the corresponding Os(IV)-azidoimido complexes, [OsIV(L2)(Cl)3(NN3)]- (L2 = bpy = [2]-, L2 = Me2bpy = [3]-, L2 = phen = [4]-, and L2 = Ph2phen = [5]-) as their PPN+ salts. The formulation of the N42- ligand has been substantiated by 15N-labeling, IR, and 15N NMR measurements. Hydroxylation of [2]- at Nalpha with O<--NMe3.3H2O occurs to give the Os(IV)-azidohydroxoamido complex, [OsIV(bpy)(Cl)3(N(OH)N3)] ([6]), which, when deprotonated, undergoes dinitrogen elimination to give the Os(II)-dinitrogen oxide complex, [OsII(bpy)(Cl)3(N2O)]- ([7]-). They are the first well-characterized examples of each kind of complex for Os.     

Bis(amido)ruthenium(IV) Complexes with 2,3-Diamino-2,3-dimethylbutane. Crystal Structure and Reversible Ru(IV)-Amide/Ru(III)-Amine and Ru(IV)-Amide/Ru(II)- Amine Redox Couples in Aqueous Solution

Two bis(amido)ruthenium(IV) complexes, [Ru(IV)(bpy)(L-H)(2)](2+) and [Ru(IV)(L)(L-H)(2)](2+) (bpy = 2,2'-bipyridine, L = 2,3-diamino-2,3-dimethylbutane, L-H = (H(2)NCMe(2)CMe(2)NH)(-)), were prepared by chemical oxidation of [Ru(II)(bpy)(L)(2)](2+) and the reaction of [(n-Bu)(4)N][Ru(VI)NCl(4)] with L, respectively. The structures of [Ru(bpy)(L-H)(2)][ZnBr(4)].CH(3)CN and [Ru(L)(L-H)(2)]Cl(2).2H(2)O were determined by X-ray crystal analysis. [Ru(bpy)(L-H)(2)][ZnBr(4)].CH(3)CN crystallizes in the monoclinic space group P2(1)/n with a = 12.597(2) ?, b = 15.909(2) ?, c = 16.785(2) ?, beta = 91.74(1) degrees, and Z = 4. [Ru(L)(L-H)(2)]Cl(2).2H(2)O crystallizes in the tetragonal space group I4(1)/a with a = 31.892(6) ?, c = 10.819(3) ?, and Z = 16. In both complexes, the two Ru-N(amide) bonds are cis to each other with bond distances ranging from 1.835(7) to 1.856(7) ?. The N(amide)-Ru-N(amide) angles are about 110 degrees. The two Ru(IV) complexes are diamagnetic, and the chemical shifts of the amide protons occur at around 13 ppm. Both complexes display reversible metal-amide/metal-amine redox couples in aqueous solution with a pyrolytic graphite electrode. Depending on the pH of the media, reversible/quasireversible 1e(-)-2H(+) Ru(IV)-amide/Ru(III)-amine and 2e(-)-2H(+) Ru(IV)-amide/Ru(II)-amine redox couples have been observed. At pH = 1.0, the E degrees is 0.46 V for [Ru(IV)(bpy)(L-H)(2)](2+)/[Ru(III)(bpy)(L)(2)](3+) and 0.29 V vs SCE for [Ru(IV)(L)(L-H)(2)](2+)/[Ru(III)(L)(3)](3+). The difference in the E degrees values for the two Ru(IV)-amide complexes has been attributed to the fact that the chelating saturated diamine ligand is a better sigma-donor than 2,2'-bipyridine.     

Novel iron(III) complexes of sterically hindered 4N ligands: regioselectivity in biomimetic extradiol cleavage of catechols

The iron(III) complexes of the 4N ligands 1,4-bis(2-pyridylmethyl)-1,4-diazepane (L1), 1,4-bis(6-methyl-2-pyridylmethyl)-1,4-diazepane (L2), and 1,4-bis(2-quinolylmethyl)-1,4-diazepane (L3) have been generated in situ in CH 3CN solution, characterized as [Fe(L1)Cl 2] (+) 1, [Fe(L2)Cl 2] (+) 2, and [Fe(L3)Cl 2] (+) 3 by using ESI-MS, absorption and EPR spectral and electrochemical methods and studied as functional models for the extradiol cleaving catechol dioxygenase enzymes. The tetrachlorocatecholate (TCC (2-)) adducts [Fe(L1)(TCC)](ClO 4) 1a, [Fe(L2)(TCC)](ClO 4) 2a, and [Fe(L3)(TCC)](ClO 4) 3a have been isolated and characterized by elemental analysis, absorption spectral and electrochemical methods. The molecular structure of [Fe(L1)(TCC)](ClO 4) 1a has been successfully determined by single crystal X-ray diffraction. The complex 1a possesses a distorted octahedral coordination geometry around iron(III). The two tertiary amine (Fe-N amine, 2.245, 2.145 A) and two pyridyl nitrogen (Fe-N py, 2.104, 2.249 A) atoms of the tetradentate 4N ligand are coordinated to iron(III) in a cis-beta configuration, and the two catecholate oxygen atoms of TCC (2-) occupy the remaining cis positions. The Fe-O cat bond lengths (1.940, 1.967 A) are slightly asymmetric and differ by 0.027 A only. On adding catecholate anion to all the [Fe(L)Cl 2] (+) complexes the linear tetradentate ligand rearranges itself to provide cis-coordination positions for bidentate coordination of the catechol. Upon adding 3,5-di- tert-butylcatechol (H 2DBC) pretreated with 1 equiv of Et 3N to 1- 3, only one catecholate-to-iron(III) LMCT band (648-800 nm) is observed revealing the formation of [Fe(L)(HDBC)] (2+) involving bidentate coordination of the monoanion HDBC (-). On the other hand, when H 2DBC pretreated with 2 equiv of Et 3N or 1 or 2 equiv of piperidine is added to 1- 3, two intense catecholate-to-iron(III) LMCT bands appear suggesting the formation of [Fe(L)(DBC)] (+) with bidentate coordination of DBC (2-). The appearance of the DBSQ/H 2DBC couple for [Fe(L)Cl 2] (+) at positive potentials (-0.079 to 0.165 V) upon treatment with DBC (2-) reveals that chelated DBC (2-) in the former is stabilized toward oxidation more than the uncoordinated H 2DBC. It is remarkable that the [Fe(L)(HDBC)] (2+) complexes elicit fast regioselective extradiol cleavage (34.6-85.5%) in the presence of O 2 unlike the iron(III) complexes of the analogous linear 4N ligands known so far to yield intradiol cleavage products exclusively. Also, the adduct [Fe(L2)(HDBC)] (2+) shows a higher extradiol to intradiol cleavage product selectivity ( E/ I, 181:1) than the other adducts [Fe(L3)(HDBC)] (2+) ( E/ I, 57:1) and [Fe(L1)(HDBC)] (2+) ( E/ I, 9:1). It is proposed that the coordinated pyridyl nitrogen abstracts the proton from chelated HDBC (-) in the substrate-bound complex and then gets displaced to facilitate O 2 attack on the iron(III) center to yield the extradiol cleavage product. In contrast, when the cleavage reaction is performed in the presence of a stronger base like piperidine or 2 equiv of Et 3N a faster intradiol cleavage is favored over extradiol cleavage suggesting the importance of bidentate coordination of DBC (2-) in facilitating intradiol cleavage.     

The cyanoimido ligand as an oxo analogue. Novel approaches to the preparations of cyano(imino)-aza-phosphorus(V) and N-cyanoaziridine

The known Os(IV)-cyanoimido complexes, mer-Et4N[OsIV(bpy)(Cl)3(NalphaCNbeta)] (mer-[OsIV=N-CN]-) (bpy = 2,2'-bipyridine) and trans-[OsIV(tpy)(Cl)2(NalphaCNbeta)] (trans-[OsIV=N-CN]) (2,2':6',2' '-terpyridine), have formal electronic relationships with high oxidation state Ru and Os-oxo and -dioxo complexes. These include multiple bonding to the metal, the ability to undergo multiple electron transfer, and the availability of nonbonding electron pairs for donation. Thermodynamic, oxo-like behavior is observed for mer-[OsIV=N-CN]- in the pH-dependence of its Os(VI/V) to Os(III/II) redox couples in 1:1 (v/v) CH3CN:H2O. Oxo-like behavior is also observed in the reaction between mer-[OsVI(bpy)(Cl)3(NalphaCNbeta)]PF6 and benzyl alcohol to give mer-[OsIV(bpy)(Cl)3(NalphaCNbetaH2)]PF6 and benzaldehyde. The reaction is first order in each reactant with kbenzyl(CH3CN, 25.0 +/- 0.1 degrees C) = (8.6 +/- 0.2) x 102 M-1 s-1. Formal NCN degrees transfer, analogous to O-atom transfer, occurs in reactions with tertiary phosphine and hexenes. In CH3CN under N2, a rapid reaction occurs between trans-[OsIV=N-CN] and PPh3 (kPPh3(DMF, 25.0 +/- 0.1 degrees C) = 4.06 +/- 0.02 M-1 s-1) to form the nitrilic N-bound Os(II)-(N-cyano)iminophosphorano product, trans-[OsII(tpy)(Cl)2(NalphaCNbetaPPh3)] (trans-[OsII-NalphaC-Nbeta=PPh3]). It undergoes solvolysis at 45 degrees C after 24 h to give trans-[OsII(tpy)(Cl)2(NCCH3)] and (N-cyano)iminophosphorane (NalphaC-Nbeta=PPh3). The analogue to epoxidation, N-cyanoaziridination of cyclohexene and 1-hexene by mer-[OsIV=N-CN]- and trans-[OsIV=N-CN], occurs at Nbeta to give the Os(IV)-N-cyanoaziridino complexes, mer-Et4N[OsII(bpy)(Cl)3(NalphaCNbetaC6H10)] and trans-[OsII(tpy)(Cl)2(NalphaCNbetaC6H11)], respectively. Oxidation to mer-[OsV(bpy)(Cl)3(NalphaCNbeta)]- greatly accelerates N-cyanoaziridination of cyclohexene, which is followed by slow solvolysis to give mer-[OsIII(bpy)(Cl)3(NCCH3)] and N-cyanoaziridine (NC-NC6H10). The Os-(N-cyano)aziridino complexes are the first well-characterized examples of coordinated cyanoaziridines.     

Bivalent and trivalent iron complexes of acyclic hexadentate ligands providing pyridyl/pyrazine-amide-thioether coordination

Acyclic pyridine-2-carboxamide- and thioether-containing hexadentate ligand 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpctb), in its deprotonated form, has afforded purple low-spin (S = 0) iron(II) complex [Fe(bpctb)] (1). A new ligand, the pyrazine derivative of H(2)bpctb, 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpzctb), has been synthesized which has furnished the isolation of purple iron(II) complex [Fe(bpzctb)].CH(2)Cl(2) (4) (S = 0). Chemical oxidation of 1 by [(eta(5)-C(5)H(5))(2)Fe][PF(6)] or [Ce(NO(3))(6)][NH(4)](2) led to the isolation of low-spin (S = 1/2) green Fe(III) complexes [Fe(bpctb)][PF(6)] (2) or [Fe(bpctb)][NO(3)].H(2)O (3), and oxidation of 4 by [Ce(NO(3))(6)][NH(4)](2) afforded [Fe(bpzctb)][NO(3)].H(2)O (5) (S = 1/2). X-ray crystal structures of 1 and 4 revealed that (i) in each case the ligand coordinates in a hexadentate mode and (ii) bpzctb(2-) binds more strongly than bpctb(2-), affording distorted octahedral M(II)N(2)(pyridine/pyrazine)N'(2)(amide)S(2)(thioether) coordination. To the best of our knowledge, 1 and 4 are the first examples of six-coordinate low-spin Fe(II) complexes of deprotonated pyridine/pyrazine amide ligands having appended thioether functionality. The Fe(III) complexes display rhombic EPR spectra. Each complex exhibits in CH(2)Cl(2)/MeCN a reversible to quasireversible cyclic voltammetric response, corresponding to the Fe(III)-Fe(II) redox process. The E(1/2) value of 4 is more anodic by approximately 0.2 V than that of 1, attesting that compared to pyridine, pyrazine is a better stabilizer of iron(II). Moreover, the E(1/2) value of 1 is significantly higher (approximately 1.5 V) than that reported for six-coordinate Fe(II)/Fe(III) complexes of the tridentate pyridine-2-carboxamide ligand incorporating thiolate donor site.     

Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.