Linkage isomerism, structure, and reactivity studies of sulfenamide complexes of cobalt(III)

The S-bonded sulfenamide isomers have been prepared by the known reaction of hydroxylamine-O-sulfonate with (en)(2)Co(III) thiolate complexes of aminoethanethiol, cysteine, and penicillamine and the cis dithiolate formed by N,N'-ethylene-di-penicillamine (EDP) and Co(III). It is shown that the sulfenamides undergo linkage isomerization in alkaline solution to produce their respective N-bonded linkage isomers. The addition of acid yields the protonated N-bonded isomers. The structures of [(en)(2)Co(NH(2)S(CH(2))(2)NH(2))](2)(S(2)O(6))(3) and [Co((NH(2)S)(2)EDP)]Br have been determined by X-ray crystallography, and the pK(a) of [(en)(2)Co(NH(2)S(CH(2))(2)NH(2))](3+) has been determined by spectrophotometry. The pH dependencies of the kinetics of the linkage isomerization reactions have been studied and yield pK(a) values of the S-bonded isomers. The (en)(2)Co systems give only the acid-stable N,N' isomer at equilibrium, whereas the EDP complex gives a mixture of N,N' and N,S isomers at pH 7-9.     

Linkage and redox isomerism in ruthenium complexes of catecholate, semi-quinone, and o-acylphenolate ligands derived from tri- and tetrahydroxy-9,10-anthracenediones

The complexes Ru(CO)(2)L(2)(PHAQ-2H) (PHAQ = 1,2,4-trihydroxy-9,10-anthracenedione (PUR), 1,2,3- trihydroxy-9,10-anthracenedione (AG), and 1,2,5,8-tetrahydroxy-9,10-anthracenedione (QAL); L = PPh(3), PCy(3), PBu(3)), and Ru(CO)(dppe)(PBu(3))(PHAQ-2H), containing catecholate-type ligands were prepared. The complex Ru(CO)(2)(PBu(3))(2)(AG-2H) crystallizes in the space group P2(1)/n (No. 14 var) with a = 13.317(2), b = 15.628(2), c = 21.076(3) A, beta = 101.660(10) degrees, Z = 4; the crystal structure shows it to contain a 2,3-catecholate ligand. The electrochemistry of these complexes was examined, and the semi-quinone complexes [Ru(CO)(2)L(2)(PHAQ-2H)](1+) and [Ru(CO)(dppe)(PBu(3))(PHAQ-2H)](1+) were generated by chemical oxidation. One example of an o-acylphenolate complex, HRu(CO)(PCy(3))(2)(PUR-H), is also reported.     

Synthesis,electrochemistry, and electrocatalytic activity of thiazole-substituted phthalocyanine complexes

Journal of Solid State Electrochemistry - We report the synthesis of non-peripheral metallophthalocyanines which carry four 4-(4-methoxyphenyl)-2-thiazole-2-thio units. 1H-NMR, FT-IR, UV–Vis,...     

High-nuclearity Pt-Tl-Fe complexes: structural, electrochemistry, and spectroelectrochemistry studies

A series of heteropolynuclear Pt-Tl-Fe complexes have been synthesized and structurally characterized. The final structures strongly depend on the geometry of the precursor and the Pt/Tl ratio used. Thus, the anionic heteroleptic cis-configured [cis-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and [Pt(bzq)(C≡CFc)(2)](-) (Fc = ferrocenyl) complexes react with Tl(+) to form discrete octanuclear (PPh(3)Me)(2)[{trans,cis,cis-PtTl(C(6)F(5))(2)(C≡CFc)(2)}(2)] (1), [PtTl(bzq)(C≡CFc)(2)](2) (5; bzq = benzoquinolate), and decanuclear [trans,cis,cis-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](2) (3) derivatives, stabilized by both Pt(II)···Tl(I) and Tl(I)···η(2)(alkynyl) bonds. By contrast, Q(2)[trans-Pt(C(6)F(5))(2)(C≡CFc)(2)] (Q = NBu(4)) reacts with Tl(+) to give the one-dimensional (1-D) anionic [(NBu(4)){trans,trans,trans-PtTl(C(6)F(5))(2)(C≡CFc)(2)}](n) (2) and neutral [trans,trans,trans-PtTl(2)(C(6)F(5))(2)(C≡CFc)(2)](n) (4) polymeric chains based on [PtFc(2)](2-) platinate fragments and Tl(+) (2) or [Tl···Tl](2+) (4) units, respectively, connected by Pt(II)···Tl(I) and secondary weak κ-η(1) (2) or η(2) (4) alkynyl···Tl(I) bonding. The formation of 1-4 is reversible, and thus treatment of neutral 3 and 4 with PPh(3)MeBr causes the precipitation of TlBr, returning toward the formation of the anionic 1 and 2' (Q = PPh(3)Me). Two slightly different pseudopolymorphs were found for 2', depending on the crystallization solvent. Finally, the reaction of the homoleptic [Pt(C≡CFc)(4)](2-) with 2 equiv of Tl(+) affords the tetradecanuclear sandwich type complex [Pt(2)Tl(4)(C≡CFc)(8)] (6). Electrochemical, spectroelectrochemical, and theoretical studies have been carried out to elucidate the effect produced by the interaction of the Tl(+) with the Pt-C≡CFc fragments. The cyclic voltammetry (CV) and differential pulse voltammetry (DPV) of 1-5 reveal that, in general, neutralization of the anionic fragments increases the stability of the fully oxidized species and gives higher E(1/2) (Fc) values than those observed in their precursors, increasing with the number of Pt-Tl bonding interactions. However, the electronic communication between Fc groups is reduced or even lost upon Tl(+) coordination, as confirmed by electrochemical (CVs and DPVs voltammograms, 1-5) and spectroelectrochemical (UV-vis-NIR, 2-4) studies. Complexes 2 and 4 still display some electronic interaction between the Fc groups, supported by the presence of an IVCT band in their UV-vis-NIR spectra of oxidized species and additional comparative DFT calculations with the precursor [trans-Pt(C(6)F(5))(2)(C≡CFc)(2)](2-) and complex 3.     

Structural and isotopomeric isomerism of hydrogen- bonded complexes

Two kinds of hydrogen-bonded complex isomerism, structural and isotopomeric, are the subject of contemporary research. Structural isomerism represents an extension of the phenomenon known from organic chemistry. Isotopomeric isomerism can be considered with any complex containing, in addition to the hydrogen involved in the hydrogen bond, at least one other hydrogen atom. Then, two different, isomeric species can be created by mono-deuteration of the complex. An example is given by the water-dimer gas-phase isotopomers HOD·OHD and DOH·OHD. The isomeric systems of both types can exhibit interchanges in the relative stabilities of the structures with changing temperature. Moreover, the temperature changes can be quite pronounced so that values of temperature derivatives are obtained which are not frequently observed with other types of isomeric systems. It can be well manifested in thermodynamic terms (standard changes of enthalpy, entropy and heat capacity upon cluster formation), or at least in isomerism contributions to the latter terms, especially so for heat capacity.     

Synthesis, characterization, and electrochemistry of biorelevant photosensitive low-potential orthometalated ruthenium complexes

Redox potentials of photosensitive cyclometalated RuII derivatives of 2-phenylpyridine or 2-(4-tolyl)pyridine are controllably decreased by up to 0.8 V within several minutes. This is achieved by irradiation of the ruthena(II)cycles cis-[Ru(o-X-2-py)(LL)(MeCN)2]PF6 (2, X = C6H4 (a) or 4-MeC6H3 (b), LL = 1,10-phenanthroline or 2,2'-bipyridine). The cis geometry of the MeCN ligands has been confirmed by the X-ray structural studies. The sigma-bound sp2 carbon of the metalated ring is trans to LL nitrogen. Complexes 2 are made from [Ru(o-X-2-py)(MeCN)4]PF6 (1) and LL. This "trivial" ligand substitution is unusual because 1a reacts readily with phen in MeCN as solvent to give cis-[Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (2c) in a 83% yield, but bpy does not afford the bpy-containing 2 under the same conditions. cis-[Ru(o-C6H4-2-py)(bpy)(MeCN)2]PF6 (2e) has been prepared in CH2Cl2 (74%). Studies of complexes 2c,e by cyclic voltammetry in MeOH in the dark reveal RuII/III quasy-reversible redox features at 573 and 578 mV (vs Ag/AgCl), respectively. A minute irradiation 2c and 2e converts them into new species with redox potentials of -230 and 270 mV, respectively. An exceptional potential drop for 2c is accounted for in terms of a photosubstitution of both MeCN ligands by methanol. ESR, 1H NMR, and UV-vis data indicate that the primary product of photolysis of 2c is an octahedral monomeric low-spin (S = 1/2) RuIII species, presumably cis-[RuIII(o-C6H4-2-py)(phen)(MeOH)2]2+. The primary photoproduct of bpy complex 2e is cis-[RuII(o-C6H4-2-py)(bpy)(MeCN)(MeOH)]+, and this accounts for a lower decrease in the redox potential. Irradiation of 2c in the presence of added chloride affords [(phen)(o-C6H4-2-py)ClRuIIIORuIVCl(o-C6H4-2-py)(phen)]PF6, a first mu-oxo-bridged mixed valent dimer with a cyclometalated unit. The structure of the dimer has been established by X-ray crystallography.     

Synthesis,characterization, and electrochemistry of phosphine-substituted diiron butane-1,2-dithiolate complexes

Abstract

The reactions of the starting complex, [Fe₂(CO)₆{μ-SCH₂CH (CH₂CH₃)S}] (1), with the phosphine ligands tris(4-methylphenyl)phosphine, diphenyl-2-pyridylphosphine, tris(4-fluorophenyl)phosphine, 2-(diphenylphosphino)benzaldehyde, or benzyldiphenylphosphine in the presence of the decarbonylating agent Me₃NO·2H₂O yielded the corresponding phosphine-substituted diiron butane-1,2-dithiolate complexes [Fe₂(CO)₅(L){μ-SCH₂CH(CH₂CH₃)S}] (L?=?P(4-C₆H₄CH₃)₃, 2; Ph₂P(2-C₅H₄N), 3; P(4-C₆H₄F)₃, 4; Ph₂P(2-C₆H₄CHO), 5; Ph₂PCH₂Ph, 6) in 75%–87% yields. The complexes have been characterized by elemental analysis, IR, ¹H, and ³¹P{¹H} NMR spectroscopy, as well as by single-crystal X-ray diffraction analysis. Moreover, the electrochemistry of 2–4 was studied by cyclic voltammetry, suggesting that they can catalyze the reduction of protons to H₂ in the presence of HOAc.     

Structural and rotational isomerism in diaminocarbene complexes of iron

Primary amines react with a variety of cationic and neutral iron isocyanide complexes to yield structural and rotational diaminocarbene isomers characterized by variable temperature ¹H and ¹³C NMR spectra. Structural isomers result from the conversion of amines to isocyanide ligands via the base-catalyzed nucleophilic attack of initially formed diaminocarbenes on $\text{cis}$ isocyanides substituents, the effect on isomer populations is often marked. Factors influencing structural and rotational isomeric preferences are discussed.     

Heterocyclic thiocarboxylato complexes of iron: synthesis,characterization, electrochemistry,and reactions

Heterocyclic-thiocarboxylato complexes of iron, CpFe(CO)₂SCO-het (het?=?2-C₄H₃O, 2-C₄H₃S, CH₂-2-C₄H₃S), have been synthesized via the reaction of iron sulfides, (μ-S _x )[CpFe(CO)₂]₂ (x?=?3,?4), with heterocyclic acid chlorides het-COCl. Photolytic substitutions of these complexes CpFe(CO)₂SCO-het with triphenylphosphine, triethylphosphite, triphenylarsine, and triphenylantimony [ER₃ (E?=?P, R?=?Ph, OC₂H₅; E?=?As, Sb, R?=?Ph)] exclusively gave the monosubstituted complexes CpFe(CO)(ER₃)SCO-het in good yields. The new complexes have been characterized by elemental analysis, UV-Vis, IR, ¹H, and ³¹P NMR spectroscopies and by cyclic voltammetry for a representative family (1, 4a–d). The solid state structures of CpFe(CO)₂SCO(2-C₄H₃S) (2), CpFe(CO)(PPh₃)SCO(2-C₄H₃S) (5a), CpFe(CO)(AsPh₃)SCO(2-C₄H₃S) (5b), and CpFe(CO)(SbPh₃)SCO(2-C₄H₃S) (5c) were determined by X-ray crystal structure analysis.     

Synthesis, electrochemistry, and spectroscopic characterization of bis-dirhodium complexes linked by axial ligands

The synthesis and electrochemical and spectroscopic properties of bis-dirhodium complexes containing ap or dpf bridging ligands, (ap)(4)Rh(2)(C triple bond C)(2)Rh(2)(ap)(4) (2) and (dpf)(4)Rh(2)(CNC(6)H(4)NC)Rh(2)(dpf)(4) (4), were investigated (where ap and dpf are the 2-anilinopyridinate and N,N'-diphenylformamidinate ions, respectively). The related "simple" dirhodium species, (ap)(4)Rh(2)(C triple bond C)(2)Si(CH(3))(3) (1) and (dpf)(4)Rh(2)(CNC(6)H(5)) (3), with the same set of bridging ligands were also synthesized and their properties compared to those of the analogous bis-dirhodium complexes. Compound 1 was obtained by mixing (ap)(4)Rh(2)Cl and Li(C triple bond C)(2)Si(CH(3))(3) in refluxing THF for 16 h under vacuum while compound 2 was prepared by a reaction between (ap)(4)Rh(2)(C triple bond C)(2)Li and (ap)(4)Rh(2)Cl under similar conditions. The reaction between (CF(3)COO)(4)Rh(2) and molten Hdpf under vacuum for 24 h leads to the generation of compound 3 with a yield of 65%. The red-orange compound 4 was obtained upon addition of 0.5 equiv of CNC(6)H(4)NC at room temperature to a CH(2)Cl(2) solution containing (dpf)(4)Rh(2) which was synthesized according to a method described previously in the literature. Compound 1 crystallizes in the triclinic space group P1, with a = 10.164(3) A, b = 13.881(3) A, c = 18.805(4) A, alpha = 73.55(2) degrees, beta = 77.89(2) degrees, gamma = 84.85(2) degrees, and Z = 2. Crystals of 2 were not good enough to collect adequate data for X-ray analysis, but the identity of this compound was confirmed, along with its P1; space group. Crystals of 3 and 4 belong to the monoclinic, P2(1)/c space group and the triclinic, P1; space group, respectively, with a = 13.5254(5) A, b = 13.7387(4) A, c = 27.2011(12) A, beta = 102.637(2) degrees, and Z = 4 for 3 and a = 13.866(8) A, b = 14.756(7) A, c = 15.008(6) A, alpha = 79.91(3) degrees, beta = 87.72(4) degrees, gamma = 89.19(4) degrees, and Z = 1 for 4. Compound 1 exhibits a single reversible oxidation at E(1/2) = 0.66 V and a single reversible reduction at E(1/2) = -0.44 V vs SCE in THF, 0.2 M TBAP. Both processes involve a one-electron transfer. Compound 2 undergoes a reversible oxidation at E(1/2) = 0.60 V and two separate one-electron-transfer reductions at E(1/2) = -0.52 and -0.65 V in THF, 0.2 M TBAP. The oxidation involves two overlapped one-electron-transfer processes. Compounds 3 and 4 undergo two reversible oxidations in CH(2)Cl(2), 0.1 M TBAP located at E(1/2) = 0.23 and 1.22 V (3) or 0.22 and 1.20 V (4). Each redox reaction of 3 involves a one-electron-transfer step while each redox reaction of 4 involves two overlapping one-electron transfers. Compound 2 shows interaction between the two dirhodium cores upon reduction, while 4 gives no evidence of electronic interaction between the two dirhodium units during either reduction or oxidation. An ESR signal with axial symmetry was obtained for the neutral compounds 1 and 2, and a similar spectrum was obtained for the singly oxidized products of compounds 3 and 4, thus suggesting the electronic configuration of (sigma)(2)(pi)(4)(delta)(2)(pi)(4)(delta)(1) for the neutral compounds 1 and 2 as well as for the oxidized compounds 3 and 4. The four compounds were also characterized by FTIR and UV-visible spectroscopy as well as by mass spectrometry.     

Synthesis, spectroscopy, electrochemistry and thermal study of vanadyl tridentate Schiff base complexes

The VO(IV) complexes of tridentate ONO Schiff ligands were synthesised and characterized by IR, UV–vis and elemental analysis. The electrochemical properties of the vanadyl complexes were investigated by cyclic voltammetry. A good correlation was observed between the oxidation potentials and the electron withdrawing character of the substituents on the Schiff base ligands, showing the following trend: MeO < H < Br < NO₂ and H < Cl. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the VO(IV) complexes were carried out in the range of 20–700 °C. The VOL¹(OH₂) decomposed in two steps whereas the remaining six complexes decomposed in three steps. The thermal decomposition of these complexes is closely related to the nature of the Schiff base ligands and proceeds via first order kinetics.     

Linkage isomerism in nitrite reduction by cytochrome cd1 nitrite reductase

Nitrite reduction by cytochrome cd(1) nitrite reductase (cd(1)NIR) is currently accepted to involve coordination of the nitrite nitrogen atom to the ferrous d(1) heme. Here, density functional theory results are reported on the previously unexplored O-binding of nitrite to ferrous and ferric cd(1)NIR. Although the N-isomer (nitro) is energetically favored over the O-nitrite (nitrito), even one single strong hydrogen bond may provide the energy required to put the two isomers on level terms. When hydrogen bonding existent at the cd(1)NIR active site is accounted for in the computational model, the O-nitrite isomer is found to spontaneously protonate and thus yield a ferric-hydroxo species, liberating nitric oxide. An O-nitrite ferrous cd(1)NIR complex appears to be an energetically feasible intermediate for nitrite reduction. O-Coordination would offer an advantage since the end product of nitrite reduction would be a ferric-hydroxo/water complex, rather than the more kinetically inert iron-nitrosyl complex implied by the N-nitrite mechanism.     

Linkage and redox isomerism in ruthenium complexes of catecholate, semiquinone, and o-acylphenolate ligands derived from 1,2-dihydroxy-9,10-anthracenedione (alizarin) and related species: syntheses, characterizations, and photophysics

The complexes Ru(CO)2L2(AL-2H) (AL = alizarin; L = PPh3, PCyc3, PBu3, P(m-NaSO3C6H4)3), Ru(CO)(dppe)(PBu3)(AL-2H), and RuH(CO)L2(AL-H) (L = PPh3, PCyc3), and Ru(CO)2L2(AR-2H) (AR = anthrarobin; L = PBu3) were prepared by reactions of Ru3(CO)12, L, and AL, and the complexes RuH(CO)(PPh3)2(AL-H), RuH(CO)(PPh3)2(QN-H) (QN = quinizarin), and RuH(CO)(PPh3)2(LQN-H) (LQN = leucoquinizarin) are prepared by reactions of RuH2(CO)(PPh3)3 with AL or QN. The AL-2H and AR-2H ligands act as 1,2-catecholates, whereas the AL-H, QN-H, LQN-H ligands are 1,9-o-acylphenolate ligands. RuH(CO)(PPh3)2(AL-H) is characterized by X-ray crystallography. The electrochemistry of these complexes is examined, and the semiquinone complexes [Ru(CO)2L2(AL-2H)]+ (L = PPh3, PCyc3, PBu3) and [Ru(CO)(dppe)(PBu3)(AL-2H)]+ are generated by chemical oxidation and were characterized by EPR and IR spectroscopy. The photophysical properties are also reported.     

Two photoluminescent pentanuclear homo- and hetero-metal complexes based on benzotriazole bridge

Two new discrete Btz-bridged pentanuclear metal complexes, [HDMF][NaHg₄(Btz)₆I₄] (1) and [Zn₅(Btz)₆(L)₃(Ac)]?·?0.5MeOH?·?0.5H₂O (2) (Btz?=?deprotonated benzotriazole, L?=?p-aminobenzoate, HDMF?=?protonated DMF, and Ac?=?acetate), were synthesized using three-layered diffusion and natural evaporation methods, respectively. In 1, the pentanuclear anion [NaHg₄(Btz)₆I₄]^? is composed of a tetrahedral arrangement of four four-coordinate Hg(II) ions centered on the six-coordinate Na(I), and thereby forming a rare Btz-bridged hetero-metal complex. Compound 2 is a neutral pentanuclear homo-metal complex, consisting of a tetrahedral arrangement of four five-coordinate Zn(II) ions centered on the fifth six-coordinate Zn(II). The thermal stabilities and solid-state photoluminescence of the two complexes have been investigated.     

Synthesis, characterization and electrochemistry of diruthenium complexes linked by aryl acetylide bridges

The reactions between Ru₂(ap)₄Cl and the appropriate lithiated aryl acetylene resulted in the complexes Ru₂(ap)₄(CC4-C₆H₄CCX) with X as SiMe₃ (1), H (2) and Ru₂(ap)₄ (3), 1,3-[Ru₂(ap)₄(CC)]₂(C₆H₄) (4), 1,3-[{Ru₂(ap)₄(CC)}₂]C₆H₃5-CCH (5) and 1-[Ru₂(ap)₄(CC)]C₆H₃3,5-(CCH)₂ (6), where ap is 2-anilinopyridinate. The spectroscopic and electrochemical properties of the new complexes have been assessed. Complexes 3, 4 and 6 display two-electron oxidation and reductions, implying the absence of any significant electronic interaction between the two Ru₂(ap)₄ units in these complexes.     

Novel fluorescent fluorine-boron complexes: synthesis, crystal structure, photoluminescence, and electrochemistry properties

Two novel fluorine-boron cored fluorescent complexes were designed and synthesized. These two complexes displayed well-ordered molecular packing, intense fluorescence, and low LUMO levels. The results indicated their potential use as electron-transport materials in electroluminescent (EL) devices.     

Synthesis,structures, and electrochemistry of diiron toluene-3,4-dithiolate complexes containing phosphine ligands

Transition Metal Chemistry - In this paper, four diiron toluene-3,4-dithiolate complexes with phosphine ligands were synthesized and characterized. Treatment of complex...