Chromium(III) complexes for photochemical nitric oxide generation from coordinated nitrite: synthesis and photochemistry of macrocyclic complexes with pendant chromophores, trans-[Cr(L)(ONO)(2)]BF(4)

Several new dinitritochromium(III) complexes of the type trans-[Cr(L)(ONO)(2)]BF(4), where L is a derivative of the macrocyclic ligand cyclam having pendant aromatic chromophores attached (L = 5,7-dimethyl-6-(substituted)-1,4,8,11-tetraazacyclotetradecane), have been prepared and characterized. Photoexcitation of aqueous solutions containing these complexes at wavelengths corresponding to the pendant chromophore absorption bands led to the generation of NO as detected by an electrochemical sensor. Photophysical data show that the expected fluorescence of the pendant chromophores is largely quenched when the macrocyclic ligand is coordinated to these Cr(III) centers, and this is interpreted in terms of fast energy transfer processes from the ligand-centered pipi states to the Cr(III)-centered ligand field states leading to subsequent cleavage of the Cr(III)-coordinated nitrito ligand. Thus, the chromophores tethered to the coordinated cyclam serve as light-gathering antennae for the intramolecular sensitization of the NO-generating photoreactions at the metal center.     

Scrutinizing low-spin Cr(II) complexes

The oxidation state of the chromium center in the following compounds has been probed using a combination of chromium K-edge X-ray absorption spectroscopy and density functional theory: [Cr(phen)(3)][PF(6)](2) (1), [Cr(phen)(3)][PF(6)](3) (2), [CrCl(2)((t)bpy)(2)] (3), [CrCl(2)(bpy)(2)]Cl(0.38)[PF(6)](0.62) (4), [Cr(TPP)(py)(2)] (5), [Cr((t)BuNC)(6)][PF(6)](2) (6), [CrCl(2)(dmpe)(2)] (7), and [Cr(Cp)(2)] (8), where phen is 1,10-phenanthroline, (t)bpy is 4,4'-di-tert-butyl-2,2'-bipyridine, and TPP(2-) is doubly deprotonated 5,10,15,20-tetraphenylporphyrin. The X-ray crystal structures of complexes 1, [Cr(phen)(3)][OTf](2) (1'), and 3 are reported. The X-ray absorption and computational data reveal that complexes 1-5 all contain a central Cr(III) ion (S(Cr) = (3)/(2)), whereas complexes 6-8 contain a central low-spin (S = 1) Cr(II) ion. Therefore, the electronic structures of 1-8 are best described as [Cr(III)(phen(?))(phen(0))(2)][PF(6)](2), [Cr(III)(phen(0))(3)][PF(6)](3), [Cr(III)Cl(2)((t)bpy(?))((t)bpy(0))], [Cr(III)Cl(2)(bpy(0))(2)]Cl(0.38)[PF(6)](0.62), [Cr(III)(TPP(3?-))(py)(2)], [Cr(II)((t)BuNC)(6)][PF(6)](2), [Cr(II)Cl(2)(dmpe)(2)], and [Cr(II)(Cp)(2)], respectively, where (L(0)) and (L(?))(-) (L = phen, (t)bpy, or bpy) are the diamagnetic neutral and one-electron-reduced radical monoanionic forms of L, and TPP(3?-) is the one-electron-reduced doublet form of diamagnetic TPP(2-). Following our previous results that have shown [Cr((t)bpy)(3)](2+) and [Cr(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine) to contain a central Cr(III) ion, the current results further refine the scope of compounds that may be described as low-spin Cr(II) and reveal that this is a very rare oxidation state accessible only with ligands in the strong-field extreme of the spectrochemical series.     

Spectroscopic characterization of chromium(III), manganese(II) and nickel(II) complexes with a nitrogen donor tetradentate, 12-membered azamacrocyclic ligand

The complexes of Cr(III), Mn(II) and Ni(II) were synthesized with macrocyclic ligand i.e. 5,11-dimethyl-6,12-diethyl-dione-1,2,4,7,9,10-hexazacyclododeca -1,4,6,10-tetraene. The ligand (L) was prepared by [2+2] condensation reaction of 2,3-pentanedione and semicarbazide hydrochloride. These complexes were found to have the general composition [Cr(L)X(2)]X and [M(L)X(2)] (where M=Mn(II) and Ni(II); X=Cl(-), NO(3)(-), (1/2)SO(4)(2-), NCS(-) and L=ligand [N(6)]). The ligand and its transition metal complexes were characterized by the elemental analysis, molar conductance, magnetic susceptibility, mass, IR, electronic and EPR spectral studies. On the basis of IR, electronic and EPR spectral studies, an octahedral geometry has been assigned for these complexes except sulphato complexes which are of five coordinated geometry.     

trans-[Ru(II)(dpp)Cl2]: a convenient reagent for the preparation of heteroleptic Ru(dpp) complexes, where dpp is 2,9-di(pyrid-2'-yl)-1,10-phenanthroline

The reaction of 2,9-di(pyrid-2'-yl)-1,10-phenanthroline (dpp) with [RuCl(3)·3H(2)O] or [Ru(DMSO)(4)Cl(2)] provides the reagent trans-[Ru(II)(dpp)Cl(2)] in yields of 98 and 89%, respectively. This reagent reacts with monodentate ligands L to replace the two axial chlorides, affording reasonable yields of a ruthenium(II) complex with dpp bound tetradentate in the equatorial plane. The photophysical and electrochemical properties of the tetradentate complexes are strongly influenced by the axial ligands with electron-donating character to stabilize the ruthenium(III) state, shifting the metal-to-ligand charge-transfer absorption to lower energy and decreasing the oxidation potential. When the precursor trans-[Ru(II)(dpp)Cl(2)] reacts with a bidentate (2,2'-bipyridine), tridentate (2,2';6,2'-terpyridine), or tetradentate (itself) ligand, a peripheral pyridine on dpp is displaced such that dpp binds as a tridentate. This situation is illustrated by an X-ray analysis of [Ru(dpp)(bpy)Cl](PF(6)).     

Spectroscopic studies of transition metal complexes with a N-donor tetradentate(N4) 12-membered macrocylic ligand

Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), copper(II), ruthenium(III), iridium(III), palladium(II) and platinum(II) complexes were synthesized with a 12-membered 1,4,7,10-tetraazadodeca-5,6,11,12-tetraene macrocylic ligand (L) and characterized by elemental analysis, molar conductance, magnetic susceptibility, IR, electronic, EPR and M?ssbauer [Fe(III)] spectral studies. The molar conductance measurements of all the complexes in DMF solution correspond to non-electrolytic nature for M(L)Cl2 complexes [where M=Mn(II), Co(II), Ni(II), Cu(II)], 1:1 electrolytes for M'(L)Cl3 complexes [where M'=Cr(III), Fe(III), Ru(III) and Ir(III)] and 1:2 electrolytes for M'(L)Cl2 complexes [where M'=Pd(II) and Pt(II)]. Thus, the complexes may be formulated as [M(L)C1(2)], [M'(L)C1(2)]C1 and [M'(L)]C1(2), respectively [where L=ligand]. All complexes were of the high-spin type and found to have six-coordinate octahedral geometry except the Pd(II) and Pt(II) complexes which were four coordinate, square planar and diamagnetic.     

Synthesis and reactivity of the aquation product of the antitumor complex trans-[Ru(III)Cl4(indazole)2]-

Aquation of the investigational anticancer drug trans-[Ru(III)Cl4(Hind)2](-) (1, KP1019) results in the formation of mer,trans-[Ru(III)Cl3(Hind)2(H2O)] (2), which was isolated in high yield (85%) and characterized by spectroscopic methods and X-ray crystallography. Dissolution of 2 in acetone, led to its dimerization into [Ru(III)2(mu-Cl)2Cl4(Hind)4] x 2 (Me)2CO (3) in 79% yield, with release of two water molecules. Complex 2 reacts readily with nucleophilic organic molecules, viz., methanol or dimethyl sulfide, at room temperature by replacement of the aqua ligand to give mer,trans-[Ru(III)Cl3(Hind)2(MeOH)] (4) and mer,trans-[Ru(III)Cl3(Hind)2(Me2S)] (5) in 58 and 64% yield, respectively. By reaction of 2 with DMSO at room temperature or dimethyl sulfide at elevated temperatures trans,trans,trans-[Ru(II)Cl2(Hind)2(Me2S)2] (6) and trans,trans,trans-[Ru(II)Cl2(Hind)2(S-DMSO)2] (7) were prepared in 64 and 75% yield, respectively. Dissolution of 2 in acetonitrile or benzonitrile gave rise to mer,trans-[Ru(III)Cl3(Hind)(HNC(Me)ind)] (8a), mer,trans-[Ru(III)Cl3(Hind)(HNC(Ph)ind)] (8b), and trans,trans-[Ru(III)Cl2(HNC(Me)ind)2]Cl (9) in 67, 50, and 23% yield, respectively, upon metal-assisted iminoacylation of indazole, which is unprecedented for ruthenium(III). Furthermore, complex 2 reacts with the DNA-model bases 9-methyladenine (9-meade) and N6,N6-dimethyladenine (6-me2ade) to yield mer,trans-[Ru(III)Cl3(Hind)2(9-meade)] (10) and mer,trans-[Ru(III)Cl3(Hind)2(6-me2ade)] (11) with the purine bases bound to the Ru(III) center via N7 and N3, respectively. Complex 11 represents the first ruthenium complex in which the coordination of the purine ligand N6,N6-dimethyladenine occurs via N3. In addition, the polymer [Na(EtOAc)2Ru(III)(mu-Cl)4(Hind)2]n (12) was crystallized from ethyl acetate/diethyl ether solutions of Na[trans-Ru(III)Cl4(Hind)2] x 1.5 H2O (1a). The reported complexes were characterized by elemental analysis, IR and UV-vis spectroscopy, ESI mass spectrometry, cyclic voltammetry, and X-ray crystallography. Electrochemical investigations give insight into the mechanistic details of the solvolytic behavior of complex 2. The lability of the aqua ligand in 2 suggests that this complex is a potential active species responsible for the high antitumor activity of trans-[Ru(III)Cl4(Hind)2](-).     

Special effects of ortho-isopropylphenyl groups. Diastereoisomerism in platinum(II) and palladium(II) complexes of helically chiral PAr3 ligands

The coordination chemistry of the four phosphines, P{C6H3(o-CH3)(p-Z)}3 where Z = H (1a) or OMe (1b) and P{C6H3(o-CHMe2)(p-Z)}3 Z = H (1c) or OMe (1d) with platinum(II) and palladium(II) is reported. Mononuclear complexes trans-[PdCl2L2](L = 1a,b) and trans-[PtCl2L2](L = 1a-c) have been prepared and the crystal structures of trans-[PdCl2(1b)2] and trans-[PtCl2(1c)2] as their dichloromethane solvates have been determined. The structures show that in these complexes, the ligands adopt g+ g+ a conformations. Examination of the Cambridge Structural Database confirms this to be one of only two conformer types that tri-o-tolylphosphines adopt and the only viable conformer in 4 and 6 coordinate complexes. The binuclear complexes trans-[Pd2Cl4L2](L = 1c,d) are formed even when an excess of the bulky 1c,d is used in the synthesis and the crystal structure of trans-[Pd2Cl4(1c)2] as its chloroform solvate is reported. Reaction of [PtCl2(NCBu(t))2] with 1b-d in refluxing toluene gave the cycloplatinated species [Pt2Cl2(L - H)2] where L - H is phosphine 1b-d deprotonated at one of the ortho-methyl carbon atoms. Variable temperature 31P and 1H NMR spectroscopy reveals that all the complexes reported are fluxional. The processes are analysed in terms of restricted P-C and P-M rotations that give rise to diastereoisomeric rotamers because of the helically chiral orientations of the aryl substituents. For the complexes of the bulky ligands 1c,d, rotation about the P-C bond is slow on the NMR timescale even up to 75 degrees C. The crystal structure of the cyclometallated complex [Pt2Cl2(1d - H)2] has been determined.     

Versatile chemical transformations of benzoxazole based ligands on complexation with 3d-metal ions

Two benzoxazoles derivative ligands were synthesized from the condensation of 3,5-di-tert-butyl-o-benzoquinone (DTBBQ) with ethanolamine or 1,3-diamino-2-hydroxypropane in methanol. Condensation of DTBBQ with ethanolamine gives the expected 5,7-di-tert-butyl-2-methylenhydroxylbenzoxazole (HL1) while with 1,3-diamino-2-hydroxypropane it gives (2-hydroxyethyl-2-{2,4-bis(1,1-dimethylethyl)-1-phenol-6 amino}-2{5,7-di-tert-butyl-benzoxazole}) (H(2)L2) with only one benzoxazole ring instead of the symmetric bis-benzoxazole derivative. The structure of HL1 and H(2)L2 were confirmed by NMR-spectroscopy and X-ray diffraction on a single crystal for HL1. The reaction of HL1 with CuCl(2) gives a mononuclear [Cu(II)(HL1)(2)Cl(2)] (1) complex for which the crystal structure shows that HL1 is preserved. In contrast, upon reaction with nickel(II), cobalt(II), and manganese(II) H(2)L2 is further oxidized and transformed in new ligands HL3 in mononuclear complexes [M(II)(L3)(2)] (M = Ni(II) (2); M = Co(II) (3)) and H(2)L4 in tetranuclear complex [Mn(II)(4)(HL4)(4)Cl(4)] (4) as found from the crystal structures of complexes 2-4. Electrochemical studies for complexes 2 and 3 evidence complicated redox properties. [Mn(II)(4)(HL4)(4)Cl(4)] (4) has a cubane-like structure with a "4 + 2" fashion The magnetic susceptibility of 4 is well fitted considering one Mn---Mn interaction J(a)(Mn(II)-Mn(II)) = -0.50(1) cm(-1) with g = 2.00(7).     

Synthesis of cis and trans bis-alkynyl complexes of Cr(III) and Rh(III) supported by a tetradentate macrocyclic amine: a spectroscopic investigation of the M(III)-alkynyl interaction

Alkynyl complexes of the type [M(cyclam)(CCR)(2)]OTf (where cyclam = 1,4,8,11-tetraazacyclotetradecane; M = Rh(III) or Cr(III); and R = phenyl, 4-methylphenyl, 4-trifluoromethylphenyl, 4-fluorophenyl, 1-naphthalenyl, 9-phenanthrenyl, and cyclohexyl) were prepared in 49% to 93% yield using a one-pot synthesis involving the addition of 2 equiv of RCCH and 4 equiv of BuLi to the appropriate [M(cyclam)(OTf)(2)]OTf complex in THF. The cis and trans isomers of the alkynyl complexes were separated using solubility differences, and the stereochemistry was characterized using infrared spectroscopy of the CH(2) rocking and NH bending region. All of the trans-[M(cyclam)(CCR)(2)]OTf complexes exhibit strong Raman bands between 2071 and 2109 cm(-1), ascribed to ν(s)(C≡C). The stretching frequencies for the Cr(III) complexes are 21-28 cm(-1) lower than for the analogous Rh(III) complexes, a result that can be interpreted in terms of the alkynyl ligands acting as π-donors. UV-vis spectra of the Cr(III) and Rh(III) complexes are dominated by strong charge transfer (CT) transitions. In the case of the Rh(III) complexes, these CT transitions obscure the metal centered (MC) transitions, but in the case of the Cr(III) complexes the MC transitions are unobscured and appear between 320 and 500 nm, with extinction coefficients (170-700 L mol(-1) cm(-1)) indicative of intensity stealing from the proximal CT bands. The Cr(III) complexes show long-lived (240-327 μs), structureless, MC emission centered between 731 and 748 nm in degassed room temperature aqueous solution. Emission characteristics are also consistent with the arylalkynyl ligands acting as π-donors. The Rh(III) complexes also display long-lived (4-21 μs), structureless, metal centered emission centered between 524 and 548 nm in degassed room temperature solution (CH(3)CN).     

Cr(III)(salen)Cl catalyzed asymmetric epoxidations: insight into the catalytic cycle

Intermediates of chromium-salen catalyzed alkene epoxidations were studied in situ by EPR, (1)H and (2)H NMR, and UV-vis/NIR spectroscopy (where chromium-salens were (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (1) and racemic N,N'-bis(3,4,5,6-tetra-deuterosalicylidene)-1,2-cyclohexanediamino chromium(III) chloride (2)). High-valence chromium complexes, intermediates of epoxidation reactions, were detected and characterized by EPR and NMR. They are the reactive mononuclear oxochromium(V) intermediate (A) Cr(V)O(salen)L (where L = Cl(-) or a solvent molecule) and an inactive chromium-salen binuclear complex (B) which acts as a reservoir of the active species. The latter complex demonstrates an EPR signal characteristic of oxochromium(V)-salen species and (1)H NMR spectra typical for chromium(III)-salen complexes, and it is identified as mixed-valence binuclear L(1)(salen)Cr(III)OCr(V)(salen)L(2) (L(1), L(2) = Cl(-) or solvent molecules). The intermediates Cr(V)O(salen)L and L(1)(salen)Cr(III)OCr(V)(salen)L(2) exist in equilibrium, and their ratio can be affected by addition of donor ligands (DMSO, DMF, H(2)O, pyridine). Addition of donor additives increases the fraction of A over that of B. The same two complexes can be obtained with m-CPBA as oxidant. Reactivities of the Cr(V)O(salen)L complexes toward E-beta-methylstyrene were measured in DMF. The L(1)(salen)Cr(III)OCr(V)(salen)L(2) intermediate has been proposed to be a reservoir of the true reactive chromium(V) species. The chromium-salen catalysts demonstrate low turnover numbers (ca. 5), probably due to ligand degradation processes.     

Molecular and electronic structures of bis-(o-diiminobenzosemiquinonato)metal(II) complexes (Ni, Pd, Pt), their monocations and -anions, and of dimeric dications containing weak metal-metal bonds

Two series of square planar, diamagnetic, neutral complexes of nickel(II), palladium(II), and platinum(II) containing two N,N-coordinated o-diiminobenzosemiquinonate(1-) pi radical ligands have been synthesized and characterized by UV-vis and (1)H NMR spectroscopy: [M(II)((2)L(ISQ))(2)], M = Ni (1), Pd (2), Pt (3), and [M(II)((3)L(ISQ))(2)] M = Ni (4), Pd (5), Pt (6). H(2)[(2)L(PDI)] represents 3,5-di-tert-butyl-o-phenylenediamine and H(2)[(3)L(PDI)] is N-phenyl-o-phenylenediamine; (L(ISQ))(1-) is the o-diiminobenzosemiquinonate pi radical anion, and (L(IBQ))(0) is the o-diiminobenzoquinone form of these ligands. The structures of complexes 1, 4, 5, and 6 have been (re)determined by X-ray crystallography at 100 K. Cyclic voltammetry established that the complete electron-transfer series consisting of a dianion, monoanion, neutral complex, a mono- and a dication exists: [M(L)(2)](z)z = -2, -1, 0, 1+, 2+. Each species has been electrochemically generated in solution and their X-band EPR and UV-vis spectra have been recorded. The oxidations and reductions are invariably ligand centered. Two o-diiminobenzoquinones(0) and two fully reduced o-diiminocatecholate(2-) ligands are present in the dication and dianion, respectively, whereas the monocations and monoanions are delocalized mixed valent class III species [M(II)(L(ISQ))(L(IBQ))](+) and [M(II)(L(ISQ))(L(PDI))](-), respectively. One-electron oxidations of 1 and trans-6 yield the diamagnetic dications [cis-[Ni(II)((2)L(ISQ))((2)L(IBQ))](2)]Cl(2) (7) and [trans-[Pt(II)((3)L(ISQ))((3)L(IBQ))](2)](CF(3)SO(3))(2) (8), respectively, which have been characterized by X-ray crystallography; both complexes possess a weak M.M bond and the ligands adopt an eclipsed configuration due to weak bonding interactions via pi stacking.     

Synthesis and photophysical properties of new chromium(III) complexes of N-derivatized 1,4,8,11-tetraazacyclotetradecane ligands cis-[Cr(1,8-R(2)cyclam)Cl(2)]Cl,where R is a pendant chromophore. exclusive formation of the cis isomer

Several new chromium(III) complexes have been synthesized utilizing derivatives of the macrocyclic ligand cyclam (1,4,8,11-tetraazacyclotetradecane) with various N-substituted chromophores in the 1 and 8 positions (1,8-R(2)cyclam) where R = CH(3), CH(2)Ph, CH(2)Nph (Nph = naphthyl), and CH(2)Anth (Anth = anthracyl). X-ray crystal structures were determined for all four complexes, and these are formed exclusively in the cis configuration with the two tertiary amines in the "hinge" positions (i.e., along the folding axis) of the coordinated ligand. As a result, the cis isomers appear to be inert to isomerization under conditions dramatically more forcing than needed to effect the cis to trans isomerization of the unsubstituted Cr(cyclam)Cl(2)(+) ion. Photophysical studies demonstrated that emission occurs solely from the metal-centered ligand field doublet excited states regardless of whether initial excitation is into the quartet ligand field bands or into the pi-pi bands of the pendant chromophore. Thus, excitation of the pendant chromophore results in efficient intramolecular energy transfer to the metal centered ligand field excited states.     

Stereoselective preparation, structures, and reactivities of phosphine-bridged mixed-metal trinuclear and pentanuclear complexes with tris[2-(diphenylphosphino)ethyl]phosphine

The phosphine-bridged linear trinuclear and pentanuclear complexes with Pd(II)-Pt(II)-Pd(II), Ni(II)-Pt(II)-Ni(II), and Rh(III)-Pd(II)-Pt(II)-Pd(II)-Rh(III) metal-ion sequences were almost quantitatively formed by the stepwise phosphine-bridging reaction of the terminal phosphino groups of tris[2-(diphenylphosphino)ethyl]phosphine (pp3), which is the tetradentate bound ligand of the starting Pd(II) and Ni(II) complexes. The solid-state structures of the trinuclear complexes were determined by X-ray structural analyses, and the structures of the polynuclear complexes in solution were characterized by NMR spectroscopy. The trans and cis isomers of the trinuclear and pentanuclear complexes, which arise from the geometry around the Pt(II) center, were selectively obtained simply by changing the counteranion of the starting complexes: the tetrafluoroborate salts, [MX(pp3)](BF4) [M = Pd(II) or Ni(II), X = Cl- or 4-chlorothiophenolate (4-Cltp-)], gave only the trans isomers, and the chloride salt, [PdCl(pp3)]Cl, gave only the cis isomers. The formation of the trinuclear complex with the 4-Cltp- and chloro ligands, trans-[Pt(4-Cltp)2{PdCl(pp3)}2](BF4)2, proceeded with exchange between the thiolato ligand in the starting Pd(II) complex, [Pd(4-Cltp)(pp(3))](BF4), and the chloro ligands in the starting Pt(II) complex, trans-[PtCl2(NCC6H5)2], retaining the trans geometry around the Pt(II) center. In contrast, the formation reaction between [PdCl(pp3)]Cl and trans-[PtCl2(NCC6H5)2] was accompanied by the trans-to-cis geometrical change on the Pt(II) center to give the trinuclear complex, cis-[PtCl2{PdCl(pp3)}2]Cl2. The mechanisms of these structural conversions during the formation reactions were elucidated by the 31P NMR and absorption spectral changes. The differences in the catalytic activity for the Heck reaction were discussed in connection with the bridging structures of the polynuclear complexes in the catalytic cycle.     

Iron(II) complexes with tetradentate bis(aminophenolate) ligands: synthesis and characterization, solution behavior, and reactivity with O(2)

Tetradentate bis(aminophenolate) ligands H(2)salan(X) and H(2)bapen(X) (where X refers to the para-phenolate substituent = H, Me, F, Cl) react with [Fe{N(SiMe(3))(2)}(2)] to form iron(II) complexes, which in the presence of suitable donor ligands L (L = pyridine or THF) can be isolated as the complexes [Fe(salan(X))(L)(2)] and [Fe(bapen(X))(L)(2)]. In the absence of donor ligands, either mononuclear complexes, for example, [Fe(salan(tBu,tBu))], or dinuclear complexes of the type [Fe(salan(X))](2) are obtained. The dynamic coordination behavior in solution of the complexes [Fe(salan(F))(L)(2)] and [Fe(bapen(F))(L)(2)] has been investigated by VT (1)H and (19)F NMR spectroscopy, which has revealed equilibria between isomers with different ligand coordination topologies cis-α, cis-β and trans. Exposure of the iron(II) salan(X) complexes to O(2) results in the formation of oxo-bridged iron(III) complexes of the type [{Fe(salan(X))}(2)(μ-O)] or [{Fe(salan(X))(L)}(2)(μ-O)]. The lack of catalytic activity of the iron(II) salan and bapen complexes in the oxidation of cyclohexane with H(2)O(2) as the oxidant is attributed to the rapid formation of stable and catalytically inactive oxo-bridged iron(III) complexes.     

En route to osmium analogues of KP1019: synthesis, structure, spectroscopic properties and antiproliferative activity of trans-[Os(IV)Cl4(Hazole)2

By controlled Anderson type rearrangement reactions complexes of the general formula trans-[Os(IV)Cl(4)(Hazole)(2)], where Hazole = 1H-pyrazole, 2H-indazole, 1H-imidazole, and 1H-benzimidazole, have been synthesized. Note that 2H-indazole tautomer stabilization in trans-[Os(IV)Cl(4)(2H-indazole)(2)] is unprecedented in coordination chemistry of indazole. The metal ion in these compounds possesses the same coordination environment as ruthenium(III) in (H(2)ind)[Ru(III)Cl(4)(Hind)(2)], where Hind = 1H-indazole, (KP1019), an investigational anticancer drug in phase I clinical trials. These osmium(IV) complexes are appropriate precursors for the synthesis of osmium(III) analogues of KP1019. In addition the formation of an adduct of trans-[Os(IV)Cl(4)(Hpz)(2)] with cucurbit[7]uril is described. The compounds have been comprehensively characterized by elemental analysis, EI and ESI mass spectrometry, spectroscopy (IR, UV-vis, 1D and 2D NMR), cyclic voltammetry, and X-ray crystallography. Their antiproliferative acitivity in the human cancer cell lines CH1 (ovarian carcinoma), A549 (nonsmall cell lung carcinoma), and SW480 (colon carcinoma) is reported.     

Probing the effects of ligand structure on activity and selectivity of Cr(III) complexes for ethylene oligomerisation and polymerisation

A series of distorted octahedral Cr(III) complexes containing tridentate S-, S/O- or N-donor ligands comprised of three distinct architectures: facultative {S(CH(2)CH(2)SC(10)H(21))(2) (L(1)) and O(CH(2)CH(2)SC(10)H(21))(2) (L(2))}, tripodal {MeC(CH(2)S(n)C(4)H(9))(3) (L(3)), MeC(CH(2)SC(10)H(21))(3) (L(4))} and macrocyclic {(C(10)H(21))[9]aneN(3) (L(5)), (C(10)H(21))(3)[9]aneN(3) (L(6)), with [9]aneN(3)=1,4,7-triazacyclononane} are reported and characterised spectroscopically. Activation of [CrCl(3)(L)] with MMAO produces very active ethylene trimerisation, oligomerisation and polymerisation catalysts, with significant dependence of the product distribution upon the ligand type present. The properties of the parent [CrCl(3)(L)] complexes are probed by cyclic voltammetry, UV-visible, EPR, EXAFS and XANES measurements, and the effects upon activation with Me(3)Al investigated similarly. Treatment with excess Me(3)Al leads to substitution of Cl ligands by Me groups, generation of an EPR silent Cr species (consistent with a change in the oxidation state of the Cr to either Cr(II) or Cr(IV)) and substantial dissociation of the neutral S and S/O-donor ligands.     

Anionic Fischer-type carbene complexes as bidentate (N,O) ligands

New polynuclear complexes, (L1)3M2 [M2 = Cr(III) (4a,4b), Fe(III) (5), Co(III) (8)], (L1)2M2(L2)2 [M2 = Co(II) (7), Ni(II) (9)], (L1)2M2(O)L2 [M2 = V(IV) (6)] and L1M2Cp2 [M2 = Ti(III) (10)] with L1 = (CO)5M1=C[C=NC(CH3)=CHS](O-)(M1 = Cr or W) and L2 = 4-methylthiazole or THF, are described. The molecular structures of these complexes determined by X-ray diffraction show that the Fischer-type carbene complexes act as bidentate ligands towards the second metal centre, coordinating through C(carbene)-attached O-atoms and imine N-atoms of the thiazolyl groups to form five-membered chelates with the oxygen atoms in the mer configuration. Isostructural complexes have similar characteristic band patterns in their far-IR spectra. Cyclic voltammetry of selected complexes reveals the oxidation of the carbene complex ligand between 1.01 and 1.29 V. Oxidation of the central metal (M2) takes place at 0.56 and 0.86 V for 7 and 9, respectively. Three stepwise reductions of Cr(III) to Cr(0) occur for 4a and 4b in the region -0.51 to -1.58 V. These new ligand types and other variants thereof should find application in ligand design with the first metal -- and other ligands attached thereto -- in the carbene complex ligand, playing an important role.     

Square planar vs tetrahedral coordination in diamagnetic complexes of nickel(II) containing two bidentate pi-radical monoanions

The reaction of three different 1-phenyl and 1,4-diphenyl substituted S-methylisothiosemicarbazides, H(2)[L(1-6)], with Ni(OAc)(2).4H(2)O in ethanol in the presence of air yields six four-coordinate species [Ni(L(1-6)(*))(2)] (1-6) where (L(1-6)(*))(1-) represent the monoanionic pi-radical forms. The crystal structures of the nickel complexes with 1-phenyl derivatives as in 1 reveal a square planar structure trans-[Ni(L(1)(-3)(*))(2)], whereas the corresponding 1,4-diphenyl derivatives are distorted tetrahedral as is demonstrated by X-ray crystallography of [Ni(L(5)(*))(2)] (5) and [Ni(L(6)(*))(2)] (6). Both series of mononuclear complexes possess a diamagnetic ground state. The electronic structures of both series have been elucidated experimentally (electronic spectra magnetization data). The square planar complexes 1-3 consist of a diamagnetic central Ni(II) ion and two strongly antiferromagnetically coupled ligand pi-radicals as has been deduced from correlated ab initio calculations; they are singlet diradicals. The tetrahedral complexes 4-6 consist of a paramagnetic high-spin Ni(II) ion (S(Ni) = 1), which is strongly antiferromagnetically coupled to two ligand pi-radicals. This is clearly revealed by DFT and correlated ab initio calculations. Electrochemically, complexes 1-6 can be reduced to form stable, paramagnetic monoanions [1-6](-) (S = (1)/(2)). The anions [1-3](-) are square planar Ni(II) (d,(8) S(Ni) = 0) species where the excess electron is delocalized over both ligands (class III, ligand mixed valency). In contrast, one-electron reduction of 4, 5, and 6 yields paramagnetic tetrahedral monoanions (S = (1)/(2)). X-band EPR spectroscopy shows that there are two different isomers A and B of each monoanion present in solution. In these anions, the excess electron is localized on one ligand [Ni(II)(L(4-6)(*))(L(4-6))](-) where (L(4-6))(2-) is the closed shell dianion of the ligands H(2)[L(4-6)] as was deduced from their electronic spectra and broken symmetry DFT calculations. Oxidation of 1 and 5 with excess iodine yields octahedral complexes [Ni(II)(L(1,ox))(2)I(2)] (7), [Ni(II)(L(1,ox))(3)](I(3))(2) (8), and trans-[Ni(II)(L(5,ox))(2)(I(3))(2)] (9), which have been characterized by X-ray crystallography; (L(1-)(6,ox)) represent the neutral, two-electron oxidized forms of the corresponding dianions (L(1-6))(2-). The room-temperature structures of complexes 1, 5, and 7 have been described previously in refs 1-5.     

Antimicrobial and antioxidant activities of new metal complexes derived from 3-aminocoumarin

3-Aminocoumarin (L) has been synthesized and used as a ligand for the formation of Cr(III), Ni(II), and Cu(II) complexes. The chemical structures were characterized using different spectroscopic methods. The elemental analyses revealed that the complexes where M=Ni(II) and Cu(II) have the general formulae [ML(2)Cl(2)], while the Cr(III) complex has the formula [CrL(2)Cl(2)]Cl. The molar conductance data reveal that all the metal chelates, except the Cr(III) one, are non-electrolytes. From the magnetic and UV-Visible spectra, it is found that these complexes have octahedral structures. The stability for the prepared complexes was studied theoretically using Density Function Theory. The total energy for the complexes was calculated and it was shown that the copper complex is the most stable one. Complexes were tested against selected types of microbial organisms and showed significant activities. The free radical scavenging activity of metal complexes have been determined by measuring their interaction with the stable free radical DPPH and all the compounds have shown encouraging antioxidant activities.     

Palladium(II), platinum(II), rhodium(III) and iridium(III) complexes coordinated with 2-aryl-4,5-dimethyl-1,2,3-triazoles as bidentate nitrogen-carbon chelate ligands

Summary Cyclometallations of 2-aryl-4,5-dimethyl-1,2,3-triazoles [H(C-N)] occur with palladium(II), platinum(II), rhodium(III) and iridium(III) chloride. Pallaciation and platination form [MCI(C-N)]₂, and rhodation and iridation [MCI(C-N)₂]₂ species. These complexes react with monodentate ligands, L, such as pyridine and tri-n-butylphosphine to give MCl(C-N)L and MCl(C-N)₂ L complexes. Corresponding bromo and iodo complexes are prepared by metathesis with lithium bromide and iodide. Spectroscopic data suggest that MX(C-N)L compounds (X = Cl, Br or I) have a structure withtrans-C,X andtrans-N,L, while [MX(C-N)₂ L] has atrans-N,N,cis-C,C, andcis-X,L structure.Author to whom all correspondence should be directed.