Cyclopentadienyl Ruthenium(II) Complexes with Bridging Alkynylphosphine Ligands: Synthesis and Electrochemical Studies

The reaction of [CpRuCl(PPh₃)₂] (Cp=cyclopentadienyl) and [CpRuCl(dppe)] (dppe=Ph₂PCH₂CH₂PPh₂) with bis‐ and tris‐phosphine ligands 1,4‐(Ph₂PC≡C)₂C₆H₄ ( 1 ) and 1,3,5‐(Ph₂PC≡C)₃C₆H₃ ( 2 ), prepared by Ni‐catalysed cross‐coupling reactions between terminal alkynes and diphenylchlorophosphine, has been investigated. Using metal‐directed self‐assembly methodologies, two linear bimetallic complexes, [{CpRuCl(PPh₃)}₂(μ‐dppab)] ( 3 ) and [{CpRu(dppe)}₂(μ‐dppab)](PF₆)₂ ( 4 ), and the mononuclear complex [CpRuCl(PPh₃)(η¹‐dppab)] ( 6 ), which contains a “dangling arm” ligand, were prepared (dppab=1,4‐bis[(diphenylphosphino)ethynyl]benzene). Moreover, by using the triphosphine 1,3,5‐tris[(diphenylphosphino)ethynyl]benzene (tppab), the trimetallic [{CpRuCl(PPh₃)}₃(μ₃‐tppab)] ( 5 ) species was synthesised, which is the first example of a chiral‐at‐ruthenium complex containing three different stereogenic centres. Besides these open‐chain complexes, the neutral cyclic species [{CpRuCl(μ‐dppab)}₂] ( 7 ) was also obtained under different experimental conditions. The coordination chemistry of such systems towards supramolecular assemblies was tested by reaction of the bimetallic precursor 3 with additional equivalents of ligand 2 . Two rigid macrocycles based on cis coordination of dppab to [CpRu(PPh₃)] were obtained, that is, the dinuclear complex [{CpRu(PPh₃)(μ‐dppab)}₂](PF₆)₂ ( 8 ) and the tetranuclear square [{CpRu(PPh₃)(μ‐dppab)}₄](PF₆)₄ ( 9 ). The solid‐state structures of 7 and 8 have been determined by X‐ray diffraction analysis and show a different arrangement of the two parallel dppab ligands. All compounds were characterised by various methods including ESIMS, electrochemistry and by X‐band ESR spectroscopy in the case of the electrogenerated paramagnetic species.     

NEW RUTHENIUM(II) COMPLEXES CONTAINING ORGANODISULFIDE LIGANDS

Abstract

The new complexes [CpRu(PPh₃)₂(RSSR)PF₆ R=CH₃, iso-Pr, CH₂C₆H₅ and C₆H₅ have been prepared from the reaction of CpRu(PPh₃)₂Cl with RSSR in CH₃OH in presence of NH₄Cl. This result contrasts with the oxidative additions of RSSR to CpFe(dppe)1 dppe=PPh₂ (CH₂)₂PPh₂ to give [CpFe(dppe)SR]PF₆ (C. Diaz et al., J. Organomet. Chem. 516, 59 (1996)). Huckel calculations on model fragments CpFe(PPh₃)₂ and CpRu(PPh₃)₂ suggest that the higher electron density of iron could explain the differences observed in reactivity. Possible biological implications are discussed.     

Syntheses,Spectral and Electrochemical Investigation of Coordination Complexes of Octakis(benzylthio)tetraazaporphyrinmaganese(II)

Synthesis of [Mn(OBTTAP)], 1 and bichromophoric, di- and pentanuclear complexes with diimine-ruthenium(II) of the type [{Mn(OBTTAP)}{Ru(bpy)₂}][PF₆]₂, 2, [{Mn(OBTTAP)}{Ru(phen)₂}][PF₆]₂, 3, [{Mn(OBTTAP)}{RuCp(PPh₃)}][PF₆], 4, [{Mn(OBTTAP)}{Ru(bpy)₂}₄]- [PF₆]₈, 5, [{Mn(OBTTAP)}{Ru(phen)₂}₄][PF₆]₈, 6 and [{Mn(OBTTAP)}{RuCp(PPh₃)}₄][PF₆]₄, 7, (OBTTAP = octakis(benzylthio)tetraazaporphyrin) have been described. They were characterized using IR, ¹H NMR, UV–visible, and mass spectral data. In the electronic absorption spectra the relative intensities and positions of the Soret and Q-bands, in the di- and pentanuclear complexes were observed shifted vis-à-vis that in the precursor complex 1. They all exhibit strong S₂ emission. The emission intensity of the equimolar solutions of complexes 2, 3, 4 and 7 were found to be significantly higher than that of 1. The excitation-emission behaviors of the complexes are indicative of interchromophore energy transfer. Complexes 2–7 exhibited good electrode activity, particularly with multiple reversible redox waves in oxidative CV scans. The OBTTAP ring oxidations were observed as one or two reversible waves, depending upon number and nature of the peripheral metal units. Particularly, with four (bpy)₂Ru^II units bonded to the [Mn(OBTTAP)] periphery, it was observed as two reversible, one electron oxidation waves at E _1/2 0.81 and 1.02 V vs. Ag/AgCl. Also the Ru(II)/Ru(III) oxidations were observed at significantly lower potential, in this complex, at E_1/2 0.49 V vs Ag/AgCl due to weaker π-inteaction with dπ(S) orbitals.     

Synthesis and structural characterization of Ni(II) complexes with the chiral CpH(PNMent) tripod ligand

Treatment of NiCl₂ with the tripod ligand (L_Ment,S_C)-1H led to (L_Ment,S_C)-[Cp(PN_Ment)NiCl] in which the potentially tridentate ligand coordinated to the metal center in a bidentate way via the cyclopentadienyl system and the phosphorus atom. In the presence of NH₄PF₆ [(L_Ment,S_C)-[Cp(PN_Ment)NiCl] readily underwent Cl/PPh₃ exchange to give (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆. Reaction of (L_Ment,S_C)-[Cp(PN_Ment)NiCl] with 0.5 eq. of dppe afforded [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂. (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆ and [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂ were characterized by NMR and MS spectroscopy, and also by single crystal X-ray diffraction. The cyclopentadienyl ligand of (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆ shows a distortion intermediate between the ene-allyl and diene types, while the two cyclopentadienyl ligands of [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂ have intermediate and diene distortions, respectively. According to the temperature dependent NMR spectra of (L_Ment,S_C)-[Cp(PN_Ment)NiPPh₃]PF₆ and [{(L_Ment,S_C)-[Cp(PN_Ment)Ni]}₂dppe](PF₆)₂ two different conformations of the tether in the Cp(PN_Ment)Ni system could be frozen out at low temperatures.     

Reactivity Studies of η5‐ Indenyl and η5‐Cp* Ruthenium(II) Complexes towards some Polypyridyl Ligands

The reaction of [(η⁵‐L³)Ru(PPh₃)₂Cl], where; L³ = C₉H₇ ( 1 ), C₅Me₅ (Cp*) ( 2 ) with acetonitrile in the presence of [NH₄][PF₆] yielded cationic complexes [(η⁵‐L³)Ru(PPh₃)₂(CH₃CN)][PF₆]; L³= C₉H₇ ([3]PF₆) and L³ = C₅Me₅ ([4]PF₆), respectively. Complexes [3]PF₆ and [4]PF₆ reacts with some polypyridyl ligands viz, 2,3‐bis (α‐pyridyl) pyrazine (bpp), 2,3‐bis (α‐pyridyl) quinoxaline (bpq) yielding the complexes of the formulation [(η⁵‐L³)Ru(PPh₃)(L²)]PF₆ where; L³ = C₉H₇, L² = bpp, ([5]PF₆), L³ = C₉H₇, L² = bpq, ([6]PF₆); L³ = C₅Me₅, L² = bpp, ([7]PF₆) and bpq, ([8]PF₆), respectively. However reaction of [(η⁵‐C₉H₇)Ru(PPh₃)₂(CH₃CN)][PF₆] ([3]PF₆) with the sterically demanding polypyridyl ligands, viz. 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tptz) or tetra‐2‐pyridyl‐1,4‐pyrazine (tppz) leads to the formation of unexpected complexes [Ru(PPh₃)₂(L²)(CH₃CN)][PF₆]₂; L² = tppz ([9](PF₆)₂), tptz ([11](PF₆)₂) and [Ru(PPh₃)₂(L²)Cl][PF₆]; L² = tppz ([10]PF₆), tptz ([12]PF₆). The complexes were isolated as their hexafluorophosphate salts. They have been characterized on the basis of micro analytical and spectroscopic data. The crystal structures of the representative complexes were established by X‐ray crystallography.     

Syntheses and Structures of Ruthenium Complexes Containing a Ru‐H‐Tl Three‐Center–Two‐Electron Bond

Treatment of CpRuH(PP) (PP=dppm, dppe) with TlPF₆ produced [CpRu(H)(Tl)(PP)]PF₆. X‐ray diffraction and computational studies suggest that the complexes contain a Ru?H?Tl 3c–2e bond and can be viewed as the first σ‐complexes of period 6 main‐group hydrides [CpRu{η²‐(H?Tl)}(PP)]PF₆ or [Tl{η²‐H?RuCp(PP)}]PF₆. The complexes can be stored as a solid at room temperature for days without appreciable decomposition, but are unstable in solution and evolved to the trimetallic complexes [{CpRu(PP)}₂(μ‐Tl)]PF₆.     

Organometallic gold(I)–nickel(II)–aryldiethynyl (–C≡C(Ar)C≡C–) phosphine complexes: synthesis and multinuclear n.m.r. study

Silver triflate [AgOTf] assisted de-bromination gives [Ni(dppm/dppe/(PPh₃)₂)(OTf)₂], which on reaction with aryldiethynyls and gold(I) phosphines in CH₂Cl₂ medium, by the self assembly technique, leads to [{Ni(dppm/dppe/(PPh₃)₂}{(1,4-AB)Au(PPh₃)}₂] [{Ni₄(dppm/dppe/(PPh₃)₂)₄(1,4AB)₄}] [dppm/dppe = diphenyl phosphino-methane (1), -ethane (2), where OSO₂CF₃ is the triflate anion]. The maximum molecular peak of the corresponding molecule is observed in the ESI mass spectrum. I.r. spectra of the complexes show –C=C– and –C=N–, as well as phosphine stretching. The ¹H-n.m.r. spectra as well as ³¹P(¹H)-n.m.r. suggest solution stereochemistry, proton movement, phosphorus proton interaction. Considering all the moities there are a lot of carbon atoms in the molecule reflected by the ¹³C-n.m.r. spectrum. In the ¹H–¹H-COSY spectrum of the present complexes and contour peaks in the ¹H–¹³C-HMQC spectrum, assign the solution structure and stereo-retentive transformation in each step.     

Einelektronen-Redox-Reaktionen von Octamethyl[4]radialen: Nachweis der Alternanz geradzahliger Radialene

One-Electron Redox Reactions of Octamethyl[4]radialene: Proof of the Alternancy of Even-Membered Radialenes The photoelectron spectrum of octamethyl[4]radialene ( = tetrakis(dimethylmethylidene)cyclobutane) yields the rather low first vertical ionization of only 7.30 eV and, therefore, the molecule can be oxidized by AlCl₃/CH₂Cl₂ to its radical cation. The ESR and ENDOR signal patterns recorded are almost identical with those of the radical anion, generated in a [2.2.2]cryptand THF solution by reduction at a potassium metal mirror. Their near congruency is in accord with the alternant π molecular properties of even-membered radialenes as predicted by HMO theory, and larger changes of the D_2d structure of C₈(CH₃)₈ during the redox reactions are presumably hindered by the steric overcrowding in persubstituted [4]radialenes.     

Syntheses and characterization of some new 2-picolylpalladium(II) complexes

The 2-picolylpalladium(II) complex [{Pd(CH₂Py)Cl(PPh₃)}₂] (CH₂Py=2-picolyl) (I), prepared from 2-picolyl chloride and [Pd(PPh₃)₄], was treated with lithium bromide, silver acetate, 4-picoline (pic) and silver perchlorate, thallium acetylacetonate{Tl(acac)}, sodium dimenthyldithiocarbamate-water-(1/2) {Na(dmdc). 2 H₂O}, and 1,2-bis(diphenylphospino)ethane (dppe) to yield [{PdBr(CH₂Py)(PPh₃)}₂] (II), [{Pd(CH₂Py)OAc(PPh₃)}₂] (III), [{Pd(Ch₂Py)(pic)(PPh₃)}₂](ClO₄)₂ (IV), [Pd(CH₂Py)(acac)(PPh₃)] (V), [Pd(CH₂Py)(dmdc)(PPh₃)] (VI), and [Pd(Ch₂Py)Cl(dppe)] (VII), respectively. Halogen abstraction from VII using silver perchlorate afforded an ionic complex [{Pd(CH₂Py)(dppe)}₂](ClO₄)₂ (VIII). It was concluded that the 2-picolyl groups in these eight complexes are σ-bonded to palladium, and that in the dinuclear complexes I, II, III, IV, and VIII, they serve as bridging ligands.     

Cyclopentadienyl Ruthenium–Nickel Catalysts for Biomimetic Hydrogen Evolution: Electrocatalytic Properties and Mechanistic DFT Studies

The new dinuclear nickel–ruthenium complexes [Ni(xbsms)RuCp(L)][PF₆] (H₂xbsms=1,2‐bis(4‐mercapto‐3,3‐dimethyl‐2‐thiabutyl)benzene; Cp^?=cyclopentadienyl; L=DMSO, CO, PPh₃, and PCy₃) are reported and are bioinspired mimics of NiFe hydrogenases. These compounds were characterized by X‐ray diffraction techniques and display novel structural motifs. Interestingly, [Ni(xbsms)RuCpCO][PF₆] is stereochemically nonrigid in solution and an isomerization mechanism was derived with the help of density functional theory (DFT) calculations. Because of an increased electron density on the metal centers [Eur. J. Inorg. Chem. 2007 , 18 , 2613–2626] with respect to the previously described [Ni(xbsms)Ru(CO)₂Cl₂] and [Ni(xbsms)Ru(p‐cymene)Cl]⁺ complexes, [Ni(xbsms)RuCp(dmso)][PF₆] catalyzes hydrogen evolution from Et₃NH⁺ in DMF with an overpotential reduced by 180 mV and thus represents the most efficient NiFe hydrogenase functional mimic. DFT calculations were carried out with several methods to investigate the catalytic cycle and, coupled with electrochemical measurements, allowed a mechanism to be proposed. A terminal or bridging hydride derivative was identified as the active intermediate, with the structure of the bridging form similar to that of the Ni? C active state of NiFe hydrogenases.     

Influence of Central Metalloligand Geometry on Electronic Communication between Metals: Syntheses,Crystal Structures,MMCT Properties of Isomeric Cyanido‐Bridged Fe2Ru Complexes,and TDDFT Calculations

To investigate how the central metalloligand geometry influences distant or vicinal metal‐to‐metal charge‐transfer (MMCT) properties of polynuclear complexes, cis‐ and trans‐isomeric heterotrimetallic complexes, and their one‐ and two‐electron oxidation products, cis/trans‐ [Cp(dppe)Fe^IINCRu^II(phen)₂CN‐Fe^II(dppe)Cp][PF₆]₂ (cis/trans‐ 1 [PF₆]₂), cis/trans‐[Cp(dppe)Fe^IINCRu^II(phen)₂CNFe^III‐(dppe)Cp][PF₆]₃ (cis/trans‐ 1 [PF₆]₃) and cis/trans‐[Cp(dppe)Fe^IIINCRu^II(phen)₂CN‐Fe^III(dppe)Cp][PF₆]₄ (cis/trans‐ 1 [PF₆]₄) have been synthesized and characterized. Electrochemical measurements show the presence of electronic interactions between the two external Fe^II atoms of the cis‐ and trans‐isomeric complexes cis/trans‐ 1 [PF₆]₂. The electronic properties of all these complexes were studied and compared by spectroscopic techniques and TDDFT//DFT calculations. As expected, both mixed valence complexes cis/trans‐ 1 [PF₆]₃ exhibited different strong absorption signals in the NIR region, which should mainly be attributed to a transition from an MO that is delocalized over the Ru^II‐CN‐Fe^II subunit to a Fe^III d orbital with some contributions from the co‐ligands. Moreover, the NIR transition energy in trans‐ 1 [PF₆]₃ is lower than that in cis‐ 1 [PF₆]₃, which is related to the symmetry of their molecular orbitals on the basis of the molecular orbital analysis. Also, the electronic spectra of the two‐electron oxidized complexes show that trans‐ 1 [PF₆]₄ possesses lower vicinal Ru^II→Fe^III MMCT transition energy than cis‐ 1 [PF₆]₄. Moreover, the assignment of MMCT transition of the oxidized products and the differences of the electronic properties between the cis and trans complexes can be well rationalized using TDDFT//DFT calculations.     

Hexaaryl[3]radialenes

Reactions of diarylmethyl anions whose conjugate acids are more acidic than diphenylmethane with tetrachlorocyclopropene are found to afford hexaaryl-[3]radialenes in modest to good yields, thus leading to the first synthesis of hexaphenyl[3]radialene itself too; X-ray crystalographic analysis of hexakis(p-cyanophenyl)[3]radialene reveals a double three-bladed conformation.     

PREPARATION AND PROPERTIES OF DIAZENIDO,HYDRAZIDO(2-), AND HYDRIDO-HYDRAZIDO(2-) COMPLEXES OF TUNGSTEN. X-RAY PHOTOELECTRON SPECTROSCOPY OF DINITROGEN AND HYDRAZIDO(2-) COMPLEXES OF MOLYBDENUM AND TUNGSTEN

Abstract

Reactions of HBr with trans-[W(N₂)₂(dppe)PPh₂Me)₂] (1) (dppe = Ph₂CH₂CH₂PPh₂) result in protonation of coordinated N₂ but no formation of ammonia or hydrazine. The tungsten-containing product depends upon the reaction conditions: (i) in MeOH, the product formed is [WBr(NNH₂) (dppe)(PPh₂Me)₂]HBr₂ (2) which converts to the hydride, [WBr₂(H)(NNH₂(dppe)(PPh₂Me)](Br(3), with loss of phosphine in THF or CH₂Cl₂, (ii) in THF or CH₂Cl₂, the hydride (3) is formed directly. Reaction of 2 with Na₂CO₃ in MeOH results in the loss of HBr and the formation of the diazenido complex [WBr(NNH)(dppe)(PPh₂Me)₂] which reacts further with Na₂CO₃ in benzene under N₂ to lose HBr and form a mixture of 1 and trans-[W(N₂)(dppe)₂]. The reaction of 1 with aqueous HF forms [WF(NNH₂)(dppe)(PPh₂Me)₂]BF₄. The X-ray photoelectron spectra of trans-[M(N₂)₂ (dppe)₂], [MBr(NNH₂)(dppe)₂Br (M = Mo, W), [WCl(NNH₂)(dppe)₂]Cl, [WCl(N)(dppe)₂]Cl and [WCl(NH) (dppe)₂] are reported. In all of these complexes, nitrogen is in a highly reduced form.     

New organometallic Ru(II) and Fe(II) complexes with tetrathia-[7]-helicene derivative ligands

A series of organometallic complexes possessing new tetrathia-[7]-helicene nitrile derivative ligands [TH-7] as chromophores, of general formula [MCp(P–P)(NC{TH-[7]-Y}Z)][PF₆] (M = Ru, Fe, P–P = DPPE, Y = H, NO₂, Z = H, C≡N; M = Ru, L–L = 2PPh₃, Y = H, Z = H) has been synthesized and fully characterized. ¹H NMR, FT-IR and UV–Vis. spectroscopic data were analyzed with in order to evaluate the existence of electronic delocalization from the metal centre to the coordinated ligand to have some insight on the potentialities of these new compounds as non-linear optical molecular materials. Slow crystallization of compound [RuCp(PPh₃)₂(NC{TH-[7]-H}H)][PF₆] 2Ru revealed an interesting isomerization of the helical ligand with formation of two carbon-carbon bonds between the two terminal thiophenes, leading to the total closure of the helix (2*Ru).     

Tertiary phosphine-appended transition metal ferrocenyl dithiocarbamates: Syntheses,Hirshfeld surface,and electrochemical analyses

Five new heteroleptic complexes of Cu(I), Ag(I), and Ni(II) having formulae [Cu₃(dtc)₂(dppf)₂]PF₆ ( Cu-I ), [Cu₃(dtc)₂(dppe)₂]PF₆ ( Cu-II ), [Cu(PPh₃)₂(dtc)] ( Cu-III ), [Ag₃(dtc)₂(PPh₃)₂]NO₃ ( Ag-I ), and [Ni(dtc)(dppf)]PF₆ ( Ni-I ) (dtc = N-ethanol-N-methylferrocenyl-dithiocarbamate; dppf = 1,1′-bis(diphenylphosphino)ferrocene; dppe = 1,1′-bis(diphenylphosphino)ethane; PPh₃ = tripheylphosphine) have been synthesized and characterized using elemental analysis, Fourier-transform infrared, multinuclear nuclear magnetic resonance, UV–Vis spectroscopy, and single-crystal X-ray diffraction. The single-crystal X-ray diffraction studies indicate that Ag-I forms a rare trinuclear cluster in which the geometry around the two silver centers Ag1 and Ag3 is distorted tetrahedral, whereas the third silver center Ag2 shows a distorted trigonal planar geometry. The Ni-I complex has a distorted square-planar geometry around the Ni center. In addition, a side product [Ag₂{S₂(dppf)₂}] ( Ag-II ) was obtained during an attempt to synthesize [Ag(dppf)(dtc)], where the two Ag centers are bridged by two sulfido centers and coordinated with two phosphorus centers of the dppf ligand to give rise to a distorted tetrahedral geometry. The solid-state structures of Ag-I , Ni-I , and Ag-II are stabilized by a variety of weak interactions. The nature of these interactions has been addressed with the help of Hirshfeld surface analyses. In addition, the weak argentophilic interaction in Ag-I and Ag-II have been studied using quantum theory of atoms in molecules and natural bond orbital calculations. The electrochemical properties of the complexes have been investigated using cyclic voltammetry, where Cu-I and Cu-II exhibited two quasi-reversible waves, whereas Cu-III , Ag-I , Ag-II , and Ni-I exhibited only one quasi-reversible peak.     

Spectral, structural and DFT studies of platinum group metal 3,6-bis(2-pyridyl)-4-phenylpyridazine complexes and their ligand bonding modes

Reactions of 3,6-bis(2-pyridyl)-4-phenylpyridazine (L^ph) with [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = C₆H₆, p-ⁱPrC₆H₄Me and C₆Me₆), [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂, (M = Rh and Ir) and [(η⁵-Cp)Ru(PPh₃)₂Cl] (Cp = C₅H₅, C₅Me₅ and C₉H₇) afford mononuclear complexes of the type [(η⁶-arene)Ru(L^ph)Cl]PF₆, [(η⁵-C₅Me₅)M(L^ph)Cl]PF₆ and [(Cp)Ru(L^ph)(PPh₃)]PF₆ with different structural motifs depending on the π-acidity of the ligand, electronic properties of the central metal atom and nature of the co-ligands. Complexes [(η⁶-C₆H₆)Ru(L^ph)Cl]PF₆1, [(η⁶-p-ⁱPrC₆H₄Me)Ru(L^ph)Cl]PF₆2, [(η⁵-C₅Me₅)Ir(L^ph)Cl]PF₆5, [(η⁵-Cp)Ru(PPh₃)(L^ph)]PF₆, (Cp = C₅H₅, 6; C₅Me₅, 7; C₉H₇, 8) show the type-A binding mode (see text), while complexes [(η⁶-C₆Me₆)Ru(L^ph)Cl]PF₆3 and [(η⁵-C₅Me₅)Rh(L^ph)Cl]PF₆4 show the type-B binding mode (see text). These differences reflect the more electron-rich character of the [(η⁶-C₆Me₆)Ru(μ-Cl)Cl]₂ and [(η⁵-C₅Me₅)Rh(μ-Cl)Cl]₂ complexes compared to the other starting precursor complexes. Binding modes of the ligand L^ph are determined by ¹H NMR spectroscopy, single-crystal X-ray analysis as well as evidence obtained from the solid-state structures and corroborated by density functional theory calculations. From the systems studied here, it is concluded that the electron density on the central metal atom of these complexes plays an important role in deciding the ligand binding sites.     

Reaction of [CpRu(CH3CN)3]PF6 with bidentate ligands: structural characterization of [{CpRu(CH3CN)2}2(μ-η-dppe)](PF6)2 [dppe=1,2-bis(diphenylphosphino)ethane]

The reaction of [CpRu(CH₃CN)₃]PF₆ with the bidentate ligands L-L=1,2-bis(diphenylphosphino)ethane, dppe, and (1-diphenylarsino-2-diphenylphosphino)ethane, dpadppe, affords mononuclear or dinuclear complexes of formula [CpRu(η²-L-L)(CH₃CN)]PF₆, [{CpRu(CH₃CN)₂}₂(μ-η^1:1-L-L)](PF₆)₂ and [{CpRu(CH₃CN)}₂(μ-η^1:1-L-L)₂](PF₆)₂ (L-L=dppe, dpadppe). All of the compounds are characterized by microanalysis and NMR [¹H and ³¹P{¹H}] spectroscopy. The crystal structure of [{CpRu(CH₃CN)₂}₂(μ-η^1:1-dppe)](PF₆)₂ has been determined by X-ray diffraction analysis. The complex exhibits a dppe ligand bridging two CpRu(CH₃CN)₂ fragments.     

Hydroxylation of azomethine carbon: isolation of complexes of η5 and η6-cyclic hydrocarbon platinum group metals with a new Schiff-base ligand

A new Schiff base, (pyridin-2-yl)-N-(3,5-di(pyridin-2-yl)-4H-1,2,4-triazol-4-yl)methanimine, (L), was synthesized. Reaction of [(η⁶-arene)Ru(µ-Cl)Cl]₂ and [Cp*M(µ-Cl)Cl]₂ (M = Rh and Ir) with one equivalent of L in the presence of NH₄PF₆ in methanol yielded dinuclear complexes, [(η⁶-arene)₂Ru₂(L-OH)Cl](PF₆)₂ {arene = C₆H₆ (1), p-ⁱPrC₆H₄Me (p-cymene) (2) and C₆Me₆ (3)}, and [Cp*₂M₂(L-OH)Cl](PF₆)₂ [M = Rh (4) and Ir (5)], respectively, leading to the formation of five new chiral complexes with –OH on the azomethine carbon. L is a pentadentate ligand where one of the metal centers is coordinated to two nitrogen atoms in a bidentate chelating fashion while the other metal is bonded tridentate to three nitrogen atoms. Although the ligand is neutral before coordination, after complexation it is anionic (uni-negative) with negative charge on the azo nitrogen {see the structures: N(5) in 2[PF₆]₂ and N(3) for 4[PF₆]₂}. The complexes have been characterized by various spectroscopic methods including infrared and ¹H NMR and the molecular structures of the representative complexes are established by single-crystal X-ray diffraction studies.     

Ruthenium(II) complexes of aroylhydrazones: structural,electrochemical and electrostatic interactions with DNA

Four Ru(II) complexes with tridentate ligands viz. (4-hydroxy-N′-(pyridin-2-yl-ethylene) benzohydrazide [Ru(L¹)(PPh₃)₂(Cl)] (1), N′-(pyridin-2-yl-methylene) nicotinohydrazide [Ru(L²)(PPh₃)₂(Cl)] (2), N′-(1H-imidazol-2-yl-methylene)-4-hydroxybenzohydrazide [Ru(L³)(PPh₃)₂(Cl)] (3), and N′-(1H-imidazol-2-yl-methylene) nicotinohydrazide [Ru(L⁴)(PPh₃)₂(Cl)] (4) have been synthesized and characterized. The methoxy-derivative of L³H (abbreviated as L³H*) exists in E configuration with torsional angle of 179.4° around C₇-N₈-N₉-C₁₀ linkage. Single crystal structures of acetonitrile coordinated ruthenium complexes of 1 and 3 having compositins as [Ru(L¹)(PPh₃)₂(CH₃CN)]Cl (1a) and [Ru(L³)(PPh₃)₂(CH₃CN)]Cl (3a) revealed coordination of tridentate ligands with significantly distorted octahedral geometry constructed by imine nitrogen, heterocyclic nitrogen, and enolate amide oxygen, forming a cis-planar ring with trans-placement of two PPh₃ groups and a coordinated acetonitrile. Ligands (L¹H-L⁴H) and their ruthenium complexes (1–4) are characterized by ¹H, ¹³C, ³¹P NMR, and IR spectral analysis. Ru(II) complexes have reversible to quasi-reversible redox behavior having Ru(II)/Ru(III) oxidation potentials in the range of 0.40–0.71 V. The DNA binding constants determined by absorption spectral titrations with Herring Sperm DNA (HS-DNA) reveal that L⁴H and 1 interact more strongly than other ligands and Ru(II) complexes. Complexes 1–3 exhibit DNA cleaving activity possibly due to strong electrostatic interactions while 4 displays intercalation.