Equilibria in complexes ofN-heterocyclic molecules,part X. The pH dependent racemization of tris-(1,10-phenanthroline)nickel(II)

Summary Circular dichroism and electronic spectral measurements have established the existence of a covalent hydrate and a pseudobase arising from attack of H₂O or HO^– at the ligand in tris-(1,10-phenanthroline)nickel(II). In anhydrous solvents and strongly acidic solution, the complex is largely unsolvated. Over a large pH range the dominant species present in aqueous solution is the covalent hydrate while at high pH, this is converted into the pseudo-base. The existence of these species, and the equilibria between them in aqueous solution elegantly explains the pH dependent dissociation and racemization of the parent molecule. It further explains the non-linear variation of these reactions in mixed solvents and indicates that more than one mechanism is responsible over the range of solvents studied here and previously.Part IX,Transition Met. Chem., 2, 12 (1977).This ready change was pointed out to one of us (R.D.G.) some years ago by Professor B. Bosnich.     

Equilibria in complexes ofN-heterocyclic molecules,part IX. Circular dichroism study of nucleophilic attack at tris-(5-nitro1,10-phenanthroline)ruthenium(II)

Summary The reactions between Ho^–, CN^–, MeO^– and EtO^– and -(-)-tris-(5-vitro-1,10-phenantliroline)ruthenium(II) ion in solution were followed by c.d. measurements. The results support the earlier findings that these reactions proceed through the formation of pseudo-bases with the ligand.Part VIII: R. D. Gillard, L. A. P. Kane-Maguire and P. A. Williams,J. Chem. Soc. Dalton Trans. in press.     

Molecular orbital calculations of iron(II) complexes of diimine ligands

Summary Molecular orbital calculations using-, the INDO method have been carried out fm the [FeL(CN)₄]² and [FeLH(CN)₄] complexes, as well as for the tree ligands, with L 2 × pyridine, 1,10-phenanthroline.2,2-bipyridyl. 2,2-rimidine, 2, 3,3-bipyridazine and 4.4-bipyrimidine. Calculations of residual charge at carbon atoms in the ligand rings. correlating with relative nucleophilicity of the compounds, corresponds with observed differences of rate of reaction of the complex [FeI;]² With nucleophiles.     

Equilibria in complexes ofN-heterocyclic molecules,part XX. The reaction of hydroxide ion with bis-[2,4,6-tri-(2-pyridyl)-1,3,5-triazine] iron(II) and ruthenium(II)

Summary [Ru(TPT)₂]²⁺ undergoes nucleophilic attack at the ligand in aqueous solutions of HO^–. The reaction is reversible and the equilibrium can be followed spectrophotometrically. In acid solution, the free nitrogen atoms of the uncoordinated pyridine residues are protonated to form a new species. Two reactions of [Fe(TPT)₂]²⁺ take place in H₂O over extended periods. The first is the well-known dissociative process, but the second appears to involve reaction at the ligand. The results are used to reinterpret some of the chemistry of complexes of TPT and related ligands.Part XIX: J. A. Arce Sagüés, R. D. Gillard, R. J. Lancashire and P. A. Williams,J. Chem. Soc. Dalton Trans., in press.     

Equilibria in complexes ofN-heterocyclic molecules,Part XXIV. The reaction of nucleophiles with tris-(2,2′-bipyrimidine)iron(II) ion and its ruthenium(II) analogue

Summary The reactions of [Fe(bipym)₃]²⁺ and [Ru(bipym)₃]²⁺ with hydroxide ion in aqueous solution have been followed. The [Ru(bipym)₃]²⁺ species undergoes nucleophilic attack at the ligand to yield [Ru(bipym)₂(pyrimidine)(OH)]⁺ and [HCO₂]^– ion, involving cleavage of one pyrimidyl ring. Intermediates can be observed in the reaction of [Fe(bipym)₃]²⁺ with HO^–, N₃ ^– and SCN^–. The kinetics of the first reaction have been followed and the results are compared with those known for the reactions of [Fe(bipy)₃]²⁺, [Fe(phen)₃]²⁺ and similar compounds.Part XXIII: P. A. Williams,Transition Met. Chem., 78/84.     

Equilibria in complexes ofN-heterocyclic molecules. Part XXXII. Dissociation oftris-(5-halo-1,10-phenanthroline)iron(III) ions in acid solution

Summary The kinetics of reaction of thetris-(5-X-1,10-phenanthroline) iron(III) ions where X=Br or Cl have been studied in detail in 0–100% sulphuric acid solutions. Relationships between the rates of reactions and the activity of water have been examined. No reaction occurs without water present. The reactions are interpreted in terms of covalent hydrate and pseudo-base formation. By taking into account previous studies, rates and magnitudes of hydrate formation for these and some other related complexes can be estimated.phen 1,10-phenanthroline - bipy 2,2-bipyridyl - terpy 2,2; 6,2-terpyridyl Part XXXI: R. D. Gillard, D. W. Knight and P. A. Williams,Transition Met. Chem., 5, 321 (1980)     

Equilibria in complexes ofN-heterocyclic molecules,part XXII. The reaction of triaquo(2,4,6-tri-(2-pyridyl)-1,3,5-triazine) copper(II) and its nickel(II) and cobalt(II) analogues with water and hydroxide ion

Summary The kinetics of the reaction of [Cu(TPT)(H₂O)₃]²⁺ and [Ni(TPT)(H₂O)₃]²⁺ with H₂O have been followed and it has been shown that the formation of covalent hydrates is important in the understanding of these systems. The [Co(TPT)(OH)₃]^– compound and its Ni analogue are attacked by HO^– initially to form pseudo-base species and in, the case of Ni , the ligand then hydrolyses to yield a compound related to the carboximate formed when HO^– reacts with [Cu(TPT)(OH)₃]^–. In this reaction too, the formation of a pseudo-base, involving attack of HO^– at the triazine ring in the ligand is significant.Part XXI, ref. 2.     

Ethylene oligomerization by diimine iron(II) complexes/EAO

The catalytic properties of a series of Fe(II) diimine complexes (diimine=N,N′-o-phenylenebis(salicylideneaminato), N,N′-ethylenebis(salicylideneaminato), N,N′-o-phenylenebisbenzal, N,N′-ethylenebisbenzal) in combination with ethylaluminoxane (EAO) for ethylene oligomerization have been investigated. Treatment of the iron(II) complexes with EAO in toluene generates active catalytic systems in situ that oligomerize ethylene to low-carbon olefins. The effects of reaction temperature, ratios of Al/Fe and reaction periods on catalytic activity and product distribution have been studied. The activity of complex FeCl₂(PhCH=o-NC₆H₄N=CHPh) with EAO at 200°C is 1.35×10⁵ g oligomers/mol Fe·h, and the selectivity of C_4–10 olefins is 84.8%.     

Heteroleptic platinum(II) and palladium(II) complexes with thiacrown and diimine ligands

We wish to report the synthesis, crystal structures, spectroscopic and electrochemical properties of several new Pt(II) heteroleptic complexes containing the thiacrown, 9S3 (1,4,7-trithiacyclononane) with a series of substituted phenanthroline ligands and related diimine systems. These five ligands are 5,6-dimethyl-1,10-phenanthroline(5,6-Me₂-phen), 4,7-dimethyl-1,10-phenanthroline(4,7-Me₂-phen), 4,7-diphenyl-1,10-phenanthroline(4,7-Ph₂-phen), 2,2′-bipyrimidine(bpm), and pyrazino[2,3-f]quinoxaline or 1,4,5,8-tetraazaphenanthrene(tap). All complexes have the general formula [Pt(9S3)(N₂)](PF₆)₂ (N₂ = diimine ligand) and form similar structures in which the Pt(II) center is surrounded by a cis arrangement of the two N donors from the diimine chelate and two sulfur atoms from the 9S3 ligand. The third 9S3 sulfur in each structure forms a longer interaction with the platinum resulting in an elongated square pyramidal structure, and this distance is sensitive to the identity of the diimine ligand. In addition, we report the synthesis, structural, electrochemical, and spectroscopic properties of related Pd(II) 9S3 complex with tap. The ¹⁹⁵Pt NMR chemical shifts for the six Pt(II) complexes show a value near −3290 ppm, consistent with a cis-PtS₂N₂ coordination sphere although more electron-withdrawing ligands such as tap show resonances shifted by almost 100 ppm downfield. The physicochemical properties of the complexes generally follow the electron-donating or withdrawing properties of the phenanthroline substituents.     

Unsymmetrical diimine complexes of iron(II) and manganese(II): synthesis, structure and photoluminescence of an isomer

Two bis(unsymmetrical diimine) complexes of (L(NO(2))(?1))(L(NO(2))(?2))M(II)Cl(2) family with M = Fe and Mn, are reported (L(NO(2))(?) = (E)-3-nitro-N-(pyridine-2-ylmethylene)aniline; ? = dihedral angle between the diimine unit including pyridine ring and the phenyl ring planes). Pure tcc-(L(NO2)(33.6))(L(NO2)(79.3))Fe(II)Cl(2)·0.5H(2)O (1) and tcc-(L(NO2)(32.0))(L(NO2)(79.4))Mn(II)Cl(2)·0.5H(2)O (2) isomers have been successfully isolated in high yields and characterized by elemental analyses, variable temperature magnetic susceptibility measurements, IR, mass, UV-vis and M?ssbauer spectra including the single-crystal X-ray structure determinations that identified strong intermolecular non-bonding interactions in lattice (tcc refers to trans-cis-cis positions with respect to pyridine N-imine N-Cl donors). Geometries optimizations of all possible tcc, ttt, ctc, ccc and cct isomers of iron at the B3LYP/DFT level in gas-phase have shown that the tcc-isomer incorporating two non-equivalent ligands as in (L(NO(2))(42))(L(NO(2))(61))Fe(II)Cl(2), 1 (g), is stabilized by 6-20 kJ mol(-1) compared to other isomers where two ligands are equivalent. The frozen methanol glasses of 1 and 2 are luminescent at 77 K (1: λ(ext) = 370, λ(em) = 521 nm, χ(2) = 1.3, τ(avg) = 0.57 ns; 2: λ(ext) = 368, λ(em) = 524 nm, χ(2) = 1.1, τ(avg) = 0.90 ns). The DFT calculations have identified four closely spaced localized π(*) orbitals comprising of two non-equivalent ligands as UPMOs. The features contrast the tcc-isomer of (L(?))(2)Fe(II)Cl(2) (3), congener of 1 without -NO(2) substitution and non-emissive (bpy)(2)Fe(II)Cl(2) (4) where two ligands are equivalent. TD-DFT calculations have assigned intra-ligand (IL) and ligand to ligand charge transfer (LLCT) dominated excited states as the origin of luminescence of 1 and 2.     

Equilibria in complexes of N-heterocyclic molecules. Part 40. Electron densities in orbitals of iron(II) bound by N-heterocycles

Summary Calculated electron densities based on INDO molecular orbital calculations for aromatic carbon atoms and for iron 3d-orbitals in a series of complexes of chelating N-heterocycles (e.g. 2,2-bipyridyl) form the basis of a discussion for possible sites of nucleophilic substitution. Calculated charges on the ring atoms of quaternized and coordinated 1,10-phenanthroline are also compared.     

Equilibria in complexes of N-heterocyclic molecules,part XXI. Kinetics of reaction of hydroxide with bis [2,4,6-tri (2-pyridyl)-1,3,5-triazine] iron (II) and ruthenium(II)

Summary The kinetics of reaction of HO^– with [Ru(TPT)₂]²⁺ and [Fe(TPT)₂]²⁺ have been studied in detail. The former participates in an equilibrium with HO^– yielding a pseudo-base by attack at the ligand and, at very high concentrations of HO^–, dissociates to yield pure TPT quantitatively. [Fe(TPT)₂]²⁺ dissociates rapidly in basic solution, even at 273 K, however, [Fe(TPT)(TPT · OH)]+ does in fact exist and the Fell and Ru^ll reactions are quite similar, although that of Fell is much faster. The implications of these findings for the dissociation of [Fe(TPT)₂]²⁺ over a wide range of pH are discussed.Patt XX, ref. 1.     

Gaseous iron(II) and iron(III) complexes with BINOLate ligands

Electrospray ionization (ESI) of dilute solutions of 1,1'-bi-2-naphthol (BINOL) and iron(II) or iron(III) sulfate in methanol/water allows the generation of monocationic complexes of iron and deprotonated BINOL ligands with additional methanol molecules in the coordination sphere, and the types of complexes formed can be controlled by the valence of the iron precursors used in ESI. Thus, iron(II) sulfate leads to [(BINOLate)Fe(CH3OH)n]+ complexes (n=0-3), whereas usage of iron(III) sulfate allows the generation of [(BINOLdiate)-Fe(CH3OH)n]+ cations (n=0-2); here, BINOLate and BINOLdiate stand for singly and doubly deprotonated BINOL, respectively. Upon collision-induced dissociation, the mass-selected ions with n>0 first lose the methanol ligands and then undergo characteristic fragmentations. Bare [(BINOLdiate)Fe]+, a formal iron(III) species, undergoes decarbonylation, which is known as a typical fragmentation of ionized phenols and phenolates either as free species or as the corresponding metal complexes. The bare [(BINOLate)Fe]+ cation, on the other hand, preferentially loses neutral FeOH to afford an organic C20H12O+* cation radical, which most likely corresponds to ionized 1,1'-dinaphthofurane.     

Equilibria in complexes ofn-heterocyclic molecules,part XXVI. Reactions of hydroxide and water with the tris-(2,2′-bipyrazine)iron(II) and tris-[2,2′-bis-(5,6-dihydro-4-H-1,3-oxazine)]iron(II) ions

Summary The reactions of [Fe(bipyz)₃]²⁺ (bipyz = 2,2-bipyrazine) and [Fe(box)₃]²⁺ [box = 2,2-bis-(5,6-dihydro-4-H-1,3-oxazine] with H₂O and HO^– in aqueous solution have been followed. The [Fe(bipyz)₃]²⁺ ion is attacked at the ligand with both nucleophiles and the ligand is cleaved. A similar reaction between HO^– and [Fe(box)₃]²⁺ is observed. Detailed kinetics for all reactions are reported.phen 1,10-phenanthroline - bipy 2,2-bipyridyl - bipym 2,2-bipyrimidine Part XXV: R. D. Gillard, W. S. Walters and P. A. Williams,J. Chem. Soc. Dalton Trans., in press.     

Binding of pi-acceptor ligands to (triamine)iron(II) complexes

A series of (Me3TACN)FeII derivatives with soft coligands have been investigated, where Me3TACN is N,N',N"-trimethyl-1,4,7-triazacyclononane. Treatment of Me3TACN with FeCl2 afforded a compound with the empirical formula (Me3TACN)FeCl2 (1). Compound 1, which is a versatile precursor reagent, was shown by single-crystal X-ray diffraction to be the salt [(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3], containing isolated [(Me3TACN)2Fe2Cl3]+ and [(Me3TACN)FeCl3]- subunits. Treatment of 1 with NaBPh4 gave the known [(Me3TACN)2Fe2Cl3]BPh4, while the addition of Me3TACN to FeCl4(2-) gave [(Me3TACN)FeCl3]-. Oxygenation of 1 afforded [(Me3TACN)FeCl2]2(mu-O), which was shown crystallographically to be centrosymmetric with a pair of distorted octahedral Fe centers. The Fe-N bond trans to the Fe-O bond is elongated by 02 A relative to the other Fe-N distances. Solutions of 1 and thiolates absorb CO to give [(Me3TACN)Fe(SPh)(CO)2]BPh4 and (Me3TACN)Fe(S2C2H4)(CO) (nu CO = 1896 cm-1). Treatment of 1 with excess CN- afforded [(Me3TACN)Fe(CN)3]-, isolated as its PPh4+ salt 5. Crystallographic and spectroscopic studies show that 5 is low spin with a C3v structure; its Fe-N distances contracted by 023 A relative to those in [(Me3TACN)FeCl3]-. Aqueous solutions of 1 bind CO upon the addition of CN- to produce (Me3TACN)Fe(CN)2(CO) (6) Analogous to 6 is (Me3TACN)Fe(CN)2(CNMe), prepared by methylation of 5. The metastable dicarbonyl [(Me3TACN)FeI(CO)2]I was prepared by treatment of FeI2(CO)4 with Me3TACN and was crystallographically characterized as its BPh4- salt. Values of E1/2 for [(Me3TACN)FeCl3]-, 5, and 6 are -0409, -0640, and 0533 V vs Fc/Fc+, respectively.     

Spin-state splittings of iron(II) complexes with trispyrazolyl ligands

We report a computational study at the OPBE/TZP level on the chemical bonding and spin ground-states of mono-nuclear iron(II) complexes with trispyrazolylborate and trispyrazolylmethane ligands. We are in particular interested in how substitution patterns on the pyrazolyl-rings influence the spin-state splittings, and how they can be rationalized in terms of electronic and steric effects. One of the main observations of this study is the large similarity of the covalent metal–ligand interactions for both the borate and methane ligands. Furthermore, we find that the spin-state preference of an individual transition-metal (TM) complex does not always concur with that of an ensemble of TM-complexes in the solid-state. Finally, although the presence of methyl groups at the 3-position of the pyrazolyl groups leads to ligand–ligand repulsion, it is actually the loss of metal–ligand bonding interactions that is mainly responsible for shifts in spin-state preferences.     

DNA binding, prominent DNA cleavage and efficient anticancer activities of tris(diimine)iron(II) complexes

The complexes rac-[Fe(diimine)(3)](ClO(4))(2)1-4, where diimine = 2,2'-bipyridine (bpy) 1, 1,10-phenanthroline (phen) 2, 5,6-dimethyl-1,10-phenanthroline (5,6-dmp) 3 and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) 4, have been isolated, characterized and their interaction with calf thymus DNA studied by using a host of physical methods. The X-ray crystal structure of rac-[Fe(5,6-dmp)(3)](ClO(4))(2)3 has been determined and the packing diagram shows the presence of two enantiomeric forms of the complex cations in the same unit cell. The structures of 1-4 in solution have also been studied using UV-Visible, Cyclic Voltammetry and ESI-MS data and all data available suggests that they retain their solid state structures even in solution. The absorption spectral titrations of the iron(ii) complexes with CT DNA reveal that the DNA binding affinities of the complexes vary in the order, 4 (K(b): 9.0 × 10(3)) > 2 (6.8 × 10(3)) > 3 (4. 8 × 10(3)) > 1 (2.9 × 10(3) M(-1)). The DNA interaction of dpq complex (4) involves partial insertion of the extended phen ring in between the DNA base pairs, which is deeper than that of phen (2). The 5,6-dmp (3) complex is involved in groove binding in the major groove of DNA. The lower DNA binding affinity of 1 is due to electrostatic interaction of the cationic complexes with exterior phosphates of DNA. The EthBr displacement assay and DNA viscosity study support these DNA binding modes and the above trend in DNA binding affinities. The complexes of 1 and 2 show induced CD (ICD) upon interaction with CT DNA while 3 and 4 bound to DNA exhibit inversion in the positive band with the helicity band showing very small changes, which implies that 3 and 4 bind enantiopreferentially to DNA. The DNA cleavage abilities of 1-4 have been observed at 10 μM concentration of complexes in the presence of 100 μM H(2)O(2) and the DNA cleavage efficiency (> 90%) follows the order 3 > 1 > 2 > 4. The anticancer activity of 1-4 against human breast cancer cell line (MCF-7) has also been studied. The IC(50) values of the complexes at different incubation time intervals of 24 and 48 h follow the order, 3 (0.8, 0.6) < 4 (20.0, 17.0) < 2 (28.0, 22.0) < 1 (32.0, 29.0 μM). Interestingly, 3 exhibits anticancer activity more potent than 1, 2 and 4 and cisplatin for both 24 and 48 h. It induces cell death both through apoptosis and necrosis mechanisms, as revealed by morphological assessment data obtained by using AO/EB and Hoechst 33258 fluorescence staining methods.     

Photophysics of diimine platinum(II) bis-acetylide complexes

A comprehensive photophysical investigation has been carried out on a series of eight complexes of the type (diimine)Pt(-C=C-Ar)(2), where diimine is a series of 2,2'-bipyridine (bpy) ligands and -C=C-Ar is a series of substituted aryl acetylide ligands. In one series of complexes, the energy of the Pt --> bpy metal-to-ligand charge transfer (MLCT) excited state is varied by changing the substituents on the 4,4'- and/or the 5,5'-positions of the bpy ligand. In a second series of complexes the electronic demand of the aryl acetylide ligand is varied by changing the para substituent (X) on the aryl ring (X = -CF(3), -CH(3), -OCH(3), and -N(CH(3))(2)). The effect of variation of the substituents on the excited states of the complexes has been assessed by examining their UV-visible absorption, variable-temperature photoluminescence, transient absorption, and time-resolved infrared spectroscopy. In addition, the nonradiative decay rates of the series of complexes are subjected to a quantitative energy gap law analysis. The results of this study reveal that in most cases the photophysics of the complexes is dominated by the energetically low lying Pt --> bpy (3)MLCT state. Some of the complexes also feature a low-lying intraligand (IL) (3)pi,pi excited state that is derived from transitions between pi- and pi-type orbitals localized largely on the aryl acetylide ligands. The involvement of the IL (3)pi,pi state in the photophysics of some of the complexes is signaled by unusual features in the transient absorption, time-resolved infrared, and photoluminescence spectra and in the excited-state decay kinetics. The time-resolved infrared difference spectroscopy indicates that Pt --> bpy MLCT excitation induces a +25 to + 35 cm(-)(1) shift in the frequency of the C=C stretching band. This is the first study to report the effect of MLCT excitation on the vibrational frequency of an acetylide ligand.     

Equilibria in complexes of N-heterocyclic ligands. Part 33. Ruthenium(II) complex ions with chelating pyridyl-imidazoles

Summary The complex salts [RuL₃] (ClO₄)₂ · nH₂O have been made, where L = 2-(2-pyridyl)imidazole and n = 2 or 2-(2-pyridyl)-benzimidazole, n = 3. Spectra are discussed, including circular dichroism (the complex ions having resulted from asymmetric syntheses).Author to whom correspondence should be directed.