Chiral metal complexes. Part 22. Stereoisomers of the dichloro [3,6-diaza-2S,7S-di(2-pyridyl)octane] - cobalt(III) ion and related species

The reaction of 3,6-diaza-2S,7S-di(2-pyridyl)- octane, S,S-peaen, with Co(II) and O₂ in aqueous solution yields a mixture, from which may be isolated three chelate diastereomers after the addition of HCl and HClO₄. These are δ-α-[Co(S,S-peaen)Cl₂]- ClO₄ and its Λ-α and Δ-β analogues. Previous workers had reported that a second β-diastereoisomer could be obtained but it has been shown that this is in fact an isomeric mixture of both Δ-α- and Λ-α- [Co(S,S-peaen)Cl₂]ClO₄. All three isomers react with oxalate anions to form an apparently unique product Λ-α-[Co(S,S-peaen)ox]⁺ in aqueous solution and which can be crystallized as its perchlorate salt. Two of the reactions reported represent unusual examples of octahedral inversions.     

The synthesis and reaction kinetics of some Co(IIl) and Cr(III) chloro complexes of 1,4,8-Triazaoctane (2,3-tri) and the isolation of chiral trans-dichloro [CoCl2(NH3)(2,3-tri)] ClO4

The reaction of 2,3-tri with CrCl₃·6H₂O₁, dehydrated in boiling DMF, results in the formation of mer-CrCl₃(2,3-tri) and anation of hydrolysed solutions of mer-MCl₃(2,3,-tri) (M=Co, Cr) with 6 M HCl containing HClO₄, forms trans-dichloro- mer-[MCl₂(2,3-tri)(OH₂)]ClO₄·H₂O (M=Cr, Co; I, II). trans-Dinitro-mer-[Co(NO₂)₂(NH₃)(2,3-tri)] ClO₄ crystallises from the reaction between mer-Co(NO₂)₃(2,3-tri) and aqueous 7 M ammonia, on addition of NaClO₄·H₂O, and trans-dichloro-mer-[CoCl₂(NH₃)(2,3-tri)]ClO₄ (III) can be isolated by treatment of the dinitro with 12 M HCl. Reaction of mer-CoCl₃(2,3-tri) with C₂O₄₂⁻, followed by addition of aqueous NH₃ and NaClO₄·H₂O results in the isolation of racemic mer-[Co(ox)(NH₃)(2,3-tri)]ClO₄· H₂O. This complex was resolved into its enantiomeric forms and treatment of these with SOCl₂/MeOH/ HClO₄ gave the chiral forms of trans-dichloro-mer- [CoCl₂(NH₃)(2,3-tri)]ClO₄ (R or S at the see-NH center). The rates of loss of the first chloro ligand from these dichloro complexes have been measured spectrophotometrically in 0.1 M HNO₃ over a 15 K temperature range to give the following kinetic parameters; (I) k_H(298)=7.25 × 10⁻⁵ s⁻¹, E_a=78.5 kJ mol⁻¹, δS₂₉₈^#=₋69 J K⁻¹ mol⁻¹; (II) k_H(298)=4.00 × 10⁻³ s⁻¹, E_a=89.9, δS₂₉₈^#= +87.5; (III) k_H(298)=3.09 × 10⁻⁴ s⁻¹, E_a=103, δS₂₉₈^#=+27. Treatment of the dichloro cations with Hg²⁺/HNO₃ results in the generation of mer- M(2,3-tri)(OH₂)₃³⁺ (M=Cr, Co; IV, V) and trans- diaqua-mer-Co(NH₃)(2,3-tri)(OH₂)₂³⁺ (VI). The Co(III) cations isomerise to the fac configuration with (V) K_isom(298) μ=1.0 M)=2.97 × 10⁻⁵ s⁻¹, E_a=115, δS₂₉₈^#=+46. (VI) K_isom(298) (μ=1.0 M)=4.13 × 10⁻⁵ s⁻¹, E_a=113, δS₂₉₈^#=+52.     

Chromium(III) complexes with 1,5,9-triazanonane (3,3-tri) - CrX3(3,3-tri)n+ and CrCl(diamine)(3,3-tri)2+

The reaction of CrCl₃ · 6H₂O (dehydrated in DMSO) with 1,5,9-triazanonane (3,3-tri) gives mer- CrCl₃(3,3-tri), the configuration being established by isomorphism with the corresponding Co(III) complex. This non-electrolyte is hydrolyzed in aqueous acidic solution and mer-[CrCl₂(3,3-tri)- (OH₂)]ClO₄ can be isolated by anation with HCl in the presence of HClO₄. Reaction of mer-CrCl₃- (3,3-tri) in DMF with diamines produces complexes of the type [CrCl(diamine)(3,3-tri)] Cl₂ [diamine= 1,2-diaminoethane (en), 1.2-diaminopropane (pn), 1,3-diaminopropane (tn), 2,2-dimethyl-1,3-diaminopropane (Me₂tn) and cyclohexanediamine (chxn, cis plus trans mixture; two isomers A and B)] and these have been characterized as the ZnCl₄²⁻ salts. The configuration of the triamine ligand in these complexes has been established as mer-(H↓)- by a single crystal X-ray analysis of [CrCl(en)(3,3-tri)]- ZnCl₄, monoclinic, P2₁, a=7.932, b= 14.711, c= 8.312 Å, β=104.6° and Z=2, refined to a conventional R factor of 0.034. The kinetics of the Hg²⁺- assisted chloride release from [CrCl(diamine)(3,3- tri)]ZnCl₄ salts were measured spectrophotometrically (μ=1.0 M HClO₄ or HNO₃) over 15 K temperature ranges to give, in order, 10⁴k_Hg (298.2 K) (M⁻¹ s⁻¹), E_a(kJ mol⁻¹), ΔS^# (J K⁻¹ mol⁻¹): en- (HClO₄): 5.95, 78.1, -53; pn(HClO₄); 5.24, 81.2; -44; tn(HClO₄): 26.7, 85.6, -15; Me₂tn(HClO₄): 21.8, 78.6, -40; A-chxn(HNO₃): 7.60, 81.0,-41; B-chxn(HNO₃): 18.3, 56.8, -115. A ‘non-replaced ligand effect’ on the rate is observed for the first time in this series of homologous Cr(III) complexes. The kinetics of the thermal aquation (k_H, 0.1 M HClO₄) were measured titrimetrically for CrCl(diamine) (3,3-tri)²⁺ to give the following kinetic parameters: diamine=en: 10⁷ k_H (298.2)=5.34 s⁻¹, E_a=99.2 kJ mol⁻¹, ΔS^#=-40 J K⁻¹ mol^-1; diamine =tn: 10⁷ k_H (298.2)=5.04 s⁻¹, E_a= 82.8, ΔS^#= -96.     

Chiral metal complexes. 25. Cobalt(III) complexes of some linear mesomeric tetramine ligands

The complexes of Λ-α-[Co(R,S-picbn)Cl₂] ClO₄ (where R,S-picbn is 3R,4S-dimethyl-1,6-di(2-pyridyl)-2,5-diazahexane) together with its Δ-Λ-α and Δ,Λ-β exo congeners,Δ-Λ-β-exo-[Co(picchmn)Cl₂] ClO₄ (where picchmn is N,N'-di(2-picolyl)-1R, 2S-diaminocyclohexane) as well as Δ,Λ-β-endo-[Co(R,S-picstien)Cl₂] ClO₄·2H₂O, [Co(R,S-picstien)(ox)] ClO₄·0.5H₂O and [Co(R,S-picstien)(mal)] ClO₄·3H₂O (where picstien is 3R,4S-diphenyl-1,6-di(2-pyridyl)-2,5-diazahexane, ox is the oxalate dianion and mal is the malonate dianion) have been synthesised. The nature of the compounds was determined using a combination of ¹H NMR and, for certain chiral species, chiroptical techniques. In the various β complexes, the tetradentate is observed to adopt either the exo or endo geometry, specifically. Factors which influence coordination geometry include steric interactions and hydrophobic bonding effects.A number of chemical transformations between dinitro and dichloro complexes of Co(III) with R,S- picbn have been examined, as has the reaction of Δ,Λ-β-exo-[Co(R,S-picbn)Cl₂]⁺ with S-alanine in aqueous solution. The resulting product mixture contains eight of the sixteen possible β diastereoisomers, of which three have been isolated and characterised. The eight are composed of four β₁ and four β₂ isomers, however, and it is noted that isomerisation at the inplane amine nitrogen atom is restricted by the overall geometry of the complexes formed. Discriminatory forces in these complexes are small in magnitude, and exo/endo isomerisation is somewhat dependent upon the choice of ligand(s) used to complete the coordination sphere.     

Shape selectivity in outer-sphere electron transfer reactions

Chiral induction has been examined in the four diastereomeric products formed in a series of outer-sphere electron transfer reactions between the oxidants [Co(ox)₃]³⁻, [Co(edta)]⁻, [Co(gly)(ox)₂]²⁻, C₁-cis(N)-[Co(gly)₂(ox)]⁻, [Co(en)(ox)₂]⁻, C₂-cis(N)-[Co(gly)₂(ox)]⁻ and trans(N)-[Co(gly)₂(ox)]⁻ with [Co((RR,SS)-chxn)₃]²⁺ and [Co((R, S)-pn)₃]²⁺ as reductants. The products; [Co((RR,SS)-chxn)₃-lel₃]³⁺, [Co((RR,SS)-chxn)₃-lel₂ob]³⁺, [Co((RR,SS)-chxn)₃-lelob₂]³⁺, [Co((RR,SS)-chxn)₃-ob₃]³⁺ and corresponding species for [Co((R, S)-pn)₃]³⁺ show patterns of selectivity which are analyzed in terms of the size and structure of the reactants. The presence of a pseudo-C₃ carboxylate face on the oxidant enhances selectivity but the pattern is quite different for those oxidants that contain oxalate as one of their ligands compared with non-oxalate containing species such as [Co(edta)]⁻. A very simple model is developed in which the reductant employs a limited set of interactions corresponding to the major symmetry axes. The unrestricted reductant has very low aggregate selectvity. Steric and hydrogen bonding patterns in both oxidant and reductant enhance individual interactions resulting in the observed selectivities.     

Coordination chemistry of the heterotopic 1,2-phenylenebis(thio)diacetic acid ligand: Rhodium(I), palladium(II) and nickel(II) complexes

Starting from the heterotopic multidentate ligand 1,2-phenylenebis(thio)diacetic acid (1), cis-rac-[PdCl₂{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}] (2), cis-rac-[Rh{1,2-(HOOCCH₂S)₂C₆H₄-κ²S,S′}(cod)]BF₄ (3) and cis-rac-[Ni{1,2-(OOCCH₂S)₂C₆H₄-κ⁴O,O′S,S′}{cis-(C₃H₄N₂)}₂] (4) were prepared and characterised by X-ray diffraction and conventional spectroscopic techniques. Compounds 1-4 show extensive hydrogen-bonded networks (XH?O, X = O, N) in the solid state.     

Manganese (III) cyclam complexes with aqua, iodo, nitrito, perchlorato and acetic acid/acetato axial ligands

The syntheses, structures and magnetic properties of five new manganese (III) cyclam complexes, trans-[Mn(cyclam)(OH₂)₂](CF₃SO₃)₃ · H₂O, trans-[Mn(cyclam)I₂]I, trans-[Mn(cyclam)(ONO)₂]ClO₄, trans-[Mn(cyclam)(OClO₃)₂]ClO₄ and trans-[Mn(cyclam)(CH₃COO)(CH₃COOH)](ClO₄)₂, are reported. Cyclam is the tetradentate amine ligand 1,4,8,11-tetraazacyclotetradecane. The complexes all exhibit pronounced tetragonal elongation of the coordination octahedron with the four cyclam nitrogens occupying the four equatorial positions. The magnetic properties are consistent with the formulation of the complexes as high-spin d⁴ systems. trans-[Mn(cyclam)(OH₂)₂](CF₃SO₃)₃ · H₂O is shown to be a convenient starting material for the syntheses of trans cyclam complexes. [Mn(cyclam)(CH₃COO)(CH₃COOH)](ClO₄)₂ exhibits extremely short intermolecular hydrogen bonds resulting in a pseudo-chain structure. The tilt of the axial ligands with respect to the equatorial plane containing the manganese and the cyclam nitrogen atoms is discussed.     

Discovery of (1R,6S)-5-[4-(1-cyclobutyl-piperidin-4-yloxy)-phenyl]-3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one (R,S-4a): Histamine H3 receptor inverse agonist demonstrating potent cognitive enhancing and wake promoting activity

A series of fused cyclopropyl-4,5-dihydropyridazin-3-one (3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one) phenoxypiperidine analogs was designed and synthesized, leading to the identification of (1R,6S)-5-[4-(1-cyclobutyl-piperidin-4-yloxy)-phenyl]-3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one (R,S-4a) as a second-generation pyridazin-3-one H₃R antagonist. Compound R,S-4a was a potent H₃R functional antagonist in vivo in the rat dipsogenia model, demonstrated potent wake activity in the rat EEG/EMG model, and enhanced short-term memory in the rat social recognition memory model at doses as low as 0.03–0.3 mg/kg po.     

Complexes of N-thiophosphorylthioureas RNHC(S)NHP(S)(OiPr)2 (HL) (R = pyridin-2-yl, pyridin-3-yl, 6-amino-pyridin-2-yl) with copper(I): Crystal structures of Cu(PPh3)nL (n = 1, 2)

Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula RNHC(S)NHP(S)(OiPr)₂ [R = pyridin-2-yl (HL^a), pyridin-3-yl (HL^b), 6-amino-pyridin-2-yl (HL^c)] with Cu(PPh₃)₃I in aqueous EtOH/CH₂Cl₂ leads to mononuclear [Cu(PPh₃)₂L^a,b-S,S′] (1, 2) and [Cu(PPh₃)L^c-S,S′] (3) complexes. Using copper(I) iodide instead of Cu(PPh₃)₃I, polynuclear complexes [Cu_n(L-S,S′)_n] (4-6) were obtained. The structures of these compounds were investigated by IR, ¹H, ³¹P{¹H} NMR spectroscopy, ES-MS and elemental analyses. The crystal structures of Cu(PPh₃)₂L^b (2) and Cu(PPh₃)L^c (3) were determined by single-crystal X-ray diffraction.     

Fabacyl acetate, a germination stimulant for root parasitic plants from Pisum sativum

A germination stimulant, fabacyl acetate, was purified from root exudates of pea (Pisum sativum L.) and its structure was determined as ent-2′-epi-4a,8a-epoxyorobanchyl acetate [(3aR,4R,4aR,8bS,E)-4a,8a-epoxy-8,8-dimethyl-3-(((R)-4-methyl-5-oxo-2,5-dihydrofuran-2-yloxy)methylene)-2-oxo-3,3a,4,5,6,7,8,8b-decahydro-2H-indeno[1,2-b]furan-4-yl acetate], by 1D and 2D NMR spectroscopic, ESI- and EI-MS spectrometric, X-ray crystallographic analyses, and by comparing the ¹H NMR spectroscopic data and relative retention times (RR_t) in LC-MS and GC-MS with those of synthetic standards prepared from (+)-orobanchol and (+)-2′-epiorobanchol. The ¹H NMR spectroscopic data and RR_t of fabacyl acetate were identical with those of an isomer prepared from (+)-2′-epiorobanchol except for the opposite sign in CD spectra. This is the first natural ent-strigolactone containing an epoxide group. Fabacyl acetate was previously detected in root exudates of other Fabaceae plants including faba bean (Vicia faba L.) and alfalfa (Medicago sativa L.).     

Synthesis and antioxidant evaluation of (S,S)- and (R,R)-secoisolariciresinol diglucosides (SDGs)

Secoisolariciresinol diglucosides (SDGs) (S,S)-SDG-1 (major isomer in flaxseed) and (R,R)-SDG-2 (minor isomer in flaxseed) were synthesized from vanillin via secoisolariciresinol (6) and glucosyl donor 7 through a concise route that involved chromatographic separation of diastereomeric diglucoside derivatives (S,S)-8 and (R,R)-9. Synthetic (S,S)-SDG-1 and (R,R)-SDG-2 exhibited potent antioxidant properties (EC₅₀ = 292.17 ± 27.71 μM and 331.94 ± 21.21 μM, respectively), which compared well with that of natural (S,S)-SDG-1 (EC₅₀ = 275.24 ± 13.15 μM). These values are significantly lower than those of ascorbic acid (EC₅₀ = 1129.32 ± 88.79 μM) and α-tocopherol (EC₅₀ = 944.62 ± 148.00 μM). Compounds (S,S)-SDG-1 and (R,R)-SDG-2 also demonstrated powerful scavenging activities against hydroxyl [natural (S,S)-SDG-1: 3.68 ± 0.27; synthetic (S,S)-SDG-1: 2.09 ± 0.16; synthetic (R,R)-SDG-2: 1.96 ± 0.27], peroxyl [natural (S,S)-SDG-1: 2.55 ± 0.11; synthetic (S,S)-SDG-1: 2.20 ± 0.10; synthetic (R,R)-SDG-2: 3.03 ± 0.04] and DPPH [natural (S,S)-SDG-1: EC₅₀ = 83.94 ± 2.80 μM; synthetic (S,S)-SDG-1: EC₅₀ = 157.54 ± 21.30 μM; synthetic (R,R)-SDG-2: EC₅₀ = 123.63 ± 8.67 μM] radicals. These results confirm previous studies with naturally occurring (S,S)-SDG-1 and establish both (S,S)-SDG-1 and (R,R)-SDG-2 as potent antioxidants and free radical scavengers for potential in vivo use.     

Copper and manganese complexes with C2-multitopic ligands. X-ray crystal structure of [Cu(N,N′-bis[(S)-prolyl]phenylenediamine)H2O]. Catalytic properties

Eight mononuclear complexes with multitopic C₂-symmetry ligands, [Cu(L)]ClO₄, [Mn(L)Cl(H₂O)]PF₆, (L=N,N′-bis[(S)-prolyl]phenylenediamine (1), N,N′-bis[(S)-N-benzylprolyl]phenylenediamine (2), N,N′-bis{[(S)-pyrrolidin-2-yl]methyl}phenylenediamine (3), N,N′-bis-{[(S)-N-benzyl-pyrrolidin-2-yl]methyl}phenylenediamine (4)) have been prepared and characterised by analytical (elemental analysis, and mass spectroscopy) and FT IR, NMR and electronic spectroscopies. The data show that the ligands are neutral and coordinate to the metal in a tetradentate manner. The N,N′-bis[(S)-prolyl]phenylenediamine ligand also appears as an anionic species, (LH-2), and the single crystal structure determination of the respective complex, [Cu(1)]H₂O, is reported. This new family of Cu-complexes catalyse the cyclopropanation of styrene with ethyl and t-butyl diazoacetate to afford cis/trans 2-phenylcyclopropan-1-carboxylates with good yields and selectivity against dimerisation and low ee (<10%). On the other hand, the manganese and copper complexes also catalyse the oxidation of organic sulfides to sulfoxides with high selectivity, and moderate to low enantioselectivity. If an excess of oxidant were used the reaction yields sulfone as only product with excellent yield.     

Homogeneous CO hydrogenation and transfer hydrogenation catalyzed by ruthenium(II) complexes containing optically active Ph2PCH(Ph)CH(Me)NH2 and 1,2-C5H8(PPh2)2 ligands

Combination of (1S,2S)-cyclopentanediylbis(diphenylphosphine) with [Ru(η⁴-C₈H₁₂){η³-(CH₂)₂CMe}₂] afforded the chelate complex [Ru{η³-(CH₂)₂CMe}₂{(1S,2S)-C₅H₈(PPh₂)₂}] (1), which gave (OC-6-13)-[RuCl₂{(1S,2S)-C₅H₈(PPh₂)₂}{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂}] (2) upon reaction with methanolic HCl in acetone, followed by the addition of the β-aminophosphine in DMF. The (P ∩ N)₂-chelated complexes (OC-6-13)-[RuCl₂{(1S,2S)-Ph₂PCH(Ph)CH(Me)NH₂}₂] (3) and (OC-6-13)-[RuCl₂{(1R,2S)-Ph₂PCH(Ph)CH(Me)NH₂}₂] (4) resulted from RuCl₃ · 3H₂O and the P,N ligands under reducing conditions. The crystal structures of 3 and 4 were determined by single-crystal X-ray diffraction. Following activation by KOBu-t in isopropanol, compounds 2–4 catalyzed the enantioselective transfer hydrogenation of acetophenone with i-PrOH as the hydrogen source as well as the direct hydrogenation of the ketone by H₂ in low to moderate e.e. (up to 67%).     

Synthesis of (R,S)-[4-11C]baclofen via Michael addition of nitromethane labeled with short-lived 11C

The synthesis of (R,S)-[4-¹¹C]baclofen, the first ¹¹C-labeled GABA_B agonist, was demonstrated via Michael addition of nitro[¹¹C]methane as a key step. A tetrabutylammonium fluoride promoted Michael addition of nitro[¹¹C]methane to methyl p-chlorocinnamate, followed by the nitro-group reduction in the presence of NiCl₂ and NaBH₄ in aqueous MeOH and alkaline hydrolysis yielded (R,S)-[4-¹¹C]baclofen in 36.4 ± 1.8% radiochemical conversion in three steps within 20 min.     

Synthesis of (R,S)-isoproterenol,an inhibitor of tau aggregation,as an 11C-labeled PET tracer via reductive alkylation of (R,S)-norepinephrine with [2-11C]acetone

(R,S)-Isoproterenol inhibits the formation of toxic granular tau oligomers associated with neuronal loss and development of cognitive disorders, and is an attractive drug candidate for Alzheimer’s disease. To elucidate its behavior in the brain by positron emission tomography, we synthesize (R,S)-[¹¹C]isoproterenol by reductive alkylation of (R,S)-norepinephrine with [2-¹¹C]acetone, which was in turn synthesized in situ under improved conditions afforded a decay-corrected radiochemical yield of 54%. The reductive alkylation using NaBH(OAc)₃ as reducing agent in the presence of benzoic acid in DMSO/DMF (60:40 v/v) at 100 °C for 10 min gave (R,S)-[¹¹C]isoproterenol in an 87% radio-high performance liquid chromatography (HPLC) analytical yield. HPLC separation using a strong cation exchange column, followed by pharmaceutical formulation in the presence of d/l-tartaric acid, afforded (R,S)-[¹¹C]isoproterenol with a total radioactivity of 2.0 ± 0.2 GBq, a decay-corrected radiochemical yield of 19 ± 2%, chemical and radiochemical purities of 71% and >99%, respectively, and a molar activity of 100 ± 13 GBq/μmol (n = 3). The overall synthesis time from the end of the bombardment to pharmaceutical formulation was 48 min. A preliminary preclinical PET study in a rat demonstrated the potential of the radioligand for the evaluation of the penetration of (R,S)-isoproterenol in human brain.     

UV-Vis absorption study of some tetragonal chromium (III) complexes

A UV-Vis absorption study was performed in order to elucidate the electronic energy levels of three tetragonal chromium (III) complexes, namely trans-[Cr(en)₂(CN)₂]ClO₄, trans-[Cr(cyclam)(CN)₂]ClO₄, and trans-[Cr(NH₃)₄(CN)₂]ClO₄. The absorption spectra of the preceding complexes have been analyzed via Gaussian analysis to locate the quartet band maxima of the tetragonal components. The deconvoluted band maxima were then fitted with the tetragonal energy matrices of d³ configuration with full configuration interaction, neglecting spin-orbit interaction. The ligand field parameters D_q, D_t, and D_s along with the electron correlation parameters have been extracted via the fitting procedure. The significance of these parameters and the translated angular overlap model parameters has been discussed. We have also uncovered in the spectrum of the ethylenediamine complex the low intensity doublet absorption bands and a high intensity charge transfer band which have been tentatively assigned.     

Alteration of molecular conformations and spectral properties for nickel(II), zinc(II) and copper(II) complexes having 3,8-di(thiophen-2′,2′′-yl)-1,10-phenanthroline ligands

Four transition metal complexes of 3,8-di(thiophen-2′,2″-yl)-1,10-phenanthroline (dtphen), formulated as [Ni(dtphen)₂(H₂O)₂]·(ClO₄)₂ (1), [Zn(dtphen)₂(H₂O)]·(ClO₄)₂ (2) [Cu(dtphen)₂(H₂O)]·(ClO₄)₂ (3), [Cu(dtphen)(phen)₂]·(ClO₄)₂ (4) (phen = 1,10-phenanthroline) with different metal-to-ligand ratios, were synthesized and characterized herein. The X-ray single-crystal diffraction studies of 1-4 exhibit that different molecular configurations for the dtphen ligand can be observed where the side thiophene rings adopt the trans/trans, trans/cis, trans/disorder and cis/cis conformations relative to the central 1,10-phenanthroline unit in different compounds. Fluorescence emission spectra of 1-4 in methanol show that the fluorescence emission of 2 is much stronger than the other three metal complexes, which is mainly due to its full d¹⁰ electronic configuration of Zn(II) ion.     

Synthesis, structure, and catalytic activity of chiral Cu(II) and Ag(I) complexes with (S,S)-1,2-diaminocyclohexane-based N4-donor ligands

Condensation of (S,S)-1,2-cyclohexanediamine with 2 equiv. of 2-pyridine carboxaldehyde in toluene in the presence of molecular sieves at 70 °C gives N,N′-bis(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine (S,S-1) in 95% yield. Reduction of 1 with an excess of NaBH₄ in MeOH at 50 °C gives N,N′-bis(pyridin-2-ylmethyl)-(S,S)-1,2-cyclohexanediamine (S,S-2) in 90% yield. Reaction of 1 or 2 with 1 equiv. of CuCl₂ · 2H₂O in methanol gives complexes [N-(pyridin-2-ylmethylene)-(S,S)-1,2-cyclohexanediamine]CuCl₂ (3) and [Cu(S,S-2)(H₂O)]Cl₂ · H₂O (4), respectively, in good yields. Complex 4 can further react with 1 equiv. of CuCl₂ · 2H₂O in methanol to give [Cu(S,S-2)][CuCl₄] (5) in 75% yield. The rigidity of the ligand coupled with the steric effect of the free anion plays an important role in the formation of the helicates. Treatment of ligand S,S-1 with AgNO₃ induces a polymer helicate {[Ag(S,S-1)][NO₃]}_n (6), while reaction of ligand 2 with AgPF₆ or AgNO₃ in methanol affords a mononuclear single helicate [Ag(S,S-2)][PF₆] (7) or a dinuclear double helicate [Ag₂(S,S-2)₂][NO₃]₂ · 2CH₃OH (8) in good yields, respectively. All compounds have been characterized by various spectroscopic data and elemental analyses. Compounds 1, 3-5, 7 and 8 have been further subjected to single-crystal X-ray diffraction analyses. The Cu(II) complexes do not show catalytic activity for allylation reaction, in contrast to Ag(I) complexes, but they do show catalytic activity for Henry reaction (nitroaldol reaction) that Ag(I) complexes do not.     

Enlarging the family of ferrocenylphosphine dinuclear rhodium complexes: synthesis and X-ray structure of a novel “A-frame”-type trimetallic Rh/Fe/Rh complex

The symmetrically substituted ligand 1,1^′-bis[di(5-methyl-2-furyl)phosphino]ferrocene (1) has been obtained from the bromophosphine BrP(Fu^Me)₂ and the dilithioferrocene/TMEDA adduct. The quantitative addition of this ferrocene derivative to the tetracarbonyl dimer [(CO)₄Rh₂{μ-(S^tBu)₂}] leads, through decarbonylation, to the dinuclear rhodium complex [(CO)₂Rh₂{μ-(S^tBu)₂}{μ-P,P-Fc[P(Fu^Me)₂]₂}] (2) in high yield. A X-ray structure [orthorhombic, space group P2₁2₁2₁; a=11.2982(2) Å, b=13.3165(3) Å, c=27.2687(7) Å] and the solution multinuclear NMR characterization are reported, which show that the rare “quasi-closed bridging” A-frame structure of the complex is rather similar to the one reported for [(CO)₂Rh₂{μ-(S^tBu)₂}{μ-P,P-dppf}] in solid state. However, in solution the furyl-containing ferrocenylphosphine complex presents a greater fluxionality, together with an electronic environment at phosphorus very different from the dppf analogue (δ_P=−10 and 27 ppm, respectively).     

Preparation and characterization of (9-methyladenine)triammineplatinum(II) and trans-dihydroxo(9-methyladenine)triammineplatinum(IV) complexes

The preparation is reported of [(NH₃)₃Pt(9- MeA)] X₂ (9-MeA = 9-methyladenine) with XCl (1a) and XClO₄ (1b) and of trans-[(OH)₂Pt(NH₃)₃- (9-MeA)]X₂ with XCl (2a) and XClO₄ (2b), and the crystal structure of 1b. [(NH₃)₃Pt(C₆H₇N₅)](ClO₄)₂ crystallizes in space group P2₁/n with a = 20.810(7) Å, b = 7.697(3) Å, c = 10.567(4) Å, β = 91.57(6)°, Z = 4. The structure was refined to R = 0.054, R_w = 0.063. In all four compounds Pt coordination is through N7 of 9-MeA, as is evident from ³J coupling between H8 of the adenine ring and ¹⁹⁵Pt. Pt(II) and Pt(IV) complexes can be differentiated on the basis of different ³J values, larger for Pt(II) than for Pt(IV) by a factor of 1.57 (av). In Me₂SO-d₆, hydrogen bonding occurs between Cl^? and C(8)H of 9-MeA as weil as between Cl^? and the NH₃ groups in the case of the Pt(II) complex 1a. Protonation of the 9-MeA ligands was followed using ¹H NMR spectroscopy and pK_a values for the N1 protonated 9-MeA ligands were determined in D₂O. They are 1.9 for 1a and 1.8 for 2a, which compares with 4.5 for the non-platinated 9-MeA. Possible consequences for hydrogen bonding with the complementary bases thymine or uracil are discussed briefly. Protonation of the OH groups in the Pt(IV) complexes has been shown not to occur above pH 1.