Coordination chemistry of H-spirophosphorane ligands towards pentacarbonylchlororhenium(I) – synthesis,structure and catalytic activity of complexes

Synthesis of a group of carbonyl rhenium coordination compounds with hydrospirophosphorane ligands was carried out and described. Different symmetrical HP(OCH₂CH₂NH)₂ L1 , HP(OCH₂CMe₂NH)₂ L2 , HP(OC₆H₄NH)₂ L3 , and unsymmetrical ligands HP (OCMe₂CMe₂O)(OC₆H₄NH) L4 were found to coordinate to the rhenium center as bidentate P,N donor ligands yielding fac-[ReCl (CO)₃ Ln ], where n = 1 – 4. Furthermore, monodentate coordination was also observed in some cases, as was clearly presented in the case of [ReCl(CO)₂( L4- κ²P,N)( L4- κP)] complex. All of the complexes were characterized using optical spectroscopy. Single-crystalX-ray diffraction was also performed in the case of fac-[ReCl(CO)₃ L3 ], fac-[ReCl(CO)₃ L4 ], [Re(CO)₂( L2 )₂]Cl and [ReCl (CO)₂( L4- κ²P,N)( L4- κP)] samples. Complexes [ReCl(CO)₃ L3 ] and [ReCl (CO)₃ L4 ], both bearing rings of conjugated double bonds within hydrospirophosphorane ligands, exhibited luminescence. Catalytic properties of rhenium complexes were assessed using the representative fac-[ReCl (CO)₃ L2 ] complex in the dimerization reaction of terminal alkynes. An efficient and selective procedure for synthesis of the E - enynes was developed. Coupling of (2-chlorophenyl)acetylene was mediated by [ReCl (CO)₃ L2 ]/TBAF system with a 100% conversion rate. Different substituents within aromatic alkynes were tolerated and the resulting products were dependent on the nature of the substituents.     

Voltammetric behaviour of rhenium(I) complexes with phosphine and carbon monoxide ligands in acetonitrile solvent

Summary The anodic and cathodic behaviour of the complexesmer-[ReCl(CO)₃(PMe₂Ph)₂],fac[ReCl(CO)₃(PMe₂Ph)₂],mer-[ReCl(CO)₃(PPh₃)₂], and [ReCl(CO)₂(PMe₂Ph)₃] in acetonitrile solvent were studied using platinum and mercury electrodes. Cyclic voltammetry and controlled potential coulometry were the main electroanalytical techniques employed. The nature of the electrolysis products and of the electrode oxidation and reduction processes were investigated. In particular, [ReCl(CO)(MeCN)₂(PMe₂Ph)₃][ClO₄]₂, [ReCl₃(CO)₂(PMe₂Ph)₂], and a not completely defined rhenium(-I) complex were electrochemically synthesized and characterized by means of i.r. and¹H n.m.r. spectroscopy, and by elemental analysis.     

Electroanalytical study of the kinetics of thefac-mer isomerization of [ReCl(CO)3(PMe2Ph)2]+ in acetonitrile

Summary The isomerization offac-[ReCl(CO)₃(PMe₂Ph)₂]⁺ to the corresponding meridional-trans isomer has been studied by electroanalytical techniques in MeCN solvent. Chronoamperometric and cyclic voltammetric data relative to the oxidation offac- andmer-[ReCl(CO)₃(PMe₂Ph)₂] allow the accurate determination of the very high kinetic rate constant for the isomerization and permit discussion of thermodynamic aspects of redox homogeneous chemical reactions involving species of the different redox couples arising from the anodic processes.     

Spectroscopic and DFT studies of photoactivatable Mn(I) tricarbonyl complexes

A combined experimental study and density functional theory calculations of fac‐[MnBr (CO)₃L] complexes (L = 2‐(2′‐pyridyl)benzimidazole ligand, furnished with either morpholine (L^morph) or phthalimido (L^phth) side‐chain) were performed using different spectral and analytical tools. The synthesized complexes released carbon monoxide upon the exposure to LED source light at 468 nm. Illumination of fac‐[MnBr (CO)₃L] (10 μM) in the myoglobin solution (Mb) produced about 25 μM MbCO. The plateau of the CO release process is attained within 25 min. With the aid of time‐dependent density functional theory calculations, the observed lowest energy absorption transition at ~ 400 nm has a ground‐state composed of d (Mn)/π (pyridyl) and excited‐state of ligand π*‐orbitals forming MLCT/π‐π^*. Natural population analyses of fac‐[MnBr (CO)₃L] were carried out to get information about the strength of Mn–CO bonds, electronic arrangment and natural charge of manganese ion.     

The optical sensor fac-tri­carbonyl­chloro­(di-2-pyridyl­methanone p-nitro­phenyl­hydrazone)­rhenium(I) di­methyl sulfoxide solvate

The first metal complex of di-2-pyridyl­methanone p-nitro­phenyl­hydrazone (dpknph), i.e. the title compound, fac-[ReCl(C₁₇H₁₃N₅O₂)(CO)₃]·C₂H₆OS, crystallizes as well separated pseudo-tetrahedral DMSO (DMSO is di­methyl sul­foxide) and pseudo-octahedral fac-[ReCl(dpknph)(CO)₃] moieties. Two N atoms from dpknph, three C atoms from the carbonyl groups and one chloride ion occupy the coordination sphere around rhenium. The coordinated dpknph ligand forms a six-membered ring in a boat conformation, with the pyridine rings in a butterfly formation. The p-nitro­phenyl­hydrazone moiety is planar, with all C and N atoms in sp²-hybridized forms. The mol­ecules pack as stacks of interlocked fac-[ReCl(dpknph)(CO)₃]·DMSO units via a network of non-covalent bonds that include solute–solute, solvent–solute and π–π interactions.     

Solution fluxionality of some pyridine-2,6-dialdehydes, -diketones and -diesters when acting as bidentate ligands in rhenium(I) and platinum(IV) complexes. Crystal structure of [ReBr(CO)3L] (L=methylethyldipicolinate)

2,6-Disubstituted pyridines, where the substituents are aldehyde, ketone or ester functions, form bidentate chelate complexes with the transition metal moieties fac-Re^IX(CO)₃ (X=halogen). 2-Substituted pyridines, where the substituents are aldehyde or ester functions, form similar types of complexes with the isoelectronic transition metal moieties fac-Re^IX(CO)₃ and Pt^IVXMe₃. The fac-Re^IX(CO)₃ complexes of the 2,6-disubstituted pyridine ligands were shown by ¹H NMR spectra to undergo metallotropic shifts whereby the Re coordination switches between adjacent ON pairs of the ONO ligand donor set. Rates and activation energies of these fluxional shifts were measured by dynamic NMR bandshape analysis. Magnitudes of ΔG³ (298.15 K) were in the range 59–64 kJ mol⁻¹ for the diketone and diester ligands. The dialdehyde ligand, 2,6-pyridinedicarboxaldehyde, formed an appreciably less-stable Re^I complex that was highly fluxional and showed a tendency to dissociation at ambient solution temperatures. The unsymmetrical diester ligand, methylethyldipicolinate, formed two distinct Re^I complex species in solution, in the approximate abundance ratio of 2:1, the more abundant structure involving coordination to the carbonyl of the ethyl ester function. This particular complex forms exclusively in the solid state and an X-ray crystal structure of [ReBr(CO)₃L] (L=methylethyldipicolinate) is reported.     

Synthesis,structure, and photochemistry of a rhenium(I) enolate complex

The rhenium(I) enolate complex fac-(CO)₃(P(CH₃)₃)₂Re(OC(CH₃)C₅H₄) (4 was prepared from the reaction of (η⁵-C₅H₄C(O)CH₃)Re(CO)₃ (3) with P(CH₃)₃. Compound 4 was characterized structurally in the solid state by X-ray crystallography and in solution by IR and ¹H, ¹³C, and ³¹P NMR spectroscopy. Photolysis of 4 at 337 nm in CH₂Cl₂ solution cleaves the ReO bond: smooth conversionto fac-(CO)₃(P(CH₃)₃)₂ReCl (5) is observed with a quantum yield of 0.04.     

[M(CO)2(NO)], a new core in bioorganometallic chemistry: model complexes of [Re(CO)2(NO)] and [Tc(CO)2(NO)]

In this study selected bidentate (L²) and tridentate (L³) ligands were coordinated to the Re(I) or Tc(I) core [M(CO)₂(NO)]²⁺ resulting in complexes of the general formula fac-[MX(L²)(CO)₂(NO)] and fac-[M(L³)(CO)₂(NO)] (M = Re or Tc; X = Br or Cl). The complexes were obtained directly from the reaction of [M(CO)₂(NO)]²⁺ with the ligand or indirectly by first reacting the ligand with [M(CO)₃]⁺ and subsequent nitrosylation with [NO][BF₄] or [NO][HSO₄]. Most of the reactions were performed with cold rhenium on a macroscopic level before the conditions were adapted to the n.c.a. level with technetium (^99mTc). Chloride, bromide and nitrate were used as monodentate ligands, picolinic acid (PIC) as a bidentate ligand and histidine (HIS), iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) as tridentate ligands. We synthesised and describe the dinuclear complex [ReCl(μ-Cl)(CO)₂(NO)]₂ and the mononuclear complexes [NEt₄][ReCl₃(CO)₂(NO)], [NEt₄][ReBr₃(CO)₂(NO)], [ReBr(PIC)(CO)₂(NO)], [NMe₄][Re(NO₃)₃(CO)₂(NO)], [Re(HIS)(CO)₂(NO)][BF₄], [⁹⁹Tc(HIS)(CO)₂(NO)][BF₄], [^99mTc(IDA)(CO)₂ (NO)] and [^99mTc(NTA)(CO)₂(NO)]. The chemical and physical characteristics of the Re and Tc-dicarbonyl-nitrosyl complexes differ significantly from those of the corresponding tricarbonyl compounds.     

Chelating and Tellurolate Ligand‐Transfer Studies of the Complex fac‐[Fe(CO)3(TePh)3]−: Crystal Structures of Heterodinuclear (CO)3Mn(μ‐TePh)3Fe(CO)3 and CpNi(TePh)(PPh3)

Complex fac‐[Fe(CO)₃(TePh)₃]^? was employed as a “metallo chelating” ligand to synthesize the neutral (CO)₃Mn(μ‐TePh)₃Fe(CO)₃ obtained in a one‐step synthesis by treating fac‐[Fe(CO)₃(TePh)₃]^? with fac‐[Mn‐(CO)₃(CH₃CN)₃]⁺. It seems reasonable to conclude that the d⁶ Fe(II) [(CO)₃Fe(TePh)₃]^? fragment is isolobal with the d⁶ Mn(I) [(CO)₃Mn(TePh)₃]^2? fragment in complex (CO)₃Mn(μ‐TePh)₃Fe(CO)₃. Addition of fac‐[Fe(CO)₃(TePh)₃]^? to the CpNi(I)(PPh₃) in THF resulted in formation of the neutral CpNi(TePh)(PPh₃) also obtained from reaction of CpNi(I)(PPh₃) and [Na][TePh] in MeOH. This investigation shows that fac‐[Fe(CO)₃(TePh)₃]^? serves as a tridentate metallo ligand and tellurolate ligand‐transfer reagent. The study also indicated that the fac‐[Fe(CO)₃(SePh)₃]^? may serve as a better tridentate metallo ligand and chalcogenolate ligand‐transfer reagent than fac‐[Fe(CO)₃(TePh)₃]^? in the syntheses of heterometallic chalcogenolate complexes.     

Ligand exchange and complex formation kinetics studied by NMR exemplified on fac-[(CO)3M(H2O)] (M = Mn, Tc, Re)

In this review ligand exchange and complex formation reactions on fac-[(CO)₃M(H₂O)₃]⁺ (M = Mn, Tc, Re) and on fac-[(CO)₂(NO)Re(H₂O)₃]²⁺ are presented. A variety of experimental NMR techniques are described and it is shown that sometimes combinations of techniques applied at variable temperature or variable pressure allowed to measure exchange rate constants and their activation parameters as well as thermodynamic parameters. Furthermore, the use of uncommon nuclei for NMR like ¹⁷O or ⁹⁹Tc extends considerably the range of applications especially in aqueous solutions when ¹H NMR is often not very useful.Tricarbonyl triaqua complexes of technetium(I) and rhenium(I) became important precursors for a variety of radiopharmaceuticals under development. It has been shown that the fac-[(CO)₃M]-unit is kinetically inert and that water molecules bound to it can be easily replaced. Reactivity of the Re^I complexes is one to two orders of magnitude slower than its Tc^I analogues. Furthermore, it shows a marked acidity dependence which has not been observed for Tc^I and Mn^I species.     

Reaktionen des Gallium‐haltigen Heterocyclus [Me2Ga{HNC(Me)}2CCN]

Reactions of the Gallium‐containing Heterocycle [Me₂Ga{HNC(Me)}₂CCN] The reaction of [Me₂Ga{HNC(Me)}₂CCN] ( 1 ) with fac‐[Mo(CO)₃(MeCN)₃] leads after addition of TMEDA to the molybdenum complex fac‐[Mo(CO)₃( 1 )(TMEDA)] ( 2 ). Under identical reaction conditions with fac‐[W(CO)₃(MeCN)₃] only the tetracarbonyle complex [W(CO)₄(TMEDA)] ( 3 ) could be isolated. Treatment of dilithiated 1 with Me₂SiCl₂ or InCl₃ initiate a fragmentation of the skeleton in 1 . Obtained were the salt [Me₂Ga(TMEDA)][Me₂GaCl₂] ( 4 ) and the indium complex [Me₂InCl(TMEDA)] ( 5 ), respectively. 2 — 5 were investigated by spectroscopical and spectrometrical methods as well as by X‐ray structure determinations. According to these 1 occupies a facial site in 2 by donation of the N‐Atom from the NC group in 1 . The molecules 2 are forming a network of hydrogen bonds. In 3 , the TMEDA ligand acts as an intramolecular chelate ligand. In the salt 4 , the cation as well as the anion are coordinated in a distorted tetrahedral environment, while in 5 a distorded trigonal‐bipyramidal coordination‐sphere is present, leading to a elongated In1‐Cl1 distance of 261.74(9) pm.     

Structures of rhenium(I) complexes with 3‐hydroxyflavone and benzhydroxamic acid as O,O′‐bidentate ligands and confirmation of π‐stacking by solid‐state NMR spectroscopy

The synthesis and crystal structures of two new rhenium(I) complexes obtained utilizing benzhydroxamic acid (BHAH) and 3‐hydroxyflavone (2‐phenylchromen‐4‐one, FlavH) as bidentate ligands, namely tetraethylammonium fac‐(benzhydroxamato‐κ²O,O′)bromidotricarbonylrhenate(I), (C₈H₂₀N)[ReBr(C₇H₆NO₂)(CO)₃], 1 , and fac‐aquatricarbonyl(4‐oxo‐2‐phenylchromen‐3‐olato‐κ²O,O′)rhenium(I)–3‐hydroxyflavone (1/1), [Re(C₁₅H₉O₃)(CO)₃(H₂O)]·C₁₅H₁₀O₃, 3 , are reported. Furthermore, the crystal structure of free 3‐hydroxyflavone, C₁₅H₁₀O₃, 4 , was redetermined at 100 K in order to compare the packing trends and solid‐state NMR spectroscopy with that of the solvate flavone molecule in 3 . The compounds were characterized in solution by ¹H and ¹³C NMR spectroscopy, and in the solid state by ¹³C NMR spectroscopy using the cross‐polarization magic angle spinning (CP/MAS) technique. Compounds 1 and 3 both crystallize in the triclinic space group P with one molecule in the asymmetric unit, while 4 crystallizes in the orthorhombic space group P2₁2₁2₁. Molecules of 1 and 3 generate one‐dimensional chains formed through intermolecular interactions. A comparison of the coordinated 3‐hydroxyflavone ligand with the uncoordinated solvate molecule and free molecule 4 shows that the last two are virtually completely planar due to hydrogen‐bonding interactions, as opposed to the former, which is able to rotate more freely. The differences between the solid‐ and solution‐state ¹³C NMR spectra of 3 and 4 are ascribed to inter‐ and intramolecular interactions. The study also investigated the potential labelling of both bidentate ligands with the corresponding fac‐^99mTc‐tricarbonyl synthon. All attempts were unsuccessful and reasons for this are provided.     

The ONN-complexes of dioxomolybdenum(VI) with dibasic 2-hydroxy-1-naphthaldehyde<Emphasis Type="Italic"> S</Emphasis>-methyl/allyl-4-phenyl-thiosemicarbazones

New dioxomolybdenum(VI) complexes were prepared by reacting S-methyl/allyl-4-phenyl-thiosemicarbazones of 2-hydroxy-1-naphthaldehyde (L ¹ H₂ and L ² H₂) and [MoO₂(acac)₂] in methyl, ethyl and propylalcohols. In the complexes the doubly deprotonated ligands are coordinated to molybdenum as tridentate ONN-donors through phenolic-oxygen, azomethine- and thioamide-nitrogen. The solid complexes of general formula [MoO₂L(ROH)] which contain an alcohol (ROH) as second ligand were characterized by physico-chemical and spectroscopic methods. The fluorescence emission intensities of the compounds were recorded in chloroform, and the intensity changes were evaluated depending on chelation and time. The structure of the S-allyl-4-phenyl-thiosemicarbazone complex has been determined by the single crystal X-ray diffraction method. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Imidazole-based bifunctional chelates for the “fac-[Re(CO)3]” core

Three monocationic rhenium(I) complexes of the type [Re(CO)₃(L)]Br, containing the bis-imidazole tridentate ligands bis-(2-(1-methylimidazolyl)methyl)amine (L¹), bis-(2-(1-methylimidazolyl)methyl)aminoethanol (L²) and bis-(2-(benzimidazolyl)ethyl)sulfide (L³), were prepared and characterized by ¹H NMR and IR spectroscopy. The complex salt [Re(CO)₃(L²)]Br (2) was also characterized by X-ray crystallography. The structure consists of discrete monocationic monomers with a fac-[Re(CO)₃]⁺ coordination unit, and the remaining three sites are occupied by one amine and two imidazolyl nitrogen donor atoms.     

Tricarbonylrhenium(I) complexes with <Emphasis Type="Italic">N,N′</Emphasis>-bis(2- and 4-nitrobenzaldehyde)-1,2-diiminoethane Schiff base ligands: synthesis,spectroscopic and crystal structure studies

fac-[Re(CO)₃(2-nben)Cl] and fac-[Re(CO)₃(4-nbzen)Cl] complexes consisting of 2-nbzen = N,N′-bis(2-nitrobenzaldehyde)-1,2-diiminoethane and 4-nbzen = N,N′-bis(4-nitrobenzaldehyde)-1,2-diiminoethane were synthesized by the reaction of Re(CO)₅Cl with nbzen ligands. These complexes were characterized by physico-chemical, spectroscopic methods and X-ray crystallography. The electrochemical behavior of the two complexes was investigated by cyclic voltammetry. In the crystal structure of [Re(CO)₃(4-nbzen)Cl], the neighbouring molecules are linked together by intermolecular C–H···Cl interactions to form 1D extended chains along the b-axis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Syntheses,structural studies and spectroscopic characterisation of pyridyl–phthalimide complexes of fac-(CO)3ReI-diimines

The mono-dentate ligands, 3-aminomethyl-N-phthalimido-pyridine (L¹) and 3-amino-N-phthalimido-pyridine (L²), were synthesised using a solvent-free melt method. These ligands were then used to access three pairs of functionalised luminescent Re^I complexes of the generic type fac-{Re(CO)₃(diimine)(Lⁿ)}(BF₄) [where diimine = 4,4′-dimethyl-2,2′-bipyridine (dmb); 2,2′-bipyridine (bpy); 1,10-phenanthroline (phen)]. X-ray crystallography has been used to structurally characterise five of the complexes showing that in the cases of the L¹ species the phthalimide unit is adjacent to and co-planar with the coordinated diimine ligand. Solution state UV–Vis absorption, electrochemistry and IR studies confirm that the proposed formulations and coordination modes exist in solution. The photophysical studies show that the visible emission from each of the six complexes is ³MLCT at room temperature. Within each pair of complexes the precise energy of the emission was subtly dependent upon the axial ligand, Lⁿ with luminescence lifetimes in the range 121–288 ns.     

The preparation and synthetic value of fac-[M(CO)3(NCR)3]+ cations (M  Mn or Re; R  Et,Pr OR PhCH2)

Treatment of MBr(CO)₅ (M = Mn or Re) with AgClO₄ and an organonitrile in a suitable solvents affords the complexes fac-[M(CO)₃(NCR)₃][ClO₄], (R = Et, Pr or PhCH₂). The use of these complexes as synthetic precursors has been illustrated by the preparation of fac-[M(CO)₃L₃][ClO₄], (M = Mn, L = NH₃ or L₃ = dien; M = Re, L₃ = triphos). Pure fac-[Re(CO)₃(NH₃)₃][ClO₄] could not be prepared using this nitrile displacement route, but may be isolated, as the PF₆^? salt, from the reaction of [Re(CO)₃(toluene)][PF₆] and ammonia in chloroform.     

Electro-optical properties of the first rhenium-hydrazone complex,fac-Re(CO)3(dpknph)*Cl

Reaction between Re(CO)₅Cl and dpknph in PhMe under reflux gave fac-Re(CO)₃(dpknph)Cl in good yield. Both dpknph and fac-Re(CO)₃(dpknph)Cl exhibit rich electro-optical properties that are sensitive to their surroundings and point to the potential use of these compounds in nonlinear optics and molecular sensing. Spectroscopic and electrochemical measurements on solutions of dpknph and fac-Re(CO)₃(dpknph)Cl show that the metal complex undergoes faster electron/charge-transfer than the free ligand. Solvent variations show that the rate increases in the following order: DMSO>DMF>MeCN.     

The unprecedented role of a Cu<Superscript>II</Superscript> cryptand in the luminescence properties of a Eu<Superscript>III</Superscript> cryptate complex

Abstract  A Eu^III cryptate complex constructed from a Cu^II cryptand with an L ^tBu ligand, [Eu^IIICu₂^II(L ^tBu)₂(NO₃)₃(MeOH)], and the corresponding Ca^II and Na^I cryptates, [Ca^IICu₂^II(L ^tBu)₂(NO₃)₂(MeOH)₂] and [Na^ICu₂^II(L ^tBu)₂(Me₂CO)](BPh₄), have been synthesized and characterized in order to shed light on the essential role of Cu^II in the luminescence of a Eu^III cryptate. The unprecedented role of a Cu^II cryptand makes it possible to produce lanthanide luminescence in a Eu^III cryptate complex and is successfully elucidated by comparison with the corresponding Ca^II and Na^I cryptates. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and Characterization of Di‐ and Tricarbonylhydridomanganese(I) Complexes

Hydrido complexes [MnH(CO)₃L^1–3] [L¹ = 1,2‐bis‐(diphenylphosphanoxy)‐ethane ( 1 ); L² = 1,2‐bis‐(diisopropylphosphanoxy)ethane ( 2 ); L³ = 1,3‐bis‐(diphenylphosphanoxy)‐propane ( 3 )] were prepared by treating [MnH(CO)₅] with the appropriate bidentate ligand by heating to reflux. Photoirradiation of a toluene solution of complexes 1 and 2 in the presence of PPh_n(OR)_3–n (n = 0, 1; R = Me, Et) leads to the replacement of a CO ligand by the corresponding monodentate phosphite or phosphonite ligand to give new hydrido compounds of formula [MnH(CO)₂(L^1–2)(L)] [L = P(OMe)₃ ( 1a – 2a ); P(OEt)₃ ( 1b – 2b ); PPh(OMe)₂ ( 1c – 2c ); PPh(OEt)₂ ( 1d – 2d )]. All complexes were characterized by IR, ¹H, ¹³C and ³¹P NMR spectroscopy. In case of compounds 2 and 3 , suitable crystals for X‐ray diffraction studies were isolated.