Metal-organic frameworks constructed from 2,4,6-Tris(4-pyridyl)-1,3,5-triazine

Five new metal-organic frameworks based on 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt) ligand have been hydrothermally synthesized. Reaction of tpt and AgNO 3 in an acidic solution at 180 degrees C yields {[Ag(Htpt)(NO3)]NO(3).4H2O}n (1).Ag(I) is trigonally coordinated by two pyridyl nitrogen and one nitrato oxygen to form a 1D zigzag chain. Reaction of tpt with CuSO4 affords {[Cu2(tpt)2(SO4)2(H2O)2].4H2O}n (2). Copper(II) is bonded to two pyridyl nitrogen, two sulfato oxygen, and two water oxygen atoms to form an elongated octahedral geometry. Each H2O ligand bridges two copper(II), whereas sulfate bridges copper(II) via micro-1,3 and micro-1,1 fashions. The copper(II)-sulfate-H2O2D layers are linked by bidentate tpt to form a 3D polymeric structure. Reaction of Cu(SO4)2, tpt, and 1,2,4,5-benzenetetracarboxylic acid (H4btec) in the presence of piperidine gives [Cu(tpt)(H2btec)1/2]n (3). Copper(I) is located in a trigonal-pyramidal coordination environment and coordinated by three pyridyl nitrogen of tpt in a plane, whereas a carboxylate oxygen is coordinated to the copper(I) axially. The tpt-Cu forms a layer, and the layers are linked through H 2btec2- to form a 2D double-layered coordination polymer. Replacing CuSO4 with ZnI2 in the synthesis gives {[Zn(tpt)(btec)1/2].H2O}n (4). Zinc(II) is in a distorted tetrahedral geometry and linked through bidentate tpt and exotetradentate btec4- to form a 2D coordination grid. Reaction of tpt with CuCN leads to the assembly of a 3D metal-organic framework [Cu3(CN)3(tpt)]n (5). Copper(I) is trigonally coordinated by one pyridyl nitrogen and two cyanides to form an intriguing honeycomb architecture. Luminescence study shows that 1, 3, 4, and 5 have blue fluorescence, which can be assigned to be ligand-centered emissions. Thermal analysis shows that all of these complexes are quite stable, and especially for 4, the framework is stable up to 430 degrees C.     

Syntheses,structures, luminescent and magnetic properties of two coordination polymers based on a fl exible multidentate carboxylate ligand

Two coordination polymers,{[Cu_3(tci)_2(DMAc)_3]-6DMAc 2H_2O}_n(1) and {[Cu_3(tci)_2(tpt)_2(H_2O)_2].2DMAc-2H_2O}_n(2)(H_3tci = tris(2-carboxyethyI)isocyanurate,tpt = 2,4,6-tris(4-pyridyl)-l,3,5-triazine,DMAc = N,/V-dimethylacetamide),have been constructed under solvothermal conditions.Both polymers were structurally characterized by single crystal X-ray diffraction,elemental analyses,IR spectra,thermogravimetric(TG) analyses and powder X-ray diffraction(RXPD).1 shows a(3,4)-connected 2D layer structure comprising Cu_2(CO_2)4 paddle-wheel units,which are further bridged by C-H…O interactions to give a 3D supramolecular network.The introduction of tpt produces different framework for 2 that comprises a dinuclear and a mononuclear Cu(Ⅱ) building units,which are further bridged together by tci~(3-) and tpt ligands to give a 4-connected 2D topological net.Adjacent 2D layers are packed together via C-H…O interactions and π…π stacking interactions to form a 3D supramolecular structure.In addition,the luminescent properties and the solid-state UV-vis spectra of 1 and 2 were explored.Furthermore,antiferromagnetic exchange interactions were unveiled in the Cu_2(COO)_4 units of 1.     

Cu(I) or Cu(I)-Cu(II) mixed-valence complexes of 2,4,6-Tri(2-pyridyl)-1,3,5-triazine: syntheses, structures, and theoretical study of the hydrolytic reaction mechanism

The reactions of 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tpt) with copper(I) halides under solvothermal or traditional conditions yielded two polymeric Cu(I) complexes [Cu2I2(tpt)]n (1) and [Cu3I3(tpt)]n (2), one mixed-valence Cu(I)-Cu(II) complex [Cu4Cl2I4(tpt)2] (3), and two Cu(II) complexes [CuBr(bpca)] (4) and [CuI(bpca)] (5) (bpca = bis(2-pyridylcarbonyl)amine). Complex 1 is a zigzag chain with tpt in a bis-bipyridine-like coordination mode, whereas complex 2 with tpt chelating three Cu(I) cations is a ladderlike coordination polymer. Complex 3 is mixed-valence, with Cu(I) in a distorted tetrahedral geometry and Cu(II) in a distorted square pyramidal geometry, forming a ladderlike supramolecular chain. Complexes 4 and 5 are the products of in situ hydrolysis of tpt involving the oxidation of Cu(I). The synthesis and characterization of complex 1, 2, and 5 indicated that Cu(I) cannot promote the hydrolysis of tpt. The theoretical study shows that the main effect for hydrolysis of tpt is the electron-withdrawing effect of metal ions.     

Complexes having the fac-[M(CO)3]+ core (M=Tc, Re) useful in radiopharmaceuticals: X-ray and NMR structural characterization and density functional calculations of species containing two sp3 N donors and one sp3 O donor

Radiopharmaceuticals containing the "fac-[M(CO)3]+ " core (M=99mTc, 186Re, or 188Re) have potential as diagnostic or therapeutic agents. Complexes with this core with sp3 amine donors have received little attention. We have studied adducts formed by ENDACH2 (HO2CCH2NHCH2CH2NHCH2CO2H) and ENACH (NH2CH2CH2NHCH2CO2H). Re(CO)3(ENDACH)-A (1A) and Re(CO)3(ENDACH)-B (1B) isomers were obtained by the reaction of ENDACH2 with Re(CO)5Cl. Re(CO)3(ENAC) (2) was obtained by the reaction of ENACH with aqueous [Re(CO)3(H2O)3]+. From single-crystal X-ray data, the three new neutral complexes, 1A, 1B, and 2, have a six-coordinate, pseudo-octahedral Re center with facially coordinated carbonyl ligands. ENDACH- and ENAC- bind facially to Re through both amine nitrogens and one carboxyl oxygen, forming two five-membered chelate rings. The Re(CO)3(ENDACH) isomers have an uncoordinated, dangling -CH2CO2H group, which is an ideal coupling site for attachment to biomolecules. The isomers differ by the configuration of the NH center bearing this dangling group. The H atom of the amine (N2) is endo (near the carbonyl ligands in the basal plane) in 1A and exo (away from carbonyl ligands) in isomer 1B. Isomers reach equilibrium (1A:1B, 70:30) after 3 days at high pH. Density functional structure optimizations were performed for isolated molecules of the type Tc(I)/Re(I)(CO)3(N2O): [Re(CO)3(NH3)2(H2O)]+, [Tc(CO)3(NH3)2(H2O)]+, [Re(CO)3(EN)(H2O)]+ (EN, ethylenediamine), [Tc(CO)3(EN)(H2O)]+, and various models for 1A, 1B, and 2. The computed structures are in good agreement with the X-ray structures. The theoretical and experimental Re-N bond distances usually agree within 0.045 A. The total electronic energy values for the computed 1A and 1B models differ by 0.815 kcal mol(-1), giving an isomer ratio of 80:20, in good agreement with the 1A/1B ratio (70:30) found.     

fac-[Re(CO)3(dmso-O)3](CF3SO3): a new versatile and efficient Re(I) precursor for the preparation of mono and polynuclear compounds containing fac-[Re(CO)3]+ fragments

We show here that the new complex fac-[Re(CO)3(dmso-O)3](CF3SO3) (1), efficiently prepared in one step from [ReBr(CO)5] and featuring a broad range of solubility, is, in general, a better precursor for the one-step synthesis of mono- and polynuclear inorganic compounds containing fac-[Re(CO)3]+ fragments compared to the commonly used (NEt4)2fac-[ReBr3(CO)3] and fac-[Re(CO)3(CH3CN)3](Y) (Y = PF6, BF4, ClO4) species. Compound 1 is the first example of a Re(I)-dmso complex structurally characterized and confirms the rule that dmso is always O-bonded when trans to CO. The reactivity of 1 was tested in the one-step preparation of several new and known complexes. The O-bonded sulfoxides of 1 are replaced under mild conditions by tri- (L3) and bidentate ligands (L2) to produce fac-[Re(CO)3(L3)]+ and fac-[Re(CO)3(L2)(dmso-O)]+ compounds, respectively. An excess of monodentate ligands (L) and more forcing conditions are needed to prepare fac-[Re(CO)3(L)3]+ compounds. The new compounds include fac-[Re(CO)3(bipy)(dmso-O)](CF3SO3) (4), that turned out to be an excellent precursor for binding the luminescent fac-[Re(CO)3(bipy)]+ fragment to polytopic ligands for the construction of more elaborate assemblies. One example reported here is the two-step preparation of fac-[{Re(CO)3(bipy)}(mu-4,4'-bipy){Ru(TPP)(CO)}](CF3SO3) (8) (TPP = tetraphenylporphyrin). The X-ray structures of the new compounds 1, 4, of the bis-porphyrin complex fac-[Re(CO)3Cl(4'MPyP)2] (13) (4'MPyP = 5-(4'pyridyl)-10,15,20-triphenylporphyrin), and of the rhenium-cyclophane [{(CO)3Re(mu-OH)2Re(CO)3}2(micro-4,4'-bipy)2] (15), among others, are described. Compound 1 might find useful applications in supramolecular chemistry (metal-mediated assembly of large architectures), in the in situ preparation of stable Re compounds to be used in nuclear medicine, and for the labeling of biomolecules.     

Involvement of a binuclear species with the Re-C(O)O-Re moiety in CO2 reduction catalyzed by tricarbonyl rhenium(I) complexes with diimine ligands: strikingly slow formation of the Re-Re and Re-C(O)O-Re species from Re(dmb)(CO)3S (dmb = 4,4'-dimethyl-2,2'-bipyridine, S = solvent)

Excited-state properties of fac-[Re(dmb)(CO)(3)(CH(3)CN)]PF(6), [Re(dmb)(CO)(3)](2) (where dmb = 4,4'-dimethyl-2,2'-bipyridine), and other tricarbonyl rhenium(I) complexes were investigated by transient FTIR and UV-vis spectroscopy in CH(3)CN or THF. The one-electron reduced monomer, Re(dmb)(CO)(3)S (S = CH(3)CN or THF), can be prepared either by reductive quenching of the excited states of fac-[Re(dmb)(CO)(3)(CH(3)CN)]PF(6) or by homolysis of [Re(dmb)(CO)(3)](2). In the reduced monomer's ground state, the odd electron resides on the dmb ligand rather than on the metal center. Re(dmb)(CO)(3)S dimerizes slowly in THF, k(d) = 40 +/- 5 M(-1) s(-1). This rate constant is much smaller than those of other organometallic radicals which are typically 10(9) M(-1) s(-1). The slower rate suggests that the equilibrium between the ligand-centered and metal-centered radicals is very unfavorable (K approximately 10(-4)). The reaction of Re(dmb)(CO)(3)S with CO(2) is slow and competes with the dimerization. Photolysis of [Re(dmb)(CO)(3)](2) in the presence of CO(2) produces CO with a 25-50% yield based on [Re]. A CO(2) bridged dimer, (CO)(3)(dmb)Re-CO(O)-Re(dmb)(CO)(3) is identified as an intermediate. Both [Re(dmb)(CO)(3)](2)(OCO(2)) and Re(dmb)(CO)(3)(OC(O)OH) are detected as oxidation products; however, the previously reported formato-rhenium species is not detected.     

Re(2)(CO)(10)-promoted S-binding, C-S bond cleavage, and hydrogenation of benzothiophenes: organometallic models for the hydrodesulfurization of thiophenes

In hydrodesulfurization model reactions of dinuclear metal complexes with thiophenes, we observe that ultraviolet photolysis of Re(2)(CO)(10) and benzothiophenes (BT) in hexanes solution produces the ring-opened BT complexes Re(2)(CO)(7)(mu-BT) (1a-d) (BT = benzothiophene (BT) 1a, 2-methylbenzothiophene (2-MeBT) 1b, 3-methylbenzothiophene (3-MeBT) 1c, and 3,5-dimethylbenzothiophene (3,5-Me(2)BT) 1d). The eta(1)(S)-bound BT complexes Re(2)(CO)(9)(eta(1)(S)-BT) (2a-d), prepared from Re(2)(CO)(9)(THF) and BT, are readily converted into 1a-d in good yields (40-60%) during UV photolysis in hexanes solution, which suggests that the eta(1)(S)-bound complexes 2a-d are precursors to 1a-d in the reactions of Re(2)(CO)(10) with BT. Irradiation of Re(2)(CO)(10) and 3,5-Me(2)BT with UV light in decane solution under an atmosphere of H(2) produces complex 1d and the partially hydrogenated BT complex Re(2)(CO)(7)(mu-3,5-Me(2)BT-H)(eta-H) (3d). Reactions of 1a with phosphines yield further ring-opened BT-Re complexes of the types Re(2)(CO)(7)(PMe(3))(3)(mu-BT) (4) and Re(2)(CO)(7)(PR(3))(2)(mu-BT) (R = Me (5), (i)Pr (6), Cy (7), and bis(diethylphosphino)ethane (8)). Structures of 1d, 2c, 3d, and 6, which demonstrate various bonding modes of benzothiophene and its C-S cleaved derivatives to two metal centers, were determined by X-ray crystallographic studies.     

Towards carbohydrate derivatives of the ReI(CO)3 fragment

With the [Re(CO)(3)Br(3)](2-) ion as a precursor for the Re(I)(CO)(3) fragment, the diols (1R,2R)-cyclohexane-1,2-diol [(1R,2R)-Chxd], anhydroerythritol (AnEryt), and (1S,2S)-cyclopentane-1,2-diol [(1S,2S)-Cptd] form dinuclear monoanions in the salts (NBu(4))[(Re(2)(CO)(6){mu-(1R,2R)-ChxdH(-1)}(3)] (1), [K([18]crown-6)][Re(2)(CO)(6)(mu-OMe)(2)(mu-AnErytH(-1))] (2) and (NBu(4))[Re(2)(CO)(6){mu-(1S,2S)-CptdH(-1)}(3)] (3). The monoanionic diolato ligands in these triply bridged dirhenates(I) are monodentate. Bridging triolato ligation in the trirhenates(I) is supported by the anions of glycerol (Glyc) and methyl beta-D-ribopyranoside (Me-beta-D-Ribp), the latter binding in its (1)C(4) conformation, in (DBUH)(2)[Re(3)(CO)(9)(mu(3)-O)(mu(3)-GlycH(-3))]0.5 MeCN (4 a), (NEt(4))[Re(3)(CO)(9)(mu(3)-OMe)(mu(3)-GlycH(-3))] (4 b) and (DBUH)[Re(3)(CO)(9)(mu(3)-OMe)(mu(3)-(1)C(4)-Me-beta-D-Ribp2,3,4H(-3))] (5). The chiral sugar alcohols L-threitol (L-Thre) and D-arabitol (D-Arab) act as tetra- and pentadentate ligands, respectively, in (NEt(4))[Re(2)(CO)(6)(L-ThreH(-3))]MeCN (6) and (NEt(4))(2)(DBUH)(2)[Re(6)(CO)(18)(D-ArabH(-5))(2)] (7). Complexes 6 and 7 are free of supporting oxo or methoxo ligands and use solely the O-atom pattern of the polyol for the connection of the Re(I)(CO)(3) moieties.     

Oxacalix[3]arene complexes with the ReI(CO)3 fragment

Oxacalix[3]arenes p-methyloxacalix[3]arene (L(1)), p-isopropyloxacalix[3]arene (L2), and p-ethoxycarbonyloxacalix[3]arene (L3) are able to bind the Re(I)(CO)3 moiety with two of their three phenol-O atoms and one of their ether-O atoms. The monoanionic complexes were isolated in the salts (DBUH)[Re(CO)3(L1H-2)].L1 (1) and (NEt4)[Re(CO)3(L2H-2)].L2.0.5 MeCN (2) (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene). Over the course of its reaction with (NEt4)(2)[Re(CO)3Br(3)] and DBU, p-ethoxycarbonyloxacalix[3]arene decomposes to form [{Re(CO)3(L4H-2)}2] (3) {L4 = 1-(5-ethoxycarbonyl-2-hydroxy-3-hydroxymethyl-benzyl)-2,3,4,6,7,8,9,10-octahydro-pyrimido[1,2-a]azepin-1-ium. The expected monoanion [Re(CO)3(L3H-2)]- (4) was identified by 13C NMR and mass spectra.     

Why is Re-Re bond formation/cleavage in [Re(bpy)(CO)3]2 different from that in [Re(CO)5]2? Experimental and theoretical studies on the dimers and fragments

The Re(NN)(CO)3(THF) (NN=bpy=2,2'-bipyridine or dmb=4,4'-dimethyl-2,2'-bipyridine) radical, produced by homolysis of [Re(NN)(CO)3]2 in THF solution by visible irradiation, dimerizes with rate constants kd=20 +/- 3 and 11 +/- 4 M(-1) s(-1) for NN=dmb and bpy, respectively. The dimerization processes are strikingly slow compared to those of typical metal radicals including Re(CO)5 (kd approximately 10(9) M(-1) s(-1)). In order to explain such slow reactions, we have performed B3LYP hybrid DFT and fully ab initio RHF and MP2 calculations on several conformations of [Re(bpy)(CO)3]2 (cis, trans, skewed cis, skewed trans) and [Re(CO)5]2 (staggered) and on their constituent monomer radicals and anions. The calculations show that the most stable geometry of [Re(bpy)(CO)3]2 is skewed cis, and the experimental infrared spectrum and photochemical properties of the [Re(bpy)(CO)3]2 dimer are best described by the calculated properties of the skewed cis conformer in which there is no low-lying unoccupied orbital that is predominantly sigma(MM) in character. The Re(bpy)(CO)3(THF) ligand radical is more stable than the 5-coordinate "17-electron" metal radical, Re(bpy)(CO)3, suggesting that the extremely slow dimerization rate most likely arises from the solvent blocking the binding site (i.e., the estimated fraction of the five-coordinate monomer is 1.6 x 10(-2)). Theoretical results are consistent with our experimental results that the dimerization process proceeds via the Re centered radical, which is involved in a pre-equilibrium favoring the ligand-centered radical. Furthermore, time-dependent DFT calculations on [Re(bpy)(CO)3]2 and [Re(bpy)(CO)3]- identify the origin of UV-vis absorption in THF.     

Systematic synthesis, isolation, and photophysical properties of linear-shaped Re(I) oligomers and polymers with 2-20 units

Systematic synthesis routes have been developed for the linear-shaped rhenium(I) oligomers and polymers bridged with bidentate phosphorus ligands, [Re(N--N)(CO)3-PP-{Re(N--N)(CO)2-PP-}(n)Re(N--N)(CO)3](PF6)(n+2) (N--N = diimine, PP = bidentate phosphine, n = 0-18). These were isolated by size exclusion chromatography (SEC) and identified by (1)H NMR, IR, electrospray ionization Fourier transform mass spectrometry, analytical SEC, and elemental analysis. Crystal structures of [Re(bpy)(CO)3-Ph2PC[triple bond]CPPh2-Re(bpy)(CO)3](PF6)2, [Re(bpy)(CO)3-Ph2PC[triple bond]CPPh2-Re(bpy)(CO)2-Ph2PC[triple bond]CPPh2-Re(bpy)(CO)3](PF6)3 and [Re(bpy)(CO)3-Ph2PC2H4PPh2-{Re(bpy)(CO)2Ph2PC2H4PPh2-}(n)Re(bpy)(CO)3](PF6)(n+2) (bpy = 2,2'-bipyridine, n = 1, 2) were obtained, showing that they have interligand pi-pi interaction between the bpy ligand and the phenyl groups on the phosphorus ligand. All of the oligomers and polymers synthesized were emissive at room temperature in solution. For the dimers, broad emission was observed with a maximum at 523-545 nm, from the (3)MLCT excited-state of the tricarbonyl complex unit, [Re(N--N)(CO)3-PP-]. Emission from the longer oligomers and polymers with > or = 3 Re(I) units was observed at wavelengths 50-60 nm longer than those of the corresponding dimers. This fact and the emission decay results clearly show that energy transfer from the edge unit to the interior unit occurs with a rate constant of (0.9 x 10(8))-(2.5 x 10(8)) s(-1). The efficient energy transfer and the smaller exclusive volume of the longer Re(I) polymers indicated intermolecular aggregation for these polymers in an MeCN solution.     

Second-sphere interaction of anions with a weakly binding metal complex host: probing the effect of counteranions

The reaction of [Re(OTf)(CO)5] with N-methylimidazole (MeIm) afforded [Re(CO)3(MeIm)3]OTf (1). The reactions of 1 with KPF6, NaBPh4 and NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl) afforded [Re(CO)3(MeIm)3]PF6 (2) [Re(CO)3(MeIm)3]BPh4 (3) and [Re(CO)3(MeIm)3]BAr'4 (4) respectively. An analogous reaction using N-phenylimidazole (PhIm) yielded [Re(CO)3(PhIm)3]BAr'4 (7). These new compounds were characterized by IR and NMR, and the structures of 1 and 2 were determined by X-ray diffraction. Compounds [Re(CO)3(MeIm)3]2[PtCl6] (5), [Re(CO)3(MeIm)3][HSO4] (6), [Re(CO)3(PhIm)3][Br] (8) and [Re(CO)3(PhIm)3][NO3] (9) were crystallized from equimolar mixtures of either 4 or 7 and the tetrabutylammonium salt of the corresponding anion, and their structures were determined by X-ray diffraction. The solution behavior of 1-4, 7 toward several anions was studied spectroscopically, including the quantitative determination of binding constants by 1H NMR. The cationic tris(imidazole)complexes are stable against imidazole-by-anion substitution, and the main hydrogen bonding interactions involve the imidazole NC(H)N groups. The binding constants for compounds 1-4 with several external anions follow the order 1<2<3<4, indicating that the strength of the cationic complex-counteranion interaction follows the order OTf(-) > PF6(-) > BPh4(-) > BAr'4(-).     

Tuning the reactivity in classic low-spin d6 rhenium(I) tricarbonyl radiopharmaceutical synthon by selective bidentate ligand variation (L,L'-Bid; L,L'= N,N', N,O, and O,O' donor atom sets) in fac-[Re(CO)3(L,L'-Bid)(MeOH)]n complexes

A range of fac-[Re(CO)(3)(L,L'-Bid)(H(2)O)](n) (L,L'-Bid = neutral or monoanionic bidentate ligands with varied L,L' donor atoms, N,N', N,O, or O,O': 1,10-phenanthroline, 2,2'-bipydine, 2-picolinate, 2-quinolinate, 2,4-dipicolinate, 2,4-diquinolinate, tribromotropolonate, and hydroxyflavonate; n = 0, +1) has been synthesized and the aqua/methanol substitution has been investigated. The complexes were characterized by UV-vis, IR and NMR spectroscopy and X-ray crystallographic studies of the compounds fac-[Re(CO)(3)(Phen)(H(2)O)]NO(3)·0.5Phen, fac-[Re(CO)(3)(2,4-dQuinH)(H(2)O)]·H(2)O, fac-[Re(CO)(3)(2,4-dQuinH)Py]Py, and fac-[Re(CO)(3)(Flav)(CH(3)OH)]·CH(3)OH are reported. A four order-of-magnitude of activation for the methanol substitution is induced as manifested by the second order rate constants with (N,N'-Bid) < (N,O-Bid) < (O,O'-Bid). Forward and reverse rate and stability constants from slow and stopped-flow UV/vis measurements (k(1), M(-1) s(-1); k(-1), s(-1); K(1), M(-1)) for bromide anions as entering nucleophile are as follows: fac-[Re(CO)(3)(Phen)(MeOH)](+) (50 ± 3) × 10(-3), (5.9 ± 0.3) × 10(-4), 84 ± 7; fac-[Re(CO)(3)(2,4-dPicoH)(MeOH)] (15.7 ± 0.2) × 10(-3), (6.3 ± 0.8) × 10(-4), 25 ± 3; fac-[Re(CO)(3)(TropBr(3))(MeOH)] (7.06 ± 0.04) × 10(-2), (4 ± 1) × 10(-3), 18 ± 4; fac-[Re(CO)(3)(Flav)(MeOH)] 7.2 ± 0.3, 3.17 ± 0.09, 2.5 ± 2. Activation parameters (ΔH(k1)(++), kJmol(-1); ΔS(k1)(), J K(-1) mol(-1)) from Eyring plots for entering nucleophiles as indicated are as follows: fac-[Re(CO)(3)(Phen)(MeOH)](+) iodide 70 ± 1, -35 ± 3; fac-[Re(CO)(3)(2,4-dPico)(MeOH)] bromide 80.8 ± 6, -8 ± 2; fac-[Re(CO)(3)(Flav)(MeOH)] bromide 52 ± 5, -52 ± 15. A dissociative interchange mechanism is proposed.     

Reactions of the Re(CO)3(H2O)3(+) synthon with monodentate ligands under aqueous conditions

The reactions of ammonia, pyridine (py), N-methyl imidazole (N-MeIm), tetrahydrothiophene (tht), and piperidine (pip) with Re(CO) 3(H 2O) 3 (+), 1 ( + ), were investigated employing aqueous conditions under atmospheric dioxygen. The reaction of [ 1]Br in aqueous ammonia led to [Re(CO) 3(NH 3) 3]Br ([ 2]Br) as the only product isolated. For the aqueous reactions of [ 1]Br with py, N-MeIm, and tht, mixtures of products are formed because of competition between the bromide and added ligand, even when the ligand is present in excess. Substitution of the PF 6 (-) anion for Br (-) leads to the clean formation of [Re(CO) 3L 3][PF 6] ([ 3][PF 6]-[ 5][PF 6]) for py, N-MeIm, and tht, respectively, as the only products observed. Reaction of [ 1][PF 6] with pip produces the dimeric species, (pip)(CO) 3Re(micro-OH) 2Re(CO) 3(pip), 6. Reactions of [ 1]Br were also performed in methanol for comparison purposes. The reaction with pip in this solvent led to the analogous dimer, (pip)(CO) 3Re(micro-OMe) 2Re(CO) 3(pip), 7; however, reactions with py, N-MeIm, and tht gave Re(CO) 3L 2Br, 8- 10, respectively, as the only products. The crystal structures of compounds [ 2]Br- 10 are reported.     

Hydrogenation and carbon-sulfur bond hydrogenolysis of benzothiophene promoted by Re2(CO)10 and H4Re4(CO)12

In the search for metal complexes that promote the cleavage of C-S bonds in thiophenes, we observe that the reaction of Re(2)(CO)(10) and benzothiophene (BT) under a hydrogen atmosphere gives the trinuclear cluster Re(3)(mu-H)(2)(mu(3)-S-2-EtC(6)H(4))(mu-2,3-DHBT)(CO)(9) (1), which contains a hydrogenated BT ligand and a thiolate ligand resulting from the hydrogenation and cleavage of a C-S bond in BT. A detailed study of the reaction shows that Re(2)(CO)(10) initially reacts with H(2) to give H(3)Re(3)(CO)(12), which subsequently converts to H(4)Re(4)(CO)(12), which finally reacts with BT to give 1.     

Reactivity of molybdenum and rhenium hydroxo-carbonyl complexes toward organic electrophiles

The hydroxo compounds [Re(OH)(CO)(3)(N-N)] (N-N=bipy, 2 a; Me(2)-bipy, 2 b) were prepared in a biphasic H(2)O/CH(2)Cl(2) medium by reaction of [Re(OTf)(CO)(3)(N-N)] with KOH. In contrast, when anhydrous CH(2)Cl(2) was used, the binuclear hydroxo-bridged compound [[Re(CO)(3)(bipy)](2)(mu-OH)]OTf (3-OTf) was obtained. Compound [Re(OH)(CO)(3)(Me(2)-bipy)] (2 b) reacted with phenyl acetate or vinyl acetate to afford [Re(OAc)(CO)(3)(Me(2)-bipy)] (4) and phenol or acetaldehyde, respectively. The reactions of [Mo(OH)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1), 2 a, and 2 b toward several unsaturated organic electrophiles were studied. The reaction of 1 with (p-tolyl)isocyanate afforded an adduct of N,N'-di(p-tolyl)urea and the carbonato-bridged compound [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(mu-eta(1)(O),eta(1)(O)-CO(3))] (5). In contrast, the reaction of 2 a with phenylisocyanate afforded [Re(OC(O)NHPh)(CO)(3)(bipy)] (6); this results from formal PhNCO insertion into the O-H bond. On the other hand, compounds [Mo[SC(O)NH(p-tolyl)](eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (7), [Re[SC(O)NH(p-tolyl)](CO)(3)(Me(2)-bipy)] (8 a), and [Re[SC(O)NHEt](CO)(3)(Me(2)-bipy)] (8 b) were obtained by reaction of 1 or 2 b with the corresponding alkyl or aryl isothiocyanates. In those cases, RNCS was inserted into the M-O bond. The reactions of 1, 2 a, and 2 b with dimethylacetylenedicarboxylate (DMAD) gave the complexes [Mo[C(OH)-C(CO(2)Me)C(CO(2)Me)-O](eta(3)-C(3)H(4)-Me-2)(CO)(phen)] (9) and [Re[C(OH)C(CO(2)Me)C(CO(2)Me)O](CO)(2)(N-N)] (N-N=bipy, 10 a; Me(2)-bipy, 10 b). The molecules of these compounds contain five-membered metallacycles that are the result of coupling between the hydroxo ligand, DMAD, and one of the CO ligands. The new compounds were characterized by a combination of IR and NMR spectroscopy, and for [[Re(CO)(3)(bipy)(2)(mu-OH)]BF(4) (3-BF(4)), 4, 5, 6, 7, 8 b, 9, and 10 b, also by means of single-crystal X-ray diffraction.     

Thiol- and thioether-based bifunctional chelates for the {M(CO)3}+ core (M = Tc, Re)

By analogy to the recently described single amino acid chelate (SAAC) technology for complexation of the {M(CO)3}+ core (M = Tc, Re), a series of tridentate ligands containing thiolate and thioether groups, as well as amino and pyridyl nitrogen donors, have been prepared: (NC5H4CH2)2NCH2CH2SEt (L1); (NC5H4CH2)2NCH2CH2SH (L2); NC5H4CH2N(CH2CH2SH)2 (L3); (NC5H4CH2)N(CH2CH2SH)(CH2CO2R) [R = H (L4); R = -C2H5 (L5). The {Re(CO)3}+ core complexes of L1-L5 were prepared by the reaction of [Re(CO)3(H2O)3]Br or [NEt4]2[Re(CO)3Br3] with the appropriate ligand in methanol and characterized by infrared spectroscopy, 1H and 13C NMR spectroscopy, mass spectrometry, and in the case of [Re(CO)3(L2)] (Re-2) and [Re(CO)3(L1)Re(CO)3Br2] (Re-1a) by X-ray crystallography. The structure of Re-2 consists of discrete neutral monomers with a fac-Re(CO)3 coordination unit and the remaining coordination sites occupied by the amine, pyridyl, and thiolate donors of L2, leaving a pendant pyridyl arm. In contrast, the structure of Re-1a consists of discrete binuclear units, constructed from a {Re(CO)3(L1)}+ subunit linked to a {Re(CO)3Br2}- group through the sulfur donor of the pendant thioether arm. The series of complexes establishes that thiolate donors are effective ligands for the {M(CO)3}+ core and that a qualitative ordering of the coordination preferences of the core may be proposed: pyridyl nitrogen approximately thiolate > carboxylate > thioether sulfur > thiophene sulfur. The ligands L1 and L2 react cleanly with [99mTc(CO)3(H2O)3]+ in H2O/DMSO to give [99mTc(CO)3(L1)]+ (99m)Tc-1) and [99mTc(CO)3(L2)] (99mTc-2), respectively, in ca. 90% yield after HPLC purification. The Tc analogues 99mTc-1 and 99mTc-2 were subjected to ligand challenges by incubating each in the presence of 1000-fold excesses of both cysteine and histidine. The radiochromatograms showed greater than 95% recovery of the complexes.     

Novel carbohydrate-appended metal complexes for potential use in molecular imaging

Seven discrete sugar-pendant diamines were complexed to the {M(CO)(3)}(+) ((99m)Tc/Re) core: 1,3-diamino-2-propyl beta-D-glucopyranoside (L(1)), 1,3-diamino-2-propyl beta-D-xylopyranoside (L(2)), 1,3-diamino-2-propyl alpha-D-mannopyranoside (L(3)), 1,3-diamino-2-propyl alpha-D-galactopyranoside (L(4)), 1,3-diamino-2-propyl beta-D-galactopyranoside (L(5)), 1,3-diamino-2-propyl beta-(alpha-D-glucopyranosyl-(1,4)-D-glucopyranoside) (L(6)), and bis(aminomethyl)bis[(beta-D-glucopyranosyloxy)methyl]methane (L(7)). The Re complexes [Re(L(1)-L(7))(Br)(CO)(3)] were characterized by (1)H and (13)C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L(2))(CO)(3)Br] and [Re(L(3))(CO)(3)Br], were characterized in the solid state by X-ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H(2)O established that the complexes exist as [Re(L(1)-L(7))(H(2)O)(CO)(3)]Br in aqueous conditions. Radiolabelling of L(1)-L(7) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period.     

Rhenium-mediated coupling of acetonitrile and pyrazoles. New molecular clefts for anion binding

The reaction of fac-[ReBr(CO)3(NCMe)2] (1) with either pyrazole (Hpz) or 3,5-dimethylpyrazole (Hdmpz) in a 1:2 Re/pyrazole ratio affords the known complexes fac-[ReBr(CO)3(Hpz)2] (2) and [ReBr(CO)3(Hdmpz)2] (3). Using a 1:1 ratio, MeCN as solvent, and longer reaction times led to a mixture in which the major components are the pyrazolylamidino complexes fac-[ReBr(CO)3(HN=C(CH3)pz-kappa2N,N)] (4) and fac-[ReBr(CO)3(HN=C(CH3)dmpz-kappa2N,N)] (5). The complexes fac-[ReBr(CO)3(Hpz)(NCMe)] (6) and fac-[ReBr(CO)3(Hdmpz)(NCMe)] (7) (along with 2 and 3) were found to be minor components of these reactions. Analogous reactions of fac-[Re(OClO3)(CO)3(NCMe)2] yielded fac-[Re(NCCH3)(CO)3(HN=C(CH3)pz-kappa2N,N)]ClO4 (8), fac-[Re(NCCH3)(CO)3(HN=C(CH3)dmpz-kappa2N,N)]ClO4 (9), fac-[Re(Hpz)(CO)3(HN=C(CH3)pz-kappa2N,N)]ClO4 (10), and fac-[Re(Hdmpz)(CO)3(HN=C(CH3)dmpz-kappa2N,N)]ClO4 (11). The X-ray structure of 11 showed the perchlorate anion to be hydrogen-bonded by the N-H groups of the pyrazole and pyrazolylamidino ligands. The behavior of the compound fac-[Re(Hdmpz)(CO)3(HN=C(CH3)dmpz-kappa2N,N)]BAr'4 (13) (synthesized by reaction of [ReBr(CO)3(Hdmpz)2] (3) with (i) AgOTf and (ii) NaBAr'(4)/MeCN) as an anion receptor has been studied in CD3CN solution. In addition, the structure of the supramolecular adduct fac-[Re(CO)3(Hdmpz)(HN=C(CH3)dmpz-kappa2N,N)].Cl (14), featuring chloride binding by the two N-H groups, was determined by X-ray diffraction.     

pH-Dependent spectroscopic and luminescent properties, and metal-ion recognition studies of Re(I) complexes containing 2-(2'-pyridyl)benzimidazole and 2-(2'-pyridyl)benzimidazolate

A series of Re(I) complexes, [Re(CO)(3)Cl(HPB)] (1), [Re(CO)(3)(PB)H(2)O] (2), [Re(CO)(3)(NO(3))(PB-AuPPh(3))] (3), and [Re(CO)(3)(NO(3))(PB)Au(dppm-H)Au](2) (4) [HPB = 2-(2'-pyridyl)benzimidazole; dppm = 2,2'-bis(diphenylphosphinomethane)], have been synthesized and characterized by X-ray diffraction. Complex 1, which exhibits interesting pH-dependent spectroscopic and luminescent properties, was prepared by reacting Re(CO)(5)Cl with an equimolar amount of 2-(2'-pyridyl)benzimidazole. The imidazole unit in complex 1 can be deprotonated to form the imidazolate unit to give complex 2. Addition of 1 equiv of AuPPh(3)(NO(3)) to complex 2 led to the formation of a heteronuclear complex 3. Addition of a half an equivalent of dppm(Au(NO(3)))(2) to complex 2 yielded 4. In both 3 and 4, the imidazolate unit acts as a multinuclear bridging ligand. Complex 4 is a rare and remarkable example of a Re(2)Au(4) aggregate in combination with μ(3)-bridging 2-(2'-pyridyl)benzimidazolate. Finally, complex 2 has been used to examine the Hg(2+)-recognition event among group 12 metal ions. Its reversibility and selectivity toward Hg(2+) are also examined.