Molecular Structures Of 2a Research Articles

Isomers of Cyclometalated Macrocycles Constructed through Olefinic C–H Activation

A new series of dinuclear complexes [(Cp*M)2{(2-pyridyl)-C═C-(2-pyridyl)}Cl2] (M = Rh (1a), Ir (1b)) and tetranuclear metallamacrocycles [{(Cp*M)2{(2-pyridyl)-C═C-(2-pyridyl)}(pyrazine)}2](OTf)4 (M = Rh (2a), Ir (2b)), [{(Cp*M)2{(2-pyridyl)-C═C-(2-pyridyl)}(bpy)}2](OTf)4 (M = Rh (3a), Ir (3b); bpy = 4,4′-bipyridine), and [{(Cp*M)2{(2-pyridyl)-C═C-(2-pyridyl)}(bpe)}2](OTf)4 (M = Rh (4a), Ir (4b); 4,4′-bpe = trans-1,2-bis(4-pyridyl)ethylene) were constructed stepwise through double-site C–H activation on the olefinic C═C bond of 1,2-bis(2-pyridyl)ethylene. Isomers were observed in both the dinuclear species and tetranuclear macrocyclic complexes and were confirmed by single-crystal X-ray diffraction. The molecular structures of 1a–c, (R,R)-(S,S)-3b, (R,R)-(S,S)-4a, (R,R)-(R,R)-/(S,S)-(S,S)-4a, and (R,R)-(S,S)-4b were characterized by single-crystal X-ray crystallography. All complexes were fully characterized by 1H NMR spectroscopy, ESI-MS, and elemental analysis.

Dynamics of H-atom exchange in stable cis-dihydrogen/hydride complexes of ruthenium(ii) bearing phosphine and N–N bidentate ligands

Synthesis and characterization of cis,trans-[RuH(η(2)-H2)(PPh3)2(N-N)][OTf] (N-N = 2,2'-bipyridyl (bpy) 1a, 2,2'-bipyrimidine (bpm) 2a; OTf = trifluoromethane sulfonate (CF3SO3)) complexes are reported. The cis-H2/hydride ligands are involved in H-atom site exchange between the two moieties. This dynamics was investigated by variable temperature NMR spectral studies based on which the mechanism of the exchange process was deduced. The ΔG(≠) for the exchange of H-atoms between the η(2)-H2 and hydride ligands was determined to be around 8 and 13 kJ mol(-1), respectively, for 1a and 2a. The H-H distances (d(HH), Å) in complexes 1a and 2a have been calculated from the T1(minimum) and (1)J(H,D) and are found to be 1.07 Å (slow) and 0.95 Å for 1a and 1.04 Å (slow) and 0.94 Å for 2a, respectively. The molecular structure of 1a was determined by X-ray crystallography.

Synthesis and Structural Analysis of (Imido)vanadium(V) Dichloride Complexes Containing Imidazolin-2-iminato- and Imidazolidin-2-iminato Ligands, and their Use as Catalyst Precursors for Ethylene (Co)polymerization

A series of (imido)vanadium(V) dichloride complexes containing 1,3-imidazolin-2-iminato or 1,3-imidazolidin-2-iminato ligands of the type, V(NR')Cl2(L) [R' = 2,6-Me2C6H3, L = 1,3-R2(CHN)2C═N (1a-c,e) or 1,3-R2(CH2N)2C═N (2a-d), R = (t)Bu (a), 2,6-Me2C6H3 (b), 2,6-(i)Pr2C6H3 (c), C6H5 (d), 2,6-(Ph2CH)2-4-MeC6H2 (e); L = 1,3-(2,6-(i)Pr2C6H3)2(CHN)2C═N, R' = 1-adamantyl (Ad, 3c), C6H5 (4c); L = 1,3-(2,6-(i)Pr2C6H3)2(CH2N)2C═N, R' = Ad (5c)], were prepared and characterized. The molecular structures of 1a, 2a,c,d, 3c, 4c, and 5c were determined by X-ray crystallography. All complexes showed high catalytic activity for ethylene polymerization especially in the presence of Et2AlCl cocatalyst; the 2,6-R2C6H3 analogues (R = Me, (i)Pr; 1b,c, 2b,c) exhibited higher catalytic activities than the (t)Bu analogues (1a, 2a), which display rather unique (small) V-N-C(imido) bond angles in the solid state. A good correlation between the activity and the (51)V NMR chemical shift was found for the (arylimido)vanadium precatalysts (1a-c,e, 2a-d, and 4c). These complexes showed high catalytic activity for the copolymerization of ethylene with norbornene (NBE), affording ultrahigh molecular weight copolymers with uniform molecular weight distributions. The activities were affected by the imido ligand as well as by the substituents in the anionic ligand, and the 2,6-(i)Pr2C6H3 analogues (especially 2c and 4c) showed the higher activities. The complexes 2c and 4c also showed high activities with efficient comonomer incorporation for the ethylene copolymerization with 5-ethylidene-2-norbornene (ENB) in the presence of Et2AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB).

C–S and C–Se Bond Formation at Bridging Vinyliminium Ligands in Diiron Complexes

AbstractThe vinyliminium complexes [Fe2{μ‐η1:η3‐C(R)C(R)CN(Me)2}(μ‐CO)(CO)(Cp)2][SO3CF3] (R = Me, 3a; R = CO2Me, 3b; R = Ph, 3c) were treated with S8 in the presence of tBuLi, undergoing fragmentation and affording the corresponding six‐membered metallacyclic complexes [Fe(Cp)(CO){SC(R)=C(R)C(NMe2)S}] (5a–c). Complexes 5a–c result from cleavage of the diiron precursor and addition of S to the vinyliminium ligand to generate a dithiochelating ligand. Analogous reactions of the vinyliminium complexes [Fe2{μ‐η1:η3‐C(R)C(R)CN(Me)(Xyl)}(μ‐CO)(CO)(Cp)2][SO3CF3] (R = Me, 3d; R = CO2Me, 3e), which contain a Xyl group (Xyl = 2,6‐Me2C6H3) in place of a methyl, displayed a different outcome. Complex 3d afforded the diiron complex [Fe2{μ‐η1:η3‐C(Me)=C(CS2)C=N(Me)(Xyl)}(μ‐CO)(CO)(Cp)2] (10), whereas 3e led to the formation of the five‐membered metallacycle [Fe(Cp)(CO){C{N(Me)(Xyl)}C(CO2Me)C(CO2Me)S}] (11) together with the diiron complex [Fe2{μ‐η1:η3‐C(CO2Me)=C(S)C=N(Me)(Xyl)}(μ‐CO)(CO)(Cp)2] (12). The formation of 10 and 12 implies C–H and C–C cleavage, respectively, and C–S bond formation without rupture of the diiron framework. The vinyliminium complexes 3a–d and also [Fe2{μ‐η1:η3‐C(Et)C(Et)CN(Me)(CH2Ph)}(μ‐CO)(CO)(Cp)2][SO3CF3] (3f) reacted with gray selenium in the presence of tBuLi to afford the five‐membered metallacycles [Fe(Cp)(CO){C{N(Me)R}C(R′)C(R′)Se}] (R = R′ = Me, 13a; R = Me, R′ = CO2Me, 13b; R = Me, R′ = Ph, 13c; R = Xyl, R′ = Me, 13d; R = CH2Ph, R′ = Et, 13f) in which one Se atom has been incorporated into the chelating ligand. The X‐ray molecular structures of 5a and 13a have been determined.

Aminoarenethiolate Aluminum Complexes: Synthesis, Characterization, and Use in l-Lactide Polymerization

Reaction of AlMe3 with S(SiMe3)(C6H3-2-CH2NRR′-5-tBu) (RR′ = C5H10 (1a), C4H8 (1b), Me2 (1c)), at ambient temperature, affords the amino adducts [AlMe3{S(SiMe3)(C6H3-2-CH2NRR′-5-tBu)}-κN] (RR′ = C5H10 (2a), C4H8 (2b), Me2 (2c)), which undergo TMS elimination upon heating to give the monomeric aminoarenethiolate aluminum complexes [AlMe2{S(C6H3-2-CH2NRR′-5-tBu)-κ2S,N}] (RR′ = C5H10 (3a), C4H8 (3b), Me2 (3c)). Following the same procedure, treatment of AlCl2Me and AlCl3 with 1 yields analogous aminoarenethiolate aluminum complexes with different degrees of methylation, the chloro methyl and dichloro complexes [AlClMe{S(C6H3-2-CH2NRR′-5-tBu)-κ2S,N}] (RR′ = C5H10 (4a), C4H8 (4b), Me2 (4c)) and [AlCl2{S(C6H3-2-CH2NRR′-5-tBu)}-κ2S,N] (RR′ = C5H10 (5a), C4H8 (5b) Me2 (5c)), respectively. These complexes have been characterized by multinuclear NMR spectroscopy and elemental analysis. Moreover, the molecular structures of 3a,b have been determined by X-ray diffraction methods. Aluminum complexes 3 have been investigated for the ring-opening polymerization (ROP) of l-lactide, achieving high conversions in relatively short periods of time. The PLAs obtained feature an aminoarenethiolate end functionality, as inferred from MALDI-TOF mass analysis.

2-Pyridylmetallocenes, part IV. Cycloplatination of 2-pyridyl-ferrocene, -ruthenocene and –cymantrene. Molecular structures of σ-Pt{CpM[C5H3(2-C5H4N)]}Cl (DMSO) (M = Fe, Ru) and σ-Pt{CpFe[C5H3(2-C5H4N)]}(acac)

The 2-pyridylmetallocenes [C5H3R(2-C5H4N)]MLn (1a–e, MLn=FeCp, RuCp, Mn(CO)3, R=H, CH3) react with cis-[PtCl2(DMSO)2] to give the cycloplatinated complexes σ-Pt{LnM[C5H2(2-C5H4N)(R)]}Cl (DMSO) (MLn=FeCp (R=H: 2a; R=Me: 2b), RuCp (R=H, 3a; R=Me, 3b), Mn(CO)3 (R=H, 4)). The reaction of 1a with the chiral sulfoxide complexes cis-[PtCl2{S(O)Me(p-C6H4Me)}2] or K[PtCl3S(O)Me(p-C6H4Me)] yields a mixture of σ-Pt{CpFe[C5H2(2-C5H4N)(R)]}Cl[S(O)Me(p-C6H4Me)] diastereomers (RpRS/SpSS)- and (RpSS/SPRS)-5. Treatment of 2a with sodium pentane-2,4-dionate (“Na(acac)”) gives the bischelate σ-Pt{CpFe[C5H3(2-C5H4N)]}(acac) (6a). Refluxing solutions of 2a with glycine in the presence of sodium methoxide yields the amino acidato complex Pt{CpFe[C5H3(2-C5H4N)]}(gly) 6b. The molecular structures of 2a, b, 3a and 6a have been determined by X-ray diffraction. 2a, b and 3a show a trans-N, S configuration of the pyridine nitrogen and the DMSO sulfur atoms.

Synthesis, structure, interaction with DNA and cytotoxicity of a luminescent copper(II) complex with a hydrazone ligand

A luminescent copper(II) complex [CuII(L)H2O]2SO4,1a was synthesized with the acyclic tridentate 2-hydroxy naphthaldehyde-2-pyridylhydrazone ligand, HL, 1. The molecular structure of 1a clearly shows that it is a monomeric copper(II) complex with CuN2OOW coordination with slightly distorted square planar geometry. The asymmetric unit of 1a contains two independent complex molecules and a sulfate anion. DNA binding interactions of 1a have been investigated by absorption, emission, viscosity and thermal denaturation studies. The cytotoxic activity of 1a was measured in vitro against the HeLa cells. The LD50 value was calculated as 4.97μM. There was no nuclear fragmentation observed after treatment with 1a, which revealed that the copper(II) complex 1a was not capable of inducing apoptosis. The cell cycle analysis of 1a indicated a dose dependent decrease of G0/G1 and S-phase cell population and dose-dependent increase of G2/M population compared with untreated control cell.

(NHC)-Pd(II) complexes with hydrophilic Nitrogen ligands;catalytic properties in neat water

The cleavage reactions of the dimers [(NHC)PdX_2]_2 with hydrophilic N-donors, L, afforded the mixed-ligand complexes of the type trans-[(NHC)LPdX_2] (X = Cl or Br; NHC = 1,3-dialkylbenzimidazol-2-ylidene (BIm) or bis(imino)acenaphthene-annulated bis(2,6-diisopropylphenyl)imidazol-2-ylidene (BIAN-IPr); L = diethanolamine (DEA), morpholine (MOR), and 3-pyridinecarboxylic acid (3-PCA)). The new complexes (1--3) were characterized by elemental analysis and spectroscopic methods and the molecular structure of 1a was determined by X-ray diffraction studies. These complexes were applied in the Suzuki--Miyaura cross-coupling reaction of phenylboronic acid with aryl halides in neat water. The activities of catalysts were monitored by gas chromatography--flame ionization detector and nuclear magnetic resonance. Whereas the complexes with DEA or 3-PCA ligands did not show significant difference in the activity, the BIAN-IPr complexes 1b and 3b bearing DEA and 3-PCA, displayed the highest catalytic activity at 100 °C.

Stepwise formation of organometallic macrocycles and triangular prisms containing 2,2′-bisbenzimidazole ligands

A series of organometallic macrocycles have been constructed by an efficient “bottom-up” assembly methodology at ambient temperature. Treatment of [Cp*MCl2]2 (1a: M = Ir, 1b: M = Rh) with pyrazine or 4,4′-bipyridine (bpy) (1:1; Cp* = pentamethylcyclopentadienyl) at room temperature resulted in the formation of binuclear complexes [Cp*MCl2]2(pyrazine) and [Cp*MCl2]2(bpy) (M = Ir or Rh), which were then further reacted with AgOTf (Tf = O2SCF3) and 2,2′-bisbenzimidazole ligand (BiBzIm). Four organometallic macrocyclic complexes formulated as [Cp*4Ir4(BiBzIm)2(pyrazine)2](OTf)4 (2a), [Cp*4Rh4(BiBzIm)2(pyrazine)2](OTf)4 (2b), [Cp*4Ir4(BiBzIm)2(bpy)2](OTf)4 (2c) and [Cp*4Rh4(BiBzIm)2(bpy)2](OTf)4 (2d) each bearing 2,2′-bisbenzimidazole ligand and the half-sandwich Ir, Rh fragments were finally obtained in good yields. In a similar process, if a rigid ligand L (3-pyridyl-bian) was used as the linker, two novel metallacycles (3a and 3b) which enchased a silver atom in the centre were obtained. Organometallic triangular prisms 4a were synthesized via methods similar to those of the rectangles. [Cp*IrCl2]2 reacted with tridentate ligand 2,4,6-tri(4-pyridyl)-1,3,5-triazine (tpt) to give the corresponding trinuclear complexes [Cp*IrCl2]3(tpt), then further reacted with AgOTf and 2,2′-bisbenzimidazole ligand, leading to the formation of the prism-like complexes formulated as [Cp*6M6(BiBzIm)6(tpt)2](OTf)6 (3a: M = Ir, 3b: M = Rh). All complexes were well characterized by 1H NMR and IR spectroscopy, as well as elemental analyses. The molecular structures of 2a, 2b, 2c, 3a, 3b and 4a were characterized by single-crystal X-ray crystallography. We found that the prism-like hexanuclear complexes 4a displayed interesting host–guest chemistry.

Coordination self-assembly of tetranuclear Pt(ii) macrocycles with an organometallic backbone for sensing of acyclic dicarboxylic acids

Coordination self-assembly of a series of tetranuclear Pt(II) macrocycles containing an organometallic backbone incorporating ethynyl functionality is presented. The 1:1 combination of a linear acceptor 1,4-bis[trans-Pt(PEt3)2(NO3)(ethynyl)]benzene (1) with three different dipyridyl donor ‘clips’ (La–Lc) afforded three [2 + 2] self-assembled Pt(II)4 macrocycles (2a–2c) in quantitative yields, respectively [La = 1,3-bis(3-pyridyl)isothalamide; Lb = 1,3-bis(3-pyridyl)ethynylbenzene; Lc = 1,8-bis(4-pyridyl)ethynylanthracene]. These macrocycles were characterized by multinuclear NMR (1H and 31P); ESI-MS spectroscopy and the molecular structures of 2a and 2b were established by single crystal X-ray diffraction analysis. These macrocycles (2a–2c) are fluorescent in nature. The amide functionalized macrocycle 2a is used as a receptor to check the binding affinity of aliphatic acyclic dicarboxylic acids. Such binding affinity is examined using fluorescence and UV-Vis spectroscopic methods. A solution state fluorescence study showed that macrocycle 2a selectively binds (K(SV) = 1.4 × 10(4) M(-1)) maleic acid by subsequent enhancement in emission intensity. Other aliphatic dicarboxylic acids such as fumaric, succinic, adipic, mesaconic and itaconic acids caused no change in the emission spectra; thereby demonstrating its potential use as a macrocyclic receptor in distinction of maleic acid from other aliphatic dicarboxylic acids.

Syntheses of Pd(ii)/Pt(ii) complexes with non-chelating 4-pyridylselenolate ligand ranging from mononuclear to macrocyclic structures and their utility as catalysts in Suzuki C–C coupling reaction

Treatment of Na2PdCl4 or [MCl2(PhCN)2] with bis(4-pyridyl)diselenide yielded an insoluble product of composition [MCl2(4,4′-(C5H4N)2Se2)]n (1). The reactions of Na2PdCl4 with one and two eq. of Na(4-SeC5H4N) afforded insoluble products [PdCl(4-SeC5H4N)]n (2) and [Pd(4-SeC5H4N)2]n (3), respectively. On treatment with PPh3, 2 and 3 gave trans-[PdCl(4-SeC5H4N)(PPh3)2] (4a) and trans-[Pd(4-SeC5H4N)2(PPh3)2] (5a), respectively. The oxidative addition of bis(4-pyridyl)diselenide to Pt(PPh3)4 exclusively yielded trans-[Pt(4-SeC5H4N)2(PPh3)2] (5b). The treatment of two eq. of Na(4-SeC5H4N) with cis-[PtX2(PR3)2] afforded 5b (X = Cl) and trans-[Pt(4-SeC5H4N)2(PEt3)2] (5c) (X = Cl or CF3SO3). The reactions of cis-[MCl2(P∩P)] and [M2Cl2(μ-Cl)2(PR3)2] with two eq. of Na(4-SeC5H4N) exclusively yielded cis-[M(4-SeC5H4N)2(P∩P)] (M/P∩P = Pd/dppe (6a), Pt/dppm (6b) and Pt/dppp (6c)) and [MCl(4-SeC5H4N)(PR3)]n (7), respectively. The complex trans-[PtCl(4-SeC5H4N)(PEt3)2] (4b) was isolated from the redistribution reaction between 5c and cis-[PtCl2(PEt3)2]. The complex [PdCl(4-SeC5H4N)(PPh3)]n (7b) exists in bi- and tri-nuclear forms, whereas [MCl(4-SeC5H4N)(PEt3)]n (7a, 7c) and [PtCl(4-SeC5H4N)(PMe2Ph)]n (7d) retain their trinuclear structure in solution. Molecular structures of 4a, 4b, 5a, 5c, 6a, 6c, 7a, 7b and 7c were established by single crystal X-ray diffraction analyses. The complexes trans-[PdCl(4-SeC5H4N)(PPh3)2] and [PdCl(4-SeC5H4N)(PPh3)]n can act as catalysts for Suzuki C–C cross coupling reaction.

Change in Coordination of NCN Pincer Iron Complexes Containing Bis(oxazolinyl)phenyl Ligands

The coordination of bis(oxazolinyl)phenyl (phebox) ligands to an Fe center was investigated in the reaction of (phebox-R)Fe(CO)2Br (1a: R = Me2; 1b: R = i-Pr) with phosphine and isocyanide compounds. Reaction of 1 with an excess amount of PMe3 in toluene proceeded at 50 °C to give the corresponding cationic complexes [(phebox-R)Fe(CO)(PMe3)2]Br [2a: R = Me2 (79%); 2b: R = i-Pr (83%)]. The molecular structures of 2a and 2b were confirmed by X-ray diffraction analysis that revealed the pseudo-octahedral geometry with NCN meridional coordination of the phebox ligand. In contrast, reaction of 1 with PMe2Ph gave the neutral phosphine complexes (η2-phebox-R)Fe(CO)(PMe2Ph)2Br [3a: R = Me2 (87%); 3b: R = i-Pr (79%)], in which the phebox ligand was coordinated to Fe as an NC bidentate ligand with the oxazoline and phenyl groups. Subsequent reaction of the neutral phosphine complex 3a resulted in the formation of the corresponding cationic complexes [(phebox-Me2)Fe(CO)(PMe2Ph)2]Br (4) via change in coordination to the tridentate mode. The reaction of 1 with tert-butylisocyanide CN(t-Bu) gave a mixture of neutral isocyanide complexes (phebox-Me2)Fe(CO)[CN(t-Bu)]Br (5, 6) in 57 and 10% yields, respectively, via exchange of one of the CO ligands. Subsequent reaction of 5 with CN(t-Bu) resulted in formation of the cationic complex {(phebox-Me2)Fe[CN(t-Bu)]3}Br (7a). Similarly, treatment of 1 with an excess amount of CN(t-Bu) afforded {(phebox-R)Fe[CN(t-Bu)]3}Br [7a: R = Me2 (83%); 7b: R = i-Pr (69%)].

Sawhorse-type diruthenium tetracarbonyl complexes containing biologically relevant acids

The reaction between the biologically active acids probenecid (HO2CC12H18NO2S), indomethacin (HO2CC18H15ClNO2) and sulindac (HO2CC19H16FOS) with Ru3(CO)12, followed by addition of axial ligands (L), such as pyridine, triphenylphosphine, or 5-(4-pyridyl)-10,15,20-triphenylporphyrin, generates a series of stable diruthenium tetracarbonyl complexes of the formula Ru2(CO)4(μ2-η2-O2CC12H18NO2S)2L2, Ru2(CO)4(μ2-η2-O2CC18H15ClNO2)2L2 and Ru2(CO)4(μ2-η2-O2CC19H16FOS)2L2, respectively. The molecular structure of 1a · C6H6 was solved by single-crystal X-ray structure analysis and a typical diruthenium tetracarbonyl backbone bridged by the carboxylato ligands and two axial triphenylphosphine ligands was revealed. The benzene molecule sits between two probenecid units, and is involved in π-stacking interactions with the aromatic part of probenecid. Despite the presence of biologically relevant derivatives and carbonyl groups within the sawhorse-type dinuclear complexes, all systems show no cytotoxicity towards human cancer cells, presumably due to the high lipophilicity of these neutral complexes.

DNA binding, nuclease and superoxide scavenging activity studies on mononuclear cobalt complexes derived from tridentate ligands

A new family of mononuclear cobalt complexes was synthesized using tridentate ligands Pyimpy (Pyimpy=1-phenyl-1-(pyridin-2-yl)-2-(pyridin-2-ylmethylene)hydrazine) and PampH (PampH=N′-phenyl-N′-(pyridin-2-yl)picolinohydrazide). The complexes [Co(Pyimpy)Cl2] (1a), [Co(Pyimpy)2](ClO4)2 (1b), [Co(Pamp)Cl2] (2a) and [Co(Pamp)2](ClO4) (2b) were characterized by elemental analysis, UV–Vis, IR, NMR, ESI-MS spectral studies and conductivity measurements. Molecular structure of 1a was determined by X-ray crystallography. Redox properties of the complexes were examined by cyclic voltammetry. Superoxide dismutase (SOD) activity of the complexes was assayed by xanthine/xanthine oxidase/nitroblue tetrazolium assay. We investigated the DNA binding properties of these complexes by absorption spectral, fluorescence quenching and circular dichroism spectral studies. Nuclease activity and their mechanism were also investigated.

Influence of steric effect on the structural aspects of N,N′,N″-triarylguanidine derived six-membered [C,N] palladacycles

Guanidine derived six-membered [C,N] palladacycles of the types [(C,N)Pd(μ-OC(O)R)]2 (1a–d), [(C,N)Pd(μ-Br)]2 (2a,b), cis-[(C,N)PdBr(L)] (3a–d, 4, and 5), and ring contracted guanidine derived five-membered [C,N] palladacycle, [(C,N)PdBr(CNXy)] (6) were prepared in high yield following the established methods with a view aimed at understanding the influence of the substituents on the aryl rings of the guanidine upon the solid state structure and solution behaviour of palladacycles. Palladacycles were characterised by microanalytical, IR, NMR and mass spectral data. The molecular structures of 1a, 1c, 2a, 2b, 3a, 3c, 3d, and 4–6 were determined by single crystal X-ray diffraction data. Palladacycles 1a and 1c were shown to exist as a dimer in transoid in–in conformation in the solid state but as a mixture of a dimer in major proportion and a monomer (κ2-O,O′-OAc) in solution as deduced from 1H NMR data. Palladacycles 2a and 2b were shown to exist as a dimer in transoid conformation in the solid state but the former was shown to exist as a mixture of a dimer and presumably a trimer in solution as revealed by a variable temperature 1H NMR data in conjunction with ESI-MS data. The cis configuration around the palladium atom in 3a, 3c, and 3d was ascribed to steric influence of the aryl moiety of NAr unit and that in 4–6 was ascribed to antisymbiosis. The solution behaviour of 3d was studied by a variable concentration (VC) 1H NMR data.

5-[4-(Dimethylamino)phenyl]-2-benzamidopyrazines: fluorescent dyes based on Cypridina oxyluciferin

To clarify the acyl substitution effect on the fluorescent property of Cypridina oxyluciferin analogs, which have the 4-(dimethylamino)phenyl group at C5, we compared the spectroscopic properties of benzamide 1b and its 2,6-dimethylphenyl derivative 1c in various solvents with those of acetamide 1a. Similarity of the fluorescence wavelengths of 1a–c indicates that the π-electronic conjugation in the excited singlet (S1) state is terminated at the acyl group and that the benzamide moiety in 1b has little effect on modulating the florescence color. The similar fluorescence solvatochromism of 1a–c reveals that their S1 states have a similar intramolecular charge transfer character. The fact that 1a–c have various fluorescence quantum yields and lifetimes depending on solvent polarity and hydrogen bonding interactions in solutions provides information about the decay processes competing with the fluorescence process in the S1 states. Among 1a–c, benzamide 1b exhibits the most sensitive variation of the fluorescence intensity depending on the solvent used. Similarity of the fluorescence spectra of 1a–c adsorbed in NaY zeolites was also observed, which indicates that the S1 states of 1a–c give mobile conformers in the NaY supercages. The relationship between the molecular structures of 1a–c and their spectroscopic properties will provide a guide for designing a new fluorophore based on Cypridina oxyluciferin.

Synthesis, Characterisation and Catalytic Application of Oxidorhenium Complexes Bearing H‐Spirophosphorane Ligands

AbstractThe coordination properties of the H‐spirophosphorane ligands HP(OCMe2CMe2O)2 (L1), HP(OCHMeCHMeO)2 (L2) and HP(OCH2CMe2NH)2 (L3) towards rhenium have been studied, and the complexes cis‐[ReOCl2{P(OCMe2CMe2O)OCMe2CMe2O}pic] (1a), cis‐ and trans‐[ReOCl2{P(OCMe2CMe2O)OCMe2CMe2O}lut] (2a and 2b), cis‐ and trans‐[ReOBr2{P(OCMe2CMe2O)OCMe2CMe2O}PPh3] (3a and 3b), [nBu4N][ReOCl3{P(OCMe2CMe2O)OCMe2CMe2O}] (4), cis‐[ReOCl2{P(OCHMeCHMeO)OCHMeCHMeO}py] (5), and [ReOCl3{P(OCH2CMe2NH)OCH2CMe2NH2}] (6) have been prepared. The H‐spirophosphoranes coordinate to the rhenium moiety as bidentate, ionic chelating ligands in 1–5 and as a molecular chelating ligand in 6. The chemical compositions of all the complexes were established by spectroscopic methods and the molecular structures of 1a, 2b, 3a, 3b, 5 and 6 were determined by single‐crystal X‐ray diffraction. It was proved that some of the complexes 1–6 and their previously obtained congeners are very good cocatalyst precursors for the oxidation of aldehydes using molecular oxygen as oxidant and N‐hydroxyphthalimide as catalyst. The impact of the structures of the complexes on their catalytic activity was studied. The presence of spirophosphorane ligands in the structures seems to be essential for stabilising the active form of the cocatalyst.

Reactions and properties of the dinuclear molybdenum complex [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)6

Reactions of the title complex (1), which features the rigid doubly-bridged biscyclopentadienyl ligand and the unusually long Mo–Mo bond in the structure, with a variety of classic substrates are explored. Complex 1 reacts with I2 in CH2Cl2 to give the expected Mo–Mo cleaved product [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)6I2 (2A) with a Mo–Mo distance of 5.329Å. While the same reaction in benzene forms the product 2B, which has the same structural formula as 2A but a different conformation, in which the Mo–Mo distance is 6.442Å. Reaction of 1 with Ph2E2 (E=S, Se) in refluxing toluene or under UV irradiation yields products with the carbonyls completely removed, [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(EPh)2(μ-EPh)2 (3a–b). Reaction of 1 with [Et2NC(S)S]2 results in the di-substituted product [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)4(Et2NC(S)S)2 (4). Reaction of 1 with C2Ph2 affords the acetylene-bridged derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)4(μ-C2Ph2) (5). Reaction of 1 with an excess of PPh3 in refluxing toluene only provides the mono-substituted derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)5(PPh3) (6), while the reaction of 1 with excess P(OPh)3 under the same conditions produces not only the mono-substituted derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)5(P(OPh)3) (7), but also the di-substituted derivative [(η5-C5H3)2(CMe2)(SiMe2)]Mo2(CO)4(P(OPh)3)2 (8). The reactivity and properties of the doubly-bridged molybdenum complex 1 and the corresponding non-bridged and singly-bridged analogs are compared. The molecular structures of 2A, 2B, 3a, 5 and 8 have been determined by single crystal X-ray diffraction.

Synthesis, crystal structure, computational study of 1-(6-chloro-pyridin-2-yl)-5-hydroxy-1H-pyrazole-3-carboxylic acid methyl ester and its 5-acetoxy analogs

Two new pyrazole derivatives of 1-(6-chloro-pyridin-2-yl)-5-hydroxy-1H-pyrazole-3-carboxylic acid methyl ester 1a and 5-acetoxy-1-(6-chloro-pyridin-2-yl)-1H-pyrazole-3-carboxylic acid methyl ester 2 were synthesized and characterized by 1H, 13C NMR, IR spectroscopies and HRMS analyses. The molecular structure of 1a and 2 were studied by X-ray diffraction and compared to density-functional-theory (DFT) calculations. The gauge-including atomic orbital (GIAO) method for calculating 1H and 13C NMR nuclear magnetic shielding tensors at the DFT method with 6-31+G* basis set were applied to the compounds 1a and 2. Additionally, thermodynamic properties of the cyclization of the compound 3 to these compounds (1a,1b,1c,4) were investigated by theoretical calculations. These theoretical calculations was shown that the compound 1a was readily formed and was the most stable one. Tautomeric forms of the compound 1a were optimized at the same methods and basis set. The calculated relative Gibbs free energies of the tautomeric forms of 1a were used to estimate the equilibrium constants. It was shown that the 1a was the most stable than tautomer of 1b and 1c in the gas phase.

Coordination-Driven Self-Assembly of 2D-Metallamacrocycles Using a New Carbazole-Based Dipyridyl Donor: Synthesis, Characterization, and C60 Binding Study

A new carbazole-based 90° dipyridyl donor 3,6-di(4-pyridylethynyl)carbazole (L) containing carbazole-ethynyl functionality is synthesized in reasonable yield using the Sonagashira coupling reaction. Multinuclear NMR, electrospray ionization-mass spectrometry (ESI-MS), including single crystal X-ray diffraction analysis characterized this 90° building unit. The stoichiometry combination of L with several Pd(II)/Pt(II)-based 90° acceptors (1a-1d) yielded [2 + 2] self-assembled metallacycles (2a-2d) under mild conditions in quantitative yields [1a = cis-(dppf)Pd(OTf)(2); 1b = cis-(dppf)Pt(OTf)(2); 1c = cis-(tmen)Pd(NO(3))(2); 1d = 3,6-bis{trans-Pt(C≡C)(PEt(3))(2)(NO(3))}carbazole]. All these macrocycles were characterized by various spectroscopic techniques, and the molecular structure of 2a was unambiguously determined by single crystal X-ray diffraction analysis. Incorporation of ethynyl functionality to the carbazole backbone causes the resulted macrocycles (2a-2d) to be π-electron rich and thereby exhibit strong emission characteristics. The macrocycle 2a has a large internal concave aromatic surface. The fluorescence quenching study suggests that 2a forms a ~1:1 complex with C(60) with a high association constant of K(sv) = 1.0 × 10(5) M(-1).