The crucial importance of agostic interactions in intermediates formed in propylene polymerization using neutral salicyladiminato palladium(II) and nickel complexes as catalysts

The structures of intermediates formed in propylene polymerisation using neutral salicyladiminato palladium(II) and nickel(II) complexes as catalysts have been investigated using density functional theory. Calculations show that all low energy intermediates contain agostic interactions either between the metal and a hydrogen from the added propylene forming four- or five-membered chelate rings, or, when a phenyl ring is present, between the metal and an aromatic C-C bond. The agostic interactions with the metal are concomitant with changes in ligand dimensions and electronic properties. In particular when a metal to hydrogen bond is formed, there is a lengthening of the C-H bond. Significant differences are found for the agostic interactions with palladium and nickel in that for Pd there is a clear preference for specific intermediates but for Ni there are several different structures with similar energies which are likely to lead to a greater variety of products on further polymerisation. (c) 2007 Elsevier B.V. All rights reserved.

Copper(II) complexes of tetradentate N2S2 donor sets: synthesis, crystal structure characterization and reactivity

Two mononuclear and one dinuclear copper(II) complexes, containing neutral tetradentate NSSN type ligands, of formulation [Cu-II(L-1)Cl]ClO4 (1), [Cu-II(L-2)Cl]ClO4 (2) and [Cu-2(II)(L-3)(2)Cl-2](ClO4)(2) (3) were synthesized and isolated in pure form [where L-1 = 1,2-bis(2-pyridylmethylthio)ethane, L-2 = 1,3-bis(2-pyridylmethylthio)propane and L-3 = 1,4-bis(2-pyridylmethylthio)butane]. All these green colored copper(II) complexes were characterized by physicochemical and spectroscopic methods. The dinuclear copper(II) complex 3 changed to a colorless dinuclear copper(I) species of formula [Cu-2(1)(L-3)(2)](ClO4)(2),0.5H(2)O (4) in dimethylformamide even in the presence of air at ambient temperature, while complexes I and 2 showed no change under similar conditions. The solid-state structures of complexes 1, 2 and 4 were established by X-ray crystallography. The geometry about the copper in complexes 1 and 2 is trigonal bipyramidal whereas the coordination environment about the copper(I) in dinuclear complex 4 is distorted tetrahedral. (C) 2008 Elsevier Ltd. All rights reserved.

Isomeric olefin tetracarbonyl complexes of tungsten(I): an infrared spectroelectrochemical study at low temperatures

In situ electrolysis within an optically transparent thin-layer electrochemical (OTTLE) cell was applied at 293-243 K in combination with FTIR spectroscopy to monitor spectral changes in the carbonyl stretching region accompanying oxidation of four tetracarbonyl olefin complexes of tungsten(0), viz., trans-[W(CO)(4)(eta(2)-ethene)(2)], trans-[W(CO)(4)(eta(2)-norbornene)(2)], [W(CO)(4)(eta(4)-cycloocta-1,5-diene)], and [W(CO)(4)(eta(4)-norbornadiene)]. In all cases, the one-electron-oxidized radical cations (17-electron complexes) have been identified by their characteristic nu(CO) patterns. For the bidentate diene ligands, the cis stereochemistry is essentially fixed in both the 18- and 17-electron complexes. The radical cation of the trans-bis(ethene) complex was observed only at 243 K, while at room temperature it isomerized rapidly to the corresponding cis-isomer. The thermal stability of the three studied radical cations in the cis configuration correlates with the relative strength of the W-CO bonds in the positions trans to the olefin ligand, which are more affected by the oxidation than the axial W-CO bonds. For the bulky norbornene ligands, their trans configuration in the bis(norbornene) complex remains preserved after the oxidation in the whole temperature range studied. The limited thermal stability of the radical cations of the trans-bis(alkene) complexes is ascribed to dissociation of the alkene ligands. The spectroelectrochemical results are in very good agreement with data obtained earlier by DFT (B3LYP) calculations.

Excited states of nitro-polypyridine metal complexes and their ultrafast decay. Time-resolved IR absorption, spectroelectrochemistry, and TD-DFT calculations of fac-[Re(Cl)(CO)3(5-Nitro-1,10-phenanthroline)]

The lowest absorption band of fac-[Re(Cl)(CO)(3)(5-NO2-phen)] encompasses two close-lying MLCT transitions. The lower one is directed to LUMO, which is heavily localized on the NO2 group. The UV-vis absorption spectrum is well accounted for by TD-DFT (G03/PBEPBE1/CPCM), provided that the solvent, MeCN, is included in the calculations. Near-UV excitation of fac-[Re(Cl)(CO)(3)(5-NO2-phen)] populates a triplet metal to ligand charge-transfer excited state, (MLCT)-M-3, that was characterized by picosecond time-resolved IR spectroscopy. Large positive shifts of the v(CO) bands upon excitation (+70 cm(-1) for the A'(1) band) signify a very large charge separation between the Re(Cl)(CO)3 unit and the 5-NO2-phen ligand. Details of the excited-state character are revealed by TD-DFT calculated changes of electron density distribution. Experimental excited-state v(CO) wavenumbers agree well with those calculated by DFT. The (MLCT)-M-3 state decays with a ca. 10 ps lifetime (in MeCN) into another transient species, that was identified by TRIR and TD-DFT calculations as an intraligand (3)n pi* excited state, whereby the electron density is excited from the NO2 oxygen lone pairs to the pi* system of 5-NO2-phen. This state is short-lived, decaying to the ground state with a similar to 30 ps lifetime. The presence of an n pi* state seems to be the main factor responsible for the lack of emission and the very short lifetimes of 3 MLCT states seen in all d(6)-metal complexes of nitro-polypyridyl ligands. Localization of the excited electron density in the lowest (MLCT)-M-3 states parallels localization of the extra electron in the reduced state that is characterized by a very small negative shift of the v(CO) IR bands (-6 cm(-1) for A'(1)) but a large downward shift of the v(s)(NO2) IR band. The Re-Cl bond is unusually stable toward reduction, whereas the Cl ligand is readily substituted upon oxidation.

Cobalt(III) complexes of some aromatic thiohydrazides – Synthesis, characterization and structure

Co(NH3)(5)Cl]Cl-2 forms neutral 1:3 complex by reaction with aromatic thiohydrazides, i.e. thiobenzhydrazide, o-hydroxythiobenzhydrazide, thiophen-2-thiohydrazide and furan-2-thiohydrazide. All these complexes are diamagnetic and have been characterized by elemental analysis and combination of spectroscopic methods. Cyclic voltammometry of the complexes shows irreversible metal centered and ligand centered electron transfer reactions. One complex, tris-o-hydroxythiobenzhydrazidocobalt(III),has been crystallized from DMSO solution to produce solvated crystals and its structure has been established by X-ray crystallography. Cobalt(III) ion is linked through three hydrazinic nitrogen and three sulfur atoms of three identical deprotonated ligand molecules in a distorted octahedral environment. Involvement of -OH group in intramolecular and intermolecular hydrogen bonding is crucial for crystal formation.

Divinyldisiloxane and divinylsilane complexes of rhodium(I)

Reaction of the tetrakis(cyclooctene)rhodium(I) complex [{Rh(C8H14-c)2(μ-Cl)}2] with the appropriate divinyldisiloxane molecules (ViSiR2)2O (R=Me or Ph) yields, by displacement of the cycloctene ligands, the complexes [{Rh(ViSiR2)2O(μ-Cl)}2] (R=Me (1) or Ph (2)). These react further with a tertiary phosphine PR3 to give cis-[Rh{(ViSiR2)2O}(PR′3)Cl] (R′=Ph or C6H4Me-p). The complex cis-[{Rh(Vi2SiMe2)(μ-Cl)}2] (7) was similarly prepared by the displacement of ethylene from [{Rh(C2H4)2(μ-Cl)}2] by the divinyldimethylsilane Vi2SiMe2. X-ray molecular structures of the crystalline complexes 1, 2 and 7 show a distorted square planar Rh(I) environment, the CH2CH groups being orthogonal to this plane; 1 and 2 have the Rh–(ViSiR2)2O metallacycle in the chair conformation, but differ in the nature of the central Rh(Cl)RhCl core, which is planar for 1 and puckered for 2, but each of 1 and 2 is the rac-diastereoisomer, whereas 7 has the meso-configuration. In solution 1 and 2 exist as a mixture of isomers, probably the rac- and meso-pairs as established by multinuclear NMR spectral studies. A series of saturation transfer NMR spectroscopic experiments showed that the divinyldisiloxane ligands in [{Rh(ViSiPh2)2O(μ-Cl)}2] underwent a dynamic process involving the dissociation, rotation and then reassociation of the vinyl groups.

Cooperative metal-ligand-induced properties of heteroleptic copper(I) xanthate/dithiocarbamate PPh3 complexes

Four new heteroleptic mononuclear complexes, [Cu(PPh3)2L1](1) {L1 = (C9H11O2CS2), [2-(4-methoxyphenyl)ethyl]xanthate}, [Cu(PPh3)2L2] (2) [L2 = (C6H7OCS2), benzylxanthate], [Cu(PPh3)2L3] (3) [L3 = (C5H9OCS2), (cyclobutylmethyl)xanthate] and [Cu(PPh3)2L4] (4) [L4 = (NC13H13NCS2), N-benzyl-N-(4-pyridylmethyl)dithiocarbamate], have been synthesized and characterized by using microanalysis, IR, UV/Vis, 1H, 13C and 31P NMR spectroscopy and X-ray crystallography; their photoluminescent behaviour and molecular electrical conductivity have been investigated. CuI possesses four-coordinate distorted tetrahedral geometry in all the complexes. All are weakly conducting and exhibit semiconductor behaviour in the studied 303363 K temperature range. Complex 4 shows striking luminescent behaviour emitting bluish green light at 480 nm in CH2Cl2 solution at room temperature

N-(Aryl)picolinamide complexes of rhodium : synthesis, structure and, spectral and electrochemical properties

Reaction of a series of N-(aryl)picolinamide ligands (HL-R, where II denotes the acidic proton and R (R = OCH3, CH3, H, Cl and NO2) is the para substituent in the aryl fragment) with RhCl3 center dot 3H(2)O in refluxing ethanal in the presence of a base (NEt3) affords two groups of yellow complexes of type [Rh(H-R)(L-R)Cl-2] and [Rh(L-R)(2)(H2O)Cl]. In [Rh(HL-R)(L-R)Cl-2], HL-R is coordinated as neutral N,O-donor and L-R as monoanionic N,N-donor, and the two chlorides are mutually trans. In [Rh(L-R)(2)(H2O)CI] both the amide ligands are coordinated as monoanionic N,N-donor, and the chloro and aquo ligands are mutually cis. Structures of the [Rh(HL-OCH3)(L-CH3)Cl-2] and [Rh(L-Cl)(2)(H2O)CI] complexes have been determined by X-ray crystallography. All the complexes show characteristic H-1 NMR signals and intense LLCT transitions in the ultraviolet region. Cyclic voltammetry on the complexes shows an oxidation of the coordinated amide ligand within 0.78-1.80 V vs SCE and a reductive response within -0.20 to -0.75 V vs SCE. DFT calculations have been done to explain the electronic spectral and electrochemical properties.

Effect of an ancillary ligand on single helix-double helix interconversion in copper complexes. Copper(I)-water bond

Reaction of Cu(ClO(4))(2)center dot 6H(2)O with the 1:2 condensate of benzildihydrazone and 2-acetylpyridine, in methanol in equimolar ratio yields a green compound which upon recrystallisation from 1:1 CH(2)Cl(2)-C(6)H(6) mixture affords [CuL(H(2)O)](ClO(4))(2)center dot 1/2C(6)H(6). The complex crystallises in the space group P-1 with a = 8.028(11) angstrom, b = 12.316(17) angstrom, c = 18.14(3) angstrom, alpha = 97.191(10)degrees, beta = 94.657(10)degrees and gamma = 108.039(10)degrees. It is single helical with the metal having a distorted trigonal bipyramidal N(4)O coordination sphere. The acid dissociation constant of the Cu(I) complex in CH(3)CN is 3.34 +/- 0.19. The X band EPR spectrum of the compound is rhombic with g(1) = 2.43, g(2) = 2.10 g(3) = 2.02 and A(1) = 79.3 x 10(-4) cm(-1). The Cu(II/I) potential of the complex in CH(2)Cl(2) at a glassy carbon electrode is 0.43 V vs SCE. It is argued that the copper-water bond persists in the corresponding copper(I) species. Its implications on the single helix-double helix interconversion in copper helicates are discussed. DFT calculations at the B3LYP/6-311G** level shows that the binding energy of water in the single helicol live-coordinate copper(I) species [CuL(H(2)O)](+) is similar to 40 kJ mol(-1).

Temperature-dependent reduction pathways of complexes fac-[Re(CO)3(N-R-imidazole)(1,10-phenanthroline)]+ (R = H, CH3)

Peculiar reduction pathways of the complexes fac-[Re(imH)(CO)3(phen)]+ and fac-[Re(imCH3)(CO)3(phen)]+ (imH = imidazole, imCH3 = N-methylimidazole and phen = 1,10-phenanthroline) have been unravelled by performing combined cyclic voltammetric and in situ IR spectroelectrochemical experiments. In the temperature range of 293–233 K, the initial reduction of the phen ligand in [Re(imH)(CO)3(phen)]+ results in irreversible conversion of the imidazole ligand to 3-imidazolate by a rapid phen•−→ imH intramolecular electron transfer coupled with N H bond cleavage. This process is followed by second phen-localized 1e− reduction producing [ReI(3-im−)(CO)3(phen•−)]−, similar to the analogous 2,2'-bipyridine complex. In contrast to the bpy analogue, the stability of the phen•−-containing complexes is significantly affected by lowering the temperature. At 233 K, a secondary reaction occurs in both [Re(3-im−)(CO)3(phen•−)]− and [Re(imCH3)(CO)3(phen•−)]. The resulting products exhibit v(CO) wavenumbers indistinguishable from those of the parent phen•− complexes; however, their oxidation occurs at a considerably more positive electrode potential. It is proposed that these species are produced by a new C C bond formation between the C(2) site of 3-im− or imCH3 and the C(2) site of the phen•−ligand.

Dithiocarbazate complexes with the [M(PPh(3))](2+) (M=Pd or Pt) moiety Synthesis, characterization and anti-Tripanosoma cruzi activity

New neutral Pd(II) and Pt(II) complexes of the type [M(L)(PPh(3))] (M Pd or Pt) were prepared in crystalline form in high-yield synthesis with the S-benzyldithiocarbazates and S-4-nitrobenzyldithiocarbazates derivatives from 2-hydroxyacetophenone, H(2)L(1a) and H(2)L(1b), and benzoylacetone, H(2)L(2a) and H(2)L(2b). The new complexes [Pt(L(1a))(PPh(3))] (1), [Pd(L(1a))(PPh(3))] (2), [Pt(L(1b))(PPh(3))] (3), [Pd(L(1b))(PPh(3))] (4), [Pt(L(2a))(PPh(3))] (5), [Pd(L(2a))(PPh(3))] (6), [Pt(L(2b))(PPh(3))] (7) and [Pd(L(2b))(PPh(3))] (8) were characterized on the basis of elemental analysis, conductivity measurements, UV-visible, IR, electrospray ionization mass spectrometry (ESI-MS), NMR ((1)H and (31)P) and by X-ray diffraction studies. The studies showed that differently from what was observed for the H(2)L(1a) and H(2)L(1b) ligands, H(2)L(2a) and H(2)L(2b) assume cyclic forms as 5-hydroxypyrazolinic. Upon coordination, H2L2a and H2L2b suffer ring-opening reaction, coordinating in the same manner as H(2)L(1a) and H(2)L(1b), deprotonated and in O,N,S-tridentate mode to the (MPPh(3))(2+) moiety. All complexes show a quite similar planar fourfold environment around the M(II) center. Furthermore, these complexes exhibited biological activity on extra and intracellular forms of Trypanosoma cruzi in a time- and concentration-dependent manner with IC(50) values ranging from 7.8 to 18.7 mu M, while the ligand H(2)L(2a) presented a trypanocidal activity on trypomastigote form better than the standard drug benznidazole. (C) 2010 Elsevier Inc. All rights reserved.

Formation of out of plane oxime metallacycles in [Cu(2)] and [Cu(4)] complexes

The reaction Of Cu(ClO(4))(2)center dot 6H(2)O with dimethylglyoxime (H(2)dmg) in a 1:1 mole ratio in aqueous methanol at room temperature affords the dinuclear complex [Cu(2)(mu-Hdmg)(4)] (1). Reaction of 1 with [Cu(bpy)(H(2)O)(2)](ClO(4))(2) (bpy = 2,2`-bipyridine) in a 1:1 mole ratio in aqueous methanol at room temperature yields the tetranuclear complex [Cu(2)(mu-HdMg)(2)(mu-dMg)(2)(bpy)(2)(H(2)O)(2)](ClO(4))(2) (2). The direct reaction of Cu(ClO(4))(2)center dot 6H(2)O with H(2)dmg and bpy in a 2:21 mole ratio in aqueous methanol at room temperature also yields 2 quantitatively. The complexes 1 and 2 were structurally characterized by X-ray crystallography. Unlike the binding in Ni/Co-dmg, two different types of N-O bridging modes during the oxime based metallacycle formation and stacking of square planar units have been identified in these complexes. The neutral dinuclear complex 1 has CuN(4)O coordination spheres and complex 2 consists of a dicationic [Cu(2)(mu-HdMg)(2)(mu-dMg)(2)(bpy)(2)(H(2)O)(2)](2+) unit and two uncoordinated ClO(4)(-) anions having CuN(4)O and CuN(2)O(3) coordination spheres. The two copper(II) ions are at a distance of 3.846(8) angstrom in 1 for the trans out of plane link and at 3.419(10) and 3.684(10) angstrom in 2 for the trans out of plane and cis in plane arrangements, respectively. The average Cu-N(oxime) distances are 1.953 and 1.935 angstrom, respectively. The average basal and apical Cu-N(oxime) distances are 1.945, 2.295 and 2.429 angstrom. The UV-Vis spectra of 2 is similar to the spectrum of the reaction mixture of 1 and [Cu(bpy)(H(2)O)(2)](2+). Variable temperature magnetic properties measurement shows that the interaction between the paramagnetic copper centers in complex I is antiferromagnetic in nature. The EPR spectra of frozen solution of the complexes at 77 K consist of axially symmetric fine-structure transitions (Delta M(S) = 1) and half-field signals (Delta M(S) = 2) at ca. 1600 G, suggesting the presence of appreciable Cu-Cu interactions. (C) 2009 Elsevier Ltd. All rights reserved.

Photoswitches and Luminescent Rigidity Sensors Based on fac-[Re(CO)(3)(Me(4)phen)(L)](+)

The fac-[Re(CO)(3)(Me(4)phen)(trans-L)](+) complexes, Me(4)phen = 3,4,7,8-tetramethyl-1,10-phenanthroline and L = 4-styrylpyridine, stpy, or 1,2-bis(4-pyridyl)ethylene, bpe, were synthesized and characterized by their spectroscopic, photochemical, and photophysical properties. The complexes exhibit trans-to-cis isomerization upon 313, 334, 365, and 404 nm irradiation, and the true quantum yields can be efficiently determined by absorption changes combined with (1)H NMR data. For fac-[Re(CO)(3)(Me(4)phen)(trans-bpe)](+) similar quantum yields were determined at all wavelengths investigated. However, a lower value (phi(true) = 0.35) was determined for fac-[Re(CO)(3)(Me(4)phen)(trans-stpy)](+) at 404 nm irradiation, which indicates different pathways for the photoisomerization process. The photoproducts, fac-[Re(CO)(3)(Me(4)phen)(cis-L)](+), exhibit luminescence at room temperature with two maxima ascribed to the (3)IL(Me4phen) and (3)MLCT(Re -> Me4phen) excited states. The luminescence properties were investigated in different media, and the behavior in glassy EPA at 77 K showed that the contribution of each emissive state is dependent on the excitation wavelength. The photochemical and photophysical behavior of the complexes were rationalized in terms of the energy gap of excited states and can be exploited in photoswitchable luminescent rigidity sensors.

You know how I know you're gay? : masculinity and homophobia in mainstream comedy

You Know How I Know You're Gay?: Masculinity and Homophobia in Contemporary Mainstream Comedy is a three-part senior scholars project that consists of a critical analysis of homophobic humor in contemporary mainstream comedy, an original feature-length comedy script entitled Don 't Be that Freshman, and a DVD of selected scenes from Don't Be that Freshman. The critical analysis first establishes the existence of homophobic humor in mainstream comedy and then links this homophobia to masculine anxiety, applying the ideas set forth in Michael Kimmel's essay, "Masculinity as Homophobia," to contemporary, mainstream, homosocial comedies. The paper goes on to examine audience reactions to this homophobic humor, focusing on audience members who enjoy these movies, yet consider themselves to be accepting of homosexuality and against homophobia. I discuss ways of resistance and the importance of opposing homophobic humor, and finally, I look at comedy as a potentially transgressive medium that could be used to fight homophobia and social inequality. The critical analysis, therefore, leads into Don't Be that Freshman, a film that uses progressive humor to oppose homophobia and expose the potential dangers and pitfalls of conforming to social constructions of gender. Don't Be that Freshman is a film about three pairs of college roommates in their first semester at college who become each other's first friends on campus. It is a character-driven comedy that attempts to normalize non-heterosexual sexual orientation and gender non-conformity, to advocate a type of living that does not conform to problematic social constructions and cultural ideologies, and at the same time to appeal to a mainstream audience. The film version is twenty-five minutes long and consists of ten scenes from the script.

New palladium(II) complexes with pyrazole ligands Part I. Synthesis, spectral and thermal studies, and antitumor evaluation

The pyrazole ligand 3,5-dimethyl-4-iodopyrazole (HdmIPz) has been used to obtain a series of palladium(II) complexes (1-4) of the type [PdX(2)(HdmIPz)(2)] {X = Cl(-) (1); Br(-) (2); I(-) (3); SCN(-) (4)}. All compounds have been isolated, purified, and characterized by means of elemental analysis, IR spectroscopy, (1)H and (13)C{(1)H}-NMR experiments, differential thermal analysis (DTA), and thermogravimetry (TG). The TG/DTA curves showed that the compounds released ligands in the temperature range 137-605 A degrees C, yielding metallic palladium as final residue. The complexes and the ligand together with cisplatin have been tested in vitro by MTT assay for their cytotoxicity against two murine cancer cell lines: mammary adenocarcinoma (LM3) and lung adenocarcinoma (LP07).