Synthesis, Crystal Structure and Bioactivity of Phenazine-1-carboxylic Acylhydrazone Derivatives.

A phenazine-1-carboxylic acid intermediate was synthesized from the reaction of aniline and 2-bromo-3-nitro-benzoic acid. It was then esterified and reacted with hydrazine hydrate to afford phenazine-1-carboxylic hydrazine. Finally, 10 new hydrazone compounds 3a-3j were obtained by the condensation reaction of phenazine-1-carboxylic acid hydrazide and the respective aldehyde-containing compound. The structures were characterized by 1H and 13C NMR spectroscopy, MS and single crystal X-ray diffraction. The antitumor activity of the target compounds in vitro (HeLa and A549) was determined by thiazolyl blue tetrazolium bromide. The results showed that compound (E)-N'-(2-hydroxy-4-(2-(piperidine-1-yl) ethoxy) benzyl) phenazine-1-carbonyl hydrazide 3d exhibited good cytotoxic activity.

Scandium calix[n]arenes (n = 4, 6, 8): structural, cytotoxicity and ring opening polymerization studies.

Interaction of [Sc(OR)3] (R = iPr or triflate) with p-tert-butylcalix[n]arenes, where n = 4, 6, or 8, affords a number of intriguing structural motifs, which are relatively non-toxic (cytotoxicity evaluated against cell lines HCT116 and HT-29) and a number were capable of the ring opening polymerization (ROP) of cyclohexene oxide.

Comparative assessment of marine weathering of ROP-derived biopolymers against conventional plastics.

Bio-based plastics were designed to replace single-use plastics and to cause less post-consumer environmental damage. This paper assesses the weathering of four bio-based polymers created by ring opening polymerization (ROP) promoted by a previously reported Ti-based catalyst, to detect any problems before production was scaled up. Samples were aged in seawater to identify degradation products and monitor structural changes. Surfaces evidenced degradation and a range of leaching products was observed. Aside from compounds used in the preparation of the plastics (i.e. residual monomers and benzyl alcohol), the degradation products included carboxylic acids (often found in plastic leachate), oxacyclohexadecan-2-one (potentially toxic to aquatic life) and triphenylmethane (potential carcinogen). Overall, there were fewer structural changes in the fossil fuel based polymer (PS) and in the commercially available bio-based plastic studied for comparison purposes than the lab based bio-based polymers.

Water-Soluble Rhenium Phosphine Complexes Incorporating the Ph2C(X) Motif (X = O-, NH-): Structural and Cytotoxicity Studies.

Reaction of [ReOCl3(PPh3)2] or [ReO2I(PPh3)2] with 2,2'-diphenylglycine (dpgH2) in refluxing ethanol afforded the air-stable complex [ReO(dpgH)(dpg)(PPh3)] (1). Treatment of [ReO(OEt)I2(PPh3)2] with 1,2,3-triaza-7-phosphaadamantane (PTA) afforded the complex [ReO(OEt)I2(PTA)2] (2). Reaction of [ReOI2(PTA)3] with dpgH2 led to the isolation of the complex [Re(NCPh2)I2(PTA)3]·0.5EtOH (3·0.5EtOH). A similar reaction but using [ReOX2(PTA)3] (X = Cl, Br) resulted in the analogous halide complexes [Re(NCPh2)Cl2(PTA)3]·2EtOH (4·2EtOH) and [Re(NCPh2)(PTA)3Br2]·1.6EtOH (5·1.6EtOH). Using benzilic acid (2,2'-diphenylglycolic acid, benzH) with 2 afforded the complex [ReO(benz)2(PTA)][PTAH]·EtOH (6·EtOH). The potential for the formation of complexes using radioisotopes with relatively short half-lives suitable for nuclear medicine applications by developing conditions for [Re(NCPh2)(dpg)I(PTA)3] (7)[ReO4]- in a 4 h time scale was investigated. A procedure for the technetium analog of complex [Re(NCPh2)I2(PTA)3] (3) from 99mTc[TcO4]- was then investigated. The molecular structures of 1-7 are reported; complexes 3-7 have been studied using in vitro cell assays (HeLa, HCT116, HT-29, and HEK 293) and were found to have IC50 values in the range of 29-1858 µM.

Molecular Tweezers-like Calix[4]arene Based Alkaline Earth Metal Cation (Ca2+, Sr2+, and Ba2+) Chemosensor and Its Imaging in Living Cells and Zebrafish.

Although alkaline earth metal cations play an important role in our daily life, little attention has been paid to the field of fast quantitative analysis of their content due to a lack of satisfactory precision and a fast and convenient means of detection. In this study, we have designed a set of molecular tweezers based on the calix[4]arene chemosensor L, which was found to exhibit high selectivity and sensitivity toward Ca2+, Sr2+, and Ba2+ (by UV-vis and fluorescence methods) with low detection limits of the order of 10-7 to 10-8 M and high association constants (of the order of 106). More significantly, sensor L not only can recognize Ca2+, Sr2+, and Ba2+ but also can further discriminate between these three cations via the differing red shifts in their UV-vis spectra (560 nm for L·Ca2+, 570 nm for L·Sr2+, and 580 nm for L·Ba2+ complex) which is attributed to their different atomic radii. A rare synergistic effect for the recognition mechanism has been demonstrated by 1H NMR spectroscopic titration. Sensor L constructed a high shielding field by the cooperation of Tris with alkaline earth metal ion after complex. Additionally, the presence of acetoxymethyl group in sensor L results in enhancement of cell permeability, and as a consequence, sensor L exhibited excellent sensing and imaging (in vivo) in living cells and in zebrafish.

An efficient ICT-based ratio/colorimetric tripodal azobenzene probe for the recognition/discrimination of F-, AcO- and H2PO4- anions.

The tripodal probe L was readily prepared via introducing rhodamine and azobenzene groups in a two-step procedure. Studies of the recognition properties indicated that probe L exhibited high sensitivity and selectivity towards F-, AcO- and H2PO4- through a ratiometric colorimetric response with low detection limits of the order of 10-7 M. The complexation behaviour was fully investigated by spectral titration, 1H NMR spectroscopic titration and mass spectrometry. Probe L not only recognizes F-, AcO- and H2PO4-, but can also distinguish between these three anions via the different ratiometric behaviour in their UV-vis spectra (387/505 nm for L-H2PO4-, 387/530 nm for L-AcO- and 387/575 nm for L-F- complex) or via different colour changes (light coral for L-H2PO4-, light pink for L-AcO- and violet for the L-F- complex). Additionally, given the presence of NH and OH groups in probe L, which can be protonated and deprotonated, probe L further exhibited an excellent pH response over a wide pH range (pH 3 to pH 12).

Cyclotrimerization of alkynes catalyzed by a self-supported cyclic tri-nuclear nickel(0) complex with α-diimine ligands.

A cyclic tri-nuclear α-diimine nickel(0) complex [{Ni(µ-LMe-2,4)}3] (2) was synthesized from a "pre-organized", trimerized trigonal LNiBr2-type precursor [Ni3(µ2-Br)3(µ3-Br)2(LMe-2,4)3]·Br (1; LMe-2,4 = [(2,4-Me2C6H3)NC(Me)]2). In complex 2, the α-diimine ligands not only exhibit the normal N,N'-chelating mode, but they also act as bridges between the Ni atoms through an unusual π-coordination of a C[double bond, length as m-dash]N bond to Ni. Complex 2 is able to catalyze the cyclotrimerization of alkynes to form substituted benzenes in good yield and regio-selectivity for the 1,3,5-isomers, which is found to vary with the nature of the alkyne employed. This complex represents a convenient self-supported nickel(0) catalyst with no need for additional ligands and reducing agent.

Erratum: Chen, L.X., et al. Synthesis and Structure of the Inclusion Complex {NdQ[5]K@Q[10](H2O)4}•4NO3•20H2O. Molecules 2017, 22, 1147.

The authors wish to make the following correction to their paper [...].

A quinoline-based fluorometric and colorimetric dual-modal pH probe and its application in bioimaging.

The compound (E)-8-hydroxyl-2-[(E)-2-(2, 4-dihydroxyphenyl)vinyl]-quinoline (1) has been developed as a fluorometric and colorimetric dual-modal probe for pH detection in solution and in vivo. Remarkable changes in the fluorescence intensity with large Stokes shifts and colorimetric responses were observed as a function of pH. The sensing mechanisms involving protonation and deprotonation processes over the acidic and alkaline pH ranges were confirmed by 1H NMR and IR spectroscopic analysis. Furthermore, the application of probe 1 for the imaging of live PC3 cells was successfully achieved. Test strips based on probe 1 were fabricated, and were found to act as a convenient and efficient pH test kits.

A chemosensor for micro- to nano-molar detection of Ag+ and Hg2+ ions in pure aqueous media and its applications in cell imaging.

The pyridine substituted thiourea derivative PTB-1 was synthesized and characterized by spectroscopic techniques as well as by single crystal X-ray crystallography. The metal ion sensing ability of PTB-1 was explored by various experimental (naked-eye, UV-Vis, fluorescence, mass spectrometry and 1H NMR spectroscopy) and theoretical (B3LYP/6-31G**/LANL2DZ) methods. PTB-1 exhibited a highly selective naked-eye detectable color change from colorless to dark brown and UV-Vis spectral changes for the detection of Ag+ with a detection limit of 3.67 µM in aqueous medium. The detection of Ag+ ions was achieved by test paper strip and supported silica methods. In contrast, PTB-1 exhibited a 23-fold enhanced emission at 420 nm in the presence of Hg2+ ions with a nano-molar detection limit of 0.69 nM. Finally, the sensor PTB-1 was applied successfully for the intracellular detection of Hg2+ ions in a HepG2 liver cell line, which was monitored by the use of confocal imaging techniques.

Characterization of the Aggregation-Induced Enhanced Emission of N,N'-bis(4-methoxysalicylide)benzene-1,4-diamine.

N,N'-bis(4-methoxysalicylide)benzene-1,4-diamine (S1) was synthesized from 4-methoxysalicylaldehyde and p-phenylenediamine and it was found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics. In aprotic solvent, S1 displayed very weak fluorescence, whilst strong emission was observed when in protic solvent. The morphology characteristics and luminescent properties of S1 were determined from the fluorescence and UV absorption spectra, SEM, fluorescence microscope and grading analysis. Analysis of the single crystal diffraction data infers that the intramolecular hydrogen bonding constitutes to a coplanar structure and orderly packing in aggregated state, which in turn hinders intramolecular C-N single bond rotation. Given that the three benzene rings formed a large plane conjugated structure, the fluorescence emission was significantly enhanced. The absolute fluorescence quantum yield and fluorescence lifetime also showed that radiation transition was effectively enhanced in the aggregated state. Moreover, the AIEE behavior of S1 suggests there is a potential application in the fluorescence sensing of some volatile organic solvents.

Vanadyl calix[6]arene complexes: synthesis, structural studies and ethylene homo-(co-)polymerization capability.

Treatment of p-tert-butylcalix[6]areneH6 (L(6)H6) with in situ [LiVO(Ot-Bu)4] afforded, after work-up, the dark green complex [Li(MeCN)4][V2(O)2Li(MeCN)(L(6)H2)2]·8MeCN (1·8MeCN). On one occasion, the reaction led to the formation of a mixture of products, the bulk of which differing from 1 only in the amount of solvate, viz.2·9.67MeCN. The second minor, yellow product has the formula {[(VO2)2(L(6)H2)(Li(MeCN)2)2]·2MeCN}n (3·2MeCN), and comprises a 1D polymeric structure with links through the L(6)H2 ligand and Li2O2 units. When the reverse order of addition was employed such that lithium tert-butoxide (7.5 equivalents) was added to L(6)H6, and subsequently treated with VOCl3 (2 equiv.), the complex {[VO(THF)][VO(µ-O)]2Li(THF)(Et2O)][L(6)]}·2Et2O·0.5THF (4·2Et2O·0.5THF), which contains a trinuclear motif possessing a central, octahedral vanadyl centre linked via oxo bridges to two tetrahedral (C3v) vanadyl centres, was isolated. The calix[6]arene in 4 is severely twisted and adopts a 'down, down, down, down, out, out' conformation. Use of excess lithium tert-butoxide led to a complex very similar to 4, differing only in the solvent of crystallization, namely 5·Et2O·2THF. The ability of 1 and 5 to act as pre-catalysts for ethylene polymerization in the presence of a variety of co-catalysts and under various conditions has been investigated. Co-polymerization of ethylene with propylene and with 1-hexene have also been conducted; results are compared versus VO(OEt)Cl2.

Vanadium(V) Oxo and imido calix[8]arene complexes: synthesis, structural studies, and ethylene homo/copolymerisation capability.

Interaction of p-tert-butylcalix[8]areneH8 (L(8) H8 ) with [NaVO(OtBu)4 ] (formed in situ from VOCl3 ) afforded the complex [Na(NCMe)5 ][(VO)2 L(8) H]⋅4 MeCN (1⋅4 MeCN). Increasing [NaVO(OtBu)4 ] to 4 equiv led to [Na(NCMe)6 ]2 [(Na(VO)4 L(8) )(Na(NCMe))3 ]2 ⋅10 MeCN (2⋅10 MeCN). With adventitious oxygen, reaction of 4 equiv of [VO(OtBu)3 ] with L(8) H8 afforded the alkali-metal-free complex [(VO)4 L(8) (µ(3) -O)2 ] (3); solvates 3⋅3 MeCN and 3⋅3 CH2 Cl2 were isolated. For the lithium analogue, the order of addition had to be reversed such that lithium tert-butoxide was added to L(8) H8 and then treated with 2 equiv of VOCl3 ; crystallisation afforded [(VO2 )2 Li6 [L(8) ](thf)2 (OtBu)2 (Et2 O)2 ]⋅Et2 O (4⋅Et2 O). Upon extraction into acetonitrile, [Li(NCMe)4 ][(VO)2 L(8) H]⋅8 MeCN (5⋅8 MeCN) was formed. Use of the imido precursors [V(NtBu)(OtBu)3 ] and [V(Np-tolyl)(OtBu)3 ] and L(8) H8 , afforded [tBuNH3 ][{V(p-tolylN)}2 L(8) H]⋅3 1/2 MeCN (6⋅3 1/2 MeCN). The molecular structures of 1 to 6 are reported. Complexes 1, 3, and 4 were screened as precatalysts for the polymerisation of ethylene in the presence of cocatalysts at various temperatures and for the copolymerisation of ethylene with propylene. Activities as high as 136 000 g (mmol(V) h)(-1) were sometimes achieved; higher molecular weight polymers could be obtained versus the benchmark [VO(OEt)Cl2 ]. For copolymerisation, incorporation of propylene was 7.1-10.9 mol % (compare 10 mol % for [VO(OEt)Cl2 ]), although catalytic activities were lower than [VO(OEt)Cl2 ].

Tri- and tetra-dentate imine vanadyl complexes: synthesis, structure and ethylene polymerization/ring opening polymerization capability.

Reaction of the ligand 2,4-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenol (L(1)H) with [VOCl3] in the presence of triethylamine afforded the complex [VOCl2L(1)] (1), whereas use of [VO(OnPr)3] led to the isolation of [VO2L(1)] (2) or [VO2L(1)]·2/3MeCN (2·2/3MeCN). Reaction of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8-ylimino)methyl)-4,6-R(1),R(2)-phenols (R(1) = R(2) = (t)Bu; L(2)H), (R(1) = R(2) = Me; L(3)H) or (R(1) = Me, R(2) = Ad; L(4)H) with [VO(OnPr)3] afforded complexes of the type [L(2-4)VO] (where L(2) = 3, L(3) = 4, L(4) = 5). The molecular structures of 1 to 3 are reported; the metal centre adopts a distorted octahedral, trigonal bipyramidal or square-based pyramidal geometry respectively. In Schlenk line tests, all complexes have been screened as pre-catalysts for the polymerization of ethylene using diethylaluminium chloride (DEAC) as co-catalyst in the presence of ethyltrichloroacetate (ETA), and for the ring opening polymerization (ROP) of ε-caprolactone in the presence of benzyl alcohol. All pre-catalyst/DEAC/ETA systems are highly active ethylene polymerization catalysts affording linear polyethylene with activities in the range 3000-10,700 g (mol h bar)(-1); the use of methylaluminoxane (MAO) or modified MAO as co-catalyst led to poor or no activity. In a parallel pressure reactor, 3-5 have been screened as pre-catalysts for ethylene polymerization in the presence of either DEAC or DMAC (dimethylaluminium chloride) and ETA at various temperatures and for the co-polymerization of ethylene with propylene. The use of DMAC proved more promising with 3 achieving an activity of 63,000 g (mol h bar)(-1) at 50 °C and affording UHMWPE (M(w) ~ 2,000,000). In the case of the co-polymerization, the incorporation of propylene was 6.9-8.8 mol%, with 3 exhibiting the highest incorporation when using either DEAC or DMAC. In the case of the ring opening polymerization (ROP) of ε-caprolactone, systems employing complexes 1-5 were virtually inactive at temperatures <110 °C; on increasing the CL : V ratio at 110 °C, conversions of the order of 80% were achievable.

A novel fluorescent "turn-on" chemosensor for nanomolar detection of Fe(III) from aqueous solution and its application in living cells imaging.

An electronically active and spectral sensitive fluorescent "turn-on" chemosensor (BTP-1) based on the benzo-thiazolo-pyrimidine unit was designed and synthesized for the highly selective and sensitive detection of Fe(3+) from aqueous medium. With Fe(3+), the sensor BTP-1 showed a remarkable fluorescence enhancement at 554 nm (λex = 314 nm) due to the inhibition of photo-induced electron transfer. The sensor formed a host-guest complex in 1:1 stoichiometry with the detection limit down to 0.74 nM. Further, the sensor was successfully utilized for the qualitative and quantitative intracellular detection of Fe(3+) in two liver cell lines i.e., HepG2 cells (human hepatocellular liver carcinoma cell line) and HL-7701 cells (human normal liver cell line) by a confocal imaging technique.

Synthesis, characterization and ethylene polymerization behaviour of binuclear nickel halides bearing 4,5,9,10-tetra(arylimino)pyrenylidenes.

Pyrene-4,5,9,10-tetraone was prepared via the oxidation of pyrene, and reacted with various anilines to afford a series of 4,5,9,10-tetra(arylimino)pyrenylidene derivatives (L1-L4). The tetraimino-pyrene compounds L1 and L2 were reacted with two equivalents of (DME)NiBr2 in CH2Cl2 to afford the corresponding dinickel bromide complexes (Ni1 and Ni2). The organic compounds were fully characterized, whilst the bi-metallic complexes were characterized by FT-IR spectra and elemental analysis. The molecular structures of representative organic and nickel compounds were confirmed by single-crystal X-ray diffraction studies. These nickel complexes exhibited high activities towards ethylene polymerization in the presence of either MAO or Me2AlCl, maintaining a high activity over a prolonged period (longer than previously reported dinickel complex pre-catalysts). The polyethylene obtained was characterized by GPC, DSC and FT-IR spectroscopy and was found to possess branched features.

Vanadyl complexes bearing bi-dentate phenoxyimine ligands: synthesis, structural studies and ethylene polymerization capability.

Reaction of [VO(OnPr)3] with the Schiff bases 3,5-(tBu)2-2-OH-C6H2CH(N(x-OR-C6H4)) (R = Me; x = 2, L(1)H; x = 3, L(2)H; x = 4, L(3)H; R = Et (L(4)H), CF3 (L(5)H), Ph (L(6)H)) or 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2'-(2''-(OR1)C6H4)C6H4) (R = adamantyl, R(1) = Ph (L(7)H) or R = C(Me)2Ph, R(1) = Ph (L(8)H)) afforded the bis(chelate) vanadium(iv) complexes [VO(L(n))2] (n = 1 (1·2MeCN); n = 2 (2); n = 3 (3·2MeCN); n = 4 (4); n = 5 (5); n = 6 (6); n = 6, (7·1.5MeCN); n = 7, (8); n = 8, (9)); in the case of L(6)H, the oxo-bridged vanadium(v) complexes [VO(µ-O)(L(6))]2 (10) was also isolated. By contrast, interaction of 4-methyl-3-(R)-2-(OH)-C6H4C[double bond, length as m-dash]N(2'-(2''-(OR1)C6H4)C6H4) (R = adamantyl, R(1) = Me (L(9)H); R = tBu, R(1) = Me (L(10)H); R = C(Me)2Ph, R(1) = Me (L(11)H)) with [VO(OnPr)3] led to the isolation of the dinuclear complexes [VO(µ-OH)(µ-OnPr)(L(n))]2 (n = 9, (·4MeCN); 10, (12); 11, (13)), respectively. The molecular structures of 1 to 13 are reported. All complexes have been screened as pre-catalysts for the polymerization of ethylene in the presence of the co-catalyst diethylaluminium chloride (DEAC) with or without ethyltrichloroacetate (ETA) present at 1 or 10 bar of ethylene. Under high pressure, all pre-catalysts exhibited high activity and afforded high molecular weight (Mw ≈ 200 000 to 675 000 g mol(-1)), linear polyethylene with activities (in the presence of ETA) in the range 4960-16 400 g mmol(-1) h(-1); at one bar, the products were generally of lower molecular weight. The use of methylaluminoxane (MAO) or modified MAO (MMAO) as co-catalyst led to trace or poor (≤110 g mmol(-1) h(-1)) activity, respectively.

2-(1-(2-Benzhydrylnaphthylimino)ethyl)pyridylnickel halides: synthesis, characterization, and ethylene polymerization behavior.

A series of 2-(1-(2-benzhydrylnaphthylimino)ethyl)pyridine derivatives (L1-L3) was synthesized and fully characterized. The organic compounds acted as bi-dentate ligands on reacting with nickel halides to afford two kinds of nickel complexes, either mononuclear bis-ligated L2NiBr2 (Ni1-Ni3) or chloro-bridged dinuclear L2Ni2Cl4 (Ni4-Ni6) complexes. The nickel complexes were fully characterized, and the single crystal X-ray diffraction revealed for Ni2, a distorted square pyramidal geometry at nickel comprising four nitrogens of two ligands and one bromide; whereas for Ni4, a centrosymmetric dimer possessing a distorted octahedral geometry at nickel was formed by two nitrogens of one ligand, two bridging chlorides and one terminal chloride along with oxygen from methanol (solvent). When activated with diethylaluminium chloride (Et2AlCl), all nickel complexes performed with high activities (up to 1.22 × 10(7) g (PE) mol(-1) (Ni) h(-1)) towards ethylene polymerization; the obtained polyethylene possessed high branching, low molecular weight and narrow polydispersity, suggestive of a single-site active species. The effect of the polymerization parameters, including the nature of the ligands/halides on the catalytic performance is discussed.

Highly active, thermally stable, ethylene-polymerisation pre-catalysts based on niobium/tantalum-imine systems.

The reactions of MCl5 or MOCl3 with imidazole-based pro-ligand L(1)H, 3,5-tBu2-2-OH-C6H2-(4,5-Ph2-1H-)imidazole, or oxazole-based ligand L(2)H, 3,5-tBu2-2-OH-C6H2 (1H-phenanthro[9,10-d])oxazole, following work-up, afforded octahedral complexes [MX(L(1,2))], where MX=NbCl4 (L(1), 1a; L(2), 2a), [NbOCl2(NCMe)] (L(1), 1b; L(2), 2b), TaCl4 (L(1), 1c; L(2), 2c), or [TaOCl2(NCMe)] (L(1), 1d). The treatment of α-diimine ligand L(3), (2,6-iPr2C6H3N=CH)2, with [MCl4(thf)2] (M=Nb, Ta) afforded [MCl4(L(3))] (M=Nb, 3a; Ta, 3b). The reaction of [MCl3(dme)] (dme=1,2-dimethoxyethane; M=Nb, Ta) with bis(imino)pyridine ligand L(4), 2,6-[2,6-iPr2C6H3N=(Me)C]2C5H3N, afforded known complexes of the type [MCl3(L(4))] (M=Nb, 4a; Ta, 4b), whereas the reaction of 2-acetyl-6-iminopyridine ligand L(5), 2-[2,6-iPr2C6H3N=(Me)C]-6-Ac-C5H3N, with the niobium precursor afforded the coupled product [({2-Ac-6-(2,6-iPr2C6H3N=(Me)C)C5H3N}NbOCl2)2] (5). The reaction of MCl5 with Schiff-base pro-ligands L(6)H-L(10)H, 3,5-(R(1))2-2-OH-C6H2CH=N(2-OR(2)-C6H4), (L(6)H: R(1)=tBu, R(2)=Ph; L(7)H: R(1)=tBu, R(2)=Me; L(8)H: R(1)=Cl, R(2)=Ph; L(9)H: R(1)=Cl, R(2)=Me; L(10)H: R(1)=Cl, R(2)=CF3) afforded [MCl4(L(6-10))] complexes (M=Nb, 6a-10a; M=Ta, 6b-9b). In the case of compound 8b, the corresponding zwitterion was also synthesised, namely [Ta(-)Cl5(L(8)H)(+)]·MeCN (8c). Unexpectedly, the reaction of L(7)H with TaCl5 at reflux in toluene led to the removal of the methyl group and the formation of trichloride 7c [TaCl3(L(7-Me))]; conducting the reaction at room temperature led to the formation of the expected methoxy compound (7b). Upon activation with methylaluminoxane (MAO), these complexes displayed poor activities for the homogeneous polymerisation of ethylene. However, the use of chloroalkylaluminium reagents, such as dimethylaluminium chloride (DMAC) and methylaluminium dichloride (MADC), as co-catalysts in the presence of the reactivator ethyl trichloroacetate (ETA) generated thermally stable catalysts with, in the case of niobium, catalytic activities that were two orders of magnitude higher than those previously observed. The effects of steric hindrance and electronic configuration on the polymerisation activity of these tantalum and niobium pre-catalysts were investigated. Spectroscopic studies ((1)H NMR, (13)C NMR and (1)H-(1)H and (1)H-(13)C correlations) on the reactions of compounds 4a/4b with either MAO(50) or AlMe3/[CPh3](+)[B(C6F5)4](-) were consistent with the formation of a diamagnetic cation of the form [L(4)AlMe2](+) (MAO(50) is the product of the vacuum distillation of commercial MAO at +50 °C and contains only 1 mol% of Al in the form of free AlMe3). In the presence of MAO, this cationic aluminium complex was not capable of initiating the ROMP (ring opening metathesis polymerisation) of norbornene, whereas the 4a/4b systems with MAO(50) were active. A parallel pressure reactor (PPR)-based homogeneous polymerisation screening by using pre-catalysts 1b, 1c, 2a, 3a and 6a, in combination with MAO, revealed only moderate-to-good activities for the homo-polymerisation of ethylene and the co-polymerisation of ethylene/1-hexene. The molecular structures are reported for complexes 1a-1c, 2b, 5, 6a, 6b, 7a, 8a and 8c.

Synthesis, characterization and catalytic behavior toward ethylene of 2-[1-(4,6-dimethyl-2-benzhydrylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylmetal (iron or cobalt) chlorides.

A series of 2-[1-(4,6-dimethyl-2-benzhydrylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridines was synthesized and used to prepare the iron(II) and cobalt(II) chloride complexes thereof. All organic compounds were fully characterized by elemental analysis, IR and NMR ((1)H/(13)C) spectroscopy, whilst the metal complexes were characterized by elemental analysis and IR spectroscopy as well as by single-crystal X-ray diffraction studies (for two representative cobalt complexes), which revealed that the geometry at the metal was either pseudo-square-pyramidal or trigonal bipyramidal. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all metal complex pre-catalysts exhibited high activities for ethylene polymerization. The iron pre-catalysts show much higher activity than did their cobalt analogues; however, the iron catalytic systems generally produced polyethylene of wide molecular weight polydispersity. At elevated reaction temperature, the polyethylene was of lower molecular weight, but revealed narrow polydispersity.