Cyclopentadienylaluminum thiolates - synthesis and structure

The dicyclopentadienylaluminum thiolates [Cp₂Al(μ-SR)]₂, where R = Et (1), ⁱPr (2), were obtained by reacting Cl₂AlSR with CpNa at the molar ratio 1:2, respectively. Use of CpLi instead of CpNa at the same molar ratio of reagents leads to the formation of cyclopentadienyl(chloro)aluminum thiolates [Cp(Cl)Al(μ-SR)]₂, exclusively, where R = Et (3), ⁱPr (4), ⁱBu (5), and ⁿBu (6). The compounds were characterized by ¹H, ¹³C, and ²⁷Al NMR spectroscopy. The structures of the compounds 1 and 4 were determined by X-ray crystallography.     

Polyketides from the mangrove-derived endophytic fungus Acremonium strictum

Five new polyketide derivatives, 6′-hydroxypestalotiopsone C (1), acropyrone (2), bicytosporone D (3), waol acid (4), and pestalotiopene C (5), together with seven known metabolites (6–12), were obtained from extracts of the endophytic fungus Acremonium strictum, isolated from the mangrove tree Rhizophora apiculata. The structures of the isolated compounds were elucidated on the basis of comprehensive NMR and MS analysis. Compounds 6, 7, and 9 showed moderate cytotoxic activity against human cisplatin-sensitive (IC₅₀ values 27.1, 76.2, and 8.3 μM, respectively) and resistant A2780 cell lines (IC₅₀ values 12.6, 30.1, and 19.0 μM, respectively), whereas only 9 exhibited antibacterial activity against Staphylococcus aureus (MIC value 14.3 μM).     

Synthesis of the first examples of stable heterometallic isopropoxides of an organometallic RSn(IV) moiety

Five-, six-, and seven-coordinate volatile butyltin(IV) heterobimetallic derivatives, respectively of the types, [BuSn{(μ-OPrⁱ)₂Al(OPrⁱ)₂}Cl₂] (1), [BuSn{(μ-OPrⁱ)₂Al(OPrⁱ)₂}₂Cl] (2), and BuSn{(μ-OPrⁱ)₂M(OPrⁱ)_x − 2}₃ (3:M = Al (x = 4); 4:M = Ga (x = 4); 5:M = Nb (x = 6)) have been synthesized by the reactions of BuSnCl₃ with potassium tetraisopropoxoaluminate in 1:1, 1:2, and 1:3 molar ratios. Replacement reactions of chloride in (1) and (2) with appropriate alkoxometallate (tetraisopropoxoaluminate, tetraisopropoxogallate, or hexaisopropoxoniobate) ligands result in the formation of novel BuSn(IV) heterotri- and tetra-metallic derivatives. All of these derivatives have been characterized by elemental analyses, molecular weight measurements, and spectroscopic (IR, ¹H, ²⁷Al, and ¹¹⁹Sn NMR) studies. Based on these studies, plausible structures for the new derivatives involving bidentate ligation of the alkoxometallate ligands have been suggested.     

Fascioquinols A-F: bioactive meroterpenes from a deep-water southern Australian marine sponge, Fasciospongia sp.

Chemical investigation of a southern Australian deep-water marine sponge, Fasciospongia sp., returned the new meroterpene sulfate fascioquinol A (1) together with a series of acid mediated hydrolysis/cyclization products, fascioquinols B (2), C (3) and D (4), and strongylophorine-22 (5). Additional co-metabolites include the new meroterpenes fascioquinol E (6) and fascioquinol F (8), together with the known sponge metabolite geranylgeranyl 1,4-hydroquinone (7). Structures were assigned to 1-8 on the basis of detailed spectroscopic analysis, chemical interconversion, mechanistic and biosynthetic considerations, and literature comparisons. The known 1,4-hydroquinone 7 was identified as the dominant cytotoxic principle in the Fasciospongia sp. extract, with selective inhibitory activity against gastric adenocarcinoma (AGS, IC₅₀ 8 μM) and neuroblastoma (SH-SY5Y, IC₅₀ 4 μM) cell lines. By contrast, while the fascioquinols displayed little or no inhibitory activity towards human cell lines, 1 and 2 displayed promising Gram-positive selective antibacterial activity towards Staphylococcus aureus (IC₅₀ 0.9-2.5 μM) and Bacillus subtilis (IC₅₀ 0.3-7.0 μM).     

Synthesis and pharmacological evaluation of 6a,7-dihydro-6H,13H-pyrazino[1,2-a;4,5-a′]diindole analogs as melatonin receptor ligands

The synthesis of two melatonin-derived analogs of the novel 6a,7-dihydro-6H,13H-pyrazino[1,2-a;4,5-a′]diindole ring system is described. The non-methoxy and methoxy analogs, 4a and 4b were prepared in seven steps starting from indoline-2-carboxylic acid 5a and 5-methoxyindoline-2-carboxylic acid 5b, respectively. While 4a exhibited micromolar affinities for both melatonin receptors, the methoxy analog 4b displayed moderate affinity for MT₂ receptors (K_i=0.41 μM) being 4.4-fold higher than for the MT₁ subtype.     

24-Thiacycloartanol, a potent mechanism-based inactivator of plant sterol methyltransferase

The rationally designed substrate mimic of cycloartenol, 24-thiacycloartanol (24-TC) 4A, and its corresponding sulfonium salt 5A were tested against the recombinant sterol methyltransferase (SMT) from Glycine max (soybean). Analog 4A was found to irreversibly inactivate the enzyme generating competitive- and time-dependent inhibition of activity accompanied by a K_i value of 2 μM and k_inact of 0.3 min⁻¹. Analog 5A, a presumptive high-energy intermediate of the SMT catalyzed reaction, was found to be a reversible, non-competitive-type inhibitor generating a K_i value of 55 nM.     

Isolation of secondary metabolites from Hortia oreadica (Rutaceae) leaves through high-speed counter-current chromatography

High-speed counter-current chromatography (HSCCC) with a two-phase solvent system (hexane–ethanol–acetonitrile–water 10:8:1:1, v/v) was applied to examine the leaves of Hortia oreadica, which afforded the known limonoid guyanin (1), the alkaloids rutaecarpin (2) and dictamnine (6), the dihydrocinnamic acid derivatives methyl 5,7-dimethoxy-2,2-dimethyl-2H-1-benzopyran-6-propanoate (3), 5,8-dimethoxy-2,2-dimethyl-2H-1-benzopyran-6-propanoic acid (4), together with the new E-3,4-dimethoxy-α(3-hydroxy-4-carbomethoxyphenyl)cinnamic acid (5). The recovery of compounds 1–6 was determined by comparison with LC-atmospheric pressure chemical ionization MS/MS data: 66.2%, 93.1%, 102.5%, 101.2%, 99.0% and 84.9%, respectively. Compound 3 showed IC₅₀ of 23.6 μM against Plasmodium falciparum and 15.6 μM against Trypanosoma brucei rhodesienses and was not toxic to KB cells (IC₅₀ > 100 μM).     

Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

Neosappanone A, a xanthine oxidase (XO) inhibitory dimeric methanodibenzoxocinone with a new carbon skeleton from Caesalpinia sappan

A novel dimeric methanodibenzoxocinone, named neosappanone A (1), possessing a unique unprecedented novel carbon framework, has been isolated from the heartwood of Caesalpinia sappan L. of Vietnam, and its structure was elucidated on the basis of spectroscopic analysis. Neosappanone A (1) competitively inhibited xanthine oxidase in a concentration-dependent manner (IC₅₀, 29.7 μM; K_i, 16.3 μM).     

Substituted lithiumtrimethylsiloxysilanides LiSiRR′(OSiMe3) - Investigations of their synthesis, stability and reactivity

The reactions of the trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-h: R′ = Ph, 1a: R = H, 1b: R = Me, 1c: R = Et, 1d: R = ⁱPr, 1e: R = ^tBu, 1f: R = Ph, 1g: R = 2,4,6-Me₃C₆H₂ (Mes), 1h: R = 2,4,6-(Me₂CH)₃C₆H₂ (Tip); 1i: R = R′ = Mes) with lithium metal in tetrahydrofuran (THF) at −78 °C and in a mixture of THF/diethyl ether/n-pentane in a volume ratio 4:1:1 at −110 °C lead to mixtures of numerous compounds. Dependent on the substituents silyllithium derivatives (Me₃SiO)RR′SiLi (2b-i), Me₃SiO(RR′Si)₂Li (3a-g), Me₃SiRR′SiLi (4a-h), (LiO)RR′SiLi (12e, 12g-i), trisiloxanes (Me₃SiO)₂SiRR′ (5a-i) and trimethylsiloxydisilanes (6f^∗, 6h^∗, 6i^∗) are formed. All silyllithium compounds were trapped with Me₃SiCl or HMe₂SiCl resulting in the following products: (Me₃SiO)RR′SiSiMe₂R″ (6b-i: R″ = Me, 7c-i: R″ = H), Me₃SiO(RR′Si)₂SiMe₂R″ (8a-g: R″ = Me, 9a-g: R″ = H), Me₃SiRR′SiSiMe₂R″ (10a-h: R″ = Me, 11a-h: R″ = H) and (HMe₂SiO)RR′SiSiMe₂H (13e, 13g-i). The stability of trimethylsiloxysilyllithiums 2 depends on the substituents and on the temperature. (Me₃SiO)Mes₂SiLi (2i) is the most stable compound due to the high steric shielding of the silicon centre. The trimethylsiloxysilyllithiums 2a-g undergo partially self-condensation to afford the corresponding trimethylsiloxydisilanyllithiums Me₃SiO(RR′Si)₂Li (3a-g). (Me₃)Si-O bond cleavage was observed for 2e and 2g-i. The relatively stable trimethylsiloxysilyllithiums 2f, 2g and 2i react with n-butyllithium under nucleophilic butylation to give the n-butyl-substituted silyllithiums ⁿBuRR′SiLi (15g, 15f, 15i), which were trapped with Me₃SiCl. By reaction of 2g and 2i with 2,3-dimethylbuta-1,3-diene the corresponding 1,1-diarylsilacyclopentenes 17g and 17i are obtained.X-ray studies of 17g revealed a folded silacyclopentene ring with the silicon atom located 0.5 Å above the mean plane formed by the four carbon ring atoms.     

Montamine, a unique dimeric indole alkaloid, from the seeds of Centaurea montana (Asteraceae), and its in vitro cytotoxic activity against the CaCo2 colon cancer cells

Reversed-phase HPLC analysis of the methanol extract of the seeds of Centaurea montana afforded a flavanone, montanoside (4), six epoxylignans, berchemol (7), berchemol 4′-O-β-d-glucoside (5), pinoresinol (10), pinoresinol 4-O-β-d-glucoside (8), pinoresinol 4,4′-di-O-β-d-glucoside (6), pinoresinol 4-O-apiose-(1→2)-β-d-glucoside (9), two quinic acid derivatives, trans-3-O-p-coumaroylquinic acid (1), cis-3-O-p-coumaroylquinic acid (2), and eight indole alkaloids, tryptamine (3), N-(4-hydroxycinnamoyl)-5-hydroxytryptamine (11), cis-N-(4-hydroxycinnamoyl)-5-hydroxytryptamine (12), centcyamine (16), cis-centcyamine (17), moschamine (13), cis-moschamine (14) and a dimeric indole alkaloid, montamine (15). While the structures of two new compounds, montanoside (4) and montamine (15), were established unequivocally by UV, IR, MS and a series of 1D and 2D NMR analyses, all known compounds were identified by comparison of their spectroscopic data with literature data. The antioxidant properties of these compounds were assessed by the DPPH assay, and their toxicity towards brine shrimps and cytotoxicity against CaCo-2 colon cancer cells were evaluated by the brine shrimp lethality and the MTT cytotoxicity assays, respectively. The novel dimer, montamine (15), showed significant in vitro anticolon cancer activity (IC₅₀=43.9 μM) while that of the monomer, moschamine (13), was of a moderate level (IC₅₀=81.0 μM).     

m-Ferrocenylbenzoate-bridged lanthanide coordination polymers: Syntheses, structures, electrochemical and magnetic properties

A series of m-ferrocenylbenzoate [m-ferrocenylbenzoate = m-NaOOCH₄C₆Fc, Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)] lanthanide coordination polymers, namely [Ln(μ₂-OOCH₄C₆Fc)(η²-OOCH₄C₆Fc)(μ₂-η²-OOCH₄C₆Fc)(CH₃OH)₂]_n [Ln = La (1), Pr (2), Nd (3), Sm (4) and Gd (5)], have been synthesized by reactions of m-ferrocenylbenzoate with Ln(NO₃)₃·nH₂O. X-ray crystallographic analyses reveal that 1, 2 and 5 are essentially isostructural with unique one-dimensional linear chain structure. Three types of coordination modes for m-ferrocenylbenzoate are observed in the unit structure which consists of the eight-membered metallacycle Ln₂(COO)₂ and the rhomboid Ln₂O₂. Electrochemical studies indicate that 1-5 exhibit a reversible redox wave of Fe^II/Fe^III and the half-wave potentials of 1-5 are slightly more positive than that of m-ferrocenylbenzoic acid. Magnetic investigations show that an antiferromagnetic interaction between Gd(III) ions exists in 5.     

Mono and dinuclear half-sandwich platinum group metal complexes bearing pyrazolyl-pyrimidine ligands: Syntheses and structural studies

Reactions of 0.5 eq. of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ (arene = η⁶-C₆H₆, η⁶-p-ⁱPrC₆H₄Me) and [(Cp∗)M(μ-Cl)Cl]₂ (M = Rh, Ir; Cp∗ = η⁵-C₅Me₅) with 4,6-disubstituted pyrazolyl-pyrimidine ligands (L) viz. 4,6-bis(pyrazolyl)pyrimidine (L1), 4,6-bis(3-methyl-pyrazolyl)pyrimidine (L2), 4,6-bis(3,5-dimethyl-pyrazolyl)pyrimidine (L3) lead to the formation of the cationic mononuclear complexes [(η⁶-C₆H₆)Ru(L)Cl]⁺ (L = L1, 1; L2, 2; L3, 3), [(η⁶-p-ⁱPrC₆H₄Me)Ru(L)Cl]⁺ (L = L1, 4; L2, 5; L3, 6), [(Cp∗)Rh(L)Cl]⁺ (L = L1, 7; L2, 8; L3, 9) and [(Cp∗)Ir(L)Cl]⁺ (L = L1, 10; L2, 11; L3, 12), while reactions with 1.0 eq. of the dinuclear complexes [(η⁶-arene)Ru(μ-Cl)Cl]₂ and [(Cp∗)M(μ-Cl)Cl]₂ give rise to the dicationic dinuclear complexes [{(η⁶-C₆H₆)RuCl}₂(L)]²⁺ (L = L1, 13; L2, 14; L3, 15), [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(L)]²⁺ (L = L1, 16; L2, 17; L3, 18), [{(Cp∗)RhCl}₂(L)]²⁺ (L = L1, 19; L2, 20; L3, 21) and [{(Cp∗)IrCl}₂(L)]²⁺ (L = L1 22; L2, 23; L3 24). The molecular structures of [3]PF₆, [6]PF₆, [7]PF₆ and [18](PF₆)₂ have been established by single crystal X-ray structure analysis.     

Chemically modified oximato complexes of titanium(IV) isopropoxide as new precursors for the sol-gel preparation of nano-sized titania: Crystal and molecular structure of [Ti{ONC10H16}4·2CH2Cl2]

Reactions of [Ti(OPrⁱ)₄] with various oximes, in anhydrous refluxing benzene yielded complexes of the type [Ti{OPrⁱ}_4−n{L}_n], where, n = 1-4 and LH = (CH₃)₂CNOH (1-4), C₉H₁₆CNOH (5-8) and C₉H₁₈CNOH (9-12). The compounds were characterized by elemental analyses, molecular weight measurements, FAB-mass, FT-IR and NMR (¹H, ¹³C{¹H}) spectral studies. The FAB-mass spectra of mono- (1), and di- (2), (6), (10) substituted products indicate their dimeric nature and that of tri- (3) and tetra- (4), (8) substituted derivatives suggest their monomeric nature. Crystal and molecular structure of [Ti{ONC₁₀H₁₆}₄·2CH₂Cl₂] (8A) suggests that the oximato ligands bind the metal in a dihapto η²-(N, O) manner, leading to the formation of an eight coordinated species. Thermogravimetric curves of (3), (6) and (10) exhibit multi-step decomposition with the formation of TiO₂ as the final product in each case, at 900 °C. Low temperature (∼600 °C) sol-gel transformations of (2), (3), (4), (6), (7) and (8) yielded nano-sized titania (a), (b), (c), (d), (e) and (f), respectively. Formation of anatase phase in all the titania samples was confirmed by powder XRD patterns, FT-IR and Raman spectroscopy. SEM images of (a), (b), (c), (d), (e) and (f) exhibit formation of nano-grains with agglomer like surface morphologies. Compositions of all the titania samples were investigated by EDX analyses. The absorption spectra of the two representative samples, (a) and (f) indicate an energy band gap of 3.17 eV and 3.75 eV, respectively.     

Synthesis and reactivity of asymmetrically substituted ansa-bridged zirconocene complexes: X-ray crystal structures of [Zr{R(H)C(η-C5Me4)(η-C5H4)}Cl2] (R = Bu, Bu) and [Zr{Bu(H)C(η-C5Me4)(η-C5H4)}(CH2Ph)2]

The dialkyl complexes, (R = Prⁱ, R′ = Me (2a), CH₂Ph (3a); R = Buⁿ, R′ = Me (2b), CH₂Ph (3b); R = Bu^t, R′ = Me (2c), CH₂Ph (3c); R = Ph, R′ = Me (2d), CH₂Ph (3d)), have been synthesized by the reaction of the ansa-metallocene dichloride complex, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (R = Prⁱ (1a), Buⁿ (1b), Bu^t (1c), Ph (1d)), and two molar equivalents of the alkyl Gringard reagent. The insertion reaction of the isocyanide reagent, CNC₆H₃Me₂-2,6, into the zirconium-carbon σ-bond of 2 gave the corresponding η²-iminoacyl derivatives, [Zr{R(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}{η²-MeCNC₆H₃Me₂-2,6}Me] (R = Prⁱ (4a), Buⁿ (4b), Bu^t (4c), Ph (4d)). The molecular structures of 1b, 1c and 3b have been determined by single-crystal X-ray diffraction studies.     

Three new sulfur-containing alkaloids, polycarpaurines A, B, and C, from an Indonesian ascidian Polycarpa aurata

Three new sulfur-containing alkaloids, polycarpaurines A (1), B (2), and C (3) were isolated from the tropical ascidian Polycarpa aurata collected in Indonesia, together with six known compounds (4-9). The structures of new compounds were assigned on the basis of their spectral data. Compounds 1, 3, 4, and 8 inhibited colony formation of Chinese hamster V79 cells with EC₅₀ values of 6.8, 8.6, 3.8, and 10 μM, respectively. Compounds 2 and 7 showed modest activity against V79 cells (EC₅₀>10 μM).     

Antileukemic α-pyrone derivatives from the endophytic fungus Alternaria phragmospora

Four new (1–4) and two known (5 and 6) α-pyrone derivatives have been isolated from Alternaria phragmospora, an endophytic fungus from Vinca rosea, leaves. The isolated compounds were chemically identified to be 5-butyl-4-methoxy-6-methyl-2H-pyran-2-one (1), 5-butyl-6-(hydroxymethyl)-4-methoxy-2H-pyran-2-one (2), 5-(1-hydroxybutyl)-4-methoxy-6-methyl-2H-pyran-2-one (3), 4-methoxy-6-methyl-5-(3-oxobutyl)-2H-pyran-2-one (4), 5-(2-hydroxyethyl)-4-methoxy-6-methyl-2H-pyran-2-one (5), and 5-[(2E)-but-2-en-1-yl]-4-methoxy-6-methyl-2H-pyran-2-one (6). Compounds 2 and 4 showed moderate antileukemic activities against HL60 cells with IC₅₀ values of 2.2 and 0.9 μM and against K562 cells with IC₅₀ values of 4.5 and 1.5 μM, respectively.     

Thermal hydrosilylation of olefin with hydrosilane. Preparative and mechanistic aspects

The reaction of trichlorosilane (1a) at 250 °C with cycloalkenes, such as cyclopentene (2a), cyclohexene (2b), cycloheptene (2c), and cyclooctene (2d), gave cycloalkyltrichlorosilanes [C_nH_2n−1SiCl₃: n = 5 (3a), 6 (3b), 7 (3c), 8 (3d)] within 6 h in excellent yields (97-98%), but the similar reactions using methyldichlorosilane (1b) instead of 1a required a longer reaction time of 40 h and afforded cycloalkyl(methyl)dichlorosilanes [C_nH_2n−1SiMeCl₂: n = 5 (3e), 6 (3f), 7 (3g), 8 (3h)] in 88-92% yields with 4-8% recovery of reactant 2. In large (2, 0.29 mol)-scale preparations, the reactions of 2a and 2b with 1a (0.58 mol) under the same condition gave 3a and 3b in 95% and 94% isolated yields, respectively. The relative reactivity of four hydrosilanes [HSiCl_3−mMe_m: m = 0-3] in the reaction with 2a indicates that as the number of chlorine-substituent(s) on the silicon increases the rate of the reaction decreases in the following order: n = 3 > 2 > 1 ? 0. In the reaction with 1a, the relative reactivity of four cycloalkenes (ring size = 5-8) decreases in the following order: 2d > 2a > 2c > 2b. Meanwhile linear alkenes like 1-hexene undergo two reactions of self-isomerization and hydrosilylation with hydrosilane to give a mixture of the three isomers (1-, 2-, and 3-silylated hexanes). In this reaction, the reactivity of the terminal 1-hexene is higher than the internal 2- and 3-hexene. The redistribution of hydrosilane 1 and the polymerization of olefin 2 occurred rarely under the thermal reaction condition.     

Electronically variable imino-phenanthrolinyl-cobalt complexes; synthesis, structures and ethylene oligomerisation studies

The 2-imino-1,10-phenanthroline ligands, 1,10-C₁₂H₇N₂-2-CRN(2,6-i-Pr₂-4-R¹-C₆H₂) [R = R¹ = H (L1); R = H, R¹ = Br (L2); R = H, R¹ = CN (L3); R = H, R¹ = i-Pr (L4); R = Me, R¹ = H (L5); R = Me, R¹ = i-Pr (L6)], have been prepared in high yield from the condensation reaction of 1,10-C₁₂H₇N₂-2-CRO (R = H, Me) with one equivalent of the corresponding 4-substituted 2,6-diisopropylaniline. The molecular structures of L2, L5 and L6 reveal the imino nitrogen atoms to adopt a transoid configuration with respect to the phenanthrolinyl nitrogen atoms. Treatment of Lx with one equivalent of CoCl₂ in n-BuOH at 90 °C gives the high spin complexes, (Lx)CoCl₂ [Lx = L1 (1a), L2 (1b), L3 (1c), L4 (1d), L5 (1e), L6 (1f)], in which the metal centres exhibit distorted square pyramidal geometries. Activation of 1a-1f with excess methylaluminoxane (MAO) gives catalysts that are modestly active for the oligomerisation of ethylene affording mainly linear α-olefins along with some degree of internal olefins. While the donor capability of the 4-position of the N-aryl group does not appear to affect the activity of the catalyst, it does have an influence on the ratio of α-olefins to internal olefins. Single crystal X-ray diffraction studies have been performed on L2, L5, L6, 1a, 1c and 1f.