Studies on ruthenium(II) and osmium(II) paracyclophane compounds

This thesis describes studies on ruthenium(II) and osmium(II) [22]paracyclophane compounds. Chapter 1 introduces the work, giving a historical background to the development of [22]paracyclophane chemistry. The properties of this compound and the syntheses of derived metal complexes are reviewed. Chapter 2 describes the synthesis of [Os(η6-C16H16)Cl2]2. Chapter 3 reports reactions of [Ru(η6-C16H16)C12]2 which lead to the formation of binuclear triply-bridged compounds of the type [(η6-C16H16)Ru(OMe)3Ru(η6-C16H16)][X] (Y=OMe-, OEt-, OH-, Cl-). Chapter 4 presents studies on the compounds [M(η6-arene)(η6-C16H16)][X]2. Chapter 5 presents the syntheses of organometallic chain compounds containing [22]paracyclophane. Chapter 6 draws together structural and spectroscopic data on the coordinated [22]paracyclophane ligand

Mixed-magnesium/zinc calix[4]arene complexes: Structure, and ring opening polymerisation studies

Different combinations of organomagnesium reagents and zinc bromide react with either 1,3-dimethoxy-4-tert-butylcalix[4]areneH2 (L(OMe)2H2) or trialkoxycalix[4]arenes (L(OR)3H) (R = n-Pr, n-pentyl) to afford mixed-metal calix[4]arene systems. Intruiging molecular structures are formed and the systems are capable of the ring opening polymerisation of ε-caprolactone under N2, air, or as melts

Pillared MOFs: structure and ring opening polymerization of cyclic esters

The solvothermal reaction of Zn(NO3)2·6H2O with 5-aminoisophthalic acid and 4,4′-bipyridyl (4,4′-bipy) led to the self-assembly of the known 3-D hybrid H-bonded/covalent structure {[Zn(5-AIP)(4,4′-bipy)0.5]·DMF}n (1·DMF), but with DMF here (rather than H2O as previously): an analogous reaction using the related 4,4′-azopyridine (4,4′-azopy) in place of 4,4′-bipyridyl afforded the structurally related framework {[Zn(5-AIP)(4,4′-azopy)0.5]·0.75DMF}n (2·0.75DMF). Similar solvothermal reactions of Co(NO3)·6H2O, Mn(NO3)·4H2O and Cd(NO3)·4H2O with 5-aminoisophthalate and the potential linkers 4,4′-bipy, 2-di(4-pyridyl)ethylene (DPE), and 4,4′-azopy afforded the porous 3-D structures {[Co2(NO3)2(5-AIP)(4,4′-bipy)2]·2EtOH}n (3·2EtOH), {[Co(5-AIP)(DPE)]·2DMF}n (4·2DMF), {[Co(5-AIP)(4,4′-azopy)]·2DMA}n (5·2DMA), {[Mn(5-AIP)(4,4′-bipy)]·2DMA}n (6·2DMA), {[Mn(5-AIP)(DPE)]·6DMF}n (7·6DMF), {[Mn(5-AIP)(4,4′-azopy)]·2.5DMF}n (8·2.5DMF), the previously reported {[Cd(5-AIP)(4,4′-bipy)]·3DMF}n (9·3DMF), {[Cd(5-AIP)(DPE)]·DMF}n (10), and {Cd(5-AIP)(4,4′-azopy)(DMF)}n (11), with structures 4-10 bearing the same network topologies with metal atoms and 5-AIP ligands in sheets, bipy ligands acting as pillars, and solvent molecules of crystallisation located around the bipy ligands. The activated MOFs were employed as catalysts for the ring opening polymerization (ROP) of ϵ-caprolactone and δ-valerolactone. ROPs were conducted as melts, and under N2 only 1 with δ-VL (∼93% conversion) was active. In the case of ϵ-CL under air, all the systems were active with 1, 2, and 11 affording >90% conversion. Molecular weights (Mn) were in the range 3760-17 940 Da and the products formed were identified as both cyclic and linear PCL. For δ-VL, the catalysts performed somewhat better, with all systems (except 8) affording ∼90% conversion or more under air. Molecular weights (Mn) were in the range 2180-7940 and as for PCL, the products formed were identified as both cyclic and linear PCL

Insights into the structures adopted by titanocalix[6 and 8]arenes and their use in the ring opening polymerization of cyclic esters

Interaction of p-tert-butylcalix[6]areneH6, L1H6, with [TiCl4] afforded the complex [Ti2Cl3(MeCN)2(OH2)(L1H)][Ti2Cl3(MeCN)3(L1H)]∙4.5MeCN (1∙4.5MeCN), in which two pseudo octahedral titanium centres are bound to one calix[6]arene. A similar reaction but employing THF resulted in the THF ring-opened product [Ti4Cl2(μ3-O)2(NCMe)2(L)2(O(CH2)4Cl)2]∙4MeCN (2∙4MeCN), where LH4 = p-tert-butylcalix[4]areneH4. Interaction of L1H6 with TiF4 (3 equiv.) led, after work-up, to the complex [(TiF)2(μ -F)L1H]2∙6.5MeCN (3∙6.5MeCN). Treatment of p-tert-butylcalix[8]areneH8, L2H8, with [TiCl4] led to the isolation of the complex [(TiCl)2(TiClNCMe)2(μ3-O)2(L2)]∙1.5MeCN (4∙1.5MeCN). From a similar reaction, a co-crystallized complex [Ti4O2Cl4(MeCN)2(L2)][Ti3Cl6(MeCN)5(OH2)(L2H2)]·H2O∙11MeCN (5·H2O 11MeCN) was isolated. Extension of the L2H8 chemistry to [TiBr4] afforded, depending on the stoichiometry, the complexes [(TiBr)2(TiBrNCMe)2(μ3-O)2(L2)]∙6MeCN (6∙6MeCN) or [Ti(NCMe)2Br]2[Ti(O)Br2(NCMe)](L2)]∙7.5MeCN (7∙7.5MeCN), whilst use of [TiF4] afforded complexes containing Ca2+ and Na+, thought to originate from drying agents, namely [Ti8CaF20(OH2)Na2(MeCN)4(L2)2]∙14MeCN (8∙14MeCN), [Na(MeCN)2][Ti8CaF20NaO16(L2)2]∙7MeCN (9∙7MeCN) or [Na]6[Ti8F20Na(MeCN)2(L2)][Ti8F20Na(MeCN)0.5(L2)]∙15.5(C2H3N) (10∙15.5MeCN). In the case of TiI4, the ladder [(TiI)2(TiINCMe)2(μ3-O)2(L2)]∙7.25CH2Cl2 (11∙7.25CH2Cl2) was isolated. These complexes have been screened for their potential to act as catalysts in the ring opening polymerization (ROP) of ε-caprolactone (ε-CL), δ-valerolactone (δ-VL) and rac-lactide (r-LA), both in air and N2. For ε-CL and δ-VL, moderate activity at 130 oC over 24 h was observed for 1, 9 and 11; for r-LA, only 1 exhibited reasonable activity. In the case of the co-polymerization of ε-CL with δ-VL, the complexes 1 and 11 afforded reasonable conversions and low molecular weight polymers, whilst 4, 6, and 9 were less effective. None of the complexes proved to be active in the co-polymerization of ε-CL and r-LA under the conditions employed herein

Trinuclear zinc calix[4]arenes: Synthesis, structure, and ring opening polymerization studies

The trinuclear zinc calix[4]arene complexes [Zn3(O2CCH3)2(L(O)2(OMe)2)2·xMeCN (x = 7.5, 1; x = 6, 1′), [Zn3(O2CCH3)2(L(O)2(OnPr)2)2·5MeCN (2·5MeCN), [Zn3(OEt)2(L(O)2(OMe)2)2]·4MeCN (3·4MeCN), [Zn3(OEt)2(L(Opentyl)2)2]·4.5MeCN (4·4.5MeCN) and [Zn3(OH)2(L(O)2(On-pentyl)2]·8MeCN (5·8MeCN) have been isolated from reaction of [(ZnEt)2(L(O)2(OR)2)2] (L(OH)2(OR)2 = 1,3-dialkoxy-4-tert-butylcalix[4]arene; R = methyl, n-propyl or pentyl) and the reagents acetic acid, ethanol, and presumed adventitious water, respectively. Attempts to make 5 via a controlled hydrolysis led only to the isolation of polymorphs of (L(OH)2(Opentyl)2·MeCN. Reaction of [Zn(C6F5)2] with L(OH)2(Opentyl)2, in the presence of K2CO3, led to the isolation of the complex [Zn6(L(On-pentyl))2(OH)3(C6F5)3(NCMe)3]·3MeCN (6·3MeCN). The molecular structures of 1–6 reveal they all contain a near linear (163 to 179°) Zn3 motif. In 1–5, a central tetrahedral Zn centre is flanked by trigonal bipyramidal Zn centres, whilst in 6, for the linear Zn3 unit, a central distorted octahedral zinc centre is flanked by trigonal planar and a tetrahedral zinc centres. Screening for the ring opening polymerization (ROP) of ε-caprolactone at 90 °C revealed that they are active with moderate to good conversion affording low to medium molecular weight products with at least two series of ions. For comparative studies, the trinuclear aminebis(phenolate) complex [Zn3(Oi-Pr)2L/] (L/ = n-propylamine-N,N-bis(2-methylene-4,6-di-tert-butylphenolate) I was prepared. Kinetics revealed the rate order I > 4 > 6 ≈ 2 ≈ 1 > 3

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

Vanadium complexes derived from oxacalix[6]arenes: structural studies and use in the ring opening homo-/co-polymerization of ε-caprolactone/δ-valerolactone and ethylene polymerization

Reaction of Na[VO(tBuO)4] (generated in-situ from VOCl3 and NaOtBu) with p-tert-butyltetrahomodioxacalix[6]areneH6 (L1H6) afforded, after work-up (in MeCN), the mixed-metal complex [(VO)2(μ-O)Na2(L1)(MeCN)4]·5(MeCN) (1·5MeCN), whilst the oxo complex {[VO]4L1} (2·6MeCN) was isolated via the use of [VO(OnPr)3]. Reaction of L1H6 with [V(Np-CH3C6H4)(OtBu)3] afforded the complex {[V(Np-CH3C6H4)]2L1} (3·7MeCN·0.5CH2Cl2). Use of similar methodology afforded the imido complexes {[V(Np-RC6H4)]2L1} (R = OMe (4); CF3(5); Cl (6); F (7)); on one occasion, reaction of [V(Np-CH3C6H4)(OEt)3] with L1H6 afforded the product [VO(L2)]2·4MeCN (8·4MeCN) (L2 = 2-(p-CH3-C6H4NCH)-4-tBu-C6H2O-6-CH2)-4-tBuC6H2OH) in which L1 has been cleaved. For comparative catalytic ring opening polymerization (ROP) studies, the known complexes [VOL3] (L3 = oxacalix[3]arene) (I), [V(Np-CH3-C6H4)L3]2 (II), [Li(MeCN)4][V2(O)2Li(MeCN)(L6H2)2] (L6H6 = p-tert-butylcalix[6]areneH6) (III) and [(VO)2L8H] (L8H8 = p-tert-butylcalix[8]areneH8) (IV) have also been prepared. ROP studies, with or with external alcohol present, indicated that complexes 1 to 8 exhibited moderate to good conversions for ε-Cl, δ-VL and the co-polymerization thereof. Within the imido series, a positive influence was observed when electron withdrawing substituents were present. These systems afforded relatively low molecular weight products and were also inactive toward the ROP of rac-lactide. In the case of ethylene polymerization, complexes 3, 5 and 7 exhibited highest activity when screened in the presence of dimethylaluminium chloride/ethyltrichloroacetate; the activity of 4 was much lower. The products were highly linear polyethylene with Mw in the range 74-120x103 Da

Allosteric binding properties of a 1,3-alternate thiacalix[4]arene-based receptor having phenylthiourea and 2-pyridylmethyl moieties on opposite faces

The synthesis of three new heteroditopic receptors (5a-c) which are based on thiacalix[4]arenes in the 1,3-alternate conformation is reported herein. These new receptors each have two thiourea moieties linking phenyl groups, two of which are substituted with electron-withdrawing groups at their para-positions, and at the opposite side of the thiacalix[4]arene cavity, with two 2-pyridylmethyl groups. One example (5a) was also characterized by X-ray crystallography. A limited 1H-NMR and UV-vis anion complexation study was conducted. DFT computational determinations indicated that 5c, which has strongly electron-withdrawing NO2 groups, had the most effective recognition ability towards the selected anions. The binding of Ag+ at the 2-pyridyl moieties, and the binding of the anions at the two thiourea NH groups of the p-substituted phenylthioureido moieties, respectively, was also investigated. The appearance of a positive allosteric effect with receptor 5b was also found using 1H-NMR titration experiments

Alternating α‑Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

The catalytic oligomerization of ethylene with chromium-based complexes containing bis­(benzimidazolemethyl)­amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained (>100 000 g mmol^–1 h^–1 bar^–1) with <i>N</i>-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1–4 bar) and by the cocatalyst to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor second distribution (<5 wt %) of 2-ethyl-1-alkenes is obtained under certain conditions, resulting from incorporation of 1-butene. DFT studies (M06L) and experimental observations regarding the reaction between AlMe₃ and the <i>N</i>-methyl BIMA ligand <b>2</b> have shown that deprotonation of the benzimidazole N–H units can occur, which suggests a change in coordination of the BIMA ligand under oligomerization conditions

Alternating α‑Olefin Distributions via Single and Double Insertions in Chromium-Catalyzed Ethylene Oligomerization

The catalytic oligomerization of ethylene with chromium-based complexes containing bis­(benzimidazolemethyl)­amine (BIMA) ligands results in alternating distributions of linear α-olefins (LAOs). Extremely high activities are obtained (>100 000 g mmol^–1 h^–1 bar^–1) with <i>N</i>-alkyl-substituted BIMA ligands, whereas bulky groups on the central nitrogen or alternative central donors result in much lower activities. Variations in the ligand backbone, as well as methylation of the benzimidazole units, lead to reduction in activity. The alternating LAO distributions have been mathematically analyzed using second-order recurrence relations. The shape of the distributions is affected by ethylene pressure (1–4 bar) and by the cocatalyst to some degree. On the basis of the results and analysis presented herein, we propose that the alternating behavior originates from the ability of these chromium BIMA catalysts to undergo single as well as double ethylene insertion reactions. A minor second distribution (<5 wt %) of 2-ethyl-1-alkenes is obtained under certain conditions, resulting from incorporation of 1-butene. DFT studies (M06L) and experimental observations regarding the reaction between AlMe₃ and the <i>N</i>-methyl BIMA ligand <b>2</b> have shown that deprotonation of the benzimidazole N–H units can occur, which suggests a change in coordination of the BIMA ligand under oligomerization conditions