Andrew L. Johnson

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Organization: University of Bath , England

Department: Department of Chemistry

Title: (PhD)

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Inorganic Chemistry

Chemicals
References

Deposition of SnS Thin Films from Sn(II) Thioamidate Precursors

Co-reporter:Amanda L. Catherall, Shasa Harris, Michael S. Hill, Andrew L. Johnson, and Mary F. Mahon

Crystal Growth & Design October 4, 2017 Volume 17(Issue 10) pp:5544-5544

Publication Date(Web):September 7, 2017

DOI:10.1021/acs.cgd.7b01100

Two thioamide pro-ligands, R1N(H)C(═S)R2 (R1 = t-Bu, R2 = i-Pr and R1 = i-Pr, R2 = i-Pr), were synthesized by treatment of the corresponding amides with Lawesson’s reagent. Reactions of [Sn{N(SiMe3)2}2] with two molar equivalents of each thioamide pro-ligand yielded the tin(II) thioamidate species, bis(2-methyl-N-(1-methylethyl)-propanethioamide)tin(II) and Bis[N-(1,1-dimethylethyl)-2-methylpropanethioamide]tin(II). Both of the new tin compounds have been characterized by 1H, 13C{1H}, and 119Sn NMR spectroscopy and elemental analysis. In addition, the solid-state structure of bis(2-methyl-N-(1-methylethyl)-propanethioamide)tin(II) has been determined through a single crystal X-ray diffraction analysis and shown to display a monomeric constitution in which the tin(II) center occupies a distorted pseudo square pyramidal geometry defined by the N2S2 donors and the stereochemically active lone pair. Both tin(II) derivatives have been assessed for their potential as single source precursors to SnS by TGA and by NMR spectroscopic analysis of the volatile organic products produced during their thermolysis. Both compounds have been utilized in the growth of thin films by aerosol-assisted chemical vapor deposition (AACVD). These latter studies provided film growth at temperatures as low as 200 °C. The films have been analyzed by PXRD, Raman spectroscopy, XPS, AFM, and SEM and are shown to comprise primarily the orthorhombic (Herzenbergite) phase of SnS, which is contaminated by only low levels of residual carbon (<5 at %). Although further films deposited onto Mo-coated substrates produced only limited photocurrents when illuminated, these results demonstrate the potential of such simple thioamidate derivatives to act as single source precursors to useful metal sulfide thin film materials.

Aerosol-Assisted Chemical Vapor Deposition of CdS from Xanthate Single Source Precursors

Co-reporter:Mark A. Buckingham, Amanda L. Catherall, Michael S. HillAndrew L. Johnson, James D. Parish

Crystal Growth & Design 2017 Volume 17(Issue 2) pp:

Publication Date(Web):January 6, 2017

DOI:10.1021/acs.cgd.6b01795

Bis-3-methylpyridine and bis-4-methylpyridine complexes of cadmium(II) ethylxanthate have been characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis. The single crystal X-ray structures of both methylpyridine derivatives have also been determined and shown to display a cis, cis, cis-configuration of the N- and S-donor ligands. The compounds have been utilized as single source precursors to deposit CdS films on silica-coated glass substrates at 220 and 350 °C by aerosol-assisted chemical vapor deposition. The surface morphology of the films has been examined by scanning electron microscopy analysis and the crystalline phases were studied by powder X-ray diffraction. The films deposited from the 3-methylpyridine adduct comprised more densely packed and more highly crystalline hexagonal CdS than those provided by either of the other two precursors. The crystallite sizes were found to be <20 nm for films deposited from the pyridine and 4-methylpyridine adducts but to display a dimension of ca. 30 nm when deposited from the 3-methylpyridine precursor. Despite these differences in morphology and crystalline composition, the electronic properties of all the CdS films were deduced by UV–vis spectroscopy to be very similar and to display absorption behavior and band gaps (Eg = 2.25–2.40 eV) consistent with bulk CdS.

Cobalt(I) Olefin Complexes: Precursors for Metal–Organic Chemical Vapor Deposition of High Purity Cobalt Metal Thin Films

Co-reporter:Jeff A. Hamilton, Thomas Pugh, Andrew L. Johnson, Andrew J. Kingsley, and Stephen P. Richards

Inorganic Chemistry 2016 Volume 55(Issue 14) pp:7141-7151

Publication Date(Web):June 27, 2016

DOI:10.1021/acs.inorgchem.6b01146

We report the synthesis and characterization of a family of organometallic cobalt(I) metal precursors based around cyclopentadienyl and diene ligands. The molecular structures of the complexes cyclopentadienyl–cobalt(I) diolefin complexes are described, as determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis and thermal stability studies of the complexes highlighted the isoprene, dimethyl butadiene, and cyclohexadiene derivatives [(C5H5)Co(η4-CH2CHC(Me)CH2)] (1), [(C5H5)Co(η4-CH2C(Me)C(Me)CH2)] (2), and [(C5H5)Co(η4-C6H8)] (4) as possible cobalt metal organic chemical vapor deposition (MOCVD) precursors. Atmospheric pressure MOCVD was employed using precursor 1, to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere (760 torr) of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 325, 350, 375, and 400 °C, respectively, by scanning electron microscopy and atomic force microscopy reveal temperature-dependent growth features. Films grown at these temperatures are continuous, pinhole-free, and can be seen to be composed of hexagonal particles clearly visible in the electron micrograph. Powder X-ray diffraction and X-ray photoelectron spectroscopy all show the films to be highly crystalline, high-purity metallic cobalt. Raman spectroscopy was unable to detect the presence of cobalt silicides at the substrate/thin film interface.

Synthesis, Structure and Chemical Vapour Deposition Studies on the Group 13 Complexes [Me2M{tfacnac}] [M = Al, Ga, In; Htfacnac = F3CC(OH)CHC(CH3)NCH2CH2OCH3]

Co-reporter:Samuel D. Cosham;Jeff A. Hamilton;Michael S. Hill;Kieran C. Molloy

European Journal of Inorganic Chemistry 2016 Volume 2016( Issue 11) pp:1712-1719

Publication Date(Web):

DOI:10.1002/ejic.201600023

Abstract

A family of group 13 metal dimethyl complexes of the general formula [Me₂M{MeC(O)CHC(NCH₂CH₂OMe)CF₃}] [M = Al (2), Ga (3) or In (4)] was synthesised by reaction of the isolated free ligand 1 with the corresponding trimethyl metal reagents. The isolated complexes 2–4 were characterised by elemental analysis and NMR spectroscopy, and the molecular structures of the complexes were determined by single-crystal X-ray diffraction, which revealed them to be monomeric five-coordinate complexes with coordination of the pendent ether-bearing lariat in the solid state. Thermogravimetric analysis showed complexes 2–4 all to have residual masses at 200 °C of 2.4 % or less, well below the value for the respective metal oxides, and vapour pressure measurements showed the indium complex 4 to be an order of magnitude less volatile (0.09 Torr at 80 °C) than the Al (2) and Ga (3) analogues, despite their being isoleptic systems. Complexes 2–4 were investigated for their utility in the low-pressure metal organic chemical vapour deposition of the respective metal oxides in the absence of additional oxidant at 400 °C on silicon substrates.

N-Heterocyclic Carbene Adducts of Molybdenum Tetracarboxylate Complexes

Co-reporter:Thomas P. Robinson, Andrew L. Johnson, Paul R. Raithby, and Gabriele Kociok-Kohn

Organometallics 2016 Volume 35(Issue 15) pp:2494-2506

Publication Date(Web):July 21, 2016

DOI:10.1021/acs.organomet.6b00386

Treatment of the quadruply bonded dimolybdenum complexes [Mo2(μ-O2CCF3)4] (1), [Mo2(μ-O2CCH3)4] (2), and [Mo2(μ-O2CBut)4] (3) with the N-heterocyclic carbenes (NHCs) L (La = IPr, Lb = IMes, Lc = IiPr2Me2, and Ld = IEt2Me2) results in the formation of a series of 1:1 and 1:2 adducts. In the case of the larger, and more sterically demanding, carbene ligands, i.e. La and Lb, coordination exclusively occurs axially with respect to the [Mo2] complexes and occurs only once in the case of La, [Mo2(μ-O2CR)4(La)] (R = Me, tBu, CF3) (1a–3a), and twice in the case of Lb, [Mo2(μ-O2CCF3)4(Lb)2] (2b). For the less sterically demanding carbene ligands (Lc and Ld) coordination to the [Mo2] core occurs twice, with a transoidal distribution about the [Mo2] unit and is exclusively in equatorial positions, resulting in partial displacement of two of the bridging {μ-O2CR} ligands in each complex. In the case of complexes 1a–3a, 2b, [Mo2(μ-OTFA)2(OTFA)2(Lc)2] (1c), [Mo2(μ-OTFA)2(OTFA)2(Ld)2] (1d), and [Mo2(μ-OAc)2(OAc)2(Ld)2] (2d) the solid-state molecular structures have been unambiguously characterized by single-crystal X-ray diffraction. As part of our study into the reactivity of NHC ligands with [Mo2(μ-O2CCH3)4], the heteroleptic NHC adduct [Mo2(μ-OAc)2Cl2(Ld)2] (5) formed from the reaction of complex 2d with trimethylsilyl chloride has also been isolated and structurally characterized using single-crystal X-ray diffraction. As part of our study the Mo–Mo stretching frequencies of these complexes have been analyzed by Raman spectroscopy.

Polymorph-Selective Deposition of High Purity SnS Thin Films from a Single Source Precursor

Co-reporter:Ibbi Y. Ahmet, Michael S. Hill, Andrew L. Johnson, and Laurence M. Peter

Chemistry of Materials 2015 Volume 27(Issue 22) pp:7680

Publication Date(Web):October 15, 2015

DOI:10.1021/acs.chemmater.5b03220

Metal chalcogenide thin films have a wide variety of applications and potential uses. Tin(II) sulfide is one such material which presents a significant challenge with the need for high quality SnS, free of oxide materials (e.g., SnO2) and higher tin sulfides (e.g., Sn2S3 and SnS2). This problem is compounded further when the target material exhibits a number of polymorphic forms with different optoelectronic properties. Unlike conventional chemical vapor deposition (CVD) and atomic layer deposition (ALD), which rely heavily on having precursors that are volatile, stable, and reactive, the use of aerosol assisted CVD (AA-CVD) negates the need for volatile precursors. We report here, for the first time, the novel and structurally characterized single source precursor (1), (dimethylamido)(N-phenyl-N′,N′-dimethylthiouriate)tin(II) dimer, and its application in the deposition, by AA-CVD, of phase-pure films of SnS. A mechanism for the oxidatively controlled formation of SnS from precursor 1 is also reported. Significantly, thermal control of the deposition process allows for the unprecedented selective and exclusive formation of either orthorhombic-SnS (α-SnS) or zinc blende-SnS (ZB-SnS) polymorphs. Thin films of α-SnS or ZB-SnS have been deposited onto Mo, fluorine doped tin oxide (FTO), Si, and glass substrates at the optimized deposition temperatures of 375 and 300 °C, respectively. The densely packed polycrystalline thin films have been characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy analysis. These data confirmed the phase purity of the SnS formed. Optical analysis of the α-SnS and ZB-SnS films shows distinctly different optical properties with direct band gaps of 1.34 and 1.78 eV, respectively. Furthermore, photoelectrochemical and external quantum efficiency (EQE) measurements were undertaken to assess the optoelectronic properties of the deposited samples. We also report for the first time the ambipolar properties of the ZB-SnS phase.

Tailoring Precursors for Deposition: Synthesis, Structure, and Thermal Studies of Cyclopentadienylcopper(I) Isocyanide Complexes

Co-reporter:A. M. Willcocks, T. Pugh, S. D. Cosham, J. Hamilton, S. L. Sung, T. Heil, P. R. Chalker, P. A. Williams, G. Kociok-Köhn, and A. L. Johnson

Inorganic Chemistry 2015 Volume 54(Issue 10) pp:4869-4881

Publication Date(Web):May 4, 2015

DOI:10.1021/acs.inorgchem.5b00448

We report here the synthesis and characterization of a family of copper(I) metal precursors based around cyclopentadienyl and isocyanide ligands. The molecular structures of several cyclopentadienylcopper(I) isocyanide complexes have been unambiguously determined by single-crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl isocyanide complex [(η5-C5H5)Cu(CNiPr)] (2a) and the tert-butyl isocyanide complex [(η5-C5H5)Cu(CNtBu)] (2b) as possible copper metal chemical vapor deposition (CVD) precursors. Further modification of the precursors with variation of the substituents on the cyclopentadienyl ligand system (varying between H, Me, Et, and iPr) has allowed the affect that these changes would have on features such as stability, volatility, and decomposition to be investigated. As part of this study, the vapor pressures of the complexes 2b, [(η5-MeC5H4)Cu(CNtBu)] (3b), [(η5-EtC5H4)Cu(CNtBu)] (4b), and [(η5-iPrC5H4)Cu(CNtBu)] (5b) over a 40–65 °C temperature range have been determined. Low-pressure chemical vapor deposition (LP-CVD) was employed using precursors 2a and 2b to synthesize thin films of metallic copper on silicon, gold, and platinum substrates under a H2 atmosphere. Analysis of the thin films deposited onto both silicon and gold substrates at substrate temperatures of 180 and 300 °C by scanning electron microscopy and atomic force microscopy reveals temperature-dependent growth features: Films grown at 300 °C are continuous and pinhole-free, whereas films grown at 180 °C consist of highly crystalline nanoparticles. In contrast, deposition onto platinum substrates at 180 °C shows a high degree of surface coverage with the formation of high-density, continuous, and pinhole-free thin films. Powder X-ray diffraction and X-ray photoelectron spectroscopy (XPS) both show the films to be high-purity metallic copper.

Why are the {Cu4N4} rings in copper(I) phosphinimide clusters [Cu{μ-NPR3}]4 (R = NMe3 or Ph) planar?

Co-reporter:Thomas P. Robinson, Richard D. Price, Matthew G. Davidson, Mark A. Fox and Andrew L. Johnson

Dalton Transactions 2015 vol. 44(Issue 12) pp:5611-5619

Publication Date(Web):12 Feb 2015

DOI:10.1039/C5DT00255A

The copper phosphinimide complexes [Cu{μ-NPR3}]4 (1, R = NMe2 and 2, R = Ph) were obtained in good yields from the reactions of Cu[Mes] (Mes = mesityl, C6H2Me3-2,4,6) with the corresponding iminophosphoranes, HNPR3. The molecular structures of 1 and 2 reveal the presence of planar eight-membered {Cu4N4} rings which contrasts with the saddle-shaped {M4N4} rings found in related metal phosphinimide complexes. According to computations, there is negligible aromaticity in the planar {Cu4N4} rings in 1 and 2 and the saddle shape observed in related {M4N4} rings is due to steric factors.

Synthesis and Characterization of Fluorinated -Ketoiminate Zinc Precursors and Their Utility in the AP-MOCVD Growth of ZnO:F

Co-reporter:Samuel D. Cosham;Gabriele Kociok-Köhn;Jeff A. Hamilton;Michael S. Hill;Kieran C. Molloy;Rémi Castaing

European Journal of Inorganic Chemistry 2015 Volume 2015( Issue 26) pp:4362-4372

Publication Date(Web):

DOI:10.1002/ejic.201500536

Abstract

A novel family of zinc bis(β-ketoiminate) complexes 2b–2h have been synthesized by reaction of the isolated free ligands 1a–h with dimethylzinc. The isolated zinc complexes were characterized by elemental analysis, NMR spectroscopy, and in the case of 2b–d and 2f–h, the molecular structures of the complexes were determined by single-crystal X-ray diffraction which reveals the compounds to be pseudo-octahedral six-coordinate, monomeric homoleptic complexes in the solid state. TG analysis showed complexes 2b–f all to have residual masses at 400 °C of 10 % or less, well below the value for ZnO and thus indicative of volatility. Of these systems 2b [Zn{MeC(O)CHC(NCH₂CH₂OMe)CF₃}₂] has been investigated for its utility in the AP-MOCVD growth of F-doped ZnO (ZnO:F) in the absence of additional oxidant at 400 °C on glass and silicon substrates.

New organo- and amidozinc derivatives of primary amines

Co-reporter:Samuel D. Cosham, Michael S. Hill, Andrew L. Johnson and Kieran C. Molloy

Dalton Transactions 2014 vol. 43(Issue 2) pp:859-864

Publication Date(Web):15 Oct 2013

DOI:10.1039/C3DT52602J

Five new zinc derivatives of primary amines [R′ZnN(H)R]2 [R = SiPh3, R′ = Me (1), N(SiMe3)2 (4); R = Si(NMe2)3, R′ = Me (2), Et (3), N(SiMe3)2 (5)] have been synthesised by reaction of R′2Zn and H2NR. All five species are dimers in which the N–H groups are disposed in a trans manner about a central Zn2N2 ring. In 1 and 4 the coordination at zinc is trigonal planar, while in 2, 3, 5 the zinc is in a distorted tetrahedral environment due to additional Me2N: → Zn coordination from one SiNMe2 group. 5 was found to be generally resistant to NH deprotonation by bases such as MN(SiMe3)2 (M = Li, K) or Zn[N(SiMe3)2]2, but reacts with Sn[N(SiMe3)2]2 to give the tin-free, tetrameric mixed zinc-imido/amido species, [{(Me3Si)2N}{(Me2N)3SiN(H)}{(Me2N)3SiN}Zn2]2 (6) which can be viewed as part of a hexameric Zn6N6 drum which has lost a Zn2N2 ring.

Synthesis, structural and thermal characterisation of titanium silylamido complexes

Co-reporter:Samuel D. Cosham, Andrew L. Johnson, Gabriele Kociok-Köhn, Kieran C. Molloy

Journal of Organometallic Chemistry 2014 Volumes 772–773() pp:27-33

Publication Date(Web):1 December 2014

DOI:10.1016/j.jorganchem.2014.08.026

•A number of titanium silylamido complexes have been synthesised and characterised.•Several complexes have been characterized using single crystal X-ray diffraction.•The thermal profiles of these complexes have been examined using TGA.The titanium silylamido complexes [{R2Si(NtBu)2}2Ti] (R = Me (3) and R = Ph (4)), [{(R2Si(NtBu)2)Ti(μ2-NtBu)}2] (R = Me (5) and R = Ph (6) have been synthesised from the reaction of the lithio-silylamide ligands [{R2Si(NtBu)2}Li2] (R = Me; (1), R = Ph; (2)) with TiCl4 and [Ti(NtBu)Cl2(Py)2] respectively. In the case of complexes 2, 3 and 5 the complexes have been structurally characterised by single crystal X-ray diffraction. The thermal profiles of the four silylamido (3–6) complexes have also been investigated by thermogravimetric analysis.The titanium silylamido complexes [{R2Si(NtBu)2}2Ti] (R = Me (3) and R = Ph (4)), [{(R2Si(NtBu)2)Ti(μ2-NtBu)}2] (R = Me (5) and R = Ph (6)) have been synthesised and structurally characterised and assessed at potential single source precursors for Ti–Si–N materials. During the course of our work the C–H activated spirocyclic complex , has been synthesised and also structurally characterised by single crystal X-ray diffraction. Figure optionsDownload full-size imageDownload as PowerPoint slideFigure optionsDownload full-size imageDownload as PowerPoint slide

Cobalt(III) Diazabutadiene Precursors for Metal Deposition: Nanoparticle and Thin Film Growth

Co-reporter:Thomas Pugh ; Samuel D. Cosham ; Jeff A. Hamilton ; Andrew J. Kingsley

Inorganic Chemistry 2013 Volume 52(Issue 23) pp:13719-13729

Publication Date(Web):November 15, 2013

DOI:10.1021/ic402317g

We report the synthesis and characterization of a family of cobalt(III) metal precursors, based around cyclopentadienyl and diazabutadiene ligands. The molecular structure of the complexes cyclopentadienyl-Cobalt(III)(N,N′-dicyclohexyl-diazabutadiene) (2c) and cyclopentadienyl-Cobalt(III)(N,N′-dimesityl-diazabutadiene) (2d) are described, as determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl derivative CpCo(iPr2-dab) (2a) as a possible cobalt metal chemical vapor deposition (CVD) precursor. Atmospheric pressure CVD (AP-CVD) was employed using precursor 2a to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 250 °C, 275 °C, 300 °C, 325 °C, and 350 °C, respectively, by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal temperature dependent growth features: films grown at 325 and 350 °C are continuous and pinhole free, whereas those films grown at substrate temperatures of 250 °C, 275 °C, and 300 °C consist of crystalline nanoparticles. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic cobalt. Raman spectroscopy has also been used to prove the absence of cobalt silicides at the substrate/thin film interface.

CVD of pure copper films from novel iso-ureate complexes

Co-reporter:Alexander M. Willcocks, Thomas Pugh, Jeff A. Hamilton, Andrew L. Johnson, Stephen P. Richards and Andrew J. Kingsley

Dalton Transactions 2013 vol. 42(Issue 15) pp:5554-5565

Publication Date(Web):21 Feb 2013

DOI:10.1039/C3DT00104K

We report the synthesis and characterisation of a new family of copper(I) metal precursors based around alkoxy-N,N′-di-alkyl-ureate ligands, and their subsequent application in the production of pure copper thin films. The molecular structure of the complexes bis-copper(I)(methoxy-N,N′-di-isopropylureate) (1) and bis-copper(I)(methoxy-N,N′-di-cyclohexylureate)(5) are described, as determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted complex 1 as a possible copper CVD precursor. Low pressure chemical vapour deposition (LP-CVD) was employed using precursor 1, to synthesise thin films of metallic copper on ruthenium substrates under an atmosphere of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 225 °C, 250 °C and 300 °C, respectively, by SEM and AFM reveal the films to be continuous and pin hole free, and show the presence of temperature dependent growth features on the surface of the thin films. Energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic copper.

Synthesis and Characterization of Zinc Ketoiminate and Zinc Alkoxide/PhenoxideKetoiminate Complexes

Co-reporter:Carlo Di Iulio;Mathew Middleton;Gabriele Kociok-Köhn;Matthew D. Jones

European Journal of Inorganic Chemistry 2013 Volume 2013( Issue 9) pp:1541-1554

Publication Date(Web):

DOI:10.1002/ejic.201201114

Abstract

Dimeric methylzinc ketoiminate complexes bis{4-[(2,6-diisopropylphenyl)imido]pentan-1-one}methylzinc, [{L¹}ZnMe]₂, and bis{1-phenyl-3[(2,6-diisopropylphenyl)imido]butan-1-one}methylzinc, [{L²}ZnMe]₂ have been synthesized and completely characterized along with the homoleptic zinc complex bis{1-phenyl-3[(2,6-diisopropylphenyl)imido]butan-1-one}zinc, [{L²}₂Zn] by means of single-crystal X-ray structure analysis and NMR spectroscopy. The related dimeric zinc phenoxide–ketoiminate complexes [{L³}Zn]₂·(dmso)₂, [{L⁴}Zn]₂·(dmso)₂, [{L⁵}Zn]₂·(dmso)₂, [{L⁶}Zn]₂·(dmso)₂ and [{L⁴}Zn]₂·(hmpa)₂ (dmso = dimethyl sulfoxide; hmpa = hexamethylphosphoramide) have also been synthesized along with the tetrameric zinc alkoxide–ketoiminate complex [{L⁷}Zn]₄. In preliminary studies the complexes described in this report were assessed for their activity in the ring-opening polymerization of rac-lactide, either in the solution state (in the presence of benzyl alcohol initiator), or under industrially preferred melt conditions (130 °C no solvent). It could be shown that these compounds are able to act as initiators for lactide polymerization, with molecular weights (M_n) of up to 102050 g/mol.

Multinuclear Copper(I) Guanidinate Complexes

Co-reporter:Alexander M. Willcocks, Thomas P. Robinson, Christopher Roche, Thomas Pugh, Stephen P. Richards, Andrew J. Kingsley, John P. Lowe, and Andrew L. Johnson

Inorganic Chemistry 2012 Volume 51(Issue 1) pp:246-257

Publication Date(Web):December 14, 2011

DOI:10.1021/ic201602m

A series of multinuclear Copper(I) guanidinate complexes have been synthesized in a succession of reactions between CuCl and the lithium guanidinate systems Li{L} (L = Me2NC(iPrN)2 (1a), Me2NC(CyN)2 (1b), Me2NC(tBuN)2(1c), and Me2NC(DipN)2 (2d) (iPr = iso-propyl, Cy = cyclohexyl, tBu = tert-butyl, and Dip = 2,6-disopropylphenyl) made in situ, and structurally characterized. The di-copper guanidinates systems with the general formula [Cu2{L}2] (L = {Me2NC(iPrN)2} (2a), {Me2NC(CyN)2} (2b), and {Me2NC(DipN)2} (2d) differed significantly from related amidinate complexes because of a large torsion of the dimer ring, which in turn is a result of transannular repulsion between adjacent guanidinate substituents. Attempts to synthesis the tert-butyl derivative [Cu2{Me2NC(tBuN)2}2] result in the separate formation and isolation of the tri-copper complexes [Cu3{Me2NC(tBuN)2}2(μ-NMe2)] (3c) and [Cu3{Me2NC(tBuN)2}2(μ-Cl)] (4c), both of which have been unambiguously characterized by single crystal X-ray diffraction. Closer inspection of the solution state behavior of the lithium salt 1c reveals a previously unobserved equilibrium between 1c and its starting materials, LiNMe2 and N,N′-di-tert-butyl-carbodiimide, for which activation enthalpy and entropy values of ΔH⧧ = 48.2 ± 18 kJ mol–1 and ΔS⧧ = 70.6 ± 6 J/K mol have been calculated using 1D-EXSY NMR spectroscopy to establish temperature dependent rates of exchange between the species in solution. The molecular structures of the lithium complexes 1c and 1d have also been determined and shown to form tetrameric and dimeric complexes respectively held together by Li–N and agostic Li···H–C interactions. The thermal chemistry of the copper complexes have also been assessed by thermogravimetric analysis.

Synthesis and Structure of 6-Aminofulvene-2-aldiminate Complexes

Co-reporter:Alexander M. Willcocks ; Alexander Gilbank ; Stephen P. Richards ; Simon K. Brayshaw ; Andrew J. Kingsley ; Raj Odedra

Inorganic Chemistry 2011 Volume 50(Issue 3) pp:937-948

Publication Date(Web):January 5, 2011

DOI:10.1021/ic101524b

We report here a synthetic route to bis(N,N′-aryl)-6-aminofulvene-2-aldimine (AFA) ligand systems, specifically Ph2-AFAH and Dip2-AFAH. The synthesis and structural characterization of a series of Cu(I) complexes [(Ph2-AFA)Cu(CNPh)2] (2), [(Ph2-AFA)Cu(CNiPr)] (3), and [(Dip2-AFA)Cu(CNiPr)] (4), from the reaction of the corresponding lithiated AFA systems with Cu−Cl derivatives are reported; notably in the case of [(Ph2-AFA)Cu(CNPh)2] studies have revealed the existence of two structural isomers (2a and 2b), both of which can be isolated and structurally characterized. Density functional theory (DFT) calculations suggest that the two crystal forms are comparatively close in energy, and geometry optimization reveals a convergence of these two forms to a geometry that more closely resembles the solid-state structure of isomer 2b, having a CH···π interaction. The reactions of the AFA compounds Ph2-AFAH and Dip2-AFAH with ZnMe2 and AlMe3 have also been investigated, and the results of these reactions are described here.

Synthesis, Characterization, and Materials Chemistry of Group 4 Silylimides

Co-reporter:S. D. Cosham ; A. L. Johnson ; K. C. Molloy ;Andrew J. Kingsley

Inorganic Chemistry 2011 Volume 50(Issue 23) pp:12053-12063

Publication Date(Web):November 4, 2011

DOI:10.1021/ic2015644

This paper focuses on the development of potential single source precursors for M–N–Si (M = Ti, Zr or Hf) thin films. The titanium, zirconium, and hafnium silylimides (Me2N)2MNSiR1R2R3 [R1 = R2 = R3 = Ph, M = Ti(1), Zr (2), Hf (3); R1 = R2 = R3 = Et, M = Ti (4), Zr (5), Hf (6); R1 = R2 = Me, R3 = tBu, M = Ti (7), Zr (8), Hf (9); R1 = R2 = R3 = NMe2, M = Ti (10), Zr (11), Hf (12)] have been synthesized by the reaction of M(NMe2)4 and R3R2R1SiNH2. All compounds are notably sensitive to air and moisture. Compounds 1, 2, 4, and 7–10 have been structurally characterized, and all are dimeric, with the general formula [M(NMe2)2(μ-NSiR3)]2, in which the μ2-NSiR3 groups bridges two four-coordinate metal centers. The hafnium compound 3 possesses the same basic dimeric structure but shows additional incorporation of liberated HNMe2 bonded to one metal. Compounds 11 and 12 are also both dimeric but also incorporate additional μ2-NMe2 groups, which bridge Si and either Zr or Hf metal centers in the solid state. The Zr and Hf metal centers are both five-coordinated in these species. Aerosol-assisted CVD (AA-CVD) using 4–7 and 9–12 as precursors generates amorphous films containing M, N, Si, C, and O; the films are dominated by MO2 with smaller contributions from MN, MC and MSiON based on XPS binding energies.

Synthesis, Isolation and Structural Characterisation of Alkoxytitanium Triflate Complexes

Co-reporter:Matthew G. Davidson

European Journal of Inorganic Chemistry 2011 Volume 2011( Issue 33) pp:5151-5159

Publication Date(Web):

DOI:10.1002/ejic.201100830

Abstract

Treatment of [Ti(OiPr)₄] with trimethylsilyl triflate results in the formation of [Ti(OiPr)₃(OTf)] (2) in high yield. Subsequent treatment of the triflate derivative 2 with a series of facially coordinating N₃-donor ligands results in the production of a series of charge-separated metal alkoxide salts of the general formula [{L}Ti(OiPr)₃][OTf] {L = tris(pyrazolyl)methane (3a), 1,3,5-triethyl-1,3,5-triazacyclohexane (3b), 1,3,5-tribenzyl-1,3,5-triazacyclohexane (3c), 1,3,5-tris(p-fluorobenzyl)-1,3,5-triazacyclohexane (3d), and 1,3,5-tris[(1S)-1-phenylethyl]-1,3,5-triazacyclohexane (3e)}. The products were characterized by ¹H and ¹³C NMR spectroscopy and in the case of 3a–c by single-crystal X-ray diffraction. Reaction of 2 with 1,3,5-triphenyl-1,3,5-triazacyclohexane results in the formation of complex 4 [{L′}₂Ti(OiPr)₂(OTf)₂], which contains two 3,4-dihydroquinazoline ligands (L′), a result of catalytic activation of the triazacyclohexane ligands by [Ti(OiPr)₃(OTf)] towards electrophilic aromatic substitution.

Plasma deposited metal Schiff-base compounds as antimicrobials

Co-reporter:Neil Poulter, Matthew Donaldson, Geraldine Mulley, Luis Duque, Nicholas Waterfield, Alex G. Shard, Steve Spencer, A. Tobias A. Jenkins and Andrew L. Johnson

New Journal of Chemistry 2011 vol. 35(Issue 7) pp:1477-1484

Publication Date(Web):04 May 2011

DOI:10.1039/C1NJ20091G

This paper details the synthesis, characterisation including crystal structure, and testing for antimicrobial efficacy of two compounds: a zinc centred bis(N-allylsalicylideneiminato)-zinc (ZSB) and its known copper analogue, bis(N-allylsalicylideneiminato)-copper (CSB). Differences in antimicrobial efficacy of the two compounds were observed, suggesting possible mechanisms for antimicrobial activity. The ZSB system was plasma deposited under various pulse conditions onto non-woven fabric, and the antimicrobial efficacy of the resultant film measured for Staphylococcus aureus and Pseudomonas aeruginosa. These results suggest the potential utility of this compound as an effective antimicrobial thin film, and confirm the critical role the ligands play in effecting antimicrobial activity.

Synthesis of complexes with the polydentate ligand N,N′-bis(2-hydroxyphenyl)-pyridine-2,6-dicarboxamide

Co-reporter:Yolanda Pérez, Andrew L. Johnson, Paul R. Raithby

Polyhedron 2011 30(2) pp: 284-292

Publication Date(Web):

DOI:10.1016/j.poly.2010.10.012

Acid activation of titanium alkoxide systems – Structural characterisation of Ti(IV) sulfonyl-imide complexes

Co-reporter:Andrew L. Johnson, Matthew G. Davidson, Matthew D. Jones, Matthew D. Lunn

Inorganica Chimica Acta 2010 Volume 363(Issue 10) pp:2209-2214

Publication Date(Web):20 June 2010

DOI:10.1016/j.ica.2010.03.027

Treatment of [Ti(OiPr)4] with the sulfonyl-imine systems Tos2NH ([(p-Me-C6H4SO2)2NH]) and Tf2NH ([(CF3SO2)2NH]) results in the formation of the new Lewis acidic titanium sulfonyl-imide complexes [Ti(OiPr)2(O,O′-Tos2N)2] (1) and [Ti(OiPr)2(HOiPr)2(O-Tf2N)2] (2), respectively. The molecular structures of the complexes have been determined by single crystal X-ray diffraction. The reaction of [Ti(OiPr)3(OAr)] (Ar = 2,6-di-tert-butyl-4-methyl phenyl) with Tf2NH results in the formation of the dimeric complex [Ti(OiPr)3(O,O′-Tf2N)]2 (3), which has also been structurally characterised. The ability of the complexes to catalyst the Friedel–Crafts acylation of anisole has also been assessed.The structurally characterised titanium sulfonyl-imide complexes [Ti(OiPr)2(O,O′-Tos2N)2] (1) and [Ti(OiPr)2(HOiPr)2(O-Tf2N)2] (2) have been synthesised from the reaction of [Ti(OiPr)4] with the N–H acids Tos2NH and Tf2NH, respectively. The dimeric complex [Ti(OiPr)3(O,O′-Tf2N)]2 (3), has also been synthesised and structurally characterised and the ability of the complexes (1–3) to catalyst the Friedel–Crafts acylation of anisole has been assessed.

Synthesis and Structures of Group 11 Metal Triazenide Complexes: Ligand Supported Metallophilic Interactions

Co-reporter:Andrew L. Johnson ; Alexander M. Willcocks ;Stephen P. Richards

Inorganic Chemistry 2009 Volume 48(Issue 17) pp:8613-8622

Publication Date(Web):July 28, 2009

DOI:10.1021/ic901051f

A homologous and homoleptic series of stable Group 11 metal triazenide complexes with the general formula [M(L′)]n (M = Cu or Au, n = 2; M = Ag, n = 3) featuring the bulky triazenide ligand N,N′-bis(2,6-di-isopropylphenyl)triazene, L′H, have been prepared by the reaction of Li[L′] with the metal chlorides, CuCl, AgCl, and [(THT)AuCl], respectively, in a 1:1 stoichiometric ratio. The compounds [Cu2(L′)2] and [Au2(L′)2] crystallized as dimers with M···M separations of 2.4458(4) Å and 2.6762(4) Å, respectively. In comparison, the reaction of AgCl with Li[L′] results in the formation of the tri-silver complex [Ag3(L′)3] with Ag···Ag separations of 3.01184(17) Å, 2.95329(17) Å, and 2.92745(16) Å. Attempts to react the parent triazene system L′H with [Cu(Mes)] resulted in the formation of the novel tri-copper system [Cu3(L′)2(Mes)]. In all cases the molecular structures of the resultant complexes have been unambiguously determined by single crystal X-ray diffraction experiments.

Synthesis and structure of aluminium amine-phenolate complexes

Co-reporter:Andrew L. Johnson, Matthew G. Davidson, Yolanda Pérez, Matthew D. Jones, Nicolas Merle, Paul R. Raithby and Stephen P. Richards

Dalton Transactions 2009 (Issue 28) pp:5551-5558

Publication Date(Web):08 Jun 2009

DOI:10.1039/B904534A

Reaction of Al(OiPr)3 with the tris-phenol amine ligand L1H3 in toluene at ambient temperature results in the formation of the iso-propanol adduct [HOiPr·Al(L1)]. Single crystal X-ray diffraction analysis reveals the structure to be a hydrogen bonded dimer. Reaction of Al(OiPr)3 (or AlMe3) with L1H3 in THF affords the related, and structurally characterised THF adduct, [THF·Al(L1)]. Similar reaction of Al(OiPr)3 (or AlMe3) with the bis-phenol amine and tetra-phenol diamine ligands, L2H3 and L3H4, results in the formation and isolation of the complexes [Al(L2)]2 and [Al(L3)H] respectively, both of which have been structurally characterised viasingle crystal X-ray diffraction studies. Reaction of the alkoxide bridged dimer [Al(L2)]2 with the strong Lewis base HMPA results in the formation of the monomeric HMPA adduct [HMPA·Al(L2)] which was also structurally characterised. The adduct [HOiPr·Al(L1)] and the dimer [Al(L2)]2 were tested for their activity in the ring-opening polymerisation (ROP) of rac-lactide under solvent-free conditions (130 °C). Under the conditions employed [Al(L2)]2 failed to produce polymer after 48 h, in stark contrast to [HOiPr·Al(L1)] which after 24 h and 48 h produced narrow molecular weight polymer (24 h: yield = 25%, Mn = 14500 and PDI = 1.05; 48 h: yield = 65%, Mn = 47700 and PDI = 1.06).

Unprecedented double migratory insertion of phenyl isocyanide into cyclopentadienyl C–H bonds

Co-reporter:Andrew L. Johnson, Alexander M. Willcocks, Paul R. Raithby, Mark. R. Warren, Andrew J. Kingsley and Raj Odedra

Dalton Transactions 2009 (Issue 6) pp:922-924

Publication Date(Web):06 Jan 2009

DOI:10.1039/B822337H

The reaction of [(η5-C5H5)Cu(CNPh)] with phenyl-isocyanide results in an unprecedented double migratory insertion into two sp2 C–H bonds of a η5-coordinated cyclopentadienyl group, and formation of the 6-aminofulvene-2-aldimine complexes [(CNPh)Cu{κ2-N,N-C5H3-1,2-(CHNPh)2}] and [(CNPh)2Cu{κ2-N,N-C5H3-1,2-(CHNPh)2}], respectively, both of which have been structurally characterised.

Reactivity of boranes with a titanium(IV) amine tris(phenolate) alkoxide complex; formation of a Ti(IV) tetrahydroborate complex, a Ti(III) dimer and a Ti(IV) hydroxide Lewis acid adduct

Co-reporter:Andrew L. Johnson, Matthew G. Davidson and Mary F. Mahon

Dalton Transactions 2007 (Issue 46) pp:5405-5411

Publication Date(Web):27 Sep 2007

DOI:10.1039/B708378E

Treatment of the titanium(IV) alkoxide complex [Ti(OiPr)(OC6Me2H2CH2)3N] (2) with BH3·THF, as part of a study into the utility and reactivity of (2) in the metal mediated borane reduction of acetophenone, results in alkoxide–hydride exchange and formation of the structurally characterised titanium(IV) tetrahydroborate complex [Ti{BH4}(OC6Me2H2CH2)3N] (3). Complex (3) readily undergoes reduction to form the isolable titanium(III) species [Ti(OC6Me2H2CH2)3N]2 (4). Reaction of (2) with B(C6F5)3 results in formation of the Lewis acid adduct [Ti(OC6Me2H2CH2)3N][HO·B(C6F5)3] (5). In comparison, treatment of the less sterically encumbered alkoxide Ti(OiPr)4 with B(C6F5)3 results in alkoxide–aryl exchange and formation of the organometallic titanium complex [Ti(OiPr)3(C6F5)]2 (6). The molecular structures of 3, 4, 5 and 6 have been determined by X-ray diffraction.

Synthesis, Isolation and Structural Investigation of Schiff-Base Alkoxytitanium Complexes: Steric Limitations of Ligand Coordination

Co-reporter:Andrew L. Johnson;Matthew G. Davidson;Matthew D. Lunn;Mary F. Mahon

European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 15) pp:

Publication Date(Web):7 JUN 2006

DOI:10.1002/ejic.200600113

This paper reports the reaction of Ti(OiPr)₄ with a series of Schiff-base ligands. The Schiff-base proligands 1a–l are synthesised by the condensation of salicylaldehyde with a range of primary alkylamine and aniline derivatives. The treatment of 1a–f with Ti(OiPr)₄ yields the octahedral bis(aryloxy–imine)Ti(OiPr)₂ complexes 2a–f. X-ray crystal structure analysis of 2c, 2d and 2e reveals complexes with a trans-aldiminato oxygen atom and cis-N,cis-alkoxide ligand arrangement about the central metal atom. The reactions of Ti(OiPr)₄ with the ligands 1g and 1h result in a sterically induced ligand rearrangement to form the octahedral complexes 2g and 2h, also characterised by X-ray diffraction experiments, in which the nitrogen atoms of the O,N-chelate are now trans-orientated at the titanium centre. ¹H NMR analysis reveals significant deshielding of the isopropoxide methine proton, induced by this coordination mode. In contrast, reactions of 1i and 1j with Ti(OiPr)₄ result in the formation and isolation of the complexes 2i and 2j. X-ray crystal structure analysis shows complex 2j to have a previously unobserved ligand orientation, in which both ligands are trans-orientated, with respect to the aldiminato oxygen atoms, about the titanium centre, but steric bulk of the ligand inhibits the bidentate coordination of both O,N-ligands. Further increase in thesteric bulk of the imine substituent results in a reduced reactivity for ligands 1k and 1l, such that Ti(OiPr)₄ reacts with 1k to form the dimeric mono(Schiff-base) complex 2k (characterised by X-ray analysis). No reaction is observed for 1l. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)