Harry Adams
The University of Sheffield, Chemistry, Department Member
ABSTRACT Three new ligands have been prepared in which two terdentate chelating pyrazolyl-bipyridine units are connected by a central aromatic spacer via methylene “hinges”: the spacers are o-phenylene (LPh), 2,6-pyridine-diyl (LPy) and... more
ABSTRACT Three new ligands have been prepared in which two terdentate chelating pyrazolyl-bipyridine units are connected by a central aromatic spacer via methylene “hinges”: the spacers are o-phenylene (LPh), 2,6-pyridine-diyl (LPy) and 2,3-naphthalenediyl (Lnaph). The ligands act as potentially hexadentate bridging ligands, with the central pyridyl N atom of LPy not involved in coordination. The following complexes were prepared and structurally characterised: [M2(LPh)2][ClO4]4 (M = Ni, Cu), which are dinuclear double helicates; [Ag2(LPh)(MeCN)2][BF4]2, a dinuclear complex with an Ag···Ag bond in which the ligand adopts a helical twist around the pair of metal ions; [Ni2(LPy)2][BF4]4, an achiral “mesocate” with a box-like structure and a face-to-face arrangement of ligands; [Ag3(Lnaph)2](BF4)3, which contains a linear trinuclear array of AgI ions with the two ligands arranged in a shallow helical twist, each ligand spanning one terminal and the central metal ion; and [Cd6(Lnaph)6](ClO4)12, a cyclic hexanuclear helicate with a perchlorate anion in the central cavity. Both [Cu2(LPh)2][ClO4]4 and [Cd6(Lnaph)6](ClO4)12, which have architecturally similar bridging ligands, show evidence by electrospray mass spectrometry for formation of a range of cyclic oligomers in solution up to 11-mers for the CdII/Lnaph system.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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Reaction of a tris-bidentate ligand L(1) (which can cap one triangular face of a metal polyhedron), a bis-bidentate ligand L(2) (which can span one edge of a metal polyhedron), and a range of M(2+) ions (M = Co, Cu, Cd), which all have a... more
Reaction of a tris-bidentate ligand L(1) (which can cap one triangular face of a metal polyhedron), a bis-bidentate ligand L(2) (which can span one edge of a metal polyhedron), and a range of M(2+) ions (M = Co, Cu, Cd), which all have a preference for six coordination geometry, results in assembly of the mixed-ligand polyhedral cages [M12(mu(3)-L(1))4(mu-L(2))12](24+). When the components are combined in the correct proportions [M(2+):L(1):L(2) = 3:1:3] in MeNO2, this is the sole product. The array of 12 M(2+) cations has a cuboctahedral geometry, containing six square and eight triangular faces around a substantial central cavity; four of the eight M3 triangular faces (every alternate one) are capped by a ligand L(1), with the remaining four M3 faces having a bridging ligand L(2) along each edge in a cyclic helical array. Thus, four homochiral triangular {M3(L(2))3}(6+) helical units are connected by four additional L(1) ligands to give the mixed-ligand cuboctahedral array, a topology which could not be formed in any homoleptic complex of this type but requires the cooperation of two different types of ligand. The complex [Cd3(L(2))3(ClO4)4(MeCN)2(H2O)2](ClO4)2, a trinuclear triple helicate in which two sites at each Cd(II) are occupied by monodentate ligands (solvent or counterions), was also characterized and constitutes an incomplete fragment of the dodecanuclear cage comprising one triangular {M3(L(2))3}(6+) face which has not yet reacted with the ligands L(1). (1)H NMR and electrospray mass spectrometric studies show that the dodecanuclear cages remain intact in solution; the NMR studies show that the Cd 12 cage has four-fold (D2) symmetry, such that there are three independent Cd(II) environments, as confirmed by a (113)Cd NMR spectrum. These mixed-ligand cuboctahedral complexes reveal the potential of using combinations of face-capping and edge-bridging ligands to extend the range of accessible topologies of polyhedral coordination cages.
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The and CHEMICAL SCIENCES
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Three new complexes [Ni(β-dkt)2(NH2-quin)] {β-dkt = 2,2,6,6-tetramethylheptane-3,3-dionate (tmhd) 1, hexafluoroacetylacetonate (hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} have been prepared by reacting [Ni(β-dkt)2(H2O)2] with... more
Three new complexes [Ni(β-dkt)2(NH2-quin)] {β-dkt = 2,2,6,6-tetramethylheptane-3,3-dionate (tmhd) 1, hexafluoroacetylacetonate (hfac) 2, 1,3-diphenylpropanedionate (dbm) 3} have been prepared by reacting [Ni(β-dkt)2(H2O)2] with 8-aminoquinoline (NH2-quin). [Ni(tmhd)2(NH2-quin)] is found to be solvatochromic exhibiting a square planar geometry in CH2Cl2, acetone, and acetonitrile with the tmhd ligand acting unusually as a counteranion while in THF and DMSO the complex is octahedral. In contrast, 2 and 3 are octahedral in all solvents. Single crystal X-ray diffraction studies reveal octahedral nickel centres with a cis arrangement of the β-diketonates. The molecular packing consists of hydrogen bonded dimers which in the case of 2 and 3 are connected to one another via π···π and C–H⋯π interactions, respectively. Cyclic voltammetry shows 1 and 3 oxidise irreversibly at 0.46 and 1.17 V, respectively.A series of novel [Ni(β-dkt)2(NH2-quin)] complexes is reported. The complexes are octahedral in the solid state but in the case of the electron rich and steric bulky tmhd ligand are square planar in non- and weakly coordinating solvents. The change in coordination geometry is found to radically alter the redox behaviour of [Ni(tmhd)2(NH2-quin)].► Nickel aminoquinoline β-diketonates as molecular switches. ► Octahedral in the solid state, square planar in solution. ► Geometry dependent on β-diketonate and then the solvent. ► Redox activity of the square planar and octahedral complexes radically different.
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CO laser‐induced multiphoton absorption of fluoroform‐d: The effects of collisions. [The Journal of Chemical Physics 78, 5990 (1983)]. Robert D. McAlpine, DK Evans, HM Adams. Abstract. Studies of the multiphoton absorption ...
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Reaction of [Rh(CO)2I]2 (1) with MeI in nitrile solvents gives the neutral acetyl complexes, [Rh(CO)(NCR)(COMe)I2]2 (R=Me, 3a; tBu, 3b; vinyl, 3c; allyl, 3d). Dimeric, iodide-bridged structures have been confirmed by X-ray crystallography... more
Reaction of [Rh(CO)2I]2 (1) with MeI in nitrile solvents gives the neutral acetyl complexes, [Rh(CO)(NCR)(COMe)I2]2 (R=Me, 3a; tBu, 3b; vinyl, 3c; allyl, 3d). Dimeric, iodide-bridged structures have been confirmed by X-ray crystallography for 3a and 3b. The complexes are centrosymmetric with approximate octahedral geometry about each Rh centre. The iodide bridges are asymmetric, with Rh–(μ-I) trans to acetyl longer than
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Thermal dissociation of CO from cis,fac-[Ir(CO)(2)I(3)Me](-) (1a) gives the iodide-bridged dimer [{Ir(CO)I(2)(mu-I)Me}(2)](2-), which was characterized crystallographically as its Ph(4)As(+) salt. This dimer reacts with CO at ambient... more
Thermal dissociation of CO from cis,fac-[Ir(CO)(2)I(3)Me](-) (1a) gives the iodide-bridged dimer [{Ir(CO)I(2)(mu-I)Me}(2)](2-), which was characterized crystallographically as its Ph(4)As(+) salt. This dimer reacts with CO at ambient temperature to give the acetyl complex trans,mer-[Ir(CO)(2)I(3)(COMe)](-). An intermediate in this reaction is the previously unobserved cis,mer-[Ir(CO)(2)I(3)Me](-) (1b), which was characterized by IR and NMR spectroscopy. Carbonylation of 1b is much faster (t(1/2) approximately 1 min at 25 degrees C) than for the cis,fac isomer 1a and also faster than the neutral tricarbonyl [Ir(CO)(3)I(2)Me]. The observations show that the relative positioning of carbonyl ligands influences reactivity more than than their number, and that CO insertion is particularly accelerated when a CO ligand is placed trans to the migrating methyl group. DFT calculations indicate that the Ir-CO bond trans to methyl contracts significantly as 1b approaches the transition state for methyl migration, facilitating stronger pi-backbonding from Ir to the spectator CO ligand, which stabilizes the transition state. The results confirm the recently proposed CO-loss mechanism for the photochemical carbonylation of 1a and suggest that the cis,mer isomer may play a minor role in the catalytic cycle for methanol carbonylation.
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Reaction of cyclometalated halide-bridged Pd(II) complexes 1-4 with the tertiary triphosphine ligand (Ph2PCH2CH2)2PPh (triphos) yielded complexes [((Ph2PCH2CH2)2PPh-P,P,P)Pd(N(Cy)=(H)C)C6H2(C(H)=N(Cy))Pd((Ph2PCH2CH2)2PPh-P,P,P)][ClO4]2 5,... more
Reaction of cyclometalated halide-bridged Pd(II) complexes 1-4 with the tertiary triphosphine ligand (Ph2PCH2CH2)2PPh (triphos) yielded complexes [((Ph2PCH2CH2)2PPh-P,P,P)Pd(N(Cy)=(H)C)C6H2(C(H)=N(Cy))Pd((Ph2PCH2CH2)2PPh-P,P,P)][ClO4]2 5, [Pd(C6H4-N=NC6H5)((Ph2PCH2CH2)2PPh-P,P,P)][ClO4] 6, and [Pd(R-C6H3C(H)=NCy)((Ph2PCH2CH2)2PPh-P,P,P)][ClO4] (7; R = 4-CHO, 8; 3-CHO). Spectroscopic and analytic data suggest five-coordination on the palladium atom, which, for complexes 5, 6, and 7, was confirmed by X-ray crystallography. The geometry around palladium may be view as a distorted trigonal bipyramid, with the palladium, nitrogen, and terminal phosphorus atoms in the equatorial plane. Compound 5 is the first doubly cyclometalated palladium(II) compound with two pentacoordinated metal centers. The structure of 6 comprises two discrete cations with slightly different geometries, showing the importance of crystal packing forces in order to determine the coordination arrangement.
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The synthesis of dinuclear [Ru(II)([n]aneS(4))] (where n = 12, 14) complexes of the bridging ligand 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine are reported. The X-ray structures of both of the new complexes are compared to a newly obtained... more
The synthesis of dinuclear [Ru(II)([n]aneS(4))] (where n = 12, 14) complexes of the bridging ligand 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine are reported. The X-ray structures of both of the new complexes are compared to a newly obtained structure for a dinuclear [Ru(II)([9]aneS(3))]-based analogue, whose synthesis has previously been reported. A comparison of the electrochemistry of the three complexes reveals that the first oxidation of the [Ru(II)([n]aneS(4))]-based systems is a ligand-based couple, indicating that the formation of the radical anion form of the bridging ligand is stabilized by metal center coordination. Spectroelectrochemistry studies on the mixed-valence form of the new complexes suggest that they are Robin and Day Class II systems. The electrochemical and electronic properties of these complexes is rationalized by a consideration of the pi-bonding properties of thiacrown ligands.
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Page 1. JOURNAL OF PHYSICAL ORGANIC CHEMISTRY J. Phys. Org. Chem. 2007; 17: 10071016 Published online 13 August 2004 in Wiley InterScience (www.interscience.wiley. com). DOI: 10.1002/poc.820 Kinetics and thermodynamics of C----Cl bond ...
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The syntheses of novel tricyclic pyrrolo[2,3-d]pyrimidine analogues of O(6)-methylguanine and S(6)-methylthioguanine are described. The crystal structures and pK(a) values of these analogues are reported. In a standard substrate assay... more
The syntheses of novel tricyclic pyrrolo[2,3-d]pyrimidine analogues of O(6)-methylguanine and S(6)-methylthioguanine are described. The crystal structures and pK(a) values of these analogues are reported. In a standard substrate assay with the human repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) only the oxygen-containing analogue displayed activity.
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Trinuclear Ni(II), Co(II) and Mn(II) complexes have been prepared from the asymmetric compartmental proligands 2-alkyliminomethyl-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol(alkyl=ethyl, n-propyl and n-butyl) and... more
Trinuclear Ni(II), Co(II) and Mn(II) complexes have been prepared from the asymmetric compartmental proligands 2-alkyliminomethyl-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol(alkyl=ethyl, n-propyl and n-butyl) and 2-[(2-methoxy-ethylimino)-methyl]-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol, which provide adjacent tridentate N2O and bidentate NO donor sets. The crystal structures of [Ni3(L6)2(OAc)2(NCS)2]·CH3OH·H2O, [Co3(L4)2(OAc)2(NCS)2], and [Mn3(L7)2(OAc)2(NCS)2]·CH3OH·H2O were determined and show that the metals provide an isosceles triangle with M1–M2=M1–M3≈3.2 Å and M2-M3≈5.0 Å. The cryomagnetic properties of the
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ABSTRACT [Rh(eta5-C5Me5) (eta5-C5H5)]+ (1a) was deprotonated (by potassium tert-butoxide) to give the neutral tetramethylfulvene complex [Rh(eta4-C5Me4:CH2)(eta5-C5H5)] (2a), which was a good nucleophile toward Me3SiCl, CH2=CHCH2Br,... more
ABSTRACT [Rh(eta5-C5Me5) (eta5-C5H5)]+ (1a) was deprotonated (by potassium tert-butoxide) to give the neutral tetramethylfulvene complex [Rh(eta4-C5Me4:CH2)(eta5-C5H5)] (2a), which was a good nucleophile toward Me3SiCl, CH2=CHCH2Br, PhCH2Br, Cl2, I2, CO2 (+MeI), and Ph2CO, giving [Rh(eta5-C5Me4CH2X)(eta5-C5H5)]+ (X = Me3Si-, CH2=CHCH2-, PhCH2-, Cl, I, MeO2C-, and Ph2C(OH)-, respectively). The complex 2a also yielded 1a both on protonation and on treatment with the ferrocenium ion in THF. Similar reactions were carried out on [lr(eta5-C5Me5)(eta5-C5H5)]+ (1b), deprotonated by lithium diisopropylamide in THF, yielding[Ir(eta5-C5Me4CH2X)(eta5-C5H5)]+ (X = Me3Si-, PhCH2-, or Ph2C(OH)-) with Me3SiCl, PhCH2Br, or Ph2CO; these reactions presumably proceeded via [Ir(eta4-C5Me4:CH2)(eta5-C5H5)] (2b). While both 2a and 2b reacted with MeI, 2a gave a mixture of complexes, [Rh(C5H5)(C5MenEt5-n)]+ (7a, n = 1-5), whereas the iridium complex 2b gave just [Ir(eta5-C5Me4Et)(eta5-C5H5)]+. Possible mechanisms for this process are reviewed.
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Division of Chemistry, School of Science, Sheffield Hallam University, Pond Street, Sheffield S1 1WB, UK Fax +44 114 2533085; (MAKhan@shu.ac.uk) ... Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK ... Received: 17... more
Division of Chemistry, School of Science, Sheffield Hallam University, Pond Street, Sheffield S1 1WB, UK Fax +44 114 2533085; (MAKhan@shu.ac.uk) ... Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK ... Received: 17 November 1995 / Accepted :17 ...
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Multicomponent synthesis of 3-aminoimidazo[1,2-a]pyrimidines usually affords a product mixture containing varying amounts of the corresponding 2-amino regioisomer. Modified methods, particularly microwave heating, have been employed to... more
Multicomponent synthesis of 3-aminoimidazo[1,2-a]pyrimidines usually affords a product mixture containing varying amounts of the corresponding 2-amino regioisomer. Modified methods, particularly microwave heating, have been employed to suppress formation of this side-product, but none of the revised protocols are readily amenable to scale. A continuous flow adaptation was found to offer improved regioselectivity toward the targeted 3-amino regioisomer with significantly shorter reaction times and also widened the scope of the reaction to permit the use of aliphatic aldehyde building blocks.
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Formation of the alkoxyalkyl complexes [M{CHMe(OMe)}(CO)2(?-C5H4R)](M = Mo, R = H; M = W, R = H or Me) and their transformations by loss of MeOH into ?3-propenoyl or vinyl complexes. Crystal structures of [Mo{CHMe(PPh3)}(CO)2(PPh3)(?-C5H5)]BF4, [Mo(?3-CH2CHC?O)(CO)(PPh3)(?-C5H5)] and [W(?-CH?CH2)...more
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... Soc., Dalton Trans., 1992, 11 RSC Article . 21, RJ Goodfellow, in Multinuclear NMR, ed. J. Mason, Plenum Press, New York, 1987, ch. 21; ; PM Hendricks, in NMR of Newly Accessible Nuclei, ed. P. Laszlo, Academic Press, London, 1983,... more
... Soc., Dalton Trans., 1992, 11 RSC Article . 21, RJ Goodfellow, in Multinuclear NMR, ed. J. Mason, Plenum Press, New York, 1987, ch. 21; ; PM Hendricks, in NMR of Newly Accessible Nuclei, ed. P. Laszlo, Academic Press, London, 1983, ch. 12. . ...
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Abstract Three new binuclear Ni(II) complexes [{Ni(L22py)Cl}2](ClO4)2 (1), [{Ni(L23py)Cl}2](ClO4)2 (2), and [{Ni(L33py)Cl}2](ClO4)2 (3), {L22py = N-(2-pyridylmethyl)-N-(2-aminoethyl)-1,2-diaminoethane,... more
Abstract Three new binuclear Ni(II) complexes [{Ni(L22py)Cl}2](ClO4)2 (1), [{Ni(L23py)Cl}2](ClO4)2 (2), and [{Ni(L33py)Cl}2](ClO4)2 (3), {L22py = N-(2-pyridylmethyl)-N-(2-aminoethyl)-1,2-diaminoethane, L23py = N-(2-pyridylmethyl)-N-(2-aminoethyl)-1,3-diaminopropane, L33py = N-(2-pyridylmethyl)-N-(3-aminopropyl)-1,3-diaminopropane} have been synthesized. Single crystal X-ray structure analysis showed that in each complex two distorted octahedral Ni(II) ions are bridged asymmetrically by a pair of chloride anions. Variable temperature magnetic susceptibility measurements of 1 and 3 revealed dominant ferromagnetic exchange interactions.
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Multicomponent synthesis of 3-aminoimidazo[1,2-a]pyrimidines usually affords a product mixture containing varying amounts of the corresponding 2-amino regioisomer. Modified methods, particularly microwave heating, have been employed to... more
Multicomponent synthesis of 3-aminoimidazo[1,2-a]pyrimidines usually affords a product mixture containing varying amounts of the corresponding 2-amino regioisomer. Modified methods, particularly microwave heating, have been employed to suppress formation of this side-product, but none of the revised protocols are readily amenable to scale. A continuous flow adaptation was found to offer improved regioselectivity toward the targeted 3-amino regioisomer with significantly shorter reaction times and also widened the scope of the reaction to permit the use of aliphatic aldehyde building blocks.
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A novel [3+2]-cycloaddition reaction of alkynylboronates and nitrile oxides gave the title compound, C(22)H(32)BNO(3), as a single regioisomer. The X-ray crystal structure analysis of this compound shows two independent molecules in the... more
A novel [3+2]-cycloaddition reaction of alkynylboronates and nitrile oxides gave the title compound, C(22)H(32)BNO(3), as a single regioisomer. The X-ray crystal structure analysis of this compound shows two independent molecules in the asymmetric unit, each with approximately coplanar isoxazole and boronate rings.
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Unexpected ring contraction in the barium-assisted cyclocondensation of 2,6-diformylpyridine and N, N=bis( Zaminoethyl)=2-phenylethylamine ... Harry Adams," Neil A. Bailey," Philippe Bertrand," Simon R. Collinson,'... more
Unexpected ring contraction in the barium-assisted cyclocondensation of 2,6-diformylpyridine and N, N=bis( Zaminoethyl)=2-phenylethylamine ... Harry Adams," Neil A. Bailey," Philippe Bertrand," Simon R. Collinson,' David E. Fenton *-' and Simon J. Kitchen