Boere, Rene

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    1,3-Diphenylisobenzofuran
    (International Union of Crystallography, 2008) Boeré, René T.; Dibble, Peter W.; Fischer, Kristapher E.
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    1,5-(4,4'-Dipyridyl)naphthalene
    (MDPI, 2015) Hassan, Mohammad R.; Boeré, René T.
    The title compound has been prepared from 1,5-dibromonaphthalene (obtained from 1,5-diaminonaphthalene) using Suzuki-Miyaura cross-coupling to 4-pyridylboronic acid. The crystal and molecular structure was determined by single-crystal X-ray diffraction.
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    1-methyl-4-thiocarbamoylpyridin-1-ium iodide
    (International Union of Crystallography, 2018) Shotonwa, Ibukun O.; Boeré, René T.
    In the title compound, C7H9N2S+·I−, the thioamide moiety is twisted out of the aromatic plane by 38.98 (4)° and forms N—H...I hydrogen bonds. In the crystal, hydrogen-bonded centrosymmetric dimers [C7H9N2S+·I−]2 are linked via additional short contacts from an aromatic CH group to the iodide anion into ribbons parallel to the (010) plane.
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    2'-acetonaphthone
    (International Union of Crystallography, 2012) Shotonwa, Ibukun O.; Boeré, René T.
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    3,5-diphenyl-1,2,4-dithiazolium tetrabromidoferrate(III)
    (International Union of Crystallography, 2013) Shotonwa, Ibukun O.; Boeré, René T.
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    3,7-Di-tert-butyl-1,5,2,4,6,8-dithiatetrazocine
    (International Union of Crystallography, 1995) Parvez, Masood; Boeré, René T.; Derrick, Sean; Moock, Klaus H.
    The eight-membered ring in the title compound, C10HI8N4S2, lies about an inversion centre and is essentially planar with normal bond lengths and angles [mean C--S 1.569 (2) and mean C--N 1.326 (3)A].
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    4-hydrazinopyridinium chloride
    (International Union of Crystallography, 2009) Boeré, René T.; Hassan, Mohammad R.
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    4-methyl-N'-(2,2,2-trichloroethanimidoyl)benzene-1-carboximidamide
    (International Union of Crystallography, 2011) Roemmele, Tracey L.; Boeré, René T.
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    4-thiocarbamoylpyridin-1-ium iodide
    (International Union of Crystallography, 2014) Shotonwa, Ibukun O.; Boeré, René T.
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    (5Z,7Z,9Z)-5,10-dibromobenzo[8]-annulene
    (International Union of Crystallography, 2013) Bender, Christopher O.; Boeré, René T.
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    Accurate crystal structures of C12H9CN, C12H8(CN)2, and C16H11CN valence isomers using nonspherical atomic scattering factors
    (RSC Publishing, 2022) Hill, Nathan D. D.; Lilienthal, Elaura; Bender, Christopher O.; Boeré, René T.
    Fourteen crystal structures, mostly from good-quality datasets but including some marginal and twinned exemplars, from a series of novel polycyclic benzo- and naphtho-fused organic nitriles are presented and accurately described, including some related structures of a bromo-substituted and partially hydrogenated analogues. These structures represent a considerable increase in the number of published structures within their archetypes. This work highlights the significant advancement in structural refinement software proffered by NoSpherA2, which enables Hirshfeld Atom Refinement (HAR) of the structures within Olex2 v1.5. This results in the determination of C–H bond lengths with near to neutron diffraction accuracies at far lower experimental cost, and with an average improvement in C–C bond precision of 42% compared to Independent Atom Model refinements. H-atoms (apart from disordered components) refined well with anisotropic displacement parameters. Nonclassical H-bonding (C–H···N≡C) in this series is analyzed, and dipolar nitrile–nitrile interactions (C≡N···C≡N) in three major motifs described by (Wood, P. A. Acta Cryst. B, 2008, 64, 393−396) are found in 9 out of 13 nitrile-containing compounds of this series, a much higher proportion than the global average of 21% of nitrile-containing compounds. The HAR/NoSpherA2 approach shows increasing benefits with better data quality without apparent discontinuities.
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    Are monophospha(III)amidines and -guanidines with ionizable hydrogens tautomeric? Towards a deeper understanding of two related hetero-element functional groups
    (Wiley, 2023) Masuda, Jason D.; Amrei, Leila M.; Boeré, René T.
    This paper presents definitive structural evidence for N,P(III)-monophosphaamidines in P=C and N=C isomeric forms from a combination of new syntheses, single-crystal X-ray diffraction (SC-XRD), solid-state NMR and FTIR. Evidence is also provided for C-amino-(σ2,λ3)-phosphaalkene and C-(σ3,λ3)-phosphinoimine tautomerism in solution using multi-nuclear NMR methods. Synthesis and SC-XRD structure determination of a trisubstituted N,N’,P(III)-monophosphaguanidine is presented, the first structure of a phospha(III)guanidine with two ionizable H atoms. The structural evidence is convincing for an N=C geometry, resulting in both N−H and P−H in the molecule. A detailed computational investigation using DFT methods is presented, with the goal of understanding the tautomeric structure preferences both at the fundamental level (parent molecules with all substituents on the heteroatoms being hydrogen) and using the full structures containing the very bulky 2,6-diisopropylphenyl (Dipp) substituents employed in this study. Arguments are espoused for treating phospha(III)amidines and -guanidines as new types of functional groups, similar to but distinct from the familiar organic analogues. Limited reactivity studies and a voltammetry study of one phospha(III)amidine are included with the supporting information.
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    Backbone-substituted ß-ketoimines and ketoiminate clusters: transoid Li2O2 squares and D2-symmetric Li4O4 cubanes. Synthesis, crystallography and DFT calculations
    (MDPI, 2017) Gietz, Twyla M.; Boeré, René T.
    The preparation and crystal structures of four β-ketoimines with bulky aryl nitrogen substituents (2,6-diisopropylphenyl and 2,4,6-trimethylphenyl) and varying degrees of backbone methyl substitution are reported. Backbone substitution “pinches” the chelate ring. Deprotonation with n-butyllithium leads to dimeric Li2O2 clusters, as primary laddered units, with an open transoid geometry as shown by crystal structures of three examples. The coordination sphere of each lithium is completed by one tetrahydrofuran ligand. NMR spectra undertaken in either C6D6 or 1:1 C6D6/d8-THF show free THF in solution and the chemical shifts of ligand methyl groups experience significant ring-shielding which can only occur from aryl rings on adjacent ligands. Both features point to conversion to higher-order aggregates when the THF concentration is reduced. Recrystallization of the materials from hydrocarbon solutions results in secondary laddering as tetramericLi4O4 clusters with a cuboidal core, three examples of which have been crystallographically characterised. These clusters are relatively insoluble and melt up to 250 ◦C; a consideration of the solid-state structures indicates that the clusters with 2,6-diisopropylphenyl substituents form very uniform ball-like molecular structures that will only be weakly solvated.
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    Bulky 2,6-disubstituted aryl siloxanes and a disilanamine
    (International Union of Crystallography (IUCr), 2020) Marszaukowski, Flavia; Wohnrath, Karen; Boeré, René T.
    The crystal structures of 5-bromo-1,3-di-tert-butyl-2-[(tri­methyl­sil­yl)­oxy]benzene, C17H29BrOSi, (I), 1,3-di-tert-butyl-2-[(tri­methyl­sil­yl)­oxy]benzene, C17H30OSi, (II), and N-(2,6-diiso­propyl­phen­yl)-1,1,1-trimethyl-N-(tri­methyl­sil­yl)silanamine, C18H35NSi2, (III), are reported. Compound (I) crystallizes in space group P21/c with Z′ = 1, (II) in Pnma with Z′ = 0.5 and (III) in Cmcm with Z′ = 0.25. Consequently, the mol­ecules of (II) are constrained by m and those of (III) by m2m site symmetries. Despite this, both (I) and (II) are distorted towards mild boat conformations, as is typical of 2,6-di-tert-butyl-substituted phenyl compounds, reflecting the high local steric pressure of the flanking alkyl groups. Compound (III) by contrast is planar and symmetric, and this lack of distortion is compatible with the lower steric pressure of the flanking 2,6-diisopropyl substituents.
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    Butylbis[µ-4-(2,4,6-trimethylphenylamino)pent-3-en-2-onato][4-(2,4,6-trimethylphenylamino)pent-3-en-2-onato]dimagnesium
    (International Union of Crystallography, 2009) Boeré, René T.; Gietz, Twyla M.
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    Chalcogen controlled redox behaviour in peri-substituted S, Se and Te naphthalene derivatives
    (RSC Publishing, 2022) Roemmele, Tracey L.; Knight, Fergus R.; Crawford, Ellis; Robertson, Stuart D.; Bode, Bela E.; Bühl, MIchael; Slawin, Alexandra M. Z.; Woollins, J. Derek; Boeré, René T.
    Cyclic and square wave voltammetry of (PhE)2peri-disubstituted naphthalene[1,8-cd]dichalcoganyls and acenaphthene[5,6-diyl]dichalcoganyls (E = S, Se, Te, 12 compounds) is reported. Mixed (E1 = Se, Te; E2 = Br, I) naphthalene[1,8-cd]halochalcoganyls were also investigated, as well as an exemplar bearing two PhS([double bond, length as m-dash]O) groups and another bearing one PhSe and one Ph2P([double bond, length as m-dash]S) substituent. The voltammetry, in CH2Cl2/0.4 M [nBu4N][PF6] at both platinum and glassy carbon macro-disk working electrodes, shows two sequential chemically reversible and electrochemically quasi-reversible oxidation processes, and the lack of accessible reductions. Additional oxidations above +1.5 V vs. Fc+/0 have not been investigated in detail. In situ and ex situ EPR spectroscopy conclusively demonstrate that both anodic processes are 1e transfers; persistent radical cations could be generated for all the dichalcoganyls except when E1 = E2 = Te; for the latter case thermally stable dications are generated instead. The complex possible solution conformations of these compounds in 0, +1 and +2 charge states were modelled with DFT at the B3LYP-D3(BJ)/6-31+G(d) level of theory in a CH2Cl2 PCM continuum solution model and adiabatic ionisation energies calculated, which correlate linearly (R = 0.88) with the Ea1p values. Crystal structures of four solvolysis and hydrolysis products of the ditellurium dications are reported and were modelled computationally. Interpretative comparisons to unsubstituted naphthalene[1,8-cd]dichalcogenoles are reported and the crystal structure of naphtho(1,8-cd)(1,2-dithiolium) tetrafluoroborate has been obtained. This is the first structure reported for any salt of this cation radical. Electron transfer mechanisms of both the (PhE)2 and E2peri-disubstituted naphthalene series are correlated using a redox molecular orbital interpretative framework.
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    Challenging an old paradigm by demonstrating transition metal-like chemistry at a neutral nonmetal center
    (Nature Portfolio, 2023) Biskup, David; Schnakenburg, Gregor; Boeré, René T.; Ferao, Arturo E.; Streubel, Rainer K.
    We describe nonmetal adducts of the phosphorus center of terminal phosphinidene complexes using classical C- and N-ligands from metal coordination chemistry. The nature of the L-P bond has been analyzed by various theoretical methods including a refined method on the variation of the Laplacian of electron density ∇2ρ along the L-P bond path. Studies on thermal stability reveal stark differences between N-ligands such as N-methyl imidazole and C-ligands such as tert-butyl isocyanide, including ligand exchange reactions and a surprising formation of white phosphorus. A milestone is the transformation of a nonmetal-bound isocyanide into phosphaguanidine or an acyclic bisaminocarbene bound to phosphorus; the latter is analogous to the chemistry of transition metal-bound isocyanides, and the former reveals the differences. This example has been studied via cutting-edge DFT calculations leading to two pathways differently favored depending on variations in steric demand. This study reveals the emergence of organometallic from coordination chemistry of a neutral nonmetal center.
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    Chemical and electrochemical oxidations of tris(3,5-di-tert-butylphenyl)phosphine. High Z’ crystal structures and conformational effects associated with bulky meta substituents
    (2018) Guimaraes, Ivelise Dimbarre Lao; Garcia, Jarem Raul; Wohnrath, Karen; Boeré, René T.
    Synthesis and single crystal X-ray diffraction structures of (3,5-tBu2-C6H3)3P, (3,5-tBu2-C6H3)3PO∙H2O, (3,5-tBu2C6H3)3PS and (3,5-tBu2-C6H3)3PSe are reported. The structure of (3,5-tBu2-C6H3)3P has Z' = 4, with both M and P enantiomers of a helical conformation and a conformation with one flat ring in the same lattice. The pyramidality index, ∑{CPC}, is smaller for the helical compared to the flat conformers. All four have structures that are more pyramidal than the corresponding Ph3P(E) derivatives, which is attributed to stronger intramolecular dispersion forces. The oxide crystallizes with Z' = 2 as a water-bridged dimer that is the most separated such dimer amongst 26 known structures, providing evidence for a distal (or perimeter) steric effect. Cyclic voltammetry in CH3CN/[nBu4N][ClO4] indicated anodic peak potentials of +0.785 V for (3,5tBu2-C6H3)3P, +0.745 for (3,5-Me2-C6H3)3P, +0.735 V for (4-MeO-3,5-Me2-C6H3)3P and +0.535 V for (4-MeOC6H3)3P, all relative to Fc+/0. On this scale, Ph3P oxidizes at +1.04 V. The unexpectedly high oxidation potentials for the first three phosphines is attributed to a more pyramidal structure resulting in lowering of the HOMO energy compared to expectations from Hammett constants and 1J(P,Se) NMR coupling constants.
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    Coordination complexes of thiazyl rings: Synthesis, structure and DFT computational analysis of CpCr(CO)x (x = 2,3) complexes of fluorinated and non-fluorinated 1lamda^3-1,2,4,6-thiatriazinyls, with differing Cr—S bond orders.
    (NRC Research Press, 2015) Ang, Chwee Y.; Kuan, Seah L.; Tan, Geok K.; Goh, Lai Y.; Roemmele, Tracey L.; Yu, Xin; Boeré, René T.
    Reaction of [3,5-Ph2-C2N3S]2 with [CpCr(CO)3]2 in toluene at RT forms an adduct via a Cr—S bond, formulated as CpCr(CO)3SN3C2Ph2, which has fitting NMR, IR and combustion analysis data. The structure was determined by a single-crystal X-ray structure diffraction study (P21/n, a = 8.4611(17)Å; b = 20.509(4) Å, c = 11.757(2) Å,  = 104.453(7)°). The Cr—S bond-length = 2.4908(11) Å corresponds to a bond-order of 1.0 from > 90 values for CpCr(CO)x or Cp*Cr(CO)x moieties (x = 2,3) bonded to S which are used to establish a Pauling-type bond order scale specific to this class of compounds. Similar reactions of fluorinated thiatriazinyls derived from [3-Ph-5-CF3-C2N3S]2 or [4-MeOC6H4-5-CF3-C2N3S]2 are accompanied by the loss of CO to produce CpCr(CO)2SN3C2PhCF3 (P, a = 8.0929(8) Å; b = 10.3160(10) Å, c = 11.2405(11),  = 70.032(2)°, = 72.076(2)°, = 82.375(2)° ) and CpCr(CO)2SN3(CCF3)(C6H4OCH3) (P21/c, a = 8.1311(7)Å; b = 24.284(2) Å, c = 9.1025(8) Å,  = 97.218(2)°), also fully characterized by spectroscopy and crystallography. Their measured Cr—S bond-lengths, 2.2987(14) Å and 2.2965(11) Å, correspond to bond orders of 1.5. (U/R)B3PW91/6-311+G(2df,2p)//B3PW91/6-31G(2d,p) hybrid DFT calculations show that the tricarbonyl complex has an unusual  bond. However, the dicarbonyl complexes of the fluorinated thiatriazinyls are -bonded.