Computation Provides Chemical Insight into the Diverse Hydride NMR Chemical Shifts of [Ru(NHC)₄(L)H]^0/+ Species (NHC = N-heterocyclic carbene; L = vacant, H₂, N₂, CO, MeCN, O₂, P₄, SO₂, H^-, F^- and Cl^-) and their [Ru(R₂PCH₂CH₂PR₂)₂(L)H]⁺ Congeners

Relativistic density functional theory calculations, both with and without the effects of spin–orbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H−, F− and Cl−), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+ (R = iPr, Cy; L = vacant, O2). Inclusion of spin–orbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Cl−, F−) being reinforced by the contribution from spin–orbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru dπ orbitals and the unoccupied σ*Ru–H orbital. In [Ru(NHC)4(η2-O2)H]+ a δ-interaction with the O2 ligand results in a low-lying LUMO of dπ character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dπ orbital under the Lz angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(iPr2PCH2CH2PiPr2)2(η2-O2)H]+ (δ = −6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+ (ca. −32 ppm, R = iPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of −41 ppm, similar to the [Ru(NHC)4H]+ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BArF4− salts of [Ru(IMe4)4(L)H]+ (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF = 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported

An element through the looking glass: Exploring the Au-C, Au-H and Au-O energy landscape

Gold, the archetypal “noble metal”, used to be considered of little interest in catalysis. It is now clear that this was a misconception, and a multitude of gold-catalysed transformations has been reported. However, one consequence of the long-held view of gold as inert metal is that its organometallic chemistry contains many “unknowns”, and catalytic cycles devised to explain gold's reactivity draw largely on analogies with other transition metals. How realistic are such mechanistic assumptions? In the last few years a number of key compound classes have been discovered that can provide some answers. This Perspective attempts to summarise these developments, with particular emphasis on recently discovered gold(III) complexes with bonds to hydrogen, oxygen, alkenes and CO ligands

Thermally stable gold(III) alkene and alkyne complexes: Synthesis, structures, and assessment of the trans‐influence on gold‐ligand bond enthalpies

The reaction of [C^C)Au(OEt2)2]+ with 1,5‐cyclooctadiene or norbornadiene affords the corresponding olefin complexes [(C^C)Au(COD)]SbF6 and [(C^C)Au(NBD)]SbF6, which are thermally stable in solution and the solid state (C^C = 4,4′‐di‐t‐butylbiphenyl‐2,2′‐diyl). The crystal structures of these complexes have been determined. By contrast, dienones such as dibenzylideneacetone are O‐ rather than C=C‐bonded. The reactions of (C^C)Au(OAcF)(L) (L = PMe3 or CNxyl) with B(C6F5)3 in the presence of bis(1‐adamantyl)acetylene give the mixed‐ligand alkyne complexes [(C^C)Au(AdC≡CAd)(L)]+, the first complexes of their type in gold chemistry. In the presence of an excess of acetylene these compounds are thermally stable in solution and as solids. The bonding of n‐ and π‐donor ligands to Au(III) fragments and the effect of the trans influence exerted by N‐ and C‐donors was explored with the aid of DFT calculations. Results show that the Au‐L bond enthalpies trans to anionic C are 35 ‐ 60% of the enthalpies trans to N, with strong π‐acceptors being particularly affected. In comparison with [Me2Au]+, the [(C^C)Au]+ fragment is more polar and in bond enthalpy terms resembles Me2Pt

Computation Provides Chemical Insight into the Diverse Hydride NMR Chemical Shifts of [Ru(NHC)₄(L)H]^0/+ Species (NHC = N-heterocyclic carbene; L = vacant, H₂, N₂, CO, MeCN, O₂, P₄, SO₂, H^-, F^- and Cl^-) and their [Ru(R₂PCH₂CH₂PR₂)₂(L)H]⁺ Congeners

International audienceRelativistic density functional theory calculations, both with and without the effects of spin–orbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H−, F− and Cl−), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+ (R = iPr, Cy; L = vacant, O2). Inclusion of spin–orbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Cl−, F−) being reinforced by the contribution from spin–orbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru dπ orbitals and the unoccupied σ*Ru–H orbital. In [Ru(NHC)4(η2-O2)H]+ a δ-interaction with the O2 ligand results in a low-lying LUMO of dπ character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dπ orbital under the Lz angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(iPr2PCH2CH2PiPr2)2(η2-O2)H]+ (δ = −6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+ (ca. −32 ppm, R = iPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of −41 ppm, similar to the [Ru(NHC)4H]+ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BArF4− salts of [Ru(IMe4)4(L)H]+ (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF = 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported

Probing the interactions of gold(I) cations with multiple bonds

Abstract A major part of this thesis is devoted to studies on the interaction of gold(I) cations with 1,3- dienes, arenes and allyl- and vinylsilanes. There are two self contained chapters, one on the synthesis of a simple Ag(I)-enyne cation and the other on the attempted synthesis of the cyaphide anion. Synthesis and characterisation of four cationic gold(I)-l ,3-diene complexes are described. In the solid state, gold(l) cations bind to only one of the double bonds of the 1,3-diene unit. Depending upon the substituents on the diene, the gold adopts either a 112- or 11'- bonding mode. Solution VT-NMR spectroscopy indicated fluxionality via an intramolecular pathway. With regard to acyclic 1,3-dienes a low energy pathway for gold(I) cations migration along the diene backbone has been suggested based on calculations. Cyclic 1,3-dienes were readily polymerised when treated with gold(I) catalysts under mild conditions. A detailed characterisation of isolated polymers has been carried out. Four gold(I)-arene complexes of the type [(112-arene)Au(P(But)2(o-biphenyl»][SbF6] were synthesised and characterised. Solution VT NMR spectroscopy indicated fluxionality in the interaction. The solid state UV -Vis absorption spectra of naphthalene, anthracene and pyrene displayed a large red-shift upon coordination to the gold(I) cation. The solid-state fluorescence emissions of the complexes have been studied. The interaction of gold(I) cations with allyl- and vinylsilanes has been studied by the synthesis and characterisation of five new complexes of the type [(112- allylsilane/vinylsilane)Au(P(But)2(o-biphenyl»][SbF6]. The influence of p-silyl effect has been highlighted in terms of metal fragment slippage across the C=C bond. Binding energies for all the complexes have been calculated. A simple Ag(I)-(l ,3-enyne) cation has been synthesised and structurally characterised. Both in solid state and solution silver binds exclusively to the alkyne moiety. A greater insight into , binding has been obtained oy calculating binding energies for alkyne coordination vs. alkene coordination. Synthesis of the cyaphide anion CC=P) has been attempted. The precursor phosphaalkyne complex, [Ru(IMe4)4(Me3SiC=P)H][BAl4], has been synthesised and characterised. 3'p NMR spectroscopy evidence for the formation of the cyaphide anion has been obtained. The interaction of gold(I) cations with phosphaalkyne was studied with the isolation and characterisation of the complex, [(ButC=P) Au(P(But)2(o-biphenyl»][SbF6]'.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Hybrid structures formed by lead 1,3-cyclohexanedicarboxylates

By the employment of hydrothermal methods, four lead 1,3-cyclohexanedicarboxylates with the compositions Pb(1,3-CHDC)(H2O), I, [(OPb4)2(OH)2(C2O4)(1,3-CHDC)4]·H2O, II, Pb2(1,3-CHDC)2(H2O), III, and (OPb3)(1,3-CHDC)2, IV, have been prepared and characterized. Of these, I and II have layered structures while III and IV have three-dimensional structures. I-III are hybrid structures possessing extended inorganic connectivity in one or two-dimensions (In, n=1 or 2) involving infinite Pb-O-Pb linkages along with zero or one-dimensional organic connectivity (Om, m=0 or 1). I contains two types of layers with different connectivities (I1O1 and I2O0). III is a truly 3-D hybrid compound with I2O1 type connectivity. IV has three-dimensional organic connectivity (O3) but no inorganic connectivity (I0). The conformation of the CHDC anion is e,e in I-III and a,e in IV. In all these compounds, the lead atom has hemi- or holodirected coordination geometry