A Gold(I)-Acetylene Complex Synthesised using Single-Crystal Reactivity.

Using single-crystal to single-crystal solid/gas reactivity the gold(I) acetylene complex [Au(L1)(η2-HC≡CH)][BArF 4] is cleanly synthesized by addition of acetylene gas to single crystals of [Au(L1)(CO)][BArF 4] [L1=tris-2-(4,4'-di-tert-butylbiphenyl)phosphine, ArF=3,5-(CF3)2C6H3]. This simplest gold-alkyne complex has been characterized by single crystal X-ray diffraction, solution and solid-state NMR spectroscopy and periodic DFT. Bonding of HC≡CH with [Au(L1)]+ comprises both σ-donation and π-backdonation with additional dispersion interactions within the cavity-shaped phosphine.

A comparison of non-covalent interactions in the crystal structures of two σ-alkane complexes of Rh exhibiting contrasting stabilities in the solid state.

Non-covalent interactions surrounding the cationic Rh σ-alkane complexes within the crystal structures of [(Cy2PCH2CH2PCy2)Rh(NBA)][BArF4], [1-NBA][BArF4] (NBA = norbornane, C7H12; ArF = 3,5-(CF3)2C6H3), and [1-propane][BArF4] are analysed using Quantum Theory of Atoms in Molecules (QTAIM) and Independent Gradient Model approaches, the latter under a Hirshfeld partitioning scheme (IGMH). In both structures the cations reside in an octahedral array of [BArF4]- anions within which the [1-NBA]+ cation system exhibits a greater number of C-H⋯F contacts to the anions. QTAIM and IGMH analyses indicate these include the strongest individual atom-atom non-covalent interactions between the cation and the anion in these systems. The IGMH approach highlights the directionality of these C-H⋯F contacts that contrasts with the more diffuse C-H⋯π interactions. The accumulative effects of the latter lead to a more significant stabilizing contribution. IGMH %δGatom plots provide a particularly useful visual tool to identify key interactions and highlight the importance of a -{C3H6}- propylene moiety that is present within both the propane and NBA ligands (the latter as a truncated -{C3H4}- unit) and the cyclohexyl rings of the phosphine substituents. The potential for this to act as a privileged motif that confers stability on the crystal structures of σ-alkane complexes in the solid-state is discussed. The greater number of C-H⋯F inter-ion interactions in the [1-NBA][BArF4] system, coupled with more significant C-H⋯π interactions are all consistent with greater non-covalent stabilisation around the [1-NBA]+ cation. This is also supported by larger computed δGatom indices as a measure of cation-anion non-covalent interaction energy.

In crystallo lattice adaptivity triggered by solid-gas reactions of cationic group 7 pincer complexes.

The group 7 complexes [M(κ3-2,6-(R2PO)2C5H3N)(CO)2L][BArF4] [M = Mn, R = iPr, L = THF; M = Re, R = tBu, L = vacant site] undergo in crystallo solid-gas reactivity with CO to form the products of THF substitution or CO addition respectively. There is a large, local, adaptive change of [BArF4] anions for M = Mn, whereas for M = Re the changes are smaller and also remote to the site of reactivity.

Chasing the agostic interaction in ligand assisted cyclometallation reactions of palladium(ii).

A 500 MHz NMR study of the reaction between 1-tetralone oxime and PdCl42- in CD3OD shows resonances attributable to a potential agostic intermediate prior to the formation of the insoluble cyclopalladated product which itself was characterised by X-ray crystallography. Calculated structural, spectroscopic, QTAIM, NBO and NCI analysis results obtained from density functional theory (DFT) calculations give a full description of the putative agostic intermediate [PdCl2(1-tetralone oxime)] (1) which is shown to include a previously unrecognised π-electron density donation from the aromatic ring to the metal in close proximity to the agostic carbon atom. Changing the (N)-OH donor to (N)-OMe does not effect the magnitude of these interactions. (N)-OH and (N)-OMe acetophenone imines in which the aromatic ring has the potential to rotate show similar agostic and π-electron donation to the alicyclic ring counterparts. 1-Tetralone which coordinates to the metal by a Pd-O bond that is much weaker than the Pd-N complexes has a slightly stronger agostic component and slightly weaker π-electron donation than the oxime counterpart.

New complexity for aromatic ring agostic interactions.

Density functional theory (DFT) calculations reveal that for ligand directed aromatic ring C-H bond activation, the agostic donation can share the same antibonding acceptor orbitals as a previously unrecognised π-donation from the aromatic ring of the ligand. The recognition of carbon based orbitals assisting the agostic interaction has significant implication for C-H bond activation chemistry.