MicroED characterization of a robust cationic σ-alkane complex stabilized by the [B(3,5-(SF5)2C6H3)4]− anion, via on-grid solid/gas single-crystal to single-crystal reactivity

Microcrystalline (∼1 μm) [Rh(Cy2PCH2CH2PCy2)(norbornadiene)][S-BArF4], [S-BArF4] = [B(3,5-(SF5)2C6H3)4]−, reacts with H2 in a single-crystal to single-crystal transformation to form the σ-alkane complex [Rh(Cy2PCH2CH2PCy2)(norbornane)][S-BArF4], for which the structure was determined by microcrystal Electron Diffraction (microED), to 0.95 Å resolution, via an on-grid hydrogenation, and a complementary single-crystal X-ray diffraction study on larger, but challenging to isolate, crystals. Comparison with the [BArF4]− analogue [ArF = 3,5-(CF3)2(C6H3)] shows that the [S-BArF4]− anion makes the σ-alkane complex robust towards decomposition both thermally and when suspended in pentane. Subsequent reactivity with dissolved ethene in a pentane slurry, forms [Rh(Cy2PCH2CH2PCy2)(ethene)2][S-BArF4], and the catalytic dimerisation/isomerisation of ethene to 2-butenes. The increased stability of [S-BArF4]− salts is identified as being due to increased non-covalent interactions in the lattice, resulting in a solid-state molecular organometallic material with desirable stability characteristics.


S.1 EXPERIMENTAL DETAILS
All manipulations (unless stated otherwise) were performed under an argon atmosphere, using standard Schlenk techniques on a dual vacuum/argon manifold or by using an argon filled glovebox (MBraun). Glassware was flame dried under vacuum prior to use. Pentane and dichloromethane (CH2Cl2) were dried using an Innovative Technology Pure-Solv™ (PS-400-3) solvent purification system and degassed by freeze-pump-thaw cycles. Deuterated solvents were dried using an appropriate drying agent: dichloromethane-d2 (CD2Cl2) with CaH2; acetonitrile-d3 (MeCN-d3) with 3 Å molecular sieves. After drying, these solvents were degassed by freeze-pump-thaw cycles and then stored over 3 Å molecular sieves. Hydrogen (H2) and deuterium (D2) gases were purchased in lecture bottles from Sigma-Aldrich and used as received.
[Rh(Cy2P(CH2)2PCy2)Cl]2 was prepared by a previously reported method. 1 All other chemicals were purchased from commercial vendors and used as received.
Solution NMR data were collected on either a Bruker AVIIIHD 500 MHz or 600 MHz spectrometer at 298 K unless otherwise started. Residual protio solvent resonances were used as a reference for 1 H NMR spectra. 2 31 P{ 1 H} NMR spectra were referenced externally to 85 % H3PO4 (D2O). All chemical shifts (δ) are quoted in ppm and coupling constants in Hz.
Solid state NMR (SSNMR) samples were prepared by packing powdered microcrystalline samples into a 4 mm zirconia solid state rotor inside an argon filled glove box. SSNMR spectra were obtained on a Bruker AVIIIHD 400 spectrometer, with a magic-angle spinning (MAS) rate of 10 kHz, referenced externally to triphenylphosphine ( 31 P: δ = -9.3) or adamantane ( 13 C{ 1 H}: upfield methine resonance, δ 29.5). 3 Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) measurements were performed in a thermal analyser (Netzsch STA 449 F5 Jupiter ® ) using an alumina crucible. The samples were heated up to 1000 °C at a ramp rate of 10 °C min −1 under an atmosphere of He flowing at 20 mL min −1 .
The powder X-ray crystallography was performed on a Panalytical Aeris X-ray diffractometer equipped with a 600 W copper source and a PIXcel1D-Medipix3 detector. The instrument was operated in transmission mode with the sample in a 0.6mm OD borosilicate capillary.
Elemental microanalyses were carried out by Dr Graeme McAllister at the University of York using an Exeter Analytical CE-440 analyser.  were treated with CD2Cl2 (0.5 mL) and MeCN-d3 (10.6 µL, 40 eq.), immediately resulting in a yellow solution, from which a yellow solid precipitated. The volatiles containing liberated dx-NBA were vacuum transferred to an empty NMR tube, then sealed under an Ar atmosphere for subsequent NMR analysis.         , then suspended in pentane (1 mL). After three freeze-pump-thaw degassing cycles, the ampoule was charged and sealed under an atmosphere of ethene (20 PSI, ~9 cm 3 , ~66 eq. per Rh) and stirred at 500 rpm. After 20 hr, an internal reference, adamantane (15 mg, 0.11 mmol), was added to the mixture, which was then filtered through a 0.2 µm pore PTFE syringe filter into a J. Young NMR tube. 1 H NMR analysis of this pentane solution, integrated relative to the adamantane reference, revealed liberated NBA, 2-butenes, 1-butene and unreacted ethene ( Table 1). The ampoule containing the remaining solids was subsequently recharged with pentane (1 mL) and ethene (20 PSI) as before. The mixture was stirred for a further 20 hr, then quantified once more by 1 H NMR, relative to additional adamantane. To examine whether any trace, unobservable but active, soluble species were present, the filtered solution taken after the first 20 hr was recharged with ethene, stirred for 20 hr, then reanalysed by 1 H NMR: no additional 2-butenes or 1-butene had formed over this time. The analogous reaction with [1-NBA][BAr F 4] yielded less than 0.1 equivalents of 2-butene per Rh.   in a pentane suspension was conducted primarily to assess the solid reaction product by SS NMR analysis, however, the mixture was also assessed for 2-butenes and 1-butene by 1 H NMR analysis of the pentane supernatant, using the quantitatively displaced NBA (1 eq. per Rh) as an internal reference. After 20 hr, a 0.5 mL aliquot was removed prior to isolation of the solids for SS NMR characterisation ( Table 2). The

S.3 CRYSTALLOGRAPHIC AND REFINEMENT DATA
Selected crystallographic data are summarized in the text and full details are given in the supplementary deposited CIF files. This data can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.

S.3.1 Single-crystal X-ray diffraction methods
Single-crystal X-ray diffraction data for were collected on an Oxford Diffraction SuperNova diffractometer with Cu-Kα (λ = 1.54184 Å) radiation equipped with a nitrogen gas Oxford Instruments Cryojet cooler. Raw frame data was reduced using CrysAlisPro, solved using Superflip 4 , and refined using full-matrix least squares refinement on all F 2 data using SHELXL-18 5 within the OLEX2 program. 6 All non-hydrogen atoms were refined anisotropically and hydrogen atoms were geometrically placed unless otherwise stated and allowed to ride on their parent atoms.
Distances and angles were calculated using the full covariance matrix. F 4] was finely ground and deposited onto Quantifoil Cu R1/4 grids that had been assembled into autogrid cartridges. These grids were then treated with H2 crystals were highly radiation sensitive and it was only possible to collect 20-30° of data before visible loss of diffraction quality occurred. Over the course of this work 111 datasets were collected from this sample but the S19 highest quality data were recorded from 29 crystals across 2 duplicate grids from the same microscope session.

Micro-crystalline [1-NBD][S-BAr
All data were processed using DIALS 7 . The images recorded on Ceta-D camera show mean negative background values at high resolution which hampers background modelling so a pedestal of 64 ADU was added to every pixel value. Initially the detector distance was fixed to 958.5 mm (determined using powder diffraction from an aluminium powder calibration grid). The structures were solved ab initio using SHELXT. 8 Structure refinement was performed using SHELXL. 5 Electron scattering factors from Peng 9 were used in refinement. Anisotropic ADPs were refined for all non-hydrogen atoms and all hydrogen atoms were geometrically placed using the idealised (inter-nuclear) X-H distances used in refinement of structures against neutron diffraction data with SHELXL 10 and allowed to ride on their parent atoms. For components (SIMU instruction) and enhanced rigid-body restraints where the relative motion of a bonded pair of atoms is restrained to be perpendicular to the bond between them (RIGU instruction 11 ) were applied to fragments of the structure. These restraints, together with refinement of an extinction parameter (EXTI instruction), enabled anisotropic refinement of all non-hydrogen atoms without resorting to use of ISOR or XNDP instructions to prevent ADPs of some atoms becoming non-positive definite during refinement.

S27
Short inter-ion contacts were analysed using the Crystal Explorer package, 26