Towards clustered carbonyl cations [M3(CO)14]2+ (M = Ru, Os): the need for innocent deelectronation

To access the hitherto almost unknown class of clustered transition metal carbonyl cations, the trimetal dodecacarbonyls M3(CO)12 (M = Ru, Os) were reacted with the oxidant Ag+[WCA]−, but yielded the silver complexes [Ag{M3(CO)12}2]+[WCA]− (WCA = [Al(ORF)4]−, [F{Al(ORF)3}2]−; RF = –OC(CF3)3). Addition of further diiodine I2 to increase the redox potential led for M = Ru non-specifically to divalent mixed iodo-RuII-carbonyl cations. With [NO]+, even the N–O bond was cleaved and led to the butterfly carbonyl complex cation [Ru4N(CO)13]+ in low yield. Obviously, ionization of M3(CO)12 with retention of its pseudo-binary composition including only M and CO is difficult and the inorganic reagents did react non-innocently. Yet, the radical cation of the commercially available perhalogenated anthracene derivative 9,10-dichlorooctafluoroanthracene (anthraceneHal) is a straightforward accessible innocent deelectronator with a half-wave potential E1/2 of 1.42 V vs. Fc0/+. It deelectronates M3(CO)12 under a CO atmosphere and leads to the structurally characterized cluster salts [M3(CO)14]2+([WCA]−)2 including a linear M3 chain. The structural characterization as well as vibrational and NMR spectroscopies indicate the presence of three electronically independent sets of carbonyl ligands, which almost mimic M(CO)5, free CO and even [M(CO)6]2+ in one and the same cation.


General procedure
All manipulations were carried out by using standard Schlenk technique or a nitrogen filled glovebox (O 2 /H 2 O < 0.1 ppm). All the reactions were performed in Schlenk tubes with grease free PTFE-valves. The solvent 1,2,3,4-Tetrafluorobenzene (TFB, C 6 F 4 H 2 , from Fluorochem) was stirred over a few days over calcium hydride (CaH 2 ) and distilled. The distillate was stirred over Ag + [Al(OR F ) 4 ] − and condensed to remove traces of less fluorinated benzenes. This leads to a minor contamination of R F OH, which does not affect the reactions. n-pentane was dried using a Grubbs apparatus. TFB and n-pentane were stored over 3 Å molar sieves. Iodine (I 2 , Acros) was sublimed under static vacuum before use. Triruthenium dodecacarbonyl (Sigma Aldrich), 9,10-Dichlorooctafluoroanthrace (Sigma Aldrich) and triosmium dodecacarbonyl (ABCR) were bought from commercial sources. Ag + [WCA] − and [NO] + [WCA] − were synthezised according to literature procedures. 1 Vibrational Spectroscopy FTIR spectra were recorded inside a glovebox with a Bruker ALPHA equipped with QuickSnap Eco ATR module and ZnSe crystal. The spectra were measured at RT in the range of 4000-550 cm -1 with 32 scans and a resolution of 2 cm -1 . The data were processed with the Bruker OPUS 7.5 software package and, if not stated otherwise, a baseline correction with 3 iterations was performed. FT Raman spectra were recorded with a VERTEX 70 with Bruker RAM II Modul (1064 nm exciting line of a Nd-YAG laser) and liquid nitrogen cooled Ge detector. The samples were flame-sealed in soda-lime glass Pasteur pipettes and were measured at RT in the range of 4000-80 cm -1 with up to 10,000 scans and a resolution of 4 cm -1 . The data were processed with the Bruker OPUS 7.5 software package. The graphical representations were created with OriginPro 2021.
NMR Spectroscopy NMR spectra were recorded at RT either on a Bruker Avance II Widebore 400 MHz, Bruker Avance III HD 300 MHz or Bruker Avance DPX 200 MHz. The samples were dissolved with 4FB (0.6 ml) in a 5 mm thickwalled NMR tube with J. Young PTFE valve. The spectra were calibrated by using the 1 H signal of the solvent 4FB ( = 6.97 ppm, rel. to Tetramethylsilane). The field corrections of other nuclei were adjusted accordingly. Typically, small impurities of HOC(CF 3 ) 3 were detected in the 19 F NMR at -76.0 ppm. The MestReNova software package was used for measuring, processing and creation of the graphical representations of the spectra. 1 H and 13 C NMR spectra are referenced against TMS and 19 F NMR spectra against CFCl 3 .

EPR Spectroscopy
The continuous wave (cw) EPR spectrum of a solution of [6] +• [F{Al(OR F ) 3 } 2 ] − in TFB was recorded at the X-band (9.75 GHz) on a Bruker EMXnano benchtop EPR spectrometer at room temperature. The modulation frequency was set to 100 kHz and the modulation amplitude to 0.01 mT at a microwave power of 1 mW (20 dB). After data acquisition, the spectrum was baseline-corrected, frequency-corrected to 9.75 GHz and field-corrected using a carbon fibre standard with g = 2.002644. 2 The numerical simulation of the experimental spectrum using EasySpin functions in MATLAB yielded g = 2.0065. 3 The hyperfine coupling constants were calculated with DFT by using the ORCA program package version 4.0. 4 The structure was optimised using B3LYP/def2-TZVP and the hyperfine coupling constants were then calculated at the B3LYP/EPR-II (6-31G** for Cl) level of theory.
Single Crystal X-ray Diffraction The data were collected on a Bruker D8 VENTURE dual wavelength Mo/Cu three-circle diffractometer with a microfocus sealed X-ray tube using mirror optics as monochromator and a Bruker PHOTON III detector. Single crystals were selected at RT under perfluoropolyalkylether oil (AB128330, ABCR GmbH & Co. KG), mounted on CryoLoops with a diameter of 0.1 to 0.2 mm and shock-cooled using an Oxford Cryostream 800 low temperature device. The data were gathered at 100(2) K using Mo K α radiation (λ = 0.71073 Å). All data were integrated with SAINT (version 8.38A) and a multi-scan absorption correction using SADABS or TWINABS was applied. The structures were solved by direct methods using SHELXT 5 and refined by full-matrix least-squares methods against F 2 by SHELXL-2018/3 6 using the GUI software ShelXle. 7 Disordered moieties were refined using bond lengths restraints and displacement parameter restraints and were modelled with the program DSR. 8 The gathered data were finalized with the tool FinalCif. 9 The graphical representations of the crystal structures were generated with Mercury (version 4.0). 10 Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre. 11 Copies of the data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.

Powder X-ray Diffraction
Powder diffractograms were recorded on a STOE STADI P powder diffractometer with Mo K α1 radiation (λ = 0.709300 Å), Ge-(111) monochromator and Mythen 1K detector at 100(10) K. The samples were sealed in a 0.5 mm thick capillary (Hilgenberg GmbH, wall thickness 0.01 mm) with silicon grease. Data acquisition, processing, and the calculation of powder diffractograms from single-crystal data was performed using the STOE WinXPOW® package.

Computational Details
Geometry optimizations were performed with the TURBOMOLE software 12 (v7.2 or v7.5) using the DFT functionals B3LYP 13 with the def2-TZVPP 14 basis set, the resolution-of-identity (RI) approximation, 15 dispersion correction (D3BJ), 16 a fine integration grid (m4 or 5 for NMR chemical shift calculations) and the default SCF convergence criteria (10 -6 a.u.). All structures were checked for proper spin occupancies and imaginary frequencies with the integrated EIGER and AOFORC 17 modules. IR and Raman spectra were simulated on B3LYP(D3BJ)/def2-TZVPP level with a scaling factor of 0.968 for all TMCCs, the spectra for the other molecules were simulated without scaling factor. QTAIM-charges were calculated with MultiWFN. 18 The EDA-NOCV analyses where carried out with the ADF software package. 19

Vibrational Modes of the 50 VE Trimetal Tetradecacarbonyls
Because the interaction between the carbonyl-ligands in the -M(CO) 5 fragments (k out-out ) is needed for the calculation of k out,ax , this is calculated before: , -, This gives finally k out,ax : [7a/7b] 2+ [Al(OR F ) 4 The pXRD shows, that the [7a] 2+ [Al(OR F ) 4 ] − 2 •2 C 6 F 4 H 2 is not phase-pure. Because the same material was used for the NMR-spectroscopy, which showed no significant impurities, we expected, that the phase decomposes under vacuum, because the co-crystallized 1,2,3,4-Tetrafluorobenzene (bp. = 95 °C) evaporates. When the experiment is repeated with a longer vacuum exposure, the crystalline phase is even more decomposed, which validates the theory. The effect is even more pronounced at [7b] 2+ [Al(OR F ) 4 ] − 2 •2 C 6 F 4 H 2 .

EPR-Spectroscopy
The isotropic hyperfine coupling constants obtained from DFT calculations at the B3LYP/EPR-II level of theory are shown in Figure S 24. For the simulation of the continuous wave EPR spectrum shown in the main text using EasySpin functions in MATLAB, the computed hyperfine coupling constants of the eight fluorine atoms were divided into two groups, each consisting of four fluorine atoms. The DFT values were used as the starting values for the fit of the experimental spectrum: Initially, the hyperfine coupling constants were assumed to be 6 MHz for the fluorine atoms in β-position and 21 MHz for the fluorine atoms in α-position and an isotropic hyperfine coupling constant of 5 MHz was assumed for each of the two chlorine atoms. During the fitting procedure of the experimental cw EPR spectrum, the hyperfine coupling constants were only adjusted by applying an identical scaling factor to all values computed by DFT. The best fit was obtained for hyperfine coupling constants of 5.82 MHz and 20.37 MHz for the two groups of fluorine atoms and 4.85 MHz for the two chlorine atoms (scaling factor of 0.97). The excellent agreement with the experimental data confirms the assignment of the hyperfine couplings and the accuracy of the calculated spin density.

Cyclic Voltammetry
Cyclic voltammetry was performed in a setup with a platinum working electrode, platinum mesh counter electrode and a platinum quasi-reference electrode. The measurements were done with a 10 mM solution of 6 in 1,2-Difluorobenzene and 1,2,3,4-Tetraflurobenzene. [ 4 ] − (10 mM) + Fc (10 mM) as internal reference. The half-wave potential is almost independent from the scan rate ν (Table S 1 + Table S 2). The redox reaction is electrochemically reversible under the given conditions, because the anodic peak current is I ac is proportional to the squareroot of the scan rate ν 1/2 ( Figure    12.