Light-Driven Ring Slippage in [Re(η7-C7H7)(η5-C7H9)]+ and the Inertness of Its Technetium Homologue

Here, we present the light-driven reactions of [Re(η7-C7H7)(η5-C7H9)]+ (1+) with nitriles, phosphines, and isocyanides, which are added to 1+ via a ring slippage of the tropylium cation from η7 to η3, forming [Re(η3-C7H7)(η5-C7H9)(L)2]+ (L= acetonitrile 2+; 2-phenylacetonitrile 3+; 1,3,5-triaza-5-phosphoadamantane (PTA) 4+; tert-butyl isocyanide 6+; benzyl isocyanide 7+) and [Re(η3-C7H7)(η5-C7H9)(L)]+ with L = (ethane-1,2-diyl)bis(diphenylphosphane) (dppe) 5+. To compare the reactivities of rhenium and technetium, we also investigated the synthesis of [99Tc(η6-C10H8)2]+, its substitution of naphthalene with cyclohepta-1,3,5-triene to obtain [99Tc(η7-C7H7)(η5-C7H9)]+, and its reactivity (or lack thereof) with light.


Table of contents
As both coordination modes consist of a set of diastereomers, all proton signals (2 x 7 aromatic protons and 2 x methyl groups) are accounted for.The 1 H-1 H COSY spectrum shows four distinct coupling systems form the aromatic protons (two coupling systems for one molecule or set of enantiomers respectively).The two low field shifted coupling systems consist of six protons (respectively three protons for one coupling system; in Figure S1., green box), meaning that they belong to the methylsubstituted ring system.In fact, the two high field shifted coupling systems consist of eight protons (respectively four protons for one coupling system; in Figure S1 red box), which belongs to the unsubstituted ring.Since many reports have shown that coordination of an arene to a 99 Tc or Re core leads to an high field shift of its 1 H signals, [1][2][3][4] the unsubstituted naphthalene ring coordinates the 99 Tc-atom (8a + and 8b + ).Similar stereochemical results were obtained for the preparations of [M( 6 -1,4-dimethylnaphthalene)2] (M = Mo, Cr).The reactions yield the symmetrical isomer exclusively, with coordination of the metal to the unsubstituted ring. 5,6gure S1. 1 H-1 H COSY spectrum in in acetone-d6. of [ 99 Tc(η 6 -C11H10)2] + (8 + ).The two boxes represent the coupling systems of the aromatic protons.The green box includes two coupling systems with three protons each.The red box contains two coupling systems with four protons each.
Due to a small coupling between the protons at the naphthalene positions 4 and 5 (Figure S2), the 1 H-1 H COSY spectrum allowed to connect the coupling systems of the methyl-substituted and unsubstituted ring system, giving the complete 1 H signal set for one diastereomer.However, 1 H-1 H COSY spectrum could not indicate which set of 1 H signals belonged to which diastereomer.In addition, NOESY experiments were also inconclusive.The correct assignment was achieved by comparing the chemical shifts of the protons belonging to the coordinating ring system (H5, H8 vs H5', H8' and H6, H7 vs H6', H7', respectively).While protons H5 and H8 have very distinct chemical shifts, those of H5' and H8' are very similar.This is even clearer when comparing H6 and H7 with H6' and H7', which overlap.This means that, on the one side, the chemical environment of protons H5 and H8 (which are H6 and H7) must be distinctly S4 different, while, on the other side, the chemical environment for H5' and H8' (H6' and H7') must be very similar.The proximity to the two methyl groups is the only possible difference in chemical environment for these protons.Examination of the protons at naphthalene positions 5 and 8 of 8a + shows that position 8 is in proximity to both methyl-groups, while 5 is further away from both methylgroups.In the case of 8b + , the proton at position 8 is in close to the methyl-group located on the same naphthalene ligand and further away from the CH3-group of the opposing naphthalene ligand.On the other hand, the proton at position 5 is close to the methyl-group on the opposing naphthalene ligand, but further away from the CH3-group located on the same naphthalene ligand.Thus, the chemical shifts of protons at positions 5 and 8 of 8b + should be more similar than the chemical shifts of the corresponding signals of 8a + .The same is true for positions 6 and 7, thus, the correct set of 1 H signals can be assigned to the correct diastereomer.
For the 13 C NMR, only the signals of the non-coordinated ring could be assigned to the corresponding structure.The 13 C signals of the coordinated ring could not be resolved and only appear as a very broad signal ( = 80 -85 ppm).This is originated from coupling with the 99 Tc nucleus (S = 9/2) and was also found for other [ 99 Tc( 6 -C6R6)2] + systems: 2 the scalar coupling propagates to the 13 C-cores through the -bonds due to large T1 relaxation times of the 99 Tc nucleus.In the case of long pulse 13 C NMR experiments on the bis- 6 -toluene complex 8 + , a scalar coupling of J ≈ 34 Hz was found for the aromatic ipso-carbon in the toluene ligand (Figure S3).

Syntheses
General procedure for light reaction: 1PF6 (2 mg, 0.056 mmol) was dissolved in 550 µL of methanol-d4 in an NMR tube; 10 eq of the ligand were added and the NMR tube was put into the light reactor.The reaction was followed by 1 H NMR until full conversion of 1 + to the product was observed.

X-ray crystallography
Single-crystal X-ray diffraction data were collected at 160(1) K on a Rigaku OD Synergy-Hypix diffractometer (2 + , 4 + ), or on a Rigaku OD Supernova/Atlas diffractometer (5 + , [Re(CN-benzyl)6] + ) or on a Rigaku OD Synergy/Pilatus diffractometer (9 + ) using a single wavelength X-ray source (Cu Kα radiation: λ= 1.54184Å) using the copper X-ray radiation (λ = 1.54184Å) from a dual wavelength X-ray source and an Oxford Instruments Cryojet XL cooler.The selected suitable single crystal was mounted using polybutene oil on a flexible loop fixed on a goniometer head and immediately transferred to the diffractometer.Pre-experiment, data collection, data reduction and analytical absorption correction 10 were performed with the program suite CrysAlisPro. 11Using Olex2, 12 the structure was solved with the SHELXT 13 small molecule structure solution program and refined with the SHELXL2018/3 program package 14 by full-matrix least-squares minimization on F2.PLATON 15 was used to check the result of the X-ray analysis.CCDC 2308424-2308428 contain the supplementary crystallographic data for this paper.These data are provided free of charge by The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/structures.

Special features 2:
There is a mixture of counter anions in the crystal.PF6 -and ReO4 -share the same sites with siteoccupancy factors of 0.9278 (12) and 0.0722 (12), respectively.

4:
There is a mixture of counter anions in the crystal.PF6 -and ReO4 -share the same sites with siteoccupancy factors of 0.9159(9) and 0. 0.0841 (9), respectively.
[Re(CN-benzyl)6]PF6: The ions are located on a three-fold axis and on a center of inversion.The asymmetric unit contains about one sixth of the molecule, the rest is reproduced by the corresponding symmetry operations.

9:
The ligand η 5 -C7H9 is fully disordered over two sets of positions with a site-occupancy factor of 0.580 (9) for the major part.

S28
Table S3.Crystal data and data collection of complexes [9]OTf.

S29
The nature of [Re(η 3 -C7H7)(η 5 -C7H9)(CN-t Bu)2] + (6 + ) was also confirmed by an X-ray structural determination but the data was of insufficient quality.The structure has not been fully refined and has not been deposited.

Figure S5 .
Figure S5.Emission spectra of each lamp: blue lamp (blue line), orange lamp (orange line), red lamp (red line), white lamp (black line).Wavelengths are listed on the table.