Catalytic Hydrodefluorination of Fluoroarenes ... - ACS Publications

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Catalytic Hydrodefluorination of Fluoroarenes Using Ru(IMe4)2L2H2 (IMe4 = 1,3,4,5-Tetramethylimidazol-2-ylidene; L2 = (PPh3)2, dppe, dppp, dppm) Complexes Mateusz K. Cybulski, Jessica E. Nicholls, John P. Lowe, Mary F. Mahon, and Michael K. Whittlesey* Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K. S Supporting Information *

ABSTRACT: The all-trans isomer of Ru(IMe4)2(PPh3)2H2 (ttt-4; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene) reacts with C6F6 at 70 °C to afford the hydride fluoride complex Ru(IMe4)2(PPh3)2HF (ttt-6). At room temperature, ttt-6 reacts with Et3SiH to give a mixture of products, one of which is assigned as the silyl trihydride complex Ru(IMe4)2(PPh3)(SiEt3)H3 (8) by comparison to the isolated and structurally characterized analogue Ru(IMe4)2(PPh3)(SiPh3)H3 (9). As ttt-4 was re-formed cleanly upon heating ttt-6 with Et3SiH, it was tested in the catalytic hydrodefluorination (HDF) of C6F6 (10 mol %, 90 °C), along with 9, Ru(IMe4)2(P-P)HF (P-P = Ph2P(CH2)2PPh2 (dppe, cct-13), Ph2P(CH2)3PPh2 (dppp, cct-14), Ph2PCH2PPh2 (dppm, cct-15)), Ru(IEt2Me2)2(PPh3)2HF (cct-7; IEt2Me2 = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)), and Ru(IEt2Me2)2(dppe)2HF (cct-16) for comparison. Both cct-13 and cct-14 brought about near-quantitative conversion to C6FH5 in 24 h, in comparison to ca. 50% conversion with ttt-4 in 144 h.

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INTRODUCTION Catalytic hydrodefluorination (HDF), the (transition) metalmediated replacement of a C−F group by a C−H group, has been proposed1,2 as being an approach that could allow the preparation of partially fluorinated compounds of value to the pharmaceutical and agrochemical industries.3 However, in order for HDF to progress into a truly viable synthetic tool for accessing the specific substitution patterns found, for example, in fluorinated drug molecules, studies of small model substrates are first required to provide a greater understanding of the factors that (i) influence catalyst activity, (ii) control the regioselectivity of C−F bond activation, and (iii) help to favor C−F cleavage over competitive C−H bond activation. Over the past few years, we have reported the use of ruthenium N-heterocyclic carbene (NHC) dihydride complexes as precursors for the catalytic HDF of model aromatic fluorocarbons such as C6F6 and C6F5H. In our initial work,4 we showed that Ru(IPr)(PPh3)2(CO)H2 (1; IPr = 1,3-bis(2,6diisopropylphenyl)imidazol-2-ylidene) exhibited a remarkably high (98%) and very unusual ortho regioselectivity,5 which resulted in conversion of C6F5H to the 1,2,3,4-isomer of tetrafluorobenzene at 70 °C. Catalysis was proposed to be initiated by loss of PPh3 from 1, C−F activation by Ru(IPr)(PPh3)(CO)H2 to form the hydride fluoride complex Ru(IPr)(PPh3)(CO)HF (2), and, last, reaction of 2 with the terminal reductant Et3SiH to re-form Ru(IPr)(PPh3)(CO)H2, along with Et3SiF (Scheme 1). Computational studies both established the viability of the postulated pathway and, more importantly, helped to rationalize the ortho regioselectivity on the basis of a nucleophilic attack pathway © XXXX American Chemical Society

Scheme 1. Mechanism of Catalytic Hydrodefluorination by Ru(IPr)(PPh3)2(CO)H2 (1)

involving the Ru−H ligand in Ru(IPr)(PPh3)(CO)H2.6 In fact, as shown in Scheme 2, two pathways were characterized, one involving a one-step, concerted process and the other a lower energy, stepwise mechanism. Additional DFT calculations were subsequently employed to investigate the broader scope and selectivity of HDF for a range of fluoroarenes C6F6−nHn (n = 0−5).7 It was established that, for the stepwise pathway, stabilization of the departing fluorine atom from the activated C−F bond through F···H−C interactions with the NHC N substituents lowered the energy of the key C−F bond breaking transition state connecting C and D in Scheme 2 and that this effect was very pronounced for a C−F bond when it was ortho to just a single C−F substituent (i.e., also ortho to H).5 The concerted process showed a complementary kinetic selectivity, taking place preferentially at a C−F bond that was ortho to two other C−F groups. In the case of C6F5H HDF shown in Scheme 2, reaction at the site para to H proved to be most favored, leading to 1,2,4,5-C6F4H2. Received: April 1, 2017

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DOI: 10.1021/acs.organomet.7b00243 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Scheme 2. Concerted and Stepwise Pathways for Ruthenium Hydride Catalyzed HDF

Scheme 4. Representative Examples To Show the Isomer Labeling Scheme Adopted in This Work

although high regioselectivity might be compromised by the likelihood of reactions taking place along pathways with and without ligand dissociation. An earlier, preliminary study on cis,cis,trans-Ru(IEt2Me2)2(PPh3)2H2 (cct-5; IEt2Me2 = 1,3diethyl-4,5-dimethylimidazol-2-ylidene)10 provided support for these assumptions. Thus, while cct-5 was able to catalyze up to four HDF cycles from C6F6, both 1,2,3,4- and 1,2,4,5-isomers of C6F4H2 were formed in the initial stages of the reactions. Herein, we show that ttt-4 is able to bring about the HDF of C6F6 all the way down to fluorobenzene and that the activity can be enhanced through the use of the chelating phosphine complexes Ru(IMe4 )2 (P-P)HX (P-P = Ph2 P(CH 2) 2PPh2 (dppe), Ph2P(CH2)3PPh2 (dppp); X = H, F). None of the compounds show the high selectivities of 1 or 3.

In an effort to validate the computational predictions, we employed the trans-dihydride complex Ru(IMe4)4H2 (3; IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene)8 on the basis that, as dissociation of the strongly bound NHC ligands was unlikely, the enforced coordinative saturation would exclude the possibility of any reaction via a stepwise pathway. Moreover, the combination of four σ-donating N-alkyl-substituted IMe4 ligands, together with the trans H−Ru−H geometry, should help to enhance the nucleophilicity of the Ru−H ligand, generating high catalytic activity. HDF of C6F6 by 3 was shown experimentally to proceed without any NHC dissociation, while enhanced activity was apparent by the fact that up to four HDF cycles to form difluorobenzene were now possible even at room temperature. The first two HDF steps, which were complete within minutes, proceeded with the anticipated high para regioselectivity associated with a concerted pathway to give 1,2,4,5-C6F4H2 (Scheme 3). HDF of lower fluorine-containing

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RESULTS AND DISCUSSION Stoichiometric C−F Activation Chemistry of ttt-4 and Silane Reactivity of Ru(IMe4)2(PPh3)2HF (ttt-6). Thermolysis of Ru(IMe4)2(PPh3)2H2 (ttt-4)11 and C6F5H (2 equiv) in benzene for 48 h at 70 °C resulted in conversion to a single ruthenium-containing species which, on the basis of the 1H, 31P{1H}, 19F, and 13C{1H} NMR spectra, was assigned as the hydride fluoride complex Ru(IMe4)2(PPh3)2HF (ttt-6; Scheme 5). This retained the trans-carbene/trans-phosphine

Scheme 3. Catalytic HDF by Ru(IMe4)4H2 (3) Scheme 5. Interconversion of Ru(IMe4)2(PPh3)2H2 (ttt-4) and Ru(IMe4)2(PPh3)2HF (ttt-6)

substrates is known to be challenging,7,9 and it was unsurprising to find that formation of 1,4-C6F2H4 was very slow at room temperature, although it could be accelerated under more forcing conditions. No additional HDF of 1,4-C6F2H4 to fluorobenzene was possible, although C6FH5 was found to be accessible (both experimentally and computationally) by starting from 1,2-C6F2H4. We now attempt to bridge the gap between 1 and 3 with studies of the mixed carbene/phosphine dihydride complex trans,trans,trans-Ru(IMe4)2(PPh3)2H2 (ttt-4; assignment of the isomers of compounds reported in this paper is based on the geometric relationship of the NHC, phosphine, and H/F ligands, respectively: see Scheme 4) and a series of closely related derivatives. We anticipated that the trans arrangement of the hydride ligands should impart high reactivity to ttt-4,

geometry found in ttt-4, as implied by the appearance of a lone, broad singlet phosphine resonance (δ 50.1) and a triplet carbenic carbon signal (δ 192.9; 2JCP = 14 Hz). The trans H−Ru−F arrangement was apparent from the large 19F splitting on a doublet of triplets Ru−H signal (δ −21.94; 2JHF = 48.0 Hz, 2 JHP = 21.0 Hz). The Ru−F resonance itself appeared as a broad singlet at a characteristic low frequency (δ −332). We were unable to resolve any couplings on the fluoride signal, even upon addition of CsF.12 An alternative and synthetically quicker route to ttt-6 involved the reaction of ttt-4 with Et3N·3HF (or TREAT-HF) in THF solution at room temperature. This pathway afforded ttt-6 in B


Article

Organometallics

of 4 gave only trace amounts of 8 even after 12 h (Supporting Information). We have been unable to isolate and fully characterize 8, as it cannot be made by reacting ttt-4 with Et3SiH. However, ttt-4 did react with Ph3SiH (upon heating at 90 °C) to give the triphenylsilyl analogue Ru(IMe4)2(PPh3)(SiPh3)H3 (9), which exhibited two comparable low-frequency doublet proton NMR signals at δ −4.82 (2JHP = 11.0 Hz) and δ −6.13 (2JHP = 9.9 Hz) in a 1:2 ratio.14,15 The interaction of silanes with ruthenium dihydride complexes has been a topic of much debate, particularly in how to differentiate a Ru σ-silane dihydride from a Ru silyl trihydride.16 Sabo-Etienne has argued that NMR metrics (particularly the magnitude of JSiH),17 the value of νSiH in the IR spectrum, and crystallographically determined values of dSi−H and dRu−Si all have to be considered to best assess the nature of the Ru−Si interaction.16c Somewhat limited information about 9 was derived from the X-ray diffraction analysis (Figure 2), since it

81% yield. The X-ray structure (Figure 1) confirmed the spectroscopically determined arrangement of the ligands. The trans

Figure 1. Molecular structure of ttt-6, with ellipsoids represented at 30% probability. Hydrogen atoms, with the exception of the hydride ligand, and the minor disordered fluorine component have been omitted for clarity.

H−Ru−F geometry helps to rationalize the long Ru−F distance of 2.2694(18) Å, which is comparable to those in both Ru(IEt2Me2)2(PPh3)2HF (cct-7; 2.264(2) Å)10 and Ru(IMe4)4HF (2.3070(18) Å).8 When the reaction of ttt-4 and C6F5H was monitored spectroscopically at shorter reaction times, C−F activation to give ttt-6 was found to take place alongside C−H activation to generate the fluoroaryl hydride complex Ru(IMe4)2(PPh3)(C6F5)H (Scheme 5). This was assigned from the similarity of its Ru−H and 31P NMR signals (Ru−H, δ −34.04 (dt, 2JHP = 32.0 Hz, 4JHF = 7.3 Hz); 31P{1H}, δ 59.5, br s) to those of the known IEt2Me analogue Ru(IEt2Me2)2(PPh3)(C6F5)H.10 Ultimately, after 48 h of reaction, Ru(IMe4)2(PPh3)(C6F5)H was no longer observed, most likely due to its reaction with the H2 released during C−H activation. In support of this, when ttt-4 was reacted with C6F5H under a pressure (4 atm) of H2, Ru(IMe4)2(PPh3)(C6F5)H was not formed at all.13 To assess the viability of catalytic HDF starting with ttt-4, the reaction of ttt-6 with alkylsilane was probed. 31P{1H} NMR spectra recorded upon addition of excess Et3SiH (3 equiv) to 6 showed complete disappearance of the latter within 20 min at room temperature and formation of two new species, neither of which was ttt-4. One was identified as tcc-4,11 while the other was formulated as the silyl trihydride complex Ru(IMe4)2(PPh3)(SiEt3)H3 (8; vide infra). Over a period of 2 days, both of these species disappeared and were replaced by a series of new resonances arising from both the cct and ctc isomers of 4, as well as ttt-4.11 Heating the mixture to 70 °C brought about full conversion to the latter over ca. 2 h. Characterization of Ru(IMe4)2(PPh3)(SiR3)H3 Complexes. The assignment of 8 was based upon the presence of two low-frequency doublet Ru−H NMR resonances at δ −6.00 (d, 2JHP = 12.0 Hz) and δ −6.86 (d, 2JHP = 11.3 Hz) in a 1:2 ratio. Its formation at very early times in the reaction of ttt-6 and Et3SiH suggests that it may result from substitution of one of the phosphine ligands trans to hydride in tcc-4, which is the other main species present at the same early stage of the reaction (Supporting Information). As tcc-4 is not isolable,11 we cannot confirm this, but we were able to show that neither cct- nor ctc-4 was the main precursor to 8, as addition of Et3SiH to an in situ generated mixture of these two isomers

Figure 2. Molecular structure of 9, with ellipsoids represented at 30% probability. Disordered atoms have been omitted for clarity, as have hydrogens, with the exception of those bound to Ru1. Selected bond lengths (Å) and angles (deg): Ru(1)−P(1) 2.430(5), Ru(1)−Si(1) 2.311(6), Ru(1)-P(1A) 2.414(5), Ru(1)−Si(1A) 2.318(6), Ru(1)− C(1) 2.091(3), Ru(1)−C(8) 2.082(2); P(1)−Ru(1)−Si(1) 155.72(14), C(1)−Ru(1)−C(8) 173.48(10), C(8)−Ru(1)−Si(1) 95.96(13).

was impossible to differentiate between the PPh3 and SiPh3 ligands (see the X-ray crystallography part of the Experimental Section). However, the structure affords a shortest possible Si··· H distance (H1−Si1A) of 2.075 Å,15,16c which is outside the 1.7−1.9 Å range indicative of a σ-Si−H interaction, although given that it is still shorter than the sum of the Si and H van der Waals radii (3.4 Å),16c the presence of some (albeit weak) interaction between the two centers, akin to that seen in Ru(PMe3)3(SiPh3)H3, seems likely.15,18c An IR band at 1776 cm−1 provides further support for the presence of a Si···H interaction. Arguably, the most telling data came from the lowtemperature (233 K) 1H−29Si HMBC spectrum (Supporting Information), which showed coupling of the two proton resonances at δ −4.84 and −6.13 to a doublet 29Si resonance (2JSiP = 29.3 Hz) at δ 22.7 with JSiH values of 45 and 16 Hz, respectively. The magnitudes of the Si−H couplings are well below the 65 Hz cutoff that has been proposed as the lower limit to indicate a Ru σ-Si−H interaction.16c Clearly, therefore, 9 (and by extension also 8) is in something of a region of ambiguity as regards an exact structural formulation, C


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Organometallics

was extended by inclusion of the IEt2Me2 complexes cct-519 and Ru(IEt2Me2)2(dppe)HF (cct-16), which was prepared by substitution of the PPh3 ligands in Ru(IEt2Me2)2(PPh3)2HF (cct-7)10 by dppe. Both solution-phase and solid-state characterization (Figure 3) showed retention of a cct geometry in 16. Table 1 summarizes the catalytic findings. Using the combination of forcing conditions (90 °C) and a large excess of reductant (80 equiv of alkylsilane relative to Ru), ttt-4 (along with cct-5) produced a mixture of products consisting mainly of both 1,2- and 1,4-isomers of C6F2H4, as well as C6FH5 (entries 1−3). The ability of both complexes to bring about up to five HDF steps is interesting in that there are only very few HDF catalysts that can reduce C6F6 to this extent.21 Addition of H2 improved the level of conversion to fluorobenzene, whereas the presence of excess PPh3 retarded it (entries 4 and 5). However, given the high temperature and long reaction times (72−144 h) necessary, the mixed carbene/phosphine complexes are clearly poorer catalysts than the all-carbene derivative 3. Moreover, the appearance of both 1,2- and 1,4-isomers of difluorobenzene indicates poorer control of regioselectivity in comparison to that seen with 3. A comparison of ttt-4 and the silyl trihydride complex 9 (entries 1 and 7) revealed comparable amounts of difluoro- and monofluorobenzene products, but poorer regiocontrol with the latter. The dppe and dppp derivatives cct-13 and cct-14 (entries 8 and 11), along with the IEt2Me2 dppe complex cct-16 (entry 15), proved to be more active than either ttt-4 or cct-5, giving 85−95% conversions to fluorobenzene in only 24 h, albeit still at 90 °C.20 Monitoring reactions with cct-13 at early times revealed (i) higher initial selectivity for the formation of 1,2,3,4-C6F4H2 in comparison to the 1,2,4,5-isomer and (ii) products resulting from subsequent HDF ortho to H (Supporting Information). Consistent with (ii), prolonged heating brought about no further HDF of 1,4-C6F2H4; there was also no further reduction of C6FH5 to benzene (Supporting Information). The dppm derivative cct-15 displayed only poor activity (entry 13). The results in Table 1 also highlight that the extent of conversion to C6FH5 for ttt-4 and cct-13−16 showed a strong dependence on the silane used as the reductant (entries 6, 9, 10, 12, 14, 16). For both cct-13 and cct-14, replacing Et3SiH by i Pr3SiH gave near-quantitative yields of fluorobenzene. This remains a perplexing feature of a number of HDF reactions,2z,4a,22 and even in cases in which the mechanism of the C−F activation step is very well understood (e.g., Ru(IMe4)4H2) variations in catalytic performance as a function of the silane can be difficult to rationalize.8

although the data provide stronger support for a silyl trihydride complex, analogous to the all-phosphine derivatives Ru(PR3)3(SiR3)H3.15,18 Preparation of Ru(IMe4)2(P-P)HF (P-P = dppe, dppp, dmpm). Attempts to synthesize the chelating phosphine dihydride complexes Ru(IMe4)2(P-P)H2 (P-P = Ph2P(CH2)2PPh2 (dppe, cct-10), Ph2P(CH2)3PPh2 (dppp, cct-11), Ph2PCH2PPh2 (dppm, cct-12)) by direct substitution of the chelating phosphines into ttt-4 was found to be problematic. Although NMR spectroscopy showed that all three complexes were formed cleanly as the cct isomers and as the only metalcontaining products when ttt-4 was heated at 70 °C with 5 equiv of the respective P-P ligands (Scheme 6), the similar solubilities Scheme 6. Synthesis of Ru(IMe4)2(P-P)HX (P-P = dppe, dppp, dppm; X = H, F)

of the products and the PPh3 released upon substitution thwarted clean separation and isolation. Thankfully, the synthesis and workup of the corresponding hydride fluoride complexes Ru(IMe4)2(P-P)HF (P-P = dppe (cct-13), dppp (cct-14), dppm (cct-15)) proved to be far more straightforward and could be achieved by simply stirring ttt-6 with 1 equiv of the appropriate chelating phosphine at room temperature (Scheme 6), followed by removal of PPh3 with pentane. The yellow Ru(IMe4)2(P-P)HF products were isolated in yields of 49, 64, and 31% for cct-13−15 respectively. The X-ray structures (Figure 3) all showed retention of a trans H−Ru−F geometry, although the presence of the bidentate phosphines caused the two IMe4 ligands to now become cis. There was little that was notable about the X-ray structures, although there was a slight shortening of the Ru−F distance in the dppm complex cct-15 (2.2109(16) Å) in comparison to the dppe and dppp analogues (2.2520(17) Å in cct-13; 2.2684(13) Å in cct-14). In solution, all three complexes displayed a Ru−H NMR resonance within ±2 ppm of that of ttt-6, alongside a Ru−F signal in the range δ −330 to −342 (Table S2 in the Supporting Information). Complexes cct-13−15 reacted cleanly with Et3SiH at room temperature (Scheme 6) to give cct-10−12 respectively (see the Supporting Information for the X-ray structure of cct-12). The dppe complex cct-10 was found to undergo slow isomerization in solution to form the highly insoluble ccc isomer (see the Supporting Information for the X-ray structure). Catalytic HDF of C6F6. The catalytic abilities (10 mol %) of ttt-4 and 9, along with the cct isomers of the chelating phosphine hydride fluoride complexes 13−15, were compared for the HDF of C6F6 with Et3SiH. The scope of the catalysis

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SUMMARY AND CONCLUSIONS A series of trans-dihydride complexes of the form Ru(NHC)2L2H2 (NHC = IMe4, IEt2Me2; L2 = (PPh3)2, dppe, dppp, dppm) have been studied for the catalytic hydrodefluorination (HDF) of hexafluorobenzene. In most cases, the Ru(NHC)2L2H2 systems exhibit good activity (TONs 40−50; cf. 80 for Ru(IMe4)4H2 (3)) but are only moderately selective, given that both 1,2- and 1,4-C6F2H4 are present at the end of catalytic runs. In the absence of detailed kinetic studies, computational investigations, or studies with fluoroarenes other than C6F6, any discussion of what the formation of different regioisomers means as far as the roles of ligand loss pathways (as found for Ru(IPr)(PPh3)(CO)H2 (1)) versus nondissociative pathways (seen with 3) is probably unwise, but we feel that our results do strengthen the conclusion presented D


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Organometallics

Figure 3. Molecular structures of cct-13−16. Ellipsoids are shown at the 30% probability level. In all cases, hydrogen atoms, with the exception of the hydride ligand, have been omitted for clarity. In addition, the minor disordered fluorine component has been omitted for both cct-13 and cct-16.

at the end of the previous work with 3 that “controlling the mechanism...controls the synthetic outcome” of HDF.8

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as a pale yellow solid (374 mg, 82%). 1H and 31P{1H} NMR data matched those in the literature.11 Ru(IEt2Me2)2(PPh3)2H2 (cct-5). A modification of the synthesis of cct-5 from that previously reported was adopted.11 A benzene solution (2 mL) of IEt2Me2 (130 mg, 0.86 mmol) was added to a benzene suspension (4 mL) of Ru(PPh3)4H2 (0.45 g, 0.39 mmol), and the mixture was stirred for 5 min. It was then filtered by cannula and the filtrate reduced to dryness. The resultant sticky residue was washed with pentane (3 × 5 mL) to afford cct-5 as a pale yellow solid (280 mg, 77%). 1H and 31P{1H} NMR data matched those in the literature.11 Ru(IMe4)2(PPh3)2HF (ttt-6). A benzene solution (2 mL) of IMe4 (142 mg, 1.14 mmol) was cannula-filtered into a benzene suspension (4 mL) of Ru(PPh3)4H2 (0.6 g, 0.52 mmol), and the mixture was stirred for 2 days at 323 K. After the mixture was cooled to room temperature, a THF solution (2 mL) of Et3N·3HF (42 μL, 0.26 mmol) was added and the resultant solution stirred at room temperature for 2 h. CsF (158 mg, 1.04 mmol) was then added and the suspension stirred overnight at room temperature. It was then cannula-filtered and the filtrate reduced to dryness. The resulting solid was washed with Et2O (3 × 5 mL) and dried in vacuo to afford 376 mg (81%) of ttt-6 as a pale yellow solid. Crystals suitable for X-ray diffraction were obtained upon slow evaporation of a saturated THF solution of the compound at 238 K. 1H NMR (500 MHz, C6D6): δ 7.85 (br, 12H, PC6H5), 6.97 (br, 18 H, PC6H5), 3.94 (s, 3H, NCH3), 3.92 (s, 3H, NCH3), 3.26 (s, 6H, NCH3), 1.37 (s, 6H,

EXPERIMENTAL SECTION

All manipulations were carried out using standard Schlenk, highvacuum, and glovebox techniques. Solvents were purified using an MBraun SPS solvent system (hexane, pentane, Et2O) or under a nitrogen atmosphere from sodium benzophenone ketyl (benzene). C6D6 and C6D5CD3 were vacuum-transferred from potassium. NMR spectra were recorded on Bruker Avance 400 and 500 NMR spectrometers at 25 °C (unless otherwise stated) and referenced to residual solvent signals for 1H/13C (benzene (1H, δ 7.15; 13C{1H}, δ 128.0), toluene (δ 2.09, δ 21.3)), externally to 85% H3PO4 for 31P (δ 0.0), and externally to CFCl3 for 19F (δ 0.0). Elemental analyses were performed by Elemental Microanalysis Ltd., Okehampton, Devon, U.K.. Ru(PPh3)4H223 and IMe424 were prepared according to literature methods. Ru(IMe4)2(PPh3)2H2 (ttt-4). A modification of the synthesis of ttt-4 from that previously reported was adopted.11 A benzene solution (2 mL) of IMe4 (142 mg, 1.14 mmol) was added to a benzene suspension (4 mL) of Ru(PPh3)4H2 (0.6 g, 0.52 mmol), and the mixture was stirred for 2 days at 323 K. After the mixture was cooled, the solution was filtered by cannula and reduced to dryness. The resultant sticky residue was washed with pentane (3 × 5 mL) to afford ttt-4 E


Article

Organometallics Table 1. Ruthenium NHC/Phosphine Complex Catalyzed HDF of C6F6a distribn of product (%)d entry

Ru source

silane

t (h)

1,4C6F2H4

1,2C6F2H4

C6FH5

1 2 3 4b 5c

ttt-4 ttt-4 cct-5 ttt-4 ttt-4

Et3SiH Et3SiH Et3SiH Et3SiH Et3SiH

72 144 144 144 144

10 9 32 10 0

65 36 32 25 10

16 52 25 65 0

6 7 8 9 10 11 12 13 14

ttt-4 9 cct-13 cct-13 cct-13 cct-14 cct-14 cct-15 cct-15

i

Pr3SiH Et3SiH Et3SiH i Pr3SiH Ph3SiH Et3SiH i Pr3SiH Et3SiH i Pr3SiH

144 72 24 24 72 24 24 24 24

4 34 5 3 12 2 1 29 5

66 42 10 0 0 3 0 49 12

24 20 85 97 0 95 99 18 0

15 16

cct-16 cct-16

Et3SiH Pr3SiH

24 24

9 8

6 38

85 54

i

other products 1,2,3-C6F3H3 (5%), 1,3-C6F2H4 (4%) 1,3-C6F2H4 (3%) 1,3-C6F2H4 (11%) 1,2,3,4-C6F4H (36%), 1,2,4,5-C6F4H2 (8%), 1,2,3-C6F3H3 (45%), 1,2,4C6F3H3 (8%) 1,2,3-C6F3H3 (6%) 1,3-C6F2H4 (4%)

1,2,4,5-C6F4H (35%), 1,2,4-C6F3H3 (15%), 1,2,3-C6F3H3 (35%)

1,3-C6F2H4 (3%) C6F6 (1%), 1,2,3,4-C6F4H2 (31%), 1,2,4,5-C6F4H2 (4%), 1,2,3,-C6F3H3 (27%), 1,2,4-C6F3H3 (20%)

TON

TOF (h−1)

41 45 43 46.5 27

0.6 0.3 0.3 0.3 0.2

42 48.5 50 28 49.5 50 42 44

0.6 2.0 2.1 0.4 2.1 2.1 1.7 0.6

48.5 45

2.0 1.9

Reaction conditions: 10 mol % of Ru, 0.005 mmol of substrate, 0.04 mmol of silane, toluene, 90 °C. bReaction run under 4 atm of H2. cReaction performed in the presence of 10 equiv of PPh3. dProduct assignments and yields (product distribution is (% of product)/(total % of all HDF products)) determined from 19F NMR spectra recorded in C6H5CH3 (protio solvent was used to avoid any H/D at Ru).

a

NCCH3CNCH3), 1.33 (s, 6H, NCCH3CNCH3), −21.94 (dt, 1H, 2JHF = 48.0 Hz, 2JHP = 21.0 Hz, RuH).31P{1H} NMR (C6D6, 162 MHz): δ 50.1 (br s). 13C{1H} NMR (126 MHz, C6D6): δ 192.9 (t, 2JCP = 14 Hz, Ru-CNHC; the Ru-CNHC resonance was measured using a very concentrated sample at 100 MHz), 141.3 (“vt”, J = 11 Hz, PC6H5), 135.2 (“vt”, J = 10 Hz, PC6H5), 126.5 (“vt”, J = 8 Hz, PC6H5), 124.0 (s, NCCH3CNCH3), 122.5 (s, NCCH3CNCH3), 35.5 (s, NCH3), 35.4 (s, NCH3), 33.4 (s, NCH3), 33.0 (s, NCH3), 9.9 (s, NCCH3), 8.9 (s, NCCH3). 19F NMR (C6D6, 376 MHz): δ −331.5 (br, 1F, RuF). Anal. Calcd (found) for C50H55N4FP2Ru: C, 67.17 (66.84); H, 6.20 (6.56); N, 6.27 (6.16). Ru(IMe4)2(PPh3)(SiPh3)H3 (9). A benzene (0.5 mL) solution of ttt-4 (0.030 g, 34.3 μmol) and Ph3SiH (0.044 g, 0.17 mmol) was heated overnight at 363 K in a J. Young resealable NMR tube. The sample was then left at room temperature for 1 week, during which time colorless crystals of 9 were deposited. These were recrystallized from toluene/pentane. Yield: 0.027 g (91%). 1H NMR (C6D5CD3, 500 MHz): δ 7.67−7.64 (br m, 5H, P/SiC6H5), 7.53−7.47 (br m, 6H, P/SiC6H5) (HMBC/HSQC confirmed the remaining aryl protons were obscured by toluene resonances), 3.49 (s, 6H, NCH3), 3.16 (s, 6H, NCH3), 1.59 (s, 6H, NCCH3CNCH3), 1.15 (s, 6H, NCCH3 CNCH3), −4.84 (d, 2JHP = 11.0 Hz, 1H, RuH), −6.13 (d, 2JHP = 9.9 Hz, 2H, RuH). 31P{1H} NMR (202 MHz, C6D5CD3, 298 K): δ 59.6 (s). 13C{1H} NMR: (C6D5CD3, 125 MHz): δ 192.2 (d, 2JCP = 11 Hz, Ru-CNHC), 150.9 (d, JCP = 2 Hz, i-SiPh3), 141.2 (d, 1JCP = 30 Hz, i-PPh3), 136.7 (s, Ph), 134.0 (d, JCP = 12 Hz, PPh3), 127.8 (s, P/SiC6H5), 127.0 (d, JCP = 8 Hz, PPh3), 126.1 (s, P/SiC6H5), 125.8 (s, P/SiC6H5), 123.3 (s, NCCH3CNCH3), 122.6 (s, NCCH3 CNCH3), 37.7 (s, NCH3), 36.0 (s, NCH3), 9.9 (s, NCCH3), 9.2 (s, NCCH3). Anal. Calcd (found) for C50H57N4SiPRu·0.5C6H5CH3: C, 69.83 (69.86); H, 6.68 (6.76); N, 6.09 (6.01). Ru(IMe4)2(dppe)HF (cct-13). A toluene (0.4 mL) solution of ttt-6 (80 mg, 0.089 mmol) and dppe (42 mg, 0.107 mmol) was shaken vigorously for 1 h at room temperature in a J. Young resealable NMR tube. It was then filtered, concentrated, and layered with pentane to afford cct-13 as pale yellow crystals (34 mg, 49%). 1H NMR (400 MHz, C6D6): δ 8.70 (br, 4H, PC6H5), 7.36 (br m, 4H, PC6H5), 7.23 (m, 4H, PC6H5), 7.09 (m, 2H, PC6H5), 6.93 (br, 6H, PC6H5), 4.39 (s, 3H, NCH3), 4.37 (s, 3H, NCH3), 2.91 (s, 6H, NCH3), 2.37 (m, 4H, Ph2P(CH2)2PPh2), 1.47 (s, 6H, NCCH3CNCH3), 1.42 (s, 6H, NCCH3CNCH3), −22.9 (dt, 2JHF = 51.9 Hz, 2JHP = 22.1 Hz,

RuH). 31P{1H} NMR (162 MHz, C6D6): δ 64.8 (br s). 19F NMR (376 MHz, C6D6): δ −330.4 (br s). 13C{1H} NMR (125 MHz, C6D6): δ 191.5 (dd, 2JCP = 95 Hz, 2JCP = 18 Hz, Ru-CNHC), 146.7 (m, i-PC6H5), 143.8 (m, i-PC6H5), 135.7 (br, PC6H5), 131.6 (br, PC6H5), 124.2 (s, NCCH3CNCH3), 122.7 (s, NCCH3CNCH3), 35.0 (br t, J = 10 Hz, NCH3), 33.8 (br m, NCH3), 33.3 (t, 2JHP = 24 Hz, Ph2P(CH2)2PPh2), 9.7 (s, NCCH3), 8.8 (s, NCCH3). Anal. Calcd (found) for C40H49N4FP2Ru: C, 62.57 (62.76); H, 6.43 (6.66); N, 7.29 (6.98). Ru(IMe4)2(dppp)HF (cct-14). ttt-6 (80 mg, 0.089 mmol) and dppp (44 mg, 0.11 mmol) were dissolved in toluene (0.4 mL) in a J. Young resealable NMR tube, and the mixture was shaken vigorously at room temperature for 1 h. After filtration, the filtrate was concentrated and layered with pentane to afford cct-14 as pale yellow crystals. Yield: 45 mg (64%). 1H NMR (C6D6, 500 MHz): δ 8.05 (br m, 4H, PC6H5), 7.88 (br m, 4H, PC6H5), 7.09−6.84 (br m, 12H, PC6H5), 4.04 (s, 3H, NCH3), 4.02 (s, 3H, NCH3), 3.54 (br m, 2H, (C6H5)2P(CH2)3P(C6H5)2), 3.46 (s, 3H, NCH3), 2.40 (br m, 2H, (C6 H5 )2 P(CH2 ) 3P(C 6H 5) 2), 1.97 (m, 1H, (C6 H5 )2 P(CH2 ) 3P(C6H5)2)), 1.70 (m, 1H, (C6H5)2P(CH2)3P(C6H5)2)), 1.40 (s, 6H, NCCH3CNCH3), 1.39 (s, 6H, NCCH3CNCH3), −21.90 (dt, 2 JHF = 52.7 Hz, 2JHP = 20.0 Hz, 1H, RuH). 31P{1H} NMR (C6D6, 202 MHz): δ 32.9 (s). 19F NMR (C6D6, 470 MHz): δ −332.9 (br s, RuF). 13C{1H} NMR (C6D6, 126 MHz): δ 193.0 (dd, 2JCP = 102 Hz, 2 JCP = 30 Hz, Ru-CNHC), 144.7 (‘t’, JCP = 12 Hz, i-PC6H5), 142.5 (‘t’, JCP = 14 Hz, i-PC6H5), 133.2 (br m, PC6H5), 126.9 (br m, PC6H5), 123.6 (s, NCCH3CNCH3), 122.0 (s, NCCH3CNCH3), 35.6 (m, NCH3), 33.5 (m, NCH3), 28.8 (br, Ph2P(CH2)PPh2), 19.9 (br s, Ph2P(CH2)PPh2), 9.6 (s, NCCH3), 8.9 (s, NCCH3). Anal. Calcd (found) for C41H51N4FP2Ru: C, 62.96 (63.14); H, 6.58 (6.50); N, 7.17 (7.43). Ru(IMe4)2(dppm)HF (cct-15). A toluene (0.4 mL) solution of ttt-6 (80 mg, 0.089 mmol) and dppm (41 mg, 0.107 mmol) was shaken vigorously in a J. Young resealable NMR tube for 1 h at room temperature. The solution was filtered, concentrated, and layered with pentane to afford cct-15 as pale yellow crystals (21 mg, 31%). 1H NMR (C6D5CD3, 400 MHz, −45 °C): δ 8.66 (br, 4H, PC6H5), 7.41 (br, 4H, PC6H5), 7.23−7.15 (m, 6H, PC6H5), 7.13−6.96 (m, 6H, PC6H5), 4.57 (m, 1H, PCH2P), 4.45 (m, 1H, PCH2P), 4.18 (s, 3H, NCH3), 4.17 (s, 3H, NCH3), 3.14 (s, 6H, NCH3), 1.48 (s, 6H, F


Article

Organometallics NCCH3CNCH3), 1.38 (s, 6H, NCCH3CNCH3), −19.68 (dt, 2 JHF = 52.8 Hz, 2JHP = 20.3 Hz, 1H, RuH). 31P{1H} NMR (C6D6, 162 MHz, −45 °C): δ 3.5 (s). 19F NMR (C6D6, 376 MHz): δ −342.2 (t, 2JHF = 47 Hz). 13C{1H} NMR (C6D5CD3, 100 MHz, −45 °C): δ 192.4 (dd, 2JCP = 115 Hz, 2JCP = 33 Hz, Ru-CNHC), 144.6 (‘t’, JCP = 17 Hz, i-PC6H5), 142.3 (‘t’, JCP = 7 Hz, o-PC6H5), 135.4 (s, m-PC6H5), 131.8 (s, p-PC6H5), 123.7 (s, NCCH3CNCH3), 122.1 (s, NCCH3CNCH3), 56.8 (t, 1JCP = 19 Hz, PCH2P), 35.9 (s, NCH3), 33.9 (s, NCH3), 33.6 (s, NCH3), 9.4 (s, NCCH3), 8.8 (s, NCCH3). Anal. Calcd (found) for C39H47N4FP2Ru: C, 62.14 (63.25); H, 6.28 (6.31); N, 7.43 (7.43). Ru(IMe4)2(dppe)H2 (cct-10). Et3SiH (6 μL, 0.038 mmol) was syringed into a J. Young resealable NMR tube containing a C6D6 solution (0.4 mL) of Ru(IMe4)2(dppe)HF (cct-13; 16 mg, 0.019 mmol) and the sample left overnight at room temperature to afford cct-10 as indicated by NMR spectroscopy. 1H NMR (C6D6, 500 MHz): δ 7.90 (t, 3JHP = 7.5 Hz, 8H, PC6H5), 7.12 (m, 8H, PC6H5), 7.05 (m, 4H, PC6H5), 3.82 (s, 12 H, NCH3), 2.31 (d, 2JHP = 17.0 Hz, 4H, P(CH2)2P), 1.50 (s, 12H, NCCH3CNCH3), −7.20 (t, 2 JHP = 19.1 Hz, 2H, RuH). 31P{1H} NMR (C6D6, 202 MHz): δ 86.0 (s). 13C{1H} NMR (C6D6, 126 MHz): δ 197.7 (dd, 2JCP = 90 Hz, 2 JCP = 20 Hz, Ru-CNHC), 146.1 (m, i-PC6H5), 133.1 (br m, PC6H5), 127.3 (br s, PC6H5), 127.2 (br m, PC6H5), 122.5 (s, NCCH3 CNCH3), 37.0 (s, NCH3), 33.9 (‘t’, JCP = 24 Hz, Ph2PCH2CH2PPh2), 9.9 (s, NCCH3). Leaving the sample to stand at room temperature for a further few days afforded a small amount of pale yellow crystals of the all-cis isomer of 10, which proved insoluble in all common NMR solvents. Yield: 7 mg (49%). Anal. Calcd (found) for C40H50N4P2Ru: C, 64.05 (64.39); H, 6.72 (6.76); N, 7.47 (7.35). Ru(IMe4)2(dppp)H2 (cct-11). Et3SiH (8.1 μL, 51.0 μmol) was added to a C6D6 solution (0.4 L) of Ru(IMe4)2(dppp)HF (cct-14, 20 mg, 25.5 μmol) and the sample left for 2 days at room temperature to afford cct-11 as indicated by NMR spectroscopy. No attempt was made to isolate the complex. 1H NMR (C6D6, 500 MHz): δ 7.99 (br, 8H, PC6H5), 7.03 (m, 8H, PC6H5), 6.95 (m, 4H, PC6H5), 3.87 (s, 12H, NCH3), 2.82 (br, 4H, Ph2PCH2CH2CH2PPh2), 1.70 (m, 2H, Ph2PCH2CH2CH2PPh2), 1.40 (s, 12H, NCCH3CNCH3), −6.64 (t, 2 JHP = 19.2 Hz, 2H, RuH). 31P{1H} NMR (C6D6, 500 MHz): δ 47.0 (s). 13C{1H} NMR (C6D6, 126 MHz): δ 197.7 dd, 2JCP = 99 Hz, 2JCP = 32 Hz, Ru-CNHC), 145.0 (‘t’, JCP = 12 Hz, i-PC6H5), 133.1 (‘t’, JCP = 5 Hz, o-PC6H5), 126.6 (m, overlapping m/p-PC6H5), 122.0 (s, NCCH3CNCH3), 37.1 (s, NCH3), 35.4 (‘t’, JCP = 14 Hz, Ph 2 PCH 2 CH 2 CH 2 PPh 2 ), 20.3 (‘t’, J CP = 5 Hz, Ph 2 PCH 2 CH2CH2PPh2), 9.8 (s, NCCH3). Ru(IMe4)2(dppm)H2 (cct-12). Et3SiH (8.4 μL, 52.9 μmol) was added to a C6D6 solution (0.4 L) of Ru(IMe4)2(dppm)HF (cct-15, 20 mg, 26.4 μmol) and the sample left for 2 days at room temperature to afford cct-12 as indicated by NMR spectroscopy. A small number of X-ray-quality crystals were isolated upon layering a toluene solution of cct-12 with pentane. 1H NMR (C6D6, 500 MHz): δ 8.38 (br, 8H, PC6H5), 7.12 (m, 6H, PC6H5), 7.05 (m, 6H, PC6H5), 4.79 (t, 2JHP = 9.1 Hz, 2H, Ph2P(CH2)PPh2), 3.70 (s, 12H, NCH3), 1.52 (s, 12H, NCCH3CNCH3), −5.37 (t, 2JHP = 16.9 Hz, 2H, RuH). 31P{1H} NMR (C6D6, 500 MHz): δ 10.9 (s). 13C{1H} NMR (C6D6, 126 MHz): δ 199.3 (dd, 2JCP = 111 Hz, 2JCP = 38 Hz, Ru-CNHC), 146.3 (‘t’, JCP = 11 Hz, i-PC6H5), 133.3 (‘t’, JCP = 6 Hz, o-PC6H5), 127.7 (s, p-PC6H5), 127.5 (‘t’, JCP = 4 Hz, m-PC6H5), 122.2 (s, NCCH3CNCH3), 61.3 (t, 1JCP = 17 Hz, Ph2PCH2PPh2), 36.8 (s, NCH3), 9.8 (s, NCCH3). Ru(IEt2Me2)2(PPh3)2HF (cct-7). An alternative approach to that previously reported for cct-7 was adopted.10 A benzene solution (2 mL) of IEt2Me2 (116 mg, 0.76 mmol) was added to a benzene suspension (4 mL) of Ru(PPh3)4H2 (0.4 g, 0.34 mmol) and the mixture stirred for 5 min before addition of a THF solution (2 mL) of Et3N·3HF (28 μL, 0.17 mmol). After the mixture was stirred for a further 2 h, CsF (105 mg, 0.69 mmol) was added and the suspension was then stirred overnight. After cannula filtration, the filtrate was reduced to dryness, washed with pentane (3 × 5 mL), and dried in vacuo to afford a pale yellow solid (170 mg, 53%). 1H, 31P{1H}, and 19 F NMR data matched those in the literature.10

Ru(IEt2Me2)2(dppe)HF (cct-16). A toluene (0.4 mL) solution of cct-7 (50 mg, 0.053 mmol) and dppe (25 mg, 0.063 mmol) was shaken vigorously for 1 h at room temperature in a J. Young resealable NMR tube. The solution was filtered, concentrated, and layered with pentane to afford cct-16 as pale yellow crystals (19 mg, 44%). 1H NMR (C6D6, 500 MHz): δ 8.35 (br m, 4H, (C6H5)2PCH2CH2P(C6H5)2), 7.46 (br m, 4H, (C6H5)2PCH2CH2P(C6H5)2), 7.19−7.13 (br m, 4H, (C6H5)2PCH2CH2P(C6H5)2), 7.09−6.97 (br m, 8H, (C6H5)2PCH2CH2P(C6H5)2), 6.13 (br m, 2H, NCH2CH3), 4.69 (m, 2H, NCH2CH3), 3.84 (m, 2H, NCH2CH3), 3.13 (m, 2H, NCH2CH3), 2.38 (m, 4H, (C6H5)2PCH2CH2P(C6H5)2), 1.67 (s, 6H, NCCH3 CNCH3), 1.61 (s, 6H, NCCH3CNCH3), 1.10 (t, 3JHH = 6.9 Hz, 6H, NCH2CH3), 0.62 (t, 3JHH = 6.9 Hz, 6H, NCH2CH3), −22.32 (dt, 2 JHF = 54.5 Hz, 2JHP = 21.6 Hz, 1H, RuH). 31P{1H} NMR (C6D6, 202 MHz): δ 63.8 (s). 19F NMR (C6D6, 470 MHz): δ −348.1 (br s, RuF). 13C{1H} NMR (C6D6, 126 MHz): δ 191.1 (ddd, 2JCP = 98 Hz, 2 JCP = 18 Hz, 2JCF = 4 Hz, Ru-CNHC), 145.8 (m, i-PC6H5), 143.3 (m, i-PC6H5), 135.0 (br m, PC6H5), 132.2 (‘t’, JCP = 4 Hz, PC6H5), 127.4 (‘t’, JCP = 4 Hz, PC6H5), 127.3 (‘t’, JCP = 4 Hz, PC6H5), 127.2 (s, PC6H5), 124.6 (s, NCCH3CNCH3), 123.1 (s, NCCH3CNCH3), 42.7 (s, NCH2CH3), 41.7 (s, NCH2CH3), 41.4 (s, NCH2CH3), 32.8 (‘t’, JCP = 23 Hz, Ph2PCH2CH2PPh2), 17.0 (s, NCH2CH3), 14.8 (s, NCH2CH3), 9.7 (s, NCCH3), 9.1 (s, NCCH3). Anal. Calcd (found) for C44H57N4FP2Ru: C, 64.14 (63.98); H, 6.97 (6.89); N, 6.80 (6.54). Procedure for Catalytic HDF Experiments. A stock solution of ruthenium complex (e.g., 11.7 mg (15 μmol) of cct-14 in 1.5 mL of C6H5CH3) was prepared, and 2 × 0.5 mL aliquots were syringed into J. Young resealable NMR tubes. C6F6 (5.8 μL, 50 μmol) and Et3SiH (64 μL, 400 μmol) or iPr3SiH (82 μL, 400 μmol) were placed in each tube. The tubes were subsequently placed in an oil bath preheated to the required temperature (90 °C). Progress was monitored by 19F NMR spectroscopy, and HDF products were identified by comparison to authentic samples from commercial suppliers. X-ray Crystallography. Data for ttt-6, 9, ccc-10, cct-13, and cct-15 were obtained using an Agilent SuperNova instrument and a Cu Kα source, while those for cct-12, cct-14, and cct-16 were garnered using an Agilent Xcalibur diffractometer and Mo Kα radiation (Table S1 in the Supporting Information). All experiments were conducted at 150 K, and hydride ligands were refined at a distance of 1.6 Å from the metal center throughout, with the exception of those in 9. All convergences were achieved using full-matrix least squares in SHELXL-9725 via the Olex-2 software suite.26 Only points of note are mentioned hereafter. In addition to one molecule of the complex, one THF moiety was also found in the asymmetric unit of ttt-6. The assignment of the oxygen therein is based on the relative Uiso values upon testing all five positions. The current assignment was optimal in this regard, also resulting in the lowest residuals. However, there is likely to be some unmodeled disorder present in the crystal at large, given the anisotropic displacement parameters (ADPs) associated with the solvent atoms. The trans hydride/fluoride ligands were also seen to exhibit disorder to the tune of 13%. F1 and F1A were refined subject to being equidistant from the central metal atom. ADP restraints were also included for F1A. While the major hydride component (H1) was readily located, there was (unsurprisingly) no compelling evidence for the other 13% occupancy disordered component of this ligand, which was therefore omitted from the refinement. H1 was refined with full site occupancy. The asymmetric unit in 9 was seen to comprise one molecule of the ruthenium complex and an area of very disordered solvent. The latter was treated using a solvent mask in Olex-2,26 and on the basis of this analysis, an allowance has been made for two guest molecules of toluene per unit cell in the formula as presented. Aside from this, the refinement of the model in this structure was uneventful, although it was impossible to differentiate between the silicon- and phosphoruscontaining ligands in terms of any local geometry about the maingroup metal, or indeed via the residuals. Hence, the model herein accounts for 50:50 disorder of the two ligands bearing these atoms. The Ru−Si and Ru−P distances were each restrained to being similar in the final least squares, and some ADP restraints were also included G


Organometallics

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for the partial occupancy atoms, to assist in convergence. The hydride positions (H1−H3) have been refined freely. However, the Si/P disorder in addition to the limitations of accurately locating hydrogen atoms using X-ray diffraction techniques bathes these assignments in a degree of uncertainty. Nonetheless, prior to the hydride inclusions, the three assigned positions represented the highest diffraction maxima in the difference Fourier electron density map. The ensuing refinement was entirely stable, and the arising Uiso values are credible. The crystal was of premium quality and the data, overall, boast an I/σ value of ca. 34. One molecule of benzene was found to accompany the complex in the asymmetric unit in cct-12, while in cct-13, the asymmetric unit was seen to house one molecule of THF in addition to one molecule of the target compound. The fluoride ligand in the latter was found to be disordered in a 90:10 ratio. The hydride trans to the major fluoride component ligand was located and refined, with full occupancy. The THF moiety was seen to be disordered over two proximate sites, in a 50:50 ratio. Electron density in this region is somewhat smeared. Consequently, solvent C−C and O−C distances were refined subject to separate similarity restraints in the final least-squares cycles. ADP restraints were also included for fractional occupancy atoms, to assist convergence. The methyl hydrogen atoms attached to C7 and C14 in cct-14 were included at calculated positions, but the Uiso values for all six were allowed to refine freely to lend some credibility to their potential hydrogen-bonding interactions with F1. Finally, disorder of 87:13 was modeled for the fluoride ligand between locations F1 and F1A, respectively, in cct-16. The hydride ligand was located and refined at full occupancy (trans to F1) rather than attempt to artificially model it in the same disorder ratio as that which pertained to the halide. Crystallographic data for all compounds have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC 1537146−1537153. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax(+44) 1223 336033, e-mail: deposit@ ccdc.cam.ac.uk).

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ACKNOWLEDGMENTS J.P.L. and M.K.W. wish to dedicate this paper to the memory of Dr. Roger Mawby, who was an inspirational undergraduate educator and doctoral supervisor of both of us. We acknowledge the EPSRC for a Doctoral Training Award for M.K.C. and thank Professor Stuart Macgregor for continued fruitful discussions.

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REFERENCES

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00243. NMR spectra of ttt-6, 9, and cct-10-16, NMR spectra of reactions relating to the formation of 8 and catalytic HDF with cct-13, crystal data/structural refinement details for ttt-6, 9, ccc-10, and cct isomers of 12−16, and X-ray structures of ccc-10 and cct-12 (PDF) Accession Codes

CCDC 1537146−1537153 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*M.K.W.: e-mail, [email protected]; tel, 44 1225 383748. ORCID

Michael K. Whittlesey: 0000-0002-5082-3203 Notes

The authors declare no competing financial interest. H


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Organometallics

(23) Young, R.; Wilkinson, G. Inorg. Synth. 1990, 28, 337−338. (24) Ansell, M. B.; Roberts, D. E.; Cloke, F. G. N.; Navarro, O.; Spencer, J. Angew. Chem., Int. Ed. 2015, 54, 5578−5582. (25) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990, 46, 467. Sheldrick, G. M. SHELXL-97, a computer program for crystal structure refinement; University of Gö ttingen, Gö ttingen, Germany, 1997. (26) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339−341.

(7) Macgregor, S. A.; McKay, D.; Panetier, J. A.; Whittlesey, M. K. Dalton Trans. 2013, 42, 7386−7395. (8) Cybulski, M. K.; McKay, D.; Macgregor, S. A.; Mahon, M. F.; Whittlesey, M. K. Angew. Chem., Int. Ed. 2017, 56, 1515−1519. (9) Pike, S. D.; Crimmin, M. R.; Chaplin, A. B. Chem. Commun. 2017, 53, 3615−3633. (10) Cybulski, M. K.; Riddlestone, I. M.; Mahon, M. F.; Woodman, T. J.; Whittlesey, M. K. Dalton Trans. 2015, 44, 19597−19605. (11) Davies, C. J. E.; Lowe, J. P.; Mahon, M. F.; Poulten, R. C.; Whittlesey, M. K. Organometallics 2013, 32, 4927−4937. (12) Addition of CsF as a scavenger (of adventitious moisture and/or HF) has been shown to resolve couplings involving metal fluoride ligands in some cases: (a) Macgregor, S. A.; Roe, D. C.; Marshall, W. J.; Bloch, K. M.; Bakhmutov, V. I.; Grushin, V. V. J. Am. Chem. Soc. 2005, 127, 15304−15321. (b) Reade, S. P.; Nama, D.; Mahon, M. F.; Pregosin, P. S.; Whittlesey, M. K. Organometallics 2007, 26, 3484− 3491. (c) Guard, L. M.; Ledger, A. E. W.; Reade, S. P.; Ellul, C. E.; Mahon, M. F.; Whittlesey, M. K. J. Organomet. Chem. 2011, 696, 780− 786. (13) (a) Johnson, S. A.; Huff, C. W.; Mustafa, F.; Saliba, M. J. Am. Chem. Soc. 2008, 130, 17278−17280. (b) Hauser, S. A.; Prokes, I.; Chaplin, A. B. Chem. Commun. 2015, 51, 4425−4428. (14) The low-frequency region of the spectrum of 9 remained unchanged at both 298 and 223 K. Measurement of T1 values (at room temperature as well as low temperature) for both of the low-frequency signals (298 K, 400 MHz, 350 ms (δ −4.77), 361 ms (δ −6.16); 223 K, 400 MHz, 387 ms (δ −4.82), 432 ms (δ −6.06)) ruled out any possibility of 9 being a dihydrogen complex, such as Ru(IMe4)2(PPh3) (η2-H2)(SiPh3)H. As the sample used in the experiment also contained a small amount of the species proposed as Ru(IMe4)2(PPh3)(SiPh3)H in ref 15, we were able to measure a T1 value for the hydride signal of this for comparison: 298 K, 400 MHz, 358 ms (δ −33.01); 223 K, 400 MHz, 366 ms (δ −32.82). (15) Prolonged exposure of an isolated sample of 9 to vacuum brought about a color change from near colorless to red-purple, which was accompanied by the appearance of a new hydride signal at δ −33.01 (d, 2JHP = 15.5 Hz). Both the color and very low frequency are indicative of a coordinatively unsaturated ruthenium species, which we propose is Ru(IMe4)2(PPh3)(SiPh3)H resulting from reductive elimination of H2. For precedents, see: Dioumaev, V. K.; Procopio, L. J.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 2003, 125, 8043− 8058. (16) (a) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151−187. (b) Nikonov, G. I. Adv. Organomet. Chem. 2005, 53, 217−309. (c) Lachaize, S.; Sabo-Etienne, S. Eur. J. Inorg. Chem. 2006, 2115− 2127. (d) Corey, J. Y. Chem. Rev. 2011, 111, 863−1071. (17) For a recent discussion of how both sign and magnitude of JSiH can be used to characterize σ-silane complexes, see: Scherer, W.; Meixner, P.; Batke, K.; Barquera-Lozada, J. E.; Ruhland, K.; Fischer, A.; Eickerling, G.; Eichele, K. Angew. Chem., Int. Ed. 2016, 55, 11673− 11677. (18) (a) Kono, H.; Wakao, N.; Ito, K.; Nagai, Y. J. Organomet. Chem. 1977, 132, 53−67. (b) Haszeldine, R. N.; Malkin, L. S.; Parish, R. V. J. Organomet. Chem. 1979, 182, 323−332. (c) Dioumaev, V. K.; Yoo, B. R.; Procopio, L. J.; Carroll, P. J.; Berry, D. H. J. Am. Chem. Soc. 2003, 125, 8936−8948. (19) Catalytic HDF with cct-5 was previously only reported in benzene rather than toluene, and over a shorter time. See ref 10. (20) Attempts to bring about the catalytic HDF of C6F6 with cct-13 (10 mol%) with Et3SiH in toluene at 70 °C led to only a very small amount of conversion even to pentafluorobenzene after 80 min. (21) (a) Wu, J.; Cao, S. ChemCatChem 2011, 3, 1582−1586. (b) Reference 2f.. (22) There are only a few studies on the apparent simple “metathesis” of a metal fluoride complex and reducing agent such as an alkyl silane: (a) Vergote, T.; Nahra, F.; Peeters, D.; Raint, O.; Leyssens, T. J. Organomet. Chem. 2013, 730, 95−103. (b) Reference 8. Both of these examples support the idea that such reactions are, in fact, far from simple. I


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