Article Cite This: Organometallics XXXX, XXX, XXX-XXX
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Direct Chlorination of Trispyrazolyl Borate Ligands in Tp-Ruthenium Complexes Hiroyuki Hattori, Dong Hyun Koo, and Jeremy A. May* Department of Chemistry, University of Houston, 3585 Cullen Blvd., Fleming Building Room 112, Houston, Texas 77204-5003, United States S Supporting Information *
ABSTRACT: Trispyrazolyl borate (Tp) ligands are highly modifiable to vary their steric and electronic properties, and the ability to selectively modify them after metal complexation would allow for rapid catalyst diversification. To this end, stable ruthenium complexes TpRu(cod)Cl (cod = 1,5-cyclooctadiene) and TpRu(nbd)Cl (nbd = norbornadiene) were selectively chlorinated at the 4-positions of the Tp pyrazole rings in high yields to afford TpClRu(cod)Cl and TpClRu(nbd)Cl. The chlorinated complexes could then undergo diene ligand exchange to afford phosphine complexes TpClRu(phosphine)Cl and TpClRu(phosphine)Cl2. Complexes were characterized via NMR spectroscopy, X-ray crystallography, UV−vis spectroscopy, and cyclic voltammetry.
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INTRODUCTION Ruthenium complexes are useful catalysts for many organic reactions, including olefin1 and enyne metatheses,2 allylations,3 and propargylations.4,5 These transformations often take advantage of stable intermediates containing Ru−C multiple bonds, such as carbenes, vinylidenes, and allenylidenes. In addition to phosphine,6 N-heterocyclic carbene (NHC),7 arene,8,9 and cyclopentadiene (Cp) ligands10 for reactive complexes, recent reports11 have demonstrated the viability of trispyrazolyl borate (Tp) ligands12 to access these reactive organo-ruthenium intermediates. Tp ligands are more easily accessed synthetically than NHC and Cp-based ligands, allowing significant variation in their steric and electronic properties. Since the oxidation potential of Ru bears on its catalytic reativity,13 facile adjustment of the electron donation by ligands would allow for greater control of catalyst properties. Here, we report the selective on-metal modification of Tp ligands and observations of the effect of these changes at the metal through changes in the complexes’ redox potential. The ability to modify ligands after complexation to a metal will allow for rapid catalyst diversification relative to independently synthesizing ligands and forming metal complexes from them.
chloropyrazolyl isomers are from Trofimenko’s original work.16 These examples were synthesized from the respective chloropyrazoles. In light of the goals expressed above to functionalize ligands while ligated to a metal, work to regioselectively chlorinate a TpRu complex was initiated. While the bromination of 3,5-dialkyltrispyrazolyl borate ligands on Ir has been reported,17 halogenation of unsubstituted trispyrazolyl borates has not. In this paper, we show that selective electrophilic substitution of unfunctionalized Tp ligands is possible, which creates precedent for myriad onmetal ligand electrophilic functionalizations. Jiménez-Tenorio and Puerta’s procedure14 was used to obtain intermediate 1a. We initially looked at the removal of the cod ligand from 1a, but found that neither hydrogenation nor elevated temperatures allowed for a discrete product to be obtained. In looking to cod removal after electrophilic Ru oxidation, it was found that reaction occurred exclusively at the Tp ligand. The pyrazoles were regioselectively chlorinated in the presence of sulfuryl chloride to give TpClRu(cod)Cl (2a). Figure 1 shows the crystal structures of 1a and 2a. Chlorination of Tp did not significantly alter any of the bond lengths or angles between the ruthenium and the nitrogen, carbon, or chlorine atoms. A plane of symmetry bisects the olefins of cod, passes through Ru, and is coplanar with one pyrazole ring. This symmetry is confirmed by the 1:2 1H NMR integration ratio of the H3 and H5 peaks (7.7 and 8.0 ppm, respectively) of the pyrazole on the plane and the peaks of the pyrazoles located off of the plane (7.5 and 7.6 ppm). The chemical shifts of the peaks of 2a moved upfield relative to those of 1a by 0.2−1 ppm. The regioselectivity of the chlorination was demonstrated by the
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RESULTS AND DISCUSSION TpRu(cod)Cl (1a) was synthesized as a strategic intermediate14 to access a variety of halogenated complexes since the diene ligand could be later removed by hydrogenation or heating,15 or the diene could be exchanged for a variety of phosphine ligands (Scheme 1). The unfunctionalized Tp ligand also offered potential diversification via electrophilic reactions, and so we initially targeted chlorination as a representative transformation. Three instances of chlorinated Tp ligands have appeared in the literature, and both that deal with 4© XXXX American Chemical Society
Received: July 19, 2017
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DOI: 10.1021/acs.organomet.7b00546 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Scheme 1. Synthesis of 2a and 2b
Two mechanistic pathways are possible for the chlorination of Tp with SO2Cl2: direct electrophilic aromatic substitution (EAS) or initial chlorine formation, followed by EAS. To differentiate between these hypothetical mechanisms, 1a was treated with trifluoromethane sulfonyl chloride as an alternate source of electrophilic chloride (Scheme 2). This reaction did Scheme 2. Mechanistic Investigation of Chlorination Figure 1. ORTEP diagrams of complexes 1a (left) and 2a (right).18 Thermal ellipsoids are shown at the 50% probability level.
disappearance of the pyrazole H4 peaks in the 1H NMR. The 13 C NMR spectrum of 2a showed a peak from the chlorinated carbon of Tp at 111 ppm. In comparison with 1a, this peak shifted 5 ppm downfield due to the electron withdrawing nature of Cl. The nbd derivative 1b was synthesized via the same route as 1a (see Scheme 1). The yield for the addition of KTp to 4b to form 1b was twice as high as that for 4a to 1a. This could be explained by impeded isomerization of the double bonds in nbd or by stronger metal coordination to the diene.19 The nbd complex 1b was chlorinated with sulfuryl chloride in THF to give 2b in 81% yield (Scheme 1). The complex 2b was analyzed via X-ray crystallography (Figure 2). The average Ru−C bond
not give detectable amounts of 2a. Ruthenium complex 1a also was treated with Cl2 gas introduced into the head space of the flask, and 2a was formed in 52% yield. Although the yield was not as high as for SO2Cl2-derived chlorination, chlorine seems to be the active reagent. This observation corresponds to the use of Br2 as the active reagent in the bromination of 3,5-dialkyl Tp Ir complexes.17 With the new chlorinated complexes 2a and 2b in hand, we looked at diene replacement to form a library of phosphine complexes. TpRu(PPh3)Cl2 (5) has been synthesized by heating a mixture of 1a and PPh3 in DMF to 150 °C, followed by the addition of CCl4 in the presence of oxygen.20 The chlorinated complex 6 was similarly synthesized from 2a or 2b in 57% or 62% yield, respectively (Scheme 3). The crystal structure of 6 was obtained (see Figure 3).21 The average Ru−N bond length for 6 was 2.085(15) Å, which is slightly shorter than the Ru−N bond in Ru(II) complexes 2a and 2b (2.1028(20) Å and 2.111(17) Å, respectively), reflecting
Figure 2. ORTEP diagram of TpClRu(nbd)Cl (2b).18 Thermal ellipsoids are shown at the 50% probability level.
Scheme 3. Exchange of Diene Ligands with Phosphines lengths were 2.233(6) Å for 2a and 2.2002(11) Å for 2b. The shorter distance for the latter confirms that the bonding between ruthenium and nbd was slightly stronger, as has been pointed out previously. 19 Analysis of 2b reveals the disappearance of 1H NMR peaks for the pyrazole H4 peaks at 6.2 and 6.3 ppm upon chlorination. The 13C NMR spectrum of 2b showed a peak at 111 ppm from the chlorinated carbon, which was shifted downfield by 5 ppm relative to that peak in 1b. These changes in the NMR spectra of 2b are similar to those found in the formation of 2a. B
DOI: 10.1021/acs.organomet.7b00546 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
Figure 3. ORTEP diagram of TpClRu(PPh3)Cl2 (6).16 Thermal ellipsoids are shown at the 50% probability level. Figure 5. Cyclic voltammetry of 5 (top) and 6 (bottom). The plot was calibrated against Fc+/Fc.
the electron deficiency of Ru(III) and the additional chloride ligand. The Ru−Cl bond was similarly 0.1 Å shorter. Previous studies have shown that electron density at ruthenium, which is catalogued via the complex’s oxidation potential, affects the formation of vinylidene and allenylidene intermediates and the ability of these intermediates to proceed to a variety of products.13 Given this correlation between oxidation potentials and organometallic reactivity, the oxidation potentials of the newly synthesized complexes were measured. The Ru(II)/(III) redox potential of 1a was 0.81 V (vs ferrocene: Fc+/Fc) (Figure 4). Interestingly, chlorinated
Scheme 4. Synthesis of Diphosphine Complexes 7a−d
Thus, it is concluded that varying the length of the diphosphine linker does not significantly influence the electronic properties of complexes 7a−d.
Figure 4. Cyclic voltammetry of 1a (top), 1b (middle), and 2b (bottom). The plot was calibrated against Fc+/Fc.
complex 2a showed irreversible oxidation that implied decomposition of the complex (see the Supporting Information). The nbd complexes 1b and 2b showed reversible peaks at 0.82 and 1.22 V, respectively. The increased resistance of 2b to oxidation might be explained by the electron withdrawing effect of Cl on Tp; it presumably reduces the electron donation to ruthenium. With the resulting decreased electron density on Ru, it is harder to remove an electron. Comparison of the CVs for 5 and 6 showed Ru(II)/(III) redox potentials at −0.51 V for 5 and −0.34 V for 6 (Figure 5). The presence of the pyrazole chlorine atom thus substantially increased the oxidation potential for the TpClRu(III) complex relative to the unchlorinated Tp, also. The negative potentials are reflective of the electron donation of the phosphine ligands and additional chloride ligand relative to the diene ligands. Diphosphine complexes 7a−d were synthesized to examine the effect of phosphine ligands on the properties of the complexes. The yields of the light-yellow products were about 70%. X-ray crystallography elucidated the structures to be those illustrated in Scheme 4.22 The CV showed the Ru(II)/(III) oxidation potential to be about 0.3 V for all of these diphosphine complexes (Figure 6).
Figure 6. Cyclic voltammograms of complexes 7a−d (from top to bottom).
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CONCLUSION In summary, the chlorination of on-metal Tp ligands was achieved in high yields. The diene complexes were then allowed to react with phosphines to generate Tp/phosphine complexes in moderate yields. These complexes were characterized with X-ray crystallography and NMR. Absorption bands and redox potentials of these complexes were measured to assess their properties. This approach demonstrates the potential to selectively modify redox potentials and access diverse structures from a common intermediate to facilitate catalyst development.
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EXPERIMENTAL SECTION
General Considerations. All reactions were carried out in flamedried Schlenk flasks under an Ar atmosphere. THF and toluene were C
DOI: 10.1021/acs.organomet.7b00546 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
d) δ 30.3, 30.96, 87.58, 95.08, 106.66, 106.75, 135.4, 138.1, 142.29, 145.57. Preparation of TpRu(nbd)Cl (1b). TpRu(nbd)Cl was prepared as is TpRu(cod)Cl, but replacing [Ru(cod)Cl]x with [Ru(nbd)Cl]x (2 g, 7.6 mmol). The product was orange needle-like crystals (1.48 g, 44% yield). 1H NMR (500 MHz, chloroform-d) δ 8.43 (d, J = 2.3 Hz, 1H), 7.76 (d, J = 2.3 Hz, 1H), 7.64 (d, J = 2.3 Hz, 2H), 7.30 (d, J = 2.3 Hz, 2H), 6.33 (t, J = 2.3 Hz, 1H), 6.22−6.14 (m, 2H), 5.29 (t, J = 3.4 Hz, 2H), 4.52−4.37 (m, 2H), 4.25 (dd, J = 4.6, 3.4 Hz, 2H), 1.70 (s, 2H). 13C NMR (500 MHz, chloroform-d) δ51.8, 60.8, 70.9, 80.8, 106.4, 106.8, 135.2, 137.6, 141.5, 145.5. Synthesis of TpClRu(cod)Cl (2a). TpRu(cod)Cl (568 mg, 1.24 mmol) was added to a flame-dried 50 mL Schlenk flask. THF (10 mL) and SO2Cl2 (0.5 mL, 6.2 mmol, 5.0 equiv) were added in that order. The reaction was complete in 45 min, and the mixture was purified via column chromatography. The product was eluted with Hex/DCM/ EtOAc = 20:2:1. The orange fractions were collected and concentrated in a flask. The residue was recrystallized from DCM/pentane to give orange plate-like crystals that, when vacuumed, became an opaque solid (698.2 mg, 100% yield). 1H NMR (500 MHz, chloroform-d) δ 8.05 (s, 1H), 7.77 (s, 1H), 7.60 (s, 2H), 7.50 (s, 2H), 4.88−4.78 (m, 2H), 4.07−3.97 (m, 2H), 2.98−2.85 (m, 2H), 2.72−2.59 (m, 2H), 2.42 (d, J = 8.6 Hz). 13C NMR (500 MHz, chloroform-d) δ30.1, 30.6, 87.8, 95.9, 110.9, 111.1, 134.0, 136.8, 141.1, 144.2. Anal. Calcd for H19C17N6BCl4Ru (560.75 g/mol): H,3.42; C, 36.39; N, 14.98; Cl, 25.28; Found: H, 3.40; C, 35.44; N, 14.51; Cl, 27.64. Synthesis of TpClRu(nbd)Cl (2b). TpRu(nbd)Cl (550.0 mg, 1.2 mmol) was added to a flame-dried 50 mL Schlenk flask. THF (10 mL) and SO2Cl2 (0.5 mL, 6.2 mmol, 5 equiv) were added in this order. Volatiles were removed under vacuum after 1 h of stirring. The residue was dissolved in DCM and purified via column chromatography. The product was eluted with Hex/DCM/EtOAc = 16:2:1. The orange fractions were collected and concentrated in a flask. The residue was recrystallized from DCM/pentane to give orange needle-like crystals (546.7 mg, 81% yield). 1H NMR (500 MHz, chloroform-d) δ 8.37 (s, 1H), 7.74 (s, 1H), 7.59 (s, 2H), 7.23 (s, 2H), 5.28−5.23 (m, 2H), 4.46 (t, J = 3.4 Hz, 2H), 4.29−4.19 (m, 2H), 1.71 (d, J = 1.7 Hz, 2H). 13C NMR (500 MHz, chloroform-d) δ51.8, 61.2, 71.3, 81.6, 110.9, 111.0, 133.8, 136.5, 140.4, 144.1. Anal. Calcd for H35C37N6BP2Cl4Ru (546.61 g/mol): H, 2.77; C, 35.26; N, 15.42; Cl, 26.02; Found: H, 2.77; C, 35.07; N, 15.38; Cl, 26.30. Synthesis of TpClRuPPh3Cl2 (6). Either TpClRu(cod)Cl (245.0 mg, 0.44 mmol) or TpClRu(nbd)Cl (238.8 mg, 0.44 mmol) with PPh3 (114.6 mg, 0.44 mmol, 1.0 equiv) was added to a flame-dried 10 mL Schlenk flask. DMF (4.0 mL) was added to the flask, and the suspension was slowly heated to 150 °C. The temperature was maintained for 2 h. The mixture was then cooled to room temperature, and the solvent as removed under vacuum. CCl4 (1 mL) and DCM (3 mL) were added to the flask. After overnight, the mixture was purified via column chromatography, and the product was eluted with Hex:DCM:EtOAc = 20:2:1. The red fractions were collected and recrystallized from DCM/pentane to give dark red needles (181.1 mg, 57% yield from 2a) (20 mg, 62% yield from 2b). Anal. Calcd for H22C27N6BPCl5Ru (750.63 g/mol): H, 2.95; C, 43.2; N, 11.2; Cl, 23.62; Found: H, 2.96; C, 43.43; N, 11.18; Cl, 23.45. Synthesis of TpClRu(dppm)Cl (7a). TpClRu(cod)Cl (245.0 mg, 0.46 mmol) and 1,1-bis(diphenylphosphino)methane (168.1 mg, 0.46 mmol, 1.0 equiv) were added to a flame-dried 10 mL Schlenk flask. DMF (4 mL) was added to the flask, and the suspension was slowly heated to 150 °C. The temperature was maintained for 2 h. The mixture was then cooled to room temperature, and the solvent as removed under vacuum. The residue was recrystallized form DCM/ pentane to give yellow needle-like crystals (295.1 mg, 78% yield). 1H NMR (500 MHz, chloroform-d) δ 7.83−7.74 (m, 4H), 7.68 (d, J = 14.9 Hz, 2H), 7.50 (s, 1H), 7.48−7.36 (m, 8H), 7.31 (t, J = 7.4 Hz, 2H), 7.25−7.13 (m, 4H), 7.08 (dd, J = 10.6, 6.6 Hz, 4H), 5.27−5.15 (m, 1H), 5.10 (d, J = 14.3 Hz, 1H), 5.00−4.88 (m, 1H), 4.28 (s, 1H). 13 C NMR (500 MHz, chloroform-d) δ 48.2−48.5 (t, JC‑P = 83 Hz), 107.5, 110.2, 128.8, 128.8, 128.8, 128.9, 128.9, 130.2, 130.7, 131.4− 131.7 (t, JC‑P = 73 Hz), 132.9, 133.3, 133.4, 133.4, 133.7, 134.3−134.6
purged with argon and dried over activated alumina columns and used after degassing by repetitive vacuum and Ar purges (×3). The synthesis of [Ru(COD)Cl]x has been reported before,23 but is reproduced below. KTp was prepared by a known method.12 TpRu(COD)Cl was prepared by the same procedure as previously reported,14 but was purified differently. The rest of the reagents are commercially available, and were degassed before usage as necessary. Flash column chromatography was performed on 60 Å silica gel (Sorbent Technologies Inc.). Analytical thin layer chromatography was performed on 250 mm EMD silica gel/TLC plates with a fluorescent indicator (F254). The 1H and 13C NMR spectra were recorded on a JEOL ECA 500 spectrometer using the residual solvent peak as an internal standard (CDCl3: 7.26 ppm for 1H NMR and 77.6 ppm for 13 C NMR and 400 MHz for 31P NMR). The crystallography measurements were made with a Bruker DUO platform diffractometer equipped with a 4K CCD APEX II detector using MoK/a radiation at 123 K. The reflections were collected using a narrow-frame algorithm with scan widths of 0.50/% in omega and phi and an exposure time of 20 s/frame at a 6 cm detector distance. The data were integrated using the Bruker Apex-II program, with the intensities corrected for Lorentz factor, polarization, air absorption, and absorption due to variation in the path length through the detector faceplate. The data were scaled, and an absorption correction was applied using SADABS. Redundant reflections were averaged. The structure was solved by direct method and refined with the program SHELXL 2014. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were refined isotropically with riding displacement parameters. UV−vis spectroscopy was collected on a Cary 6000 UV−vis NIR spectrophotometer over the 200−800 nm spectral range in DCM at room temperature. Cyclic voltammetry (CV) measurements were perforned at the scan rate of 0.1 V/s with a CH Instruments 602E potentiostat interfaced with a nitrogen glovebox via wire feedthroughs. Samples were dissolved in DCM with 0.1 M TBAPF6 as a supporting electrolyte. A 3 mm diameter glassy carbon working electrode, platinum wire counter electrode, and a silver wire pseudoreference electrode were used. Elemental analyses (H, C, N, Cl) were performed by Atlantic Microlab, Inc. of Norcross, GA. Preparation of [Ru(cod)Cl]x (4a). A flame-dried 500 mL roundbottom flask was charged with RuCl3(H2O)x (10 g, 45.2 mmol) under an inert atmosphere. Ethanol (240 mL) and 1,5-cyclooctadiene (9.5 mL, 77.1 mmol, 1.6 equiv) were added to the flask. The mixture was heated to reflux, and the mixture was boiled 24 h. The suspension was cooled to room temperature and filtered. The precipitate was rinsed with ether and dried under vacuum to give a brown powder (11.02 g, 82% yield). This powder was not characterized due to poor solubility in organic solvents. Preparation of [Ru(nbd)Cl]x (4b). [Ru(nbd)Cl]x, 4b, was prepared following the same procedure as [Ru(cod)Cl]x, but using norbornadiene instead (7.8 mL, 77.1 mmol, 1.6 equiv). The reaction gave a reddish powder (2.03 g, 80% yield). The product was not characterized due to poor solubility in organic solvents. Preparation of TpRu(cod)Cl (1a). [Ru(cod)Cl]x (2 g, 7.1 mmol) was added to a flame-dried 50 mL Schlenk flask. Toluene (25 mL) and TMEDA (2.5 mL, 16.8 mmol, 2.2 equiv) was added to the flask. The mixture was stirred in an oil bath at 80 °C for 3 days. Volatiles were removed under vacuum, and KTp (1.3 g, 5.2 mmol, 0.7 equiv) and acetone (13 mL) were added to the residue in a glovebox. The flask was stirred in an oil bath at 55 °C for 2 h, and the solvent was removed under reduced pressure. DCM was added to the flask, and the mixture was stirred under air overnight. The DCM solution was purified via column chromatography, and the product was eluted with DCM/ EtOAc = 40:1. The major orange band was collected and concentrated. The residue was recrystallized from DCM/pentane over 2 days to give orange plate-like crystals (809.2 g, 25% yield). 1H NMR (500 MHz, chloroform-d) δ 8.13 (d, J = 2.3 Hz, 1H), 7.79 (d, J = 2.3 Hz, 1H), 7.65 (d, J = 2.3 Hz, 2H), 7.57 (d, J = 1.7 Hz, 2H), 6.32 (t, J = 2.3 Hz, 1H), 6.21 (t, J = 2.3 Hz, 2H), 4.96−4.87 (m, 2H), 4.07− 3.98 (2H), 3.01−2.89 (m, 2H), 2.75−2.62 (m, 2H), 2.42 (q, J = 7.6 Hz, 2H), 2.25 (q, J = 7.4 Hz, 2H). 13C NMR (500 MHz, chloroformD
DOI: 10.1021/acs.organomet.7b00546 Organometallics XXXX, XXX, XXX−XXX
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Organometallics (t, JC‑P = 78 Hz), 134.8, 142.7, 146.8. 31P NMR (400 MHz, chloroform-d) δ 8.2 Anal. Calcd for H29C34N6BP2Cl4Ru (840.65 g/ mol): H, 3.49; C, 48.77; N, 10.03; Cl, 16.94; Found: H, 3.59; C, 48.87; N, 10.11; Cl, 16.79. Synthesis of TpClRu(dppe)Cl (7b). It was synthesized in analogy with TpClRu(dppm)Cl, but using 1,2-bis(diphenylphosphino)ethane (174.1 mg, 0.46 mmol, 1.0 equiv). The recrystallization gave yellow needle-like crystals (269.2 mg, 72.1% yield). 1H NMR (500 MHz, chloroform-d) δ 7.67 (s, 2H), 7.57 (t, J = 8.0 Hz, 4H), 7.44 (s, 1H), 7.43−7.31 (m, 6H), 7.23 (t, J = 7.4 Hz, 2H), 7.12−7.03 (m, 6H), 6.72 (t, J = 8.0 Hz, 4H), 4.86 (s, 1H), 4.72−3.98 (1H), 3.20−2.99 (m, 2H), 2.94−2.77 (m, 2H). 13C NMR (500 MHz, chloroform-d) δ 29.2−29.5 (t, JC‑P = 93 Hz), 108, 110.2, 128.2−128.3, 128.7, 130, 130.3, 131.4− 131.8 (m), 132.7, 133.5, 133.9, 134.1, 136.1−136.4 (m), 142.7, 147. 31 P NMR (400 MHz, chloroform-d) δ 70.7 Anal. Calcd for H31C35N6BP2Cl4Ru (854.78 g/mol): H, 3.67; C, 49.38; N, 9.87; Cl, 16.65; Found: H, 3.73; C, 49.12; N, 9.85; Cl, 16.38. Synthesis of TpClRu(dppp)Cl (7c). It was synthesized in analogy with TpClRu(dppm)Cl, but using 1,3-bis(diphenylphosphino)propane (181.0 mg, 0.46 mmol, 1.0 equiv). The recrystallization gave yellow needle-like crystals (276.3 mg, 73% yield). 1H NMR (500 MHz, chloroform-d) δ 7.71 (t, J = 8.0 Hz, 4H), 7.55 (s, 2H), 7.38 (t, J = 7.2 Hz, 2H), 7.35−7.27 (m, 5H), 7.19 (t, J = 7.4 Hz, 2H), 7.03 (t, J = 7.4 Hz, 4H), 6.55 (t, J = 7.7 Hz, 4H), 6.33 (s, 2H), 4.81 (s, 1H), 4.63− 3.82 (1H), 3.00 (td, J = 15.8, 7.1 Hz, 2H), 2.79 (t, J = 12.9 Hz, 3H), 2.21 (q, J = 12.8 Hz, 1H). 13C NMR (500 MHz, chloroform-d) δ 21.2, 28.9−29.2 (t, JC‑P = 59 Hz), 108.2, 109.6, 127.9−128, 128.5, 129.8, 131.0−131.3 (t, JC‑P = 73.5 Hz), 132.3, 133.3, 134.1, 134.2, 135.5− 135.9 (t, JC‑P = 83 Hz), 143.1, 148.3. 31P NMR (400 MHz, chloroform-d) δ 34.1 Anal. Calcd for H33C36N6BP2Cl4Ru (868.90 g/ mol): H, 3.84; C, 50.00; N, 9.71; Cl, 16.39; Found: H, 3.90; C, 49.53; N, 9.69; Cl, 17.51. Synthesis of TpClRu(dppb)Cl (7d). It was synthesized in analogy with TpClRu(dppm)Cl, but using 1,4-bis(diphenylphosphino)butane (186.7 mg, 0.46 mmol, 1.0 equiv). The recrystallization gave yellow needle-like crystals (278.1 mg, 72% yield). 1H NMR (500 MHz, chloroform-d) δ 7.62 (s, 4H), 7.53 (d, J = 10.9 Hz, 2H), 7.36 (t, J = 7.2 Hz, 2H), 7.29 (t, J = 8.0 Hz, 5H), 7.22−7.11 (m, 2H), 6.99 (t, J = 7.7 Hz, 4H), 6.60−6.40 (m, 6H), 5.55 (s, 1H), 4.54−3.83 (1H), 2.87 (d, J = 10.9 Hz, 2H), 2.77−2.54 (m, 4H), 2.18 (d, J = 5.7 Hz, 2H). 13C NMR (500 MHz, chloroform-d) 23.1, 27.8−28.0 (t, JC‑P = 49 Hz), 108.5, 109.7, 127.7−127.8, 128.2, 129.6, 132.5, 133.2−133.5 (t, JC‑P = 73.5 Hz), 133.7, 134.2, 134.4, 137.6−137.9 (t, JC‑P = 76 Hz), 143.8, 148.6. 31P NMR (400 MHz, chloroform-d) δ 35.9 Anal. Calcd for H35C37N6BP2Cl4Ru (883.03 g/mol): H, 4.01; C, 50.5; N, 9.56; Cl, 16.12; Found: H, 4.07; C, 50.61; N, 9.55; Cl, 16.03.
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ORCID
Jeremy A. May: 0000-0003-3319-0077 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are thankful to the Welch Foundation (grant E-1744) and the ACS Petroleum Research Fund for supporting this research (grant 55652-ND1). We are also grateful to Dr. Wang Xiqu for support in solving X-ray crystal structures.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00546. Full characterization data for 2a, 2b, 6, 7a, 7b, 7c, and 7d and experimental procedures for all reactions (PDF) Accession Codes
CCDC 1551227−1551233 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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REFERENCES
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*E-mail:
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DOI: 10.1021/acs.organomet.7b00546 Organometallics XXXX, XXX, XXX−XXX
Article
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DOI: 10.1021/acs.organomet.7b00546 Organometallics XXXX, XXX, XXX−XXX
