Borane-Bridged Ruthenium Complex Bearing a PNP Ligand

Article pubs.acs.org/Organometallics

Borane-Bridged Ruthenium Complex Bearing a PNP Ligand: Synthesis and Structural Characterization Yijing Xu, Christoph A. Rettenmeier, Gudrun T. Plundrich, Hubert Wadepohl, Markus Enders, and Lutz H. Gade* Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: Reaction of the precursor complex [RuHCl(CO)(PPh3)3] with the PNP protioligand CbzdiphosH in toluene resulted in the formation of two stereoisomeric hydrido complexes, [(CbzdiphosH)RuHCl(CO)] (A). The addition of a strong base (KOtBu or LiEt3BH), on the other hand, led to the formation of the 1,2dehydrochlorination product [(Cbzdiphos)RuH(CO)]. The reaction of the latter with BH3·THF at room temperature led to the 1,2-addition of the BH3 moiety to the Ru−N function, forming a RuNBH cycle in [(CbzdiphosHBH2)RuH(CO)] (B). The same borane-bridged compound was obtained when complex A was treated with NaBH4 in THF. The BH2 group forms a bridging unit between the carbazole-N atom and one of the ruthenium-bound hydrides.

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INTRODUCTION Metal complexes containing tridentate meridionally coordinating ligands, commonly referred to as pincers,1 have been studied extensively in recent years.2 Among these, ruthenium PNP pincer complexes are of special interest because of their diverse coordination chemistry and their application as catalysts in a variety of transformations.3 Inspired by the work by Milstein et al.4 a variety of different ruthenium PNP complexes have been developed that show metal ligand cooperation in the bond activation of small molecules and have been found to be active catalysts for hydrogenation and dehydrogenation reactions.5 Some of these systems have been found to form borane adducts exhibiting different binding modes of the BHx unit (complexes I−III, Figure 1). Next to their application as catalysts,6 these complexes allow the investigation of the coordination modes of borane ligands to transition metal complexes.7,8

in the formation of two stereoisomeric hydrido complexes, [(CbzdiphosH)RuHCl(CO)] (2 and 2′). The major isomer 2, could be isolated and fully characterized (Scheme 1). The Scheme 1. Synthesis of the Complexes [(CbzdiphosH)RuHCl(CO)] (2) and [(Cbzdiphos)RuH(CO)] (3)

complex contains a metal-bound hydrido ligand as well as a protic NH function at the carbazole backbone of the pincer ligand similar to previously described ruthenium species by Takasago,8 Schneider,11 and Gusev12 et al. Complex 2 was found to be thermally stable toward hydrogen elimination at 110 °C even in the presence of PPh3 as a potential donor ligand. The addition of a strong base (KOtBu or LiEt3BH), on the other hand, led to the formation of the 1,2-dehydrochlorination product [(Cbzdiphos)RuH(CO)] (3). An analogous reactivity

Figure 1. PNP-type ruthenium-based borohydride pincer complexes.6c,7,8

Recently, we reported the synthesis of a new PNP ligand, CbzdiphosH (1), and investigated its coordination chemistry in Ni, Pd, and Ir complexes.9

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RESULTS AND DISCUSSION The reaction of the precursor complex [RuHCl(CO)(PPh3)3]10 with the PNP protioligand CbzdiphosH (1)9a in toluene resulted © XXXX American Chemical Society

Received: August 12, 2015

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DOI: 10.1021/acs.organomet.5b00699 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

is observed [1.830(2) Å (2); 1.848(3) Å, (3)]. The proton at the carbazole nitrogen atom in 2 also leads to a wider angle [47.11(6)° (2); 31.0(1)° (3)] between the plane of the carbazole backbone and the CbzdiphosH-Ru coordination plane than in complex 3. In the case of complex 2 an intermolecular hydrogen-bonding interaction via the Cl and carbazole NH atoms was found, resulting in a dimeric arrangement with an H2Cl2 cycle as the centerpiece (Figure 3). This attractive interaction leads to a

of amino chlorido complexes has been reported for comparable ruthenium systems.11 Both compounds 2 and 3 were isolated and structurally characterized by X-ray diffraction (Figure 2). Crystals of complex

Figure 3. Dimeric structure of complex 2 in the solid state.

displacement of the chlorine atom from the axial position of an ideal octahedral coordination geometry toward the carbazole NH (N−Ru−Cl 81.9° and C−Ru−Cl 105.0°). An analogous dimeric aggregation was observed in the case of Schneider’s iron PNP pincer complex.13 In the IR spectra (KBr) of both complexes 2 and 3 the characteristic CO vibrational band was observed at 1933 and 1930 cm−1, while the Ru−H bands were found at 1999 and 2060 cm−1, respectively. The observed frequencies for the Ru−H vibration are well in the region of values obtained from comparable Ru−H complexes.14 When the isolated stereoisomer 2, the major product of the PNP-metalation represented in Scheme 2, was dissolved in

Figure 2. Molecular structure of complex 2 (above) and 3 (below) (thermal ellipsoids are shown at the 50% probability level; hydrogen atoms with the exception of H and H1 omitted for clarity). Principal bond lengths [Å] and angles [deg] of complex 2: Ru−H 1.68(3), Ru− Cl(1) 2.5245(5), Ru−P(1) 2.3273(5), Ru−P(2) 2.3318(5), Ru−N(1) 2.3011(17), Ru−C(48) 1.830(2), N(1)−H(1) 0.87(3), Cl(1)−Ru−H 167.8(11), P(1)−Ru−H 94.7(11), P(1)−Ru−Cl(1) 87.000(18), P(1)−Ru−P(2) 173.235(19), P(2)−Ru−H 92.1(11), P(2)−Ru− Cl(1) 86.269(18), N(1)−Ru−H 86.0(11). Complex 3: Ru−H 1.41(4), Ru−Cl(1) 2.6535(12), Ru−P(1) 2.3311(10), Ru−P(2) 2.3321(11), Ru−N(1) 2.173(2), Ru−C(48) 1.848(3), Cl(1)−Ru−H 173.3(18), P(1)−Ru−H 81.0(17), P(1)−Ru−Cl(1) 92.64(3), P(1)− Ru−P(2) 168.44(2), P(2)−Ru−H 87.5(17), P(2)−Ru−Cl(1) 98.85(3), N(1)−Ru−H 94.1(17).

Scheme 2. Equilibrium between Complex 2 and Its Stereoisomer 2′

3 were obtained by crystallization from a dichloromethane solution, resulting in a weakly bound dichloromethane molecule occupying the sixth binding site at the ruthenium center. In both compounds 2 and 3 the pincer ligand is meridionally coordinated to the ruthenium center. Similar to the previously described Ir and Ni Cbzdiphos complexes, the carbazole plane in the backbone of the ligand frame is tilted with respect to the coordination plane spanned by the donor atoms and the metal center.9b The different binding mode of the carbazole N functionality in both compounds is a key factor that affects the structural properties of complexes 2 and 3. In complex 2 the pincer ligand coordinates in its protonated neutral form, whereas in 3 it binds as an anionic ligand, leading to a significantly shorter Ru−N distance [2.301 Å (2); 2.173 Å (3)]. Notably, only a small difference in the Ru−CO bond distances trans to the carbazole-N

toluene-[D8], only one set of signals was observed in the 1H NMR spectrum, but when heated to 100 °C its partial conversion to the minor component 2′ was observed. At 110 °C a steadystate ratio of 2:2′ of 1.5:1 was reached after 24 h, which changed to 2.1:1 again when the sample was held at room temperature for 2 days. This reversible isomerization of 2 to 2′ was too slow to give rise to dynamic behavior on the NMR time scale. However, the addition of NEt3 led to a drastic enhancement of the rate of interconversion. Under these base-catalyzed conditions the chemical exchange correlation between corresponding resonances of 2 and 2′ was observable in the EXSY NMR spectrum at room temperature (see Supporting Information). B


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Organometallics The configuration of the second stereoisomer 2′ could not be established beyond doubt, and we were unable to obtain crystals of this form that were suitable for X-ray diffraction. However, in view of the base-catalyzed enhancement of the interconversion of 2 and 2′, it is most likely that they differ in the relative configuration of the NH and the RuH functionality. While in 2 both H atoms are located on the opposite sides of the coordination plane spanned by the pincer ligand (anti), they are thought to be on the same side (syn) of the ligand plane in the isomer 2′ (Scheme 2). The formation of two anti and syn isomers like 2 and 2′ has also been reported by Schneider et al. for iron PNP complexes.13 In their case the syn isomer was found to be the kinetic product of the complex formation reaction, while the anti isomer was thermodynamically favored and was slowly formed quantitatively with time. Both stereoisomers 2 and 2′ react with LiEt3BH to give complex 3. The reaction of complex 3 with BH3·THF at room temperature led to the 1,2-addition of the BH3 moiety to the Ru−N function, forming a RuNBH cycle in [(CbzdiphosHBH2)RuH(CO)] (4) (Scheme 3). The same borane-bridged

Figure 4. Molecular structure of complex 4 (thermal ellipsoids are shown at the 50% probability level; nonhydridic hydrogen atoms omitted for clarity). Principal bond lengths [Å] and angles [deg]: Ru−H 1.58(3), Ru−Ha 1.80(3), Ru····B 2.458(2), Ru−P(1) 2.3457(5), Ru− P(2) 2.3400(5), Ru−N(1) 2.2478(16), Ru−C(48) 1.826(2), B−Ha 1.33(3), B−Hb 1.14(2), B−Hc 1.08(2), Ha−Ru−H 171.0(13), P(1)− Ru−B 94.40(6), P(2)−Ru−B 88.55(6), P(2)−Ru−Ha 93.1(9), P(1)− Ru−P(2) 177.045(18), N(1)−Ru−P(1) 91.43(4), N(1)−Ru−P(2) 91.02(4).

Scheme 3. Syntheses of the Borane Complex [(CbzdiphosHBH2)RuH(CO)] (4)

The length of the B−N distance (1.594(3) Å) matches the sum of the covalent radii for a N−B single bond (1.58(2) Å),20 which indicates that there is little BN π-bond character as expected for a boron bond with a quaternary nitrogen center.21 In solution at room temperature, three 1H NMR resonances (Figure 5) can be assigned to the BH2 unit (3.00 ppm, 2H, 11B

compound was obtained when complex 2 was treated with NaBH4 in THF. Complexes bearing such an azaborametallacycle are known for early transition metals,15 but only a few examples of late transition metal complexes have been reported.16 Single crystals of compound 4 were obtained that were suitable for X-ray diffraction analysis. The ruthenium atom was found to be in a distorted octahedral environment with the phosphorus donors (P1 and P2), the N atom, and CO ligand in the equatorial plane and the two hydrogen atoms (Ha and H) in the axial position (Figure 4). The BH2 group forms a bridging unit between the carbazole-N atom and one of the ruthenium-bound hydrides (Ha). This Ru−Ha bond is elongated (1.80 Å) compared to the other Ru−H bond (1.58 Å). The Ru···B distance of 2.458(2) Å is significantly longer than the sum of the covalent radii (2.09 Å)17 and longer than those found in other bis(σ-B−H) borane ruthenium complexes.18 However, it is shorter than those of 1η-B−H σ-type complexes such as the [Ru(xantphos)(PPh3)(H3B·NH2tBu)H][BArF4].19 The Ru···B distance in 4 appears to reflect the geometric demands of the coordination mode of the BH3 unit to the Ru−N function in the complex rather than additional attractive interactions between the Ru and the B centers.

Figure 5. Variable-temperature 1H NMR spectra of complex 4 (400 MHz, 230−360 K in toluene-d8). At 230 K the 1H NMR peak of the BH2 unit is superimposed with the one of the tBu groups.

decoupled) as well as the ruthenium-bound hydrides (−4.50 ppm (Ha) and −10.46 ppm (H)). The chemical shifts of both the BH2 and RuH signals are within the region of comparable compounds.22 A variable-temperature 1H NMR study was performed to investigate the dynamic behavior of the exchange of the Ha by Hb/Hc via the rotation of the BH3 unit around the B−N bond (see Supporting Information). At room temperature and below the exchange was slow, and the high-temperature limit of the exchange was not reached even at 420 K (dichlorobenzene). Nevertheless, the chemical exchange peak between the Ha resonance and the BH2 proton signal observed in the EXSY experiment was used to determine the activation barrier of ΔG# = 70 ± 1 kJ mol−1 for the hydrogen exchange process at 295 K (see Supporting Information). The value for the activation barrier was found to be comparable to those reported for azaborametallacycles (ΔG# = 48−71 kJ mol−1).15a,b C


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Organometallics

a versatile reactivity from these new ruthenium Cbzdiphos complexes.

Furthermore, the assignments of Ha−c and the RuH resonances of complex 4 were verified by the preparation and analysis of the partially deuterated complex 4-D3 (Figure 6). The

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EXPERIMENTAL SECTION

General Experimental Procedures. All manipulations were carried out under an inert atmosphere of dry argon (Argon 5.0, purchased from Messer Group GmbH and dried over Granusic granulated phosphorus pentoxide) using standard Schlenk techniques or by working in a glovebox. Solvents were dried according to literature procedures23 and stored in glass ampules under an argon atmosphere. Et2O and n-pentane were distilled from sodium/potassium alloy. nHexane was distilled from potassium; CH2Cl2, from calcium hydride; and toluene, from sodium. The same procedures were used to dry the deuterated solvents. Degassed solvents were obtained by three successive freeze−pump−thaw cycles. The ligand CbzdiphosH was synthesized according to the literature.9a All other chemicals were purchased and used as received without further purification. NMR spectra were recorded on Bruker Avance III (600 MHz) and Bruker Avance II (400 MHz) instruments. Chemical shifts (δ) are given in parts per million (ppm) and are referenced to residual proton or the carbon resonance solvent signals.24 H3PO4 (31P) was used as an external standard. The following abbreviations were used: s (singlet), d (doublet), t (triplet), m (multiplet), br (broad signal), vt (virtual triplet). Mass spectra were acquired on a JEOL JMS-700 magnetic sector (LIFDI) spectrometer at the mass spectrometry facility of the Institute of Organic Chemistry, the University of Heidelberg. IR elemental analysis was carried out in the Microanalysis Laboratory of the Heidelberg Chemistry Department. Synthetic Protocols and Characterization Data. Preparation of [PNP] RuHCl(CO) (2). RuHClCO(PPh3)3 (476.2 mg, 0.50 mmol) was added to a solution of [PNP] [PNP = 3,6-di-tert-butyl-1,8-bis((diphenylphosphino)methyl)-9H-carbazole−Cbzdiphos-H] protioligand (357.9 mg, 0.53 mmol) in 20 mL of toluene, and the solution was stirred at 110 °C overnight. After the solvent was removed under a reduced pressure, the crude product was washed with a mixture of toluene and n-pentane (4:1) to give the product as a white solid. The crude product was recrystallized from CH2Cl2/hexane at −34 °C to give complex 2 as a crystalline solid (345.3 mg, 0.41 mmol, 82%). 1H NMR (600.1 MHz, CD2Cl2, rt): δ (ppm) −14.9 (t, 1H, JPH = 15.4 Hz, Ru−H), 1.16 (s, 18H, C(CH3)3), 3.70−3.73 (m, 2H, CH2), 4.43 (d, 2H, 2JHH = 12.5 Hz, CH2), 6.74 (s, 2H, CHCarb‑2), 7.22 (t, 4H, 3JHH = 7.4 Hz, CHm‑Ph), 7.30 (s, 2H, 3JHH = 7.3 Hz, CHp‑Ph), 7.41−7.42 (m, 6H, CHm‑Ph, CHp‑Ph), 7.53−7.56 (m, 5H, CHo‑Ph, N−H), 7.70−7.74 (m, 6H, CHo‑Ph, CHCarb‑4). 13C NMR (150.9 MHz, CD2Cl2, rt): δ (ppm) 31.6 (s, C(CH3)3), 32.3 (vt, CH2), 34.9 (s, C(CH3)3), 115.8 (s, CHCarb‑4), 123.0 (s, CCarb‑1), 127.0 (vt, CHCarb‑2), 128.3 (vt, CHm‑Ph), 128.4(vt, CHm‑Ph), 129.2 (s, CCarb‑4a), 130.0 (s, CHp‑Ph), 130.8 (s, CHp‑Ph), 132.5 (vt, CHo‑Ph), 132.7 (vt, CPh), 134.6 (vt, CHo‑Ph), 135.8 (vt, CPh), 143.8 (vt, CCarb‑9a), 149.0 (s, CCarb‑3), 204.9 (vt, CO). 31P{1H} NMR (242.9 MHz, C 6 D6 , rt): δ (ppm) 60.0. MS (LIFDI): m/z (%) calcd for C47H48ClNOP2Ru 841.2, found 841.2 (100) ([M]+). We were unable to detect the molecular ion peak by other HR-MS methods. Anal. Calcd for C47H48ClNOP2Ru+CH2Cl2: C, 62.24; H, 5.44; N, 1.51. Found: C, 61.95; H, 5.41; N, 1.48. Partial Isomerization of Complex 2. A sample of complex 2 (5 mg) in 0.5 mL of toluene-d8 was heated to 100 °C for 5 h and subsequently analyzed by NMR spectroscopy. 1H NMR (600.1 MHz, toluene-d8, rt): δ (ppm) −13.26 (t, 1H, JPH = 19.2 Hz, Ru−H), 1.35 (s, 18H, C(CH3)3), 3.62−3.65 (m, 2H, CH2), 4.04−4.06 (m, 2H, CH2), 6.79−6.81 (m, 4H, CHph), 6.83−6.85 (m, 4H, CHPh), 6.98−7.08 (m, 4H, CHCarb‑2, CHPh), 7.11−7.14 (m, 2H, CHPh), 7.19−7.22 (m, 4H, CHPh), 7.83 (s, 1H, N− H), 8.03 (s, 2H, CHCarb‑4), 8.19−8.22 (m, 4H, CHPh). 13C NMR (150.9 MHz, toluene-d8, rt): δ (ppm) 31.9 (s, C(CH3)3), 32.5 (vt, CH2), 34.9 (s, C(CH3)3), 115.7 (s, CHCarb‑4), 123.5 (s, CCarb‑1), 127.7 (vt, CHCarb‑2), 127.8 (vt, CHPh), 128.6 (vt, CHPh), 129.4 (s, CCarb‑4a), 130.0 (s, CHPh), 130.2 (s, CHPh), 132.6 (t, CHPh), 133.5 (vt, CHPh), 135.5 (vt, CPh), 135.9 (vt, CHPh), 144.5 (s, CCarb‑9a), 147.4 (s, CCarb‑3), 205.1 (vt, CO). 31 1 P{ H} NMR (242.9 MHz, toluene-d8, rt): δ (ppm) 55.89.

Figure 6. 2H NMR spectra of complexes 4-D4 (above) and 4-D3 (middle) as well as the 1H NMR spectrum of complex 4 (below).

reaction of [(CbzdiphosH)RuHCl(CO)] (2) with NaBD4 led to the formation of [(CbzdiphosDBD2)RuHCl(CO)] (4-D3). The 2 H NMR spectrum of 4-D3 in toluene displayed two sharp B−D resonances with relative integrals of 1 to 2 at −4.57 and 3.00 ppm, respectively. In addition, the formation of 4-D3 was confirmed by mass spectrometric analysis (LIFDI). The IR spectrum (CH2Cl2) of complex 4 shows two bands at 2460 and 2378 cm−1, which were assigned to the asymmetric and the symmetric stretching vibration of the bridging BH2 unit by comparing the experimental data to the frequency analysis of the DFT-optimized structure (DFT B3LYP/def2TZVP; see Supporting Information). Accordingly, these vibrational bands were shifted in the spectra of the deuterated complexes 4-D3 and 4-D4 (as well as isotopomers of partially deuterated species, Scheme 4) to the region of 1853 to 1756 cm−1. The terminal Ru−H and the stretching resonance of complex 4 appear to be overlapping with the CO band at 1940 cm−1. Scheme 4. Syntheses of the Deuterated Borohydrido Complex [(CbzdiphosDBD2)RuHCl(CO)] (4-D3) and [(CbzdiphosDBD2)RuDCl(CO)] (4-D4)

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CONCLUSION In this first report on ruthenium hydrido complexes bearing the carbazole-based PNP ligand developed in our group the addition of a BH3 unit to the hydrido complex 3 led to the formation of a rare borane-bridged adduct, which is the first late transition metal derivative of this type that could be structurally characterized by X-ray diffraction analysis. In view of these results, one can expect D


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Organometallics Preparation of [PNP] RuH(CO) (3). To a solution of 2 (84 mg, 0.10 mmol) in THF was added LiEt3BH (1.1 equiv, 0.11 mmol) at −78 °C. After 10 min, the cooling bath was removed and the reaction was stirred overnight. After removal of the solvents, the residue was treated with a toluene/pentane mixture (4:1) and the suspension was filtered through a pad of Celite. The solvents of the filtrate were removed, and the crude product was recrystallized from CH2Cl2/pentane at −34 °C to give complex 3 as a crystalline solid (72 mg, 0.089 mmol, 90%). 1H NMR (399.9 MHz, CD2Cl2, rt): δ (ppm) −17.52 (m, 1H, JPH = 15.4 Hz, Ru− H), 1.44 (s, 18H, C(CH3)3), 3.66−3.70 (m, 2H, CH2), 4.11−4.17 (m, 2H, CH2), 7.33 (s, 2H, CHCarb‑2), 7.37−7.40 (m, 6H, CHm‑Ph), 7.48− 7.49 (m, 6H, CHm‑Ph, CHp‑Ph), 7.82−7.89 (m, 8H, CHo‑Ph), 7.92 (m, 2H, CHCarb‑4). 13C NMR (100.6 MHz, CD2Cl2, rt): δ (ppm) 32.2 (s, C(CH3)3), 32.4 (vt, CH2), 34.6 (s, C(CH3)3), 114.8 (s, CHCarb‑4), 119.1 (s, CCarb‑1), 124.6 (vt, CHCarb‑2), 125.8 (s, CCarb‑4a), 128.8 (vt, CHm‑Ph), 129.0 (vt, CHm‑Ph), 130.3 (s, CHp‑Ph), 130.6 (s, CHp‑Ph), 132.9 (vt, CHo‑Ph), 133.6 (vt, CHo‑Ph), 134.5 (vt, CPh), 136.7 (vt, CPh), 139.4 (s, CCarb‑3), 150.0 (vt, CCarb‑9a), 203.8 (vt, CO). 31P{1H} NMR (161.9 MHz, toluene-d8, rt): δ (ppm) 46.8 (s). MS (LIFDI): m/z (%) calcd for C47H47NOP2Ru 805.2, found 805.2 (100) ([M]+). We were unable to detect the molecular ion peak by other HR-MS methods. Anal. Calcd for C48H49Cl2NOP2Ru: C, 64.79; H, 5.55; N, 1.57. Found: C, 64.36; H, 5.64; N, 1.55. Preparation of [PNP] RuHBH2CO (4). To a solution of 2 (42 mg, 0.05 mmol) in THF was added a solution of NaBH4 (9.5 mg, 0.25 mmol) in THF (3.0 mL), and the reaction mixture was stirred at room temperature overnight. After removal of the solvents, the residue was treated with a toluene/pentane mixture (4:1) and the suspension was filtered through a pad of Celite. The solvents of the filtrate were removed, and the crude product was recrystallized from CH2Cl2/hexane at −34 °C to give complex 4 as a crystalline solid (39 mg, 0.047 mmol, 93%). 1H NMR (399.9 MHz, C6D6, rt): δ (ppm) −10.3 (t, JHP = 17.4 Hz, 1H, Ru−H), − 4.35 (br, 1H, Ru−H−B), 1.26 (s, 18H, C(CH3)3), 3.17 (br, 2H, BH2), 3.34−3.40 (m, 2H, CH2), 4.78 (d, 2JHH = 13.5 Hz, 2H, CH2), 6.82−6.90 (m, 8H, CHCarb‑2, CHm‑Ph), 7.01−7.07 (m, 6H, CHm‑Ph, CHp‑Ph), 7.69−7.81 (m, 10H, CHo‑Ph, CHCarb‑4), 13C NMR (100.6 MHz, CD2Cl2, rt): δ (ppm) 31.7 (s, C(CH3)3), 31.8 (vt, CH2), 34.7 (s, C(CH3)3), 115.3 (s, CHCarb‑4), 122.2 (s, CCarb‑1), 127.9 (s, CHCarb‑2), 128.4 (vt, CHm‑Ph), 128.9 (vt, CHm‑Ph), 129.2 (s, CCarb‑4a), 130.1 (s, CHp‑Ph), 130.5 (s, CHp‑Ph), 132.5 (vt, CHo‑Ph), 133.8 (vt, CHo‑Ph), 134.0 (vt, CPh), 137.3 (vt, CPh), 146.5 (s, CCarb‑3), 150.5 (vt, CCarb‑9a), 204.9 (vt, CO). 31P{1H} NMR (161.9 MHz, C6D6, rt): δ (ppm) 53.7. 11B{1H} NMR (128.3 MHz, o-C6D4Cl2, 420 K): δ (ppm) −20.8. MS (LIFDI): m/z (%) calcd for C47H50BNOP2Ru 819.3, found 819.3 (100) ([M]+). We were unable to detect the molecular ion peak by other HR-MS methods. Anal. Calcd for C47H50BNOP2Ru: C, 68.95; H, 6.16; N, 1.71. Found: C, 68.83; H, 6.25; N, 1.68. X-ray Crystal Structure Determinations. Crystal data and details of the structure determinations are compiled in Table S1 (Supporting Information). Full shells of intensity data were collected at low temperature with a Bruker AXS Smart 1000 CCD diffractometer (Mo Kα radiation, sealed X-ray tube, graphite monochromator; compound 3) and an Agilent Technologies Supernova-E CCD diffractometer (Mo Kα radiation, microfocus X-ray tube, multilayer mirror optics; compounds 2 and 4). Data were corrected for air and detector absorption and Lorentz and polarization effects;25,26 absorption by the crystal was treated numerically (Gaussian grid; compounds 2 and 4)26,27 or with a semiempirical multiscan method (compound 3).28,29 The structures were solved by the charge flip procedure30 and refined by fullmatrix least-squares methods based on F2 against all unique reflections.31 All non-hydrogen atoms were given anisotropic displacement parameters. Hydrogen atoms were generally input at calculated positions and refined with a riding model. The positions of some hydrogen atoms (those on N, Ru, and B) were taken from difference Fourier syntheses and fully refined. Disordered solvent of crystallization (methylene chloride) in the structure of 2 was subjected to suitable geometry and adp restraints. Computational Study. DFT calculations were performed using the Gaussian 09, revision D.01,32 software package on the bwforcluster JUSTUS. The geometry optimization and the harmonic frequency

analysis were carried out at the B3LYP33/def2TZVP34 level of theory using the “tight” convergence criteria for SCF calculations.

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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.5b00699. Additional experimental and spectroscopic details (PDF) Crystallographic data (CIF) Chemical structure (XYZ)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Overseas Study Program of Guangzhou Elite Project (JY201311) for financial support. We acknowledge funding by the Deutsche Forschungsgemeinschaft (Ga 488/9-1). We are grateful for the generous computational resources provided by the bwForCluster JUSTUS, funded by the Ministry of Science, Research and Arts and the Universities of the State of Baden-Württemberg, Germany, within the framework program bwHPC-C5.

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REFERENCES

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