Tris(boratabenzene) Lanthanum Complexes: Synthesis, Structure, and

Article pubs.acs.org/Organometallics

Tris(boratabenzene) Lanthanum Complexes: Synthesis, Structure, and Reactivity Chunhong Wang, Xuebing Leng, and Yaofeng Chen* State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, P. R. China S Supporting Information *

ABSTRACT: A series of tris(boratabenzene) lanthanum complexes were synthesized and structurally characterized. Salt elimination of anhydrous LaCl3 with Li[C5H5BR] (R = H, NEt2) provided tris(boratabenzene) lanthanum complexes [C5H5BH]3LaLiCl (1) and [C5H5BNEt2]3LaLiCl(THF) (2) in high yields. Hydroboration of 1-hexene or 3-hexyne with 1 gave the alkyl- or alkenyl-functionalized boratabenzene lanthanum complexes, [C5H5B(CH2)5CH3]3LaLiCl(THF) (3) and [C5H5BC(C2H5) CH(C2H5)]3LaLiCl(THF) (4), in good yields. Hydroboration of N,N′-diisopropylcarbodiimide with 1 gave the monohydroboration product [C5H5BN(iPr)CHN(iPr)][C5H5BH]2La (5) due to the steric bulk of the [C5H5BN(iPr)CHN(iPr)]− ligand. Complex 5 can undergo further hydroboration with 3-hexyne or dehydrogenative coupling with phenyl acetylene to afford [C5H5BN(iPr)CHN(iPr)][C5H5BC(C2H5)CH(C2H5)]2La (6) or [C5H5BN(iPr)CHN(iPr)][C5H5BCCPh)]2La (7).

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INTRODUCTION

RESULTS AND DISCUSSION Synthesis. Anhydrous LaCl3 and Li[C5H5BH] or Li[C5H5BNEt2] were heated at 75 °C in THF. After 1 week, THF was removed under vacuum, and the residue was extracted with toluene. Removal of the solvent of the extract gave tris(boratabenzene) lanthanum complex [C5H5BH]3LaLiCl (1) (82% yield) or [C5H5BNEt2]3LaLiCl(THF) (2) (83% yield) (Scheme 1). Reaction of anhydrous LaCl3 with Li[C5H5BOiPr] was also carried out. However, no identified product was obtained. Attempts to obtain the alkali-metal free

Boratabenzenes are heterocyclic, 6π-electron aromatic anions that have been introduced into organometallic chemistry as counterparts of Cp-type ligands with poorer electron-donating properties.1 A larger number of transition-metal complexes bearing boratabenzenes, in particular, the derivatives of Group 4, 6, and 8 metals, have been reported.2 On the other hand, only a handful of examples of boratabenzene derivatives of rareearth metals have been synthesized before 2007, and most of them are chloride derivatives.3 It was surprising, considering the wide use of Cp-type ligands in the organometallic chemistry of rare-earth metals. Therefore, our group carried out a study to investigate if boratabenzenes are as powerful ligands as Cp-type ligands in the synthesis of various types of rare-earth organometallic complexes. We were able to synthesize a series of bis(boratabenzene) trivalent rare-earth metal chlorides, amides and alkyl complexes,4 bis(boratabenzene) divalent rare-earth metal complexes,5 mono(boratabenzene) rare-earth metal dialkyl complexes,6 amidino-boratabenzene rare-earth metal complexes,7 and ansa-heteroborabenzene divalent ytterbium complexes,8 some of which show interesting reactivity.4c,d,5,6,8 Herein, we report the synthesis, structural characterization, and reactivity of tris(boratabenzene) lanthanum complexes. These complexes represent the first examples of the transition-metal complexes in which one metal ion is coordinated by three boratabenzenes. © XXXX American Chemical Society

Scheme 1. Synthesis of Complexes 1−5

Received: March 26, 2015

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DOI: 10.1021/acs.organomet.5b00262 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

complex [C 5 H 5 BN( i Pr)CHN( i Pr)][C 5 H 5 BCCPh)][C5H5BH]La (8), which contains three different boratabenzenes, by controlling the molar ratio of 5 to phenyl acetylene were unsuccessful. The reaction gave a mixture of 5, 7, and 8. It was known that tris(cyclopentadienyl) rare-earth metal complexes may undergo addition reaction with unsaturated substrates through the metal−carbon bond.9 For example, the reaction of [C5H5]3Y with N,N′-diisopropylcarbodiimide gives a functionalized Cp ligand with an amidinate fragment linked to the aromatic ring through the C−C bond via the addition of the Y−C(cp) bond to the NCN unit.9a The tris(1-H-boratabenzene) lanthanum complex undergoes hydroboration reaction through the B−H bond rather than an addition reaction through the metal−carbon bond, indicating that the B−H bond is more reactive than the La−C(Boratabenzene) bond of the complex. Reaction of complex 5 with 3-hexyne provides the hydroboration product, but that with phenyl acetylene gives the dehydrogenative coupling product, presumably due to the greater acidity of the terminal acetylene. Crystal Structures. Recrystallization of 1 in a mixture of THF and toluene gave single crystals suitable for X-ray diffraction analysis. X-ray diffraction analysis revealed that it is a THF solvated discrete cation−anion pair [Li(THF)4][(C5H5BH)3La(μ-Cl)La(C5H5BH)3] (1′). Complex 1 perhaps exits as a dimer and contains a [LiClLi]+ unit, and the LiCl elimination occurs during recrystallization of 1 to afford 1′ due to coordination of THF to the lithium ion. There are two crystallographically independent molecules in the unit cell of 1′; the ORTEP diagram of the [(C5H5BH)3La(μ-Cl)La(C5H5BH)3]− anion in molecule one is shown in Figure 1. Each lanthanum ion is coordinated by three [C5H5BH]− ligands, and two [C5H5BH]3La fragments are bridged by a chloride to form the [(C5H5BH)3La(μ-Cl)La(C5H5BH)3]−

tris(boratabenzene) complexes by the sublimation of complexes 1 and 2 under vacuum failed. Our previous study disclosed the hydroboration of unsaturated substrates with 1-H-boratabenzene metal complexes to access new boratabenzene complexes.4c Herein, this strategy was employed for the synthesis of new tris(boratabenzene) lanthanum complexes from 1. Hydroboration of 1hexene or 3-hexyne with 1 in a toluene−THF mixture at 75 °C for 3 days gave the corresponding hydroboration product [C 5 H 5 B(CH 2 ) 5 CH 3 ] 3 LaLiCl(THF) (3) (81% yield) or [C 5 H 5 BC(C 2 H 5 )CH(C 2 H 5 )] 3 LaLiCl(THF) (4) (79% yield) (Scheme 1). Complexes 3 and 4 are alkyl- and alkenylfunctionalized boratabenzene complexes, respectively. Hydroboration of N,N′-diisopropylcarbodiimide with 1 provided [C5H5BN(iPr)CHN(iPr)][C5H5BH]2La (5) in 83% yield. In the reaction, one 1-H-boratabenzene was functionalized into amidino-boratabenzene, while the other two remained intact. The addition of excess N,N′-diisopropylcarbodiimide to 1 did not yield the complex [C5H5BN(iPr)CHN(iPr)]2[C5H5BH]La or [C5H5BN(iPr)CHN(iPr)]3La even after 1 week, which can be attributed to the steric bulk of the [C5H5BN(iPr)CHN(iPr)]− ligand. As 5 has two 1-H-boratabenzenes, it can be further functionalized into new boratabenzene complexes, as shown in Scheme 2. Complex 5 reacted with 3-hexyne in Scheme 2. Hydroboration or Dehydrogenative Coupling with Complex 5

Figure 1. ORTEP diagram of the [(C 5 H 5 BH) 3 La(μ-Cl)La(C5H5BH)3]− anion with thermal ellipsoids set at 30% probability. Hydrogen atoms have been omitted for clarity. Selected bond distances [Å] and angles [deg]: La1−Cl1 2.821(3), La1−B1 3.052(13), La1−C1 2.993(12), La1−C2 2.988(11), La1−C3 2.920(12), La1−C4 2.921(11), La1−C5 2.979(11), La1−B2 3.088(14), La1−C6 2.998(11), La1−C7 2.934(11), La1−C8 2.924(11), La1−C9 3.003(11), La1−C10 3.002(11), La1−B3 3.032(13), La1−C11 2.988(15), La1−C12 2.955(15), La1−C13 2.951(12), La1−C14 2.968(13), La1−C15 2.956(14), La2−Cl1 2.818(3), La2−B4 3.098(14), La2−C16 3.018(11), La2−C17 2.929(11), La2−C18 2.883(11), La2−C19 2.960(13), La2−C20 3.001(11), La2−B5 3.048 (15), La2−C21 3.024 (12), La2−C22 2.962(14), La2−C23 2.899(11), La2−C24 2.968(12), La2−C25 2.967(13), La2−B6 3.120(15), La2−C26 3.006 (13), La2−C27 2.953(13), La2−C28 2.889(11), La2−C29 2.944(11), La2−C30 3.019 (11), La1−Cl1−La2 162.43(12).

toluene to give the corresponding hydroboration product [C5H5BN(iPr)CHN(iPr)][C5H5BC(C2H5)CH(C2H5)]2La (6) in 75% yield. The reaction is slow, requiring long reaction times (4 days) and a high reaction temperature (110 °C) to complete the reaction. The reaction of 5 with 1-hexene is even slower, and was not complete after 1 week. Reaction of 5 with terminal alkyne phenyl acetylene did not afford the hydroboration product but a dehydrogenative coupling product [C5H5BN(iPr)CHN(iPr)][C5H5BCCPh)]2La (7) in 95% yield. Such dehydrogenative coupling is interesting, as it can be potentially used for the synthesis of metallopolymers featuring boratabenzenes with the −CC− unit as the linkage or part of the linkage.2l Efforts to synthesize lanthanum B


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Organometallics anion. Slippage of the lanthanum ion away from the boron atom results in long La−B distances (3.032(13)−3.120(15) Å), and the lanthanum ion is closer to the para carbon atoms than to the ortho carbon atoms. This structural feature is similar to that observed for [C5H5BH]2YCl, but significantly different from [C5H5BH]Rh(COD), where the distances from the rhodium ion to the boron atom (2.277(12) Å) and to the para carbon atom (2.278(15) Å) are almost the same.4c The La− C(boratabenzene) bond lengths of 1′ are in the range of 2.883(11)−3.024(12) Å. The La1−Cl1 and La2−Cl1 bond lengths are 2.821(3) and 2.818(3) Å, respectively, and the La1−Cl1−La2 angle is 162.43(12)°. Single crystals of 5 and 7 suitable for X-ray diffraction analysis were grown from the toluene−hexane mixture solutions. ORTEP diagrams of 5 and 7 are shown in Figures 2 and 3, respectively. Complex 5 is a mononuclear complex; the

Figure 3. ORTEP diagram of 7 with thermal ellipsoids set at 30% probability. Hydrogen atoms have been omitted for clarity. Selected bond distances [Å] and angles [deg]: La1−B1 3.020(10), La1−C1 2.997(8), La1−C2 2.982(8), La1−C3 2.980(9), La1−C4 3.046(8), La1−C5 3.026(9), La1−B2 3.132(11), La1−C6 3.040(8), La1−C7 2.954(8), La1−C8 2.926(8), La1−C9 2.962(8), La1−C10 3.021(9), La−N1 2.544(6), La−B3 2.962(10), La1−C11 2.967(8), La1−C12 2.992(7), La1−C13 2.967(7), La1−C14 2.999(8), La1−C15 2.972(8), B3−N2 1.519(12), C32−N1 1.324(10), C32−N2 1.317(9), B1−C16 1.557(15), B2−C24 1.564(15), C16−C17 1.205(13), C24−25 1.208(13); B1−C16−C17 171.8(1), B2−C24−C25 176.7(1), C16− C17−C18 176.8(1), C24−C25−C26 178.8(1).

It is noteworthy that the bonding mode of the boratabenzene ring of the [C5H5BN(iPr)CHN(iPr)]− ligand is different from that of the [C5H5BH]− ligand. The distance from the lanthanum ion to the para carbon atom (2.947(2) Å) is similar to those to the ortho carbon atoms (2.958(2) and 2.966(2) Å); the La−B3 bond length (2.953(2) Å) is much shorter than the La−B1 and La−B2 bond lengths (3.112(14) and 3.043(3) Å). For complex 7, the C16−C17 and C24−25 bond lengths (1.205(13) and 1.208(13) Å) are consistent with those of the C−C triple bonds, whereas the B1−C16 and B2−C24 bond lengths (1.557(15) and 1.564(15) Å) display single-bond character. Accordingly, the B1−C16−C17 (171.8(1)°), B2− C24−C25 (176.7(1)°), C16−C17−C18 (176.8(1)°), and C24−C25−C26 (178.8(1)°) angles are close to 180°. Other structural features of 7 are similar to those of 5 and will not be discussed in detail.

Figure 2. ORTEP diagram of 5 with thermal ellipsoids set at 30% probability. Hydrogen atoms have been omitted for clarity. The [B1C1-C2-C3-C4-C5] boratabenzene ring is disordered over two positions, and only one is shown. Selected bond distances [Å]: La− B1 3.112 (14), La−C1 3.014(14), La−C2 2.976(14), La−C3 2.953(15), La−C4 3.025(16), La−C5 3.012(22), La−B2 3.043 (3), La−C6 3.007(3), La−C7 2.999(2), La−C8 2.960(2), La−C9 2.971(2), La−C10 3.015(2), La−B3 2.953(2), La−C11 2.958(2), La−C12 2.983(2), La−C13 2.947(2), La−C14 2.988(2), La−C15 2.966(2), La−N2 2.557(2), B3−N1 1.513(3), C16−N1 1.327(3), C16−N2 1.313(3).

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CONCLUSIONS A series of tris(boratabenzene) lanthanum complexes were synthesized via the salt elimination of anhydrous LaCl3 with lithium salts of boratabenzene, the hydroboration of unsaturated substrates with the 1-H-boratabenzene lanthanum complex, or the dehydrogenative coupling of terminal alkyne with the 1-H-boratabenzene lanthanum complex. The boron substituents of the synthesized tris(boratabenzene) lanthanum complexes include hydrogen, alkyl, alkenyl, alkynyl, and amidino. The hydroboration and dehydrogenative coupling strategies provided the complexes containing two different kinds of boratabenzenes, which are difficult to be synthesized by the salt elimination method.

lanthanum ion is coordinated by one [C5H5BN(iPr)CHN(iPr)]− ligand and two [C5H5BH]− ligands. The coordination fashion between the lanthanum ion and the [C5H5BH]− ligands in 5 is very similar to that in 1′; the lanthanum ion slips away from the boron atom and toward the para carbon atom. The [C5H5BN(iPr)CHN(iPr)]− ligand coordinates to the lanthanum ion through both the boratabenzene ring and one amidinate nitrogen, showing a similar constrained geometry to that observed for the linked amido-cyclopentadienyl ligands [C5R4SiMe2NR′]2− (R = Me, H)10 and its boratabenzene analogue [4-(SiMe2N(tBu))C5H5BN(iPr)2]2−.11 The amidinate fragment displays a delocalized electronic frame. The C16−N1 and C16−N2 bond lengths (1.327(3) and 1.313(3) Å) are intermediate between those of typical single and double bonds, and the C17, N1, C16, N2, and C20 atoms are coplanar. This plane is nearly perpendicular to the boratabenzene ring with a dihedral angle of 88°, thus offering a minimum overlap between the π orbitals of the amidinate and those of the boratabenzene.

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EXPERIMENTAL SECTION

General. All operations were carried out under an atmosphere of argon using Schlenk techniques or in a nitrogen-filled glovebox. Toluene, THF, hexane, C6D6, and THF-d8 were dried over Na/K C


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Organometallics

°C): δ (ppm) 139.4, 134.2, 112.4, 73.0, 33.6, 32.7, 29.0, 25.6, 23.4, 22.9, 14.6. 11B NMR (128 MHz, C6D6, 25 °C): δ (ppm) 42.4. Anal. Calcd for C37H62B3ClLaLiO: C, 60.33; H, 8.48. Found: C, 60.41; H, 8.68.

alloy, transferred under vacuum, and stored in the glovebox. [C5H5BH]Li and [C5H5BNEt2]Li were prepared as we previously reported.4a,c 1-Hexene and 3-hexyne were dried over CaH2 and transferred under vacuum. Phenyl acetylene and N,N′-diisopropylcarbodiimide were dried over 4 Å molecular sieves and degassed by three freeze−pump−thaw cycles before use. 1H NMR and 13C NMR spectra were recorded on a VARIAN Mercury 300 or 400 MHz spectrometer at 300 or 400 MHz, and 75 or 100 MHz, respectively. 11B NMR spectra were recorded on a Bruker DXP 400 MHz spectrometer at 128 MHz. All chemical shifts were reported in δ units with references to the residual solvent resonance of the deuterated solvents for proton and carbon chemical shifts, to external BF3·OEt2 for boron chemical shifts. Elemental analysis was performed by the Analytical Laboratory of Shanghai Institute of Organic Chemistry. Synthesis of [C5H5BH]3LaLiCl (1). [C5H5BH]Li (371 mg, 4.42 mmol) and LaCl3 (357 mg, 1.46 mmol) were mixed in 15 mL of THF, and the reaction mixture was stirred for 7 days at 75 °C. The volatiles of the reaction mixture were removed in vacuo, and the residue was extracted with 3 × 5 mL of toluene. Removal of the solvent of the extract in vacuo gave 1 as a white solid (500 mg, 82% yield). 1H NMR (300 MHz, THF-d8, 25 °C): δ (ppm) 7.36 (t, 3JH−H = 8.7 Hz, 6H; H2), 6.60 (dd, 3JH−H = 9.0 Hz, 3JH−H(B) = 3.9 Hz, 6H; H1), 6.30 (t, 3 JH−H = 6.9 Hz, 3H; H3), 5.75−4.45 (br, 3H; H4). 13C NMR (75 MHz, THF-d8, 25 °C): δ (ppm) 140.7, 132.2, 115.4. 11B NMR (128 MHz, THF-d8, 25 °C): δ (ppm) 32.3. Anal. Calcd (%) for C15H18B3LaLiCl: C, 43.72; H, 4.40. Found: C, 43.60; H, 4.31.

Synthesis of [C5H5BC(C2H5)CH(C2H5)]3LaLiCl(THF) (4). Following the procedure described for 3. Reaction of 1 (100 mg, 0.24 mmol) with 3-hexyne (199 mg, 2.42 mmol) for 3 days at 75 °C gave 4 as a yellow oil (140 mg, 79% yield). 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) 7.20 (t, 3JH−H = 8.4 Hz, 6H; H2), 6.92 (d, 3JH−H = 9.2 Hz, 6H; H1), 6.13 (t, 3JH−H = 6.8 Hz, 3H; H3), 6.10 (t, 3JH−H = 7.6 Hz, 3H; H4), 3.47 (m, 4H; OCH2CH2 of THF), 2.60 (quart, 3JH−H = 7.6 Hz, 6H; BCCH 2 CH 3 ), 2.32 (quint, 3 J H−H = 7.6 Hz, 6H; BCCHCH2CH3), 1.33 (m, 4H; OCH2CH2 of THF), 1.24 (t, 3JH−H = 7.6 Hz, 9H; BCCH2CH3), 1.16 (t, 3JH−H = 7.6 Hz, 9H; BCCHCH2CH3) . 13C NMR (100 MHz, C6D6, 25 °C): δ (ppm) 147.0, 140.6, 138.0, 130.9, 112.3, 72.2, 25.6, 24.0, 22.3, 15.8, 15.1. 11B NMR (128 MHz, C6D6, 25 °C): δ (ppm) 38.0. Anal. Calcd (%) for C37H56B3ClLaLiO: C, 60.83; H, 7.73. Found: C, 61.30; H, 7.82.

Synthesis of [C5H5BNEt2]3LaLiCl(THF) (2). Following the procedure described for 1. Reaction of [C5H5BNEt2]Li (232 mg, 1.50 mmol) with LaCl3 (123 mg, 0.50 mmol) for 7 days at 75 °C gave 2 as an orange oil (290 mg, 83% yield). 1H NMR (300 MHz, C6D6, 25 °C): δ (ppm) 7.17 (t, 3JH−H = 7.2 Hz, 6H; H2), 5.99 (d, 3JH−H = 10.2 Hz, 6H; H1), 5.71 (br, 3H; H3), 3.56 (m, 4H; OCH2CH2 of THF), 3.35 (br, 6H; NCH2), 3.10 (br, 6H; NCH2), 1.34 (m, 4H; OCH2CH2 of THF), 1.20 (t, 3JH−H = 7.2 Hz, 18H; NCH2CH3). 13C NMR (75 MHz, C6D6, 25 °C): δ (ppm) 141.5, 116.9, 102.4, 72.8, 42.9, 25.7, 16.2. 11B NMR (128 MHz, C6D6, 25 °C): δ (ppm) 32.1. Anal. Calcd for C31H53B3LaN3OLiCl: C, 53.38; H, 7.66. Found: C, 54.85; H, 7.77. A satisfactory elemental analysis result for 2 could not be obtained. There are small amounts of impurities, which show signals at 0.8−1.0 ppm in the 1H NMR spectrum. As 2 is an oil, the impurities could not be removed by recrystallization. The NMR (1H, 13C, 11B) spectra of the complex are provided as the Supporting Information.

Synthesis of [C5H5BN(iPr)CHN(iPr)][C5H5BH]2La (5). A toluene solution of N,N′-diisopropylcarbodiimide (420 mg, 3.33 mmol in 4 mL of toluene) was added to 1 (275 mg, 0.67 mmol) in 1 mL of THF, and the reaction mixture was stirred for 8 h at 75 °C. The volatiles of the reaction mixture were removed in vacuo, and the residue was extracted with 2 × 2 mL of toluene. Removal of the solvent of the extract in vacuo gave a yellow residue. The residue was washed with 2 × 1 mL of hexane and dried in vacuo to afford 5 as a yellow solid (275 mg, 83% yield). 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) 7.44 (t, 3 JH−H = 7.2 Hz, 2H; H6), 7.27 (t, 3JH−H = 8.0 Hz, 4H; H2), 7.26 (s, 1H; H8), 7.16−7.00 (br, 4H, H1), 6.42−6.36 (m, 4H; H3 and H5), 6.32 (t, 3 JH−H = 7.2 Hz, 1H, H7), 3.09 (sept, 3JH−H = 6.8 Hz, 1H; CH(CH3)2), 3.01 (sept, 3JH−H = 6.8 Hz, 1H; CH(CH3)2), 1.05 (d, 3JH−H = 6.8 Hz, 6H; CH(CH3)2), 0.93 (d, 3JH−H = 6.8 Hz, 6H; CH(CH3)2), the H4 signal is too abroad to be assigned. 13C NMR (100 MHz, C6D6, 25 °C): δ (ppm) 163.9, 141.8, 138.5, 135.1, 114.8, 112.4, 52.2, 50.7, 24.1, 23.9. 11B NMR (128 MHz, C6D6, 25 °C): δ (ppm) 36.9, 34.4. Anal. Calcd for C22H32B3LaN2: C, 53.29; H, 6.50. Found: C, 53.74; H, 6.34.

Synthesis of Complex [C5H5B(CH2)5CH3]3LaLiCl(THF) (3). A toluene solution of 1-hexene (408 mg, 4.85 mmol in 4 mL of toluene) was added to 1 (100 mg, 0.24 mmol) in 1 mL of THF, and the reaction mixture was stirred for 3 days at 75 °C. The volatiles of the reaction mixture were removed in vacuo, and the residue was extracted with 2 × 2 mL of toluene. Removal of the solvent of the extract in vacuo gave 3 as a yellow oil (145 mg, 81% yield). 1H NMR (300 MHz, C6D6, 25 °C): δ (ppm) 7.18 (t, 3JH−H = 6.9 Hz, 6H; H2), 6.85 (d, 3 JH−H = 9.0 Hz, 6H; H1), 6.15 (t, 3JH−H = 6.6 Hz, 3H; H3), 3.42 (m, 4H; OCH2CH2 of THF), 1.92−1.83 (m, 6H; BCH2), 1.68−1.40 (m, 24H, BCH2(CH2)4CH3), 1.26 (m, 4H; OCH2CH2 of THF), 0.98 (t, 3 JH−H = 7.5 Hz, 9H; BCH2(CH2)4CH3). 13C NMR (75 MHz, C6D6, 25

Synthesis of [C 5 H 5 BN( i Pr)CHN( i Pr)][C 5 H 5 BC(C 2 H 5 )CH(C2H5)]2La (6). 3-Hexyne (364 mg, 4.4 mmol) and 5 (110 mg, 0.22 mmol) were mixed in 3 mL of toluene. After stirring for 4 days at 110 °C, the reaction mixture was filtered. Evaporation of the orange filtrate in vacuo afforded 6 as an orange oil (110 mg, 75% yield). 1H NMR D


Organometallics

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(300 MHz, C6D6, 25 °C): δ (ppm) 7.54 (t, 3JH−H = 8.4 Hz, 2H; H6), 7.31 (s, 1H; H8), 7.28 (d, 3JH−H = 8.1 Hz, 2H; H1), 7.11 (m, 4H; H2), 6.96 (d, 3JH−H = 9.0 Hz, 2H; H1), 6.51 (t, 3JH−H = 7.2 Hz, 2H; H4), 6.43 (t, 3JH−H = 7.5 Hz, 1H; H7), 6.38 (d, 3JH−H = 9.6 Hz, 2H; H5), 6.14 (t, 3JH−H = 6.6 Hz, 2H; H3), 3.16 (sept, 3JH−H = 6.9 Hz, 1H; CH(CH3)2), 3.06 (sept, 3JH−H = 6.9 Hz, 1H; CH(CH3)2), 2.76 (quart, 3 JH−H =7.2 Hz, 4H; BCCH2CH3), 2.44 (quint, 3JH−H = 7.2 Hz, 4H; BCCHCH2CH3), 1.33 (t, 3JH−H = 7.2 Hz, 6H; BCCH2CH3), 1.23 (t, 3 JH−H = 7.2 Hz, 6H; BCCHCH2CH3), 0.98 (t, 3JH−H = 6.9 Hz, 12H; CH(CH3)2). 13C NMR (75 MHz, C6D6, 25 °C): δ (ppm) 163.8, 147.02, 141.8, 139.4, 137.5, 137.1, 132.5, 131.2, 129.2, 114.1, 112.6, 52.3, 50.7, 24.2, 24.1, 22.3, 16.0, 15.2. 11B NMR (128 MHz, C6D6, 25 °C): δ (ppm) 37.2, 11B signals from two different boratabenzene rings are overlapped. Anal. Calcd for C34H52B3LaN2: C, 61.86; H, 7.94. Found: C, 60.68; H, 7.87.

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ASSOCIATED CONTENT

S Supporting Information *

CIF files giving X-ray crystallographic data for complexes 1′, 5, and 7; a table giving crystallographic data and refinement parameters for complexes 1′, 5, and 7; and figures giving 1H (13C, 11B) NMR spectra of complexes 1−7. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00262.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: (+86) 021-54925149. Notes

The authors declare no competing financial interests.

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ACKNOWLEDGMENTS This work was supported by the State Key Basic Research & Development Program (Grant No. 2011CB808705), the National Natural Science Foundation of China (Grant Nos. 21272256, 21132002, 21325210, and 21421091), and the Chinese Academy of Sciences.

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REFERENCES

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Synthesis of [C5H5BN( Pr)CHN( Pr)][C5H5BCCPh)]2La (7). Following the procedure described for 6. Reaction of 5 (150 mg, 0.30 mmol) with phenyl acetylene (154 mg, 1.51 mmol) for 1.5 days at 75 °C gave 7 as a yellow solid (200 mg, 95% yield). 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) 7.76−7.72 (m, 6H; Ph-H), 7.33−7.03 (m, 14H; Ph-H, H1, H2, H5, and H7), 6.61 (t, 3JH−H = 7.2 Hz, 1H; H6), 6.56 (d, 3JH−H = 9.6 Hz, 2H; H4), 6.47 (br, 2H; H3), 3.05 (m, 2H; CH(CH3)2), 1.11 (d, 3JH−H = 6.4 Hz, 6H; CH(CH3)2), 0.94 (d, 3JH−H = 6.4 Hz, 6H; CH(CH3)2). 13C NMR (100 MHz, C6D6, 25 °C): δ (ppm) 164.2, 142.7, 137.7, 137.2, 131.9, 129.3, 128.6, 127.6, 126.3, 115.3, 114.1, 106.7, 102.1, 52.24, 50.9, 24.2, 24.1. 11B NMR (128 MHz, C6D6, 25 °C): δ (ppm) 36.1, 29.0. Anal. Calcd for C38H40B3LaN2: C, 65.57; H, 5.79. Found: C, 64.90; H, 5.51.

X-ray Crystallography. Single crystals of 1′, 5, and 7 were mounted under a nitrogen atmosphere on a glass fiber, and data collection was performed on a Bruker APEX2 diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The SMART program package was used to determine the unit cell parameters. The absorption correction was applied using SADABS. The structures were solved by direct methods and refined on F2 by full-matrix least-squares techniques with anisotropic thermal parameters for non-hydrogen atoms. Hydrogen atoms were placed at calculated positions and were included in the structure calculation. Calculations were carried out using the SHELXL-97 program. The software used is listed in ref 12. Crystallographic data and refinement for 1′, 5, and 7 are provided in the Supporting Information. E


Article

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