Reaction of a Zirconocene–Carboryne Complex with Pyridines

ARTICLE pubs.acs.org/Organometallics

Reaction of a Zirconocene Carboryne Complex with Pyridines: Ligand C H Activation§ Shikuo Ren† and Zuowei Xie*,†,‡ †

Department of Chemistry and Center of Novel Functional Molecules, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China ‡ State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin, China

bS Supporting Information ABSTRACT: Reactions of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 (1) with various N-heterocycles derived from pyridine were studied. Treatment of 1 with pyridine, 2-bromopyridine, 2, 4-lutidine, quinoline, and 2-(1-hexynyl)pyridine generated α-C H activation (σ-bond metathesis) products Cp2Zr(η2-C, N-C5H4N)(σ-C2B10H11) (2), Cp2Zr[η2-C,N-(6-Br-C5H3N)](σC2B10H11) (3), Cp2Zr[η2-C,N-(4,6-Me2-C5H2N)](σ-C2B10H11) (4), Cp2Zr(η2-C,N-C9H6N)(σ-C2B10H11) (5), and Cp2Zr{η2-C,N-[6-(nBuCtC)-C5H3N]}(σ-C2B10H11) (7), respectively. On the other hand, reaction of 1 with acridine gave the addition product 1,2-[Cp2Zr(10,9-C13H9N)]-1,2-C2B10H10 (6) in 85% isolated yield. Complex 1 reacted with 3-(1-hexynyl)pyridine to afford α-C H activation species Cp2Zr{η2-C,N-[5-(nBuCtC)C5H3N]}(σ-C2B10H11) (8a) and Cp2Zr{η2-C,N-[3-(nBuCtC)C5H3N]}(σ-C2B10H11) (8b) in a molar ratio of 42:58, as determined by the 1H NMR spectrum. In the presence of CuI, however, the CtC insertion products zirconacyclopentenes 1,2-[Cp2ZrC(2-C5H4N)dCR]-1,2-C2B10H10 [R = Bun (9), Ph (10)] were obtained in 74 77% yields. It is suggested that the coordination of pyridine to the Zr atom is crucial for α-C H activation (σ-bond metathesis). The presence of CuI can alter the reaction path by preventing the coordination of pyridine to the Zr atom, which blocks the α-C H activation path, leading to the alkyne insertion reaction. All complexes were characterized by 1H, 13C, and 11B NMR spectra as well as elemental analyses. Their structures were further confirmed by single-crystal X-ray analyses.

’ INTRODUCTION Carboryne (1,2-dehydro-o-carborane) is a three-dimensional relative of benzyne.1 Its reactivity pattern toward unsaturated molecules can be modified by transition metals.2 For example, nickel carboryne complex (η2-C2B10H10)Ni(PPh3)2 can undergo regioselective [2 + 2 + 2] cycloaddition reactions with 2 equiv of alkynes to afford benzocarboranes,3 react with 1 equiv of alkene to generate alkenylcarborane coupling products,4 and a three-component [2 + 2 + 2] cyclotrimerization with 1 equiv of activated alkene and 1 equiv of alkyne to give dihydrobenzocarboranes.5 The reaction of carboryne with alkynes can also be catalyzed by Ni species.6 In contrast, the zirconium carboryne species, generated in situ from Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 (1), reacts with only 1 equiv of alkyne,7 or polar unsaturated organic substrates,8 to give monoinsertion zirconacycles. Many attempts to isolate the expected intermediate Cp2Zr(η2-C2B10H10) failed, although zirconium carboryne complexes supported by other π or σ ligands are known.9 In view of the isolation and structural characterization of Cp2Zr(η2-C6H4)(PMe3) in which the reactive intermediate Cp2Zr(η2-C6H4) can be stabilized by the Lewis base PMe3,10 we speculated that a Lewis base stabilized zirconium carboryne, Cp2Zr(η2-C2B10H10)(L), might be isolated in a similar manner. Unfortunately, after examination of a series of phosphines and r 2011 American Chemical Society

amines, we did not obtain any pure products. However, when pyridine was used as a Lewis base, a C H activation product, Cp2Zr(η2-C,N-C5H4N)(σ-C2B10H11) (2) was isolated in 90% yield. This unexpected result prompted us to investigate the reactions of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 (1) with various pyridine derivatives. These results are reported in this article.

’ RESULTS AND DISCUSSION Reaction. Treatment of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 (1) with 1.2 equiv of pyridine in toluene at room temperature gave the zirconocene pyridinyl complex Cp2Zr(η2-C,N-C5H4N)(σ-C2B10H11) (2) in 90% isolated yield via α-C H activation (σ-bond metathesis of pyridine) (Scheme 1). The characteristic cage CH proton was observed at 3.29 ppm as a broad singlet in the 1 H NMR spectrum. The four protons of the pyridinyl unit were observed at 8.44, 7.16, 6.91, and 6.50 ppm, respectively. The most distinctive change was the α-carbon of pyridinyl, which was largely downfield shifted to 201.6 ppm from the value of about 150 ppm for pyridine in the 13C NMR spectrum because of its connection to the Zr atom. This measured value is comparable to that of 200.9 ppm Received: August 18, 2011 Published: October 11, 2011 5953

dx.doi.org/10.1021/om200772q | Organometallics 2011, 30, 5953–5959

Organometallics

ARTICLE

Scheme 1. Reaction of 1 with Pyridines

Scheme 2. Reaction of 1 with Pyridine-Substituted Alkynes

reported for Cp2Zr[η2-C,N-C5H4N](BPh4).11 Its 11B NMR spectrum showed a 1:1:2:2:4 pattern, which is different from that of 1.8 The above results suggested that the α-proton of pyridine was transferred to the o-carboranyl unit during the reaction. Such an assumption was supported by deuterium-labeled experiments. When pyridine-d5 was used in the reaction, the corresponding deuterated product Cp2Zr[η2-C,N-C5D4N](σ-C2B10H10D) (2-d5) was obtained in 87% isolated yield (Scheme 1). Its 1H NMR spectrum exhibited only Cp protons at 5.20 ppm as a singlet, whereas the 2H NMR spectrum showed a broad singlet at 3.25 ppm assignable to the cage C-D and four peaks at 8.45, 7.18, 6.93, and 6.52 corresponding to the pyridinyl unit. The 11B NMR spectrum of 2-d5 was essentially the same as that of 2. We then examined a series of N-heterocycles derived from pyridine. Reaction of 1 with 2-bromo-pyridine or 2,4-lutidine in toluene at room temperature afforded the corresponding α-C H activation product Cp2Zr[η2-C,N-(6-Br-C5H3N)](σ-C 2 B 10 H 11 ) (3) or Cp 2 Zr[η 2 -C,N-(4,6-Me 2 -C5 H 2 N)](σ-C2B10H11) (4) in >80% isolated yields. When 2,4-lutidine was replaced by 2,6-lutidine in the above reaction, a mixture of inseparable products was generated. Complex 1 reacted slowly with quinoline in toluene at room temperature, which proceeded well in refluxing toluene to give α-C H activation product Cp2Zr(η2-C,N-C9H6N)(σ-C2B10H11) (5) in 85% isolated yield. However, interaction of 1 with acridine in refluxing toluene

generated a 9,10-insertion product 1,2-[Cp2Zr(9,10-C13H9N)]1,2-C2B10H10 (6) in 75% isolated yield, which is very different from the reaction of Cp2ZrMe(THF)(BPh4) with acridine.12 In the 1H NMR spectrum of 6, the 9-proton was largely shifted to high field at 4.85 ppm as a singlet from 8.7 ppm in acridine. The aforementioned reactions are outlined in Scheme 1. We have recently reported that the reaction of 1 with alkynes gave the monoinsertion products 1,2-[Cp2ZrC(R1)dC(R2)]1,2-C2B10H10.7 Treatment of 1 with 1 equiv of 2-(1-hexynyl)pyridine in toluene at room temperature afforded the α-C H activation product Cp2Zr{η2-C,N-[6-(nBuCtC)-C5H3N]} (σ-C2B10H11) (7) in 56% isolated yield (Scheme 2). No alkyne insertion product 1,2-[Cp2ZrC(2-C5H4N)dCBun]-1,2-C2B10H10 was observed even in refluxing toluene. Under the same reaction condition, two regioisomers of α-C H activation products Cp2Zr{η2-C,N-[5-(nBuCtC)C5H3N]}(σ-C2B10H11) (8a) and Cp2Zr{η2-C,N-[3-(nBuCtC)C5H3N]}(σ-C2B10H11) (8b) were obtained in a molar ratio of 42:58 as determined by the 1H NMR spectrum when 3-(1-hexynyl)pyridine was used as a substrate. These two isomers were separated by recrystallization from toluene in 33% and 35% isolated yields for 8a and 8b, respectively. However, if 2 equiv of CuI were added to the above reaction, α-C H activation reactions were completely blocked, and the alkyne insertion product was observed. Such an insertion reaction was accelerated by high temperatures. Under refluxing toluene conditions, the monoinsertion products 1,2-[Cp2ZrC(2-C5H4N)dCR]-1,2-C2B10H10 [R = Bun (9), Ph (10)] were isolated in 74 77% yields. Hydrolysis of 9 and 10 generated the corresponding alkenylcarboranes 11 and 12. Scheme 2 summarizes the above reactions. 5954

dx.doi.org/10.1021/om200772q |Organometallics 2011, 30, 5953–5959

Organometallics

ARTICLE

Figure 1. Molecular structure of Cp2Zr(η2-C,N-C5H4N)(σ-C2B10H11) (2) (thermal ellipsoids drawn at the 35% probability level). Figure 3. Molecular structure of Cp2Zr(η2-C,N-C9H6N)(σ-C2B10H11) (5) (thermal ellipsoids drawn at the 35% probability level).

Figure 2. Molecular structure of Cp2Zr[η2-C,N-(4,6-Me2-C5H2N)](σ-C2B10H11) (4) (thermal ellipsoids drawn at the 35% probability level).

Complexes 2, 3, 7, and 8 are soluble in toluene, benzene, pyridine, and THF, whereas complexes 4 6, 9, and 10 are only soluble in THF and pyridine. They are all insoluble in ethyl ether and hexane. Complexes 2 8 are moisture-sensitive, but 9 and 10 are stable in open air for several hours in the solid state probably due to the very crowded coordination environment of the Zr atom in the latter. They were fully characterized by 1H, 13C, and 11 B NMR spectra as well as elemental analyses. Structure. The molecular structures of complexes 2, 4, 5, 6, 7, 8a, and 10 were further confirmed by single-crystal X-ray analyses and are shown in Figures 1 7, respectively. Selected bond lengths and angles are summarized in Table 1. The Zr N C ring in complexes 2, 4, 5, 7, and 8a is structurally similar to that observed in Cp2Zr[η2-C,N-(6-Me-C5H3N)](PMe3)(BPh4),11 and the Sc N C ring in Cp*2Sc[η2-C,N-C5H4N].13 The Zr Ccage distances fall in the range of 2.495(3) 2.529(6) Å, which is slightly larger than the corresponding values found in Zr carboranyl complexes.14 The Zr Npyr distances vary from 2.125(3) to 2.402(6) Å. Such large deviations suggest that the interactions between the Zr atom and pyridine are affected by the ligands. These measured values can be compared to that of 2.21(1) Å in Cp2Zr[η2-C,N-(6-Me-C5H3N)](PMe3)(BPh4),11 2.26(1) Å

Figure 4. Molecular structure of 1,2-[Cp2Zr(9,10-C13H9N)]-1,2C2B10H10 (6) (thermal ellipsoids drawn at the 35% probability level).

Figure 5. Molecular structure of Cp2Zr{η2-C,N-[6-(nBuCtC)C5H3N]}(σ-C2B10H11) (7) (thermal ellipsoids drawn at the 35% probability level). 5955

dx.doi.org/10.1021/om200772q |Organometallics 2011, 30, 5953–5959

Organometallics

Figure 6. Molecular structure of Cp2Zr{η2-C,N-[5-(nnBuCtC)C5H3N]}(σ-C2B10H11) (8a) (thermal ellipsoids drawn at the 35% probability level).

Figure 7. Molecular structure of 1,2-[Cp2ZrC(2-C5H4N)dCR]-1,2C2B10H10 (10) (thermal ellipsoids drawn at the 35% probability level).

in [ArN(CH2 )3 NAr]Zr(η 2 -C,N-C 5 H 4 N)(CH 2 CMe2 Ph), 15a 2.24(1) Å in Cp* 2 ZrH(η 2 -C,N-C 5 H4 N), and 2.21(1) Å in Cp* 2 ZrCl(η 2 -C,N-C 5 H4 N). 15b The Zr Cpyr distances fall in the range of 2.208(4) 2.302(6) Å, which is comparable to those observed in Cp2Zr[η2-C,N-(6-Me-C5H3N)](PMe3)(BPh4) (2.29(2) Å), 11 [ArN(CH2 )3 NAr]Zr[η 2 -C,N-C 5 H 4 N](CH2 CMe2Ph) (2.22(1) Å),15a Cp*2ZrH[η2-C,N-C5H4N] (2.26(1) Å), and Cp*2ZrCl[η2-C,N-C5H4N] (2.23(1) Å).15b The highly acute Cpyr Zr Npyr angles [33.6(2) 34.7(2)o] are very close to those reported in Cp2Zr[η2-C,N-6-Me-C5H3N](PMe3)(BPh4) (34.2(4)o),11 [ArN(CH2)3NAr]Zr[η2-C,N-C5H4N](CH2CMe2Ph) (34.2(4)o),15a Cp*2ZrH[η2-C,N-C5H4N] (34.7(1)o), and Cp*2ZrCl[η2-C,N-C5H4N] (34.8(1)o).15b The geometry around the Zr atom in 10 (Figure 7) is similar to that observed in 1,2[Cp2ZrC(PPh2)dC(Bun)]-1,2-C2B10H107a with an intramolecular coordination. The Zr Npyr/Zr Ccage distances of 2.402(6)/ 2.529(6) Å in 10 are slightly longer than the corresponding values found in 2 8 due probably to steric reasons. The Zr Ccage/ Ccage Ccage distances of 2.529(6)/1.711(8) Å in 10 are comparable to those of 2.507(3)/1.721(4) Å in 1,2-[Cp2ZrC(PPh2)d C(Bun)]-1,2-C2B10H10.7a Mechanism. Addition of CuI can alter the reaction pathway of 1 with alkynylpyridines (Scheme 2), leading to the formation of alkyne insertion products. These results suggest that the coordination of pyridine to the Zr atom is essential for the α-C H activation reaction to proceed. The Cu atom can compete for Zr’s

ARTICLE

binding site and push the Zr atom off the pyridine molecule, thus blocking the α-C H activation path and facilitating the alkyne insertion. In the presence of CuI, 1 does not react with pyridine, which further supports the above assumption. Scheme 3 shows a proposed reaction mechanism for α-C H activation and insertion reactions. Elimination of LiCl from 1 gives the zirconocene carboryne intermediate,8 which is best described as a resonance hybrid of Zr C σ- and π-bonded species.9 Coordination of pyridine to the Zr atom activates the α-C H bond, leading to the formation of α-C H activation (σ-bond metathesis) products. This process is similar to that observed in the reaction of [Cp2ZrMe][BPh4]11 or organoyttrium alkyl16 with pyridine. However, in the presence of CuI, the coordination of N to the Cu atom blocks the activation process, resulting in the inertness of 1 toward pyridine. On the other hand, the Cu alkynylpyridine complex can coordinate to the Zr atom via its CtC unit, leading to the alkyne insertion.7 For the formation of 6, a possible pathway may involve direct nucleophilic attack of the carborane anion on the C-9 of acridine, followed by the formation of a new Zr N bond with the elimination of LiCl. This mechanism is supported by the isolation and structural characterization of 1-(9,10-dihydroacridine)1,2-C2B10H11 prepared from an equimolar reaction of Li2C2B10H10 with acridine in toluene at room temperature.17

’ CONCLUSION Reactions of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 with Nheterocycles derived from pyridine gave α-C H activation products in high yields. These reactions may involve the pyridine coordinated zirconocene carboryne intermediate. The coordination of pyridine to the Zr atom is crucial for α-C H activation. The presence of CuI can alter the reaction path by preventing the coordination of pyridine to the Zr atom, which blocks the αC H activation path, leading to the alkyne insertion reaction. ’ EXPERIMENTAL SECTION General Procedures. All reactions were performed under an atmosphere of dry nitrogen with the rigid exclusion of air and moisture using standard Schlenk or cannula techniques, or in a glovebox. All organic solvents were freshly distilled from sodium benzophenone ketyl immediately prior to use. The 1H NMR spectra were recorded on either a Bruker DPX 300 spectrometer at 300 MHz or a Bruker DPX 400 spectrometer at 400 MHz. 13C{1H} NMR spectra were recorded on either a Bruker DPX 300 spectrometer at 75 MHz or a Bruker DPX 400 spectrometer at 100 MHz. 11B{1H} NMR spectra were recorded on either a Bruker DPX 300 spectrometer at 96 MHz or a Varian Inova 400 spectrometer at 128 MHz. All chemical shifts were reported in δ units with reference to the residual protons and carbons of the deuterated solvents for proton and carbon chemical shifts, and to external BF3 3 OEt2 (0.00 ppm) for boron chemical shifts. Infrared spectra were obtained from KBr pellets prepared in the glovebox on a PerkinElmer 1600 Fourier transform spectrometer. Elemental analyses were performed by the Shanghai Institute of Organic Chemistry, CAS, China. Mass spectra were obtained on a Thermo Finnigan MAT 95 XL spectrometer. Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2,8 (2-pyridnyl)CtCBun, and (2-pyridinyl)CtCPh18 were prepared according to the literature methods. All other chemicals were purchased from either Aldrich or Acros Chemical Co. and used as received unless otherwise specified. Preparation of Cp2Zr[η2-C,N-C5H4N](σ-C2B10H11) (2). To a solution of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 (1; 554 mg, 1.0 mmol) 5956

dx.doi.org/10.1021/om200772q |Organometallics 2011, 30, 5953–5959

Organometallics

ARTICLE

Table 1. Selected Bond Lengths (Å) and Angles (deg)

a

compd

av. Zr Centa

av. Zr Ccp

Zr Ccage

Zr Cpyr

Zr Npyr

Ccage Ccage

Cpyr Npyr

Cent Zr Cent

Cpyr Zr Npyr

2

2.222

2.520(4)

2.511(4)

2.208(4)

2.273(3)

1.713(7)

1.326(5)

127.1

34.4(1)

4

2.242

2.538(4)

2.512(4)

2.252(5)

2.195(4)

1.738(7)

1.327(6)

130.1

34.7(2)

5

2.230

2.529(4)

2.505(6)

2.271(6)

2.191(4)

1.720(9)

1.292(8)

127.9

33.6(2)

6

2.229

2.528(3)

2.495(3)

2.125(3)

1.723(4)

125.5

88.9(1)c 34.6(1)

7

2.239

2.532(3)

2.522(3)

2.267(3)

2.200(2)

1.699(4)

1.330(3)

128.1

8a

2.236

2.531(12)

2.512(16)

2.221(10)

2.306(9)

1.67(2)

1.325(16)

127.4

34.0(4)

10

2.241

2.532(7)

2.529(6)

2.302(6)b

2.402(6)

1.711(8)

1.340(8)

128.1

56.9(2)

Cent = the centroid of the Cp ring. b Zr Cvinyl. c Ccage Zr Npyr.

Scheme 3. Proposed Reaction Mechanism

C5H5), 3.57 (brs, 1H, cage H). 13C{1H} NMR (100 MHz, benzene-d6): δ 198.8, 144.4, 139.7, 131.3, 127.1 (pyridinyl C), 111.3 (C5H5), 84.2, 67.8 (cage C). 11B{1H} NMR (96 MHz, benzene-d6): δ 0.5 (1B), 1.6 (1B), 6.5 (2B), 7.5 (2B), 11.0 (4B). IR (KBr, cm 1): ν 2560 (B H). Anal. Calcd for C17H24B10BrNZr (3): C, 39.15; H, 4.64; N, 2.69. Found: C, 39.11; H, 4.49; N, 2.29.

Preparation of Cp2Zr[η2-C,N-(4,6-Me2-C5H2N)](σ-C2B10H11) (4). This complex was prepared as pale yellow crystals from 1 (554 mg,

in toluene (15 mL) was added pyridine (95 mg, 1.2 mmol) at room temperature, and the mixture was stirred at room temperature for 48 h. After removal of the precipitate, the filtrate was concentrated in vacuum to about 5 mL. Complex 2 was crystallized out as pale yellow crystals after this solution stood for 2 days at room temperature (400 mg, 90%). 1H NMR (400 MHz, benzene-d6): δ 8.44 (d, J = 5.1 Hz, 1H), 7.16 (d, J = 7.2 Hz, 1H), 6.91 (m, 1H), 6.50 (m, 1H) (pyridinyl H), 5.20 (s, 10H, C5H5), 3.29 (brs, 1H, cage H). 13C{1H} NMR (100 MHz, benzene-d6): δ 201.6, 144.5, 136.2, 129.1, 123.8 (pyridinyl C), 109.4 (C5H5), 85.6, 66.1 (cage C). 11B{1H} NMR (96 MHz, benzene-d6): δ 0.1 (1B), 1.0 (1B), 6.0 (2B), 7.2 (2B), 10.9 (4B). IR (KBr, cm 1): ν 2573, 2545 (B H). Anal. Calcd for C17H25B10NZr (2): C, 46.12; H, 5.69; N, 3.16. Found: C, 46.08; H, 5.88; N, 2.88.

Preparation of Cp2Zr[η2-C,N-C5D4N](σ-C2B10H10D) (2-d5). This complex was prepared as pale yellow crystals from 1 (554 mg, 1.0 mmol) and pyridine-d5 (101 mg, 1.2 mmol) in toluene (15 mL) using the same procedures reported for 2. Yield: 390 mg (87%). 1H NMR (400 MHz, benzene-d6): δ 5.20 (s, 10H, C5H5). 2H NMR (400 MHz, benzene): δ 8.45 (1D), 7.18 (1D), 6.93 (1D), 6.52 (1D) (pyridinyl D), 3.25 (1D, cage C-D). 11B{1H} NMR (96 MHz, benzene-d6): δ 0.2 (1B), 0.9 (1B), 5.9 (2B), 7.1 (2B), 10.8 (4B).

Preparation of Cp2Zr[η2-C,N-(6-Br-C5H3N)](σ-C2B10H11) (3). This complex was prepared as a pale yellow solid from 1 (554 mg, 1.0 mmol) and 2-bromopyridine (190 mg, 2.0 mmol) using the same procedures reported for 2. Yield: 422 mg (81%). 1H NMR (400 MHz, benzene-d6): δ 7.50 (m, 1H), 6.70 (m, 2H) (pyridinyl H), 5.42 (s, 10H,

1.0 mmol) and 2,4-lutidine (128 mg, 1.2 mmol) using the same procedures reported for 2. Yield: 385 mg (82%). 1H NMR (400 MHz, pyridine-d5): δ 7.70 (s, 1H), 6.81 (s, 1H), (pyridinyl H), 5.98 (s, 10H, C5H5), 4.39 (brs, 1H, cage H), 2.45 (s, 3H), 2.22 (s, 3H), (CH3). 13 C{1H} NMR (100 MHz, pyridine-d5): δ 187.0, 152.2, 149.2, 129.1, 124.9 (pyridinyl C), 110.5 (C5H5), 85.7, 68.3 (cage C), 20.4, 19.7 (CH3). 11 1 B{ H} NMR (96 MHz, pyridine-d5): δ 1.5 (1B), 2.4 (1B), 7.2 (4B), 11.2 (4B). IR (KBr, cm 1): ν 2562 (B H). Anal. Calcd for C19H29B10NZr (4): C, 48.48; H, 6.21; N, 2.98. Found: C, 48.41; H, 6.22; N, 2.72. Preparation of Cp2Zr(η2-C,N-C9H6N)(σ-C2B10H11) (5). This complex was prepared as pale yellow crystals from 1 (554 mg, 1.0 mmol) and quinoline (155 mg, 1.2 mmol) using the same procedures reported for 2, but in refluxing toluene. Yield: 418 mg (85%). 1H NMR (400 MHz, pyridine-d5): δ 8.26 (d, J = 8.0 Hz, 1H), 8.17 (d, J = 8.0 Hz, 1H), 8.14 (d, J = 8.0 Hz, 1H), 8.04 (d, J = 8.0 Hz, 1H), 7.88 (m, 1H), 7.68 (m, 1H) (quinolinyl H), 6.04 (s, 10H, C5H5), 4.47 (brs, 1H, cage H). 13 C{1H} NMR (75 MHz, pyridine-d5): δ 194.7, 142.7, 136.3, 131.0, 129.0, 128.9, 127.1, 126.7, 122.3 (quinolinyl C + C5H5), 85.4, 68.2 (cage C). 11 1 B{ H} NMR (96 MHz, pyridine-d5): δ 0.9 (1B), 0.2 (1B), 4.9 (4B), 9.0 (4B). IR (KBr, cm 1): ν 2567 (B H). Anal. Calcd for C21H27B10NZr (5): C, 51.19; H, 5.52; N, 2.84. Found: C, 51.58; H, 5.46; N, 2.71.

Preparation of 1,2-[Cp2Zr(9,10-C13H9N)]-1,2-C2B10H10 (6). This complex was prepared as yellow crystals from 1 (554 mg, 1.0 mmol) and acridine (215 mg, 1.2 mmol) using the same procedures reported for 5. Yield: 407 mg (75%). 1H NMR (400 MHz, pyridine-d5): δ 7.43 (d, J = 7.6 Hz, 2H), 7.37 (d, J = 7.6 Hz, 2H), 7.26 (m, 2H), 7.08 (m, 2H), (acridinyl H), 6.31 (s, 10H, C5H5), 4.85 (brs, 1H, cage H). 13C{1H} NMR (100 MHz, pyridine-d5): δ 156.6, 133.7, 128.1, 126.9, 122.0 (aromatic C), 115.9 (C5H5), 86.3, 85.4 (cage C), 53.4 (CH). 11B{1H} NMR (96 MHz, pyridine-d5): δ 1.7 (2B), 6.8 (8B). IR (KBr, cm 1): ν 2554 (B H). Anal. Calcd for C25H29B10NZr (6): C, 55.32; H, 5.38; N, 2.58. Found: C, 55.58; H, 5.46; N, 2.71.

Preparation of Cp 2 Zr{η 2 -C,N-[6-(n BuC;C)-C 5 H 3 N]}(σ-C2B10H11) (7). This complex was prepared as pale yellow crystals from 1 (554 mg, 1.0 mmol) and 2-(1-hexynyl)pyridine (191 mg, 1.2 mmol) using the same procedures reported for 2. Yield: 293 mg (56%). 1 H NMR (300 MHz, benzene-d6): δ 7.52 (d, J = 6.9 Hz, 1H), 6.99 (m, J = 6.9 Hz, 1H), 6.87 (d, J = 6.9 Hz, 1H) (pyridinyl H), 5.55 (s, 10H, C5H5), 3.74 (brs, 1H, cage H), 2.17 (t, J = 6.6 Hz, 2H, CH2), 1.40 (m, 4H, CH2), 0.86 (t, J = 7.2 Hz, CH3). 13C{1H} NMR (75 MHz, benzened6): δ 190.8, 139.1, 136.8, 130.8, 126.8 (pyridinyl C), 111.0 (C5H5), 97.3, 84.7 (CtC), 77.4, 68.5 (cage C), 30.6, 22.2, 19.0, 13.6 (Bun). 5957

dx.doi.org/10.1021/om200772q |Organometallics 2011, 30, 5953–5959

Organometallics B{1H} NMR (96 MHz, benzene-d6): δ 0.3 (1B), 1.4 (1B), 6.1 (2B), 7.5 (2B), 10.6 (4B). IR (KBr, cm 1): ν 2601, 2550 (B H). Anal. Calcd for C23H33B10NZr (7): C, 52.84; H, 6.36; N, 2.68. Found: C, 52.84; H, 6.35; N, 2.72. 11

Preparation of Cp 2 Zr{η 2 -C,N-[5-(n BuC;C)C 5 H 3 N]}(σ-C2B10H11) (8a) and Cp2Zr{η2-C,N-[3-(nBuC;C)C5H3N]}(σ-C2B10H11) (8b). These two complexes were prepared as pale yellow crystals from 1 (554 mg, 1.0 mmol) and 3-(1-hexynyl)pyridine (191 mg, 1.2 mmol) using the same procedures reported for 2. They were separated by recrystallization from toluene. Yield: 170 mg (33%) for 8a and 185 mg (35%) for 8b. 8a: 1H NMR (300 MHz, benzene-d6): δ 8.91 (s, 1H), 7.38 (d, J = 7.6 Hz, 1H), 7.15 (d, J = 7.6 Hz, 1H) (pyridinyl H), 5.24 (s, 10H, C5H5), 3.30 (brs, 1H, cage H), 2.22 (t, J = 6.8 Hz, 2H, CH2), 1.45 (m, 4H, CH2), 0.86 (t, J = 7.2 Hz, CH3). 13C{1H} NMR (75 MHz, benzene-d6): δ 201.7, 146.7, 138.8, 128.8, 121.9 (pyridinyl C), 109.5 (C5H5), 95.1, 85.5 (CtC), 77.2, 66.0 (cage C), 30.7, 22.3, 19.3, 13.7 (Bun). 11B{1H} NMR (96 MHz, benzene-d6): δ 0.8 (1B), 0.0 (1B), 5.2 (2B), 6.1 (2B), 10.2 (4B). Anal. Calcd for C23H33B10NZr (8a): C, 52.84; H, 6.36; N, 2.68. Found: C, 52.51; H, 6.38; N, 2.51. 8b: 1 H NMR (300 MHz, benzene-d6): δ 8.24 (d, J = 7.6 Hz, 1H), 7.20 (d, J = 7.6 Hz, 1H), 6.45 (m, 1H) (pyridinyl H), 5.40 (s, 10H, C5H5), 3.30 (brs, 1H, cage H), 2.29 (t, J = 7.2 Hz, 2H, CH2), 1.48 (m, 4H, CH2), 0.88 (t, J = 7.2 Hz, CH3). 13C{1H} NMR (75 MHz, benzene-d6): δ 205.3, 142.6, 138.2, 126.8, 123.8 (pyridinyl C), 109.5 (C5H5), 94.4, 85.4 (CtC), 79.7, 66.1 (cage C), 31.1, 22.2, 19.3, 13.7 (Bun). 11B{1H} NMR (96 MHz, benzene-d6): δ 0.5 (1B), 1.0 (1B), 6.0 (2B), 7.1 (2B), 10.9 (4B). IR (KBr, cm 1): ν 2560 (B H). Anal. Calcd for C23H33B10NZr (8b): C, 52.84; H, 6.36; N, 2.68. Found: C, 52.58; H, 6.73; N, 2.40.

Preparation of 1,2-[Cp2ZrC(2-C5H4N)dCBun]-1,2-C2B10H10 (9). To a solution of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 (1; 554 mg, 1.0 mmol) in toluene (15 mL) was added 2-(1-hexynyl)pyridine (191 mg, 1.2 mmol) and CuI (381 mg, 2.0 mmol), and the mixture was heated to reflux for 48 h. After filtration, the resultant clear solution was concentrated under vacuum to about 5 mL. Complex 9 was isolated as light yellow crystals after this solution stood at room temperature for 2 days (387 mg, 74%). 1H NMR (300 MHz, CD2Cl2): δ 8.13 (d, J = 7.5 Hz, 1H), 7.78 (t, J = 7.5 Hz, 1H), 7.20 (t, J = 7.5 Hz, 1H), 7.03 (d, J = 7.5 Hz, 1H) (pyridinyl H), 6.03 (s, 10H, C5H5), 2.43 (t, J = 7.2 Hz, 2H, CH2), 1.51 (m, 4H, CH2), 0.96 (t, J = 7.2 Hz, 3H, CH3). 13C{1H} NMR (75 MHz, CD2Cl2): δ 164.7, 161.8, 155.2, 148.4, 139.0, 122.1, 119.6 (pyridinyl C + olefinic C), 111.9 (C5H5), 97.0, 96.2 (cage C), 33.9, 31.0, 23.6, 13.9 (Bun). 11B{1H} NMR (128 MHz, CD2Cl2): δ 1.9 (1B), 5.4 (3B), 7.2 (4B), 11.5 (2B). IR (KBr, cm 1): ν 2550 (B H). Anal. Calcd for C23H33B10NZr (9): C, 52.84; H, 6.36; N, 2.68. Found: C, 52.97; H, 6.53; N, 2.59.

Preparation of 1,2-[Cp2ZrC(2-C5H4N)dCPh]-1,2-C2B10H10 (10). This complex was prepared as light brown crystals from 1 (554 mg, 1.0 mmol) and 2-(1-phenylacetylenyl)pyridine (215 mg, 1.2 mmol) using the same procedures reported for 9. Yield: 418 mg (77%). 1H NMR (300 MHz, CD2Cl2): δ 8.08 (d, J = 5.4 Hz, 1H), 7.42 (m, 4H), 7.10 (m, 3H), 5.81 (d, J = 8.1 Hz, 1H) (aromatic H), 6.12 (s, 10H, C5H5). 13C{1H} NMR (75 MHz, CD2Cl2): δ 166.3, 164.7, 152.8, 148.2, 140.2, 138.5, 129.0, 128.4, 127.9, 122.8 (aromatic C + olefinic C), 118.9 (C5H5), 96.6, 95.6 (cage C). 11B{1H} NMR (128 MHz, CD2Cl2): δ 1.9 (1B), 5.4 (3B), 7.1 (4B), 11.7 (2B). IR (KBr, cm 1): ν 2556 (B H). Anal. Calcd for C25H29B10NZr (10): C, 55.32; H, 5.38; N, 2.58. Found: C, 55.16; H, 5.65; N, 2.30.

Preparation of 1-[trans-(2-C5H4N)CHdCBun]-1,2-C2B10H11 (11). To a solution of complex 9 (157 mg, 0.3 mmol) in ethyl acetate (10 mL) was added aqueous HCl solution (1M, 10 mL). After the mixture was stirred at room temperature for 1 h, it was then treated with 1 M NaHCO3 aqueous solution (10 mL). The organic layer was separated, and the aqueous solution was extracted with ethyl acetate (10 mL  2). The organic phase was combined, washed with saturated brine aqueous

ARTICLE

solution (20 mL), and dried over anhydrous Na2SO4. After removal of the solvent under vacuum, the residue was purified by flash column chromatography on silica gel using hexane/ethyl acetate (4/1 in v/v) as the eluent to give 11 as a white solid (79 mg, 87%). 1H NMR (400 MHz, CDCl3): δ 8.61 (d, J = 4.0 Hz, 1H), 7.72 (m, 1H), 7.21 (m, 2H), (pyridinyl H), 6.72 (s, 1H, CdCH), 3.91 (brs, 1H, cage H), 2.70 (t, J = 8.0 Hz, 2H, CH2), 1.54 (m, 2H, CH2), 1.38 (m, 2H, CH2), 0.93 (t, J = 7.2 Hz, 3H, CH3). 13C{1H} NMR (100 MHz, CDCl3): δ 154.5, 149.4, 139.6, 136.3, 131.3, 124.9, 122.3 (olefinic and pyridinyl C), 79.1, 59.6 (cage C), 31.2, 31.1, 22.7, 13.6 (Bun). 11 1 B{ H} NMR (96 MHz, CDCl3): δ 2.9 (1B), 4.3 (1B), 9.3 (2B), 11.2 (4B), 13.4 (2B). HRMS: m/z Calcd for C13H2311B810B2N+: 303.2985. Found: 303.2969. Anal. Calcd for C13H23B10N (11): C, 51.80; H, 7.69; N, 4.65. Found: C, 51.86; H, 7.65; N, 4.50.

Preparation of 1-[trans-(2-C5H4N)CHdCPh]-1,2-C2B10H11 (12). This compound was prepared as a white solid from 10 (163 mg, 0.3 mmol) using the same procedures reported for 11. Yield: 86 mg (89%). 1H NMR (400 MHz, CDCl3): δ 8.50 (d, J = 4.4 Hz, 1H), 7.44 (m, 3H), 7.28 (m, 1H), 7.15 (m, 2H), 7.02 (dd, J = 4.4, 4.8 Hz, 1H), 6.35 (d, J = 8.0 Hz, 1H) (aromatic H), 7.21 (s, 1H, CdCH), 3.36 (brs, 1H, cage CH). 13C{1H} NMR (75 MHz, CDCl3): δ 153.5, 149.1, 137.7, 135.9, 135.3, 135.2, 129.6, 129.3, 123.4, 122.5, (olefinic + aromatic C), 77.2, 58.4 (cage C). 11B{1H} NMR (128 MHz, CDCl3): δ 3.3 (1B), 4.0 (1B), 8.6 (2B), 10.3 (2B), 12.2 (2B), 13.5 (2B). HRMS: m/z Calcd for C15H2111B810B2N+: 322.2593. Found: 322.2595. Anal. Calcd for C15H21B10N (12): C, 55.70; H, 6.54; N, 4.33. Found: C, 55.51; H, 6.68; N, 4.10. X-ray Structure Determination. All single crystals were immersed in Paraton-N oil and sealed under nitrogen in thin-walled glass capillaries. Data were collected at 293 K on a Bruker SMART 1000 CCD diffractometer using Mo Kα radiation. An empirical absorption correction was applied using the SADABS program.19 All structures were solved by direct methods and subsequent Fourier difference techniques and refined anisotropically for all non-hydrogen atoms by full-matrix least-squares on F2 using the SHELXTL program package.20 All hydrogen atoms were geometrically fixed using the riding model. Further details are included in the Supporting Information.

’ ASSOCIATED CONTENT

bS

Supporting Information. Crystallographic data in CIF format for 2, 4 7, 8a, 10, and 1-(9,10-dihydroacridine)-1,2C2B10H11; table of crystal data and details of data collection and structure refinements; and 1H NMR spectra of compounds 11 and 12. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: +852 26035057.

’ ACKNOWLEDGMENT The work described in this paper was supported by grants from the Research Grants Council of the Hong Kong Special Administration Region (Project No. 404108), The Chinese University of Hong Kong, NSFC/RGC Joint Research Scheme (Project No. N_CUHK470/10), and State Key Laboratory of ElementoOrganic Chemistry, Nankai University (Project No. 0314). We thank Ms. Hoi-Shan Chan for single-crystal X-ray analyses.

’ DEDICATION § This paper is dedicated to Professor Christian Bruneau on the occasion of his 60th birthday. 5958

dx.doi.org/10.1021/om200772q |Organometallics 2011, 30, 5953–5959

Organometallics

ARTICLE

’ REFERENCES (1) (a) Gingrich, H. L.; Ghosh, T.; Huang, Q.; Jones, M., Jr. J. Am. Chem. Soc. 1990, 112, 4082. (b) Ghosh, T.; Gingrich, H. L.; Kam, C. K.; Mobraaten, E. C. M.; Jones, M., Jr. J. Am. Chem. Soc. 1991, 113, 1313. (c) Huang, Q.; Gingrich, H. L.; Jones, M., Jr. Inorg. Chem. 1991, 30, 3254. (d) Cunningham, R. J.; Bian, N.; Jones, M., Jr. Inorg. Chem. 1994, 33, 4811. (e) Ho, D. M.; Cunningham, R. J.; Brewer, J. A.; Bian, N.; Jones, M., Jr. Inorg. Chem. 1995, 34, 5274. (f) Barnett-Thamattoor, L.; Zheng, G.; Ho, D. M.; Jones, M., Jr.; Jackson, J. E. Inorg. Chem. 1996, 35, 7311. (g) Jeon, J.; Kitamura, T.; Yoo, B.-W.; Kang, S. O.; Ko, J. Chem. Commun. 2001, 2110. (h) Kiran, B.; Anoop, A.; Jemmis, E. D. J. Am. Chem. Soc. 2002, 124, 4402. (i) Lee, T.; Jeon, J.; Song, K. H.; Jung, I.; Baik, C.; Park, K.-M.; Lee, S. S.; Kang, S. O.; Ko, J. J. Chem. Soc., Dalton Trans. 2004, 933. (2) For reviews, see: (a) Qiu, Z.; Ren, S.; Xie, Z. Acc. Chem. Res. 2011, 44, 299. (b) Qiu, Z.; Xie, Z. Sci. China, Ser. B: Chem. 2009, 52, 1544. (3) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2006, 128, 7728. (4) Qiu, Z.; Xie, Z. Angew. Chem., Int. Ed. 2008, 47, 6572. (5) Qiu, Z.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 2084. (6) Qiu, Z.; Wang, S. R.; Xie, Z. Angew. Chem., Int. Ed. 2010, 49, 4649. (7) (a) Ren, S.; Chan, H.-S.; Xie, Z. Organometallics 2009, 28, 4106. (b) Ren, S.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2009, 131, 3862. (8) Deng, L.; Chan, H.-S.; Xie, Z. J. Am. Chem. Soc. 2005, 127, 13774. (9) (a) Wang, H.; Li, H.-W.; Huang, X.; Lin, Z.; Xie, Z. Angew. Chem., Int. Ed. 2003, 42, 4347. (b) Ren, S.; Deng, L.; Chan, H.-S.; Xie, Z. Organometallics 2009, 28, 5749. (10) Buchwald, S. L.; Watson, B. T. J. Am. Chem. Soc. 1986, 108, 7411. (11) Jordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990, 9, 1546. (12) (a) Jordan, R. F.; Guram, A. S. Organometallics 1990, 9, 2116. (b) Jordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (13) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. Soc. 1987, 109, 203. (14) (a) Wang, H.; Wang, Y.; Li, H.-W.; Xie, Z. Organometallics 2001, 20, 5110. (b) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 3850. (c) Wang, H.; Chan, H.-S.; Okuda, J.; Xie, Z. Organometallics 2005, 24, 3118. (d) Xie, Z. Coord. Chem. Rev. 2006, 250, 259. (e) Hong, E.; Kim, Y.; Do, Y. Organometallics 1998, 17, 2933. (f) Zi, G.; Li, H.-W.; Xie, Z. Organometallics 2002, 21, 1136. (15) (a) Scollard, J. D.; McConville, D. H.; Vittal, J. J. Organometallics 1995, 14, 5478. (b) Krut’ko, D. P.; Kirsanov, R. S.; Belov, S. A.; Borzov, M. V.; Churakov, A. V.; Howard, J. A. K. Polyhedron 2007, 26, 2864. (16) (a) Duchateau, D.; Brussee, E. A. C.; Meetsma, A.; Teuben, J. H. Organometallics 1997, 16, 5506. (b) Arndt, S.; Elvidge, B. R.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Organometallics 2006, 25, 793. (17) 1-(9,10-Dihydroacridine)-1,2-C2B10H11 was isolated in 94% yield. 1H NMR (400 MHz, CDCl3): δ 7.30 (m, 4H), 7.03 (m, 2H), 6.89 (d, J = 7.2 Hz, 2H) (aromatic H), 6.30 (s, 1H, NH), 4.94 (s, 1H, CH), 3.12 (brs, 1H, cage H). 13C{1H} NMR (100 MHz, CDCl3): δ 139.5, 130.0, 129.2, 121.3, 117.9, 114.8 (aromatic C), 81.3, 59.1 (cage C), 48.5 (CH). 11B{1H} NMR (128 MHz, CDCl3): δ 3.7 (1B), 5.8 (1B), 9.9 (2B), 12.2 (2B), 14.0 (4B). HRMS: m/z Calcd for C15H2111B810B2+N: 323.2672. Found: 323.2661. Its structure was confirmed by single-crystal X-ray analyses, which is included in the Supporting Information. (18) Lautens, M.; Yoshida, M. J. Org. Chem. 2003, 68, 762. (19) Sheldrick, G. M. SADABS: Program for Empirical Absorption Correction of Area Detector Data; University of G€ottingen: G€ ottingen, Germany, 1996. (20) Sheldrick, G. M. SHELXTL 5.10 for Windows NT: Structure Determination Software Programs; Bruker Analytical X-ray Systems, Inc.: Madison, WI, 1997.

5959

dx.doi.org/10.1021/om200772q |Organometallics 2011, 30, 5953–5959