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Enhanced Activity of [Ni(NHC)CpCl] Complexes in Arylamination Catalysis Anthony R. Martin, Yusuke Makida, Sébastien Meiries, Alexandra M. Z. Slawin, and Steven P. Nolan* EaStCHEM School of Chemistry, University of St Andrews, North Haugh, St Andrews KY16 9ST, U.K. S Supporting Information *

ABSTRACT: Seven new air- and moisture-stable nickel complexes bearing flexible bulky NHC (N-heterocyclic carbene) ancillary ligands (NHC = IPr*, IPr*Tol, IPr*OMe, IPent) are reported. Using experimentally determined crystal structures, the steric environments of [Ni(NHC)CpCl] complexes were analyzed. A survey of their catalytic activity in Buchwald−Hartwig arylamination has been performed. In comparison to less sterically demanding analogues (NHC = IMes, SIMes, IPr, SIPr), an increase in the ligand bulkiness was found to correlate to a dramatic enhancement of the C−N bond formation efficiency. Finally, the catalytic activity of the most active precatalyst, [Ni(IPr*OMe)CpCl], was further explored and the scope and limitations of this complex were examined.

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substituted Cp moiety14 or the halide has been abstracted/ replaced.15 However, since we reported their low activity in Buchwald− Hartwig arylamination, no further attempts to improve their reactivity have been published. Nicasio suggested16 that the reason for this moderate catalytic activity may arise from the difficulty in reducing the NiII precatalyst to its active Ni0 form. While Nicasio replaced the Cp ligand with the more labile η3allyl, we hypothesized that the use of a very bulky NHC ancillary ligand could increase the steric pressure on the Cp moiety and hence favor its decoordination during the reduction process. Moreover, bulky NHCs could improve the stability of the [Ni0-NHC] active species and thus enhance its catalytic performance. However, steric hindrance about the metal center could be detrimental for the coordination of incoming substrates. Therefore, the use of a bulky yet flexible NHC ancillary ligand could constitute a solution. For this purpose, we employed the IPent ligand and IPr*type NHC ligands which have been studied by Hillhouse on Ni17 and by us on Au,18 Ru,19 Ni,19b and Pd.20 Herein, we report the activity of [Ni(NHC)CpCl] complexes 1−4 in Buchwald−Hartwig arylamination (NHC = IPr* (1), IPr*Tol (2), IPr*OMe (3), IPent (4)) and compare it to that of the previously reported catalysts7 of the same general formula (NHC = IMes (5), SIMes (6), IPr (7), SIPr (8)) (Figure 1).21

INTRODUCTION Cross-coupling reactions are some of the most powerful synthetic chemistry tools. Palladium-catalyzed transformations have attracted particular attention, culminating in the 2010 Nobel Prize being awarded to Suzuki, Heck, and Negishi for “palladium catalyzed cross-coupling reactions in organic synthesis”.1 Much less research has been devoted to the first-row counterpart of palladium, nickel. Nevertheless, nickel has proven to be a cost-effective and viable alternative for most of the achievable transformations using palladium.2 Many Nibased systems have been developed for C−C and C−N bond formation and other coupling reactions.3 While in situ prepared Ni/NHC catalysts have been studied profusely in C−N bond formation,4 the use of well-defined [Ni(NHC)] precatalysts has been explored to a lesser extent despite the interesting activity of such systems.5 [Ni(NHC)CpCl] complexes are particularly attractive, partially due to their air and moisture stability and straightforward preparation. Following the seminal publication by Cowley, describing the synthesis of [Ni(IMes)CpCl],6 our group reported a simple, general route to this catalyst family,7 which has been studied comprehensively by Chetcuti and others for the hydrosilylation of ketones and aldehydes,8 Suzuki−Miyaura coupling,9 hydrothiolation of alkynes,10 C−H activation of acetonitrile11 or acetone ligands,12 and intramolecular C−H activation.13 Analogues have been reported where the Cp ligand was replaced with an indenyl or © XXXX American Chemical Society

Received: May 29, 2013

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ligand (4) was found to be smaller than the IPr* ligands and the SIPr ligand (8). This may arise from the flexibility of IPent; the pent-3-yl moieties are positioned away from the metal center. As a general trend, the %Vbur value is closely correlated to the reaction time required for the synthesis of the complexes: the bulkier the NHC ligand, the longer the reaction time. 1−4 were assessed in Buchwald-Hartwig arylamination. To compare their catalytic performance directly with that of the reported precatalysts 5−8, the coupling between morpholine and 4-chlorotoluene was selected as a benchmark reaction. The previous conditions7 were used (Table 3). As previously reported,7 precatalysts 5−8 performed poorly (16−32% conversion). Complex 4, which bears the flexible IPent ligand, exhibits a catalytic activity in the same range. Complexes bearing the flexible yet bulky IPr*-based ligands (1−3) showed improved performance, with conversion of up to 90%. The %Vbur values of the complexes correlate to their catalytic performance. This trend agrees with our working hypothesis that an increase in NHC bulk could lead to improved catalytic properties, possibly through the stabilization of the putative Ni0 active species. We then prepared an additional three nickel complexes bearing IPr*OMe as an ancillary ligand to prove the effect of the chloride moiety on the nickel center in Buchwald−Hartwig coupling (Table 4). Halogen-exchanged analogues were synthesized under Finkelstein’s conditions from 3 ([Ni(IPr*OMe)CpX] (X = Br (9), I (10)). An acetonitrilecoordinated cationic complex was also prepared from 3 according to the reported procedure9 ([Ni(IPr*OMe)(NCCH3)Cp](PF6) (11)). The catalytic activities of 9−11 were evaluated in the benchmark reaction, and these complexes showed moderate to good performance (62−84% conversion). Although similar active species would be expected to form from 3 as well as 9−11, slightly less reactive tendencies of 9−11 in comparison to 3 were caused by a variation in the thermal stability of these precatalysts. 3 was found to be the most active precatalyst. After optimization of the reaction parameters, full conversion was reached in the benchmark reaction (Table 5, 12a) using 5 mol % of 3, KOtAm, and toluene at 110 °C.24 Although the use of other well-defined nickel complexes for the coupling of aryl chlorides16,26 or bromides27 with amines has been reported, the use of air- and moisture-stable [Ni(NHC)CpCl] complexes represents a significant advance. We next surveyed the scope and limitations of the present catalytic system (Table 5). The reactivity appears to depend on the substitution pattern of the aryl chloride. Slightly hindered or unhindered aryl chlorides were well tolerated (Table 5, 12a,b). In contrast, methyl groups at the ortho position of the chlorobenzene ring led to lower yields (Table 5, 12c,d); the reaction did not proceed with chloromesitylene (Table 5, 12d). To circumvent this lack of reactivity, bromomesitylene was used. Even though bromide derivatives are known to perform better during the oxidative addition step, no arylated product was formed but 50% dehalogenation product was observed by GC, suggesting that oxidative addition of the C−halide bond to the catalyst is still possible, while the sterics of the aryl halide play a crucial role. The electronic properties of the aryl chloride did not significantly influence the reaction; activated and deactivated chlorobenzene derivatives afforded the products in good yields (Table 5, 12e−g). We also investigated several amines. Cyclic dialkylamines (Table 5, 12a−g,k,l), N-

Figure 1. [Ni(NHC)CpCl] precatalysts examined in the Buchwald− Hartwig amination reaction.

In addition, we examine the reactivity of [Ni(IPr*OMe)CpCl] derived complexes, [Ni(IPr*OMe)CpX] (X = Br (9), I (10)) and [Ni(IPr*OMe)(NCCH3)Cp](PF6) (11), to explore the anionic ligand effect on the nickel center.

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RESULTS AND DISCUSSION The imidazolium chloride salts of the IPr*, IPr*Tol, IPr*OMe, and IPent ligands (NHC·HCl) were prepared according to the literature reports.20a,22 The synthesis of 1−4 was undertaken via a previously described procedure.7 Nickelocene and the respective NHC·HCl salt were refluxed in THF for 3−16 h to afford 1−4 in good isolated yields (Table 1). Notably, the more Table 1. Synthesis of [Ni(NHC)CpCl] Complexes 1−4

complex

NHC·HCl

reaction time (h)

yield (%)

1 2 3 4

IPr*·HCl IPr*Tol·HCl IPr*OMe·HCl IPent·HCl

16 16 16 3

79 67 84 76

sterically demanding NHC ligands IPr*, IPr*Tol, and IPr*OMe required prolonged reaction times (ca. 16 h) in comparison to IPent (Table 1, entry 4), and (S)IMes and (S)IPr (only 3 h in literature reports). 1−4 were characterized by 1H and 13C{1H} NMR spectroscopy; their purities and structures were confirmed by elemental analysis and single-crystal X-ray diffraction,23 respectively (Figure 2). All exhibit the same two-legged piano-stool geometry around the metal center, considering the NHC ligand, the chloride ion, and the centroid of the Cp moiety. The NHC ligand does not affect the spatial disposition of the Cp moiety,24 suggesting that no steric pressure is exerted on the Cp ligand by the NHC ligands, in the solid state. The angle among the carbene carbon, the nickel center, and the chloride (C1−Ni−Cl1) lies in the range 92.4−94.0°. The bond distances between the carbene (C1) and the metal center (Ni1) for 1−4 are in the range 1.865−1.904 Å and are close to the literature data for 5−823 (Table 2). On the basis of the crystal structures, the percent buried volume (%Vbur) was calculated using the “SambVca” application.25 Values were obtained for the NHC ligands in 1−4 and also for 5−8 for comparative purposes (Table 2). As expected, IPr*-based NHC ligands (1−3) featured the highest buried volume (39.8−40.1%). In contrast, the IPent B

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Figure 2. Molecular structures of complexes 1−4. H atoms are omitted for clarity.

Table 2. Comparison of Bond Lengths and Angles and %Vbur Values for 1−8 complex [Ni(IPr*)CpCl] (1) [Ni(IPr*Tol)CpCl] (2) [Ni(IPr*OMe)CpCl] (3) [Ni(IPent)CpCl] (4) [Ni(IMes)CpCl] (5)b,c [Ni(SIMes)CpCl] (6)b,d [Ni(IPr)CpCl] (7)d [Ni(SIPr)CpCl] (8)d

Ni1−C1 (Å)

C1−Ni1−Cl1 (deg)

%Vbura

1.904(5) 1.865(6) 1.887(3)

92.65(5) 93.05(3) 94.04(5)

39.9 39.8 40.1

1.873(7) 1.873(5), 1.877(5)

92.41(7) 96.89(5), 96.79(3) 98.1(6), 99.4(6)

36.1 33.1, 33.7

93.86(3) 92.06(5)

35.8 36.9

1.861(16), 1.882(16) 1.8748(11) 1.8752(16)

Table 3. Efficiency of Precatalysts 1−8 in Buchwald− Hartwig Couplinga

34.1, 34.2

precatalyst

conversionb (%)

[Ni(IPr*)CpCl] (1) [Ni(IPr*Tol)CpCl] (2) [Ni(IPr*OMe)CpCl] (3) [Ni(IPent)CpCl] (4) [Ni(IMes)CpCl] (5) [Ni(SIMes)CpCl] (6) [Ni(IPr)CpCl] (7) [Ni(SIPr)CpCl] (8)

75 51 90 23 17 16 28 32

a

%Vbur values were calculated using a Ni1−C1 value of 2.00 Å, a sphere radius of 3.5 Å, Bondi radii scaled by 1.17, and mesh spacing of 0.05. H atoms were excluded. bTwo independent molecules are present in the asymmetric unit. cSee ref 23. dSee ref 7.

a

methylaniline (Table 5, 12h), and 2,6-dimethylaniline (Table 5, 12i) were tolerated. In contrast to the case for hindered aryl chlorides (Table 5, 12d), hindered anilines reacted smoothly (Table 5, 12i). However, in the case of n-octylamine, the coupling product was isolated in only 23% yield (Table 5, 12j). Attempts to couple unhindered 4-chlorotoluene with noctylamine were also unsuccessful (only 31% conversion by GC). Finally, we investigated the use of heteroaryl chloride coupling partners. Surprisingly, 2-chloropyridine, which is known to undergo facile arylamination, did not permit full conversion (Table 5, 12k), whereas the more challenging 3chloropyridine achieved full conversion and 80% isolated yield (Table 5, 12l). The results in Table 5 underline the efficiency of 3 for C−N bond formation, regardless of the electronics of the aryl

Table 4. Ni Precatalysts 9−11 and Their Catalytic Activity in Buchwald−Hartwig Couplinga

Reaction conditions: 4-chlorotoluene (0.42 mmol), morpholine (0.63 mmol), KOtBu (0.84 mmol), [Ni] (5 mol %), dioxane (1 mL), 105 °C. bConversion to coupling product based on starting material determined by GC; average of two runs.

precatalyst conversion (%)

9 72

10 62

11 84

a

Reaction conditions and their assessments were identical with those in Table 3.

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analysis were grown by slow diffusion of pentane into a staurated solution of 1 in chloroform. 1H NMR (CD2Cl2, 300 MHz): δ 2.34 (s, 6H, CH3), 4.59 (s, 5H, CHCp), 5.02 (s, 2H, CHimid), 5.77 (s, 4H, CH(Ph)2), 6.70−6.74 (m, 8H, HAr), 7.03 (s, 4H, HAr), 7.07−7.10 (m, 12H, HAr), 7.22−7.33 (m, 20H, HAr). 13C NMR (CD2Cl2, 75 MHz): δ 22.1 (CH3), 51.7 (CH), 93.5 (CHCp), 125.6 (CHAr), 126.8 (CHAr), 127.0 (CHAr), 128.6 (CHAr), 128.7 (CHAr), 129.8 (CHAr), 130.8 (CHAr), 130.9 (CHAr), 137.0 (CAr), 139.3 (CAr), 142.6 (CAr), 143.9 (CAr), 145.1 (CAr), 167.9 (CAr). Anal. Calcd for C74H61N2ClNi: C, 82.88; H, 5.73; N, 2.61. Found: C, 82.91; H, 5.81; N, 2.74. [Ni(IPr*Tol)CpCl] (2). Following the general procedure, using 200 mg of nickelocene and 1.124 g of IPr*Tol·HCl, 2 was isolated as a purplepink powder (839 mg) in 67% yield. Suitable crystals for X-ray diffraction analysis were grown by slow diffusion of pentane into a saturated solution of 2 in toluene. 1H NMR (CD2Cl2, 300 MHz): δ 2.23 (s, 12H, CH3), 2.32−2.34 (m, 18H, CH3), 4.59 (s, 5H, CHCp), 5.12 (s, 2H, CHimid), 5.72 (s, 4H, CH(Ph)2), 6.58 (d, J = 8.1 Hz, 8H, HAr), 6.87 (d, J = 7.9 Hz, 8H, HAr), 7.02 (s, 4H, HAr), 7.07 (d, J = 8.0 Hz, 8H, HAr), 7.19 (d, J = 8.1 Hz, 8H, HAr). 13C NMR (CD2Cl2, 75 MHz): δ 21.2 (CH3), 21.3 (CH3), 22.1 (CH3), 51.0 (CH), 93.6 (CHCp), 125.6 (CHAr), 129.2 (CHAr), 129.3 (CHAr), 129.6 (CHAr), 130.5 (CHAr), 130.8 (CHAr), 136.3 (CAr), 136.5 (CAr), 137.0 (CAr), 138.9 (CAr), 141.3 (CAr), 142.3 (CAr), 142.6 (CAr), 166.9 (CAr). Anal. Calcd for C82H77N2ClNi: C, 83.14; H, 6.55; N, 2.36. Found: C, 83.12; H, 6.53; N, 2.46. [Ni(IPr*OMe)CpCl] (3). Following the general procedure, using 200 mg of nickelocene and 1.039 g of IPr*OMe·HCl, 3 was isolated as a purple-pink powder (983 mg) in 84% yield. Suitable crystals for X-ray diffraction analysis were grown by slow evaporation of a concentrated solution of 3 in dichloromethane. 1H NMR (CD2Cl2, 300 MHz): δ 3.65 (s, 6H, OCH3), 4.64 (s, 5H, CHCp), 4.96 (s, 2H, CHimid), 5.77 (s, 4H, CH(Ph)2), 6.71 (s, 4H, HAr), 6.73−6.76 (m, 8H, HAr), 7.07−7.10 (m, 12H, HAr), 7.22−733 (m, 20H, HAr). 13C NMR (CD2Cl2, 75 MHz): δ 52.0 (CH), 55,7 (OCH3) 93.4 (CHCp), 115,4 (CHAr), 125.7 (CHAr), 126.9 (CHAr), 127.2 (CHAr), 128.7 (CHAr), 129.7 (CHAr), 130.9 (CHAr), 132.5 (CAr), 143.7 (CAr), 144.5 (CAr), 144.9 (CAr), 159.7 (CAr), 168.7. Anal. Calcd for C74H61N2O2ClNi: C, 80.47; H, 5.57; N, 2.54. Found: C, 80.53; H, 5.65; N, 2.67. [Ni(IPent)CpCl] (4). Following the general procedure, using 200 mg of nickelocene and 531 mg of IPent·HCl, 4 was isolated as a purplepink powder (468 mg) in 76% yield. Suitable crystals for X-ray diffraction analysis were grown by slow evaporation of a saturated solution of 4 in pentane. 1H NMR (CD2Cl2, 300 MHz): δ 0.73 (t, J = 7.5 Hz, 12H, CH3), 1.02 (t, J = 7.3 Hz, 12H, CH3), 1.43−1.58 (m, 8H, CH2), 1.83−2.04 (m, 8H, CH2), 2.46−2.54 (m, 4H, CH), 4.48 (s, 5H, CHCp), 7.09 (s, 2H, CHimid), 7.32 (d, J = 7.8 Hz, 4H, HAr), 7.52 (t, J = 7.7 Hz, 2H, HAr). 13C NMR (CD2Cl2, 75 MHz): δ 10.4 (CH3), 12.9 (CH3), 26.6 (CH2), 27.6 (CH2), 41.3 (CH), 92.8 (CHCp), 125.9 (CHAr), 126.4 (CHAr), 129.2 (CHAr), 145.0 (CAr), 167.5 (CAr). Anal. Calcd for C40H57N2ClNi: C, 72.79; H, 8.70; N, 4.24. Found: C, 72.68; H, 8.82; N, 4.33. General Procedure for the Preparation of Complexes 9 and 10. This reaction was conducted under aerobic conditions. [Ni(IPr*OMe)CpCl] (1 equiv) and an excess amount of the corresponding sodium salt were placed in a vial equipped with a magnetic stirring bar. Acetone was added, followed by sealing with a screw cap. The resulting suspension was stirred at 60 °C for 24 h. The solvent was roughly evaporated, and the crude residue was dissolved in CH2Cl2 before being passed through a pad of Celite. The collected filtrate was concentrated to dryness and triturated with pentane. The complexes were finally dried overnight under high vacuum at 60 °C. [Ni(IPr*OMe)CpBr] (9). Following the general procedure, using 21.1 mg of 3 and 500 mg of NaBr, 9 was isolated as a purple-pink powder (18.3 mg) in 83% yield. 1H NMR (CD2Cl2, 400 MHz): δ 3.64 (s, 6H, OCH3), 4.76 (s, 5H, CHCp), 4.98 (s, 2H, CHimid), 5.88 (s, 4H, CH(Ph)2), 6.71 (s, 4H, HAr), 6.72−6.76 (m, 8H, HAr), 7.04−7.11 (m, 12H, HAr), 7.22−7.31 (m, 12H, HAr), 7.33−7.38 (m, 8H, HAr). 13 C{1H} NMR (CD2Cl2, 100 MHz): δ 52.1 (CH(Ph)2), 55.7 (OCH), 93.9 (CHCp), 115.5 (CHAr), 125.7 (CHAr), 126.9 (CHAr), 127.2 (CHAr), 128.7 (CHAr), 128.8 (CHAr), 129.7 (CHAr), 130.9 (CHAr),

Table 5. Scope and Limitations of the Arylamination Reactiona,b

a

Reaction conditions: aryl chloride (0.38 mmol), amine (0.57 mmol), KOtAm (0.76 mmol), 3 (5 mol %), toluene (1 mL), 110 °C, 16 h. b Conversion (%) to coupling product, shown in parentheses, based on starting material determined by GC; average of two runs.

chloride partner. However, the use of hindered aryl halide derivatives is problematic. While a bulkier NHC ligand led to improved performance, it appears that more flexible NHC ligands are required to accommodate incoming substrates.

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CONCLUSION In summary, we have reported the preparation of seven new airand moisture-stable nickel complexes bearing NHC ligands with flexible bulk, namely IPr*, IPr*Tol, IPr*OMe, and IPent. These complexes were fully characterized by NMR, and crystal structures of [Ni(NHC)CpCl] were elucidated by X-ray diffraction analyses. A survey of their catalytic properties in Buchwald−Hartwig amination was presented. The bulkiness of the ligand appeared to dramatically affect the catalytic properties, as bulkier NHC ligands allowed higher conversions. We assume that the considerable steric demand of the bulky IPr*-based NHC ligand could prevent the rapid decay of the [Ni0-NHC] active species and thus enhance its catalytic efficiency. At the same time, in order to allow the coordination of the coupling partners, the flexibility of the NHC ligand about the metal center proved to play a major role.

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EXPERIMENTAL SECTION

General Procedure for the Preparation of Complexes 1−4. In a glovebox, a 50 mL Schlenk flask equipped with a magnetic stirring bar was charged with nickelocene (200 mg, 1.06 mmol), NHC·HCl (1.0 equiv, 1.06 mmol), and 20 mL of THF. Outside of the glovebox, the reaction mixture was connected to a Schlenk line and stirred at 70 °C for 3−16 h. The solvent was eventually evaporated off, and the crude residue was dissolved in CH2Cl2 (15 mL) before being passed through a bed of Celite over silica (4 cm of each). The collected filtrate was concentrated until 3 mL of solution remained (except for IPent, which was concentrated to dryness and did not need further purification). Addition of pentane resulted in the precipitation of the complexes. The supernatant was removed, and the residue was washed twice with 25 mL of pentane. The complexes were finally dried overnight under high vacuum at 80 °C. [Ni(IPr*)CpCl] (1). Following the general procedure, using 200 mg of nickelocene and 1.006 g of IPr*·HCl, 1 was isolated as a purple-pink powder (896 mg) in 79% yield. Suitable crystals for X-ray diffraction D

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132.7(CAr), 143.8 (CAr), 144.2 (CAr), 144.8 (CAr), 159.6 (CAr), 168.9 (Cimid.). Anal. Calcd for C74H61N2O2BrNi: C, 77.36; H, 5.35; N, 2.44. Found: C, 77.29; H, 5.21; N, 2.34. [Ni(IPr*OMe)CpI] (10). Following the general procedure, using 21.2 mg of 3 and 600 mg of NaI, 10 was isolated as a brown-purple powder (19.0 mg) in 83% yield. 1H NMR (CD2Cl2, 400 MHz): δ 3.62 (s, 6H, OCH3), 4.95 (s, 5H, CHCp), 5.02 (s, 2H, CHimid), 6.01 (s, 4H, CH(Ph)2), 6.69 (s, 4H, HAr), 6.70−6.75 (m, 8H, HAr), 7.01−7.11 (m, 12H, HAr), 7.23−7.28 (m, 4H, HAr), 7.29−7.34 (m, 8H, HAr), 7.37− 7.43 (m, 8H, HAr). 13C{1H} NMR (CD2Cl2, 100 MHz): δ 52.3 (CH(Ph)2), 55.7 (OCH), 94.5 (CHCp), 115.6 (CHAr), 125.8 (CHAr), 126.9 (CHAr), 127.2 (CHAr), 128.7 (CHAr), 128.8 (CHAr), 129.6 (CHAr), 131.1 (CHAr), 133.1(CAr), 143.8 (CAr), 143.9 (CAr), 144.5 (CAr), 159.6 (CAr). Anal. Calcd for C74H61N2O2INi: C, 74.32; H, 5.14; N, 2.34. Found: C, 74.25; H, 5.03; N, 2.28. Procedure for the Preparation of the Complex [Ni(IPr*OMe)(NCMe)Cp](PF6) (11). In a glovebox, a vial containing a magnetic stirring bar was charged with [Ni(IPr*OMe)CpCl] (110.4 mg, 0.1 mmol), KPF6 (184.1 mg, 10 equiv), 2.0 mL of CH3CN, and 1.0 mL of CH2Cl2 and sealed with a screw cap. Outside of the glovebox, the reaction mixture was stirred at room temperature for 1 h. The solvent was evaporated off, and the residue was dissolved in CH2Cl2 (2.0 mL) before being passed through a pad of Celite. The filtrate was concentrated to ca. 0.25 mL and treated with pentane (2.0 mL) to yield a yellow solid. The solid was collected by filtration, washed with pentane, and dried overnight under high vacuum at 60 °C to give 11 as a yellow powder (103.9 mg) in 83% yield. 1 H NMR (CDCl3, 400 MHz): δ 1.10 (s, 3H, NCCH3), 3.67 (s, 6H, OCH3), 5.12 (s, 5H, CHCp), 5.37 (s, 2H, CHimid), 5.59 (s, 4H, CH(Ph)2), 6.71−6.78 (m, 8H, HAr), 6.78 (s, 4H, HAr), 7.07−7.18 (m, 12H, HAr), 7.27−7.35 (m, 12H, HAr), 7.36−7.45 (m, 8H, HAr). 13 C{1H} NMR (CD2Cl2, 100 MHz): δ 4.0 (NCCH3), 52.2 (CH(Ph)2), 55.6 (OCH3) 96.3 (CHCp), 115.0 (CHAr), 126.4 (CHimid), 127.0 (CHAr), 127.7 (CHAr), 128.6 (CHAr), 128.9 (CHAr), 129.2 (CHAr), 130.8 (CAr), 133.8 (NCCH3) 142.2 (CAr), 142.9 (CAr), 160.1 (CAr), 165.0 (Cimid). Anal. Calcd for C76H64N3O2F6PNi: C, 72.73; H, 5.14; N, 3.35. Found: C, 72.62; H, 5.10; N, 3.45. General Procedure for the Buchwald−Hartwig Amination Reaction. In a glovebox, a vial containing a stirring bar was charged with KOtAm (96 mg, 0.76 mmol, 2.0 equiv) and [Ni(IPr*OMe)CpCl] (3; 1.90 × 10−5 mol, 21 mg, 5 mol %) and sealed with a screw cap fitted with a septum. The amine (0.57 mmol, 1.5 equiv) and/or the aryl chloride (0.38 mmol, 1.0 equiv) were added at this point if solids. Outside of the glovebox, the solvent (toluene, 1 mL) was added, followed by the amine and/or the aryl chloride if liquids. Finally, the vial was heated to 110 °C for 16 h. The solution was then cooled to room temperature, diluted with 5 mL of dichloromethane, and passed through a plug of Celite which was subsequently washed twice with 5 mL of dichloromethane. The collected filtrate was concentrated and adsorbed on silica gel prior to purification via flash column chromatography.

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ACKNOWLEDGMENTS We thank the ERC (FUNCAT) and the EPSRC for funding and the EPSRC NMSSC in Swansea for mass spectrometric analyses. S.P.N. is a Royal Society Wolfson Research Merit Award holder. David J. Nelson and Alba Collado are acknowledged for fruitful discussions.

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

Text, figures, a table, and CIF files giving crystallographic data for 1−5, structure overlays of 1−5, optimization reaction study, compound characterization data, and 1H and 13C{1H} NMR spectra for all the synthesized compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Fax: +44 (0) 1334 463 808. E-mail: [email protected]. Notes

The authors declare no competing financial interest. E

dx.doi.org/10.1021/om4004863 | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

(19) (a) Manzini, S.; Urbina-Blanco, C. A.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2012, 31, 6514−6517. (b) Balogh, J.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2012, 31, 3259−3263. (20) (a) Martin, A. R.; Chartoire, A.; Slawin, A. M. Z.; Nolan, S. P. Beilstein J. Org. Chem. 2012, 8, 1637−1643. (b) Chartoire, A.; Lesieur, M.; Falivene, L.; Slawin, A. M. Z.; Cavallo, L.; Cazin, C. S. J.; Nolan, S. P. Chem. Eur. J. 2012, 18, 4517−4521. (c) Chartoire, A.; Frogneux, X.; Nolan, S. P. Adv. Synth. Catal. 2012, 354, 1897−1901. (d) Chartoire, A.; Frogneux, X.; Boreux, A.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2012, 31, 6947−6951. (e) Chartoire, A.; Boreux, A.; Martin, A. R.; Nolan, S. P. RSC Adv. 2013, 3, 3840−3843. (f) Meiries, S.; Chartoire, A.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2012, 31, 3402−3409. (21) Abbreviations: IPr*, 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene; IPr*Tol, 1,3-bis(2,6-bis(di-p-tolylmethyl)-4methylphenyl)imidazol-2-ylidene; IPr*OMe, 1,3-bis(2,6-bis(diphenylmethyl)-4-methoxyphenyl)imidazol-2-ylidene; IPent, 1,3-bis(2,6-bis(pentan-3-yl)phenyl)imidazol-2-ylidene; IMes, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; SIMes, 1,3-bis(2,4,6-trimethylphenyl)-4,5dihydroimidazol-2-ylidene; IPr, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; SIPr, 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene. (22) (a) Berthon-Gelloz, G.; Siegler, M. A.; Spek, A. L.; Tinant, B.; Reek, J. N. H.; Markó, I. E. Dalton Trans. 2010, 39, 1444−1446. (b) Meiries, S.; Speck, K.; Cordes, D. B.; Slawin, A. M. Z.; Nolan, S. P. Organometallics 2013, 32, 330−339. (c) Collado, A.; Balogh, J.; Meiries, S.; Slawin, A. M. Z.; Falivene, L.; Cavallo, L.; Nolan, S. P. Organometallics 2013, 32, 3249−3252. (23) CCDC 940977−940981 contains the crystallographic data for 1−5. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_ request/cif. Data for 6−8 can be obtained from ref 7. (24) See the Supporting Information for structure overlays of complexes 1−5. (25) Poater, A.; Cosenza, B.; Correa, A.; Giudice, S.; Ragone, F.; Scarano, V.; Cavallo, L. Eur. J. Inorg. Chem. 2009, 2009, 1759−1766. (26) (a) Chen, C.; Yang, L.-M.. Org. Lett. 2005, 7, 2209−2211. (b) Gao, C.-Y.; Cao, X.; Yang, L.-M. Org. Biomol. Chem. 2009, 7, 3922−3925. (27) Matsubara, K.; Ueno, K.; Koga, Y.; Hara, K. J. Org. Chem. 2007, 72, 5069−5076.

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dx.doi.org/10.1021/om4004863 | Organometallics XXXX, XXX, XXX−XXX