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Structurally Similar, Thermally Stable Copper(I), Silver(I), and Gold(I) Ethylene Complexes Supported by a Fluorinated Scorpionate H. V. Rasika Dias* and Jiang Wu Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019, United States S Supporting Information *

ABSTRACT: Treatment of Li[PhBH3] with excess 3(C2F5)PzH led to the B-phenylated tris(pyrazolyl)borate ligand as its lithium salt [PhB(3-(C2F5)Pz)3]Li. This ligand enabled the isolation of thermally stable group 11 metal ethylene adducts [PhB(3-(C2F5)Pz)3]M(C2H4) (M = Au, Ag, Cu). They were characterized by spectroscopy and by X-ray crystallography. These ethylene adducts are structurally similar and feature three-coordinate trigonal-planar metal sites and a κ2-bonded tris(pyrazolyl)borate ligand. They are ideal for examining the trends involving ethylene complexes of the group 11 triad. The ethylene 13C NMR resonance of the [PhB(3(C2F5)Pz)3]M(C2H4) adducts in C6D12 appear at δ 58.9, 101.6, and 85.5 ppm, respectively, for M = Au, Ag, Cu. The M−C and M−N bond distances are largest in the silver complex and smallest in the copper complex.

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INTRODUCTION Tris(pyrazolyl)borateswhich belong to a class of ligands generally referred to as scorpionatesare some of the most widely utilized metal ion chelators in chemistry.1−4 They are very popular because the steric and electronic properties of these ligands can be modified quite readily by varying the substituents on the pyrazolyl moieties or on the boron center. Indeed, a vast array of tris(pyrazolyl)borates are now known, including fluorinated versions such as [HB(3-(CF3)Pz3]− and [HB(3,5-(CF3)2Pz)3]− as well as B-alkylated and B-arylated systems such as [MeB(3-(CF3)Pz)3]− and [PhB(3-(CF3)Pz)3]−.1,5−7 Tris(pyrazolyl)borates have played a particularly important role in coinage-metal (Cu, Ag, Au) alkene chemistry.3,8 For instance, the first structurally authenticated coinage-metal ethylene complexes reported in the literature (i.e., [HB(3,5(CH3)2Pz)3]Cu(C2H4),9 [HB(3,5-(CF3)2Pz)3]Ag(C2H4),10 and [HB(3,5-(CF3)2Pz)3]Au(C2H4)11) involve tris(pyrazolyl)borate supporting ligands. Isolation of [HB(3,5-(CF3)2Pz)3]Cu(C2H4)12 completed the isoleptic ethylene complexes of the group 11 triad (Figure 1).3,8 Interestingly, however, the gold adduct [HB(3,5-(CF3)2Pz)3]Au(C2H4) (1) displays a rare κ2 coordination of the tris(pyrazolyl)borate ligand (i.e., one very long and two short Au−N distances and trigonal-planar gold center), while the corresponding ethylene complexes of the lighter coinage metals (2 and 3)silver and copperexhibit typical κ3-tris(pyrazolyl)borate coordination in the solid state. In this paper, we describe the outcome of an effort to obtain an isostructural series of group 11 ethylene adducts for a group trend study. Indeed, we show that it is possible to synthesize the complete set of [PhB(3-(C2F5)Pz)3]M(C2H4) complexes (M = Au, Ag, Cu) (see 4−6, Figure 1) that have very similar © 2012 American Chemical Society

Figure 1. Coinage-metal ethylene complexes supported by [HB(3,5(CF3)2Pz)3]− and [PhB(3-C2F5)Pz)3]−. Special Issue: Fluorine in Organometallic Chemistry Received: November 27, 2011 Published: January 18, 2012 1511

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adducts, respectively. These separations are within the sum of van der Waals radii of M and C (for comparison, the sums of van der Waals radii of M and C are 3.36, 3.42, and 3.10 Å for M = Au, Ag, Cu, respectively). However, these contacts do not appear to be significant enough to distort the coordination geometry at the metal center, because all three [PhB(3(C2F5)Pz)3]M(C2H4) complexes feature trigonal-planar metal sites, as is evident from the sum of angles at the metal center (360°). The NMN and CMC planes, however, are not exactly coplanar, and the torsion angles between the two planes are 2.3, 17.2, and 8.9° for the Au, Ag, and Cu adducts, respectively. Overall, unlike the previously reported series [HB(3,5(CF3)2Pz)3]M(C2H4) (M = Cu, Ag, Au) (where the Cu and Ag adducts have κ3-bonded tris(pyrazolyl)borate and pseudotetrahedral metal sites while the Au adduct has a trigonal-planar metal site and a κ2-bonded tris(pyrazolyl)borate ligand; see Figure 1),10−12 [PhB(3-(C2F5)Pz)3]M(C2H4) complexes have similar structures in the solid state (Figures 2−4). The CC, Au−C, and Au−N bond distances of [PhB(3(C2F5)Pz)3]Au(C2H4) (see Table 2) are similar to the corresponding distances observed for [HB(3,5-(CF3)2Pz)3]Au(C2H4)11 (CC = 1.380(10) Å, Au−C = 2.096(6), 2.108(6) Å, and Au−N = 2.224(5), 2.221(5) Å) and [HB(3-(CF3),5(Ph)Pz)3]Au(C2H4)11 (CC = 1.387(9) Å, Au−C = 2.093(5), 2.096(5) Å, and Au−N = 2.175(4), 2.205(4) Å). This is not surprising, as all three adducts feature three-coordinate, trigonal-planar gold centers. Structurally authenticated gold ethylene complexes such as [PhB(3-(C2F5)Pz)3]Au(C2H4) are rare.3,8,11,13,14 A limited number of silver ethylene adducts supported by tris(pyrazolyl)borates are available in the literature.3 Thus, it is possible to compare Ag−C and Ag−N distances of threecoordinate [PhB(3-(C2F5)Pz)3]Ag(C2H4) with those of fourcoordinate, tetrahedral silver ethylene complexes such as [HB(3,5-(CF3)2Pz)3]Ag(C2H4) and [MeB(3-(C2F5)Pz)3]Ag(C2H4). The average Ag−C bond distances of these adducts show no significant variations and are 2.282(3), 2.300(7), and 2.300(2) Å, respectively. The Ag−N distances are, however, significantly longer in the four-coordinate adducts (e.g., average Ag−N distances of three-coordinate [PhB(3-(C2F5)Pz)3]Ag(C2H4) and four-coordinate [HB(3,5-(CF3)2Pz)3]Ag(C2H4)10 and [MeB(3-(C2F5)Pz)3]Ag(C2H4)6 are 2.282(2), 2.358(4), and 2.3544(14) Å, respectively). The ethylene CC distance change as a result of coordination to silver(I) in these (and many of other reported) adducts is small and is often overshadowed by the high esd values, libration effects, and the anisotropy of the electron density.3,8,15 For comparisons, the CC bond length in free gaseous ethylene is estimated to be 1.3305(10) Å, while the corresponding distance from X-ray data is 1.313 Å.16,17 A comparison of structural data of [PhB(3-(C2F5)Pz)3]Cu(C2H4) (Table 2) to those for [HB(3,5-(CF3)2Pz)3]Cu(C2H4)12 and [MeB(3-(CF3)Pz)3]Cu(C2H4),5 with fourcoordinate, tetrahedral copper sites, shows that Cu−N distances are significantly shorter in [PhB(3-(C2F5)Pz)3]Cu(C2H4) (e.g., average Cu−N bond distances of [HB(3,5(CF3)2Pz)3]Cu(C2H4) and [MeB(3-(CF3)Pz)3]Cu(C2H4) are 2.111(3) and 2.113(2) Å, respectively, while the average Cu−N bond length in [PhB(3-(C2F5)Pz)3]Cu(C2H4) is 2.008(3) Å). The Cu−C distances, however, do not show a significant difference (e.g., average Cu−C distances of these adducts range from 2.022(6) to 2.038(3) Å). Although there are a number of structurally authenticated copper ethylene adducts in the

structures in the solid state by manipulating the substituent on the boron.

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RESULTS AND DISCUSSION The lithium salt of the ligand [PhB(3-(C2F5)Pz)3]− used in this work was synthesized from Li[PhBH3] and the free pyrazole 3(C2F5)PzH. After purification (mainly to remove extra pyrazole), [PhB(3-(C2F5)Pz)3]Li can be used directly in the synthesis of the coinage-metal adducts. For example, the treatment of [PhB(3-(C2F5)Pz)3]Li with AuCl under an atmosphere of ethylene in hexane led to the formation of [PhB(3-(C2F5)Pz)3]Au(C2H4) (4; Scheme 1) in good yield. It Scheme 1. Synthetic Route to [PhB(3-(C2F5)Pz)3]Au(C2H4) using Li[PhBH3], 3-(C2F5)PzH, AuCl, and Ethylene

is a colorless solid. Crystals of this compound can be handled in open air for short periods without any apparent signs of decomposition. The analogous Ag(I) and Cu(I) adducts 5 and 6 can also be prepared via a similar metathesis process using silver and copper salts, CF3SO3Ag and CuCl, instead of AuCl. [PhB(3-(C2F5)Pz)3]Ag(C2H4) can be purified by recrystallization in hexane at −20 °C. The solid sample of [PhB(3(C2F5)Pz)3]Ag(C2H4) is stable for days in air without protection from light. The copper ethylene complex [PhB(3(C2F5)Pz)3]Cu(C2H4) is also fairly air stable and can even be purified by running a hexane solution through a short silica gel column in open air. X-ray analysis of [PhB(3-(C2F5)Pz)3]M(C2H4) (M = Au, Ag, Cu; Table 1) revealed that all three coinage-metal adducts have rather similar structures in the solid state (Figures 2−4). Crystals of the copper adduct show nonmerohedral twinning, which was resolved satisfactorily by using the Cell_Now program. The tris(pyrazolyl)borate ligand of [PhB(3-(C2F5)Pz)3]M(C2H4) coordinates to the metal ion in a κ2 fashion via nitrogen atoms of two pyrazolyl arms and adopts a boat configuration. The third pyrazolyl ring occupies the apical position and adopts an orientation where the donor-nitrogen site points away from the metal site. The phenyl group on boron sits above the metal center. The metal to ipso carbon distances are 3.10, 2.79, and 2.81 Å in the Au, Ag, and Cu 1512

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Table 1. Crystal Data and Summary of Data Collection and Refinement empirical formula formula wt temp (K) wavelength (Å) cryst syst space group unit cell dimens a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z calcd density (Mg/m3) abs coeff (mm−1) final R indices (I > 2σ(I)) R1 wR2 R indices (all data) R1 wR2

[PhB(3-(C2F5)Pz)3]Au(C2H4)

[PhB(3-(C2F5)Pz)3]Ag(C2H4)

[PhB(3-(C2F5)Pz)3]Cu(C2H4)

C23H15AuBF15N6 868.19 100(2) 0.710 73 orthorhombic P212121

C23H15AgBF15N6 779.09 100(2) 0.710 73 monoclinic P21/n

C23H15CuBF15N6 734.76 100(2) 0.710 73 monoclinic P21/n

13.2540(10) 14.1925(11) 14.9711(12) 90 90 90 2816.2(4) 4 2.048 5.351

11.2741(7) 12.8593(8) 19.3139(11) 90 90.280(1) 90 2800.0(3) 4 1.848 0.847

11.052(3) 12.721(3) 19.714(5) 90 91.960(3) 90 2770.0(11) 4 1.762 0.917

0.0381 0.0863

0.0368 0.0957

0.0507 0.1338

0.0479 0.0911

0.0391 0.0985

0.0611 0.1403

Figure 2. ORTEP diagram of [PhB(3-(C2F5)Pz)3]Au(C2H4) (left; thermal ellipsoids set at 50% probability) and a view showing the κ2-bonded tris(pyrazolyl)borate ligand (right).

the copper complex. These M−C and M−N distances thus follow the trend of covalent radii of the M(I) ions (e.g., covalent radii of two-coordinate copper(I), gold(I), and silver(I) are 1.13, 1.25, and 1.33 Å, respectively).18,19 The ethylene CC bond distance is relatively long in the gold and copper adducts compared to that in the silver complex. However, these differences are not very significant because they are within the 3σ level of esd values. Nevertheless, the CC distance is expected to increase in the order Ag < Cu < Au on the basis of computational studies and M−ethylene bond strength data of various related and unrelated coinage-metal ethylene systems (i.e., in coinage-metal adducts, Au(I) forms the strongest bond with ethylene while Ag(I) forms the weakest bond).14,15,20−22 As noted below, 13C NMR data of the ethylene moiety ae a good indicator of the σ/π metal−ethylene interaction and observed data for [PhB(3-(C2F5)Pz)3]M(C2H4) are in agreement with the expected group trend.20,23−25

literature, those supported by tris(pyrazolyl)borate ligands are limited in number. Among these, [PhB(3-(C2F5)Pz)3]Cu(C2H4) and [(C2H4)Cu(Pz)2BH(Pz)CuCl]2 are rare (tris(pyrazolyl)borato)copper(I) ethylene complexes that feature three-coordinate copper−ethylene sites.9 [(C2H4)Cu(Pz)2BH(Pz)CuCl]2, however, has a relatively less bulky and electron rich tris(pyrazolyl)borate ligand. The Cu−N distances (1.934(2), 1.941(2) Å) of this adduct are shorter than the corresponding distances in [PhB(3-(C2F5)Pz)3]Cu(C2H4). The Cu−C distances of [(C2H4)Cu(Pz)2BH(Pz)CuCl]2 (1.995(3), 2.003(3) Å) are only marginally shorter in comparison to those found in [PhB(3-(C2F5)Pz)3]Cu(C2H4). [PhB(3-(C2F5)Pz)3]M(C2H4) adducts possess similar structures and are more suitable for direct comparisons and for examination of group trends of metal ethylene complexes. The M−C and M−N distances of the [PhB(3-(C2F5)Pz)3]M(C2H4) adducts are largest in the silver complex and smallest in 1513

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Figure 3. ORTEP diagram of [PhB(3-(C2F5)Pz)3]Ag(C2H4) (left; thermal ellipsoids set at 50% probability) and a view showing the κ2-bonded tris(pyrazolyl)borate ligand (right).

Figure 4. ORTEP diagram of [PhB(3-(C2F5)Pz)3]Cu(C2H4) (left; thermal ellipsoids set at 50% probability) and a view showing the κ2-bonded tris(pyrazolyl)borate ligand (right).

Table 2. Selected Crystallographic and NMR Data for [PhB(3-(C2F5)Pz)3]M(C2H4) NMR (ppm; C6D12)

compd

CC (Å)

C−M−C (deg)

[PhB(3(C2F5)Pz)3] Au(C2H4) [PhB(3(C2F5)Pz)3] Ag(C2H4) [PhB(3(C2F5)Pz)3] Cu(C2H4)

1.366(12)

38.0(3)

1.311(5) 1.354(7)

N−M−N (deg)

∑ angles at M involving N and centroid of CC (deg)

M−N (Å)

C−M (Å)

M···B (Å)

84.7(2)

2.213(6), 2.216(6)

2.089(8), 2.105(7)

3.231

360

2.85

58.9

33.38(14)

86.02(7)

2.279(2), 2.286(2)

2.279(3), 2.286(3)

3.129

360

4.62

101.6

38.96(19)

93.76(13)

2.008(3), 2.009(3)

2.027(4), 2.033(4)

2.949

360

3.71

85.5

1

H

13

C

The 1H NMR spectrum of [PhB(3-(C2F5)Pz)3]Au(C2H4) in C6D12 exhibited a resonance at δ 2.85 ppm, which could be assigned to the protons of the ethylene moiety. The 1H NMR spectrum taken in CDCl3 also displays this peak at δ 2.89 ppm. The 13C NMR signal of the bonded ethylene in C6D12 was detected at δ 58.9 ppm, which is shifted significantly upfield relative to that of the free ethylene (δ 123.3 ppm). For comparison, [HB(3-(CF3),5-(Ph)Pz)3]Au(C2H4)11 displays the ethylene proton resonance in the 1H NMR spectrum at δ 3.69 ppm (which is about 0.8 ppm downfield from the signal

Although solid-state structures of [PhB(3-(C2F5)Pz)3]M(C2H4) show two types of pyrazolyl moieties (two metal bound and one free), 1H and 19F NMR data at room temperature suggest fluxional behavior in solution, as is evident from the presence of an averaged set of signals. We have seen similar fluxionality with [HB(3,5-(CF3)2Pz)3]Au(C2H4).11 Casarin et al. have studied somewhat related tris(pyrazolyl)methane complexes of silver(I) and copper(I) ions using DFT and reported that the κ2 to κ3 interconversion is an essentially barrierless process.26 1514

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Cu(C2H4), as was evident from the appearance of a signal at δ 3.71 corresponding to the 1H NMR signal of the CuI−C2H4 moiety. In summary, we have reported the isolation and characterization of a series of thermally stable, isoleptic, and structurally similar coinage-metal−ethylene adducts, [PhB(3-(C2F5)Pz)3]M(C2H4) (M = Au, Ag, Cu). They display trigonal-planar metal sites. The tris(pyrazoyl)borate ligand coordinates to the metal atom in a κ2 fashion. The M−C and M−N distances of the [PhB(3-(C2F5)Pz)3]M(C2H4) complexes follow the same trend as the covalent radii of M(I). The gold−ethylene adduct shows large upfield NMR shifts of the ethylene proton and carbon signals, indicating relatively high Au→ethylene back-bonding. We are presently examining the tris(pyrazolyl)borate ligand electronic effects on the M−ethylene interaction and spectroscopic properties. Coinage-metal adducts of fluorinated scorpionates are also of current interest as potential catalysts for C−H and C−halogen bond activation chemistry.12,28−38

observed for [PhB(3-(C2F5)Pz)3]Au(C2H4)). However, the 13 C NMR signal of the ethylene carbons of [HB(3-(CF3),5(Ph)Pz)3]Au(C2H4) appears at δ 59.3 ppm, which is very similar to that of [PhB(3-(C2F5)Pz)3]Au(C2H4). This unusually large upfield shift of the ethylene protons of [PhB(3(C2F5)Pz)3]Au(C2H4) suggests that these protons experience the shielding cone of the B-phenyl group in solution.7 1 H NMR signals corresponding to the coordinated ethylene of [PhB(3-(C2F5)Pz)3]Ag(C2H4) and [PhB(3-(C2F5)Pz)3]Cu(C2H4) in C6D12 appear at δ 4.62 and 3.71 ppm, respectively (Table 2). Overall, the gold adduct shows the largest upfield shift of the ethylene proton signal from that of free ethylene protons, while the silver adduct shows the smallest shift. The 13 C NMR data show that coinage-metal-bound ethylene carbon signals also show a similar trend. The ethylene carbon resonance of the [PhB(3-(C2F5)Pz)3]M(C2H4) adducts in C6D12 appear at δ 58.9, 101.6, and 85.5 ppm, respectively, for M = Au, Ag, Cu. The upfield shift of the carbon resonance in the gold adduct is particularly large. For example, Δδ(C) values (where Δδ(C) = δ(C)complex − δ(C)ethylene) for these Au, Ag, and Cu adducts are −64, −22, and −38 ppm, respectively. The upfield shift of the 13C and 1H NMR resonance of the ethylene signal has been attributed to the increased metal-to-ethylene πback-donation contribution.13,20,25,27 The 13C NMR data are particularly useful, since they are less affected by the ring current effects. Overall, these NMR data point to a π-backdonation component in the gold(I)−ethylene bond that is significantly higher than in the lighter members and are in good agreement with the latest computational work and NMR spectroscopic studies of gold(I) ethylene adducts. We have also examined some of the properties, chemistry, and solution behavior of [PhB(3-(C2F5)Pz)3]M(C2H4). [PhB(3-(C2F5)Pz)3]Ag(C2H4) and [PhB(3-(C2F5)Pz)3]Cu(C2H4) lose coordinated ethylene if hexane or CH2Cl2 solutions of these compounds are concentrated under reduced pressure, possibly yielding the aggregates {[PhB(3-(C2F5)Pz)3]Ag}n and {[PhB(3-(C2F5)Pz)3]Cu}n (e.g., dimers, polymers). The corresponding ethylene complexes can be regenerated by bubbling ethylene into solutions of these aggregates. Similar behavior was observed for [PhB(3-(CF3)Pz)3]Ag(C2H4).7 We have also reported the isolation of ethylene-free {[PhB(3(CF3)Pz)3]Ag}n, which has a helical, polymeric structure.7 The addition of excess ethylene to CDCl3 or C6D12 solutions of [PhB(3-(C2F5)Pz)3]Ag(C2H4) in an NMR tube at room temperature led to the coalescence of 1H NMR signals of the coordinated ethylene, with the free ethylene producing a sharp new signal at a weighted average position (see Figure S1 in the Supporting Information). The copper adduct shows similar behavior, but the resulting coalesced peak was much broader. We have also treated C6D12 solutions of the Au(I) analogue with excess ethylene. The 1H NMR spectrum of this mixture at room temperature shows two sharp signals, one at the coordinated ethylene chemical shift value of the gold adduct and the second peak at δ 5.39 ppm corresponding to the free ethylene, signifying that there is no associative ethylene exchange on the NMR time scale. We also examined some metathesis chemistry. For example, the addition of AuCl to a C6D12 solution of [PhB(3(C2F5)Pz)3]Ag(C2H4) resulted in the formation of [PhB(3(C2F5)Pz)3]Au(C2H4) within 1 h, as was evident from the appearance of a AuI−C2H4 (δ 2.85) signal in the 1H NMR spectrum. Similarly, the treatment of [PhB(3-(C2F5)Pz)3]Ag(C2H4) with CuCl in C6D12 resulted in [PhB(3-(C2F5)Pz)3]-

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EXPERIMENTAL SECTION

All manipulations were carried out under an atmosphere of purified nitrogen using standard Schlenk techniques or in a Vacuum Atmosphere single-station glovebox equipped with a −25 °C refrigerator. Solvents were purchased from commercial sources and purified prior to use. NMR spectra were recorded at 25 °C on a JEOL Eclipse 500 and JEOL Eclipse 300 spectrometer (1H, 500.16 and 300.53 MHz; 13C, 125.78 and 75.59 MHz; 11B, 160.47 and 96.42 MHz; 19F, 470.62 and 282.78 MHz). 1H and 13C chemical shifts are reported in ppm versus Me4Si. 19F NMR values were referenced to external CFCl3. 11B NMR values were referenced to external BF3·Et2O. Melting points were obtained on a Mel-Temp II apparatus. Silver(I) triflate, AuCl, and CuCl were purchased from Aldrich, and ethylene gas was purchased from Matheson. [PhBH3]Li and 3-(C2F5)PzH were prepared as reported previously.39,40 [PhB(3-(C2F5)Pz)3]Li. Li[PhBH3] (0.40 g, 4.14 mmol) kept at −25 °C in a freezer attached to a glovebox was added into a precooled Schlenk tube containing 3-(C2F5)PzH (18.6 mmol) at −25 °C. The reaction mixture was brought outside the glovebox, and the temperature was raised slowly while keeping the mixture under nitrogen to 140 °C with stirring. It was kept at this temperature for 6 h (from time to time, the heat gun was used to melt down the pyrazole collecting on the wall of the flask). The mixture was cooled to room temperature, and the resulting solid was transferred to a sublimation apparatus and sublimed at 50 °C under vacuum to remove excess 3(C2F5)PzH to give [PhB(3-(C2F5)Pz)3]Li as a pale green-white sticky solid (yield 90% based on Li[PhBH3]). This product was used directly in the following steps. It is hygroscopic and readily forms [PhB(3(C2F5)Pz)3]Li·H2O if exposed to the atmosphere, even during sample preparation for analyses. Mp: 94 °C. 1H NMR (CDCl3): δ 7.46−7.30 (8 H, m, Pz-H and Ph-H), 6.44 (3 H, d, 3J(H−H) = 2.41 Hz, Pz-H), 2.22 (2 H, s, H2O). 19F NMR (CDCl3): δ −84.9 (s, 9F, CF3), −113.1(s, 6F, CF2). 11B NMR (CDCl3): δ 0.54 (br s). [PhB(3-(C2F5)Pz)3]Au(C2H4). Solid [PhB(3-(C2F5)Pz)3]Li (0.20 g, 0.31 mmol) and gold(I) chloride (0.072 g, 0.31 mmol) were placed in a Schlenk flask (protected from light by covering with some aluminum foil). To this mixture was added 20 mL of hexane saturated with ethylene at 20 °C, and the resulting mixture was stirred for 1 h. Ethylene gas was gently bubbled through the solution about two to three times (30 s each time) during this period. The yellow solution gradually turned gray, and an off-white precipitate was formed. The mixture was filtered under N2 through a bed of Celite, and the filtrate was collected and dried under reduced pressure to give [PhB(3(C2F5)Pz)3]Au(C2H4) as a colorless solid (0.21 g, 77%). X-ray-quality crystals were obtained from a hexane solution saturated with ethylene at −20 °C. Mp: decomposes around 45 °C. Anal. Calcd for C23H15AuBF15N6: C, 31.82; H, 1.74; N, 9.68. Found: C, 31.74; H, 1.93; N, 10.17. 1H NMR (CDCl3, 298 K): δ 2.89 (s, 4H, C2H4), 6.63 1515

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Organometallics (br, 3H, 4-CH), 6.68 (m, 2H, Ph), 7.26 (m, 2H, Ph), 7.48 (m, 1H, Ph), 7.65 (br, 3H, 5-CH). 1H NMR (C6D12, 298 K, selected): δ 2.85 (s, 4H, C2H4). 13C NMR (CDCl3, selected): δ 59.3 (t, 1JCH = 165 Hz, C2H4). 13 C{1H} NMR (C6D12, selected): δ 58.9 (s, C2H4). 19F NMR (CDCl3, 298 K): δ −84.4 (s), −113.0 (br). [PhB(3-(C2F5)Pz)3]Ag(C2H4). [PhB(3-(C2F5)Pz)3]Li (0.3 g, 0.46 mmol) and AgOTf (0.12 g, 0.46 mmol) were mixed in a Schlenk tube covered with aluminum foil. Hexane (30 mL) saturated with ethylene was added to the mixture at room temperature. The mixture turned pale yellow during the stirring. The resulting mixture was filtered, and the solvent was removed from the filtrate under an ethylene atmosphere to give the product as a white solid in approximate yield of 70%. It was recrystallized from hexane (containing added ethylene) at −20 °C to give colorless crystals of [PhB(3-(C2F5)Pz)3]Ag(C2H4). Mp: crystals darken and melt starting at 85 °C. Anal. Calcd for C23H15AgBF15N6: C, 35.46; H, 1.94; N, 10.79. Found: C, 35.44; H, 1.95; N, 10.71. 1H NMR (C6D12): δ 4.62 (s, 4H, C2H4), 6.44 (d, 3JHH = 2.41 Hz, 3H, 4-CH), 6.84 (m, 2H, Ph), 7.28 (m, 3H, Ph), 7.55 (br, 3H, 5-CH). 13C NMR (CDCl3, selected): δ 102.0 (t, 1JCH = 162 Hz, C2H4). 13C{1H} NMR (C6D12, selected): δ 101.6 (s, C2H4). 19F NMR (CDCl3, 298 K): δ −85.1 (s), −113.6 (br). [PhB(3-(C2F5)Pz)3]Cu(C2H4). Solid [PhB(3(C2F5)Pz)3]Li (0.20 g, 0.31 mmol) and CuCl (0.04 g, 0.40 mmol) were placed in a Schlenk flask. To this mixture was added 20 mL of hexane saturated with ethylene at 20 °C, and the solution was stirred for 1 h. Ethylene gas was gently bubbled through the solution about two to three times (30 s each time) during this period. The mixture was filtered under N2 through a bed of Celite and dried under reduced pressure using a stream of ethylene gas to give [PhB(3-(C2F5)Pz)3]Cu(C2H4) as a white solid (0.18 g, 80%). The product was crystallized from hexane containing ethylene at −20 °C. Mp: 113 °C. Anal. Calcd for C23H15CuBF15N6: C, 37.60; H, 2.06; N, 11.44. Found: C, 37.11; H, 1.94; N, 11.17. 1H NMR (CDCl3): δ 3.70 (s, 4H, C2H4), 6.58 (br, 3H, 4-CH), 6.75 (m, 2H, Ph), 7.29 (m, 3H, Ph), 7.57 (br, 3H, 5-CH). 1H NMR (C6D12, selected): δ 3.71 (s, 4H, C2H4). 13C{1H} NMR (C6D12, selected): δ 85.5 (s, C2H4). 19F NMR (CDCl3, 298 K): δ −84.4 (s), −112.6 (br). X-ray Crystallographic Data. A suitable crystal covered with a layer of cold hydrocarbon oil was selected and mounted with Paratone-N oil in a cryo-loop and immediately placed in the lowtemperature nitrogen stream. The X-ray intensity data were measured at 100(2) K on a Bruker SMART APEX CCD area detector system equipped with a Oxford Cryosystems 700 Series cooler, a graphite monochromator, and a Mo Kα fine-focus sealed tube (λ = 0.710 73 Å). The data frames were integrated with the Bruker SAINT-Plus software package. Data were corrected for absorption effects using the multiscan technique (SADABS or TWINABS). Structures were solved and refined using the Bruker SHELXTL (version 6.14) software package. [PhB(3-(C2F5)Pz)3]Cu(C2H4) crystals show nonmerohedral twinning, which was resolved by using the Cell_Now program. [PhB(3-(C2F5)Pz)3]Au(C2H4) shows some disorder at one of the C2F5 groups. All the non-hydrogen atoms were refined anisotropically. Further details are given in Table 1 and in the Supporting Information.

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ACKNOWLEDGMENTS

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REFERENCES

This work was supported by the National Science Foundation (No. CHE-0845321) and the Robert A. Welch Foundation (Grant No. Y-1289). The NSF (No. CHE-0840509) is thanked for providing funds to upgrade the NMR spectrometer used in this work. The X-ray crystallography was performed at the Center for Nanostructured Materials (CNM) at the University of Texas at Arlington.

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ASSOCIATED CONTENT

S Supporting Information *

CIF files giving X-ray crystallographic data for [PhB(3(C2F5)Pz)3]M(C2H4) (M = Cu, Ag, Au) and figures giving 1 H NMR spectra that show the effects of excess ethylene in a solution of [PhB(3-(C2F5)Pz)3]M(C2H4). This material is available free of charge via the Internet at http://pubs.acs.org.

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Corresponding Author

*E-mail: [email protected]. 1516

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Organometallics

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(33) Lovely, C. J.; Flores, J. A.; Meng, X.; Dias, H. V. R. Synlett 2009, 129. (34) Rangan, K.; Fianchini, M.; Singh, S.; Dias, H. V. R. Inorg. Chim. Acta 2009, 362, 4347. (35) Braga, A. A. C.; Caballero, A.; Urbano, J.; Diaz-Requejo, M. M.; Perez, P. J.; Maseras, F. ChemCatChem 2011, 3, 1646. (36) Conde, A.; Mar Diaz-Requejo, M.; Perez, P. J. Chem. Commun. 2011, 47, 8154. (37) Caballero, A.; Despagnet-Ayoub, E.; Mar Diaz-Requejo, M.; Diaz-Rodriguez, A.; Gonzalez-Nunez, M. E.; Mello, R.; Munoz, B. K.; Ojo, W.-S.; Asensio, G.; Etienne, M.; Perez, P. J. Science 2011, 332, 835. (38) Diaz-Requejo, M. M.; Perez, P. J. Chem. Rev. 2008, 108, 3379. (39) Singaram, B.; Cole, T. E.; Brown, H. C. Organometallics 1984, 3, 774. (40) Tang, X.-Q.; Hu, C.-M. J. Chem. Soc., Perkin Trans. 1994, 2161.

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