Reactivity of an Unsaturated Iridium(III) Phosphoramidate Complex

Jul 22, 2015 - Treatment of [1] with Na[BArF4], [BArF4] = [B(C6H3(CF3)2)4], led to the formation of the 16-electron two-legged piano stool species [Cp...
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Reactivity of an Unsaturated Iridium(III) Phosphoramidate Complex, [Cp*Ir{κ2‑N,O}][BArF4] Marcus W. Drover,†,‡ Heather C. Johnson,‡ Laurel L. Schafer,† Jennifer A. Love,† and Andrew S. Weller*,‡ †

Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1 Chemistry Research Laboratories, Department of Chemistry, The University of Oxford, Mansfield Road, Oxford, U.K. OX1 3TA

‡

S Supporting Information *

ABSTRACT: The three-legged piano stool complex [Cp*Ir(κ2-N,O-Xyl(N)P(O)(OEt)2)(Cl)], [1] (Cp* = η5-C5Me5, Xyl = 2,6-dimethylphenyl), was prepared from reaction of 0.5 equiv of [Cp*IrCl2]2 with the sodiated phosphoramidate ligand Na[Xyl(N)P(O)(OEt)2]. Treatment of [1] with Na[BArF4], [BArF4] = [B(C6H3(CF3)2)4], led to the formation of the 16electron two-legged piano stool species [Cp*Ir(κ2-N,O-Xyl(N)P(O)(OEt)2)][BArF4], [2][BArF4], which was characterized in both solution and solid state. Reactivity screening revealed that complex [2][BArF4] undergoes addition of a variety of Lewis bases to afford the corresponding 18-electron adducts with concomitant movement of the phosphoramidate ligand from κ2-N,O to κ1-N, [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(L)2][BArF4]; L = CNtBu, [3][BArF4], CNXyl, [4][BArF4], MeCN, [7][BArF4], bipy, [8][BArF4]; bipy = 2,2′-bipyridine. For complex [7][BArF4], variable-temperature 31P{1H} NMR spectroscopy revealed that MeCN coordination was reversible between 238 and 190 K. To probe E−H (E = Si, B) bond activation, complex [2][BArF4] was treated with H2SiPh2, providing the five-membered iridacycle [Cp*Ir(κ2-N,Si-Xyl(N)P(OSiPh2)(OEt)2)][BArF4], [9][BArF4], via geminal Si−H activation, while use of mesityl borane, H2BMes (Mes = 2,4,6-trimethylphenyl), afforded the six-membered phosphoramidate-stabilized borane complex [Cp*Ir(κ3-N,H,H-Xyl(N)P(OBH2Mes)(OEt)2)][BArF4], [10][BArF4]. Complexes [3][BArF4] and [9][BArF4] were additionally characterized by single-crystal X-ray diffraction.

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Chart 1. Relevant N,O-Chelated Group 9 Complexes

INTRODUCTION For some time now there has been growing interest in the synthesis of coordinatively unsaturated fragments of d6 metals having the general formula Cp*MLn (Cp* = η5-C5Me5, M = Ru, Rh, Ir).1 Generally speaking, the reactivity of these 16electron complexes toward two-electron donors is noteworthy, provoking application in both catalysis and stoichiometric bond activation.2 Toward this end, many research groups have focused their attention on the identity of “Ln”, where both symmetric and unsymmetric bidentate ligands have been considered in order to tune subsequent reactivity at the metal center. For group 8 and 9 metals, examples of Cp*-containing complexes having 1,2-bis(diphenylphosphino)ethane,3 tetramethylethylenediamine (TMEDA),4 1,2-dithiolate,5 1,2-dialkoxo (e.g., catecholate),6 1,3-diketiminate,7,8 amidinate [R′NC(R)NR′ ]−,1,9−11 and phosphinoamidinate12−14 ligands are known. Moreover, although two-legged piano stool complexes of the type Cp*IrLn have been described, those supported by anionic heterobidentate 1,3-bis(N,O-chelating) ligands are rare, being limited to a sole example formed via cycloaddition of Cp*Ir NtBu and CO2 (complex B, Chart 1).15 In the context of late transition metals (TMs) bearing heterobidentate ligands, some of us recently reported the preparation of amidate-ligated [R′NC(O)R]− Rh(I) complexes for use in O2 and S8 activation (complex A, Chart 1).16 © XXXX American Chemical Society

Continuing this study of N,O-chelated late TM complexes, but wishing to expand our work beyond amidate ligands, the phosphoramidates [R(N)P(O)(R′)2]− presented themselves as suitable ligand candidates. Similar to amidates, these scaffolds offer several benefits including the possibility for hemilability (Chart 2), facile substituent interchangeability (e.g., R and R′) allowing for steric and electronic manipulation, and acute (ca. 70°) N−M−O bite angles permitting augmented reactivity. We also postulated that these scaffolds might stabilize an unsaturated 16-electron d6 metal fragment through use of a Received: June 3, 2015

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Organometallics

complexes of the type [η6-(C6R6)Ru{κ2-N,N-AM}][X] (R = H or Me, [X] = [PF6] or [BArF4], AM = amidinate) could also be prepared on treatment of η6-(C6R6)Ru{κ2-N,N-AM}(Cl) with Na[BArF4] or AgPF6.9 Addition of Na[BArF4] to complex [1] in CH2Cl2 at 25 °C gave a deep red solution of [Cp*Ir(κ2-N,O-Xyl(N)P(O)(OEt)2)][BArF4] ([2][BArF4]). Complex [2][BArF4] can also be accessed in a one-pot reaction of [Cp*IrCl2]2, ligand, and Na[BArF4] without the need for prior isolation of [1]. In CD2Cl2 at 298 K the 1H NMR spectrum of complex [2][BArF4] was found to be similar to that of its precursor [1]; eight resonances were observed in total: five of which arise from the phosphoramidate ligand framework, one for the coordinated η5C5Me5 group, and two from the [BArF4]− counterion. For this 16-electron low-coordinate complex, 1H{31P} NMR spectroscopy additionally showed that the phosphorus-bonded ethoxy methylene groups, P-(OCH2CH3)2, were observed as a coincident dq at δ 4.13 [2JH,H = 4.0 Hz, 3JH,H = 7.0 Hz, 4H]. The phosphoramidate ethoxy methyl groups, P-(OCH2CH3)2, were observed as a single downfield-shifted resonance at δ 1.33 [t, 3JH,H = 7.0 Hz, 6H]. In the 31P{1H} NMR spectrum, a single low-field signal was observed at δ 41.5, a difference of Δδ = +30.4 ppm compared with [1], consistent with a significant change in the coordination environment of the phosphoramidate ligand. Finally, ESI (electrospray mass spectrometry)22 showed a parent ion at m/z = 584.1920 (calcd 584.1901) with the expected isotope pattern for [2]+. Despite numerous attempts, suitable crystalline material of [2][BArF4] could not be obtained. However, use of the [BArCl24]− (ArCl2 = 3,5Cl2C6H3) anion23 for the synthesis of [2]+ afforded single crystals of [2][BAr Cl2 4 ] that were suitable for X-ray crystallography. The solid-state structure of [2][BArCl24] shows a two-legged piano stool complex that is formally a 16-electron species, consistent with the NMR spectroscopic data (Figure 1). In comparison to the protio-ligand,19 the

Chart 2. Possible Phosphoramidate Coordination Modes

sterically hindered N-substituent and π- and σ-donation, all requisite features noted by Caulton et al. for the preparation of unsaturated Ru(II) piano stool complexes.4 Only a few examples of phosphoramidate-ligated complexes are known including κ1-O-bonded main group complexes of Sn(IV) and Al(III),17,18 a Ta(V) phosphoramidate complex that has recently been utilized in catalytic room-temperature hydroaminoalkylation,19 and a Co(III) complex that results from hydrolysis of 2,4-dinitrophenyl phosphate at [Co(NH3)5]3+.20

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RESULTS AND DISCUSSION Treatment of 0.5 equiv of [Cp*IrCl2]2 with the sodiated phosphoramidate ligand salt Na[Xyl(N)P(O)(OEt)2]19 (Xyl = 2,6-dimethylphenyl) in CH2Cl2 at 25 °C gave access to the neutral Ir(III) complex [Cp*Ir(κ2-N,O-Xyl(N)P(O)(OEt)2)(Cl)], [1], as an orange solid following workup (Scheme 1). In Scheme 1. Preparation of Cationic Ir(III) Phosphoramidate Complex [2][BArF4]

CD2Cl2 at 298 K, the 1H NMR spectrum of [1] reveals seven resonances in total including two multiplets for the ethoxy methylene groups, P-(OCH2CH3)2 each of integration 2H, which are observed at δ 3.79 and 3.91, and a single ethoxy methyl resonance at δ 1.13 [t, 3JH,H = 7.0 Hz, 6H] for P(OCH2CH3)2. The Cp* group resonates at δ 1.64 (15H). For the −N(Xyl) group, a singlet of integration 6H is observed, consistent with two equivalent CH3 groups; decoalescence is not observed down to 190 K, indicating free C−N bond rotation. The 31P{1H} NMR spectrum shows a slightly downfield-shifted singlet at δ 10.1 (compared with δ 5.0 for the protio-ligand). With complex [1] in hand, the related cationic two-legged piano stool complex can be prepared by simple chloride abstraction. This route has previously been adopted by Carmona and co-workers, who accessed [Cp*Ir{κ2-N,NAP}][BArF4] ([BArF4] = [B(C6H3(CF3)2)4], AP = aminopyridinate) from [Cp*Ir{κ2-N,N-AP}(Cl)] using Na[BArF4].21 Nagashima et al. have also shown that cationic 16-electron Ru

Figure 1. ORTEP depiction of the solid-state molecular structure of [Cp*Ir{κ2-N,O-Xyl(N)P(O)(OEt)2}][BArCl24], [2][BArCl24] (displacement ellipsoids are shown at 50% probability, hydrogens and [BArCl24] counterion omitted for clarity). Selected bond lengths [Å] and angles [deg]: Ir(1)−O(1) 2.142(2), Ir(1)−N(1) 1.989(3), P(1)− O(1) 1.523(2), P(1)−N(1) 1.612(3), N(1)−Ir(1)−O(1) 70.8(1), O(1)−P(1)−N(1) 99.6(1).

P(1)−O(1) bond length is elongated from 1.4727(9) Å to 1.523(2) Å, while the P(1)−N(1) bond length is shortened from 1.6388(10) Å to 1.612(3) Å. Upon coordination, the N(1)−P(1)−O(1) bond angle is also reduced from 113.01(5)° to 99.6(1)°. Notably, the N(1)−Ir(1)−O(1) bite angle is small (70.8(1)°), but larger than that found for related rhodium(I) amidate complexes (e.g., O(1)−Rh(1)−N(1) 61.16(4)° for B

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Organometallics complex A, Chart 1).16 Additionally, the Ir(I)−N(1) bond length is short (1.989(3) Å), likely owing to joint Ir−N σ,πdonor character, while the Ir(I)−O(1) bond is considerably longer (2.142(2) Å). In a related κ2-N,O Ir(III) complex (Chart 1, complex B) the Ir(I)−N(1) bond length is similar (1.943(6) Å); however, the Ir(I)−O(1) bond in complex B is slightly shorter (2.049(6) Å), generating a tighter N(1)−Ir(1)−O(1) bond angle of 65.35(22)° (cf. 70.8(1)° for [2][BArCl24]).15 With a reliable route to the 16-electron complex [2][BArF4], its reactivity toward two-electron Lewis bases was explored. Addition of 1 equiv of the isonitriles CNR (R = tBu or Xyl) to CD2Cl2 solutions of [2][BArF4] at 298 K resulted in the formation of two products in a 1:1 ratio as determined by NMR spectroscopy (Scheme 2): the starting material [2][BArF4] and

Single crystals of [3][BArF4] suitable for analysis were obtained from a saturated hexanes-layered CH2Cl2 solution at −35 °C. The structure, presented in Figure 2, features an 18-

Scheme 2. Reaction of [2][BArF4] with Isonitriles

Figure 2. ORTEP depiction of the solid-state molecular structure of [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(CNtBu)2][BArF4], [3][BArF4] (displacement ellipsoids are shown at 50% probability, hydrogens and [BArF4] counterion omitted for clarity). Selected bond lengths [Å] and angles [deg]: Ir(1)−N(1) 2.143(5), Ir(1)−C(15) 1.988(5), Ir(1)−C(20) 1.950(5), P(1)−O(1) 1.461(5), P(1)−N(1) 1.618(5), O(1)−P(1)−N(1) 117.1(3).

the 18-electron Ir(III) bis-isonitrile adduct [Cp*Ir(κ1-NXyl(N)P(O)(OEt)2)(CNR)2][BArF4] (R = tBu, [3][BArF4], or Xyl, [4][BArF4]), for which a single-crystal X-ray diffraction study on [3][BArF4] confirmed the κ1-N coordination mode (vide inf ra). To the best of our knowledge, complex [3][BArF4] is the first example of a κ1-N-bonded phosphoramidate complex. When complex [2][BArF4] was treated with 2 equiv of CNR, the quantitative formation of the bis-isonitrile adducts results. This demonstrates the ability of the phosphoramidate ligand to act in a hemilabile manner.24 The change in coordination mode from κ2-N,O to κ1 is revealed in the 31 1 P{ H} NMR spectrum, which shows upfield-shifted resonances compared with [2][BArF4] at δ 7.00 (Δδ = −34.5) for [3][BArF4] and δ 7.70 (Δδ = −33.8) for [4][BArF4]. It is noteworthy, however, that in the absence of solid-state data it is difficult to distinguish between κ1-O and κ1-N phosphoramidate-ligated metal complexes. These signals are also similar to those observed in the 31P{1H} NMR spectrum of [1] and the free protio-ligand. In addition, for [3][BArF4], the ethoxy methylene (P(OCH2CH3)2) groups are observed as a single coincident environment at δ 3.72, while a single tBu environment is observed at δ 1.39 that corresponds to two CNtBu ligands in the 1H NMR spectrum. Solution-phase infrared (IR) spectroscopic analysis of the isonitrile stretching frequency (νCN) for these complexes showed broad bands at 2188 and 2212 cm−1 for [3][BArF4] and 2167 cm−1 for [4][BArF4], indicating a slight blue-shift of 54, 78, and 44 cm−1 respectively in comparison to the neat isonitriles. An increase in stretching frequency suggests donation of the isonitrile lone pair, which has some antibonding character, to Ir. Accordingly, these Ir(III) phosphoramidate complexes can be considered poor π-donors. ESI-MS also provided [M]+ signals for [3]+ and [4]+ at m/z = 750.3318 (calcd 750.3376) and 846.3311 (calcd 846.3376), respectively, of the appropriate isotope pattern. Consistent with the poor π-donating capacity of complex [2][BArF4], no adduct formation was observed between [2][BArF4] and excess cyclooctene, styrene, tert-butylethylene, or ethylene (3 atm) from 298 to 190 K.

electron, three-legged piano stool complex, consistent with NMR and MS analysis. In comparison to [2][BArF4], the Ir− Nphosphoramido bond is lengthened significantly (2.143(5) Å). Ring-opening also results in a drastic change in O(1)−P(1)− N(1) angle from 99.6(1)° for κ2-N,O [2][BArF4] to 117.1(3)° for κ1-N [3][BArF4], close to that found for the protio-ligand (113.01(5)°). It is additionally noteworthy that the κ1-Nphosphoramide atom in [3][BArF4] is nearly planar, with the sum of angles about nitrogen close to 360° (359.4°). By contrast, use of MeCN as an alternative Lewis base did not result in the clean isolation of a bis-adduct at 298 K. Instead, equilibria were established between bis- and monoadducts and complex [2][BArF4] (Scheme 3). Addition of 5 equiv of MeCN to a CD2Cl2 solution of [2][BArF4] resulted in no apparent color change, whereas a characteristic yelloworange color was observed for the 18-electron complexes [3][BArF4] and [4][BArF4]. Furthermore, 1H and 31P{1H} NMR spectroscopy at 298 K showed broadened signals Scheme 3. Proposed Reactivity of [2][BArF4] with Acetonitrile

C

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Organometallics attributable to [2][BArF4] along with a slightly broadened resonance at δ 1.98 due to free CH3CN.25 Progressive cooling to 190 K and monitoring the 31P{1H} NMR spectrum revealed the presence of a number of fluxional processes. At 190 K, the signal for [2][BArF4] (δP 41.5) is broadened (ω1/2 = 230 Hz) and became upfield-shifted to δP ca. 32, while a new signal at δP 8.31 (ΔδP = −33.2) was observed; these two signals were in a 1:6 relative ratio (Figure 3). On the basis of the data obtained

(bipy), an orange solution resulted, which was characterized by NMR spectroscopy as [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(2,2′bipy)][BArF4], [8][BArF4] (Scheme 4). In the 1H NMR Scheme 4. Reaction of [2][BArF4] with Substituted Pyridines

spectrum, signals assignable to a Cs-symmetric Ir(III) complex were apparent, including signals for the coordinated Cp*, phosphoramidate (notably a coincident signal for the ethoxy methylene groups at δ 3.68), and bipy auxiliary ligands. The 31 1 P{ H} NMR spectrum showed a diagnostic upfield shift from [2][BArF4] to give a new signal at δP 8.48 (ΔδP = −33.0). ESIMS also provided a molecular ion ([M]+) signal for [8]+ at m/z = 740.2527 (calcd 740.2589) with the appropriate isotope pattern. By contrast, reaction of [2][BArF4] with 2-phenylpyridine (phpyr) in MeCN/CH2Cl2 provided the known cycloiridated adduct [Cp*Ir{κ2-N,C-phpyr}(MeCN)][BArF4]26 (confirmed by 1H NMR spectroscopy) and protio-ligand in a 1:1 ratio. This outcome suggests that a phosphoramidate ligand may serve as an intramolecular base, acting to cleave C−H bonds with aid from Ir(III), likely via a C−H agostic interaction.27 In terms of reactivity with phosphines, when 1 equiv of PR3 (R = Ph, Me, Cy) was added to CD2Cl2 solutions of [2][BArF4], analysis by 31P{1H} NMR spectroscopy showed protio-ligand and several high-field chemical resonances, indicating a mixture of species was produced. We suggest this mixture may be due to the formation of cyclometalated Ir(III)phosphine complexes.28 These products might be formed following a concerted metalation−deprotonation process,29 whereby phosphine coordination is followed by phosphoramidate-aided deprotonation of an adjacent C−H bond, culminating in the elimination of protio-ligand and a cyclometalated Ir(III) product. The use of the diphosphine ligands 1,2-bis(diphenyl)phosphinoethane or -methane yielded similar results. Given that complex [2][BArF4] underwent C−H activation of 2-phenylpyridine, we were interested to explore other potential E−H (E = Si, B) activation pathways. Such complexes represent attractive targets owing to their implication in catalytic E−H activation chemistry, for example.30 Treatment of [2][BArF4] with 1 equiv of H2SiPh2 in CD2Cl2 at 298 K resulted in the immediate effervescence of H2 and the formation of an olive green solution of a complex characterized as [Cp*Ir(κ2-N,Si-Xyl(N)P(OSiPh2)(OEt)2)][BArF4], [9][BArF4] (Scheme 5). Following 15 min of reaction time, 31 1 P{ H} NMR spectroscopy revealed complete conversion of the starting material and a new signal at δP 33.5, consistent with

Figure 3. Variable-temperature 31P{1H} NMR spectra for the reaction of MeCN (5 equiv) with [2][BArF4] (CD2Cl2, 202 MHz).

for [3][BArF4] and [4][BArF4], the latter signal was assigned to the new complex [Cp*Ir(κ 1 -N-Xyl(N)P(O)(OEt) 2 )(MeCN)2][BArF4], [7][BArF4] (Scheme 3). The relative ratio of [2][BArF4] to [7][BArF4] was found to increase in favor of the latter as temperature decreased, e.g., 1:0.3 at 258 K and 1:6 at 190 K. We attribute this behavior to two competing equilibria. The first results from rapid, but reversible, addition of 1 equiv of MeCN to [2][BArF4] giving (R/S)-[Cp*Ir(κ2N,O-Xyl(N)P(O)(OEt)2)(MeCN)][BArF4], [5][BArF4]. This accounts for broadening and the upfield shift of [2][BArF4] on cooling, in which the time-averaged position of the equilibrium between [2][BArF4] and [5][BArF4] shifts to favor the mononitrile adduct. The second is a relatively slow equilibrium established between [2][BArF4] and the bis-nitrile adduct [7][BArF4], presumably operating via a κ1-bonded intermediate [6][BArF4], which at low temperature favors the latter (Scheme 3). The favoring of the nitrile adduct species [5][BArF4] and [7][BArF4] at low temperature is consistent with entropic arguments, while the relatively slow equilibrium to establish [7][BArF4] is consistent with the requirement for accessing the κ1-N phosphoramidate ligand coordination mode. In the absence of MeCN, the VT 1H and 31P{1H} NMR spectra of [2][BArF4] (CD2Cl2, 298−190 K) showed no change. Comparable solvent reactivity using 5 equiv of tetrahydrofuran (THF) or diethyl ether was not observed, suggesting an order of relative binding constants with [2][BArF4] as CNR > MeCN ≫ THF, Et2O. Nagashima et al. have reported similar behavior with the 16-electron fragment [Cp*Ru{κ2-N,N-AM}] (AM = amidinate), which undergoes reversible addition of pyridine to give [Cp*Ru{κ2-N,N-AM}(py)].10 To probe ligand hemilability, and in particular the κ1-Nligated phosphoramidate binding mode, trapping with a bidentate (four-electron donor) ligand system was probed. When complex [2][BArF4] was treated with 2,2′-bipyridine D

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Organometallics Scheme 5. Reaction of [2][BArF4] with H2SiPh2

elimination, an Ir(III) silylene might result, which could undergo intramolecular attack by the phosphoramidate ligand, followed by H2 elimination (or vice versa) to provide complex [9][BArF4]. Oro et al. proposed a similar pathway for the activation of H2SiPh2 using Ir(TFB)(κ1-O-O2CCH3)(PR3) (TFB = tetrafluorobarrelene) to provide Ir(TFB)(κ1-SiSiPh2O2CCH3)(PR3)(H)2, which intriguingly, unlike [9][BArF4], was resistant to H2 reductive elimination.30h Having observed facile C−H and Si−H activation, we next sought to explore the reactivity of [2][BArF4] with a monoborane, H2BMes (Mes = 2,4,6-trimethylphenyl). Treatment of a CD2Cl2 solution of [2][BArF4] with H2BMes at 25 °C immediately resulted in a color change from red to orange, giving complex [Cp*Ir(κ 3 -N,H,H-Xyl(N)P(OBH 2 Mes)(OEt)2)][BArF4], [10][BArF4] (Scheme 6), in 90% yield Scheme 6. Reaction of [2][BArF4] with H2BMes and H2

an increase in iradacycle ring size (ΔδP = −8 ppm) and not the formation of a κ1-bonded complex. By 1H NMR spectroscopy, a signal assigned to free H2 (δ 4.62)25 was also observed along with those corresponding to the Cp*, phosphoramidate, and −SiPh2 ligands. A 1H−29Si{1H} HMBC NMR experiment additionally provided a cross-peak for the silicon-containing metallacycle at δ 61.3. ESI-MS also provided a signal at m/z = 766, consistent with H2 elimination and incorporation of an −SiPh2 unit. The crystal structure of [9][BArF4] (Figure 4),

following workup. Although attempts to obtain crystalline [10][BArF4] have not yet been successful, we propose this species results as a consequence of ligand hemilability, whereupon a κ1-N intermediate provides stabilization to the H2BMes unit. This assignment comes from a combination of 1 H, 13C, 11B, and 31P NMR spectroscopies and elemental analysis. As of yet, obtaining a 11B{1H} NMR spectrum of [10][BArF4] has proven difficult using both direct and indirect methods, prompting us to prepare the analogue [Cp*Ir(κ3N,H,H-Xyl(N)P(OBH2Dur)(OEt)2)][BArF4] (Dur = 2,3,5,6tetramethylphenyl), for which a 11B{1H} NMR spectrum was measured giving δ 44 (ω1/2 = 510 Hz), characteristic of metal coordination.32 Notably, Stradiotto reported an analogous oxygen-stabilized Ru(η2-H2BMes) complex for which the 11 1 B{ H} NMR spectrum gave δ 59.14 1H NMR spectroscopy provided additional evidence for coordination of H2BMes. In addition to a coincident signal for the two sets of phosphorusbonded ethoxy methylene groups, P-(OCH2CH3)2, at δ 4.17, a broad signal, which sharpens upon 11B decoupling, at δ −8.03 (2H) was observed, supporting the existence of an Ir−H−B bonding motif. ESI-MS also provided a [M]+ signal for [10]+ at m/z = 715 with the appropriate isotope pattern. Furthermore, an upfield-shifted signal at δ 16.5 was noted in the 31P{1H} NMR spectrum, supporting the formation of a six-membered ring system. It is noteworthy that δP is a good indicator of iridacycle ring size and, thus, phosphoramidate coordination mode. For instance, δP decreases as a function of metallacycle

Figure 4. ORTEP depiction of the solid-state molecular structure of [Cp*Ir{κ2-N,Si-Xyl(N)P(OSiPh2)(OEt)2}][BArF4], [9][BArF4] (displacement ellipsoids are shown at the 50% probability, hydrogens and [BArF4] counterion omitted for clarity). Selected bond lengths [Å] and angles [deg]: Ir(1)−N(1) 1.992(2), Ir(1)−Si(1) 2.343(1), Si(1)− O(1) 1.758(2) P(1)−O(1) 1.531(3), P(1)−N(1) 1.629(3), N(1)− Ir(1)−Si(1) 85.18(8), O(1)−P(1)−N(1) 108.0(1), Ir(1)−Si(1)− O(1) 102.07(8).

obtained at −35 °C from hexanes-layered CH2Cl2, shows a noncrystallographically imposed Cs-symmetric Ir(III) complex bonded to both the phosphoramidate N atom and a Si atom of the activated H2SiPh2 unit. For this genuine heterocycle31 (a ring system containing only one atom of each element), the Ir(1)− Si(1) (2.343(1) Å) and Si(1)−O(1) (1.758(2) Å) bond lengths are consistent with those found in related Ir-SiPh2OR complexes, while an augmented O(1)−P(1)−N(1) angle of 108.0(1)° is consistent with ring expansion.30h−j Scheme 5 illustrates a possible reaction manifold for the formation of this complex. We suggest that the first step involves Si−H oxidative addition to provide a κ1-N Ir(III) hydride. Following αE

DOI: 10.1021/acs.organomet.5b00397 Organometallics XXXX, XXX, XXX−XXX

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Organometallics ring size: δP 41.5 ([2][BArF4]: four-membered), 33.5 ([9][BArF4]: five-membered), 16.5 ([10][BArF4]: six-membered), and ca. 7−8 ([3,4,7,8][BArF4]: κ1-N). Indeed, isolation of [10][BArF4] and not the direct B−H activation product is consistent with the proposal of κ1-N-phosphoramidate C−H agostic intermediates during C−H activation using [2][BArF4]. The borane adduct [10][BArF4] was found to be unstable following 1 week at 25 °C in CD2Cl2, giving protio-ligand and a mixture of Cp*Ir-containing products including [Cp*2Ir2(μH)3][BArF4], [11][BArF4], for which there is a single high-field resonance, δ −15.52 (μ2-H). Additionally, X-ray quality crystals of [11][BArF4] were isolated from a pentane-layered CH2Cl2 solution of [10][BArF4] at 25 °C, the product of Ir(III)facilitated B−H activation and protio-ligand elimination (see the SI). Dimeric Ir(III) complex [11][BArF4] has been previously reported by hydrogenation of several different Cp*Ir(III)-containing complexes, although no X-ray structure has been provided.21b,33 By comparison, exposure of a CD2Cl2 solution of [2][BArF4] to an H2 atmosphere resulted in the irreversible formation of [11][BArF4] along with protio-ligand. In summary, we have reported the first systematic preparation of an unsaturated Ir(III) complex stabilized by a phosphoramidate ligand, which exists as a monomeric entity in both solution and solid state. In contrast to conventionally employed amidinate ligands, the use of such N,O-1,3heterobidentate ligands permits access to rich coordination behavior, providing κ1-N complexes in the presence of Lewisbasic ligands. For example, reaction of [2][BArF4] with twoelectron donors including CNR (R = tBu, Xyl), MeCN, and 2,2′-bipyridine provided stable 18-electron complexes [3][BArF4], [4][BArF4], [7][BArF4], and [8][BArF4], respectively. We suggest this flexibility is derived as a consequence of the weakly donating PO moiety to Ir(III), allowing for ease in ligand displacement. This is an important factor for the design of ligand frameworks which favor the generation of coordinatively unsaturated complexes. This hemilability is further highlighted by treatment of [2][BArF4] with H2SiPh2 or H2BMes, which gave the five-membered [9][BArF4] or sixmembered [10][BArF4] iridacycle, respectively. 31P{1H} NMR spectroscopy was also found to be a valuable diagnostic tool for the assessment of the phosphoramidate binding mode. Efforts toward understanding these reactivity trends as well as developing the related chemistry of analogous Rh(III) and Ru(II) fragments are currently under way.

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Columbia. Infrared data were obtained using a PerkinElmer Frontier FT-IR spectrometer. The 13C{1H} NMR data in CD2Cl2 for the [BArF4] counterion21b are identical for all complexes reported herein and are as follows: 13C{1H} NMR: δ = 162.1 (q, 1JC,B = 37 Hz), 135.3, 129.2 (q, 2JC,F = 31 Hz), 124.9 (q, 1JC,F = 273 Hz), 117.8. [Cp*Ir(κ2-N,O-Xyl(N)P(O)(OEt)2)(Cl)], [1]. In the glovebox, [IrCp*(μ-Cl)(Cl)]2 (20.0 mg, 0.025 mmol) and sodium N-[diethyl(2,6dimethylphenyl)phosphoramidate] (14.0 mg, 0.050 mmol) were added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, and the dark orange-brown solution was allowed to stir for 2 h at 25 °C. Following this period, the solution was filtered through a Celite filter and the solvent was removed in vacuo to afford a dark orange solid (29 mg, 93%). 1H NMR (400 MHz, CD2Cl2, 298 K): δ = 6.91 (d, 3JH,H = 7.4 Hz, 2H; Ar(CH)), 6.79 (t, 3JH,H = 7.4 Hz, 1H; Ar(CH)), 3.91 (m, 2H; OCH2CH3) 3.79 (m, 2H; OCH2CH3), 2.04 (s, 6H; Ar(CH3)), 1.64 (s, 15H; Cp*), 1.13 (t, 3JH,H = 7.0 Hz, 6H; OCH2CH3). 13C{1H} NMR (100 MHz, CD2Cl2, 298 K): δ = 151.37, 135.79, 127.41, 124.32, 88.65 (Cp*), 62.74 (d, 2JP,C = 6.2 Hz; OCH2CH3), 20.38 (ArCH3), 16.54 (d, 3JP,C = 7.9 Hz; OCH2CH3), 10.23 (Cp*). 31P{1H} NMR (161.9 MHz, CD2Cl2, 298 K): δ = 10.1. EI-MS: m/z 619 [M]+, 583 [M − HCl]+, 555 [M − HCl − Et]+. Anal. Calcd for C22H34ClIrNO3P (619.16): C, 42.68; H, 5.54; N, 2.26. Found: C, 43.02; H, 5.57; N, 2.39. [Cp*Ir(κ2-N,O-Xyl(N)P(O)(OEt)2)][BArF4], [2][BArF4]. In the glovebox, [IrCp*(μ-Cl)(Cl)]2 (42.0 mg, 0.053 mmol), sodium N[diethyl(2,6-dimethylphenyl)phosphoramidate] (30.0 mg, 0.108 mmol), and Na[BArF4] (96 mg, 0.108 mmol) were all added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, and the bright red solution was allowed to stir for 1 h at 25 °C. Following this period, the solution was cannula filtered (to remove NaCl) and the solvent was removed in vacuo to afford an orange solid. Recrystallization from hexane-layered CH2Cl2 at −18 °C gave bright red crystals (80 mg, 50%). 1H NMR (400 MHz, CD2Cl2, 298 K): δ = 7.74 (br s, 8H; BArF4), 7.58 (br s, 4H; BArF4), 7.49 (d, 3JH,H = 7.2 Hz, 2H; Ar(CH)), 7.05 (t, 3JH,H = 7.2 Hz, 1H; Ar(CH)), 4.13 (m, 3JH,H = 7.0 Hz, 2H + 2H coincident signals; OCH2CH3), 2.30 (s, 6H ; Ar(CH3)), 1.60 (s, 15H; Cp*), 1.33 (t, 3JH,H = 7.0 Hz, 6H; OCH2CH3). 13C{1H} NMR (400 MHz, CD2Cl2, 298 K): δ = 138.54, 134.14, 129.35, 124.32, 88.72 (Cp*), 68.00 (d, 2JP,C = 8.0 Hz; OCH2CH3) 19.04 (ArCH3), 16.30 (d, 3JP,C = 6.1 Hz; OCH2CH3), 10.09 (Cp*). 31P{1H} NMR (161.9 MHz, CD2Cl2, 298 K): δ = 41.5. 11B{1H} NMR (160.4 MHz, CD2Cl2, 298 K): δ = −6.59 (s, BArF4). 19F{1H} NMR (376.5 MHz, CD2Cl2, 298 K): δ = −62.9. ESI(+)-MS (40 V, 180 °C): calcd 584.1901, found 584.1920 for C22H34IrNO3P+, [2]+. Anal. Calcd for C54H46BF24IrNO3P (1447.19): C, 44.83; H, 3.20; N, 0.97. Found: C, 44.73 H, 3.12 N, 1.04. [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(CNtBu)2][BArF4], [3][BArF4]. In the glovebox [Cp*Ir(κ2-N,O)][BArF4], [2][BArF4] (15 mg, 0.010 mmol), was added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, followed by the addition of CNtBu (2.8 mg, 0.034 mmol), which caused an immediate color change to yellow. After stirring for 15 min at 25 °C, the solvent was removed in vacuo, and the yellow oil was washed with 3 × 5 mL of hexanes to give a yellow solid (16 mg, 96%). X-ray quality crystals were grown from a hexanes-layered CH2Cl2 solution at −35 °C. 1H NMR (400 MHz, CD2Cl2, 298 K): δ = 7.74 (br s, 8H; BArF4), 7.58 (br s, 4H; BArF4), 6.99 (d, 3JH,H = 7.4 Hz, 2H; Ar(CH)), 6.85 (t, 3 JH,H = 7.4 Hz, 1H; Ar(CH)), 3.72 (m, 2H + 2H coincident signals; OCH2CH3), 2.26 (s, 6H; Ar(CH3)), 1.97 (s, 15H, Cp*), 1.39 (s, 18H; CNtBu), 1.10 (t, 3JH,H = 7.1 Hz, 6H; OCH2CH3). 13C{1H} NMR (100 MHz, CD2Cl2, 298 K): δ = 138.58, 136.68, 126.57, 123.86, 100.52 (Cp*), 62.85 (d, 2JP,C = 6.8 Hz; OCH2CH3), 30.38 (CNtBu), 20.77 (Ar(CH3)), 16.65 (d, 3JP,C = 7.3 Hz; OCH2CH3), 10.05 (Cp*). 31 1 P{ H} NMR (161.9 MHz, CD2Cl2, 298 K): δ = 7.00. 11B{1H} NMR (160.4 MHz, CD2Cl2, 298 K): δ = −6.59 (s, BArF4). 19F{1H} NMR (376.5 MHz, CD2Cl2, 298 K): δ = −62.9. ESI(+)-MS (40 V, 180 °C): calcd 750.3376, found 750.3318 for C32H52IrN3O3P+, [3]+. FT-IR ATR (CH2Cl2, cm−1): 2188 (br, νC≡N), 2212 (br, νC≡N). Anal. Calcd

EXPERIMENTAL SECTION

General Methods. All experiments were carried out employing standard Schlenk techniques under an atmosphere of dry nitrogen or argon using degassed, dried solvents. [Cp*IrCl2]2,34 Na[BArF4],35 and H2BMes36 were prepared using a literature procedure. CD2Cl2 was dried over CaH2 and degassed by three freeze−pump−thaw cycles. The proligand 1a-H19 was prepared according to literature procedures. NMR spectra were recorded on a Bruker Avance 300, 400, 500, or 600 MHz spectrometer. 1H NMR spectra are reported in parts per million (ppm) and were referenced to residual solvent: 1H (CD2Cl2): δ 5.32; 13 C (CD2Cl2): δ 53.84; coupling constants are reported in Hz. 13C and 31 P NMR spectra were performed as proton-decoupled experiments and are reported in ppm. The multiplicities are abbreviated as follows: s = singlet, d = doublet, dd = doublet of doublets, h = heptet (septet). NMR spectra are shown using Topspin 3.2 NMR processing software (see the SI). EI-MS or ESI-MS data were obtained using a Kratos MS50 spectrometer (70 eV source) and a Bruker micrOTOF instrument interfaced with a glovebox, respectively. Microanalysis was performed at London Metropolitan University and the University of British F

DOI: 10.1021/acs.organomet.5b00397 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

95.98 (Cp*), 68.82 (d, 2JP,C = 8.7 Hz; OCH2CH3), 19.77 (Ar(CH3)2), 15.64 (d, 3JP,C = 6.4 Hz; OCH2CH3), 9.57 (Cp*). 31P{1H} NMR (161.9 MHz, CDCl3, 298 K): δ = 33.5. 29Si{1H} NMR (79.5 MHz, CDCl3, 298 K): δ = 61.3. 11B{1H} NMR (160.4 MHz, CD2Cl2, 298 K): δ = −6.59 (s, BArF4). 19F{1H} NMR (376.5 MHz, CD2Cl2, 298 K): δ = −62.9. ESI(+)-MS (40 V, 180 °C): m/z 766 for C 33 H 44 IrNO 3 PSi [9] + . Anal. Calcd for C 66 H 56 BF 24 IrNO 3 PSi (1629.23): C, 48.66; H, 3.46; N, 0.86. Found: C, 49.75; H, 3.58; N, 1.71. Satisfactory microanalysis was not obtained for this compound; see the SI for NMR/MS data indicating sample homogeneity. [Cp*Ir(κ3-N,H,H-Xyl(N)P(OBH2Mes)(OEt)2)][BArF4], [10][BArF4]. [Cp*Ir(κ2-N,O)][BArF4], [2][BArF4] (15 mg, 0.010 mmol), was added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, followed by the addition of H2BMes (1.4 mg, 0.010 mmol, 1 equiv), which caused an immediate color change to orange-yellow. After stirring for 15 min at 25 °C, the solvent was removed in vacuo and the green oil was washed with 4 × 5 mL of hexanes to give an orange solid (14.7 mg, 90%). 1H NMR (400 MHz, CD2Cl2, 298 K): δ = 7.70 (br s, 8H; BArF4), 7.53 (br s, 4H; BArF4), 7.13 (d, 3JH,H = 7.5 Hz, 2H; Ar(CH)), 7.06 (t, 3JH,H = 7.5 Hz, 1H; Ar(CH)), 6.91 (s, 2H; Mes), 4.17 (m, 2H + 2H coincident signals; OCH2CH3), 2.42 (s, 6H), 2.34 (s, 3H), 2.26 (s, 6H), 1.39 (s, 15H, Cp*), 1.31 (t, 3JH,H = 7.0 Hz, 6H; OCH2CH3), −8.03 (s, 2H; η2BH2). 13C{1H} NMR (100 MHz, CD2Cl2, 298 K): δ = 140.38, 137.69, 136.31 (d, 3JP,C = 5.6 Hz; OCH2CH3), 128.92, 128.19, 126.13, 123.42, 95.10 (Cp*), 67.97 (d, 2JP,C = 8.8 Hz; OCH2CH3), 21.58 (Ar(CH3)2), 21.29 (Ar(CH3)2), 19.04 (Ar(CH3)2), 15.99 (d, 3JP,C = 6.7 Hz; OCH2CH3), 8.59 (Cp*). 31P{1H} NMR (161.9 MHz, CD2Cl2, 298 K): δ = 16.5. 11B{1H} NMR (160.4 MHz, CD2Cl2, 298 K): δ = −6.59 (s, BArF4). 19F{1H} NMR (376.5 MHz, CD2Cl2, 298 K): δ = −62.9. ESI(+)-MS (40 V, 180 °C): m/z 715 for C31H47BIrNO3P [10]+. Anal. Calcd for C63H59B2F24IrNO3P (1578.94): C, 47.92; H, 3.77; N, 0.89. Found: C, 48.10; H, 3.87; N, 0.89.

for C64H64BF24IrN3O3P (1613.20): C, 47.65; H, 4.00; N, 2.60. Found: C, 47.78; H, 4.14; N, 2.60. [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(CNXyl)2][BArF4], [4][BArF4]. In the glovebox [Cp*Ir(κ2-N,O)][BAr F4], [2][BArF4] (15 mg, 0.010 mmol), was added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, followed by the addition of CNXyl (2.8 mg, 0.021 mmol), which caused an immediate color change to yellow. After stirring for 15 min at 25 °C, the solvent was removed in vacuo, and the yellow oil was washed with 3 × 5 mL of hexanes to give a yellow solid (17 mg, 96%). 1H NMR (400 MHz, CD2Cl2, 298 K): δ = 7.75 (br s, 8H; BArF4), 7.57 (br s, 4H; BArF4), 7.27 (t, 3JH,H = 7.6 Hz, 2H; Xyl(CH)), 7.19 (d, 3JH,H = 7.2 Hz, 4H; Xyl(CH)), 6.85 (t, 3JH,H = 7.3 Hz, 2H; Ar(CH)), 6.67 (t, 3JH,H = 7.0 Hz, 1H; Ar(CH)), 3.71 (m, 2H + 2H coincident signals; OCH2CH3), 2.42 (s, 12H; Xyl(CH3)2) 2.35 (s, 6H; Ar(CH3)2), 2.00 (s, 15H, Cp*), 0.99 (t, 3JH,H = 6.9 Hz, 6H; OCH2CH3). 13C{1H} NMR (150 MHz, CD2Cl2, 298 K): δ = 137.85, 136.08, 130.95, 130.57, 126.23, 125.67, 124.73, 123.50, 101.71 (Cp*), 62.26 (d, 2JP,C = 6.8 Hz; OCH2CH3), 20.55 (Ar(CH3)2), 18.73 (CNAr(CH3)2), 15.86 (d, 3JP,C = 7.2 Hz; OCH2CH3), 9.64 (Cp*). 31P{1H} NMR (161.9 MHz, CD2Cl2, 298 K): δ = 7.70. 11B{1H} NMR (160.4 MHz, CD2Cl2, 298 K): δ = −6.59 (s, BArF4). 19F{1H} NMR (376.5 MHz, CD2Cl2, 298 K): δ = −62.9. ESI(+)-MS (40 V, 180 °C): calcd 846.3376, found 846.3311 for C40H52IrN3O3P+ [4]+. FT-IR ATR (CH2Cl2, cm−1): 2167 (br, νC≡N). Anal. Calcd for C72H64BF24IrN3O3P (1709.28): C, 50.59; H, 3.77; N, 2.46. Found: C, 50.29; H, 3.89; N, 2.65. [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(MeCN)2][BArF4], [7][BArF4]. In the glovebox [Cp*Ir(κ2-N,O)][BArF4], [2][BArF4] (10.0 mg, 0.007 mmol), was added to a J. Young NMR tube. Next, MeCN (1.5 μL, ∼5 equiv) was added, resulting in no observable color change. 31P{1H} NMR (161.9 MHz, CD2Cl2, 190 K): δ = 8.31. [Cp*Ir(κ1-N-Xyl(N)P(O)(OEt)2)(2,2′-bipy)][BArF4], [8][BArF4]. In the glovebox [Cp*Ir(κ2-N,O)][BArF4], [2][BArF4] (15 mg, 0.010 mmol), was added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, followed by the addition of 2,2′-bipyridine (2.4 mg, 0.015 mmol), which caused an immediate color change to yellow. After stirring for 15 min at 25 °C, the solvent was removed in vacuo and the orange oil was washed with 3 × 5 mL of hexanes to give an orange solid (15 mg, 90%). 1H NMR (400 MHz, CD2Cl2, 298 K): δ = 8.78 (d, 3JH,H = 5.3 Hz, 2H), 8.02 (t, 3 JH,H = 7.8 Hz, 2H), 7.97 (t, 3JH,H = 7.7 Hz, 2H), 7.72 (br s, 8H; BArF4), 7.55 (br s, 4H; BArF4), 7.47 (t, 3JH,H = 6.5 Hz, 2H), 6.54 (br s, 3H; Ar(CH)), 3.68 (m, 2H + 2H coincident signals; OCH2CH3), 1.65 (s, 6H; Ar(CH3)), 1.48 (s, 15H, Cp*), 1.08 (t, 3JH,H = 7.1 Hz, 6H; OCH2CH3). 13C{1H} NMR (150 MHz, CD2Cl2, 298 K): δ = 155.89, 153.06, 140.11, 138.09, 128.62, 128.22, 126.39, 123.90, 122.73, 90.39 (Cp*), 62.26 (d, 2JP,C = 6.8 Hz; OCH2CH3), 19.49 (Ar(CH3)2), 16.47 (d, 3JP,C = 7.2 Hz; OCH2CH3), 8.87 (Cp*). 31P{1H} NMR (161.9 MHz, CD2Cl2, 298 K): δ = 8.48. 11B{1H} NMR (160.4 MHz, CD2Cl2, 298 K): δ = −6.59 (s, BArF4). 19F{1H} NMR (376.5 MHz, CD2Cl2, 298 K): δ = −62.9. ESI(+)-MS (40 V, 180 °C): calcd 740.2589, found 740 .2 527 f or C 3 2 H 4 2 I r N 3 O 3 P + [8 ] + . A n a l . C a l c d fo r C64H54BF24IrN3O3P (1603.12): C, 47.95; H, 3.40; N, 2.62. Found: C, 47.99; H, 3.37; N, 2.74. [Cp*Ir(κ2-N,Si-Xyl(N)P(OSiPh2)(OEt)2)][BArF4], [9][BArF4]. [Cp*Ir(κ2-N,O)][BArF4], [2][BArF4] (19.5 mg, 0.013 mmol), was added to a small Schlenk flask equipped with a stir bar. Approximately 5 mL of CH2Cl2 was added via cannula, followed by the addition of H2SiPh2 (12.4 mg, 0.067 mmol, 5 equiv), which caused an immediate color change to green. After stirring for 15 min at 25 °C, the solvent was removed in vacuo and the green oil was washed with 4 × 5 mL of hexanes to give a green solid (12 mg, 55%). X-ray quality crystals were grown from a hexanes-layered CH2Cl2 solution at −35 °C. 1H NMR (400 MHz, CDCl3, 298 K): δ = 7.70 (br s, 8H; BArF4), 7.67 (m, 6H, SiPh2), 7.53 (m, 6H, SiPh2), 7.52 (br s, 4H; BArF4), 7.27 (d, 3JH,H = 7.5 Hz, 2H; Ar(CH)), 7.09 (t, 3JH,H = 7.5 Hz, 1H; Ar(CH)), 3.98 (m, 2H; OCH2CH3), 3.87 (m, 2H; OCH2CH3), 2.41 (s, 6H), 1.10 (t, 3JH,H = 7.1 Hz, 6H; OCH2CH3), 1.09 (s, 15H, Cp*). 13C{1H} NMR (100 MHz, CDCl3, 298 K): δ = 146.84, 135.99 (d, 3JP,C = 4.4 Hz), 138.23, 133.20 (d, 3JP,C = 4.7 Hz), 131.55, 128.90, 126.13, 123.42, 120.71,

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ASSOCIATED CONTENT

S Supporting Information *

1

H, 13C, and 31P{1H} NMR spectra for all complexes as well as crystallographic data for [2][BarCl24], [3][BArF4], [9][BArF4], and [11][BArF4]. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.organomet.5b00397. CCDC 1061938 ([2][BArCl24]), 1403652 ([3][BArF4]), 1403651 ([9][BArF4]), and 1061937 ([11][BArF4]) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc. cam.ac.uk/data_request/cif.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the following for support of this research: NSERC (Discovery, Research Tools, and Instrumentation Grants to J.A.L. and L.L.S.; a MSFSS travel award to M.W.D.), the University of British Columbia (VPRI travel award to M.W.D.), the Peter Wall Institute for Advanced Studies, and the government of Canada (Vanier Scholarship to M.W.D.). This work was undertaken, in part, thanks to funding from the Canada Research Chairs program (L.L.S.). EPSRC is also thanked for funding (H.C.J.). G

DOI: 10.1021/acs.organomet.5b00397 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

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DOI: 10.1021/acs.organomet.5b00397 Organometallics XXXX, XXX, XXX−XXX