CuI-Catalyzed Conjugate Addition of Silyl Boronic Esters: Retracing

Article pubs.acs.org/Organometallics

CuI‑Catalyzed Conjugate Addition of Silyl Boronic Esters: Retracing Catalytic Cycles Using Isolated Copper and Boron Enolate Intermediates Jacqueline Plotzitzka and Christian Kleeberg* Institut für Anorganische und Analytische Chemie, Technische Universität Carolo-Wilhelmina zu Braunschweig, Hagenring 30, 38106 Braunschweig, Germany S Supporting Information *

ABSTRACT: Copper(I)-catalyzed conjugate additions of silyl boronic esters to α,β-unsaturated aldehydes, ketones, and esters are synthetically well-established reactions. For the first time central reactive intermediates as well as the boron enolates as the primary reaction products are isolated and employed in order to deduce catalytic cycles on an experimental basis. Employing an NHC CuI complex as a model catalyst, it is possible to perform efficient catalytic transformations as well as to isolate and characterize the formed copper enolate complexes as the key intermediates. It is shown that for this catalytic system the nature of this enolateO- or C-enolateis crucial for the catalytic process. For α,β-unsaturated aldehydes and ketones the O-enolate is formed predominantly, while for α,β-unsaturated esters the C-enolate is the major product. Catalytic turnover is only facile for copper O-enolates, as they react efficiently with the silyl boronic ester under (re)formation of the catalytically active Cu−Si species and a thermodynamically favored boric acid ester. Thus, the formation of copper C-enolates is inhibiting the catalytic process, and effective turnover is possible only after solvolysis by an alcohol additive. The individual catalytic processes were retraced by performing stepwise stoichiometric reactions monitored by in situ NMR spectroscopy.

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INTRODUCTION Silyl boronic esters, especially pinB−SiMe2Ph (1) (pin = OCMe2CMe2O), are well-established reagents in transitionmetal-catalyzed silylation reactions (e.g., Pt, Pd, Cu, Ni, Rh, CuII). More recently, transition-metal-free Lewis-base-promoted silylation and borylation reactions employing 1 have also emerged.1−4 Furthermore, copper(I)-catalyzed silylation reactions employing 1 with various organic substrates such as α,β-unsaturated carbonyl and carboxyl compounds, aldehydes, imines, amides, but also, for example, allyl/propargyl chlorides have been reported in the past few years.1a,2 Using α,βunsaturated carbonyl and carboxyl compounds as substrates, the products obtained, possibly after hydrolytic workup, are the corresponding β-silyl carbonyl/carboxyl compounds, respectively (Scheme 1). A generalized catalytic cycle was proposed in agreement with the experimental data, well-established stoichiometric cuprate chemistry, and the apparently closely related CuI-catalyzed diboration reactions (Scheme 2).1a,2,4−8,9a,b While diverse catalyst systems and reaction conditions are employed in these transformations, two general points regarding the (pre)catalyst are to be noted: The CuI source may be a preformed, isolated copper complex. More often, a CuI salt and a ligand or ligand precursor, possibly under addition of an auxiliary reagent (e.g., a base in the case of imidazolium salt in © XXXX American Chemical Society

Scheme 1. General Scheme of Copper(I)-Catalyzed Silylation Reactions of α,β-Unsaturated Carbonyl (R = H, Alkyl; R′ = H, Alkyl, Aryl) and Carboxyl (R = Alkoxido, R′ = H, Alkyl, Aryl) Compounds Employing the Silyl Boronic Ester 1

order to furnish a (NHC)Cu species), is employed. In a simple and yet versatile catalytic system CuCN is used in the absence of any additional ligand.1a,2,4 The second general observation is that catalytic amounts of an alkali metal alkoxide are required. It has been conclusively argued that the alkoxide is necessary (besides the possible generation of an NHC ligand, vide supra) to form a copper alkoxido species that is crucial for an initial B−Si bond activation step in order to generate the catalytically Received: September 29, 2014

A

dx.doi.org/10.1021/om500989w | Organometallics XXXX, XXX, XXX−XXX

Organometallics

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and finally to study their reactivity and retrace the catalytic cycle stepwise by stoichiometric reactions. We reasoned that using a model catalyst based on the (IDipp)CuI fragment is advantageous in order to have welldefined, mononuclear species and to prevent the formation of aggregates and/or polynuclear complexes as suggested by the long-discussed aggregation behavior known from, for example, alkyl and aryl cuprates.6 Furthermore, the (IDipp)CuI system has already been successfully employed as a model catalyst studying 1,2-addition reactions of 1 to aldehydes and CO2 as well as in a number of related studies.5,9

Scheme 2. Proposed Catalytic Cycle for the CuI-Catalyzed Conjugate Silylation of α,β-Unsaturated Carbonyl and Carboxyl Compounds with 1a

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RESULTS AND DISCUSSION Catalytic Experiments. The exemplary α,β-unsaturated carbonyl and carboxyl compounds 3a−f as substrates were reacted with 1 in the presence of catalytic amounts of (IDipp)CuOtBu (2). The substrates were selected in order to cover carbonyl and carboxyl compounds (ketones, aldehydes, esters) and different substitution patterns at the β-carbon atom (Table 1). Table 1. Conjugate Addition of 1 to α,β-Unsaturated Substrates in the Presence of 2

a

Adopted from ref 1a.

crucial Cu−Si species (Scheme 2). The effectiveness of ligand control especially by NHC ligands has been demonstrated by Hoveyda et al.: Using a chiral NHC-Cu complex as catalyst, the conjugate silyl addition to α,β-unsaturated ketones and esters results in high yields and enantioselectivity.4a The commonly accepted catalytic process consists of three distinct steps (Scheme 2): (1) formation of the central copper(I) silyl complex (via σ-bond metathesis) from the silyl boronic ester and a copper alkoxido species, initially formed from the primary copper source and the alkali metal alkoxide. (2) This copper(I) silyl complex reacts in an addition reaction with the α,β-unsaturated substrate to give a β-silylated copper enolate. (3) The reaction of this enolate with the silyl boronic esters regenerates the copper(I) silyl complex (and, hence, completes the catalytic cycle), and the primary product of the catalytic process, a β-silylated boron O-enolate, is released. Finally, hydrolytic workup of the latter results in the formation of the finally isolated β-silylated carbonyl/carboxyl compounds. The individual steps within the catalytic cycle are also, as far as plausible, in agreement with computational data on a CuI/amine-cocatalyzed enantioselective conjugate silylation of α,β-unsaturated carbonyl compounds and with experimental studies on the 1,2-addition of 1 to aldehydes and CO2.4g,5,10 For a further rational development of CuI-catalyzed conjugate addition of silyl boronic esters with α,β-unsaturated carbonyl and carboxyl compounds a more detailed understanding of the species present during the individual reaction steps and of their reactivity is highly desirable. Hence, we set out to study the CuI-catalyzed reaction of 1 with exemplary α,βunsaturated aldehydes, ketones, and esters employing a (IDipp)CuI complex (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as model catalyst. In particular we aimed to isolate and thoroughly characterize the central intermediates

substrate R = Et, R′ = H R = Me, R′ = Me cyclohexenone R = H, R′ = H R = H, R′ = Me R = OMe, R′ = H

3a 3b 3c 3d 3e 3f

t/h

4 (E/Z)a

5a

3 6−8 6 2 16 4

87% (1:7) 67% not isolated 93% (2:5) 0%b

77% 87% 82% 68% 0%b 79%c

a

Isolated yields. E/Z ratio determined by 1H NMR spectroscopy. b1,2Addition product in 92% (7)/83% (8) yield (vide infra, Scheme 3). cIn the presence of iPrOH.

For the ketones 3a−c and the mono-β-substituted aldehyde 3d the expected β-silylated boron enolates (4a,b,d) and after hydrolytic workup the corresponding β-silylated carbonyl compounds (5a−d) were isolated in good yields. This demonstrates that 2 is indeed an efficient precatalyst and that further studies may be fruitful to gain more mechanistic insight. Moreover, to the best of our knowledge, the β-silyl boron enolates as the primary reaction products of a CuI-catalyzed silyl conjugate addition reaction of a silyl boronic ester have so far not been obtained in substance and characterized in any detail.11 The conjugate addition reactions of 1 to 3a, 3b, and 3d were studied by in situ 1H NMR spectroscopy under conditions closely resembling the conditions used above but employing 10 mol % of (IDipp)Cu−SiMe2Ph (6) or (IDipp)Cu−OtBu (2) as precatalysts and C6D6 as solvent. As, according to the proposed catalytic cycle (Scheme 2) and in agreement with our studies on related 1,2-addition chemistry, the alkoxide complex 2 is rapidly converted to 6 upon reaction with 1, both precatalysts eventually lead to the same catalytically active species.5 For all substrates the formation of the boron enolate as the virtually exclusive reaction product is observed (Figure 1). B

dx.doi.org/10.1021/om500989w | Organometallics XXXX, XXX, XXX−XXX

Organometallics

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Figure 1. Details of in situ 1H NMR spectra of conjugate addition reactions of 1 (1.2 equiv, ■) to hex-4-en-3-one (3a), mesityloxide (3b, □), and crotonaldehyde (3d) (1.0 equiv) (from top) in the presence of 10 mol % precatalyst (6 (●) for 3a,b and 2 for 3d) at room temperature (300 MHz, rt, C6D6). Signals of the minor isomers are denoted by a prime; only selected NOESY contacts are shown (○: pinB−OtBu; ×: 5a); † denotes that only a part of the signal is visible due to overlapping.

and in particular with reported values for related silyl enol ethers.12 In addition to the signals of the silylation products 4a,b,d signals indicative for complex 6 as well as for residual 1 are observed in all reactions. Moreover, unreacted starting material is observed in the reaction of 3b as well as pinB−OtBu in the reaction of 3d. The latter results from the initial conversion of the precatalyst 2 to the silyl complex 6 in order to enter the catalytic cycle (vide supra).5 In the case of the reaction of 3a a small amount (95%) the E isomer. All solvents were dried using a solvent purification systems, deoxygenated using the freeze−pump−thaw method, and stored under purified nitrogen. All manipulations were performed using standard Schlenk techniques under an atmosphere of purified nitrogen or in a nitrogen-filled glovebox. Air-sensitive samples were measured in NMR tubes equipped with screw caps. Chemical shifts (δ) are given in ppm, using the residual resonance signal of the solvents (C6D6: 99.5% deuteration, 1H NMR: 7.16 ppm, 13C NMR: 128.06 ppm).20 11B chemical shifts are reported relative to external BF3·Et2O. 11B NMR spectra were processed applying a back linear prediction in order to suppress the broad background signal due to the borosilicate glass of the NMR tube and a Lorentz-type window function (LB = 10 Hz); the spectra were carefully evaluated to ensure that no genuinely broad signals of the sample were suppressed. If necessary 2D NMR techniques were employed to establish connectivity and to assign the individual signals (1H−1H NOESY (1 s mixing time), 1H−1H COSY, 1H−13C HSQC, and 1H−13C HMBC). Complicated coupling patterns were analyzed with the aid of simulations. The same numbering scheme as in Figures 1−4 and 6/ 7 is used in the experimental part. Melting points were determined in flame-sealed capillaries under nitrogen and are not corrected. Elemental analyses were performed at the Institut für Anorganische and Analytische Chemie of the Technische Universität CaroloWilhelmina zu Braunschweig. GC/MS measurements were performed in positive EI mode (70 eV, 60−700 m/z) with the following conditions: injection temperature 250 °C; interface temperature 280 °C; temperature program: start temperature 50 °C for 3 min, heating rate 12 °C min−1, end temperature 300 °C for 8 min; column type: 5% phenyl-arylene/95% dimethylpolysiloxane, 30 m × 0.25 mm, 0.25 μm film thickness; He carrier gas (1.5 mL min−1). For HRMS measurements a time-of-flight mass spectrometer operating in EI mode (70 eV) coupled to a gas chromatograph was used. Infrared (IR) spectra were recorded using an ATR unit. Analytical thin-layer chromatography (TLC) was performed on precoated silica gel polyester sheets; flash column chromatography (⦶ 3 cm × 20 cm) on silica gel 60. Preparation of 4a,b,d and 7 (General Procedure). In a nitrogen-filled glovebox 2 (18 mg, 34 μmol, 3 mol %) and 1 (300 mg, 1.14 mmol, 1.0 equiv) were mixed in dry toluene (5 mL). The α,βunsaturated substrate (1.14 mmol, 1.0 equiv) was added, and the mixture stirred at room temperature. The progress of the reaction was monitored by GC/MS analysis of an aliquot of the reaction mixture (0.05 mL) after dilution with Et2O (2 mL) and filtration over Celite. After complete consumption of 1 the solvent and excess α,βunsaturated carbonyl substrate were evaporated at room temperature under vacuum (10−3 mbar), and the residue was extracted with npentane (2 × 2 mL) and filtered over Celite, in order to remove insoluble NHC-Cu complexes, to give a clear solution. Evaporation of the solvent and possibly residual α,β-unsaturated carbonyl substrate at room temperature under vacuum (10−3 mbar) yielded the reaction products. pinB-O-C6H10-SiMe2Ph (4a): hex-4-en-3-one (3a) (112 mg, 1.14 mmol); 3 h; pale yellow, sticky oil (357 mg, 0.99 mmol, 87%). Despite all efforts the contamination of 4a with a small amount (100 °C. Anal. Calcd for C40H55CuN2O2Si: C, 69.88; H, 8.06; N, 4.07. Found: C, 69.72; H, 8.02; N, 4.21. In Situ NMR Experiments: Catalytic Conjugate Silyl Addition to 3a,b,d,e,f (Figure 1−3). In a nitrogen-filled glovebox a screw cap NMR tube was charged with 3a,b,d,e or f (57 μmol, 1.0 equiv), 1 (18 mg, 68 μmol, 1.2 equiv), and 2 (3.3 mg, 5.7 μmol, 10 mol %) or 6 (3.0 mg, 5.7 μmol, 10 mol %) and C6D6 (0.7 mL). 1H NMR spectra were recorded after the given time intervals at rt: 3a: 5.6 mg, 6 h. 3b: 5.6, 20

Hz, 3JHH = 4.2 Hz, 1 H, CH), 0.97 (d, 3JHH = 7.6 Hz, 3 H, CH3), 0.28 (s, 6 H, Si(CH3)2).21c 1H NMR (300 MHz, C6D6, rt): δ 7.41−7.35 (m, 2 H, CHPh), 7.20−7.15 (m, 3 H, CHPh), 3.32 (s, 3 H, OCH3), 2.33 (dd, 3JHH = 15.3 Hz, 3JHH = 4.2 Hz, 1 H, CH2), 2.02 (dd, 3JHH = 15.3 Hz, 3JHH = 10.8 Hz, 1 H, CH2), 1.53 (dqd, 3JHH = 10.8 Hz, 3JHH = 7.3 Hz, 3JHH = 4.2 Hz, 1 H, CH), 0.97 (d, 3JHH = 7.3 Hz, 3 H, CH3), 0.13 (s, 3 H, Si(CH3)2), 0.12 (s, 3 H, Si(CH3)2). MS (GC/MS, EI): 236 [M]+, 221 [M − CH3]+, 205 [M − OCH3]+, 159 [M − Ph]+, 135 [SiMe2Ph]+.21c Preparation of 9a-d,f (General Procedure). In a nitrogen-filled glovebox 6 (50 mg, 85 μmol, 1 equiv) was dissolved in toluene (2 mL), and a small excess of the α,β-unsaturated carbonyl compound 3a−d,f was added. After the given reaction time at room temperature the mixture was layered with n-pentane (approximately 2 mL) and stored at −40 °C. After separation of a (crystalline) solid the supernatant solution was decanted and the residue washed with npentane (approximately 2 × 1 mL) and dried in vacuo. (IDipp)Cu-O-C6H10-SiMe2Ph (9a): hex-4-en-3-one (3a) (9 mg, 92 μmol, 1.1 equiv); 3 h; light brown microcrystals (64 mg, 74 μmol, 87%). 1H NMR (600 MHz, C6D6, rt): δ 7.74−7.70 (m, 2 H, o-CHPh), 7.28−7.22 (m, 3 H, m,p-CHPh), 7.19 (t, JHH = 7.8 Hz, 2 H, p-CHDipp), 7.04 (d, JHH = 7.8 Hz, 4 H, m-CHDipp), 6.25 (s, 2 H, NCH), 3.97 (d, JHH = 9.5 Hz, 1 H, 2-CH), 2.72 (dq, 3JHH = 9.5 Hz, 3JHH = 7.5 Hz, 2 H, 3-CH), 2.54 (sept., 3JHH = 6.9 Hz, 4 H, CH(CH3)2), 1.96 (q, 3JHH = 15.0 Hz, 3JHH = 7.5 Hz, 1 H, 1-CH2), 1.93 (dq, 3JHH = 16.0 Hz, 1 H, 1CH2), 2 × 1.36 (d, JHH = 6.9 Hz, 6 H, CH(CH3)2), 1.14 (d, JHH = 7.6 Hz, 3 H, 4-CH3), 1.06 (bd, 3JHH = 6.9 Hz, 12 H, CH(CH3)2), 1.02 (t, 3 JHH = 7.5 Hz, 3 H, 1a-CH3), 0.41 (s, 3 H, Si(CH3)2), 0.39 (s, 3 H, Si(CH3)2). 13C{1H} NMR (150 MHz, C6D6, rt): δ 182.8 (CCarbene), 162.1 (O-CCH), 145.7 (ipso-CDipp), 142.1 (ipso-CPh), 135.2 (ipsoNCDipp), 134.8 (o-CHPh), 130.7 (p-CHDipp), 128.2 (m/p-CHPh), 127.6 (m/p-CHPh), 124.4 (m-CHDipp) 122.6 (NCH), 95.5 (2-CH), 35.5 (1CH2), 29.0 (CH(CH3)2), 24.9 (CH(CH3)2), 23.9 (CH(CH3)2), 17.8 (3-CH), 16.8 (4-CH3), 13.6 (1a-CH3), −2.7 (Si(CH3)2), −4.8 (Si(CH3)2). Mp: 110−114 °C. Anal. Calcd for C41H57CuN2OSi: C, 71.83; H, 8.38; N, 4.09. Found: C, 69.56; H, 8.23; N, 4.17. Repeated elemental analysis for different, independently prepared samples failed to give more satisfactory results; all samples gave consistent values but were low in carbon. It may be speculated that this is caused by SiC and/or carbide/carbonate formation.22 (IDipp)Cu-O-C6H10-SiMe2Ph (9b): mesityl oxide (3b) (9 mg, 92 μmol, 1.1 equiv); 20 h; off-white microcrystals (39 mg, 57 μmol, 67%). 1 H NMR (600 MHz, C6D6, rt): δ 7.78−7.74 (m, 2 H, o-CHPh), 7.26− 7.18 (m, 3 H, m,p-CHPh), 7.20 (t, 3JHH = 7.8 Hz, 2 H, p-CHDipp), 7.05 (d, JHH = 7.8 Hz, 4 H, m-CHDipp), 6.26 (s, 2 H, NCH), 3.87 (bs, 1 H, 2-CH), 2.53 (sept., 3JHH = 6.9 Hz, 4 H, CH(CH3)2), 1.59 (s, 3 H, 1CH), 1.36 (d, 3JHH = 6.9 Hz, 12 H, CH(CH3)2), 1.36 (s, 6 H, 4-CH3), 1.06 (d, 3JHH = 6.9 Hz, 12 H, CH(CH3)2), 0.52 (s, 3 H, Si(CH3)2). 13 C{1H} NMR (150 MHz, C6D6, rt): δ 182.7 (CCarbene), 157.0 (O-C CH), 145.7 (ipso-CDipp), 142.6 (ipso-CPh), 135.2 (o-CHPh), 135.1 (ipsoNCDipp), 130.7 (p-CHDipp), 127.9 (m/p-CHPh), 127.3 (m/p-CHPh), 124.3 (m-CHDipp), 122.6 (NCH), 102.6 (2-CH), 30.4 (1-CH2), 29.0 (CH(CH3)2), 26.8 (4-CH3), 24.9 (CH(CH3)2), 23.9 (CH(CH3)2), 22.6 (3-CH), −3.0 (Si(CH3)2). Mp: 128−134 °C. Anal. Calcd for C41H57CuN2OSi: C, 71.83; H, 8.38; N, 4.09. Found: C, 70.70; H, 8.29; N, 4.22. Repeated elemental analysis for different, independently prepared samples failed to give more satisfactory results; all samples gave consistent values but were low in carbon. It may be speculated that this is caused by SiC and/or carbide/carbonate formation.22 (IDipp)Cu-O-C6H8-SiMe2Ph (9c): cyclohexenone (3c) (9 mg, 94 μmol, 1.1 equiv); 1 h; crystallization at −78 °C, colorless microcrystals (36 mg, 53 μmol, 62%). 1H NMR (600 MHz, C6D6, rt): δ 7.64−7.60 (m, 2 H, o-CHPh), 7.25−7.21 (m, 3 H, m,p-CHPh), 7.20 (t, 3JHH = 7.7 Hz, 2 H, p-CHDipp), 7.04 (d, JHH = 7.7 Hz, 4 H, m-CHDipp), 6.23 (s, 2 H, NCH), 4.56 (bs, 1 H, O−CCH), 2 × 2.53 (sept., 3JHH = 6.9 Hz, 2 H, CH(CH3)2), 2.05−1.97 (m, 2 H, CH-Si and CH2), 1.94−1.89 (m, 1 H, CH2), 1.79−1.69 (m, 2 H, CH2), 1.66−1.56 (m, 1 H, CH2), 1.49−1.43 (m, 1 H, CH2), 1.34 (d, 3JHH = 6.9 Hz, 6 H, CH(CH3)2), 1.33 (d, 3JHH = 7.0 Hz, 6 H, CH(CH3)2), 2 × 1.06 (d, 3JHH = 6.9 Hz, 6 H, CH(CH3)2), 0.32 (s, 3 H, Si(CH3)2), 0.31 (s, 3 H, Si(CH3)2).

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h. 3d: 4.0 mg, 2 h. 3e: 4.8 mg, 6 h. 3f: 5.7 mg, 8 h; a separate, identical experiment was performed under addition of iPrOH (approximately 3.4 mg, 57 μmol, 1.0 equiv, 0.5 h). In Situ NMR Experiments: Formation of 9a,b,d,f (Figure 4). In a nitrogen-filled glovebox a screw cap NMR tube was charged with 6 (15 mg, 26 μmol, 1.0 equiv), 3a,b,d or f (26 μmol, 1.0 equiv), and C6D6 (0.7 mL). 1H NMR spectra were recorded after the given time intervals at rt. 3a: 2.8 mg, 1.5 h. 3b: 2.8 mg, 16 h. 3d: 2.0 mg, 0.5 h. 3f: 2.8 mg, 0.5 h. In Situ NMR Experiments: Formation of 4a,b,d/5f and 6 from 9a,b,d,f and 1 (Figure 6,7). In a nitrogen-filled glovebox a screw cap NMR tube was charged with 9a,b,d or f (15 mg, 1 equiv), 1 (7 mg, 27 μmol, 1.2 equiv), and C6D6 (0.7 mL). 1H NMR spectra were recorded after 2 h at rt. 9a: 22 μmol. 9b: 22 μmol. 9d: 23 μmol. 9f: 22 μmol; after 2 h a 1H NMR spectrum was recorded, iPrOH (approximately 2 mg, 3 μmol, 1.5 equiv) was added, and another 1H NMR spectrum was recorded.

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ASSOCIATED CONTENT

S Supporting Information *

The SI available contains additional NMR spectroscopic and crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC 1019946−1019951. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44(1223) 336-033; e-mail: deposit@ccdc. cam.ac.uk].

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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 gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG). C.K. thanks the Fonds der Chemischen Industrie for a Liebig-Stipendium. The authors wish to thank Oliver Haslett (RISE program, DAAD) for help with the laboratory work.

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REFERENCES

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dx.doi.org/10.1021/om500989w | Organometallics XXXX, XXX, XXX−XXX

Organometallics

Article

(14) The molecular structure of 7 has also been established by an Xray structure analysis; see SI for details. (15) Crystallization of 9d proved especially challenging as repeatedly crystals of (IDipp)CuPh were obtained from samples containing 9d and that were originally free of (IDipp)CuPh. Moreover, formation of (IDipp)CuPh was also observed in C6D6 solution after prolonged periods of time. The intriguing observations regarding 9d, its decomposition to (IDipp)CuPh, the formation of 10, and the equilibrium of the E/Z isomersmay it be related or notare subjects of ongoing studies.16 For the spectroscopic data of (IDipp) CuPh see ref 9d. (16) See SI for details. (17) In all cases but 9d the refinement of suitable split atom models was successful. Similarity restraints had to be employed and a common ADP was refined for each disordered atom pair. The refined occupancies of the main component were 9a: 0.950(1), 9b: 0.811(1), and 9d(10)PhMe: 0.656(3). Only the geometrical data of the major component are discussed.16 (18) Wiberg, N. Holleman-Wiberg, Lehrbuch der Anorganischen Chemie; Walter de Gruyter: Berlin/New York, 2007; p 2006. (19) (a) Mankad, N. P.; Laitar, D. S.; Sadighi, J. P. Organometallics 2004, 23, 3369−3371. (b) Hintermann, L. Beilstein J. Org. Chem. 2007, 3, No. 22. (c) Jarkauskas, V.; Sadighi, J. P.; Buchwald, S. L. Org. Lett. 2003, 5, 2417−2420. (d) Andersen, M. W.; Hildebrandt, B.; Köster, G.; Hoffmann, R. W. Chem. Ber. 1989, 122, 1777−1782. (e) Suginome, M.; Matsuda, T.; Ito, Y. Organometallics 2000, 19, 4647−4649. (20) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organometallics 2010, 29, 2176−2179. (21) (a) Lipshutz, B. H.; Sclafani, J. A.; Takanami, T. J. Am. Chem. Soc. 1998, 120, 4021−4022. (b) Ito, H.; Ishizuka, T.; Tateiwa, J.; Sonoda, M.; Hosomi, A. J. Am. Chem. Soc. 1998, 120, 11196−11197. (c) Lipshutz, B. H.; Tanaka, N.; Taft, B. R.; Lee, C.-T. Org. Lett. 2006, 8, 1963−1966. (22) (a) Culmo, R. F. Application Note Elemental Analysis; Perkin Elmer, Inc.: Shelton, CT, 2013. (b) Gawargious, Y. A.; MacDonald, A. M. G. Anal. Chim. Acta 1962, 27, 300−302.

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dx.doi.org/10.1021/om500989w | Organometallics XXXX, XXX, XXX−XXX