Mono- and Bis-Cyclometalated Palladium Complexes: Synthesis

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Mono- and Bis-Cyclometalated Palladium Complexes: Synthesis, Characterization, and Catalytic Activity Sebastian Molitor, Christopher Schwarz, and Viktoria H. Gessner* Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany S Supporting Information *

ABSTRACT: Cyclometalated palladium complexes have found a variety of applications, above all in homogeneous catalysis. Most complexes include mono-cyclometalated ligands, particularly systems with P- or N-donors. Herein, we report the preparation of a series of mono- and biscyclometalated palladium complexes with a silyl-substituted thiophosphinoyl ligand. The complexes have been synthesized via oxidative addition and dehydrohalogenation reactions. Thereby, dehydrohalogenation selectively results in the second cyclometalation and not in the formation of a carbene species. In the formed square-planar palladacycles the ligands exhibit S,C- and S,C,C-coordination modes, respectively. Depending on the silyl moiety, cyclometalation occurs via an aryl or even a methyl group, thus also giving way to unusual silapalladacyclobutanes with an open-book geometry. The complexes have been characterized in solution as well as in the solid state. Preliminary catalytic studies show that both the mono- and bis-cyclometalated complexes can be applied as catalysts in C−C coupling reactions.

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INTRODUCTION Transition metal carbene complexes have fascinated chemists for many years due to their diverse reactivity and applicability in stoichiometric as well as catalytic transformations.1 Nucleophilic carbenes of late transition metals are a unique subclass of carbene complexes that diverge from the prototypic Fischer and Schrock systems.2,3 Hence, only in 2002 did Hillhouse report on the first isolation of a group 10 metal alkylidene.4 Yet, in the past couple of years these complexes have found increasing attention. Due to the unusual electronic properties of the metal−carbon interaction, these complexes were found to be applicable in a number of bond activation reactions.5 For example, the groups of Piers and Iluc applied PCsp2P nickel and palladium complexes B (Chart 1) in the activation of a series of E−H bonds as well as the H−H bond in dihydrogen.6,7 Besides using PCsp2P pincer ligands for the stabilization of late transition metal alkylidenes, also dilithiomethanes8 as well as lithium carbenoids9 have been found to be suitable precursors to access such unusual carbene species. The “carbenoid route” has first been reported by Le Floch and co-workers with the preparation of palladium complex C (Chart 1b).10,11 Limitations of this synthetic strategy, however, were observed by our group.12 Employing the more reactive silyl-substituted carbenoids, mixtures of the unusual T-shaped carbene complex D and thioketone E were observed depending on the substitution pattern at silicon. Because of the unique structure of D, we were interested in alternative routes to the carbenoid method to selectively access the carbene species D. Dehydrohalogenation such as used for the PCsp2P pincer systems (e.g., A to B, Chart 1a) seemed to be a suitable synthetic strategy. © 2015 American Chemical Society

Chart 1. Nucleophilic Group 10 Carbene Complexes Based on PCsp2P Pincer Ligands and Lithium Carbenoids

Herein, we show that contrary to previous reports on related ligands13 no carbene complex formation is observed by dehydrogenation of the methanide complexes (Chart 1c). Instead, bis-cyclometalated complexes are readily formed by metalation of silicon-bound aryl and also methyl groups, Received: October 27, 2015 Published: December 31, 2015 159

DOI: 10.1021/acs.organomet.5b00903 Organometallics 2016, 35, 159−167

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Organometallics

All complexes 2a−2f are stable toward air and moisture and were characterized by multinuclear NMR spectroscopy, highresolution mass spectrometry, and X-ray diffraction analysis. The complexes showed similar spectroscopic properties. Thus, only the data of complex 2a are discussed in more detail. 2a is characterized by two doublets in the 31P{1H} NMR spectrum at δP = 46.3 and 22.4 ppm with a coupling constant of 3JPP = 17.5 Hz. The 1H NMR spectrum exhibits two sets of signals for the diastereotopic protons of the phosphorus-bound phenyl groups and the characteristic signal at δH = 2.17 ppm for the central hydrogen atom at the PCSi backbone. This signal appears as a doublet of doublets with coupling constants of 2JPH = 8.8 Hz and 3JPH = 5.4 Hz, respectively. The signal for the central carbon atom experiences an upfield shift in the 13C{1H} NMR spectrum upon metalation and appears at δC = −9.9 ppm as a doublet of doublets (1JCP = 83.6 Hz and 2JCP = 33.6 Hz). The silicon signal resonates at δSi = −16.1 ppm in the 29Si{1H} NMR spectrum. Similar NMR spectroscopic features are observed for all other complexes 2b−2f.14 Single crystals of 2a−2f suitable for X-ray diffraction analysis were obtained by slow vapor diffusion of pentane into highly concentrated solutions of the complexes in THF or diethyl ether. Important bond lengths and angles are listed in Table 1. Figure 1 exemplarily shows the molecular structures of complexes 2a and 2c, which crystallize in the monoclinic space group P21/n and the triclinic space group P1̅, respectively (for further details, see the Supporting Information). The palladium atom in 2a exhibits a slightly distorted square-planar geometry [sum of angles around Pd: 359.4(1)°] with angles between 80.1(1)° and 94.7(1)°. The Pd−C bond length of 2.158(2) Å is slightly longer than typical Pd−C single bonds reported for other palladium(II) alkyl complexes.15,16 This suggests a weaker Pd−C bond with presumably a higher degree of electrostatic interaction due to the strong electronwithdrawing nature of the thiophosphinoyl moiety. Compared to the halogenated precursor 1a (see the Supporting Information) the P−S bond elongates from 1.948(2) Å in 1a to 2.028(1) Å in 2a, while the P−C1 [1a: 1.803(3); 2a: 1.752(2) Å] and the C1−Si [1a: 1.899(3); 2a: 1.879(2) Å] bonds slightly shorten. This can be explained by the negative partial charge at the central carbon atom C1 in the palladium complex, which leads to electrostatic interactions within the P− C−Si linkage as well as to negative hyperconjugation effects into the antibonding orbital of the P−S bond. This holds true for all complexes 2a−2f. After successful preparation of the oxidative addition products 2 we addressed the synthesis of the corresponding carbene complexes by dehydrohalogenation. At first, this was tested by means of the triphenylsilyl-substituted derivative 2a employing a series of different metal bases. While no reaction was observed with sodium or potassium hydride, selective transformation to a single new product was achieved employing

respectively (Chart 1c). This strategy also gives way to unusual palladacycles with palladacyclobutane moieties.

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RESULTS AND DISCUSSION Synthesis and Characterization. Earlier studies by our group have shown that the use of lithium carbenoids for the synthesis of palladium carbene complexes of type D results in the formation of mixtures of D and the corresponding thioketone E (Chart 1b) via transfer of sulfur from the thiophosphinoyl moiety to the carbenoid carbon atom. DFT studies suggested that this sulfur transfer can be prevented by coordination of the thiophosphinoyl moiety to the metal prior to the formation of the PdC bond.12b Thus, we attempted the synthesis of the α-silyl-substituted carbene complexes via dehydrohalogenation of the palladium complexes 2a−2f analogous to synthesis of other nucleophilic carbene complexes with late transition metals.6,13 The halogenated precursors 1 were prepared according to a protocol previously established by our group including deprotonation of the diprotonated precursors and halogenation with hexachloroethane and iodine, respectively (see the Supporting Information for experimental as well as analytical details).12 Different silyl moieties were chosen to explore the influence of electronic and steric effects (Me vs Ph in 1a−1d) as well as the impact of additional donor functions (OMe and NMe2 in 1e and 1f) on the complex formation. Treatment of the chlorinated compounds with [Pd(PPh3)4] at elevated temperatures for 5 h gave way to the desired oxidative addition products. The complexes 2a, 2c, 2e, and 2f could thus be isolated as yellow solids in 55−91% yield as racemic mixtures (Scheme 1). Reactions of the iodo compounds expectedly Scheme 1. Synthesis of the Pd(II) Complexes 2a

a Conditions: (i) Toluene, [Pd(PPh3)4], reflux for X = Cl; T = RT for X = I.

proceeded more smoothly. Complexes 2b and 2d could be isolated in good yields (81% and 82%) after only 1 h reaction time at room temperature as orange and reddish solids, respectively.

Table 1. Selected Bond Lengths [Å] and Angles [deg] of the Molecular Structures of Complexes 2a−2f complex

Si−C1

P1−C1

P1−S

Pd−C1

Pd−S

Pd−X

P−C1−Si

S−Pd−X

C1−Pd−P2

∑Pd

2a 2b 2c 2d 2e 2f

1.879(2) 1.885(2) 1.878(4) 1.881(3) 1.867(3) 1.868(3)

1.752(2) 1.755(2) 1.750(4) 1.760(3) 1.749(3) 1.758(3)

2.028(1) 2.027(1) 2.027(2) 2.033(1) 2.036(1) 2.023(1)

2.158(2) 2.171(2) 2.123(3) 2.147(3) 2.142(3) 2.163(3)

2.343(1) 2.364(1) 2.328(1) 2.350(1) 2.324(1) 2.320(1)

2.342(1) 2.632(1) 2.329(1) 2.612(3) 2.344(1) 2.329(1)

126.3(1) 123.4(1) 119.8(2) 119.3(2) 120.4(2) 127.5(2)

166.2(1) 171.2(1) 168.3(1) 170.2(1) 170.9(1) 173.5(1)

173.3(1) 173.2(1) 178.1(1) 176.0(1) 172.1(1) 176.1(1)

359.4(1) 360.0(1) 359.9(1) 359.9(1) 359.1(1) 359.8(1)

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diastereotopic protons of the phosphorus- and silicon-bound phenyl groups and the characteristic doublet of doublets at δH = 1.46 ppm for the central hydrogen atom (2JPH = 8.6 Hz and 3 JPH = 5.8 Hz) in the 1H NMR spectrum. The central carbon atom and the metalated carbon atom of the phenylene group are also both involved in coupling with both phosphorus nuclei and appear as a doublet of doublets at δC = −5.7 and 154.0 ppm, respectively in the 13C{1H} NMR spectrum. The constitution of 3 was unequivocally confirmed by X-ray diffraction analysis (Figure 2). In the molecular structure the

Figure 2. Molecular structure of complex 3 in the solid state. Thermal ellipsoids are displayed at the 50% probability level. Hydrogen atoms (except for H1 at C1) have been omitted for clarity. Selected bond lengths [Å] and angles [deg]: P1−C1 1.750(2), P1−S 2.017(2), Pd− C1 2.157(2), Pd−S 2.439(1), Pd−C31 2.043(2), P−C1−Si 132.4(1), S−Pd−C31 166.9(1), C1−Pd−P2 176.2(1).

Figure 1. Molecular structures of complexes 2a (top) and 2c (bottom) in the solid state. Thermal ellipsoids are displayed at the 50% probability level. Hydrogen atoms (except for H1 at C1 and hydrogens at the SiMe3 group) have been omitted for clarity. Selected bond lengths and angles are given in Table 1.

ligand acts as a dianionic S,C,C pincer ligand. The central structural motif is formed by fused four- and five-membered rings with the palladium atom exhibiting a slightly distorted square-planar geometry [sum of angles around Pd: 359.9(1)°]. While most of the bond distances and angles in 3 are comparable to those found in the chloro and iodo precursors 2a and 2b, the Pd−S distance undergoes a considerable elongation upon cyclometalation [2.343(1) Å in 2a compared to 2.439(1) Å in 3]. This is due to the stronger trans effect of the aryl ligand in 3 compared to the halide ligand in 2a or 2b. While cyclometalation reactions are well documented for phosphorus-bound aryl groups,17 far fewer reports have appeared with silyl or silyl-substituted ligands.18 In the case of palladium there areto the best of our knowledgeonly two examples known, which additionally make use of a pyridyl substituent as a directing group for cyclometalation.19 Due to the facile formation of the bis-cyclometalated complex 3, we next addressed the influence of the substitution pattern at silicon on the cyclometalation process. Therefore, complexes 2c−2f were applied in an synthetic protocol analogous to that used for the formation of 3. Independent of the silyl group, dehydrohalogenation always resulted in the formation of bis-cyclometalated complexes. Despite the presence of further donor functions (2e and 2f) or the presence of only methyl groups at silicon (2c and 2d), no carbene complex formation was observed. In the case of the

alkali metal hexamethyldisilazanes (LiHMDS, NaHMDS, KHMDS). Refluxing a toluene solution of 2a with LiHMDS for 5 h resulted in the complete consumption of 2a and the formation of a complex characterized by two doublets at δP = 60.1 and 29.4 ppm (3JPP = 14.4 Hz) in the 31P{1H} NMR spectrum (Scheme 2). Workup to remove excess base and Scheme 2. Synthesis of the Cyclometalated Complex 3

byproducts formed gave the complex as a brown solid in 35% yield. Higher yields (77%) were achieved when starting from the iodo precursor 2b. NMR spectroscopic studies of the formed product, however, clearly showed that dehydrohalogenation of 2a and 2b does not result in the formation of the corresponding carbene species D (Chart 1), but the biscyclometalated complex 3. Palladcycle 3 is characterized by the 161


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analysis of complex 5 confirmed the metalation of the methyl group and the formation of the bis-cyclometalated complex (Figure 3). In the molecular structure the methanide ligand

anisol derivative 2f the formation of two isomers was observed due to the competing metalation of the phenyl (4a) or anisolyl substituents (4b). Because of the similar solubility behavior, the complexes could not be separated. Their formation, however, was evidenced by means of their NMR spectroscopic data. Chart 2. Palladium Complexes 4a and 4b

Cyclometalation was also observed using the trimethylsilyl (2c and 2d)- and anilino (2e)-functionalized systems. Treatment of a THF solution of the chlorido complexes with a slight excess of LiHMDS at 60 °C resulted in the selective metalation of one of the methyl groups and the formation of complexes 5 and 6 with an unusual silapalladacyclobutane moiety as central structural motif (Scheme 3). Both complexes could be isolated Figure 3. Molecular structure of complex 5 in the solid state. Thermal ellipsoids are displayed at the 50% probability level. Hydrogen atoms (except H1 at C1, hydrogens at C2, and the hydrogens of the SiMe2 group) have been omitted for clarity. Selected bond lengths [Å] and angles [deg]: P1−C1 1.734(3), P1−S 2.027(1), Pd−C1 2.179(3), Pd−S 2.497(1), Pd−C2 2.087(3), P−C1−Si 135.3(2), S−Pd−C2 160.5(1), C1−Pd−P2 170.7(1), Si−C2−Pd 90.4(1), P1−S−Pd−C1 21.9, C1−Pd−C2−Si 16.4.

Scheme 3. Synthesis of the Cyclometalated Complexes 5 and 6

adopts an “open-book” conformation with a large P−C−Si angle of 135.3(2)°, resulting from the small bite of the two fused four-membered rings. The most striking difference compared to the chloro precursor 2c concerns again the elongation of the Pd−S bond to 2.497(1) Å due to the stronger trans effect of the alkyl ligand. Overall, complex 5 is the first example of a structurally characterized 1,3-palladasilacyclobutane and the first bis-cyclometalated palladium complex with two fused palladacyclobutanes. So far, palladasilacyclobutanes have been discussed only in the context of palladium-catalyzed reactions of siliranes with alkynes, but have never been isolated.20,21 Mechanistically, the observed cyclometalation reactions can in principal proceed via two alternative pathways: (A) direct C−H activation of the phenyl or methyl group in the formed carbene complex with subsequent hydrogen shift to the carbene carbon atom or (B) deprotonative metalation of the phenyl or methyl group via an amido intermediate such as 5-Int (Scheme 3). Although pathway A has found to be active in several cyclometalation reactions involving methandiide-derived carbene complexes,17a−c this mechanism can be excluded in the case of the formation of 5. Recent studies by our group have shown that the T-shaped carbene complexes D (Chart 1) are stable. Even at elevated temperatures no cyclometalation but the formation of other products was observed.12b Thus, the cyclometalation has to proceed via mechanism B. Indeed, in the case of the bis-cyclometalated complex 5 formation of the amido intermediate 5-Int could be observed by NMR monitoring of the transformation of 2c to 5. As such, treatment of complex 2c with KHMDS for 3 h at 60 °C resulted in the formation of the bis-cyclometalated complex 5 accompanied by a further product characterized by two doublets at δP = 20.0

as yellow solids in 75% and 62% yield. Most characteristic for both complexes are the diastereotopic protons of the metalated methylene unit, which give rise to an AB system at δ = −0.45 ppm and −0.27 ppm for complex 5 (δ = 0.11 and 0.18 ppm for 6). The proton at the central carbon atom appears as a doublet of doublets at δH = −0.62 ppm (5) and −0.08 ppm (6), respectively. Both signals of the metalated carbon atoms C1 and C2 resonate at high field (5: δC = −26.5 and −12.2 ppm, 6: δC = −24.3 and −6.4 ppm) in the 13C NMR spectrum. It is interesting to note that cyclometalation of the aniline derivative 2e proceeds regio- and diastereoselectively. No metalation of the aryl or the second methyl group was observed. As such, all NMR spectra featured only one set of signals, suggesting that the stereogenic central carbon atom C1 determines which of the two methyl groups is metalated. The molecular structure of the starting chloro complex 2a suggests that only the (SC,RSi) and (RC,SSi) isomers should be formed due to steric repulsion between the anilino substituent and the phosphorus-bound phenyl groups (Figure S56 in the Supporting Information). While all crystallization attempts of 6 failed, single crystals of 5 were obtained by slow diffusion of pentane into a highly concentrated THF solution of 5 at −28 °C. X-ray diffraction 162


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Organometallics and 50.6 ppm in the 31P{1H} NMR spectrum. Longer reaction times resulted in the consumption of this intermediate and the complete conversion to 5. 1H NMR spectroscopy confirmed the formation of the amido complex 5-Int as an intermediate showing additional singlets for the methyl groups of the N(TMS)2 moiety together with a set of signals analogous to the starting complex 2c. The fact that the amido intermediate does not deliver the corresponding carbene complex suggests that deprotonation of the phenyl group is preferred over deprotonation of the methanide carbon. This might be the result of the higher acidity of the methyl and phenyl proton or due to the close proximity of the methyl/aryl group to the internal base (amido ligand).

Table 2. Suzuki−Miyaura Coupling of 4-Bromoanisole and Phenylboronic Acida

no.

catalyst

catalyst conc [mol %]

reaction time [h]

NMR yieldsb [%]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

[Pd(PPh3)4] 2a 2a 2a 2a 2a 2a 2a 2a 2a 5 5 5 5 5 5 3 3

0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.05 0.005 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

2 0.5 1 1.75 3 4 8 21 3 3 1 2 3 4 8 10 3 8

25 39 69 79 91 95 98 98 89 85 34 45 56 71 87 92 73 92

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CATALYTIC ACTIVITY Metalacycles have become the subject of intense research due to their applications in a variety of different fields of research.22 Catalytic applications have found increased attention, ever since the discovery that the enhanced activity of palladium catalysts with P(o-Tol)3 instead of the commonly applied PPh3 ligand relies on the formation of cyclometalated complexes.23 Palladacycles are particularly interesting, because of their remarkable catalytic activity in a number of different transformations, for example, in Suzuki, Heck, or other C−C and C−N cross-coupling reactions.24 Prominent examples are the Herrmann−Beller precatalyst F (Chart 3) or the Buchwald a

Reaction conditions: 4-bromoanisole (1 mmol), phenyl boronic acid (1.5 mmol), catalyst, K2CO3 (2 mmol), methanol, 80 °C. bNMR conversion with respect to 4-bromoanisole.

Chart 3. Palladacycles Active as (Pre-)catalysts in Coupling Reactions

Interestingly, the oxidative addition product 2a turned out to be the best (pre)catalyst, being superior compared to the biscyclometalated systems 3 and 5. With 2a as catalyst complete conversion was already obtained after 4 h reaction time and TONs of up to 17 000 could be obtained in only 3 h (entry 10). The lower activity of the bis-cyclometalated systems becomes evident from time−conversion profile of the coupling reactions with 2a and 5 as catalysts (Figure 4). While 2a

palladacycle G, which have been shown to possess higher activity and stability compared to other palladium catalysts with simple phosphine ligands.25 Although most of the reported palladacycles feature cyclometalated phosphine and amine ligands, also other donor functions have been used for the construction of cyclometalated complexes, which were also applied in a series of different coupling reactions (e.g., H).26 With the cyclometalated complexes 2 and the doublecyclometalated compounds 3 and 5 in hand, we turned our attention toward their catalytic ability. We particularly focused on the question of whether the second cyclometalation would lead to a further enhancement of the catalytic performance and thus provide a new concept for ligand design. As many cyclometalated species have been employed in Suzuki−Miyaura coupling reactions, we chose this reaction as the first test reaction. Thereby, the catalytic performance of the palladacycles was probed by the coupling of 4-bromoanisole and phenylboronic acid. Experiments were conducted under mild reaction conditions (refluxing methanol) in the presence of two equivalents of K2CO3, followed by evaporation of solvent under reduced pressure. As shown in Table 2, all complexes were found to be catalytically active, exhibiting higher activity compared to the standard Pd(0) catalyst [Pd(PPh3)4]. Yields over 90% were obtained after a 10 h reaction time with all palladacycles (entries 7, 16, and 18).

Figure 4. Time−conversion profile for the Suzuki−Miyaura crosscoupling of 4-bromoanisole with phenylboronic acid: percent conversion monitored by NMR spectroscopy with respect to 4bromoanisole. 163


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Organometallics

128.5 (d, 3JCP = 10.1 Hz; CHPdPPh,meta), 129.1 (CHSiPh,para), 129.1 (d, JCP = 12.5 Hz, CHPPh,meta), 130.3 (d, 2JCP = 12.0 Hz; CHPPh,ortho), 130.5 (d, 4JCP = 2.3 Hz; CHPdPPh,para), 131.1 (d, 1JCP = 41.1 Hz; CPdPPh,ipso), 131.9 (d, 2JCP = 11.0 Hz; CHPPh,ortho), 131.95 (d, 4JCP = 3.0 Hz; CHPPh,para), 132.03 (d, 4JCP = 3.0 Hz; CHPPh,para), 134.8 (d, 2JCP = 11.6 Hz; CHPdPPh,ortho), 136.5 (dd, 3JCP = 3.8 Hz, 4JCP = 2.0 Hz; CSiPh,ipso), 136.5 (d, 1JCP = 83.1 Hz; CPPh,ipso), 136.9 (d, 1JCP = 86.0 Hz; CPPh,ipso), 137.3 (CHSiPh,ortho). 29Si{1H} NMR (C6D6, 99.4 MHz): δ = −16.1 (dd, 2JSiP = 8.1 Hz, 3JSiP = 4.7 Hz). 31P{1H} NMR (C6D6, 162.0 MHz): δ = 22.5 (d, 3JPP = 17.5 Hz; PdPPh3), 46.3 (d, 3JPP = 17.4 Hz; PS). Anal. Calcd for C49H41ClP2PdSSi: C, 65.84; H, 4.62; S, 3.59. Found: C, 64.51; H, 4.41; S, 3.35. HRMS (ESI): calcd for C49H41P2PdSSi ([M − Cl]+•) m/z = 857.1203; found m/z = 857.1195. Synthesis of Complex 2b. This complex was synthesized according to the general procedure. Yield: 82%. 1H NMR (C6D6, 400.1 MHz): δ = 3.16 (dd, 2JHP = 8.7 Hz, 3JHP = 5.2 Hz, 1H; CH), 6.59−6.63 (m, 2H, CHPPh,meta), 6.75−6.79 (m, 1H, CHPPh,para), 6.96−7.11 (m, 23H; CHarom.), 7.50−7.54 (m, 6H, CHPdPPh,ortho), 8.05−8.08 (m, 6H, CHSiPh,ortho), 8.14−8.18 (m, 2H; CHPPh,ortho). 13C{1H} NMR (C6D6, 100.6 MHz): δ = −16.8 (dd, 1JCP = 85.6 Hz, 2JCP = 32.7 Hz; CH), 127.6 (CHSiPh,meta), 128.0 (d, 3JCP = 12.2 Hz; CHPPh,meta), 128.2 (d, 3JCP = 10.1 Hz; CHPdPPh,meta), 128.7 (d, 3JCP = 12.5 Hz, CHPPh,meta), 129.0 (CHSiPh,para), 129.5 (d, 2JCP = 12.1 Hz; CHPPh,ortho), 130.0 (d, 4JCP = 2.3 Hz; CHPdPPh,para), 131.0 (d, 4JCP = 3.0 Hz; CHPPh,para), 131.2 (d, 4JCP = 3.0 Hz; CHPPh,para), 132.4 (d, 2JCP = 11.0 Hz; CHPPh,ortho), 132.6 (d, 1 JCP = 42.3 Hz; CPdPPh,ipso), 135.3 (d, 2JCP = 11.4 Hz; CHPdPPh,ortho), 136.6 (dd, 3JCP = 3.7 Hz, 4JCP = 2.0 Hz; CSiPh,ipso), 137.5 (d, 1JCP = 85.0 Hz; CPPh,ipso), 137.8 (CHSiPh,ortho), 138.5 (dd, 1JCP = 54.7 Hz, 4JCP = 7.0 Hz; CPPh,ipso). 29Si{1H} NMR (C6D6, 99.4 MHz): δ = −17.1 (dd, 2JSiP = 8.2 Hz, 3JSiP = 4.3 Hz). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 23.6 (d, 3JPP = 16.6 Hz; PdPPh3), 43.6 (d, 3JPP = 16.6 Hz; PS). Anal. Calcd for C56H49IP2PdSSi: C, 62.43; H, 4.58; S, 2.98. Found: C, 62.42; H, 4.57; S, 2.68. HRMS (ESI): calcd for C49H41P2PdSSi ([M − I]+•) m/z = 857.120 28; found m/z = 857.120 25. Synthesis of Complex 2c. This complex was synthesized according to the general procedure. Yield: 91%. 1H NMR (C6D6, 500.1 MHz): δ = 0.44 (s, 9H; SiCH3), 1.66 (dd, 2JHP = 8.9 Hz, 3JHP = 4.5 Hz, 1H; CH), 6.89−7.07 (m, 15H, CHarom.), 7.31−7.36 (m, 2H, CHPPh,ortho), 7.81−7.86 (m, 6H; CHPdPPh,ortho). 8.09−8.14 (m, 2H; CHPPh,ortho). 13 C{1H} NMR (C6D6, 125.8 MHz): δ = −4.8 (dd, 1JCP = 89.5 Hz, 2JCP = 24.6 Hz; CH), 3.5 (dd, 3JCP = 3.7 Hz, 4JCP = 2.2 Hz; SiCH3), 128.51 (d, 3JCP = 11.9 Hz; CHPPh,meta), 128.54 (d, 3JCP = 9.9 Hz; CHPdPPh,meta), 128.9 (d, 3JCP = 12.3 Hz; CHPPh,meta), 130.1 (d, 2JCP = 12.5 Hz; CHPPh,ortho), 130.2 (d, 4JCP = 2.4 Hz; CHPdPPh,para), 131.5 (d, 4JCP = 3.0 Hz; CHPPh,para), 131.9 (d, 4JCP = 3.0 Hz; CHPPh,para), 132.0 (d, 2JCP = 11.2 Hz; CHPPh,ortho), 132.1 (d, 1JCP = 39.0 Hz; CPdPPh,ipso), 135.1 (d, 2 JCP = 11.6 Hz; CPdPPh,ortho), 136.7 (d, 1JCP = 79.8 Hz; CPPh,ipso), 137.7 (dd, 1JCP = 55.1 Hz, 4JCP = 8.0 Hz; CPPh,ipso). 29Si{1H} NMR (C6D6, 99.4 MHz): δ = −1.7 (dd, 2JSiP = 8.0 Hz, 3JSiP = 2.9 Hz). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 20.6 (d, 3JPP = 15.8 Hz; PdPPh3), 50.7 (d, 3JPP = 15.8 Hz; PS). Anal. Calcd for C34H35ClP2PdSSi: C, 57.71; H, 4.99; S, 4.53. Found: C, 58.08; H, 5.13; S, 4.30. HRMS (ESI): calcd for C34H35P2PdSSi ([M − Cl]+•) m/z = 671.0733; found m/z = 671.0727. Synthesis of Complex 2d. This complex was synthesized according to the general procedure. Yield: 81%. 1H NMR (C6D6, 500.1 MHz): δ = 0.43 (s, 9H; SiCH3), 2.17 (dd, 2JHP = 8.5 Hz, 3JHP = 4.9 Hz, 1H; CH), 6.90−7.05 (m, 15H, CHarom.), 7.32−7.36 (m, 2H, CHPPh,ortho), 7.76−7.81 (m, 6H; CHPdPPh,ortho). 8.11−8.15 (m, 2H; CHPPh,ortho). 13 C{1H} NMR (C6D6, 125.8 MHz): δ = −11.3 (dd, 1JCP = 88.0 Hz, 2 JCP = 27.1 Hz; CH), 4.2 (dd, 3JCP = 3.6 Hz, 4JCP = 2.2 Hz; SiCH3), 128.3 (d, 3JCP = 10.0 Hz; CHPdPPh,meta), 128.5 (d, 3JCP = 11.8 Hz; CHPPh,meta), 128.7 (d, 3JCP = 12.4 Hz; CHPPh,meta), 129.7 (d, 2JCP = 12.1 Hz; CHPPh,ortho), 130.1 (d, 4JCP = 2.2 Hz; CHPdPPh,para), 131.4 (d, 4JCP = 2.9 Hz; CHPPh,para), 131.8 (d, 4JCP = 3.0 Hz; CHPPh,para), 132.3 (d, 2JCP = 11.4 Hz; CHPPh,ortho), 132.8 (d, 1JCP = 40.2 Hz; CPdPPh,ipso), 135.3 (d, 2 JCP = 11.5 Hz; CPdPPh,ortho), 136.9 (d, 1JCP = 81.4 Hz; CPPh,ipso), 139.2 (dd, 1JCP = 53.5 Hz, 4JCP = 8.5 Hz; CPPh,ipso). 29Si{1H} NMR (C6D6, 99.4 MHz): δ = −2.1 (dd, 2JSiP = 8.0 Hz, 3JSiP = 2.4 Hz). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 23.0 (d, 3JPP = 14.8 Hz; PdPPh3), 48.3

reaches full conversion after a 4 h reaction time, only 73% of coupling products were obtained with 3 and only 56% with silapalladabutane 5 in the same period of time. This suggests that the second cyclometalation hampers the formation of the catalytically active species in the reaction process due to the strong binding of the pincer ligand.

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CONCLUSION In summary, we have reported the preparation of a series of mono- and bis-cyclometalated palladium complexes with a silylsubstituted thiophosphinoyl ligand. The complexes have been synthesized via oxidative addition of the halogenated ligand followed by dehydrohalogenation with a metal base. Thereby, dehydrohalogenation does not deliver the formation of a carbene speciesas has been observed for related systems but selectively results in the second cyclometalation. In the formed palladacycles the ligands exhibit S,C- and S,C,Ccoordination modes, respectively, with a square-planar-coordinated palladium. Depending on the silyl moiety, cyclometalation occurs at the silicon-bound aryl or at a simple methyl group. The latter results in the formation of unusual silapalladacyclobutane structures with an open-book geometry. Preliminary catalytic studies showed that both the mono- and bis-cyclometalated complexes can be applied as (pre)catalysts in Suzuki−Miyaura coupling reactions, with the monocyclometalated complex being more active than its bis-cyclometalated counterparts. Current studies are focusing on further catalytic applications of the synthesized palladacycles.

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EXPERIMENTAL SECTION

General Methods. All experiments were carried out under a dry, oxygen-free argon atmosphere using standard Schlenk techniques. Involved solvents were dried over sodium or potassium and distilled prior to use. H2O is distilled water. 1H, 13C{1H}, 29Si{1H}, and31P{1H} NMR spectra were recorded on Avance-500 or Avance-400 spectrometers at 22 °C if not stated otherwise. All values of the chemical shift are in ppm regarding the δ-scale. All spin−spin coupling constants (J) are reported in hertz (Hz). To display multiplicities and signal forms correctly, the following abbreviations were used: s = singlet, d = doublet, t = triplet, m = multiplet, br = broad signal. Signal assignment was supported by DEPT and HMQC experiments. Elemental analyses were performed on an Elementarvario MICROcube elemental analyzer. High-resolution mass spectra (ESI, APCI) were recorded on an Exactive Plus Orbitrap mass spectrometer from Thermo Scientific. For a better ionization in the cases of 2c, 2d, and 6 acetonitrile was added to the solutions of the complexes. All All reagents were purchased from Sigma-Aldrich, ABCR, Rockwood Lithium, or Acros Organics and used without further purification. Experimental details and analytical data for the halogenated precursors 1a−1f are given in the Supporting Information. General Procedure for the Oxidative Addition to the Complexes 2a−2f. The corresponding chlorinated precursor and 1 equiv of [Pd(PPh3)4] were dissolved in toluene and refluxed for 4 h (1 h at room temperature for the iodinated precursors). After cooling to room temperature the solvent was removed in vacuo and the residue was washed with diethyl ether (2 × 10 mL) and hexane (2 × 10 mL) to yield the palladium complexes as air-stable yellow to orange solids. Synthesis of Complex 2a. This complex was synthesized according to the general procedure. Yield: 52%. 1H NMR (CD2Cl2, 500.1 MHz): δ = 2.17 (dd, 2JHP = 8.8 Hz, 3JHP = 5.5 Hz, 1H; CH), 7.05−7.17 (m, 11H, CHarom.), 7.22−7.32 (m, 15H; CHarom.), 7.37−7.42 (m, 3H; CHarom.), 7.45−7.49 (m, 6H, CHPdPPh,ortho), 7.48−7.53 (m, 2H; CHPPh,meta), 7.58−7.62 (m, 1H; CHPPh,para), 7.65−7.68 (m, 6H, CHSiPh,ortho), 8.00−8.06 (m, 2H; CHPPh,ortho). 13C{1H} NMR (CD2Cl2, 125.8 MHz): δ = −9.9 (dd, 1JCP = 83.4 Hz, 2JCP = 33.8 Hz; CH), 127.5 (CHSiPh,meta), 128.4 (d, 3JCP = 12.3 Hz; CHPPh,meta), 164


Article

Organometallics

and refluxed for 5 h. After filtration followed by evaporation of the solvent the residue was washed with pentane (4 × 10 mL) and dried in vacuo to yield the product as a brown solid (65 mg, 75.8 μmol, 75%). 1 H NMR (CD2Cl2, 500.1 MHz): δ = 1.46 (dd, 2JHP = 8.6 Hz, 3JHP = 5.8 Hz, 1H; CH-1), 6.40−6.43 (m, 1H; CH-18), 6.68−6.71 (m, 1H; CH-16/CH-17), 6.75−6.77 (m, 1H; CH-15), 6.97−7.00 (m, 2H; CH8/CH-8′), 7.02−7.04 (m, 1H; CH-16/CH-17), 7.15−7.20 (m, 3H; CHarom.), 7.34−7.37 (m, 7H; CHarom.), 7.40−7.51 (m, 13H; CHarom.), 7.54−7.58 (m, 6H; CH-11), 7.65−7.67 (m, 2H, CH-7/CH-7′), 7.78− 7.83 (m, 2H; CH-3/CH-3′). 13C{1H} NMR (CD2Cl2, 125.8 MHz): δ = −5.7 (dd, 1JCP = 51.9 Hz, 2JCP = 48.6 Hz; C-1), 122.6 (C-16/C-17), 126.3 (d, 4JCP = 3.5 Hz; C-18), 127.2 (C-8/C-8′), 128.1 (C-8′/C-8), 128.5 (d, 3JCP = 12.3 Hz; C-4/C-4′), 128.6 (C-9/C-9′), 128.6 (d, 3JCP = 9.8 Hz; C-12), 128.9 (d, 3JCP = 11.7 Hz; C-4′/C-4), 129.3 (C-9′/C9), 130.0 (d, 2JCP = 10.8 Hz; C-3/C-3′), 130.4 (d, 4JCP = 2.1 Hz; C-13), 131.1 (d, 2JCP = 11.9 Hz; C-3′/C-3), 131.5 (d, 4JCP = 2.9 Hz; C-5/C5′), 131.7 (d, 4JCP = 2.9 Hz; C-5′/C-5), 132.6 (d, 1JCP = 38.2 Hz; C10), 133.7 (C-16/C-17), 135.1 (d, 2JCP = 12.5 Hz; C-11), 135.6 (C-7/ C-7′), 136.0 (dd, 1JCP = 66.6 Hz, 4JCP = 4.4 Hz; C-2/C-2′), 136.6 (C6/C-6′), 137.2 (C-7′/C-7), 137.7 (d, 2JCP = 12.0 Hz; C-15), 138.5 (dd, 1 JCP = 70.8 Hz, 4JCP = 1.5 Hz; C-2′/C-2), 140.1 (dd, 3JCP = 2.1 Hz, 4JCP = 0.9 Hz; C-6′/C-6), 154.0 (dd, 2JCP = 11.9 Hz, 3JCP = 1.1 Hz; C-14), 169.0 (dd, 3JCP = 6.5 Hz, 3JCP = 2.8 Hz; C-19). 29Si{1H} NMR (CD2Cl2, 99.4 MHz): δ = −21.8 (br d, 2JSiP = 7.4 Hz). 31P{1H} NMR (CD2Cl2, 202.5 MHz): δ = 29.4 (d, 3JPP = 14.4 Hz; PdPPh3), 60.1 (d, 3 JPP = 14.4 Hz; PS). Anal. Calcd for C49H40P2PdSSi: C, 68.64; H, 4.70; S, 3.74. Found: C, 68.44; H, 4.89; S, 3.28. HRMS (APCI): calcd for C49H41P2PdSSi ([M + H]+•) m/z = 857.1203; found m/z = 857.1201. Synthesis of Silapalladacycles 4a and 4b. Complex 2f (18.6 mg, 20.1 μmol) and LiHMDS (3.7 mg, 22.1 μmol) were dissolved in THF (1 mL) in a J. Young NMR tube and heated for 16 h at 60 °C. After removal of the solvent in vacuo the remaining residue was washed twice with pentane (2 × 10 mL) and subsequently with toluene (10 mL) to remove the formed salt. Drying in vacuo afforded the silapalladacycles 4a and 4b in an approximately 1:1 mixture as a yellow solid (quantitative yield). 1H NMR (C6D6, 500.1 MHz): δ = 1.59 (dd, 2 JHP = 8.5 Hz, 3JHP = 6.9 Hz, 1H; PCHSi isomer a), 2.00 (dd, 2JHP = 8.7 Hz, 3JHP = 5.0 Hz, 1H; PCHSi isomer b), 2.92 (s, 3H; OCH3 isomer a), 3.13 (s, 3H; OCH3 isomer b), 6.43 (br, 1H; CHAnisole isomer a), 6.61 (br, 1H; CHAnisole isomer b), 6.65−7.28 (m, CHarom.), 7.20 (br, 1H; CHAnisole isomer a), 7.32 (br, 1H; CHAnisole isomer b), 7.57−7.59 (m, CHarom.), 7.67−7.93 (m, CHarom.), 7.99−8.01 (m, CHarom.), 8.34−8.39 (m, 1H; CHAnisole isomer a). 13C{1H} NMR (C6D6, 125.8 MHz): δ = −1.1 (dd, 1JCP = 51.5 Hz, 2JCP = 48.5 Hz; PCSi isomer a), − 5.8 (dd, 1JCP = 51.9 Hz, 2JCP = 47.8 Hz; PCSi isomer b), 54.2 (OCH3 isomer a), 54.6 (OCH3 isomer b), 109.6 (CHAnisole isomer a), 110.6 (CHAnisole isomer b), 120.4 (CHAnisole isomer a), 120.7 (CHAnisole isomer b), 122.5 (CHAnisole isomer a), 123.1 (CHAnisole isomer b), 125.97 (Cq), 126.03 (Cq), 126.4 (CHarom.), 127.0 (CHarom. isomer b), 127.0 (CHarom.), 127.8 (CHarom. isomer a), 127.9 (d, J = 12.0 Hz; CHarom. isomer a), 128.1 (d, J = 12.0 Hz; CHarom. isomer b), 128.4 (CHarom.), 128.4 (d, J = 9.9 Hz; CHarom. isomer a), 128.4 (Cq), 128.5 (d, J = 9.6 Hz; CHarom. isomer b), 128.5 (d, J = 11.9 Hz; CHarom. isomer b), 128.6 (d, J = 11.6 Hz; CHarom. isomer a), 128.8 (CHarom.), 129.9 (CHarom.), 129.9 (CHarom.), 130.1 (CHarom.), 130.1 (CHarom.), 130.3 (CHarom.), 130.4 (CHarom.), 130.7 (CHarom.), 130.8 (CHarom.), 130.8 (CHarom.), 130.9 (CHarom.), 131.0 (CHarom.), 131.2 (CHarom.), 131.3 (CHarom.), 133.0 (d, J = 37.0 Hz; Cq isomer b), 133.2 (d, J = 37.5 Hz; Cq isomer a), 135.3 (d, J = 12.5 Hz; CHarom. isomer b), 135.3 (d, J = 12.8 Hz; CHarom. isomer a), 136.7 (dd, J = 66.1 Hz, 4.3 Hz; Cq isomer b), 137.3 (CHarom. isomer a), 137.8 (d, J = 11.9 Hz; CHarom. isomer a), 137.9 (d, J = 11.9 Hz; CHarom. isomer b), 138.0 (CHarom. isomer b), 138.2 (Cq), 138.5 (dd, J = 65.0 Hz, 5.4 Hz; Cq isomer a), 139.3 (dd, J = 69.5 Hz, 1.7 Hz; Cq isomer b), 139.4 (dd, J = 72.6 Hz, 1.4 Hz; Cq isomer a), 140.1 (CHarom. isomer b), 142.2 (br d, J = 1.8 Hz; Cq isomer b), 154.3 (dd, J = 11.7 Hz, 1.1 Hz; Cq isomer b), 155.4 (dd, J = 12.8 Hz, 0.9 Hz; Cq isomer a), 164.8 (Cq isomer a), 169.1 (dd, J = 6.4 Hz, 2.8 Hz; Cq isomer b), 169.5 (dd, J = 6.4 Hz, 2.8 Hz; Cq isomer a). 29Si{1H} NMR (C6D6, 99.4 MHz): δ = −22.1 (dd, 2JSiP =

(d, 3JPP = 14.8 Hz; PS). Anal. Calcd for C34H35IP2PdSSi: C, 51.11; H, 4.41 S, 4.01. Found: C, 51.53; H, 4.41; S, 3.02. HRMS (ESI): calcd for C34H35P2PdSSi ([M − I]+•) m/z = 671.0733; found m/z = 671.0720. Synthesis of Complex 2e. This complex was synthesized according to the general procedure. Yield: 62%. 1H NMR (C6D6, 500.1 MHz): δ = 0.67 (s, 3H; SiCH3), 1.33 (d, 4JHP = 0.8 Hz, 3H; SiCH3), 2.51 (dd, 2 JHP = 8.6 Hz, 3JHP = 3.5 Hz, 1H; CH), 2.57 (s, 6H; N(CH3)2), 6.71− 7.15 (m, 16H; CHarom.), 7.74−7.78 (m, 1H; CHarom.), 7.86−7.90 (m, 6H, CHPdPPh,ortho), 8.14−8.18 (m, 2H, CHPPh,ortho). 13C{1H} NMR (C6D6, 125.8 MHz): δ = −6.4 (dd, 1JCP = 84.8 Hz, 2JCP = 28.9 Hz; CH), 1.5 (SiCH3), 5.6 (d, 3JCP = 9.1 Hz; SiCH3), 47.1 (N(CH3)2), 121.6 (CHAniline), 124.7 (CHAniline), 128.1 (d, 3JCP = 11.9 Hz; CHPPh,meta), 128.5 (d, 3JCP = 9.8 Hz; CHPdPPh,meta), 128.9 (d, 3JCP = 12.2 Hz, CHPPh,meta), 129.7 (d, 2JCP = 12.0 Hz; CHPPh,ortho), 129.9 (CHAniline), 130.1 (d, 4JCP = 2.2 Hz; CHPdPPh,para), 131.3 (br; 2×CHPPh,para), 131.8 (d, 2JCP = 11.0 Hz; CHPPh,ortho), 132.2 (d, 1JCP = 38.6 Hz; CPdPPh,ipso), 135.2 (d, 2JCP = 11.6 Hz; CHPdPPh,ortho), 135.5 (CHAniline), 136.6 (dd, 1JCP = 54.9 Hz, 4JCP = 8.6 Hz; CPPh,ipso), 137.1 (d, 1JCP = 78.9 Hz; CPPh,ipso), 139.2 (d, 3JCP = 4.8 Hz; CSiPh,ipso), 161.1 (CN(CH3)2Aniline). 29Si{1H} NMR (C6D6, 99.4 MHz): δ = −10.0 (dd, 2 JSiP = 7.9 Hz, 3JSiP = 3.9 Hz). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 20.8 (d, 3JPP = 15.7 Hz; PdPPh3), 52.3 (d, 3JPP = 15.7 Hz; PS). Anal. Calcd for C41H42ClNP2PdSSi: C, 60.59; H, 5.21; N, 1.72; S, 3.95. Found: C, 59.98; H, 5.06; N, 1.38; S, 3.49. HRMS (ESI): calcd for C41H41NP2PdSSi ([M − Cl]+•) m/z = 776.1312; found m/z = 776.1308. Synthesis of Complex 2f. This complex was synthesized according to the general procedure. Yield: 83%. 1H NMR (CD2Cl2, 500.1 MHz): δ = 2.18 (dd, 2JHP = 8.3 Hz, 3JHP = 6.2 Hz, 1H; CH), 3.38 (s, 3H; OCH3), 6.39 (m, 1H; CHAnisole), 6.77 (dt, 3JHH = 7.3 Hz, 5JHH = 0.8 Hz, 1H; CHAnisole), 7.02−7.06 (m, 2H, CHPPh,meta), 7.14 (ddd, 3JHH = 8.2 Hz, 3JHH = 7.3 Hz, 4JHH = 1.7 Hz, 1H; CHAnisole), 7.17−7.32 (m, 21H; CHarom.), 7.33−7.35 (m, 1H; CHAnisole), 7.37−7.40 (m, 3H; CHarom.), 7.52−7.57 (m, 2H; CHPPh,meta), 7.61−7.65 (m, 1H, CHPPh,para), 7.75−7.77 (m, 2H, CHSiPh,ortho), 7.86−7.88 (m, 2H, CHSiPh,ortho), 8.02−8.06 (m, 2H; CHPPh,ortho). 13C{1H} NMR (CD2Cl2, 125.8 MHz): δ = −10.3 (dd, 1JCP = 85.9 Hz, 2JCP = 32.0 Hz; CH), 54.6 (OCH3), 110.3 (CHAnisole), 120.2 (CHAnisole), 125.3 (dd, 3JCP = 4.0 Hz, 4 JCP = 2.7 Hz; CSiPhAnisole), 127.1 (CHSiPh,meta), 127.3 (CHSiPh,meta), 127.8 (d, 3JCP = 12.1 Hz; CHPPh,meta), 128.4 (d, 3JCP = 10.0 Hz; CHPdPPh,meta), 128.8 (CHSiPh,para), 128.8 (CHSiPh,para), 129.1 (d, 3JCP = 12.3 Hz, CHPPh,meta), 129.7 (d, 2JCP = 12.0 Hz; CHPPh,ortho), 130.4 (d, 4 JCP = 2.3 Hz; CHPdPPh,para), 130.8 (d, 2JCP = 11.9 Hz; CHPPh,ortho), 131.27 (CHAnisole), 131.28 (d, 1JCP = 40.4 Hz; CPdPPh,ipso), 131.7 (d, 2 JCP = 10.7 Hz; CHPPh,ortho), 131.9 (d, 4JCP = 3.0 Hz; CHPPh,para), 132.0 (d, 4JCP = 3.0 Hz; CHPPh,para), 134.9 (d, 2JCP = 11.6 Hz; CHPdPPh,ortho), 136.3 (d, 1JCP = 82.2 Hz; CPPh,ipso), 136.3 (dd, 1JCP = 55.4 Hz, 4JCP = 6.6 Hz; CPPh,ipso), 136.8 (d, 3JCP = 6.5 Hz; CSiPh,ipso), 137.0 (CHAnisole), 137.3 (br d, 3JCP = 2.5 Hz; CSiPh,ipso), 137.4 (CHSiPh,ortho), 137.7 (CHSiPh,ortho), 164.2 (COCH3Aniline). 29Si{1H} NMR (CD2Cl2, 99.4 MHz): δ = −17.3 (dd, 2JSiP = 7.5 Hz, 3JSiP = 3.5 Hz). 31P{1H} NMR (CD2Cl2, 202.5 MHz): δ = 21.6 (d, 3JPP = 14.9 Hz; PdPPh3), 51.7 (d, 3 JPP = 14.8 Hz; PS). Anal. Calcd for C54H51ClO2P2PdSSi: C, 65.12; H, 5.16; S, 3.22. Found: C, 64.85; H, 5.36; S, 3.44. HRMS (ESI): calcd for C50H43OP2PdSSi ([M − Cl]+•) m/z = 887.1309; found m/z = 887.1296. Synthesis of Silapalladacycle 3. Complex 2a (101 mg, 103 μmol) and LiHMDS (85.7 mg, 513 μmol) were dissolved in toluene (11 mL)

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Organometallics 7.2 Hz, 3JSiP = 1.5 Hz, isomer a), − 20.3 (br d, 2JSiP = 7.3 Hz, isomer b). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 29.5 (d, 3JPP = 14.6 Hz; PdPPh3 isomer b), 30.1 (d, 3JPP = 14.5 Hz; PdPPh3 isomer a), 57.3 (d, 3 JPP = 14.4 Hz; PS isomer a), 60.1 (d, 3JPP = 14.6 Hz; PS isomer b). Synthesis of Silapalladacycle 5. Complex 2c (91.2 mg, 129 μmol) and LiHMDS (23.7 mg, 142 μmol) were dissolved in THF (12 mL)

Hz; C-11), 134.6 (C-7/C-8/C-9/C-10), 134.7 (d, 2JCP = 12.7 Hz; C12), 135.7 (d, 1JCP = 78.7 Hz; C-15/C-15′), 142.8 (dd, 1JCP = 63.3 Hz, 4 JCP = 5.4 Hz; C-15′/C-15), 143.2 (d, 3JCP = 3.6 Hz; C-6), 160.1 (C-5). 29 Si{1H} NMR (C6D6, 99.4 MHz): δ = −14.3 (dd, 2JSiP = 11.8 Hz, 3JSiP = 6.4 Hz). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 26.3 (d, 3JPP = 23.8 Hz; PdPPh3), 53.9 (d, 3JPP = 23.8 Hz; PS). HRMS (ESI): calcd for C41H42NP2PdSSi ([M + H + H3CCN]+•) m/z = 776.1312; found m/z = 776.1308. General Procedure for the Suzuki−Miyaura Coupling Reactions. A mixture of phenyl boronic acid (1.50 mmol), 4bromoanisole (1.00 mmol), catalyst (see Table 2 for catalyst concentrations), K2CO3 (2.00 mmol), and methanol (3 mL) was heated to 80 °C (see Table 2 for the corresponding reaction time) and cooled to room temperature. The solvent was removed at room temperature under reduced pressure (20 mbar), and the conversion was determined via 1H NMR spectroscopy with respect to 4bromoanisole. X-ray Crystallographic Studies. Single crystals were selected from a Schlenk flask or a vial under an argon atmosphere and covered with an inert oil (perfluoropolyalkyl ether, ABCR Chemicals). Data were collected on a Bruker APEX-CCD (D8 three-circle goniometer) (Bruker AXS). Integration was conducted with SAINT, and an empirical absorption correction (SADABS) was applied. The structures were solved by direct methods and refined by full-matrix least-squares methods against F2 (SHELXL-08).27 All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were placed in calculated positions and refined using the riding model. Details about the structure refinements are given in Table S1−S26 (Supporting Information). Crystallographic data (including structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-1432200−1432212. Copies of the data can be obtained free of charge on application to the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK [fax: (+44) 1223336-033; e-mail: [email protected]].

and stirred for 16 h at 59 °C. After removal of the solvent in vacuo the remaining residue was washed twice with pentane (2 × 10 mL) and subsequently with toluene (10 mL) to remove the formed salt. Drying in vacuo afforded the silapalladacycle 5 as a yellow solid (64.9 mg, 96.7 μmol, 75%). 1H NMR (C6D6, 500.1 MHz): δ = −0.62 (dd, 2JHP = 10.1 Hz, 3JHP = 8.7 Hz, 1H; CH-1), − 0.45 (dd, 2JHH = 11.0 Hz, 4JHP = 2.1 Hz 1H; CH2), − 0.27 (ddd, 3JHP = 14.4 Hz, 2JHH = 11.0 Hz, 4JHP = 3.3 Hz 1H; CH2), −0.20 (s, 3H; SiCH3), 0.30 (s, 3H; SiCH3), 7.02−7.11 (m, 15H, CHarom.), 7.76−7.80 (m, 6H, CH-6), 7.86−7.91 (m, 2H; CH-10/CH-10′). 8.13−8.17 (m, 2H; CH-10′/CH-10). 13C{1H} NMR (C6D6, 125.8 MHz): δ = −26.5 (dd, 1JCP = 60.8 Hz, 2JCP = 37.5 Hz; C1), −12.2 (d, 3JCP = 4.2 Hz; C-2), − 0.5 (C-3/C-4), 11.3 (d, 3JCP = 5.1 Hz; C-3/C-4), 128.0 (d, 3JCP = 12.3 Hz; C-11/C-11′), 128.5 (d, 3JCP = 11.8 Hz; C-11′/C-11), 128.6 (d, 3JCP = 9.6 Hz; C-7), 128.8 (d, 2JCP = 11.5 Hz; C-10/C-10′), 129.1 (d, 4JCP = 2.0 Hz; C-8), 131.0 (pt, C-12 and C-12′), 132.9 (d, 2JCP = 11.7 Hz; C-10′/C-10), 134.0 (d, 1JCP = 36.7 Hz; C-5), 134.7 (d, 2JCP = 12.6 Hz; C-6), 136.1 (d, 1JCP = 80.0 Hz; C-9/C-9′), 142.5 (dd, 1JCP = 63.5 Hz, 4JCP = 5.6 Hz; C-9′/C-9). 29 Si{1H} NMR (C6D6, 99.4 MHz): δ = −4.6 (dd, 2JSiP = 11.9 Hz, 3JSiP = 6.1 Hz). 31P{1H} NMR (C6D6, 202.5 MHz): δ = 26.0 (d, 3JPP = 23.9 Hz; PdPPh3), 52.0 (d, 3JPP = 23.9 Hz; PS). HRMS (ESI): calcd for C34H35P2PdSSi ([M + H]+•) m/z = 671.0733; found m/z = 671.0725. Synthesis of Silapalladacycle 6. Complex 2e (90.0 mg, 111 μmol) and LiHMDS (23.5 mg, 140 μmol) were dissolved in THF (13 mL)

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00903. Experimental procedures and NMR spectra of all isolated compounds (PDF) Crystallographic details (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

and stirred for 16 h at 57 °C. After removal of the solvent in vacuo the remaining residue was washed twice with pentane (2 × 10 mL) and subsequently with toluene (10 mL) to remove the formed salt. Drying in vacuo afforded the silapalladacycle 6 as a yellow solid (53.5 mg, 68.7 μmol, 62%). 1H NMR (C6D6, 500.1 MHz): δ = −0.08 (dd, 2JHP = 10.1 Hz, 3JHP = 7.9 Hz, 1H; CH-1), 0.11 (br d, 1H; CH2), 0.16−0.22 (m, 1H; CH2), 0.26 (s, 3H; SiCH3), 2.49 (s, 6H; N(CH3)2), 6.99−7.06 (m, 10H, CHarom.), 7.08−7.12 (m, 6H, CH-13), 7.19−7.22 (m, 1H; CH-7/CH-8/CH-9/CH-10), 7.24−7.27 (m, 1H; CH-7/CH-8/CH-9/ CH-10), 7.78−7.82 (m, 6H; CH-12.), 7.95−8.00 (m, 3H; CH-16/CH16′ and CH-7/CH-8/CH-9/CH-10), 8.23−8.28 (m, 2H; CH-16′/CH16). 13C{1H} NMR (C6D6, 125.8 MHz): δ = −24.3 (dd, 1JCP = 59.7 Hz, 2JCP = 38.3 Hz; C-1), −6.4 (d, 3JCP = 5.6 Hz; C-2), −0.5 (C-3), 46.8 (C-4), 120.3 (C-7/C-8/C-9/C-10), 124.3 (C-7/C-8/C-9/C-10), 128.1 (d, 3JCP = 12.3 Hz; C-17/C-17′), 128.5 (d, 3JCP = 11.6 Hz; C17′/C-17), 128.6 (d, 3JCP = 9.6 Hz; C-13),129.1 (d, 2JCP = 11.4 Hz; C16/C-16′), 129.9 (C-7/C-8/C-9/C-10), 129.9 (d, 4JCP = 2.0 Hz; C-14), 130.9 (d, 4JCP = 2.8 Hz; C-18/C-18′), 131.1 (d, 4JCP = 3.0 Hz; C-18′/ C-18), 133.1 (d, 2JCP = 11.7 Hz; C-16′/C-16), 134.1 (d, 1JCP = 36.5

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the DFG (Emmy Noether Grant to V.H.G.) and the Fond der Chemischen Industrie. We also thank Rockwood Lithium for the supply of chemicals and Christoph Mahler for conducting the HRMS studies.

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REFERENCES

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Mono- and Bis-Cyclometalated Palladium Complexes: Synthesis

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