TOMPP-Catalyzed Telomerization of 1, 3

Article pubs.acs.org/Organometallics

Mechanistic Study of the Pd/TOMPP-Catalyzed Telomerization of 1,3Butadiene: Influence of Aromatic Solvents on Bis-Phosphine Complex Formation and Regioselectivity Peter J. C. Hausoul,†,‡ Martin Lutz,*,§ Johann T. B. H. Jastrzebski,† Pieter C. A. Bruijnincx,‡ Bert M. Weckhuysen,‡ and Robertus J. M. Klein Gebbink*,† †

Organic Chemistry & Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands ‡ Inorganic Chemistry & Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands § Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands S Supporting Information *

ABSTRACT: A study of the influence of reaction conditions on the Pd/TOMPP-catalyzed (TOMPP = tris(2methoxyphenyl)phosphine) telomerization of 1,3-butadiene with phenols revealed that the composition of the reaction medium strongly influences the regioselectivity of the telomer products. Mechanistic studies show this effect to be related to the stability of the key catalytic intermediate cis-[Pd((1−3η)-octa-2,7-dien-1-yl)(TOMPP)2]+ (E), which mainly depends on the solvent composition. The crotyl analogue cis-[Pd((1−3η)-but-2-en-1-yl)(TOMPP)2]BF4 (4) was synthesized as a model for E and was fully characterized, including by an X-ray crystal structure determination. Comparison of the crystal structures of 4 and [Pd((1−3,7,8η)-octa-2(E),7-dien-1-yl)(TOMPP)]BF4 (1), an analogue of intermediate C, shows that the difference in regioselectivity for nucleophilic attack of these complexes is not reflected in the structure of the allyl moiety. Furthermore, Pd/ TOMPP-catalyzed n/iso equilibration reactions of telomers show that all product formation routes in the Pd-catalyzed telomerization mechanism are reversible. Telomer product equilibration studies resulted in complete conversion to 1,3,7octatriene, with the selectivity changing over time in favor of formation of the Z isomer of octatriene.

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compounds (NuH), the σ-allylic fragment of B acts as a base and is protonated at the 6-position of the octadienyl chain, resulting in the ionic complex [Pd((1−3,7,8η)-octa-2(E),7dien-1-yl)(PR3)]Nu (C). The 1- and 3-positions of the π-allylic fragment of C are susceptible to nucleophilic attack and after addition of Nu− result in product complexes [Pd((2,3,7,8η)-1Nu-octa-2(E),7-diene)(PR3)] (Dn) and [Pd((1,2,7,8η)-3-Nuocta-1,7-diene)(PR3)] (Diso, not shown), respectively. Intermediate C shows a clear preference for attack at the 1-position, and as a result, telomers with high n/iso ratios are typically observed. After displacement of the ligated telomer by butadiene, A is regenerated and the cycle completed. Depending on the ligand to metal ratio (P/Pd) used in the reaction, the η2 olefin ligand of C can be substituted by PR3, resulting in the formation of the bis-phosphine complex cis[Pd((1−3η)-octa-2(E),7-dien-1-yl)(PR3)2]Nu (E). Like C, E is susceptible to nucleophilic attack of Nu−. Owing to its different electronic and steric properties, the regioselectivity of E differs considerably from that of C. Indeed, stoichiometric reactions have shown that the nucleophilic addition of Nu− to E results in much lower n/iso ratios.5

INTRODUCTION The Pd-catalyzed telomerization of 1,3-butadiene, originally developed by Smutny,1 is currently an integral part of the 1octene process (i.e., via methoxyoctadiene) commercialized by the Dow Chemical Co.2 The reaction readily converts a wide variety of protic compounds such as water, alcohols, amines, and acids to the corresponding octadienyl derivatives and as such provides an attractive route for the production of surfactants and polymer components. In this regard, the Pdcatalyzed telomerization reaction is also increasingly being explored as a potential route for the valorization of biomassbased substrates.3 The mechanism of this reaction has been studied extensively, and most of the relevant catalytic intermediates have been identified and characterized.4−6 The studies of Jolly et al.4 and Beller et al.5 have particularly contributed to the current understanding of the reaction mechanism (Scheme 1). As depicted, the reaction yields n and iso telomers in a 100% atom-efficient manner. The mechanism starts with a postulated zerovalent monophosphine, bis-butadiene species [Pd((1,2η)-scis-buta-1,3-diene)((1,2η)-s-trans-buta-1,3-diene)(PR3)] (A), which is formed in situ. Oxidative coupling of the butadiene ligands yields the bis-allylic species [Pd((1,6−8η)-octa-2(Z),6(E)-dien-1,8-diyl)(PR3)] (B).7 In the presence of protic © XXXX American Chemical Society

Received: March 21, 2013

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dx.doi.org/10.1021/om400246a | Organometallics XXXX, XXX, XXX−XXX

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Scheme 1. Overall Reaction and General Mechanism of the Pd/PR3-Catalyzed Telomerization of 1,3-Butadiene with Nucleophiles (NuH)

C or Pd(acac)2). ESI-MS studies on the Pd/TOMPP-catalyzed telomerization of 1,3-butadiene with methanol by Patton et al. also showed that G is already clearly present during the initial, productive stage of the reaction.8 This confirms that, under reversible conditions, G indeed acts as a ligand reservoir and that a high concentration of G does not necessarily result in deactivation. Deactivation in this case was found to be caused by irreversible side reactions of G. Similar observations have also been reported for TPPTS-derived phosphonium salts.12 Recently, we have studied the activity of lignin-type phenols in the Pd/TOMPP-catalyzed telomerization of 1,3-butadiene and the subsequent conversion of the telomer products via a thermal Claisen rearrangement (Scheme 3).13 Very low n/iso ratios (3−5) were observed for phenol telomerization, and it was shown that the n/iso ratio decreases from 9 to 4 during the catalytic run. For guaiacol it was found that variation of the P/ Pd ratio has little effect on the n/iso ratio (22−26), whereas variation of the butadiene to substrate ratio (Bu/S) has a strong influence on the n/iso ratio (7−39). These observations are difficult to rationalize using the generally accepted mechanism. This prompted mechanistic studies to gain more insight into the species and equilibria involved in these processes as well as the factors that control the regioselectivity of the Pd/TOMPP catalyst. Here we present the results of stoichiometric coordination reactions of [Pd((1−3,7,8η)-octa-2(E),7-dien-1-yl)(TOMPP)]BF4 (1),11 an analogue of C, with TOMPP in solvents such as MeOH and toluene/MeOH (4/1), the preparation and characterization of the model compound cis-[Pd((1−3η)-but2(E)-en-1-yl)(TOMPP)2]BF4 (4), a comparison of the crystal structures of 1 and 4, and the results of Pd/TOMPP-catalyzed telomer equilibration reactions.

The formation of byproducts, such as 1,3,7-octatriene, is also commonly observed and is considered to proceed via a formal proton abstraction from complex C.4,6 Since the n telomer is generally the desired product, considerable effort has been devoted to the development of ligands that result in high regioand chemoselectivities. Recent examples show that particularly catalysts based on ligands that bear o-methoxy substituents (or related groups such as xanthene moieties) display very high activities and good selectivities toward the n-telomer product.8 It has also been shown that N-heterocyclic carbene ligands provide very active and chemoselective catalysts for the Pdcatalyzed telomerization reaction.9 Previously, we have reported on the activity of the Pd/ TOMPP catalyst in the telomerization of 1,3-butadiene with biomass-based substrates such as diols, sugar alcohols, and carbohydrates.10 In the case of carbohydrates, it was established that the presence of a hemiacetal group in the substrate led to premature catalyst deactivation. Mechanistic studies showed that deactivation correlated with the fate of the (excess) phosphine present in the reaction mixture. The phosphine was found to be converted via C to ligand-derived octadienylphosphonium species (G), eventually depleting the amount of available ligand (Scheme 2).11 Stoichiometric coordination reactions also showed that this reaction is fully reversible in the presence of Pd(0) and a catalytic amount of ligand. On this basis, the observed deactivation was attributed to the incompatibility between G and cationic Pd(II) species (e.g., Scheme 2. Formation of (Octa-2,7-dien-1-yl)phosphonium (G) from [Pd(1-3,7,8η-octa-2,7-dien-1-yl)(PR3)]Nu (C) and PR3

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RESULTS AND DISCUSSION Solvent-Dependent Reaction of [Pd((1−3,7,8η)-octa2(E),7-dien-1-yl)(TOMPP)]BF4 (1) with TOMPP. The B


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Scheme 3. Pd/TOMPP-Catalyzed Telomerization of 1,3-Butadiene with Lignin-Type Phenols and Thermal Claisen Rearrangement

catalytic results reported for the Pd/TOMPP-catalyzed telomerization of 1,3-butadiene with guaiacol showed that the solvent composition of the reaction medium has a distinct influence on the course of catalysis,13 emphasized in particular by the low n/iso ratios at high substrate concentrations and the high n/iso ratios at low substrate concentrations. Drawing from the observations of Beller et al., these results point to the participation of cis-bisphosphine complex E in the reaction to different extents.5 Given the large cone angle of TOMPP, (exo2: θ = 176°), it was anticipated that cis-bisphosphine complexes of TOMPP would be rather crowded and unstable. To determine the stability and properties of complex E (Nu− = BF4−), the reaction of [Pd((1−3,7,8η)-octa-2(E/Z),7-dien-1-yl)(TOMPP)]BF4 (1)11 with 1 equiv of TOMPP was studied by variable-temperature 31P NMR. In solvents such as CDCl3, CD2Cl2, and d6-acetone, the reaction rapidly produces phosphonium species 3 and several unidentified Pd complexes (Scheme 4). When the reaction was instead performed in Scheme 4. Solvent-Dependent Reaction of [Pd(1-3,7,8-ηocta-2(E/Z),7-dien-1-yl)(TOMPP)]BF4 (1) with TOMPPa

Figure 1. 31P NMR spectra of the stoichiometric reaction of [Pd((1− 3,7,8η)-octa-2(E/Z),7-dien-1-yl)(TOMPP)]BF4 (1) with 1 equiv of TOMPP in d4-methanol and d8-toluene/d4-methanol (4/1 v/v). Conditions: 5 min at room temperature, subsequently −50 °C.

a

small peak at 25.0 ppm, which correspond to slightly shifted signals of 3 (E isomer, 25.0 ppm; Z isomer, 25.5 ppm).11a In addition, two small doublets with equal intensity and coupling constants were observed at 10.7 and 6.0 ppm, which confirms the presence of the bis-phosphine complex cis-[Pd((1−3η)octa-2(E/Z),7-dien-1-yl)(TOMPP)2]BF4 (2). In d8-toluene/d4methanol (4/1 v/v), the peak of 3 was much less intense and the doublets attributed to 2 were much more intense. The high proportion of toluene in the mixture thus causes a shift of the equilibria toward 2. Due to this solvent dependency, attempts to isolate complex 2 by precipitation or slow vapor diffusion using various nonsolvents resulted in mixtures of 1 and 3 but not 2. These results demonstrate that, even with a large cone angle ligand such as TOMPP, complex E can be formed during catalysis and that the equilibria among C, G, and E are sensitive to the proportion of aromatic solvent in the reaction medium (Scheme 4). This is well in line with the observations discussed above that low n/iso ratios are obtained in catalysis at high

R = 2-MeOPh.

solvents that mimic the catalytic conditions of (neat) telomerization reactions such as d4-methanol and d8-toluene/ d4-methanol (4/1 v/v), only three distinct new 31P signals were observed in addition to the peaks of 1 (10−11 ppm) and TOMPP (−38.2 ppm) (Figure 1). The reaction run in d4methanol (i.e., 5 min at room temperature, subsequently cooled to −50 °C) displayed an intense sharp peak at 24.7 ppm and a C


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concentrations of aromatic substrate and that variation of the P/Pd ratio has little effect on the n/iso ratio.13 Moreover, these results show that at low aromatic solvent concentrations the equilibrium is shifted toward C and G and leads to high n/iso ratios due to the high regioselectivity of C. Variation of the P/ Pd ratio, therefore, has little effect on the n/iso ratio, as any excess phosphine is converted to G. Conversely, at high concentrations of aromatic solvent, the equilibrium is shifted toward E, which exhibits lower regioselectivity and as a result lower n/iso ratios are obtained. Preparation and Characterization of cis-[Pd((1−3η)but-2-en-1-yl)(TOMPP)2]BF4 (4). As the isolation of 2 was unsuccessful due to equilibration with species 1 and 3, the butenyl analogue cis-[Pd((1−3η)-but-2-en-1-yl)(TOMPP)2]BF4 (4) was synthesized as a model for complex 2. Previously we demonstrated that microreversibility can be employed for the preparation of complex 1 from 2,7-octadienol in the presence of 1 equiv of [HPR3]BF4.11 For the preparation of 4 a similar synthetic approach was used (Scheme 5). Stoichiometric

Figure 2. Molecular structure of cis-[Pd((1−3η)-but-2(E)-en-1yl)(TOMPP)2]BF4 (4) in the crystal. Hydrogen atoms, the BF4− anion, and severely disordered solvent molecules are omitted for clarity. Ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å): Pd1−C1 = 2.167(2), Pd1−C2 = 2.183(3), Pd1−C3 = 2.244(3), Pd1−P1 = 2.3662(6), Pd1−P2 = 2.3525(6), C1−C2 = 1.359(4), C2−C3 = 1.395(4), C3−C4 = 1.459(4). Selected angles (deg): P1−Pd1−P2 = 110.63(2), P1−Pd1−C3 = 92.59(7), P2−Pd1− C1 = 90.45(8), C1−C2−C3 = 122.6(3).

Scheme 5. One-Pot Synthesis of cis-[Pd((1−3η)-but-2(E)en-1-yl)(TOMPP)2]BF4 (4) from Pd(dba)2, PR3, [HPR3]BF4, and Crotyl Alcohola

a

provide useful information, due to severe line broadening. Full assignment of these isomers is complicated due to multiple overlapping signals in the 1H NMR spectrum, but additional 1 H−1H COSY and 1H−31P heteronuclear correlation measurements provided sufficient information to allow a tentative assignment (see the Supporting Information). At −80 °C the methyl signals of the butenyl ligands of isomers 4a−d are all observed separately, and on the basis of shift positions and coupling constants it is proposed that isomers 4a,c,d are syn isomers and that isomer 4b is an anti isomer. 1H−31P heteronuclear correlation data show that the coupling of protons on C1 and C3 to P1 or P2 of isomer 4b is opposite to that of 4a,c, providing evidence for different orientations of the butenyl ligand. Coalescence of these signals at 20 °C therefore supports the proposition that the dynamic processes of 4 include syn/anti isomerization and apparent allyl rotation. These processes are known to occur via an η3−η1−η3 rearrangement of the allyl16,17 and rearrangements of the ligands via ligand exchange and conformational changes. For 4 it is possible that hemilabile coordination of the o-methoxy groups occurs during the dissociative η3−η1−η3 rearrangement of the allyl ligand. Scheme 6 shows four different η1 isomers, in which one TOMPP ligand displays a κO,P chelate and whereby the phosphines are positioned either cis or trans. Possible evidence for the η1/cis κO,P complexes is provided in the 31P NMR spectrum at −80 °C, which shows two minor isomers with a very large upfield shift (at −7 and −14 ppm) in comparison to the signals found for η3 isomers 4a−d (found between 2 and 10 ppm). On the basis of these data it proposed that the numerous isomers of 4 found at low temperatures are the result of apparent allyl rotation and syn/anti isomerization. 31 P NMR spectra of the reaction of 4 with excess TOMPP in CDCl3 showed that (but-2(E)-en-1-yl)(tris(2methoxyphenyl))phosphonium tetrafluoroborate (5) is only formed in minute amounts and that the equilibrium is on the side of the starting materials in this case (Scheme 7). This lack of phosphonium formation is in sharp contrast to the case for complex 1, which under the same conditions reacts to give the phosphonium species 3. It can therefore be inferred that the

R = 2-MeOPh.

amounts of Pd(dba)2, TOMPP, and [HPR3]BF4 (R = 2MeOPh) were reacted at 60 °C for 2 h in the presence of an excess amount of crotyl alcohol (16 equiv). Subsequent isolation by precipitation yielded 66% of 4 as a slightly yellow powder. Single crystals of 4 were obtained via slow vapor diffusion of Et2O into a MeOH solution of 4, and its structure was determined by X-ray crystallography (Figure 2). The result shows a Pd complex with a distorted-square-planar geometry around Pd1 defined by C1, C3, P1, and P2. The phosphine ligands are arranged in a cis fashion, and both ligands exhibit an exo 2 configuration. 14 The wide P1−Pd1−P2 angle of 110.63(2)° shows that the large steric bulk of the ligands exerts considerable strain on the geometry of the complex. The ortho protons of the two endo-oriented 2-methoxyphenyl rings are positioned in close proximity to the metal (Pd−H = 2.88 (P1), 3.07 Å (P2)), indicative of anagostic interactions with the metal center (Figure 3).15 It is also noteworthy that, unlike most π-allyl complexes, the butenyl ligand of 4 could be refined as a single isomer without a disorder model. The 1H and 31P NMR spectra of complex 4 are severely broadened at room temperature, indicating that the complex shows dynamic behavior in solution. The variable-temperature 1H and 31P NMR spectra (−80 °C to room temperature) showed that 4 is in dynamic exchange between numerous isomers, four of which (4a−d) are considerably more abundant. Of these, 4a is the major species (relative abundances: 7.4 (4a), 1.6 (4b), 1.4 (4c), 1.0 (4d), based on 1H and 31P NMR at −80 °C). Lowtemperature 13C NMR spectra were also recorded but did not D


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Figure 3. Illustration of the anagostic hydrogen-bonding interactions in the molecular structure of cis-[Pd((1−3η)-but-2(E)-en-1-yl)(TOMPP)2]BF4 (4).

Scheme 6. Possible κO,P Chelate Isomers of 4 Formed during η3−η1−η3 Rearrangement of the Butenyl Ligand

geometry of the Pd−allyl moiety in these complexes and possibly a correlation to changes in their reactivity. Electronic and steric differences are assessed by comparing the bond lengths and angles of the coordination environments of 1 and 4 (Figure 4). Examination of the allyl moieties shows that the C1−C2 (1.399(6) Å) and C2−C3 bond lengths (1.397(6) Å) are almost equal in 1, whereas in 4 the C1−C2 bond length (1.359(4) Å) is 0.036(7) Å shorter than that of C2−C3 (1.395(4) Å). In fact, the C1−C2 bond length of 4 is comparable to the C7−C8 bond length (1.364(5) Å) of the η2 olefin in 1. Interestingly, the lengths of metal−allyl bonds Pd1− C1, Pd1−C2, and Pd1−C3 are comparable in both complexes, whereas the metal−phosphine bonds Pd1−P1 (2.3662(6) Å) and Pd1−P2 (2.3525(6) of 4 are considerably longer than that of 1 (2.3390(8) Å). The angle between P1 and the midpoint of the η2 olefin (P1−Pd1−midpoint(C7−C8)) of 107.19(7)° in 1 is only slightly less than the P1−Pd1−P2 angle (110.63(2)°) in 4. In addition, the difference in C1−C2−C3−C4 torsion angles of 1 (168.1(4)°) and 4 (178.1(4)°) and the relatively long P1− C7 bond (2.300(3) Å) in comparison to Pd1−C8 (2.236(3) Å) provide evidence for the existence of ring strain in 1.

Scheme 7. Formation of (But-2(E/Z)-en-1-yl)(tris(2methoxyphenyl))phosphonium (5) from cis-[Pd((1−3η)but-2(E/Z)-en-1-yl)(TOMPP)2]BF4 (4) and 5 equiv of TOMPPa

a

Conditions: (i) CDCl3, 1 h, room temperature. R = 2-MeOPh.

electrophilicity of 4 is significantly decreased by the strong electron donation of the second TOMPP ligand. Importantly, in light of the solvent-dependent reaction of 1 with TOMPP (Scheme 4), these results confirm that 3 is primarily formed from 1. Structural Comparison of [Pd((1−3,7,8η)-octa-2(E),7dien-1-yl)(TOMPP)]BF4 (1) and cis-[Pd((1−3η)-but-2(E)en-1-yl)(TOMPP)2]BF4 (4). The availability of two high-quality crystal structures of both 111 and 4 now allows a detailed comparison of the influence of ligand substitution on the E


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Figure 4. ORTEP diagrams displaying bond lengths (Å) of the coordination spheres of [Pd((1−3,7,8η)-octa-2(E),7-dien-1-yl)(TOMPP)]BF4 (1)11 (left) and cis-[Pd((1−3η)-but-2(E)-en-1-yl)(TOMPP)2]BF4 (4) (right). Ellipsoids are drawn at the 50% probability level.

is not observed, and the metal−allyl bond lengths of 1 rather indicate an allyl bonding which is comparable to that in 4. In addition, contrary to expectation, the significantly shorter Pd1− P bond of 1 shows that the ligand substitution has a pronounced effect on the ligand cis to the substitution site. These results therefore raise the question if the C1−C2 and C2−C3 bond lengths can be used to access changes in allyl bonding, let alone changes in reactivity. Numerous studies on allylic substitution reactions have shown that the regiochemical outcome of nucleophilic attack can depend on a variety of factors, including the steric and electronic properties of the allyl, donor/acceptor properties of the trans ligands,19 bite angle of chelate ligands,20 syn/anti ratio,21 cyclic constraints,22 and dynamic processes. It should also be noted that, as a result of different kinetics, the regiochemical outcome of stoichiometric reactions are not necessarily equivalent to the outcome of catalytic reactions. Nevertheless, experimental and theoretical studies on complexes with P,N-type ligands have shown that changes in allyl reactivity are better correlated to the metal− allyl bond lengths due to similarities with the resulting transition state geometries.23 For cis-bis-phosphine complexes of type E, the steric and electronic effects of the opposing ligands on the allylic termini can be considered as equal and the regioselectivity for nucleophilic attack on these complexes is then mainly determined by the properties of the allyl ligand. The relatively long Pd1−C3 bond in 4 suggests an electronic preference for the iso product, whereas the decreased steric hindrance around the 1-position could favor formation of the n product.20 Goux et al. studied the allylation of phenols via complexes resembling E using allylic carbonates as substrates. Under kinetic conditions, n/iso ratios of approximately 0.6−1.5 were found irrespective of the employed phosphine, solvent, or reactant (i.e., n or iso allylic carbonates), with the iso product typically slightly dominating the distribution.24a This indicates that for complexes of type E the regioselectivities for attack at the 1and 3-positions are quite comparable and are the result of a tradeoff between electronic preference and steric hindrance. For complexes of type C, however, very high n/iso ratios are typically observed and point to an enhanced reactivity of the 1position. Studies on complexes with bidentate P,N-type ligands have shown that attack typically occurs at the allylic position trans to the π-acceptor ligand (i.e., the phosphine). The reactivity difference induced by this class of ligands has effectively been used to direct the regioselectivity of nucleophilic attack toward the iso product. For C-type complexes both trans ligands possess π-acceptor properties

In 4 the C1−C2 bond is significantly shorter than the C2− C3 bond and the Pd1−C1 bond is significantly shorter than the Pd1−C3 bond. In comparison to fully symmetric π-allyl complexes which generally exhibit equal C1−C2/C2−C3 and Pd1−C1/Pd1−C3 bonds, methyl substitution at one allylic terminus apparently results in a distorted allyl system. The shorter Pd1−C1 bond in comparison to the Pd1−C3 bond can be interpreted as being the result of increased σ character of C1 and increased π character of C3 (i.e., σ-alkyl bonds are typically much shorter than π-alkene bonds) and bonding of the allyl to the metal is distorted toward η1:η2. In line with this, an elongation of the C1−C2 bond and a contraction of the C2− C3 bond would also be expected. Nevertheless, the C1−C2 and C2−C3 bonds of 4 rather show an opposite distortion of the allyl toward η2:η1. This distortion together with the difference in metal−allyl bond lengths can be rationalized by considering the butenyl fragment as a radical three-electron ligand separately from the metal−phosphine fragment. In this way it becomes clear that inductive stabilization within the butenyl structure leads to an inherent distortion of the resonance structure such that C1−C2 displays a higher bond order than C2−C3. The significantly longer Pd1−C3 bond in comparison to the Pd1−C1 bond can then be interpreted as being the result of decreased electronic demand of C3 due to the donating effect of the methyl group. In addition, the C1−C2−C3−C4 torsion angle of 4 of 178.1(4)° shows that the butenyl structure is planar and that C3 is sp2 hybridized. Regardless of the differences in bond lengths between C1−C2/C2−-C3 and Pd1−C1/Pd1−C3, it is thus proposed that the bonding of the butenyl ligand is still best described as η3. Similar observations regarding asymmetry in the bonding of the allyl to palladium induced by substitution at one allylic terminus have been described by Welch et al.18 On the basis of comparisons of crystal structures of complexes with sterically different, symmetric opposing ligands it was proposed that the elongation of P1−C3 is caused by electronic effects rather than steric. In comparison to 4, the longer C1−C2 bond length of 1 points to a decrease in bond order resulting from the change in trans effect of σ-donor/π-acceptor for TOMPP to π-donor/πacceptor for the η2 olefin. The equal bond lengths of C1−C2 and C2−C3 of 1 also suggest that the electrons of the allyl ligand are fully delocalized over C1 and C3. This, in turn, can be interpreted as an increase in reactivity of the 1-position toward nucleophilic addition, which is well in line with previous observations.5 Nevertheless, if the bonding of the allyl is indeed changed, than a elongation of the Pd1−C1 bond and/or contraction of the Pd1−C3 bond would also be expected. This F


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ratio of 4.4. Both of these ratios are then maintained throughout the remainder of the reaction. In addition to this rapid equilibration of the n/iso ratio, the formation of p-cresol (6) and 1,3,7-octatriene (9(E/Z)) is also observed. Interestingly, the E/Z ratio of octatriene changes during the reaction. Initially 9(E) is the main product, but as the reaction progresses, 9(Z) becomes the main product and a final E/Z ratio of 0.7 is observed. When a P/Pd ratio of 6 was employed, the reaction proceeded identically. The 31P NMR spectra of the reaction mixtures showed no signal for phosphonium species 3 during or after the reaction. On the basis of the reactivity of 4 (Scheme 7), this indicates that the equilibration reaction likely proceeds via complex E. For the guaiacol telomer (7a(E/Z)) (Figure 6) a similar behavior is observed. The telomer composition is rapidly equilibrated within 0.5 h, and an n/iso ratio of 2.3 and E/Z ratio of 3.8 are observed throughout the remainder of the reaction. However, the conversion toward octatriene is markedly faster. The creosol telomer (8a(E/Z)) also shows equilibration and ultimately conversion to octatriene. Unfortunately, the signals of the cis telomer (8a(Z)) and the iso telomer (8b) overlap in the 1H NMR spectra in this case and the relative compositions could not be quantified. Nevertheless, the same general behavior was observed as for the previous reactions. The conversion toward octatriene proceeded faster than for 6a(E/Z) and a bit slower than for 7a(E/Z) (Figure 7). These results show that the product formation route is reversible for Pd/TOMPP and that equilibration of the telomer composition is possible for all of the studied substrates. With regard to the catalytic process, this shows that the telomerization reaction proceeds under kinetic control via C, since the n/iso ratios observed for phenolic substrates are all higher than the equilibrium compositions.13 Also, as a result of the sluggish telomerization rates of phenol and p-cresol, the equilibration is relatively fast and leads to a lowering of the n/ iso ratio during the run. Although reversibility via C cannot be excluded, on the basis of these results, i.e. the preferred formation of E in aromatic solvents and the regioselectivity of E-type complexes, we propose that n/iso equilibration proceeds preferentially via intermediate E. The formation of 1,3,7-octatriene in the case of Pd-catalyzed telomerization of 1,3-butadiene is well-known and was already reported in the initial studies by Smutny and Takahashi et al.1,25,26 The mechanistic details behind octratriene formation have not yet been completely resolved, however. On the basis of deuterium labeling studies, Jolly suggested that the formation of octatriene may proceed either via a β-hydrogen abstraction from C or directly from B.4 Conversely, it has also been shown that η3 allyl complexes are formed from the reaction of metal hydride complexes, e.g., [PdH(PR3)2]+, with 1,3-dienes17,27 and from that of diene complexes, e.g., [Pd((1,2η)-diene)(PR3)2], with acids.28 The kinetic product in the former cases was found to be the anti product, which implies that the diene was in an scis shape prior to protonation, typical for a η4 bonding mode. Nevertheless, a study by Jolly regarding neutral [M(buta-1,3diene)(PR2CH2CH2PR2)] complexes (M = Ni, Pd, Pt) showed that for nickel and palladium the bonding mode of butadiene is highly fluxional and a stable η4 state was not observed. In the case of platinum both η2 and η1:η1 bonding modes were stable, depending on the substituents of the phosphine.29 A report on the formation of dienes via Pd-catalyzed elimination of allylic acetates also points to a preference for the anti β-hydride elimination pathway.30 On the other hand, evidence for a syn β-

and it is unclear whether their differences are substantial enough to create a strong bias for attack at the 1-position. As indicated above, the metal−allyl bond lengths of 1 are comparable to those of 4 and suggest a similar reactivity of the allyl. Nevertheless, studies by Krafft et al. and Norrby et al. on similar “wrap around” complexes have shown that cyclic constraints dominate the regioselectivity of these complexes.22 Moreover, it was shown that the size of the metallacycle can be used to direct the attack toward the 1-position or the 3position, whereby the electronic effects of the trans ligands are completely overruled. Therefore, in contrast to complexes of type E, crystallographic data of the allyl moiety of complexes C do not provide conclusive insight into the observed regioselectivity. n/iso Equilibration and 1,3,7-Octatriene Formation. Kinetic measurements on the Pd/TOMPP-catalyzed telomerization of phenol showed that the n/iso ratio is low and even decreases during the reaction, pointing to an equilibration of the telomer composition. The results of Goux et al. furthermore showed that the etherification of phenols is reversible at 60 °C. The increased stability of E in aromatic solvents, as shown in the solvent-dependent reaction of 1 with 1 equiv of TOMPP, makes it likely that this intermediate is present in the telomerization reaction with phenols and influences the n/iso ratio either via equilibration of the telomer composition or via its low inherent regioselectivity. The reversibility of the product formation route under neutral conditions was therefore studied in d6-benzene at 60 °C. Isolated n telomers of p-cresol (6a(E/Z)), guaiacol (7a(E/ Z)), and creosol (8a(E/Z))) were heated in the presence of 1.7−1.8 mol % of Pd(dba)2 and TOMPP (P/Pd = 2), and the reaction was monitored by 1H NMR (Scheme 8).13 The results of p-cresol telomer (6a(E/Z)) (Figure 5) show that the initial telomer composition (n/iso = 18.6, E/Z = 4.9) is rapidly equilibrated within 1 h to give an n/iso ratio of 2.5 and a E/Z Scheme 8. Pd/TOMPP-Catalyzed Equilibration of n (a(E/ Z)) and iso (b) Telomers and Conversion to ROH and 1,3,7-Octatriene (9(E/Z))a

a

R = 2-MeOPh. G


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Figure 5. Pd/TOMPP-catalyzed equilibration of p-cresol telomers (6a(E/Z) and 6b) and conversion to 1,3,7-octatriene (9(E/Z)). Conditions: 2.5 mL of d6-benzene, 0.85 mmol of 6a(E/Z), 1.75 mol % of Pd(dba)2, TOMPP, P/Pd = 2.1, 60 °C.

Figure 6. Pd/TOMPP-catalyzed equilibration of guaiacol telomers (7a(E/Z) and 7b) and conversion to 1,3,7-octatriene (9(E/Z)). Conditions: 2.5 mL of d6-benzene, 0.83 mmol of 7a(E/Z), 1.82 mol % of Pd(dba)2, P/Pd = 2.0, 60 °C.

isomer.33 Therefore, in line with this reasoning, we propose that also for our system the reaction proceeds via a η4 diene intermediate. The key regioselectivity-determining step then likely involves the reversible formation of the anti η3 allyl complex from a η4 s-cis diene complex (Scheme 9). For this reaction, both associative and dissociative pathways can be envisaged; however, computational data on the syn β-hydride elimination pathway suggest that the dissociative route is preferred. Thus starting from E(anti) or C(anti), a vacant site is created by the decoordination of L, which allows a βhydrogen of the η3 allyl ligand to approach the metal. Depending on the orientation of R′, two transition states are possible and after β-hydride elimination result in the formation of (E)- and (Z)-diene hydride complexes, respectively. In the

hydride elimination pathway (a route that has also been proposed on the basis of computational studies for the formation of octatriene in the case of the Pd-catalyzed telomerization6b) has been provided by Shimizu et al.31 The results of the equilibration reactions discussed above show that the E/Z selectivity of 1,3,7-octatriene changes in favor of the Z isomer during the reaction. Beller et al. also reported a final E/Z ratio of 0.6 at the end of the reaction in the case of the Pd/NHC-catalyzed dimerization of butadiene.32 Interestingly, a recent paper by Hilt et al. shows that the conversion of (E)-dienes toward the thermodynamically less favored Z isomer can be catalyzed by cobalt complexes. It was proposed that this conversion is the result of the highly strained formation of the η4 s-cis diene complex in the case of the Z H


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mediate C in the telomerization mechanism) with 1 equiv of TOMPP ligand in different solvents confirm that cis-[Pd((1− 3η)-octa-2(E),7-dien-1-yl)(TOMPP)2]BF4 (2, corresponding to intermediate E in the telomerization mechanism) is stabilized in aromatic solvents. On the basis of this and catalytic results it is proposed that intermediate E participates in the telomerization reaction with aromatic substrates. The butenyl analogue cis-[Pd((1−3η)-but-2(E)-en-1-yl)(TOMPP)2]BF4 (4) was prepared as a model for 2 (and E by analogy) and was fully characterized, including an X-ray crystal structure determination. The reaction of 4 with TOMPP shows that the phosphonium salt 3 is exclusively formed from 1 and not from 2. Comparison of the crystal structures of 4 and 1 shows that the regioselecivity difference for nucleophilic attack between complexes E and C cannot be deduced from the structural details of these Pd−allyl complexes. The reversibility of the product formation route under neutral conditions was studied using n telomers of p-cresol, guaiacol, and creosol. The results show that equilibration of the n/iso ratio is completed within the first 1 h. Together with catalytic data, this led to the conclusion that telomer formation proceeds kinetically via C and that variations of the n/iso ratios are likely the result of equilibration reactions via complex E. Conversion of the telomers toward 1,3,7-octatriene was also observed, and it was found that the E/Z selectivity changes in favor of the Z isomer during the reaction. A mechanism involving a β-hydride elimination reaction of the anti η3 allyl complex is proposed to account for the observed results.

Figure 7. Pd/TOMPP-catalyzed conversion of phenol telomers 6− 8a(E/Z) to phenols 6−8.

Scheme 9. Proposed Mechanism for 1,3(E/Z),7-Octatriene (9(E/Z)) Formation and Equilibration

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EXPERIMENTAL SECTION

General Procedures. All reactions were carried out under an oxygen-free, dry nitrogen atmosphere using standard Schlenk techniques unless stated otherwise. Tris(2-methoxyphenyl)phosphonium tetrafluoroborate was prepared according to previously published procedures.11 1H/1H{31P}/1H−1H-COSY, 13C{1H}, and 31 1 P{ H} NMR spectra were recorded on a Varian AS400 instrument. Chemical shifts are reported in ppm relative to residual solvent signals. High-resolution ESI-MS spectra were recorded on a Waters LCT Premier XE Micromass system. Elemental analysis was carried out by Kolbe, Microanalytische laboratorium, Mülheim a/d Ruhr, Germany. cis-[Pd((1−3η)-but-2(E)-en-1-yl)(TOMPP)2]BF4 (4). Pd(dba)2 (1.15 g, 2.0 mmol), TOMPP (0.71 g, 2.0 mmol), tris(2methoxyphenyl)phosphonium tetrafluoroborate (0.90 g, 2.0 mmol), and crotyl alcohol (2 mL, 32 mmol) were sequentially dissolved in 75 mL of a (4/1 v/v) toluene/methanol mixture. The solution was stirred and heated to 60 °C for 2 h. Subsequently the solution was concentrated in vacuo at 65 °C. The obtained residue was dissolved in MeOH, filtrered over Celite, and precipitated with excess Et2O. The solution was decanted, and the obtained solids were washed with Et2O and dried in vacuo. 1.27 g (1.33 mmol, 66.2%) of 4 was obtained as a slightly yellow powder. Additional recrystallization via slow vapor diffusion from MeOH/Et2O yielded crystals suitable for X-ray diffraction. 1H NMR (400 MHz, CD2Cl2, −80 °C): δ (ppm) 8.15 (dd, 3J(HAr6d−P1d) = 18.7, 3J(HAr6d−HAr5d) = 7.4 Hz, HAr6d), 8.06 (dd, 3 J(HAr6c−P1c) = 19.0, 3J(HAr6c−HAr5c) = 7.7 Hz, HAr6c), 7.97 (dd, overlapping signals, 3J(HAr6b−HAr5b) = 7.9 Hz, HAr6b), 7.93 (dd, 3 J(HAr6a−P1a) = 19.5, 3J(HAr6a−HAr5a) = 7.7 Hz, HAr6a), 7.53 (t, 3J = 7.6 Hz, HAr), 7.48−6.47 (m, overlapping signals, HAr3−6a−d), 6.36 (t, 3 J(HAr5a/c−HAr6/4a/c) = 7.4 Hz, HAr5a/c), 6.32 (t, overlapping signals 3 J(HAr5b−HAr6/4b) = 7.4 Hz, HAr5b), 6.19 (dd, 3J(HAr3a−P2a) = 5.1 Hz, 3 J(HAr3a−HAr4a) = 7.9 Hz, HAr3a), 6.07 (t, 3J = 7.8 Hz, HAr), 5.41 (td, 3J = 8.1, 8.1, 15.3 Hz, H3b), 5.36−5.25 (m, overlapping signals, H3a/c/d), 5.14 (dd, 3J(HAr6−P) = 16.5, 3J(HAr6−HAr5) = 7.8 Hz, HAr6), 4.34 (m, H4b), 3.98 (s, HOMe), 3.94 (s, HOMe), 3.92 (s, HOMe1a), 3.90 (s, HOMe), 3.85 (s, HOMe), 3.82 (s, HOMe2a), 3.80−3.49 (m, overlapping signals), 3.48 (s, HOMe3d), 3.44 (s, HOMec), 3.36 (s, HOMe3b), 3.32 (s, HOMe3a),

(E)-diene complex the R′ group points away from the diene, but, for the (Z)-diene complex, the R group points in the direction of the diene and as such leads to a highly strained and unstable intermediate. Subsequent deprotonation by Nu− and decoordination, in turn, result in the formation NuH and liberation of the diene. The equilibration of 7a(E/Z) clearly shows that the E pathway is favored kinetically, as the initial selectivity toward E is higher than that of Z. However, as the reaction progresses, the selectivity toward the Z isomer increases and, in the case of 6a(E/Z), ultimately exceeds that of the E isomer. This is rather counterintuitive, as the E product is also the thermodynamically favored product. This can be rationalized by considering that the E pathway is fully reversible, whereas in the case of the Z pathway, the rates of the forward and reverse reactions differ to such an extent that a net production of Z isomer is obtained. Nevertheless, the exact pathway through which the reaction proceeds is not yet clear and warrants a further detailed study.

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CONCLUSIONS Stoichiometric coordination reactions of [Pd((1−3,7,8η)-octa2(E),7-dien-1-yl)(TOMPP)]BF4 (1, corresponding to interI


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3.30−3.11 (m, overlapping signals), 3.10 (s, HOMe), 3.07 (s, HOMe4a), 3.05 (s, HOMe), 3.04 (s, HOMe5a), 3.02 (s, HOMe), 3.00−2.88 (m, overlapping signals), 1.91 (s, HOMe6a), 1.75 (s, HOMe6c), 1.68 (s, HOMe6b),1.59 (t, 3J(H2c−P1c) = 11.2 Hz, 3J(H2c−H3c) = 11.2 Hz, H2c), 0.82 (td, 4J(HMea−P1a) = 6.4 Hz, 4J(HMea−P2a) = 6.4 Hz, 3J(HMea− H4a) = 10.5 Hz, HMea), 0.71 (td, 4J(HMed−P1d) = 6.3 Hz, 4J(HMed−P2d) = 6.3 Hz, 3J(HMed−H4d) = 10.4 Hz, HMed), 0.49 (td, 4J(HMec−P1c) = 5.8 Hz, 4J(HMec−P2c) = 5.8 Hz, 3J(HMec−H4c) = 11.1 Hz, HMec), 0.02 (q, 4J(HMeb−P1b) = 6.4 Hz, 4J(HMeb−P2b) = 6.4 Hz, 3J(HMeb−H4b) = 6.6 Hz, HMeb). 19F NMR (376 MHz, CD2Cl2, −80 °C): δ (ppm) −152.23 (s), −152.38 (s). 31P NMR (162 MHz, CD2Cl2, −90 °C): δ (ppm) 9.99 (d, 2J(P2c−P1c) = 41.9 Hz, P2c), 8.88 (d, 2J(P2d−P1d) = 40.6 Hz, P2d) 8.66 (d, 2J(P2a−P1a) = 39.8, P2a), 8.53 (d, 2J(P2b−P1b) = 38.7 Hz, P2b), 5.78 (d, 2J(P1d−P2d) = 41.2 Hz, P1d), 3.96 (d, 2J(P1a− P2a) = 39.8 Hz, P1a), 2.67 (d, 2J(P1b−P2b) = 38.6 Hz, P1b), 2.19 (d, 2 J(P1c−P2c) = 41.9 Hz, P1c). HR-ESI-MS: calcd for [C46H49O6P2Pd]+ e/z 865.2039, found 865.2056. Anal. Calcd for C46H49BF4O6P2Pd: C, 57.97; H, 5.18; P, 6.50; Pd, 11.17. Found: C, 57.3; H, 5.34; P, 6.4; Pd, 11.01. Kinetic NMR Study of the n/iso Equilibration. TOMPP (10.5 mg, 29,8 μmol) and Pd(dba)2 (8.8 mg, 15.3 μmol) were dissolved in degassed d6-benzene (2.5 mL) and left to react for 5 min at room temperature. Isolated n telomer (0.75 mmol) was added and the solution briefly stirred. A 1 mL aliquot was taken and introduced in a NMR tube under an N2 atmosphere and sealed. Quantitative 1H NMR spectra (5 s relaxation delay) were recorded at 60 °C at regular intervals. Peak integrals were corrected for total response. X-ray Crystal Structure Determination of 4. Crystal data: [C46H49O6P2Pd]BF4 + disordered solvent, fw = 953.00,38 yellow block, 0.36 × 0.24 × 0.18 mm3, monoclinic, P21/c (No. 14), a = 11.5357(3), b = 22.0424(2), c = 21.0432(2) Å, β = 116.986(1)°, V = 4768.15(15) Å3, Z = 4, Dx = 1.328 g/cm3,38 μ = 0.52 mm−1.38 A total of 90485 reflections were measured on a Nonius KappaCCD diffractometer with rotating anode and graphite monochromator (λ = 0.71073 Å) up to a resolution of (sin θ/λ)max = 0.65 Å−1 at a temperature of 150(2) K. Intensity data were integrated with Eval15 software.34 Absorption correction and scaling was performed on the basis of multiple measured reflections with SADABS35 (0.68−0.75 correction range). A total of 10941 reflections were unique (Rint = 0.024), of which 9520 were observed (I > 2σ(I)). The structure was solved with direct methods using the program SHELXS-9736 and refined with SHELXL9736 against F2 values of all reflections. All other non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were introduced in calculated positions and refined with a riding model. The structure contains solvent-accessible voids (626 Å3/unit cell). These voids were filled with disordered solvent molecules. Their contribution to the structure factors was taken into account by backFourier transformation using the SQUEEZE routine of the PLATON software,37 resulting in 109 electrons/unit cell. A total of 548 parameters were refined with no restraints. Minor disorder of the coordinated butenyl moiety was ignored. R1/wR2 (I > 2σ(I)): 0.0379/0.1012. R1/wR2 (all reflections): 0.0452/0.1053. S = 1.071. The residual electron density was between −1.20 and 1.56 e/Å3. Geometry calculations and checking for higher symmetry were performed with the PLATON program.38

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Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank ACTS-ASPECT for financial support.

(1) Smutny, E. J. J. Am. Chem. Soc. 1967, 89, 6793−6794. (2) (a) Briggs, J.; Patton, J.; Vermaire-Louw, S.; Margl, P.; Hagen, H.; Beigzadeh, D. (Dow) WO 2010019360 A2, 2009. (b) Van Leeuwen, P.; Tschan, M.; Garcia-Suarez, E. J., Freixa, Z., Hagen, H. (Dow) WO 2010120846 A2, 2010. (3) (a) Behr, A.; Becker, M.; Beckmann, T.; Johnen, L.; Leschinski, J.; Reyer, S. Angew. Chem., Int. Ed. 2009, 48, 3598−3614. (b) Bouquillon, S.; Muzart, J.; Pinel, C.; Rataboul, F. Top. Curr. Chem. 2010, 295, 93−119. (c) Bruijnincx, P. C. A.; Jastrzebski, R.; Hausoul, P. J. C.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. Top. Organomet. Chem. 2012, 39, 45−102. (d) Mutlu, H.; Parvulescu, A. N.; Bruijnincx, P. C. A.; Weckhuysen, B. M.; Meier, M. A. R. Macromolecules 2012, 45, 1866−1878. (4) (a) Benn, R.; Jolly, P. W.; Mynott, R.; Raspel, B.; Schenker, G.; Schick, K. P.; Schroth, G. Organometallics 1985, 4, 1945−1953. (b) Jolly, P. W.; Mynott, R.; Raspel, B.; Schick, K. P. Organometallics 1986, 5, 473−481. (5) Vollmüller, F.; Krause, J.; Klein, S.; Mägerlein, W.; Beller, M. Eur. J. Inorg. Chem. 2000, 1825−1832. (6) (a) Huo, C.-F; Jackstell, R.; Beller, M.; Jiao, H. J. Mol. Model. 2010, 16, 431−436. (b) Jabri, A.; Budzelaar, P. H. M. Organometallics 2011, 30, 1374−1381. (7) Storzer, U.; Walter, O.; Zevaco, T.; Dinjus, E. Organometallics 2005, 24, 514−520. (8) (a) Palkovits, R.; Nieddu, I.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. ChemSusChem 2008, 1, 193−196. (b) Tschan, M.J.-L.; Garcia-Suarez, E. J.; Freixa, Z.; Launay, H.; Hagen, H.; BenetBuchholz, J.; van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2010, 132, 6463−6473. (c) Briggs, J. R.; Hagen, H.; Samir, J.; Patton, J. T. J. Organomet. Chem. 2011, 696, 1677−1686. (d) Tschan, M.J.-L.; LopezValbuena, J.-M.; Freixa, Z.; Launay, H.; Hagen, H.; Benet-Buchholz, J.; van Leeuwen, P. W. N. M. Organometallics 2011, 30, 792−799. (9) (a) Jackstell, R.; Harkal, S.; Jiao, H.; Spannenberg, A.; Borgmann, C.; Roettger, D.; Nierlich, F.; Elliot, M.; Niven, S.; Cavell, K.; Navarro, O.; Viciu, M. S.; Nolan, S. P.; Beller, M. Chem. Eur. J. 2004, 10, 3891− 3900. (b) Jackstell, R.; Andreu, G. A.; Frisch, A.; Selvakumar, K.; Zapf, A.; Klein, H.; Spannenberg, A.; Rottger, D.; Briel, O.; Karch, R.; Beller, M. Angew. Chem. 2002, 114, 1028−1031; Angew. Chem., Int. Ed. 2002, 41, 986−989. (10) (a) Palkovits, R.; Nieddu, I.; Kruithof, C. A.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. Chem. Eur. J. 2008, 14, 8995−9005. (b) Palkovits, R.; Parvulescu, A. N.; Hausoul, P. J. C.; Kruithof, C. A.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. Green Chem. 2009, 11, 1155−1160. (c) Parvulescu, A. N.; Hausoul, P. J. C.; Bruijnincx, P. C. A.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. Catal. Today 2010, 158, 130−138. (d) Hausoul, P. J. C.; Bruijnincx, P. C. A.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. ChemSusChem 2009, 2, 855− 858. (11) (a) Hausoul, P. J. C.; Parvulescu, A. N.; Lutz, M.; Spek, A. L.; Bruijnincx, P. C. A.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. ChemCatChem 2011, 3, 845−852. (b) Hausoul, P. J. C.; Parvulescu, A. N.; Lutz, M.; Spek, A. L.; Bruijnincx, P. C. A.; Weckhuysen, B. M.; Klein Gebbink, R. J. M. Angew. Chem., Int. Ed. 2010, 49, 7972−7975. (12) (a) Basset, J.-M.; Bouchu, D.; Godard, G.; Karamé, I.; Kuntz, E.; Lefebvre, F.; Legagneux, N.; Lucas, C.; Michelet, D.; Tommasino, J. B. Organometallics 2008, 27, 4300−4309. (b) Kuntz, E.; Basset, J.-M.; Bouchu, D.; Godard, G.; Lefebvre, F.; Legagneux, N.; Lucas, C.; Michelet, D. Organometallics 2010, 29, 523−526. (13) Hausoul, P. J. C.; Tefera, S. D.; Blekxtoon, J.; Bruijnincx, P. C. A.; Klein Gebbink, R. J. M.; Weckhuysen, B. M. Catal. Sci. Technol. 2013, 3, 1215−1223.

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S Supporting Information *

Figures giving detailed NMR assignments and additional 2D NMR spectroscopic data and CIF files giving crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for M.L.: [email protected] (correspondence pertaining to crystallographic studies). *E-mail for R.J.M.K.G.: [email protected]. J


Organometallics

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TOMPP-Catalyzed Telomerization of 1, 3

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