Synthesis, characterization, and C–H activation reactions of novel organometallic O-donor ligated Rh(III) complexes

Journal of Organometallic Chemistry 696 (2011) 551e558

Contents lists available at ScienceDirect

Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem

Synthesis, characterization, and CeH activation reactions of novel organometallic O-donor ligated Rh(III) complexes William J. Tenn III a, Brian L. Conley a, Steven M. Bischof b, Roy A. Periana b, * a b

Donald P. and Katherine B. Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California, Los Angeles, CA 90089, United States The Scripps Energy Laboratories, Department of Chemistry, The Scripps Research Institute, Jupiter, FL 33458, United States

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 July 2010 Received in revised form 3 September 2010 Accepted 7 September 2010 Available online 17 September 2010

The synthesis and characterization of the O-donor ligated, air and water stable organometallic complexes trans- (2), and cis-(hfac-O,O)2Rh(CH3)(py) (3), trans-(hfac-O,O)2Rh(C6H5)(py) (4), cis-(hfac-O,O)2Rh(C6H5)(py) (5), and cis-(hfac-O,O)2Rh(Mes)(py) (6) (where hfac-O,O ¼ k2-O,O-1,1,1,5,5,5-hexafluoroacetylacetonato) are reported. These compounds are analogues to the O-donor iridium complexes that are active catalysts for the hydroarylation and CeH activation reactions as well as the bis-acetylacetonato rhodium complexes, which we recently reported. The trans-complex 2 undergoes a quantitative trans to cis isomerization in cyclohexane to form 3, which activates CeH bonds in both benzene and mesitylene to form compounds 5 and 6, respectively. All of these compounds are air and water stable and do not lead to decomposition products. Complex 5 promotes hydroarylation of styrene by benzene to generate dihydrostilbene. Ó 2010 Elsevier B.V. All rights reserved.

Keywords: CH activation Hydroarylation Rhodium Hydrophenylation Hydrocarbons Catalysis

1. Introduction The design of highly efficient and selective catalysts for the functionalization of arenes remains an important challenge [1]. One approach to this challenge is based on the design of homogeneous catalysts that operate by the CeH activation reaction [2]. In this reaction, the CeH bond of unactivated hydrocarbons can selectively react with homogeneous, ligated, metal complexes to break the CeH bond under mild conditions to generate MeC intermediates by a non-radical, concerted CeH bond cleavage. Currently, many stoichiometric examples of this reaction are known; however, the key challenge today when developing catalysts is coupling the CeH activation reaction with functionalization of the MeC intermediate to generate a useful product [2]. Developing the correct ligand is crucial in facilitating the successful coupling of CeH activation and functionalization reactions by mediating the properties of the metal center and stabilizing the complex. In this regard, while N, P, and C-donor ligands have been extensively examined [3], fewer examples exist for Odonor ligated complexes for both early [4] and late [5] transition metals. In addition, to the possibility that O-donor ligands could be more stable to the acidic and oxidizing conditions required for * Corresponding author. Tel.: þ1 561 228 2457. E-mail address: [email protected] (R.A. Periana). 0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2010.09.021

functionalization [6], some other reasons for focus on O-donor ligands are the weak p-donor properties and electron-withdrawing “hard” characteristics that could also facilitate both the CeH activation reaction and functionalization of the MeC intermediates [7]. Recently, we showed [8] a class of thermally and acid stable k2-acacO,O-donor ligated Ir(III) complexes (where acac ¼ acetylacetonato or 2,4-pentanedione) that are efficient catalysts for the regioselective hydroarylation [9] of olefins via a reaction mechanism involving reversible CeH activation and rate determining MeC functionalization by olefin insertion by both experimental [10] and density functional theory (DFT) studies [11]. The results from DFT calculations show that unfavorable O-donor ligand-pp to metal-dp interactions (the so-called “p conflict”) with the d6 center could stabilize the transition state for CeH bond cleavage through ligand p-donation [12]; while the electron-withdrawing characteristics of the acac-O,O ligands could facilitate the rate determining olefin insertion step. Specifically, these studies showed that substituting the eCH3 group on the acetylacetonato ligands of the (acac-O,O)2Ir(III)(R)(L) complex (where R is an alkyl or aryl group) with strongly withdrawing eCF3 groups as in cis(hfac-O,O)2Ir(R)(L) (where hfac-O,O ¼ k2-O,O-1,1,1,5,5,5-hexafluoroacetylacetonato) could facilitate a facile insertion of the olefin into the MePh bond [11b]. In an attempt to examine the prediction from the DFT studies, we sought to synthesize the k2-acac-O,O-donor ligated Ir(III) complexes where the eCH3 groups of the acac-O,O ligands were substituted

552

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558

with eCF3 groups. However, we could not obtain well characterized materials using Ir and no analogs have been previously reported. Given the usual parallels between Ir and Rh [13], we synthesized the eCF3 analogs of the Rh(III) derivatives as a starting point for examining the chemistry of fluorinated k2-acac-O,O ligands and the impact on CeH activation and olefin arylation. Herein, we report the synthesis and characterization of cis(hfac-O,O)2Rh(CH3)(py) (3), and examine its reactivity with sp2 and sp3 CeH bonds. The complex is competent for CeH activation and the cis-(hfac-O,O)2Rh(Ph)(py) (5) and cis-(hfac-O,O)2Rh(Mes)(py) (6) complexes generated by reaction with benzene and mesitylene, respectively, were isolated and fully characterized. Since complex 5 is an analog of both the (acac-O,O)2Rh(Ph)(CH3OH) complex which we recently reported [7d], and of the original (acac-O,O)2Ir(R)(L) complexes [8,10], we contrast the reactivity of these compounds. 2. Results and discussion 2.1. Synthesis of complexes The syntheses of new Rh(III) complexes with the b-diketonate (hfac-O,O) are summarized in Scheme 1. The synthesis of 1 has been previously reported [14]. Treatment of rhodium(III) trichloride hydrate with hexafluoroacetylacetone in refluxing anhydrous ethanol for 4 h, followed by recrystallization from methanol yields the complex trans-(hfac-O,O)2Rh(CH3OH)(Cl) (1). Complex 1 is an air and water stable mustard-yellow microcrystalline compound. The 1H NMR spectrum of 1 shows a single resonance signal for the methine proton of the hfac ligands at 6.60 ppm, which implies a symmetric environment for the two hfac ligands as expected for the trans geometry; whereas, a cis geometry would reveal two distinct methine signals. Coordinated MeOH could not be detected due to rapid scrambling with the solvent. Furthermore, analysis of the 19F NMR revealed a singlet at 71.87 ppm for the eCF3, which is also consistent with a symmetric trans environment of the hfac-O,O ligands. This assignment was later confirmed by a low temperature, single crystal, X-ray diffraction study of 1 as shown in Fig. 1. Although the aquo analog of 1 was previously reported, no definitive structure of the complex had been previously reported. Complex 1 was heated with (CH3)2Hg in methanol at 75  C for 12 h, followed by treatment with pyridine. This afforded the methyl complex, trans-(hfac-O,O)2Rh(CH3)(py) (2), which has also been characterized by 1H, 13C NMR spectroscopy, elemental analysis, and single crystal X-ray diffraction (Fig. 2). Analysis by 1H NMR revealed a doublet at 2.43 ppm with a RheH coupling of 2.2 Hz corresponding to the eCH3 group. X-ray diffraction studies revealed

k2-O,O-1,1,1,5,5,5-hexafluoroacetylacetonate

Fig. 1. ORTEP structure of 1 (50% probability thermal ellipsoids). A molecule of cocrystallized methanol and hydrogen atoms has been omitted for clarity. Selected bond lengths ( A): Rh(1)eCl(1), 2.2747(16); Rh(1)eO(1), 1.989(3); Rh(1)eO(2), 1.992(3); Rh (1)eO(3), 1.992(3); Rh(1)eO(4), 1.997(3); Rh(1)eO(5), 2.064(3). Selected bond angles ( ): O(1)eRh(1)eO(2), 94.55(11); O(2)eRh(1)eO(4), 86.36(13); C(11)eO(5)eRh(1), 119.3(3).

a bond length for the RheCH3 bond of 2.031(3)  A. Interestingly, comparison with two previously reported iridium species highlights the contraction of the metalemethyl bond in the rhodium analog relative to the previously reported iridium derivatives: 1) trans-(acac-O,O)2Ir(CH3)(py) [15] and 2) trans-(tropolone-O,O)2Ir (CH3)(py) [16] where the IreCH3 bond lengths are 2.041 and 2.047  A, respectively (Fig. 2). Having previously shown that our trans-bis-acac motif is active for CeH activation after undergoing a trans to cis isomerization, we were interested in generating the cis isomer of complex 2. Indeed, heating complex 2 in cyclohexane at 130  C for 12 h induced the desired trans to cis isomerization to yield the cis-(hfac-O,O)2Rh (CH3)(py) isomer, complex 3 (Fig. 3). Carrying out the reaction in a sealed NMR tube with a resealable PTFE valve containing a coaxial, external standard of 1,3,5-trimethoxybenzene in CCl4, revealed the trans to cis isomerization was quantitative by comparison to the external standard and the methyl and methine signals integration by 1H NMR after 12 h at 130  C. The isomerization is also characterized by a downfield shift of the eCH3 signal to 2.48 ppm as a doublet due to coupling with the rhodium center with a coupling constant of 2.5 Hz. Also, there is a minor contracA in the crystal tion of the RheN(C5H5) from 2.236(3) to 2.017(5) 

Scheme 1. Synthesis of (hfac-O,O)2Rh(III) complexes.

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558

553

Initial investigations with this molecule revealed that a decomposition pathway was readily accessible leading to intractable rhodium materials. Upon heating in arene solutions or methanol, 4 was found to decompose readily and generate biphenyl (identified by GCeMS and NMR analysis) and a new (hfac-O,O)2Rh complex which we were unable to characterize. Attempts to carry out the trans to cis isomerization analogous to cases of 2 and 3 were also unsuccessful and readily afforded the decomposition products of biphenyl and uncharacterized (hfac-O,O)Rh complexes. 2.2. Hydrocarbon activation

Fig. 2. ORTEP plot of 2 (50% probability thermal ellipsoids) with hydrogen atoms removed for clarity. Selected bond lengths ( A): Rh(1)eN(1), 2.236(3); Rh(1)eC(16), 2.031(3); Rh(1)eO(1), 1.998(2); Rh(1)eO(2), 2.001(2); Rh(1)eO(3), 2.007(2); Rh(1)eO  (4), 2.003(2). Selected bond angles ( ): O(1)eRh(1)eO(2), 94.58(9); O(1)eRh(1)eO(3), 85.12(9); N(1)eRh(1)eC(16), 178.88(11).

structures upon isomerization of and the RheCH3 bond from 2.031 (3) to 2.026(5)  A, although this is minor and within experimental error. This is most likely a trans influence phenomenon and exchange of the trans methyl/pyridine moiety for both the methyl and pyridine groups in an orientation trans to the oxygen from the “hard” hfac-O,O ligands leads to the contraction in the bond distances due to electron withdrawal effects of the eCF3 groups mediated by the rhodium center. We were also interested in making the phenyl analog of 2, by treating 1 with Ph2Hg, instead of Me2Hg, in CHCl3/CH3OH at 100  C for 12 h, followed by treatment with pyridine, gave the air and water stable phenyl complex trans-(hfac-O,O)2Rh(Ph)(py) (4).

The reactivity of (hfac-O,O)2Rh(III) complexes towards CeH bonds was subsequently studied. Heating a solution of 3 in benzene at 190  C for 14 h readily generates the cis-(hfac-O,O)2Rh(Ph)(py) (5) species, which can be isolated in 78% yield; as shown in Scheme 2. The 1H NMR spectrum revealed the disappearance of the distinctive doublet of the Rh-CH3 resonance at 2.48 ppm, which is accompanied by the appearance of two new multiplets at 7.10 and 6.36 ppm corresponding to a new set of phenyl protons with an integration of 3:2, respectively. Monitoring the reaction in C6D6 using a sealed NMR tube with resealable PTFE valve reveals an upfield 1:1:1 triplet at 0.18 ppm due to the formation of CH3D. Some decomposition of the starting material is observed, especially when the reactions were carried out at temperatures greater than 190  C. Complex 5 has been fully characterized by 1H, 13C NMR spectroscopy, and elemental analysis. In a closely related reaction to the one reported above (Scheme 2), after complex 3 is heated in mesitylene at 190  C for 14 h it is converted to the cis-(hfac-O,O)2Rh(Mes)(Py) (6) species. Compound 6 was obtained in 51% yield from the reaction of 3. Complex 6 can be characterized by two methine signals at 5.96 and 5.68 ppm corresponding to the cis geometry and the two double of doublets at 5.05 and 4.46 ppm representing the methylene linker bound to the rhodium in the 1H NMR. Further analysis of the 1H NMR spectrum after reaction in a sealed J-Young NMR tube revealed the generation of CH3D when run in deuterated mesitylene again characterized by the upfield 1:1:1 triplet at 0.18 ppm. We were able to further characterize 6 by 13C NMR spectroscopy, high-resolution mass spectrometry, and X-ray crystallography (Fig. 4). 2.3. Catalytic CeH activation After establishing that 3 can activate the sp2 and sp3 CeH bonds of benzene and mesitylene to generate the respective aryl complexes, we examined the catalytic CeH activation of benzene with 3. The rate of H/D exchange was monitored in a reaction mixture of C6H6 and toluene-d8 (1:1 v/v), at 190  C catalyzed by the methanol analog of 2, trans-(hfac-O,O)2Rh(CH3)(CH3OH) (2-CH3OH), which is used as the crude residue mixture (see Experimental section). The reaction

Fig. 3. ORTEP structure of 3 (50% probability thermal ellipsoids) with hydrogen atoms removed for clarity. Selected bond lengths ( A): Rh(1)eN(1), 2.017(5); Rh(1)eC(16), 2.026(5); Rh(1)eO(1), 1.996(4); Rh(1)eO(2), 2.017(4); Rh(1)eO(3), 2.171(4); Rh(1)eO  (4), 2.000(3). Selected bond angles ( ): O(1)eRh(1)eO(2), 94.34(15); O(3)eRh(1)eO(4), 91.98(14); O(2)eRh(1)eN(1), 176.34(16); O(3)eRh(1)eO(3), 177.18(19).

Scheme 2. Hydrocarbon activation by 3.

554

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558

expected reactivity and experimental simplicity we limited the feasibility studies to liquid styrene. A 2 mL Schlenk tube fitted with a resealable PTFE valve was charged with 5.7 mg (8.47  103 mmol) of 5, styrene (0.2 mL), and benzene (1 mL) and placed in a temperature regulated oil bath set at 190  C for 30 min (Scheme 3). The contents of the reactor were then analyzed by GCeMS followed by evaporation of the volatiles and dissolution in benzene-d6 for NMR analysis. The complex was found to promote stoichiometric hydroarylation to generate dihydrostilbene as compared to an internal standard of cyclohexane. Short reaction times (<1 h) led primarily to dihydrostilbene. Monitoring the reaction for extended periods (>1 h) revealed the production of significant quantities of polystyrene, as evidenced by 1H NMR and MS analysis. Given the relatively low rates with this system, we did not extend the studies to other olefins. Interestingly, no olefinic products, such as stilbenes, which could result from b-hydride elimination of the products from the metal center, were detected in the analysis of the reaction mixture. Our previously reported hydroarylation system based on the (acacO,O)2Ir(R)(L) motif also showed no formation of b-hydride elimination products [8,10]. In both systems, this is likely due to the occurrence of reversible and unproductive b-hydride elimination reactions. The previously reported TpRu(CO)(CH3CN)(R) complex (where Tp ¼ trispyrazolylborate) [19], also showed the lack of b-hydride elimination reactions when R ¼ ethylbenzene to generate styrene; however, on the substitution of ethyl to propylor hexylbenzene facile b-hydride elimination reactions were seen. This effect was attributed to the rapid dissociation of higher order olefins from the Ru center. We are currently examining these b-hydride elimination reactions in more detail to understand the relative differences in selectivities to products and isomers. Fig. 4. ORTEP plot of 6 (50% probability thermal ellipsoids) with selected hydrogens removed for clarity. Selected bond lengths ( A): Rh1eN1, 2.021(4); Rh1eC16, 2.062(4); Rh(1)eO(1), 2.202(3); Rh(1)eO(2), 2.006(3); Rh(1)eO(3), 2.002(3); Rh(1)eO(4), 2.016 (3). Selected bond angles ( ): O(1)eRh(1)eO(2), 92.03(11); O(3)eRh(1)eO(4), 94.18 (11); O(4)eRh(1)eN(1), 174.76(12); O(1)eRh(1)eC(16), 177.98(15); Rh(1)eC(16)eC(17), 114.7(3).

mixture is stable over 11.5 h and obtains 114 turn-over-numbers (TON) with a turn-over-frequency (TOF) of 2.8  103 s1 based on added catalyst by monitoring deuterium incorporation into benzene via GCeMS using a program developed with Microsoft Excel (see Experimental section for further explanation) [17]. In addition, when the reaction was carried out using the pyridyl complex, 2, a TOF of 2.0  103 s1 was observed. These catalytic rates are roughly equivalent to our previously reported cis-(acac-O,O)2Ir(Ph)(py) system, which yielded a TOF of 2  104 s1 at 160  C for exchange between toluene and benzene, given the temperature difference between the two runs (190 versus 160  C, respectively). Unfortunately, this is slower than the trans (acac-O,O)2Ir isomer which, as previous studies have shown reacts via the same transition state for CeH activation as the cis isomer but since it has a less stable ground state, is more active for H/D exchange [11,18]. The inhibition by pyridine, a more tightly binding ligand, also supports a metalmediated mechanism involving pre-equilibrium dissociation of a labile ligand from the metal center to form a reactive, 5-coordinate intermediate followed by hydrocarbon coordination followed by CeH bond cleavage.

2.5. RheCH3 bond distance We reasoned that our lack of catalytic activity, compared to the previously reported Ir systems, might be due to the significant increase in electron deficiency at the Rh center. Our previously reported prediction [11] suggested that making the metal center more electron deficient should facilitate the olefin insertion step and improve overall catalytic rates. However, those calculations were performed on the (hfac-O,O)2Ir(III) complexes, and even with the similarities between Rh and Ir, it was not obvious how this would affect catalysis. In the case of Rh, only the stoichiometric reaction between benzene and styrene to generate dihydrostilbene is observed. Thus, the (hfac-O,O)2RheCH3 metric parameters were compared to known RheCH3 complexes to understand the lack of reactivity. Interestingly, when we compare the RheCH3 bond distances (Table 2) from X-Ray studies of numerous Rh complexes, we find that both the trans- and cis-(hfac-O,O)2Rh complexes have two of A, the shortest RheCH3 bond distances at 2.031(3) and 2.026(5)  respectively. The short RheCH3 bond distance highlights the

2.4. Hydroarylation of styrene with benzene Having demonstrated the stoichiometric and catalytic capability of 3 for the CeH activation reaction of benzene, we examined the competency of 5 for hydroarylation reactions. Based on the higher

Scheme 3. Anti-Markovnikov hydroarylation of styrene promoted by 5.

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558

555

Table 1 Crystal data and summary of collection and refinement details for 1e3, and 6.

Empirical formula Formula weight Crystal color Temperature (K) Crystal system Space group Crystal size (mm) a ( A) b ( A) c ( A) a ( ) b ( ) g ( ) V ( A3) Z Dcalcd (g/cm3) m (mm1) Absorp. correction Reflect. collected Independent reflections R1 wR2 GOF Refinement method

1

2

3

6

C11H6ClF12O5Rh 584.50 Brown 123(2) Orthorhombic Pca2(1) 0.50  0.29  0.10 8.6144(10) 19.986(2) 11.7027(13) 90.00 90.00 90.00 2014.8(4) 4 2.029 1.117 None 11495 4341 [R(int) ¼ 0.0298] 0.0494 0.0842 1.042 Full-matrix least-squares on F2

C16H10F12NO4Rh 611.16 Orange 143(2) Triclinic P1 0.19  0.09  0.02 10.8849(12) 10.9005(12) 10.9681(12) 117.822(2) 108.698(2) 99.217(2) 1012.91(19) 2 2.004 0.977 None 6284 4373 [R(int) ¼ 0.0225] 0.0448 0.0921 1.056 Full-matrix least-squares on F2

C16H10F12NO4Rh 611.16 Yellow 153(2) Monoclinic P2(1)/c 0.20  0.18  0.01 8.0941(15) 29.962(6) 8.7770(17) 90.00 97.310(3) 90.00 2111.2(7) 4 1.923 0.937 None 12955 4737 [R(int) ¼ 0.0511] 0.0849 0.1387 1.043 Full-matrix least-squares on F2

C24H18F12NO4Rh 715.34 Orange 143(2) Monoclinic P2(1)/c 0.5  0.4  0.2 7.9459(8) 38.117(4) 8.8400(9) 90.00 96.506(2) 90.00 2660.2(5) 4 1.786 0.759 None 16330 5987 [R(int) ¼ 0.0380] 0.0543 0.1309 1.043 Full-matrix least-squares on F2

significant electron-withdrawing capabilities that hfac-O,O ligands have on mediating the electronic character of the rhodium. Although it was reported that an increase in the electron deficiency of the metal center should facilitate the olefin insertion step with minimal effect on the CeH activation barrier [11], the reactivity of the (hfac-O,O)2Rh complex reveals that the interplay between the two barriers can have a profound impact on catalysis. We are therefore exploring further modifications of the ligand system to improve the reactivity of this class of catalysts. 3. Conclusion Here we have prepared several new Rh(III) compounds based on hard, O-donor, bis-hexafluoroacetylacetonato ligands. This is an extension of our previous work on Rh and Ir systems based on the bis-acetylacetonato motif. The cis-(hfac-O,O)2Rh(CH3)(py) (3) species is produced in near quantitative yield via trans to cis isomerization. Reaction of 3 with benzene or mesitylene generates the corresponding phenyl- or mesityl-complexes in good yields. The phenyl analog, 5, was found to promote stoichiometric, antiMarkovnikov hydroarylation of styrene with benzene to generate dihydrostilbene; unfortunately, no catalytic hydroarylation products were observed due to lack of catalyst activity. We are currently working on modifications to the Rh complexes in an attempt to improve their catalyst activity. Also, we are working towards expanding our Ir system containing hfac-O,O ligands for the development of non-free radical reactions for the functionalization of MeR bonds. 4. Experimental section 4.1. Warning! Organomercury compounds are highly toxic! There is a danger of cumulative effects. These compounds may cause serious and irreversible effects on skin contact. These compounds may be fatal if absorbed through the skin e even in small amounts. A single drop may cause serious injury or potentially be fatal. They may cause metal fume fever if inhaled or swallowed. Chronic exposure may

cause irreversible CNS damage, sensitization, weight loss, immunological disease and other serious effects. Dimethylmercury is volatile and dangerous concentrations can readily build up in poorly ventilated areas. Work with these toxic compounds must not begin until a full assessment of the risks has been made and suitable protocols established. 4.2. General methods All air and water sensitive procedures were carried out either in an MBraun inert atmosphere glovebox or using standard Schlenk techniques under argon. The glovebox atmosphere was maintained by periodic nitrogen purges and monitored by an oxygen analyzer {O2 < 15 ppm}. Methanol was dried from Mg/I2 and benzene was distilled from Na/benzophenone under dinitrogen. All deuterated solvents (Cambridge Isotopes) were used as received. 1,1,1,5,5,5hexafluoroacetylacetone (Synquest) was stored under argon. GCeMS analysis was performed on a Shimadzu GCeMS QP5000 (ver. 2) equipped with cross-linked methyl silicone gum capillary column (DB5) for liquid samples and on a GasPro column for gas analyses. The retention times of the products were confirmed by comparison to authentic samples. NMR spectra were obtained on a Bruker AM-360 spectrometer, measured at 360.138 MHz for 1H and 90.566 MHz for 13C or on a Bruker AC-250 spectrometer, measured at 250.134 MHz for 1H and 62.902 MHz for 13C, or Varian Mercury-400 spectrometer, measured at 399.96 MHz for 1H, 100.57 MHz for 13C, and 376.34 MHz for 19F at 25  C. All chemical shifts are reported in units of ppm and referenced to the residual proteated solvent unless otherwise stated. High-resolution mass spectra were obtained by UCLA Pasarow Mass Spectrometry Laboratory on an ESI mass spectrometer. Elemental analysis was performed by Desert Analytics (Columbia Analytical Services) of Tucson, Arizona. 4.3. X-ray crystallography Table 1 summarizes the crystallographic data for all structurally characterized compounds. X-ray data were collected at 85 K for complexes 1, 2, and 6 at 149 K for complex 3, on a SMART APEX CCD

556

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558

Table 2 A) for various Rh(III) methyl complexes. RheCH3 bond distances ( Molecule

Bond dist. ( A)

Ref.

cis-(hfac-O,O)2Rh(CH3)(py) trans-(hfac-O,O)2Rh(CH3)(py) (Oetaethylporphinato)Rh(CH3) (octa-n-pentylphthalocyaninato)Rh(CH3) (PCP)Rh(CH3)Cla (POCOP)Rh(CH3)(FBF3)b TpRh(PPh3)(CH3)Ic cis-[(acac-O,O)Rh(PPh3)2(CH3)(CH3CN)][BPh4] cis-[Rh(BA)(PPh3)2(CH3)(CH3CN)][BPh4]d cis-[(acac-O,O)Rh(PPh3)2(CH3)(NH3)][BPh4] (fctfa)Rh(CO)(PPh3)(CH3)Ie [(acac-O,O)Rh(PPh3)2(CH3)(CH3CN)][BPh4] Cp*Rh(Me2SO)(CH3)2 cis,cis-(dmb)Rh(CH3)2(I)(CO)g (ArN]C(CH3)eC(CH3)]NAr)Rh(CO)(CH3)I2h trans-(BPHA)Rh(P(OPh)3)2(CH3)Ii (PyPCP)Rh(CH3)(PEt3)Ij

2.026(5) 2.031(3) 2.031(6) 2.031(8) 2.044(4) 2.050(3) 2.05(3) 2.059(3) 2.062(3) 2.075(3) 2.076(8) 2.085(7) 2.091(4)f 2.102(3) 2.115(13) 2.137(20) 2.156(5)

This one This one [20] [21] [22] [23] [24] [25] [25] [25] [26] [25] [27] [28] [29] [30] [31]

a PCP ¼ 1-((diethylamino)methyl)-3-((di-tertbutylphosphino)methyl)-2,4,6trimethylbenzene. b POCOP ¼ C6H3(CH3)[OP(iPr)2]2. c Tp ¼ trispyrazoleborate. d BA ¼ benzoylacetonato. e fctfa ¼ ferrocenoylacetonato. f Average of the methyl bond lengths. g Only one of two methyls is reported due to methyl/carbonyl disorder in the crystal structure. h Ar ¼ 2-iPrC6H4. i BPHA ¼ N-benzoyl-N-phenylhydroxyamino. j Pyt PCP ¼ pyrrolylphoshinoxylene.

diffractometer with graphite-monochromated Mo-Ka radiation A). The cell parameters for each compound were (l ¼ 0.71073  obtained from the least-squares refinement of the spots (from 60 collected frames) using the SMART program [32]. In each case, a hemisphere of data was collected up to a resolution of 0.75  A, and intensity data were processed using the SAINT PLUS program [33]. Empirical absorption corrections were applied using SADABS [34], and all calculations for the structural analyses were carried out using the SHELXTL package [35]. Initial positions of the Rh atoms were located by direct methods, and the rest of the atoms were found using conventional heavy atom techniques. The structures were refined by least-squares methods using data in the range of 2è ¼ 3.5e55.0 . All non-hydrogen atoms in the three complexes were anisotropically refined, and calculated hydrogen positions were varied in a riding manner along with their attached carbons. There was some disorder present in the fluorines of the eCF3 groups in compounds 3 and 6.

4.4. Synthesis of trans-(hfac-O,O)2Rh(Cl)(CH3OH) (1) This synthesis can be followed as reported by Chattoraj and Sievers [14] by heating 4.0 g RhCl3(H2O)3 and 11.0 mL 1,1,1,5,5,5-hexafluoropentanedione (Hhfac) in 50 mL absolute ethanol under argon or dinitrogen. However, this makes the workup rather difficult. After removing the bulk solvent in vacuo, the residue must be thoroughly dried, either by exposure to vacuum (30 mTorr) for w24 h or by gently heating at 40e50  C on a high vacuum line (2 mTorr) for several hours. Upon removal of all excess ethanol, deionized water was added. A large excess of water was added as the desired product is very insoluble. The complex precipitated from solution as mustardyellow microcrystals, which were then washed on a medium porosity frit with copious amounts of water. A second crop of crystals was also recovered from the mother-liquor as they precipitated. The crops of crystals were then combined. Smaller scale reactions were run using 1.0 g RhCl3$(H2O)x and 3.0 mL Hhfac in 15 mL of absolute ethanol.

These reactions are easier to dry and yields averaged w48%. A common impurity is free hfac ligand as characterized by a 1H NMR resonance upfield of the methine proton in the bound ligand. Recrystallization from methanol gives trans-(hfac-O,O)2Rh(Cl) (CH3OH). 1H NMR (CD3OD, 400 MHz): d 6.60 (s, 2H, hfac C3H). 19F NMR (CD3OD, ref. to CFCl3, 360 MHz): d 71.87 (s, 12F, hfac-CF3). 13C {1H} NMR (C6D6, 100 MHz): d 179.1 (q, 2JCF ¼ 146.8 Hz, hfac C]O), 116.8 (q, 1 JCF ¼ 1132.8 Hz, hfac-CF3), 93.3 (s, hfac methine). Single crystals suitable for X-ray diffraction were obtained from a concentrated solution in methanol stored at 30  C overnight. 4.5. Synthesis of trans-(hfac-O,O)2Rh(CH3)(py) (2) Approximately 1.0 g of 1 was dissolved in 15 mL of methanol in a 30 mL Schlenk tube fitted with a resealable PTFE valve. This compound is highly soluble and does not require much methanol to dissolve large quantities of the compound. Dimethylmercury was added in a 2:1 molar ratio with respect to the compound. The reaction mixture was then heated for 14 h at 75  C under argon after 5 successive freezeepumpethaw cycles to degas the solution. Excess dimethylmercury and methanol were removed in vacuo after the reaction was complete. The condensed material in the trap was treated with HNO3 to convert excess dimethylmercury to (CH3)Hg (NO3) for safer disposal. The remaining residue in the reaction flask was redissolved in a minimal amount of methanol and kept at 30  C overnight to precipitate methylmercuric chloride (grayish black) which was removed by filtration. 2-MeOH was isolated by filtration of the mercuric salt precipitates and removal of the solvent from the filtrate by high vacuum in the glovebox. 1H NMR of 2-MeOH (CDCl3, 400 MHz): d 6.4 (s, 2H, hfac methine), 3.5 (s, 3H, bound methanol CH3), 3.0 (d, 3H, Rh-CH3). Neat pyridine was added to the methanol adduct and the solution immediately turned red. Heating 65  C for 30 min converts the methanol adduct to the pyridyl complex. Analytical TLC revealed an impurity that stuck to neutral alumina when run in CH2Cl2. Preparatory TLC or an alumina plug was employed at this point to remove to isolate the product. Excess pyridine was removed in vacuo. When nearly all the pyridine was removed, a small amount of chloroform was added to dissolve the solid formed in the flask and the remaining traces of pyridine. This solution was then fully evaporated. Crystals suitable for X-ray diffraction were grown from methanol at low temperature (30  C). 1 H NMR (CDCl3, 400 MHz): d 8.49 (d, 2H, o-py), 7.93 (t, 1H, p-py), 7.54 (t, 2H, m-py), 6.14 (s, 2H, hfac methine), 2.43 (d, 3H, RheCH3, 2 JRhH ¼ 2.2 Hz). 19F NMR (CD3OD, ref. to CFCl3, 360 MHz): d 72.2 (s,12F, hfac-CF3). 13C {1H} NMR (C6D6, 100 MHz): d 175.2 (q, 2JFC ¼ 35.6 Hz, hfac C]O), 148.9 (m, py), 138.8 (m, py), 125.8 (s, py), 115.3 (q, 1 JFC ¼ 285.4 Hz, hfac-CF3), 92.2 (m, hfac methine), 5.9 (d, 1JRhC ¼ 16 Hz, CH3). Anal. Calcd. for RhC16H10F12NO4: C, 31.44; H, 1.65; N, 2.29. Found: C, 31.58; H, 1.58; N, 2.24. 4.6. Synthesis of cis-(hfac-O,O)2Rh(CH3)(py) (3) Quantitative isomerization of the trans-complex, 2, to the cisanalog, 3, occurs upon heating 2 in cyclohexane under argon. Complex 2 (45.0 mg) was dissolved upon heating in cyclohexane (6.0 mL) at 95  C and after 14 h was completely converted to the cis isomer, 3, as evidenced by 1H NMR. The yield of the reaction was measured by comparison with an internal standard (1,3,5-trimethoxybenzene). Decomposition may occur if the solution is not fully degassed prior to carrying out the isomerization procedure. 1H NMR (CDCl3, 400 MHz): d 8.26 (d, 2H, o-py), 7.88 (t, 1H, p-py), 7.43 (t, 2H, m-py), 6.22 (s, 1H, hfac methine), 5.99 (s, 1H, hfac methine), 2.48 (d, 3H, RheCH3, 2JRhH ¼ 2.5 Hz). 19F NMR (CDCl3, ref. to CFCl3, 360 MHz): d 76.32 (s, 3F, hfac-CF3), 74.79 (s, 3F, hfac-CF3), 74.70 (s, 3F, hfac-CF3), 74.37 (s, 3F, hfac-CF3). 13C {1H} NMR (CDCl3,

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558

400 MHz): d 177.3 (q, hfac C]O, 2JCF ¼ 35.0), 175.3 (m, hfac C]O, overlapping resonances), 151.7 (s, o-py), 138.7 (s, p-py), 125.6 (s, mpy), 117.4 (m, CF3, 1JCF ¼ 284 Hz), 116.4 (m, CF3, 1JCF ¼ 284 Hz), 115.9 (q, CF3, 1JCF ¼ 284 Hz), 115.7 (q, CF3, 1JCF ¼ 284 Hz), 92.1 (s, hfac methine), 89.0 (s, hfac methine), 7.2 (d, RheCH3, 1JRhC ¼ 26 Hz). 4.7. Synthesis of trans-(hfac-O,O)2Rh(Ph)(py) (4) In a Schlenk tube fitted with a resealable PTFE valve, 1 (0.10 g) was heated with diphenyl mercury (0.10 g, w1.2 mol eq) in 1:1 CHCl3/CH3OH (15 mL) at 100  C for 12 h after 5 freezeepumpethaw cycles and filled with argon. The solution became dark orange. The solvent was then removed in vacuo. The residue was treated with 7 mL of dry pyridine and the solution was heated for 15 min at 50  C. The solution was concentrated by removal of solvent, then 1.0 mL of water was added and a yellow/orange compound precipitated. The solid was filtered and washed with two 5 mL portions of cold water. The compound was then dried on the vacuum line and stored under argon. The compound was found to be air and water stable. 1H NMR (CDCl3, 250 MHz): d 8.62 (d, 2H, o-py), 7.96 (t, 1H, p-py), 7.57 (t, 2H, m-py), 7.14 (m, 3H, Ph-H), 7.05 (d, 2H, Ph-H), 5.91 (s, 2H, hfac methine). 19F NMR (CD3OD, ref. to CFCl3, 360 MHz): d 74.98 (s, 12F, hfac-CF3). Anal. Calcd for C21H18F12NO4Rh: C, 37.47; H, 1.80; N, 2.08. Found: C, 37.73; H, 1.80; N, 2.02. 4.8. Synthesis of cis-(hfac-O,O)2Rh(Ph)(py) (5) In a Schlenk flask with a resealable PTFE valve, 3 (0.25 mg) was heated in neat benzene (15 mL) under argon at 190  C for 24 h. Removal of the volatiles followed by sublimation of this compound at w60  C left behind some Rh metal and afforded cis-(hfac)2Rh(Ph)(py) in 75% yield. 1H NMR (CDCl3, 400 MHz): d 8.17 (d, 2H, o-py), 7.87 (t,1H, p-py), 7.36 (t, 2H, m-py), 7.10 (m, m/p-phenyl overlaping), 6.86 (d, ophenyl), 6.09 (s, 2H, hfac methine), 6.06 (s, 2H, hfac methine). 13C NMR {1H} (CDCl3, 100 MHz): d 177.1 (m, hfac C]O, overlapping resonances), 152.4 (Ph or Py), 147.7 (d, i-phenyl 1JRhC ¼ 28.6 Hz), 139.0 (Ph or Py), 134.4 (Ph or Py), 127.7 (Ph or Py), 125.5 (Ph or Py), 125.2 (Ph or Py), 118.0 (m, hfac-CF3 overlapping resonances), 92.3 (s, hfac methine), 89.5 (s, hfac methine). Anal. Calcd for C21H18F12NO4Rh: C, 37.47; H, 1.80; N, 2.08. Found: C, 37.80; H, 2.00; N, 2.08. 4.9. Synthesis of cis-(hfac-O,O)2Rh(Mes)(py) (6) In a Schlenk flask with a resealable PTFE valve, 3 (0.25 mg) was heated in neat mesitylene (10 mL) under argon at 195  C for 14 h. After removal of the solvent cis-(hfac-O,O)2Rh(Mes)(py) was isolated in 51% yield by sublimation at 60  C. 1H NMR (CDCl3, 400 MHz): d 8.26 (d, 2H, o-py), 7.90 (t, 1H, p-py), 7.45 (t, 2H, m-py), 6.79 (s, 1H, p-mesityl), 6.69 (s, 1H, o-mesityl), 5.96 (s, 1H, hfac methine), 5.68 (s, 1H, hfac methine), 5.05 (dd, 1H, mesityl methylene), 4.46 (dd, 1H, mesityl methylene), 2.15 (s, 3H, mesityl methyl). 13C NMR (CDCl3, 100 MHz): d 176.0 (m, C]O hfac overlapping resonances), 151.7, 145.1, 138.7, 137.6, 128.0, 127.3, 125.7 (phenyl and mesityl aromatic carbons), 117.0 (m, hfac-CF3 overlapping resonances), 91.4 (s, hfac methine), 89.1 (s, hfac methine), 30.9 (s, mesityl methyl), 30.7 (s, mesityl methyl), 20.9 (d, mesityl methylene, 1JRhC ¼ 25.1 Hz). HR-MS (ESI): Calculated for C24H19NO4F12Rhþ1 (M þ H) 716.0172, found 716.0170. Single crystals suitable for X-ray diffraction were grown from evaporation of a concentrated solution in methanol. 4.10. H-D exchange Catalytic H-D exchange reactions were quantified by monitoring the increase of deuterium into C6H6 by GCeMS analyses. This was achieved by deconvoluting the mass fragmentation pattern obtained

557

from the MS analysis, using a program developed with Microsoft EXCEL [36]. An important assumption made with this method is that there are no isotope effects on the fragmentation pattern for the various benzene isotopologs. Fortunately, because the parent ion of benzene is relatively stable towards fragmentation, it can be used reliably to quantify the exchange reactions. The mass range from 78 to 84 (for benzene) was examined for each reaction and compared to a control reaction where no metal catalyst was added. The program was calibrated with known mixtures of benzene isotopologs. The results obtained by this method are reliable to within 2.5%. Thus, analysis of a mixture of C6H6, C6D6 and C6H5D1 prepared in a molar ratio of 40:50:10 resulted in a calculated ratio of 41.2(C6H6):47.5 (C6D6):9.9(C6H5D1). Catalytic H/D exchange reactions were thus run for sufficient reaction times to be able to detect changes >5% exchange. The methanol analog of complex 2, trans-(hfac-O,O)2Rh(CH3)(CH3OH), was used for most H/D exchange experiments unless otherwise stated. In a typical experiment, a 2 mL Schlenk tube fitted with a resealable PTFE valve was charged with 5 mg of methanol analog 2, benzene (1.0 mL), and toluene-d8 (1.0 mL) under an atmosphere of argon. The tube was then placed in a temperature controlled oil bath maintained at 190  C and deuteration was then measured via GCeMS analysis as described previously. 4.11. Hydroarylation of styrene with benzene A 2 mL Schlenk tube fitted with a resealable PTFE valve was charged with 5.7 mg (8.47  103 mmol) of 5, styrene (0.2 mL), and benzene (1 mL) and placed in a temperature regulated oil bath set at 190  C for 30 min. The contents of the reactor were then analyzed by GCeMS followed by evaporation of the volatiles and dissolution in benzene-d6 for NMR analysis. The retention times, mass spectra, and NMR spectra of the species detected were compared to that of authentic samples. Acknowledgment The authors acknowledge Muhammed Yousufuddin, Timothy J. Stewart, and Prof. Robert Bau for solving the crystal structures. Dr. Brian G. Hashiguchi and Dr. Kapil S. Lokare are thanked for their helpful discussions during the preparation of this manuscript. We thank the National Science Foundation (CHE-0328121), Chevron Corporation, the Loker Hydrocarbon Research Institute, the University of Southern California, The Scripps Research Institute, and Center for Catalytic Hydrocarbon Functionalization, a DOE Energy Frontier Research Center (DOE DE-SC000-1298) for financial support. Appendix A. Supporting information CCDC 790213, 790214, 790215, and 790216 contain the supplementary crystallographic data for this paper. This data can be obtained free of charge from The Cambridge Crystallographic Data Center via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jorganchem.2010.09.021. References [1] J. Haggin, Chem. Eng. News 71 (1993) 23. [2] (a) B.A. Arndtsen, R.G. Bergman, T.A. Mobley, T.H. Peterson, Acc. Chem. Res. 28 (1995) 154; (b) A.E. Shilov, G.B. Shulpin, Activation and Catalytic Reactions of Saturated Hydrocarbons in the Presence of Metal Complexes. Kluwer Academic, Dordrecht, 2000; (c) C.G. Jia, T. Kitamura, Y. Fujiwara, Acc. Chem. Res. 38 (2001) 633; (d) W.D. Jones, Acc. Chem. Res. 36 (2003) 140; (e) R.H. Crabtree, J. Chem. Soc., Dalton Trans. 19 (2001) 2437;

558

[3]

[4] [5] [6]

[7]

[8] [9]

W.J. Tenn III et al. / Journal of Organometallic Chemistry 696 (2011) 551e558 (f) J.A. Labinger, J.E. Bercaw, Nature 417 (2002) 507; (g) R.A. Periana, G. Bhalla, W.J. Tenn III, K.J.H. Young, X.Y. Liu, O. Mironov, C.J. Jones, V.R. Ziatdinov, J. Mol. Catal. A: Chem. 220 (2004) 7; (h) B.L. Conley, W.J. Tenn III, K.J.H. Young, S.K. Ganesh, S.K. Meier, V.R. Ziatdinov, O. Mironov, J. Oxgaard, J. Gonzales, W.A. Goddard III, R.A. Periana, J. Mol. Catal. A: Chem. 251 (2006) 8; (i) I.A. Mkhalid, J.H. Barnard, T.B. Marder, J.M. Murphy, J.F. Hartwig, Chem. Rev. 110 (2010) 890; (j) D.A. Colby, R.G. Bergman, J.A. Ellman, Chem. Rev. 110 (2010) 624. For example see: (a) J.R.A. Fulton, W.D. Holland, J. Fox, R.G. Bergman, Acc. Chem. Res. 35 (2002) 44; (b) W.D. Jones, F.J. Feher, Acc. Chem. Res. 22 (1989) 91; (c) T.G.P. Harper, R.S. Shinomoto, M.A. Deming, T.C. Flood, J. Am. Chem. Soc. 110 (1988) 7915; (d) C.M. Wang, J.W. Ziller, T.C. Flood, J. Am. Chem. Soc. 117 (1995) 1647; (e) M.W. Holtcamp, J.A. Labinger, J.E. Bercaw, J. Am. Chem. Soc. 119 (1997) 848; (f) R.A. Periana, D.J. Taube, S. Gamble, H. Taube, T. Satoh, H. Fujii, Science 280 (1998) 560; (g) L. Johansson, O.B. Ryan, M. Tilset, J. Am. Chem. Soc. 121 (1999) 1974; (h) U. Fekl, K.I. Goldberg, Adv. Inorg. Chem. 5454 (2003) 259; (i) F.C. Liu, E.B. Pak, B. Singh, C.M. Jensen, A.S. Goldman, J. Am. Chem. Soc. 121 (1999) 4086; (j) S. Nuckel, P. Burger, Angew. Chem. Int. Ed. 42 (2003) 1632; (k) A. Gunay, K.H. Theopold, Chem. Rev. 110 (2010) 1060 and references therein; (l) B.C. Bales, P. Brown, A. Dehstani, J.M. Mayer, J. Am. Chem. Soc. 127 (2005) 2832; (m) M.A. Lockwood, K. Wang, J.M. Mayer, J. Am. Chem. Soc. 121 (1999) 11894. Y. Taniguchi, T. Hayashida, H. Shibasaki, D. Piao, T. Kitamura, T. Yamaji, Y. Fujiwara, Org. Lett. 1 (1999) 557. M.J. Burk, R.H. Crabtree, J. Am. Chem. Soc. 109 (1987) 8025. (a) J. Riehl, Y. Jean, O. Eisenstein, M. Pélissier, Organometallics 11 (1992) 9; (b) J.T. Poulton, K. Folting, W.E. Streib, K.G. Caulton, Inorg. Chem. 31 (1992) 3190; (c) F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, fifth ed. John Wiley & Sons, New York, 1988, pp. 1189e1194; (d) J.P. Collman, Acc. Chem. Res. 1 (1968) 136; (e) D.M. Tellers, S.J. Skoog, R.G. Bergman, T.B. Gunnoe, W.D. Harman, Organometallics 19 (2000) 2428; (f) D.M. Tellers, R.G. Bergman, J. Am. Chem. Soc. 122 (2000) 954; (g) J.S. Owen, J.A. Labinger, J.E. Bercaw, J. Am. Chem. Soc. 126 (2004) 8247. (a) H.E. Bryndza, W. Tam, Chem. Rev. 88 (1988) 1163; (b) R.G. Bergman, Polyhedron (1995) 3221; (c) J.M. Mayer, Polyhedron (1995) 3273; (d) X.Y. Liu, W.J. Tenn III, G. Bhalla, R.A. Periana, Organometallics 23 (2004) 3584; (e) S.M. Bischof, D.H. Ess, S.K. Meier, J. Oxgaard, R.J. Nielsen, G. Bhalla, W.A. Goddard III, R.A. Periana, Organometallics 29 (2010) 742. T. Matsumoto, D.J. Taube, R.A. Periana, H. Taube, H. Yoshida, J. Am. Chem. Soc. 122 (2000) 7414. (a) S. Murai, F. Kakiuchi, S. Sekine, Y. Tanaka, A. Kamatani, M. Sonoda, N. Chatani, Nature 366 (1993) 529; (b) S. Murai, N. Chatani, F. Kakiuchi, Pure Appl. Chem. 69 (1997) 589; (c) X. Zhang, M. Kanzelberger, T.J. Emge, A.S. Goldman, J. Am. Chem. Soc. 126 (2004) 13192; (d) K. Krogh-Jespersen, M. Czerw, K. Zhu, B. Singh, M. Kanzelberger, N. Darji, P.D. Achord, K.B. Renkema, A.S. Goldman, J. Am. Chem. Soc. 124 (2002) 10797; (e) X. Zhang, M. Kanzelberger, T.J. Emge, A.S. Goldman, J. Am. Chem. Soc. 126 (2004) 13192; (f) S.I. Kozhushkov, D.S. Yufit, L. Ackermann, Org. Lett. 10 (2008) 3409; (g) C. Jia, T. Kitamura, Y. Fujiwara, Acc. Chem. Res. 34 (2001) 633; (h) R.A. Windenhoefer, Chem. Eur. J. 14 (2008) 5382; (i) L.A. Goj, T.B. Gunnoe, Curr. Org. Chem. 9 (2005) 671; (j) K.A. Pittard, J.P. Lee, T.R. Cundari, T.B. Gunnoe, J.L. Petersen, Organometallics 23 (2004) 5514; (k) R. Martinez, J.P. Genet, S. Darses, Chem. Commun. (2008) 3855; (l) Z. Zhang, X. Wang, R.A. Widenhoefer, Chem. Commun. (2006) 3717; (m) N.A. Foley, J.P. Lee, Z. Ke, T.B. Gunnoe, T.R. Cundari, Acc. Chem. Res. 42 (2009) 585; (n) A.R. Luedtke, K.I. Goldberg, Angew. Chem. Int. Ed. 47 (2008) 7694;

[10]

[11]

[12]

[13] [14] [15] [16]

[17]

[18]

[19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36]

(o) D. Karshtedt, A.T. Bell, T.D. Tilley, Organometallics 23 (2004) 4169; (p) D. Karshtedt, J.L. McBee, A.T. Bell, T.D. Tilley, Organometallics 25 (2006) 1801. (a) R.A. Periana, X.Y. Liu, G. Bhalla, Chem. Commun. (2002) 3000; (b) G. Bhalla, J. Oxgaard, W.A. Goddard III, R.A. Periana, Organometallics 24 (2005) 3229; (c) G. Bhalla, X.Y. Liu, J. Oxgaard, W.A. Goddard III, R.A. Periana, J. Am. Chem. Soc. 127 (2005) 11372. (a) J. Oxgaard, R.P. Muller, W.A. Goddard III, R.A. Periana, J. Am. Chem. Soc. 126 (2004) 352; (b) J. Oxgaard, W.A. Goddard III, J. Am. Chem. Soc. 126 (2004) 442; (c) J. Oxgaard, R.A. Periana, W.A. Goddard III, J. Am. Chem. Soc. 126 (2004) 11658. (a) D.M. Lunder, D.B. Lobkovsky, W.B. Strieb, K.G. Caulton, J. Am. Chem. Soc. 113 (1991) 1837; (b) T.C. Flood, J.K. Lim, M.A. Deming, W. Keung, Organometallics 19 (2000) 1166. N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, second ed. Butterworth-Heinemann, Boston, Massachusetts, 1998. S.C. Chattoraj, R.E. Sievers, Inorg. Chem. 6 (1967) 408. A.G. Wong-Foy, G. Bhalla, X.Y. Liu, R.A. Periana, J. Am. Chem. Soc. 125 (2003) 14292. (a) G. Bhalla, R.A. Periana, Angew. Chem. Int. Ed. 44 (2005) 1540; (b) G. Bhalla, J. Oxgaard, W.A. Goddard III, R.A. Periana, Organometallics 24 (2005) 3229. Turnover frequency (TOF) is defined as ([product]/[catalyst]) per second. Turnover number (TON) is defined as [product]/[catalyst] when the reaction is stopped. The concentration of catalyst for the above calculations is based on moles of added rhodium. (a) C.E. Webster, Y. Fan, M.B. Hall, D. Kunz, J.F. Hartwig, J. Am. Chem. Soc. 125 (2003) 858; (b) J.F. Hartwig, K.S. Cook, M. Hapke, C.D. Incarvito, Y. Fan, C.E. Webster, M.B. Hall, J. Am. Chem. Soc. 127 (2005) 2538; (c) S.M. Ng, W.H. Lam, C.C. Mak, C.W. Tsang, G. Jia, Z. Lin, C.P. Lau, Organometallics 22 (2003) 641; (d) W.H. Lam, G. Jia, Z. Lin, C.P. Lau, O. Eisenstein, Chem. Eur. J. 9 (2003) 2775 For a recent review see:; (e) R.N. Perutz, S. Sabo-Etieene, Angew. Chem. Int. Ed. 46 (2007) 2578. M. Lail, C.M. Bell, D. Conner, T.R. Cundari, T.B. Gunnoe, J.L. Petersen, Organometallics 23 (2004) 5007. A. Takenaka, S.K. Syal, Y. Sasada, T. Omura, H. Ogoahi, Z.-I. Yoshida, Acta. Cryst. B32 (1976) 62. M.J. Chen, J.W. Rathke, J.C. Huffman, Organometallics 12 (1993) 4673. M. Gandelman, A. Vigalok, L.J.W. Shimon, D. Milstein, Organometallics 16 (1997) 3981. H. Salem, Y. Ben-David, L.J.W. Shimon, D. Milstein, Organometallics 25 (2006) 2292. J.-C. Chambron, D.M. Eichhorn, T.S. Franczyk, D.M. Stearns, Acta. Cryst. C47 (1991) 1732. E.P. Shestakova, Y.S. Varashavsky, K.A. Lyssenko, A.A. Korlyukov, V.N. Khrustalev, M.V. Andreeva, J. Organomet. Chem. 689 (2004) 1930. J. Conradie, G.J. Lamprecht, A. Roodt, J.C. Swarts, Polyhedron 26 (2007) 5075. E. Fooladi, T. Graham, M.L. Turner, B. Dalhus, P.M. Maitlis, M. Tilset, Dalton Trans. (2002) 975. J. van Slageren, A.L. Vermeer, D.J. Stufkens, M. Lutz, A.L. Spek, J. Organomet. Chem. 626 (2001) 118. L. Gonsalvi, J.A. Gaunt, H. Adams, A. Castro, G.J. Sunley, A. Haynes, Organometallics 22 (2003) 1047. G.J. Lamprecht, G.J. Van Zyl, J.G. Leipoldt, Inorg. Chim. Acta 164 (1989) 69. E. Kossoy, B. Rybtchinski, Y. Diskin-Posner, L.J.W. Shimon, G. Leitus, D. Milstein, Organometallics 28 (2009) 523. Smart V 5.625 Software System for the CCD Detector System. Bruker AXS, Madison, WI, 2001. Saint V 6.22 Software System for the CCD Detector System. Bruker AXS, Madison, WI, 2001. R.H. Blessing, Acta Crystallogr. A51 (1995) 33. G.M. Sheldrick, SHELXTL, Version 5.1. Bruker Analytical X-ray System, Inc., Madison, WI, 1997. For the Microsoft Excel deconvolution tables see: K.J.H. Young, S.K. Meier, J. Gonzales, J. Oxgaard, W.A. Goddard III, R.A. Periana Organometallics 25 (2006) 4734.