Pesci, Peters, or Deacon? - American Chemical Society

Article pubs.acs.org/Organometallics

Who Wins: Pesci, Peters, or Deacon? Intrinsic Reactivity Orders for Organocuprate Formation via Ligand Decomposition Lenka O’Connor Sraj,† George N. Khairallah,† Gabriel da Silva,‡ and Richard A. J. O’Hair*,† †

School of Chemistry, Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Melbourne, Victoria 3010, Australia ‡ Department of Chemical and Biomolecular, The University of Melbourne, Melbourne, Victoria 3010, Australia S Supporting Information *

ABSTRACT: There are three metal-mediated ligand decomposition reactions that give rise to organometallics: (i) decarboxylation of a metal carboxylate, “the Pesci reaction”; (ii) desulfination of a metal sulfinate, “the Peters reaction”; (iii) desulfonation of a metal sulfonate, “the Deacon reaction”. Despite growing interest in their use in applications in organic synthesis, little is known about the relative ease of thermal extrusion of CO2 versus SO2 versus SO3 in metal complexes. Here the intrinsic reactivity orders for organocuprate formation via ligand decomposition have been studied in the gas phase for the first time. A combination of low-energy collision-induced dissociation experiments in an ion trap mass spectrometer and DFT calculations was used. Simple ligand competition experiments in the heterocopper complexes [MeXOCuOYMe]− (where X = CO or SO and Y = SO or SO2), formed via electrospray ionization, show that desulfination occurs more easily than decarboxylation, which in turn is more facile than desulfonation. This is consistent with DFT calculations at the M06/SDD/cc-pVTZ//M06/cc-pVDZ level of theory, which show that the barriers associated with the transition states follow the order SO2 < CO2 < SO3.

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INTRODUCTION The Pesci reaction, first reported in 1901,1 is a metal-mediated process that involves reaction of a carboxylic acid with a metal salt to yield a metal carboxylate (eq 1, Scheme 1) followed by thermal decarboxylation to produce an organometallic species (eq 2). It has been widely studied in both the condensed2 and gas phases.3 Recent work has focused on exploring potential catalytic reactions of relevance in organic synthesis.4,5 Useful transformations that have been uncovered include protodecarboxylation (eq 3)6 together with various C−C bond coupling reactions, such as Heck reactions (eq 4), aryl coupling (eq 5), Michael addition reactions (eq 6), and acetylenic coupling (eq 7).4,5 Carboxylates are not the only ligands that can undergo metal-mediated thermal extrusion of a small molecule to yield an organometallic species. Sulfinic acids (RSO2H), sulfonyl chlorides (RSO2Cl), and sulfonic acids (RSO3H), which are readily available organic substrates,7 can react with metal salts to produce metal sulfinates (eqs 8 and 9 of Scheme 1)8 and metal sulfonates (eq 11),9 which in turn can undergo thermal extrusion of SO2 (eq 10) and SO3 (eq 12). Indeed, the Peters desulfination reaction (eq 10)10,11 was reported only 4 years after the Pesci reaction, while the Deacon reaction (eq 12) was first reported in 1971.12−14 Recent work on metal-mediated desulfination15,16 and desulfonation17 reactions has focused on exploring many of the same catalytic reactions of relevance to © 2012 American Chemical Society

organic synthesis as have been explored for metal-mediated decarboxylation.4 Despite the common theme of forming an organometallic reagent, there are few examples where metal-mediated decarboxylation has been directly compared with desulfination or desulfonation.17 Indeed, no one appears to have attempted to address the following fundamental question: For organic ligands, which f unctional groups are more suitable for the formation of organometallics RMLn via extrusion of an oxide (eq 13)carboxylates (X = CO), sulf inates (X = SO), or sulfonates (X = SO2)? Here we answer this question via a gas phase study that uses a combination of low-energy collision-induced dissociation (CID) tandem mass spectrometry experiments and DFT calculations.18,19 The heteroligated copper anions [RXOCuOYR]− (where R = Me, X = CO or SO, and Y = SO or SO2) are examined since (i) previous studies on the lowenergy CID of heterocopper carboxylates, [MeCO2CuO2CR]−, have shown that these systems readily provide information on which of the competing decarboxylation reactions involving the different carboxylate ligands is kinetically preferred;3h (ii) Received: November 23, 2011 Published: February 10, 2012 1801

dx.doi.org/10.1021/om2011722 | Organometallics 2012, 31, 1801−1807

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to as M06/SDD/cc-pVTZ//M06/cc-pVDZ throughout this article. The combination of the M06 functional with a triple-ζ quality basis set that incorporates relativistic corrections for transition metals is expected to result in relative energies with mean uncertainties of around 2 to 3 kcal mol−1.22,23 Comparing all reaction energies with and without the effective core potential, we observe a mean unsigned difference of only 0.8 kcal mol−1, which is consistent with a small relativistic effect in Cu, a first-row transition metal. Use of the triple-ζ basis set cc-pVTZ versus the double-ζ basis set cc-pVDZ for the final single-point energy, however, results in a larger mean unsigned difference of 3.3 kcal mol−1 over all reactions. Initial geometry optimizations and IRC calculations (confirming transition-state connectivity) were carried out at the B3LYP/SDD/6-31G* level of theory, in order to allow a comparison to our previous work at this level of theory,3h and the structures associated with eqs 14−17 are given in Table S1 in the Supporting Information. These structures do not differ significantly from those obtained with the M06 functional. The B3LYP energies show a mean unsigned difference of 5.1 kcal mol−1 from the M06/SDD/cc-pVTZ//M06/cc-pVDZ results.

Scheme 1. Metal-Catalyzed Ligand Decomposition Reactions with Potential Applications in Organic Synthesis4,5

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RESULTS AND DISCUSSION Our previous studies on the low-energy CID of heterocopper carboxylates, [MeCO2CuO2CR]−, have shown that these systems readily provide information on which of the competing decarboxylation and ligand loss reactions involving the different carboxylate ligands is kinetically preferred.3h Thus, here we report on the CID spectra of the heteroligated copper anions [RXOCuOYR]− (where R = Me, X = CO or SO, and Y = SO or SO2), which can potentially undergo four different competing reactions: extrusion of XO (eq 14); loss of the anionic ligand, RXO− (eq 15); extrusion of YO (eq 16); and loss of the anionic ligand, RYO− (eq 17).

copper is one of the metals of choice for promoting decarboxylation reactions.2b

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RXOML n → RML n + XO

(13)

METHODS

Experiments. Experiments were carried out using a Thermo Finnigan LTQ linear ion trap mass spectrometer equipped with electrospray ionization. All reagents were used as received. Copper(II) acetate was dissolved in methanol with a concentration of 0.5−1.0 mM, and methane sulfinic acid, methane sulfonic acid, and acetic acid were added appropriately to a final concentrations of 0.5−1.0 mM. The relative ratio of the reactants was important in order to generate the appropriate ions. These solutions were pumped via a syringe into the electrospray source at a rate of 5 μL/min. Typical electrospray source conditions involved needle potentials of 2.5−3.5 kV. The heated capillary temperature was between 250 and 300 °C. Mass selection and collision-induced dissociation were carried out using standard isolation and excitation procedures of the LTQ software. The copper (63Cu 69.2%, 65Cu 30.8%) and sulfur (32S 94.93%, 34S 4.29%) isotope patterns were used to identify copper- and/or sulfurcontaining anions. Threshold energy-resolved CID studies were undertaken on a LCQ mass spectrometer (3D ion trap, Finnigan) as described previously by Colorado and Brodbelt.20 In brief, these experiments measure the appearance of desulfination, desulfonation, or decarboxylation products by varying the CID energy imparted on the mass-selected precursors [MeXOCuOYMe]− and observing the changes in product ion intensity as a function of collision energy. Reaction delays and scan window ranges were held constant throughout each experiment. Theory. DFT calculations were carried out within Gaussian 09,21 utilizing the M06 hybrid meta-GGA functional.22 This functional has been shown to exhibit excellent performance for transition metals and for thermochemical kinetics more broadly,22,23 making it well-suited to studying the energetics of organocuprate reactions. Geometry optimizations and frequency calculations were performed using the double-ζ cc-pVDZ basis set. Single-point energy calculations were subsequently performed on all structures using the large cc-pVTZ triple-ζ quality basis set, with the Stuttgart-Dresden SDD basis set and effective core potential used for the copper centers, so as to account for scalar relativistic effects. The complete model chemistry is referred

Low-Energy CID Experiments on Ligand Decomposition Reactions. Three heteroligated copper anions were examined: [MeCO2CuO2SMe]− (i.e., X = CO and Y = SO); [MeCO2CuO3SMe]− (i.e., X = CO and Y = SO2); and [MeSO2CuO3SMe]− (i.e., X = SO and Y = SO2). Their lowenergy CID spectra in a LTQ-FT mass spectrometer are given in Figure 1. A simple comparison of the abundances of the product ions arising from eqs 14 and 16 readily allows the relative ease of decarboxylation (Pesci reaction), desulfination (Peters reaction), and desulfonation (Deacon reaction) to be established.19 Figure 1A shows that desulfination of [MeCO2CuO2SMe]− (m/z 201) yields [MeCO2CuMe]− (m/z 137, eq 16), which dominates over decarboxylation (virtually no [MeCuO2SMe]− (m/z 157, eq 14) is formed). Decarboxylation is favored over desulfonation, as indicated by the dominance of [MeCuO3SMe]− (m/z 173, eq 14) over [MeCO2CuMe]− (m/ z 137, eq 16) in the CID spectrum of [MeCO2CuO3SMe]− (Figure 1B, m/z 217). These results imply that desulfination is preferred over desulfonation, which is confirmed by the CID spectrum of [MeSO2CuO3SMe]− (Figure 1C, m/z 237), where the yield of [MeCuO3SMe]− (m/z 173, eq 14) is substantially greater than that of [MeSO2CuMe]− (m/z 157, eq 16). These qualitative results were confirmed by energy-resolved CID experiments on the same three heteroligated copper complexes, conducted using a 3D ion trap mass spectrometer 1802


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branching ratios are 92.3% for the loss of SO2 and 7.7% for the loss of CH3SO3−. Apart from ligand decomposition, the ligand loss reactions (eqs 15 and 17) appear to be unfavorable fragmentation channels, as shown in the LTQ-FT mass spectrometer experiments. Only minor losses of MeSO3− (m/z 95) are observed for [MeCO2CuO3SMe]− (Figure 1B) and [MeSO2CuO3SMe]− (Figure 1C). In contrast, losses of MeCO2− (m/z 59) and MeSO2− (m/z 79) are below 0.1% relative abundance in the CID spectra. The preference for MeSO3− ligand loss over MeCO2− and MeSO2− ligand losses is consistent with MeSO3H being a stronger acid than MeSO2H and MeCO2H in the gas phase.26 Theoretical Insights into Fragmentation Mechanisms. Ab initio calculations were carried out with the M06 density functional to gain further insights into the energetics and mechanisms of these fragmentation reactions. Figure 2 shows the potential energy diagram associated with eqs 14−17 for [MeCO2CuO2SMe]−, while the related potential energy diagrams for [MeCO2CuO3SMe]− and [MeSO2CuO3SMe]− are given in Figures 3 and 4, respectively. Table 1 lists the energies for the reactions associated with eqs 14−17 for all three anions. Figure 2 represents the potential energy diagram for the competing decarboxylation/desulfination reactions. An examination of this diagram shows that the transition state and final product energies are higher than the entrance channel (1a1) by 1.12 (TS 1a1−2a1) and 1.33 (3a1 + SO2) eV, respectively, in the case of SO2 loss, whereas they are 1.47 (TS 1a1−2b1) and 0.71 (3b1 + CO2) eV higher in the case of CO2 loss, and hence, this experiment is kinetically controlled. Clearly, in this case, desulfination is preferred over decarboxylation. An analysis of the structures involved in these mechanisms shows that the monodentate O-bound isomer (1a1) is the lowest energy structure of the precursor ion ([MeCO2CuO2SMe]−) with an S-bound isomer (1b1) close in energy at +0.23 eV. Additionally, transition states in both processes are four-centered involving an S−Me (TS 1a1−2a1) and C−Me (TS 1a1−2b1) bond breaking and Cu−Me bond making. Interestingly, in the case of TS 1a1−2a1 we observe the rotation of the SO2 group to allow the interaction between the sulfur atom and copper. Figure 3 shows the potential energy diagram for the competing decarboxylation/desulfonation reactions for the heterocomplex [MeCO2CuO3SMe]−. The transition state and final product energies are higher than the entrance channel (1a2) by 1.42 (TS 1a2−2a2) and 0.63 (3a2 + CO2) eV, respectively, in the case of CO2 loss, whereas they are 1.69 (TS 1a2−2b2) and 2.82 (3b2 + SO3) eV higher in the case of SO3 loss, and hence, this experiment is both kinetically and thermodynamically favoring the loss of CO2. Analysis of the structures involved in these mechanisms shows that a monodentate O-bound isomer is the lowest energy structure of the precursor ion ([MeCO2CuO3SMe]−). It is worth noting that all attempts to calculate a S-bound isomer reverted to the O-bound isomer. Similarly to the previous case, the transition states in both processes are four-centered, involving an S−Me (TS 1a2−2a2) and C−Me (TS 1a2−2b2) bond breaking and Cu−Me bond making. Interestingly also here, in the case of TS 1a2−2b2 rotation of the SO3 group occurs to allow the interaction between the sulfur atom and copper. The modes of binding of the acetate ligand and the nature of the transition states for decarboxylation in [MeCO2CuO2SMe]− and [MeCO2CuO3SMe]− are consistent

Figure 1. Low-energy collision-induced dissociation spectra of (A) [MeCO2CuO2SMe]−; (B) [MeCO2CuO3SMe]−; and (C) [MeSO2CuO3SMe]−. * represents the monoisotopic peaks corresponding to 63Cu and 32S isotopes that were mass selected. Spectra were obtained using the LTQ-FT mass spectrometer.

(LCQ).20 These experiments provided apparent thresholds for desulfination, desulfonation, and decarboxylation. At the 10% relative ratios, desulfination is occurring at a normalized collision energy (NCE) of ca. 13 (arb. units) in the case of [MeCO2CuO2SMe]− and a NCE of ca. 14 (arb. units) in the case of [MeSO 2 CuO 3 SMe] − . In the case of [MeCO2CuO3SMe]− desulfonation is occurring at ca. 20 (arb. units). It is clear from these results that desulfination requires the least energy, whereas desulfonation requires the most (see Supporting Information Figure S1). How does this reactivity order compare with the fragmentation chemistry associated with the bare anions, MeXO−? Since the bare methyl anion formed via eq 18 is below the low mass cutoff of the ion trap, we are unable to carry out these experiments. An examination of the literature, however, reveals that while the acetate anion undergoes decarboxylation (eq 18, where X = CO),24 MeSO3− undergoes a range of other fragmentation reactions, with no loss of SO3 (eq 18) occurring.19a To gain further insights into Me− anion formation, the thermochemistry associated with eq 18 has been calculated.25 Although the endothermicity follows the order MeCO2− < MeSO2− < MeSO3−, it is clear that desulfonation is considerably more endothermic than either decarboxylation or desulfination. MeXO− → Me− + XO

(18)

In addition to the thresholds for dissociation of the three heteroligated copper complexes, branching ratios of the unimolecular reaction products can be extracted from these energy-resolved CID experiments. Thus, for [MeCO2CuO2SMe]− the branching ratios are 98% for the loss of SO2 and 2% for the loss of CO2; for [MeCO2CuO3SMe]− the branching ratios are 95.5% for the loss of CO2 and 4.5% for the loss of CH3SO3−, and in the case of [MeSO2CuO3SMe]− the 1803


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Figure 3. M06/SDD/cc-pVTZ//M06/cc-pVDZ calculated potential energy diagram for the fragmentation reactions of [MeCO2CuO3SMe]−: (a) desulfination (eq 14); methylsulfinate loss (eq 15); desulfonation (eq 16); and methylsulfonate loss (eq 17). (b) Key structures associated with desulfination and desulfonation.

Figure 2. M06/SDD/cc-pVTZ//M06/cc-pVDZ calculated potential energy diagram for the fragmentation reactions of [MeCO2CuO2SMe]−: (a) desulfination (eq 14); methylsulfinate loss (eq 15); desulfonation (eq 16); and methylsulfonate loss (eq 17). (b) Key structures associated with desulfination and desulfonation.

CuOYMe]−·(XO) complexes that are essentially linear (e.g., the bond angle of Me−Cu−O3SMe in 2b3 is 174.3°). In contrast, desulfonation gives rise to a three-coordinate copper complex (the bond angle of Me−Cu−S(O2)Me in 2a3 is 93.9°), which involves a formal oxidation of the Cu center to Cu(III) and is consistent with a stronger interaction between the S and Cu. Thus while the Cu−S bond length in the case of the SO2 complex is 2.44 Å (2a3 of Figure 4b), it is only 2.16 Å in the case of the SO3 complex (2b3 of Figure 4b). A comparison of the low-energy CID spectra shown in Figure 1 with the DFT-predicted lowest energy fragmentation pathways listed in Table 1 shows good agreement. Thus the DFT-predicted barriers for desulfination (1.12 and 1.26 eV) are lower than decarboxylation, (1.42 and 1.47 eV), which in turn are lower than the barriers for desulfonation (1.69 and 2.01 eV). Interestingly the DFT-predicted barriers for decarboxylation at the B3LYP/SDD6-31+G(d) level are 1.72 and 1.70 eV (Supporting Information Table S1), which are very similar

with the wide range of copper carboxylates, [MeCO2CuO2CR]−, previously reported.3g The methane sulfinate ligand can, however, bind to copper through either the O or S atoms. 8 For both [MeCO 2 CuO 2 SMe] − and [MeSO2CuO3SMe]−, the O-bound isomer is favored over the S isomer by 0.12 and 0.23 eV, respectively (1a1 and 1b1 of Figure 2b and 1a3 and 1b3 of Figure 4b). The methanesulfonate anion binds in a monodentate fashion in both [MeCO2CuO3SMe]− and [MeSO2CuO3SMe]−.9 The transition states for desulfination (TS1a3−2a3) and desulfonation (TS1a3−2b3) are four centered and involve S−Me bond breaking and Cu−Me bond making. Both transition states also involve rotation of the SOx group to allow the interaction between the sulfur and copper (Figure 4b). In all three cases there are interesting structural differences in the product complexes formed upon ligand decomposition. Decarboxylation and desulfination give rise to [Me1804


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Finally, the ligand loss channels are all higher in energy, consistent with these reactions being very minor channels in the CID spectra.

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CONCLUSIONS Here we have shown that heteroligated copper anions, [RXOCuOYR]− (where R = Me, X = CO or SO, and Y = SO or SO2), provide a powerful experimental and theoretical platform to determine the fundamental ease of formation of an organocuprate via thermal extrusion of the oxides XO (eq 14) versus YO (eq 16). Using this approach we have shown for the first time that thermally induced copper-mediated desulfination occurs more easily than decarboxylation, with desulfonation being the least preferred. This may be due to the formation of Cu(III) intermediate species in the case of desulfonation. While further studies are required to test the generality of this reactivity order for other metals, it is worth noting that this appears to be consistent with literature reports, where there are more published examples for desulfination and decarboxylation than for desulfonation,2,4,14 and with the observations that Pd(II)-catalyzed protodecarboxyation occurs more readily than protodesulfonation and that Pd(II)-catalyzed desulfitative aryl addition to nitriles does not require activating ortho substituents, whereas the related decarboxylative do.17 Of all these substrates, carboxylic acids and their salts remain attractive reagents for use in metal-catalyzed decarboxylation reactions in organic synthesis due to their ready availability, but there is clearly renewed interest in the applications of the Peters reaction in organic synthesis.15,16

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ASSOCIATED CONTENT

S Supporting Information *

Complete details for ref 21, Figure S1, Table S1, and the Cartesian coordinates of the DFT-optimized structures of isomers 1−7. This material is available free of charge via the Internet at http://pubs.acs.org.

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Figure 4. M06/SDD/cc-pVTZ//M06/cc-pVDZ calculated potential energy diagram for the fragmentation reactions of [MeSO2CuO3SMe]−: (a) desulfination (eq 14); methylsulfinate loss (eq 15); desulfonation (eq 16); and methylsulfonate loss (eq 17). (b) Key structures associated with desulfination and desulfonation.

Corresponding Author

*E-mail: [email protected]. Phone: +61 3 8344-2452. Fax: +61 3 9347-5180.

Table 1. M06/SDD/cc-pVTZ//M06/cc-pVDZ Energies Associated with the Fragmentation Reactions of the Heteroligated Copper Anions, [MeXOCuOYMe]− (eqs 14−17)

ion

ligand fragmentation (eq 14)a,b

ligand loss (eq 15)a,c

ligand fragmentation (eq 16)a,b

ligand loss (eq 17)a,c

[MeCO2CuO2SMe]− [MeCO2CuO3SMe]− [MeSO2CuO3SMe]−

1.47 (0.71) 1.42 (0.63) 1.26 (1.27)

2.27 2.32 2.22

1.12 (1.33) 1.69 (2.82) 2.01 (2.83)

2.09 1.68 1.76

AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the ARC for financial support via grants DP110103844 (to R.A.J.O. and G.N.K.) and DP1096134 (G.N.K.). R.A.J.O. thanks Dr. Nicoletta Nicolini for providing background information on Leone Pesci and Prof. Lothar Beyer and Dr. Konrad Koszinowski for providing background information on Walter Peters. We also thank the Victorian Partnership for Advanced Computing for generous allocation of computer time.

a In eV (1 eV = 96.485 kJ mol−1). bActivation energy for ligand fragmentation reactions. The values in parentheses refer to the overall endothermicity of the reaction. cReaction endothermicity for ligand loss (assumed as barrierless).

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DEDICATION Dedicated to Professor Glen B. Deacon on the occasion of his 75th birthday.

to those calculated at the same level of theory for decarboxylation of the acetate ligand in a wide range of heterocomplexes, [MeCO2CuO2CR]−, which fall in the range 1.67−1.68 eV.3g The DFT calculations are consistent with the experimental order for organocuprate formation given in Figure 1, which follows the order SO2 loss > CO2 loss > SO3 loss.

REFERENCES

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1805


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went on to become Professor of Pharmaceutical Chemistry at the Univeristy of Balogna. For his obituary see: Proc. Ital. Chem. Soc., 1917, 44−46. (2) For earlier reviews on the use of decarboxylation reactions to produce organometallics in the condensed phase see: (a) Deacon, G. B. Organomet. Chem. Rev. A 1970, 5, 355. (b) Deacon, G. B.; Faulks, S. J.; Pain, G. N. Adv. Organomet. Chem. 1986, 25, 237. (3) (a) Fiedler, A.; Schröder, D.; Zummack, W.; Schwarz, H. Inorg. Chim. Acta 1997, 259, 227. (b) Bachrach, S. M.; Hare, M.; Kass, S. R. J. Am. Chem. Soc. 1998, 120, 12646. (c) O’Hair, R. A. J. Chem. Commun. 2002, 20. (d) James, P. F.; O’Hair, R. A. J. Org. Lett. 2004, 6, 2761. (e) O’Hair, R. A. J.; Vrkic, A. K.; James, P. F. J. Am. Chem. Soc. 2004, 126, 12173. (f) Jacob, A. P.; James, P. F.; O’Hair, R. A. J. Int. J. Mass Spectrom. 2006, 255−256, 45. (g) O’Hair, R. A. J.; Waters, T.; Cao, B. Angew. Chem., Int. Ed. 2007, 46, 7048. (h) Rijs, N. J.; Khairallah, G. N.; Waters, T.; O’Hair, R. A. J. J. Am. Chem. Soc. 2008, 130, 1069. (i) Thum, C. C. L.; Khairallah, G. N.; O’Hair, R. A. J. Angew. Chem., Int. Ed. 2008, 47, 9118. (j) Khairallah, G. N.; Waters, T.; O’Hair, R. A. J. Dalton Trans. 2009, 2832. (k) Rijs, N. J.; O’Hair, R. A. J. Organometallics 2009, 29, 2684. (l) Khairallah, G. N.; Thum, C.; O’Hair, R. A. J. Organometallics 2009, 28, 5002. (m) Rijs, N. J.; Yates, B. F.; O’Hair, R. A. J. Chem.Eur. J. 2010, 16, 2674. (n) Khairallah, G. N.; Yoo, J. H.; O’Hair, R. A. J. Organometallics 2010, 29, 1238. (o) Rijs, N. J.; O’Hair, R. A. J. Organometallics 2010, 29, 2282. (p) Rijs, N. J.; Sanvido, G. B.; Khairallah, G. N.; O’Hair, R. A. J. Dalton Trans. 2010, 39, 8655. (q) Meyer, M. M.; Chan, B.; Radom, L.; Kass, S. R. Angew. Chem., Int. Ed. 2010, 49, 5161. (r) Attygale, A. B.; Chan, C.-C.; Axe, F. U.; Bolgar, M. J. Mass Spectrom. 2010, 45, 72. (s) Chan, C.-C.; Axe, F. U.; Bolgar, M.; Attygale, A. B. J. Mass Spectrom. 2010, 45, 1130. (t) Butschke, B.; Schwarz, H. Organometallics 2010, 29, 6002. (u) Woolley, M.; Khairallah, G. N.; Donnely, P. S.; O’Hair, R. A. J. Rapid Commun. Mass Spectrom. 2011, 25, 2083. (v) Leeming, M. G.; Khairallah, G. N.; da Silva, G.; O’Hair, R. A. J. Organometallics 2011, 30, 4297. (w) Brunet, C.; Antoine, R.; Broyer, M.; Dugourd, P.; Kulesza, A.; Petersen, J.; Röhr, M. I. S.; Mitrić, R.; Bonačić-Koutecký, V.; O’Hair, R. A. J. J. Phys. Chem. A 2011, 115, 9120. (x) Rijs, N. J.; Yoshikai, N.; Nakamura, E.; O’Hair, R. A. J., J. Am. Chem. Soc., in press (DOI: 10.1021/ja2069032). (y) Rijs, N. J.; O’Hair, R. A. J. Dalton Trans., in press (DOI:10.1039/C2DT12117D). (4) For reviews see: (a) Gooßen, L. J.; Gooßen, K.; Rodriguez, N.; Blanchot, M.; Linder, C.; Zimmermann, B. Pure Appl. Chem. 2008, 80, 1725. (b) Gooßen, L. J.; Rodriguez, N.; Gooßen, K. Angew. Chem., Int. Ed. 2008, 47, 3100. (5) The source of the metal carboxylate has also included metalcatalyzed insertion into allyl and benzyl esters. For a review see: Weaver, J. D.; Recio, A. III; Grenning, A. J.; Tunge, J. A. Chem. Rev. 2011, 111, 1846. (6) Goossen, L. J.; Linder, C.; Rodriguez, N.; Lange, P. P.; Fromm, A. Chem. Commun. 2009, 46, 7173. (7) For monographs on the chemistry of sulfinic and sulfonic acids see: (a) The Chemistry of Sulphinic Acids, Esters and Their Derivatives; Patai, S., Ed.; Wiley: Chichester, NY, 1990. (b) The Chemistry of Sulphonic Acids, Esters, and Their Derivatives; Patai, S.; Rappoport, Z., Eds.; Wiley: Chichester, NY, 1991. (8) Sulfinate anions can bind to metals via either the oxygen or the sulfur atom. For an older review of metal sulfinates including their synthesis and structures see: Vitzthum, G.; Lindner, E. Angew. Chem., Int. Ed. Engl. 1971, 10, 315. (9) For reviews on the coordination chemistry of sulfonates see: (a) Lawrance, G. A. Chem. Rev. 1986, 86, 17. (b) Cote, A. P.; Shimizu, G. K. H. Coord. Chem. Rev. 2003, 245, 49. (10) Peters, W. Ber. Dtsch. Chem. Ges. 1905, 38, 2565. Walter Peters (1876−?) obtained his Ph.D. from the University of Strassbourg in 1903. He then carried out research under the guidance of Arthur Hantzsch at the University of Leipzig, which is where he discovered the reaction that bears his name. While the main part of his work for his habilitation thesis was carried out at Leipzig, he received his habilitation from the University of Rostock.

(11) The opposite reaction, insertion of SO2 into metal−carbon bonds, has been studied for a number of organometallics: (a) Wojcicki, A. Adv. Organomet. Chem. 1974, 12, 31. (b) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books, Sausalito, CA, 2010; pp 462−465. (12) (a) Cookson, P. G.; Deacon, G. B. J. Organomet. Chem. 1971, 27, C9. (b) Cookson, P. G.; Deacon, G. B. Aust. J. Chem. 1973, 26, 541. (c) Cookson, P. G.; Deacon, G. B. Aust. J. Chem. 1973, 26, 1893. (d) Deacon, G. B.; Miller, J. M.; Taylor, B. S. F. Aust. J. Chem. 1975, 28, 1499. (13) The opposite reaction, insertion of SO3 into metal−carbon bonds, has been studied for a number of organometallics: (a) Kitching, W.; Fong, C. W. Organomet. Chem. Rev. Sect. A 1970, 5, 281. (b) Olapinski, H.; Weidlein, J.; Hausen, H. D. J. Organomet. Chem. 1974, 64, 193. (c) Smith, K.; Hou, D. J. Org. Chem. 1996, 61, 1530. (14) The Pesci, Peters, and Deacon reactions were all reported as stoichiometric reactions involving the reaction of carboxylic acids, sulfinic acids, and sulfonic acids (or their alkali metal salts) with mercury salts. These reactions proceed via thermal extrusion of CO2, SO2, or SO3 under vacuum and have generally been used in the synthesis of arylmercuric and diarylmercuric compounds. Due to the toxicity of mercury and organomercury compunds, their recent synthetic applications have been limited. For reviews on the synthesis of organomercury compounds via decarboxylation, desulfination, and desulfonation reactions see: (a) Makarova, L. G.; Nesmeyanov, A. N. The Organic Compounds of Mercury, Translated from the Russian by Scripta Technica, ltd.; North-Holland Pub. Co.: Amsterdam, 1967; pp 254−257 and 259−264. (b) Larock, R. C. Organomercury Compounds in Organic Synthesis; Springer-Verlag: Berlin, 1985; pp 101−109. (15) For an early report on C−C coupling reactions of organopalladium intermediates formed via desulfination of aromatic sulfinic acids see: (a) Garves, K. J. Org. Chem. 1970, 35, 3273. For recent reports see: (b) Miao, T.; Wang, G. W. Chem. Commun. 2011, 47, 9501. (c) Liu, J.; Zhou, X. Y.; Rao, H. H.; Xiao, F. H.; Li, C. J.; Deng, G. J. Chem.Eur. J. 2011, 17, 7996. (d) Chen, R.; Liu, S.; Liu, X.; Yang, L.; Deng, G. J. Org. Biomol. Chem. 2011, 9, 7675. (16) For the use of metal-catalyzed desulfination of sulfinyl chlorides in C−C coupling applications see: (a) Dubbaka, S. R.; Vogel, P. Angew. Chem., Int. Ed. 2005, 44, 7674. (b) Rao Volla, C. M.; Vogel, P. Angew. Chem., Int. Ed. 2008, 47, 1305. (17) For a rare recent example that compares palladium-catalyzed protodecarboxyation and protodesulfonation reactions, see: (a) Núñez Magro, A. A.; Eastham, G. R.; Cole-Hamilton, D. J. Dalton Trans. 2009, 4683. Larhed has published separate reports on Pd(II)catalyzed decarboxylative and desulfitative aryl addition to nitriles and notes that desulfination does not require activating ortho substituents: (b) Lindh, J.; Sjoberg, P. J. R.; Larhed, M. Angew. Chem., Int. Ed. 2010, 49, 7733. (c) Behrends, M.; Savmerker, J.; Sjoberg, P. J. R.; Larhed, M. ACS Catal. 2011, 1, 1455. (18) For a review on the use of decarboxylation and other types of reactions to produce organometallic ions in the gas phase see: O’Hair, R. A. J. Gas Phase Ligand Fragmentation to Unmask Reactive Metallic Species. In MS Investigations of Reactive Intermediates in Solution; Santos, L. S., Ed.; Wiley-VCH: Weinheim, 2010; Chapter 6, pp 199− 227. ISBN: 978-3-527-32351-7. (19) The present report appears to be the first gas phase study of metal-mediated desulfination and desulfonation reactions using MS. (a) For CID of bare sulfonate anions, see: Smith, J. D.; O’Hair, R. A. J.; Williams, T. D. Phos. Sulf. Silicon Relat. Elements 1996, 119, 49. (b) For Fe+ insertion into the C−S bond of methanesulfonic acid followed by SO2 loss to give [CH3FeOH]+ see: Schröder, D.; Fiedler, A.; Hrušaḱ , J.; Schwarz, H. J. Am. Chem. Soc. 1992, 114, 1215. (20) Colorado, A.; Brodbelt, J. J. Am. Soc. Mass Spectrom. 1996, 7, 1116. (21) Frisch, M. J.; et al. Gaussian_09; Gaussian, Inc: Pittsburgh, PA, 2003. (22) Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215. (23) Zhao, Y.; Truhlar, D. G. Acc. Chem. Res. 2008, 41, 157. 1806


Organometallics

Article

(24) For studies on the gas phase decarboylation of the acetate anion see: (a) Graul, S. T.; Squires, R. R. J. Am. Chem. Soc. 1988, 110, 607. (b) Graul, S. T.; Squires, R. R. J. Am. Chem. Soc. 1989, 111, 892. (c) O’Hair, R. A. J.; Gronert, S.; DePuy, C. H.; Bowie, J. H. J. Am. Chem. Soc. 1989, 111, 3105. (d) Graul, S. T.; Squires, R. R. J. Am. Chem. Soc. 1990, 112, 2506. (25) The endothermicity for the fragmentation reaction shown in eq 18 can be calculated from known thermochemistry (see Supporting Information Table S2) or from DFT calculations using data from the Supporting Information. They are (a) X = CO: experiment 2.61 eV; theory 2.54 eV. (b) X = SO: experiment 3.36 eV; theory 3.27 eV. (c) X = SO2: experiment 5.11 eV; theory 5.17eV. (26) The gas phase acidities are ΔG°acidity(CH3CO2H) = 1427.0 ± 8.4 kJ mol−1; ΔG°acidity(CH3SO2H) = 1341.0 ± 22.0 kJ mol−1; ΔG°acidity(CH3SO3H) = 1318.0 ± 8.4 kJ mol−1. Data from http:// webbook.nist.gov (retrieved November 2011).

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Pesci, Peters, or Deacon? - American Chemical Society

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