Formation and Structure of a Cobalt (III) Complex Containing a

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Formation and Structure of a Cobalt(III) Complex Containing a Nonstabilized Pyridinium Ylide Ligand Patrizia Siega, Renata Dreos,* Giovanna Brancatelli, Nicola Demitri,† and Silvano Geremia Department of Chemical and Pharmaceutical Sciences, University of Trieste, Via L. Giorgieri 1, 34127 Trieste, Italy S Supporting Information *

ABSTRACT: The reaction of [CoIII(4,4′dmsalen)(CH2Cl)(S)], where 4,4′dmsalen = 4,4′-dimethylsalen and S = solvent, with pyridine led to the formation of [CoIII(4,4′dmsalen)(CH2py)(Cl)], containing a nonstabilized pyridinium ylide as axial ligand. The complex has been unambiguously characterized by single-crystal X-ray diffraction analysis. Time-resolved 1H NMR spectra showed that the formation of [CoIII(4,4′dmsalen)(CH2py)(Cl)] occurs in a two-step process involving a metallacyclized intermediate, cis-β-[CoIII(4,4′dmsalenCH2)(py)(S)]+. A similar experiment carried out in the presence of different nitrogen bases having higher pKa values (4-Me-py or 4-t-Bu-py) allowed a better separation of the two consecutive reactions. The almost complete conversion of [CoIII(4,4′dmsalen)(CH2Cl)(S)] in the cyclized intermediate before the formation of the ylide indicates that the ylide complex forms exclusively through the nucleophilic attack of the nitrogen base at the −CH2O− carbon of the cyclized species, whereas a parallel direct conversion through the displacement of Cl− from the axial CH2Cl group of [CoIII(4,4′dmsalen)(CH2Cl)(S)] may be ruled out.

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INTRODUCTION

benzoyl group on the Cα atom. The former complex was prepared by oxidative addition of the pyridinium salt [pyCH2C(O)Ph]Cl to the CoII(dmgH)2 derivative,3 the latter by substitution of the sulfide group by the preformed ylide in [CoIII(dmgH)2(Me)(SMe2)].4 Some years ago we reported the synthesis and the structural characterization of the cis-β-[CoIII(4,4′,7,7′tmsalenCH2)(py)(H2O)]+ complex (salen = 2,2′- ethylenebis(nitrilomethylidene)diphenol and 4,4′,7,7′tmsalen = 4,4′,7,7′tetramethylsalen), where S = H2O, in which the tetradentate ligand forms a seven-membered ring by intramolecular reaction of the axial chloromethyl group of [CoIII(4,4′,7,7′tmsalen)(CH2Cl)(S)], S = solvent, with the equatorial chelate in the presence of pyridine (Scheme 1).5 More recently,6 we decided to extend this study to complexes with differently substituted salen chelates with the aim of evaluating the effect of the presence of methyl groups in the equatorial chelate on the rate of the cyclization reaction. The reaction of [CoIII(4,4′dmsalen)(CH2Cl)(S)], 1, with pyridine, however, led to the formation, besides the desired cis β complex 2a, of the trans species 3a, containing a nonstabilized pyridinium ylide as axial ligand (Scheme 2).

Ylides behave as good ligands toward transition metals owing to the charge density centered on the ylidic carbon.1 The major part of the reported ylide−metal complexes concerns ylides in which the heteroatoms are P, S, or N and the metals belong to the middle or late transition metals. Pyridinium ylides show interesting characteristics due to their appreciable stability, quite exceptional for nitrogen ylides, which is attributed to the delocalization of the charge on the heterocycle.2 To the best of our knowledge, only two X-ray structures of Co(III) complexes containing a pyridinium ylide have been described, and both refer to [CoIII(dmgH)2{benzoyl(1-pyridinio)methanide}(X)] complexes, with dmgH = dimethylglyoximate and X = Cl3 or Me4 (Chart 1), in which the ylide ligand is stabilized by a Chart 1. Structurally Characterized CoIII(dmgH)2 Complexes Containing an Ylide Group (X = Cl or Me)

Received: July 18, 2014

© XXXX American Chemical Society

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Scheme 1. Cyclization Reaction of [CoIII(4,4′,7,7′tmsalen)(CH2Cl)(S)] in the Presence of py

Scheme 2. Two-Step Reaction for the Formation of the Ylide Complexes

Information). The CH3 and the CH2-CH2 protons of the equatorial ligand resonate as singlets at 2.19 and 3.94 ppm, respectively, whereas the CH2-py gives a singlet at 5.35 ppm. The doublet at 6.78 ppm is assigned to H-C3, and the multiplet at 7.01 ppm to H-C2 and H-C5. The py protons resonate at 7.42 (meta), 8.19 (para), and 8.46 ppm (ortho). The H-C7 protons give a singlet at 8.08 ppm. The ROESY spectrum (Figure S2) shows, beside others, a cross-peak between pyridine ortho and Co-CH2 protons, confirming the spatial closeness of the pyridinyl residue and the axial CH2 group. The ESI-MS spectrum of 3a in water shows the base peak at m/z+ 446.4, corresponding to the cation [Co(4,4′dmsalen)(CH2py)]+. Conductance measurements carried out on a 5 × 10−4 M solution of [Co(4,4′dmsalen)(CH2py)(Cl)] in water afford a molar conductivity value of 122 S cm2 mol−1, in agreement with the presence of a 1:1 electrolyte, indicating the dissociation of the axial chloride in solution and the formation of the cation [Co(4,4′dmsalen)(CH2py)(S)]+. The conductance value is stable with time, suggesting that the dissociation of chloride is fast. The crystal structure determination of compound 3a showed that the orthorhombic crystals consist of neutral octahedral [CoIII(4,4′dmsalen)(CH2py)(Cl)] complexes. The ORTEP drawing of the molecular structure of 3a is depicted in Figure 1, and selected bond lengths and angles are listed in Table S1. The asymmetric unit contains a single crystallographic independent molecule of the [CoIII(4,4′dmsalen)(CH2py)(Cl)] complex. The 4,4′dmsalen acts as a tetradentate ligand through its N2O2 donor set chelating the CoIII ion at the equatorial plane. The metal coordination sphere is completed by the presence of a chloride and a CH2py ylide group at the trans-axial positions. The coordination of the ylide group is slightly bent with a C(17)−Co−Cl angle of 177.9(1)°. The salen ligand adopts an overall stepped conformation, with dihedral angles between the planes of the salicylidene rings and the equatorial plane of the cobalt center (N2O2Co) of 171.42(7)° and 169.80(7)°, respectively. The Co(III) ion exhibits a distorted octahedral geometry with a slight displacement of 0.0061(5) Å of the Co ion from the equatorial

The synthesis of metal complexes containing nonstabilized ylides by reaction of a halomethyl metallic precursor7 with the appropriate nucleophile EZn has been widely applied with platinum, palladium, rhodium, and iron complexes8 but not, to our knowledge, with cobalt complexes. The only notable exception is the reaction of [CpCo(PMe3)(L)(CH2Cl)]+ with PMe3, which produces [CpCo(PMe3)(L)(CH2PMe3)]2+.9 Recently, the formation of a halomethyl intermediate that reacts with PR3 to afford the −CH2PR3 group has been proposed in the double C−Cl bond activation of CH2Cl2 by CoCl2 in the presence of metallic Zn.10 Therefore, in view of the peculiarity of the formation of 3a from 1, we decided to further investigate this reaction. The synthesis and the characterization both in solution and in the solid state of 3a and the 1H NMR study of the formation reaction are reported herein.

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RESULTS AND DISCUSSION Complex 3a was initially obtained as a byproduct in the course of a reaction intended to yield 2a, by heating a solution of 1 in methanol in the presence of an excess of pyridine at 40 °C for 2 h. Subsequently, it was obtained in better yield at higher temperatures and with longer reaction times. The progress of the reaction was monitored by TLC on silica gel using 3:1 CHCl3/EtOH as eluent. At the beginning, the TLC evidenced only the brown spot corresponding to 1, but a red spot corresponding to 2a and, finally, a green spot corresponding to 3a developed with time. After about 4 h, the starting product was completely consumed and 3a was the prevailing species in solution, although 2a was still present. The reaction was stopped at this point to avoid the incipient decomposition of 3a, and the reaction mixture evaporated to dryness under vacuum. The products were separated by flash chromatography on silica gel using 3:1 CHCl3/EtOH as eluent, and 3a was recovered from the green fraction by evaporation. The 1H NMR spectrum in CD3OD of 3a is quite simple, having a relatively small number of signals owing to the C2h symmetry of the complex in solution (Figure S1, Supporting B

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suspension was recorded at room temperature (Figure 3). Complex 1 originated, besides the other signals, a singlet at

Figure 1. Molecular structure of complex 3a, showing ellipsoids at the 50% of probability level and the atomic labeling scheme.

plane toward the ylide group. The Co−N and Co−O bond lengths [1.876(3)−1.887(3) and 1.903(2)−1.883(3) Å] are comparable within their esd’s to those found in the structure of the already reported complex [CoIII(4,4′dmsalen)(CH2Cl)]2.6 The axial Co−C(17) and Co−Cl bond lengths are 1.981(4) and 2.465(1) Å, respectively, and significantly differ from the bond distances reported for the ylide dimethylglyoximate cobalt analogue (Chart 1),3 where the Co−C and Co−Cl lengths were 2.07(1) and 2.285(4) Å, respectively. The absence of the electron-withdrawing phenone moiety linked to the C(17) leads to a more pronounced trans-influence exerted by the CH2-py frame, as witnessed by the value of the Co−Cl distance. Among the few metal−ylide structures, a similar strong transinfluence exhibited by the CH2-py fragment has been previously observed only in a rhenium complex.11 The C(17)−N(3) bond lies over the equatorial Co−O(2) bond, and the CH2py mean plane is tilted by 30° with respect to the nearest salicylidene moiety Therefore, there are no significant intramolecular stacking interactions, the distance between the centroids of aromatic rings being equal to 4.16 Å. On the contrary, the ylide ligand establishes a π−π stacking interaction with a symmetrical molecule (distance between centroids of aromatic rings: 3.54 Å) generated by an inversion center, as shown in Figure 2. Molecular pillars are generated by

Figure 3. Time-resolved 1H NMR spectra in CD3OD of (a) complex 1 at room temperature; (b) immediately after the addition of a 200-fold excess of py-d5 at room temperature; (c) at 45 °C; (d) at 60 °C. Successive spectra were recorded at intervals of 10 min. Signals of 1 are indicated by the symbol ■, those of 2a by ◆, and those of 3a by ▲.

Figure 2. Pattern of noncovalent interactions at the solid state: π−π stacking interactions between the CH2py ligands from symmetryrelated molecules and weak hydrogen bonds between the axial CH2 fragment and the chloride atom of adjacent complexes are depicted in orange and magenta, respectively.

3.78 ppm (CH2-CH2 protons) and a further singlet at 5.35 ppm (CH2Cl). Subsequently, an excess of py-d5 was added to the suspension in the NMR tube at room temperature. As a consequence of the addition of py, the suspension dissolved completely. The spectrum of the resulting solution showed two multiplets in the range 3.35−3.70 ppm for the CH2-CH2 protons, whereas the singlet of CH2Cl shifted downfield to 5.68 ppm. The spectral variation was attributed to the axial

the presence of a weak hydrogen-bonding interaction (Table S2) that involves the axial CH2 fragment and the chloride atom of two adjacent complex molecules, as shown in Figure 2. The formation of complex 3a from 1 was monitored by 1H NMR spectroscopy under experimental conditions as close as possible to those of the preparative reaction. The complex 1 was suspended in CD3OD, and the 1H NMR spectrum of the C

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accumulation of the cyclized intermediate. Indeed, for both 4Me-py and 4-t-Bu-py, the patterns of the signal intensities versus time were similar to that above-described, but the two consecutive steps are less overlapped (Figures S5−S8, Supporting Information). The exponential decay of 1 is almost complete before the initial appearance of the ylide complex and the signal of the intermediate goes through a maximum whose intensity is very close to the initial intensity of 1. For L = 4-Me-py, the ka and kb values were estimated directly from the exponential plots of signal intensities versus time, disregarding the time interval in which the two steps overlap (Table 1). For L = 4-t-Bu-py the first step was too fast to allow an estimation of ka with this experimental method; the value obtained for kb is reported in Table 1.

coordination of py to form [Co(4,4′dmsalen)(CH2Cl)(py)].6,13 The temperature was then raised to 60 °C, and sequential NMR spectra at this temperature were recorded at intervals of 10 min (Figure 3). The signal at 5.68 ppm, whose position was scarcely affected by the rising of the temperature, decreased and finally vanished with time, whereas a new singlet appeared at 5.42 ppm, which was assigned to one of the two diastereotopic CH2Co protons of the metallacyclized intermediate 2a.5 This signal intensity increased at first and then decreased to zero with time. The spectrum of 3a, appeared after an induction period and increased with time. The formation of two multiplets in the range 3.60−3.90 ppm for the CH2-CH2 protons, instead of the singlet at 3.94 ppm present in the spectrum of 3a in CD3OD (see above), and the downfield shift of the singlet of CH2Co from 5.35 to 5.58 ppm have been attributed to the axial coordination of pyridine, in line with the interpretation for 1. The kinetic study of the reaction was carried out using the signal of the geminal CH2-Co protons, chosen as their signal does not overlap with others in the course of the reaction. The integrated intensities of these signals relative to the residual ortho protons of py-d5 versus time are reported in Figure 4.

Table 1. Kinetic Constants for the Consecutive Steps of Scheme 2 and pKa Values of the Relative Nitrogen Base

a

L

ka/s−1

kb/s−1

pKaa

py 4-Me-py t-Bu-py

7.5 × 10−4 21 × 10−4 not determined

3.2 × 10−4 1.2 × 10−4 0.85 × 10−4

5.17 6.02 5.99

Ref 14.

The almost complete conversion of 1 in the cyclized intermediate during the course of the reaction suggests that the formation of the ylide complex occurs exclusively through the nucleophilic attack of L at the −CH2O− carbon of the cyclized species, whereas a parallel direct conversion of 1 to the ylide complex through the displacement of Cl− from the axial CH2Cl group by the incoming nitrogen ligand may be ruled out. This result is in accord with the scarce reactivity of the C− Cl bond in the macrocyclic Co halogenomethyl complexes, which generally require harsh conditions for the removal of the halogen.15 The question remains whether the nucleophilic attack of L at the −CH2O− carbon of the cyclized species occurs in an intramolecular fashion or intermolecularly: further kinetic and computational studies are in progress in order to elucidate this point.

Figure 4. Integrated intensities of the axial CH2 1H NMR signal (relative to the residual signal of py-d5) versus time for complexes 1 (■), 2a (◆), and 3a (▲).

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The simplest reaction scheme that accounts for this kinetic behavior is that of two consecutive reactions (Scheme 2). The intensity of the singlet due to 1 decays exponentially with time. The intensity of this signal versus time was fitted to a single-exponential function to yield the rate constant for the disappearance of 1 (ka = 7.5 × 10−4 s−1). The rate constant for the formation of 3a, kb, was estimated by taking into account that at the maximum concentration of 2a, d[2a]/dt = 0 and ka[1] = kb[2a].12 The ratio [1]/[2a] was evaluated from the signal intensity ratio in correspondence with the maximum ([1]/[2a] = 0.43 at 50 min) giving a kb value of 3.2 × 10−4 s−1. The above results do not allow ruling out a parallel pathway that proceeds via the direct attack of the pyridine at the CH2Cl group. In order to test this hypothesis, we decided to repeat the 1 H NMR experiment under similar experimental conditions but with different nitrogen bases. In fact, it has been previously found that the metallacyclization rate constants, ka, increase noticeably with increasing the pKa of L.13 We reasoned that if this effect would be less marked or absent for the second step, the change of L from py (pKa = 5.17)14 to 4-Me-py (pKa = 6.02)14 or 4-t-Bu-py (pKa = 5.99)14 should result in a better separation of the two consecutive reactions and in an

EXPERIMENTAL SECTION

General Methods. [CoIII(4,4′dmsalen)(CH2Cl)]2 was synthesized as already reported by us.6 All other reagents were analytical grade and used without further purification. 1D and 2D NMR spectra were recorded on a Jeol EX-400 (1H at 400 MHz and 13C at 100.4 MHz) and a Varian 500 INOVA (1H at 499 MHz and 13C at 125 MHz) spectrometer with the solvent as internal reference. Electrospray mass spectra were recorded in positive mode by using a Bruker Esquire 4000 mass spectrometer. Synthesis of [CoIII(4,4′dmsalen)(CH2py)(Cl)], 3a. A 0.130 g amount (0.161 mmol) of [CoIII(4,4′dmsalen)(CH2Cl)]2 was dissolved in 100 mL of methanol, and 10 mL of pyridine was added. The solution was warmed to 60 °C in the dark, and the progress of the reaction was monitored by TLC on silica gel using 3:1 CHCl3/EtOH as eluent. After ca. 4 h the heating was stopped and the solvent was evaporated in vacuo. The mixture was separated by flash chromatography on a silica gel column using 3:1 CHCl3/EtOH as eluent. The first red fraction was discarded, and the green fraction afforded the desired product after evaporation of the solvent. Yield: 0.0363 g (0.0752 mmol), 23.3%. ESI MS (MeOH, 116.4 V): m/z calcd for C24H25CoN3O2Cl 481.9; found 446.1 (−Cl−). 1H NMR (400 MHz, CD3OD): δ 2.19 (6H, s, CH3-C4), 3.94 (4H, s, H-C8), 5.35 (2H, s, H2C-py), 6.78 (2H, d, H-C3), 7.01 (4H, m, H-C2 and H-C5), 7.42 (2H, m, meta H py), 8.08 (2H, s, H-CN), 8.19 (1H, m, para H py), 8.46 (2H, m, ortho H py). 13C NMR (100.4 MHz, CD3OD): δ D

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C 20.2 (CH3-C4), 41.3 (H2C-py), 59.4 (C8), 120.0 (quaternary carbon), 123.2(C3), 125.4 (quaternary carbon), 127.4 (meta C py), 134.6 (C2 or C5), 137.0 (C2 or C5), 143.7 (para C py), 144.8 (ortho C py), 163.8 (quaternary carbon), 167.5 (H-CN). Conductivity Measurement. Measurements were performed on a 5 × 10−4 M solution of 3a in Milli-Q water in a thermostated (25 ± 0.1 °C) vessel with a Radiometer CDM92 810 conductimeter. The cell constant was determined with a potassium chloride solution (2 × 10−2 M) of known ionic conductivity. X-ray Diffraction Analysis of the Complex 3a. Complex 3a crystals (dimensions ∼0.3 × 0.3 × 0.2 mm3) were grown by slow evaporation from water solutions at 4 °C. Data collection was performed at the X-ray diffraction beamline of Elettra Synchrotron, Trieste (Italy) (monochromatic wavelength λ = 0.774 91 Å), using a Pilatus 2M image plate detector using a phi scan strategy. The crystal of 3a soaked in a drop of Paratone N was mounted in a loop and flash frozen to 100 K with a nitrogen stream. The diffraction data were indexed and integrated using MOSFLM16 and scaled with SCALA.17 The structures was solved by direct methods using SIR200218 and Fourier analyzed and refined by the full-matrix least-squares based on F2 using SHELXL-97.19 In the final refinement, all non-hydrogen atoms were treated anisotropically and the hydrogen atoms were included at calculated positions with isotropic U factors = 1.2Ueq. The experimental data have been corrected empirically for X-ray absorption using the XABS2 program.20 Essential crystal and refinement data are given in Table S3. CCDC 998823 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www. ccdc.cam.ac.uk/data_request/cif. 1 H NMR Evaluation of the Cyclization Rate. In a typical experiment 1 (3.0 mg) was suspended in CD3OD (0.6 mL), and the spectrum was recorded at room temperature. A 1:200 (py-d5) or 1:50 (4-Me-py or 4-t-Bu-py) excess of the nitrogen ligand was added to the suspension, and the spectrum of the resulting solution was recorded at room temperature. The temperature was then gradually raised to 60 °C, and spectra were acquired at different times at this temperature. The progress of the reaction with time was monitored by integration of nonoverlapping signals, relative to the residual signal of py-d5 or of the solvent.

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ACKNOWLEDGMENTS We thank FRA 2013 of University of Trieste for support. REFERENCES

(1) Urriolabeitia, E. P. Top. Organomet. Chem. 2010, 30, 15−48 and references therein. (2) Jacobs, J.; Van Hende, E.; Claessens, S.; De Kimpe, N. Curr. Org. Chem. 2011, 15, 1340−1362. (3) Saito, T. Bull. Chem. Soc. Jpn. 1978, 51, 169−173. (4) Saito, T.; Urabe, H.; Sasaki, Y. Transition Met. Chem. 1980, 5, 35−39. (5) Dreos, R.; Nardin, G.; Randaccio, L.; Siega, P.; Tauzher, G.; Vrdoljak, V. Inorg. Chem. 2003, 42, 6805−6811. (6) Siega, P.; Dreos, R.; Brancatelli, G.; Zangrando, E.; Tavagnacco, C.; Vrdoljak, V.; Hrenar, T. Organometallics 2014, 33, 909−920. (7) Friedrich, H. B.; Moss, J. R. Adv. Organomet. Chem. 1991, 33, 235−290. (8) (a) Kermode, N. J.; Lappert, M. F.; Skelton, B. W.; White, A. H.; Holton, J. J. Organomet. Chem. 1982, 228, C71−C75. (b) Hoover, J. F.; Stryker, J. M. Organometallics 1988, 7, 2082−2084. (c) Ferguson, G.; Li, Y.; McAlees, A. J.; McCrindle, R.; Xiang, K. Organometallics 1999, 18, 2428−2439. (d) McCrindle, R.; Ferguson, G.; McAlees, A. J.; Arsenault, G. J.; Gupta, A.; Jennings, M. C. Organometallics 1996, 14, 2741−2748. (e) Werner, H.; Hofmann, L.; Paul, W.; Schubert, U. Organometallics 1988, 7, 1106−1111. (f) Leoni, P.; Marchetti, F.; Paoletti, M. Organometallics 1997, 16, 2146−2151. (g) Marder, T. B.; Fultz, W. C.; Calabrese, J. C.; Harlow, R. L.; Mistein, D. J. Chem. Soc., Chem. Commun. 1987, 1543−1545. (9) (a) Werner, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 927−949. (b) Werner, H.; Hofman, L. J. Organomet. Chem. 1985, 289, 141−155. (10) (a) Pattacini, R.; Jie, S.; Braunstein, P. Chem. Commun. 2009, 890−892. (b) Algarra, A. G.; Braunstein, P.; Macgregor, S. A. Dalton Trans. 2013, 42, 4208−4217. (11) Zhang, C.; Guzei, I. A.; Espenson, J. H. Organometallics 2000, 19, 5257−5259. (12) Wilkins, R. G. Kinetics and Mechanism of Reactions of Transition Metal Complexes; VCH: Weinheim, Germany, 1991; p 19. (13) Dreos, R.; Siega, P. Organometallics 2006, 25, 5180−5183. (14) Brown, H. C.; Mihm, X. R. J. Am. Chem. Soc. 1955, 77, 1723− 1726. (15) (a) Ricroh, M. N.; Bied-Charreton, C.; Gaudemer, A. Tetrahedron Lett. 1971, 30, 2859−2862. (b) Marzilli, L. G.; Bayo, F.; Summers, M. F.; Thomas, L. B.; Zangrando, E.; Bresciani Pahor, N.; Mari, M.; Randaccio, L. J. Am. Chem. Soc. 1987, 109, 6045−6052. (c) Schrauzer, G. N.; Ribeiro, A. L.; Lee, L. P.; Ho, R. K. Y. Angew. Chem., Int. Ed. Engl. 1971, 10, 807−808. (d) Dreos, R.; Felluga, A.; Nardin, G.; Randaccio, L.; Siega, P.; Tauzher, G. Inorg. Chem. 2001, 40, 5541−5546. (e) Dreos, R.; Felluga, A.; Nardin, G.; Randaccio, L.; Tauzher, G. Organometallics 2003, 22, 2486−2491. (f) Dreos, R.; Randaccio, L.; Siega, P.; Vrdoljak, V. Croat. Chem. Acta 2009, 82, 455− 461. (16) Battye, G. G.; Kontogiannis, L.; Johnson, O.; Powell, H. R.; Leslie, A. G. W. Acta Crystallogr. 2011, D67, 271−281. (17) (a) Evans, P. R. Acta Crystallogr. 2006, D62, 72−82. (b) Winn, M. D.; Ballard, C. C.; Cowtan, K. D.; Dodson, E. J.; Emsley, P.; Evans, P. R.; Keegan, R. M.; Krissinel, E. B.; Leslie, A. G. W.; McCoy, A.; McNicholas, S. J.; Murshudov, G. N.; Pannu, N. S.; Potterton, E. A.; Powell, H. R.; Read, R. J.; Vagin, A.; Wilson, K. S. Acta Crystallogr. 2011, D67, 235−242. (18) Burla, M. C.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2003, 36, 1103. (19) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (20) Parkin, S.; Moezzi, B.; Hope, H. J. Appl. Crystallogr. 1995, 28, 53−56.

ASSOCIATED CONTENT

S Supporting Information *

Figure S1: 1H NMR spectrum in CD3OD of the complex 3a. Figure S2: ROESY 2D NMR spectrum of 3a in CD3OD. Figure S3: 13C NMR spectrum of 3a in CD3OD. Figure S4: gHSQCed spectrum of 3a in CD3OD. Figure S5: Time-resolved 1H NMR spectra in CD3OD of complex 1 in the presence of an excess of 4-Me-py. Figure S6: Integrated intensities of the 1H NMR signals versus time of 1, 2b, and 3b. Figure S7: Time-resolved 1 H NMR spectra in CD3OD of complex 1 in the presence of an excess of 4-t-Bu-py. Figure S8: Integrated intensities of the 1H NMR signals versus time of 1, 2c, and 3c. Table S1. Bond lengths and angles for complex 3a. Table S2. Weak hydrogen bonds found in the crystal packing of complex 3a. Table S3: Crystallographic details and refinement data for complex 3a. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address †

Nicola Demitri, Elettra, Sincrotrone Trieste, S.S. 14 Km 163.5 in Area Science Park, 34149 Basovizza, Trieste, Italy. Notes

The authors declare no competing financial interest. E

dx.doi.org/10.1021/om5007374 | Organometallics XXXX, XXX, XXX−XXX