Rhodium(III) Azuliporphyrins - Organometallics (ACS Publications)

Jul 23, 2015 - Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States. Organometallics ... The o-, m-, and p-x...
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Rhodium(III) Azuliporphyrins Leah M. Stateman, Gregory M. Ferrence, and Timothy D. Lash* Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, United States S Supporting Information *

ABSTRACT: The organometallic chemistry of azuliporphyrins has been extended to the first syntheses of rhodium(III) derivatives. Reaction of [Rh(CO)2Cl]2 with an azuliporphyrin in refluxing xylenes gave rhodium(III) azuliporphyrins in 62− 67% yield. These derivatives incorporate solvent molecules as axial ligands and thereby introduce two carbon−rhodium bonds in a three-component reaction. The methylbenzyl ligands that are derived from xylenes overlie the π system of the porphyrinoid macrocycle, and proton NMR spectra show that these units are strongly shielded. The o-, m-, and p-xylene-derived complexes were characterized by X-ray crystallography, and this confirmed the presence of the central rhodium atom and the axial benzylic ligands. Additionally, when the azuliporphyrin was reacted with [Rh(CO)2Cl]2 in refluxing acetonitrile and then treated with acetone and basic alumina, a rhodium(III) azuliporphyrin with an acetone-derived axial ligand was generated. These results demonstrate that azuliporphyrins are superior organometallic ligands and therefore merit further investigation.

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INTRODUCTION

acetic acid, followed by oxidation with DDQ (Scheme 1). This strategy has been quite successful in synthesizing tert-butyl and Scheme 1. 3 + 1 Synthesis of Azuliporphyrins

phenyl-substituted azuliporphyrins 5b and 5c.16 An alternative “3 + 1” strategy was also developed,17 and this method was applied to the synthesis of azuliporphyrins, 15−17 their heteroanalogues,15,18 and related benzoazuliporphyrins.19 In addition, a “2 + 2” method for preparing azuliporphyrins has been reported,20 and a direct route to tetraaryl azuliporphyrins has been described.21−23 In 2002, azuliporphyrins were reported to react with nickel(II) acetate, palladium(II) acetate, or platinum(II) chloride to give good yields of stable organometallic derivatives 8 (Scheme 2).14 However, despite these promising early results, the organometallic chemistry of azuliporphyrins has not been explored in detail. Recently, we reported that [Ir(COD)Cl]2 reacted with azuliporphyrins 5a and 5b in refluxing o- or p-xylenes to give low yields of unusual iridium(III) derivatives 9 (Scheme 2).24 These reactions

Carbaporphyrinoid systems are porphyrin-like systems that have one or more carbon atoms in place of interior nitrogen atoms.1−4 These include N-confused porphyrins 15 and carbaporphyrins such as 2,6 benziporphyrins (3),7 and azuliporphyrins (4).8 These porphyrin analogues exhibit unusual reactivity and spectroscopic properties, and for these reasons have been widely investigated.1−4 Carbaporphyrinoids such as 1−4 readily form organometallic derivatives,9−11 particularly with late transition metal ions such as Ni(II), Pd(II), Pt(II), Cu(III), Ag(III), and Au(III). Although the early work on the organometallic chemistry of carbaporphyrinoids primarily focused on N-confused porphyrins (1),10,11 carbaporphyrins,12 benziporphyrins,13 and azuliporphyrins14 have all been shown to be versatile organometallic ligands. Azuliporphyrins (e.g., 5a), which are porphyrin analogues with an azulene unit in place of a pyrrole moiety,8,15 were first obtained in 1997 using a “3 + 1” methodology by reacting azulene dialdehyde 6a with tripyrranes 7 in the presence of trifluoro© XXXX American Chemical Society

Received: June 1, 2015

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DOI: 10.1021/acs.organomet.5b00433 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Scheme 2. Metalation of Azuliporphyrins

Scheme 3. Synthesis of Rhodium(III) Azuliporphyrins

involve not only the insertion of iridium into the porphyrinoid cavity to form a metal−azulene bond but also the generation of a second metal−carbon bond by incorporation of the xylene solvent. Even though the reactions were carried out under nitrogen, oxidation of the xylene fragment occurred to form a carbonyl unit, and the Ir(I) reagent yielded an Ir(III) product.24 Metalloporphyrinoids such as 8 and 9 incorporate metal cations with well-known catalytic properties that could potentially lead to applications. In 2014, examples of ruthenium(II) tetraphenylazuliporphyrins were disclosed.25 In addition, copper(II) salts react with tetraarylazuliporphyrins to give oxidative metalation products,26 and similar ruthenium(II) derivatives have recently been reported.27 Clearly, the potential of azuliporphyrins in this field provides numerous opportunities for further research. Rhodium(III) porphyrins are well-known and have demonstrated efficient and selective carbon−hydrogen bond activation.28−30 In addition, rhodium(III) N-confused porphyrins have been prepared,31 and related organometallic complexes derived from expanded porphyrins such as hexaphyrins(1.1.1.1.1.1) have been described.32 Rh(IV) complexes of N-confused porphyrins also effectively promote stereoselective cyclopropanation reactions with alkenes.33 Given the significance of these reports, we have extended our studies to explore the formation of rhodium derivatives of azuliporphyrins. Efficient syntheses of rhodium(III) azuliporphyrins are reported, and three of these complexes have been structurally characterized by single crystal X-ray diffraction.34

Figure 1. UV−vis spectrum of o-xylene-derived rhodium(III) azuliporphyrin 10a in chloroform.

demonstrated that rhodium and a xylene molecule had been incorporated into the product, but unlike in the case of iridium, the methylene unit had not been oxidized. The high-resolution mass spectrum for this compound was consistent with the molecular formula C48H52N3Rh. The proton NMR spectrum in CDCl3 gave a 2H doublet (J = 3.8 Hz) at −1.88 ppm and a 3H singlet at −0.31 ppm (Figure 2). The doublet was assigned to the presence of a methylene unit that was directly connected to the rhodium cation and the splitting results from two-bond coupling with 103Rh (I = 1/2). The upfield shifts to these resonances indicates that these protons lie over the macrocyclic ring and thereby fall into a strongly shielding zone. A complete analysis of the NMR data demonstrated that 2methylbenzylrhodium(III) azuliporphyrin 10a had been generated. The protons directly attached to the benzene ring showed up at 3.52 (1H, d), 5.77 (2H, m), and 6.22 ppm (1H, dt), and the degree of shielding can be directly correlated to the proximity of the arene protons to the azuliporphyrin macrocycle. The meso-protons on the azuliporphyrin fragment gave rise to two 2H singlets at 8.42 and 9.07 ppm, values that are slightly downfield from the resonances in azuliporphyrin 5b, indicating that the organometallic system has comparable or slightly increased macrocyclic aromaticity. For the 13C NMR spectrum in d5-pyridine, the benzylic-CH2 gave rise to a doublet (J = 25.6 Hz) at 5.6 ppm caused by direct 103Rh−carbon coupling. In addition, a downfield doublet was observed at 200.6 ppm (J = 31.5 Hz) because of the inner carbon of the azulene unit that is directly bonded to the rhodium ion. Comparable downfield shifts are seen for benzene carbons directly linked to rhodium(III) in pincer complexes,35 although the values reported for rhodium(III) N-confused porphyrins were near 150 ppm.31 Azuliporphyrin 5b reacted with [Rh(CO)2Cl]2 in m- or p-xylenes to give the related organometallic complexes 10b and 10c (Scheme 3). These derivatives were rather insoluble in most organic solvents, and

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RESULTS AND DISCUSSION In our earlier work on the synthesis of iridium(III) azuliporphyrins 9, complexes derived from azuliporphyrin 5a proved to be highly insoluble and difficult to characterize.24 However, much better results were obtained using tertbutylazuliporphyrin 5b.24 For this reason, 5b16 was used as the precursor to the desired rhodium organometallic derivatives. Initially, [Rh(COD)Cl]2 was used in these studies, but significantly better results were subsequently obtained using the related Rh(I) reagent [Rh(CO)2Cl]2. Azuliporphyrin 5b was refluxed with [Rh(CO)2Cl]2 in o-xylene under an atmosphere of nitrogen for 2 days (Scheme 3). The resulting product was purified by column chromatography on grade-3 basic alumina and afforded a deep maroon colored band. Derivative 10a gave a distinctive UV−vis spectrum showing a strong band at 377 nm and weaker absorptions that extended to beyond 800 nm (Figure 1). The NMR and MS data B

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Figure 2. Proton NMR spectrum (500 MHz) of o-xylene-derived rhodium(III) azuliporphyrin 10a in CDCl3. * = solvent impurities.

NMR data could only be obtained in d5-pyridine. Otherwise, these complexes gave results similar to those of 10a, and the NMR data only differed for the resonances corresponding to the benzylic fragment. Attempts to carry out the reaction in toluene were unsuccessful, possibly because of the lower boiling point for this solvent. Although the mechanism for the incorporation of the benzylic units is not known, rhodium(III) porphyrins are known to form similar complexes under basecatalyzed conditions.29 In contrast, aryl C−H activation to give aryl rhodium complexes has also been observed for Rh(III) porphyrins,28 but this process was not noted for the azuliporphyrin reactions. All three of the xylene-derived rhodium(III) azuliporphyrin complexes were characterized by single-crystal X-ray diffraction analysis (Figures 3−5). These both confirm the presence of the methylbenzyl ligands and show that the structures of the three isomers are very similar with the most significant variation being the orientation of the axial ligands. This is clearly

Figure 4. Color POV-Ray-rendered ORTEP III drawing of m-xylene derived complex 10b (50% probability level; selected hydrogen atoms and secondary occupancies of disordered atoms omitted for clarity).

Figure 5. Color POV-Ray-rendered ORTEP III drawing of p-xylene derived rhodium complex 10c (50% probability level, selected hydrogen atoms omitted for clarity). Figure 3. Color POV-Ray-rendered ORTEP III drawing of o-xylenederived rhodium(III) complex 10a (50% probability level, selected hydrogen atoms and secondary occupancies of disordered atoms omitted for clarity). Only one of two crystallographically independent molecules is shown.

illustrated by the overlay of structures of each isomer, which were generated by a least-squares fit of the Rh, C21, N22, N23, N24, and C2c atoms (Figure 6). No significance beyond crystal-packing forces is attributed to the differing orientations C

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phenyltolylporphyrinato)rhodium(III).40 These new structures add to the very limited repertoire of metalated porphyrinoids containing a benzyl ligand. A search of the CSD returned only seven such structures,41 of which three are the aforementioned rhodium complexes39,40 and three others are tetra-p-tolylporphyrinatoiridium complexes.42 The remaining structure is an unusual eight-coordinate zirconium complex.43 When reactions with 5b, [Rh(CO)2Cl]2, and xylenes were carried out for shorter periods of time and the crude product was run through a grade-3 basic alumina column with acetone− toluene mixtures, low yields of alternative product 10d (Scheme 4) with an appended acetone unit were noted. It

Figure 6. Mercury-rendered overlay of nonhydrogen atoms of structures of 10a (red), 10b (green), and 10c (blue).

Scheme 4. Synthesis of Rhodium Complexes Derived from Methyl Ketones

of the methylbenzyl ligands. The p-methylbenzyl isomer, 10c, has a well-ordered structure with the p-methylbenzyl group roughly bisecting the trans pyrrolic unit (Figure 5). The mmethylbenzyl isomer, 10b, has the methyl group situated roughly over a meso carbon atom and exhibits 180° flip disorder about the C25−C26 axis (Figure 4). Evidently, optimal packing for the o-methylbenzyl isomer, 10a, is more complex (Figure 3). In addition to 180° flip disorder about the C25−C26 axis, other segments of the molecule display disordered packing. More remarkably, the structure includes two-molecule translational modulation, where the pseudotranslation between the two crystallographically independent molecules arises from slightly different atomic positions and markedly different relative occupancies of the pseudotranslationally related disordered parts. Refinement details regarding modeling of the modulation are described in the Supporting Information. Aside from the orientation of the methylbenzyl moieties, all three structures display remarkably similar corresponding bond lengths and angles for all framework atoms. In fact, all corresponding framework bond lengths between structures are the same within error (e.g., the C2−C2a bond lengths are the same for 10a−c). The organic bond parameters were found by Mogul to be generally typical.36 As expected, all three structures gave pyrrolic Cβ−Cβ bond lengths about 0.1 Å shorter than the adjacent Cα−Cβ bond lengths, indicating that the Cβ−Cβ units are somewhat isolated from the rest of the macrocycle’s π systems. In common with the six other metalated azuliporphyrinoid structures that we have reported,14,24,26,37,38 all the C−C bond lengths of the azulene’s cyclopentadienyl rings are rather distended with lengths between 1.42 and 1.45 Å, suggesting that they all have significant single-bond character. The small deviations of the 29 atoms comprising each azuliporphyrinoid framework from the planes defined by Rh, C21, N22, N23, and N24 quantify the planar nature of the porphyrinoid ligands. For example, in 10b, the root-mean-square distance is 0.21 Å with the azulene C2b (0.474 Å), C2c (0.594 Å), and C3b (0.507 Å) atoms being farthest from the plane. In each complex, the rhodium(III) ion is situated in a square plane defined by C21, N22, N23, and N24 but is slightly off-center from the macrocylic cavity because of the Rh−N23 bond lengths being 0.11 Å longer than the corresponding Rh−C21 bond lengths. In each complex, the methylbenzyl ligands occupy a fifthcoordination site, thereby placing the metal centers in distinctly square pyramidal coordination environments. The 2.07 Å (in 10a and 10b) and 2.06 Å (in 10c) Rh−C25 bond lengths are as expected and very similar to the corresponding 2.09 Å bond in (4-tert-butylbenzyl)-(tetra-p-tolylporphyrinato)-rhodium(III),39 2.06 Å bond in (4-fluorobenzyl)-(tetra-p-tolylporphyrinato)rhodium(III),39 and 2.06 Å bond in (4-nitrobenzyl)-(tetra-

was hypothesized that intermediary rhodium(III) species 11 (possibly a cationic species with no axial ligand X) was formed initially and that this reacted with the acetone to give 10d (Scheme 4). To avoid the formation of xylene derivatives, 5b and [Rh(CO)2Cl]2 were reacted in refluxing chlorobenzene and then treated with acetone, but only trace amounts of 10d were isolated. Better results were obtained when the reaction was carried out in refluxing acetonitrile, but only low yields of 10d were obtained. Because 10d was originally observed when the products were being purified by column chromatography on basic alumina, we speculated that a basic catalyst was required to promote the reaction. The crude intermediate from the reaction in acetonitrile was taken up in a mixture of toluene and acetone and stirred with basic alumina for 2 h. After workup and purification by column chromatography, 10d was isolated in >60% yield. The acetone derivative gave spectroscopic properties similar to those of 10a−c. The rhodium−CH2 unit gave a doublet (J = 4.2 Hz) at −3.15 ppm, whereas the remaining methyl group on the acetone fragment gave a 3H singlet at −1.25 ppm. In the 13C NMR spectrum, the Rh−CH2 gave a doublet at 6.9 ppm, whereas the carbonyl group was observed at 207 ppm. The low solubility of the sample did not allow internal C−Rh resonance to be identified in this solvent. However, in d5-pyridine a doublet (1JRh−C = 29.5 Hz) was identified for this unit at 197.0 ppm. The identity of 10d was further confirmed by high-resolution mass spectrometry, which gave a molecular ion at m/z 725.2838 (m/z calculated for C42H48N3ORh: 725.2847). D

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spectroscopy. 2D experiments were carried out using standard software. High-resolution mass spectra (HRMS) were carried out using a double-focusing magnetic sector instrument. 1H and 13C NMR spectra for all new compounds are reported in the Supporting Information. o-Xylene-Derived Rhodium(III) Azuliporphyrin 10a. tertButylazuliporphyrin 5b (20.0 mg, 0.0353 mmol) was dissolved in anhydrous o-xylene (40 mL). [Rh(CO)2Cl]2 (13.7 mg, 0.035 mmol) was added, and nitrogen was bubbled through the solution for 5 min. The mixture was stirred under reflux for 2 days. The solvent was removed under reduced pressure, and the residue was run through a grade-3 basic alumina column eluting with dichloromethane. Further purification on grade-2 basic alumina, eluting with dichloromethane, gave the product as a deep maroon band, and following evaporation of the solvent, the rhodium(III) complex (18.4 mg, 0.024 mmol, 67%) was obtained as a dark solid. A sample was recrystallized from chloroform−hexanes to give dark purple crystals. mp: >300 °C; UV− vis (CHCl3): λmax nm (log ε) 377 (4.78), 440 (4.45), 463 (4.50), 535 (4.53), 625 (sh, 4.04), 683 (sh, 3.88), 778 (sh, 3.35); 1H NMR (500 MHz, CDCl3, δ): −1.88 (2H, d, 2JRh−H = 3.8 Hz, Rh−CH2), −0.31 (3H, s, 2′-CH3), 1.56 (9H, s, t-Bu), 1.59 (6H, t, J = 7.6 Hz), 1.62 (6H, t, J = 7.6 Hz, 4 × CH2CH3), 3.13 (6H, s, 7,18-CH3), 3.28−3.49 (8H, m, 4 × CH2CH3), 3.52 (1H, d, J = 8.0 Hz, 6′-H), 5.76−5.79 (2H, m, 3′,5′-H), 6.22 (1H, dt, J = 1.2, 7.3 Hz, 4′-H), 7.55 (2H, d, J = 10.9 Hz, 22,32-H), 8.42 (2H, s, 10,15-H), 8.83 (2H, d, J = 10.9 Hz, 21,31-H), 9.07 (2H, s, 5,20-H); 13C NMR (125 MHz, 333 K, d5-pyridine, δ): 5.6 (Rh−CH2, d, 1JRh−C = 25.6 Hz), 10.9 (7,18-CH3), 16.7 (2 × CH2CH3), 17.7 (2′-CH3), 17.8 (2 × CH2CH3), 19.3 (2 × CH2CH3), 19.7 (2 × CH2CH3), 31.1 (C(CH3)3), 38.3 (C(CH3)3), 96.0 (10,15CH), 109.7 (5,20-CH), 121.3 (4′-CH), 123.4 (aryl-CH), 126.6 (21,31CH), 127.8 (aryl CH), 128.2 (6′-CH), 132.7, 135.3 (22,32-CH), 136.9, 140.8, 143.4, 144.1, 146.5, 148.1, 150.8, 155.5, 158.6, 200.6 (21-C, d, 1 JRh−C = 31.5 Hz); HR-MS (ESI-MS) calcd for C48H52N3Rh: 773.3211, found: 773.3198 (accuracy 1.7 ppm). m-Xylene-Derived Rhodium(III) Azuliporphyrin 10b. tertButylazuliporphyrin 5b (20.0 mg, 0.0353 mmol), [Rh(CO)2Cl]2 (13.7 mg, 0.035 mmol), and m-xylene (40 mL) were reacted under the foregoing conditions to give rhodium(III) derivative 10b (17.0 mg, 0.022 mmol, 62%) as a dark solid. mp: >300 °C; UV−vis (CHCl3): λmax nm (log ε) 377 (4.69), 440 (4.38), 462 (4.43), 533 (4.44), 624 (sh, 3.97), 686 (sh, 3.80), 779 (sh, 3.29); 1H NMR (500 MHz, d5pyridine, δ): −1.96 (2H, br d, 2JRh−H = 2.7 Hz, Rh−CH2), 1.41 (9H, s, t-Bu), 1.66−1.73 (12H, 2 overlapping triplets, 4 × CH2CH3), 1.82 (3H, s, 3′-CH3), 3.15 (6H, s, 7,18-CH3), 3.38−3.55 (8H, m, 4 × CH2CH3), 4.11 (1H, s, 2′-H), 4.18 (1H, d, J = 7.6 Hz, 6′-H), 6.11 (1H, t, J = 7.4 Hz, 5′-H), 6.26 (1H, d, J = 7.4 Hz, 4′-H), 7.35 (2H, d, J = 10.5 Hz, 22,32-H), 8.60 (2H, s, 10,15-H), 8.74 (2H, d, J = 10.5 Hz, 21,31-H), 9.26 (2H, s, 5,20-H); 13C NMR (125 MHz, d5-pyridine, 333 K, δ): 10.5 (Rh−CH2, d, 1JRh−C = 25.0 Hz), 10.8 (7,18-CH3), 16.7 (2 × CH2CH3), 17.8 (2 × CH2CH3), 19.4 (2 × CH2CH3), 19.7 (2 × CH2CH3), 21.2 (3′-CH3), 31.1 (C(CH3)3), 38.3 (C(CH3)3), 95.7 (10,15-CH), 109.5 (5,20-CH), 121.9 (4′-CH), 123.1 (6′-CH), 125.6 (5′-CH), 126.5 (21,31-CH), 126.6 (4′-CH), 127.0, 134.1 (22,32-CH), 136.9, 140.8, 143.3, 143.9, 147.9, 150.6, 155.5, 158.5, 200.9 (21-C, d, 1 JRh−C = 31.4 Hz); HR-MS (ESI-MS) calcd for C48H52N3Rh: 773.3211, found: 773.3202 (accuracy 1.1 ppm). p-Xylene-Derived Rhodium(III) Azuliporphyrin 10c. tertButylazuliporphyrin 5b (20.0 mg, 0.0353 mmol), [Rh(CO)2Cl]2 (13.7 mg, 0.035 mmol), and p-xylene (40 mL) were reacted under the foregoing conditions to give 10c (18.3 mg, 0.0235 mmol, 67%) as a dark solid. mp: >300 °C; UV−vis (CHCl3): λmax nm (log ε) 377 (4.62), 439 (4.33), 462 (4.36), 533 (4.36), 626 (sh, 3.91), 684 (sh, 3.75), 781 (sh, 3.29); 1H NMR (500 MHz, d5-pyridine, δ): −1.92 (2H, br d, 2JRh−H = 2.6 Hz, Rh−CH2), 1.41 (9H, s, t-Bu), 1.66−1.71 (12H, 2 overlapping triplets, 4 × CH2CH3), 1.84 (3H, s, 4′-CH3), 3.15 (6H, s, 7,18-CH3), 3.32−3.56 (8H, m, 4 × CH2CH3), 4.27 (2H, d, J = 7.7 Hz, 3′,5′-H), 6.01 (1H, d, J = 7.7 Hz, 2′,6′-H), 7.35 (2H, d, J = 10.7 Hz, 22,32-H), 8.56 (2H, s, 10,15-H), 8.75 (2H, d, J = 10.7 Hz, 21,31-H), 9.28 (2H, s, 5,20-H); 13C NMR (125 MHz, d5-pyridine, 333 K, δ): 10.0 (Rh−CH2, d, 1JRh−C = 25.0 Hz), 10.8 (7,18-CH3), 16.7 (2 ×

Attempts to react the intermediate with acetophenone under the same conditions gave low yields (300 °C; UV−vis (CHCl3): λmax nm (log ε) 371 (4.75), 448 (4.53), 527 (4.36), 623 (sh, 4.03), 676 (sh, 3.94), 753 (sh, 3.47); 1H NMR (500 MHz, CDCl3, δ): −3.15 (2H, d, 2JRh−H = 4.2 Hz, Rh−CH2), −1.25 (3H, s, C(O)CH3), 1.59 (9H, s, t-Bu), 1.64 (6H, t, J = 7.7 Hz), 1.71 (6H, t, J = 7.7 Hz, 4 × CH2CH3), 3.13 (6H, s, 7,18CH3), 3.48−3.59 (8H, m, 4 × CH2CH3), 7.64 (2H, d, J = 10.8 Hz, 22,32-H), 8.72 (2H, s, 10,15-H), 8.83 (2H, d, J = 10.8 Hz, 21,31-H), 9.06 (2H, s, 5,20-H); 1H NMR (500 MHz, d5-pyridine, δ): −2.59 (2H, br d, 2JRh−H = 2.6 Hz, Rh−CH2), −0.57 (3H, s, C(O)CH3), 1.41 (9H, s, t-Bu), 1.67 (6H, t, J = 7.6 Hz), 1.72 (6H, t, J = 7.6 Hz, 4 × CH2CH3), 3.16 (6H, s, 7,18-CH3), 3.49−3.58 (8H, m, 4 × CH2CH3), 7.39 (2H, d, J = 10.8 Hz, 22,32-H), 8.78 (2H, d, J = 10.8 Hz, 21,31-H), 8.84 (2H, s, 10,15-H), 9.42 (2H, s, 5,20-H); 13C NMR (125 MHz, CDCl3, δ): 6.9 (Rh−CH2, d, 1JRh−C = 31.6 Hz), 11.1 (7,18-CH3), 16.6 (2 × CH2CH3), 17.6 (2 × CH2CH3), 19.4 (2 × CH2CH3), 19.7 (2 × CH2CH3), 25.5 (C(O)CH3), 31.7 (C(CH3)3), 38.8 (C(CH3)3), 97.5 (10,15-CH), 110.2 (5,20-CH), 127.38 (22,32-CH), 127.45, 134.4 (21,31-CH), 137.3, 140.8, 143.4, 143.5, 147.6, 150.5, 154.2, 159.8, 207.0 (CO); 13C NMR (125 MHz, d5-pyridine, δ): 10.9 (7,18CH3), 14.4 (Rh−CH2, d, 1JRh−C = 31.6 Hz), 16.9 (2 × CH2CH3), 17.9 (2 × CH2CH3), 19.4 (2 × CH2CH3), 19.7 (2 × CH2CH3), 26.8 (C(O)CH3), 31.0 (C(CH3)3), 38.2 (C(CH3)3), 95.8 (10,15-CH), 109.8 (5,20-CH), 127.6 (22,32-CH), 135.6 (21,31-CH), 137.5, 141.1, 143.6, 143.7, 147.6, 155.5, 159.6, 197.0 (21-C, d, 1JRh−C = 29.5 Hz), 210.4 (CO); HR-MS (ESI-MS) calcd for C42H48N3ORh: 725.2847, found: 725.2838 (accuracy 1.2 ppm).

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X-ray diffractometer and Dr. Mathias Zeller of Youngstown State University for useful discussion.

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic data for 10a−c in CIF format, experimental crystallographic details, and copies of selected UV−vis, 1H NMR, 1H−1H COSY, HSQC, DEPT-135, and 13C NMR spectra are provided. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00433.

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REFERENCES

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Science Foundation (NSF) under grant no. CHE-1212691 and the Petroleum Research Fund, administered by the American Chemical Society. We also thank NSF (CHE-1039689) for funding the F

DOI: 10.1021/acs.organomet.5b00433 Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.5b00433 Organometallics XXXX, XXX, XXX−XXX