ARTICLE pubs.acs.org/Organometallics
Photochemistry of π- and n-Donor Bifunctional Monosubstituted Derivatives of Cyclopentadienylmanganese Tricarbonyl Complexes Containing an Allyl Group and Photo- and Thermoisomerization of the Corresponding Dicarbonyl Chelates Elena S. Kelbysheva, Mariam G. Ezernitskaya, Tatyana V. Strelkova, Yurii A. Borisov, Aleksandr F. Smol’yakov, Zoya A. Starikova, Fedor M. Dolgushin, Aleksey N. Rodionov, Boris V. Lokshin, and Nikolay M. Loim* A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov street, GSP-1, 119991 Moscow, Russia
bS Supporting Information ABSTRACT:
Photochemical properties of a series of bifunctional monosubstituted derivatives of cymantrene containing a C-, N-, or O-bound πallyl group, along with n-donating carbamate, amide, or pyridine fragments were investigated. The results obtained demonstrate that the nature and thermodynamic stability of the cyclopentadienylmanganese dicarbonyl chelates derived from bifunctional monosubstituted cymantrene derivatives depend substantially on both the nature of the functional groups and on their position in the substituent at the Cp ring. Thus, for the six-membered chelates, the thermodynamic stability increases in the series carbamates < amides < pyridines < olefins. Some of the dicarbonyl chelates studied form reversible photochromic systems due to linkage isomerization between different donating groups of the bifunctional substituent and the manganese atom with a wide range of times of thermal isomerization.
’ INTRODUCTION Photochemical ligand exchange in cyclopentadienylmanganese tricarbonyl (cymantrene) derivatives is one of the most important methods for the synthesis of mono- and binuclear compounds containing n- and π-donor ligands at the manganese atom.1 When the cymantrene derivatives have fragments in the cyclopentadienyl ring that are able to coordinate to the manganese atom, their photolysis gives dicarbonyl intramolecular chelates having different thermodynamic and kinetic stability.2,3a In recent years, it has been reported that these types of semilabile complexes are capable of forming photochromic systems due to reversible intra- or intermolecular ligand exchange processes and linkage isomerization of chelating bifunctional ligands with the metal atom.3 With the aim of searching for new compounds exhibiting photochromic properties, in this paper we for the first time report the synthesis of novel monosubstituted bifunctional derivatives of cymantrene, 17 (Figure 1), and a study of their photochemical behavior. The general feature of these cymantrene derivatives is the presence of the π-donating allyl fragment in the side chain of a substituent, along with n-donating carbamate, amide, or pyridine groups that can play the role of ligands in metal complexes. The influence of the nature of ligands and their r 2011 American Chemical Society
Figure 1. Compounds studied: 4, R = OBu-t, R0 = Me; 5, R = R0 = Me; 6, R = OBu-t, R0 = H; 7, R = Me, R0 = H.
position in the substituent on the type and photochromic properties of the chelated dicarbonyl photoproducts formed is discussed. Received: May 17, 2011 Published: July 26, 2011 4342
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Figure 2. Molecular structure of tricarbonyl complexes 5 and 7 (thermal ellipsoids drawn at the 50% probability level). Selected bond lengths (Å): for 5, Mn(1)C(1) = 2.1621(14), Mn(1)C(6) = 1.793(2), C(1)C(9) = 1.516(2), C(9)N(1) = 1.480(2), N(1)C(14) = 1.359(2), C(6)O(1) = 1.146(2); for 7, Mn(1)C(1) = 2.154(1), Mn(1)C(6) = 1.796(1), C(1)C(9) = 1.506(1), C(9)N(1) = 1.464(1), N(1)C(13) = 1.356(1), C(6)O(1) = 1.149(1).
Scheme 1
Scheme 2
’ RESULTS AND DISCUSSION Compounds 1 and 2 were prepared by metalation of cymantrene and R-picoline with n-BuLi and the subsequent reaction of their organolithium derivatives with 2-formylpyridine and cymantrenecarbaldehyde,4 respectively, followed by alkylation of secondary cymantrenylcarbinols formed with allyl bromide. The synthesis of 3 was performed by metalation of N-Boc-Nmethyl-1-aminoethylcymantrene3d with n-BuLi at 70 °C in THF and quenching of the lithium derivative with allyl bromide. Compounds 47 were prepared by alkylation of the corresponding acetamides and tert-butylcarbamates of aminomethyl- and 1-aminoethylcymantrenes3d,4 with allyl bromide in the presence of NaH in DMF. Compounds 5 and 7 were characterized by X-ray diffraction (Figure 2). These amides in solution exist as a mixture of two rotamers with respect to the partial double NCO bond in a ratio of 1:5; in the case of carbamates 4 and 6, approximately equal amounts of isomers are observed at room temperature, and their coalescence temperature is 340 K. Both racemic 1-aminoethylcymantrene and its optically pure R enantiomer were used for the synthesis of chiral compounds 4 and 5.4,5 It was found earlier that photolysis of the allyl ether of cymantrenylcarbinol 8 gives the dicarbonyl chelate 9 with a Mnolefin bond (Scheme 1).6 In the case of the bifunctional compound 1, where there are both allyl and pyridine groups in the substituent, photolysis
of its hexane or benzene solutions mainly gives chelate 10 with an MnN bond, whereas the yield of olefin isomer 11 does not exceed 14% (Scheme 2). IR and 1H NMR data for these chelates match the literature data.1j,3c,3d,6 Chelate 10 was isolated, and its structure was also confirmed by X-ray crystallography (Figure 3). IR and 1H NMR monitoring of this reaction indicates that full conversion of 1 occurs, but the ratio of 10 to 11 is constant and equal to 1:0.16 at all irradiation stages. Therefore, the formation of each chelate occurs kinetically independently and the chelates do not seem to isomerize to one another. Actually, upon irradiation of benzene, hexane, or THF solutions of the isolated chelate 10 for 1040 min, no formation of chelate 11 was detected; only slow degradation of 10 to unidentified products was observed. However, under irradiation of a mixture of 10 and 11 in THF, the intensities of the bands assigned to 11 at 1964 and 1906 cm1 decrease and those of 10 at 1925 and 1857 cm1 grow parallel. Thus, irreversible photoisomerization of the olefin chelate 11 into 10 takes place. In a dark process, no isomerization of 10 into 11 was observed for 72 h. The geometry and full energy of chelates was calculated by B3LYP/6-31G* methods7 (Table 1 and the Supporting Information). The geometry calculated is in agreement with the X-ray structure for chelate 10 (Supporting Information). 4343
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Figure 3. Molecular structure of dicarbonyl chelates 10 and 12a (thermal ellipsoids drawn at the 50% probability level). Selected bond lengths (Å); for 10A, Mn(1)C(1) = 2.129(2), Mn(1)C(6) = 1.766(2), Mn(1)N(1) = 2.022(1), C(1)C(11) = 1.502(2), C(12)N(1) = 1.355(2), N(1)C(16) = 1.353(2), C(6)O(1) = 1.164(2); for 13aA, Mn(1)C(1) = 2.162(3), Mn(1)C(6) = 1.765(3), Mn(1)C(8) = 2.139(3), Mn(1)C(9) = 2.148(3), C(1)C(11) = 1.495(4), C(11)O(3) = 1.431(3), N(1)C(13) = 1.354(4), N(1)C(17) = 1.341(4), C(6)O(1) = 1.159(3).
Table 1. Calculated Energies of the Starting Compounds and the Photoproducts E, au
ΔE, kcal/mola
1 10
2162.8043 2049.4772
0.0
11
2049.4728
2.8
2
2202.1070
12
2088.7903
1.7
13a (1S,R/1R,S)
2088.7930
0.0
13a (1R,R/1S,S)
2088.7853
4.8
13t (1S,R/1R,S)
2088.7861
4.3
13t (1R,R/1S,S) 4
2088.7856 2281.0106
4.6
17
2167.6591
2.3
18
2167.6628
0.0
5
2087.8449
19
1974.4783
9.8
20
1974.4940
0.0
6
2241.7081
21 21ab
2128.3616 2128.3446
7
2048.5337
22
1935.1851
0.0
23
1935.1693
9.9
compd
0.0 10.7
ΔE is the relative energy of isomeric chelates. b The carbamate isomer of chelate 21. a
The increase in the number of bonds between the Cp cycle and the pyridine nitrogen atom from three in 1 to four in 2 significantly changes the picture of photolysis. Irradiation of 2 in hexane, benzene, or THF up to 6070% conversion results in simultaneous formation of the isomeric chelates 12 and 13 in a ratio of 1:2, respectively (Scheme 3). Thus, the formation of the
Scheme 3
six-membered pyridine chelate 12 from 2 is kinetically less favorable than that of the five-membered chelate 10 in the case of photolysis of 1. Extended irradiation of solutions of 2 up to its full conversion leads to formation of a mixture of 12 and 13 in a ratio of 1:1. That means that photoinduced linkage isomerization of chelate 13 to chelate 12 takes place. Olefin chelate 13, having chiral centers at the carbon atom bound to the Cp ring and the methyne carbon of the allyl group, is a 3:1 mixture of the two stereoisomers 13a,b, which have close but not identical spectral characteristics. Both stereoisomers turned out to be stable compounds and were isolated, whereas pyridine chelate 12, in contrast to 10, rapidly decomposes in the course of separation. Irradiation of a 13a,b mixture or each isomer separately results in a decrease of the amount of 13 and formation of 12, which also exists as a mixture of the two stereoisomers 12a,b (according to IR in hexane, Figure 4). A dark reaction of the mixture of chelates 12 and 13 formed in a ratio of 3:1, respectively, results in thermal isomerization of dicarbonyl pyridine complex 12 to the 4344
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Figure 4. IR spectral changes for a 10 mM solution of a mixture of 13b and 13a in a ratio of ca. 9:1 (according to NMR, Figure 5) in hexane: (a) before UV irradiation; (b) after 2 min irradiation; (c) after 4 min irradiation; (d) 72 h without irradiation (dark reaction).
Figure 5. Fragments of 1H NMR spectra at 27 °C in benzene-d6: (a) 13a; (b) 13b (containing ca. 10% 13a); (c) after 2 months of a dark reaction of neat 13b at room temperature.
thermodynamically more stable olefin chelates 13 with a halfconversion time of 150 h. Monitoring of the photolysis of 13a or 13b in benzene, hexane, or THF by IR and 1H NMR methods revealed reversible phototransformations between these olefin chelates occurring parallel to their isomerization to 12. Moreover, thermal isomerization of chelate 13b to isomer 13a takes place not only in solution (Figure 4) but also without solvent (Figure 5). The dark reaction of a chelate mixture in a closed system when CO removal is prohibited, along with isomerization, gives simultaneously the parent complex 2 (Scheme 3). Thus, isomeric chelates 12 (λmax 434 nm) and 13 (λmax 330 nm) are components of a reversible photochromic system. Estimation of the quantum yield for the photoisomerization of 13 into 12 relative to ϕ 0.96 obtained for the photolysis of 1-(tert-butyloxycarbonylamino)ethylcymantrene (14)3d gives a value of about 0.8. The molecular structure of the chelate (1S,R/1R,S)-13a was established by X-ray analysis (Figure 3). Close geometrical parameters were obtained for the optimized structure of this
Figure 6. Optimized structures of isomers of compound 13. The distances are given in Å.
diastereomer calculated by the DFT method (Table 1 and Figure 6). In both cases, the coordinated oxyallyl group is 4345
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Organometallics Scheme 4
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Scheme 6
Scheme 5
arranged in the cisoid conformation with a torsional angle CH2dCHCH2O of ca. 30°. Since isomer 13b is a noncrystallizing liquid, we performed the DFT calculations of geometry and energies for the most probable stereoisomers of 13a. As a result, three structures were revealed whose the full energies are 4.334.83 kcal/mol higher than that for (1S,R/1R,S)-13a: the 1S,S/1R,R diastereomer of 13a and diastereomers (1R,S/1S,R)13t and (1S,S/1R,R)-13t with the transoid conformation of the oxyallyl group with a torsional angle CH2dCHCH2O of about 130° (Table 1, Figure 6). Although (1R,S/1S,R)-13t proved to be the most stable among the three calculated structures, the energy difference between them is only 0.5 kcal/mol. This does not permit us to draw a conclusion as to the structure of 13b. Nevertheless, significant differences in the δ values for diastereotopic protons of the oxyallyl OCH2 fragment in the 1H NMR spectra of chelates 13a (3.01 and 4.29 ppm) and 13b (1.98 and 4.26 ppm) allow us to suppose that, most probably, 13b has a structure close to that of (1R,S/1S,R)-13t. Recently we found that photolysis of tert-butylcarbamates of primary and secondary 1-aminoalkylcymantrenes give dicarbonyl chelate complexes. They are thermodynamically stable in solution and in a closed system form reversible photochromic pairs with the corresponding starting tricarbonyl compound.3d Photolysis of carbamate 3 containing the allyl group at the C1 atom of the substituent in benzene or hexane preferably gives the carbamate chelate 15 (the ratio of 15 to 16 was 5:1 at irradiation of 3 in benzene up to 95% conversion). However, under dark conditions, 15 slowly (in 34 h) and fully isomerizes into the thermodynamically more stable olefin chelate 16; in a closed system, it concurrently reacts with carbon monoxide to form the starting tricarbonyl complex 3 (Scheme 4). IR and NMR
Figure 7. Molecular structure of dicarbonyl chelates 21 and 22 (thermal ellipsoids drawn at the 50% probability level). Selected bond lengths (Å): for 21, Mn(1)C(1) = 2.154(1), Mn(1)C(6) = 1.784(1), Mn(1)C(8) = 2.153(1), Mn(1)C(9) = 2.171(1), C(1) C(11) = 1.496(2), C(11)N(1) = 1.458(2), N(1)C(12) = 1.361(2), C(8)C(9) = 1.397(2), C(6)O(1) = 1.150(2); for 22, Mn(1)C(1) = 2.172(2), Mn(1)C(6) = 1.773(2), Mn(1)C(8) = 2.145(3), Mn(1)C(9) = 2.157(3), C(1)C(11) = 1.502(4), C(11)N(1) = 1.450(5), N(1)C(12) = 1.364(3), C(8)C(9) = 1.404(4), C(6) O(1) = 1.156(3).
monitoring of photolysis of a hexane solution of chelate 16 under monochromatic irradiation at λmax 365 nm shows no isomerization of 16 into 15. This means that chelate 15 is a kinetic product of the photolysis of 3. A different picture is observed for photolysis of N-allylcarbamate 4, where the number of bonds between the Cp ring and vinyl group is increased from two in 3 to three in 4. Irradiation of 4 in benzene or hexane results in simultaneous formation of both 4346
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Table 2. UVVis Characteristics of Photochromic Pairs in Benzene photochromic pair
13/12
16/15
18/17
20/19
22/23
λmax, nm
330/434
326/503
341/516
331/509
333/519
τ1/2 for dark reacn, min
9 103
180240
3
5
5
carbamate 17 and olefin 18 dicarbonyl chelates in the ratio 1:3, respectively, at 2530% conversion of 4 (Scheme 5). However, under dark conditions, already in the course of IR, 1H NMR, and UVvis monitoring of the reaction mixtures, the content of chelate 17 gradually decreases up to full isomerization of 17 into the thermodynamically more stable chelate 18 (Table 1). Thus, complete conversion of 4 results in chelate 18 as the sole product. Further irradiation of the solution obtained of 18 results in the following changes in the IR spectra in theν(MCO) region: the intensities of the bands at 1975 and 1915 cm1 of chelate 18 decrease while those at 1945 and 1869 cm1 corresponding to chelate 17 appear, which indicates photoinduced linkage isomerization of chelate 18 to 17. After irradiation ceases, the latter transforms back to 18 with τ1/2 = 3 min. The starting concentration of olefin chelate 18 practically remains the same after three to four cycles of the irradiationdark reactions. Therefore, dicarbonyl chelates 17 (λmax 516 nm) and 18 (λmax 341 nm) form a reversible photochromic system due to linkage isomerization between different donating groups of the bifunctional substituent and the manganese atom (Scheme 5). When the reaction was performed in a closed system without removal of carbon monoxide, neither chelate was virtually transformed into the starting tricarbonyl complex 4. Photolysis of N-allylamide 5 (Scheme 5) predominantly gives the crimson red 19 (λmax 509 nm) in the early stages of the reaction. The ratio of 19 to 20 was 5:1 at ca. 25% convertion of 5 in benzene. However the amide chelate 19 fully thermally isomerizes into the yellow olefin chelate 20 (λmax 331 nm) for 30 min (τ1/2 5 min). Thus, full conversion of 5 results in chelate 20 as the single product. Obviously, the replacement of tertbutoxyl in 4 for the less bulky methyl in 5 makes the amide chelate 19 more kinetically stable than the carbamate chelate 17. Repeated photolysis of 20 gives dicarbonyl chelate 19 back. This means that there is also reversible photochromic transformation between chelates 20 and 19. While photolysis of 4 that contains the methyl group at the C-1 position of the substituent gives two dicarbonyl chelates, irradiation of allyl carbamate 6 in hexane, benzene, or THF gives the olefin chelate 21 only (Scheme 6, Figure 7). Under experimental conditions, this chelate is a thermo- and photostable compound. Photolysis of allylamide 7 in hexane (in contrast to photolysis of 5) exclusively gives olefin chelate 22 (Figure 7). However, irradiation of 7 in benzene or THF at room temperature results in both chelates: 22 and the amide isomer 23 in a ratio of 4:1, respectively. Moreover, at the first reaction stages (up to 2030% conversion of the tricarbonyl complex) and at a temperature below 10 °C, isomer 23 is the major kinetic product, which after several minutes (τ1/2 = 5 min) thermally isomerizes to 22. Repeated irradiation of a benzene solution of 22 (λmax 333 nm) results in its isomerization to chelate 23, having a crimson red color (λmax 519 nm), which in a dark reaction transforms into the starting chelate. Therefore, there is a reversible photochromic transformation between these chelates, the rate of thermal isomerization of 22 to 23 being temperature and solvent dependent. The results presented above demonstrate that the nature and thermodynamic stability of cyclopentadienylmanganese
dicarbonyl chelates derived from bifunctional monosubstituted cymantrene derivatives depend substantially on both the nature of functional groups and on their position in the substituent at the Cp ring. Thus, for the six-membered chelates, the thermodynamic stability increases in the series carbamates < amides < pyridines < olefins. Although amide and carbamate chelates are thermodynamically less stable, their predominant formation at the first stages indicates that they are kinetic products. This is probably associated with the greater spatial accessibility of the Mn atom in an intermediate coordinatively unsaturated dicarbonyl complex for the oxygen lone pair of the fragment OdCN of the substituent as compared to that for the bulky vinyl group. The presence of the methyl group at the C-1 position of the substituent substantially increases the kinetic stability of the carbamate and amide chelates and the duration of their isomerization to the olefin chelates. Thus, the design of functional groups in the substituent as well as solvent and temperature effects allowed us to obtain novel organometallic photochromic systems based on cymantrene derivatives 13, 16, 18, 20, and 22 with a wide range of times of thermal isomerization (Table 2). It is remarkable that, in these cases, in the presence of carbon oxide in a closed cell, reversible three-component photochromic systems are obtained due to transformation of dicarbonyl chelates to the parent tricarbonyl complexes 2, 4, 5, and 7, respectively. The structures of dicarbonyl chelates were established from analysis of IR, 1H and 13C NMR, and UVvis spectra, elemental analysis for isolated chelates, and X-ray studies for compounds 10, 13a, 21, and 22 (Figures 3 and 7). The IR spectrum of each chelated complex obtained has two ν(CO) bands in the range of 19801850 cm1. However, in case of chiral pyridine 12 and olefin chelates 16, 18, and 20 (except chelate 10) in hexane, these bands are split by two components of different intensities (Δν ≈ 4 cm1, Experimental Section and Figure 4). This splitting is probably associated with asymmetrical coordination of the functional groups in the substituent to the manganese atom to form the diastereomeric dicarbonyl complexes with a nonequivalent arrangement of the ligand carbonyl groups in two diastereomers. This type of coordination is observed in the X-ray structures of 13a, 21, and 22 and obtained in the optimized structures of the products of photolysis of 1 and 47. It also follows from the 1H and 13C NMR spectra of olefin chelates 21 and 22 formed from achiral tricarbonyl complexes 6 and 7, respectively. The 1H NMR spectra of the latter contain four two-proton signals from the protons in the R- and β-positions of the Cp ring and the methylene groups of the CpCH2 and NCH2 fragments. At the same time, the spectra of 21 and 22 display four one-proton signals from the protons of the Cp ring and two doublets (AB systems) from the prochiral protons of these CH2 groups. On going from the tricarbonyl complexes to the dicarbonyl chelates studied, the following changes were observed in the 13C NMR spectra: the number of signals from the carbon nuclei of the Cp ring increased from three to five, respectively, and in addition, two signals from the prochiral CO ligands were observed for chelates 21 and 22, whereas the spectra of complexes 6 and 7 had one signal. 4347
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Organometallics Formation of chelated complexes is accompanied by substantial and typical changes in the chemical shifts of proton and carbon nuclei for the functional groups participating in coordination to the manganese atom, as well as for the CO ligands. In contrast, the signals of the H and C nuclei for the second functional group that does not coordinate to manganese change insignificantly. In particular, in the 1H NMR spectra of olefin chelates in benzene, there are two broadened doublets in the range of 1.62.1 ppm from the cis and trans protons of the CH2 fragment of the coordinated CHdCH2 group and a complex multiplet in the range of 2.52.8 ppm from the proton of the CH fragment of the same group. In the case of pyridine chelates, there are three multiplets in the range of 5.76.5 ppm from the protons at the 3-, 4-, and 5-positions of the heterocycle. This picture allows us to reliably confirm the coordination type of chelates and unambiguously assign the majority of the signals in the NMR spectra of photolysis products. However, in the case of chelates 1520 containing the carbamate or amide group, full assignment of the signals in their 1H NMR spectra cannot be done because, as was mentioned above, these chelates are mixtures of diastereomers and/or geometrical isomers with respect to the partial double NCO bond. As a result, many signals overlap to give complex multiplet fragments in the spectra.
’ CONCLUSION With the aim of searching for new organometallic compounds exhibiting photochromic properties, we first report the synthesis of a series of monosubstituted bifunctional derivatives of cymantrene, 17, containing a C-, N-, or O-bound π-allyl group, along with n-donating carbamate, amide, or pyridine fragments, which can play the role of ligands in metal complexes. The different structures of these compounds provided an opportunity to elucidate the influence of the nature of ligands and their position in the substituent on the coordination type and photochromic properties of chelated dicarbonyl photoproducts formed. The structures of dicarbonyl chelates were established from the analysis of IR, 1H and 13C NMR, and UVvis spectra, elemental analysis for isolated chelates, and X-ray studies for compounds 10, 13a, 21, and 22. Furthermore, computed geometric parameters for the optimized structures and full energies of chelates as well as for tricarbonyl compounds 1, 2, and 47 were obtained by the DFT method. The study has shown that the nature and thermodynamic stability of cyclopentadienylmanganese dicarbonyl chelates derived from bifunctional monosubstituted cymantrene derivatives substantially depend on both the nature of functional groups and on their position in the substituent of the Cp ring. Thus, for the six-membered chelates, the thermodynamic stability increases in the series carbamates < amides < pyridines < olefins. Some of the dicarbonyl chelates studied form reversible photochromic systems due to linkage isomerization between different donating groups of the bifunctional substituent and the manganese atom with a wide range of times of thermal isomerization. ’ EXPERIMENTAL SECTION 1
H and 13C NMR spectra were measured on a Bruker Avance 400 (400.13 and 100.61 MHz, respectively) spectrometer. Chemical shifts δ were referenced to TMS in ppm using residual solvent protons as an internal standard. The signal assignment was performed by analogy with similar compounds.1j,3c,3d,6 If necessary, the signals in 1H NMR spectra were assigned using 2D COSY and NOESY experiments. IR spectra
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were recorded on a Magna 750-IR (Nicolet) IR Fourier spectrometer with a resolution of 2 cm1 in KBr cells. UVvis spectra were recorded on a Specord M-40 spectrophotometer. EI mass spectra were recorded on Kratos MS 890 and Finnigan POLARIS Q spectrometers at 70 eV, with the temperature of the ionization chamber being 250 °C. Specific rotation angles were measured using a Perkin-Elmer 341 polarimeter at a wavelength of 589 nm. Silica gel 60 (Merck) was used for column chromatography. Tetrahydrofuran (THF), hexane, and benzene were purified by conventional methods and distilled from sodium benzophenone ketyl under an argon atmosphere. The photochemical reactions were carried out using a Hereaus TQ 150 Hg immersion lamp. 2-Formylpyridine was purchased from Sigma-Aldrich Chemicals. 1-Allyloxy-1-pyrid-2-yl-1-cymantrenylmethane (1). (A) n-BuLi (1.6 M in hexane, 40 mL, 64 mmol) was added dropwise to a solution of cymantrene (10 g, 49 mmol) in dry THF (100 mL) under an argon atmosphere at 70 °C; after 40 min the reaction was quenched by 2-pyridylcarbaldehyde (7.0 mL. 73.3 mmol). Then the temperature was raised to 10 °C, the reaction mixture was poured into cold water (300 mL), and the products were extracted with CH2Cl2 (3 150 mL). The combined extracts were washed with water (2 100 mL) and brine (100 mL) and dried with Na2SO4. The yield of 1-pyrid-2-yl-1-cymantrenylmethanol (24) was 4 g (26%); mp 9293 °C (hexane). 1H NMR (acetone-d6): δ 4.81 (m, 1H, H-Cp), 4.89 (m, 1H, H-Cp), 5.12 (m, 1H, H-Cp), 5.21 (m, 1H, H-Cp). 5.57 (s, 1H, CH), 7.36 (ddd, J = 7.6, 4.8, 1.1 Hz, 1H, Py), 7.59 (ddd, J = 7.9, 1.8, 1.1 Hz, 1H, Py), 7.88 (ddd, J = 7.9, 7.6, 1.8 Hz, 1H, Py), 8.58 (br d, J = 4.8 Hz, 1H, Py). Anal. Calcd for C14H10MnNO4: C, 54.04; H, 3.24; N, 4.50;. Mn, 17.66. Found: C, 54.11; H, 3.15; N, 4.59; Mn, 17.40. (B) A solution of 24 (2 g, 6.4 mmol) in dry THF (50 mL) was added dropwise to a suspension of 60% sodium hydride (0.6 g, 15 mmol) at 0 °C under an argon atmosphere. Then the suspension was stirred for 15 min and allyl bromide (1.0 mL, 11.5 mmol) in dry THF (10 mL) was added through a septum. The solution was brought to room temperature and stirred for 3 h. The reaction mixture was quenched with 10% aqueous NH4Cl (50 mL), the layers were separated, and the aqueous layer was extracted with ethyl acetate (3 100 mL). The organic layers were combined, washed with brine (100 mL), and dried with Na2SO4. The solvent was removed under vacuum, and the product was isolated by column chromatography on silica gel (hexane/ethyl acetate 3/1). The yield of 1 (yellow oil) was 1.0 g (45%).1H NMR (benzene-d6): δ 3.74 (dd, J = 12.9, 5.5 Hz, 1H, OCH2), 3.79 (m, 1H, H-Cp), 3.83 (dd, J = 12.9, 4.9 Hz, 1H, OCH2), 3.88 (m, 1H, H-Cp), 4.64 (m, 1H, H-Cp), 4.68 (m, 1H, H-Cp), 5.03 (dd, J = 10.4, 2 Hz, 1H, dCH2), 5.17 (s, 1H, OCH), 5.21 (dd, J = 17.2, 2 Hz, 1H, dCH2), 5.78 (dddd, J = 17.2, 10.4, 5.5, and 4.9 Hz, 1H, dCH), 6.63 (dd, J = 7.6, 4.8 Hz, 1H, Py), 7.13 (ddd, J = 7.6, 7.9, and 1.5 Hz, 1H, Py), 7.38 (d, J = 7.9 Hz, 1H, Py), 8.39 (d, J = 5.0 Hz, 1H, Py). 13C NMR (benzene-d6): δ 71.13 (CHPy), 78.92 (CH2O), 80.33 (Cp), 82.21 (Cp), 84.36 (Cp), 85.24 (Cp), 105.92 (C1Cp), 117.37 (CH2d), 120.73 (C5Py), 123.44 (C3Py), 135.02 (CHd), 137.33 (C4Py), 149.80 (C6Py), 161.87 (C2Py), 226.03 ((CO)3). IR (benzene, cm1): ν (CO) 2020, 1935. UVvis (benzene, λ [nm]; ε [l/mol•cm]): 330; 230. Anal. Calcd for C17H14MnNO4: C, 58.13; H, 4.02; N, 3.99; Mn, 15.64. Found: C, 58.15; H, 4.09; N, 3.984; Mn, 15.59. 1-Allyloxy-2-pyrid-2-yl-1-cymantrenylethane (2). (A). n-BuLi (1.6 M in hexane, 40 mL, 64 mmol) was slowly added to a solution of freshly distilled 2-picoline (5 mL, 50 mmol) in dry THF (100 mL) under an argon atmosphere at 70 °C. Then the reaction mixture was equilibrated to 0 °C and cooled again to 30 °C and cymantrenylcarbaldehyde4 (11.6 g, 50 mmol) in 20 mL of dry THF was added dropwise. The reaction mixture was brought to room temperature and quenched with water (300 mL). The aqueous layer was extracted with CH2Cl2 (3 150 mL), and the organic layers were washed with water (2 100 mL) and brine (100 mL) and dried with Na2SO4. The solvent 4348
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Organometallics was removed under vacuum, and the residue was purified by column chromatography on silica gel (hexane/ethyl acetate 5/1). The yield of 1-hydroxy-1-(pyrid-2-ylmethyl)-1-cymantrenylmethane (25) was 3.7 g (23%); mp 6667 °C (hexane). 1H NMR (benzene-d6): δ 2.66 (br d, J = 14.2 Hz, 1H, CH2), 2.77 (dd, J = 14.2, 8.7 Hz, 1H, CH2), 3.92 (m, 1H, H-Cp), 3.95 (m, 1H, H-Cp), 4.46 (m, 1H, H-Cp), 4.58 (m, 1H, H-Cp), 4.66 (d, J = 8 Hz, 1H, OCH), 5.94 (br s, 1H, OH), 6.486.55 (m, 2H, Py), 6.94 (t, J = 7.7 Hz, 1H, Py), 8.08 (br d, 1H, Py). Anal. Calcd for C15H12MnNO4: C, 55.40; H, 3.72; N, 4.31; Mn, 16.89. Found: C, 55.24; H, 3.56; N, 4.18; Mn, 16.78. (B) Allylation of 25 (2.4 g, 7.4 mmol) was performed similarly to the preparation of 1 from 24. The yield of 2 (oil) was 1.0 g (37%). 1H NMR (benzene-d6): δ 2.91 (dd, J = 13.6, 5.6 Hz, 1H, CH2Py), 3.07 (dd, J = 13.6, 7.2 Hz, 1H, CH2Py), 3.79 (dm, J = 12.7 Hz, 1H, OCH2), 3.82 (m, 1H, H-Cp), 3.85 (m, 1H, H-Cp), 3.93 (dm, J = 12.7 Hz, 1H, OCH2), 4.09 (m, 1H, H-Cp), 4.47 (m, 1H, H-Cp), 4.58 (dd, J = 5.6, 7.2 Hz, 1H, CHO), 4.96 (dm, J = 10.4 Hz, 1H, dCH2), 5.14 (dm, J = 17.2 Hz, 1H, dCH2), 5.71 (ddt, J = 17.2, 10.4, 5.3 Hz, 1H, dCH), 6.59 (dd, J = 7.6, 4 Hz, 1H, Py), 6.72 (d, J = 7.6 Hz, 1H, Py), 6.99 (t, J = 7.6 Hz, 1H, Py), 8.42 (br.d, J = 4 Hz, 1H, Py). 13C NMR (benzene-d6): δ 46.47 (CH2Py), 71.18 (CH2O), 75.17 (CHO), 80.02 (Cp), 81.63 (Cp), 82.41 (Cp), 83.42 (Cp), 106.65 (C1Cp), 116.49 (CH2d), 121.45 (Py), 124.40 (Py), 135.03 (CHd), 135.74 (Py), 149.58 (Py), 158.42 (C2Py), 225.55 (3CO). IR (hexane, cm1): ν(CO) 2005, 1945. UVvis (benzene; λ, nm; ε, L/(mol cm)): 333; 1063. Anal. Calcd for C18H16MnNO4: C, 59.19; H, 4.42; N, 3.84; Mn, 15.04. Found: C, 59.31; H, 4.45; N, 3.67; Mn, 15.00. N-Boc-N-methyl-1-allyl-1-cymantrenylethylamine (3). n-BuLi (1.6 M in hexane, 7 mL, 11.2 mmol) was added dropwise to a solution of N-Boc-N-methyl-1-cymantrenylethylamine3d (2 g, 5.5 mmol) in dry THF (50 mL) under an argon atmosphere at 70 °C, and the mixture was kept at this temperature for 30 min. Then allyl bromide (1 mL, 11.1 mmol) was added. The reaction mixture was brought to 0 °C, stirred for 90 min, and poured into cold water (150 mL). The products were extracted with ether (3 150 mL), and the organic layers were dried over Na2SO4. The solvent was removed under vacuum, and the brown oil was isolated. The product was purified by column chromatography on silica gel (hexane/ ethyl acetate 3/1). The yield was 1.4 g (64%). 1H NMR (benzene-d6): δ 1.27 (s, 3H, CCH3), 1.33 (s, 9H, CMe3), 2.11 (dd, J = 13.5, 7.7 Hz, 1H, CH2CH), 2.68 (s, 3H, CH3N), 3.67 (dd, J = 13.5, 6.7 Hz, 1H, CH2CH), 3.79 (m, 2H, H-Cp), 4.59 (m, 1H, H-Cp), 4.64 (m, 1H, H-Cp), 5.03 (d, J = 10.1 Hz, 1H, dCH2), 5.07 (d, J = 13.5 Hz, 1H, dCH2), 5.68 (dddd, J = 13.9, 10.1, 7.7, 6.7 Hz, 1H, dCH). IR (benzene, cm1): ν(CO) 2014, 1933, ν(CdO) 1697. UV (benzene; λ, nm; ε, L/(mol cm)): 329; 1244. Anal. Calcd for C19H24MnNO5: C, 56.86; H, 6.03; N, 3.49; Mn, 13.69. Found: C, 56.64; H, 6.15; N, 3.36; Mn, 13.04. N-Boc-N-allyl-1-cymantrenylethylamine (4). A 60% suspension of NaH (0.4 g, 10 mmol) was added with stirring to a solution of N-Boc-1-cymantrenylethylamine3d (1.0 g, 2.9 mmol) in DMF (20 mL) under an argon atmosphere at 0 °C, and the mixture was kept at 0 °C for 30 min. Then allyl bromide (2.0 mL, 23 mmol) was added dropwise, and the reaction mixture was brought to room temperature and stirred for 1 h. The mixture was poured into icewater (50 mL), the products were extracted with CH2Cl2 (3 75 mL), the extracts were dried with MgSO4, the solvent was removed under vacuum, and 4 (yellow oil) was isolated by column chromatography (hexane/ethyl acetate 4/1). The yield was 0.6 g (55%). 1H NMR (benzene-d6, 340 K): δ 1.14 (d, J = 7 Hz, 3H, CHCH3), 1.41 (s, 9H, CMe3), 3.49 (dd, J = 15.9, 5.7 Hz, 1H, CH2CHd), 3.63 (br d, J = 16 Hz, 1H, CH2CHd), 3.91 (m, 1H, H-Cp), 4.06 (m, 1H, H-Cp), 4.32 (m, 1H, H-Cp), 4.54 (m, 1H, H-Cp), 4.89 (dm, 1H, dCH2), 4.94 (dm, J = 18 Hz, 1H, dCH2), 4.97 (m, 1H, CHCH3), 5.65 (m, 1H, CHd). IR (hexane, cm1): ν(CO) 2026, 1935, ν(CdO) 1700. UVvis (benzene; λ, nm; ε, L/(mol cm)): 328; 793. [R]D25 = 70.2° (c 0.47, ethanol) for the R enantiomer. Anal. Calcd for
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C18H22MnNO5: C, 55.82; H, 5.72; N, 3.62; Mn, 14.18. Found: C, 55.11; H, 6.01; N, 3.45; Mn, 14.01. MS (EI; m/z (relative intensity, %)): 303 [M 3CO]+, 247 [M C4H9], 203 [M CO2]+ . N-Acetyl-N-allyl-1-cymantrenylethylamine (5). (A) A solution of 1-cymantrenylethylamine (26;5 2 g, 8.1 mmol) in CH2Cl2 (50 mL) was cooled to 20 °C under argon, and Et3N (2.3 mL, 16.3 mmol) and acetyl chloride (0.9 mL, 12.2 mmol) were successively added. The reaction mixture was brought to room temperature and stirred for an additional 2 h, and then a saturated solution of NH4Cl was added dropwise and the reaction mixture was stirred for 20 min. The organic layer was separated, washed with 20% H3PO4 and with aqueous NaHCO3, dried with MgSO4, and the solvent was removed under vacuum. The residue was crystallized from hexane. The yield of N-acetyl1-cymantrenylethylamine (27) was 1.9 g (83%); mp 9192 °C. 1H NMR (benzene-d6): δ 0.96 (d, J = 6.6 Hz, 3H, CHCH3), 1.65 (s, 3H, COCH3), 3.92 (m, 2H, H-Cp), 4.31 (m, 1H, H-Cp), 4.41 (m, 1H, H-Cp), 4.90 (br s, 1H, CHCH3), 4.90 (br s, 1H, NH). 1H NMR (acetone-d6): δ 1.37 (d, J = 6.8 Hz, 3H, CHCH3), 1.88 (s, 3H, COCH3), 4.78 (m, 1H, H-Cp), 4.83 (br dq, 1H, CHCH3), 4.86 (m, 1H, H-Cp), 5.09 (m, 1H, H-Cp), 7.32 (br d, 1H, NH). IR (benzene, cm1): ν(CO) 2021, 1936, ν(CdO) 1685. UVvis (benzene; λ, nm; ε, L/(mol cm)): 331; 1309. [R]D25 = +25.4° (c 0.23, ethanol) for R enantiomer. Anal. Calcd for C12H12MnNO4: C, 49.83; H, 4.15; N, 4.84; Mn, 19.03. Found: C, 49.89; H, 4.08; N, 4.75; Mn, 19.00. (B) The synthesis of 5 was performed analogously to that of 4, starting from 27 (0.5 g, 1.7 mmol) in DMF (20 mL) using a 60% suspension of NaH (0.3 g, 7.5 mmol) and allyl bromide (1.2 mL, 14 mmol). The product was purified by column chromatography on silica gel (hexane/ethyl acetate 4/1). The yield was 0.3 g (53%); mp 4243 °C. 1H NMR (benzene-d6; mixture of two rotamers in the ratio 1:5): major conformer, δ 0.98 (d, J = 7.2 Hz, 3H, CHCH3), 1.73 (s, 3H, CH3), 3.13 (m, 2H, CH2CHd), 3.75 (s, 1H, H-Cp), 3.90 (s, 1H, H-Cp), 4.16 (s, 1H, H-Cp), 4.46 (m, 1H, H-Cp), 4.69 (d, J = 17.6 Hz, 1H, dCH2), 4.75 (d, J = 10.7 Hz, 1H, dCH2), 5.17 (ddt, J = 17.6, 10.7, 5.1 Hz, 1H, CHd), 5.52 (qu, J = 7.2 Hz, 1H, CHCH3); minor conformer, 0.87 (d, J = 6 Hz, 3H, CHCH3), 1.82 (s, 3H, CH3), 3.41 (m, 1H, CH2CHd), 3.77 (m, 1H, H-Cp), 3.79 (m, 1H, CH2CHd), 3.89 (m, 1H, H-Cp), 3.98 (m, 1H, H-Cp), 4.31 (qu, J = 6 Hz, 1H, CHCH3), 4.78 (m, 2H, CH2), 4.86 (m, 1H, H-Cp), 5.76 (m, 1H, CHd). IR (hexane, cm1): ν(CO) 2027, 1941, ν(CdO) 1667. UVvis (benzene; λ, nm; ε, L/(mol cm)): 329; 1208. [R]D25 75.9° (c 0.74, ethanol) for R enantiomer. Anal. Calcd for C15H16MnNO4: C, 54.72; H, 4.90; N, 4.26; Mn, 16.69. Found: C, 54.57; H, 4.81; N, 4.18; Mn, 16.60. N-Boc-N-allylcymantrenylmethylamine (6). This compound was obtained according to the procedure for allylation of compound 26 from N-Boc-1-cymantrenylmethylamine3d (1.1 g, 3.0 mmol), a 60% suspension of NaH (0.4 g, 10 mmol), and allyl bromide (2.1 mL, 23 mmol). The yield was 0.8 g (72%, yellow oil). 1H NMR (benzene-d6, 330 K): δ 1.40 (s, 9H, CMe3), 3.69 (m, 2H, CH2CHd), 3.76 (s, 2H, CH2Cp), 3.95 (m, 2H, H-Cp), 3.98 (m, 2H, H-Cp), 4.92 (dm, J = 11 Hz, 1H, dCH2), 4.94 (dm, J = 17 Hz, 1H, dCH2), 5.55 (ddt, J = 17, 11, and 6 Hz, 1H, CHd). 13C NMR (benzene-d6; mixture of two rotamers in the ratio 1:1.5) major conformer, 28.33 (3CH3), 43.84 (NCH2), 49.94 (CH2Cp), 79.78 (CMe3), 81.78 (2C, Cp), 84.52 (2C, Cp), 101.19 (C1Cp), 116.23 (dCH2), 134.16 (CHd), 155.26 (OCdO), 225.30 ((CO)3); minor conformer, δ 28.33 (3CH3), 43.61 (NCH2), 49.14 (CH2Cp), 79.89 (CMe3), 81.78 (2C, Cp), 84.12 (2C, Cp), 101.19 (C1Cp), 117.06 (CH2d), 134.16 (CHd), 154.59 (OCdO), 225.30 ((CO)3). IR (benzene, cm1): ν(CO) 2021, 1935, ν(CdO) 1700. UVvis (benzene; λ, nm; ε, L/(mol cm)): 329; 1037. Anal. Calcd for C17H20MnNO5: C, 54.70; H, 5.40; Mn, 14.72. Found: C, 54.78; H, 5.49; Mn, 14.80. N-Acetyl-N-allylcymantrenylmethylamine (7). (A) N-Acetylcymantrenylmethylamine (28) was obtained by the procedure for the 4349
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Organometallics synthesis of amide 27 from cymantrenylmethylamine3d,8 (3 g, 13 mmol). The yield was 2.8 g (80%); mp 9394 °C (hexane/ethyl acetate). 1H NMR (acetone-d6): δ 1.90 (s, 3H, CH3), 4.01 (d, J = 5.9 Hz, 2H, CH2N), 4.84 (m, 2H, H-Cp), 5.01 (m, 2H, H-Cp), 7.63 (br t, 1H, NH). Anal. Calcd for C11H10MnNO4: C, 48.02; H, 3.66; N, 5.09; Mn, 19.97. Found: C, 47.86; H, 3.73; N, 5.02; Mn, 19.7. (B) Allylation of amide 28 (1.4 g, 5.0 mmol) was performed similarly to the synthesis of 5 using a 60% suspension of NaH (0.4 g, 10 mmol) and allyl bromide (3.8 mL, 45 mmol). The yield was 0.7 g (47%); mp 5657 °C (hexane). 1H NMR (benzene-d6; mixture of two conformers in a ratio of 1:6): major conformer, δ 1.69 (s, 3H, CH3), 3.30 (dd, J = 4.8, 1.6 Hz, 2H, CH2CHd), 3.81 (s, 2H, CH2N), 3.87 (m, 2H, H-Cp), 4.42 (m, 2H, H-Cp), 4.76 (dqv, J = 17.2, 1.3 Hz, 1H, dCH2), 4.84 (dqv, J = 10.4, 1.3 Hz, 1H, dCH2), 5.21 (ddt, J = 17.2, 10.4, 4.9 Hz, 1H, CHd); minor conformer, 1.75 (s, 3H, CH3), 3.44 (s, 2H, CH2N), 3.82 (m, 2H, CH2Cp), 3.87 (m, 2H, H-Cp), 3.89 (m, 2H, H-Cp), 4.93 (dm, J = 16 Hz, 1H, dCH2), 4.97 (dm, J = 9 Hz, 1H, dCH2), 5.60 (m, 1H, CHd). 13C NMR (benzene-d6): major conformer, δ 20.98 (CH3), 42.91 (CH2Cp), 50.85 (CH2N), 81.69 (2C, Cp), 85.05 (2C, Cp), 100.83 (C1Cp), 116.28 (dCH2), 133.14 (CHd), 170.15 (broad NCdO), 225.39 (3CO); minor conformer, 21.41 (CH3), 44.59 (CH2N), 47.38 (CH2Cp), 82.16 (2C, Cp), 83.16 (2C, Cp), 100.42 (C1Cp), 117.39 (dCH2), 134.17 (CHd), 168.54 (broad NCdO), 225.01 (3CO). IR (benzene, cm1): ν(CO) 2021, 1936, ν(CdO) 1659. IR (THF, cm1): ν(CO) 2019, 1934, ν(CdO) 1656. UVvis (benzene; λ, nm; ε, L/(mol cm)): 329; 1110. MS (EI): m/z (related intensity, %) 289 (4) [M + 2H ]+, 231 (100) [M 2CO]+. Anal. Calcd for C14H14MnNO4: C, 53.35; H, 4.48; N, 4.44; Mn, 17.43. Found: C, 53.49; H, 4.58; N, 4.41; Mn, 17.3. (Allyloxy)methylcymantrene (8). 8 was prepared according to a procedure similar to that for compound 1 from hydroxymethylcymanrene9 (5.2 g, 22.2 mmol), NaH (60% suspension, 1.6 g, 40 mmol), and allyl bromide (2.9 mL, 33.3 mmol). The yield was 4.3 g (72%). 1H NMR (benzene-d6): δ 3.63 (s, 2H, CH2), 3.65 (dm, J = 5.3 Hz, 2H, CH2CH), 3.86 (m, 2H, H-Cp), 4.18 (m, 2H, H-Cp), 4.99 (ddd, J = 10.2, 2.2, 1.6 Hz, 1H, dCH2), 5.14 (ddd, J = 17.3, 2.2, 1.6 Hz, 1H, dCH2), 5.73 (ddt, J = 17.3, 10.2, 2.2 Hz, 1H, dCH). IR (hexane, cm1): ν(CO) 2026, 1944 (lit.10 IR: 2030, 1950).
General Procedure for Obtaining Dicarbonyl Chelates 10, 13a,b, 21, and 22. A solution of a tricarbonyl compound in THF (250 mL) was irradiated for 3040 min with an Hg lamp under argon in an immersion-well photochemical reactor at 710 °C. The reactions were monitored by IR spectra of probes of the reaction solution. The solvent was removed by rotary evaporation at low temperature; the residue was separated by silica gel column chromatography with hexane as an eluent and crystallized from hexane. [(1-Allyloxy-1-kN-pyrid-2-ylmethyl)-η5-cyclopentadienyl](dicarbonyl)manganese (10). After the general irradiation procedure, compound 1 (0.30 g, 0.85 mmol) gave orange crystals of 10 (yield 0.2 g, 74%). Mp: 6768 °C. 1H NMR (benzene-d6): δ 3.32 (m, 1H, H-Cp), 3.68 (ddt, J = 12.8, 6.1, 1.3 Hz, 1H, OCH2), 3.91 (m, 1H, H-Cp), 4.09 (ddt, J = 12.8, 4.8, 1.4 Hz, 1H, OCH2), 4.51 (s, 1H, OCH), 5.04 (dd, J = 10.4, 1.4 Hz, 1H, dCH2), 5.08 (m, 1H, H-Cp), 5.17 (dd, J = 17.2, 1.4 Hz, dCH2), 5.20 (m, 1H, H-Cp), 5.695.82 (2H, H-Py and CHd), 6.45 (m, J = 7.9, 1.5 Hz, 1H, Py), 6.47 (m, 1H, Py), 7.89 (d, J = 5.9 Hz, 1H, Py). 13C NMR (benzene-d6): δ 69.56 (CHO), 75.78 (CH2O), 77.75 (Cp), 78.79 (Cp), 83.10 (Cp), 82.53 (Cp), 113.08 (C1Cp), 117.27 (dCH2), 122.82 (Py), 123.43 (Py), 134.43 (CHd), 134.93 (Py), 156.18 (Py), 171.11 (C2Py), 234.40 (CO), 235.31 (CO). IR (benzene, cm1): ν(CO) 1928, 1860. IR (hexane, cm1): ν(CO) 1940, 1878. IR (THF, cm1): ν(CO) 1924, 1857. UVvis (benzene; λ, nm; ε, L/(mol cm)): 441; 6429. Anal. Calcd for C16H14MnNO3: C, 59.45; H 4.37; N, 4.33; Mn, 17.00. Found: C, 59.68; H 4.26; N, 4.21; Mn, 16.90.
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[(1-η2-Allyloxy-2-pyrid-2-ylethyl)-η5-cyclopentadienyl]dicarbonylmanganese (13). An oily mixture of 13a,b in the ratio 3.5:1 was obtained from compound 2 (505 mg, 1.4 mmol) by the general irradiation procedure and separated by column chromatography on silica gel with hexane/EtOAc (3/1) as an eluent. The first yellow band was 13a as orange crystals; the second yellow band was 13b (an oil). Data for 13a (153 mg, 32% yield) are as follows. Mp: 108109 °C (hexane). 1H NMR (benzene-d6): δ 1.73 (d, J = 8.9 Hz, 1H, CH2d), 2.33 (d, J = 12.3 Hz, 1H, CH2d), 2.71 (m, 1H, CHd), 2.83 (dd, J = 13.6, 6.0 Hz, 1H, CH2Py), 3.01 (dd, J = 14.7, 1.8 Hz, 1H, OCH2), 3.03 (dd, J = 13.6, 7.9 Hz, 1H, CH2Py), 3.56 (m, 1H, H-Cp), 3.67 (m, 1H, H-Cp), 3.81 (dd, J = 7.9, 5.9 Hz, 1H, CHCp), 4.29 (dd, J = 14.7, 1.1 Hz, 1H, OCH2), 4.31 (m, 1H, H-Cp), 4.72 (m, 1H, H-Cp), 6.55 (dd, J = 7.5, 4.4 Hz, 1H, Py), 6.68 (d, J = 7.8 Hz, 1H, Py), 6.92 (dt, J = 7.5, 1.8 Hz, 1H, Py), 8.43 (m, 1H, Py). 13C NMR (benzene-d6): δ 29.07 (CH2Py), 45.81 (OCH2), 59.83 (OCH), 67.78 (dCH2), 70.53 (dCH), 76.76 (Cp), 85.21 (Cp), 87.05 (Cp), 87.10 (Cp), 95.68 (C1Cp), 121.38 (Py), 123.96 (Py), 135.62 (Py), 149.61 (Py), 158.55 (C1-Py), 233.46 (CO), 235.15 (CO). IR (benzene, cm1): ν(CO) 1965, 1902. IR (hexane, cm1): 1974, 1917. UVvis (THF; λ, nm; ε, L/(mol cm)): 329; 940, 365; 470. MS (EI): m/z (related intensity, %) 337 (1) [M]+, 281 (31) [M 2CO]+, 225 (42), 223 (78), 168 (100). Anal. Calcd for C17H16MnNO3: C, 60.54; H, 4.78; N, 4.15; Mn, 16.29. Found: C, 60.49; H 4.87; N, 4.07; Mn, 16.0. Data for 13b (38 mg, 8% yield) are as follows. 1H NMR (benzene-d6): δ 1.74 (d, J = 8.1 Hz, 1H, CH2d), 1.98 (dd, J = 13.2, 8.8 Hz, 1H, OCH2), 2.03 (d, J = 11.9 Hz, 1H, CH2d), 2.96 (m, 1H, H-Cp), 3.13 (dd, J = 14.0, 5.7 Hz, 1H, CH2Py), 3.263.37 (m, 2H, CHd and CH2Py), 3.74 (m, 1H, H-Cp), 4.03 (dd, J = 7.9, 5.7 Hz, 1H, CHCp), 4.26 (dd, J = 13.2, 5.1 Hz, 1H, OCH2), 4.39 (m, 1H, H-Cp), 4.89 (m, 1H, H-Cp), 6.56 (dd, J = 6.5, 5.1 Hz, 1H, Py), 6.84 (d, J = 7.6 Hz, 1H, Py), 7.02 (ddd, J = 7.6, 6.5, 1.5 Hz, 1H, Py), 8.43 (br d, J = 4.4 Hz, 1H, Py). 13C NMR (benzene-d6): δ 38.14 (CH2Py), 42.75 (OCH2), 58.38 (OCH), 68.16 (dCH2), 71.83 (Cp), 72.26 (dCH), 83.36 (Cp), 84.94 (Cp), 87.66 (Cp), 103.54 (C1Cp), 121.38 (Py), 124.08 (Py), 135.74 (Py), 149.64 (Py), 159.03 (C1Py), 233.19 (CO), 234.57 (CO). IR (hexane, cm1): ν(CO) 1978, 1921. UVvis (benzene; λ, nm; ε, L/(mol cm)): 331 sh; 1170, 365; 380. MS (EI): m/z (related intensity, %) 337 (1) [M]+, 281 (45) [M 2CO]+, 225 (75), 223 (100), 168 (98). N-Boc-N-(η2-allyl)(1-aminomethyl-η5-cyclopentadienyl)dicarbonylmanganese (21). Compound 21 was obtained from 6 (374 mg, 1 mmol) by the general irradiation procedure as yellow crystals (210 mg, yield 67%). Mp: 9698 °C (hexane). 1H NMR (benzene-d6, 340 K): δ 1.42 (s, 9H, 3CH3), 1.81 (d, J = 8.5 Hz, 1H, dCH2), 2.15 (d, J = 12.3 Hz, 1H, dCH2), 2.70 (d, J = 14.5 Hz, 1H, CH2N), 2.81 (m, 1H, CHd), 2.96 (dd, J = 15.9, 2.3 Hz, 1H, CH2CHd), 3.66 (m, 1H, H-Cp), 3.70 (m, 1H, H-Cp), 3.93 (br d, J = 15, 2.3 Hz, 1H, CH2CHd), 4.20 (d, J = 14.5 Hz, 1H, CH2N), 4.48 (m, 1H, H-Cp), 4.51 (m, 1H, H-Cp). 13C NMR (benzene-d6, 293 K): major rotamer, δ 28.33 (3CH3), 41.74 (CH2N), 46.16 (CH2Cp), 57.37 (dCH2), 70.05 (CHd), 79.48 (CMe3), 86.55 (2Cp), 87.26 (1C Cp), 88.26 (1C Cp), 95.00 (C1Cp), 128.38 (CHd), 154.81 (OC=O), 233.58 (CO), 235.19 (CO). IR (benzene, cm1): ν(CO) 1964, 1901, ν(CdO) 1700. UVvis (benzene; λ, nm; ε, L/(mol cm)): 334; 885. MS (EI): m/z (related intensity, %) 347 (2) [M + 2H]+, 289 (48) [M 2CO]+, 233 (68), 189 (100). Anal. Calcd for C16H20MnNO4: C, 55.66; H, 5.84; N, 4.06; Mn, 15.91. Found: C, 55.64; H, 5.78; N, 4.07; Mn, 15.80. N-Acetyl-N-(η2-allyl)(1-aminomethyl-η5-cyclopentadienyl)dicarbonylmanganese (22). Compound 22 was obtained from 7 (474 mg, 1.5 mmol) by the general irradiation procedure as yellow crystals (375 mg, 87% yield). Mp: 120121 °C (hexane). 1H NMR (benzene-d6; mixture of two rotamers in the ratio 6:1): major isomer, δ 1.57 (d, J = 8.5 Hz, 1H, CH2d), 1.65 (C, 3H, CH3), 1.79 (d, J = 12.2 Hz, 1H, CH2d), 2.13 (d, 1H, J = 14.1 Hz, CH2Cp), 2.45 (m, 1H, CHd), 2.63 (dd, J = 17.0, 2.2 Hz, 1H, NCH2), 3.44 (dd, J = 17.0, 2.2 Hz, 1H, NCH2), 3.58 (m, 1H, H-Cp), 3.63 (m, 1H, H-Cp), 4.32 (m, 1H, H-Cp), 4.63 (m, 1H, H-Cp), 4.99 (d, J = 14.2 Hz, 1H, CpCH2); minor isomer, 1.54 (s, 3H, CH3), 1.85 (d, J = 8 4350
dx.doi.org/10.1021/om200407c |Organometallics 2011, 30, 4342–4353
Organometallics Hz, 1H, CH2d), 1.99 (d, J = 13.5 Hz, 1H, CH2d), 2.23 (d, 1H, J = 15.2 Hz, CH2Cp), 2.51 (dm, J = 12.6 Hz, 1H, NCH2), 2.75 (m, 1H, CHd), 3.15 (m, 1H, H-Cp), 3.24 (d, J = 15.2 Hz, 1H, CH2Cp), 3.59 (m, 1H, H-Cp), 4.29 (m, 1H, H-Cp), 4.63 (m, 1H, H-Cp), 4.80 (dm, J = 12.6 Hz, 1H, NCH2). 13C NMR (benzene-d6): major isomer, δ 29.37 (CH3), 40.13 (NCH2), 47.48 (CpCH2), 55.84 (CH2d), 70.28 (CHd), 87.01 (2Cp), 87.22 (Cp), 88.16 (Cp), 93.67 (C1Cp), 169.30 (br NCdO), 233.93 (CO), 234.03 (CO); minor isomer, 20.61 (CH3), 32.02 (CH2N), 44.44 (CpCH2), 56.54 (CH2d), 70.08 (CHd), 86.52 (Cp), 86.76 (Cp), 87.17 (2Cp), 93.81 (C1Cp), 169.3 (br, NCdO), 233.61 (CO), 234.03 (CO). IR (benzene, cm1): ν(CO) 1965, 1903, ν(CdO) 1659. IR (THF, cm1): ν(CO) 1965, 1903, ν(CdO) 1656. UVvis (benzene; λ, nm; ε, L/(mol cm)): 333; 934. MS (EI): m/z (related intensity, %) 289 (3) [M + 2H], 231 (100) [M 2CO]+. Anal. Calcd for C13H14MnNO3: C, 54.37; H, 4.91; N, 4.77; Mn, 19.13. Found: C, 54.52; H, 5.16; N, 4.87; Mn, 19.00.
General Procedure for Spectral Studies of Photochemical Reactions of Tricarbonyl Complexes 18 and Dicarbonyl Chelates and Their Isomerization. Solutions of tricarbonyl compounds in the required solvent (benzene, hexane, or THF; c 24 mM) were placed, under an argon atmosphere, into IR or UV cells and irradiated with an Hg lamp (steady radiation of the lamp was achieved in 2 min before irradiation); the spectra were registered every 12 min. Then irradiation of the sample was repeated up to full conversion of tricarbonyl complexes or 50% isomerization of dicarbonyl chelates. The total irradiation time for compounds 18 was from 10 to 25 min. To prepare samples for NMR monitoring, solutions of compounds (c 1015 mM) were filtered into an NMR tube, bubbled with argon, and irradiated with the Hg lamp at 810 °C for 4 min up to 2530% conversion. The distance between the lamp and the sample was 5 cm in all cases. The width of the irradiation window was 2 cm in the IR cell, 1 cm in the UV cell, and 5 mm in the NMR tube. Monitoring of all dark reactions of irradiated samples was carried out similarly at least for 72 h. The “irradiationdark reaction” procedure for ca. 2 mM solutions of 13a,b and 22 in benzene or hexane was repeated three to four times in the IR cell. In the case of chelates 18 and 20, this procedure was carried out using irradiated solutions of compounds 4 and 5, respectively, after full conversion of tricarbonyl complexes. Samples were irradiated in IR, NMR, or UV cells having free volume for the accumulation of carbon monoxide liberated (open system). In the case of irradiation in a closed system, there is no free volume in the IR cells (closed system). [(η2-Allyloxymethyl)-η5-cyclopentadienyl]dicarbonylmanganese (9). 1 H NMR (benzene-d6): δ 1.7 (d, J = 8.6 Hz, 1H, CH2d), 2.27 (d, J = 12.4 Hz, 1H, CH2d), 2.76 (m, 1H, CHd), 2.85 (d, J = 12.8 Hz, 1H, CH2Cp), 2.96 (dm, J = 14.4 Hz, 1H, OCH2), 3.50 (m, 1H, H-Cp), 3.63 (m, 1H, H-Cp), 3.92 (d, J = 12.8 Hz, 1H, CH2Cp), 4.02 (d, J = 14.4 Hz, 1H, OCH2), 4.33 (m, 1H, H-Cp), 4.68 (m, 1H, H-Cp). IR (hexane, cm1): ν(CO) 1975, 1917. [(1-η2-Allyloxy-1-pyrid-2-yl-methyl)-η5-cyclopentadienyl]dicarbonylmanganese (11). 1H NMR (benzene-d6): δ 1.75 (d, J = 9.4 Hz, 1H, CH2d), 2.38 (d, J = 11.9 Hz, 1H, CH2d), 2.80 (m, 1H, CHd), 3.17 (d, J = 16 Hz, 1H, OCH2), 3.57 (m, 1H, H-Cp), 4.36 (s, 1H, CHCp), 4.59 (d, J = 16 Hz, 1H, OCH2), 4.75 (m, 1H, H-Cp), 6.52 (m, 1H, Py), 7.07 (m, 1H, Py), 7.28 (d, J = 7.8 Hz, 1H, Py), 8.27 (br d, J = 4.2 Hz, 1H, Py). IR (benzene, cm1): ν(CO) 1960, 1903. IR (hexane, cm1): ν(CO) 1971, 1915. IR (THF, cm1): ν(CO) 1964, 1906. [(1-Allyloxy-2-kN-pyrid-2-ylethyl)-η5-cyclopentadienyl]dicarbonylmanganese (12). 1H NMR (benzene-d6): δ 2.64 (dd, J = 14,3 Hz, 1H, CH2Py), 2.81 (dd, J = 14,9 Hz, 1H, CH2Py), 3.52 (m, 1H, H-Cp), 3.63 (m, 1H, H-Cp), 3.67 (m, 1H, OCH2), 3.75 (dd, J = 8.8, 3.3 Hz, 1H, CHCp), 3.94 (dd, J = 13.5, 4.8 Hz, 1H, OCH2), 4.54 (m, 1H, H-Cp), 4.99 (d, J = 9.5 Hz, 1H, dCH2), 5.11 (m, 1H, H-Cp), 5.13 (d, J = 17.2 Hz, 1H, dCH2), 5.75 (m, 1H, CHd), 5.82 (t, J = 5.5, 1H, Py), 6.25
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(d, J = 7.9, 1H, Py), 6.47 (t, J = 7.8, 1H, Py), 9.07 (d, J = 5.4 Hz, 1H, Py). IR (benzene, cm1): ν(CO) 1927, 1853. IR (hexane, cm1): 1936, 1933, 1870, 1867 sh. UVvis (benzene; λ, nm; ε, L/(mol cm)): 434; >1460. [N-Methyl-2-(tert-butyloxy-kO-carbonylamino)pent-4-en-2-yl-η5cyclopentadienyl]dicarbonylmanganese (15). 1H NMR (benzene-d6): δ 1.01 (s, 3H, CH3), 1.05 (s, 9H, CMe3), 2.23 (d, J = 8 Hz, 1H, CH2C), 2.29 (s, NCH3), 2.96 (m, 1H, H-Cp), 3.16 (m, 1H, H-Cp), 4.78 (m, 1H, CH2C), 4.85 (d, J = 10.1 Hz, 1H, dCH2), 4.86 (d, J = 17.3 Hz, 1H, dCH2), 4.94 (m, 1H, H-Cp), 5.54 (m, 1H, dCH). IR (benzene, cm1): ν(CO) 1927, 1853, ν(CdO) 1632. IR (hexane, cm1): ν(CO) 1938, 1871. UVvis (benzene; λ, nm; ε, L/(mol cm)): 503; >1300. N-Boc-[(1-η2-allyl-1-methylaminoethyl)-η5-cyclopentadienyl]dicarbonylmanganese (16). 1H NMR (benzene-d6): major isomer, δ 1.31 (s, 9H, CMe3), 1.59 (s, 3H, CCH3), 1.68 (d, J = 7.4 Hz, 1H, CH2d), 1.77 (m, 1H, CCH2), 2.37 (m, 1H, CHd), 2.46 (s, NCH3), 2.92 (m, 1H, CH2d), 3.19 (m, 1H, H-Cp), 3.45 (m, 1H, H-Cp), 4.47 (m, 1H, H-Cp), 5.17 (m, 1H, H-Cp). IR (benzene, cm1): ν(CO) 1963, 1896, ν(CdO) 1695. IR (hexane, cm1): ν(CO) 1974, 1912; minor isomer, ν(CO) 1974, 1914 sh. UVvis (benzene; λ, nm; ε, L/(mol cm)): 326; 1230. N-Allyl-[1-(tert-butyloxy-kO-acetylamino)ethyl-η5-cyclopentadienyl]dicarbonylmanganese (17). 1H NMR (benzene-d6): δ 0.88 (d, J = 7.0 Hz, 3H, CHCH3), 1.04 (s, 9H, CMe3), 2.57 (m, 1H, H-Cp), 2.91 (q, J = 7.0 Hz, 1H, CHCH3), 3.38 (m, 2H, NCH2), 3.56 (m, 1H, Cp), 4.8 5.0 (m, 2H, dCH2), 5.09 (m, 1H, H-Cp), 5.14 (m, 1H, H-Cp), 5.39 (m, 1H, dCH). IR (hexane, cm1): ν(CO) 1939, 1870. UVvis (benzene; λ, nm): 516. N-Boc-N-(η2-allyl)(1-aminoethyl-η5-cyclopentadienyl)dicarbonylmanganese (18). Mixture of two isomers 1:1.2. Data for the major isomer are as follows. 1H NMR (benzene-d6): δ 0.78 (d, J = 7.0 Hz, 3H, CHCH3), 1.58 (s, 9H, CMe3), 1.72 (d, J = 7.8 Hz, 1H, dCH2), 2.02 (d, J = 11.8 Hz, 1H, dCH2), 2.67 (m, 1H, CHd), 2.75(m, 1H, H-Cp), 2.83 (br d, J = 17 Hz, 1H, NCH2), 3.59 (m, 1H, H-Cp), 4.27 (br.d, J = 16.8 Hz, 1H, NCH2), 4.34 (m, 1H, H-Cp), 4.89 (m, 1H, H-Cp), 5.10 (br q, 1H, CHCH3). IR (hexane, cm1): ν(CO) 1977, 1914, ν(CdO) 1700. UVvis (benzene; λ, nm; ε, L/(mol cm)): 341; >700. Data for the minor isomer are as follows. 1H NMR (benzene-d6): δ 0.69 (d, J = 7 Hz, 3H, CHCH3), 1.42 (s, 9H, CMe3), 1.731.9 (1H, dCH2), 2.152.3 (1H, dCH2), 3.41 (m, 2H, NCH2 and CHd), 3.65 (m, 1H, H-Cp), 3.82 (m, 1H, H-Cp), 4.30 (m, 1H, Cp-H), 4.65 (m, 1H, NCH2), 4.67 (m, 1H, H-Cp), 5.05 (br m, 1H, CHCH3). IR (hexane, cm1): ν(CO) 1972, 1918, ν(CdO) 1700. UVvis (benzene; λ, nm; ε, L/(mol cm)): 341; >700. N-Allyl-[1-(kO-acetylamino)ethyl-η5-cyclopentadienyl]dicarbonylmanganese (19). 1H NMR (benzene-d6): δ 0.82 (d, J = 6.5 Hz, 3H, CHCH3), 1.09 (s, 3H, COCH3), 2.53 (m, 1H, H-Cp), 2.66 (br.d, J = 6.5 Hz, 1H, NCH2), 2.87 (br d, J = 6.5 Hz, 1H, NCH2), 3.32 (q, J = 6.5 Hz, 1H, CHCH3), 5.01 (m, 1H, H-Cp), 5.05 (m, 1H, H-Cp). IR (hexane, cm1): ν(CO) 1941, 1872, ν(CdO) 1605. UVvis (benzene; λ, nm; ε, L/(mol cm)): 509; >900. N-Acetyl-N-(η2-allyl)-(1-aminoethyl-η5-cyclopentadienyl)dicarbonylmanganese (20). Mixture of two isomers 1:4. 1H NMR (benzene-d6): major isomer, δ 0.65 (d, J = 7 Hz, 3H, CHCH3), 1.55 (d, J = 8.4 Hz, 1H, dCH2), 1.68 (s, 3H, COCH3), 1.84 (d, J = 11.2 Hz, 1H, dCH2), 2.45 (m, 1H, CHd), 2.86 (br d, J = 17 Hz, NCH2), 3.38 (br.d, J = 17 Hz, NCH2), 3.59 (m, 1H, H-Cp), 3.64 (m, 1H, H-Cp), 4.27 (m, 1H, H-Cp), 4.58 (m, 1H, H-Cp), 5.52 (br q, 1H, CHCH3). IR (hexane, cm1): major isomer, ν(CO) 1975, 1917, ν(CdO) 1663; minor isomer, 1978, 1921, ν(CdO) 1663. UVvis (benzene; λ, nm; ε, L/(mol cm)): 331; 1200. N-Allyl-[(kO-acetylaminomethyl)-η5-cyclopentadienyl]dicarbonylmanganese (23). 1H NMR (benzene-d6): δ 1.08 (s, 3H, COCH3), 2.68 (br d, J = 5 Hz, 2H, NCH2), 2.87 (s, 2H, CH2Cp), 3.17 (m, 2H, H-Cp), 4.88 (m, 2H, H-Cp). IR (benzene, cm1): ν(CO) 1931, 1856. IR 4351
dx.doi.org/10.1021/om200407c |Organometallics 2011, 30, 4342–4353
Organometallics (THF, cm1): ν(CO) 1927, 1854, ν(CdO) 1615. UVvis (benzene; λ, nm): 519.
Estimation of Quantum Yield of Isomerization of 13a into 12. A 3.9 mL portion of a 1.73 103 M solution of 13a in THF (ε328
1090, ε365 471) was added to 5.0 mL of a 1.68 103 M solution of 1-(tert-butyloxycarbonylamino)ethylcymantrene (14)3d in THF (ε325 1048, ε365 380), and the mixture was saturated with argon. Aliquots of the solution prepared with the total absorption 0.714 at 365 mn with that of 0.36 for each component were transferred into an IR cell (KBr, 0.21 mm, 3 1.5 cm2) and irradiated with the 365 nm band of a Hg lamp by application of UVS-6 + BS-7 filters (made in Russia) from a distance of 5 cm. The concentration decrease for both complexes was determined from the integral intensities of the IR band 2020 cm1 for carbamate and 1900 cm1 for 13a, which do not overlap with ν(CO) bands of the products. At 1012% conversion of carbamate 14 to corresponding dicarbonyl chelate (ε365 650), 89% isomerization of 13a to the pyridine chelate 12 (ε365 1100) occurred (the result of two experiments). These data together with ϕ 0.98 determined for photolysis of 14 allowed us to obtain a quantum yield of 0.8 for photoisomerization of 13a to 12. X-ray Study of 5, 7, 10, 13a, 21, and 22. Single-crystal X-ray diffraction experiments were carried out with a Bruker SMART APEX II diffractometer (graphite-monochromated Mo KR radiation, λ = 0.710 73 Å, ω-scan technique, T = 100 K). The APEX II software11 was used for collecting frames of data, indexing reflections, determining lattice constants, integrating intensities of reflections, scaling ,and absorption correction, and SHELXTL12 was used for space group and structure determination, refinements, graphics, and structure reporting. The structures were solved by direct methods and refined by the fullmatrix least-squares technique against F2 with anisotropic displacement parameters for all non-hydrogen atoms. All hydrogen atoms were placed geometrically and included in the structure factor calculations in the riding motion approximation. The principal experimental and crystallographic parameters are presented in Figures 2, 3, and 7. Crystal data and data collection and structure refinement parameters for 5, 7, 10, 13a, 21, and 22 are presented in the Supporting Information (Table S1). The chelate 10 crystallizes in the centrosymmetric space group P1 with two independent molecules A and B in the unit cell (the molecule of 10A is presented in Figure 3), which differ from each another in the oxyallyl group orientation (the C(11)O(3)C(10)C(9) torsion angle is equal to 72.8 and 172.9° in molecules A and B, respectively). The chelate five-membered cycle Mn(1)C(1)C(11)C(12)N(1) is planar, and its plane is perpendicular to the plane of the Cp ring (the dihedral angle between these two planes is equal to 88.4 and 89.8° in molecules A and B, respectively). The Mn(1)N(1) distance (2.022(1) and 2.010(1) Å in molecules A and B, respectively) is close to that (2.014(1) Å) observed in the complex with the quinolyl moiety13 and is slightly shortened in comparison to that (2.067(1) Å) observed in the complex with a six-membered chelate cycle.3b Formation of a strained five-membered chelate cycle in 10 leads to significant deviation of the C(11) atom from the plane of the Cp ring directed toward the manganese atom (0.278 and 0.295 Å in molecules A and B, respectively). The complex 13a crystallizes in the noncentrosymmetric space group Pna21 with two independent molecules A and B in the unit cell (the molecule of 13aA is presented in Figure 3), which have similar structures.
’ ASSOCIATED CONTENT Supporting Information. CIF files giving crystallographic data and a table giving crystal data and data collection and structure refinement parameters for 5, 7, 10, 13a, 21, and 22 and tables, text, and figures giving results of DFT calculations for compounds 10 and 11 and stereoisomers of chelate 13
bS
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(coordinates of atoms, one-electron energy, and Mulliken population analysis). This material is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
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