Investigation of the photochemical behaviour of tricarbonyl(cyclopentadienyl)manganese derivatives with carbamate groups

Article abstract of DOI:10.1002/ejic.200900458

Photochemical properties of cymantrene carbamates were for the first time investigated. It was found that UV irradiation of Boc-substituted 1-aminoalkylcymantrenes yields dicarbonyl chelate complexes as a result of the coordination of the oxygen atom of t

Full text of DOI:10.1002/ejic.200900458

FULL PAPER
DOI: 10.1002/ejic.200900458
Investigation of the Photochemical Behaviour of Tricarbonyl-
(cyclopentadienyl)manganese Derivatives with Carbamate Groups
Lyudmila N. Telegina,[a] Mariam G. Ezernitskaya,[a] Ivan A. Godovikov,[a]
Kirill K. Babievskii,[a] Boris V. Lokshin,[a] Tatiayana V. Strelkova,[a] Yuriy A. Borisov,[a] and
Nikolay M. Loim*[a]
Keywords: Photolysis / Carbonyl ligands / Cyclopentadienyl ligands / Manganese
Photochemical properties of cymantrene carbamates were for
the first time investigated. It was found that UV irradiation of
Boc-substituted 1-aminoalkylcymantrenes yields dicarbonyl
chelate complexes as a result of the coordination of the oxy-
gen atom of the carbamate ligand to the manganese atom.
These complexes show high thermodynamic and kinetic sta-
bility in solution at room temperature and in closed systems
can be used for the creation of photochromic systems based
on cymantrene carbamates.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Introduction
Results and Discussion
Photochemical substitution of CO ligands in transition-
UV irradiation of a colourless solution of Boc-substi-
metal carbonyl complexes is a well-known, simple and ef- tuted 1-aminoethylcymantrene (3) in benzene resulted in the
ficient method for modification of these compounds. In appearance of a crimson colour, which persisted at 10–
particular, in a series of tricarbonyl(cyclopentadienyl)- 25 °C for several hours. The analysis of the photolysis prod-
manganese (cymantrene) complexes, this method is tradi- ucts of 3 by TLC indicated the full disappearance of the
tionally used for the preparation of derivatives containing initial compound (Rf = 0.53; hexane/ethyl acetate, 3:1). A
phosphanes, phosphites, olefins, acetylenes, amines, sul- similar picture was observed in the case of the photolysis
fides, nitriles and other n- and π-donor molecules as ligands of carbamates 4 and 5.
at the manganese atom.[1a–1f,2–9] Some compounds having
Monitoring of the photolysis of compounds 3–5 in ben-
phosphane, pyridine, nitrile, sulfide and thioamide substitu- zene by IR spectroscopy showed that, parallel with the dis-
ents in the Cp ring can form stable intramolecular che- appearance of two ν(CO) bands of the initial tricarbonyl
lates.[1j,3–7] Recently, it was shown that cymantrene-based complexes, two new ν(CO) bands of equal intensities ap-
chelate complexes open new possibilities for the creation peared that are associated with dicarbonyl manganese de-
of photochromic systems.[7] With the aim of searching for rivatives (Table 1). Simultaneously the ν(CO) band of the
cymantrene derivatives, which can be used for the creation carbamate group in the range of 1700 cm–1 shifted to a low
of reversible photochromic systems, we studied the photo- frequency range by ca. 50 cm–1; in the case of carbamates
chemical behaviour of tert-butylcarbamates of α-aminoalk- 3 and 4 the centre of the ν(NH) band was about 5–10 cm–1
ylcymantrenes (Scheme 1).
downshifted (Table 1).
Similar spectral changes were observed in the case of
photolysis of carbamates in hexane and THF (Table 1). The
similarity of spectral parameters for complex 6 in benzene,
hexane and THF indicates that, even with irradiation of the
carbamates in THF, the carbamate group occupies a free
coordination site of the manganese atom. In all solvents,
isosbestic points were observed (Figure 1) indicating that,
within the IR timescale, only two types of complexes exist
in solution, namely, with three and two carbonyl ligands at
the manganese atom. Thus, the IR spectra show that stabili-
zation of dicarbonyl complexes 6–8 occurs as a result of
intramolecular bonding between the manganese atom and
the CO group in the carbamate substituent. The capacity
of carbamates to act as a ligand at intermolecular interac-
Scheme 1.
[a] A. N. Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences,
28 Vavilova Street, 119991 Moscow, Russian Federation
Fax: +7-499-135-5085
E-mail: loim@ineos.ac.ru
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900458.
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Photochemistry of Tricarbonyl(cyclopentadienyl)manganese Derivatives
Table 1. ν(CO) frequencies for carbamates 3–5 and dicarbonyl into a quartet at δ = 3.06 ppm (J = 6.7 Hz), the doublet for
complexes 6–8.
the CH2 protons of complex 4 at δ = 3.52 ppm (J = 5.8 Hz)
transforms into a singlet at δ = 3.11 ppm (Figure 2 and Ex-
perimental Section). In the H NMR spectrum of carba-
Compound
ν(CO)
ν(CO) of
carbamate
group
ν(NH) of
carbamate
group
1
mate 5, there are two sets of signals for two conformers
resulting from the rotation about the C–N bond of the sub-
stituent. After photolysis only one signal set is observed for
complex 8, which is indicative of the lack of conformational
isomerism in the coordinated carbamate group. Upon
transformation of carbamates 3–5 into corresponding di-
carbonyl compounds 6–8, the signals for the β-protons of
the Cp ring undergo an upfield shift, whereas the signals
for the α-protons of the Cp ring are shifted downfield, so
that anisotropy increases by an average value of 2 ppm.
(The signal assignment for the α- and β-protons of the Cp
ring is given in the Experimental Section.) In the case of
chiral compounds, the chemical shifts for the diastereotopic
α-H and αЈ-H, as well as for the β- and βЈ-protons of the
Cp ring become significantly nonequivalent. For complexes
6 and 8, the differences between the signals for β-H and βЈ-
H are 0.49 and 0.94 ppm, whereas those for α-H and αЈ-H
are 0.06 and 0.01 ppm, respectively. Significant differences
between nonequivalent Cp signals were observed earlier for
cymantrene and benzenetricarbonyl chromium derivatives
and were considered characteristic properties of this type of
chelate complex.[3–7,10] The formation of the rigid chelate
cycle hinders the internal rotation about the Mn–Cp-ring
centroid bond. This creates two anisotropic areas in the cy-
clopentadienyl ring, one of which is under the influence of
the CO groups and the other is affected by the coordinated
carbamate groups.
3
6
2040,1930[a]
2018,1932[b]
2025,1948[c]
1930,1857[a]
1929,1854[b]
1943,1874[c]
2022,1933[a]
1933,1856[a]
2020,1935[a]
2027,1947[c]
1955,1854[a]
1940,1871[c]
1717[a]
1714[b]
1727[c]
1666[a]
1658[b]
1675[c]
1719[a]
1668[a]
1694[a]
1708[c]
1640[a]
1649[c]
≈3424 (br.)[a]
≈3310 (br.)[b]
≈3451 (br.)[c]
≈3405 (br.)[a]
≈3275 (br.)[b]
≈3441 (br.)[c]
≈3438 (br.)[a]
≈3421 (br.)[a]
4
7
5
8
[a] The spectra were measured in benzene. [b] The spectra were
measured in THF. [c] The spectra were measured in hexane.
tion is low. We found that photolysis of cymantrene in ben-
zene in the presence of Boc-substituted phenylethylamine
(10) resulted in the appearance of a light crimson colour
due to the formation of the dicarbonyl complex, and this
colour change was only observed with a cymantrene/10 ra-
tio of no less than 1:10.
Figure 1. IR spectra in the ν(CO) range for 3 (2.6 m in THF) over
the course of irradiation. Overall irradiation time was 6 min.
The 1H NMR spectra registered in the course of photoly-
sis of carbamates 3–5 in benzene also indicated that only
two types of complexes existed throughout the reaction.
Coordination of the CO group of the carbamate fragment
to the manganese atom results in a substantial difference in
the spectra of tricarbonyl and dicarbonyl compounds. In
particular, during the photolysis of carbamates 3 and 4, the
position and multiplicity of the signal for the protons at the
1-carbon of the substituent change. In the case of com-
pound 3, a doublet of quartets at δ = 4.58 ppm (J = 6.8 Hz
1
Figure 2. H NMR spectra of 3 (15 m in [D6]benzene) at 23 °C:
between CH-CH3 and J = 5.9 Hz between CH-NH) turns (a) before irradiation, (b) after 5 min irradiation.
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N. M. Loim et al.
FULL PAPER
The formation of dicarbonyl compounds 6–8 exhibits
itself in the UV spectra, where two new absorption bands
appear near 420 (shoulder) and 520 nm (Figure 3). The po-
sition and intensity of these bands weakly depend on the
nature of the solvent (hexane, benzene, ethanol and THF;
see the Experimental Section). The parameters of the UV
spectra are similar to those for cymantrene derivatives con-
taining THF or alkylamines coordinated to the manganese
atom; these cymantrene derivative have an absorption band
at about 500 nm assigned to LF bands associated with “d–
d” transitions rather than to metal–ligand charge trans-
fer.[8,9] This fact provides reason to suppose that in our case,
these transitions have the same nature. This supposition is
confirmed by DFT calculations. It follows from analysis of
HOMO and LUMO coefficients that low-energy transitions
of UV spectra have dominant d–d character. Nevertheless,
collaboration of the carbamate group AO in forming of the
first and second LUMO did not accept a partial CT charac-
ter of transition.
Figure 4. (a,b) CD spectra of (R)-3 (2.45 m in benzene) and (c,d)
(S)-3 (6.7 m in benzene) at room temperature: (a and c) before
irradiation, (b) after 5 min irradiation and (d) after 3 min irradia-
tion.
However, the DFT calculations for these complexes con-
firm the proposed structure, and the global minimum dif-
fers in energy from the tricarbonyl complexes by
30 kcalmol–1 (Figure 5 and Table 2). The calculated values
for the position and intensity of the ν(CO) bands of the
carbamate group agreed with the experimental data
(Table 2).
Irradiation of carbamates 3–5 by a UV lamp in the
closed system, in which the CO formed was not removed
from the reaction, yielded complexes 6–8, which trans-
formed into parent tricarbonyl complexes in a dark process
at room temperature. After three- and fourfold repetition of
the process: irradiation–dark reaction, both the total view
of the IR spectrum and the stretching mode intensities for
CO groups in the starting compound and the product did
not change with the experimental accuracy (Scheme 2).
Direct reaction of the resulting dicarbonyl chelate pro-
Figure 3. UV/Vis spectra of 3 (3.5 m in benzene) at room tem-
perature: (a) before irradiation, (b) after 5 min irradiation (100%
conversion by IR spectra).
The circular dichroism (CD) spectra measured during ir- ceeded with approximately the same rate whether the reac-
radiation of the (R) enantiomer of compound 3 in benzene, tion mixture was irradiated with the full spectrum of the
ethanol or THF show that, instead of one negative Cotton UV lamp or with a wavelength of 300–400 nm, which corre-
effect near 360 nm, three Cotton effects with alternating sponds to the position of the longwave absorption band in
signs arise, the positions of which coincide with the absorp- the UV spectrum of the parent carbamate. In both cases,
tion bands in the UV spectra. An increase in the rotary the half-conversion time was about 3 min, counting from
force of the Cotton effects for the dicarbonyl complex indi- the moment of switching on the lamp, or 30 s, counting
cates that local symmetry around the Mn atom changes as from the moment of stabilization of the work of the lamp
a result of chelation of the side chiral substituent. A mirror- (10 min). The quantum yield for 366 nm irradiation is
like picture of spectral changes in the CD spectra is ob- 0.98Ϯ0.04 in all cases, which is in accord with the literature
served upon irradiation of the (S) enantiomer of 3. When data.[9,11] The reverse reaction proceeded much slower: the
the conversion of (S)-3 achieves 50%, the Cotton effect half-conversion time was 60–90 min, but a sharp accelera-
bands are observed only for two compounds: the dicarbonyl tion of the reverse reaction occurred (half-conversion time
and tricarbonyl complexes (Figure 4).
was about 10 min) when the reaction mixture was irradiated
The data considered above have led to the conclusion with a wavelength of 480–530 nm corresponding to the
that photolysis of cymantrenyl carbamates resulted in ther- maximum of the first longwave band in the UV spectra of
modynamically stable chelate dicarbonyl complexes, in chelates (Scheme 2).
which the Mn atom is coordinated to the O atom of the
Thus, we found that photolysis of cymantrenyl carb-
carbamate substituent. Unfortunately, our attempts to ob- amates in closed systems can be used for the creation of
tain crystals of chelate complexes for X-ray analysis failed. novel photochromic systems. Availability of cymantrenyl
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Photochemistry of Tricarbonyl(cyclopentadienyl)manganese Derivatives
Figure 5. The calculated structure of chelate complex 6.
Table 2. Calculated energies and ν(CO) for carbamates 3–5 and dicarbonyl complexes 6–8.
Com-
pound
E [a.u.], ∆E
EЈ [a.u.], ∆EЈ
G [a.u.], ∆G [kcalmol–1] Calculated ν(CO)
[kcalmol–1]
[kcalmol–1]
3
6
4
7
5
8
–1117.15, –
–1003.80, +182.88
–1077.84, –
–964.49, +180.67
–1156.45, –
–1043.11, +159.08
–1116.84, –
–1003.50, +171.08
–1077.55, –
–964.21, +170.00
–1156.05, –
–1042.72, +145.35
–1116.89, –
–1003.55, +127.11
–1077.61, –
–964.26, +129.41
–1156.10, –
–1042.77, +113.38
1991(770), 1930 (922), 1920 (909), 1678 (579)
1933 (897), 1876 (1041), 1651 (449)
1989 (768), 1926 (914), 1921 (920), 1690 (593)
1936 (901), 1878 (1058), 1650 (560)
1993 (772), 1934 (925), 1919 (902), 1660 (570)
1934 (895), 1874 (1030), 1654 (401)
at 30–40 °C for 4–5 h. In this case, unreacted dicarbonyl
complex 6 results in the formation of a product with Rf =
0.85 (hexane/ethyl acetate, 3:1). The generation of this prod-
uct takes place in a yield of 60% at the irradiation of com-
pound 3 without PPh3. It was isolated by column
chromatography as a yellow oil. The IR spectrum of this
oil has no bands in the range of 1800–2100 cm–1 (MCO
stretch), but there was a strong absorption at 1700 cm–1 as-
Scheme 2.
1
sociated with the CO groups of the carbamates. In the H
NMR spectrum, there were six resonances from olefin pro-
tons in the range of 6–7 ppm, as well as the signals from
the protons of the CH3, tBu, CH and NH groups (see Ex-
perimental Section). These data, as well as the presence of
the molecular ion at m/z = 209 in the mass spectrum gave
reason to believe that the fraction with Rf = 0.85 (hexane/
ethyl acetate, 3:1) mainly contained two isomeric olefins
10a,b in a ratio of 1:1.3. Unfortunately, we failed to prepare
pure samples for analysis, because these olefins partially de-
composed in the course of chromatographic purification.
Apparently, olefins 10a,b are formed due to decomplexation
of the cyclopentadienyl ligand from the intermediate dicar-
bonyl manganese complex during isolation of photolysis
products. Earlier, we observed the formation of cyclopenta-
dienes in the photolysis of diphenylcymantrenylphos-
phane.[2] Recently the photolysis of cymantrene derivatives
carbamates in the optically active form allows their use for
selective excitation of circular polarized light.
The slow rate of the reverse reaction without initiation
by visible light points to rather high thermodynamic and
kinetic stability of chelates in ligand-substitution reactions.
Thus, irradiation of compound 3 in the closed system in
the presence of triphenylphosphane (1.5 equiv.) yields only
chelate dicarbonyl complex 6. Moreover, the only product
of the dark reaction of this chelate is the parent carbamate.
Nevertheless, the substitution of CO for PPh3 occurred in
a yield of 41% after 45 min, when the photolysis of an equi-
molecular mixture of carbamate 3 and triphenylphosphane
was run in the photoreactor under an intensive argon flow.
The yield of triphenylphosphane complex 9 increased to
83% when the irradiation of carbamate 3 was followed by
the addition of PPh3, then the dark reaction was performed in proton donor solvents has been reported as an efficient
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N. M. Loim et al.
FULL PAPER
logues. These deuterated compounds were prepared from α-deuter-
iocymantrenecarbaldehyde[14] and 1-(N,N,N-trimethylammonium)-
ethyl(α-deuteriocymantrene) iodide (12)[13,15] according to
Scheme 4.
method for the synthesis of substituted cyclopentadi-
enes.[12a,12b] Actually, the photolysis of carbamate 3 in a
mixture of diethyl ether/methanol (1:2) gives the same mix-
ture 10a,b with a product yield of 86%. A similar picture
was observed in the case of the photolysis of carbamates 4
and 5. In the case of compound 5, triphenylphosphane
complex 11 was isolated and characterized (Scheme 3).
Scheme 4.
1-Azidoethyl(α-deuteriocymantrene) (13): Sodium azide (8.1 g,
120 mmol) was dissolved in 75% aqueous diglyme (100 mL) with
heating. The solution was filtered, then compound 12 (5 g,
12 mmol) was added. The reaction mixture was heated at 100 °C
under an argon atmosphere in darkness for 55 h. Water (200 mL)
was added and the organics were extracted with diethyl ether
(3ϫ200 mL). The organic layer was washed with water to pH 7
and dried with MgSO4; then, the solvent was evaporated. The resi-
due was distilled in vacuo. B.p. 101–102 °C/0.08 Torr. Yield: 2 g
Scheme 3.
1
(61%). H NMR (400.13 MHz, CDCl3): δ = 1.45 (d, J = 6.6 Hz, 3
H, CH3), 4.24 (qd, J = 6.6 Hz, 1 H, CHCH3), 4.65 (m, 1 H, Cp-
H), 4.81 (m, 2 H, Cp-H) ppm. C10H8MnN3O3 (273.13): calcd. C
43.90, H 2.95, Mn 20.12; found C 44.09, H 3.02, Mn 19.93.
Conclusions
Photochemical properties of cymantrene carbamates
were for the first time investigated by IR, NMR, UV and
1-Aminoethylethyl(α-deuteriocymantrene) (1-D): NaBH4 (0.68 g,
CD spectroscopic methods. It was found that UV irradia- 18 mmol) was added in portion to a solution of 13 (2 g, 7.3 mmol)
in 2-propanol (30 mL), and the reaction mixture was heated at re-
flux for 16 h. Then, 20% H3PO4 (100 mL) was added dropwise,
and the organics were extracted with diethyl ether. The aqueous
layer was brought to pH 10 with 2  NaOH, and the organics were
extracted with diethyl ether. The combined ether layers were
washed with water to pH 8 and dried with MgSO4, and the solvent
was evaporated. The residue was distilled in vacuo. B.p. 87–88 °C/
8ϫ10–2 Torr (ref.[15] b.p. 80–81 °C/6ϫ10–2 Torr). Yield: 1 g (55%).
1H NMR (400.13 MHz, CDCl3): δ = 1.28 (d, J = 6.4 Hz, 3 H,
CH3), 3.74 (qd, J = 6.4 Hz, 1 H, CHCH3), 4.58 (m, 1 H, βH-Cp),
4.64 (m, 1 H, βH-Cp), 4.71, 4.81 (m, 0.5 H, αH-Cp) ppm.
tion of Boc-substituted 1-aminoalkylcymantrenes yields di-
carbonyl chelate complexes as a result of the coordination
of the oxygen atom of the carbamate ligand to the manga-
nese atom. The possibility for the formation of chelate com-
plexes was confirmed by DFT calculations. Dicarbonyl che-
lates show high thermodynamic stability in solution at
room temperature and in closed systems can be used for
the creation of photochromic systems based on cymantrene
carbamates due to reverse dissociation and recombination
of CO ligand.
Cymantrenecarbaldehyde Oxime (14): Cymantrenecarbaldehyde
(14 g, 60 mmol), NH2OH·HCl (6.4 g, 91 mmol) and sodium acetate
(9.3 g, 113 mmol) were dissolved in ethanol (100 mL), and the reac-
tion mixture was heated at reflux for 1 h. Then the reaction mixture
was cooled and concentrated to 1/4 volume. Water (100 mL) was
added to the residue, and the organics were extracted with diethyl
ether (3ϫ100mL). The organic layer was washed with 2  H2SO4
(75 mL) and water to pH 7 and dried with MgSO4. The solvent was
evaporated, and the residue was crystallized from benzene. Yellow
crystalline oxime was isolated. M.p. 144–145 °C. Yield: 11.2 g
Experimental Section
General Data: 1H and 31P NMR spectra were registered with a
Bruker Avance 400 (400.13 and 161.98 MHz, respectively) spec-
trometer. Chemical shifts were referenced to TMS by using residual
solvent protons as an internal standard. ESI mass spectra were
obtained with a Finnigan LCQ Advantage instrument. IR spectra
were measured with a Magna 750-IR (Nicolet) IR Fourier spec-
trometer in a cell with KBr windows. UV spectra were recorded
with a Specord M-40 UV/Vis spectrophotometer. CD spectra were
measured with an automatic recording spectrometer SKD-2 (Insti-
tutes of Molecular Biology and Spectroscopy, RAS). Specific rota-
tion angles were measured by using a Perkin–Elmer 341 polarime-
ter at a wavelength of 589 nm. Photochemical reactions were car-
ried out by using a UV immersion lamp Normag TQ 150 (running
of stationary conditions were realized in 3 min.) and filters passing
bands of 300–400 nm and 480–530 nm. Tetrahydrofuran (THF),
hexane and benzene were purified by conventional methods and
distilled from sodium benzophenone ketyl under an atmosphere of
argon. 1-Aminoethylcymantrene (1) and its (R) and (S) enantio-
mers and cymantrenecarbaldehyde were prepared according to the
methods reported earlier.[13,14] The signals for the α- and β-protons
of the Cp ring were assigned by using phase-sensitive 2D NOESY,
as well as comparing with the NMR spectra of deuterated ana-
1
(76%). H NMR (400.13 MHz, [D6]acetone) showed a mixture of
two isomers in a ratio of 2:1. Major isomer: δ = 5.05 (m, 2 H, Cp-
H), 5.69 (m, 2 H, Cp-H), 7.16 (s, 1 H, CH), 11.01 (s, 1 H, NOH)
ppm; minor isomer: δ = 5.05 (m, 2 H, Cp-H), 5.39 (m, 2 H, Cp-
H), 7.82 (s, 1 H, CH), 10.51 (s, 1 H, NOH) ppm. MS (ESI): m/z =
247 [M+], 163 [M+/3CO]. C9H6MnNO4 (247,15): calcd. C 43.76, H
2.45, N 5.66, Mn 22.25; found C 44.01, H 2.38, N 5.70, Mn 21.95.
Aminomethylcymantrene (2): Zn (13.5 g, 206 mmol) was gradually
added to a solution of oxime 15 (8.5 g, 34.4 mmol) in acetic acid
(35 mL) and water (2.5 mL). The process was exothermic. Then,
the reaction mixture was heated at reflux for 30 min, cooled to
80 °C and filtered off. The precipitate on the filter was washed with
acetic acid. The combined filtrates were neutralized to pH 9 with
25% ammonia water, and the organics were extracted with diethyl
ether. The organic layer was washed with 2  NaOH (50 mL) and
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Photochemistry of Tricarbonyl(cyclopentadienyl)manganese Derivatives
dried with MgSO4, and the solvent was evaporated. The residue
hour later the solution became yellow, and its TLC showed two
zones. The solution was filtered, the solvent was evaporated. 1.3 g
of the crude product was obtained. The mixture of two products
was distilled in vacuo. B.p. 110–111 °C/8ϫ10–2 Torr (ref.[16] b.p. 80–
81 °C/6ϫ10–2 Torr). Product 2 was isolated as a yellow oil. Yield:
1
6 g (75%). H NMR (400.13 MHz, [D8]toluene): δ = 0.75 (br. s, 2 was separated by column chromatography on SiO2 (benzene). Two
H, NH2), 3.05 (m, 2 H, CH2), 4.05 (m, 2 H, Cp-H), 4.21 (m, 2 H, fractions were isolated: complex 9 in a yield of 500 mg (41%) Rf =
Cp-H) ppm. MS (ESI): m/z = 233 [M+], 149 [M+/3CO].
0.64 (hexane/ethyl acetate, 3:1) and olefin 10 in a yield of 250 mg
(48%) Rf = 0.85 (hexane/ethyl acetate, 3:1). Complex 6 exists as
yellow crystals. M.p. 176–178 °C. 1H NMR (400.13 MHz, [D6]ben-
zene): δ = 1.51 (d, J = 6.6 Hz, 3 H, CHCH3), 1.75 [s, 9 H, C(CH3)],
4.05 (m, 2 H, Cp-Hβ), 4.65 (m, 2 H, Cp-Hα), 4.92 (br. s, 1 H, NH),
5.11 (m, 1 H, CHCH3), 7.29 (m, 10 H, PPh3), 7.83 (m, 5 H, PPh3)
ppm. 31P NMR (161.98 MHz, [D6]benzene): δ = 92.6 (s, PPh3)
Boc-Substituted 1-Aminoethylcymantrene (3): A solution of 1- ami-
noethylcymantrene (1; 2.47 g, 10 mmol) and (Boc)2O (2.5 g,
11.5 mmol) in THF (30 mL) was stirred for 1 h. Then, the solvent
was evaporated, and the residue was crystallized from hexane. Yel-
low crystals of 3 were isolated. M.p. 76–77 °C. Yield: 3.33 g (96%).
1H NMR (400.13 MHz, [D6]benzene): δ = 0.91 (d, J = 6.8 Hz, 3
H, CHCH3), 1.54 (s, 9 H, C(CH3)), 3.67 (m, 2 H,Cp-Hβ), 4.26 (m,
2 H, αH-Cp), 4.35 (br. s, 1 H, NH), 4.58 (m, 1 H, CHCH3) ppm.
ppm. IR (CH Cl ): ν = 1940, 1875 [ν(CO)] cm–1. C H MnNO P
˜
2
2
32 33
4
(581.65): calcd. C 66.09, H 5.71, N 2.41, P 5.33; found C 66.12, H
5.64, N 2.35, P 5.19.
IR (benzene): ν = 2040 [ν(CO)], 1930 (MCO), 1717 [ν(C=O)] cm–1.
˜
˜
IR (hexane): ν = 2025, 1948 [ν(CO)]; 1727 [ν(C=O)] cm–1. IR
Method B: A solution of compound 3 (870 mg, 2.5 mol) in benzene
(300 mL) was cooled to 7 °C under an atmosphere of argon with
stirring. The solution was then irradiated using the UV immersed
lamp. Just after the beginning of irradiation the solution gained a
crimson colour. The irradiation was run at 7–9 °C for 30 min.
Then, PPh3 (980 mg, 0.00375 mol) was added, and the reaction
mixture was stirred at 35–40 °C for 4 h and kept overnight. Two
products were formed. The solution was filtered, the solvent was
evaporated. 1.4 g of an oily residue was obtained. This oil was sepa-
rated by column chromatography on SiO2 (benzene). Two fractions
were isolated: complex 9 in a yield of 1 g (83%) and olefin 8 in a
yield of 80 mg (15%). The spectral characteristics of this complex
were identical to those of 6 obtained by method A.
(THF): ν = 2018, 1932 [ν(CO)], 1714 [ν(C=O)] cm–1. UV (benzene):
˜
λ (ε, Lmol–1) = 330 (531) nm. UV (THF): λ (ε, Lmol–1) = 331 (946)
nm. C15H18MnNO5 (347.33): calcd. C 51.88, H 5.22, N 4.03, Mn
15.82; found C 51.99, H 5.22, N 4.09, Mn 15.9.
Boc-Substituted Aminomethylcymantrene (4): The compound was
synthesized by the same procedure as 3 starting from 2 (6 g,
26 mmol) and Boc2O (6.5 g, 30 mmol). The yield of 4 was 8.3 g
1
(96%). Yellow solid. M.p. 86–87 °C. H NMR (400.13 MHz, [D6]-
benzene): δ = 1.51 [s, 9 H, C(CH3)], 3.52 (m, J = 5.8 Hz, 2 H,
CH2), 3.88 (m, 2 H, βH-Cp), 4.22 (m, 2 H, αH-Cp), 4.31 (br. s, 1
H, NH) ppm. IR (benzene): ν = 2022, 1933 [ν(CO)]; 1719 [ν(C=O)]
˜
cm–1. UV (benzene): λ (ε, Lmol–1) = 332 (1372) nm. C14H16MnNO5
(333.3): calcd. C 50.46, H 4.84, N 4.20, Mn 16.49; found C 50.63,
H 4.88, N 4.15, Mn 16.65.
Boc-Substituted 1-Aminoethylcyclopentadienes (10a,b): A solution
of compound 3 (501 mg, 1.4 mmol) in benzene (300 mL) or diethyl
ether/methanol (1:2) was cooled to 7 °C under an atmosphere of
argon with stirring. The solution was then irradiated using the UV
immersed lamp. Immediately after the beginning of irradiation the
solution became crimson. The reaction mixture was irradiated at
7–9 °C for 45 min and kept in darkness overnight. The solution
was filtered, the solvent was evaporated and the crude product
(350 mg) was purified by column chromatography on SiO2 (ben-
zene). Compounds 10a,b were isolated as yellow oils. Yield in ben-
zene: 177 mg (59%). Yield in diethyl ether/MeOH: 251 mg (86%).
1H NMR (400.13 MHz, [D6]benzene) revealed a mixture of two
isomers in a ratio of 1:1.3. Major isomer: δ = 1.33 (d, J = 6.6 Hz,
3 H, CHCH3), 1.65 [s, 9 H, C(CH3)], 2.85 (m, 2 H, CH2-Cp), 4.48
(m, 1 H, CHCH3), 6.04 (m, 1 H, CH-Cp), 6.33 (m, 1 H, CH-Cp),
6.60 (m, 1 H, CH-Cp) ppm; minor isomer: δ = 1.26 (d, J = 6.6 Hz,
3 H, CHCH3), 1.65 [s, 9 H, C(CH3)], 2.85 (m, 2 H, CH2-Cp), 4.40
(m, 1 H, CHCH3), 4.89 (br. s, 1 H, NH), 6.22 (m, 1 H, CH-Cp),
6.42 (m, 1 H, CH-Cp), 6.49 (m, 1 H, CH-Cp) ppm. IR (CH2Cl2):
Boc-Substituted (N-Methyl-1-aminoethyl)cymantrene (5): A solu-
tion of 3 (3.47 g, 10 mmol) in DMFA (20 mL) was cooled to 0 °C
under an atmosphere of argon with stirring. Then, a 60% suspen-
sion of sodium hydride (1.2 g, 30 mol) was gradually added, and
the mixture was kept at 0 °C for 1 h. Methyl iodide (5.04 mL,
80 mmol) was added. The mixture was heated to room temperature
and stirred for 2 h and then poured into water (50 mL); the or-
ganics were extracted with diethyl ether (3ϫ75mL). The organic
layer was dried with MgSO4, the solvent was evaporated and a
yellow oil was isolated. The product was purified by silica gel col-
umn chromatography (benzene). Yield: 2.6 g (71%). 1H NMR
(400.13 MHz, [D6]benzene): revealed a mixture of two conformers
in a ratio of 3:2. Major conformer: δ = 1.01 (d, J = 7.1 Hz, 3 H,
CHCH3), 1.55 [s, 9 H, C(CH3)], 2.46 (s, 3 H, NCH3), 3.84 (m, 1
H, Cp-Hβ), 4.01 (m, 1 H, Cp-HβЈ), 4.24 (m, 1 H, Cp-Hα), 4.46 (m,
1 H, Cp-HαЈ), 5.38 (m, 1 H, CHCH3) ppm; minor conformer: δ =
1.01 (d, J = 7.1 Hz, 3 H, CHCH3), 1.55 [s, 9 H, C(CH3)], 2.53 (s,
3 H, NCH3), 3.84 (m, 1 H, Cp-Hβ), 4.01 (m, 1 H, Cp-HβЈ), 4.17
(m, 1 H, Cp-Hα), 4.52 (m, 1 H, Cp-HαЈ), 5.07 (m, 1 H, CHCH3)
ν = 1700 [ν(C=O)] cm–1. MS (ESI): m/z = 209 [M+].
˜
ppm. IR (benzene): ν = 2020, 1935 [ν(CO)]; 1694 [ν(C=O)] cm–1.
Boc-Substituted
Dicarbonyl(N-methyl-1-aminoethylcyclopentadi-
˜
IR (hexane): ν = 2027, 1947 [ν(CO)]; 1708 [ν(C=O)] cm–1. UV (ben-
enyl)(triphenylphosphane)manganese (11): As in the case of the syn-
thesis of 6 by method B, compound 5 (0.90 g, 0.0025 mol) and PPh3
(0.98 g, 0.00375 mol) gave an oily residue, from which complex 11
was isolated as a yellow powder by column chromatography on
SiO2 (benzene) in a yield of 0.8 g (54%). M.p. 148–149 °C. 1H
NMR of 7 (400.13 MHz, [D6]benzene) showed a mixture of two
conformers in a ratio of 1:1.2. Major isomer: δ = 1.20 (d, J =
˜
zene): λ (ε, Lmol–1) = 330 (725) nm. UV (hexane): λ (ε, Lmol–1) =
330 (301) nm. C16H20MnNO5 (361.36): calcd. C 53.18, H 5.54, N
3.88, Mn 15.24; found C 53.77, H 5.98, N 3.85, Mn 14.83.
Boc-Substituted
(1-Aminoethylcyclopentadienyl)dicarbonyl(tri-
phenylphosphane)manganese (9)
Method A: A solution of compound 3 (870 mg, 2.5 mmol) and 6.1 Hz, 3 H, CHCH3), 1.50 [s, 9 H, C(CH3)], 2.76 (s, 3 H, NCH3),
PPh3 (650 mg, 2.5 mmol) in benzene (300 mL) was placed in a pho-
toreactor and cooled to 7 °C under an atmosphere of argon with
stirring. The solution was then irradiated using the UV immersion
lamp. Just after the beginning of irradiation the solution colour
became crimson. The irradiation was run at 7–9 °C for 45 min. An
4.05 (m, 1 H, Cp-Hβ), 4.53 (m, 1 H, Cp-HβЈ), 4.64 (m, 1 H, Cp-
Hα), 4.82 (m, 1 H, Cp-HαЈ), 5.61 (m, 1 H, CHCH3), 7.29 (m, 10
H, PPh3), 7.80 (m, 5 H, PPh3) ppm; minor isomer: δ = 1.20 (d, J
= 6.1 Hz, 3 H, CHCH3), 1.50 [s, 9 H, C(CH3)], 2.86 (s, 3 H, NCH3),
4.05 (m, 1 H, Cp-Hβ), 4.53 (m, 1 H, Cp-HβЈ), 4.64 (m, 1 H, Cp-
Eur. J. Inorg. Chem. 2009, 3636–3643
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3641

N. M. Loim et al.
FULL PAPER
Hα), 4.82 (m, 1 H, Cp-HαЈ), 5.86 (m, 1 H, CHCH3), 7.29 (m, 10 tional (LYP)] density functional theory with the default pruned fine
H, PPh3), 7.80 (m, 5 H, PPh3) ppm. 31P NMR (161.98 MHz, [D6]-
grids for energies with geometry optimization. The basis set for
benzene): δ = 93.2 (s, PPh3) ppm. C33H35MnNO4P (595.68): calcd. manganese was LanL2DZ.
C 66.54, H 5.93, N 2.35, P 5.20; found C 66.65, H 5.99, N 2.22, P
5.25.
Supporting Information (see footnote on the first page of this arti-
cle): Table of molecular orbital coefficients and figure of the struc-
The General Irradiation Procedure for the Spectral Study of Intra-
molecular Dicarbonyl Carbamate Complexes: Solutions of tricar-
bonyl compounds 3–5 in a required solvent (benzene, hexane, etha-
nol or THF; c = 2–4 m) were placed under an argon atmosphere
into an IR or UV cell, and the samples were irradiated with UV
light for 1–2 min with turning of lamp followed by the registration
of the spectra, then were repeated. To prepare samples for NMR
spectra, these solutions (c = 10–15 m) were filtered into an NMR
tube, bubbled with argon and irradiated with the UV lamp for
4 min. Distance between lamp and sample was 5 cm in all cases.
Width of irradiation window was 2 cm in IR cell, 1 cm in UV cell
and 5 mm in NMR tube.
Ferrioxalate actinometry was used for 366-nm irradiation.[17] Pho-
toproduct was identified by UV/Vis and IR spectra by comparison
with spectra for authentic samples. Quantitative analyses were
made by monitoring electronic spectral changes. Quantum yields
were determined from initial spectral changes where optical density
changes were linear with irradiation time. The quantum yield is
0.98Ϯ0.04 in all cases. This value is for conversion of Ͻ15%.
ture of dicarbonyl chelate complex 6 with number of atoms.
Acknowledgments
This study was partly supported by the Department of Chemistry
and Material Science of Russian Academy of Science (grants Pro-
gram P-18 and Program OCh-1). We would like to thank Dr.
Yury I. Lyakhovetsky for helpful discussions.
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Intramolecular Complex 6: 1H NMR (400.13 MHz, [D6]benzene): δ
= 0.75 (d, J = 6.7 Hz, 3 H, CHCH3), 1.13 [s, 9 H, C(CH3)], 2.87
(m, 1 H, Cp-Hβ), 3.06 (q, J = 6.7 Hz, 1 H, CHCH3), 3.36 (m, 1
H, Cp-HβЈ), 3.94 (br. s, 1 H, NH), 5.04 (m, 1 H, αH-Cp), 5.10 (m,
1 H, αЈH-Cp) ppm. IR (benzene): ν = 1930, 1857 [ν(CO)]; 1666
˜
[ν(C=O)] cm–1. IR (hexane): ν = 1943, 1874 [ν(CO)]; 1674 [ν(C=O)]
˜
cm–1. IR (THF): ν = 1929, 1854 [ν(CO)]; 1658 [ν(C=O)] cm–1. UV
˜
(benzene): λ (ε, Lmol–1) = 330 (1651), 426 (178), 516 (245) nm. UV
(THF): λ (ε, Lmol–1) = 331 (2760), 426 (212), 511 (246) nm.
Intramolecular Complex 7: 1H NMR (400.13 MHz, [D6]benzene): δ
= 1.09 [s, 9 H, C(CH3)], 2.72 (m, 2 H, Cp-Hβ), 3.11 (s, 2 H, CH2),
3.70 (br. s, 1 H, NH), 5.07 (m, 2 H, Cp-Hα) ppm. IR (benzene): ν
˜
= 1933, 1856 [ν(CO)]; 1668 [ν(C=O)] cm–1. UV (benzene): λ (ε,
Lmol–1) = 332 (4253), 426 (271), 516 (200) nm.
Intramolecular Complex 8: 1H NMR (400.13 MHz, [D6]benzene): δ
= 0.91 (d, J = 7.0 Hz, 3 H, CHCH3), 1.12 [s, 9 H, C(CH3)], 2.21
(s, 3 H, NCH3), 2.71 (m, 1 H, Cp-Hβ), 3.25 (m, 1 H, CHCH3),
3.65 (m, 1 H, Cp-Hβ), 5.17 (m, 2 H, Cp-Hα) ppm. IR (benzene):
ν = 1955, 1854 [ν(CO)]; 1640 [ν(C=O)] cm–1. IR (hexane): ν = 1940,
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˜
˜
1841 [ν(CO)]; 1649 [ν(C=O)] cm–1. UV (benzene): λ (ε, Lmol–1) =
330 (1649), 426 (179), 515 (179) nm. UV (hexane): λ (ε, Lmol–1) =
330 (546), 426 (177), 523 (136) nm.
The General Irradiation Procedure in Closed Systems: Solutions of
2–4 m tricarbonyl compounds 3–5 in benzene were saturated with
argon and placed into an IR cell, then the samples were irradiated
with UV light of full spectra or 300–400 nm band followed by the
registration of the spectra. Irradiated solutions were kept in the
darkness or were irradiated with visible light of 480–530 nm at
room temperature followed by the registration of spectra. Distance
between lamp and sample was 5 cm in all cases. Width of irradia-
tion window was 2 cm in IR cell. Both the total view of the IR
spectrum and the stretching mode intensities for CO groups in the
starting compound and the product after three- and fourfold repeti-
tion of the process: irradiation–dark reaction did not change.
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Calculation: Theoretical calculations were carried out using the
Gaussian98[18] implementions of B3LYP [Becke three-parameter
exchange functional (B3) and Lee–Yang–Parr correlation func-
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Eur. J. Inorg. Chem. 2009, 3636–3643

Photochemistry of Tricarbonyl(cyclopentadienyl)manganese Derivatives
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Received: May 20, 2009
Published Online: July 8, 2009
Eur. J. Inorg. Chem. 2009, 3636–3643
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3643