Synthesis, characterisation and reactivity of novel bis(tosyl)imidoruthenium(VI) porphyrin complexes; X-ray crystal structure of a tosylamidoruthenium(IV) porphyrin

Article abstract of DOI:10.1039/a702093g

Bis(tosyl)imidoruthenium(VI) porphyrin complexes are prepared and characterised by spectroscopic means; [Ru^VI-(tpp)(NTs)₂] can undergo imido group transfer reactions with alkenes to afford aziridines, as well as C-H bond oxidation of

Full text of DOI:10.1039/a702093g

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis, characterisation and reactivity of novel bis(tosyl)imidoruthenium(vi)
porphyrin complexes; X-ray crystal structure of a tosylamidoruthenium(iv)
porphyrin
Sze-Man Au,a Wai-Hong Fung,a Ming-Chuan Cheng,a Chi-Ming Che*a and Shie-Ming Peng†b
a Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
b Department of Chemistry, National Taiwan University, Taipei, Taiwan
Bis(tosyl)imidoruthenium(VI) porphyrin complexes are pre-
pared and characterised by spectroscopic means; [RuVI-
(tpp)(NTs)2] can undergo imido group transfer reactions
with alkenes to afford aziridines, as well as C–H bond
oxidation of benzyl alcohol to give benzaldehyde; a tosyl-
amido ruthenium(IV) complex is also isolated and charac-
terised by X-ray diffraction.
doublets at d 6.45 and 4.87. The pyrrolic protons for 1 (d 8.82)
appear at higher field than that for [RuVI(tpp)O2] (d 9.1),10 this
coincides with the fact that the (tosyl)imido ligand is a stronger
p donor than the oxo ligand.12
At room temp., 1 reacts readily with alkenes to give aziridines
in good yields (Table 1). With the addition of pyrazole (Hpz),
apart from aziridines [RuIV(tpp)(NHTs)(pz)] 3 (NHTs = tosy-
lamido) was also isolated and characterised.‡ The UV–VIS and
IR absorption spectra of 3 (oxidation marker band at 1012
cm21) are very similar to those observed for [RuIV(tpp-(OMe)3-
The transition metal catalysed aziridination of alkenes by
PhINTs provides direct access to aziridines from alkenes. This
reaction can be performed selectively and, in some cases, high
enantioselectivity can be attained.1–3 However, the mechanism
of the reaction remains elusive, it becomes difficult to improve
the catalysis in a rational manner. Although both the metal–
imido species [MNNTs] and the Lewis-acid PhINTs adduct
[M–N(Ts)(IPh)] have been proposed to be the reactive inter-
mediates, neither has been isolated or spectroscopically charac-
terised.1 Reports on imidoruthenium complexes remain sparse,
notable examples include [RuVI(tpp)(NBut)O],4 trans-
3,4,5)(NPh2)2][tpp-(OMe)3-3,4,5
= dianion of meso-tetra-
kis(3,4,5-trimethoxyphenyl)porphyrin].13 Together with the
magnetic susceptibility measurement [meff = 3.20 mB (300 K),
Evans method], the formulation as ruthenium(iv) with two
unpaired electrons in the ground state is confirmed. The
0.35
14
12
(a)
(b)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
6
[RuIV(NBut)2(PMe3)4]5 and [RuII·NC6H2But3-2,4,6)(h -p-
cymene)],6 but none of them are known for imido group transfer
reactions with alkenes. Indeed, there are few reports in the
literature concerning alkene aziridination reactions using a well
characterised metal–imido complex.7 Herein we describe the
synthesis, spectroscopic characterisation and reactivities of the
bis(tosyl)imidoruthenium(vi) porphyrin complexes [RuVI-
(tpp)(NTs)2] 1 and [RuVI(oep)(NTs)2] 2 (tpp = dianion of
10
8
450 500 550 600 650 700
λ / nm
6
4
2
5,10,15,20-tetraphenylporphyrin, oep
=
dianion of
2,3,7,8,12,13,17,18-octaethylporphyrin, Ts = tosyl).
0
200
300
400
500
600
700
Complexes 1 and 2 were prepared by the treatment of the
λ / nm
corresponding
[RuII(por)(CO)(MeOH)]
complexes8
(por = dianion of porphyrin, 0.2 mmol) with PhINTs9 (0.6
mmol) in dried CH2Cl2 (20 ml) for 5 min at room temp. under
an inert atmosphere. Removal of the solvent followed by
washing with MeOH afforded the desired products as red–violet
solids. The complexes were further purified by chromatography
on a short neutral alumina column with CH2Cl2 as the eluent
(overall yield 60%†).
Fig. 1 (a) UV–VIS spectrum of [RuVI(tpp)(NTs)2] 1; (b) UV–VIS spectral
trace for the reaction of 1 with styrene in CH2Cl2 (2% pyrazole) (450–700
nm)
Table 1 Stoichiometric alkene aziridination and C–H oxidation of benzyl
alcohol by [RuVI(tpp)(NTs)2]
Entry
1
Substrate
Product
NTs
Yielda (%)
75
The imidoruthenium(vi) complexes 1 and 2 are stable in the
solid state at 220 °C for days, whereas in purified CH2Cl2 the
compounds can be kept for hours at room temp. without
significant decomposition. Their UV–VIS absorption spectra
highly resemble those of structurally related dioxoruthe-
nium(vi) porphyrin complexes10,11 (Fig. 1). The IR spectra of 1
and 2 exhibit intense nas(RuNNTs) stretching absorptions at 914
and 900 cm21 respectively, which are at lower wavenumbers
than the nas(OsNNTs) absorption at 924 cm21 found in
[OsVI(tpp)(p-NC6H4NO2)2].12 It is important to note that the
oxidation state markers for 1 and 2 appear at 1016 and 1018
cm21 respectively, which is in accordance with the formulation
of the ruthenium(vi) oxidation state.10a,11 The diamagnetic
behaviour of the complexes, together with the above findings,
Ph
Ph
NTs
2
3
78
71
p-MeC6H4
p-MeC6H4
p-ClC6H4
NTs
p-ClC6H4
NTs
4
5
68
95
PhCHO
TsNH2
a Isolated yield based on the amount of [RuVI(tpp)(NTs)2].
Ph
OH
1
strongly suggest a terminal d2 metal–imido system. H NMR
100
spectra reveal that 1 and 2 possess pseudo D4h symmetry, and
the aromatic protons of the Ts groups (HA and HB) appear as
Chem. Commun., 1997
1655

View Article Online
was found to be: rate = k2[RuVI][PhCH2OH], with the second-
order rate constant of (3.6 ± 0.1) 3 1021 dm3 mol21 s21 at 298
K. It is noteworthy that a large primary kinetic isotope effect
was observed using PhCD2OH (kH/ kD = 7.4) indicating that the
reaction should proceed via a hydrogen atom abstraction
pathway.
C(50)
C(48)
C(49)
C(47)
C(51)
C(23)
O(1)
C(22)
C(45)
C(46)
C(24)
C(25)
S
C(21)
N(5)
O(2)
C(2)
C(3)
C(5)
C(7)
We acknowledge support from The University of Hong Kong
and the Hong Kong Research Grants Council.
C(31)
C(32)
C(41)
C(40)
C(8)
C(6)
C(26)
C(4)
C(9)
C(39)
C(20)
N(1)
N(2)
C(1)
C(42)
C(30)
C(29)
N(4)
C(11)
Footnotes and References
N(3)
Ru
C(10)
C(27)
C(19)
C(16)
* E-mail: cmche@hkucc.hku.hk
† For correspondence regarding the crystallography.
C(34)
C(14)
N(6)
C(15)
C(44)
C(43)
C(18)
C(28)
C(12)
C(13)
C(17)
C(35)
‡ Satisfactory elemental analyses were obtained for all compounds. UV–
VIS [lmax/nm (log emax/dm3mol21cm21)] (CH2Cl2): 1 416 (5.14), 536
(4.18), 568 (3.77); 2 406 (5.07), 520 (4.21), 551 (4.16); 3 412 (5.07), 530
(3.96). 1H NMR (300 MHz, TMS, CD2Cl2): 1 dH 2.17(s, Me, 6H), 4.87(d,
4H), 6.45(d, 4H), 7.79(m, 12H), 8.18(m, 8H), 8.82(s, 8H); 2 dH 1.99(t,
24H), 2.29(s, 6H), 4.07(q, 16H), 4.63(d, 4H), 6.48(d, 4H), 10.0(s, 4H). IR
C(33)
C(52)
C(53)
N(7)
C(36)
C(38)
C(54)
C(37)
Fig. 2 A perspective view of 3 with atom labelling scheme. Selected bond
distances (Å) and angles (°): Ru–N(5) 2.025(11), Ru–N(6) 2.111(11), Ru–
N(1) 2.041(8), Ru–N(2) 2.032(9), Ru–N(3) 2.033(8), Ru–N(4) 2.037(9);
N(5)–Ru–N(6) 176.2(4), Ru–N(5)–S 136.4(7).
(Nujol) 1 914, 1016 cm21; 2 900, 1018 cm21; 3 1012 cm21
§ Crystal data for 3: C54H39N7O2RuS, M = 951.09, monoclinic, space
group P21/c, a 13.308(2), b 14.473(5), c 25.678(6) Å, b
.
=
=
=
= 90.05(2)°, U = 4945.7(22) Å3, Z = 4, Dc = 1.277 g cm23, m = 33.162
cm21, F(000) = 1952, crystal dimensions 0.03 3 0.10 3 0.50 mm.
Intensity data were collected at 298 K on a Enraf-Nonius CAD4
diffractometer with graphite-monochromated Mo-Ka radiation (l = 1.5418
Å). A total of 7540 unique reflections were measured and 4438 with
I > 2s(I) were used as refinement; R = 0.061, Rw = 0.087, GOF = 1.43.
The final Fourier difference map showed residual extrema in the range 1.36
to 20.650 e Å23. CCDC 182/535.
structure of 3 has been established by X-ray crystal analysis.‡
As shown in Fig. 2, the Ru–N(5) bond distance of 2.025(11) Å
is comparable to the RuIV–N(amide) distances of
1.987–2.044(5)
Å
found in [RuIV(chbae)(PPh3)(py)]
[chbae = 1,2-bis(3,5-dichloro-2-hydroxybenzamido)ethane
tetraanion].14 The Ru–N(5)–S(1) bond angle of 136.4(7)° is not
unexpected for a coordinated amide ligand since a similar value
of 138.4(6)° has been reported for [RuII(Et2dtc)(PPh3)2-
(CO)(NHSO2C6H2Pri3-2,4,6)] (Et2dtc = N,N’-diethyldithio-
carbamate).15
1 D. A. Evans, M. M. Faul and M. T. Bilodeau, J. Am. Chem. Soc., 1994,
116, 2742.
2 J. P. Mahy, G. Bedi, P. Battioni and D. Mansuy, J. Chem. Soc., Perkin
Trans. 2, 1988, 1517.
3 R. Breslow and S. H. Gellman, J. Chem. Soc., Chem. Commun., 1982,
1400.
The UV–VIS spectral trace for the reaction of 1 with excess
styrene in CH2Cl2 containing pyrazole (2% m/m) exhibited
clean isosbestic points [Fig. 1(b)]. The reactions of 1 with
alkenes followed the second-order rate law, rate = k2[RuVI]-
[alkene]. The second-order rate constants k2 measured at 298 K
are (9.7 ± 0.3) 3 1023 and (1.1 ± 0.1) 3 1023 dm3 mol21 s21for
styrene and norbornene, respectively. The activation parameters
for the styrene aziridination by 1 were determined to be
DH‡ = 4.7 ± 0.1 kcal mol21 and DS‡ = 252.4 ± 0.2 cal K21
mol21 (1 cal = 4.184J). The negative value of DS‡ is consistent
with an associative mechanism. For the aziridination of various
para-substituted styrenes (p-OMe, -Me, -F, -Cl, -CF3) by 1, the
k2 values were found to span a narrow range. The log krel
[krel = k2(p-substituted styrene)/k2(styrene)] values correlate
linearly with the s+ values with a small magnitude of r+ = 21.1
(R = 0.98); this indicates a minor development of positive
charge in the transition state.
4 J. S. Huang, C. M. Che and C. K. Poon, J. Chem. Soc., Chem. Commun.,
1992, 161.
5 A. A. Danopoulos, G. Wilkinson, B. Hussain-Bates and M. B.
Hursthouse, Polyhedron, 1992, 11, 2961.
6 A. K. Burrell and A. J. Steedman, J. Chem. Soc., Chem. Commun., 1995,
2109.
7 J. T. Groves and T. Takahashi, J. Am. Chem. Soc., 1983, 105, 2073.
8 R. C. Young, J. K. Nagle, T. J. Meyer and P. G. Whitten, J. Am. Chem.
Soc., 1978, 100, 4473.
9 Y. Yamada, T. Yamamoto and M. Okawara, Chem. Lett., 1975, 361.
10 (a) W. H. Leung and C. M. Che, J. Am. Chem. Soc., 1989, 111, 8812; (b)
C. Ho, W. H. Leung and C. M. Che, J. Chem. Soc., Dalton Trans., 1991,
2933.
11 J. T. Groves and K. H. Ahn, Inorg. Chem., 1987, 26, 3831.
12 J. A. Smieja, K. M. Omberg and G. L. Breneman, Inorg. Chem.,1994,
33, 614.
13 J. S. Huang, C. M. Che, Z. Y. Li and C. K. Poon, Inorg. Chem.,1992, 31,
1315.
14 C. M. Che, W. K. Cheng, W. H. Leung and T. C. W. Mak, J. Chem. Soc.,
Chem. Commun., 1987, 418.
Stoichiometric oxidation of benzyl alcohol by 1 in dichloro-
methane containing pyrazole (2% m/m) gave benzaldehyde and
tosyl amine quantitatively (Table 1), and 3 was formed as the
product of the reduction of the imidoruthenium(vi) complex.
The observed rate law for the reaction of benzyl alcohol with 1
15 W. H. Leung, M. C. Wu, J. L. C. Chim and W. T. Wong, Inorg. Chem.,
1996, 35, 4801.
Received in Cambridge, UK, 26th March 1997, 7/02093G
1656
Chem. Commun., 1997