The first organoruthenium(IV) complexes containing nitrogen donor ligands by oxidative addition of allylic substrates to coordinatively unsaturated Ru(II) complexes

Article abstract of DOI:10.1039/b002927k

Oxidative addition of allylic substrates to coordinatively unsaturated ruthenium(II), (n⁵-C₅Me₅)Ru(amidinate) complexes, afford cationic ruthenium(IV) compounds, [(n⁵-C₅Me₅)Ru(amidinate)(n<

Full text of DOI:10.1039/b002927k

The first organoruthenium(IV) complexes containing nitrogen donor ligands by
oxidative addition of allylic substrates to coordinatively unsaturated Ru(II
)
complexes†
Hideo Kondo, Yoshitaka Yamaguchi and Hideo Nagashima*
Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816-8580, Japan and CREST, Japan
Science and Technology Corporation (JST), Japan. E-mail: nagasima@cm.kyushu-u.ac.jp
Received (in Cambridge, UK) 12th April 2000, Accepted 8th May 2000
Oxidative addition of allylic substrates to coordinatively
room temperature. After 1 h, the solvent was removed in vacuo.
Spectroscopic evidence suggests that the resulting yellow solid
5
unsaturated ruthenium(II), (h -C5Me5)Ru(amidinate) com-
5
5
3
plexes, afford cationic ruthenium(IV) compounds, [(h -
is [(h -C5Me5)Ru(amidinate)(h -allyl)]Cl 2a (yield of the crude
3
5 3
C5Me5)Ru(amidinate)(h -allyl)]+, which have been charac-
product > 95%) containing ca. 5% of (h -C5Me5)Ru(h -
4a 3
terized by spectroscopic analysis and X-ray structure
determination.
allyl)Cl2. This new h -allyl complex 2a is not very stable in
solution and gradually decomposes to a mixture of intractable
products. In contrast, 3a, a stable analogue of 2a, was
successfully isolated as a yellow solid in 48% yield by exchange
Studies on the structures and reactions of coordinatively
unsaturated transition metal complexes have received much
attention from organometallic chemists, because these com-
pounds are believed to be involved in many transition metal-
mediated organic reactions as important intermediates.1 In
particular, the structures and reactions of coordinatively
unsaturated ruthenium(II) complexes have been actively investi-
gated recently;1 these studies contribute to the understanding of
the factors leading to the stabilization of these complexes, e.g.
steric effects, presence of p-donor ligands, metal-bond strength
and their tendency towards oxidative addition of H2 and
HSiR3.1–3 Although the oxidative addition of allylic substrates
to ruthenium(II) complexes4 is an important elementary reaction
in the catalytic transformation of an allyl moiety,5 that to
isolated coordinatively unsaturated ruthenium compounds has
not, as yet, been studied.1–3 We have recently reported a novel
in CHCl3 of the counter anion Cl2 to PF6 followed by
2
recrystallization of the crude product. Complex 3a could also be
obtained directly from 1a by treatment with allyl chloride in the
presence of NaPF6. The oxidative addition of allyl acetate or
allyl methyl carbonate in the presence of NaPF6 offers an
alternative synthetic method for 3a without formation of by-
products; 3a was isolated in quantitative yield. In a similar
fashion, 3b, a methallyl analogue of 3a, and a compound 3c,
bearing a different amidinate ligand, were successfully prepared
and characterized as shown in Table 1.
Table 1
Isolated
Precursor
R2
X
Method Product yield (%)
5
reactive complex, (h -C5Me5)Ru(amidinate) 1, which shows
1a
1a
1c
1a
1a
1c
1a
1a
H
Me
H
H
Me
H
Cl
Cl
Cl
Cl
Cl
Cl
A
A
A
B
B
B
B
B
3a
3b
3c
3a
3b
3c
3a
3a
48
55
62
64
39
62
97
97
signs of coordinative unsaturation, in which the amidinate
ligand contributes to stabilizing the formally 16-electron
configuration.6 The fact that 1 is highly reactive towards the
reaction with a variety of two-electron donor ligands stimulated
us to explore the possibility that 1 may also be reactive towards
oxidative addition reactions.6 Here, we report that 1 readily
reacts with an allylic substrate to give the corresponding
cationic Ru(IV) allylic compound as shown in Scheme 1. This is
the first example, to the best of our knowledge, of oxidative
addition of allylic substrates to isolable coordinatively un-
saturated ruthenium complexes. Additionally, the product is a
rare example of an organoruthenium(IV) compound coordinated
to nitrogen donor ligands.
H
H
OCOMe
OCO2Me
Complex 3a was fully characterized by spectroscopic
methods (1H NMR, 13C NMR, IR),‡ elemental analyisis and an
X-ray crystal structure determination§ and an ORTEP drawing
of 3a is shown in Fig. 1. Complex 3a has a square-pyramidal
structure, with two nitrogen atoms of the amidinate ligand and
3
terminal carbons of the h -allyl ligand at the basal positions.
Complex 1a was treated with a stoichiometric amount of allyl
chloride at 278 °C and the mixture was allowed to warm to
The orientation of the allyl group is endo, and variable
temperature NMR studies showed that there is no equilibrium
with the corresponding exo isomer. This endo orientation is also
5
3
seen in (h -C5Me5)Ru(h -allyl)X2 reported previously.4a The
† Electronic supplementary information (ESI) available: typical procedures
and spectroscopic data. See http://www.rsc.org/suppdata/cc/b0/b002927k/
crystal structure of 3a, in comparison with that of the starting
Scheme 1 Method A; allyl–Cl in pentane followed by NH4PF6 in CHCl3; method B; allyl–X (X = Cl, OAc, OCO2Me) and NaPF6 in THF. For 1–3: a, R
= But, R1 = Ph, R2 = H; b, R = But, R1 = Ph, R2 = Me; c, R = Pri, R1 = Me, R2 = H.
DOI: 10.1039/b002927k
Chem. Commun., 2000, 1075–1076
This journal is © The Royal Society of Chemistry 2000
1075

Scheme 2
We are grateful to Kouki Matsubara (Kyushu Univ.) for his
help in the X-ray analyses. Part of this work is financially
supported by the Japan Society of the Promotion of Science
(Grant-in-Aid for Scientific Research 10450343).
Notes and references
‡ Representative spectroscopic evidence: 3a; 1H NMR (CDCl3): d 0.95 [s,
18H, C(CH3)3], 1.81 [s, 15H, C5(CH3)5], 2.22 (d, J = 10.2 Hz, 2H, anti-CH
of the allyl group), 4.53 (d, J = 6.1 Hz, 2H, syn-CH of the allyl group), 5.36
(dt, J = 6.1, 10.2 Hz, 1H, central-CH of the allyl group), 7.16 (m, 1H,
C6H5), 7.24 (m, 1H, C6H5), 7.32 (m, 1H, C6H5), 7.35 (m, 1H, C6H5), 7.44
(m, 1H, C6H5). 13C{1H} NMR (CDCl3): d 10.9 [C5(CH3)5], 35.5 [C(CH3)3],
58.0 [C(CH3)3], 59.7 (CH2 of the allyl group), 97.2 (CH of the allyl group),
106.6 [C5(CH3)5], 127.4, 127.6, 127.8, 129.9, 132.8, 138.6 (C6H5), 178.9
(NCN). Anal. Calc. for C28H43N2PF6Ru: C, 51.45; H, 6.63; N, 4.29. Found:
C, 51.22; H, 6.62; N, 4.34%.
Fig. 1 ORTEP drawing of 3a showing 50% thermal ellipsoids. PF62 omitted
for clarity. Selected bond lengths (Å) and angles (°): Ru(1)–C(1–5)av
2.263(4), Ru(1)–N(1), 2.128(3), Ru(1)–N(2) 2.125(3), Ru(1)–C(11)
2.193(5), Ru(1)–C(12) 2.132, Ru(1)–C(13) 2.206, C(11)–C(12) 1.385(8),
C(12)–C(13) 1.379(8); N(1)–Ru(1)–N(2) 61.98(12), C(11)–Ru(1)–C(12)
64.1(2), C(11)–C(12)–C(13) 115.2(5).
§ Crystal data for C28H43F6N2PRu 3a: M = 653.68, orthorhombic, space
group Pbca, a = 31.771(6), b = 14.038(4), c = 13.366(5) Å, V =
5961(3) Å3, T = 293 K, Z = 8, m = 0.637 mm21, 6849 reflections
material 1a reveals that the Ru–N and Ru–C bonds (average)
become longer [1a: Ru–N 2.073(3) Å, Ru–Cav 2.158(4) Å].
The chemical reactivity of the h -allyl moiety is an
measured, 6848 unique (Rint
= 0.0409), 4403 observed ( > 2s), final
3
residuals R1 = 0.0492, wR2 = 0.1418 [I > 2s(I)]; R1 = 0.0917, wR2 =
0.1620 (all data). CCDC 182/1633. See http://www.rsc.org/suppdata/cc/b0/
b002927k/ for crystallographic files in .cif format.
interesting problem for the exploration of stoichiometric and
catalytic reactions mediated by 1 or 2. Preliminary studies on
the reactivity of 3a revealed that it reacted with nucleophiles
such as PhLi and sodium dimethyl methylmalonate but not with
electrophiles such as aldehydes and unsaturated molecules such
as ethylene and CO. The stoichiometric reaction of 3a with PhLi
in THF gave a mixture of 1-phenylprop-1-ene and 1-phenyl-
prop-2-ene in a ratio of 1+2. Similarly, treatment of 3a with
sodium dimethyl methylmalonate resulted in formation of
dimethyl allylmethylmalonate. In both of the reactions, re-
generation of 1a was also observed. The latter allylation
reaction can be extended to a catalytic reactions when allyl
methyl carbonate is used as the allylic substrate; 1a (10 mol%)
successfully catalyzed the reaction of allyl methyl carbonate
with dimethyl methyl malonate in THF at room temperature to
give the product in 90% yield (Scheme 2).
1 For a recent extensive review, see: R. Poli, Chem. Rev., 1996, 96, 2135
and references therein.
2 For a review on coordinatively unsaturated Ru(II) complexes, see: K. G.
Caulton, New. J. Chem., 1994, 18, 25 and references therein.
3 For recent studies of coordinatively unsaturated ruthenium(II) complexes
stabilized by nitrogen donor ligands, see the following literature and
references cited therein: C. Gemel, K. Mereite, R. Schmid and K.
Kirchner, Organometallics, 1997, 16, 5601; K.-J. Haack, S. Hayashi, A.
Fujii, T. Ikariya and R. Noyori, Angew. Chem., Int. Ed. Engl., 1997, 36,
285; C. Gemel, J. C. Huffman, K. G. Caulton, K. Mauthner and K.
Kirchner, J. Organomet. Chem., 2000, 593, 342.
4 (a) H. Nagashima, K. Mukai and K. Itoh, Organometallics, 1984, 3,
1314; H. Nagashima, K. Mukai, Y. Shiota, K. Yamaguchi, K. Ara, T.
Fukahori, H. Suzuki, M. Akita, Y. Moro-oka and K. Itoh, Organome-
tallics, 1990, 9, 799; (b) M. O. Albers, D. C. Liles, D. J. Robinson, A.
Shaver and E. Singleton, Organometallics, 1987, 6, 2347; (c) P. J. Fagan,
W. S. Mahoney, J. C. Calabrese and I .D. Williams, Organometallics,
1990, 9, 1843; (d) E. Rüba, W. Simanko, K. Mauthner, K. M. Soldouzi,
C. Slugovc, K. Mereiter, R. Schmid and K. Kirchner, Organometallics,
1999, 18, 3843 and references therein.
In conclusion, oxidative addition of allylic substrates to the
5
isolable coordinatively unsaturated complex (h -C5Me5)Ru(h-
amidinate), has been observed which leads to a new cationic
5
3
organoruthenium(IV) complex [(h -C5Me5)Ru(h -allyl)(h-ami-
dinate)]+ stabilized by a nitrogen-donor ligand. This oxidative
addition is envisioned to be extendable to stoichiometric and
catalytic transformations of allylic substrates mediated by 1–3,
as already evidenced by our preliminary studies on the reactions
of 3a with nucleophiles.
5 T. Kondo, H. Ono, N. Sataka, T. Mitsudo and Y. Watanabe, Organome-
tallics, 1995, 14, 1945; T. Kondo, Y. Morisaki, S. Uenoyama, K. Wada
and T. Mitsudo, J. Am. Chem. Soc., 1999, 121, 8657 and references
therein.
6 Y. Yamaguchi and H. Nagashima, Organometallics, 2000, 19, 725.
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Chem. Commun., 2000, 1075–1076