Unexpected coupling between an η5-indenyl ligand and alkenyl-vinylidene fragments: Synthesis of unprecedented (η6-indene)ruthenium(II) metallacycles

Article abstract of DOI:10.1039/b212406h

Vinylidene complexes [Ru{=C=C(H)CR¹R²CH₂C(Me)= CH₂}(η⁵-C₉H₇)(PPh ₃)₂][BF₄] undergo an intramolecular coupling between the alkenyl-vinylidene frag

Full text of DOI:10.1039/b212406h

Unexpected coupling between an h5-indenyl ligand and
alkenyl-vinylidene fragments: synthesis of unprecedented
(h6-indene)ruthenium(II) metallacycles†
Victorio Cadierno,a Salvador Conejero,a Josefina Díez,a M. Pilar Gamasa,a José Gimeno*a and
Santiago García-Grandab
a Departamento de Química Orgánica e Inorgánica/I.U.Q.O.E.M., Facultad de Química, Universidad de
Oviedo-C.S.I.C, 33071 Oviedo, Spain. E-mail: jgh@sauron.quimica.uniovi.es; Fax: +34985103446
b Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, 33071
Oviedo, Spain
Received (in Cambridge, UK) 17th December 2002, Accepted 14th February 2003
First published as an Advance Article on the web 28th February 2003
Vinylidene complexes [Ru{NCNC(H)CR1R2CH2C(Me)N
CH2}(h5-C9H7)(PPh3)2][BF4] undergo an intramolecular
coupling between the alkenyl-vinylidene fragment and the
h5-indenyl ligand to afford indene-metallacyclic compounds
(6a,b) in which the resulting functionalised indene group is
h6-coordinated to the metal.
Demetalation of vinylidenes 3a–d in refluxing acetonitrile
proceeds as expected (except for 3a), yielding the novel
1,5-enynes 4b–d (90–94% isolated yields) and the nitrile
5
complex [Ru(h -C9H7)(N·CMe)(PPh3)2][BF4] (5) quantita-
tively
(Scheme
1).‡
All
attempts
to
prepare
HC·CCPh2CH2C(Me)NCH2 by heating acetonitrile solutions of
3a failed, resulting instead, besides free PPh3, in complicated
mixtures of uncharacterized species. However, stirring a
solution of 3a in acetonitrile or dichloromethane at room
temperature gives in ca. 3 h the unprecedented cyclometalated
The reactivity of transition-metal allenylidene complexes
[M]NCNCNCR2 has attracted a great deal of attention in the last
decade1 and important applications in organic synthesis are now
emerging.2 In this context, we have recently reported an easy
entry to terminal 1,5-enynes HC·CCR1R2CH2CHNCH2 starting
from indenyl-ruthenium(II) allenylidenes [Ru(NCNCNCR1R2)-
6
(h -indene)ruthenium(II) complex 6a, isolated from the reaction
mixture as an air-stable orange solid (87% yield) (Scheme 2).§
Similarly, vinylidene derivatives 3b–d give also analogous
metallacycles although longer reaction times are required (ca.
72 h), and only complex 6b is obtained with analytical purity
(85% yield) (Scheme 2).§ Complexes 6a,b formally result from
the coupling of the terminal carbon atom of the alkenyl group
5
(h –C9H7)(PPh3)2][PF6] and allylmagnesium bromide.3 The
following processes are involved in this synthetic route: (i)
regioselective nucleophilic addition of the Grignard reagent at
the electrophilic Cg atom of the allenylidene chain to give s-
5
5
alkynyl derivatives [Ru(C·CCR1R2CH2CHNCH2)(h -C9H7)-
with the h -indenyl ligand after a ring closure of the alkenyl-
1
(PPh3)2], (ii) selective Cb protonation of these s-alkynyl
vinylidene moiety. Apparently, the competitive h -vinylidene–
2
complexes to afford the corresponding alkenyl-vinylidene
h -alkyne tautomerization, a key step in the demetalation
5
derivatives
[Ru{NCNC(H)CR1R2CH2CHNCH2}(h -C9H7)-
process,3 is a faster process for vinylidenes 3b–d allowing the
isolation of the terminal 1,5-enynes 4b–d.
(PPh3)2]+, and finally (iii) demetalation of the vinylidene
complexes in refluxing acetonitrile to give the free 1,5-enynes,
recovering the metal fragment as the acetonitrile solvate
Analytical and spectroscopic data of complexes 6a,b support
the proposed formulation.§ Note that formation of these
metallacycles involves the generation of three stereogenic
centers (Scheme 2). 31P-{1H} NMR spectroscopy reveals that
the reactions proceed stereoselectively since only one diaster-
eoisomer is observed, the spectra consisting of two doublet
resonances in accordance with the nonequivalence of the
5
[Ru(h -C9H7)(N·CMe)(PPh3)2]+.
In order to investigate the scope of this synthetic approach,
the reactivity of [Ru(NCNCNCR1R2)(h -C9H7)(PPh3)2][PF6]
5
(1a–d)4 towards 2-methylallylmagnesium chloride was ex-
plored. Thus, following the same synthetic protocol used in our
previous report,3 s-alkynyl derivatives 2a–d and alkenyl-
vinylidene complexes 3a–d were prepared in 77–86% and
91–95% yields, respectively (Scheme 1).‡
1
phosphorus nuclei. H and 13C-{1H} NMR spectra are also in
agreement with the proposed structures. In particular, the
alkenyl Ru–CNCH carbons resonate at ca. dC 150 (dd, 2J(CP) =
9.4–16.9 Hz) and 138 (s) ppm, respectively.5
In addition, the structure of 6b has been determined by a
single-crystal X-ray diffraction study (Fig. 1).¶ As expected, the
two enantiomers are present in the unit cell displaying
R
C1SC10SC11 and SC1RC10RC11 configurations (two molecules
for each one; only one of the molecules displaying RC1SC10SC11
configuration is shown in Fig. 1). The molecular structure
shows the typical pseudooctahedral three-legged piano-stool
coordination around the ruthenium atom, which is bonded to the
6
functionalised indene unit acting as a h -ligand, the phosphorus
atoms from PPh3, and a 1-cyclohexenyl ring (the bond length
Ru–C(16) of 2.138(5) Å is consistent with a ruthenium–carbon
5
5
Scheme
1
[Ru]
=
[Ru(h -C9H7)(PPh3)2]; complex
Reagents and
5
=
[Ru(h -
C9H7)(N·CMe)(PPh3)2][BF4].
CH2NC(Me)CH2MgCl (1 equiv.), THF, 220 °C; ii, HBF4 (1 equiv.), Et2O,
conditions: i,
220 °C; iii, MeC·N, reflux.
† Electronic supplementary information (ESI) available: experimental
section. See http://www.rsc.org/suppdata/cc/b2/b212406h/
Scheme 2
840
CHEM. COMMUN., 2003, 840–841
This journal is © The Royal Society of Chemistry 2003

(6b) h. The solution was then evaporated to dryness and the resulting solid
residue washed with diethyl ether (3 3 10 cm3) and vacuum-dried. Selected
spectroscopic data (numbering for protons and carbons follows the
crystallographic scheme shown in Fig. 1): 6a: dP (CD2Cl2) 28.66 and 34.40
(d, 2J(PP) = 54.0); dH (CD2Cl2) 1.09 (d, 3 H, J(HH) = 6.3, H-12), 1.72 (m,
1 H, H-13), 2.03 (dd, 1 H, J(HH) = 12.5 and 12.5, H-13), 3.20 (m, 1 H, H-
11), 3.93 (m, 1 H, H-10), 4.01 (m, 1 H, H-1), 4.57 (br, 1 H, H-15), 5.10 (br,
1 H, H-3), 5.57, 5.93, 6.01 and 6.20 (br, 1 H each, H-5, H-6, H-7 and H-8),
6.60 (br, 1H, H-2), 6.71–7.41 (m, 40 H, Ph); dC (CD2Cl2) 22.60 (s, C-12),
35.78 (s, C-11), 43.51 (s, C-13), 51.13 (s, C-1), 52.80 (s, C-14), 80.78 (s, C-
10), 86.90, 93.50, 95.57 and 98.32 (s, C-5, C-6, C-7 and C-8), 101.26 (s, C-4
or C-9), 111.63 (d, 2J(CP) = 7.7, C-4 or C-9), 125.95–150.31 (m, Ph),
129.99 and 144.66 (s, C-2 and C-3), 137.91 (s, C-15), 153.95 (dd, 2J(CP) =
16.9 and 11.7, C-16). 6b: dP (CD2Cl2) 27.75 and 29.48 (d, 2J(PP) = 60.2);
dH (CD2Cl2) 1.31 (d, 3 H, J(HH) = 6.2, H-12), 1.72 (m, 1 H, H-13), 1.99
(dd, 1 H, J(HH) = 13.3 and 13.3, H-13), 2.73 (m, 1 H, H-11), 3.90 (m, 1 H,
H-10), 4.04 (m, 1 H, H-1), 4.89 (br, 1 H, H-15), 5.00 (br, 1 H, H-3), 5.44,
5.52, 5.73 and 5.80 (br, 1 H each, H-5, H-6, H-7 and H-8), 6.41–7.97 (m, 38
H, Ph and C12H8), 6.90 (br, 1H, H-2); dC (CD2Cl2) 22.90 (s, C-12), 38.17
(s, C-11), 42.67 (s, C-13), 53.61 (s, C-1), 55.21 (s, C-14), 77.59 (s, C-10),
82.90, 94.94, 96.03 and 99.21 (s, C-5, C-6, C-7 and C-8), 103.66 (s, C-4 or
C-9), 107.27 (d, 2J(CP) = 9.4, C-4 or C-9), 120.36–152.86 (m, Ph and
C12H8), 131.00 and 142.73 (s, C-2 and C-3), 138.10 (s, C-15), 148.23 (dd,
2J(CP) = 15.7 and 9.4, C-16).
¶ Crystal data for 6b: C64H53BF4P2Ru·3/2THF, M = 1180.04, orange prism
¯
(0.175 3 0.15 3 0.075 mm), triclinic, P1, a = 14.7232(5), b = 18.8325(7),
c = 21.3164(9) Å, a = 70.118(2), b = 80.999(2), g = 83.676(2)°, V =
5479.4(4) Å3, Z = 4, Dcalc = 1.430 g cm23, m(Cu-Ka) = 3.364 mm21
,
Fig. 1 Molecular structure and numbering scheme of 6b (only one of the
independent molecules is shown; bond lengths and angles are only for this
molecule). Tetrafluoroborate anion, THF molecules and phenyl groups of
the PPh3 ligands have been omitted for clarity. Selected bond distances (Å)
and angles (°): Ru–C* 1.814(16); Ru–P(1) 2.3755(13); Ru–P(2)
2.3736(13); Ru–C(16) 2.138(5); C(1)–C(2) 1.516(7); C(2)–C(3) 1.327(7);
C(1)–C(10) 1.559(16); C(10)–C(11) 1.530(7); C(10)–C(16) 1.547(7);
C(11)–C(13) 1.530(7); C(13)–C(14) 1.531(7); C(14)–C(15) 1.528(7);
C(15)–C(16) 1.349(6); C*–Ru–P(1) 123.84(16); C*–Ru–P(2) 125.81(17);
C*–Ru–C(16) 116.07(21); P(1)–Ru–P(2) 98.48(5); P(1)–Ru–C(16)
92.02(13); P(2)–Ru–C(16) 91.81(13). C* = centroid of C(4), C(5), C(6),
C(7), C(8) and C(9).
Nonius Kappa CCD diffractometer, Cu-Ka radiation (l = 1.54184 Å).
158352 reflections collected, 20043 unique (12474 with I > 2s(I)). R1
=
0.0564; wR2 = 0.1298 both for I > 2s(I). CCDC 199722. See http://
www.rsc.org/suppdata/cc/b2/b212406h/ for crystallographic data in CIF or
other electronic format.
1 M. I. Bruce, Chem. Rev., 1998, 98, 2797; V. Cadierno, M. P. Gamasa and
J. Gimeno, Eur. J. Inorg. Chem., 2001, 571.
2 Ruthenium(II) allenylidene complexes have shown to be active catalysts
in: (a) ROMP: I. A. Abdallaoui, D. Sémeril and P. H. Dixneuf, J. Mol.
Catal. A, 2002, 182–183, 577; (b) RCM: R. Akiyama and S. Kobayashi,
Angew. Chem., Int. Ed., 2002, 41, 2602; (c) dimerization of tin hydrides:
S. M. Maddock and M. G. Finn, Angew. Chem., Int. Ed., 2001, 40, 2138;
(d) propargylic substitutions: Y. Nishibayashi, M. Yoshikawa, Y. Inada,
M. Hidai and S. Uemura, J. Am. Chem. Soc., 2002, 124, 11846; (e)
cycloaddition reactions: Y. Nishibayashi, Y. Inada, M. Hidai and S.
Uemura, J. Am. Chem. Soc., 2002, 124, 7900.
single bond). The C(2)–C(3) and C(15)–C(16) distances
(1.327(7) and 1.349(6) Å, respectively) show the expected
values for a double carbon–carbon bond.
The most remarkable feature of this coupling is the
3 V. Cadierno, S. Conejero, M. P. Gamasa and J. Gimeno, Organome-
tallics, 2002, 21, 3837.
6
generation of a functionalised h -coordinated indene derivative
5
5
6
from a h -indenyl complex. Although h ? h haptotropic
4 (a) V. Cadierno, M. P. Gamasa, J. Gimeno, M. González-Cueva, E.
Lastra, J. Borge, S. García-Granda and E. Pérez-Carreño, Organome-
tallics, 1996, 15, 2137; (b) S. Conejero, J. Díez, M. P. Gamasa, J. Gimeno
and S. García-Granda, Angew. Chem., Int. Ed., 2002, 41, 3439.
5 These chemical shifts are typical of alkenyl-ruthenium(II) derivatives.
See for example: K. Bieger, J. Díez, M. P. Gamasa, J. Gimeno, M.
Pavlisˆta, Y. Rodríguez-Álvarez, S. García-Granda and R. Santiago-
García, Eur. J. Inorg. Chem., 2002, 1647.
6 M. Y. Hung, S. M. Ng, Z. Zhou, C. P. Lau and G. Jia, Organometallics,
2000, 19, 3692 and references therein.
7 (a) No intermediates could be detected by 31P-{1H} NMR spectroscopy
(b) transformation of 3a,b into 6a,b proceeds in the presence of the
radical-scavenger 2,6-di-tert-butyl-4-methylphenol, discarding the in-
volvement of free radicals in this coupling process.
rearrangements have been reported as the result of protonation
of h -indenyl complexes,6 as far as we know these are the first
5
rearrangements mediated by a C–C coupling. We note that the
related
alkenyl-vinylidene
derivative
5
[Ru{NCNC(H)CPh2CH2CHNCH2}(h -C9H7)(PPh3)2][BF4]3
6
does not rearrange in solution, to afford the corresponding (h -
indene)ruthenium(II) metallacycle, even in refluxing dichloro-
methane. This fact seems to indicate that electron-rich alkenyl
units, i.e. C(CH3)NCH2, are required in this coupling process.
Further studies concerning the scope and mechanism7,8 of
this unusual carbocyclization, as well as reactivity studies on the
resulting metallacycles, are now under active investigation.
We thank the Ministerio de Ciencia y Tecnología of Spain
(Project BQU2000-0227) and the Gobierno del Principado de
Asturias (Project PR-01-GE-6) for financial support, and for a
Ph.D. fellowship (to S. C.).
8 Although the exact mechanism of this reaction is still unknown, the
following processes could be involved: (a) intramolecular [2 + 2]
cycloaddition between the two CNC double bonds of the alkenyl-
vinylidene group. A process of this type has been recently reported: P.
Álvarez, E. Lastra, J. Gimeno, M. Bassetti and L. R. Falvello, J. Am.
Chem. Soc., 2003, 125, 2386; (b) direct carbocyclization of the electron-
rich double bond at the Ca of the vinylidene unit. A process of this type
has been proposed in the catalytic cyclization of dienyl alkynes: C. A.
Notes and references
‡ Compounds 2–4a–d have been characterized by NMR spectroscopy and
elemental analyses or HRMS. See ESI.
5
Merlic and M. E. Pauly, J. Am. Chem. Soc., 1996, 118, 11319; (c) h to
3
h slippage of the indenyl ligand: M. J. Calhorda and L. F. Veiros, Coord.
§ A solution of the corresponding vinylidene complex [Ru{N
Chem. Rev., 1999, 185–186, 37; V. Cadierno, J. Díez, M. P. Gamasa, J.
Gimeno and E. Lastra, Coord. Chem. Rev., 1999, 193–195, 147; M. J.
Calhorda, C. C. Romao and L. F. Veiros, Chem. Eur. J., 2002, 8, 868.
5
CNC(H)CR1R2CH2C(Me)NCH2}(h -C9H7)(PPh3)2][BF4] (3a,b; 1 mmol) in
dichloromethane (30 cm3) was stirred at room temperature for 3 (6a) or 72
CHEM. COMMUN., 2003, 840–841
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