A new class of tethered-arene ruthenium(II) complexes with pendant P and C donor atoms: Synthesis of η6:η1:η1 phosphonio-azabutadienyl ruthenabicycles via allenylidene intermediates

Article abstract of DOI:10.1039/b404971c

The activation of 1,1-diphenyl-2-propyn-1-ol by complexes [RuCl(η⁶-p-cymene){η²-P,N-Ph₂PCH ₂P(=NR)Ph₂}]⁺ (1a-d) results in the formation of the unusual tethered (η⁶-arene)-ruthenium(II) derivatives 2a-d, via an unprecedented iminophosphorane-allenylidene coupling process.

Full text of DOI:10.1039/b404971c

A new class of tethered-arene ruthenium(II) complexes with pendant P
and C donor atoms: synthesis of h6:h1:h1 phosphonio-azabutadienyl
ruthenabicycles via allenylidene intermediates†
Victorio Cadierno,* Josefina Díez, Joaquín García-Álvarez and José Gimeno*
Departamento de Química Orgánica e Inorgánica, I.U.Q.O.E.M., Facultad de Química, Universidad de
Oviedo, 33071, Oviedo, Spain. E-mail: jgh@fq.uniovi.es; vcm@fq.uniovi.es; Fax: +34985103446;
Tel: +34985103461
Received (in Cambridge, UK) 5th April 2004, Accepted 4th June 2004
First published as an Advance Article on the web 20th July 2004
The activation of 1,1-diphenyl-2-propyn-1-ol by complexes
[RuCl(h6-p-cymene){h2-P,N-Ph2PCH2P(NNR)Ph2}]+ (1a–d) re-
sults in the formation of the unusual tethered (h6-arene)–
ruthenium(II) derivatives 2a–d, via an unprecedented imino-
phosphorane–allenylidene coupling process.
consistent with the presence of single metal–carbon and double
nitrogen–carbon bonds, respectively.9
Complexes 2a–d formally result from the coupling of the
uncoordinated iminophosphorane unit –Ph2PNN–RF of 1a–d with
the allenylidene chain (resulting from the dehydration of the
coordinated propargylic alcohol) with concomitant exchange of the
6
Since the isolation of the first allenylidene–ruthenium(II) com-
plexes,1 the development of their chemistry has shown them to
form one of the cornerstones of the synthetic applications of
carbene–ruthenium complexes. Their applications in both stoichio-
metric2 and catalytic3 organic transformations are among the most
appealing in ruthenium-mediated organic synthesis,4 featuring a
versatile reactivity including nucleophilic, electrophilic as well as
cycloaddition reactions. In the context of our studies on the utility
of ruthenium(II)–allenylidenes for promoting regio- and ster-
eoselective C–C and C–heteroatom couplings,5 we now report a
synthetic methodology for unprecedented tethered arene–rutheniu-
m(II) complexes 2 (see Fig. 1). They have been generated from the
intramolecular coupling of an iminophosphorane group –Ph2PNN–
RF with the allenylidene chain NCNCNCPh2 and concomitant
coordination of one of the terminal phenyl groups to ruthenium. To
the best of our knowledge, these complexes represent the first
examples of tethered-arene derivatives in which the pendant arm is
linked to the metal by both P and C-donor atoms displaying a rare
h -p-cymene ligand by one phenyl group of the alkynol. Re-
markably, an unusual migration of the fluoroaromatic substituent
RF from the imino group NN–RF to the Cb atom of the allenylidene
chain also takes place.
Although no intermediates could be detected by NMR spectros-
copy, the involvement of allenylidene species in this unusual
coupling process has been confirmed by using the closely related
mesitylene–ruthenium(II) complex 3 as starting material (Scheme
2). Thus, the treatment of 3 with 10 equiv. of HC·CC(OH)Ph2, in
CH2Cl2 at room temperature generates (ca. 12 h) the diph-
2
enylallenylidene derivative 5. The hemilabile properties of the h -
P,N-iminophosphorane-phosphine ligand provide the required
vacant site for the coordination of the propargylic alcohol.7
Complex 5 slowly converts (ca. 10 days) into the phosphonio-
6
1
1
h :h :h coordination mode.6
The process takes place by reaction of the iminophosphorane
complexes 1a–d7 with a 10-fold excess of 1,1-diphenyl-2-propyn-
1-ol in dichloromethane at room temperature (ca. 48 h), yielding
the bicyclic phosphonio-azabutadienyl–ruthenium(II) derivatives
2a–d (Scheme 1), which have been isolated as air-stable orange
solids in 78–88% yield.8 Analytical and spectroscopic data of
complexes 2a–d support the proposed formulation.‡ In particular
the H and 13C-{1H} NMR data indicate: (i) the disappearance of
1
Scheme 1 Activation of 1,1-diphenyl-2-propyn-1-ol by complexes 1a–d.
the isopropyl and methyl resonances of the p-cymene ligand, and
(ii) the formation of the Ru–C bond in the azabutadienyl chain as
reflected by the appearance of a characteristic low-field doublet of
doublets resonance at ca. dC 234 ppm [2J(CP) = 14.3–18.1 and
1.7–4.5 Hz].8
Moreover, the structure of complex 2d has been determined by a
single-crystal X-ray diffraction study (Fig. 2).§ The most remark-
able features of the structure are the Ru–C(23) and N(1)–C(23)
bond lengths (2.026(10) and 1.297(11) Å, respectively) which are
Fig. 2 Molecular structure of 2d. SbF62 anion, hydrogen atoms and phenyl
groups of the P,N-ligand have been omitted. Selected bond distances (Å)
and angles (°): Ru–Cl(1) 2.399(2); Ru–P(2) 2.302(3); Ru–C(23) 2.026(10);
P(1)–N(1) 1.638(6); N(1)–C(23) 1.297(11); C(23)–C(14) 1.490(12);
C(14)–C(7) 1.373(13); C(23)–Ru–P(2) 86.7(3); C(23)–Ru–Cl(1) 88.4(2);
P(2)–Ru–Cl(1) 90.29(9); Ru–C(23)–N(1) 132.6(7); C(23)–N(1)–P(1)
130.3(7); Ru–C(23)–C(14) 114.1(7); C(23)–C(14)–C(7) 118.1(9).
Fig. 1 Structure of the tethered-arene complexes reported in this paper.
† Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/cc/b4/b404971c/
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C h e m . C o m m u n . , 2 0 0 4 , 1 8 2 0 – 1 8 2 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

azabutadienyl metallacycle 2a, via allenylidene–iminophosphorane
coupling and mesitylene–phenyl ring exchange (Scheme 2).
The allenylidene complex 5 could be isolated in 79% yield,‡ and
its structure was confirmed unequivocally by X-ray crystallography
(Fig. 3).¶
This work was supported by the Ministerio de Ciencia y
Tecnología (MCyT) of Spain (Project BQU2003–00255). V.C.
thanks the MCyT for the award of a Ramón y Cajal contract.
Notes and references
Although the overall mechanism for this coupling reaction is still
unknown it seems that the first step, in which the –Ph2PNN–RF unit
is added to the allenylidene chain, depends on the electrophilicity of
the Ca atom of the allenylidene ligand. This could explain the
observed slower reaction rate in the transformation of the more
electron-rich mesitylene vs the p-cymene complex (3 vs 1a),
allowing the isolation of allenylidene 5 in which the electrophilicity
of the a-carbon is clearly reduced. In accord with this, the
analogous hexamethylbenzene complex 6‡ (Scheme 2) remains
unchanged under similar reaction conditions. It should be noted
that, although the addition of X–H (X = O, N, S, P) bonds to the
CaNCb of transition-metal allenylidenes is a well-established
transformation which generally yields Fischer-type a,b-unsat-
urated carbenes2 or in some cases azoniabutadienyl species (X =
N),8 no X–C bond additions to allenylidene chains have been
reported to date. This reaction pathway constitutes a novel example
of the usefulness of transition-metal allenylidene complexes as
building blocks for the preparation of unusual organometallic
skeletons.
‡ Compounds 1c–d, 2a–d, 5 and 6 have been characterized by NMR
spectroscopy and elemental analyses. See ESI.
§ Crystal data for 2d: RuC48H32F9N3P2ClSb, M = 1141.98, orange prism
(0.125 3 0.075 3 0.025 mm), monoclinic, C2/c, a = 39.587(7) Å, b =
12.430(2) Å, c = 20.522(4) Å, a = 90°, b = 117.306(7)°, g = 90°, V =
8973(3) Å3, Z = 8, Dcalc = 1.691 g cm23, m(Cu-Ka) = 9.392 mm21
,
Nonius Kappa CCD diffractometer, Cu–Ka radiation (l = 1.54184 Å).
54554 reflections collected, 5843 unique (Rint = 0.095). R1 = 0.0603; wR2
= 0.1392 both for I > 2s(I). CCDC 236842. See http://www.rsc.org/
suppdata/cc/b4/b404971c/ for crystallographic files in .cif format.
¶ Crystal data for 5: RuC54H44F10N2P2ClSb, M = 1231.12, violet prism
(0.25 3 0.25 3 0.10 mm), monoclinic, P21/a, a = 16.4727(16) Å, b =
17.1842(17) Å, c = 20.571(2) Å, a = 90°, b = 112.879(2)°, g = 90°, V =
5364.9(3) Å3, Z = 4, Dcalc = 1.524 g cm23, m(Mo–Ka) = 0.966 mm21
,
Bruker Smart CCD diffractometer, Mo–Ka radiation (l = 0.71073 Å).
43447 reflections collected, 16052 unique (Rint = 0.1035). R1 = 0.0728;
wR2 = 0.1988 both for I > 2s(I). CCDC 236843. See http://www.rsc.org/
suppdata/cc/b4/b404971c/ for crystallographic files in .cif format.
1 J. P. Selegue, Organometallics, 1982, 1, 217.
2 M. I. Bruce, Chem. Rev., 1998, 98, 2797; V. Cadierno, M. P. Gamasa
and J. Gimeno, Eur. J. Inorg. Chem., 2001, 571.
6
1
1
In summary, a readily accessible route to unprecedented h :h :h
tethered-arene–ruthenium(II) complexes, in which the pendant
arms involve both P and C donor atoms, is described. The chemistry
of transition-metal complexes containing tethered-type ligands is
growing rapidly because of their potential contribution to the
configurational stability around the metal centre, and for promoting
selective stoichiometric and catalytic transformations.6,10 Further
studies concerning the scope and mechanism of this coupling
process, as well as reactivity studies on the new type of tethered-
arene–ruthenium(II) complexes 2, are now under active investiga-
tion.
3 Ruthenium(II
) allenylidene complexes have shown to be active
precatalysts in: (a) ROMP: R. Castarlenas and P. H. Dixneuf, Angew.
Chem., Int. Ed., 2003, 42, 4524; (b) RCM: M. Bassetti, F. Centola, D.
Sémeril, C. Bruneau and P. H. Dixneuf, Organometallics, 2003, 22,
4459; (c) Dimerization of tin hydrides: S. M. Maddock and M. G. Finn,
Angew. Chem., Int. Ed., 2001, 40, 2138; (d) Propargylic substitutions:
Y. Nishibayashi, H. Imajima, G. Onodera, M. Hidai and S. Uemura,
Organometallics, 2004, 23, 26; (e) Allenylidene–ene reactions: Y.
Nishibayashi, Y. Inada, M. Hidai and S. Uemura, J. Am. Chem. Soc.,
2003, 125, 6060; (f) Cycloaddition reactions: Y. Nishibayashi, Y. Inada,
M. Hidai and S. Uemura, J. Am. Chem. Soc., 2002, 124, 7900.
4 T. Naota, H. Takaya and S.-I. Murahashi, Chem. Rev., 1998, 98, 2599;
B. M. Trost, F. D. Toste and A. B. Pinkerton, Chem. Rev., 2001, 101,
2067; V. Ritleng, C. Stirling and M. Pfeffer, Chem. Rev., 2002, 102,
1731.
5 V. Cadierno, S. Conejero, M. P. Gamasa and J. Gimeno, Dalton Trans.,
2003, 3060 and references therein.
6
6 Tethered (h -arene)–Ru(II) complexes containing pendant N,N- and
N,O-donor arms have been recently reported: J. Hannedouche, G. J.
Clarkson and M. Wills, J. Am. Chem. Soc., 2004, 126, 986.
7 We have described the synthesis and hemilabile behaviour of complexes
1a–b and 3–4: V. Cadierno, J. Díez, S. E. García-Garrido, S. García-
Granda and J. Gimeno, J. Chem. Soc., Dalton Trans., 2002, 1465; V.
Cadierno, P. Crochet, J. García-Álvarez, S. E. García-Garrido and J.
Gimeno, J. Organomet. Chem., 2002, 663, 32.
Scheme 2 RF = p-C5F4N. Reagents and conditions: i, HC·CC(OH)Ph2 (10
equiv.), CH2Cl2, rt; ii, R = H, CH2Cl2, rt, 10 days.
8 Only
the
azabutadienyl–ruthenium(II
)
derivatives
5
[Ru{C(CHNCPh2)NNR}(h -C5H5)(CO)(PiPr3)] (R
=
Ph, nPr,
CH2C·CH), obtained by deprotonation of the corresponding azoniabu-
tadienyl
5
species
[Ru{C(CHNCPh2)NNHR}(h -C5H5)(CO-
)(PiPr3)][BF4], are known: (a) D. J. Bernad, M. A. Esteruelas, A. M.
López, J. Modrego, M. C. Puerta and P. Valerga, Organometallics,
1999, 18, 4995; (b) M. L. Buil, M. A. Esteruelas, A. M. López and E.
Oñate, Organometallics, 2003, 22, 162.
9 The P(1)–N(1) distance (1.638(6) Å) shows also the expected value for
a P–N single bond. See for example: F. H. Allen, O. Kennard, D. G.
Watson, A. G. Orpen, L. Brammer and R. Taylor, J. Chem. Soc., Perkin
Trans. 2, 1987, S1. These structural parameters seem to rule out any
important contribution from the carbenic resonance form:
Fig. 3 Molecular structure of 5. SbF62 anion, hydrogen atoms and phenyl
groups of the P,N-ligand have been omitted. Selected bond distances (Å)
and angles (°): Ru–Cl(1) 2.3887(17); Ru–P(1) 2.3237(18); Ru–C(1)
1.896(7); C(1)–C(2) 1.242(9); C(2)–C(3) 1.366(10); P(1)–C(37) 1.842(6);
C(37)–P(2) 1.814(6); P(2)–N(1) 1.560(6); N(1)–C(50) 1.379(9); C(1)–Ru–
P(1) 86.0(2); C(1)–Ru–Cl(1) 88.4(2); P(1)–Ru–Cl(1) 89.37(6); Ru–C(1)–
C(2) 178.7(6); C(1)–C(2)–C(3) 176.6(8).
10 See for example: H. Butenschon, Chem. Rev., 2000, 100, 1527; J. W.
Faller and D. G. D’Alliessi, Organometallics, 2003, 22, 2749; B.
Çetinkaya, S. Demir, I. Özdemir, L. Toupet, D. Sémeril, C. Bruneau and
P. H. Dixneuf, Chem. Eur. J., 2003, 9, 2323.
C h e m . C o m m u n . , 2 0 0 4 , 1 8 2 0 – 1 8 2 1
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