Formation of a coordinated 2-aminoethylidene ligand and its rearrangement by deprotonation into a phosphinoallyl ligand containing a pyrrolidin-2-yl ring

Article abstract of DOI:10.1021/ic801302z

The activation of 1,1-diphenyl-2-propyn-1-ol by the metallic fragment [(η⁵-C₅Me₅)Ru(dippae)]⁺ {dippae = 1,2-bis[(diisopropylphosphanyl)amino]ethane}, followed by dehydration, produces a cationic complex that, by deprotonation and rearrangement, leads to a neutral complex with a phosphinoallyl ligand containing a pyrrolidin-2-yl ring.

Full text of DOI:10.1021/ic801302z

Inorg. Chem. 2008, 47, 8598-8600
Formation of a Coordinated 2-Aminoethylidene Ligand and Its
Rearrangement by Deprotonation into a Phosphinoallyl Ligand
Containing a Pyrrolidin-2-yl Ring
M. Carmen Puerta, Pedro Valerga,* and M. Dolores Palacios
Departamento de CMIM y Qu´ımica Inorga´nica, Facultad de Ciencias, UniVersidad de Ca´diz,
Campus del R´ıo San Pedro, Puerto Real 11510, Spain
Received July 11, 2008
The activation of 1,1-diphenyl-2-propyn-1-ol by the metallic fragment
[(η -C5Me5)Ru(dippae)]+ {dippae ) 1,2-bis[(diisopropylphospha-
nyl)amino]ethane}, followed by dehydration, produces a cationic
complex that, by deprotonation and rearrangement, leads to a
neutral complex with a phosphinoallyl ligand containing a pyrrolidin-
2-yl ring.
electron species but is also a function of the propargyl alcohol
substituents.9 During the last years, we have studied the
reactivity of several half-sandwich ruthenium complexes
toward 1-alkynes and propargyl alcohols, and we have
reported the irreversible rearrangement of half-sandwich
ruthenium hydridoalkynyl complexes to their vinylidene
isomers.10 In the course of our studies on the activation of
1,1-diphenyl-2-propyn-1-ol by [Cp*RuCl(L2)] [Cp* )
C5Me5, L2 ) 2PEt311 or 1,2-bis(diisopropylphosphino)ethane
(dippe)12], we have described the sequence of species
involved.13 In both cases, the η5-C5Me5 ligand plays a key
role in the isolation of the intermediate species, which finally
leads to stable allenylidene compounds.11-13 Very recently,
we have reported chloride abstraction from complexes
[Cp*RuCl(R,R-dippach)] {R,R-dippach ) (R,R)-1,2-bis[(di-
isopropylphosphanyl)amino]cyclohexane}and[Cp*RuCl(dippae)]
{dippae ) 1,2-bis[(diisopropylphosphanyl)amino]ethane}
under dinitrogen or argon. The reaction carried out under
argon yields the expected 16-electron complex
[Cp*Ru(dippae)]+, but in the case of R,R-dippach, a complex
5
It is well-known that propargyl alcohol activation by means
of organometallic complexes yields allenylidene compounds.1
Ruthenium allenylidene complexes show versatile chemical
behavior in relation to the unsaturated character of the carbon
chain.2 They exhibit electrophilic reactivity at the R- and
γ-carbon atoms;3 thus, ruthenium allenylidene complexes are
excellent substrates for C-C and C-heteroatom coupling
by cycloaddition reactions.4,5 The ꢀ-carbon shows nucleo-
philic character.6-8 The allenylidene reactivity greatly
depends on the electron richness of the in situ generated 16-
*
To whom correspondence should be addressed. E-mail:
pedro.valerga@uca.es.
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8598 Inorganic Chemistry, Vol. 47, No. 19, 2008
10.1021/ic801302z CCC: $40.75  2008 American Chemical Society
Published on Web 08/26/2008

COMMUNICATION
Scheme 1
Scheme 2
which appears at 1.84 ppm. All of these spectroscopic data
agree well with those reported for other vinylalkylidene
complexes in spite of the fac that they do not have N bonded
to Cꢀ.15 Two doublets at 100.4 and 102.3 ppm in the 31P{1H}
NMR spectrum indicate the nonequivalence of the two
phosphorus atoms.
In order to establish the sequence of intermediates in the
activation of alkynols by the moiety [Cp*Ru(dippae)]+, we
have studied the reaction between the dinitrogen compound
[Cp*Ru(dippae)(N2)][BAr′4]14 and 1,1-diphenyl-2-propyn-
1-ol in CD2Cl2 by monitoring the process by 1H and 31P{1H}
NMR at variable temperature.
The formation of 1 can be rationalized as follows: The
dissociation of a labile dinitrogen ligand and the C-H
activation of the propargyl alcohol should afford a, in
[Cp*Ru{κ3-P,P′,N-η2-P,N(R,R-dippach)}]+ was obtained,
showing a novel terdentate coordination mode of this
ligand.14
1
agreement with a triplet at -7.9 ppm in H and a singlet at
104.78 ppm in 31P{1H} NMR spectra at 5 °C. The hydroxy-
alkynyl hydride a is likely in equilibrium with π-alkynol
species not detected. Carbene complex b is generated from
π-alkynol by an intramolecular nuclephilic attack of a
nitrogen atom on the π-alkynol ligand. At a temperature of
We report now the activation of 1,1-diphenyl-2-propyn-
1-ol by the metallic fragment [Cp*Ru(dippae)]+. In the
course of the reaction with [Cp*Ru(dippae)Cl], using Na-
BAr′4, sodium tetrakis{3,5-bis(trifluoromethyl)phenyl}borate,
as a chloride abstractor, a heterocyclic vinylcarbene complex
[Cp*Ru{dCHC(NHPPri CHCH2NHPPri )dCPh2-κ3-
1
25 °C in the low-field region of the H spectrum, the most
2
2
noticeable resonances appear near 16.0 ppm. These signals
correspond to carbene species b (probably two stereoisomers
b1 and b2 with the vicinal hydrogen in two different
orientations exchange between them). These resonances
should appear as multiplets, but they remain unresolved. In
the 31P{1H} spectra, isomer b1 shows two doublets at 101.3
and 104.0 ppm (JPP ) 37 Hz) and isomer b2 shows two
doublets at 98.5 and 100.3 ppm (JPP ) 34 Hz). After 19 h at
room temperature (25 °C), the proton carbenic signals of b
isomers are very weak and the signal at 15.3 ppm is strongest,
indicating the formation of the final carbene complex 1. In
31P{1H} NMR spectra, the presence of 1 is indicated by two
doublets at 100.4 and 102.3 ppm (JPP ) 36 Hz).
P,P,C}]+ (1) was obtained instead of an allenylidene or an
aminocarbene derivative. Ruthenium alkenylalkylidene com-
plexes have already been obtained by the reaction of hydride
precursor complexes and propargyl alcohols followed by
proton addition to vinylalkenyl derivatives.15 On the other
hand, the addition of a nucleophile to η2-coordinated alkynes
affording vinylruthenium complexes (or more exactly alk-
enylphosphonio complexes) is less usual.16 However, as far
as we know, heterocyclic vinylalkylidenes bearing an aminic
nitrogen atom bonded to the ꢀ-carbon atom have not been
previously reported. The formation of 1 according to eq 1
in Scheme 1 is remarkable.
The formulation as a alkenylcarbene derivative is consis-
tent with the NMR data. The presence of the carbene moiety
RudCH is confirmed by the 13C{1H} spectrum, which shows
the typical low-field resonance of the carbonic carbon nucleus
at 289.5 ppm and resonances assignable to Cꢀ and Cγ at 148.5
Deprotonation of 1 with KOH produces in one step an
uncommon rearrangement, leading to a tetrasubstituted
i
i
trihaptoallylcomplex[Cp*Ru{η3-CHC[(CHCH2NPPr2)NHPPr2]CPh2-
κ4-P,C,C′,C′′}] (2), which is a very unusual transformation
that lacks precedent in the literature (Scheme 2).
1
and 120.5 ppm, respectively. In the H NMR spectrum, the
most remarkable features are the downfield resonance (15.3
ppm) of the RudCH proton and the corresponding to N-H,
The reaction leading to neutral compound 2 is relatively
fast and takes place in hetereogeneous media. It should
involve a sequence of internal rearrangements and C-E
couplings. The reaction of 1 with KtBuO produced in a less
clean manner compound 2 with very low yield.
It is not possible to propose mechanistic routes based on
our experimental data. Only a description of broken and
formed bonds follows: In the final product, a C-N bond is
formed over the already existing carbon 1 on the 3,3-
diphenylprop-2-enylidene moiety. Carbon 2 results coupled
(14) Palacios, M. D.; Puerta, M. C.; Valerga, P.; Lledo´s, A.; Veilly, E.
Inorg. Chem. 2007, 46, 6958.
(15) (a) Esteruelas, M. A.; Lahoz, F.; On˜ate, E.; Oro, L. A.; Zeier, B.
Organometallics 1994, 13, 4258. (b) Esteruelas, M. A.; Liu, F.; On˜ate,
E.; Sola, E.; Zeier, B. Organometallics 1997, 16, 2919. (c) Wilhelm,
T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R. H. Organometallics
1997, 16, 3867. (d) Gamasa, M. P.; Gimeno, J.; Mart´ın-Vaca, B. M.
Organometallics 1998, 17, 3707.
(16) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Gonza´lez-Bernardo, C.;
Pe´rez-Carren˜o, E.; Garc´ıa-Granda, S. Organometallics 2001, 20, 5177.
Inorganic Chemistry, Vol. 47, No. 19, 2008 8599

COMMUNICATION
Scheme 3
pentamethylcyclopentadienyl ligand and the isopropyl and
phenyl groups, some features of interest appear and they will
be discussed. In the 31P{1H} NMR spectrum, two singlets
at 79.33 and 126.8 ppm correspond to noncoordinated and
coordinated phosphorus, respectively. HETCOR and HSQC
Figure 1. Crystal structure of 2. The thermal ellipsoids are scaled to the
50% probability level. Hydrogen atoms are omitted for clarity.
1
experiments contributed to explain 13C{1H} and H NMR
with one carbon from the ethylene chain. Subsequently, a
five-membered N-heterocycle is formed and the vicinal
Ru-P bond is cleaved.
Crystals suitable for X-ray crystallography were obtained.
The single-crystal analysis revealed the unusual structure of
this compound (Figure 1).
spectra.
The allylic hydrogen Ha (Scheme 3) exhibits a multiplet
at 4.50 ppm (main constant JHaP ) 27.5 Hz and some
additional coupling with isopropyl group hydrogens). For
the cationic ruthenium(IV) complex [Ru(Cp*)Cl(Ph2POMe)(η3-
CH2CMeCH2)][PF6],20 with 2.01-3.8 ppm for the allylic
hydrogens using CD2Cl2 as the solvent, in neutral allyl
compounds of ruthenium, the interval is even larger,
1.35-5.79 ppm, although it includes changes by the solvent
(C6D6 and CDCl3 were used).17 Hb originates a doublet at
6.08 ppm (JH -H ) 8.78 Hz). This coupling constant points
In this “semisandwich” molecule, the “in situ” formed
ligand acts formally as a terdentate chelating ligand, with
the allyl moiety occupying two positions of coordination and
the phosphorus atom the third one. The bond lengths
Ru(1)-P(1) and P(1)-N(1) included in the five-membered
chelating ring are 2.2815(6) and 1.689(2) Å, respectively,
with the P-N distance being slightly shorter than the
analogous distance P(2)-N(2), 1.721(2) Å, found for the
noncoordinated phosphorus. The allyl moiety bonds the metal
in a trihapto mode, with bond lengths Ru-C being 2.231(2),
2.153(2), and 2.237(2) Å. The distances C(11)-C(12) and
C(12)-C(13) are 1.411(3) and 1.449(3) Å, respectively.
These structural parameters are similar to those found for
the comparable Cp*Ru complexes containing η3-allyl or η3-
butadienyl entities.17-19 The allyl carbon atoms C(11) and
C(12) form with C(32), C(33), and N(2) a five-membered
heterocycle derived of pyrrolidine, which is almost planar.
The allyl plane C(11)-C(12)-C(13) and the cyclopentadi-
enyl ring C(1)>C(5) form a dihedral angle of 66.6(2)°. The
plane formed by the central atom C(12) in the allyl entity
with Ru(1) and P(1) intersects nearly perpendicularly the
cyclopentadienyl ring with a dihedral angle equal to 83.09(7)°.
It was confirmed by means of NMR spectroscopy that this
solid-state molecular structure is essentially maintained also
in solution. In addition to the signals corresponding to the
b
c′
out a transoid arrangement for Hb and Hc′. A doublet at 2.66
ppm (JH -H ) 11.13 Hz) was assigned to Hc and a multiplet
c
c′
at 3.44 ppm (JH -H ) 11.13 Hz, JH -H ) 8.78 Hz) to Hc′
c′
c
c′
b
(the roughly estimated shift for this type of hydrogen is
around 3.00 ppm). The carbon related to Hc and Hc′ appears
at 59.8 ppm and the allylic carbon related to Ha at 59.4 ppm.
The two other allylic carbons around 60 ppm were not clearly
observed. The carbon related to Hb appears at 99.5 ppm.
The formation of complex 2 containing a pyrrolidin-2-yl
ring of interest in biochemistry and medicine is facilitated
by the flexibility of the ethylene chain in the phosphinoamine
ligand dippae.
Acknowledgment. This work was supported by spanish
MEC (Project CTQ2007-60137/BQU) and Junta de Andalu-
c´ıa (Grants FQM 188 and FQM 00094). We thank Johnson
Matthey plc for generous loans of ruthenium trichloride.
Supporting Information Available: Experimental details (PDF)
and X-ray data for complex 2 (CIF). This material is available free
of charge via the Internet at http://pubs.acs.org.
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N. N. J. Chem. Soc., Dalton Trans. 2000, 2279.
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IC801302Z
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8600 Inorganic Chemistry, Vol. 47, No. 19, 2008