Ruthenium-mediated insertion of an unsaturated C4 unit into the P-N bond of an aminophosphine ligand

Article abstract of DOI:10.1021/om050688u

The reactions of 1,6-heptadiyne and 1,7-octadiyne with [RuCp(PPh ₂NEt₂)(CH₃CN)₂]⁺ afford the η³-phosphaallyl-η²-vinylamine complexes [RuCp(η³-(P,C,C)-PPh₂CH

Full text of DOI:10.1021/om050688u

Organometallics 2005, 24, 4899-4901
4899
Ruthenium-Mediated Insertion of an Unsaturated C4
Unit into the P-N Bond of an Aminophosphine Ligand
Sonja Pavlik,† Florian Jantscher,† Kurt Mereiter,‡ and Karl Kirchner*,†
Institute of Applied Synthetic Chemistry and Institute of Chemical Technologies and Analytics,
Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
Received August 9, 2005
Scheme 1
Summary: The reactions of 1,6-heptadiyne and 1,7-
octadiyne with [RuCp(PPh2NEt2)(CH3CN)2]+ afford the
η3-phosphaallyl-η2-vinylamine complexes [RuCp(η3-
(P,C,C)-PPh2CHdC(CH2)n-η2(C,C)-CdCHNEt2)]+ (n ) 3,
4), which cleanly rearrange to give the η1-phosphaallyl-
η3-azaallyl complexes [RuCp(η1(P)-PPh2CHdC(CH2)n-η3-
(C,C,N)-CCHNEt2)]+ (n ) 3, 4).
The labile complexes [RuCp(PR3)(CH3CN)2]PF6 (R )
alkyl, aryl) are synthons for the 14-electron fragments
[RuCp(PR3)]+, promoting the oxidative coupling of
alkynes to eventually give ruthenium allyl carbenes.1
These, in turn, behave as masked 16e complexes which
are capable of activating C-H bonds of alkyl and aryl
substituents of the phosphine ligands to afford η4-
butadiene complexes according to Scheme 1.2 With
aminophosphine ligands of the type PR2NHR′ instead
of PR3, N-H bond activation rather than C-H bond
activation is observed. In this way amido-η4-butadiene
complexes are obtained (Scheme 2).3,4 In this context
we found it interesting to switch over to aminophos-
phine ligands lacking N-H bonds in order to see
whether C-H bond activation processes become pre-
dominant again. Here we give a preliminary account of
these investigations and report the reaction of [RuCp-
(PPh2NEt2)(CH3CN)2]PF6 (1) with diynes, revealing an
unusual insertion of an unsaturated carbon C4 chain
into the P-N bond of the aminophosphine ligand. As a
result of this transformation, phosphaallyl and azaallyl
complexes are formed.
Scheme 2
Treatment of 1 with 1,6-heptadiyne results within a
few minutes in the formation of the η3-phosphaallyl-
η2-vinylamine [RuCp(η3(P,C,C)-PPh2CHC(CH2)3-η2(C,C)-
CdCHNEt2)]+ (2a) in high yield (Scheme 3).6,7 At
elevated temperature (80 °C) 2a isomerizes cleanly to
afford the thermodynamically more stable η1-phos-
phaallyl-η3-azaallyl complex [RuCp(η1(P)-PPh2CHd
C(CH2)3-η3(C,C,N)-CCHNEt2)]+ (3a) in 85% isolated
yield.8 With 1,7-octadiyne the analogous phosphaallyl-
azaallyl complex 2b is formed, as monitored by 1H and
31P{1H} NMR spectroscopy, but rearranges already at
room temperature to give the corresponding η1-phos-
phaallyl-η3-azaallyl complex 3b. Compounds 2a, 3a,
and 3b, which are air-stable both in solution and in the
solid state, were fully characterized by 1H, 13C{1H}, and
31P{1H} NMR spectroscopy as well as by elemental
analysis. The 1H NMR spectroscopic data for 2a include
characteristic resonances at 4.01 (d, 2JHP ) 4.7 Hz) and
† Institute of Applied Synthetic Chemistry.
‡ Institute of Chemical Technologies and Analytics.
(1) Schmid, R.; Kirchner, K. Eur. J. Inorg. Chem. 2004, 2609.
(2) Ru¨ba, E.; Mereiter, K.; Schmid, R.; Kirchner, K.; Bustelo, E.;
Puerta, M. C.; Valerga, P. Organometallics 2002, 21, 2912.
(3) Pavlik, S.; Mereiter, K.; Schmid, R.; Kirchner, K. Organometallics
2003, 22, 1771.
(4) Jimenez-Tenorio, M.; Puerta, M. C.; Valerga, P. Eur. J. Inorg.
Chem. 2005, 2631.
(5) For related ruthenium η3-phosphaallyl complexes see: (a) Ji, H.
L.; Nelson, J. H.; DeCian, A.; Fischer, J.; Solujic, L.; Milosavljevic, E.
B. Organometallics 1992, 11, 401. (b) Barthel-Rosa, L. P.; Maitra, K.;
Fischer, J.; Nelson, J. H. Organometallics 1997, 16, 1714. (c) Durac-
zynska, D.; Nelson, J. H. Dalton Trans. 2003, 449. (d) Duraczynska,
D.; Nelson, J. H. Dalton Trans. 2005, 92.
F. Mercier, F.; Hugel-LeGoff, C.; Ricard, L.; Mathey, F. J. Organomet.
Chem. 1990, 398, 389. (h) Hugel-LeGoff, C.; Mercier, F.; Ricard, L.;
Mathey, F. J. Organomet. Chem. 1989, 363, 325. (i) Mercier, F.;
Mathey, F. Organometallics 1990, 9, 863.
(7) For a recent review of azaallyl complexes see: Caro, C. F.;
Lappert, M. F.; Merle, P. G. Coord. Chem. Rev. 2001, 219-221, 605.
(8) Watson, L. A.; Franzman, B.; Bollinger, J. C.; Caulton, K, G.
New J. Chem. 2003, 27, 1769.
(6) (a) Appel, R.; Schuhn, W.; Knoch, F. Angew. Chem., Int. Ed. Engl.
1985, 24, 420. (b) Mathey, F. J. Organomet. Chem. 1990, 400, 149. (c)
Nixon, J. F. Chem. Rev. 1988, 88, 1353. (d) Mercier, F.; Fischer, J.;
Mathey, F. Angew. Chem., Int. Ed. Engl. 1986, 25, 357. (e) Mercier,
F.; Hugel-LeGoff, C.; Mathey, F. Organometallics 1988, 7, 955. (f)
Niecke, E.; Kramer, B.; Nieger, M. Organometallics 1991, 10, 10. (g)
10.1021/om050688u CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/10/2005

4900 Organometallics, Vol. 24, No. 21, 2005
Communications
Scheme 3
Figure 1. Structural view of 2a showing 30% thermal
-
ellipsoids (PF6 and most H atoms omitted for clarity).
Selected bond lengths (Å): Ru-P(1) ) 2.2690(9), Ru-C(18)
) 2.231(3), Ru-C(19) ) 2.227(3), Ru-C(23) ) 2.239(4),
Ru-C(24) ) 2.547(3), P(1)-C(18) ) 1.764(4), C(18)-C(19)
) 1.412(5), C(19)-C(23) ) 1.425(5), C(23)-C(24) ) 1.392(5),
C(24)-N ) 1.358(4).
3.58 ppm (d, 1H, JHP ) 5.7 Hz) assignable to the protons
H1 and H4 of the η3-phosphaallyl and η2-vinylamine
units, respectively. In the 13C{1H} NMR spectrum the
coordinated sp2 carbon atoms C1, C2, C3, and C4 of the
η3-phosphaallyl-η2-vinylamine moiety exhibit charac-
1
teristic resonances at 40.8 (d, JCP ) 24.2 Hz), 75.8,
117.4 (d, JCP ) 4.6 Hz), and 117.8 ppm (d, JCP ) 6.9
Hz), respectively. In the 31P{1H} NMR spectrum the
phosphaallyl ligand exhibits a singlet at 4.3 ppm.
Concurrent NMR spectra are observed for 2b. However,
due to spectral overlap with 3b, not all signals could be
unequivocally assigned.
The NMR data of 3a are quite different from those of
2a. The 1H NMR spectrum exhibits resonances at 6.35
(d, JHP ) 9.8 Hz) and 6.03 ppm, which can be assigned
to the olefinic hydrogen atom H1 and the allyl proton
H4. The most characteristic features in the 13C{1H}
NMR spectrum are a low-field doublet resonance at
172.0 ppm (d, JCP ) 27.2 Hz) and doublet resonances
at 117.4 (d, JCP ) 47.9 Hz), 91.3 (d, JCP ) 3.1 Hz), and
79.1 ppm (d, JCP ) 1.5 Hz) assignable to the terminal
allyl carbon atom C3, the two olefinic carbon atoms C1
and C2, and the central allyl carbon atom C4 bearing
the NEt2 unit. In the 31P{1H} NMR spectrum the η1-
(P)-phosphaallyl ligand exhibits a singlet at 74.1 ppm
(cf. 4.3 ppm in 2a). The NMR spectra of 3b are similar
to those of 3a and are not discussed here.
The solid-state structures of 2a and 3b were deter-
mined by single-crystal X-ray diffraction. ORTEP dia-
grams are depicted in Figures 1 and 2, respectively, with
important bond distances reported in the captions. The
structure of 2a can be described as a three-legged piano-
stool coordination with the η3(P)-phosphaallyl moiety
and the carbon atoms of the vinylamine unit as the legs.
The η3-phosphaallyl functionality is nearly symmetri-
cally bonded to the metal, with the Ru-P, Ru-C(18),
and Ru-C(19) bond distances being 2.269(1), 2.231(3),
Figure 2. Structural view of 3b showing 30% thermal
-
ellipsoids (PF6 and most H atoms omitted for clarity).
Selected bond lengths (Å): Ru-N ) 2.212(2), Ru-C(25) )
2.083(2), Ru-C(24) ) 2.203(3), Ru-P(1) ) 2.2758(6), P(1)-
C(18) ) 1.806(2), C(18)-C(19) ) 1.323(4), C(19)-C(24) )
1.498(4), C(24)-C(25) ) 1.420(3), C(25)-N ) 1.424(3).
and 2.227(3) Å, respectively. The C-C part of the moiety
is strongly asymmetrically bonded to the metal center,
with the Ru-C bonds to the carbon atoms C(23) and
C(24) being 2.239(4) and 2.547(3) Å, respectively. Strong
alteration of olefin binding by π-donor substituents has
been also observed in [FeCp(CO)2(H2CdCHNMe2)]+,
where the vinylamine is essentially η1 bound (the
nonbonded Fe‚‚‚C separation is 2.823(11) Å).8 In turn,
the C(24)-N bond already exhibits double-bond char-
acter, being 1.358(4) Å (cf. 1.456(5) and 1.474(5) Å for
N-C(25) and N-C(27), respectively), and the N atom
is essentially planar. The bonding situation of the -Cd
CHNEt2 unit might be described as intermediate be-
tween the limiting vinylamine and imine forms or
alternatively perhaps even as η1(C)-azaallyl. Accord-
ingly, rotation about the C(23)-C(24) bond is expected
to be facile, putting the NEt2 substituent rapidly in a

Communications
Organometallics, Vol. 24, No. 21, 2005 4901
syn conformation for steric reasons (conversion of C to
2 in Scheme 3).
B takes place with concomitant P-N bond cleavage.9
In this way RuCp η3-phosphaallyl-η2-vinylamine com-
plexes C are afforded with the NEt2 substituent initially
in an anti position. However, rotation about the C-C
bond to give the more stable syn isomers 2 is facile, since
the Ru-C4 bond is weak or even nonbonding. Com-
plexes 2 are the kinetic products, which rearrange
eventually to the thermodynamically more stable η1-
phosphaallyl-η3-azaallyl complexes 3. The final conver-
sion again requires a syn-anti isomerization of the NEt2
substituent. Detailed mechanistic investigations, sup-
ported by theoretical DFT calculations, are currently
underway and will be reported in due course.
The structure of 3b is also of the three-legged piano-
stool type, with the η3-azaallyl moiety and the P atom
as the legs. The η3-azaallyl unit, being exo oriented with
respect to the phosphine moiety, is asymmetrically
bonded to the metal with the Ru-C bond distance to
the central allyl carbon atom C(25) (2.083(2) Å) dis-
tinctly shorter than the Ru-N and Ru-C(24) bonds to
the terminal allyl atoms N and C(24) (2.212(2) and
2.203(3) Å, respectively).
For the present conversions, unfortunately, no inter-
mediates could be detected spectroscopically. However,
from previous experimental data it is apparent that the
formation of η3-phosphaallyl-η2-vinylamine and η1-
phosphallyl-η3-azaallyl complexes proceeds via the
intermediacy of the highly electrophilic metallacyclo-
pentatriene A and the allyl carbene complex B, as
depicted in Scheme 3.1 There is apparently migration
of the κ1(P)-coordinated PPh2NEt2 ligand, analogously
to the η3-allyl carbene complexes already described.1 In
contrast, however, instead of C-H bond activation
involving either the phenyl or ethyl subtituents of the
aminophosphine ligand, P-N bond activation occurs.
Preliminary DFT/B3LYP calculations strongly suggest
that direct NEt2 attack at the carbene carbon atom of
Acknowledgment. Financial support by the “Fonds
zur Fo¨rderung der wissenschaftlichen Forschung” is
gratefully acknowledged (Project No. P16600-N11).
Supporting Information Available: Text giving experi-
mental procedures and CIF files giving complete crystal-
lographic data and technical details for 2a and 3b. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM050688U
(9) For P-N bond cleavage reactions involving aminophosphines
see: Fei, Z.; Biricik, N.; Zhao, D.; Scopelliti, R.; Dyson, P. Inorg. Chem.
2004, 43, 2228. Priya, S.; Balakrishna, M. S.; Mague, J. T.; Mobin, S.
M. Inorg. Chem. 2003, 42, 1272.