Half-Sandwich Ruthenium-Phosphine Complexes with Pentadienyl
and Oxo- and Azapentadienyl Ligands
Amira Reyna-Madrigal,
†
Anabel Moreno-Gurrola,
†
Odilia Perez-Camacho,
‡
M. Elena Navarro-Clemente,
§
Patricia Jua ́ rez-Saavedra,
†
Marco A. Leyva-Ramirez,
†
Atta M. Arif,
∥
Richard D. Ernst,
∥
and M. Angeles Paz-Sandoval*
,†
†
Departamento de Química, Centro de Investigació n y de Estudios Avanzados del IPN, Av. IPN # 2508, San Pedro Zacatenco,
Me ́ xico 07360, D.F., Mexico
‡
Centro de Investigació n en Química Aplicada, Blvd. Enrique Reyna Hermosillo #140 Saltillo, Coahuila 25250, Mexico
§
Escuela Superior de Ingeniería Química e Industrias Extractivas, IPN, Unidad Profesional Adolfo Ló pez Mateos,
San Pedro Zacatenco, Me ́ xico 07738, D. F., Mexico
∥
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, United States
* S Supporting Information
ABSTRACT: Treatment of RuCl
2
(PPh
3
)
3
and RuHCl(PPh
3
)
3
with the tin compound
CH
2
C(Me)CHC(Me)CH
2
SnMe
3
gives the corresponding acyclic pentadienyl half-
sandwich (η
5
-CH
2
C(Me)CHC(Me)CH
2
)RuX(PPh
3
)
2
[X = Cl, (2); H, (3)]. The
steric congestion in 2 is most effectively relieved by formation of the cyclometa-
lated complex (η
5
-CH
2
C(Me)CHC(Me)CH
2
)Ru(C
6
H
4
PPh
2
)(PPh
3
)(4). Addition of
1 equiv of PHPh
2
to (η
5
-CH
2
CHCHCHCH
2
)RuCl(PPh
3
)
2
(1)affords the chiral com-
plex (η
5
-CH
2
CHCHCHCH
2
)RuCl(PPh
3
)(PHPh
2
)(5), while compound (η
5
-CH
2
C-
(Me)CHC(Me)CH
2
)RuCl(PPh
3
)(PHPh
2
)] (6) is directly obtained from the reaction
of RuCl
2
(PPh
3
)
3
with CH
2
C(Me)CHC(Me)CH
2
Sn(Me)
3
and PHPh
2
. Treatment of
RuCl
2
(PPh
3
)
3
with the corresponding Me
3
SnCH
2
CHCHCHNR (R = Cy, t-Bu)
affords (1-3,5-η-CH
2
CHCHCHNCy)RuCl(PPh
3
)
2
(7) and [1-3,5-η-CH
2
CHCHCHN-
(t-Bu)]RuCl(PPh
3
)
2
(8). The hydrolysis of 7, on a silica gel chromatography column,
allows the isolation of RuCl(η
5
-CH
2
CHCHCHO)(PPh
3
)
2
(9). The azapentadienyl
complex 7 reacts with 1 equiv of PHPh
2
to afford [1-3,5-η-CH
2
CHCHCHN(Cy)]RuCl(PPh
3
)(PHPh
2
)(10), while the corre-
sponding product [1-3,5-η-CH
2
CHCHCHN(t-Bu)]RuCl(PPh
3
)(PHPh
2
)(11) from 8 is only observed through
1
H and
31
P NMR
spectroscopy as a mixture of isomers. Two equivalents of PHPh
2
gives spectroscopic evidence of [η
3
-CH
2
CHCHCHN(t-Bu)]-
RuCl(PHPh
2
)
3
. A mixture of products [η
5
-CH
2
C(Me)CHC(Me)O]RuCl(PPh
3
)
2
(12) and [η
5
-CH
2
C(Me)CHC(Me)O]RuH-
(PPh
3
)
2
(13) is obtained from reaction of RuCl
2
(PPh
3
)
3
with Li[CH
2
C(Me)CHC(Me)O]. In contrast, the oxopentadienyl compound
13 is cleanly formed from RuHCl(PPh
3
)
3
and Li[CH
2
C(Me)CHC(Me)O]. An attempt to separate compounds 12 and 13 by
crystallization gives an orthometalated product [η
5
-CH
2
C(Me)CHC(Me)O]Ru(C
6
H
4
PPh
2
)(PPh
3
)(14), which is the oxopentadienyl
analogue to 4. The bulky [1-3,5-η-CH
2
C(t-Bu)CHC(t-Bu)O]RuH(PPh
3
)
2
(15) analogue to 13 has also been prepared from
RuHCl(PPh
3
)
3
and Li[CH
2
C(t-Bu)CHC(t-Bu)O]. Compounds 3, 5, 6, 7, and 12−15 have been structurally characterized. The
preferred heteropentadienyl orientations and the relative positions of the H, Cl, PPh
3
, and PHPh
2
ligands have been established in the
piano-stool structures for all compounds, and it can be definitively surmised that the chemistry involved in the heteropentadienyl half-
sandwich compounds studied is dominated by steric effects.
■
INTRODUCTION
In efforts to gain a better understanding of acyclic versus cyclic
pentadienyl ligands, many “half-open ruthenocenes” have been
prepared and comparisons between complexes having both types of
coordinated ligands have been carried out, including CpRu-
(2,4-Me
2
-η
5
-pentadienyl),
1a
Cp*Ru(η
5
-pentadienyl),
1b
Cp*Ru(2,4-
Me
2
-η
5
-pentadienyl),
1b
and [Cp*RuH(2,4-Me
2
-η
5
-pentadienyl)]-
[BF
4
].
1c
The chemistry of pentadienyl ligands has shown interesting
and new possibilities of reactivity compared to the chemistry of the
well-known cyclopentadienyl ligand, due to the former’ s unique
properties, such as the ability to adopt a variety of bonding modes
and to shift easily among them.
2
The incorporation of heteroatoms
such as sulfur, oxygen, and nitrogen into the pentadienyl frag-
ment has led to a wider scope in the chemistry of the Cp′Ru-
(heteropentadienyl) (Cp′ = Cp, Cp*) complexes, and the coor-
dinated heteropentadienyl ligands display a much wider range of
ligand substitutions and additions, oxidative additions, and cou-
pling reactions, among others.
3
The interesting reaction chemistry
displayed by their simple pentadienyl analogues follows from
their differences in electronic structure. It was then of con-
siderable interest to continue the study and development of
Received: July 12, 2012
Published: October 3, 2012
Article
pubs.acs.org/Organometallics
© 2012 American Chemical Society 7125 dx.doi.org/10.1021/om300657z | Organometallics 2012, 31, 7125−7145