Synthesis, structure, and reactivity of trigonal bipyramidal ruthenium(IV) trialkyl complexes

Article abstract of DOI:10.1021/om400183n

The alkylation of [Ru(NPPh₃)(PPh₃)₂Cl ₃] with Me₃SiCH₂MgCl afforded the Ru ^IV trialkyl complex [Ru(CH₂SiMe₃) ₃(PPh₃)Cl] (1), which exhibits a trigonal bipyramidal geometry with the three alkyl groups occupying the equatorial plane. DFT calculations reveal that 1 possesses a (d_xz,d_yz)4 singlet ground state, consistent with the observed diamagnetism of the complex. The electronic spectrum of 1 displayed two absorptions at 455 and 505 nm, which, on the basis of TDDFT calculations, are attributed to metal-centered d-d transitions with a significant contribution from the alkyl ligands. Chloride abstraction of 1 with Ag(OTf) (OTf^- = triflate) provided the triflate complex [Ru(CH₂SiMe₃)₃(PPh₃)(OTf)] (2) that proved to be a useful starting material for Ru^IV trialkyl complexes. Substitution of 2 with NaX afforded [Ru(CH₂SiMe ₃)₃(PPh₃)(X)] (X = N₃^- (3) or SCN^- (4)). Treatment of 2 with excess sodium 2,3,5,6-tetrafluorophenoxide (NaOR_f) in tetrahydrofuran resulted in desilylation of two alkyl groups, and formation of the dimethyl complex [Ru(CH₂SiMe₃)Me₂(PPh₃)(OR _f)] (5). 2 underwent reductive elimination of the C-C bond with 1,10-phenanthroline (phen) in CH₂Cl₂ to give cis-[Ru(phen)₂(PPh₃)Cl](OTf) (6). The crystal structures of 1, 2, 4, and 5 have been determined.

Full text of DOI:10.1021/om400183n

Article
pubs.acs.org/Organometallics
Synthesis, Structure, and Reactivity of Trigonal Bipyramidal
Ruthenium(IV) Trialkyl Complexes
Enrique Kwan Huang,† Wai-Man Cheung,† Sharon Lai-Fung Chan,*,‡ Herman H. Y. Sung,†
Ian D. Williams,† and Wa-Hung Leung*,†
†Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P. R.
China
‡Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong,
P. R. China
S
* Supporting Information
ABSTRACT: The alkylation of [Ru(NPPh3)(PPh3)2Cl3] with
Me3SiCH2MgCl afforded the RuIV trialkyl complex [Ru-
(CH2SiMe3)3(PPh3)Cl] (1), which exhibits a trigonal
bipyramidal geometry with the three alkyl groups occupying
the equatorial plane. DFT calculations reveal that 1 possesses a
(dxz,dyz)4 singlet ground state, consistent with the observed diamagnetism of the complex. The electronic spectrum of 1 displayed
two absorptions at 455 and 505 nm, which, on the basis of TDDFT calculations, are attributed to metal-centered d−d transitions
with a significant contribution from the alkyl ligands. Chloride abstraction of 1 with Ag(OTf) (OTf− = triflate) provided the
triflate complex [Ru(CH2SiMe3)3(PPh3)(OTf)] (2) that proved to be a useful starting material for RuIV trialkyl complexes.
−
Substitution of 2 with NaX afforded [Ru(CH2SiMe3)3(PPh3)(X)] (X = N3 (3) or SCN− (4)). Treatment of 2 with excess
sodium 2,3,5,6-tetrafluorophenoxide (NaORf) in tetrahydrofuran resulted in desilylation of two alkyl groups, and formation of
the dimethyl complex [Ru(CH2SiMe3)Me2(PPh3)(ORf)] (5). 2 underwent reductive elimination of the C−C bond with 1,10-
phenanthroline (phen) in CH2Cl2 to give cis-[Ru(phen)2(PPh3)Cl](OTf) (6). The crystal structures of 1, 2, 4, and 5 have been
determined.
thylphenyl)11 are well documented. In this paper, we describe
INTRODUCTION
■
the synthesis and structures of the RuIV trialkyl complexes
High-valent late transition metal alkyl complexes are of interest
[RuIV(CH2SiMe3)3(PPh3)X] that exhibit trigonal bipyramidal
due to their involvement in metal-catalyzed C−H activation
g e o m e t r y . T h e t r i fl a t e ( O T f −
)
c o m p l e x
and functionalization.1 Compared with the earlier transition
metal counterparts, the chemistry of polyalkyl complexes of late
transition metals, particularly Ru,2−8 is not well developed.
Wilkinson and co-workers pioneered the synthesis of
homoleptic alkyls of Ru.2−4 Tetrahedral [RuIV(c-C6H11)4]2
and ethane-like [RuIII2(CH2EMe3)6] (E = C, Si)3 containing
RuRu triple bonds have been obtained by alkylation of
[Ru2(OAc)4Cl] (OAc− = acetate) with Grignard reagents.
Anionic permethyl complexes such as [Li(tmed)]3[RuIIIMe6]
and [Li(tmed)]2[(nbd)RuIIMe4] (tmed = N,N,N′,N′-tetrame-
thylethylenediamine; nbd = norbornadiene) have also been
synthesized.4,8 These Ru homoleptic alkyls are very air
sensitive, and their reaction chemistry has not been studied
in detail. It is well-known that multiply bonded ligands can
stabilize high-valent organometallic complexes. Thus, stable
[RuIV(CH2SiMe3)3(PPh3)(OTf)] (2) was found to display
interesting reactivity. The desilylation of 2 with sodium 2,3,5,6-
tetrafluorophenoxide and ligand-induced reductive elimination
of 2 will be reported.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were carried out
under nitrogen by standard Schlenk techniques. Solvents were purified
by standard procedures and distilled prior to use. NMR spectra were
recorded on a Bruker AV 400 MHz NMR spectrometer operating at
400, 376.5, and 162.0 MHz for 1H, 19F and 31P, respectively. Chemical
shifts (δ, ppm) were reported with reference to SiMe4 (1H and 13C),
CF3C6H5 (19F), and H3PO4 (31P). Infrared spectra (KBr) were
recorded on a Perkin-Elmer 16 PC FT-IR spectrophotometer and ESI
mass spectra on an Applied Biosystem QSTAR mass spectrometer and
quadrupole-time-of-flight tandem mass spectrometer (QTOF Premier,
Waters Micromass, Manchester, UK). GC−MS was carried out with
an Aglient 5957C gas chromatograph−mass spectrometer. UV−visible
spectra were recorded on a Perkin-Elmer LAMBAD 900 UV/vis/NIR
spectrophotometer. Elemental analyses were performed by Medac
Ltd., Surrey, U.K.
9
RuVI nitrido (e.g., [Ru(N)R4]− where R = Me or CH2SiMe3 )
and oxo (e.g., [Ru(O)(CH2SiMe3)4]−)10 alkyl complexes have
been synthesized.
In the above-mentioned Ru polyalkyl complexes, the metal
centers are in either pseudo tetrahedral or octahedral/square
pyramidal coordination environments. To our knowledge, Ru
alkyl complexes in trigonal bipyramidal geometry have not been
isolated to date, although related RuIV tetrakis(thiolate)
complexes such as [Ru(SR)4(MeCN)] (R = 2,3,4,6-tetrame-
Received: March 5, 2013
Published: August 14, 2013
© 2013 American Chemical Society
4483
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489

Organometallics
Article
The compound [Ru(NPPh3)(PPh3)2Cl3]12 was prepared according
to a literature method. Sodium 2,3,5,6-tetrafluorophenoxide (NaORf)
was prepared by reaction of 2,3,5,6-tetrafluorophenol with 1 equiv of
sodium hydride (60% in mineral oil) in tetrahydrofuran (THF) at
room temperature.
7.39−7.43 (m, 6H, PPh3), 7.44−7.45 (m, 3H, PPh3). 31P {1H} NMR
(162 MHz, THF-d8): δ 58.73 (s). 19F NMR (376 MHz, THF-d8): δ
−162.22 (m), −146.10 (m). Anal. Calcd for C30H33F4OPRuSi: C,
55.80; H, 5.15. Found: C, 55.50; H, 5.06.
cis-[Ru(phen)2(PPh3)Cl][OTf] (6). To a solution of 2 (50.0 mg, 0.065
mmol) in CH2Cl2 (5 mL) was added 1,10-phenanthroline (23.4 mg,
0.13 mmol) at room temperature. The resulting orange mixture was
stirred at room temperature overnight. The volatiles were removed in
vacuo, and the residue was extracted with CH2Cl2. Recrystallization
from CH2Cl2/hexane gave orange crystals which were suitable for X-
Syntheses. [Ru(CH2SiMe3)3(PPh3)Cl] (1). To a brown suspension
of [Ru(NPPh3)(PPh3)2Cl3] (100 mg, 0.094 mmol) in THF (5 mL)
was added Me3SiCH2MgCl (0.67 mL of a 0.7 M solution in THF,
0.469 mmol) at −78 °C. The resulting deep red mixture was stirred
overnight at room temperature, and the volatiles were removed in
vacuo. The residue was extracted with hexane. Concentration and
cooling at −4 °C afforded air stable red crystals which were suitable for
1
ray analysis. Yield: 26.5 mg (45%). H NMR (400 MHz, CDCl3): δ
7.02 (m, 9H, PPh3), 7.31 (m, 6H, PPh3), 7.46 (s, 1H, phen), 7.56 (s,
1H, phen), 7.79 (s, 1H, phen), 7.86 (d, J = 4.2 Hz, 1H, phen), 8.09 (d,
J = 4.6 Hz, 1H, phen), 8.15 (d, J = 4.4 Hz, 1H, phen), 8.23 (d, J = 4.2
Hz, 1H, phen), 8.54 (d, J = 3.8 Hz, 1H, phen). 31P {1H} NMR (162
MHz, CDCl3): δ 42.31 (s). 19F NMR (376 MHz, C6D6): δ −78.24 (s).
1
X-ray analysis. Yield: 44.7 mg (72%). H NMR (400 MHz, C6D6): δ
0.30 (s, 27H, SiMe3), 3.20 (d, J = 3.2 Hz, 6H, CH2SiMe3), 6.95 (m,
6H, PPh3), 7.02 (m, 3H, PPh3), 7.26−7.35 (m, 6H, PPh3). 31P {1H}
NMR (162 MHz, C6D6): δ 54.83 (s). MS (ESI): m/z 625.3 (M+ −
Cl). UV/vis (CH2Cl2): λmax/nm (εmax/M−1 cm−1): 455 (730), 505
(692). Anal. Calcd for C30H48PRuSi3Cl·0.5Et2O: C, 52.43; H, 7.29.
Found: C, 52.44; H, 7.02.
MS (ESI): m/z 758 (M+
- OTf). Anal. Calcd for
C43H31ClF3N4O3PRuS: C, 56.86; H, 3.44 ; N, 6.17. Found: C,
56.88; H, 3.50; N, 6.27.
[Ru(CH2SiMe3)3(PPh3)OTf] (2) (OTf− = Triflate). To a solution of 1
(50.0 mg, 0.072 mmol) in THF (5 mL) was added AgOTf (18.5 mg,
0.072 mmol) at room temperature. The resulting red mixture was
stirred at room temperature overnight and filtered. The volatiles were
removed in vacuo, and the residue was washed with hexane and then
extracted with Et2O. Concentration and cooling at −4 °C afforded red
crystals which were suitable for X-ray analysis. Yield: 48.5 mg (87%).
1H NMR (400 MHz, C6D6): δ 0.19 (s, 27H, SiMe3), 3.59 (d, J = 4.0
Hz, 6H, CH2SiMe3), 6.87−6.92 (m, 6H, PPh3), 6.95−7.02 (m, 6H,
PPh3), 7.19−7.23 (m, 3H, PPh3). 31P {1H} NMR (162 MHz, C6D6): δ
Computational Details. All calculations were performed with the
Gaussian 09 program package.13 The 6-31+G* basis set14 was
employed for all atoms except Ru, which was described by the
Stuttgart small-core relativistic effective-core potential with its
accompanying basis set.15 The M06L16 functional developed by
Truhlar and Zhao was employed for all DFT calculations. A full
geometry optimization using B3LYP17 functional has also been
performed on 1 for comparison in which M06L showed a better
agreement, especially on the Ru−carbon bond length, with
experimental data of 1 (Table S2, Supporting Information). Therefore,
only the M06L-calculated results would be discussed here. Full
geometry optimizations without symmetry constraints were carried out
in the gas phase for both the singlet and triplet ground states of 1
followed by frequency calculations to ensure that the optimized
structures were true energy minima. In addition, full geometry
optimizations and time-dependent density functional theory (TD-
DFT) calculations have been performed on 1 with C3 symmetry
imposed. The use of C3 symmetry can provide a simple model to
interpret the nature of molecular orbitals, and it is justified because 1
possesses pseudo C3 symmetry in solution on the NMR time scale.
The integral equation formalism model (IEFPCM)18 has also been
applied to account for solvent effects upon the electronic transition
(solvent = dichloromethane).
X-ray Crystallography. Intensity data were collected on a Bruker
APEX 1000 CCD diffractometer using graphite-monochromated Mo
Kα radiation (λ = 0.71073 Å). The collected frames were processed
with the software SAINT. Structures were solved by the direct
methods and refined by full-matrix least-squares on F2 using the
SHELXTL software package.19,20 Atomic positions of non-hydrogen
atoms were refined with anisotropic parameters and with suitable
restraints. However, disordered atoms were refined isotropically.
Hydrogen atoms were generated geometrically and allowed to ride on
their respective parent carbon atoms before the final cycle of least-
squares refinement.
1
58.03 (s). 19F NMR (376 MHz, C6D6): δ −75.41 (s). H NMR (400
MHz, THF-d8): δ −0.06 (s, 9 H, SiMe3), 3.37 (d, J = 3.6 Hz, 2H,
CH2SiMe3), 7.22−7.27 (m, 6H, PPh3), 7.43−7.47 (m, 6H, PPh3),
7.52−7.56 (m, 3H, PPh3). 31P {1H} NMR (162 MHz, THF-d8): δ
56.32 (s). 19F NMR (376 MHz, THF-d8): δ −75.68 (s). MS (ESI): m/
z 624.3 (M+ − OTf). UV/vis (CH2Cl2): λmax/nm (εmax/M−1 cm−1):
455 (1034), 505 (980). Anal. Calcd for C31H48F3O3PRuSSi3: C, 48.10;
H, 6.25. Found: C, 48.20; H, 6.30.
[Ru(CH2SiMe3)3(PPh3)(N3)] (3). To a solution of 2 (50.0 mg, 0.065
mmol) in THF (5 mL) was added NaN3 (4.2 mg, 0.065 mmol) at
room temperature. The resulting deep purple mixture was stirred at
room temperature overnight and filtered. The volatiles were removed
in vacuo, and the residue was extracted with hexane. Concentration
1
and cooling at −4 °C gave purple crystals. Yield: 37.3 mg (86%). H
NMR (400 MHz, C6D6): δ 0.24 (s, 27H, SiMe3), 3.07 (d, J = 7.2 Hz,
6H, CH2SiMe3), 6.92−6.96 (m, 6H, PPh3), 6.99 (m, 3H, PPh3), 7.25
(m, 6H, PPh3). 31P {1H} NMR (162 MHz, C6D6): δ 52.37 (s). IR
(KBr, cm−1): 2020 [ν(N3)]. Anal. Calcd for C30H48N3PRuSi3: C,
54.02; H, 7.25; N, 6.30. Found: C, 53.65; H, 7.21; N, 6.36.
[Ru(CH2SiMe3)3(PPh3)(SCN)] (4). This compound was prepared
similarly as for 3 using NaSCN (6.3 mg, 0.065 mmol) in place of
1
NaN3. Yield: 40.0 mg (90%). H NMR (400 MHz, C6D6): δ 0.25 (s,
27H, SiMe3), 3.06 (d, J = 7.6 Hz, 6H, CH2SiMe3), 6.91 (m, 6H, PPh3),
6.98 (m, 3H, PPh3), 7.17 (m, 6H, PPh3). 31P {1H} NMR (162 MHz,
C6D6): δ 54.20 (s). Anal. Calcd for C31H48NPRuSSi3: C, 54.51; H,
7.08; N, 2.05. Found: C, 54.35; H, 6.74; N, 2.08.
RESULTS AND DISCUSSION
■
[Ru(CH2SiMe3)(Me)2(PPh3)(ORf)] (Rf = C6F4H) (5). To a solution of
2 (50.0 mg, 0.065 mmol) in THF (5 mL) was added NaORf (153 mg,
0.81 mmol) at room temperature. The resulting deep red solution was
stirred at room temperature overnight. The volatiles were removed in
vacuo, and the residue was extracted with hexane. The red extracts
were concentrated and cooled at −4 °C to give a red solid, which was
further recrystallized from hexane at −4 °C four times to give red
[RuIV(CH2SiMe3)3(PPh3)Cl] (1). Treatment of the RuIV
phosphoraminato complex [RuIV(NPPh3)(PPh3)2Cl3] with
excess Me3SiCH2MgCl in tetrahydrofuran, followed by
recrystallization from hexane, afforded red crystals characterized
as the trialkyl complex [RuIV(CH2SiMe3)3(PPh3)Cl] (1).
Complex 1 is remarkably stable and can be purified by column
chromatography in air without decomposition. It may be noted
that dimeric RuI I I trimethylsilylmethyl complex
[Ru2(CH2SiMe3)6] containing a Ru−Ru triple bond has been
obtained from the alkylation of [Ru2(OAc)4Cl] with
Me3SiCH2MgCl.3 Attempts to prepare analogous trialkyl
complexes by treatment of [RuIV(NPPh3)(PPh3)2Cl3] with
other alkylating agents, including PhMgCl, PhCH2MgCl,
1
single crystals. Yield: 18.9 mg (45%). H NMR (400 MHz, C6D6): δ
0.06 (s, 9H, SiMe3), 2.41 (d, J = 4.4 Hz, 6H, Me), 3.43 (d, J = 6.8 Hz,
2H, CH2SiMe3), 6.11 − 6.17 (m, 1H, OC6F4H), 6.92 (m, 6H, PPh3),
6.98 (m, 3H, PPh3), 7.07−7.12 (m, 6H, PPh3). 31P {1H} NMR (162
MHz, C6D6): δ 59.15 (s). 19F NMR (376 MHz, C6D6): δ −160.94
1
(m), −144.12 (m). H NMR (400 MHz, THF-d8): δ −0.083 (s, 9H,
SiMe3), 2.32 (d, J = 4.8 Hz, 6H, Me), 3.33 (d, J = 6.4 Hz, 2 H,
CH2SiMe3), 6.25−6.34 (m, 1H, OC6F4H), 7.20−7.24 (m, 6H, PPh3),
4484
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489

Organometallics
Article
Me3CCH2Li, and MeLi, failed; these reactions only yielded
hexane-insoluble dark materials that did not crystallize. The 1H
NMR spectrum of 1 in C6D6 showed sharp peaks, indicative of
the diamagnetic nature of the complex. A single set of
resonances [δ 0.30 (s), 3.20 (d)] was found for the alkyl groups
in 1, consistent with its solid-state structure (vide infra). The
methylene resonance of 1 occurred at a more upfield position
than those for reported Ru trimethylsilylmethyl complexes,
such as [Ru2(CH2SiMe3)6] (δ 1.51 ppm)3 and mer-[Ru-
(dtbpy)(NO)(CH2SiMe3)3] (δ 1.24, 1.59 ppm; dtbpy = 4,4′-
di-tert-butyl-2,2′-bipyridyl).7 The 31P {1H} NMR spectrum of 1
showed a singlet at δ 54.83 ppm. The UV−visible spectrum of
1 in CH2Cl2 displayed d−d absorption bands (vide infra) with
maxima at ca. 455 (ε = 730 M−1 cm−1) and 505 nm (ε = 692
M−1 cm−1). The cyclic voltammogram of complex 1 in CH2Cl2
exhibited an irreversible wave at ca. 0.79 V versus ferrocenium−
ferrocene, which is tentatively assigned as the RuIV−RuV
oxidation.
steric effects. The Ru−C distances [2.026(4)−2.037(4) Å] are
similar to those in [Ru2(CH2SiMe3)6] [av 2.031(5) Å].3 The
Ru−Cl bond is rather long (2.4109(13) Å cf. 2.3643(8) Å in
[Ru(SR)3(MeCN)Cl] where R = 2,6-dimethylphenyl22)
presumably due to steric effects and/or trans influence of PPh3.
DFT and TD-DFT Calculations. DFT calculations were
performed in order to gain insight into the ground state
electronic structure of 1. Figure 2 shows the frontier orbitals of
The solid-state structure of complex 1 is shown in Figure 1.
The geometry around Ru is pseudo trigonal bipyramidal with
Figure 2. Frontier orbitals of 1 imposed with C3 symmetry (isovalue of
0.05).
1. DFT calculations reveal that the ground state of complex 1 is
a singlet, (dyz,dxz),4 consistent with the observed diamagnetism
of the complex. The optimized triplet ground state is 26.8 kcal
mol−1 higher than the singlet state. The HOMO of 1 is a
nonbonding Ru dxz orbital whereas the LUMO is an
2
2
antibonding orbital formed from the Ru dx −y and alkyl ligands.
Time-dependent DFT (TD-DFT) calculations were also
performed to elucidate the nature of electronic absorption
bands associated with 1 at 455 and 505 nm (Figure 3 insert).
Calculated excitation energies, oscillator strengths, and
absorption spectrum constructed by convolution of these
calculated transitions with Gaussian functions are depicted in
Figure 3. Details of the composition of the molecular orbitals
Figure 1. Molecular structure of complex 1. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at 30% probability.
Selected bond lengths (Å): Ru1−C1 2.026(4), Ru1−C2 2.037(4),
Ru1−C3 2.026(4), Ru1−Cl1 2.4109(13), Ru1−P1 2.2692(14).
the three alkyl groups occupying the equatorial positions.
Although organometallic RuIV complexes are well-known, to
our knowledge, complex 1 is the first example of a trigonal
bipyramidal RuIV alkyl complex. It should be noted that similar
trigonal bipyramidal structures have been found for isoelec-
tronic [RuIV(SR)4(MeCN)] (R = 2,4,5,6-tetramethylphenyl or
2,4,6-triisopropylphenyl)11 and [ReIIIPh3(PEt2Ph)2].21 In
[RuIV(SR)4(MeCN)], the R substituents of the three equatorial
thiolate ligands adopt a “two-up one-down” arrangement, as a
consequence of dπ(Ru)−pπ(S) interactions.11 Metal−ligand π
interactions have also been proposed for [ReIIIPh3(PEt2Ph)2],
in which the three equatorial phenyl ligands are approximately
coplanar.21 By contrast, trigonal bipyramidal 1 contains pure σ
ligands at the equatorial positions. The three trimethylsilyl
groups in 1 point toward the chloride apparently because of
Figure 3. Calculated absorption spectrum for 1 from TD-DFT (M06L
functional)/PCM calculations. Excitation energies and oscillator
strengths are shown by the blue vertical lines; spectrum (in black) is
convoluted with Gaussian function having full width half-maximum of
0.2 eV. Inset: UV/vis spectrum of 1 in CH2Cl2 at 25 °C.
4485
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489

Organometallics
Article
involved in the lowest-energy electronic transition of 1 are
summarized in Table S3 of the Supporting Information. The
profiles of the convoluted absorption spectrum resemble those
observed in the experimental data. The lowest energy
absorption bands at around 500 nm for 1 originate from
three vertical transitions, which explain the splitting of lowest-
energy absorption bands for 1. These transitions are attributed
to the mixing of HOMO−1 → LUMO (Ru(dyz) →
2
2
Ru(dx −y )−Calkyl(σ*)), HOMO−1 → LUMO+1 (Ru(dyz) →
Ru(dxy)−Calkyl(σ*)), HOMO → LUMO (Ru(dxz) → Ru-
2
2
(dx −y )−Calkyl(σ*)), and HOMO → LUMO+1 (Ru(dxz) →
Ru(dxy)−Calkyl(σ*)) transitions. Therefore, the lowest-transi-
tion absorption bands for 1 are best described as metal-
centered transitions with a significant contribution from the
alkyl ligands.
Chloride Substitution of 1. Treatment of 1 with
[ A g ( O T f ) ] ( O T f −
=
t r i fl a t e ) a ff o r d e d
[RuIV(CH2SiMe3)3(PPh3)(OTf)] (2), which can serve as a
good starting material for RuIV trialkyl complexes. The triflate
ligand in 2 is labile and can be easily replaced with other
anionic ligands. The reactivity of 2 is summarized in Scheme 1.
a
Scheme 1. Synthesis and Reactivity of 2
Figure 4. Molecular structure of complex 2. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at 30% probability.
Selected bond lengths (Å): Ru1−C1 2.046(5), Ru1−C2 2.021(5),
Ru1−C3 2.034(5), Ru1−O1 2.207(4), Ru1−P1 2.2402(10).
a
Reagents and conditions: (i) AgOTf, THF; (ii) NaX, THF; (iii) 10
equiv of NaORf, THF; (iv) 2 equiv of phen, CH2Cl2.
Reaction of 2 with NaX yielded [RuIV(CH2SiMe3)3(PPh3)-
(X)] [X− = N3 (3), NCS− (4)]. The H NMR spectra of
complexes 2−4 are similar to that of 1, each showing a singlet
and a doublet due to the methyl and methylene protons,
respectively. Complexes 2 and 4 have been characterized by X-
ray diffraction, and their structures are shown in Figures 4 and
5, respectively. Like 1, both 2 and 4 exhibit trigonal bipyramidal
geometry with the alkyl groups at the equatorial positions. The
Ru−C and Ru−P distances in 2 [av 2.034 and 2.2402(10) Å]
and 4 [av 2.017 and 2.2763(13) Å] are similar to those in 1.
The thiocyanate ligand in 4 is N-bound and essentially linear
[Ru−N−C and N−C−S bond angles are 175.3° and 179.1(6)°,
respectively].
Desilylation of [Ru(CH2SiMe3)3(PPh3)(OTf)]. Reactions of
2 with alkoxides and aryloxides such as KO-t-Bu and NaOPh
yielded dark orange materials that did not crystallize. On the
other hand, treatment of 2 with excess (∼10-fold) sodium
2,3,5,6-tetrafluorophenoxide (NaORf) in THF gave a red oily
material, which, after recrystallization from hexane, yielded a
dark red crystalline solid characterized as the dimethyl complex
[RuIV(CH2SiMe3)Me2(PPh3)(ORf)] (5). 5 is stable in the solid
state but is somewhat air sensitive in solution. The crude
product of 5 was found to contain an impurity that exhibited a
−
1
Figure 5. Molecular structure of complex 4. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at 30% probability.
Selected bond lengths (Å) and angles (deg): Ru1−C1 2.001(6), Ru1−
C2 2.022(5), Ru1−C3 2.029(5), Ru1−N1 2.082(4), Ru1−P1
2.2763(13); Ru1−N1−C13 175.3, N1−C13−S1 179.1(6).
31P resonance at δ 60.42 ppm in THF and a doublet at δ 2.43
1
ppm assignable to methyl protons (vide infra) in the H NMR
spectrum. This impurity, possibly a trimethyl complex (vide
infra), could be removed by repeated (at least four times)
recrystallization of the crude product from hexane. The 31P
{1H} NMR spectrum of a purified sample of 5 showed a singlet
4486
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489

Organometallics
Article
at δ 58.73 ppm only. In the 1H NMR spectrum of 5, the methyl
protons appeared as a doublet at δ 2.32 ppm, which is more
upfield than that for the methylene protons of the
trimethylsilylmethyl ligand (δ 3.43 ppm). Attempts to
i s o l a t e t h e m o n o - o r t r i m e t h y l c o m p l e x
[RuIV(CH2SiMe3)3−xMex(PPh3)(ORf)] (x = 1 or 3) by reacting
2 with 1 equiv or a large excess of NaORf failed, although NMR
spectroscopy and ESI MS indicated that these complexes
should be present in the reaction mixture (vide infra).
spectrum of the mixture displayed three major peaks at m/z
625.1417, 553.1468, and 481.1049, which can be assigned to
[Ru(CH2SiMe3)3(PPh3)]+ (calcd m/z 625.1876), [Ru-
(CH2SiMe3)2Me(PPh3)]+ (calcd m/z 553.1457), and [Ru-
(CH2SiMe3)Me2(PPh3)]+ (calcd m/z 481.1061), respectively.
As the reaction progressed, the intensity of the first two peaks
dropped, while that for the third one increased. After 17 h, the
peak at m/z 481.1061 was predominant. In addition, a minor
peak at m/z 409.0641 assignable to [RuMe3(PPh3)]+ was
detected. On the basis of the above results, we tentatively assign
the resonances at δ 52.33 and 57.04 ppm in 31P NMR spectrum
as [Ru(CH2SiMe3)3(PPh3)X] and [Ru(CH2SiMe3)2Me(PPh3)-
X], respectively, where X− is possibly RfO−. The minor product
with δ = 60.42 ppm is attributed to the trimethyl species,
[RuMe3(PPh3)X]. Therefore, it is reasonable to assume that
the desilylation of 2 into 5 involves a monomethyl
intermediate, presumably [Ru(CH2SiMe3)2Me(PPh3)(ORf)].
Although the hydrolysis of trimethylsilylmethyl acyl com-
plexes to acetyl complexes is well precedented,23,24 to our
knowledge, the desilylation of the σ-bonded trimethylsilyl-
methyl ligand under mild conditions has not been reported.
Previously, Hoffman and co-workers reported that the reaction
of [Re(O){C(O)CH2SiMe3}(CH2SiMe3)2(PMe3)] with bases
such as sodium acetate and excess water gave the acetyl
complex [Re(O){C(O)Me}(CH2SiMe3)2(PMe3)] via hydrol-
ysis of the C−Si bond of the acyl group. It was proposed that
the C−Si bond activation results from the attack of the Si atom
by the base or water hydrogen-bonded to the base, followed by
protonation of a resonance-stabilized enolate ion, [Re(O){C-
(O)CH2}(CH2SiMe3)2(PMe3)]−.23 In this work, the silylether
Me3SiORf has been detected by GLC in the reaction of 2 with
NaORf, indicating that the desilylation involves the nucleophilic
attack of the Si atom by the phenoxide.
Figure 6 shows the molecular structure of 5. The trigonal
bipyramidal geometry is retained after the desilylation of the
A plausible mechanism for the formation of complex 5 is
shown in Scheme 2. Substitution of 2 with NaORf gives
[Ru(CH2SiMe3)3(PPh3)(ORf)]. Nucleophilic attack (possibly
Ru-assisted) of the Si atom of an alkyl group by RfO−, followed
by elimination of RfOSiMe3, affords a methylene intermediate,
A. This transient methylene species is apparently very reactive
and has not been observed by NMR spectroscopy. Protonation
of A by moisture in the solvent or the phenol25 provides a
Figure 6. Molecular structure of complex 5. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are drawn at 30% probability.
Selected bond lengths (Å) and angle (deg): Ru1−C41 2.021(2), Ru1−
C42 2.022(2), Ru1−C7 2.0128(19), Ru1−P1 2.2511(5), Ru1−O1
2.0954(14); Ru1−O1−C1 127.26(13).
Scheme 2. Plausible Mechanism for Formation of 5
alkyl ligands in 2. The Ru−C distances [2.021(2) and 2.022(2)
Å] for the two methyls are similar to that for the
trimethylsilylmethyl ligand [2.0128(19) Å], which compares
well with those in 1. The rather big Ru−O−C angle
[127.26(13)°] in 5 is suggestive of dπ(Ru)−pπ(O) interaction
for the phenoxide ligand.
The reaction of 2 with NaORf has been monitored by NMR
spectroscopy and ESI mass spectrometry (see Supporting
Information). Upon addition of excess (10-fold) NaORf to 2 in
THF, two singlets at δ 52.33 and 57.04 ppm along with the
signal of 5 at δ 58.73 ppm were observed in the 31P {1H} NMR
spectrum. As the reaction proceeded, the intensity of the signal
at δ 52.33 decreased, whereas that for δ 57.04 ppm and 5
increased. Later on, the peak at δ 57.04 ppm also dropped as 5
became the predominant species in the mixture. After 17 h,
only the signal of 5 along with a small peak at δ 60.42 ppm was
found in the 31P NMR spectrum. Therefore, it seems
reasonable to assume that the complex with δ = 52.33 ppm
was converted to 5 via an intermediate with δ = 57.04 ppm. At
the beginning of the reaction, the high-resolution ESI mass
4487
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489

Organometallics
Article
monomethyl complex, B. Similarly, the desilylation of the
second alkyl group in B, followed by protonation, yields the
dimethyl complex 5. It is not clear why the desilylation of the
third alkyl in 2 to give the trimethyl complex is more difficult
than that of the first two alkyls.
mass spectrometry. The high performance computing service
provided by the University of Hong Kong is gratefully
acknowledged.
REFERENCES
■
Reductive Elimination of [Ru(CH2SiMe3)3(PPh3)(OTf)].
No reaction was found when 2 was reacted with dihydrogen or
ethylene in CDCl3. Treatment of 2 with nitric oxide resulted in
a dark intractable material whereas that with carbon monoxide
yielded a yellow solid, possibly a Ru carbonyl complex/cluster,
which showed C−O bands at 1994 and 2054 cm−1 in the IR
spectrum. We have not been able to crystallize this carbonyl
complex/cluster for structure determination. Treatment of 2
with pyridine gave a green material that did not crystallize. On
the other hand, reaction of 2 with 1,10-phenanthroline (phen)
in CH2Cl2 afforded the RuII complex cis-[RuII(phen)2(PPh3)-
Cl][OTf] (6).26 Me3SiCH2CH2SiMe3 was detected by GC−
MS in the reaction mixture, indicating that 6 was formed by
ligand-induced reductive coupling of the alkyl groups in 2. It
seems likely that the reductive elimination of the C−C bond
from 2 affords a monoalkyl intermediate, possibly [Ru-
(phen)2(PPh3)(CH2SiMe3)]+, which reacts with CH2Cl2 to
yield chloride product 6. Under the same conditions, no
reaction was found between 1 and phen, suggesting that
dissociation of the labile triflate ligand in 2 to provide a vacant
coordination site is essential for the reductive elimination of the
RuIV trialkyl complex. 6 also underwent reductive elimination
with phen in THF. Unfortunately, we have not been able to
crystallize the product for characterization.
(1) (a) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879.
(b) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154. (c) Labinger, J. A.; Bercaw, J. E. Nature
2002, 417, 507. (d) Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471.
(e) Ishiyama, T.; Takagi, J.; Ishida, K.; Miyaura, N.; Anastasi, N. R.;
Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 390. (f) Hashiguchi, B. G.;
Bischof, S. M.; Konnick, M. M.; Periana, R. A. Acc. Chem. Res. 2012,
45, 885.
(2) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.;
Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1992, 3477.
(3) Tooze, R. P.; Wilkinson, G.; Motevalli, M.; Hursthouse, M. B. J.
Chem. Soc., Dalton Trans. 1986, 2711.
(4) Savage, P. D.; Wilkinson, G.; Motevalli, M.; Hursthouse, M. B. J.
Chem. Soc., Dalton Trans. 1988, 669.
(5) Hay-Motherwell, R. S.; Wilkinson, G.; Hussain-Bates, B.;
Hursthouse, M. B. Polyhedron 1990, 9, 2071.
(6) Shapley, P. A.; Kim, H. S.; Wilson, S. R. Organometallics 1988, 7,
928.
(7) Chan, K.-W.; Huang, E. K.; Williams, I. D.; Leung, W.-H.
Organometallics 2009, 28, 5794.
(8) Jeffries, P. M.; Ellenwood, R. E.; Girolami, G. S. Inorg. Chim. Acta
2008, 361, 3165.
(9) Shapley, P. A.; Kim, H. s.; Wilson, S. R. Organometallics 1988, 7,
928.
(10) Marshman, R. W.; Bigham, W. S.; Wilson, S. R.; Shapley, P. A.
Organometallics 1990, 9, 1341.
(11) (a) Koch, S. A.; Millar, M. J. Am. Chem. Soc. 1983, 105, 3362.
(b) Millar, M.; O’Sullivan, T.; de Vries, N.; Koch, S. A. J. Am. Chem.
Soc. 1985, 107, 3714.
(12) Pawson, D.; Griffith, W. P. J. Chem. Soc., Dalton Trans. 1975,
417−423.
CONCLUSIONS
■
In summary, we have synthesized and structurally characterized
the RuIV trialkyl complexes [Ru(CH2SiMe3)3(PPh3)X] (X− =
monoanionic ligand) that exhibit unique trigonal bipyramidal
geometry. [Ru(CH2SiMe3)3(PPh3)(OTf)] (2) containing a
labile triflate ligand was found to display interesting organo-
metallic chemistry. For example, treatment of 2 with NaORf led
to desilylation of the alkyl groups and formation of a dimethyl
complex, whereas that with phen resulted in reductive
elimination of the C−C bond. The investigation of the reaction
chemistry and catalytic activity of 5-coordinated, 14-electron
RuIV trialkyl complexes is underway.
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, Jr., J. A.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.;Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
ASSOCIATED CONTENT
* Supporting Information
Crystallographic data and cif files for complexes 1, 2, 4, and 5,
computational details for 1, and ESI mass and 31P {1H} NMR
spectra for the reaction of 2 with NaORf. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
̈
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,
Revision C.01; Gaussian, Inc.: Wallingford, CT, 2009.
(14) Francl, M. M.; Peitro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon,
M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
(15) Dolg, M.; Wedig, U.; Stoll, H.; Preuss, H. J. Chem. Phys. 1987,
86, 866.
(16) Zhao, Y.; Truhlar, D. G. J. Chem. Phys. 2006, 125, 194101.
(17) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.;
Yang, W.; Parr, R. G. Phys. Rev. B. 1988, 37, 785.
(18) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999.
(19) Bruker SMART and SAINT+, version 6.02a; Siemens Analytical
X-ray Instruments Inc.: Madison, WI, 1998.
(20) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(21) Carroll, W. E.; Bau, R. J. Chem. Soc., Chem. Commun. 1978, 825.
(22) Zhang, Q.-F.; Lai, C.-Y.; Wong, W.-Y.; Leung, W.-H.
Organometallics 2002, 21, 4017.
AUTHOR INFORMATION
Corresponding Author
*E-mail: chleung@ust.hk; sharonlf.chan@polyu.edu.hk
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Hong Kong Research Grants Council (to W.-
H.L., Project 601708), the Hong Kong University of Science
and Technology, and the Hong Kong Polytechnic University
for support, and Prof. C.-M. Che and Dr. Kevin Wai-Pong Tao,
the University of Hong Kong, for the help in high-resolution
4488
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489

Organometallics
Article
(23) Hofmann, D. M.; Lapas, D.; Wierda, D. A. Polyhedron 1996, 15,
3309.
(24) (a) Carmona, E.; San
Atwood, J. L.; Priester, R. D.; Rogers, R. D. J. Am. Chem. Soc. 1984,
106, 3214. (b) Carmona, E.; Contreras, L.; Poveda, M. K.; Sanchez, L.
J.; Atwood, J. L.; Rogers, R. D. Organometallics 1991, 10, 61.
́
chez, L.; Marín, J. M.; Poveda, M. L.;
́
(25) As suggested by one reviewer, an alternative proton source is
Na[H(ORf)2] (Rf = C6F4H) where one phenol hydrogen bonds to the
phenoxide oxygen, which is an intermediate product from the
deprotonation of RfOH.
(26) The identity of 6 has been established by an X-ray diffraction
study. However, the crystal structure of 6 has not refined satisfactorily
due to poor quality of the crystal.
4489
dx.doi.org/10.1021/om400183n | Organometallics 2013, 32, 4483−4489