2,2,2-tris(pyrazolyl)ethoxide (EpOX) ruthenium(II) complexes, (EpOX)RuCl(L)(L′): Synthesis, structure, and reactivity

Article abstract of DOI:10.1021/ic3024474

Treatment of RuCl₂(PPh₃)₃ with sodium 2,2,2-tris(pyrazolyl)ethoxide [NaOCH₂C(pz)₃; pz = pyrazolyl] affords the asymmetric heteroscorpionate complex cis-(Ep ^OX)RuCl(PPh₃)₂

Full text of DOI:10.1021/ic3024474

Article
pubs.acs.org/IC
2,2,2-Tris(pyrazolyl)ethoxide (EpOX) Ruthenium(II) Complexes,
(EpOX)RuCl(L)(L′): Synthesis, Structure, and Reactivity
Brandon Quillian,†,∥ Evan E. Joslin,† T. Brent Gunnoe,*,† Michal Sabat,‡ and William H. Myers§
†Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
‡Nanoscale Material Characterization Facility, Department of Materials Science and Engineering, University of Virginia,
Charlottesville, Virginia 22904, United States
§Department of Chemistry, University of Richmond, Richmond, Virginia 23173, United States
S
* Supporting Information
ABSTRACT: Treatment of RuCl2(PPh3)3 with sodium 2,2,2-
tris(pyrazolyl)ethoxide [NaOCH2C(pz)3; pz = pyrazolyl]
affords the asymmetric heteroscorpionate complex cis-(EpOX)-
RuCl(PPh3)2 (1), (EpOX = κ3-N,N,O-OCH2C(pz)3), which
can be converted to Ru(II) compounds (2−6), (EpOX)RuCl-
(L)(L′) [(2) L = PPh3, L′ = P(OCH2)3CEt; (3) L = L′ = P(OCH2)3CEt; (5) L, L′ = PPh3, CO; (6) L = L′ = CO]. Compounds
1 and 3 react with CHCl3 at 60 and 100 °C, respectively, to yield cationic tris(pyrazolyl)methane Ru(II) complexes, [(κ3-N,N,N-
Mp)RuCl(L)2]Cl [Mp = HC(pz)3; (7) L = PPh3; (8) L = P(OCH2)3CEt]. The complexes have been characterized by 1H, 13C,
and 31P{1H} NMR spectroscopy, elemental analysis, high resolution mass spectrometry, and cyclic voltammetry. Complexes 1
and 3 have also been characterized by single crystal X-ray analysis.
(pyrazolyl)methane ligands on d6-octahedral centers may
provide insights into incorporating these ligands in catalytic
Trofimenko’s early studies of poly(pyrazolyl) ligands1−3 has
processes that require such stabilization.36,37
INTRODUCTION
■
played a major role in the development of transition metal
We elected to study 2,2,2-tris(pyrazolyl)ethanol [HOCH2C-
chemistry.4−11 The H(4−n)B(pz)n (n = 2, 3, 4) architecture is
(pz)3, {EpOH}]14 on ruthenium as a model system. Reger et al.
easily modified by varying the number and identity of the
initially disclosed the synthesis of EpOH as a synthon for the
pyrazolyl fragments, which has allowed the preparation of a
14
t
preparation of Bu(C6H4)CH2OCH2C(pz)3, and it has since
been used as a building block for more elaborate ligands.38−41
The parent ligand, EpOH, has had limited use as a κ3-N,N,N-
coordinating ligand in transition metal coordination chem-
istry,42−44 but to our knowledge it has never been examined as
a k3-N,N,O-heteroscorpionate. Herein, we discuss the proper-
ties and some reactions of Ru(II) complexes supported by
2,2,2-tris(pyrazolyl)ethoxide (EpOX) bound in a κ3-N,N,O-
coordination mode.
variety of poly(pyrazolyl)borate ligands.11−13 In addition,
poly(pyrazolyl) ligands with carbon8,14,15 or silicon16,17 have
been prepared. Replacing one of the pyrazolyl substituents of
HE(pz*)3 (E = B, C, Si; pz* = pyrazolyl or substituted
pyrazolyl) with a nonpyrazolyl moiety provides mixed
heteroscorpionate (HS) ligands.18 The bis(pyrazolyl)methane
heteroscorpionate ligands (HSMe) [HC(pz*)2X, X = functional
group] often possess anionic X functional groups such as
phenoxide,19−21 alkoxide,20−24 thiolate,20 acetate,14,25−27 or
dithioacetate.24,27 These ligands have been used to prepare
biomimetic models for enzyme active sites such as 2-his-1-
carboxylate facial triad enzymes,28,29 liver alcohol dehydrogen-
ase,22 and dimethylsulfoxide reductase.19,20 The utility of the
acetate functionalized HSMe ligands has been especially well-
documented in transition metal coordination chemistry;23,30,31
however, less attention has been drawn to the study of alkoxy
functionalized HSMe ligands beyond the early transition
metals.20−24 Caulton et al. have studied the effects of alkoxy
fragments on five-coordinate d6-systems and found that
(PR3)2Ir(H)2(OR) complexes are more stabilized by alkoxy
functional groups than acetate, which is proposed to be a
consequence of increased π-donation of the alkoxy lone
pairs.32,33 Although the alkoxy fragment induces relative
stability, the influence does not engender inertness, but instead
maintains “operational” unsaturation.34,35 Obtaining a better
understanding of the impact of alkoxy functionalized bis-
RESULTS AND DISCUSSION
■
Preparation of cis-(EpOX)RuCl(PPh3)2 and Reaction
with P(OCH2)3CEt. The reaction of RuCl2(PPh3)3 with
NaEpOX (EpOX
=
−OCH2C(pz)3) (eq 1),38 prepared in situ
Received: November 8, 2012
© XXXX American Chemical Society
A
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by treating 2,2,2-tris(pyrazolyl)ethanol14 with excess sodium
hydride, gives cis-(EpOX)RuCl(PPh3)2 (1) in 48% isolated yield.
NMR spectra (1H, 13C, and 31P) of 1 are consistent with an
asymmetric complex, which indicates a PPh3 ligand trans to the
alkoxide of the EpOX ligand. No evidence of a second isomer
with the chloride ligand trans to the alkoxide fragment was
detected. In a previous study, the similar heteroscorpionate
ruthenium complex, (HSA)RuCl(PPh3)2 [HSA = bis(pyrazolyl)-
Scheme 1. Reactions of 1 with P(OCH2)3CEt
−
acetate {HC(pz)2CO2 }], was isolated as mixture of cis/trans
isomers.45
Complex 1 decomposes above 70 °C to intractable products
and exhibits air- and moisture-sensitivity at room temperature
in both solution (methylene chloride, chloroform, benzene,
tetrahydrofuran (THF), and toluene) and in the solid-state.
The methylene protons of 1 are observed as two resonances at
2
2
4.32 ppm and 4.75 ppm (d, JHH = 8 Hz and dd, JHH = 8 Hz
protons and the resonances observed for the diastereotopic
methylene protons of the alkoxy fragment of 3 are consistent
with an asymmetric complex. A pair of doublets at 4.18 ppm
4
and JHP = 7 Hz, respectively). Solvent identity has a
pronounced effect on the multiplicity and chemical shift of
the 31P resonances. 31P NMR spectra recorded at room
temperature in THF-d8, CDCl3, CD2Cl2, and NCCD3 display
two doublets exhibiting an AB splitting pattern (2JPP = 26 Hz)
(Figure 1). In contrast, in benzene and toluene only a single
1
and 4.26 ppm (3JPH = 4 Hz) in the H NMR spectrum is
assigned to the phosphite methylene protons. These resonances
1
collapse to singlets in the phosphorus decoupled H NMR
spectrum.
The reaction of 1 with excess of P(OCH2)3CEt (5 equiv) in
CD2Cl2 at room temperature results in the formation of
multiple products (determined by 31P NMR spectroscopy),
including free PPh3. The 31P spectrum also reveals a broad
resonance (116 ppm), a virtual triplet (133 ppm), and a large
singlet (130 ppm). In addition, two doublets at 129 ppm and
130 ppm are observed for complex 3. No evidence of 2 is
detected; however, the reaction of 2 with excess phosphite
results in the formation of 3. Cooling the solution to −50 °C
results in decoalescence of the broad peak at 116 ppm into two
doublet of doublets (2JPP = 786 and 69 Hz) (Figure 2). The
Figure 1. 31P{1H} NMR spectra of cis-(EpOX)RuCl(PPh3)2 (1)
showing different chemical shifts and multiplicities as a function of
solvent identity.
resonance is observed, which we presume is a result of a
dynamic exchange of the two phosphine ligands. Consistent
with this suggestion, the single resonance in toluene
decoalesces into two broad doublets in the 31P NMR spectrum
of 1 at −5 °C.
The reaction of 1 with 1.1 equiv of 4-ethyl-2,6,7-trioxa-1-
phosphabicyclo[2.2.2]octane [P(OCH2)3CEt]46 in THF results
in the formation of the mixed phosphine/phosphite complex
(EpOX)RuCl[P(OCH2)3CEt](PPh3) (2) in 83% isolated yield
(Scheme 1). A diagnostic pair of doublets in the 31P NMR
Figure 2. 31P{1H} NMR spectra of the reaction of 1 with excess
P(OCH2)3CEt; room temperature (bottom) and −50 °C (top)
spectra (units are in ppm).
2
2
spectrum (48 ppm and 129 ppm, JPP = 58 Hz) is consistent
large JPP coupling constant for the doublet of doublets (786
with phosphine and phosphite ligands in a cis conformation.
Alternatively, combining 1 with excess P(OCH2)3CEt in
refluxing THF results in the precipitation of (EpOX)RuCl[P-
(OCH2)3CEt]2 (3) (Scheme 1). The mixed phosphine/
phosphite complex 2 is not observed (vide infra) while
monitoring the formation of 3 by 1H and 31P NMR
spectroscopy. The nine distinct signals for the pyrazolyl
Hz) was validated by a 31P COSY NMR experiment (see
2
Supporting Information). Complexes with JPP couplings as
large as 1100 Hz have been reported.47,48 The two doublet of
doublets at 119.0 ppm and 113.6 ppm are coupled to the virtual
triplet at 133 ppm,49,50 which remains a triplet at lower
temperature. The sharp singlet at 130 ppm observed at room
temperature broadens (128−132 ppm) and becomes a complex
B
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Scheme 2. Reaction of 1 with Excess P(OCH2)3CEt to Produce (mer-κ2-N,O-EpOX)RuCl[P(OCH2)3CEt]3 and Proposed
Fluxional Ring-Flip of the EpOX Ligand to Explain Variable Temperature 31P NMR Spectra
multiplet at lower temperature, indicative of a dynamic
process.51 These variable temperature spectra (Figure 2) are
consistent with the complex (mer-κ2-N,O-EpOX)RuCl[P-
(OCH2)3CEt]3 having three phosphite ligands about the
metal center in a meridional configuration (Scheme 2). The
additional singlet at ∼130 ppm in the room temperature 31P
NMR spectrum is due to an uncharacterized species, which we
were unable to isolate.
ppm), suggesting a more electron-rich metal center. This is
inconsistent with the formation of [(EpOX)Ru-
(PPh3)2(NCMe)][Cl] through chloride/NCMe exchange, as
it is expected the cationic complex would result in a downfield
chemical shift for the methylene hydrogen atoms. The 31P
NMR, in addition to the diastereotopic signals for the
methylene hydrogen atoms, is consistent with an asymmetric
complex with the PPh3 ligands arranged in a cis-configuration.
The absolute configuration of the ligands about ruthenium is
not known. The isolation of 4 suggests the phosphine ligands in
1 are more strongly bound to Ru than the chelated nitrogen
atoms. This reactivity is different from the reaction of
(HSA)RuCl(PPh3)2 with NCMe to produce the acetonitrile
complex (k3-N,N,O,-HSA)RuCl(PPh3)(NCMe).53
Transition metal complexes possessing multiple phosphorus
ligands are commonly characterized on the premise that 2JPP(cis)
< 2JPP(trans) 52 On this basis, the small coupling constant (2JPP
. =
67 Hz) for the triplet at 133 ppm is attributed to a phosphite
ligand in the N−O−Cl plane coupled to the two cis-phosphite
ligands, and the two doublets at 119.0 ppm and 113.6 ppm with
a large 2JPP(trans) (786 Hz) and smaller 2JPP(cis) (67 Hz) coupling
constant are assigned to the trans-phosphite ligands. The broad
peak (116 ppm) at room temperature is a consequence of the
two trans phosphite ligands approaching chemical equivalence,
likely because of conformational fluxionality of the κ2-N,O-EpOX
ligand, where the complex rapidly converts between two
conformers via a low-energy “flip” of the free noncoordinating
pyrazolyl units (Scheme 2).
Single Crystal X-ray Structures of 1 and 3. Single crystal
X-ray structural analyses were performed on yellow and
colorless crystals of 1 (Figure 3) and 3 (Figure 4). The unit
All efforts to isolate the tris-phosphite complex (mer-κ2-N,O-
EpOX)RuCl[P(OCH2)3CEt]3 led to the formation of 3. This
suggests (mer-κ2-N,O-EpOX)RuCl[P(OCH2)3CEt]3 is only
stable in the presence of excess phosphite. As evidence of
this hypothesis, reaction of 3 with 1 equiv of P(OCH2)3CEt
revealed only minor formation of (mer-κ2-N,O-EpOX)RuCl[P-
(OCH2)3CEt]3, signified by a broad peak at 116 ppm in the 31
P
NMR spectrum. The resonances for (mer-κ2-N,O-EpOX)RuCl-
[P(OCH2)3CEt]3 are much larger when 3 is reacted with 16
equiv of P(OCH2)3CEt. Using NMR spectra, an equilibrium
constant of 4.1(4) × 10−3 was calculated for the formation of
(mer-κ2-N,O-EpOX)RuCl[P(OCH2)3CEt]3.
Figure 3. ORTEP of cis-(EpOX)RuCl(PPh3)2 (1) (30% probability
with hydrogen atoms omitted). Selected bond lengths (Å): Ru(1)−
Cl(1), 2.4242(8); Ru(1)−P(1), 2.3218(9); Ru(1)−P(2), 2.3235(8);
Ru(1)−O(1), 2.096(2); Ru(1)−N(1), 2.071(3), Ru(1)−N(3),
2.099(3). Selected bond angles (deg): N(1)−Ru(1)−O(1),
87.14(9); N(1)−Ru(1)−N(3), 85.9(1); O(1)−Ru(1)−N(3),
79.1(1); N(1)−Ru(1)−P(1), 96.38(8); O(1)−Ru(1)−P(1),
84.74(7); N(1)−Ru(1)−P(2), 90.23(7); P(1)−Ru(1)−P(2),
103.71(3); O(1)−Ru(1)−Cl(1), 86.99(6); N(3)−Ru(1)−Cl(1),
86.99(8); P(1)−Ru(1)−Cl(1), 89.21(3); P(2)−Ru(1)−Cl(1),
94.67(3); N(7)−Ru(2)−N(9), 86.7(1); N(7)−Ru(2)−O(2),
86.1(1); N(9)−Ru(2)−O(2), 81.8(1); N(7)−Ru(2)−P(4), 90.95(7).
Reaction of cis-(EpOX)RuCl(PPh3)2 (1) with NCMe.
Heating 1 in neat acetonitrile for 36 h produces (κ2-N,O,-
1
EpOX)RuCl(PPh3)2(NCMe) (4) (characterized by H and 31P
NMR spectroscopy) (eq 2). This complex is characterized by a
pair of doublets in the 31P NMR spectrum (48.1 ppm and 50.1
cell of 1 contains two similar but crystallographically unique
molecules, while that of 3 contains only one independent
molecule. The initial discussion of 1 will be limited to one
structure; differences between the two structures will be
addressed below. The Ru(II) metal centers in 1 and 3 reside
in a slightly distorted octahedral geometry and confirm an
intact Ru−O bond with nearly identical bond lengths (Ru−O
2
ppm, JPP = 26 Hz), which are shifted upfield relative to those
1
of 1, and a singlet in the H NMR spectrum at 2.34 ppm
assigned to coordinated NCMe. The resonances attributed to
the diastereotopic methylene hydrogen atoms of 4 are
separated by more than 1 ppm (4.29 ppm and 3.25 ppm)
and shifted upfield compared to those of 1 (4.75 and 4.31
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coplanarity relative to the C(1)−C(2) bond in 1a. The
Ru(2)−O(2)−C(48) bond angle [121.0(2)°] in 1b is slightly
larger than the Ru(1)−O(1)−C(1) bond angle [118.0(2)°] in
1a. Transition metal M−O−R bond angles can vary greatly
depending on the π-interaction of the −OR lone pairs with the
metal or substituents, with larger bond angles usually
correlating to a greater degree of π-bonding. For example,
TpRu(PMe3)2(OPh)54 has a larger Ru−O−R bond angle [Ru−
O−C = 133.2(2)°] than TpRu(PMe3)2(OMe), [Ru−O−C =
109.5(2)°],55 possibly because of π-bonding of the oxygen lone
pairs into the phenyl ring of TpRu(PMe3)2(OPh).
Reaction of 1 with Carbon Monoxide. (EpOX)RuCl-
(PPh3)(CO) (5) is isolated in 90% yield from the reaction of 1
with CO (60 psi) at room temperature (Scheme 3).
Scheme 3. Reactions of 1 with CO (60 psi) for 30 min and 4
weeks
Figure 4. ORTEP of (EpOX)RuCl[P(OCH2)2CEt]2 (3) (30%
probability with hydrogen atoms omitted). Selected bond lengths
(Å): Ru(1)−Cl(1), 2.3990(9); Ru(1)−P(1), 2.1899(7); Ru(1)−P(2),
2.1905(8); Ru(1)−O(1), 2.086(2); Ru(1)−N(1), 2.140(2); Ru(1)−
N(3). 2.055(3). Selected bond angles (deg): Cl(1)−Ru(1)−P(1),
96.03(3); Cl(1)−Ru(1)−P(2), 87.91(3); Cl(1)−Ru(1)−O(1),
84.85(6); Cl(1)−Ru−N(1), 90.75(7); Cl(1)−Ru−N(3), 172.80;
P(1)−Ru−O(1), 92.45(6); P(1)−Ru(1)−P(2), 90.34(3); P(1)−
Ru(1)−N(1), 169.18(7); P(1)−Ru(1)−N(3), 89.86(7); P(2)−
Ru(1)−O(1), 172.48(6); O(1)−Ru(1)−N(1), 79.74(9).
bond = 2.092(2) Å in 1 and 2.086(2) Å in 3). The close
similarity between these bond lengths implies that the trans-
effect influence of the different phosphorus ligands has little
bearing on Ru−O bond distance. The Ru−O bonds of 1 and 3
are shorter than that found in (HSA)RuCl(PPh3)2 (Ru−O =
2.181(2) Å) by almost 0.1 Å.45 The shorter Ru−O bond
distance found in 1 and 3 is expected since the oxygen atom of
the alkoxy unit is not involved in delocalized π-bonding as with
acetate.
The two independent molecules (vide supra) found in the
unit cell of 1 have distinctions such as variation of the Ru−O−
C−C dihedral angle and the orientation of the free pyrazolyl
fragment (Figure 5). For example, the morphology of 1a shown
in Figure 5 displays a Ru(1)−O(1)−C(1)−C(2) dihedral angle
of 37.21°, while that for 1b [Ru(2)−O(2)−C(48)−C(49)] is
7.28°. The free pyrazolyl fragment of 1b is nearly coplanar with
the C(48)−C(49) bond, while it is slightly bent from
Monitoring the reaction by 31P NMR spectroscopy reveals
complete conversion of 1 to 5 within 30 min. The nine well-
resolved pyrazolyl resonances and the two resonances for
methylene protons (two doublets; 4.98 ppm and 5.14 ppm,
1
2JHH = 9 Hz) in the H NMR spectrum are consistent with an
asymmetric complex. A single resonance (44.0 ppm) is
observed in the 31P NMR spectrum, while a strong absorption
at 1940 cm−1 in the IR spectrum of 5 is assigned to the CO
stretch. Comparison of the νCO (cm−1) for 5 with those of
similar octahedral Ru(II) complexes bearing CO, Cl, and PPh3
ligands (Table 1) suggests the EpOX ligand is an overall better
electron-donor than Tp56 and Cp;57 however, it appears that
the electron donating ability of the EpOX ligand is less than that
of Cp* (C5Me5 ).58 As expected, the νCO (1940 cm−1) stretch
−
for 5 also implies that the EpOX ligand is a stronger electron-
donating ligand than its acetate bearing analogue (HSA)RuCl-
(CO)(PPh3) (νCO = 1969 cm−1).59
Table 1. Carbonyl Stretching Frequencies of Octahedral
Ruthenium(II) Complexes with CO and PPh3 Ligands
complex
νCO (cm−1
)
ref.
(EpOX)RuCl(PPh3)(CO) (5)
1940
1918
1944
1958
1965
1969
2012
2027
this work
Cp*RuCl(PPh3)(CO)
(η5-indenyl)RuCl(PPh3)(CO)
CpRuCl(PPh3)(CO)
58
60
57
56
59
61
62
TpRuCl(PPh3)(CO)
(HSA)RuCl(PPh3)(CO)
[(η6-C6Me6)RuCl(PPh3)(CO)][PF6]
[(η6-p-cymene)RuCl(PPh3)(CO)][OTf]
Figure 5. Depiction of dihedral angle of the C−C−O−Ru fragments
of two crystallographically independent molecules found in the unit 1a
and 1b. Atoms of the phosphorus ligands are omitted for clarity.
D
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Prolonged reaction of 1 with CO (60 psi) at room
temperature produces (EpOX)RuCl(CO)2 (6) over several
weeks (Scheme 3). The half-life of this reaction at room
temperature is approximately 21 days. Increasing CO pressure
(100 psi) at room temperature and/or exposure to slightly
elevated temperatures (50 °C) leads to the formation of
multiple intractable products. Complex 6 is asymmetric, as
indicated by the nine pyrazolyl and two methylene resonances
alkoxide fragment of the EpOX ligand is likely converted into a
carbonyl unit upon phosphine dissociation followed by β-
hydride elimination.70,71 The net loss of the CHO fragment of
the EpOX ligand could involve decarbonylation.72−74 The
observation of C(D)HCl2 in the 1H NMR spectrum in
CDCl3 is evidence of hydrogen/chloride exchange between 1
and solvent.75 Reactions with metal-hydrides with chloroform
to generate a metal-chloride and methylene chloride are
known.76,77 Thus, the observation of CHDCl2 is consistent
with the formation of a Ru−H intermediate. The intimate
details for the conversion of 1 to 7 cannot be known with
available data, but Scheme 4 portrays a pathway consistent with
experimental observations and established precedent.
2
(two doublets, 4.77 ppm and 4.94 ppm, JHH = 9 Hz). Two
absorptions at 2060 cm−1 and 1986 cm−1 in the IR spectrum of
6 confirm the presence of cis-dicarbonyl ligands. Comparison
of the average value of the symmetric and asymmetric
absorptions for a series of Ru(II) complexes (Table 2) places
Table 2. Carbonyl Stretching Frequencies of Octahedral
Ruthenium(II) Complexes with Bis-carbonyl Ligands
Scheme 4. Possible Pathway for the Conversion of 1 to 7
complex
νCO (cm−1
)
avg νCO (cm−1
)
ref
(EpOX)RuCl(CO)2 (5)
2060, 1986
2025, 1975
2052, 1995
2059, 2008
2071, 2011
2066, 1996
2023
2000
2023
2033
2041
2031
this work
Cp*RuCl(CO)2
(η5-indenyl)RuCl(CO)2
CpRuCl(CO)2
63
64
65
66
67
TpRuCl(CO)2
(bdmpza)RuCl(CO)2
the donor ability of the EpOX ligand greater than Tp and Cp,
similar to indenyl, and less than Cp*. The recently reported
(bdmpza)RuCl(CO)2 (bdmpza =2,5-dimethylpyrazolyl ace-
tate) complex,67 which bears an acetate heteroscorpionate
ligand, has a slightly higher energy average CO absorption than
6.
Reactivity of (EpOX)RuCl(L)2 Complexes with Chloro-
form. Heating 1 in chloroform at 60 °C results in the
formation of the previously reported68 tris(pyrazolyl)methane
ruthenium(II) complex [{HC(pz)3}RuCl(PPh3)2]Cl (7) (eq
3). The identity of compound 7 was confirmed by independent
Similar to the formation of 7, heating a CHCl3 solution of 3
(100 °C) yields [{κ3-HC(pz)3}RuCl[P(OCH2)3CEt]2]Cl (8)
1
in quantitative yield (determined by H NMR spectroscopy).
1
Monitoring the reaction with H and 31P NMR spectroscopy
suggests differences in formation pathways for 7 and 8. For
example, while free PPh3 is observed during the formation of 7,
no evidence of P(OCH2)3CEt dissociation is obtained during
the formation of 8. In addition, the reaction of 3 with CDCl3
produces [{DC(pz)3}RuCl{P(OCH2)3CEt}2]Cl (8-d1), as
indicated by the absence of the methine proton resonance at
12.36 ppm for the tris(pyrazolyl)methane ligand, and C(D)-
HCl2 is not observed when CDCl3 is used as reaction medium
for the conversion of 3 to 8. This suggests that the deuterium/
proton incorporation at the methine position in 8 comes
directly from the solvent. Heating 3 in 13CHCl3 does not afford
synthesis. Monitoring the reaction of 1 with CHCl3 to generate
7 by 31P NMR spectroscopy revealed initial appearance of free
PPh3, followed by the emergence of a singlet at 39.2 ppm for
complex 7. Ruthenium intermediates were not observed by 31
P
or 1H NMR spectroscopy, although during the reaction
a
13C-labeled complex 8.
1
resonances in the H NMR spectrum were broadened. Upon
Electrochemistry. To determine relative electron density
completion of the reaction, the free PPh3 was completely
consumed. Performing the reaction in CDCl3 results in the
production of CHDCl2 (1:1:1 triplet, 5.32 ppm). Additionally,
when heating 1 in the presence of excess PPh3 the rate of
formation of 7 is reduced. For example, heating 1 in the
presence of PPh3 (5 equiv) in CDCl3 for 2 h results in 10%
conversion of 1 into 7, whereas heating 1 without added PPh3
results in a more expedient reaction with 33% conversion in 2
h. These observations are consistent with a mechanism that
involves PPh3 dissociation.
of the Ru(II) complexes we sought to compare redox
potentials. The results of cyclic voltammetry studies of
complexes 1−3, 5, 7, and 8 are listed in Table 3 (reported
versus NHE). Cyclic voltammogram (CV) data for all
complexes show either irreversible or quasi-reversible Ru(III/
II) redox potentials. A quasi-reversible couple at +0.47 V is
assigned to the Ru(III/II) redox potential of 1. As expected,
based on the νCO stretch of TpRuCl(CO)(PPh3) and
(EpOX)RuCl(PPh3)(CO) (3) (νCO = 1965 cm−1 and 1940
cm−1, respectively), the Ru(III/II) potential of 1 is negative to
that of the less electron-rich TpRuCl(PPh3)2,78 observed at
0.84 V. In relation to 1, Ru (III/II) potentials of compounds 2
Given that the addition of free PPh3 slows the reaction and
the precedent for Ru(II)-based decarbonylation reactions,69 the
E
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Article
residues of the EpOX ligand are listed by chemical shift and multiplicity
only (all coupling constants are less than 3 Hz).
Table 3. Cyclic Voltammetry Data for (κ3-L)RuCl(L′)(L″)
Complexes [L = EpOX or tris(pyrazolyl)methane (Mp)]
Electrochemical experiments were performed under a nitrogen
atmosphere using a BAS Epsilon Potentiostat. Cyclic voltammograms
were recorded in NCMe using a standard three electrode cell from
−1700 to 1700 mV at 100 mV/s (unless otherwise noted) with a
glassy carbon working electrode and tetrabutylammonium hexafluor-
ophosphate as electrolyte. All potentials are reported versus NHE
(normal hydrogen electrode) using cobaltocenium hexafluorophos-
phate as the internal standard. High-resolution electrospray ionization
mass spectrometry (ESI-MS) analyses were obtained on a Bruker
BioTOF-Q spectrometer at the University of Richmond. Samples were
dissolved in acetonitrile then mixed 3:1 with 0.1 M aqueous sodium
trifluoroacetate (NaTFA) using [Na(NaTFA)x]+ clusters as an internal
standard. These data are reported using the most intense peaks from
the isotopic envelope for either [M]+, [M + H]+, or [M + Na]+. The
data are listed as m/z with the intensity relative to the most abundant
peak of the isotopic envelope given in parentheses for both the
calculated and the observed peaks. The difference between calculated
and observed peaks is reported in ppm. Single crystal X-ray intensity
data were collected on a Bruker SMART APEX II CCD diffractometer
using MoKα radiation. The structure was solved by direct methods in
Bruker SHELXTL.80 Hydrogen atoms were included in calculated
positions without further refinement. The preparation and character-
ization of 2,2,2-(pyrazol-1-yl)ethanol,14,40 2,2,2-(pyrazol-1-yl)ethoxide
sodium38 and RuCl2(PPh3)381 have been reported. P(OCH2)3CEt was
obtained from a commercial source and purified by extraction and
recrystallization in hexane. All other reagents were used as purchased
from commercial sources.
complex [L′/L″]
1 [PPh3]2
ligand
E1/2, {Ep,a}
EpOX
EpOX
EpOX
EpOX
Mp
+0.47
2 [PPh3/P(OCH2)3CEt]
3 [P(OCH2)3CEt]2
5 [PPh3/CO]
{+0.70}
{+0.73}
{+1.21}
+1.24
7 [PPh3]2
8 [P(OCH2)3CEt]2
Mp
{+1.29}
and 3 are more positive, showing irreversible Ru(III/II)
potentials at +0.70 V and +0.73 V, respectively. These data
suggest that the net result of substituting PPh3 with
P(OCH2)3CEt is a reduction of electron-density at the metal
center. This correlates well with the known π-accepting ability
of bicyclic phosphites.79 The CV of 5 reveals a Ru(III/II)
potential at +1.21 V, which reflects the expected reduction of
electron-density upon coordinating CO. The CVs for the
cationic tris(pyrazolyl)methane ruthenium compounds, 7 and
8, show considerably more positive Ru(III/II) redox potentials
(+1.24 V and +1.29 V, respectively) compared to the neutral
EpOX ruthenium complexes 1−5.
SUMMARY
■
cis-(EpOX)RuCl(PPh3)2 (1). To a 100 mL round-bottom flask
containing HOCH2C(pz)3 (643 mg, 2.52 mmol) in THF (18 mL), a
slurry of NaH (73.8 mg, 3.08 mmol) in THF (8 mL) was added. The
reaction mixture was stirred at room temperature for 45 min. The
solution was passed through a short column of Celite to remove excess
NaH, and the filtrate was added to a THF solution (20 mL) of
RuCl2(PPh3)3 (2.35 g, 2.45 mmol). The reaction was stirred at room
temperature overnight then all volatiles were removed in vacuo. The
remaining red-brown residue was reconstituted in a minimum amount
of methylene chloride, loaded on a short column of Celite, and washed
with additional methylene chloride (15 mL). The filtrate was collected
and reduced to ∼3−5 mL in vacuo, and hexane was added to induce
precipitation. The yellow precipitate was collected on medium
porosity frit and washed with diethyl ether and pentane. The solid
was collected, reconstituted in methylene chloride, and loaded on a
silica column (prewashed with diethyl ether). A red material was
eluted with diethyl ether and discarded. The column was then washed
with THF to elute a yellow band. This eluate was collected, reduced in
vacuo unto dryness, reconstituted in methylene chloride (5 mL), and
treated with hexanes to precipitate a yellow solid. The yellow solid was
collected on a fine frit, washed with a minimum amount of diethyl
ether followed by copious amounts of pentane, and dried in vacuo
(791 mg, 35%). 1H NMR (300 MHz, CDCl3) δ: 4.31 (d, 1H,
−CH2ORu-, 2JHH = 7 Hz), 4.75 (dd, 1H, −CH2ORu-, 2JHH = 8 Hz and
4JHP =7 Hz), 5.35 (m, 2H, overlapping 3- or 5-pz), 5.96 (dd, 1H, 4-pz),
6.61 (m, 2H, overlapping, 4-pz), 6.96−7.06 (m, 12H, PPh3), 7.06−
7.18 (m, 6H, PPh3), 7.20−7.26 (m, 6H, overlapping pz and PPh3),
7.47 (br s, 1H, 3- or 5-pz), 7.80 (t, 6H, o-PPh3, 3JHH = 9 Hz), 7.88 (d,
1H, 3- or 5-pz), 7.99 (br s, 1H, 3- or 5-pz). 13C{1H} NMR (125 MHz,
CDCl3) δ: 75.6 (s, -OCH2C(pz)3), 91.2 (s, -OCH2C(pz)3), 105.7,
Ruthenium(II) compounds 1−6 supported by 2,2,2-
tris(pyrazolyl)ethoxide (NaOCH2C(pz)3, {EpOX}, pz = pyr-
azolyl) with phosphorus and CO ligands have been reported.
For complexes 1, 3, and 6, the asymmetric cis-isomers with the
chloride ligand cis to the alkoxy ligand are isolated. Compounds
1 and 3 react with CHCl3 at 60 and 100 °C, respectively, to
produce cationic tris(pyrazolyl)methane Ru(II) products (7
and 8). Conversions of the ruthenium(II) EpOX complexes 1
and 3 to tris(pyrazolyl)methane Ru(II) products 7 and 8
highlight the potential incompatibility of the EpOX ligand with
late transition metal complexes that can mediate β-hydride
elimination and decarbonylation. Using νCO of monocarbonyl
complexes as a gauge, the EpOX ligand is more electron-
donating than Cp, Tp and η6-arenes.
EXPERIMENTAL SECTION
■
Unless otherwise noted, all synthetic procedures were performed
under anaerobic conditions in a nitrogen filled glovebox or by using
standard Schlenk techniques. Glovebox purity was maintained by
periodic nitrogen purges and was monitored by an oxygen analyzer
(O2 < 15 ppm for all reactions). Tetrahydrofuran was dried by
distillation from sodium/benzophenone. Pentane was distilled over
P2O5. Acetonitrile and diethyl ether were dried by distillation from
CaH2. Benzene, hexanes, and methylene chloride were purified by
passage through a column of activated alumina. Acetonitrile-d3,
benzene-d6, chloroform-d1, methylene chloride-d2 and toluene-d8
were stored under a nitrogen atmosphere over 4 Å molecular sieves.
1H NMR spectra were recorded on a Varian Mercury Plus 300 MHz or
a Varian Inova 500 MHz spectrometer, and 13C NMR spectra were
recorded on Varian Mercury Plus 300 MHz and Varian Inova 500
MHz spectrometers (operating frequency 75 and 126 MHz,
respectively). All 1H and 13C NMR spectra are referenced against
residual proton signals (1H NMR) or the 13C resonances of the
deuterated solvent (13C NMR). 31P NMR spectra were obtained on a
Varian Mercury Plus 300 MHz (operating frequency 121 MHz)
spectrometer and referenced against an external standard of H3PO4 (δ
= 0). Variable Temperature 31P NMR and 31P COSY experiments
were recorded on a Varian Inova 500 MHz spectrometer (202 MHz).
Pyrazolyl has been abbreviated as pz. Resonances due to the pyrazolyl
3
106.6, 108.4 (each a singlet, 4-pz), 127.2, 127.6 (each d, JCP = 9 Hz,
m-PPh3), 128.5, 128.9 (each a singlet, p-PPh3), 130.7, 130.9, 130.8
(each a singlet, 3- or 5-pz), 134.4, 135.1 (each a doublet, 2JCP = 9 Hz,
o-PPh3), 136.0 (s, 1JCP = 6 Hz, i-PPh3), 136.4 (s, i-PPh3, 1JCP = 2 Hz),
142.9, 145.8, 148.9 (each s, 3- or 5-pz). 31P{1H} NMR (121 MHz,
2
2
CDCl3) δ: 46.9 (d, JPP = 27 Hz), 48.1 (d, JPP = 27 Hz). CV: E1/2
=
+0.47 V, [Ru(III/II), quasi-reversible]. HRMS: [M + H]+ obs’d (%),
calc’d (%), ppm: 903.16439 (43.7), 903.1638 (41.9), 0.7; 904.16405
(66), 904.16389 (61.4), 0.2; 905.16457 (100), 905.16313 (100), 1.6;
906.16477 (67.3), 906.16462 (56.8), 0.2; 907.16289 (77.7), 907.163
(75.9), −0.1.
F
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Inorganic Chemistry
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(EpOX)RuCl(PPh3)[P(OCH2)3CEt] (2). P(OCH2)3CEt (46.4 mg,
0.286 mmol) dissolved in THF was added to a THF solution (25 mL)
of 1 (235 mg, 0.260 mmol) and stirred for 3 h at room temperature.
All solvent was removed under vacuum, the yellow residue was taken
up in a minimum amount of methylene chloride, and hexanes were
added to induce precipitation. The pale-yellow solid was collected on a
fine porosity frit, washed with pentane, and dried under reduced
pressure (173 mg, 83%). 1H NMR (500 MHz, CD2Cl2) δ: 0.73 (t, 3H,
−CH2CH3, 3JHH = 7 Hz), 1.09 (q, 2H, −CH2CH3, 3JHH = 7 Hz), 3.96
(EpOX)RuCl(CO)(PPh3) (5). cis-(EpOX)RuCl(PPh3)2 (1) (101 mg,
0.111 mmol) was dissolved in THF (30 mL) and added to a glass
pressure reactor equipped with a stir bar. The reactor was pressurized
with CO (60 psi) and stirred at room temperature for 30 min. The
initial homogeneous yellow solution became colorless. The contents of
the reactor were transferred to a round-bottom flask, and the solvent
was removed under reduced pressure to afford a brown residue. The
residue was dissolved in methylene chloride, loaded on a short column
of silica gel, and eluted with THF. The eluate was collected, reduced in
vacuo ∼3 mL, and hexanes were added to give a precipitate. The white
precipitate was collected on a fine porosity frit, washed with diethyl
ether and pentane, and dried in vacuo (67.1 mg, 90%). IR (Thin film
3
2
(d, 6H, (POCH2)3-, JHP = 5 Hz), 4.82 (d, 1H, −CH2ORu-, JHH = 8
Hz), 5.04 (t, 1H, −CH2ORu-, 2JHH = 8 Hz), 5.69 (dd, 1H, 3- or 5-pz),
6.40 (br s, 1H, 4-pz), 6.63 (m, 2H, overlapping 4-pz), 6.67 (d, 1H, 3-
or 5-pz), 7.17 (d, 1H, 3- or 5-pz), 7.20−2.30 (m, 9H, PPh3), 7.86−
7.95 (m, 6H, PPh3), 7.97 (d, 1H, 3- or 5-pz), 8.06 (d, 1H, 3- or 5-pz),
8.29 (d, 1H, 3- or 5-pz). 13C{1H} NMR (125 MHz, CD2Cl2) δ: 7.2 (s,
−CH2CH3), 23.8 (s, -CH2CH3), 35.1 (d, (−CH2)3CEt, 3JCP = 31 Hz),
74.1 (d, P(OCH2)3, 2JCP = 7 Hz), 92.0 (s, C(pz)3), 106.0, 106.6, 108.7
(each a singlet, 4-pz) 127.4 (d, o-PPh3, 2JCP = 9 Hz), 130.8 (s, p-PPh3),
1
KBr): νCO = 1940 cm−1. H NMR (CD2Cl2, 500 MHz), δ: 4.98 (dd,
2
4
1H, −CH2ORu- JHH = 9 Hz and JHP =1 Hz), 5.15 (d, 1H,
2
−CH2ORu-, JHH = 9 Hz), 5.90 (vt, 1H, 4-pz), 6.45 (m, 1H, 3- or 5-
pz), 6.63 (dd, 1H, 3- or 5-pz), 6.68 (vt, 1H, 4-pz), 6.91 (dd, 1H, 3- or
5-pz), 7.28 (dd, 1H, 3- or 5-pz), 7.29 (m, 6H, PPh3), 7.41 (m, 3H,
PPh3), 7.74−7.93 (m, 6H, PPh3), 8.02 (d, 1H, 3- or 5-pz), 8.09 (d, 1H,
3- or 5-pz), 8.19 (br s, 1H, 3- or 5-pz). 13C{1H} NMR (125 MHz,
CD2Cl2) δ: 76.1 (s, C(pz)3), 92.9 (s,-CH2ORu-), 107.8, 108.0, 109.9
3
131.2 (s, 3- or 5-pz), 135.1 (d, m-PPh3, JCP = 10 Hz), 136.5 (d, i-
1
PPh3, JCP = 42 Hz), 143.3, 145.8, 148.4 (each a singlet, 3- or 5-pz).
2
31P{1H} NMR (121 MHz, CD2Cl2) δ: 48.1 (d, PPh3, JPP = 57 Hz),
2
(each a singlet, 4-pz), 128.7 (d, m-PPh3, JCP = 10 Hz), 131.0 (s, p-
129.1 (d, P(OCH2)3CEt, JPP = 57 Hz). CV: Ep,a = +0.70 V [Ru(III/
PPh3), 134.1 (d, i-PPh3, 1JCP = 48 Hz), 134.9 (d, o-PPh3, 2JCP = 10 Hz)
2
II), irreversible]. HRMS: [M+H+] obs’d (%), calc’d (%), ppm:
804.11488 (50.5), 804.11706 (60.8), −2.7; 805.11449 (100),
805.11626 (100), −2.2; 806.11614 (49.6), 806.11763 (48.3), −1.8;
807.11501 (81.2), 807.11603 (75.6), −1.3; 808.11862 (24.1),
808.11864 (27.9), 0.
132.0, 132.1, 132.7, 144.5, 145.4, 147.5 (each a singlet, 3- or 5-pz),
2
201.6 (d, CO, JCP = 15 Hz). 31P{1H} NMR (CD2Cl2, 121 MHz) δ:
44.00. HRMS: [M + Na]+ obs’d (%), calc’d (%), ppm: 692.04849
(50), 692.04921 (60.6), −1; 693.04907 (100), 693.04838 (100), 1;
694.05024 (33.3), 694.04963 (44.1), 0.9; 695.04545 (85.7), 695.04812
(EpOX)RuCl[P(OCH2)3CEt]2 (3). Compound 1 (101 mg, 0.111
mmol) and P(OCH2)3CEt (101 mg, 0.623 mmol) were combined,
dissolved in THF (40 mL), and refluxed for 8 h. The flask was allowed
to cool to room temperature, and hexanes were added to induce
precipitation. The white solid was collected on a fine porosity frit,
washed successively with diethyl ether and pentane, and dried under
(75.3), −3.8; 696.04491 (12.5), 696.05077 (24.4), −8.4. CV: E1/2
+1.21 V.
=
(EpOX)RuCl(CO)2 (6). Compound 1 (444 mg, 0.491 mmol) was
dissolved in THF (30 mL) and added to a pressure reactor equipped
with a stir bar. The reactor was pressurized with CO (60 psi) and
allowed to stir at room temperature for 30 days. The initial
homogeneous yellow reaction solution became colorless. The contents
were placed in a round-bottom flask, and the solvent was removed
under reduced pressure to afford a brown residue. The residue was
dissolved in minimal THF and eluted with THF through a short
column of silica. This portion contained complex 5. The column was
then washed with a THF/MeOH (90/10, v/v%) mixture to elute a
reddish-brown band. The filtrate was collected, and the solvent was
removed in vacuo. The residue was taken up in methylene chloride,
and hexanes were added to induce precipitation. The off-white solid
was collected on a frit by filtration, washed with pentane and dried
1
reduced pressure (72.1 mg, 93%). H NMR (300 MHz, CD2Cl2) δ:
3
0.81 (overlapping triplets, 6H, −CH2CH3, JHH = 7 Hz), 1.18 (q, 2H,
−CH2CH3, 3JHH = 7 Hz), 1.20 (q, 2H, −CH2CH3, 3JHH = 7 Hz), 4.21
2
2
(d, 6H, P(OCH2)3-, JHP = 4 Hz), 4.26 (d, 6H, P(OCH2)3-, JHP = 4
Hz), 4.58 (d, 1H, −CH2ORu-, 2JHH = 9 Hz), 4.77 (t, 1H, −CH2ORu-,
2JHH = 9 Hz), 6.16 (dt, 1H, 4-pz), 6.39 (br s, 1H, 4-pz), 6.61 (dt, 1H,
4-pz), 6.71 (d, 1H, 3- or 5-pz), 7.15 (d, 1H, 3- or 5-pz), 7.88 (d, 1H, 3-
or 5-pz), 7.98 (br s, 2H, overlapping resonances, 3- or 5-pz), 8.26 (br
s, 1H, 3- or 5-pz). 13C{1H} NMR (75 MHz, CDCl3) δ: 7.3 (s,
3
−CH2CH3), 23.7 (s, -CH2CH3), 35.1 (dd, JCP = 20 Hz,
2
(−CH2)3CEt), 74.0 (d, (P(OCH2)3, JCP = 6 Hz), 76.0 (s,
under reduced pressure (12.3 mg, 5%). IR (thin film on KBr): νCO =
1
OCH2C(pz)3), 91.7 (s, C(pz)3), 105.9, 106.6, 108.4 (each a singlet,
4-pz), 130.4, 131.0, 142.9, 146.0, 148.7 (each a singlet, 3- or 5-pz).
31P{1H} NMR (121 MHz, CD3CN) δ: 129.2 (d, 2JPP = 99 Hz), 130.7
2060 cm−1 and 1986 cm−1. H NMR (CDCl3, 300 MHz) δ: 4.77 (d,
1H, −CH2ORu-, 2JHH = 9 Hz), 4.94 (d, 1H, −CH2ORu-, 2JHH = 9 Hz)
6.45 (t, 1H, 4-pz), 6.53 (t, 1H, 4-pz), 6.72 (dd, 1H, 4-pz), 7.11(dd, 1H,
3- or 5-pz), 7.20 (dd, 1H, 3- or 5-pz), 7.77 (dd, 1H, 3- or 5-pz), 8.02
(d, 1H, 3- or 5-pz), 8.08 (d, 1H, 3- or 5-pz), 8.28 (d, 1H, 3- or 5-pz).
HRMS: [M + Na]+obs’d (%), calc’d (%), ppm: 457.9524 (56.3),
457.95263 (59.9), −0.5; 458.95164 (100), 458.95169 (100), −0.1;
459.95238 (13.1), 459.95218 (29.9), 0.4; 460.95174 (79.5), 460.9515
(77.1), 0.5; 462.95523 (26.3), 462.95036 (16.6), 10.5.
2
(d, JPP = 99 Hz). EA calcd (found) for C24H34Cl4N6O7P2Ru: C,
35.01(35.46); H, 4.16(4.52); N, 10.29(10.01). Note: contains 1 equiv
1
of CHCl3 determined by H NMR. CV: Ep,a = +0.73 V Ru(III/II)
(irreversible), +1.10 V (irreversible). HRMS: [M+H+] obs’d (%),
calc’d (%), ppm: 804.11488 (50.5), 804.11706 (60.8), −2.7;
805.11449 (100), 805.11626 (100), −2.2; 806.11614 (49.6),
806.11763 (48.3), −1.8; 807.11501 (81.2), 807.11603 (75.6), −1.3;
808.11862 (24.1), 808.11864 (27.9), 0.
[HC(pz)3RuCl(PPh3)2]Cl (7). A solution of compound 1 (302 mg,
0.334 mmol) in chloroform (25 mL) was placed in a pressure tube and
stirred at 60 °C overnight. The solvent was removed under reduced
pressure, and the remaining residue was reconstituted in a minimum
amount of methylene chloride. Hexanes were added to induce
precipitation of pale-yellow solid, which was collected on a fine
porosity frit and washed with diethyl ether followed by pentane. The
crude product was reconstituted in THF and eluted through a short
column of silica. The filtrate was collected, solvent reduced in vacuo
until ∼3−5 mL remained, and hexanes were added to induce
precipitation. The pale-yellow solid was collected on a fine porosity frit
and washed with diethyl ether and pentane and dried under reduced
pressure (236 mg, 71%). The spectroscopic data for 7 is identical to
that previously reported.68 CV: E1/2 = +1.24 V Ru(III/II)(quasi-
reversible).
(κ2-N,O-EpOX)RuCl(PPh3)2(NCMe) (4). Compound 1 (99.0 mg,
0.110 mmol) was dissolved in NCMe (10 mL) and stirred at room
temperature for 36 h. The yellow solution was filtered through a plug
of Celite. The filtrate was collected, and then solvent removed under
reduced pressure. The residue was reconstituted in a minimum
amount of methylene chloride and treated with hexanes to give a pale
yellow solid. The solid was collected by filtration on a fine porosity frit
1
and dried in vacuo (72.2 mg, 70%). H NMR (CD2Cl2, 300 MHz) δ:
2.34 (s, 3H, NCMe), 3.22 (d, 1H, −CH2ORu-, 2JHH = 9 Hz), 4.29 (dd,
1H, −CH2ORu-, 2JHH = 9 Hz, 4JHP = 7 Hz), 5.75 (dd, 1H, 4-pz), 6.18
(dd, 1H, 4-pz), 6.20 (br dd, 1H, 4-pz), 6.38 (d, 1H, 3- or 5-pz), 6.56
(d, 1H, 3- or 5-pz), 6.69 (d, 1H, 3- or 5-pz), 7.06 (t, 6H, p-PPh3, 3JHH
= 9.06), 7.18−7.49 (m, 25H, overlapping o-m-PPh3 and one 3- or 5-
pz), 7.74 (d, 1H, 3- or 5-pz,), 8.04 (d, 1H, 3- or 5-pz). 31P{1H} NMR
(CD2Cl2, 121 MHz) δ: 48.1 (d, 2JPP = 25 Hz), 50.1 (d, 2JPP = 25 Hz).
[HC(pz)3RuCl[P(OCH2)3CEt]2]Cl (8). Compound 3 (140 mg, 0.199
mmol) was dissolved in CHCl3 (10 mL), transferred to a pressure
G
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Inorganic Chemistry
Article
tube, and heated at 100 °C overnight. The solution was treated with
hexanes and a white solid formed. The solid was collected on a fine
porosity frit, washed with diethyl ether and pentane, and dried under
(16) Vepachedu, S.; Stibrany, R. T.; Knapp, S.; Potenza, J. A.;
Schugar, H. J. Acta Crystallogr., Sect. C 1995, 51, 423−426.
(17) Pullen, E. E.; Rabinovich, D.; Incarvito, C. D.; Concolino, T. E.;
Rheingold, A. L. Inorg. Chem. 2000, 39, 1561−1567.
1
reduced pressure (86.7 mg, 62%). H NMR (CD2Cl2, 300 MHz) δ:
0.83 (t, 6H, −CH2CH3, 3JHH = 8 Hz), 1.24 (q, 4H, −CH2CH3, 3JHH
=
́
(18) Otero, A.; Fernandez-Baeza, J.; Antinolo, A.; Tejeda, J.; Lara-
̃
8 Hz), 4.30 (vt, 12H, -(OCH2)3, 3JPH = 3 Hz), 6.27 (t, 1H, 4-pz), 6.40
(vt, 2H, 4-pz), 7.84 (d, 1H, 3- or 5-pz), 8.13 (d, 1H, 3- or 5-pz), 8.70
(br s, 2H, 3- or 5-pz), 8.80 (br s, 1H, 3- or 5-pz), 12.36 (br s, 1H,
HC(pz)3). 13C{1H} NMR (CD2Cl2, 126 MHz) δ: 7.3 (−CH2CH3),
23.6 (−CH2CH3), 35.8 (t, C(CH2CH3), 3JCP = 16 Hz), 74.1 (C(pz)3),
75.0 ({OCH2}3), 107.4, 107.7 (each a singlet, 4-pz), 133.5, 135.0,
146.6, 150.0 (each a singlet, 3- or 5-pz). 31P{H} (CDCl3, 121 MHz) δ:
131.0 (s). CV: E1/2 = +1.5 V Ru(III/II) (quasi-reversible), Ep,a = +1.28
(irreversible). HRMS: [M]+obs’d (%), calc’d (%), ppm: 672.0607
(29.6), 672.0603 (32.9), 0.6; 673.0592 (37.6), 673.0593 (40), 0.1;
674.0588 (58.3), 674.0597 (60.3), 1.3; 675.0589 (100), 675.0588
(100), 0.1; 676.0598 (35.8), 676.0598 (38.2), 0; 677.0581 (74.6),
677.0586 (76.3), 0.7.
Sanchez, A. Dalton Trans. 2004, 1499−1510.
́
(19) Kail, B. W.; Basu, P. Dalton. Trans. 2006, 1419−1423.
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Carrano, C. J. Inorg. Chem. 2004, 43, 7800−7806.
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Hermosilla, F.; Díez-Barra, E.; Lara-San
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́
dez-Baeza, J.; Tejeda, J.; Antonío, A.; Carrillo-
́
chez, A.; Fernandez-Lopez, M.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic data in CIF format. Further details are given in
Figures S1−S7. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: tbg7h@virginia.edu.
■
(28) Papish, E. T.; Taylor, M. T.; Jernigan, F. E., III; Rodig, M. J.;
Shawhan, R. R.; Yap, G. P. A.; Jove, F. A. Inorg. Chem. 2006, 45, 2242−
2250.
Present Address
∥Department of Chemistry and Physics, Armstrong Atlantic
State University, 11935 Abercorn St., Savannah, Georgia 31419,
United States.
(29) Beck, A.; Barth, A.; Hubner, E.; Burzlaff, N. Inorg. Chem. 2003,
42, 7182−7188.
(30) Higgs, T. C.; Ji, D.; Czernuscewicz, R. S.; Carrano, C. J. Inorg.
Chim. Acta 1999, 286, 80−92.
Notes
(31) Burzlaff, N.; Hegelmann, I.; Weibert, B. J. Organomet. Chem.
2001, 626, 16−23.
The authors declare no competing financial interest.
(32) Riehl, J. F.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organometallics
1992, 11, 729−737.
ACKNOWLEDGMENTS
■
We thank the Department of Energy (DE-SC0000776) for
support of this work. B.Q. thanks the Ford Foundation for
support through a postdoctoral fellowship. We acknowledge
Dr. John G. Verkade (Iowa State University) for helpful
discussions.
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