6498 Inorganic Chemistry, Vol. 48, No. 14, 2009
Ghosh et al.
(C5Bz5)Ru(CO)2H. Cationic dihydrogen complexes were
observed by NMR at low temperatures from protonation
25.7 (d, 1JCH=133 Hz, CHMe2); 25.5 (q, 1JCH=126 Hz, CHMe2);
25.4 (d, 1JCH=127 Hz, CHMe2); 25.2 (q, 1JCH=126 Hz, CHMe2).
IR (hexane) ν(CO): 2015 (s) cm-1, 1956 (s) cm-1. Anal. Calcd
for C19H30O2Ru: C 58.27%; H 7.72%. Found: C 58.45%;
of (CpiPr )Ru(CO)2H, Cp*Ru(CO)2H, or CpRu(CO)[P-
4
(OPh)3]H by HOTf. At higher temperatures the H2 ligand
is lost, generating ruthenium triflate complexes. These new
Ru complexes were usedascatalyst precursors inthe presence
of added HOTf for the catalytic deoxygenation of 1,2-
propanediol to give n-propanol. Increasing the electron
density at the metal can improve performance of the catalyst,
as shown by the higher conversion to products obtained with
CpRu(CO)(PMe3)H, CpRu(CO)(PCy3)H, or CpRu(CO)[P-
(p-C6H4F)3]H, compared to {[CpRu(CO)2]2(μ-H)}+OTf -.
Similarly, changing from Cp to Cp* improves performance,
as {[Cp*Ru(CO)2]2(μ-H)}+OTf - provides better results than
{[CpRu(CO)2]2(μ-H)}+OTf -. Too much electron density at
the metal (and perhaps increased steric interference), how-
ever, results in a poorer performance since Cp*Ru(CO)-
(PMe3)H gives worse results than those obtained from either
{[CpRu(CO)2]2(μ-H)}+OTf - or CpRu(CO)(PMe3)H. Simi-
larly, the bis-phosphite complex CpRu[P(OPh)3]2H does not
give high conversions as a catalyst precursor, suggesting that
the lower acidity of the corresponding dihydrogen or dihy-
dride complex, or increased steric demands of the ligands, is
deleterious to catalytic activity.
H 7.67%.
iPr4
Synthesis of [(CpiPr )Ru(CO)(μ-CO)]2. A solution of (Cp )-
4
Ru(CO)2H (0.100 g, 0.255 mmol) and Gomberg’s dimer
(0.062 g, 0.128 mmol) were stirred in hexane (15 mL) at room
temperature in the dark for 1 day, giving a yellow precipitate.
The reaction mixture was concentrated to 10 mL for further
precipitation, and the precipitate was isolated by filtration to
give [(CpiPr )Ru(CO)(μ-CO)]2 as a yellow solid (0.052 g, 52%).
4
1H NMR (C6D6): δ 4.51 (s, 1H, HC5 ), 3.07 (sept, JHH
=
7 Hz, 2H, CHMe2); 2.87 (sept, 3JHH=7 Hz, 2H, CHMe2); 1.58
(d, 3JHH=7 Hz, 6H, CHMe2); 1.27 (d, 3JHH=7 Hz, 6H, CHMe2);
iPr4
3
3
3
1.23 (d, JHH=7 Hz, 6H, CHMe2); 1.06 (d, JHH=7 Hz, 6H,
CHMe2). 13C NMR (C6D6): δ 229 (br, CO); 118.0 (s, Cp-ring-
C-Pri); 111.1 (s, Cp-ring-C-Pri); 82.4 (dt, 1JCH=171 Hz, 2JCH=4
1
Hz, Cp-ring-CH); 26.8 (d, JCH=126 Hz, CHMe2); 26.3
(q, 1JCH = 126 Hz, CHMe2); 25.3 (d, 1JCH=131 Hz, CHMe2);
3
24.7 (q, 1JCH=126 Hz, CHMe2); 24.5 (q, 1JCH=126 Hz, CHMe2);
22.7 (q, 1JCH=126 Hz, CHMe2). IR (C6D6) ν(CO): 1936 (s) cm-1
,
.
1761 (s) cm-1. IR (toluene) ν(CO): 1938 (s) cm-1, 1762 (s) cm-1
IR (hexane) ν(CO): 1943 (s) cm-1, 1768 (s) cm-1. Anal. Calcd
for C38H58O4Ru2: C 58.42%; H 7.48%. Found: C 58.17%;
H 7.79%.
Protonation of (CpiPr )Ru(CO)2H by HOTf at Low Tempera-
4
tures. HOTf (4.0 μL, 0.045 mmol) was added to (CpiPr )Ru-
4
Experimental Section
(CO)2H (0.015 g, 0.038 mmol) in CD2Cl2 (0.69 mL) at -80 ꢀC in
an NMR tube, and the reaction was monitored by H NMR
All manipulations were carried out under an atmosphere
of argon using Schlenk or vacuum-line techniques, or in a
Vacuum Atmospheres drybox. Quantitative analysis of the
intermediates and products was carried out by gas chromato-
graphy, using an internal standard for integration, follow-
1
spectroscopy. At -80 ꢀC, the dihydrogen complex {(CpiPr )Ru-
4
(CO)2(η2-H2)}+OTf- (65%) was found to be in equilibrium with
(CpiPr )Ru(CO)2H (35%) and with the unreacted HOTf [TfO
-
4
H-OTf and (HOTf)n]. The equilibrium constant (Keq) for the
ing protocols previously described in detail.4,5 Preparations of
3 3 3
reaction was found to be 51 M-1 at -80 ꢀC. There was only a
small change in the observed equilibrium constant on warming
HCpiPr 13
,
HC5Bz5,28 1,2,3-trimethylindene,39 Tp*Ru(COD)H,40
4
Tp*Ru(CO)2H,40 Cp*Ru(CO)2H,41 and {[CpRu(CO)2]2-
(μ-H)}+OTf -9 were carried out according to the literature
procedures. CpRu(CO)(PCy3)H was prepared by a minor
modification of the route described by Heinekey.33 The head-
to-tail dimer of trityl radical (Gomberg’s dimer,18 1-diphenyl-
methylene-4-triphenylmethyl-2,5-cyclohexadiene;see Scheme2)
was prepared by reaction of Ph3CBr with Cu, as described for a
to -60 ꢀC as the Keq value only changed to 61 M-1. Upon further
elevating the temperature, broadening of {(CpiPr )Ru-(CO)2(η -
2
4
H2)}+OTf - and (CpiPr )Ru(CO)2H resonances were observed,
4
suggesting the occurrence of proton transfer exchange between
these complexes. Coalescence of the HC5
iPr4
resonances was
4
observed at -40 ꢀC, and decomposition to (CpiPr )Ru(CO)2OTf
iPr4
(HC5 resonance at δ 5.08), accompanied by the formation of
substituted derivative.19
H2 (δ 4.60), was observed upon warming to 27 ꢀC. {(CpiPr )Ru-
4
iPr4
Synthesis of (CpiPr )Ru(CO)2H. A solution of HCp (0.300 g,
4
(CO)2(η2-H2)}+OTf -: H NMR (CD2Cl2) -80 ꢀC: δ 5.48 (s,
1
iPr4
1.28 mmol) and Ru3(CO)12 (0.273 g, 0.427 mmol) in heptane
(25 mL) was refluxed for 9 h, and the extent of the reaction was
monitored by IR spectroscopy. The dark brown reaction mixture
was filtered, and the filtrate was evaporated to give an oil, which
was dissolved in pentane and filtered though silica gel to obtain
a clear yellow solution. The solvent was evaporated to give obtain
1H, HC5 ), 2.3-3.0 (CHMe2 not resolved); 0.8-1.5
(CHMe2 not resolved); -5.85 (s broad w1/2=69 Hz, 2H, Ru-
(η2-H2)).
Synthesis of (C5Bz5)Ru(CO)2H. Asolutionof HC5Bz5 (0.500g,
0.969 mmol) and Ru3(CO)12 (0.207 g, 0.324 mmol) in heptane
(25 mL) was refluxed for 10 days, and the extent of the reaction was
monitored by IR spectroscopy. The brownish-yellow reaction
mixture was filtered through alumina inside a drybox, and the
solvent was evaporated to give a dark brown oil. The oil was
dissolved in pentane (5 mL), and cooled to-30 ꢀC. A brown oily
solid precipitated. The supernatant pentane extract was decanted,
and the solvent was evaporated to obtain (C5Bz5)Ru(CO)2H as an
oily yellow solid (0.154 g, 24%). 1H NMR (C6D6): δ 7.02-6.87 (m,
25H, C6H5), 3.61 (s, 10H, CH2C6H5), -9.92 (s, 1H, Ru-H).
a yellow oil, which was cooled at -40 ꢀC to give (CpiPr )Ru(CO)2H
4
as a yellow solid (0.226 g, 45%). 1H NMR (C6D6): δ 4.80 (s, 1H,
iPr4
HC5 ), 2.57 (sept, 3JHH=7 Hz, 2H, CHMe2); 2.49 (sept, 3JHH=7
Hz, 2H, CHMe2); 1.24 (d, 3JHH=7 Hz, 6H, CHMe2); 1.18 (d, 3JHH
=7 Hz, 6H, CHMe2); 1.11 (d, 3JHH=7 Hz, 6H, CHMe2); 0.94 (d,
3JHH=7 Hz, 6H, CHMe2); -10.3 (s, 1H, Ru-H). 13C NMR (C6D6):
δ 203.6 (d, 2JCH=9 Hz, CO); 113.7 (s, Cp-ring-C-Pri); 112.4 (s, Cp-
ring-C-Pri); 75.9 (dt, 1JCH=171 Hz, 2JCH=5 Hz, Cp-ring-CH); 26.7
1
1
IR (hexane) ν(CO): 2020 (s) cm-1, 1963 (s) cm-1
.
(q, JCH = 127 Hz, CHMe2); 26.2 (q, JCH = 126 Hz, CHMe2);
Synthesis of CpRu(CO)[P(OPh)3]H. A solution of freshly
cracked cyclopentadiene (9.00 mL, 109 mmol) and Ru3(CO)12
(0.900 g, 1.41 mmol) was refluxed in heptane (70 mL) for 4.5 h.15
The color of the solution changed from dark orange to lemon
yellow. An aliquot taken for IR spectroscopy showed predomi-
nant formation of CpRu(CO)2H (2033 and 1973 cm-1) along
(39) (a) O’Hare, D.; Green, J. C.; Marder, T.; Collins, S.; Stringer, G.;
Kakkar, A. K.; Kaltsoyannis, N.; Kuhn, A.; Lewis, R.; Mehnert, C.; Scott,
P.; Kurmoo, M.; Pugh, S. Organometallics 1992, 11, 48–55. (b) Miyamoto, T.
K.; Tsutsui, M.; Chen, L.-B. Chem. Lett. 1981, 729–730.
(40) Moreno, B.; Sabo-Etienne, S.; Chaudret, B.; Rodriguez, A.; Jalon,
F.; Trofimenko, S. J. Am. Chem. Soc. 1995, 117, 7441–7451.
(41) (a) Cheng, T.-Y.; Bullock, R. M. Organometallics 2002, 21, 2325–
2331. (b) Fagan, P. J.; Mahoney, W. S.; Calabrese, J. C.; Williams, I. D.
Organometallics 1990, 9, 1843–1852.
with the minor amounts of [CpRu(CO)2]2 (1944 and 1793 cm-1
)
and (η4-C5H6)Ru(CO)3 (2064, 1998, and 1987 cm-1).15 The
reaction mixture was cooled to -78 ꢀC, and a solution of