Hydrogenolysis of a ruthenium carbene complex to yield dihydride-dihydrogen tautomers: Mechanistic implications for tandem ROMP-hydrogenation catalysis

Article abstract of DOI:10.1021/ic000102q

Conversion of Grubbs's catalyst 1 into a hydrogenation catalyst is described. Hydrogenolysis of the Rucarbene bond in CH₂Cl₂ yields Ru(IV) species 2; in other solvents, a mixture of 2 and its dihydrogen tautomer 4 is formed, even in the presence of base. Further reaction gives hydridochloro complex RuHCl(H₂)(PCy₃)₂ 3, which reverts to 2 in CH₂Cl₂.

Full text of DOI:10.1021/ic000102q

5412
Inorg. Chem. 2000, 39, 5412-5414
NMR (δ, C6D6, Ar): 91.3 (s, 2), 54.2 (s, 4). A third singlet appeared
under H2: 40.3 (s, 7). In solution, trace impurities can be seen by 31P-
{1H} NMR. 1H NMR (δ, C6D6, Ar): -16.2 (br s, Ru(H2), 4), -12.0 (t,
3J(H,P) ) 31.5 Hz, Ru(H)2, 2), 0.9-2.3 (m, Cy). Under H2: -13.0 (br
Hydrogenolysis of a Ruthenium Carbene
Complex to Yield Dihydride-Dihydrogen
Tautomers: Mechanistic Implications for
Tandem ROMP-Hydrogenation Catalysis
3
s, Ru(H2), 4), -12.0 (t, J(H,P) ) 31.5 Hz, Ru(H)2, 2), -9.8 (br s,
Ru(H2), 7), 0.9-2.3 (m, Cy). No signal for 3 (δΗ -14.0) was observed.
Hydride T1 min for 4 (C7D8, H2, 500 MHz, 268K) 18.8 ms. Anal. Calcd
for C36H68Cl2P2Ru: C, 58.84; H, 9.33. Found: C, 58.91; H, 9.23.
RuCl2(H2)(PCy3)2[η1-OdC(NMe2)Me] (6). (a) A suspension of 1
(100 mg, 122 µmol) in Et2O-DMA (10:1, total volume 20 mL) was
stirred under 1000 psi H2 for 20 h. The resulting pale yellow solid was
filtered off, washed with Et2O and hexanes, and dried. Yield: 70 mg
(71%). Solid state 31P{1H} NMR (δ): 32.2 (s); a small peak at 47.5
ppm is assigned to 4. Solution 31P{1H} NMR reveals only 2/4 (vide
infra). 1H NMR (δ, C6D6, Ar): -16.2 (br s, Ru(H2), 4), -12.0 (t,
3J(H,P) ) 31.5 Hz, Ru(H2, 2), 0.9-2.6 (m, Cy, DMA). Integration vs
MeOH as internal standard: hydride (2 + 4): aliphatics (Cy + DMA)
) 2:75. Hydride T1 min (C7D8, H2, 500 MHz, 268 K) 18.5 ms. IR
(Nujol): ν(CO) 1630 cm-1. Anal. Calcd for C40H77Cl2NOP2Ru: C,
58.45; H, 9.44; N, 1.70. Found: C, 58.95; H, 9.67; N, 1.66. (b) A
solution of 1 (50 mg, 61 µmol) and PS (13 mg, 61 µmol) in benzene-
DMA (3:1, 20 mL total) was stirred under 1 atm H2 for 16 h, until
only the 31P{1H} NMR singlet for 4 was present. Removal of benzene
in vacuo gave a yellow suspension, which was filtered off, washed
with methanol and cold hexanes, and dried. Yield: 20 mg (44%). Some
PS/DMA remained after this treatment. The C6D6 solution slowly
deposited crystals of 6.
Samantha D. Drouin, Glenn P. A. Yap, and
Deryn E. Fogg*
Center for Catalysis Innovation and Research,
Department of Chemistry, University of Ottawa, Ottawa,
ON, Canada K1N 6N5
ReceiVed February 1, 2000
Introduction
Ring-opening metathesis polymerization (ROMP), followed
by hydrogenation, affords a “back-door” route to polyolefins
inaccessible via conventional Ziegler-Natta or metallocene
catalysis. We and others1 have been exploring tandem poly-
merization-hydrogenation, in which both processes are effected
by a single catalyst precursor, as an exceptionally efficient
variant on this approach. Here we report the transformation of
ROMP catalyst 1 into dihydride, dihydrogen, and hydride
species, under conditions relevant to the hydrogenation chem-
istry.
Ru(H)(D)Cl2(PCy3)2 (2HD) and RuCl2(HD)(PCy3)2 (4HD). A sample
of 6 (10 mg, 12 µmol) in 1 mL of C6D6 was freeze-thaw-degassed
twice and then thawed under D2. 31P{1H} NMR (δ, C6D6): 90.8, 90.6
Experimental Section
1
(s, two isomers of 2HD),2a 54.2 (s, 4HD), 40.1 (s, 7HD). H NMR (δ,
General Considerations. All operations were performed under N2,
Ar, or vacuum, using standard Schlenk or drybox techniques. Dry,
oxygen-free hexanes, benzene, and Et2O were obtained using an
Anhydrous Engineering solvent purification system, and stored over
Linde 4 Å molecular sieves. Methanol was distilled under N2 from
Mg(OCH3)2, DMA and CH2Cl2 from CaH2. CD2Cl2, C6D6, and C7D8
were dried over activated sieves (Linde 4 Å) and degassed by
consecutive freeze/pump/thaw cycles. Hydrogen (Praxair UHP grade)
was purified by passage through a Deoxo cartridge and an indicating
Drierite column in series. All other reagents were used as received.
Solution 31P NMR spectra were recorded on a Varian XL-300, solid-
3
3
C6D6): -11.86 (t, J(H,P) ) 31.5; 2HD), -11.91 (t, J(H,P) ) 31.5;
1
2
HD), -13.1 (br t, J(H,D) ) 22.5; 4HD). Deuterium splitting of the
broad, low-intensity signal for 7 prevents observation of the hydride
in 7HD
.
RuHCl(H2)(PCy3)2 (3). A solution of 1 (60 mg, 73 µmol) and PS
(47 mg, 220 µmol) in CH2Cl2 (20 mL) was stirred under 1000 psi H2
for 14 h. Removal of solvent in vacuo gave an orange solid, which
was extracted with cold hexanes, filtered, and washed with cold
methanol and hexanes. Yield: 42 mg (82%). 31P{1H} NMR (δ, C6D6):
54.2 (s). 1H NMR (δ, C6D6, Ar): -16.3 (br s, RuH3), 0.9-2.3 (m, Cy).
Under H2: -14.0 (br s, RuH3), 0.9-2.3 (m, Cy). A broad singlet for
dihydrogen adduct 8 (δΗ -7.9)2b is observed only on cooling to 193 K
(CD2Cl2).
1
state spectra on a Bruker ASX-200 spectrometer. H NMR data were
measured on a Varian Gemini 200 NMR or Bruker ASX-500
spectrometer. 31P and 1H NMR shifts are referenced to 85% aq H3PO4
or the residual protons of the deuterated solvent, respectively. Mi-
croanalytical data were obtained using a Perkin-Elmer Series II
CHNS/O instrument. High-pressure hydrogenations were carried out
in glass-lined Parr autoclaves.
X-ray Crystallographic Data Collection for 6. Single-crystal X-ray
diffraction measurements were performed with Mo KR radiation (λ )
0.71073 Å) on a Bruker AX SMART 1k CCD diffractometer. Crystal
data: orthorhombic, space group Pnma, Z ) 4, a ) 17.831(2) Å, b )
23.980(3) Å, c ) 9.6048(9) Å, V ) 4106.9(9) Å3, Fcalcd ) 1.326 gcm-3
,
Ru(H)2Cl2(PCy3)2 (2). (a) A solution of 1 (5 mg, 6.1 µmol) in CD2-
Cl2 (0.7 mL) showed clean, quantitative conversion to 2 after 24 h
1.70° e Θ e 24.71°; λ(Mo KR) ) 0.71073 Å, 0.3° ω scans with CCD
area detector, T ) 203 K, 32693 reflections measured [3589 observed
unique (I > 2σI) 227 parameters refined], F2 refinement, RF(wRF2) )
0.0670 (0.1568).
under H2 (1 atm). 31P{1H} NMR (δ, CD2Cl2): 91.3 (s). H NMR (δ,
1
3
CD2Cl2): -12.4 (t, J(H,P) ) 31.6 Hz, 2H, RuH), 0.9-2.3 (m, 66H,
Cy), 2.4 (s, 3H, toluene CH3), 7.2 (m, 5H, Ph). (b) A solution of 1 (50
mg, 60.8 µmol) in CH2Cl2 (20 mL) was stirred under 1000 psi H2 for
14 h. The orange solution was used directly in subsequent experiments.
RuCl2(H2)(PCy3)2 (4). A suspension of 1 (100 mg, 122 µmol) in
hexanes (10 mL) was stirred under 1000 psi H2 at 50 °C for 40 h. The
resulting pale yellow solid was filtered off and dried under vacuum.
Yield 60 mg (67%). Solid state 31P{1H} NMR (δ): 47.5 ppm. 31P{1H}
Results and Discussion
Hydrogenolysis of 1 in CH2Cl2 effects clean conversion into
known2a Ru(IV) species 2 (Scheme 1). Hydrogenolysis in
nonchlorinated solvents, in the presence or absence of base
(DMA; PS-DMA; DMA ) dimethylacetamide, PS ) Proton
* Corresponding author. E-mail: dfogg@science.uottawa.ca. Fax: (613)
562-5170.
(2) (a) Rodriguez, V.; Sabo-Etienne, S.; Chaudret, B.; Thoburn, J.; Ulrich,
S.; Limbach, H.-H.; Eckert, J.; Barthelat, J.-C.; Hussein, K.; Marsden,
C. J. Inorg. Chem. 1998, 37, 3475. (b) Christ, M. L.; Sabo-Etienne,
S.; Chaudret, B. Organometallics 1994, 13, 3800. (c) Guari, Y.; Ayllon,
J. A.; Sabo-Etienne, S.; Chaudret, B. Inorg. Chem. 1998, 37, 640. (d)
Chaudret, B.; Chung, G.; Eisenstein, O.; Jackson, S. A.; Lahoz, F. J.;
Lopez, J. A. J. Am. Chem. Soc. 1991, 113, 2314.
(1) (a) McLain, S. J.; McCord, E. F.; Arthur, S. D.; Hauptman, E.;
Feldman, J.; Nugent, W. A.; Johnson, L. K.; Mecking, S.; Brookhart,
M. Proceed. PMSE 1997, 76, 246. (b) Watson, M. D.; Wagener, K.
B. Polym. Prepr. 1997, 38, 474. (c) Dias, E. L.; Grubbs, R. H.
Organometallics 1998, 17, 2758. (d) Drouin, S. D.; Zamanian, F.;
Fogg, D. E. Macromolecules, to be submitted.
10.1021/ic000102q CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/27/2000

Notes
Inorganic Chemistry, Vol. 39, No. 23, 2000 5413
Table 1. Crystallographic Data for 6
chemical formula: C40H75Cl2NOP2Ru formula weight ) 820.0
a ) 17.831(2) Å
b ) 23.980(3) Å
c ) 9.6048(9) Å
space group: Pnma (No. 62)
T ) -70 °C
λ ) 0.71073 Å
F
calcd ) 1.326 gcm-3
V ) 4106.9 Å3
Z ) 4
µ ) 6.21 cm-1
R1a ) 0.0670
wR2b ) 0.1568
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
Scheme 1
Figure 1. Molecular structure of 6 (thermal ellipsoids depicted at 50%
probability level, hydrogens omitted for clarity). Selected bond lengths
(Å) and angles (deg): Ru-O1 2.323(7), Ru-P1 2.3707(16), Ru-Cl1
2.423(4), Ru-Cl2 2.428(6), O1-C19 1.212(13), O1-Ru-P1 97.78-
(4), P1-Ru-P1A 164.29(8), O1-Ru-Cl1 90.21(19), O1-Ru-Cl2
83.35(19), Cl1-Ru-Cl2 173.55(13).
Sponge, 1,8-bis(dimethylamino)naphthalene), reveals a dihy-
drogen complex, either alone or accompanying 2. By analogy
with related work,3 hydridochloro complex 32b was expected.
Heterolytic activation of dihydrogen is well known to give such
species. Indeed, the generally accepted role of base in promoting
catalytic hydrogenation via transition-metal dihalides involves
abstraction of HX to give hydridohalo intermediates that afford
entry into the catalytic cycle.4 We were thus surprised to observe
as the kinetically favored reaction path not loss of HCl, but
conversion into previously unreported dichloro complex 4, or
its DMA adduct 6. We isolate base-free 4 via hydrogenolysis
of 1 in hexanes. Complicating its isolation from “better” solvents
is its instability toward slow loss of H2, tautomerism to 2-4
mixtures in solution (vide infra), and loss of HCl to afford 3 as
the thermodynamic product from H2/base treatment. Complex
4 is almost certainly implicated in other chemistry of 2, possibly
including catalytic dechlorination of aryl chlorides,5 but its
presence has gone unrecognized, owing to its 31P NMR
equivalence with 3.2b
The identity of 4 is supported by T1, J(H-D), and microana-
lytical data. The T1 minimum value (18.8 ms at 268 K and 500
MHz, corresponding to an H-H distance of 0.84 Å for fast-
spinning H2)6a is significantly shorter than that for 3 (30 ms at
243 K, 250 MHz; 60 ms at 500 MHz).2b The comparatively
long relaxation time for 3 is characteristic of η2-H2 perturbed
by interaction with cis-hydride.6b The HD derivative of 4
exhibits a coupling constant of 22.5 Hz, corresponding to an
H-H distance of 1.04 Å.6c The discrepancy with the T1-derived
value may reflect the intermediacy between fast and slow
spinning of the dihydrogen ligand (the H-H distance calculated
for nonspinning H2 is 1.06 Å).6a
confirms retention of both chloride ligands. Crystals were grown
from benzene/DMA solutions of 4 (generated from 1/H2/PS).
These reaction conditions eliminate any possibility that “shut-
tling” between hydridochloro and dichloro species is mediated
by CH2Cl2 solvent.3a We formulate the structure as an octahedral
complex with mutually trans phosphines and chlorides in the
basal plane, and O-bound DMA trans to H2. Although the H2
ligand is not located, spectroscopic data support its retention in
6. A precedent for this transformation is the reaction of Os-
(H)2Cl2(PiPr3)2 with pyrazole to give a six-coordinate dihydrogen
complex as a base adduct.7 The weak interaction implied by
the long Ru-O bond in 6 is consistent with minimal perturbation
of the ν(CO) IR resonance (1630 cm-1, vs 1640 cm-1 for free
DMA).
In solution, we favor a five-coordinate structure resulting from
dissociation of DMA (i.e., 4, rather than 6), on the basis of the
spectroscopic resemblance to base-free 4. NMR spectra of the
two in C6D6 are identical (disregarding peaks for free DMA in
the case of 6), and the dihydrogen T1 values are also identical
within experimental error, differing by 0.3 ms. A structural
difference between solid and solution state is manifest in 31P-
{1H} NMR spectra of 6: solid-state NMR reveals a signal at
32 ppm, where the corresponding solution spectrum exhibits
only the singlets assigned to 4 and 2 (δP 54 and 91, respectively).
In comparison, the solid state 31P{1H} NMR spectrum of base-
free 4 consists of a peak at 47.5 ppm. (Chemical shift differences
between solid state and solution NMR data are common;
structures are considered qualitatively similar for differences
of ca. 6 ppm.8) Inspection of either 4 or 6 in solution under H2
1
reveals new 31P{1H} and H NMR singlets (δP 40; δH -9.8),
both of which disappear on evacuation and backfilling with Ar.
31P EXSY experiments indicate a correlation between the peaks
at δ 54 and 40, consistent with chemical exchange between
Single-crystal X-ray analysis of DMA adduct 6 (Figure 1)
(3) (a) Olivan, M.; Caulton, K. G. Inorg. Chem. 1999, 38, 566. (b) Wolf,
J.; Stuer, W.; Grunwald, C.; Gevert, O.; Laubender, M.; Werner, H.
Eur. J. Inorg. Chem. 1998, 1827.
(4) James, B. R., in ComprehensiVe Organometallic Chemistry; Wilkinson,
G., Ed.; Pergamon Press: New York, 1982; Vol. 8, p 285.
(5) Cucullu, M. E.; Nolan, S. P.; Belderrain, T. R.; Grubbs, R. H.
Organometallics 1999, 18, 1299.
(6) (a) Bautista, M. T.; Cappellani, E. P.; Drouin, S. D.; Morris, R. H.;
Schweitzer, C. T.; Sella, A.; Zubkowski, J. J. Am. Chem. Soc. 1991,
113, 4876. (b) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992,
121, 155. (c) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J.;
Morris, R. H.; Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J.
Am. Chem. Soc. 1996, 118, 5396.
1
coordinatively unsaturated 4 and its bis(H2) derivative 7. H
EXSY likewise correlates the hydride peaks at -9.8 and -13
ppm. The latter is assigned to 4, its downfield shift relative to
the value under Ar (-16.2 ppm) arising from exchange
averaging with 7.
(7) Esteruelas, M. A.; Lahoz, F. J.; Oro, L. A.; Onate, E.; Ruiz, N. Inorg.
Chem. 1994, 33, 787.
(8) Bemi, L.; Clark, H. C.; Davies, J. A.; Fyfe, C. A.; Wasylishen, R. E.
J. Am. Chem. Soc. 1982, 104, 438.

5414 Inorganic Chemistry, Vol. 39, No. 23, 2000
Whereas dissolving 4 or 6 in benzene or toluene gives an
equilibrium mixture of dihydride and dihydrogen species, solely
2 is observed in CH2Cl2. (Complex 3 likewise gives 2 in CH2-
Cl2, but only on extended exposure). We identify the 4f2
conversion as tautomerism, rather than reaction with chlorinated
solvent,3a as dissolving 4 in CD2Cl2 does not effect incorporation
of deuterium (1H and 2H evidence). The barrier to interconver-
sion is presumably due to movement of the heavy atoms,
possibly involving compression of the P-Ru-P angle in 2
relative to 4. An iodo analogue of 3 exhibits a P-Ru-P angle
of 175°,2d vs angles of ∼112° determined computationally for
2,2a and crystallographically for [Ru(H)2Cl2(PiPr3)2].9 Dihydro-
gen-dihydride tautomeric equilibria have been spectroscopically
observed in other systems, and solvent effects on the position
of equilibrium have been described.6b
under partial H2 atmosphere by variations in the extent of
exchange averaging of 3 with its bis(H2) derivative 8 are
resolved at 193 K.
The spectroscopic similarity between 3 and the new complex
4 means that chemistry thought to involve the former must be
reconsidered to take into account the possible implication of 4.
The accessibility of the latter via tautomerism is a further
development in the emerging chemistry of Ru(IV) species of
type 2. Finally, the facile transformation of ROMP catalyst 1
into potentially interconvertible dihydride, dihydrogen, and
hydridochloro species is of particular interest with regard to
tandem ROMP-hydrogenation chemistry. We have indications
that small variations in reaction conditions lead to dramatic
changes in hydrogenation activity, and that optimum results are
not necessarily associated with the use of strong base.1d
Hydrogenolysis of 1 in the presence of strong base such as
PS, or further reaction of 4, affords a route to 3. The
dehydrohalogenation reaction is particularly facile in neat CH2-
Cl2 solvent. Complexes 3 and 4 are indistinguishable by 31P
NMR or 1H NMR under Ar. The hydride signals can, however,
be distinguished at RT under 1 atm H2. Ambiguities introduced
Acknowledgment. This work was supported by the Natural
Sciences and Engineering Research Council of Canada, the
Canada Foundation for Innovation, and the Ontario Innovation
Trust.
Supporting Information Available: An X-ray crystallographic file
in CIF format for the structure determination of 6. This material is
available free of charge via the Internet at http://pubs.acs.org.
(9) Grunwald, C.; Gevert, O.; Wolf, J.; Gonzalez-Herrero, P.; Werner,
H. Organometallics 1996, 15, 1960.
IC000102Q
Ad d ition s a n d Cor r ection s
1999, Volume 38
S. C. Gibney, G. Ferraudi, and M. Shang: Ultraviolet
Photochemistry of CoIIIL(H2O)SO3 [L ) Me6[14]dieneN4,
+
[14]andN4] Complexes. Quandaries about the Linkage
Isomerization to O-Bonded Sulfite and the Photogeneration
of Cobalt(I) in Sequential Biophotonic Photolysis.
Page 2904: There is an error in the reported value of the
rate constants. kxchg ) 6 × 107 M-1 s-1 must be replaced by
kxchg ) (6.0 ( 0.7) M-1 s-1, and kxchg ) (4 ( 3) × 107 M-1
s-1 must be replaced by kxchg ) (4 ( 3). These sentences should
read as follows:
2-
A rate constant kxchg ) (4 ( 3) M-1 s-1 for the SO3•-/SO3
self-exchange was reported in the literature on the basis that
some electron-transfer reactions obey the Marcus theory.43,44
This value of the self-exchange rate constant and those
calculated in this work by using other reactions, e.g., the
oxidation of SO32- by Cl2-, were in good agreement, e.g., kxchg
) (6.0 ( 0.7) M-1 s-1 45,46
.
IC001047O
Published on Web 10/21/2000