Convenient synthesis of ruthenium(II) dihydride phosphine complexes Ru(H)2(PP)2 and Ru(H)2(PR3)x (x = 3 and 4)

Article abstract of DOI:10.1021/om9706673

A novel and convenient one-pot synthesis of ruthenium(II) dihydride phosphine complexes from the air-stable [RuCl₂(COD)]_x, the appropriate phosphine, and NaOH in sec-butyl alcohol under argon at 80 °C is reported. A series of chelating (dcpm, dcpe, dppe, dppb, dppp, dppf, and depe) and monodentate phosphine (PEt₃ and PPh₃) complexes have been synthesized using this methodology. The crystalline products are isolated in high yield. These dihydride complexes have been shown to be useful precursors to cationic dihydrogen hydride complexes, some of which exhibit significant activity as hydrogenation catalysts.

Full text of DOI:10.1021/om9706673

Organometallics 1997, 16, 5569-5571
5569
Con ven ien t Syn th esis of Ru th en iu m (II) Dih yd r id e
P h osp h in e Com p lexes Ru (H)2(P P )2 a n d Ru (H)2(P R3)x (x )
3 a n d 4)
Steven P. Nolan,1 Toma`s R. Belderrain, and Robert H. Grubbs*
The Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and
Chemical Engineering, California Institute of Technology, Pasadena, California 91125
Received August 1, 1997X
A novel and convenient one-pot synthesis of ruthenium(II) dihydride phosphine complexes
from the air-stable [RuCl2(COD)]x, the appropriate phosphine, and NaOH in sec-butyl alcohol
under argon at 80 °C is reported. A series of chelating (dcpm, dcpe, dppe, dppb, dppp, dppf,
and depe) and monodentate phosphine (PEt3 and PPh3) complexes have been synthesized
using this methodology. The crystalline products are isolated in high yield. These dihydride
complexes have been shown to be useful precursors to cationic dihydrogen hydride complexes,
some of which exhibit significant activity as hydrogenation catalysts.
+
In tr od u ction
reactivity of these RuH(PP)2 (PP ) chelating diphos-
phine) complexes extends from hydrogenation of
alkynes12 (eq 1) to asymmetric transfer hydrogenation
of prochiral olefins bearing carboxylic acids13 (eq 2).
The use of metal hydride complexes is prevalent
throughout organometallic chemistry and homogeneous
catalysis since these complexes play a prominent role
as active catalysts in the isomerization, polymerization,
and hydrogenation of olefins.2-5 In most cases, the
ancillary ligation associated with these metal hydride
moieties is comprised of tertiary phosphine ligands.
These ligands have been shown to possess a wide range
of tunable steric and electronic properties.6 Bidentate
phosphine ligands7 of the type R2PCH2CH2PR2 (R )
alkyl and aryl) have also proven the be a useful class of
supporting ligands in organometallic complexes and
catalysis.2,4 Significant research efforts have been
devoted to the investigation of ruthenium hydrides
bearing bidentate phosphines.8,9 This interest stems
from the catalytic activity displayed by these complexes
in hydrogenation processes. Chiral biphosphines such
as BINAP10 and DuPhos11 have recently been included
to the list of chelating diphosphines capable of support-
ing mononuclear hydrides of ruthenium. The displayed
Multistep synthetic routes to these complexes have
been described in the literature (vide infra). In the
present contribution, we report a straightforward syn-
thetic methodology leading to gram quantities of a
variety of Ru(H)2(PP)2 (PP ) chelating diphosphine)
complexes, from an air-stable precursor. These com-
plexes are immediate synthetic precursors to the cat-
ionic complexes displaying catalytic behavior.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations involving
organoruthenium complexes were performed under inert
atmospheres of argon or nitrogen using standard high-vacuum
or Schlenk-tube techniques or in a Vacuum Atmospheres
glovebox containing less than 1 ppm of oxygen and water.
Ligands were purchased from Strem Chemicals and used as
received. Sec-butyl alcohol was purchased from Aldrich as
anhydrous grade (99.5%) and purged with Ar prior to use.
NMR spectra were recorded using a GE 400 MHz spectrom-
eter. Solvents were purified using procedures previously
reported.14
X Abstract published in Advance ACS Abstracts, November 15, 1997.
(1) Permanent address: University of New Orleans, Department of
Chemistry, New Orleans, LA 70148.
(2) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry, 2nd
ed.; University Science: Mill Valley, CA, 1987.
(3) Homogeneous Catalysis with Metal Phosphine Complexes;
Pignolet, L. H., Ed.; Plenum: New York, 1983.
(4) (a) Noyori, R. Asymmetric Catalysis in Organic Synthesis; Wiley
and Sons, Inc.: New York, 1994 and references cited. (b) Burk, M. J .;
Harper, G. P.; Kalberg, C. S. J . Am. Chem. Soc. 1995, 117, 4423-
4424 and references cited.
(5) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis; Wiley
Interscience: New York, 1992.
Syn th esis. The identity of Ru(H)2(dppe)2 (1),15 Ru(H)2-
(dppf)2 (4),16 Ru(H)2(dcpe)2 (5),17 Ru(H)2(depe)2 (7),15 Ru(H)2-
(6) (a) Tolman, C. A. Chem. Rev. 1977, 77, 313-348. (b) White, D.;
Coville, N. Adv. Organomet. Chem. 1994, 36, 95-158.
(7) Abbreviations used in the text for chelating phosphines: PPh2-
CH2CH2PPh2 (dppe), PPh2(CH2)3PPh2 (dppp), PPh2(CH2)4PPh2 (dppb),
(PPh2C5H4)2Fe (dppf), PCy2CH2PCy2 (dcpm), PCy2CH2CH2PCy2 (dcpe),
PEt2CH2CH2PEt2 (depe).
(8) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97-102.
(9) (a) Geneˆt, J . P. ACS Symp. Ser. 1996, 641, 31-51. (b) Geneˆt, J .
P.; Ratovelomanana-Vidal, V.; Can˜o de Andrade, M. C.; Pfister, X.;
Guerreiro, P.; Lenoir, J . Y. Tetrahedron Lett. 1995, 36, 4801-4808.
(10) Saburi, M.; Takeuchi, H.; Ogasawa, M. T.; Tsukahara, Y. I.;
Ikariya, T.; Takahashi, T. J . Organomet. Chem. 1992, 428, 155-167.
(11) Schlaf, M.; Lough, A. J .; Morris, R. H. Organometallics 1997,
16, 1253-1259.
(12) Albers, M. O.; Singleton, E.; Viney, M. M. J . Mol. Catal. 1985,
33, 77-82.
(13) Saburi, M.; Ohnuki, M.; Ogasawa, M. T.; Takahashi, T.; Uchida,
Y. Tetrahedron Lett. 1992, 33, 5783-5786.
(14) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518-1520.
(15) 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, 4876-4887.
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D’Agostino, C. Inorg. Chem. 1994, 33, 6278-6288.
S0276-7333(97)00667-5 CCC: $14.00 © 1997 American Chemical Society

5570 Organometallics, Vol. 16, No. 25, 1997
Nolan et al.
(PEt3)4 (8),18 Ru(H)2(PPh3)3 (9),19 and [RuH(dcpe)2]BF4 (10)17
was confirmed by comparing experimental to reported spec-
troscopic information. [RuCl2(COD)]x was synthesized accord-
ing to the literature procedure.20 Experimental synthetic
procedures, leading to isolation of crystalline materials, for all
complexes are reported below.
Ru (H)2(d p p e)2 (1). A 250 mL Schlenk flask containing a
Teflon-coated magnetic stirring bar was charged with NaOH
(1.0 g, 25 mmol). The flask was then taken into the glovebox
where [RuCl2(COD)]x (0.352 g, 1.25 mmol) and PPh2CH2CH2-
PPh2 (dppe) (1.0 g, 2.5 mmol) were added to the reaction vessel.
The vessel was removed from the glovebox and connected to a
Schlenk line where degassed sec-butyl alcohol (80 mL) was
added using a cannula. The reaction vessel was then sealed
and heated to 80 °C for 3 h. The system was then allowed to
cool to room temperature, and degassed water (100 mL) was
added to dissolve the excess NaOH. The suspension was then
transferred using a cannula onto a medium porosity collection
frit where the yellow solid was further washed with 3 × 20
mL portions of degassed methanol and finally dried in vacuo
to yield 0.95 g (85%) of Ru(H)2(dppe)2.
Ru (H)2(P P h 3)3 (9). In an identical fashion as for the
synthesis of 1, but using 3 equiv of PPh3, 9 was isolated as an
orange-brown microcrystalline solid in 88% yield.
[Ru H(d cp e)2]BF 4 (10). A 50 mL Schlenk flask containing
a Teflon-coated magnetic stirring bar was charged with 5
(0.250g, 0.264 mmol) and tetrahydrofuran (20 mL). To this
solution was added HBF4 (40 µL of a 54% solution, Aldrich).
After 10 min, the volatiles were removed in vacuo and the
residue washed with Et2O (2 × 20 mL) and dried in vacuo.
This procedure yields 220 mg (80%) of the product as a yellow
solid. NMR data are the same as those reported for PF6 salt.
[Ru H(d p p p )2]BF 4 (11). In the glovebox, an NMR tube was
charged with 2, C6D6, and 1 equiv of HBF4 and was then fitted
1
with a septum cap. The H and 31P both provide spectroscopic
evidence of the complete conversion to 11 (see Discussion).
[Ru H(d p p b)2]BF 4 (12). A similar procedure as for the
synthesis of 11 was used for 12 but using 3. Complete
conversion was observed by 1H and 31P NMR spectroscopy (see
Discussion).
Resu lts a n d Discu ssion
Ru (H)2(d p p p )2 (2). In an identical fashion as for the
synthesis of 1, but using PPh2(CH2)3PPh2 (dppp), 2 was
isolated as a yellow microcrystalline solid in 84% yield. 1H
NMR (400 MHz, C6D6, 25 °C): -7.60 (m). 31P NMR (161.9
Researchers at Du Pont have recently reported the
use of [RuCl2(COD)]x and NaOH in the isolation of
ruthenium hydride (dihydrogen) complexes, eq 3.21 The
MHz, C6D6, 25 °C): 29.12 (t, J P-P ) 28 Hz), 33.92 (t, J P-P
)
[RuCl2(COD)]x + 2PCy3 + xs NaOH toluene8
27 Hz). Anal. Calcd for C54H54P4Ru: C, 69.89; H, 5.87. Found:
C, 69.92; H, 5.99.
H2
Ru (H)2(d p p b)2 (3). In an identical fashion as for the
synthesis of 1, but using PPh2(CH2)4PPh2 (dppb), 3 was
isolated as a yellow microcrystalline solid in 88% yield. 1H
NMR (400 MHz, C6D6, 25 °C): -9.54 (m). 31P NMR (161.9
MHz, C6D6, 25 °C): 35.81 (m), 50.27 (m). Anal. Calcd for
[Ru(H)2(H2)2(PCy3)2] + 2NaCl + C8H16 (3)
reported experimental conditions required elevated
pressures of hydrogen (69 atm) and prolonged heating
of the toluene/water solution in the presence of a phase-
transfer agent. The use of a strong base was necessary
for complete conversion of Ru-Cl into Ru-H. This
point was recently illustrated in the synthesis of ruthe-
nium hydrido chloride complexes, eq 4.22 This approach
C
55H56P4Ru: C, 70.13; H, 5.99. Found: C, 69.78; H, 6.17.
Ru (H)2(d p p f)2 (4). In an identical fashion as for the
synthesis of 1, but using (PPh2C5H4)2Fe (dppf), 4 was isolated
as an orange microcrystalline solid in 85% yield.
Ru (H)2(d cp e)2 (5). In an identical fashion as for the
synthesis of 1, but using PCy2CH2CH2PCy2 (dcpe), 5 was
isolated as a white microcrystalline solid in 80% yield.
Ru (H)2(d cp m )2 (6). In an identical fashion as for the
synthesis of 1, but using PCy2CH2PCy2 (dcpm), 6 was isolated
as an off-white microcrystalline solid in 54% yield. 1H NMR
(400 MHz, C6H6, 25 °C): -11.49 (m). 31P NMR (161.9 MHz,
C6D6, 25 °C): 66.10 (s). Anal. Calcd for C50H94P4Ru: C, 65.26;
H, 10.29. Found: C, 65.10; H, 10.32. Exact mass (HRMS)
calcd for C50H94P4Ru (M+), 919.5271, found 919.5254.
Ru (H)2(d ep e)2 (7). A 250 mL Schlenk flask containing a
Teflon-coated magnetic stirring bar was charged with NaOH
(1.0 g, 25 mmol). The flask was then taken into the glovebox
where [RuCl2(COD)]x (0.340 g, 1.20 mmol) and PEt2CH2CH2-
PEt2 (depe) (0.500 g, 2.40 mmol) were charged into the reaction
vessel. The vessel was removed from the glovebox and
connected to a Schlenk line where degassed sec-butyl alcohol
(80 mL) was added by cannula. The reaction vessel was sealed
and heated to 80 °C for 2 h. The system was allowed to cool
to room temperature, and degassed water (100 mL) was added
to dissolve the excess NaOH. The orange organic layer was
decanted by cannula into a 200 mL Schlenk, where the
volatiles were removed in vacuo. The product was recrystal-
lized from methanol to yield 0.87 g (70%) of Ru(H)2(depe)2.
Ru (H)2(P Et3)4 (8). In a manner analogous to the procedure
leading to the isolation of 7, 8 was obtained in 60% yield after
recrystallization from methanol.
[RuCl2(COD)]x + 2PCy3 + NEt3 sec-BuOH8
H2
[Ru(H)(Cl)(H2)2(PCy3)2] + HNEt3Cl + C8H16 (4)
suggested that the synthesis of Ru(H)2(PP)2 complexes
might also be possible in this fashion. Initially, reac-
tions were conducted under a hydrogen atmosphere, but
the use of hydrogen sometimes led to the over-reduction
of the ruthenium center. This problem was circum-
vented by the use of alcohols as the hydrogen source in
ruthenium chemistry.8,23 Reactions involving [RuCl2-
(COD)]x, NaOH, and 2 equiv of a chelating phosphine
in sec-butyl alcohol were carried out in the absence of
hydrogen and led to high yields of Ru(H)2(PP)2 com-
plexes, eq 5. This simple process represents a marked
xs NaOH
1/x[RuCl2(COD)]x + 2PP
8
sec-BuOH
Ru(H)2(PP)2 + C8H16 + 2NaCl
PP ) Chelating Phosphine
(5)
improvement on the reported synthetic routes to these
complexes.
(17) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Farnetti, E. J . Chem. Soc.,
Dalton Trans. 1991, 1525-1530.
(21) Beatty, R. P.; Paciello, R. A. U.S. Patent 5,444,778, 1996.
(22) (a) Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R.
H. Organometallics 1997, 16, 3867-3869. (b) Belderrain, T. R.; Grubbs,
R. H. Organometallics 1997, 16, 4001-4003. (c) Wilhelm, T. E.;
Belderrain, T. R.; Nolan, S. P.; Grubbs, R. H. Organomet. Synth. 1997,
in press.
(18) Gusev, D.; Hu¨bener, R.; Burger, P.; Orama, O.; Berke, H. J .
Am. Chem. Soc. 1997, 119, 3716-3731.
(19) Levison, J . J .; Robinson, S. D. J . Chem. Soc A, 1970, 2947-
2954.
(20) Albers, M. O.; Ashworth, T. V.; Oosthuizen, E.; Singleton, E.
Inorg. Synth. 1989, 26, 68-77.
(23) J ohnstone, R. A. W.; Wilby, A. H.; Entwistle, I. D. Chem. Rev.
1985, 85, 129-170.

Ru(II) Dihydride Phosphine Complexes
Organometallics, Vol. 16, No. 25, 1997 5571
The Ru(H)2(PP)2 complexes themselves have demon-
strated catalytic activity, but their cationic derivatives
display greater reactivities.24 Two major routes to the
cationic complexes have been employed. The first series
of reactions leads to the Ru(H)2(PP)2 in three steps, eqs
6-8.15 A number of dihydrides have been isolated by a
solid, and drying affords the products in high yields and
in high enough purity that NMR analysis does not
detect the presence of any side products.
The protonation step of one Ru(H)2(PP)2 product was
carried out with HBF4 and afforded the desired cationic
complex in 80% yield, eq 14.29 All NMR data for 10
RuCl3 + xs DMSO f RuCl2(DMSO)4
(6)
RuCl2(DMSO)4 + 2dppe f RuCl2(dppe)2 + 4DMSO
(7)
RuCl2(dppe)2 + 2NaOEt f Ru(H)2(dppe)2 + 2NaCl
(8)
-
proved identical to that reported for the PF6 salt.
simple substitution reaction with the Ru(H)2(PPh3)4
synthon.25 The example given in eq 9 affords the
product in 61% yield.17 Once the dihydride compounds
Confirmation of the composition of complexes 2 and 3
was further obtained by identification of their protona-
tion product by NMR.24a,29
In view of the important catalytic behavior of ruthe-
nium complexes bearing monodentate phosphines1 and
in order to test the generality of the methodology,
reactions were carried out in an analogous manner with
monodentate phosphines, eq 15. It should be noted that
Ru(H)2(PPh3)4 + 2dcpe f Ru(H)2(dcpe)2 + 4PPh3
(9)
have been isolated, simple protonation with acids af-
fords the cationic monohydride complexes, eq 10.17,26
NaOH
1/x[RuCl2(COD)]x + nPR3 sec-BuOH8
Ru(H)2(PR3)n + C8H16 + 2NaCl
n ) 3; R ) Ph; 88% yield
n ) 4; R ) Et; 60% yield
(15)
The second pathway to complexes of type A is also a
multistep process, eqs 11-13, the last of which involves
direct phosphine substitution from a cationic ruthenium
hydrazine complex.12,27
the new methodology possesses significant advantages
over reported routes where metal hydrides30 (PPh3 case)
and excess phosphine18 (PEt3 case) had to be used, eq
16.
RuCl3‚xH2O + COD f 1/x[RuCl2(COD)]x (11)
[NBu4]BH4
RuCl3‚nH2O + xs PEt3
8 Ru(H)2(PEt3)4 (16)
NH4PF6
[RuCl2(COD)]x + 3NH2NMe2
8
Con clu sion
[(COD)RuH(NH2NMe2)3]PF6 (12)
A simple synthetic procedure that produces a high
yield of high-purity Ru(H)2(PP)2 complexes has been
developed. These complexes can be readily converted
into an important class of hydrogenation catalysts. The
ease of preparation of the [RuCl2(COD)]x starting com-
plex, the low cost of the solvent and base, and the ease
of workup make this methodology quite attractive for
the synthesis of ruthenium hydride complexes. The
generality of the methodology is presently being tested
for other ruthenium and late transition metal com-
plexes.
[(COD)RuH(NH2NMe2)3]PF6 + 2dppb f
[RuH(dppb)2] PF6 + 3NH2NMe2 + COD (13)
The usefulness of the reported methodology should
now become apparent. An air-stable complex, synthe-
sized in air with yields of >85% (eq 11), can be directly
used with sodium hydroxide, the appropriate phosphine,
and sec-butyl alcohol. Reaction times were usually kept
constant at 3 h.28 Addition of degassed water, filtration
of the reaction mixture, a methanol rinse of the collected
Ack n ow led gm en t. The National Science Founda-
tion is gratefully acknowledged for financial support of
this work.
(24) (a) Saburi, M.; Aoyagi, K.; Takahashi, T.; Uchida, Y. Chem. Lett.
1990, 601-604. (b) Farnetti, E.; Graziani, M.; Mezzetti, A.; Del Zotto,
A. J . Mol. Catal. 1992, 73, 147-155. (c) Ogasawa, M.; Saburi, M.
Organometallics 1994, 13, 1911-1917.
OM9706673
(25) A recent report makes use of RuHCl(PPh3)3 as a substitution
precursor, see: Field, L. D.; Wilkinson, M. P. Organometallics 1997,
16, 1841-1845.
(29) Protonation following this protocol was performed for Ru(H)2-
(dppp)2 (2) and Ru(H)2(dppb)2 (3). Spectroscopic data for both cationic
species 11 and 12, respectively, match those reported in ref 24a. These
(26) In a closed system, the complex formed is best formulated as a
dihydrogen adduct of A.
(27) (a) Ashworth, T. V.; Singleton, E. J . Chem. Soc., Chem.
Commun. 1976, 705-706. (b) Ashworth, T. V.; Singleton, E; Hough,
J . J . J . Chem. Soc., Dalton Trans. 1977, 1809-1815.
(28) Reactions often are completed in shorter times, as is apparent
by the dramatic color changes associated with reaction completion.
syntheses were performed using evacuation of volatiles in a last
isolation step; H2 is also removed in this step, as in the synthesis of
10.
(30) Harris, R. O.; Hota, N. K.; Sadavoy, L.; Yuen, J . M. C. J .
Organomet. Chem. 1973, 54, 259-264.