Ruthenium(II) hydrido complexes of 2,6-(diphenylphosphinomethyl)pyridine

Article abstract of DOI:10.1021/om970811k

A series of PNP-ruthenium(II) complexes Ru(OCOMe)₂(PNP) (1), Ru(OCOMe)₂(PNP)-(PPh₃) (2), the monohydrides RuHX(PNP)(PPh₃) (X = OCOMe (3); X = Cl (4)), and dihydride RuH₂(PNP)(PPh₃) (5) (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine) were synthesized and characterized by microanalysis as well as NMR, IR, and mass spectroscopies. The solution dynamics of complex 1 were studied by variable-temperature ¹H and ³¹P{¹H} NMR spectroscopies. The crystal structure of RuHCl(PNP)(PPh₃) (4) was determined by X-ray crystallography, showing that the PNP ligand coordinates the Ru atom in a meridional mode. The hydrido complexes RuH(OCOMe)(PNP)(PPh₃) (3) and RuH₂(PNP)(PPh₃) (5) undergo deuterium exchange reactions with CD₃OD to give substitution of both the hydrides and PNP methylene protons by deuterium. The probable intermediates involved in these exchange processes are molecular dihydrogen complexes of Ru(II).

Full text of DOI:10.1021/om970811k

2470
Organometallics 1998, 17, 2470-2476
Ru th en iu m (II) Hyd r id o Com p lexes of
2,6-(Dip h en ylp h osp h in om eth yl)p yr id in e
Noureddine Rahmouni,†,‡ J ohn A. Osborn,*,† Andre´ De Cian,§ J ean Fischer,§ and
Aziz Ezzamarty‡
Laboratoire de Chimie des Me´taux de Transition et de Catalyse and
Laboratoire de Cristallochimie et Chimie Structurale, URA 424 CNRS, Institut Le Bel,
Universite´ Louis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg Cedex, France, and
Laboratoire de Catalyse, Faculte´ des Sciences Ain Chok, Universite´ Hassan II, BP 5366,
Maaˆrif, Casablanca, Morocco
Received September 12, 1997
A series of PNP-ruthenium(II) complexes Ru(OCOMe)2(PNP) (1), Ru(OCOMe)2(PNP)-
(PPh3) (2), the monohydrides RuHX(PNP)(PPh3) (X ) OCOMe (3); X ) Cl (4)), and dihydride
RuH2(PNP)(PPh3) (5) (PNP ) 2,6-bis(diphenylphosphinomethyl)pyridine) were synthesized
and characterized by microanalysis as well as NMR, IR, and mass spectroscopies. The
1
solution dynamics of complex 1 were studied by variable-temperature H and 31P{1H} NMR
spectroscopies. The crystal structure of RuHCl(PNP)(PPh3) (4) was determined by X-ray
crystallography, showing that the PNP ligand coordinates the Ru atom in a meridional mode.
The hydrido complexes RuH(OCOMe)(PNP)(PPh3) (3) and RuH2(PNP)(PPh3) (5) undergo
deuterium exchange reactions with CD3OD to give substitution of both the hydrides and
PNP methylene protons by deuterium. The probable intermediates involved in these
exchange processes are molecular dihydrogen complexes of Ru(II).
In tr od u ction
variety of transition metals (Ru, Pd, Rh, Ir). This PNP
tridentate system is designed so as to allow meridional
coordination to the metal center, where the C2 sym-
metrical environment of the ligand may be preserved
in octahedral catalytic intermediates. This arrange-
ment allows the substrate to approach and bind along
the C2 axis, thus interacting directly with the substit-
uents on the phosphorus donor atoms and experiencing
the quadrant effect shown in Figure 1. Additionally,
the nitrogen atom should modify the properties of the
resulting complexes and their catalytic reactivities
relative to that found for their triphosphine- or trini-
trogen-based ligands.
We initially investigated the coordination chemistry
of the simplest achiral member of this family, 2,6-bis-
(diphenylphosphinomethyl)pyridine (hereafter desig-
nated as PNP, Figure 1), and reported certain catalytic
properties of the resultant complexes.4 In this paper,
we describe our results concerning the synthesis and
characterization of a new series of ruthenium(II) hy-
drido complexes containing the PNP ligand, including
a structural analysis by X-ray diffraction of one such
hydrido complex.
In recent years, chiral polydentate ligands have
attracted much attention as ligands of transition-metal
catalysts in a variety of asymmetric transformations.1
Thus, several ruthenium diphosphine and triphosphine
complexes have been shown to display rich catalytic
behavior, including high enantioselectivity using chiral
chelating diphosphine ligands2 such as BINAP. We3a,b
and others5-9 have recently developed a new type of
tridentate PNP ligand with an axial element of sym-
metry, and we have studied its coordination to a wide
† Laboratoire de Chimie des Me´taux de Transition et de Catalyse,
Universite´ Louis Pasteur.
‡ Universite´ Hassan II.
§ Laboratoire de Cristallochimie et Chimie Structurale, Universite´
Louis Pasteur.
(1) For example see: (a) Kagan, H. B. Comprehensive Organome-
tallic Chemistry; Wilkinson, G., Stone, F. G. A., Eds.; Pergamon:
Oxford, 1982; Vol. 8. (b) Brunner, H. Angew. Chem., Int. Ed. Engl.
1983, 17, 897-1012. (c) Knowles, W. S. Acc. Chem. Res. 1983, 16, 106-
112. (d) Whitesell, J . K. Chem. Rev. 1989, 89, 1581-1590. (e) Noyori,
R. Asymmetric Catalysis in Organic Synthesis; Wiley: New York, 1994.
(2) Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345 and
references therein.
(3) (a) Sablong, R.; Newton, C.; Dierkes, P.; Osborn, J . A. Tetrahe-
dron Lett. 1996, 37, 4933. (b) Sablong, R.; Osborn, J . A. Tetrahedron
Lett. 1996, 37, 4937.
(4) Barloy, L.; Ku, S. Y.; De Cian, A.; Fischer, J .; Osborn, J . A.
Polyhedron 1997, 16, 291.
Exp er im en ta l Section
(5) J iang, Van Plew, D.; Murtuza, S.; Zhang, X. Tetrahedron Lett.
1996, 37, 797.
Gen er a l Con sid er a tion s. All experiments were carried
out under a nitrogen or argon atmosphere, using a vacuum
line or Vacuum Atmospheres glovebox equipped with a Dri-
Train HE-493 inert gas purifier. 1H (300 MHz) and 31P{1H}
(121.5 MHz, broadband decoupled) NMR spectra were recorded
(6) (a) Giannoccaro, P.; Vasapollo, G.; Sacco, A. J . Chem. Soc., Chem.
Commun. 1980, 1136. (b) Vasapollo, G.; Giannoccaro, P.; Nobile, C.
F.; Sacco, A. Inorg. Chim. Acta 1981, 48, 125. (c) Giannoccaro, P.;
Vasapollo, G.; Nobile, C. F.; Sacco, A. Inorg. Chim. Acta 1982, 61, 69.
(d) Sacco, A.; Giannoccaro, P.; Vasapollo, G. Inorg. Chim. Acta 1984,
83, 125.
(7) (a) Vasapollo, G.; Nobile, C. F.; Sacco, A. J . Organomet. Chem.
1985, 296, 435. (b) Sacco, A.; Vasapollo, G.; Nobile, C. F.; Piergiovanni,
A.; Pellinghelli, M. A.; Lanfranchi, M. J . Organomet. Chem. 1988, 356,
397.
(8) Steffey, B. D.; Miedaner, A.; Maciejewski-Farmer, M. L.; Ber-
natis, P. R.; Herring, A. M.; Allured, V. S.; Carperos, V.; DuBois, D. L.
Organometallics 1994, 13, 4844.
(9) Hahn, C.; Sieler, J .; Taube, R. Chem. Ber. 1997, 130, 939.
S0276-7333(97)00811-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/19/1998

Ru(II) Hydrido Complexes
Organometallics, Vol. 17, No. 12, 1998 2471
pentane, and dried in vacuo. Complex 2 was recrystallized
from CH2Cl2/pentane, giving a yellow microcrystalline product.
Yield: 360 mg, 90%. Anal. Calcd for C54H50NP3Cl2O4Ru: C,
62.25; H, 4.84; N, 1.34; P, 8.92. Found: C, 61.61; H, 4.99; N,
1.19; P, 8.41. 1H NMR δ (298 K, CDCl3, ppm): 7.60-6.87 (m,
38 H, H arom), 4.48 (t, 2 × 2H, CH2), 1.15 (s, 2 × 3H, MeCO2),
5.28 (s, 2 H, CH2Cl2). 31P{1H} NMR (298 K, CDCl3, ppm):
MXX′ spectrum with (δX + δX′) at 40.18 (d, 2 P, PNP); δM 33.78
(t, 1 P, PPh3); J (M,X) ) 30 Hz.
Syn th esis of Ru H(OCOMe)(P NP )(P P h 3) (3). Meth od
I. A solution of PNP (200 mg, 0.420 mmol) in 10 mL of THF
was added dropwise to a solution of RuH(OCOMe)(PPh3)3 (400
mg, 0.421 mmol) in 15 mL of THF. The mixture was stirred
for 3 h, and then the yellow solution obtained was concentrated
in vacuo and excess pentane added. The resulting yellow
precipitate was collected by filtration, washed with pentane
and dried in vacuo. Yield: 320 mg, 80%. Anal. Calcd for
C
51H46NP3O2Ru: C, 68.14; H, 5.16; N, 1.56. Found: C, 67.24;
H, 5.12; N, 1.58. FAB-MS m/z (assignment, relative inten-
sity): 898.1 ([M - H]+, 37), 838.1 ([M - H - OCOMe]+, 25),
636.0 ([M - H - PPh3]+, 100), 576.0 ([M - H - OCOMe -
PPh3]+, 40). IR (Nujol mull, cm-1): ν(Ru-H) 2064. 1H NMR
δ (298 K, C6D6, ppm): 7.87-6.37 (m, 38 H, H arom), 5.30 and
3.74 (2 dt, 2 × 2H, CH2), 2.21 (s, 3H, MeCO2), -18.47 (q, 1H,
Ru-H, J (H,P) ) 22 Hz). 31P{1H} NMR (298 K, C6D6, ppm):
MXX′ spectrum, δM 59.12 (t, 1P, PPh3); δX 30.46 (d, 2P, PNP);
J (M,X) ) 30 Hz.
Meth od II. A solution of Ru(OCOMe)2(PNP)(PPh3) (40 mg,
0.042 mmol) in 10 mL of benzene was transferred in a 50 mL
stainless steel autoclave. After degassing 3 times with H2, the
mixture was maintained at 25 °C under 20 bar of H2 for 2 h.
The resulting yellow solution obtained was concentrated under
vacuo, and excess pentane was added. The resulting yellow
precipitate was collected by filtration and dried in vacuo.
Yield: 35 mg, 93%.
Syn th esis of Ru HCl(P NP )(P P h 3)‚CH2Cl2 (4). Meth od
I. A solution of PNP (200 mg, 0.420 mmol) in 10 mL of THF
was added dropwise to a solution of RuHCl(PPh3)3 (390 mg,
0.422 mmol) in 20 mL of THF. After being stirred for 4 h, the
violet solution turned yellow. The solution was concentrated
in vacuo, and excess pentane was added. The resulting yellow
precipitate was collected by filtration, washed with pentane,
and dried in vacuo. Complex 5 was recrystallized from CH2-
Cl2/pentane, giving an orange microcrystalline product.
Yield: 310 mg, 84%. Anal. Calcd for C50H45NP3Cl3Ru: C,
62.54; H, 4.72; N, 1.46; P, 9.68. Found: C, 63.14; H, 4.73; N,
1.58; P, 9.14. IR (Nujol mull, cm-1): ν(Ru-H) 1987. 1H NMR
δ (298 K, CDCl3, ppm): 7.76-7.70 and 7.34-6.78 (m, 38 H, H
arom), 4.76 and 3.96 (2 dt, 2 × 2H, CH2), -17.26 (q, 1H, Ru-
H, J (H, P) ) 21 Hz), 5.29 (s, 2H, CH2Cl2). 31P{1H} NMR (298
K, CDCl3, ppm): δM 58.09 (t, 1P, PPh3); δX 48.98 (d, 2P, PNP);
J (M,X) ) 30 Hz.
Meth od II. A suspension of LiAlH4 (45 mg, 1.185 mmol)
in 5 mL of THF was added dropwise to a solution of RuCl2-
(PNP)(PPh3) (500 mg, 0.549 mmol) in 20 mL of THF. The
mixture was stirred for 2 h at room temperature. After
addition of ethanol (30 mL), the solution was concentrated and
the resulting yellow solution cooled to -20 °C to give yellow-
orange crystals. Yield: 390 mg, 81%.
F igu r e 1. Quadrant effects of tridentate ligands and the
PNP ligand.
on a Bruker AC300 instrument and referenced to Me4Si and
85% aqueous H3PO4, respectively. FT-IR spectra were re-
corded on a Perkin-Elmer 1600 Series spectrometer on KBr
pellets or in Nujol. FAB-MS spectra and elemental analyses
were carried out by the corresponding facilities at the Chem-
istry Research Centre at Universite´ Louis Pasteur, Strasbourg.
Methylene chloride and acetonitrile were distilled under
nitrogen over calcium hydride; pentane, THF, and benzene
over sodium and benzophenone. Ru2(OCOMe)4,10 RuCl2-
(PPh3)3,11 RuHCl(PPh3)3,12 Ru(OCOMe)2(PPh3)2,13 RuH(OC-
OMe)(PPh3)3,14 RuH2(PPh3)4,15 and PNP16 were prepared fol-
lowing the literature methods.
Syn th esis of Ru (OCOMe)2(P NP ) (1). A solution of PNP
(200 mg, 0.420 mmol) and Ru2(OCOMe)4 (100 mg, 0.228 mmol)
in 50 mL of CH3OH was refluxed for 6 h. After the mixture
was cooled to room temperature, the green solution obtained
was evaporated to dryness, the resulting solid was extracted
with CH2Cl2, and the extracts were filtered to remove excess
Ru2(OCOMe)4. The resulting green solution was concentrated
in vacuo, and on addition of excess Et2O, a crystalline green
product precipitated, which was collected by filtration and
dried under vacuum. Yield: 220 mg, 75%. Anal. Calcd for
C
35H33NP2O4Ru: C, 60.52; H, 4.79; N, 2.02; P, 8.92. Found:
C, 60.47; H, 5.00; N, 2.27; P, 8.89. FAB-MS m/z (assignment,
relative intensity): 636.0 ([M - OAc]+, 90), 576.1 ([M -
2OAc]+, 100). 1H NMR δ (298 K, CD2Cl2, ppm): 8.20-6.4 (m,
23 H, H arom), 4.35 (s, 2 × 2H, CH2), 1.89 (s, 2 × 3H, CH3-
CO2). 31P{1H} NMR (CD2Cl2, ppm): at 298 K δ 28.14 (s, PNP);
at 200 K 2 broad singlets (relative intensities ca. 2:1) at δ 31.76
and 24.56. 31P{1H} NMR (CD3OD, ppm): at 298 K δ 25.54 (s,
PNP); at 200 K 2 broad singlets (relative intensities ca. 9:1)
at δ 29.78 and 23.14.
Syn th esis of Ru (OCOMe)2(P NP )(P P h 3)‚CH2Cl2 (2). A
solution of PNP (200 mg, 0.420 mmol) in 10 mL of THF was
added dropwise to a solution of Ru(OCOMe)2(PPh3)2 (313 mg,
0.420 mmol) in 20 mL of THF. The mixture was stirred for 4
h, and then the yellow-orange solution obtained was concen-
trated in vacuo and excess of pentane added. The resulting
yellow precipitate was collected by filtration, washed with
Syn th esis of Ru H2(P NP )(P P h 3) (5). A solution of PNP
(200 mg, 0.420 mmol) in 10 mL of THF was added dropwise
to a solution of RuH2(PPh3)4 (485 mg, 0.420 mmol) in 20 mL
of THF with stirring. After 1 h, the yellow-orange solution
obtained was concentrated in vacuo and excess pentane added.
The resulting yellow precipitate was collected by filtration,
washed with pentane and dried in vacuo. Yield: 240 mg, 68%.
Anal. Calcd for C49H44NP3Ru: C, 70.00; H, 5.27; N, 1.67.
Found: C, 70.53; H, 4.63; N, 1.72. FAB-MS m/z (assignment,
relative intensity): 839.1 ([M - 2H]+, 100); 576.0 ([M - 2H -
PPh3]+, 50). IR (Nujol mull, cm-1): ν(Ru-H) 1977. 1H NMR
δ (298 K, C6D6, ppm): 7.97-6.21 (m, 38H, H arom), 3.86 (t, 2
(10) Legzdins, P.; Mitchell, R. W.; Rempel, G. L.; Ruddick, J . D.;
Wilkinson, G. J . Chem. Soc. A 1970, 3322.
(11) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 238.
(12) Hallman, B.; MacGarvey, B. R.; Wilkinson, G. J . Chem. Soc. A
1968, 3143.
(13) Mitchell, R. W.; Spencer, A.; Wilkinson, G. J . Chem. Soc., Dalton
Trans. 1973, 846.
(14) Young, R.; Wilkinson, G. Inorg. Synth. 1977, 17, 79.
(15) Young, R.; Wilkinson, G. Inorg. Synth. 1977, 17, 75.
(16) Dahlhoff, W. V.; Nelson, S. M. J . Chem. Soc. A 1971, 2184.

2472 Organometallics, Vol. 17, No. 12, 1998
Rahmouni et al.
Ta ble 1. X-r a y Exp er im en ta l Da ta
× 2H, CH2), -4.87 (q, 2H, Ru-H, J (H, P) ) 19 Hz). 31P{1H}
NMR (298 K, C6D6, ppm): MXX′ spectrum with δM 78.46 (t,
1P, PPh3); δX 70.71 (d, 2P, PNP); J (M,X) ) 31 Hz.
formula
mol wt
C49H43NP3ClRu‚CH2Cl2
960.27
Deu ter iu m Exch an ge Reaction s of 3 an d 5 with CD3OD.
For 3: In an NMR tube complex 3 (0.01 g, 11.12 mmol) was
dissolved in 0.5 mL of CD3OD. The reaction was followed by
1H and 31P NMR spectroscopies. After 1 h, the 1H NMR
spectrum showed peaks at δ (298 K, CD3OD, ppm) 7.68-6.90
(m, 38 H, Harom), 4.57 and 3.94 (2 dt, 2 × 2H, CH2), 1.84 (s,
3H, CH3CO2); the 31P{1H} NMR (298 K, CD3OD, ppm) showed
the following resonances: δM 61.41 (s (br), 1 P, PPh3); δA 51.83
(s (br), 2 P, PNP). The spectra were taken at regular intervals,
and after 144 h, no further changes were observed, i.e., the
following spectra were obtained: 1H NMR δ (298 K, CD3OD,
ppm) 7.68-6.90 (m, 38 H, H arom), 1.84 (s, 3 H, CH3CO2);
31P{1H} NMR (298 K, CD3OD, ppm) δM 61.47 (s (br), 1 P, PPh3);
cryst system
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
color
triclinic
P1h
10.525(3)
13.477(4)
18.350(5)
69.56(2)
79.12(2)
68.44(2)
2262(1)
2
orange
cryst dimens (mm)
0.46 × 0.28 × 0.22
D
calc (g cm-3
)
1.41
F000
984
0.657
0.970/1.000
294
0.710 73
Mo KR graphite-monochromated
Enraf Nonius CAD4
µ (mm-1
)
δX 51.74 (s (br), 2 P, PNP). The FAB-MS of the final product
trans min and max
temp (K)
showed m/z (assignment, relative intensity): 844.8 ([M -
OAc]+, 100), 579.8 ([M - D - OAc - PPh3]+, 25).
wavelength (Å)
radiation
diffractometer
scan mode
For 5: 5 (0.01 g, 11.9 mmol) was dissolved in 0.5 mL of CD3-
OD and syringed into an NMR tube, and the reaction was
followed by both 1H and 31P NMR spectroscopies. After ca. 5
min, the following spectra were obtained: 1H NMR δ (298 K,
CD3OD, ppm) 7.60-6.70 (m, 38H, H arom); 31P{1H} NMR (298
K, CD3OD, ppm): δM 61.89 (t, 1P, PPh3); δX 56.08 (2P, d, PNP);
J (M,X) ) 27 Hz. The exchange reactions had already gone to
completion. The FAB-MS spectrum of the product showed m/z
(assignment, relative intensity): 845.2 ([M - D]+, 100).
Cr ysta llogr a p h ic Da ta Collection a n d Str u ctu r e De-
ter m in a tion of Ru HCl(P NP )(P P h 3)‚CH2Cl2 (4). Single
crystals of 4 (C49H43NP3ClRu‚CH2Cl2, MW ) 960.3) were
obtained as described above. Data were collected at room
temperature using Mo KR graphite-monochromated radiation,
λ ) 0.7107 Å, on a Nonius CAD4-F diffractometer. The orange
compound crystallizes in the triclinic system, space group P1h,
with a ) 10.525(3) Å, b ) 13.477(4) Å, c ) 18.350(5) Å, R )
θ/2θ
hkl limits
-14,14; -18,17; -25,0
θ limits (deg)
no. of data measd
no. of data with I/3σ(I)
weighting scheme
no. of variables
R(F)
2.5/29.97
13 526
8873
4Fo2/(σ2(Fo2) + 0.0064Fo
4
520
0.044
0.066
1.286
0.905
Rw(F)
GOF
largest peak in final
difference (e Å-3
)
resonance at 1.89 ppm assigned to two acetate groups,
which upon cooling to 200 K separates into two singlets
at 2.11 and 1.86 ppm. The 31P{1H} NMR spectrum of
this compound in CD2Cl2 solution at room temperature
exhibits a broad singlet at δ 28.14 ppm, which at 200 K
appears as two separate singlets at δ 31.76 and 24.56
ppm with relative intensities of approximately 2:1. At
ambient temperature, the 31P{1H} NMR spectrum of 1
in a polar solvent, CD3OD, exhibits a broad singlet at δ
25.54 ppm, which at 200 K separates again into two
singlets at δ 29.78 and 23.14 ppm, which now have a
relative intensity of ca. 9:1. The FAB MS spectrum
shows m/z at 636.0, [M - OCOMe]+ (90), and 576.1, [M
- 2OCOMe]+ (100), indicating the presence of mono-
meric species. We propose that two isomers 1a and 1b
exist in equilibrium in solution where the PNP ligand
is coordinated to the metallic center in a tridentate mer
fashion in both isomers. The octahedral isomer, 1a ,
contains both monodentate and bidentate acetate ligands,
whereas 1b is a pentacoordinate cationic species with
a chelating acetate ligand formed by the dissociation of
one acetate ligand (Scheme 1) or perhaps a solvated
hexacoordinate complex. This would account for the
observation that in a polar solvent the equilibrium is
shifted toward 1b.
69.56(2), â ) 79.12(2)°, γ ) 68.44(2)°, V ) 2262.9 Å3, dcalcd
)
1.409 g cm-3, Z ) 2, µ ) 6.568 cm-1. A total number of 13 526
reflections were collected over the range 2° < θ < 29°. Three
standard reflections measured every hour during the data
collection period showed no significant trend. The data were
corrected for Lorentz, polarization, and absorption factors (ψ
scan of 4 reflections). There were 8862 reflections with I >
3σ(I) used. The structure was solved using direct methods.
The CH2Cl2 solvation molecule is disordered over two positions
(ratio 0.7/0.3). Nonsolvent hydrogen-atom positions were
calculated (C-H ) 0.95 Å, B(H) ) 1.3Beqv(C) Å2), solvent
protons were omitted and the proton attached to Ru was
located from a difference map. All hydrogen atoms were
introduced as fixed contributors. For all computations the
Nonius MolEN package17 was used. Crystal data and details
on intensity collection parameters are indicated in Table 1.
Full-matrix least-squares led to the final values of R(F) )
0.044, and Rw(F) ) 0.66.
Resu lts a n d Discu ssion
The synthetic results described in this paper are
shown in Scheme 1.
Syn th esis a n d NMR Stu d ies on Ru (OCOMe)2-
(P NP ) (1). Treatment of Ru2(OCOMe)4 with 1 equiv
of PNP in refluxing methanol for 6 h produces 1 as green
crystals after recrystallization from CH2Cl2/pentane.
Microanalysis is in full agreement with the proposed
formulation of Ru(OCOMe)2(PNP).
The variable-temperature 1H and 31P NMR data show
that rapid exchange occurs between 1a and 1b even at
low temperatures, thereby equilibrating the phosphorus
environments. The high-temperature process observed
in the 1H spectra may involve an exchange between
terminal and chelating acetate ligands in 1a via an
intermediate (η1-OCOMe)2Ru(PNP) species.
Syn th esis a n d Ch a r a cter iza tion of Com p lex Ru -
(OCOMe)2(P NP )(P P h 3) (2). Complex 2 has been
isolated by the reaction between PNP and Ru(OCOMe)2-
The 1H NMR spectrum of 1 in CD2Cl2 solution at room
temperature exhibits a broad singlet for the methyl
(17) Fair, C. K. In MoLEN, An Intelligent System for Crystal
Structure Analysis; Enraf-Nonius: Delft, The Netherlands 1990.

Ru(II) Hydrido Complexes
Organometallics, Vol. 17, No. 12, 1998 2473
Sch em e 1
(PPh3)2 in THF at room temperature and characterized
by spectroscopic techniques.
dride complex RuH(OCOMe)(PNP)(PPh3) (3) can be
synthesized by two methods: either by reaction of PNP
ligand and 1 equiv of RuH(OCOMe)(PPh3)3 in THF at
room temperature or by reaction of complex 2 in benzene
under a H2 pressure (20 bar) in a stainless steel
autoclave. Complex 3 was isolated in good yield and
characterized by spectroscopic techniques.
The 31P{1H} NMR spectrum of 2 in CDCl3 solution
shows an MXX′ system (δX ) 40.18 ppm, 1P, PNP; δM
) 33.78 ppm, 1P, PPh3) with a J (M,X) coupling constant
of 30 Hz, indicating that the triphenylphosphine is in a
cis position to the two phosphorus atoms of the PNP
1
ligand. The H NMR spectrum exhibits a singlet at δ
The IR spectrum exhibits an absorption with weak
intensity at ν(Ru-H) ) 2064 cm-1, assigned to a
terminal hydride ligand. The31P{1H} NMR spectrum
in C6D6 solution of 3 shows an MXX′ system (δX ) 30.46
ppm, 2P, PNP; δM ) 59.12 ppm, 1P, PPh3) with a J (M,X)
coupling constant of 30 Hz, indicating that the PPh3
1.15 ppm for the methyl groups of the two acetate
ligands and a virtual triplet at δ 4.48 ppm attributed
to the methylene protons on the PNP ligand. This
triplet results from an AA′XX′ system where each proton
is virtually coupled to the two equivalent phosphorus
4
nuclei (2J HP + J HP′ ) 8.7 Hz). Such a situation has
1
ligand is cis to the PNP ligand. The H NMR spectrum
been frequently described in the literature concerning
other PNP coordination compounds7,8 and is character-
istic of a meridional coordination, where the two protons
of each CH2 moiety are equivalent. Consequently, the
molecule possesses a plane of symmetry that includes
the three donor atoms of PNP, so that PPh3 necessarily
lies trans to the pyridine nitrogen.
exhibits a singlet at δ 2.21 ppm attributed to the methyl
of the acetate group and a high-field quartet at δ )
-18.47 ppm, which confirms the presence of a terminal
metal hydride. The observed multiplicity originates
from the nearly identical J (H,P) coupling of 22 Hz to
the cis phosphorus atoms of PPh3 and to the two
equivalent PPh2 groups of the PNP ligand. However,
The molecular structure of analogous complex RuCl2-
(PNP)(PPh3) has been previously determined by X-ray
diffraction methods4 and shows that the PNP ligand
coordinates to the metallic center in a tridentate me-
ridional mode with the triphenylphosphine ligand trans
to the pyridine nitrogen, the two chlorides lying mutu-
ally trans; 2 clearly has an analogous structure.
Syn th esis an d Ch ar acter ization of Hydr ide Com -
p lex, Ru H(OCOMe)(P NP )(P P h 3) (3). The monohy-
1
the PNP methylene signals now appear in the H NMR
spectrum as a set of two doublets of triplets centered
at δ 5.30 and 3.74 ppm, corresponding to an AA′BB′XX′
system. The two methylene protons borne by each
carbon are now unequivalent, with a gem coupling
constant of 15.9 Hz, and virtually coupled to the
phosphorus atoms with different coupling constants
4
(2J HP + J HP′ ) 8.6 and 9.4 Hz). Further, the reaction

2474 Organometallics, Vol. 17, No. 12, 1998
Rahmouni et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg)
Ru-H
1.46
Ru-N(1)
2.150(2)
1.354(3)
1.367(3)
1.839(3)
1.853(3)
Ru-Cl
2.5795(7)
2.3070(6)
2.3077(6)
2.2881(6)
C(14)-N(1)
C(18)-N(1)
C(19)-P(2)
C(13)-P(1)
Ru-P(1)
Ru-P(2)
Ru-P(3)
Cl-Ru-H
178
80
96
88
81
34
101.32(2)
84.55(6)
90.08(2)
98.34(2)
81.32(6)
155.97(3)
99.78(2)
78.77(6)
176.60(6)
99.38(2)
C(1)-P(1)-H
90
90
34
139
123
78
101.0(1)
103.3(1)
99.0(1)
119.8(2)
121.3(2)
109.7(2)
102.1(1)
104.6(1)
98.1(1)
117.6(2)
P(1)-Ru-H
N(1)-Ru-H
P(2)-Ru-H
P(3)-Ru-H
Ru-P(1)-H
Cl-Ru-P(1)
Cl-Ru-N(1)
Cl-Ru-P(2)
Cl-Ru-P(3)
P(1)-Ru-N(1)
P(1)-Ru-P(2)
P(1)-Ru-P(3)
N(1)-Ru-P(2)
N(1)-Ru-P(3)
P(2)-Ru-P(3)
C(13)-P(1)-H1
Ru-P(3)-H1
C(32)-P(3)-H
C(38)-P(3)-H
C(44)-P(3)-H
C(1)-P(1)-C(7)
C(1)-P(1)-C(13)
C(7)-P(1)-C(13)
P(1)-C(1)-C(6)
P(1)-C(1)-C(2)
C(18)-C(19)-P(2)
C(19)-P(2)-C(20)
C(19)-P(2)-C(26)
C(20)-P(2)-C(26)
P(2)-C(20)-C(21)
there are no standard deviations for bond distances and
angles involving this proton (Table 2). In general, the
bond lengths and angles are unexceptional, but it is
interesting to compare the structure of 4 with that found
for RuCl2(PNP)(PPh3) which we have previously re-
ported.4 Although the two structures are very similar,
some differences are apparent, in particular the Ru-
Cl bond is considerably longer in 4, being 2.579 Å (cf.
2.412 Å in the dichloride complex), as a result of a
ground-state trans effect of the hydride ligand. Further,
all Ru-P bonds are shorter in 4 by ca. 0.06 Å, and some
of the bond angles are correspondingly larger, e.g., the
P-Ru-Cl angles have increased by 5-12°. Little
difference is found for the P-Ru-P angle of the PNP
ligand in the two complexes (156° vs 157.9°). Intu-
itively, electrostatic considerations would lead to the
prediction of shorter Ru-P bonds in the dichloride Ru
complex, which is not observed. Apparently, the shorter
Ru-Cl bonds found in this latter complex must provide
greater steric repulsion and cause the lengthening of
the Ru-P bonds. These results are similar to those
obtained by Bianchini18,19 in the closely related com-
plexes mer-RuCl2[nPrN(CH2CH2PPh2)2](PPh3) and mer-
RuHCl[(nPr)N(CH2CH2PPh2)2](PPh3).
F igu r e 2. ORTEP drawing of RuHCl(PNP)(PPh3)‚CH2Cl2.
Hydrogen atoms and CH2Cl2 are omitted.
of 3 with CDCl3 on heating for 2 h at 60 °C yields 7, as
1
confirmed by H and 31P NMR.
Syn th esis an d Ch ar acter ization of Hydr ide Com -
p lex Ru HCl(P NP )(P P h 3) (4). The monohydride com-
plex RuHCl(PNP)(PPh3) (4) was also synthesized by two
methods: either by reaction directly between PNP and
1 equiv of RuHCl(PPh3)3 in THF at room temperature
or by reacting RuCl2(PNP)(PPh3) in THF at room
temperature with excess LiAlH4. An orange microcrys-
talline crop of 4 was obtained by recrystallization from
CH2Cl2/pentane and characterized by spectroscopic
techniques. The IR spectrum exhibits an absorption
with weak intensity at ν(Ru-H) ) 1987 cm-1, assigned
to a terminal hydride ligand. The 31P{1H} NMR spec-
trum of 4 in CDCl3 solution shows an MXX′ system (δX
) 48.98, 2P, PNP; δM ) 58.09 ppm, 1P, PPh3) with a
J (M,X) coupling constant of 30 Hz, again indicating a
mer coordination geometry for the PNP ligand with
PPh3 trans to pyridine. The 1H NMR spectrum in high-
field region shows a quartet at δ -17.26 ppm, which
confirms the presence of a terminal hydride (J (H,P) )
21 Hz). The PNP methylene signals appear as a set of
two doublets of triplets centered at 4.76 and 3.96 ppm,
corresponding to an AA′BB′XX′ system. The two me-
thylene protons borne by each carbon are not equivalent,
and a gem coupling constant of 15.9 Hz is observed, each
proton is virtually coupled to the phosphorus atoms with
slighly different coupling constants (2J HP + 4J HP′ ) 7.2
and 9.2 Hz).
Syn th esis a n d Ch a r a cter iza tion of Dih yd r id o
Com p lex Ru H2(P NP )(P P h 3) (5). The dihydride com-
plex 5 was prepared by addition of 1 equiv of PNP to
RuH2(PPh3)4 in THF. The IR spectrum exhibits an
absorption of medium intensity at ν(Ru-H) ) 1977
cm-1, which is assigned to the presence of terminal
hydrides. 31P{1H} NMR of 5 in C6D6 solution shows an
MXX′ system (δX ) 70.71 ppm, 2P, PNP; δM ) 78.46
ppm, 1P, PPh3), and a J (M,X) coupling constant of 31
Hz indicates that the PPh3 ligand is cis to the P atoms
1
X-r a y Diffr a ction Stu d y of 4. An ORTEP plot of 4
is shown in Figure 2. Selected bond distances and angles
are given in Table 2. The monohydride 4 is monomeric
with a distorted octahedral geometry around the ruthe-
nium and confirms that the PNP ligand is coordinated
to the metallic center in a tridentate meridional mode,
with the triphenylphosphine ligand trans to the nitrogen
atom of the pyridine group. The hydride ligand is trans
to the chloride ligand with Ru-H ) 1.46 Å. Ru-H was
located in a difference map but not refined. Therefore,
of the PNP ligand. The H NMR spectrum exhibits a
single resonance attributed to the methylene protons
2
of the PNP ligand as a triplet at 3.86 ppm, with J HP
+
4J HP′ ) 6.5 Hz. The quartet signal at high field δ -4.87
ppm (J (H,P) ) 19 Hz), therefore, must result from the
two hydride ligands being in a trans arrangement. The
(18) Bianchini, C.; Masi, D.; Peruzzini, M.; Romerosa, A.; Zanobini,
F. Acta Crystallogr. 1995, C15, 2514.
(19) Bianchini, C.; Innocenti, P.; Masi, D.; Peruzzini, M.; Zanobini,
F. Gaz. Chim. Ital. 1992, 122, 461.

Ru(II) Hydrido Complexes
Organometallics, Vol. 17, No. 12, 1998 2475
Sch em e 2
possibility of a 5 being a molecular dihydrogen com-
pound would seem to be excluded since the CH2 reso-
nances would not be equivalent. trans-Dihydrido com-
plexes are rare but not unknown, and the pronounced
reactivity of 5 may result from this rather rare stereo-
chemical arrangement.
Rea ction s of Hyd r id e Com p lexes 4 a n d 5: Deu -
ter iu m Exch a n ge Rea ction s w ith CD3OD. The
dihydride complex RuH2(PNP)(PPh3) (5) reacts im-
mediately in CD2Cl2 or CDCl3, yielding the monohydride
complex 4 by substitution of one hydride with a chloride
ligand. Moreover, a very rapid reaction of 5 occurs at
ambient temperature in a CD3OD solution. After a few
minutes, 1H NMR studies of the dihydride complex show
the disappearance of the resonances due to the hydrides
but more surprisingly the protons of the PNP methyl-
enic groups have also been totally replaced by deuterons.
No exchange with aromatic protons is detected. Growth
of the CD3OH peak in the 1H NMR confirms that
exchange has occurred with the O-D function of the
CD3OD. The IR spectrum shows the disappearance of
the ν(Ru-H) vibration, but the resultant Ru-D absorp-
tion could not be observed due to it overlapping with
strong pyridine vibrations. However, a FAB mass
spectrum study of the resultant complex 6 shows a peak
at m/z ) 845.2 corresponding to M - D+, where M is
5-d6, showing that the exchange of six hydrogens by
deuterium has taken place.
F igu r e 3. 1H NMR signals of the PNP methylene protons
of RuH(OAc)(PNP)(PPh3) in CD3OD at ambient tempera-
ture; (a) after 1 h; (b) after 30 h; (c) after 144 h.
The monohydride complex RuH(OAc)(PNP)(PPh3) (3)
also displays a similar behavior in CD3OD but the H/D
exchange is much slower (Scheme 2). Analysis by H
scribed here. It is clear that two separate processes are
involved: the exchange with the Ru-H function which
is fast for both complexes and the slow exchange with
the CH2 groups which is considerably faster for the
dihydrido species 5 than for the monohydrido species
3.
In the exchange process involving the Ru-H function,
it would seem highly unlikely that the hydride ligand
would be removed as a proton in these electron-rich
complexes, particularly by a relatively weak base such
as methanol. It is known, however, that certain metal
hydride complexes can be protonated by alcohols directly
on the hydride ligand to form molecular dihydrogen
1
NMR (see Figure 3) shows the decrease of the hydride
resonance over a few minutes to give RuD(OAc)(PNP)-
(PPh3), 3a , but the total exchange of the CH2 groups to
yield RuD(OAc)(PNP-d4)(PPh3), 3b, is only complete
1
after ca. 6 days, with a concomitant increase of the H
resonance of CD3OH. The IR spectrum also showed the
disappearance of the ν(Ru-H) vibration.
The deuterium exchange reactions of CD3OD were
only observed with the hydride complexes 3 and 5, no
exchange being detected for the other compounds de-

2476 Organometallics, Vol. 17, No. 12, 1998
Rahmouni et al.
unlikely for stereochemical reasons. The most feasible
explanation for this exchange is that if a dihydrogen
complex is formed in low concentration in solution as
discussed above, the resultant MeO- present would then
deprotonate (reversibly) the methylene protons. The
deprotonation of a methylene group on PNP coordinated
to Pt(II) and Pd(II) by MeO- has been observed.7b Since
5 is more basic than 3, the methylene proton exchange
would be expected to occur more readily for this dihy-
drido species 5 as more dihydrogen complex and MeO-
would be formed in solution. In summation, these
exchange processes would appear to be most reasonably
explained by the formation of intermediate Ru(II) di-
hydrogen complexes but confirmation of this proposal
must await further experimentation.
F igu r e 4.
complexes.20 Such a dihydrogen intermediate is prob-
ably reversibly formed by the same mechanism in the
exchange process observed here (Figure 4a), which
would allow rapid exchange at the hydride ligand.
Although we have not observed such an intermediate,
very recently stable Ru(II) dihydrogen complexes closely
similar to those suggested here have been reported.21
An alternative mechanism where exchange takes place
by a four-center interaction, equivalent to a σ-bond
metathesis reaction, between the O-D bond of the
alcohol and the Ru-H bond (Figure 4b), however,
cannot be totally excluded. Such an intermediate or
transition state would avoid the charge separation
involved in the formation of MeO- and the intermediate
cationic dihydrogen complex and may explain the rapid-
ity of the exchange process. Labeling experiments and
studies using more acidic and sterically encumbered
alcohols will be necessary to clarify this point.
Con clu sion s
The above complexes have been synthesized in order
to test the activity of the Ru-PNP systems as catalysts
in a variety of reactions, particularly in the hydrogena-
tion of olefins, ketones, and imines. Our preliminary
results using the hydrido complexes 3 and 5 are very
promising. Such studies are the prelude to the synthe-
sis and study of the analogue compounds containing
chiral PNP ligands, which will be the subject of a
forthcoming publication.
Ack n ow led gm en t. We thank A. A. Bahsoun and R.
Gauvin for helpful contributions, N. Kyritsakas for aid
in the X-ray analysis, and a referee for an important
suggestion. We thank the C.N.R.S. for financial support
and the Morroccan Government for a research leave
accorded to N. Rahmouni.
The methylene protons on the PNP ligand coordinated
to Ru(II) are relatively acidic, since they are attached
to a phosphonium center. Although we observe the
deuterium incorporation in these methylene protons
only with the hydrido complexes, direct exchange of the
CH2 groups with the Ru-D formed would appear
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, displacement parameters, bond distances, and
bond angles (20 pages). Ordering information is given on any
current masthead page.
(20) See, for example: Bampos, N.; Field, L. D. Inorg. Chem. 1990,
29, 587.
(21) J ia, G.; Lee, H. M.; Williams, I. D.; Lau, C. P.; Chen, Y.
Organometallics 1997, 16, 3941.
OM970811K