Reactions of an amido hydrido complex of osmium, OsH(NHCMe 2CMe2NH2)(PPh3)2: HX addition, HX transfer, and ketone H2 Hydrogenation

Article abstract of DOI:10.1021/om048998k

Summary: The new amido complex OsH(NHCM₂CMe₂ NH ₂(PPh₃)₂ (2) reacts with weak acids HX to give complexes OsHX(tmen)(PPh₃) (1; X = Cl, 3; X = NCCHCN; and X = H; tmen = NH₂CM₂

Full text of DOI:10.1021/om048998k

Organometallics 2005, 24, 479-481
479
Reactions of an Amido Hydrido Complex of Osmium,
OsH(NHCMe2CMe2NH2)(PPh3)2: HX Addition, HX
Transfer, and Ketone H2 Hydrogenation
Sean E. Clapham and Robert H. Morris*
Department of Chemistry, University of Toronto, 80 St. George Street, Toronto,
Ontario M5S 3H6, Canada
Received December 16, 2004
Scheme 1. Synthesis of Complex 2 and Structures
of 1 and 2 from X-ray Diffraction Studiesa
Summary: The new amido complex OsH(NHCMe2CMe2-
NH2)(PPh3)2 (2) reacts with weak acids HX to give
complexes OsHX(tmen)(PPh3)2 (1; X ) Cl, 3; X )
NCCHCN; and X ) H; tmen ) NH2CMe2CMe2NH2) and
is an active ketone hydrogenation catalyst. HX is com-
pletely transferred from Os to Ru in the reactions of the
amido complex RuH(NHCMe2CMe2NH2)(PPh3)2 with
complexes 1 and 3.
Ruthenium amido hydrido complexes have been iden-
tified as active catalysts for the H2 hydrogenation and
asymmetric hydrogenation of ketones and imines.1-3 In
this paper we make an initial comparison of the proper-
ties of the title osmium amido hydrido complex 2 with
those4 of the reported ruthenium analogue RuH-
(NHCMe2CMe2NH2)(PPh3)2 (4)1 as both a ketone hy-
drogenation catalyst and as a compound reactive toward
weak acids. The reactivity of other late-transition-metal
amido complexes toward weak acids has been studied5-9
and is important in catalytic conjugate addition reac-
tions.10 We also report a novel HX transfer reaction that
promises to allow us to rank the reactivity of amido
groups on different metals.
a Most of the phenyl atoms have been removed for clarity.
ligands and toward the less bulky diamine ligand. The
1
triplet at -20.9 ppm in the hydride region of the H
NMR spectrum and the singlet observed at 17.9 ppm
in the 31P{1H} NMR spectrum suggest that this struc-
ture is maintained in solution. The dehydrohalogenation
of 1 by reaction with potassium tert-butoxide produces
the amido hydrido complex OsH(NHCMe2CMe2NH2)-
(PPh3)2 (Scheme 1). A broad peak at -23.7 ppm in the
1H NMR and two broad peaks at 29.8 and 27.1 ppm in
the 31P{1H} NMR indicate that the complex is fluxional
at room temperature with magnetically inequivalent
phosphorus nuclei. The X-ray crystal structure of 2
(Scheme 1) is almost the same as the structure of the
previously reported ruthenium analogue 4: e.g. Os1d
N2 ) 1.958(3) Å, Os1-N1 ) 2.181(2) Å, and P2-Os1-
N1 ) 165.97(8)° vs RudN ) 1.967(2) Å, Ru-N )
2.176(1) Å, and P-Ru-N ) 164.98(5)°.1 The geometry
around osmium in 2 is best viewed as distorted trigonal
bipyramidal with axial atoms N1 and P2 and equatorial
atoms N2, P1, and H1Os. The amido nitrogen N2 is
trigonal planar and positioned for optimum dative pπ-
(N)fdπ(Os) bonding. This π bonding distorts the equa-
torial geometry from trigonal to Y-shaped with a small
H1Os-Os1-P1 angle (80.3°).12 As expected, the os-
mium-amido bond is significantly shorter than the
osmium-amine bond.
The complex 2 is generated in two steps from OsHCl-
11
(PPh3)3 by first reacting it with 2,3-diamino-2,3-
dimethylbutane to give OsHCl(tmen)(PPh3)2 (1; tmen
) NH2CMe2CMe2NH2). The X-ray crystal structure
(Scheme 1) has a distorted-octahedral geometry with
trans hydride and chloride, cis phosphines, and cis
amine ligands. The smaller Cl-Os-N angles of 80.78-
(12) and 82.95(12)° and the larger Cl-Os-P angles of
96.00(5) and 106.65(5)° indicate that the chloride ligand
is moved away from the bulky triphenylphosphine
* To whom correspondence should be addressed. E-mail:
rmorris@chem.utoronto.ca. Fax: (416) 978-6962.
(1) Abdur-Rashid, K.; Clapham, S. E.; Hadzovic, A.; Harvey, J. N.;
Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2002, 124, 15104-15118.
(2) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Organometallics
2000, 19, 2655-2657.
(3) Sandoval, C. A.; Ohkuma, T.; Mun˜iz, K.; Noyori, R. J. Am. Chem.
Soc. 2003, 125, 13490-13503.
(4) Clapham, S. E.; Lough, A. J.; Rasool, N.; Zimmer-De Iuliis, M.;
Morris, R. H. Manuscript in preparation.
(5) Fulton, J. R.; Sklenak, S.; Bouwkamp, M. W.; Bergman, R. G. J.
Am. Chem. Soc. 2002, 124, 4722-4737.
(6) Fox, D. J.; Bergman, R. G. Organometallics 2004, 23, 1656-1670.
(7) Conner, D.; Jayaprakash, K. N.; Wells, M. B.; Manzer, S.;
Gunnoe, T. B.; Boyle, P. D. Inorg. Chem. 2003, 42, 4759-4772.
(8) Eckert, N. A.; Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Inorg.
Chem. 2004, 43, 3306-3321.
Like the ruthenium analogue 4, the new osmium
amido complex 2 is an active ketone hydrogenation
catalyst. With an acetophenone concentration of 0.17
M in benzene, a ratio of acetophenone to 2 of 347:1, and
(9) Soper, J. D.; Bennet, B. K.; Lovel, S.; Mayer, J. M. Inorg. Chem.
2001, 40, 1888-1893.
(10) Murata, K.; Konishi, H.; Ito, M.; Ikariya, T. Organometallics
2002, 21, 253-255.
(12) Riehl, J. F.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organome-
tallics 1992, 11, 729-737.
(11) Ferrando, G.; Caulton, K. G. Inorg. Chem. 1999, 38, 4168-4170.
10.1021/om048998k CCC: $30.25 © 2005 American Chemical Society
Publication on Web 01/14/2005

480 Organometallics, Vol. 24, No. 4, 2005
Communications
the mild conditions of 5 atm of hydrogen and 20 °C, the
TOF continuously increases, reaching a maximum of 0.4
s-1 with 98% conversion to 1-phenylethanol in 20 min.
Under the same conditions using the ruthenium catalyst
4, the TOF continuously decreases from an initial
maximum TOF of 1 s-1, achieving 99% conversion in
20 min. The differences in the kinetic behavior and the
mechanism of hydrogenation are under study. The
hydrido chloro complex 1 is a precatalyst that is
activated by reaction with KOtBu. This combination can
be used to hydrogenate neat acetophenone to 1-phe-
nylethanol under the mild conditions of 1 atm of
dihydrogen and room temperature. Reported osmium
catalysts for the hydrogenation of ketones require
higher temperatures (>80 °C).13,14
Like the ruthenium analogue 4,1 complex 2 in benzene
under 1 atm of H2(g) splits dihydrogen, a very weak acid
with pKR
> 44,15 into a hydride on osmium and a
THF
proton on the nitrogen of the diamine ligand, to produce
the reactive trans-dihydride complex trans-OsH2(tmen)-
(PPh3)2. This has a triplet at -6.8 ppm (JPH ) 12 Hz)
Figure 1. X-ray crystal structure of 3. Some atoms have
been removed for clarity.
1
for the hydride in the H NMR spectrum and a singlet
Scheme 2. Transfer of HX from
OsHX(tmen)(PPh3)2 to 4 (X ) Cl, NCCHCN)
in the 31P{1H} spectrum at 36.8 ppm.
THF
Malononitrile is a weak acid with pKR
) 24.15 It
reacts with 2 according to eq 1 to give OsH(NCCHCN)-
(tmen)(PPh3)2 (3). The triplet at -15.9 ppm in the
hydride region of the 1H NMR spectrum and the singlet
at 19.7 ppm in the 31P{1H} NMR spectrum indicate
equivalent phosphorus atoms. The ν(C-N) signal at
2126 cm-1 is lower than that reported for the carbon-
bound dicyanomethyl complex Co(salpn)(CH(CN)2)(py)
(salpn ) the dianion of N,N′-bis(salicylideneimine)-1,2-
propane), suggesting that the NCCHCN ligand is bonded
via nitrogen to osmium in 3.16,17 Indeed, the X-ray
crystal structure of 3 (Figure 1) is the first to show a
dicyanomethyl ligand that is not carbon-bonded to a
transition metal. A structure has been reported for a
dimeric palladium complex with two dicyanomethyl
ligands that bridge by forming Pd-N and Pd-C bonds.18
We conclude that the negative charge on the dicyanom-
ethyl ligand in 3 is delocalized over the entire ligand
on the basis of the following bond angle and distance
data. The central carbon, C9, has a planar geometry
with a C7-C9-C8 angle of 123.3(4)°. The C-N bonds
C7-N4 ) 1.156(5) Å and C8-N3 ) 1.151(4) Å are
similar, as are the C-C bonds C7-C9 ) 1.389(6) Å and
C8-C9 ) 1.388(5) Å. In the crystal lattice the molecules
of 3 occur in hydrogen-bonded pairs with the terminal
nitrogen of the dicyanomethyl ligand of one molecule
forming a hydrogen bond with the amine proton of a
partner molecule and vice versa.
With analogous amido complexes of ruthenium and
osmium and their adducts in hand, we were interested
in determining, by competition experiments, which
amido complex has the higher affinity for the weak acid
HX. A slight excess of 1 was added with 4 to an NMR
tube, and both were dissolved in benzene-d6. The
reaction mixture was observed by 1H and 31P{1H} NMR.
Over a period of 24 h all of 4 was converted to RuHCl-
(tmen)(PPh3)2, while 1 was converted to 2 (Scheme 2, X
) Cl). The excess 1 remained at the end of this period.
Similarly, after a slight excess of 3 was added to an
NMR tube with 4 dissolved in benzene-d6, all of 4 was
converted to trans-RuH(NCCHCN)(tmen)(PPh3)2 4 while
3 was converted to 2 within 20 min. It is somewhat
surprising that HX is transferred completely from
osmium to ruthenium. With the greater extent of their
valence orbitals, third-row transition metals generally
form stronger bonds than second-row transition metals.
The formation of a stronger OsdN bond versus RudN
(13) Rosales, M.; Gonzalez, A.; Mora, M.; Nader, N.; Navarro, J.;
Sanchez, L.; Soscun, H. Transition Met. Chem. 2004, 29, 205-211.
(14) Sanchez-Delgado, R. A.; Rosales, M.; Esteruelas, M. A.; Oro,
L. A. J. Mol. Catal. A: Chem. 1995, 96, 231-243.
(15) Abdur-Rashid, K.; Fong, T. P.; Greaves, B.; Gusev, D. G.;
Hinman, J. G.; Landau, S. E.; Morris, R. H. J. Am. Chem. Soc. 2000,
122, 9155-9171.
(16) Bailey, N. A.; Higson, B. M.; McKenzie, E. D. Inorg. Nucl. Chem.
Lett. 1971, 7, 591.
(17) Baddley, W. H.; Choudhury, P. J. Organomet. Chem. 1973, 60,
C74-C76.
(18) Ruiz, J.; Rodriguez, V.; Lopez, G.; Casabo, J.; Molins, E.;
Miravitlles, C. Organometallics 1999, 18, 1177-1184.

Communications
Organometallics, Vol. 24, No. 4, 2005 481
bond appears to drive these novel HX transfer reactions.
It is known that 5d metals form stronger multiple bonds
than 4d metals.19,20 This will be checked in future
calculations.
In summary, the new osmium complex 1 with added
base, or complex 2 without added base, actively cata-
lyzes the hydrogenation of ketones under milder condi-
tions than for other known osmium catalysts. Complex
3 has a novel nitrogen-bonded dicyanomethyl ligand.
The complexes 1 and 3 display the interesting behavior
of donating HCl and CH2(CN)2, respectively, to the
ruthenium analogue of 2. This may be attributed to a
strong 2pπf5dπ bond formed between the amido nitro-
gen and osmium(II).
Acknowledgment. We thank the NSERC and the
donors of the Petroleum Research Fund, administered
by the American Chemical Society, for funding this
research. We thank Dr. D. Song for his work in acquir-
ing the X-ray data and Dr. K. Abdur-Rashid for pre-
liminary results.
Supporting Information Available: Text and a figure
giving experimental details and a CIF file giving X-ray
crystallographic data. This information is available free of
charge via the Internet at http://pubs.acs.org.
(19) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1988.
(20) Tucci, G. C.; Donahue, J. P.; Holm, R. H. Inorg. Chem. 1998,
37, 1602-1608.
OM048998K