Synthesis and structure of new osmium-PCP complexes. Osmium-mediated C-C bond activation

Article abstract of DOI:10.1021/om000878z

The new complex Os{1,3-(ⁱPr₂PCH₂)₂ C₆H₃}(Cl)(PPh₃) (2) was obtained from the reaction between the diphosphine {1,3-(ⁱPr₂ PCH₂)₂C₆

Full text of DOI:10.1021/om000878z

Organometallics 2001, 20, 1719-1724
1719
Articles
Syn th esis a n d Str u ctu r e of New Osm iu m -P CP
Com p lexes. Osm iu m -Med ia ted C-C Bon d Activa tion
Re´gis M. Gauvin,† Haim Rozenberg,‡ Linda J . W. Shimon,‡ and David Milstein*,†
Departments of Organic Chemistry and Chemical Services, The Weizmann Institute of Science,
Rehovot, 76100, Israel
Received October 13, 2000
The new complex Os{1,3-(iPr2PCH2)2C6H3}(Cl)(PPh3) (2) was obtained from the reaction
between the diphosphine {1,3-(iPr2PCH2)2C6H4} (1) and OsCl2(PPh3)3. 2 reacts with H2 to
yield the dihydrido species Os{1,3-(iPr2PCH2)2C6H3}(H)2(Cl)(PPh3) (3). Addition of 1 equiv
of carbon monoxide to 2 led to the formation of Os{1,3-(iPr2PCH2)2C6H3}(CO)(Cl)(PPh3) (4),
while in the presence of excess CO, the bis-carbonyl complex Os{1,3-(iPr2PCH2)2C6H3}(CO)2-
(Cl) (5) was formed. Both 2 and 5 were structurally characterized by X-ray diffraction studies.
The reaction of OsCl2(PPh3)3 (under hydrogen pressure) and OsHCl(PPh3)3 with the
diphosphine {1,3,5-(CH3)3-2,6-(iPr2PCH2)2C6H} (6) led to the formation of the C-C activation
products Os{3,5-(CH3)-2,6-(iPr2PCH2)2C6H}(H2)(Cl)(PPh3) (7) and Os{3,5-(CH3)-2,6-(iPr2-
PCH2)2C6H}(Cl)(PPh3) (8), respectively.
In tr od u ction
plexes have been reported.5 Following our interest in
the exploration of the chemistry of the PCP complexes,
in particular regarding their potential in the field of
strong bonds activation,6 we describe here the synthesis
and structure of new osmium complexes bearing the
PCP ligand {1,3-(iPr2PCH2)2C6H3}-, as well as our first
results regarding the intramolecular activation of car-
bon-carbon bonds with osmium.
Since their first use by Shaw and co-workers in the
1970s,1 pincer ligands bearing a PCP donor set have
attracted considerable attention. Upon coordination to
transition metals, the rigid bis-chelated framework may
confer on such complexes interesting reactivities, as well
as allow the stabilization of uncommon species.2
Efficient catalytic transformations by PCP-containing
systems have also been reported.3 Although a variety
of late transition metals have been complexed with PCP
ligands, of the iron triad only the ruthenium derivatives
have been the subject of thorough studies.4 To our
knowledge, only two examples of osmium-PCP com-
Resu lts a n d Discu ssion
The complex Os{1,3-(iPr2PCH2)2C6H3}(Cl)(PPh3) (2)
was obtained as a green solid from the reaction between
the diphosphine {1,3-(iPr2PCH2)2C6H4} (1) and the
7
dichloride complex OsCl2(PPh3)3 (Scheme 1). The cy-
clometalation occurs at room temperature and requires
the use of triethylamine as a base. In its absence, the
reaction proceeds sluggishly.
The geometry of complex 2 in the solid state was
determined by an X-ray diffraction study (Figure 1).
The structure of the compound, similar to the one
recently reported for Os{1,3-(Ph2PCH2)2C6H3}(Cl)-
(PPh3),5a is of the distorted square-pyramidal type. The
* Corresponding author. E-mail: david.milstein@weizmann.ac.il.
† Department of Organic Chemistry.
‡ Department of Chemical Services.
(1) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020.
(2) Some examples: (a) Vigalok, A.; Shimon, L. J . W.; Milstein, D.
J . Am. Chem. Soc. 1998, 120, 477. (b) Vigalok, A.; Rybtchinski, B.;
Shimon, L. J . W.; Ben-David Y.; Milstein, D. Organometallics 1999,
18, 895. (c) Rybtchinski, B.; Ben-David Y.; Milstein, D. Organometallics,
1997, 16, 3786. (d) van der Boom, M. E.; Ben-David, Y.; Milstein, D.
J . Am. Chem. Soc. 1999, 121, 6652. (e) Ashkenazi, N.; Vigalok, A.;
Parthiban, S.; Ben-David, Y.; Shimon, L. J . W.; Martin, J . M. L.;
Milstein, D. J . Am. Chem. Soc. 2000, 122, 8797.
(3) (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J . Am.
Chem. Soc. 1997, 119, 11687. (b) J ensen, C. M. Chem. Commun. 1999,
2443. (c) Morales-Morales, D.; Redon, R.; Yung, C.; J ensen, C. M. Chem.
Commun. 2000, 1620. (d) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali,
S.; Van Koten, G. Angew. Chem., Int. Ed. 2000, 39, 743.
(4) (a) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten,
G. Organometallics 1996, 15, 5687. (b) J ia, G.; Lee, H. M.; Xia, H. P.;
Williams, I. D. Organometallics 1996, 15, 5453. (c) Dani, P.; Karlen,
T.; Gossage, R. A.; Smeets, W. J . J .; Spek, A. L.; van Koten, G. J . Am.
Chem. Soc. 1997, 119, 11317. (d) Steenwinkel, P.; Kolmschot, S.;
Gossage, R. A.; Dani, P.; Veldman, N.; Spek, A. L.; van Koten, G. Eur.
J . Inorg. Chem. 1998, 477. (e) van der Boom, M. E.; Kraatz, H.-B.;
Hassner, L.; Ben-David, Y.; Milstein, D. Organometallics 1999, 18,
3873.
(5) (a) Wen, T. B.; Cheung, Y. K.; Yao, J .; Wong, W.-T.; Zhou, Z. Y.;
J ia, G. Organometallics 2000, 19, 3803. (b) For an earlier example of
a PCP-Os complex formed by successive electrophilic additions of a
carbene on PPh3 ligands, see: Hoskins, S. V.; Rickard, C. E. F.; Roper,
W. R. J . Chem. Soc., Chem. Commun. 1984, 1000.
(6) (a) For a review on C-C bond activation with a particular
emphasis on PCP systems, see: Rybtchinski B.; Milstein, D. Angew.
Chem., Int. Ed. 1999, 38, 870. (b) C-O activation: van der Boom, M.
E.; Liou, S.-Y.; Ben-David, Y.; Shimon, L. J . W.; Milstein, D. J . Am.
Chem. Soc. 1998, 120, 6531. van der Boom, M. E.; Liou, S.-Y.; Ben-
David, Y.; Vigalok, A.; Milstein, D. Angew. Chem., Int. Ed. 1997, 36,
625.
(7) (a) Hoffmann, P. R.; Caulton, K. G. J . Am. Chem. Soc. 1975, 97,
4221. (b) Elliott, G. P.; McAuley, N. M.; Roper W. R. Inorg. Synth. 1989,
26, 184.
10.1021/om000878z CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/31/2001

1720 Organometallics, Vol. 20, No. 9, 2001
Gauvin et al.
oxide. Flushing of a green benzene solution of 2 with
1
H2 leads to a rapid color change to yellow. H, 31P{1H},
and 13C{1H} NMR indicate the quantitative formation
of Os{1,3-(iPr2PCH2)2C6H3}(H)2(Cl)(PPh3) (3, Scheme 2).
The spectroscopic features of 3 in deuterated benzene
comprise in the 31P{1H} NMR the expected doublet and
triplet at 29.61 and -6.91 ppm, respectively, for the PCP
and PPh3 ligands, as well as in 1H NMR two sets of
doublets of virtual triplets for the CH2 groups, at 3.95
and 3.03 ppm. Moreover, the presence of two equivalent
hydrogen ligands is confirmed by the observation of a
doublet of triplets centered at -12.11 ppm. The low T1
value of 132 ms at 213 K (C7D8) obtained for the hydride
in 3 is borderline between a H2 adduct and a dihydride.8
To determine the nature of the H2 moiety, we generated
the complex 3-d by reaction between 2 and HD for the
1
1
determination of the J HD value. However, the H NMR
spectrum of the new complex merely exhibits a high-
field signal similar to the one observed for 3, but
differing in its intensity relative to the other peaks (1H
F igu r e 1. ORTEP drawing of 2 (30% probability). Selected
bonds lengths (Å): Os(1)-C(4) ) 2.064(3); Os(1)-Cl(2) )
2.4146(11); Os(1)-P(3) ) 2.3322(10); Os(1)-P(5) ) 2.3495-
(11); Os(1)-P(6) ) 2.2189(9). Selected bond angles (deg):
C(4)-Os(1)-Cl(2) ) 144.49(8); P(3)-Os(1)-P(5) ) 156.31-
(3); C(4)-Os(1)-P(3) ) 82.04(8); C(4)-Os(1)-P(5) ) 80.66-
(8); C(4)-Os(1)-P(6) ) 89.63(8); P(6)-Os(1)-Cl(2) ) 125.74-
(3).
1
instead of 2H for 3). The signal obtained on the H{31P}
NMR spectrum is a singlet, and no splitting due to
proton-deuterium coupling was observed. This suggests
a structure of the dihydride type, i.e., a seven-coordi-
nated species with two equivalent hydrides. Leaving a
sample of 3-d in C6D6 solution at room temperature for
a few hours resulted in an increase of the intensity of
the hydride signal. The 2H NMR spectrum reveals a
statistical redistribution of the deuterium between the
hydride and the ortho protons of the aromatic rings of
the triphenylphosphine at 8.06 ppm, thus showing the
existence of a scrambling process that exchanges those
protons, similarly to what was reported for RuHCl-
(PPh3)3.9 An NOE experiment carried out at 243 K
(C7D8, 400 MHz) indicates that the hydrides are located
cis to the triphenylphosphine ligand. Moreover, the
absence of a large coupling constant between the Cipso
of the PCP and the phosphorus nucleus of the PPh3 is
indicative that the latter lies in a cis position relative
to the Os-C bond. Thus, it can be assumed that in this
heptacoordinate complex the two hydrides are pseudo-
trans to the PCP Cipso, in the meridional plane defined
by the Os-PCP framework, with the chloride trans to
the triphenylphosphine. Slow loss of hydrogen gradually
converts 3 back to 2, both in solution and in the solid
state. Noteworthy, 3 is also slowly formed by reaction
between 2 and MeOH, most probably by dehydrogena-
tion of the primary alcohol. Such a process is reminis-
cent of a key step in the catalytic hydrogen transfer
reaction from alcohols to unsaturated substrates.3d,10 No
decarbonylation was observed (no carbonyl complex was
detected by infrared spectroscopy).
Sch em e 1
basal plane comprises the PCP ligand and the chlorine
atom, while the apical position is occupied by the PPh3
ligand. Noteworthy, the methyl groups of the isopropyl
substituents on the PCP are pointing away from the
triphenylphosphine, to reduce the steric interactions.
The bond distances and angles are within the expected
ranges. More particularly, the osmium-aryl bond dis-
tance, 2.064(3) Å, is comparable to the corresponding
distance of the phenyl phosphine PCP analogue (2.04-
(1) Å).5a However, the PCP bite angle (P(3)-Os(1)-P(5))
of 156.31(3)° is slightly larger than the one reported for
Os{1,3-(Ph2PCH2)2C6H3}(Cl)(PPh3) (149.9(1)°), probably
due to the larger steric hindrance generated by the
bulkier isopropyl substituents. The spectroscopic fea-
tures of 2 in solution are in agreement with the crystal
structure. The 31P{1H} NMR spectrum in C6D6 at room
temperature consists of a doublet and a triplet in a 2:1
ratio, centered at 33.88 and 5.17 ppm, respectively, with
1
a coupling constant of 12.1 Hz. The H NMR exhibits
two sets of doublets of virtual triplets at 2.85 and 1.98
ppm, the consequence of the diastereotopicity of the
methylene protons. Moreover, the ipso carbon of the
pincer ligand resonates at 153.20 ppm as a triplet with
In a similar fashion, 2 reacts at room temperature
in benzene with 1 equiv of CO to yield quantitatively
(by NMR) the carbon monoxide adduct Os{1,3-(iPr2-
PCH2)2C6H3}(CO)(Cl)(PPh3) (4). The carbonyl ligand
gives rise to a characteristic absorption band in the IR
spectrum at 1921 cm-1. NMR data confirm the formula-
tion, with notably the expected A2B system in the 31P-
{1H} spectrum (doublet centered at 25.81 ppm for the
a
2J PC coupling constant of 7.8 Hz. The multiplicity of
this signal and the low value of the coupling constant
indicates the absence of a phosphorus trans to the
osmium-bound carbon, thus confirming the position of
the triphenylphosphine at the apex of the coordination
polyhedron.
The formal electronic unsaturation of the 16-electron
complex 2 is demonstrated by its reactivity toward small
donor molecules such as dihydrogen and carbon mon-
(8) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789.
(9) Stolzenberg, A. M.; Muetterties, E. L. Organometallics 1985, 4,
1739.
(10) Zassinovich, G.; Mestroni, G.; Gladiali, S. Chem. Rev. 1992, 95,
1051.

New Osmium-PCP Complexes
Organometallics, Vol. 20, No. 9, 2001 1721
Sch em e 2
the CO and PPh3 ligands. We can then conclude that
in the octahedral complex 4 the chloride and the
triphenylphosphine occupy the positions cis to the PCP
ipso carbon, the carbonyl being coordinated trans to the
metal-aryl bond. 4 reacts further with an additional
equivalent of CO to give the bis-carbonyl complex Os-
{1,3-(iPr2PCH2)2C6H3}(CO)2(Cl) (5), with elimination of
the triphenylphosphine ligand. 5 can be directly gener-
ated by pressurizing 2 with 3 bar CO or from the
reaction of 3 with CO under mild conditions. Slow
evaporation of a concentrated pentane solution of the
reaction mixture led to the formation of colorless single
crystals of the bis-carbonyl compound. An X-ray diffrac-
tion study unambiguously confirmed the formulation
(Figure 2). The geometry around the osmium is distorted
octahedral, with the PCP ligand coordinating in a
meridional fashion, and two carbonyls occupying mutu-
ally cis positions.
The PCP bite angle (P(2)-Os(1)-P(3)) of 160.59(6)°
is significantly larger than in 2, which could originate
from the lesser distortion of the PCP framework in the
pseudo-octahedral complex 5. The Os-Caryl bond length
(Os(1)-C(11) ) 2.154(6) Å) is longer than in 2, as
expected from the strong trans influence of the carbonyl
ligand. It is similar to the value of 2.162(5) Å found in
the isostructural complex Os(2-naphthyl)(Cl)(CO)2-
(PPh3)2,11 but shorter than the corresponding distance
F igu r e 2. ORTEP drawing of 5 (30% probability). Selected
bonds lengths (Å): Os(1)-C(1) ) 1.941(8); Os(1)-C(2) )
1.855(15); Os(1)-C(11) ) 2.154(6); Os(1)-Cl(4) ) 2.474-
(2); Os(1)-P(2) ) 2.3798(18); Os(1)-P(3) ) 2.3816(17);
C(1)-O(1) ) 1.136(8); C(2)-O(2) ) 1.16(2). Selected bond
angles (deg): P(2)-Os(1)-P(3) ) 160.59(6); C(2)-Os(1)-
C(1) ) 90.9(3); C(2)-Os(1)-C(11) ) 92.8(3); C(11)-Os(1)-
Cl(4) ) 84.76(17).
PCP ligand, triplet at 3.71 ppm for the PPh3, with
respective intensities 2:1) and the two sets of doublets
of virtual triplets for the diastereotopic methylene PCP
5b
in Os{(o-PPh2C6H4)2(CH)}(Cl)(CO)2 (2.215(8) Å), as
expected for a switch from a Os-C sp2 to Os-C sp3
bond. However, the osmium-carbonyl bond distances
are very similar: 1.941(8) and 1.855(5) Å for 5, 1.939-
(7) and 1.855(7) Å for Os(2-naphthyl)(Cl)(CO)2(PPh3)2,
and 1.918(10) and 1.878(10) Å for Os{(o-PPh2C6H4)2-
(CH)}(Cl)(CO)2, for the CO ligands respectively trans
and cis to the Os-CPCP bond. Infrared spectroscopy
shows two characteristic carbonyl absorption bands at
2001 and 1922 cm-1 of equal intensity, indicating a
C(1)-Os(1)-C(2) angle of 90°, in agreement with the
X-ray structure. The NMR features of 5 in C6D6 solution
are those expected for the solid state structure, namely
a singlet in 31P{1H} NMR at 46.63 ppm, and two sets of
doublets of virtual triplets for the methylenic protons
at 3.95 and 3.03 ppm, the latter as a result of the lack
of equatorial symmetry in the PCP framework. The two
different CO give rise to two triplets centered at 187.90
and 180.30 ppm in the 13C{1H} spectrum.
1
protons at 4.00 and 3.14 ppm in the H NMR spectrum.
In the 13C{1H} NMR the ipso carbon resonates at 150.51
2
ppm, with a J PC coupling constant of 7.8 Hz, which is
consistent with the absence of a phosphine in the
position trans to the metal-aryl bond of the octahedral
complex. The CO ligand appears in the 13C{1H} spec-
trum at 194.80 ppm as a doublet of triplets. The low
coupling constant with the triphenylphosphine phos-
phorus allows us to conclude on a mutual cis postion of
(11) Baker, L.-J .; Clark, G. R.; Rickard, C. E. F.; Roper, W. R.;
Woodgate, S. D.; Wright, L. J . J . Organomet. Chem. 1998, 551, 247.
(12) C-C cleavage by â-alkyl elimination in a Os complex has been
postulated: (a) Edwards, A. J .; Esteruelas, M. A.; Lahoz, F. J .; Lopez,
A. M.; Onate, E.; Oro, L. A.; Tolosa, J . I. Organometallics 1997, 16,
1316. For C-C activation by Os clusters, see: (b) Chi, Y.; Chung, C.;
Chou, Y. C.; Su, P. C.; Chiang, S. J .; Peng, S. M.; Lee, G. H.
Organometallics 1997, 16, 1702. (c) Adams, R. D.; Qu, X. S. Organo-
metallics 1995, 14, 4172. (d) Park, T. J .; Woo, B. W.; Chung, J . H.;
Shim, S. C.; Lee, J . H.; Lim, S. S.; Suh, I. H. Organometallics 1994,
13, 3384. (e) Deeming, A. J .; Felix, M. S. B.; Nuel, D. Inorg. Chim.
Acta 1993, 213, 3.
Having shown that osmium-PCP complexes were
stable and synthetically accessible via C-H bond acti-

1722 Organometallics, Vol. 20, No. 9, 2001
Gauvin et al.
Sch em e 3
(Scheme 3). GC analysis of the gas phase showed
methane formation. 8 has spectroscopic features very
similar to those of 2. The 31P{1H} displays a doublet and
a triplet at 37.60 (2P) and 3.01 (1P) ppm, respectively,
1
and the H NMR is almost identical, with the notable
exception of the singlet at 2.25 ppm for the two methyl
groups on the PCP backbone. The methylene protons
resonate at 2.86 and 1.73 ppm as doublets of virtual
triplets. Placing a solution of 8 under hydrogen cleanly
converted it to 7, as expected from the reactivity of 2
with H2.
Su m m a r y
New osmium complexes bearing a bulky PCP ligand
have been synthesized, and two of them have been
structurally characterized by X-ray diffraction. More-
over, we have reported the first example of osmium
insertion into an unstrained strong aryl-C bond in
solution. Our efforts are currently directed toward the
broadening of the scope of this reaction, as well as
toward mechanistic understanding of this process.
vation, we chose to study the ability of this metal to
promote intramolecular cleavage of C-C bonds.
We have recently reported such a reaction in the case
of ruthenium,4e while osmium insertion into a strong,
nonstrained C-C bond12 has not been reported yet.
Heating of an equimolar mixture of the complex OsCl2-
(PPh3)3 and the diphosphine {1,3,5-(CH3)3-2,6-(iPr2-
PCH2)2C6H} (6) under 3 bar of hydrogen leads to the
formation of the pincer complex Os{3,5-(CH3)-2,6-(iPr2-
PCH2)2C6H3}(H)2(Cl)(PPh3) (7) in 80% yield by NMR
(Scheme 3).
Separation of the products from the reaction mixture,
especially from the residual triphenylphosphine, was
prevented by the very similar solubilities of those
compounds in organic solvents. However, the similarity
of the spectroscopic features of 7 and 3, from which it
differs only by the presence of the two methyl groups
on the PCP aromatic moiety, is in agreement with the
formulation. The 31P{1H} NMR spectrum consists of a
doublet at 29.65 ppm and a triplet at -7.33 ppm in a
2:1 respective proportion. The 1H NMR spectrum ex-
hibits notably a doublet of triplets at -12.09 ppm for
the two osmium-bound hydrides, along with two dou-
blets of triplets centered at 3.89 and 3.02 ppm for the
CH2 groups. The two methyls on the PCP aromatic ring
resonate as a singlet at 2.36 ppm. This new osmium
complex results from the selective activation of the
Csp2-Csp3 Ar-CH3 bond located between the two phos-
phine arms.
No activation of the two other analogous Csp2-Csp3
bonds was detected. This tends to indicate that the C-C
activation requires an initial bis-coordination of the
diphosphine substrate, as in the similar ruthenium
system.4e
CH4 formation was confirmed by GC analysis of the
reaction gas phase. This product most probably origi-
nates from the reaction of a chelated diphosphine-
osmium hydride species, in which the irreversible
cleavage of the aryl-methyl bond yields a cyclometa-
lated complex and CH4. Indeed, it is known that OsCl2-
(PPh3)3 reacts with hydrogen to yield hydride-containing
complexes.13
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were carried out under
an inert atmosphere in a glovebox or using standard Schlenk
techniques. Solvents were dried, distilled, and degassed before
use. 1H, 31P{1H}, and 13C{1H} spectra were recorded on a
Bruker AMX400 spectrometer at 400, 162, and 100 MHz,
respectively, or on a Bruker DPX250 spectrometer at 250, 101,
and 62 MHz, respectively. NMR solvent is C6D6. 1H and 13C
chemical shifts are reported in ppm downfield from TMS and
referenced to the residual solvent h1 (7.15 ppm for benzene-
d6) and all-d solvent peaks (128.00 ppm for benzene), respec-
tively. 31P NMR chemical shifts are in ppm downfield from
H3PO4 and referenced to an external 85% H3PO4 sample. All
1
measurements were performed at 20 °C. Assignments of H
and 13C{1H} NMR signals were done with 1H{31P} and 13C-
DEPT-135 NMR, respectively. Infrared spectra were collected
on a Nicolet Prote´ge´ 460 spectrometer. GC analyses were
performed on a Hewlett-Packard HP6890 gas chromatograph
equipped with a molecular sieves column. Elemental analyses
were carried out at the Hebrew University, J erusalem, and
by H. Kolbe, Mu¨lheim an der Ruhr, Germany. Mass spectros-
copy analyses were carried out at the Ludwig-Maximilians
Universita¨t, Mu¨nchen, Germany.
Os{1,3-(iP r 2P CH2)2C6H3}(Cl)(P P h 3) (2). To a deep green
solution of 253 mg (0.241 mmol) of OsCl2(PPh3)3 and 50 µL
(0.359 mmol) of NEt3 in 10 mL of benzene was added a solution
of 82 mg (0.243 mmol) of 1 in 5 mL of benzene. Stirring the
mixture overnight at room temperature caused the precipita-
tion of NEt3HCl out of the emerald green supernatant.
Filtration and evaporation to dryness followed by repeated
washings of the resulting green solid with pentane led to the
isolation of 182 mg of the desired complex (yield: 91%). X-ray
quality crystals were obtained by slow evaporation of a THF
1
solution of the complex. H NMR (250 MHz): δ 7.60 (m, 6H,
PPh3), 7.05 (d, J ) 7.1 Hz, CHmeta PCP), 6.95 (m, 9H, PPh3),
2
6.84 (t, J ) 7.3 Hz, 1H, CHpara PCP), 2.85 (dvt, J HH ) 16.6
v
i
Hz, J HP ) 5.0 Hz, 2H, ArCHHP), 2.76 (m, 2H, CH Pr), 1.98
A similar reaction is obtained by heating an equimolar
mixture of the hydridochloride complex Os(H)(Cl)-
2
v
(dvt, J HH ) 16.6 Hz, J HP ) 4.0 Hz, 2H, ArCHHP), 1.41 (m,
i
6H, CH3 iPr), 1.26 (m, 2H, CH Pr), 1.23 (m, 6H, CH3 iPr), 1.09
13
(PPh3)3 and the diphosphine (6) in the absence of
(m, 6H, CH3 iPr), 0.75 (m, 6H, CH3 iPr). 31P{1H} NMR (100
hydrogen in a closed vessel. In this case, we observed
the formation of the pincer complex Os{3,5-(CH3)-2,6-
(iPr2PCH2)2C6H}(Cl)(PPh3) (8) in 65% yield by NMR
2
2
MHz): δ 33.88 (d, J PP ) 12.1 Hz, 2P, PCP), 5.17 (t, J PP
)
12.1 Hz, 1P, PPh3). 13C{1H} NMR (62 MHz): δ 153.20 (t, J PC
v
) 7.8 Hz, Cipso PCP), 135.22-120.66 (C Ar), 37.89 (vt, J PC
)
v
i
15.0 Hz, ArCH2P), 28.01 (vt, J PC ) 11.5 Hz, CH Pr), 26.41
v
i
(13) Ferrando, G.; Caulton, K. G. Inorg. Chem. 1999, 38, 4168.
(vt, J PC ) 10.4 Hz, CH Pr), 20.65 (CH3 iPr), 20.25 (CH3 iPr),

New Osmium-PCP Complexes
Organometallics, Vol. 20, No. 9, 2001 1723
19.19 (CH3 iPr), 18.00 (CH3 iPr). Anal. Found (calcd): C, 55.51
(55.29); H, 5.91 (6.11).
Ta ble 1. Cr ysta l Da ta for 2 a n d 5
2
5
Os{1,3-(iP r 2P CH2)2C6H3}(H)2(Cl)(P P h 3) (3). A 30 mg
(0.036 mmol) sample of 2 was dissolved in 5 mL of benzene.
Hydrogen was bubbled through the solution, whose color
turned rapidly from deep green to yellow. Evaporation to
dryness yielded an analytically pure pale yellow solid in
quantitative yield. 1H NMR (400 MHz): δ 8.06 (m, 6H, PPh3),
formula
fw
C
36H50ClOsP3
C22H36O2ClOsP2
620.10
801.32
space group
cryst syst
a, Å
P1h
Pbca
triclinic
10.430(2)
10.944(2)
17.643(4)
72.55(3)
81.04(3)
66.51(3)
1760.5(6)
1.512
orthorhombic
10.5700(3)
15.5690(4)
28.8730(7)
90
b, Å
c, Å
2
7.4-7.0 (m, 12H, H Ar), 3.95 (dvt, J HH ) 15.7 Hz, J HP ) 3.7
2
R, deg
â, deg
γ, deg
V, Å3
D
Z
Hz, 2H, ArCHHP), 3.03 (dvt, J HH ) 15.7 Hz, J HP ) 3.7 Hz,
i
i
90
90
2H, ArCHHP), 2.20 (m, 2H, CH Pr), 1.41 (m, 2H, CH Pr),
2
1.04 (m, 6H, CH3 iPr), 0.75 (m, 1H, CH3 iPr), -12.11 (dt, J PH
4751.5(2)
1.734
) 16.2 Hz, J PH ) 13.0 Hz, 2H, Os(H)2). 31P{1H} NMR (162
2
calcd, g cm-3
2
2
MHz): δ 29.61 (d, J PP ) 12.4 Hz, 2P, PCP), -6.91 (t, J PP
)
2
8
12.4 Hz, 1P, PPh3). 13C{1H} NMR (100 MHz): δ 147.48 (dt,
2J PC ) 7.1 Hz, 1.3 Hz, Cipso PCP), 140.82-120.99 (C Ar), 39.86
(dvt, J PC ) 16.4 Hz, 6.0 Hz, ArCH2P), 25.19 (vt, J PC ) 13.3
µ(Mo KR), mm-1
cryst size, mm-3
T, K
3.857
5.630
0.3 × 0.1 × 0.1
0.1 × 0.07 × 0.03
120(2)
120(2)
i
i
no. of reflns collected 32 315
14 052
Hz, CH Pr), 24.32 (vt, J PC ) 10.8 Hz, CH Pr), 20.47 (vt, J PC
) 1.9 Hz, CH3 iPr), 20.06 (CH3 iPr), 19.19 (CH3 iPr), 18.90 (CH3
iPr). Anal. Found (calcd): C, 55.04 (55.16); H, 6.26 (6.33).
Os{1,3-(iP r 2P CH2)2C6H3}(CO)(Cl)(P P h 3) (4). To 96 mg
(0.115 mmol) of 2 dissolved in 10 mL of benzene in a closed
vessel was added with a syringe 2.8 mL (0.116 mmol) of CO.
The green solution turned gradually to yellow. Evaporation
to dryness followed by repeated washing with 10 mL portions
of pentane led to the isolation of 84 mg of analytically pure 4
no. of indep reflns
11 563
[R(int) ) 0.053]
R1 ) 0.0318,
wR2 ) 0.0632
R1 ) 0.0435,
wR2 ) 0.0662
3402
[R(int) ) 0.092]
R1 ) 0.0334,
wR2 ) 0.0817
R1 ) 0.0498,
wR2 ) 0.0869
final R indices
[I>2σ(I)]
R indices (all data)
attempts led to decomposition of 7. 1H NMR (400 MHz): δ 8.07
(m, 6H, PPh3), 7.00 (9H, PPh3), 6.81 (s, 1H, Hpara PCP), 3.89
1
2
v
(yield: 86%). H NMR (250 MHz): δ 7.55 (m, 6H, PPh3), 6.90
(dvt, J HH ) 15.3 Hz, J HP ) 3.4 Hz, 2H, ArCHHP), 3.02 (dvt,
(m, 12H, H Ar PCP + PPh3), 4.00 (dvt, 2J HH ) 15.1 Hz, vJ HP
)
)
2J HH ) 15.3 Hz, J HP ) 3.3 Hz, 2H, ArCHHP), 2.36 (s, 6H,
i
2
i
i
4.6 Hz, 2H, ArCHHP), 3.68 (m, 2H, CH Pr), 3.14 (dvt, J HH
ArCH3), 2.17 (m, 2H, CH Pr), 1.44 (m, 2H, CH Pr), 1.03 (m,
v
15.0 Hz, J HP ) 3.1 Hz, 2H, ArCHHP), 1.54 (m, 6H, CH3 iPr),
6H, CH3 iPr), 0.81 (m, 6H, CH3 iPr), 0.74 (m, 12H, CH3 iPr),
i
1.15 (m, 6H, CH3 iPr), 1.00 (m, 2H, CH Pr), 0.87 (m, 6H, CH3
-12.09 (dt, J PH ) 14.9 Hz, J PH ) 13.0 Hz, 2H, Os(H)2). 31P-
2
2
iPr), 0.61 (m, 6H, CH3 iPr). 31P{1H} NMR (162 MHz): δ 25.81
{1H} NMR (162 MHz): δ 29.65 (d, 2J PP ) 10.5 Hz, PCP), -7.33
2
2
(t, J PP ) 10.5 Hz, PPh3). 13C{1H} NMR (100 MHz): δ 143.25
2
(d, J PP ) 8.6 Hz, 2P, PCP), 3.71 (t, J PP ) 8.6 Hz, 1P, PPh3).
13C{1H} NMR (62 MHz): δ 194.80 (dt, J PC ) 9.5 Hz, 4.8 Hz,
CO), 150.51 (t, J PC ) 7.8 Hz, Cipso PCP), 138.57-121.73
(C Ar), 42.02 (vt, J PC ) 17.2 Hz, CH2 PCP), 26.46 (vt, J PC
10.1 Hz, CH Pr), 25.22 (vt, J PC ) 13.2 Hz, CH Pr), 21.07 (CH3
iPr), 20.50 (CH3 iPr), 20.12 (CH3 iPr), 19.79 (CH3 iPr). IR (NaCl,
film, cm-1): 1921, νCO. Anal. Found (calcd): C, 54.75 (54.89);
H, 5.87 (5.91).
2
2
(dt, J PC ) 7.1 Hz, 1.0 Hz, Cipso Ar), 140.70-127.37 (m, C Ar),
2
v
3
36.89 (dvt, J PC ) 16.8 Hz, J PC ) 6.1 Hz, ArCH2P), 25.40 (vt,
vJ PC ) 13.5 Hz, CH Pr), 24.43 (vt, J PC ) 10.8 Hz, CH Pr),
22.74 (s, CH3 Ar), 20.52 (CH3 iPr), 19.90 (CH3 iPr), 19.17 (CH3
iPr), 18.86 (CH3 iPr). MS (EI+): 855 ([M - H]+).
i
i
)
i
i
Os{3,5-(CH3)-2,6-(iP r 2P CH2)2C6H}(Cl)(P P h 3) (8). A mix-
ture of 20 mg of Os(H)(Cl)(PPh3)3 (0.020 mmol) and 7.5 mg of
6 (0.020 mmol) in 5 mL of THF was heated at 90 °C in a closed
vessel for 16 h. A color change from brown to deep green was
observed. Volatiles were evaporated from the green reaction
mixture to yield a green solid, which contains 8 as the major
species. Attempts to separate this product from excess PPh3
were not successful due to the very similar solubility properties
of these compounds in organic solvents such as pentane,
diethyl ether, or ethanol. Chromatography attempts led to
decomposition of 8. Hydrogen bubbling through a C6D6 solution
of this solid resulted in rapid conversion of 8 to 7. 1H NMR
(250 MHz): δ 7.51 (m, 6H, PPh3), 6.93 (m, 9H, PPh3), 6.52 (s,
Os{1,3-(iP r 2P CH2)2C6H3}(CO)2(Cl) (5). Stirring benzene
solutions of 2, 3, or 4 under CO pressure (3 bar) at room
temperature for 3 h yielded yellow solutions of 5. Evaporation
to dryness gave yellow solids containing both the expected
complex and free triphenylphosphine. Analytically pure mate-
rial was obtained by recrystallization from diethyl ether at -30
°C. Colorless single crystals of 5 were formed by slow evapora-
1
tion of a concentrated pentane solution. H NMR (250 MHz):
2
v
δ 7.00 (m, 3H, CH Ar PCP), 3.66 (dvt, J HH ) 15.8 Hz, J HP
)
2
v
4.7 Hz, 2H, ArCHHP), 3.19 (dvt, J HH ) 15.8 Hz, J HP ) 3.7
i
i
Hz, 2H, ArCHHP), 2.94 (m, 2H, CH Pr), 2.00 (m, 2H, CH -
Pr), 1.26 (m, 6H, CH3 iPr), 1.05 (m, 6H, CH3 iPr), 0.95 (m, 12H,
CH3 iPr). 31P{1H} NMR (100 MHz): δ 46.63 (s, PCP). 13C{1H}
2
v
1H, Hpara PCP), 2.86 (dvt, J HH ) 17.0 Hz, J HP )5.0 Hz, 2H,
i
ArCHHP), 2.81 (m, 2H, CH Pr), 2.24 (s, 6H, ArCH3), 1.73 (dvt,
2
2J HH ) 17.0 Hz, J HP ) 3.5 Hz, 2H, ArCHHP), 1.43 (m, 6H,
CH3 iPr), 1.27 (m, 8H, CH + CH3 iPr), 1.09 (m, 6H, CH3 iPr),
0.77 (m, 6H, CH3 iPr). 31P{1H} NMR (101 MHz): δ 37.60 (d,
NMR (62 MHz): δ 187.89 (t, J PC ) 4.9 Hz, OsCO), 180.30 (t,
2J PC ) 7.8 Hz, OsCO), 149.19 (t, J PC ) 7.4 Hz, Cipso PCP),
2
v
138.06-122.17 (C Ar), 41.34 (vt, J PC ) 17.3 Hz, ArCH2P),
v
i
v
2J PP ) 11.3 Hz, 2P, PCP), 3.01 (t, J PP ) 11.3 Hz, 1P, PPh3).
2
26.04 (vt, J PC ) 13.2 Hz, CH Pr), 23.6 (vt, J PC ) 13.9 Hz,
CH Pr), 20.30 (CH3 iPr), 19.87 (CH3 iPr), 19.48 (CH3 iPr), 17.98
i
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 2. Red crys-
tals suitable for X-ray diffraction studies were obtained by slow
evaporation of a THF solution. A crystal (0.3 × 0.1 × 0.1 mm3)
was mounted on a nylon loop and flash frozen in a cold
nitrogen stream (at 120 K) on a Nonius KappaCCD diffracto-
meter mounted on a FR590 generator equipped with a sealed
tube with Mo KR radiation (λ ) 0.71073 Å) and a graphite
monochromator. The SHELX-97 program package was used
for structure solution and refinement. The structure was solved
using direct methods and refined by full-matrix least-squares
techniques based on F2. The final cycle of the least-squares
refinement for 2 gave an agreement factor R ) 0.032 (based
on F2) for data with I > 2σ(I) and R ) 0.044 for all data (11 563
reflections). Idealized hydrogens were placed and refined in a
(CH3 iPr). IR (NaCl, film, cm-1): 2001, 1922, νCO. Anal. Found
(calcd): C, 42.60 (42.68); H, 5.63 (5.70).
Os{3,5-(CH3)-2,6-(iP r 2P CH2)2C6H}(Cl)(H)2(P P h 3) (7). In
a Fischer-Porter bottle, 66 mg (0.063 mmol) of OsCl2(PPh3)3
and 24 mg (0.063 mmol) of 6 were dissolved in 5 mL of THF.
The solution was pressurized with 3 bar of hydrogen and
heated at 100 °C for 16 h. The gas phase was collected by
regular Schlenk techniques, and the resulting yellow solution
was evaporated to dryness. NMR showed the presence of 7 as
the major species. Attempts to separate this product from
excess PPh3 were not successful due to the very similar
solubility properties of these compounds in organic solvents
such as pentane, diethyl ether, or ethanol. Chromatography

1724 Organometallics, Vol. 20, No. 9, 2001
Gauvin et al.
riding mode. ORTEP views of the molecular structures and
the adopted numbering are shown in Figure 1. Table 1 gives
details of the crystal structure determination.
refined in a riding mode. ORTEP views of the molecular
structures and the adopted numbering are shown in Figure
2. Table 1 gives details of the crystal structure determination.
X-r a y Cr ysta l Str u ctu r e Deter m in a tion of 5. Colorless
crystals suitable for X-ray diffraction studies were obtained
by slow evaporation of a pentane solution. A crystal (0.1 ×
0.07 × 0.03 mm3) was mounted on a nylon loop and flash frozen
in a cold nitrogen stream (at 120 K) on a Nonius KappaCCD
diffractometer mounted on a FR590 generator equipped with
a sealed tube with Mo KR radiation (λ ) 0.71073 Å) and a
graphite monochromator. The SHELX-97 program package
was used for structure solution and refinement. The structure
was solved using direct methods and refined by full-matrix
least-squares techniques based on F2. The final cycle of the
least-squares refinement for 5 gave an agreement factor R )
0.0334 (based on F2) for data with I > 2σ(I) and R ) 0.0498
for all data (3402 reflections). No constraints were used.
During the structure solution, it appeared that a chlorine atom
(denoted as Cl(5) in Supporting Information) was located
between C(2) and O(2) with a 10% occupancy. The structure
was refined with such dicrete disorder modeled; however the
corresponding carbonyl that would have been located near Cl-
(4) could not be located. Idealized hydrogens were placed and
Ack n ow led gm en t. This work was supported by the
U.S-Israel Binational Science Foundation and by the
Israeli Ministry of Science (Tashtiot program). We thank
Dr. Leonid Konstantinovsky for assistance with NMR
spectroscopy. Dr. Dominik Hermann is acknowledged
for the mass spectroscopy analyses. D.M. is the holder
of the Israel Matz Professorial Chair of Organic Chem-
istry.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
6 and 7 with PPh3, tables of crystal data and structure
refinement, atomic coordinates, bond lengths and angles,
anisotropic displacement parameters, and hydrogen coordi-
nates for 2 and 5. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM000878Z