Reaction pathways for fac-Os(CO)3(MeCN)Me2 with mono- and bidentate ligands

Article abstract of DOI:10.1021/om061022i

The reactions of fac-Os(CO)₃(L)Me₂ (1a, L = MeCN; 1b, L = THF) with monodentate and bidentate ligands have been studied for the first time. Treatment of 1a or 1b with PPh₃ gives fac-Os(CO) ₃(PPh₃)-Me₂ (2), which may be further reacted with Me₃NO in acetonitrile to give the unexpected isomer cis-Os(CO)₂(PPh₃)(MeCN)Me₂ (3). Subsequent reaction of 3 with PPh₃ gives cis,trans-Os(CO)₂(PPh ₃)₂Me₂ (4), with a further isomerization accompanying the ligand substitution. Oxidative decarbonylation of 4 with Me₃NO was found not to be possible. Treatment of 1a or 1b with bidentate ligands gives different reaction products, depending on the choice of ligand, the reaction conditions, and the stoichiometry. Reactions with small-bite-angle bidentate ligands (L-L) gave the compounds cis-Os(CO) ²(L-L)(COMe)-Me (5a, L-L = dppm; 5b, L-L = dppe; 5c, L-L = 2,2′-bipy). These mixed methyl acetyl complexes are formed by displacement of the labile ligand and subsequent chelation, accompanied by methyl migration onto carbonyl. Reaction of 1a with 1 equiv of dppp, however, resulted in a series of reactions which led to the formation of the decarbonylated product cis-Os(CO)₂(dppp)Me₂ (7). However, reaction of la with 0.5 equiv of dppp gave the bimetallic dppp-bridged complex [fac-Os(CO) ₃Me₂]₂(μ-dppp) (8). In addition to characterization of all the new compounds by analytical and spectroscopic techniques, the molecular structures of 5a and 8 have been determined by X-ray diffraction.

Full text of DOI:10.1021/om061022i

1256
Organometallics 2007, 26, 1256-1260
Reaction Pathways for fac-Os(CO)3(MeCN)Me2 with Mono- and
Bidentate Ligands
Matthew J. Overett,† Hong Su, and John R. Moss*
Department of Chemistry, UniVersity of Cape Town, Rondebosch 7701, South Africa
ReceiVed NoVember 7, 2006
The reactions of fac-Os(CO)3(L)Me2 (1a, L ) MeCN; 1b, L ) THF) with monodentate and bidentate
ligands have been studied for the first time. Treatment of 1a or 1b with PPh3 gives fac-Os(CO)3(PPh3)-
Me2 (2), which may be further reacted with Me3NO in acetonitrile to give the unexpected isomer cis-
Os(CO)2(PPh3)(MeCN)Me2 (3). Subsequent reaction of 3 with PPh3 gives cis,trans-Os(CO)2(PPh3)2Me2
(4), with a further isomerization accompanying the ligand substitution. Oxidative decarbonylation of 4
with Me3NO was found not to be possible. Treatment of 1a or 1b with bidentate ligands gives different
reaction products, depending on the choice of ligand, the reaction conditions, and the stoichiometry.
Reactions with small-bite-angle bidentate ligands (L-L) gave the compounds cis-Os(CO)2(L-L)(COMe)-
Me (5a, L-L ) dppm; 5b, L-L ) dppe; 5c, L-L ) 2,2′-bipy). These mixed methyl acetyl complexes are
formed by displacement of the labile ligand and subsequent chelation, accompanied by methyl migration
onto carbonyl. Reaction of 1a with 1 equiv of dppp, however, resulted in a series of reactions which led
to the formation of the decarbonylated product cis-Os(CO)2(dppp)Me2 (7). However, reaction of 1a with
0.5 equiv of dppp gave the bimetallic dppp-bridged complex [fac-Os(CO)3Me2]2(µ-dppp) (8). In addition
to characterization of all the new compounds by analytical and spectroscopic techniques, the molecular
structures of 5a and 8 have been determined by X-ray diffraction.
Scheme 1
Introduction
Although the reactions of metal carbonyl alkyls of the type
M(CO)5R (M ) Mn, Re) have been extensively studied,1
relatively few reactions of metal carbonyl dialkyls such as cis-
Os(CO)4R2 (R ) Me, Et, etc.)2 have been reported. Thermal
decomposition of cis-Os(CO)4Me2 gives methane as the primary
organic product, which is believed to form via a radical
pathway.3 Reactions with Br2, HF, and CO have also been
described, and these reactions yield Os(CO)4MeBr,2b cis-Os-
(CO)4F2,4 and Os(CO)5,2b respectively. Little is known about
the reactivity of such systems with monodentate or multidentate
neutral ligands; the literature only describes the substitution of
cis-Os(CO)4Me2 with PPh3 by thermal5 or oxidative2a decar-
bonylation to give fac-Os(CO)3(PPh3)Me2. No carbonyl insertion
reactions have been observed.
Since LnOsMe2 (where Ln ) other ligands) could be a model
for
surface sites in heterogeneous catalysis, we have explored the
reactions of Os(CO)3Me2 species. We have recently described
the synthesis of fac-Os(CO)3(L)Me2 (1a, L ) MeCN; 1b, L )
THF) and the reaction of these compounds with PPh3 to give
fac-Os(CO)3(PPh3)Me2 (2).6 The presence of a labile MeCN or
THF ligand effectively activates the dialkylosmium carbonyl
for substitution reactions. We report here a study of some of
the rich coordination chemistry that results from the reactions
of 1 or 2 with simple mono- and bidentate ligands.
* To whom correspondence should be addreseed. E-mail:
John.Moss@science.uct.ac.za. Fax: +27 (0)21 689 7499. Tel:
+27(0)21 650 2535.
† Present address: Sasol Technology R&D, 1 Klasie Havenga Rd.,
Sasolburg 1947, South Africa.
(1) (a) Wilkinson, G.; Stone; F. G. A.; Abel, E. W. ComprehensiVe
Organometallic Chemistry; Pergamon Press: Oxford, U.K., 1982; Wilkin-
son, G.; Stone; F. G. A.; Abel, E. W. ComprehensiVe Organometallic
Chemistry II; Pergamon Press: Oxford, U.K., 1995. (b) Moss, J. R. J. Mol.
Catal. A: Chem. 1996, 107, 169. (c) Ford, P. C.; Boese, W. T. AdV. Chem.
Ser. 1997, No. 253, 221.
(2) (a) Carter, W. J.; Kelland, J. W.; Okrasinski, S. J.; Warner, K. E.;
Norton, J. R. Inorg. Chem 1982, 21, 3955. (b) L’Eplattenier, F.; Pelichet,
C. HelV. Chim. Acta 1970, 53, 1091. (c) George, R. D.; Knox, S. A. R.;
Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1973, 972.
(3) (a) Evans, J.; Okrasinski, S. J.; Pribula, A. J.; Norton, J. R. J. Am.
Chem. Soc. 1977, 99, 5835. (b) Carter, W. J.; Okrasinski, S. J.; Norton, J.
R. Organometallics 1985, 4, 1376.
Results and Discussion
Oxidative decarbonylation of 2 using Me3NO was found to
be possible under mild conditions (Scheme 1). Thus, treatment
of 2 with excess Me3NO in acetonitrile gives a single new
(4) Brewer, S. A.; Buggey, L. A.; Holloway, J. H.; Hope, E. G. J. Chem.
Soc., Dalton Trans. 1995, 2941.
(5) L’Eplattenier, F. Inorg. Chem. 1969, 8, 965.
(6) Overett, M. J.; Moss, J. R. Inorg. Chim. Acta 2005, 358, 1715.
10.1021/om061022i CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/01/2007

Reaction Pathways for fac-Os(CO)3(MeCN)Me2
Organometallics, Vol. 26, No. 5, 2007 1257
Scheme 2
carbonyl compound, which was identified by IR and NMR
spectroscopy as cis-Os(CO)2(PPh3)(MeCN)Me2 (3). Interest-
ingly, decarbonylation and phosphine coordination is ac-
companied by rearrangement, presumably through loss of
octahedral configuration in the pentacoordinate transition state.
The tertiary phosphine ligand shifts to a trans,cis orientation
with respect to the methyls and the labile MeCN substituent
coordinates cis to both methyls (Scheme 1). This may be
deduced from the 3J(PH) couplings for the methyl peaks in the
1H NMR: the methyl trans to phosphine, located upfield (0.49
ppm) from the cis methyl (1.25 ppm), has a significantly greater
3J(PH) coupling (8 Hz vs 4 Hz). Compound 3 is moderately
thermally unstable, both as an isolated solid and in solution,
due to the lability of the acetonitrile ligand.
Figure 1. Molecular structure of cis-Os(CO)2(dppm)(COMe)Me
(5a). Thermal ellipsoids are drawn at the 35% probability level.
Selected interatomic distances (Å) and angles (deg): Os1-C1,
1.901(3); Os1-C2, 1.884(3); Os1-C3, 2.104(3); Os1-C5, 2.218-
(3); Os1-P1, 2.4094(7); Os1-P2, 2.4156(7); C1-O1, 1.138(3);
C2-O2, 1.147(3); C3-O3, 1.209(3); C3-C4, 1.531(4); P1-Os1-
P2, 69.98(2); P1-C18-P2, 97.4(1); Os1-C3-C4, 120.2(2).
Reaction of 3 with triphenylphosphine gives, as expected,
Os(CO)2(PPh3)2Me2, although the ligand displacement reaction
is again accompanied by a selective isomerization. This may
be observed by monitoring the reaction in situ using IR
spectroscopy. After reaction of 3 with 1 equiv of PPh3 for 1 h
at 60 °C in toluene, new bands characteristic of a cis-dicarbonyl
species were observed at 2006 and 1915 cm-1; however, before
complete conversion of 3, a further set of bands attributable to
another cis-discarbonyl species appeared at 1985 and 1912 cm-1.
After 16 h, complete conversion to this new product was
apparent. After isolation, the compound was identified as
cis,trans-Os(CO)2(PPh3)2Me2 (4) by NMR spectroscopy (Scheme
1). The IR-observed intermediate is presumably the kinetically
favored cis,cis-Os(CO)2(PPh3)2Me2, formed by direct displace-
ment of MeCN by PPh3. The subsequent isomerization to the
thermodynamically favored product is due to steric repulsion
of the bulky phosphines (Scheme 1).
displacement of the labile ligand and subsequent chelation was
accompanied by a methyl migration onto an adjacent carbonyl
to give compounds of the type cis-Os(CO)2(L-L)(COMe)Me
(5a, L-L ) dppm; 5b, L-L ) dppe; 5c, L-L ) bipy).
These products were fully characterized by spectroscopic and
analytical techniques, and in addition, the structure of 5a was
determined by X-ray diffraction (Figure 1).
Compound 5a crystallizes as a racemate in the monoclinic
crystal system with a C2/c space group and eight repeating units
per unit cell (four of each mirror image). The molecular structure
has a distorted-octahedral geometry, with the bite angle of dppm
being 69.98°. The acyl C-O bond length of 1.209 Å is, as
expected, greater than the carbonyl C-O bond lengths (1.138
and 1.147 Å).
To the best of our knowledge, compounds 5a-c are the first
isolated and structurally characterized osmium complexes with
both acyl and alkyl groups. Decomposition of such acetyl methyl
compounds could lead to useful organic products.
Further reaction of 4 with Me3NO proved impossible, even
under harsh conditions (large excess of Me3NO, in refluxing
acetonitrile). This is in agreement with the “rule of thumb” that
only metal carbonyls with CO stretches above 2000 cm-1 are
susceptible to oxidative carbonylation using Me3NO.7
The bidentate ligands thus far employed were all characterized
by relatively small bite angles and a tendency toward chelation.
Our attention now turned to bidentate ligands with larger bite
angles with the potential to coordinate in a bridging mode across
a bimetallic system. Such a ligand is 1,3-bis(diphenylphosphi-
no)propane (dppp). Thus, treatment of 1a with 1 equiv of dppp
in toluene at 70 °C led to the formation of a new product
(Scheme 3), identified as fac-Os(CO)3(dppp)Me2 (6). Although
6 was not isolated, its structure as a fac-tricarbonyl species with
monodentate phosphine substitution (and therefore a pendant
free phosphine as well) may be deduced by comparison of the
Having thus established the limit of substitution for mono-
dentate ligands achievable by oxidative decarbonylation, our
attention now turned to the reaction of 1 with bidentate ligands
(L-L). Since only one labile ligand is available for substitution,
a number of different reactions are possible after the initial
displacement of MeCN (or THF). Possible reactions include
decarbonylation and chelation to form Os(CO)2(L-L)Me2, meth-
yl migration onto carbonyl (alternatively carbonyl insertion into
Os-Me) and chelation to form Os(CO)2(L-L)(COMe)Me, and
formation of bimetallic compounds of the form [Os(CO)3Me2]2-
(µ-L-L). Our investigations show that all of these reactions can
take place, depending on the choice of ligand, the reaction
conditions, and the stoichiometry. Thus, reaction of 1a or 1b
with bidentate ligands such as bis(diphenylphosphino)methane
(dppm), bis(diphenylphosphino)ethane (dppe), and 2,2′-bipyridyl
(bipy) under mild conditions gave in each case a single new
compound in high yield (Scheme 2). In these reactions,
IR spectrum with that of 2 (νCO 2068, 1993, and 1960 cm-1
;
cf. 2068, 1994, and 1960 cm-1 for 2). Monitoring the reaction
by NMR in C6D6 is also instructive. The formation of 6 is
indicated by the presence of singlets at -6.5 ppm (coordinated
phosphine) and -17.4 ppm (free phosphine) in the 31P NMR
spectrum. After a prolonged reaction time at 70 °C, formation
of cis-Os(CO)2(dppp)(COMe)Me (5d) is apparent (Scheme 3),
by both IR spectrocopy (νCO 2013 and 1949 cm-1; cf. 2005
and 1940 cm-1 for 5b) and in situ 31P NMR spectroscopy
(doublets at -24.0 and -24.8 ppm). However, under the forcing
conditions required to drive the reaction to completion (110 °C),
(7) (a) Blumer, D. J.; Barnett, K. W.; Brown, T. L. J. Organomet. Chem.
1979, 173, 71. (b) Koelle, U. J. Organomet. Chem. 1977, 133, 53.

1258 Organometallics, Vol. 26, No. 5, 2007
OVerett et al.
Scheme 3
Figure 2. Molecular structure of [fac-Os(CO)3Me2]2(µ-dppp) (8).
Thermal ellipsoids are drawn at the 35% probability level. Hydrogen
atoms are omitted for clarity. Selected interatomic distances (Å)
and angles (deg): Os1-C16, 1.922(5); Os1-C17, 1.935(5); Os1-
C18, 1.904(5); Os1-C19, 2.196(4); Os1-C20, 2.199(4); Os1-P1,
2.410(1); Os1-P1-C1, 117.0(1); Os1-P1-P2-Os2, 139.8(6).
Scheme 4
bidentate ligands. The “activated” compound fac-Os(CO)3-
(MeCN)Me2 (1a) was found to be a convenient point of
departure. A maximum of two substitutions by triphenylphos-
phine can be performed on this system by further oxidative
decarbonylation with Me3NO. Thus, cis,trans-Os(CO)2(PPh3)2-
Me2 (4) was prepared in three steps from 1a, and further reaction
with Me3NO could not be achieved. Treatment of 1a with
bidentate ligands (L-L) resulted in a variety of different
reactions, depending on the choice of ligand, the reaction
conditions, and the stoichiometry employed. These include new
examples of several classical organometallic reactions, including
methyl migration to carbonyl and acyl decarbonylation. Thus,
compounds of the form cis-Os(CO)2(L-L)(COMe)Me (5a-d),
fac-Os(CO)3(L-L)Me2 (6), cis-Os(CO)2(L-L)Me2 (7), and [fac-
Os(CO)3Me2]2(µ-L-L) (8) could all be prepared and identified.
In the future, we plan to explore the reactions of other
dialkylosmium compounds with a wider range of ligands, to
determine the underlying reasons for the selective isomerization
reactions and to explore the thermal decomposition of the acyl
alkyl complexes.
a further transformation taking place simultaneously was
indicated by IR spectroscopy (νCO 2005 and 1929 cm-1). After
prolonged reflux to allow completion of the reaction, a new
product, identified as cis-Os(CO)2(dppp)Me2 (7), was isolated
in low yield (Scheme 3). Compound 7 is formed by decarbo-
nylation of the acyl moiety in 5d under the high-temperature
conditions required to drive the chelation of the dppp ligand to
the osmium. Similar thermally mediated decarbonylation reac-
tions have been observed for other organometallic acyl species.8
Given the high stability of 6 against chelation, the formation
of a bimetallic species with bridging dppp was accessible. Thus,
reaction of 1a with 0.5 equiv of dppp under mild conditions
gave the expected bimetallic product [fac-Os(CO)3Me2]2(µ-
dppp) (8) in good yield (Scheme 4).
The bimetallic nature of 8 and its stereochemistry was
confirmed by an X-ray crystal structure determination (Figure
2).
Experimental Section
General Considerations. All reactions were carried out under
nitrogen or argon using standard Schlenk techniques. fac-Os(CO)3-
(MeCN)Me2 (1a), fac-Os(CO)3(THF)Me2 (1b), and fac-Os(CO)3-
(PPh3)Me2 (2) were prepared as described previously.6 Me3-
NO‚2H2O was purified by sublimation under vacuum at 60 °C onto
a dry ice cooled finger. All other reagents were obtained from
Sigma-Aldrich and used without purification. Toluene was dried
and purified by distillation from sodium. Acetonitrile and dichlo-
romethane were dried and purified by distillation from calcium
hydride. Melting points were recorded on a Kofler hotstage
microscope (Reichert Thermovar) and are uncorrected. Microanaly-
sis data were obtained from the University of Cape Town
Microanalytical Laboratory. Infrared spectra were recorded on a
Perkin-Elmer 983 spectrometer as solutions in cells with NaCl
windows. NMR spectra were recorded on a Varian Unity-400
Compound 8 crystallizes in the monoclinic crystal system
with a P21/c space group and four repeating units per unit cell.
The coordination geometry around the two osmium atoms is
that of an irregular octahedron. Bimetallic metal carbonyl
compounds with bridging dppp ligands have been reported with
several metals, including tungsten,9 molybdenum,9a,10 chromi-
um,9a,10 and rhenium;11 however, to the best of our knowledge,
8 is the first example of a bimetallic osmium compound with a
bridging diphosphine ligand and is certainly the only example
of a bimetallic dimethylosmium compound.
Conclusions
In conclusion, we have explored the reactivity of dimethyl
osmium carbonyl compounds with a range of simple mono- and
(9) (a) Hor, T. S. A. J. Organomet. Chem. 1988, 340, 51. (b) Dickson,
C.; McFarlane, W.; Coville, N. Inorg. Chim. Acta 1989, 158, 205.
(10) Gan, K.-S.; Lee, H. K.; Hor, T. S. A. J. Organomet. Chem. 1993,
460, 197.
(11) Lee, K.-W.; Hanckel, J. M.; Brown, T. L. J. Am. Chem. Soc. 1986,
108, 2266.
(8) (a) Calerazzo, F. Angew. Chem., Int. Ed. Engl. 1977, 16, 299. (b)
Kuhlmann, E. J.; Alexander, J. J. Coord. Chem. ReV. 1980, 33, 195. (c)
Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and
Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; p 362.

Reaction Pathways for fac-Os(CO)3(MeCN)Me2
Organometallics, Vol. 26, No. 5, 2007 1259
spectrometer (1H, 13C) or a Varian Mercury-300 spectrometer (1H,
13C, 31P). Mass spectrometry was carried out using electron impact
(EI) or fast atom bombardment (FAB) ionization by Dr. Phillip
Boshoff of the Cape Technikon, and the reported m/z value
corresponds to the most abundant isotopes for each element. In
each case the observed isotopic distribution corresponds to the
theoretical distribution. The X-ray diffraction data were collected
at room temperature on a Nonius Kappa CCD diffractometer with
1.5 kW graphite-monochromated Mo radiation.
romethane/hexane, 5b was obtained as a white crystalline solid
(yield 118 mg, 81%). Mp: 184-187 °C. Anal. Found: C, 53.2; H,
4.0. Calcd for C31H30O3P2Os: C, 53.0; H, 4.3. IR (νmax/cm-1
;
dichloromethane): 2005 s (CO), 1940 s (CO), 1588 w (COMe).
1H NMR (δ; 300 MHz, CDCl3): 7.94-7.31 (20H, m, Haryl), 2.78
(2H, m, PCH2CH2P), 2.49 (3H, s, COMe), 2.41 (2H, m, PCH2CH2P),
-0.65 (3H, dd, 3J(PH) ) 9 Hz, 3J(PH) ) 9 Hz, Os-Me). 13C{1H}
NMR (δ; 75 MHz, CDCl3); 186.8 (dd, 2Jtrans(PC) ) 5 Hz, 2Jcis(PC)
2
2
) 4 Hz, COMe), 185.6 (dd, Jtrans(PC) ) 5 Hz, Jcis(PC) ) 4 Hz,
2
CO trans to PPh2), 181.8 (t, Jcis(PC) ) 4 Hz, CO trans to Me),
cis-Os(CO)2(PPh3)(MeCN)Me2 (3). A stirred solution of 2 (100
mg, 0.177 mmol) in acetonitrile (5 mL) was treated with Me3-
NO‚2H2O (76 mg, 0.68 mmol) in acetonitrile (2 mL), added in 0.5
mL aliquots over 48 h, after which the reaction was judged to be
complete by IR spectroscopy. After removal of the volatiles in
vacuo and column chromatography (silica, 40% dichloromethane
in hexane, Rf ) 0.24), 3 was obtained as a white crystalline material
which decomposes slowly in solution or as an isolated solid (yield
69 mg, 67%). Mp: 133-136 °C. IR (νmax/cm-1; dichloromethane):
135.7-127.8 (Caryl), 53.0 (d, 3Jtrans(PC) ) 18 Hz, COMe), 28.2 (dd,
1J(PC) ) 33 Hz, 2J(PC) ) 16 Hz, PCH2CH2P), 27.5 (dd, 1J(PC) )
28 Hz, 2J(PC) ) 10 Hz, PCH2CH2P), -19.7 (dd, 2J(PC) ) 14 Hz,
2J(PC) ) 9 Hz). MS (m/z; FAB): 705 (M+ + H, 5%), 689 (M+
-
Me, 69%)
cis-Os(CO)2(2,2′-bipy)(COMe)Me (5c). From 1a. A stirred
mixture of 1a (52 mg, 0.15 mmol) and 2,2′-bipyridyl (27 mg, 0.17
mmol) in toluene (5 mL) was heated to 50 °C for 5 days. A bright
orange color developed in the solution, and the reaction was
monitored by IR spectroscopy. The volatiles were removed in
vacuo, and after purification by preparative TLC (alumina, ethyl
acetate, Rf ) 0.56), 5c was obtained as an orange crystalline solid
(yield 61 mg, 87%). Mp: 169-172 °C. Anal. Found: C, 39.0; H,
3.0; N, 6.1. Calcd for C15H14N2O3Os: C, 39.1; H, 3.1; N, 6.1%.
IR (νmax/cm-1; toluene): 1992 s (CO), 1916 s (CO), 1584 w
(COMe). 1H NMR (δ; 300 MHz, C6D6): 10.34 (1H, m, bipy), 8.61
(1H, m, bipy), 7.06 (2H, m, bipy), 6.87 (2H, m, bipy), 6.58 (1H,
m, bipy), 6.27 (1H, m, bipy), 3.15 (3H, s, -COMe), -0.01 (3H, s,
Os-Me). 13C{1H} NMR (δ; 75 MHz, CDCl3): 190.5 (COMe),
188.8 (CO), 181.7 (CO), 155.7 (1-Cbipy), 154.9 (1′-Cbipy), 153.7 (3-
1
1992 s, 1921 s. H NMR (δ; 300 MHz, C6D6): 7.68-6.95 (15H,
m, Haryl), 1.25 (3H, d,3J(PC) ) 4 Hz, Os-Me trans to CO), 0.49
(3H, d, 3J(PC) ) 8 Hz, Os-Me trans to PPh3), 0.26 (3H, d, 4J(PC)
) 1.5 Hz, -NCMe). 31P{1H} NMR (δ; 120 MHz, C6D6): 9.38.
MS (m/z; FAB): 582 (M+ + H, 3%), 542 (M+ + 2H - MeCN,
11%), 526 (M+ + H - MeCN - Me, 10%).
cis,trans-Os(CO)2(PPh3)2Me2 (4). A stirred mixture of 3 (82
mg, 0.14 mmol) and PPh3 (48 mg, 0.18 mmol) in toluene (15 mL)
was heated to 60 °C. The reaction was monitored by IR spectros-
copy. After 1 h, the bands at 1993 and 1926 cm-1 (3) were replaced
by new bands at 2006 and 1915 cm-1, along with a minor band at
1985 cm-1. After 3 h, bands at bands at 1985 and 1912 cm-1 were
dominant, with the band at 2006 cm-1 still evident. After 16 h,
only bands at 1985 and 1911 cm-1 were apparent. The volatiles
were removed in vacuo, and after column chromatography (silica,
25% dichloromethane in hexane, Rf ) 0.27) and recrystallization
(dichloromethane/hexane), 4 was obtained as a white crystalline
solid (yield 68 mg, 60%). Mp: 222-224 °C. Anal. Found: C, 60.2;
H, 4.3. Calcd for C40H36O2P2Os: C, 60.0; H, 4.5. IR (νmax(CO)/
Cbipy), 153.4 (3′-Cbipy), 137.8 (5-Cbipy), 137.2 (5′-Cbipy), 126.0 (Cbipy),
125.8 (Cbipy), 122.6 (Cbipy), 122.3 (Cbipy), 53.9 (COMe), 1.9 (Os-
Me). MS (m/z; EI): 907 (2M+ - Me, 10%), 879 (2M+ - Me -
CO, 7%), 461 (M+ - H, 3%) 447 (M+ - Me, 40%), 419 (M+
Me - CO, 100%), 391 (M+ - Me - 2CO, 27%).
-
From 1b. A solution of 1b was prepared by treatment of cis-
Os(CO)4Me2 (50 mg, 0.15 mmol) with excess Me3NO‚2H2O in THF
and filtration through silica after completion of the reaction.6 2,2′-
Bipyridyl (24 mg, 0.15 mmol) was added, and the mixture was
refluxed for 48 h. A dark orange color formed in solution. The
reaction was monitored by IR spectroscopy. After removal of the
volatiles in vacuo and purification by preparative TLC (alumina,
dichloromethane) an orange crystalline solid was recovered and
identified as 5c by comparison of its IR and NMR spectra with
those of an authentic sample (yield 44 mg, 64%).
1
cm-1; dichloromethane): 1985 s, 1909 s. H NMR (δ; 400 MHz,
CDCl3): 7.56-7.34 (30H, m, Haryl), -0.65 (6H, t, 3J(PH) ) 8 Hz,
2
Os-Me). 13C{1H} NMR (δ; 100 MHz, CDCl3): 183.6 (t, J(PC)
) 8 Hz, CO), 134.2 (Caryl), 132.8 (Caryl), 129.8 (Caryl), 127.8 (Caryl),
2
-13.8 (t, J(PC) ) 8 Hz, Os-Me). 31P{1H} NMR (δ; 120 MHz,
CDCl3): 5.84 (s).
cis-Os(CO)2(dppm)(COMe)Me (5a). A stirred mixture of 1a
(78 mg, 0.22 mmol) and dppm (86 mg, 0.22 mmol) in toluene (5
mL) was heated to 70 °C. The reaction was monitored by IR
spectroscopy and was judged to be complete after 3 days. The
volatiles were removed in vacuo, and after recrystallization from
dichloromethane/hexane, 5a was obtained as a white crystalline
solid (yield 142 mg, 91%). X-ray-quality crystals were obtained
by slow diffusion of hexane into a concentrated dichloromethane
solution of 5a. Mp: 186-189 °C. Anal. Found: C, 52.6; H, 3.8.
Calcd for C30H28P2O3Os: C, 52.3; H, 4.1. IR (νmax/cm-1; dichlo-
romethane): 2003 s (CO), 1939 s (CO), 1588 w (COMe). 1H NMR
(δ; 300 MHz, CDCl3): 7.81-7.31 (20H, m, Haryl), 4.7 (2H, m,
PCH2P), 2.58 (3H, s, COMe), -0.15 (3H, t, 3J(PH) ) 20 Hz, Os-
Me). 13C{1H} NMR (δ; 75 MHz, CDCl3) 186.9 (CO), 185.6 (d,
cis-Os(CO)2(dppp)Me2 (7). A stirred mixture of 1a (101 mg,
0.292 mmol) and dppp (121 mg, 0.292 mmol) in toluene (10 mL)
was heated to 70 °C. The reaction was monitored by IR spectros-
copy. After 16 h, 1a was consumed, and new bands at 2068, 1993,
and 1960 cm-1 indicated formation of a new fac-tricarbonyl species,
assigned as the pendant η2-dppp intermediate 6. Simultaneously,
new bands at 2013 and 1949 cm-1, which grew in strength relative
to the bands at 2068, 1994, and 1960 cm-1, indicated formation of
a dicarbonyl species, assigned as 5d. After 72 h the reaction was
still incomplete, and the mixture was refluxed for 24 h. Significant
decomposition was observed, and IR spectroscopy indicated forma-
tion of a third product, a dicarbonyl species with bands at 2005
and 1930 cm-1, present in solution with both 6 and 5d. After
additional reflux for 72 h, the reaction was judged to be complete.
The volatiles were removed in vacuo, the residue was taken up in
dichloromethane, and this solution was filtered through silica. After
removal of the volatiles in vacuo and two recrystallizations from
dichloromethane/hexane, a white crystalline solid was recovered
and identified as 7 (yield 55 mg, 27%). Mp: 242-245 °C. Anal.
Found: C, 54.2; H, 4.5. Calcd for C31H32O2P2Os: C, 54.1; H, 4.7%.
2
2J(PC) ) 7 Hz, CO), 182.9 (d, J(PC) ) 8 Hz, COMe), 135.7-
127.9 (Caryl), 52.9 (d, 3J(PC) ) 19 Hz, -COMe), 43.3 (dd, 1J(PC)
1
2
) 29 Hz, J(PC) ) 24 Hz, PCH2P), -20.6 (dd, J(PC) ) 9 Hz,
2J(PC) ) 6 Hz, Os-Me). 31P{1H} NMR (δ; 75 MHz, CDCl3):
2
2
-48.2 (d, J(PP) ) 10 Hz), -54.3 (d, J(PP) ) 10 Hz).
cis-Os(CO)2(dppe)(COMe)Me (5b). A stirred mixture of 1a (71
mg, 0.21 mmol) and dppe (83 mg, 0.21 mmol) in toluene (5 mL)
was heated to 70 °C. The reaction was monitored by IR spectros-
copy and was judged to be complete after 3 days. The volatiles
were removed in vacuo, and after recrystallization from dichlo-
1
IR (νmax(CO)/cm-1; dichloromethane): 2001 s, 1924 s. H NMR
(δ; 300 MHz, CDCl3): 7.52-7.20 (20H, m, Haryl), 2.74-1.58 (6H,

1260 Organometallics, Vol. 26, No. 5, 2007
OVerett et al.
m, PCH2CH2CH2P), -0.14 (3H, dd, 3Jcis(PC) ) 8 Hz, 3Jcis(PC) )
crystalline material (yield 73 mg, 43%), X-ray-quality crystals were
obtained by slow diffusion of hexane into a concentrated dichlo-
romethane solution of 8. Mp: 205-208 °C. Anal. Found: C, 43.7;
H, 3.6. Calcd for C37H38O6P2Os2: C, 43.5; H, 3.8. IR (νmax(CO)/
cm-1; toluene): 2069 vs, 1993 s, 1961 s. 1H NMR: (δ; 300 MHz,
CDCl3): 7.38-7.27 (20H, m, Haryl), 2.38 (4H, m, PCH2CH2CH2P),
1.01 (2H, m, PCH2CH2CH2P), -0.46 (12H, d, 3J(PH) ) 8 Hz, Os-
Me). 31P{1H} NMR (δ; 120 MHz, CDCl3): -7.8 (s). MS (m/z;
FAB): 1023 (M+ + H, 20%).
3
3
7 Hz, Me trans to CO), -0.29 (3H, dd, Jtrans(PC) ) 8 Hz, Jcis-
(PC) ) 4 Hz, Me trans to P). 13C{1H} NMR (δ; 75 MHz, CDCl3):
2
186.4 (t, J(PP) ) 7 Hz, CO trans to Me), 185.3 (m, CO trans to
1
P), 136.9-127.5 (Caryl), 24.3 (d, J(PC) ) 26 Hz, PCH2-), 23.4
(dd, 1J(PC) ) 30 Hz, 3J(PC) ) 4 Hz, PCH2-), 19.5 (m, PCH2CH2-
2
2
CH2P), -20.1 (dd, Jcis(PC) ) 10 Hz, Jcis(PC) ) 6 Hz, Me trans
to CO), -23.5 (dd, 2Jtrans(PC) ) 42 Hz, 2Jcis(PC) ) 8 Hz, Me trans
to P). 31P{1H} NMR (δ; 120 MHz; CDCl3): -16.7 (d, J(PP) )
2
2
24 Hz), -24.1 (d, J(PP) ) 24 Hz). MS (m/z; FAB): 689 (M+
-
H, 6%), 675 (M+ - Me, 11%), 658 (M+ - H - 2Me, 100%), 631
Acknowledgment. Sasol Technology (Pty) Ltd. is gratefully
acknowledged for a bursary for M.J.O.; Johnson Matthey and
Anglo Platinum Corp. are acknowledged for PGM compounds.
(M+ - H - 2Me - CO, 34%).
[fac-Os(CO)3Me2]2(µ-dppp) (8). A stirred mixture of 1a (117
mg, 0.339 mmol) and dppp (68 mg, 0.17 mmol) in toluene (10
mL) was heated to 70 °C. A brown color indicated some
decomposition in solution. The reaction was monitored by infrared
spectroscopy and was judged complete after 72 h. After removal
of the volatiles in vacuo, purification by column chromatography
(silica, 25% dichloromethane in hexane, Rf ) 0.30), and recrys-
tallization (dichloromethane/hexane), 8 was obtained as a white
Supporting Information Available: CIF files giving full details
of the crystal structure analyses for compounds 5a and 8. This
material is available free of charge via the Internet at http://
pubs.acs.org.
OM061022I