C-H Bond Activation in the Formation of an Osmium(IV) Metallacycle

Article abstract of DOI:10.1021/om980852w

The osmium methylimido complex [(η⁵C₅H₅)O_S(NCH ₃)(CH₂SiMe₃)₂(SO₃CF ₃], 1, reacts with PPh₃ to give both the methyleneamido complex (η⁵C₅H₅)Os(NCH₂)(CH ₂SiMe₃)₂, 2, and the unique osmium(IV) hydride [(η⁵-C₅H₅)Os(H)(PPh ₃){CHSiMe₃PPh₂(C₆H ₄)][SO₃CF₃], 4. A single-crystal X-ray diffraction study of 4 shows that this molecule has a distorted square pyramidal structure with the center of the cyclopentadienyl ring at the apex. This molecule results from a series of reactions that includes two C-H activation steps: α-hydrogen elimination and orthometalation.

Full text of DOI:10.1021/om980852w

814
Organometallics 1999, 18, 814-816
C-H Bon d Activa tion in th e F or m a tion of a n
Osm iu m (IV) Meta lla cycle
J ennifer L. Koch and Patricia A. Shapley*
Department of Chemistry, University of Illinois, Urbana, Illinois 61801
Received October 13, 1998
Summary: The osmium methylimido complex [(η5-
C5H5)Os(NCH3)(CH2SiMe3)2][SO3CF3], 1, reacts with
PPh3 to give both the methyleneamido complex (η5-
C5H5)Os(NCH2)(CH2SiMe3)2, 2, and the unique osmium-
(IV) hydride [(η5-C5H5)Os(H)(PPh3){CHSiMe3PPh2(C6-
H4)}][SO3CF3], 4. A single-crystal X-ray diffraction study
of 4 shows that this molecule has a distorted square
pyramidal structure with the center of the cyclopenta-
dienyl ring at the apex. This molecule results from a
series of reactions that includes two C-H activation
steps: R-hydrogen elimination and orthometalation.
F igu r e 1. SHELXTL plot of 4 showing 35% probability
ellipsoids for non-H atoms. H atoms have been left out for
clarity except for the hydride and H6, which were both
independently refined. Selected bond distances (Å): Os-
C6 ) 2.129(8), Os-C40 ) 2.129(8), Os-H ) 1.614(77), Os-
Cp ) 2.231(8), Os-P2 ) 2.306(2). Selected bond angles
(deg): C40-Os-C6 ) 81.2(3), C40-Os-P2 ) 84.7(2), C6-
Os-P2 ) 96.3(2), Cp-Os-C6 ) 129.7(3), Cp-Os-P2 )
132.1(3), Cp-Os-C6 ) 129.7(3), Cp-Os-P2 ) 132.1(3).
Cp is the centroid of carbon atoms in the cyclopentadienide
ring.
Imido ligands in transition metal imido complexes can
react with nucleophiles, electrophiles, and unsaturated
molecules in a number of ways depending on the nature
of the complex. Acids add to some imides, forming amide
complexes.1 Bases can deprotonate some imido groups
to form alkylideneamido complexes.2,3 In some cases,
nucleophiles add to the imido nitrogen atom.2,4 Alkenes
and alkynes add to the amide ligand in a few com-
plexes.2,5 Studies on the reaction chemistry of organo-
metallic imido complexes have an added complication
because alkyl ligands may react under the same condi-
tions as imido ligands.
We recently described the reaction chemistry of the
osmium methylimido complex [(η5-C5H5)Os(NCH3)(CH2-
SiMe3)2][SO3CF3], 1.2 Various bases deprotonate the
methylimido ligand and form an osmium(IV) methyl-
eneamido complex (η5-C5H5)Os(NdCH2)(CH2SiMe3)2, 2.
Triphenylphosphine reacts with 1 as both a base and a
nucleophile. The reaction of 1 with 1.5 equiv of triphen-
ylphosphine gives nearly equal amounts of 2 and [(η5-
C5H5)Os(CH2SiMe3)2(PPh3)][SO3CF3], 3, by 1H NMR,
along with [HPPh3][SO3CF3] and MeNdPPh3 (Scheme
1, R ) CH2SiMe3). There is an intermediate species
between 1 and 3, which we presume to be [(η5-C5H5)-
Os(CH2SiMe3)2(MeNdPPh3)][SO3CF3] on the basis of
(1) (a) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;
J ohn Wiley & Sons: New York, 1988; Chapter 5, pp 223-226. (b)
Antinolo, A.; Carrillohermosilla, F.; Otero, A.; Fajardo, M.; Garces, A.;
Gomezsal, P.; Lopezmardomingo, C.; Martin, A.; Miranda, C. J . Chem.
Soc., Dalton Trans. 1998, 59-65. (c) Adachi, T.; Hughes, D, L.; Ibrahim,
S. K.; Okamoto, S.; Pickett, C. J .; Yabanouchi, N.; Yoshida, T. J . Chem.
Soc., Chem. Commun. 1995, 1081-1083. (d) Sundermeyer, J .; Puttelik,
J .; Foth, M.; Field, J . S.; Ramesar, N. Chem. Ber. 1994, 127, 1201-
1212.
(2) Shapley, P. A.; Shusta, J . M.; Hunt, J . L. Organometallics 1996,
15, 1622-1629.
(3) (a) Chatt, J .; Dosser, R. J .; King, F.; Leigh, G. J . J . Chem. Soc.,
Dalton Trans. 1976, 2435-2443. (b) Powell, K. R.; Pe´rez, P. J .; Luan,
L.; Feng, S. G.; White, P. S.; Brookhart, M.; Templeton, J . L.
Organometallics 1994, 13, 1851-1864.
(4) (a) Moubaraki, B.; Murray, K. S.; Nichols, P. J .; Thomson, S.;
West, B. O. Polyhedron 1994, 13, 485-495. (b) Arntdsen, B. A.;
Sleiman, H. F.; McElwee-White, L. Organometallics 1993, 12, 2440-
2444. (c) Dobbs, D. A.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115,
3836-3837. (d) Huang, J .-S.; Che, C.-M.; Poon, C.-K. J . Chem. Soc.,
Chem. Commun. 1992, 161-163. (e) Fourquet, J . L.; Leblanc, M.;
Saravanamuthu, A.; Bruce, M. R. M.; Bruce, A. E. Inorg. Chem. 1991,
30, 3241-3243. (f) Harlan, E. W.; Holm, T. H. J . Am. Chem. Soc. 1990,
112, 186-193. (g) Sleiman, H. F.; Mercer, S.; McElwee-White, L. J .
Am. Chem. Soc. 1989, 111, 8007-8009. (h) Elliot, R. L.; Nichols, P. J .;
West, B. O. Polyhedron 1987, 6, 2191-2192.
(5) (a) Walsh P. J .; Hollander, F. J .; Bergman, R. G. Organometallics
1993, 12, 3705-3723. (b) De With, J .; Horton, A. D.; Orpen, A. G.
Organometallics 1993, 12, 1493-1496. (c) Chong. A. O.; Oshima, K.;
Sharpless, K. B. J . Am. Chem. Soc. 1977, 99, 3420-3426. (d) Schofield,
M. H.; Kee, T. P.; Anhaus, J . T.; Schrock, R. R.; J ohnson, K. H., Davis,
W. M. Inorg. Chem. 1991, 30, 3595-3604. (e) Groves, J . T.; Takahashi,
T. J . Am. Chem. Soc. 1983, 105, 2073-2074.
1
data from IR, H NMR, and 31P NMR spectroscopy of
the reaction mixture.
However, when 1 reacts with an excess quantity of
PPh3 in dichloromethane solution, 3 is not a product.
The organometallic products are the methyleneamido
complex, 2, and a new metallocycle [(η5-C5H5)Os(H)-
(PPh3){CHSiMe3PPh2(C6H4)}][SO3CF3], 4. Complex 2 is
readily extracted from the reaction mixture by removing
the dichloromethane under vacuum and extracting the
residue with hexane.2 Complex 4 crystallizes from
tetrahydrofuran/diethyl ether solutions at -30 °C. Com-
plex 4 also forms by the reaction between 3 and PPh3.
Elemental analysis and spectroscopic methods char-
acterized complex 4. The presence of a metal hydride is
2
confirmed by the resonance at -11.63 ppm (dd, J PH
)
37.8 Hz, J PH ) 5.4 Hz, 1H, OsH) in the 1H NMR
spectrum. Integration shows that there is only one
trimethylsilyl group. The inequivalent phosphorus at-
oms differ by 38.5 ppm in the 31P NMR spectrum.
X-ray-quality crystals were obtained by slow addition
of hexane to a tetrahydrofuran/dichloromethane (5:1
ratio) solution of 4 at -30 °C. Figure 1 shows the
structure of 4. The osmium center is in a four-legged
3
10.1021/om980852w CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/05/1999

Communications
Organometallics, Vol. 18, No. 5, 1999 815
Sch em e 1
Sch em e 2
of excess phosphine, the phosphinimine is lost, resulting
in the formation of [(η5-C5H5)Os(PPh3)(CH2SiMe3)2][SO3-
CF3], 3. Complex 3 is coordinatively unsaturated with
a 16-electron count but it can be isolated from solution.
In this proposed mechanism, complex 3 reacts with
additional PPh3 in solution. Phosphine coordination
induces R-hydrogen elimination and loss of tetrameth-
ylsilane from the complex.10 Triphenyl phosphine adds
to the electron-deficient carbon of the resulting alky-
lidene. Examples of attack by a tertiary phosphine on
an unsaturated carbon producing a phosphoylide are
known, and this type of reaction has been used to trap
methylidene intermediates.11 The phosphoylide inter-
mediate in this reaction forms the observed metalla-
cycle, 4, via orthometalation.
The reaction between triphenylphosphine and [(η5-
C5H5)Os(NCH3)(CH2SiMe3)2][SO3CF3] is complex and
depends strongly on the concentration and relative
quantity of the phosphine. The methylimido ligand is
acidic and the phosphine deprotonates it. The nitrogen
atom of the methylimido ligand is also electrophilic and
the nucleophilic phosphine adds to form an unstable
coordinated phosphinimine complex. If additional PPh3
is available, it adds to the osmium center and displaces
the phosphinimine. Excess PPh3 promotes R-hydride
elimination, adds to the resulting alkylidene at the
alkylidene carbon, and ultimately leads to the formation
of a stable metallocycle [(η5-C5H5)Os(H)(PPh3){CHSiMe3-
PPh2(C6H4)}][SO3CF3].
piano stool environment. The cyclopentadienyl ligand
is bound to the osmium in an η5 fashion and shows no
distortion. Nitridoosmium(VI) cyclopentadienyl com-
plexes show a significant distortion toward the η3
coordination mode.6
The carbon and the hydrogen atom derived from the
orthometalated phenyl group are trans to one another.
Both C40 and H have smaller Cp-Os-L angles [CpOs-
C(40) ) 111.5(3)°; Cp-Os-H ) 113.0(3)°],where Cp is
the centroid of the cyclopentadienyl moiety, than do C6
and P2 [Cp-Os-C(6) ) 129.7(3)°; Cp-Os-P(2) ) 132.1-
(3)°]. This distortion from ideal pseudo-square-pyrami-
dal geometry is common in compounds of the general
formula CpML4 in which the four L ligands are not
identical.7 The metal-hydride was located and indepen-
dently refined. The Os-H bond distance, 1.614(77) Å,
falls within the expected range (1.62-1.68 Å) for
terminal osmium hydrides.8
A proposal for the formation of 4 is shown in Scheme
3. Several transition metal imido complexes react with
phosphines at the imido nitrogen to give either a
coordinated or free phosphinimine and a reduced metal
species.9 In this case, nucleophilic attack of PPh3 on the
imido nitrogen of 1 likely forms a coordinated phos-
phinimine complex, [(η5-C5H5)Os(MeNPPh3)(CH2SiMe3)2]-
[SO3CF3]. This complex is unstable and in the presence
(9) (a) Pe´rez, P. J .; White, P. S.; Brookhart, M.; Templeton, J . L.
Inorg. Chem. 1994, 33, 6050-6056. (b) Moubaraki, B.; Murray, K. S.;
Nichols, P. J .; Thomson, S.; West, B. O. Polyhedron 1994, 13, 485-
495. (c) Dobbs, D. A.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115,
3836-3837. (d) Harlan, E. W.; Holm, R. H. J . Am. Chem. Soc. 1990,
112, 186-193. (e) Fourquet, J . L.; Leblanc, M.; Saravanamuthu, A.;
Bruce, M. R. M.; Bruce, A. E. Inorg. Chem. 1991, 30, 3241-3243. (f)
Anhaus, J . T.; Kee, T. P.; Schofield, M. H.; Schrock, R. R. J . Am. Chem.
Soc. 1990, 112, 1642-1643. (g) Sleiman, H. F.; Mercer, S.; McElwee-
White, L. J . Am. Chem. Soc. 1989, 111, 8007-8009. (h) Elliott, R. L.;
Nichols, P. J .; West, B. O. Polyhedron 1987, 6, 2191-2192.
(10) In other complexes, phosphine addition to the metal increases
steric bulk at the metal center and promotes R-elimination. Examples
include: (a) Churchill, M. R.; Wasserman, H. J .; Turner, H. W.;
Schrock, R. R. J . Am. Chem. Soc. 1982, 104, 1710-1716. (b) Rupprecht,
G. A.; Messerle, L. W.; Fellmann, J . D.; Schrock, R. R. J . Am. Chem.
Soc. 1980, 102, 6236-6244. (c) Clark, D. N.; Schrock, R. R. J . Am.
Chem. Soc. 1978, 100, 6774-6776.
(11) (a) Holmes, S. J .; Schrock, R. R.; Churchill, M. R.; Wasserman,
H. J . Organometallics 1984, 3, 476-484. (b) Churchill, M. R.; Wasser-
man, H. J . Inorg. Chem. 1982, 21, 3913-3916. (c) Hayes, J . C.; Pearson,
G. D. N.; Cooper, N. J . J . Am. Chem. Soc. 1981, 103, 4648-4650. (d)
Canestrari, M.; Green, M. L. H. J . Chem. Soc., Chem. Commun. 1979,
913-914. (e) Cooper, J . N.; Green, M. L. H. J . Chem. Soc., Dalton
Trans. 1979, 1121-1127. (f) Cooper, N. J .; Green, M. L. H. J . Chem.
Soc., Chem. Commun. 1974, 208-209. (g) Cooper, N. J .; Green, M. L.
H. J . Chem. Soc., Chem. Commun. 1974, 761-762. (h) Kreissl, F. R.;
Kreiter, C. G.; Fischer, E. O. Angew. Chem., Int. Ed. Engl. 1972, 11,
643-644.
(6) (a) Marshman, R. W.; Shusta, J . M.; Wilson, S. R.; Shapley, P.
A. Organometallics 1991, 10, 1671-1676. (b) Koch, J . L.; Shapley, P.
A. Organometallics 1997, 16, 4071-4076.
(7) (a) Cole, A. A.; Mattamana, S. P.; Poli, R. Polyhedron 1996, 15,
2351-2361. (b) Abugideiri, F.; Fettinger, J . C.; Keogh, D. W.; Poli, R.
Organometallics 1996, 15, 4407-4416. (c) Fettinger, J . C.; Kraatz, H.-
B.; Poli, R.; Rheingold, A. L. Acta Crystallogr., Sect. C 1995, C51, 364-
367. (d) Lin, Z.; Hall, M. B. Organometallics 1993, 12, 19-23.
(8) (a) J ohnson, T. J .; Albinati, A.; Koetzle, T. F.; Ricci, J .; Eisenstein,
O.; Huffman, J . C.; Caulton, K. G. Inorg. Chem. 1994, 33, 4966-4976.
(b) Bianchini, C.; Linn, K.; Masi, D.; Peruzzini, M.; Polo, A.; Vacca, A.;
Zanobini, F. Inorg. Chem. 1993, 32, 2366-2376. (c) Hart, D. W.; Bau,
R.; Koetzle, T. F. J . Am. Chem. Soc. 1977, 99, 7557-7564.

816 Organometallics, Vol. 18, No. 5, 1999
Communications
Sch em e 3
collected at 198 K on a Siemens Platform/CCD automated
diffractometer. Crystal and refinement details are given in
Table 1 (Supporting Information). Systematic conditions sug-
gested the ambiguous space group P1h; refinement confirmed
the presence of a symmetry center. Standard intensities
showed no decay during frame collection. Intensity data were
reduced by 3D-profile analysis using SAINT and corrected for
Lorentz-polarization effects and for absorption. Scattering
factors and anomalous dispersion terms were taken from
standard tables.
The structure was solved by direct methods; correct posi-
tions for 47 non-H atoms were deduced from an E-map. One
cycle of isotropic least-squares refinement followed by an
unweighted difference Fourier synthesis revealed positions for
the remaining non-H atoms. Atomic parameters for atoms H
and H(6) were independently refined. Methyl H atom positions,
Si-CH3, were optimized by rotation about Si-C bonds with
idealized C-H, Si-H, and H-H distances. Remaining H atoms
were included as fixed idealized contributors. H atom U’s, were
assigned as 1.2 times Ueq of adjacent non-H atoms. Non-H
atoms were refined with anisotropic thermal coefficients.
Successful convergence of the full-matrix least-squares refine-
ment on F2 was indicated by the maximum shift/error for the
last cycle. The highest peaks in the final difference Fourier
map were in the vicinity of Os and Cl atoms; the final map
had no other significant features. A final analysis of variance
between observed and calculated structure factors showed no
dependence on amplitude or resolution.
Exp er im en ta l Da ta
All reactions were done under nitrogen atmosphere, using
standard air-sensitive techniques with a Schlenk line or in a
Vacuum Atmospheres glovebox unless otherwise stated. Di-
ethyl ether, THF, and hexane were distilled from Na/ben-
zophenone. Methylene chloride was distilled from CaH2. All
solvents were stored over 4 Å molecular sieves. Deuterated
methylene chloride was purchased from Cambridge Isotope
Laboratories and was used without further purification.
[CpOs(NCH3)(CH2SiMe3)2][SO3CF3] was synthesized according
to literature procedure.2 All reagents were purchased from
Aldrich.
NMR spectra were recorded on a Varian Unity 500, a Varian
Unity 400, or a General Electric QE-300. Chemical shifts for
1H and 13C NMR spectra were referenced to internal solvent
resonances. IR spectra were recorded on a Perkin-Elmer 1600
series FTIR. Mass spectra were recorded on a VG ZAB-SE
(FAB). Elemental analyses were performed by the University
of Illinois microanalytical service.
P r ep a r a tion of [Cp (P P h 3)Os(CHSiMe3P P h 2(C6H4))]-
[SO3CF3], 4. One equivalent of [CpOs(NCH3)(CH2SiMe3)2][SO3-
CF3], 1, (0.092 g, 0.201 mmol) was dissolved in 30 mL of
CH2Cl2. Two equivalents of PPh3 (0.105 g, 0.400 mmol) was
added to the CH2Cl2 solution, and the reaction mixture was
stirred for 24 h. The reaction was then filtered through Celite,
and the solvent was removed from the filtrate. The residue
was washed with diethyl ether to extract CpOs(NCH2)(CH2-
SiMe3)2, 2, and MeNdPPh3. The remaining residue was taken
up in either CH2Cl2 or THF. Crystals were obtained by slowly
adding diethyl ether or hexane to the solution (0.025 g, 0.025
mmol, 12.4%). 1H NMR data (400 MHz, CD2Cl2, 18.9 °C): δ
7.96-6.72 (m, 29H, P(C6H5) and P(C6H4)), 4.94 (s, 5H, C5H5),
1.05 (d, J ) 21.6 Hz, 1H, CHSiMe3), -0.14 (s, 9H, Si(CH3)3),
-11.63 (dd, 2J PH ) 37.8 Hz, 3J PH ) 5.4 Hz, 1H, OsH). Crystals
grown from THF/hexane solution also had two multiplets at
δ 3.85 and 1.80 in the 1H NMR spectrum due to residual THF,
while crystals grown from CHCl3 had a singlet at δ 7.25 due
to residual CHCl3. 13C NMR data (125.7 MHz, CD2Cl2, 19.9
°C): δ 298.2 (m, CHSiMe3), 146.91-123.80, 83.42 (s, C5H5),
3.12 (s, Si(CH3)3). 31P{1H} NMR data (161.9 MHz, CD2Cl2, 18.9
°C): δ 57.7, 19.2. IR (KBr pellet, cm-1): 3059 (m, Cp νCH), 2961
(m, νCH), 1435 (m, δCH), 1422 (m), 1271 (s), 1221 (m), 1150 (s,
Ack n ow led gm en t. We gratefully acknowledge the
financial support of the National Science Foundation
(CHE 95-26350). NMR spectra were obtained in the
Varian Oxford Instrument Center for Excellence in
NMR Laboratory. Funding for this instrumentation was
provided in part from the W. M. Keck Foundation, the
National Institutes of Health (PHS 1 S10 RR10444-01),
and the National Science Foundation (NSF CHE 96-
10502). Purchase of the Siemens Platform/CCD diffrac-
tometer by the School of Chemical Sciences was sup-
ported by National Science Foundation Grant CHE
9503145. We thank Scott R. Wilson and Theresa Prus-
sak-Wieckowska for collection of crystal data and helpful
discussions in the solving of the crystal structures.
ν
SO), 1033 (s, νSO), 833 (m, νSiC), 638 (m, Cp δCC). Mass
spectroscopy (FAB, MB, m/z): 867.2 (M+), 605.2 (M+ - PPh3).
Anal. Calcd for OsC46H45P2SiSO3F3‚C4H8O: C, 55.24: H, 4.91;
P, 5.7. Found: C, 55.13; H, 5.15; P, 5.79.
Su p p or tin g In for m a tion Ava ila ble: For 4, tables of
additional crystal data collection and refinement parameters,
atomic coordinates, thermal parameters, and complete tables
of distances and angles are provided. This material is available
free of charge via the Internet at http://pubs.acs.org.
Cr ysta l Da ta a n d Str u ctu r e Refin em en t Su m m a r y for
4•(CH2Cl2)2. The data crystal was mounted using oil (Para-
tone-N, Exxon) to a thin glass fiber. Diffraction data were
OM980852W