Dissociative and nondissociative pathways in the endo to exo isomerization of tetramethyl-o-xylylene complexes of ruthenium and osmium, ML3{η4o-C6Me4(CH 2)2} (M = Ru, L = PMe3; M = Os, L = PMe3, PMe2Ph).

Article abstract of DOI:10.1021/om9804226

Treatment of the (η⁶-hexamethylbenzene)ruthenium(II) and -osmium(II) salts [M(O₂-CCF₃)L₂(η⁶-C ₆Me₆)]PF₆ (M = Ru, L = PMe₃; M = Os, L = PMe₃, PMe₂Ph) in the presence of L with KO-t-Bu gives exclusively the endo- (tetramethyl-o-xylylene)metal(0) complexes ML₃{η⁴-endo-o-C₆Me₄(CH ₂)₂}, endo-1, -2, and -3, respectively, in high yield; these are protonated by an excess of triflic acid (CF₃SO₃H, TfOH) to give the (η⁶-hexamethylbenzene)metal(II) salts [ML₃(η⁶-C₆Me₆)](OTf)₂ [M = Ru, L = PMe₃ (4); M = Os, L = PMe₃ (5); M = Os, L = PMe₂Ph (6)). Complexes 4-6 revert to endo-1-3 on treatment with KO-t-Bu, whereas for M=Ru, L=PMe₂Ph the complexes [ML₃(η⁶-C₆Me₆)]²⁺ and [M(O₂CCF₃)L₂(η⁶-C ₆-Me₆)]⁺/L react with KO-t-Bu to give exclusively the exo isomer, Ru(PMe₂Ph)₃{η⁴-exo-o-(CH₂) ₂C₆Me₄} (exo-7). The endo complexes 1-3 are converted quantitatively into the corresponding exo isomers in toluene in the temperature range 65-106°C, the process being first order in endo complex. Kinetics studies in the presence of PMe₃ (for 1 and 2) or PMe₂-Ph (for 3) indicate that two pathways are available: one depends on initial dissociation of L and proceeds through a bis(ligand) intermediate or intermediates, e.g., ML₂{endo-o-C₆-Me₄(CH₂)₂} and ML₂{exo-o-(CH₂)₂C₆Me₄}, and the other does not. The dissociative mechanism is predominant for M = Ru, L = PMe₃, whereas the nondissociative or direct mechanism plays the dominant, possibly exclusive, role for M = Os, L = PMe₃. The osmium(0) compound exo-2 adds PMe₃ irreversibly to give the σ-bonded (hexamethylbenzene-1,2-diyl)osmium(II) complex Os(PMe₃)₄{κ²-o-(CH₂) ₂C₆Me₄} (8), whereas the corresponding PMe₂Ph derivative 9 is in equilibrium with exo-3 and PMe₂Ph and cannot be isolated; the ruthenium(0) compound exo-1 is inert toward PMe₃. Density functional calculations on the model compounds ML₃-{η⁴-exo-o-(CH₂)₂C ₆H₄} and ML₄{κ²-o-(CH₂)₂C ₆H₄}(M = Ru, Os; L = PH₃) correctly reflect the observed stability order Os > Ru for the diyl complex but predict the latter to be more stable than the η⁴ complex for both elements. In this case, the usual computational simplification of replacing a tertiary phosphine by PH₃ is probably unjustified. The molecular structures of the η⁴ complexes endo-3, exo-3, and exo-1 and of the diyl complex 8 have been determined by X-ray crystallography. The endo- to exo-o-xylylene isomerizations are compared with the intramolecular migrations that occur in Fe(CO)₃(η⁴-polyene) and Cr(CO)₃(η⁶-substituted-naphthalene) complexes.

Full text of DOI:10.1021/om9804226

3784
Organometallics 1998, 17, 3784-3797
Dissocia tive a n d Non d issocia tive P a th w a ys in th e en d o
to exo Isom er iza tion of Tetr a m eth yl-o-xylylen e
Com p lexes of Ru th en iu m a n d Osm iu m ,
ML3{η4-o-C6Me4(CH2)2} (M ) Ru , L ) P Me3; M ) Os, L )
P Me3, P Me2P h ). F or m a tion of
Hexa m eth ylben zen e-1,2-d iyl Com p lexes by Liga n d
Ad d ition to th e exo-Osm iu m Com p lexes
Martin A. Bennett,*,† Mark Bown,† David C. R. Hockless,† J ohn E. McGrady,‡
Harold W. Schranz,† Robert Stranger,‡ and Anthony C. Willis†
Research School of Chemistry and the Department of Chemistry, Australian National
University, Canberra, ACT 0200, Australia
Received May 26, 1998
Treatment of the (η6-hexamethylbenzene)ruthenium(II) and -osmium(II) salts [M(O2-
CCF3)L2(η6-C6Me6)]PF6 (M ) Ru, L ) PMe3; M ) Os, L ) PMe3, PMe2Ph) in the presence of
L with KO-t-Bu gives exclusively the endo- (tetramethyl-o-xylylene)metal(0) complexes
ML3{η4-endo-o-C6Me4(CH2)2}, endo-1, -2, and -3, respectively, in high yield; these are
protonated by an excess of triflic acid (CF3SO3H, TfOH) to give the (η6-hexamethylbenzen-
e)metal(II) salts [ML3(η6-C6Me6)](OTf)2 [M ) Ru, L ) PMe3 (4); M ) Os, L ) PMe3 (5); M )
Os, L ) PMe2Ph (6)). Complexes 4-6 revert to endo-1-3 on treatment with KO-t-Bu,
whereas for M)Ru, L)PMe2Ph the complexes [ML3(η6-C6Me6)]2+ and [M(O2CCF3)L2(η6-C6-
Me6)]+/L react with KO-t-Bu to give exclusively the exo isomer, Ru(PMe2Ph)3{η4-exo-o-
(CH2)2C6Me4} (exo-7). The endo complexes 1-3 are converted quantitatively into the
corresponding exo isomers in toluene in the temperature range 65-106 °C, the process being
first order in endo complex. Kinetics studies in the presence of PMe3 (for 1 and 2) or PMe2-
Ph (for 3) indicate that two pathways are available: one depends on initial dissociation of
L and proceeds through a bis(ligand) intermediate or intermediates, e.g., ML2{endo-o-C6-
Me4(CH2)2} and ML2{exo-o-(CH2)2C6Me4}, and the other does not. The dissociative mecha-
nism is predominant for M ) Ru, L ) PMe3, whereas the nondissociative or direct mechanism
plays the dominant, possibly exclusive, role for M ) Os, L ) PMe3. The osmium(0) compound
exo-2 adds PMe3 irreversibly to give the σ-bonded (hexamethylbenzene-1,2-diyl)osmium(II)
complex Os(PMe3)4{κ2-o-(CH2)2C6Me4} (8), whereas the corresponding PMe2Ph derivative 9
is in equilibrium with exo-3 and PMe2Ph and cannot be isolated; the ruthenium(0) compound
exo-1 is inert toward PMe3. Density functional calculations on the model compounds ML3-
{η4-exo-o-(CH2)2C6H4} and ML4{κ2-o-(CH2)2C6H4}(M ) Ru, Os; L ) PH3) correctly reflect the
observed stability order Os > Ru for the diyl complex but predict the latter to be more stable
than the η4 complex for both elements. In this case, the usual computational simplification
of replacing a tertiary phosphine by PH3 is probably unjustified. The molecular structures
of the η4 complexes endo-3, exo-3, and exo-1 and of the diyl complex 8 have been determined
by X-ray crystallography. The endo- to exo-o-xylylene isomerizations are compared with
the intramolecular migrations that occur in Fe(CO)3(η4-polyene) and Cr(CO)3(η6-substituted-
naphthalene) complexes.
In tr od u ction
In its mononuclear complexes, o-xylylene (o-quino-
dimethane, xylene-1,2-diyl) can bind as a η4 conjugated
diene to transition-metal atoms either via the endocyclic
pair of double bonds (Figure 1a), as in M(η6-C6Me6){η4-
o-C6Me4(CH2)2} (M ) Fe,1,2 Ru3,4), or via the exocyclic
F igu r e 1. Coordination modes for o-xylylene.
pair of double bonds (Figure 1b), as in Fe(CO)3{η4-o-
(CH2)2C6H4}5,6 and Co(η5-C5H5){η4-o-(CH2)2C6H4}.7 As
† Research School of Chemistry.
‡ Department of Chemistry.
(1) Madonic, A. M.; Astruc, D. J . Am. Chem. Soc. 1984, 106, 2437.
(2) Astruc, D.; Mandon, D.; Madonik, A.; Michaud, P.; Ardoin, N.;
Varret, F. Organometallics 1990, 9, 2155.
(3) Hull, J . W., J r.; Mann, C.; Gladfelter, W. L. Organometallics
1992, 11, 3117.
(4) Hull, J . W., J r.; Gladfelter, W. L. Organometallics 1982, 1, 1716.
S0276-7333(98)00422-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 07/21/1998

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3785
shown in Figure 1c, o-xylylene can also behave as a two-
electron σ-donor ligand via the exocyclic methylene
groups, mainly to metal atoms in medium to high
oxidation states; examples of mononuclear κ2 complexes
of this type are Pt{o-(CH2)2C6H4}(1,5-COD),8 M(η5-
C5H5)2{η4-o-(CH2)2C6H4} (M ) Ti, Zr, Hf),9 and W{η4-
o-(CH2)2C6H4}3.10
osmium with PMe3 and PMe2Ph as coligands and show
that in these compounds thermal isomerization occurs
much more easily; further, for osmium with PMe2Ph,
the η4-exo and κ2 bonding modes are interconvertible.
Exp er im en ta l Section
We have shown that the 4d8 fragment Ru(PMe2Ph)3
is capable of coordinating o-xylylene in both exo and
endo modes. Deprotonation of the (arene)ruthenium-
(II) monocationic salts [Ru(O2CCF3)(PMe2Ph)2(η6-are-
ne)]PF6 (arene ) C6Me6, 1,2-C6H4Me2) with KO-t-Bu or
Na[N(SiMe3)2] in the presence of PMe2Ph gives the
corresponding exo-o-xylylene complexes (eq 1),11 whereas
Gen er a l P r oced u r es. The following instruments were
used: Varian XL200 (13C NMR at 50.29 MHz), Varian VXR-
300S and Varian Gemini 300 (1H NMR at 300 MHz, 31P NMR
at 121.42 MHz, 13C NMR at 75.43 MHz), Varian VXR-500S
(1H NMR at 500 MHz), VG AutoSpec (EI mass spectra at 70
eV) and VG ZAB-2SEQ (EI at 70 eV, FAB at 30 kV, Cs ions
using a NBA matrix), VG Quattro II (electrospray triple
quadrupole), and Perkin-Elmer 683 (infrared). The NMR
spectroscopic data for the tetramethyl-o-xylylene complexes
are collected in Tables 1 and 2.
Organic solvents of reagent grade were dried by published
procedures17 and distilled under nitrogen before use. All
operations with endo- and exo-tetramethyl-o-xylylene com-
plexes were carried out under argon by standard Schlenk
techniques. The (η6-hexamethylbenzene)-ruthenium(II) and
-osmium(II) precursors were handled in air. Elemental analy-
ses were carried out in-house. The compounds [Ru(O2CMe)2-
(η6-C6Me6)]‚H2O,18 [OsCl2(η6-C6Me6)]2,19,20 and [Ru(PMe2Ph)3-
11
(C6Me6)](CF3SO3)2 were prepared as described.
P r ep a r a tion s. (a ) Ru (O2CCF 3)2(P Me3)(η6-C6Me6). This
compound has been prepared previously by treatment of
RuMe2(PMe3)(η6-C6Me6) with an excess of CF3CO2H.21 We
made it as follows. A sample of [Ru(O2CMe)2(η6-C6Me6)]‚H2O
(200 mg, 0.501 mmol) was treated with trifluoroacetic acid (4
mL) at room temperature for 4 h. The excess acid was
removed under reduced pressure and the orange crystalline
product, presumed to be [Ru(O2CCF3)2(η6-C6Me6)], was dis-
solved in dichloromethane (10 mL) to give a yellow-orange
solution. Addition of PMe3 (52 µL, 0.502 mmol) gave an orange
solution, which was stirred at room temperature for 17 h. The
solvent was removed under reduced pressure, and the residue
was washed with n-hexane (3 × 20 mL). Yellow microcrystals
of Ru(O2CCF3)2(PMe3)(η6-C6Me6) (257 mg, 92%) were obtained
by crystallization from dichloromethane/n-hexane. 1H NMR
(CD2Cl2, 300 MHz): δ 2.08 (d, J PH ) 1.0 Hz, C6Me6), 1.33 (d,
J PH ) 10.8 Hz, PMe3). Lit.21 1H NMR (C6H6, 60 MHz): δ 1.69
(d, J PH ) 0.8 Hz, C6Me6), 1.06 (d, J PH ) 8.3 Hz, PMe3). 31P{1H}
NMR (CD2Cl2, 121.42 MHz): δ 6.30. Lit.21 31P{1H} NMR
(C6H6, 36.43 MHz): δ 3.64. 13C{1H} NMR (CD2Cl2, 75.43
treatment of the dicationic salts [M(η6-o-C6H4Me2)(PMe2-
Ph)3](PF6)2 (M ) Ru, Os) with KO-t-Bu gives exclusively
the endo-o-xylylene complexes M(PMe2Ph)3{η4-o-(CH2)2-
C6H4} (eq 2).12 The exo complexes have also been made
independently by reaction of RuCl2(PMe2Ph)4 with the
appropriate o-methylbenzyl Grignard or lithium
reagents.13-15 Density functional calculations on the
model compound Ru(PH3)3{η4-o-(CH2)2C6H4} show that
the exo compound is ca. 60 kJ mol-1 more stable than
its endo isomer, mainly because of aromatic stabilization
in the former;16 however, since no thermal interconver-
sion of the isomers was observed, it was assumed that
the process must be thermally forbidden. In this report,
we extend our studies to tetramethyl-o-xylylene com-
plexes of ruthenium with PMe3 as coligand and of
MHz): δ 95.09 (s, C6Me6), 16.37 (s, C6Me6), 13.87 (d, J PC
29.65 Hz, PMe3).
)
This compound was converted into [Ru(O2CCF3)(PMe3)2(η6-
C6Me6)]PF6 by treatment with PMe3/NH4PF6.21
(b) Os(O2CCF3)2(P Me3)(η6-C6Me6). A mixture of [OsCl2(η6-
C6Me6)]2 (100 mg, 0.181 mmol) and silver acetate (85 mg, 0.50
mmol) was stirred for 12 h in benzene (20 mL). The resulting
solution was filtered through Celite to remove AgCl, solvent
was removed under reduced pressure, and the solid yellow
residue was treated with trifluoroacetic acid (4 mL) for 30 min
to give a blue solution (the color probably arises from traces
of osmium trifluoroacetato complexes formed by loss of arene).
The excess of acid was removed under reduced pressure, and
the residue was dissolved in dichloromethane (10 mL) to give
a deep blue solution. Addition of PMe3 (40 µL, 0.386 mmol)
(5) Roth, W. R.; Meier, J . D. Tetrahedron Lett. 1967, 2053.
(6) J ohnson, B. F. G.; Lewis, J .; Thompson, D. J . Tetrahedron Lett.
1974, 3789.
(7) Hersh, W. H.; Hollander, F. J .; Bergman, R. G. J . Am. Chem.
Soc. 1983, 105, 5834.
(8) Lappert, M. F.; Martin, T. R.; Raston, C. L.; Skelton, B. W.;
White, A. H. J . Chem. Soc., Dalton Trans. 1982, 1959.
(9) Bristow, G. S.; Lappert, M. F.; Martin, T. R.; Atwood, J . L.;
Hunter, W. F. J . Chem. Soc., Dalton Trans. 1984, 399.
(10) Lappert, M. F.; Raston, C. L.; Rowbottom, G. L.; Skelton, B.
W.; White, A. H. J . Chem. Soc., Dalton Trans. 1984, 883.
(11) Bennett, M. A.; Goh, L. Y.; McMahon, I. J .; Mitchell, T. R. B.;
Robertson, G. B.; Turney, T. W.; Wickramasinghe, W. A. Organome-
tallics 1992, 11, 3069.
(12) Bennett, M. A.; Bown, M.; Goh, L. Y.; Hockless, D. C. R.;
Mitchell, T. R. B. Organometallics 1995, 14, 1000.
(13) Chappell, S. D.; Cole-Hamilton, D. J .; Galas, A. M. R.; Hurst-
house, M. B. J . Chem. Soc., Dalton Trans. 1982, 1867.
(14) Simpson, N. J .; Cole-Hamilton, D. J . Polyhedron 1988, 19/ 20,
1945.
(15) Simpson, N. J .; Cole-Hamilton, D. J . J . Chem. Soc., Dalton
Trans. 1990, 1329.
(16) McGrady, J . E.; Stranger, R.; Bown, M.; Bennett, M. A.
Organometallics 1996, 15, 3109.
(17) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 4th ed.; Butterworth-Heinemann: Oxford, U.K., 1996.
(18) Tocher, D. A.; Gould, R. O.; Stephenson, T. A.; Bennett, M. A.;
Ennett, J . P.; Matheson, T. W.; Sawyer, L. S.; Shah, V. K. J . Chem.
Soc., Dalton Trans. 1983, 1571.
(19) Bown, M.; Fontaine, X. L. R.; Greenwood, N. N.; Kennedy, J .
D. J . Organomet. Chem. 1987, 325, 233.
(20) Kiel, W. A.; Ball, R. G.; Graham, W. A. G. J . Organomet. Chem.
1990, 383, 481.
(21) Werner, H.; Kletzin, H. J . Organomet. Chem. 1982, 228, 289.

Ta ble 1. 1H, 13C{1H}, a n d 31P {1H} NMR Da ta for o-Xylylen e Com p ou n d s en d o-1-3 a n d exo-1-3a ,b
o-xylylene
phosphine
assgt
δ(13C{1H})
δ(1H)
δ(31P{1H})
δ(1H)
δ(13C)
Ru(PMe3)3{η4-endo-o-
C6Me4(CH2)2}c (1)
dCH2
C1,2
C3,6
90.74
4.57 (m), 5.29 (m)
-4.6 (d, 2P)
-12.8 (t, 1P, J PP ) 11.5 Hz)
PMe3: 1.25 (dd, 9H, J PH ) 1.1,
6.9 Hz), 0.97 (m, 18H)
PMe3: 25.04 (appt td, 6C,
3.3,11.0 Hz), 19.33 (d,
3C, 20.9 Hz)
154.16 (d, J PC ) 4.4 Hz)
25.03 (td, J PC ) 3.3, 10.7 Hz)
80.30 (d, J PC ) 3.3 Hz)
C4,5
H-C31,61 22.86
H-C41,51 17.87
1.71 (m)
1.90 (m)
Os(PMe3)3{η4-endo-o-
dCH2
92.10
4.53 (m), 5.28 (m)
-54.2 (d, 2P)
-55.1 (t, 1P, J PP ) 6.1 Hz)
PMe3: 1.37 (dd, 9H, J PH ) 1.0,
8.0 Hz), 1.15 (dd, 18H,
J PH ) 1.0, 6.6 Hz)
PMe3: 25.56 (sym m, 6C),
20.35 (appt dt, 3C, 29.0,
2.1 Hz)
C6Me4(CH2)2}]d,e (2) C1,2
156.02 (d, J PC ) 4.2 Hz)
47.97 (td, J PC ) 4.6, 12.5 Hz)
86.04 (dt, J PC ) 5.0, 2.1 Hz)
C3,6
C4,5
H-C31,61 23.53
H-C41,51 17.39
1.71 (d, J PH ) 3.6 Hz)
2.00 (dt, J PH ) 2.4, 0.7 Hz)
Os(PMe2Ph)3{η4-endo-o- dCH2
94.70
4.43 (s), 5.29 (s)
-36.6 (d, 2P)
-39.1 (t, 1P, J PP ) 8.7 Hz)
PMe2Ph: 1.91 (d, 6H, J PH ) 7.9
Hz), 1.57 (d, 6H, J PH ) 6.9
Hz), 1.27 (d, 6H, J PH ) 6.4 Hz)
PMe2Ph: 6.9-7.7 (m, 15H)
PMe2Ph: 23.60 (d, 2C, 1.6
Hz), 23.32 (m, 2C), 19.47
(m, 2C)
C6Me4(CH2)2}f-h (3) C1,2
155.29 (d, J PC ) 4.1 Hz)
46.96 (td, J PC ) 4.6, 12.8 Hz)
86.96 (d, J PC ) 5.2 Hz)
C3,6
C4,5
PMe2Ph: 125-147 (m)
H-C31,61 23.11
H-C41,51 15.59 (d, J PC ) 1.9 Hz)
1.38 (t, J PH ) 3.4 Hz)
1.59 (d, J PH ) 2.4 Hz)
Ru(PMe3)3{η4-exo-o-
dCH2
27.61 (m)
102.3 (q, J PC ) 2.2 Hz)
132.82
-0.38 (m, Hanti), 2.09 (m, Hsyn) -7.4 (d, 2P)
14.5 (t, 1P, J PP ) 7.3 Hz)
PMe3: 1.35 (d, 9H, J PH ) 7.8
PMe3: 23.37 (appt t, 6C, 10.4
Hz), 25.26 (appt dt, 3C,
23.3, 2.9 Hz)
2
(CH2)2C6Me4}d,f,i (1) C1,2
Hz), 0.91 (vt, 18H, J PH
+
C3,6
C4,5
4J PH ) 5.7 Hz)
132.03
H-C31,61 18.40
H-C41,51 17.66
2.36 (s)
2.13 (s)
Os(PMe3)3{η4-exo-o-
(CH2)2C6Me4}j (2)
dCH2
C1,2
C3,6
22.40 (m)
97.86 (q, J PC ) 2.6 Hz)
132.57
-0.02 (m, Hanti), 2.50 (m, Hsyn) -55.0 (d, 2P)
PMe3: 1.50 (d, 9H, J PH ) 8.8
Hz), 1.08 (d, 18H, J PH ) 6.5
Hz)
PMe3: 24.09 (appt td, 6C,
15.4, 3.9 Hz), 25.51 (appt
dt, 3C, 31.3, 3.0 Hz)
-38.0 (t, 1P, J PP ) 11.5 Hz)
C4,5
130.07
H-C31,61 19.10
2.14 (s)
2.41 (s)
H-C41,51 17.38
Os(PMe2Ph)3{η4-exo-o- dCH2
22.99 (m)
99.54 (q, J PC ) 2.3 Hz)
132.82
-0.06 (m, Hanti), 2.51 (m, Hsyn) -39.7 (d, 2P)
PMe2Ph: 1.89 (d, 6H, J PH ) 8.6
Hz), 1.33 (d, 6H, J PH ) 6.4 Hz),
1.26 (d, 6H, J PH ) 6.1 Hz)
PMe2Ph: 23.38 (appt dt,
3C, 32.63, 2.3 Hz), 22.67
(d, 3C, 12.2 Hz), 22.46 (d,
3C, 11.2 Hz)
(CH2)2C6Me4}f,h (3)
C1,2
C3,6
-26.6 (t, 1P, J PP ) 14.8 Hz)
C4,5
132.03
PMe2Ph: 6.5-7.6 (m, 15H)
PMe2Ph: 126-147 (m)
H-C31,61 18.40
H-C41,51 17.66
2.09 (s)
2.14 (s)
a
Numbering of o-xylylene nuclei:
b 1H NMR at 300 MHz, 31P NMR at 121.42 MHz, and 13C NMR at 75.43 MHz in benzene-d6 at 298 K, except where stated otherwise. c 1H and 13C resonances were assigned by comparison with
d
the spectra of endo-3 and endo-2. 1H NMR at 500 MHz. e Assignments of 1H and 13C resonances were obtained from multiple-bond 2D [1H-13C]-GHMQC experiments at 500 MHz. f In toluene-
h
d8 at 298 K. g 13C NMR at 50.29 MHz. 1H and 13C resonances were assigned from single- and multiple-bond 2D [1H-13C]-GHMQC experiments at 500 MHz. i 1H and 13C resonances were
assigned from a multiple-bond 2D [1H-13C]-GHMQC experiment at 500 MHz and a [1H-13C] COSY experiment at 75.43 MHz. j 1H and 13C resonances were assigned by comparison with the
spectra of exo-3.

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3787
gave an orange solution, which was stirred at room temper-
ature for 1 h. The solvent was removed under reduced
pressure and the residue washed with n-hexane (3 × 20 mL).
Yellow microcrystals of Os(O2CCF3)2(PMe3)(η6-C6Me6) (175 mg,
74%) were obtained by crystallization from dichloromethane/
n-hexane. 1H NMR (CD2Cl2, 300 MHz): δ 2.11 (s, C6Me6), 1.36
2
(d, J PH ) 10.5 Hz, PMe3). 31P{1H} NMR (CD2Cl2, 121.42
MHz): δ 30.35 (s). MS (FAB): m/z 656, [M]+. Anal. Calcd
for C19H27F6O4OsP: C, 34.86; H, 4.16. Found: C, 34.83; H,
4.05.
(c) [Os(O2CCF 3)(P Me3)2(η6-C6Me6)]P F 6. A sample of
[Os(O2CCF3)2(PMe3)(η6-C6Me6)] in methanol (5 mL), which had
been made directly, without isolation, from [OsCl2(η6-C6Me6)]2
(249 mg, 0.293 mmol), was treated successively with PMe3 (125
µL, 1.23 mmol) and NH4PF6 (1.65 g, 10.12 mmol) in water (1.5
mL) to give the product as a pale yellow precipitate. After
filtration, washing with water, and drying under vacuum, 323
mg (72%) of the product was obtained. 1H NMR (CD2Cl2, 300
MHz): δ 2.20 (s, C6Me6), 1.59 (vt, 2J PH + 4J PH ) 10.0 Hz, PMe3).
31P{1H} NMR (CD2Cl2, 121.42 MHz) δ -40.7 (s, PMe3), -143.8
(spt, PF6, J PF ) 711 Hz). MS (FAB): m/z 619, [M - PF6]+.
Anal. Calcd for C20H36F9O2OsP3: C, 31.50; H, 4.76; P, 12.18.
Found: C, 31.03; H, 4.75; P, 12.08.
(d ) [Os(O2CCF 3)(P Me2P h )2(η6-C6Me6)]P F 6. A mixture of
[OsCl2(η6-C6Me6)]2 (213 mg, 0.252 mmol) and silver acetate
(168 mg, 1.01 mmol) was stirred for 69 h in benzene (50 mL)
and treated with trifluoroacetic acid (4 mL) as described in
(b). The blue residue obtained after removal of the excess acid
was dissolved in methanol (10 mL) to give a red-blue dichroic
solution. Successive addition of PMe2Ph (142 µL, 1.00 mmol)
and a solution of NH4PF6 (600 mg) in water (500 µL) precipi-
tated the required compound as a yellow solid (175 mg), which
was collected by filtration, washed with water, and dried in
vacuo. The mother liquor was evaporated to dryness under
reduced pressure. The residue was washed with water and
extracted with dichloromethane (ca. 10 mL). The filtered
extract was concentrated under reduced pressure to ca. 2 mL.
Addition of ether gave a second crop of product (176 mg) as a
crystalline yellow solid. The total amount of [Os(O2CCF3)(PMe2-
Ph)2(η6-C6Me6)]PF6 was 351 mg (79%). 1H NMR (CD2Cl2, 300
2
MHz): δ 7.7-7.4 (m, PMe2Ph), 1.83 (s, C6Me6), 1.81 (vt, J PH
4
2
4
+ J PH ) 9.3 Hz), 1.63 (vt, J PH + J PH ) 10.2 Hz) (PMe2Ph).
31P{1H} NMR (CD2Cl2, 121.42 MHz): δ -35.7 (s, PMe2Ph),
-143.8 (spt, PF6, J PF ) 711 Hz). MS (FAB): m/z 743, [M -
PF6]+. Anal. Calcd for C30H40F9O2OsP3: C, 40.63; H, 4.55.
Found: C, 40.46; H, 4.35.
(e) Ru (P Me3)3{η4-en do-o-C6Me4(CH2)2}, en do-1. A stirred
suspension of [Ru(O2CCF3)(PMe3)2(η6-C6Me6)]PF6 (176 mg, 0.26
mmol) in THF (30 mL) was treated successively with PMe3
(27 µL, 0.265 mmol) and an excess of KO-t-Bu (293 mg, 2.6
mmol), and the mixture was stirred at room temperature for
18 h. The THF was removed under reduced presure, and the
yellow residue was extracted with ether (2 × 20 mL). The
solution was filtered through Celite, and the solvent was
removed under reduced pressure to give endo-1 as a yellow,
crystalline solid (112 mg, 88%). IR (KBr disk): 1510 cm-1 (ν-
(free CdC)). MS (EI): m/z 490 (parent ion). Anal. Calcd for
C
21H43RuP3: C, 51.52; H, 8.85. Found: C, 51.23; H, 8.85.
(f) Ru (P Me3)3{η4-o-exo-(CH2)2C6Me4}, exo-1. A sample of
endo-1 (ca. 30 mg) in toluene-d8 (ca. 600 µL) was heated at
110 °C for 16 h, during which time the solution changed from
yellow to deep gold. Monitoring by 1H and 31P{1H} NMR
spectroscopy showed the endo to exo isomerization was quan-
titative and complete. The solvent was removed under reduced
pressure to give exo-1 as yellow crystals. X-ray-quality crystals
were grown by slow evaporation of the toluene-d8 solution. MS
(EI): m/z 490 (parent ion). Anal. Calcd for C21H43RuP3: C,
51.52; H, 8.85. Found: C, 51.25; H, 8.62.
(g) Os(P Me3)3{η4-en d o-o-C6Me4(CH2)2}, en d o-2. This was
obtained as a yellow, crystalline solid similarly to endo-1 from
[Os(O2CCF3)(PMe3)2(η6-C6Me6)]PF6 (312 mg, 0.41 mmol) in

3788 Organometallics, Vol. 17, No. 17, 1998
Bennett et al.
THF (40 mL), PMe3 (41 µL, 0.40 mmol), and an excess of KO-
t-Bu (449 mg, 4.0 mmol). The yield was 228 mg (96%). IR
for C23H45F6O6OsP3S2: C, 31.43; H, 5.16; P, 10.57. Found: C,
31.56; H, 5.31; P, 10.46.
(KBr disk): 1572 cm-1 (ν(free CdC)). MS (EI): m/z (parent
(m ) [Os(P Me2P h )3(η6-C6Me6)](CF 3SO3)2 (6). (i) Addition
of an excess of triflic acid (120 µL, 1.3 mmol) to a stirred
solution of endo-3 (53 mg, 0.069 mmol) in ether (20 mL) gave
a deep yellow precipitate, which was separated by filtration,
washed with ether (2 × 5 mL), and dried under vacuum.
Yellow crystals of 6 (41 mg, 56%) were obtained by vapor
diffusion of ether into an acetone solution.
12
ion) calcd for
C
1H43192Os31P3 580.2193, found 580.2179.
21
Anal. Calcd for C21H43OsP3: C, 43.59; H, 7.49; P, 16.06.
Found: C, 43.01; H, 8.02; P, 15.82.
(h ) Os(P Me3)3{η4-exo-o-(CH2)2C6Me4}, exo-2. This was
prepared as yellow microcrystals from endo-2 by following the
procedure for exo-1. MS (EI): m/z (parent ion) calcd for
12
C
1H43192Os31P3 580.2193, found 580.2179. Anal. Calcd for
(ii) A sample of exo-3 (80 mg, 0.105 mmol) in ether (40 mL)
was treated with two 100 µL portions of triflic acid, as
described for exo-1 and exo-2. After recrystallization from
acetone/ether, 6 was obtained as an off-white solid (56 mg,
50%). 1H NMR (CD2Cl2, 300 MHz): δ 7.7-7.2 (m, Ph), 2.13
(s, C6Me6), 2.06 (vt, 2J PH + 4J PH ) 8.9 Hz, PMe2). 31P{1H} NMR
(CD2Cl2, 121.42 MHz): δ -48.9 (s). MS (FAB): m/z 917, [M
- CF3SO3]+. Anal. Calcd for C38H52F6OsO6P3S2: C, 42.85; H,
4.83; S, 6.02. Found: C, 42.43; H, 4.51; S, 5.90.
(n ) Os(P Me3)4{K2-o-(CH2)2C6Me4} (8). A solution of exo-2
(48 mg, 0.083 mmol) in toluene-d8 (600 µL) was treated with
PMe3 (20 µL, 0.196 mmol). Removal of the volatile materials
under reduced pressure gave 8 as a white crystalline solid (50
mg, 92%). X-ray-quality crystals were grown by slow evapora-
21
C21H43OsP3: C, 43.59; H, 7.49. Found: C, 43.72; H, 7.32.
(i) Os(P Me2P h )3{η4-en d o-o-C6Me4(CH2)2}, en d o-3. This
was obtained as a yellow solid similarly to endo-1 from [Os-
(O2CCF3)(PMe2Ph)2(η6-C6Me6)]PF6 (173 mg, 0.195 mmol) in
THF (40 mL), PMe2Ph (28µL, 0.197 mmol), and an excess of
KO-t-Bu (66 mg, 0.585 mmol), the mixture being stirred at
room temperature for 24 h. The yield was 125 mg (84%).
X-ray-quality crystals were grown by diffusion of pentane into
a benzene solution. IR (KBr disk): 1584 cm-1 (ν(free CdC)).
12
MS (EI): m/z (parent ion) calcd for
C
1H49192Os31P3 766.2662,
36
found 766.2664. Anal. Calcd for C36H49P3Os: C, 56.53; H,
6.46. Found: C, 56.43; H, 6.42.
(j) Os(P Me2P h )3{η4-exo-o-(CH2)2C6Me4}, exo-3. This was
obtained similarly to exo-1 by heating endo-3 in toluene-d8 at
70 °C for 16 h. X-ray-quality crystals were grown from
tion of a solution in toluene-d8. MS (EI): m/z (parent ion) calcd
12
for
C
C
1H52190Os31P4 654.2604, found 654.2607; calcd for
24
1H52192Os31P4 656.2634, found 656.2624. Anal. Calcd for
12
isopentane at -78 °C. MS (EI): m/z (parent ion) calcd for
24
12
1H49192Os31P3 766.2662, found 766.2656. Anal. Calcd for
C
24H52OsP4: C, 44.03; H, 8.01; P, 18.92. Found: C, 44.29; H,
C
36
8.32; P, 18.67.
C
36H49OsP3: C, 56.53; H, 6.46. Found: C, 55.80; H, 6.51.
(k ) [Ru (P Me3)3(η6-C6Me6)](CF 3SO3)2 (4). (i) A solution of
(o) Os(P Me2P h )4{K2-o-(CH2)2C6Me4} (9). A solution of
exo-3 (16 mg, 0.021 mmol) in toluene-d8 (600 µL) was treated
with PMe2Ph (5 µL, 0.031 mmol). The solution was shown by
31P NMR spectroscopy to contain an equilibrium mixture of
exo-3, 9, and PMe2Ph. Complex 9 could not be isolated by
column chromatography; it was therefore identified by com-
parison of its spectroscopic parameters with those of 8 (Table
2).
Dep r oton a tion of [ML3(η6-C6Me6)]2+. (a) A stirred sus-
pension of complex 4 (M ) Ru, L ) PMe3; 135 mg, 0.113 mmol)
in THF (30 mL) was treated with an excess of KO-t-Bu (135
mg, 1.20 mmol) for 2 h. The solvent was removed under
reduced pressure, and the resulting yellow residue was
extracted with ether (3 × 10 mL). The extracts were filtered
through Celite, and the ether was pumped off to give endo-1
(50 mg, 91%).
endo-1 (71 mg, 0.145 mmol) in THF (20 mL) was treated with
an excess of triflic acid (130 µL, 1.15 mmol). The resulting
yellow precipitate was separated by filtration, washed with
ether (2 × 20 mL), and dried under vacuum. Yellow crystals
of 4 (96 mg, 84%) were obtained by diffusion of ether vapor
into an acetone solution.
(ii) A suspension of exo-1 (46 mg, 0.094 mmol) in ether (20
mL) was treated with triflic acid (50 µL, 0.565 mmol). The
resulting pale yellow precipitate was separated by filtration
1
and washed with ether. Since the H NMR spectrum showed
the presence of some monoprotonated product,11 the solid was
dissolved in methanol (5 mL) and treated with another 50 µL
portion of triflic acid to give a yellow solution. The solvent
was removed under reduced pressure to give a brown oil, which
solidified on addition of ether (20 mL). The product was
recrystallized from acetone/ether to give 4 (64 mg, 86%). 1H
NMR (acetone-d6, 300 MHz): δ 2.52 (q, J PH ) 0.7 Hz, C6Me6),
1.86 (vt, 2J PH + 4J PH ) 9.7 Hz, PMe3). 31P{1H} NMR (acetone-
d6, 121.42 MHz): δ 5.83 (s). MS (electrospray (MeOH)): m/z
641, [M - CF3SO3]+. Anal. Calcd for C23H45F6O6RuP3S2: C,
34.98; H, 5.74. Found: C, 34.60; H, 5.66.
(b) A stirred suspension of [Ru(PMe2Ph)3(η6-C6Me6)](CF3-
SO3)2 (400 mg, 0.410 mmol) in THF (50 mL) was treated with
an excess of KO-t-Bu (460 mg, 4.10 mmol) for 30 min. Workup
as described above gave Ru(PMe2Ph)3{η4-exo-(CH2)2C6Me4} (7;
(212 mg, 77%), which was identified by its 1H and 31P{1H}
NMR spectra.11
(l) [Os(P Me3)3(η6-C6Me6)](CF 3SO3)2 (5). (i) Treatment of
a solution of endo-2 (160 mg, 0.272 mmol) in ether (80 mL)
with triflic acid (250 µL, 2.83 mmol) gave a brown solid, which
was separated by filtration and washed with ether. The solid
was redissolved in methanol (10 mL), and another 250 µL
portion of triflic acid was added. Removal of the solvent under
reduced pressure gave a brown oil which solidified on addition
of ether (20 mL). Yellow crystals of 5 (190 mg, 80%) were
obtained by vapor diffusion of ether into an acetone solution.
(ii) Treatment of a solution of exo-2 (48 mg, 0.083 mmol) in
ether (20 mL) with triflic acid (50 µL, 0.565 mmol) gave
immediately an off-white precipitate, which was separated by
filtration, washed with ether, and dissolved in methanol (5
mL). Addition of more triflic acid (50 µL, 0.565 mmol) gave a
yellow solution. The solvent was removed under reduced
pressure to give a brown oil, which solidified on addition of
ether (20 mL). Recrystallization from acetone/ether gave off-
white crystals of 5 (67 mg, 92%). 1H NMR (acetone-d6, 300
MHz): δ 2.53 (s, C6Me6), 1.93 (vt, 2J PH + 4J PH ) 9.7 Hz, PMe3).
31P{1H} NMR (acetone-d6, 121.42 MHz): δ -49.0 (s). MS
(electrospray (MeOH)): m/z 731, [M - CF3SO3]+. Anal. Calcd
(c) Treatment of complex 5 (M ) Os, L ) PMe3; 160 mg,
0.182 mmol) in THF (30 mL) with an excess of KO-t-Bu (204
mg, 1.82 mmol) for 15 h as described above gave endo-2 (99
mg, 94%). Similarly, complex 6 (M ) Os, L ) PMe2Ph; 500
mg, 0.469 mmol) in THF (30 mL) with KO-t-Bu (526 mg, 4.69
mmol) for 16 h gave endo-3 (242 mg, 67%).
Kin etics of en d o to exo Isom er iza tion . A sample of the
endo isomer was dissolved under argon in toluene-d8 in a 5
mm NMR tube. The initial concentrations (mmol per liter)
were 34.0 (1), 20.2 (2), and 21.8 (3). The tube was placed in a
Varian VXR-300S NMR spectrometer set at the desired
temperature. The temperature was regulated by cooled gas
flow and measured from the control panel after calibration
with ethylene glycol and methanol NMR thermometers.22 The
rates of the isomerization were determined from the decrease
1
of the integral of the well-separated higher field H resonance
at δ ca.4.5 of the pair associated with the exo-methylene
protons of the endo isomer (see Table 1); data were collected
at 15 min intervals. Line fitting and calculation of errors in
(22) Duerst, R.; Merbach, A. Rev. Sci. Instrum. 1965, 36, 1896.

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3789
Ta ble 3. Cr ysta l a n d Refin em en t Da ta for en d o-1, en d o-3, exo-3 a n d 8
endo-1 endo-3 exo-3
(a) Crystal Data
8
chem formula
fw
C
21H43P3Ru
C36H49P3Os
764.90
C36H49P3Os
764.90
C24H52OsP4
654.77
489.56
cryst syst
unit cell dimens
a (Å)
b (Å)
c (Å)
orthorhombic
monoclinic
triclinic
triclinic
16.638(4)
18.233(6)
16.635(4)
15.956(2)
13.159(4)
16.262(3)
10.031(2)
11.124(3)
17.111(3)
96.17(2)
90.88(2)
115.92(1)
1703.2(7)
P1h
9.290(3)
12.936(3)
13.085(2)
86.48(2)
72.78(2)
78.02(2)
1469.3(6)
P1h
R (deg)
â (deg)
101.25(1)
γ (deg)
V (Å3)
5046(2)
Pbca
1.289
8
3355(1)
P21/n
1.514
4
space group
Dc (g cm-3
Z
)
1.491
2
1.480
2
F(000)
2064
1544
772
664
color, habit
yellow plate
0.88 × 0.18 × 0.32
8.00 (Mo KR)
yellow plate
0.32 × 0.28 × 0.06
87.06 (Cu KR)
yellow plate
colorless block
cryst dimens
0.20 × 0.15 × 0.03
0.53 × 0.32 × 0.24
µ (cm-1
)
39.05 (Mo KR)
45.67 (Mo KR)
(b) Data Collection and Processing
Rigaku AFC 6R Philips PW1100/20
diffractometer
X-radiation
scan mode
ω-scan width
2θ limits (deg)
min, max h,k,l
no. of rflns
total
Rigaku AFC 6S
Mo KR
Rigaku AFC 6S
Mo KR
Cu KR
Mo KR
ω-2θ
ω-2θ
ω-2θ
ω-2θ
1.20 + 0.34 tan θ
50.1
0-19, 0-21, 0-19
1.30 + 0.34 tan θ
120.2
1.00 + 0.34 tan θ
48.0
0.80 + 0.34 tan θ
50.1
0-18, 0-15, -18 to +18 -11 to +11, -12 to +12, 0 to +19 0-11, -14 to +15, -14 to +15
4980
5449
5346
5557
unique (Rint/%) 4980
obsd (I > 3σ(I)) 3238
5241 (8.1)
3750
azimuthal scans
0.3398, 1.0000
5346
3786
DIFABS
0.7600, 1.0000
5206 (1.4)
4469
azimuthal scans
0.6300, 1.0000
abs cor
min, max cor
azimuthal scans
0.7896, 1.0000
(c) Structure Analysis and Refinement
structure solution Patterson methods
(DIRDIF92 PATTY)
Patterson methods
(DIRDIF92 PATTY)
Patterson methods
(DIRDIF92 PATTY)
Direct methods
(SHELXS86)
full-matrix least squares
279
refinement
full-matrix least squares full-matrix least squares full-matrix least squares
no. of params
224
361
373
weighting scheme w ) 4Fo2/[σ2(Fo2) +
w ) 4Fo2/[σ2(Fo2) +
w ) 4Fo2/[σ2(Fo2) +
w ) 4Fo2/[σ2(Fo2) +
(0.0040Fo2)2]
2.5
(0.0200Fo2)2]
(0.0040Fo
3.7
3.3
)
(0.0004Fo2)2]
2
R(obsd data) (%) 3.2
Rw(obsd data) (%) 3.7
3.7
3.0
2.3
the activation parameters were performed with the IGOR PRO
program.23 The data are listed in the form kobs (error) (106
s-1) [T (K)]. endo-1 f exo-1: no added PMe3, 9.8 (0.3) [338.5],
15.6 (0.4) [343.0], 23.4 (0.6) [348.0], 37.0 (0.8) [353.0], 80.4 (4.6)
[357.5], 100.7 (2.8) [361.5], 162.1 (3.9) [366.5], 209.2 (5.8)
[368.5], 254.3 (8.1) [370.5], 324.3 (12.3) [373.0], 338.5 (11.3)
[375.0], 393.3 (13.1) [377.0], 501.7 (18.9) [379.5]; with 20 equiv
of added PMe3, 13.1 (0.5) [348], 23.5 (0.5) [353.0], 27.6 (0.6)
[357.5], 38.5 (1.0) [361.5], 71.8 (1.7) [366.5], 147.5 (3.6) [370.5],
263.4 (7.5) [375.0]. endo-2 f exo-2: no added PMe3, 6.5 (0.3)
[357.5], 10.5 (0.3) [361.5], 18.9 (0.5) [366.5], 38.3 (0.8) [370.5],
66.3 (1.3) [375.0], 100.7 (2.3) [379.5]; with 20 equiv of added
PMe3, 7.5 (0.4) [353.0], 9.3 (0.4) [357.5], 12.8 (0.4) [361.5], 22.3
(0.5) [366.5], 30.6 (0.6) [370.5], 56.7 (1.0) [375.0]. endo-3 f
exo-3: no added PMe2Ph, 3.0 (0.4) [338.5], 4.7 (0.5) [343.0],
12.6 (0.4) [348.0], 21.4 (2.2) [353.0], 42.5 (1.4) [357.5], 81.9 (3.5)
[361.5], 179.6 (5.4) [366.5], 478.1 (19.0) [370.5], 994.5 (48.6)
[375.0]; with 20 equiv of added PMe2Ph, 3.3 (0.2) [343.0], 7.1
(0.4) [348.0], 13.0 (0.5) [353.0], 27.1 (0.9) [357.5], 46.1 (1.1)
[361.5], 89.7 (2.4) [366.5], 136.3 (3.2) [370.5], 274.6 (8.2) [375.0].
The influence on the rate of isomerization kobs of 0.5-20 mol
of phosphine per mol of endo complex was studied. The data
are listed in the form kobs (error) (106 s-1) [no. of equivalents
of added phosphine]. endo-1 f exo-1 (T ) 357.5 K): 80.4 (4.6)
[0.0], 72.1 (2.9) [0.5], 46.6 (3.1) [1.0], 38.8 (2.7) [2.0], 23.3 (1.5)
[4.0], 22.6 (1.1) [10.0], 27.5 (1.3) [20.0]. endo-2 f exo-2 (T )
379.5 K): 100.7 (2.3) [0.0], 109.8 (2.1) [1.0], 111.4 (2.3) [2.0],
114.5 (2.3) [4.0], 109.8 (2.1) [10.0], 117.3 (2.3) [20.0]. endo-3
f exo-3 (T ) 357.5 K): 42.5 (1.4) [0.0], 41.5 (0.9) [0.5], 36.6
(0.9) [1.0], 34.8 (0.8) [2.0], 32.3 (0.8) [4.0], 31.8 (0.8) [10.0], 32.1
(0.8) [20.0].
The validity of the steady-state approximation (SSA) model
used in the discussion of mechanism (see text) was checked
by numerical simulations using two very different computa-
tional methods. The first was the deterministic approach,24
in which the time dependence of the concentration of the
various species is written as a set of coupled differential
equations; these were integrated by means of the program
REACT3.25 The second was the stochastic method, in which
changes in a reacting system are modeled by random selection
among probability-weighted reaction steps; the program CKS
was used for this purpose.24,26-28
Cr ysta llogr a p h y. The crystal and refinement data for
ML3{η4-o-C6Me4(CH2)2} (M ) Ru, L ) PMe3, exo-1; M ) Os, L
) PMe2Ph, endo- and exo-3) and Os(PMe3)4{κ2-o-(CH2)2C6Me4}
(8) are summarized in Table 3. Crystals of exo-1, exo-3, and 8
were mounted under argon in Lindemann capillaries in
silicone grease to prevent movement during data collection; a
crystal of endo-3 was mounted on a glass fiber with Araldite.
(24) Steinfield, J . I.; Francisco, J . S.; Hase, W. L. Chemical Kinetics
and Dynamics; Prentice Hall: Englewood Cliffs, NJ , 1989.
(25) Whitbeck, M. Numerical Modeling of Reaction Mechanisms. In
Tetrahedron Comput. Methodol. 1992, 3 (No. 6B), 497.
(26) Hinsberg, B.; Houle, F. A. CKS; IBM Research Division,
Almaden Research Center, San J ose, CA 95120-6099.
(27) Bunker, D. L.; Garrett, B.; Kliendienst, T.; Long, G. S., III.
Combust. Flame 1974, 23, 373.
(23) IGOR PRO; Wave Metrics Inc., Lake Oswego, OR 97035, 1995.
(28) Gillespie, D. T. J . Comput. Phys. 1976, 22, 403.

3790 Organometallics, Vol. 17, No. 17, 1998
Bennett et al.
The structures of endo- and exo-3 and of exo-1 were solved by
Patterson methods (DIRDIF92, PATTY),29 while the structure
of 8 was solved by direct methods (SHELXS86).30 All the
structures were refined by full-matrix least-squares analysis.
Hydrogen atoms were included at calculated positions (C-H
) 0.95 Å) except for the methylene hydrogen atoms attached
to carbon atoms C11 and C21 of exo-3, exo-1, and 8, for which
the coordinates were determined from an inner-data difference
map and refined. Calculations were generally performed using
the teXsan crystal structure analysis package.31 The initial
data reduction for exo-3 was performed with the XTAL
package.32
Com p u ta tion s. The electronic structure calculations are
based on approximate density functional theory and were
performed by use of the Amsterdam density functional (ADF)
program developed by Baerends and co-workers.33,34 The
valence orbitals of the main-group elements were expanded
in double-ú Slater-type basis sets, augmented with a single
p-type polarization function for hydrogen and a single d
function for carbon and phosphorus. The orbitals of ruthenium
were represented by a triple-ú basis.35 An auxiliary set of s,
p, d, f, and g Slater functions was used to fit the molecular
electron density.36 Electrons in orbitals up to and including
1s (C), 2p (P), and 4p (Ru) were considered as cores and treated
using the frozen-core approximation. Calculations were per-
formed with the local exchange-correlation potential of Vosko,
Wilk, and Nusair,37 along with the gradient corrections of
Becke38 and Perdew.39 Quasi-relativistic corrections were
made for both ruthenium and osmium. Geometries were
optimized in C2v (κ2-M(PH3)4(C8H8)), Cs (endo- and exo-M(PH3)3-
(C8H8)), and C3v (PH3) symmetry using the gradient algorithm
of Versluis and Ziegler.40
by single-crystal X-ray structure analysis (see below).
As in M(PMe2Ph)3{η4-endo-o-C6H4(CH2)2} (M ) Ru,
Os),12 the trigonal ML3 fragment is bound to the endo-
diene unit, a pair of tertiary phosphine ligands being
related by a mirror plane that bisects the tetramethyl-
o-xylylene, and a unique tertiary phosphine lying in the
mirror plane below the coordinated diene.
The spectroscopic properties of endo-1-3 are gener-
ally similar to those of M(PMe2Ph)3{η4-endo-o-C6H4-
(CH2)2} (M ) Ru, Os).12 The IR spectra contain a weak
band in the 1500-1600 cm-1 region assignable to ν(Cd
C) of the uncoordinated exo-diene. The 1H NMR spectra
show a characteristic pair of multiplets at δ ca. 4.5 and
5.3 due to the exo-methylene protons, and a singlet at
δ ca. 90 in the 13C NMR spectra is assigned to the exo-
methylene carbon atoms. The inner carbon atoms of
the exo-diene give rise to a doublet at δ ca. 155, being
coupled to only one of the three phosphorus atoms (2J PC
ca. 4 Hz). The inner carbon atoms C4,5 of the coordi-
nated endo-diene appear at δ ca. 80; for endo-1 and
endo-3 this resonance is a doublet owing to coupling
with the unique phosphorus atom (P1), whereas for
endo-2 the resonance is a doublet of triplets because of
additional weaker coupling with the other two, equiva-
lent phosphorus atoms (P2, P3). For similar reasons, the
outer carbon atoms C3,6 of the endo-diene also appear
as a doublet of triplets, at δ ca. 25 for endo-1 and at 50
for endo-2 and endo-3; surprisingly, the trend of chemi-
cal shifts is opposite to that shown for the outer diene
carbon atoms in M(CO)3(η4-1,3-diene) (M ) Fe, Ru, Os),
which become progressively more shielded with increas-
ing atomic number of the metal.41 The ring methyl
protons (Me-C3,6 and Me-C4,5) appear as a pair of well-
resolved multiplets owing to 31P coupling. The 31P{1H}
NMR spectra of endo-3 show a well-resolved doublet and
triplet (2J PP ca. 5-11 Hz) in the expected 2:1 intensity
ratio; in contrast to M(PMe2Ph)3{η4-endo-o-C6H4(CH2)2}
(M ) Ru, Os), rotation of the tertiary phosphine ligands
relative to the coordinated diene is slow on the NMR
time scale at room temperature.
Resu lts
In contrast with the behavior of the Ru-PMe2Ph
system (eq 1),11 treatment of [Ru(O2CCF3)(PMe3)2(η6-
C6Me6)]PF6 with KO-t-Bu in the presence of trimeth-
ylphosphine gives exclusively the endo-(tetramethyl-o-
xylylene)ruthenium(0) complex Ru(PMe3)3{η4-endo-o-
C6Me4(CH2)2} (endo-1) in 88% yield as a yellow, air-
sensitive, crystalline solid. Similarly, reaction of the
osmium(II) salts [Os(O2CCF3)L2(η6-C6Me6)]PF6 (L )
PMe3, PMe2Ph) with KO-t-Bu and L gives the corre-
sponding endo-(tetramethyl-o-xylylene)osmium(0) com-
plexes OsL3{η4-endo-o-C6Me4(CH2)2} (L ) PMe3 (endo-
2), PMe2Ph (endo-3)) (eq 3). The new compounds have
been characterized by elemental analysis, mass spec-
trometry, infrared and NMR (1H, 13C, and 31P) spec-
troscopy (Table 1) and, in the case of endo- and exo-3,
(29) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Symkalla, C. The
DIRDIF Program System; Technical Report of the Crystallography
Laboratory; University of Nijmegen, Nijmegen, The Netherlands, 1992.
(30) Sheldrick, G. M. SHELX-86. In Crystallographic Computing 3;
Sheldrick, G. M., Kru¨ger, C., Goddard, R., Eds.; Oxford University
Press: Oxford, England, 1985; pp 175-189.
(31) TEXSAN: Single-Crystal Structure Analysis Software, Version
1.6c; Molecular Structure Corp., The Woodlands, TX 77381, 1993.
(32) Hall, S. R.; Flack, H. D.; Stewart, J . M. XTAL3.2 Reference
Manual; Universities of Western Australia, Geneva and Maryland;
Lamb: Perth, Australia, 1992.
(33) Baerends, E. J .; Ellis, D. E.; Ros, P. Chem. Phys. 1973, 2, 41.
(34) te Velde, G. B.; Baerends, E. J . J . Comput. Phys. 1992, 99, 84.
(35) Vernooijs, P.; Snijders, G. J .; Baerends, E. J . Slater Type Basis
Functions for the Whole Periodic System; Free University of Amster-
dam: Amsterdam, The Netherlands, 1981.
(36) Krijn, J .; Baerends, E. J . Fit Functions in the HFS Method; Free
University of Amsterdam: Amsterdam, The Netherlands, 1984.
(37) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J . Phys. 1980, 58, 1200.
(38) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
Treatment of complexes endo-1-3 with an excess of
triflic acid (CF3SO3H, TfOH) in ether precipitates the
triflate salts of the hexamethylbenzene-metal(II) cat-
ions, [ML3(η6-C6Me6)](OTf)2 (L ) PMe3, M ) Ru (4), Os
(5); L ) PMe2Ph, M ) Os (6)) (eq 4). These have been
characterized by elemental analysis and by their spec-
troscopic properties, which are unexceptional (see Ex-
perimental Section). Reaction of complexes 4-6 with
KO-t-Bu re-forms the tetramethyl-o-xylylene complexes
endo-1-3, just as the parent endo-o-xylylene complexes
M(PMe2Ph)3{η4-endo-o-C6H4(CH2)2} are generated from
the corresponding (o-xylene)metal dications [M(PMe2-
Ph)3(η6-C6H4Me2)]2+ 12
.
In contrast, treatment of a
(39) Perdew, J . P. Phys. Rev. B 1986, 33, 8822.
(40) Versluis, L.; Ziegler, T. J . Chem. Phys. 1988, 88, 322.
(41) Zobl-Ruh, S.; von Philipsborn, W. Helv. Chim. Acta 1980, 63,
773.

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3791
Sch em e 1
suspension of [Ru(PMe2Ph)3(η6-C6Me6)](OTf)211 in THF
with KO-t-Bu forms exclusively the exo-tetramethyl-o-
xylylene complex M(PMe2Ph)3{η4-exo-o-(CH2)2C6Me4}
(7) (eq 5).
acid regenerates the triflate salts of the (hexamethyl-
benzene)metal dications 4-6, which were isolated in
good yield (eq 5).
We reported previously12 that the unsubstituted
complex Ru(PMe2Ph)3{η4-endo-o-C6H4(CH2)2} does not
isomerize to the exo compound in toluene at or above
60 °C, even though the exo isomer is predicted to be the
more stable.16 We now find that this isomerization
proceeds quantitatively in the molten state (ca. 300 °C);
the osmium compound decomposes under these condi-
tions.
While studying the effect of added tertiary phosphine
on the kinetics of the thermal endo to exo isomerization
of the osmium complexes 2 and 3 (see below), we
realized that the products under these conditions are
the κ2-3,4,5,6-tetramethyl-o-xylylene tetrakis(tertiary
phosphine) complexes OsL4{κ2-o-(CH2)2C6Me4} (L )
PMe3 (8), PMe2Ph (9)) rather than the tris(tertiary
phosphine) complexes exo-2 and exo-3. The added
ligand can be considered to displace the coordinated
formal double bond of the aromatic ring of the o-xylylene
(Scheme 1). Complex 8 can be isolated in 92% yield as
a colorless, crystalline solid from the reaction of PMe3
with exo-2 at room temperature. It has been character-
ized by elemental analysis, mass spectrometry, NMR
(1H, 13C, and 31P) spectroscopy, and single-crystal X-ray
diffraction (see below). Complex 9 cannot be isolated
and has been characterized only on the basis of its NMR
spectroscopic data. It is in rapid equilibrium with exo-3
and free PMe2Ph, the equilibrium constant for the
reaction
This remarkable difference of regioselectivity in depro-
tonation for the Ru-PMe2Ph and Os-PMe2Ph systems
suggested that endo to exo isomerization might be
observable in tetramethyl-o-xylylene complexes. In-
deed, heating in toluene above 65 °C causes quantitative
isomerization of the endo complexes 1-3 to the corre-
sponding exo complexes ML3{η4-exo-o-(CH2)2C6Me4} (L
) PMe3, M ) Ru (exo-1), Os (exo-2); L ) PMe2Ph, M )
Os (exo-3)) (eq 6), whose NMR properties (Table 1) are
Os(PMe2Ph)3{η4-exo-o-(CH2)2C6Me4} + PMe2Ph a
Os(PMe2Ph)4{κ2-o-(CH2)2C6Me4}
measured by 31P NMR spectroscopy being 1.10 ( 0.02
at 25 °C. The highest mass peak in the EI mass
spectrum of toluene solutions of 9 is that due to 3,
showing that 9 is stable only in the presence of free
PMe2Ph. In contrast, there is no evidence for the
presence of exo-2 and PMe3 in solutions of 8 and there
is no observable reaction between the ruthenium com-
plex exo-1 and PMe3.
The 1H NMR spectra of 8 and 9 each show a
resonance at δ ca. 2.3, which appears as a triplet of
triplets owing to coupling with two pairs of inequivalent
31P nuclei, and is assigned to the equivalent methylene
protons. The 31P{1H} NMR spectra consist of a pair of
1:2:1 triplets of equal intensity (2J PP ) 16.5 Hz for 8
and 13.1 Hz for 9) arising from two pairs of tertiary
phosphines: one mutually trans, the other cis. In the
13C NMR spectra the methylene carbon atoms give
resonances at δ ca. 9, which for 9 is a triplet with
separations of 16.5 Hz and for 8 is a double triplet of
doublets with separations of 45.5, 9.1, and 4.8 Hz. The
similar to those of previously described analogues, such
as complex 7.11 In particular, the 1H NMR spectra show
a characteristic pair of multiplets at δ 0 to -0.4 and
2.0-2.5 due to anti and syn protons of the coordinated
exo-1,3-diene. A multiplet at δ 22-27 in the 13C NMR
spectrum is assigned to the exo-methylene carbon
atoms, shifted by ca. 70 ppm to lower frequency of the
corresponding resonance in endo-1-3. The inner diene
carbon atoms C1,2 resonate at δ ca. 100, ca. 50 ppm to
low frequency of their chemical shift in 1-3. The 31P-
{1H} NMR spectra of the exo complexes, like those of
their endo isomers, show a well-resolved doublet and
triplet (2J PP ) ca. 6-12 Hz) in an intensity ratio of 2:1.
The structures of exo-1 and exo 3 have been confirmed
by single-crystal X-ray diffraction analysis (see below).
Treatment of the exo-isomers with an excess of triflic

3792 Organometallics, Vol. 17, No. 17, 1998
Bennett et al.
F igu r e 2. Molecular structure of Os(PMe2Ph)3{η4-endo-
o-C6Me4(CH2)2} (endo-3) with 50% ellipsoids.
F igu r e 3. Molecular structure of Ru(PMe3)3{η4-exo-o-
(CH2)2C6Me4} (exo-1) with 50% ellipsoids.
signals due to carbon atoms C1 and C2 to which the
methylene groups are attached occur as doublets of
triplets at δ ca. 153 with separations of ca. 10 and 5
Hz, while the signals due to the remaining ring carbon
atoms C3,6 and C4,5 appear in the normal aromatic
region at δ ca. 130. Relative to the corresponding
chemical shifts in exo-2 and exo-3, the ca. 14 ppm shift
to low frequency of the methylene carbon atoms in 8
and 9, and the ca. 55 ppm shift to high frequency of the
now uncoordinated carbon atoms C1 and C2, are diag-
nostic of the change from η4-exo to κ2 binding of the
tetramethyl-o-xylylene unit.
Cr ysta l a n d Molecu la r Str u ctu r es. The molecular
structures of Os(PMe2Ph)3{η4-endo-o-C6Me4(CH2)2} (endo-
3), Ru(PMe3)3{η4-exo-o-(CH2)2C6Me4} (exo-1), Os(PMe2-
Ph)3{η4-exo-o-(CH2)2C6Me4} (exo-3), and Os(PMe3)4{κ2-
o-(CH2)2C6Me4} (8) are shown in Figures 2-5, with the
atom numbering; selected bond distances and inter-
atomic angles are given in Tables 4-7. The geometry
of endo-3 is very similar to that of the unsubstituted
compound Os(PMe2Ph)3{η4-endo-o-C6H4(CH2)2}.12 The
Os(PMe2Ph)3 moiety is bound to the endocyclic diene
unit, the metal atom being slightly closer to the inner
than to the outer carbon atoms (Os-C(4),C(5) ) 2.230
Å (average), Os-C(3),C(6) ) 2.279 Å (average)). These
distances are, respectively, ca. 0.06 and 0.03 Å greater
than the corresponding separations in the unsubstituted
compound.12 The o-xylylene ring in endo-3 has the
characteristic folded conformation, the dihedral angle
between the C(3) to C(6) and C(6)-C(1)-C(2)-C(3)
planes being 42.9° (cf. 37.0 and 39.5° in the unsubsti-
tuted Ru and Os compounds12 and 33.8° in Ru(η6-C6-
Me6){η4-endo-o-C6Me4(CH2)2}.4
F igu r e 4. Molecular structure of Os(PMe2Ph)3{η4-exo-o-
(CH2)2C6Me4} (exo-3) with 50% ellipsoids.
Å (average) in exo-1; Os-C(11),C(21) ) 2.172 Å (aver-
age), Os-C(1),C(2) ) 2.324 Å (average) in exo-3). As
discussed previously,16 this reversal of the normal trend
for (1-4-η)-diene complexes can be ascribed to the
tendency toward aromatization of the six-membered
ring in the exo-η4 complexes. The Ru-C(diene) dis-
tances in exo-1 are close to those observed in Ru(PMe2-
Ph)3{η4-exo-o-(CH2)2C6H4};13 i.e., they are unaffected by
the methyl substitution in the six-membered ring. As
in other exo-o-xylylene complexes, such as Co(η5-C5H5)-
{η4-o-(CH2)2C6H4}7 and Fe(CO)3{η4-o-(CH2)2C6H2Me2-
4,5},42 but in contrast with endo-3, the o-xylylene ring
In the exo isomers of 1 and 3, the ML3 fragments are
bound to the exocyclic diene unit, the geometries being
similar to that of the unsubstituted compound Ru(PMe2-
Ph)3{η4-exo-o-(CH2)2C6H4}.13 In contrast to endo-3, the
metal atoms in exo-1 and exo-3 are considerably closer
to the outer than to the inner diene carbon atoms (Ru-
C(11),C(21) ) 2.173 Å (average), Ru-C(1),C(2) ) 2.291
(42) Girard, L.; Decken, A.; Blecking, A.; McGlinchey, M. J . J . Am.
Chem. Soc. 1994, 116, 6427.

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3793
Ta ble 6. Selected Bon d Len gth s (Å) for
Os(P Me2P h )3 {η4-exo-(CH2)2C6Me4}(exo-3)
Os(1)-P(1)
Os(1)-P(3)
Os(1)-C(2)
Os(1)-C(21)
P(1)-C(111)
P(1)-C(131)
P(2)-C(221)
P(3)-C(311)
P(3)-C(331)
C(1)-C(11)
C(2)-C(21)
C(3)-C(31)
C(4)-C(41)
C(5)-C(51)
C(6)-C(1)
2.257(2)
2.316(2)
2.310(7)
2.157(8)
1.839(9)
1.826(8)
1.824(8)
1.843(8)
1.843(8)
1.45(1)
Os(1)-P(2)
Os(1)-C(1)
Os(1)-C(11)
2.308(2)
2.337(7)
2.187(9)
P(1)-C(121)
P(2)-C(211)
P(2)-C(231)
P(3)-C(321)
1.821(9)
1.857(8)
1.840(8)
1.839(8)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(61)
1.444(9)
1.429(9)
1.384(10)
1.43(1)
1.367(10)
1.51(1)
1.44(1)
1.51(1)
1.51(1)
1.50(1)
1.420(10)
Ta ble 7. Selected Bon d Len gth s for
Os(P Me3)4{K2-o-(CH2)2C6Me4} (8)
F igu r e 5. Molecular structure of Os(PMe3)4{κ2-o-(CH2)2C6-
Me4} (8) with 50% ellipsoids.
Os(1)-P(1)
Os(1)-P(3)
Os(1)-C(11)
P(1)-C(111)
P(1)-C(131)
P(2)-C(221)
P(3)-C(311)
P(3)-C(331)
P(3)-C(421)
C(1)-C(11)
C(2)-C(21)
C(3)-C(31)
C(4)-C(41)
C(5)-C(51)
C(6)-C(1)
2.308(2)
2.343(2)
2.170(5)
1.835(6)
1.842(6)
1.835(6)
1.830(6)
1.853(6)
1.857(6)
1.527(6)
1.498(7)
1.534(7)
1.524(7)
1.524(7)
1.394(6)
Os(1)-P(2)
Os(1)-P(4)
Os(1)-C(21)
P(1)-C(121)
P(2)-C(211)
P(2)-C(231)
P(3)-C(321)
P(4)-C(411)
P(4)-C(431)
C(1)-C(2)
2.349(2)
2.316(1)
2.185(5)
1.854(7)
1.826(6)
1.846(6)
1.852(6)
1.847(6)
1.834(6)
1.398(6)
1.413(6)
1.384(7)
1.401(7)
1.404(6)
1.507(7)
Ta ble 4. Selected Bon d Len gth s (Å) for
Os(P Me2P h )3{η4-en d o-o-C6Me4(CH2)2} (en d o-3)
Os(1)-P(1)
Os(1)-P(3)
Os(1)-C(4)
Os(1)-C(6)
P(1)-C(111)
P(1)-C(131)
P(2)-C(221)
P(3)-C(311)
P(3)-C(331)
C(1)-C(11)
C(2)-C(21)
C(3)-C(31)
C(4)-C(41)
C(5)-C(51)
C(6)-C(1)
2.296(2)
2.328(2)
2.226(8)
2.276(8)
1.868(8)
1.845(9)
1.843(8)
1.884(9)
1.855(8)
1.32(1)
Os(1)-P(2)
Os(1)-C(3)
Os(1)-C(5)
2.338(2)
2.281(8)
2.234(8)
P(1)-C(121)
P(2)-C(211)
P(2)-C(231)
P(3)-C(321)
1.806(10)
1.843(8)
1.840(8)
1.824(9)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(61)
1.47(1)
1.45(1)
1.45(1)
1.38(1)
1.47(1)
1.50(1)
C(6)-C(61)
1.34(1)
1.52(1)
1.53(1)
1.53(1)
in Os(PMe3)4{κ2-o-(CH2)2SiMe2}.44 The Os-C distances
in 8 differ slightly (2.170(5), 2.185(5) Å), possibly as a
consequence of solid-state effects; they are somewhat
less than those in Os(PMe3)4{κ2-o-(CH2)2SiMe2} (2.24-
(1) Å) but are similar to the Os-CH3 distances in OsI-
(Me)(CO)2(PMe3)2 (2.174(15) Å) and [OsMe(CO)2(NCMe)-
(PMe3)2]BPh4 (2.198(17) Å).45 As in Os(PMe3)4{κ2-o-
(CH2)2SiMe2}, the Os-P bond lengths for phosphorus
trans to phosphorus (2.349(2), 2.343(2) Å) in 8 are
greater than those for phosphorus trans to carbon
(2.308(2), 2.316(1) Å). The bond distances within the
six-membered ring (C(1)-C(6)) of 8 fall in a closer range
(1.384-1.413 Å) than those in exo-3 (1.367-1.444 Å),
consistent with the greater aromatic character of the
ring in the former compound. The o-xylylene ring in 8
is almost flat, the dihedral angle between the planes
C(11)-C(1)-C(2)-C(21) and Os(1)-C(11)-C(21) being
only 6.6° (cf. 89.4° in exo-3). The magnitude of this fold
angle in the compounds formulated as κ2-o-xylylene
complexes is remarkably variable, e.g., 3.9° in Mn-
(dmpe)2{κ2-o-(CH2)2C6H4},43 41-53° in M(η5-C5H5)2{o-
(CH2)2C6H4} (M ) Ti, Zr, Hf),9 44° in Nb(η5-C5H4SiMe3)2-
{o-(CH2)2C6H4},9 66 and 42° in Mg(thf)4[OW{o-(CH2)2-
C6H4}2],10 and 83° in W{o-(CH2)2C6H4}3.10 It has been
suggested10 that the larger values reflect a π-interaction
of the aromatic ring with the metal center.
1.47(1)
Ta ble 5. Selected Bon d Len gth s (Å) for
Ru (P Me3)3{η4-exo-(CH2)2C6Me4} (exo-1)
Ru(1)-P(1)
Ru(1)-P(3)
Ru(1)-C(2)
Ru(1)-C(21)
P(1)-C(111)
P(1)-C(121)
P(1)-C(131)
P(2)-C(211)
P(2)-C(311)
P(3)-C(321)
C(1)-C(11)
C(2)-C(21)
C(3)-C(31)
C(4)-C(41)
C(5)-C(51)
C(6)-C(1)
2.238(1)
2.311(1)
2.297(4)
2.175(4)
1.869(1)
1.82(1)
Ru(1)-P(2)
Ru(1)-C(1)
Ru(1)-C(11)
2.306(1)
2.284(4)
2.170(4)
P(1)-C(111′)
P(1)-C(121′)
P(1)-C(131′)
P(2)-C(221)
P(3)-C(311)
P(3)-C(331)
C(1)-C(2)
1.81(1)
1.84(1)
1.85(1)
1.82(2)
1.824(5)
1.837(5)
1.841(5)
1.461(6)
1.451(5)
1.498(6)
1.539(6)
1.516(6)
1.433(6)
1.829(5)
1.837(5)
1.812(6)
1.428(5)
1.440(6)
1.362(6)
1.414(6)
1.376(6)
1.519(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-C(61)
in exo-1 and exo-3 is almost flat, the dihedral angle
between the C(3) to C(6) and C(6)-C(1)-C(2)-C(3)
planes being 1.9° (exo-1) and 4.3° (exo-3). In all three
tetramethyl-o-xylylene complexes, the C-C bond lengths
within the uncoordinated diene fragment show the
expected short-long-short alternation, whereas those
in the coordinated diene unit are almost equal.
In agreement with the spectroscopic studies, the X-ray
structure analysis of 8 shows that the tetramethyl-o-
xylylene is bound to the Os(PMe3)4 unit via the two
exocyclic methylene groups, so that the ligand behaves
as a two-electron σ-donor. The distorted-octahedral
geometry about the metal atom is similar to that
observed in Mn(dmpe)2{κ2-o-(CH2)2C6H4} (dmpe ) 1,2-
bis(dimethylphosphino)ethane, Me2PCH2CH2PMe2)43 and
Com p u ta tion a l Resu lts. In an effort to understand
better the different behavior of the o-xylylene complexes
of ruthenium(0) and osmium(0) with ligands, we carried
(43) Howard, C. G.; Girolami, G. S.; Wilkinson, G.; Thornton-Pett,
M.; Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1983, 2631.
(44) Behling, T.; Girolami, G. S.; Wilkinson, G.; Somerville, R. G.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1984, 877.
(45) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Zanazzi, P. Inorg.
Chem. 1993, 32, 547.

3794 Organometallics, Vol. 17, No. 17, 1998
Bennett et al.
F igu r e 7. First-order rate plots from NMR spectroscopy
for the endo to exo isomerization of Os(PMe2Ph)3{η4-o-C6-
Me4(CH2)2} (3).
F igu r e 6. Energy level diagram showing the calculated
relative energies of η4-endo-, η4-exo-, κ2-o-xylylene com-
plexes of ruthenium and osmium.
Ta ble 8. Ca lcu la ted Tota l En er gies (eV) of en d o-
a n d exo-ML3{η4-o-C6H4(CH2)2} a n d of
ML4{K2-o-(CH2)2C6H4} (M ) Ru , Os; L ) P H3)
molecular fragment
energy
PH3
-15.19
-152.89
-152.25
-168.42
-153.49
-152.81
-169.24
exo- Ru(PH3)3(o- xylylene)
endo- Ru(PH3)3(o- xylylene)
Ru(PH3)4(o- xylylene)
exo- Os(PH3)3(o- xylylene)
endo- Os(PH3)3(o- xylylene)
Os(PH3)4(o- xylylene)
out density functional calculations on the model systems
M(PH3)3{η4-endo-o-C6H4(CH2)2} + PH3, M(PH3)3{η4-exo-
o-(CH2)2C6H4} + PH3, and M(PH3)4{κ2-o-(CH2)2C6H4} (M
) Ru, Os). The energies are listed in Table 8 and
represented graphically in Figure 6, where the energies
are plotted relative to those of M(PH3)3{η4-exo-o-
(CH2)2C6H4}. For both ruthenium and osmium the exo
isomer is more stable than the endo isomer by ca. 60
kJ mol-1. As shown earlier,16 this can be attributed
largely to the tendency toward aromatization of the six-
membered ring; hence, the identity of the metal atom
plays only a small role in determining the relative
stability of the endo and exo isomers. For both metals,
the κ2 complex is found to be more stable than (η4-exo-
complex + PH3), by ca. 36 kJ mol-1 for Ru and ca. 53
kJ mol-1 for Os. The relationship of these predictions
to the experimental results is discussed below.
F igu r e 8. Eyring plot for the endo to exo isomerization of
Os(PMe2Ph)3(η4-o-C6Me4(CH2)2} (3).
a constant, limiting value in the presence of >4 mmol
of PMe3. A similar but less pronounced effect is evident
for the isomerization of the osmium-PMe2Ph complex,
endo-3, in the presence of added PMe2Ph (Figure 10).
In contrast, the rate of disappearance of the osmium-
PMe3 complex, endo-2, is almost independent of added
PMe3 (Figure 11).
For endo-1 and endo-3, the observations are consistent
with the hypothesis that isomerization occurs by two
pathways, one of which requires initial dissociation of
tertiary phosphine while the other does not. A plau-
sible, tractable model for the process is shown in Scheme
2. In the dissociative process, a reversible preequilib-
rium generates the 16-electron intermediate ML2{η4-
endo-Me4-o-xylylene} (B) by dissociation of tertiary
phosphine (L) from the endo-ML3 complex (A), with rate
constants k1 and k-1 for the forward and reverse
reactions. The ML2 fragment in B migrates irreversibly
from the endo to the exo pair of double bonds with the
rate constant k2, generating the second intermediate
ML2{η4-exo-Me4-o-xylylene} (C), which picks up L rap-
idly and irreversibly with a rate constant k3 to form the
exo-ML3 complex (D). In the nondissociative process,
Kin etics of Isom er iza tion . The endo to exo isomer-
izations of complexes 1-3 in toluene-d8 exhibit good
first-order kinetics in the temperature range 65-106
1
°C, as established by H NMR spectroscopy. Figure 7
shows typical first-order rate plots at eight tempera-
tures for the disappearance of endo-3, Figure 8 shows
the derived Eyring plot, and Table 9 summarizes the
activation parameters for the endo- to exo-isomerizations
of 1-3.
As shown in Figure 9, the rate of isomerization of the
ruthenium-PMe3 complex, endo-1, is reduced exponen-
tially by addition of small amounts of PMe3; the rate
constant is approximately halved in the presence of 2
mmol of PMe3 per mmol of endo-1, but it rapidly reaches

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3795
Ta ble 9. Activa tion P a r a m eter s for en d o to exo Isom er iza tion of ML3{η4-o-C6Me4(CH2)2} (M ) Ru , L ) P Me3
(1); M ) Os, L ) P Me3 (2); M ) Os, L ) P Me2P h (3))
process
∆Hq (kJ mol-1
)
∆Sq (J mol-1 K-1
)
Eact (kJ mol-1
)
ln A
endo-1 f exo-1a
103.9(0.7)
147.8(1.8)
168.1(1.7)
123.3(3.9)
105.6(1.6)
107.4(1.8)
142.9(1.5)
-36.0(2.0)
+67.2(4.8)
+141.5(4.8)
+12.5(10.5)
-36.9(4.9)
-42.4(4.9)
+65.4(4.1)
106.8(0.7)
153.6(1.8)
171.1(1.7)
126.3(3.9)
108.6(1.8)
110.5(1.8)
199.7(7.0)
26.3(0.2)
38.8(0.6)
47.7(0.6)
32.2(1.3)
26.2(0.5)
25.6(0.6)
56.3(2.5)
endo-2 f exo-2a
endo-3 f exo-3a
endo-1 f exo-1 (dissoc pathway)b
endo-1 f exo-1 (direct pathway)c
endo-2 f 8c
endo-1 f 9c
a
b
In the absence of added L. Rate data obtained by subtraction of observed rate in the presence of an excess of L (20 equiv) from that
in the absence of added L. c Rate data in the presence of an excess of L (20 equiv).
F igu r e 11. Dependence of kobs on added PMe3 for the endo
F igu r e 9. Dependence of kobs on added PMe3 for the endo
to exo isomerization of Ru(PMe3)3{η4-o-C6Me4(CH2)2} (1) at
357.5 K. The dotted line represents the calculated curve
(see text).
to exo isomerization of Os(PMe3)3{η4-o-C6Me4(CH2)2} (2) at
379.5 K. The dotted line represents the calculated curve
(see text).
Sch em e 2
F igu r e 10. Dependence of kobs on added PMe2Ph for the
endo to exo isomerization of Os(PMe2Ph)3{η4-o-C6Me4-
(CH2)2} (3) at 357.5 K. The dotted line represents the
calculated curve (see text).
OsL4{κ2 -Me4-o-xylylene} (E), the forward and reverse
rate constants being k4 and k-4
.
Application of the steady-state approximation (SSA)
to the concentration of B yields eqs 7 and 8. If L is small
or changes slowly with time, this corresponds with the
observed first-order behavior (eq 9). Clearly, kobs ) k1
+ k5 when [L] ) 0 and kobs ) k5 when Lf ∞.
A isomerizes directly to D with the rate constant k5; this
process is assumed to be irreversible. In the case of
osmium, complex D is in equilibrium with added L and
The validity of the SSA model has been checked by

3796 Organometallics, Vol. 17, No. 17, 1998
k1[A]
Bennett et al.
convert in solution under normal conditions; hence, it
was not possible to verify experimentally the theoretical
prediction of the greater stability for the exo isomer.16
The presence of methyl substituents at the 3-6-posi-
tions of the o-xylylene lowers the barrier to the endo to
exo isomerization to such an extent that (a) Ru(PMe2-
Ph)3{η4-endo-o-C6Me4(CH2)2} (endo-7) cannot be isolated
or detected and (b) the kinetics of the isomerization can
be studied in an experimentally readily accessible
temperature range for ML3{η4-o-C6Me4(CH2)2} (L )
PMe3, M ) Ru (1), Os (2); L ) PMe2Ph, M ) Os (3)).
These effects can probably be traced in part to a ground-
state destabilization of the endo isomer. Comparison
of the bond lengths of Os(PMe2Ph)3{η4-endo-o-C6R4-
(CH2)2} (R ) H, Me) shows that the four methyl groups
in 3 cause a significant lengthening of the Os-C bonds,
presumably weakening the Os-diene interaction. The
effect is similar to that observed in metal-alkene
complexes and may be ascribed to a combination of
steric hindrance and weakening of metal-alkene back-
bonding resulting from the electron-donating effect of
the methyl groups.46,47
In contrast to their ruthenium(0) analogues, the η4-
exo-o-xylylene complexes of osmium(0), exo-2 and exo-
3, take up an additional molecule of tertiary phosphine
(reversibly for 3 and PMe2Ph, irreversibly for 2 and
PMe3) to give the κ2 complexes 8 and 9. The density
functional calculations reproduce the greater stability
of the κ2 complexes for the heavier element, which
probably reflects the greater stability of metal-carbon
σ-bonds for 5d relative to 4d elements,48,49 but they
predict incorrectly that the κ2 complexes should be the
stable species in the presence of an excess of ligand for
both metals. The most likely source of systematic error
lies in an overestimate of the strength of the M-P
bonds. This will not affect the comparison of the
relative energies of the endo and exo isomers, but it will
be significant in comparing ML4 with ML3 complexes.
Moreover, steric interactions are likely to be greater in
the ML4 complexes, so that the calculations will tend
to overestimate the stability of ML4 relative to ML3.
Clearly, the common device of replacing PR3 by PH3 in
order to simplify computations is misleading in this
case. The marked differences resulting from replace-
ment of PMe2Ph by PMe3, which are likely to be of
largely steric origin, are evident in the chemistry
reported here.
[B] )
(7)
(8)
k2 + k-1[L]
d[A]
) -(k1 + k5)[A] + k-1[B][L]
dt
d[A]
) -kobs[A]
dt
(9)
1
kobs ) k5 + k1
(10)
{
}
1 + k-1[L]/k2
numerical simulations (see Experimental Section and
Supporting Information), which show that, for the endo
to exo isomerization of 1 and 3, the rate constant kobs
and the extracted kinetic parameters are insensitive to
the formation of the κ2 complex E. We have therefore
used the SSA model to extract kinetic parameters from
the experimental data for 1 and 3 by iterative curve
fitting to eq 10. The calculated curves are compared
with the experimental data in Figures 9 and 10. The
derived kinetic parameters at 357.5 K are k1 ) (6.56 (
0.86) × 10-5 s-1, k5 ) (1.78 ( 0.62) × 10-5 s-1, and k-1
/
k2 ) 0.95 ( 0.44 equiv-1 (regression coefficient 0.968)
for 1, k1 ) (1.27 ( 0.17) × 10-5 s-1, k5 ) (3.04 ( 0.13)
× 10-5 s-1, and k-1/k2 ) 0.83 ( 0.39 equiv-1 (regression
coefficient 0.967) for 3.
It seems likely that the reversible dissociative process
plays little if any role in the isomerization of endo-2, in
view of the lack of dependence of the rate on PMe3
concentration. In this case, therefore, we consider only
the following processes occurring in nondissociative
isomerization:
A {kk } D
5
-5
k4
D + L
98 E (L ) PMe3)
Applying the SSA to the concentration of D and assum-
ing (1) that the concentration of L is small or changing
only slowly with time and (2) that the steady-state
concentration of L is near its initial value, we obtain
eqs 11 and 12. The following values allowed a reason-
d[A]
dt
) -kobs[A]
(11)
(12)
The endo- to exo-isomerizations of complexes 1 - 3
are examples of haptotropic rearrangements, in which
a metal-ligand fragment, such as M(CO)3, migrates
between coordinated and uncoordinated CdC bonds.50
In some cases the processes occur at rates on the NMR
time scale,51,52 but the examples reported here are more
k5
kobs
)
1 + k-5/k4[L]
able representation of the results at 379.5 K: k5 ) 1.14
× 10-4 s-1, k-5 ) 0.049 × 10-4 s-1, and k4 ) 0.59 ×
10-4 s-1 equiv-1. The concentration profiles show, not
surprisingly, that the SSA is poor for [L] ) 0, 1, or 2
equiv per equiv of [A], so these values must be treated
with caution.
(46) Yamamoto, A. Organotransition Metal Chemistry, Fundamental
Concepts and Applications; Wiley-Interscience: New York, 1986; pp
212-222.
(47) Pruchnik, F. P. Organometallic Chemistry of the Transition
Elements; Plenum: New York, 1990; pp 343-346.
(48) Reference 46, pp 47-51.
(49) Reference 47, p 201.
Discu ssion
(50) Albright, T. A.; Hofmann, P.; Hoffmann, R.; Lillya, C. P.;
Dobosh, P. A. J . Am. Chem. Soc. 1983, 105, 3396 and references
therein.
The observations reported here extend earlier work
on o-xylylene complexes in two respects. First, although
the endo and exo isomers of η4-o-xylylene with Ru(PMe2-
Ph)3 had been characterized,11,12 these did not inter-
(51) Mann, B. E. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford,
U.K., 1982; Vol. 3, p 90.
(52) Mann, B. E. Chem. Soc. Rev. 1986, 15, 167.

Isomerization of Xylylene Complexes of Ru and Os
Organometallics, Vol. 17, No. 17, 1998 3797
akin energetically to the 1,3-rearrangements in Fe(CO)3
complexes of η4-1,3,5-cycloheptatriene and substituted
cycloheptatrienes,53,54 acyclic polyene iron tricarbonyls
(e.g., that shown in eq 13),55-61 and Cr(CO)3 complexes
of η6-naphthalene and substituted naphthalenes (eq
14).62,63 For the iron tricarbonyls, the rearrangements
to any simple interpretation. The Ea and ∆Hq values
for the endo to exo isomerization of 1 are smaller than
those for 2 and 3, consistent with the stronger metal-
ligand bonds and lower lability of 5d-element complexes
relative to their 4d-element analogues. The small,
positive activation entropy ∆Sq for the dissociative
pathway in the isomerization of endo-1 is also as
expected for this type of process.64-66 However, the
value of ∆Sq for the net process, in the absence of PMe3,
is negative, even though ca. 75% of the isomerization
proceeds by the dissociative route. Even more surpris-
ing are the large positive values of ∆Sq for the isomer-
ization of endo-2 in the absence of added PMe3 and
endo-3 in the absence of added PMe2Ph, where the route
depending on dissociation of L appears to play little role
(in the case of 3, ca. 25%) or no role. The results may
indicate that aromatic solvent plays a specific role in
the isomerizations of the endo osmium complexes.
At this stage, one can only speculate about intermedi-
ates or transition states. For the ligand-independent
process, a concerted loosening of one of the endo double
bonds via species 10 seems plausible. Loss of a ligand
are believed to occur via a 16-electron intermediate or
transition state Fe(CO)3(η2-polyene), although a path-
way proceeding via a dicarbonyl, Fe(CO)2(η4-polyene),
seems to have been explicitly eliminated only in the case
of the substituted cycloheptatriene complexes Fe(CO)3-
(η4-exo- C7H7R) (R ) Me3Si, Me3Ge, Ph3Ge).54 Theoreti-
cal calculations50 on the mechanism of the degenerate
η6 f η6 rearrangement of Cr(CO)3(η6-C10H8) support a
circuitous pathway in which naphthalene undergoes
partial dissociation to a η2-exocyclic intermediate.
As expected, in the endo to exo isomerization of 1 and
3, the ligand-dependent dissociative pathway plays a
more significant role for the bulkier ligand PMe2Ph than
for PMe3 and, perhaps less predictably, for ruthenium
compared with osmium. However, the activation pa-
rameters listed in Table 9 do not seem to be amenable
L could generate formally 18-electron ML2 complexes
having structures such as 11 or 12; current research is
directed to the possible stabilization of such intermedi-
ates by use of sterically bulky tertiary phosphines.
Ack n ow led gm en t. We thank J ohnson-Matthey Co.,
Royston, U.K., for a loan of hydrated ruthenium(III)
chloride, and Professors Denis Evans and Alan Sargeson
for helpful discussions.
(53) Karel, K. J .; Albright, T. A.; Brookhart, M. Organometallics
1982, 1, 419.
(54) LiShingMan, L. K. K.; Reuvers, J . G. A.; Takats, J .; Deganello,
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(58) Whitlock, H. W.; Markezich, R. L. J . Am. Chem. Soc. 1971, 93,
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Su p p or tin g In for m a tion Ava ila ble: Tables giving crys-
tallographic data, atomic coordinates and equivalent isotropic
displacement parameters, anisotropic displacement param-
eters, interatomic distances and angles for non-hydrogen
atoms, interatomic distances, angles, and torsion angles for
hydrogen atoms, and selected least-squares planes for endo-
3, exo-3, exo-1, and 8 and text and tables giving details of the
kinetics simulation (134 pages). Ordering information is given
on any current masthead page.
(59) Goldschmidt, Z.; Bakal, Y. J . Organomet. Chem. 1984, 269, 191.
(60) Hafner, A.; von Philipsborn, W.; Salzer, A. Angew. Chem., Int.
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S. Organometallics 1987, 6, 1173.
(63) Oprunenko, Y. T.; Malyugina, S. G.; Ustynyuk, Y. A.; Ustynyuk,
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