Photochemistry of M(PP3)H2 (M = Ru, Os; PP3 = P(CH2CH2PPh2)3): Preparative, NMR, and time-resolved studies

Article abstract of DOI:10.1021/ja963797w

Photochemical reaction of Ru(PP₃)H₂ (PP₃ = P(CH₂CH₂PPh₂)₃) in THF under a rigorously inert atmosphere yields the cyclometalated complex Ru[(Ph₂PCH₂CH₂)₂P(CH₂CH₂PPhC₆H₄)]H. The latter is converted back to Ru(PP₃)H₂ under H₂ and reacts even with traces of N₂ to yield Ru(PP₃)(N₂). The dinitrogen complex may be synthesized directly by a number of methods. NMR spectroscopy shows that photolysis of Ru(PP₃)H₂ under C₂H₄ and CO yields Ru(PP₃)(C₂H₄) and Ru(PP₃)(CO), respectively, Photolysis of Ru(PP₃)H₂ with HSiEt₃ in THF yields Ru(PP₃)(SiEt₃)H, while photolysis in mixtures of THF and benzene at low temperature yields Ru(PP₃)(Ph)H. The latter is also generated by reduction of Ru(PP₃)Cl₂ in the presence of benzene. Os(PP₃)(Ph)H is formed either by photolysis of Os(PP₃)H₂ or by reduction of Os(PP₃)Cl₂ in the presence of benzene. Irradiation of Os(PP₃)H₂ in THF or THF/hexane mixtures initially yields the THF C-H activation product, Os(PP₃)(2-C₄H₇O)H. This complex is also generated by reduction of Os(PP₃)Cl₂ with sodium naphthalenide under N₂ in the presence of THF. Os(PP₃)-(2-C₄H₇O)H is converted to the cyclometalated complex, Os[(Ph₂PCH₂CH₂)₂P(CH₂CH₂PPhC₆H₄)]H, on irradiation in THF and to Os(PP₃)(Ph)H on irradiation in benzene. Reaction of Os(PP₃)H₂ with CH₃OTf (Tf = triflate) yields Os(PP₃)(OTf)H, which is converted to the labile Os(PP₃)(CH₃)H on reaction with methyllithium. Laser flash photolysis of Ru(PP₃)H₂ in cyclohexane (laser wavelength 308 nm) yields transient Ru(PP₃) with an absorption maximum at 395 nm. The transient reacts with H₂, C₆H₆, HSiEt₃, CO, N₂, C₂H₄, and THF with little discrimination; the second-order rate constants for these reactions lie in the range 5 x 10⁵-2 x 10⁶ dm³ mol^-1 s^-1 at 295 K. Kinetic isotope effects have been determined for the reaction with benzene and THF, as 1.5 (0.2) and 1.1 (0.2), respectively. Activation parameters for reaction of Ru(PP₃) are as follows: with HSiEt₃ ΔH≠ = 35 (2) kJ mol^-1, ΔS≠ = -18 (6) J K^-1 mol^-1; with C₆H₆ ΔH≠ = 39 (4) kJ mol^-1, ΔS≠ ~0 J K^-1 mol^-1. The reaction with THF yields a short-lived adduct, probably bound through oxygen, which is rapidly converted to the cyclometalated product. Laser flash photolysis of Os(PP₃)H₂ generates transient Os(PP₃) (λ(max) = 390 nm). The transient kinetics of Os(PP₃) are substantially different from its ruthenium analogue. It reacts with alkanes and shows different behavior toward THF but is unaffected by addition of H₂. Rate constants in the range 6 x 10⁴-6 x 10⁵ dm³ mol^-1 s^-1 (295 K) are presented for reaction with C₆H₆, THF, HSiEt₃, CO, C₂H₄, N₂, and several alkanes. Kinetic isotope effects have been determined for the reactions with methylcyclohexane and benzene as 5.6 (1.5) and 0.6 (0.1), respectively. The rate constants for reaction with alkanes rise in the order, methylcyclohexane < pentane < heptane < methane. The rate constants for reaction with methane and benzene are insignificantly different. Following reaction of Os(PP₃) with THF to form Os(PP₃)-(THF), C-H insertion occurs with a first-order rate constant of 4.2 (8) x 10³ s^-1 with k(H)/k(D) = 2.6 (0.4). The activation parameters for reaction of Os(PP₃) with substrates are as follows: with pentane ΔH≠ = 27 (1) kJ mol^-1, ΔS≠ = -59 (4) J K^-1 mol^-1; with HSiEt₃ ΔH≠ = 31 (5) kJ mol^-1, ΔS≠ = -27 (12) J K^-1 mol^-1; with C₆H₆ ΔH≠ = 38 (₃) kJ mol^-1, ΔS≠ = -7 (9) J K^-1 mol^-1.

Full text of DOI:10.1021/ja963797w

J. Am. Chem. Soc. 1997, 119, 8459-8473
8459
Photochemistry of M(PP3)H2 (M ) Ru, Os; PP3 )
P(CH2CH2PPh2)3): Preparative, NMR, and Time-Resolved
Studies
Robert Osman,† David I. Pattison,† Robin N. Perutz,*,† Claudio Bianchini,*,‡
Juan A. Casares,‡,§ and Maurizio Peruzzini‡
Contribution from the Department of Chemistry, UniVersity of York, Heslington, York,
YO1 5DD, U.K., and the Istituto per lo Studio della Stereochimica ed Energetica dei
Composti di Coordinazione, ISSECC-CNR, Via J. Nardi 39, 50132 Firenze, Italy
ReceiVed October 31, 1996X
Abstract: Photochemical reaction of Ru(PP3)H2 (PP3 ) P(CH2CH2PPh2)3) in THF under a rigorously inert atmosphere
yields the cyclometalated complex Ru[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H. The latter is converted back to
Ru(PP3)H2 under H2 and reacts even with traces of N2 to yield Ru(PP3)(N2). The dinitrogen complex may be
synthesized directly by a number of methods. NMR spectroscopy shows that photolysis of Ru(PP3)H2 under C2H4
and CO yields Ru(PP3)(C2H4) and Ru(PP3)(CO), respectively. Photolysis of Ru(PP3)H2 with HSiEt3 in THF yields
Ru(PP3)(SiEt3)H, while photolysis in mixtures of THF and benzene at low temperature yields Ru(PP3)(Ph)H. The
latter is also generated by reduction of Ru(PP3)Cl2 in the presence of benzene. Os(PP3)(Ph)H is formed either by
photolysis of Os(PP3)H2 or by reduction of Os(PP3)Cl2 in the presence of benzene. Irradiation of Os(PP3)H2 in THF
or THF/hexane mixtures initially yields the THF C-H activation product, Os(PP3)(2-C4H7O)H. This complex is
also generated by reduction of Os(PP3)Cl2 with sodium naphthalenide under N2 in the presence of THF. Os(PP3)-
(2-C4H7O)H is converted to the cyclometalated complex, Os[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H, on irradiation
in THF and to Os(PP3)(Ph)H on irradiation in benzene. Reaction of Os(PP3)H2 with CH3OTf (Tf ) triflate) yields
Os(PP3)(OTf)H, which is converted to the labile Os(PP3)(CH3)H on reaction with methyllithium. Laser flash photolysis
of Ru(PP3)H2 in cyclohexane (laser wavelength 308 nm) yields transient Ru(PP3) with an absorption maximum at
395 nm. The transient reacts with H2, C6H6, HSiEt3, CO, N2, C2H4, and THF with little discrimination; the second-
order rate constants for these reactions lie in the range 5 × 105-2 × 106 dm3 mol-1 s-1 at 295 K. Kinetic isotope
effects have been determined for the reaction with benzene and THF, as 1.5 (0.2) and 1.1 (0.2), respectively. Activation
parameters for reaction of Ru(PP3) are as follows: with HSiEt3 ∆Hq ) 35 (2) kJ mol-1, ∆Sq ) -18 (6) J K-1
mol-1; with C6H6 ∆Hq ) 39 (4) kJ mol-1, ∆Sq ≈ 0 J K-1 mol-1. The reaction with THF yields a short-lived adduct,
probably bound through oxygen, which is rapidly converted to the cyclometalated product. Laser flash photolysis
of Os(PP3)H2 generates transient Os(PP3) (λmax ) 390 nm). The transient kinetics of Os(PP3) are substantially
different from its ruthenium analogue. It reacts with alkanes and shows different behavior toward THF but is unaffected
by addition of H2. Rate constants in the range 6 × 104-6 × 105 dm3 mol-1 s-1 (295 K) are presented for reaction
with C6H6, THF, HSiEt3, CO, C2H4, N2, and several alkanes. Kinetic isotope effects have been determined for the
reactions with methylcyclohexane and benzene as 5.6 (1.5) and 0.6 (0.1), respectively. The rate constants for reaction
with alkanes rise in the order, methylcyclohexane < pentane < heptane < methane. The rate constants for reaction
with methane and benzene are insignificantly different. Following reaction of Os(PP3) with THF to form Os(PP3)-
(THF), C-H insertion occurs with a first-order rate constant of 4.2 (8) × 103 s-1 with kH/kD ) 2.6 (0.4). The
activation parameters for reaction of Os(PP3) with substrates are as follows: with pentane ∆Hq ) 27 (1) kJ mol-1
∆Sq ) -59 (4) J K-1 mol-1; with HSiEt3 ∆Hq ) 31 (5) kJ mol-1, ∆Sq ) -27 (12) J K-1 mol-1; with C6H6 ∆Hq
) 38 (3) kJ mol-1, ∆Sq ) -7 (9) J K-1 mol-1
,
.
Introduction
iridium, and osmium complexes.4-6 One advantage of the
photochemical method lies in the ability to obtain kinetic data
by laser flash photolysis. We recently exploited this in our
Photochemical elimination of dihydrogen from metal dihy-
dride complexes dates back to the discovery of the photoreaction
of W(η5-C5H5)2H2 with benzene by Giannotti and Green.1 The
photochemical methods2 were soon found to complement the
more traditional reductive syntheses, for instance of dimers of
Mo(η5-C5H5)2.3 In recent years, photochemical elimination of
dihydrogen has become one of the key routes into carbon-
hydrogen bond activation especially by half-sandwich rhodium,
(2) (a) Berry, M.; Elmitt, K.; Green, M. L. H.; Simpson, S. J. J. Chem.
Soc., Dalton Trans. 1979, 1950. (b) Berry, M.; Cooper, N. J.; Green, M. L.
H. J. Chem. Soc., Dalton Trans. 1980, 29. (c) Geoffroy, G. L.; Bradley, M.
G. Inorg. Chem. 1978, 17, 2410. (d) Belmore, K. A.; Vanderpool, R. A.;
Tsai, J. C.; Khan, M. A.; Nicholas, K. M. J. Am. Chem. Soc. 1988, 110,
2004. (e) Grebenik, P.; Grinter, R.; Perutz, R. N. Chem. Soc. ReV. 1988,
17, 453.
(3) (a) Thomas, J. L.; Brintzinger, H. H. J. Am. Chem. Soc. 1972, 94,
1386. (b) Thomas, J. L. J. Am. Chem. Soc. 1973, 95, 1838. (c) Bashkin, J.;
Green, M. L. H.; Poveda, M. L.; Prout, K. J. Chem. Soc., Dalton Trans.
1982, 2485. (d) Chatt, J.; Davidson, J. M. J. Chem. Soc. 1965, 843.
(4) (a) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984, 106, 1650.
(b) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91. (c) Periana, R.
A.; Bergman, R. G. J. Am. Chem. Soc. 1986, 108, 7332. (d) Chin, R. M.;
Dong, L.; Duckett, S. B.; Partridge, M. G.; Jones, W. D.; Perutz, R. N. ibid
1993, 115, 7685.
† University of York.
‡ ISSECC, Florence.
§ Present address: Departamento de Quimica Inorganica, Universidad
de Valladolid, Spain.
X Abstract published in AdVance ACS Abstracts, August 15, 1997.
(1) Giannotti, C.; Green, M. L. H. J. Chem. Soc. Chem. Commun. 1972,
1114.
S0002-7863(96)03797-3 CCC: $14.00 © 1997 American Chemical Society

8460 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Scheme 1. Structures of M(PP3) and M(dmpe)2
Osman et al.
cation, [Rh(PP3)H2]+, which is isoelectronic with Ru(PP3)H2,
has also been isolated and can be converted to the triflate-
stabilized RhI species, [Rh(PP3)(OSO2CF3)]+.11a The latter
coordinates CO, phosphines, and halides and also undergoes
oxidative addition with dihydrogen. However, [Rh(PP3)(OSO2-
CF3)]+ neither undergoes cyclometalation nor reaction with
benzene. Intermolecular C-H activation of benzene or THF
can be achieved with [Ir(PP3)]+ 11b or [Rh(NP3)]+ (NP3
)
studies of complexes of the type Ru(R2PCH2CH2PR2)2H2 (R
) Me, Et, Ph, C2F5).7,8 We showed that each of these
complexes undergoes photodissociation of dihydrogen to yield
16-electron Ru(R2PCH2CH2PR2)2 fragments with characteristic
multiband UV/vis spectra. The fragments, Ru(dmpe)2, Ru-
(depe)2, and Ru(dppe)2 (those with R ) Me, Et, and Ph,
respectively, collectively abbreviated to Ru(drpe)2), are close
to square planar and each exhibits a very low energy absorption
band at ca. 740 nm. The lowest energy absorption of Ru(dfepe)2
(the analogue with R ) C2F5) is shifted to 620 nm and may be
perturbed by F-coordination. The reactivity of Ru(dmpe)2 varies
with substrate according to the pattern k(H2) > k(CO) > k(C2H4)
≈ k(HSiEt3). The rate constant for reaction with H2 is 6.2 ×
109 dm3 mol-1 s-1, remarkably close to the diffusion limit. The
reactivity of Ru(depe)2 follows the same pattern as for Ru-
(dmpe)2, but the rate constants are a factor of 15 lower for H2
and 200 times lower for HSiEt3. The phenyl analogue, Ru-
(dppe)2, is less reactive still; k(H2) is 250 times smaller than
for Ru(dmpe)2 and k(C2H4) is 3700 times smaller, while there
is no detectable reaction toward HSiEt3. NMR studies of the
photoproducts complement the flash photolysis measurements
by allowing conclusive identification of the final products. The
flash photolysis and NMR measurements agree for Ru(depe)2,
Ru(dppe)2, and Ru(dfepe)2 in showing no reaction with benzene.
However, there is a discrepancy between the methods for
Ru(dmpe)2: no reaction with benzene is found by laser flash
photolysis, but NMR studies show formation of Ru(dmpe)2-
(Ph)H.
N(CH2CH2PPh2)3).11a The fluxional behavior of complexes of
the type [M(PP3)H2]n+ has been reported.9,10,12
In this paper we explore the photochemistry of Ru(PP3)H2
(1Ru) and Os(PP3)H2 (1Os) by preparative and by in situ NMR
methods. We show that some of the products can also be
obtained by thermal routes involving reduction of M(PP3)Cl2
in the presence of suitable substrates or reaction of Os(PP3)H2
with methyl triflate. The rates of reaction of M(PP3) are
quantified by laser flash photolysis. Striking features include
(a) the scavenging of N2 by the product of cyclometalation of
Ru(PP3); (b) the completely different kinetic selectivity of Ru-
(PP3) and Os(PP3) compared to Ru(dppe)2; (c) the enhanced
reactivity of Ru(PP3) toward benzene and HSiEt3 compared to
Ru(dppe)2; and (d) the insertion of Os(PP3) into aliphatic C-H
bonds of THF and alkanes, most notably of methane itself. Some
of the results with Os(PP3) have been published as a com-
munication.13
Experimental Section
Laser Flash Photolysis. The laser flash photolysis apparatus at York
has been fully described previously.7 In summary, a XeCl excimer
laser (308 nm) is used as the excitation source, while detection is
achieved with a pulsed Xe arc lamp, monochromator, and photomul-
tiplier. The photomultiplier is linked to a digital oscilloscope (Tektronix
TDS520), and the system is controlled by a Dell PC with in-house
software. Typically, transient data are collected as averages of between
two and ten shots. Pseudo-first-order decays were analyzed by fitting
a straight line plot of ln ∆A against time using in-house software, while
Microcal Origin was used to fit decays to complex analytical expres-
sions, and Simula was used to model decays where no analytical
function could be derived.
Samples were prepared in a 10 mm quartz cuvette, fitted with a
Young’s PTFE stopcock and a degassing bulb. Solid was loaded into
these cells in an argon atmosphere glovebox. Solvents (Aldrich HPLC
grade) were dried over CaH2 at reflux and stored under argon. These
were transferred to the flash cells via cannula through a silicone septum
on a Schlenk line fitted with a mercury diffusion pump. The
concentration of the samples was adjusted to obtain an absorbance of
0.6-1.0 at 308 nm and then degassed by three freeze-pump-thaw
cycles (to 10-4 mbar), before backfilling with the required atmosphere.
Gas mixtures were made up manometrically in 1 L bulbs to a pressure
of typically 700 Torr. Liquid quenchers were usually prepared as 1
mol dm-3 stock solutions, before addition to the samples with a
microliter syringe. UV/visible spectra were recorded before and after
laser flash photolysis on a Perkin-Elmer Lambda 7G spectrometer.
General Procedures. Solvents (THF, benzene, hexane) were of
AR grade and dried by distillation over sodium/benzophenone under
an Ar or N2 atmosphere, while THF was also dried and purified by
distillation under nitrogen over LiAlH4. The solvents were stored over
The synthesis of M(PP3)H2 (PP3 ) P(CH2CH2PPh2)3, M )
Ru, Os) complexes9,10 offered the opportunity to study how the
reactivity and spectra of the constrained M(PP3) unit compare
with those of Ru(drpe)2. The tetradentate ligand allows the
M(PP3) transient to adopt pyramidal (C3V) or butterfly (Cs)
geometries but prevents adoption of the square planar (D2h)
structure characteristic of Ru(drpe)2 (Scheme 1). The numbering
of the compounds is shown in Chart 1.
Chart 1. Key to the Compound Numbering System
compound
M(PP3)H2
M(PP3)Cl2
[Ru(PP3)(H)(N2)]BPh4 3Ru
number
1Ru/1Os Os(PP3)(2-C4H7O)H 8Os
2Ru/2Os M(PP3)(Cl)H 9Ru/9Os
M(PP3)(C2H4)
compound
number
10Ru/10Os
11Ru
M[(Ph2PCH2CH2)2P-
(CH2CH2PPhC6H4)]H
M(PP3)(Ph)H
M(PP3)(N2)
M(PP3)(CO)
4Ru/4Os Ru(PP3)(SiEt3)H
5Ru/5Os Os(PP3)(OTf)H
6Ru/6Os Os(PP3)(Me)H
7Ru/7Os
12Os
13Os
The Florence group has already obtained considerable
information concerning the conversion of M(PP3)H2 to dihy-
drogen hydride cations, [M(PP3)(η2-H2)H]+, and other cationic
complexes, [M(PP3)(L)H]+ (M ) Ru, Os; L ) CO, N2).9,10 The
(7) Hall, C.; Jones, W. D.; Mawby, R. J.; Osman, R.; Perutz, R. N.;
Whittlesey, M. K. J. Am. Chem. Soc. 1992, 114, 7425.
(8) Cronin, L.; Nicasio, M. C.; Perutz, R. N.; Peters, R. G.; Roddick, D.
M.; Whittlesey, M. K. J. Am. Chem. Soc. 1995, 117, 10047.
(9) Bianchini, C.; Perez, P. J.; Peruzzini, M.; Zanobini, F.; Vacca, A.
Inorg. Chem. 1991, 30, 279.
(10) Bianchini, C.; Linn, K.; Masi, D.; Peruzzini, M.; Polo, A.; Vacca,
A.; Zanobini, F. Inorg. Chem. 1993, 32, 2366.
(11) (a) Bianchini, C.; Masi, D.; Meli, A.; Peruzzini, M.; Zanobini, F. J.
Am. Chem. Soc. 1988, 110, 6411. (b) Bianchini, C.; Peruzzini, M.; Zanobini,
F. J. Organomet. Chem. 1987, 326, C79.
(5) (a) Janowicz, A. H.; Bergman, R. G. J. Am. Chem. Soc. 1983, 105,
3929. (b) Buchanan, J. M.; Stryker, J. M.; Bergman, R. G. J. Am. Chem.
Soc. 1986, 108, 1537. (c) Sponsler, M. B.; Weiller, B. H.; Stoutland, P. O.;
Bergman, R. G. J. Am. Chem. Soc. 1989, 111, 6841. (d) Bloyce, P. E.;
Rest, A. J.; Whitwell, I. J. Chem. Soc., Dalton Trans. 1990, 813. (e)
Partridge, M. G.; McCamley, A.; Perutz, R. N. J. Chem. Soc., Dalton Trans.
1994, 3519.
(6) (a) Kiel, W. A.; Ball, R. G.; Graham, W. A. G. J. Organomet. Chem.
1990, 383, 481. (b) Brough, S. A.; Hall, C.; McCamley, A.; Perutz, R. N.;
Stahl, S.; Wecker, U.; Werner, H. J. Organomet. Chem. 1995, 504, 33.
(12) Heinekey, D. M.; van Roon, M. J. Am. Chem. Soc. 1996, 118, 12134.
(13) Osman, R.; Pattison, D. I.; Perutz, R. N.; Bianchini, C.; Peruzzini,
M. J. Chem. Soc., Chem. Commun. 1994, 513.

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8461
molecular sieves or under argon in ampoules fitted with a PTFE
stopcock. tert-Butyllithium (1.7 mol dm-3 solution in pentane) and
phenyllithium (1.8 mol dm-3 solution in cyclohexane-diethyl ether)
were purchased from Aldrich and used as received. The complexes
Ru(PP3)H2 (1Ru),9 Os(PP3)H2 (1Os),10 Ru(PP3)Cl2 (2Ru),9 Os(PP3)-
Cl2 (2Os),10 and [Ru(PP3)(H)(N2)]BPh4 (3Ru)9 were prepared as
described in the literature. The gases (N2, Ar, C2H4, CH4, H2, CO)
were of BOC Research grade (99.999%) or high purity grade (He),
while 15N2 (99%) was obtained from MSD Isotopes. Deuterated
solvents for NMR measurements (Aldrich, Merck and Goss Scientific
Instruments Ltd.) were dried over molecular sieves, or by stirring over
potassium/benzophenone before being distilled and stored under
vacuum. All reactions and manipulations were routinely performed
under a dry nitrogen or argon atmosphere using standard Schlenk, high
vacuum line and glovebox techniques. The solid complexes were
collected on sintered glass-frits and washed with hexane before being
dried in a stream of nitrogen.
31P{1H} NMR spectroscopy: the cyclometalated complex Ru[(Ph2PCH2-
CH2)2P(CH2CH2PPhC6H4)]H (4Ru) was the only ruthenium product.
1
After 2 h, 31P{1H} and H NMR spectra showed ca. 85% conversion
of 1Ru into 4Ru.
(B) Preparative Experiment in THF. A solution of 1Ru (200 mg,
0.26 mmol) in THF (20 mL) was irradiated with UV light at 293 K
under helium. After 2 h, addition of hexane (30 mL) to the resulting
light orange solution led to the precipitation of 4Ru as pale yellow
microcrystals. Yield 75%. Anal. Calcd for C42H42P4Ru: C, 65.37;
H, 5.49. Found: C, 65.21; H, 5.39. IR: ν(Ru-H) 1950 cm-1 (m).
Photolysis of Ru(PP3)H2 in Benzene/THF-d8. A solution of 1Ru
in C6H6/THF-d8 (25:75 v/v) prepared under argon in a 5-mm NMR
tube was irradiated with UV light at 243 K for ca 5 h. The sample
was kept at 243 K, and low temperature 31P{1H} and 1H NMR
spectroscopy (223 K) showed that 1Ru had disappeared to give a new
product Ru(PP3)(Ph)H (5Ru). On warming to 273 K, 5Ru decomposed
rapidly to reform 1Ru, in addition to 4Ru and other products.
Preparative photochemical reactions were performed by using a
Helios Italquartz UV 13F apparatus. The photolysis source was a 135
W (principal emission wavelength at 366 nm) high-pressure mercury
vapor immersion lamp equipped with a wave filter to remove excess
heat or a 150 W high-pressure mercury vapor lamp with a water filter
(10 cm) to remove excess heat. In some cases a Schott UG11 filter
was used to photolyze in the range 290 nm < λ < 376 nm. Photolysis
NMR experiments were carried out in quartz NMR tubes (Wilmad) or
in glass tubes fitted with a PTFE stopcock for manipulation under
reactive atmospheres. Low temperature photolysis was achieved by
passing the gas evaporating from liquid nitrogen through a thermostated
dewar, using a 300 W xenon arc lamp as the photolysis source.
Photolysis and product characterization in York was achieved by loading
the compound into an NMR tube with a PTFE stopcock in a glovebox
with an argon atmosphere. Dry solvents were added by cannula, and
the sample was degassed by three freeze-pump-thaw cycles before
backfilling with the required atmosphere. After photolysis the solvent
was removed in Vacuo before condensing deuterated solvent onto the
product mixture. The products were analyzed by 1H and 31P{1H} NMR
spectroscopy.
1H and 13C{1H} NMR spectra were recorded on Varian VXR 300,
Bruker AC200P, Bruker AVANCE DRX 500, Jeol EX270, or Bruker
AMX500 spectrometers operating at 200.13, 270.05, 299.94 or 500.13
MHz (1H) and 50.32, 75.42, and 125.80 MHz (13C). Chemical shifts
are given relative to tetramethylsilane and were calibrated against the
residual solvent resonance (1H) or the deuterated solvent multiplet (13C).
31P{1H} NMR spectra were measured relative to external 85% H3PO4
with downfield values taken as positive. 15N{1H} NMR spectra were
acquired on a Bruker AMX500 and calibrated relative to dissolved 15N2
at δ 309.5. 13C-DEPT experiments were run on the Bruker AC 200P
spectrometer. 1H,13C-2D HETCOR NMR experiments were recorded
on either the Bruker AC 200P spectrometer using the XHCORR pulse
program or the Bruker AVANCE DRX 500 spectrometer equipped with
a 5-mm triple resonance probe-head (inverse correlation mode, HMQC
experiment). The 1H,1H-2D COSY NMR experiments were conducted
routinely on the Bruker AC 200P instrument in the absolute magnitude
mode using a 45° or 90° pulse after the incremental delay or were
acquired on the AVANCE DRX 500 Bruker spectrometer using the
gradient-accelerated version of the conventional COSY sequence
(COSYPS). 1H,1H-2D NOESY NMR experiments on 8Os were
conducted on the same instrument operating in the phase-sensitive TPPI
mode in order to discriminate between positive and negative cross peaks.
The proton NMR spectra, with broadband and selective phosphorus
decoupling, were recorded on the Bruker AC 200P instrument equipped
with a 5-mm inverse probe and a BFX-5 amplifier device using the
decoupling sequence GARP. Infrared spectra were recorded as Nujol
mulls or in solution on a Perkin-Elmer 1600 series or a Mattson-Unicam
RS FT-IR spectrophotometer between KBr plates. Elemental analyses
(C, H, N) were performed using a Carlo Erba Model 1106 elemental
analyzer.
Photolysis of Ru(PP3)H2 under Nitrogen in THF. A solution of
1Ru (200 mg, 0.26 mmol) in THF (20 mL) was irradiated with UV
light at 293 K under nitrogen. After 50 min, a sample of the resulting
red orange solution (0.6 mL) was transferred Via syringe into a 5-mm
screw-cap NMR tube containing 0.3 mL of degassed THF-d8 and
studied by 31P{1H} NMR spectroscopy. The NMR analysis showed
the partial conversion (ca. 30%) of 1Ru to Ru(PP3)(N2) (6Ru) (see
below). Trace amounts of 4Ru (∼2%) were also detected. After 2 h
of photolysis the 31P{1H} NMR analysis gave the following composi-
tion: 6Ru (44%), 4Ru (8%), 1Ru (48%).
Synthesis of Ru(PP3)(N2) (6Ru). (A). A solution of sodium
naphthalenide prepared in THF (30 mL) from 130 mg (1.04 mmol) of
naphthalene and 50 mg of freshly cut sodium (2.20 mmol) was added
in small portions with stirring to a THF (10 mL) suspension of Ru-
(PP3)Cl2 (2Ru) (400 mg, 0.48 mmol) at 273 K. The pale yellow
suspension turned red-brown immediately, while the starting dichloride
dissolved completely. After stirring for 30 min at 273 K, the ice-bath
was removed, and the solution was slowly brought to room temperature
and stirred for an additional 30 min. The red-brown solution was
filtered and concentrated to about 15 mL under vacuum. Addition of
hexane (30 mL) gave red microcrystals of Ru(PP3)(N2) (6Ru). Yield
78%. Anal. Calcd for C42H42N2P4Ru: C, 63.07; H, 5.30; N, 3.50.
Found: C, 62.95; H, 5.25; N, 3.31. IR: ν(NtN) 2080 cm-1 (m).
(B). Phenyllithium (0.072 mmol; 40 µL of a solution 1.8 M in
diethyl ether-cyclohexane) was syringed into a screw-cap NMR tube
containing a solution of [Ru(PP3)(H)(N2)]BPh4 (3Ru) (36 mg, 0.033
mmol) in THF-d8 (0.8 mL) at 195 K. The yellow solution immediately
turned red-brown. The 31P{1H} NMR spectrum showed that 6Ru was
the main product (80%). Two other unidentified products were formed,
neither of which contained hydride ligands.
(C). Nitrogen was bubbled into a solution of 4Ru in THF-d8 (1.0
mL) prepared by photolysis of 1Ru (30 mg, 0.039 mmol) under argon
in a 5-mm NMR quartz tube. The reaction was monitored by 31P{1H}
NMR spectroscopy which showed the selective formation of 6Ru. A
complete transformation occurred after 24 h in the dark.
Several experiments were carried out to study the thermal behavior
of 6Ru in both THF and C6H6 under either N2 or Ar atmosphere.
Extensive decomposition of the compound invariably occurred to
unidentified products. In particular, the formation of 4Ru or 5Ru was
never observed.
Synthesis of Ru(PP3)(CO) (7Ru). A solution of sodium naphtha-
lenide prepared in THF (10 mL) from 65 mg (0.52 mmol) of
naphthalene and 25 mg of freshly cut sodium (1.10 mmol) was added
in small portions with stirring under a positive pressure of carbon
monoxide to a THF solution (8 mL) of 2Ru (200 mg, 0.24 mol) cooled
to 273 K. The pale yellow suspension turned dark yellow immediately
while the starting dichloride dissolved. After stirring for 5 min at 273
K, the solution was evaporated to dryness under vacuum to yield a
dark yellow solid which was washed with CO-saturated pentane (3 ×
5 mL) before being dried under vacuum. Yield 92%. Anal. Calcd
for C43H42OP4Ru: C, 64.58; H, 5.29. Found: C, 64.72; H, 5.11. IR:
NMR data (1H and 31P{1H}) for the complexes synthesized as below
are listed in Tables 1 (Ru) and 2 (Os).
ν(CtO) 1866 cm-1 14 13C{1H} NMR (295 K, THF-d8, 50.32 MHz,
.
Photolysis of Ru(PP3)H2 under Helium. (A) NMR Experiment
in THF-d8. A solution of 1Ru (20 mg, 0.026 mmol) in THF-d8 (1.0
mL) prepared under helium in a 5-mm NMR quartz tube was irradiated
with UV light at 293 K. The photolysis reaction was monitored by
(14) Compare with [Ru(CO)(QP)] (QP ) P(o-C6H4PPh2)3): ν(CtO)
1891 cm-1, see: Halfpenny, M. T.; Venanzi, L. M. Inorg. Chim. Acta 1971,
5, 91.

8462 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Osman et al.
CO atmosphere in a sealed NMR tube): δ 224.0 (dq, JCPb 72.1 Hz,
JCPt 12.0 Hz, RuCO (Pb ) bridgehead; Pt ) terminal in C3V)).15
(B) Preparation of Os(PP3)(CH3)H (13Os). A Schlenk tube was
charged with 200 mg of 1Os (0.23 mmol) and 10 mL of benzene
previously degassed under argon. After the solution was cooled to ca.
279 K, 1 equiv of both MeOTf and MeLi were added via syringe in a
quick sequence with stirring. Removal of the solvent in Vacuo gave a
solid residue which was washed with pentane (2 × 3 mL) and
characterized as a mixture of 5Os (45%), 1Os (25%), 13Os (25%),
and 12Os (5%) (31P and 1H NMR integration). IR data for 13Os:
Reduction of Os(PP3)Cl2 (2Os) with Sodium Naphthalenide. A
slight excess of sodium naphthalenide prepared in THF (30 mL) from
130 mg (1.04 mmol) of naphthalene and 50 mg of freshly cut sodium
(2.20 mmol) was added in portions with stirring to a suspension of
2Os (150 mg, 0.16 mmol) in THF (10 mL) thermostated at 273 K
under N2. The starting dichloride dissolved to give a dark red solution.
After 15 min, the solution was concentrated in vacuo to give a dark
red oil. Due to the extreme air- and moisture-sensitivity of this product
neither a satisfactory elemental analysis nor a complete spectroscopic
characterization was obtained. However, based on the 31P{1H} NMR
spectrum (253 K) as well as the chemical behavior (see below) and a
comparison with the analogous Ru chemistry, this product was assigned
the formula Os(PP3)(N2) (6Os).
ν(Os-H) 2042 cm-1
.
Synthesis of the (Phenyl)hydride Complex Os(PP3)(Ph)H (5Os)
via 12Os. A Schlenk tube was charged with 200 mg of 1Os (0.23
mmol) and 10 mL of benzene previously degassed under argon. After
the solution was cooled to ca. 279 K, 1 equiv of both MeOTf (26 µL)
and MeLi (145 µL, 1.6 mol dm-3 solution in Et2O) was added via
syringe in a quick sequence with stirring. Addition of hexane (5 mL)
and slow concentration under argon gave off-white crystals of 5Os.Yield
85%.
Synthesis of Os(PP3)(2-C4H7O)H (8Os). On standing at room
temperature for 30 min, the red solution of 6Os obtained as described
above, turned orange and, after addition of hexane and concentration
under nitrogen, pale orange microcrystals of the (tetrahydrofuranyl)-
hydride (8Os) separated in about 60% yield. Anal. Calcd for
C46H49P4OsO: C, 59.15; H, 5.25. Found: C, 58.89; H, 5.16. IR:
Results
1. Product Studies of the Photochemical Reactions of Ru-
(PP3)H2 and Related Reductive Syntheses. NMR studies of
Ru(PP3)H2 (1Ru) show the hydride resonance as a broad doublet
in the proton spectrum at δ -6.66. The 31P{1H} NMR spectrum
reveals the bridgehead phosphorus (Pb) as a quartet at δ 157.0
and the three terminal phosphorus nuclei (Pt) of the tripodal
ligand as a doublet at δ 76.7. The fluxional behavior of 1Ru
has been investigated previously.9 (See Table 1 for details of
NMR spectra of complexes of Ru(PP3).)
A sample of 1Ru was dissolved in THF and placed under an
atmosphere of Research Grade argon. After photolysis for ca.
20 h (290 nm < λ < 376 nm) the 31P{1H} NMR spectrum
showed a product with an AMQX splitting pattern, and the
proton spectrum revealed a new hydride resonance. The same
product was made on a preparative scale by taking a solution
of 1Ru in THF and irradiating with UV light at 293 K under
helium. The yellow microcrystalline product is identified as
the cyclometalated species, Ru[(Ph2PCH2CH2)2P(CH2CH2-
PPhC6H4)]H (4Ru), on the basis of the large upfield shift
(approximately 80 ppm) of one of the phosphorus resonances16
and the relatively low field resonance of the hydride (Scheme
2). This complex reacted thermally under 1 atm of hydrogen
to reform 1Ru within a few minutes (Scheme 3), behavior which
is similar to that of Fe(Ph2PCH2CH2PPh2)(C6H4PPhCH2CH2-
PPh2)H with H2.17
ν(Os-H) ) 1996 cm-1 13C{1H} NMR (295 K, C6D6, 125.77 MHz,
.
assigned by HETCOR) C4H7O ring: δ 59.0 (dd, JCPtr 57.1 Hz, JCPcis
10.4 Hz, C1(Ptr ) terminal P trans to one P in Cs, Pcis ) terminal P cis
to all other P in Cs), δ 47.8 (s, C2), δ 28.2 (s, C3), δ 71.0 (d, JCPtr 5.2
Hz, C4). The compound is extremely sensitive to air and moisture and
decomposes in THF at 343 K (sealed NMR tube) without formation
of any known product.
Photochemical Behavior of 8Os in THF Solution. A solution of
8Os (40 mg, 0.05 mmol) in THF-d8 (0.8 mL) was irradiated with UV
light in a quartz NMR tube for 90 min at room temperature. 31P{1H}
and 1H spectroscopy showed the transformation of 8Os into the
cyclometalated complex Os[(Ph2PCH2CH2)2P(CH2CH2PPhC6H4)]H (4Os).
Decomposition to unidentified products (ca. 20%) was also observed.
Synthesis of the (Phenyl)hydride Complex Os(PP3)(Ph)H (5Os).
(A). A solution of 2Os (100 mg, 0.12 mmol) in C6H6 (15 mL) was
stirred for 4 h in the presence of an excess of sodium amalgam (1.5%
of Na) under nitrogen. Afterwards, the yellow solution was filtered to
remove the amalgam, and the solvent was removed in vacuo to give a
solid residue that was characterized as the (phenyl)hydride complex
Os(PP3)(Ph)H (5Os) (86%) (IR: ν(Os-H) ) 2054 cm-1), occasionally
contaminated by the known complex Os(PP3)(Cl)H (9Os).9
(B). A solution of 8Os (40 mg, 0.05 mmol) in C6D6 (0.8 mL) in a
sealed NMR tube was monitored periodically by 31P{1H} NMR
spectroscopy at room temperature. After 4 days, all the starting material
8Os was transformed into Os(PP3)(D)(C6D5) (5Os-d6). (C). A solution
of 8Os (40 mg, 0.05 mmol) in C6D6 (0.8 mL) was irradiated with UV
light in a quartz NMR tube for 90 min at room temperature. 31P{1H}
and 1H spectroscopy showed the complete transformation of 8Os into
5Os-d6.
The cyclometalated complex (4Ru) also reacts thermally with
nitrogen (1 atm) at ambient temperature to form the dinitrogen
complex, Ru(PP3)(N2) (6Ru) (Scheme 3). Ru(PP3)(N2) was
generated by several other means: (i) by direct photolysis of
1Ru in THF under N2, giving 6Ru and 4Ru in 40% and 25%
yields, respectively (Scheme 2); (ii) by the addition of sodium
naphthalenide to a solution of Ru(PP3)Cl2 (2Ru) under an N2
atmosphere; and (iii) by adding phenyllithium to a solution of
[Ru(PP3)(H)(N2)]BPh4 (3Ru) in THF-d8 at 195 K (Scheme 4).
Ru(PP3)(N2) is a red crystalline complex (ν(NtN) ) 2080
cm-1; λmax ) 410 nm) which was fully characterized by 31P-
Synthesis of the (η1-O-Triflate)hydride Complex Os(PP3)(OTf)H
(12Os). A solution of 1Os (200 mg, 0.23 mmol) in benzene (25 mL)
prepared under argon was treated with 1 equiv of MeOTf (26 µL) under
vigorous stirring. On evaporation of the solvent under a brisk current
of argon, pale yellow needles of Os(PP3)(OTf)H (12Os) separated
within a few minutes. Addition of ice-cold hexane previously degassed
under argon completed the precipitation of 12Os. Yield 90%. Anal.
Calcd for C43H43F3O3P4OsS: C, 51.08; H, 4.29. Found: C, 51.16; H,
4.42. IR: ν(Os-H) 2027 cm-1; ν(S-O)coord 1314 cm-1
.
1
{1H} and H NMR. The 31P{1H} NMR spectrum (Figure 1a)
Reaction of 12Os with MeLi. (A) In situ Generation of Os(PP3)-
(CH3)H (13Os). To a solution of 12Os in C6D6 in a 5-mm screw-cap
NMR tube at room temperature, 1.25 equiv of MeLi (1.6 mol dm-3
solution in Et2O) were added with a syringe. A 31P{1H} NMR spectrum
of the resulting light orange solution was recorded immediately. The
NMR analysis revealed the quantitative formation of the (methyl)-
hydride complex Os(PP3)(CH3)H (13Os). On standing, Os(PP3)-
(C6D5)D (5Os-d6) was formed at the expense of 13Os.
shows an AM3 pattern with a large P-P coupling (23.5 Hz). In
addition, the labeled complex, Ru(PP3)(15N2) (6Ru-15N2) was
formed by photolysis. The 31P{1H} spectrum displayed the extra
couplings to two 15N nuclei (Figure 1b). The 15N{1H} spectrum
showed three resonances. A large sharp singlet at δ 309.5 is
assigned to 15N2 gas in solution. The inequivalent 15N nuclei
of 6Ru-15N2 appear as a doublet of quintets at δ 317.9 and a
broad peak at δ 356.7 (Figure 1c). These splitting patterns
confirm the structure as the η1-N2 complex. Previous 15N{1H}
NMR data for dinitrogen complexes are sparse. However,
(15) Compare with [(triphos)Ru(CO)2] (triphos ) MeC(CH2PPh2)3):
δRuCO 221.8 (m), see: Hommeltoft, S. I.; Baird, M. C. Organometallics
1986, 5, 190. The synthesis of [(triphos)Ru(CO)2] was originally reported
by Siegl, W. O.; Lapporte, S. J.; Collman, J. P. Inorg Chem. 1973, 12,
674.
(16) Garrou, P. E. Chem. ReV. 1981, 81, 229.
(17) Azizian, H.; Morris, R. H. Inorg. Chem. 1983, 22, 6.

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8463
1
Table 1. Selected H, 15N{1H}, and 31P{1H}NMR Data for the Ru(PP3)L and Ru(PP3)(X)H compoundse,f
coupling constant, J/Hz
complex
nucleus
δ/ppm
assignment
Ru(PP3)H2
1Ru
1Ha
-6.66
157.0
76.7
-0.25
145.0
83.7
br d
q
d
dq
dd
ddd
dd
ddd
br d
q
fluxional
J(Pt) 7.2
J(Pb) 7.0
J(Pb) 80.5, J(Pcy, Pcis, Ptr) 17.5
J(Pcy) 9.7, J(Ptr) 6.2
J(Pcy) 275.7, J(Pcis) 15.2, J(Pb) 6.1
J(Ptr) 15.2, J(Pcy) 24.3
J(Ptr) 275.0, J(Pcis) 24.3, J(Pb) 9.4
fluxional
hydride
Pb
Pt
hydride
Pb
Ptr
Pcis
Pcy
hydride
Pb
Pt
31Pa
cyclometalated
complex
4Ru
1Hb
31Pb
76.6
-7.7
-8.22
142.9
59.4
Ru(PP3)(Ph)H
(300 K)
5Ru
1Ha
31Pa
J(Pt) 9.2
fluxional
br
49.7
br
dtd
td
ps t
td
q
fluxional
Pt
Ru(PP3)(Ph)H
(273 K)
5Ru
1Hc
-8.22
141.1
55.7
47.4
159.4
69.4
159.5
69.4
317.9
356.7
163.7
79.5
-7.95
150.2
48.3
38.4
2.49
160.9
73.9
-9.77
0.74
0.82
153.2
69.7
J(Pcis) 81.2, J(Ptr) 24.7, J(Pb) 12.9
J(Ptr) 11.3, J(Pcis) 2.2
J(Pb, Pcis) 11.8
J(Ptr) 11.6, J(Pb) 2.1
J(Pt) 23.5
hydride
Pb
Ptr
Pcis
Pb
Pt
Pb
Pt
NR
Nâ
Pb
Pt
hydride
Pb
Ptr
Pcis
C2H4
Pb
31Pc
Ru(PP3)(14N2)
6Ru
31Pb
31Pb
15Nb
31Pa
d
J(Pb) 23.5
Ru(PP3)(15N2)
6Ru-15N2
dqd
ddd
dquin
br
q
d
dq
td
ps t
td
dq
q
J(NR) 29.8, J(Pt) 23.6, J(Nâ) 2.2
J(Pb) 23.6, J(NR) 4.8, J(Nâ) 1.8
J(Pb) 29.4, J(Pt, Nâ) 4.7
Ru(PP3)(CO)
7Ru
Ru(PP3)(Cl)H
9Ru
J(Pt) 30.5
J(Pb) 30.5
1Ha
J(Pb) 96.8, J(Ptr, Pcis) 23.8
J(Ptr) 14.1, J(Pcis) 6.8
J(Pb, Pcis) 14.2
J(Ptr) 14.6, J(Pb) 6.9
J(Pb) 3.8, J(Pt) 0.8
J(Pt) 30.0
31Pa
Ru(PP3)(C2H4)
10Ru
1Ha
31Pa
d
J(Pb) 30.0
Pt
Ru(PP3)(SiEt3)H
(300 K)
11Ru
1Hb
dqd
t
J(Pb) 8.8, J(Ptr, Pcis) 5.4, fluxional
J(Si(CH2CH3)3) 7.5
J(Si(CH2CH3)3) 7.5
J(Pt) 14.7
J(Pb) 14.6
J(Pcis) 66.7, J(Ptr) 24.8, J(Pb) 7.8
hydride
silyl CH3’s
silyl CH2’s
Pb
q
q
d
31Pb
Pt
Ru(PP3)(SiEt3)H
(175 K)
11Ru
1Hb
-9.63
156.9
75.9
dtdd
br
hydride
Pb
Ptr or Pcis
Ptr or Pcis
31Pb
br
br
70.7
a In C6D6. b In THF-d8. c In 3:1 mixture THF-d8: C6H6. d See text for comments on signs of coupling constants. e Key to subscripts: Pb ) bridgehead;
Pt ) terminal (in C3V); Pcis ) terminal P cis to all other P in Cs; Ptr ) terminal P trans to one P in Cs; Pcy ) cyclometalated P; NR ) nitrogen
attached to metal center; Nâ ) nitrogen furthest away from metal center. f 1H NMR data for the PP3 ligands excluded.
RhCl(N2)(PPri3)2 shows similar shifts and couplings to 6Ru-
15N2.18 Like the cyclometalated complex (4Ru), 6Ru reacts
thermally with H2 at room temperature, to form 1Ru over a
few minutes (Scheme 3). Experiments designed to study the
thermal behavior of 6Ru in THF under either N2 or Ar
atmosphere invariably resulted in decomposition. Photolysis
of 1Ru in THF under argon atmospheres containing only trace
amounts of N2 (BOC Pureshield Argon, 99.995%) still yields
6Ru in small amounts. At such low concentrations this must
be attributed to the efficient scavenging of N2 by the cyclom-
etalated complex (4Ru).
spectrum of 5Ru at 233 K exhibited a hydride resonance at δ
-8.22 with a doublet of triplets of doublets splitting, while the
31P{1H} NMR showed three broad triplets. At higher temper-
atures (273 K) the 31P{1H} NMR spectrum sharpened to give a
triplet of doublets at δ 141.1, a pseudo triplet at δ 55.7 and a
triplet of doublets at δ 47.4, which is a characteristic AMQ2
pattern. The stereochemistry of 5Ru was determined by
selective phosphorus decoupling of the 1H NMR spectrum. This
revealed that the hydride was trans to Pcis, with the large trans
coupling destroyed by irradiation at δ 47.4. As the solution is
warmed to 293 K, 5Ru reacts with expelled H2 to reform 1Ru;
formation of 4Ru together with small amounts of a new species
is also observed.
In contrast to the low temperature experiments, photolysis
of 1Ru in benzene (AR Grade) under an atmosphere of argon
(99.995%) at room temperature led to a mixture of products by
31P{1H} and 1H NMR analysis, in which the major product was
identified as 4Ru. When Ru(PP3)Cl2 (2Ru) was stirred with a
Na/Hg amalgam in benzene at room temperature, a mixture of
5Ru and 4Ru were formed (Scheme 5). On placing this mixture
under nitrogen the products were converted to Ru(PP3)(N2)
(6Ru). Conversely, 5Ru could not be formed by thermal
reaction of 6Ru with benzene.
Photolysis of 1Ru in a large volume of hexane under an
atmosphere of CO for 1 h resulted in the formation of a product
which showed an AM3 pattern in the 31P{1H} NMR spectrum
and a large coupling constant (JPP ) 30.5 Hz) suggestive of a
Ru(0) product with local C3V symmetry. A doublet of quartets
at δ 224.0 in the 13C{1H} NMR spectrum assigned to the
carbonyl carbon atom confirms the trigonal bipyramidal structure
of Ru(PP3)(CO) (7Ru, IR, hexane: ν(CO) ) 1890 cm-1
,
UV/visible: λmax ) 380 nm). Complex 7Ru could be made
on a preparative scale by reduction of 2Ru in the presence of
carbon monoxide (Scheme 4).
When 1Ru was photolyzed for 5 h in a 3:1 (v/v) mixture of
THF-d8 and C6H6 at 243 K, low temperature 31P{1H} NMR
spectra of the resulting orange-yellow solution showed selective
A sample of 1Ru in toluene was photolyzed (90 min) under
an atmosphere of ethene and redissolved in C6D6. The 31P{1H}
NMR spectrum featured an AM3 pattern with a large coupling
1
formation of Ru(PP3)(Ph)H (5Ru) (Scheme 2). The H NMR

8464 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Scheme 2. Photochemical Reactions of Ru(PP3)H2
Osman et al.
Scheme 3. Reactions of the Cyclometalated Ru(PP3)
Figure 1. (a) 31P{1H} NMR spectrum of Ru(PP3)(14N2); (b) 31P{1H}
NMR spectrum of Ru(PP3)(15N2); and (c) 15N{1H} NMR spectrum of
Ru(PP3)(15N2). Resonances marked * due to residual Ru(PP3)(14N2).
Scheme 4. Thermal Routes to Ru(PP3)(N2) and Ru(PP3)(CO)
constant (JPP ) 30.0 Hz), which is typical of a C3V Ru(0) species.
1
The H NMR spectrum showed a doublet of quartets which
collapsed to a singlet on selective phosphorus decoupling. This
resonance is assigned to four equiv ethene protons coupled to
the unique apical phosphorus and the three equiv terminal
phosphorus donor atoms. The product is assigned as the η2-
ethene complex (10Ru) (Scheme 2). No attempt was made to
isolate the product.
1
(PP3)H2 and Related Syntheses. The H NMR spectrum of
Os(PP3)H2 (1Os) shows a broad hydride resonance at δ -7.85.
The 31P{1H} NMR spectrum shows an AM3 pattern with a
quartet at δ 134.8 (J ) 5.0 Hz) and a doublet at δ 45.8 (J )
4.9 Hz). These observations indicate that the dihydride is
fluxional (cf. Ru(PP3)H2).10 The NMR data for complexes of
Os(PP3) are listed in Table 2.
A sample of 1Ru dissolved in a 2:1 (v/v) mixture of THF-d8
and HSiEt3 was photolyzed for 2 h. The resulting solution was
evaporated to dryness, washed with hexane (to remove involatile
organosilanes), and redissolved in THF-d8. The 1H NMR
spectrum at 175 K showed a hydride resonance as a doublet of
triplets of doublets, and the 31P{1H} NMR spectrum exhibited
three broad resonances. The product is assigned as the silyl
hydride complex, Ru(PP3)(SiEt3)H (11Ru). Selective phos-
A sample of 1Os in benzene solution was photolyzed for 1
h (290 nm < λ < 376 nm). The H NMR spectrum of the
1
1
phorus decoupling of the H NMR spectrum revealed that the
product showed a doublet of triplets of doublets in the hydride
region and new multiplets in the aromatic region which
integrated in the ratio 1:2:2 relative to the hydride resonance.
The 31P{1H} NMR spectrum can be analyzed in terms of an
AMQ2 pattern with some unresolvable couplings. The product
of the reaction can therefore be identified as Os(PP3)(Ph)H (5Os)
(Scheme 6). Confirmation is obtained by synthesis of the
compound via reduction of Os(PP3)Cl2 (2Os) in benzene with
Na/Hg amalgam (Scheme 7).
hydride ligand of 11Ru is trans to Pcis. Complex 11Ru proved
to be highly fluxional. At room temperature, the 31P{1H} NMR
spectrum showed an AM3 pattern, and the 1H spectrum showed
a doublet of quartets for the hydride resonance. The hydride
couplings to Pcis and Ptr for 11Ru at room temperature (JPH
)
8.8, 5.4 Hz) agree with the average of those at 175 K, provided
that the coupling J(Pcis) is taken as the opposite sign of J(Ptr).
2. Product Studies of the Photochemical Reactions of Os-

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
Scheme 5. Thermal Synthesis of Ru(PP3)(Ph)H
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8465
needles of 12Os. When MeLi was added immediately after
the MeOTf to a C6D6 solution of 1Os, the solution became light
orange. A 31P{1H} NMR spectrum of the solution revealed the
quantitative formation of 13Os. The solution was left to stand,
and 31P{1H} NMR spectra showed the conversion of 13Os to
5Os-d6 by reductive elimination of methane and reaction with
solvent (Scheme 7).
Photolysis of 1Os in THF under an ethene atmosphere gave
1
a new species in high yield. The H NMR spectrum showed
no resonances due to a new hydride, while the 31P{1H} NMR
spectrum showed a product with an AM3 splitting pattern. This
product can be assigned as the η2-ethene complex (10Os) which
is fluxional, hence making the three terminal phosphorus atoms
equivalent (Scheme 6).
Addition of sodium naphthalenide to Os(PP3)Cl2 (2Os) in
THF at 273 K under a N2 atmosphere yielded an extremely air
and moisture sensitive red oil, which was provisionally char-
acterized by 31P{1H} NMR as Os(PP3)(N2) (6Os) (Scheme 7).
However, photolysis of 1Os under a N2 atmosphere did not
generate 6Os. Solutions of the phenyl hydride (5Os) and
cyclometalated complexes (4Os) did not convert thermally or
photochemically to 6Os under an atmosphere of N2 (in contrast
with the behavior of the Ru analogues).
3. Transient Photochemistry of Ru(PP3)H2. Ru(PP3)H2
(1Ru) is a pale yellow solid; its UV/visible spectrum shows an
absorption which increases into the UV with a resolved shoulder
at 335 nm in cyclohexane (333 nm in THF). At the laser
wavelength of 308 nm, it has an extinction coefficient of 7300
dm3 mol-1 cm-1 (THF solution). It is only slightly soluble in
cyclohexane but dissolves readily in THF.
Laser flash photolysis of samples of 1Ru in cyclohexane
solution (ca. 10-4 mol dm-3) under an atmosphere of H2 (in
order to ensure reversibility) generated a transient within the
risetime of the apparatus (ca. 100 ns). The transient showed a
broad maximum centered at 395 nm (Figure 3) with no other
absorption maxima out to 900 nm. The absorption maximum
was shifted to 390 nm on changing the solvent to pentane (also
under H2). All subsequent data were recorded at 400 nm unless
otherwise stated.
Products of the photolysis of 1Os in alkane solvents proved
unsuitable for analysis by NMR as the solubilities were poor,
and hence concentrations of the product were too low. The
photolysis of 1Os for 1.5 h in hexane/THF (3:2 v/v) was
attempted in order to overcome low solubility in alkane and
give the alkane activated product in yields suitable for NMR
analysis. The 31P{1H} NMR spectrum showed an AMNQ
pattern, with the resonances assigned to the two trans phos-
phorus atoms appearing as a second-order quartet. The 1H NMR
spectrum showed a new hydride resonance coupled to two
inequivalent phosphorus nuclei (Pb and Pcis) and equally coupled
to the two inequivalent trans phosphorus nuclei (Ptr) leading to
a doublet of triplets of doublets. Photolysis in THF alone for
about 2 h yielded the same product as that observed in a hexane/
THF mixture, while photolysis in THF-d8 yielded the same
product, except that there is no hydride resonance and the
resonance assigned to Pcis is broadened. This product is assigned
not as the alkyl hydride complex as hoped, nor as the
cyclometalated product (4Os) as described previously,13 but as
the tetrahydrofuranyl hydride complex, Os(PP3)(2-C4H7O)H
(8Os) (Scheme 6). In addition, 8Os has been synthesized by
reducing Os(PP3)Cl2 (2Os) with sodium naphthalenide at 273
K under N2 and leaving the red product (see below) to stand in
THF solution for a short period at room temperature to give
orange microcrystals. The compound is extremely air and
moisture sensitive and decomposes thermally (343 K). The
effect of deuteration allows us to determine the stereochemis-
try: the hydride must be trans to Pcis and the tetrahydrofuranyl
ring trans to the bridgehead phosphorus. A combination of
COSY and NOESY spectra of the purified compound allows
full assignment of the stereochemistry of the tetrahydrofuranyl
ring (Figure 2, Scheme 6).
In cyclohexane solution under an argon atmosphere, the
transient signal decayed over several milliseconds and did not
return to the baseline, indicating the formation of a longer-lived
photoproduct. The decay fitted a plot of ln ∆A against time
and gave a first-order rate constant of 350 s-1 19
.
In heptane
solution under an argon atmosphere, the behavior was similar
but the rate constant increased to 610 s-1
.
Laser flash photolysis of 1Ru in cyclohexane was carried
out under varying pressures of H2 (200-760 Torr), always made
up to ca. 1 atm with argon (Figure 4). The decay now returned
to the baseline with pseudo-first-order kinetics in hundreds of
microseconds, an observation consistent with a reaction which
reverses thermally. A plot of kobs against [H2] yielded a straight
line and a second-order rate constant of (2.0 ( 0.4) × 106 dm3
mol-1 s-1 (Table 3, Figure S1 in Supporting Information). A
similar rate constant was obtained with hydrogen in pentane.
Addition of benzene (0.1-1.5 mol dm-3) to cyclohexane
solutions under argon of 1Ru quenched the transient, but the
signal did not return completely to the baseline. A plot of kobs
against [benzene] is linear (Table 3, Figure 5). The experiments
were repeated with benzene-d6 (0.09-0.74 mol dm-3) and
yielded a kinetic isotope effect, kH/kD ) 1.5 ( 0.2 (Tables 3
and 4, Figure 5).20 The quenching kinetics with triethylsilane
(0.01-0.06 mol dm-3) in cyclohexane solutions of 1Ru gave a
second-order rate constant, k2 ) (5.4 ( 1.1) × 105 dm3 mol-1
s-1 (Table 3).
Prolonged photolysis (ca. 15 h) of 1Os in THF solution
destroyed 8Os and yielded a new product which shows four
resonances in the 31P{1H} NMR spectrum, including one which
was shifted upfield by about 80 ppm from the terminal
resonances in 1Os. In addition the 1H NMR spectrum showed
a new hydride resonance at relatively low field, δ -2.03. These
two factors allow assignment of this product as the cyclometa-
lated complex (4Os) (see comments for reaction of Ru(PP3)H2
with THF). Selective phosphorus decoupling showed that the
hydride is trans to the bridgehead phosphorus in this complex.
Thermal and photochemical experiments on purified 8Os show
that the conversion to 4Os only occurs photochemically (Scheme
8).
The solubility of 1Os in alkanes is too low for study by NMR
spectroscopy. Therefore, the methyl hydride complex, Os(PP3)-
(Me)H (13Os), was synthesized from 1Os via the triflate hydride
complex, Os(PP3)(OTf)H (12Os) (Scheme 7). Addition of
methyl triflate to a benzene solution of 1Os yielded pale yellow
Flash photolysis in the presence of THF (0.008-0.068 mol
dm-3) yielded an instantaneous rise when monitored at 470 nm,

8466 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Osman et al.
1
Table 2. Selected H and 31P{1H} NMR Data for Os(PP3)L and Os(PP3)(X)H Complexes
coupling constant, J/Hz
complex
Os(PP3)H2
1Os
nucleus
δ/ppm
assignment
1Ha
-7.85
134.8
45.7
-2.03
128.4
53.6
br
q
d
dq
dd
ddd
ddd
dd
dtd
m
m
m
d
dt
fluxional
J(Pt) 5.0
J(Pb) 4.9
J(Pb) 58, J(Ptr, Pcis, Pcy) 14
J(Ptr) 9, J(Pcis) 10
J(Pcy) 258, J(Pb) 9, J(Pcis) 4
J(Pcy) 19, J(Pb) 10, J(Ptr) 4
J(Ptr) 258, J(Pcis) 9
J(Pcis) 67.8, J(Ptr) 29.4, J(Pb) 8.7
hydride
Pb
Pt
hydride
Pb
Ptr
Pcis
Pcy
hydride
phenyl
phenyl
phenyl
Pb
Pcis
Ptr
Pb
Pt
hydride
H1
31Pa
cyclometalated
complex
4Os
1Hb
31Pb
50.6
-36.4
-8.68
8.41
7.89
6.58
122.1
25.8
23.9
136.9
39.2
-9.12
6.17
Os(PP3)(Ph)H
5Os
1Ha
31Pa
J(Pcis) 9.0
J(Pb) 9.0, J(Ptr) 4.5
J(Pcis) 4.5
J(Pt) 12.1
J(Pb) 12.1
d
q
d
dtd
m
Os(PP3)(N2)
6Os
Os(PP3)(2-C4H7O)H
8Os
31Pc
1Hb
J(Pcis) 65.5, J(Ptr) 28.9, J(Pb) 8.3
2.55
2.80
m
m
H2
H3
2.05
3.92
4.32
123.6
31.0
28.1
23.0
140.2
42.4
m
td
td
ddd
ddd
ddd
dt
q
d
second order, masked by PP3 ligand
J(H6-H7) 7.8
H4, H5
H6
H7
Pb
Ptr1
Ptr2
Pcis
Pb
Pt
J(H6-H7) 7.8
31Pb
J(Pcis) 10.6, J(Ptr1) 2.0, J(Ptr2) 3.3
J(Ptr2) 243.1, J(Pcis) 6.0, J(Pb) 2.0
J(Ptr1) 243.1, J(Pcis) 6.0, J(Pb) 3.3
J(Pb) 10.6, J(Ptr1,Ptr2) 6.0
J(Pt) 12.1
Os(PP3)(C2H4)
10Os
Os(PP3)(OTf)H
12Os
31Pb
J(Pb) 12.9
1Ha
-5.82
104.1
30.1
dtd
dt
dt
J(Pcis) 74.5, J(Ptr) 25.3, J(Pb) 13.6
J(Pcis) 8.3, J(Ptr) 4.2
J(Pb) 8.3, J(Ptr) 5.7
hydride
Pb
Pcis
31Pa
26.9
-9.37
1.24
127.4
26.7
dd
dtd
dq
d
J(Pcis) 5.7, J(Pb) 4.2
Ptr
Os(PP3)(CH3)H
13Os
1Ha
J(Pcis) 68.3, J(Ptr) 28.3, J(Pb) 9.1
J(Pb) 18.8, J(Pcis, Ptr) 7.5
J(Pcis) 8.6
hydride
methyl
Pb
31Pa
d
J(Pcis) 6.4
Ptr
20.3
dt
J(Pb) 8.6, J(Ptr) 6.4
Pcis
a,bKey to subscripts and superscripts as Table 1. c In THF-d8 at 253 K.
Scheme 6. Photochemical Reactions of Os(PP3)H2
Scheme 7. Thermal Syntheses with Os(PP3)Cl2 and
Os(PP3)H2
followed by a further rise over tens of microseconds (Figure
6a). This growth showed a linear dependence on THF
concentration (Table 3, Figure 6c). The resulting photoproduct
(λmax 435 nm) decayed over a few milliseconds (Figure 6b),
with a rate constant which showed an inverse dependence on
the THF concentration (Figure 6d). The reactions were repeated
with THF-d8 (0.003-0.054 mol dm-3) and identical behavior
was observed (Table 3). The kinetic isotope effect proved
insignificant (Table 4). The lifetime of the photoproduct is
extended to approximately 200 ms in pure THF (12.3 mol
dm-3).
total pressure of ca. 1 atm with argon. The transient decayed
with pseudo-first-order kinetics, but a long-lived photoproduct
absorbed strongly at the usual monitoring wavelength. By
monitoring the solutions at 440 nm, decay signals were obtained
with minimum product absorption and maximum decay ampli-
tude (cf. λmax for Ru(PP3)(CO) ) 380 nm). A plot of observed
rate constant against CO concentration is linear (Figure S1,
Table 3). As a test for a spin triplet state for the transient, a
sample was prepared under 11 Torr of CO filled to 1 atm with
The rate of reaction of the transient with CO was determined
under varying pressures of CO (10-650 Torr) made up to a

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8467
Figure 3. (a) Transient spectrum recorded 10 µs after the laser flash
photolysis of Ru(PP3)H2 in cyclohexane (9). (b) Transient spectrum
recorded 13 µs after the laser flash photolysis of Os(PP3)H2 in
cyclohexane (2). The spectra were recorded under atmospheres of H2.
The reactivity of the transient with ethene was investigated,
and a long-lived photoproduct was observed which absorbed
strongly at 400 nm as with quenching by CO. Even at 440 nm
the difference in extinction coefficients between the transient
and photoproduct was low, but small amplitude decays were
obtained at three different partial pressures (Table 3). The
reactivity of the transient toward nitrogen (60-770 Torr) was
monitored in a similar way. Flash photolysis generated a
transient which decayed with pseudo-first-order kinetics to a
photoproduct which absorbed very strongly at 400 nm (cf. λmax
for Ru(PP3)(N2) ) 410 nm). Kinetic measurements were made
at 390 nm (Figure S1, Table 3).
Reactivity toward methane was investigated with two samples
side-by-side of 1Ru in cyclohexane, under argon and methane,
respectively. The transients produced on flash photolysis
decayed with identical rates.
The temperature dependences of the rate constants for the
decay of the transient in cyclohexane in the presence of HSiEt3
(0.013 to 0.018 mol dm-3) and benzene (0.15 mol dm-3) were
studied from 285-338 and 280-327 K, respectively. Eyring
plots of ln(k2/T) against 1/T yielded straight lines (Table S1,
Figure 7). From these plots the activation parameters were
determined (Table 5).
Figure 2. (a) Contour plot of a section of the 1H,1H-COSY spectrum
of Os(PP3)(2-C4H7O)H showing the scalar couplings for the protons
of the tetrahydrofuranyl ring. The relevant cross-peak between protons
H1 and H2 is marked. (b) Section of the phase sensitive 1H,1H-NOESY
spectrum (with both positive and negative contours shown) of Os(PP3)-
(2-C4H7O)H, showing the spatial relationships between the protons of
the tetrahydrofuranyl ring. The relevant negative cross peaks pertaining
to the H1 proton are marked. Note that resonances due to the phosphine
alkyl backbone are also present in this region.
The transient observed on laser flash photolysis is readily
assigned as Ru(PP3) on consideration of (i) the regeneration of
1Ru under H2, (ii) the quenching behavior with simple
substrates, and (iii) the consistency with the NMR studies of
the photochemistry. The transient behavior is summarized by
Scheme 9 for all substrates except THF. The more complex
behavior on laser flash photolysis of 1Ru in the presence of
THF may be understood through Scheme 10a, where Ru(PP3)
reacts reversibly to form Ru(PP3)(OC4H8), which acts as a
temporary sink. Meanwhile Ru(PP3) is converted irreversibly
to the cyclometalated complex (4Ru). Both Ru(PP3) and Ru-
(PP3)(OC4H8) contribute to the transient absorption, but the latter
has λmax at much longer wavelength (435 nm). Figure 6
represents a fit to this scheme. Although we have no direct
evidence, we surmise that the product of photolysis of 1Ru in
pure alkanes is the cyclometalated complex (4Ru).
4. Transient Photochemistry of Os(PP3)H2. Os(PP3)H2
(1Os) is a creamy-white solid; its UV/visible spectrum shows
no visible absorption maximum but an absorption which
increases into the UV region with a shoulder at 310 nm. It has
an extinction coefficient of 4600 dm3 mol-1 cm-1 at the laser
wavelength (308 nm) in THF solution. It is only slightly soluble
in alkanes but dissolves readily in THF and benzene.
Scheme 8. Reactions of Os(PP3)(2-C4H7O)H
Xe rather than Ar. Xe has a significantly higher solubility21
than Ar, and its heavy atom effect should assist in overcoming
the spin selection rules. However, the rate constants for reaction
with CO in the presence of Ar and Xe were not significantly
different.
(18) Thorn, D. L.; Tulip, T. H.; Ibers, J. A. J. Chem. Soc., Dalton Trans.
1979, 2022.
(19) The experiment was repeated in cyclohexane-d12, and the pseudo-
first-order rate constant was determined as kobs ) 550 s-1, yielding a kinetic
isotope effect of 0.6. Assuming cyclohexene-d10 reacts with a similar rate
constant to ethene (k2 ≈ 5 × 105 dm3 mol-1 s-1), the rate increase can also
be accounted for by small amounts of cyclohexene-d10 (1 mM) impurity in
the cyclohexane-d12. Consequently we do not place any emphasis on this
result.
(20) Similar arguments regarding cyclohexene-d10 impurities were
considered as for Ru(PP3)H2,19 but the observed rate constant was an order
of magnitude greater than expected for quenching by 1 mM cyclohexene-
d10, derived on the basis of the rate constant for reaction with ethene and
heptene. Consequently we believe that the observed kinetic isotope effect
is reliable.
Flash photolysis (308 nm) of a cyclohexane solution of 1Os
(ca. 8 × 10-5 mol dm-3) under argon resulted in a transient
absorption with an instrument-limited risetime (ca. 100 ns). The
maximum absorption was observed at approximately 390 nm
(Figure 3), with no further absorption maxima at longer
(21) Wilhelm, E.; Battino, R. Chem. ReV. 1973, 73, 1.

8468 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Osman et al.
Table 3. Second-Order Rate Constants for Reaction of M(PP3) (M ) Ru, Os) with Quenchers at 296 K
gas solubilityb/
k/dm3 mol-1 s-1
k/dm3 mol-1 s-1
quenchera
mol dm-3 atm-1
Ru(PP3)c
Os(PP3)c
H2
3.8 × 10-3
(2.0 ( 0.4) × 106
cyclohexane
cyclohexane-d12
pentane
1.5 × 103d
5.3 × 102d
(6.0 ( 1.0) × 104
(9.5 ( 1.4) × 104
(3.1 ( 0.5) × 104
(5.5 ( 1.5) × 103
(3.2 ( 0.5) × 105
(5.7 ( 1.0) × 105
(3.2 ( 0.6) × 105
(4.5 ( 1.1) × 105
(3.3 ( 0.7) × 105
6.5 × 105
heptane
methylcyclohexane
methylcyclohexane-d14
benzene
benzene-d6
THF
THF-d8
HSiEt3
CO
ethene
N2
methane
(1.3 ( 0.1) × 106
(6.8 ( 0.7) × 105
(1.6 ( 0.2) × 106
(1.5 ( 0.1) × 106
(5.4 ( 1.1) × 105
(1.0 ( 0.1) × 106
7.6 × 105
9.3 × 10-3
0.14
(3.2 ( 0.4) × 105
2.2 × 106
7.1 × 10-3
(7.5 ( 1.8) × 105
3.0 × 10-2
(2.6 ( 0.4) × 105
a All measurements were taken in cyclohexane solution. b Reference 21 for gas solubility. c Error bars as 95% probability on least squares fit.
When no error bars are shown, rate constant based on measurements with 1 atm gas only. d The rate constants for reaction with cyclohexane are
taken from measurements in neat cyclohexane.
By varying the concentration of pentane in cyclohexane (0.24-
1.32 mol dm-3) and repeating the experiment it was found that
kobs varied linearly with pentane concentration (Figures 8 and
9a) giving a second-order rate constant of (6.0 ( 1.0) × 104
dm3 mol-1 s-1 (Table 3). Similar experiments were undertaken
with heptane (0.11-0.98 mol dm-3), methylcyclohexane (0.08-
1.26 mol dm-3) (Table 3, Figure 9a), and methylcyclohexane-
d14 (0.09-7.84 mol dm-3) (Table 3). The results with
methylcyclohexane allowed a kinetic isotope effect to be
calculated of kH/kD ) 5.6 ( 1.5 (Table 4). The striking results
with pentane, heptane, and methylcyclohexane led to investiga-
tion of methane as a quencher (see below).
Figure 4. Decay of the transient formed on the flash photolysis of
In benzene solution, the decay of the transient formed on
flash photolysis of 1Os was too fast to observe. By varying
the concentration of benzene in cyclohexane (0.12-0.94 mol
dm-3), it was shown that the rate of decay of the transient varied
linearly with [benzene] (Table 3, Figure 9b). The experiments
were repeated with benzene-d6 (0.09-0.87 mol dm-3) to give
a second-order rate constant (Table 3, Figure 9b) and a kinetic
isotope effect of kH/kD ) 0.6 ( 0.1 (Table 4). The quenching
kinetics of 1Os in cyclohexane with added HSiEt3 (0.004-0.067
mol dm-3) proved to be linear with respect to [HSiEt3] (Table
3).
Ru(PP3)H2 in cyclohexane solution under 500 Torr of hydrogen + 260
Torr of argon. The decay is first-order (inset), and the signal decays to
the baseline.
Quenching with tetrahydrofuran (0.006-0.060 mol dm-3
)
yielded a double exponential decay (Figure 10a). The fast
component showed a linear dependence on THF concentration
(Table 3, Figure 10b). The longer-lived product (λmax 440 nm)
decayed with a first-order decay constant of (4.2 ( 0.8) × 103
s-1 which showed no dependence on the THF concentration
(Figure 10c). Experiments with THF-d8 (0.007-0.016 mol
dm-3) demonstrated similar double exponential behavior (Table
3). The longer-lived product decayed with a first-order decay
constant of (1.6 ( 0.5) × 103 s-1 which again proved
independent of [THF-d8]. The resulting kinetic isotope effect
for the fast component was not significant, but for the slow
component the kinetic isotope effect is kH/kD ) 2.6 ( 0.4 (Table
4).
Quenching by hydrogen was investigated by preparing two
samples of 1Os in cyclohexane solution, under atmospheres of
argon and hydrogen, respectively. The transient signals ob-
served on flash photolysis decayed with identical rates. Even
when the H2 pressure was increased to 3 atm ([H2] ) 1.1 ×
10-2 mol dm-3), there was no change in the rate of decay
relative to an argon atmosphere.
Figure 5. Plot of pseudo-first-order decay constant against concentra-
tion of benzene (9) and benzene-d6 (b) for the transient formed on
flash photolysis of Ru(PP3)H2.
wavelength. All subsequent kinetic data were recorded at 390
nm unless otherwise stated.
In cyclohexane under an argon atmosphere the transient signal
decayed over several hundred microseconds and did not return
to the baseline, indicating the formation of a longer-lived
photoproduct. The decay was first-order as shown by the
linearity of a plot of ln ∆A against time, kobs ) 1.4 × 104 s-1
.
The experiment was repeated in cyclohexane-d12, and the
pseudo-first-order rate constant, kobs ) 4.9 × 103 s-1 was
determined; thus the approximate kinetic isotope effect for this
reaction is kH/kD ) 2.8 (Table 4).20
When pentane was used as a solvent, a transient signal was
observed with a similar λmax to that observed in cyclohexane.
However, the signal now decayed in just a few microseconds
(kobs ) 7.3 × 105 s-1) and still did not return to the baseline.
Quenching by CO was investigated by preparing two samples
in cyclohexane under atmospheres of argon and CO respectively.

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8469
Figure 6. Analysis of photoreaction of Ru(PP3)H2 with THF in cyclohexane: (a) fitted data (λ ) 470 nm, [THF-d8] ) 0.018 mol dm-3) on short
timescale, showing growth of Ru(PP3)(OC4H8); (b) fitted data (λ ) 470 nm, [THF-d8] ) 0.018 mol dm-3) on long time scale, showing decay of
Ru(PP3)(OC4H8); (c) kobs for fast growth against [THF] (9) and [THF-d8] (b); and (d) 1/kobs for slow decay against [THF] showing experimental
data (9) and modeled data (2).
Scheme 10. Transient Photochemistry of M(PP3)H2 in the
Presence of THF: (a) M ) Ru and (b) M ) Os
Figure 7. Eyring plots for the reaction of Ru(PP3) with triethylsilane
(b) and benzene (2).
Scheme 9. Transient Photochemistry of Ru(PP3)H2
Table 4. Kinetic Isotope Effects (KIE) for the Reaction of M(PP3)
Transients with Selected Quenchers
quenchera
KIE Ru(PP3)b
KIE Os(PP3)b
cyclohexane
methylcyclohexane
C6H6
THF: growth of M(PP3)(OC4H8)
THF: decay of M(PP3)(OC4H8)
2.8
5.6 ( 1.5
0.6 ( 0.1
0.7 ( 0.2
2.6 ( 0.4
1.5 ( 0.2
1.1 ( 0.2
0.9 ( 0.1
a All measurements were taken in cyclohexane solution, except for
cyclohexane where neat solvent was used. b Error bars as 95%
probability on least squares fit. When no error bars are shown, rate
constant based on measurements with one concentration only.
In the presence of CO, the decay was slightly, but reproducibly,
faster (kobs ) 2.0 × 104 s-1) than that under argon (kobs ) 1.4
× 104 s-1). These data can be used to give an approximate
value for the second-order rate constant for the reaction of the
transient with CO (Table 3).
the transient decay was slightly faster under an atmosphere of
methane than under argon (kmethane ) 2.2 × 104 s-1, kargon
)
A similar experiment with a methane atmosphere showed that
1.4 × 104 s-1). The experiment was repeated with 2 and 3

8470 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Osman et al.
Figure 8. Decay of osmium transient in the presence of 0.47 mol dm-3
pentane in cyclohexane and first-order plot (inset). The decay is more
than twice as fast as in cyclohexane alone.
Figure 10. Analysis of photoreaction of Os(PP3)H2 with THF in
cyclohexane: (a) fitted transient with [THF] ) 0.025 mol dm-3; (b)
kobs for fast decay against [THF] (9) and [THF-d8] (b); (c) kobs for
slow decay against [THF] (9) and [THF-d8] (b).
Table 5. Activation Parameters for the Reactions of M(PP3) (M )
Ru, Os) and Related Compounds with Various Quenchersa
∆Hq/
∆Sq/
∆Gq
/
298
kJ mol-1
J mol-1 K-1
kJ mol-1
Ru(PP3) + HSiEt3
Ru(PP3) + benzene
Os(PP3) + pentane
Os(PP3) + HSiEt3
Os(PP3) + benzene
Ru(dmpe)2 + HSiEt3
35 ( 2
39 ( 4
27 ( 1
31 ( 5
38 ( 3
9 ( 1
-18 ( 6
+1 ( 13
-59 ( 4
-27 ( 12
-7 ( 9
-53 ( 4
-87 ( 6
-112 ( 4
40 ( 4
38 ( 6
45 ( 2
39 ( 6
40 ( 4
25 ( 2
48 ( 3
44 ( 1
Figure 9. Plots of observed pseudo-first-order decay constant against
quencher concentration for the decay of the transient formed on flash
photolysis of Os(PP3)H2: (a) pentane (2), heptane (b) and methylcy-
clohexane (9) inset: methane ([); (b) benzene (9) and benzene-d6
(b).
b
c
Fe(dmpe)2 + HSiEt3
22 ( 2
11 ( 3
d
Ru(depe)2 + HSiEt3
a Error bars as 95% probability on least squares fit. b See ref 7. c See
ref 24b. d See ref 8.
atm pressure of methane yielding a linear plot of kobs against
methane concentration (Table 3, Figure 9a, inset).
Quenching with nitrogen (1 and 2 atm) and ethene (60-760
Torr) was investigated (Table 3). The decays did not return to
the baseline and had a large residual absorption.
Scheme 11. Transient Photochemistry of Os(PP3)H2
The temperature dependences of the rate constants for the
decay of the transient with pentane (1.64 mol dm-3), triethyl-
silane (0.004-0.04 mol dm-3), and benzene (0.19 mol dm-3
)
were studied from 280-325, 283-337, and 287-326 K,
respectively. Eyring plots of ln(k2/T) against 1/T were used to
extract the activation parameters (Tables 5 and S2, Figure S2).
The laser photochemistry of 1Os can be interpreted in terms
of Os(PP3) as the principal transient. The argument for the
assignment is similar to that for Ru(PP3) except that the
precursor is not regenerated under a hydrogen atmosphere. The
quenching behavior is summarized in Scheme 11 for all
quenchers except THF. Unlike Ru(PP3), the transient behavior
of Os(PP3) provides direct evidence for reaction of heptane,
pentane, methylcyclohexane, and methane. The kinetic isotope
effect in cyclohexane provides evidence for the formation of
Os(PP3)(C6H11)H, although the cyclometalated species (4Os)
cannot be excluded as a possible product. The double expo-
nential behavior in the presence of THF is suggestive of
conversion of Os(PP3) to the oxygen-bound THF adduct,
followed by conversion to the C-H insertion product (80s)
observed by NMR. This sequence represented in Scheme 10b
forms the basis for the fit to the kinetic data shown in Figure
10a. It also accounts for the kinetic isotope effect on the slower
step but the lack of KIE on the fast step.
Discussion
The photochemistry of both Ru(PP3)H2 (1Ru) and Os(PP3)-
H2 (1Os) in solution proves to be extensive, leading to many
products which can also be obtained by reductive synthesis from
M(PP3)Cl2 (2Ru/2Os). In some cases the photochemical route
is preferred, while reductive routes are more facile for others.
Product Studies. Photolysis of 1Ru in THF under a
rigorously inert atmosphere yields the cyclometalated complex

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8471
(4Ru). This reacts readily with H2 to regenerate 1Ru and also
acts as an efficient scavenger for N2 to give Ru(PP3)(N2) (6Ru).
Hence 4Ru can be considered as a store for some of the photon
energy in the absence of other quenchers. We deduce an order
of thermodynamic stability: 4Ru < 6Ru < 1Ru. However,
Ru(PP3)(Ph)H (5Ru) cannot be produced thermally by addition
of benzene to a solution of 4Ru. Ru(PP3)(Ph)H is best formed
photochemically at low temperature in THF/C6H6 mixtures,
which also generates some of the cyclometalated species.
Although dinitrogen complexes of Ru(II) are abundant, 6Ru is
a rare example of a dinitrogen complex of Ru(0).
The photochemistry of 1Os proved substantially different
from its ruthenium analogue. Photolysis in THF yielded the
tetrahydrofuranyl hydride complex (8Os), which could also be
formed by reductive synthesis from Os(PP3)Cl2, and has no
ruthenium analogue. Secondary photolysis of 8Os was found
to be the only route to the cyclometalated complex (4Os). The
formation of Os(PP3)(N2) (6Os) proved inaccessible by photo-
chemical routes. However, 6Os could be generated in THF at
low temperature by a thermal method but reacted with THF
upon warming. Finally, in contrast to the ruthenium analogue,
Os(PP3)(Ph)H (5Os) is thermally stable and can be obtained
by both photochemical and reductive routes.
Figure 11. Schematic diagram showing the rate constants for reaction
of M(PP3) compared to those for Fe(dmpe)2, Ru(dppe)2, and Ru(depe)2.
characteristic of the square planar geometry adopted by the M0
complexes with two bidentate phosphine ligands. An additional
influence on the UV/visible spectrum may come from an
interaction of the metal with a phenyl group of the PP3 ligand
(see below). These conclusions are also consistent with
observations on Fe(dmpe)2 which exhibits a UV/visible spectrum
with a single maximum at 390 nm.24b The proposed geometry
of the transient Fe(dmpe)2 is Cs rather than the square planar
D2h for the ruthenium analogues.
Reactivity of Transients. The rate constants for reaction
of M(PP3) are shown schematically in Figure 11, together with
those for Fe(dmpe)2, Ru(depe)2, and Ru(dppe)2. A notable
feature is the narrow range of rate constants, varying for Ru-
(PP3) between 5.4 × 105 and 2.0 × 106 dm3 mol-1 s-1 and for
Os(PP3) between 1.5 × 103 and 6.5 × 105 dm3 mol-1 s-1. This
lack of selectivity contrasts with the behavior of Ru(dppe)2 and
Ru(depe)2.8 Thus the ratio of rate constants for reaction with
H2 and C2H4, k(H2)/k(C2H4) is 2.6 for Ru(PP3) but 410 for Ru-
(dppe)2. The comparison with selectivity for H2 over HSiEt3
is even more dramatic: k(H2)/k(HSiEt3) is 3.7 for Ru(PP3) but
3600 for Ru(depe)2.
The reactivity of Ru(PP3) is also enhanced toward some key
substrates compared to Ru(depe)2 and Ru(dppe)2. The species
with the tetradentate ligand reacts rapidly with HSiEt3 and
benzene. The closest analogue with bidentate ligands, Ru-
(dppe)2, reacts with neither HSiEt3 nor C6H6 in the presence of
photogenerated hydrogen. Ru(depe)2 reacts with HSiEt3 but not
with C6H6. Thus the striking reactions of Ru(PP3) are as a result
of reduced selectivity for hydrogen coupled with enhanced
reactivity toward other species.
When we consider Os(PP3), the changed reactivity is even
more remarkable. The back reaction of Os(PP3) with H2 fails
to compete with solvent activation even under 3 atm H2. Instead
we observe a first-order decay of the transient in cyclohexane
with a rate constant of 1.4 × 104 s-1. This measurement enables
us to calculate an upper limiting rate constant for reaction of
Os(PP3) with H2 of ca. 106 dm3 mol-1 s-1. The rate constants
for reaction of Os(PP3) with CO, HSiEt3, and ethene are all
reduced marginally relative to Ru(PP3). However, the striking
feature is that Os(PP3) reacts with alkanes containing a primary
alkyl group and with methane itself. The rate constants increase
in the order methylcyclohexane < pentane < heptane < methane
< benzene. The large kinetic isotope effect for the reaction
with methylcyclohexane (kH/kD ) 5.6) provides evidence that
the observed quenching by alkanes involves C-H bond breaking
and the formation of new alkyl hydride species. Remarkably,
the rate constant for reaction with methane is only about 20%
Dahlenburg et al. have studied the reduction of a variety of
related MP4Cl2 (M ) Ru, Os) complexes in which the
phosphines have methyl rather than phenyl substituents.22 They
have employed the tetradentate phosphines P(CH2CH2CH2-
B
PMe2)3 (P4A), P((C6H4)PMe2)3 (P4 ), and combinations of bi-
and tridentate phosphines with PMe3. The RuP4Cl2 species
invariably yield RuP4(Ph)H on reduction in the presence of
benzene, while a photochemical route from the dihydride has
also been employed for Ru(P4A)(Ph)H. Unlike our Ru(PP3)-
(Ph)H these are stable, isolable complexes. The reduction of
Ru(P4A)Cl2 in THF yields Ru(P4A)(2-C4H7O)H, which is an
exact analogue of 8Os.
The methyl hydride complex, Os(PP3)(Me)H, was generated
from Os(PP3)(OTf)H in benzene solution but proved unstable
with respect to Os(PP3)(Ph)H. The low solubility of Os(PP3)-
H2 prevented us from carrying out product studies by NMR in
alkane solvents.
For comparison, Flood et al. have studied the thermolysis of
Os(PMe3)4(CH2CMe3)H with hydrocarbons, isolating C-H
activation products, Os(PMe3)4(R)H, from benzene, Me4Si,
mesitylene, and methane.23 In the absence of these substrates
a cyclometalation product is formed. The reaction with benzene
proceeds via oxidative addition of benzene to Os(PMe3)3(CH2-
CMe3)H to form an OsIV intermediate, whereas reaction with
Me4Si involves oxidative addition to Os(PMe3)3.
Transient Photochemistry. Laser flash photolysis of M(PP3)-
H2 yields transients within the instrumental risetime (ca. 100
ns) which are assigned to M(PP3). They exhibit a single
absorption maximum at 395 nm (M ) Ru) and 390 nm (M )
Os), respectively. These spectra contrast with those of Ru-
8
(drpe)2 and Os(dmpe)2,24a all of which show a series of
absorption bands across the visible spectrum including one at
very long wavelength between 700 and 800 nm. We deduce
that the C3V or Cs geometry (Scheme 1) enforced by the
tetradentate PP3 ligand removes the long wavelength bands
(22) (a) Antberg, M.; Dahlenburg, L. J. Organomet. Chem. 1986, 312,
C67. (b) Dahlenburg, L.; Frosin, K.-M. Chem. Ber. 1988, 121, 865. (c)
Dahlenburg, L.; Kerstan, S.; Werner, D. J. Organomet. Chem. 1991, 411,
457.
(23) (a) Desrosiers, P. J.; Shinomoto, R. S.; Flood, T. C. J. Am. Chem.
Soc. 1986, 108, 1346 and 7964. (b) Harper, T. G. P.; Shinomoto, R. S.;
Deming, M. A.; Flood, T. C. J. Am. Chem. Soc. 1988, 110, 7915. (c)
Shinomoto, R. S.; Desrosiers, P. J.; Harper, T. G. P.; Flood, T. C. J. Am.
Chem. Soc. 1990, 112, 704. (d) Ermer, S. P.; Shinomoto, R. S.; Deming,
M. A.; Flood, T. C. Organometallics 1989, 8, 1377.
(24) (a) Nicasio, M. C.; Perutz, R. N. Unpublished observations. (b)
Whittlesey, M. K.; Mawby, R. J.; Osman, R.; Perutz, R. N.; Field, L. D.;
Wilkinson, M. P.; George, M. W. J. Am. Chem. Soc. 1993, 115, 8627.

8472 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
Osman et al.
lower than that with benzene. The kinetic isotope effect
measured for the reaction of Os(PP3) with cyclohexane (kH/kD
) 2.8) suggests that the transient is even capable of activating
secondary C-H bonds in the absence of more reactive
substrates, despite the possibility for intramolecular activation
to form the cyclometalated species. The rate constant for
reaction with cyclohexane is, however, at least 20 times smaller
than that for the reaction with alkanes containing methyl groups.
It is this selectivity which has enabled us to determine full
kinetic quenching plots for reactions with alkanes in the presence
of cyclohexane as solvent. Thus Os(PP3) brings reduced
reactivity toward H2 but enhanced reactivity toward alkanes,
with substantial selectivity for CH4 over primary C-H bonds,
and primary over secondary C-H bonds.
Kinetic selectivities for different alkanes have been deter-
mined previously for Tp′Rh(CNR) (Tp′ ) HB(3,5-dimethyl-
pyrazolyl)3). The selectivity for primary over secondary C-H
bonds of Os(PP3) is at least five times higher than that for
Tp′Rh(CNR) which previously displayed the highest kinetic
selectivities for hydrocarbons.25 The kinetic selectivities are
calculated as a ratio of the rate constants for the hydrocarbon
involved and normalized with respect to the number of C-H
bonds of interest present in the hydrocarbon. The kinetic
selectivity of Os(PP3) for methane over cyclohexane is at least
520 times greater than for Tp′Rh(CNR), where reaction with
methane was not observed at atmospheric pressure. Reactions
of osmium complexes with alkanes, including methane, have
been recorded previously in arene half-sandwich complexes6
and in other phosphine complexes.23
dependence on the THF concentration which was consistent with
the observed KIE for the second mechanism.
The kinetic isotope effects are collected in Table 4. All
significant KIEs are normal except for Os(PP3) with benzene
for which an inverse effect is observed (kH/kD ) 0.6 ( 0.1).
Inverse isotope effects are usually interpreted in terms of a pre-
equilibrium to form an η2-C6H6 complex. However, ab initio
calculations of kinetic isotope effects suggest a considerable
need for caution in deducing mechanisms from inverse kinetic
isotope effects.27
The differing reactivities of M(PP3) and Ru(drpe)2 should be
apparent through activation parameters. The enthalpies of
activation (Table 5) vary between 35 and 39 kJ mol-1 for Ru-
(PP3) and between 27 and 38 kJ mol-1 for Os(PP3). All these
values are much higher than those for reactions of Ru(dmpe)2
or Ru(depe)2 with HSiEt3. The entropies of activation are
surprisingly close to zero for bimolecular processes, the most
negative being for Os(PP3) + pentane. The small value of ∆Sq
for Ru(PP3) and HSiEt3 contrasts with much more negative
values for the reactions of the bidentate analogues. The
entropies of activation for M(PP3) + HSiEt3 are similar to that
for CpMn(CO)2S (S ) solvent) + HSiEt3 (-28 ( 10 J K-1
mol-1),28 which has been interpreted in terms of an early
transition state.
Key differences in the reactivity of Ru(PP3) and Os(PP3) may
be summarized as follows: (a) Ru(PP3) cyclometalates ther-
mally, Os(PP3) cyclometalates only via secondary photolysis
of 8Os; (b) Ru(PP3) reacts with H2 under our conditions, Os-
(PP3) does not; and (c) only Os(PP3) undergoes C-H activation
reactions with alkanes and THF. The ability to undergo C-H
activation reactions is associated with the increased strength of
M-H and M-C bonds among the third row elements.29
Structural Implications of Reactivity. The reactivity pat-
terns of M(PP3) may be summarized as low selectivity with
reduced reactivity toward H2 but enhanced reactivity toward
other substrates relative to Ru(drpe)2. Where comparisons are
possible, the value of ∆Hq is higher than for Ru(drpe)2 and the
value of ∆Sq is less negative. We have considered three
explanations of these phenomena involving (i) a spin triplet
ground state, (ii) specific solvation, and (iii) a barrier created
by the position of the phosphine phenyl groups.
The reactions of M(PP3) with THF require analysis of more
complex kinetics. For Ru(PP3) the oscilloscope traces measured
at 470 nm (near the maximum for the O-bound THF adduct)
showed a rapid growth (ca. 10-5 s, Figure 6a) followed by a
slow decay (ca. 10-2 s, Figure 6b). Each trace could be fitted
to a simple exponential function to yield kobs(fast) for the growth,
or kobs(slow) for the decay. The data were analyzed according
to the mechanism of Scheme 10a. A plot of kobs(fast) versus
[THF] was linear and yielded the rate constant for reaction of
Ru(PP3) with THF to form an O-bound adduct, k1 ) (1.6 (
0.2) × 106 dm3 mol-1 s-1 (Figure 6c). A plot of 1/kobs(slow)
versus THF was linear. This reciprocal plot could be modeled
most satisfactorily when k-1 ) 2 × 104 s-1 and k2 ) 400 s-1
(Figure 6d). The kinetic modeling does not represent a unique
solution but is consistent with the measurements in pure
cyclohexane which give a value for kobs of 350 s-1. This slow
step is attributed to cyclometalation of the fragment. The values
of k1 and k-1 combine to give an equilibrium constant for
formation of Ru(PP3)(THF) of ca. 80. The lifetime of Ru(PP3)-
(THF) in pure THF of ca. 200 ms also suggests a weakly bound
adduct.
The possibility of a triplet ground state for M(PP3) requires
serious consideration since Co(NP3)+ (NP3 ) N(CH2CH2PPh2)3)
exhibits such a ground state in the solid phase.30a However,
spin crossover effects should result in an entropic barrier as for
Fe(CO)4.30b Moreover, the absence of a heavy atom effect when
(26) The analytical equation derived for fitting the double exponential
decay traces (Figure 10a) to the proposed mechanism (Scheme 10b) for
the reaction of Os(PP3) in the presence of THF is shown below:
bk1
ck1k3
∆A ) e-(k +k )t a +
-
-
1
3
{
(k2 - k1 - k3) (k2 - k1 - k3)(k1 + k3)
The reactivity of Os(PP3) in THF follows a different pattern.
The kinetics are fitted to Scheme 10b. The model was fitted
using an analytical expression26 for multistep irreversible
reactions, as derived from the first-order differential equations.
Here, trapping of Os(PP3) to form an oxygen bound adduct
(which displays no kinetic isotope effect, Tables 3 and 4)
competes with the decay process found in pure cyclohexane
(which is probably C-H activation, see earlier). The oxygen
bound adduct converts to Os(PP3)(tetrahydrofuranyl)H with a
rate constant of k2 ) 4.2 × 103 s-1. This step exhibits a kinetic
isotope effect of kH/kD ) 2.6 ( 0.4. We also considered a
reaction scheme in which the oxygen-bound adduct is formed
reversibly and Os(PP3)(tetrahydrofuranyl)H is formed directly
from Os(PP3). However, we were unable to obtain a rate
dk3
(c - b)k1
ck1 + dk3
(k1 + k3)
+ e-k t
+
2
}
{
}
(k1 + k3)
(k2 - k1 - k3)
where k1 is the pseudo-first-order rate constant and k3 was assumed to take
the same value as that observed in neat cyclohexane (1.4 × 104 s-1). The
other variables are defined as a ) ꢀ(Os(PP3)) × [Os(PP3)]0; b ) ꢀ(Os-
(PP3)(OC4H8)) × [Os(PP3)]0; c ) ꢀ(Os(PP3)(2-C4H7O)H) × [Os(PP3)]0;
and d ) ꢀ(Os(PP3)(C6H11)H) × [Os(PP3)]0 where [Os(PP3)]0 is the initial
concentration of Os(PP3) generated by the laser. The values of k1, k2, a, b,
c, and d were fitted to the observed kinetic traces for each concentration of
THF.
(27) (a) Abu-Hasanayn, F.; Goldman, A. S.; Krogh-Jesperson, K. J. Phys.
Chem. 1993, 97, 5890. (b) Hall, C.; Perutz, R. N. Chem. ReV. 1996, 96,
3125.
(28) Hill, R. H.; Wrighton, M. S. Organometallics 1987, 6, 632.
(29) Martinho-Simoes, J. A.; Beauchamp, J. C. Chem. ReV. 1990, 90,
629.
(30) (a) Sacconi, L.; Orlandini, A.; Midollini, S. Inorg. Chem. 1974, 13,
2850. (b) Weitz, E. J. Phys. Chem. 1987, 91, 3945.
(25) Jones, W. D.; Hessel, E. T. J. Am. Chem. Soc. 1993, 115, 554.

M(PP3)H2 (M ) Ru; Os; PP3 ) P(CH2CH2PPh2)3)
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8473
Xe was dissolved in a solution of Ru(PP3)H2 + CO lends no
support to this hypothesis. Of course, high spin ground states
for ruthenium and osmium complexes would be highly unusual.
For these reasons a spin triplet ground state for M(PP3) is
excluded.
The presence of a solvent molecule coordinated to a reactive
intermediate is characteristic of many d6 species such as
Cr(CO)5S (S ) solvent)31 and CpMn(CO)2S.32 Solvent coor-
dination has also been observed for Ru(CO)2(PMe3)2S33 but not
for Ru(drpe)2. If this model is correct, the barrier to reaction
would arise principally by displacement of the solvent molecule
by the incoming substrate. Since M(PP3) species are so reactive
and the parent dihydrides are not soluble in perfluoroalkanes,
this model has proved hard to test. We note that the rate
constant for reaction of Ru(PP3) with H2 increased significantly
between cyclohexane and heptane as solvents, but the change
was within the limits of general solvent effects.
In the third model, motion of the phenyl groups to a less
favorable conformation where they are out of the way of an
incoming ligand gives rise to the high ∆Hq, and an early
transition state, and hence low ∆Sq. The steric effects of the
phenyl groups in either C3V or Cs structures may be modeled
by an examination of the crystal structures of analogous 18
electron rhodium and iridium complexes.34 Moreover, there is
the additional possibility that a phenyl group may act as an
agostic ligand to ruthenium or osmium in M(PP3). The
plausibility of an agostic interaction is made clear by model
building and by analogy with the structures of [Re(triphos)-
(CO)2]BF4 (triphos ) MeC(CH2PPh2)3)35 and Ru(PPh3)3Cl2.36
If correct, the agostic interaction will certainly affect the UV/
visible spectrum of M(PP3). Although the agostic model cannot
be distinguished experimentally at this stage from solvent
coordination, we consider that it offers the most satisfactory
explanation of the observed behavior.
of their reactions with a range of substrates have been
determined. Key features are summarized below: (a) Photolysis
of Ru(PP3)H2 in THF under an inert atmosphere yields the
cyclometalated complex (4Ru), which acts as an energy store,
and scavenges N2 and H2. (b) Photolysis of Os(PP3)H2 in THF
yields the tetrahydrofuranyl hydride complex (8Os), which is
better synthesized reductively. The cyclometalated osmium
complex (4Os) is only formed on photolysis of 8Os. (c)
Benzene activation leads to formation of M(PP3)(Ph)H com-
plexes. The osmium product is isolable, but the ruthenium
product is thermally labile. Os(PP3)(Me)H has been synthesized
but proves unstable with respect to reductive elimination of
methane. (d) The UV/visible spectra of the M(PP3) intermedi-
ates are quite different from the square planar transients such
as Ru(dppe)2. The change reflects the enforced C3V or Cs
structure and the likely agostic interaction of a phenyl group.
(e) The reactivity of Ru(PP3) is quite different from Ru(dppe)2
and Ru(depe)2 with a more rapid reaction with HSiEt3 but a
much slower reaction with H2. Of these three transients, only
Ru(PP3) reacts with benzene. (f) Os(PP3) inserts into C-H
bonds of alkanes in addition to those of benzene and THF. The
high sensitivity of UV/visible spectroscopy coupled with the
use of kinetic isotope effects enable these reactions to be
established despite very low solubility of the precursors in
alkanes. The rate constants follow the order: cyclohexane <
methylcyclohexane < pentane < heptane < methane < benzene
≈ THF. The selectivity for primary alkyl groups and methane
over cyclohexane is sufficient that full quenching experiments
can be carried out. The rate of reaction with methane is only
about 20% slower than that with benzene. (g) The enforced
C3V or Cs structure successfully prepares Ru(PP3), and more
especially Os(PP3), for C-H activation. The barrier to inter-
molecular C-H or Si-H activation must be lower than for
square planar analogues because of the prearranged geometry.
Most remarkably, the barrier to cyclometalation is high enough
that this process does not compete effectively with intermo-
lecular processes for Ru(PP3) and is only accessible photo-
chemically for Os(PP3). It is equally significant that the
reactions of M(PP3) with H2 are not fast enough to inhibit C-H
activation.
Acknowledgment. The York group thanks EPSRC and
British Gas for financial support, while the Florence group
thanks the EC for support (contract ERB CHRXCT 930147).
We appreciated helpful discussions with Dr M. K. Whittlesey
and Dr M. C. Nicasio and would like to acknowledge Prof. K.
G. Caulton for bringing an error in our communication to our
attention. Thanks are expressed to Mr F. Zanobini for his
assistance in the synthesis of the starting materials and Miss C.
L. Higgitt for running NMR spectra in York.
Conclusion
A range of complexes, M(PP3)L and M(PP3)(X)Y (M ) Ru,
Os), have been synthesized by reduction of M(PP3)Cl2 and by
photolysis of M(PP3)H2. The transient intermediates, M(PP3),
have been detected by laser flash photolysis, and the kinetics
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1995, 14, 3268.
(34) (a) Di Varia, M.; Rovai, D.; Stoppioni, P.; Peruzzini, M. J.
Organomet. Chem. 1991, 420, 135. (b) Bianchini, C.; Masi, D.; Mealli, C.;
Meli, A.; Sabat, M. Organometallics 1985, 4, 1014. (c) Di Varia, M.;
Peruzzini, M.; Stoppioni, P. Inorg. Chem. 1991, 30, 1001.
(35) Bianchini, C.; Marchi, A.; Marvelli, L.; Peruzzini, M.; Romerosa,
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Supporting Information Available: Tables S1 and S2 show
the temperature dependence data for flash photolysis with
Ru(PP3) and Os(PP3), respectively and Figures S1 and S2 show
quenching of Ru(PP3) with gaseous quenchers and Eyring plots
for Os(PP3), respectively (5 pages). See any current masthead
page for ordering and Internet access instructions.
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