Nitrous oxide mediated oxygen atom insertion into a ruthenium-hydride bond. Synthesis and reactivity of the monomeric hydroxoruthenium complex (DMPE)2Ru(H)(OH)

Article abstract of DOI:10.1021/om960991i

Treatment of (DMPE)₂Ru(H)₂ with 1 equiv of N₂O affords the hydroxoruthenium complex (DMPE)₂Ru(H)(OH) (1) in 41% yield; further treatment with an atmosphere of N₂O affords the bis(hydroxo) complex (DMPE)₂Ru(OH)₂ (4) in 17% yield. The addition of protic reagents to 1 results in the replacement of the OH group with several other ligands, including aryloxo, thiolato, siloxo, C-bound enolate, acetylide, and triphenylstannyl; more deep-seated changes take place when 1 reacts with p-tolualdehyde and hexafluoroacetone.

Full text of DOI:10.1021/om960991i

1106
Organometallics 1997, 16, 1106-1108
Nitr ou s Oxid e Med ia ted Oxygen Atom In ser tion in to a
Ru th en iu m -Hyd r id e Bon d . Syn th esis a n d Rea ctivity of
th e Mon om er ic Hyd r oxor u th en iu m Com p lex
(DMP E)2Ru (H)(OH)
Anne W. Kaplan and Robert G. Bergman*
Department of Chemistry, University of California, Berkeley, California 94720
Received November 22, 1996X
Summary: Treatment of (DMPE)2Ru(H)2 with 1 equiv
of N2O affords the hydroxoruthenium complex (DMPE)2-
Ru(H)(OH) (1) in 41% yield; further treatment with an
atmosphere of N2O affords the bis(hydroxo) complex
(DMPE)2Ru(OH)2 (4) in 17% yield. The addition of
protic reagents to 1 results in the replacement of the OH
group with several other ligands, including aryloxo,
thiolato, siloxo, C-bound enolate, acetylide, and triphen-
ylstannyl; more deep-seated changes take place when 1
reacts with p-tolualdehyde and hexafluoroacetone.
(DMPE)2Ru(H)(OH) (1) via the oxidative addition of
water to the Ru(0) complex (DMPE)2Ru(C2H4) (2) and
subsequent H2O removal with 4 Å molecular sieves.
Elevated temperatures and extended reaction times
were necessary to effect this reaction,23 so the possible
use of N2O to directly transfer an oxygen atom into a
ruthenium hydride bond seemed like an attractive
alternative. Hillhouse and co-workers have found that
N2O can be used to insert oxygen atoms into nickel-
carbon and the relatively oxophilic (group 4) early
metal-hydrogen bonds, but to our knowledge oxygen-
ation of late metal-hydrogen bonds has not been
observed.24-28
We wish to report the first observation of oxygen atom
transfer from N2O into a late transition metal-
hydrogen bond and the chemistry of the hydroxohydri-
doruthenium complex produced in this reaction.
Many catalytic processes involve intermediates that
are proposed to contain late transition metal-hetero-
atom (N, O, S) bonds.1-3 Recent work has been directed
toward the synthesis of these potentially reactive spe-
cies, but there remain few examples of monomeric late
metal hydroxide complexes,3-18 species which are thought
to be important in the hydration of olefins to alcohols,
the hydration of nitriles to carboxamides, and the
Wacker process.3,19-22
We have now found that N2O may be used to mediate
oxygen atom insertion into the Ru-H bond of (DMPE)2-
29
Ru(H)2 (3). Treatment of the dihydride with 1 equiva-
lent of N2O affords the hydroxoruthenium complex 1 in
41% yield after crystallization.30 Treatment of either
dihydride 3 or the isolated monoinsertion product 1 with
an atmosphere of N2O affords the bis(hydroxo) complex
(DMPE)2Ru(OH)2 (4), which can be obtained 95% pure
in 17% yield (eq 1).31
We recently reported the preparation and character-
ization of the monomeric hydroxoruthenium complex
X Abstract published in Advance ACS Abstracts, February 15, 1997.
(1) Masters, C. Homogeneous Transition-Metal Catalysis; Chapman
and Hall: New York, 1981.
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1985, 68, 101.
We have also studied the exchange chemistry of 1 and
have demonstrated that a number of complexes contain-
ing ruthenium-heteroatom bonds are accessible by
treatment with protic reagents at room temperature.
Addition of phenols, thiols, and silanols to 1 yield the
(12) J ames, B. R.; Preece, M.; Robinson, S. D. Adv. Chem. Ser. 1982,
No. 196, 145.
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Soc. 1979, 101, 2027.
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Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 5875.
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1995, 14, 456.
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(29) An improved preparative method for 3 has been used which
involves Na reduction of (DMPE)2RuCl2 in the presence of an atmo-
sphere of H2. This affords 3 in >95% yield. We thank Prof. L. Field for
this suggestion.
(22) Bottomley, F.; Sutin, L. Adv. Organomet. Chem. 1988, 28, 339.
S0276-7333(96)00991-0 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 6, 1997 1107
Sch em e 1
While the aforementioned reactions may be thought
of as proceeding by protonation of the hydroxide moiety,
this is not the only mode of reactivity available to the
hydroxoruthenium complex 1. The addition of Ph3SnH,
which does not contain an acidic hydrogen, to 1 affords
the stannyl hydride complex 14 in 86% yield (Scheme
1). Both Sn-P and Sn-H coupling are observed by
NMR spectroscopy.44
An interesting reaction is observed when 1 is treated
with 1 equiv of p-tolualdehyde (eq 2). The hydroxide
oxygen is retained, the aldehydic C-H bond is broken,
and the ruthenium carboxylate complex 15 is obtained
in 28% yield.34 The structural assignment of 15 was
confirmed by X-ray crystallography; an ORTEP diagram
corresponding (aryloxo)-,32 (thiolato)-,33 and siloxoru-
thenium complexes 5-9 in 25-40% yield (Scheme 1).34
Complex 1 is also reactive toward molecules containing
acidic C-H bonds. The treatment of 1 with acetone
affords the C-bound enolate complex 1035 in 34% yield.34
Terminal alkynes react with 1 to give the ruthenium
acetylide complexes 1136 and 12 in ca. 30% yield.34
Interestingly, reactivity can be affected at both ends of
1,7-octadiyne to give the bimetallic complex 13 (68%
yield). The reactivity of the hydroxoruthenium com-
plexes 1 and 4 toward the C-H bonds of conjugated
alkynes could provide a convenient, controlled route into
extended conjugated organometallic systems.37-43
(35) Conditions for the synthesis and isolation of 10 given in this
footnote are applicable for the synthesis of 16. A 50-mL thick-walled
glass vessel fused to a vacuum stopcock was charged with a stir bar
and a solution of (DMPE)2Ru(H)(OH) (104 mg, 0.25 mmol) in C6H6
(10 mL). The bomb was degassed via three freeze-pump-thaw cycles,
and acetone (0.27 mmol) was condensed in. The solution was warmed
to 25 °C and stirred for 1 h. Volatile materials were removed in vacuo
to afford 108 mg (95% yield) of 10 as a tan powder which was pure by
NMR spectroscopy. The product was washed with pentane (3 × 3 mL)
and then dissolved in toluene for crystallization by slow pentane vapor
diffusion into the solution. Recrystallization afforded 39 mg (34% yield)
of 10 as tan crystals. 1H NMR (C6D6): δ 2.13 (s, 3 H, C(O)CH3), 1.57
(m, 6 H, Ru-CH2 and P-CH2), 1.38 (s, 12 H, P-CH3), 1.21 (m, 4 H,
P-CH2), 1.14 (s, 12 H, P-CH3), -16.67 (qn, J HP ) 22.2 Hz, 1 H, Ru-
H); 31P{1H} NMR (C6D6): δ 43.0 (s). 13C{1H} NMR (C6D6): δ 210.7 (C),
31.0 (qn, J CP ) 13.7 Hz, p-CH2), 30.6 (COCH3), 25.7 (qn, J CP ) 7.6 Hz,
p-CH3), 18.0 (qn, J CP ) 4.2 Hz, Ru-CH2), 15.2 (qn, J CP ) 5.0 Hz,
p-CH3). IR (KBr): 2958 (m), 2922 (m), 2897 (s), 1928 (s), 1713 (w),
1475 (m), 1444 (m), 1419 (s), 1365 (m), 1288 (w), 1279 (m), 1232 (w),
1074 (w), 991 (w), 935 (s), 889 (s), 862 (w), 840 (m), 795 (w), 727 (s),
702 (s), 683 (w), 644 (m), 459 (w) cm-1. MS-EI: m/z ) 459 [(M)+]. Anal.
Calcd for C15H38OP4Ru: C, 39.21; H, 8.34. Found: C, 39.20; H, 8.32.
(36) Conditions for the synthesis and isolation of 11 given in this
footnote are applicable for the synthesis of 13. Complex 12 was
synthesized by passing acetylene gas through a solution of 1 in benzene
for 25 min. Complex 12 was isolated similarly to 11. To a solution of
(DMPE)2Ru(OH)(H) (1) (98 mg, 0.23 mmol) in C6H6 (5 mL) was added
dropwise a solution of phenylacetylene (26 mg, 0.26 mmol) in C6H6 (5
mL). The tan solution turned peach after 0.5 h at 25 °C. Lyophilization
of the reaction solution, followed by dissolution in pentane, filtration
through Celite, and concentration in vacuo afforded 88 mg (74% yield)
of 11 as an orange solid which was pure by NMR spectroscopy.
Analytically pure yellow needles of 11 (33 mg, 28% yield) were obtained
by two successive recrystallizations from pentane at -70 °C. 1H NMR
(C6D6): δ 7.47 (d, J HH ) 6.9 Hz, 2 H, o-C6H5), 7.18 (s, 2 H, m-C6H5),
6.95 (t, J HH ) 7.4 Hz, 1 H, p-C6H5), 1.50 (s, 12 H, P-CH3), 1.51 (m, 4
H, P-CH2), 1.29 (m, 4 H, P-CH2), 1.24 (s, 12 H, P-CH3), -11.95 (qn,
J HP ) 20.0 Hz, 1 H, Ru-H). 31P{1H} NMR (C6D6): δ 45.5 (s). 13C{1H}
NMR (C6D6): δ 133.5 (m, Ru-C), 132.5 (Ru-CC), 130.5 (CH), 127.9
(CH), 122.0 (CH), 109.3 (ipso-C), 31.6 (qn, J CP ) 14.1 Hz, p-CH2), 23.7
(qn, J CP ) 7.0 Hz, p-CH3), 17.1 (qn, J CP ) 7.0 Hz, p-CH3). IR (KBr):
3064 (w), 2960 (w), 2926 (w), 2899 (m), 2058 (s), 1759 (w), 1632 (w),
1591 (m), 1479 (w), 1417 (m), 1290 (w), 1277 (w), 935 (s), 926 (s), 889
(30) An 800-mL thick-walled glass vessel fused to a vacuum stopcock
was charged with a stir bar and a colorless solution of (DMPE)2Ru-
(H)2 (2.30 g, 5.71 mmol) in C6H6 (100 mL). The bomb was degassed
via three freeze-pump-thaw cycles, and N2O (6.29 mmol) was
condensed in. The solution was warmed to 25 °C and stirred for 12 h.
The resulting brown solution was concentrated in vacuo to a dark
brown residue and washed with pentane (4 × 5 mL) to remove
unreacted (DMPE)2Ru(H)2. The residue was dissolved in minimal
toluene (10 mL) and layered with pentane (40 mL). After 1 d at 25 °C,
the tan solution was decanted from a dark brown residue and the
solution was cooled to -35 °C for 2 d. The tan crystals obtained were
washed with pentane (3 × 1 mL) and dried in vacuo to afford 980 mg
(41% yield) of 1. Characterization data for 1 are identical with the
literature values given in ref 23.
(31) The synthesis of 4 differs from the synthesis of 1 in that 1 atm
of N2O was used and the solution was stirred for 2 d. Analytically pure
material was not obtained after repeated recrystallizations.
(32) Conditions for the synthesis and isolation of 5 listed below are
general for complexes 6, 7, 8, 9, 14, and 15. To a solution of
(DMPE)2Ru(OH)(H) (1) (89.3 mg, 0.10 mmol) in C6H6 (10 mL) was
added phenol (20.9 mg, 0.11 mmol). After 1 h at 25 °C, the solution
was concentrated to a beige powder, which was dissolved in toluene
for crystallization by slow pentane vapor diffusion into the solution.
Recrystallization afforded 24.8 mg (25% yield) of 5 as white crystals.
1H NMR (C6D6): δ 7.35 (t, J HH ) 7.8 Hz, 2 H, m-OC6H5), 6.62 (t, J HH
) 6.8 Hz, 1 H, p-OC6H5), 6.43 (d, J HH ) 7.6 Hz, 2 H, o-OC6H5), 1.65
(m, 4 H, P-CH2), 1.30 (s, 12 H, P-CH3), 1.23 (m, 4 H, P-CH2), 1.09
(s, 12 H, P-CH3), -23.3 (qn, J HP ) 21.8 Hz, 1 H, Ru-H). 31P{1H} NMR
(C6D6): δ 45.4 (s). 13C{1H} NMR (C6D6): δ 174.0 (C), 129.1 (CH), 120.5
(CH), 109.5 (CH), 31.3 (qn, J CP ) 12.3 Hz, CH2), 22.9 (m, PCH3), 15.5
(qn, J CP ) 5.4 Hz, PCH3). IR (KBr): 3058 (w), 2958 (w), 2897 (m), 1928
(m), 1589 (m, br), 1562 (w, br), 1489 (m), 1479 (m, br), 1421 (w, br),
1290 (m, br), 1279 (m, br), 1164 (w, br), 1124 (w, br), 1101 (w, br),
1072 (w, br), 1020 (w, br), 989 (w, br), 935 (s, br), 910 (m, br), 889 (m),
841 (m), 795 (w), 760 (w), 727 (m), 698 (m), 644 (m), 523 (w), 459 (w)
(m), 841 (w), 795 (w), 748 (m), 725 (m), 702 (m), 646 (m), 461 (w) cm-1
.
MS-EI: m/z ) 503 [(M - 1)+]. Anal. Calcd for C20H38P4Ru: C, 47.71;
H, 7.61. Found: C, 47.50; H, 7.67.
(37) Yam, V. W.-W.; Lau, V. C.-Y.; Cheung, K.-K. Organometallics
1996, 15, 1740.
(38) Weng, W.; Bartik, T.; Brady, M.; Bartik, B.; Ramsden, J . A.;
Arif, A. M.; Gladysz, J . A. J . Am. Chem. Soc. 1995, 117, 11922.
(39) Narvor, N. L.; Toupet, L.; Lapinte, C. J . Am. Chem. Soc. 1995,
117, 7129.
(40) Khan, M. S.; Kakkar, A. K.; Ingham, S. L.; Raithby, P. R.; Lewis,
J . J . Organomet. Chem. 1994, 472, 247.
(41) Atherton, Z.; Faulkner, C. W.; Ingham, S. L.; Kakkar, A. K.;
Khan, M. S.; Lewis, J .; Long, N. J .; Raithby, P. R. J . Organomet. Chem.
1993, 462, 265.
cm-1. MS-EI: m/z ) 496 [M+]. HRMS (EI) (m/z): Calcd for C18H38
-
OP4Ru, 496.0917; obsd, 496.0924. Anal. Calcd for C18H38OP4Ru: C,
43.64; H, 7.73. Found: C, 43.99; H, 8.22.
(33) Burn, M. J .; Fickes, M. G.; Hollander, F. J .; Bergman, R. G.
Organometallics 1995, 14, 137.
(34) Yields refer to doubly recrystallized material and do not reflect
percent conversions to spectroscopically pure material which are >90%.
(42) Faulkner, C. W.; Ingham, S. L.; Khan, M. S.; Lewis, J .; Long,
N. J .; Raithby, P. R. J . Organomet. Chem. 1994, 482, 139.
(43) Sponsler, M. B. Organometallics 1995, 14, 1920.

1108 Organometallics, Vol. 16, No. 6, 1997
Communications
This is most easily applied to the reaction of 1 with weak
protic acids H-X, perhaps including alkynes and ac-
etone. In the reaction of triphenyltin hydride, we
suggest that the Sn-H bond adds to the cationic
ruthenium center and then hydroxide removes a proton
from Ru to arrive at the observed product 14.
Assuming the hydroxide ligand is labile, it should be
possible to trap the resulting [(DMPE)2Ru(H)]+ cation
17. When the hydroxoruthenium complex 1 is exposed
to an atmosphere of ethylene in benzene at 105 °C for
1 d, the ruthenium ethylene complex 2 is formed
(Scheme 1). There is strong evidence that the reverse
reaction (treatment of 2 with an excess of water at
elevated temperatures to form the hydroxoruthenium
complex 1) proceeds via a cationic hydridoruthenium
ethylene complex 18 which loses ethylene and forms 2
by anion addition.33 We believe that we are observing
the microscopic reverse of this process: dissociation of
hydroxide, coordination of ethylene, and deprotonation
of the metal center to afford the observed product 2.
Initial ion pair formation can also be used to rational-
ize the apparent oxidations of p-tolualdehyde and
hexafluoroacetone to the corresponding carboxylate
complexes. O-coordination of the aldehyde to the ru-
thenium center and subsequent hydroxide attack at the
carbonyl carbon would form metallaacetal species 19
(Scheme 2). This species is likely to be unstable with
respect to â-elimination, leading to the dihydride com-
plex 3 and the carboxylic acid, which quickly react to
give 15 (vide supra). Hexafluoroacetone leads to inter-
mediate 20 which undergoes C-C cleavage followed by
proton transfer to give 16.
F igu r e 1. ORTEP diagram of (DMPE)2Ru(H)(OC(O)C6H4-
Me) (15).
Sch em e 2
In summary, we have demonstrated that N2O is
capable of mediating oxygen atom insertion into a late
metal-hydrogen bond to afford hydroxoruthenium com-
plexes 1 and 4. Additional complexes containing ru-
thenium-heteroatom bonds may be prepared via ex-
change reactions with 1. Complex 1 has been shown to
activate C-H, Sn-H, and C-C bonds under mild
conditions, partially due to the lability of the hydroxide
ligand. Further reactivity and mechanistic studies of
the hydroxoruthenium complex 1 and its derivatives,
as well as the bis(hydroxo)ruthenium complex 4, are
underway.
of the complex is shown in Figure 1.45 The structure
reveals that there is no apparent interaction between
the carbonyl oxygen and the ruthenium center in the
solid state. We have found independently that 3 and
p-toluic acid react to generate complex 15 with loss of
dihydrogen (Scheme 2). Similar reactivity is observed
when 1 is treated with hexafluoroacetone to afford 16
in 39% yield (eq 2).34 In this case, the C-C bond is
broken and the release of trifluoromethane is observed
by NMR spectroscopy.
Ack n ow led gm en t. We thank the National Insti-
tutes of Health (Grant No. GM-25459) and the Arthur
C. Cope Fund administered by the American Chemical
Society for generous financial support of this work. We
are grateful to Dr. F. J . Hollander, director of the
University of California Berkeley College of Chemistry
X-Ray diffraction facility (CHEXRAY), for solving the
crystal structure of 15. We also thank Prof. R. A.
Andersen for suggesting the use of N2O in the synthesis
of 1 and for helpful discussions and Prof. R. N. Perutz
for disclosure of results prior to publication.
Much of the observed reactivity of 1 can be rational-
ized using the assumption that the first step involves
reversible formation of a metal cation/OH- ion pair (17).
Su p p or tin g In for m a tion Ava ila ble: Text describing
spectroscopic and analytical data for complexes 4-8 and 10-
16, tables of structural data for 15, and NMR spectra for
complexes 4, 7, 13, and 14 (22 pages). Ordering information
is given on any current masthead page.
2
(44) 2J PSn ) 174.6 Hz; J HSn ) 216.1 Hz.
(45) Perutz and co-worker(s) have recently solved the X-ray struc-
ture for the related complex (DMPE)2Ru(H)(OCOH): Organometallics
1996, 15, 5166.
OM960991I