Water-promoted reaction of a platinum(II) oxo complex with ethylene

Article abstract of DOI:10.1021/om010868d

Treatment of [(dppp)Pt(μ-O)]₂(LiOTf)₂ (dppp = Ph₂P(CH₂)₃PPh₂) with ethylene in the presence of trace amounts of water results in oxygen atom transfer to one arm of the bidentate phosphine ligand and formation of(dpppO)Pt(η²-CH₂=CH₂)₂ (dpppO = Ph₂P(CH₂)₃P(O)-Ph₂). Further investigation reveals that the reaction of [L₂Pt(μ-O)]₂(LiOTf)₂ with water forms (dppp)Pt(OH)₂, which acts as a catalyst for the oxygen atom transfer reaction. The analogous oxo complex [(PPh₃)₂Pt(μ-O)]₂-(LiBF₄)₂ does not react with ethylene under similar conditions. These results indicate that hydroxo complex intermediates should be considered in oxygen atom transfer reactions.

Full text of DOI:10.1021/om010868d

Organometallics 2002, 21, 997-1000
997
Wa ter -P r om oted Rea ction of a P la tin u m (II) Oxo Com p lex
w ith Eth ylen e†
Bruce Flint, J ian-J un Li, and Paul R. Sharp*
Department of Chemistry, University of MissourisColumbia, Columbia, Missouri 65211
Received October 3, 2001
Summary: Treatment of [(dppp)Pt(µ-O)]2(LiOTf)2 (dppp
) Ph2P(CH2)3PPh2) with ethylene in the presence of trace
amounts of water results in oxygen atom transfer to one
arm of the bidentate phosphine ligand and formation
of (dpppO)Pt(η2-CH2dCH2)2 (dpppO ) Ph2P(CH2)3P(O)-
Ph2). Further investigation reveals that the reaction of
[L2Pt(µ-O)]2(LiOTf)2 with water forms (dppp)Pt(OH)2,
which acts as a catalyst for the oxygen atom transfer
reaction. The analogous oxo complex [(PPh3)2Pt(µ-O)]2-
(LiBF4)2 does not react with ethylene under similar
conditions. These results indicate that hydroxo complex
intermediates should be considered in oxygen atom
transfer reactions.
in our system, a hydroxo complex produced from the
water catalyzes the process, suggesting the involvement
of a hydroxo group in the oxygen atom transfer.
Resu lts
In dry THF, [(dppp)Pt(µ-O)]2(LiOTf)2 (1) displays no
measurable reactivity toward ethylene. However, upon
addition of trace amounts of water (0.03 equiv), 1 reacts
readily with ethylene to form (dpppO)Pt(η2-CH2dCH2)2
2 (eq 1).
In tr od u ction
The chemistry of transition-metal oxo complexes has
been of interest to chemists for many years.1 Chemical
industries use late-transition-metal catalysts in a va-
riety of processes.2 Many of these processes involve the
reaction of molecules with a metal surface, where
oxygen atoms (oxo groups) are formed and transferred
to other species. The chemistry occurring at the surface
is poorly understood and is more easily studied through
the use of soluble model complexes. Of particular
interest to us is the synthesis and reactivity of late-
transition-metal oxo complexes with small molecules.1c,d
In this paper we report studies of the reactivity of
dimeric [(dppp)Pt(µ-O)]2(LiOTf)2 (dppp ) Ph2P(CH2)3-
PPh2, OTf ) CF3SO3) and the discovery of its reaction
with ethylene in THF that contains trace amounts of
water. This ability of water contamination to activate
the platinum oxo complex toward alkenes is remarkable.
Furthermore, to our surprise, oxygen atom transfer to
the phosphine ligand occurs rather than oxidation3 of
the alkene or insertion4 of the alkene into the Pt-O
bond. Oxygen atom transfers from transition metal oxo
complexes to phosphines are not uncommon;5 however,
The reaction mixture containing complex 2 and LiOTf
reduces to an orange oil in vacuo, and 2 cannot be
isolated in crystalline form. Efforts to isolate solid 2 by
trituration and column chromatography were unsuc-
cessful. Similar diphosphine oxide complexes have been
reported6 in which crystallization and purification have
posed problems. However, the NMR spectroscopic data
clearly establish (dpppO)Pt(CH2dCH2)2 (2) as a member
of the known class of complexes of formula LPt(CH2d
CH2)2 (L ) a phosphine).7 With the exception of the
signals from the “dangling” OPPh2 end of the dpppO
ligand, all spectroscopic data closely resemble that for
(Ph2PMe)Pt(CH2dCH2)2.7 The 31P NMR spectrum of 2
in the THF reaction mixture shows a singlet at 16.7 ppm
with Pt satellites for the Ph2P end of the dpppO group
bonded to Pt(0) and a singlet at 31 ppm without
satellites for the “dangling” OPPh2 end of the dpppO
ligand. The shift of 31 ppm is similar to that of other
1
reported diphosphine oxides.6,8 The H NMR spectrum
(4) For examples of alkene or alkyne insertion into late-transition-
metal-oxygen bonds see: (a) Bryndza, H. E.; Calabrese, J . C.; Wreford,
S. S. Organometallics 1984, 3, 1603-1604. (b) Woerpel, K. A.; Berg-
man, R. G. J . Am. Chem. Soc. 1993, 115(17), 7888-7889.
(5) For examples of phosphine oxidation by late-transition-metal oxo
complexes see: (a) Brownlee, G. S.; Carty, P.; Cash, D. N.; Walker, A.
Inorg. Chem. 1975, 14, 323-327. (b) Vilmer, M. C. M.S. Thesis,
University of Missouri, Columbia, MO, 1986. (c) McGhee, W. D.; Foo,
T.; Hollander, F. J .; Bergman, R. G. J . Am. Chem. Soc. 1988, 110, 8543.
(d) Dobbs, D. A.; Bergman, R. G. Organometallics 1994, 13, 4594-
4605. (e) Shan, H.; J ames, A. J .; Sharp, P. R. Inorg. Chem. 1998, 37,
5727-5732. (f) Obias, H. V.; Lin, Y.; Murthy, N. N.; Pidcock, E.;
Solomon, E. I.; Ralle, M.; Blackburn, N. J .; Neuhold, Y. M.; Zuber-
buhler, A. D.; Karlin, K. D. J . Am. Chem. Soc. 1998, 120, 12960-12961.
For other transition-metal systems see: Seymore, S. B.; Brown, S. N.
Inorg. Chem. 2000, 39, 325-332 and references therein.
† Taken in part from the Ph.D. thesis of J ian-J un Li (1996).
(1) (a) Griffith, W. P. Coord. Chem. Rev. 1970, 5, 459-517. (b)
Mehrotra, R. C.; Singh, A. Chem. Soc. Rev. 1996, 25(1), 1-13. (c) Sharp,
P. R. Comments Inorg. Chem. 1999, 21(1-3), 85-114. (d) Sharp, P. R.
J . Chem. Soc. Dalton Trans. 2000, 16, 2647-2884. (e) West, B.
Polyhedron 1989, 219-274. (f) Bottomley, F.; Sutin, L. Adv. Organomet.
Chem. 1988, 28, 339-387.
(2) (a) Brown, W. A.; King, D. A. J . Phys. Chem. B 2000, 104, 2578-
2595. (b) Farrauto, R. J .; Bartholomew, C. H. Fundamentals of
Industrial Catalytic Processes; Blackie Academic & Professional: New
York, 1997. (c) Madix, R. J .; Roberts, J . T. In Surface Reactions; Madix,
R. J ., Ed.; Springer-Verlag: New York, 1994; pp 5-53. (d) Guo, X.-C.;
Madix, R. J . J . Am. Chem. Soc. 1995, 117, 5523-30. (e) Hamed, O.;
Henry, P. M. Organometallics 1997, 16, 4903-4909. Schmatloch, V.;
Kruse, N. Surf. Sci. 1992, 269-270, 488-494.
(6) Higgins, S. J .; Taylor, R.; Shaw, B. L. J . Organomet. Chem. 1987,
325, 285-292.
(7) Harrison, N. C.; Murray, M.; Spencer, J . L.; Stone, G. A. J . Chem.
Soc., Dalton Trans. 1978, 1337-1342.
(3) For a rare example of alkene oxidation by an isolated late-
transition-metal oxo complex see: Hosokawa, T.; Takano, M.; Mura-
hashi, S. I. J . Am. Chem. Soc. 1996, 118, 3990-3991.
10.1021/om010868d CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/31/2002

998 Organometallics, Vol. 21, No. 5, 2002
Notes
of 2 in CD2Cl2 shows the ethylene ligands as a broad
1
singlet at 2.3 ppm with H-195Pt coupling of 58 Hz. The
broadness of the peak is due to rotation of the ethylene
ligands, common to this class of complexes.7 This was
1
confirmed by a low-temperature H NMR study, which
showed collapse of this peak (Tc ≈ -40 °C) as the
temperature was lowered and emergence of two broad
peaks on each side of the original peak position. The
13C NMR spectrum shows an ethylene peak at 39 ppm
with 13C-195Pt coupling of 141 Hz. The 31P NMR
spectrum of 2 in CD2Cl2 is similar to that in THF, with
the exception that the OPPh2 peak at 31 ppm is notably
broadened. This broadness is most likely due to hemi-
labile9 activity of the phosphine oxide ligand (a weak
interaction of the phosphine oxide portion of the dpppO
ligand with the platinum metal center) in the poor
donor solvent CD2Cl2. Confirmation of the presence of
the dpppO ligand is obtained by the addition of dppe to
a THF solution of 2, which yields Pt0(dppe)2,10 free
dpppO11 (by 31P NMR spectroscopy), and presumably
ethylene (eq 2).
F igu r e 1. ORTEP drawing of the cationic portion of
[(dppp)Pt(OH)2(Li)(THF)]2[OTf]2 (3′), showing two (dppp)-
Pt(OH)2 units bridged by two Li(THF)+ units.
Ta ble 1. Selected Dista n ces (Å) a n d An gles (d eg)
for [(d p p p )P t(OH)2(Li)(THF )]2[OTf]2 (3′)
Pt1-O1
Pt1-O2
Pt1-P1
Pt1-P2
2.039(4)
2.070(4)
2.2157(13)
2.2267(14)
O1-Li1
O2-Li1
Li1-O3
1.890(10)
1.912(10)
1.932(11)
O1-Pt1-O2
O1-Pt1-P1
O1-Pt1-P2
O2-Pt1-P2
O2-Pt1-P2
P1-Pt1-P2
79.48(16)
93.65(12)
173.72(11)
173.72(12)
91.28(12)
92.57(5)
Li1-O1-Pt1
Li1-O2-Pt1
O1-Li1-O2
O2-Li1-O3
O1-Li1-O3
97.5(3)
92.4(3)
115.2(5)
119.9(5)
118.3(5)
Mass spectral analysis also shows the presence of
dpppO.
Careful examination of the eq 1 reaction mixture by
31P NMR spectroscopy reveals trace amounts of another
platinum-containing product, 3. This same complex is
formed in high yield from the reaction of 1 in THF with
2 molar equiv of H2O (eq 3).
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
Deta ils for [(d p p p )P t(OH)2(Li)(THF )]2[OTf]2 (3′)
empirical formula
fw
C28H28F3LiO5P2PtS
797.55
temp (K)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
173
triclinic
P1h
10.507(2)
13.627(3)
15.891(3)
100.512(3)
106.577(3)
111.330(3)
1924.0(7)
2
1.63
0.7107
3.844
0.0498, 0.0111
Yellow crystals are deposited from the reaction solution.
X-ray crystallography shows the crystalline material to
be the hydroxo complex [(dppp)Pt(OH)2(Li)(THF)]2[OTf]2
(3′) (Figure 1). An abbreviated summary of the crystal
data collection and processing is given in Table 1.
Selected distances and angles are listed in Table 2. The
Pt portion of the structure consists of two square-planar
(dppp)Pt(OH)2 units bridged through the hydroxo groups
by two Li(THF)+ units. The average Pt-O distance (2.05
Å) falls in the low end of the range (2.02-2.19 Å) for
the few structurally characterized Pt(II) terminal hy-
droxo complexes12 and is slightly longer than the Pt-O
Z
Dcalcd (g/cm3)
λ (Å)
µ (mm-1
)
R1,a wR2b
a
R1 ) (∑||Fo| - |Fc||)/∑|Fo|. b wR2 ) [(∑w(Fo2 - Fc2)2/∑w(Fc2)2]1/2
with weight ) 1/[σ2(Fo2) + (0.0459P)2 + 15.9835P]; P ) (Fo
2Fc2)/3.
+
2
distance found in the only structurally characterized Pt-
(II) complex with a terminal hydroxo group trans to a
phosphine center (2.03 Å).12e The Pt-O distances in 3′
2+
(8) Appleton, T. G.; Bryiel, K. A.; Hall, J . R.; Kennard, C. H. L.;
Lynch, D. E.; Sinkinson, J . A.; Smith, G. Inorg. Chem. 1994, 33, 444-
455.
(9) Slone, C. S.; Wienberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233.
(10) Al-Resayes, S. I.; Hitchcock, P. B.; Meidine, M. F.; Nixon, J . F.
J . Organomet. Chem. 1988, 341, 457-472.
(11) Grushin, V. V. J . Am. Chem. Soc. 1999, 121, 5831-2.
(12) (a) Britten, J . F.; Lippert, B.; Lock, C. J . L.; Pilon, P. Inorg.
Chem. 1982, 21, 1936-1941. (b) Miyamoto, T. K. Chem. Lett. 1994,
1971. (c) Navarro, J . A. R.; Romero, M. A.; Salas, J . M.; Quiros, M.
Inorg. Chem. 1997, 36, 3277-3283. (d) Klein, A.; Klinkhammer, K.
W.; Scheiring, T. J . Organomet. Chem. 1999, 592, 128-135. (e) Straub,
B. F.; Rominger, F.; Hofmann, P. Inorg. Chem. Commun. 2000, 3, 214-
217.
are shorter than those found in [(dppp)Pt(OH)]2
,
where the hydroxo groups bridge the two Pt centers
(Pt-O ) 2.10 Å).13 The interaction of the hydroxo groups
with the Li ions in 3 evidently does not greatly perturb
the Pt-O distances from that of a terminal hydroxo
group. For simplicity in the following considerations,
dimeric 3′ is assumed to behave as the monomer (dppp)-
Pt(OH)2 (3) in solution.
(13) Bandini, A. L.; Banditelli, G.; Demartin, F.; Manassero, M.;
Minghetti, G. Gazz. Chim. Ital. 1993, 123, 417-423.

Notes
Organometallics, Vol. 21, No. 5, 2002 999
Sch em e 1
Sch em e 2
Discu ssion
The catalysis of the oxygen atom transfer reaction of
the oxo complex 1 by the hydroxo complex 3 is note-
worthy. Oxygen atom transfers to phosphines from
transition-metal oxo complexes, including late-transi-
tion-metal oxo complexes, have been reported previously
but apparently do not involve hydroxo species.5 If we
had not noticed the need for traces of water in the
reaction of 1, we would not have been aware of the
involvement of hydroxo complexes in this system. A
possible pathway for the catalytic reaction of oxo
complex 1 is given in Scheme 1 and begins with the
reaction of 1 with the catalyst 3 to produce the detected
complex formulated as 4 or 5. Complex 4 or 5 is given
as the species that undergoes reaction with ethylene.
This follows from the observation that neither 1 nor 3
reacts with ethylene by itself and that the intermediate
4 or 5, produced from the reaction of 1 and 3, is observed
in the ethylene reaction mixtures up until the end of
the reaction. Since no other species are observed during
the reaction, the slow step is assigned to the reaction
of ethylene with 4 or 5. It is possible that another low-
concentration, undetected species is responsible for the
ethylene reaction; however, lacking any further evi-
dence, 4 and 5 are the best candidates.
The details of the ethylene reaction step are unknown
but may involve ethylene-induced reductive elimination
of a phosphine center and a hydroxo ligand, as il-
lustrated for 4 in Scheme 2. Similar reductive elimina-
tions of a hydroxo group or an acetate group and a
phosphine ligand have been suggested by Amatore and
co-workers in the reduction of Pd(II) to Pd(0).15 π-Acid-
ligand-induced reductive eliminations are known,16
consistent with the ethylene-induced elimination pro-
posed here. Proton transfer from the P-OH group to
the oxo group and reaction with another ethylene would
give the observed product 2 and re-form the catalyst 3.
A similar process may be involved in the Pd-catalyzed
synthesis of bis-phosphine monoxides from diphos-
phines, NaOH, and BrCH2CH2Br.17
Complex 3 does not react with ethylene in THF or
CH2Cl2. However, small amounts of 3 (0.1 equiv) induce
a reaction of 1 with ethylene in dry THF, where the
product is again 2 with 3 remaining at the end of the
reaction. Thus, 3 is a catalyst for the reaction of 1 with
ethylene (eq 4).
To further investigate the role of 3 in the reaction,
solid 3′ was added to a solution of 1 (2:1 molar ratio) in
d8-THF. (Solid 3′ only partially dissolved.) The 31P NMR
spectrum of the mixture showed 1, 3, and what is
believed to be [(dppp)Pt(OH)]2(µ-O) (4) or [(dppp)2Pt2-
(µ-O)(µ-OH)][OH] (5) (Scheme 1), which appears as two
doublets (J P-P ) 27 Hz). The 195Pt-31P coupling con-
stants are consistent with one P center trans to a strong
donor oxo ligand (-4.5 ppm, J Pt-P ) 2571 Hz) and
another P center trans to a weaker donor hydroxo ligand
(-11.0 ppm, J Pt-P ) 3774 Hz).14 These same peaks are
observed in the catalyzed reactions of 1 with ethylene
(eqs 1 and 4) but are absent at the end of the reactions;
only 3 remains.
To test the phosphine ligand requirements, [(PPh3)2-
Pt(µ-O)]2(LiBF4) was pressurized with ethylene in the
presence and in the absence of traces of water. No
reaction occurred in either case. Treatment of [(Ph3P)2-
Pt(µ-O)]2(LiBF4) with 1 molar equiv of water yields a
product that appears to be similar to 4 or 5 (31P NMR,
250 MHz, THF: 8 ppm (d, J P-P ) 17 Hz, J Pt-P ) 4462
Hz) and 15 ppm (d, J Pt-P ) 2761 Hz)), but this species
apparently does not catalyze the reaction of the oxo
complex with ethylene. The dppp oxo complex [(dppb)-
Pt(µ-O)]2(LiOTf)2 (dppb ) Ph2PCH2CH2CH2CH2PPh2)
was also examined. Like the dppp complex 1, trace
amounts of water are required to observe a reaction with
ethylene. The reaction appears to be analogous to that
of 1 with ethylene (eq 1).
Finally, in the above discussion we have neglected
possible solution-phase Li ion interactions with the oxo
(15) (a) Amatore, C.; J utand, A.; Medeiros, M. J . New J . Chem. 1996,
20, 1143-1148. (b) Amatore, C.; Carre, E.; J utand, A.; M’Barki, M. A.
Organometallics 1995, 14, 1818-1826. (c) Amatore, C.; J utand, A.;
Thuilliez, T. Organometallics 2001, 20, 3241-3249.
(14) Li, J . J .; Li, W.; Sharp, P. R. Inorg. Chem. 1996, 35, 604-613.
Recent observations in our laboratories suggest that mixed hydroxo/
oxo cores such as in 5 are distorted such that the oxo ligand is a
stronger donor and the hydroxo ligand is a weaker donor than in the
unmixed dioxo and dihydroxo complexes. This results in more extreme
values of J P-Pt than expected from the dioxo and dihydroxo complexes.
(16) (a) Goliaszewski, A.; Schwartz, J . J . Am. Chem. Soc. 1984, 106,
5028-5030. (b) Hill, A. F.; Hulkes, A. G.; White, A. J . P.; Williams, D.
J . Organometallics 2000, 19, 371-373.
(17) Vladimir, V. G. J . Am. Chem. Soc. 1999, 121, 5831-5832.

1000 Organometallics, Vol. 21, No. 5, 2002
Notes
[(d p p p )P t(OH)2(Li)(THF )]2[OTf]2 (3′). Water (24 µL,
0.013 mmol) was added by syringe to a solution of [(dppp)Pt-
(µ-O)]2(LiOTf)2 (0.020 g, 0.013 mmol) in 1.0 mL of THF. The
initially pale yellow solution immediately darkened slightly.
After 1 h, crystals began to form and the solution was chilled
to 0 °C overnight. The yellow crystals were collected, washed
with diethyl ether, and dried in vacuo. The crystals are
unstable to solvent loss and become a powder in vacuo. Yield:
and hydroxo ligands of the complexes, such as the
interactions observed in the solid-state structure of the
dihydroxo complex 3 and the dioxo complex [(Ph3P)2Pt-
(µ-O)]2(LiBF4).14 Such Li ion interaction may play a role
in the solution chemistry by stabilizing complexes and
ionic species such as the hydroxide ion in proposed 5.
That such interactions are important is shown by the
reaction of the Li-free dioxo complex [L2Pt(µ-O)]2-
(NaOTf)x (L2 ) dppp) with ethylene in the presence of
ca. 0.1 equiv of water. Only a very slow reaction occurs,
giving the ethylene complex 2, suggesting that the
weaker Na ion interactions with the oxo and hydroxo
ligands are not as effective at stabilizing key species.
Consistent with this, the 31P NMR spectrum of the
mixture shows the presence of the dioxo complex and
L2Pt(OH)2 (3) but no signals for the proposed reaction
intermediate, 4 or 5, could be detected.
12 mg (60%). 31P{1H} NMR (101 MHz, CD2Cl2): -9.0 (J Pt-P
)
3262 Hz). 31P NMR (101 MHz, THF): -7.7 (J Pt-P ) 3246 Hz).
1H NMR (250 MHz, CD2Cl2): 7.55-7.28 (m, 20H, Ph), 2.59
(broad, 4H), 1.88 (broad, 2H), -0.44 (s, 2H, OH). Anal. Calcd
(found) for PtP2C28H28LiF3SO5‚0.4C4H8O: C, 43.02 (43.12); H,
3.81 (3.86).
(d p p p O)P t(η2-CH2dCH2)2 (2). A solution of [(dppp)Pt(µ-
O)]2(LiOTf)2 (0.050 g, 0.032 mmol) and (dppp)Pt(OH)2(LiOTf)
(ca. 1 mg) in 2 mL of THF was treated with ethylene gas (12
atm) in a Parr pressure vessel for 24 h. The resulting solution
was evaporated under a stream of ethylene, and the oily
residue was redissolved in CD2Cl2 for NMR measurements.
31P NMR (101 MHz, CD2Cl2): 35.2, 15.6 (J Pt-P ) 3330 Hz). 1H
NMR (250 MHz, CD2Cl2): 7.3-7.7 (m, 20H, Ph), 2.6 (broad,
4H, PCH2CH2CH2P), 2.3 (broad, 8H, J H-Pt ) 58 Hz, CH2dCH2),
1.7 (broad, 2H, PCH2CH2CH2P). 31P NMR (101 MHz, THF):
32.9 (s, 1P), 16.7 (s, 1P, J Pt-P ) 3349 Hz). 13C NMR (250 MHz,
THF/C6D6): 127-135 (m, 30C, Ph), 39 (s, 2C, J C-Pt ) 141 Hz,
CH2dCH2), 33 (broad, 2C, PCH2CH2CH2P), 19 (broad, 1C,
PCH2CH2CH2P). LD(ToF) MS: m/z 201 ([P(O)Ph2]+), 243
([P(O)Ph2CH2CH2CH2]+), 249 ([P(C2H4)2]+), 451 ([CH2P(Ph)2-
Pt(C2H4)2]+), 605 ([Pt(PPh2CH2CH2CH2PPh2)]+), 621 ([Pt(PPh2-
CH2CH2CH2P(O)Ph2]+).
Cr ysta l Str u ctu r e An a lysis. Crystal data, reflection col-
lection, and processing parameters and solution and refine-
ment data are summarized in Table 2 and as a CIF file in the
Supporting Information. The crystal was grown as described
above and is sensitive to solvent loss. The crystal was mounted
by pipetting a sample of crystals and mother liquor into a pool
of heavy oil. A crystal was selected and removed from the oil
with a glass fiber. With the oil-covered crystal adhering to the
end of the glass fiber, the sample was transferred to an N2
cold stream on the diffractometer.
Con clu sion s
An oxygen atom transfer reaction of [L2Pt(µ-O)]2-
(LiOTf)2 (L2 ) dppp, dppb; OTf ) CF3SO3) is catalyzed
by the hydroxo complex L2Pt(OH)2 (3). Observations on
the reaction are consistent with mediation of the oxygen
atom transfer by a hydroxo group. These results indicate
that oxygen atom transfer reactions of basic oxo com-
plexes may occur through hydroxo species generated by
trace amounts of water or other protic species. By
analogy, nitrene transfers from imido complexes may
also occur through amido species.
Exp er im en ta l Section
Unless stated otherwise, all experiments were performed
under a dinitrogen atmosphere using a VAC drybox or by
Schlenk techniques. Degassed THF and Et2O were passed
through activated alumina solvent drying columns before use.18
The complexes [(dppp)Pt(µ-O)]2(LiOTf)2 (1), [(dppb)Pt(µ-O)]2-
(LiOTf)2, and [(PPh3)2Pt(µ-O)]2(LiBF4) were prepared as previ-
ously reported.14 The bidentate phosphine ligands dppp and
dppe were purchased from Aldrich Chemical Co. CP grade
ethylene was purchased from Scott Specialty Gases. Experi-
ments involving ethylene were performed in either a Parr
pressure vessel or a Fisher-Porter pressure bottle. NMR
spectra were recorded on a Bruker ARX-250 NMR instrument
at ambient temperatures. Mass spectra were recorded on a
Laser Desorption (ToF) instrument in the linear mode using
2,5-dihydroxybenzoic acid as an external reference. Infrared
spectra were obtained with a Nicolet Magna-550 spectrometer.
1H and 31P NMR chemical shifts are reported in parts per
million and are referenced to TMS (internal) and 85% H3PO4
(external) standards, respectively. Desert Analytics performed
the elemental analyses.
Ackn owledgm en t. We thank the Division of Chemi-
cal Sciences, Office of Basic Energy Sciences, Office of
Energy Research, U.S. Department of Energy (Grant
DF-FG02-88ER 13880), for support of this work. Grants
from the National Science Foundation (Grant No. CHE
89-08304) provided a portion of the funds for the
purchase of NMR equipment. We also thank Charles
Barnes for assistance with the crystal structure and
Anandi Upendran for the variable-temperature NMR
data and the reactions of the sodium derivatives.
Su p p or tin g In for m a tion Ava ila ble: An X-ray crystal-
lographic file in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
(18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15(5), 1518-1520.
OM010868D