Reactivity and stability of 2-platinaoxetanes

Article abstract of DOI:10.1021/om900828k

The influence of ancillary ligands, Lewis acids, carbon substituents and oxidants on the stability and reactivity of 2-platinaoxetanes was investigated through the reactions of 2-platinaoxetanes Pt(L₂)(AOC ₇H₁₀) (L₂

Full text of DOI:10.1021/om900828k

Organometallics 2009, 28, 6935–6943 6935
DOI: 10.1021/om900828k
Reactivity and Stability of 2-Platinaoxetanes
Jianguo Wu and Paul R. Sharp*
125 Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211
Received September 24, 2009
The influence of ancillary ligands, Lewis acids, carbon substituents, and oxidants on the stability and
reactivity of 2-platinaoxetanes was investigated through the reactions of 2-platinaoxetanes Pt(L2)(AOC7H10)
(L2 = COD, 2PEt3, 2PPh3, dppe, But2bpy, Me2bpy; A = nothing or a Lewis acid; C7H10 = norbornene)
with Lewis acids, alkenes, H2O2, and Br2. Addition of catalytic or stoichiometric amounts of BF3 to
2-platinaoxetanes PtL2(C7H10OBF3) (L2 =2PEt3 (7),2PPh3 (8), dppe (9),But2bpy (10),Me2bpy (11)) inthe
presence of benzonorbornene diacetate (NB2) does not give alkene exchange, as observed previously for
Pt(COD)(C7H10OBF3) (2), but only norbornene extrusion. The Pt products are hydroxo complexes
[PtL2(μ-OH)]2(BF3OH)2 for L = PPh3 and PEt3 or unidentified compounds. Treatment of Pt(COD)-
(BF3OC7H10) (2) with ethylene in the presence of catalytic or stoichiometric amounts of BF3 affords
norbornene, acetaldehyde, and allyl complex [Pt(COD)(η3-CH2CHCHCH3)]X (X = BF3OH or BF4, 12).
Similar reactions of 2 or 2-platinaoxetane [Pt2(COD)2(OC7H10)Cl]BF4 (1) with isobutylene give norbor-
nene, allyl complex [Pt(COD)(η3-CH2C(CH3)CH2)]BF4 (13), Pt(COD)Cl2 (for 1 only), and presumably
water. To investigate the stability of 2-platinaoxetanes with different oxygen-coordinated Lewis acids,
Pt(COD)(C7H10O) (6) was treated with 1,2-C6F4(BAr2)2 (Ar=C6F5), HBF4, MeOTf, or Ph3PAuOTf, and
PtL2(C7H10O) (L2 = 2PEt3 (5), 2PPh3 (18), dppe (19)) were treated with HBF4. In each case, norbornene
(NB) extrusion is observed. (Complexes 18 and 19 are reported here for the first time.) In contrast, the
reaction of 6 with HCl(g) in toluene/water yields Pt(COD)(Cl)(C7H10OH) (20). NB extrusion is observed in
dry C6D6. Both processes occur in CD2Cl2 or CD3OD. Complex 20 also forms in the reaction of 2-platina-
oxetane 1with HCl(aq). Treatment of 6with Br2 gives rapid elimination of norbornene oxide with formation
of Pt(COD)Br2. H2O2(aq) and 6 give Pt(COD)(OH)(C7H10OH) (21), an OH analogue of 20.
Introduction
have been prepared and studied,5,7-28 but complete explora-
tion of their chemistry and validation of their involvement in
1-Metalla-2-oxacyclobutanes (2-metallaoxetanes)1 have
long been thought to be important in both homogeneous
and heterogeneous alkene oxidations, epoxide reactions, and
other transition metal-mediated transformations.2-6 Over
the years a number of transition metal 2-metallaoxetanes
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*Corresponding author. E-mail: SharpP@missouri.edu.
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r
2009 American Chemical Society
Published on Web 11/06/2009
pubs.acs.org/Organometallics

6936 Organometallics, Vol. 28, No. 24, 2009
Wu and Sharp
these transition metal (TM)-meditated reactions remains to
be fully achieved.
oxygen-bonded acid. Solvent-dependent reactivity is also
observed.
Many of the reported studies of 2-metallaoxetanes are
related to alkene oxidation. In some cases it has been
shown that 2-metallaoxetanes can form from oxidation
of alkene complexes.5,11,17,18,23 Of further relevance to
TM-mediated olefin oxidation (e.g., the Wacker process)
is the formation of 2-metallaoxetanes by coupling of an
alkene with an oxo or hydroxo complex.21,22,25,28 In some
reactions the coupling can be reversible.24,25,28 However,
alkene coupling to give 2-metallaoxetanes appears to be
rare for oxo and hydroxo complexes, and the factors
involved are not clear.
Our work in this area began with the synthesis of
2-platinaoxetane (1) by combination of an oxo complex with
an alkene (eq 1).21 Most recently we have shown that this
reaction is proton catalyzed and that the key species that
couples with the alkene is a hydroxo complex.28
Results
BF3 Reactions in the Presence of Alkenes. In an effort to
expand the alkene exchange chemistry of eq 2 to other
alkenes, the reaction of several alkenes with 2-platina-
oxetanes 1 and 2 was explored. Ethylene pressurization of
a colorless dichloromethane solution of 2 containing 10%
BF3 results in a slow (6 h) reaction ultimately leading to a
pale yellow solution (eq 3). Acetaldehyde (14% yield
by NMR) is readily identified by NMR spectroscopy
as one of the products. The known allyl complex
[Pt(COD)(η3-(CH3)CHCHCH2)]þ (12)30 is also observed
and was isolated in crude form. 19F NMR data and IR
absorption bands are consistent with BF3(OH)- as the
counterion for 12. (BF3OH- and related anions have been
previously encountered in reactions with BF3.31-34) Only
small amounts of free NB are observed. A much cleaner
reaction occurs in C6D6, and only acetaldehyde (27%
yield) and free norbornene are detected in solution,
while allyl complex 12 precipitates as a white solid in
54% yield.
In addition, 2-platinaoxetane 1 undergoes acid-catalyzed
reversible alkene extrusion from the 2-platinaoxetane ring,
allowing alkene exchange in the ring (eq 2).
Excess isobutylene addition to a mixture of 2 and 1 equiv
of BF3 in C6D6 or CD2Cl2 affords only known allyl
complex [Pt(COD)(η3-CH2C(CH3)CH2)]þ (13)30 and free
norbornene (eq 4). No aldehyde or ketone is observed.
-
Allyl complex 13 precipitates as the BF4 salt (84%)
in C6D6 and has been characterized by single-crystal
X-ray crystallography (see Supporting Information).
If only 10% BF3 is used, the reaction stops at ∼10%
conversion, suggesting that the BF3 catalyst is con-
sumed in the formation of 13. 1H NMR spectroscopic
monitoring of the reaction shows no sign of alkene
exchange or alkene insertion for either the 10% or 1 equiv
reactions.
Complex 1 is also a useful starting material for the
preparation of other 2-platinaoxetanes by displacement
of the ancillary COD ligand and/or the oxygen-bonded
Pt(COD)Clþ Lewis acid fragment. The resulting family of
2-platinaoxetanes27 provides an opportunity to examine
changes in the chemistry as a function of the ancillary
ligands and the oxygen-bonded Lewis acid. Small mole-
cule insertion chemistry of these 2-platinaoxetanes has
been reported.29 Herein, we reported our investigation of
the effect of ancillary ligands, oxygen-bonded acids, al-
kenes, and oxidation state on the reactivity and stability of
2-platinaoxetanes. Our studies show that stability depends
on the ancillary ligands, the alkenes from which they
are formed, the presence or absence of an acid (or two)
on the oxygen atom, and, when present, the identity of the
In contrast to 2, 2-platinaoxetane 1 reacts completely
with isobutylene with only a catalytic amount of BF3
in CD2Cl2, giving again allyl complex 13 and Pt(COD)Cl2
(eq 5). In this case 1 supplies the BF4 anion and the
BF3 catalyst is not consumed. Even without added
(30) Boag, N. M.; Green, M.; Spencer, J. L.; Stone, F. G. A. J. Chem.
Soc., Dalton Trans. 1980, 1200–1207.
(31) Kerber, R. C.; Reis, K. P. J. Org. Chem. 1989, 54, 3550–3553.
(32) Liang, K.-W.; Li, W.-T.; Peng, S.-M.; Wang, S.-L.; Liu, R.-S. J.
Am. Chem. Soc. 1997, 119, 4404–4412.
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(34) Suzaki, Y.; Osakada, K. Organometallics 2006, 25, 3251–3258.
(29) Wu, J.; Sharp, P. R. Organometallics 2008, 27, 4810–4816.

Article
Organometallics, Vol. 28, No. 24, 2009 6937
BF3, 1 slowly reacts with isobutylene to give the same
products.
NB2. The role of NB2 in the reaction is not clear, but it may
bring in the needed H2O or stabilize intermediate fragments.
With 1 equiv of BF3 Et2O, 2-platinaoxetanes 7 and 8 again
Following the procedure for the alkene exchange of 1 and
2, the reactions of 2-platinaoxetanes 7-11 with NB2 in the
3
extrude norbornene. In the case of 8, the Pt-containing
product is again the hydroxo complex 16, but for 7 new
unidentified products that change with the solvent are
obtained. In CD2Cl2, the reaction mixture remains homo-
geneous and shows a major 31P NMR peak at 15.3 ppm with
JPt-P = 2926 Hz. In C6D6, an off-white precipitate is
obtained, which dissolves in CD2Cl2 to give an unknown
single 31P NMR peak at 19.0 ppm with JPt-P = 3587 Hz.
2-Platinaoxetanes 9-11 are poorly soluble in benzene, and
their reactions with acids were conducted in CD2Cl2. In
presence of BF3 Et2O were examined. However, the reac-
3
tions did not yield alkene reaction products and were gen-
erally the same as those with only the Lewis acid BF3 and are
therefore considered in the following section.
Acid Reactions. 2-Platinaoxetanes with two Lewis acids on
the oxygen atom have been implicated in Lewis acid-cata-
lyzed alkene exchange reactions (eq 1).24 In an attempt
to obtain a stable complex with two Lewis acid centers
coordinated to the oxygen atom, the bidendate Lewis acid
C6F4(BC6F5)2 (Ar = C6F5)35 was added to 2-platinaoxetane
6 (eq 6). The only identifiable products are norbornene and
the anion 14, identified by comparison its 1H and 19F NMR
spectrum with those previously reported.35
reactions with 10% BF3 Et2O, NB2 was also present but
3
did not appear to be involved in the reactions (eq 8).
Norbornene extrusion was observed in all cases (1H NMR).
Removal of the volatiles in vacuo followed by washing of the
residue with toluene to remove the NB2 yielded solid pro-
1
ducts, which were dissolved in CD2Cl2 or DMSO. The H
NMR spectra of these solutions show only unidentified
peaks associated with the PtL2 fragment (see Experimental
Section). No NB2-derived peaks are detected.
In contrast to C6F4(BC6F5)2, excess BF3 simply converts 6
to 2-platinaoxetane 2, which is stable in the presence of BF3
but susceptible to alkene exchange via coordination of a
second BF3 (eq 1).24 Stability to excess BF3 is lost when the
COD ligand of 2 is replaced by phosphine ligands. Addition
of 10% BF3 Et2O to a C6D6 mixture of 2-platinaoxetane
3
Pt(PPh3)2(C7H10OBF3) (8) causes the 1H NMR signals for 8
to disappear, signals for free norbornene to appear, and the
formation of a white precipitate (eq 7). NMR spectroscopy
of the precipitate dissolved in CD2Cl2 shows it to be a salt of
Protonation reactions were also investigated. Treatment
of Lewis-acid-free 6 with 1 equiv of HBF4 in C6D6 gave
norbornene extrusion and a white precipitate of the
BF4 salt of hydroxo complex [Pt(COD)(μ-OH)]x (17),
characterized by comparison of the 1H and 195Pt NMR
spectroscopic data with the triflate analogue [Pt(COD)-
(μ-OH)]x[OTf]x (eq 9), which has a tetrameric (x = 4)
solid-state structure but may be dimeric (x = 2) in solution.28
2þ
the hydroxo dimer [Pt(PPh3)2(μ-OH)]2 (16).36 The same
products are observed in the presence of excess NB2 or in
CD2Cl2. The identity of the counterion for 16 is unknown
but may be BF3OH-, formed by addition of adventitious
water across the O-B bond of 8.
-
xþ
The PEt3 2-platinaoxetane 7 reacts similarly with
BF3 Et2O in the presence of excess NB2 (eq 7) to give
Norbornene extrusion is also observed on HBF4 addition
to phosphine-coordinated 2-platinaoxetane 5 and newly
prepared (see Experimental Section) PPh3 and dppe analo-
gues 18 and 19 (eq 10). The identity of the Pt-containing
products has not been established, but the known hydroxo
complexes [PtL2(μ-OH)2]2þ (L2 = 2PEt3 (15), 2PPh3 (16),
dppe) are apparently not formed.36-40 Similarly, addition of
3
2þ
[Pt(PEt3)2(μ-OH)]2 (15, identified by 31P NMR spectro-
scopy37,38) but gives a mixture of products in the absence of
(35) Williams, V. C.; Piers, W. E.; Clegg, W.; Elsegood, M. R. J.;
Collins, S.; Marder, T. B. J. Am. Chem. Soc. 1999, 121, 3244–3245.
(36) Belluco, U.; Bertani, R.; Meneghetti, F.; Michelin, R. A.;
Mozzon, M. J. Organomet. Chem. 1999, 583, 131–135.
(37) Hara, K.; Taguchi, M.; Yagasaki, A. Polyhedron 2001, 20, 1903–
1905.
(39) Scarcia, V.; Furlani, A.; Longato, B.; Corain, B.; Pilloni, G.
Inorg. Chim. Acta 1988, 153, 67–70.
(40) Longato, B.; Corain, B.; Bonora, G. M.; Pilloni, G. Inorg. Chim.
(38) Mintcheva, N.; Nishihara, Y.; Tanabe, M.; Hirabayashi, K.;
Mori, A.; Osakada, K. Organometallics 2001, 20, 1243–1246.
Acta 1987, 137, 75–79.

6938 Organometallics, Vol. 28, No. 24, 2009
Wu and Sharp
PPh3AuOTf to a C6D6 solution of 6 liberates norbornene,
Scheme 1
but again known [(COD)Pt(μ-OAuPPh3)]2 ,
2þ 41 which might
be expected, could not be detected. MeOTf and 6 also gives
norbornene extrusion along with an unidentified precipitate.
toluene solution of 6 results in cleavage of the Pt-O bond,
giving Pt(II) complex 21 (eq 14). Spectral data for 21 are
almost identical to those for 20 except for the appearance of
the Pt-bonded OH proton as a singlet at 1.37 ppm in the 1H
NMR spectrum. A broad IR peak at 3455 cm-1 is assigned to
the OH groups. 1H-13C COSY reveals the norbornol OH as
a doublet at 3.31 ppm with JH-H = 7 Hz. Curiously,
although 21 is formally an H2O addition product of 6,
H2O2 is required to form 21. There is no reaction bet-
ween 6 and water under similar conditions. The H2O2 may
simply lower the pH, as H2O2 is more acidic than water,43
thereby initiating protonation of the 2-platinaoxetane
oxygen center.
The course of the reaction of 2-platinaoxetane 6 with
HCl(g) is solvent dependent. In benzene, HCl(g) addition
to 6 gives norbornene and an unidentified precipitate (eq 11).
When the reaction is performed in CD2Cl2 or CD3OD,
mixtures of HCl addition product 20 and norbornene are
observed, and in toluene/H2O only 20 forms. 2-Platina-
oxetane 1 and HCl(aq) in CH2Cl2 also give 20.
Discussion
Thermal Stability and Oxidation Reactions. In the absence
of additional Lewis acids the 2-platinaoxetanes are thermally
robust. 2-Platinaoxetane 6 and BF3 adducts 2 and 7-11 can
be heated for days at 100 °C with excess norbornene without
noticeable decomposition. 2-Platinaoxetane 1 is less stable,
and exo-2,3-epoxynorbornane is detected along with
Acid Reactivity. The acid (protic and Lewis) reactivity of
2-metallaoxetanes, both those studied here and from reports
in the literature, is summarized in Scheme 1. The coordina-
tion of an acid to the oxygen center of a 2-metallaoxetane can
give stable adducts or adducts that decompose by one of two
pathways. C-O bond cleavage (path b) results in alkene
extrusion, giving either alkene complex D or free alkene and
the fragment E. M-O bond cleavage (path a) gives hydroxo
alkyl complex C. Including the examples reported here, the
most common appears to be alkene extrusion (path b). The
2-ruthenaoxetanes, RuL4(OC(Me)(Ph)CH2) (L = a phos-
phine), react with a variety of protic and Lewis acids by path
b, extruding R-methylstyrene and giving Ru complexes from
capture of a fragment of type E.15,16 Reversible alkene
extrusion is observed for the protonated 2-platinaoxetanes
Pt(dpms)(HOC7H10) and Pt(dpms)(HOC8H14) (dpms =
dipyridylmethanesulfonate)25 and in the alkene exchange
reactions of BF3 adduct Pt(COD)(BF3OC7H10) 2 catalyzed
by BF3.24 In the latter case coordination of two BF3 appears
to be required for alkene extrusion. This is also true of the
other BF3 adducts reported here, where the presence of
additional BF3 is required for alkene extrusion. Alkene
extrusion path b is also followed for most acid reactions of
the other 2-platinaoxetanes reported here. It should be noted
that 2-molybdaoxetanes extrude alkenes even in the absence
of acids.14
42
Pt(COD)Cl2 and Pt(norbornene)3 on heating a mixture
of 1 and excess norbornene for 7 h at 60 °C (eq 12). The yield
of volatile exo-2,3-epoxynorbornane was not determined
prior to workup. After workup 1H NMR analysis indicated
only a small amount.
In contrast, treatment of 6 with 1 equiv of Br2 in CD2Cl2
immediately affords exo-2,3-epoxynorbornane in 70% yield
and Pt(COD)Br2 in quantitative yield by 1H NMR spectro-
scopy (eq 13).
These remarkably facile C-O bond cleavage reactions
contrast with the acid reactions of 2-rhodaoxetanes [Rh(N4)-
(OCH2CH2)]þ (N4 = N,N,N-tri(2-pyridylmethyl)amine or
No reaction is observed when 6 is treated with O2 or
AuCl3. However, 30% H2O2(aq) addition to a CH2Cl2 or
(41) Shan, H.; James, A. J.; Sharp, P. R. Inorg. Chem. 1998, 37, 5727–
5732.
(42) Drew, D.; Doyle, J. R. Inorg. Synth. 1990, 28, 346–9.
(43) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5
ed.; John Wiley and Sons: New York, 1988.

Article
Organometallics, Vol. 28, No. 24, 2009 6939
Scheme 2
The ethylene-derived 2-rhodaoxetanes discussed above are
in this category and have shown only ring-opening albeit in
polar solvents.
N-[(6-methyl-2-pyridyl)methyl]-N,N-di(2-pyridylmethyl)-
amine).44,45 On protonation or alkylation, these 2-rhoda-
oxetanes yield either stable adducts of type B or products
resulting from ring-opening (path a) to complexes of type C.
The C-O bond is also retained in the CO2 insertion into
the Ir-O bond of 2-iridaoxetane Cp*Ir(OC(Me2)CH2).9
Insertion likely occurs through an adduct of type B that
rearranges to the insertion product via C.
The absence of β-hydride elimination products (e.g.,
norbornone) from our norbornene-based 2-platinaoxetanes
is unexpected. This is especially so with the Lewis acid
adducts, where a relatively labile Pt-O bond should result
in facile ring-opening (path a, Scheme 1), making a site
available for β-elimination. The rigidity of the norbornene
system is certainly important in suppressing β-elimination.
Putative 2-platinaoxetanes from the more flexible alkenes
ethylene and propylene are not observed, while products
(acetaldehyde and acetone) associated with β-elimination
are. Similarly, 2-rhodaoxetanes from ethylene undergo
β-elimination on protonation, giving acetaldehyde. Yet,
the rigid Rh complex 22, which is a ring-opened protonated
2-rhodaoxetane of type C, undergoes β-elimination, giving
norbornenone.48 The difference is likely the position of the
nonbridgehead β-hydrogen atom. In our 2-platinaoxetanes,
where the ring is formed by intramolecular addition of a
Pt-O bond across the norbornene double bond,28 the Pt and
O atoms are syn with both atoms exo on the norbornane
skeleton (F). The β-hydrogen atom is therefore anti to the Pt
atom and inaccessible for elimination.49 In contrast, 22 is
formed by intramolecular OH- attachment on coordinated
norbornadiene. As a result, the Rh and oxygen atoms are
anti and the Rh and β-hydrogen atoms are syn (G), thus
facilitating elimination. Interestingly, this suggests that
rigid alkene oxidation through an intramolecular addition
mechanism will not readily give ketones, and alternate
products such as epoxides may form instead.
Alkene Extrusion Products. Scheme 3 shows proposed
pathways for the various products formed from BF3-induced
alkene extrusion from 2-platinaoxetanes 2, 7, and 8. Previous
results suggest that coordination of a second BF3 to the
oxygen atom of 2 induces C-O bond scission to give inter-
mediate 23 (L2 = COD). A similar reaction is presumed
for the other 2-platinaoxetanes. The fate of 23 apparently
depends on the identity of the ancillary ligands (L/L2). For
COD, 2 and 23 are in equilibrium, with 2 favored, but in the
presence of an alkene norbornene is displaced from 23 to give
24, which then goes on to follow one of two reaction channels
depending on the presence or absence of an allylic hydrogen
atom. With an allylic hydrogen atom (isobutylene) proton
transfer from the alkene to the oxygen center of 24 yields
observed allyl complex 13. Ethylene, lacking an allylic
hydrogen atom, follows the second channel, giving acetalde-
hyde oxo-alkene coupling. The low yield of acetaldehyde
and the formation of allyl complex 12 indicate that other
The solvent-dependent reactivity of 2-platinaoxetane 6
with HCl is noteworthy. Under polar conditions ring-
opening (path a) to hydroxo alkyl complex 20 (path a) is
observed, while under nonpolar conditions norbornene is
extruded (path b). The dissociation state of the HCl in the
hydrogen-bonding solvents could be important in the diver-
gent reactivity, but the observation of both products in
CH2Cl2 suggests that this is not a major factor. Instead,
solvent stabilization of the expectedly more polar ring-opened
product (C) is probably the cause. Greater solvent stabiliza-
tion of the ring-opened product would favor its formation over
norbornene extrusion. We recently reported spectroscopic
evidence of a solvent-induced weakening of the Pt-O bond
in 2-platinaoxetane 5.27 This was detected as a decrease in the
195Pt-31P coupling for the P atom trans to the oxygen atom as
the solvent was changed from CD2Cl2 to C6D6, suggesting
solvent stabilization of a more polar form (Scheme 2).46
These results suggest that the chemistry of other 2-metal-
laoxetanes may change with solvent. The 2-ruthenaoxetane
acid reactions, where alkene extrusion was observed, were
conducted in nonpolar solvents and may show a shift in
reactivity in polar solvents. On the other hand, the 2-rho-
daoxetane acid reactions, where C-O bond retention was
observed, were conducted in polar solvents. Alkene extru-
sion may be observed in low-polarity solvents. Solvent-
dependent 2-metallaoxetane ring-opening has implications
for Wacker alkene oxidation. If formation of a protonated
2-palladaoxetane occurs in Wacker chemistry, either by OH
coordination of an intermediate hydroxyethyl complex or by
internal Pd-OH attachment on a coordinated alkene,6 the
stability of the C-O bond should be most favorable in polar
solvents, exactly the conditions used for Wacker chemistry.47
Another potential factor in competitive ring-opening and
alkene extrusion is the rigidity of the metallaoxetane ring
system. The norbornene-derived 2-platinaoxetanes lack
C-C bond rotation, so that even when ring-opening occurs,
the oxygen atom is held in close proximity to the Pt center.
This would encourage ring-reclosing and promote alkene
extrusion over ring-opening. More flexible ring systems
allow C-C bond rotation of the O atom away from the
metal center, decreasing the opportunity for ring-reclosing.
(44) de Bruin, B.; Boerakker, M. J.; De Gelder, R.; Smits, J. M. M.;
Gal, A. W. Angew. Chem., Int. Ed. 1999, 38, 219–222.
(45) de Bruin, B.; Boerakker, M. J.; Verhagen, J. A. W.; de Gelder, R.;
Smits, J. M. M.; Gal, A. W. Chem.;Eur. J. 2000, 6, 298–312.
(46) Allen, F. H.; Pidcock, A. J. Chem. Soc. A 1968, 2700–2704.
(47) Takacs, J. M.; Xun-tian Jiang, J. M. Curr. Org. Chem. 2003, 7,
369.
(48) Hetterscheid, D. G. H.; Smits, J. M. M.; de Bruin, B. Organo-
metallics 2004, 23, 4236–4246.
(49) A related norbornene-derived azametallaoxetane also appears to
be resistant to β-elimination: Casalnuovo, A. L.; Calabrese, J. C.;
Milstein, D. J. Am. Chem. Soc. 1988, 110, 6738–44.

6940 Organometallics, Vol. 28, No. 24, 2009
Wu and Sharp
Scheme 3
Scheme 4
the PtIV 2-platinaoxetanes 29 (Scheme 4). Low stability
of the PtIV oxidation state of 29 would be expected
with the π-acid COD ligand and the high stability of the
Pt(COD)Br2 product.
These thermal reactions should be contrasted with
the photolytic extrusion of acetone from the IrIII 2-metalla-
oxetane Cp*Ir(OC(Me2)CH2), leaving a stable methylene
complex.10
Conclusions
Acid reactions of 2-metallaoxetanes appear to have three
possible outcomes: (1) formation of a stable oxygen adduct,
(2) alkene extrusion, or (3) formation of a hydroxo alkyl
complex. While the rigidity of the 2-metallaoxetane ring
system may be important in the direction the reaction takes,
in at least some cases reactivity can be switched from alkene
extrusion to hydroxo alkyl formation by increased solvent
polarity. Reversible alkene extrusion appears uncommon
and has been observed only for PtII 2-platinaoxetanes with
COD or dpms ancillary ligands. In the absence of acids, PtII
2-platinaoxetane are thermally robust, but oxidation to a
PtIV 2-platinaoxtane facilitates epoxide reductive elimina-
tion, supporting the viability of late metal 2-metallaoxetane
intermediates in alkene oxidation to epoxides.22,25
pathways are also operative. With other L or L2, including
the dppe and diimine complexes 9-11, norbornene is lost
from 23 and the resulting PtL2(O(BF3)2) fragment is not
captured by another alkene. Instead, the electrophilic PtL2-
(O(BF3)2) fragment must follow other uncharacterized reac-
tion pathways. In the case of L = PEt3 and PPh3 the
fragment scavenges adventitious water, yielding the hydroxo
complexes [PtL2(μ-OH)]22þ 15 and 16.
Experimental Section
Norbornene extrusion from the 2-platinaoxetane reac-
tions with Hþ, Meþ, and PPh3Auþ give identified products
only in the case of 6 and Hþ. Known hydroxo 17 is produced
presumably via the fragment [Pt(COD)(OH)]þ. With the
phosphine and bypiridine complexes the known39,50,51 di-
meric hydroxo complexes are not observed, suggesting that
the [PtL2(OH)]þ fragment for these ligands do not survive
long enough to dimerize. Similarly, known41 [Pt(COD)-
Experiments were performed under a dinitrogen atmosphere
in a Vacuum Atmospheres Corporation drybox or on a Schlenk
line. Solvents were dried by standard techniques and stored
under dinitrogen over 4 A molecular sieves or sodium metal.
Alkenes, PPh3, dppe, BF3 Et2O, 30% H2O2, HBF4 Et2O, and
3
3
MeOTf were purchased from Aldrich or Acros. Anhydrous
hydrogen chloride was obtained from Scott Specialty Gases,
Inc. All commercial chemicals were used as received except
where noted. PPh3AuOTf was prepared by metathesis of
PPh3AuCl with AgOTf in CH2Cl2. Deuterated solvents were
obtained from Cambridge Isotope Laboratories. CD2Cl2 was
dried over activated alumina. C6D6 and toluene-d8 were dried
over sodium metal. The bidentate Lewis acid C6F4(BArF2)2 was
prepared by a literature procedure.35 Complexes 1, 2, and 5-11
were synthesized as described previously.21,24,27 Complexes 18
and 19 were prepared as described below following procedures
for related 5.27 GC-MS experiments were performed using an
HP 6890 GC-5973 MSD instrument. NMR spectra were re-
corded on Bruker AMX-250, -300, or -500 spectrometers at
ambient probe temperatures. Data are given in ppm relative
2þ
(μ-OAuPPh3)]2 is not observed in the reaction of 6 with
PPh3Auþ; even this would be expected to form from the
[Pt(COD)(μ-OAuPPh3)]þ fragment resulting from norbor-
nene extrusion.
Epoxide Formation. Epoxides are the most desirable pro-
ducts from alkene oxidation. Their formation from 2-metal-
laoxetanes has only recently been observed and appears
difficult for d8-complexes. Epoxide elimination from a d8-
AuIII 2-auraoxetane22 takes days at room temperature, and
our d8-PtII 2-platinaoxetanes are quite stable, with only 1
showing evidence of epoxide elimination on thermolysis.
Recently PtIV 2-platinaoxetanes, prepared by oxidation of
PtII 2-platinaoxetanes with H2O2 or O2, were reported to
eliminate epoxides.25 Even these complexes required heating
for hours at 60-80 °C to observe elimination. In contrast,
the Br2-induced elimination of epoxide from 6 is immediate
at room temperature. Elimination presumably occurs from
1
to solvent signals referenced to TMS for H and 13C spectra
or relative to external standards for 195Pt (K2PtCl4/D2O
at -1624 ppm), 31P (85% H3PO4 at 0.0 ppm), and 19F (CFCl3
at 0.0 ppm). Atom numbering for the peak assignments is given
below. IR samples were prepared by evaporation of a CH2Cl2
solution onto a NaCl plate. Desert Analytics, Inc. performed the
elemental analyses (inert atmosphere). Inclusion of solvent of
crystallization in the elemental analyses was confirmed by NMR
spectroscopy.
(50) Bushnell, G. W.; Dixon, K. R.; Hunter, R. G.; McFarland, J. J.
Can. J. Chem. 1972, 50, 3694.
(51) Singh, A.; Anandhi, U.; Cinellu, M. A.; Sharp, P. R. Dalton
Pt(PPh3)2(OC7H10) (18). From Pt(COD)(OC7H10) (6). PPh3
(9.5 mg, 0.036 mmol) in 0.1 mL of C6D6 was added dropwise to
Trans. 2008, 2314–2327.

Article
Organometallics, Vol. 28, No. 24, 2009 6941
an agitated solution of 6 (7.5 mg, 0.018 mmol) in 0.4 mL of
C6D6. After 5 min, the volatiles were removed in vacuo. The
resulting oily residue was dissolved in toluene, and the mixture
was evaporated to dryness and left in vacuo for 2 h. This
procedure was repeated two or three times until residual COD
was eliminated and a solid residue was obtained. The residue
was washed with cold hexane and dried in vacuo to give white
solid 18. Yield: 12.1 mg (81%). From [Pt2(COD)2(OC7H10)-
Cl]BF4 (1). PPh3 (12.3 mg, 0.047 mmol) in 0.1 mL of CH2Cl2 was
added to a solution of 1 (8.0 mg, 0.0095 mmol) in 0.4 mL of
CH2Cl2. After 10 min, excess hexane was added and a white
precipitate of [Pt(PPh3)3(Cl)]BF4 formed. The clear solution was
decanted off the precipitate and evaporated in vacuo to give
white solid 18. Yield: 6.2 mg, 78%. Anal. Calcd (found) for
1.28 (m, 1H, H5), 0.96 (d, JH-H = 8.7 Hz, 1H, H70), 0.77 (br m,
2H, H40 and H50), 0.66 (br m with satellites, JPt-H = 44 Hz, 1H,
1
H2). Overlapping peaks detected by H-13C HMQC. Assign-
ments by DEPT-135 and 1H-1H COSY. 13C{1H} NMR
(75.5 MHz, CD2Cl2): 133.4 (dd, JP-C = 11, 4 Hz, Ph), 133.3
(s, Ph), 133.1 (s, Ph), 132.9 (s, Ph), 132.8 (s, Ph), 132.5(s, Ph),
131.0 (d, JP-C = 6 Hz, Ph), 130.8 (s, Ph), 129.2 (dd, JP-C
=
10 and 2 Hz, Ph), 129.0 (s, Ph), 128.8 (s, Ph), 128.7 (s, Ph) 102.1
(s, C1), 45.6 (C6), 40.4 (C3), 36.5 (C7), 33.5 (d, JP-C = 12 Hz,
C4), 30.2 (dd, 1JP-C = 38 Hz, 3JP-C = 20 Hz, CH2PPh2), 24.7
(dd, 1JP-C = 32 Hz, 3JP-C = 9 Hz, CH2PPh2), 23.4 (s, C5). 31
P
NMR (101 MHz, CD2Cl2): 39.0 (d with satellites, JPt-P = 1611
Hz, JP-P = 11 Hz), 29.0 (d with satellites, JPt-P = 3497 Hz,
JP-P = 11 Hz). 195Pt NMR (64 MHz, CD2Cl2): -3926 (dd,
C43H40OP2Pt 0.75CH2Cl2: C, 58.81 (58.59); H, 4.68 (5.10).
J
Pt-P = 1643 and 3552 Hz).
3
Reaction of Pt(COD)(BF3OC7H10) (2) with Ethylene and
Catalytic BF3. A medium-walled NMR tube was charged with
a solution of 2 (7.2 mg, 0.0075 mmol) and 5% BF3 Et2O (1.2 μL
3
of a solution prepared by adding 15 μL of BF3 Et2O to 485 μL of
3
CDCl3) in CD2Cl2 (0.5 mL). The tube was connected to a
vacuum line, immersed into liquid nitrogen, and evacuated.
Ethylene (5 mL, 0.2 mmol at 25 °C, 1 atm) was added by vacuum
transfer, and then the tube was flame-sealed and allowed to
warm to room temperature. The reaction was monitored by 1H
NMR spectroscopy. Free norbornene, acetaldehyde, and a
transient with a peak at 8.93 ppm (t, JH-H = 7 Hz) were
observed early in the reaction. Free norbornene and the tran-
sient disappeared and acetaldehyde increased as the reaction
progressed. After ∼6 h the reaction was complete, yielding
1H NMR (300 MHz, CD2Cl2): 7.42 (m), 7.26 (m) and 7.16 (m)
(30H, Ph), 6.02 (br s with poorly resolved satellites (shoulders),
JPt-H ≈ 30 Hz, 1H, H1), 2.78 (d, JH-H = 10 Hz, 1H, H7), 1.91
(br s, 1H, H6), 1.17 (br s, 3H, overlapping H3, H4, and H5), 0.89
(d, JH-H = 10 Hz, 1H, H70), 0.66 (br m, 1H, H50), 0.36 (br m,
1H, H40), 0.23 (br s with poorly resolved satellites (shoulders),
JPt-H ≈ 30 Hz, 1H, H2). Overlapping peaks detected by 1H-13C
HMQC. Assignments by DEPT-135 and 1H-1H COSY
(unresolved coupling between H1 and H2 observed). 13C{1H}
NMR (75.5 MHz, CD2Cl2): 134.2 (d, JP-C = 11.3 Hz, Ph),
129.7 (s, Ph), 129.3(s, Ph), 127.2 (dd, JP-C = 10.1 and 30.2 Hz,
Ph), 99.7 (s, C1), 45.4 (s, C6), 39.2 (s, C3), 35.5 (s, C7), 32.2 (s,
C4), 22.4 (s, C5). 31P NMR (101 MHz, CD2Cl2): 20.9 (br s with
1
∼17% acetaldehyde by H NMR spectroscopy. The volatiles
were removed in vacuo, and the residue was dissolved in
minimum CH2Cl2. Addition of excess ether gave an off-white
solid consisting of crude allyl complex [Pt(COD)(η3-CH2-
CHCH(CH3))]þBF3OH- (12) with other minor products.
Increasing the amount of BF3 Et2O from 5% to 10% gave the
3
same result.
With 1 equiv of BF3 the amount of the transient increased and
it became persistent, but about the same yield of acetaldehyde
was obtained. Both the acetaldehyde and the intermediate
disappeared when the reaction mixture was left overnight.
In C6D6, the reaction of 2 and ethylene with catalytic amounts
satellites, JPt-P = 1502 Hz), 15.1 (br s with satellites, JPt-P
=
3796 Hz). 31P NMR (101 MHz, CD2Cl2, -70 °C): 20.06 (d with
satellites, JPt-P = 1527 Hz, JP-P = 4 Hz), 15.10 (d with
satellites, JPt-P = 3773 Hz, JP-P = 4 Hz). 31P NMR (101
MHz, C6D6): 19.84 (br s with satellites, JPt-P = 1489 Hz), 16.54
(br s with satellites, JPt-P = 3721 Hz). 195Pt NMR (64 MHz,
C6D6): -3861 (dd, JPt-P = 1522 and 3793 Hz).
of BF3 Et2O gives a white precipitate of 12 (54% yield). The 1H
3
NMR spectrum of the solution showed the presence of acet-
aldehyde (∼28%) and free NB. Allyl complex 12 was identified
Pt(dppe)(OC7H10) (19).
A solution of dppe (7.5 mg,
1
by comparison of its H NMR spectrum with previously re-
0.018 mmol) in 0.1 mL of CD2Cl2 was added dropwise to an
agitated solution of Pt(COD)(OC7H10) (6) (7.3 mg, 0.018 mmol)
in 0.4 mL of CD2Cl2. After 15 min, the volatiles were removed in
vacuo. The resulting oily residue was dissolved in toluene, and
the mixture was evaporated to dryness and left in vacuo for 2 h.
This procedure was repeated two or three times until residual
COD was eliminated and a solid residue was obtained. The
residue was dissolved in minimum CH2Cl2, and excess hexane
was added to precipitate white solid 19. The solution was
carefully decanted off the product, which was washed with
hexane and dried in vacuo. Yield: 10.8 mg (84%).
ported [Pt(COD)(η3-CH2CHCH(CH3))]BF4.18 IR absorption
bands at 1440, 1200-1060, 880, 802, and 3442 (br) cm-1 and 19
F
NMR shifts (235 MHz, CDCl3) of -151.19 (10B) and -151.24
(11B) ppm suggest that the counteranion for 12 is BF3OH-.31-34
195Pt NMR (64 MHz, CD2Cl2): -4397.
Reaction of Pt(COD)(BF3OC7H10) (2) with Isobutylene and
BF3: [Pt(COD)(η3-CH2C(CH3)CH2)][BF4] (13). A medium-
walled NMR tube was charged with a solution of 2 (5.7 mg,
0.012 mmol) and BF3 Et2O (1.4 μL, 0.012 mmol) in C6D6
3
(0.5 mL). The tube was connected to the vacuum line, immersed
into liquid nitrogen, and evacuated. Isobutylene (5 mL,
0.2 mmol at 25 °C) was added by vacuum transfer. The tube
was then flame-sealed and allowed to warm to room tempera-
ture. The NMR tube was shaken by hand. A precipitate formed
and the reaction appeared complete after ca. 20 min. Free
norbornene was observed by 1H NMR spectroscopy. The
volatiles were removed in vacuo. The residue was dissolved in
minimum CH2Cl2, and excess diethyl ether addition gave a
white precipitate of [Pt(COD)(η3-CH2C(CH3)CH2)][BF4] (13).
The solution was carefully decanted off the product, which was
washed with hexane and dried in vacuo. Yield: 4.5 mg (83%).
Spectroscopic data match those previously reported.18 Colorless
single crystals for X-ray analysis were grown by slow evapora-
tion of a CH2Cl2 solution of 13 at -30 °C. A reaction in CD2Cl2
gave similar results. 195Pt NMR (64 MHz, CD2Cl2): -4374.
Anal. Calcd (found) for C33H34OP2Pt: C, 56.3 (56.0); H, 4.9
(5.3). 1H NMR (500 MHz, CD2Cl2): 7.85 (m), 7.63 (m) and 7.43
(m) (20H, Ph), 6.30 (br s with satellites, JPt-H = 45 Hz, 1H, H1),
2.68 (d, JH-H = 8.7 Hz, 1H, H7), 2.39 (m, 1H, PCH2), 2.09
(m, 1H, PCH2), 2.05 (m, 2H, PCH2), 1.98 (m, 1H, H6), 1.70
(br s with satellites, JPt-H = 39 Hz, 1H, H3), 1.41 (m, 1H, H4),

6942 Organometallics, Vol. 28, No. 24, 2009
Wu and Sharp
Reaction of [Pt2(COD)2(OC7H10)Cl]BF4 (1) with Isobutylene
and Catalytic BF3. A medium-walled NMR tube was charged
with a solution of 1 (18 mg, 0.021 mmol) in CD2Cl2 (0.5 mL) and
(300 MHz) of the filtrate showed complete loss of the peak at
6.08 ppm for 9 and appearance of free NB. The volatiles were
removed in vacuo. The resulting residue was washed with
toluene (to remove NB2) and dried in vacuo. A 1H NMR
spectrum of the solid in CD2Cl2 gave 1H peaks at 7.75 (m),
7.63 (m), 7.40 (m), 2.34 (s), and 2.37 (s) ppm. The 31P NMR
spectrum showed peaks at 48.7, 47.9, and 34.4 ppm with no 195Pt
satellites.
BF3 Et2O (8.5 μL of a solution of 15 μL in 485 μL of CDCl3,
3
0.0021 mmol). The tube was connected to the vacuum line,
immersed into liquid nitrogen, and evacuated. Isobutylene
(5 mL, 0.2 mmol at 25 °C) was added by vacuum transfer, and
then the tube was flame-sealed and allowed to warm to room
temperature. The tube was shaken, and the reaction was com-
plete after 6 h, over which time the solution changed from
colorless to pale yellow and finally yellow. The 1H NMR
spectrum of the reaction mixture showed the presence of free
norbornene, Pt(COD)Cl2, and allyl complex 13 (62% by
1H NMR spectroscopy).
L2 = But2bpy (10). Excess NB2 (2.4 mg, 9.2 ꢀ 10-3 mmol) was
added to a solution of 10 (0.3 mg, 4.7 ꢀ 10-4 mmol) in 0.4 mL of
CD2Cl2, and then 0.2 μL of a solution of 15 μL of BF3 Et2O in
3
485 μL of CDCl3 was added. After 20 min, a 1H NMR spectrum
of the mixture showed free NB and other new peaks. The
volatiles were removed in vacuo, and the resulting residue was
dissolved in minimum CH2Cl2 and excess hexane was added.
A white precipitate formed, which was isolated by decantation.
The solid was washed with toluene and dried in vacuo. 1H NMR
(500 MHz) data for the solid in CD2Cl2: 8.86 (d, JH-H = 7 Hz,
0.67H), 8.68 (d, JH-H = 7 Hz, 0.53H), 8.35 (d, JH-H = 7 Hz,
0.78H), 8.17 (d, JH-H = 2 Hz, 0.58H), 7.89 (m, 0.58H), 7.66 (m,
0.73H), 6.78 (s, 0.37H), 6.64 (s, 0.26H), 6.30 (br s, 0.94H), 3.90
(br s, 0.55H), 3.06 (m, 1.26H), 2.72 (d, JH-H = 9 Hz, 1.25H),
2.44 (s, 0.43H), 2.34 (s, 0.48H), 2.30 (s, 0.45H), 1.54 (s, 0.84 H),
1.48 (s, 2.59H), 1.45 (s, 1.56H).
Reaction of Pt(COD)(C7H10O) (6) with C6F4(BAr2)2 (Ar =
C6F5). C6F4(BAr2)2 (14.2 mg, 0.017 mmol) was added to a
solution of 6 (7.0 mg, 0.017 mmol) in 0.5 mL of CD2Cl2. After
1
5 min, the H and 19F NMR spectra showed the presence of
[C6F4(BAr2)2(μ-OH)]- (14).23
Reaction of Pt(PPh3)2(C7H10OBF3) (6) with BF3. Formation
of [Pt(PPh3)2(μ-OH)]22þ (16). In C6D6. Catalytic BF3 (2.5 μL
of a solution prepared by adding 15 μL of BF3 Et2O to 485 μL of
CDCl3) was added to a solution of 6 (5.5 mg, 0.0060 mmol) in
3
1
0.4 mL of C6D6. Free norbornene was observed by H NMR
spectroscopy, and a white precipitate formed. After the solution
was carefully decanted off, the precipitate was dissolved in
CD2Cl2 and a 31P NMR spectrum showed the formation of 16.36
In CD2Cl2. Catalytic BF3 (2.5 μL of a solution prepared by
L2 = Me2bpy (11). Excess NB2 (2.4 mg, 9.2 ꢀ 10-3 mmol) was
added to a solution of 11 (2.4 mg, 3.8 ꢀ 10-3 mmol) in 0.4 mL of
CD2Cl2, and then 0.7 μL of a solution of 15 μL of BF3 Et2O in
3
485 μL of CDCl3 was added. After 1 h, a pale yellow precipitate
formed. The mixture was filtered, and a 1H NMR spectrum of
the filtrate showed free NB. The precipitate was washed with
toluene and dried in vacuo. A 1H NMR spectrum of the
precipitate in DMSO showed only Me2bpy peaks: 9.46 (d,
JH-H = 6 Hz, 1H), 9.15 (d, JH-H = 6 Hz, 1H), 8.88 (d,
adding 15 μL of BF3 Et2O to 485 μL of CDCl3) or stoichio-
3
metric BF3 (0.7 μL of BF3 Et2O) was added to a solution of 6
3
(5.5 mg, 0.0060 mmol) in 0.5 mL of CD2Cl2. Free NB was
observed in the H NMR spectra of the mixtures, and the 31P
NMR spectra showed only one peak at 7.8 ppm with JPt-P =
3745 Hz, indicating the presence of known [Pt(PPh3)2-
1
JH-H = 6 Hz, 1H), 9.46 (d, JH-H = 6 Hz, 1H), 8.69 (s, 1.5H),
(μ-OH)]22þ (16).36
8.64 (s, 1.5H), 8.52 (d, JH-H = 6 Hz, 1H), 8.23 (s, 1H), 7.83 (m,
3H), 7.28 (m, 1H), 2.30 (s, 6H).
Reaction of Pt(COD)(C7H10O) (6) with HBF4, PPh3AuOTf,
Excess NB2. Excess NB2 (19.3 mg, 7.5 ꢀ 10-2 mmol) was
added to a solution of platinoxetane 6 (7.5 ꢀ 10-3 mmol) in
0.5 mL of CD2Cl2, and then 3 μL of a solution of 15 μL of
or MeOTf in C6D6. HBF4. HBF4 Et2O (1.5 μL, 0.011 mmol)
3
BF3 Et2O in 485 μL of CDCl3 (7.5 ꢀ 10-4 mmol) was added.
was added to an agitated solution of 6 (4.7 mg, 0.011 mmol) in 0.4
mLofC6D6. Theclearsolutionimmediatelybecame cloudy. After
20 min, a yellow precipitate formed and a 1H NMR spectrum of
the mixture showed the presence of free norbornene. The clear
solution was carefully decanted off the precipitate, which was
washed with ether and dried in vacuo. NMR data identified the
3
After 10 min a 31P NMR spectrum showed the formation of
[Pt(PPh3)2(μ-OH)]22þ (16).36
Reaction of Pt(PEt3)2(C7H10OBF3) (5) with BF3. 1 equiv of
BF3 in CD2Cl2. One equivalent of BF3 Et2O (0.9 μL, 7.5 ꢀ 10-3
3
mmol) was added to a solution of 5 (4.6 mg, 7.5 ꢀ 10-3 mmol) in
0.5 mL of CD2Cl2. Free NB was observed in the 1H NMR
spectrum of the solution, and the 31P NMR spectrum showed a
major peak at 15.3 ppm with JPt-P = 2926 Hz.
precipitate (17) as the BF4- salt of [Ptx(COD)x(μ-OH)4]xþ 28 1
H
.
NMR (300 MHz, CD3NO2): 5.65 (s, JPt-H = 69 Hz, 4H, COD
CH), 2.81 (br s, 4H, COD CH2), 2.37 (m, 4H, COD CH2). 195Pt
NMR (64 MHz, CD3NO2): -2794. 19F NMR (235 MHz,
CD3NO2): -151.4.
1 equiv of BF3 in C6D6. As above but in C6D6 instead of
CD2Cl2. An off-white precipitate was obtained, which dissolves in
=
CD2Cl2 to give a single 31P NMR peak at 19.0 ppm with JPt-P
PPh3AuOTf. PPh3AuOTf (7.4 mg, 0.012 mmol) was added to
an agitated solution of 6 (5.0 mg, 0.012 mmol) in 0.5 mL of
C6D6. After 10 min, a 1H NMR spectrum of the mixture showed
the presence of free norbornene. A 31P NMR spectrum showed a
major peak at 29.4 ppm with no satellites and a very minor peak
at 44.5 ppm. The same reaction in CD2Cl2 gave a black
3587 Hz.
10% BF3. Addition of catalytic BF3 (8 μL of a solution of 15
μL of BF3 Et2O in 485 μL of CDCl3) to a solution of 5 (11 mg,
3
0.022 mmol) in 0.5 mL of CH2Cl2 gave two major 31P NMR
peaks at 7.90 ppm (JPt-P = 3799 Hz) and 6.80 ppm (JPt-P =
1
3771 Hz).
10% BF3 and Excess NB2: Formation of [Pt(PEt3)2(μ-
precipitate, and a H NMR spectrum of the mixture showed
the presence of free norbornene. A 195Pt NMR spectrum gave
two peaks at -2965 and -3099 ppm. The 31P NMR spectrum
showed no peaks.
2þ
OH)]2 (15). Excess NB2 (19.3 mg, 7.5 ꢀ 10-2 mmol) was
added to a solution of the platinaoxetane (7.5 ꢀ 10-3 mmol) in
0.5 mL of CD2Cl2, and then 3 μL of a solution of 15 μL of
MeOTf. MeOTf (0.9 μL, 0.008 mmol) was added to an
agitated solution of 6 (3.3 mg, 0.008 mmol) in 0.5 mL of
C6D6. After 10 min, a 1H NMR spectrum indicated the reaction
was only partially completed. New peaks at 5.74 (m), 4.18
(d, JH-H = 5.2 Hz), 2.18 (d, JH-H = 5.5 Hz), and 2.05 (m)
together with minor free NB peaks were observed. After 3 h, a
white precipitate formed and a 1H NMR spectrum of the
mixture showed large amounts of free NB.
BF3 Et2O in 485 μL of CDCl3 (7.5 ꢀ 10-4 mmol) was added.
3
1
After 10 min a H NMR spectrum of the solution showed the
presence of free NB, and a 31P NMR spectrum showed the
2þ
formation of [Pt(PEt3)2(μ-OH)]2 (15) as a singlet with satel-
lites at 7.2 ppm (JPt-P = 3481 Hz).37,38
Reaction of PtL2(C7H10OBF3) with Catalytic BF3. L2 = dppe
(9). Excess NB2 (2.8 mg, 1.1 ꢀ 10-2 mmol) was added to a
solution of 9 (2.4 mg, 3.1 ꢀ 10-3 mmol) in 0.5 mL of CD2Cl2,
Reaction of PtL2(C7H10O) with HBF4. L = PEt3 (5). Addi-
tion of 1 equiv of HBF4 Et2O to a solution of 5 in C6D6 results in
and then 0.6 μL of a solution of 15 μL of BF3 Et2O in 485 μL
3
3
of CDCl3 was added. After 20 min, a 1H NMR spectrum
a white precipitate and free NB. 31P NMR data for a solution of

Article
Organometallics, Vol. 28, No. 24, 2009 6943
the precipitate in CDCl3: 19.6 (s, JPt-P = 3585 Hz, 1P), 11.9 (s,
JPt-P = 2393 Hz, 1P).
L = PPh3 (18). Addition of 1 equiv of HBF4 Et2O to
a solution of 18 in C6D6 resulted in a white precipitate and
free NB. 31P NMR data for a solution of precipitate in CDCl3:
23.64 ppm (d, JPt-P = 2484 Hz, JP-P = 19 Hz, 2P), 13.02 ppm
(t with satellites, JP-P = 19 Hz, JPt-P = 3826 Hz, 1P).
Thermolysis of [Pt2(COD)2(OC7H10)Cl]BF4 (1) with Excess
NB. Complex 1 (54 mg, 0.064 mmol), 4 mL of CH2Cl2, and
excess NB (70 mg, 0.73 mmol) were placed in a sealable 25 mL
Schlenk tube. The tube was sealed, and the mixture was heated
at 60 °C for 7 h. The solvent and excess NB were removed by
placing the sample under high vacuum for 4 h. The resulting
solid was extracted with 2 ꢀ 5 mL of hexane. The combined
extracts were evaporated to dryness. A proton NMR spectrum
in CD2Cl2 showed the presence of Pt(NB)3 with trace amounts
of exo-2,3-epoxynorbornane. A 1H and 195Pt NMR spectra
of the hexane insoluble residue showed the presence of
Pt(COD)Cl2.
3
L2 = dppe (19). HBF4 Et2O (1 equiv) was added to a solution
3
of 19 in CH2Cl2, giving free NB. 31P NMR data for the mixture:
42.4 (s, JPt-P = 3585 Hz, 1P), 44.6 (d, JP-P = 30 Hz, 1P),
29.5 (d, JP-P = 30 Hz, 1P). Pt-P coupling was not observed for
the last two phosphine peaks.
Reaction of Pt(COD)(C7H10O) (6) with H2O/HCl: Pt(COD)-
(C7H10OH)Cl (20). H2O (0.8 μL, 0.044 mL) was injected into
a solution of 6 (4.5 mg, 0.011 mmol) in 0.5 mL of toluene-d8.
The mixture was monitored by 1H NMR spectroscopy. No
reaction was observed overnight. Anhydrous HCl gas (0.24 mL,
0.011 mmol) was injected into the mixture. Complex 20 was
immediately formed. The solution was evaporated to dryness to
give 20 as a white solid (quantitative). Anal. Calcd (found) for
C15H23ClOPt: C, 40.1 (40.9); H, 5.1 (4.4).
Reaction of [Pt(COD)(OC7H10) (6) with Br2. Br2 (1.4 μL,
0.027 mmol) was injected into an agitated solution of 6 (11 mg,
0.027 mmol) in 0.5 mL of CD2Cl2. A 1H NMR spectrum of the
homogeneous reaction mixture showed the presence of exo-2,3-
epoxynorbornane in ca. 70% yield. The pale yellow mixture was
reduced to ∼0.1 mL, and some precipitate appeared. Addition
of excess hexane gave complete precipitation of Pt(COD)Br2.
The filtrate was used for GC-MS analysis. The exo-2,3-epox-
ynorbornane peak showed Mþ = 110 (tR = 4.97 min) and was
compared with an authentic sample.
Pt(COD)(OH)(C7H10OH) (21). A 6.0 μL (0.058 mmol)
amount of 30% aqueous H2O2 was added to a stirred solution
of 6 (11 mg, 0.027 mmol) in 1 mL of CH2Cl2. After 5 min the
reaction mixture was evaporated to dryness. The resulting
residue was extracted with 2 ꢀ 1 mL of benzene. The extract
was evaporated to dryness to give 21 as a white solid. Yield:
6.7 mg, 59%. The reaction is much slower in toluene but gives
similar results.
1H NMR (300 MHz, C6D6): 5.27 (m, 2H, COD CH),
4.15 (apparent t, JH-H = 6.9 Hz, 1H, H1), 4.08 (td with satellites,
JH-H = 7.5, 3 Hz, JPt-H = 75 Hz, 1H, COD CH), 3.96 (td with
satellites, JH-H = 7.5, 3 Hz, JPt-H = 75 Hz, 1H, COD CH), 3.30
(d, JH-H = 7.2 Hz, 1H, OH), 2.65 (d, JH-H = 10.0 Hz, 1H, H7),
2.52 (br s, 1H, H6), 2.20 (d with satellites, JH-H = 1.8 Hz, JPt-H =
24 Hz, 1H, H3), 2.16 (dd, JH-H = 6.3, 1.8 Hz, 1H, H2), 1.78, 1.56,
1.46, and 1.31 (m’s, 8H total, COD CH2), 1.45 (m, 2H, H4 and H5),
1.18 (d, JH-H = 10.0 Hz, 1H, H70), 0.99 (m, 2H, H40 and H50).
Assignments were made by comparison to the spectra for the OH
analogue 21 (see below). 195Pt NMR (64 MHz, C6D6): -3459.
Reaction of Pt(COD)(C7H10O) (6) with HCl(g). Anhydrous
HCl(g) (0.27 mL, 0.012 mmol) was injected into a solution of 6
(5.0 mg, 0.012 mg) in 0.5 mL of the following deuterated solvents,
and the reaction was monitored by 1H NMR spectroscopy.
C6D6. A precipitate formed, and only free NB was detected in
solution. Complex 20, which is soluble in C6D6, was not
observed. The precipitate dissolved in CDCl3 to give 1H NMR
(300 MHz, CDCl3): 5.59 (s, JPt-H = 68 Hz, COD CH), 2.69 (br
m, COD CH2), 2.26 (m, COD CH2).
Anal. Calcd (found) for C15H24O2Pt: C, 41.76 (42.25); H, 5.61
(5.22). IR (cm-1): 3455 (br, νOH). 1H NMR (500 MHz, C6D6):
5.27 (m, 2H, COD CH), 4.15 (apparent br t, JH-H = 7 Hz, 1H,
H1), 4.08 (m, 1H, COD CH), 3.97 (m, 1H, COD CH), 3.31(d,
J
H-H = 7.0 Hz, 1H, C-OH), 2.65 (d, JH-H = 9.5 Hz, 1H, H7),
2.53 (br s, 1H, H6), 2.20 (br s, 1H, H3), 2.16 (d, JH-H = 6.5 Hz,
1H, H2), 1.84, 1.72, 1.66, 1.55, and 1.33 (m’s, 8H total, COD
CH2), 1.45 (m, 2H, H4 and H5), 1.37 (s, 1H, PtOH), 1.18 (d,
J
H-H = 9.5 Hz, 1H, H70), 0.99 (m, 2H, H40 and H50). Assign-
ments by 1H-13C HMQC, DEPT-135, and 1H-1H COSY. 13
C
NMR (75 MHz, C6D6): 114.8 (COD CH), 114.7 (COD CH),
84.0 (COD CH), 83.3 (COD CH), 81.4 (C1), 50.6 (C2), 44.5 (C6),
40.2 (C3), 35.8 (C7), 32.6 (C4), 31.6 (COD CH2), 30.9 (COD
CH2), 27.3 (COD CH2), 26.7 (COD CH2), 24.5 (C5). Assign-
ments by 1H-13C HMQC and DEPT-135. 195Pt NMR
(64 MHz, C6D6): -3460.
CD2Cl2. The mixture remained homogeneous. Complex 20
and free NB were detected in a 4:3 ratio by H NMR spectro-
1
scopy. Peaks at 5.56 (m, JPt-H ≈ 68 Hz), 2.68 (m), and 2.28 (m),
overlapping with those for 20, were also observed.
CD3OD. The mixture remained homogeneous, and 20 and
free NB were detected in a 3:1 ratio by 1H NMR spectroscopy.
Peaks at 5.54 (m, JPt-H ≈ 70 Hz), 2.58 (m), and 2.36 (m),
overlapping with those for 20, were also observed.
Reaction of [Pt2(COD)2(OC7H10)Cl]BF4 (1) with H2O/HCl.
Dilute aqueous HCl solution (4.5 μL of a 1 mL 37% hydro-
chloric acid solution in 5 mL of H2O) was added to a solution of
1 (7.5 mg, 0.0089 mmol) in 0.5 mL of CH2Cl2. The mixture was
stirred for 10 min. The solution was evaporated to dryness in
vacuo. The resulting residue was extracted with benzene. The
extraction was evaporated to dryness to give crude 20 identified
by 1H NMR spectroscopy.
Acknowledgment. Support from the U.S. Department
of Energy, Office of Basic Energy Sciences (DE-FG02-
88ER13880), is gratefully acknowledged. We thank a
reviewer for helpful comments and Dr. C. Barnes for
the X-ray structure determination.
Supporting Information Available: Crystallographic data
in cif format is available free of charge via the Internet at
http://pubs.acs.org.