Synthesis, structure, and characterization of a bridging ethylidene (perfluoroalkyl)phosphine platinum complex

Article abstract of DOI:10.1021/om0107237

Thermolysis of (dfepe)Pt(Et)(O₂CCF₃) (dfepe = (C₂F₅)₂PCH₂CH₂P (C₂F₅)₂) in benzene at 80°C results in the formation of (dfepe)Pt(η²-C₂H₄). However, at 120°C in CF₃CO₂ H a bridging ethylidene platinum dimer, [(dfepe)₂Pt₂(μ-CHMe)(μ-H)][O₂ CCF₃], is produced instead. Product isolation by precipitation with diethyl ether afforded the neutral dimer (dfepe)₂Pt₂(μ-CHMe₃). Alternatively, (dfepe)₂Pt₂(μ-CHMe) may be prepared at 20°C by treatment of [(dfepe)Pt(μ-H)]₂(H)⁺ with 1 atm of ethylene. Complete characterization of this species was accomplished by ¹H, ¹³C, and ³¹P NMR spectroscopy, as well as X-ray diffraction. Investigations probing the mechanism of formation for this μ-alkylidene product are presented. The synthesis of the benzyl complex (dfepe)Pt(CH₂Ph)(O₂CCF₃) and its reversible rearrangement to the η³-benzyl complex [(dfepe)Pt(η³-CH₂Ph)]⁺ upon labilization of trifluoroacetate anion is also reported.

Full text of DOI:10.1021/om0107237

Organometallics 2001, 20, 5731-5737
5731
Syn th esis, Str u ctu r e, a n d Ch a r a cter iza tion of a Br id gin g
Eth ylid en e (P er flu or oa lk yl)p h osp h in e P la tin u m Com p lex
Shannon White, Eric W. Kalberer, Byron L. Bennett, and Dean M. Roddick*
Department of Chemistry, Box 3838, University of Wyoming, Laramie, Wyoming 82071
Received August 8, 2001
Thermolysis of (dfepe)Pt(Et)(O2CCF3) (dfepe ) (C2F5)2PCH2CH2P(C2F5)2) in benzene at
80 °C results in the formation of (dfepe)Pt(η2-C2H4). However, at 120 °C in CF3CO2H a
bridging ethylidene platinum dimer, [(dfepe)2Pt2(µ-CHMe)(µ-H)][O2CCF3], is produced
instead. Product isolation by precipitation with diethyl ether afforded the neutral dimer
(dfepe)2Pt2(µ-CHMe3). Alternatively, (dfepe)2Pt2(µ-CHMe) may be prepared at 20 °C by
treatment of [(dfepe)Pt(µ-H)]2(H)+ with 1 atm of ethylene. Complete characterization of this
species was accomplished by 1H, 13C, and 31P NMR spectroscopy, as well as X-ray diffraction.
Investigations probing the mechanism of formation for this µ-alkylidene product are
presented. The synthesis of the benzyl complex (dfepe)Pt(CH2Ph)(O2CCF3) and its reversible
rearrangement to the η3-benzyl complex [(dfepe)Pt(η3-CH2Ph)]+ upon labilization of trifluo-
roacetate anion is also reported.
In tr od u ction
formation of previously reported (dfepe)Pt(η2-C2H4).3
However, thermolysis in trifluoroacetic acid at 120 °C
for 2 h resulted in the complete disappearance of
starting material resonances and the appearance of new
proton signals at δ 8.97 and 2.78, a Pt2(µ-H) hydride
resonance at δ 0.26 (tt, 1J PtH ) 635 Hz, 1J PH ) 163 Hz),
and a distinctive carbon resonance at 152.4 ppm coupled
to two platinum centers and two phosphorus atoms (t,
We have recently reported the catalytic dimerization
of ethylene by (perfluoroalkyl)phosphine complexes of
platinum and palladium in trifluoroacetic acid.1 A key
feature of the proposed catalytic cycle is the stability of
alkyl intermediates (dfepe)M(R)X (R ) Et, Bu) toward
further protonolysis under catalytic reaction conditions
(CF3CO2H, 80 °C) (Scheme 1).
1
2J PC ) 130 Hz, J PtC ) 491 Hz; Pt(µ-CHMe)). Two 31P
Since related work with (dfepe)Pt(Me)(O2CCF3) showed
that protonolysis to form (dfepe)Pt(O2CCF3)2 only occurs
at significant rates above 150 °C,2 we also wished to
examine the thermal stability of the dimerization
catalytic resting state, (dfepe)Pt(Et)(O2CCF3), to estab-
lish an effective upper thermal limit for Pt-alkyl
insertion chemistry in trifluoroacetic acid. Surprisingly,
we find that thermolysis of (dfepe)Pt(Et)(O2CCF3) at 120
°C does not result in ethane evolution and production
of (dfepe)Pt(O2CCF3)2 as expected but, rather, leads to
the quantitative formation of an ethylidene-bridged
dimeric product, [(dfepe)2Pt2(µ-CHMe)(µ-H)][O2CCF3],
which is readily deprotonated to form (dfepe)2Pt2(µ-
CHMe). In this paper we present the synthesis, struc-
ture, and characterization of these µ-alkylidene products
and some observations regarding the mechanism of
dimer formation. We also report the synthesis of the
benzyl complex (dfepe)Pt(CH2Ph)(O2CCF3) and its re-
versible rearrangement to the η3-benzyl complex [(dfepe)-
Pt(η3-CH2Ph)]+ upon abstraction of trifluoroacetate
anion.
NMR resonances for this new product 2 appeared at δ
73.5 (m, 1J PtP ) 4894 Hz) and 67.8 (m, 1J PtP ) 2045 Hz),
consistent with a dfepe chelate coordinated trans to
weak and strong sigma-donors, respectively. Attempted
isolation of 2 by either precipitation with diethyl ether
or removal of trifluoroacetic acid under vacuum yielded
the yellow solid product 3, which, apart from the lack
of a hydride resonance, exhibited very similar spectro-
scopic properties. Dissolution of 3 in trifluoroacetic acid
1
resulted in a quantitative reversion to 2. Both H and
13C data are consistent with the presence of a bridging
ethylidene moiety (µ-CHMe) for both complexes 2 and
3 (Scheme 2). In addition to the formation of ethylidene
dimer products, ca. 0.5 equiv of 2-(trifluoroacetato)-
butane was also observed by NMR in the thermolysis
mixture. This butyl ester product comes from the
platinum-catalyzed dimerization of released ethylene,
followed by 1,2-acid addition,1 and satisfactorily ac-
counts for the mass balance required in Scheme 2.
A number of hydrocarbyl ligand-bridged dimeric
platinum complexes are known;4-7 the most closely
(3) Bennett, B. L.; Roddick, D. M. Inorg. Chem. 1996, 35, 4703.
(4) (a) Anderson, G. K. Adv. Organomet. Chem. 1993, 35, 1. (b)
J effrery, J . C.; Moore, I.; Murray, M.; Stone, F. G. A. J . Chem. Soc.,
Dalton Trans. 1982, 1741. (c) Ashworth, T. V.; Berry, M.; Howard, J .
A. K.; Laguna, M.; Stone, F. G. A. J . Chem. Soc., Dalton Trans. 1980,
1615.
Resu lts a n d Discu ssion
Warming (dfepe)Pt(Et)(O2CCF3) (1) in benzene to 80
°C results in reversible CF3CO2H elimination and the
(5) (a) Bandini, A. L.; Banditelli, G.; Minghetti, G. J . Organomet.
Chem. 2000, 595, 224. (b) Minghetti, G.; Albinati, A.; Bandini, A. L.;
Banditelli, G. Angew. Chem., Int. Ed. Engl. 1985, 24, 120.
(6) Zhuravel, M. A.; Glueck, D. S.; Liable-Sands, L. M.; Rheingold,
A. L. Organometallics 1998, 17, 574.
(1) White, S.; Bennett, B. L.; Roddick, D. M. Organometallics 1999,
18, 2536.
(2) Bennett, B. L.; Hoerter, J . M.; Houlis, J . F.; Roddick, D. M.
Organometallics 2000, 19, 615.
10.1021/om0107237 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 11/20/2001

5732 Organometallics, Vol. 20, No. 26, 2001
White et al.
Sch em e 1
Sch em e 2
comparable µ-alkylidene systems are [Pt2(dppe)2(µ-
CHCH2R)(µ-H)]+ (R ) H, Ph)5 and [Pt2(dppf)2(µ-CHCH2-
Ar)(µ-H)]+ (dppf ) Ph2PC5H4FeC5H4PPh2, Ar ) p-MeO-
1
C6H4).6 13C and H NMR alkylidene resonances reported
for these compounds are shifted uniformly upfield
relative to data for 2, reflecting the significantly lower
platinum electron density induced by the dfepe ligands.
The presence of a bridging ethylidene group in
compound 3 was confirmed by an X-ray crystallographic
study (Figure 1). A summary of data collection param-
eters and a listing of selected metrical parameters are
presented in Tables 1 and 2, respectively. Disorder of
the bridging ethylidene group between the sides of the
plane defined by Pt(1), Pt(2), and the bridging carbon
reduced the precision of this structure. However, a
general comparison between the diplatinum core of this
molecule with related structures can be made. The
observed Pt-Pt distance, 2.6540(8) Å, for 3 is substan-
tially shorter than metal-metal distances reported for
µ-methylene complexes without a supporting Pt-Pt
bond (>3 Å)7 and for the cationic hydride-bridged di-
mers [Pt2(dppe)2(µ-CHCH2Ph)(µ-H)]+ (2.735(1) Å)5 and
[Pt2(dppf)2(µ-CHCH2Ar)(µ-H)]+ (2.7314(4) Å)6 but simi-
lar to Pt-Pt distances reported for the neutral trimeric
complexes Pt3[µ-C(OMe)Ar]3(CO)3 (2.621(1) Å) and (tBu2-
MeP)2Pt2[µ-C(OMe)Ph]W(CO)6 (2.628(1) Å).8,9 The geo-
metry about each platinum center is distorted square
planar, with each (dfepe)Pt chelate moiety twisted ∼20°
F igu r e 1. Molecular structure of (dfepe)2Pt2(µ-CHMe) (3)
with the atom-labeling scheme (30% probability ellipsoids).
Only one of the disordered ethylidene groups is shown.
from the plane defined by Pt2(µ-C(21b)). The Pt-P bonds
opposite to the ethylidene bridge (2.253(5) and 2.245(3)
Å) are somewhat longer than the Pt-P bonds opposite
to the Pt-Pt bond (2.211(4), 2.206(4) Å) and are indica-
tive of a stronger trans influence for the alkylidene
bridge relative to the neighboring platinum center.
The reported synthesis of [Pt2(dppe)2(µ-CHCH2R)(µ-
+
H)]+ from (dppe)Pt2(H)3 and alkene suggested an
(7) (a) Azam, K. A.; Frew, A. A.; Lloyd, B. R.; Manojlovic-Muir, L.;
Muir, K. W.; Puddephatt, R. J . Organometallics 1985, 4, 1400. (b)
Arnold, D. P.; Bennett, M. A.; McLaughlin, G. M.; Robertson, G. B. J .
Chem. Soc., Chem. Commun. 1983, 34.
(8) J effery, J . C.; Moore, L.; Murray, M.; Stone, F. G. A. J . Chem.
Soc., Dalton Trans. 1982, 1741.
(9) Ashworth, T. V.; Berry, M.; Howard, J . A. K.; Laguna, M.; Stone,
F. G. A. J . Chem. Soc., Chem. Commun. 1979, 45.

A Pt Ethylidene (Perfluoroalkyl)phosphine Complex
Organometallics, Vol. 20, No. 26, 2001 5733
Ta ble 1. Cr ysta llogr a p h ic Da ta for
Sch em e 3
(d fep e)2P t2(µ-CHMe) (3)
chem formula
fw
C22H12F40P4Pt2
1550.38
Pbca (No. 61)
16.880(2)
16.1793(13)
29.049(5)
7933(2)
8
space group
a (Å)
b (Å)
c (Å)
V (Å3)
Z
λ (Å)
0.710 73
-102
T (°C)
F
calcd (g cm-3
)
2.596
R1 (I > 2σ(I))a
0.0767
R1 (all data)
0.1412
a
R1 ) ∑(|Fo| - |Fc|)/∑|Fo|.
peratures.1 Although R-H elimination is not generally
favored for late-transition-metal systems,10 a consider-
able body of work by Stone et al. provides ample
precedent for the bimolecular trapping step.11
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (d fep e)2P t2(µ-CHMe) (3)
Pt(1)-Pt(2)
Pt(1)-C(21b)
Pt(2)-C(21b)
Pt(1)-P(2)
2.6540(8)
2.03(4)
Pt(1)-C(21a)
Pt(2)-C(21a)
Pt(1)-P(1)
2.11(3)
2.02(2)
2.211(4)
2.245(4)
1.48(5)
2.01(4)
Since any potential R-H elimination equilibrium oc-
curring in (dfepe)Pt(Et)O2CCF3 would be effectively
masked by competing reversible â-H processes, we have
considered the thermal chemistry of related (dfepe)Pt-
(R)X systems, where â-H elimination is not possible. In
previous work we have noted that (dfepe)Pt(Me)O2CCF3
is thermally stable in CF3CO2H at temperatures below
150 °C for extended periods and converts solely to
(dfepe)Pt(O2CCF3)2 at higher temperatures.2 The ab-
sence of any significant deuterium scrambling into the
methyl group of (dfepe)Pt(Me)O2CCF3 in CF3CO2D prior
to protonolysis argues against an energetically acces-
sible R-H elimination mechanism. Since the mechanism
outlined in Scheme 3 requires a (dfepe)Pt0 trap, we have
also reexamined the thermal stability of (dfepe)Pt(Me)-
O2CCF3 in CF3CO2H in the presence of (dfepe)2Pt. Only
(dfepe)Pt(O2CCF3)2 was observed in solution after 4 days
at 100 °C (eq 2). The effect of an added [(dfepe)Pt(0)]
2.253(5)
2.206(4)
1.55(7)
Pt(2)-P(3)
Pt(2)-P(4)
C(21a)-C(22a)
C(21b)-C(22b)
P(1)-Pt(1)-P(2)
86.3(2)
48.5(6)
51.5(7)
P(3)-Pt(2)-P(4)
86.3(2)
48.5(10)
49.2(12)
C(21a)-Pt(1)-Pt(2)
C(21a)-Pt(2)-Pt(1)
C(21b)-Pt(1)-Pt(2)
C(21b)-Pt(2)-Pt(1)
P(1)-Pt(1)-C(21a) 104.9(12) P(1)-Pt(1)-C(21b) 107.7(10)
P(2)-Pt(1)-C(21a) 168.8(6)
P(3)-Pt(2)-C(21a) 163.9(8)
P(4)-Pt(2)-C(21a) 102.7(7)
P(2)-Pt(1)-C(21b) 158.0(13)
P(3)-Pt(2)-C(21b) 168.3(13)
P(4)-Pt(2)-C(21b) 104.9(12)
Pt(1)-C(21a)-Pt(2)
80.0(8)
Pt(1)-C(21b)-Pt(2)
82(2)
alternative route to 2 and 3.5 As described previously,3
treatment of [(dfepe)Pt(µ-H)]2 in aprotic media with 1
atm of ethylene results in H2 loss and formation of
(dfepe)Pt(η2-C2H4). In CF3CO2H, however, the trihy-
dride cation [(dfepe)Pt(µ-H)]2(H)+ (4) is present as the
major species in solution (see Experimental Section). In
the presence of 1 atm of ethylene at 20 °C, 4 quantita-
tively converts to [(dfepe)2Pt2(µ-CHMe)(µ-H)]+ after 24
h (eq 1). It is significant that some catalytic dimerization
source on the thermolysis of (dfepe)Pt(Et)(O2CCF3) was
also investigated. Warming (dfepe)Pt(Et)(O2CCF3) in
the presence of 1 equiv of (dfepe)2Pt to 100 °C for 10
days in CF3CO2H produced no detectable µ-ethylidene
product; rather, (dfepe)Pt(O2CCF3)2 (3) was again ob-
served as the sole product. A control experiment was
carried out to test the effect of added dfepe to (dfepe)-
Pt(R)X systems: addition of dfepe to a solution of
(dfepe)Pt(Et)(O2CCF3) in CF3CO2H resulted in the rapid
of ethylene to form 2-(trifluoroacetato)butane (ca. 3
equiv) was also observed under these mild reaction
conditions.
Mech a n ism of Eth ylid en e Dim er F or m a tion . A
common mechanism to explain the formation of 2 from
the thermolysis of (dfepe)Pt(Et)O2CCF3 as well as from
the trihydride cation 4 is not readily apparent. Accord-
ingly, we shall consider each of these transformations
separately. One possible mechanism to explain the
formation of products 2 and 3 from (dfepe)Pt(Et)(O2-
CCF3) is outlined in Scheme 3. Here, R-H elimination
by (dfepe)Pt(Et)(O2CCF3) followed by acid loss affords
the platinum carbene complex (dfepe)PtdC(H)Me, which
is trapped by (dfepe)Pt(C2H4). Previous studies indicate
that a rapid equilibrium between (dfepe)Pt(Et)(O2CCF3)
and (dfepe)Pt(C2H4) must exist at superambient tem-
(10) (a) Foley, P.; DiCosimo, R.; Whitesides, G. M. J . Am. Chem.
Soc. 1980, 102, 6713. (b) Burk, M. J .; McGrath, M. P.; Crabtree, R. H.
J . Am. Chem. Soc. 1988, 110, 620.
(11) (a) Stone, F. G. A. Acc. Chem. Res. 1981, 14, 318. (b) Green,
M.; Howard, J . A. K.; J ames, A. P.; J elfs, A. N. de M.; Nunn, C. M.;
Stone, F. G. A. J . Chem. Soc., Chem. Commun. 1984, 1623. (c) Awang,
M. R.; Barr, R. D.; Green, M.; Howard, J . A. K.; Marder, T. B.; Stone,
F. G. A. J . Chem. Soc., Dalton Trans. 1985, 2009. (d) Green, M.;
Howard, J . A. K.; J ames, A. P.; Nunn, C. M.; Stone, F. G. A. J . Chem.
Soc., Dalton Trans. 1986, 187.

5734 Organometallics, Vol. 20, No. 26, 2001
White et al.
Sch em e 4
evolution of ethylene and the formation of (dfepe)2Pt at
room temperature. Heating this resulting solution to
100 °C resulted in a quantitative conversion to (dfepe)-
Pt(O2CCF3)2 after several days. From these observa-
tions, we conclude that the role of added (dfepe)2Pt in
the thermolysis of (dfepe)Pt(R)X systems is most likely
as a source of free dfepe. Interestingly, the thermal
conversion of (dfepe)Pt(Me)(O2CCF3) to (dfepe)Pt(O2-
CCF3)2 in trifluoroacetic acid is somewhat accelerated
in the presence of (dfepe)2Pt.
change was noted in the 31P NMR and 1H NMR
corresponding to the generation of 6. The lack of any
1H or 31P NMR spectroscopic changes down to -75 °C
confirm that the benzylic unit in 6 is highly fluxional.
Despite the additional complication introduced by the
benzallylic equilibrium, the potential for reversible R-H
elimination for this system was examined. Warming a
solution of 6 in CF3CO2D to 80 °C for 24 h resulted in
a 50% decrease in the integrated intensity of the
aromatic resonance at δ 6.76, with no significant
changes in the other aromatic signals or the methylene
resonance at δ 3.71. After 2 days at 120 °C the signal
at δ 6.76 was ∼10% of its initial intensity and the
remainder of the spectrum was unchanged. No (dfepe)-
Pt(O2CCF3)2 was observed. From these data, we con-
clude that R-H elimination is not significant in this
system but that deuterium exchange with the ortho
protons of the benzyl group is occurring instead via an
intramolecular metalation process (Scheme 5).
Two plausible alternative pathways for the formation
of [(dfepe)2Pt2(µ-CHMe)(µ-H)]+ from (dfepe)Pt(Et)(O2-
CCF3) are given in Schemes 6 and 7. In the first scheme,
intramolecular vinyl C-H activation from (dfepe)Pt(η2-
C2H4) to give (dfepe)Pt(CHdCH2)(H) and subsequent
bimolecular trapping by “(dfepe)Pt” and hydride migra-
tion leads to the observed product. C-H bond activation
is known for (R3P)2Pt0 systems,13 and vinylic activation
is precedented for other late transition metals.14
We have also examined [(dfepe)Pt(µ-H)]2(H)+ as an
alternative source of (dfepe)Pt0. A 1:1 mixture of (dfepe)-
Pt(Et)(O2CCF3) and [(dfepe)Pt(µ-H)]2 in trifluoroacetic
acid did not react at ambient temperature. However,
warming to 90 °C for 30 min did result in a complete
conversion to [(dfepe)2Pt2(µ-CHMe)(µ-H)][O2CCF3].
As a further test for the viability of any R-H-mediated
processes, we have prepared (dfepe)Pt(CH2Ph)O2CCF3
(5) and examined its thermal and protolytic stability.
Spectroscopic data for 5 are fully consistent with an
(dfepe)Pt(R)X formulation in benzene. In neat trifluo-
roacetic acid, however, a dramatic change in 31P NMR
1
chemical shifts and J PtP values occurs, which indicates
that simple σ-benzyl coordination is not present under
these conditions (see Experimental Section). Removal
of CF3CO2H under vacuum and dissolution in benzene
results in the regeneration of 5. On the basis of our
previous work in strongly acidic solvents,2b we conclude
that acid-induced labilization of trifluoroacetate anion
and an accompanying allylic rearrangement to form
[(dfepe)Pt(η3-CH2Ph)]+ (6) is taking place in CF3CO2H
(Scheme 4). The equivalence of ortho and meta aryl
The key step in Scheme 7 is intermolecular attack on
coordinated ethylene by an unsaturated (dfepe)Pt0
center to generate [(dfepe)2Pt2(µ-η1:η1-C2H4)(H)]+, fol-
lowed by â-H elimination to form a µ,η1:η2-vinyl complex
which serves as a common intermediate in both Schemes
6 and 7. A number of examples of metal-centered
nucleophilic attack on LnM(η2-C2H4) lend precedent to
this key bimolecular step.15 With few exceptions,16
however, most of these reports have involved addition
of anionic metal centers to cationic ethylene complexes.
In principle, nucleophilic attack on coordinated ethylene
1
protons in ambient-temperature H NMR spectra indi-
cate that rotation about the CH2-Ph bond must be
rapid, in accord with a fluxional benzylic unit (see
below). All attempts to isolate 6 from solution resulted
in the regeneration of 5.
In an effort to favor the η3-benzyl complex under
aprotic conditions, we have examined the effect of added
SbF5(SO2), a potent anion abstraction agent.12 Pen-
tafluoropyridine proved to be a suitable weakly coordi-
nating solvent for this reaction. Upon addition of
SbF5(SO2) to (dfepe)Pt(CH2Ph)O2CCF3, an immediate
(13) (a) Hofmann, P.; Unfried, G. Chem. Ber. 1992, 125, 659. (b)
Hofmann, P.; Heiss, H.; Neiteler, P.; Mu¨ller, G.; Lachmann, J . Angew.
Chem., Int. Ed. Engl. 1990, 29, 880. (c) Hackett, M.; Whitesides, G.
M. J . Am. Chem. Soc. 1988, 110, 1449.
(14) (a) Faller, J . W.; Smart, C. J . Organometallics 1989, 8, 602. (b)
Stoutland, P. O.; Bergman, R. G. J . Am. Chem. Soc. 1988, 110, 5732.
(c) J anowicz, A. H.; Bergman, R. G. J . Am. Chem. Soc. 1983, 105, 3929.
(d) Baker. M. V.; Field, L. D. J . Am. Chem. Soc. 1986, 108, 7433. (e)
Wenzel, T. T.; Bergman, R. G. J . Am. Chem. Soc. 1986, 108, 4856.
(12) (a) Houlis, J . F.; Roddick, D. M. J . Am. Chem. Soc. 1998, 120,
11020. (b) Moore, J . W.; Baird, H. W.; Miller, H. B. J . Am. Chem. Soc.
1968, 90, 1358.

A Pt Ethylidene (Perfluoroalkyl)phosphine Complex
Organometallics, Vol. 20, No. 26, 2001 5735
Sch em e 5
Sch em e 6
Sch em e 7
may occur at either [(dfepe)Pt(η2-C2H4)(H)]+, as shown,
or on the neutral Pt(0) ethylene complex (dfepe)Pt(η2-
C2H4). We believe that the former is most likely, since
a Pt(II) cationic alkene complex is expected to be more
reactive and ethylidene formation is only observed
under acidic conditions.17
A vinyl-bridged intermediate similar to that proposed
in Schemes 6 and 7 has been prepared by the reaction
of (PR3)2Ir(CO)(OTf) with (PPh3)2Pt(η2-C2H4) (eq 3).18
Although this report claimed the first example of
intermolecular, homogeneous transition-metal vinylic
C-H activation of a π-complexed alkene, no evidence
was presented to support this assertion.
(15) (a) Gafoor, M. A.; Hutton, A. T.; Moss, J . R. J . Organomet.
Chem. 1996, 510, 233. (b) Raab, K.; Nagel, U.; Beck, W. Z. Naturforsch.,
B 1983, 38, 1466. (c) Olgemo¨ller, B.; Beck, W. Chem. Ber. 1981, 114,
867.
(16) (a) Anderson, O. P.; Bender, B. R.; Norton, J . R.; Larson, A. C.;
Vergamini, P. J . Organometallics 1991, 10, 3145. (b) Motyl, K. M.;
Norton, J . R.; Schauer, C. K.; Anderson, O. P. J . Am. Chem. Soc. 1982,
104, 7325.
(17) We have recently characterized a related Pt(II) alkene complex,
(dfepe)Pt(H2CdC(H)Me)(OSO2F)+: Kalberer, E.; Roddick, D. M. Un-
published observations.
(18) (a) Stang, P. J .; Huang, Y.-H.; Arif, A. M. Organometallics 1992,
11, 845. (b) Huang, Y.-H.; Stang, P. J .; Arif, A. M. J . Am. Chem. Soc.
1990, 112, 5648.

5736 Organometallics, Vol. 20, No. 26, 2001
White et al.
and/or glovebox techniques. Dry oxygen-free solvents were
prepared using standard procedures. Aprotic deuterated sol-
vents used in NMR experiments were dried over activated 3
Å molecular sieves. CF3CO2D was obtained from Cambridge
Isotope Laboratories (Cambridge, MA), and used as received.
Elemental analysis was performed by Desert Analytics. NMR
spectra were obtained with a Bruker DRX-400 instrument. 31
P
NMR spectra were referenced to an 85% H3PO4 external
standard. (dfepe)Pt(Et)(O2CCF3),1 (dfepe)Pt(Me)(O2CCF3),19
(cod)Pt(benzyl)2 (cod ) 1,5-cyclooctadiene),22 and dfepe23 were
prepared using literature methods.
[(d fep e)2P t 2(µ-CH Me)](µ-H )]+ (2) a n d (d fep e)2P t 2(µ-
CHMe) (3). A solution of (dfepe)Pt(Et)(O2CCF3) (0.122 g, 0.135
mmol) in 5 mL of trifluoroacetic acid was warmed to 120 °C.
After 2 h, 31P NMR data indicated that conversion to
[(dfepe)2Pt2(µ-CHMe)(µ-H)][O2CCF3] was complete. Spectro-
scopic data for 2: 1H NMR (CF3CO2H, 400 MHz, 23 °C) δ 8.93
(br s, 1H; Pt(µ-CHMe), 3.13 (m, 4H, PCH2), 2.90 (m, 4H; PCH2),
All mechanisms proposed thus far for the synthesis
of µ-ethylidene products require a bimolecular trapping
by “(dfepe)Pt”. As discussed earlier, (dfepe)2Pt is not an
effective trap, due to the noninnocence of dfepe released
under the reaction conditions. The use of [(dfepe)Pt(µ-
H)(H)]2 as a (dfepe)Pt0 source in the thermolysis of
+
1
2.72 (br s, 3H, Pt(µ-C(H)CH3), 0.26 (tt, 1H, J PtH ) 635 Hz,
(dfepe)Pt(Et)(O2CCF3) did afford 2 in CF3CO2H under
milder conditions, but it is possible that ethylidene
product formation in this case derives from the reaction
of released ethylene with [(dfepe)Pt(µ-H)]2(H)+.
1J PH ) 163 Hz, Pt(µ-H)); 13C NMR (CF3CO2D, 100.6 MHz, 23
2
1
°C) δ 151.8 (t, J PC ) 130 Hz, J PtC ) 491 Hz; Pt(µ-CHMe)),
114.7-124.4 (overlapping mm, 8C, CF2CF3), 30.2 (s, C(H)CH3),
25.6 (s, 4C, PCH2), 21.8 (s, 4C, PCH2); 31P NMR (CF3CO2H,
1
1
161.9 MHz, 23 °C) δ 73.2 (m, J PtP ) 4866 Hz), 68.0 (m, J PtP
) 1845 Hz). Attempts to isolate this protonated dimer from
CF3CO2H were unsuccessful, due to facile loss of CF3CO2H
under vacuum. After the mixture was cooled to ambient
temperature, all volatiles were removed and Et2O (5 mL) was
added to dissolve the yellow solid. Filtration was performed
to isolate the product from any unreacted starting material 1,
followed by a cold filtration (-78 °C) to yield a pure yellow
solid, which was dried under vacuum (0.06 g, 57%). Anal. Calcd
for C22H12F40P4Pt2: C, 17.04; H, 0.78. Found: C, 17.08; H, 0.85.
1H NMR (acetone-d6, 400 MHz, 23 °C): δ 9.07 (br s, 1H; Pt-
(µ-C(H)CH3)), 2.99 (m, 2H; PCH2), 2.80 (m, 3H; Pt(µ-C(H)CH3)),
2.44 (m, 2H; PCH2). 13C NMR (acetone-d6, 100.6 MHz, 23 °C):
Any mechanism to account for the formation of
µ-ethylidene product from (dfepe)2Pt2(µ-H)2H+ must
explain the much milder reaction conditions required
in this synthetic route. A proposed mechanism is shown
+
in Scheme 8. While fragmentation of the dimeric Pt2H3
induced by ethylene addition is possible, this would
simply lead to (dfepe)Pt(Et)O2CCF3 formation. A likely
alternative lower energy pathway involves a dimeric
ethylene intermediate, [(dfepe)2Pt2(H)(η2-C2H4)]+. Analo-
gous carbonyl complexes have been produced in the
reaction of L4Pt2H3+ with CO.19 Conversion of (dfepe)2Pt2-
(H)(η2-C2H4)+ to a bridged ethylene complex leads to an
ethylidene mechanism analogous to Schemes 6 and 7.
An unexplained observation in the reaction of
2
1
δ 157.6 (t, J PC ) 139 Hz, J PtC ) 814 Hz; Pt(µ-C(H)CH3)),
123.7-112.2 (overlapping mm, 8C, CF2CF3), 30.3 (s, C(H)CH3),
25.3 (s, 4C, PCH2), 21.5 (s, 4C, PCH2). 31P NMR (acetone-d6,
161.9 MHz, 23 °C): δ 85.2 (m, 1J PtP ) 1153 Hz), 74.5 (m, 1J PtP
) 2199 Hz).
+
(dfepe)2Pt2(H)3 with ethylene is the formation of the
butyl ester under these mild conditions. It is possible
that ethylene dimerization for this system involves a
bimetallic reaction pathway similar to that proposed for
(dfepe)2Ir2H4.20
[(d fep e)P t(µ-H)]2(H)+ (4). A 10 mg portion of [(dfepe)Pt-
(µ-H)]2 was dissolved in 0.5 mL of CD2Cl2, and 30 µL of CF3-
CO2H was added via microliter syringe. An immediate color
change from orange-brown to light yellow was observed. 1H
and 31P NMR indicate complete conversion to a new species
Su m m a r y
1
assigned as [(dfepe)2Pt2(µ-H)2(H)]+. H NMR (CD2Cl2, 400.13
The underlying mechanism of Pt2(µ-CHR) complex
formation remains open to question. A pathway involv-
ing R-H elimination and carbene trapping does not
appear reasonable in light of other (dfepe)Pt(R)X reac-
tivity data. We cannot rule out C-H vinylic activation
(Scheme 6) but currently favor the convergent processes
outlined in Schemes 7 and 8, which can more readily
explain the formation of alkylidene products from both
(dfepe)Pt(Et)(O2CCF3) and [(dfepe)Pt(µ-H)]2(H)+ precur-
sors. The chemistry of coordinatively unsaturated
bridged-alkene complexes M2(µ-η1:η1-C2H4) such as those
proposed in Schemes 7 and 8 is currently undeveloped
and merits future study.
MHz, 27 °C): δ 3.02 (m, 8H; PCH2), -2.60 (m, 1J PtH ) 517 Hz,
2J PH ) 50 Hz; 3H; Pt(µ-H)). 31P NMR (CD2Cl2, 161.97 MHz,
1
25 °C): δ 85.3 (m, J PtP ) 3010 Hz).
(d fep e)P t(CH2P h )(O2CCF 3) (5). Trifluoroacetic acid (30
µL, 0.044 g, 0.45 mmol) was added to a solution of (cod)Pt-
(benzyl)2 (0.010 g, 0.025 mmol) in 15 mL of methylene chloride
at -78 °C via syringe under N2 and stirred at -78 °C for 1 h.
When the mixture was warmed to ambient temperature, dfepe
(0.1 mL, 0.22 g, 0.39 mmol) was added via syringe under N2
and the resulting mixture stirred for 4 h. A cold filtration (-78
°C) was done to isolate a white solid, which was dried under
vacuum (0.18 g, 54%). Anal. Calcd for C19H11F23P2Pt: C, 23.64;
1
H, 1.15. Found: C, 23.25; H, 1.03. H NMR (C6D6, 400 MHz,
23 °C): δ 7.37 (m, 2H, o-C6H5), 7.18 (m, 1H, p-C6H5), 7.00 (m,
2
2H, m-C6H5), 3.78 (s, J PtH ) 28 Hz; Pt-CH2Ph), 1.62 (m, 2H,
PCH2), 1.41 (m, 2H, PCH2). 31P NMR (C6D6, 161 MHz, 23 °C):
Exp er im en ta l Section
2
2
δ 76.8 (m, J PtP ) 1200 Hz), 56.4 (m, J PtP ) 4830 Hz). NMR
data for (dfepe)Pt(benzyl)(O2CCF3) in CF3CO2D: 1H NMR δ
7.97 (t, 3J CH ) 7.7 Hz, 2H; m-C6H5), 7.49 (m, 1H; p-C6H5), 6.71
Gen er a l P r oced u r es. All manipulations were conducted
under an atmosphere of purified nitrogen using high-vacuum
(19) Minghetti, G.; Bandini, A. L.; Banditelli, G.; Bonati, F.; Szostak,
R.; Strouse, C. E.; Knobler, C. B.; Kaesz, H. D. Inorg. Chem. 1983, 22,
2332.
(20) Hoerter, J . M.; Schnabel, R. C.; Roddick, D. M. Organometallics
1999, 18, 5717-5720.
(21) Bennett, B. L.; Birnbaum, J .; Roddick, D. M. Polyhedron 1995,
14, 187.
(22) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411.
(23) Ernst., M. F.; Roddick, D. M. Inorg. Chem. 1989, 28, 1624.

A Pt Ethylidene (Perfluoroalkyl)phosphine Complex
Organometallics, Vol. 20, No. 26, 2001 5737
Sch em e 8
2
(m, 2H; o-C6H5), 3.66 (AB pattern, J PH ) 9.7 Hz, 2H; PtCH2-
Ph), 2.94 (m, PCH2), 2.72 (m, PCH2); 31P NMR: δ 74.3 (pseudo
p, 2J PtP ) 3240 Hz, 2J PF ) 63 Hz), 71.3 (pseudo p, 2J PtP ) 5190
crystallized in the centrosymmetric orthorhombic space group
Pbca (Z ) 8). All non-hydrogen atoms except for those noted
below were refined anisotropically. The C(3) and C(4) perfluo-
roethyl carbons were restrained (DFIX) during refinement
with fixed C-F bond distances, due to some positional disorder
in this perfluoroethyl group. In addition, the bridging eth-
ylidene group was disordered with respect to the disposition
of the methyl group above and below the plane defined by the
bridging carbon and the two platinum centers. A large aniso-
tropic displacement of the bridging C(21) carbon also suggested
disorder in this position, so the two independent bridging
CHMe sets C(21a), C(22a) and C(21b), C(22b) were modeled
isotropically; a population refinement gave sof’s of 0.56 and
0.44, respectively, for the A and B ethylidene sets. Hydrogen
atom positions were added in ideal calculated positions and
with fixed isotropic thermal parameters set at 1.5 times the
isotropic equivalent of the attached carbon atom for the
disordered methyl groups and 1.2 times that for the remaining
hydrogen atoms. The final R factor values were R1 ) 0.0767
and wR2 ) 0.1374 for 7682 data with F > 4σ(F), with a
goodness of fit on F2 of 1.038. The maximum and minimum
residual electron densities were 1.70 and -2.69 e Å3. Selected
metrical parameters for 3 are presented in Table 2.
2
Hz, J PF ) 66 Hz).
[(d fep e)P t(η3-CH2P h )][(CF 3CO2)SbF 5] (6). SbF5(SO2) (5
mg, 0.012 mmol) was added to a solution of (dfepe)Pt(CH2Ph)-
(O2CCF3) (15 mg, 0.012 mmol) in 1 mL of pentafluoropyridine.
Immediate conversion to 6 was observed by 31P NMR spec-
troscopy. Isolation of this compound was not accomplished. 1H
3
NMR (pentafluoropyridine, 400 MHz, 23 °C): δ 7.99 (t, J CH
) 6.0 Hz, 2H; m-C6H5), 7.51 (m, 1H; p-C6H5), 6.75 (m, 2H;
2
o-C6H5), 3.70 (AB pattern, J PH ) 9.1 Hz, 2H; PtCH2Ph), 2.91
(m, PCH2), 2.67 (m, PCH2). 31P NMR (pentafluoropyridine, 161
2
2
MHz, 23 °C): δ 74.6 (pseudo p, J PtP ) 3234 Hz, J PF ) 62
2
2
Hz), 71.4 (pseudo p, J PtP ) 5188 Hz, J PF ) 66 Hz).
Cr ysta l Str u ctu r e of (d fep e)2P t2(µ-CHMe) (3). Slow
evaporation from benzene afforded yellow plates of 3. A crystal
of suitable size was mounted on a glass fiber using grease.
Data were collected using a Siemens SMART CCD diffracto-
meter using monochromatic molybdenum radiation and an
LT-2 low-temperature apparatus operating at 171 K. A sum-
mary of crystal data is presented in Table 1. Cell parameters
were obtained from a least-squares fit to the angular coordi-
nates of 51 reflections of a series of oscillation frames. Data
were measured using ω scans of 0.3° per frame for 30 s. The
first 50 frames were recollected at the end of data collection
to monitor for decay. The data were corrected for Lorentz and
polarization effects. Absorption corrections were applied using
SADABS.
Ack n ow led gm en t. This work has been supported
by the National Science Foundation (Grants CHE-
9615985 and CHE-009049), and the Wyoming DOE-
EPSCoR Program.
The structure was solved by direct methods and standard
difference Fourier techniques and refined by full-matrix least-
squares techniques on F2 using structure solution programs
from the SHELXTL system (version 5.04).24 The compound
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates and temperature factors, and in-
tramolecular bond distances and angles of complex 3. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(24) Sheldrick, G. M. SHELXTL Crystallographic System, version
5.04/Iris; Siemens Analytical X-ray Instruments, Inc., Madison, WI.
OM0107237