Synthesis of [(dfepe)Pt(Me)(NC5F5)] +B(C6F5)4_, a highly active ethylene dimerization catalyst

Article abstract of DOI:10.1021/om8003509

The synthesis of cationic adducts (dfepe)Pt(Me)(L)₊ (dfepe = (C₂F₅)₂PCH₂CH₂P(C ₂F₅)₂; L = MeCN, CO, C₂H ₄, C₅F₅N

Full text of DOI:10.1021/om8003509

Organometallics 2008, 27, 3659–3665
3659
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Synthesis of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 , a Highly Active
Ethylene Dimerization Catalyst
Sayanti Basu, Navamoney Arulsamy, and Dean M. Roddick*
Department of Chemistry, Box 3838, UniVersity of Wyoming, Laramie, Wyoming 82071
ReceiVed April 18, 2008
The synthesis of cationic adducts (dfepe)Pt(Me)(L)+ (dfepe ) (C2F5)2PCH2CH2P(C2F5)2; L ) MeCN,
CO, C2H4, C5F5N, µ-Cl) are reported. Treatment of (cod)Pt(Me)Cl with AgSbF6 in acetonitrile followed
by the addition of dfepe afforded (dfepe)Pt(Me)(CH3CN)+SbF6-. Addition of B(C6F5)3 to (dfepe)Pt-
(Me)(O2CCF3) in methylene chloride afforded the structurally characterized borane association product
(dfepe)Pt(Me)[(O2CCF3)B(C6F5)3] in high yield. Attempts to displace the [(O2CCF3)B(C6F5)3]- anion
with donor ligands resulted in loss of borane and regeneration of (dfepe)Pt(Me)(O2CCF3). Addition of
-
the mesitylenium acid (1,3,5-C6H4Me3)+B(C6F5)4 to (dfepe)PtMe2 in methylene chloride at ambient
temperatures resulted in chloride abstraction and the precipitation of the chloride-bridged dimeric complex
[{(dfepe)Pt(Me)}2(µ-Cl)]+B(C6F5)4-, which has been structurally characterized. In contrast, treatment
of (dfepe)PtMe2 with (1,3,5-C6H4Me3)+B(C6F5)4- in pentafluoropyridine at ambient temperature resulted
in the precipitation of the structurally characterized pentafluoropyridine adduct [(dfepe)Pt(Me)-
-
-
(NC5F5)]+B(C6F5)4 in good yield. Exposure of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 to 1 atm of CO in
o-difluorobenzene gave the carbonyl complex [(dfepe)Pt(Me)(CO)]+B(C6F5)4-. In marked contrast to
previously reported platinum systems, [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 is a very active ethylene
-
dimerization catalyst at ambient temperature (600 psi ethylene, 22 °C in ortho-difluorobenzene, 150
-
turnovers h-1). The ethylene adduct [(dfepe)Pt(Me)(η2-C2H4)]+B(C6F5)4 has been spectroscopically
characterized at -20 °C.
(hydrogen bonding) with the neat acid media. This strategy to
generate reactive organometallic cations, though fruitful, is
limited since the use of increasingly stronger acid media to
generate more labile metal cations places restrictions on which
coordination substrates can be used. In superacidic media in
particular, only extremely weakly basic substrates such as CO
and H2 are stable and readily examined.4f
Introduction
Cationic group 10 compounds of the general formula
L2M(alkyl)(L′)+, L2M(L′)22+, or L3M(L′)2+ are of continuing
interest due in part to their role in alkene oligomerization,1
alkene/CO copolymerization,2 and a wide variety of metal-
mediated catalytic organic transformations.3 A key requirement
of many active catalyst systems is the use of very weakly
coordinating counteranions (WCAs), solvents, and ancillary
neutral donor ligands L′. In our prior work exploring the
chemistry of perfluoroalkylphosphine (“PFAP”) group 10
systems, we have taken advantage of the remarkable resistance
of (dfepe)M(CH3)(X) (dfepe ) (C2F5)2PCH2CH2P(C2F5)2) and
trans-(dfmp)2Pt(CH3)(X) (dfmp ) (C2F5)2PMe) complexes
toward protonolysis and have examined their chemistry in acidic
and superacidic solvents.4 Under acidic conditions the anionic
ligand X- is labilized both by virtue of being the conjugate
base of a very strong acid, HX, and by homoconjugation
Several years ago we reported that (dfepe)Pt(Me)O2CCF3 is
a modestly active ethylene dimerization catalyst (∼6 turnovers
h
-1) in trifluoroacetic acid at 80 °C.4e Although much less active
than the corresponding (dfepe)2Pd/CF3CO2H system, this was
the first example of catalytic ethylene dimerization by a well-
defined platinum complex. Brookhart and Templeton have
recently reported ethylene dimerization by (diimine)Pt(H)(η2-
C2H4)+BAr′4 at 100 °C with a slow turnover rate of ∼0.1 h-1 5
.
A direct comparison of the intrinsic metal-carbon bond
insertion reactivity of electron-poor (dfepe)Pt(R)+ and the more
electron-rich (diimine)Pt(R)+ moieties is clearly of interest.
However, the catalyst resting state for ethylene dimerization
by (dfepe)Pt(Me)(O2CCF3) in CF3CO2H was identified as
(dfepe)Pt(Et)(O2CCF3), rather than (dfepe)Pt(Et)(η2-C2H4)+ or
(dfepe)Pt(H)(η2-C2H4)+, and indicated that trifluoroacetate anion
loss was rate-determining. This contrasts with the (diimine)Pt(II)
* Corresponding author. E-mail: dmr@uwyo.edu.
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000,
100, 1169–1203. (b) Mecking, S. Coord. Chem. ReV. 2000, 203, 325–351.
(c) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995,
117, 6414–6415. (d) Conley, M. P.; Burns, C. T.; Jordan, R. F. Organo-
metallics 2007, 26, 6750–6759.
(2) (a) Kochi, T. K.; Nakamura, A.; Ida, H.; Nozaki, K. J. Am. Chem.
Soc. 2007, 129, 7770–7771. (b) Catalytic Synthesis of Alkene-Carbon
Monoxide Copolymers and Cooligomers; Sen, A., Ed.; Kluwer Academic
Publishers: Dordrecht, The Netherlands, 2003. (c) Drent, E.; Budzelaar,
P. H. M. Chem. ReV. 1996, 96, 663–681. (d) Sen, A. Acc. Chem. Res. 1993,
26, 303–310.
(3) (a) Fu¨rstner, A.; Davies, P. W. Angew. Chem., Int. Ed. 2007, 46,
3410–3449. (b) Chianese, A. R.; Lee, S. J.; Gagne´, M. R. Angew. Chem.,
Int. Ed. 2007, 46, 4042–4059. (c) Doherty, S.; Knight, J. G.; Smyth, C. H.;
Harrington, R. W.; Clegg, W. Organometallics 2007, 26, 5961–5966. (d)
Liu, C.; Bender, C. F.; Han, X.; Widenhoefer, R. A. Chem. Commun. 2007,
3607–3618. (e) Hahn, C. Chem.-Eur. J. 2004, 10, 5888–5899.
(4) (a) Butikofer, J. L.; Parson, T. G.; Roddick, D. M. Organometallics
2006, 25, 6108–6114. (b) Kalberer, E. W.; Houlis, J. F.; Roddick, D. M.
Organometallics 2004, 23, 4112–4115. (c) Butikofer, J. L.; Hoerter, J. M.;
Peters, R. G.; Roddick, D. M. Organometallics 2004, 23, 400–408. (d)
Bennett, B. L.; Hoerter, J. M.; Houlis, J. F.; Roddick, D. M. Organometallics
2000, 19, 615–621. (e) White, S.; Bennett, B. L.; Roddick, D. M.
Organometallics 1999, 18, 2536–2542. (f) Houlis, J. F.; Roddick, D. M.
J. Am. Chem. Soc. 1998, 120, 11020–11021.
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10.1021/om8003509 CCC: $40.75
2008 American Chemical Society
Publication on Web 07/17/2008

3660 Organometallics, Vol. 27, No. 15, 2008
Basu et al.
catalyst resting state (diimine)Pt(Et)(η2-C2H4)+, which allowed
trapping ligands.8 No reaction was observed between (dfepe)Pt-
Me2 and B(C6F5)3 in dichloromethane at ambient temperature.
No (dfepe)Pt(Me)(CO)+ was formed in the presence of CO as
the barrier to ethylene insertion to be directly determined.5
To address this specific issue and to more broadly extend
the chemistry of labile PFAP complex metal cations, we have
begun to examine routes to isolable, labile complex platinum
cations employing WCAs such as fluorinated aryl borates and
halocarboranes. In this paper we present the synthesis and
characterization of the labile electron-poor methyl cation
complex [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4- and a preliminary
survey of its reactivity with ethylene. We anticipated that weakly
coordinating pentafluoropyridine would be readily displaced by
ethylene and that dimerization via a (dfepe)Pt(Et)(η2-C2H4)]+
catalyst resting state would be significantly more facile. Indeed,
a trapping ligand under these conditions. (dfepe)PtMe2 was
-
similarly unreactive with the trityl reagent Ph3C+B(C6F5)4
.
No reaction was also observed between excess B(C6F5)3 and
the monoalkyl complexes (dfepe)Pt(Me)(OTf) or (dfepe)Pt-
(Me)Cl. However, when (dfepe)Pt(Me)(O2CCF3) was treated
with 1.2 equiv of B(C6F5)3 in methylene chloride, the association
product (dfepe)Pt(Me)[(O2CCF3)B(C6F5)3] (2) was isolated in
high yield (eq 2).
-
we find that [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 reacts with
ethylene at low temperatures to form a discrete adduct,
[(dfepe)Pt(Me)(η2-C2H4)]+B(C6F5)4-. This platinum system
exhibits unusually high catalytic activity for ethylene dimer-
ization at room temperature.
NMR data clearly support the formation of a borane adduct:
The methyl resonance of 2 is shifted upfield by 0.54 ppm from
that of 1, and the coupling constant for Pt-P trans to the adduct
(1JPt-P) 5220 Hz) is significantly higher than that of the Pt-P
trans to O2CCF3 in (dfepe)Pt(Me)(O2CCF3) (1JPt-P) 4575 Hz),
indicating a weakened interaction of the acetate moiety with
the Pt center. 19F NMR spectra exhibit peaks that are charac-
teristic of the presence of a coordinated borane ligand (-134.4,
-160.7, -163.5) and are shifted from those of the free borane.
Infrared data show a ν(CO) shift from 1704 cm-1 in
(dfepe)Pt(Me)(O2CCF3) to 1653 cm-1 in 2. Spectroscopic
evidence is in accord with X-ray crystallographic data (see
below).
Results and Discussion
Synthesis of [(dfepe)Pt(Me)(MeCN)]+SbF6- (1). Conven-
tional halide abstraction has been examined as a route to labile
Pt(II) alkyl cation solvates, (dfepe)Pt(Me)(solV)+. Treatment of
(dfepe)Pt(Me)Cl with AgSbF6 in acetonitrile does not result in
halide abstraction, presumably due to strong Pt-Cl binding to
the electrophilic (dfepe)Pt(II) moiety. (dfepe)Pt(Me)(MeCN)+
can, however, be prepared via an indirect synthesis: addition
of AgSbF6 to (cod)Pt(Me)Cl in acetonitrile followed by the
-
addition of dfepe afforded (dfepe)Pt(Me)(CH3CN)+SbF6 (1)
(eq 1).
Treatment of (dfepe)Pt(Me)(O2CCF3) in methylene chloride
with 2 atm of BF3 similarly resulted in the formation a BF3
adduct, (dfepe)Pt(Me)[(O2CCF3)(BF3)] (3), as evidenced by a
0.98 ppm downfield shift of the methyl resonance and an
increase of the 1JPtP value trans to the trifluoroacetate ligand to
5380 Hz. In contrast to 2, however, 3 was not isolable and
reverted back to the starting complex upon removal of BF3 under
vacuum (eq 3).
The intermediate (cod)Pt(Me)(CH3CN)+ was not isolated.
However, the formation of (cod)Pt(Me)(CH3CN)+ was con-
firmed by 1H NMR, where a 0.08 ppm upfield shift of the methyl
resonance relative to the starting material (cod)Pt(Me)Cl was
1
noted. JPtP data are diagnostic for the strength of the trans
Pt-ligand interaction and is useful for establishing relative trans
ligand influences.6 For 1, 31P resonances appear at 64.8 (1JPtP
) 4680 Hz) and 81.9 (1JPtP ) 1400 Hz) ppm for the phosphorus
atoms trans to the CH3CN ligand and the methyl group,
1
The large JPtP value for 2 indicated that (dfepe)Pt(Me)-
(O2CCF3)B(C6F5)3 might be a potential labile source of the 14-
electronmoiety(dfepe)Pt(Me)+.However,exposureof(dfepe)Pt(Me)-
[(O2CCF3)B(C6F5)3] to CO or dissolution in acetone or aceto-
nitrile resulted in regeneration of (dfepe)Pt(Me)(O2CCF3). These
observations suggest that borane adduct formation in eq 2 is
also reversible and [(C6F5)3B(O2CCF3)]- is not a sufficiently
innocent anion for platinum cation studies.
1
respectively. The JPtP value of 4680 Hz is higher than that
reported for [(dppe)Pt(Me)(CH3CN)]+ (1JPtP ) 4370 Hz),6
indicating that the acetonitrile ligand is more weakly coordinated
in 1. However, treatment of 1 with 1 atm of CO or ethylene in
acetonitrile at ambient temperature does not result in acetonitrile
displacement and indicates that 1 is not a sufficiently labile
source of the (dfepe)Pt(Me)+ moiety.
(dfepe)PtMe2 Protonolysis Studies with (1,3,5-C6H4Me3)+B-
(C6F5)4-: Synthesis and Characterization of [{(dfepe)Pt(Me)}2(µ-
Synthesis and Characterization of (dfepe)Pt(Me)[(O2CCF3)-
B(C6F5)3] (2). The Lewis acid B(C6F5)3 has been widely used
as an alkyl abstraction reagent in coordination chemistry, giving
rise to cationic complexes with [RB(C6F5)3]- as the counterion.7
This reaction has been more commonly employed with more
carbanionic early transition metal alkyls, but methyl abstraction
from (bu2bpy)PtMe2 has been reported in the presence of
-
-
Cl)]+B(C6F5)4 (4) and [(dfepe)Pt(Me)(L)]+B(C6F5)4 (L )
C5F5N (5); CO (6)). Previous research in our group has focused
on the formation of (dfepe)Pt(Me)(X) and trans-(dfmp)2Pt(Me)X
products by HX protonolysis of (dfepe)PtMe2 and cis-
(dfmp)2PtMe2 with the strong acids CF3CO2H, H2SO4,
CF3SO3H, and FSO3H. These conjugate base derivatives, while
(6) Appleton, T. G.; Bennett, M. A. Inorg. Chem. 1978, 17, 738–747.
(7) (a) Piers, W. E. AdV. Organomet. Chem. 2005, 52, 1–77. (b) Chen,
E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391–1434.
(8) (a) Hill, G. S.; Manojlovic-Muir, L.; Muir, K. W.; Puddephatt, R. J.
Organometallics 1997, 16, 525–530. (b) Hill, G. S.; Rendina, L. M.;
Puddephatt, R. J. J. Chem. Soc., Dalton Trans. 1996, 1809–1813.

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Synthesis of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4
Organometallics, Vol. 27, No. 15, 2008 3661
relatively labile, involve significant Pt-X covalent bonding and
only form the anion displacement adducts such as [(dfepe)Pt-
(Me)(CO)]+ and [trans-(dfmp)2Pt(Me)(CO)]+ in neat acid
solutions for the stronger acids HX ) CF3SO3H and FSO3H.4a,f
Reed and co-workers have reported stable arenium acids
(areneH+) with very weakly coordinating counterions such as
-
B(C6F5)4 and CB11H6Cl6-, which can serve as protonolysis
reagents in organometallic chemistry,9 although their use for
this purpose has only recently been reported.10 In particular,
(1,3,5-C6H4Me3)+B(C6F5)4- is a readily prepared arenium acid
that is sufficiently stable for protonation studies.9b Addition of
diffraction, have confirmed the formulation of 5. In addition to a
δ 1.33 downfield shift of the methyl proton resonance relative to
(dfepe)PtMe2, characteristic phosphorus resonances were observed
1
trans to the methyl group (δ 82.4 ppm, JPtP ) 1490 Hz) and
-
1.2 equiv of (1,3,5-C6H4Me3)+B(C6F5)4 to (dfepe)PtMe2 in
1
pentafluoropyridine (δ 60.9 ppm, JPtP ) 4950 Hz). 19F NMR
methylene chloride at ambient temperatures resulted in the
precipitation of the chloride-bridged dimeric complex [{(dfepe)Pt-
(Me)}2(µ-Cl)]+B(C6F5)4- (4) (eq 4). The reaction of Cp2M(Ph)2
confirmed the presence of coordinated pentafluoropyridine, whose
resonances (ortho: δ -106.8; meta: δ -153.7) were shifted
significantly from free pentafluoropyridine (ortho: δ -87.0; para:
δ -133.5; meta: δ -161.0). The pentafluoropyridine ligand in 5
is labile: treatment of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4- with 1
atm of CO in o-difluorobenzene gave the carbonyl complex
-
(M ) Zr, Hf) with (1,3,5-C6H4Me3)+B(C6F5)4 in CH2Cl2
similarly forms [{(Cp2M(Ph)}2(µ-Cl)]+B(C6F5)4-; this analo-
gous reaction likely proceeds via the intermediacy of a dichlo-
romethane solvate and has been shown to involve the formation
of [(arene)CH2Cl]+.10 31P NMR spectra of 4 in SO2 display two
resonances at δ 82.1 (1JPtP) 1460 Hz) and 62.6 (1JPtP ) 5030
Hz) corresponding to phosphorus groups trans to the methyl
and bridging chloride ligands, respectively. 19F spectra reso-
-
[(dfepe)Pt(Me)(CO)]+B(C6F5)4 (6) (eq 6). 31P NMR data for 6
show a characteristic 1JPtP (trans to CO) of 3710 Hz, which closely
corresponds to the value for [(dfepe)Pt(Me)(CO)]+(OSO2F)- (3700
Hz).4f ν(CO) for 6 is 2174 cm-1, which is also essentially identical
to values found for [(dfepe)Pt(Me)(CO)]+(OTf)- and [(dfepe)Pt(Me)-
(CO)]+(OSO2F)- (2176 and 2174 cm-1) in their respective neat
acid solutions.
-
nances for the B(C6F5)4- counterion integrate as one B(C6F5)4
unit per two dfepe ligands, consistent with a monocation dimeric
formulation, which has been verified by X-ray diffraction data
(see later). Although 4 may be viewed as a 14-electron
(dfepe)PtMe+ unit stabilized by donor base coordination with
(dfepe)Pt(Me)Cl, its chemistry does not reflect this description.
For instance, treatment of a solution of 4 in CD2Cl2 with CO
does not give (dfepe)Pt(Me)Cl and (dfepe)Pt(Me)(CO)+, but
instead produces a complex product mixture.
Crystallographic Studies. All three structurally characterized
compounds 2, 4, and 5 contain square-planar (dfepe)Pt(Me)(X)
moieties (Figures 1–3). As anticipated, Pt-P bond distances
trans to the methyl ligand are all substantially lengthened by
the methyl ligand trans influence: 2.312 (av) Å for (2), 2.300
(av) Å for 4, and 2.329(1) Å for 5. These values are much
greater than the 2.233(2) Å value found for (dfepe)Pt(Me)2 and
similar to the 2.301(2) Å Pt-P bond distance trans to methyl
in (dfepe)Pt(Me)(OTf).13 There is a corresponding shortening
of the Pt-P bond trans to the more weakly coordinating X group
relative to (dfepe)Pt(Me)2: 2.158 (av) Å for 2, 2.166 (av) Å for
4, and 2.175(1) Å for 5; the Pt-P bond distance trans to OTf
in (dfepe)Pt(Me)(OTf) is 2.149(2) Å.
Bercaw and co-workers have reported that pentafluoropyridine
is both a weakly coordinating solvent and a ligand for cationic
platinum systems such as [(tmeda)Pt(Me)(NC5F5)]+BArf-.11
Accordingly, we have examined pentafluoropyridine as a
compatible solvent for our own platinum cation work. Treatment
of (dfepe)PtMe2 with (1,3,5-C6H4Me3)+B(C6F5)4- in pentafluo-
ropyridine at ambient temperature resulted in the preci-
pitation of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4- (5) in good yield
(eq 5).
A promising weakly coordinating polar aprotic solvent for
cationic transition metal complexes is ortho-difluorobenzene
(ODB), which has been previously utilized as an electrochemical
solvent.12 1H, 31P, and 19F NMR data in ODB, along with X-ray
A variety of coordination complexes having the Lewis acid
(C6F5)3B ligated to oxo groups,14 acyls,15 or amides16 are known.
Most relevant to the (dfepe)Pt(Me)(O2CCF3)B(C6F5)3 structure
are (C6F5)3B adducts with carboxylate ligands.17 The Pt-O bond
length in 2 (2.117 (av) Å) is slightly larger than Pt-O bonds
(13) Bennett, B. L.; Birnbaum, J.; Roddick, D. M. Polyhedron 1995,
14, 187–195.
(14) (a) Sa´nchez-nieves, J.; Royo, P.; Mosquera, M. E. G. Eur. J. Inorg.
Chem. 2006, 12, 7–132. (b) Sarsfield, M. J.; Helliwell, M. J. Am. Chem.
Soc. 2004, 126, 1036–1037. (c) Barrado, G.; Doerrer, L.; Green, M. L. H.;
Leech, M. A. J. Chem. Soc., Dalton Trans. 1999, 1061–1066.
(15) (a) Llewellyn, S. A.; Green, M. L. H.; Cowley, A. R. Dalton Trans.
2006, 1776–1783. (b) Anderson, G. D. W.; Boys, O. J.; Cowley, A. R.;
Green, J. C.; Green, M. L. H.; Llewellyn, S. A.; M.; von, Beckh, C. M.;
Pascu, S. I.; Vei, I. C. J. Organomet. Chem. 2004, 689, 4407–4419.
(16) Mountford, A. J.; Clegg, W.; Coles, S. J.; Harrington, R. W.;
Horton, P. N.; Humphrey, S. M.; Hursthouse, M. B.; Wright, J. A.;
Lancaster, S. J. Chem.-Eur. J. 2007, 13, 4535–4547.
(17) (a) Wasilke, J.-C.; Komon, Z. J. A.; Bu, X.; Bazan, G. C.
Organometallics 2004, 23, 4174–4177. (b) Shim, C. B.; Kim, Y. H.; Lee,
B. Y.; Dong, Y.; Yun, H. Organometallics 2003, 22, 4272–4280. (c) Komon,
Z. J. A.; Bu, X.; Bazan, G. C. J. Am. Chem. Soc. 2000, 122, 12379–12380.
(18) Pantcheva, I.; Osakada, K. Organometallics 2006, 25, 1735–1741.
(9) (a) Reed, C. A.; Kim, K.-C.; Stoyanov, E. S.; Stasko, D.; Tham,
F. S.; Mueller, L. J.; Boyd, P. D. W. J. Am. Chem. Soc. 2003, 125, 1796–
1804. (b) Reed, C. A.; Fackler, N. L. P.; Kim, K.-C.; Stasko, D.; Evans,
D. R.; Boyd, P. D. W.; Rickard, C. E. F. J. Am. Chem. Soc. 1999, 121,
6314–6315.
(10) Sydora, O. L.; Kilyanek, S. M.; Jordan, R. F. Organometallics 2007,
26, 4746–4755.
(11) Holtcamp, M. W.; Henling, L. M.; Day, M. W.; Labinger, J. A.;
Bercaw, J. E. Inorg. Chim. Acta 1998, 270, 467–478.
(12) (a) O’Toole, T. R.; Younathan, J. N.; Sullivan, B. P.; Meyer, T. J.
Inorg. Chem. 1989, 28, 3923–3926. (b) Sun, H.; Biffinger, J. C.; DiMagno,
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4509.

3662 Organometallics, Vol. 27, No. 15, 2008
Basu et al.
Figure 3. Molecular structure of [(dfepe)Pt(Me)(NC5F5)]+B-
-
(C6F5)4 (5) (borate anion and hydrogen atoms are omitted for
clarity) with atom-labeling scheme (ellipsoids are drawn at 30%
probability). Selected metrical data (Å, deg): Pt(1)-P(1): 2.1747(10);
Pt(1)-P(2): 2.3294(11); Pt(1)-C(11): 2.080(4); Pt(1)-N(1): 2.153(4);
C(11)-Pt(1)-N(1): 85.40(14).
Figure 1. Molecular structure of (dfepe)Pt(Me)(O2CCF3)B(C6F5)3
(2) (hydrogen atoms are omitted for clarity) with atom-labeling
scheme (ellipsoids are drawn at 30% probability; only the Pt(2)
unit with its associated atoms is shown). Selected metrical data
(Å, deg): Pt(2)-P(3) 2.314(2); Pt(2)-P(4) 2.161(2); Pt(2)-O(3)
2.115(5); Pt(2)-C(32) 2.084(7); O(3)-C(43) 1.245(9); C(43)-O(4)
1.258(9); O(4)-B(2) 1.571(10); C(32)-Pt(2)-O(3) 85.4(3);
P(3)-Pt(2)-P(4)85.57(8);C(43)-O(3)-Pt(2)133.5(5);O(3)-C(43)-O(4)
126.4(7); C(43)-O(4)-B(2) 127.6(6).
C-OB bond length of 1.260 (av) Å and the O-COB bond
length of 1.242 (av) Å for 2 fall within the range of reported
values,17 the O-B bond length is 1.58 (av) Å, which is slightly
elongated (∼0.04 Å) compared to other borane-carboxylate
adducts.
Dimeric platinum compounds bridged by a single chlorine
atom are not common.20 The main structural details of chloro-
bridged dimeric 4 are in accord with previously reported
systems. Observed Pt-Cl bond distances (2.378(3) and 2.381(3)
Å) are slightly shorter than values for platinum compounds with
trans alkyl and aryl phosphines (range: 2.390-2.421 Å)20a,c,e
and much longer than the 2.296(1) Å bond length reported for
the diimine system {[ArNdC(Me)C(Me)dNAr]Pt(Me)}2(η-
Cl)+.20b This ordering is consistent with the relative trans
influence of diimines, PFAPs, and donor phosphines. The angle
between the least-squares planes defined by each platinum
square-planar environment (69.8°) falls within the reported range
for other [(chelate)Pt(Me)]2(η-Cl)+ structures (65.6-73.4°); the
Pt-Cl-Pt angle (122.32(12)°) is slightly greater than the
112.7-120.2° range for these compounds.
Only two other pentafluoropyridine transition metal com-
plexeshavebeenreported.11,21 ThePt-Nbondin[Pt(dfepe)(Me)-
(NC5F5)]+B(C6F5)4- (2.153(4) Å) is significantly longer than
the Pt-N bond (2.043(6) Å) of [(tmeda)Pt(Me)(NC5F5)]+-
BArf-. This 0.11 Å difference in bond lengths is comparable
to the ∼0.08 Å bond length increase found for Pt-Cl in 4
compared to {[ArNdC(Me)C(Me)dNAr]Pt(Me)}2(η-Cl)+,
and as such could be largely attributed to the greater trans
Figure 2. Molecular structure of [{(dfepe)Pt(Me)}2(µ-
Cl)]+B(C6F5)4- (4) (borate anion and hydrogen atoms are omitted
for clarity) with atom-labeling scheme (ellipsoids are drawn at 30%
probability). Selected metrical data (Å, deg): Pt(1)-P(1): 2.165(3);
Pt(2)-P(4): 2.168(3); Pt(1)-P(2): 2.298(3); Pt(2)-P(3): 2.303(3);
Pt(1)-Cl(1): 2.381(3); Pt(2)-Cl(1): 2.378(3); Pt(1)-C(1): 2.082(11);
Pt(2)-C(2): 2.094(11); Pt(2)-Cl(1)-Pt(1): 122.32(12).
(19) Scriban, C.; Glueck, D. S.; Golen, J. A.; Rheingold, A. L.
Organometallics 2007, 26, 1788–1800.
(20) (a) Oberbeckmann-Winter, N.; Braunstein, P.; Welter, R. Orga-
nometallics 2004, 23, 6311–6318. (b) Albano, V. G.; di Serio, M.; Monari,
M.; Orabona, I.; Panunzi, A.; Ruffo, F. Inorg. Chem. 2002, 41, 2672–2677.
(c) Wile, B. M.; Burford, R. J.; McDonald, R.; Ferguson, M. J.; Stradiotto,
M. Organometallics 2006, 25, 1028–1035. (d) Charmant, J. P. H.; Fan, C.;
Norman, N. C.; Pringle, P. G. Dalton Trans. 2007, 114–123. (e) Dahlenburg,
L.; Mertel, S. J. Organomet. Chem. 2001, 630, 221–243.
(21) Huhmann-Vincent, J.; Scott, B. L.; Kubas, G. J. Inorg. Chem. 1999,
38, 115–124.
found in (dppe)Pt(O2CCF3)2 (2.078(4), 2.096(4) Å),18 (dfepe)Pt-
(Me)(OSO2CF3) (2.090(6) Å),13 and [Pt(Me-Duphos)(Ph)]2(µ-
CO3) (2.044(9), 2.079(8) Å)19 and is consistent with a weaken-
ing of the metal-carboxylate ligand interaction. While the

-
Synthesis of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4
Organometallics, Vol. 27, No. 15, 2008 3663
Scheme 1
consistent with initial production of propene was observed. All
platinum-bound alkyl resonances were obscured by a broadened
butene aliphatic resonance at 0.8 ppm. 31P NMR revealed a
single solution species with resonances at δ 77.3 (1JPtP ) 1220
Hz) and 66.0 (1JPtP ) 4730 Hz), shifted significantly from those
in 7 but consistent with an alkyl alkene complex, (dfepe)P-
t(alkyl)(η2-alkene)+ (8). After complete consumption of ethyl-
ene, resonances for 8 were replaced by broad poorly resolved
peaks at 80.0 and 76.3 ppm. After 1 day, three (dfepe)Pt
products with resonances at δ 81.7 (1JPtP ) 3600 Hz), 75.8 (1JPtP
) 3940 Hz), and 73.1 (1JPtP ) 3920 Hz) in a 1:3:1.4 ratio were
influence of dfepe relative to tmeda. The twist angle of the
NC5F5 aryl plane with respect to the Pt-centered square plane
is 78°, which is comparable to that found for [(tmeda)Pt(CH3)-
(NC5F5)]+[BArf]- (88°).
1
observed. The similarity of JPtP magnitudes to that for the
previously reported Pt(0) ethylene complex (dfepe)Pt(η2-C2H4)
Dimerization and Oligomerization of Ethylene by
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4-. Ni(II) and Pd(II) systems
can exhibit very high catalytic activities for ethylene dimerization,
oligomerization, or polymerization.1,22 Only limited catalytic
ethylene dimerization activity has been reported for Pt(II) com-
plexes (dfepe)Pt(Me)(O2CCF3) (dichloromethane, 65 °C, ∼1
1
(δ 81.2, JPtP ) 3643 Hz) suggests that these terminal species
are (dfepe)Pt(η2-alkene) products. The eventual formation of
Pt(0) species from Pt(II) precursors is likely due to proton
transfer from acidic (dfepe)Pt(H)(alkene)+ intermediates to the
more electron-rich alkene products.
turnover h-1; CF3CO2H, 80 °C, 6 turnover h-1 4e
and (di-
)
imine)Pt(H)(η2-C2H4)+BArf- (dichloroethane, 100 °C, ∼0.1 turn-
overs h-1).5 In stark contrast, [(dfepe)Pt(Me)(NC5F5)]+B-
(C6F5)4- is orders of magnitude more reactive than these related
systems: Exposure of a solution of [(dfepe)Pt(Me)(NC5F5)]+-
Conclusions
-
The preparation of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 (5)
provides an effective labile precursor to the (dfepe)Pt(Me)+
moiety, which can be studied under aprotic conditions in weakly
coordinating aprotic solvents. For group 10 nickel and palladium
diimine systems, the barriers to ethylene migratory insertion
are 13-14 and 17-19 kcal mol-1, respectively, much lower
than the corresponding 29.8 kcal mol-1 barrier reported for
platinum.5 Details on the underlying mechanism of ethylene
dimerization by 5 await further study. However, the clean
formation of [(dfepe)Pt(Me)(η2-C2H4)]+ in o-difluorobenzene
prior to the onset of dimerization activity at 10 °C is consistent
with a RDS involving ethylene insertion. From the greatly
enhanced observed rate of dimerization for 5 relative to
(diimine)Pt(Et)(η2-C2H4)+ we can conclude either (i) the barrier
to insertion in electron-poor (dfepe)Pt(Et)(η2-C2H4)+ is signifi-
cantly lower or (ii) a different mechanism is operative for
ethylene dimerization by this more electrophilic system. Alkene
oligomerization by electrophilic metal centers may proceed by
carbocationic intermediates or metal-stabilized carbenium ion
intermediates.24 Recently Vitagliano et al. have reported that
ethylene complexed to dicationic (PNP)Pt(II) is activated toward
external nucleophilic attack by electron-rich alkenes to form
coupled products.25 Further studies are underway to determine
the operative mechanism of ethylene dimerization and subse-
quent oligomerization of the butene products by [(dfepe)Pt-
(Me)(NC5F5)]+ and to more broadly explore the reactivity of
this and related systems.
-
B(C6F5)4 (ca. 0.02 M) to 600 psi of ethylene at 22 °C in
o-difluorobenzene results in the production of a thermodynamic
(∼2:1) trans:cis mixture of 2-butenes at an approximate initial rate
of 150 turnovers h-1 (Scheme 1). In a subsequent slower process,
70% consumption of butenes over a period of 20 h produced an
oligomeric product with aliphatic resonances between 0.6 and 2.0
ppm and vinylic resonances between 4.7 and 5.3 ppm in an
integrated ratio of 69 to 1. The Mn estimated from 1H NMR data
was ∼1000 (about 35 ethylene units).23 Preliminary GPC measure-
ments on the oily material yielded an approximate Mn value of
∼1600.
The reaction between [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4- and
ethylene in o-difluorobenzene was monitored by VT NMR.
Addition of 2 atm ethylene at -20 °C resulted in a clean
conversion to a new platinum complex with 31P NMR reso-
nances at δ 75.7 (1JPtP ) 1360 Hz) and 64.6 (1JPtP ) 4370 Hz).
Platinum coupling for the upfield resonance is reduced 590 Hz
relative to 5, indicative of replacement of pentafluoropyridine
by ethylene to form [(dfepe)Pt(Me)(η2-C2H4)]+B(C6F5)4 (7).
-
1H spectra show dfepe backbone multiplet resonances at δ 1.95
and 1.72 and a platinum-coupled methyl resonance at δ 0.30
(2JPtH ) 48 Hz) shifted slightly upfield compared to the methyl
resonance in 5. Under excess ethylene (∼2 equiv), an exchanged-
broadened ethylene resonance without platinum coupling was
observed at 4.4 ppm. The freezing point of o-difluorobenzene
(-34 °C) does not allow us to determine the slow exchange
limit between free and bound ethylene in this solvent. However,
solutions of 5 at -20 °C exposed to limiting amounts (<10
mol %) of ethylene showed partial conversion to 7 and a
broadened singlet resonance at δ 4.92 with platinum satellites
(2JPtH ) 56 Hz), which is assigned to the η2-C2H4 ligand.
The nature of the catalyst was monitored by 1H and 31P NMR
under the catalytic conditions (o-difluorobenzene, 22 °C, 600
psi of ethylene (ca. 125 equiv)). After mixing and warming to
Experimental Section
General Procedures. All manipulations were conducted under
an atmosphere of purified nitrogen using high-vacuum and/or
glovebox techniques. Dry, oxygen-free solvents were prepared using
standard procedures. Deuterated solvents used in NMR experiments
were dried over activated 3 Å molecular sieves. Elemental analyses
were performed by Desert Analytics. NMR spectra were obtained
with a Bruker DRX-400 instrument. IR spectra were taken with a
Bomem MB100 instrument as Nujol mulls using KCl plates. 31P
1
ambient temperature, initial H NMR spectra showed 6 equiv
of butene products, as well as a downfield shift of the dfepe
backbone resonances to δ 2.36 and 2.14. A vinylic resonance
(24) (a) Baird, M. C. Chem. ReV. 2000, 100, 1471–1478. (b) Albietz,
P. J.; Yang, K.; Lachicotte, R. J.; Eisneberg, R. Organometallics 2000, 19,
3543–3555. (c) Sen, A.; Lai, T.-W. J. Am. Chem. Soc. 1981, 103, 4627–
4629.
(25) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem.
Soc. 1976, 98, 6521–6528.
(22) (a) Speiser, F.; Braunstein, P.; Saussine, L. Acc. Chem. Res. 2005,
38, 784–793. (b) Schro¨der, D. L.; Keim, W.; Zuideveld, M. A.; Mecking,
S. Macromolecules 2002, 35, 6071–6073.
(23) Daugulis, O.; Brookhart, M.; White, P. S. Organometallics 2002,
21, 5935–5943.

3664 Organometallics, Vol. 27, No. 15, 2008
Basu et al.
-
Table 1. Crystallographic Data for (dfepe)Pt(Me)(O2CCF3)B(C6F5)3 (2), [{(dfepe)Pt(Me)}2(µ-Cl)]+B(C6F5)4 (4), and
-
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 (5)
-
-
(dfepe)Pt(Me)(O2CCF3)B(C6F5)3
[{(dfepe)Pt(Me)}2(µ-Cl)]+B(C6F5)4
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4
chemical formula
fw
T, K
C31H7BF38O2P2Pt
1401.20
100(2)
C46H14BClF60P4Pt2
2266.89
298(2)
C40H7F45P2Pt
1624.31
100(2)
λ, Å
space group
a, Å
b, Å
c, Å
0.71073
P21/c
37.2880(7)
11.7590(2)
37.4162(7)
90
91.4960(10)
90
16400.3(5)
8
0.71073
P1
0.71073
Cc
30.6236(6)
10.3226(2)
17.6987(4)
90
122.8130(10)
90
4702.13(17)
4
j
13.3406(14)
15.748(2)
17.943(2)
67.388(8)
75.126(9)
75.726(10)
3316.6(7)
2
2.270
4.556
0.0560
0.1448
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
Dcalc, Mg m-3
µ, mm-1
R1[I > 2σ(I)]a
wR2[I > 2σ(I)]b
2.270
3.708
0.0407
0.0790
2.294
3.269
0.0269
0.0529
2
2 2
a R1 ) ∑||Fo - |Fc||/∑|Fo|. b wR2 ) {∑[w(Fo - Fc ) ]∑w(Fo2)2] }1/2
.
spectra were referenced to an 85% H3PO4 external standard. 19F
spectra were referenced to CF3CO2Et as an external standard
(-75.32 ppm vs CFCl3 with downfield chemical shifts taken to be
positive). GPC measurements were taken on a Waters SEC equipped
with two 300 mm Waters Styrogel columns (molecular weight
ranges: 5 × 102 to 3 × 104, 5 × 103 to 6 × 105) and a Waters
2414 refractive index detector. (cod)PtCl2,25 (dfepe)Pt(Me)2,26
(dfepe)Pt(Me)(O2CCF3)(BF3) (3). A 20 mg amount of
(dfepe)Pt(Me)(O2CCF3) and 5 mL of CD2Cl2 were placed in a
Teflon valve NMR tube that was pressurized with ca. 2 atm of
BF3. NMR data for the resulting solution were consistent with the
formation of (dfepe)Pt(Me)(O2CCF3)(BF3). 1H NMR (CD2Cl2,
400.13 MHz, 20 °C): δ 2.85 (m, 2H; PCH2), 2.54 (m, 2H; PCH2),
0.33 (t, 3H, PtCH3). 31P NMR (161.70 MHz, CD2Cl2, 20 °C): δ
-
dfepe, and (C6Me3H4)+B(C6F5)4 were prepared according to
1
81.8 (P trans to CH3, m, JPt-P ) 1530 Hz), 56.2 (P trans to
literature methods.9b
1
O2CCF3(BF3), m, JPt-P ) 5380 Hz). 19F NMR (376.5 MHz,
-
[(dfepe)Pt(Me)(CH3CN)]+SbF6 (1). To a flask charged with
CD2Cl2, 20 °C): δ -77.8 (s, 3F; O2CCF3), -78.7 (s, 6F; PCF2CF3),
-78.9 (s, 6F; PCF2CF3), -107 to -110 (overlapping ABX
multiplets), -139.0 (s, 3F; BF3).
(cod)Pt(Me)(Cl) (0.75 g, 2.1 mmol) and AgSbF6 (0.73 g, 2.12
mmol) was added 15 mL of CH3CN. After 1 h of stirring at ambient
temperature the resulting precipitate was filtered off and washed
several times with acetonitrile. dfepe (1.44 g, 2.54 mmol) was added
to the filtrate, and after stirring the reaction mixture for 1 h, the
volatiles were removed and the residue was slurried in 10 mL of
methylene chloride. Filtration and washing of the white solid with
methylene chloride following by drying under vacuum yielded 1.732
g (80%) of 1. Anal. Calcd: C, 14.82; H, 0.95; N, 1.33. Found: C,
-
[{(dfepe)Pt(Me)}2(µ-Cl)]+B(C6F5)4 (4). To a flask charged
with 0.263 g of (dfepe)Pt(Me)2 (3.32 × 10-4 mol) and 0.32 g of
-
(C6Me3H4)+B(C6F5)4 (4.0 × 10-4 mol) was added 15 mL of
CH2Cl2. After 2 h of stirring, the resulting white solid was collected
by filtration, washed, and dried under vacuum to yield 0.31 g
(23.4%) of 4. Crystals suitable for diffraction analysis were grown
by slow diffusion of m-difluorobenzene into a solution of {[Pt(d-
fepe)Me]2(µ-Cl)}+[B(C6F5)4]- in o-difluorobenzene. Anal. Calcd
for C46H14F60BClP4Pt2: C, 24.40; H, 0.62. Found: C, 23.54; H, 0.68.
1H NMR (SO2, 400.13 MHz, 20 °C): δ 3.31 (m, 2H; PCH2), 3.02
(m, 2H; PCH2), 1.66 (d, 3JPH ) 6 Hz, 2JPtH ) 45 Hz, 3H, PtCH3).
31P NMR (161.70 MHz, SO2, 20 °C): δ 82.1 (P trans to CH3, m,
1
14.88; H, 0.77; N, 1.30. H NMR (acetone-d6, 400.13 MHz, 20
°C): δ 3.60 (m, 2H; PCH2), 3.30 (m, 2H; PCH2) 2.93 (s, 3H,
2
3
CH3CN), 1.43 (d, JPtH ) 51 Hz, JPH ) 7 Hz, 3H, PtCH3). 31P
NMR (161.70 MHz, acetone-d6, 20 °C): δ 81.9 (P trans to CH3,
1
1
m, JPtP ) 1400 Hz), 64.8 (P trans to CH3CN, m, JPtP ) 4680
Hz). 19F NMR (376.5 MHz, acetone-d6, 20 °C): δ -78.3 (s, 6F;
PCF2CF3), -79.1 (s, 6F; PCF2CF3), -106 to -110 (overlapping
ABX multiplets, 8F; PCF2CF3).
1
1JPtP ) 1460 Hz), 62.6 (P trans to µ-Cl, m, JPtP ) 5030 Hz). 19F
NMR (376.5 MHz, SO2, 20 °C): δ -79.1 (s, 6F; PCF2CF3), -79.6
(s, 6F; PCF2CF3), -107 to -111 (overlapping ABX multiplets),
(dfepe)Pt(Me)(O2CCF3)B(C6F5)3 (2). To a flask charged with
(dfepe)Pt(Me)(O2CCF3) (0.19 g, 2.2 × 10-4 mol) and B(C6F5)3
(0.135 g, 2.64 × 10-4 mol) was added 15 mL of methylene
chloride. After 3 h of stirring the resulting white solid 2 was
collected by filtration, washed, and dried under vacuum to yield
0.33 g of borane adduct (82%). Crystals suitable for diffraction
analysis were grown by slowly cooling a warm, saturated dichlo-
romethane solution. Anal. Calcd for C31H7F38BO2P2Pt: C, 26.57;
H, 0.50. Found: C, 26.20; H, 0.33. IR (cm-1): 1653(s), 1226(br,
3
-132.0 (br s, 8F; o-ArF), -162.9 (t, JFF ) 20 Hz, 4F; p-ArF),
3
-166.5 (t, JFF ) 20 Hz, 4F; m-ArF).
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4- (5). To a flask charged with
-
(dfepe)Pt(Me)2 (0.25 g, 3.2 × 10-4 mol) and (C6Me3H4)+B(C6F5)4
(0.33 g, 4.1 × 10-4 mol) was added 25 mL of pentafluoropyridine.
After 2 h of stirring the resulting white solid 5 (0.45 g, 88%) was
collected by filtration, washed, and dried under vacuum. Crystals
suitable for diffraction analysis were grown by slow diffusion of
m-difluorobenzene into a solution of [(dfepe)Pt(Me)(NC5F5)]+-
B(C6F5)4- in o-difluorobenzene. Anal. Calcd for C40H7F45BNP2Pt:
C, 29.57; H, 0.43. Found: C, 29.56; H, 0.71. 1H NMR (400.13
MHz, o-difluorobenzene, 20 °C): δ 2.01 (m, 2H; PCH2), 1.71 (m,
1
s), 1156(m), 984(s). H NMR (CD2Cl2, 400.13 MHz, 20 °C): δ
2
2.82 (m, 2H; PCH2), 2.52 (m, 2H; PCH2), 0.78 (d, JPtH ) 40.17
Hz, 3JPH ) 7.07 Hz, 3H, PtCH3). 31P NMR (161.70 MHz, CD2Cl2,
20 °C): δ 81.9 (P trans to CH3, m, 1JPtP ) 1530 Hz), 62.1 (P trans
to (O2CCF3)B(C6F5)3, m, 1JPtP ) 5220 Hz). 19F NMR (376.5 MHz,
CD2Cl2, 20 °C): δ -78.0 (s, 6F; PCF2CF3), -79.0 (s, 6F; PCF2CF3),
-106 to -110 (overlapping ABX multiplets, 8F; PCF2CF3), -134.4
(br s, 8F; o-ArF), -160.7 (br s, 4F; p-ArF), -163.5 (br s, 8F;
m-ArF).
2H; PCH2), 0.17 (br s, JPtH ) 43 Hz, 3H, PtCH3). 31P NMR
2
(161.70 MHz, o-difluorobenzene, 20 °C): δ 82.4 (P trans to CH3,
m, 1JPtP ) 1490 Hz), 60.9 (P trans to NC5F5, m, 1JPtP ) 4950 Hz).
19F NMR (376.5 MHz, o-difluorobenzene, 20 °C): δ -77.9 (s, 6F;
PCF2CF3), -78.4 (s, 6F; PCF2CF3), -105 to -109 (overlapping
ABX multiplets, 8F; PCF2CF3), -115.2 (p, J ) 20 Hz, 1F;
p-C5F5N), -130.8 (br s, 8F; o-B(C6F5)4), -153.7 (br s, 2F; meta-
(26) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411–
428.

-
Synthesis of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4
Organometallics, Vol. 27, No. 15, 2008 3665
C5F5N; ortho-C5F5N obscured by solvent resonance at -139 ppm),
2θ range of 3.68° to 50.00° with the data collected having -1 e
h e 15, -17 e k e 17, -20 e l e 21 using the XSCANS
program.29 Three standard reflections measured after every 97
reflections exhibited no significant loss of intensity. The structure
was solved by direct methods and refined by least-squares
techniques adapting the full-matrix weighted least-squares scheme,
w-1 ) σ2Fo2 + (0.0851P)2 + 20.4914P, where P ) (Fo2 + 2Fc2)/
3, on F2 using the SHELXTL program suite.27,30 The asymmetric
unit consists of discrete well-separated [{(dfepe)Pt(Me)}2(µ-Cl)]+
and B(C6F5)4- ions located on general positions. All non-hydrogen
atoms were located in the difference maps during successive cycles
of least-squares and refined anisotropically. The (C11-C12)
perfluoroethyl group is partially disordered with no satisfactory
model; therefore, the two carbon atoms and their associated fluorine
atoms were assigned fixed positional and thermal parameters. All
hydrogen atoms were placed in calculated positions and refined
isotropically with a riding model. The final refinement parameters
were R1 ) 0.0560 and wR2 ) 0.1448 for data with F > 4σ(F) and
R1 ) 0.0767 and wR2 ) 0.1591 for all data with the data to
parameter ratio of 12.
3
-162.0 (t, JFF ) 20 Hz, 4F; p-B(C6F5)4), -165.9 (m, 8F;
m-B(C6F5)4).
-
[(dfepe)Pt(Me)(CO)]+B(C6F5)4 (6). To a flask charged with
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 (5) (0.11 g, 6.8 × 10-5 mol)
-
was added 10 mL of o-difluorobenzene. After 2 h of stirring at
room temperature under 1 atm of CO, the solution was concentrated
and precipitated with methylene chloride to give a white solid,
which was isolated by filtration and dried under vacuum (0.51 g,
50%). Anal. Calcd for C36H7F40BOP2Pt: C, 29.15; H, 0.48. Found:
C, 28.81; H, 0.76. IR (o-difluorobenzene): 2174 cm-1. H NMR
1
(o-difluorobenzene, 400.13 MHz, 20 °C): δ 2.16 (m, 2H; PCH2),
2.03 (m, 2H; PCH2), 0.66 (t, 2JPtH ) 59.3 Hz, 3JPH ) 10.7 Hz, 3H,
PtCH3). 31P NMR (161.70 MHz, o-difluorobenzene, 20 °C): δ 84.7
(P trans to CH3, m, 1JPtP ) 1350 Hz), 70.9 (P trans to CO, m, 1JPtP
) 3710 Hz).
Preparation of [(dfepe)Pt(Me)(η2-C2H4)]+B(C6F5)4- (7). In a
typical experiment, a 5 mm NMR tube fitted with a Teflon valve
(Chemglass CG-512 or New Era NE-CAV-VBP) was charged with
ca. 20 mg of 5 and 0.5 mL of o-difluorobenzene and cooled to
-80 °C. Approximately 2 atm of ethylene was added via syringe,
and the solution was warmed to -20 °C with stirring. Low-
temperature NMR data confirmed the clean formation of [(dfepe)Pt-
(Me)(η2-C2H4)]+B(C6F5)4-. 1H NMR (400.13 MHz, o-difluoroben-
zene, -20 °C): δ 1.95 (m, 2H; PCH2), 1.72 (m, 2H; PCH2), 0.30
X-ray diffraction data were collected for [(dfepe)Pt(Me)(NC5F5)]+-
-
B(C6F5)4 (5) on a Bruker AXS SMART CCD diffractometer
employing Mo KR radiation (graphite monochromator) at 100 K.
Standard Bruker control and integration software were employed, and
Bruker SHELXTL software was used for structure solution, refinement,
and graphics. The unit cell parameters were obtained from a least-
squares fit to the angular coordinates of all reflections. Intensities were
integrated from a series of frames (0.3° ω rotation) covering more
than a hemisphere of reciprocal space. Absorption and other corrections
were applied using TWINABS.31 5 crystallizes in the monoclinic space
group Cc. The asymmetric unit consists of well-separated and well-
2
(br. s, JPtH ) 48 Hz, 3H, PtCH3). 31P NMR (161.70 MHz,
o-difluorobenzene, -20 °C): δ 75.7 (P trans to CH3, m, 1JPtP ) 1360
1
Hz), 64.6 (P trans to ethylene, m, JPtP ) 4370 Hz).
X-ray Crystallographic Studies. X-ray diffraction data were
collected for (dfepe)Pt(Me)[(O2CCF3)B(C6F5)3] (2) on a Bruker AXS
SMART CCD diffractometer employing Mo KR radiation (graphite
monochromator) at 173 K. Standard Bruker control (SMART, 1997)
and integration (SAINT, 1997) software were employed, and Bruker
SHELXTL software (Sheldrick, 1997) was used for structure solution,
refinement, and graphics.27 The unit cell parameters were obtained
from a least-squares fit to the angular coordinates of all reflections.
Intensities were integrated from a series of frames (0.3° ω rotation)
covering more than a hemisphere of reciprocal space. Absorption and
other corrections were applied using SADABS (Sheldrick, 1996).28
Compound 2 crystallizes in the monoclinic space group C2/c. The
asymmetric unit contains two well-separated independent molecules.
One molecule (Pt(1) and its associated atoms) exhibits some disorder
in the difluoromethylene carbon atoms (C8 and C10), as reflected in
their high thermal parameters. The remainder of this molecule and
the second molecular unit are well-ordered. All non-hydrogen atoms
were located in the Fourier maps and refined anisotropically. The H
atoms were placed in calculated positions and were refined isotropically
by a riding model.
-
ordered [(dfepe)Pt(Me)(NC5F5)]+ and B(C6F5)4 ions. All non-
hydrogen atoms were located in the Fourier maps and refined
anisotropically. The H atoms were placed in calculated postions and
refined isotropically using a riding model. The final refinement
parameters were R1 ) 0.0269 and wR2 ) 0.0529 for data with F >
4σ(F) and R1 ) 0.0312 and wR2 ) 0.0552 for all data with the data
to parameter ratio of 13. The absolute configuration of the formula
unit was verified satisfactorily by refining the Flack parameter close
to zero (-0.003(3)).32 Crystallographic data collection parameters and
refinement data for compounds 2, 4, and 5 are summarized in Ta-
ble 1.
Acknowledgment. We thank The National Science Foun-
dation (CHE-0457435) and DOE/EPSCoR (DE-FG02-
05ER46185) for financial support.
Supporting Information Available: Complete tables of atomic
coordinates, thermal parameters, and bond distances and angles for
complexes 2, 4, and 5. This material is available free of charge via
the Internet at http://pubs. acs.org.
X-ray diffraction data were collected for [{(dfepe)Pt(Me)}2(µ-
-
Cl)]+B(C6F5)4 (4) on a Bruker P4 diffractometer equipped with
a molybdenum tube and a graphite monochromator at 298 K. A
colorless crystal of approximate dimensions 0.64 mm × 0.48 mm
× 0.20 mm in a sealed glass capillary was used for data collection.
A total of 11 469 (Rint ) 0.0590) reflections were gathered in the
OM8003509
(27) SAINT-NT (Ver. 5/6.0), Software for the CCD Detector System;
Bruker AXS: Madison, WI, 1997. SMART (Ver. 5.631), Software for
the CCD Detector System; Bruker AXS: Madison, WI, 1997. Sheldrick,
G. M. SHELXS97 and SHELXL97; University of Go¨ttingen, Germany,
1997.
(28) Sheldrick, G. M. SADABS, A Program for Area Detector Absorption
Corrections; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(29) Bruker, G. XSCANS (Ver. 2.31): Bruker AXS, Inc.: Madison, WI,
1993.
(30) Bruker, G. SHELXTL (Ver. 5.10): Bruker AXS, Inc.: Madison, WI,
1997.
(31) Sheldrick, G. M. TWINABS; University of Go¨ttingen: Go¨ttingen,
Germany, 2002.
(32) Flack, H. D. Acta Crystallogr. 1983, A39, 876–881.