Acceptor pincer coordination chemistry of platinum: reactivity properties of ((CF3PCP)Pt(L)+ (L = NC5F5, C2H4)

Article abstract of DOI:10.1021/om8008876

Synthetic strategies toward the synthesis of electron-poor pincer complexes (^CF3PCP)PtH and (^CF3PCP)Pt(η² H ²⁺) are described. Metathesis of (^CF3PCP)PtCl with hydride reagents does not lead to (^C

Full text of DOI:10.1021/om8008876

1148
Organometallics 2009, 28, 1148–1157
Acceptor Pincer Coordination Chemistry of Platinum: Reactivity
Properties of (CF3PCP)Pt(L)+ (L ) NC5F5, C2H4)
Jeramie J. Adams, Navamoney Arulsamy, and Dean M. Roddick*
Department of Chemistry, Box 3838, UniVersity of Wyoming, Laramie, Wyoming 82071
ReceiVed September 11, 2008
Synthetic strategies toward the synthesis of electron-poor pincer complexes (CF PCP)PtH and
3
CF3
CF3
2
+
3
(
(
PCP)Pt(η -H2) are described. Metathesis of (CF PCP)PtCl with hydride reagents does not lead to
PCP)PtH; (CF3PCP)PtCl with KH in tetrahydrofuran (THF) afforded an unusual metallated bimetallic
1
3-
pincer product (CF PCP)Pt[κ -C,κ P,C,P-2,6-(CHP(CF3)2)(CH2P(CF3)2)-C6H3]PtCl, which has been
3
CF3
structurally characterized. Chloride abstraction from (CF PCP)PtCl or protonolysis of ( PCP)PtMe in
3
+
the presence of H2 gives the structurally characterized hydride-bridged dimer {(CF PCP)Pt}2(µ-H) . In
3
the presence of trapping ligands H2O, C2H4, or pentafluoropyridine, the corresponding complexes
CF3
(
PCP)Pt(L)+ (L ) H2O, C2H4, NC5F5) are cleanly produced and have been structurally characterized.
The C2H4 and NC5F5-adducts may be alternatively prepared by methide abstraction from (CF PCP)PtMe
3
with Ph3C+B(C6F5)4 in the presence of trapping ligand. Evidence for the transient formation of
CF3
CF3
-
(
(
PCP)PtH from treatment of (CF3PCP)PtCl or (CF3PCP)Pt(NC5F5)+ with Et3Si+B(C6F5)4 is presented.
PCP)Pt(C2H4)+ serves as a catalyst for ethylene hydrogenation (0.30 turnovers h-1, 70 °C) and
hydrosilation with Et3SiH (460 turnovers h-1, RT) and Cl3SiH (5 turnovers h-1, RT). At elevated
+
-1
temperatures, (CF PCP)Pt(C2H4) also exhibits limited ethylene dimerization activity (0.07 turnovers h ,
3
155 °C) and 1-butene isomerization (0.9 turnovers h-1, 80 °C).
as a stable strongly electrophilic 14 e- metal center for mediating
Introduction
substrate activation processes. Initial targets for this work
Research involving monoanionic terdentate PCP “pincer”
(PCP ) 2,6-C6H3(EPR2)2; E ) CH2 or O) ligands has expanded
to include a diverse range of steric and electronic tuning
effects.1,2 Most PCP ligands incorporate donating phosphine
groups such as EPR2 ) CH2PR2 (R ) Ph, Pr, Bu), but more
recently phosphinite, perfluoroaryl-, and pyrrolyl-substituted
PCP ligands have been introduced which have significant
π-acceptor abilities.3-5 We have recently reported the synthesis
2
+
2
+
included (CF PCP)Pt(η -H2) and (CF PCP)Pt(η -alkene) .
3
3
We report here efforts to prepare the hydride or dihydrogen
CF3
2
+
complexes (CF PCP)PtH and ( PCP)Pt(η -H2) and the syn-
3
thesis of the adducts (CF PCP)Pt(NC5F5) and (CF PCP)-
+
3
3
i
t
Pt(η2-C2H4)+. (CF PCP)Pt(η -C2H4) serves as a catalyst for
2
+
3
ethylene hydrogenation (0.30 turnovers h-1, 70 °C) and also
exhibits limited ethylene dimerization activity (0.07 turnovers
+
h-1, 155 °C). We find that (CF PCP)Pt(NC5F5) reacts rapidly
3
and coordination properties of a new strong π-acceptor PCP
at subambient temperatures with Et3SiH to give redistribution
products. In the presence of excess ethylene or propylene,
6
ligand, 1,3-C6H4(CH2P(CF3)2)2 (CF PCPH). Initial work focused
3
on the synthesis of platinum derivatives (CF PCP)Pt(X) (X )
3
catalytic hydrosilation is observed with Et3SiH and Cl3SiH and
Cl, Me); of particular interest was the synthesis of the carbonyl
CF3
(
PCP)Pt(η2-C2H4)+ under ambient conditions. The underlying
cation (CF PCP)Pt(CO) by halide abstraction by Ag , since this
+
+
3
mechanism of these reactions is discussed.
demonstrated access to the (CF PCP)Pt moiety. We are inter-
+
3
ested in exploring the chemistry of (CF PCP)Pt and its potential
+
3
Results and Discussion
(1) (a) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003, 103, 1759–
1792. (b) Singleton, J. T. Tetrahedron 2003, 59, 1837–1857. (c) Albrecht,
M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750–3781.
(2) (a) Bedford, R. B.; Betham, M.; Blake, M. E.; Coles, S. J.; Draper,
S. M.; Hursthouse, M. B.; Scully, P. N. Inorg. Chem. Acta. 2006, 359,
1870–1878. (b) Gomez-Benitez, V.; Baldovino-Pantaleon, O.; Herrera-
Alvarez, C.; Toscano, R. A.; Morales-Morales, D. Tetrahedron Lett. 2006,
47, 5059–5062. (c) Wang, Z.; Sugiarti, S.; Morales, C. M.; Jensen, C. M.;
Morales-Morales, D. Inorg. Chim. Acta 2006, 359, 1923–1928. (d) Ceron-
Camacho, R.; Gomez-Benitez, V.; Le Lagadec, R.; Morales-Morales, D.;
Toscano, R. A. J. Mol. Catal. A: Chem. 2006, 247, 124–129.
(3) Chase, P. A.; Gagliardo, M.; Lutz, M.; Spek, A. L.; van Klink,
G. P. M.; van Koten, G. Organometallics 2005, 24, 2016–2019.
(4) Kossoy, E.; Iron, M. A.; Rybtchinski, B.; Ben-David, Y.; Shimon,
L. J. W.; Konstantinovski, L.; Martin, J. M. L.; Miltsein, D. Chem.sEur.
J. 2005, 11, 2319–2326.
CF3
Attempted
Synthesis
of
(
PCP)Pt(H)
and
t
CF3
(
(
PCP)Pt(η2-H2)+. The synthesis of (BuPCP)PtH from
t
BuPCP)PtCl and NaBH4 or LiAlH4 is well known.7 However,
treatment of (CF PCP)PtCl with hydride reagents NaBH4, LiAlH4,
and LiEt3BH led to uncharacterized product mixtures with no
3
associated 1H NMR hydride resonances. Treatment of
CF3
(
PCP)PtCl or (CF3PCP)PtMe with either stoichiometric or
excess Et3SiH similarly did not afford identifiable products. The
reaction of (CF PCP)PtCl with excess PhSiH3 in benzene resulted
3
in vigorous hydrogen evolution; after 5 h, the solution was a
deep red color, and 31P NMR showed only uncoordinated
CF3
PCPH. Some insight into these observations is given by the
reaction of (CF PCP)PtCl with KH in tetrahydrofuran (THF):
(5) (a) Gagliardo, M.; Havenith, R. W. A.; van Link, G.; van Koten, G.
J. Organomet. Chem. 2006, 691, 4411–4418. (b) Gagliardo, M.; Chase,
P. A.; Lutz, M.; Spek, A. L.; Hartl, F.; Havenith, R. W. A.; van Klink,
G. P. M.; van Koten, G. Organometallics 2005, 24, 4553–4557.
(6) Adams, J. J.; Lau, A.; Arulsamy, N.; Roddick, D. M. Inorg. Chem.
2007, 46, 11328–11334.
3
(7) (a) Kimmich, B. F. M.; Bullock, R. M. Organometallics 2002, 21,
1504–1507. (b) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans.
1976, 1020–1024.
10.1021/om8008876 CCC: $40.75
2009 American Chemical Society
Publication on Web 01/26/2009

Acceptor Pincer Coordination Chemistry of Pt
Organometallics, Vol. 28, No. 4, 2009 1149
Scheme 1
+
AgSbF6 yielded the aquo complex (CF PCP)Pt(H2O) SbF6- (3).
3
In the presence of 1 atm of H2, the hydride-bridged cation
{(CF PCP)Pt}2(µ-H) SbF6- (4a) was cleanly produced. Monitor-
+
3
ing the reaction between (CF PCP)PtCl and AgSbF6 by NMR in
3
CD2Cl2, acetone-d6, THF, and 1,2-difluorobenzene under 1-3
atm of H2 showed only 4a being formed, with no evidence for
the intermediacy of (CF PCP)Pt(η -H2) or ( PCP)PtH. There
was no change in the course of the reaction in the presence of
excess (∼4 equiv) added Et3N. The formulation of 4a as a
hydride-bridged cation is clearly indicated by 1H NMR, which
exhibits a pentet (2JPH ) 10 Hz) hydride resonance at δ -5.33
with a characteristic 1:8:18:8:1 splitting due to two equivalent
platinum centers with natural abundance 195Pt (1JPtH ) 254 Hz).
The molecular structure of 4a has been determined (see later).
2
+
CF3
3
1
Figure 1. Molecular structure of (CF PCP)Pt[κ -C,κ3-P,C,P-2,6-
(CHP(CF3)2)(CH2P(CF3)2)-C6H3]PtCl (1) with partial atom labeling
scheme (50% probability ellipsoids). Only one of the independent
molecular units is shown. Aromatic hydrogen atoms and the CF3
groups on P1 and P2 are omitted for clarity. Selected metrical data:
Pt(1)-P(1), 2.2475(8); Pt(1)-P(2), 2.2206(8); Pt(1)-Cl(1), 2.100(3);
Pt(1)-C(22), 2.182(3); Pt(2)-P(3), 2.2292(8); Pt(2)-P(4), 2.2356(7);
Pt(2)-C(13), 2.033(3); Pt(2)-Cl(1), 2.2656(7). P(1)-Pt(1)-P(2),
153.59(3); C(1)-Pt(1)-C(22), 174.61(11); P(3)-Pt(2)-P(4),
163.08(3); C(13)-Pt(2)-Cl(1), 179.05(9).
3
Protonolysis of (CF PCP)PtMe by the mesitylenium acid
3
reagent (C6Me3H4)+B(C6F5)4- was also examined. In methylene
chloride, the chloride-bridged dimer {(CF PCP)Pt}2(µ-
3
slow evaporation of a dichloromethane filtrate extract of the
Cl)+B(C6F5)4 (2b) was cleanly produced in the absence of
-
initial complex product mixture afforded a small amount (<5%)
of an unusual metallated bimetallic product (CF PCP)Pt[κ -C,κ -
P,C,P-2,6-(CHP(CF3)2)(CH2P(CF3)2)C6H3]PtCl (1) which was
characterized by X-ray crystallography (eq 1, Figure 1). The
origin of this metallated product is likely due to deprotonation
of a benzylic CH2 group by KH, which is rendered acidic by
1
3
3
hydrogen gas (Scheme 1). We have recently reported the
analogous production of {(dfepe)Pt(Me)}2(µ-Cl)+ from (dfepe)Pt-
Me2 and (C6Me3H4)+B(C6F5)4- in CH2Cl2.8 In the less reactive
solvent 1,2-difluorobenzene under 1 atm of H2, {(CF PCP)Pt}2(µ-
3
H)+B(C6F5)4 (4b) was exclusively produced.
-
+
-
The protonolysis of (CF PCP)PtMe by (C6Me3H4) B(C6F5)4
3
the adjacent P(CF3)2 center, followed by alkylation of unreacted
CF3
in 1,2-difluorobenzene was monitored by VT NMR. Upon
thawing at -30 °C, evolution of methane was observed and a
new major species (ca. 70-80%) was produced. This product
had significant shifts in 1H, 19F, and 31P NMR resonances relative
(
PCP)PtCl. This sensitivity of the CF3PCP ligand to benzylic
deprotonation may explain a lack of success with hydridic/basic
reagents, though we note that (CF PCP)PtCl is cleanly alkylated,
3
6
not deprotonated, by MeMgBr to form (CF PCP)PtMe.
3
to (CF PCP)PtMe (see Experimental Section) and persisted in
3
solution at ambient temperatures. Attempts to isolate the major
product from this reaction, however, were unsuccessful. In the
presence of 3 atm of H2, -30 °C spectra again show the same
major product with no associated hydride resonances. Upon
warming to 10 °C, however, the hydride-bridged dimer 4b was
formed. At 25 °C, ∼60% had converted to 4b, and complete
conversion occurred after 20 min at 25 °C.
CF3
2
An alternative approach to (CF PCP)PtH and ( PCP)Pt(η -
3
Interestingly, the elusive hydride complex (CF PCP)PtH has
3
H2)+ via chloride abstraction from (CF PCP)PtCl in the presence
3
been observed as a transient species in the reaction of
CF3
PCP)PtCl with Et3Si+B(C6F5)4- in 1,2-difluorobenzene. After
of dihydrogen was also examined. In the absence of added
(
hydrogen, (CF PCP)PtCl combined with AgSbF6 in CH2Cl2
several minutes at ambient temperatures 1H NMR spectra
3
cleanly produced the chloride-bridged dimer, {(CF PCP)Pt}2(µ-
3
Cl)+SbF6- (2a) (Scheme 1), which was structurally characterized
(8) Basu, S.; Arulsamy, N.; Roddick, D. M. Organometallics 2008, 27,
3659–3665.
(see later). In the presence of water, halide abstraction by

1150 Organometallics, Vol. 28, No. 4, 2009
Adams et al.
Scheme 2
showed a 2:1 mixture of hydride-bridged dimer 4b and a new
species with a triplet hydride resonance at δ -5.73 (1JPtH ) 7
data for the product from protonolysis in the absence of trapping
ligands. We are not able to account for this difference. 13C NMR
spectra for 7 show an ethylene resonance at δ 87.3 with a 1JCH
coupling of 168 Hz, somewhat higher than the free ethylene
value of 157 Hz. This is consistent with the very high ν(CO)
value observed for the analogous carbonyl complex
Hz, 2JPH ) 224 Hz) which we assign to (CF PCP)PtH (5). After
3
3 h at ambient temperature, 5 quantitatively converted to the
hydride-bridged dimer. VT NMR experiments confirmed the
formation of the hydride complex 5: at -30 °C, an ∼80:20
8
mixture of (CF PCP)PtH and 4b was observed, and at -20 °C a
(
PCP)Pt(CO)+ (2143 cm-1) and similarly reflects limited
CF3
3
1
50% conversion to the cationic dimer had occurred. The ultimate
source of the hydride was not identified. Attempts to extract
metal backbonding in this system. A VT H NMR experiment
with 7 and 1 equiv of C2H4 was carried out: some broadening
and shifting of the free and coordinated C2H4 resonances were
observed, but no coalescence occurred up to 100 °C in 1,2-
difluorobenzene.
+
-
neutral complex 5 from the (CF PCP)PtCl and Et3Si B(C6F5)4
3
reaction mixture into benzene or pentafluoropyridine resulted
in the precipitation of 4b.
Control experiments were carried out: treating
Crystallographic Studies. All structurally characterized
complexes consist of square planar platinum units with minor
deviations from planarity stemming from steric influences. The
κ1,κ3 metallated bridging mode observed in 1 has not been
previously observed in PCP ligand coordination chemistry,
though R-carbon phosphine metalation and dimer formation is
known for dppm,9 dmpe,10 and Ph2P(cyclopentadienyl) phos-
phine systems.11 In 1, the environment around the platinum
attached to the benzylic position (Pt1) is distorted with the
phosphorus atoms bent slightly (0.20, 0.21 Å from the least-
squares Pt coordination plane) toward the less sterically crowded
PCP arene ring and away from the P(CF3)2 group adjacent to
the point of metalation (Figure 1). The planar coordination
environment about Pt(2), in contrast, has deviations less than
0.07 Å and reflects less sterically induced distortion. A metrical
CF3
-
(
PCP)Pt(NC5F5)+B(C6F5)4 , a labile source of the (CF3PCP)Pt+
moiety (see below), with Et3SiCl in 1,2-difluorobenzene resulted
in no reaction after heating at 100 °C for 24 h. However, reaction
of (CF PCP)Pt(NC5F5) B(C6F5)4- with Et3Si+B(C6F5)4- gave the
+
3
hydride complex 5 in 70% yield after 10 min at RT, as judged
by NMR spectroscopy. Interestingly, after 48 h, 5 had reverted
back to primarily (CF PCP)Pt(NC5F5) B(C6F5)4- (90%) and only
+
3
1
∼10% of the hydride-bridged dimer 4b was observed. VT H
and 13C NMR spectra showed a series of resonances in the
ethylsilyl region which suggest that the silyl cation from
Et3Si+B(C6F5)4- undergoes complex reactivity and is likely the
source for the hydride ligand.
+
Synthesis of (CF PCP)Pt(L) (L ) NC5F5, C2H4). The
3
+
transient (CF PCP)Pt moiety can be efficiently trapped by added
3
ligands. Thus, the reaction between (CF PCP)PtMe and
parameter that exhibits a good correlation with (CF PCP)Pt steric
3
3
(C6Me3H4)+B(C6F5)4- in the presence of pentafluoropyridine or
environment is the P-Pt-P bond angle. In relatively undistorted
square planar complexes and in the Pt(2) unit of 1, P-Pt-P
angles range between 161° and 163°. For the Pt(1) center in 1
(153.6°) and the dimeric bridged complexes 2a (158.7° ave)
and 4a (153.6° ave), this angle decreases due to bending the
pendant phosphine pincer arms out of the platinum coordination
plane.
ethylene cleanly afforded (CF PCP)Pt(NC5F5) B(C6F5)4- (6) and
+
3
CF3
-
(
PCP)Pt(η2-C2H4)+B(C6F5)4 (7), respectively (Scheme 2).
In our recently reported syntheses of (dfepe)Pt(Me)(L)+
complexes, we noted that methide abstraction from (dfepe)PtMe2
by trityl cation did not readily occur. In contrast, (CF PCP)PtMe
3
-
does react with Ph3C+B(C6F5)4 in the presence of C2H4 or
pentafluoropyridine to also give 6 and 7, presumably due to
the greater trans-labilizing ability of the PCP aryl unit. In the
absence of trapping ligand, 80% conversion to a new species
was observed by NMR; 31P NMR spectra show a major
resonance at 65.8 ppm (1JPtP ) 3480 Hz), 19F NMR spectra show
a corresponding new PCF3 multiplet at -55.8, and a new
benzylic proton resonance was observed at 2.75 ppm. The
methyl resonance of 1,1,1-triphenylethane was also observed
at 0.89 ppm in 1H NMR spectra. The spectroscopic data obtained
For all complexes, the C(aryl)-Pt distances vary according
to the trans influence of the remaining ligand. The longest
C(aryl)-Pt distance is observed for Pt(1) in 1 (2.100(3) Å),
where the trans group is the benzyl group of the pincer ligand
(9) Brown, M. P.; Yavari, A. J. Organomet. Chem. 1983, 256, C19-
C22.
(10) Cotton, F. A.; Hunter, D. L.; Frenz, B. A. Inorg. Chim. Acta 1975,
15, 155–160.
(11) Fallis, K. A.; Anderson, G. K.; Lin, M.; Rath, N. P. Organometallics
1994, 13, 478–488.
for the reaction of (CF PCP)PtMe and trityl cation does not match
3

Acceptor Pincer Coordination Chemistry of Pt
Organometallics, Vol. 28, No. 4, 2009 1151
+
Figure 2. [(CF PCP)Pt]2(µ-Cl) SbF6- (2a) with partial atom labeling scheme (50% probability ellipsoids). Phosphine CF3 groups have been
omitted for clarity. Selected metrical data: Pt(1)-P(1), 2.2372(7); Pt(1)-P(2), 2.2483(6); Pt(1)-C(1), 2.035(2); Pt(1)-C1(1), 2.4196(6);
Pt(2)-P(3), 2.2423(7); Pt(2)-P(4), 2.2421(7); Pt(2)-C(13), 2.029(3); Pt(2)-Cl(1), 2.4144(6); Pt(1)-Pt(2), 4.0872(2); P(1)-Pt(1)-P(2),
158.59(3); C(1)-Pt(1)-Cl(1), 175.91(7); P(3)-Pt(2)-P(4), 158.80(3); C(13)-Pt(2)-Cl(1), 176.75(7); Pt(1)-Cl(1)-Pt(2), 115.45(3).
3
+
-
Figure 3. Molecular structure of (CF PCP)Pt(H2O) SbF6 (3) with partial atom labeling scheme (50% probability ellipsoids). Only one of
the independent molecular units is shown. Selected metrical data: Pt(1)-C(1), 2.016(2); Pt(1)-O(1W), 2.145(2); Pt(1)-P(2), 2.2446(7);
Pt(1)-P(1), 2.2449(7). C(1)-Pt(1)-O(1W), 176.25(10); P(2)-Pt(1)-P(1), 163.29(2).
3
on Pt(2). Of intermediate length are C(aryl)-Pt in the hydride-
bridged dimer 4a (2.066(2), 2.067(2) Å) and in ethylene
complex 7 (2.051(3) Å), and the shortest bond distances are
observed for Pt(2) in 1 (2.033(3) Å), 2a (2.029(3), 2.035(2)
Å), 3 (2.016(2) Å), and 6 (2.0302(19) Å) for terminal chloride,
bridging chloride, water, and pentafluoropyridine adducts,
respectively.
Complexes 2a and 4a consist of two bridged square planar
platinum centers bridged by a chlorine and a hydrogen atom,
respectively (Figures 2 and 4). The C(aryl)-Pt-H angles in 4a
(170.1, 170.6°) and the C(aryl)-Pt-Cl angles in 2a (175.9,
176.8°) reflect an essential linear coordination geometry, with
the smaller angle in the hydride dimer ascribed to a greater steric
interaction between the two metal units. Relief of steric
crowding is achieved by canting the platinum centers by 85.4°
for 2a and 74.8° for 4a. The interplatinum distance in 4a is
2.832 Å, which is on the low end of the range reported for
similar {(X)(R3P)2Pt}2(µ-H)+ structures (2.710-3.237 Å).12,13
Venanzi et al. has noted that hydride-bridged dimers in this class
of compounds have shorter Pt-Pt distances for less electron-

1152 Organometallics, Vol. 28, No. 4, 2009
Adams et al.
Figure 4. Molecular structure of [(CF PCP)Pt]2(µ-H) SbF6- (4a) with partial atom labeling scheme (50% probability ellipsoids). Phosphine
CF3 groups have been omitted for clarity. Selected metrical data: Pt(1)-Pt(2), 2.8324; Pt(1)-P(1), 2.2461(5); Pt(1)-P(2), 2.2244(5);
Pt(1)-C(1), 2.066(2); Pt(1)-H(1), 1.79(4); Pt(2)-P(3), 2.2227(5); Pt(2)-P(4), 2.2486(5); Pt(2)-C(13), 2.067(2); Pt(2)-H(1), 1.67(4).
P(1)-Pt(1)-P(2), 153.56(2); C(1)-Pt(1)-H(1), 170.1(13); P(3)-Pt(2)-P(4), 153.662(19); C(13)-Pt(2)-H(1), 170.6(16); Pt(1)-H(1)-Pt(2),
110.05.
+
3
rich metal centers.12 While a significant metal-metal interaction
can be inferred in 4a, where the Pt(1)-H-Pt(2) bond angle is
110°, the Pt-Cl-Pt bond angle in 2a of 115.45° combined with
long Pt-Cl bond lengths results in a nonbonding Pt-Pt distance
of 4.087 Å.
The observed Pt-N bond distance of 2.1727(16) Å is very
-
similar to that found for (dfepe)Pt(Me)(NC5F5)+B(C6F5)4
(2.153(4) Å),8 in keeping with the strong trans influence of both
phosphorus and hydrocarbyl groups. The NC5F5 aryl plane is
essentially perpendicular to the Pt coordination plane (interplanar
angle ) 89.6°) and is comparable to that found for (tmeda)Pt(Me)-
(NC5F5)+B[m-(CF3)2C6H3]4- (88°) and (dfepe)Pt(Me)(NC5F5)+B-
The asymmetric unit for 3 contains two independent
CF3
(
PCP)Pt(H2O)+ cations (Figure 3). In the Pt(1) unit, a C2 twist
-
of 13.2° of the PCP aromatic backbone and benzyl carbons with
respect to the plane defined by the platinum and attached atoms
is observed, whereas in the Pt(2) unit the PCP dibenzyl plane
is not twisted but canted 9.9° above the platinum square plane.
These two distinct types of distortions serve to relieve chelate
(C6F5)4 (78°).
(
CF3
-
PCP)Pt(η2-C2H4)+B(C6F5)4 (7) is the first structurally
characterized ethylene complex in the PCP Pt motif (Figure 6).
The ethylene adduct is symmetrically bonded to the Pt metal
center with identical Pt-C(C2H4) bonds of 2.305(5) and 2.306(4)
Å, and the ethylene Pt plane is nearly perpendicular to the aryl
plane with an interplanar angle of 88.26°. The ethylene C-C
bond (1.305(7) Å) is significantly shorter than the complex
(PhPNP)Pt(C2H4)2+ (1.359(10) Å).20 In contrast, the Pt-C(C2H4)
bonds are ∼0.13 Å longer, consistent with the greater trans
influence of the aryl backbone compared to the pyridine
backbone.
strain in the (PCP)Pt moiety.
A number of trans-
(R3P)2Pt(X)(H2O)+ complexes have been reported with X )
H,14 Cl,15 aryl,16 or vinyl group as the trans ligand.17 The Pt-O
bond lengths found for (CF PCP)Pt(H2O) SbF6- of 2.145(2) and
+
3
2.133(2) Å are somewhat shorter than the 2.175-2.19 Å range
reported for complexes with X ) aryl and are consistent with
a stronger water-platinum interaction in this more electrophilic
acceptor phosphine system.
CF3
(
PCP)Pt(NC5F5)+B(C6F5)4- (6) is only the fourth structur-
Reactivity Studies
ally characterized pentafluoropyridine complex (Figure 5).8,18,19
+
-
Reactivity of (CF PCP)Pt(NC5F5) B(C6F5)4 with H2 and
3
CF3
R3SiH. The pentafluoropyridine adduct
(
PCP)Pt-
(12) Albinati, A.; Chaloupka, S.; Eckert, J.; Venanzi, L. M.; Wolfer,
M. K. Inorg. Chim. Acta 1997, 259, 305–316.
(NC5F5)+B(C6F5)4 (6) serves as a convenient source of the
-
electrophilic 16-electron (CF PCP)Pt moiety for study. Earlier,
+
3
(13) (a) Novio, F.; Gonzalez-Duarte, P.; Lledos, A.; Mas-Balleste, R.
Chem.sEur. J. 2007, 13, 1047–1063. (b) Bandini, A. L.; Banditelli, G.;
Manassero, M.; Albinati, A.; Colognesi, D.; Eckert, J. Eur. J. Inorg. Chem.
2003, 3958–3967. (c) Albinati, A.; Bracher, G.; Carmona, D.; Jans, J. H. P.;
Klooster, W. T.; Koetzle, T. F.; Macchioni, A.; Ricci, J. S.; Thouvenot, R.;
Venanzi, L. M. Inorg. Chim. Acta. 1997, 265, 255–265. (d) Bachechi, F.
Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1993, 49, 460–464. (e)
Carmona, D.; Thouvenot, R.; Venanzi, L. M.; Bachechi, Zambonelli, L. J.
Organomet. Chem. 1983, 250, 589–608.
(14) Parkins, A. W.; Richard, C. J.; Steed, J. W. Inorg. Chim. Acta 2005,
358, 2827–2832.
(15) Rath, N. P.; Fallis, K. A.; Anderson, G. K. Acta Crystallogr., Sect.
C: Cryst. Struct. Commun. 1993, 49, 2079–2081.
we noted that generation of (CF PCP)Pt in the presence of H2
+
3
resulted in the formation of the hydride-bridged dimer,
+
CF3
{(CF PCP)Pt}2(µ-H) . VT NMR studies of
(
PCP)Pt-
3
(NC5F5)+B(C6F5)4 in 1,2-difluorobenzene under 3 atm of H2
-
at -20 °C did not show any displacement of pentafluoropyridine
to form observable η2-H2 or classical hydride intermediates, but
+
rather slow conversion to {(CF PCP)Pt}2(µ-H) at ambient
3
temperature over the course of 3 days. In contrast, 6 reacts more
rapidly with silanes: addition of 10 equiv of Et3SiH in
(16) (a) Kryschenko, Y. K.; Seidel, S. R.; Muddiman, D. C.; Nepo-
mucemo, A. I.; Stang, P. J. J. Am. Chem. Soc. 2003, 125, 9647–9652. (b)
Ito, M.; Ebihara, M.; Kawamura, T. Inorg. Chim. Acta 1994, 218, 199–
202.
(17) Siedle, A. R.; Gleason, W. B.; Newmark, R. A.; Pignolet, L. H.
Organometallics 1986, 5, 1969–1975.
1,2-difluorobenzene at 27 °C resulted in the rapid generation
+
of (CF PCP)Pt}2(µ-H) . Initial spectra after 2 min showed a 1:1.4
3
CF3
+
mixture of (CF PCP)Pt(H)/{( PCP)Pt}2(µ-H) , which after 10
min had completely converted to the cationic hydride dimer.
Over the course of 45 min, a slow redistribution reaction was
3
(18) Holtcamp, M. W.; Henling, L. M.; Day, M. W.; Labinger, J. A.;
Bercaw, J. E. Inorg. Chim. Acta 1998, 270, 467–478.
(19) Huhmann-Vincent, J.; Scott, B. L.; Kubas, G. J. Inorg. Chem. 1999,
38, 115–124.
(20) Hahn, C.; Morviallo, P.; Herdtweck, E.; Vitagliano, A. Organo-
metallics 2002, 21, 1807–1818.

Acceptor Pincer Coordination Chemistry of Pt
Organometallics, Vol. 28, No. 4, 2009 1153
+
Figure 5. Molecular structure of (CF PCP)Pt(NC5F5) B(C6F5)4- (6) with partial atom labeling scheme (50% probability ellipsoids). Selected
metrical data: Pt(1)-C(1), 2.030(2); Pt(1)-N(1), 2.173(2); Pt(1)-P(1), 2.2443(5); Pt(1)-P(2), 2.2424(5); P(1)-Pt(1)-P(2), 161.34(2);
C(1)-Pt(1)-N(1), 179.19(7).
3
observed to generate a new ethylsilyl product, which was
identified by 1H and 13C NMR as tetraethylsilane. After 22.5 h,
the Et3SiH/Et4Si ratio was 1.67:1. Observation of a singlet at δ
3.43 confirmed the generation of free H2 in this reaction.
Hydrosilation
and
Hydrogenation
Activity
of
CF3
-
(
PCP)Pt(η2-alkene)+B(C6F5)4 Complexes. 16-Electron
(PCP)Pt(L)+ complexes are formally coordinatively saturated
Pt(II) systems, with no readily accessible site for coreactant
A-B bond oxidative addition and subsequent reaction with
Hydrosilation of propene with Et3SiH promoted by (CF PCP)-
3
Pt(η2-C2H4)+ is regioselective: reaction of 6 equiv of Et3SiH
with 22 equiv of propene at room temperature for 40 min
resulted in complete conversion to the n-propyl product,
Et3Si(CH2CH2CH3), with no isopropyl isomer Et3Si(CH(CH3)2),
2
+
-
substrate L. Nevertheless, (CF PCP)Pt(η -C2H4) B(C6F5)4 (7)
has some limited alkene hydrogenation catalyst activity. At
ambient temperature, 1.7 equiv of ethane were produced from
43 equiv of C2H4 and 3 atm of H2 after 77 h. Heating this
reaction mixture for 16 h at 70 °C generated 6.5 equiv of
CH3CH3. Thus, the rate of hydrogenation is 0.02 turnovers h-1
at ambient temperature and 0.30 turnovers h-1 at 70 °C.
3
1
as judged by H and 13C NMR (eq 3). During the course of
reaction, 7 underwent clean conversion to the propylene complex
CF3
(
PCP)Pt(η2-H2CdC(H)Me)+B(C6F5)4- (8), which was spec-
troscopically characterized and independently prepared from the
reaction of the pentafluoropyridine complex 6 and propene. The
attempted hydrosilation of the more sterically hindered tertiary
olefin 1-methyl-1-cyclohexene resulted in complicated mixtures.
Many metal systems efficiently catalyze hydrosilation of
olefins with tertiary silanes;21 however, to our knowledge, no
2
PCP-based catalysts are known. We report that (CF PCP)Pt(η -
3
C2H4)+ is a modestly active hydrosilation catalyst (eq 2).
Treatment of 7 with 70 equiv of C2H4 and 15 equiv of Et3SiH
as a limiting reagent in 1,2-difluorobenzene gave complete
conversion to the hydrosilation product Et4Si after 2 min at
ambient temperature. The chlorosilane Cl3SiH reacted much
more slowly to give 91% conversion to EtSiCl3 after 5 h (∼5
turnovers h-1). Monitoring the reaction of 7 with 8.9 equiv of
ethylene with 14.8 equiv of Et3SiH at -10 °C in 1,2-
difluorobenzene by 1H NMR showed a first order disappearance
of ethylene with an apparent rate constant of 0.005 s-1 (∼18
turnovers h-1).
Ethylene Dimerization and Isomerization of 1-Butene
2
+
-
by (CF PCP)Pt(η -C2H4) B(C6F5)4 . Ni(II) and Pd(II) systems
exhibit high catalytic activities for ethylene dimerization,
oligomerization, or polymerization.22 Limited activity for di-
merization has been reported for Pt(II) complexes
(dfepe)Pt(Me)(O2CCF3) at 80 °C and (diimine)Pt(H)(η2-
3
(21) For recent examples, see. (a) Hamze, A.; Provot, O.; Brion, J.-D.;
Alami, M. Tetrahedron Lett. 2008, 49, 2429–2431. (b) Deglmann, P.; Ember,
E.; Hofmann, P; Pitter, S.; Walter, O. Chem.sEur. J. 2007, 13, 2864–
2879. (c) Bruner, H. Angew. Chem., Int. Ed. 2004, 43, 2749–2750. (d) Field.,
L. D.; Ward, A. J. J. Organomet. Chem. 2003, 681, 91–97. (e) Glaser, P. B.;
Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 13640–13641.

1154 Organometallics, Vol. 28, No. 4, 2009
Adams et al.
Alkene isomerization catalysis generally proceeds via metal
hydride or metal-allyl hydride intermediates25 and involves the
availability of an adjacent hydride ligand or an additional site
of coordinative unsaturation to support an equilibrium between
LnM(alkene) and Ln-1M(allyl)(H). Nevertheless, 7 exhibits
modest alkene isomerization activity: warming a mixture of 7
and 10 equiv of 1-butene to 80 °C in 1,2-difluorobenzene
produced 3.6 equiv of a ∼1:1 mixture of cis- and trans-2-butene.
A single platinum species was observed during the course of
2
reaction and was tentatively assigned as (CF PCP)Pt(η -
3
H2CdC(H)CH2Me)+B(C6F5)4-).
Summary
+
The initial goal of preparing a labile source of the (CF PCP)Pt
3
moiety has been partially realized with the preparation of the
+
pentafluoropyridine adduct (CF PCP)Pt(NC5F5) . The reactions
3
of (CF PCP)PtMe with (C6Me3H4) B(C6F5)4- or Ph3C+B(C6F5)4
+
-
3
in 1,2-difluorobenzene afford major species which are similar
yet not spectroscopically identical. A preliminary assignment
+
-
of these products as either the ion pair (CF PCP)Pt B(C6F5)4
3
or solvate (CF PCP)Pt (solv)B(C6F5)4- is not supported by their
+
3
lackofreactivitywithH2 atlowtemperaturetoform(CF PCP)Pt(η -
H2)+, and work is continuing to further characterize these
products.
2
3
In contrast to (tBuPCP)Pt(η2-H2)+, which is moderately stable
under a H2 atmosphere,7a the unobserved dihydrogen adduct
Figure 6. Molecular structure of (CF PCP)Pt(C2H4) B(C6F5)4 (7)
with partial atom labeling scheme (50% probability ellipsoids). The
anion and hydrogens are omitted for clarity. Selected metrical data:
Pt(1)-C(1), 2.051(3); Pt(1)-P(1), 2.2510(10); Pt(1)-P(2), 2.2543(9);
Pt(1)-C(14), 2.306(4); Pt(1)-C(13), 2.305(5); C(13)-C(14),
1.305(7). C(1)-Pt(1)-P(1), 80.78(11); C(1)-Pt(1)-P(2), 79.74(10);
P(1)-Pt(1)-P(2), 160.36(4).
+
-
PCP)Pt(η2-H2)+ is unstable with respect to proton loss and
CF3
3
(
formation of the cationic hydride-bridged dimer {(CF PCP)Pt}2(µ-
H)+B(C6F5)4- (4). Thus far, all attempts to cleanly prepare and
3
isolate the neutral hydride (CF PCP)PtH have been unsuccessful.
3
We believe that any (CF PCP)PtH formed in the presence of a
3
potential source of (CF PCP)Pt is efficiently trapped to give 4.
+
3
The result that (CF PCP)Pt (generated initially either by Cl-
+
3
abstraction from (CF PCP)PtCl or by pentafluoropyridine dis-
3
C2H4)+BArf- at 100 °C.23,24 More recently, our research group
has shown the system [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4- to be
orders of magnitude more reactive than these related systems.8
Interestingly, despite the absence of an adjacent alkyl ligand to
initiate and promote insertion, 7 exhibited limited catalytic
activity for the dimerization of ethylene at high temperatures
to a ∼2:1 trans/cis mixture of 2-butenes (0.07 turnovers h-1,
155 °C, 1:1 1,2-difluorobenzene/benzene (eq 4)). After 60 h at
155 °C, about 10% decomposition of complex 7 was noted.
placement from (CF PCP)Pt(NC5F5) ) reacts with the electro-
+
3
philic reagent Et3Si+B(C6F5)4 to form substantial amounts of
-
CF3
(
PCP)PtH is quite surprising and not readily explained.
Hydrosilation catalysis by late transition metal systems
generally follows a classic or modified Chalk-Harrod mech-
anism involving oxidative addition of Si-H bonds to a
coordinatively unsaturated metal center.26 While hydrosilation
by labile (phen)Pd(Me)(L)+ systems proceed via alkene adducts,
27
(phen)Pd(SiR3)(η2-alkene)+, the16-e-Pt(II)complex(CF PCP)Pt(η -
C2H4)+ lacks a readily accessible site for silyl coordination.
Nevertheless, hydrosilation (and olefin hydrogenation) is ob-
served to occur. No silane addition intermediates have been
observed at -30 °C which would support a tentative reaction
mechanism. We speculate that either (a) direct addition of Si-H
bonds to alkene activated by the electrophilic metal center is
occurring, (b) Si-H bond addition to form tetravalent platinum
intermediates takes place, or (c) dissociation of a pendant
phosphine group and/or Si-H addition across the PCP aryl-Pt
2
3
bond is occurring.28 The release of PCPH from reaction of
CF3
(25) Herrmann, W. A.; Prinz, M. Double-bond Isomerization of Olefins.
In Applied Homogeneous Catalysis with Organometallic Compounds, 2nd
ed.; Cornils, B., Herrmann, W. A., Eds.; Wiley-VCH: Weinheim, Germany,
2002; Vol. 3, pp 1119-1130.
(26) (a) Chalk, A. J.; Harrod, J. F. J. Am. Chem. Soc. 1965, 87, 16–21.
(b) Duckett, S. B.; Perutz, R. N. Organometallics 1992, 11, 90–98.
(27) LaPointe, A. M.; Rix, F. C.; Brookhart, M. J. Am. Chem. Soc. 1997,
119, 906–917.
(28) H2 addition and H migration to a PCP aryl-metal bond have been
reported: van der Boom, M. E.; Iron, M. A.; Atasoylu, O.; Shimon, L. J. W.;
Rozenberg, H.; Ben-David, Y.; Konstantinovski, L.; Martin, J. M. L.;
Milstein, D. Inorg. Chim. Acta 2004, 357, 1854–1864.
(22) (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. (c) Conley, M. P.; Burns, C. T.; Jordan, R. F. Organo-
metallics 2007, 26, 6750–6759. (d) Speiser, F.; Braunstein, P.; Saussine,
L. Acc. Chem. Res. 2005, 38, 784–793. (e) Schro¨der, D. L.; Keim, W.;
Zuideveld, M. A.; Mecking, S. Macromolecules 2002, 35, 6071–6073.
(23) White, S.; Bennett, B. L.; Roddick, D. M. Organometallics 1999,
18, 2536–2542.
(24) Shiotsuki, M.; White, P. S.; Brookhart, M.; Templeton, J. L. J. Am.
Chem. Soc. 2007, 129, 4058–4067.

Acceptor Pincer Coordination Chemistry of Pt
Organometallics, Vol. 28, No. 4, 2009 1155
mmol) and (C6Me3H4)+B(C6F5)4- (0.041 g, 0.0.51 mmol) at -195
°C. Upon thawing, vigorous bubbling was observed and the reaction
was allowed to warm to ambient temperature. Colorless needles
began to precipitate after ∼4 h, and slow evaporation to ∼0.3 mL
and removal of the supernatant gave 0.029 g (63%) of 2b. 1H, 31P,
and CF3 19F NMR data for 2b were identical to 2a data.
CF3
(
PCP)PtCl with excess PhSiH3 may reflect the latter reaction
pathway. The greater reactivity of (CF PCP)Pt(η -C2H4) toward
the more electron-rich silane Et3SiH relative to Cl3SiH is in
qualitative support of a nucleophilic silane addition reaction path.
In a similar fashion, conventional alkene hydrogenation, dimer-
ization, and isomerization catalysis by 7 requires additional
2
+
3
CF3
+
-
PCP)Pt(H2O) SbF6 (3). (CF PCP)PtCl (0.113 g, 0.168
3
(
coordination sites by either expanding the coordination sphere
of (CF PCP)Pt(alkene) or partial dissociation of the PCP
+
mmol) was added to AgSbF6 (0.200 g, 0.585 mmol) wetted with
water (50 µL, 2.77 mmol). Methylene chloride (20 mL) was added,
and the reaction mixture was stirred at ambient temperature for
5 h. The resulting AgCl precipitate was filtered off, and crystalline
white product (0.127 g, 85%) was precipitated from the filtrate by
addition of ∼75 mL of hexanes. Crystals suitable for X-ray
diffraction were grown by the slow diffusion of hexane into a
methylene chloride solution of 3. Anal. Calcd for C12H9P2F18OSbPt:
3
framework.
Experimental Section
General Procedures. All manipulations were conducted under
N2 or vacuum using high-vacuum line and glovebox techniques
unless otherwise noted. All ambient pressure chemistry was carried
out under a pressure of approximately 590 torr (elevation ∼2195
m). All solvents were dried using standard procedures and stored
under vacuum. Pentafluoropyridine and 1,2-difluorobenzene (Syn-
quest, Inc.) were dried over activated 4 Å molecular sieves. Et3SiH,
Cl3SiH, Et3SiCl, and KH were purchased from Aldrich and used
as received. Aprotic deuterated solvents used in NMR experiments
were dried over activated 3 Å molecular sieves. Ethylene (Airgas),
H2 (US Welding), and propene (Aldrich) were used as received.
Elemental analyses were performed by Desert Analytics. NMR
spectra were obtained with a Bruker DRX-400 instrument. 1H NMR
spectra in 1,2-difluorobenzene were locked and referenced to the
residual protons of acetone-d6 sealed in a capillary. 31P NMR spectra
were referenced to an 85% H3PO4 external standard. 19F NMR
spectra were referenced to CF3CO2CH2CH3 (δ -75.32).
1
C, 16.20%; H, 1.02%. Found: C, 17.44%; H, 0.83%. H NMR
(CD2Cl2, 400.13 MHz, 20 °C): δ 7.32 (m, 3H; Ar), 4.08 (m, 4H;
ArCH2), 2.19 (br.s, 2H; H2O). 31P NMR (CD2Cl2, 161.97 MHz, 20
1
°C): δ 64.4 (m, JPtP ) 3660 Hz). 19F NMR (acetone-d6, 376.50
MHz, 20 °C): δ -53.5 (m, PCF3). IR (Nujol, cm-1): ν(H2O) )
3453 cm-1
.
+
-
{(CF PCP)Pt}2(µ-H) SbF6 (4a). (CF PCP)PtCl (0.250 g, 0.373
mmol) and AgSbF6 (0.127 g, 0.373 mmol) were dissolved in 30
mL of methylene chloride at -78 °C, and the mixture was stirred
under 1 atm of H2 in the dark. The reaction was allowed to warm
to ambient temperature and then stirred for an additional 20 h. The
solid mixture was filtered off and then redissolved in ∼10 mL
acetone. AgCl was removed by filtration, and the acetone was
removed from the filtrate and replaced by ∼10 mL methylene
chloride. Trituration and filtration afforded a pale yellow crystalline
solid (0.136 g, 48% yield). Crystals suitable for X-ray diffraction
were grown by slow evaporation from methylene chloride. Anal.
Calcd for C24H15P4F30SbPt2: C, 19.10%; H, 1.00%. Found: C,
3
3
29
29
Ph3C+B(C6F5)4
,
(C6Me3H4)+B(C6F5)4
,
(
PCP)PtCl, and
-
-
CF3
6
CF3
(
PCP)PtMe were prepared following literature procedures.
Et3Si+B(C6F5)4 was prepared from Ph3C+B(C6F5)4 and Et3SiH
following a modified literature procedure, isolated by triturating
with petroleum ether, and stored at -25 °C in an inert atmosphere
-
-
1
19.11%; H, 0.99%. H NMR (acetone-d6, 400.13 MHz, 20 °C): δ
dry box.29 Ph3C+B(C6F5)4 was prepared from KB(C6F5)4 and
-
7.69 (m, 4H; Ar), 7.60 (m, 2H; Ar), 4.89 (m, 8H; CH2), -5.33
1
2
(pp, JPtH ) 254 Hz, JPH ) 10 Hz, 1H; Pt2(µ-H)). 31P NMR
Ph3CCl following a modified procedure.30
(acetone-d6, 161.97 MHz, 20 °C): δ 70.6 (m, 1JPtP ) 3470 Hz). 19
NMR (acetone-d6, 376.50 MHz, 20 °C): δ -54.7 (m, PCF3).
{(CF PCP)Pt}2(µ-H) B(C6F5)4 (4b).
F
Reaction of (CF PCP)PtCl with KH. ( PCP)Pt(Cl) (0.100 g,
0.149 mmol) was dissolved in 30 mL of THF, and 6 mg of KH
(0.149 mmol) was added at ambient temperature. Vigorous bubbling
occurred, and the solution turned initially purple and then pale
yellow with a white precipitate. The solvent was removed; 1H NMR
spectra of the residue in C6D6 revealed a complex product mixture
with no characteristic high field hydride resonances. The residue
was dissolved in ∼3 mL methylene chloride, filtered, and hexane
was layered on top and allowed to slowly diffuse at ambient
temperature. Less than a 5% yield of colorless crystals was obtained
CF3
3
+
-
3
Method A. 1,2-Difluorobenzene (20 mL) was condensed onto a
CF3
mixture of
(
PCP)PtMe (0.250 g, 0.384 mmol) and
(C6Me3H4)+B(C6F5)4- (0.338 g, 0.422 mmol) at -78 °C and placed
under 1 atm of H2. Upon thawing, vigorous bubbling was observed
and the reaction mixture was allowed to warm with stirring to
ambient temperatures and stirred an additional 4 h. The solvent
volume was reduced to ∼5, and 25 mL of petroleum ether was
slowly added to precipitate an off-white solid (0.221 g, 59% yield).
1H, 31P, and CF3 19F NMR data for 4b were identical to 4a data.
which was subsequently identified as (CF PCP)Pt[κ -C,κ3-P,C,P-
2,6-(CHP(CF3)2)(CH2P(CF3)2)C6H3]PtCl (1) by X-ray analysis.
1
3
{(CF PCP)Pt}2(µ-Cl) SbF6- (2a). (CF PCP)PtCl (0.200 g, 0.298
mmol) and AgSbF6 (0.101 g, 0.298 mmol) were dissolved in 30
mL of methylene chloride and stirred for 24 h in the absence of
light. AgCl and was filtered off, and the filtrate was reduced to ∼7
mL and cooled to -78 °C, producing a white precipitate which
was collected and dried under vacuum (0.197 g, 86% yield). Slow
evaporation from methylene chloride yielded crystals suitable for
X-ray diffraction. Anal. Calcd for C24H14P4F30ClSbPt2: C, 18.68%;
H, 0.92%. Found: C, 18.68%; H, 0.82%. 1H NMR (CD2Cl2, 400.13
MHz, 20 °C): δ 7.32 (m, 3H; Ar), 4.06 (m, 4H; ArCH2). 31P NMR
+
3
3
Method B. A mixture of (CF PCP)PtCl (0.150 g, 0.224 mmol)
3
and Et3Si+B(C6F5)4 (0.195 g, 0.246 mmol) were dissolved in 20
-
mL of benzene. The initially colorless solution turned yellow after
1 h, and a precipitate began to form. The reaction mixture was
stirred for 24 h and filtered to give pale yellow crystalline solid 4b
(0.200 g, 92% crude yield, ∼90% purity by NMR).
+
Reaction of (CF PCP)PtMe with (C6Me3H4) B(C6F5)4-. The
3
reaction between (CF PCP)PtMe and (C6Me3H4) B(C6F5)4 was
monitored by VT NMR. A 5 mm NMR tube fitted with a Teflon
+
-
3
valve was charged with (CF PCP)PtMe (0.018 g, 0.028 mmol),
3
(CD2Cl2, 161.97 MHz, 20 °C): δ 63.0 (m, J,PtP ) 3640 Hz). 19F
1
(C6Me3H4)+B(C6F5)4 (0.024 g, 0.030 mmol), and 0.5 mL of 1,2-
-
NMR (CD2Cl2, 376.50 MHz, 20 °C): δ -54.8 (m, PCF3).
difluorobenzene and then placed under 3 atm of H2. Upon thawing
{(CF PCP)Pt}2(µ-Cl) B(C6F5)4 (2b). Methylene chloride (1.5
+
-
3
at -30 °C, gas evolution was observed and the production of
mL) was condensed onto a mixture of (CF PCP)PtMe (0.030 g, 0.046
3
1
methane was confirmed by H NMR (δ -1.07). A single major
(∼70-80%) product was characterized spectroscopically. 1H NMR:
1
δ 2.53 (m, 4H; CH2). 31P NMR: δ 62.2 (m, JPtP ) 3760 Hz). 19F
(29) 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–
NMR: δ -53.7 (m, 12F; PCF3), -131.8 (br.s, 8F; ortho-B(C6F5)4),
-162.4 (t,3JFF ) 19 Hz, 4F; para-B(C6F5)4), -166.4 (m, 8F; meta-
B(C6F5)4).
6315.
(30) Lambert, J. B.; Zhang, S.; Ciro, S. M. Organometallics 1994, 13,
2430–2443.

1156 Organometallics, Vol. 28, No. 4, 2009
Adams et al.
+
Reaction of (CF PCP)PtMe with Ph3C B(C6F5)4-. The reaction
of 7 to 2b. Anal. Calcd for BC38H11P2F32Pt: C, 33.95%; H, 0.83%.
Found: C, 33.38%; H, 0.54%. 1H NMR (CD2Cl2, 400.13 MHz, 20
°C): δ 7.60 (br.s, 3H; Ar), 5.20 (t, 2JPtH ) 33 Hz, 4H; C2H4), 4.36
(m, 4H, ArCH2). 13C{1H} NMR (CD2Cl2, 100.61 MHz, 20 °C):
87.2 (t, 3JCP ) 13 Hz, 2JCH ) 168 Hz; Pt(C2H4)), 34.3 (m; CH2P).
3
between (CF PCP)PtMe and Ph3C B(C6F5)4 was monitored at
+
-
3
ambient temperature by NMR. A 5 mm NMR tube fitted with a
Teflon valve (Chemglass, CG-512) was charged with (CF PCP)PtMe
3
(0.021 g, 0.032 mmol), Ph3C+B(C6F5)4 (0.030 g, 0.032 mmol),
-
1
31P NMR (CD2Cl2, 161.97 MHz, 20 °C): δ 63.9 (m, JPtP ) 3380
and 0.5 mL of 1,2-difluorobenzene. Approximately half of
CF3
Hz). 19F NMR (CD2Cl2, 376.50 MHz, 20 °C): δ -54.5 (m, 12F;
PCF3), -133.2 (br.s, 8F; ortho-B(C6F5)4), -163.7 (t,3JFF ) 20 Hz,
(
PCP)PtMe was converted to a major species after 30 min, and
after 5 h the reaction mixture showed 85+% conversion to a major
species as judged by NMR. H NMR: δ 2.75 (m, 4H; CH2). 31P
1
4F; para-B(C6F5)4), -167.6 (m, 8F; meta-B(C6F5)4).
NMR: δ 65.8 (m, JPtP ) 3480 Hz). 19F NMR: δ -55.8 (m, 12F;
1
CF3
(
PCP)Pt(η2-H2CdC(H)Me)+B(C6F5)4- (8). One atm of pro-
PCF3), -131.5 (br.s, 8F; ortho-B(C6F5)4), -162.7 (t,3JFF ) 19 Hz,
4F; para-B(C6F5)4), -166.5 (m, 8F; meta-B(C6F5)4). 1H NMR for
1,1,1-triphenylethane: δ 0.90 (s, 3H; CH3), 6.79 (m), 6.44 (m), 6.27
pene was introduced into a flask containing 6 (0.150 g, 0.101 mmol)
dissolved in 7 mL of 1,2-difluorobenzene. The reaction mixture
was stirred at room temperature for 16 h, and the solution remained
colorless. The volatiles were removed, and the remaining viscous
oil was triturated in 15 mL to give a white solid, which was
collected by filtration (0.086 g, 63% crude yield, 90% pure by
NMR). 1H NMR (1,2-difluorobenzene, 400.13 MHz, 20 °C):
aromatic resonances obscured by 1,2-difluorobenzene; δ 4.45 (dt,
(m).
+
Reaction of (CF PCP)PtCl with Et3Si B(C6F5)4-. A NMR tube
3
charged with (CF PCP)PtCl (0.030 g, 0.044 mmol), Et3Si B(C6F5)4
+
-
3
(0.043 g, 0.054 mmol), and 0.5 mL of 1,2-difluorobenzene was
monitored by NMR. After 15 min at ambient temperature, 31P NMR
spectra showed a ∼2:1 mixture of hydride-bridged dimer 4b and a
3
2
3JHH ) 15.6 Hz, JPH ) 4 Hz, JPtH ) 34 Hz, 1H; CH2CHCH3),
new species tentatively assigned as the neutral hydride, (CF PCP)PtH
3.22 (d, 3JHH ) 8.2, 2JPtH ) 40 Hz, 1H; CH2CHCH3), 2.90 (m, 5H;
3
overlapping benzylic and CH2CHCH3 resonances), 0.77 (d, 3JHH
)
(5). After 3 h, the hydride complex had quantitatively converted to
1
6.1 Hz, JPtH ) 17 Hz, 3H; CH2CHCH3). 31P NMR (1,2-
difluorobenzene, 161.97 MHz, 20 °C): δ 65.3 ppm (m, 1JPtP ) 3460
Hz). 19F NMR (1,2-difluorobenzene, 376.50 MHz, 20 °C): δ -54.6
(m, 12F; PCF3), -131.4 (br.s, 8F; ortho-B(C6F5)4), -162.8 (t,3JFF
) 20 Hz, 4F; para-B(C6F5)4), -166.5 (br.t, 8F; meta-B(C6F5)4).
Catalysis NMR Studies. The following describe specific NMR
experiments for hydrogenolysis, hydrosilation, dimerization, and
isomerization. Liquid reagents were added via microliter syringe.
All gaseous reagents (C2H4, C3H7, C4H8) were condensed into
valved NMR tubes at -195 °C. The stated equivalents were
determined by solution integration.
3
4b. Data for 5: H NMR (400.13 MHz, 20 °C): δ 2.88 (m, 4H;
CH2), -5.73 (t, 1JPtH ) 7 Hz, 2JPH ) 224 Hz, 1H; PtH). 31P NMR
(161.97 MHz, 20 °C): δ 63.7 (m, JPtP ) 3570 Hz). 19F NMR
1
(376.50 MHz, 20 °C): δ -55.7 (m, 12F; PCF3).
CF3
-
(
PCP)Pt(NC5F5)+B(C6F5)4 (6).
Method A. Pentafluoropyridine (7 mL) was condensed onto a
CF3
mixture of
(
PCP)PtMe (0.300 g, 0.461 mmol) and
(C6Me3H4)+B(C6F5)4 (0.405 g, 0.506 mmol) at -195 °C. Upon
thawing, vigorous bubbling was observed and the reaction mixture
was allowed to warm to ambient temperature and then stirred for
an additional 4 h. The white precipitate of 6 (0.571 g, 83%) was
collected via filtration and dried under vacuum. Crystals suitable
for X-ray diffraction were grown by slow evaporation from a 1:1.5
mixture of 1,2-difluorobenzene/pentafluoropyridine. Anal. Calcd for
BNC41H7P2F37Pt: C, 33.16%; H, 0.48%; N, 0.94%. Found: C,
33.54%; H, 0.69%; N, 0.88%. 1H NMR (1,2-difluorobenzene,
400.13 MHz, 20 °C): aromatic resonances obscured by 1,2-
difluorobenzene; δ 2.90 (m, 4H, CH2). 31P NMR (1,2-difluoroben-
-
Hydrogenation of C2H4 by 7. A NMR tube was charged with
7 (0.025 g, 0.019 mmol), 0.5 mL of 1,2-difluorobenzene, C2H4 (43
equiv), and 3 atm of H2. The only metal species present throughout
the reaction was 7, as judged by NMR. After 77 h, 1.7 equiv of
1
CH3CH3 was observed by H NMR spectroscopy. Warming to 70
°C for 16 h produced a total of 6.5 equiv of ethane.
Hydrosilation of C2H4 and Et3SiH by 7 at 20 °C. A NMR
tube was charged with 7 (0.019 g, 0.014 mmol), 0.5 mL of 1,2-
difluorobenzene, C2H4 (70 equiv), and Et3SiH (15 equiv) at 77 K
and thawed immediately before taking spectra at 20 °C. Initial NMR
spectra showed quantitative conversion of Et3SiH to Et4Si (∼2 min
acquisition time). Complex 7 was the sole metal species observed.
Hydrosilation of C2H4 and Et3SiH by 7 at -10 °C. A NMR
tube was charged with 7 (0.019 g, 0.014 mmol), 0.5 mL of 1,2-
difluorobenzene, C2H4 (8.9 equiv), and Et3SiH (14.8 equiv) and
zene, 161.97 MHz, 20 °C): δ 63.2 ppm (m, JPtP ) 3540 Hz). 19F
1
NMR (1,2-difluorobenzene, 376.50 MHz, 20 °C): δ -55.3 (m, 12F;
PCF3), -79.9 (m, 2F; ortho-NC5F5), -116.2 (p, JFF ) 19 Hz, 1F;
meta-NC5F5), -131.4 (br.s, 8F; ortho-B(C6F5)4), -154.4 (d,3JFF
)
19 Hz, 2F; para-NC5F5), -162.8 (t,3JFF ) 20 Hz, 4F; para-
B(C6F5)4), -166.6 (br.t, 8F; meta-B(C6F5)4).
Method B. A mixture of (CF PCP)PtMe (0.100 g, 0.153 mmol)
3
and Ph3C+B(C6F5)4- (0.141 g, 0.153 mmol) was dissolved in 7 mL
pentafluoropyridine. The yellow solution was stirred at ambient
temperature for 2 h, at which point a precipitate began to form.
The reaction mixture was allowed to stand undisturbed for 16 h,
giving a pale yellow crystalline solid 6, which was then collected
by filtration (0.140 g, 62%, ∼95+% purity by NMR).
1
warmed to -10 °C. After 44 min, H NMR spectra showed the
conversion of 7.0 equiv of ethylene to Et4Si. A plot of ln{[C2H4]/
[C2H4]0} versus time over two half-lives gave a first order rate
constant of 0.005 s-1 (R2 ) 0.998).
Hydrosilation of C2H4 and HSiCl3 by 7. A NMR tube was
charged with 7 (0.020 g, 0.015 mmol), 0.5 mL of 1,2-difluoroben-
zene, C2H4 (40 equiv), and HSiCl3 (27 equiv) and warmed to 20
°C. Complex 7 remained the sole metal species during the course
of the reaction, and after 5 h 91% conversion of HSiCl3 to
CF3
-
(
PCP)Pt(η2-C2H4)+B(C6F5)4 (7). 1,2-Difluorobenzene (20
mL) was condensed onto a mixture of (CF PCP)PtMe (0.500 g, 0.768
3
mmol) and (C6Me3H4)+B(C6F5)4 (0.613 g, 0.768 mmol), and 1
-
atm of C2H4 was admitted. Upon thawing, vigorous bubbling was
observed and the reaction mixture was allowed to warm up to
ambient temperature and stirred for an additional 6 h. The solvent
was removed, 20 mL of hexanes was added, and the solid residue
was triturated. The hexanes were removed, and the solid was
dissolved in ∼40 mL of methylene chloride. The solution volume
was reduced to ∼7 mL and cooled to afford a white precipitate
(0.544 g, 53%), which was isolated and dried under vacuum.
Crystals suitable for X-ray diffraction were grown by slow diffusion
of 2-methyl-2-butene into a methylene chloride solution of 7.
2-Methyl-2-butene, initially examined as a potential reactant, was
found to promote crystal growth and also slowed decomposition
1
CH3CH2SiCl3 was observed. Spectroscopic data for EtSiCl3: H
3
NMR (1,2-difluorobenzene, 400.13 MHz, 20 °C): δ 0.17 (q, JHH
3
) 8 Hz, 2H; CH2,), -0.00 (t, JHH ) 8 Hz, 3H; CH3). 13C NMR
(1,2-difluorobenzene, 100.61 MHz, 20 °C): δ 16.64 (s; CH2), 5.30
(s; CH3).
Hydrosilation of Propene and Et3SiH by 7. A NMR tube was
charged with 7 (0.018 g, 0.013 mmol), 0.5 mL of ODF, propene
(22 equiv), and Et3SiH (6 equiv, 12.9 µL, 0.078 mmol). NMR
spectra taken 15 min after warming the reaction mixture to 20 °C
showed clean conversion of 7 to 8 and quantitative conversion
of SiEt3H to Et3Si(CH2CH2CH3). Spectroscopic data for

Acceptor Pincer Coordination Chemistry of Pt
Organometallics, Vol. 28, No. 4, 2009 1157
+
-
+
-
+
-
Table 1. Crystallographic Data for (1), [(CF PCP)Pt]2(µ-Cl) SbF6 (2a), (CF PCP)Pt(H2O) B(C6F5)4 (3), [(CF PCP)Pt]2(µ-H) SbF6 (4a),
3
3
3
CF3
+
-
2
+
3
(
PCP)Pt(NC5F5) B(C6F5)4 (6), and (CF PCP)Pt(η -C2H4) B(C6F5)4- · C5H10 (7)
CF3
(
PCP)Pt(η2-
[(CF PCP)Pt]2(µ-
(
PCP)Pt
[(CF PCP)Pt]2(µ-
(
PCP)Pt(NC5F5)+B
C2H4)+B
CF3
CF3
3
3
-
-
-
-
compound
1 · 1/2C6H6
Cl)+SbF6
(H2O)+SbF6
H)+SbF6
(C6F5)4
(C6F5)4- · C5H10
chemical formula
fw
T, °C
λ, Å
space group
C27H16ClF24P4Pt2
1345.91
-123
0.71073
P21/n
C24 H14Cl F30P4Pt2Sb
1543.61
-123
0.71073
P21/n
C12 H9 F18OP2PtSb
889.97
-123
0.71073
C2/c
C24H15F30P4Pt2Sb
1509.17
-123
0.71073
P21/n
C41H7BF37NP2Pt
1484.32
-123
0.71073
P21/c
C43H21BF32P2Pt
1413.44
-123
0.71073
P21/c
a, Å
b, Å
c, Å
16.4459(2)
20.6746(3)
22.0032(3)
90
90.6980(10)
90
7480.81(17)
8
2.390
14.0640(5)
16.9140(6)
17.9834(6)
90
106.098(2)
90
4110.1(2)
4
2.495
41.9243(8)
10.4572(2)
22.5118(4)
90
110.5430(10)
90
9241.8(3)
16
2.559
13.5979(3)
17.6629(3)
16.7502(3)
90
103.5910(10)
90
3910.38(13)
4
2.563
13.9317(2)
17.1374(3)
19.2130(3)
90
98.2910(10)
90
4539.22(12)
4
2.172
11.4117(5)
22.9772(10)
16.9942(8)
90
98.609(3)
90
4405.8(3)
4
2.131
R, °
ꢀ, °
γ, °
V, Å3
Z
Dcalc, mg m-3
µ, mm-1
R1 [I > 2σ(I)]a
wR2 [I > 2σ(I)]b
7.857
0.0306
0.0611
7.821
0.0350
0.0698
7.504
0.0273
0.0598
8.152
0.0236
0.0476
3.351
0.0248
0.0505
3.430
0.0429
0.1020
b
a R1 ) Σ||Fo - |Fc||/Σ|Fo|. wR2 ) {Σ[w(Fo - Fc2)2]Σ[w(Fo )2]}1/2
.
2
2
1
Et3Si(CH2CH2CH3): H NMR (1,2-difluorobenzene, 400.13 MHz,
crystal. Crystals were attached to a MiTeGen micromount using
Paratone N oil.
3
20 °C): δ 0.22 (m, 2H; CH2), 0.16 (t, JHH ) 8 Hz, 12H; CH3),
-0.60 (q, 3JHH ) 8 Hz, 12H; CH3). 13C NMR (1,2-difluorobenzene,
100.61 MHz, 20 °C, DEPT 90 and 135): δ 18.24 (s; CH3), 17.54
(s; CH2), 14.14 (s; CH2), 7.03 (s, 3C; CH3), 3.33 (s, 3C; CH2).
Ethylene Dimerization by 7. A NMR tube was charged with 7
(0.025 g, 0.019 mmol), 0.5 mL of ODF, 0.5 mL of benzene, and
C2H4 (30 equiv). The reaction mixture was heated at 155 °C for
60 h. About 10% of 7 and the anion B(C6F5)4 underwent
decomposition as judged by 19F NMR. Eight equivalents of were
C2H4 consumed, producing 4 equiv of a 2:1 mixture of trans and
cis butenes and a trace amount of 1-butene.
A series of narrow frames of data were collected with a scan
width of 0.5° in ω or φ and an exposure time of 10 s per frame.
The frames were integrated with the Bruker SAINT software
package31 using a narrow-frame integration algorithm. The data
were corrected for absorption effects by the numerical face-indexing
technique (SADABS). A summary of crystallographic data collec-
tion parameters and refinement data are collected in Table 1.
Structures were solved by direct methods using the Bruker
SHELXTL (v. 6.10) software package.31 All non-hydrogen atoms
were located in successive Fourier maps and refined anisotropically.
The hydrogen atoms were placed in calculated positions and refined
isotropically employing a riding model. The asymmetric unit of 1
1-Butene Isomerization by 7. A NMR tube was charged with
7 (0.014 g, 0.009 mmol), 0.5 mL of 1,2-difluorobenzene, and
1-butene (10 equiv). After 4 h at 80 °C, 3.6 equiv of a ∼1:1 mixture
of cis- and trans-2-butene was produced (36% conversion). A single
consists
of
two
crystallographically
distinct
[Pt2(C12H7P2F12)(C12HP2F12)Cl] molecules and a well-ordered ben-
zene molecule. 2a crystallizes as two independent [Pt(pcp)(H2O)]+
metal species was observed during the reaction which has
CF3
PCP)Pt(η2-
-
been
tentatively
assigned
as
(
cations and two SbF6 anions. The asymmetric unit of 7 consists
H2CdC(H)CH2Me)+B(C6F5)4-). 1H NMR (1,2-difluorobenzene,
400.13 MHz, 20 °C): aromatic resonances obscured by 1,2-
difluorobenzene; δ 4.56 (dm, JHH ) 14.8 Hz, JPtH ) 50 Hz, 1H;
of well-ordered [Pt(pcp)(C2H4)]+ and borate anions and a disordered
2-methyl-2-butene molecule. The hydrogen atoms of the 2-methyl-
2-butene molecule were not located or placed in calculated positions.
The carbon atoms of the 2-methyl-2-butene were refined isotropically.
3
2
3
2
CH2CHCH2CH3), 3.37 (d, JHH ) 7.6, JPtH ) 41 Hz, 1H;
CH2CHCH2CH3), 3.00 (m, 5H; overlapping benzylic and
CH2CHCH2CH2CH3 resonances), 0.61 (m, 2H; CH2CHCH2CH3),
Acknowledgment. We thank The National Science Foun-
dation (CHE-0457435) and DOE/EPSCoR (DE-FG02-
05ER46185) for financial support.
0.03 (t, JHH ) 8.3 Hz, 3H; CH2CHCH2CH3). 31P NMR (1,2-
3
1
difluorobenzene, 161.97 MHz, 20 °C): δ 64.8 (m, JPtP ) 3420
Hz). 19F NMR (1,2-difluorobenzene, 376.50 MHz, 20 °C): δ -54.3
(m, 6F; PCF3), -54.8 (m, 6F; PCF3), -131.4 (br.s, 8F; ortho-
B(C6F5)4), -162.8 (t,3JFF ) 20 Hz, 4F; para-B(C6F5)4), -166.6
(br.t, 8F; meta-B(C6F5)4).
Supporting Information Available: Complete tables of atomic
coordinates, thermal parameters, and bond distances and angles for
complexes 1, 2a, 3, 4a, 6, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org.
X-ray Crystallography. X-ray diffraction data for 1, 2a, 3, 4a,
6, and 7 were measured on a Bruker SMART APEX II CCD area
detector system equipped with a graphite monochromator and a
Mo KR fine-focus sealed tube operated at 1.5 kW power (50 kV,
30 mA) with the detector placed at a distance of 5.9 cm from the
OM8008876
(31) APEX2 Software Suite, v. 2.1-0; Bruker AXS: Madison, WI, 2004.