Synthesis and Structural Characterization of an Unusual Platinum π-Arene Complex: (η6-C6H3Me3)Pt[(C2F5)2PMe]Me+

Article abstract of DOI:10.1021/acs.organomet.5b00410

Treatment of cis-(dfmp)₂PtMe₂ (dfmp = (C₂F₅)₂PMe) with the mesitylenium acid (C₆Me₃H₄)⁺B(C₆F₅)₄^- in 1,2-difluorobenzene cleanly produces an unusually stable arene complex, [(η⁶-C₆Me₃H₃)Pt(dfmp)(CH₃)]⁺(B(C₆F₅)₄)^- (1). Facile arene exchange and competitive binding equilibria have been quantified for mesitylene relative to toluene (K = 0.0030(3)) and durene (K = 20(2)). Reaction of 1 with H₂ at 80°C results in hydrogenolysis to form the arene hydride (η⁶-C₆Me₃H₃)Pt(dfmp)(H)⁺ (2), while treatment of 1 with CO gives trans-(dfmp)₂Pt(CO)Me⁺ as the major phosphine product. Addition of excess Me₃P to 1 results in both arene and dfmp displacement to form (Me₃P)₃PtMe⁺. (η⁶-C₆Me₃H₃)Pt(dfmp)(CH₃)⁺ is a moderately active ethylene dimerization catalyst to form 2-butenes (～7 TO h^-1, 20°C). (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00410

Article
pubs.acs.org/Organometallics
Synthesis and Structural Characterization of an Unusual Platinum
6
+
π‑Arene Complex: (η ‑C H Me )Pt[(C F ) PMe]Me
6
3
3
2 5 2
Bhusan Thapaliya, Suman Debnath, Navamoney Arulsamy, and Dean M. Roddick*
Department of Chemistry, University of Wyoming, Dept. 3838, 1000 E. University Avenue, Laramie, Wyoming 82071, United States
*
S Supporting Information
ABSTRACT: Treatment of cis-(dfmp) PtMe (dfmp =
2
2
+
(
(
C F ) PMe) with the mesitylenium acid (C Me H ) B-
2 5 2 6 3 4
−
C F ) in 1,2-difluorobenzene cleanly produces an unusually
stable arene complex, [(η -C Me H )Pt(dfmp)(CH )] (B-
C F ) ) (1). Facile arene exchange and competitive binding
6
5 4
6
+
6
3
3
3
−
(
6 5 4
equilibria have been quantified for mesitylene relative to
toluene (K = 0.0030(3)) and durene (K = 20(2)). Reaction of 1 with H at 80 °C results in hydrogenolysis to form the arene
2
6
+
+
hydride (η -C Me H )Pt(dfmp)(H) (2), while treatment of 1 with CO gives trans-(dfmp) Pt(CO)Me as the major phosphine
product. Addition of excess Me P to 1 results in both arene and dfmp displacement to form (Me P) PtMe . (η -
C Me H )Pt(dfmp)(CH ) is a moderately active ethylene dimerization catalyst to form 2-butenes (∼7 TO h , 20 °C).
6
3
3
2
+
6
3
3
3
+
−1
6
3
3
3
INTRODUCTION
to effect a clean Pt−Me protonolysis. In an extension on this
■
6
1
work we have examined routes to monodentate phosphine
Since Fischer’s initial report of (η -benzene) Cr, metal-arene
2
+
analogues of the general form (PFAP) Pt(R) . Here we report
n
complexes have played an important role in organometallic
coordination chemistry as both supporting ancillary ligands and
key intermediates in metal-mediated arene functionalization
19
that treatment of cis-(dfmp) PtMe (dfmp = (C F ) PMe)
with [C Me H ] (B(C F ) ) does not afford anticipated
2
2
2 5 2
+
−
6
3
4
6 5 4
+
2
(dfmp)
PtMe (L) products, but rather incorporates the
2
chemistry. π-Arene complex chemistry across the d-block is
released mesitylene group to form an unusual stable 18-
extensive for the middle transition metals (groups 6−9).
6
+
electron arene complex, (η -C Me H )Pt(dfmp)(CH ) . This
6
6
3
3
3
Literature reports of η -arene complexes for the group 10 triad,
product is interesting in several respects: it is not only a very
6
in contrast, are much less common. η -Arene complexes of
6
rare example of a stable platinum η -arene complex, but it also
6
Ni(0) of the general form (η -arene)Ni(L) (L =
possesses Pt−CH functionality that affords the possibility of
1
t
t
3
+
4
5
6
3
κ - Bu PCH P Bu , NO , N+HC, SiR ) and the Ni(II)
2
2
2
2
metal−alkyl bond chemistry. In this paper we detail the
6
6
complexes (η -arene)Ni(allyl) and (η -arene)Ni(X) (X =
C F , SiX ) are known. In contrast, there is only a single clear
6
2
structural and spectroscopic properties of (η -C Me H )Pt-
7
,8
6
3
3
+
6
5
3
(
dfmp)(CH ) and present a preliminary survey of its thermal
6
+
9
3
example of a Pd(II) analogue, (η -arene)M(allyl) . For
platinum only a single Pt(II) arene complex has been isolated
stability, ligand exchange chemistry, and reactions with
dihydrogen, CO, and ethylene.
6
4
2+ 10
and structurally characterized, (η -C Me )Pt(η -C Me ) ,
6
6
4
4
6
3
+
and (η -C Me )Pt(η -2-methylallyl) has been characterized
6
6
1
1
RESULTS AND DISCUSSION
as a thermally unstable solution species by NMR. We have
more recently reported the formation of the complex
■
6
Synthesis and Characterization of (η -C
H
Me
with 1 equiv
of mesitylenium acid in 1,2-difluorobenzene (abbreviated as
)Pt-
6
3
3
6
2+
+
(
dfepe)Pt(η -C H ) (dfepe = (C F ) PCH CH P(C F ) )
(dfmp)Me . The reaction of cis-(dfmp) PtMe
2 2
6
6
2
5 2
2
2
2 5 2
12
with limited solution stability under superacidic conditions.
In 2008 we reported a highly active chelating perfluor-
oalkylphosphine (PFAP) platinum ethylene dimerization
catalyst, [(dfepe)Pt(Me)(NC F )] (B(C F ) ) . This com-
plex was shown to be orders of magnitude more reactive than the
corresponding diimine platinum analogue; considering the
extensive use of diimine ancillary ligands in group 10 alkene
1
31
ODFB) was monitored by H and P NMR spectroscopy. As
13
noted previously, ODFB is an exceptional solvent (liquid
+
−
13
range: −34 to +92 °C) for studying highly electrophilic metal
5
5
6 5 4
complex chemistry due to its high dielectric constant (D =
s
20
1
4
1
3.8, 28 °C) and ability to solubilize complex ions, its large
21
electrochemical window (+2.0 V to −2.2 V vs SSCE), its
relative inertness to halide extraction side reactions,
2
2,23
15
and its
oligomerization chemistry, and the recognized importance of
1
6
weakly coordinating nature (see later). After 15 min at ambient
group 10 alkene oligomerization catalysts, the expansion of
group 10 alkyl cation chemistry to a broader range of ligand
sets such as phosphines, and more specifically PFAPs, is clearly
temperature 31P NMR spectra indicate a clean conversion to a
1
:1 mixture of free dfmp and a Pt−dfmp resonance at 18.6 ppm
1
1
7
with an unusually large ( J = 6380 Hz) platinum coupling
warranted.
The key to accessing the labile cationic platinum alkyl
PtP
+
−
complex [(dfepe)Pt(Me)(NC F )] (B(C F ) ) was the use of
Reed’s mesitylenium acid reagent, [C Me H ] (B(C F ) ) ,
Received: May 13, 2015
5
5
6 5 4
+
−
18
6
3
4
6 5 4
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00410
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
constant. Proton spectra confirmed the formation of methane
Pt(II)−PFAP systems, this bond distance falls within the
range 2.135−2.186 Å found for Pt(II)−PFAP with weak trans
and free dfmp and the appearance of new Pt-coupled methyl
3
2
13,19
26
resonances at δ 0.73 ( J = 64 Hz, J = 11 Hz) and δ 0.08
influence groups such as trifluoroacetate,
triflate,
PtH
PH
2
3
13
(
JPtH = 81 Hz, J = 3 Hz), which are assigned to the dfmp
pentafluoropyridine, and fluoroarsenate as well as antimonate
PH
27
and Pt-bound methyl groups, respectively. A new mesitylene
anions, suggesting that the effective trans influence of the π-
arene ligand in complex 1 is low.
1
95
methyl resonance was observed at δ 1.29 displaying
Pt
3
coupling ( J
coordination. For comparison, J
= 15 Hz), which confirmed platinum−arene
π-Arene Exchange Study. The relative labilities of the
mesitylene and dfmp ligands in complex 1 are of interest, since
this addresses the question of whether 1 can serve as an
PtH
3
couplings to the methyl
PtH
2+
4
6
4
6
3
protons in (η -C Me )Pt(η -C Me ) and (η -C Me )Pt(η -2-
6
6
4
6
6
+
10,11
2
6
+
methylallyl) are 17 and 16 Hz, respectively.
No J
effective source of 16-electron (η -C H Me )PtMe and/or 12-
PtH
6 3 3
+
coupling is observed for the coordinated mesitylene aromatic
C−H resonance at δ 5.61. Together these data are consistent
with the quantitative conversion of cis-(dfmp) PtMe to the
electron Pt(dfmp)Me fragments. Accordingly, a brief survey of
phosphine and π-arene exchange chemistry for (η -C H Me )-
Pt(dfmp)Me has been carried out (Scheme 1). No degenerate
6
6
3
3
+
2
2
6
novel cationic arene methyl complex (η -C H Me )Pt(dfmp)-
Me (1) (eq 1). Complex 1 is readily isolated as a pale yellow
6
3
3
+
Scheme 1
crystalline solid and is stable in solution in the absence of added
mesitylene. The stability of 1 is exceptional: only 10%
decomposition with release of mesitylene is observed after
warming to 80 °C in ODFB for 6 h. The observation of a single
phosphine exchange with excess added dfmp (14 equiv) in
ODFB solutions of 1 at 20 °C was observed on the NMR time
scale. Similarly, NMR monitoring of 1 in the presence of 1.5
equiv of the more sterically demanding monodentate PFAP
mesitylene methyl resonance for this C symmetric complex
s
down to −30 °C is consistent with rapid arene ring rotation/
equilibration on the NMR time scale.
t
35
ligand (C F ) P( Bu) at 20 °C showed no evidence of arene
2
5 2
or dfmp substitution after several hours. Addition of the strong
The structure of 1 was confirmed by X-ray crystallography
Figure 1). The Pt−C(arene) bond distance average, 2.448 Å,
donor phosphine Me P does, however, result in rapid
(
3
displacement of both the dfmp and mesitylene ligands (see
later, Scheme 3).
Scheme 2
6
+
Figure 1. Crystal structure of (η -C H Me )Pt(dfmp)Me (1) with
6
3
3
thermal ellipsoids at the 35% probability level. Selected metrical data:
Pt(1)−C(1): 2.072(3) Å, Pt(1)−P(1): 2.1620(7) Å, Pt(1)−C(2):
2
.470(3) Å, Pt(1)−C(3): 2.439(3) Å, Pt(1)−C(4): 2.520(3) Å,
Pt(1)−C(5): 2.475(3) Å, Pt(1)−C(6): 2.390(3) Å, C(2)−C(3):
1
.404(4) Å, C(3)−C(4): 1.421(4) Å, C(4)−C(5): 1.394(4) Å, C(5)−
C(6): 1.410(4) Å, C(6)−C(7): 1.417(4) Å, C(7)−C(2): 1.413(4) Å;
Pt(1)−C(7): 2.395(3) Å; P(1)−Pt(1)−C(1): 87.38(10)°.
Scheme 3
is significantly longer and also has a wider Pt−C(aryl) bond
6
length range (2.395(3)−2.520(3) Å) than that reported for (η -
4
+
10
C Me )Pt(η -C Me ) (2.319(5)−2.380(6) Å, 2.351 Å av).
6
6
4
4
This bonding asymmetry is not correlated with any significant
C(aryl)−C(aryl) bond alternation (1.394(4)−1.421(4) Å) or
with trans influence effects of the dfmp and methyl ligands, but
may be indicative of facile ring slippage and arene exchange/
dissociation, as has been noted for similar palladium and nickel
9
,24
systems. The short Pt−P bond distance of 2.1620(7) Å is in
keeping with the generally observed trend for PFAP
2
5
complexes. Relative to other structurally characterized
B
DOI: 10.1021/acs.organomet.5b00410
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Arene lability trends for (η -arene)ML systems have been
Article
6
These observations are consistent with either disproportiona-
tion or efficient scavenging of dfmp by an initially formed arene
displacement product such as (dfmp)Pt(CO) Me to form
trans-(dfmp) Pt(CO)Me . H NMR spectral broadening under
n
28,29
the subject of numerous studies.
In general, the arene
+
lability dramatically increases going from group 6 to group 10
2
+
1
metals ranging from thermally robust (arene)M(CO) (M =
3
2
Cr, Mo) complexes, which require elevated temperatures and/
or added donor solvents as catalysts to effect arene displace-
ment, to (arene)Ni(C F ) compounds, which undergo
excess CO is likely due to dfmp/CO exchange. Solution IR
spectra of 1 treated with excess CO in dichloromethane show a
−
1
sharp band at 2150 cm assignable to trans-(dfmp) Pt(CO)-
6
5
2
2
30
6
+
−1
uncatalyzed exchange at ambient temperatures, and (η -
Me , as well as a broad ν(CO) band at 2099 cm ; since no
significant PFAP product other than trans-(dfmp) Pt(CO)Me
+
+
C H Me )Pd(allyl) , which undergoes exchange with free
6
3
3
2
7b
mesitylene on the NMR time scale down to −77 °C. In all
cases the order of arene binding affinity has followed increased
donor ability: C Me > C H Me > C H Me > C H Me >
toluene > benzene > fluorobenzenes. Facile arene exchange
between the mesitylene ligand of 1 and free arenes occurs
within minutes at ambient temperatures and has allowed us to
readily measure competitive equilibrium constants for
is observed, we tentatively attributed this additional band to an
as yet unidentified dfmp-free platinum carbonyl species (see
Figure S11).
6
6
6
2
4
6
3
3
6
4
2
29
6
Reaction of 1 with Me P. The clean formation of (η -
3
+
C H Me )Pt(dfmp)Me in eq 1 is facilitated by the lability and
6
3
3
the electron-poor nature of the perfluorinated dfmp ligand.
Reaction of the analogous donor phosphine complex cis-
(Me P) PtMe with mesitylenic acid in ODFB produced a 1:1
+
31
mesitylene relative to toluene and 1,2,4,5-tetramethylbenzene
3
2
2
1
6
+
(
durene). The H NMR chemical shifts for the free arene
mixture of (η -C H Me )Pt(PMe )Me and [(Me P) PtMe ]
6 3 3 3 3 3
6
methyl groups and the Pt−CH resonances for each (η -
arene)Pt(dfmp)Me complex are well separated and allow for
due to efficient trapping of initially formed protonolysis
3
+
+
product (Me P) PtMe(solv) by released Me P (Scheme 3).
3
2
3
+
6
quantification of all solution species by integration (representa-
tive examples are given in Figures S3 and S4). In accord with
previous studies a clear preference for binding to electron-rich
(Me P) PtMe may be cleanly generated by treatment of (η -
C H Me )Pt(dfmp)Me with excess Me P. The absence of
detectable Me PH suggests that protonation of Me P by
3 3
+
6
3
3
3
+
3
3
6
+
arenes also exists for (η -arene)Pt(dfmp)Me : at 20 °C the
equilibria for exchange of 1 with toluene (K = 0.0030(3) and
durene (K = 20(2) are fully established within 30 min. No
evidence of mesitylene displacement by the ODFB aromatic
solvent is observed, consistent with its electron-poor nature.
Comparison of these values to corresponding ones reported by
unreacted mesitylenium acid is not competitive with the
kinetics of platinum cation trapping. For the poorly donating
dfmp ligand, neither competitive trapping of platinum nor
+
32
protonation to form dfmpH takes place. It is likely that
other, less donating and more sterically demanding phosphine
systems (Ar P, (RO) P, (pyr) P, (C F ) P, etc.) may also favor
3
3
3
6 5 3
6
Muetterties for the exchange of (η -C H Me )Mo(CO) with
arene product formation over protonolysis trapping and also
lead to exclusive arene product formation.
6
3
3
3
toluene (K = 0.034) and durene (K = 1.2) indicates a much
6
more significant (∼10-fold) preference of (η -arene)Pt(dfmp)-
Complex 1 has been surveyed for ethylene dimerization
activity. Addition of ethylene (∼27 equiv) to 1 in ODFB at 20
°C resulted in the complete displacement of mesitylene as well
as a significant amount (∼50%) of dfmp and the appearance of
very broad resonances at 0.7 and −1.0 ppm (ν ≈ 100 Hz).
+
Me systems for more electron-rich arenes.
Reactions of 1 with H and CO. Facile arene exchange
2
suggests that the formally coordinatively saturated 18-electron
complex 1 may react under mild conditions with other
1/2
potential substrates such as H and CO and serve as a source
Monitoring the progress of reaction showed the appearance of
stoichiometric propene and formation of a 2:1 thermodynamic
2
+
of the 12-electron moiety “(dfmp)PtMe ”. The reaction
6
+
−1
between (η -C H Me )Pt(dfmp)Me and hydrogen (∼3 atm)
mixture of trans- and cis-2-butene at a rate of ∼7 TO h . The
6
3
3
1
31
in ODFB was monitored by H and P NMR. After 12 h at
ambient temperature, methane loss and 10% conversion to a
absence of significant amounts of 1-butene in ethylene
dimerization by 1 was also noted in dimerization catalysis by
6
+
13
new species having (η -C H Me )Pt resonances at δ 5.57 and
[(dfepe)Pt(Me)(NC F )]
and contrasts with the compet-
6
3
3
5 5
1
.41, a dfmp methyl doublet at δ 0.73, and an associated
itive production of 1-butene by Brookhart and Templeton’s
1
2
+
14
1
platinum-coupled doublet at δ −23.21 ( J = 1640 Hz, J
3
C H Me )Pt(dfmp)H (2) (Scheme 2). Warming the reaction
mixture to 80 °C for 3 h resulted in 55% conversion to 2, while
further warming for 12 h resulted in a 3:1 mixture of hydride
complex to starting complex with an accompanying 50%
decomposition with the release of free mesitylene.
=
[(diimine)Pt(Et)(C H )] system.
H NMR spectra of a
HPt
HP
2
4
6
7 Hz) confirmed the formation of the arene hydride, (η -
mixture of 1 and excess ethylene in ODFB cooled to −30 °C
+
after reacting for 5 min at 25 °C revealed a distinctive Pt−CH
6
3
3
3
3
2
31
resonance at δ −1.42 ( J = 20 Hz, J = 59 Hz), and P
HP
HPt
NMR displayed free dfmp and two Pt-bound resonances at 26.2
1
1
( J = 3400) and 4.4 ppm ( J = 990) assignable to dfmp
PPt
PPt
ligands trans to Pt−ethylene and Pt−CH groups, respectively
3
6
+
The reaction of (η -C H Me )Pt(dfmp)Me with CO in
(Figures S9 and S10). On the basis of these data we tentatively
assign the initial major (dfmp)Pt species formed under catalytic
6
3
3
ODFB has also been examined. After 10 min exposure to 1 atm
of CO at ambient temperature, free mesitylene was observed as
well as ill-defined broad resonances in H NMR spectrum at δ
+
conditions as cis-(dfmp) Pt(C H )Me . It is notable that, even
2
2
4
1
though the major identified platinum-bound species is a bis-
dfmp adduct, which requires scavenging of an additional
equivalent of dfmp from the catalyst precursor 1, 50% of the
total dfmp under catalytic conditions is dissociated. As a result,
1
.21 and 0.26. A single major resonance (∼40% of the
31 31
integrated total of all P resonances) appeared in the P NMR
1
spectra at 34.5 ppm (m, J = 3130 Hz), and no free dfmp was
observed. A separate NMR experiment with 0.5 equiv of added
PtP
+
we cannot discriminate between cis-(dfmp) Pt(C H )Me and
2
2
4
CO revealed a distinctive Pt−Me proton resonance at δ 0.15
some phosphine-free compound as the catalyst resting state.
2
3
(
J
= 58 Hz, J = 9 Hz) and a ∼1:1 mixture of the 34.5
Summary. The ligand substitution and reaction chemistry
PtH
PH
6
+
ppm phosphorus species and unreacted 1: NMR data for this
of (η -C H Me )Pt(dfmp)Me is dependent on the nature of
6 3 3
new dfmp product closely match data for the previously
the incoming substrate: for reactions with arene, clean exchange
is observed, which maintains an intact Pt(dfmp)Me moiety.
+
18
+
reported bis-phosphine complex trans-(dfmp) Pt(CO)Me .
2
C
DOI: 10.1021/acs.organomet.5b00410
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Degenerate phosphine exchange with added dfmp on the NMR
time scale is not observed; quantification of a potential slower
degenerate phosphine exchange rate utilizing deuterated dfmp
or another appropriate competitive added ligand merits further
(s, 6F; PCF
2
CF
3
), −112 to −115 (overlapping ABX multiplets, 4F;
3
PCF CF ), −133.1 (s, br, 8F; ortho-(C F ) B), −163.7 (t, J = 19
2
3
6
5
4
FF
3
Hz, 4F; para-(C F ) B), −167.6 (t, br,
J = 19 Hz, 8F; meta-
6
5
4
FF
(
C F ) B). NMR data in dichloromethane (10% CD Cl in CH Cl ; δ
6 5 4 2 2 2 2
1
5
.32 CH Cl used as internal reference): H NMR (400.13 MHz, 25
2 2
study. The reaction of 1 with the strongly donating Me3P
6
3
6
°
C): δ 6.86 (s, 3H; (η -C H Me )Pt), 2.48 (s, J = 15 Hz, 9H; (η -
6 3 3 PtH
ligand results in rapid loss of both arene and dfmp to form
3
2
C H Me )Pt), 1.92 (d, J = 64 Hz, J = 11 Hz, 3H; Me(C F ) P),
1
+
6
3
3
HPt
HP
2 5 2
(
Me P) PtMe . The reaction of 1 with CO is less well defined,
2
3
31
3
3
.21 (d, J = 81 Hz, J = 3 Hz, 3H; Pt(CH )). P NMR (161.97
HPt HP 3
but surprisingly forms a bis-dfmp product trans-(dfmp) Pt-
1
3
3
2
MHz, 25 °C): δ 19.9 (ps. p, J = 6360 Hz, J ≈ J = 62 Hz).
6 + −
PPt
PFa
PFb
+
6
+
(
CO)Me . The reaction of (η -C H Me )Pt(dfmp)Me with
6 3 3
{(η -C
6
H
3
Me
3
)Pt[(C
2
F
5
)
2
MeP]H} (B(C
2
6
F
5
)
4
)
(2). The reaction
1
31
H is moderately selective toward Pt−Me bond hydrogenolysis,
between complex 1 and H was monitored by H and P NMR: A
5 mm Teflon-valved NMR tube containing 10 mg of 1 and 0.5 mL of
2
but requires heating and is accompanied by significant
decomposition. The most probable mechanism of hydro-
genolysis requires either dfmp loss or partial arene displace-
1,2-difluorobenzene was cooled to −195 °C, and 1 atm H was
2
admitted. After warming to ambient temperature (∼3 atm H
2
1
4
pressure), H NMR indicated ∼10% reaction after 12 h. Warming
ment (i.e., formation of a 16-electron (η -C H Me )Pt(dfmp)-
6
3
3
6
+
to 80 °C for 3 h resulted in 55% conversion to {(η -C H Me )Pt-
6
3
3
Me intermediate). The modest catalytic activity observed for
η -C H Me )Pt(dfmp)Me is lower than reported for
(dfepe)Pt(Me)(NC F )] (B(C F ) ) (150 TO h ) but is
+
−
6
+
[(C F ) MeP]H} (B(C F ) ) (2). Further warming for 12 h resulted
2 5 2 6 5 4
(
[
6 3 3
in a 3:1 mixture of 2 to 1 with an accompanying 50% decomposition
with the release of free mesitylene. NMR data for 2: H NMR (400.13
+
−
−1
5
5
6 5 4
1
still much higher than the only two other reported platinum
6
MHz, 1,2-difluorobenzene, 25 °C): δ 5.57 (s, 3H; (η -C H Me )Pt),
14,33
6
3
3
ethylene dimerization catalysts.
Future research is directed
3
6
3
1
.41 (s, J = 15 Hz, 9H; (η -C H Me )Pt), 0.73 (d, J = 82 Hz,
PtH 6 3 3 HPt
2
1
2
toward extending this new class of group 10 arene complexes
JHP = 11 Hz, 3H), −23.21 (d, J = 1640 Hz, J = 37 Hz, 1H;
HPt
HP
+
3
1
and exploring the utility of (π-arene)M(PFAP)R systems as
Pt(H)). P NMR (161.97 MHz, 1,2-difluorobenzene, 25 °C): δ 14.1
effective synthons for electrophilic 12-electron (PFAP)MR+
moieties. In a broader context, the strategy of employing Reed’s
arenium or halocarborane acids to generate unsaturated metal
cations through protonolysis, combined with the unique
combination of polarity and ion solvation of weakly
coordinating 1,2-difluorobenzene, may serve as a convenient
1
(m, J = 5780 Hz).
PPt
Reaction of cis-(Me
typical experiment, (nbd)PtMe
Me P were combined in 0.5 mL of benzene-d . Complete conversion
P)
3
PtMe
with [C
Me H F )
]+(B(C )−. In a
6 3 4 6 5 4
2
2
(10 mg) and excess (∼20 equiv)
2
3
6
31
1
to cis-(Me P) PtMe was confirmed by P NMR (δ −23.9, J
=
3
2
2
PPt
1
785 Hz). Removal of volatiles and addition of 0.5 mL of 1,2-
difluorobenzene with an acetone-d locking capillary gave spectro-
scopically pure cis-(Me P) PtMe : H NMR (400.13 MHz, 1,2-
difluorobenzene, 25 °C): δ 0.23 (ps. d, J = 20 Hz, J = 8 Hz, 18H;
6
general synthetic route to very labile cationic metal complexes
1
+
3
2
2
with very weakly coordinating L′ trapping ligands, L M(L′) .
3
n
HPt
HP
3
31
(
Me P) Pt), −0.37 (m, J = 66 Hz, 6H; PtMe ). P NMR (161.97
3
2
HPt
2
1
EXPERIMENTAL DETAILS
MHz, 1,2-difluorobenzene, 25 °C): δ −25.6 (s, JPPt = 1792 Hz). After
removal of volatiles, 1.2 equiv of [C Me H ] (B(C F ) ) was added,
■
+ −
6
3
4
6 5 4
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. Aprotic deuterated solvents used in NMR experiments were
dried over activated 3 Å molecular sieves. Elemental analyses were
performed by ALS Environmental. IR spectra were recorded on a
Varian FTS-800 FTIR. NMR spectra were obtained with a Bruker
Avance-III-400 instrument using 5 mm NMR tubes fitted with Teflon
valves (New Era Enterprises, Inc., NE-CAV5). Spectra taken in 1,2-
and 0.5 mL of 1,2-difluorobenzene was added while maintaining the
temperature at −30 °C. Upon warming to 20 °C for 30 min, a clean
conversion to a 1:1 mixture of (η -C H Me )Pt(Me P)Me and
6
+
6
3
3
3
+
1
31
6
(
Me P) PMe was indicated by H and P NMR. NMR data for (η -
3 3
+
1
C H Me )Pt(Me P)Me : H NMR (400.13 MHz, 1,2-difluoroben-
6
3
3
3
6
3
zene, 25 °C): δ 5.31 (s, 3H; (η -C H Me )Pt), 1.15 (s, J = 11 Hz,
6
3
3
PtH
6
9
H; (η -C H Me )Pt), 0.4 to 0.2 (m, 9H; Me P overlapping with
6 3 3 3
+
2
(
Me P) PMe trimethylphosphine resonances), −0.31 (d, J = 87
3
3
HPt
3
3
1
Hz, J = 2.4 Hz, 3H; Pt(CH )). P NMR (161.97 MHz, 1,2-
HP
3
1
difluorobenzene, 25 °C): δ −28.7 (s, J = 5260 Hz). NMR data for
PPt
+
1
(
Me P) PtMe (comparable to literature values): H NMR (400.13
difluorobenzene were externally locked and referenced to acetone-d
3 3
6
capillaries (acetone-d5 set to 2.07 ppm). 3 P NMR spectra were
1
MHz, 1,2-difluorobenzene, 25 °C): δ 0.4 to 0.2 (m, 27H;
(Me P) PMe trimethylphosphine resonances overlapped with the
3 3
+
19
referenced to an 85% H PO external standard. F NMR spectra were
3
4
6
+
2
Me P resonance of (η -C H Me )Pt(Me P)Me ), −0.74 (dt, J
=
P
=
=
referenced to a CF CO CH CH (−75.32 ppm) external standard.
3
6
3
3
3
HPt
31
3
2
2
3
3
3
5
8 Hz, J (cis) = 8.2 Hz, J (trans) = 6.5 Hz, 3H; Pt(CH )).
1
,2-Difluorobenzene was purchased from Synquest Laboratories, Inc.
HP HP 3
1
NMR (161.97 MHz, 1,2-difluorobenzene, 25 °C): δ −20.3 (d, J
All reagents, unless otherwise noted, were purchased from Aldrich and
PPt
3
4
2
1
2
1
570 Hz, J = 23.5 Hz, 2P; Me P’s cis to Pt-Me), −26.4 (t, J
were used without further purification. (nbd)PtMe , (C F ) PMe
PP
3
PPt
2
2 5 2
1
9
t
35
2
790 Hz, J = 23.5 Hz, 1P; Me P trans to Pt-Me).
(
[
dfmp) and cis-(dfmp) Pt(Me) ,
(C F ) P( Bu),
C Me H ] (B(C F ) ) were prepared following literature proce-
and
PP
3
2
2
2
5 2
+
−
Catalytic Ethylene Dimerization Using 1. In a typical
experiment, a Teflon-valved 5 mm NMR tube containing a sealed
acetone-d capillary was charged with 10 mg of 1 and 0.5 mL of 1,2-
6
3
4
6 5 4
1
8
dures.
6
+
−
{
(η -C H Me )Pt[(C F ) MeP]Me} (B(C F ) ) (1). (dfmp) Pt-
Me)2 (330 mg, 0.416 mmol) and [C Me H ] (B(C F ) ) (333
6
6
3
3
2
5 2
6
5 4
2
+
−
(
difluorobenzene, and excess ethylene was condensed in at 77 K.
Integration of initial H NMR spectra quantified the initial amount of
added ethylene, which was typically ∼25 equiv. NMR spectra at 25 °C
were taken at 5 min intervals using both the residual acetone-d and
the 1,2-difluorobenzene as reference standards. Integration of cis- and
trans-2-butene product methyl resonances was used to determine
TONs. The catalytic activity was taken from the time period
subsequent to complete propene formation.
X-ray Crystallography. X-ray diffraction data for {(η -C
6
3
4
6 5 4
1
mg, 0.416 mmol) were dissolved in 10 mL of 1,2-difluorobenzene and
stirred for 1 h at ambient temperature. All volatiles were removed, and
the solid residue was dissolved in 10 mL of petroleum ether (35−60
5
°
C); precipitation at −78 °C and cold filtration afforded 1 as an
analytically pure pale yellow crystalline solid (375 mg, 70%). Anal.
Calcd for C H F BPPt: C, 36.22; H, 1.40. Found: C, 36.10; H, 1.81.
39
18 30
1
H NMR (400.13 MHz, 1,2-difluorobenzene, 25 °C): δ 5.61 (s, 3H;
6
3
6
6
(η -C H Me )Pt), 1.29 (s, J = 15 Hz, 9H; (η -C H Me )Pt), 0.73
6
H
3
Me
3
)-
6
3
3
PtH
6
3
3
3
2
2
+
−
(
d, J = 64 Hz, J = 11 Hz, 3H; Me(C F ) P), 0.08 (d, J = 81
Pt[(C F ) MeP]Me} (B(C F ) ) (1) were measured at 150 K on a
2 5 2 6 5 4
HPt
HP
2
5
2
HPt
3
31
Hz, JHP = 3 Hz, 3H; Pt(CH )). P NMR (161.97 MHz, 1,2-
difluorobenzene, 25 °C): δ 18.6 (pseudopentet, J = 6380 Hz, J
≈
Bruker SMART APEX II CCD area detector system equipped with a
graphite monochromator and a Mo Kα fine-focus sealed tube operated
at 1.5 kW power (50 kV, 30 mA). Crystals were attached to glass fibers
3
1
3
PPt
PFa
3
19
JPFb = 60 Hz). F NMR (CD Cl , 376.50 MHz, 25 °C): δ −77.8
2
2
D
DOI: 10.1021/acs.organomet.5b00410
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
using Paratone N oil. Collection and refinement details are included in
the Supporting Information.
(16) Camacho, D. H.; Guan, Z. Chem. Commun. 2010, 46, 7879−
7893.
(17) A separate paper examining the effects of phosphine versus
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00410.
diimine ancillary effects on alkene insertion barriers is in preparation:
Schmidt, B. M.; Adams, J. J.; Basu, S.; Thapaliya, B.; Arulsamy, N.;
Roddick, D. M. Manuscript in preparation.
■
*
S
(18) 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,
6
314−6315.
Representative NMR spectra and tables giving X-ray
(19) Butikofer, J. L.; Hoerter, J. M.; Peters, R. G.; Roddick, D. M.
Organometallics 2004, 23, 400−408.
20) Mansingh, A.; McLay, D. B. J. Chem. Phys. 1971, 54, 3322−
325.
21) O’Toole, T. R.; Younathan, J. N.; Sullivan, B. P.; Meyer, T. J.
Inorg. Chem. 1989, 28, 3923−3926.
22) Gianetti, T. L.; Bergman, R. G.; Arnold, J. Chem. Sci. 2014, 5,
2517−2524.
23) ODFB is susceptible to C−F bond activation by fluorophilic
metals; see ref 22.
24) Walter, M. D.; Moorhouse, R. A.; White, P. S.; Brookhart, M. J.
Polym. Sci., Part A: Polym. Chem. 2009, 47, 2560−2573.
diffraction data collection and refinement details for 1
(
3
(
(
PDF)
CIF data for complex 1 (CIF)
AUTHOR INFORMATION
Corresponding Author
Phone: +1 307 766 2535. E-mail: dmr@uwyo.edu.
(
■
(
*
Notes
(
The authors declare no competing financial interest.
(25) Ernst, M. F.; Roddick, D. M. Organometallics 1990, 9, 1586−
ACKNOWLEDGMENTS
We thank The National Science Foundation (CHE-0911739)
for financial support.
■
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E
DOI: 10.1021/acs.organomet.5b00410
Organometallics XXXX, XXX, XXX−XXX