Platinum ethylene dimerization catalysts: Diphosphine vs. diimine ancillary ligand effects

Article abstract of DOI:10.1016/j.poly.2020.114461

Kinetic and mechanistic studies are presented for the (dfepe)Pt(Me)(NC₅F₅)⁺ (dfepe = (C₂F₅)₂PCH₂CH₂P(C₂F₅)₂) ethylene dimerization catalyst system. New labile complexes (dfepe)PtMe(L)⁺ (L = NC₅F₅, C₆F₅CN, C₆F₅NH₂, C₆F₅NO₂) have been prepared. A general extension to a variety of other chelating diphosphine analogues (PP)Pt(Me)(C₂H₄)⁺ has been accessed by methyl abstraction from donor (PP)PtMe₂ precursors with Ph₃C⁺B(C₆F₅)₄^? in the presence of ethylene to cleanly afford (PP)Pt(Me)(C₂H₄)⁺ products. Catalysis studies for these more electron-rich diphosphine systems demonstrate moderate dimerization activity which is uniformly higher than reported for (diimine)Pt(Me)(C₂H₄)⁺. In several cases allylic catalyst decomposition products (PP)Pt(η³-C₃H₄Me)⁺ have been identified. A DFT study of insertion barriers for diimine and diphosphine systems is presented which suggests that weakening of Pt-ethylene ground state binding by strong-field diphosphine ligands is a major contributing factor to the lower ethylene insertion barriers for PP systems.

Full text of DOI:10.1016/j.poly.2020.114461

Journal Pre-proofs
Platinum Ethylene Dimerization Catalysts: Diphosphine vs. Diimine Ancil‐
lary Ligand Effects
Suman Debnath, Sayanti Basu, Bradley M. Schmidt, Jeramie J. Adams,
Navamoney Arulsamy, Dean M. Roddick
PII:
S0277-5387(20)30118-2
DOI:
Reference:
https://doi.org/10.1016/j.poly.2020.114461
POLY 114461
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
5 January 2020
17 February 2020
17 February 2020
Please cite this article as: S. Debnath, S. Basu, B.M. Schmidt, J.J. Adams, N. Arulsamy, D.M. Roddick, Platinum
Ethylene Dimerization Catalysts: Diphosphine vs. Diimine Ancillary Ligand Effects, Polyhedron (2020), doi:
https://doi.org/10.1016/j.poly.2020.114461
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Revised
Platinum Ethylene Dimerization Catalysts: Diphosphine vs.
Diimine Ancillary Ligand Effects
Suman Debnath, Sayanti Basu, Bradley M. Schmidt, Jeramie J. Adams, Navamoney
Arulsamy, and Dean M. Roddick*
Department of Chemistry, University of Wyoming
Dept. 3838, 1000 E University Ave., Laramie, WY 82071

Abstract
Kinetic and mechanistic studies are presented for the previously reported
(dfepe)Pt(Me)(NC5F5)+ (dfepe = (C2F5)2PCH2CH2P(C2F5)2) ethylene dimerization catalyst
system. New labile complexes (dfepe)PtMe(L)+ (L = NC5F5, C6F5CN, C6F5NH2, C6F5NO2)
have been prepared. A general extension to a variety of other chelating diphosphine
analogues (PP)Pt(Me)(C2H4)+ has been accessed by methyl abstraction from donor
-
(PP)PtMe2 precursors with Ph3C+B(C6F5)4 in the presence of ethylene to cleanly affords
(PP)Pt(Me)(C2H4)+ products. Catalysis studies for these more electron-rich diphosphine
systems demonstrate moderate dimerization activity which is uniformly higher than
reported for (diimine)Pt(Me)(C2H4)+. In several cases allylic catalyst decomposition
products (PP)Pt(3-C3H4Me)+ have been identified. A DFT study of insertion barriers for
diimine and diphosphine systems is presented which suggests that weakening of Pt-
ethylene ground state binding by strong-field diphosphine ligands is a major contributing
factor to the lower ethylene insertion barriers for PP systems.
†Submitted in honor of Prof. John E. Bercaw, on the occasion of his 75th birthday
Keywords (platinum organometallics; ethylene complex; phosphine coordination; DFT
analysis; dimerization catalysis; kinetics)

Introduction
Catalytic olefin oligomerization/polymerization continues to be a subject of
considerable academic as well as industrial interest. Ziegler-Natta and chromium-based
Phillips catalyst systems are well known and have been used for the past 60 years to
facilitate olefin polymerization at low pressures and moderately high temperatures
resulting in millions of tons of polyethylene and polypropylene each year.1 Large scale
linear alpha olefin production using the Shell higher olefin process is also well-
established.2 One major limitation of early-transition metal polymerization catalysts is their
strong Lewis-acidic nature and oxophilicity, which makes them incompatible for use in
polymerization or co-polymerization of many functionalized olefins. While late transition
metal systems in principle are more tolerant of alkene functional groups because of their
reduced affinities for heteroatoms (N, O, halides), late transition metal systems are still
mostly limited to dimerization or oligomerization of simple alkenes.3
Pioneering work by Brookhart and coworkers in 1995 on highly active nickel (II)
and palladium (II) α-diimine complexes has driven interest in late transition metal systems
as efficient olefin oligomerization catalysts.4,5 In stark contrast, the analogous platinum
diimine complex, (diimine)Pt(Et)(C2H4)+, was found to exhibit very limited ethylene
dimerization activity (100 °C, ~ 0.1 turnovers hr-1).6 The rate-limiting ethylene insertion
barrier for platinum in this system was determined to be 29.8 kcal mol-1, which is much
higher than the corresponding barriers found for palladium (17-19 kcal mol-1) and nickel
(13-14 kcal mol-1). In 1999 our research group reported modest ethylene dimerization
activity for the perfluoroalkylphosphine (PFAP) system (dfepe)Pt(Me)(O2CCF3) (80 °C,
-
TOF = 6 hr-1; dfepe = (C2F5)2PCH2CH2P(C2F5)2).7 Noting that CF3CO2 anion loss was
likely the rate determining step, in 2008 we reported a labile platinum alkyl cation

-
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 which converts to the desired ethylene adduct
(dfepe)Pt(Me)(C2H4)+ °C.8
upon
exposure
to
ethylene
at
-20
-
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 is an active ethylene dimerization pre-catalyst at
ambient temperature (600 psi ethylene, 27 °C in o-difluorobenzene (DFB), TOF = 42
hr-1).9 This activity is many orders of magnitude greater than the corresponding diimine
catalyst and provided motivation for the further development of PFAP-based group 10
alkene oligomerization catalysts.
In this paper, we have examined the properties and dimerization kinetics of the
(dfepe)Pt(Me)(C2H4)+ catalyst in more detail, and also surveyed the ethylene dimerization
activity for a range of chelating donor phosphine complexes (PP)Pt(Me)(C2H4)+ with
varying chelate backbones and pendant phosphine groups (Chart 1).
While the electron-poor PFAP complex (dfepe)PtMe2 reacts only slowly with trityl
-
cation, more electron-rich (PP)PtMe2 complexes react readily with Ph3C+B(C6F5)4 in the
presence of ethylene to cleanly afford (PP)Pt(Me)(C2H4)+ products. Ethylene dimerization
activity of the donor phosphine systems was found to be significantly less than

(dfepe)Pt(Et)(C2H4)+, but still considerably more active than the platinum diimine system.
DFT calculations are presented which provide some insight into the generally higher
catalytic activity of group 10 phosphine-supported catalysts.
Results and Discussion
(dfepe)Pt(Me)(L)+ Chemistry
a) (dfepe)PtMe(L)+ (L = NC5F5, C6F5CN, C6F5NH2, C6F5NO2) Synthesis. We have briefly
examined pentafluorobenzonitrile, pentafluoroaniline, and pentafluoronitrobenzene as
-
alternative labile ligands for (dfepe)PtMe(L)+ chemistry. [(dfepe)PtMe(NC5F5)]+B(C6F5)4
(1) is only slightly soluble in pentafluorobenzonitrile at ambient temperature, but warming
to 80 ºC for 30 mins followed by cooling produced crystals of
-
[(dfepe)Pt(Me)(C6F5CN)]+B(C6F5)4 (2) suitable for X-ray diffraction (Figure 1) which
confirmed conversion to the pentafluorobenzonitrile adduct (Equation 1).
C18
C17
C12
C13
P1
C16
N1
Pt1
C14
C15
P2
C11

-
Figure 1. Molecular plot of [(dfepe)Pt(Me)(NCC6F5)]+B(C6F5)4 (2) (borate anion not
shown) showing 50% probability thermal ellipsoids and partial labeling scheme. Selected
metrical data (bond lengths in Å and angles in deg): Pt(1)-N(1): 2.044(3); Pt(1)-C(11):
2.104(3); N(1)-C(12): 1.133(4); Pt(1)-P(1): 2.2974(8); Pt(1)-P(2): 2.1736(9); P(1)-Pt(1)-
N(1): 97.42(8); P(1)-Pt(1)-C(11): 175.2(1). P(2)-Pt(1)-N(1): 176.06(8), P(2)-Pt(1)-C(11):
91.16(12).
Reaction of 1 with 3 equiv. pentafluoroaniline in o-difluorobenzene at room
temperature similarly resulted in the displacement of the pentafluoropyridine ligand to
-
yield [(dfepe)Pt(Me)(NH2C6F5)]+B(C6F5)4 (3). Adducts 2 and 3 were not isolated on a
preparative scale. Pentafluoronitrobenzene was also examined as both a potential
weakly-coordinating solvent and a useful ancillary ligand. No displacement of
pentafluoropyridine was indicated by NMR spectra of
1
dissolved in
pentafluoronitrobenzene;
however,
protonolysis
of
(dfepe)PtMe2 with
-
[H(mesitylene)]+B(C6F5)4 in pentafluoronitrobenzene as the solvent cleanly yielded a pale
-
green product [(dfepe)Pt(Me)(C6F5NO2)]+B(C6F5)4 (4), which was isolated in 76% yield
(Equation 2).
For (dfepe)PtMe(L)+ complexes the relative ordering of 1JPtP magnitudes (trans to
L) is: 5480 Hz (C6F5NO2) >> 4950 (NC5F5) ~ 4940 (C6F5CN) >> 4450 (C6F5NH2) > 4370
(C2H4)8, which parallels the qualitative ligand lability trend. While several platinum adducts
of pentafluoroaniline and pentafluorobenzonitrile have been reported,10,11 to our

knowledge complex 4 is the only reported example of an isolated pentafluoronitrobenzene
adduct.
b) (dfepe)PtEt(L)+ Synthesis and Dynamics. In our initial report we noted that
(dfepe)PtMe(C2H4)+ cleanly formed upon treatment of the labile pentafluoropyridine
-
adduct [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 with ethylene at -20 ºC (31P NMR:  75.7 (1JPtP
31
= 1360 Hz), 64.6 (1JPtP = 4370 Hz)).8 Monitoring the course of reaction by P NMR
showed conversion to a catalyst resting state with similar spectroscopic features (-20 °C:
 74.6 (1JPtP = 1220 Hz), 63.6 (1JPtP = 4730 Hz)), which we had tentatively assigned as
the ethyl complex (dfepe)Pt(Et)(C2H4)+. We have now confirmed this assignment:
protonolysis of (dfepe)PtEt2 by [H(mesitylene)]+(B(C6F5)4)- in pentafluoropyridine cleanly
-
generates [(dfepe)Pt(Et)(NC5F5)]+B(C6F5)4 (5) which was isolated as a white solid
containing 0.79 equiv. of unassociated pentafluoropyridine. Addition of excess (~ 5
equiv.) ethylene to 5 in DFB at -30 °C resulted in complete displacement of
pentafluoropyridine within minutes to generate a product with 31P resonances essentially
identical to those previously ascribed to (dfepe)Pt(Et)(2-C2H4)+ (6) (Equation 3, Figure
2). Under excess ethylene 1H NMR spectra show a single broadened ethylene resonance
at 4.3 ppm due to rapid exchange. Exposure of 5 to a limiting (~10%) amount of ethylene
resulted in partial conversion to 6 and the appearance of a 195Pt-coupled C2H4 resonance
at  4.76 (2JPtH = 55 Hz).

P trans to ethylene
P trans to Et
P trans to NC5F5
ppm 85
80
75
70
65
60
55
50
45
40
-
Figure 2. Bottom: 31P NMR spectrum of {(dfepe)Pt(Et)(NC5F5)+}B(C5F6)4 in DFB at -30
°C. Top: treatment with excess ethylene at -30 °C, 30 min., conversion to
-
[(dfepe)Pt(Et)(C2H4)]+B(C5F6)4 .
The pentafluoropyridine adduct (dfepe)Pt(Et)(NC5F5)+ displays dynamic NMR
behavior. Ambient temperature spectra for (dfepe)Pt(Et)(NC5F5)+ in o-difluorobenzene
exhibit a single broad resonance at 0.4 ppm for all five ethyl protons. A coalescence point
is reached at 0 °C and further cooling to -50 °C results in separate methylene and methyl
resonances at  1.01 and -0.29, respectively (Supplemental Figure S10). A slow
3
exchange limit with fully resolved JHH splitting was not accessible due to the freezing
point limit of the solvent (-34 C). Coordinated pentafluoropyridine resonances for
(dfepe)Pt(Et)(NC5F5)+ are not observed in ambient temperature 19F NMR spectra due to
rapid ligand exchange with free residual pentafluoropyridine, but cooling to -50 °C
revealed both free and coordinated C5F5N resonances (Supplemental Figure S12). Line
shape analysis for both Pt-ethyl proton exchange and NC5F5 ligand exchange (Figures
S11, S13) give intra- and intermolecular kinetic barriers of 12.6(2) kcal mol-1 and 11.8(2)

kcal mol-1, respectively, which are consistent with an ethyl site exchange mechanism
involving initial NC5F5 ligand loss followed by reversible -H elimination.
Dynamic exchange processes for (dfepe)Pt(Et)(2-C2H4)+ could not be evaluated
due to the onset of ethylene insertion chemistry above -30 °C.12 Formation of
(dfepe)Pt(Et)(2-C2H4)+ followed by removal of excess ethylene led to uncharacterized
product mixtures and no evidence of platinum hydride formation. Since treatment of
(diimine)PtEt2 with [H(OEt2)2][BAr’4] (Ar’ = 3,5-(CF3)2C6H3) in diethyl ether at -78 °C is
reported to produce a stable ethylene hydride product, (diimine)Pt(H)(2-C2H4),6 the
analogous reaction of (dfepe)PtEt2 with the arenium acid [C6Me3H4]+(B(C6F5)4)- in a 1:1
mixture of CD2Cl2 and DFB at -60 °C was examined. Ethane loss and the formation of a
primary (dfepe)Pt product with a 31P resonance at  78.4 (1JPtP = 3330 Hz) and a partially-
resolved shoulder at  79.5 was observed, which upon warming to -40 °C collapsed to a
single broad resonance at  79.0. 1H NMR spectra from -60 to +10 °C showed a range of
broad poorly-defined resonances between 0 – 2 ppm. No clear evidence supporting the
formation of either an ethylene hydride or agostic ethyl complex was obtained.
c) Hydride Trapping Studies. In our initial 2008 report we observed that the catalyst
resting state (dfepe)Pt(Et)(2-C2H4)+ converted upon consumption of available ethylene
to a mixture of Pt(0) alkene species (dfepe)Pt(2-alkene), presumably due to proton
transfer from acidic (dfepe)Pt(H)(alkene)+ intermediates to more basic (relative to
ethylene) butene products. To probe the Brønsted acidity of platinum hydride
intermediates, the effect of added proton traps was investigated. Tilley and coworkers
have reported Me3SiPh and Me3SnPh as efficient non-nucleophilic proton traps for an
electrophilic Pt(II) bis-triflate hydroamination system.13 However, the presence of 1.2

equiv. Me3SiPh did not affect the rate of butene product formation by
(dfepe)Pt(Me)(NC5F5)+ under standard catalyst conditions, and addition of 1.2 equiv.
Me3SnPh to (dfepe)Pt(Me)(NC5F5)+ in o-difluorobenzene instead resulted in methylation
to form (dfepe)Pt(Me)2.
Typical proton traps are sterically-hindered amines which have high proton
affinities combined with low nucleophilicity toward sterically-hindered Lewis acid sites.
2,2,6,6-tetramethylpiperidine, 2,6-diphenylpyridine and triethylamine were found to be
ineffective and gave uncharacterized products when added to solutions of
(dfepe)Pt(Me)(NC5F5)+ in o-difluorobenzene. Addition of 1.2 equivalents of 2,6-lutidine to
a solution of (dfepe)Pt(Me)(NC5F5)+ in o-difluorobenzene resulted in pentafluoropyridine
31
displacement to yield [(dfepe)Pt(Me)(2,6-lutidine)]+, tentatively identified by P NMR (
76.3, 1JPtP = 1340 Hz; trans to CH3,  62.6, 1JPtP = 4000 Hz; trans to 2,6-lutidine). Finally,
the more sterically-hindered base 2,6-di-tbutylpyridine, which has been extensively used
as proton trap in living carbocationic polymerization systems,14,15 was examined. No
significant changes in the spectra of 5 in o-difluorobenzene occurred upon addition of one
equiv. 2,6-di-tbutylpyridine, indicating that 2,6-di-tbutylpyridine does not displace
pentafluoropyridine from (dfepe)Pt(Me)(NC5F5)+. Upon addition of ethylene, however, the
clean stoichiometric production of 2,6-di-tbutylpyridinium, propene, and the neutral
ethylene complex (dfepe)Pt(C2H4) was observed, consistent with efficient base
interception of the hydride intermediates (dfepe)Pt(H)(alkene)+ or (dfepe)Pt(H)(solv)+.
The initial formation of propene from (dfepe)Pt(Me)(C2H4)+ during catalytic
dimerization runs has also been verified by a 13C labeling study: treatment of
-
[(dfepe)Pt(13CH3)(NC5F5)]+B(C6F5)4 with ethylene in the presence of 2,6-di-tbutylpyridine

cleanly afforded (dfepe)Pt(2-C2H4) and free 13CH3CH=CH2 (Equation 4), which was
identified by 13C NMR.
d)
(dfepe)Pt(Me)(L)+ Ethylene Dimerization Kinetic Studies. The ethylene
-
dimerization activity of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 reported briefly in our previous
-
paper has been examined in more detail. The activity of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4
was followed by 1H NMR under 600 psi ethylene (~175 equiv. dissolved ethylene) at 27
°C using a previously-described sapphire NMR sample tube assembly.16 The deviation
from linearity noted prior to the 10 minute mark is due to the initial conversion of
[(dfepe)Pt(Me)(C2H4)]+ to propene and the active catalyst resting state,
[(dfepe)Pt(Et)(C2H4)]+ (Figure 3). The measured steady-state rate of 2-butenes (trans:cis
~ 2:1) production of 0.700(5) mol-1 min-1 corresponds to a G‡(300 K) of 20.2(1) kcal
mol-1, considerably less than that reported for (diimine)Pt(Et)(C2H4)+ (G‡(373 K) = 29.8
kcal mol-1).6
-
Figure 3.
Plot of butenes production by [(dfepe)Pt(Me)(NC5F5)]+B(C5F6)4 in
o-difluorobenzene (0.018 M) under 600 psi (~175 equiv., 3.2 M) ethylene at 27 °C. The
rate of butenes production excluding the initial 10 mins. of data was 0.700(5) mol-1 min-1.

-
The catalytic activity of [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 was also measured at
-10, 0 and +10 °C in the presence of excess ethylene (see Supplementary Materials for
0 and +10 °C kinetic plots). As shown in Figure 4, Plot (a), significant non-linearity is
apparent at -10 °C due to the competitive conversion of [(dfepe)Pt(Me)(C2H4)]+ under
these conditions to the [(dfepe)Pt(Et)(C2H4)]+ catalyst resting state. Monitoring by 31P
NMR gave a first-order rate constant for this conversion step of kinit = 0.0022(4) min-1),
corresponding to a G‡ of 20.7 kcal mol-1 for ethylene insertion into the Pt-Me bond.
Applying this correction (dividing butenes production by the [Pt(Et)]/[Pt(Me)]0 ratio as a
function of time) gave Plot 4b with an associated rate of 0.00638(6) min-1 with a slightly
lower G‡ of 20.1 kcal mol-1 for ethylene insertion into the Pt-Et bond. The limited stability
-
of [(dfepe)Pt(Et)(NC5F5)]+B(C6F5)4 prevented us from directly examining dimerization
kinetics without the added complication of Pt-Me to Pt-Et conversion.
Figure
4.
Plot
(a):
Uncorrected
plot
of
2-butenes
production
by
{(dfepe)Pt(Me)(NC5F5)+}B(C5F6)4 (0.014 M) in o-difluorobenzene in the presence of 23
equivs. ethylene at -10 °C. Plot (b): 2-butenes production divided by catalyst fraction
[Pt(Et)]/[Pt(Me)]0, calculated from [PtEt] = [PtMe]0e-kt, with k = 0.0022(4) min-1, giving an
effective conversion rate of 0.00638(6) min-1.
-

The kinetic order in ethylene was examined by monitoring the initial rate of butene
formation as a function of ethylene concentration. Monitoring butenes production at 27
-
°C by [(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 in o-difluorobenzene in the presence of 12 and
175 equiv. ethylene revealed only a slight difference in activity during the initial conversion
to the Pt-ethyl catalyst resting state, but a significant difference in activity (~ 3-fold) under
high ethylene concentration (Figure 5). This unusual behavior differs from the ethylene-
independent rate observed previously for (diimine)Pt(Et)(C2H4)+.6 Control of ethylene
concentration throughout our studies was problematic: variation of ethylene condensation
into 5 mm NMR tubes was sensitive to time and mixing. At the highest concentrations
(i.e., 175 equiv.) this introduces ethylene concentration-dependent kinetic behavior, but
at lower concentrations the assumption of ethylene independence and rate-determining
ethylene insertion appears to be reasonable (see below).
Figure 5. Ethylene dependence of butenes production by {(dfepe)Pt(Me)-
-
(NC5F5)+}B(C5F6)4 (0.018 M) in o-difluorobenzene in the presence of 12 equiv. (, 0.22
M,) and 175 equiv, (, 3.2 M, 0.700(5) min-1) ethylene at 27 °C. Rates taken from the
linear regions after 16 min. are 0.241(8) min-1 and , 0.700(5) min-1, respectively.

An Eyring plot of -10, 0, 10, and 27 °C data is revealing (Figure 6): The rate
dependence under limited amounts (6 - 23 equiv.) of ethylene is well-behaved, but the
increased butenes production rate under high ethylene concentration is a significant
outlier and suggests a competing associative pathway. The obtained activation values of
H‡ = +15.4(1) kcal mol-1 and S‡ = -7.0(5) EU are in reasonable agreement with DFT
calculated values for ethylene insertion into the Pt-Me bond of the model complex
[(CF3)2PCH2CH2P(CF3)2]Pt(Me)(C2H4)]+ of H‡ = +19.9(1) kcal mol-1 and S‡ = -7.1 EU
(see later).
Figure 6. Eyring plot of ethylene dimerization activity by {(dfepe)Pt(Me)-
-
(NC5F5)+}B(C5F6)4 under limited ethylene (, 2-23 equiv.), showing the outlier data at 27
°C with 175 equiv. ethylene ().
(PP)Pt(Me)(L)+ Chemistry
There is an unresolved question in (dfepe)Pt(Me)(L)+ chemistry: Is the dramatic
ethylene dimerization catalytic rate enhancement achieved by replacing the diimine
ancillary ligand by dfepe unique to PFAP ligands, or a more general feature in phosphine

catalyst analogues? To address this issue, we have prepared a broad range of
diphosphine platinum systems and examined their catalytic activity.
a) (PP)PtMe2 Syntheses. A series of (PP)PtMe2 diphenylphosphine complexes with
varying chelate backbone length (dppm, dppe, dppp, dppb), as well as the methyl- and
isopropyl-substituted C2-bridged chelates dmpe and dippe are readily prepared from
(cod)PtMe2 and the appropriate diphosphine.17 (dfppe)PtMe2, previously prepared by
methylation of (dfppe)PtCl2,18 was prepared in a similar manner from (cod)PtMe2, as were
the dimethyl complexes incorporating the carboranyl backbone chelates 1,2-
bis(dimethylphosphino)carborane (dmpc) and 1,2-bis(diphenylphosphino)carborane
(dppc). The diphosphines examined in this study are summarized in Chart 1.
b) (PP)PtMe(CO)+ Syntheses. (CO) values provide useful qualitative information on
relative net metal electron density for the diphosphine systems used in this study (Table
- 19
1). Methyl abstraction from (PP)PtMe2 precursors by the trityl cation, [Ph3C]+B(C6F5)4 ,
in the presence of 1 atm CO in the polar poorly-coordinating solvent o-difluorobenzene
(DFB) is a convenient route to the corresponding donor phosphine carbonyl cations
(PP)Pt(Me)(CO)+ (Equation 5). In the case of (dppm)PtMe2, abstraction using
-
[Ph3C+]B(C6F5)4 under CO didn’t produce the expected monomeric product
(dppm)Pt(Me)(CO)+ (18), but rather a single major (~65%) species that has been
tentatively assigned as the bimetallic complex [(-dppm)2Pt2(Me)2(CO)2]2+.20 Carbonyl
-
complex 18 was obtained as a minor component using [Ph3C]+SbF6 as the methyl
abstraction reagent and was characterized by 31P NMR and IR. [(dippe)Pt(Me)(CO)]+
-
B(C6F5)4 (17) has been crystallographically characterized (see Supplemental Section).

No corresponding methyl abstraction by trityl cation from the
perfluoroalkylphosphine (PFAP) derivative (dfepe)PtMe2 occurs in the presence of CO,
presumably due to its significantly reduced metal electron density, but
(dfepe)Pt(Me)(CO)+
has
been
prepared
by
CO
substitution
of
- 8
[(dfepe)PtMe(NC5F5)]+B(C6F5)4 , or by methyl abstraction in the presence of CO using
the more powerful SbF5(SO2) reagent.21
c) (PP)PtMe2 Ethylene Dimerization Studies. In contrast to the dfepe system, which is
accessed via the labile pentafluoropyridine adduct (dfepe)Pt(Me)(NC5F5)+, the
corresponding donor phosphine catalyst systems are more conveniently accessed by
direct methyl abstraction with trityl cation in the presence of ethylene to form in situ
(PP)Pt(Me)(C2H4)+ products (Equation 6). For (dfepe)PtMe2, trityl abstraction in the
presence of ethylene is very slow and not quantitative (see later). Continued exposure
to excess ethylene at ambient temperatures results in conversion to the corresponding
ethyl complexes, (PP)Pt(Et)(C2H4)+. A general trend noted for all examined
(PP)Pt(Me)(C2H4)+/ (PP)Pt(Et)(C2H4)+ pairs is a consistent increase in 1JPtP of 160 – 360
Hz for the phosphorus trans to the ethylene ligand and decrease of 140 – 170 Hz for the
phosphorus trans to the alkyl ligand going from the methyl to the ethyl complexes.

Initial Pt-methyl ethylene insertion rates and ethylene dimerization activities of the
complexes 25 – 33 were evaluated by 1H NMR under excess (20 - 90 equiv.) ethylene in
DFB and are summarized in Table 1, along with the time dependent distribution of butene
products. Dimerization activities span a ~30-fold range of activity from 0.06 TO/hr for
(dmpe)Pt(Et)(C2H4)+ to 1.90 TO/hr for the perfluoroaryl complex (dfppe)Pt(Et)(C2H4)+. For
(dppm)Pt(Me)(C2H4)+ the disappearance of the Pt-Me resonance could be monitored, but
the dimerization activity could not be determined due to the competitive appearance of a
new species with a 31P resonance at -1.6 ppm which we tentatively assign as the
bimetallic complex [(-dppm)2Pt2(Me)2(C2H4)2]2+ based on its similarity to the analogous
carbonyl adduct [(-dppm)2Pt2(Me)2(CO)2]2+.12
The activity of (dppe)Pt(Et)(C2H4)+ is anomalous: after three days, broad 1H NMR
resonances at  1.2 and 0.8 begin to appear due to oligomerized ethylene, and after the
complete consumption of all ethylene in 7 days a ~1:1 integrated mixture of butenes and
oligomeric product is obtained; this behavior is similar to that observed for
(dfepe)Pt(Et)(C2H4)+ and has been attributed previously to acid catalysis rather than
multiple insertion chemistry. No oligomerization activity is observed for any of the other
diphosphine systems examined.

Unlike the (dfepe)Pt(Me)(C2H4)+ system, which generates isomerized 2-butene as
the sole observed product, significant amounts of 1-butene are observed in all donor
phosphine systems; over time the ratio of 2-butenes/1-butene was found to increase in
all cases. The penultimate accepting phosphine system (dfppe)Pt(Me)(C2H4)+ most
closely approaches the behavior of (dfepe)Pt(Me)(C2H4)+ both in terms of dimerization
and butene isomerization activity.
Table 1. Summary of (PP)Pt(Me)(L)+ (L = CO, C2H4) comparative data
diphosphine (PP)Pt(Me)(L)+
Pt-Me
Total butenes % selectivity for
system
insertion
rate, hr-1
activity, TOF
hr-1
2-butenes
(elapsed hours)
(CO) (cm-1,
DCM solvent)
(22 ºC, DFB
solvent)
(22 ºC, DFB
solvent)
dmpe
dippe
2112
2106
0.00176(5)
0.115(1)
0.06(1)
0.32(3)
36(191), 60(408)
54(46)
dppm
dppe
dppp
dppb
dmpc
dppc
dfppe
dfepe
2110
2114
2117
2118
2132
2133
2149
21748
0.00248(3)
0.0422(3)
0.169(2)
0.107(1)
0.413(8)
0.45(1)
1.63(3)
---
---
---
0.07(1)
0.24(2)
0.45(4)
0.68(3)
0.94(9)
1.90(10)
42.0(3)a
53(47), 90(168)
77(4), 97(284)
79(16), 93(46)
92(19), 98(41)
55(19), 84(71)
85(21), 96(28)
100
aThis study, T = 27 ºC.
d) (PP)Pt(3-C3H4Me)+ formation from (PP)Pt(Et)(C2H4)+. As was observed for
(dfepe)Pt(Et)(C2H4)+, the (PP)Pt(Et)(C2H4)+ catalyst resting states for all other phosphine
systems examined persist in the presence of excess ethylene. The ultimate fate of the
catalyst after ethylene consumption, however, is variable. The majority of diphosphine

systems decompose to uncharacterized platinum product mixtures. In the cases where
PP = dppb, dmpc, and dippe, however, conversion to a single major product occurred.
The products formed from dppb and dippe were only partially characterized: single broad
1
31P resonances were observed with JPtP = 3530 and 3520 Hz, respectively, and the
corresponding 1H NMR spectra exhibited only a series of broad features between 0 and
2 ppm (apart from the 1- and 2-butene product resonances) and new methyl singlets. The
behavior of (dmpc)Pt(Et)(C2H4)+ was more definitive: 12 hrs after consumption of ethylene
a clean (~95%) conversion to a single product was indicated by the appearance of an AB
31
1
set of P resonances at 47.3 ppm (JPP = 15.5 Hz) with very similar JPtP values (3732,
3722 Hz). Isolation of single crystals from the dmpc product solution and characterization
by X-ray diffraction showed this product to be the 1-methylallyl product [(dmpc)Pt(3-
-
C3H4Me)]+B(C6F5)4 (34) (Equation 7, Figure 7). From this result we conclude that the
single 31P resonances observed for the dppb and dippe catalyst products are likely due
to isochronous (or dynamically exchanged) P centers in analogous (dppb)Pt(3-C3H4Me)+
and (dippe)Pt(3-C3H4Me)+ products.

B10
C8
C1
P2
B9
B8
B7
C2
C3
B6
Pt1
B3
C7
B4
P1
B1
B2
C5
B5
C4
-
Figure 7. Crystal structure of [(dmpc)Pt(3-C3H4Me)]+B(C6F5)4 (34) with thermal
ellipsoids at the 35% probability level. The borate anion is not shown. Selected metrical
data (bond lengths in Å and angles in deg): Pt(1)-C(1): 2.197(6); Pt(1)-C(2): 2.147(7);
Pt(1)-C(3): 2.229(7); Pt(1)-P(1): 2.247(1); Pt(1)-P(2): 2.238(1); P(1)-Pt(1)-C(1): 168.9(2);
P(1)-Pt(1)-C(3): 100.7(2); P(2)-Pt(1)-C(1): 98.3(2); P(2)-Pt(1)-C(3): 164.7(3).
Interestingly, although attempts to directly access (dfepe)Pt(R)(C2H4)+ products
from trityl methyl abstraction from (dfepe)PtMe2 in the presence ethylene were
unsuccessful, after prolonged standing crystals of the corresponding methylallyl complex
-
[(dfepe)Pt(3-C3H4Me)]+B(C6F5)4 (35) were obtained and also crystallographically
characterized (see Supplementary Section). A tentative mechanism to account for the
formation of these allylic products is shown in Scheme 1. Overlaid on the standard
ethylene dimerization mechanism is a competition between associative interchange (kdisp
)
of butene with ethylene, which continues the dimerization pathway, and irreversible allylic
activation (kallyl) of the intermediate butene adduct. As long as a sufficient concentration
of ethylene persists, the allylic deactivation step is suppressed.

R2
P
Scheme 1
Pt Bu
P
R2
R2
P
R2
P
kallyl
Pt
Pt
R2
-H2
Et
P
R2
P
R2
P
H
Pt
P
R2
kdisp
isomerize
R2
P
Pt
P
R2
H
R2
P
Pt
Et
P
R2
DFT modeling of ethylene insertion barriers.
A key issue to consider is: why are platinum diphosphine catalysts generally more
active than the corresponding diimine system? To probe this question, the barriers to
ethylene insertion for Brookhart’s diimine catalyst and a range of model PP chelate
systems have been evaluated by DFT methods (M06l functional, def2 basis sets). A
comparative natural bond order (NBO) analysis of the model perfluoroalkylphosphine
complex
(dfmpe)Pt(Me)(C2H4)+
(dfmpe
=
(CF3)2PCH2CH2P(CF3)2)
versus
(diimine)Pt(Me)(C2H4)+ (diimine = [(2,6-Me2C6H3)N=C(An)-C(An)=N(2,6-Me2C6H3)], An =
1,8-naphylenediyl)) has also been carried out. DFT results are summarized in Table 2.

Table 2. Summary of DFT results (M06l, def2 basis sets) for (PP)Pt(Me)(C2H4)+ and
(diimine)Pt(Me)(C2H4)+ insertion barriers to form agostic Pt(C3H7)+ products (diimine =
[(2,6-Me2C6H3)N=C(An)-C(An)=N(2,6-Me2C6H3)], An = 1,8-naphylenediyl).
L2Pt(Me)(C2H4)+ G
for C2H4 binding,
kcal mol-1
ligand system
L2Pt(Me)(C2H4)+
L2Pt(Me)(C2H4)+
G‡ for insertion, G for insertion,
kcal mol-1
kcal mol-1
(dmpm)Pt
(dmpe)Pt
26.3
23.3
0.0
0.1
13.0
13.3
(dmpp)Pt
23.3
23.2
25.1
22.0
30.1
-2.0
-2.6
1.9
12.3
10.1
14.8
20.5
33.4
cis-(Me3P)2Pt
(dppe)Pt
(dfmpe)Pt
(diimine)Pt
1.6
12.9
Calculated activation barriers for (dfmpe)Pt(Me)(C2H4)+ (22.0 kcal mol-1) and
(diimine)Pt(Me)(C2H4)+ (30.1 kcal mol-1) are in reasonable agreement with experimental
values found for (dfepe)Pt(Et)(C2H4)+ (20.2(1) kcal mol-1, 300 K) and
(diimine)Pt(Et(C2H4)+ (29.8 kcal mol-1, 373 K). Insertion barriers for donor phosphine
systems, with the exception of chelate-constrained (dmpm)Pt(Me)(C2H4)+, are slightly
higher than found for the dfmpe model complex and are insensitive to chelate chain length
or replacement by unconstrained Me3P groups. The high insertion barrier for
(diimine)Pt(Me)(C2H4)+ correlates with a significantly higher ethylene binding energy than
donor phosphine analogues (33.4 vs. 10.1 – 14.8 kcal mol-1), which should contribute to
stabilization of the reactant ground state. Interestingly, the ethylene bonding energy for
(dfmpe)Pt(Me)(C2H4)+ (20.5 kcal mol-1) is significantly higher than in donor phosphine
complexes despite the lower overall insertion barrier. This might reflect reduced ethylene
backbonding counterbalanced by a weaker phosphine trans-influence and greater sigma
electrostatic attraction.

Some insight into relative ethylene insertion barriers into Pt-Me bonds is provided
by calculated transition state geometries and relative bond orders (Figure 8). Overall,
changes in bond lengths are very similar: for (dfmpe)Pt(Me)(C2H4)+, Pt-Me bond-
lengthening to form the 4-center transition state is 0.22 Å and the formed Pt-C(ethylene)
bond length of 2.10 Å closely matches the reactant Pt-Me bond length. The corresponding
values for (diimine)Pt(Me)(C2H4)+ (0.21 Å lengthening, Pt-C(ethylene) = 2.03 Å) mirror
these changes. Changes in spectator dfmpe and diimine ligated atom metal bond lengths
(i.e., the trans influence) as the degree of Pt-C sigma bonding bonding evolves is also
similar: Elongated Pt-P and Pt-N bonds trans to Pt-Me (2.35, 2.20 Å, respectively)
contract to 2.23 and 2.04 Å as the Pt-Me bond is partially broken, and the Pt-P and Pt-N
bonds initially trans to Pt-ethylene elongate to a similar degree: Pt-P = 2.32, Pt-N = 2.20
Å.
Figure 8. Selected metrical parameters (Å) for (dfmpe)Pt(Me)(C2H4)+ and
(diimine)Pt(Me)(C2H4)+ reactant and transition state calculated geometries (DFT, M06l,
def2 basis sets).

The most significant differences in the diphosphine and diimine complex
approaches to the transition state are (1) The much shorter Pt-ethylene bond lengths for
the diimine complex (2.13 Å vs. 2.30 Å for (dfmpe)Pt(Me)(C2H4)+), and (2) the shorter Me-
ethylene bond length in the transition state for the diimine complex, 1.93 vs. 2.05 Å,
indicative of more extensive Me migration to ethylene (i.e., a later transition state).
Overall, while the bond-breaking cost for the Pt-Me bond lost is effectively
counterbalanced by Pt-C(ethylene) sigma bond formation in both ligand systems, the loss
of the stronger binding energy of (diimine)Pt(Me)+ to ethylene (33.4 kcal mol-1) compared
to the 20.5 kcal mol-1 binding energy for (dfmpe)Pt(Me)+ could explain the difference in
insertion barriers. This can be rephrased in classic coordination chemistry terms: the
greater trans-influence of ancillary phosphine ligands relative to diimine ligands
substantially weakens ethylene binding and raises the reactant ground state energy.
Changes in bonding energetics can also be evaluated by considering Wiberg bond
order indices,22 which are available from natural bond order analysis. For
(dfmpe)Pt(Me)(C2H4)+, the calculated index for the Pt-C(ethylene) bonds is 0.350, which
diverges at the transition state to 0.574 (sigma bond forming to Pt) and 0.174 (sigma bond
forming to migrating Me). For (diimine)Pt(Me)(C2H4)+, however, the calculated index for
the Pt-C(ethylene) bonds is significantly higher, 0.522, and diverges in the transition state
to 0.703 (sigma bond forming to Pt) and 0.167 (sigma bond forming to migrating Me). The
“bond order gain” in forming the new Pt-C sigma bond for (dfmpe)Pt(Me)(C2H4)+ (+0.224)
is higher than the +0.181 gain for (diimine)Pt(Me)(C2H4)+. In other words, there is an
energetic advantage in forming a new Pt-C sigma bond from the more weakly-bound

ethylene ligand in (dfmpe)Pt(Me)(C2H4)+ relative to the same ethylene insertion process
for (diimine)Pt(Me)(C2H4)+.
Summary
Building upon our initial reported work for the special case of PP =
perfluoroalkylphosphine,
this
paper
more
generally
establishes
that
(PP)Pt(alkyl)(ethylene)+ systems are significantly more activated toward migratory
insertion relative to (diimine)Pt(alkyl)(ethylene)+. Further (dfepe)Pt(R)(L)+ investigations
have (a) demonstrated more labile adducts, (b) confirmed (dfepe)Pt(Et)(C2H4)+ as the
catalyst resting state, and (c) verified propene as the initial product following Pt-Me
insertion. Base trapping studies with 2,6-di-tbutylpyridine implicate the intermediacy of
acidic hydride intermediates in the ethylene dimerization catalytic cycle.
Kinetics studies confirm the significantly lower insertion barrier for
(dfepe)Pt(Et)(C2H4)+ (20.2(1) kcal mol-1) relative to (diimine)Pt(Et)(C2H4)+ (29.8 kcal
mol-1), and variable temperature kinetics gave activation values (H‡ = +15.4(1) kcal mol-1
and -7.0(5) EU) in reasonable agreement with calculated values. Under moderate
amounts of excess ethylene, the rate of dimerization is zero-order in alkene but at higher
pressures a modest but significant rate acceleration is observed which suggests a
competing associate reaction pathway.
A broad range of phosphine chelate systems (PP)Pt(Me)(C2H4)+ have been
prepared in situ by trityl abstraction of methyl from (PP)PtMe2 in the presence of ethylene
and their activity has been examined (Table 1). No other diphosphine system approaches
PP = dfepe in activity, but a clear trend of increased activity with decreasing diphosphine
donor ability is established: (CO) data confirm that the most active dimerization catalysts

(PP = dmpc, dppc, dfppe, dfepe) are also the most electron poor. Beyond the low activity
of the highly constrained (dppm)Pt chelate, a modest increase in activity follows
increasing chelate chain length (dppe, dppp, dppb). Steric influence is best demonstrated
by the (dippe)Pt(Me)(C2H4)+ system, which is ~65 times more active toward insertion into
the Pt-Me bond than (dmpe)Pt(Me)(C2H4)+. Several instances where catalyst
decomposition to an inactive allylic final product have been noted, exemplified most
clearly by structurally-characterized (dmpc)Pt(3-C3H4Me)+.
DFT studies have been carried out in order to shed light on the (diphosphine)Pt
versus (diimine)Pt activity issue (Table 2). All propyl insertion products exhibit a modest
degree of agostic binding of the pendant methyl group. Calculated Pt-Me insertion
barriers agree well with the experimentally-determined barrier for (dfepe)Pt(Et)(C2H4)+
and the reported value for (diimine)Pt(Et)(C2H4)+. Only slight differences in insertion
barriers for donor phosphine systems are found; all donor phosphine systems have
calculated ethylene binding energies between 10 and 15 kcal mol-1. The only outliers in
ethylene binding energy happen to be the most active (dfepe) and least active (diimine)
analogues; both of these have significantly higher ethylene ligand binding energies. The
diimine system is also an outlier in G for the insertion process: whereas all diphosphine
systems are close to thermoneutral, G for (diimine)Pt(Me)(C2H4)+ is +12.9 kcal mol-1.
Qualitatively, the higher barrier for ethylene insertion for the diimine system can be
attributed to a later transition state and the accompanying loss of strong Pt-ethylene
binding.

In summary, the lower insertion barrier noted for diphosphine systems relative to
diimine systems can be reduced down to a simple “back of the envelope” explanation that
is rooted in well-known coordination chemistry trends: symmetric chelating strong-field
and weak-field ancillary ligand trans binding sites are both thermoneutral with respect to
the conversion of a reactant Pt-alkyl bond into a product Pt-alkyl bond. However, the
conversion of a Pt-ethylene binding site to a weak Pt--(agostic -Me) binding site is not
thermoneutral: stronger Pt-ethylene binding trans to a weak-field ligand (such as diimine)
leads to an energetically uphill process which effects the activation barrier to insertion.
We suggest that further explorations of ligand field effects, particularly in square planar
group 10 catalyst systems, would be a worthwhile undertaking.
Experimental
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 instrument. 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 o-difluorobenzene were externally
locked and referenced to acetone-d6 capillaries (acetone-d5 set to 2.07 ppm). 31P spectra
were referenced to an 85% H3PO4 external standard. 19F spectra were referenced, to a
CF3CO2CH2CH3 (-75.32 ppm) external standard. o-difluorobenzene (DFB),

pentafluoropyridine, pentafluorobenzonitrile, pentafluoroaniline, and pentafluoro-
nitrobenzene were purchased from Synquest Labs, Inc. All other reagents, unless
otherwise noted, were purchased from Aldrich and were used without further purification.
- 8
[(dfepe)Pt(Me)(NC5F5)]+B(C6F5)4 ,
(cod)PtMe2,23 (dippe)PtMe2,17b, (dmpe)PtMe2,24
17c, 17d
(PP)PtMe2 (PP = dppm, dppe, dppp, dppb),17a,
1,2-bis(diphenylphosphino)
carborane
(dppc),25
1,2-bis(dimethylphosphino)carborane
(dmpc),26
- 19
- 28
7
[C6Me3H4]+(B(C6F5)4)-,27 [Ph3C]+B(C6F5)4 , [Ph3C]+SbF6 , and (dfepe)PtEt2 were
13
prepared following literature procedures. The synthesis of CH3Li is described in the
Supplementary Section.
-
-
[(dfepe)Pt(Me)(NCC6F5)]+B(C6F5)4 (2). 20 mg of (dfepe)Pt(Me)(NC5F5)+B(C6F5)4 and 1
mL of NCC6F5 were placed in a NMR tube fitted with a Teflon valve and heated at 80 ºC
for half an hour. Upon cooling to room-temperature, colorless crystals were deposited
along the walls of the NMR tube and were collected for X-ray diffraction (see
Supplemental Section). NMR data for the remaining solution were consistent with the
-
clean formation of [(dfepe)Pt(Me)(NCC6F5)]+B(C6F5)4 (2). Preparatory-scale isolation of
2 was not attempted. 1H NMR (o-difluorobenzene, 400.13 MHz, 27 ºC, external acetone-
d6 reference):  2.03 (m, 2H; PCH2), 1.72 (m, 2H; PCH2), 0.18 (br. s, 2JPtH = 43 Hz, 3H;
PtCH3). 31P NMR (o-difluorobenzene, 161.70 MHz, 27 ºC):  79.9 (m, 1JPtP = 1490 Hz, P
trans to CH3), 58.4 (m, 1JPtP = 4940 Hz, P trans to NCC6F5).
-
[(dfepe)Pt(Me)(NH2C6F5)]+B(C6F5)4 (3). To a 5 mm NMR tube fitted with a Teflon valve
-
containing 15 mg of (dfepe)Pt(Me)(NC5F5)+B(C6F5)4 in 1 mL of o-difluorobenzene was
added 2 mg (~3 equiv.) of pentafluoroaniline. NMR data for the resulting solution
1
confirmed the formation of 3. H NMR (o-difluorobenzene, 400.13 MHz, 27 ºC):  1.97

(m, 2H; PCH2), 1.75 (m, 2H; PCH2), 0.10 (br. s, 1JPtH = 42 Hz, 3H; PtCH3). 31P NMR (o-
difluorobenzene, 161.70 MHz, 27 ºC):  76. 8 (m, 1JPtP = 1480 Hz; P trans to CH3), 60.9
(m, 1JPtP = 4450 Hz; P trans to NCC6F5). 19F NMR (376.5 MHz, o-difluorobenzene, 27 oC):
 -80.8 (s, 6F; PCF2CF3), -81.4 (s, 6F; PCF2CF3), -108 to -112 (overlapping ABX
-
multiplets, 8F; PCF2CF3), -133.7 (br. s, 8F; o-B(C6F5)4 ), -150.8 (br. s, 2F; C6F5NH2),
3
-153.6 (br. s, 1F; C6F5NH2), -160.6 (br. s, 2F; C6F5NH2), -165.0 (t, JFF =20 Hz, 4F; p-
-
-
B(C6F5)4 ), -168.8 (m, 8F; m-B(C6F5)4 ).
-
[(dfepe)Pt(Me)(O2NC6F5)]+B(C6F5)4 (4). 15 mL of pentafluoronitrobenzene was added to
-
a flask charged with (dfepe)Pt(Me)2 (0.24 g, 0.30 mmol) and (C6Me3H4)+B(C6F5)4 (0.29
g, 0.36 mmol). After 2 h of stirring, the resulting pale-green solid 4 (0.385 g, 76.2%) was
collected by filtration, and dried under vacuum. Anal. Calcd for C41H7BF45NO2P2Pt: C,
29.52; H, 0.42; Anal. found: C, 29.60; H, 0.74; 1H NMR (o-difluorobenzene, 400.13 MHz,
20 oC):  2.00 (m, 2H; PCH2), 1.70 (m, 2H; PCH2), 0.29 (br. s,  = 40 Hz, 3H, PtCH3).
½
31P NMR (161.70 MHz, o-difluorobenzene, 20 oC):  83.8 (m, 1JPtP = 1600 Hz; P trans to
1
CH3)  53.6 (m, JPtP = 5480 Hz; P trans to O2NC6F5). 19F NMR (376.5 MHz, o-
difluorobenzene, 20 oC):  -80.7 (s, 6F; PCF2CF3), -81.8 (s, 6F; PCF2CF3), -108 to -113
-
(overlapping ABX multiplets, 8F; PCF2CF3), -133.7 (br. s, 8F; o-B(C6F5)4 ), -134.5 (br. s,
 = 250 Hz, 2F; C6F5NO2), -157.0 (br. s,  = 250 Hz, 2F; C6F5NO2 (p-C6F5NO2 not
½
½
-
-
observed), -165.0 (t, 3JFF =20 Hz, 4F; p-B(C6F5)4 ), -168.8 (br. s, 8F; m-B(C6F5)4 ).
-
[(dfepe)Pt(Et)(NC5F5)]+B(C6F5)4 (5). To a flask charged with (dfepe)PtEt2 (0.250 g,
0.305 mmol) and [C6Me3H4]+(B(C6F5)4)- (0.370 g, 0.462 mmol) was added 15 mL of
pentafluoropyridine. After stirring the mixture for 2 hrs the resulting white solid (0.470 g)