d8 Nickel and palladium difluorocarbenes derived from trifluoromethyl POCOP-type pincer complexes

Article abstract of DOI:10.1016/j.jorganchem.2017.04.013

In this study, trifluoromethyl POCOP-type pincer complexes (^iPrPOCOP)Ni(CF₃) (1-CF3) and (^iPrPOCOP)Pd(CF₃) (2-CF3) are prepared. These complexes undergo Lewis acid-mediated fluoride abstraction to furnish cation

Full text of DOI:10.1016/j.jorganchem.2017.04.013

Accepted Manuscript
8
d Nickel and palladium difluorocarbenes derived from trifluoromethyl POCOP-type
pincer complexes
Graham M. Lee, Ilia Korobkov, R. Tom Baker
PII:
S0022-328X(17)30240-1
10.1016/j.jorganchem.2017.04.013
JOM 19900
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 7 March 2017
Revised Date: 12 April 2017
Accepted Date: 13 April 2017
8
Please cite this article as: G.M. Lee, I. Korobkov, R.T. Baker, d Nickel and palladium difluorocarbenes
derived from trifluoromethyl POCOP-type pincer complexes, Journal of Organometallic Chemistry
(2017), doi: 10.1016/j.jorganchem.2017.04.013.
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ACCEPTED MANUSCRIPT

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d8 Nickel and Palladium Difluorocarbenes Derived from Trifluoromethyl POCOP-type
Pincer Complexes
Graham M. Lee, Ilia Korobkov, and R. Tom Baker*
Department of Chemistry and Biomolecular Sciences and Centre for Catalysis Research and
Innovation, University of Ottawa, 30 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
*Corresponding author. E-mail address: rbaker@uottawa.ca (R. T. Baker)
Abstract
In this study, trifluoromethyl POCOP-type pincer complexes (iPrPOCOP)Ni(CF3) (1-CF3) and
(iPrPOCOP)Pd(CF3) (2-CF3) are prepared. These complexes undergo Lewis acid-assisted
fluoride abstraction to furnish cationic d8 difluorocarbene complexes of the type
[(iPrPOCOP)M(=CF2)]+[X]-, which are characterized in solution and for M = Ni using single-
crystal X-ray diffraction analysis. The electrophilic nature of these difluorocarbene complexes is
discussed, including their reactivity with pyridines.
Keywords
Nickel, Palladium, Fluorine, Fluorocarbene complexes, Pincer ligands
1. Introduction
Metal complexes with fluorinated ligands are of significant interest due to their applications in
the synthesis of fluorinated organic products.[1] The successful synthesis, characterization, and
controlled reactivity of M=CF2 complexes, however, remains a challenging and ongoing area of
research. Reported strategies for M=CF2 synthesis include 2-electron reduction of metal
perfluoroalkyl complexes [2], direct transfer of CF2 to a metal center [3], and α-fluoride
abstraction from metal perfluoroalkyl ligands.[4] One method of controlling the reactivity of
M=CF2 complexes is by changing the oxidation state of the metal, as first demonstrated by

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Roper et al. whereby a Ru0=CF2 (d8) complex reacts as a nucleophile at the carbene carbon, and
RuII=CF2 (d6) reacts as an electrophile.[5] Our group has shown that a similar dynamic exists
between nucleophilic CoI (d8) fluorocarbenes (Figure 1A) [6] and electrophilic CoIII (d6)
fluorocarbenes (Figure 1B).[7] While examples of fluorocarbene complexes have also been
documented based on metals from group 6 (Mo [8]), and group 7 (Mn [4]), only recently have
any examples from group 10 been reported.
Figure 1. Selected examples of metal difluorocarbene complexes.
The first example of a group 10 fluorocarbene complex was the base-stabilized Pt complex
[NBu4][Pt(CF3)2(κ-C,κ-S-CF2NC5H4S)] (formally d8) (Figure 1C), although the reactivity of this
complex was not discussed.[9] Our group recently published the first isolated examples of nickel
difluorocarbene complexes (Figure 1D), which are also the first examples of M=CF2 complexes
with formal d10 electronic configuration; these were shown to exhibit nucleophilic reactivity

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through [2 + 2] cycloaddition reactions with tetrafluoroethylene (TFE).[10] Previous to this,
nickel difluorocarbenes had only been studied in the gas phase [11] or proposed as intermediates
in the catalytic reaction of highly fluorinated epoxides with halogens.[12] To date, there are no
reported examples of experimentally observed palladium fluorocarbene complexes, although
they have been proposed as key species in the catalytic synthesis of (difluoromethyl)arenes.[13]
Finally, an important study by Ozerov et al. described the formation of a PNP-type pincer
complex of rhodium bearing a difluorocarbene ligand (Figure 1E), which can serve as a
precursor to a rhodium fluorocarbyne. [3b]
Nickel and palladium complexes bearing diphosphinito pincer-type POCOP [POCOP =
κP,κC,κP–(2,6-(R2PO)2-C6H3)] ligands have been used for catalytic transformations such as
hydroamination of acrylonitrile and olefination of aryl chlorides.[14] These complexes feature
strong terdentate metal-ligand bonding and one free coordination site at the metal, which can be
occupied by either an anionic or neutral ligand, affording neutral (POCOP)MIIX or cationic
[(POCOP)MIIL]+ species, respectively. Therefore, we hypothesized that POCOP complexes of
group 10 metals would be a stable platform for interconversion between anionic CF3 and neutral
CF2 ligands, via potentially reversible fluoride abstraction using a Lewis acid. The goal of the
present study is to prepare and characterize the first examples of M=CF2 complexes of nickel and
palladium with formal d8 electronic configurations, and explore what we expect to be
electrophilic-type reactivity.
2. Results and discussion
2.1 Preparation of (POCOP)M(CF3) (M = Ni, Pd)

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We began by preparing nickel and palladium iPrPOCOP [iPrPOCOP = κP,κC,κP–(2,6-(iPr2PO)2-
C6H3)] complexes (iPrPOCOP)MCl (M = Ni (1-Cl), Pd (2-Cl)), 1-Cl according to a direct, one-
pot method, [15] and 2-Cl using standard stepwise procedures (Scheme 1).[16]
Scheme 1. Previously reported syntheses of 1-Cl and 2-Cl.
Zargarian and co-workers recently reported the synthesis of fluoro and trifluoromethyl
derivatives of POCOP nickel complexes, including trifluoromethyl complex (iPrPOCOP)Ni(CF3)
(1-CF3) by treating 1-Cl with Me3SiCF3/AgF overnight at 45 °C in THF.[17] Here, we report an
alternative synthetic protocol for the preparation of nickel and palladium trifluoromethyl POCOP
complexes. Treatment of both 1-Cl and 2-Cl with Me3SiCF3/CsF for 2 h at room temperature in
DMF results in formation of the trifluoromethyl pincer complexes 1-CF3 (yellow solid, 80%
isolated yield) and (iPrPOCOP)Pd(CF3) (2-CF3) (white solid, 74% isolated yield), respectively
(Scheme 2).

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Scheme 2. Synthesis of trifluoromethyl Ni and Pd (iPrPOCOP) complexes 1-CF3 and 2-CF3.
Complex 2-CF3 was characterized using elemental analysis, multinuclear NMR
spectroscopy, and single crystal X-ray diffraction. The 19F and 31P NMR spectra of 2-CF3 are
highly characteristic. The 19F spectrum displays a single resonance appearing as a triplet at -8.24
ppm (JFP = 14 Hz), and the 31P{1H} spectrum shows a single resonance for equivalent
1
phosphinite groups coupled to the CF3 ligand, appearing as a quartet at 191.6 ppm. The H
spectrum displays the typical resonances associated with the iPrPOCOP ligand. The X-ray
structure of 2-CF3 confirms the Pd center has square planar geometry (Figure 1), with typical
angular distortions about the Pd center consistent with the small bite angle of the POCOP ligand
(P-Pd-P < CPOCOP-Pd-CF; CPOCOP-Pd-P < P-Pd-CF) (Table 1). The Pd-CF3 bond distance in 2-
CF3 is 2.1139(17) Å, in comparison with the corresponding distance in (POCOP-iPr)Pd-CH3 of
2.125(3) Å.[14e]
Figure 2. ORTEP drawing of complex 2-CF3. Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are set to the 50% probability level.

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2.2 Preparation of [(POCOP)M(=CF2)]+ (M = Ni, Pd)
Our strategy to prepare d8 Ni and Pd difluorocarbene complexes consisted of abstracting
a fluoride from a trifluoromethyl ligand using a Lewis acid. The reactivity of cationic d8 nickel
and palladium difluorocarbene complexes is expected to be electrophilic, different than the
nucleophilic type reactivity observed for d10 nickel difluorocarbene complexes previously
studied.[10] We began our investigation by treating complex 3 with 1 equiv of Me3SiOTf (OTf =
SO3CF3) in CH2Cl2 (Figure 3).
Figure 3. Reaction of 1-CF3 with Me3SiOTf, analyzed using 31P{1H} NMR.

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After 10 minutes of stirring, analysis of the reaction mixture using 31P and 31F NMR
spectroscopy indicated the formation of the cationic nickel difluorocarbene complex
[(iPrPOCOP)Ni(=CF2)][OTf] (1-CF2a) with concomitant formation of Me3SiF, along with
(iPrPOCOP)Ni(OTf) (1-OTf) and unreacted starting material 1-CF3. Within 1.5 h trifluoromethyl
complex 1-CF3 was completely consumed, and over the course of 20 h difluorocarbene complex
1-CF2a was all converted to 1-OTf. The difluorocarbene complex reacts with trace moisture
(despite rigorous attempts to remove water from solvents) to furnish 2 equiv of HF and a
carbonyl complex (1-COa), which is not detected using NMR spectroscopy as the CO ligand is
immediately displaced by the triflate group. The 19F and 13P{1H} NMR signals for 1-CF2a are
highly characteristic. The 19F NMR signal for the difluorocarbene ligand appears as a highly de-
shielded broad singlet at 169.1 ppm, typical for metal difluorocarbene complexes with
electrophilic reactivity patterns, along with the signal for outer-sphere triflate at -78.3 ppm. The
13P{1H} signal appears at 206.4 ppm as a triplet, due to coupling with the CF2 ligand (3JPF = 14
Hz). The distinct changes in chemical shift and splitting pattern of the 31P{1H} NMR signals
between (POCOP)M(CF3) and [(POCOP)M(=CF2)] complexes makes this a particularly useful
tool for evaluating reactivity. Repeated attempts at growing single crystals of 1-CF2a suitable
for X-ray diffraction were unsuccessful.
The observed sensitivity of complex 1-CF2a to hydrolysis is a clear indication that
choice of solvent, drying method, and reaction concentration are crucial factors in determining
the reaction yield. A quantitative study of common organic solvents subjected to a variety of
desiccants showed the combination of CH2Cl2 and activated 3 Å molecular sieves (10% m/v) for
24 h produced extremely dry solvent, with residual water content of 0.1
± 0.1 ppm as determined
by Karl Fischer titration.[18] Indeed, when complex 1-CF3 was reacted with Me3SiOTf in

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solvents other than dry CH2Cl2 (toluene, C6D6, hexane, or MeCN) yields of 1-CF2a suffered
dramatically, or the reaction was quenched entirely. Therefore, CH2Cl2 (and occasionally CD2Cl2
and CD3Cl) is the solvent of choice for investigations of d8 nickel and palladium difluorocarbene
complexes.
In an effort to establish a reliable, high yielding route for the formation of
difluorocarbene complexes, we explored the reactivity of complex 1-CF3 with a variety of Lewis
acids. When 1 equiv of BF3
·
Et2O was added to a solution of 1-CF3 in CH2Cl2 and analyzed
h, 31P{1H} NMR revealed the formation of
using NMR spectroscopy after
2
[(iPrPOCOP)Ni(=CF2)][BF4] (1-CF2b) in approximately 67% yield. After 16 h, however, 1-
CF2b was no longer detected, having undergone hydrolysis to form [(iPrPOCOP)Ni(CO)][BF4]
(1-COb). When complex 1-CF3 was treated with the weaker Lewis acid BPh3, no reaction took
place. Similarly, complex 1-CF3 did not react with NaBPh4.
Tris(pentafluorophenyl)borane B(C6F5)3 is a strong Lewis acid which has been reported
to facilitate C-F activation.[7, 19] When complex 1-CF3 was treated with 1 equiv of B(C6F5)3
(added as a solid), an immediate color change from yellow to orange was observed, and
[(iPrPOCOP)Ni(=CF2)][FB(C6F5)3] (1-CF2c) was formed cleanly in 98% yield as determined by
NMR analysis (Scheme 4).
Scheme 3. Formation of cationic difluorocarbene complexes 1-CF2c and 2-CF2.

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Furthermore, 1-CF2c was still present in 85% yield after 11 h. After 26 h, however, 1-
CF2c had been completely hydrolysed to [(iPrPOCOP)Ni(CO)][FB(C6F5)3] (1-COc). It is
noteworthy that 5c-COc is significantly more stable in solution than 1-COa, apparently due to
the reduced ability of the bulky [FB(C6F5)3] anion to coordinate to Ni relative to [OTf]. The
NMR spectra of 1-CF2c are highly characteristic, and similar to those of OTf and BF4
derivatives 1-CF2a and 1-CF2b. The 19F spectrum features the Ni=CF2 signal at 167.3 ppm,
which appears as a well resolved triplet due to coupling with the phosphinite groups (3JFP = 14
Hz). The 19F signals associated with the [FB(C6F5)3] anion are characteristic of the tetrahedral
geometry at boron, including a broad B-F resonance at ca. -190 ppm for the abstracted fluoride,
and consistent with those previously reported. The 31P{1H} spectrum features a triplet resonance
at 206.4 ppm with the corresponding coupling to the CF2 group. 1-COc is identified by a
characteristic sharp singlet in the 31P{1H} spectrum at 209.1 ppm, and a carbonyl stretching
frequency at 2095 cm-1 in the IR spectrum.
The reactivity of palladium trifluoromethyl complex 2-CF3 with B(C6F5)3 was also
investigated. A concentrated CH2Cl2 solution of 2-CF3 was treated with 1 equiv B(C6F5)3,
resulting in an immediate colour change from a colourless solution to yellow. After 10 minutes,
NMR analysis revealed the cationic difluorocarbene [(iPrPOCOP)Pd(=CF2)][FB(C6F5)3] (2-CF2)
was formed in 76% yield, along with [(iPrPOCOP)Pd(CO)][FB(C6F5)3] (2-CO) in 26% yield.
31
After 17 h, the distribution was 63% of 2-CF2 and 37% of the hydrolysis product. The P{1H}
NMR spectrum for 2-CF2 consists of a broad singlet at 199.2 ppm at room temperature (23 °C).
The 19F NMR spectrum features the characteristic downfield Pd=CF2 peak at ca. 185 ppm, which
also appears as a broad singlet at 23 °C. The coupling between the phosphinite groups and

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Pd=CF2 could be resolved by cooling the NMR sample to -30 °C (Figure 3), revealing a coupling
constant of 13 Hz. This observation indicates a reduced barrier for rotation of the CF2 ligand in
2-CF2 compared to 1-CF2.
Figure 4. Variable-temperature 31P{1H} and 19F NMR spectra of 2-CF2.
Yellow crystals of 1-CF2c were grown from a concentrated CH2Cl2 solution at -35 °C,
and analyzed using single crystal X-ray crystallography (Figure 4). The structure of 1-CF2c
reveals square planar geometry at the Ni center, and overall C2v symmetry of the complex. The
Ni=CF2 bond is 1.780(3) Å, compared to 1.9296(15) Å for the Ni-CF3 bond of 1-CF3. As a
further comparison, the Ni=CF2 bond of tetrahedral d10 nickel fluorocarbene complex
Ni(DPPE)[P(OMe)3](=CF2) (DPPE = Ph2P(CH2)2PPh2) is 1.771(4).[10] The carbene carbon of
1-CF2c is sp2 hybridized, with the fluorine atoms oriented above and below the plane of the
POCOP ligand. The C-F bonds are 1.277(4) Å and 1.304(4) Å, significantly shorter than those

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of the CF3 group in complex 1-CF3 (average of 1.3668 Å). Repeated attempts at growing
crystals of palladium difluorocarbene complex 2-CF2 suitable for X-ray diffraction were
unsuccessful.
Figure 5. ORTEP drawing of complex 1-CF2c. Hydrogen atoms are omitted for clarity. Thermal
ellipsoids are set to the 50% probability level.
Table 1. Selected bond distances (Å) and angles (o) of 1-CF3a, 2-CF3, and 1-CF2c.
[(POCOP)Ni(CF3)]
1-CF3
[(POCOP)Pd(CF3)]
2-CF3
[(POCOP)Ni(=CF2)]+
1-CF2c
M-C(POCOP)
M-P(POCOP)
1.9076(13)
2.0143(14)
1.902(3)
2.1518(4), 2.1591(4)
2.2758(4), 2.2774(4)
2.1629(8), 2.1684(8)

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M-CF
C-F
1.9296(15)
2.1139(17)
1.362(2), 1.349(2),
1.340(2)
1.780(3)
1.3653(18), 1.3721(19),
1.363(2)
1.277(4), 1.304(4)
P-O
1.6579(11), 1.6577(11)
1.3893(18), 1.3883(17)
177.53(6)
1.6474(11), 1.6553(11)
1.3943(17), 1.3902(19)
178.09(6)
1.633(2), 1.622(2)
1.391(4), 1.389(4)
177.46(14)
O-C
CPOCOP-M-CF
P-M-P
163.660(16)
159.136(15)
162.72(3)
CPOCOP-M-P
CF-M-P
81.72(4), 82.02(4)
98.00(5), 98.31(5)
79.69(4), 79.61(4)
99.79(4), 100.98(4)
81.39(9), 81.34(9)
97.45(10), 99.83(10)
101.83(13), 102.01(15), 104.68(15), 104.94(15),
101.47(13) 103.87(13)
F-CF-F
104.9(3)
a The x-ray structure of 1-CF3 was determined independently from the structure reported by
Zargarian et al., with virtually identical unit cell and structural parameters.[17]
2.3 Reactivity of [(POCOP)M(=CF2)] (M = Ni, Pd) with pyridines
The facile hydrolysis of the difluorocarbene ligands in 1-CF2c and 2-CF2 to furnish CO
ligands is unavoidable, even when using rigorously dried solvents. Therefore, reactivity studies
are conducted on a freshly prepared mixture of difluorocarbene complexes 1-CF2c or 2-CF2 and
31
19
1-COc or 2-CO in CH2Cl2, and analyzed using P{1H} and F NMR spectroscopy before and
after the reaction (Scheme 6). When 1-CF2c is treated with 1 equiv of pyridine, there is near
quantitative conversion to the adduct [(iPrPOCOP)Ni(CF2(NC5H5))][FB(C6F5)3] (1-CF2-py). The
identity of complex 1-CF2-py is suggested especially by a characteristic 19F NMR signal for the
Ni-CF2N fragment, which appears as a triplet at ca. -31 ppm (3JFP = 23 Hz). This resonance in 1-

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CF2-py is shifted up-field dramatically relative to the Ni=CF2 peak in 1-CF2c, due to the change
at the carbon atom to sp3 from sp2 hybridization upon formation of the C-N bond. In addition, the
31P{1H} NMR spectrum for 1-CF2-py appears as a triplet at ca. 191 ppm with coupling to the
CF2 moiety. The other products present in the reaction mixture include
[(iPrPOCOP)Ni(NC5H5)][FB(C6F5)3] , formed via displacement of the CO ligand on the
hydrolyzed complex by pyridine, and a small amount of 1-CF3. The formation of 1-CF3 is
proposed to result from the reaction of 1-CF2c with F-, generated via displacement of the B-F
bond in the [FB(C6F5)3] anion by pyridine, resulting in concomitant formation of the pyridine-
B(C6F5)3 adduct. Treatment of 1-CF2c with 1 equiv of 2-phenylpyridine gives 1-CF3 as the
major product, along with formation of the 2-phenylpyridine-B(C6F5)3 adduct. The added steric
hindrance at the 2 position of pyridine prevents formation of the C(F2)-N bond, as well as the
displacement of the CO ligand on 1-COc.
Scheme 4. Reactivity of 5c and 6 with pyridine and 2-phenylpyridine.

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The reactivity patterns of palladium difluorocarbene complex 2-CF2 with pyridine and 2-
phenylpyridine are similar to that of 1-CF2c. Treatment of 2-CF2 with pyridine yields
[(iPrPOCOP)Pd(CF2(NC5H5))][FB(C6F5)3] (2-CF2-py) as the major product. The Pd-CF2N
fragment in 2-CF2-py appears in the 19F NMR spectrum as a triplet at ca. -34 ppm (3JFP = 18
Hz), and the phosphinite groups appear in the 31P{1H} NMR spectrum as a triplet at ca. 189 ppm.
When 2-phenylpyridine is allowed to react with 2-CF2, trifluoromethyl complex 2-CF3 is the
major product along with 2-phenylpyridine-B(C6F5)3. In contrast to the analogous nickel
complex, 2-phenylpyridine readily displaces the CO ligand of 2-CO to form the Pd-N complex.
3. Conclusions
Here, we demonstrated that (iPrPOCOP)Ni(CF3) (1-CF3) and (iPrPOCOP)Pd(CF3) (2-CF3) react
cleanly
with
B(C6F5)3
to
furnish
cationic
d8
difluorocarbene
complexes
[(iPrPOCOP)Ni(=CF2)][FB(C6F5)3] (1-CF2c) and [(iPrPOCOP)Pd (=CF2)][FB(C6F5)3] (2-CF2).
The identity of these complexes was confirmed unambiguously using 19F and 31P{1H} NMR
spectroscopy, as well as single crystal X-ray diffraction for 1-CF2c. The use of B(C6F5)3 as the
Lewis acid was significant, as the resulting [FB(CF6F5)3]- anion contained sufficient steric bulk
so as to prolong 1-CF2c in solution. The expected electrophilic reactivity of these
difluorocarbene complexes was confirmed by their observed high-sensitivity to hydrolysis by
adventitious moisture, as well as their reactivity with the N-donor pyridine. Overall, we have
shown that trifluoromethyl pincer-type complexes are a robust platform for the formation of
difluorocarbene complexes via
α-fluoride abstraction by a sterically bulky Lewis acid, and can
serve as the basis for future structural and reactivity studies.

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4. Experimental section
4.1 General Procedures
Experiments were conducted under nitrogen, using Schlenk techniques or an MBraun
glove box. All solvents were deoxygenated by purging with nitrogen. Toluene, hexanes, diethyl
ether (Et2O) and tetrahydrofuran (THF) were dried on columns of activated alumina using a J. C.
Meyer (formerly Glass Contour®) solvent purification system. Benzene-d6 (C6D6) and were
dried by standing over activated alumina (ca. 10 wt. %) overnight, followed by filtration.
Dichloromethane (DCM) was dried by storing over activated (heated at ca. 250 °C for >10 h
under vacuum) 4 Å molecular sieves for 24 h. Acetonitrile (MeCN), acetonitrile-d3 (CD3CN) and
CD2Cl2 were dried by refluxing over calcium hydride under nitrogen. After distillation, they
were dried further by filtration through activated alumina (ca. 5-10 wt. %). Dichloromethane-d2
(CD2Cl2) was vacuum-transferred before use. All solvents were stored over activated (heated at
ca. 250 °C for >10 h under vacuum) 4 Å molecular sieves. Glassware was oven-dried at 150 °C
for >2 h or flame-dried using a torch. The following chemicals were obtained commercially, as
indicated: Me3SiCF3 (Oakwood Chemical, 98%), Me3SiOTf (Tf = SO2CF3, Aldrich, 98%),
B(C6F5)3 (Strem, 97%), chlorodiphenylphosphine (ClPPh2, Aldrich, 99%), resorcinol (Aldrich,
98%), pyridine (Aldrich, anhydrous, 99.8%), 2-phenylpyridine (Aldrich, 98%), Ni powder
(Strem, 99.5%), Pd[COD]Cl2 (Aldrich, 99%), CsF (Aldrich, 99%) (CsF was dried under vacuum
1
19
31
at 250 °C for several h). H, F and P{1H}NMR spectra were recorded on either a 300 MHz
1
Bruker Avance or 300 MHz Bruker Avance II instrument at room temperature (21-23 °C). H
NMR spectra were referenced to the residual proton peaks associated with the deuterated
19
solvents (C6D6: 7.16 ppm, CDCl3: 7.26 ppm, CD3CN: 1.94 ppm, CD2Cl2: 5.32 ppm). F NMR
spectra were referenced to internal 1,3- bis(trifluoromethyl)benzene (BTB) (Aldrich, 99%,

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deoxygenated by purging with nitrogen, stored over activated 4 Å molecular sieves), set to –63.5
ppm. 1H NMR data for BTB: (300 MHz, C6D6)
δ 6.60 (m, 1H, Ar-5-H), 7.12 (m, 2H, Ar-4,6-H),
7.76 (m, 1H, Ar-2-H); (300 MHz, CD3CN) 7.76-7.84 (m, 1H, Ar–H), 7.95-8.04 (m, 3H, Ar–
δ
H). 31P{1H}NMR data were referenced to external H3PO4 (85% aqueous solution), set to 0.0
ppm. Elemental analyses were performed by the CENTC Elemental Analysis Facility at the
University of Rochester.
4.2 Synthesis of [(iPrPOCOP)Ni(CF3)] 1-CF3
A solution of [(iPrPOCOP)Ni(Cl)] (610 mg, 1.40 mmol) was stirred in DMF (6 mL) and CsF (850
mg, 5.60 mmol) was added as a solid. After 5 minutes of additional stirring, Me3SiCF3 (800 mg,
5.60 mmol) was added drop-wise to the suspension, over a span of 5 minutes. After stirring for
1.5 h, hexane (10 mL) was added to the solution and the mixture was filtered over a pad of
Celite, washing with hexane (5 mL). The resulting yellow solution was dried under vacuum, and
the remaining residue was extracted with toluene and hexane (10 mL, 1:1) and filtered through a
o
plug of Celite. The filtrate was concentrated to 1 mL and placed at -35 C for 24 h. Yellow
crystals formed, and were collected by filtration and washed with cold hexane (5 mL), giving
[(iPrPOCOP)Ni(CF3)] (530 mg, 80% isolated yield). Slow evaporation of a concentrated
THF/Et2O solution gave crystals suitable for X-ray diffraction. X-ray and spectroscopic data are
in agreement with those previously published. 1H NMR (CDCl3, 300 MHz)
CH3), 2.42 (m, JHH = 7.1 Hz, 4H, CH(CH3)2), 6.46 (d, J = 7.9 Hz, 2H, m-H), 6.98 (t, J = 7.9 Hz,
δ 1.24-1.37 (m, 24H,
3
31
1H, p-H). 19F NMR (CDCl3, 282 MHz)
196.3 (q, 3JPF = 14.9 Hz).
δ
-6.7 (t, JFP = 14.9 Hz). P{1H} NMR (CDCl3, 121
MHz)
δ

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4.3 Synthesis of [(iPrPOCOP)Pd(CF3)] 2-CF3
A solution of [(iPrPOCOP)Pd(Cl)] (450 mg, 0.93 mmol) was stirred in DMF (6 mL) and CsF
(550 mg, 3.62 mmol) was added as a solid. After 5 minutes of additional stirring, Me3SiCF3 (610
mg, 4.28 mmol) was added drop-wise to the suspension, over a span of 5 minutes. After stirring
for 1.5 h, hexane (10 mL) was added to the solution and the mixture was filtered over a pad of
celite, washing with hexane (5 mL). The resulting yellow solution was dried under vacuum, and
the remaining residue was extracted with toluene and hexane (10 mL, 1:1) and filtered through a
o
plug of Celite. The filtrate was concentrated to 1 mL and placed at -35 C for 24 h. White
crystals formed, and were collected by filtration and washed with cold hexane (5 mL), giving
[(iPrPOCOP)Pd(CF3)] (356 mg, 74% isolated yield). 1H NMR (CDCl3, 300 MHz)
δ 1.20-1.33 (m,
24H, CH3), 2.39 (m, JHH = 7.2 Hz, 4H, CH(CH3)2), 6.56 (d, JHH = 7.8, 2H, m-H), 6.98 (tm, JHH
=
7.8 Hz, 1H, p-H). 19F NMR (CDCl3, 282 MHz)
δ
-8.2 (t, 3JFP = 13.8 Hz). 31P{1H} NMR (CDCl3,
3
121 MHz)
δ
191.6 (q, JPF = 13.8 Hz). Anal. Calcd for C19H31F3O2P2Pd: C, 44.16; H, 6.05%.
Found: C, 44.45; H, 5.63.
4.4 Synthesis and characterization of [(iPrPOCOP)Ni(=CF2)][OTf]1-CF2a in situ
To a solution of (POCOP-iPr)Ni(CF3) (20 mg, 0.0426 mmol) in CH2Cl2 (0.5 mL) and C6D6 (60
µ
L) was added neat Me3SiOTf (1 equiv, 8
analyzed using 19F and 31P{1H} NMR spectroscopy, which revealed the formation of
[(iPrPOCOP)Ni(=CF2)][OTf](1-CF2a) in 82% yield.19F NMR (282 MHz, CH2Cl2)
2F, CF2), -78.3 (br. s, 3F, OTf). 31P{1H} (121 MHz, CH2Cl2) 206.4 (t, 2P, 3JPF = 14 Hz).
µL). After 15 minutes, the reaction mixture was
δ
169.1 (br. s,
δ
4.5 Synthesis and characterization of [(iPrPOCOP)Ni(=CF2)][BF4]1-CF2b in situ

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To a solution of (POCOP-iPr)Ni(CF3) (20 mg, 0.0426 mmol) in CH2Cl2 (0.5 mL) and C6D6 (60
µ
L) was added BF3· Et2O (1 equiv, 6 µL, 0.0486 mmol). After 2 h, the mixture was analyzed
using 19F and 31P{1H} NMR spectroscopy, which revealed the formation of
19
[(iPrPOCOP)Ni(=CF2)][BF4] (1-CF2b) in 67% yield. F NMR (282 MHz, CH2Cl2)
δ 172.3 (br.
s, 2F, CF2), -149.6 (br. s, 4F, BF4). 31P{1H} (121 MHz, CH2Cl2)
δ 207.1 (br, s).
4.6 Synthesis of [(iPrPOCOP)Ni(=CF2)][BF(C6F5)3] 1-CF2c
To a solution of [(iPrPOCOP)Ni(CF3)] (20 mg, 0.043 mmol) in CH2Cl2 (0.5 mL) was added
B(C6F5)3 (22 mg, 0.043 mmol) as a solid, resulting in an immediate colour change from yellow
to orange. After 15 minutes, analysis of the crude mixture using NMR spectroscopy revealed the
formation
of
[(iPrPOCOP)Ni(=CF2)][BF(C6F5)3]
in
98%
yield,
along
with
19
[(iPrPOCOP)Ni(CO)][BF(C6F5)3] (1-COc) (2% yield). F NMR (282 MHz, CH2Cl2)
δ
167.3 (t,
3JFP = 14 Hz, 2F, CF2), -135.2 (m, JFF = 12.6 Hz, o-F, 6F), -162.5 (t, JFF = 19.8 Hz, p-F, 3F), -
166 (m, JFF = 19.8 Hz, m-F, 6F), -190.3 (br. s, B-F). 31P{1H} (121 MHz, CH2Cl2)
δ
206.4 (t, 2P,
3JPF = 14 Hz). Addition of H2O results in nearly quantitative conversion to
31
[(iPrPOCOP)Ni(CO)][BF(C6F5)3] (1-COc): IR (neat): 2095 cm-1. P{1H} (121 MHz, CH2Cl2)
δ
209.1 (s).
4.7 Synthesis of [(iPrPOCOP)Pd(=CF2)][BF(C6F5)3] 2-CF2
To a solution of [(iPrPOCOP)Pd(CF3)] (20 mg, 0.039) in CH2Cl2 (0.5 mL) was added B(C6F5)3
(20 mg, 0.039 mmol) as a solid, resulting in an immediate colour change from colourless to dark
yellow-orange. After 15 minutes, analysis of the crude mixture using NMR spectroscopy
revealed the formation of [(iPrPOCOP)Pd(=CF2)][BF(C6F5)3] in 98% yield, along with

ACCEPTED MANUSCRIPT
[(iPrPOCOP)Pd(CO)][BF(C6F5)3] (2-CO) (2% yield). 19F NMR (282 MHz, CH2Cl2)
δ 185.2 (t,
3JFP = 14 Hz, 2F, CF2), -135.2 (m, JFF = 12.6 Hz, o-F, 6F), -162.5 (t, JFF = 19.8 Hz, p-F, 3F), -
166 (m, JFF = 19.8 Hz, m-F, 6F), -190.3 (br. s, B-F). 31P{1H} (121 MHz, CH2Cl2)
δ
199.2 (23 °C:
br. s, 2P; -30 °C: t, 2P, 3JPF = 13 Hz). Addition of H2O results in nearly quantitative conversion
to [(iPrPOCOP)Pd(CO)][BF(C6F5)3] (2-CO): IR (CH2Cl2): 2110 cm-1. 31P{1H} (121 MHz,
CH2Cl2) δ 201.1 (s).
4.8 Reaction of 1-CF2c with pyridine
To a solution of [(iPrPOCOP)Ni(CF3)] (15 mg, 0.032 mmol) in CH2Cl2 (0.5 mL) was added
B(C6F5)3 (17 mg, 0.032 mmol) as a solid. After 5 minutes, the orange solution was transferred to
an NMR tube and analyzed using 19F and 31P{1H} NMR spectroscopy to establish the formation
of 1-CF2c. Pyridine (3 µL, 1.1 equiv) was then added to the solution, resulting in an immediate
19
31
colour change to yellow-orange, and analyzed again using F and P{1H} NMR, revealing the
formation of [(iPrPOCOP)Ni(CF2(NC5H5))][FB(C6F5)3] (1-CF2-py). See supporting information
for spectra. [(iPrPOCOP)Ni(CF2(NC5H5))][FB(C6F5)3]: 31P{1H} (121 MHz, CH2Cl2)
3JPF = 23 Hz). 19F NMR (282 MHz, CH2Cl2) -30.6 (t, 2F, 3JFP = 23 Hz) -135.2 (m, JFF = 12.6
δ 191.2 (t,
δ
Hz, o-F, 6F), -162.5 (t, JFF = 19.8 Hz, p-F, 3F), -166 (m, JFF = 19.8 Hz, m-F, 6F), -190.3 (br. s,
B-F).
4.9 Reaction of 2-CF2 with pyridine
To a solution of [(iPrPOCOP)Pd(CF3)] (11 mg, 0.021 mmol) in CH2Cl2 (0.5 mL) was added
B(C6F5)3 (11 mg, 0.021 mmol) as a solid. After 5 minutes, the orange solution was transferred to
an NMR tube and analyzed using 19F and 31P{1H} NMR spectroscopy to establish the formation

ACCEPTED MANUSCRIPT
of 2-CF2. Pyridine (2
µ
L, 1.1 equiv) was then added to the solution, resulting in an immediate
19
31
colour change to yellow-orange, and analyzed again using F and P{1H} NMR, revealing the
formation of [(iPrPOCOP)Pd(CF2(NC5H5))][FB(C6F5)3] (2-CF2-py). See supporting information
for spectra. [(iPrPOCOP)Pd(CF2(NC5H5))][FB(C6F5)3]: 31P{1H} (121 MHz, CH2Cl2)
3JPF = 18 Hz). 19F NMR (282 MHz, CH2Cl2) -33.9 (t, 2F, 3JFP = 18 Hz) -135.2 (m, JFF = 12.6
δ 189.3 (t,
δ
Hz, o-F, 6F), -162.5 (t, JFF = 19.8 Hz, p-F, 3F), -166 (m, JFF = 19.8 Hz, m-F, 6F), -190.3 (br. s,
B-F).
4.10 Reaction of 1-CF2c with 2-phenylpyridine
To a solution of [(iPrPOCOP)Ni(CF3)] (15 mg, 0.032 mmol) in CH2Cl2 (0.5 mL) was added
B(C6F5)3 (17 mg, 0.032 mmol) as a solid. After 5 minutes, the orange solution was transferred to
an NMR tube and analyzed using 19F and 31P{1H} NMR spectroscopy to establish the formation
of 1-CF2c. 2-phenylpyridine (4 µL, 1.1 equiv) was then added to the solution, resulting in an
immediate colour change to yellow-orange, and analyzed again using 19F and 31P{1H} NMR,
revealing the formation of 1-CF3 as the major product. See supporting information for spectra.
4.11 Reaction of 2-CF2 with 2-phenylpyridine
To a solution of [(iPrPOCOP)Pd(CF3)] (11 mg, 0.021 mmol) in CH2Cl2 (0.5 mL) was added
B(C6F5)3 (11 mg, 0.021 mmol) as a solid. After 5 minutes, the orange solution was transferred to
an NMR tube and analyzed using 19F and 31P{1H} NMR spectroscopy to establish the formation
of 2-CF2. 2-phenylpyridine 3 µL, 1.1 equiv) was then added to the solution, resulting in an
immediate colour change to yellow-orange, and analyzed again using 19F and 31P{1H} NMR,
revealing the formation of 2-CF3 as the major product. See supporting information for spectra.

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4.12 X-ray crystallographic studies
Colourless single crystals of 2-CF3 suitable for X-ray diffraction were grown by slow
evaporation from a concentrated THF/Et2O solution. Yellow single crystals of 1-CF2c suitable
for X-ray diffraction were grown at -35 °C from a concentrated CH2Cl2 solution. The crystals
were mounted on thin glass fibers using paraffin oil and were cooled to 200°K prior to data
collection. Data were collected on a Bruker AXS KAPPA single crystal diffractometer equipped
with a sealed Mo tube source (wavelength 0.71073 Å) APEX II CCD detector. Raw data
collection and processing were performed with APEX II software package from BRUKER
AXS.7 Diffraction data were collected with a sequence of 0.5°
ω scans at 0, 90, 180, and 270° in
ϕ. Initial unit cell parameters were determined from 60 data frames collected at the different
sections of the Ewald sphere. Semi-empirical absorption corrections based on equivalent
reflections were applied. Systematic absences in the diffraction data set and unit-cell parameters
were consistent with triclinic systems. Solutions in centrosymmetric space group yielded
chemically reasonable and computationally stable results of refinement. The structures were
solved by direct methods, completed with difference Fourier synthesis, and refined with full-
matrix least-squares procedures based on F2. In the structure, compound molecules are situated
in the general position. All non-hydrogen atoms were refined anisotropically with satisfactory
thermal parameters values. To achieve satisfactory thermal parameters, it was not necessary to
use constraints. Additional crystallographic data and selected data collection parameters are
reported in Table 3. The cif files for the following structures are available as Supporting
Information.

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Table 2. Crystal refinement data for 2-CF3 and 1-CF2c.
Identification code
Empirical formula
CCDC deposition number
Formula weight
Temperature
Wavelength
Crystal system
Space group
a, Å
2-CF3
1-CF2c
C19 H31 F3 O2 P2 Pd
1543097
C37 H31 B F18 Ni O2 P2
1543098
516.78
981.08
200(2) K
200(2) K
0.71073 Å
0.71073 Å
Triclinic
Triclinic
P -1
P -1
8.1848(2)
11.6548(4)
12.7644(4)
13.8891(4)
92.4984(18)
95.9449(17)
101.9326(18)
b, Å
10.3310(3)
14.6517(4)
100.5912(12)
104.3629(11)
101.6362(12)
c, Å
α
, deg
, deg
β
γ
, deg
Volume
3
3
2006.22(11) Å
1139.26(5) Å
Z
2
2
Density (calculated)
3
3
1.506 Mg/m
1.624 Mg/m
Absorption coefficient
-1
-1
0.990 mm
0.681 mm
988
F(000)
528
Crystal size
3
3
0.390 x 0.240 x 0.100 mm
0.215 x 0.111 x 0.080 mm
1.634 to 28.383°
Theta
range
for
data 2.077 to 28.332°
collection

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Index ranges
-9<=h<=10
-15<=h<=15
-13<=k<=13
-19<=l<=19
17505
-17<=k<=16
-18<=l<=14
Reflections collected
27389
Independent reflections
5502 [R(int) = 0.0145]
9743 [R(int) = 0.0408
Completeness to theta = 98.6 %
25.242°
98.0 %
Absorption correction
Semi-empirical
from
Semi-empirical from
equivalents
equivalents
Max. and min. transmission
Refinement method
0.7457 and 0.6537
0.7457 and 0.6750
Full-matrix least-squares on Full-matrix least-squares on
2
F
2
F
Data / restraints / parameters 5502 / 0 / 244
1.034
Final R indices [I>2sigma(I)] R1 = 0.0201, wR2 = 0.0522
9743 / 0 / 550
1.012
2
Goodness-of-fit on F
R1 = 0.0497, wR2 = 0.1221
R1 = 0.0870, wR2 = 0.1402
n/a
R indices (all data)
R1 = 0.0224, wR2 = 0.0535
n/a
Extinction coefficient
Largest diff. peak and hole
-3
-3
0.529 and -0.360 e.Å
0.383 and -0.325 e.Å
Acknowledgements

ACCEPTED MANUSCRIPT
We thank the NSERC and the Canada Research Chairs program for generous financial support
and the University of Ottawa, Canada Foundation for Innovation, and Ontario Ministry of
Economic Development and Innovation for essential infrastructure. Dr. Glenn Facey and Dr.
Eric Ye are thanked for helpful discussions and assistance with NMR experiments. G.M.L.
gratefully acknowledge support from NSERC. Thank you also to Prof. John Gladysz for his
many contributions to organometallic chemistry and its community.
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Highlights
In this study, trifluoromethyl POCOP-type pincer complexes (iPrPOCOP)Ni(CF3) (1-CF3) and
(iPrPOCOP)Pd(CF3) (2-CF3) are prepared. These complexes undergo Lewis acid-assisted
fluoride abstraction to furnish cationic d8 difluorocarbene complexes of the type
[(iPrPOCOP)M(=CF2)]+[X]-, which are characterized in solution and for M = Ni using single-
crystal X-ray diffraction analysis. The electrophilic nature of these difluorocarbene complexes is
discussed, including their reactivity with pyridines.