Synthesis and molecular structure of a perfluoroalkyl complex of platinum containing a PCP pincer ligand

Article abstract of DOI:10.1021/om010569o

Treatment of (TMEDA)Pt(C₃F₇)Me (TMEDA = tetramethylethylenediamine) with 1,3-bis[(diphenylphosphino)methyl]benzene (PCPH) in mesitylene under reflux affords the first known pincer complex of a group 10 metal with a fluoroalkyl ligand.

Full text of DOI:10.1021/om010569o

Organometallics 2001, 20, 4741-4744
4741
Notes
Syn th esis a n d Molecu la r Str u ctu r e of a P er flu or oa lk yl
Com p lex of P la tin u m Con ta in in g a P CP P in cer Liga n d
Russell P. Hughes,*,† Alex Williamson,† Christopher D. Incarvito,‡ and
Arnold L. Rheingold‡
Departments of Chemistry, 6128 Burke Laboratory, Dartmouth College,
Hanover, New Hampshire 03755, and University of Delaware, Newark, Delaware 19716
Received J une 26, 2001
Summary: Treatment of (TMEDA)Pt(C3F7)Me (TMEDA
) tetramethylethylenediamine) with 1,3-bis[(diphen-
ylphosphino)methyl]benzene (PCPH) in mesitylene under
reflux affords the first known pincer complex of a group
10 metal with a fluoroalkyl ligand.
plexes, in view of renewed interest in their structures
and chemistry.17-24 To the best of our knowledge there
are only two examples of transition metal pincer com-
plexes that contain a metal-fluoroalkyl linkage, both
of which involve rhodium.5,9 Complex 1a was made by
heating the ligand 2,6-(CH2PtBu2)2C6H3CF3 in the pres-
ence of [RhCl(L2)]2, a reaction in which a remarkable
insertion of rhodium into the strong aryl-CF3 bond was
observed. Alternatively, the iodide analogue 1b was
synthesized by an oxidative addition reaction of Rh{2,6-
(CH2PtBu2)2C6H3}(η1-N2) with CF3I.
In tr od u ction
Since the first reported example in 1976,1 there have
been many reports of complexes involving anionic mer-
tridentate “pincer” ligands.2 Ligands of the general type
[2,6-(CH2PR2)2C6H3]- (PCP) are generally synthesized
by ligand displacement reactions at elevated tempera-
tures and require not only binding by the two phospho-
rus atoms but also the activation of a bond from a carbon
atom of the core arene to H, O, or C.3-16
Resu lts a n d Discu ssion
We have recently reported the synthesis of square
planar palladium(II)19 and platinum(II)25 complexes 2
by oxidative addition of fluoroalkyl iodides to the
dimethyl precursors 3, followed by reductive elimination
of CH3I. The TMEDA ligand can be displaced by 1,2-
bis(diphenylphosphino)ethane to give a diphosphine
analogue 4.25 In an attempt to approach the synthesis
of bis[(diphenylphosphino)methyl]phenyl (PCP) pin-
cer26-29 analogues by a similar route, we prepared the
We have been interested recently in developing
synthetic routes to transition metal fluoroalkyl com-
* Corresponding author. E-mail: rph@dartmouth.edu. Fax: (603)
646-3946.
† Dartmouth College.
‡ University of Delaware.
(1) Moulton, C. J .; Shaw, B. L. J . Chem. Soc., Dalton Trans. 1976,
1020-1024.
(2) An overview of complexes containing such ligands can be found
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1282-1291.
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3186.
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Concolino, T. E.; Rheingold, A. L. Organometallics 2000, 19, 5190-
5201.
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1999, 18, 2413-2419.
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A. L. Organometallics 2001, 20, 363-366.
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(26) Rimml, H.; Venanzi, L. M. J . Organomet. Chem. 1983, 259, C6-
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10.1021/om010569o CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/22/2001

4742 Organometallics, Vol. 20, No. 22, 2001
Notes
F igu r e 1. ORTEP diagram of the non-hydrogen atoms of
6, showing atom-labeling scheme. Thermal ellipsoids are
shown at the 30% level.
Sch em e 1
previously reported methyl complex 5a .30 Attempts at
preparation of Pt(IV) or Pt(II) fluoroalkyl complexes by
treatment of 5a with n-C3F7I afforded a mixture of
products, the dominant component of which appeared
to be (PCP)PtI, which could be converted back to 5a by
treatment with MeLi. As we have remarked previ-
ously,19,25 the oxidative addition reactions of fluoroalkyl
iodides with Pd(II) and Pt(II) precursors are often
capricious in avoiding reproducibility from one system
to another.
We next turned to a ligand displacement route, which
proved to be successful. Treatment of the previously
reported complex 2b25 with the pincer ligand precursor
in refluxing mesitylene afforded the Pt(II) complex 6.
The probable mechanistic sequence of this reaction is
shown in Scheme 1 and involves initial displacement
of the TMEDA ligand by the relatively soft chelating
diphosphine PCPH, followed by metalation of the aryl
C-H bond to form the Pt(IV) intermediate 7, which
undergoes facile reductive elimination of methane to
form the Pt(II) complex 6. The solution structure of 6
is defined spectroscopically; the 19F NMR spectrum
exhibits the expected three resonances for the perfluo-
ropropyl group, with the R-CF2 resonance at δ -84.4
ppm showing strong coupling to 195Pt (2J FPt ) 248 Hz),
and the 31P{1H} NMR spectrum a single resonance at
δ 40.0 ppm, which appears as a triplet of triplets with
coupling to the R- and â-CF2 groups (3J PF ) 21 Hz, 4J PF
) 6 Hz), with additional 195Pt satellites (1J PPt ) 3041
Hz).
X-ray quality crystals of 6 were grown from CH2Cl2/
heptane. An ORTEP diagram of the structure is shown
in Figure 1, with a different view of the coordination
sphere around platinum in Figure 2. Details of the
crystallographic determination are provided in Table 1,
and representative bond lengths and angles appear in
Table 2. The pincer ligand adopts an overall arrange-
ment similar to that reported for the corresponding
chloride complex 5b,30 with the arene portion of the
pincer ligand canted with respect to the coordination
plane by approximately 15°, as shown in Figure 2. The
distance from Pt to the arene carbon, Pt(1)-C(19), is
2.072(7) Å, significantly longer than the 1.998(8) Å
observed for 5b,30 and indistinguishable from the 2.066-
(3) Å reported for 5c,27 illustrating the expected order
of structural trans-influences; perfluoropropyl ≈ CO2H
> Cl.31 The P(1)-Pt(1)-P(2) angle of 162.89(8)° is
identical to that found in 5b [162.0(1)°],30 and only very
slightly larger than the 161.87(4)° found in 5c,27 il-
lustrating that a significant change in the Pt-aryl
(30) Gorla, F.; Venanzi, L. M.; Albinati, A. Organometallics 1994,
13, 43-54.
(31) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335-422.

Notes
Organometallics, Vol. 20, No. 22, 2001 4743
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 6
Bond Lengths (Å)
Bond Angles (deg)
Pt(1)-C(19)
2.072(7)
2.186(8)
C(19)-Pt(1)-C(33)
177.1(3)
81.67(19)
97.96(16)
81.35(19)
98.89(16)
162.89(8)
120.2(5)
104.2(6)
104.8(6)
120.7(7)
110.5(10)
108.9(9)
106.3(8)
Pt(1)-C(33)
Pt(1)-P(2)
Pt(1)-P(1)
C(33)-C(34)
C(34)-C(35)
F(1)-C(33)
F(2)-C(33)
F(3)-C(34)
F(4)-C(34)
F(5)-C(35)
F(6)-C(35)
F(7)-C(35)
C(19)-Pt(1)-P(2)
C(33)-Pt(1)-P(2)
C(19)-Pt(1)-P(1)
C(33)-Pt(1)-P(1)
P(2)-Pt(1)-P(1)
C(34)-C(33)-Pt(1)
F(2)-C(33)-F(1)
F(4)-C(34)-F(3)
C(33)-C(34)-C(35)
F(5)-C(35)-F(7)
F(5)-C(35)-F(6)
F(7)-C(35)-F(6)
2.2770(18)
2.2818(18)
1.376(12)
1.547(13)
1.374(8)
1.370(7)
1.412(9)
1.388(9)
1.274(11)
1.351(11)
1.340(11)
Attempts to further functionalize complex 6 by treat-
ment with n-C3F7I or MeI failed to give oxidative
addition products, and the starting complex was recov-
ered unchanged.
F igu r e 2. ORTEP diagram of the coordination sphere of
6, with thermal ellipsoids shown at the 30% level. Only
the ipso-carbon atoms of phenyl rings bound to phosphorus
are shown for clarity.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Unless otherwise noted, all
reactions were performed in oven-dried glassware, using
standard Schlenk techniques, under an atmosphere of nitro-
gen, which had been deoxygenated over BASF catalyst and
dried using Aquasorb, or using drybox techniques. THF,
diethyl ether, hexanes, and CH2Cl2 were dried and degassed
over alumina columns under N2.33 1H NMR (300 MHz) and
19F (282 MHz) were recorded on a Varian UNITY plus 300
System in the solvent indicated. 1H NMR chemical shifts were
referenced to TMS using the protio impurity in the solvent
peak, and 19F chemical shifts were referenced to CFCl3.
Microanalyses were performed by Schwarzkopf Microanalyti-
cal Laboratory (Woodside, NY). Perfluoropropyl iodide was
purchased from Aldrich, treated with Na2S2O3 to remove
residual I2, and vacuum distilled before use. (TMEDA)Pt(CH3)-
(C3F7) was prepared as previously reported.25
P r ep a r a tion of {1,3-(CH2P P h 2)2C6H4}. Bis[(diphenylphos-
phino)methyl]benzene is commonly prepared by treatment of
1,3-bis(bromomethyl)benzene with Ph2PNa in liquid am-
monia.26-29 However, we found it more convenient to prepare
by the following method.
Dropwise addition of 0.5 equiv of 1,3-bis(chloromethyl)-
benzene in THF to a solution of PPh2Li in THF/hexane
(prepared by dropwise addition of PPh2H in THF to a solution
of BuLi in hexanes at -40 °C) afforded a pale yellow solution,
which was stirred overnight. The volatiles were removed, and
the oily white solid was washed with hot EtOH. The residue
was purified by extraction into Et2O, filtration, and removal
of solvent from the filtrate.
Ta ble 1. Cr ysta l Da ta a n d Su m m a r y of X-r a y Da ta
Collection for 6
formula
fw
C35H27F7P2Pt
837.60
space group
a, Å
b, Å
P21/c
10.192(3)
18.106(8)
17.018(3)
90
91.008(17)
90
c, Å
R, deg
â, deg
γ, deg
V, Å3
3140.0(17)
4
Z
D(calcd), g/cm3
abs coeff, mm-1
temp, K
diffractometer
radiation
R(F), %a
R(wF2), %a
1.772
4.637
293(2)
Siemens P4
Mo KR 0.71073 Å
3.95
10.03
Quantity minimized ) R(wF2) ) ∑[w(Fo2 - Fc2)2]/∑[(wFo2)2]1/2
R ) ∑∆/∑(Fo), ∆ ) |(Fo - Fc)|.
;
a
distance does not result in a significant change in the
diphosphine bite angle at the metal. The distance from
Pt to the fluorinated carbon, Pt(1)-C(33), of 2.186(8) Å
is longer than that observed in the square planar
complexes 8a [2.067(7) Å] and 8b [2.087(6) Å].25 It is
difficult to distinguish whether this longer distance is
a result of the stronger trans-influence of the aryl ligand
in 6 compared to the trans-phosphorus ligand in com-
plexes 8 or the combined steric effects of two cis-PPh2
groups in 6. The perfluoropropyl ligand itself exhibits
the same pattern of acute F-C-F angles and obtuse
Pt-C-C and C-C-C angles previously observed in a
variety of transition metal complexes containing this
ligand.19,20,25,32
P r ep a r a tion of {2,6-(CH2P P h 2)2C6H3}P t(Me). To a solu-
tion of (PCP)PtCl (100 mg, 0.148 mmol) in THF (15 mL) at
-40 °C was added a solution of MeLi (0.15 mL, 1.4 M, 0.21
mmol) in Et2O. The mixture was allowed to warm to room
temperature and then stirred for 30 min. Addition of EtOH
and removal of the THF in vacuo gave a yellow precipitate,
which was collected on a glass frit and washed with EtOH and
hexanes.
1H NMR (CDCl3, 300 MHz, 21 °C): δ 0.51 (t, 3J HP ) 5.0 Hz,
2J HPt ) 54.6 Hz, 3H, PtMe), 4.00-4.20 (m, 4H, CH2), 7.00-
7.21 (m, 3H, C6H3), 7.37-7.41 (m, 12H, Ph), 7.68-7.75 (m, 8H,
1
Ph). 31P NMR (CDCl3, 121.4 MHz, 21 °C): δ 37.1 (s, J PPt
3035 Hz).
)
(32) Hughes, R. P.; Lindner, D. C.; Smith, J . M.; Zhang, D.; Incarvito,
C. D.; Lam, K.-C.; Liable-Sands, L. M.; Sommer, R. D.; Rheingold, A.
L. J . Chem. Soc., Dalton Trans. 2001, 2270-2278.
(33) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518-1520.

4744 Organometallics, Vol. 20, No. 22, 2001
Notes
P r ep a r a tion of {2,6-(CH2P P h 2)2C6H3}P t(C3F 7). A mix-
ture of 2,6-(CH2PPh2)2C6H4 (0.179 g, 0.401 mmol) and (TMEDA)-
Pt(C3F7)Me (0.100 g, 0.202 mmol) was stirred in mesitylene
under reflux for 16 h to give a pale yellow solution. Removal
of solvent in vacuo gave a yellow-white tar, which was treated
with a 3:1 mixture of hexanes and EtOH to afford a white
precipitate, which was collected on a glass frit and washed
with hexanes. Yield: 0.078 g, 46%. Anal. Calcd for C31H23F7P2-
Pt: C, 50.19; H, 3.25. Found: C, 50.59; H, 3.32.
ture was solved using direct methods, completed by subsequent
difference Fourier syntheses, and refined by full-matrix least-
squares procedures. A DIFABS absorption correction was
applied. All non-hydrogen atoms were refined with anisotropic
displacement coefficients, and hydrogen atoms were treated
as idealized contributions. All software and sources of the
scattering factors are contained in the SHELXTL (5.10)
program library.
1H NMR (CDCl3, 300 MHz, 21 °C): δ 4.00-4.09 (m, 4H,
CH2), 6.99-7.11 (m, 3H, C6H3), 7.41-7.43 (m, 12H, Ph), 7.72-
Ack n ow led gm en t. R.P.H. is grateful to the Na-
tional Science Foundation and to the Petroleum Re-
search Fund, administered by the American Chemical
Society, for generous financial support.
7.75 (m, 8H, Ph). 19F NMR (CDCl3, 282.3 MHz, 21 °C):
δ
)
3
2
-117.4 (m, â-CF2, J FPt ) 53 Hz), -84.4 (brs, R-CF2, J FPt
248 Hz), -79.5 (t, 4J FF ) 10.5 Hz, CF3). 31P{1H} NMR (CDCl3,
3
4
121.4 MHz, 21 °C): δ 40.0 (tt, J PF ) 20.5 Hz, J PF ) 5.8 Hz,
Su p p or tin g In for m a tion Ava ila ble: Atomic fractional
coordinates, bond distances and angles, and anisotropic ther-
mal parameters for complex 6 are available free of charge via
the Internet at http://pubs.acs.org.
1J PPt ) 3041 Hz).
Cr ysta llogr a p h ic Str u ctu r a l Deter m in a tion . Crystal,
data collection, and refinement parameters are collected in
Table 1. The systematic absences in the diffraction data are
uniquely consistent for the reported space groups. The struc-
OM010569O