First example of B-C bond cleavage in the BAr(F) (B[C6H3(CF3)2-3,5]4) anion mediated by a transition metal species, trans-[(Ph3P)2Pt(Me)(OEt2)]+

Article abstract of DOI:10.1039/a902274k

The first example of transition metal-mediated decomposition of the widely used BAr(F) anion (BAr(F) = B[C₆H₃(CF₃)₂-3,5]₄) has been accomplished by mild heating of the cationic platinum complex trans-[(Ph₃P)₂Pt(Me)(OEt₂)]⁺(BAr(F))- in low-coordinating solvents to form the diarylated product trans-(Ph₃P)₂Pt(Ar(F))₂ in good yield, thus demonstrating that such non-interacting anions can react with electrophilic transition metal complexes.

Full text of DOI:10.1039/a902274k

First example of B–C bond cleavage in the BArF (B[C6H3(CF3)2-3,5]4) anion
mediated by a transition metal species, trans-[(Ph3P)2Pt(Me)(OEt2)]+
Wayde V. Konze, Brian L. Scott and Gregory J. Kubas*
Chemical Science and Technology Division, MS J514, Los Alamos National Laboratory, Los Alamos, NM 87545,
USA. E-mail: kubas@lanl.gov
Received (in Bloomington, IN, USA) 22nd March 1999, Revised version received 26th July 1999, Accepted 28th
July 1999
The first example of transition metal-mediated decomposi-
tion of the widely used BArF anion (BArF = B[C6H3(CF3)2-
3,5]4) has been accomplished by mild heating of the cationic
platinum complex trans-[(Ph3P)2Pt(Me)(OEt2)]+(BArF)2 in
low-coordinating solvents to form the diarylated product
trans-(Ph3P)2Pt(ArF)2 in good yield, thus demonstrating
that such non-interacting anions can react with electrophilic
transition metal complexes.
relative peak heights; the BArF anion has peaks at d 7.73 and
7.58 in a 2+1 ratio, while the coordinated ArF group in 2
exhibits peaks at d 8.25 and 8.05 in a 1+2 ratio. The molecular
structure of 2 (Fig. 1) shows that the platinum is in a square
planar environment, with the bis(trifluoromethyl)phenyl groups
located trans to each other and at an angle of 72.6° to the plane
defined by Pt(1), P(1), P(1A), C(19) and C(19A).‡
The incorporation of non-coordinating, low-interacting anions
for the stabilization of reactive transition metal cations has
proven to be very useful for carrying out interesting bond-
cleavage reactions, catalytic polymerization reactions and for
stabilizing weakly coordinating ligands.1 In order for these
reactions to be successful, the anion must not coordinate to the
vacant site, and must not react with the metal center. The BArF
(B[C6H3(CF3)2-3,5]4) anion has been used widely in this respect
because of its ease of preparation and extremely robust
character toward a variety of reactive transition metal cations.2
Recently, however, the BArF anion was found to coordinate to
various metal complexes in either h -, h - or h -fashion,3
indicating that this anion can coordinate to suitable transition
metal fragments.
3
4
6
Although the non-fluorinated BPh42 anion has been shown to
be relatively reactive, displaying a marked tendency to act as a
phenylating agent toward transition metal cations,4 there have
been no reported examples of arylation reactions between the
BArF anion and transition metal centers. We herein report the
first example of the reaction of the BArF anion with a transition
metal cation in the complex trans-[(Ph3P)2Pt(Me)(OEt2)]+
(BArF)2 1a, which decomposes to form the diarylated complex
trans-(Ph3P)2Pt(ArF)2 2 under mild conditions.
Fig. 1 Molecular structure of 2 showing the atom numbering scheme (50%
probability ellipsoids). Selected bond distances (Å) and angles (°): Pt(1)–
C(19) 2.083(2), Pt(1)–P(1) 2.3180(5), C(19)–Pt(1)–P(1) 91.73(6), C(19)–
Pt(1)–P(1A) 88.27(6).
The formation of 2 entails the net transfer of two 3,5-bis(tri-
fluoromethyl)phenyl groups from the BArF anion to the
platinum center, constituting the first example of aryl group
transfer from the BArF anion. Although this reaction is
unprecedented for the BArF anion, similar reactions have been
carried out with the BPh4 anion; the metathesis reaction [eqn.
(2)] of [(PhMe2P)2Pt(Me)(solv)]+ with NaBPh4 results in the
The complex trans-[(Ph3P)2Pt(Me)(OEt2)]+(BArF)2 1a was
prepared by reacting (Ph3P)2Pt(Me)2 with [H(OEt2)2]+BArF2 in
Et2O at room temperature. Compound 1a is stable in Et2O
solution for several weeks at 230 °C, and is stable indefinitely
at 230 °C as an isolated solid. However, when 1a was placed in
benzene and allowed to stand at room temperature for 5 days,
the compound trans-(Ph3P)2Pt(ArF)2 2 formed as colorless
crystals [eqn. (1)].† The reaction was also more conveniently
formation of the neutral bis(phenyl)platinum derivative
(PhMe2P)2Pt(Ph)2.5 It was determined from these studies that
weakly bound ligands (e.g., F2CNCFH) in place of the
coordinated solvent molecules enhanced the phenylation reac-
tion. In a separate study,6 the mechanism of phenyl transfer
from the BPh4 anion to the dicationic platinum species
[Pt(solv)2(L)2]2+ (L = PMe3, PEt3, PPh3; solv = H2O, MeOH)
to form [Pt(Ph)(solv)(L)2]+ was investigated. It was found that
carried out by refluxing 1a in toluene for 20 min. Complex 2
was characterized by elemental analysis, 1H NMR and 31P{1H}
NMR,† and the structure was determined by X-ray diffraction
studies.‡ A characteristic feature of the 1H NMR spectrum of 2
is the downfield shift of the ArF resonances and the change in
Chem. Commun., 1999, 1807–1808
1807

the actual phenylating species is BPh3, which was formed from
proton-induced decomposition of the BPh4 anion to form BPh3
and PhH. The coordinated solvent molecules in
[Pt(solv)2(L)2]2+ were assumed to be acidic enough to cause the
decomposition of the BPh4 anion. It is doubtful that a similar
mechanism is occurring in the decomposition of 1a, as the
coordinated Et2O molecule does not contain acidic protons
which could cause the decomposition of the BArF anion.
Instead, this reaction most likely proceeds through an initial step
that involves electrophilic attack of the platinum cation on one
of the aryl groups of the BArF anion. The fate of the methyl
ligand is not known, but no methane was evolved during the
reaction.
In order to determine the effects of the ligands on the
arylation reaction, both the coordinated solvent and the
phosphine ligands were varied in 1a. Complexes containing
both coordinated MeCN and MeOH were prepared by dissolv-
ing 1a in MeCN and MeOH, respectively, and precipitating out
trans-[(Ph3P)2Pt(Me)(NCMe)]+(BArF)2 1b and trans-
[(Ph3P)2Pt(Me)(MeOH)]+ (BArF)2 1c as solids.† The 1H NMR
spectrum of 1b was almost identical to the known compound
trans-[(Ph3P)2Pt(Me)(NCMe)]+(BF4)2,7 and exhibited a singlet
at d 1.157 corresponding to coordinated MeCN, which
disappeared when CD3CN was added. Complex 1c exhibited a
signal at d 2.684 corresponding to coordinated MeOH, which
disappeared when CD3OD was added. When 1b was refluxed in
either benzene or toluene under identical conditions to that of
1a, there was no evidence for formation of 2. However, when 1c
was refluxed in toluene under identical conditions, 2 formed in
roughly the same yield as from the reaction of 1a. Evidently, the
more weakly bound Et2O and MeOH ligands allow the aryl
group transfer to occur in order to form 2, while the more
stongly bound MeCN ligand prevents this reaction from taking
place.
In order to examine the effects of the phosphine ligand on the
aryl group transfer, the complexes trans-[(Pri3P)2Pt(Me)(O-
Et2)]+(BArF)2 1d and trans-[(Et3P)2Pt(Me)(OEt2)]+(BArF)2 1e
were synthesized analogously to the preparation of 1a. After
refluxing 1d in toluene for several hours, there was no evidence
of B–C bond cleavage. However, the less sterically encumbered
1e reacted after refluxing for 10 min in benzene. A mixture of
platinum complexes formed which could not be identified, but
clear crystals were obtained from benzene which were charac-
terized by X-ray diffraction to be B[C6H3(CF3)2-3,5]3 3, the
structure of which has not been previously reported.‡ Although
this reaction gave different results than the decomposition of 1a,
it still indicates that B–C cleavage takes place with this more
basic, less steric phosphine. Evidently, bulky phosphines do not
allow this reaction to take place, which is consistent with the
transition metal cation attacking the bulky BArF anion.
The aryl group transfer from the BArF anion to the platinum
metal center in trans-[(Ph3P)2Pt(Me)(OEt2)]+(BArF)2 1a repre-
sents the first example of a transition metal-mediated decom-
position of the normally non-interacting BArF anion and serves
to alert those who use this anion to the possibility of its
reactivity. The mechanism of this reaction is unclear, but we
have found that the coordinated solvent must be a weak ligand
(Et2O, MeOH), the solvent for the decomposition reaction must
be non-coordinating, and the phosphine ligands must not be too
bulky in order for this reaction to proceed. Preliminary results
indicate that analogs of 1a containing isocyanides instead of
phosphines allow similar B–C bond cleavage reactions to
proceed immediately at room temperature. These results
indicate that the initial step of this reaction is electrophilic attack
of the platinum cation on an aryl group of the BArF anion, which
is consistent with the fact that both a sterically accessible metal
center and a weakly occupied coordination site are necessary for
aryl group transfer to occur.
Notes and references
† Experimental procedures: 1a: to a stirred Et2O solution (10 mL) of
[H(OEt2)2]+BArF (0.135 g, 0.133 mmol) at room temp. was added
2
(Ph3P)2Pt(Me)2 (0.100 g, 0.133 mmol) as a solid. Evolution of methane
began immediately, and after 5 min the solution was clear and colorless. The
volume was reduced to 3 mL, and 10 mL of hexanes was then added. The
volume was reduced to ca. 8 mL and placed in a 230 °C freezer for 1 day
to obtain a white, crystalline solid. The filtrate was decanted off, the solids
were washed with 3 3 5 mL of hexanes at 230 °C and dried under vacuum
to give 1a (0.195 g, 87%). 1H NMR (CD2Cl2, 280 °C): d 7.73 (s, 8H, BArF),
7.21–7.62 (34H, Ph + BArF), 3.53 (br, 4H, ether CH2), 1.16 (t, JHH = 7.05
Hz, 6H, ether CH3), 0.73 (t, JHP 6.75, JHPt 71.0 Hz, 3H, Pt–Me). 31P{1H}
NMR (CD2Cl2, 280 °C): d 31.3 (s, JPPt 3195 Hz). Anal. Calc. for
C75H55BF24OP2Pt: C, 52.44; H, 3.32. Found: C, 52.43; H, 3.59%.
1b and 1c: complex 1a (0.100 g, 0.0598 mmol) was dissolved in 10 mL
of either MeCN (for 1b) or MeOH (for 1c) at room temp. and stirred for 15
min. The solvent was removed under vacuum, the oily residue was
dissolved in 2 mL of CH2Cl2 and 15 mL of hexanes was then added. After
cooling overnight at 230 °C, off-white crystals formed which were isolated
by removing the filtrate and drying under vacuum to give 1b (0.0905 g,
92%) or 1c (0.0854 g, 90%). For 1b: 1H NMR (CD2Cl2, 25 °C): d 7.53–7.75
(42H, Ph + BArF), 1.16 (br, 3H, MeCN), 0.28 (t, 3H, JHP 7.05, JHPt 78.3 Hz,
Pt–Me). 31P{1H} NMR (CD2Cl2, 25 °C): d 27.2 (s, JPPt 3008 Hz). Anal.
Calc. for C71H48BF24NP2Pt: C, 52.03; H, 2.95; N, 0.85. Found: C, 52.41; H,
3.04; N, 0.84%. For 1c: 1H NMR (CD2Cl2, 25 °C): d 7.53–7.75 (42H, Ph +
BArF), 2.68 (br, 3H, CH3OH), 0.612 (t, 3H, JHP 6.90, JHPt 87.6 Hz, Pt–Me).
31P{1H} NMR (CD2Cl2, 25 °C): d 32.4 (s, JPPt 3114 Hz). Anal. Calc. for
C
70H49BF24OP2Pt: C, 51.58; H, 3.03. Found: C, 51.63; H, 3.03%.
2: complex 1a (0.200 g, 0.120 mmol) was dissolved in toluene (5 mL) and
heated to reflux for 20 min. The solution turned orange during this time. The
solution was cooled, the solvent was removed under vacuum and 5 mL of
MeOH was added. The mixture was cooled to 230 °C for 4 h, the white
precipitate was collected on a frit, washed with cold MeOH and dried in
vacuum to yield pure 2 (0.0875 g, 63%). 1H NMR (CD2Cl2, 25 °C): d 8.25
(s, 2H, BArF), 8.05 (s, 4H, BArF), 7.35–7.18 (30H, Ph). 31P{1H} NMR
(CD2Cl2, 25 °C): d 20.6 (s, JPPt 2998 Hz). Anal. Calc. for C52H36F12P2Pt:
C, 54.51; H, 3.17. Found: C, 54.47; H, 3.28%.
‡ Crystal data: for 2: C52H36F12P2Pt·2 C6H6, M = 1302.05, triclinic,
¯
space group P1, a = 11.3973(6), b = 11.4539(5), c = 12.8260(6) Å, a =
105.675(1), b = 111.466(1), g = 103.393(1)°, V = 1394.5(1) Å3, Z = 1,
T
=
203 K, m
= = 0.0473 (5227 independent
2.654 mm21, wR2
reflections), R = 0.0186 [I > 2s(I)].
¯
3: C24H9BF18, M = 650.12, triclinic, space group P1, a = 9.5433(9), b
= 11.656(1), c = 12.775(1) Å, a = 100.544(2), b = 110.146(1), g =
97.299(2)°, V = 1283.4(2) Å3, Z = 2, T = 203 K, m = 1.89 cm21. The final
refinement (5459 reflections collected, 4206 independent) included aniso-
tropic temperature factors on all non-hydrogen atoms and converged to R1
= 0.0628 and wR2 = 0.1820.
CCDC 182/1365. See http://www.rsc.org/suppdata/cc/1999/1807/ for
crystallographic files in .cif format.
1 S. H. Strauss, Chem. Rev., 1993, 93, 927.
2 M. Brookhart, B. Grant and A. F. Volpe, Organometallics, 1992, 11,
3920; See also: M. D. Butts, B. L. Scott and G. J. Kubas, J. Am. Chem.
Soc., 1996, 118, 11831; P. J. Alaimo, B. A. Arndtsen and R. G. Bergman,
J. Am. Chem. Soc., 1997, 119, 5269; M. W. Holtcamp, L. M. Henling,
M. W. Day, J. A. Labinger and J. E. Bercaw, Inorg. Chim. Acta, 1998,
270, 467.
3 J. Powell, A. Lough and T. Saeed, J. Chem. Soc., Dalton Trans., 1997,
4137.
4 M. Aresta, E. Quaranta and I. Tommasi, New J. Chem., 1997, 21, 595.
5 H. C. Clark and J. D. Ruddick, Inorg. Chem., 1970, 9, 1226; H. C. Clark
and L. E. Manzer, Inorg. Chem., 1971, 10, 2699.
6 K. Siegmann, P. S. Pregosin and L. M. Venanzi, Organometallics, 1989,
8, 2659.
7 R. A. Michelin, M. Mozzon, P. Berin, R. Bertani, F. Benetollo, G.
Bombieri and R. J. Angelici, Organometallics, 1994, 13, 1341.
Communication 9/02274K
1808
Chem. Commun., 1999, 1807–1808