Hydrocarbyl ligand tuning of the PtII/IV redox potential

Article abstract of DOI:10.1021/ic034731m

The potentially tridentate macrocycle [2.1.1]-(2,6)-pyridinophane (L) enables the transient LPt^II(CH₃)⁺ to cleave the C-H bond of two molecules of C₆F₅H. The resulting product has two aryl groups on Pt but, in contrast to nonfluorinated analogue, varies in its location of the cleaved H, as is evident from the two products (HL⁺)Pt^IIR₂ and (η³-L)-pt ^IVH(R)₂⁺. At equilibrium, the related example where R = CH₃ is purely the Pt^IV redox isomer, which with R = C₆H₅ shows detectable populations of both isomers, and with R = C₆F₅ is purely the pyridine-protonated (HL⁺)Pt^II redox isomer. All species show a hydrogen bond from the pyridinium proton to Pt^II. Consistent with the idea that electron-withdrawing R makes platinum(II) more resistant to oxidation (i.e., a proton on Pt), and thus less Bronsted basic, the ¹J _ptH coupling constant falls in the series R = Me (90 Hz), R = C ₆H₅ (86 Hz), and R = C₆F₅ (63 Hz).

Full text of DOI:10.1021/ic034731m

Inorg. Chem. 2004, 43, 3642−3646
Hydrocarbyl Ligand “Tuning” of the PtII/IV Redox Potential
Andrei N. Vedernikov,* Maren Pink, and Kenneth G. Caulton*
Department of Chemistry, Indiana UniVersity, Bloomington, Indiana 47405
Received June 26, 2003
The potentially tridentate macrocycle [2.1.1]-(2,6)-pyridinophane (L) enables the transient LPtII(CH )+ to cleave the
3
C−H bond of two molecules of C F H. The resulting product has two aryl groups on Pt but, in contrast to nonfluorinated
6
5
analogue, varies in its location of the cleaved H, as is evident from the two products (HL+)PtIIR and (η3-L)-
2
PtIVH(R)2+. At equilibrium, the related example where R ) CH is purely the PtIV redox isomer, which with R )
3
C H shows detectable populations of both isomers, and with R ) C F is purely the pyridine-protonated (HL+)PtII
6
5
6 5
II
redox isomer. All species show a hydrogen bond from the pyridinium proton to Pt . Consistent with the idea that
electron-withdrawing R makes platinum(II) more resistant to oxidation (i.e., a proton on Pt), and thus less Brønsted
basic, the 1JPtH coupling constant falls in the series R ) Me (90 Hz), R ) C H (86 Hz), and R ) C F (63 Hz).
6
5
6 5
Introduction
hydrogen (eq 2), which requires a base to remove H+ from
R-H σ-bonded to PtII.
Transition-metal basicity, nucleophilicity, and reducing
power are often strongly correlated parameters which can
therefore influence a broad range of chemical reactivity. We
have reported earlier that a CH2Cl2-solvated transient
LPt(CH3)+, involving the preorganized-geometry macrocyclic
ligand L,1 has the ability to cleave a wide range of C-H
bonds, including alkanes.2,3
L′PtIIX + R-H f L′PtIV(R)(H)X
(1)
(2)
solv
L′PtIIX + R-H
+8 L′PtII(R)X
-Hsolv
One of these mechanisms, eq 1, is also known in
platinum(II)/arene chemistry.6,7 In principle, either product
might be obtained in a single system because it has been
shown that the two different products in eqs 1 and 2 can
2
coexist in equilibrium, eq 3 (R ) Ph). Thus, in (η2-L)-
Two limiting cases of mechanistic extremes are considered
for alkane (R-H) activation with PtII.4,5 Oxidative addition,
eq 1, involving a change of metal oxidation state is an
alternative to the nonredox electrophilic substitution of
PtR+, the pendant pyridine of η2-L can participate either by
binding to the emerging PtIV center during C-H oxidative
addition or by binding H+ during electrophilic hydrogen
substitution. With (η2-L)PtR+ with R ) Ph as a reference,
we can expect that small changes of electronic or steric
* Authors to whom correspondence should be addressed. E-mail:
caulton@indiana.edu (K.G.C.).
(1) Vedernikov, A. N.; Pink, M.; Caulton, K. G. J. Org. Chem. 2003, 68,
4806.
(2) Vedernikov, A. N.; Huffman, J. C.; Caulton, K. G. Chem. Commun.
(6) (a) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J. L.
Organometallics 2001, 20, 1709. (b) Norris, C. M.; Reinartz, S,; White,
P. S.; Templeton, J. L. Organometallics 2002, 21, 5649.
(7) (a) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc.
2002, 124, 1378. (b) Johansson, L.; Tilset, M.; Labinger, J. A.; Bercaw,
J. E. J. Am. Chem. Soc. 2000, 122, 10846. (c) Peters, R. G.; White,
S.; Roddick, D. M. Organometallics 1998, 17, 4493.
2003, 358.
(3) Vedernikov, A. N.; Huffman, J. C.; Caulton, K. G. New J. Chem.
2003, 27, 665.
(4) Wick, D. D.; Goldberg, K. I. J. Am. Chem. Soc. 1997, 119, 10235.
(5) Siegbahn, P. E. M.; Crabtree, R. H. J. Am. Chem. Soc. 1996, 118,
4442.
3642 Inorganic Chemistry, Vol. 43, No. 12, 2004
10.1021/ic034731m CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/04/2004

Hydrocarbyl “Tuning” of the PtII/IV Redox Potential
effects in the complex can affect the product distribution in
equilibrium 3. Here we demonstrate a concrete example of
this effect. Concurrently, we show how the basicity of PtII
in the corresponding product of electrophilic hydrogen
substitution, (HL+)PtIIR2, is reflected in the observed value
of the Pt‚‚‚HN+ coupling constant.
Results
Electrophilic Hydrogen Substitution in C6F5H. Penta-
fluorobenzene (50:1 mole ratio) reacted with a CD2Cl2
solution of LPtMe2H+ (BArF4 salt) at 22 °C in the course of
24 h to produce cleanly the N-protonated bispentafluoro-
phenylplatinum(II) complex, eq 4 (Ar ) C6F5). Methane (1H
Figure 1. ORTEP drawing of the non-hydrogen atoms of (LH+)Pt(C6F5)2,
showing selected atom labeling and the hydrogen bonding of the pyridinium
acidic proton to Pt.
ArH
ArH
Table 1. Crystal Data and Structure Refinement for
LPtIVMe2H+ -MeH8 LPtIV(Ar)MeH+
8 (HL+)PtIIAr2
[(LH+)Pt(C6F5)2](BArF4) in CH2Cl2
-MeH
(b)
(a)
empirical formula
fw
C63H30BF34N3Pt
1680.80
(4)
cryst color, shape, size
colorless block,
0.20 × 0.15 × 0.13 mm3
137(2) K
NMR evidence) evolution was accompanied by the complete
disappearance of the high-field H NMR hydride signal of
1
temp
wavelength
cryst syst, space group
unit cell dimens
LPtMe2H+ at -21.65 ppm. Growth of a low-field signal
(+16.3 ppm), very broad at 22 °C and more narrow at -40
°C, was evidence of the NH+ proton, with satellites due to
Pt-H coupling of 63 Hz. The latter chemical shift and
coupling are diagnostic of hydrogen bonding to the metal,8-11
which is evidence of the basicity of square-planar PtII via
0.71073 Å
monoclinic, P2(1)/c
a ) 18.9201(19) Å
b ) 13.3663(12) Å
c ) 28.588(4) Å
7194.0(15) Å3
4
R ) 90°
â ) 95.691(7)°
γ ) 90°
vol
Z
density(calcd)
abs coeff
F(000)
1.552 Mg/mm3
2.077 mm-1
3272
2
the doubly occupied dz orbital. Heating the reaction mixture
for 96 h at 80 °C did not affect its composition; no high-
field Pt-H resonances and thus no traces of hydridoplatinum
complexes were detected, consistent with (HL+)PtIIAr2 being
the thermodynamic product in the case of Ar ) C6F5. In
contrast to the phenyl analogue,2 no intermediate LPt(Ar)-
MeH+ (Ar ) C6F5 vs Ph, eq 4) was observed by NMR
spectroscopy. Its lower stability is presumably due to the
stronger electron-withdrawing character and bulkiness of
C6F5 versus Ph. The 19F NMR spectrum shows four broad
signals due to the m- and o-fluorines, indicating slowed
rotation about Pt-aryl bonds at 22 °C along with two sharp
triplets of p-fluorines of two nonequivalent pentafluorophenyl
ligands. At -40 °C the rotation becomes very slow on the
NMR time scale, so that signals of m- and o-fluorines appear
as eight sharp multiplets.
no. of independent reflns
21015 [R(int) ) 0.0529]
no. of data/restraints/params 21015/24/948
GOF on F2
1.065a
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole
R1 ) 0.0375b
R1 ) 0.0476b
3.387 and -1.594 e‚Å-3
wR2 ) 0.0909c
wR2 ) 0.0949c
a GOF ) [∑[w(Fo - Fc )2]/(Nobservns - Nparams)]1/2, all data. b R1 )
2
2
2
2
2
∑(|Fo| - |Fc|)/∑|Fo|. c wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for the Cation
(LH+)Pt(C6F5)2
Pt1
Pt1
Pt1
Pt1
Pt1
C26
C20
N3
N2
H1n
2.016(3)
2.020(3)
2.091(2)
2.100(2)
2.428
C26
C26
C20
C26
C20
N3
C11
C7
C17
C13
N1
Pt1
Pt1
Pt1
Pt1
Pt1
Pt1
N2
N2
N3
N3
H1n
C20
N3
N3
N2
N2
N2
Pt1
Pt1
Pt1
Pt1
Pt1
87.98(13)
172.01(10)
93.49(12)
92.96(10)
170.71(11)
84.35(9)
112.91(17)
128.02(18)
126.9(2)
X-ray Diffraction Structure Determination of the BArF
4
Salt of (HL+)Pt(C6F5)2. Slow evaporation of a CH2Cl2-
pentane solution of [(HL+)Pt(C6F5)2]BArF yields small
4
crystals suitable for X-ray diffraction structure determination
(Figure 1 and Tables 1 and 2) using long frame times and a
SMART 6000 system.
The coordination geometry around Pt is faithful to cis-
disubstituted planar; cis angles around Pt sum to 358.8°. The
species lacks mirror symmetry because the pendant pyri-
113.78(19)
167.52
dinium moiety is tethered by one CH2 and one (CH2)2 link.
Because of the single CH2 link between N2 and N3, the N2-
Pt-N3 angle is small (84.35(9)°). Macrocycle ring con-
straints also cause ∼8° misalignment of the N2 and N3
pyridine lone pairs from an ideal Pt-N-C(ortho) of 120°.
The pyridinium ring orients the N-H proton toward (not
away from) Pt, with a H+-Pt distance, 2.428 Å, which is
(8) Puddephatt, R. J. Coord. Chem. ReV. 2001, 219-221, 157.
(9) Casas, J. M.; Falvello, L. R.; Fornies, J.; Martin, A.; Welch, A. J.
Inorg. Chem. 1996, 35, 6009.
(10) (a) Canty, A. J.; van Koten, G. Acc. Chem. Res. 1995, 28, 406. (b)
Hambley, T. W. Inorg. Chem. 1998, 37, 3767.
(11) (a) Yao, W.; Eisenstein, O.; Crabtree, R. H. Inorg. Chim. Acta 1997,
254, 105. (b) Braga, D.; Grepioni, F.; Tedesco, E.; Biradha, K.;
Desiraju, G. R. Organometallics 1997, 16, 1846.
Inorganic Chemistry, Vol. 43, No. 12, 2004 3643

Vedernikov et al.
among the shortest observed9,11 for such hydrogen bonding
to planar PtII. The angle Pt-H1n-N1 is 167.52° as is
common for hydrogen-bonded platinum(II) compounds.9-11
There are no short contacts of this proton with C6F5 fluorines.
strate R-H bond to a PtII center in a complex of RH15 in
the proposed reactive transient (η2-L)PtR(R-H)+,2,3 eqs 6a
and 6b.
Attempted Use of (HL+)PtII(C6F5)2 for Conversion of
Alkane. The equilibrium pair in eq 3 (R ) Ph) has shown
the ability to react with ethane and cyclopentane to give the
corresponding LPtH(olefin)+ and benzene.2 This is because
LPtPh2H+ is able to slowly eliminate benzene at 22 °C and
the resulting transient LPtPh+ adds ethane, then loses
benzene, and eliminates â-H. The contrasting reluctance of
(HL+)Pt(C6F5)2 to eliminate C6F5H is shown by the fact that,
when heated with 25 vol % cyclopentane in a sealed NMR
1
tube at 80 °C for 24 h, it shows no change in its H NMR
spectrum. Thus, no LPtH(olefin)+ complex forms.
In eq 6a, the pendant nitrogen can lower the activation
energy by incipient formation of the third Pt-N bond. In eq
6b, the H-R bond orientation permits CH bond cleavage
assisted by the pendant nitrogen. The latter product is then
stabilized by an intramolecular metal-hydrogen bond, Pt‚‚
(HL+)Pt(C6F5)2 + cyclo-C5H10 N
LPtH(cyclopentene)+ + 2C6F5H
+
10
2
‚HN , to the platinum dz orbital.
This is consistent with the preferential strengthening of
the M-C6X5 vs X5C6-H bond12 when X ) F, which strongly
disfavors ArH elimination from LPtAr2H+ in the case of Ar
) C6F5 as compared with Ar ) C6H5.
Formation and Isomerization of (HL+)PtIIMe2. This
molecule is both thermodynamically and kinetically unstable
even at -50 °C. Protonation of LPtIIMe2 with triflic acid in
CH2Cl2 in the presence of NaBArF4 at -80 °C (eq 5)13 forms
Considering eq 6b (R ) C6F5) from the point of view of
synthetic utility, we believe it represents the first example
of the synthesis of pentafluorophenylplatinum(II) complexes
by direct metalation of the corresponding fluorohydro-
carbon.16
Consider now formation of (HL+)PtIIR2 and LPtIVR2H+
isomers by a different method: protonation of species LPtIIR2
with R ) C6F5, Ph, and Me, eq 7.2,3 All of these LPtIIR2
LPtIIMe2 + HOTf -80 °C 8
NaBArF
4
(HL+)PtIIMe2 + LPtIVMe2H+ + NaOTfV (5)
(HL+)PtMe2 in 8% yield along with two isomeric LPtIVMe2H+
complexes, symmetrical (4%) and unsymmetrical (88%). The
1H NMR data reveal the former to have the unsymmetrical
binding of the pyridinophane to Pt, as is true of the reagent
LPtMe2,14 and the observed 1H NMR signal at +17.17 ppm
is consistent with concerted protonation directly at the
pendant pyridine. This species shows a NH‚‚‚Pt coupling
constant of 90 Hz, this being larger than that of either the
C6H5 (86 Hz) or C6F5 (63 Hz) analogue.
species are characterized by virtually the same basicity of
the pendant nitrogen but by different basicities of the metal
atom bearing different ligands R. The steric size of R may
also influence the site of protonation. For example, 1H NMR
data show that rotation about the Pt-Ar bond in (HL+)PtIIAr2
at 22 °C is fast for Ar ) Ph, but slowed for Ar ) C6F5, thus
indicating larger steric bulk and/or Pt-aryl π bonding in the
latter case.
Raising the temperature to -45 °C causes rapid (τ1/2 ) 8
min) isomerization of (HL+)PtMe2 into the thermodynami-
cally more stable product sym-LPtIVMe2H+.3 Thus, the
equilibrium in eq 3 lies to the left side for R ) Me.
Discussion
Addition of a proton to the more electron-rich platinum
atom in LPtIIMe2 leads ultimately to the formation of the
CH Bond Activation with LPtR+: Oxidative Addition
versus Electrophilic Substitution. Analyzing the second
step in eq 4, we can consider two orientations of a sub-
(15) (a) Jones, W. D. Acc. Chem. Res. 2003, 36, 140. (b) Flood, T. C.;
Janak, K. E.; Iimura, M.; Zhen, H. J. Am. Chem. Soc. 2000, 122, 6783.
(c) Childs, G. I.; Colley, C. S.; Dyer, J.; Grills, D. C.; Sun, X.-Z.;
Yang, J.; George, M. W. J. Chem. Soc., Dalton Trans. 2000, 1901.
(d) Hall, C.; Perutz, R. N. Chem. ReV. 1996, 96, 3125. (e) Bengali, A.
A.; Arndtsen, B. A.; Burger, P. M.; Schultz, R. H.; Weiller, B. H.;
Kyle, K. R.; Moore, C. B.; Bergman, R. G. Pure Appl. Chem. 1995,
67, 281.
(12) Clot, E.; Besora, M.; Maseras, F.; Megret, C.; Eisenstein, O.; Oelckers,
B.; Perutz, R. N. Chem. Commun. 2003, 490.
(13) Triflate coordinates to the PtII transient, quenching the C-H cleavage
F
F
chemistry. The sodium in NaBAr4 precipitates NaOTf, and (BAr4
)
leaves the transient highly unsaturated.
(14) Vedernikov, A. N.; Huffmann, J. C.; Caulton, K. G. Inorg. Chem.
2003, 41, 6867.
(16) Clot, E.; Oelckers, B.; Klahn, A. H.; Eisenstein, O.; Perutz, R. N. J.
Chem. Soc., Dalton Trans. 2003, 4065.
3644 Inorganic Chemistry, Vol. 43, No. 12, 2004

Hydrocarbyl “Tuning” of the PtII/IV Redox Potential
most stable, platinum(IV) isomer, sym-LPtIVR2H+,3 eq 7a,
while in the case of the electron-poor platinum center in
LPtII(C6F5)2 the most stable product of its protonation should
be the (HL+)PtIIR2 species, eq 7b. In the case of R ) Ph,
platinum(II) and platinum(IV) redox isomers are formed, by
protonation at low temperature, in a 9:1 thermodynamic
ratio.2 Thus, increasing the electron-withdrawing character
and steric bulk of R thermodynamically favors the product
of reaction 6b (7b) over that of reaction 6a (7a).
Experimental Section
General Procedures. All manipulations were carried out under
purified argon using standard Schlenk and glovebox techniques.
Solvents were dried and distilled following standard protocols and
stored in gastight bulbs under argon. All reagents for which a
synthesis is not given are commercially available from Aldrich or
Pressure Chemicals and were used as received without further
purification. All NMR solvents were dried, vacuum-transferred, and
stored in an argon-filled glovebox. [2.1.1]-(2,6)-Pyridinophane1 and
14
PtII-HX Hydrogen Bonding in L′′PtIIR2 Complexes.
Another measure of the relative basicity of the PtII center in
LPtIIR2 species, besides the value of the equilibrium constant
of eq 3, might be the magnitude of the Pt-H coupling
constant in (HL+)PtIIR2. This decreases according to R )
Me > Ph > C6F5 and is the same trend for (HL+)PtIIR2,
becoming more dominant over the platinum(IV) isomer
LPtIVR2H+. There are several literature examples of anionic
pentafluorophenylplatinum(II) complexes [Pt(C6F5)3L′′]-,
with L′′ containing a potential hydrogen bond donor group
HX located in proximity to the metal atom.9,17 In the case
of structurally similar substituted pyridine ligands with
weakly acidic HX donors, such as H-C(sp3), H-C(sp2), and
H-O-C(sp3), no H-Pt coupling was observed, and thus,
no hydrogen bonding by this criterion was found in solu-
tion.17 In contrast, L′′ with the more acidic phenolic hydroxyl,
H-O-C(sp2), showed the presence of such an interaction.9
Since the pyridinium fragment NH+ is more acidic than the
phenolic OH, we can rationalize why the uncharged and less
electron-rich platinum(II) center in (HL+)PtII(C6F5)2 exhibits
Pt‚‚‚H hydrogen bonding. Some degree of flexibility of the
macrocycle L allows certain variation of the Pt-HN+
separation. The platinum(II) center in the case of R ) Me is
so electron-rich that the platinum(II) isomer, eq 3, is no
longer thermodynamically preferred and can be observed
only under conditions of kinetic control.
LPtMe2 have been synthesized according to the published
1
procedures. H and 19F NMR spectra were recorded on an Inova
700 spectrometer (1H, 400 MHz; 19F, 376.43 MHz). H and 19F
1
NMR chemical shifts are reported in parts per million and
referenced to residual solvent resonance peaks in the first two cases
or the BArF peak.
4
Synthesis of [(HL+)PtII(C6F5)2]BArF . A 2 mL Schlenk flask
equipped with a Kontes Teflon valve and magnetic stirring bar was
charged in an argon-filled glovebox with 20 mg of NaBArF (22
4
4
µmol), 20 µmol of LPtMe2, and 0.6 mL of a 3:1 CD2Cl2-
pentafluorobenzene mixture. The flask was then removed from the
glovebox and immersed into an acetone bath cooled to -95 °C.
The Teflon valve was replaced with a serum cap, and a solution of
3.0 mg of HSO3CF3 in 0.1 mL of CD2Cl2 (20 µmol) was added to
the stirred suspension dropwise with a syringe. After 5 min of
stirring at -95 °C the resulting liquid was warmed to room
temperature and transferred to a Teflon-sealed NMR tube. Reaction
1
was monitored by H NMR spectroscopy. In 1 day at 22 °C the
reaction was complete. Heating the reaction mixture at 80 °C in a
sealed NMR tube for 96 h did not change its composition. Colorless
crystals suitable for X-ray analysis were obtained by adding
cyclohexane and allowing the mixture to evaporate slowly. Yield:
90%.
[(HL)Pt(C6F5)2]BArF , Data for the Cationic Part. H NMR
1
4
(CD2Cl2, 22 °C): δ 3.31 (m, 1H, C2H4), 3.50 (ddd, J ) 3.1, 13.5,
2
19.8 Hz, 1H, C2H4), 4.11 (m, 1H, C2H4), 4.22 (d, JH-H ) 14.1
Hz, 1H, CH2), 4.54 (d, 2JH-H ) 15.3 Hz, 1H, CH2), 4.81 (ddd, J )
2.9, 13.6, 15.9 Hz, 1H, C2H4), 5.46 (d, 2JH-H ) 14.0 Hz, 1H, CH2),
6.17 (d, 2JH-H ) 15.2 Hz, 1H, CH2), 7.42 (d, 3JH-H ) 7.8 Hz, 1H,
m-CH, py), 7.54 (d, 3JH-H ) 7.8 Hz, 1H, m-CH, py), 7.59 (d, 3JH-H
Thus, the basicities of a platinum(II) center toward two
different acids, external H+ (as reflected by the position of
equilibrium 3) and NH+ (as reflected by the value of the
1JPt-H coupling constant in (HL+)PtR2 species), correlate one
with the other.
3
) 8.0 Hz, 1H, m-CH, py), 7.65 (d, JH-H ) 7.8 Hz, 1H, m-CH,
py), 7.66 (d, 3JH-H ) 7.9 Hz, 1H, m-CH, py), 7.83 (t, 3JH-H ) 7.9
3
Hz, 1H, p-CH, py), 7.86 (t, JH-H ) 7.8 Hz, 1H, p-CH, py), 8.19
(t, 3JH-H ) 8.0 Hz, 1H, p-CH, py), 16.33 (br s, 1H, NH). The NH+
proton signal is very broad at 22 °C (half-width of 57 Hz), thus
making locating platinum satellites unreliable. The narrower signal
of the NH+ proton observed at -40 °C (half-width of 21 Hz)
Conclusions
While this paper began by describing two distinct mecha-
nistic possibilities for C-H cleavage, eqs 1 and 2, the fact
that our compounds show equilibrium interconVersion
between the distinct products of these two mechanisms means
that we are unable to make a mechanistic determination in
our examples, from the available observations of CH bond
cleavage. However, the evidence that these products, PtII and
PtIV, are in hydrocarbyl-ligand-dependent equilibrium is an
exceptional case of intramolecular migration between two
redox states via bond breaking and making to H. Such redox
isomerization is certainly facilitated by the hydrogen bonding,
which in turn is another benefit of the “preorganized”
geometry of the pyridinophane ligand on PtII.1
1
resolved the value of JPt-H ) 63 Hz. 19F NMR (CD2Cl2, -40
°C): δ -164.40 (ddd, J ) 8.1, 20.3, 29.7 Hz, 1F, m-CF), -164.09
(ddd, J ) 8.3, 20.6, 29.7 Hz, 1F, m-CF), -163.14 (ddd, J ) 8.3,
20.8, 29.2 Hz, 1F, m-CF), -162.90 (ddd, J ) 8.1, 20.5, 29.2 Hz,
3
1F, m-CF), -161.05 (t, JF-F ) 20.3 Hz, 1F, p-CF), -160.93 (t,
3JF-F ) 20.3 Hz, 1F, p-CF), -122.12 (d, JF-F ) 29.2 Hz, JPt-F
3
3
3
3
) 443 Hz, 1F, o-CF), -121.78 (d, JF-F ) 29.2 Hz, JPt-F ) 446
Hz, 1F, o-CF), -119.31 (m, 3JPt-F ) 408 Hz, 1F, o-CF), -118.68
3
(m, JPt-F ) 416 Hz, 1F, o-CF). 19F NMR (CD2Cl2, 22 °C): δ
-164.17 (br m, 2F, m-CF), -163.22 (br m, 2F, m-CF), -160.96
3
3
(t, JF-F ) 20.0 Hz, 1F, p-CF), -160.79 (t, JF-F ) 20.0 Hz, 1F,
p-CF), -122.11 (br s, 3JPt-F ) 440 Hz, 2F, o-CF), -119.01 (br m,
3JPt-F ) 400 Hz, 2F, o-CF).
Attempted Reaction of [(HL+)PtII(C6F5)2]BArF4 with Cyclo-
pentane. In an argon-filled glovebox a Teflon-capped NMR tube
was charged with 16.8 mg of (HL+)Pt(C6F5)2BArF4 (10 µmol) and
(17) Casas, J. M.; Fornies, J.; Martin, A. J. Chem. Soc., Dalton Trans.
1997, 1559.
Inorganic Chemistry, Vol. 43, No. 12, 2004 3645

Vedernikov et al.
0.6 mL of a 3:1 CD2Cl2-cyclopentane mixture. The tube was then
removed from the glovebox and immersed into an oil bath preheated
to 80 °C. After 24 h of heating the reaction mixture showed no
changes in the 1H NMR spectrum. In particular, no high-field Pt-H
resonance due to LPtH(cyclopentane)+ 2 was observed.
mm3) was placed onto the tip of a 0.1 mm diameter glass capillary
and mounted on a SMART6000 (Bruker) at 137(2) K.
The data collection was carried out using Mo KR radiation
(graphite monochromator) with a frame time of 10 s and a detector
distance of 5.1 cm. A randomly oriented region of two spheres in
reciprocal space was surveyed. Six major sections of frames were
collected with 0.30° steps in ω at six different æ settings and a
detector position of -43° in 2θ. An additional set of 50 frames
was collected to model decay. Data to a resolution of 0.71 Å were
considered in the reduction. Final cell constants were calculated
from the xyz centroids of 9604 strong reflections from the actual
data collection after integration (SAINT).18 The intensity data were
corrected for absorptions (SADABS).19 Table 1 contains additional
crystal and refinement information.
Protonation of LPtIIMe2 and Thermal Transformation of
[(HL+)PtIIMe2]BArF . A 2 mL Schlenk flask equipped with a
4
Kontes Teflon valve, sealed NMR tube, and magnetic stirring bar
was charged in an argon-filled glovebox with 20 mg of NaBArF
4
(22 µmol), 20 µmol of LPtMe2, and 0.6 mL of CD2Cl2. The flask
was then removed from the glovebox and immersed into an acetone
bath cooled to -95 °C. The Teflon valve was replaced with a serum
cap, and a solution of 3.0 mg of HSO3CF3 in 0.1 mL of CD2Cl2
(20 µmol) was added to the stirred suspension dropwise with a
syringe. After 5 min of stirring at -95 °C the resulting liquid was
transferred into a sealed NMR tube precooled with the acetone bath.
The flask was connected to a vacuum line, and the NMR tube was
Structure Solution and Refinement. The space group P21/c
was determined on the basis of intensity statistics and systematic
absences. The structure was solved using SIR-9220 and refined with
SHELXL-97.21 A direct-methods solution was calculated which
provided most non-hydrogen atoms from the E-map. Full-matrix
least-squares/difference Fourier cycles were performed which
located the remaining non-hydrogen atoms. All non-hydrogen atoms
were refined with anisotropic displacement parameters. The hy-
drogen atoms were placed in ideal positions and refined as riding
atoms with relative isotropic displacement parameters with the
exception of H1n, which was refined with an individual displace-
ment parameter. The structure contains large voids (1576 Å3 per
unit cell) that are occupied by dichloromethane molecules. Their
contribution to the structure factors was assessed by back Fourier
transformation to 132 electrons per unit cell; for comparison,
dichloromethane occupies 83 Å3 with 78 electrons.22 The data were
modified accordingly. The refinement using the modified dataset
improved the overall structure and the R values significantly. The
remaining electron density is located in the vicinity of the CF3
groups. One CF3 group is disordered over two positions.
1
flame-sealed. Reaction was monitored by H NMR spectroscopy
in a precooled NMR probe starting from -80 °C. The temperature
was raised by 10° increments. At -80 °C three isomeric products
were observed, (HL+)PtIIMe2 (8%), unsym-LPtIVMe2H+ (88%), and
sym-LPtIVMe2H+ (4%).3 They underwent quantitative isomerization
into sym-LPtIVMe2H+ in the temperature range of -50 to -30 °C.
To follow the (HL+)PtIIMe2 to sym-LPtIVMe2H+ isomerization,
spectra were taken every 10 min at a constant temperature, -45
°C. The approximate half-life for (HL+)PtIIMe2 undergoing isomer-
ization into sym-LPtIVMe2H+ at the temperature given was calcu-
lated to be 8 min.
1
[(HL)PtIIMe2]BArF , Data for the Cationic Part. H NMR
4
2
(CD2Cl2, -65 °C): δ: 0.64 (s, JPt-H ) 84 Hz, 3H, PtMe), 0.69
(s, 2JPt-H ) 86 Hz, 3H, PtMe), 4.03 (d, 2JH-H ) 15.4 Hz, 1H, CH2),
2
2
4.21 (d, JH-H ) 14.0 Hz, 1H, CH2), 4.88 (d, JH-H ) 15.4 Hz,
2
3
1H, CH2), 5.26 (d, JH-H ) 14.0 Hz, 1H, CH2), 7.21 (d, JH-H
)
3
7.8 Hz, 1H, m-CH, py), 7.36 (d, JH-H ) 7.8 Hz, 1H, m-CH, py),
7.40 (d, 3JH-H ) 7.8 Hz, 1H, m-CH, py), 7.44 (d, 3JH-H ) 7.8 Hz,
1H, m-CH, py), 7.95 (t, 3JH-H ) 7.8 Hz, 1H, p-CH, py), 17.17 (br
Acknowledgment. This work was supported by the DOE.
A.N.V. is on leave from the Chemical Faculty, Kazan State
University, Kazan, Russia. This work has been made possible
in part due to support from the Russian Foundation for Basic
Research (Grant 01.03.32692).
1
s, JPt-H ) 90 Hz, 1H, Pt‚‚‚HN); signals of two m-CH and two
p-CH groups presumably overlap with the other signals.
1
[unsym-LPtIVMe2H]BArF , Data for the Cationic Part. H
4
1
NMR (CD2Cl2, -65 °C): δ -22.23 (s, JPt-H ) 1373 Hz, 1H,
PtH), 1.17 (s, 2JPt-H ) 69 Hz, 3H, PtMe), 1.45 (s, 2JPt-H ) 69 Hz,
3H, PtMe), 3.08 (m, 1H, C2H4), 3.09 (m, 1H, C2H4), 3.47 (m, 1H,
C2H4), 4.09 (d, 2JH-H ) 15.1 Hz, 1H, CH2), 4.32 (d, 2JH-H ) 15.0
Hz, 1H, CH2), 4.53 (m, 1H, C2H4), 4.71 (d, 2JH-H ) 15.0 Hz, 1H,
Supporting Information Available: Full crystallographic
details (CIF, PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
2
3
CH2), 4.82 (d, JH-H ) 15.0 Hz, 1H, CH2), 7.13 (d, JH-H ) 8.0
Hz, 1H, m-CH, py), 7.27 (d, 3JH-H ) 8.0 Hz, 1H, m-CH, py), 7.30
(d, 3JH-H ) 8.0 Hz, 1H, m-CH, py), 7.32 (d, 3JH-H ) 8.0 Hz, 1H,
m-CH, py), 7.48 (d, 3JH-H ) 8.0 Hz, 1H, m-CH, py), 7.49 (d, 3JH-H
) 8.0 Hz, 1H, m-CH, py), 7.54 (t, 3JH-H ) 7.8 Hz, 1H, p-CH, py),
IC034731M
(18) SAINT 6.1, Bruker Analytical X-ray Systems, Madison, WI.
(19) Blessing, R. Acta Crystallogr. 1995, A51, 33.
(20) Altomare, A.; Cascarno, G.; Giacovazzo, C.; Gualardi, A. J. Appl.
Crystallogr. 1993, 26, 343.
(21) SHELXTL-Plus V5.10, Bruker Analytical X-ray Systems, Madison,
WI.
3
3
7.64 (t, JH-H ) 7.8 Hz, 1H, p-CH, py), 7.77 (t, JH-H ) 7.8 Hz,
1H, p-CH, py).
X-ray Structure Determination of [(LH+)Pt(C6F5)2](BArF ).
4
A colorless crystal (approximate dimensions 0.20 × 0.15 × 0.13
(22) Immirzi, A.; Perini, B. Acta Crystallogr. 1977, A33, 216.
3646 Inorganic Chemistry, Vol. 43, No. 12, 2004