Structural investigations of platinum(II) styrene and styryl complexes and mechanistic study of vinylic deprotonation

Article abstract of DOI:10.1021/om900482k

The X-ray structures of the π-complex [Pt(PNP)(CH₂=CHPh)] (BF₄)₂ and the σ-complex [Pt(PNP)((E)-CH=CHPh)] BF₄ are reported (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine). The styrene complex undergoes vinylic

Full text of DOI:10.1021/om900482k

Organometallics 2010, 29, 1331–1338 1331
DOI: 10.1021/om900482k
Structural Investigations of Platinum(II) Styrene and Styryl Complexes
and Mechanistic Study of Vinylic Deprotonation
Christine Hahn*
Department of Physical Sciences, University of Texas of the Permian Basin, 4901 East University Boulevard,
Odessa, Texas 79762
Received June 7, 2009
The X-ray structures of the π-complex [Pt(PNP)(CH2dCHPh)](BF4)2 and the σ-complex [Pt(PNP)-
((E)-CHdCHPh)]BF4 are reported (PNP = 2,6-bis(diphenylphosphinomethyl)pyridine). The styrene
complex undergoes vinylic deprotonation by reaction with the weakly basic nucleophiles ROH (R = Me,
1
Et, H), which was monitored by H and 31P NMR. The mechanistic pathway includes nucleophilic
addition of the oxygen donor nucleophiles to the coordinated styrene. The resulting addition products
[Pt(PNP)(CH2CHPhOR)]BF4 transformed to the styryl complex only when protons are present. Simi-
larly, the related 1-vinylnaphthalene complex [Pt(PNP)(CH2dCHC10H7)](BF4)2 undergoes vinylic
deprotonation in the presence of methanol, forming the corresponding σ-complex [Pt(PNP)((E)-
CHdCHC10H7)]BF4.
Introduction
while substitution of the alkene by the nucleophile is less compe-
titive.1b,2 Although the dicationic PdII and PtII alkene complexes
are highly reactive they are stable enough for complete character-
ization in solution and in solid state. [Pd(PNP)(CH2dCH-
Ph)](BF4)2 and [Pt(PNP)(CH2dCH2)](BF4)2 are the first dica-
tionic monoalkene complexes of PdII and PtII being investigated
by X-ray structure analysis.1a,2
Dicationic palladium(II) and platinum(II) monoalkene
complexes1,2 have recently gained increasing interest in
C-C, C-N, and C-O bond formations.3-6 Due to the high
positive complex charge, the coordinated C-C double bond
in these complexes is highly activated, and the complexes add
readily even very weak nucleophiles such as internal alkenes
and activated arenes. These C-C bond formations were
observed in stoichiometric and catalytic reactions.4
In the course of the investigation of nucleophilic addition
of dicationic platinum alkene complexes [Pt(PNP)(CHRd
CHR0)](BF4)2 (R/R0 = H/H, H/Me, H/Et, H/Ph (1), (E)-/
(Z)-Me/Me) with nitrogen and oxygen donor molecules, it
was observed that only in the case of the styrene derivatives
[Pt(PNP)(CH2CHPhOR)]BF4 (R = H (2a), Me (2b)) did
spontaneous decomposition occur at room temperature.2
The resulting product was identified as [Pt(PNP)((E)-CHd
Equilibrium studies of dicationic PdII and PtII alkene com-
plexes[M(PNP)(CHRdCHR0)](BF4)2 (PNP=2,6-bis(diphenyl-
phosphinomethyl)pyridine) with protic nucleophiles (HNR2,
HOR) showed that the nucleophilic addition is thermodynami-
cally highly favored compared to neutral or cationic complexes,
1
CHPh)]BF4 (3) by H and 13C NMR spectroscopy. It was
found that the platinum(II) styrene complex 1 underwent in
the presence of weakly basic nucleophiles such as methanol
and water a vinylic deprotonation. Complex 1 displays the
most reactive alkene complex known, with regard to olefinic
C-H bond activation.
*To whom correspondence should be addressed. E-mail: hahn_c@
utpb.edu.
(1) (a) Hahn, C.; Vitagliano, A.; Giordano, F.; Taube, R. Organo-
metallics 1998, 17, 2060–2066. (b) Hahn, C.; Morvillo, P.; Vitagliano, A.
Eur. J. Inorg. Chem. 2001, 419–429.
(2) Hahn, C.; Morvillo, P.; Herdtweck, E.; Vitagliano, A. Organo-
Vinylic deprotonation has been studied for a few alkene
complexes of other transition metals.7,8 The only platinum-
(II) alkene complex from which a vinylic proton could be
removed, [PtCl(CH2dCHPh)(tmeda)]ClO4 (tmeda = N,N,
N0,N0-tetramethylethylenediamine), was reported recently.9
The activation of an olefinic C-H bond by transition metals
not only is a useful method to prepare σ-vinyl complexes
metallics 2002, 21, 1807–1818.
(3) Chianese, A. R.; Lee, S. J.; Gagne, M. R. Angew. Chem., Int. Ed.
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(4) (a) Hahn, C.; Cucciolito, M. E.; Vitagliano, A. J. Am. Chem. Soc.
2002, 124, 9038–9039. (b) Cucciolito, M. E.; D'Amora, A.; Vitagliano, A.
Organometallics 2005, 24, 3359–3361. (c) Cucciolito, M. E.; D'Amora, A.;
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r
2010 American Chemical Society
Published on Web 02/25/2010
pubs.acs.org/Organometallics

1332 Organometallics, Vol. 29, No. 6, 2010
Hahn
from parent alkene complexes but also has considerable
importance for organic synthesis.10 Platinum vinyl com-
plexes are relevant intermediates in catalytic processes, e.g.
hydrosilylation of alkynes,11 and are commonly prepared by
oxidative addition of the vinyl halide X-CHdCHR to a Pt0
center,12 from Grignard or lithium reagents,13 or by insertion
of an alkyne into Pt-H bond.14
In this paper the X-ray structure analysis of
[Pt(PNP)(CH2dCHPh)](BF4)2 (1) is reported. An overview
of the characteristic structural parameters of all isostructural
complexes15 [M(PNP)(CH2dCHR)]nþ (M = RhI, PdII, PtII;
R = H, Ph) will be given and discussed. The process of
vinylic deprotonation of complex 1 which was observed with
oxygen donor nucleophiles2 has been reinvestigated, and the
results of more detailed 1H NMR studies as well as the solid-
state structure of the styryl complex [Pt(PNP)((E)-
CHdCHPh)]BF4 (3) are reported in this paper.
Results and Discussion
Figure 1. ORTEP view of the complex dication of 1, [Pt(PNP)-
(CH2dCHPh)]2þ. Thermal ellipsoids are drawn at the 50% proba-
bility level. Selected bond lengths (A) and angles (deg): Pt-P(1)=
2.3309(15), Pt-P(2) = 2.3105(14), Pt-N = 2.076(4), Pt-C(1) =
2.188(6), Pt-C(2) = 2.282(6), C(1)-C(2) = 1.350(10), P(1)-
C(27) = 1.811(6), P(2)-C(14) = 1.842(6); P(1)-Pt-P(2) =
162.79(5), P(1)-Pt-N = 81.15(12), P(2)-Pt-N = 81.64(12),
N-Pt-C(1) = 159.7(2), N-Pt-C(2) = 164.7(2), C(1)-Pt-
C(2) = 35.1(3), C(1)-C(2)-C(3) = 127.6(7), Pt-C(2)-C(3) =
112.5(5).
Molecular Structure of [Pt(PNP)(CH2dCHPh)](BF4)2 (1).
Single crystals of the dicationic platinum styrene complex 1,
suitable for X-ray analysis, were obtained from a solution in
dichloromethane after slow evaporation of the solvent at
room temperature over a period of several days. No addi-
tional free styrene was added for stabilization which was
otherwise necessary for crystal growth of the isostructural
palladium complex.1a An ORTEP view of the dication of 1,
[Pt(PNP)(CH2dCHPh)]2þ, is shown in Figure 1. The overall
geometry of complex 1 is quite similar to that of [Pt(PNP)-
(CH2dCH2)]2þ and related alkene PNP complexes of RhI
and PdII.1a,2,15 Characteristic structural parameters for all
PNP alkene complexes of RhI, PdII, and PtII are summa-
rized in Table 1. The P(1)-Pt-P(2) angle in complex 1 is
found to be 162.8ꢀ, which is within the range observed in the
other M(PNP) complexes. The two five-membered rings
are very constrained, which forces an inclination of the
pyridine ring from the coordination plane by 21ꢀ. Similar
values were observed for the isostructural RhI and PdII
complexes.1a,15
˚
The C-C double bond of the coordinated styrene is tilted
by 11ꢀ from the normal plane in complex 1. This angle is
somewhat smaller than that in the isostructural styrene com-
plexes (RhI, 15ꢀ; PdII, 16ꢀ).15,1a This trend was also noted for
the PtII andRhI ethylenecomplexes (cf. Table 1).2,15 However,
the coordinated ethylene in these complexes is overall less
tilted than the styrene due to fewer steric interactions with the
phenyl groups of the PNP ligand.
The C-C double-bond length in complex 1 (C(1)-C(2) =
1.350(10) A) is somewhat longer than that found in the iso-
˚
structural PdII styrene complex1a (1.292(10) A) and is not
˚
significantly shorter than that in the monocationic RhI styrene
complex15 (1.383(7) A) (cf. Table 1). While the Pt-CH2 bond
˚
(10) (a) Selective Hydrocarbon Activation; Davies, J. A., Watson, P. L.,
Greenberg, A., Liebman, J. F., Eds.; VCH: New York, 1990. (b) Handbook
of C-H Transformations, Applications in Organic Synthesis; Dyker, G.,
Ed.; Wiley-VCH: Weinheim, Germany, 2005. (c) Pfeffer, M.; Spencer, J. In
Comprehensive Organometallic Chemistry III; Mingos, D. M. P., Crabtree,
R. H., Eds.; Elsevier: Amsterdam, 2007; Vol. 10, p 155. (d) Faller, J. W.;
Felkin, H. Organometallics 1985, 4, 1488–1490. (e) Mori, H.; Matsuo, T.;
Yoshioka, Y.; Katsumura, S. J. Org. Chem. 2006, 71, 9004–9012.
(11) (a) Green, M.; Spencer, J. L.; Stone, G. A. J. Chem. Soc., Dalton
Trans. 1977, 1525–1529. (b) Widenhoefer, R. A.; Bender, C. F. Compre-
hensive Organometallic Chemistry III; Mingos, D. M. P., Crabtree, R. H.,
Eds.; Elsevier: Amsterdam, 2007; Vol. 11, p 371.
(12) (a) Rajaram, J.; Pearson, R. G.; Ibers, J. A. J. Am. Chem. Soc.
1974, 96, 2103–2108. (b) Cook, C. D.; Jauhal, G. S. Can. J. Chem. 1967, 45,
301–304.
(13) Cardin, C. J.; Cardin, D.; Parge, H. E.; Sullivan, A. C. J. Chem.
Soc., Dalton Trans. 1986, 2315–2320.
˚
length (Pt-C(1) = 2.188(6) A) is the same as the Pt-C dis-
tances in the analogous PtII ethylene complex,2 the Pt-CHPh
˚
bond (Pt-C(2) = 2.282(6) A) is significantly longer. The same
˚
strong elongation of the M-CHPh bond by 0.1 A was also
observed in the dicationic PdII styrene complex,1a whereas in
the monocationic RhI styrene complex this elongation is much
less pronounced.15 In comparison to other PtII styrene com-
plexes, similar differences between the two Pt-C bond lengths
˚
of about 0.1 A and similar C-C double-bond lengths were
reported for [Pt(η3-CH2CMeCH2)(PPh3)(CH2dCHPh)]PF6
16
˚
˚
˚
(Pt-C = 2.203(12) A, 2.301(12) A; C-C = 1.341(17) A)
˚
and [PtCl2(CH2dCHPh)2] (Pt-C = 2.156(7), 2.2705(5) A;C-
C = 1.382(9) A).17 In a monocationic PtII styrene complex con-
˚
(14) (a) Osakada, K. In Comprehensive Organometallic Chemistry III;
Mingos, D. M. P., Crabtree, R. H. Eds.; Elsevier: Amsterdam, 2007; Vol. 8, p
471. (b) Anderson, G. K. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, A., Wilkinson, G., Eds.; Pergamon Press: London, 1995;
Vol. 9, p 483. (c) West, N. M.; Peter, S.; Templeton, J. L. Organometallics
2008, 27, 5252–5262. (d) Ohtaka, A.; Kuniyasu, H.; Kinomoto, M.; Kur-
osawa, H. J. Am. Chem. Soc. 2002, 124, 14324–14325. (e) Knorr, M.;
Strohmann, C. Eur. J. Inorg. Chem. 2000, 241–252. (f) Steinborn, D.;
Becke, S.; Bruhn, C.; Heinemann, F. W. J. Organomet. Chem. 1998, 556,
189–196.
taining an anionic chelating ligand with relatively strong C and
N donor functions18 the Pt-C distances (2.160(5), 2.218(5) A)
˚
˚
have a difference of about 0.06 A while the C-C double-bond
(16) Miki, K.; Kai, Y.; Kasai, N.; Kurosawa, H. J. Am. Chem. Soc.
1983, 105, 2482–2483.
(17) Albinati, A.; Caseri, W. R.; Pregosin, P. S. Organometallics 1987,
6, 788–793.
(18) Baar, C. R.; Jenkins, H. A.; Jennings, M. C.; Yap, G. P. A.;
(15) For isostructural alkene RhI complexes see: Hahn, C.; Sieler, J.;
Taube, R. Chem. Ber./Recl. 1997, 130, 939–945.
Puddephatt, R. J. Organometallics 2000, 19, 4870–4877.

Article
Organometallics, Vol. 29, No. 6, 2010 1333
Table 1. Structural Parameters of Related Alkene Complexes [M(PNP)(CH2dCHR)]nþ (M = RhI, PdII, PtII; R = H, Ph)
CdC, A M-CH2, A M-CHR, A M-N, A M-P(1), A M-P(2), A P(1)-M-P(2), deg —CdC, dega
˚
˚
˚
˚
˚
˚
complex
[Rh(PNP)(CH2dCH2)]þb
1.351(11)
[Rh(PNP)(CH2dCHPh)]þb 1.383(7)
[Pd(PNP)(CH2dCHPh)]2þc 1.292(10)
2.132(6)
2.144(5)
2.165(7)
2.180(6)
2.188(6)
2.157(6)
2.201(4)
2.273(7)
2.181(8)
2.282(6)
2.092(4)
2.102(3)
2.058(4)
2.051(4)
2.076(4)
2.2690(13)
2.2916(10)
2.314(1)
2.3059(13)
2.3105(14)
2.3001(13)
2.3004(11)
2.330(2)
2.3063(13)
2.3309(14)
161.39(5)
161.96(4)
162.4(1)
163.57(5)
162.79(5)
6
16
15
2
[Pt(PNP)(CH2dCH2)]2þd
[Pt(PNP)(CH2dCHPh)]2þ
(cation of 1)
1.359(10)
1.350(10)
11
a Angle between the coordinated C-C double bond and the normal to the complex plane, which is the best plane of P(1), N, Pt, and P(2). b See ref 15.
c See ref 1a. d See ref 2.
Scheme 1. Formation of an Incipient Carbocation by Slipping of
the Alkene from η2 to η1 Coordination Mode
Ph)]BF4 (3). Similarly, the addition products [Pt(PNP)(CH2-
CHPhOR)]BF4 (R = H (2a), Et (2c)), formed in situ by treat-
ment of the styrene complex 1 with water and ethanol, respec-
tively, also transformed slowly to complex 3. In each case the E
isomer was formed, which is stable as a solid and in solution
without showing any indication for isomerization to the Zform.
This process was monitored by 1H and 13P NMR spectros-
copy. For this purpose a solution of 20 mM of the styrene
complex 1in CD3OD was prepared, generating complex 2b-d3 in
situ (cf. Scheme 2). The change of concentrations of 2b-d3 and 3
over time, which is shown in Figure 2, was determined by inte-
gration of 1H NMR signals in the respective spectra. The graph
in Figure 3 shows a plot of pseudo-first-order kinetics of the
transformation of 2b-d3 to 3. The observed rate constant was
determined as kobs =1.25ꢀ 10-4 s-1, and the half-life of 2b-d3 is
t1/2 = 90 ( 3 min. In Figure 4, selected 1H NMR spectra recor-
ded over the course of the reaction show the slow transformation
of 2b-d3 to 3. Notable in these spectra, the signals at δ 2.02 and
2.17 (PtCHaHb), 3.71 (CHPh),4.56(PCH2),and6.62(CPh-o) of
complex 2b-d3 appear relatively broad. A similar broadening of
the 31P NMR signal at δ 30.5 was also observed for 2b-d3 in this
reaction mixture (w1/2 = 13 Hz). In contrast, all signals in the 1H
NMR spectrum of a solution of isolated 2b dissolved in CD3OD
are sharp and show complex H-H, H-P, and H-Pt coupling
patterns, respectively (see the Experimental Section). The iso-
lated methoxyalkyl complex 2b is completely stable in CD3OD
solution over several days. No indication for any decomposition
or transformation to the styryl complex 3 was noted.
Another kinetic experiment was performed with the in situ
prepared ethoxyalkyl complex [Pt(PNP)(CH2CHPhOCH2-
CH3)]BF4 (2c) (from 20 mM complex 1 in ethanol), where
kobs = 1.00 ꢀ 10-5 s-1 and t1/2 = 1155 ( 150 min were ob-
served for the transformation to complex 3. The change of
concentrations of 2c and 3 was recorded by integration of the
respective 31P NMR signals at δ 29.7 (JP-Pt = 3077 Hz) and
27.0 (JP-Pt = 2922 Hz), respectively.
When complex [Pt(PNP)(CH2CHPhOR)]BF4 (2) is gen-
erated in situ, it always forms a stoichiometric amount of
protons by instant dissociation from the primarily formed
addition product I (cf. Scheme 2). The equilibrium between I
and 2 lies on the very right side; however, the broad NMR
signals observed for 2b-d3 suggest a dynamic interaction
between the methoxy group of 2b-d3 and the stoichiometric
proton on the NMR time scale. This suggests that only the
presence of additional protons in solution allows the trans-
formation of 2 to the styryl complex 3, which involves the
reassociation of the proton at the hydroxy or alkoxy group
and dissociation of ROH from intermediate I. In other
words, the transformation from 2 to 3 is a proton-catalyzed
process, and its rate depends on the proton concentration.
Upon treatment of the styryl complex 3 with an excess of
II
length (1.380(8) A) falls within the range of the Pt styrene
˚
complexes mentioned above. These complexes seem to have a
relatively moderate degree of π-back-donation in their Pt-
(CdC) bond. Strong π-back-donation in the neutral four- and
five-coordinate PtII styrene complexes [PtCl2(NC5H4Me)-
(CH2dCHPh)]19 and [PtCl2(diimine)(CH2dCHPh)]20 is sug-
gested by the relatively long C-C double-bond length
˚
˚
(1.454(17) A and 1.53(5) A, respectively). The Pt-C distances
˚
are only different by about 0.05 A.
From the structural parameters of the coordinated styrene
and ethylene at the Pt(PNP)2þ fragment it can be seen in
comparison to the isostructural PdII and RhI alkene com-
plexes that the Pt2þ center has no particular influence on the
C-C double-bond length. While the C-C double-bond
length is commonly sought to estimate the degree of
π-back-donation contribution in the metal-alkene bond,21
it does not appear to be very diagnostic for the dicationic PtII
alkene complexes. As pointed out earlier, the high positive
charge in the dicationic complexes rather affects the M-C
bond lengths.22 In particular, in the case of monosubstituted
alkenes such as styrene, the unequally stronger lengthening of
the M-CHR bond may indicate the degree of activation by
increasing the positive net charge. These structural features
are supported by 13C NMR spectroscopic data: (i) the signal
for M-CHPh is shifted less upfield than that for M-CH2 in
comparison to the signals of the free styrene and (ii) JC-Pt
-
(Pt-CHPh) < JC-Pt(Pt-CH2).2 These data indicate a great-
er weakening of the M-CHR bond. Overall, the structural
parameters observed for the dicationic PtII styrene complex
confirm the general picture of the enhanced “slipping” of the
alkene with higher positive complex charge, thus promoting
the formation of an incipient carbocation preferably located
at the substituted carbon atom (cf. Scheme 1).
Vinylic Deprotonation. When styrene complex 1 was dis-
solved in methanol, the addition product [Pt(PNP)(CH2CH-
PhOCH3)]BF4 (2b) was formed immediately and quantitatively
(cf. Scheme 2) and could be isolated in high yield and analyti-
cally pure form.2 However, if the methoxyalkyl complex 2b
was not isolated within 10 min from the solution, it started
transforming to the styryl complex [Pt(PNP)((E)-CHdCH-
(19) Nyburg, S. C.; Simpson, K.; Wong-Ng, W. J. Chem. Soc., Dalton
Trans. 1976, 1865–1870.
(20) van der Poel, H.; van Koten, G.; Kokkes, M.; Stam, C. H. Inorg.
Chem. 1981, 20, 2941–2950.
(21) Elschenbroich, C. Organometallics, 3rd ed.; Wiley-VCH: Wein-
heim, Germany, 2006; p 403.
HBF4 Et2O in CD3OD, the styrene complex 1 was re-formed
3
(22) Hahn, C. Chem. Eur. J. 2004, 10, 5888–5899.
in an equilibrium reaction (cf. Scheme 2). The reaction of the

1334 Organometallics, Vol. 29, No. 6, 2010
Scheme 2. Mechanistic View of the Vinylic Deprotonation of Styrene Complex 1
Hahn
Figure 2. Plot of the concentrations [2b-d3] and [3] against time.
Figure 4. Time-dependent 1H NMR spectra showing the trans-
formation of 2b-d3 to 3 in CD3OD.
substituent at the β-carbon atom, providing an extended
π-conjugation. Notably, no spontaneous vinylic deprotona-
tion was observed for the analogous ethylene and alkyl alkene
derivatives [Pt(PNP)(CH2CHROCH3)]BF4 (R = H, Me, Et)
in the presence of a stoichiometric amount of protons.2
In order to broaden the scope of the vinylic deprotonation,
the 1-vinylnaphthalene complex [Pt(PNP)(CH2dCHC10H7)]-
(BF4)2 (4) was investigated. Complex 4 was prepared from
[Pt(PNP)(CH2dCH2)](BF4)2 by substitution of ethylene2 by
1-vinylnaphthalene and characterized by 1H, 13C, and 31PNMR
spectroscopy (see the Experimental Section).23 When complex
Figure 3. Pseudo-first-order plot for the transformation of
2b-d3 to 3.
methoxyalkyl complex 2b with an excess of HBF4 Et2O in
3
CD3OD led first to the formation of the styryl complex 3 as the
kinetic product, which then slowly transformed to the styrene
complex 1as the thermodynamic product. The formation of the
styryl complex 3even in the presence of a large excess of the acid
indicates that the vinylic deprotonation must be a very fast
intramolecular process, whereas the protonation of the styryl
complex 3 is a much slower equilibrium.
(23) Compounds 4-6 seem to be slightly unstable in solution and form
some black platinum precipitate. The platinum metal impurities are most
likely the reason for the light gray-brownish color of the isolated com-
pounds 4-6, which were difficult to remove. This also may explain the
lower values of the elemental analyses (C, H, N) by 4-11% found for these
compounds. In case of compound 6 no sufficient amount was available for
analysis, due to strong electrostatic problems during weighing.
Thermodynamically, the formation of the σ-vinyl complex
3 is thought to be considerably facilitated due to the phenyl

Article
Organometallics, Vol. 29, No. 6, 2010 1335
Scheme 3. Vinylic Deprotonation of 1-Vinylnaphthalene Complex 4
4 was dissolved in methanol, its characteristic yellow color dis-
appeared immediately, giving a colorless solution. This indi-
cates the immediate addition of methanol at the C-C double
bond, forming the corresponding methoxyalkyl complex 5
(see Scheme 3), which could be trapped by addition of
NaHCO3 to remove the stoichiometric proton. The isolated
complex 5 was characterized by 1H, 13C, and 31P NMR
spectroscopy (see the Experimental Section).23 In the 31P
the high thermodynamic stability of the σ-vinyl complexes [Pt-
(PNP)(CHdCHAr)]BF4 (Ar= Ph (3), C10H7 (6)). In contrast,
treatment of the methoxyethyl complex [Pt(PNP)(CH2CH2-
OCH3)]BF4 with excess HBF4 in methanol led directly to the
formation of the ethylene complex [Pt(PNP)(CH2dCH2)]-
(BF4)2, while the corresponding vinyl complex was not ob-
served.2
These results suggest that at the stage of intermediate I (or
complexes 2 þ Hþ and 5 þ Hþ; cf. Schemes 2 and 3) there
exist two pathways in the reverse direction: (i) reverse nucleo-
philic addition (according to the principle of microscopic
reversibility) and (ii) the formation of complexes 3 and 6 by
simultaneous dissociation of ROH2þ. In the case of ethylene
and alkenes with aliphatic substituents the activation barrier
of path ii is presumably so high that no indication for vinylic
deprotonation has been observed. However, if extended
π-conjugation is introduced in the alkene, then the activation
barrier of path ii decreases considerably so that it becomes
readily available. In the reaction of complexes 1 and 4 with
ROH overall, the species [2 þ Hþ] and [5 þ Hþ] represent
kinetic products, while the σ-vinyl complexes 3 and 6 are the
thermodynamic products, respectively. The kinetic products
can be trapped simply by proton removal with NaHCO3 but
react further in the presence of protons.
NMR spectrum a characteristic signal at δ 31.2 (JP-Pt
=
3057 Hz) was observed. Very similar to the case for the in situ
generated complex 2b-d3, the methoxyalkyl complex 5-d3
prepared by dissolution of the π-complex 4 in CD3OD also
transformed slowly to the corresponding σ-vinyl complex 6
[Pt(PNP)(CHdCHC10H7)]BF4 (cf. Scheme 3).23 The process
was monitored by 31P NMR spectroscopy, showing a new
signal at δ 27.1 (JP-Pt = 2931 Hz) which is similar in chemical
shift and P-Pt coupling constant to those of the styryl
complex 3. In the 1H NMR spectrum a doublet at δ 6.97 with
characteristic platinum satellites (2JH-Pt=79 Hz) and a H-H
coupling constant of 16.6 Hz appears for the R-vinyl proton,
which indicates the formation of the E isomer. The observed
rate constant of the transformation of 5-d3 to 6 with an initial
concentration of 15 mM of 5-d3 in CD3OD was determined as
kobs=9.67 ꢀ 10-5 s-1, and the half-life of 5-d3 was found to be
t1/2 = 120 ( 10 min. Considering the somewhat lower initial
concentration of 5-d3 due to the limited solubility in methanol,
the rate constant of transformation of 5-d3 to 6 can be
estimated to be practically the same as that observed for the
vinylic deprotonation of the styrene derivative. This experi-
ment demonstrates that the extended π-conjugation of the
alkenethrough an aromatic groupis crucial toobserve the loss
of the vinylic proton, while the naphthyl group does not seem
to have much influence on the rate. Similarly, treatment of
Despite their mechanistic implications as nucleophiles with
formation of intermediates [2 þ Hþ] or [5 þ Hþ], alcohols or
water can be seen as efficient enough Brønsted bases in the
overall reaction of the vinylic deprotonation. Considering their
low basicity, for example for methanol with pKa(MeOH2þ) =
-2.2, and the low acidity of the free styrene (pKa = 40), it can
be concluded that the coordination of the styrene at the Pt2þ
center allows an extreme enhancement of the acidity of the
vinylic proton by about 43 orders of magnitude.
complex 5 with a large excess of HBF4 Et2O led to the instant
3
Vinylic deprotonation of alkenes in transition-metal com-
plexes can occur by different pathways, depending on elec-
tronic conditions at the metal center. Monocationic PtII
alkene complexes, in comparison, are quite inert toward
methanol and react only with stronger basic nucleophiles
(e.g., OH-, MeO-) to form the corresponding addition
products.24 Vinylic deprotonation of [PtCl(CH2dCHPh)-
(tmeda)]ClO4 occurred with NEt3 and anhydrous Na2CO3
by external proton abstraction.9 The resulting styryl complex
which forms E and Z isomers can be also reversibly repro-
tonated, showing an overall Brønsted acid-base equilibrium
similar to that observed between complexes 1 and 3.
formation of complex 6.
The mechanistic pathway of the vinylic deprotonation of the
dicationic alkene complexes complex 1 and 4 can be described
as follows. Although the styrene and 1-vinylnaphthalene mo-
lecules are highly activated in the dicationic platinum(II) com-
plexes 1 and 4 in terms of a promoted slipping from the η2 to η1
coordination mode, no direct spontaneous dissociation of the
vinylic proton has been observed in acceptor solvents such as
CH2Cl2 and CH3NO2. However, alcohols or water, which may
actually act as Brønsted bases for a direct vinylic deprotona-
tion, add preferably at the C-C double bond. Thus, the oxygen
donor nucleophile helps first to unfold the styrene molecule
from the η2 to η1 coordination mode by formation of the
thermodynamically labile oxonium intermediate I. The alcohol
or water molecules are, on the other hand, also good leaving
groups. As the kinetic studies showed, they display individual
rates: methanol dissociates somewhat faster than ethanol.
The leaving ROH molecule acts probably as the closest and
most efficient base to promote a very fast intramolecular,
vicinal deprotonation. That this deprotonation occurs even in
Vinylic deprotonation of coordinated alkenes in cationic
ReII complexes of the type [Re(η5-C5H5)(NO)(PPh3)(CH2d
CHR)]BF4 has been studied in detail using t-BuO-Kþ as the
Brønsted base (pKa(t-BuOH) = 19).7 In this case proton-
ation of the resulting vinyl complex with HBF4 Et2O did not
3
give back the parent stryene complex, but a cationic alkyli-
dene rhenium complex was formed.
(24) Maresca, L.; Natile, G.; Rizzardi, G. Inorg. Chim. Acta 1980, 38,
53–57.
the presence of excess HBF4 Et2O (pKa = -5) demonstrates
3

1336 Organometallics, Vol. 29, No. 6, 2010
Hahn
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for
[Pt(PNP)(CHdCHPh)]BF4 (3; Molecules 3A and 3B)
molecule 3A
molecule 3B
Pt-P(1)
2.2896(18)
2.2893(18)
2.125(4)
2.005(6)
1.322(9)
1.478(9)
1.824(6)
1.854(6)
164.36(6)
81.81(13)
82.91(13)
98.56(18)
96.89(18)
176.6(2)
128.0(7)
130.3(6)
2.2775(19)
2.2840(18)
2.110(4)
2.012(6)
1.322(8)
1.458(9)
1.836(6)
1.844(6)
165.12(5)
83.00(13)
82.27(13)
96.21(17)
98.53(17)
179.1(2)
128.5(7)
127.9(5)
Pt-P(2)
Pt-N
Pt-C(1)
C(1)-C(2)
C(2)-C(3)
P(1)-C(14)
P(2)-C(27)
P(1)-Pt-P(2)
P(1)-Pt-N
P(2)-Pt-N
P(1)-Pt-C(1)
P(2)-Pt-C(1)
N-Pt-C(1)
C(1)-C(2)-C(3)
Pt-C(1)-C(2)
double bond. Packing forces may be likely responsible for the
respective distortions.
Figure 5. ORTEP view of the complex cation [Pt(PNP)(CHd
CHPh)]þ (3A).
Conclusion
A spontaneous vinylic C-H bond activation occurred
when the iridium(I) cyclooctene complex [{Ir(COE)2Cl}2]
was reacted with the tridentate PNP ligand 2,6-bis((di-tert-
butylphosphino)methyl)pyridine.8a An iridium(III) hydrido
vinyl complex formed by oxidative addition of the vinylic
C-H bond. In contrast, the analogous rhodium(I) complex
[{Rh(COE)2Cl}2] did not undergo vinylic C-H bond activa-
tion. This is analogous to the case for the “active” platinum
complex [Pt(PNP)(CH2dCHPh)]2þ (1), while no indication
of a vinylic deprotonation was observed with the isostructur-
al palladium complex [Pd(PNP)(CH2dCHPh)]2þ under si-
milar conditions (see above).
The X-ray structure analysis of the platinum styrene
complex [Pt(PNP)(CH2dCHPh)]2þ shows close structural
similarities to that of the analogous palladium styrene com-
plex, in particular the significantly different metal-carbon
bond lengths of M-CH2 and M-CHPh. This feature in-
dicates an incipient slipping of the C-C double bond and
carbocationic character at the substituted carbon atom.
Vinylic deprotonation was observed, however, only with
the platinum styrene complex. Platinum may probably form
a stronger M-C σ-bond in the resulting styryl complex than
palladium does. The spontaneous vinylic deprotonation is
also limited to the complexes of aromatic alkenes. It did not
occur with the analogous ethylene or other alkyl alkene
complexes. The aryl group has a strong stabilizing effect in
the vinyl complex through extended π-conjugation and
provides the main thermodynamic driving force of the
equilibrium system. A further factor, which opens this
particular reaction path, is the use of water or alkohols
(MeOH, EtOH) as weakly basic nucleophiles. The rate-
limiting factor in this process seems to be the ease of the
reversible dissociation of the nucleophile from the former
olefinic carbon atom. The rate of the process is determined
by the type of nucleophile and even the proton concentra-
tion: the higher the proton concentration, the faster the
reversible nucleophilic addition and hence the faster the
vinylic deprotonation! Although amines are stronger bases
than water or alcohols, they are much poorer leaving groups,
and thus the addition products are quite stable and do not
undergo vinylic deprotonation. Overall it can be concluded
that the vinylic C-H bond is highly activated in the dica-
tionic platinum(II) complex. The proton release depends just
on a very subtle interplay of thermodynamic and kinetic
factors. NMR spectroscopy and X-ray crystal structure
analysis confirm the formation of exclusively the E isomer
in each case.
Molecular Structure of the Platinum(II) σ-Styryl Complex
[Pt(PNP)(CHdCHPh)]BF4 (3). Single crystals of the styryl
complex 3 were grown from a reaction solution of styrene
complex 1 in methanol at room temperature over the course
of 3 days. The unit cell contains two independent molecules
of the styryl complex 3, which display a nearly square-planar
geometry around the metal center. In both molecules the
styryl moiety is in the E configuration, confirming the NMR
spectroscopic data. The structure of the cation 3A is shown in
Figure 5. Selected structural parameters of 3A and 3B are
summarized in Table 2. The average Pt-C bond length in
complex 3 is comparable with Pt-C σ-bonds in other
˚
platinum(II) vinyl complexes (e.g., 2.022 A in trans-[PtBr-
((Z)-CHdCHPh)(PPh3)2]12a and 2.032 A in trans-[PtCl-
˚
(CHdCH2)(PMe2Ph)2]25). In both molecules (3A and 3B)
˚
the C-C double bond has the same length of 1.322 A, which
˚
falls in the range of bond lengths (1.31-1.34 A) found in
vinyl ligands coordinated in other metal complexes. The
˚
˚
C(2)-C(3) bond length (3A, 1.478(9) A; 3B, 1.458(9) A) is
typical for a single bond between two sp2 carbon atoms. The
vinylic double bond in molecule 3A is tilted 47ꢀ from the
normal plane of the complex, and the phenyl group lies
practically in plane with the double bond. In contrast, in
molecule 3B the angle between the double bond and the
normal plane of the complex is observed to be only 27ꢀ,
whereas the phenyl group lies 15ꢀ out of the plane of the
These studies furthermore demonstrate a facile way to
prepare cationic platinum(II) aryl vinyl complexes using
alcohols or water for effective deprotonation of the dicatio-
nic PtII aryl alkene complexes. The PtII complexes 3 and 5 can
be used for further reaction studies representing key inter-
mediates in catalytic cycles.
(25) Cardin, C. J.; Muir, K. W. J. Chem. Soc., Dalton Trans. 1977,
1593–1596.

Article
Organometallics, Vol. 29, No. 6, 2010 1337
Experimental Section
Table 3. Crystal Data and Structure Refinement Details for
[Pt(PNP)(CH2dCHPh)](BF4)2 (1) and
[Pt(PNP)(CHdCHPh)]BF4 (3)
General Consideration. Complexes 1, 2b, 3, and [Pt(PNP)-
(CH2dCH2)](BF4)2 were prepared and isolated under condi-
tions described previously.2 The NMR studies were performed
on a Bruker 250 MHz instrument. CD2Cl2 and CD3OD were
1
3
empirical formula
formula wt
temp (K)
wavelength (A)
cryst syst
C39H35B2F8NP2Pt
948.33
110(2)
1.541 84
monoclinic
P21/c
13.684(3)
11.966(3)
22.420(6)
90
96.020(15)
90
3651.0(15)
4
1.725
8.647
1864
C39H34BF4NP2Pt
860.51
293(2)
0.710 73
triclinic
P1h
12.534(6)
17.101(8)
17.919(8)
70.036(8)
82.643(8)
78.659(8)
3532(3)
˚
received from Aldrich and dried over 3 A molecular sieves. The
1H NMR shifts were referenced to the resonance of the residual
protons. The 31P NMR shifts were referenced to an external
85% H3PO4 standard. The following abbreviations were used
for NMR signals: s, singlet; d, doublet; t, triplet; ps.t, pseudo
triplet; m, multiplet; br, broad.
˚
space group
˚
a (A)
˚
b (A)
X-ray Structure Determination of [Pt(PNP)(CH2dCH-
Ph)](BF4)2 (1) and [Pt(PNP)(CHdCHPh)]BF4 (3).26-28 Details
of the X-ray experiment, data collection and reduction, and final
structure refinement calculation for complexes 1 and 3 are
summarized in Table 3. Suitable crystals of complexes 1 and 3
were selected and fixed to a nylon loop, which in turn was
attached to a copper mounting pin. The crystal of complex 1 was
coated in a cryogenic protectant (Paratone) and was placed in a
cold nitrogen stream maintained at 110 K. Bruker D8 GADDS
and SMART 1000 three-circle X-ray diffractometers and gra-
˚
c (A)
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
4
1.618
4.114
1696
F
calcd (g cm-3
)
μ (mm-1
F000
)
cryst size (mm)
θ range for data
collecn (deg)
0.09 ꢀ 0.09 ꢀ 0.01
0.40 ꢀ 0.30 ꢀ 0.20
3.97-59.99
2.03-25.00
˚
phite-monochromated Cu KR (λ = 1.541 84 A, 40 kV, 40 mA)
˚
and Mo KR radiation (λ = 0.701 73 A, 50 kV, 40 mA) were
index ranges (h, k, l)
h, (15; k, (13;
l, (25
27 490
5335/0.1084
98.4
h, (14; k, (20;
l, (25
32 873
12 170/0.0524
97.7
employed for sample screening and data collection, respectively,
for complexes 1 and 3. Sixty data frames were taken at widths of
0.5ꢀ (1) and 0.3ꢀ (3) with an exposure time of 10 s. Over 200
reflections were centered, and their positions were determined.
These reflections were used in the autoindexing procedure to
determine the unit cell. A suitable cell was found and refined by
nonlinear least-squares and Bravais lattice procedures and
reported in Table 3. The standard data collection consisted of
collection of one hemisphere of data collected using ω scans,
involving the collection of 2520 0.5ꢀ (1) and 2400 0.3ꢀ (3) frames
at fixed angles for φ, 2θ, and χ (2θ = -28ꢀ, χ = 54.73ꢀ), while
varying ω. Each frame was exposed for 10 s (1) or 30 s (3). The
total data collection was performed for a duration of approxi-
mately 24 h at 110 K (1) and 293 K (3). All non-hydrogen atoms
were calculated in ideal positions. The tetrafluoroborate anions
in complex 3 were found disordered over several positions,
which is a common feature for this anion.29 Bond restraints
and distances were applied to model the disorder.
no. of rflns collected
no. of indep rflns/Rint
completeness to
θ = 59.99ꢀ (%)
abs cor
semiempirical from equivalents
0.4934/0.2899
max/min transmissn
refinement method
no. of data/restraints/
params
0.9185/0.5100
full-matrix least squares on F2
5335/0/481
12 170/196/957
goodness of fit on F2
R1 (obsd, I > 2σ(I)/all)
wR2 (obsd, I > 2σ(I)/all)
1.008
1.000
0.0348/0.0499
0.0672/0.0694
0.846/-1.318
0.0342/0.0609
0.0725/0.0867
1.145/-0.611
-3
˚
max/min ΔF (e A
)
1H, OCHaHb), 2.93 (t, 2JH-H = 6.5 Hz, 1H, OCHaHb), 3.89 (m,
2JH-Pt = 49 Hz, 1H, CHPhO), 4.21 (m, 2H, PCHaHb), 4.66 (m,
2H, PCHaHb), 6.61 (m, 2H, CPh), 7.08 (m, 3H, CPh), 7.52-8.06
(m, 23H, PPh2, py). 31P NMR (101.25 MHz, EtOH): δ 29.7 (s,
Synthesis and NMR Studies. Synthesis of [Pt(PNP)(CH2-
CHPhOR)]BF4 (R = Me (2b), Et (2c)). The styrene complex 1
(112 mg, 0.118 mmol) was dissolved in 3 mL of methanol (for 2b)
or ethanol (for 2c), and the mixture was stirred for 10 min in the
presence of 3 equiv of NaHCO3. The solution was filtered. The
white product was precipitated by dropwise addition of diethyl
ether to the filtrate. The product was filtered off, washed twice
with 3 mL of diethyl ether, and dried under vacuum.
J
P-Pt = 3077 Hz).
In Situ Preparation of [Pt(PNP)(CH2CHPhOCD3)]BF4
3
-
DþBF4 (2b-d3). A 20 mM solution of styrene complex 1 in
CD3OD was prepared which produces quantitatively 2a-d3 and
1 equiv of DþBF4-. NMR spectra were recorded upon mixing.
1H NMR (250 MHz, CD3OD): δ 2.01 (br, 1H, PtCHaHb), 2.16
(br, 1H, PtCHaHb), 3.69 (br, 1H, PtCHaHb, CHO), 4.62 (m, 4H,
PCH2), 6.63 (br, 2H, Ph), 7.05 (m, 3H, Ph), 7.54-7.68 (m, 8H,
PPh2), 7.80-7.93 (m, 14H, PPh2, py), 8.02 (t, 1H, 3JH-H = 8 Hz,
py). 31P NMR (101.25 MHz, CD3OD): δ 30.5 (s br, w1/2 = 13
Hz, JP-Pt = 3048 Hz).
[Pt(PNP)(CH2CHPhOCH3)]BF4 (2b). Yield: 91% (88 mg,
0.107 mmol). 1H NMR (250 MHz, CD3OD): δ 2.01 (m, 2JH-Pt
=
88 Hz, 1H, PtCHaHb), 2.16 (m, 2JH-Pt = 85 Hz, 1H, PtCHaHb),
2.61 (s, 3H, OCH3), 3.69 (m, 2JH-Pt = 39 Hz, 1H, CHPhO), 4.62
(m, 4H, PCH2), 6.61 (m, 2H, CPh), 7.05 (m, 3H, CPh), 7.54-7.68
(m, 8H, PPh2), 7.80-7.93 (m, 14H, PPh2, 3,5-py), 8.02 (t, 1H,
3JH-H = 8 Hz, 4-py). 31P NMR (101.25 MHz, CD3OD): δ 30.5 (s,
[Pt(PNP)(CHdCHPh)]BF4 (3). Complex 3 was formed in situ
from a solution of 2b-d3 DþBF4- and analyzed after 24 h by NMR
3
spectroscopy. 1H NMR (250 MHz, CD3OD): δ4.76 (ps t, 2þ4JH-P
=
5 Hz, 4H, PCH2), 6.08 (d, 2JH-Pt = 78 Hz, JH-H = 17 Hz, 1H,
PtCHd), 6.78 (m, 2H, Ph), 7.04-7.10 (m, 3H, Ph), 7.53-7.87 (m,
22H, PPh2, 3,5-py), 8.01 (t, 1H, 3JH-H = 8 Hz, 4-py). 31P NMR
(101.25 MHz, CD3OD): δ 27.0 (s, JP-Pt = 2922 Hz).
JP-Pt = 3054 Hz).
[Pt(PNP)(CH2CHPhOCH2CH3)]BF4 (2c). Yield: 95% (102
mg, 0.112 mmol). Anal. Calcd for C41H40BF4NOP2Pt: C, 54.32;
H, 4.45; N, 1.54. Found: C, 53.77; H, 4.38; N, 1.57. 1H NMR (250
MHz, CD2Cl2): δ 0.96 (t, 2JH-H = 6.5 Hz, 3H, CH3), 2.09 (m,
1H, PtCHaHb), 2.12 (m, 1H, PtCHaHb), 2.77 (t, 2JH-H = 6.5 Hz,
[Pt(PNP)(CH2dCHC10H7)](BF4)2 (4). To a solution of
480 mg (0.550 mmol) of [Pt(PNP)(CH2dCH2)](BF4)2 in 50 mL
of dichloromethane was added 3 equiv of 1-vinylnaphthalene
(245 μL, 1.65 mmol). Argon was gently bubbled through the
reaction mixture for 1 h with stirring. The yellow reaction solution
was filtered, and the volume of the filtrate was reduced to 10 mL.
The product was precipitated by dropwise addition of diethyl
ether. The product was filtered off, washed three times with
5 mL of diethyl ether, and dried under vacuum. The product was
obtained as a yellow solid. Yield: 503 mg (0.504 mmol, 92%). Anal.
(26) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(27) Barbour, L. J. J. Supramol. Chem. 2001, 189–191.
(28) (a) SMART (5.632); Bruker Analytical X-ray Instruments Inc.,
Madison, WI, 2000. (b) SAINT (6.45); Bruker Analytical X-ray Instru-
ments Inc., Madison, WI, 2003.
(29) Ishida, H.; Nakai, T.; Kumagae, N.; Kubozono, Y.; Kashino, S.
J. Mol. Struct. 2002, 606, 273-279 and references therein.

1338 Organometallics, Vol. 29, No. 6, 2010
Hahn
PtCHd), 6.99 (d, 1H, JH-H = 8.2 Hz, C10H7), 7.04 (d, 1H,
3
Calcd for C43H37B2F8NP2Pt CH2Cl2: C, 50.90; H, 3.78; N, 1.34.
3
Found: C, 49.09; H, 3.38; N, 1.35. 1H NMR(250 MHz, CD3NO2):
3JH-H = 7.3 Hz, C10H7), 7.11 (dt, 1H, JH-H = 1.3 Hz, 3JH-H
=
δ 4.89 (d ps t, 2H, 2JH-H = 17.6 Hz, 2þ4JH-P = 4.8Hz, PCHaHb),
=
8.5 Hz, C10H7), 7.21 (t, 1H, 3JH-H = 7.5 Hz, C10H7), 7.31 (dt,
4.95 (m, 1H, dCH), 5.31(d ps t, 2H, 2JH-H = 17.6 Hz, 2þ4JH-P
1H, JH-H = 1.2 Hz, JH-H = 8.1 Hz, C10H7), 7.41-8.04 (m,
3
4.8 Hz, PCHaHb), 5.36 (dt, 1H, 3JH-H = 15.2 Hz, 3JH-P = 4.7
Hz, dCH2), 5.53 (d, 1H, 3JH-H = 8.7 Hz, dCH2), 7.03 (d, 1H,
25H, C10H7, =CH, Ph, 3,5-py), 8.11 (t, 1H, 3JH-H = 8.0 Hz, 4-
=
py). 13C NMR (62.89 MHz, CD3OD): δ 45.4 (ps.t, 1þ3JC-P
3JH-H = 7.1 Hz, C10H7), 7.21 (t, 1H, 3JH-H = 7.6 Hz, C10H7),
17.2 Hz, PCH2), 123.4 (s, C10H7), 123.9 (t, JC-P = 8.6 Hz,
PtCHd), 124.0 (ps t, 4JC-P = 5.5 Hz, 3,5-py), 124.7 (s, C10H7),
126.2 (s, C10H7), 126.3 (s, C10H7), 126.6 (s, C10H7), 127.2 (s,
2
3
7.36-8.14 (m, 27H, C10H7, Ph, 3,5-py), 8.27 (t, 1H, JH-H
=
7.7 Hz, 4-py). 13C NMR (62.89 MHz, CD3NO2): δ 45.2 (ps t,
1þ3
J
C-P
= 17.3 Hz, PCH2), 69.6 (s, dCH2), 108.6 (s, dCH), 123.6
0
C10H7), 128.7 (s, C10H7), 129.1 (s, C10H7), 130.8 (ps t, 3þ5JC-P
=
(ps.t, 1JC-P = 30.8 Hz, PPhi), 124.1 (ps t, 1JC-P = 30.8 Hz, PPhi ),
5.6 Hz, PPhm), 133.5 (s, PPhp), 134.5 (ps.t, 2þ4JC-P = 6.8 Hz,
PPho), 135.0 (s, C10H7), 137.4 (t, 3JC-P = 5.2 Hz, dCH), 140.1
3þ5
124.4 (s, C10H7), 126.4 (ps.t,
J
C-P
= 5.5 Hz, 3,5-py), 127.3
(s, C10H7), 127.4 (s, C10H7), 129.2 (s, C10H7), 130.3 (s, C10H7),
(s, 4-py), 141.6 (s, C10H7), 162.1 (t, 3JC-P = 3.6 Hz, 2,6-py). 31
(101.25 MHz, CD3OD): δ 27.1 (s, JP-Pt = 2931 Hz).
P
131.5 (s, C10H7), 131.5 (ps t, 3þ5JC-P = 6.1 Hz, PPhm), 132.1 (s,
C10H7), 132.4 (ps.t, 3þ5JC-P = 5.6 Hz, PPhm ), 134.0 (s, C10H7),
NMR Studies. The progressive formation of complex 3 from
in situ prepared solutions of 20 mM 2b-d3 in CD3OD and 20 mM
2c in EtOH was monitored over time by 1H and 31P NMR
spectroscopy at T = 298 K. In case of the conversion of 2c only
31P NMR spectra were recorded. Similarly, the progressive
formation of complex 6 starting from a 15 mM solution of
5-d3 in CD3OD was monitored by 31P NMR spectroscopy. The
error of the obtained kinetic data is (10%. For monitoring of
the equilibrium of the back-formation of complex 1, a 20-fold
0
2þ4
135.7 (s, PPhp), 134.9 (ps t,
J
C-P
= 6.0 Hz, PPho), 135.9 (s,
0
C10H7), 135.9 (ps.t, 2þ4JC-P = 7.0 Hz, PPho ), 136.2 (s, C10H7),
3
136.4 (s, PPhp ), 146.7 (s, 4-py), 162.9 (ps t, JC-P < 3 Hz, 2,6-py).
0
31P (101.25 MHz, CD2Cl2): δ 37.0 (s, JP-Pt = 2329 Hz).
[Pt(PNP){CH2CH(C10H7)(OCH3)}]BF4 (5). The 1-vinyl-
naphthalene complex 4 (106 mg (0.106 mmol) was dissolved in 2
mL of methanol, and 3 equiv of NaHCO3 was added. After it was
stirred for 5 min, the mixture was filtered through Celite. The
solvent was removed under vacuum. The light brown solid residue
was washed twice with 2 mL of diethyl ether and dried under vacu-
um. Yield: 82 mg (0.092 mmol, 87%). Anal. Calcd for C44H40-
BF4NOP2Pt: C, 56.06; H, 4.28; N, 1.49. Found: C, 52.79; H, 4.06;
N, 1.43. 1H NMR (250 MHz, CD3OD): δ 2.33 (m, 2JH-Pt = 78.9
Hz, 2H, PtCH2), 2.71 (s, 3H, OCH3), 3.82 (m, 1H, CH), 4.43 (m,
4H, PCH2), 6.79 (d, 1H, JH-H = 6.8 Hz, C10H7), 6.98 (dt, 1H,
excess of HBF4 Et2O was added to (i) complex 2b and (ii)
3
complex 3, respectively, in CD3OD.
Acknowledgment. Spring Carlisle, Alicia Lopez,
Bhavisha Bhakta, Jason B. Bracken, and Mayra Miranda
are acknowledged for their experimental contributions.
Dr. J. H. Reibenspies (Texas A&M University, College
Station) is acknowledged for X-ray structure analyses.
This work has been supported by the donors of the
Petroleum Research Fund, administered by the American
Chemical Society (No. 48223-GB3), the Welch Founda-
tion (No. AW-0013), and the NSF-LSAMP program of
the UT system.
JH-H = 6.7 Hz, C10H7), 7.22 (t, 1H, JH-H = 7.3 Hz, C10H7), 7.31
(t, 1H, JH-H = 7.0 Hz, C10H7), 7.53-7.75 (m, 14H, PPh2, 3,5-py),
7.83-7.97 (m, 8H, PPh2), 8.00 (t, 1H, 3JH-H = 7.8 Hz, 4-py). 31
(101.25 MHz, CD2Cl2): δ 31.2 (s, JP-Pt = 3057 Hz).
P
[Pt(PNP)(CHdCHC10H7)]BF4 (6). The vinylnaphthalene
complex 4 (53 mg, 0.053 mmol) was dissolved in 2 mL of
CH3OH. After the solution was stirred for 24 h at room
temperature, the solvent was removed under reduced pressure.
The residue was dissolved in 2 mL of CH2Cl2, and the solution
was filtered through Celite. Diethyl ether (6 mL) was added to
the filtrate, and the product precipitated as a light gray solid.
Yield: 37 mg (0.041 mmol, 78%). Anal. Calcd for C43H36BF4-
NOP2Pt: C, 56.72; H, 3.98; N, 1.54. Found: C, 50.5; H, 3.5; N,
Supporting Information Available: CIF files giving all crystal
data and refinement parameters, atomic coordinates, bond
length, bond angles, and thermal displacement parameters for
complexes 1 and 3 and figures giving NMR spectra of com-
pounds 4-6. This material is available free of charge via the
Internet at http://pubs.acs.org.
1.3. 1H NMR (250 MHz, CD3OD): δ 4.76 (ps t, 4H, 2þ4JH-P
4.0 Hz, PCH2), 6.97 (d, 1H, 3JH-H = 16.6 Hz, 2JH-Pt = 79 Hz,
=