Rearrangement of a σ-2-(cycloprop-2-enyl)vinyl- to an η3-cyclopentadienylplatinum(II) complex. Selective protonolysis of the platinum-methyl bond

Article abstract of DOI:10.1021/om0206507

The σ-2-(cycloprop-2-enyl)vinylplatinum(II) complex (PEt₃)₂Pt(Me)(CH=CH-cyclo-C₃HPh₂) (5) was prepared and characterized by NMR spectroscopy and X-ray crystallography. Treatment of 5 with Bronsted acids results in selective splitting of the Pt - methyl bond to give chloro derivative (PEt₃)₂Pt(Cl)(CH=CH-cyclo-C₃HPh₂) (6), or the rearranged η³-diphenylcyclopentadienyl cation 7⁺, depending on the acid employed. Formation of cation 7⁺ could also be accomplished by treatment of 6 with TIPF₆. Monitoring the protonolysis reactions by NMR spectroscopy at -60 °C, however, showed no evidence for platinabenzene or platinabenzvalene intermediates.

Full text of DOI:10.1021/om0206507

5394
Organometallics 2002, 21, 5394-5400
Rea r r a n gem en t of a σ-2-(Cyclop r op -2-en yl)vin yl- to a n
η3-Cyclop en ta d ien ylp la tin u m (II) Com p lex. Selective
P r oton olysis of th e P la tin u m -Meth yl Bon d
Volker J acob, Timothy J . R. Weakley, and Michael M. Haley*
Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253
Received August 12, 2002
The σ-2-(cycloprop-2-enyl)vinylplatinum(II) complex (PEt3)2Pt(Me)(CHdCH-cyclo-C3HPh2)
(5) was prepared and characterized by NMR spectroscopy and X-ray crystallography.
Treatment of 5 with Bronsted acids results in selective splitting of the Pt-methyl bond to
give chloro derivative (PEt3)2Pt(Cl)(CHdCH-cyclo-C3HPh2) (6), or the rearranged η3-
diphenylcyclopentadienyl cation 7+, depending on the acid employed. Formation of cation
7+ could also be accomplished by treatment of 6 with TlPF6. Monitoring the protonolysis
reactions by NMR spectroscopy at -60 °C, however, showed no evidence for platinabenzene
or platinabenzvalene intermediates.
Sch em e 1. Ap p r oa ch to P la tin a ben zen es a n d
Va len ce Isom er s th r ou gh
In tr od u ction
In our laboratory we have developed a general method
for the synthesis of metallabenzenes1 and their valence
isomers starting from Z-3-(2-iodoethenyl)cyclopropenes
such as 1.2-5 Conversion of this compound to its orga-
nolithium derivative followed by ligand metathesis with
Vaska-type complexes possessing small and/or electron-
donating phosphines yields iridabenzvalenes (e.g., 2)
with a σ-bond to the vinyl group of the vinylcyclopropene
and π-coordination of the cyclopropene CdC double
bond.3,4 Cyclopropene-vinylalkylidene rearrangement,6
initiated either through gentle heating or by use of
larger phosphines, leads to formation of the correspond-
ing iridabenzenes (e.g., 3).2 As part of our efforts to
extend this methodology to other metal complexes, we
recently reported the first example of a platinabenzene
(4)7 in which an (η5-cyclopentadienyl)Pt(II) unit is part
of the metalla-aromatic ring. Interestingly, both the
cyclopentadienyl and metalla-aromatic rings in 4 are
derived from 1 in its reaction with (1,5-cod)PtCl2.
cis-(P R3)2P t(Z-CHdCH-cyclo-C3HP h 2)Y
In ter m ed ia tes
(phosphine)platinum(II) unit, cis-(PR3)2Pt, appeared to
be a good choice to attempt the synthesis of platina-
benzvalenes and -benzenes, as a broad variety of di-
organo complexes of this template with a square-planar
coordinated d8 platinum center are known.8 This tem-
plate should geometrically be well suited for accom-
modation of one σ-/π-coordinated vinylcyclopropene
precursor 1 as well as for the incorporation in the
metalla-aromatic ring of a putative platinabenzene
(Scheme 1). However, a systematic approach to com-
plexes with only one vinylcyclopropene ligand bonded
to the cis-(PR3)2Pt unit is required, as straightforward
stoichiometric reaction of dihalogeno complexes with
organolithium or Grignard compounds often results in
complicated mixtures of starting material, mono- and
To extend this chemistry, we decided to investigate
the reactions with other Pt(II) precursors. The cis-bis-
* To whom correspondence should be addressed. Fax: (541) 346-
0487. E-mail: haley@oregon.uoregon.edu.
(1) Bleeke, J . R. Chem. Rev. 2001, 101, 1205-1227.
(2) (a) Gilbertson, R. D.; Weakley, T. J . R.; Haley, M. M. J . Am.
Chem. Soc. 1999, 121, 2597-2598. (b) Wu, H.-P.; Gilbertson, R. D.;
Lau, T. L.; Lanza, S.; Weakley, T. J . R.; Haley, M. M. Unpublished
results.
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Int. Ed. Engl. 1989, 28, 610-611. (b) Nguyen, S. T.; J ohnson, L. K.;
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tallics 1992, 11, 3933-3935.
(7) J acob, V.; Weakley, T. J . R.; Haley, M. M. Angew. Chem., Int.
Ed. 2002, 41, 3470-3473.
(3) Gilbertson, R. D.; Weakley, T. J . R.; Haley, M. M. Chem. Eur. J .
2000, 6, 437-441.
(8) (a) Organometallic Compounds of Nickel, Palladium, Platinum,
Copper, Silver and Gold; Cross, R. J ., Mingos, D. M. P., Eds.; Chapman
and Hall: London, UK, 1985, pp 163-243. (b) Hartley, F. R. In
Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G.
A., Abel, E. W., Eds.; Pergamon Press: New York, 1982; Vol. 6, pp
471-762.
(4) Wu, H.-P.; Lanza, S.; Weakley, T. J . R.; Haley, M. M. Organo-
metallics 2002, 21, 2824-2826.
(5) Wu, H.-P.; Weakley, T. J . R.; Haley, M. M. Organometallics 2002,
21, 4320-4322.
10.1021/om0206507 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 11/01/2002

Preparation of (PEt3)2Pt(Me)(CHdCH-cyclo-C3HPh2)
Organometallics, Vol. 21, No. 24, 2002 5395
a
Ta ble 1. NMR Sp ectr oscop ic Da ta of Com p ou n d s 5, 6, a n d 7‚O2COCF 3
1H NMR
13C NMR
31P NMRb
PEt3
Ph group
vinylcyclopropene
PEt3
vinylcyclopropene
Ph group
PEt3
5 (CDCl3) 7.79 br d, 4H
3J HH ) 7.5
7.24 m, 1H, PtCH
6.11 m, 1H, CH
1.94 m, 6H 153.1 dd, PtCH
2J PC ) 115, 16
1J PtC ) 789
131.2
129.5
128.7
127.9
s
s
s
s
16.9 m, CH2
9.6 (1825)
8.9 (1766)
2J PP ) 13.5
7.45 t, 4H
1.84 m, 6H 134.8 d, CH
16.1 m, CH2
3J HH )7.5
3J PC ) 4
119.2 br s, CPh
7.33 d, 2H
3.11 br d, 1H, CHCpr 1.14 m, 18H 28.3 d, CHCpr
8.6 d, CH3
2J PC ) 6
3J HH ) 7.5
3J HH ) 8.4
4J PC ) 6
3J PtC ) 110
-0.84 dd, 3H, CH3
3J PH ) 91.2, 7.0
2J PtH ) 574
0.4 dd, CH3
2J PC ) 100, 17
1J PtC ) 566
6 (CDCl3) 7.90 br s, 4H
6.64 ddd, 1H, PtCH 2.00 m, 12H 142.2 dd, PtCH
130.9 br s 17.3 m, CH2
14.6 (1671)
7.6 (4147)
2J PP ) 14.3
3J HH ) 10.2, 9.0
2J PC ) 107, 11,
1J PtC ) 544
1.12 m, 18H 139.1 s, CH
3J PH ) 22
7.46 t, 4H
6.14 ddd, 1H, CH
3J HH ) 10.2,
130.1 br s 15.8 m, CH2
128.8 br s
3J HH ) 7.5
118.0 br s, CPh
4J PH ) 6, 4.5,
3J PtH ) 78
7.32 d, 2H
3.32 br d, 1H, CHCpr
27.9 d, CHCpr
4J PC ) 6
128.1
s
8.7 d, CH3
2J PC ) 7
3J HH ) 7.5
3J HH ) 9.0
3J PtC ) 70
7‚O2CCF3 7.41 m, 4H
(CD2Cl2)
6.25 t, 1H, CHCp′
3J HH ) 3.0
1.73 m, 12H 122.4 s, CPhCp′
96.1 s, CHCp′
132.7
129.4
s
s
19.6 m, CH2
1.1 (4229)
2J PtH ) 37
7.27 m, 6H
5.76 br d, 2H, CHCp′ 0.96 m, 18H 91.1 t, CHCp′
128.9
128.6
s
s
8.2 br s, CH3
3J PtC ) 22
3J HH ) 3.0
2J PC ) 4
a
b
Coupling constants in Hz; data for 7‚BF4 and 7‚PF6 are given in the Experimental Section. 1J PtP values in parentheses.
Sch em e 2
disubstituted products, and low yields.9,10 One possible
route starts with “asymmetric” (PR3)2Pt(X)Y (Scheme
1). Only one of the ligands, X, will be substituted for a
vinylcyclopropene unit while Y remains unchanged. In
the following step Y- is cleaved from the σ-vinyl
compound (PR3)2Pt(Y)(CHdCH-cyclo-C3HPh2), allowing
for coordination of the cyclopropene double bond. De-
pending on its stability either this cationic platinaben-
zvalene or rearranged products such as a platinaben-
were accompanied by considerable decomposition,9
5
zene or a cyclopentadienyl platinum compound will be
was isolated by crystallization from Et2O/hexanes in
isolated. Use of the (PEt3)2Pt template and a halogeno
ligand as primary leaving group X allows for employing
Y ) Me as the secondary anionic leaving group. This
unexpected choice is based on the high degree of
selectivity reported for protonolysis of the chemically
different platinum-carbon bonds in (PEt3)2Pt(alkyl)aryl
compounds.11,12 We report herein our investigations
utilizing the strategy outlined above.
64% yield. In the 31P NMR spectrum (CDCl3) two
1
doublets with nearly identical chemical shifts and J PtP
coupling constants support the cis-(PEt3)2Pt configura-
1
tion in 5 (Table 1). In the H NMR spectrum multiplet
signals for the vinylic protons are found at δ 7.24 and
6.11. The signal for the cyclopropene sp3 proton is a
broad doublet (δ 3.11), different from the broad, shape-
less signal typical for metallabenzvalenes.3-5 Four
signals attributable to the carbon atoms of the σ-coor-
dinated C5 precursor are found in the 13C NMR spec-
trum of 5, along with signals for the aromatic carbons,
ethyl groups, and the Pt-bonded methyl group.
Synthesis of 5 provided the desired starting material
in which the cis-(PEt3)2Pt moiety is affixed to one
σ-bonded vinylcyclopropene. Selective removal of the
secondary leaving group Y ) Me was attempted by
treatment with an equimolar amount of Bronsted acid.
To accomplish this in 5, however, required discrimina-
tion between the Pt-Me bond and the Pt-C(sp2) bond
to the vinylcyclopropene ligand instead of a Pt-C(sp2)
bond to the aryl ligand in (PEt3)2Pt(alkyl)aryl com-
pounds.11,12 After successful cleavage of the Pt-Me
bond, products can result from coordination of either
the cyclopropene double bond (noncoordinating acid
anion case, e.g. BF4-) or the acid anion A- (e.g. Cl-) by
the Pt center. The latter case has the systematic
Resu lts a n d Discu ssion
Lithiation of vinylcyclopropene 1 with BuLi followed
by reaction with trans-(PEt3)2Pt(Me)I13 yielded cis-
(PEt3)2Pt(Me)(Z-CHdCH-cyclo-C3HPh2), 5 (Scheme 2).
While attempts to purify the product by chromatography
(9) Hackett, M.; Whitesides, G. M. J . Am. Chem. Soc. 1988, 110,
1449-1462.
(10) Cardin, C. J .; Cardin, D. J .; Parge, H. E.; Sullivan, A. C. J .
Chem. Soc., Dalton Trans. 1986, 2315-2320.
(11) J awad, J . K.; Puddephatt, R. J .; Stalteri, M. A. Inorg. Chem.
1982, 21, 332-336.
(12) (a) Romeo, R.; Plutino, M. R.; Elding, L. I. Inorg. Chem. 1997,
36, 5909-5916. (b) Alibrandi, G.; Minniti, D.; Scolaro, L. M.; Romeo,
R. Inorg. Chem. 1988, 27, 318-324. (c) Alibrandi, G.; Minniti, D.;
Romeo, R.; Uguagliati, P.; Calligari, L.; Belluco, U.; Crociani, B. Inorg.
Chim. Acta 1985, 100, 107-113.
(13) (a) Michelin, R. A.; Mozzon, M.; Berin, P.; Bertani, R.; Benetollo,
F.; Bombieri, G.; Angelici, R. J . Organometallics 1994, 13, 1341-1350.
(b) Chatt, J .; Shaw, B. L. J . Chem. Soc. 1959, 705-716.

5396 Organometallics, Vol. 21, No. 24, 2002
J acob et al.
Sch em e 3. Rea ction of 5 w ith Br on sted Acid
Rea gen ts
advantage that it may allow for the isolation of an
intermediate cis-(PEt3)2Pt(A)(Z-CHdCH-cyclo-C3HPh2).
Removal of the anionic leaving group A- can be per-
formed in a separate second step in the absence of
protons, which the desired platinabenzenes and -benz-
valenes might well be sensitive toward.
A method for the replacement of methyl for chloride
ligands at a Pt(II) center has been introduced by Clark
and Manzer.14 Their in situ generation of hydrochloric
acid proved convenient for the conversion of 5 into 6
(Scheme 3). Treatment of a solution of 5 in Et2O/MeOH
(3:1) with an equimolar amount of acetyl chloride led
to formation of cis-(PEt3)2Pt(Cl)(Z-CHdCH-cyclo-C3-
HPh2), 6. The compound precipitated from the reaction
solution and was isolated in good yield. Small amounts
of 1,2-diphenyl-3-vinylcyclopropene and trans-(PEt3)2-
Pt(Me)Cl, derived from protonolysis of the Pt-C(sp2)
bond, as well as cis-(PEt3)2PtCl2, were formed as byprod-
ucts. The 31P NMR spectrum of 6 (CDCl3) shows two
F igu r e 1. Molecular structure of 6; ellipsoids are drawn
at the 30% probability level.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in Com p ou n d s 5 a n d 6
5 (Y ) Me)
6 (Y ) Cl)
Pt-P1
Pt-P2
Pt-Y
Pt-C1
C1-C2
C2-C3
C3-C4
C3-C5
C4-C5
2.305(3)
2.290(3)
2.119(12)
2.043(9)
1.318(14)
1.473(15)
1.535(15)
1.519(20)
1.297(21)
2.356(2)
2.224(2)
2.399(2)
2.043(8)
1.334(11)
1.480(12)
1.486(12)
1.495(12)
1.304(11)
1
doublets with strongly different J PtP coupling constants
(Table 1); the signal at δ 7.6 is assigned to the phos-
phorus nucleus trans to the hydrocarbon ligand. Mul-
tiplets for the vinyl protons and a doublet signal for the
cyclopropenyl proton are observed in the 1H NMR
spectrum, along with the ethyl groups and aromatic
protons. The signal of the ortho phenyl protons at δ 7.90,
however, does not display the expected doublet shape
but is extremely broadened. This is mirrored in the 13C
NMR spectrum by the ortho and ipso phenyl carbons
as well as by the quaternary carbon atoms of the
cyclopropene ring, which give rise to similarly broad-
ened signals. This observation can be attributed to a
possible influence of the Pt center on the tethered
cyclopropene moiety in close proximity. NMR data for
5 and 6, however, differ from those of iridabenzvalenes
(e.g. 2), excluding the existence of five-coordinate Pt
species in solution.
P1-Pt-P2
P1-Pt-Y
P2-Pt-C1
Y-Pt-C1
P1-Pt-C1
P2-Pt-Y
Pt-C1-C2
C1-C2-C3
100.73(9)
86.3(3)
90.2(3)
105.53(7)
84.99(7)
84.2(2)
83.0(4)
85.5(2)
167.7(3)
172.8(3)
132.1(8)
126.2(9)
169.5(2)
169.00(7)
125.5(6)
127.8(7)
groups. The overall features of the solid state structures
are very similar (Table 2); therefore, only the structure
of 6 is depicted in Figure 1. The vinylcyclopropene
moiety is σ-bonded to a square-planar coordinated Pt-
(II) center. The Pt-C(sp2) bond (2.043 Å) is of the same
length in 5 and 6 and significantly shorter than the Pt-
Me bond (2.119 Å) in 5.15 As expected, the Pt-P bond
lengths in 5 are nearly identical, while in 6 the Pt-P1
bond trans to the hydrocarbon ligand is distinctly longer
than Pt-P2 trans to the chloro ligand owing to different
trans influences (2.356 Å vs 2.224 Å). The angles around
the Pt(II) center show a pattern dominated by the steric
bulk of the ligands. The Z-configuration of the vinylic
CdC double bond is retained throughout the complete
Crystals suitable for X-ray crystallography were
obtained both for the methyl derivative 5 (pentane, 0
°C) and the chloro derivative 6 (Et2O, 0 °C). Both
compounds crystallize without inclusion of solvent
molecules, yet in different crystal systems and space
(14) Clark, H. C.; Manzer, L. E. J . Organomet. Chem. 1973, 59, 411-
428.
(15) Cardin, C. J .; Muir, K. W. J . Chem. Soc., Dalton Trans. 1977,
1593-1596.

Preparation of (PEt3)2Pt(Me)(CHdCH-cyclo-C3HPh2)
Organometallics, Vol. 21, No. 24, 2002 5397
reaction sequence leading from 1 to 6. The fact that the
tethered cyclopropene double bond, which could easily
move into a favorable position for η2-coordination by
rotation about the C3-C4 bond (Figure 1), is bent away
from the metal center can be attributed to the propen-
sity of Pt(II) for square-planar geometry. Therefore, a
well-defined Pt-cyclopropene bonding interaction in
solution cannot account for the observed signal broad-
1
ening in the H and 13C NMR spectra of 5 and 6.
A change in product composition is observed when
CF3CO2H with the less well coordinating trifluoroac-
etate anion is used as the proton source (Scheme 3).
Addition of 1 equiv of CF3CO2H to a light yellow solution
of 5 in Et2O results in a color change to orange-yellow.
After the reaction mixture was stirred overnight, 7‚O2-
CCF3 precipitated and was isolated by filtration as an
orange solid in 52% yield. Two signals at δ 5.76 and 6.25
(ratio 2:1, Table 1) in the 1H NMR spectrum of this
compound show that Pt-mediated rearrangement16 of
the C5-vinylcyclopropene precursor, presumably through
the stages of an intermediate platinabenzvalene and
-benzene, which undergoes metal extrusion followed by
ring closure,4,7 to the 1,2-diphenylcyclopentadienyl
ligand17 has taken place. Comparison with the corre-
sponding signals of 4, in which the 1,2-diphenylcyclo-
pentadienyl ligand is η5-coordinated to a Pt(II) center
2
(δ 5.09 (1H) and 5.36 (2H); J PtH not resolved),7 shows
two differences: (1) a coupling 2J PtH ) 37 Hz is observed
for the signal of the single proton in 7‚O2CCF3, and (2)
the sequence of chemical shifts is reversed, so that this
signal appears downfield of the doublet for the two
protons. These two findings advocate allylic η3- rather
than η5-coordination of the 1,2-diphenylcyclopentadienyl
ligand of 7+ in solution.18,19 To identify possible inter-
mediates, the protonolysis reaction was carried out at
-60 °C and monitored by 1H and 31P NMR spectroscopy;
cis-(PEt3)2Pt(OCOCF3)(CHdCH-cyclo-C3HPh2) (8) formed
exclusively as the initial product. While this compound
was stable in solution at low temperature, warming
resulted in formation of 7‚O2CCF3 and of isomerized
trans-(PEt3)2Pt(OCOCF3)(CHdCH-cyclo-C3HPh2) in a
ratio of 3:2 after equilibration at room temperature for
15 h. The 1H NMR spectra, however, do not provide any
F igu r e 2. Molecular structure of 7‚O2CCF3; ellipsoids are
drawn at the 30% probability level. Left: Cation 7+.
Right: Reduced view of 7+ parallel to the cyclopentadienyl
plain (ethyl and phenyl carbon atoms are omitted for
clarity; C2 and C3 are eclipsed by C1 and C5, respectively).
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) in th e Ca tion P or tion of 7‚O2CCF 3
Pt-C1
Pt-C2
Pt-C3
Pt-C4
Pt-C5
Pt-P1
Pt-P2
2.508(3)
2.587(3)
2.319(3)
2.258(3)
2.252(3)
2.255(1)
2.253(1)
C1-C2
C2-C3
C1-C5
C3-C4
C4-C5
P1-Pt-P2
1.405(4)
1.461(4)
1.451(4)
1.413(5)
1.400(5)
97.59(3)
(16) (a) Hughes, R. P.; Lambert, J . M. J .; Rheingold, A. L. Organo-
metallics 1985, 4, 2055-2057. (b) Grabowski, N. A.; Hughes, R. P.;
J aynes, B. S.; Rheingold, A. L. J . Chem. Soc., Chem. Commun. 1986,
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Group; Rappoport, Z., Ed.; Wiley: New York, 1995; Vol. 2, pp 495-
695. (d) Binger, P.; Bu¨ch, H. M. Top. Curr. Chem. 1987, 135, 77-155.
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S.-G.; Lee, H.-K.; Lee, S. S.; Chung, Y. K. Organometallics 1997, 16,
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Chem. Soc., Dalton Trans. 1980, 1200-1207, 1208-1219, and 1220-
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Lewis, J . J . Chem. Soc., Dalton Trans. 1973, 1848-1852. (d) Mann,
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evidence for postulated platinabenzvalene or platina-
benzene intermediates in the vinylcyclopropene-cyclo-
pentadienyl rearrangement.
X-ray structure analysis of 7‚O2CCF3 was performed
on red crystals grown by vapor-phase diffusion of Et2O
into a CH2Cl2 solution of the compound. In the solid
state the (PEt3)2Pt moiety is coordinated to a 1,2-
diphenylcyclopentadienyl (Cp′) ligand (Figure 2) with
noncoordinated trifluoroacetate serving as the counte-
rion (not shown). Since the Pt(CH)Cp′ distances are
distinctly shorter than the Pt(CPh)Cp′ distances (Table
3), the 1,2-diphenylcyclopentadienyl ligand has to be
regarded as η3-coordinated. Nothing comparable was
observed for the structure of 47 or [CpPt(dppe)]SO3-
CF3,20 where all Pt-C distances are of essentially equal
length; thus, the authors claim η5-coordination in both
cases. No steric interactions that would force ring-
(20) Fallis, S.; Rodriguez, L.; Anderson, G. K.; Rath, N. P. Organo-
metallics 1993, 12, 3851-3855.

5398 Organometallics, Vol. 21, No. 24, 2002
J acob et al.
slipping are apparent in either case. The distances
CHCp′-CHCp′ and CPhCp′-CPhCp′ are significantly shorter
than CHCp′-CPhCp′, so that the 1,2-diphenylcyclopen-
tadienyl ligand in 7+ is bisected into the coordinating
C3H3- and the more distant CPhdCPh unit. Compari-
son of the η3-coordinated allyl unit in 7+ with structural
data for [(η3-C3H5)Pt(PCy3)2]+ 21 consequently reveals
distinct similarities. Again, the results of solid-state
structural analysis are in agreement with NMR data
obtained for solutions of 7+, thus excluding that the
observed ring-slipping could be regarded as exclusively
attributable to crystal packing effects.
cis-(PEt3)2Pt(Cl)(Z-CHdCH-cyclo-C3HPh2), was com-
pletely converted into two new compounds displaying
singlet signals at δ )1.0 (4236 Hz) and 16.1 (2742 Hz).
Assignment of the first signal to the cation 7+ is
supported by the corresponding cyclopentadienyl reso-
nances in the 1H NMR spectrum. The latter signal
belongs to the rearranged complex trans-(PEt3)2Pt(Cl)-
(Z-CHdCH-cyclo-C3HPh2). Resonances for the protons
of the σ-coordinated vinylcyclopropene ligand of this
compound are also present. These results are in good
agreement with observations in the low-temperature
CF3CO2H protonolysis of 5. They can be interpreted
toward competition between the two irreversible pro-
cesses of cis-trans isomerization and ligand exchange/
vinylcyclopropene-cyclopentadienyl rearrangement. No
evidence for platinabenzvalene or -benzene intermedi-
ates is found even when these mild reaction conditions
are applied.
Use of HBF4 with the very poorly coordinating tet-
rafluoroborate anion did not lead to the product mixture
observed with CF3CO2H. Addition of 1 equiv of ethereal
HBF4 solution to a solution of 5 in Et2O cooled to -60
°C was followed by immediate gas evolution and forma-
tion of a light yellow precipitate, which turned orange
above -30 °C. After the solution was warmed to room
temperature and filtered, orange 7‚BF4 was isolated in
a yield of 86%. Comparison of the NMR spectra of 7‚
BF4 and 7‚O2CCF3 shows identical chemical shifts and
coupling parameters; therefore, the coordination mode
of the cyclopentadienyl ligand in 7+ does not depend on
the counterion present. Protonolysis with HBF4 was
carried out as a low-temperature NMR experiment in
the manner described for the reaction of 5 with CF3-
CO2H, using CD2Cl2 as the solvent for reasons of
solubility. In this case the reaction led to immediate and
exclusive formation of the cyclopentadienyl compound
7‚BF4 at -60 °C. Again, no signals attributable to
postulated platinabenzvalene and platinabenzene in-
Con clu sion s
The platinum(II) center in cis-(PEt3)2Pt(Me)(CHdCH-
cyclo-C3HPh2) (5) displays square-planar coordination
and does not interact with the CdC double bond of the
cyclopropene ring. Protonolysis of 5 with different
Bronsted acids shows distinct similarities with corre-
sponding methyl (aryl) compounds in that the Pt-Me
bond is cleaved selectively.12 The observed dependence
of the product composition from the acid anion is in
accord with the reported influence of anion coordination
propensity on the mechanism of this type of reaction.12
While in the case of poorly coordinating counterions
(BF4-) salts of cation 7+ were formed exclusively, the
main product of protonolysis with hydrochloric acid was
complex 6 containing a σ-bonded vinylcyclopropene and
coordinated chloride. Reaction of 5 with CF3CO2H gave
7‚O2CCF3 as the main product; however, trans-(PEt3)2-
Pt(OCOCF3)(CHdCH-cyclo-C3HPh2) was generated as
an additional product.
The formation of the (η3-1,2-diphenylcyclopentadi-
enyl)Pt(PEt3)2 cation 7+ is best explained by Pt-medi-
ated rearrangement of the coordinated vinylcyclopro-
pene,7 presumably passing through the stages of a
highly reactive platinabenzvalene and/or platinaben-
zene (Scheme 1). The role of the Pt center in this process
has been established by chloride abstraction from 6
working in the absence of reactants more acidic than
methanol, thus excluding mere acid catalysis. Platina-
benzvalene or -benzene intermediates could be observed
in none of the investigated cases; consequently, the cis-
(PEt3)2Pt unit is not capable of stabilizing a platina-
benzene moiety in a way comparable to that of the (η5-
cyclopentadienyl)Pt unit in 4.7 The known examples of
square-planar bis(phosphine)platinum complexes with
simultaneous coordination of σ-alkyl and carbene ligands,
requisite for platinabenzene formation, have the trans
configuration.23 Stabilization through formation of the
metalla-aromatic ring system is obviously not sufficient
to compensate for adopting the less favorable cis con-
1
termediates were found in the H NMR spectra.
In compound 6, the methyl moiety introduced to direct
reactivity toward monosubstitution in the synthesis of
5 is replaced by the “conventional” anionic leaving group
Y ) Cl. Abstraction of this ligand can be effected by a
variety of reagents, TlPF6 being one representative
example. Reaction of 6 with an equimolar amount of
TlPF6 in THF results in immediate formation of cyclo-
pentadienyl complex 7‚PF6, indicated by a change of
color to red. 31P and 1H NMR spectra of the CD2Cl2
extract show that the reaction proceeds cleanly without
considerable formation of byproducts.
Studies on the isomerization of cis-(PEt3)2Pt(Cl)R to
the corresponding trans complexes22 in protic solvents
capable of stabilizing chloride anions by solvation
postulate a dissociative mechanism involving 14-elec-
tron intermediates [(PEt3)2PtR]+. Solvolysis should
therefore provide a way to open the coordination site
occupied by the chloride and avoid use of both Lewis
and Bronsted acids stronger than the solvent. The
cyclopropene double bond in 6 should be preorganized
in an extremely favorable position to trap such an
unsaturated intermediate intramolecularly by coordina-
tion, leading to ligand exchange rather than cis-trans
rearrangement.
Dissolving colorless 6 in CD3OD at room temperature
resulted in an orange solution. Investigation by 31P
NMR spectroscopy showed that the starting material,
(23) (a) Clark, H. C.; J ain, V. K.; Rao, G. S. J . Organomet. Chem.
1983, 259, 275-282. (b) Belluco, U.; Bertani, R.; Fornasiero, S.;
Michelin, R. A.; Mozzon, M. Inorg. Chim. Acta 1998, 275-276, 515-
520. (c) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M.; Benetollo,
F.; Bombieri, G.; Angelici, R. J . Inorg. Chim. Acta 1995, 240, 567-
574. (d) Stang, P. J .; Huang, Y.-H. J . Organomet. Chem. 1992, 431,
247-254.
(21) Smith, J . D.; Oliver, J . D. Inorg. Chem. 1978, 17, 2585-2589.
(22) (a) Romeo, R.; Minniti, D.; Lanza, S. Inorg. Chem. 1980, 19,
3663-3668. (b) Blandamer, M. J .; Burgess, J .; Romeo, R. Inorg. Chim.
Acta 1982, 65, L179-L180. (c) Blandamer, M. J .; Burgess, J .; Minniti,
D.; Romeo, R. Inorg. Chim. Acta 1985, 96, 129-135.

Preparation of (PEt3)2Pt(Me)(CHdCH-cyclo-C3HPh2)
Organometallics, Vol. 21, No. 24, 2002 5399
was isolated by filtration, washed with Et2O (1 mL), and dried
in vacuo (61 mg, 40%). A second crop of product (18 mg, 12%)
was isolated from the ether filtrate after an additional 24 h of
stirring. Compound 7‚O2CCF3 crystallized from CH2Cl2/Et2O
in red blocks suitable for X-ray structural analysis. IR (KBr)
ν 1685 (vs), 1196 (s), 1154 (s), 1116 (s) cm-1. UV/vis (CH2Cl2)
λmax (ꢀ) 460 nm (750). MS (ESI-Pos, MeOH) m/z 648 (100, M+
- O2CCF3). Anal. Calcd for C31H43F3O2P2Pt‚CH2Cl2 (858.64):
C, 46.16; H, 5.28. Found: C 46.37, H 5.69.
P r oton olysis of 5 w ith CF 3CO2H a t -60 °C. Complex 5
(20.6 mg, 0.031 mmol) was suspended in THF-d8 (0.5 mL) in
an NMR tube and cooled to -60 °C. CF3CO2H (3 µL, 0.039
mmol) was added via syringe. The sample was transferred into
the pre-cooled spectrometer and investigated by 1H and 31P
NMR spectroscopy at -60 °C, which revealed exclusive forma-
tion of cis-(PEt3)2Pt(OCOCF3)(CHdCH-cyclo-C3HPh2) (8): 1H
figuration as metal extrusion with concomitant ring
closure to form the cyclopentadienyl ligand occurs
instead.
Exp er im en ta l Section
Gen er al. Reactions were carried out using standard Schlenk
technique in an inert atmosphere (dry Ar or N2) when
necessary. THF and Et2O were distilled from Na/benzophenone
under nitrogen prior to use. Unless stated otherwise solvents
and reagents were purchased commercially and used as
received. Z-1,2-Diphenyl-3-(2-iodoethenyl)cyclopropene (1)2 and
trans-(PEt3)2Pt(Me)I12 were prepared by literature methods.
1H (299.94 MHz), 13C (75.43 MHz), and 31P (121.42 MHz) NMR
spectra were recorded using a Varian Inova 300 NMR spec-
trometer. Chemical shifts are expressed in ppm downfield from
tetramethylsilane using the residual solvent as internal
NMR (C4D8O, 213 K) δ 7.78 (d, 4H, CHarom
,
3J HH ) 7.0 Hz),
3
3
1
1
standard (CDCl3, H 7.27 ppm and 13C 77.2 ppm; CD2Cl2, H
7.41 (pt, 4H, CHarom, J HH ) 7.3 Hz), 7.28 (t, 2H, CHarom, J HH
3
5.32 ppm and 13C 54.0 ppm; CD3OD, 1H 4.87 and 3.31 ppm
) 7.3 Hz), 6.76 (m, 1H, PtCH), 5.92 (ddd, 1H, CH, J HH ) 8.8,
4
3
and 13C 49.2 ppm; C4D8O, H 3.57 and 1.72 ppm and 13C 67.4
1
10.5 Hz, J PH ) 21.1 Hz), 3.41 (d, 1H, CHCpr, J HH ) 8.8 Hz),
2.06 (m, 6H, CH2), 1.81 (m, 6H, CH2), 1.21 (m, 18H, CH3). 31P
and 25.3 ppm). 31P NMR shifts are expressed in ppm downfield
to 85% H3PO4/H2O as external standard. Coupling constants
are expressed in Hz. IR spectra were recorded using a Nicolet
Magna-FTIR 550 spectrometer. UV/vis spectra were recorded
in CH2Cl2 using a Hewlett-Packard 8453 UV-vis spectropho-
tometer. Mass spectra were recorded using an Agilent 1100
Series LC/MSD spectrometer (API-ES, APCI). Melting points
were determined on a Meltemp II apparatus and are uncor-
rected. Elemental analyses were performed by Robertson
Microlit Laboratories, Inc.
2
1
NMR (C4D8O, 213 K) δ 2.9 (d, J PP ) 12 Hz, J PtP ) 4412 Hz),
2
1
19.8 (d, J PP ) 12 Hz, J PtP ) 1774 Hz).
The yellow solution turned orange upon warming to room
temperature. Additional NMR spectra were taken, showing
the complete disappearance of 8 after 15 h and formation of
compounds 7‚O2CCF3 and trans-(PEt3)2Pt(OCOCF3)(CHdCH-
cyclo-C3HPh2) in ca. 3:2 ratio. 7‚O2CCF3: 1H NMR (C4D8O) δ
3
2
6.39 (t, 1H, CHCp′, J HH ) 3.0 Hz, J PtH ) 37 Hz), 6.02 (br d,
3
2H, CHCp′, J HH ) 3.0 Hz), 0.98 (m, 18H, CH3), aromatic CH
and ethyl CH2 resonances not assigned. 31P NMR (C4D8O) δ
cis-(P Et3)2P t(Me)(Z-CHdCH-cyclo-C3HP h 2) (5). Cyclo-
propene 1 (546 mg, 1.59 mmol) was dissolved in dry Et2O (20
mL) under Ar and cooled to -78 °C. BuLi (0.635 mL, 2.5 M in
hexanes, 1.60 mmol) was added dropwise and the resulting
yellow solution was stirred for 15 min. The cooled lithiate
solution was transferred via cannula into a Schlenk flask
charged with trans-(PEt3)2Pt(Me)I (867 mg, 1.51 mmol). The
mixture was allowed to warm to room temperature and stirred
for 12 h before quenching with a few drops of H2O and
filtration through a thin pad of silica. The yellow filtrate was
evaporated to ca. 1 mL, layered with hexanes (5 mL), and
stored at 0 °C overnight to yield pale yellow crystals of 5 (550
mg, 55%). A second crop of crystals (93 mg, 9%) was obtained
from the mother liquor upon concentration and cooling, for an
overall yield of 64%. Crystals suitable for X-ray analysis were
obtained by cooling a saturated pentane solution of 5 to 0 °C;
mp 109 °C dec. IR (KBr) ν 1811 (m) cm-1. MS (ESI-Pos, MeOH)
1.5 (s, J PtP ) 4265 Hz). trans-8: 1H NMR (C4D8O) δ 6.84 (dt,
1
3
3
3
1H, PtCH, J HH ) 10.0, J PH ) 3.0 Hz), 5.57 (t, 1H, CH, J HH
) 10.0 Hz, J PtH ) 136 Hz), 3.26 (d, 1H, CHCpr,
3J HH ) 10.0
3
Hz), 1.20 (m, 18H, CH3), aromatic CH and ethyl CH2 reso-
nances not assigned. 31P NMR (C4D8O) δ 19.4 (s, J PtP ) 2864
1
Hz).
[(η3-C5H3P h 2)P t(P Et3)2]BF 4 (7‚BF 4). Complex 5 (68 mg,
0.102 mmol) was dissolved in Et2O (3 mL) and cooled to -60
°C. HBF4 (0.014 mL, 54% in Et2O, 0.101 mmol) was added
dropwise. The resulting yellow suspension was stirred at -60
°C for 15 min, then allowed to warm. At -30 °C the color of
the precipitate changed from light yellow to orange. After the
mixture was stirred for 2 h at room temperature the orange
precipitate of 7‚BF4 was collected by filtration, washed with
Et2O (2 mL), and dried in vacuo (64 mg, 86%). Compound 7‚
BF4 crystallizes from CH2Cl2/Et2O as red blocks. 1H NMR (CD2-
m/z 648 (100, M+ - Me), 663 (32, M+ - H), 678 (55, M+
+
Cl2) δ 7.47 (m, 4H), 7.36 (m, 4H), 7.33 (m, 2H), 6.31 (t, 1H,
2
CHCp′
,
3J HH ) 3.0 Hz, J PtH ) 37 Hz), 5.80 (br d, 2H, CHCp′
,
Me). Anal. Calcd for C30H46P2Pt (663.71): C, 54.29; H, 6.99;
P, 9.33. Found: C, 54.06; H, 6.86; P, 8.89.
3J HH ) 3.0 Hz), 1.79 (m, 12H, CH2), 1.04 (m, 18H, CH3). 13C
NMR (CD2Cl2) δ 132.7 (s), 129.4 (s), 128.9 (s), 128.6 (s), 122.5
cis-(P Et3)2P t(Cl)(Z-CHdCH-cyclo-C3HP h 2) (6). Complex
5 (128 mg, 0.193 mmol) was dissolved in Et2O/MeOH (3:1, 3
mL) and cooled to -60 °C. Acetyl chloride (0.014 mL, 0.196
mmol) was added dropwise. The resulting yellow solution was
stirred at -60 °C for 5 min and then allowed to warm to room
temperature. A light-yellow precipitate of 6 formed, which was
isolated by filtration after concentration of the mixture to ca.
1 mL. The product was washed with MeOH (0.5 mL) and
pentane (1 mL) and dried in vacuo (86 mg, 65%). Colorless
crystals suitable for X-ray analysis were obtained by cooling
saturated Et2O solutions of 6 to 0 °C; mp 116 °C dec. IR (KBr)
2
3
(s), 96.0 (s), 91.1 (t, J PC ) 4.0 Hz), 19.7 (m), 8.2 (br s, J PtC
)
22.0 Hz). 31P NMR (CD2Cl2) δ 1.1 (s, 1J PtP ) 4229 Hz). IR (KBr)
ν 1084 (vs), 1058 (vs) cm-1. UV/vis (CH2Cl2) λmax (ꢀ) 457 (715)
nm. MS (ESI-Pos, MeOH) m/z 648 (100, M+ - BF4). Anal.
Calcd for C29H43BF4P2Pt (735.48): C, 47.36; H, 5.90; P, 8.42.
Found: C, 47.11; H, 5.91; P, 8.41.
[(η3-C5H3P h 2)P t(P Et3)2]P F 6 (7‚P F 6). Solid TlPF6 (52 mg,
0.15 mmol) was added to a solution of 6 (96 mg, 0.14 mmol) in
THF (3 mL) at room temperature. The mixture turned into
an orange suspension immediately. After the mixture was
stirred for 15 min the solvent was evaporated and the residue
filtered through Celite with CH2Cl2 (5 mL). The filtrate was
evaporated, washed with Et2O (10 mL), and dried in vacuo,
giving 7‚PF6 (95 mg, 86%) as a red-orange solid. The compound
was crystallized from CH2Cl2/Et2O as red plates. 1H NMR (CD2-
ν 1811 (m) cm-1. MS (ESI--Pos, MeOH) m/z 648 (100, M+
-
Cl). Anal. Calcd for C29H43P2ClPt (684.13): C, 50.91; H, 6.35;
P, 9.05. Found: C, 50.86; H, 6.34; P, 9.03.
[(η3-C5H3P h 2)P t(P Et3)2]O2CCF 3 (7‚O2CCF 3). Complex 5
(134 mg, 0.202 mmol) was dissolved in Et2O (3 mL) and cooled
to -60 °C. CF3CO2H (0.016 mL, 0.207 mmol) was added
dropwise and the orange solution was stirred at -60 °C for
10 min, then allowed to warm to room temperature. Stirring
overnight at room temperature led to formation of a red
solution containing an orange precipitate of 7‚O2CCF3, which
Cl2) δ 7.47 (m, 4H), 7.33 (m, 6H), 6.32 (t, 1H, CHCp′, )
3J HH
2
3
3.0 Hz, J PtH ) 37 Hz), 5.82 (br d, 2H, CHCp′, J HH ) 3.0 Hz),
1.81 (m, 12H, CH2), 1.04 (m, 18H, CH3). 13C NMR (CD2Cl2) δ
132.4 (s), 129.4 (s), 128.9 (s), 128.6 (s), 122.4 (s), 96.1 (s), 91.1
(t, J PC ) 6 Hz), 19.7 (m), 8.2 (br s, J PtC ) 22 Hz). 31P NMR
2
3

5400 Organometallics, Vol. 21, No. 24, 2002
Ta ble 4. Cr ysta l Da ta for Com p lexes 5, 6, a n d 7‚O2CCF 3
J acob et al.
5
6
7‚O2CCF3
mol formula
mol wt
C
663.7
30H46P2Pt
C29H43ClP2Pt
684.2
C31H43F3O2P2Pt
761.7
crystal dimens (mm)
cryst syst
space group
Z
0.11 × 0.13 × 0.32
monoclinic
P21
0.33 × 0.40 × 0.43
orthorhombic
P212121
4
0.23 × 0.27 × 0.29
triclinic
P1h
2
2
a (Å)
b (Å)
c (Å)
9.466(2)
16.583(2)
9.8661(13)
90
92.97(2)
90
1546.6(5)
1.425
46.4
10.423(2)
14.476(2)
20.385(3)
90
90
90
3075.7(9)
1.477
47.5
52
1.0-5.5
8.4097(6)
10.9877(6)
17.8086(11)
103.727(5)
90.644(6)
94.374(5)
1593.2(2)
1.588
R (deg)
â (deg)
γ (deg)
V (Å3)
Fcalcd (g cm-3
)
µ (cm-1
)
45.3
52
1.1-5.5
2θmax (deg)
54
0.9-4.1
scan speed (deg min-1
no. of reflns
)
independent
3319
3413
6252
obsd [I g σ(I)]
2712
3258
668
3386
2995
1368
5904
6252(all)
760
used in refinementa
F000
rel corr factors
0.824-1.000
0.683-1.000
0.798-1.000
no. of refined parameters
R(F)/wR [I g σ(I)]
297
299
353
0.033/0.034
0.053/0.070
1.77 (near Pt)/-1.73
0.025/0.028
0.042/0.065
1.11 (near Pt)/-0.77
0.022/0.028
0.036/0.055
0.77 (near Pt)/-0.58
R(F2)/wR (F2) (all)
residual electron density [e Å-3
]
a
Based on (F2); all reflections not systematically absent.
1
1
(CD2Cl2) δ 0.9 (s, J PtP ) 4236 Hz), -143.4 (sept, PF6-, J PF
)
X-r a y Str u ctu r es of 5, 6, a n d 7‚O2CCF 3. Data (Table 4)
were obtained on an Enraf-Nonius CAD-4 Turbo diffractome-
ter, Mo KR radiation, λ ) 0.71073 Å; graphite monochromator;
T ) 298 K; scan mode ω-2θ. Structure refinement (C atoms
anisotropic, H atoms riding) was accomplished with the teXsan
program suite (version 1.7 for SGI workstations).
703 Hz). IR (KBr) ν 841 (vs) cm-1. UV/vis (CH2Cl2) λmax (ꢀ) 458
(670) nm. MS (ESI-Pos, MeOH) m/z 648 (100, M+ - PF6). Anal.
Calcd for C29H43F6P3Pt (793.65): C, 43.89; H, 5.45. Found: C,
44.03; H, 5.21.
Isom er iza tion of 6 in CD3OD. Complex 6 (7 mg, 0.010
mmol) was suspended in CD3OD (1 mL) in an NMR tube and
sonicated for 30 min. The clear orange solution was investi-
gated by H and 31P NMR spectroscopy. 7‚Cl: 1H NMR (CD3-
Ack n ow led gm en t. This research was supported by
the National Science Foundation (CHE-0075246). V.J .
gratefully acknowledges the Alexander von Humboldt
Foundation for a Feodor Lynen Fellowship.
1
3
2
OD) δ 6.39 (t, 1H, CHCp′, J HH ) 3.0 Hz, J PtH ) 37 Hz), 6.06
3
(br d, 2H, CHCp′, J HH ) 3.0 Hz), 1.86 (m, 12H, CH2), 1.04 (m,
18H, CH3), aromatic CH resonances not assigned. 31P NMR
Su p p or tin g In for m a tion Ava ila ble: X-ray structures of
5, 6, and 7‚O2CCF3, structure refinement details, and tables
of atomic coordinates, thermal parameters, bond lengths, bond
angles, torsion angles, and mean planes. This material is
available free of charge via the Internet at http://pubs.acs.org.
(CD3OD) δ 1.0 (s, J PtP ) 4236 Hz). trans-6: 1H NMR (CD3-
1
3
3
OD) δ 6.89 (dt, 1H, Pt-CH, J HH ) 10.0, J PH ) 2.8 Hz), 5.70
(t, 1H, CH, 3J HH ) 10.0 Hz, 3J PtH ) 143 Hz), 3.20 (d, 1H, CHCpr
,
3J HH ) 10.0 Hz), 2.05 (m, 12H, CH2), 1.24 (m, 18H, CH3),
aromatic CH resonances not assigned. 31P NMR (CD3OD) δ
1
16.1 (s, J PtP ) 2742 Hz).
OM0206507