Synthesis of a novel volatile platinum complex for use in CVD and a study of the mechanism of its thermal decomposition in solution

Article abstract of DOI:10.1021/ja9526527

The synthesis, characterization, chemical vapor deposition, and mechanistic investigation of the thermal decomposition in aromatic solvents of cis-bis(η²,η¹-pent-4-en-1-yl)platinum (1) are described. Complex 1 has a unique chelated structure, giving rise to enhanced volatility, and has proved useful for the chemical vapor deposition of thin platinum films under mild conditions. Films deposited on a glass slide in a hot walled glass tube at 175°C have an elemental composition of 82% Pt and 18% C. Kinetic, deuterium labeling and chemical trapping experiments indicate that the decomposition of 1 in aromatic solvents proceeds by reversible β-hydride elimination followed by reversible dissociation of 1,4-pentadiene to give a 3-coordinate platinum hydride intermediate (9). Reductive elimination of 1-pentene from 9 deposits metallic platinum. The rate of decomposition exhibits a significant β-deuterium isotope effect of k_H/k_D=3.8±0.3. Added olefins are rapidly isomerized during the decomposition of 1: trapping experiments with diphenylacetylene indicate that intermediate 9 is the highly active catalyst that is responsible for the alkene isomerization. The synthesis, characterization, chemical vapor deposition, and mechanistic investigation of the thermal decomposition in aromatic solvents of cis-bis(η²,η¹-pent-4-en-1-yl)platinum (1) are described. Complex 1 has a unique chelated structure, giving rise to enhanced volatility, and has proved useful for the chemical vapor deposition of thin platinum films under mild conditions. Films deposited on a glass slide in a hot walled glass tube at 175°C have an elemental composition of 82% Pt and 18% C. Kinetic, deuterium labeling, and chemical trapping experiments indicate that the decomposition of 1 in aromatic solvents proceeds by reversible β-hydride elimination followed by reversible dissociation of 1,4-pentadiene to give a 3-coordinate platinum hydride intermediate (9). Reductive elimination of 1-pentene from 9 deposits metallic platinum. The rate of decomposition exhibits a significant β-deuterium isotope effect of k(H)/k(D) = 3.8 ± 0.3. Added olefins are rapidly isomerized during the decomposition of 1; trapping experiments with diphenylacetylene indicate that intermediate 9 is the highly active catalyst that is responsible for the alkene isomerization.

Full text of DOI:10.1021/ja9526527

2634
J. Am. Chem. Soc. 1996, 118, 2634-2643
Synthesis of a Novel Volatile Platinum Complex for Use in
CVD and a Study of the Mechanism of Its Thermal
Decomposition in Solution
Christopher D. Tagge,† Robert D. Simpson,† Robert G. Bergman,*,†
Michael J. Hostetler,‡ Gregory S. Girolami,*,‡ and Ralph G. Nuzzo*,‡
Contribution from the Department of Chemistry, UniVersity of California,
Berkeley, California 94720-1460, and Department of Chemistry, Department of Material Science
and Engineering, and Frederick Seitz Materials Research Laboratory, UniVersity of Illinois,
UrbanasChampaign, Urbana, Illinois 61801
ReceiVed August 7, 1995. ReVised Manuscript ReceiVed NoVember 16, 1995X
Abstract: The synthesis, characterization, chemical vapor deposition, and mechanistic investigation of the thermal
decomposition in aromatic solvents of cis-bis(η2,η1-pent-4-en-1-yl)platinum (1) are described. Complex 1 has a
unique chelated structure, giving rise to enhanced volatility, and has proved useful for the chemical vapor deposition
of thin platinum films under mild conditions. Films deposited on a glass slide in a hot walled glass tube at 175 °C
have an elemental composition of 82% Pt and 18% C. Kinetic, deuterium labeling, and chemical trapping experiments
indicate that the decomposition of 1 in aromatic solvents proceeds by reversible â-hydride elimination followed by
reversible dissociation of 1,4-pentadiene to give a 3-coordinate platinum hydride intermediate (9). Reductive
elimination of 1-pentene from 9 deposits metallic platinum. The rate of decomposition exhibits a significant
â-deuterium isotope effect of kH/kD ) 3.8 ( 0.3. Added olefins are rapidly isomerized during the decomposition of
1; trapping experiments with diphenylacetylene indicate that intermediate 9 is the highly active catalyst that is
responsible for the alkene isomerization.
Introduction
number of organoplatinum complexes exhibit sufficient volatility
necessary for the CVD technique, and even fewer undergo clean
thermal decomposition to give platinum films. Puddephatt and
co-workers recently reviewed several precursors for platinum
CVD and reported that (MeNC)2PtMe2 produced films of the
highest purity in the absence of added reagents: 88% Pt and
11% C.8 Further studies showed that the addition of H2 as a
carrier gas drastically reduced the carbon contamination in
platinum films for all organoplatinum precursors.13
We wish to report the synthesis of cis-bis(η2,η1-pent-4-en-
1-yl)platinum (1), a novel, volatile organoplatinum complex that
has proved useful for the deposition of unusually pure thin
platinum films. We attribute the high volatility of 1 to the small,
compact shape and low molecular weight imparted by the
chelating pentenyl ligands. We have studied the thermolysis
reactions of 1 in aromatic solvents extensively in both the
presence and absence of added reagents. We have found
evidence that a transient intermediate is a highly active olefin
isomerization catalyst.
Chemical Vapor Deposition (CVD) is an important and
widely used method of fabricating metal thin films from
organometallic precursors. The technique involves the vola-
tilization of an organometallic complex, which is then passed
over a substrate and thermolyzed to deposit a metal film.1
Ideally, the organic remnants of the thermolysis reaction remain
in the gas phase and are easily removed. The temperatures of
the thermolysis reactions are typically thousands of degrees
lower than the temperatures required to generate films by other
techniques. However, often the precursor decomposition reac-
tions are not clean and heteroatoms from the ligands become
incorporated into and reduce the quality of the resulting metal
film. A fundamental understanding of the decomposition
process should lead to the design of precursor complexes that
undergo cleaner thermolysis reactions to produce higher quality
metal films.
Due to the importance of thin platinum films for micro-
electronic2-5 and catalytic6 applications, there has been much
interest in the design and study of organoplatinum complexes
for use as precursors for CVD.7-12 However, only a small
Results
Preparation and Characterization of 1. Treatment of
(COD)PtCl2 with pent-4-en-1-ylmagnesium bromide at 0 °C in
Et2O leads to the formation of 1 and free COD and precipitation
of MgCl2 (eq 1). Complex 1 was purified by sublimation and
† University of California.
‡ University of Illinois.
X Abstract published in AdVance ACS Abstracts, February 15, 1996.
(1) Jensen, K. S.; Kern, W. In Thin Film Processes; Vossen, J. L., Kern,
W., Eds.; Academic Press: Boston, 1991; Vol. II, pp 283-353.
(2) Bindra, P.; Roldan, J. J. Electrochem. Soc. 1985, 132, 2581-2589.
(3) Green, M. L.; Levy, R. A. J. Met. 1985, 37, 63-71.
(4) Shibli, S. M. A.; Noel, M. J. Power Sources 1993, 45, 139-152.
(5) Zimmerman, J. H. J. Power Sources 1991, 36, 253-267.
(6) Dossi, C.; Psaro, R.; Bartsch, A.; Fusi, A.; Sordelli, L.; Ugo, R.;
Bellatreccia, M.; Zanoni, R.; Vlaic, G. J. Catal. 1994, 145, 377-383.
(7) Bradley, D. C. Polyhedron 1994, 13, 1111-1121.
(8) Dryden, N. H.; Kumar, R.; Ou, E.; Rashidi, M.; Roy, S.; Norton, P.
R.; Puddephatt, R. J. Chem. Mater. 1991, 3, 677-685.
(9) Gozum, J. E.; Pollina, D. M.; Jensen, J. A.; Girolami, G. S. J. Am.
Chem. Soc. 1988, 110, 2688-2689.
(10) Puddephatt, R. J. Polyhedron 1994, 13, 1233-1234.
(11) Xue, Z.; Strouse, M. J.; Shuh, D. K.; Knobler, C. B.; Kaesz, H. D.;
Hicks, R. F.; Williams, R. S. J. Am. Chem. Soc. 1989, 111, 8779-8784.
0002-7863/96/1518-2634$12.00/0 © 1996 American Chemical Society

Synthesis of a NoVel Volatile Platinum Complex
J. Am. Chem. Soc., Vol. 118, No. 11, 1996 2635
pentene (5) is shown in Scheme 1. A solution of diethyl (allyl)-
malonate in D2O in the presence of a catalytic amount of acid
was heated at reflux for 1 day. Monodeuterated diacid 2 was
detected by 1H NMR spectroscopy, but was not isolated.
Continued heating for an additional 4 days led to the complete
conversion of 2 to dideuterated acid 3. Reduction with LiAlH4
followed by treatment with PPh3Br2 gave bromide 5. Integration
Figure 1. ORTEP drawing of 1.
1
of the resonances in the H NMR spectrum of 5 indicated that
Scheme 1
2
deuterium incorporation was greater than 95%. A H NMR
spectrum of 5 confirmed that deuterium was present exclusively
in the â-position.
Bromide 5 was treated with Mg, then (COD)PtCl2 to give
1-â-d4 in 50% yield after sublimation (eq 1). Resonances at δ
1.85 (s, broad, 1 D) and 2.17 (s, 1 D, JPtD ) 18 Hz) are the
only two features present in the 2H NMR spectrum; the
deuterium atoms remain exclusively in the â-position of the
pentenyl ligand upon coordination to platinum. Based on the
assumption that the through-bond coupling along Pt-C5-
C4-H is maximized when the dihedral angle is 180° and
smallest when the angle is 90°, the resonance at δ 2.17
(exhibiting JPtD ) 18 Hz) has been assigned to the deuterium
atoms in the pseudo-equatorial position of the puckered chelate
ring. The broadness of the second deuterium resonance
probably results from a smaller, unresolved coupling to plati-
num. In the 13C NMR spectrum of 1-â-d4, the resonance at δ
28.70 (quin, JCD ) 20 Hz) confirms that the deuterium atoms
are present in the â-position. The mass spectrum of 1-â-d4
exhibits the molecular ion at m/e at 337 (195Pt), 4 amu greater
than that for 1. Since no scrambling or D-H exchange was
detected, we conclude that the deuterium incorporation in 1-â-
d4 is similar to that for bromide 5 (greater than 95%).
isolated as yellow crystals in 85% yield. Recrystallization from
an ethanol/pentane (1/1) solution at -15 °C resulted in crystals
that were suitable for X-ray diffraction. Complex 1 is an air-
and moisture-stable, low-melting (40-41 °C), volatile solid,
which is moderately thermally sensitive in the solid state. It
decomposes within 2 weeks at room temperature, but is stable
indefinitely at -15 °C.
1
The H NMR spectrum of 1 displays three distinct alkene
resonances at δ 3.25 (d, 2 H, JHH ) 9 Hz, JPtH ) 28 Hz), 3.65
(d, 2 H, JHH ) 16 Hz, JPtH ) 40 Hz), and 4.45 (m, 2 H). The
upfield shift of the resonances from those of the free alkene
and the magnitude of the Pt-H coupling constants are consistent
with π-coordination of the terminal CdC bond of the pentenyl
ligand to platinum. The alkyl resonances appear as overlapping
multiplets centered at δ 2.00 (m, 12 H) and could not be
resolved. The five resonances present in the 13C NMR spectrum
all exhibit 195Pt coupling and have been assigned based on the
chemical shifts, the magnitude of the C-Pt coupling constants,
and DEPT experiments: δ 28.70 (s, JCPt ) 40 Hz, â-CH2), 32.31
(s, JCPt ) 811 Hz, R-CH2), 33.76 (s, JCPt ) 24 Hz, γ-CH2),
80.00 (s, JCPt ) 50 Hz, dCH2), 113.1 (s, JCPt ) 40 Hz, CH).
The assignment for the â-carbon resonance is further supported
by a deuterium labeling study (vide infra). The molecular ion
appears in the electron ionization mass spectrum at m/e ) 333
Chemical Vapor Deposition. (a) Platinum Films. Chemi-
cal vapor deposition studies were performed in both a hot wall,
low pressure (10-3 Torr) glass tube and a hot stage, high vacuum
(10-7 Torr) stainless steel reaction vessel. Film formation in
the hot tube experiments results from a combination of gas phase
and surface decomposition pathways, whereas the hot stage
emphasizes surface reactivity.1 Because of the high volatility
of 1, it was not necessary to heat the precursor reservoir to obtain
a reasonable rate of film growth.
There was no indication of substrate selectivity for experi-
ments performed with the hot stage reactor; similar platinum
films were obtained on copper and glass substrates held at 200
°C. The elemental composition of the films on a copper
substrate, determined by Auger electron spectroscopy, were
consistently 65% Pt, 25% C, and 10% Cu. The composition
remained constant to a depth of 1250 Å, at which point the
percentage of copper increased dramatically.
(
195Pt), which is consistent with a monomeric structure.
A single crystal X-ray diffraction study confirmed that 1 is
monomeric, having two pentenyl ligands bound to platinum in
a chelated fashion (Figure 1). The platinum is essentially
square-planar coordinate; the two π-bound alkenes are oriented
cis to one another and each is trans to a σ-bound carbon. The
chelating pentenyl rings are related by a C2 axis of symmetry.
The thermolysis of 1 in a vertical hot tube reactor (Figure
2a) resulted in the formation of a highly reflective platinum
mirror at temperatures as low as 175 °C on a glass substrate.
The purity of the resulting films showed no temperature
dependence, as AES showed similar atomic compositions for
experiments at 220 and 275 °C. After sputtering away the upper
400 Å of the film to remove contamination from contact with
lab atmosphere, film composition was consistently 82% Pt and
18% C. These values remained constant to a depth of 4000 Å,
at which point the depth profile analysis was terminated. A
scanning electron micrograph of a film formed on a glass slide
at 275 °C shows an approximate average particle diameter of
60 nm and no indication of a predominant crystallographic
orientation (Figure 3). The lower level of carbon contamination
in these films (as compared to the hot stage experiments)
indicates that gas phase decomposition pathways are significant
for this process.
The chelated structure of 1 results in several interesting
structural features. As the pentenyl ring is puckered, aliphatic
hydrogens may appear in a pseudo-axial or pseudo-equatorial
position. The dihedral angle between the alkenes and the square
plane is 69°; the π-bound alkenes are tipped 21° from the
perpendicular (generally the most stable for platinum π-com-
plexes)14 conformation. Finally, the molecule is very compact,
measuring less than 6.3 Å across its widest span (C3-C8).
Preparation and Characterization of 1-â-d4. Isotopically
labeled 1-â-d4 was prepared from the corresponding labeled
alkyl bromide. The synthesis of 5-bromo-4,4-dideuterio-1-
(12) Xue, Z.; Thridanam, H.; Kaesz, H. D.; Hicks, R. F. Chem. Mater.
1992, 4, 162-166.
(13) Kumar, R.; Roy, S.; Rashidi, M.; Puddephatt, R. J. Polyhedron 1989,
8, 551-553.
(14) Albright, T. A.; Hoffmann, R.; Thibeault, J. C.; Thorn, D. L. J.
Am. Chem. Soc. 1979, 101, 3801-3812.

2636 J. Am. Chem. Soc., Vol. 118, No. 11, 1996
Tagge et al.
The labeled olefin 1,1-dideuterio-1-pentene was introduced
through the secondary inlet into the horizontal reactor both
during and after the deposition of 1. In both cases, none of the
recovered labeled olefin (analyzed by 1H and 2H NMR
spectroscopy) had isomerized.
Thermolysis of 1 in Aromatic Solvents. The thermolysis
of 1 in benzene-d6 at 75 °C for 8 h results in the deposition of
colloidal platinum and a mixture of olefins: 1-pentene (0.06
equiv), 2-pentene (1.2 equiv), 1,4-pentadiene (0.06 equiv), and
1,3-pentadiene (0.38 equiv) (total ) 1.7 equiv) (eq 3). These
ratios remained constant throughout the thermolysis and were
independent of temperature. No higher alkenes, which could
result from the coupling of radicals, were detected. Thermolysis
of 1 in the presence of added mercury, which has been shown
to trap colloidal platinum species,15 did not affect the distribution
of the organic products. Similar results were obtained when
the thermolysis was conducted in the presence of O2, H2O, and
CHCl3, in different solvents (toluene-d8 and cyclooctane), and
in silylated and lead glass reaction vessels.
Figure 2. Schematic representations of (a) a vertical hot tube reactor
and (b) a horizontal hot tube reactor equipped with a cold trap.
Added olefins (1-hexene, trans-3-hexene, and 1,1-dideuterio-
1-pentene) were isomerized to a mixture of their isomers during
the thermolysis of 1, but were not isomerized when added to
the reaction mixture after the decomposition of 1 was complete.
Similarly, 1,4-pentadiene was isomerized to a mixture of cis-
and trans-1,3-pentadiene when thermolyzed with 1. Kinetic
studies of the 1,4-pentadiene isomerization have shown that the
isomerization rate of the diene exhibits first-order behavior and
is similar to the rate of decomposition of 1. Furthermore, added
1,4-pentadiene strongly inhibits the decomposition of 1 (vide
infra).
Thermolysis of 1 in toluene-d8 in the presence of 3,3-
dimethyl-1,4-pentadiene completely inhibited the formation of
colloidal platinum (eq 4). While free 1,3- and 1,4-pentadiene
1
were evolved, no 1- or 2-pentene was detected by H NMR
spectroscopy. Unfortunately, the resulting organoplatinum
complexes (formed in a ratio of 5:1:1) could not be completely
purified. However, the similarity of the 1H NMR spectrum of
the major product to that of 1 is consistent with the structural
formulation for 6. Resonances at δ 3.17 (dd, 2 H, JHH ) 9 Hz,
JPtH ) 25 Hz), 3.62 (dd, 2 H, JHH ) 15 Hz, JPtH ) 40 Hz), and
4.14 (m, 2 H) are characteristic of a chelated pentenyl ligand.
Two singlets at δ 1.06 (s, 6 H) and 1.23 (s, 6 H) correspond to
the axial and equatorial methyl groups of 6. The tetramethyl
substituted analog has a greater thermal stability than 1, as
temperatures greater than 105 °C are required for the decom-
position of 6.
Figure 3. Scanning electron micrograph of the thin Pt film formed
from the CVD of 1 on a glass slide at 275 °C.
(b) Organic Products. A horizontal hot tube reactor
equipped with a U-tube cold trap (-196 °C) and a secondary
inlet was employed to isolate the volatile products formed under
CVD conditions (Figure 2b). The organic products from the
thermolysis of 1 at 220 °C and 10 mTorr were analyzed by 1H
NMR spectroscopy and gas chromatography. The olefins
1-pentene, 2-pentene, 1,3-pentadiene, and 1,4-pentadiene were
formed in approximately equal amounts (eq 2). This distribution
Thermolysis of 1 with Diphenylacetylene. Thermolysis of
1 in the presence of diphenylacetylene at 75 °C in toluene-d8
completely inhibited the deposition of colloidal Pt(0), leading
to the formation of organoplatinum complexes 7 and 8 (eq 5).
did not change with temperature or pressure. Similar results
were observed for the thermolysis of 1 in a lead glass reactor
(used to minimize wall effects).

Synthesis of a NoVel Volatile Platinum Complex
J. Am. Chem. Soc., Vol. 118, No. 11, 1996 2637
Kinetics. The thermolysis of 1 was monitored by following
1
the disappearance of 1 (0.069 M in toluene-d8) by H NMR
spectroscopy in a sealed tube at 87 °C. In the absence of added
reagents, the decomposition of 1 to colloidal platinum, pentenes,
and pentadienes obeyed clean first-order kinetics (kobs ) 4.15
× 10-4 s-1). There was no induction period, nor any evidence
of an autocatalytic reaction. The decomposition of 1 is slightly
accelerated by added diphenylacetylene (kobs ) 1.1 × 10-3 s-1
;
[PhCtCPh] ) 0.34 M), and strongly inhibited by added 1,4-
pentadiene (kobs ) 1.9 × 10-5 s-1; [1,4-pentadiene] ) 0.97 M).
No intermediates were detected in any of the preceding
reactions.
The effect of diphenylacetylene concentration on the rate of
decomposition of 1 has been thoroughly investigated. As 1,4-
pentadiene is produced during the course of the reaction, free
1,4-pentadiene was added in order to maintain pseudo-first-order
conditions. The decomposition of 1 (0.028 M in toluene-d8;
[1,4-pentadiene] ) 0.32 M; monitored by 1H NMR spectroscopy
at 77 °C) is accelerated by diphenylacetylene, but the rate
appears to saturate at higher concentrations of the alkyne (Figure
5a). Because of concentration limitations (due to solubility and
detection), the saturation point could not be reached under these
conditions.
Fortunately, the maximum diphenylacetylene-independent or
“saturation” rate was achieved in the experiments conducted
without added 1,4-pentadiene. In the absence of added 1,4-
pentadiene, the rate of decomposition of 1 at 77 °C showed no
dependence on the concentration of diphenylacetylene (Figure
5b). These data were combined with those from the experiments
in the presence of 1,4-pentadiene to construct an inverse plot
of 1/kobs vs [1,4-pentadiene]/[PhCtCPh] (Figure 5c).23 The rate
at saturation for the decomposition of 1 (ksat ) 3.08 ( 0.25 ×
10-4 s-1) was calculated from the intercept of the inverse plot.
The activation parameters (∆Hq ) 32.3 ( 0.4 kcal/mol and ∆Sq
) 18 ( 1 eu, 77 °C) for the decomposition of 1 under saturation
conditions were determined from a temperature dependence
study (62.5-93 °C).
Figure 4. ORTEP drawing of one of the two independent molecules
in the asymmetric unit of 8.
In addition, the ratio of 1-pentene and 1,4-pentadiene to their
thermodynamically favored isomers, 2-pentene and 1,3-penta-
diene, is drastically increased. The distribution of the pentenes
and pentadienes, as well as the yields of 7 and 8, is markedly
dependent on the concentration of diphenylacetylene. At low
concentrations of diphenylacetylene (5 equiv), bis(diphenyl-
acetylene)platinum (7), which has been characterized previ-
ously,16 is the major organoplatinum product. As the concentra-
tion of diphenylacetylene is increased, the yields of 1-pentene,
2-pentene, 1,3-pentadiene, and 7 all approach zero, while the
yields of novel organoplatinum product (8) and 1,4-pentadiene
both approach 1 equiv.
Complex 8 was isolated from the reaction mixture in 51%
yield by chromatography on silica followed by recrystallization
from a toluene/hexane solution. The low temperature (255 K)
1H NMR spectrum of 8 exhibits alkyl resonances at δ 1.50 (m,
3 H) and 2.00 (m, 3 H), and olefinic resonances at δ 3.24 (d, 1
H, JHH ) 9 Hz, JPtH ) 41 Hz), 3.92 (d, 1 H, JHH ) 15 Hz, JPtH
) 49 Hz), and 5.38 (m, 1 H) that are characteristic of a chelated
pentenyl ligand.17 In addition, there is a vinyl resonance at δ
5.95 (s, 1 H, JPtH ) 18 Hz) and several aryl resonances having
a cumulative integration of 20 protons. There are 25 distinct
carbon resonances in the 13C NMR spectrum. The molecular
ion appears at m/e ) 691 in the mass spectrum.
A single crystal X-ray diffraction study indicates that 8 has
retained one chelating pentenyl ligand and has added a chelating
1,2,3,4-tetraphenylbuta-1,3-dien-1-yl ligand (Figure 4). There
is one toluene solvate molecule, which has different intermo-
lecular contacts to the two independent molecules of 8 in the
asymmetric unit. The molecules have very similar structural
parameters and are related by a pseudo-2-fold screw axis. Each
Pt is essentially square-planar coordinate in which the two
σ-bound carbons are oriented cis to one another and each is
trans to a coordinated π-bond. The stereochemistry about the
terminal double bond of the tetraphenylbutadienyl ligand is
trans.18-22
Thermolysis of 1-â-d4. The decomposition of 1-â-d4 (0.028
M in toluene-d8) under saturation conditions ([PhCtCPh] )
0.60 M; [1,4-pentadiene]0 ) 0 M) at 77 °C was monitored by
1H NMR spectroscopy. The measured rate constant was 0.80
( 0.02 × 10-4 s-1, showing that the reaction exhibits a
substantial â-deuterium isotope effect of kH/kD ) 3.8. The only
organic product, 2-deuterio-1,4-pentadiene, was identified by
1H NMR spectroscopy and GC/MS. The organoplatinum
1
products, identified by H NMR spectroscopy, were a mixture
1
2
of 7 and 8. From the H and H NMR spectra it is apparent
that deuterium atoms are present only in the pentenyl ligand of
8; no deuterium atoms were detected in the terminal vinyl
position of the butadienyl ligand. A mass spectrum of the
mixture of organoplatinum products indicates that both 8-d2 and
8-d3 are present.
Reaction with H2. Upon treatment with H2, solid 1
decomposes rapidly at room temperature to yield colloidal
(18) Isomerization to give the E isomer is common for alkyne insertion
reactions (see refs 19-22).
(19) Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 3002-
3011.
(20) Samsel, E. G.; Norton, J. R. J. Am. Chem. Soc. 1984, 106, 5505-
5512.
(15) Whitesides, G. M.; Hackett, M.; Brainard, R. L.; Lavalleye, J. P. P.
M.; Sowinsky, A. F.; Izumi, A. N.; Moore, S. S.; Brown, D. W.; Staudt, E.
M. Organometallics 1985, 4, 1819-1830.
(16) Green, M.; Grove, D. M.; Howard, J. A. K.; Spencer, J. L.; Stone,
F. G. A. J. Chem. Soc., Chem. Commun. 1976, 759-760.
(17) At room temperature the NMR spectra are broad. At low temperature
a small amount (<5%) of a minor isomer was detected. The fluxional
process was not investigated.
(21) Attig, T. G.; Clark, H. C.; Wong, C. S. Can. J. Chem. 1977, 55,
189-198.
(22) Clark, H. C.; Fiess, P. L.; Wong, C. S. Can. J. Chem. 1977, 55,
177-188.
(23) Since 1,4-pentadiene is produced during the course of the reaction,
the value for [1,4-pentadiene] was set to 0.014 M, the average of the amount
produced. However, use of values ranging from 0.0001 to 0.028 M for this
concentration gives similar plots.

2638 J. Am. Chem. Soc., Vol. 118, No. 11, 1996
Tagge et al.
Scheme 2
(a)
deposited rapidly at room temperature and the organic products
were collected at 77 K. Spectroscopic analysis showed that
1-pentene and 2-pentene were formed in approximately equal
amounts (eq 6).
Discussion
Chemical Vapor Deposition. The pent-4-en-1-yl ligand has
shown great promise as a ligand for the preparation of
organometallic CVD precursors. The chelating ligand has a
low molecular weight and leads to a compact structure enhanc-
ing the volatility of the resulting organometallic complex. Most
important for CVD applications, we have demonstrated that the
chelated bis-pentenyl complex of platinum undergoes a facile,
low energy, relatively clean decomposition reaction that deposits
thin platinum films. Thermolysis of 1 in a hot tube CVD reactor
(Figure 2a) produced films of unusually high purity for an
organoplatinum precursor, comparable to Puddephatt’s (MeNC)2-
PtMe2 complex (vide supra).8 In addition, 1 decomposes under
unusually mild conditions. Unfortunately, the facile reaction
of 1 with dihydrogen at 25 °C precluded detailed CVD studies
using dihydrogen as a carrier gas with the present CVD
apparatus.
(b)
Mechanism. Initially, we expected the thermal decomposi-
tion of 1 to involve â-hydride elimination and dissociation of
1,4-pentadiene to give a three-coordinate platinum hydride
intermediate (9), followed by reductive elimination of 1-pentene
to deposit a platinum film (Scheme 2). However, analysis of
the volatile products from CVD experiments showed a mixture
of the expected kinetic products (1-pentene and 1,4-pentadiene)
and an approximately equivalent amount of their thermody-
namically favored isomers 2-pentene and 1,3-pentadiene (pre-
dominately trans isomers). While control experiments are
difficult to rigorously conduct in a heterogeneous system, we
made a serious effort to determine whether alkene isomerization
is catalyzed by the platinum film. The fact that an isotopically
labeled alkene (1,1-dideuterio-1-pentene) did not isomerize when
introduced into the CVD reactor both during and after the
decomposition of 1 suggests that the film is not a catalyst for
alkene isomerization.
(c)
In order to study the thermolysis of 1 as quantitatively as
possible, we investigated the decomposition of 1 in aromatic
solvents, a relatively nonpolar medium. The thermolysis of 1
in benzene-d6 gives the same organic products as those observed
under CVD conditions. However, the ratio of the expected
kinetic products, 1-pentene and 1,4-pentadiene, to 2-pentene and
1,3-pentadiene is very low. The decomposition obeys clean,
first-order kinetics. There is no evidence for autocatalysis by
either colloidal platinum or other products. As no decadienes
are produced and no free radical abstraction of hydrogen or
chlorine atoms was observed when the reaction was conducted
in the presence of CHCl3, a mechanism involving homolytic
cleavage of the Pt-C σ-bond to give pentenyl radicals is
unlikely.
Figure 5. Kinetic data for the decomposition of 1 in the presence of
PhCtCPh (77 °C, toluene-d8): (a) the plot of the observed rate constant
for the decomposition of 1 with respect to the concentration of
diphenylacetylene in the presence of added 1,4-pentadiene; (b) the plot
of the observed rate constant for the decomposition of 1 with respect
to the concentration of diphenylacetylene in the absence of added 1,4-
pentadiene; (c) the inverse plot.
platinum. Because of our reactor design (Figure 2a), this facile
reaction prevented detailed CVD studies as platinum deposited
before reaching the substrate (a suitable gas inlet/substrate
arrangement will permit film analysis). In a closed system in
both solution and the solid state, the final organic product was
pentane, presumably resulting from hydrogenation of the olefins
catalyzed by Pt(0). Hydrogenation was avoided by treating the
vapor of 1 with hydrogen gas under dynamic vacuum (0.2 Torr)
using the apparatus shown in Figure 2b. Again, platinum
Added 1,4-pentadiene severely retards the rate of decomposi-
tion of 1, which could reflect either of two equilibria for the
decomposition process: association of 1,4-pentadiene with 1,
or reversible dissociation of 1,4-pentadiene from 1. Since we

Synthesis of a NoVel Volatile Platinum Complex
J. Am. Chem. Soc., Vol. 118, No. 11, 1996 2639
Scheme 3
mediate 9. In the gas phase or in solution in the absence of
traps, reductive elimination of 1-pentene from 9 deposits metallic
platinum. In aromatic solvents diphenylacetylene rapidly traps
9 to give alkyne adduct 12. Intermediate 12 may then
reductively eliminate 1-pentene, and be trapped by a second
equivalent of diphenylacetylene to give 7, or consecutively insert
two molecules of diphenylacetylene to yield 8. Our evidence
indicates that 9 is a highly active isomerization catalyst and
catalyzes the isomerization of kinetic products 1-pentene and
1,4-pentadiene to 2-pentene and 1,3-pentadiene, respectively.
The lower than theoretical yield of organic products (ca. 85%)
in the absence of diphenylacetylene presumably results from a
secondary decomposition pathway.
Using the steady-state assumption, the rate law associated
with the mechanism illustrated in Scheme 3 can be derived; it
is given in eq 7. At high ratios of [PhCtCPh]/[1,4-pentadiene],
do not detect the formation of a 1,4-pentadiene adduct (or the
disappearance of 1), we exclude the associative mechanism.
Thus, reversible dissociation of 1,4-pentadiene from 1 must
precede (or be) the rate determining step in the mechanism of
decomposition of 1.24-30 That 3,3-dimethyl-1,4-pentadiene is
incorporated into the platinum complex (to form 6) during the
thermolysis of 1 is further evidence for the reversibility of 1,4-
pentadiene dissociation.
Although added 1,4-pentadiene inhibits the decomposition
of 1, it is slowly isomerized to cis- and trans-1,3-pentadiene.
Similarly, added alkenes (1-hexene and 1,1-dideuterio-1-pen-
tene) rapidly isomerize to a mixture of their isomers during,
but not before or after, the thermal decomposition of 1 in
aromatic solvents. Since alkene isomerization occurs only
during the decomposition of 1 and obeys first-order kinetics,
we conclude that a transient intermediate platinum complex that
is a highly active olefin isomerization catalyst is formed during
the thermolysis.
The catalytically active intermediate can be trapped chemi-
cally with diphenylacetylene. As the alkyne concentration is
increased, the yields of the expected kinetic products 1-pentene
and 1,4-pentadiene increase at the expense of the isomerized
products 2-pentene and 1,3-pentadiene, indicating that diphen-
ylacetylene inhibits olefin isomerization. At very high con-
centrations of the alkyne, only 1,4-pentadiene is produced;
alkene isomerization and the formation of 1-pentene have been
eliminated.
A kinetic study showed that added diphenylacetylene results
in only a slight rate acceleration for the decomposition and clean
first-order behavior in 1. The reaction is inhibited by added
1,4-pentadiene, and at high ratios of alkyne to diene the reaction
reaches saturation (the rate is no longer dependent on the
concentration of diphenylacetylene). These data indicate that
the alkyne captures a platinum intermediate and does not create
a new decomposition pathway by direct reaction with 1.
The results summarized above for the decomposition of 1
can be rationalized by the mechanism shown in Scheme 3.
Initial, reversible pentenyl de-chelation to give 10, followed by
â-hydride elimination to yield 11 and reversible 1,4-pentene
dissociation, leads to three-coordinate platinum hydride inter-
the [1,4-pentadiene] term becomes negligible and the expression
for kobs becomes a constant value (eq 8). Thus, the rate law
for the above mechanism predicts the experimentally observed
rate saturation at high ratios of [PhCtCPh]/[1,4-pentadiene].
Furthermore, the large, positive entropy of activation (18 ( 1
eu) suggests that substantial rotational and/or translational
freedom is acquired in or before the rate determining transition
state. This is consistent with the presence of de-chelation in
the pre-equilibrium steps and with the proposed rate-limiting
dissociation of 1,4-pentadiene.
While alkene de-chelation cannot be detected kinetically, there
is much theoretical and experimental evidence that direct
â-hydride elimination from a four-coordinate square-planar d8
complex with a constrained configuration, such as 1, must be a
high energy process. In a theoretical investigation, Thorn and
Hoffmann concluded that â-hydride elimination proceeds much
more readily from a three-coordinate d8 intermediate.31 White-
sides and co-workers have extensively studied the decomposition
reactions of L2PtR2 (L ) phosphine; R ) alkyl) complexes and
have found that the lowest energy â-hydride eliminations occur
in systems where a phosphine dissociates to give a three-
coordinate LPtR2 intermediate.32-34 When phosphine dissocia-
tion is inhibited by using a chelating phosphine, â-hydride
elimination does not take place until much higher temperatures
are reached.34 Furthermore, Thorn and Hoffmann have calcu-
lated that the lowest energy transition state for â-hydride
elimination involves a PtCCH dihedral angle of 0°.31 Whitesides
and co-workers have shown that â-hydride elimination is
severely retarded in constrained platinum metallacycles that
cannot achieve this angle.35,36 Finally, Flood and co-workers
have estimated the Pt-alkene bond strength to be less than 28
(24) There are several examples of square-planar d8 organometallic
complexes, having strong σ-donating, trans-activating alkyl ligands, which
undergo substitution by dissociation of a neutral ligand to give a three-
coordinate 14-electron intermediate (see refs 25-30).
(25) Alibrandi, G.; Bruno, G.; Lanza, S.; Minniti, D.; Romeo, R.; Tobe,
M. L. Inorg. Chem. 1987, 26, 185-190.
(26) Brainard, R. L.; Miller, T. M.; Whitesides, G. M. Organometallics
1986, 5, 1481-1490.
(27) Frey, U.; Helm, L.; Merbach, A. E.; Romeo, R. J. Am. Chem. Soc.
1989, 111, 8161-8165.
(31) Thorn, D. L.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 2079-
2090.
(32) Brainard, R. L.; Whitesides, G. M. Organometallics 1985, 4, 1550-
1557.
(33) McCarthy, T. J.; Nuzzo, R. G.; Whitesides, G. M. J. Am. Chem.
Soc. 1981, 103, 1676-1678.
(34) Whitesides, G. M.; Gaasch, J. F.; Stedronsky, E. R. J. Am. Chem.
Soc. 1972, 94, 5258-5270.
(28) Lanza, S.; Minniti, D.; Romeo, R.; Moore, P.; Sachinidis, J.; Tobe,
M. L. J. Chem. Soc., Chem. Commun. 1984, 542-543.
(29) Minniti, D.; Alibrandi, G.; Tobe, M. L.; Romeo, R. Inorg. Chem.
1987, 26, 3956-3958.
(35) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem.
Soc. 1976, 98, 6521-6528.
(36) Miller, T. M.; Whitesides, G. M. Organometallics 1986, 5, 1473-
1480.
(30) Minniti, D. Inorg. Chem. 1994, 33, 2631-2634.

2640 J. Am. Chem. Soc., Vol. 118, No. 11, 1996
Tagge et al.
kcal/mol for a complex with a chelating pentenyl ring similar
to that in complex 1.37 Under the reaction conditions employed
for the thermolysis of 1 (77 °C), there would be sufficient energy
to break such a bond.
Scheme 4
We propose that â-hydride elimination occurs in a pre-
equilibrium step, prior to the rate determining dissociation of
1,4-pentadiene. The observed â-deuterium isotope effect (kH/
kD ) 3.8) is of a magnitude normally interpreted as evidence
for direct involvement of C-H bond-breaking in the rate
determining step. However, Whitesides and co-workers have
reported similar values (2.3 and 3.0) for equilibrium kinetic
isotope effects for platinum dialkyl complexes.26,32 Furthermore,
Jones and Feher have observed an equilibrium kinetic isotope
effect of kH/kD ) 2.7 in a rhodium system.38
In the presence of diphenylacetylene we cannot rigorously
exclude an associative mechanism in which there is a direct
equilibrium between 11 and 12 (in such a mechanism the rate
would saturate at k2, the â-hydride elimination step). However,
diphenylacetylene does not react directly with 1 and our kinetic
results obtained in the absence of diphenylacetylene have shown
that substitution of 1,4-pentadiene in 11 proceeds by a dissocia-
tive mechanism. Thus, we believe that a mechanism involving
the associative attack of diphenylacetylene on 11 and the reverse
reaction of attack by 1,4-pentadiene on 12 is unlikely.
conclude that the alkyne trapping and insertion steps must be
faster than reductive elimination of the alkene.40
Isomerization of Kinetic Alkene Products. Many transition
metal hydride complexes have been shown to catalyze alkene
isomerization through consecutive steps of alkene insertion and
â-hydride elimination.41 Our kinetic studies have indicated that
alkene insertion/â-hydride elimination is a reversible step in the
decomposition of 1. The fact that added olefins are isomerized
exclusively during the thermolysis of 1 necessitates the presence
of a transient intermediate that is a highly active alkene
isomerization catalyst. It is reasonable to conclude that
intermediate 9 is responsible for the isomerization of the
expected kinetic products of the thermolysis of 1, 1-pentene,
and 1,4-pentadiene. The fact that the trapping of 9 with
diphenylacetylene leads to a drastic reduction in isomerization
supports this conclusion. Furthermore, 9 has an open coordina-
tion site, which would facilitate the complexation and isomer-
ization of added alkenes. Presumably, diphenylacetylene
inhibits alkene isomerization through preferential occupation of
the open coordination site.
Relationship between the Thermal Decomposition of 1
Under Nonpolar Solution and CVD Conditions. Detailed
kinetic studies of the decomposition of 1 are more straightfor-
ward to carry out in solution than in the CVD reactor itself. In
the absence of direct mechanistic studies under CVD conditions,
we cannot be certain that the mechanism that we have elucidated
in solution is necessarily the same as that which operates under
CVD conditions. However, the pentene and pentadiene products
observed in the hot tube experiments are the same as those seen
in solution. The differences observed in the product ratios
between the CVD and solution phase reactions can be attributed
to the increased contact time in solution. Thus, it is likely that
an intermediate platinum hydride is formed during the hot tube
thermolysis reaction and that its behavior parallels that seen in
nonpolar solutions. While we cannot determine if the platinum
hydride complex is present in the gas phase or on the platinum
surface, our CVD experiments indicate that gas phase decom-
position pathways are significant for the hot tube reactions (vide
supra). The carbon contamination of the Pt films presumably
results from the secondary decomposition pathway proposed
for the decomposition of 1 in aromatic solvents in the absence
of diphenylacetylene.
Organoplatinum Products. The conversion of intermediate
alkyne adduct 12 to products 7 and 8 occurs after the rate
determining step, making direct investigation of this part of the
process difficult. However, we can draw some conclusions
about the reaction pathways from the fact that the ratio of 8/7
increases with increasing diphenylacetylene concentration.
Presumably, 7 results from reductive elimination of 1-pentene
from 12 followed by rapid reaction with diphenylacetylene.
Product 8 appears to result from the insertion of diphenylacety-
lene into the platinum-hydride bond of 12 followed by the
insertion of a second molecule of alkyne into the resulting
platinum-vinyl bond to give the chelated product.
A mechanism involving the direct attack of diphenylacetylene
on 12 to accelerate alkyne insertion (and prevent reductive
elimination) would account for the observed dependence of the
relative yields of 7 and 8 on alkyne concentration. However,
theoretical calculations indicate that the low energy pathway
for alkyne insertions in platinum(II) systems proceeds from four-
coordinate square-planar complexes.31 There is much experi-
mental evidence to substantiate this prediction.19,20,22,39 In
addition, as mentioned above, we have not obtained any
evidence for the associative attack of diphenylacetylene on 1
or any 4-coordinate intermediate in this system. Thus, we
disfavor an associative mechanism for the conversion of 12 to
8.
A second, more plausible mechanism that accounts for the
observed dependence of the product yields on alkyne concentra-
tion is shown in Scheme 4. Rapid, reversible de-chelation of
the pentenyl ligand generates transient intermediate 13. Reac-
tion with free diphenylacetylene forms 14, and accounts for the
observed alkyne concentration dependence. Irreversible alkyne
insertion produces 15 and prevents reductive elimination. A
second insertion of diphenylacetylene into the platinum vinyl
bond of 15 gives 8. Because reductive elimination of 1-pentene
could potentially occur from 12 and 14 as well as 13, we
Summary
We have described the synthesis of a novel, volatile orga-
noplatinum(II) complex (1), which has proved useful for the
(37) Ermer, S. P.; Struck, G. E.; Bitler, S. P.; Richards, R.; Bau, R.;
Flood, T. C. Organometallics 1993, 12, 2634-2643.
(38) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1984, 106, 1650-
1663.
(39) Chaudhury, N.; Puddephatt, R. J. J. Organomet. Chem. 1975, 87,
C45-C47.
(40) A mechanism involving rapid, reversible alkyne insertion would
also account for the observed effect of diphenylacetylene concentration.
However, to our knowledge, there have been no reports of facile â-hydride
elimination from a vinyl complex.
(41) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.; John
Wiley and Sons, Inc.: New York, 1992.

Synthesis of a NoVel Volatile Platinum Complex
J. Am. Chem. Soc., Vol. 118, No. 11, 1996 2641
(η1,η2-C5H9)2Pt (1). A 100-mL Schlenk flask was charged with
Mg (0.122 g, 5.02 mmol), 1 crystal of I2, and Et2O (20 mL). The
mixture was stirred under N2 for 1 h, and 5-bromo-1-pentene (0.60
mL, 5.1 mmol) was added by syringe. The mixture was stirred for 6
h, then cooled to 0 °C. The solution was transferred away from the
undissolved Mg by cannula to a 100-mL Schlenk flask containing
(COD)PtCl2 (0.53 g, 1.4 mmol) in Et2O (20 mL) under nitrogen at 0
°C. The mixture was stirred at 0 °C for 30 min. The excess Grignard
reagent was quenched with distilled H2O (0.5 mL) and the mixture
was allowed to warm to room temperature. The solution was dried
with magnesium sulfate and filtered through Celite, which was washed
with Et2O (60 mL). The combined filtrates were concentrated by rotary
evaporation to a viscous yellow oil. The oil was purified by sublimation
(25 °C, 10 mTorr) to yield yellow crystals (0.390 g, 83%). MS (EI)
m/e Calcd: 332 (88%, 194Pt), 333 (100%, 195Pt). Found: 332 (90%),
333 (65%), indicating a mixture of M+ and (M - H)+. The base peak
appeared at m/e ) 259 (100%). 1H NMR (400 MHz, C6D6, 298 K):
δ 2.00 (m, 12 H), 3.25 (d, 2 H, JHH ) 9 Hz, JPtH ) 28 Hz), 3.65 (d, 2
H, JHH ) 16 Hz, JPtH ) 40 Hz), 4.45 (m, 2 H). 13C{1H} NMR (101
MHz, C6D6, 298 K): δ 28.70 (s, JPtC ) 40 Hz), 32.31 (s, JPtC ) 811
chemical vapor deposition of thin platinum films of relatively
high purity (82% Pt). We attribute the unusual volatility of 1
to the compact structure imparted by the two chelating pent-
4-en-1-yl ligands. A comprehensive investigation of the mech-
anism of decomposition of 1 in aromatic solvents revealed the
presence of a transient three-coordinate platinum hydride (9)
that catalyzes the isomerization of the kinetic products 1-pentene
and 1,4-pentadiene to 2-pentene and 1,3-pentadiene. The
intermediate isomerization catalyst was chemically trapped with
diphenylacetylene.
Experimental Section
General. For a description of the instrumentation and general
procedures used, please see earlier papers from these laboratories.42,43
Unless otherwise specified all reagents were purchased from
commercial suppliers and used without subsequent purification. Diethyl
ether, toluene, hexamethyldisiloxane, and benzene were distilled from
sodium benzophenone ketyl under nitrogen. Deuterated solvents were
vacuum transferred from sodium benzophenone ketyl. Diphenylacety-
lene was purified by sublimation. The reagents (COD)PtCl2,35 2,2-
dimethyl-3-butenal,44 and R2CdPPh3 (R ) H, D) were prepared
according to literature procedures. Powderless gloves were worn during
all sample or CVD chamber manipulations. All CVD substrates (glass
slide, silicon wafer, or copper foil) were washed with 2-propanol and
distilled H2O and dried under a stream of argon prior to use. Argon
(99.9%) and hydrogen (99.999%) were used as received.
Chemical Vapor Deposition. Three types of CVD chambers were
used in this study: a hot stage reactor, a vertical hot wall reactor, and
a horizontal hot wall reactor equipped with a U-tube cold trap. The
hot stage reactor consisted of an evacuated (10-7 Torr) stainless steel
chamber equipped with a heatable sample stage (a copper block
resistively heated by a current passing through a tungsten wire) and a
sample/carrier gas/reactive gas inlet placed ∼5 cm from the hot stage.
In this device, only the sample stage was heated. The remainder of
the chamber was kept at ambient temperature.
The vertical hot wall reactor consisted of a dynamically pumped
(10-3 Torr) 60 cm long Pyrex tube, at one end of which was placed
the CVD precursor. This section of the tube was kept at room
temperature during the CVD run. Approximately 20 cm from this area
was a 20 cm long hot zone in which the CVD substrate was placed.
The hot zone of the reaction chamber was wrapped with a layer of
heating tape and then a layer of aluminum foil. The temperature was
interactively controlled and monitored via a thermocouple placed
between the heating tape and the glass tube. The system was heated
at 300 °C for 1 h prior to use (the precursor reservoir was cooled to
-196 °C during this period). The system was designed so that a
controlled flow of either a carrier gas (Ar) or a reactive gas (H2) could
pass over the precursor and toward the hot zone.
The precursor reservoir and hot zone of the horizontal hot tube
reactor were similar to those for the vertical reactor. In addition, the
horizontal reactor was equipped with a secondary inlet between the
precursor reservoir and the hot zone. Volatile products were collected
in a U-tube (cooled to -196 °C) connected to the end of the hot tube.
The experiments were conducted under both static and dynamic vacuum
(10 mTorr). At the conclusion of each type of CVD experiment
(typically 1 h), the reaction chamber or hot stage was slowly cooled
(while under dynamic vacuum) to room temperature.
Hz), 33.76 (s, JPtC ) 24 Hz), 80.00 (s, JPtC ) 50 Hz), 113.1 (s, JPtC
)
40 Hz). DEPT90: δ 113.1 (CH). Mp 40-41 °C. Anal. Calcd for
C10H18Pt: C, 36.03; H, 5.44. Found: C, 36.23; H, 5.48.
(η1,η2-C5H7D2)2Pt (1-â-d4). Complex 1-â-d4 was prepared by the
same method used for its protiated analog, replacing 5-bromo-1-pentene
with 5-bromo-4,4-dideuterio-1-pentene. MS (EI) m/e Calcd: 336 (88%,
194Pt), 333 (100%, 195Pt). Found: 336 (100%), 337 (96%), indicating
a mixture of M+ and (M - H)+. This mixture precluded analysis of
deuterium incorporation by examination of the mass spectrum. 1H
NMR (400 MHz, C6D6, 298 K): same as 1 except for δ 2.00 (m, 8 H).
2H NMR (60 MHz, C6H6, 298 K): δ 1.86 (s, 1 D, broad), 2.17 (s, 1 D,
JPtD ) 18 Hz). 13C NMR (75.5 MHz, C6D6, 298 K): δ 28.2 (quin, JDC
) 20 Hz, JPtC could not be resolved), 32.1 (s, JPtC ) 811 Hz), 33.6 (s,
JPtC ) 26 Hz), 80.0 (s, JPtC ) 45 Hz), 113.1 (s, JPtC ) 45 Hz).
DEPT45: δ 32.1, 33.6, 80.0, 113.1.
Thermolysis of 1 with PhCtCPh: (η2-PhCtCPh)2Pt (7). A glass
bomb was charged with 1 (0.034 g, 0.102 mmol), PhC≡CPh (0.085 g,
0.48 mmol), and benzene (6 mL) under nitrogen. The solution was
heated at 75 °C for 15 h and then evaporated to dryness. The brown
residue was dissolved in Et2O (3 mL) and stored at -35 °C for 15 h.
The resulting white crystals were washed with Et2O (2 × 1 mL) and
dried in Vacuo giving 0.028 g (0.051 mmol, 50%) of 7. The identity
of 7 was confirmed by comparison of 13C NMR and IR spectral data
with literature values.16
Thermolysis of 1 with PhCtCPh: (η1,η2-C5H9)(η1,η2-C4Ph4H)-
Pt‚0.5 toluene (8). A 30-mL glass bomb was charged with 1 (0.064
g, 0.19 mmol), PhC≡CPh (2.25 g, 12.6 mmol), and toluene (5 mL)
under nitrogen. The solution was heated at 75 °C for 5 h and then
was evaporated to dryness. The yellow residue was chromatographed
on a column of silica (2 cm × 10 cm) under nitrogen using a solution
of 90/10 hexanes/toluene as eluent. The excess diphenylacetylene
eluted first, followed by a bright yellow band which was evaporated
to dryness (0.080 g). The yellow solid was crystallized from a 75/25
hexanes/toluene solution (5 mL) stored at -35 °C for 4 days to yield
0.065 g (0.097 mmol, 51%) of yellow block-like crystals of 8. MS
(EI) m/e Calcd for 195Pt: 621. Found: 621 (M+, 78%). The base peak
appeared at m/e ) 552 (M+ - C5H9, 100%). 1H NMR (300 MHz,
CH2Cl2, 255 K): major isomer (there is a small amount (5%) of what
appears to be a minor isomer) δ 1.50 (m, 3H), 2.00 (m, 3H), 3.24 (d,
1 H, JHH ) 9 Hz, JPtH ) 41 Hz), 3.92 (d, 1 H, JHH ) 15 Hz, JPtH ) 49
Hz), 5.38 (m, 1 H), 5.91 (s, 1 H, JPtH ) 19 Hz), 6.94 (m, 2 H), 7.05
(m, 6 H), 7.30 (m, 8 H), 7.66 (m, 2H), 7.80 (m, 2H). 13C NMR (101
MHz, CH2Cl2, 255 K, JPtC could not be resolved in this experiment):
δ 22.7, 26.7, 32.4, 76.4, 98.3, 103.0, 108.2, 124.7, 124.9, 126.6, 126.9,
127.1, 128.0, 128.1, 128.2, 128.5, 128.8, 129.1, 138.3, 138.6, 138.9,
140.7, 143.1, 156.4. IR (KBr): 555 (w), 694 (s), 729 (w), 750 (w),
763 (m), 1381 (w), 1441 (m), 1483 (w), 1492 (w), 1597 (w), 2850
(w), 2922 (w), 3018 (w), 3057 (w). Anal. Calcd for C36.5H34Pt (8‚
0.5toluene): C, 65.65; H, 5.13. Found: C, 65.40; H, 5.18.
The compositions of the platinum films from the hot stage and
vertical hot tube experiments were determined by Auger electron
spectroscopy, the film adherence was tested with Scotch tape (passed
in all cases), and the film morphology was analyzed by scanning
electron microscopy at the University of Illinois Materials Research
Lab. Volatile products from the horizontal hot wall reactor experiments
were vacuum transferred into a solvent (benzene or benzene-d6) and
analyzed by NMR spectroscopy and gas chromatography.
(42) Hostetler, M. J.; Nuzzo, R. G.; Girolami, G. S. J. Am. Chem. Soc.
1995, 117, 1814-1827.
(43) Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc. 1994, 116,
3822-3835.
H2CdCHCH2CD2CO2H (3). A 200-mL two-neck round-bottomed
flask equipped with a reflux condenser was charged with D2O (75 mL)
under nitrogen. Acetyl chloride (0.40 mL, 5.6 mmol) was added
(44) Crawford, R. J.; Lutener, S.; Tokunaga, H. Can. J. Chem. 1977,
55, 3951-3954.

2642 J. Am. Chem. Soc., Vol. 118, No. 11, 1996
Tagge et al.
dropwise by syringe and the mixture was stirred for 5 min to generate
a catalytic amount of acid. Diethyl (allyl)malonate (7.5 mL, 38 mmol)
was added by syringe and the mixture was heated at reflux. The
progress of the reaction was monitored by 1H NMR spectroscopic
analysis of aliquots from the reaction mixture. The reaction was
complete after 5 days. The solution was cooled to room temperature
and was extracted with Et2O. The organic solution was dried over
magnesium sulfate, filtered through Celite, and concentrated by rotary
evaporation to give 3.35 g (87%) of 3 as a viscous off-white liquid.
The 1H NMR spectrum of 3 was compared to that of the parent
4-pentenoic acid. Spectroscopic data for 3: 1H NMR (400 MHz,
CDCl3, 298 K) δ 2.35 (d, 2 H, JHH ) 6 Hz), 5.00 (dd, 1 H, JHH ) 1
Hz, JHH ) 10 Hz), 5.06 (dd, 1 H, JHH ) 1 Hz, JHH ) 17 Hz), 5.80 (m,
1 H). Spectroscopic data for H2CdCHCH2CH2CO2H: 1H NMR (400
MHz, CDCl3, 298 K) δ 2.35 (m, 2 H), 2.44 (m, 2 H), 5.00 (dd, 1 H,
JHH ) 1 Hz, JHH ) 10 Hz), 5.06 (dd, 1 H, JHH ) 1 Hz, JHH ) 17 Hz),
5.80 (m, 1 H).
external 100% ethylene glycol standard). The reaction was monitored
at 300 s intervals to greater than 3.5 half-lives by 1H NMR spectroscopy.
3,3-Dimethyl-1,4-pentadiene.45 A 50-mL Schlenk tube was charged
with Ph3PCH2 (1.05 g, 3.80 mmol) and toluene (10 mL) under nitrogen.
The yellow solution was cooled to 0 °C and 2,2-dimethyl-3-butenal
(0.375 g, 3.81 mmol) in toluene (5 mL) was added by syringe. The
resulting clear solution was filtered through acidic alumina, which was
washed with toluene (2 × 2 mL). Distillation of the combined filtrates
at 72 °C afforded 0.14 g (1.4 mmol, 37%) of 3,3-dimethyl-1,4-
pentadiene as a clear liquid. 1H NMR (300 MHz, CDCl3, 298 K): δ
1.09 (s, 6 H), 4.95 (m, 4 H), 5.80 (m, 2 H). Bp 72 °C (experimental),
70 °C (reported).45
Thermolysis of 1 with 3,3-Dimethyl-1,4-pentadiene: Spectro-
scopic Evidence for (η1,η2-CH2CH2C(Me)2CHdCH2)2Pt (6). A 30-
mL glass bomb was charged with 1 (0.048 g, 0.14 mmol), 3,3-dimethyl-
1,4-pentadiene (80 µL, 0.6 mmol), and benzene (5 mL) under nitrogen.
The solution was heated for 15 h at 75 °C, filtered through silica, and
evaporated to dryness affording a yellow solid (0.040 g). Despite
repeated chromatography and crystallization, the major product could
only be partially separated from two minor products (ca. 15%). 1H
NMR (300 MHz, C6D6, 298 K): δ 1.06 (s, 6 H), 1.23 (s, 6 H), δ 3.17
(dd, 2 H, JHH ) 9 Hz, JPtH ) 25 Hz), 3.62 (dd, 2 H, JHH ) 15 Hz, JPtH
) 40 Hz), 4.14 (m, 2 H).
H2CdCHCH2CD2CH2OH (4). A 100-mL three-neck round-
bottomed flask equipped with a reflux condenser was charged with
LiAlH4 (1.50 g, 39.5 mmol) and Et2O (50 mL) under nitrogen.
Complex 3 (2.0 g, 19 mmol) was added dropwise by syringe and the
mixture was heated at reflux for 12 h. The flask was cooled to room
temperature and 8 mL of 3% NaOH (aq) was added and the mixture
was stirred for 30 min. The solution was filtered through Celite and
concentrated by rotary evaporation to yield 1.54 g (17.5 mmol, 92%)
Thermolysis of 1-â-d4 with PhCtCPh. Under a nitrogen atmo-
sphere at 21 °C a 1-mL volumetric flask was charged with 1-â-d4
(0.0094 g, 0.028 mmol), diphenylacetylene (0.153 g, 0.858 mmol), and
hexamethyldisiloxane (0.8 µL, internal standard). The mixture was
diluted to a volume of 1.0 mL with toluene-d8. The light yellow
solution was transferred to a 5-mm NMR tube, which was then flame-
sealed under nitrogen. The sample was placed in a NMR probe (Bruker
AMX 300 MHz) preheated to 77 °C (temperature calibrated with an
external 100% ethylene glycol standard). The reaction was monitored
at 300-s intervals to greater than 3.5 half-lives by 1H NMR spectroscopy.
After the reaction had reached completion (7 h) the volatile materials
were vacuum transferred to another 5-mm NMR tube and analyzed by
1H NMR spectroscopy and GC/MS. The spectroscopic data were
consistent with those expected for 2-deuterio-1,4-pentadiene. The yield
based on 1H NMR integration was 92%. 1H NMR (300 MHz, toluene-
d8, 298 K): δ 2.60 (d, 2 H, JHH ) 6 Hz), 4.92 (m, 4 H), 5.70 (m, 1H).
GC/MS: m/e ) 69 (M+). The non-volatile materials were analyzed
1
of 4 as a clear liquid. The H NMR spectrum of 4 was compared to
that of the parent 4-penten-1-ol. Spectroscopic data for 4: 1H NMR
(400 MHz, CDCl3, 298 K) δ 1.67 (br s, 1 H), 2.10 (d, 2 H, JHH ) 7
Hz), 3.62 (s, 2 H), 4.97 (m, 2H), 5.80 (m, 1 H). Spectroscopic data
for H2CdCHCH2CH2CH2OH: 1H NMR (400 MHz, CDCl3, 298 K) δ
1.63 (m, 3 H, the resonances for the acidic proton and â-protons
overlap), 2.10 (vq, 2 H, JHH ) 8 Hz), 3.62 (t, 2 H, JHH ) 7 Hz), 5.97
(m, 2 H), 5.80 (m, 1 H).
H2CdCHCH2CD2CH2Br (5). A 300-mL three-neck round-bot-
tomed flask equipped with a pressure-equalizing addition funnel was
charged with N-bromosuccinimide (11.5 g, 64.6 mmol) and CH2Cl2
(100 mL) under nitrogen. The orange slurry was cooled to 0 °C and
a solution of PPh3 (16.0 g, 61.1 mmol) in CH2Cl2 was added by addition
funnel over 20 min. Pyridine (2.2 g, 28 mmol) was added by syringe.
To the maroon mixture, a solution of 4 (1.54 g, 17.5 mmol) in CH2Cl2
(50 mL) was added by addition funnel over 30 min. The mixture was
stirred for 40 h at room temperature, then diluted with pentane (75
mL), filtered through Celite, and concentrated to a volume of 10 mL.
The clear solution was vacuum transferred to a 25-mL round-bottomed
flask. Pentane was removed by distillation (40 °C). Vacuum transfer
of the remaining volatile materials afforded 0.400 g (2.64 mmol, 15%)
of 5 as a clear liquid. The 1H NMR spectroscopic and GC/MS data of
5 were compared to that of the parent 5-bromo-1-pentene. Spectro-
scopic data for 5: GC/MS m/e (relative intensity) 111 (CH2CD281Br+,
8%), 109 (CH2CD279Br+, 9%), 71 (CH2dCHCH2CD2CH2+, 100%), 70
1
by H NMR spectroscopy and mass spectrometry. The spectroscopic
data were consistent with a mixture of 7 and 8-dx, where x ) 2 or 3.
1
The yield of 8-dx, based on H NMR spectroscopy, was 60%. The
yield of 7 could not be determined due to overlap of resonances in the
1H NMR spectrum. 1H NMR (500 MHz, C6D6, 298 K): notable
features consistent with 8-dx, δ 1.50 (m), 3.24 (d, JHH ) 9 Hz, platinum
coupling was not resolved), 3.92 (d, JHH ) 15 Hz, platinum coupling
was not resolved), 5.38 (br), 5.91 (s, platinum coupling was not
resolved), 7.66 (m), 7.80 (m); resonance consistent with 7, δ 7.98 (d,
7 Hz); other resonances were obscured by the large concentration of
free diphenylacetylene in the sample. MS (EI): m/e ) 623 (60%) and
624 (60%), indicating a mixture of 8-d3 and 8-d2.
X-ray Crystallographic Analysis of (η1,η2-C5H9)2Pt (1). Clear
yellow blocks of 1 were obtained by slow crystallization from a pentane/
ethanol (1/1) solution at -15 °C. A fragment cut from one of these
crystals was mounted on a glass fiber using Paratone N hydrocarbon
oil. The crystal was then transferred to an Enraf-Nonius CAD-4
diffractometer and centered in the beam. It was cooled to -100 °C
by a nitrogen flow low-temperature apparatus, which had been
previously calibrated by a thermocouple placed at the sample position.
Crystal quality was evaluated by measurement of intensities and
inspection of peak scans. Automatic peak search and indexing
procedures yielded a triclinic reduced primitive cell. Inspection of the
Niggli values revealed no conventional cell of higher symmetry.
The 1737 raw intensity data were converted to structure factor
amplitudes and their esd’s by correction for scan speed, background,
and Lorentz and polarization affects. No corrections for crystal
movement or decomposition were necessary. An empirical correction
was made to the data based on the combined differences of Fobs and
1
(23%), 69 (30%), 68 (13%). The molecular ion was not detected. H
NMR (300 MHz, CDCl3, 298 K): δ 2.18 (d, 2 H, JHH ) 7 Hz), 3.37
(s, 2 H), 5.02 (m, 2 H), 5.78 (m, 1 H), no resonance was observed at
δ 1.93, indicating greater than 95% deuterium incorporation. 2H NMR
(61 MHz, C6H6, 298 K): δ 1.42 (s). The GC data showed that
contaminants were present in the sample of 5. Spectroscopic data for
1-d4 indicated that the contaminants did not effect the incorporation of
the pentenyl-d2 ligand into the metal complex. Spectroscopic data for
H2CdCHCH2CH2CH2Br: GC/MS m/e (relative intensity) 150 (M+,
81Br, 2%), 148 (M+, 79Br, 2%), 109 (CH2CH281Br+, 7%), 107 (CH2-
CH281Br+, 8%), 69 (CH2dCHCH2CH2CH2+, 100%), 68 (24%), 67
(34%). 1H NMR (300 MHz, CDCl3, 298 K): δ 1.93 (m, 2 H), 2.18
(vq, 2 H, JHH ) 7 Hz), 3.37 (t, 2 H, JHH ) 7 Hz), 5.02 (m, 2 H), 5.78
(m, 1 H).
Thermolysis of 1 with PhCtCPh: Sample Kinetic Trial. Under
a nitrogen atmosphere at 21 °C a 1-mL volumetric flask was charged
with 1 (0.0093 g, 0.028 mmol), diphenylacetylene (0.056 g, 0.31 mmol),
and hexamethyldisiloxane (0.8 µL, internal standard). The mixture was
diluted to a volume of 1.0 mL with toluene-d8. The light yellow
solution was transferred to a 5-mm NMR tube, which was then flame-
sealed under nitrogen. The sample was placed in a NMR probe (Bruker
AMX 300 MHz) preheated to 77 °C (temperature calibrated with an
Fclc following refinement of all atoms with isotropic thermal parameters
(45) Lukes, R.; Hofman, J. Chem. Ber. 1960, 93, 2556-2561.

Synthesis of a NoVel Volatile Platinum Complex
J. Am. Chem. Soc., Vol. 118, No. 11, 1996 2643
(Tmax ) 1.66, Tmin ) 0.75, no θ dependence).46 The choice of the centric
group P1h was confirmed by the successful solution and refinement of
the structure.
The structure was solved by Patterson methods and refined by
standard least-squares and Fourier techniques. The final residuals for
50 variables refined against the 1563 accepted data for which F2 >
3σ(F2) were R ) 4.5%, wR ) 5.8%, and GOF ) 2.81. The R value
for all 1737 data was 5.0%.
The quantity minimized by the least-squares program was ∑w(|Fo|
- |Fc|)2, where w is the weight of a given observation. The p-factor,
used to reduce the weight of intense reflections, was set to 0.03 in the
last cycles of refinement. The analytical forms of the scattering factor
tables for the neutral atoms were used and all scattering factors were
corrected for both the real and imaginary components of anomalous
dispersion.47
Inspection of the residuals ordered in ranges of sin(θ/λ), |Fo|, and
parity and the value of the individual indexes showed no unusual
features or trends. The largest peak in the final difference Fourier map
had an electron density of 4.07 e-/Å3, and the lowest excursion -2.24
e-/Å3.
the successful solution and refinement of the structure. Removal of
the bad data (as above) left 7063 unique data in the final data set.
The structure was solved by Patterson methods and refined by
standard least-squares and Fourier techniques. Hydrogen atoms were
assigned idealized locations and values of Biso approximately 1.3 times
the Beqv of the atoms to which they were attached. They were included
in structure factor calculations, but not refined. After inclusion of the
hydrogen atoms it became obvious that some regions of data were
systematically low in intensity. A total of 282 reflections were removed
from the data set in 8 regions of consecutive collection numbers. After
these were removed, the DIFABS absorption correction was performed.
Attempts to refine the carbon atoms with anisotropic thermal parameters
yielded chemically unreasonable results, probably due to high correla-
tion between the two independent molecules in the unit cell. Thus,
only the platinum atoms were refined with anisotropic thermal
parameters.
The final residuals for 311 variables refined against the 5213 accepted
data for which F2 > 3σ(F2) were R ) 4.88%, wR ) 5.68%, and GOF
) 1.86. The R value for all 7063 data was 7.10%. Data analysis was
conducted as described for 1. The largest peak in the final difference
Fourier map had an electron density of 1.96 e-/Å3, and the lowest
excursion was -0.27 e-/Å3. There was no indication of secondary
extinction in the high-intensity low-angle data.
X-ray Crystallographic Analysis of (η1,η2-C5H9)(η1,η2-C4Ph4H)-
Pt‚0.5 toluene (8). Clear yellow blocks of 8 were obtained by slow
crystallization from a hexane/toluene (3/1) solution at -35 °C as
described above. A fragment cut from one of these crystals was
mounted in the X-ray beam and cooled to -110 °C as described for 1.
Automatic peak search and indexing procedures yielded a triclinic
reduced primitive cell. Inspection of the Niggli values revealed no
conventional cell of higher symmetry.
Acknowledgment. We are grateful for financial support of
this work by the National Science Foundation through Grant
No. CHE-9113261 to R.G.B., Grant No. CHE-9300995 to
R.G.N., and a Graduate Research Fellowship to C.D.T. We also
acknowledge partial support from the Department of Energy
through Grant No. DEFG02-91ER45439 to R.G.N. We thank
Dr. Frederick J. Hollander for determining the crystal structure
of 1, Noo Li Jeon for the SEM, and Dr. Thomas H. Peterson
and Dr. David J. Schwartz for helpful discussions.
The 7345 raw intensity data were converted to structure factor
amplitudes and their esd's by correction for scan speed, background,
and Lorentz and polarization effects. No correction for crystal
decomposition was performed, as the intensity standards varied
randomly by approximately (10%, far larger than any secular variation.
Inspection of the azimuthal scan data showed a variation Imin/Imax
)
Supporting Information Available: Tables of crystal and
data collection parameters for 1 and 8, positional parameters
for 1, tables of bond distances and angles, and representative
kinetic data (17 pages). This material is contained in many
libraries on microfiche, immediately follows this article in the
microfilm version of the journal, can be ordered from the ACS,
and can be downloaded from the Internet; see any current
masthead page for ordering information and Internet access
instructions.
0.82 for the average curve, but also showed effects which suggested
(together with the intensity standard variations) that the crystal was
moving in the beam. An empirical correction was made to the data
based on the combined differences of Fobs and Fclc following refinement
of all atoms with isotropic thermal parameters and removal of 282 data
in eight groups (see below) (Tmax ) 1.31, Tmin ) 0.82, no θ
dependence).46 The choice of the centric group P1h was confirmed by
(46) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 159.
(47) Cromer, D. T.; Waber, J. T. International Tables for X-Ray
Crystallography; The Kynoch Press: Birmingham, England, 1974; Vol.
IV.
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