Alkyne insertion into the Pt-H bond of Pt(H)(1-pentene)(β-diiniinate) initiates a reaction cascade that results in C-H activation or C-C coupling

Article abstract of DOI:10.1021/om800521x

The lability of the 1-pentene ligand in (Cl-nacnac)Pt(H)(1-pentene) (1; Cl-nacnac = bis(W-aryl)-β-diiminate), which has been synthesized from the reaction of Me₄Pt₂(μ-SMe2)2 with Cl-nacnacH in pentane, allows the reactivity of the (Cl-nacnac)Pt(H) fragment to be probed. The reaction of 1 with alkynes was explored. Alkynes displace pentene and rapidly undergo insertion into the Pt-H bond of 1 to initiate a reaction cascade. The identity of the final platinum product depends on the substituents on the alkyne reagent. Reaction of 1 with 2-butyne results in hydrogen migration after insertion and yields an η³-allyl product, (Cl-nacnac) Pt(η³-C₃H₄Me) (2). When reacted with 1, terminal silyl alkynes R₃SiC≡CH (R₃Si = Me ₃Si, Ph₃Si) undergo C-H activation of one of the silyl substituents after initial alkyne insertion into the Pt-H bond, resulting in net hydrogenation of the alkyne. The result is formation of (Cl-nacnac)Pt((o-C ₆H₄)SiPh₂(CH=CH₂)) (3) or (Cl-nacnac)Pt((CH₂)SiMe₂(CH=CH₂)) (5), which contains either an aryl or an alkyl ligand with a chelated vinylsilane substituent; complex 3 was characterized by X-ray crystallography. These products are the result of 2,1-insertion of the alkyne into the Pt-H bond, thus placing the silyl group and Pt on the same carbon, which positions the substituents on the silicon proximal to Pt and ripe for C-H activation. In contrast to the silylalkyne reagents, terminal alkynes lacking propargylic hydrogens, PhC≡CH and r-BuC≡CH, insert into the Pt-H bond in a 1,2- rather than a 2,1-fashion, which places the alkyne substituent β to the metal and precludes facile C-H activation. Instead, a second alkyne enters the coordination sphere and couples with the adjacent vinyl group in a head-to-tail fashion to form (Cl-nacnac)Pt(η¹:η²-C(H)=C(R)C(H)= C(H)(R)) (7), which has a chelated η¹:η²- butadienyl ligand with R groups at the 2- and 4-positions.

Full text of DOI:10.1021/om800521x

5252
Organometallics 2008, 27, 5252–5262
Alkyne Insertion into the Pt-H Bond of
Pt(H)(1-pentene)(ꢀ-diiminate) Initiates a Reaction Cascade That
Results in C-H Activation or C-C Coupling
Nathan M. West, Peter S. White, and Joseph L. Templeton*
Department of Chemistry, UniVersity of North Carolina at Chapel Hill, Chapel Hill,
North Carolina 27599-3290
ReceiVed June 5, 2008
The lability of the 1-pentene ligand in (Cl-nacnac)Pt(H)(1-pentene) (1; Cl-nacnac ) bis(N-aryl)-ꢀ-
diiminate), which has been synthesized from the reaction of Me4Pt2(µ-SMe2)2 with Cl-nacnacH in pentane,
allows the reactivity of the (Cl-nacnac)Pt(H) fragment to be probed. The reaction of 1 with alkynes was
explored. Alkynes displace pentene and rapidly undergo insertion into the Pt-H bond of 1 to initiate a
reaction cascade. The identity of the final platinum product depends on the substituents on the alkyne
reagent. Reaction of 1 with 2-butyne results in hydrogen migration after insertion and yields an η3-allyl
product, (Cl-nacnac)Pt(η3-C3H4Me) (2). When reacted with 1, terminal silyl alkynes R3SiCt CH (R3Si
) Me3Si, Ph3Si) undergo C-H activation of one of the silyl substituents after initial alkyne insertion
into the Pt-H bond, resulting in net hydrogenation of the alkyne. The result is formation of
(Cl-nacnac)Pt((o-C6H4)SiPh2(CHdCH2)) (3) or (Cl-nacnac)Pt((CH2)SiMe2(CHdCH2)) (5), which contains
either an aryl or an alkyl ligand with a chelated vinylsilane substituent; complex 3 was characterized by
X-ray crystallography. These products are the result of 2,1-insertion of the alkyne into the Pt-H bond,
thus placing the silyl group and Pt on the same carbon, which positions the substituents on the silicon
proximal to Pt and ripe for C-H activation. In contrast to the silylalkyne reagents, terminal alkynes
lacking propargylic hydrogens, PhCt CH and t-BuCt CH, insert into the Pt-H bond in a 1,2- rather
than a 2,1-fashion, which places the alkyne substituent ꢀ to the metal and precludes facile C-H activation.
Instead, a second alkyne enters the coordination sphere and couples with the adjacent vinyl group in a
head-to-tail fashion to form (Cl-nacnac)Pt(η1:η2-C(H)dC(R)C(H)dC(H)(R)) (7), which has a chelated
η1:η2-butadienyl ligand with R groups at the 2- and 4-positions.
tail fashion.4-7 Reductive dimerization of terminal alkynes to
Introduction
yield 1,3-butadienes is somewhat less common, but once again
head-to-tail coupling is rare.8-10 Most couplings favor head-
to-head coupling so that the R groups from RCt CH reside at
the 1- and 4-positions in the organic product.8,9,11-19 Regardless
Dehydrogenation of n-pentane with a (nacnac)PtMe fragment
formed in situ provides a convenient route to (nacnac)Pt(H)(1-
pentene), and the pentene ligand is labile.1,2 The ꢀ-diiminate
ligands used here have phenyl rings on the nitrogens with no
substituents at the ortho positions, and the absence of bulky
ortho substituents allows facile ligand exchange. Similar
compounds reported by Goldberg used bulky substituents in the
ortho position on the phenyl rings of the ꢀ-diiminate ligands,
which inhibited ligand exchange because the metal was too
sterically crowded to readily undergo associative ligand ex-
change.3 The simple synthesis of these olefin hydride complexes
coupled with the ease of displacing the R-olefin ligand allowed
access to a range of (nacnac)Pt(H)(L) complexes. Given the
propensity for alkynes to insert into M-H bonds, we have
undertaken a systematic study of alkyne reactions with (Cl-
nacnac)Pt(H)(1-pentene).
(4) Trost, B. M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ruhter, G.
J. Am. Chem. Soc. 1997, 119, 698.
(5) Schafer, M.; Wolf, J.; Werner, H. Organometallics 2004, 23, 5713.
(6) Gao, Y.; Puddephatt, R. J. Inorg. Chim. Acta 2003, 350, 101.
(7) Sans, V.; Trzeciak, A. M.; Luis, S.; Ziolkowski, J. J. Catal. Lett.
2006, 109, 37.
(8) Ananikov, V. P.; Mitchenko, S. A.; Beletskaya, I. P. J. Organomet.
Chem. 2000, 604, 290.
(9) Ananikov, V. P.; Mitchenko, S. A.; Beletskaya, I. P. Russ. J. Org.
Chem. 2002, 38, 636.
(10) Kong, J. R.; Krische, M. J. J. Am. Chem. Soc. 2006, 128, 16040.
(11) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.; Zanobini, F.
Organometallics 1994, 13, 4616.
(12) Weng, W.; Guo, C.; Celenligil-Cetin, R.; Foxman, B. M.; Ozerov,
O. V. Chem. Commun. 2006, 197.
(13) Ciclosi, M.; Estevan, F.; Lahuerta, P.; Passarelli, V.; Perez-Prieto,
J.; Sanau, M. AdV. Synth. Catal. 2008, 350, 234.
(14) Ghosh, R.; Zhang, X.; Achord, P.; Emge, T. J.; Krogh-Jespersen,
K.; Goldman, A. S. J. Am. Chem. Soc. 2007, 129, 853.
(15) Ogoshi, S.; Ueta, M.; Oka, M.-A.; Kurosawa, H. Chem. Commun.
2004, 2732.
(16) Slugovc, C.; Mereiter, K.; Zobetz, E.; Schmid, R.; Kirchner, K.
Organometallics 1996, 15, 5275.
(17) Li, X.; Vogel, T.; Incarvito, C. D.; Crabtree, R. H. Organometallics
2005, 24, 62.
Though many transition-metal complexes have been shown
to dimerize terminal alkynes, few favor coupling in a head-to-
* To whom correspondence should be addressed. E-mail: joetemp@
unc.edu.
(1) West, N. M.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 2007,
129, 12372.
(2) West, N. M.; Templeton, J. L. Can. J. Chem., in press.
(3) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc. 2003,
125, 15286.
(18) Li, X.; Incarvito, C. D.; Crabtree, R. H. J. Am. Chem. Soc. 2003,
125, 3698.
10.1021/om800521x CCC: $40.75
2008 American Chemical Society
Publication on Web 09/18/2008

Alkyne Insertion Products with Pt(H)(1-pentene)(ꢀ-diiminate)
Organometallics, Vol. 27, No. 20, 2008 5253
Scheme 1. Alkyne Coupling Pathways Favoring Head-to-
Head Coupling Products
with C adjacent to the Ct C unit and 2,1-insertion into the Pt-H
bond when a Si atom is adjacent to the Ct C triple bond.
Multiple insertions of alkynes into metal-hydride bonds are
rare because the second insertion, a C-C forming step, is usually
significantly higher in energy than the first insertion, a C-H
forming step; only a few examples of these multiple insertions
have been reported.17-19,21-24
Results and Discussion
Reaction of (Cl-nacnac)Pt(H)(1-pentene) (1) with CH3Ct
CCH3. We previously reported that olefin insertion into the
Pt-H bond of (nacnac)Pt(H)(olefin) was surprisingly slow.1,2
Use of aryl rings that are unsubstituted at the ortho position on
the nacnac ligand allows access to the platinum center and
promotes facile ligand displacement. Thus, reactivity patterns
of ligands other than olefins can be explored. To further explore
insertion chemistry accessible to the Pt-H bond, we report here
reactions with alkynes. Alkynes tend to be much more reactive
toward metal hydrides than alkenes; thus, we expect their
insertion into the Pt-H bond to be rapid even though alkene
insertion is slow.
For this study we chose to use p-Cl-substituted aryl rings on
the nacnac ligand, due to their slightly lower solubility in
nonpolar solvents, making the compounds easier to isolate as
solids than the previously reported phenyl nacnac complex.1,2
The chlorine atoms at the para position do not appear to
influence the reactivity dramatically relative to the unsubstituted
phenyl. The chloride substituents are located far away from the
metal, and they do not influence the steric environment. In
addition the hydride resonance closely mimics the parent nacnac
analogue: the chemical shift changes by only 0.17 ppm and the
1JPt-H value changes by only 3 Hz out of 1200 Hz.
of whether the new C-C bond is formed via reductive
elimination or alkyne insertion into an M-C bond, the head-
to-head product is usually heavily favored due to the steric bulk
of the R group on the tail carbon of the alkyne.
A recent report by Goldman showed that even though
migration of hydride to the terminal carbon of phenylacetylene
was favored, no reductive elimination with C-C bond formation
occurred from the phenylacetylide intermediate due to the steric
bulk at the C-C bond formation site (mechanism 1; Scheme
1).14 Reductive elimination occurred only when the opposite
alkyne insertion product was formed as an intermediate.
Terminal alkyne dimerization has been accomplished with an
Ir-H reagent, and it occurs by migration of the hydride to the
most substituted alkyne position, yielding the less sterically
hindered metal-bound vinyl group which then migrates to a
second alkyne, but the second migration goes to the least
substituted carbon and so the head-to-head product is formed
upon ꢀ-H elimination (mechanism 2; Scheme 1).13 Thus, 1,3-
disubstituted 1,3-butadienes or enynes have proven far more
elusive than than the 1,4-disubstituted analogues. As described
in detail in this article, our results are particularly surprising,
because we strongly favor coupling even with the bulky tert-
butyl substituent on the alkyne. Aside from dimerization, alkynes
can be used to synthesize more complex unsaturated compounds
via reductive coupling to heteroatom containing unsaturated
molecules.10,20
Alkynes react rapidly with the olefin hydride Pt(II) reagent,
and they then undergo rapid insertion into the Pt-H bond. The
fate of the unsaturated platinum vinyl intermediate depends on
alkyne identity. Internal alkynes with protons on the carbons
adjacent to the triple bond, such as 2-butyne, form Pt allyls.
Terminal alkynes with no protons adjacent to the triple bond
form one of two products, depending on the R group of the
alkyne. Silylacetylenes, such as (triphenylsilyl)acetylene and
(trimethylsilyl)acetylene, produce a cyclometalated vinylsilane
where the alkyne has been reduced to an alkene and C-H
activation of either the silyl methyl or phenyl has occurred.
Carbon-substituted alkynes, such as phenylacetylene and tert-
butylacetylene, couple in a head-to-tail fashion to form η1:η2-
butadienyl complexes with substituents on the 2- and 4-carbons.
The products of terminal alkyne addition reflect 1,2-insertion
We first tested the reactivity of the pentene hydride complex
1 with 2-butyne; hydride migration was indeed rapid. Addition
of 1 equiv of 2-butyne to a CD2Cl2 solution of 1 at room
temperature resulted in a rapid color change from yellow to
light orange. The 1H NMR showed free 1-pentene, and no
hydride signal remained. The product was identified as the
1-methylallyl adduct, (Cl-nacnac)Pt(anti-η3-C3H4Me) (2) (eq 1).
1
The H NMR displayed signals indicative of one methylallyl
isomer: a doublet of triplets at 4.6 ppm, a pseudo quintet at 2.4
ppm, and two doublets of doublets near 1.9 ppm, all with Pt
satellites. These signals correspond to the central proton on C2,
to the proton on C3, and to the two inequivalent protons on
C1, respectively. The proton on C3 and one of the protons on
C1 exhibit a syn coupling of 6.6 Hz to the central CH proton.
The other proton on C1 exhibits an anti coupling of 10.8 Hz;
therefore, the methyl on C3 must reside in the anti position.
Typically only the anti isomer is observed when allyls are
formed via alkyne insertion into a metal-hydride bond, since
the alkyne insertion step is stereoselective for cis addition so
that the vinyl geometry is poised to form the anti allyl product.25
The 1,2-proton shift probably occurs by C-H activation of the
methyl group adjacent to platinum to form an η2-allene followed
by hydride migration to the internal carbon to from the allyl
ligand.
(21) Esteruelas, M. A.; Garcia-Yebra, C.; Olivan, M.; Onate, E.; Tajada,
M. A. Organometallics 2000, 19, 5098.
(22) Kishimoto, Y.; Eckerle, P.; Miyatake, T.; Kainosho, M.; Ono, A.;
Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1999, 121, 12035.
(23) Burrows, A. D.; Green, M.; Jeffery, J. C.; Lynam, J. M.; Mahon,
M. F. Angew. Chem., Int. Ed. 1999, 38, 3043.
(24) Chin, C. S.; Lee, H.; Park, H.; Kim, M. Organometallics 2002,
21, 3889.
(25) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; 3rd ed.; Wiley: New York, 2000.
(19) Selnau, H. E.; Merola, J. S. J. Am. Chem. Soc. 1991, 113, 4008.
(20) Ngai, M.-Y.; Barchuk, A.; Krische, M. J. J. Am. Chem. Soc. 2007,
129, 12644.

5254 Organometallics, Vol. 27, No. 20, 2008
West et al.
Reaction of (Cl-nacnac)Pt(H)(1-pentene) (1) with R3SiCt
CH (R3 ) Me3, Ph3, MePh2). Reactions with terminal alkynes
lacking propargylic protons were also explored. Since silicon-
containing alkynes lead to single platinum products following
alkyne incorporation we consider R3SiCt CH reagents before
R3Ct CH reagents. Reaction of 1 equiv of Ph3SiCt CH with a
CD2Cl2 solution of 1 resulted in formation of complex 3. The
reaction was complete in less than 1 h and formed a single
Figure 1. X-ray crystal structure of (Cl-nacnac)Pt((o-C6H4)-
Si(Ph)2(CHdCH2)) (3). Selected bond distances (Å) and angles
(deg): Pt1-C39 ) 2.031; Pt1-C20 ) 2.142; Pt1-C21 ) 2.140;
Pt1-N1 ) 2.044; Pt1-N5 ) 2.120; C20-C21 ) 1.404;
C39-Pt1-C20 ) 82.62; C39-Pt1-C21 ) 86.12; C34-Si1-C21
) 100.2; N1-Pt1-C20 ) 150.97; N1-Pt1-C21 ) 169.33;
N1-Pt1-N5 ) 91.02.
1
product quantitatively, as monitored by H NMR. Complex 3
displayed diagnostic 1H NMR signals characteristic of a
Pt-bound vinyl group. Compound 3 has a doublet of doublets
at 3.7 ppm (J ) 10.8 and 14.4 Hz), a doublet at 3.2 ppm (J )
10.8 Hz), and a doublet at 3.1 ppm (J ) 14.4 Hz); each signal
2
3
displays a JPt-H coupling in the 50-70 Hz range. The JH-H
values are indicative of cis and trans couplings. This classic
terminal olefin pattern reflects addition of another hydrogen in
addition to the original Pt-H in order to generate (R3Si)-
CHdCH2 from R3SiCt CH. The hydrogen does not originate
in another 1 equiv of alkyne, as only 1 equiv of alkyne was
consumed in the reaction. The platinum complex was purified
by silica gel chromatography, yielding a yellow solid of pure
Scheme 2. Formation of 3 via 2,1-Insertion of Ph3SiCt CH
into the Pt-H Bond of 1
1
3. After purification the aromatic region of the H NMR was
clean, and it was clear that the three phenyl rings on the SiPh3
group had been desymmetrized. In addition to the aromatic Cl-
nacnac p-C6H4Cl signals, two distinct C6H5 groups were
observed, and there were also two doublets and two triplets in
this region with each of the signals integrated for one proton.
This indicates that one of the phenyls lost an ortho proton and
each of the four remaining protons is unique in the product.
Fitting these pieces together, it appeared that after alkyne
insertion into the Pt-H bond the Pt activated an aromatic C-H
bond on one of the SiPh3 phenyl groups and then reductively
eliminated the vinyl group to form a complex having a phenyl
ligand with an o-diphenylvinylsilyl substituent chelating the Pt
atom (eq 2).
plane, these two angles would be the same. The C34-Si1-C21
bond angle is compressed to 100.2°, reflecting a small amount
of ring strain. The Pt1-C39-C34-Si1-C21 ring exhibits a
classic envelope structure with the Pt1, C39, C34, and Si1 atoms
virtually coplanar and C21 out of the plane. The Cl-nacnac
ligand is somewhat twisted to place the nitrogens as close to
directly trans to the aryl and olefin ligands as possible; this is
evidenced by a torsion angle of 19.2° between the two Cl-nacnac
methyl bonds (C6-C2 and C4-C7). The aryl-Pt bond distance,
C39-Pt1, is 2.03 Å and the olefin-Pt bond lengths, C21-Pt1
and C20-Pt1, are both 2.14 Å. The Pt1-N5 bond trans to the
phenyl is 2.12 Å, while the Pt1-N1 bond trans to the olefin is
only 2.04 Å, indicating the stronger trans influence of the aryl
group relative to the olefin. The Cl-nacnac Ar and the Pt-bound
aryl adjacent to each other are stacked parallel to one another,
and the distance between the two ipso carbons is only 2.94 Å,
which rationalizes the hindered rotation of one Cl-nacnac Ar
Recrystallization of 3 from pentane at -30 °C yielded yellow
crystals suitable for X-ray crystallography, and the resulting
structure confirms the proposed geometry of 3 (Figure 1). The
1
group evident in the H NMR.
Regarding the mechanism of the formation of 3 (Scheme 2),
an attractive hypothesis is that reaction of 1 with Ph3SiCt CH
leads to 2,1-insertion of the alkyne into the Pt-H bond,
affording a Pt-vinyl intermediate in which a SiPh3 substituent
is bound to the same carbon as the Pt atom. This positions a
phenyl group close to the metal and allows for facile arene
o-C-H activation. When the resulting platinum hydride ligand
migrates to the vinyl substituent, the result is a Pt-aryl bearing
an o-diphenylvinylsilyl substituent. In constrast, 1,2-insertion
structure of (Cl-nacnac)Pt((o-C6H4)Si(Ph)2(CHdCH2)) (3) shows
that the Pt geometry deviates only slightly from an ideal square
-planar geometry. The olefin is aligned virtually orthogonal to
the square plane, as is typical for such Pt(II) complexes, but
the olefin is not centered along the z axis. The olefin location is
constrained by ring limitations, as evinced by the N1-Pt1-C21
and N1-Pt-C20 angles of 151.0 and 169.3°; if the olefin was
orthogonal to the square plane with its midpoint in the N2CPt

Alkyne Insertion Products with Pt(H)(1-pentene)(ꢀ-diiminate)
Organometallics, Vol. 27, No. 20, 2008 5255
1
Figure 2. H NMR of (Cl-nacnac)Pt(CH2SiMe2CHdCH2) (5) (CD2Cl2, 300 MHz, room temperature).
of the alkyne into the Pt-H bond would leave Pt bound to the
terminal carbon of the vinyl group and place the SiPh3 group γ
to the metal, rendering arene C-H activation less likely.
If CO is bubbled into a solution of 3, the coordinated olefin
tail is rapidly displaced by CO. The reaction proceeds quanti-
tatively by 1H NMR in less than 5 min to produce (Cl-
nacnac)Pt(CO)((o-C6H4)Si(Ph)2(CHdCH2)) (4). The dechelated
vinylsilane olefinic protons appear at 7.2, 6.2, and 5.6 ppm and
display trans, cis, and geminal coupling constants of 20.0, 14.4,
and 3.6 Hz, respectively. The Pt-bound aryl resonances shift
only slightly and still appear as four distinct signals: two
doublets and two triplets. The CO stretch for 4 appears at 2080
cm-1 in hexanes.
The methylene residue of the activated methyl group displays
high-field signals for the diastereotopic protons due to coordina-
tion to platinum and to shielding from the Cl-nacnac Ar group.
Like the SiPh3 analogue, Me3SiCt CH must undergo 2,1-
insertion prior to C-H activation of one of the silyl methyl
groups (eq 3); a 1,2-insertion would place the methyl hydrogens
far from the metal. Related chelated dimethylvinylsilane com-
plexes of Pt(II) have been made by Young via metathesis of
the Grignard reagent ClMgCH2SiMe2CHdCH2 with Pt(II)
1
chlorides; they exhibit similar H NMR signals.26,27
Addition of Me3SiCt CH to a CD2Cl2 solution of 1 resulted
in a reaction that formed a new product, 5, quantitatively in
less than 1 h, as monitored by 1H NMR. Only 1 equiv of alkyne
was consumed in the reaction. The product contained several
signals integrating for a total of three protons in the chemical
shift region indicative of bound olefins; the protons show a
second-order coupling pattern. Simulated 1H NMR matched the
experimental data well and yielded coupling constants of 15.2,
10.2, and 3.2 Hz for the trans, cis, and geminal couplings,
respectively. Surprisingly, the 1H NMR spectrum also displays
four inequivalent methyl signals: two due to the Cl-nacnac ligand
and another two upfield at 0.16 and -0.26 ppm for diaste-
reotopic Me groups at Si. In addition, roofed doublets appeared
at -0.89 and -1.34 ppm with 12.4 Hz coupling to each other,
and they exhibit 68 and 78 Hz Pt coupling, respectively (Figure
2). These Pt coupling constants are typical for two-bond
coupling values, and these unique signals were assigned to
diastereotopic protons on a Pt-bound methylene group. This
assignment was consistent with both the chemical shifts and
the magnitude of the H-H coupling constant. It appeared that
the alkyne had inserted into the Pt-H bond and then activated
a C-H bond of one of the silyl methyl groups to form a chelated
Addition of CO to a solution of 5 resulted in displacement
of the chelating olefin and replacement by CO to form (Cl-
1
nacnac)Pt(CO)(CH2SiMe2CHdCH2) (6) quantitatively by H
1
NMR in less than 5 min (eq 4). The H NMR of 6 displays
terminal olefin signals at 6.10, 5.82, and 5.51 ppm with trans,
cis, and geminal coupling constants of 20.1, 14.6, and 3.9 Hz,
respectively. As a result of dechelation, the two silyl methyl
groups (δ -0.10 ppm) are equivalent, since they are related by
the mirror plane of the Cs-symmetrical complex, as are the two
PtCH2 protons (δ -0.08 ppm, 2JPt-H ) 78 Hz). The CO stretch
(26) Kelly, R. D.; Young, G. B. J. Organomet. Chem. 1989, 361, 123.
(27) Kelly, R. D.; Young, G. B. Polyhedron 1989, 8, 433.
alkyl olefin complex, (Cl-nacnac)Pt(CH2SiMe2CHdCH2) (5).

5256 Organometallics, Vol. 27, No. 20, 2008
West et al.
Figure 3. X-ray crystal structure of (Cl-nacnac)Pt(CH2SiMe2-
CHdCH2)(CO) (6). Selected bond distances (Å) and angles (deg):
Pt1-C22 ) 2.104; Pt1-C20 ) 1.844; Pt1-N1 ) 2.048; Pt1-N5
) 2.096; C20-O21 ) 1.131; C25-C26 ) 1.324; C20-Pt1-C22
) 82.79; C34-Si1-C21 ) 100.2; N1-Pt1-C20 ) 173.95;
N5-Pt1-C22 ) 175.23; N1-Pt1-N5 ) 89.63.
appears at 2072 cm-1 in hexanes, indicating that the chelated
alkyl group donates more electron density to the metal than the
chelated arene in 4, where the CO stretch is slightly higher at
2080 cm-1. The complex was characterized by X-ray crystal-
lography, and the Pt-CH2(SiR3) bond length of 2.104 Å is
noticeably longer than the Pt-Caryl bond length of 2.031 Å in
complex 3 and the Pt-CH3 bond length of 2.082 Å in
(nacnac)Pt(CH3)(CO) (Figure 3).1
1
Figure 4. Olefinic region of the H NMR of 7a.
competitive with or favored over arene C-H activation.29-32
While the present case is admittedly special, due to the silicon
substituent on the methyl/phenyl groups it is noteworthy
nonetheless.
Reaction of (Cl-nacnac)Pt(H)(1-pentene) (1) with RCt CH
(R ) t-Bu, Ph). Addition of 1 equiv of t-BuCt CH to a CD2Cl2
solution of the pentene hydride complex 1 at room temperature
resulted in a color change from yellow to light orange. After
about 1 h the 1H NMR spectrum showed a 1:1 ratio of unreacted
1 and a (Cl-nacnac)Pt product that contained no hydride ligand.
Addition of another 1 equiv of tert-butylacetylene promotes
complete conversion of 1 to the new Pt product 7a. Note that
1-pentene was displaced during the reaction and did not react
with the product. The 1H NMR spectrum for 7a exhibits a singlet
at 4.01 ppm with 32 Hz Pt coupling in addition to two coupled
doublets, one at 3.50 ppm and the other at 2.89 ppm with 53
We hoped to compare phenyl activation and methyl activation
processes by employing Ph2MeSiCt CH as a reagent. Reaction
of Ph2MeSiCt CH with the labile Pt(II) pentene reagent 1 results
in formation of a mixture of all three possible products: the
methyl activation product and both diastereomers of the phenyl
activation products. The two diastereomers resulting from phenyl
activation are present in equal amounts, indicating that there is
no preference for one phenyl relative to the other. Unexpectedly,
the complex reflecting methyl activation is present in about a
1:1 ratio with the two phenyl activation isomers combined. This
product ratio indicates that methyl C-H activation is about 1.33
times more likely than phenyl C-H activation, since if there
were no preference, the number of o-phenyl (4) and methyl
protons (3) would lead to the ratio 4/3 in favor of phenyl
activation. We expected that the five-membered chelate structure
would be significantly more stable than the four-membered ring
and that this would thermodynamically favor phenyl activation.
Platinum(II)-aryl bonds have been reported to be stronger than
platinum(II)-methyl bonds, which would add further thermo-
dynamic stability to the arene activation product.28 The reaction
products are probably determined kinetically, in which case the
methyl activation may be favored because this conformer would
have the large phenyl groups rotated away from the metal and
avoid unfavorable steric interactions with the Cl-nacnac Ar
groups. It should be noted that in most cases d8 transition metals
strongly favor arene C-H activation over sp3 C-H activation;
there are only a few cases in which sp3 C-H activation is
3
and 47 Hz Pt coupling, respectively, as well as 8.8 Hz JH-H
coupling (Figure 4). The 1H NMR spectrum also displayed two
distinct tert-butyl groups, confirming that 2 equiv of alkyne is
incorporated into 7a. We postulated that the vinyl fragment
formed by 1,2-insertion into the Pt-H bond has coupled in a
head-to-tail fashion to a second equivalent of alkyne to yield
an η1-butadienyl ligand which could then chelate to Pt through
the second double bond to form an η1:η2-butadienyl complex
(Scheme 3). A similar η1:η2-butadienyl complex was observed
for the insertion of diphenylacetylene into a Pt-H bond followed
by migration of the resulting vinyl to another 1 equiv of
diphenylacetylene; this complex was characterized crystallo-
graphically.33 Complex 7a, (Cl-nacnac)Pt((H)CdC(t-Bu)(H)Cd
C(H)(t-Bu)), would contain three olefinic hydrogens for the η1:
η2-butadienyl ligand, two of which would couple to one another
and one that would stand alone, as observed. To confirm the
identity of the product, 13C{1H}, HMQC, and HMBC 13C
(29) Zhu, Y.; Fan, L.; Chen, C.-H.; Finnell, S. R.; Foxman, B. M.;
Ozerov, O. V. Organometallics 2007, 26, 6701.
(30) Hofmann, P.; Heiss, H.; Neiteler, P.; Muller, G.; Lachmann, J.
Angew. Chem., Int. Ed. 1990, 29, 880.
(31) Zhong, H. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc.
2002, 124, 1378.
(32) Rybtchinski, B.; Cohen, R.; Ben-David, Y.; Martin, J. M. L.;
Milstein, D. J. Am. Chem. Soc. 2003, 125, 11041.
(28) Al Takhin, G.; Skinner, H. A.; Zaki, A. A. J. Chem. Soc., Dalton
Trans. 1984, 371.
(33) Tagge, C. D.; Simpson, R. D.; Bergman, R. G.; Hostetler, M. J.;
Girolami, G. S.; Nuzzo, R. G. J. Am. Chem. Soc. 1996, 118, 2634.

Alkyne Insertion Products with Pt(H)(1-pentene)(ꢀ-diiminate)
Scheme 3. Reductive Coupling of 2 Equiv of t-BuCt CH
Organometallics, Vol. 27, No. 20, 2008 5257
displayed the same pattern, with two doublets and one singlet
(all with Pt satellites), but they were shifted about 1 ppm
downfield relative to 7a. This complex was less stable than the
tert-butyl analogue and degraded over 1 day in solution to an
unidentified product. The tert-butyl analogue, on the other hand,
was stable in solution and was purified via silica gel chroma-
tography, yielding a yellow solid.
For further proof of the compound’s identity and to explore
its reactivity, we attempted to displace the η2-olefin tail by
addition of another ligand, thereby forming an η1-butadienyl
complex. Compound 7a was found to be unreactive toward most
ligands, including CO, which usually displaces olefins rapidly
and irreversibly, but trimethylphosphine did displace the olefin
and yielded (Cl-nacnac)Pt(PMe3)(η1-butadienyl) (8) quantita-
tively by NMR spectroscopy (eq 5). The vinyl proton on C1 in
8 shifted down 1.4 ppm from 4.0 ppm in 7a to 5.4 ppm but
2
retained an almost identical JPt-H coupling of 34 Hz. The
downfield shift of this proton was probably due to the fact that
in the chelated species this proton would be oriented directly
toward the Cl-nacnac aryl ring and thus was heavily shielded,
resulting in the high field signal at 4 ppm (anisotropic chemical
shifts reflecting shielding effects due to aryl substituents on
nacnac ligands have been reported by Porschke45); once the
ligand was dechelated, it could rotate away from the aryl and
out of the shielding cone. The olefinic hydrogens on C3 and
C4 shifted down to 5.2 and 5.5 ppm, respectively, and they no
longer exhibited Pt coupling. The coupling between these two
protons increased to 13.2 Hz, indicative of a trans geometry in
accord with Pt-H addition to the triple bond. The carbon signals
for C3 and C4 shifted downfield to 130 and 140 ppm,
respectively, again with loss of Pt coupling; they were no longer
coordinated to the metal. The resonance for C1 shifted only
slightly downfield to 120 ppm, and now phosphorus coupling
of 15 Hz was evident; C2 also underwent a small shift (to 144
experiments were conducted. The olefinic signals at 4.0, 3.5,
and 2.9 ppm correlated with carbons at 114, 64, and 104 ppm;
the 13C signal at 114 ppm had a Pt coupling of 740 Hz, and the
1
signal at 104 ppm had a Pt coupling of 248 Hz. A JPt-C
coupling constant of 740 Hz is typical of a Pt-C σ bond and
is consistent with an η1-vinyl ligand;1,34-41 the coupling of 248
1
Hz is typical of JPt-C for a Pt-(η2-olefin),1,36,37 further sup-
porting the proposed η1:η2-butadienyl structure. The 13C
resonance at 64 ppm had a Pt coupling constant of only 24 Hz,
indicating that coordination of the η2-olefin is not symmetrical
because it is constrained by the ring size. The remaining vinyl
carbon, with no protons attached, was found via HMBC to
resonate at 151 ppm, compatible with our formulation of this
product.
The tert-butyl alkyne is sterically similar to Me3SiCt CH;
thus, the regiochemistry of the insertion appears to be dominated
by the electronic effect of the atom bound to the Ct CH
fragment atom. The silicon atom makes the adjacent Pt-C bond
stronger and thus the insertion selectivity reverses from 1,2 with
carbon to 2,1 with silicon, just as observed by Trost.4 Such a
reversal in insertion regioselectivity indicates that there is a
subtle balance between the two pathways, and the stability of
the vinyl intermediates formed from the initial insertion into
the Pt-H bond likely determines the regiochemistry of insertion.
This simple insertion guideline may be useful for alkyne
coupling, since replacement of C by Si would reverse the C-C
linkage in the product. Few catalyst systems can be modified
to yield either 1,4- or 1,3-disubstituted alkynes, and those that
can usually produce a mixture of isomers.42-44
3
1
ppm) and exhibited a 3 Hz JP-C coupling. The H NMR for
the butadienyl ligand resembles that of the free 1,3-di-tert-butyl-
1,3-butadiene.46
When phenylacetylene was reacted with 1, the analogous
coupled product, 7b, was observed. The three olefinic protons
(34) Fekl, U.; Kaminsky, W.; Goldberg, K. I. J. Am. Chem. Soc. 2001,
123, 6423.
(35) Ananikov, V. P.; Mitchenko, S. A.; Beletskaya, I. P. J. Organomet.
Chem. 2001, 636, 175.
(36) Iwayanagi, T.; Saito, Y. Chem. Lett. 1976, 5, 1193.
(37) Shiotsuki, M.; White, P. S.; Brookhart, M.; Templeton, J. L. J. Am.
Chem. Soc. 2007, 129, 4058.
(38) MacDonald, M. G.; Kostelansky, C. N.; White, P. S.; Templeton,
J. L. Organometallics 2006, 25, 4560.
(39) Reinartz, S.; Baik, M. H.; White, P. S.; Brookhart, M.; Templeton,
J. L. Inorg. Chem. 2001, 40, 4726.
(40) Reinartz, S.; White, P. S.; Brookhart, M.; Templeton, J. L.
Organometallics 2000, 19, 3854.
(41) Kostelansky, C. N.; MacDonald, M. G.; White, P. S.; Templeton,
J. L. Organometallics 2006, 25, 2993.
We noticed that during the synthesis of the t-BuCt CH
coupled product 7a a minor product formed in about 5% yield,
as assessed by 1H NMR. This minor product displayed Pt-
coupled doublets at -0.22 and -0.74 ppm with 8 Hz JH-H
coupling and Pt satellites with approximately 70 Hz coupling.
We were not able to isolate this compound for further
characterization, but it was clear that these doublets were due
to the same type of species as the Me3SiCt CH product 5. Thus,
(42) Yi, C. S.; Liu, N. Organometallics 1996, 15, 3968.
(43) Baratta, W.; Herrmann, W. A.; Rigo, P.; Schwarz, J. J. Organomet.
Chem. 2000, 593-594, 489.
(45) Tian, X.; Goddard, R.; Porschke, K.-R. Organometallics 2006, 25,
5854.
(46) Hopf, H.; Lipka, H.; Traetteberg, M. Angew. Chem., Int. Ed. 1994,
33, 204.
(44) Yang, C.; Nolan, S. P. J. Org. Chem. 2002, 67, 591.

5258 Organometallics, Vol. 27, No. 20, 2008
Scheme 4. Two Possible Insertion Pathways for t-BuCt CH
West et al.
it appears that a small amount of the Me3CCt CH underwent
2,1-insertion before C-H activation of one of the tert-butyl
methyl groups to form the chelated neohexenyl compound 7a′
(Scheme 4). It appears that when 2,1-insertion occurs, C-H
activation of the R group, either methyl or phenyl, is faster than
coordination and insertion of a second alkyne. When 1,2-
insertion occurs, there is no alkyne substituent in position to be
easily activated, and so the unsaturated vinyl intermediate binds
a second alkyne and C-C coupling occurs. A similar mechanism
is probably operative for the insertion of internal alkynes such
as 2-butyne; once insertion occurs, the metal can rapidly activate
the C-H bonds of the methyl group. This would yield a Pt
allene hydride intermediate which would rapidly undergo
hydride migration to the central carbon to form the observed
Pt allyl complex.
with the bulky group away from the metal. A switch from 1,2-
insertion to 2,1-insertion on moving from CMe3 to SiMe3 was
observed for the Pd(OAc)2-catalyzed alkyne dimerization reac-
tion reported by Trost.4
Once the alkyne has inserted into the Pt-H bond, a second
alkyne coordinates to the metal and a 1,2-insertion of the alkyne
into the Pt-C bond of the vinyl group occurs, yielding the
complex that places the R group of the alkyne farther from the
metal. It is notable that, while 1-pentene was available to trap
the vinyl intermediate, we did not observe any pentene binding.
Attempts to observe reaction intermediates via low-temperature
1H NMR failed. The reaction of the phenylacetylene with 1 was
1
monitored by VT H NMR, but only loss of 1 and appearance
of 7b and 1-pentene were observed. This indicates that displace-
ment of 1-pentene is rate limiting. We observed earlier (vide
supra) that the second alkyne addition is faster than the first by
adding 1 equiv of alkyne to 1 and getting a 1:1 ratio of 1 to 7;
thus, rate-limiting olefin displacement is not surprising because
hydride migration should be rapid. Considering that olefin
displacement is fairly rapid, the barrier to C-C bond formation
in this system is quite low for a Pt species.
It is worth noting that the structures of 7a′ and 5 are similar
to the geometry of the vinyl-alkyne coupling products 7. Both
products link the internal olefin carbon to the metal through
four-membered chelate rings. Also, both products are bound in
an η1:η2 fashion through one Pt-C σ bond and one η2-olefin.
The only difference between the four-atom skeleton of the
ligands, equating Si and C, is the double bond between C1 and
C2 in 7. The sp2-hybridized carbons in 7 are more rigid than
the sp3 atoms in 7a′ and 5. This rigidity probably increases the
ring strain in 7 somewhat. While it seems like the four-
membered rings would have substantial ring strain, the experi-
mental evidence indicates that it is quite stable. All of the
alkynes lead to chelated σ and π ligands after insertion into the
Pt-H bond. These products appear to be a thermodynamic sink,
as different reaction mechanisms and stoichiometries converge
to remarkably similar structures.
Deuterium labeling studies were conducted to test for
scrambling between the Pt-H and the acetylenic protons. Two
equivalents of PhCCH was added to a CD2Cl2 solution of (Cl-
nacnac)Pt(D)(1-pentene-d10) (1-d11) and the resulting η1:η2-
butadienyl complex exhibited integrations for the protons on
C1, C3, and C4 as follows: singlet, ∼0.5 H; doublet over singlet,
∼1 H; doublet, ∼0.5 H. This indicates that the Pt-D is
scrambled between the C1 and C4 positions. When PhCCD was
reacted with (Cl-nacnac)Pt(H)(1-pentene) (1), the 1H NMR
spectrum showed a singlet integrating for about half a proton
for the C1 and C4 signals and no signal was seen for the C3
proton. This again shows that the original Pt-H is ultimately
scrambled between the C1 and C4 sites. Reaction of t-BuCCD
with 1 yielded slightly different results. In this case the initial
1H NMR showed only a small amount of scrambling between
the positions on C1 and C4: ∼20% H at C1 and ∼20% D at
C4. Upon standing in solution for several hours the spectrum
showed complete scrambling: ∼50% H at C1 and ∼50% D at
C4.
Mechanistic Considerations for Head-to-Tail Coupling
of RCt CH (R ) t-Bu, Ph). To form the observed head-to-tail
coupled product, the first alkyne must insert into the Pt-H bond
in a 1,2-fashion, giving a Pt vinyl intermediate in which the R
group is distal from the metal. Not only is a 1,2-insertion
required to yield the observed head-to-tail coupling but it also
prohibits C-H activation of the t-Bu substituent, indirectly
allowing alkyne coupling to occur. We believe that the elec-
tropositive nature of the Si atom is the cause for the reversal
between 2,1- and 1,2-insertion. Steric factors are not likely to
dictate 2,1-insertion of the silyl alkynes, because the SiMe3
group on the 2-carbon is sterically similar to the CMe3 group
of t-BuCt CH, an alkyne that favors 1,2-insertion. The silyl
group will stabilize the Pt-C bond formed by 2,1-insertion of
the alkyne into the Pt-H, favoring this product thermodynami-
cally even though it is more sterically crowded relative to the
1,2-insertion product. There is no significant electronic stabiliza-
tion of the Pt-C bond from C-based groups such as t-Bu or
Ph; thus, in those cases the most stable Pt-C bond is the one
The labeling results indicate that the protons do not have to
scramble along the reaction path forming 7 but rather that they
can scramble once the product is formed. This is probably true
for the phenylacetylene product as well; in that case the
scrambling just happens too fast to catch it before completion.
There are several plausible mechanisms for C1-C4 proton
scrambling. The protons could be scrambled via acetylenic C-H
activation before the alkynes are coupled, and if the coupling
step is reversible, then scrambling after 7 is formed would occur.

Alkyne Insertion Products with Pt(H)(1-pentene)(ꢀ-diiminate)
Organometallics, Vol. 27, No. 20, 2008 5259
Scheme 5. Possible Mechanisms for Proton Scrambling in 7
Alternatively, the protons could scramble after alkyne coupling
via some type of vinylic C-H activation mechanism.
to C1 and C4 in 7. A possible variant of this mechanism is
rehybridization to form the alkyl carbene metallacyclopentadiene
with the proton and t-Bu group on the C4 methylene carbon
and a 1,3-proton shift from C4 to C1, yielding the same Cs-
symmetric intermediate for proton equilibration; it is not possible
to distinguish between these two variants experimentally.
Mechanism A (Scheme 5) involves C-H activation of the
first alkyne rather than insertion into the Pt-H bond. This yields
a five-coordinate Pt(IV) dihydride which could rapidly equili-
brate the hydrides. Reductive elimination of the alkyne will re-
form the Pt(II) hydride alkyne adduct with the hydride and
acetylide protons scrambled. From here the second alkyne will
insert into the Pt-H(D) bond to yield a Pt(II) vinyl alkyne
intermediate. This Pt(II) vinyl alkyne species will then undergo
migratory insertion to give the η1:η2-butadienyl product 7. This
mechanism would suffice if all of the scrambling occurred before
formation of 7, but since we observed scrambling of the protons
in the already formed product when t-BuCt CD is used, it does
not seem sufficient. The alkyne coupling could conceivably be
reversible, but that seems unlikely. Note that alkyne deinsertion
from the Pt-H would be necessary to scramble the protons.
There is a large thermodynamic driving force to reduce the
alkyne; therefore, deinsertion seems unlikely. Though there are
numerous reports of alkyne insertion into metal hydrides, there
are few examples of alkyne deinsertion to generate a metal
hydride.14,47
Mechanism B (Scheme 5) involves scrambling of the
hydrogens on C1 and C4 in 7 via isomerization of the butadienyl
ligand. Activation of the C4-H bond would yield a Pt(IV)
hydride metallacyclopentadiene species. Hydride migration to
C1 instead of C4 would form the opposite isomer of the η1:
η2-butadienyl, in which C1 and C2 are now bound as the η2-
olefin. At this stage H,D exchange has not yet been accom-
plished, but isomerization of this intermediate to a carbene
metallacyclopentadiene would create an sp3-hybridized meth-
ylene group at C1. This complex is Cs symmetric with the mirror
plane relating the protons on C1 to one another and thus
equilibrating them. Isomerization back to the original geometry
of 7 then results in scrambling of the original hydrogens attached
There are a number of metallacyclopentadiene complexes of
d8 transition metals in the literature;48-53 thus, postulating such
a species as an intermediate has precedence. A Rh(I) catalyst
was recently reported to C-H activate the terminal vinyl C-H
bond in a η1:η2-eneiminyl ligand to form a Rh(III) metallapy-
rrole hydride species;54 this transformation is analogous to the
Pt(II) η1:η2-butadienyl to Pt(IV) metallacyclopentadiene trans-
formation proposed here. A similar transformation has been
proposed for a Rh(I) η1-butadienyl complex.22 One might hope
to observe some of the other isomer in solution, but we believe
that the isomer in which C1 and C2 form the η2-olefin will be
energetically less favorable than the observed isomer. Even
though a terminal olefin typically binds more tightly to Pt than
an internal olefin, here the t-Bu group on C4 would be forced
to point directly toward the Cl-nacnac aryl ring and the result
would be an unfavorable steric interaction. Mechanism B seems
more attractive because, unlike A, it does not require either C-C
bond cleavage or alkyne deinsertion.
(48) Muller, C.; Lachicotte, R. J.; Jones, W. D. Organometallics 2002,
21, 1118.
(49) van Belzen, R.; Elsevier, C. J.; Dedieu, A.; Veldman, N.; Spek,
A. L. Organometallics 2003, 22, 722.
(50) Eisch, J. J.; Ma, X.; Han, K. I.; Gitua, J. N.; Kruger, C. Eur. J. Inorg.
Chem. 2001, 77.
(51) Campora, J.; Palma, P.; Carmona, E. Coord. Chem. ReV. 1999, 195,
207.
(52) Otsuka, S.; Nakamura, A. AdV. Organomet. Chem. 1976, 14, 245.
(53) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M. J. Orga-
nomet. Chem. 2000, 600, 37.
(47) Gao, Y.; Jennings, M. C.; Puddephatt, R. J. Dalton Trans. 2003,
261.
(54) Colby, D. A.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc.
2008, 130, 3645.

5260 Organometallics, Vol. 27, No. 20, 2008
West et al.
Scheme 6. Addition of Various Alkynes to (Cl-nacnac)Pt(H)(1-
pentene) (1)
ꢀ-enamineimine) were synthesized via published procedures.
Silylalkynes Ph3SiCt CH and Ph2MeSiCt CH were synthesized via
published procedures.58 The t-BuCt CD was formed by stirring
t-BuCt CH with NaOD/D2O for 2 days. All other reagents were
used as received from Sigma Aldrich.
1H NMR and 13C NMR spectra were recorded on Bruker AMX
300 MHz, Bruker Avance 400 MHz, and Bruker DRX 500 MHz
spectrometers. 1H NMR and 13C NMR chemical shifts were
referenced to residual 1H and 13C signals of the deuterated solvents.
Infrared spectra were recorded on an ASI ReactIR 1000 instrument.
For clarity the NMR data for the Cl-nacnac ligand for all of the
complexes has been omitted from the synthesis of each complex
and given in Table 1.
Cl-nacnacPt(H)(1-pentene) (1). The complex was synthesized
in a manner analogous to that for nacnacPt(H)(1-pentene). To a
Schlenk flask was added 200 mg (0.348 mmol) of Me4Pt2(µ-SMe2)2
and 245 mg (0.766 mmol, 2.2 equiv) of Cl-nacnacH. Methylene
chloride and pentane were added, and the solution was stirred
overnight. The bright yellow solution gradually changed to a darker
orange color. The resulting oil was chromatographed on a silica
column pretreated with a 3% NEt3 in CH2Cl2 solution, using 80:
20 hexanes-CH2Cl2 solution as the mobile phase. The first yellow
band contains the product and free ligand; this product was collected
and rotavapped to dryness. The product was chromatographed again
using an untreated silica column and 100% CH2Cl2 to yield 106
mg (30%) of pure 1. IR (CH2Cl2): νPt-H 2217 cm-1. 1H NMR (δ,
CD2Cl2, 400 MHz): 3.24 (1H, sextet, Pt-CH2dCHPr, 3JH-H ) 6.8
Hz); 3.06 (1H, d, cis-Pt-CH2dCHPr, 3JH-H,trans ) 12.8 Hz, 2JPt-H
Conclusions
The (Cl-nacnac)Pt(H)(1-pentene) complex 1 is a useful
starting material to assess the reactivity of the (Cl-nacnac)Pt(H)
fragment, as the 1-pentene is easily displaced by other ligands.
Complex 1 reacts with alkynes to displace 1-pentene, followed
by rapid insertion of the alkyne into the Pt-H bond. Once
insertion occurs, the electron-rich Pt reacts with alkyl or aryl
C-H bonds on the newly formed vinyl group if they are in
close proximity to the metal. This results in the formation of Pt
allyls when alkynes with protons on the C adjacent to the triple
bond, such as 2-butyne, are used. Alternatively, chelating alkyl/
aryl olefins are formed when there are no protons adjacent to
the triple bond, such as with Ph3SiCt CH or Me3SiCt CH
(Scheme 6). These silyl alkynes insert into the Pt-H bond in a
2,1-manner, probably because the Si atom stabilizes the Pt-C
bond when the silicon is ꢀ to the metal, placing the silyl
substituents proximal to the Pt center for C-H activation. The
1,2-insertion of t-BuCt CH places the alkyne substituents away
from the metal such that C-H activation is disfavored and so
the metal binds another alkyne and a second 1,2-insertion occurs,
yielding an η1:η2-butadienyl complex. The product that results
reflects head-to-tail reductive dimerization of two terminal
alkynes.
3
) 48 Hz); 2.75 (1H, d, trans-Pt-CH2dCHPr, JH-H,cis ) 7.6 Hz,
2JPt-H ) 62.4 Hz); 1.71, 1.58, 1.46, 1.33 (1H, m, Pt-CH2d
CHCH2CH2CH3); 0.83 (3H, t, Pt-CH2dCHCH2CH2CH3, 3JH-H
7.4 Hz); -21.57 (s, 1H, JPt-H ) 1216 Hz, Pt-H). Anal. Calcd
for C22H26N2Cl2Pt: C, 45.21; H, 4.48; N, 4.79. Found: C, 45.31;
H, 4.28; N, 4.68.
)
1
(Cl-nacnac)Pt(anti-η3-C3H4Me) (2). In a vial was dissolved 30
mg (0.051 mmol) of 1 in 2 mL of pentane. To the solution was
added 5.0 µL (3.5 mg, 0.065 mmol, 1.1 equiv) of 2-butyne. The
vial was capped and shaken; after 30 min the solvent was evacuated,
giving 2 as a yellow solid in quantitative yield. The product can
be purified via liquid chromatography using silica gel treated with
97:3 CH2Cl2-NEt3 and a mobile phase of 4:1 hexanes-CH2Cl2.
1H NMR (δ, CD2Cl2, 400 MHz, room temperature): 4.63 (dt, 1H,
3
2
3JH-H,syn ) 6.6 Hz, JH-H,anti ) 10.8 Hz, JPt-H ) 78 Hz,
H2CCHC(H)(Me)); 2.46 (quin, 1H, 3JH-H,syn ) 3JH-H(Me) ) 6.6 Hz,
2JPt-H ) 40 Hz, H2CCHC(H)(Me)); 1.93 (dd, 1H, 3JH-H ) 6.6 Hz,
2JH-H ) 2 Hz, JPt-H ) 24 Hz, syn-H2CCHC(H)(Me)); 1.89 (dd,
1H, JH-H ) 10.8 Hz, JH-H ) 2 Hz, JPt-H ) 24 Hz, anti-
2
3
2
2
3
3
H2CCHC(H)(Me)); 0.60 (d, 3H, JH-H ) 6.4 Hz, JPt-H ) 13.6
Hz, H2CCHC(H)(CH3)). 13C NMR (δ, CD2Cl2, 100 MHz, room
temperature): 98.1 (1JPt-C ) 63 Hz, H2CCHC(H)Me)); 59.3 (1JPt-C
Experimental Section
)
242 Hz, H2CCHC(H)Me)); 40.1 (1JPt-C
) 253 Hz,
H2CCHC(H)Me)); 14.0 (2JPt-C ) 49 Hz, H2CCHC(H)(CH3)).
(Cl-nacnac)Pt(o-C6H4-SiPh2CHdCH2) (3). In a vial was dis-
solved 30 mg (0.058 mmol) of 1 in 2 mL of pentane. To the solution
was added 1 equiv of Ph3SiCt CH. The vial was capped and shaken,
and then after 1 h the solvent was evacuated, yielding compound
3. The product can be purified via liquid chromatography using
silica gel treated with 97:3 CH2Cl2-NEt3 and a mobile phase of
4:1 hexanes-CH2Cl2. X-ray-quality crystals were formed by
General Procedures. Unless otherwise stated, all reactions were
performed under an atmosphere of dry nitrogen or argon using
standard Schlenk and drybox techniques. Argon and nitrogen were
purified by passage through columns of BASF R3-11 catalyst and
4 Å molecular sieves. All glassware was flame-dried under vacuum
and cooled under N2 before use. Diethyl ether, methylene chloride,
toluene, and pentane were purified under an argon atmosphere and
passed through a column packed with activated alumina.55 Tet-
rahydrofuran was distilled from sodium/benzophenone ketyl. Me-
thylene chloride-d2 was vacuum-transferred from calcium hydride
and degassed by several freeze-pump-thaw cycles. Me4Pt2(µ-
SMe2)256 and Cl-nacnacH57 (Cl-nacnacH ) bis(N-(p-Cl-phenyl))-
1
recrystallization from pentane at -30 °C. H NMR (δ, CD2Cl2,
400 MHz, room temperature): 7.82 (m, 2H, o-SiPh); 7.54 (m, 3H,
m,p-SiPh); 7.31 (m, 1H, p-SiPh′); 7.23 (m, 4H, o,m-SiPh′); 6.84
(d, 1H, 3JH-H ) 6.8 Hz, C3-H Pt-PhSi); 6.74 (d, 1H, 3JH-H ) 7.6
(55) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(56) Hill, G. S.; Irwin, M. J.; Levy, C. J.; Rendina, L. M.; Puddephatt,
R. J. Inorg. Synth. 1998, 32, 149.
(57) Budzelaar, P. H. M.; de Gelder, R.; Gal, A. W. Organometallics
1998, 17, 4121.
(58) Ochida, A.; Ito, H.; Sawamura, M. J. Am. Chem. Soc. 2006, 128,
16486.

Alkyne Insertion Products with Pt(H)(1-pentene)(ꢀ-diiminate)
Organometallics, Vol. 27, No. 20, 2008 5261
Table 1. 1H and 13C NMR Data for the Cl-nacnac Ligand of Complexes 1-8
nacnac p-Cl-Ph (δ, ppm) nacnac backbone (δ, ppm)
complex
1
1H: m 7.34 d, 2H, 8.4 Hz; m 7.23 d, 2H, 8.4 Hz; o 6.93 d, 2H, 8 Hz; o 1H: CH 5.06 s, 1H; CH3 1.74, 1.68 s, 3H
6.83 d, 1H, 8.4 Hz; o 6.79 d, 1H, 8.4 Hz
2
1H: 7.30 m, 4H; 7.1-6.9 m, 4H
1H: CH 4.92 s, 1H; CH3 1.65, 1.64 s, 3H
3
13C: N-C 156.7, 156.3; CH/CCl 128.3, 128.3, 128.3, 128.3, 124.8,
124.8, 124.6, 124.6, 124.3, 124.1
13C: CdN 158.5, 156.2; CH 98.7, JPt-H ) 61 Hz; CH3 23.9, 23.6
3
1H: m 7.34 br d, 2H; o 7.03 br, 1H; o 6.95 br, 1H; m 6.70 d, 2H, 8.4
Hz; o 6.28 d, 2H, 8.4 Hz
1H: CH 5.08 s, 1H; CH3 1.75, 1.72 s, 3H
13C: N-C 151.4, 148.4; CH/CCl 139.2-122.4a
13C: CdN 160.9, 158.2; CH 100.8, JPt-H ) 48 Hz; CH3 26.0, 25.7
3
4
5
1H: m 7.23 d, 2H, 8.4 Hz; m 6.86 d, 2H, 8.4 Hz; m 6.62 br, 2H; o 6.20 1H: CH 5.07 s, 1H; CH3 1.81, 1.62 s, 3H
br, 2H
1H: 7.30 m, 4H; 6.87 m, 1H; 6.81 m, 3H
1H: CH 5.02 s, 1H; CH3 1.75, 1.63 s, 3H
13C: N-C 152.4, 148.1; CH/CCl 130.6, 129.8, 128.2, 128.2, 128.1,
128.1, 127.6, 127.6, 127.2, 127.2
13C: CdN 159.6, 156.9; CH 99.4, JPt-H ) 48 Hz; CH3 26.0, 25.7
3
6
1H: 7.35 d, 2H, 8.4 Hz; 7.31 d, 2H, 8.4 Hz; 7.02 d, 2H, 8.7 Hz; 6.86 d, 1H: CH 5.01 s, 1H; CH3 1.78, 1.71
2H, 8.7 Hz
7a
1H: 7.32 d, 2H, 8 Hz; 7.30 d, 2H, 8 Hz; 6.86 br d, 2H; 6.80 d, 2H, 8.1 1H: CH 4.91 s, 1H; CH3 1.73, 1.67
Hz
3
13C: N-C 152.2, 151.2; CH/CCl 130.2, 129.9, 128.5, 128.5, 128.5,
128.5, 128.2, 128.2, 127.3, 127.3
13C: CdN 160.0, 156.2; CH 98.9, JPt-H ) 50 Hz; CH3 25.3, 25.0
7b
8
1H: 7.6-6.9b
1H: CH 5.10 s, 1H; CH3 1.85, 1.84 s, 3H
13C: CdN 160.1, 156.4; CH 99.0; CH3 25.3, 24.9
1H: CH 4.70 s, 1H; CH3 1.59, 1.57 s, 3H
13C: N-C 153.6, 152.6; CH/CCl 129-122c
1H: 7.24 d, 2H, 8.8 Hz; 7.22 d, 2H, 8.8 Hz; 7.03 d, 2H, 8 Hz; 6.96 d,
2H, 8 Hz
3
13C: N-C 155.0, 150.1; CH/CCl 129.3, 129.1, 129.1, 129.0, 129.0,
128.1, 128.1, 127.6, 127.6, 124.1
13C: CdN 158.2, 157.5; CH 99.4, JPt-H ) 43 Hz; CH3 25.0, 25.0
a p-Cl-Ph carbons are indistinguishable from SiPh3 carbons; all are given in the Experimental Section. b p-Cl-Ph protons are indistinguishable from
aromatic phenylacetylene protons. c p-Cl-Ph carbons and aromatic phenylacetylene carbons were not individually identified.
Hz, C6-H Pt-PhSi); 6.61 (t, 1H, 3JH-H ) 7.2 Hz, C5-H Pt-PhSi);
(SiMe(CH3)up); -14.1 ((CH2)SiMe2, 1JPt-C ) 504 Hz). Anal. Calcd
for C22H26N2Cl2PtSi: C, 43.14; H, 4.28; N, 4.57. Found: C, 43.50;
H, 3.93; N, 4.33.
6.54 (t, 1H, 3JH-H ) 7.2 Hz, C4-H Pt-PhSi); 3.70 (dd, 1H, 3JH-H,cis
3
) 10.8 Hz, JH-H,trans ) 14.8 Hz, (SiR3)HCdCH2); 3.24 (d, 1H,
3
3JH-H,cis ) 10.8 Hz, (SiR3)HCdCH2); 3.07 (d, 1H, JH-H,trans
)
(Cl-nacnac)Pt(CO)(CH2SiMe2CHdCH2) (6). In an NMR tube
was dissolved 10 mg (0.016 mmol) of 5 in 2 mL of pentane. CO
gas was bubbled into the solution, and then the tube was shaken,
giving compound 6 in quantitative yield by 1H NMR. IR (hexanes,
room temperature): νCO 2072 cm-1. 1H NMR (δ, CD2Cl2, 300 MHz,
14.8 Hz, (SiR3)HCdCH2). 13C NMR (δ, CD2Cl2, 125 MHz, RT):
139.2, 136.5, 135.8, 135.8, 135.8, 135.5, 135.5, 135.5, 133.2, 133.1,
133.1, 131.2, 130.3, 130.2, 130.0, 129.9, 129.1, 128.4, 128.4, 128.4,
128.1, 128.1, 128.1, 126.6, 126.6, 124.1, 122.4 (28C, Ar/Ph C);
1
80.8 (SiPh2CHdCH2, JPt-C ) 193 Hz); 66.8 (SiPh2CHdCH2,
room temperature): 6.10 (dd, 1H, 3JH-H,trans ) 20.1 Hz, 3JH-H,cis
)
1JPt-C ) 198 Hz). Anal. Calcd for C37H32N2Cl2PtSi: C, 55.64; H,
4.04; N, 3.51. Found: C, 55.92; H, 3.92; N, 3.29.
14.6 Hz, (SiR3)HCdCH2); 5.81 (dd, 1H, JH-H,cis ) 14.6 Hz,
3
3
3JH-H,gem ) 3.2 Hz, (SiR3)HCdCH2); 5.51 (dd, 1H, JH-H,trans
)
(Cl-nacnac)Pt(CO)(o-C6H4-SiPh2CHdCH2) (4). In an NMR
tube was dissolved 10 mg (0.013 mmol) of 3 in 2 mL of pentane.
CO gas was bubbled into the solution, and then the tube was shaken,
giving compound 4 in quantitative yield by 1H NMR. IR (hexanes,
room temperature): νCO 2080 cm-1. 1H NMR (δ, CD2Cl2, 400 MHz,
20.1 Hz, 3JH-H,gem ) 3.2 Hz, (SiR3)HCdCH2); -0.08 (s, 2H, 2JPt-H
) 78 Hz, Pt-CH2Si); -0.10 (s, 6H, SiMe2). Anal. Calcd for
C23H26N2Cl2OPtSi: C, 43.13; H, 4.09; N, 4.37. Found: C, 43.40;
H, 3.81; N, 4.10.
(Cl-nacnac)Pt(η1:η2-C(H)dC(t-Bu)C(H)dC(H)(t-Bu)) (7a). In
a vial was dissolved 30 mg (0.058 mmol) of 1 in 2 mL of pentane.
To the solution was added 21.4 µL (14.2 mg, 3 equiv) of
3,3-dimethyl-1-butyne. The vial was capped and shaken, and then
after 3 h the solvent was evacuated, yielding compound 7a. The
product can be purified via liquid chromatography using silica gel
treated with 97:3 CH2Cl2-NEt3 and a mobile phase of 4:1
3
room temperature): 7.46 (d, 4H, JH-H ) 6.8 Hz, o-SiPh2); 7.38
(m, 4H, m-SiPh2); 7.30 (m, 2H, p-SiPh2); 7.24 (dd, 1H, 3JH-H,cis
)
14.4 Hz, 3JH-H,trans ) 20.0 Hz, (SiR3)HCdCH2); 7.03 (d, 1H, 3JH-H
3
) 6.8 Hz, C6-H Pt-PhSi); 6.74 (d, 1H, JH-H ) 7.2 Hz, C3-H
3
Pt-PhSi); 6.69 (t, 1H, JH-H ) 7.2 Hz, C5-H Pt-PhSi); 6.51 (t,
3
3
1H, JH-H ) 7.0 Hz, C4-H Pt-PhSi); 6.23 (dd, 1H, JH-H,cis
)
3
1
14.4 Hz, JH-H,gem ) 3.6 Hz, (SiR3)HCdCH2); 5.57 (dd, 1H,
3JH-H,trans ) 20.0 Hz, 3JH-H,gem ) 3.6 Hz, (SiR3)HCdCH2). Anal.
Calcd for C38H32N2Cl2OPtSi: C, 55.21; H, 3.90; N, 3.39. Found:
C, 55.42; H, 3.83; N, 3.11.
hexanes-CH2Cl2. H NMR (δ, CD2Cl2, 300 MHz, room temper-
2
ature): 4.01 (s, 1H, JPt-H ) 32 Hz, Pt-C(H)dC(t-Bu)-); 3.50
3
2
(d, 1H, JH-H ) 8.8 Hz, JPt-H ) 53 Hz, -C(H)dC(H)(t-Bu));
3
2
2.89 (d, 1H, JH-H ) 8.8 Hz, JPt-H ) 47 Hz, -C(H)dC(H)(t-
Bu)); 0.87 (s, 9H, -C(H)dC(H)(C(CH3)3)); 0.82 (s, 9H, -C(H)d
C(C(CH3)3)-). 13C NMR (δ, CD2Cl2, 100 MHz, room temperature):
151.2 (Pt-C(H)dC(t-Bu)-); 113.7 (1JPt-C ) 740 Hz, Pt-C(H)dC(t-
Bu)-); 104.0 (1JPt-C ) 248 Hz, -C(H))C(H)(t-Bu)); 63.7 (1JPt-C
) 24 Hz, -C(H)dC(H)(t-Bu)); 37.3 (3JPt-C ) 77 Hz, Pt-
(Cl-nacnac)Pt(CH2SiMe2CHdCH2) (5). In a vial was dissolved
30 mg (0.058 mmol) of 1 in 2 mL of pentane. To the solution was
added 1 equiv of Me3SiCt CH. The vial was capped and shaken,
and then after 1 h the solvent was evacuated, yielding compound
5. The product can be purified via liquid chromatography using
silica gel treated with 97:3 CH2Cl2-NEt3 and a mobile phase of
4:1 hexanes-CH2Cl2. 1H NMR (δ, CD2Cl2, 400 MHz, room
C(H)dC(CMe3)-); 36.0 (2JPt-C
) 21 Hz, -C(H)dC(H)-
(CMe3)); 32.0 (3JPt-C ) 24 Hz, -C(H)dC(H)(C(CH3)3)-); 28.3
(Pt-C(H)dC(C(CH3)3)-). Anal. Calcd for C29H36N2Cl2PtSi: C,
51.33; H, 5.35; N, 4.13. Found: C, 51.41; H, 5.29; N, 3.99.
(Cl-nacnac)Pt(η1:η2-C(H)dC(Ph)C(H)dC(H)(Ph)) (7b). In an
NMR tube was dissolved 10 mg (0.017 mmol) of 1 in 0.6 mL of
CD2Cl2. To the solution was added 3.8 µL (3.5 mg, 2 equiv) of
phenylacetylene. The tube was capped and shaken, and the 1H NMR
spectrum recorded after 20 min displayed complex 7b. 1H NMR (δ,
CD2Cl2, 400 MHz, room temperature): 7.6-6.9 (18H, Ph); 5.22 (s,
2
temperature): 3.34 (m, 1H, JPt-H ) 68 Hz, (SiR3)HCdCH2 cis);
3
3.02 (m, 2H, (SiR3)HCdCH2 trans (simulated J values: JH-H,trans
3
2
) 15.2 Hz, JH-H,cis ) 10.2 Hz, JH-H ) 3.2 Hz)); 0.16, (s, 3H,
Si(Me2)up); -0.26 (s, 3H, Si(Me2)down); -0.89 (d, 1H, 2JH-H ) 12.4
Hz, 2JPt-H ) 67.6 Hz, Pt-(CH2)downSi);-1.34 (d, 1H, 2JH-H ) 12.4
2
Hz, JPt-H ) 77.6 Hz, Pt-(CH2)upSi). 13C NMR (δ, CD2Cl2, 125
MHz, room temperature): 75.3 (SiMe2CHdCH2, 1JPt-C ) 242 Hz);
63.9 (SiMe2CHdCH2, 1JPt-C ) 75 Hz); 7.6 (SiMe(CH3)down); -2.3

5262 Organometallics, Vol. 27, No. 20, 2008
West et al.
Table 2. Crystal Data and Structure Refinement Details for 3 and 6
3
6
empirical formula
mol wt
C37H32Cl2N2PtSi
798.73
C23H26Cl2N2OPtSi
640.54
temp, K
100(2)
100(2)
wavelength, Å
cryst syst
space group
a, Å
b, Å
c, Å
0.710 73
triclinic
P1
1.541 78
monoclinic
P21/c
12.6224(5)
9.5550(4)
20.1223(8)
90
91.486(2)
90
2426.07(17)
4
j
10.2345(2)
11.6447(2)
14.6854(3)
97.484(1)
90.520(1)
91.588(1)
1734.45(6)
2
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
calcd density, Mg/m3
1.529
4.261
788
1.754
13.451
1248
µ, mm-1
F(000)
crystal size, mm3
2θ range, deg
index ranges
no. of rflns collected
no. of indep rflns
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
largest diff peak and hole, e Å-3
0.59 × 0.12 × 0.10
0.25 × 0.05 × 0.05
1.40-25.68
3.50-69.51
-12 e h e 12, -13 e k e 14, -17 e l e 11
15 681
6559 (R(int) ) 0.0330)
6559/0/390
-15 e h e 15, -11 e k e 11, -24 e l e 24
24 550
4485 (R(int) ) 0.0351)
4485/0/275
1.101
1.139
R1 ) 0.0274, wR2 ) 0.0733
R1 ) 0.0314, wR2 ) 0.0751
1.291 and -0.693
R1 ) 0.0256, wR2 ) 0.0615
R1 ) 0.0278, wR2 ) 0.0626
2.059 and -0.988
2
3
1H, JPt-H ) 34 Hz, Pt-C(H)dC(Ph)-); 4.41 (d, 1H, JH-H ) 7.6
100 MHz, room temperature): 143.6 (3JP-C ) 3 Hz, Pt-C(H)dC(t-
Bu)-); 140.4 (-C(H)dC(H)(t-Bu)); 129.9 (-C(H)dC(H)(t-Bu));
120.1 (2JP-C ) 15 Hz, Pt-C(H)dC(t-Bu)-); 38.4 (3JPt-C ) 70
Hz, Pt-C(H)dC(CMe3)-); 32.6 (-C(H)dC(H)(CMe3)); 30.9
(Pt-C(H)dC(C(CH3)3)-); 30.1 (-C(H)dC(H)(C(CH3)3)); 16.8
2
3
Hz, JPt-H ) 46 Hz, -C(H)dC(H)(Ph)); 4.29 (d, 1H, JH-H ) 7.6
Hz, 2JPt-H ) 50 Hz, -C(H)dC(H)(Ph)). 13C NMR (δ, CD2Cl2, 100
MHz, room temperature): 142.7 (Pt-C(H)dC(Ph)-); 140.0, 138.6
(C-Ph ipso C); 129-122 (15C, Ph C); 123.4 (Pt-C(H)dC(Ph)-);
92.5 (-C(H)dC(H)(Ph)); 63.7 (-C(H)dC(H)(Ph)).
2
(1JP-C ) 40 Hz, JPt-C ) 53 Hz, P(CH3)3).
(Cl-nacnac)Pt(η1-C(H)dC(t-Bu)C(H)dC(H)(t-Bu))(PMe3)
(8). A CH2Cl2 solution of the butadienyl complex 7 was placed in
a flask in the drybox. The flask was removed from the box and
placed under positive N2 pressure. Trimethylphosphine was added
via microliter syringe; upon addition the light orange solution turned
bright yellow. After 30 min the solvent was removed and the
Crystallographic Data for 3 and 6. Crystal data and structure
refinement details for 3 and 6 are given in Table 2.
Acknowledgment. We acknowledge Elise Traversa for
help in obtaining the X-ray structure of 6. This research was
supported by funding from the National Science Foundation
(Grant No. CHE-0717086).
1
product triturated with pentane, giving 8 in quantitative yield. H
NMR (δ, CD2Cl2, 400 MHz, room temperature): 5.50 (d, 1H, 3JH-H
2
) 13 Hz, -C(H)dC(H)(t-Bu)); 5.39 (s, 1H, JPt-H ) 34 Hz,
Pt-C(H)dC(t-Bu)-); 5.23 (d, 1H, 3JH-H ) 13 Hz, -C(H)dC(H)(t-
Supporting Information Available: CIF files giving structural
data for complexes 3 and 6. This material is available free of charge
via the Internet at http://pubs.acs.org.
2
Bu)); 1.21, (s, 9H, -C(H)dC(C(CH3)3)-); 0.87 (d, 9H, JP-H
)
3
10.4 Hz, JPt-H ) 30 Hz, P(CH3)3); 0.73 (s, 9H, -C(H)d
C(H)(C(CH3)3)). 31P NMR (δ, CD2Cl2, 162 MHz, room tempera-
ture): -39.5 (s, JPt-P ) 4164 Hz, PMe3). 13C NMR (δ, CD2Cl2,
OM800521X
1