Coupling of terminal alkynes by RuHXL2 (X = Cl or N(SiMe3)2, L = PiPr3)

Article abstract of DOI:10.1016/j.jorganchem.2007.12.016

The compounds RuL₂HX, where L = PⁱPr₃ and X = Cl or N(SiMe₃)₂, are catalyst precursors for dimerization of terminal alkynes to enynes and also to cumulenes at 23 °C; selectivity among these products i

Full text of DOI:10.1016/j.jorganchem.2007.12.016

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1664–1673
www.elsevier.com/locate/jorganchem
Coupling of terminal alkynes by RuHXL2 (X = Cl or
N(SiMe3)2, L = PiPr3)
Joo-Ho Lee, Kenneth G. Caulton *
Department of Chemistry, Indiana University, Bloomington, IN 47405-7102, United States
Received 14 November 2007; received in revised form 7 December 2007; accepted 7 December 2007
Available online 15 December 2007
Abstract
The compounds RuL2HX, where L = PiPr3 and X = Cl or N(SiMe3)2, are catalyst precursors for dimerization of terminal alkynes to
enynes and also to cumulenes at 23 °C; selectivity among these products is X-dependent, but not high. Conversion of Ru species onto the
catalytic cycle was undetectably small, so alternative approaches to understanding the catalytic mechanism were employed: stoichiom-
etric reactions, independent synthesis of candidate intermediates, and trapping with CO. These show the intermediacy of vinylidenes and
vinyl compounds, and reveal conversion of cumulenes to the thermodynamically more stable enynes.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Terminal alkynes; Dimerization; Enynes; Cumulenes
1. Introduction
In this report, these 14e unsaturated ruthenium com-
plexes are investigated for the reactivity with terminal
alkynes, via possible intermediate vinylidene or vinyl com-
plexes. The reaction of terminal alkynes with unsaturated
divalent ruthenium or osmium complexes is known to form
vinylidene complexes (Scheme 1) [7–11]. The present report
Back donation from a metal center containing no pi acid
ligands has been shown to have the ability to isomerize
hydrocarbons to the isomeric carbene complexes, especially
from olefins (Eq. (1)).
H
L
CH3
R'
H
H
L
L
L
L
Cl
Cl
H
H
H
+
2
Cl
Ru
2
Ru
Ru
ð1Þ
L
R'
1
1
R' = H, OR, or NR R2
For example, the 14-electron ruthenium(II) complexes
RuXHL2 [1] (X = Cl, F, NHtBu, OtBu, or N(SiMe3)2,
and L = PiPr3) were investigated for their reactivity with
various vinyl compounds [2–6].
focuses especially on the reactivity of 14-electron ruthe-
nium(II) complexes RuXHL2 (X = Cl (1), or N(SiMe3)2
(2), and L = PiPr3) with various alkynes, but under cata-
lytic conditions, where the alkyne/Ru ratio is much greater
than unity. The dimerization of terminal alkynes [12–17]
has been widely studied because of its attractive, atom-eco-
nomic forming of a C–C bond which serve as a useful
building block for organic synthesis [18–20]. In addition,
*
Corresponding author.
E-mail address: caulton@indiana.edu (K.G. Caulton).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.12.016

J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
1665
and 31P{1H} NMR spectra of 2 over one day, although
there was no signal for the terminal hydrogen of
PhC„CH. Instead, when 5 equiv. of PhC„CH was
applied in that reaction mixture, an AB pattern grew at
H
L'
H
L'
C
H
Cl
L'
Ru H2
+
2
HC C R"
Cl
L'
Ru
C
H
H
H
-
R"
R"
L' = PtBu2Me R''= Ph or SiMe3
L' = PiPr3
R" = Ph or H
1
5.77 and 6.39 ppm in the H NMR spectrum which corre-
sponds cis-PhC(H)@C(H)CCPh (3a). At 20:1 mol ratio, in
3.7 h, all acetylene is converted to cis-[13], trans-[13], and
1,3-disubstituted enynes [12] and cumulene (6, 7) in the
mole ratio 79:14:7:trace. In addition, a small amount of
styrene (ꢁ3% by the ratio of integration of vinyl protons
Scheme 1.
the enyne could be a monomer unit to produce conjugated
polymers or oligomers. However, due to the possibility of
several isomers (Scheme 2), the selectivity of RCCH dimer-
ization is the biggest challenge to be addressed [21]. Here
we present the catalytic reactivity of RuXHL2 with termi-
nal alkynes together with a mechanistic study. Ruthenium
has good precedent for dimerization of terminal alkynes
[20,22–29].
1
on the H NMR) was seen in the spectra. Past reported
dimerization of terminal alkynes has yielded mainly three
kinds of enyne (Scheme 2) [12–15]. In addition, in a few
cases, the formation of cumulenes (6 and 7) has been
reported also [13–16,31,32].
2.3. R = SiMe3 and CMe3
2. Results and discussion
The reactivity of 2 towards tert-butylacetylene and tri-
methylsilylacetylene were also studied (Table 1) [12–16].
1
2.1. Reaction of 14 electron ruthenium complexes (1 and 2)
and terminal alkynes, RCCH
To periodically monitor the dimerization, H NMR and
31P{1H} NMR were used. Especially in the case of 1H
NMR, the signals of dimers in the vinyl region were
observed, as well as for the unreacted acetylene proton.
Compound 2 is a catalyst precursor for the dimerization
t
[12,14,30] of terminal alkynes (RC„CH, R = Ph (a), Bu
(b), and Me3Si (c)) with high stereoselectivities at room
temperature. 2 can be prepared in situ by addition of LiN-
(SiMe3)2 to 1; this conversion is complete within 30 min.
A hydride triplet is observed at ꢀ20.8 ppm and a
31P{1H} NMR singlet is seen at 98.8 ppm. Two doublet
Table 1
Dimerization of RC„CH by ruthenium complexes 1 and 2 in C6D6
R
Complex
Product ratio 3:4:5:6
% Yield Reaction time
Ph
tBu
Me3Si
Ph
tBu
1
1
1
2
2
2
75.9:7:17.1:trace*
Trace*
100
0
84
100
100
<28 h
i
Over 2 days
<3 days
3.7 h
of virtual triplet Me groups in Pr and two SiMe3 signals
indicate it has Cs symmetry.
21.2:trace*:73.5:5.3
78.8:13.8:7.4:trace*
85.6:trace*:5.7:8.7
<5.5 h
0.5 h
Me3Si
67.5:trace*:trace*:32.5 100
2.2. R = Ph
Reaction condition: catalyst:acetylene = 0.109 mmol:2.18 mmol, room
temperature. Trace*: signals cannot be distinguished because they are too
weak.
When equimolar 2 and PhC„CH was mixed in ben-
zene, there is no significant change observed in H NMR
1
H
C
H
H
C
R
R
C
H
cat.
RC
CH
C
C
C
C
C
C
R
H
H
RC
RC
RC
3
4
5
H
R
C
C
R
H
C
C
C
C
H
C
R
H
C
7
6
R
R=Ph(a), tBu(b), Si Me3(c)
Scheme 2.

1666
J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
In the case of tBuC„CH, 3b (86%) was the major product
(vinyl signals appeared at 5.56 ppm and 5.46 ppm with a
12.3 Hz coupling constant); a vinyl signal at 6.29 ppm, hav-
ing J = 1.5 Hz, indicates formation of 5b (6%). In addition,
the signal of a vinyl proton appeared at 5.51 ppm which
corresponds to cumulene (9%) [13,15,16]. Under the same
conditions, Me3SiC„CH produced mainly cis-enyne, 3c,
(67%) (6.22 ppm and 6.00 ppm with 14.4 Hz coupling)
and a vinyl singlet at 6.37 ppm corresponding to formation
of cumulene (32%) [13,14].
of 6c to 3c took 101 h, but dimerization was done in 0.5 h.
This isomerization is much faster for the Me3Si case. How-
1
ever, this isomerization does not take place once the H
NMR and 31P{1H} NMR signals of 2 have decayed.
Energy difference of cis-enyne and cumulene has been
studied with Me(H)C@C@C@C(H)Me for 6b (Fig. 1) [15]
and H3Si(H)C@C@C(H)SiH3 for 6c (Fig. 1) [14] which
shows cumulenes have higher energy than cis-enynes (by
17.3 kcal/mol for Me(H)C@C@C@C(H)Me, and by
18.9 kcal/mol for H3Si(H)C@C@C@C(H)SiH3).
In the case of the cumulene, it was hard to distinguish
whether it was cis (6) or trans (7) because both have the
same 1H NMR chemical shift [14]. However, since we
observed that cumulenes were isomerized to 3b and 3c
[14], respectively, after 2 dimerized all of BuC„CH or
Me3SiC„CH, this suggests that cumulenes in this case
might have cis stereochemistry, 6b and 6c.
By comparing products from 1 and 2, it was found that
Cl vs. N(SiMe3)2 significantly influences the reaction time
as well as distribution of products; this indicates that at
least one of these two anionic ligands remains attached to
Ru on the catalytic cycle. For example, the fastest reaction
by 2 (dimerization of Me3SiC„CH) is the slowest reaction
by 1 (over 78 h to completely dimerize 20 equiv. of acety-
lene). In addition, catalyst 2 produced mainly 3c, but 5c
t
1
2.4. Catalysis with the chloride analog, 1
was produced only by 1 (only a trace could be seen in H
NMR spectra catalyzed by 2). In the case of the dimeriza-
tion of tert-butylacetylene, mainly 3b was formed by 2.
Unexpectedly, the reaction of BuC„CH with 1 did not
Since detection of metal-containing intermediates was
not possible during catalysis by 2, compound 1 was stud-
ied. Because it is known that the H2 adduct of 1 consumes
2 equiv. of terminal alkyne (liberating olefin) to produce
vinylidene complex (Scheme 1) [8–12], 1 itself could also
form a vinylidene compound with acetylene which could
be one of possible intermediates for the dimerization. In
addition dimerization of alkyne with excess terminal
alkynes could be studied also, to learn the impact of lone
pair electron donor ability, Cl (1) vs. N(SiMe3)2 (2), on cat-
alyst performance. Dimerization of PhC„CH by 1 pro-
duced mainly cis-enyne (3a) with 75.9% of overall
product. In addition, small amounts of trans-(4a) (7%, dou-
blet at 6.3 ppm) and 1,3-enynes (5a) (17.1%, singlets at
t
produce any dimers which might be due to steric bulk
around the metal center after formation of its vinylidene.
1
The only product, seen by H NMR, was trace of 5b over
2 days. However, PhC„CH was not much influenced by
change from Cl to N(SiMe3)2. These gave similar distribu-
tion of products, but the reaction rate was significantly
faster for 2.
2.5. Mechanism
By various studies [12–16], mainly two pathways were
proposed for dimerization of terminal acetylene catalyzed
1
5.74 ppm and 5.69 ppm) were also seen in H NMR. Only
one vinyl signal for 4a is seen because of overlap of the
other vinyl proton signal with the phenyl signals. Unex-
pectedly, the reaction of 1 and tBuC„CH did not produce
any dimer except for a weak signal of enyne 5b. However,
dimerization of Me3SiC„CH produced 1,3-enyne (5c) as a
major dimer (73.5% of total dimers). As minor products, 3c
with 21.2% yield and cis-cumulene (6c) with 5.3% yield
were produced by 1.
Surprisingly, over a long reaction period of dimerization
by 2, isomerization of 6b or 6c to the thermodynamically
more stable 3b or 3c, respectively, occurred [14,15]. These
cumulene isomerizations are slower than the rate of alkyne
dimerization (Tables 1 and 2). For example, isomerization
H
H
C
C
C
C
H3E
EH3
19 (20.1)
H3E
C
C
H
H3EC
C
H
1.7 (1.2)
Table 2
H
Isomerization of cumulene to cis-disubstituted enyne by complex 2
C
R
Ratio of product after isomerization
3:4:5:6
Isomerization time
(h)
EH3
H3EC
C
C
tBu
87.5:trace*:6.5:6
26
<101
H
Me3Si 100:trace*:trace*:trace*
Trace*: signals cannot be distinguished because they are too weak.
Fig. 1. Relative isomer energies (kcal/mol) for E@C(Si).

J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
1667
CHR
H
H
HC
H
8
H
RC CH
RC CH
RC CH
9
[Ru]
[Ru]
C C
[Ru] C C
R
R
1 or 2
L
[Ru] =
X
L
Ru
H2 C CRH
k1
R
H
10
13
C
C
[Ru]
C
C
C
[Ru]
C
R
H
C
C
R
R
k2
H
11
R
R
H
14
C
C
C
C
[Ru]
[Ru]
C
C
C
C
R
R
k3
RC CH
RC CH
H
R
R
H
C
12
C
15
k4
C
C
[Ru]
[Ru]
RC
CH
RC CH
RC CH
RC
C
C
CH
C
C
H
R
R
H
R
R
C
C
C
C
H
H
C
C
C
C
4
3
R
R
Scheme 3.
In all cases, species 8 were identified by triplets due to
the vinylidene proton and to the hydride signal(Table 3).
This suggests that isomerization to vinylidene from acety-
lene is favorable which implicates II (above) as on the cat-
alytic cycle.
Therefore, the mechanism for formation of 3 and 4 in
Scheme 3 is proposed. Here, stereoselectivity is determined
by vinylidene conformers 10 vs. 13, which lead to 3 or 4,
respectively. Since 1 and 2 both have bulky L, when R
by metal complexes. These differ by isomeric catalyst struc-
tures I or II (below). Studying the mechanism of alkyne
dimerization catalyzed by 2 was frustrated because 1H
NMR and 31P{1H} NMR spectra showed no detectable
amount of ruthenium–substrate complex converted onto
the catalytic cycle. Therefore catalyst 1 was chosen for
mechanistic study since it reacts slower than 2 (Table 1).
1:1 mol ratio(RC„CH:1) reactions were performed to see
whether vinylidene complexes, 8 (Scheme 3), were pro-
duced (Scheme 1). In reactions of all three terminal acety-
lenes, 8 was formed.
Table 3
Chemical shift of vinylidene complexes
M
C
CR
M
C
CR
R
1H NMR
31P{1H} (ppm)
C
Hydride (ppm)
Vinylidene proton (ppm)
RC
CH
Ph
ꢀ12.53
ꢀ13.79
ꢀ15.09
4.35
2.77
2.41
51.0
50.88
51.00
CHR
tBu
I
II
Me3Si

1668
J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
was bulky, 3 was the major product (Table 1) since the for-
mation of 11 is apparently more favorable than 14 [14].
Formation of 9 was demonstrated by an osmium analog
[33], where reaction of OsH3ClL2 with 2 equiv. Me3SiCCH
produces a vinylidene compound, which is then trans-
H
R
H
R
H
C
C
C
C
C
C
C
H2
[Ru]
+
C
[Ru]
19
H
R
R
2
formed
into
the
vinyl
vinylidene
compound,
6
OsClL2(C(H)@C(H)SiMe3)(@C@C(H)SiMe3). In the pres-
ent work, when 1 or 2 equiv. of phenyl acetylene was added
to 8a in an attempt to observe any of the proposed
intermediate 9, 10 or 13, not all of 8a was consumed. Even
when 3 equiv. of phenyl acetylene was added, 8a was not
consumed completely. Instead, dimerization of acetylene
was observed, consistent with only small conversion of
Ru onto the catalytic cycle. That is, k1 limits the amount
of active catalyst formed from precatalyst.
L
-H2
[Ru] =
X
Ru
H
R
H
L
R
C
C
16
[Ru]
C
C
C
C
17
[Ru]
H
C
C
R
R
Transformation of g3-PhC4HPh ligand (16, Scheme 4),
an isomer of 11, has been suggested as the source of cumu-
lene [16,30].
R
C
H
3
11
[Ru]
C
R
C
H
C
C
H
R
Compound 16 could be isomerized to cumulenyl ligand
(17) by additional acetylene and then could be released as
cumulene by another acetylene addition. In addition, 16
serves as an entry point into a catalytic cycle to isomerize
6 to 3 (Scheme 5). Oxidative addition of cumulene to 1
or 2 yields 17 with liberation of H2 (Scheme 5).
C
C
C
C
C
C
R
6
C
R
H
R
Scheme 5.
Binding site exchange of the cumulenyl ligand in 17
causes isomerization from cumulenyl to enynyl ligand (17
to 16). When the second cumulene adds to 11, enyne is
released.
R group [33,35] with binding site exchange in Ru-vinyl
group in 11 (path 1). The other possibility is from activated
catalyst form I (path 2).
Another pathway to produce enyne, Scheme 7, involves
species I then IV. Vinyl diacetylide compound (V) could be
For the formation of 5 [12,34], compound 20 is required.
Two pathways are possible (Scheme 6). One is migration of
R
H
H
16
11
R
R
H
X
C
C
C
L
C
L
C
C
X
Ru
L
C
C
X
Ru
C
L
C
Ru
C
L
C
R
L
R
R
10
18
L
R
H
H
C
X
R
Ru
C
C
RC
R
CH
R
C
C
L
L
C
C
H
C
C
X
Ru
6
C
RC
R
L
C
CH
C
R
H
Scheme 4.

J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
1669
attempted through the addition of LiC„CPh to
RuCl2L2(@C@CHPh) [36,37] in benzene over 2 days. Slow
exchange of Clꢀ with PhC„Cꢀ was observed due to the
insolubility of LiC„CPh in the solvent. Characterization
by NMR indicates that 16a, not 10a, is the product formed.
R
CH2
C
5
RC
path 2
path 1
I
HC
CR
[Ru]
H
R
11
C
L
RC CH
While
a
triplet
of
the
vinylidene
proton
[Ru] =
C
[Ru]
C
C
R
X
Ru
(RuCl2L2(@C@CHPh)) (4.7 ppm) has disappeared,
appearance of a singlet at 7.5 ppm suggests formation of
vinyl ligand by migration of acetylide (PhCCꢀ) to C(a).
In addition, the absence of a C(a)13C NMR signal around
250–300 ppm confirms the absence of any Ru@C(a) bond.
Instead, one triplet at 163.4 ppm (JP–C = 8 Hz) is due to a
vinyl C(a) and 11 signals from 137 to 124 ppm which
include acetylene C (in addition to phenyl) are also
observed. Observing acetylene C in that region also indi-
cates the acetylene binds to Ru, as shown in 16a.
C
L
C
H
R
C
R
C
[Ru]
C
RC
CH
CR
H
C
C
R
[Ru]
RC CH
C
C
H
C
R
For complete identification of 16a, CO was added to this
compound in C6D6 at room temperature (Scheme 8) as an
analog to the formation of 12a or 18a. Two carbonyl trip-
lets at 200.7 and 198.1 ppm indicate two CO bind to Ru.
13C{1H} NMR supports formation of 21, not 22, in
R
C
[Ru]
C
20
CR
Scheme 6.
Scheme 8.
A C(a) triplet observed at 145.2 ppm
(JP–C = 4 Hz) and a C(b) triplet is seen at 141.1 ppm but
its JP–C is not fully resolved. Eight phenyl singlets and
two cumulene (C(c) and C(d)) singlets were observed
between 131.4 and 99.1 ppm. In further confirmation of
the ligand structure, protonation of 21 was performed with
HCl, which liberated cumulene (not enyne), with formation
of Ru(CO)2Cl2L2 [38,39].
formed by another acetylene addition. Enyne could be pro-
duced by migration of one of acetylide to the vinyl ligand
(V ? VI), followed by addition of acetylene. In this system,
trans vinyl product is more favorable than cis, which con-
trasts to experiment.
2.6. Independent study of the mechanism: attempted
synthesis of proposed intermediates
H
For independent study of the mechanism, synthesis of
RuClL2(@C@CHPh)(C„CPh) (10a, cf. 10 and 13) was
L
Ru
C
Ph
L
C
C
Cl
C
CHPh
Cl
Ru
C
H
H
L
L
RCCH
[Ru]
[Ru] =
[Ru]
H
C
C
L
III
X
Ru
10a
Ph
16a
Ph
L
R
-RHC=CH2
+2 RCCH
H
To test the catalytic viability of 16a, 20 equiv. of
PhC„CH was added. In 30 min, all of 16a disappeared
and three kinds of dimers appeared. Compounds 3a, 4a,
and 5a were produced in the ratio of 76.5:5:18.5 which
ratio is very similar to that from catalytic dimerization of
phenylacetylene by 1 (Table 1). However in this dimeriza-
tion, cumulene was not seen. This suggests that binding
PhC„CH to 16a generates 12 or 15 to form cis- or
trans-enyne, respectively, instead of 18; 16a is a precatalyst
for dimerization.
[Ru]
[Ru]
R
R
IV
I
R
R
R
RCCH
R
RCCH
VI
V
R
R
[Ru]
R
[Ru]
R
R
3. Discussion
R
This work has shown that CO-free, p-electron rich RuII
complexes have the ability to form C/C bonds at 23 °C. We
Scheme 7.

1670
J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
H
Ph
H
C
OC
Ph
Ph
C
C
OC
16a + 2CO
OC
[Ru]
C
C
or
21
C
C
OC
[Ru]
22
C
Ph
L
Ru
Cl
[Ru] =
L
HC
l
OC
[Ru]
+
C
HPh
C
PhHC
OC
Cl
observed
Scheme 8.
have not attempted to optimize conditions for best selectiv-
ity, but these would clearly be dependent on R group iden-
tity in RCCH. The lability of H on an sp carbon clearly
contributes to the reactivity reported here, making vinyli-
dene complex formation facile. Once the Ru@C bond is
formed, insertion of this into a Ru–acetylide bond becomes
possible. These reactions remain mechanistically obscure
because a spectroscopically undetectable amount of cata-
lyst precursor is converted onto the catalytic cycle.
A recent report [40] has provided deep insight into one
mechanism of enyne formation catalyzed by one specific
homogenous catalyst, [C6H3(CH2PtBu2)2]Ir, which is selec-
tive for trans-1,4-phenyl-but-3-ene-1-yne, 4a. The deduced
mechanism at this very sterically constrained catalyst is
H–C(sp) oxidative addition, then Ir–H addition across
the second alkyne C„C bond, then reductive coupling to
form enyne. The high regioselectivity is concluded to result
at the reductive coupling step, and the kinetically favored
r-vinyl complex (Ph on Ca) fails at C–C coupling, so the
more slowly formed alternative (Ph or Cb) is on the path
to the observed enyne regioisomer. Isotope effect measure-
ments rule out a vinylidene intermediate. No cumulene was
formed.
4. Experimental
4.1. General
All reactions and manipulations were performed using
standard Schlenk line and glovebox techniques under the
prepurified argon. All solvents were dried and distilled
from appropriate agents and stored in airtight solvent
bulbs with Teflon closures under argon. RuCl2-
(PiPr3)2(@C@CHPh) was prepared by the reported proce-
dure (using [RuCl2(COD)]x instead of [RuCl2(p-cymene)]2)
[38]. All NMR solvents were also dried with appropriate
agents and vacuum transferred and stored in the glovebox
under argon. All NMR spectra were taken by Varian Gem-
ini 2000 (300 MHz H, 121 MHz 31P) spectrometers and
1
Varian Inova (400 MHz H, 161 MHz 31P) spectrometer
1
1
and referenced by residual protio solvent peaks for H or
external standard (phosphoric acid) for 31P.
4.2. Preparation of [RuHCl(PiPr3)2]2, 1 [1]
t
1.2 mL of butylethylene (6.28 mmol) was slowly added
into 2.9 g of [RuH(H2)Cl(PiPr3)2] (6.28 mmol) with 40 mL
of toluene via syringe. Color of the solution darkened. This
solution was stirred for 40 min at room temperature, and
volatiles were removed into a liquid N2 trap. The red
brown precipitate was dried in vacuo. 1H NMR
The diversity of products formed in the present work
differentiates this from the (pincer) Ir catalyst performance
described above, and indicates the likelihood of participa-
tion here by more reaction channels than for (pincer)Ir.
The catalysts differ in that the Ru system begins with a
hydride and involves RuII, so both (vs. an IrI nonhydride)
favor Ru avoiding RuIV and thus favoring a vinylidene-
2
(300 MHz, C6D6): d ꢀ24.2 (t, JP–H = 32.8 Hz, Ru–H),
1.34 (dvt, JP–H = 3JH–H = 6.2 Hz, 18H, P(CHMe2)3), 1.36
(dvt, JP–H = 3JH–H = 6.2 Hz, 18H, P(CHMe2)3), 2.19 (m,
6H, P(CHMe2)3). 31P{1H} NMR (162 MHz, C6D6,
20 °C): d 84.1 (s).
t
forming initial step. The four Bu groups make the (pin-
cer)Ir system more dominated by steric effects than the
nonchelated PiPr3 groups on Ru; increased selectivity is
thus favored for the former. In fact, our determination that
a hydride–vinylidene is formed in a stoichiometric reaction
shows this preference for a RuII–H reagent. In short, differ-
ent complexes exhibit different catalytic performance by
different influence of structure/composition/d-electron
count (here d6 vs. d8).
4.3. Preparation of RuH(N(SiMe3)2)(PiPr3)2, 2 [1]
Fifteen grams of [RuHCl(PiPr3)2]2 (16.4 lmol) was dis-
solved with 1 mL C6D6 in a Teflon sealed NMR tube.
Then, 0.55 mg of LiN(SiMe3)2 (32.8 lmol) was added, giv-
1
ing an immediate reaction. H NMR (300 MHz, C6D6): d

J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
1671
ꢀ20.8 (t, 2JP–H = 31 Hz, 1H, Ru–H), 0.10 (s, 9H, NSiMe3),
0.52 (s, 9H, NSiMe3), 1.15 (dvt, JP–H = 3JH–H = 7 Hz, 18H,
P(CHMe2)3), 1.21 (dvt, JP–H = 3JH–H = 7 Hz, 18H,
P(CHMe2)3), 1.85 (m, 6H, P(CHMe2)3). 31P{1H} NMR
(121 MHz, C6D6): d 94.8 (s).
lene (32.8 lmol) was added via syringe. Color changed to
1
light red brown. This reaction was finished in 30 min. H
2
NMR (C6D6, 300 Hz): d ꢀ15.09 (t, JP–H = 18.2 Hz,
RuH), d 0.15 (s, CCHSi(Me3)), d 1.28 (m, P(CH(Me2))3),
4
d 2.63 ppm (m, P(CH(Me2))3), d 2.41 (t, JP–H = 3.3 Hz,
CCHSi(Me3)). 31P{1H} NMR (C6D6, 121 Hz):
d
4.4. Dimerization of terminal alkynes catalyzed by 1
51.00 (s).
49.2 lmol of 1 was dissolved in 1.5 mL of C6D6 and
equally divided among three NMR tubes equipped with a
Teflon seal. 328 lmol of phenylacetylene, tert-butylacety-
lene, or trimethylsilylacetylene were added each tube at
room temperature. By 1H NMR, the progress of dimeriza-
tion was monitored over time.
4.9. cis-PhCH@CHCCPh (3a) [13]
1H NMR (C6D6, 300 MHz): d 6.39 (d, JH–H = 12 Hz,
3
3
@CH), d 5.77 (d, JH–H = 12 Hz, @CH). d 8.10–6.80 (m,
Ph).
4.10. trans-PhCH@CHCCPh (4a) [13]
4.5. Dimerization of terminal alkynes catalyzed by 2
1H NMR (C6D6, 300 MHz): d 6.29 (d, 3JH–H = 19.9 Hz,
@CH), d 8.10–6.80 (m, Ph).
Compound 2 in 1.5 mL of C6D6 was prepared by addi-
tion of LiN(SiMe3)2 (49.2 lmol) to 1 (49.2 lmol) in C6D6
before it was used. Then, each 0.5 mL of solution
(16.4 lmol) of 2 was placed in three NMR tubes equipped
with a Teflon seal. 328 lmol of phenylacetylene, tert-butyl-
acetylene, or trimethylsilylacetylene were added each tube
4.11. CH2C(Ph)(CCPh) (5a) [12]
1H NMR (C6D6, 300 MHz): d 5.69 (s, @CHH), d 5.74 (s,
@CHH). d 8.10–6.80 (m, Ph).
1
at room temperature. By H NMR, the progress of dimer-
ization was monitored.
4.12. cis-tBuHCCHCCtBu (3b)
t
4.6. Preparation of RuHCl(PiPr3)2(CCHPh), 8a
1H NMR (C6D6, 300 MHz): d 1.18 (s, Bu), d 1.24 (s,
tBu), 5.46 ppm (d, JH–H = 12.3 Hz, @CH), d 5.56 (d,
3
Fifteen grams of [RuHCl(PiPr3)2]2 (16.4 lmol) was
placed in an NMR tube equipped with a Teflon seal and
dissolved in 0.5 mL of C6D6. 3.66 lL of phenylacetylene
(32.8 lmol) was added via syringe. The color changed to
3JH–H = 12.3 Hz, @CH).
4.13. CH2C(tBu)(CCtBu) (5b)
t
dark green. This reaction was finished in 30 min.
1H NMR (C6D6, 300 MHz): d 1.17 (s, Bu), d 1.19 (s,
1H NMR (C6D6, 300 MHz): d ꢀ12.48 (t, JP–H
=
tBu), d 5.11 (d, JH–H = 1.5 Hz, @CHH), d 5.33 (d, JH–
2
2
2
17.4 Hz, RuH), d 1.21 (m, P(CH(Me2))3), d 2.49 (m,
H = 1.5 Hz, @CHH).
4
P(CH(Me2))3), d 4.36 (t, JP–H = 3.9 Hz, CCH(Ph)), d
6.8–7.3 (m, CCH(Ph)). 31P{1H} NMR (C6D6, 121 MHz):
d 51.0 (s).
4.14. cis-(tBu)HCCCCH(tBu) (6b)
t
1H NMR (C6D6, 300 MHz): d 1.07 (s, Bu), d 5.51 (s,
4.7. Preparation of RuHCl(PiPr3)2(CCHtBu), 8b
@CH).
Fifteen grams of [RuHCl(PiPr3)2]2 (16.4 lmol) was
placed in an NMR tube equipped with a Teflon seal and
dissolved in 0.5 mL of C6D6. 4 lL of tert-butylacetylene
(32.8 lmol) was added via syringe. The color changed to
dark green. This reaction was finished in 30 min. 1H
4.15. cis-Me3SiHCCHCCSiMe3 (3c)
1H NMR (C6D6, 300 MHz): d 0.15 (s, Me3Si), d 0.22 (s,
Me3Si), d 6.00 (d, JH–H = 15.3 Hz, @CH), d 6.22 (d, JH–
H = 15.3 Hz, @CH).
3
3
2
NMR (C6D6, 300 MHz): d ꢀ13.79 (t, JP–H = 18.3 Hz,
3
RuH), d 1.09 (s, CCH(tBu)), d 1.26 (d, JH–H = 6.3 Hz,
4.16. CH2C(SiMe3)(CCSiMe3) (5c)
3
P(CH(Me2))3), d 1.30 (d, JH–H = 7.2 Hz, P(CH(Me2))3),
4
d 2.67 (m, P(CH(Me2))3), d 2.77 (t, JP–H = 3.6 Hz,
1H NMR (C6D6, 300 MHz): d 0.12 (s, Me3Si), d 0.17 (s,
Me3Si), d 5.54 (d, 2JH–H = 2.0 Hz, @CHH), d 6.10 (d, 2JH–
H = 1.7 Hz, @CHH).
CCH(tBu)). 31P{1H} NMR (C6D6, 121 MHz): d 50.88 (s).
4.8. Preparation of RuHCl(PiPr3)2(CCHSiMe3), 8c
4.17. cis-(Me3Si)HCCCCH(SiMe3) (6c)
Fifteen grams of [RuHCl(PiPr3)2]2 (16.4 lmol) was
placed in an NMR tube equipped with a Teflon seal and
dissolved in 0.5 mL of C6D6. 4.7 ll of trimethylsilylacety-
1H NMR (C6D6, 300 MHz): d 1.22 (s, Me3Si), d 6.36 (s,
@CH).

1672
J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
4.18. Preparation of RuCl(PiPr3)2(g3CCHPh(CCPh))
(16a)
(400 MHz, C6D6): 6.4 (s, 2H, CHPh), 6.92–7.46 (m, 10H,
CHPh).
Thirty-six milligrams of LiCCPh (340 lmol) was added
into the solution of 0.2 g of RuCl2(PiPr3)2(CCHPh)
(340 lmol) in 30 mL of benzene. After 2 days stirring, vol-
atiles were removed by high vacuum with a liquid N2 trap.
The crude compound was dissolved in pentane and filtered
to remove LiCl. Pentane was removed in vacuo. This com-
pound was washed with 10 ml of MeOH, three times and
dried. 0.13 g of the dark reddish brown product (56%)
was collected. 1H NMR (400 MHz, C6D6): 1.12 (dvt,
JP–H = JH–H = 6 Hz, 18H, P(CHMe2)3), 1.18 (dvt,
JP–H = 3JH–H = 6 Hz, 18H, P(CHMe2)3), 2.14 (m, 6H,
P(CHMe2)3). 7.01 (t, JH–H = 7.6 Hz, H, Ph), 7.1 (t,
JH–H = 7.6 Hz, H, Ph), 7.21 (t, JH–H = 7.6 Hz, 2H, Ph), 7.3
(t, JH–H = 7.6 Hz, 2H, Ph), 7.54 (s, H, CHPh), 8.00 (d,
JH–H = 7.6 Hz, 2H, Ph), 8.27 (d, JH–H = 7.6 Hz, 2H, Ph).
31P{1H} NMR (161 MHz, C6D6): d 27.6 (s). 13C{1H}
NMR (100.6 MHz, C6D6): 163.4 (t, JP–C = 8 Hz), 137.3,
133.1, 131.4, 129.3, 128.4, 128.1, 127.9, 127.3, 125.6,
125.3, 124.2.
4.21. Dimerization of terminal alkynes catalyzed by 16a
Twenty-eight micromoles of 16a was dissolved in 0.5 mL
of C6D6 in an NMR tube equipped with a Teflon seal.
560 lmol of phenylacetylene was added. By 1H NMR,
the progress of dimerization was monitored. The ratio of
dimers (3a, 4a, and 5a) was 76.5:5:18.5.
Acknowledgement
This work was supported by the National Science Foun-
dation (NSF) under Grant No. CHE0544829.
References
[1] J.N. Coalter III, J.C. Huffman, W.E. Streib, K.G. Caulton, Inorg.
Chem. 39 (2000) 3757.
[2] J.N. Coalter III, J.C. Bollinger, J.C. Huffman, U. Werner-Zwanziger,
K.G. Caulton, E.R. Davidson, H. Gerard, E. Clot, O. Eisenstein,
New J. Chem. 24 (2000) 9.
[3] D. Huang, J.C. Bollinger, W.E. Streib, K. Folting, V. Young Jr., O.
Eisenstein, K.G. Caulton, Organometallics 19 (2000) 2281.
[4] H. Gerard, E. Clot, C. Giessner-Prettre, K.G. Caulton, E.R.
Davidson, O. Eisenstein, Organometallics 19 (2000) 2291.
[5] J.N. Coalter III, J.C. Huffman, K.G. Caulton, Organometallics 19
(2000) 3569.
[6] J.N. Coalter III, W.E. Streib, K.G. Caulton, Inorg. Chem. 39 (2000)
3749.
[7] M. Olivan, E. Clot, O. Eisenstein, K.G. Caulton, Organometallics 17
(1998) 3091.
[8] M. Olivan, E. Clot, O. Eisenstein, K.G. Caulton, Organometallics 17
(1998) 897.
[9] J. Wolf, W. Stueer, C. Gruenwald, O. Gevert, M. Laubender, H.
Werner, Eur. J. Inorg. Chem. (1998) 1827.
[10] J. Wolf, W. Stuer, C. Grunwald, H. Werner, P. Schwab, M. Schulz,
Angew. Chem., Int. Ed. 37 (1998) 1124.
[11] M. Olivan, O. Eisenstein, K.G. Caulton, Organometallics 16 (1997)
2227.
4.19. Reaction of 16a with CO
Twenty milligrams of 16a (30 lmol) was placed with
0.5 mL of C6D6 in the NMR tube equipped with Teflon
seal stopcock. This solution was freeze-pump-thaw-
degassed three times in liquid N2 and the headspace
evacuated. 1 atm. of CO was added. The color changed
1
immediately to pale yellow. H NMR (400 MHz, C6D6):
1.14 (dvt, JP–H = JH–H = 6 Hz, 18H, P(CHMe2)3), 1.34
(dvt, JP–H = 3JH–H = 6 Hz, 18H, P(CHMe2)3), 2.66 (m,
6H, P(CHMe2)3). 6.96–7.13 (m, 4H, Ph), 7.33 (t,
JH–H = 7.6 Hz, 2H, Ph), 7.7 (d, JH–H = 7.6 Hz, 2H, Ph),
8.17 (s, H, CHPh), 8.32 (d, JH–H = 7.6 Hz, 2H, Ph).
31P{1H} NMR (161 MHz, C6D6): d 35.11 (s). 13C{1H}
NMR (100.6 MHz, C6D6): 200.7 (t, JP–C = 10 Hz), 198.2 (t,
JP–C = 10 Hz), 145.1 (t, JP–C = 4 Hz), 141.1 (t, JP–C not
resolved), 131.4, 128.7, 128.5, 128.4, 128.1, 127.9, 127.1,
126.3, 103.4, 99.1.
[12] A.K. Dash, M.S. Eisen, Org. Lett. 2 (2000) 737.
[13] C.S. Yi, N. Liu, Organometallics 15 (1996) 3968.
[14] Y. Wakatsuki, H. Yamazaki, N. Kumegawa, P.S. Johar, Bull. Chem.
Soc. Jpn. 66 (1993) 987.
[15] Y. Wakatsuki, H. Yamazaki, N. Kumegawa, T. Satoh, J.Y. Satoh, J.
Am. Chem. Soc. 113 (1991) 9604.
4.20. Reaction of RuCl(PiPr3)2(g1CCHPh(CCPh))(CO)2
with HCl
[16] Y. Wakatsuki, T. Satoh, H. Yamazaki, Chem. Lett. (1989) 1585.
[17] T. Katagiri, H. Tsurugi, A. Funayama, T. Satoh, M. Miura, Chem.
Lett. 36 (2007) 830.
[18] M. Bassetti, C. Pasquini, A. Raneri, D. Rosato, J. Org. Chem. 72
(2007) 4558.
[19] X. Chen, P. Xue, H.H.Y. Sung, I.D. Williams, M. Peruzzini, C.
Bianchini, G. Jia, Organometallics 24 (2005) 4330.
[20] C. Bianchini, P. Frediani, D. Masi, M. Peruzzini, F. Zanobini,
Organometallics 13 (1994) 4616.
[21] C. Bruneau, P.H. Dixneuf, Angew. Chem., Int. Ed. 45 (2006) 2176.
[22] C. Bianchini, M. Peruzzini, F. Zanobini, P. Frediani, A. Albinati, J.
Am. Chem. Soc. 113 (1991) 5453.
[23] Y. Wakatsuki, H. Yamazaki, J. Organomet. Chem. 500 (1995)
349.
Twenty milligrams of 16a (30 lmol) was placed with
0.5 mL of C6D6 in the NMR tube equipped with Teflon
seal stopcock. This solution was freeze-pump-thaw-
degassed three times in liquid N2 and the headspace evac-
uated. 1 atm. of CO was added. Color change was immedi-
ate. After 1 day, 30 lL of HCl (1 M in Et2O, 30 lmol) was
added
by
a
syringe.
Ru(CO)2Cl2(PiPr3)2
and
PhHCCCCHPh were produced in 1 h. Ru(CO)2Cl2(PiPr3)2:
1H NMR (400 MHz, C6D6): 1.25 (vq, J = 6 Hz, 36H,
P(CHMe2)3), 2.78 (m, 6H, P(CHMe2)3). 31P{1H} NMR
[24] S. Pavlik, C. Gemel, C. Slugovc, K. Mereiter, R. Schmid, K.
Kirchner, J. Organomet. Chem. 617–618 (2001) 301.
[25] C.S. Yi, N. Liu, Synlett (1999) 281.
1
(161 MHz, C6D6): d 38.67 (s). PhHCCCCHPh: H NMR

J.-H. Lee, K.G. Caulton / Journal of Organometallic Chemistry 693 (2008) 1664–1673
1673
[26] H. Katayama, H. Yari, M. Tanaka, F. Ozawa, Chem. Commun.
(2005) 4336.
[34] B.M. Trost, M.T. Sorum, C. Chan, G. Ruehter, J. Am. Chem. Soc.
119 (1997) 698.
[27] K. Melis, D. De Vos, P. Jacobs, F. Verpoort, J. Organomet. Chem.
659 (2002) 159.
[35] D. Huang, K. Folting, K.G. Caulton, J. Am. Chem. Soc. 121 (1999)
10318.
[28] L. Dahlenburg, K.M. Frosin, S. Kerstan, D. Werner, J. Organomet.
Chem. 407 (1991) 115.
[36] C. Gruenwald, O. Gevert, J. Wolf, P. Gonzalez-Herrero, H. Werner,
Organometallics 15 (1996) 1960.
[29] M. Bassetti, S. Marini, J. Diaz, M.P. Gamasa, J. Gimeno, Y.
Rodriguez-Alvarez, S. Garcia-Granda, Organometallics 21 (2002)
4815.
[37] H. Katayama, F. Ozawa, Organometallics 17 (1998) 5190.
[38] H.-F. Chow, X.-P. Cao, M.-k. Leung, J. Chem. Soc., Perkin Trans. 1
(1995) 193.
[30] G. Jia, A.L. Rheingold, D.W. Meek, Organometallics 8 (1989) 1378.
[31] M.A. Esteruelas, J. Herrero, A.M. Lopez, M. Olivan, Organometal-
lics 20 (2001) 3202.
[39] M. Ogasawara, S.A. Macgregor, W.E. Streib, K. Folting, O.
Eisenstein, K.G. Caulton, J. Am. Chem. Soc. 118 (1996)
10189.
[32] H. Yamazaki, J. Chem. Soc., Chem. Commun. (1976) 841.
[33] D. Huang, M. Olivan, J.C. Huffman, O. Eisenstein, K.G. Caulton,
Organometallics 17 (1998) 4700.
[40] R. Ghosh, X. Zhang, P. Achord, T.J. Emge, K. Krogh-Jespersen,
A.S. Goldman, J. Am. Chem. Soc. 129 (2007) 853.