Controlling the catalytic oligomerization of terminal alkynes promoted by organoactinides: A strategy to short oligomers

Article abstract of DOI:10.1021/ja983640z

A novel strategy has been developed for the catalytic synthesis of short oligomers, dimers and/or trimers, of terminal alkynes. The method allows control of the extent of and, in some cases, the regiospecificity in the catalyzed oligomerization of terminal alkynes promoted by bis(pentamethylcyclopentadienyl)actinide dimethyl complexes (Cp*₂AnMe₂; Cp* = C₅Me₅, An = Th, U). These metallocene precursors are known to promote the simultaneous production of a large number of differently sized oligomers in the presence of terminal alkynes. However, the addition of specific amines ensures the selective synthesis of short oligomers. Catalytic 'tailoring' to dimers or a mixture of dimers and trimers can be achieved by using nonbulky or bulky amines, respectively. The kinetics in the catalytic oligomerization of 1-hexyne, in the presence of i-BuNH₂, mediated by Cp*₂ThMe₂ are first order in [alkyne], first order in [Th], and inverse first order in [amine]. Kinetic, spectroscopic, and mechanistic data argue that the turnover-limiting step involves the formation of the mono(amido)thorium acetylide complex with rapid insertion of the alkyne and protonolysis by the amine.

Full text of DOI:10.1021/ja983640z

J. Am. Chem. Soc. 1999, 121, 3025-3034
3025
Controlling the Catalytic Oligomerization of Terminal Alkynes
Promoted by Organoactinides: A Strategy to Short Oligomers
Ariel Haskel, Ji Quan Wang, Thomas Straub, Tal Gueta Neyroud, and Moris S. Eisen*
Contribution from the Department of Chemistry, Technion-Israel Institute of Technology,
Haifa 32000, Israel
ReceiVed October 16, 1998
Abstract: A novel strategy has been developed for the catalytic synthesis of short oligomers, dimers and/or
trimers, of terminal alkynes. The method allows control of the extent of and, in some cases, the regiospecificity
in the catalyzed oligomerization of terminal alkynes promoted by bis(pentamethylcyclopentadienyl)actinide
dimethyl complexes (Cp*2AnMe2; Cp* ) C5Me5, An ) Th, U). These metallocene precursors are known to
promote the simultaneous production of a large number of differently sized oligomers in the presence of terminal
alkynes. However, the addition of specific amines ensures the selective synthesis of short oligomers. Catalytic
“tailoring” to dimers or a mixture of dimers and trimers can be achieved by using nonbulky or bulky amines,
respectively. The kinetics in the catalytic oligomerization of 1-hexyne, in the presence of i-BuNH2, mediated
by Cp*2ThMe2 are first order in [alkyne], first order in [Th], and inverse first order in [amine]. Kinetic,
spectroscopic, and mechanistic data argue that the turnover-limiting step involves the formation of the mono-
(amido)thorium acetylide complex with rapid insertion of the alkyne and protonolysis by the amine.
Introduction
of the products was previously not available. It is noteworthy
to point out that highly regioselective catalysts (early and late
transition metals) for the specific dimerization of terminal
alkynes have been reported but provide no means to generate
or to control the formation of higher oligomers.6,7
In the design of chemical reaction schemes to obtain selective
and regiospecific products, transition metals have been widely
studied, with stoichiometric and catalytic reactions, and in many
cases have resulted in efficient, selective processes which
operate under mild and easily controlled conditions.1,2 Despite
the rapid growth of activity in this field,3 controlling the extent
of catalytic oligomerization/polymerization reactions remains
challenging. For example, in the catalytic Ziegler-Natta po-
lymerization reaction, dihydrogen is added to control, to some
extent, the molecular weight of the polymeric chains,4 or, in
the polymerization of alkenes by cationic group 4 metallocenes,
the counterion affects the molecular weight of the observed
polymers.5 For the catalytic oligomerization of alkynes, the
means to control the selectiVity (extent of the oligomerization)
In the preceding contribution,8 we noted that organoactinide
complexes of the type (C5Me5)2AnMe2 (An ) Th (1), U (2))
were found to be effective precatalysts for the oligomerization
of terminal alkynes. We have shown that for bulky acetylenes,
such as t-BuCtCH or (TMS)CtCH, selective dimerization (eq
1) and trimerization (eq 2) were achieved, producing the head-
to-tail dimer and the specific head-to-tail-to-head trimer,
respectively.9
For nonbulky terminal alkynes, the oligomerization leads to
a mixture of dimers to heptamers with no regioselectivity among
the different oligomers.9 The plausible mechanism based on
kinetic experiments and accomplished by trapping some key
(1) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992.
(2) (a) Moser, R. R.; Slocum, D. W. Homogeneous Transition Metal
Catalyzed Reactions; American Chemical Society: Washington, DC, 1990.
(b) Davis, M. E.; Suib, S. L. SelectiVity in Catalysis; American Chemical
Society: Washington, DC, 1991. (c) Davies, J. A.; Watson, P. L.; Liebman,
J. F.; Greenberg, A. SelectiVe Hydrocarbon ActiVation; VCH: New York,
1990.
(3) (a) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154. (b) ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier:
New York, 1995; Vol. 12. (c) ComprehensiVe Organic Synthesis: SelectiV-
ity, Strategy and Efficiency in Modern Organic Chemistry; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: Oxford, U.K., 1991; Vols. 3 and 5.
(4) (a) Keii, T.; Soga, K. Catalytic Olefin Polymerization; Elsevier:
Amsterdam, 1990. (b) Kaminsky, W.; Sinn, H. Transition Metals and
Organometallics as Catalysts for Olefin Polymerization; Springer-Verlag:
Berlin, Heidelberg, 1988.
(5) (a) Chen, Y.-X.; Metz, M. V.; Li, L.; Stern, C. L.; Yang, S.; Marks,
T. J. J. Am. Chem. Soc. 1998, 120, 6287. (b) Chen, Y.-X.; Stern, C. L.;
Marks, T. J. J. Am. Chem. Soc. 1997, 119, 2582. (c) Chen, Y.-X.; Stern, C.
L.; Yang, S.; Marks, T. J. J. Am. Chem. Soc. 1996, 118, 12451. (d) Deck,
P. A.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 6128. (e) Giardello, M.
A.; Eisen, M. S.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1995, 117,
12114. (f) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255 and
references therein.
(6) (a) Barbaro, P.; Bianchini, C.; Peruzzini, M.; Polo, A.; Zanobini, F.;
Frediani, P. Inorg. Chim. Acta 1994, 220, 5. (b) Schaverien, C. J.
Organometallics 1994, 13, 69. (c) Heeres, H. J.; Teuben, J. H. Organo-
metallics 1991, 10, 1980. (d) Duchateau, R.; Van Wee, C. T.; Teuben, J.
H. Organometallics 1996, 15, 2291. (e) Duchateau, R.; Van Wee, C. T.;
Meetsma, A.; Teuben, J. H. J. Am. Chem. Soc. 1993, 115, 4931. (f) Heeres,
H. J.; Heeres, A.; Teuben, J. H. Organometallics 1990, 9, 1508. (g) Yoshida,
M.; Jordan, R. F. Organometallics 1997, 16, 4508. (h) Thompson, M. E.;
Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santarsiero, B. D.;
Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. Soc. 1987, 109, 203. (i) St.
Claire, M.; Schaefer, W. P.; Bercaw, J. E. Organometallics 1991, 10, 4508.
(7) (a) Horton, A. D. J. Chem. Soc., Chem. Commun. 1992, 185. (b) Yi,
C. S.; Liu, N. Organometallics 1996, 15, 3968. (c) Horton, A. D.; Orpen,
A. G. Angew. Chem., Int. Ed. Engl. 1992, 31, 876. (d) Slugovc, C.; Mereiter,
K.; Zobetz, E.; Schmid, R.; Kirchner, K. Organometallics 1996, 15, 5275.
(e) Johnson, E.; Balaich, G. J.; Fanwick, P. E.; Rothwell, I. P. J. Am. Chem.
Soc. 1997, 119, 11086. (f) van der Linden, A.; Schaverien, C. J.; Meijboom,
N.; Ganter, C.; Orpen, A. G. J. Am. Chem. Soc. 1995, 117, 3008. (g) Trost,
B. M.; Sorum, M. T.; Chan, C.; Harms, A. E.; Ru¨hter, G. J. Am. Chem.
Soc. 1997, 119, 698 and references therein.
(8) Haskel, A.; Straub, T.; Dash, A. K.; Eisen, M. S. J. Am. Chem. Soc.
1999, 121, 3014.
(9) Straub, T.; Haskel, A.; Eisen, M. S. J. Am. Chem. Soc. 1995, 117,
6364.
10.1021/ja983640z CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/17/1999

3026 J. Am. Chem. Soc., Vol. 121, No. 13, 1999
Haskel et al.
Figure 1. Trapped intermediate complexes in the oligomerization of
terminal alkynes promoted by organoactinide complexes.
(1)
with individual stoichiometric reactions. The regioselectivity of
the different oligomers can be tailored, to some extent, by the
different organoactinide metals, the pKa, and steric hindrance
imparted by the amine. This strategy provides a route to control,
in principle, oligomerization/polymerization reactions of ter-
minal alkynes producing specific enynes for further chemical
transformations toward antitumor antibiotics containing diene-
ynes or fused bicyclic [n.m.0] structural frameworks which
represent primordial substructures in many biologically interest-
ing molecules.11
(2)
intermediate complexes, 3 and 4 (see Figure 1), was outlined
in Scheme 1 in the preceding contribution.8 The turnover-
limiting step for the catalytic trimerization of (TMS)CtCH was
found to be the elimination of the organic trimer from the bis-
(dieneyne)thorium complex 4. This result argues that the rate
for σ-bond metathesis between the actinide carbyls and the
alkyne, eliminating methane, and the rate of insertion of the
CtC triple bond of the terminal alkyne into the metal acetylide
moiety (steps 1 and 2 in Scheme 1, ref 8) are much faster than
the rate for C-H σ-bond metathesis of the terminal alkyne bond
with the metal-dialkenyl complex in the catalytic cycle (step
4).
An interesting conceptual consideration is the ability to
control the proposed mechanism in such a manner as to allow
the formation of specific dimer or trimer, restraining the
formation of higher oligomers, that is, to block routes 3 and 4
(Scheme 1, preceding contribution8) and constrain the catalyst
to follow pathways 2 and 5.
Experimental Section
Materials and Methods. All manipulations of air-sensitive materials
were performed with the rigorous exclusion of oxygen and moisture
in flamed Schlenk-type glassware on a dual-manifold Schlenk line, or
interfaced to a high-vacuum (10-5 Torr) line, or in a nitrogen-filled
Vacuum Atmospheres glovebox with a medium-capacity recirculator
(1-2 ppm of O2). Argon, acetylene, and nitrogen were purified by
passage through a MnO oxygen-removal column and a Davison 4 Å
molecular sieve column. Ether solvents were distilled under argon from
sodium benzophenone ketyl. Hydrocarbon solvents (THF-d8, toluene-
d8, benzene-d6, C6D12) were distilled under nitrogen from Na/K alloy.
All solvents for vacuum-line manipulations were stored in vacuo over
Na/K alloy in resealable bulbs. Acetylenic compounds (Aldrich) were
dried and stored over activated molecular sieves (4 Å), degassed, and
freshly vacuum-distilled. Deuterium oxide was purchased from Cam-
bridge Isotopes. Amines (Fluka) were dried over Na/K alloy and stored
over activated molecular sieves (4 Å), degassed, and freshly vacuum-
distilled. 2,6-dimethylaniline-d2 was synthesized by repeated deuterium
exchange with D2O under N2 and was found to be g99% ND2 (1H
2
NMR and H NMR integrations). Cp*2AnMe2 (Th, U)12 and Cp*2U-
We report herein a principle for the selective control of the
extent of oligomerization of terminal alkynes, by an acidic chain-
transfer agent, as a basic strategy to modify the nonselective
oligomerization toward small oligomers (dimers and trimers).
This approach uses a chain-transfer reagent that does not end
up in the product (in contrast to, e.g., H2) and is also novel
since it does not require subsequent elimination from the product
to release the unsaturated oligomer (in contrast to, e.g., ethene
oligomerization by metallocene catalysts or magnesium re-
agents).10 The catalytic oligomerization is promoted by orga-
noactinide complexes with the addition of the chain-transfer
agent, producing selectiVe dimers and regiospecific trimers with
no other higher oligomers (tetramers to heptamers) as observed
for the compared nonselective oligomerization without the added
reagent. The oligomerization control was achieved by adding
an amine (primary or secondary) to the catalytic cycle, without
much altering of the turnover frequencies as compared with
those of the noncontrolled process. The selectivity control, which
is the amount of the different oligomers obtained by the different
complexes (Th, U), of the new catalytic cycle was achieved by
considering the difference in the calculated bond-disruption
energies between an actinide-alkenyl and an actinide-amido
bond and the combination of the nonselective catalytic pathways
(NHR)2 (R ) 2,6-dimethylphenyl, t-Bu, Ph, CtC(TMS)) were prepared
according to published procedures.13 NMR spectra were recorded on
Bruker AM 200 and Bruker AM 400 spectrometers. Chemical shifts
for 1H NMR and 13C NMR are referenced to internal solvent resonances
and are reported relative to tetramethylsilane. GC/MS experiments were
conducted in a GC/MS (Finnigan Magnum) spectrometer. The NMR
experiments were conducted in Teflon valve-sealed tubes (J. Young)
after vacuum transfer of the liquids in a high-vacuum line.
Kinetic Study of Controlled Oligomerization. In a typical experi-
ment, an NMR sample was prepared as described in the typical NMR-
scale catalytic reactions section but maintained at -78 °C until kinetic
measurements were initiated. The sealed tube was heated in a
temperature-controlled oil bath, and at time intervals NMR data were
acquired using eight scans per time interval with a long pulse delay to
avoid saturation of the signal. The kinetics were usually monitored by
the intensity changes in the substrate resonances and in the product
resonances over 3 or more half-lives. The substrate concentration (C)
1
was measured from the area (As) of the H-normalized signal of the
(11) (a) Grissom, J. W.; Gunawardena, G. U.; Klingberg, D. Tetrahedron
1996, 52, 6453. (b) Miller, S. J.; Kim, S.-H.; Chen, Z.-R.; Grubbs, R. H. J.
Am. Chem. Soc. 1995, 117, 2108. (c) Kim, S.-H.; Zuercher, W. J.; Bowden,
N. B.; Grubbs, R. H. J. Org. Chem. 1996, 61, 1073.
(12) Fagan, P. J.; Manriquez, J. M.; Maatta, E. A.; Seyam, A. M.; Marks,
T. J. J. Am. Chem. Soc. 1981, 103, 6650.
(13) (a) All toxic materials were disposed of in accordance with Prudent
Practices for Disposal of Chemicals from Laboratories; National Academy
Press: Washington, DC, 1983. (b) Straub, T.; Reiss, G.; Frank, W.; Eisen,
M. S. J. Chem. Soc., Dalton Trans. 1996, 2541.
(10) (a) Pelletier, J.-F.; Mortreux, A.; Olonde, X.; Bujadoux, K. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1854. (b) Samsel, E. G. U.S. Patent
Application EP 574854, 1993.

Controlled Oligomerization of Terminal Alkynes
J. Am. Chem. Soc., Vol. 121, No. 13, 1999 3027
solvent (Ab). All the data collected could convincingly be least-squares-
fit (R > 0.98) to eq 3 or 4, where C0 (C0 ) As0/Ab0) is the initial
concentration of substrate and C (As/Ab) is the substrate concentration
at time t.
of Cp*2ThMe2 to a mixture of the geminal head-to-tail 5A (57%) and
trans head-to-head 5B (43%) dimers, respectively.
1H NMR (400 MHz, C6D6) of 5A: δ 5.23 (d, 1H, 3JHH ) 1.95 Hz,
3
HHCdC), 5.06 (d, 1H, JHH ) 1.95 Hz, HHCdC), 2.31 (septet, 1H,
3
3JHH ) 6.84 Hz, Me2CHCdC), 2.30 (septet, 1H, JHH ) 6.84 Hz,
3
CtCCHMe2), 1.10 (d, 6H, JHH ) 6.84 Hz, Me2CHCdC), 1.05 (d,
mt ) log(C/C0)
(3)
(4)
3
6H, JHH ) 6.84 Hz, Me2CHCtC).
13C NMR (100 MHz, C6D6) of 5A: δ 139.2 (s, CdC), 117.1 (t,
1JCH ) 157.6 Hz, H2CdC), 96.5 (s, CdCCtC), 79.6 (s, CtCCHMe2),
35.7 (d, 1JCH ) 136.3 Hz, CdCCHMe2), 29.5 (d, 1JCH ) 142 Hz, Ct
1
1
)
+ mt
C
C0
1
1
CCHMe2), 22.3 (q, JCH ) 127.8 Hz, CdCCHMe2), 21.4 (q, JCH
126.3 Hz, CtCCHMe2).
)
The ratio of catalyst to substrate was accurately measured by
calibration with internal FeCp2. Turnover frequencies (Nt, h-1) were
calculated from the least-squares-determined slopes (m) of the resulting
plots. Typical initial amine concentrations were in the range 0.035-
0.49 M, initial alkyne concentrations were in the range 0.097-3.84
M, and typical catalyst concentrations were in the range 8.7-53 mM.
Synthesis of Cp*2ThMe(NH-2,6-Me2Ph) (15). A 50 mL Schlenk
tube was charged in the glovebox with 50 mg (0.0939 mmol) of Cp*2-
ThMe2. An 8 mL portion of THF was added to the Schlenk tube by
vacuum transfer at -78 °C, and then 0.09 mL (0.0939 mmol) of 2,6-
dimethylaniline was syringed into the Schlenk tube. The solution was
stirred at -78 °C for 4 h and at room temperature for an additional 5
h. The reaction was monitored to completion by following the
disappearance of the methyl signal of the starting complex at δ ) -0.5
ppm. The solvent was removed by vacuum distillation, the mixture
was redissolved in 20 mL of toluene, the solution was filtered, and
crystallization was accomplished by the addition of 5 mL of hexane at
-78 °C overnight.
1H NMR (400 MHz, C6D6) of 5B: δ 5.44 (dd, 1H, 3JHH ) 7.81 Hz,
3JHH ) 10.74 Hz, Me2CHHCdCH), 5.16 (d, 1H, JHH ) 10.74 Hz,
3
Me2CHHCdCH), 3.07 (m, 1H, Me2CHCHdC), 2.13 (m, 1H,
3
CtCCHMe2), 1.12 (d, 6H, JHH ) 6.84 Hz, Me2CHCdC), 1.05 (d,
3
6H, JHH ) 6.84 Hz, Me2CHCtC).
13C NMR (100 MHz, C6D6) of 5B: δ 149.1 (d, JCH ) 154.7 Hz,
1
1
CtCCHdC), 108.0 (d, JCH ) 163.2 Hz, CdCHCHMe2), 99.5 (s,
1
CdCCtC), 76.4 (s, CtCCHMe2), 35.9 (d, JCH ) 136.3 Hz,
CdCCHMe2), 29.7 (d, 1JCH ) 142 Hz, CtCCHMe2), 23.2 (q, 1JCH
)
1
127.8 Hz, CdCCHMe2), 21.8 (q, JCH ) 126.3 Hz, CtCCHMe2).
m/z: 137 (M+ + 1; 100%), 121 (M+ - CH3), 109 (M+ - CHCH3),
91 (M+ - 3CH3). High-resolution mass spectrum, m/z: calcd for C8H16
(M+), 136.2390; found, 136.2367.
(c) Oligomerization of 3-Methyl-1-butyne by Cp*2UMe2 and
Me2NH. As described above, in 0.25 mL of THF, 0.7 mL (6.8 mmol)
of 3-methyl-1-butyne was oligomerized (90% conversion after 43 h)
with 0.15 mL (2.3 mmol) of Me2NH and 5 mg (0.01 mmol) of Cp*2-
UMe2 to a mixture of the geminal head-to-tail dimer 5A (10%) and
the head-to-tail-to-tail trimer 5C (90%), respectively. Vacuum-transfer
distillation (50 °C; 1 × 10-3 mmHg) afforded clean separation of the
two compounds.
-1
1
3
Ir: ν ) 3253 cm (N-H). H NMR (THF-d8): δ 6.98 (d, 4H, J
3
) 7.4 Hz, m-H), 6.45 (t, 2H, J ) 7.4 Hz, p-H), 2. 28 (s, 31H, Cp +
NH), 0.16 (s, 3H, CH3). Anal. Calcd for C29H43NTh (MW )
637.6966): C, 54.62; H, 6.80; N, 2.20. Found: C, 54.39; H, 6.89; N,
2.40. HRMS, m/z: 637.6970. Mp (dec) ) 95-100 °C.
1H NMR (400 MHz, C6D6) of the head-to-tail-to-tail trimer 5C: δ
6.00 (s, br, 1H, H2CdCRHCdCR), 4.90 (m, br, 2H, H2CdCRHCd),
Synthesis of Cp*2Th(NH-2,6-Me2Ph)2 (13). A 50 mL Schlenk tube
was charged in the glovebox with 50 mg (0.0939 mmol) of Cp*2ThMe2.
An 8 mL portion of THF was added to the Schlenk tube by vacuum
transfer at -78 °C, and then 0.022 mL (0.229 mmol) of 2,6-
dimethylaniline was syringed into the Schlenk tube. The solution was
stirred for 4 h at -78 °C and for an additional 15 h at room temperature.
The reaction was monitored to completion by following the disappear-
ance of the methyl signals of the starting complex and of the
intermediate methylamido complex at δ ) -0.5 and 0.16 ppm,
respectively. The solvent was removed by vacuum distillation at low
temperature, the mixture was redissolved in 20 mL of toluene, the
solution was filtered, and crystallization was accomplished by the
addition of 15 mL of hexane at -78 °C overnight.
3
3
3.02 (septet, 1H, JHH ) 6.8 Hz, Me2CHCdC), 2.83 (septet, 1H, JHH
3
) 6.84 Hz, CtCCHMe2), 2.50 (septet, 1H, JHH ) 6.84 Hz,
3
CdCCHMe2), 1.05 (d, 6H, JHH ) 6.84 Hz, Me2CHCtC), 1.05 (d,
3
12H, JHH ) 6.84 Hz, Me2CHCdC).
13C NMR (100 MHz, C6D6) of the head-to-tail-to-tail trimer 5C: δ
153.3 (s, CtCCdC), 134.7 (s, H2CdC), 134.5 (d, H2CdCCHdC),
112.1 (t, 1JCH ) 156.0 Hz, H2CdCCHdC), 97.6 (s, CtCCHMe2), 81.2
1
(s, CtCCHMe2), 36.9 (d, JCH ) 127.5 Hz, CdCCHMe2), 30.7 (d,
1JCH ) 125 Hz, CtCCHMe2), 26.1 (q, 1JCH ) 125.5 Hz, CdCCHMe2),
1
1
23.5 (q, JCH ) 125.5 Hz, CdCCHMe2), 23.1 (q, JCH ) 125.5 Hz,
CtCCHMe2).
m/z: 204 (M+), 189 (M+ - CH3), 175 (M+ - CH2 - CH3), 9161
(M+ - CHMe2, 100%), 147 (M+ - CHMe2 - CH2). High-resolution
mass spectrum m/z: calcd for C15H24 (M+), 204.3585; found, 204.3556.
(d) Dimerization of 1-Hexyne by Cp*2ThMe2 and MeNH2.
According to the general procedure described above, 12 mg (0.023
mmol) of Cp*2ThMe2 was mixed with 0.2 mL (1.7 mmol) of 1-hexyne
and 0.2 mL (4.5 mmol) of MeNH2 to yield a mixture (93%) of dimers
(45% geminal (6A); 48% trans (6B)) after 46 h.
-1
1
3
Ir: ν ) 3219 cm (N-H). H NMR (THF-d8): δ 7.08 (d, 4H, J
3
) 7.6 Hz, m-H), 6.39 (t, 2H, J ) 7.6 Hz, p-H), 2.10 (br, 32H, Cp +
NH). Anal. Calcd for C36H50N2Th (MW ) 742.8338): C, 58.21; H,
6.78; N, 3.77. Found: C, 54.25; H, 6.98; N, 3.58. HRMS, m/z:
742.8342. Mp (dec) ) 97-113 °C.
Controlled Catalytic Oligomerization of HCtCR by Cp*2AnMe2
(An ) Th, U) in the Presence of Amines. (a) General Procedure.
In a typical procedure, alkyne and amine were added to an NMR tube
containing ≈7 mg (0.013 mmol) of the catalyst in ca. 0.3 mL of solvent
(C6D6 where not stated otherwise) by vacuum transfer in a high-vacuum
line. The sealed tube was heated in an oil bath (oil temperature 100
°C). For thorium, the formation of the metal bis(amido) complexes
was indicated by the change of color of the reaction mixture from
transparent to pale yellow. For uranium, the color of the reaction mixture
changed from orange to red-brown during the formation of the metal
bis(amido) complexes. After 100% conversion of the alkyne (detected
by 1H NMR), the organic products were vacuum-transferred to another
NMR tube and identified by 1H, 13C, COSY, NOESY, and C-H
correlation NMR spectroscopy and by GC/MS. Different geometrical
isomers were identified by comparing the signals of one clean isomer
and subtracting the data from those of the mixture.
1H NMR (400 MHz, C6D6) of 6A: δ 5.40 (d, 1H, 2JHH ) 1.95 Hz,
HHCdC), 5.09 (d, 1H, 2JHH ) 1.95 Hz, HHCdC), 2.16 (t, 2H, 3JHH
)
3
6.84 Hz, H2CCdC), 2.14 (t, 2H, JHH ) 6.84 Hz, H2CCtC), 1.59
3
3
(quintet, 2H, JHH ) 6.84 Hz, JHH ) 6.84 Hz, H2CCH2CdC), 1.50-
1.20 (m, 6H, CH2), 0.86 (t, 3H, 3JHH ) 6.84 Hz, CH2CH3), 0.76 (t, 3H,
3JHH ) 6.84 Hz, CH2CH3).
13C NMR (100 MHz, C6D6) of 6A: δ 126.7 (s, Cd), 119.5 (t, 1JCH
) 158 Hz, H2CdC), 94.4 (s, tCCdC), 78.1 (s, tCCH2), 37.8 (t, 1JCH
) 124 Hz, CtCCH2), 31.1 (t, 1JCH ) 128 Hz, CH2CdC), 30.7 (t, 1JCH
1
) 131 Hz, tCCH2CH2CH2), 22.3 (t, JCH ) 132 Hz, CdCCH2CH2-
1
1
CH2), 22.2 (t, JCH ) 125 Hz, CH2CH3), 19.2 (t, JCH ) 122 Hz,
CH2CH3), 14.0 (q, 1JCH ) 124 Hz, CH2CH3), 13.6 (q, 1JCH ) 124 Hz,
CH2CH3).
(b) Dimerization of 3-Methyl-1-butyne by Cp*2ThMe2 and
EtNH2. According to the general procedure described above, 0.08 mL
(0.78 mmol) of 3-methyl-1-butyne was dimerized (100% conversion
after 66 h) with 0.4 mL (6.1 mmol) of EtNH2 and 8 mg (0.015 mmol)
m/z: 164 (M+), 135 (M+ - CH2 - CH3), 121 (M+ - CH2 - CH2
- CH3), 107 (M+ - C4H9), 93 (M+ - C4H9 - CH3; 100%) High-
resolution mass spectrum, m/z: calcd for C12H20, 164.2932; found,
164.2915.

3028 J. Am. Chem. Soc., Vol. 121, No. 13, 1999
Haskel et al.
126.3 Hz,
3
1
1H NMR (400 MHz, C6D6) of 6B: δ 5.62 (dt, 1H, JHH ) 10.94
CdCCtC), 77.7 (s, tCC5H9), 47.6 (d, JCH
)
3
3
1
1
Hz, JHH ) 7.32 Hz, HCdCHCH2), 5.33 (d, 1H, JHH ) 10.94 Hz,
CdCCHC4H8), 41.3 (d, JCH ) 142 Hz, CtCCHC4H8), 33.4 (t, JCH
3
1
HCdCHCtC), 2.17 (t, 2H, JHH ) 7.32 Hz, CH2CdC), 2.10 (t, 2H,
) 126.4 Hz, CdCCHC2H4C2H4), 31.2 (t, JCH ) 134.9 Hz,
3JHH ) 7.32 Hz, CH2CtC), 1.65-1.11 (m, 8H, CH2), 0.83 (t, 3H, 3JHH
CtCCHC2H4C2H4), 25.9 (t, 1JCH ) 132.0 Hz, CdCCHC2H4C2H4), 25.1
3
1
) 7.32 Hz, CH2CH3), 0.79 (t, 3H, JHH ) 7.32 Hz, CH2CH3).
(t, JCH ) 129.2 Hz, CtCCHC2H4C2H4).
13C NMR (100 MHz, C6D6) of 6B: δ 142.1 (d, JCH ) 155 Hz,
1H NMR (400 MHz, C6D6) of the trans isomer 7B: δ 5.54 (dd, 1H,
1
tCHCd), 110.3 (d, JCH ) 163 Hz, dCHCH2), 90.1 (s, tCCdC),
3JHH ) 6.84 Hz, JHH 10.74 Hz, C5H9HCdCH), 5.38 (d, 1H, JHH
)
1
3
3
1
1
81.6 (s, tCCH2), 37.5 (t, JCH ) 124 Hz, CtCCH2), 31.3 (t, JCH
)
10.74 Hz, dCHCtC), 3.1 (m, 2H, CHC4H8), 1.9-1.3 (m, 16H,
CHC4H8).
1
128 Hz, CH2CdC), 31.2 (t, JCH ) 131 Hz, CtCCH2CH2CH2), 22.6
(t, 1JCH ) 132 Hz, CdCCH2CH2CH2), 22.2 (t, 1JCH ) 125 Hz, CH2CH3),
13C NMR (100 MHz, C6D6) of the trans isomer 7B: δ 147.0 (d,
1
1
1JCH ) 156.1 Hz, C5H9CHdCH), 108.8 (d, 1JCH ) 163.2 Hz, CdCH-
19.2 (t, JCH ) 122 Hz, CH2CH3), 14.1 (q, JCH ) 124 Hz, CH2CH3),
13.5 (q, JCH ) 124 Hz, CH2CH3).
1
1
CtC), 98.4 (s, CdCCtC), 80.1 (s, tCC5H9), 51.8 (d, JCH ) 127.7
1
(e) Dimerization of 1-Hexyne by Cp*2ThMe2 and EtNH2. As
described above, 0.08 mL (0.70 mmol) of 1-hexyne was dimerized (85%
conversion after 48 h) with 0.06 mL (0.91 mmol) of EtNH2 and 15 mg
(0.028 mmol) of Cp*2ThMe2 to a mixture of dimers (32% 6A and 53%
6B).
Hz, CdCCHC4H8), 41.3 (d, JCH ) 142 Hz, CtCCHC4H8), 34.3 (t,
1JCH ) 134.9 Hz, CdCCHC2H4C2H4), 32.3 (t, JCH ) 127.0 Hz,
1
CtCCHC2H4C2H4), 29.9 (t, 1JCH ) 130.6 Hz, CdCCHC2H4C2H4), 25.8
1
(t, JCH ) 132 Hz, CtCCHC2H4C2H4).
m/z: 188 (M+), 173 (M+ - CH3), 160 (M+ - C2H4), 145 (M+
-
(f) Dimerization of 1-Hexyne by Cp*2ThMe2 and i-BuNH2. As
described above, 0.04 mL (0.35 mmol) of 1-hexyne was dimerized (89%
conversion after 23 h) with 0.08 mL (0.81 mmol) of i-BuNH2 and 5
mg (0.01 mmol) of Cp*2ThMe2 to the geminal dimer 6A, selectively.
(g) Oligomerization of 1-Hexyne by Cp*2ThMe2 and 2,6-Di-
methylaniline. In 0.2 mL of THF, 0.1 mL (0.85 mmol) of 1-hexyne
was oligomerized (100% conversion after 72 h) with 0.14 mL (1.14
mmol) of 2,6-dimethylaniline and 10 mg (0.018 mmol) of Cp*2ThMe2
to a mixture of the geminal dimer 6A (60%) and the head-to-tail-to-
tail trimer 6C (40%), respectively.
C3H7), 131 (M+ - C4H9), 119 (M+ - C5H9), 105 (M+ - CH2 - C5H9),
91 (M+ - C2H4 - C5H9; 100%). High-resolution mass spectrum, m/z:
calcd for C14H20 (M+), 188.3155; found, 188.3108.
(k) Dimerization of 4-tert-Butylphenylacetylene by Cp*2ThMe2
and EtNH2. As described above, 0.14 mL (0.8 mmol) of 4-t-BuPh-
CtCH was dimerized (100% conversion after 69 h) with 0.08 mL (1.12
mmol) of EtNH2 and 8 mg (0.015 mmol) of Cp*2ThMe2 to the trans
head-to-head dimer 8B, exclusively.
1H NMR (400 MHz, C6D6) of the trans head-to-head dimer 8B: δ
3
3
8.00 (d, 2H, JHH ) 7.81 Hz, o-H of Ar-CtC), 7.50 (d, 2H, JHH
)
3
1H NMR (400 MHz, C6D6) of 6C: δ 6.80 (s, 1H, CtCCHdC),
7.81 Hz, o-H of ArCdC), 7.35 (d, 2H, JHH ) 7.81 Hz, m-H of Ar-
2
2
3
4.97 (d, 1H, JHH ) 1.95 Hz, HCdC), 4.88 (d, 1H, JHH ) 1.95 Hz,
CtC), 7.18 (d, 2H, JHH ) 7.81 Hz, m-H of ArCdC), 6.54 (d, 1H,
3
3
3
HCdC), 2.50 (t, 4H, JHH ) 7.81 Hz, CH2CdC), 2.45 (t, 2H, JHH
)
3JHH ) 11.72 Hz, ArCHdCH), 5.87 (d, 1H, JHH ) 11.72 Hz, Ar-
6.84 Hz, CH2CtC), 1.70 (q, 2H, 3JHH ) 7.81 Hz, CH2CH2CdC), 1.59-
CHdCHCtC), 1.27 (s, 9H, t-BuArCdC), 1.18 (s, 9H, t-BuArCtC).
13C NMR (100 MHz, C6D6) of the trans head-to-head dimer 8B: δ
3
1.12 (m, 10H), 0.98 (t, 6H, JHH ) 6.84 Hz, CH2CH3), 0.87 (t, 3H,
3JHH ) 6.84 Hz, CH2CH3).
151.7 (s, CCdC), 151.6 (s, CCtC), 138.6 (d, JCH ) 156.1 Hz,
1
1
13C NMR (100 MHz, C6D6) of 6C: δ 125.3 (s, CdCH), 122.7 (d,
o-CHCtC), 134.6 (s, p-CCtC), 131.6 (d, JCH ) 161.8 Hz, o-CH-
1JCH ) 130.6 Hz, CdCH), 115 (t, JCH ) 158 Hz, CH2dC), 93.7 (s,
CdC), 129.1 (d, 1JCH ) 158.8 Hz, CtCCHdC), 125.7 (d, 1JCH ) 160.4
1
1
1
tCCdC), 88.0 (s, tCCH2), 40.5 (t, JCH ) 127 Hz, CtCCH2), 36.1
Hz, m-CHCtC), 125.5 (d, JCH ) 161.8 Hz, m-CHCdC), 121.3 (s,
1
1
1
(t, JCH ) 128 Hz, CH2CdC), 32.2 (t, JCH ) 128 Hz, CdCCH2CH2-
p-CCdC), 107.0 (d, JCH ) 159.0 Hz, CdCHAr), 96.6 (s, CtCAr),
CH2), 31.3 (t, 1JCH ) 128 Hz, CtCCH2CH2CH2), 31.1 (t, 1JCH ) 128
88.7 (s, CdCCtC), 31.5 (s, CtCPhCMe3), 31.2 (s, CdCPhCMe3),
1
1
1
Hz, CdCCH2CH2CH2), 30.5 (t, JCH ) 128 Hz, CdCCH2CH2CH2),
19.4 (q, JCH ) 124.9 Hz, CtCPhCMe3), 12.3 (q, JCH ) 126.3 Hz,
CdCPhCMe3).
m/z: 316 (M+; 100%), 301 (M+ - CH3), 245 (M+ - CH2CMe2 -
CH3), 203 (M+ - CMe3 - CH2CMe2), 115 (M+ - t-BuC6H4 - C2H2-
CMe2). High-resolution mass spectrum, m/z: calcd for C15H24 (M+),
316.4907; found, 316.4901.
(l) Dimerization of 4-tert-Butylphenylacetylene by Cp*2UMe2 and
Me2NH. As described above, in 0.4 mL of THF, 0.15 mL (0.9 mmol)
of 4-t-BuPhCtCH was dimerized (100% conversion after 43 h) with
0.15 mL (2.3 mmol) of Me2NH and 5 mg (0.01 mmol) of Cp*2UMe2
to the trans head-to-head dimer 8B, exclusively.
1
1
22.6 (t, JCH ) 122 Hz, CH2CH3), 19.6 (t, JCH ) 122 Hz, CH2CH3),
1
1
17.5 (t, JCH ) 125 Hz, CH2CH3), 14.2 (q, JCH ) 121 Hz, CH2CH3),
1
13.9 (q, JCH ) 121 Hz, 2 × CH2CH3).
m/z: 246 (M+), 231 (M+ - CH3), 217 (M+ - CH2 - CH3), 204
(M+ - C3H8), 189 (M+ - C4H9; 100%). High-resolution mass spectrum,
m/z: calcd for C18H30 (M+), 246.4398; found, 246.4407.
(h) Oligomerization of 1-Hexyne by Cp*2ThMe2 and 2,6-
Dimethylaniline-d2. As described above, 0.06 mL (0.52 mmol) of
1-hexyne was oligomerized (100% conversion after 94 h) in 0.5 mL
of THF with 0.06 mL (0.48 mmol) of 2,6 dimethylaniline-d2 and 12
mg (0.023 mmol) of Cp*2ThMe2 to a mixture of the geminal dimer
6A (42%) and the head-to-tail-to-tail trimer 6C (58%), respectively
The same reaction with 10 times excess (0.23 mmol) of the deuterated
amine was completely inhibited.
(i) Oligomerization of 1-Hexyne by Cp*2ThMe2 and t-BuNH2.
As described above, 0.08 mL (0.70 mmol) of 1-hexyne was oligomer-
ized (100% conversion after 62 h) with 0.08 mL (0.81 mmol) of
t-BuNH2 and 12 mg (0.023 mmol) of Cp*2ThMe2 to a mixture of the
geminal dimer 6A (81%) and the head-to-tail-to-tail trimer 6C (19%),
respectively. Vacuum-transfer distillation (50 °C; 1 × 10-3 mmHg)
afforded the separation of the dimer from the trimer.
(m) Dimerization of Phenylacetylene by Cp*2ThMe2 and EtNH2.
As described above, 0.04 mL (0.4 mmol) of PhCtCH was dimerized
(67% conversion after 3 h) with 0.04 mL (0.61 mmol) of EtNH2 and
13 mg (0.024 mmol) of Cp*2ThMe2 to the trans head-to-head dimer
9B, exclusively.
1H NMR (400 MHz, THF-d8) of the trans head-to-head dimer 9B:
δ 7.94 (d, 2H, 3JHH ) 8.79 Hz, o-H of ArCCtC), 7.55-7.25 (m, 8H),
3
3
6.73 (d, 1H, JHH ) 11.72 Hz, HCdCH), 5.93 (d, 1H, JHH ) 11.72
Hz, HCdCHCtC).
13C NMR (100 MHz, THF-d8) of the trans head-to-head dimer 9B:
1
δ 140.5 (d, o-CH of ArCCtC, JCH ) 156.1 Hz), 138.6 (s, CCtC),
1
1
(j) Dimerization of Cyclopentylacetylene by Cp*2ThMe2 and
EtNH2. According to the general procedure above, 0.12 mL (1.10
mmol) of C5H9CtCH was dimerized (100% conversion after 138 h)
with 0.08 mL (1.2 mmol) of EtNH2 and 7 mg (0.013 mmol) of Cp*2-
ThMe2 to a mixture of the geminal head-to-tail 7A (75%) and trans
head-to-head 7B (25%) dimers, respectively.
133.1 (d, JCH ) 167.5 Hz, o-CH of ArCdC), 130.6 (d, JCH ) 161.8
1
Hz, m-CH of ArCCtC), 130.3 (d, JCH ) 160.4 Hz, p-CH of Ar-
CdC), 130.2 (d, 1JCH ) 160.4 Hz, m-CH of ArCCtC), 130.0 (d, 1JCH
) 160.4 Hz, p-CH of ArCdC), 128.1 (d, 1JCH ) 156.1 Hz, CHdCH),
1
126.8 (s, CCdC), 108.9 (d, JCH ) 164.7 Hz, CdCHCt), 97.5 (s,
CtC), 90.7 (s, CdCCtC).
1H NMR (400 MHz, C6D6) of the geminal head-to-tail isomer 7A:
δ 5.17 (d, 1H, 3JHH ) 1.95 Hz, HHCd), 5.06 (d, 1H, 3JHH ) 1.95 Hz,
HHCd), 1.9-1.3 (m, 18H, C5H9).
m/z: 204 (M+; 100%), 126 (M+ - C6H5), 101 (M+ - CH2CH2 -
C6H5). High-resolution mass spectrum, m/z: calcd for C16H12 (M+),
204.0939; found, 204.0901.
(n) Dimerization of t-BuCtCH by Cp*2UMe2 and t-BuNH2. As
above, in 0.4 mL of THF, 0.1 mL (0.8 mmol) of t-BuCtCH was
13C NMR (100 MHz, C6D6) of the geminal head-to-tail isomer 7A:
1
δ 136.9 (s, CH2dC), 117.7 (t, JCH ) 159.0 Hz, CH2dC), 94.9 (s,

Controlled Oligomerization of Terminal Alkynes
J. Am. Chem. Soc., Vol. 121, No. 13, 1999 3029
dimerized (50% conversion after 264 h) with 0.1 mL (1.0 mmol) of
t-BuNH2 and 5 mg (0.01 mmol) of Cp*2UMe2 to a mixture of the
geminal head-to-tail dimer 10A (40%) and the trans head-to-head 10B
dimer (60%), respectively. For characterization of the geminal head-
to-tail dimer, see ref 8.
Table 1. Controlled Catalytic Oligomerization of Terminal
Alkynes Promoted by Organoactinides in the Presence of Aminesa
% dimers
% trimer
entry catalystb
Rc
i-Pr
amine
EtNH2
Me2NH
MeNH2
EtNH2
A
B
C
1H NMR (200 MHz, C6D6) of the trans head-to-head dimer 10B: δ
1
2
3
4
5
6
7
8
9
10
11
11
13
14
15
Th
U
57
10
45
32
89
43
3
3
i-Pr
90
5.68 (d, 1H, JHH ) 11.9 Hz), 5.32 (d, 1H, JHH ) 11.9 Hz), 1.15 (s,
Th
Th
Th
Th
Th
Th
Th
Th
U
n-Bu
n-Bu
n-Bu
n-Bu
n-Bu
n-Bu
C5H9
48
53
9H), 1.00 (s, 9H).
i-BuNH2
Results
2,6 DMAd 60
2,6 DMDe 42
40
58
19
The goal of this investigation was to examine the scope,
chemoselectivity, regioselectivity, actinide metal sensitivity,
kinetics, and mechanism of the selective oligomerization of
terminal alkynes controlled by the specific addition of amines.
This study represents an extension of, and comparison to, our
previous investigation of the oligomerization of terminal alkynes
promoted by organoactinides.8 In the following discussion, we
focus on the reaction scope, metal effect, kinetics, rate law, and
thermodynamics.
Reaction Scope of the Controlled Oligomerization. Orga-
noactinide complexes of the type (C5Me5)2AnMe2 (An ) Th,
U) react with terminal alkynes in the presence of primary
amines, yielding only dimers (eq 5) and, in some cases, an
additional specific trimer (eq 6) (Table 1), contrasting the
t-BuNH2
EtNH2
81
75
f
25
100
100
67
p-t-BuPh EtNH2
p-t-BuPh Me2NHg
Th
Th
Th
U
Ph
Ph
Ph
t-Bu
EtNH2
i-BuNH2
t-BuNH2
t-BuNH2
85
100
60
40
a Solvent C6H6; [cat] ) 7.6 × 10-2 M; [alkyne] ) 2.6 M; 80 °C;
[amine] ) 2.6 M; turnover frequency range 5-18 h-1. The remaining
percentage to 100% conversion is the product formed in the inter-
molecular hydroamination of the corresponding alkyne and amine.15
b Precatalyst Cp*2AnMe2 (An ) Th, U). c R ) substituent from the
corresponding RCtCH. d 2,6-Dimethylaniline. e 2,6-Dimethylaniline-
d2. f Cyclopentyl. g The same result was obtained without amine.
Scheme 1. Stoichiometric Reactivity of (C5Me5)2ThMe2
with Amines and Terminal Alkynes
reactivity for each actinide complex toward alkynes or/and
amines is outlined in Schemes 1 and 2, for Th and U,
respectively.
oligomerization chemoselectivity and regioselectivity that has
been observed under the same conditions in the absence of
amines.8 The reactions are conveniently monitored by 1H NMR
spectroscopy. In general, the initial reaction of (C5Me5)2AnMe2
(An ) Th, U) with an alkyne yields the bis(acetylide) complex,
though, in the presence of amines, for the thorium complex,
the corresponding (C5Me5)2Th(NHR)2 (13) is formed whereas,
for the uranium complex, no bis(amido) complex is observed
unless a large excess of the amine is used.13
Stoichiometric Reactivity of Organoactinide Complexes.
The different catalytic reactivities found for similar organo-
actinides (see Table 1), which is unprecedented in the chemistry
of organoactinides, prompted us to study the stoichiometric
reactivity of these organoactinide complexes to understand the
resting state of the complexes in the catalytic cycle. The
(C5Me5)2ThMe2 (1) reacts with t-BuCtCH and (TMS)-
CtCH, producing the bis(acetylide) complexes (C5Me5)2Th-
(CtCR)2 (11) (R ) t-Bu, TMS).8 The reaction of these bis-
(acetylide) complexes (11) with equimolar amounts of 2,6-
dimethylaniline yields the corresponding bis(amido) complexes
(C5Me5)2Th(NHR)2 (13). This result argues that the second
amine insertion into the thorium mono(amido)-mono(acetylide)
complex 12 is faster than the first insertion, thwarting its
isolation. Interestingly, the reaction of (C5Me5)2ThMe2 (1) with
an equimolar amount of 2,6-dimethylaniline allows the forma-
tion of the mono(amido)thorium methyl complex 15, which can
be reacted subsequently with another equivalent of 2,6-di-
methylaniline, yielding the corresponding bis(amido) complex

3030 J. Am. Chem. Soc., Vol. 121, No. 13, 1999
Haskel et al.
Scheme 2. Stoichiometric Reactivity of (C5Me5)2UMe2 with
Amines and Terminal Alkynes
Actinide, Amine, and Alkyne Effects on the Catalytic
Process. For the thorium-catalyzed oligomerization of terminal
alkynes in the presence of primary amines, as compared to the
results in the absence of amines, a dramatic effect of reducing
the extent of oligomerization is observed. For an aliphatic
alkyne, nonbulky primary amines produce mixtures of the
corresponding geminal dimer (A) and trans dimer (B) (entries
1 and 3 in Table 1; eq 5),18 whereas for aromatic alkynes, only
the trans dimer (B) is formed (entries 10-14 in Table 1).
Increasing the bulkiness of the primary amine for aliphatic
alkynes, using, for example, 2,6-dimethylaniline or t-BuNH2,
allows the formation only of the geminal dimer A and the
specific trimer C with no traces of the trans dimer B (entries
6-8 in Table 1; eq 7). This result argues that the insertion of
13. Heating the bis(amido) complex 13, in THF, eliminates an
amine molecule, allowing the formation of the thorium imido
complex 16. This complex can also be formed by eliminating
methane by heating complex 15.14 In an excess of amine, the
bis(amido) complex 13 seems to be in rapid equilibrium with
the bis(amido)-amine complex 14,15 though the equilibrium
lies toward the bis(amido) complex (vide infra).
the second alkyne into the metalla-eneyne complex M-A,
which is presumably in the preferred stereochemistry due to
the bulky amine, and the subsequent trimer elimination (eq 7)
are much faster than either the insertion of an alkyne into the
intermediate complex M-B or the protonolysis of M-B by
either the alkyne or the amine, eliminating trimer D or dimer
B, respectively (eq 8).19 It is important to point out that the
For the corresponding uranium complex 2, a similar reactivity
has been found. Thus, the reactions with PhCtCH and
(TMS)CtCH produced the bis(acetylide) complexes (C5-
Me5)2U(CtCR)2 (17) (R ) Ph, TMS).8 In contrast to the
thorium complexes, these bis(acetylide) complexes are extremely
stable and the bis(amido) complex 19 can be formed only by
adding a large excess of the amine.13 This result argues that
the equilibrium between complexes 17 and 19 lies preferentially
toward the bis(acetylide) complexes instead of either the mono-
(amido)-mono(acetylide) complex 18 or the bis(amido) com-
plex 19. Attempts to isolate the monomethyl-amido complex
21, by reacting 1 equivalent of 2,6-dimethylamine with complex
2, yield only 0.5 equiv of the bis(amido) complex 19. Similar
to the thorium bis(amido) complex, in the presence of an excess
of amine, complex 19 is in fast equilibrium with complex 20.
Again, this equilibrium favors the bis(amido) complex (vide
infra).14 When the bis(amido) complex 19 is heated in THF,
elimination of an amine molecule is observed, allowing the
formation of the corresponding uranium imido complex 22.16,17
reactions of the thorium precursor with nonbulky secondary
amines, such as Et2NH and Me2NH, and i-PrCtCH allow the
formation of higher oligomers (up to pentamers); however, the
obtained higher oligomers are produced in lower yields, as
compared with the results obtained in the reactions in the
absence of amines. In similar oligomerization reactions, with
bulky secondary amines, such as Ph2NH, no major changes are
observed for these oligomerizations, as compared to the blank
reactions in the absence of amines. These results argue that,
for secondary amines, the rate of severing the growing oligomer
from the metal is much slower than the rate of insertion of
alkynes and severing the oligomer chain by the alkyne itself,
producing the bis(acetylide) complex. (vide infra).
(14) Haskel, A.; Straub, T.; Eisen, M. S. Organometallics 1996, 15, 3770.
(15) The intermolecular hydroaminations of terminal alkynes promoted
by these types of organoactinide complexes follow different reactivities.14
However, in both cases, the kinetics exhibit an inverse first order in amine,
which has been corroborated to be effective due to the rapid equilibrium
between the bis(amido) complex and the bis(amido)-amine complex. This
type of equilibrium has also been observed in organolanthanide chemistry
in the presence of amines: (a) Giardello, M. A.; Conticello, V. P.; Brard,
L.; Gagne´, M. R.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10241. (b)
Gagne´, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 275.
(c) Gagne´, M. R.; Brard, L.; Conticello, V. P.; Giardello, M. A.; Stern, C.
L.; Marks, T. J. Organometallics 1992, 11, 2003.
(16) (a) Eisen, M. S.; Straub, T.; Haskel, A. J. Alloys Compd. 1998,
271, 116. (b) Straub, T.; Haskel, A.; Eisen, M. S. Manuscript in Preparation.
(17) Imido structures of uranium(IV) and -(VI) have been character-
ized: (a) Warner, B. P.; Scott, B. L.; Burns, C. J. Angew. Chem., Int. Ed.
Engl. 1998, 37, 959. (b) Arney, D. S. J.; Burns, C. J. J. Am. Chem. Soc.
1995, 117, 9448 and references therein.
(18) In the absence of amines, from dimers to heptamers are observed.
See Table 1 in ref 8.
(19) The plausible equilibrium between M-A and M-B has been shown
to be nonoperative under the reaction conditions.8

Controlled Oligomerization of Terminal Alkynes
J. Am. Chem. Soc., Vol. 121, No. 13, 1999 3031
In the uranium-controlled oligomerization of nonbulky alkynes
with secondary amines (primary amines yield only the inter-
molecular hydroamination product (eq 9)), no major chemo-
selectivity is observed, but the amount of the smaller oligomers
increases as compared with that of the reactions performed in
the absence of the amines (except for entry 2 in Table 1).20
Interestingly, for tert-butylacetylene, in the absence of amine,
the geminal dimer is obtained, regioselectively, whereas in the
presence of tert-butylamine, a mixture of the two dimers is
obtained (entry 15, Table 1). This result strongly suggests that
the amine should be attached to the metal center at the time of
the alkyne insertion to induce different regioselectivities.
Previously, for the noncontrolled oligomerization reactions,
we showed that the actinide-bis(acetylide) complex is the active
species in the catalytic cycle. In the new controlled oligomer-
ization reaction, the formation of the organoactinide bis(amido)
complex, which is the predominant species as observed in the
NMR,21 argues against this actinide-bis(acetylide) complex as
being the active species and provides strong evidence that the
amine is the major protonolytic agent.
Figure 2. Plot of the observed reaction rate vs alkyne concentration
for the controlled dimerization of 1-hexyne with i-BuNH2 using Cp*2-
ThMe2 as the precatalyst in benzene-d6. The line represents the least-
squares fit to the data points.
through the metal complex, only exchanging hydrogen/
deuterium atoms.22
Kinetic Studies of the Controlled Oligomerization of
Terminal Alkynes. Kinetic measurements on the controlled
oligomerization reaction of n-BuCtCH with i-BuNH2 were
1
undertaken by in-situ H NMR spectroscopy. The reaction of
To corroborate this protonolytic theory, besides the different
regioselectivities observed and besides the kinetics of the
reaction (vide infra), and to corroborate that the amine is the
major protonolytic agent, a novel strategy was implemented to
increase the selectivity toward the trimer. This was accomplished
by providing a kinetic delay for the fast protonolysis by the
amine, to allow more trimer formation, in a reaction producing
both dimer and trimer through replacement of the amine
hydrogens by deuterium (eq 10; and entries 6 and 7 in Table
an ≈70-fold excess of n-BuCtCH and i-PrNH2 with (C5Me5)2-
ThMe2 was monitored with constant catalyst concentration until
complete substrate consumption. The disappearance of the
1
CtCH (δ ) 2.28 ppm) H resonance was normalized. The
turnover frequency of the reaction was calculated from the slope
of the kinetic plots of substrate-to-catalyst ratio vs time. The
kinetic plots as shown in Figure 2 reveal a linear dependence
of the rate of the reaction on alkyne substrate concentration over
a ∼40-fold substrate concentration range, which indicates a first-
order dependence of the catalytic rate on substrate concentration
under these conditions, in analogy to the nonselective oligo-
merization of terminal alkynes in the absence of amines.
Considering the rapidity of the An-C protonolysis by primary
amines, it seems unreasonable that intermolecular proton transfer
from either the alkyne or the amine could be turnover-limiting
under most catalytic conditions. When the concentration of the
alkyne is maintained constant and the concentration of the amine
is varied over 14-fold concentration range (Figure 3) a plot of
the rate of the reaction vs amine concentration exhibits an
inverse proportionality, indicating that the reaction is inverse
first order in amine. An inverse proportionality in catalytic
systems is well-known and consistent with a rapid equilibrium
before the rate-limiting step. Our case is consistent with the
equilibrium between the bis(amido) complex and the bis(amido)-
amine complex, as found in the hydroamination of terminal
alkynes promoted by organoactinides14,16 and early transition
metal complexes23 and in the hydroamination of olefins
promoted by organolanthanide complexes.15
(10)
1). This strategy indeed enabled us to influence the chemo-
selectivity of the oligomerization and to increase the trimer:
dimer ratio.
Following the reaction, we observed the first deuterium at
the geminal position but, at larger conversions, we observed
more olefinic proton signals exchanged by deuterium, implicat-
ing that the alkyne and the deuterated amine were in equilibrium
When the initial concentrations of the terminal alkyne and
the amine are held constant and the concentration of the catalytic
precursor is varied over a ∼10-fold concentration range (Figure
4), a plot of reaction rate vs precatalyst concentration indicates
that the reaction is first-order-dependent in precatalyst. Thus,
(20) For Cp*2U(NR2)2 (R ) Me) control is observed only toward
isopropylacetylene whereas, for other alkynes, a mixture of oligomers is
obtained. The selectivity, though, is notoriously biased toward the smaller
oligomers in comparison to that of the noncontrolled oligomerization.
(21) Cp*2U{NH[C6H3(CH3)2]}2 1H NMR (cyclohexane-d12, 296 K): δ
8.85 (d, (4/2)H, 3J ) 7.0 Hz, m-H), 5.44 (s, 30H, Cp*), 4.10 (d, (4/2)H, 3J
) 7.0 Hz, m-H), 2.70 (t, 2H, 3JHH ) 7.0 Hz, p-H), -0.78 (s, (6/3)H, CH3),
-22.4 (s, (6/3)H, CH3), -52.0 (s, br, 2H, NH). Cp*2Th(NH(t-Bu))2 1H
NMR (THF-d8, 296 K): δ 2.02 (s, 32H, Cp* + NH), 1.08 (s, 18H, t-Bu).
Cp*2U(NHEt)2 1H NMR (THF-d8, 296 K): δ 1.18 (s, 30H, Cp*), 0.05 (t,
6H, 3JHH ) 7.1 Hz, CH2CH3), -4.7 (br, 4H, CH2CH3), -76.50 (s, br, 2H,
NH). Cp*2U(NH(t-Bu))2 1H NMR (THF-d8, 296 K): δ 2.49 (s, 30H, Cp*),
-3.74 (s, 18H, t-Bu), -64.30 (s, br, 2H, NH).
(22) Blank reactions of deuterated amines and alkynes at 80 °C in the
absence of the organoactinide complexes did not induce the hydrogen/
deuterium exchange.
(23) (a) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem.
Soc. 1992, 114, 1708. (b) Baranger, A. M.; Walsh, P. J.; Bergman, R. G.
J. Am. Chem. Soc. 1993, 115, 2753.

3032 J. Am. Chem. Soc., Vol. 121, No. 13, 1999
Haskel et al.
Figure 5. Eyring plot for the controlled dimerization of 1-hexyne with
i-BuNH2 using Cp*2ThMe2 as the precatalyst in toluene-d8. The line
represents the least-squares fit to the data points.
alkynes by amines producing dimers and, depending on the
bulkiness of the amine, trimers with the absence of higher
oligomers as compared to those for the noncontrolled catalytic
cycle (tetramers-heptamers) demonstrate the ability to tailor
the extent of oligomerization catalyzed by organoactinide
complexes.24 This strategy is based on an acidic chain-transfer
mechanism as a competing reaction, modifying the nonselective
oligomerization mechanism toward small oligomers. Using this
approach, the chain-transfer reagent does not end up in the
product and does not require subsequent elimination from the
product to release the unsaturated oligomer. A substantial range
of substrates can be selectively dimerized, including bulky and
nonbulky aliphatic and aromatic terminal alkynes. Regarding
the amine effect, with aliphatic alkynes and in the thorium case,
nonbulky primary amines are able to produce a mixture of two
of the three possible dimers with no discrimination between
them, whereas bulky amines allow the production of one dimer
and one trimer. Interestingly, the formed trimer contains the
same regiochemistry as the dimer complex before it was
protonated, indicating that, for bulky primary amines, the rate
for releasing the dimer from the organometallic complex with
the regiochemistry of M-B (eq 12) is much slower than the
Figure 3. Plots of the observed reaction rate vs (a) amine concentration
and (b) 1/amine concentration for the controlled dimerization of
1-hexyne with i-BuNH2 using Cp*2ThMe2 as the precatalyst in benzene-
d6. The line represents the least-squares fit to the data points.
(12)
(13)
Figure 4. Plot of the observed reaction rate vs catalyst concentration
for the controlled dimerization of 1-hexyne with i-BuNH2 using Cp*2-
ThMe2 as the precatalyst in benzene-d6. The line represents the least-
squares fit to the data points.
the rate law for the controlled oligomerization of terminal
alkynes promoted by organoactinides is given by eq 11. The
rate of alkyne insertion into the metal complex with the
regiochemistry M-A and subsequent protonolysis to the trimer
(eq 13). This result also corroborates that the insertion of the
alkyne yielding either M-A or M-B is not reversible.
V ) k[Th][alkyne][amine]-1
derived ∆Hq and ∆Sq values from an Eyring analysis (Figure
5) are 15.1(3) kcal mol-1 and -41.2(6) eu, respectively.
(11)
(24) Other controlling reagents such as silanes (primary-tertiary) have
been demonstrated to be effective as well: (a) Eisen, M. S. Proceedings of
the XVIIIth International Conference on Organometallic Chemistry, Munich,
Germany, August 1998; Abstract BI1. (b) Wang, J. Q; Eisen, M. S.
Unpublished results.
Discussion
Catalytic Reaction Scope and Mechanism. The present
catalytic results for the controlled oligomerization of terminal

Controlled Oligomerization of Terminal Alkynes
J. Am. Chem. Soc., Vol. 121, No. 13, 1999 3033
Scheme 3. Plausible Cycle for the Controlled
Oligomerization of Terminal Alkynes Catalyzed by
Organothorium Complexes in the Presence of Primary
Amines
of a sequence of well-established elementary reactions, such as
insertion of acetylene into an M-C σ-bond and σ-bond
metathesis. The precatalyst (C5Me5)2ThMe2 in the presence of
amine and alkyne is converted to the bis(amido) complex E
and the bis(amido)-amine complex D. These complexes were
found to be in rapid equilibrium and are responsible for the
inverse kinetic dependence on the amine. Complex E, which is
the catalytic resting form of the complex under the catalytic
conditions, reacts with 1 equiv of alkyne, as the rate-limiting
step, producing complex F (step 1).27 The formulation of
complex F and not the bis(acetylide) complex is based on the
different dimer and trimer ratios obtained with different amines,
implying that at least one amine should be coordinated to the
actinide complex. Likewise, with amines, the oligomerization
of t-BuCtCH by Cp*2UMe2 produces both dimers whereas,
in the absence of amine, only the geminal dimer is formed.
Moreover, regarding the acetylenic substrates, for aromatic
alkynes, the regiochemistry of the trans dimer is preferentially
obtained whereas, for aliphatic alkynes, both dimers are
obtained. Furthermore, comparison of the results obtained for
the oligomerization of phenylacetylene in the absence of amines
(with amines, only a dimer is obtained), in which both dimers
and higher oligomers are obtained, argues that an amido-
acetylide complex and not the bis(acetylide) complex is
responsible for this fine regiodifferentiation. It is noteworthy
to point out that, for the latter case, the observed regioselectivity
can be explained not only by the higher partial charge (δ-) of
the R-carbon from the aromatic ring as compared with aliphatic
alkynes28 but also by the effective partial charge (δ+) at the
metal center due to the coordinated amine. The following rapid
step in the catalytic cycle is the insertion of an alkyne into an
actinide-carbyl σ-bond, yielding the actinide-alkenyl-amido
complex G (step 2). This complex may undergo either a σ-bond
protonolysis with the amine, to yield the corresponding dimer
and the bis(amido) complex E (step 3), or another insertion of
an alkyne and concomitant σ-bond protonolysis by the amine,
yielding the oligomeric trimer and the bis(amido) complex E.14
Thus the reaction rate law presented in eq 11 is compatible with
rapid, operationally irreversible alkyne insertion (step 2), rapid
σ-bond protonolysis of the oligomer by the amine (step 3), a
slow preequilibration involving the bis(amido) (E) and the
mono(amido)-acetylide complex (F) (step 1), and a rapid
equilibrium between the bis(amido) complex E and the bis-
(amido)-amine complex D.
Since the stereochemical approach of either the amine or the
alkyne is a side approach,25 it seems plausible that, for bulky
primary amines, the steric hindrance imparted by the pentamethyl-
cyclopentadienyl rings prevents the amine from closely ap-
proaching the metalla-eneyne complex, impeding the rapid
severance of the dimer but allowing, at the same time, the
insertion of one more alkyne with the specific regiochemistry,
in which the alkyne substituent is pointing away from the metal
center.26 For nonbulky primary amines, no major steric hin-
drance is exhibited at the metal center, allowing the formation
of both dimers. For secondary bulky amines, no real control is
achieved, indicating that the amine is unable to rapidly sever
the growing oligomeric chain, allowing a protonolysis competi-
tion with the terminal alkyne, forming the bis(acetylide)
complexes. In addition, Et2NH is able to reduce the amount of
higher oligomers, though it is unable to control the chemo- and
regioselectivity of the reaction. It seems that the equilibrium
thorium bis(acetylide) h thorium mono(amide) mono(acetylide)
is strongly affected by the bulkiness of the amine and the pKa
of its hydrogens.
Regarding the rate, the present oligomerization processes
exhibit rates (Nt ) 5-18 h-1) similar to those of the nonselective
oligomerization (Nt ) 3-10 h-1). The activation entropy ∆Sq
) -41.2(6) eu for the dimerization of 1-hexyne in the presence
of t-BuNH2 can be compared to ∆Sq ) -45.2(6) eu obtained
for the trimerization of (TMS)CtCH (eq 2). It appears that both
processes proceed with similar degrees of entropic reorganiza-
tion on approaching the transition state. Since in both oligo-
merization processes the rate-limiting steps are different, the
activation enthalpy values are not compared.
Metal Effect on the Catalytic Process. Controlling the
oligomerization has been achieved by allowing a kinetic
competition between the insertion of a new alkyne molecule
into the metal-alkenyl bond (eq 14) with the protonolysis by
the amine (eq 15). Hence, The insertion reaction produces a
larger metalla-oligomer complex, whereas the competing
protonolysis produces the organic product and the bis(amido)
organometallic complex.29 The difference in selectivity as found
for the two similar organoactinide complexes can be cor-
A plausible mechanism for the controlled oligomerization of
terminal alkynes is shown in Scheme 3. The mechanism consists
(25) (a) Fagan, P. J.; Manriquez, J. M.; Volmer, S. H.; Day, C. S.; Day,
V. W.; Marks, T. J. J. Am. Chem. Soc. 1981, 103, 2206. (b) Elschenbrich,
Ch.; Salzer, A. Organometallics, 1st ed.; VCH: Weinheim, Germany, 1989;
Chapters 15 and 17.
(26) For (TMS)CtCH, a different regiochemistry is obtained due to the
polarization effect of the silicon atom. Stockis and Hoffman have performed
calculations on the polarization of the π* orbitals in (TMS)CtCH and
CH3CtCH. Different polarizations were found for both groups, showing
the large effect of the substituent on the alkyne sp-carbon atoms. These
electronic effects are believed to be responsible for the difference in
regioselectivities of the trimerization-dimerization results: (a) Stockis, A.;
Hoffmann, R. J. Am. Chem. Soc. 1980, 102, 2952. (b) Apeloig, Y.; Stanger,
A. J. Am. Chem. Soc. 1985, 107, 2806. (c) Allen, A. D.; Krishanmunti, R.;
Surya Prakash, G. K.; Tidwell, T. T. J. Am. Chem. Soc. 1990, 112, 1291.
(d) Apeloig, Y.; Biton, R.; Abu-Freih, A. J. Am. Chem. Soc. 1993, 115, 5,
2522. (e) Frey, J.; Schottland, E.; Rappoport, Z.; Bravo-Zhivotovskii, D.;
Nakash, M.; Botoshansky, M.; Kaftory, M.; Apeloig, Y. J. Chem. Soc.,
Perkin Trans 2 1994, 2555.
(27) Steps 2 and 3 in Scheme 1 are very fast, preventing the characteriza-
tion of complexes F and G. Under the experimental conditions, the only
observable complex during the catalytic reaction is the bis(amido) complex
for either the thorium or the uranium complex. However, we have been
able to spectroscopically characterize in solution a similar alkylamido
complex of thorium, Cp*2Th(NHR)CH3 (R ) t-Bu): 1H NMR δ 2.08 (s,
31H, Cp* + NH), 1.13 (s, 9H, t-Bu), -0.22 (s, 3H, Th-CH3).
(28) The 13C NMR spectra of phenylacetylene and n-BuCtCH for the
acetylenic carbons are extremely similar.
(29) The amine concentration range should be large enough to avoid
formation of larger oligomers (the alkyne will compete for protonolysis).
We have found that a 1:1 alkyne:amine ratio allows better control. Excess
of amine will preferentially form complex D, making the reaction extremely
slow.

3034 J. Am. Chem. Soc., Vol. 121, No. 13, 1999
Haskel et al.
ization. It is important to point out that all the alkyne substrates
presented in Table 1 were reacted with both organoactinides
and only those cases in which a controlling effect was found
are presented in Table 1. For the majority of the substrates in
the uranium case, no real controlling effect was found. Hence,
the theoretical thermodynamic calculations are in agreement with
our observed results, and it seems that the results found for the
uranium complex (entries 2, 11, and 15 in Table 1) are the
outcome of a kinetic effect presumably due to the bulkiness of
the alkyne.
(14)
Conclusions
In conclusion, we have shown that it is possible to control
the extent of the oligomerization of terminal alkynes catalyzed
by organoactinide complexes, by using selected amines. This
led to the possibility of ensuring catalysis by “recycling” the
obtained organometallic bis(amido) complex back to the starting
catalytically active mono(amido)thorium acetylide species. A
detailed understanding of the thermodynamics of the single steps
in the desired reactions was the key to “designing” the catalytic
cycles. The use of different protonolytic sources are under
investigation.
(15)
roborated using bond disruption energy data.30 Thus, for
thorium, both reactions (eqs 14 and 15) are calculated to be
exothermic by almost equal amounts, allowing the control,
whereas, for uranium, the formation of the bis(amido) complex
is endothermic, impeding the control of the extent of oligomer-
Acknowledgment. This research was supported by the Israel
Science Foundation, administered by the Israel Academy of
Sciences and Humanities under Contract 69/97-1, and by the
VPR Fund for the Promotion of Research at the Technion. T.S.
thanks the Max-Planck-Gesellschaft for a MINERVA postdoc-
toral fellowship, and J.Q.W. thanks the Technion for a post-
doctoral fellowship.
(30) (a) Smith, G. M.; Susuki, H.; Sonnenberg, D. C.; Day, V. W.; Marks,
T. J. Organometallics 1986, 5, 549. (b) Giardello, M. A.; King, W. A.;
Nolan, S. P.; Porchia, M.; Sishta, C.; Marks, T. J. In Energetics of
Organometallic Species; Martinho-Simo`es, J. A., Ed.; Kluwer Academic
Press: Dodrecht, The Netherlands, 1992; pp 35-51. (c) Martinho Simo`es,
J. A.; Beauchamp, J. L. Chem. ReV. 1990, 90, 629. (d) Bruno, J. W.; Marks,
T. J.; Morss, L. R. J. Am. Chem. Soc. 1983, 105, 6824.
JA983640Z