Synthesis, structure, and hydroamination kinetics of (2,2′- diaryldipyrrolylmethane)- and bis(2-arylpyrrolyl)titanium complexes

Article abstract of DOI:10.1021/om0607088

The trifluoroacetic acid catalyzed reaction of acetone and 2-arylpyrroles results in the formation of 2,9-diaryl-5,5-dimethyldipyrrolylmethanes. Ligands bearing 3,5-(CF₃)₂C₆H₃ (H ₂dmpm^3,5-CF3 and mesityl (H₂dmpm^mes) arenes were prepared in 72% and 68% yields using this procedure. The new dipyrrolylmethanes react with Ti(NMe₂)₄ to form Ti(NMe₂)₂(dmpm^3,5-CF3) and Ti(NMe ₂)₂(dmpm^mes) in 92% and 30% yields, respectively. The solid-state structures of these complexes are quite similar to that of the sterically smaller 5,5-dimethyldipyrrolylmethane complex Ti(NMe₂)₂(dmpm) with one η⁵- and one η¹-pyrrolyl; however, the substituted derivatives display much lower barriers to pyrrolyl conformational exchange, as judged by VT ¹H NMR spectroscopy. Also synthesized were bis(pyrrolyl) complexes without the methylene connector. Reactions of 2-arylpyrroles where the aryl group was 3,5-(CF₃)₂C₆H₃, mesityl, 4-(CF₃)C₆H₄, and p-tolyl generated Ti(NMe ₂)₂(pyrr^3,5-CF3)₂, Ti(NMe ₂)₂(pyrr^mes)₂, Ti(NMe ₂)₂(pyrr^4-CF3)₂, and Ti(NMe ₂)₂(pyrr^tol)₂ in 38%, 74%, 45%, and 37% purified yields, respectively. Hydroamination catalysis rates under pseudo-first-order conditions were tested using aniline and 1-phenylpropyne at 75 °C. On the dmpm framework, 2-substitution in Ti(NMe₂) ₂(dmpm^3,5-CF3) and Ti(NMe₂) ₂(dmpm^mes) results in reduced pseudo-first-order rate constants of (780 ±30) × 10^-7 and (403 ± 80) × 10^-7 s^-1 relative to Ti(NMe₂) ₂-(dmpm) at (1976 ± 130) × 10^-7 s ^-1, which is attributed to steric constraints near the substrate-binding pocket. Testing catalysis rates on the approximately isosteric complexes Ti(NMe₂)²(pyrr^4-CF3)₂ and Ti(NMe₂)₂(pyrr^tol)₂ provided rate constants of (1255 ± 193) × 10^-7 and (880 ± 20) × 10^-7 s^-1, demonstrating that electron-withdrawing groups increase catalytic activity in these systems. Ti(NMe₂) ₂(dmpm^3,5-CF3), Ti(NMe₂)₂(dmpm ^mes), Ti(NMe₂)₂(pyrr^3,5-CF3)2, and Ti(NMe₂)₂(pyrr^mes)₂ were studied by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om0607088

Organometallics 2006, 25, 6125-6133
6125
Synthesis, Structure, and Hydroamination Kinetics of
(2,2′-Diaryldipyrrolylmethane)- and Bis(2-arylpyrrolyl)titanium
Complexes
Douglas L. Swartz II and Aaron L. Odom*
Department of Chemistry, Michigan State UniVersity, East Lansing, Michigan 48824
ReceiVed August 5, 2006
The trifluoroacetic acid catalyzed reaction of acetone and 2-arylpyrroles results in the formation of
2,9-diaryl-5,5-dimethyldipyrrolylmethanes. Ligands bearing 3,5-(CF3)2C6H3 (H2dmpm3,5-CF ) and mesityl
3
(H2dmpmmes) arenes were prepared in 72% and 68% yields using this procedure. The new dipyrrolyl-
methanes react with Ti(NMe2)4 to form Ti(NMe2)2(dmpm3,5-CF ) and Ti(NMe2)2(dmpmmes) in 92% and
3
30% yields, respectively. The solid-state structures of these complexes are quite similar to that of the
sterically smaller 5,5-dimethyldipyrrolylmethane complex Ti(NMe2)2(dmpm) with one η5- and one η1-
pyrrolyl; however, the substituted derivatives display much lower barriers to pyrrolyl conformational
exchange, as judged by VT 1H NMR spectroscopy. Also synthesized were bis(pyrrolyl) complexes without
the methylene connector. Reactions of 2-arylpyrroles where the aryl group was 3,5-(CF3)2C6H3, mesityl,
4-(CF3)C6H4, and p-tolyl generated Ti(NMe2)2(pyrr3,5-CF )2, Ti(NMe2)2(pyrrmes)2, Ti(NMe2)2(pyrr4-CF )2,
and Ti(NMe2)2(pyrrtol)2 in 38%, 74%, 45%, and 37% purified yields, respectively. Hydroamination catalysis
rates under pseudo-first-order conditions were tested using aniline and 1-phenylpropyne at 75 °C. On the
3
3
dmpm framework, 2-substitution in Ti(NMe2)2(dmpm3,5-CF ) and Ti(NMe2)2(dmpmmes) results in reduced
3
pseudo-first-order rate constants of (780 ( 30) × 10-7 and (403 ( 80) × 10-7 s-1 relative to Ti(NMe2)2-
(dmpm) at (1976 ( 130) × 10-7 s-1, which is attributed to steric constraints near the substrate-binding
pocket. Testing catalysis rates on the approximately isosteric complexes Ti(NMe2)2(pyrr4-CF )2 and Ti-
3
(NMe2)2(pyrrtol)2 provided rate constants of (1255 ( 193) × 10-7 and (880 ( 20) × 10-7 s-1, demonstrating
that electron-withdrawing groups increase catalytic activity in these systems. Ti(NMe2)2(dmpm3,5-CF ),
3
Ti(NMe2)2(dmpmmes), Ti(NMe2)2(pyrr3,5-CF )2, and Ti(NMe2)2(pyrrmes)2 were studied by single-crystal X-ray
3
diffraction.
anism for the zirconium system involves terminal imido
formation, [2 + 2] cycloaddition with alkyne, Zr-C bond
protonolysis, and Zr-N protonolysis steps, as shown in Scheme
1. Evidence regarding the mechanism of the titanium-catalyzed
reaction points to a route similar to that found for its heavier
congener.14
Introduction
Titanium-catalyzed C-N bond formation has recently seen
an explosion of activity. A large portion of the new chemistry
is based on pioneering studies by the groups of Bergman,1
Rothwell,2 and Livinghouse3 in the reactivity of group 4 imido4
complexes. Among the many functionalities available from the
new intermolecular methodologies5 are new routes to imines,6
hydrazones,7 indoles,7 pyrroles,8 R,â-unsaturated imines,9 tau-
tomers of 1,3-dimines,10 and tautomers of 1,3-iminohydra-
zones.11 In addition, a variety of nitrogenous heterocycles are
available by intramolecular cyclization.12
One can easily draw analogies between the Bergman hy-
droamination mechanism14a and the Chauvin mechanism15 for
(6) For some recent examples see: (a) Marcsekova, K.; Wegener, B.;
Doye, S. Eur. J. Org. Chem. 2005, 4843. (b) Smolensky, E.; Kapon, M.;
Eisen, M. S. Organometallics 2005, 24, 5495. (c) Heutling, A.; Pohlki, F.;
Doye, S. Chem. Eur. J. 2004, 10, 3059. (d) Ward, B. D.; Maisse-Francois,
A.; Mountford, P.; Gade, L. H. Chem. Commun. 2004, 704. (e) Lorber, C.;
Choukroun, R.; Vendier, L. Organometallics 2004, 23, 1845. (f) Ackermann,
L. Organometallics 2003, 22, 4367. (g) Zhang, Z.; Schafer, L. L. Org. Lett.
2003, 5, 4733. (h) Tillack, A.; Castro, I. G.; Hartung, C. G.; Beller, M.
Angew. Chem., Int. Ed. 2002, 41, 2541. (i) Tillack, A.; Khedkar, V.; Beller,
M. Tetrahedron Lett. 2004, 45, 8875. (j) Johnson, J. S.; Bergman, R. G. J.
Am. Chem. Soc. 2001, 123, 2923. (k) Cao, C.; Ciszewski, J. T.; Odom, A.
L. Organometallics 2001, 20, 5011. (l) Shi, Y.; Ciszewski, J. T.; Odom, A.
L. Organometallics 2001, 20, 3968. (m) Haak, E.; Bytschkov, I.; Doye, S.
Angew. Chem., Int. Ed. 1999, 38, 3389.
(7) (a) Cao, C.; Shi, Y.; Odom, A. L. Org. Lett. 2002, 4, 2853. (b)
Ackermann, L.; Born, R. Tetrahedron Lett. 2004, 45, 9541. (c) Khedkar,
V.; Tillack, A.; Michalick, M.; Beller, M. Tetrahedron Lett. 2004, 45, 3123.
(d) Khedkar, V.; Tillack, A.; Michalik, M.; Beller, M. Tetrahedron 2005,
61, 7622.
(8) Ramanathan, B.; Keith, A. J.; Armstrong, D.; Odom, A. L. Org. Lett.
2004, 6, 2957.
The mechanism13 for the reaction was elucidated by Bergman
and co-workers using a zirconocene-based system.1 The mech-
* To whom correspondence should be addressed. E-mail: odom@
cem.msu.edu.
(1) (a) Baranger, A. M.; Walsh, P. J.; Bergman, R. G. J. Am. Chem.
Soc. 1993, 115, 2753. (b) Walsh, P. J.; Baranger, A. M.; Bergman, R. G.
J. Am. Chem. Soc. 1992, 114, 1708. (c) Duncan, A. P.; Bergman, R. G.
Chem. Rec. 2002, 2, 431. (d) Lee, S. Y.; Bergman, R. G. Tetrahedron 1995,
51, 4255. (e) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem.
Soc. 1998, 120, 13405.
(2) Hill, J. E.; Profilet, R. D.; Fanwick, P. E.; Rothwell, I. P. Angew.
Chem., Int. Ed. 1990, 29, 664.
(3) (a) Fairfax, D.; Stein, M.; Livinghouse, T.; Jensen, M. Organome-
tallics 1997, 16, 1523. (b) McGrane, P. L.; Livinghouse, T. J. Am. Chem.
Soc. 1993, 115, 11485. (c) McGrane, P. L.; Jensen, M.; Livinghouse, T. J.
Am. Chem. Soc. 1992, 114, 5459. (d) McGrane, P. L.; Livinghouse, T. J.
Org. Chem. 1992, 57, 1323.
(9) Cao, C.; Li, Y.; Shi, Y.; Odom, A. L. Chem. Commun. 2004, 2002.
(10) Cao, C.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2003, 125, 2880.
(11) Banerjee, S.; Shi, Y.; Cao, C.; Odom, A. L. J. Organomet. Chem.
2005, 690, 5066.
(4) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839.
(5) Odom, A. L. Dalton Trans. 2005, 225.
10.1021/om0607088 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/16/2006

6126 Organometallics, Vol. 25, No. 26, 2006
Swartz and Odom
Scheme 1. Bergman Mechanism for Alkyne
Hydroamination
increased Lewis acidity of the metal center may expedite the
protonolysis event, which is believed to be the rate-limiting step.
Because so many of the applications listed above are based
upon the hydroamination catalytic cycle, we often still use
simple hydroamination of alkynes as a method for evaluating
the efficacy of new catalyst designs, as will be done in this
study.
Our group has been working to increase the activity of the
complexes employed in titanium hydroamination through ancil-
lary ligand studies. To do this, we have chosen as a basis a set
of ligands using pyrrole as the unit interacting with titanium.
The use of pyrrole in the ancillary ligands was driven by a
couple of factors. The first was one of expediency; pyrroles
are relatively easy to manipulate into multidentate ligands using
a set of standard condensation reactions that take advantage of
the nucleophilic nature of the ring. As a result, several classes
of multidentate ligands can be synthesized in a small number
of steps using methods such as the Mannich reaction. Second,
pyrrole is a poor π-donor relative to commonplace amides and
alkoxides when these bear typical organic substituents.20
Considering the known improvement in catalytic activity of
related d0 Schrock carbenes on increased Lewis acidity and
increased acidity of amines attached to more Lewis acidic metal
centers (vide supra), we expected increased reactivity with
decreased donor ability of the ancillary ligands.5
olefin metathesis. Both reactions are known to involve inter-
mediates with metal-ligand multiple bonds (e.g., A in Scheme
1). In addition, a key step in both mechanisms is [2 + 2]
cyclization between a C-C unsaturated bond and the metal-
ligand multiple bond (compound A to C).16 Increasing the Lewis
acidity of the metal center in d0 olefin metathesis catalysts, i.e.,
Schrock’s catalyst, is well-known to increase catalysis rates,17
which is likely due, at least in part, to stronger olefin-metal
center interactions (B in Scheme 1) prior to cycloaddition. We
anticipated that the increased Lewis acidity would be advanta-
geous for titanium hydroamination for similar reasons.18 In
addition, the Bergman mechanism involves protolytic cleavage
of an M-C bond by a coordinated amine (D to E in Scheme
1). Brønsted acidity of a coordinated amine (D in Scheme 1)
increases on coordination to a metal center.19 Consequently,
The most active precatalyst known thus far for simple alkyne
hydroamination is the dipyrrolylmethane-ligated titanium com-
plex Ti(NMe2)2(dmpm) (1),21 where dmpm is 5,5-dimethyl-
dipyrrolylmethane, and its derivatives. The ligand is readily
prepared by the reaction (eq 1) of acetone and pyrrole catalyzed
by trifluoroacetic acid (TFA) using the procedure of Lindsey
and co-workers.22
In this study, we evaluated the effects on structure and
catalysis of 2-aryl substitutions on the dmpm framework. In
addition, we prepared related bis(pyrrolyl) complexes to evaluate
the effect of the linker on the structure and catalysis.
(12) (a) Kim, H.; Lee, P. H.; Livinghouse, T. Chem. Commun. 2005,
5205. (b) Bexrud, J. A.; Beard, J. D.; Leitch, D. C.; Schafer, L. L. Org.
Lett. 2005, 7, 1959. (c) Hoover, J. M.; Petersen, J. R.; Pikul, J. H.; Johnson,
A. R. Organometallics 2004, 23, 4614. (d) Ackermann, L.; Bergman, R.
G.; Loy, R. N. J. Am. Chem. Soc. 2003, 125, 11956. (e) Li, C.; Thomson,
R. K.; Gillon, B.; Patrick B. O.; Schafer, L. L. Chem. Commun. 2003, 2462.
(f) Bytschkov, I.; Doye. S. Tetrahedron Lett. 2002, 43, 3715. (g) Ackermann,
L.; Bergman, R. G. Org. Lett. 2002, 4, 1475.
(13) There is some evidence that cationic group 4 complexes use a 1,2-
insertion mechanism similar to that found for lanthanide and group 3 based
hydroamination catalysts. For examples of cationic zirconium hydroami-
nation see: (a) Gribkov, D. V.; Hultzsch, K. C. Angew. Chem., Int. Ed.
2004, 43, 5542. (b) Knight, P. D.; Munslow, I.; O’Shaughnessy, P. N.;
Scott, P. Chem. Commun. 2004, 894. For examples of hydroamination using
the 1,2-insertion mechanism see: (c) Li, Y.; Marks, T. J. J. Am. Chem.
Soc. 1998, 120, 1757. (d) Seyam, A. M.; Stubbert, B. D.; Jensen, T. R.;
O’Donnell, J. J., III; Stern, C. L.; Marks, T. J. Inorg. Chim. Acta 2004,
357, 4029. (e) Roesky, P. W.; Stern, C. L.; Marks, T. J. Organometallics
1997, 16, 4705. (f) Gagne, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem.
Soc. 1992, 114, 275. (g) Molander, G. A.; Romera, J. A. C. Chem. ReV.
2002, 102, 2161. (h) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37,
673. (i) Kim, J. Y.; Livinghouse, T. Org. Lett. 2005, 7, 1737.
(14) (a) Straub, B. F.; Bergman, R. G. Angew. Chem., Int. Ed. 2001, 40,
4632. (b) Pohlki, F.; Doye, S. Angew. Chem., Int. Ed. 2001, 40, 2305.
(15) Herrison, J.-L.; Chauvin, Y. Makromol. Chem. 1971, 141, 161.
(16) Grubbs, R. H., Ed. Handbook of Metathesis; Wiley-VCH: Chich-
ester, U.K., 2003.
Results and Discussion
Selective generation of 2-arylpyrrole complexes is greatly
enabled by a recent methodological contribution by Sadighi and
co-workers,23 which involves coupling between chloro(pyrrolyl)-
zinc and aryl halides catalyzed by palladium (eq 2). Using this
technique, a variety of 2-arylpyrroles can be synthesized
selectively on multigram scales. For this study, we prepared
(19) For a thorough discussion of the pKa of a ruthenium amine complex
see: Fulton, J. R.; Sklenak, S.; Bouwkamp, M. W.; Bergman, R. G. J. Am.
Chem. Soc. 2002, 124, 4722.
(20) Ciszewski, J. T.; Harrison, J. F.; Odom, A. L. Inorg. Chem. 2004,
43, 3605.
(17) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare,
M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875.
(18) The added strength of dative interactions with the amines in solution
could negate some of the effects of stronger alkyne/olefin binding. There
could also be advantages to greater Lewis acidity in the [2 + 2]
cycloaddition itself.
(21) Shi, Y.; Hall, C.; Ciszewski, J. T.; Cao, C.; Odom, A. L. Chem.
Commun. 2003, 586.
(22) Littler, B. J.; Miller, M. A.; Hung, C.-H.; Wagner, R. W.; O’Shea,
D. F.; Boyle, P. D.; Lindsey, J. S. J. Org. Chem. 1999, 64, 1391.
(23) Rieth, R. D.; Mankad, N. P.; Calimano, E.; Sadighi, J. P. Org. Lett.
2004, 6, 3981.

Dipyrrolylmethane and Bis(2-arylpyrrolyl) Ti Complexes
Organometallics, Vol. 25, No. 26, 2006 6127
Scheme 2. Synthesis of H2dmpm3,5-CF and H2dmpmmes and
3
Reactions with Ti(NMe2)4 (2) To Form
Ti(NMe2)2(dmpm3,5-CF ) (3) and Ti(NMe2)2(dmpmmes) (4)
3
Figure 1. ORTEP structure from single-crystal X-ray diffraction
on Ti(NMe2)2(dmpm3,5-CF ) (3). Selected bond distances (Å) and
3
angles (deg): Ti-N(3) ) 1.875(5), Ti-N(4) ) 1.892(5), Ti-N(2)
) 2.048(5), Ti-N(1) ) 2.400(6); N(4)-Ti-N(3) ) 107.1(2),
N(4)-Ti-N(2) ) 102.6(2), N(3)-Ti-N(2) ) 104.8(2).
mol was measured.21 It is assumed that the exchange occurs
through an η1:η1 isomer, and this barrier is consistent in
magnitude with other known pyrrole η1 to η5 isomerizations25
in the literature24 and even related phospholyl isomerizations.26
In the solid state the complexes with R-aryl substitution on
the pyrrolyl rings show structures very similar to that of the
unsubstituted derivative 1. The metric parameters from 1 to the
more sterically encumbered 3 and 4 do not change significantly.
A structure for 3 is shown in Figure 1. For the structure of 4,
see the Supporting Information.
Consistent with Parkin’s results, increased sterics lower the
barrier for ring exchange in 3 and 4. For example, the
compounds are still at the fast exchange limit at -60 °C.
For comparison with the dmpm derivatives, we also prepared
unlinked bis(pyrrolyl) derivatives with the same aryl group on
3
the pyrrolyl rings. The two complexes Ti(NMe2)2(pyrr3,5-CF
)
2
4-(CF3)C6H4, 4-(CH3)C6H4, 3,5-(CF3)2C6H3, and 2,4,6-(CH3)3C6H2
substituted pyrroles.
(5) and Ti(NMe2)2(pyrrmes)2 (6) were prepared by treatment of
Ti(NMe2)4 with 2 equiv of the pyrrole (Scheme 3).
Interestingly, the solid-state structures of the bis(pyrrolyl)
complexes 5 (Supporting Information) and 6 (Figure 2) bear
pyrrolyl rings that are both in the η1:η1 configuration in the
solid state. When solutions were cooled in the NMR probe, no
new resonances could be seen in the baseline.
With these complexes in hand, we set out to answer several
questions. First, how would sterics in the 2-position affect the
catalysis rate? Second, how does the linker affect the catalysis
rate? Third, can it be shown that electron-withdrawing groups
definitively increase the rate, as argued in the Introduction?
To test the kinetic ability of the catalysts, we chose a standard
set of conditions. The reactions are run pseudo first order in
amine, which we chose as aniline. Aniline was chosen over other
possible amines because it runs at a reasonable rate with a large
variety of catalysts. For example, we hoped to compare the
efficacy of the new catalysts with that of commercially available
Ti(NMe2)4 (2), which is very effective with aniline but not with
most alkylamines.6l The limiting reagent utilized was 1-phe-
nylpropyne, which runs cleanly with good regioselectivity with
most catalysts at a moderate rate. An internal alkyne was needed,
due to the rapidity of hydroamination with catalysts such as
The usual procedure for the synthesis of dipyrrolylmethanes
involves the use of a large excess of pyrrole (eq 1). We were
quite relieved to find that the 2-arylpyrroles could be used as
the limiting reagent in the synthesis of dipyrrolylmethane
derivatives with acetone as the electrophile. The reactions are
smoothly catalyzed by TFA to generate the ligands in good
yield. We initially prepared two 5,5-dimethyldipyrrolylmethane
derivatives for study, 2,9-[3,5-(CF3)2C6H3]-5,5-dimethyldipyr-
rolylmethane (H2dmpm3,5-CF ) and 2,9-[2,4,6-(CH3)3C6H2]-5,5-
3
dimethyldipyrrolylmethane (H2dmpmmes). These complexes
react with Ti(NMe2)4 (2) to generate the new pyrrolyl complexes
Ti(NMe2)2(dmpm3,5-CF ) (3) and Ti(NMe2)2(dmpmmes) (4)
3
(Scheme 2).
Parkin and Tanski24 have shown that decreased sterics and
decreased electron density at the metal favor the η5 configuration
in 2-arylpyrrolyl complexes. Our previous studies on Ti(NMe2)2-
(dmpm) (1) showed the dipyrrolylmethane ligand was in the
η1:η5 configuration in the solid state. In cold solutions on the
NMR time scale, resonances consistent with the solid-state
structure were observed. As the solution is warmed, resonances
for the η1-pyrrolyl and η5-pyrrolyl groups coalesce. The fast
exchange limit is reached well before room temperature, and a
barrier for pyrrolyl ligand conformational exchange of 10 kcal/
(25) For a review on Cp and indenyl isomerization see: O’Conner, J.
M.; Casey, C. P. Chem. ReV. 1987, 87, 307.
(26) Hollis, T. K.; Ahn, Y. J.; Tham, F. S. Chem. Commun. 2002, 2996.
(24) Tanski, J. M.; Parkin, G. Organometallics 2002, 21, 587.

6128 Organometallics, Vol. 25, No. 26, 2006
Swartz and Odom
Figure 2. ORTEP structure from single-crystal X-ray diffraction
on Ti(NMe2)2(pyrrmes
) (6). Selected bond distances (Å) and
2
angles (deg): Ti-N(3) ) 1.844(4), Ti-N(4) ) 1.865(4), Ti-N(2)
) 1.971(4), Ti-N(1) ) 2.007(4); N(3)-Ti-N(4) ) 109.3(2),
N(3)-Ti-N(2) ) 107.5(2), N(4)-Ti-N(2) ) 108.4(2), N(3)-Ti-
N(1) ) 112.0(2), N(4)-Ti-N(1) ) 114.1(2), N(2)-Ti-N(1) )
105.2(2).
Figure 3. Plot of concentration of 1 versus pseudo-first-order rate
constant for the hydroamination reaction.
Scheme 3. Synthesis of Ti(NMe2)2(pyrr3,5-CF )2 (5) and
3
Ti(NMe2)2(pyrrmes)2 (6)
equations. Even though most of the catalysts are quite regiose-
lective for this reaction, the measurement of the disappearance
of 1-phenylpropane was preferable to measuring the appearance
of products to avoid missing potential rate contributions from
the other regioisomer. Comparisons between catalysts use the
magnitude of kobs under these constant conditions as a measure
of relative hydroamination reaction rate.
The results of the kinetic study on compounds 1 and 3-6
are shown in Table 1. The errors are based on repeated runs (at
least three), are at the 99% confidence level, and varied with
catalyst from as little as 4% to as high as 20%. The average
error on the rate constants was about 10% at this confidence
level.
It is obvious from comparison of the data in entries 1-3 of
Table 1 that substitution on the 2-position of the pyrrole rings
in the dmpm framework results in a reduction in rate constant
by a factor of about 2.5-5 times relative to the parent
framework. The increased sterics of the dipyrrolylmethane
framework near the substrate binding sites results in slower
kinetics.
Scheme 4. Conditions for the Kinetic Studies
Interestingly, the unlinked pyrrolyl catalysts were actually
faster than the dmpm derivatives by a factor of 1.5-2 times
(entries 4 and 5 versus entries 2 and 3). This increase in rate
can again be explained by the steric congestion of the substituted
dmpm derivatives. It is likely that the unlinked derivatives can
rotate the bulky substituents away from the substrate-binding
site, increasing the rate constant.
Ti(NMe2)2(dmpm) (1) with terminal alkynes. For example, the
reaction with 1-hexyne and aniline requires less than 5 min when
started at room temperature using 5 mol % of 1. Catalyst 1,
conveniently, requires less than 4 h at 75 °C to carry the reaction
to completion with 1-phenylpropyne and excess aniline. The
conditions for the catalyses are shown in Scheme 4. The
reactions were run in d8-toluene in the NMR probe.
Often, catalytic reactions show a first-order dependence on
catalyst concentration. This was shown to be true with 1 under
these conditions; changes in catalyst concentration track linearly
with rate constant (Figure 3). With catalytic conditions that are
at high concentrations of amine and with a linear dependence
on catalyst concentration, the rate law for the reaction reduces
to a pseudo-first-order expression in alkyne with standardized
conditions for the catalyst. All the catalytic reactions studied
fit well to the rate expression in Scheme 4.
However, even the complexes bearing the unlinked pyrrolyl
ligands were still slower than the parent complex Ti(dmpm)-
(NMe2)2 (1) by a factor of ∼1.5 versus the fastest member,
Ti(NMe2)2(pyrr3,5-CF )2 (5).
3
Comparison of the two catalysts Ti(NMe2)2(pyrr3,5-CF )2 (5)
3
and Ti(NMe2)2(pyrrmes)2(6) does not allow separation of steric
and electronic factors. Consequently, we prepared two additional
titanium compounds that differ only in the donor ability of a
substituent in the 4-position of an aromatic group on the
2-position of a pyrrole. The pyrroles, synthesized using the
Sadighi reaction, were 2-(4-(trifluoromethyl)phenyl)pyrrole
tol
(Hpyrr4-CF ) and 2-(4-tolyl)pyrrole (Hpyrr ). These were placed
3
A representative plot of ln[1-phenylpropyne] versus time
under the conditions shown in Scheme 4 is provided as Figure
4 for complex 1. The disappearance of the 1-phenylpropyne
starting material versus time was used to fit the first-order
on titanium by transamination (Scheme 5) on Ti(NMe2)4 (2) to
tol
form Ti(NMe2)2(pyrr4-CF )2 (7) and Ti(NMe2)2(pyrr )2 (8).
3
Using the same experimental procedure as before (Scheme
4), the activities of 7 and 8 were also tested. As shown in Figure

Dipyrrolylmethane and Bis(2-arylpyrrolyl) Ti Complexes
Organometallics, Vol. 25, No. 26, 2006 6129
Table 1. Observed Rate Constants for Pyrrolyl Catalysts
Ti(NMe2)2(dmpm) (1), Ti(NMe2)2(dmpm3,5-CF ) (3),
3
Ti(NMe2)2(dmpmmes) (4), Ti(NMe2)2(pyrr3,5-CF )2 (5), and
3
Ti(NMe2)2(pyrrmes)2 (6)
a Conditions are as shown in Scheme 4. b All errors are at the 99%
confidence limit.
Scheme 5. Synthesis of Ti(NMe2)2(pyrr4-CF )2 (7) and
3
Ti(NMe2)2(pyrrtol)2 (8)
Figure 4. (top) Representative plot of ln[1-phenylpropyne] vs time
with complex 1 as the hydroamination catalyst. (bottom) Repre-
sentative plot of [1-phenylpropyne] vs time with fit curve. See the
Experimental Section for a description of the equation used to fit
the bottom plot.
smaller rate constant at (880 ( 20) × 10-7 s-1 relative to either
CF3 complex but slightly improved activity over the more
sterically crowded mesityl-containing compound 6.
One possible complication with the bis(pyrrolyl) complexes
is disproportionation reactions to generate a mixture containing
mono(pyrrolyl) and tris(pyrrolyl) complexes.27 Are the mono-
(pyrrolyl) or the bis(pyrrolyl) complexes actually the active
catalysts? Thus far, we have only been able to isolate the mono-
(pyrrolyl) complexes as impure mixtures. Attempts to study
kinetics using these impure complexes or mono(pyrrolyl)
complexes generated in situ from Ti(NMe2)4 and Hpyrr deriva-
Figure 5. Comparison of rate constants for hydroamination of the
bis(pyrrolyl) complexes. Errors are at the 99% confidence level,
and rate constants are ×10-7 s-1
.
5, the compounds showed a dramatic difference with donor
ability of the substituent in the para position of the arene ring.
The p-CF3 complex 7 has a rate constant of (1255 ( 145) ×
10-7 s-1, similar to that of the 3,5-(CF3)2 species 5 at (1275 (
72) × 10-7 s-1. The p-methyl complex 8 had a significantly
(27) Crossover of pyrrolyl ligands is certainly possible in these com-
plexes. Taking a C6D6 solution of Ti(NMe2)2(pyrr3,5-CF )2 (5) and Ti(NMe2)2-
3
(pyrrmes)2 (6) in a 1:1 ratio leads to new resonances in the 1H NMR spectra
which are presumably due to pyrrolyl crossover. Further study is warranted
on these issues.

6130 Organometallics, Vol. 25, No. 26, 2006
Swartz and Odom
Table 2. Comparison of Various Catalyst Architectures
The results in Table 2 suggest that the pyrrolyl framework is
quite effective relative to other catalyst architectures currently
in use. As in our previous report,21 the results show that Ti-
(NMe2)2(dmpm) (1) is about a factor of 2 faster than Ti(NMe2)4
(2) (entries 1 and 2). The bis(pyrrolyl) species 6 provides activity
comparable with that of 2. The rate constant for 6 increased by
∼5 times on raising the temperature from 75 to 100 °C.
Comparison of Ti(indenyl)2(NMe2)2 with 6 under identical
conditions reveals that this pyrrolyl catalyst is about a factor of
4 times faster for these substrates.
Conclusions
Using readily available 2-substituted pyrroles, a route to 2,9-
diaryldipyrrolylmethanes has been developed where the syn-
thesized pyrroles can be used as the limiting reagent in
condensation with acetone. Placing these new ligands on
titanium is readily accomplished by reaction with Ti(NMe2)4
(2), and the resulting complexes show η5:η1 coordination of the
dipyrrolylmethane in the solid state. However, the barrier for
pyrrolyl exchange in these substituted dipyrrolylmethanes is
quite low and is below what could be measured by variable-
a Conditions are the same as shown in Scheme 4, except in entries 4
and 5, where the temperature is 100 °C instead of 75 °C. b All errors are at
the 99% confidence limit.
tives have given very large errors. While the average rate
constants are generally smaller than those of their bis(pyrrolyl)
counterparts, the errors do not allow a definitive answer to this
question at this time.
1
temperature H NMR spectroscopy. Catalysis with these new
dmpm complexes was slower than with unsubstituted 1, which
we currently assign to steric inhibition by the bulky groups near
the substrate-binding site. Consistent with this, simple bis-
(pyrrolyl) complexes without the methylene linker and with the
same substituents show faster catalysis rates, which is likely
due to free rotation of the steric bulk away from the substrate
binding site in the bis(pyrrolyl) derivatives. Using these bis-
(pyrrolyl) catalysts, we were able to show experimentally that
hydroamination activity can be increased by adding electron-
withdrawing groups to pyrrolyl substituents (Figure 5).
Comparison of various catalyst architectures shows that the
pyrrolyl catalysts are quite rapid. It should be noted that this
does not necessarily imply that these catalysts are superior for
any particular application. The “best” catalyst for any particular
application is a function of availability, selectivity, and activity
with a particular set of substrates. For example, the fastest
catalyst studied here, 1, is a poor catalyst for some applications,
e.g., hydrohydrazination,30 and is the only catalyst studied that
leads to any product for others, e.g., the synthesis of 1-phenyl-
2,5-dibenzylpyrrolyl from 1,6-diphenyl-1,5-hexadiyne and aniline.8
The aim is to optimize the activity of the most promising
catalysts for these reactions, which our current results suggest
are the dipyrrolylmethane complexes of titanium, especially Ti-
(NMe2)2(dmpm) (1). From these experiments, we are discover-
ing what electronic features and steric profiles encourage these
useful C-N bond forming reactions.
It can be said definitively that the active species is not Ti-
(NMe2)4 (2), prepared by disproportionation of the bis(pyrrolyl)
complexes. Since we do not observe Hpyrr during the reactions,
the maximum amount of 2 that can be generated via dipropor-
tionation is half of the concentration generally employed in our
kinetics runs (Scheme 4). Since the rates vary linearly with
catalyst concentration (Figure 3), the rate constant for these
reactions would have a maximum (full disproportionation to 2
and (pyrr)4Ti) of kobs ) (433 ( 47) × 10-7 s-1. Since the rates
for all of the bis(pyrrolyl) complexes are faster than this, 2
cannot be the active species in these reactions.
We can also use the same conditions to evaluate these pyrrolyl
catalysts versus several commonly employed titanium complexes
with various architectures. For this we wished to compare other
catalyst types with the parent complex Ti(NMe2)2(dmpm) (1)
and bis(pyrrolyl) species Ti(NMe2)2(pyrrmes)2 (6). An important
comparison is with Ti(NMe2)4 (2), which does not have as large
a substrate scope as many of the other catalyst types;6l however,
it is commercially available and is often the starting material
for other titanium catalysts. We also compared with triple-
recrystallized samples of Ti(indenyl)2Me2 (9), which has been
shown by Doye and co-workers to be a fairly general catalyst
for alkyne hydroamination.6c
We were able to run all the catalysts at 75 °C, with the
exception of the indenyl complex 9. While 9 was active at 75
°C, the results were inconsistent at this temperature, which was
apparently due to a sensitive catalyst activation period.28
Assuming that there was an activation problem, we incubated
the catalyst with the aniline portion at 100 °C prior to alkyne
addition. However, this still did not result in good reproducibility
of the kinetics under these conditions. Consequently, we ran
the reactions with 9 at 100 °C, which afforded plots that reliably
fit well to first-order kinetics. For comparison, Ti(NMe2)2-
(pyrrmes)2 (6), a very stable but relatively slow catalyst, was
run at the higher temperature as well.29
Good activity was obtained with simple bis(pyrrolyl) com-
plexes such as Ti(NMe2)2(pyrr3,5-CF )2 (5). Whether the some-
3
what faster rates with the dipyrrolylmethane 1 are due to
electronic factors resulting from the different ligand architecture,
smaller steric constraints in 1, or a combination of the two
effects is currently unknown, which is the subject of ongoing
scrutiny.
Further optimization of the dmpm framework is currently
under investigation. For previous studies, some data suggested
that the active species for hydroamination is the η1:η1-dmpm
isomer of 1.21 Consequently, moving the steric bulk from the
2- to the 3-position of the pyrrolyl ring may result in greater
(28) The only pyrrolyl catalyst for which an activation period was
observed was for some of the less active bis(pyrrolyl) complexes such as
(29) A comparison with Ti(NMe2)2(dmpm) (1) would have been prefer-
able. However, under these conditions at 100 °C the reaction was ∼50%
complete in <10 min, making its measurements unreliable.
(30) Banerjee, S.; Odom, A. L. Unpublished results.
Ti(NMe2)2(pyrrmes
) ) (8). However, even with
(6) and Ti(NMe2)2(pyrrtol
2
2
these, activation would occur at room temperature over a couple of hours
if samples were allowed to rest before the kinetic run.

Dipyrrolylmethane and Bis(2-arylpyrrolyl) Ti Complexes
Organometallics, Vol. 25, No. 26, 2006 6131
MHz, CDCl3): δ 8.2 (br s, 1 H, Ha), 7.37 (d, JHH ) 8.46 Hz, 2 H,
Hg or Hh), 7.18 (d, JHH ) 8.07 Hz, 2 H, Hg or Hh), 6.82 (m, 1 H,
Hb or Hd), 6.50 (m, 1 H, Hb or Hd), 6.31 (q, JHH ) 2.84, 1 H, Hc),
2.39 (s, 3 H, Hj). 13C NMR (500 MHz, CDCl3) δ 135.85 (Ci or
Cf), 132.19 (Ci or Cf), 129.97 (Ce), 129.50 (Ch or Cg), 123.77 (Ch
or Cg), 118.42 (Cd or Cb), 109.90 (Cd or Cb), 105.31 (Cc), 21.38
(Cj). Anal. (Found) calcd: C, (84.10) 84.04; H, (7.02) 7.05; N,
(8.66) 8.91.
activity as the substituent is moved away from the active site.
This assertion is currently being tested.
Experimental Section
General Considerations. All manipulations of air-sensitive
compounds were carried out in an MBraun drybox under a purified
nitrogen atmosphere. Anhydrous ether was purchased from Co-
lumbus Chemical Industries Inc., and pentane and toluene, pur-
chased from Spectrum Chemical Mfg. Corp., were purified by
sparging with dry N2 and then removing the water by running the
solvents through activated alumina systems purchased from Solv-
Tek. Hexanes and ethyl acetate were purchased from Mallinckodt-
Baker Inc., and reagent grade acetone was purchased from Fisher
Scientific and distilled from CaSO4 under N2 and stored over 4Å
molecular sieves. Trifluoracetic acid was purchased from Aldrich
and used as received. Aniline was purchased from Matheson,
Coleman and Bell Mfg. and was distilled two times from calcium
hydride under vacuum. 1-Phenylpropyne was purchased from GFS
Chemical, vacuum-distilled, and then passed over two columns of
neutral alumina. Ti(NMe2)4 (2)31 and Ti(indenyl)2(CH3)2 (9)32 were
prepared using the literature procedures. 2-(2,4,6-Trimethylphenyl)-
1H-pyrrole (Hpyrrmes) and 2-[3,5-bis(trifluoromethyl)phenyl]-1H-
Synthesis of 2-[4-(Trifluoromethyl)phenyl]-1H-pyrrole
-
(Hpyrr4-CF ).
3
Under an atmosphere of dry nitrogen, a threaded Schlenk tube was
loaded with sodium pyrrole (3.6 g, 40.4 mmol), ZnCl2 (5.5 g, 40.4
mmol), and a stirbar. To that vessel was slowly added 32 mL of
THF (Caution! exothermic). After 10 min, Pd(OAc)2 (15 mg, 0.5
mol %) and 2-(dicyclohexylphosphino)biphenyl (24 mg, 0.5 mol
%) were added to the Schlenk tube. The screw cap was replaced,
and the tube was removed from the drybox and connected to a
Schlenk line. Under a continuous flow of nitrogen the screw cap
was removed and 4-bromobenzotrifluoride (3 g, 13 mmol) was
quickly added. The screw cap was replaced, and the headspace in
the tube was evacuated. The tube was then placed in a 80 °C oil
bath, where the contents were allowed to react for 20 h. After the
reaction was complete, the tube was removed from the oil bath
and cooled to room temperature. The cap was removed, and the
solution was transferred to a separatory funnel. The tube was rinsed
with 30 mL of OEt2 and 30 mL of H2O, which were then added to
the separatory funnel. The aqueous layer was extracted with OEt2
(3 × 50 mL); the combined organic layers were collected and dried
over MgSO4. The solution was then filtered and concentrated in
vacuo. Purification of the crude product was accomplished by
column chromatography on silica gel using an eluting solution of
hexanes: ethyl acetate (9:1). Removal of volatiles yielded the
product as a white solid (2.53 g, 90%). Mp: 158 °C. 1H NMR (500
MHz, CDCl3): δ 8.46 (br s, 1 H, Ha), 7.59 (d, JHH ) 7.73 Hz, 2
H, Hh), 7.53 (d, JHH ) 7.73 Hz, 2 H, Hg), 6.91 (m, J ) 1.70 Hz,
1 H, Hd), 6.62 (m, JHH ) 1.47 Hz, 1 H, Hb), 6.33 (q, J ) 3.36 Hz,
1 H, Hc). 13C NMR (500 MHz, CDCl3): δ 135.91 (Cf), 130.6 (Ce),
127.85 (q, JCF ) 33 Hz, Ci), 125.92 (q, JCF ) 33 Hz, Ch), 124.29
(q, JCF ) 272 Hz, Cj), 123.58 (Cg), 120.1 (Cd), 110.65 (Cc), 107.7
(Cb). Anal. (Found) calcd: C, (62.22) 62.56; H, (3.54) 3.82; N,
(6.51) 6.67.
pyrrole (Hpyrr3,5-CF ) were synthesized according to literature
3
methods.23 Deuterated solvents were dried over purple sodium
benzophenone ketyl (C6D6) or phosphoric anhydride (CDCl3) and
distilled under a nitrogen atmosphere. Deuterated toluene was dried
1
by passing through two columns of neutral alumina. H and 13C
spectra were recorded on Inova-300 and VXR-500 spectrometers.
All spectra were referenced internally to residual protio solvent (1H)
or solvent (13C) resonances. 1H and 13C assignments were confirmed
when necessary by using two-dimensional 1H-1H and 1H-13C
correlation NMR experiments. Chemical shifts are reported in ppm,
and coupling constants are reported in Hz. Typical coupling
constants are not reported.
Synthesis of 2-(4-Methylphenyl)-1H-pyrrole (Hpyrrtol).
Under an atmosphere of dry nitrogen a threaded Schlenk tube was
loaded with sodium pyrrole (4.69 g, 52.6 mmol), ZnCl2 (7.17 g,
52.6 mmol), and a stirbar. To that same vessel was added 40 mL
of THF slowly (Caution! exothermic). After 10 min, Pd(OAc)2 (20
mg, 0.5 mol %) and 2-(di-tert-butylphosphino)biphenyl (26 mg,
0.5 mol %) were added to the Schlenk tube. The tube was then
capped, taken from the dry box, and connected to a Schlenk line.
Under a continuous flow of nitrogen the screw cap was removed,
and 4-bromotoluene (3 g, 17.5 mmol) was quickly added. The screw
cap was replaced after addition. The headspace in the Schlenk tube
was evacuated, and the tube was then placed in a 100 °C oil bath
for 24 h. After 24 h, the tube was removed from the oil bath and
cooled to room temperature. The cap was removed, and the solution
was transferred to a separatory funnel. The tube was rinsed with
30 mL of OEt2 and 30 mL of H2O, which were then added to the
separatory funnel. The aqueous layer was extracted with OEt2 (3
× 50 mL); the combined organic layers were collected and dried
over MgSO4. The solution was then filtered and concentrated in
vacuo. Purification of the crude product was accomplished by
column chromatography on silica gel using an eluting solution of
hexanes: ethyl acetate (9:1). Removal of volatiles yielded the
product as a white solid (1.44 g, 54%). Mp: 145 °C. 1H NMR (500
Synthesis of 2,9-Bis[3,5-bis(trifluoromethyl)phenyl]-5,5-dim-
ethyldipyrrolylmethane (H2dmpm3,5-CF ).
3
A single-necked 14/20 25 mL round-bottom flask was charged with
2-[3,5-bis(trifluoromethyl)phenyl]-1H-pyrrole (0.4 g, 1.4 mmol) and
acetone (2.08 g, 36 mmol). The flask then was sealed with a septum.
The solution was stirred at room temperature while it was degassed
under a flow of argon. After 15 min, trifluoroacetic acid (0.4 g,
3.6 mmol) was added via syringe. The solution was stirred for 3 h
under an argon atmosphere. The reaction mixture was quenched
with ∼15 mL of a 0.1 M NaOH solution. The resulting mixture
was transferred to a separatory funnel, where the aqueous layer
was extracted with Et2O (2 × 15 mL). The combined organic layers
(31) Bradley, D. C.; Thomas, I. M. J. Chem. Soc. 1960, 3859.
(32) Balboni, D.; Camuratti, G. P.; Resconi, L. Inorg. Chem. 2001, 40,
6588.

6132 Organometallics, Vol. 25, No. 26, 2006
Swartz and Odom
were dried over MgSO4 and filtered. The solvent was removed in
vacuo to give a purple oil. The oil was then tritrated with pentane
to yield a pink solid (0.311 g, 72%). Mp: 130 °C. H NMR (500
(distorted q, Ci), 119.55 (q, JCF ) 3.7 Hz, Cl), 110.22 (Ce or Cf),
109.53 (Ce or Cf), 45.88 (Cm), 39.67 (Cb)29.33 (Cc). Anal. (Found)
calcd: C, (50.45) 50.84; H, (3.75) 3.85; N, (7.48) 7.65.
Synthesis of Ti(NMe2)2(dmpmmes) (4).
1
MHz, CDCl3): δ 8.11 (br s, 2 H, Ha), 7.73 (s, 4 H, Hi), 7.6 (s, 2
H, Hl), 6.6 (m, JHH ) 2.32 Hz, 2 H, He or Hf), 6.2 (m, JHH ) 3.23
Hz, 2H, He or Hf), 1.76 (s, 6 H, Hd). 13C NMR (500 MHz, CDCl3):
δ 141.64 (Ch or Cg), 134.4 (Ch or Cg), 132.18 (q, JCF ) 31.94 Hz,
Cj), 129.03 (Cb), 123.28 (q, JCF ) 272 Hz, Ck), 123.15 (q, JCF
)
2.54 Hz, Ci), 119.1 (q, JCF ) 3.91 Hz, Cl), 108.64 (Ce or Cf), 107.09
(Ce or Cf), 35.83 (Cc), 29.09 (Cd). Anal. (Found) calcd: C, (54.63)
54.19; H, (3.14) 3.03; N, (4.52) 4.68.
Synthesis of 2,9-Bis(2,4,6-trimethylphenyl)-5,5-dimethyldipyr-
rolylmethane (H2dmpmmes).
Under an atmosphere of dry nitrogen, a threaded pressure tube was
loaded with Ti(NMe2)4 (2; 0.316 g, 1.4 mmol), H2dmpmmes (0.578
g, 1.4 mmol), and ∼8 mL of Et2O. The pressure tube was sealed
with a Teflon screw cap, taken out of the dry box, and put in a 50
°C oil bath, where it was left to react for 18 h. The pressure tube
was then removed from the oil bath and taken back into an
atmosphere of dry nitrogen, where the volatiles were removed in
vacuo to yield an orange oily solid. Crystallization from pentane
yielded an orange solid (0.225 g, 30%). Mp: 155 °C dec. 1H NMR
(500 MHz, CDCl3): δ 6.80 (s, 4 H, Hk), 6.37 (d, JHH ) 2.80 Hz,
2 H, Hf or He), 6.28 (d, JHH ) 2.77 Hz, 2H, Hf or He), 2.59 (s, 12
A single-necked 14/20 25 mL round-bottom flask was charged with
2-(2,4,6-trimethylphenyl)-1H-pyrrole (0.25 g, 1.3 mmol) and
acetone (1.96 g, 33 mmol) and then sealed with a septum. The
solution was stirred at room temperature while being degassed under
a flow of argon. After 15 min, trifluoroacetic acid (0.384 g, 3.3
mmol) was added via syringe. The solution was stirred for 1 h.
The reaction mixture was quenched with ∼15 mL of a 0.1 M NaOH
solution. The resulting mixture was transferred to a separatory
funnel, where the aqueous layer was extracted with Et2O (2 × 15
mL). The combined organic layers were dried over MgSO4 and
filtered. The solvent was removed in vacuo to give an orange oil.
The oil was then tritrated with pentane to yield an orange solid
(0.187 g, 68%). Mp: 115 °C. 1H NMR (500 MHz, CDCl3): δ 7.57
(br s, 2 H, Ha), 6.89 (s, 4 H, Hk), 5.88 (t, JHH ) 2.87 Hz, 2H, He
or Hf), 5.8 (t, JHH ) 5.86 Hz, 2 H, He or Hf), 2.2 (s, 6 H, Hm), 2.0
(s, 12 H, Hj), 1.6 (s, 6 H, Hd). 13C NMR (500 MHz, CDCl3): δ
138.54 (Cl, Ci, or Ch), 138.31 (Cl, Ci, or Ch), 137.38 (Cl, Ci, or Ch),
130.83 (Cb or Cg), 128.76, 127.98 (Ck), 107.5 (Ce or Cf), 103.4(Ce
or Cf), 35.30 (Cc), 28.95 (Cd), 20.99 (Cm), 20.52 (Cj). Anal. (Found)
calcd for C29H34N2: C, (84.85) 84.83; H, (8.37) 8.35; N, (6.78)
6.82.
H, Hn), 2.23 (s, 6 H, Hm), 2.18 (s, 12 H, Hj), 1.94 (s, 6H, Hc). 13
C
NMR (500 MHz, CDCl3) 159.15 (Ch), 138.38 (Ci or Cl), 138.26
(Ci or Cl), 136.27 (Cd or Cg), 132.54 (Cg or Cd), 128.52 (Ck), 113.70
(Ce or Cf), 107.01 (Ce or Cf), 47.45 (Cn), 39.26 (Cb), 30.15 (Cm),
21.67 (Cj), 20.92 (Cc). After many attempts at elemental analysis,
1
satisfactory results were not obtained. H and 13C NMR spectra
are included in the Supporting Information to demonstrate purity.
Synthesis of Ti(NMe2)2(pyrr3,5-CF )2 (5).
3
Under an atmosphere of dry nitrogen, a 20 mL scintillation vial
Synthesis of Ti(NMe2)2(dmpm3,5-CF ) (3).
3
was loaded with Ti(NMe2)4 (2; 0.150 g, 0.669 mmol) in ∼3 mL of
OEt2. A separate vial was loaded with Hpyrr3,5-CF (0.372 g, 1.33
3
mmol) in ∼5 mL of OEt2. The substituted arylpyrrole was then
added to the vial containing 2 at room temperature. The solution
was stirred at room temperature for 6 h. Volatiles were removed
in vacuo to yield a red oil. Crystallization from pentane yielded
the bis(pyrrolyl) species as an orange solid (0.175 g, 38%). Mp:
86 °C dec. 1H NMR (500 MHz, CDCl3): δ 7.74 (s, 4 H, Hf), 7.61
(s, 2 H, Hi), 6.89 (m, 2 H, Ha, Hb, or Hc), 6.48 (m, 2 H, Ha, Hb, or
Hc), 6.25 (m, 2 H, Ha, Hb, or Hc), 3.0 (s, 12 H, Hj). 13C NMR (500
MHz, CDCl3): δ 138.88 (Ce), 137.70 (Cd), 131.62 (q, JCF ) 33
Hz, Cg), 126.63 (Ca, Cb, or Cc), 125.96 (Cf), 123.35 (JCF ) 273
Hz, Ch), 119.1 (Ci), 111.86 (Ca, Cb, or Cc), 111.20 (Ca, Cb, or Cc),
44.53 (Cj). Anal. (Found) calcd for C28H24F12N4Ti: C, (48.48)
48.57; H, (3.53) 3.49; N, (7.78) 8.09.
Under an atmosphere of dry nitrogen a vial was loaded with Ti-
(NMe2)4 (2; 0.131 g, 0.584 mmol) in ∼3 mL of Et2O. In a 20 mL
scintillation vial was loaded 2,9-bis[3,5-bis(trifluoromethyl)phenyl]-
5,5-dimethyldipyrrolylmethane (0.350 g, 0.584 mmol) in ∼3 mL
of OEt2. The solutions were put into a cold well, where they sat
Synthesis of Ti(NMe2)2(pyrrmes)2 (6).
until nearly frozen. To a thawing solution of H2dmpm3,5-CF was
3
added the cold solution of 2. The solution was stirred at room
temperature for 4 h. Volatiles were removed in vacuo to yield an
orange solid (0.395 g, 92%). Mp: 150 °C dec. 1H NMR (300 MHz,
CDCl3): δ 7.96 (s, 4 H, Hi), 7.63 (s, 2 H, Hl), 6.55 (d, JHH ) 3.19
Hz, 2 H), 6.44 (d, JHH ) 3.18 Hz, 2 H), 2.6 (s, 12 H, Hm), 1.8 (s,
6 H, Hc). 13C NMR (500 MHz, CDCl3): δ 162.84 (Ch), 138.18 (Ca
or Cg), 138.04 (Ca or Cg), 131.17 (q, JCF ) 33.6 Hz, Cj), 126.26
Under an atmosphere of dry nitrogen a threaded pressure tube was
loaded with Ti(NMe2)4 (0.075 g, 0.334 mmol), Hpyrrmes (0.124 g,

Dipyrrolylmethane and Bis(2-arylpyrrolyl) Ti Complexes
Organometallics, Vol. 25, No. 26, 2006 6133
Table 3. Structural Parameters for Ti(NMe2)2(dmpm3,5-CF
)
3
0.667 mmol), and ∼5 mL of Et2O. The pressure tube was then
sealed with a Teflon screw cap and wrapped with Teflon tape. The
pressure tube was then taken out of the drybox and put into a 60
°C oil bath for 40 h. The pressure tube was taken back into an
atmosphere of dry nitrogen, and the volatiles were removed in vacuo
to yield a yellow solid. The compound was purified by recrystal-
(3), Ti(NMe2)2(dmpmmes) (4), Ti(NMe2)2(pyrr3,5-CF )2 (5), and
Ti(NMe2)2(pyrrmes)2 (6)
3
3
4
5
6
formula
C31H28F12- C33H44N4- C28H24F12- C30H40N4-
N4Ti
732.47
P1h
Ti
544.62
P21/n
8.840(4)
30.94(1)
11.113(5)
N4Ti
692.41
P21/c
19.534(3)
8.104(1)
19.178(3)
Ti
504.56
P1h
1
lization from pentane (0.125 g, 74%). Mp: 160 °C dec. H NMR
formula wt
space group
a (Å)
b (Å)
c (Å)
(500 MHz, CDCl3): δ 6.83 (s, 4 H, Hh), 6.81 (q, JHH ) 1.57 Hz,
2 H, Hb), 6.19 (t, J ) 2.76, Hz, 2 H, Ha or Hc), 5.91 (t, JHH ) 1.61
Hz, 2 H, Ha or Hc), 2.77 (s, 12 H, Hk), 2.28 (s, 6H, Hj), 2.1 (s, 12
H, Hg). 13C NMR (500 MHz, CDCl3): δ 139.2 (Cf), 137.54 (Ci,
Ce, or Cd), 136.85 (Ci, Ce, or Cd), 134.65 (Ci, Ce, or Cd), 127.6
(Ch), 123.09 (Cb), 108.6 (Ca or Cc), 108.3 (Ca or Cc), 44.14 (Ck),
21.04 (Cj), 20.36 (Cg). Anal. (Found) calcd: C, (70.98) 71.42; H,
(8.01) 7.99; N, (10.97) 11.10.
12.60(1)
12.63(1)
12.79(1)
78.12(1)
64.44(1)
62.66(1)
1631(2)
2
0.359
1.491
10 574
4699
7.745(1)
12.215(2)
16.177(2)
74.266(3)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
98.779(8)
105.277(3) 82.985(3)
72.952(3)
3004(2)
4
0.312
1.204
25 589
4349
2928.5(7)
4
0.395
1.570
24 219
4215
1406.8(3)
2
µ (mm-1
)
0.328
1.291
12 039
4051
Synthesis of Ti(NMe2)2(pyrr4-CF )2 (7).
3
D
calcd (g cm-3
)
total no. of rflns
no. of unique
rflns (Rint
extinction coeff
)
(0.06)
0.006(2)
0.0634
(0.31)
0.029(4)
0.0809
0.1948
(0.112)
0.0025(6)
0.0512
0.1328
(0.0651)
0.003(2)
0.0632
0.1690
R(Fo) (I > 2σ)
2
Rw(Fo ) (I > 2σ) 0.1648
General Considerations for X-ray Diffraction. Crystals grown
from concentrated solutions at -35 °C were quickly moved from
a scintillation vial to a microscope slide containing Paratone N.
Samples were selected and mounted on a glass fiber in wax and
Paratone. The data collections were carried out at a sample
temperature of 173 K on a Bruker AXS platform three-circle
goniometer with a CCD detector. The data were processed and
reduced utilizing the program SAINTPLUS supplied by Bruker
AXS. The structures were solved by direct methods (SHELXTL
v5.1, Bruker AXS) in conjunction with standard difference Fourier
techniques. Structural parameters for 3-6 are given in Table 3.
Under an atmosphere of dry nitrogen, a 20 mL scintillation vial
was loaded with Hpyrr4-CF (0.115 g, 0.544 mmol), Ti(NMe2)4 (2;
3
0.061 g, 0.272 mmol), OEt2 (3 mL), and a stir bar. The vial was
then capped and the mixture stirred for 36 h at room temperature.
The volatiles were removed in vacuo to yield an orange oil.
Crystallization from pentane yielded an orange solid (0.069 g, 45%).
1
Mp: 72 °C. H NMR (500 MHz, CDCl3): δ 7.47 (d, JHH ) 7.88
Hz, 4 H, Hg), 7.45 (d, JHH ) 7.89 Hz, 4 H, Hf), 7.00 (m, 2 H, Hc),
6.36 (m, 2 H, Ha or Hb), 6.27 (t, JHH ) 2.67 2 H, Ha or Hb), 3.16
(s, 12 H, Hj). 13C NMR (500 MHz, CDCl3): 140.43 (Ce), 139.50
(Cd), 127.64 (q, JCF ) 33 Hz, Ch), 126.56 (Cf), 126.51 (Cc), 125.12
(q, JCF ) 11.78 Hz, Cg), 124.31 (q, JCF ) 272 Hz, Ci), 111.07 (Ca
or Cb), 109.86 (Ca or Cb), 44.68 (Cj). Anal. (Found) calcd: C,
(55.83) 56.13; H, (5.11) 4.71; N, (10.29) 10.07.
General Procedure for Kinetics. All manipulations were done
in an inert atmosphere drybox. In a 2 mL volumetric flask was
loaded the catalyst (10 mol %, 0.1 mmol), aniline (0.931 g, 911
µL, 10 mmol), 1-phenylpropyne (0.116 g, 125 µL, 1 mmol), and
ferrocene (0.056 g, 0.3 mmol) as an internal standard. The solution
was then diluted to 2 mL with deuterated toluene. An ample amount
of solution (∼0.75 mL) was put into a threaded J. Young tube that
was sealed with a cap and then wrapped with Teflon tape. The
tube was then removed from the drybox and heated at 75 or 100
°C in the NMR spectrometer. The relative 1-phenylpropyne versus
ferrocene concentration was monitored as a function of time. The
fits are to the exponential decay of the starting material using the
scientific graphing programs Origin or KaleidaGraph. The exact
Synthesis of Ti(NMe2)2(pyrrtol)2 (8).
Under an atmosphere of dry nitrogen a threaded pressure tube was
loaded with Hpyrrtol (0.115 g, 0.732 mmol), Ti(NMe2)4 (2; 0.082
g, 0.366 mmol), OEt2 (3 mL), and a stirbar. The pressure tube was
then sealed with a Teflon screw cap and wrapped with Teflon tape.
The tube was removed from the drybox and placed in a 60 °C oil
bath, where the mixture was left to react for 24 h. After the reaction
was complete, the tube was taken back into an atmosphere of dry
nitrogen. The reaction mixture was transferred to a 20 mL
scintillation vial, where the volatiles were concentrated in vacuo
to yield an orange oil. Crystallization from pentane yielded an
obst
expression used to fit the data was Yt ) Y∞ + (Y0 - Y∞)exp-k
where Y ) [1-phenylpropyne] at time ) t (Yt), infinity (Y∞), or
initial (Y0).33 The variables Y∞, Y0, and kobs were optimized in the
fits. For a representative fit see Figure 4.
Acknowledgment. We greatly appreciate the financial
support of the National Science Foundation (Grant No. 0350762),
the donors of the Petroleum Research Fund, administered by
the American Chemical Society (Grant No. 45401-AC3), the
Department of Energy-Defense Programs (Grant No. PO 27856-
001-01), and Michigan State University. A.L.O. is an Alfred P.
Sloan Fellow.
1
orange solid (0.060 g, 37%). Mp: 71 °C. H NMR (500 MHz,
CDCl3): δ 7.18 (d, JHH ) 7.68 Hz, 4 H, Hh or Hg), 7.04 (d, JHH
)
7.77, 4 H, Hh or Hg), 6.90 (m, 2 H, Hd), 6.27 (m, 2 H, (Hc or Hb),
6.18 (m, 2 H, Hc or Hb), 2.99 (s, 12 H, Ha), 2.29 (s, 6 H, Hj). 13C
NMR: δ 141.11 (Ci), 135.53 (Cf), 134.57 (Ce), 128.82 (Ch or Cg),
126.97 (Ch or Cg), 125.67 (Cd), 110.05 (Cb or Cc), 107.68 (Cb or
Cc), 44.68 (Ca), 21.10 (Cj). Anal. (Found) calcd: C, (69.53) 69.94;
H, (7.60) 7.19; N, (12.17) 12.49.
Supporting Information Available: Tables and full labeling
schemes for 3-6 from X-ray diffraction studies, CIF files giving
X-ray data for 3-6, and figures giving NMR spectra for 4. This
materialisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
(33) Espenson, J. H. Chemical Kinetics and Reaction Mechanisms;
McGraw-Hill: New York, 1995.
OM0607088