Scandium, yttrium, and lanthanum benzyl and alkynyl complexes with the N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-6-amido ligand: Synthesis, characterization, and Z-selective catalytic linear dimerization of phenylacetylenes

Article abstract of DOI:10.1021/om8004228

1,4,6-Trimethyl-N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-6-amine (HL) reacts with M(CH₂Ph)₃(THF)₃ to give the dibenzyl complexes (L)M(CH₂Ph)₂ (M = Sc, 1; M = Y, 2; M = La, 3). Compounds 1,2, and 3 can

Full text of DOI:10.1021/om8004228

Organometallics 2009, 28, 719–726
719
Scandium, Yttrium, and Lanthanum Benzyl and Alkynyl Complexes
with the N-(2-Pyrrolidin-1-ylethyl)-1,4-diazepan-6-amido Ligand:
Synthesis, Characterization, and Z-Selective Catalytic Linear
Dimerization of Phenylacetylenes
Shaozhong Ge, Auke Meetsma, and Bart Hessen*
Center for Catalytic Olefin Polymerization, Stratingh Institute for Chemistry, UniVersity of Groningen,
Nijenborgh 4, 9747 AG, Groningen, The Netherlands
ReceiVed May 9, 2008
1,4,6-Trimethyl-N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-6-amine (HL) reacts with M(CH2Ph)3(THF)3
to give the dibenzyl complexes (L)M(CH2Ph)2 (M ) Sc, 1; M ) Y, 2; M ) La, 3). Compounds 1, 2, and
3 can be converted to their corresponding cationic monobenzyl species [(L)M(CH2Ph)]+ (M ) Sc, Y
and La) by reaction with [PhNMe2H][B(C6F5)4]. Reaction of (L)Sc(CH2Ph)2 with 2 equiv of pheny-
lacetylene affords the monomeric dialkynyl complex (L)Sc(Ct CPh)2 (4), while reactions of (L)M(CH2Ph)2
(M ) Y and La) give the dimeric dialkynyl complexes [(L)M(Ct CPh)(µ-Ct CPh)]2 (M ) Y, 5; M )
La, 6). The neutral complexes (2, 3, 5, and 6) and the cationic monobenzyl species [(L)M(CH2Ph)]+ (M
) Y and La) are catalysts for the Z-selective linear head-to-head dimerization of phenylacetylenes. The
cationic yttrium and the neutral lanthanum systems are the most effective catalysts in the series. The
related scandium species show poor activity and selectivity.
parameter for the trivalent rare earth metals3), ancillary ligands,
and usage of neutral versus cationic species.4,5 For the catalytic
dimerization of alkynes, however, as yet, little is known about
the influence of these parameters.
Recently, we reported a highly efficient and regioselective
cationic yttrium-based catalyst for Z-selective linear dimerization
of terminal alkynes, employing the N-(2-pyrrolidin-1-ylethyl)-
1,4-diazepan-6-amido (L).2a Here we describe the synthesis and
characterization of neutral dibenzyl, dialkynyl, and cationic
monobenzyl scandium, yttrium, and lanthanum complexes
supported by this ligand and a comparative study of their
performance in the catalytic dimerization of phenylacetylenes.
Introduction
The catalytic dimerization of terminal alkynes is a straight-
forward and atom-economical method to synthesize conjugated
enyne motifs, which are important building blocks for organic
synthesis and key units found in a variety of biologically active
compounds and synthetic conjugated polymers for optoelectronic
applications.1 Organo rare earth metal compounds have been
reported to catalyze this transformation effectively with high
selectivity.2 For olefin polymerization and hydroamination/
cyclization catalysis by organo rare earth compounds, it has been
demonstrated that the performance of this family of catalysts is
strongly influenced by the ionic radius (a uniquely tunable
Results and Discussion
Synthesis and Characterization of Dibenzyl Complexes
(L)M(CH2Ph)2 (M ) Sc, 1; M ) Y, 2; M ) La, 3). The rare
earth metal tribenzyl compounds M(CH2Ph)3(THF)3 have re-
cently emerged as convenient organo rare earth metal starting
materials, which are readily accessible from the reaction of rare
* Corresponding author. E-mail: B.Hessen@rug.nl.
(1) (a) Katayama, H.; Nakayama, M.; Nakano, T.; Wada, C.; Akamatsu,
K.; Ozawa, F. Macromelecules 2004, 37, 13. (b) Takayama, Y.; Delas, C.;
Muraoka, K.; Uemura, M.; Sato, F. J. Am. Chem. Soc. 2003, 125, 14163.
(c) Takayama, Y.; Delas, C.; Muraoka, K.; Sato, F. Org. Lett. 2003, 5,
365. (d) Tykwinski, R. R.; Zhao, Y. Synlett 2002, 1939. (e) Brønsted
Nielsen, M.; Schreiber, M.; Baek, Y. G.; Seiler, P.; Lecomte, S.; Bouden,
C.; Tykwinski, R. R.; Gisselbrecht, J.-P.; Gramlich, V.; Skinner, P. J.;
Bosshard, C.; Gu¨nter, P.; Gross, M.; Diederich, F. Chem.-Eur. J. 2001, 7,
3263. (f) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int.
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W. Science 1992, 256, 1172. (i) Trost, B. M. Science 1991, 254, 1471.
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2007, 26, 6508. (b) Liu, Y.; Nishuira, M.; Wang, Y.; Hou, Z. J. Am. Chem.
Soc. 2006, 128, 5592. (c) Komeyama, K.; Kawabata, T.; Takehira, K.;
Takaki, K. J. Org. Chem. 2005, 70, 7260. (d) Tazelaar, C. G. J.; Bambirra,
S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H. Organometallics
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Miyamoto, T. J. Am. Chem. Soc. 2003, 125, 1184. (f) Wang, J. Q.; Dash,
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117, 6364. (h) Duchateau, R.; van Wee, C. T.; Meetsma, A.; Teuben, J. H.
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2008, 130, 4984. (b) Bambirra, S.; van Leusen, D.; Tazelaar, C. G. J.;
Meetsma, A.; Hessen, B. Organometallics 2007, 26, 1014. (c) Zeimentz,
P. M.; Arndt, S.; Elvidge, B. R.; Okuda, J. Chem. ReV. 2006, 106, 2404.
(d) Arndt, S.; Okuda, J. AdV. Synth. Catal. 2005, 347, 339. (e) Bambirra,
S.; Bounkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004,
126, 9182. (f) Lawrence, S. C.; Ward, B. D.; Dubberley, S. R.; Kozak,
C. M.; Mountford, P. Chem. Commun. 2003, 2880. (g) Arndt, S.; Spaniol,
T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003, 42, 5075.
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Organometallics 2008, 27, 1242. (b) Yuen, H. F.; Marks, T. J. Organo-
metallics 2008, 27, 155. (c) Bambirra, S.; Tsurugi, H.; van Leusen, D.;
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10.1021/om8004228 CCC: $40.75
2009 American Chemical Society
Publication on Web 01/15/2009

720 Organometallics, Vol. 28, No. 3, 2009
Scheme 1. Synthesis of Compounds 1-3
Ge et al.
earth metal trihalides MX3(THF)n with benzyl potassium.6
M(CH2Ph)3(THF)3 reacts with 1,4,6-trimethyl-N-(2-pyrrolidin-
1-ylethyl)-1,4-diazepan-6-amine (HL)2a in toluene or THF to
afford the dibenzyl complex (L)M(CH2Ph)2 (M ) Sc, 1; M )
Y, 2; M ) La, 3) as yellow crystals after crystallization from
a toluene/pentane mixture (isolated yield: 77% for 1; 80% for
2; 68% for 3) (Scheme 1). When performed in C6D6 or THF-
d8, these reactions are seen by NMR spectroscopy to be
quantitative. Compounds 1, 2, and 3 are highly air and moisture
sensitive, but thermally robust and can be stored in the solid
state or solution at ambient temperature without decomposition
for a few months. The related yttrium dialkyl complex
(L)Y(CH2SiMe3)22a in benzene solution gradually decomposes
with release of TMS at ambient temperature. In C6D6 solution,
the pendant pyrrolidinyl groups in these complexes are coor-
dinated to the metal centers, as both its R- and ꢀ-H resonances
are diastereotopic at ambient temperature. The benzyl methylene
Figure 1. Molecular structure of (L)Sc(CH2Ph)2 (1). Hydrogen
atoms are omitted for clarity, and thermal ellipsoids are drawn at
the 50% probability level. Selected bond lengths (Å) and angles
(deg): Sc(1)-N(11) ) 2.382(2), Sc(1)-N(12) ) 2.585(2),
Sc(1)-N(13) ) 2.063(2), Sc(1)-N(14) ) 2.362(2), Sc(1)-C(115)
) 2.329(3), Sc(1)-C(122) ) 2.368(3), N(11)-Sc(1)-N(12) )
66.93(7), N(11)-Sc(1)-N(13) ) 77.21(8), N(11)-Sc(1)-N(14)
) 153.31(7), N(12)-Sc(1)-N(13) ) 75.33(7), N(12)-Sc(1)-C(115)
) 155.18(8), N(13)-Sc(1)-N(14) ) 76.16(8), N(13)-Sc(1)-C(122)
)154.19(9),N(14)-Sc(1)-C(115))100.05(8),N(14)-Sc(1)-C(122)
)91.20(8),Sc(1)-C(115)-C(116))116.88(18),Sc(1)-C(122)-C(123)
) 112.76(17).
1
protons in 1, 2, and 3 are diastereotopic, with H resonances
(in benzene-d6 at 25 °C) at δ 2.24 and 2.11 ppm (JHH ) 8.4
Hz) for 1, δ 2.22 and 1.96 ppm (JHH ) 7.1 Hz and JYH ) 2.7
Hz) for 2, and δ 2.34 and 2.11 ppm (JHH not resolved due to
fluxionality in benzene-d6 at 25 °C; JHH ) 7.5 Hz in toluene-d8
at -30 °C) for 3. The corresponding 13C resonances (solvent:
benzene-d6) are found at δ 52.3 (JCH ) 114.8 Hz) for 1, δ 51.4
ppm (JCH ) 120.7 Hz and JYC ) 28.2 Hz) for 2, and δ 62.6
ppm (JCH ) 134.0 Hz) for 3.
Complexes 1, 2, and 3 were characterized by single-crystal
X-ray diffraction, and their molecular structures are shown in
Figure 1, 2, and 3, respectively, together with selected bond
lengths and bond angles. All three complexes crystallize in space
j
group P1, and the crystals contain two independent molecules
in the asymmetric unit cell, which do not differ significantly;
for each compound, only one of them is explicitly discussed
here. The scandium compound 1 contains two η1-bound benzyl
groups per molecule, with Sc(1)-C(115)-C(116) ) 116.88(18)°
versus Sc(1)-C(122)-C(123) ) 112.76(17)°. Each molecule
of the yttrium compound 2 contains one η1- and one η2-bound
benzyl group per molecule, with Y(1)-C(115)-C(116) )
109.67(18)° versus Y(1)-C(122)-C(123) ) 96.60(16)°. In the
lanthanum compound 3, both benzyl groups are η2-bound with
La1-C115-C116 ) 89.4(2)° and La1-C122-C123 ) 93.8(2)°.
The η2-bonding mode of the benzyl group might account for
the aforementioned enhanced thermal stability of 2 versus its
trimethylsilylmethyl analogue. In all compounds 1-3, the
azepine moiety of the ligands is facially coordinated, with the
shortest M-N distances to the amide nitrogen N13. The other
Figure 2. Molecular structure of (L)Y(CH2Ph)2 (2). Hydrogen
atoms are omitted for clarity, and thermal ellipsoids are drawn at
the 50% probability level. Selected bond lengths (Å) and angles
(deg): Y(1)-N(11) ) 2.524(2), Y(1)-N(12) ) 2.659(2), Y(1)-N(13)
) 2.217(2), Y(1)-N(14) ) 2.512(2), Y(1)-C(115) ) 2.491(3),
Y(1)-C(122))2.544(3),Y(1)-C(123))3.071(3),N(11)-Y(1)-N(12)
) 63.81(6), N(11)-Y(1)-N(13) ) 73.38(7), N(11)-Y(1)-N(14)
) 145.31(6), N(12)-Y(1)-N(13) ) 72.10(7), N(12)-Y(1)-C(115)
) 152.35(8), N(13)-Y(1)-N(14) ) 72.07(7), N(13)-Y(1)-C(122)
)149.54(8),N(14)-Y(1)-C(115))102.51(8),N(14)-Y(1)-C(122)
)89.85(8),Y(1)-C(115)-C(116))109.67(18),Y(1)-C(122)-C(123)
) 96.60(16).
(6) Sc, Lu: (a) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A.;
Hessen, B.; Saliu, K.; Takats, J. Organometallics 2008, 27, 1501. Sc: (b)
Carver, C. T.; Montreal, M. J.; Diaconescu, P. L. Organometallics 2008,
27, 363. La: (c) Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics
2006, 25, 3454. The Y tribenzyl derivative is readily accessible via the
same procedure. A full report on the structure and properties of this
compound is in preparation.
two amine nitrogen atoms of the azepine moiety bind to the
metal center unequally, with the differences of 0.197, 0.135,
and 0.178 Å between the two M-N(amine) distances for 1, 2,

Z-SelectiVe Catalytic Linear Dimerization of Phenylacetylenes
Organometallics, Vol. 28, No. 3, 2009 721
Scheme 2. Synthesis of Dialkynyl Complexes 4-6
(52.3 ppm for 1, 51.4 ppm for 2, and 62.6 ppm for 3), associated
with the conversion to cationic species.8
Stoichiometric Reactions of Compounds 1-3 with Phe-
nylacetylene. Upon reaction with 2 equiv of phenylacety-
lene, the dibenzyl complex 1 is converted to the mononuclear
dialkynyl scandium compound (L)Sc(Ct CPh)2 (4) and the
dibenzyl complexes 2 and 3 to the dinuclear dialkynyl com-
pounds [(L)M(C-CPh)(µ-C-CPh)]2 (M ) Y, 5; M ) La, 6).
They were obtained as colorless crystalline material after crys-
tallization from a toluene/hexane mixture (isolated yield: 4, 73%;
5, 70%; 6, 66%) (Scheme 2). The 13C resonances of M-C(t C-
Ph) are found at δ 142.1 ppm for 4, 148.4 ppm for 5, and 162.1
ppm for 6. Room-temperature NMR spectra of 5 and 6 in
toluene-d8 indicate a Cs symmetrically averaged structure, and
lowering the temperature to -50 °C results in a decoalescene
of the o-Ph 1H NMR resonance for both 5 and 6, indicating the
presence of bridging and terminal alkynyl groups.
Compounds 4-6 were characterized by single-crystal X-ray
diffraction, and the structures of 4 and 5 are shown in Figures
4 and 5, respectively (see Supporting Information for the
structure of 6), together with selected bond distances and
bond angles. The structure determination of 4 at 100 K was
complicated by the occurrence of a low-temperature phase
transition, causing splitting of the diffraction peaks. To avoid
this problem, data collection was carried out at 222 K, resulting
in successful structural characterization. Compound 4 features
a distorted octahedral metal center, and the coordination sphere
is composed of four nitrogens of the ligand L and two termi-
nal alkynyl groups with Sc-C(15)-C(16) ) 172.4(3)° and
Sc-C(23)-C(24) ) 172.3(3)°. Compounds 5 and 6 are isos-
tructural, and only the structure of 5 is explicitly discussed here.
Compound 5 is a centrosymmetric dimer with two alkynyl
groups bridging the two yttrium centers. The core of the structure
is a four-membered ring Y-C(23)-Y(_a)-C(23_a), which is
essentially planar (the torsion angle Y-C(23)-Y(_a)-C(23_a)
is 0.00(12)°). The azepine-amine and terminal alkynyl ligands
in 5 adopt a trans-arrangement around the core. A cis-ar-
rangement has been reported for a closely related dialkynyl
complex, {[Me2TACN(CH2)2NtBu]La(Ct CPh)(µ-Ct CPh)}2.2d
The bridging alkynyl groups are asymmetrically bound to
the two yttrium centers, with Y-C(23) ) 2.530(5) Å and
Figure 3. Molecular structure of (L)La(CH2Ph)2 (3). Hydrogen
atoms are omitted for clarity, and thermal ellipsoids are drawn at
the 50% probability level. Selected bond lengths (Å) and angles
(deg): La(1)-N(11) ) 2.861(3), La(1)-N(12) ) 2.683(3),
La(1)-N(13) ) 2.352(3), La(1)-N(14) ) 2.653(3), La(1)-C(115)
) 2.735(4), La(1)-C(116) ) 3.074(4), La(1)-C(122) ) 2.654(4),
La(1)-C(123) ) 3.097(4), N(11)-La(1)-N(12) ) 60.38(9),
N(11)-La(1)-N(13) ) 67.42(10), N(11)-La(1)-N(14) ) 96.98(9),
N(12)-La(1)-N(13) ) 69.99(10), N(12)-La(1)-C(115) )
122.58(10), N(13)-La(1)-N(14) ) 68.69(10), N(13)-La(1)-C(122)
)102.57(11),N(14)-La(1)-C(115))87.66(10),N(14)-La(1)-C(122)
)112.37(12),La(1)-C(115)-C(116))89.4(2),La(1)-C(122)-C(123)
) 93.8(2).
and 3, respectively. The longer M-N(amine) bonds are located
approximately trans to one of the benzyl groups, as seen by
the angles N(12)-Sc(1)-C(116) ) 176.26°, N(12)-Y(1)-C(116)
) 175.18°, and N(11)-La(1)-C(123) ) 169.65°. Similar
asymmetries were observed previously in triazacyclononane-
amide rare earth metal dialkyls.7
Generation of Cationic Species [(L)M(CH2Ph)]+. Upon
reaction with 1 equiv of [PhNMe2H][B(C6F5)4] in the weakly
coordinating polar solvent C6D5Br, the dibenzyl compounds 1-3
are cleanly converted to the corresponding cationic monobenzyl
species [(L)M(CH2Ph)]+ (as seen by NMR spectroscopy) with
liberation of toluene and free PhNMe2. The cationic monobenzyl
scandium and yttrium species are sufficiently stable to allow
characterization by both 1H and 13C NMR spectroscopy at
ambient temperature. This is in contrast to the related yttrium
dialkyl compound (L)Y(CH2SiMe3)2,2a of which the corre-
sponding cationic monoalkyl compound is insufficiently stable
for characterization in the absence of a coordinating solvent
like THF. The cationic monobenzyl lanthanum species in
C6D5Br decomposes within an hour at ambient temperature and
precipitates as a brown oily material; after decomposition, only
toluene and PhNMe2 could be detected in solution by 1H NMR
spectrometry. The 13C NMR resonances of the M-CH2 groups
are found at δ 54.8 ppm for [(L)Sc(CH2Ph)]+, δ 53.7 ppm for
[(L)Y(CH2Ph)]+, and δ 63.1 ppm for [(L)La(CH2Ph)]+, showing
a typical downfield shift, relative to their dibenzyl precursors
(8) (a) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2001, 637. (b) Bambirra, S.; van Leusen, D.;
Meetsma, A.; Hessen, B.; Teuben, J. H. Chem. Commun. 2003, 522. (c)
Ge, S.; Bambirra, S.; Meetsma, A.; Hessen, B. Chem. Commun. 2006, 3320.
(d) Ge, S.; Meetsma, A.; Hessen, B. Organometallics 2007, 26, 5278.
(7) Bambirra, S.; Boot, S. J.; van, D.; Meetsma, A.; Hessen, B.
Organometallics 2004, 23, 1891.

722 Organometallics, Vol. 28, No. 3, 2009
Ge et al.
Figure 4. Molecular structure of (L)Sc(Ct CPh)2 (4). All hydrogen
atoms are omitted for clarity, and thermal ellipsoids are drawn at
the 30% probability level. Selcted bond lengths (Å) and angles
(deg): Sc-N(1) ) 2.485(2), Sc-N(2) ) 2.373(3), Sc-N(3) )
2.045(2), Sc-N(4) ) 2.333(3), Sc-(15) ) 2.262(3), Sc-C(23) )
2.296(4), C(15)-C16) ) 1.208(5), C(23)-C(24) ) 1.214(5),
N(1)-Sc-N(2))68.08(9),N(1)-Sc-N(3))75.16(9),N(1)-Sc-N(4)
) 107.3(1), N(1)-Sc-C(15) ) 159.92(10), N(2)-Sc-N(3) )
78.88(10), N(2)-Sc-N(4) ) 155.52(10), N(3)-Sc-N(4) )
76.74(10), N(3)-Sc-C(23) ) 151.79(11), Sc-C(15)-C(16) )
172.4(3), C(15)-C(16)-C(17) ) 178.7(3), Sc-C(23)-C(24) )
172.3(3), C(23)-C(24)-C(25) ) 176.8(4).
Figure 5. Molecular structure of [(L)Y(Ct CPh)(µ-Ct CPh)]2 (5).
Hydrogen atoms are omitted for clarity, and thermal ellipsoids are
drawn at the 50% probability level. Selected bond lengths (Å) and
angles (deg): Y-N(1) ) 2.680(3), Y-N(2) ) 2.609(4), Y-N(3)
) 2.223(3), Y-N(4) ) 2.609(3), Y-C(15) ) 2.456(4), Y-C(23)
) 2.530(5), Y(_a)-C(23) ) 2.701(4), N(1)-Y-N(2) ) 62.87(9),
N(1)-Y-N(3))71.82(10),N(1)-Y-N(4))127.93(9),N(2)-Y-N(3)
) 90.09(11), N(2)-Y-C(15) ) 146.12(14), N(3)-Y-N(4) )
67.70(11), N(3)-Y-C(23) ) 118.19(13), N(4)-Y-C(15) )
78.51(13), N(4)-Y-C(23) ) 81.41(12), Y-C(15)-C(16) )
172.3(4), Y-C(23)-C(24) ) 133.1(4), C(15)-C(16)-C(17) )
174.8(5), C(23)-C(24)-C(25) ) 179.6(4), C(23)-Y-C(23_a) )
76.16(4).
Y-C(23)-C(24) ) 133.1.(4)° versus Y(_a)-C(23) ) 2.701(4)
Å and Y(_a)-C(23)-C(24) ) 113.1(3)°. The geometry around
the R-carbon (Y-Ct CPh) of the bridging alkynyl group is
slightly distorted from planarity (sum of angles around C(23)
is 350.0°). The binding mode of terminal alkynyl groups deviates
only slightly from linearity with Y-C(15)-C(16) ) 172.3(4)°.
There is no significant difference in CC triple bond lengths
between terminal and bridging alkynyl groups in 5 and 6.
Catalytic Dimerization of Phenylacetylenes. Recently
we have shown that the ionic catalyst (L)Y(CH2SiMe3)2/
[PhNMe2H][B(C6F5)4] can effectively and selectively dimerize
a range of terminal alkynes to (Z)-1,4-disubstituted enynes.2a
In this contribution, dimerization of phenylacetylenes was
studied with the neutral dibenzyl complexes (L)M(CH2Ph)2 (M
) Sc, 1; M ) Y, 2; M ) La, 3), the dialkynyl complexes
[(L)M(Ct CPh)(µ-Ct CPh)]2 (M ) Sc, 4, M ) Y, 5; M ) La,
6), and the ionic species [(L)M(CH2Ph)][B(C6F5)4] (M ) Sc,
Y, La) as precatalysts (Scheme 3). The results are summarized
in Table 1. The neutral scandium compound 1 and its corre-
sponding dialkynyl compound 4 do not show catalytic activity
toward phenylacetylene in C6D6 at 80 °C (entry 1), but traces
of Z-dimer and head-to-tail gem-dimer (2,4-diphenylbut-1-en-
3-yne) are observed when the reaction mixture is heated at
120 °C for 2 h. The neutral yttrium complex 2 and the neutral
lanthanum complex 3 can efficiently dimerize phenylacetylene
(50 equiv) to Z-1,4-diphenylbut-1-en-3-yne in benzene solvent
with full conversion and selectivity. Compound 3, with the larger
metal (La), shows the higher activity of the two (entries 2 and
3). The isolated dimeric diacetylide complexes 5 and 6 dimerize
phenylacetylene at identical rates to their corresponding dibenzyl
precursors 2 and 3, respectively (entries 4 and 5). The steric
hindrance of an ortho-substituent (substrate: 2-ethynyltoluene)
Scheme 3. Catalytic Z-Selective Dimerization of Phenylacetylenes
shuts down the catalysis by the yttrium complex 2 (entry 9),
but for the lanthanum compound 3 it only slows down the
catalysis, which still proceeds to full conversion (entry 10).
The combination of the scandium compound 1 and [PhNMe2H]-
[B(C6F5)4] sluggishly dimerizes phenylacetylene, but two products
(52% Z-dimer and 48% head-to-tail gem-dimer) are observed (entry
6). The ionic yttrium catalyst system 2/[PhNMe2H][B(C6F5)4] in
bromobenzene (entries 7 and 11) shows the same activity with
phenylacetylene and 2-ethynyltoluene as the (L)Y(CH2SiMe3)2/
[PhNMe2H][B(C6F5)4] catalyst reported previously.2a The combina-
tion of the lanthanum complex 3 and [PhNMe2H][B(C6F5)4] only
sluggishly dimerizes phenylacetylenes, but still shows Z-selectivity
(entries 8 and 12). The thermolability of the cationic La-species
and its poor solubility, mentioned above, may account for this low
efficiency.
The kinetics of the dimerization of phenylacetylene by the
two most active catalyst systems, the ionic yttrium system
1/[PhNMe2H][B(C6F5)4] and the neutral lanthanum system 2,
were studied. Plots of the conversion versus time are shown in
Figure 4. The catalysis by the ionic yttrium system shows a
zero-order dependence on substrate concentration over the entire

Z-SelectiVe Catalytic Linear Dimerization of Phenylacetylenes
Organometallics, Vol. 28, No. 3, 2009 723
Table 1. Z-Selective Dimerization of Terminal Alkynes by Yttrium
These rare earth metal alkyl and alkynyl derivatives are active
in the catalytic dimerization of phenylacetylenes. Both the metal
ionic radius and the neutral or cationic nature of the catalyst
species have an influence on the catalytic performance. The
neutral and cationic yttrium and lanthanum complexes catalyze
the linear head-to-head dimerization of phenylacetylenes with
full selectivity for the Z-dimer. For yttrium, the cationic catalyst
is clearly more active than its neutral precursor, but for the larger
metal, lanthanum, the neutral catalyst shows the higher activity.
The smallest metal in the series, scandium, not only shows the
lowest catalyst activity but also lacks regioselectivity, producing
both head-to-head and head-to-tail dimerization products. For
practical application in the catalytic synthesis of Z-enynes, the
La-system is most convenient, as it obviates the use of a
fluorinated borate cocatalyst and a weakly nucleophilic polar
solvent like bromobenzene. It also is less sensitive to steric
hindrance in the substrate, which should allow for the widest
substrate scope.
and Lanthanum Catalysts
Experimental Section
General Remarks. All reactions and manipulations of air- and
moisture-sensitive compounds were performed under a nitrogen
atmosphere using standard Schlenk, vacuum line, and glovebox
techniques, unless mentioned otherwise. Toluene and hexane
(Aldrich, anhydrous, 99.8%) were passed over columns of Al2O3
(Fluka), BASF R3-11-supported Cu oxygen scavenger, and mo-
lecular sieves (Aldrich, 4 Å). THF (Aldrich, anhydrous, 99.8%)
was dried over Al2O3 (Fluka). All solvents were degassed prior to
use and stored under nitrogen. Deuterated solvents (C6D6, C7D8,
C4D8O; Aldrich) were vacuum-transferred from Na/K alloy, and
C6D5Br was dried and distilled from CaH2. NMR spectra were
recorded on Varian Gemini VXR 300, Varian Gemini VXR 400,
or Varian Inova 500 spectrometers in NMR tubes equipped with a
a Reaction conditions: catalyst (10 µmol), [PhNMe2H][B(C6F5)4] (B)
(8.0 mg, 10 µmol) activator where appropriate, substrate (0.5 mmol), 80
°C, solvent: C6D6 (0.5 mL) for neutral catalysts and C6D5Br (0.5 mL)
for ionic catalysts. b Determined by in situ NMR spectroscopy. c 48%
head-to-tail gem-dimer (2,4-diphenylbut-1-en-3-yne) was also formed.
1
Teflon (Young) valve. The H NMR spectra were referenced to
resonances of residual protons in deuterated solvents. The 13C NMR
spectra were referenced to carbon resonances of deuterated solvents
and reported in ppm relative to TMS (δ 0 ppm). Elemental analyses
were performed in the Microanalysis Department of the University
of Groningen, and the reported values are the average values of
two independent determinations. Phenylacetylene and 2-ethynyl-
toluene were purchased and dried and distilled from CaH2 prior to
use. La(CH2Ph)3(THF)36c and N-(2-pyrrolidin-1-ylethyl)-1,4-diaz-
epan-6-amine (HL)2a were prepared according to published proce-
dures. Y(CH2Ph)3(THF)3 was prepared from YCl3(THF)3.5 and
KCH2Ph following the protocol for La(CH2Ph)3(THF)3.
Synthesis of (L)Sc(CH2Ph)2 (1). A solution of HL (0.13 g, 0.52
mmol) in toluene (5 mL) was added to a solution of Sc(CH2Ph)3-
(THF)3 (0.24 g, 0.52 mmol) in toluene (20 mL), and the resulting
mixture was stirred at room temperature for 30 min. Volatiles were
removed under vacuum, and the residue was dissolved in toluene
(3 mL). Pentane (5 mL) was carefully layered on top of the resulting
red solution. Upon cooling to -30 °C, crystalline material formed.
The mother liquor was decanted, and the solid was dried under
reduced pressure, affording the title compound as a pale yellow
Figure 6. Dimerization of phenylacetylene with 1/B in C6D5Br at
room temperature (top) and with 2 in C6D6 at 35 °C (bottom).
conversion range. The neutral lanthanum system shows a zero-
order dependence on substrate concentration only over the first
50% conversion, suggesting a change in rate-determining step
at lower substrate concentrations. As yet, the precise mechanism
leading to the Z-selective dimerization is unclear. Mechanistic
investigations are in progress and will be reported separately.
1
solid (0.19 g, 0.40 mmol, 77%). H NMR (500 MHz, C6D6, 25
°C) δ: 7.28-7.20 (8H, o-H + m-H, Ph), 6.81 (t, 2H, JHH ) 6.6
Hz, p-H Ph), 2.75 (m, 2H, Py R-H), 2.71 (m, 2H, NCH2-bridge),
2.65 (m, 2H, NCH2-bridge), 2.48 (m, 2H, NCH2), 2.45 (d, 2H, JHH
) 12.0 Hz, CCH2N), 2.24 (d, 2H, JHH ) 8.4 Hz, ScCH2), 2.22 (m,
2H, Py R-H), 2.11 (d, 2H, JHH ) 8.4 Hz, ScCH2), 2.07 (s, 6H,
NCH3), 1.70 (d, 2H, JHH ) 12.0 Hz, CCH2N), 1.60 (m, 2H, NCH2),
1.35 (m, 2H, Py ꢀ-H), 1.29 (m, 2H, Py ꢀ-H), 0.59 (s, 3H, CCH3).
13C NMR (125.7 MHz, 25 °C, C6D6) δ: 155.5 (s, ipso-C Ph), 128.5
(d, JCH ) 151.0 Hz, o-C Ph), 124.4 (d, JCH ) 152.6 Hz, m-C Ph),
117.2 (d, JCH ) 159.3 Hz, p-C Ph), 74.0 (t, JCH ) 134.3 Hz,
CCH2N), 57.6 (t, JCH ) 132.2 Hz, NCH2CH2-azepine), 57.3 (s,
Conclusions
The 1,4,6-trimethyl-N-(2-pyrrolidin-1-ylethyl)-1,4-diazepan-
6-amido ligand is able to support well-defined neutral and
cationic benzyl and alkynyl scandium, yttrium, and lanthanum
complexes and thus is suitable as a monoanionic tetradentate
ancillary ligand over the full size range of the rare earth metals.

724 Organometallics, Vol. 28, No. 3, 2009
Ge et al.
Table 2. Crystal Data and Collection Parameters of Complexes 1-3
1
2
3
formula
fw
C28H43ScN4
480.63
C28H43N4Y
524.58
C28H43LaN4
574.57
cryst color
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
yellow
yellow
yellow
0.47 × 0.41 × 0.11
0.52 × 0.48 × 0.15
0.41 × 0.26 × 0.13
triclinic
triclinic
triclinic
j
j
j
P1 (No. 2)
P1 (No.2)
P1 (No. 2)
9.2415(16)
16.471(3)
17.628(3)
77.115(3)
89.025(3)
82.541(3)
2593.4(8)
4
1.231
3.07
1040
2.93, 26.02
(11, (20, (21
19 080
9831
7551
9.2345(10)
16.4721(17)
18.0513(19)
75.5247(16)
88.9232(17)
82.6102(17)
2636.5(5)
4
1.322
22.35
1112
3.01, 26.37
(11, (20, (22
20 090
10 402
7883
9.2008(8)
16.3686(15)
18.2607(17)
75.3451(15)
89.2363(15)
82.9433(15)
2640.1(4)
2
1.446
16.4
1184
2.44, 27.49
(11, -20f21, (23
22 620
11 641
9191
Z
Fcalcd (g cm-3
)
µ (cm-1
)
F(000), electrons
θ range (deg)
index ranges (h,k,l)
no. of reflns collected
no. of unique reflns
no. of reflns with Fo g 4σ(Fo)
wR(F2)
0.1347
0.0851
0.0997
a, b
R(F)
0.0637, 1.4677
0.0499
0.0445, 0
0.0342
0.0548, 0
0.0390
T (K)
100(1)
100(1)
100(1)
GOF
1.066
1.000
1.002
Table 3. Crystal Data and Collection Parameters of Compounds 4-6
4
5 · (C6H14)0.5
C33H46N4Y
587.66
6
formula
fw
C30H39N4Sc
500.62
C60H78N8La2
1189.14
cryst color
cryst size (mm)
cryst syst
space group
a (Å)
colorless
colorless
colorless
0.39 × 0.26 × 0.23
monoclinic
P21/c (14)
10.8798(17)
12.3577(19)
21.351(3)
0.39 × 0.33 × 0.28
monoclinic
P21/n (14)
12.682(2)
14.790(3)
15.914(3)
0.22 × 0.19 × 0.16
monoclinic
P21/n (14)
13.8365(16)
14.4305(16)
14.2150(16)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
101.561(2)
93.154(3)
92.3806(17)
2812.4(7)
4
1.182
2.86
1072
2.52, 26.02
(13, (15, -26f23
20 542
5501
2980.4(9)
4
1.310
19.85
1244
2.52, 26.02
(15, -16f18, (19
21 840
5856
2835.8(6)
2
1.393
15.3
1216
2.46, 26.02
(17, (17, (17
21 350
5585
Z
F
calcd, g cm-3
µ, cm-1
F(000), electrons
θ range (deg)
index ranges (h,k,l)
no. of reflns collected
no. of unique reflns
no. of reflns with Fo g 4σ(Fo)
wR(F2)
a, b
R(F)
T (K)
GOF
3133
3504
4139
0.1645
0.0757, 0
0.0577
222(1)
0.1216
0.0466, 0
0.0492
100(1)
0.0964
0.0478, 0
0.0411
100(1)
0.974
1.051
0.984
CCH3), 57.0 (t, JCH ) 135.2 Hz, azepine-NCH2-bridge), 52.5 (t,
JCH ) 138.4 Hz, R-C Py), 52.3 (t, JCH )114.8 Hz, ScCH2), 50.6
(q, JCH ) 136.2 Hz, NCH3), 45.5 (t, JCH ) 129.4 Hz, Py-CH2-
bridge), 22.4 (t, JCH ) 132.0 Hz, ꢀ-C Py), 20.3 (q, JCH ) 125.9
Hz, CCH3). Anal. Calc for C28H43N4Sc: C, 69.97; H, 9.02; N, 11.66.
Found: C, 69.50; H, 9.03; N, 11.26.
Synthesis of (L)Y(CH2Ph)2 (2). A solution of HL (0.28 g, 1.10
mmol) in toluene (5 mL) was added to a suspension of Y(CH2Ph)3-
(THF)3 (0.63 g, 1.10 mmol) in toluene (30 mL). The resulting mixture
was stirred at room temperature for 30 min and then filtered. The filtrate
was concentrated to about 3 mL. Pentane (5 mL) was carefully layered
on top of the resulting red solution. Upon cooling to -30 °C, crystalline
material formed. The mother liquor was decanted, and the solid was
dried under vacuum, yielding the title compound as a pale yellow solid
(0.45 g, 0.86 mmol, 80%). 1H NMR (400 MHz, C6D6) δ: 7.19-7.11
(8H, o-H + m-H, Ph), 6.65 (t, 2H, JHH ) 6.4 Hz, p-H Ph), 2.89 (m,
2H, R-H Py), 2.82 (m, 2H, NCH2-bridge), 2.77 (m, 2H, NCH2-bridge),
2.51 (d, 2H, JHH ) 11.7 Hz, CCH2N), 2.29 (m, 2H, R-H Py), 2.22
(dd, 2H, JHH ) 7.12 Hz, JYH ) 2.7 Hz,YCH2), 2.01 (s, 6H, NCH3),
1.96 (dd, 2H, JHH ) 7.12 Hz, JYH ) 2.7 Hz,YCH2), 1.87 (m, 2H,
NCH2), 1.71 (d, 2H, JHH ) 11.7 Hz, CCH2N), 1.48 (m, 2H, NCH2),
1.43 (m, 2H, ꢀ-H Py), 1.38 (m, 2H, ꢀ-H Py), 0.66 (s, 3H, CCH3). 13
C
NMR (100.5 MHz, 25 °C, C6D6) δ: 155.0 (s, ipso-C Ph), 129.8 (d,
JCH ) 153.6 Hz, o-C Ph), 122.3 (d, JCH ) 154.4 Hz, m-C Ph), 116.1
(d, JCH ) 159.0 Hz, p-C Ph), 74.9 (t, JCH ) 133.4 Hz, CCH2N), 59.1
(t, JCH ) 136.1 Hz, azepine-NCH2-bridge), 57.3 (t, JCH ) 137.9 Hz,
NCH2CH2-azepine), 57.0 (s, CCH3), 52.6 (t, JCH ) 138.7 Hz, R-C
Py), 51.4 (dt, JCH )120.7 Hz, JYC ) 28.2 Hz, YCH2), 49.6 (q, JCH
)
127.6 Hz, NCH3), 46.3 (t, JCH ) 126.6 Hz, Py-CH2-bridge), 23.0 (t,
JCH ) 132.4 Hz, ꢀ-C Py), 20.6 (q, JCH ) 124.0 Hz, CCH3). Anal.

Z-SelectiVe Catalytic Linear Dimerization of Phenylacetylenes
Organometallics, Vol. 28, No. 3, 2009 725
Calc for C28H43N4Y: C, 64.11; H, 8.26; N, 10.68. Found: C, 64.21;
H, 8.32; N, 10.35.
138.3 (d, JCF ) 235.0 Hz, p-C C6F5), 136.5 (d, JCF ) 242.9 Hz,
m-C C6F5), 124.2 (br, ipso-C C6F5), 118.9 (o-C Ph), 118.3 (p-C
Ph), 75.7 (CCH2-azepine), 59.4 (NCH2-bridge), 56.8 (CCH3), 56.2
(NCH2-azepine), 53.7 (br, YCH2), 52.4 (R-C Py), 48.9 (NCH3),
45.1 (NCH2-bridge), 22.8 (ꢀ-C Py), 19.2 (CCH3).
Synthesis of (L)La(CH2Ph)2 (3). To a solution of La(CH2Ph)3-
(THF)3 (0.898 g, 1.57 mmol) in THF (20 mL) was added dropwise
a solution of ligand HL (0.0.364 g, 1.57 mmol) in THF (5 mL).
After completion of addition, the mixture was stirred at room
temperature for 30 min. All the volatiles were removed under
reduced pressure. The residue was dissolved in toluene (about 3
mL) and then filtered. n-Hexane (5 mL) was carefully layered on
top of the filtrate. Upon cooling to -30 °C, crystalline material
formed, including the material suitable for single-crystal X-ray
diffraction. The mother liquor was decanted, and the solid was dried
under vacuum, yielding the title compound as a yellow solid (0.615
Reaction of 3 with [PhNMe2H][B(C6F5)4]. A solution of 3(25.8
mg, 44.9 µmol) in C6D5Br (0.6 mL) was added to [PhNMe2H]-
[B(C6F5)4] (36.0 mg, 44.9 µmol). The obtained solution was trans-
ferred to an NMR tube equipped with a Teflon (Young) valve. NMR
analysis indicated clean conversion to the corresponding cationic
1
monobenzyl species, toluene, and free PhNMe2. H NMR (500
MHz, C6D5Br, 23 °C) δ: 6.96 (t, 1H, JHH ) 7.2 Hz, p-H Ph), 6.37
(t, 2H, JHH ) 7.05 Hz, m-H Ph), 6.21 (d, 2H, JHH ) 5.92 Hz, o-H
Ph), 2.63 (m, 4H, NCH2-bridge), 2.63 (d, 2H, JHH ) 12.7 Hz, CCH2-
azepine), 2.61 (m, 2H, R-H Py), 2.43 (m, 2H, R-H Py), 2.29 (m,
2H, NCH2-azepine), 2.12 (s, 6H, NCH3), 2.10 (d, 2H, JHH ) 11.9
Hz, CCH2-azepine), 2.02 (m, 2H, NCH2-azepine), 1.94 (br, 2H,
LaCH2), 1.67 (m, 2H, ꢀ-H Py), 1.63 (m, 2H, ꢀ-H Py), 0.59 (s, 3H,
CCH3). {1H}13C NMR (125.7 MHz, C6D5Br, 23 °C) δ: 148.5 (d,
JCF ) 240.7 Hz, o-C C6F5), 138.3 (d, JCF ) 235.0 Hz, p-C C6F5),
136.5 (d, JCF ) 242.9 Hz, m-C C6F5), 132.1 (m-C, Ph), 124.2 (br,
ipso-C C6F5), 119.5 (o-C Ph), 114.8 (p-C Ph), 73.9 (CCH2-azepine),
63.1 (LaCH2), 59.1 (CCH3), 57.7 (NCH2-bridge), 56.7 (NCH2-
azepine), 52.3 (R-C Py), 48.9 (NCH3), 46.7 (NCH2-bridge), 23.0
(ꢀ-C Py), 20.0 (CCH3). The ipso-C resonance is obscured by the
solvent peaks. 19F NMR (470 MHz, C6D5Br, 23 °C) δ: -137.1 (d,
JFF ) 11.5 Hz, o-F), -167.3 (t, JFF ) 21.3 Hz, m-F), -171.2 (t,
JFF ) 17.8 Hz, p-F).
1
g, 1.07 mmol, 68%). H NMR (400 MHz, C6D6) δ: 7.07 (t, 4H,
JHH ) 7.57 Hz, m-H Ph), 6.70 (d, 4H, JHH ) 7.76 Hz, o-H Ph),
6.47 (t, 2H, JHH ) 7.17 Hz, p-H Ph), 2.88 (m, 2H, NCH2-bridge),
2.80 (m, 2H, NCH2-bridge), 2.67 (m, 2H, R-H Py), 2.62 (d, 2H,
JHH ) 12.1 Hz, CCH2N), 2.34 (br, 2H, LaCH2), 2.14 (m, 2H, R-H
Py), 2.11 (br, 2H, LaCH2), 2.10 (m, 2H, NCH2), 2.02 (s, 6H, NCH3),
1.83 (d, 2H, JHH ) 12.1 Hz, CCH2N), 1.63 (m, 2H, NCH2), 1.55
(m, 2H, Py ꢀ-H), 1.42 (m, 2H, Py ꢀ-H), 0.67 (s, 3H, CCH3). 13C
NMR (100.5 MHz, C6D6) δ: 152.2 (s, ipso-C Ph), 131.0 (d, JCH
)
153.5 Hz, m-C Ph), 120.7 (d, JCH ) 152.0 Hz, o-C Ph), 114.3 (d,
JCH ) 159.4 Hz, p-C Ph), 73.7 (t, JCH ) 134.3 Hz, CCH2N), 62.6
(t, JCH )134.0 Hz, LaCH2), 59.4 (s, CCH3), 58.5 (t, JCH ) 133.6
Hz, azepine-NCH2-bridge), 57.3 (t, JCH ) 131.9 Hz, NCH2-azepine),
52.9 (t, JCH ) 138.5 Hz, R-C Py), 49.4 (q, JCH ) 135.2 Hz, NCH3),
47.6 (t, JCH ) 128.7 Hz, Py-CH2-bridge), 23.3 (t, JCH ) 131.3 Hz,
ꢀ-C Py), 20.9 (q, JCH ) 125.0 Hz, CCH3). Anal. Calc for
C28H43LaN4: C, 58.53; H, 7.54; N, 9.75. Found: C, 58.75; H, 7.60;
N, 9.34.
Synthesis of (L)Sc(Ct CPh)2 (4). To a solution of 1 (144.2 mg,
0.3 mmol) in toluene (35 mL) was added a solution of pheny-
lacetylene (61.3 mg, 0.6 mmol) in toluene (2 mL). The resulting
solution was stirred overnight at room temperature, and then all
the volatiles were removed under vacuum. The residue was
dissolved in benzene (2 mL) and hexane (1 mL) was added,
followed by filtration. Upon standing at room temperature overnight,
crystalline material formed, including material suitable for single-
crystal X-ray diffraction. The mother liquor was decanted, and the
solid was dried under reduced pressure, yielding the title compound
as a white solid (110.2 mg, 0.22 mmol, 73%). 1H NMR (400 MHz,
C6D6, 25 °C) δ: 7.65 (d, 4H, JCH ) 7.68 Hz, o-H Ph), 7.07 (t, 4H,
JCH ) 7.91 Hz, m-H Ph), 6.97 (t, 2H, JCH ) 7.23 Hz, p-H Ph),
3.78 (m, 2H, R-H Py), 3.28 (m, 2H, NCH2), 3.03 (m, 2H, NCH2-
bridge), 2.79 (m, 2H, NCH2-bridge), 2.62 (d, 2H, JHH ) 11.6 Hz,
CCH2N), 2.58 (s, 6H, NCH3), 2.32 (m, 2H, R-H Py), 2.17 (m, 2H,
ꢀ-H Py), 1.91 (d, 2H, JHH ) 11.6 Hz, CCH2N), 1.83 (m, 2H, NCH2),
1.47 (m, 2H, ꢀ-H Py), 0.64 (s, 3H, CCH3). 13C NMR (100.5 MHz,
C6D6, 25 °C) δ: 142.1 (br, ScCt C-Ph), 132.0 (dt, JCH ) 159.5
Hz, JCH ) 6.6 Hz, o-C Ph), 128.2 (dd, JCH ) 158.9 Hz, JCH ) 7.7
Hz, m-C Ph), 125.7 (dt, JCH ) 160.1 Hz, JCH ) 7.7 Hz, p-C Ph),
102.6 (t, JCH ) 4.6 Hz, ScCt CPh), 74.7 (t, JCH ) 133.2 Hz,
CCH2N), 59.6 (t, JCH ) 135.6 Hz, azepine-NCH2-bridge), 57.8 (s,
CCH3), 57.4 (t, JCH ) 137.5 Hz, NCH2CH2-azepine), 54.4 (t, JCH
) 139.3 Hz, R-C Py), 51.4 (q, JCH ) 135.6 Hz, NCH3), 45.8 (t,
JCH ) 128.4 Hz, Py-CH2-bridge), 23.1 (t, JCH ) 133.0 Hz, ꢀ-C
Py), 19.5 (q, JCH ) 124.8 Hz, CCH3). Anal. Calc for C28H43N4Sc:
C, 71.98; H, 7.85; N, 11.19. Found: C, 71.88; H, 7.89; N, 11.09.
Synthesis of [(L)Y(Ct CPh)(µ-Ct CPh)]2 (5). A solution of 2
(104.9 mg, 0.2 mmol) in toluene (1 mL) was added to pheny-
lacetylene (40.9 mg, 0.4 mmol), and the resulting mixture was kept
for 30 min at room temperature and then at -30 °C overnight,
after which crystalline material had formed. The mother liquor was
decanted and the solid was dried under vacuum, giving the title
compound (76.2 mg, 0.07 mmol, 70%) as a colorless solid. Crystals
suitable for single-crystal X-ray diffraction were grown by crystal-
Reaction of 1 with [PhNMe2H][B(C6F5)4]. A solution of 1(18.7
mg, 38.9 µmol) in C6D5Br (0.5 mL) was added to [PhNMe2H]-
[B(C6F5)4] (31.2 mg, 38.9 µmol). The resulting mixture was ho-
mogenized by agitation and transferred to an NMR tube equipped
with a Teflon (Young) valve. NMR analysis indicated clean con-
version to the corresponding cationic monobenzyl species, toluene,
and free PhNMe2. 1H NMR (500 MHz, C6D5Br, 23 °C) δ: 7.05 (t,
2H, JHH ) 7.1 Hz, m-H Ph), 6.65 (t, 1H, JHH ) 7.2 Hz, p-H Ph),
6.04 (br, 2H, o-H Ph), 2.82 (br, 2H, NCH2-bridge), 2.70 (m, 2H,
R-H Py), 2.63 (m, 2H, R-H Py), 2.60 (d, 2H, JHH ) 12.4 Hz, CCH2-
azepine), 2.56 (br, 2H, NCH2-bridge), 2.15 (d, 2H, JHH ) 12.4 Hz,
CCH2-azepine), 2.06 (s, 6H, NCH3), 1.96 (m, 2H, NCH2-azepine),
1.87 (m, 2H, NCH2-azepine), 1.82 (br, 2H, ScCH2), 1.68 (m, 2H,
ꢀ-H Py), 1.61 (m, 2H, ꢀ-H Py), 0.44 (s, 3H, CCH3). {1H}13C NMR
(125.7 MHz, C6D5Br, 25 °C) δ: 152.4 (s, ipso-C Ph), 148.5 (d, JCF
) 240.7 Hz, o-C C6F5), 138.3 (d, JCF ) 235.0 Hz, p-C C6F5), 136.5
(d, JCF ) 242.9 Hz, m-C C6F5), 133.7 (m-C Ph), 120.7 (o-C, Ph),
120.2 (p-C Ph), 124.2 (br, ipso-C C6F5), 77.3 (CCH2N), 56.9
(azepine-NCH2-bridge), 55.6 (NCH2CH2-azepine), 55.5 (s, CCH3),
54.7 (ScCH2), 54.0 (R-C Py), 48.7 (NCH3), 44.9 (Py-CH2-bridge),
21.5 (ꢀ-C Py), 18.0 (CCH3).
Reaction of 2 with [PhNMe2H][B(C6F5)4]. A solution of 2(19.9
mg, 37.9 µmol) in C6D5Br (0.5 mL) was added to [PhNMe2H]-
[B(C6F5)4] (30.4 mg, 37.9 µmol). The resulting mixture was ho-
mogenized by agitation and transferred to an NMR tube equipped
with a Teflon (Young) valve. NMR analysis indicated clean
conversion to the corresponding cationic monobenzyl species,
toluene, and free PhNMe2. 1H NMR (500 MHz, C6D5Br, 25 °C) δ:
6.89 (br, 2H, m-H Ph), 6.48 (br, 1H, p-H Ph), 6.22 (br, 2H, o-H
Ph), 2.79 (m, 2H, R-H Py), 2.63 (m, 2H, NCH2-bridge), 2.60 (d,
2H, JHH ) 11.9 Hz, CCH2-azepine), 2.58 (m, 2H, R-H Py), 2.49
(m, 2H, NCH2-bridge), 2.30 (m, 2H, NCH2-azepine), 2.13 (d, 2H,
JHH ) 11.9 Hz, CCH2-azepine), 2.09 (m, 2H, NCH2-azepine), 2.06
(s, 6H, NCH3), 1.65 (m, 4H, ꢀ-H Py), 1.64 (br, 2H, YCH2), 0.59
(s, 3H, CCH3). {1H}13C NMR (125.7 MHz, C6D5Br, 25 °C) δ: 153.4
(ipso-C Ph), 133.4 (m-C, Ph), 148.5 (d, JCF ) 240.7 Hz, o-C C6F5),
1
lization from toluene/hexane. H NMR (500 MHz, C6D6, 25 °C)
δ: 7.76 (br, 8H, o-H Ph), 7.07 (t, 8H, JHH ) 7.24 Hz, m-H Ph),
6.95 (t, 4H, JHH ) 6.44 Hz, p-H Ph), 3.54 (m, 4H, NCH2), 3.39

726 Organometallics, Vol. 28, No. 3, 2009
Ge et al.
(br, 8H, R-H Py), 3.13 (m, 4H, NCH2-bridge), 3.05 (m, 4H, NCH2-
bridge), 2.83 (s, 12H, NCH3), 2.70 (d, 4H, JHH ) 11.0 Hz, CCH2N),
1.99 (d, 4H, JHH ) 11.0 Hz, CCH2N), 1.98 (m, 4H, NCH2), 1.80
(br, 8H, ꢀ-H Py), 0.75 (s, 6H, CCH3). 13C NMR (125.7 MHz, C7D8,
25 °C) δ: 148.4 (s, Ct CPh), 132.1 (d, JCH ) 161.6 Hz, o-C Ph),
128.3 (d, JCH ) 158.9 Hz, m-C Ph), 126.3 (d, JCH ) 160.2 Hz, p-C
Ph), 114.9 (br, Ct CPh), 77.6 (t, JCH ) 135.7 Hz, CCH2N), 58.6
(t, JCH ) 135.5 Hz, NCH2CH2-azepine), 58.3 (t, JCH ) 133.3 Hz,
azepine-NCH2-bridge), 57.7 (s, CCH3), 54.4 (t, JCH ) 137.8 Hz,
R-C Py), 52.6 (q, JCH ) 135.5 Hz, NCH3), 47.1 (t, JCH ) 128.9
Hz, Py-CH2-bridge), 23.5 (t, JCH ) 131.2 Hz, ꢀ-C Py), 19.8 (q,
JCH ) 125.4 Hz, CCH3). The ipso-C resonance is obscured by the
solvent peaks. Anal. Calc for C60H78Y2N8: C, 66.17; H, 7.22; N,
10.29. Found: C, 66.16; H, 7.37; N, 9.89.
final volume of the reaction mixture is approximately 550 µL (500
µL stock solution + ∼50 µL substrate) and [M] is ∼18.2 mM.
Catalytic Oligomerization of Phenylacetylenes by the Ionic
Catalysts (1, 2, or 3)/[PhNMe2H][B(C6F5)4]. In a Tomas tube, a
solution of 1 or 2 (10 µmol) in C6D5Br (0.5 mL) was added to
[PhNMe2H][B(C6F5)4] (8.0 mg, 10 µmol), and then the resulting
solution was treated with phenylacetylene (51.1 mg, 0.5 mmol) or
2-ethynyltoluene (58.0 mg, 0.5 mmol). The resulting mixture was
transferred to an NMR tube equipped with a Teflon (Young) valve.
The tube was inserted into an NMR spectometrometer which was
preheated to 80 °C, and a single pulse spectrum was taken every 5
min. The final volume of the reaction mixture is approximately
550 µL (500 µL stock solution + ∼50 µL substrate) and [M] is
∼18.2 mM.
Synthesis of [(L)La(Ct CPh)(µ-Ct CPh)]2 (6). To a solution
of 3 (116.4 mg, 0.2 mmol) in toluene (2 mL) was added phe-
nylacetylene (40.9 mg, 0.4 mmol). The resulting mixture was left
standing at -30 °C overnight, after which crystalline material had
formed. The mother liquor was decanted and the solid was dried
under vacuum, yielding the title compound as a colorless solid (72.8
mg, 65.8 µmol, 66%). Crystals suitable for single-crystal X-ray
Structure Determinations of Compounds 1-6. Suitable single
crystals of the compounds were obtained by crystallization as
described above. Crystals were mounted on a glass fiber inside a
glovebox and transferred under inert atmosphere to the cold nitrogen
stream of a Bruker SMART APEX CCD diffractometer. Intensity
data were collected with Mo KR radiation (λ ) 0.71073 Å).
Intensity data were corrected for Lorentz and polarization effects.
A semiempirical absorption correction was applied, based on the
intensities of symmetry-related reflections measured at different
angular settings (SADABS9). The structures were solved by
Patterson methods, and extension of the models was accomplished
by direct methods applied to difference structure factors, using the
program DIRDIF.10 In a subsequent difference Fourier synthesis
all hydrogen atoms were located, of which the positional and
isotropic displacement parameters were refined. All refinements and
geometry calculations were performed with the program packages
SHELXL11 and PLATON.12 Crystallographic data and details of
the data collections and structure refinements are listed in Table 2
(for 1-3) and Table 3 (for 4-6).
1
diffraction were grown by crystallization from THF/hexane. H
NMR (500 MHz, C7D8, 25 °C) δ: 7.81 (d, 8H, JHH ) 7.53 Hz, o-H
Ph), 7.12 (t, 8H, JHH ) 7.76 Hz, m-H Ph), 6.98 (t, 4H, JHH ) 7.42
Hz, p-H Ph), 4.12 (br, 4H, R-H Py), 3.55 (m, 4H, NCH2), 3.16 (m,
4H, NCH2-bridge), 3.08 (m, 4H, NCH2-bridge), 2.83 (s, 12H,
NCH3), 2.72 (d, 4H, JHH ) 11.6 Hz, CCH2N), 2.48 (br, 4H, R-H
Py), 2.46 (br, 4H, ꢀ-H Py), 2.06 (m, 4H, NCH2), 2.05 (d, 4H, JHH
) 11.6 Hz, CCH2N), 1.72 (br, 4H, ꢀ-H Py), 0.73 (s, 6H, CCH3).
13C NMR (125.7 MHz, C7D8, 25 °C) δ: 162.1 (s, C‘CPh), 132.2
(d, JCH ) 161.3 Hz, o-C Ph), 128.3 (d, JCH ) 167.4 Hz, m-C Ph),
126.2 (d, JCH ) 162.9 Hz, p-C Ph), 115.5 (br, Ct CPh), 76.9 (t,
JCH ) 132.3 Hz, CCH2N), 60.1 (t, JCH ) 133.9 Hz, azepine-NCH2-
bridge), 58.4 (t, JCH ) 136.0 Hz, NCH2CH2-azepine), 54.6 (t, JCH
) 138.1 Hz, R-C Py), 54.4 (s, CCH3), 51.5 (q, JCH ) 136.0 Hz,
Acknowledgment. This investigation was financially
supported by the Chemical Science Division of The Neth-
erlands Organisation for Scientific Research (NWO-CW).
NCH3), 48.0 (t, JCH ) 127.7 Hz, Py-CH2-bridge), 24.3 (t, JCH
)
131.4 Hz, ꢀ-C Py), 19.8 (q, JCH ) 126.2 Hz, CCH3). The ipso-C
resonance is obscured by the solvent peaks. Assignment of NMR
resonances was aided by COSY and HSQC experiments. Anal. Calc
for C60H78La2N8: C, 60.60; H, 6.61; N, 9.42. Found: C, 59.25; H,
6.59; N, 9.30. The rather low carbon content found (whereas H
and N values agree with the calculated values) is likely to be due
to some carbide formation. We have observed this before on a La-
acetylide compound.2d
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
OM8004228
(9) Sheldrick, G. M. SADABS Version 2, Empirical Absorption Cor-
rection Program; University of Go¨ttingen: Go¨ttingen, Germany, 2000.
(10) Beurskens, P. T.; Beurskens, G.; De Gelder, R.; Garcia-Granda,
S.; Gould, R. O.; Israel, R.; Smits, J. M. M. The DIRDIF-99 program system;
Crystallography Laboratory, Unversity of Nijmegen: Nijmegen, The
Netherlands, 1999.
(11) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(12) Spek, A. L. PLATON, program for the Automated Analysis of
Molecular Geometry; University of Utrecht: Utrecht, The Netherlands, 2000.
Catalytic Dimerization of Phenylacetylenes by 1–6. Pheny-
lacetylene (51.1 mg, 0.5 mmol) or 2-ethynyltoluene (58.0 mg, 0.5
mmol) was added to a solution of complex 1, 2, 3, or 4 (10 µmol)
or 5 or 6 (5 µmol) in C6D6 (0.5 mL). The resulting solution was
transferred to an NMR tube equipped with a Teflon (Young) valve.
The tube was inserted into an NMR spectrometer that was preheated
to 80 °C, and a single pulse spectrum was taken every 5 min. The