Tunable π-interactions in monomeric organozinc complexes: Solution and solid-state studies

Article abstract of DOI:10.1021/om070213y

A series of the calix[4]arene ligands, partially oxygen-depleted at the 1 and 3 positions via the Sonogashira cross-coupling reaction with several arylacetylenes, were prepared. Upon reaction with R₂-Zn (R = Me, Et, C₆F₅), the corresponding organozinc complexes were obtained. X-ray analysis showed weak π-interactions between the organozinc fragment and the triple bonds. In addition, the solution ¹³C NMR studies showed good correlation between the strength of these interactions and electron density at the acetylene group, with more electron-rich alkynes binding stronger to the Zn center. The latter was also supported by DFT calculations on a model compound. These results show that, albeit weak, π-interactions of organozinc compounds can be observed and fine-tuned in both solution and the solid state.

Full text of DOI:10.1021/om070213y

Organometallics 2007, 26, 4015-4020
4015
Tunable π-Interactions in Monomeric Organozinc Complexes:
Solution and Solid-State Studies
Ella Bukhaltsev,† Israel Goldberg,† Revital Cohen,‡ and Arkadi Vigalok*,†
School of Chemistry, The Sackler Faculty of Exact Sciences, Tel AViV UniVersity, Tel AViV 69978, Israel,
and Faculty of Chemistry, Chemical Research Support Unit, The Weizmann Institute of Science,
RehoVot 76100, Israel
ReceiVed March 7, 2007
A series of the calix[4]arene ligands, partially oxygen-depleted at the 1 and 3 positions via the
Sonogashira cross-coupling reaction with several arylacetylenes, were prepared. Upon reaction with R2-
Zn (R ) Me, Et, C6F5), the corresponding organozinc complexes were obtained. X-ray analysis showed
weak π-interactions between the organozinc fragment and the triple bonds. In addition, the solution 13C
NMR studies showed good correlation between the strength of these interactions and electron density at
the acetylene group, with more electron-rich alkynes binding stronger to the Zn center. The latter was
also supported by DFT calculations on a model compound. These results show that, albeit weak,
π-interactions of organozinc compounds can be observed and fine-tuned in both solution and the solid
state.
plexes from toluene gave crystalline compounds that
Introduction
showed Zn π-interactions with the toluene molecule.7a However,
Organozinc reagents are widely utilized in modern
synthetic organic chemistry, particularly in asymmetric cataly-
sis.1 In many cases, organic transformations assisted by
organozincs involve substrates bearing alkene or alkyne
functions.2 While unsaturated substrates usually show strong
π-interactions with the majority of electron-rich d10 com-
plexes,3 such interactions are noticeably scarce in the isoelec-
tronic electron-rich zinc(II) complexes. Since the Zn-alkene
or Zn-alkyne interaction virtually lacks the back-bonding
component,4,5 these complexes should be considerably
weaker for zinc compared with other d10 metals. It is, neverthe-
less, important to keep in mind that zinc does not use its
d-electrons for binding and often is not considered a transition
metal.
1
the solution H and 13C NMR spectra of these complexes7a,b
exhibit signals expected for the noncoordinated toluene.8 No
benzene incorporation into the crystal structure was observed
when bis(pentafluorophenyl)zinc was crystallized from ben-
zene.9
Circumstantial evidence for the Zn π-interactions was ob-
tained from the solution NMR studies of di-4-hexynyl- and di-
4-pentenylzinc; however, these earlier reports were not verified
by the X-ray crystallography.10,11 Although alkene coordination
to Zn appears to be responsible for the stereoselectivity of
allylzincation and zinc-assisted cyclopropanation reactions,12
formation of a π-complex between allylzinc bromide and
ethylene was calculated to be slightly endothermic,13 emphasiz-
ing the delicate balance in assessment of Zn π-interactions in
solution and the solid state. Thus far, π-interactions in mono-
meric complexes have been confirmed only for the Lewis acidic
zinc dihalides.14 In this paper, we report the first solution and
X-ray studies on the fine-tuning of the organozinc π-interactions
with an alkyne ligand.
Zinc alkene complexation was very recently reported to
exist in divinyl zinc derivatives in the solid state but not in
solution.6 Recrystallization of bis(perfluoroaryl)zinc com-
* Corresponding author. E-mail: avigal@post.tau.ac.il.
† Tel Aviv University.
‡ The Weizmann Institute of Science.
(1) von Wangelin, A. J.; Frederiksen, M. U. Zinc-mediated reactions. In
Transition Metals for Organic Synthesis: Building Blocks and Fine
Chemicals, 2nd ed.; Beller, M., Bolm, C., Eds.; Wiley-VCH: New York,
2004; p 519.
(2) For the latest references see: (a) Lorthiois, E.; Meyer, C. Cabozin-
cation of alkenes and alkynes. In The Chemistry of Organozinc Compounds;
Rappoport, Z., Marek, I., Eds.; Wiley-VCH: New York, 2006; Chapter
19, p 863. (b) Reiser, O. Angew. Chem., Int. Ed. 2006, 45, 2838. (c) Pu, L.
Tetrahedron 2003, 59, 9873.
(7) (a) Guerrero, A.; Martin, E.; Hughes, D. L.; Kaltsoyannis, N.;
Bochmann, M. Organometallics 2006, 25, 3311. (b) Walker, D. A.;
Woodman, T. J.; Hughes, D. L.; Bochmann, M. Organometallics 2001,
20, 3772.
(8) Gottlieb, H. E.; Kotlyar, V.; Nudelman, A. J. Org. Chem. 1997, 62,
7512.
(9) Sun, Y.; Piers, W. E.; Parvez, M. Can. J. Chem. 1998, 76, 513.
(10) Alkyne complexes: (a) Okninska, E.; Starowieyski, K. B. J.
Organomet. Chem. 1989, 376, 7. (b) Okninska, E.; Starowieyski, K. B. J.
Organomet. Chem. 1988, 347, 1.
(11) Alkene complexes: (a) Albright, M. J.; St. Denis, J. N.; Oliver, J.
P. J. Organomet. Chem. 1977, 125, 1. (b) St Denis, J.; Oliver, J. P.; Dolzine,
T. W.; Smart, J. B. J. Organomet. Chem. 1974, 71, 315.
(12) (a) Marek, I.; Beruben, D.; Normant, J.-F. Tetrahedron Lett. 1995,
36, 3695. (b) Beruben, D.; Marek, I.; Normant, J.-F.; Platzer, N. J. Org.
Chem. 1995, 60, 2488.
(3) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Sausalito, CA, 1987.
(4) This lack of back-donation is attributed to the large orbital promotion
energy: Elschenbroich, C.; Salzer, A. Organometallics: A Concise
Introduction, 2nd ed.; VCH Publishers Inc.: New York, 1992; p 256.
(5) (a) For relevant discussion see: Lin, J.; Jones, P.; Guckert, J.;
Solomon, E. I. J. Am. Chem. Soc. 1991, 113, 8312. (b) Hg(II) alkyne
complexes, also lacking the back-bonding component, have been reported:
Faville, S. J.; Henderson, W.; Mathieson, T. J.; Nicholson, B. K. J.
Organomet. Chem. 1999, 580, 363.
(13) (a) Marek, I.; Schreiner, P. R.; Normant, J. F. Org. Lett. 1999, 1,
929. (b) See also: Hirai, A.; Nakamura, M.; Nakamura, E. J. Am. Chem.
Soc. 2000, 122, 11791.
(14) (a) Lang, H.; Mansilla, N.; Rheinwald, G. Organometallics 2001,
20, 1592. (b) Enders, M.; Ludwig, G.; Pritzkow, H. Eur. J. Inorg. Chem.
2002, 539.
(6) Wooten, A.; Carroll, P. J.; Maestri, A. G.; Walsh, P. J. J. Am. Chem.
Soc. 2006, 128, 4624.
10.1021/om070213y CCC: $37.00 © 2007 American Chemical Society
Publication on Web 07/07/2007

4016 Organometallics, Vol. 26, No. 16, 2007
BukhaltseV et al.
Scheme 1
Scheme 2
Figure 1. ORTEP structures (50% probability) of molecules of
2a. Hydrogen atoms and solvent (pentane) molecule are omitted
for clarity. Labels C1 and C1′, and C2 and C2′, are used to allow
better comparison between the alkyne ligands on each side. The
corresponding atoms are not symmetry related. Selected distances
(Å) and angles (deg): Zn1-O1 1.971(2), Zn1-O2 1.992(2), Zn1-
C1 3.0667(37), Zn1-C2 2.7695(37), Zn1-C1′ 3.3661(36), Zn1-
C2′ 2.9545(34), Zn1-Zn2 3.067, Zn1-C3 1.941(4), Zn2-C4
1.940(4); C3-Zn1-O2 148.48(13), C3-Zn1-O1 133.25(13), O1-
Zn1-O2 78.19(9).
Results and Discussion
We recently showed that the reaction of 2 equiv of a
dialkylzinc reagent with 1,3-diethers or diesters of calix[4]arene
(calixarene) results in the bimetallic inclusion complexes where
one of the alkylzinc groups is located inside the calixarene
cavity. This internal zinc center is coordinated to two of the
oxygen atoms, while the second one remains on top of the
calixarene phenolic rim and coordinated to all four oxygen atoms
(Scheme 1).15 As a continuation of this work, we reacted Me2-
Zn with the calixarene ligand 1a, where two of the oxygen atoms
have been replaced with a phenylacetylene unit.16 The 1H NMR
spectrum of the reaction mixture indicated the quantitative
formation of the new bimetallic complex 2a, similar to that
previously reported, showing that the formation of these
complexes is not affected by the absence of the two oxygen
donors (Scheme 2).
To verify the composition of 2a, we performed crystal-
lographic studies of its crystal. The X-ray structure of 2a (Figure
1) shows that the general characteristics of this complex are
similar to the complexes with more common calixarene
ligands.15 An important feature of this structure is the relatively
short distances, shorter than the sum of the van der Waals radii
(3.09 Å), between the external zinc atom and carbon atoms of
one of the triple bonds of the calixarene ligand, 2.7695(37) and
3.0667(37) Å. There is also a noticeable difference between the
C3-Zn1-O2 and C3-Zn1-O1 bond angles, 148.48° and
133.25°, respectively, a feature not observed in other Zn
calixarene complexes.15 Although the interactions between the
zinc center and second triple bond are less apparent if only Zn-
carbon distances (2.9545(34) and 3.3661(36) Å) are counted,
the solution 1H and 13C NMR spectra show symmetrical patterns
even at -80 °C without preferential Zn coordination to either
of the triple bonds. The NMR data suggest that, in solution,
the zinc center either is equally interacting with both alkyne
groups in a five-coordinate fashion or exists in a very fast
equilibrium even at low temperatures.
To investigate the alkyne π-interactions in the organozinc
calixarene complexes, we prepared a series of ligands 1b-e
with different substituents in the aromatic ring of the alkyne
part of the molecule. Upon the reaction with Me2Zn, complexes
2b-e were obtained in quantitative yields (Scheme 2). Interest-
ingly, the 13C NMR ∆δ of the triple-bond carbon atoms’
chemical shifts between the complexes and free ligands shows
very good correlation with the σp-Hammett parameters of the
substituents in the aromatic ring (Figure 2).17 In all cases, the
signals of the carbon atoms of the triple bond are shifted
downfield, suggesting some weakening of the triple bond (Table
1). These shifts were more significant for the complexes bearing
electron-donating groups, implying stronger interactions of the
electron-rich alkynes with the zinc center.
A similar trend was observed for the 13C NMR signal of the
zinc-bound methyl group, which showed steady upfield shifts
for complexes with more electron-rich alkyne ligands. To ensure
that this trend is not a result of the direct interaction of the
aromatic ring with the methyl group, we prepared the corre-
sponding ethylzinc complexes (3, Scheme 2). The 13C NMR
analysis showed that the Zn-bound methylene group of the ethyl
ligand is more affected by the electronic properties of the
substituent in the aromatic ring than the corresponding methyl
end group. Due to its closer proximity, this group would be
more susceptible to the aromatic ring-current effects should the
latter be influencing the chemical shifts of the alkylzinc groups.
Interestingly, the triple-bond carbon atoms show weaker interac-
tions with the more electron-rich ethylzinc fragment in 3 than
with the methylzinc fragment in 2, as confirmed by the 13C
NMR ∆δ analysis (Table 2). We also prepared complexes 4,
containing pentafluorophenyl groups (Scheme 2), significantly
weaker donors than alkyls, at the Zn center. The 13C NMR
analysis showed that the triple bonds in 4 exhibit larger chemical
shifts versus the free ligands than in 2. Again, electron-donating
substituents in the aromatic ring resulted in stronger Zn-triple
bond π-interactions (Table 3). Favorable π-stacking interactions
between the electron-rich aromatic groups and pentafluorophe-
(15) (a) Bukhaltsev, E.; Goldberg, I.; Vigalok, A. Organometallics 2004,
23, 4540. (b) Bukhaltsev, E.; Goldberg, I.; Vigalok, A. Organometallics
2005, 24, 5732.
(16) (a) Al-Saraierh, H.; Miller, D. O.; Georghiou, P. E. J. Org. Chem.
2005, 70, 8273. (b) We modified the original protocols by using a more
reactive t-Bu3P/Pd(dba)2 cross-coupling catalyst. See Experimental Part for
details.
(17) Hansch, C. A.; Leo, A.; Taft, R. W. Chem. ReV. 1991, 91, 165.

Tunable π-Interactions in Monomeric Organozinc Complexes
Organometallics, Vol. 26, No. 16, 2007 4017
Figure 2. Difference in chemical shifts (∆δ, ppm) of the triple-bond carbons C1 (a) and C2 (b) in complexes 2 versus free ligands as a
function of the Hammett Fpara values.17 For 2e, twice the value of Fmeta was taken.
Table 1. 13C NMR Chemical Shifts of the Triple-Bond Carbons in Complexes 2a-e and 6 versus the Corresponding Ligands
δ CtC 13C NMR,b ppm
ligand δ CtC 13C NMR, ppm
∆δ, ppm
a
compound
σpara
C1
C2
C1
C2
C1
C2
2b
2c
2a
2d
2ec
6
-0.27
-0.17
0.00
106.59
106.43
106.05
104.16
101.96
107.32
103.58
89.10
89.57
90.10
92.17
93.01
88.94
92.42
98.26
98.37
98.14
96.51
94.81
98.52
96.28
86.73
87.40
87.95
90.32
91.35
86.55
90.63
8.33
8.06
7.91
7.65
7.15
8.80
7.30
2.37
2.17
2.15
1.85
1.66
2.39
1.79
0.54
0.86c
-0.27
0.54
b
a Taken from ref 17. All spectra were observed in C6D6 at 22 °C. c For 2e, twice the value of Fmeta was taken.
Table 2. 13C NMR Chemical Shifts of the Triple-Bond Carbons in Complexes 3a-e versus the Corresponding Ligands
δ CtC 13C NMR, ppm ligand δ CtC 13C NMR, ppm
∆δ, ppm
compound
σpara
C1
C2
C1
C2
C1
C2
3b
3c
3a
3d
3e
-0.27
-0.17
0.00
106.06
105.91
105.54
103.67
101.51
88.59
89.09
89.60
91.66
92.54
98.26
98.37
98.14
96.51
94.81
86.73
87.40
87.95
90.32
91.35
7.80
7.54
7.40
7.17
6.70
1.86
1.69
1.65
1.34
1.19
0.54
0.86c
Table 3. 13C NMR Chemical Shifts of the Triple-Bond Carbons in Complexes 4a-d versus the Corresponding Ligands
δ CtC 13C NMR, ppm ligand δ CtC 13C NMR, ppm
∆δ, ppm
compound
σpara
C1
C2
C1
C2
C1
C2
4b
4c
4a
4d
-0.27
-0.17
0.00
108.67
108.30
107.84
105.65
88.32
88.72
89.12
90.85
98.26
98.37
98.14
96.51
86.73
87.40
87.95
90.32
10.41
9.93
9.70
9.15
1.59
1.32
1.17
0.53
0.54
nylzinc moiety may also contribute to the observed large
chemical shifts.
an03 program package.19 DFT calculations at the PBE0/SDD
level of theory20-22 of 6a (the simplified analogue of 6 where
the t-Bu groups have been replaced by hydrogen atoms)
provided structural features closely resembling those observed
in the X-ray analysis of 6. In particular, the calculations show
that the external zinc center is located closer to the electron-
rich alkyne, with Zn-C2 and Zn1-C1 distances of 2.841 and
To further verify the tunability of the Zn-alkyne interactions,
we synthesized the calixarene dialkyne ligand 5, bearing
different alkyne groups at the opposite sides of the calixarene
cone. Upon reacting with 2 equiv of Me2Zn, this compound
afforded the expected bimetallic zinc complex 6 (Scheme 3).
Interestingly, comparison of the ∆δ of the 13C NMR triple-
bond signals in 6 versus 5 with the corresponding value for 2b
and 2d (versus 1b and 1d, respectively) showed that the Zn
π-interactions are stronger for the electron-rich alkyne part of
the ligand and weaker for the electron-poor alkyne group (Table
1). This unsymmetrical binding was confirmed by the X-ray
analysis of complex 6 (Figure 3), which shows that the distances
between the “electron-rich” alkyne carbons and zinc atom are
approximately 0.05 Å shorter than the corresponding distances
involving the “electron-poor” part of the molecule (2.8706(38)
versus 2.9222(39) Å for C2 and 3.1152(39) versus 3.1719(42)
Å for C1). Unlike in 2a, the arylalkyne units in 6 are aligned
parallel to each other.18
(18) We observed a similar alignment in the X-ray structure of 2b.
Although there are severe disorders in this structure at the “periphery” of
the molecule (OMe and t-Bu groups), the central part of the molecule in
the proximity of the Zn atoms was solved reliably. In addition to the parallel
positioning of the aryl groups, the crystal structure of 2b shows average
Zn-C2 and Zn-C1 distances of 2.879 and 3.092 Å, respectively, which is
similar to what was observed for the zinc interactions with the electron-
rich part of the molecule of 6.
(19) Frisch, M. J. et al. Gaussian 03, Revision C.02; Gaussian, Inc.:
Wallingford, CT, 2004.
(20) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1996, 77,
3865.
(21) Dunning, T. H., Jr.; Hay, P. J. Modern Theoretical Chemistry;
Plenum: New York, 1976; Vol. 3, p 1.
(22) Dolg, M. Effective Core Potentials. In Modern Methods and
Algorithms of Quantum Chemistry; John von Neumann Institute for
Computing: Ju¨lich, 2000; Vol. 1, p 479.
The coordination modes of the Zn-alkyne complexes were
further validated by computational methods using the Gaussi-

4018 Organometallics, Vol. 26, No. 16, 2007
BukhaltseV et al.
Table 4. Crystal Structure Information for Complexes 2a
and 6
2a
6
empirical formula
fw
tempe (K)
C62H68O2Zn2·C5H12
1048.05
110(2)
C64H69F3O3Zn2
1073.93
110(2)
wavelength (Å)
radiation type
cryst syst
space group
unit cell dimens
a (Å)
0.71073
Mo KR
monoclinic
P2/c
0.71073
Mo KR
triclinic
P1h
23.3100(3)
12.3369(2)
20.4060(5)
90.00
105.4498(6)
90.00
10.2094(4)
14.1816(4)
19.7097(7)
104.3222(12)
98.4218(17)
96.127(3)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
cell volume (Å3)
Z
5656.16(18)
4
2704.58(16)
2
calcd density (g m-3
cryst descrip
crystal size (nm)
θ range for data
collection (deg)
index ranges
)
1.231
1.319
colorless plates
0.50 × 0.30 × 0.10
2.26 to 27.51
colorless prisms
0.30 × 0.25 × 0.25
1.41 to 28.28
Figure 3. ORTEP structures (50% probability) of molecules of 6.
Hydrogen atoms are omitted for clarity. Labels C1 and C1′, and
C2 and C2′, are used to allow better comparison between the alkyne
ligands on each side. The corresponding atoms are not symmetry
related. Selected distances (Å) and angles (deg): Zn1-O1 2.006-
(3), Zn1-O2 1.973(3), Zn1-C1 3.1152(39), Zn1-C2 2.8706(38),
Zn1-C1′ 3.1719(42), Zn1-C2′ 2.9222(39), Zn1sZn2 3.0517,
Zn1-C3 1.944(5), Zn2-C4 1.929(5); C3-Zn1-O2 137.70(19),
C3-Zn1-O1 143.38(19), O1-Zn1-O2 78.72(11).
-28 e h e 27
-15 e k e 0
0 e l e 15
0 e h e 12
-17 e k e 17
-24 e l e 23
10 498/7856
no. of reflns collected/
unique
refinement method
goodness-of-fit
no. of data/restrains/
params
10 967/7889
full-matrix F2
1.012
10 967/1/628
full-matrix F2
1.044
10 498/0/658
high-purity nitrogen over activated 4 Å molecular sieves. All
deuterated solvents were stored under high-purity nitrogen over 3
Å molecular sieves. Commercially available reagents were pur-
chased from Aldrich and used as received. The NMR spectra were
recorded on Bruker AC 200 MHz and Bruker AMX 400 MHz
spectrometers. 1H and 13C NMR signals are reported in ppm
R1(I > 2σ(I))
wR2(all data)
0.0552
0.0624
0.1382a
0.1620b
2
2
2
a w ) 1/[σ2(Fo ) + (0.0807P)2 + 6.7515P] where P ) (Fo + 2Fc )/3.
2
2
2
b w ) 1/[σ2(Fo ) + (0.0967P)2 + 3.4491P] where P ) (Fo + 2Fc )/3.
1
Scheme 3
downfield from TMS. H signals are referenced to the residual
proton of a deuterated solvent (7.26 ppm for CDCl3, 7.15 ppm for
C6D6). For 13C NMR spectra, the following signals were used as a
reference: 77.36 ppm for CDCl3, 128.62 ppm for C6D6. 19F
chemical shifts are reported in ppm downfield from CClF3. All ∆δ
13C{1H} NMR measurements were performed at 22 °C in C6D6
unless stated otherwise. Elemental analyses were performed in the
laboratory for microanalysis at the Hebrew University of Jerusalem.
The high-resolution mass spectra were recorded at the Maiman
Institute for Proteome Research at Tel Aviv University.
General Procedure for the Preparation of Ligands 1a-e. All
reactions were carried out under an inert atmosphere of pure
nitrogen using 10 mol % of a Pd catalyst, 250 mol % of CuI, 4
equiv of DBU, and 3 equiv of acetylene. A typical procedure is
reported below.
3.144 Å, respectively. Interestingly, the calculations also show
a slight tilt of the methyl group toward the electron-poor alkyne
(Zn2-Zn1-C3 angle of 172.5° versus 176.4° in the experi-
mental structure), suggesting that there is some tendency of the
Zn1 center to be in a tetrahedral configuration with C3, O1,
O2, and the electron-donating alkyne moiety as ligands.
In conclusion, we showed that the organozinc π-interactions
can be directly tuned and observed in both solution and the
solid state. As no back-bonding has been shown for zinc, more
electron-rich alkynes form stronger bonds to the metal center.
Although the interactions are generally weak, our observations
support the notion that π-interactions with organozinc reagents
exist in solution and, thus, can influence their reactivity in
catalytic transformations.
1a. To a mixture of P(t-Bu)3H+BF4- (16 mg, 0.055 mmol) and
Pd2dba3 (12.5 mg, 0.014 mmol) dissolved in 10 mL of dry DMF
were added CuI (250 mg, 1.31 mmol), DBU (334 mg, 2.20 mmol),
phenylacetylene (169 mg, 1.65 mmol), and bis(OTf)-p-tert-butylcalix-
[4]arene (500 mg, 0.55 mmol), and the mixture was heated at
100 °C for 4 h. The solvent was evaporated on a rotary evaporator,
and the resulting crude product was dissolved in CH2Cl2 (40 mL)
and washed with saturated aqueous NH4Cl (20 mL) and H2O (20
mL). Drying the CH2Cl2 extract over MgSO4 followed by solvent
removal under vacuum gave the crude product. Precipitation from
CH2Cl2/MeOH afforded the pure product (400 mg, 89% yield).
1
1a. H NMR δ, ppm: 0.98 (18H, s, t-Bu), 1.36 (18H, S, t-Bu),
2
2
3.64 (4H, d, JHH ) 13.5 Hz, CH2), 4.96 (4H, d, JHH ) 13.5 Hz,
CH2), 6.04 (2H, s, OH), 6.84-6.87 (4H, m, Ar-H), 6.93 (4H, s,
Ar-H), 6.99-7.02 (2H, m, Ar-H), 7.18 (4H, s, Ar-H), 7.51-
7.55 (4H, m, Ar-H). 13C NMR δ, ppm: 30.93, 32.00 (CMe3),
34.13, 34.44 (CMe3), 37.29 (CH2), 87.95, 98.14 (CtC), all aromatic
(s): 119.48, 123.85, 124.68, 125.91, 128.19, 128.34, 129.00, 132.06,
142.15, 142.34, 150.94, 152.00.
Experimental Part
General Information. All operations with air- and moisture-
sensitive compounds were performed in a nitrogen-filled Innovative
Technology glovebox. All solvents were degassed and stored under

Tunable π-Interactions in Monomeric Organozinc Complexes
Organometallics, Vol. 26, No. 16, 2007 4019
1b. The compound was obtained in 75% yield after purification
by column chromatography. 1H NMR δ, ppm: 0.99 (18H, s, t-Bu),
δ, ppm: -14.00 (ZnCH3), -7.57 (ZnCH3), 31.16, 31.99 (CMe3),
34.27, 34.92 (CMe3), 40.12 (CH2), 90.10, 106.05 (CtC), all
aromatic (s): 123.98, 125.95, 126.08, 127.50, 128.52, 128.84,
131.24, 132.41, 141.38, 141.93, 152.13, 158.65. HR-MS M-Me:
measd (calcd) 957.3531 (957.3562), C62H68O2Zn2.
2
1.38 (18H, S, t-Bu), 3.11 (6H, s, CH3), 3.67 (4H, d, JHH ) 13.6
2
Hz, CH2), 5.03 (4H, d, JHH ) 13.6 Hz, CH2), 6.24 (2H, s, OH),
6.48 (4H, m, Ar-H), 6.95 (4H, s, Ar-H), 7.23 (4H, s, Ar-H),
7.34 (4H, m, Ar-H). 13C NMR δ, ppm: 30.95, 32.03 (CMe3), 34.13,
34.42 (CMe3), 37.28 (CH2), 54.75 (OCH3), 86.73, 98.26 (CtC),
all aromatic (s): 114.37, 119.78, 124.65, 125.86, 128.31, 129.09,
133.63, 134.43, 141.98, 142.31, 150.65, 160.02. HR-MS: M+Na
measd (calcd) 899.5072 (899.5010), C62H68O4.
1
2b. H NMR δ, ppm: -2.20 (3H, s, ZnCH3), -0.20 (3H, s,
ZnCH3), 1.10 (18H, s, t-Bu), 1.37 (18H, s, t-Bu), 3.11 (6H, s,
2
2
OCH3), 3.82 (4H, d, JHH ) 14.0 Hz, CH2), 5.33 (4H, d, JHH
)
14.0 Hz, CH2), 6.55 (4H, m, Ar-H), 7.24 (4H, s, Ar-H), 7.33
(4H, m, Ar-H), 7.35 (4H, s, Ar-H). 13C NMR δ, ppm: -14.16
(ZnCH3), -7.71 (ZnCH3), 31.30, 31.94 (CMe3), 34.27, 34.89
(CMe3), 40.34 (CH2), 54.59 (OCH3) 89.10, 106.59 (CtC), all
aromatic (s):116.18, 125.50, 128.78, 131.35, 133.41, 133.74, 134.72,
140.90, 141.83, 151.63, 158.75, 160.50. FAB-MS: measured (calcd)
1036 (1036). Anal. for C64H72O4Zn2: found (calcd) C 74.11 (74.19);
H 7.04 (7.00).
1c. The compound was obtained in 65% yield after purification
by column chromatography. 1H NMR δ, ppm: 0.99 (18H, s, t-Bu),
2
1.37 (18H, s, t-Bu), 2.08 (6H, s, CH3), 3.64 (4H, d, JHH ) 13.5
2
Hz, CH2), 5.00 (4H, d, JHH ) 13.5 Hz, CH2), 6.14 (2H, s, OH),
6.70 (4H, m, Ar-H), 6.94 (4H, s, Ar-H), 7.18 (4H, s, Ar-H),
7.50 (4H, m, Ar-H). 13C NMR δ, ppm: 21.49 (CMe3), 30.93, 32.02
(CMe3), 34.12, 34.42 (CMe3), 37.26 (CH2), 87.40, 98.37 (CtC),
all aromatic (s): 119.40, 124.65, 125.86, 129.03, 129.50, 132.10,
132.79, 137.91, 139.47, 142.05, 150.78, 152.03. HR-MS: M+Na:
measd (calcd) 867.5049 (867.5112), C62H68O2.
1
2c. H NMR δ, ppm: -2.21 (3H, s, ZnCH3), -0.24 (3H, s,
ZnCH3), 1.08 (18H, s, t-Bu), 1.37 (18H, s, t-Bu), 1.92 (6H, s, CH3),
2
2
3.81 (4H, d, JHH ) 14.0 Hz, CH2), 5.32 (4H, d, JHH ) 14.0 Hz,
CH2), 6.76 (4H, m, Ar-H), 7.23 (4H, s, Ar-H), 7.32 (4H, m, Ar-
H), 7.34 (4H, s, Ar-H). 13C NMR δ, ppm: -14.10 (ZnCH3), -7.60
(ZnCH3), 21.42 (CMe3), 31.19, 32.01 (CMe3), 34.27, 34.90 (CMe3),
40.15 (CH2), 89.57, 106.43 (CtC), all aromatic (s): 119.43, 125.93,
127.48, 129.38, 131.30, 132.43, 139.03, 139.45, 141.19, 141.85,
151.90, 158.71. FAB-MS: M-Me measd (calcd) 988 (988). Anal.
for C64H72O2Zn2: found (calcd) C 76.62 (76.56); H 7.27 (7.23).
1d. The compound was obtained in 70% yield after purification
by column chromatography. 1H NMR δ, ppm: 0.98 (18H, s, t-Bu),
1.35 (18H, s, t-Bu), 3.66 (4H, d, 2JHH ) 13.6 Hz, CH2), 4.87 (4H,
2
d, JHH ) 13.6 Hz, CH2), 5.81 (2H, s, OH), 6.94 (4H, s, Ar-H),
7.08 (4H, m, Ar-H), 7.19 (4H, s, Ar-H), 7.28 (4H, m, Ar-H).
13C NMR δ, ppm: 30.80, 30.85, 31.93 (CMe3), 34.15, 34.49
(CMe3), 37.23 (CH2), 90.32, 96.51 (CtC), all aromatic (s): 118.68,
124.86, 125.53, 126.04, 127.19, 127.82, 128.31, 132.06, 142.34,
142.85, 151.76. 19F NMR δ, ppm: -63.33 (6F, s, CF3); HR-MS:
M+Na: measd (calcd) 975.4479 (975.4546), C62H62O2F6. Anal.
for C62H62F6O2: found (calcd) C 77.65 (78.13); H 6.67 (6.56).
1
2d. H NMR δ, ppm: -2.21 (3H, s, ZnCH3), -0.39 (3H, s,
ZnCH3), 1.07 (18H, s, t-Bu), 1.36 (18H, s, t-Bu), 3.82 (4H, d, 2JHH
) 14.1 Hz, CH2), 5.19 (4H, d, 2JHH ) 14.1 Hz, CH2), 7.17 (8H, s,
Ar-H), 7.23 (4H, s, Ar-H), 7.36 (4H, s, Ar-H). 13C NMR δ,
ppm: -13.61 (ZnCH3), -7.03 (ZnCH3), 30.80 (CF3), 31.09, 31.95
(CMe3), 34.30, 35.03 (CMe3), 40.07 (CH2), 92.17, 104.16 (CtC),
all aromatic (s): 125.26, 125.50, 125.53, 126.12, 127.37, 127.65,
130.60, 132.42, 141.89, 142.38, 153.06, 158.38. 19F NMR δ, ppm:
-63.12 (6F, s, CF3). FAB-MS: M-Me measd (calcd) 1112 (1112).
Anal. for C64H66F6O2Zn2: found (calcd) C 68.97 (69.13); H 6.06
(5.98).
1e. The compound was obtained in 75% yield after purification
by column chromatography. 1H NMR δ, ppm: 0.95 (18H, s, t-Bu),
1.37 (18H, s, t-Bu), 3.60 (4H, d, 2JHH ) 13.7 Hz, CH2), 4.74 (4H,
2
d, JHH ) 13.7 Hz, CH2), 5.56 (2H, s, OH), 6.91 (4H, s, Ar-H),
7.16 (4H, s, Ar-H), 7.56 (2H, m, Ar-H), 7.81 (4H, m, Ar-H).
13C NMR δ, ppm: 30.22, 30.77, 31.92 (CMe3), 34.16, 34.51
(CMe3), 37.09 (CH2), 91.35, 94.81 (CtC), all aromatic (s): 118.04,
121.83, 124.94, 126.12, 128.94, 131.05, 131.90, 132.57, 142.56,
143.13, 151.45, 152.24. 19F NMR δ, ppm: -63.74 (12F, s, CF3).
1
2e. H NMR δ, ppm: -2.26 (3H, s, ZnCH3), -0.48 (3H, s,
ZnCH3), 1.04 (18H, s, t-Bu), 1.36 (18H, s, t-Bu), 3.77 (4H, d, 2JHH
) 14.0 Hz, CH2), 5.06 (4H, d, 2JHH ) 14.0 Hz, CH2), 7.22 (4H, s,
Ar-H), 7.33 (4H, m, Ar-H), 7.47 (2H, s, Ar-H), 7.79 (4H, s,
Ar-H). 13C NMR δ, ppm: -13.81 (ZnCH3), -6.94 (ZnCH3), 30.71
(CF3), 31.00 (CMe3), 31.58 (CF3), 31.91 (CMe3), 34.30, 35.03
(CMe3), 39.90 (CH2), 93.01, 101.96 (CtC), all aromatic (s):
121.85, 122.23, 124.36, 126.17, 130.79, 131.70, 132.13, 132.47,
142.21, 142.65, 153.73, 158.19. 19F NMR δ, ppm: -62.51 (12F,
s, CF3). FAB-MS: M-Me measd (calcd) 1231 (1231); C66H64F12O2-
Zn2.
Preparation of 5. Ligand 5 was prepared following the general
procedure but using the mixture of two acetylenes: 1.2 equiv of
4-ethynylanisole and 0.9 equiv of 4-ethynyltrifluorotoluene. After
purification by silica column chromatography (hexane/CH2Cl2 as
eluent), the pure product was obtained in 20% yield.
5. 1H NMR δ, ppm: 0.98 (9H, s, t-Bu), 0.99 (9H, s, t-Bu), 1.36
2
(18H, s, t-Bu), 3.36 (3H, s, OCH3), 3.67 (4H, d, JHH ) 13.6 Hz,
CH2), 4.91 (2H, d, 2JHH ) 13.6 Hz, CH2), 4.97 (2H, d, 2JHH ) 13.6
Hz, CH2), 6.01 (2H, s, OH), 6.51 (2H, ABm, Ar-H), 6.94 (2H, s,
Ar-H), 6.95 (2H, s, Ar-H), 7.19 (4H, s, Ar-H), 7.37 (2H, ABm,
Ar-H), 7.43 (2H, ABm, Ar-H). 13C NMR δ, ppm: 30.21 (CF3),
30.88, 30.92, 31.98 (CMe3), 34.14, 34.40, 34.43 (CMe3), 37.26
(CH2), 54.76 (OMe), 86.55, 98.52 (CtC, Ar-OMe), 90.63, 96.27
(CtC, Ar-CF3), all aromatic (s): 114.40, 115.60, 118.87, 119.61,
124.72, 124.80, 125.87, 126.01, 128.89, 129.07, 132.26, 133.47,
141.81, 142.40, 142.58, 150.78, 151.55, 151.93, 160.41, 160.66.
HR-MS: measd (calcd) 914.4888 (914.4880), C62H65O3F3.
6. 1H NMR δ, ppm: -2.21 (3H, s, ZnCH3), -0.30 (3H, s,
ZnCH3), 1.08 (9H, s, t-Bu), 1.09 (9H, s, t-Bu), 1.37 (18H, s, t-Bu),
3.07 (3H, s, OCH3), 3.80 (2H, d, 2JHH ) 14.1 Hz, CH2), 3.83 (2H,
d, 2JHH ) 13.9 Hz, CH2), 5.25 (2H, d, 2JHH ) 13.9 Hz, CH2), 5.27
2
(2H, d, JHH ) 14.1 Hz, CH2), 6.53 (2H, m, Ar-H), 7.23 (4H, s,
Ar-H), 7.28-7.35 (10H, m, Ar-H). 13C NMR δ, ppm: -13.93
(ZnCH3), -7.44 (ZnCH3), 30.21 (CF3), 31.12, 31.18, 31.98 (CMe3),
34.28, 34.91, 34.98 (CMe3), 40.08, 40.19 (CH2), 54.65 (OMe),
88.94, 107.32 (CtC, Ar-OMe), 92.42, 103.58 (CtC, Ar-CF3),
all aromatic (s): 125.93, 126.12, 126.28, 127.52, 127.58, 128.68,
129.09, 131.14, 131.21 132.38, 134.16, 134.43, 140.79, 141.98,
142.08, 151.95, 152.74, 158.59, 160.66, 160.80. Anal. for C64H69F3O3-
Zn2: found (calcd) C 71.22 (71.57); H 6.75 (6.48).
General Procedure for the Preparation of Complexes 2-4
and 6. To a solution of the free ligand (1 or 5) in 2 mL of dry
toluene was added a solution of ZnMe2 (2.0 M in toluene, 2.5 equiv,
30 µL, 0.061 mmol). The resulting mixture was stirred at room
temperature for 8 h, and the volatiles were evaporated, giving the
pure product as an air-sensitive white solid in 100% yield.
1
3a (using ZnEt2 1.0 M in hexane). H NMR δ, ppm: -1.37
2
3
(2H, q, JHH ) 7.9 Hz, ZnCH2CH3), 0.01 (3H, t, JHH ) 7.9 Hz,
1
2a. H NMR δ, ppm: -2.22 (3H, s, ZnCH3), -0.30 (3H, s,
ZnCH2CH3), 0.51 (2H, q, 2JHH ) 8.0 Hz, ZnCH2CH3), 1.14 (18H,
ZnCH3), 1.08 (18H, s, t-Bu), 1.37 (18H, s, t-Bu), 3.79 (4H, d, 2JHH
s, t-Bu), 1.24 (3H, t, JHH ) 8.0 Hz, ZnCH2CH3), 1.36 (18H, s,
3
2
2
2
) 14.0 Hz, CH2), 5.29 (4H, d, JHH ) 14.0 Hz, CH2), 6.91-6.92
t-Bu), 3.80 (4H, d, JHH ) 13.9 Hz, CH2), 5.30 (4H, d, JHH )
(6H, m, Ar-H), 7.22 (4H, s, Ar-H), 7.34 (8H, s, Ar-H). 13C NMR
13.9 Hz, CH2), 6.92-6.94 (6H, m, Ar-H), 7.31 (4H, s, Ar-H),

4020 Organometallics, Vol. 26, No. 16, 2007
BukhaltseV et al.
7.32 (4H, s, Ar-H), 7.40-7.42 (4H, m, Ar-H). 13C NMR δ,
ppm: -2.60 (ZnCH2CH3), 5.56 (ZnCH2CH3), 11.22 (ZnCH2CH3),
12.78 (ZnCH2CH3), 31.05, 32.02 (CMe3), 34.24, 35.07 (CMe3),
40.19 (CH2), 89.60, 105.54 (CtC), all aromatic (s): 123.98, 125.89,
126.25, 127.58, 128.53, 128.88, 130.74, 132.21, 141.07, 142.00,
152.57, 159.20. FAB-MS: M-Et measd (calcd) 974 (974). Anal.
for C64H72O2Zn2: found (calcd) C 76.20 (76.56); H 7.22 (7.23).
20.64 Hz), -157.31 (1F, t, JFF ) 18.6 Hz) -158.85 (1F, t, JFF )
18.6 Hz), -161.08 (2F, m), -163.28 (2F, m). HR-MS: M+H
measd (calcd) 1277.3213 (1277.3246); C72H63O2F10Zn2.
1
4b. H NMR δ, ppm: 0.72 (18H, s, t-Bu), 1.43 (18H, s, t-Bu),
3.18 (6H, s, OCH3), 3.81 (4H, d, 2JHH ) 14.2 Hz, CH2), 5.30 (4H,
d, 2JHH ) 14.2 Hz, CH2), 6.42 (4H, m, Ar-H), 6.93 (4H, m, Ar-
H), 7.32 (4H, s, Ar-H), 7.40 (4H, s, Ar-H). 13C NMR δ, ppm:
30.30, 31.89 (CMe3), 34.43, 34.59 (CMe3), 40.22 (CH2), 54.89
(OCH3), 88.32, 108.67 (CtC), all aromatic (s): 113.96, 125.55,
127.01, 129.34, 130.83, 133.66, 140.68, 143.69, 152.24, 157.36,
161.02. 19F NMR δ, ppm: -114.23 (2F, d, JFF ) 16.6 Hz), -116.23
(2F, d, JFF ) 19.0 Hz), -158.45 (1F, t, JFF ) 19.5 Hz) -160.00
(1F, t, JFF ) 19.0 Hz), -162.46 (2F, m), -164.35 (2F, m). FAB-
MS: measd (calcd) 1340 (1340); C74H66F10O4Zn2.
1
2
3b. H NMR δ, ppm: -1.34 (2H, q, JHH ) 7.9 Hz, ZnCH2-
3
2
CH3), 0.03 (3H, t, JHH ) 7.9 Hz, ZnCH2CH3), 0.62 (2H, q, JHH
) 7.9 Hz, ZnCH2CH3), 1.16 (18H, s, t-Bu), 1.33 (3H, t, overlapped
with t-Bu at 1.36), 1.36 (18H, s, t-Bu), 3.13 (6H, s, OCMe3), 3.84
(4H, d, 2JHH ) 13.8 Hz, CH2), 5.35 (4H, d, 2JHH ) 13.8 Hz, CH2),
6.56 (4H, m, Ar-H), 7.33 (8H, s, Ar-H), 7.40 (4H, m, Ar-H).
13C NMR δ, ppm: -2.75 (ZnCH2CH3), 5.12 (ZnCH2CH3), 11.27
(ZnCH2CH3), 12.94 (ZnCH2CH3), 31.09, 32.03 (CMe3), 34.23,
35.04 (CMe3), 40.27 (CH2), 54.66 (OCMe3), 88.59, 106.06 (Ct
C), all aromatic (s): 114.39, 125.86, 127.54, 128.68, 130.86, 133.88,
134.43, 140.58, 141.91, 151.07, 159.29, 160.51.
1
4c. H NMR δ, ppm: 0.71 (18H, s, t-Bu), 1.43 (18H, s, t-Bu),
2
1.95 (6H, s, CH3), 3.79 (4H, d, JHH ) 14.2 Hz, CH2), 5.30 (4H,
d, 2JHH ) 14.2 Hz, CH2), 6.66 (4H, m, Ar-H), 6.92 (4H, m, Ar-
H), 7.08 (4H, s, Ar-H), 7.39 (4H, s, Ar-H). 13C NMR δ, ppm:
30.27, 31.89 (CMe3), 34.43, 34.61 (CMe3), 40.18 (CH2), 88.72,
108.30 (CtC), all aromatic (s): 119.44, 125.56, 126.71, 128.86,
130.78, 131.89, 139.44, 139.98, 141.05, 143.74, 152.54, 160.62.
19F NMR δ, ppm: -113.24 (2F, d, JFF ) 18.3 Hz), -115.45 (2F,
d, JFF ) 21.2 Hz), -157.40 (1F, t) -160.08 (1F, t), -161.55 (2F,
t), -163.34 (2F, t).
1
2
3c. H NMR δ, ppm: -1.35 (2H, q, JHH ) 7.9 Hz, ZnCH2-
3
2
CH3), 0.02 (3H, t, JHH ) 7.9 Hz, ZnCH2CH3), 0.58 (2H, q, JHH
) 8.0 Hz, ZnCH2CH3), 1.15 (18H, s, t-Bu), 1.30 (3H, t, JHH
3
)
8.0 Hz, ZnCH2CH3), 1.36 (18H, s, t-Bu), 1.93 (6H, s, CMe3), 3.82
(4H, d, 2JHH ) 13.9 Hz, CH2), 5.34 (4H, d, 2JHH ) 13.8 Hz, CH2),
6.77 (4H, m, Ar-H), 7.31 (4H, s, Ar-H), 7.33 (4H, s, Ar-H),
7.39 (4H, m, Ar-H). 13C NMR δ, ppm: -2.68 (ZnCH2CH3), 5.36
(ZnCH2CH3), 11.25 (ZnCH2CH3), 12.88 (ZnCH2CH3), 21.44 (CMe3),
31.07, 32.03 (CMe3), 34.24, 35.06 (CMe3), 40.23 (CH2), 89.09,
105.91 (CtC), all aromatic (s): 119.44, 125.87, 127.56, 129.39,
130.81, 132.24, 139.05, 139.45, 140.88, 141.93, 151.32, 159.26.
1
4d. H NMR δ, ppm: 0.69 (18H, s, t-Bu), 1.43 (18H, s, t-Bu),
2
2
3.79 (4H, d, JHH ) 14.2 Hz, CH2), 5.17 (4H, d, JHH ) 14.2 Hz,
CH2), 6.75 (4H, m, Ar-H), 7.03 (4H, m, Ar-H), 7.08 (4H, s, Ar-
H), 7.40 (4H, s, Ar-H). 13C NMR δ, ppm: 30.17 (CMe3), 30.22
(CF3), 31.83 (CMe3), 34.46, 34.73 (CMe3), 40.72 (CH2), 90.85,
105.65 (CtC), all aromatic (s): 124.29, 126.52, 127.17, 128.92,
129.18, 130.48, 131.45, 132.62, 141.80, 144.27, 153.73, 157.01.
19F NMR δ, ppm: -62.68 (6F, s, CF3), -113.46 (2F, d, JFF ) 20
Hz), -115.36 (2F, d, JFF ) 20 Hz), -156.89 (2F, m) -160.09
(2F, m), -162.91 (2F, m). FAB-MS: measd (calcd) 1392 (1392);
C72H60F16O2Zn2.
1
2
3d. H NMR δ, ppm: -1.36 (2H, q, JHH ) 7.9 Hz, ZnCH2-
3
2
CH3), 0.00 (3H, t, JHH ) 7.9 Hz, ZnCH2CH3), 0.39 (2H, q, JHH
) 8.0 Hz, ZnCH2CH3), 1.09 (3H, m, overlapped with t-Bu at 1.13),
1.13 (18H, s, t-Bu), 1.36 (18H, s, t-Bu), 3.82 (4H, d, JHH ) 13.8
2
Hz, CH2), 5.21 (4H, d, 2JHH ) 13.8 Hz, CH2), 7.20-7.27 (8H, m,
Ar-H), 7.32 (4H, s, Ar-H), 7.34 (4H, s, Ar-H). 13C NMR δ,
ppm: -2.17 (ZnCH2CH3), 6.18 (ZnCH2CH3), 11.12 (ZnCH2CH3),
12.54 (ZnCH2CH3), 30.23, 30.719 (CF3), 30.96, 31.96 (CMe3),
34.26, 35.15 (CMe3), 40.14 (CH2), 91.66, 103.67 (CtC), all
aromatic (s): 121.77, 125.46, 126.04, 129.33, 130.11, 130.49,
130.75, 132.22, 141.57, 142.43, 152.50, 158.94. 19F NMR δ, ppm:
-63.07 (6F, s, CF3). FAB-MS: M-Et measd (calcd) 1111(1111);
C66H70F6O2Zn2.
Computational Methods. All calculations were carried out using
Gaussian 03 Revision C.02.19 Geometry optimizations were carried
out using the PBE0 DFT exchange-correlation functional together
with the SDD basis set. PBE0 is the hybride variant of PBE
(Perdew, Burke, and Ernzerhof’s nonempirical GGA functional)
and contains 25% HF exchange.20 This functional has been shown
to yield more reliable reaction barrier heights than B3LYP23 or other
“conventional” exchange-correlation functionals, without sacrific-
ing performance of other properties.24 SDD is the combination of
the Huzinaga-Dunning double-ú basis set21 on lighter elements
with the Stuttgart-Dresden basis set-RECP combination22 on
transition metals. Geometries were optimized using the default
pruned (75 302) grid.
1
2
3e. H NMR δ, ppm: -1.42 (2H, q, JHH ) 8.0 Hz, ZnCH2-
CH3), -0.06 (3H, t, 3JHH ) 8.0 Hz, ZnCH2CH3), 0.27 (2H, q, 2JHH
) 8.1 Hz, ZnCH2CH3), 1.09 (3H, t, overlapped with t-Bu), 1.11
2
(18H, s, t-Bu), 1.36 (18H, s, t-Bu), 3.77 (4H, d, JHH ) 13.9 Hz,
2
CH2), 5.07 (4H, d, JHH ) 13.8 Hz, CH2), 7.29 (4H, s, Ar-H),
7.30 (4H, s, Ar-H), 7.49 (2H, s, Ar-H), 7.86 (4H, s, Ar-H). 13
C
NMR δ, ppm: -2.31 (ZnCH2CH3), 5.89 (ZnCH2CH3), 11.01
(ZnCH2CH3), 12.07 (ZnCH2CH3), 30.22 (CF3), 30.59 (CF3), 30.89,
31.95 (CMe3), 34.29, 35.19 (CMe3), 39.98 (CH2), 92.54, 101.51
(CtC), all aromatic (s): 121.88, 122.21, 124.96, 126.12, 130.29,
131.79, 132.14, 132.48, 141.92, 142.68, 153.19, 158.71. 19F NMR
δ, ppm: -62.53 (12F, s, CF3).
Acknowledgment. We thank the US-Israel Binational
Science Foundation for financial support and Prof. Ilan Marek
for valuable discussions.
Supporting Information Available: Crystallographic informa-
tion for complexes 2a and 6 (CIF). Complete ref 19. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
4a. H NMR δ, ppm: 0.70 (18H, s, t-Bu), 1.43 (18H, s, t-Bu),
2
2
3.77 (4H, d, JHH ) 14.2 Hz, CH2), 5.27 (4H, d, JHH ) 14.2 Hz,
CH2), 6.74-6.80 (6H, m, Ar-H), 6.92-6.94 (4H, m, Ar-H), 7.07
(4H, s, Ar-H), 7.39 (4H, s, Ar-H). 13C NMR δ, ppm: 30.23,
31.86 (CMe3), 34.42, 34.62 (CMe3), 40.11 (CH2), 89.12, 107.84
(CtC), all aromatic (s): 122.24, 125.58, 125.69, 126.43, 129.25,
129.34, 130.72, 131.78, 141.24, 143.82, 152.78, 157.25. 19F NMR
OM070213Y
(23) (a) Stevens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J.
Phys. Chem. 1994, 98, 11623. (b) Becke, A. D. J. Chem. Phys. 1993, 98,
5648.
(24) Quintal, M. M.; Karton, A.; Iron, M. A.; Boese, A. D.; Martin, J.
M. L. J. Phys. Chem. A 2006, 110, 709.
δ, ppm: -113.26 (2F, d, JFF ) 19.17 Hz), -115.67 (2F, d, JFF
)