Article
Organometallics, Vol. 30, No. 1, 2011 151
base [(TMEDA)Na(μ-TMP)(μ-tBu)Zn(tBu)] (1) produced
the three new selectively ortho-zincated crystalline complexes
[(TMEDA)Na(μ-TMP){μ-2-[1-C(O)NEt2]C6H4}Zn(tBu)] (3),
[(TMEDA)Na(μ-TMP){μ-2-(1-C(O)NEt2)(3-OMe)C6H3}Zn-
(tBu)] (4), and [(TMEDA)Na(μ-TMP){μ-2-(1-OC(O)NEt2)-
C6H4}Zn(tBu)] (6). Although the metalation regioselectiv-
ities observed in these reactions are not new, it is worth
stressing that these highly chemo- and regioselective reac-
tions are being performed at ambient temperatures with no
suggestion of complications in the form of side reactions.
This increased sensitivity can be exploited to trap and isolate
the metalated intermediates (prior to electrophilic quenching)
in clean, pure crystalline forms, which allows valuable insight
to be drawn on the structure of the intermediates both in the
solid state by X-ray crystallography and in solution by NMR
spectroscopy. Collectively, these results highlight the effi-
ciency of the synergic bimetallic bases, which is leading to the
emergence of AMMZn as a novel alternative to the estab-
lished DoM reaction via lithiation.
collected, 10 077 were unique, Rint=0.0345, R=0.0326, Rw=0.0723,
GOF=0.923, 366 refined parameters, max. and min. residual
electron density=0.505 and -0.392 e A-3
.
3
Crystal data for 6: C30H57N4NaO2Zn, M =594.16, mono-
clinic, P21/c, a=18.2070(4) A, b=10.3460(2) A, c=19.9460(4) A,
β=116.629(3)o, V=3358.68(12) A3, Z=4; 27 340 reflections
collected, 8907 were unique, Rint = 0.0304, R = 0.0287, Rw =
0.0602, GOF=0.894, 393 refined parameters, max. and min.
residual electron density=0.389 and -0.271 e A-3
.
3
Synthesis of [(TMEDA)Na(μ-TMP)(μ-tBu)Zn(tBu)], 1. nBuNa
(2 mmol, 0.16 g) was suspended in hexane (10 mL) and sonicated
for 10 min to form a fine dispersion. TMP(H) (2 mmol, 0.34 mL)
was added, and the subsequent yellow suspension was allowed to
t
stir for 1 h. In a separate Schlenk tube, freshly prepared Bu2Zn
(2 mmol, 0.36 g) was dissolved in hexane (10 mL) and transferred
to the already prepared NaTMP via cannula. TMEDA was then
introduced (2 mmol, 0.3 mL), and the resulting suspension was
gently heated to produce a homogeneous yellow solution to yield
an in situ mixture of 1, which was checked against an authentic
sample of 1 via NMR spectroscopy but then repeated several times
without further checking.
Synthesis of [(TMEDA)Na(μ-TMP){μ-2-[1-C(O)NEt2]C6H4}-
Zn(tBu)], 3. X-ray quality crystalline material was prepared by
treating the aforementioned hexane solution of 1 with N,N-
diethylbenzamide (2 mmol, 0.354 g), and the reaction mixture
was allowed to stir at ambient temperature for 18 h. Following
gentle heating, the orange solution was concentrated in vacuo
and transferred to a freezer for storage (-28 °C), where colorless
crystals of 3 were deposited overnight (0.63 g, 54%). Mp: 124 °C.
1H NMR (400.1 MHz, C6D6, 300 K): δ 7.94 (1H, d, 3J(H,H) =
7.23 Hz, meta), 7.21 (1H, t, 3J(H,H)=7.06 Hz, para), 6.99 (2H,
m, meta and ortho), 3.46-3.20 (3H, m, CH2-Ethyl), 2.93 (1H, m,
CH2-Ethyl), 1.99-1.88 (4H, m, γ- and β-TMP), 1.78 (4H, s,
CH2-TMEDA), 1.71 (12H, s, CH3-TMEDA), 1.57 (2H, m, β-
TMP), 1.52 (3H, s, CH3-TMP), 1.50 (12H, s, CH3-tBu and CH3-
TMP), 1.32 (3H, s, CH3-TMP), 1.21 (3H, s, CH3-TMP), 1.02
(3H, t, 3J(H,H)=7.14 Hz, CH3-Ethyl), 0.79 (3H, t, 3J(H,H) =
7.13 Hz, CH3-Ethyl). 13C NMR (100.6 MHz, C6D6, 300 K):
δ177.9 (CdO), 168.9 (Cortho-Zn), 145.8 (Cipso), 141.3 (Cmeta),
126.8 (Cpara), 123.3 and 123.1 (Cmeta and Cortho), 57.3 (CH2-
TMEDA), 52.8 (2 ꢀ R-TMP), 45.6 (CH3-TMEDA), 43.6 (CH2-
Ethyl), 40.7 (β-TMP), 39.7 (β-TMP), 38.3 (CH2-Ethyl), 37.4
(CH3-TMP), 35.8 (CH3-tBu), 35.2 (CH3-TMP), 34.6 (CH3-
TMP), 34.4 (CH3-TMP), 20.4 (γ-TMP), 20.2 (Cq-tBu), 13.9
(CH3-Ethyl), 12.9 (CH3-Ethyl).
Synthesis of [(TMEDA)Na(μ-TMP){μ-2-(1-C(O)NEt2)
(3-OMe)C6H3}Zn(tBu)], 4. N,N-Diethyl-3-methoxybenzamide
(2 mmol, 0.415 g) was introduced to the aforementioned hexane
solution of 1. To obtain a homogeneous solution, THF (2 mL)
was added, and the resulting reaction mixture was allowed to stir
at room temperature overnight. The dark orange solution was
concentrated in vacuo and stored in a refrigerator (5 °C) preceding
the growth of small, colorless block crystals of 4 (0.54 g, 44%).
Mp: 121 °C. 1H NMR (400.1 MHz, C6D6, 300 K): δ δ7.04 (1H, t,
3J(H,H)=7.72 Hz, meta), 6.68 (1H, d, 3J(H,H)=7.21 Hz, ortho),
6.51 (1H, d, 3J(H,H) = 7.98 Hz, para), 3.51 (3H, s, OCH3),
3.41-3.18 (3H, m, CH2-Ethyl), 3.01 (1H, m, CH2-Ethyl), 2.04
(1H, m, γ-TMP), 1.84 (5H, s, γ-TMP and CH2-TMEDA), 1.77
(12H, s, CH3-TMEDA), 1.62 (3H, s, CH3-TMP), 1.59 (3H, s,
CH3-TMP), 1.46 (9H, s, CH3-tBu), 1.34 (2H, m, β-TMP) 1.31
(3H, s, CH3-TMP), 1.28 (3H, s, CH3-TMP), 1.02 (3H, t, 3J(H,H)=
7.13 Hz, CH3-Ethyl), 0.81 (3H, t, 3J(H,H) = 7.13 Hz, CH3-
Ethyl). *From 2D HSQC and COSY experiments, the second β-
TMP resonance appears to be masked by the TMEDA signals
around 1.82 ppm. 13C NMR (100.6 MHz, C6D6, 300 K): δ
δ177.4 (CdO), 167.9 (Cortho-Zn), 155.3 and 146.3 (Cipso and
Experimental Section
Hexane and THF, purchased from Sigma Aldrich, were
distilled from sodium-benzophenone. All synthetic work was
carried out under a protective inert argon atmosphere using
standard Schlenk techniques. The 1H NMR spectroscopic
experiments were performed on a Bruker DPX400 spectrometer
with an operating frequency of 400.13 MHz. The 13C NMR
spectra were recorded on the same instrument at an operating
frequency of 100.62 MHz. All chemical shifts are quoted relative
to TMS standard at 0.00 ppm. The IR spectra were recorded on
a Perkin-Elmer Spectrum 100 FT-IR spectrometer, and elemen-
tal analyses were carried out on a Perkin-Elmer 2400 elemental
analyzer. Due to the extreme air and moisture sensitivity of 3, 4,
and 6, ideal analyses could not be obtained. Melting/decom-
€
position points were measured on a Buchi melting point B-545
t
apparatus. The syntheses of Bu2Zn14 and nBuNa39 were as
previously published.
X-ray Crystallography. All data were collected at 123(2) K on
an Oxford Diffraction Gemini S diffractometer with Mo KR
radiation (λ = 0.71073 A). Structures were solved using
SHELXS-97,40 while refinements were carried out on F2 against
all independent reflections by the full-matrix least-squares
method using the SHELXL-97 program.40 With the exception
of the atoms of the minor disorder component present in 6 all
non-hydrogen atoms were refined using anisotropic thermal
parameters. CCDC 793876 (3), 793877 (4), and 793878 (6) contain
the full supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
data_request/cif.
Crystal data for 3: C30H57N4NaOZn, M=578.16, monoclin-
ic, P21/n, a=10.4215(3) A, b = 16.4560(3) A, c=19.5649(4) A,
β = 94.868(2)o, V = 3343.20(13) A3, Z = 4; 28 026 reflections
collected, 9698 were unique, Rint =0.0450, R = 0.0348, Rw =
0.0637, GOF=0.841, 347 refined parameters, max. and min.
residual electron density=0.512 and -0.412 e A-3
.
3
Crystal data for 4: C31H59N4NaO2Zn, M = 608.18, mono-
clinic, P21/c, a=16.3094(2) A, b = 10.3360(2) A, c=20.8204(4) A,
β = 98.105(2)o, V = 3474.72(10) A3, Z = 4. 34 313 reflections
(38) As found when recording NMR spectra of N,N-diethylbenza-
mide, N,N-diethyl-3-methoxybenzamide, and N,N-diethyl phenyl
O-carbamate in C6D6 solution during this work.
(39) Schade, C.; Bauer, W.; Schleyer, P. v. R. J. Organomet. Chem.
1985, 295, c25.
C
meta), 125.6 (Cmeta), 117.1 (Cortho), 107.1 (Cpara), 57.4 (CH2-
TMEDA), 53.9 (OCH3), 53.2 (2 ꢀ R-TMP), 45.7 (CH3-
TMEDA), 43.6 (CH2-Ethyl), 41.8 (β-TMP), 41.2 (β-TMP),
38.3 (CH2-Ethyl), 36.6 (CH3-TMP), 35.8 (CH3-tBu), 35.6
(40) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112.