Coordination to RMg+ and RZn+ Cations
Organometallics, Vol. 19, No. 23, 2000 4817
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temperatures37 that slow the allylic isomerization
(eq 13) that at ambient temperature is rapid relative
DMSO. H NMR (0.3 M, 300 MHz): δ 0.28 (q, J ) 8.0 Hz,
2, CH2Zn), 1.27 (t, J ) 8.0 Hz, 3, CH3CH2), 1.71 (s, 6, CH3S),
6.26 (s, 5, CH).
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HMP A. H NMR (0.3 M, 200 MHz): δ 0.29 (q, J ) 8.0 Hz,
2, CH2Zn), 1.38 (t, J ) 8.0 Hz, 3, CH3CH2), 2.20 (d, J ) 9.5
Hz, 9, CH3N), 6.53 (s, 5, CH).
P r ep a r a tion of RM(Coor d )+P h 4C5H- Solu tion s. In a
typical preparation of RZn(coord)+, an R2Zn compound (0.050
mmol) and Ph4C5H2 (18 mg, 0.050 mmol) were weighed into a
container, and a benzene-d6 solution of the coordinating agent
(0.50 mL, 0.10 M, 0.050 mmol) was added. The preparation
was stirred (stirring bar) for a few minutes, and the resulting
green solution was sealed into an NMR tube. The NMR tube
was heated at 70 °C for 2 h and then examined by 1H NMR
spectroscopy to verify that reaction was complete. The Ph4C5H-
absorptions in 1H NMR spectra, essentially identical for all
solutions, were assigned with the aid of NOE and decoupling
experiments. The absorption at δ 6.77, which because of its
position and because it is a singlet must be due to H1, has a
NOE effect with the doublet at δ 7.61 but not the doublet at δ
7.47. Therefore, the δ 7.61 doublet is assigned to the o-H of
the R-phenyl and the δ 7.47 doublet to the o-H of the â-phenyl.
Decoupling experiments that show connectivities to these H’s
then permitted assigning the other absorptions: (300 MHz) δ
6.77 (s, 1, Ph4C5H-), 6.94 (t, J ) 7.2 Hz, 2, p-H of R-Ph), 7.09
(t, J ) 7.3 Hz, 2, p-H of â-Ph), 7.23 (t, J ) 7.6 Hz, 4, m-H of
R-Ph), 7.29 (t, J ) 7.5 Hz, 4, m-H of â-Ph), 7.47 (d, J ) 7.2 Hz,
4, o-H of â-Ph), 7.61 (d, J ) 7.5 Hz, 4, o-H of R-Ph). The
preparations of RMg(coord)+ solutions followed the same
procedure except that the NMR tube was heated at no more
than 50 °C for no longer than 20-30 min before examination
by 1H NMR spectroscopy to verify that reaction was complete.
Exch a n ge of RZn (coor d )+ w ith coor d *. The general
procedure is illustrated using N3 and N4 as the coordinating
agents. A benzene-d6 solution of N3 (0.50 mL, 0.10 M, 0.050
mmol) and the contents of an NMR tube containing a benzene-
d6 solution of RZn(N4)+Ph4C5H- (0.50 mL, 0.10 M, 0.050 mmol)
were added to a vial. Similar amounts of solutions of N4 and
of RZn(N3)+Ph4C5H- were added to another vial. The resulting
solutions were stirred for a few minutes (stirring bar), each
was then placed into an NMR tube, and the NMR tubes were
sealed. When K ) [RZn(coord)+][coord*]/[RZn(coord*)+][coord]
exceeded 100, an excess (ca. 5-fold) of coord was used to make
small absorptions of RMg(coord)+ and coord* larger and
integration more accurate. The NMR tubes were maintained
to the NMR time scale. We found, however, that
solutions with N3, N4, or 14N4 exhibit at ambient
temperature the absorptions expected for nonisomeriz-
ing (CH2dCMeCH2)2Zn (although with 14N4, absorp-
tions are broad); solutions with 9N3, 12N3, or 211C have
only one broad absorption for the allylic CH2 groups.
Coordination of the Zn by N3 and N4 must be more
effective than by the cyclic coordinating agents.38,39
Exp er im en ta l Section
Procedures involving organometallic compounds were per-
formed under a nitrogen atmosphere using Schlenk tech-
niques, a glovebox, and a vacuum line. Nitrogen was purified
by passing through columns of manganese oxide oxygen
scavenger and molecular sieves (4 Å). Glassware was dried in
an oven at 200 °C for at least 4 h prior to use. Benzene-d6
(Cambridge Isotope Laboratories) was stored over molecular
sieves (4 Å). Benzene (isotopically normal), pentane, dioxane,
and organic halides were distilled from CaH2; dioxane was
stored over molecular sieves (4 Å) under a nitrogen atmos-
phere. Diethyl ether and tetrahydrofuran were distilled from
sodium benzophenone ketyl immediately prior to use. TMEDA,
DMSO, and HMPA were distilled from CaH2 at reduced
pressure. Mg was “99.95%” (Aldrich Chemical Co.). Et2Hg
(Strem Chemicals) and all other chemicals (Aldrich Chemical
Co.) were used as received. NMR spectra were taken in
benzene-d6. 1H absorptions are reported relative to internal
C6D5H (taken as δ 7.15 ppm) using the following notations:
s, singlet; d, doublet; t, triplet; q, quartet; m, a more complex
multiplet; c, complex overlapping absorptions; b, broad. 13C
absorptions are reported relative to internal C6D6 (taken as δ
128.0). Solutions for NMR analysis were prepared in the
glovebox and transferred into NMR tubes, to which an exten-
sion of routine glass tubing had been added to facilitate sealing
with a flame. The NMR tube was capped temporarily with a
rubber septum, removed from the glovebox, immersed in liquid
nitrogen, and sealed at the extension.
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at 22 ( 1 °C. H NMR data were recorded when (depending
Rea ction s of EtZn Cp w ith Coor d in a tin g Agen ts. Solu-
tions were prepared in benzene-d6 having equal concentrations
(listed for each preparation) of EtZnCp and a coordinating
on the system, several hours to 2 days) it was evident that
the NMR spectra of the two solutions no longer were changing.
For K’s of 100 or so, more than 100 scans were taken to obtain
good signal-to-noise ratios for the smaller absorptions. Values
of K (in parentheses) obtained from RZn(coord)+ with coord*:
EtZn(211C)+ with N3* (3.5); EtZn(N3)+ with 211C* (1/3.7), N4*
(3.0), 12N3* (7.5), 14N4* (180); EtZn(N4)+ with N3* (1/3.1),
12N3* (2.2), 14N4* (48); EtZn(12N3)+ with N3* (1/7.3), N4*
(1/2.3) 14N4* (18); EtZn(14N4)+ with N3* (1/155), N4* (1/43),
12N3* (1/19), 9N3* (68); EtZn(9N3)+ with 14N4* (1/64); NpZn-
(211C)+ with 14N4* (50), N3* (171); NpZn(14N4)+ with 211C*
(1/54), N4* (2.1), 12N3* (2.2), N3* (4.6); NpZn(N4)+ with 14N4*
(1/2.0), 12N3* (1.1), N3* (1.7); NpZn(12N3)+ with 14N4* (1/
2.4), N4* (1.0), N3* (1.7); NpZn(N3)+ with 211C* (1/156),
14N4* (1/4.8), N4* (1/1.8), 12N3* (1/1.6). The values of K
obtained from a pair of solutions (RZn(coord)+ + coord* and
RZn(coord*) + coord) always were very similar. In studies of
NpZn(9N3)+ with N3, 14N4, or N4, absorptions of NpZn(N3)+,
NpZn(14N4)+, and NpZn(N4)+ were not detected at equilibri-
um.
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agent. The H NMR spectrum of EtZnCp is given for purposes
of comparison: (200 MHz) δ 0.26 (q, J ) 8.1 Hz, 2, CH2), 1.40
(t, J ) 8.0 Hz, 3, CH3), 6.03 (s, 5, CH).
14N4: P r ep a r a tion of EtZn (14N4)+EtZn Cp 2-. Compo-
1
nents were initially 0.6 M, but phase separation occurred. H
NMR (360 MHz, lower phase): δ -0.44 (q, J ) 8.2 Hz, 2, CH2-
Zn+), -0.20 (q, J ) 7.9 Hz, 2, CH2Zn-), 0.90-2.00 (c, 16, most
CH2’s of 14N4+), 1.06 (t, J ) 8.2 Hz, 3, CH3CH2Zn+), 1.34 (t,
J ) 8.1 Hz, 3, CH3CH2Zn-), 1.59 (s, 12, CH3N), 2.24 (bt, 4,
CHHCH2CHH), 6.25 (s, 10, CH).
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TMEDA. H NMR (0.4 M, 200 MHz): δ -0.15 (q, J ) 8.0
Hz, 2, CH2Zn), 1.39 (t, J ) 8.0 Hz, 3, CH3CH2), 1.52 (s, 4,
CH2N), 1.78 (s, 12, CH3N), 6.49 (s, 5, CH).
(37) Benn, R.; Hoffmann, E. G.; Lehmkuhl, H.; Nehl, H. J . Orga-
nomet. Chem. l978, 146, 103. Also see: Benn, R.; Grondey, H.;
Lehmkuhl, H.; Nehl, H.; Angermund, K.; Kru¨ger, C. Angew. Chem.,
Int. Ed. Engl. l987, 26, 1279.
(38) Coordination by 18C6 effectively reduces allylic isomerization,
but that is the consequence of forming a rotaxane structure.10
(39) Although solutions of (CH2dCMeCH2)2Zn in nonpolar solvents
at ambient temperature are prone to decompose, solutions containing
N3 and N4 seemed to be indefinitely stable and solutions containing
14N4 decomposed only slowly.
Exch a n ge of RMg(coor d )+ w ith coor d *. The solutions
were prepared as for RZn(coord)+ exchange except that an R2-
Mg solution (20 mg, 0.10 M, 0.0020 mmol) was weighed into
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the vial. H NMR absorptions generally were evident for the
Np2Mg, although their positions were somewhat altered by