Reactions of diorganocadmium compounds with other dialkylmetal compounds and macrocycles: Synthesis of organocadmate anions

Article abstract of DOI:10.1021/om001020c

Combining R₂Cd (R an alkyl or Ph group), the corresponding R₂Mg compound, and 1,4,8,11-tetramethyl-1,4,8,11-tetraazatetradecane, 2,1,1-cryptand, or 2,2,1-cryptand in solution quantitatively produces R₃Cd^-1 and R

Full text of DOI:10.1021/om001020c

Organometallics 2001, 20, 1569-1574
1569
Rea ction s of Dior ga n oca d m iu m Com p ou n d s w ith Oth er
Dia lk ylm eta l Com p ou n d s a n d Ma cr ocycles: Syn th esis of
Or ga n oca d m a te An ion s1
Hui Tang and Herman G. Richey, J r.*
Department of Chemistry, The Pennsylvania State University,
University Park, Pennsylvania 16802
Received November 27, 2000
Combining R2Cd (R an alkyl or Ph group), the corresponding R2Mg compound, and 1,4,8,-
11-tetramethyl-1,4,8,11-tetraazatetradecane, 2,1,1-cryptand, or 2,2,1-cryptand in solution
quantitatively produces R3Cd- and RMg(macrocycle)+ ions. Solutions obtained by combining
the same macrocycles with R2Cd alone or with R2Cd plus the corresponding R2Zn compound
do not contain significant amounts of ions; rapid exchange of R groups in these solutions,
however, may be due to formation of trace amounts of R3Cd- ions.
Combining a polar organometallic compound and a
coordinating agent can generate ate2 anions by transfer
of an organic group to an organometallic acceptor.
Syntheses of organomagnesate anions and coordinated
RMg+ cations (e.g., eq 1) are examples.3,4 The driving
tetramethyl-1,4,8,11-tetraazatetradecane) ions and NMR
information indicating the presence of several R3Cd-
RMg(14N4)+ species in solutions. In such salts, the
metal of the cation is so enveloped by the macrocycle
that it cannot form specific bonding interactions with
the anion. This note provides further information about
R3Cd-RMg(14N4)+ species, describes additional reac-
tions that might synthesize R3Cd- anions, and provides
information about exchange of R groups in some solu-
tions.
2 R2Mg + macrocycle f
R3Mg- + RMg(macrocycle)+ (1)
force is extensive coordination between O and N atoms
of a macrocycle and the metal of the resulting cation.
This potent ability to transfer “R-” provides an attrac-
tive way of generating new organoate species. We set
out to use this approach to synthesize triorganocadmate
anions (R3Cd-). The closest analogues that had been
studied by X-ray diffraction were some halogen-contain-
ing organocadmate anions shown to have polymeric
structures with bridging halogens.5,6 The only observa-
tions of solutions were of (CF3)3Cd-,6 an anion favored
by extremely electron-withdrawing groups. NMR stud-
ies of solutions prepared from RLi and R2Cd had
suggested formation of mixed species (1:1, 2:1, and 3:1),7
but these solutions certainly do not contain true orga-
nocadmate anions free of specific bonding to lithium.
An earlier report8 gave the X-ray structure of a solid
having Me3Cd- and MeMg(14N4)+ (14N4 ) 1,4,8,11-
Resu lts a n d Discu ssion
Benzene was the solvent except where noted. It has
been useful for studies of organometalate species since
(1) they usually are stable in it, (2) they often are equally
or more soluble in it than in solvents, such as diethyl
ether or THF, often used for polar organometallic
compounds, and (3) the deuterated version needed for
1H NMR studies is relatively inexpensive.
R2Cd a n d Ma cr ocycles. 1H NMR absorptions of
solutions prepared using different ratios of Et2Cd and
14N4 are almost the same (within <0.1 ppm) as those
of Et2Cd and 14N4 when each is the only solute.
However, the effects of coupling of 111Cd (13% natural
abundance, spin 1/2) and113Cd (12%, 1/2) with the CH2
and CH3 H’s, striking in spectra of Et2Cd alone (both
J ’s ca. 50-60 Hz), are absent; only a slightly broadened
quartet and triplet are seen for the CH2 and CH3.
Therefore, the ethyl groups exchange rapidly relative
to the NMR time scale. Although the equilibrium in eq
2 lies substantially to the left, formation of a trace
* To whom correspondence should be addressed. E-mail: hgr@
chem.psu.edu.
(1) Much of this work is taken from: Tang, H. Ph.D. Dissertation,
The Pennsylvania State University, l997.
(2) Wittig, G. Angew. Chem. l958, 70, 65.
(3) Squiller, E. P.; Whittle, R. R.; Richey, H. G., J r. J . Am. Chem.
Soc. 1985, 107, 432.
(4) Richey, H. G., J r.; Kushlan, D. M. J . Am. Chem. Soc. 1987, 109,
2510. Pajerski, A. D.; Parvez, M.; Richey, H. G., J r. J . Am. Chem. Soc.
1988, 110, 2660.
2 R2Cd + macrocycle h R3Cd- + RCd(macrocycle)+
(2)
(5) Osman, A.; Tuck, D. G. J . Organomet. Chem. l979, 169, 255.
Buttrus, N. H.; Eaborn, C.; El-Kheli, M. N. A.; Hitchcock, P. B.; Smith,
J . D.; Sullivan, A. C.; Tavakkoli, K. J . Chem. Soc., Dalton Trans. l988,
381. Al-J uaid, S. S.; Buttrus, N. H.; Eaborn, C.; Hitchcock, P. B.; Smith,
J . D., Tavakkoli, K. J . Chem. Soc., Chem. Commun. l988, 1389.
(6) Naumann, D.; Tyra, W. J . Organomet. Chem. 1989, 368, 131.
(7) Toppet, S.; Slinckx, G.; Smets, G. J . Organomet. Chem. 1967, 9,
205. Seitz, L. M.; Little, B. F. J . Organomet. Chem. 1969, 18, 227.
(8) Tang, H.; Parvez, M.; Richey, H. G., J r. Organometallics l996,
15, 5281.
amount of Et3Cd-EtCd(14N4)+ may be responsible for
the rapid exchange, which would result if formation of
these ions and their reversion to Et2Cd and 14N4 is very
rapid or, alternatively, if exchange of ethyl between Et2-
Cd and Et3Cd- is very much more rapid than between
Et2Cd and Et2Cd. Increased rates of methyl exchange
10.1021/om001020c CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/23/2001

1570 Organometallics, Vol. 20, No. 8, 2001
Tang and Richey
in Me2Cd and in Me2Cd-Me2Zn solutions caused by
donor solvents have been attributed to more facile
bridging by the methyl groups when the metal is
coordinated to a solvent heteroatom.9 Such coordinated
species (e.g., R2Cd--+OR′2) have ate character.
R2Cd , R2Mg, a n d Ma cr ocycles. Another synthetic
approach10 to organocadmate anions is to use an orga-
nometallic compound that in combination with a mac-
rocycle is a stronger “R-” donor than R2Cd. R2Mg is a
likely candidate (eq 3).
R2Cd + R2Mg + macrocycle f
R3Cd- + RMg(macrocycle)+ (3)
1
F igu r e 1. 1H NMR spectrum (360 MHz) of the lower liquid
phase containing Et3Cd-EtMg(14N4)+ that separated when
equimolar amounts of Et2Cd, Et2Mg, and 14N4 were added
to benzene-d6. Absorptions of Et3Cd- are labeled A, of Et
of EtMg(14N4)+ are labeled B, and of 14N4 of EtMg(14N4)+
are labeled C.
In the absence of a macrocycle, H NMR spectra of
solutions of Et2Cd and Et2Mg have only one broad
triplet and one broad quartet, and effects of coupling of
111Cd and 113Cd are absent. In equimolar solutions, these
absorptions lie midway between the corresponding
absorptions of Et2Cd and Et2Mg. The species in solution
therefore are Et2Cd and Et2Mg, but all ethyl groups
exchange rapidly relative to the NMR time scale (al-
though not quite rapidly enough to lead to extremely
sharp absorptions).
Preparations using equimolar amounts of Et2Cd, Et2-
Mg and 14N4 are good examples to introduce the
experiments with macrocycles. For these preparations
(and for others in this note), results were essentially
identical when different initial concentrations (in the
range 0.1-0.8 M) were used. Et2Cd-Et2Mg-14N4
preparations had two liquid phases, as is often seen
when organometallic ions form in aromatic solvents.11
When equimolar amounts of the reactants were used,
1H NMR spectra showed that the upper phases contain
little solute.12 Many features of NMR spectra of a lower
phase indicate that Et3Cd- and EtMg(14N4)+ (e.g., eq
and R3Mg- 3,15 are downfield from those of the corre-
sponding R2Zn and R2Mg compounds. The 13C NMR
spectrum of the lower phase also has two sets of ethyl
absorptions and one set of 14N4 absorptions. The single
113Cd NMR absorption of the lower phase is 298 ppm
downfield from the 113Cd absorption of a solution of Et2-
Cd alone, a shift similar to that6 between the 113Cd
absorptions of (CF3)2Cd and (CF3)3Cd- Cs+. Ethyl
groups of Et3Cd- exchange rapidly since effects of
coupling of 111Cd and 113Cd with the R-H’s, â-H’s, and
R-C, prominent in 1H and 13C NMR spectra of Et2Cd
alone, are absent. Exchange conceivably could be be-
tween R3Cd- ions but more likely is between R3Cd- and
small amounts of R2Cd (R3Cd- + R2Cd* a R2Cd +
1
R3Cd*-). H NMR spectra were taken at lower temper-
1
atures (in toluene-d8) in an effort to slow the exchange
but, except for significant broadness of all absorptions
at the lowest temperatures (-40 and -60 °C), are
similar to those in ambient temperature spectra.
3) are its principal components. The H NMR spectra
(Figure 1) exhibit two sets of ethyl absorptions in 3:1
ratio. The 14N4 absorptions and the smaller set of ethyl
absorptions have intensities indicating that the groups
responsible for them are 1:1 and positions similar13 to
those previously observed14-16 for EtMg(14N4)+ in the
presence of other anions (including a CH2Mg absorption
∼0.9 ppm upfield from that of Et2Mg and all 14N4
absorptions upfield from those of free 14N4). The CH2
absorption of the larger ethyl set is ∼0.2 ppm downfield
from that of Et2Cd, just as R-H absorptions of R3Zn- 10
Et2Mg-Et2Cd-14N4 preparations using an ether as
the solvent also formed Et3Cd-EtMg(14N4)+. Two liquid
phases were present when dioxane or diethyl ether was
used. Enough solute remained in the upper phases to
1
be observed in H NMR spectra, and the spectra of the
upper and lower phases are similar. Homogeneous
solutions were obtained when THF or DME was the
solvent. All spectra exhibit two sets of ethyl absorp-
tions (3:1) and 14N4 absorptions characteristic of
Et3Cd-EtMg(14N4)+.
(9) Oliver, J . P. Adv. Organomet. Chem. l970, 8, 167. Henold, K.;
Soulati, J .; Oliver, J . P. J . Am. Chem. Soc. 1969, 91, 3171.
(10) Fabicon, R. M.; Pajerski, A. D.; Richey, H. G., J r. J . Am. Chem.
Soc. 1991, 113, 6680.
Some R2Mg-R2Cd-14N4 reactions used bulkier R
groups. All experiments using isobutyl, neopentyl (Np
) Me3CCH2), and Me3SiCH2 groups resulted in two
liquid phases, the lower containing most of the solute.
1H NMR spectra of the lower phases are those expected
for R3Cd-RMg(14N4)+. As with the ethyl preparations,
effects of coupling of 111Cd and 113Cd with R- and â-H’s
are absent, even at lower temperatures. With neopentyl
and Me3SiCH2, phase separation was slow, apparently
a result of slow R3Cd-RMg(14N4)+ formation. With
neopentyl, for example, phase separation did not begin
until several hours after preparation; 1H NMR spectra
taken soon after preparation showed broad absorptions
that must be principally of Np2Mg, Np2Cd, and 14N4,
(11) Atwood, J . L. In Inclusion Compounds; Atwood, J . L., Davies,
J . E. D., Macnicol, D. D., Eds.; Academic: London, 1984; Vol. 1, Chapter
9.
(12) Equimolar amounts of Et2Cd, Et2Mg, and 14N4 generally were
used. When more 14N4 was used, the excess 14N4 was principally in
the upper phase. Where investigated in other reactions that produced
two liquid phases, excess macrocycle also was mainly in the upper
phase.
(13) Only the position of the most downfield 1H NMR absorption of
14N4 of RMg(14N4)+ cations is very dependent on the anion.14,15 The
four H’s (NCHHCH2CHHN) responsible for this absorption lie above
one face of the 14N4, projecting into the solution at a location providing
the least hindered approach to the center of positive charge.
(14) Pajerski, A. D.; Chubb, J . E.; Fabicon, R. M.; Richey, H. G., J r.
J . Org. Chem. 2000, 65, 2231.
(15) Pajerski, A. D. Ph.D. Dissertation, The Pennsylvania State
University, 1990.
(16) Tang, H.; Parvez, M.; Richey, H. G., J r. J . Organomet. Chem.
2000, 19, 4810.

Synthesis of Organocadmate Anions
Organometallics, Vol. 20, No. 8, 2001 1571
but with positions somewhat altered by routine17
coordination of 14N4 to Mg and Cd. After the lower
phase is no longer growing (ca. 1 day), the upper
phase has weak 1H NMR absorptions attributable to
Np3Cd-NpMg(14N4)+, in fact, identical to those of a
dilute solution formed by dissolving crystals of Np3Cd--
NpMg(14N4)+ (that precipitated slowly after hexane
was layered over a benzene solution prepared from Np2-
Cd, Np2Cd, and 14N4).
fore it is likely that a trace amount of Np3Cd-Np-
Mg(222C)+ is responsible for the exchange.20 The ob-
servation of discrete Np2Mg absorptions, however,
indicates that the interconversion Np2Cd + Np2Mg +
222C a Np3Cd-NpMg(222C)+ is too slow to rapidly
interchange the neopentyl groups of Np2Cd (a conclusion
in accord with the observation that formation of
Np3Cd-NpMg(14N4)+ is slow). Therefore, by default, the
principal exchange pathway is most likely between
Np2Cd and small amounts of Np3Cd-.
A white crystalline solid precipitated rapidly when
Me2Mg, Me2Cd, and 14N4 were mixed in benzene-d6.
This solid is virtually insoluble in benzene at ambient
temperature, but two liquid phases were seen when it
was heated in benzene at 70 °C. The 1H NMR spectrum
of the upper phase has weak absorptions expected for
Me3Cd-MeMg(14N4)+ (precipitation occurred before
NMR spectra could be taken of the smaller lower phase).
Crystals formed slowly when equimolar amounts of
Ph2Mg, Ph2Cd, and 14N4 were dissolved in THF and
then a small layer of benzene and a larger layer of
hexane were added. Although Ph2Mg is virtually in-
soluble in benzene, these crystals were somewhat
soluble (ca. 0.05 M) at 70 °C; precipitation was slow
when a heated solution was cooled, permitting NMR
spectra of this single phase to be taken at ambient
1
R2Cd , R2Zn , a n d Ma cr ocycles. The H NMR spec-
trum of a solution prepared from equimolar amounts
of Et2Zn and Et2Cd has two sets of ethyl absorptions
(1:1) with positions identical to those of the components
when alone. Coupling of 111Cd and 113Cd with the R- and
â-hydrogens of Et2Cd is observed, so any exchange
involving the ethyl groups of Et2Cd is slow. Addition of
1
221C provided a solution whose H NMR spectrum has
two sets (1:1) of broad ethyl absorptions. The positions
111
of one set are identical to those of Et2Cd; effects of
-
Cd and 113Cd coupling are observable, although the
satellite absorptions are less sharp than in the system
without 221C. The positions of the other ethyl set are
shifted slightly (0.1-0.2 ppm) from those of Et2Zn, as
expected for routine coordination17 of 221C to Et2Zn.
221C therefore does not cause significant ion formation
and facilitates ethyl group exchange only to a very
limited extent. In contrast to RMg+, neither RZn+ nor
RCd+ binds strongly enough with 221C to form suf-
ficient ate anion to lead to an R group exchange that is
1
temperature. H NMR spectra indicate the solute to be
Ph3Cd-PhMg(14N4)+.8,18,19
Cryptands were used for some reactions. With 211C
(2,1,1-cryptand) or 221C (2,2,1-cryptand), R2Mg and R2-
Cd (R ) Et, Np, or Me3SiCH2) formed two liquid phases.
1H NMR spectra of the lower phases exhibit the features
observed with 14N4, including two sets of alkyl absorp-
tions (3:1), and therefore contain R3Cd-RMg(cryptand)+.
Effects of coupling of 111Cd and 113Cd are absent, even
in spectra of NpMg(211C)+Np3Cd- preparations to
which TMEDA was added (TMEDA might slow ex-
change by coordinating with Np3Cd- and any excess
Np2Cd or Np2Mg).
1
rapid relative to the NMR time scale. H NMR spectra
of Et2Zn-Et2Cd-14N4 solutions, however, show only
one broad set of ethyl absorptions and no effects of Cd
coupling, both features indicating a faster exchange of
ethyl groups. 14N4 binds more effectively than 221C to
RZn+,16 and a trace of Et3Cd-Et(14N4)+ may be respon-
sible for the rapid exchange of ethyl groups. The Et3Cd-
concentration must be low, however; the single absorp-
tion in the 113Cd NMR spectrum is the same (within 0.1
ppm) as that of a solution of Et2Cd alone, in contrast to
the 113Cd absorption of Et3Cd-EtMg(14N4)+, which is
298 ppm downfield.
Su m m a r y. R2Cd compounds do not form observable
amounts of R3Cd-RCd(macrocycle)+ with the macro-
cycles that were tried, but rapid R exchange may be due
to formation of trace amounts of these ions. The failure
to form significant amounts of ions is not surprising
since organocadmium compounds22 coordinate more
feebly than organozinc compounds to O and N donor
atoms and even conversion of R2Zn to R3Zn-RZn-
(macrocycle)+ requires both a macrocycle particularly
effective for RZn+ and an organic group particularly
effective at stabilizing R3Zn-.16 R3Cd- ions can be
synthesized from R2Cd compounds, however, by provid-
ing a stronger “R-” donor. Combinations of R2Mg and
R2Cd with 14N4, 211C, or 221C are effective. Similar
With 222C (2,2,2-cryptand), Np2Mg and Np2Cd pro-
1
duced a solution whose H NMR spectrum has two sets
of neopentyl absorptions. The positions of one set are
shifted somewhat from those of Np2Mg alone, as ex-
pected for routine coordination17 of 222C to Np2Mg. The
positions of the other set are identical to those of Np2-
Cd alone, but effects of coupling of 111Cd and 113Cd are
absent. Coordination of NpMg+ to 222C is sufficiently
weaker than to 211C or 221C to preclude formation of
observable amounts of Np3Cd-NpMg(222C)+. The ab-
sence of coupling with Cd shows that the neopentyl
groups of Np2Cd exchange rapidly, but the independent
absorptions for Np2Mg and Np2Cd indicate that this
exchange does not significantly involve Np2Mg. There-
(17) “Routine” is used here to refer to coordination of one or two
heteroatoms of the macrocycle to the metal atom, coordination similar
to that by acyclic ethers and amines. Such coordinate bonds generally
form and break rapidly relative to the NMR time scale.
(18) One THF per salt unit also is in the crystal; its absorptions
are seen in the NMR spectra.
(19) A crystal obtained by a slightly different crystallization proce-
dure was subjected to X-ray diffraction structural analysis.1 The
asymmetric unit is composed of two independent Ph3Cd- units, two
independent PhMg(14N4)+ units, and two THF molecules not involved
in any specific bonding. Discrepancy indices (R ) 0.134, Rw ) 0.144)
in the final refinement were high, but the results are adequate to show
the principal structural features; in fact, the geometry determined for
PhMg(14N4)+ is very similar to that previously found for this cation15
with a different anion and for MeMg(14N4)+.8 Ph3Cd- has an es-
sentially trigonal planar geometry, as found for Me3Cd-.8
(20) The preparations of R2Mg compounds, by precipitation of MgX2
from RMgX solutions using dioxane,21 generally leaves traces of halide,
which might have a role in the exchanges. Np2Mg was sublimed,
however, and so residual halide is particularly low.
(21) Wakefield, B. J . Organomagnesium Methods in Organic Syn-
thesis; Academic: London, l995; Section 3.4.1.
(22) Boersma, J . In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon: Oxford,
l982; Chapter 16. O’Brien, P. In Comprehensive Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, 1995; Vol. 3, Chapter 4.

1572 Organometallics, Vol. 20, No. 8, 2001
Tang and Richey
with dimethylmagnesium and diphenylmagnesium to make
them sufficiently soluble).
Dim eth ylm a gn esiu m (200 MHz): δ -0.95 (s).
Dieth ylm a gn esiu m (200 MHz): δ -0.03 (q, J ) 8.0 Hz, 2,
CH2), 1.66 (t, J ) 7.9 Hz, 3, CH3).
combinations with R2Zn in place of R2Mg do not produce
observable amounts of R3Cd-RZn(macrocycle)+, but
trace amounts may be responsible for rapid exchange
of R’s of R2Cd.
Diisobu tylm a gn esiu m (200 MHz): δ -0.11 (d, J ) 6.5 Hz,
2, CH2), 1.31 (d, J ) 6.1 Hz, 6, CH3), 2.24 (m, 1, CH).
Din eop en tylm a gn esiu m (200 MHz): δ 0.22 (s, 2, CH2),
1.27 (s, 9, CH3).
Bis(tr im eth ylsilylm eth yl)m agn esiu m (200 MHz): δ -1.31
(s, 2, CH2), 0.33 (s, 9, CH3).
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. Solutions for
NMR analysis were prepared in the glovebox and transferred
into NMR tubes to which an extension of routine glass tubing
had been added to facilitate sealing with a flame. An NMR
tube was capped temporarily with a rubber septum, removed
from the glovebox, immersed in liquid nitrogen, and sealed at
the extension. Except where noted, NMR spectra were taken
at ambient temperature. 1H NMR absorptions are reported
relative to internal C6D5H (δ 7.15 ppm) for solutions in
benzene-d6 and to internal tetramethylsilane (δ 0.00) for
solutions in other solvents. 13C NMR absorptions are reported
relative to internal C6D6 (δ 128.0 ppm) and 113Cd NMR
absorptions relative to external Et2Cd (0.4 M in benzene-d6).
The following notations are used: s, singlet; d, doublet; t,
triplet; q, quartet; m, a more complex multiplet; c, complex
Dip h en ylm a gn esiu m (300 MHz): δ 7.41 (t, J ) 7.2 Hz, 1,
p-H), 7.53 (t, J ) 6.6 Hz, 2, m-H), 8.12 (d, J ) 7.4 Hz, 2, o-H).
P r ep a r a tion of Dior ga n oca d m iu m Com p ou n d s. The
following is a typical procedure. A Et2O solution of a Grignard
reagent (0.10 M, 80 mL) was added dropwise over a period of
2 h to a stirred suspension of CdCl2 (6.4 g, 0.035 mol) in Et2O
(40 mL) in a reaction vessel protected from light with alumi-
num foil. After addition was complete, the reaction mixture
was allowed to stir for 12 h. Most of the Et2O was removed at
reduced pressure. Then all of the volatile contents were
transferred from the reaction mixture at low pressure. The
resulting material was pumped on carefully (0 °C) to remove
most residual diethyl ether. Then the remaining material was
subjected to a second vacuum transfer. The following 1H NMR
spectra are of ca. 0.1 M solutions (benzene-d6).
Dim eth ylca d m iu m : 1H NMR (200 MHz) δ 0.59* (s, CH3).
Dieth ylca d m iu m : 1H NMR (200 MHz) δ 0.29* (q, J ) 8.0
Hz, 2, CH2), 1.26* (t, J ) 8.1 Hz, 3, CH3); 13C NMR (90 MHz)
δ 12.8* (both C's).24
1
overlapping absorptions; b, broad. An * is placed on those H
and 13C NMR absorptions that have clearly evident satellite
absorptions due to coupling to 111Cd and 113Cd. Benzene-d6
(Cambridge Isotope Laboratories) was stored over molecular
sieves (4 Å). Other hydrocarbon solvents and dioxane were
distilled from CaH2 and stored over molecular sieves (4 Å)
under a nitrogen atmosphere. Immediately prior to use, diethyl
ether and tetrahydrofuran were distilled from sodium ben-
zophenone ketyl, and dimethoxyethane (DME) and tetra-
methylethylenediamine (TMEDA) were distilled under vacuum
from CaH2. All macrocyclic compounds, Et2Zn, and Mg (99.95%)
(Aldrich Chemical Co.) were used as received. Me2Cd (Orga-
nometallics, Inc.) was purified by vacuum transfer prior to use.
P r ep a r a tion of Dior ga n om a gn esiu m Com p ou n d s. The
following is a typical procedure. A solution of the alkyl halide
(distilled from CaH2 under nitrogen, 0.10 mol) in Et2O (40 mL)
was added dropwise over 2 h to a stirred mixture of Mg (3.0 g,
0.125 mol) in Et2O (40 mL). Alkyl bromides were used for all
preparations except that of bis(trimethylsilylmethyl)magne-
sium, for which the chloride was used. After addition was
complete, the reaction mixture was allowed to stir for 12 h.
The concentration of the Grignard reagent solution was
determined by hydrolyzing an aliquot, adding an excess of a
Diisobu tylca d m iu m : 1H NMR (200 MHz) δ 0.62* (d, J )
6.0 Hz, 2, CH2), 0.98 (d, J ) 7.1 Hz, 6, CH3), 2.29 (bm, 1, CH).
Din eop en tylca d m iu m : 1H NMR (200 MHz) δ 0.64* (s, 2,
CH2), 1.06 (s, 9, CH3).
Bis(tr im eth ylsilylm eth yl)ca d m iu m : 1H NMR (200 MHz)
δ 0.58* (s, 2, CH2), 0.11 (s, 9, CH3).
Dip h en ylca d m iu m : 1H NMR (300 MHz) δ 7.15-7.35 (c,
all H’s).
P r ep a r a tion of NMR Solu tion s. In the glovebox, the
diorganocadmium compound, the corresponding diorganomag-
nesium or diorganozinc compound, and the macrocycle were
weighed into a vial (in some preparations only two of these
reactants were used), and the solvent (ordinarily 0.5 mL) was
added. If a homogeneous solution was present after the
preparation had been stirred (magnetic stirrer) for a few
minutes, it was transferred into an NMR tube. When the
preparation was opaque (indicating phase separation), it was
allowed to stand unstirred until phase separation was com-
plete. To obtain enough of a lower phase to permit taking
routine NMR spectra, it was necessary to do a preparation on
a larger scale (generally using 1.2 mL of solvent). For the
representative spectra that are listed below, equimolar amounts
of all reactants were used; the concentration listed for a
spectrum is the concentration that each reactant would have
if no reaction took place (and if no phase separation occurred).
To allow comparison with spectra of other solutions, the
spectra of 14N4 and Et2Zn also are listed.
14N4 (ben zen e-d 6). 1H NMR (0.2 M, 200 MHz): δ 1.55
(quintet, J ) 6.5 Hz, 1, CH2CH2CH2), 2.13 (s, 3, CH3), 2.40 (s,
2, NCH2CH2N), 2.48 (t, J ) 6.4 Hz, 2, CH2CH2CH2).
Et2Zn (ben zen e-d 6). 1H NMR (0.1 M, 200 MHz): δ 0.12
(q, J ) 7.9 Hz, 2, CH2), 1.11 (t, J ) 7.8 Hz, 3, CH3).
Et2Cd a n d 14N4 (ben zen e-d 6). 1H NMR (0.1 M, 200
MHz): δ 0.37 (bq, J ) 8.1 Hz, 2, CH2Cd), 1.33 (bt, J ) 8.2 Hz,
3, CH3C), 1.49 (bm, 4, CH2CH2CH2), 2.08 (s, 12, CH3N), 2.34
(s, 8, NCH2CH2N), 2.42 (bt, 8, CH2CH2CH2).
standard HNO3 solution (0.10 M), and titrating with
a
standard NaOH solution (0.10 M) to a phenolphthalein red
endpoint. Halide was also determined by titration;23 to the
above solution was added 2 drops of a 5% K2CrO4 solution
followed by titration with a standard AgNO3 solution (0.10 M)
to a brick red endpoint. The diorganomagnesium compound
was prepared by the dioxane precipitation method.21 A solution
of dioxane (8.8 g, 0.10 mol) in Et2O (40 mL) was added
dropwise over 2 h to the stirred Grignard reagent solution (0.10
mol). The resulting slurry was stirred for 12 h and then
centrifuged. The clear supernatant liquid was transferred and
the solvent removed at reduced pressure, leaving a solid, which
was heated (50 °C) under vacuum (10-3 Torr) for an additional
5 h to remove residual Et2O. All diorganomagnesium com-
pounds had R/X ratios (determined by titration analysis) >
20. Dineopentylmagnesium was further purified by sublima-
1
tion (85 °C, 10-3 Torr). The following H NMR spectra are of
(24) The coincidence of the absorptions of the two C’s has been noted
before: Mu¨ller, H.; Ro¨sch, L.; Erb, W.; Zeisberg, R. J . Organomet.
Chem. l977, 140, C17. We did a 1H-13C COSY NMR experiment and
found the expected couplings of the CH2 H’s and the CH3 H’s, but to
the same 13C absorption position (δ 12.8).
ca. 0.1 M solutions in benzene-d6 (2 equiv of THF were used
(23) Day, R. A., J r.; Underwood, A. L. Quantitative Analysis, 6th
ed.; Prentice Hall: Englewood Cliffs, NJ , l991; Chapter 22.

Synthesis of Organocadmate Anions
Organometallics, Vol. 20, No. 8, 2001 1573
Et2Mg a n d Et2Cd (ben zen e-d 6). 1H NMR (0.6 M, 200
MHz): δ 0.17 (b, 2, CH2), 1.41 (b, 3, CH3), 3.30 (s, dioxane25).
Et2Mg, Et2Cd , a n d 14N4 (ben zen e-d 6); P r ep a r a tion of
EtMg(14N4)+Et3Cd -. 1H NMR (0.6 M, lower phase, 200
MHz): δ -0.95 (q, J ) 8.3 Hz, 2, CH2Mg), 0.51 (q, J ) 7.9 Hz,
6, CH2Cd), 1.19 (t, J ) 8.2 Hz, 3, CH3CMg), 1.83 (t, J ) 8.1
Hz, 9, CH3CCd), 0.90-2.10 (c, 16, most CH2’s of 14N4), 1.69
(s, 12, CH3N), 2.32 (bt, 4, CHHCH2CHH). 13C NMR (0.6 M,
lower phase, 50 MHz): δ 59.7 (NCCN), 56.1 (NCCCN), 43.3
(NCH3), 21.4 (NCCCN), 17.1 (CCCd), 14.9 (CCMg), 10.4 (CCd),
-0.7 (CMg); 113Cd NMR (0.6 M, lower phase, 67 MHz) δ 297.9.
Et2Mg, Et2Cd , a n d 14N4 (DME); P r ep a r a tion of EtMg-
produced a 0.3 M solution. Two liquid layers formed upon
gentle heating (70 °C). 1H NMR (upper layer, 300 MHz): δ
-1.61 (s, 3, CH3Mg), -0.26 (s, 9, CH3Cd, 0.90-3.00 (c, 20,
CH2’s of 14N4), 1.60 (s, 12, CH3N). Precipitation occurred
before NMR spectra could be taken of the small lower layer.
P h 2Mg, P h 2Cd , a n d 14N4 (ben zen e-d 6); P r ep a r a tion of
P h Mg(14N4)+P h 3Cd -. Besides amounts of the reagents that
would have produced a 0.2 M solution, 1 equiv of THF (to help
dissolve the Ph2Mg) also was weighed in before adding the
solvent. A large amount of precipitate was present. The 1H
NMR spectrum of the remaining solution showed it to contain
little solute. A homogeneous solution (ca. 0.05 M) resulted from
heating a portion of the precipitate in benzene to 70 °C; after
the solution was cooled to ambient temperature, it was possible
to take an NMR spectrum of the supersaturated solution before
crystals formed. 1H NMR (300 MHz): δ 0.82-1.80 (c, 16, most
CH2’s of 14N4+), 1.42 (s, 12, CH3N), 2.24 (c, 4, CHHCH2CHH),
7.26 (bs, 5, all H’s of PhMg), 7.33 (t, J ) 7.3 Hz, 3, p-H of
PhCd), 7.49 (t, J ) 7.6 Hz, 6, m-H of PhCd), 8.47 (d, J ) 7.5
Hz, 6, o-H of Ph3Cd).
1
(14N4)+Et3Cd -. H NMR (1.0 M, 200 MHz): δ -0.69 (q, J )
8.3 Hz, 2, CH2Mg), 0.10 (q, J ) 7.8 Hz, 6, CH2Cd), 1.27 (t, J )
8.1 Hz, 3, CH3CMg), 1.44 (t, J ) 8.3 Hz, 9, CH3CCd), 1.50-
2.80 (c, 16, most CH2’s of 14N4), 2.36 (s, 12, CH3N), 3.12 (bt,
4, CHHCH2CHH), 3.28 (s, CH3 of DME), 3.44 (s, CH2 of DME).
Et2Mg, Et2Cd , a n d 14N4 (THF ); P r ep a r a tion of EtMg-
1
(14N4)+Et3Cd -. H NMR (1.0 M, 200 MHz): δ -0.71 (q, J )
8.5 Hz, 2, CH2Mg), 0.16 (q, J ) 7.9 Hz, 6, CH2Cd), 1.20 (t, J )
7.8 Hz, 3, CH3CMg), 1.30 (t, J ) 8.1 Hz, 9, CH3CCd), 1.50-
2.80 (c, 16, most CH2’s of 14N4), 2.42 (s, 12, CH3N), 3.09 (bt,
4, CHHCH2CHH), 1.76 (m, CH2CO of THF), 3.62 (m, CH2O of
THF).
Et2Mg, Et2Cd , a n d 221C (ben zen e-d 6); P r ep a r a tion of
EtMg(221C)+Et3Cd -. Liquid phase separation took place
1
slowly. H NMR (0.5 M, lower phase, 200 MHz): δ -0.88 (q,
J ) 8.2 Hz, 2, CH2Mg), 0.44 (q, J ) 7.9 Hz, 6, CH2Cd), 1.18 (t,
J ) 8.4 Hz, 3, CH3CMg), 1.89 (t, J ) 7.9 Hz, 9, CH3CCd), 1.80-
3.50 (c, 32, all H’s of 221C).
E t2Mg, E t 2Cd , a n d 14N4 (d ioxa n e); P r ep a r a t ion of
EtMg(14N4)+Et3Cd -. 1H NMR (1.2 M, lower phase, 200
MHz): δ -0.78 (q, J ) 8.2 Hz, 2, CH2Mg), 0.50 (q, J ) 8.0 Hz,
6, CH2Cd), 1.17 (t, J ) 8.3 Hz, 3, CH3CMg), 1.27 (t, J ) 8.1
Hz, 9, CH3CCd), 1.40-2.72 (c, 32, most CH2’s of 14N4+), 2.38
(s, 12, CH3N), 2.97 (bt, 4, CHHCH2CHH), 3.57 (s, dioxane).
Et2Mg, Et2Cd , a n d 14N4 (Et2O); P r ep a r a tion of EtMg-
Np 2Mg, Np 2Cd , a n d 211C (ben zen e-d 6); P r ep a r a tion of
Np Mg(211C)+Np 3Cd -. Liquid phase separation was slow
(about 5 h to complete). 1H NMR (0.2 M, lower phase, 300
MHz): δ -0.63 (s, 2, CH2Mg), 0.76 (s, 6, CH2Cd), 1.20 (s, 9,
CH3CMg), 1.35 (s, 27, CH3Cd), 1.70-3.30 (c, 28, all H’s of
211C).
1
(14N4)+Et3Cd -. H NMR (1.0 M, lower phase, 200 MHz): δ
-0.40 (b, 2, CH2Mg), 0.38 (b, 6, CH2Cd), 0.82 (b, 3, CH3CMg),
1.21 (b, 9, CH3CCd), 1.40-2.70 (c, 32, most CH2’s of 14N4+),
2.40 (s, 12, CH3N), 2.90 (bt, 4, CHHCH2CHH), 1.08 (t, CH3 of
Et2O), 3.35 (q, CH2 of Et2O).
i-Bu 2Mg, i-Bu 2Cd , a n d 14N4 (ben zen e-d 6); P r ep a r a tion
of i-Bu Mg(14N4)+i-Bu 3Cd -. 1H NMR (0.4 M, lower phase,
200 MHz): δ -0.86 (d, J ) 6.7 Hz, 2, CH2Mg), 0.72 (d, J ) 5.7
Hz, 6, CH2Cd), 1.10 (d, J ) 6.0 Hz, 6, CH3CMg), 1.25 (d, J )
6.8 Hz, 18, CH3CCd), 2.60-2.80 (c, 4, CHMg and CHCd), 1.10-
2.70 (c, 16, most CH2’s of 14N4), 1.70 (s, 12, CH3N), 2.50 (bt,
4, CHHCH2CHH).
Colorless crystals of NpMg(211C)+Np3Cd- were obtained by
layering hexane (1 mL) over a solution prepared from Np2Mg
(42 mg, 0.25 mmol), Np2Cd (64 mg,0.25 mmol), and 211C (72
mg, 0.25 mmol) in benzene (0.8 mL). A homogeneous solution
resulted from dissolving the crystals (10 mg) in benzene-d6 (0.5
1
mL). H NMR (300 MHz): δ -0.63 (s, 2, CH2Mg), 0.80 (s, 6,
CH2Cd), 1.21 (s, 9, CH3CMg), 1.38 (s, 27, CH3CCd), 1.70-3.30
(c, 28, all H’s of 211C).
Np Mg(211C)+Np 3Cd - a n d TMEDA (ben zen e-d 6). Crys-
tals of NpMg(2,1,1-C)+Np3Cd- (10 mg, 0.014 mmol) were
dissolved in a benzene-d6 solution of TMEDA (0.5 mL, 0.008
Np 2Mg, Np 2Cd , a n d 14N4 (ben zen e-d 6); P r ep a r a tion of
Np Mg(14N4)+Np 3Cd -. Liquid phase separation was slow
(about 12 h to complete). 1H NMR (0.4 M, lower phase, 300
MHz): δ -0.64 (s, 2, CH2Mg), 0.71 (s, 6, CH2Cd), 1.04 (s, 9,
CH3CMg), 1.38 (s, 27, CH3CCd), 1.10-2.10 (c, 16, most CH2’s
of 14N4+), 1.78 (s, 12, CH3N), 2.30 (bt, 4, CHHCH2CHH).
Crystals of NpMg(14N4)+Np3Cd- were obtained by carefully
layering hexane (1 mL) over a solution prepared from Np2Mg
(80 mg, 0.48 mmol), Np2Cd (122 mg, 0.48 mmol), and 14N4
(123 mg, 0.48 mmol) in benzene (0.8 mL). A homogeneous
solution resulted from dissolving the crystals (10 mg) in
1
M, 0.004 mmol). H NMR (360 MHz): δ -0.62 (s, 2, CH2Mg),
0.80 (s, 6, CH2Cd), 1.19 (s, 9, CH3CMg), 1.38 (s, 27, CH3CCd),
1.60-3.20 (c, all H's of 211C), 1.48 (s, CH2 of TMEDA), 1.49
(s, CH3 of TMEDA).26
Np 2Mg, Np 2Cd , a n d 222C (ben zen e-d 6). 1H NMR (0.3 M,
360 MHz): δ 0.18 (s, 2, CH2Mg), 0.65 (s, 2, CH2Cd), 1.05 (s, 9,
CH3CCd), 1.51 (s, 9, CH3CMg), 2.38 (b, 12, CH2N), 3.37 (b, 12,
NCH2CH2O, 3.54 (b, 12, OCH2CH2O).
(Me3SiCH2)2Mg, (MeSiCH2)2Cd , a n d 221C (ben zen e-d 6);
P r ep a r a tion of Me3SiCH2Mg(221C)+(Me3SiCH2)3Cd -. Liq-
1
1
uid phase separation was slow. H NMR (0.3 M, lower phase,
benzene-d6 (0.5 mL). H NMR (300 MHz): δ -0.64 (s, 2, CH2-
200 MHz): δ -2.02 (s, 2, CH2Mg), -0.51 (s, 6, CH2Cd), -0.01
(s, 9, CH3SiCMg), 0.32 (s, 27, CH3SiCCd), 1.60-3.40 (c, all H’s
of 221C).
Mg), 0.85 (s, 6, CH2Cd), 1.11 (s, 9, CH3CMg), 1.61 (s, 27, CH3-
CCd), 1.15-2.10 (c, 16, most CH2's of 14N4+), 1.62 (s, 12,
CH3N), 2.70 (bt, 4, CHHCH2CHH).
Et2Zn a n d Et2Cd (ben zen e-d 6). 1H NMR (0.4 M, 200
MHz): δ 0.11 (q, J ) 8.0 Hz, 2, CH2Zn), 0.30* (q, J ) 8.0 Hz,
2, CH2Cd), 1.12 (t, J ) 8.1 Hz, 3, CH3CZn), 1.26* (t, J ) 7.9
Hz, 3, CH3CCd).
(Me3SiCH2)2Mg, (Me3SiCH2)2Cd , a n d 14N4 (b en zen e-
d 6); P r ep a r a tion of Me3SiCH2Mg(14N4)+(Me3SiCH2)3Cd -.
Liquid phase separation was slow (about 10 h to complete).
1H NMR (0.4 M, lower phase, 360 MHz): δ -2.20 (s, 2, CH2-
Mg), -0.50 (s, 6, CH2Cd), 0.15 (s, 9, CH3SiCMg), 0.34 (s, 27,
CH3SiCCd), 1.10-1.90 (c, 16, most CH2’s of 14N4+), 1.60 (s,
12, CH3N), 2.64 (bt, 4, CHHCH2CHH).
Me2Mg, Me2Cd , a n d 14N4 (ben zen e-d 6); P r ep a r a tion of
MeMg(14N4)+Me3Cd -. Immediate precipitation of white
crystals was observed from a preparation that would have
1
Et2Zn , Et2Cd , a n d 14N4 (ben zen e-d 6). H NMR (0.4 M,
200 MHz): δ 0.27 (b, 2, CH2Zn and CH2Cd), 1.41 (b, 3, CH3-
CZn and CH3CCd), 1.26 (bm, 1, CH2CH2CH2), 1.99 (s, 3, CH3N),
2.18 (s, 2, NCH2CH2N, 2.38 (bt, 2, CH2CH2CH2). 113Cd NMR
(0.4 M, 67 MHz): δ -0.08 (s).
(26) The absorptions of TMEDA alone in benzene-d6 are δ 2.20
(CH2) and 2.36 (CH3). The absorption positions observed here suggest
that TMEDA is coordinated to a metal.
(25) Small amounts of dioxane occasionally remained in the R2Mg
preparations.

1574 Organometallics, Vol. 20, No. 8, 2001
Tang and Richey
Et2Zn , Et2Cd , a n d 221C (ben zen e-d 6). 1H NMR (0.5 M,
360 MHz): δ 0.24 (q, J ) 8.4 Hz, 2, CH2Zn), 0.32* (q, J ) 7.8
Hz, 2, CH2Cd), 1.27* (t, J ) 8.1 Hz, 3, CH3CCd), 1.31 (t, J )
7.8 Hz, 3, CH3CZn), 2.45-2.64 (c, 6, CH2N), 3.40-3.60 (c, 10,
CH2O).
mous referee for helpful suggestions. H.G.R. acknowl-
edges a NATO Collaborative Research Grant that made
possible valuable discussions with Professor Friedrich
Bickelhaupt and co-workers at the Free University in
Amsterdam.
Ack n ow led gm en t. We thank the National Science
Foundation for supporting this research and an anony-
OM001020C