Stability and reactivity of phenylstrontium compounds in solution

Article abstract of DOI:10.1021/om900888g

Fragmentation of tetrahydrofuran (thf) and N,N,N-,N-- tetramethylethylenediamine (tmeda) by PhSrI leads to the formation of the new organostrontium compounds [(tmeda)Sr(I)(μ-Ph)₂{μ-N(Me)CH ₂CH₂NMe₂)Sr(tmeda)], [

Full text of DOI:10.1021/om900888g

2034 Organometallics 2010, 29, 2034–2039
DOI: 10.1021/om900888g
Stability and Reactivity of Phenylstrontium Compounds in Solution
€
Jens Langer, Helmar Gorls, and Matthias Westerhausen*
Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena, August-Bebel-Strasse 2,
D-07743 Jena, Germany
Received October 12, 2009
Fragmentation of tetrahydrofuran (thf) and N,N,N0,N0-tetramethylethylenediamine (tmeda) by
PhSrI leads to the formation of the new organostrontium compounds [(tmeda)Sr(I)(μ-Ph)2-
{μ-N(Me)CH2CH2NMe2)Sr(tmeda)], [(tmeda)Sr(I)(μ-Ph)(μ-I){μ-N(Me)CH2CH2NMe2)Sr(tmeda)],
and [{(tmeda)Sr}4(μ4-O)(μ-I)4(μ-Ph)2].
Indroduction
reaction is of special interest. The direct reaction of stron-
tium metal, activated with mercury, with iodobenzene in thf
to yield phenylstrontium iodide was already published by
Kocheshkov et al. in 1973.8 This reaction proceeded smo-
othly in diethyl ether or benzene only after addition of thf.9
The same approach was employed in the preparation of other
ArSrI (Ar = tolyl, naphthyl, and 2-thienyl) compounds.10
Treatment of thf solutions of phenylstrontium iodide with
In general, organostrontium compounds have received far
less attention than the organic derivatives of the lighter
alkaline earth metals magnesium and calcium. Nevertheless,
their enhanced reactivity when compared with that of these
lighter homologues makes them interesting subjects for
further investigations. Different routes to organostrontium
compounds have been reported. For instance, alkylstron-
tium compounds can be isolated from the reaction of SrI2
with a potassium alkyl if bulky triorganylsilyl groups from
the potassium alkyl protect the reactive Sr-C bond or if the
nucleophilicity of the carbanion is reduced by delocalization
of the anionic charge. Thus [(thf)3Sr{CH(SiMe3)2}2]1 and
[(thf)Sr{C(SiMe3)2(SiMe2OMe)}2]2 were prepared. In addi-
tion, the reaction of a benzylpotassium derivative with anhy-
drous SrI2 was used in the preparation of [(thf)2Sr{CH-
(SiMe3)(C6H4-2-NMe2)}2] with hexacoordinate strontium
atoms.3 The reduction of 2,3-dimethyl-1,4-diphenylbuta-
diene with strontium in thf yielded deep red (thf)4Sr(C4H2-
2,3-Me2-1,4-Ph2).4 Niemeyer and co-workers employed an
organomercury compound to transfer a C6F5 group to stron-
tium, using a shielding triazenide ligand to stabilize the
resulting F5C6Sr derivative.5 In some cases the extremely
high reactivity of organostrontium compounds impedes the
synthesis of such derivatives, and ether cleavage products are
isolated instead.6,7
N,N,N0,N0-tetramethylethylenediamine (tmeda) yielded PhSrI
3
0.5tmeda.11 A recent reinvestigation of phenylstrontium
iodide in THF showed two sets of NMR resonances, which
indicates that there is a Schlenk equilibrium between PhSrI
and SrPh2 þ SrI2 in solution.12 However, little is known
about the reactivity and structures of arylstrontium deriva-
tives in solution and solid state.
Results and Discussion
Activated strontium metal as well as organostrontium
compounds show a much higher reactivity than homologous
magnesium and calcium derivatives. Therefore, the direct
reaction of activated strontium with iodobenzene was per-
formed in THF at 0 °C under an argon atmosphere, and the
reaction mixture was always kept at temperatures below
0 °C. A solvent change to diethyl ether led to drastically
lower yields. Initial attempts to isolate arylstrontium com-
pounds from those reaction mixtures failed. The precipitate,
obtained at -90 °C, consisted mainly of [(thf)5SrI2] and con-
tained only about 10% of aryl strontium derivatives. Due
to the fact that a Schlenk-type equilibrium between PhSrI
and Ph2Sr/SrI2 (eq 1)12 obviously favored the homoleptic
However, the possibility of the straightforward synthesis
of organostrontium compounds in analogy to the Grignard
*Corresponding author. Fax: þ49 3641 948102. E-mail: m.we@
uni-jena.de.
(1) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; MacDougall,
D. J.; Mahon, M. F.; Procopiou, P. A. Chem.;Eur. J. 2008, 14, 11292–
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Nakamura, A. J. Am. Chem. Soc. 1994, 116, 6977–6978.
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Chem., Int. Ed. 2005, 44, 5871–5875.
(6) Alexander, J. S.; Ruhlandt-Senge, K.; Hope, H. Organometallics
2003, 22, 4933–4937.
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1274–1280.
(8) Kocheshkov, K. A.; Kozhemyakina, L. F.; Sheverdina, N. I. Izv.
Akad. Nauk SSSR 1973, 2400.
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Kocheshkov, K. A. Zh. Obshch. Khim. 1978, 48, 623–624.
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Dokl. Akad. Nauk SSSR 1974, 218, 1385–1386. (b) Kozhemyakina, L. F.;
Sheverdina, N. I.; Kocheshkov, K. A. Dokl. Akad. Nauk SSSR 1975, 220,
99–100. (c) Kozhemyakina, L. F.; Sheverdina, N. I.; Paleeva, I. E.; Cherno-
plekova, V. A.; Kocheshkov, K. A. Izv. Akad. Nauk SSSR 1976, 431–433.
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r
pubs.acs.org/Organometallics
Published on Web 04/01/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 9, 2010 2035
Figure 1. Temperature dependence of the 1H NMR spectrum of “[(thf)5Sr(Ph)I]” in d8-THF.
Attempts to obtain suitable crystals of an organostron-
tium compound from these solutions in THF failed not only
due to the unfavorable Schlenk equilibrium but also as a
result of the reactivity of those species toward THF. The
initial step of the degradation reaction is the R-deprotona-
tion of THF by the heavy Grignard reagent. The degradation
reaction was monitored in d8-THF, which is more stable than
THF due to a direct isotope effect and slows the decomposi-
tion of the organostrontium species (see Figure 2). The main
products observed via NMR measurement are benzene and
ethene. Additional signals detected may belong to a stron-
tium ethenolate complex, but this assignment remained
uncertain because of the very low concentration of this
species in solution. During decomposition, colorless crystals
deposited that were identified as [(thf)5SrI2] by X-ray dif-
fraction experiments.
The solid initially obtained from THF was used for further
investigations in various solvents. It was found that the
Schlenk equilibrium is operative in all ether solvents tested.
Different solvent adducts of SrI2 were isolated upon cooling
of these solutions. Depending on the solvent used, the
compounds [(thf)5SrI2] (pure THF; see also ref 14), [(thf)5-
Figure 2. Decomposition of “[(thf)5Sr(Ph)I]” in d8-THF.
compounds and, additionally, arylstrontium compounds
exhibit an even greater solubility in THF than arylcalcium
complexes,13 it was necessary to increase the concentration
of the reaction solution to enable the isolation of aryl-
strontium-richer reaction products. Following this strat-
egy we were able to nearly meet the expected formula of a
post-Grignard reagent, and a composition of the isolated
SrI2] toluene (1) (thf/toluene mixture), [(thf)3(dme)SrI2] (2),
3
[(thf)2(dme)2SrI2] (3) (mixtures of THF and 1,2-dimethoxy-
ethane (dme)), and [(dme)3SrI2] (pure dme or dme/diethyl
ether mixture; see also ref 15) were obtained (see Supporting
Information). However, no crystalline arylstrontium com-
pounds could be isolated from those solutions, even after
removal of SrI2 and further concentration.
product of [(thf)5Sr(Ph)0.96 1.04] was determined. How-
I
ever, the content of arylstrontium species varies between
different crops, indicating that the composition given
above is only an empirical one and the white powder
obtained may consist of different complexes. A saturated
solution in d8-THF shows only one signal set for metal-
1
Recently, we found that arylcalcium compounds are less
soluble in tmeda than in ethers, which enabled the crystal-
lization of [(tmeda)Ca(Ph)(μ-Ph)]2.13 Therefore tmeda was
employed as solvent, too. While the starting material was
soluble in the solvent mixtures mentioned above, it only part-
ially dissolved in tmeda. Assuming that the arylstrontium
compounds were more soluble than the strontium iodides,
the solution was further investigated. Crystals of a heavy
dinuclear Grignard reagent of strontium were obtained from
this solution by cooling to -40 °C (Chart 1).
bound phenyl groups in the H NMR spectrum, but the
broadened doublet of the o-CH groups at δ 8.04 indicates
fluxional behavior. Dilution and cooling lead to the obser-
vation of two different signal sets for the strontium-
coordinated phenyl groups (see Figure 1), and two differ-
ent doublets at δ 8.20 and 7.70 were now observed for the
o-CH groups. These results can be interpreted with respect
to the above-mentioned Schlenk-type equilibrium. How-
ever, the observation of an additional shoulder at δ 8.25 at
-50 °C indicates that this interpretation is simplified.
Obviously, there are more species participating in that
equilibrium.
(14) Ruhlandt-Senge, K.; Davis, K.; Dalal, S.; Englich, U.; Senge,
M. O. Inorg. Chem. 1995, 34, 2587–2592.
€
(15) Weber, F.; Wolmershauser, G.; Sitzmann, H. Acta Crystallogr.
€
(13) Langer, J.; Krieck, S.; Gorls, H.; Westerhausen, M. Angew.
Chem., Int. Ed. 2009, 48, 5741–5744.
2005, E61, m512–m513.

2036 Organometallics, Vol. 29, No. 9, 2010
Langer et al.
Chart 1. Schematic Representation of 4, 40, and 5
The X-ray structure determination and NMR spectro-
scopic investigations showed that the crystal consists of
dinuclear [(tmeda)Sr(I)(μ-Ph)2{μ-N(Me)CH2CH2NMe2)Sr-
(tmeda)] (4) as the major component (85%) (see Figure 3).
However, one of the bridging phenyl groups can also be ex-
changed by a bridging iodide anion, leading to [(tmeda)-
Sr(I)(μ-Ph)(μ-I){μ-N(Me)CH2CH2NMe2)Sr(tmeda)](40),which
was found to occupy 15% of the lattice sites. Both structures
contain two hexacoordinate strontium atoms. In these molecules
the phenyl groups occupy bridging positions, whereas the iodide
anion is also bound terminally. Due to the bridging position of the
phenyl groups, rather large Sr-C bond lengths (average Sr-C
2.84 A) are observed. The terminally bound iodide anion shows a
Sr1-I1 distance of 3.2608(9) A, which is comparable to those of
[(thf)5SrI2] (3.230(2) A).14 The unsymmetrical iodide bridge
shows Sr1-I2 and Sr2-I2 bond lengths of 3.441(9) and
3.240(8) A, respectively. The asymmetry of the bridge is reflected
in the amide coordination, with Sr1-N3 and Sr2-N3 values of
2.632(7) and 2.529(7) A. In contrast to these bridges the phenyl
groups exhibit only small deviations from a symmetric bonding
situation. In solution, only one set each of signals for the phenyl
groups and for the amide ligand was found, indicative of a
fluxional behavior of 4/40 in thf.
Figure 3. Molecular structures and numbering schemes of 4
(top) and 40 (bottom). The thermal ellipsoids represent a prob-
ability of 40%; H atoms are neglected for clarity reasons. Sel-
ected bond lengths (A) and angles (deg): 4: Sr1-C1 2.827(14),
Sr1-C7 2.830(8), Sr1-N3 2.632(7), Sr1-I1 3.2608(9), Sr2-C1
2.848(14), Sr2-C7 2.854(7), Sr2-N3 2.529(7), Sr2-N4 2.731(7),
Sr1-C1-Sr2 75.6(3), C2-C1-C6 113.8(14), Sr1-C7-Sr2
75.5(2), C8-C7-C12 116.3(7), Sr1-N3-Sr2 84.7(2), I1-Sr1-
C1 165.5(3), N4-Sr2-C1 150.8(3); 40: Sr1-I2 3.441(9), Sr2-I2
3.240(8), Sr1-I2-Sr2 62.69(15).
by alkyllithum compounds is well known.17-20 In addition,
the methylene transfer from N-lithiomethyl-N,N0,N00,N00-
tetramethyldiethylenetriamine to epoxides and oxetanes re-
sulting in the formation of the corresponding lithium amide
was reported by Klumpp and co-workers.21
The origin of the unexpected bridging amide ligand can be
ascribed to the fragmentation of tmeda by these extremely
reactive organostrontium reagents. GC-MS examination of
the used tmeda solvent did not show any sign of the presence
of N,N,N0-trimethylethylenediamine as an alternative source
of the observed ligand. However, such R-elimination react-
ions are well known in organolithium chemistry. For in-
stance, Ziegler and Gellert showed that the fragmentation of
dimethyl ether follows this reaction pathway.16 Here the
initial step is the metalation of a CH3 group of the ether
molecule by an alkyllithium. The related lithiation of tmeda
Another derivative, [{(tmeda)Sr}4(μ4-O)(μ-I)4(μ-Ph)2] (5),
could be crystallized from the mother liquor. These cry-
stals diffract only weakly due to an extremely large lattice
constant (c=72.9560(13) A). Therefore only the atom con-
nectivity can be given (Figure 4).
(17) Harder, S.; Lutz, M. Organometallics 1994, 13, 5173–5176.
€
(18) Hildebrand, A.; Lonnecke, P.; Silaghi-Dumitrescu, L.; Silaghi-
Dumitrescu, I.; Hey-Hawkins, E. Dalton Trans. 2006, 967–974.
(19) Gessner, V. H.; Strohmann, C. J. Am. Chem. Soc. 2008, 130,
14412–14413.
(20) Conway, B.; Garcı
ꢀ
a-Alvarez, J.; Hevia, E.; Kennedy, A. R.;
´
Mulvey, R. E.; Robertson, S. D. Organometallics 2009, 28, 6462–6468.
(21) Schakel, M.; Luitjes, H.; Dewever, F. L. M.; Scheele, J.; Klumpp,
G. W. J. Chem. Soc., Chem. Commun. 1995, 513–514.
(16) Ziegler, K.; Gellert, H.-G. Justus Liebigs Ann. Chem. 1950, 567,
185–195.

Article
Organometallics, Vol. 29, No. 9, 2010 2037
with tmeda. Phenylcalcium iodide, prepared according to a
literature procedure,24 was treated with tmeda under similar
conditions (eq 2). The isolated product was [(tmeda)2Ca-
(Ph)I] (6). Thus cleavage of tmeda had not occurred. The
molecular structure of 6 is shown in Figure 5. The hexacoor-
dinate calcium atom lies in a distorted octahedral environ-
ment with the anionic ligands in trans-positions. The Ca-C
and Ca-N bond lengths of 2.658(9) and 2.575(5)/2.590(5) A,
respectively, lie in expected ranges.
½ðthfÞ4CaðPhÞIꢀ þ 2tmeda f ½ðtmedaÞ2CaðPhÞIꢀ þ 4THF
ð2Þ
Conclusion
Tmeda molecules are able to completely displace the thf
ligands of the coordination spheres of the heavy alkaline
earth metal compounds. The enhanced reactivity of the
arylstrontium iodides leads to tmeda degradation, whereas
a similar reaction was not observed for arylcalcium iodides.
In conclusion we have shown that phenylstrontium com-
pounds show excellent solubility in THF and dme even at
low temperature probably due to the Schlenk equilibrium
that is occurring. In tmeda their solubility is considerably
lower, which allows isolation of two rare, structurally char-
acterized examples of arylstrontium compounds. Those
products arise from solvent fragmentation and underline
the higher reactivity of the strontium derivatives in compari-
son to their calcium analogues. It is also noteworthy that
phenyl groups favor bridging positions in organostrontium
compounds (leading to multinuclear derivatives), whereas in
organocalcium chemistry terminally bound phenyl groups
are common, which facilitates the isolation of mononuclear
phenylcalcium compounds.
Figure 4. Structural representation and numbering scheme of 5.
Figure 5. Molecular structure and numbering scheme of 6. The
thermal ellipsoids represent a probability of 40%; H atoms are
omitted for clarity reasons. Selected bond lengths (A) and angles
(deg): Ca1-C1 2.658(9), Ca1-N1 2.590(5), Ca1-N2 2.575(5),
Ca1-I1 3.302(1); N1-Ca1-N2 74.0(2), C1-Ca1-I1 177.6(2),
C1-Ca1-N1 93.9(2), C1-Ca1-N2 94.2(2), N1-Ca1-I1 84.7(1),
N2-Ca1-I1 87.3(1), C2-C1-C6 115.9(11), Ca1-C1-C2
121.3(8), Ca1-C1-C6 122.9(7).
Experimental Section
General Remarks. All manipulations were carried out under
an argon atmosphere using standard Schlenk techniques. The
solvents were dried according to common procedures and
distilled under argon; deuterated solvents were dried over
sodium, degassed, and saturated with argon. The yields given
are not optimized. The 1H and 13C{1H} NMR spectra were
obtained on a Bruker AC 200 or 400 MHz spectrometer. Metal
content was determined by complexometric titration with 0.05 M
EDTA (indicator: Eriochrome Black T).
The strontium tetrahedron is centered by an oxygen atom
that stems from THF cleavage. Interstitial oxygen atoms are
well known for strontium cages, as, for example, in square
Sr5(μ5-O) pyramids and in Sr4(μ4-O) tetrahedra.22,23 All
Tmeda was dried over sodium/benzophenone and distilled
before use. [(thf)4Ca(Ph)I] was prepared according to a known
procedure.24
Sr Sr edges of the Sr4 tetrahedron of 5 are bridged by
3 3 3
monovalent anions. Two opposite edges are bridged by
phenyl groups; all other edges by iodide anions. Each
strontium atom also binds to a tmeda ligand in order to
complete the coordination sphere, leading to hexacoordinate
metal atoms.
Detection of N,N,N0-trimethylethylendiamine in the used
tmeda was attempted by GC-MS analysis. A Thermo Finnigan
Trace GC-MS with a EI/CI combi source was used. Benzene (tR=
4.08 min) and toluene (tR=5.51 min) were the only detectable
impurities in tmeda (tR =6.05 min). Instrument conditions:
gas chromatograph: RTX-5 Amine capillary column (30 m ꢁ
0.25 mm, 1 μm film); injector 250 °C, surge pressure 3 kPa,
oven program 60 °C for 0.2 min, 10 °C/min to 150 °C, 25 °C/
min to 250 °C, hold for 2.8 min. Mass spectrometer: ionization
mode EIþ, scan range 61-379 amu, 3 scans per second,
detector voltage 500.0 V, source temperature 120 °C, GC
interface temperature 200 °C.
The higher reactivity of phenylstrontium iodide is best
shown in comparison to the reaction of phenylcalcium iodide
(22) Hernandez-Sanchez, B. A.; Boyle, T. J.; Baros, C. M.; Brewer,
L. N.; Headley, T. J.; Tallant, D. R.; Rodriguez, M. A.; Tuttle, B. A.
Chem. Mater. 2007, 19, 1459–1471.
€
(23) Westerhausen, M.; Digeser, M. H.; Noth, H.; Knizek, J.
Synthesis of “PhSrI”. A suspension of strontium metal (1.57 g,
17.9 mmol, activated with ammonia), together with glass balls, in
THF (40 mL) was cooled to -40 °C. Iodobenzene (2.53 g,
12.4 mmol) was added at this temperature, and the resulting
Z. Anorg. Allg. Chem. 1998, 624, 215–220.
€
€
(24) (a) Fischer, R.; Gartner, M.; Gorls, H.; Westerhausen, M.
€
€
Organometallics 2006, 25, 3496–3500. (b) Gartner, M.; Gorls, H.;
Westerhausen, M. Synthesis 2007, 725–730.

2038 Organometallics, Vol. 29, No. 9, 2010
Table 1. Crystal Data and Refinement Details for the X-ray Structure Determinations
Langer et al.
1
2
3
4/40
5
6
formula
C
27H48I2O5Sr
C16H34I2O5Sr
C16H36I2O6Sr
[0.85 (C29H55IN6Sr2)
0.15(C23H50I2N6Sr2)
0.5(C6H16N2)]
C
36H74I4N8OSr4
C18H37CaIN4
3
3
fw/g mol-1
794.07
-90(2)
monoclinic
C2/c
21.7972(7)
13.9236(6)
13.8943(3)
90
126.763(2)
90
3378.2(2)
4
1.559
34.53
11 859
2636
3876/0.0327
0.0894
0.0349
1.010
0.338/-0.860
none
738735
647.85
-90(2)
monoclinic
P21/c
17.1871(4)
8.9208(4)
16.1756(6)
90
99.600(2)
90
2445.35(15)
4
1.760
47.48
16 065
4047
5531/0.0447
0.0909
0.0369
1.014
665.87
-90(2)
monoclinic
C2/c
15.0594(11)
10.0303(7)
16.9646(15)
90
106.462(4)
90
2457.5(3)
4
1.800
47.3
7755
1773
2790/0.0707
0.0914
0.0432
0.928
1.088/-0.775
none
739482
P
855.50
1493.11
-90(2)
tetragonal
I42d
25.1714(4)
25.1714(4)
72.9560(13)
90
476.50
3
T/°C
-90(2)
orthorhombic
Pbca
12.7937(4)
18.8424(4)
33.4870(11)
90
90
90
8072.5(4)
8
1.408
35.5
48 714
4402
8791/0.1141
0.1821
0.0742
1.016
0.684/-0.752
none
738736
P
-90(2)
orthorhombic
Cmc21
13.2520(5)
11.3612(7)
15.6074(9)
90.00
90.00
90.00
2349.8(2)
4
1.347
15.88
7850
2120
2559/0.0518
0.0807
0.0359
cryst syst
space group
a/A
b/A
c/A
R/deg
β/deg
γ/deg
V/A3
Z
90
90
46224.9(13)
24
1.287
43.8
89 646
9149
25550/0.2280
0.3130
0.1112
1.044
1.491/-1.613
none
motif
F/g cm-3
3
μ/cm-1
measd data
data with I > 2σ(I)
unique data/Rint
wR2 (all data, on F2)a
R1 (I > 2σ(I))a
Sb
1.014
res dens/e A-3
absorpt method
CCDC no.
0.575/-1.030
none
0.506/-0.550
none
743858
3
739481
P
P
a Definition of the R indices: R1 = (
Fo| - |Fc )/ |Fo|; wR2 = { [w(Fo2 - Fc2)2]/ [w(Fo2)2]}1/2 with w-1 = σ2(Fo2) þ (aP)2 þ bP; P = [2Fc
þ
2
P
Max(Fo2)]/3. b S = { [w(Fo2 - Fc2)2]/(No - Np)}1/2
.
mixture was allowed to warm to 0 °C and was kept at this
temperature for 4.5 h. During this procedure the reaction flask
was shaken. The resulting brown solution was filtered, and the
solid residue was discarded. The solution (79% yield of orga-
nostrontium compounds, as determined by titration with 0.1 M
HCl of a hydrolyzed aliquot) was stored at -90 °C for 3 days.
Afterward the crystalline solid that had formed was collected on
a cooled Schlenk frit and dried in vacuo. Yield: 2.70 g (33%,
96% of the expected alkalinity of [(thf)5Sr(Ph)I] determined by
titration with 0.1 M HCl of a hydrolyzed aliquot). Two signal
sets for strontium-bound phenyl groups were observed in the
NMR spectra. 1H NMR (200 MHz, d8-THF, 300 K): δ 6.65-7.0
(m, p-CH þ m-CH Ph þ Ph*), 7.91 (br, o-CH Ph), 8.2 (v br, o-
CH Ph*). 13C NMR (50.33 MHz, d8-THF): δ 125.1 (p-CH Ph),
125.2 (p-CH Ph*), 126.4 (m-CH Ph), 126.6 (m-CH Ph*), 141.8
(o-CH Ph*), 142.3 (o-CH Ph), 193.0 (i-C Ph*), 194.5 (i-C Ph).
Formation of 4/40 and 5. Phenylstrontium iodide (650 mg)
prepared as described above was suspended in tmeda (20 mL)
at room temperature and stirred for 20 min. The remaining solid
was removed by filtration, and the mother liquor was concen-
trated to 16 mL in vacuo. Then the solution was stored for 3
weeks at -40 °C. Afterward the irregularly shaped, pale yellow
crystals of 4/40 that had formed were isolated by decantation of
Yield: 390 mg, 0.82 mmol, 97% (crude product). Suitable
crystals of 6 for X-ray diffraction experiments were obtained
by cooling a saturated solution in tmeda from rt to -40 °C.
These crystals were used for NMR measurement and elemen-
tal analysis. Anal. Calcd for C18H37CaIN4: Ca, 8.41. Found:
1
Ca, 8.7. H NMR (400 MHz, d8-THF): δ 2.16 (s, 24H, CH3
tmeda), 2.31 (s, 8H, CH2 tmeda), 6.70 (m, 1H, p-CH Ph),
6.81 (m, 2H, m-CH Ph), 7.66 (m, 2H, o-CH Ph). 13C NMR
(100.65 MHz, d8-THF): δ 46.2 (8 ꢁ NCH3 tmeda), 58.8 (4 ꢁ
NCH2 tmeda), 122.7 (p-CH Ph), 125.4 (2 ꢁ m-CH Ph), 141.1
(2 ꢁ o-CH Ph), 189.9 (i-C Ph). A second signal set of low
intensity for the phenyl group was observed. The values are
similar to the one reported for [(tmeda)Ca(Ph)(μ-Ph)]2,13
indicative of an active Schlenk equilibrium in solution. 13C
NMR: δ 125.9 (p-CH Ph*), 126.4 (m-CH Ph*), 144.3 (o-CH
Ph*), 185.2 (i-C Ph*).
Crystal Structure Determinations. The intensity data for the
compounds were collected on a Nonius KappaCCD diffract-
ometer using graphite-monochromated Mo KR radiation. Data
were corrected for Lorentz and polarization effects but not for
absorption effects.25,26 The structures were solved by direct
methods (SHELXS)27 and refined by full-matrix least-squares
techniques against Fo2 (SHELXL-97) (Table 1).28 All hydrogen
atoms were included at calculated positions with fixed thermal
parameters. All nondisordered non-hydrogen atoms were re-
fined anisotropically.28
1
the supernatant solution. Yield: 180 mg. H NMR (200 MHz,
d8-THF): δ 2.0-2.2 (br, 36H, CH3 tmeda þ 2 ꢁ NCH3), 2.30
(s, 10H, CH2 tmeda), 2.59 (br, 2H, CH2N), 2.90 (br s, 3H,
NCH3), 3.06 (br, 2H, NCH2), 6.86 (m, 2H, p-CH Ph), 7.01 (m,
4H, m-CH Ph), 8.09 (m, 4H, o-CH Ph). 13C NMR (50.3 MHz,
d8-THF): δ 43.0 (NCH3), 45.9 (2 ꢁ NCH3), 46.2 (10 ꢁ NCH3
tmeda), 57.1 (NCH2), 58.8 (5 ꢁ NCH2 tmeda), 62.3 (NCH2),
124.6 (2ꢁp-CH Ph), 126.6 (4ꢁm-CH Ph), 141.7 (4ꢁo-CH Ph),
194.4.0 (2 ꢁ i-C Ph). The mother liquor was filtered to remove
a small amount of amorphous precipitate, concentrated to
approximately 5 mL, and stored again for 3 weeks at -40 °C,
resulting in the formation of approximately 10 mg of crystal-
line 5.
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft (DFG, Bonn/Germany) for generous finan-
cial support of this research initiative. We also gratefully
(25) COLLECT, Data Collection Software; Nonius B.V.: Netherlands,
1998.
(26) Otwinowski, Z.; Minor, W. Processing of X-Ray Diffraction
Data Collected in Oscillation Mode. In Methods in Enzymology, Vol.
276, Macromolecular Crystallography, Part A; Carter, C. W.; Sweet, R. M.,
Eds.; Academic Press: San Diego, 1997; pp 307-326.
(27) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467–473.
(28) Sheldrick, G. M. SHELXL-97 (Release 97-2); University of
Synthesis of [(tmeda)2Ca(Ph)I] (6). [(thf)4Ca(Ph)I] (450 mg,
0.85 mmol) was suspended in tmeda (20 mL) at room tem-
perature and stirred for 1 h. The solvent was removed under
reduced pressure, and the residual solid was dried in vacuo.
€
Gottingen: Germany, 1997.

Article
Organometallics, Vol. 29, No. 9, 2010 2039
acknowledge the funding of the Fonds der Chemischen
Industrie (Frankfurt/Main, Germany).
http://pubs.acs.org. In addition, crystallographic data (exclud-
ing structure factors) have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications
CCDC-738735 for 1, -739481 for 2, -739482 for 3, -738736 for 4,
and -743858 for 6. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [e-mail: deposit@ccdc.cam.ac.uk].
Supporting Information Available: Crystallographic data of
the new compounds and CIF files giving data collection and
refinement details as well as positional coordinates of all atoms.
This material is available free of charge via the Internet at