Coordination behavior and coligand-dependent cis/trans isomerism of calcium bis(diphenylphosphanides)

Article abstract of DOI:10.1002/ejic.201100241

The salt metathesis reaction of KPPh₂ with CaI₂ and SrI₂ in THF yields the corresponding complexes [(THF) ₄Ae(PPh₂)₂] [Ae = Ca (1), Sr]. Depending on the crystallization conditions, cis- or trans-[(THF)₄Ca(PPh ₂)₂] can be isolated. In solution, a fast equilibrium converts these isomers into each other leading to a single set of resonances in the NMR spectra. The THF ligands can be replaced by stronger Lewis bases, such as N-methylimidazole (MeIm), which leads to the formation of [(MeIm) ₄Ae(PPh₂)₂] [Ae = Ca (2a), Sr (2b)]. The use of tetradentate hexamethyltriethylenetetramine (hmteta) fixes a cis configuration yielding [(hmteta)Ca(PPh₂)₂] (3). All compounds are very air and moisture sensitive, therefore a few crystals of the partially oxidized product [(hmteta)Ca(PPh₂)(OPPh₂)] (4) were also obtained. [(L)₄Ca(PPh₂)₂] is an effective hydrophosphanylation catalyst. To predetermine and fix a cis or trans arrangement of the phosphanide anions, the neutral coligand sphere of four Lewis base donors, such as four THF molecules or one hmteta ligand, was altered. Copyright

Full text of DOI:10.1002/ejic.201100241

FULL PAPER
DOI: 10.1002/ejic.201100241
Coordination Behavior and Coligand-Dependent cis/trans Isomerism of
Calcium Bis(diphenylphosphanides)
Jens Langer,[a] Tareq M. A. Al-Shboul,[a] Fadi M. Younis,[a] Helmar Görls,[a] and
Matthias Westerhausen*[a]
Keywords: Calcium / Strontium / Isomers / Phosphanides / Phosphinites
The salt metathesis reaction of KPPh2 with CaI2 and SrI2 in
THF yields the corresponding complexes [(THF)4Ae(PPh2)2]
[Ae = Ca (1), Sr]. Depending on the crystallization conditions,
cis- or trans-[(THF)4Ca(PPh2)2] can be isolated. In solution, a
fast equilibrium converts these isomers into each other lead-
ing to a single set of resonances in the NMR spectra. The
THF ligands can be replaced by stronger Lewis bases, such
as N-methylimidazole (MeIm), which leads to the formation
of [(MeIm)4Ae(PPh2)2] [Ae = Ca (2a), Sr (2b)]. The use of
tetradentate hexamethyltriethylenetetramine (hmteta) fixes
a cis configuration yielding [(hmteta)Ca(PPh2)2] (3). All com-
pounds are very air and moisture sensitive, therefore a few
crystals of the partially oxidized product [(hmteta)Ca(PPh2)
(OPPh2)] (4) were also obtained.
leading to exceptions from this rule. Therefore, a trans ar-
rangement of the phosphanide ligands in calcium bis(phos-
phanides) can be expected because this arrangement also
minimizes electrostatic repulsion between the anions. This
rule seems to be quite general because [(THF)4Ca-
(PPh2)2],[4,5] [(THF)4Ca{P(H)SiiPr3}2],[10] and [(THF)4Ca-
{P(SiMe3)2}2][11] crystallized with a trans arrangement
whereas the bulky 1,3,5-trimethyl-1,3,5-triazinane ligand
(tmta) enforces a bent P–Ca–P moiety with an angle of
110.2(1)° in [(tmta)2Ca{P(SiMe3)2}2] and an octa-coordi-
nate calcium atom.[12] Quantum chemical investigations on
monomeric derivatives AeX2 (X = CH3, NH2, OH, and F)
show that linear molecules can be expected for the lighter
alkaline earth metals, whereas strontium and barium tend
to form bent molecules due to small but significant d-or-
bital contributions.[13] Calcium and especially the heavier
homologous metals lie on the borderline between classic s-
block elements and early transition metals with an increas-
ing tendency to involve d-orbitals in bonding situations
from calcium to barium. Recent calculations also showed
dimethylcalcium to be bent.[14] Similar trends are valid for
unsolvated halides[15] and hydrides[16] with CaF2 being bent
whereas the heavier halides show linear CaX2 molecules in
contrast to bent BaX2. The solvation of CaI2 (which shows
a linear geometry if unsolvated) with mono-dentate Lewis
bases L, such as ethers, yields [(L)4CaI2] with a transoid
arrangement of the iodide anions.[2,3,17] The addition of tet-
Introduction
Calcium bis(phosphanides) are accessible through the
metalation of phosphanes and metathetically by the reac-
tion of potassium phosphanides with alkaline earth metal
diiodides in THF.[1] THF is an ideal solvent because it is a
strong base thus ensuring the solubility of calcium diiodide
as [(THF)4CaI2],[2,3] although the nearly quantitative pre-
cipitation of KI drives the metathesis reaction completely
in favor of calcium bis(phosphanide). This metathetical ap-
proach gave pure [(THF)4Ca(PPh2)2],[4,5] which proved to
be a valuable catalyst in hydrophosphanylation reactions of
alkynes.[6,7] Nevertheless, with catalytic amounts of [(THF)4-
Ca(PPh2)2], reactions of HPPh2 with substituted butadiynes
gave various regio- and stereoisomers. The resulting C=C
double bonds remained inactive during this procedure. In
another reaction, heteroleptic calcium diphenylphosphan-
ides showed catalytic hydrophosphanylation activity toward
activated alkenes.[7,8] Due to the importance of calcium
bis(diphenylphosphanide) in calcium-mediated hydro-phos-
phanylation reactions of alkynes, we were interested in
varying the coordination sphere to tune the reactivity and
regioselectivity of these catalysts.
Schleyer and co-workers[9] stated roughly 20 years ago
that “the preferred anion orientation in unsolvated species
will dominate the coordination geometries of the solvated
complexes as well” because “anionic ligands are bound
more strongly than neutral coligands” with bulky coligands
ramethylethylenediamine
[1,2-bis(dimethylamino)ethane,
tmeda] leads to trans-[(tmeda)2CaI2], however, tetradentate
hexamethyltriethylenetetramine (hmteta) enforces a cis ar-
rangement of the CaI2 unit.[17] Additionally, the 1,2-di-
methoxyethane adduct [(dme)2Ca(NPh2)2] adopts a cis ar-
rangement.[18]
[a] Institute of Inorganic and Analytical Chemistry, Friedrich
Schiller University,
Humboldtstrasse 8, 07743 Jena, Germany
Fax: +49-3641-948102
E-mail: m.we@uni-jena.de
3002
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Eur. J. Inorg. Chem. 2011, 3002–3007

Coordination Behavior of Calcium Bis(diphenylphosphanides)
Due to the importance of calcium bis(diphenylphos-
Due to the fact that the bis(tmeda) complex of calcium
phanide) in catalytic hydrophosphanylation reactions we in- diiodide crystallized as a trans isomer and the hmteta ad-
vestigated the coordination behavior of this complex.
duct with a cisoid iodide arrangement, we substituted the
THF ligands of 1 by hmteta. The major product was indeed
the calcium complex [(hmteta)Ca(PPh2)2] (3) with the di-
phenylphosphanide ligands in a cisoid fashion. There are
two possible isomers with this structure (Scheme 3), namely,
a complex with a cis or a trans configuration of the dimeth-
ylamino bases. Due to steric reasons, the trans isomer is
formed. Traces of oxygen (from exposure to adventitious
air) oxidized Ph2P– to Ph2P-O– anions, which were also de-
tected in solution by 31P NMR spectroscopy. A very similar
configuration was also observed for heteroanionic [(hmteta)-
Ca(PPh2)(OPPh2)] (4), which was isolated together with the
major product 3.
Results and Discussion
The metathesis reaction of KPPh2 with CaI2 in THF
yields [(THF)4Ca(PPh2)2] (1),[4,5] which can be recrys-
tallized after the removal of insoluble potassium iodide
(Scheme 1). A careful investigation of the crystal shape
showed two crystal morphologies, namely, cubic blocks and
rod-shaped crystals. Therefore, crystallization conditions
were investigated in more detail. At –40 °C, predominantly
rod-shaped crystals of cis-[(THF)4Ca(PPh2)2] (cis-1) pre-
cipitated from concentrated solutions. After removal of this
crystalline material the mother liquor was cooled and from
this diluted solution orange-red blocks of trans-[(THF)4-
Ca(PPh2)2] (trans-1) predominantly formed. These findings
were verified by X-ray structure determinations. Both iso-
mers are shown in Scheme 2. In solution, only one set of
signals can be observed by NMR spectroscopy. Upon cool-
ing the solution, however, a shift of the singlet in the 31P
NMR spectra from δ = 13.1 (293 K) to δ = 18.0 ppm
(203 K) was observed, accompanied by a slight broadening
of the signal.
Scheme 3. Possible isomers for the hmteta complex 3 of calcium
bis(diphenylphosphanide). The phosphorus atoms can be in a trans
(top) or a cis arrangement with the dimethylamino groups in a
trans (bottom, left) or cis orientation (bottom, right).
Scheme 1. Syntheses of 1–3.
The initial objective of this investigation was the elucida-
tion of the influence of a cis or trans arrangement of the
diphenylphosphanides on the structural parameters and in
a later study on the catalytic reactivity. From THF solu-
tions, both isomers can be isolated depending on the
crystallization conditions, however, an equilibrium, fast on
the NMR time scale, leads to a single set of resonances in
solution spectra. The molecular structure and numbering
scheme of cis-1 are represented in Figure 1.
Contrary to the expectation that cis-arranged bulky
anions should enhance repulsive electrostatic and steric
strain leading to enhanced bond lengths, the average Ca–P
and Ca–O distances are smaller than observed for the trans
isomer (Table 1). However, enhancement of the negative
charge on the phosphorus atoms on replacement of the
phenyl groups by trialkylsilyl substituents leads to smaller
Scheme 2. Schematic drawing of trans-[(THF)4Ca(PPh2)2] (trans-1)
and cis-[(THF)4Ca(PPh2)2] (cis-1), which precipitate depending on
the crystallization conditions. Only the Ca–P bonds are drawn, the
other lines represent the edges of the coordination octahedron.
The substitution of the coordinated THF molecules of Ca–P distances as, for example, observed for [(THF)4Ca-
[(THF)4Ca(PPh2)2] (1) with the stronger Lewis base N- {P(SiMe3)2}2] (av. Ca–P 291.8 pm[11]). In addition, smaller
methylimidazole (MeIm) was achieved by the addition of coordination numbers of calcium also lead to a contraction
this azaligand to a THF solution of 1. Recrystallization of the Ca–P bond[22] enhanced by incorporation of the phos-
from a toluene/THF mixture gave orange-red single crystals phanide functionality in a bidentate ligand system.[22,23]
of [(MeIm)4Ca(PPh2)2] (2a). A similar protocol gave Reduction of the charge on the phosphorus atom by delo-
orange-red crystals of the homologues strontium derivative calization, as in [(THF)3Ca{(Me2P)2C-SiMe3}2] {Ca–P
[(MeIm)4Sr(PPh2)2] (2b). In both cases, the crystalline sol- ranging from 303.8(1) to 304.9(1) pm[24]}, or on the calcium
ids contained the trans isomers.
atom by a covalently bound counter part, as in [(THF)4-
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M. Westerhausen et al.
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azole adducts of ytterbium,[20] europium,[21] and samarium
bis(diphenylphosphanide),[19] which are included for com-
parison in Table 1.
Figure 1. Molecularstructure and numbering scheme of cis-[(THF)4-
Ca(PPh2)2] (cis-1). The ellipsoids represent a probability of 40%,
H atoms are omitted for clarity. Symmetry-related atoms (–x, y,
–z + 1.5) are marked with the letter “A”. Selected bond lengths
[pm]: Ca1–O1 236.6(1), Ca1–O2 234.4(1), Ca1–P1 295.12(5), P1–
C1 182.3(2), P1–C7 181.1(2); angles (deg.): P1–Ca1–P1A 95.55(2),
P1–Ca1–O1 92.12(3), P1–Ca1–O2 93.41(3), P1–Ca1–O1A
170.29(3), P1–Ca1–O2A 90.43(3), O1–Ca1–O2 83.15(4), O1–Ca1–
O1A 80.93(6), O1–Ca1–O2A 92.49(4), O2–Ca1–O2A 174.28(6),
Ca1–P1–C1 117.18(5), Ca1–P1–C7 111.67(5), C1–P1–C7 106.69(7).
Figure 2. Molecular structure and numbering scheme of [(MeIm)4-
Ca(PPh2)2] (2a). Ellipsoids represent a probability of 40%, H atoms
are omitted for clarity. Symmetry-related atoms (–x, –y, –z + 1) are
marked with the letter “A”. Selected bond lengths of 2a [of isotypic
2b in square brackets] [pm]: Ae1–P1 303.8(1) [315.42(7)], Ae1–N1
245.2(3) [260.1(2)], Ae1–N3 244.1(3) [262.4(2)], P1–C9 181.0(4)
[181.0(3)], P1–C15 181.5(4) [181.5(3)]; angles (deg.): P1–Ae1–P1A
180.0 [180.0], P1–Ae1–N1 91.72(8) [90.89(6)], P1–Ae1–N3 86.39(7)
[91.66(5)], N1–Ae1–N3 85.35(10) [94.91(8)], Ae1–P1–C9 122.0(1)
[111.67(9)], Ae1–P1–C15 115.2(1) [123.36(9)], C9–P1–C15 106.1(2)
[107.0(1)].
Ca(Ph)(PPh2)] {Ca–P 301.0(2) pm[25]}, led to enlarged Ca–
P distances. The phosphorus atoms in cis-1 are in pyramidal
environments and with this geometry, crowding is reduced
by the diphenylphosphanide groups turning away from one
another. The rather short Ca–O bonds and the fact that the
Ca–O values trans to P and trans to O are similar, verify
the lack of significant intramolecular strain.
The molecular structure and numbering scheme of
Substitution of the THF ligands by N-methylimidazole [(hmteta)Ca(PPh2)2] (3) and [(hmteta)Ca(PPh2)(OPPh2)] (4)
leads to the alkaline earth metal complexes [(MeIm)4Ae- are represented in Figures 3 and 4, respectively. In both
(PPh2)2] (2a: Ae = Ca; 2b: Ae = Sr). The molecular struc- structures, the hmteta ligands show very similar conforma-
ture and numbering scheme of 2a is displayed in Figure 2, tions with the dimethylamino functionalities in a trans
values for 2b are given in the legend and listed in Table 1. alignment. The Ca–N distances to the dimethylamino bases
The alkaline earth metal atoms are in distorted octahedral are smaller than those to the inner nitrogen atoms, which
environments with trans arrangements of the diphenylphos- can be explained by an enhanced steric strain. This crowd-
phanyl ligands and form short bonds to the imidazole li- ing also enhances the Ca–P bond lengths in comparison
gands leading to an elongation of the Ae–P bonds. The with those in the THF complex of calcium bis(diphenyl-
planar imidazole ligands represent strong Lewis bases with phosphanide).[4,5] Furthermore, steric repulsion leads to in-
nearly planar coordinating N1 and N3 nitrogen atoms. creased angle sums of the phosphorus atoms as a conse-
These complexes show very similar molecular structures to quence of the fact that the diphenylphosphanyl groups are
those also observed for the corresponding N-methylimid- straightened up toward the periphery of the complex.
Table 1. Average values of selected structural parameters of adducts of mononuclear calcium and strontium bis(diphenylphosphanide) of
the type [(L)nM(PPh2)2]. For comparison reasons [(THF)4Ca(PPh2)2] (trans-1) as well as isotypic alkaline earth metal and lanthanoid
complexes are included.
Compound
M–P
M–O/N
P–C
P–M–P
M–P–C
C–P–C
ΣP
Ref.
[4,5]
trans-[(THF)4Ca(PPh2)2]
cis-[(THF)Ca(PPh2)2]
trans-[(MeIm)4Ca(PPh2)2]
cis-[(hmteta)Ca(PPh2)2]
trans-[(THF)4Sr(PPh2)2]
trans-[(MeIm)4Sr(PPh2)2]
[(THF)5Ba(PPh2)2]
298.7
295.1
303.8
301.3
314.3
315.4
333.7
334.8
299.1
302.8
312.7
313.9
237.6
235.5
244.7
254.8
252.1
261.3
274.7
278.5
243.4
249.1
260.8
262.1
182.0
181.7
181.3
183.0
181.8
181.3
181.6
181.9
184.3
181.4
181.5
180.8
180
95.55
180
99.19
177.4
180
157.1
160.8
180
109.5/120.5
111.7/117.2
115.2/122.0
110.5/123.3
101.6/106.2
111.7/123.4
105.6/115.7
97.9/101.8
110.2/119.4
114.6/123.0
113.7/123.0
112.8/124.3
103.4
106.7
106.1
103.0
107.3
107.0
106.0
105.3
103.1
106.4
106.6
106.3
333.4
335.5
343.3
336.7
316.6
342.1
327.2
306.0
332.7
343.9
343.3
343.1
[4,5]
[4]
[5]
[(18C6)Ba(PPh2)2]
[19]
[20]
[21]
[19]
trans-[(THF)4Yb(PPh2)2]
trans-[(MeIm)4Yb(PPh2)2]
trans-[(MeIm)4Eu(PPh2)2]
trans-[(MeIm)4Sm(PPh2)2]
180
180
180
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Coordination Behavior of Calcium Bis(diphenylphosphanides)
alkoxides do not provide useful data for comparison be-
cause of their complex oligomeric structures.[27]
Conclusion
THF complexes of alkaline earth metal bis(diphenyl-
phosphanides) can adopt cis and trans configurations,
which are in a fast equilibrium in solution. Depending on
the crystallization conditions, for example, the concentra-
tion of the mother liquor and crystallization temperature,
cis or trans isomers can be crystallized. The coordination
of tetradentate hexamethyltriethylenetetramine (hmteta) en-
forces a cis arrangement of the diphenylphosphanide li-
gands.
The angle sums of the phosphorus atoms reflect the
steric hindrance between the phosphanide ligands and the
neutral coligands (THF, MeIm, or hmteta). In no case is
a planar coordination of the phosphorus atom observed.
Stronger bases, such as N-methylimidazole, cause an elong-
ation of the Ca–P bonds. These alkaline earth metal com-
pounds form crystal structures that are similar to those of
the ytterbium, europium, and samarium analogues, exemp-
lifying an often-observed relationship. Future studies to
clarify the influence of the configuration on the reactivity
and catalytic behavior of these complexes will be facilitated
by the isolation of compounds with well-defined cis and
trans configurations.
Figure 3. Molecular structure and numbering scheme of [(hmteta)-
Ca(PPh2)2] (3). The ellipsoids represent a probability of 40%. H
atoms are omitted for clarity. Symmetry-related atoms (–x, y, –z +
0.5) are marked with the letter “A”. Selected bond lengths [pm]:
Ca1–P1 301.3(1), Ca1–N1 251.5(3), Ca1–N2 258.0(6), P1–C1
181.8(4), P1–C7 184.2(4); angles (deg.): P1–Ca1–P1A 99.19(5), P1–
Ca1–N1 88.56(8), P1–Ca1–N2 153.6(1), P1–Ca1–N1A 95.83(7),
P1–Ca1–N2A 99.4(1), N1–Ca1–N2 71.0(1), N1–Ca1–N1A
173.2(2), N1–Ca1–N2A 103.2(1), N2–Ca1–N2A 70.4(2), Ca1–P1–
C1 123.3(1), Ca1–P1–C7 110.5(1), C1–P1–C7 103.0(2).
Experimental Section
General: All manipulations were carried out in an argon atmo-
sphere under anaerobic conditions. Prior to use, all solvents were
thoroughly dried and distilled under an argon atmosphere. In many
cases, it was not possible to weigh out a definite amount because
the compounds were so sensitive to air and moisture that they de-
composed, at least partially, during this procedure. Therefore, the
analyses are limited to NMR spectroscopy and X-ray structure de-
terminations. 1H, 31P{1H}, and 13C NMR spectra were recorded in
[D8]THF solutions at ambient temperature on a Bruker AC
200 MHz or a Bruker AC 400 MHz spectrometer. All spectra were
referenced to 98% perdeuterated THF as an internal standard.
Starting [(THF)4Ae(PPh2)2] (Ae = Ca, Sr) was prepared metatheti-
cally according to a literature procedure[4,5] from KPPh2 and AeI2.
Figure 4. Molecular structure and numbering scheme of [(hmteta)-
Ca(PPh2)(OPPh2)] (4). The ellipsoids represent a probability of
40%, H atoms are omitted for clarity. Selected bond lengths [pm]:
Ca1–P1 302.0(1), Ca1–O1 216.7(3), Ca1–N1 252.0(4), Ca1–N2
262.1(4), Ca1–N3 263.8(4), Ca1–N4 258.3(4), P1–C13 182.9(5), P1–
C19 182.8(4), O1–P2 155.6(3), P2–C25 184.2(5), P2–C31 185.2(5);
angles (deg.): P1–Ca1–O1 103.0(1), P1–Ca1–N1 98.02(9), P1–Ca1–
N2 101.58(9), P1–Ca1–N3 152.66(9), P1–Ca1–N4 87.3(1), O1–
Ca1–N1 95.3(1), O1–Ca1–N2 153.5(1), O1–Ca1–N392.9(1), O1–
Ca1–N4 88.0(1), N1–Ca1–N2 71.5(1), N1–Ca1–N3 102.5(1), N1–
Ca1–N4 173.0(1), N2–Ca1–N3 68.8(1), N2–Ca1–N4 103.0(1), N3–
Ca1–N4 71.0(1), Ca1–O1–P2 161.4(2), Ca1–P1–C13 110.6(1), Ca1–
P1–C19 110.1(1), C13–P1–C19 103.1(2), O1–P2–C25 104.3(2), O1–
P2–C31 103.8(2), C25–P2–C31 98.4(2).
Isolation of cis-[(THF)4Ca(PPh2)2] (cis-1): A solution of KPPh2 in
THF (0.5 m, 9.7 mL, 4.85 mmol) was added to a solution of anhy-
drous CaI2 (0.71 g, 2.42 mmol) in THF (40 mL). During this pro-
cedure, a colorless precipitate of KI formed and the solution turned
orange-red. The reaction mixture was stirred an additional hour at
room temperature and filtered to remove the solid. The mother
liquor was reduced to approximately 20 mL by vacuum distillation
and stored at –40 °C overnight. The formed orange-yellow rod-like
crystals were collected on a cooled Schlenk frit and gently dried in
vacuo. The crystals tended to lose cocrystallized THF upon pro-
longed drying. Yield: 0.69 g (0.82 mmol, 34%).
In complex 4, one of the phosphanyl groups is oxidized
leading to the diphenylphosphinite anion [Ph2PO]–. In this
anion the phosphorus atom is in a pyramidal environment
with a small angle sum of 306.5°. The P–O bond length of
155.6(3) pm is very small. A larger value of 159.62(2) pm
was observed for the bridging Ph2PO– anion with a three-
coordinate oxygen atom between two calcium atoms in
[(bdi)Ca(μ-OPPh2)]2, in which bdi refers to the anion
formed by deprotonation of 2-[(2,6-diisopropylphenyl)-
amino]-4-[2,6-diisopropylphenylimino]pent-2-ene.[26] The
Ca1–O1 bond length of 216.7(3) pm in complex 4 is very
Crystals of this crop were identified as cis-1·2THF by X-ray diffrac-
tion experiments. From the mother liquor, orange-red blocks were
obtained by prolonged storage at –40 °C, identified as the trans
short due to a strong electrostatic attraction. The calcium isomer (Note that the crystal shape is not sufficient to distinguish
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M. Westerhausen et al.
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between the isomers, as under differing conditions the trans isomer
THF (10 mL) caused an immediate color change to orange. The
subsequent addition of MeIm (0.26 mL) deepened the orange
color. Filtration and removal of all volatile materials left a residue
that was washed with toluene and recrystallized from a mixture of
toluene and THF (ratio 3:1). Cooling to –30 °C gave red crystalline
2b (0.51 g, 80%). This compound is soluble in THF but insoluble
in aliphatic and aromatic hydrocarbons.
was obtained in the form of yellow needles).[5]
[(MeIm)4Ca(PPh2)2] (2a). Method A: N-Methylimidazole (MeIm,
0.13 mL, 1.69 mmol) was added to an orange solution of [(THF)4-
Ca(PPh2)2] (295 mg, 0.42 mmol) in THF (15 mL) at room tempera-
ture. After 20 min all volatiles were removed in vacuo and the resi-
due washed with hexane. Recrystallization from a mixture of tolu-
ene and THF (ratio 3:1) at –30 °C afforded red crystals of 2a
(0.23 g, 74%).
M.p. 121–123 °C (dec.). (C40H44N8P2Sr, 786.40): calcd. C 61.09, H
1
5.64, N 14.25; found C 60.00, H 5.93, N 13.64. H NMR: δ = 3.60
(s, Me), 6.4–7.0 and 7.3–7.6 (Ph, Im) ppm. 13C NMR: δ = 33.0
(Me), 120.2 (br., Ph), 120.4 (Im), 127.7 (br., Ph), 129.8 (Im), 130.9
(br., Ph), 139.4 (Im) ppm; ipso-C not found. 31P{1H} NMR: δ =
Method B:
A solution of KPPh2 in THF (0.5 m, 6.1 mL,
3.05 mmol) was added dropwise to a solution of anhydrous CaI2
(455 mg, 1.55 mmol) in THF (10 mL). The reaction mixture turned
orange. MeIm (0.51 mL) was then added dropwise to this reaction
mixture. Filtration (removal of insoluble KI), removal of all vola-
tiles, washing with hexane, and recrystallization from a mixture of
benzene and THF (ratio 3:1) gave red crystals of 2a (0.81 g, 71%).
Complex 2a is soluble in THF but insoluble in aliphatic and aro-
matic hydrocarbons.
–6.8 (s) ppm. IR (Nujol): ν = 3111 (m), 3056 (m), 2993 (w), 2953
˜
(w), 2917 (w), 2343 (w), 1965 (w), 1896 (w), 1822 (w), 1775 (w),
1631 (w), 1581 (m), 1517 (vs), 1475 (s), 1436 (s), 1421 (w), 1285 (s),
1231 (s), 1231 (s), 1191 (sh br), 1128 (w), 1079 (m), 1026 (m), 979
(w), 921 (m), 908 (m), 816 (s), 741 (s), 699 (s), 663 (s), 617 (s), 561
(m), 530 (m) cm–1.
[(hmteta)Ca(PPh2)2] (3) and [(hmteta)Ca(PPh2)(OPPh2)] (4): Hexa-
methyltriethylenetetramine (0.38 g, 1.65 mmol) was added to a
stirred suspension of trans-[(THF)4Ca(PPh2)2] (1.048 g, 1.50 mmol)
in toluene (15 mL). The resulting reaction mixture was stirred for
2 h at room temperature. The yellow precipitate of 3 was collected
on a Schlenk frit and dried in vacuo. The mother liquor was stored
at –40 °C for several days resulting in the formation of a few tiny
yellow platelets of 4·1.5toluene. Yield: 0.94 g (1.47 mmol, 98%) of
M.p. 137–140 °C (dec.). (C40H44CaN8P2, 738.86): calcd. C 65.02,
1
H 6.00, N 15.17; found C 64.82, H 6.12, N 14.93. H NMR: δ =
3.60 (s, Me), 6.8–7.7 (Ph, Im) ppm. 13C NMR: δ = 32.7 (s, Me),
120.2 (s, Im), 129.1 (s, Ph), 129.2 (d, JPC = 6.2 Hz, Ph), 129.9 (s,
Im), 134.6 (d, JPC = 17.1 Hz, Ph), 138.4 (s, Im) ppm; ipso-C signal
not visible. 31P{1H} NMR: δ = –13.6 (s) ppm. IR (Nujol): ν = 3109
˜
(w), 3052 (m), 2951 (w), 1967 (w), 1897 (w), 1828 (w), 1673 (m),
1590 (m), 1518 (s), 1437 (s), 1285 (m), 1231 (w), 1201 (sh br), 1126
(w), 1063 (m), 1027 (m), 999 (w), 923 (m), 907 (m), 818 (m), 749
(s), 720 (vs), 698 (s), 663 (s), 617 (m), 565 (m), 539 (w) cm–1.
1
yellow 3. Characterization of 3: H NMR: δ = 2.15 (s, 12 H, Me),
2.20 (s, 6 H, Me), 2.37 (m, 4 H, CH2), 2.42 (s, 4 H, CH2), 6.61 (br.,
4 H, p-CH Ph), 6.86 (br., 8 H, m-CH Ph), 7.41 (br pseudo-t, 8 H,
o-CH Ph) ppm. 13C NMR: δ = 43.3 (s, 2C, CH3), 46.1 (s, 4C, CH3),
57.3 (s, 4C, CH2), 58.8 (s, 2C, CH2), 121.0 (br., 4C, p-CH Ph), 127.7
[(MeIm)4Sr(PPh2)2] (2b). Method A: N-Methylimidazole (0.11 mL,
1.34 mmol) was added at room temperature to an orange solution
of [(THF)4Sr(PPh2)2] (250 mg, 0.334 mmol) in THF (20 mL). After
30 min the solvent was removed in vacuo and the residue washed
with toluene. Recrystallization at –30 °C from a mixture of toluene
and THF (ratio 3:1) afforded 2b (0.2 g, 77%).
3
(d, JPC = 5.2 Hz, 8C, m-CH Ph), 131.2 (m, 8C, o-CH Ph), 153.1
1
(d, JPC = 32.9 Hz, 4C, i-C Ph) ppm. 31P{1H} NMR: δ = –13.0 (s)
ppm. The NMR spectroscopic data indicate complete substitution
of hmteta by [D8]THF in solution.
Method B: Addition of a solution of KPPh2 in THF (0.5 m, 3.3 mL,
Crystal Structure Determinations: The intensity data for the com-
1.63 mmol) to a solution of [(THF)5SrI2] (577 mg, 0.82 mmol) in
pounds was collected on a Nonius KappaCCD diffractometer
Table 2. Crystal data and refinement details for the X-ray structure determinations of 1, 2a, 2b, 3, and 4.
Compound
cis-1
2a
2b
3
4
Formula
fw /gmol–1
T /°C
Crystal system
Space group
a /Å
C40H52CaO4P2·2C4H8O C40H44CaN8P2
C40H44N8P2Sr C36H50CaN4P2 C36H50CaN4OP2·1.5C7H8
843.04
738.85
786.39
640.82
795.02
–140(2)
monoclinic
C2/c
28.3842(4)
8.4877(1)
22.0814(3)
120.508(1)
4583.29(10)
4
–90(2)
monoclinic
P21/n
9.8382(8)
17.967(2)
10.9869(13)
95.765(7)
1932.3(4)
2
–90(2)
monoclinic
P21/n
–140(2)
monoclinic
C2/c
–140(2)
monoclinic
C2/c
10.0306(3)
17.5212(9)
11.2950(5)
95.213(3)
1976.86(15)
2
17.4513(7)
11.2393(7)
17.8468(7)
92.367(3)
3497.5(3)
4
42.9287(10)
11.6140(4)
17.9756(7)
97.159(2)
8892.3(5)
8
b /Å
c /Å
β /°
V /Å3
Z
ρ /gcm–3
μ /mm–1
Measured data
Data with IϾ2σ(I)
1.222
2.53
1.270
2.85
1.321
1.217
1.188
14.84
13269
3.01
9988
2.51
22387
14022
4608
11885
2913
2917
2770
7250
Unique data (Rint
)
5232/0.0233
0.1129
0.0408
1.009
0.956/–0.749
none
4378/0.0968
0.1810
0.0671
0.977
0.274/–0.409
none
4485/0.0583
0.1144
0.0440
0.940
0.316/–0.303
none
3918/0.0576
0.1739
0.0722
1.116
0.400/–0.462
none
9610/0.0535
0.2538
0.0988
1.126
0.822/–0.570
none
wR2 (all data, on F2)[a]
R1 [IϾ2σ(I)][a]
[b]
S
Residual dens. /eÅ–3
Absorption method
2
2 2
[a] Definition of the R indices: R1 = (Σ||Fo| – |Fc||)/Σ|Fo|; wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2 with w–1 = σ2(Fo2) + (aP)2. [b] s =
2
2 2
{Σ[w(Fo – Fc ) ]/(No – Np)}1/2
.
3006
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 3002–3007

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Received: March 9, 2011
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Published Online: May 24, 2011
Eur. J. Inorg. Chem. 2011, 3002–3007
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3007