Tethered cationic alkaline earth-olefin complexes

Article abstract of DOI:10.1039/c7dt03300a

The aminofluoroalcohol N,N,N-(CH₂CHCH₂CH₂-),(CH₃OCH₂CH₂-),(HOC(CF₃)₂CH₂-)N ({RO^F}H) possessing both a methoxy and an olefin dangling side arms enables the preparation of the heteroleptic charge neutral alkaline earth complexes [{μ²-RO^F}AeN(SiMe₂H)₂]₂ (Ae = Ca, 1; Sr, 2). These O-bridged dinuclear complexes were characterised by NMR spectroscopy and X-ray diffraction crystallography. XRD analysis of 1 and 2 showed that both complexes are stabilised by intramolecular Ae?F-C and β-agostic Ae?H-Si secondary interactions, and that the olefin does not bind to the alkaline earths while the methoxy side-arm does. The discrete ion pairs [({μ²-RO^F}Ae·(Et₂O)₂)₂]²⁺·2[H₂N{B(C₆F₅)₃}₂]^- (Ae = Ca, 3a; Sr, 4a) were synthesised upon treatment of the parent complexes 1 and 2 by [H·(Et₂O)₂]⁺.[H₂N{B(C₆F₅)₃}₂]^-. NMR spectroscopy showed the presence of two coordinated Et₂O molecules on each metal in these complexes. The water adduct [({μ²-RO^F}Sr·(H₂O))₂]²⁺·2[H₂N{B(C₆F₅)₃}₂]^- (4b), presumably derived from 4a upon adventitious introduction of moisture during recrystallisation, was characterised by crystallographic methods. The dication [({μ²-RO^F}Sr·(H₂O))₂]²⁺ exists as an O-bridged dinuclear species featuring very strong intramolecular Sr?F-C interactions in the range 2.788(5)-2.997(6) ?, and no interaction with the weakly coordinating anion. Perhaps more importantly, the tethered olefins are coordinated onto the metal cations, with short Sr?Cπ interactions in the range 3.066(10)-3.092(10) ?; this represents the first example of a Sr-olefin cationic complex. Hence, cationisation of the charge neutral precursor to generate the discrete ion pair increases electron deficiency at the metal centre, resulting in the first observation of the binding of an olefin onto a well-defined cationic heavy alkaline earth. On the other hand, our attempts to produce Ae-olefin cations devoid of coordinated Lewis base with this strategy have met no success so far.

Full text of DOI:10.1039/c7dt03300a

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Tethered cationic alkaline earth - olefin complexes
SorinꢀClaudiu Roꢁca, Vincent Dorcet, Thierry Roisnel,
JeanꢀFrançois Carpentier*, and Yann Sarazin*
Université de Rennes 1, CNRS, Institut des Sciences Chimiques de Rennes, UMR 6226, Campus
de Beaulieu, Fꢀ35042 Rennes Cedex, France. Eꢀmail: jeanꢀfrancois.carpentier@univꢀrennes1.fr;
yann.sarazin@univꢀrennes1.fr; Fax: (+33) 2 23 23 69 39; Tel: (+33) 2 23 23 30 19
1

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Abstract
The
aminofluoroalcohol
N,N,Nꢀ(CH2=CHCH2CH2ꢀ),(CH3OCH2CH2ꢀ),(HOC(CF3)2CH2ꢀ)N
({ROF}H) possessing both a methoxy and an olefin dangling side arms enables the preparation of
the heteroleptic charge neutral alkaline earth complexes [{ꢂ2ꢀROF}AeN(SiMe2H)2]2 (Ae = Ca, 1;
Sr, 2). These Oꢀbridged dinuclear complexes were characterised by NMR spectroscopy and Xꢀ
ray diffraction crystallography. XRD analysis of 1 and 2 showed that both complexes are
stabilised by intramolecular Ae···F–C and βꢀagostic Ae···H–Si secondary interactions, and that
the olefin does not bind to the alkaline earths while the methoxy sideꢀarm does. The discrete ion
pairs [({ꢂ2ꢀROF}Ae•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (Ae = Ca, 3a; Sr, 4a) were synthesised
upon treatment of the parent complexes 1 and 2 by [H•(Et2O)2]+.[H2N{B(C6F5)3}2]–. NMR
spectroscopy showed the presence of two coordinated Et2O molecules on each metal in these
complexes. The water adduct [({ꢂ2ꢀROF}Sr•(H2O))2]2+.2[H2N{B(C6F5)3}2]– (4b), presumably
derived from 4a upon adventitious introduction of moisture during recrystallisation, was
characterised by crystallographic methods. The dication [({ꢂ2ꢀROF}Sr•(H2O))2]2+ exists as an Oꢀ
bridged dinuclear species featuring very strong Sr···F–C interactions in the range 2.788(5)ꢀ
2.997(6) Å, and no interaction with the weakly coordinating anion. Perhaps more importantly, the
tethered olefins are coordinated onto the metal cations, with short Sr···Cπ interactions in the
range 3.066(10)ꢀ3.092(10) Å; this represents the first example of a Srꢀolefin cationic complex.
Hence, cationisation of the charge neutral precursor to generate the discrete ion pair increases
electron deficiency at the metal centre, resulting in the first observation of the binding of an
olefin onto a wellꢀdefined cationic heavy alkaline earth. On the other hand, our attempts to
produce Aeꢀolefin cations devoid of coordinated Lewis base with this strategy have met no
success so far.
2

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Introduction
The coordination chemistry of the large alkaline earths (Ae) calcium, strontium and barium has
enjoyed a remarkable growth in the past 15 years, in particular because these abundant metals
have emerged as viable alternatives to late transition metals in homogenous catalysis.1 Under the
impulse of Westerhausen, the fundamental organometallic chemistry of calcium has proved to
provide much more than just a heavier version of Grignard’s magnesium reagents, and calcium
alkyl and aryl compounds have instead demonstrated a reactivity of their own.2 Some of the
prominent examples include mesitylcalcium iodide,3 diarylcalcium,4 arylcalcium cations,5 an
exquisite inverse organocalcium(I) sandwich complex6 or 1ꢀalkenyl and alkyl calcium iodides.7
By comparison, Aeꢀcarbon bonds with stabilising electronꢀrich monoanionic groups, e.g.
cyclopentadienyls8 or allyls,9 have been known for some time, while on the other hand, very little
is known of the bonding between Ae metals and neutral π ligands.2a This situation results from
the inability to establish dꢀπ* back donation in Ae complexes owing to their d0 external electronic
configuration, by contrast with late transition metal complexes. This paucity is best expressed for
Aeꢀolefin complexes, for which only a handful of cases of olefin coordination are known.10 The
seminal example, Schumann’s [Ae(C5Me4CH2CH2CH=CH2)2] (Ae = Ca, Sr, Ba; I in Fig. 1),11
was followed by Roesky’s related [Ba(C5Me5)(C5Me4CH2C5Me5)].12 More recently, we have
reported on heteroleptic Aeꢀolefin complexes supported by fluoroalkoxides, and stabilised by a
pattern of intramolecular Ae···F–C, Ae···Cπ and βꢀagostic Ae···H–Si secondary interactions
(Fig. 1, IIꢀIII).13 Aeꢀolefin complexes are thought to be models of putative reactive intermediates
in the catalysed hydroamination and hydrophosphination of alkenes.1,14 To our surprise, the olefin
complexes II and III proved as stable as the intramolecular methoxy adducts IV and V.15
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Me2 SiMe2H
Me2 SiMe2H
Si
N
Si
F2
H
F2
C
H
F
F3C
N
F3C
N
N
C
iPr
F
Ae
O
Ca
O
O
N
O
N
iPr
Ae
Ca
Ae
F
F
C
N
C
H
N
H
CF3
CF3
F2
F2
Si
Si
HMe2Si
HMe2Si
Me2
Me2
Ae = Ca
Sr
(II-Ca)
(II-Sr)
(I-Ae)
(III)
O
tBu
O
O
O
N
O
O
N
CF3
R
N
tBu
CF3
CF2
SiMe2H
O
CF2
O
O
H
O
Ae
N
Ae
F
F
SiMe2
O
O
Ca
Ae
F
H
H
Ca
Ae
O
O
O
O
O
Me2Si
O
F2C
F3C
tBu
F
N
N
N
F2C
F3C
O
O
N
HMe2Si
R
O
O
tBu
O
O
[H2N{B(C6F5)3}2]
[H2N{B(C6F5)3}2]
2
2
R = Me (IV)
R = CH2CH2OMe (V)
(VI-Ae)
(VII-Ae)
Fig. 1 Examples of Aeꢀolefin complexes (IꢀIII), chargeꢀneutral compounds with secondary
interactions (IVꢀV), and discrete Ae cations (VIꢀVII). Ae = Ca, Sr, Ba unless otherwise stated.
Wellꢀdefined monocationic Ae complexes are another class of rare and yet useful
compounds. Compared to their neutral congeners, they show greater electronꢀdeficiency and
Lewis acidity, which has been proposed to enhance their reactivity in homogenous
polymerisation catalysis1f,16 or alkene hydrogenation,17 and, overall, to produce competent Lewis
acid catalysts.18 Yet, because of electronic depletion and high electropositivity, isolating discrete
Ae cations has been tedious. Itoh and Kitagawa reported the first examples in 2001,19 whereas we
and others have more recently developed several cationic Ae polymerisation catalysts.15,16,20
4

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Multidentate aminoetherꢀphenolato or ꢀfluoroalkoxo ligands, owing to their low propensity to
bridge multiple metal centres and generate multinuclear aggregates, have enabled substantial
advances in this area, e.g by affording very reactive, solventꢀfree Ae complexes such as VI and
VII in Fig. 1.
As part of our efforts towards implementing secondary interactions in alkaline earth
chemistry, we report here on the syntheses of the first cationic calciumꢀ and strontiumꢀolefin
complexes. It is shown how nonꢀcovalent interactions in calcium and strontium complexes21
alone can at times fail to deliver these targets, and how this can be overcome through ligand
design.
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Results and discussion
Rationale for ligand design: {ROF}H
Following a method reported earlier to obtain Ae cations,20 our initial attempts at preparing
cationic calciumꢀolefin complexes consisted of the equimolar reactions between complexes II-Ca
or III (see Fig. 1) with [H•(OEt2)2]+.[H2N{B(C6F5)3}2]– (aka Bochmann’s acid).22 Even if the
release of HN(SiMe2H)2 occurred, these reactions failed to yield the desired cationic Aeꢀolefin
adducts, and only returned species which we could not authenticate. This was assumed to result
from excessive electron deficiency in the expected products, leading to uncontrolled reactivity
and decomposition. We therefore did not pursue this route, nor did we explore the oneꢀstep
reaction of [Ca[N(SiMe2H)2]2] with the doubly acidic proꢀligand [{RO}HH]+.[H2N{B(C6F5)3}2]–
which can be obtained upon protonation of the appropriate proꢀligand {RO}H with Bochmann’s
acid.20,22,23
We have shown that the coordination of a single methoxy sideꢀarm per metal atom was
sufficient to warrant the formation of the charge neutral calcium complex IV, whereas the further
addition of a second pair of methoxy tethers as in V was superfluous as it did not interact with the
calcium centres.20c Nonetheless, this scenario changed upon cationisation, as it was found that all
methoxy sideꢀarms were metalꢀbound in the cationic complexes derived from V.
This knowledge, combined with the apparent inability to cleanly generate cations from II-Ca
or III, led us to consider the utilisation of the new mixed olefin/methoxy aminoether
fluoroalcohol {ROF}H (Scheme 1). This proꢀligand can be readily obtained (78% yield) as a
colourless oil upon reaction of Nꢀ(2ꢀmethoxyethyl)butꢀ3ꢀenꢀ1ꢀamine with 2,2ꢀ
bis(trifluoromethyl)oxirane. Its 19F NMR spectrum in benzeneꢀd6 exhibits a single sharp singlet at
6

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‒77.51 ppm. The olefinic hydrogen atoms are characterised by clear multiplets at 5.54 (CH=CH2)
and ca. 4.95 (CH=CH2) ppm in the 1H NMR spectrum.
NH
O
CF3
+
CF3
O
Et2O
N(SiMe2H)2
F3C
CF3
O
O
N
Ae
O
[Ae[N(SiMe2H)2]2 (THF)n]
CF3
CF3
OH
N
Ae
1/2
N
Et2O, 78 °C
O
2 HN(SiMe2H)2
n THF
F3C
O
CF3
(HMe2Si)2N
{ROF}H 78%
Ca
Sr
[{ 2-ROF}CaN(SiMe2H)2]2
[{ 2-ROF}SrN(SiMe2H)2]2
1
( ) 76%
Ae =
2
( ) 71%
Scheme 1 Syntheses of {ROF}H and of complexes [{ꢂ2ꢀROF}AeN(SiMe2H)2]2 (Ae = Ca, 1; Sr,
2). Secondary interactions are not represented.
Charge neutral heteroleptic complexes
The protonolysis reactions between {ROF}H and a slight (33%) excess of the alkaline earth
tetramethyldisilazido precursors [Ca[N(SiMe2H)2]2•(THF)] and [Sr[N(SiMe2H)2]2•(THF)2/3]
afforded the targeted heteroleptic charge neutral complexes [{ꢂ2ꢀROF}CaN(SiMe2H)2]2 (1) and
[{ꢂ2ꢀROF}SrN(SiMe2H)2]2 (2) upon clean release of HN(SiMe2H)2 (Scheme 1).24 Both
compounds exist as dinuclear Oꢀbridged dimer in the molecular solidꢀsate (vide infra). They were
isolated as analytically pure colourless solids after workꢀup in 76% and 71% yields, respectively.
Their identities were established by NMR spectroscopy and Xꢀray diffraction crystallography,
and their purity were corroborated by combustion analysis. These two complexes are soluble in
1
ethers and hydrocarbons, including common alkanes. In their H NMR spectra recorded in
benzeneꢀd6, the resonance for SiH hydrogens appear as multiplets at δ 4.88 (for 1) and 4.95 (for
7

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1
2) ppm. The corresponding JHꢀSi coupling constants of ca. 162 Hz testify to mild Ae···H‒Si βꢀ
agostic interactions; such interactions are now known to contribute to the stability of electron
deficient alkaline earth architectures.25 The resonances for CH=CH2 and CH=CH2 hydrogens (δ
5.57 and 5.11ꢀ4.93 ppm for 1, 5.56 and 5.09ꢀ4.97 ppm for 2) are located in the same region as
seen for the proꢀligand (5.53 and 4.98ꢀ4.91 ppm), an indication that the olefins do not bind to the
metals in solution. In their 19F NMR spectra, both complexes give rise to two well resolved
quadruplets (4JFꢀF ≈ 9.1ꢀ9.3 Hz) in the region between δ –76 and –78 ppm, indicating that the two
geminal CF3 groups in α position to the alkoxide lose magnetic equivalence upon coordination of
the ligands to the metals. In the 13C{1H} NMR spectra, the CF3 carbon atoms respectively
generate a quadruplet at δ 125.99 ppm for 1 (1JCꢀF = 288.9 Hz) and at δ 126.60 ppm for 2 (1JCꢀF
=
288.9 Hz). Heptets are found at δ ca. 79.31 (for 1) or 79.87 ppm (for 2) for the C(CF3) atoms,
2
with JCꢀF ≈ 25ꢀ26 Hz. There is hardly any change in the 13C resonances for CH=CH2 and
CH=CH2 carbon atoms compared to the proꢀligand (1, 134.95 and 116.91 ppm; 2, 134.84 and
117.03 ppm; {ROF}H, 135.61 and 116.78 ppm), another sign of the absence of significant
interaction between the olefin and the metals in these two neutral complexes.
The molecular solidꢀstate structure of 1 is depicted in Fig. 2. It shows the complex to exist as
a centrosymmetric Oꢀbridged dinuclear species, with coordination of the Namine and Oether atoms
onto calcium, but without interaction between the metal cations and the olefinic tethers. There is
considerable disorder in the olefinic sideꢀarms, and only the main components of these fragments
are depicted in Fig. 2. This disorder generated considerable difficulties in refining the positions of
the atoms in the dangling CH2CH2CH=CH2 tethers, and we could not manage to obtain reliable
C‒C and C=C bond lengths for the corresponding four carbon atoms. For this reason, a
discussion of metric parameters, in particular for the C=C double bond, is inappropriate.
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Nonetheless, it is clear that there is no interaction between Ca and the C=C bonds, as indicated by
the large Ca1‒C21A (5.174(6) Å) and Ca1‒Ca22A (6.456(11) Å) distances.
Fig. 2 Representation of the molecular solidꢀstate structure of [{ꢂ2ꢀROF}CaN(SiMe2H)2]2 (1),
showing only the main component of the disordered olefinic sideꢀarms. Hydrogen atoms other
than SiH are omitted for clarity. Secondary interactions are represented by dashed lines. Selected
bond lengths (Å) and angles (°): Ca1‒O1 = 2.3319(16), Ca1‒O1’ = 2.2921(17), Ca1‒O17 =
2.3975(18), Ca1‒N1 = 2.301(2), Ca1‒N2 = 2.587(2), Ca1‒F2’ = 3.119(2), Ca1‒F6 = 3.036(2),
Ca1‒H1 = 3.237(29), Ca1‒H2 = 3.267(21); Si1‒N1‒Ca1 = 114.09(12), Si2‒N1‒Ca1 =
117.30(13).
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Complex 1 exhibits mild βꢀagostic Ca···H–Si interactions in the solid state, with for instance
Ca1‒H1 (3.237(29) Å) and Ca1‒H2 (3.267(21) Å) distances longer than those measured in II-Ca
or III, in the range 3.08(3)ꢀ3.19(3) Å.13 This is consistent with the NMR data for this compound
(vide supra). There are also two short Ca···F–C contacts per metal cation, with Ca1‒F6 (3.036(2)
Å) and Ca1‒F2’ (3.119(2) Å) both below the accepted limit for this type of interactions.26 Again,
these are on the whole weaker than those detected in II-Ca (3.050(2) Å) and III (2.931(1) Å).
That both Ca···H–Si and Ca···F–C are weaker in 1 than in II-Ca and III attests reliably that the
Ca‒Oether interactions in 1 are stronger than the Ca···Cπ interactions in the olefin adducts, as
expected for an oxophilic element such as calcium. The Ca1‒O17 bond length of 2.3975(18) Å is
only moderately longer than the distances to the bridging anionic Oalkoxide atoms O1’ and O1
(2.2921(17) and 2.3319(16) Å). By contrast, the Ca1‒N2 interatomic distance to Namine (2.587(2)
Å) is much longer than Ca1‒N1 to the terminal Namide atom, 2.301(2) Å. Perhaps unsurprisingly,
these metric parameters in 1 actually compare very well with the corresponding ones in the
methoxy adducts IV and V.15 Overall, taking the secondary interactions into consideration, each
calcium centre achieves a formal coordination number of 9 in 1, although it has been shown that
these Ca···H–Si and Ca···F–C interactions are mostly electrostatic, with little or no covalent
character.13,25
The molecular solid state structure of the strontium complex 2 resembles that of its calcium
congener, but there are nonetheless some noticeable differences (Fig. 3). It also exists as an Oꢀ
bridged dimer, with coordination of the methoxy sideꢀarm but without interaction of the olefins
onto the strontium centres (Sr1‒C12A = 5.1897(77) Å, Sr1‒C13A = 6.4806(98) Å). There is
again considerable disorder in the olefinic sideꢀarms, with precludes discussion of the pertaining
metric parameters for these segments. The structure of 2 includes one relatively strong βꢀagostic
Sr···H–Si interaction for each strontium, with Sr1‒H1 as short as 3.0841(524) Å whereas the
10

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interatomic distance Sr1‒H2 of 3.5090(359) is much longer. Conversely, the Sr1‒N1‒Si1 angle
of 109.71(16) ° is substantially less obtuse than Si2‒N1‒Sr1 (115.83(16) °). Each strontium atom
is also stabilized by two very strong Sr···F–C interactions, as testified by the very short Sr1‒F1’
and Sr1‒F6 distances of 3.049(2) and 2.996(3) Å, respectively. Both Sr···H–Si and Sr···F–C
interactions are comparatively stronger in 2 than in the related II-Sr, which discloses longer Sr‒F
(3.050(2) and 3.136(2) Å) and Sr‒H (two interactions at 3.092(34) and 3.169(37) Å, by
opposition to a single one in 2) interatomic distances.13a
Fig. 3 Representation of the molecular solidꢀstate structure of [{ꢂ2ꢀROF}SrN(SiMe2H)2]2 (2),
showing only the main component of the disordered olefinic sideꢀarms. Hydrogen atoms other
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than SiH are omitted for clarity. Secondary interactions are represented by dashed lines. Selected
bond lengths (Å) and angles (°): Sr1‒O1 = 2.466(2), Sr1‒O1’ = 2.432(2), Sr1‒O8 = 2.535(2),
Sr1‒N1 = 2.450(3), Sr1‒N5 = 2.759(3), Sr1‒F1’ = 3.049(2), Sr1‒F6 = 2.996(3), Sr1‒H1 =
3.0841(524); Si2‒N1‒Si1 = 134.1(2), Si2‒N1‒Sr1 = 115.83(16), Si1‒N1‒Sr1 = 109.71(16).
The bond lengths to bridging Oalkoxide (2.432(2) and 2.466(2) Å), to the terminal Namide atom (Sr1‒
N1 = 2.450(3) Å), and to the Namine atoms in 2 are very similar to those measured in II-Sr. Hence,
the replacement of a metalꢀbound olefin in II-Sr by a coordinated methoxy in 2 only impacts the
number and the strength of the nonꢀcovalent Sr···H–Si and Sr···F–C interactions, and not the
bonding to the Oꢀ and Nꢀatoms.
Cationic complexes
The treatment of 1 and 2 with one equivalent of [H•(OEt2)2]+.[H2N{B(C6F5)3}2]– in Et2O at room
temperature resulted in the precipitation of [({ꢂ2ꢀROF}Ca•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (3a)
and [({ꢂ2ꢀROF}Sr•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (4a), where two molecules of Et2O are found
on each metal centre. The formulation for these ion pairs was established upon examination of
the NMR spectroscopic data. The two complexes were isolated as fine colourless powders in
moderate yields after workꢀup. They are moderately soluble in ethers and dichloromethane, but
they are not soluble in hydrocarbons. The compounds were repeatedly submitted to elemental
analysis, but we failed to obtain reliable and reproducible results, presumably because of their
extreme sensitivity.
The 1H and 13C{1H} NMR data for 3a and 4a recorded in dichloromethaneꢀd2 at 25 °C show
the presence of two molecules of diethyl ether per metal. Coordination of Et2O is unambiguous, as
all the pertaining 1H resonances are substantially shifted towards low field in comparison with free
1
13
Et2O in the same deuterated solvent. From the H and C{1H} NMR data, it was not possible to
12

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establish whether the olefin coordinates to the metal in solution. The 19F NMR spectra showed the
expected resonances for the weakly coordinating anion, with the typical resonances at δ –132.94, –
160.26 and –165.79 ppm for 3a, and at δ –132.89, –160.23 and –165.75 ppm for 4a, indicating the
19
absence of interaction between the anions and the cations in solution. The F NMR spectra for 3a
and 4a also exhibited three multiplets of approximate relative intensities 2:1:3 between δ ‒76 and ‒
78 ppm, indicating loss of equivalence of the fluorine atoms in the CF3 groups in the cationic
components; which we interpret as a result of persistent Ae···F‒C interactions. Low temperature
11
19F NMR did not provide information about the multiplicity of these resonances. In the B{1H}
spectrum of each compound, the presence of the expected single resonance at δ ca. ‒8.41 (in 3a) or
‒8.41 (in 4a) ppm revealed that the anion [H2N{B(C6F5)3}2]– remained intact during the synthesis.
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Scheme 2 Syntheses of the ion pairs [({ꢂ2ꢀROF}Ca•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (3a) and
[({ꢂ2ꢀROF}Sr•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (4a).
Recrystallisation of a concentrated solution of 4a in dichloromethane afforded a small crop
of colourless single crystals of the water adduct [({ꢂ2ꢀROF}Sr•(H2O))2]2+.2[H2N{B(C6F5)3}2]–
(4b). Despite multiple attempts, we have not been able to obtain waterꢀfree crystals for these
compounds. Although all possible care was taken to exclude the presence of moisture (including
gloveꢀbox techniques and passivation of glassware with Me3SiCl), we can only assume that the
substitution of diethyl ether in 4a by water in the single crystals of 4b resulted from the presence
of residual water during the recrystallisation procedure.
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Fig. 4 Representation of the structure of the dication 4b2+ from the recrystallised ion pair [({ꢂ2ꢀ
ROF}Sr•(H2O))2]2+.2[H2N{B(C6F5)3}2]– (4b). Anions and nonꢀinteracting molecules of CH2Cl2
not represented. Hydrogen atoms other than those on water molecule omitted for clarity. Selected
bond lengths (Å): Sr1‒O1 = 2.417(5), Sr1‒O1’ = 2.430(5), Sr1‒O19 = 2.518(6), Sr1‒O21 =
2.578(5), Sr1‒F6’ = 2.997(6), Sr1‒F10 = 2.788(5), Sr1‒N12 = 2.831(6), Sr1‒C15 = 3.066(10),
Sr1‒C16 = 3.092(10), C15‒C16 = 1.358(14).
The crystal contained two molecules of nonꢀinteracting molecules of dichloromethane per
asymmetric unit. As inferred from NMR data, there is no interaction in the molecular solid state
between the anionic and cationic components. Hence, only the structure of the cationic
component 4b2+ is discussed. The structure of [({ꢂ2ꢀROF}Sr•(H2O))2]2+ depicted in Fig. 4 shows
the dication to exist as a centrosymmetric Oꢀbridged dimer, with one molecule of water
coordinated on each strontium centre. More importantly, the dication is characterised by two
strong Sr···F‒C interactions for each strontium, as indicated by short to very short Sr1‒F6’ and
Sr1‒F10 interatomic distances, respectively 2.997(6) and 2.788(5) Å. The latter is in particular
much lower than those in the parent complex 2 (vide supra). Finally, the short Sr1‒C15
(3.066(10) Å) and Sr1‒C16 (3.092(10) Å) are good evidence of the coordination of the olefins to
the metal atoms. To our knowledge, 4b2+ is the sole example of a discrete Srꢀolefin cation known
to date. Sr···Cπ interactions were also detected in the charge neutral complex II-Sr, with
distances to the interacting Cπ atoms in this case (3.061(3) and 3.165(3) Å) commensurate with
those in 4b2+. They both are also in the range of those measured in Schumann’s
[Sr(C5Me4CH2CH2CH=CH2)2], 2.99(2)ꢀ3.25(2) Å.27 The C=C double bond in 4b2+ (C15‒C16 =
1.358(14) Å) seems elongated with respect to that in II-Sr (1.316(5) Å), but the large standard
deviation in 4b2+ precludes accurate comparison of the C=C bond lengths in the two complexes.28
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The Sr···F‒C distances in 4b2+ are shorter than in 2, with is consistent with electronic depletion
at the metal ions in the dication. However, it is remarkable that the bond lengths from Sr to
Oalkoxide (2.417(5) and 2.430(5) Å) and Namine (2.831(6) Å) atoms in the dication are at best
comparable, if not longer, than in the charge neutral 2. The Sr‒Oalkoxide bonds in 4b2+ are
nonetheless shorter than in the strontium dicationic aminoꢀazaꢀcrownꢀetherꢀfluoroalkoxide in VI-
Sr (four different Sr‒Oalkoxide bonds in the range 2.446(7)ꢀ2.516(6) Å, average 2.486 Å),20a which
is assumed to reflect greater electron deficiency of the metal in 4b2+. Although the presence of
coordinated water in 4b2+ impacts its coordination pattern, it is also evident that the presence of
strong Sr···Cπ and Sr···F‒C nonꢀcovalent interactions plays is a major factor in the stability of
the dication. The fate of the diethyl ether molecules during the crystallisation process is not
elucidated, but one should note that the intramolecular coordination of the olefins in 4b2+ hence
appears to be favoured over the binding of any of the four surrounding Et2O molecules (possibly
driven by favourable entropic considerations with formation of a six membered chelate).
Finally, attempts to recrystallise the calcium compound 3b were carried out. Crystals of low
quality that contained one ion pair of formula [({ꢂ2ꢀROF}Ca•(H2O))2]2+.2[H2N{B(C6F5)3}2]– and
another one corresponding to [({ꢂ2ꢀROF}Ca•(Et2O))2]2+.2[H2N{B(C6F5)3}2]– in the asymmetric
unit were obtained, but the quality of the best crystallographic data was insufficient and only
afforded unacceptable refinement (final R1 > 13%, see the Electronic Supporting Information).
This precludes any discussion of metric parameters for these two salts. Nonetheless, the
connectivity unambiguously shows that the olefins do not bind to calcium in the monoꢀEt2O
adduct [({ꢂ2ꢀROF}Ca•(Et2O))2]2+, whereas they do in the monoꢀwater adduct [({ꢂ2ꢀ
ROF}Ca•(H2O))2]2+, suggesting that in addition to obvious electronic considerations, the binding
of the olefin in these calcium cations may also be very influenced by steric factors.
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Conclusion
Our failed initial attempts at obtaining alkaline earth cations stabilised by olefins and free of
coordinated solvent molecules such as THF have led us to design a fluoroalkoxy ligand
possessing both a methoxy and an olefinic dangling sideꢀarms. In the corresponding heteroleptic
charge neutral calcium and strontium complexes 1 and 2, the ether moiety binds intramolecularly
to the metal, but the olefin remains fully dissociated. Olefin coordination was enforced
successfully upon cationisation, yielding the bisꢀether adducts 3a and 4a, from which crystals of
the monoꢀwater adduct [({ꢂ2ꢀROF}Sr•(H2O))2]2+ (4b2+) were isolated. Crystals of this dication
free of coordinated water could unfortunately not be obtained, despite repeated attempts.
Evidently, the complex traps even the tiniest traces of residual moisture owing to the extreme
electron deficiency of 4b2+. We are now pursuing alternative pathways for the preparation of
cationic Aeꢀolefin compounds devoid of coordinated solvent, a prelude for the computational
analysis of the bonding by DFT methods. We should also mention that in the course of the
present work, we have also prepared complexes stabilised by other π ligands, that is, where the
dangling olefin groups in {ROF}H is replaced by a phenyl group. The neutral heteroleptic
complexes akin to 1 and 2 were successfully prepared and structurally characterised, but the
resulting cations were isolated and recrystallised as monoꢀEt2O adducts which did not show
coordination of the aromatic moiety onto the alkaline earths.
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Experimental section
General procedures. All manipulations were performed under inert atmosphere using standard
Schlenk techniques or in a dry, solventꢀfree gloveꢀbox (Jacomex; O2 < 1 ppm, H2O < 5 ppm).
CaI2 and SrI2 (both from Aldrich, 99.999%, anhydrous beads), and 2,2ꢀ
bis(trifluoromethyl)oxirane (Apollo Scientific) were used as received. HN(SiMe2H)2 (ABCR)
was dried over CaH2 and distilled prior to use. [Ca[N(SiMe2H)2]2•(THF)] and
[Sr[N(SiMe2H)2]2•(THF)2/3],25a as well as the salt [H(OEt2)2]+•[H2N{B(C6F5)3}2]–,22 were
prepared following the literature protocol. Solvents (THF, Et2O, CH2Cl2, pentane and toluene)
were purified and dried (water contents all below 10 ppm) over alumina columns (MBraun SPS).
THF was further distilled under argon from sodium mirror/benzophenone ketyl. All deuterated
solvents (Eurisotop, Saclay, France) were stored in sealed ampoules over activated 3 Å molecular
sieves and were thoroughly degassed by several freezeꢀthawꢀvacuum cycles.
NMR spectra were recorded on a Bruker spectrometer Avance III 400 MHz equipped with a
BBOF pulsed fieldꢀgradient probe or a Bruker spectrometer Avance 500 MHz equipped with a
1
dual pulse field gradient probehead. All H and 13C chemicals shifts were determined using
residual signals of the deuterated solvents and were calibrated vs. SiMe4. 19F{1H} chemical shifts
were determined by external reference to an aqueous solution of NaBF4. Assignment of the
signals was carried out using 1D (1H, 13C{1H}) and 2D (COSY, edited HSQC and HMBC) NMR
experiments.
Elemental analyses were performed on a Carlo Erba 1108 Elemental Analyzer instrument at the
London Metropolitan University by Stephen Boyer and were the average of two independent
measurements; they were complicated by the extreme airꢀsensitivity of the complexes. The
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averaged values are reported together with the deviation. ESI mass spectra were recorded on a
Bruker MicrOTOFꢀQ II spectrometer with a QqoaTOF geometry.
N-(2-methoxyethyl)but-3-en-1-amine.
Adapting from a known procedure,29 a mixture of 2ꢀmethoxyethylamine (8.64 g, 11.5 mmol) and
1 equiv of 4ꢀbromoꢀ1ꢀbutene (1.55 g, 11.5 mmol) was refluxed at 110 °C for 3 days. All volatiles
were then removed under vacuum. H2O (20 mL) was added to the reaction mixture. After
separation of the two layers, the organic fraction was acidified by addition of aqueous HCl 5% to
pH = 3. The two layers were separated and the aqueous phase was backꢀextracted with Et2O (2 ×
100 mL). The aqueous phase was then neutralised by slow addition of concentrated aqueous
NaOH to pH = 12. To this solution, Et2O (100 mL) was then added. The organic phase was
separated and the aqueous phase was further extracted with Et2O (3 × 50 mL). The combined
organic layers were dried over MgSO4. Removal of the solvent yielded the secondary amine in
1
3
74% yield (1.10 g). H NMR (benzeneꢀd6, 400.13 MHz, 298 K): δ 5.75 (ddt, 1H, JHꢀH (trans) =
3
3
17.0 Hz, JHꢀH (cis) = 10.2 Hz, JHꢀH = 6.8 Hz, CH=CH2), 5.08–4.94 (m, 2H, CH=CH2), 3.29 (t,
2H, 3JHꢀH = 5.3 Hz, CH2OCH3), 3.09 (s, 3H, OCH3), 2.65 (t, 2H, 3JHꢀH = 5.3 Hz, CH2CH2OCH3),
2.54 (t, 2H, 3JHꢀH = 6.9 Hz, NCH2CH2CH=CH2), 2.16ꢀ2.07 (m, 2H, NCH2CH2CH=CH2), 1.17 (br
s, 1H, NH) ppm.
{ROF}H.
To a solution of Nꢀ(2ꢀmethoxyethyl)butꢀ3ꢀenꢀ1ꢀamine (1.10 g, 8.50 mmol) in Et2O (10 mL) was
added 2,2ꢀbis(trifluoromethyl)oxirane (1.70 g, 9.35 mmol) at room temperature. The reaction
mixture was left to stir for 4 days. Removal of the volatiles followed by drying in vacuo afforded
1
{ROF}H as a colourless oil. Yield 2.03 g (78%). H NMR (benzeneꢀd6, 400.13 MHz, 298 K):
3
3
3
6.57 (s, 1H, OH), 5.53 (ddt, 1H, JHꢀH (trans) = 19.1 Hz, JHꢀH (cis) = 9.6 Hz, JHꢀH = 6.8 Hz,
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3
CH=CH2), 4.98–4.91 (m, 2H, CH=CH2), 2.96 (s, 3H, OCH3), 2.92 (t, 2H, JHꢀH = 5.1 Hz,
3
CH2OCH3), 2.85 (s, 2H, CH2(CF3)2), 2.44‒2.38 (m, 2H, CH2CH2CH=CH2), 2.36 (t, 2H, JHꢀH
=
3
13
5.1 Hz, CH2CH2OCH3), 1.90 (q, 2H, JHꢀH = 7.5 Hz, CH2CH2CH=CH2) ppm. C{1H} NMR
1
(benzeneꢀd6, 100.62 MHz, 298 K): δ 135.61 (CH=CH2), 124.39 (q, JCꢀF = 286.7 Hz, CF3),
2
116.78 (CH=CH2), 73.47 (hept, JCꢀF = 28.7 Hz, C(CF3)2), 69.73 (CH2OCH3), 58.38 (OCH3),
54.71
(CH2CH2OCH3),
54.19
(CH2CH2CH=CH2),
53.49
(CH2C(CF3)2),
31.42
19
(CH2CH2CH=CH2) ppm. F{1H} NMR (benzeneꢀd6, 376.44 MHz, 298 K): −77.51 (s, 6F, CF3)
ppm. Elemental analysis for C11H17F6NO2 (309.12 g mol−1): theoretical, C 42.7%, H 5.5%, N
4.5%; found C 42.7%, H 5.7%, N 4.4%. Mass spectrometry ESI [M + Na+] (C11H17F6NO2Na) m/z
theoretical: 332.1061; found 332.1056.
[{µ2-ROF}CaN(SiMe2H)2]2 (1).
A solution of {RO}H (0.24 g, 0.82 mmol) in Et2O (10 mL) was added at −78 °C over a period of
1 h to a solution of [Ca[N(SiMe2H)2]2•(THF)] (0.40 g, 1.06 mmol) in Et2O (10 mL). The reaction
mixture was warmed to room temperature and, after stirring for a further 1 h, the volatiles were
removed under vacuum. The resulting oil was stripped with pentane (3 × 2 mL) and washed with
the same solvent (2 × 2 mL) to afford 1 as a colourless powder (0.25 g, 76%). Crystals suitable
1
for Xꢀray diffractometry were obtained from a pentane solution stored at –30 °C. H NMR
(benzeneꢀd6, 400.13 MHz, 298 K): δ 5.57 (ddt, 1H, 3JHꢀH (trans) = 13.7 Hz, 3JHꢀH (cis) = 10.3 Hz,
1
3JHꢀH = 6.5 Hz, CH=CH2), 5.11–4.93 (m, 2H, CH=CH2), 4.88 (s, 2H, JSiꢀH = 162 Hz, SiH), 3.11
(s, 3H, OCH3), 2.97‒2.81 (overlapping m, 3H, CH2OCH3 and C(H)HCH2OCH3), 2.82‒2.65 (m,
2H, CH2CH2CH=CH2), 2.73 (ABq, 2H, JAB = 15.1 Hz, CH2C(CF3)2), 2.04‒1.92 (m, 2H,
C(H)HCH2OCH3 and CH2C(H)HCH=CH2), 1.90‒1.75 (m, 1H, CH2C(H)HCH=CH2), 0.46 (d,
13
3JHꢀH = 2.6 Hz, 12H, SiCH3) ppm. C{1H} NMR (benzeneꢀd6, 100.63 MHz, 298 K): δ 134.95
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1
1
(CH=CH2), 125.99 (q, JCꢀF = 288.9 Hz, CF3), 125.72 (q, JCꢀF = 290.1 Hz, CF3), 116.91
2
(CH=CH2), 79.31 (hept, C(CF3)2, JCꢀF = 26.2 Hz), 69.08 (CH2OCH3), 60.36 (OCH3), 54.79
(CH2C(CF3)2), 53.97 (CH2CH2OCH3), 52.01 (NCH2CH2CH=CH2), 27.30 (NCH2CH2CH=CH2),
19
5.14 (SiCH3), 4.84 (SiCH3) ppm. F{1H} NMR (benzeneꢀd6, 376.47 MHz, 298 K): δ –76.78 (q,
4
4
6F, JF‒F = 9.3 Hz, CF3), –78.02 (q, 6F, JF‒F = 9.1 Hz, CF3) ppm. Elem. Anal. for
C15H30CaF6N2O2Si2 (480.66 g mol−1): calcd C 37.5%, H 6.3%, N 5.8%; found C 37.3%, H 6.2%,
N 5.7%.
[{µ2-ROF}SrN(SiMe2H)2]2 (2).
A solution of {RO}H (0.18 g, 0.57 mmol) in Et2O (10 mL) was added at −78 °C over 1 h to a
solution of [Sr[N(SiMe2H)2]2•(THF) ] (0.31 g, 0.76 mmol) in Et2O (10 mL). The reaction
⅔
mixture was warmed to room temperature and, after stirring a further 1 h, the volatiles were
pumped off. The resulting oil was stripped with pentane (3 × 3 mL) and washed with this solvent
(2 × 2 mL) to afford 2 as a colourless powder (0.21 g, 71%). Crystals suitable for Xꢀray
1
diffractometry were grown from a pentane solution at –30 °C. H NMR (benzeneꢀd6, 400.13
3
3
3
MHz, 298 K): δ 5.56 (ddt, 1H, JHꢀH (trans) = 17.1 Hz, JHꢀH (cis) = 10.2 Hz, JHꢀH = 6.5 Hz,
CH=CH2), 5.09–4.97 (m, 2H, CH=CH2), 4.95 (s, 2H, 1JSiꢀH = 162 Hz, SiH), 3.00 (s, 3H, OCH3),
2.92‒2.81 (m, 2H, CH2OCH3), 2.81‒2.71 (m, 1H, C(H)HCH2OCH3), 2.70‒2.57 (m, 1H,
NC(H)HCH2CH=CH2), 2.65 (ABq, 2H, JAB = 15.1 Hz, CH2C(CF3)2), 2.55‒2.42 (m, 1H,
NC(H)HCH2CH=CH2), 2.12‒1.80 (overlapping m, 3H, NCH2CH2CH=CH2 and
C(H)HCH2OCH3), 0.47 (s, 12H, SiCH3) ppm. 13C{1H} NMR (benzeneꢀd6, 100.63 MHz, 298 K):
δ 134.84 (CH=CH2), 126.60 (q, 1JCꢀF = 288.9 Hz, CF3), 126.15 (q, 1JCꢀF = 290.1 Hz, CF3), 117.03
2
(CH=CH2), 79.87 (hept, C(CF3)2, JCꢀF = 25.3 Hz), 69.20 (CH2OCH3), 59.61 (OCH3), 52.26
(CH2C(CF3)2 and CH2CH2OCH3), 52.16 (NCH2CH2CH=CH2), 28.33 (NCH2CH2CH=CH2), 5.02
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19
(SiCH3), 4.85 (SiCH3) ppm. F{1H} NMR (benzeneꢀd6, 376.47 MHz, 298 K): δ –77.37 (q, 6F,
4
4JF‒F = 9.1 Hz, CF3), ‒78.41 (q, 6F, JF‒F = 9.2 Hz, CF3) ppm. Elem. Anal. for
C15H30SrF6N2O2Si2 (528.20 g mol−1): calcd C 34.1%, H 5.7%, N 5.3%; found C 33.9%, H 5.6%,
N 5.2%.
[({µ2-ROF}Ca•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (3a).
Complex 1 (50 mg, 0.10 mmol) and [H•(OEt2)2]+.[H2N{B(C6F5)3}2]– (125 mg, 0.10 mmol) were
dissolved in Et2O (10 mL) and reacted overnight. A colourless precipitate formed immediately
upon stirring. After overnight stirring, the precipitate was isolated by filtration, washed with
pentane (3 × 10 mL) and dried in vacuo to constant weight to give 3a as a colourless powder (54
1
mg, 34%). H NMR (dichloromethaneꢀd2, 400.13 MHz, 298 K): δ 5.93ꢀ5.74 (m, 1H, CH=CH2),
5.68 (br s, 2H, NH2), 5.30ꢀ5.19 (m, 2H, CH=CH2), 4.01ꢀ3.90 (m, 1H, C(H)HOCH3), 3.82ꢀ3.75
(m, 1H, C(H)HOCH3), 3.72ꢀ3.62 (overlapping m, 11H, OCH3 and OCH2CH3), 3.43ꢀ3.32 (m, 1H,
3
C(H)H(CF3)2), 3.16ꢀ2.89 (overlapping m, 3H, C(H)H(CF3)2 and CH2CH2OCH3), 2.82 (t, JH–H
=
3
7.84 Hz, 2H, NCH2CH2CH=CH2), 2.48ꢀ2.21 (m, 2H, NCH2CH2CH=CH2), 1.27 (t, JH–H = 7.1
13
Hz, 12H, OCH2CH3) ppm. C{1H} NMR (dichloromethaneꢀd2, 100.63 MHz, 298 K): δ 149.65,
147.24, 141.03, 138.45, 138.32 (all C6F5), 136.02 (CH=CH2), 119.63 (CH=CH2), 71.03
(CH2OCH3), 66.58 (OCH2CH3), 61.85 (OCH3), 52.66 (NCH2CH2CH=CH2 or NCH2CH2OCH3 or
CH2(CF3)2), 30.28 (NCH2CH2CH=CH2), 14.87 (OCH2CH3) ppm. The resonances for CF3 and
C(CF3)2 were not detected. The resonances for either NCH2CH2OCH3, NCH2CH2CH=CH2 or
CH2(CF3)2 overlap with the solvent peak and therefore cannot be assigned. 19F{1H} NMR
(dichloromethaneꢀd2, 376.47 MHz, 298 K): δ –76.87 to –77.06 (m, 3F, CF3), –77.52 to –77.67
(m, 1F, CF3), –77.79 to –77.98 (m, 2F, CF3), –132.94 (d, 3JF–F = 18.62 Hz, 12F, oꢀC6F5), –160.26
3
3
11
(t, JF–F = 20.58 Hz, 6F, pꢀC6F5), –165.79 (t, JF–F = 19.06 Hz, 12F, mꢀC6F5) ppm. B NMR
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(dichloromethaneꢀd2, 128.40 MHz, 298 K): δ –8.41 ppm. Satisfactory elemental analysis for 3a
could not be obtained in spite of repeated attempts.
[({µ2-ROF}Sr•(Et2O)2)2]2+.2[H2N{B(C6F5)3}2]– (4a).
Complex 2 (80 mg, 0.15 mmol) and [H•(OEt2)2]+.[H2N{B(C6F5)3}2]– (180 mg, 0.15 mmol) were
dissolved in Et2O (10 mL). A colourless precipitate formed immediately upon stirring. After
overnight stirring, the precipitate was isolated by filtration, washed with pentane (3 × 10 mL) and
dried under vacuum to give 4a as a colourless powder (130 mg, 54%). Crystals of [({ꢂ2ꢀ
ROF}Sr•(H2O))2]2+.2[H2N{B(C6F5)3}2]– (4b) suitable for Xꢀray diffraction were grown from a
1
concentrated CH2Cl2 solution at room temperature. H NMR (dichloromethaneꢀd2, 400.16 MHz,
298 K): δ 5.92ꢀ5.75 (m, 1H, CH=CH2), 5.69 (br s, 2H, NH2), 5.30ꢀ5.20 (m, 2H, CH=CH2), 4.00ꢀ
3.86 (m, 1H, C(H)HOCH3), 3.78ꢀ3.65 (m, 1H, C(H)HOCH3), 3.78ꢀ3.65 (overlapping m, 11H,
2
OCH3 and OCH2CH3), 3.32 (d, JH–H = 15.7 Hz, 1H, C(H)H(CF3)2), 3.13ꢀ2.63 (overlapping m,
5H, C(H)H(CF3)2, NCH2CH2CH=CH2 and CH2CH2OCH3), 2.50ꢀ2.21 (m, 2H,
3
NCH2CH2CH=CH2), 1.22 (t, JH–H = 7.1 Hz, 12H, OCH2CH3) ppm. 13C{1H} NMR
(dichloromethaneꢀd2, 100.63 MHz, 298 K): δ 149.67, 147.32, 140.93, 138.52, 136.14 (all C6F5),
136.67 (CH=CH2), 120.06 (CH=CH2), 70.80 (CH2OCH3), 66.42 (OCH2CH3), 61.14 (OCH3),
55.66 (CH2C(CF3)2), 52.44 (NCH2CH2CH=CH2), 30.29 (NCH2CH2CH=CH2), 15.43 (OCH2CH3)
ppm. The resonances for CF3, C(CF3)2, and NCH2CH2OCH3 could not be detected; the resonance
for NCH2CH2OCH3 most likely overlaps with the solvent signals. 19F{1H} NMR
(dichloromethaneꢀd2, 376.47 MHz, 298 K): δ –76.44 to –77.76 (m, 3F, CF3), –76.94 to –77.16
(m, 1F, CF3), –77.55 to –77.80 (m, 2F, CF3), –132.89 (d, 3JF–F = 18.10 Hz, 12F, oꢀC6F5), –160.23
3
3
11
(t, JF–F = 20.10 Hz, 6F, pꢀC6F5), –165.75 (t, JF–F = 19.65 Hz, 12F, mꢀC6F5) ppm. B NMR
(dichloromethaneꢀd2, 128.40 MHz, 298 K): δ –8.43 ppm. Elemental analysis could not be
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performed reliably for this compound, most likely owing to its high sensitivity, or perhaps due to
erratic contamination by adventitious water or other Lewis bases.
X-ray diffraction crystallography. Crystals of 1, 2 and 4b suitable for Xꢀray diffraction analysis
were obtained by recrystallisation of the purified products. Diffraction data were collected at 150
K using a D8 VENTURE Bruker AXS diffractometer with graphiteꢀmonochromated MoKα
radiation (λ = 0.71073 Å). Relevant collection and refinement data are summarised in Table 1.
Crystal data and details of data collection and structure refinement for the three complexes
(CCDC 1570851ꢀ1570853) can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
The structure of 1 was solved by dualꢀspace algorithm using the SHELXT program,30 and then
refined with fullꢀmatrix leastꢀsquare methods based on F2(SHELXL).31 All nonꢀhydrogen atoms
were refined with anisotropic atomic displacement parameters. Except Siꢀlinked hydrogen atoms
that were introduced in the structural model through Fourier difference maps analysis, H atoms
were finally included in their calculated positions. A final refinement on F2 with 5457 unique
intensities and 291 parameters converged at ωR(F2) = 0.1191 (R(F) = 0.0504) for 4086 observed
reflections with I > 2σ(I).
The structure of 2 was solved by dualꢀspace algorithm using the SHELXT program,30 and then
refined with fullꢀmatrix leastꢀsquare methods based on F2(SHELXL).31 All nonꢀhydrogen atoms
were refined with anisotropic atomic displacement parameters. Except Siꢀlinked hydrogen atoms
that were introduced in the structural model through Fourier difference maps analysis, H atoms
were finally included in their calculated positions. A final refinement on F2 with 5625 unique
24

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intensities and 277 parameters converged at ωR(F2) = 0.0929 (R(F) = 0.0432) for 3892 observed
reflections with I > 2σ(I).
The structure of 4b was solved by dualꢀspace algorithm using the SHELXT program,30 and then
refined with fullꢀmatrix leastꢀsquare methods based on F2(SHELXL).31 All nonꢀhydrogen atoms
were refined with anisotropic atomic displacement parameters. Except Oꢀlinked hydrogen atoms
in water molecules that were introduced in the structural model from calculated positions by the
method of Nardelli,32 H atoms were finally included in their calculated positions. A final
refinement on F2 with 12066 unique intensities and 824 parameters converged at ωR(F2) =
0.1961 (R(F) = 0.0880) for 6574 observed reflections with I > 2σ(I).
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Table 1 Summary of crystallographic data for complexes 1, 2 and 4b.
[{ꢂ2ꢀROF}CaN(SiMe2H)2]2
(1)
[{ꢂ2ꢀROF}SrN(SiMe2H)2]2
[({ꢂ2ꢀROF}Sr•(H2O))2]2+
.2[H2N{B(C6F5)3}2]– (4b)
(2)
Formula
CCDC
C30 H64 Ca2 F12 N4 O4 Si4
C30 H64 F12 N4 O4 Si4 Sr2 C96 H44 B4 Cl4 F72 N4 O6 Sr2
1570851
965.37
1570852
1056.42
Monoclinic
P 21/n
1570853
3077.63
Monoclinic
P 21/n
Mol. wt.
Crystal system
Space group
a (Å)
Monoclinic
P 21/n
10.4222(3)
16.7411(6)
14.0517(5)
90
10.5669(6)
17.1007(9)
13.9454(8)
90
11.8244(12)
14.3892(14)
31.655(3)
90
b (Å)
c (Å)
α (o)
β (o)
102.7440(10)
90
102.799(2)
90
93.679(3)
90
γ (o)
V (Å3)
2391.33(14)
2
2457.3(2)
2
5374.9(9)
2
Z
Density (g/cm3)
Abs. coeff., (mmꢀ1)
F(000)
1.341
1.428
1.902
0.421
2.348
1.274
1016
1068
3016
Crystal size, mm
0.60 × 0.40 × 0.25
2.973 to 27.480
0.42 × 0.26 × 0.09
2.980 to 27.481
0.31 × 0.21 × 0.02
2.942 to 27.481
θ
range (°)
‒12 < h < 13
‒21 < k < 21
‒18 < l < 18
‒13 < h < 13
‒19 < k < 22
‒18 < l < 18
‒15 < h < 13
‒18 < k < 18
‒41 < l < 41
Limiting indices
R(int)
0.0418
22661
0.1001
25392
0.1405
39315
Reflections collected
4086
5625
12066
Refl. Unique [I>2
Completeness to
σ(I)]
0.995
5457 / 2 / 291
1.060
0.999
5625 / 0 / 277
1.015
0.978
12066 / 5 / 824
1.049
θ
Data/restraints/param.
Goodnessꢀofꢀfit
0.0504 (0.0758)
0.0432 (0.0820)
0.0880 (0.2113)
R1 [I>2σ (I)] (all data)
0.1191 (0.1355)
0.325 and ‒0.541
0.0929 (0.1093)
0.610 and ‒1.018
0.1961 (0.2312)
0.889 and ‒1.306
wR2 [I>2
σ (I)] (all data)
Largest diff. (e·A−3)
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Conflicts of interest. There are no conflicts of interest to declare.
Acknowledgements. S.ꢀC. R. is grateful to the French Agence Nationale de la Recherche for
a PhD grant (GreenLAkE, ANRꢀ11ꢀBS07ꢀ009ꢀ01).
Electronic Supporting Information. NMR spectra for 1ꢀ4; Molecular structures of [({ꢂ2ꢀ
ROF}Ca•(H2O))2]2+.2[H2N{B(C6F5)3}2]– and [({ꢂ2ꢀROF}Ca•(Et2O))2]2+.2[H2N{B(C6F5)3}2]–.
Notes and References
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4
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29