Synthesis and crystal structures of bis(diphenylphosphanyl)methanides of lithium and calcium as well as of their borane adducts

Article abstract of DOI:10.1039/b822530c

The reaction of Li{HC(PPh₂)₂}, which forms [(tmeda)(thf)Li{HC(PPh₂)₂}] (1) in the presence of appropriate Lewis bases, with KOtBu and CaI₂ in THF yields [(thf)₃Ca{CH(PPh₂)_2<

Full text of DOI:10.1039/b822530c

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www.rsc.org/dalton | Dalton Transactions
Synthesis and crystal structures of bis(diphenylphosphanyl)methanides of
lithium and calcium as well as of their borane adducts†
Jens Langer, Katja Wimmer, Helmar Go¨rls and Matthias Westerhausen*
Received 15th December 2008, Accepted 9th February 2009
First published as an Advance Article on the web 27th February 2009
DOI: 10.1039/b822530c
The reaction of Li{HC(PPh2)2}, which forms [(tmeda)(thf)Li{HC(PPh2)2}] (1) in the presence of
appropriate Lewis bases, with KOtBu and CaI2 in THF yields [(thf)3Ca{CH(PPh2)2}2] (2). In complexes
1 and 2 the bis(diphenylphosphanyl)methanide anions act as bidentate ligands via the phosphorus
atoms. Lithiation of H2C(PPh2-BH3)2 in diethyl ether leads to the formation of [(Et2O)2Li{CH(PPh2-
BH3)2}] (3) which can be recrystallized from 1,2-dimethoxyethane (DME) leading to the formation of
solvent-separated [(dme)3Li]+ [HC(PPh2-BH3)2]- (3¢). The reaction of 3 with KOtBu and then with
˚
anhydrous CaI2 yields [(thf)Ca{CH(PPh2-BH3)2}2] (4). In compound 4 a Ca–C bond of 2.754(3) A is
observed in the solid state to only one of the anions whereas the other anion only binds via the
borane units.
thesis of calcium bis[trimethylsilyl-bis(dimethylphosphanyl)me-
Introduction
thanide] succeeded via the metathesis reaction of Li{C(PMe2)2-
The synthesis of alkylcalcium compounds poses several challenges
which have to be overcome. Calcium metal itself is rather inert
whereas the organylcalcium compounds exhibit an enormous
reactivity which often leads to ether cleavage reactions.1–3 Metal ac-
SiMe3} with CaCl2 in THF. The anions in [(thf)3Ca{C(PMe2)2-
SiMe3}2] bind as bidentate ligands via the phosphorus bases to the
calcium atom leading to a seven-coordinate calcium center with
22
˚
an average Ca–P bond length of 3.043 A. Here we report on the
tivation, whichwas achievedvia cocondensation ofcalcium vapour
with bromo-bis(trimethylsilyl)methane, and addition of 1,4-
dioxane led to the formation of the first structurally characterized
dialkylcalcium derivative, [(diox)2Ca{CH(SiMe3)2}2].4 In order to
circumvent difficulties arising from the low reactivity of the metal,
the metathesis reaction of alkyl potassium with calcium diiodide
offers a promising procedure. This reaction pathway allowed the
isolation and structural characterization of [Ca{C(SiMe3)3}2] with
a bent C–Ca–C fragment,5 of [(thf)2Ca{CH(SiMe3)2}2],6 and of the
calciate [Ca{CH(SiMe3)2}3]- with a calcium atom in a pyramidal
environment.7 In order to stabilize the organocalcium compounds
in ether the nucleophilicity of the carbanion has to be reduced
via delocalization of anionic charge by phenyl groups (leading to
benzyl derivatives)8–13 or via backdonation of charge into a
s*(Si–C) bond of a trialkylsilyl group (negative hyperconju-
gation).4–6 Even a combination of both concepts was applied in
order to isolate soluble trialkylsilylbenzyl calcium derivatives.8,14
In carbene adducts such as complexes of CaR2 with imidazol-
2-ylidenes often dissociation equilibria were observed.15 Nev-
ertheless, crystallization of these adducts could be performed
and short calcium–C bonds were observed.16–18 Stabilization of
anionic charge was also performed by phosphoranyl substituents
as in calcium bis[bis(trimethylsilylimino-diphenylphosphoranyl)-
methanide] and in dimeric calcium bis(trimethylsilylimino-diphe-
nylphosphoranyl)methanediide19 as well as in calcium bis[bis-
(arylimino-diphenylphosphoranyl)methanide] and in calcium
bis(arylimino-diphenylphosphoranyl)methanediide.20,21 The syn-
synthesis and characterization of [(thf)3Ca{CH(PPh2)2}2] and its
borane adduct.
Results and discussion
Synthesis
Lithium bis(diphenylphosphanyl)methanide has been well-
known for nearly forty years.23 Its 1,2-bis(dimethylamino)ethane
(TMEDA) adduct is monomeric in the solid state with the lithium
atom binding to the phosphorus atoms of the anion and to
the nitrogen atoms of the bidentate TMEDA ligand.24 The Li–P
˚
distances are 2.582(4) A. Substitution of the TMEDA molecule
by a THF molecule leads to dimerization and the formation of
25
˚
a lithium–carbon bond with a length of 2.242(8) A. A similar
relation is observed for monomeric [(tmeda)Li{C(PMe2)2SiMe3}]
and dimeric [(thf)Li{C(PMe2)2SiMe3}]25 as well as for dimeric
[(thf)Li{C(PMe2)3}].26 The enhancement of the coordination num-
ber of lithium in [(tmeda)(thf)Li{HC(PPh2)2}] (1) leads to two sig-
˚
nificantly different Li–P bond lengths of 2.653(4) and 3.018(4) A.
This lithium complex 1 was reacted with KOtBu [giving potassium
bis(diphenylphosphanyl)methanide]27 and then with anhydrous
calcium diiodide yielding [(thf)3Ca{CH(PPh2)2}2] (2) according
to eqn (1). In this complex the calcium atoms show a comparable
coordination sphere as in [(thf)3Ca{C(PMe2)2SiMe3}2] of Karsch
and Reisky.22
Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-
Universita¨t Jena, August-Bebel-Str. 2, D-07743, Jena, Germany. E-mail:
m.we @ uni-jena.de; Fax: +49 (0) 3641 9–48102
(1)
† CCDC reference numbers 712109 for 1, 712110 for 2, 712111 for 3,
712112 for 3¢, and 712113 for 4. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b822530c
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In order to prevent Ca–P bonds the lone pairs at the P atoms
were blocked with borane units. The well-known28–30 borane
adduct H2C(PPh2-BH3)2 [which is isoelectronic to H2C(SiPh2-
CH3)2] was metallated in diethyl ether with butyl lithium,
yielding [(Et2O)2Li{CH(PPh2-BH3)2}] (3) with the lithium atom
coordinating to the B-bound hydrides. Recrystallization from
1,2-dimethoxyethane (DME) gave the solvent-separated ion
pair [(dme)3Li]+ [HC(PPh2-BH3)2]- (3¢). The reaction of 3 with
KOtBu and then with anhydrous CaI2 led to the formation of
[(thf)Ca{CH(PPh2-BH3)2}2] (4) with moderate yield as shown
in eqn (2). This compound is isoelectronic to yet unknown
[(thf)Ca{CH(SiPh2-CH3)2}2] but the bis(trimethylsilyl)methanides
of calcium contain quite similar structural motifs.4,6
A·2BH3 are included. The borane addition leads to a low field
shift of the 31P NMR resonance due to the enlarged coordination
number and the formation of a Lewis acid–base complex. The
P–CH2–P unit shows a low field shift for the protons and a slight
1
high field shift in the 13C{ H} NMR experiment. Deprotonation
of the methylene moieties leads to significant low field shifts of
these resonances in the NMR spectra in agreement with larger
shielding due to anionic charge on these P–CH–P fragments.
The delocalization and formation of partial double bonds also
enhances the 1J(P,C) coupling constants of the P–CH–P units.
The ipso-carbon atoms of the P-bound phenyl groups are also
affected by borane addition as well as deprotonation of the
methylene groups. In the borane adduct drastically larger 1J(P,i-C)
coupling constants are observed.
Molecular structures
The coordination behaviour of the bis(diphenylphosphanyl)-
methanide ligand is diverse. Mercury bis[bis(diphenylphos-
phanyl)methanide] shows Hg–C bonds and no short Hg–P
contacts.31 These ligands can also bind via the carbon and the
phosphorus atoms as found in dimeric lithium derivatives25,26 as
(2)
3
well as in [Cr2(Cl){CH(PPh2)2}3] and [Sm{h -CH(PPh2)2}3].32 C-
as well as P-coordination of this ligand was also observed for main
group elements such as e.g. Sn, Pb,33 Al, and Ga.34 In dinuclear
gold(I) complexes, the bis(diphenylphosphanyl)methanide anion
is in a bridging position and binds via the P-atoms.35
In compounds 1 and 2 the bis(diphenylphosphanyl)methanide
ligand binds exclusively via the phosphorus atoms. Fig. 1 and
2 display molecular structures and numbering schemes of 1
and 2, respectively. The anion of lithium derivative 1 shows
comparable parameters as in [(tmeda)Li{CH(PPh2)2}].24 The
negative charge is delocalized in the PCP fragment leading to
NMR investigations
The NMR data of these bis(diphenylphosphanyl)methanides are
summarized in Table 1. For comparison reasons the parameters
of bis(diphenylphosphanyl)methane A and its borane adduct
Table 1 Selected NMR data of bis(diphenylphosphanyl)methane derivatives. Starting H2C(PPh2)2 (A) and H2C(PPh2BH3)2 (A·2 BH3) are included for
comparison reasons
A
1
2
A·2BH3
3
K{HC(PPh2BH3)2}
4
1H
d(PCHP)
2.88
1.9
1.56
8.6
2.02
6.8
3.23
10.7
0.74
<1
0.61
6.6
1.53
14
2J(H,P)
13C{ H}
1
d(PCP)
1J(C,P)
d(i-C)
28.7
17.9
16.5
23.9
24.8
129.1
55.7
132.9
9.9
129.1
10.7
5.1
6.6
76.7
143.4
59.8
5.6
23.3
140.3
4.5
133.6
21.0
128.9
7.1
129.1
19.4
152.3
4.0
132.0
7.8
127.4
Broad
125.4
31.1
149.1
Broad
131.9
6.4
127.8
< 1
77.4
142.8
56.7
133.1
9.2
127.2
9.4
127.9
51.0
138.0
66.1
131.9
9.6
1J(C,P)
d(o-C)
2J(C,P)
d(m-C)
3J(C,P)
d(p-C)
132.7
8.7a
127.4
8.8a
128.1
128.1
b
126.6
132.0
129.2
+11.1
-31.5
1
31P({ H}
d(PCP)
-20.4
+2.9
+1.0
+14.9
+16.3
-33.6
+18.1
-33.9
1
11B{ H}
d(BH3)
—
—
—
-56.1c
28
Ref.
a Observation of a pseudo-triplet of a AA¢X spectrum type. b Coupling constant cannot be assigned due to overlap with solvent signals. c Chemical shift
given relative to BMe3; chemical shift given relative to BF3·OEt2: d = -36.6.
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a strong shortening of the P–C bonds. However, the coordination
mode of the anion in the complexes [(tmeda)Li{CH(PPh2)2}]
and [(tmeda)(thf)Li{CH(PPh2)2}] differ significantly. Whereas
in [(tmeda)Li{CH(PPh2)2}] an average Li–P bond length of
a coordination number of 4 + 1 for lithium in 1, also causes an
elongation of the Li–N bonds of approximately 0.1 A.
˚
The calcium derivatives 2 and [(thf)3Ca{C(SiMe3)(PMe2)2}2]22
are very similar. The Ca–O distances of these complexes are nearly
identical. However, the different bulk of methyl and phenyl groups
leads to a distortion of the binding mode of the anions. On the one
hand and in contrast to [(thf)3Ca{C(SiMe3)(PMe2)2}2]22 with an
2.582(6) A was observed,24 the enhanced strain due to the addition
˚
of another Lewis base leads to enhanced Li–P distances and to
˚
significantly different Li–P bond lengths of 2.653(4) and 3.018(4) A
˚
average Ca–P bond length of 3.043 A, larger Ca–P bond lengths
in 1. Thus the penta-coordination, which can best be described as
˚
of 3.062 and 3.126 A are observed. On the other hand, the P–C
˚
distances of the PCP backbone are shorter in 2 (av. C–P 1.729 A)
22
˚
than in [(thf)3Ca{C(SiMe3)(PMe2)2}2] (av. C–P 1.758 A). The
steric pressure of the trimethylsilyl group leads to a narrower PCP
angle of 106.0◦ whereas in 2 an average PCP bond angle of 113.6◦
is observed.
The addition of borane formally leads to the insertion of
BH3 units into the Li–P bonds. In [(Et2O)2Li{CH(PPh2-BH3)2}]
(3) the hexa-coordinate lithium atom is in a distorted trigonal
˚
prismatic environment of two oxygen (av. Li–O 1.977 A) and
˚
four hydrogen atoms (av. Li–H 2.06 A). Molecular structure and
numbering scheme are given in Fig. 3. The coordination of BH3 to
the P atoms leads to a strong widening of the PCP angle to 130.8◦
˚
and to a slight shortening of the P–C bonds (av. P–C 1.713 A).
˚
In H2C(PPh2BH3)2 a characteristic P–C single bond of 1.833 A is
observed with a PCP angle of 118.2◦.30
Fig. 1 Molecular structure and numbering scheme of [(tmeda)(thf)-
Li{HC(PPh2)2}] (1). The ellipsoids represent a probability of 40%. The
H atoms are omitted for clarity reasons with the exception of the
PC(H)P units. Intercalated solvent molecules are not shown. Selected
˚
bond lengths (A): Li1–P1 2.653(4), Li1–P2 3.018(4), Li1–N1 2.172(5),
Li1–N2 2.143(4), Li1–O1 1.946(4), C1–P1 1.733(2), C1–P2 1.736(2),
P1–C2 1.845(2), P1–C8 1.858(2), P2–C14 1.852(2), P2–C20 1.844(2).
Angles (◦): P1–Li1–P2 61.07(8), P1–C1–P2 113.3(1), Li1–P1–C1 95.5(1),
Li1–P2–C1 83.5(1).
Fig. 3 Molecular structure and numbering scheme of [(Et2O)2Li-
{HC(PPh2BH3)2}] (3). The ellipsoids represent a probability of 40%. The H
atoms are omitted for clarity reasons with the exception of the P–C(H)–P
˚
and borane units. Selected bond lengths (A): Li1–O1 1.971(7), Li1–O2
1.983(7), Li1–H1B1 2.08(4), Li1–H2B1 2.10(4), Li1–H1B2 2.02(4), Li1–H2B2
2.05(4), C1–P1 1.710(3), C1–P2 1.716(3), P1–B1 1.926(4), P1–C2 1.830(3),
P1–C8 1.833(3), P2–B2 1.922(4), P2–C14 1.839(3), P2–C20 1.832(3).
Angles (◦): P1–C1–P2 130.8(2), C1–P1–B1 121.6(2), C1–P2–B2 120.3(2).
The solvent-separated ion pair [(dme)3Li]+ [HC(PPh2-BH3)2]-
(3¢) crystallized with two crystallographically independent
molecules in the asymmetric unit which are distinguished by
the letters “A” and “B”. Molecular structure and numbering
scheme of molecule A is shown in Fig. 4. No short contacts exist
between anion and cation. Whereas in the contact ion pair 3 a
cisoid arrangement of the BH3 units was observed, a transoid
conformation is realized in solvent-separated 3¢. Due to this fact
repulsion between the B2A borane moiety and the P1A diphenyl-
phosphanyl fragment leads to a widening of the P1A–C1A–P2A
(133.5(2)◦) and C1A–P2A–B2A angles (121.1(2)◦).
Fig. 2 Molecular structure and numbering scheme of [(thf)3Ca{HC-
(PPh2)2}2] (2). The ellipsoids represent a probability of 40%. The
H atoms are omitted for clarity reasons with the exception of the
˚
P–C(H)–P units. Selected bond lengths (A): Ca1–P1 3.146(1), Ca1–P2
3.0654(9), Ca1–P3 3.0589(9), Ca–P4 3.107(1), Ca1–O1 2.394(2), Ca1–O2
2.428(2), Ca1–O3 2.370(2), C1–P1 1.730(3), C1–P2 1.728(3), P1–C2
1.841(3), P1–C8 1.849(3), P2–C14 1.860(3), P2–C20 1.854(3), C26–P3
1.724(3), C26–P4 1.734(3), P3–C27 1.856(3), P3–C33 1.846(3), P4–C39
1.851(3), P4–C45 1.846(3). Angles (◦): P1–Ca1–P2 55.55(2), P3–Ca1–P4
55.95(2), P1–C1–P2 113.7(2), P3–C26–P4 113.5(2), P1–Ca1–P3 89.51(3),
P1–Ca1–P4 144.92(3), P2–Ca1–P3 142.24(3), P2–Ca1–P4 153.32(3).
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Fig. 4 Structure representation and numbering scheme of molecule
A of solvent-separated [(dme)3Li]+ [HC{PPh2BH3}2]- (3¢). The other
ion pair
represent
B
a
of the asymmetric unit is omitted. The ellipsoids
probability of 40%. The phenyl and DME hydrogen
atoms are neglected for clarity reasons. Selected bond lengths of
Fig. 5 Molecular structure and numbering scheme of [(thf)Ca{HC-
PPh2BH3)2}2] (4). The ellipsoids represent a probability of 40%. The
phenyl and THF hydrogen atoms are neglected for clarity reasons. Selected
˚
the anion (A): C1A–P1A 1.704(4), C1A–P2A 1.725(4), C1A–H1A
0.84(4), P1A–B1A 1.934(4), P1A–C2A 1.839(4), P1A–C8A 1.833(4),
P2A–B2A 1.937(4), P2A–C14A 1.834(4), P2A–C20A 1.840(4). Angles
(◦): P1A–C1A–P2A 133.5(2), P1A–C1A–H1A 112(3), P2A–C1A–H1A
114(3), C1A–P1A–B1A 108.9(2), C1A–P2A–B2A 121.1(2). Selected
˚
bond lengths (A): Ca–C1 2.754(3), Ca1–O1 2.359(2), Ca1–H1B1 2.37(3),
Ca1–H3B1 2.62(3), Ca1–H2B2 2.37(3), Ca1–H1B3 2.41(3), Ca1–H3B3 2.34(3),
Ca1–H1B4 2.37(3), Ca1–H3B4 2.47(3), C1–P1 1.764(3), C1–P2 1.759(3),
P1–B1 1.933(3), P1–C2 1.825(3), P1–C8 1.821(3), P2–B2 1.919(3), P2–C14
1.828(3), P2–C20 1.823(3), C26–P3 1.712(3), C26–P4 1.712(3), P3–B3
1.926(3), P3–C27 1.825(3), P3–C33 1.834(3), P4–B4 1.930(3), P4–C39
1.830(3), P4–C45 1.825(3). Angles (◦): Ca1–C1–P1 91.3(1), Ca1–C1–P2
92.3(1), P1–C1–P2 125.0(2), C1–P1–B1 113.5(2), C1–P2–B2 113.7(2),
P3–C26–P4 129.7(2), C26–P3–B3 120.4(1), C26–P4–B4 120.8(2).
˚
bond lengths of the cation (A): Li1A–O1A 2.214(8), Li1A–O2A
2.045(7), Li1A–O3A 2.131(7), Li1A–O4A 2.244(8), Li1A–O5A 2.068(7),
Li1A–O6A 2.145(7).
In [(thf)Ca{CH(PPh2-BH3)2}2] (4) the nine-coordinate calcium
˚
atom binds to an oxygen (Ca–O 2.359 A) and one carbon atom
˚
(Ca–C 2.754 A) as well as seven hydrogen atoms (av. Ca–H
tween the [{(Me3Si)3C5H2}Ca(thf)2] unit and the [HBEt3] anion
˚
2.42 A). Despite the rather large coordination number, a small
was found.
Ca–O distance is observed. The Ca–H bond lengths are in the
expected region and larger than bridging hydride ions between two
calcium cations.36 Molecular structure and numbering scheme of
4 is displayed in Fig. 5. The Ca–C bond is longer than observed
in the bis(trialkylsilyl)methyl derivatives of calcium,4,6 the carbene
Conclusion
The rich coordination chemistry of the ligand [HC(PPh2-
BH3)2] was investigated varying from a free anion to a
ligand binding via the borane moieties and via the methine
carbon atom. The metathesis reaction of K{CH(PPh2)2}
and K{CH(PPh2-BH3)2} with anhydrous calcium diiodide
adducts,16–18 and in [(thf)2Ca{C3H3(SiMe3)2}2],37 however, similar
19
=
Ca–C bond lengths were found in [Ca{C(PPh2 NSiMe3)2]2.
The fact that one anion shows a Ca1–C1 bond whereas the other
does not offers the opportunity to elucidate the influence on the
structural parameters of the anions. The formation of the Ca–C
bond leads to a pyramidalization of the HCP2 moiety (angle sum
at C1 341◦, at C26 358◦) and to a smaller P1–C1–P2 bond angle
of 125.0◦ compared to P3–C26–P4 with 129.7◦. This structural
change hinders charge delocalization leading to larger P–C1 bonds
yields
corresponding
[(thf)3Ca{CH(PPh2)2}2]
(2)
and
[(thf)Ca{CH(PPh2-BH3)2}2] (4), respectively. In compound
2 the bis(diphenylphosphanyl)methanide anions act as bidentate
ligands via the phosphorus atoms leading to a seven-coordinate
calcium atom. The coordination mode of the [RC(PR¢2)2]- anions
in main group45 and f-block27 chemistry depends on the metal
atom, the presence of donor ligands, and the nature of the
substituents R and R¢ at carbon and phosphorus.45 Due to similar
Pauling electronegativities and a valence isoelectronic situation
the anionic carbon and phosphorus centers can compete as
Lewis bases making it difficult to foresee the coordination mode.
The formal insertion of borane into the Ca–P bonds of 2 leads
to compound 4 which is isoelectronic to [(thf)Ca{CH(SiPh2-
CH3)2}2]. In 4 one anion exclusively binds via the boron-bound
hydrides whereas the other ligand also shows an additional Ca–C
bond. However, in solution both these anions are chemically and
magnetically equivalent as a consequence of flexibility of the
molecule. The free anion was observed in the solvent-separated
ion pair [(dme)3Li]+ [HC(PPh2-BH3)2]- (3¢).
˚
˚
(av. C1–P1/2 1.762 A, C26–P3/4 1.712 A).
The metal–boron distances in the contact ion pairs
˚
3
(Li1–B1 2.478(7) and Li1–B2 2.467 A) and 4 (Ca1–B1 2.754(3),
˚
Ca1–B2 2.908(4), Ca1–B3 2.813(3), and Ca1–B4 2.833(3) A)
are comparable to those observed in other compounds. In
LiBH4 and LiNH2BH3 lithium–boron distances of 2.37 to
2.62 A and 2.50 to 2.69 A, respectively, were found. In calcium
boranate Ca(BH4)2 Ca–B distances between 2.89 and 2.96 A
were determined.40,41 Furthermore in Ca(NH2BH3), which attracts
38
39
˚
˚
˚
some interest as a hydrogen storage material, similar values
between 2.87 and 3.03 A were observed.39 In [(thf)4Ca{(Me3Si)2C–
˚
PMe2BH3}2] the calcium atom binds to the oxygen atoms of
the THF bases and to four boron-bound hydride groups of two
42
˚
borane units with a Ca–B distance of 2.751(2) A. Comparable
values were also observed in [(dme)2Ca(BH4)2]43 whereas in
The compounds [(thf)Ca{CH(PPh2-BH3)2}2] (4) and yet un-
[{(Me3Si)3C5H2}Ca(thf)2(HBEt3)]44 a rather loose contact be-
known [(thf)Ca{CH(SiPh2-CH3)2}2] are isoelectronic complexes.
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However, the coordination behaviour of the ligands shows sig-
nificant differences. Bis(triorganylsilyl)methyl groups form
Ca–C bonds as found in [(diox)2Ca{CH(SiMe3)2}2]46 (diox =
1,4-dioxane) whereas the CH(PPh2-BH3)2 group prefers a coor-
dination to calcium via the borane units due to significant basicity
of B-bound hydrogen atoms.
added slowly to the stirred suspension at room temperature. The
resulting clear, pale yellow solution was stirred for 0.5 h and then
stored at 0 ◦C over night. Afterwards the supernatant solution
was decanted from the colorless crystals of 3. Yield: 0.53 g. The
1
product loses ether on drying in vacuo. H NMR (400 MHz,
[D8]THF, 25 ◦C): d 0.50–1.40 (br, 6H, BH3), 0.74 (s, 1H, PCHP),
1.16 (CH3 Et2O), 3.42 (CH2 Et2O), 7.15 (br s, 12H, Ph), 7.76 (m,
8H, Ph). Li NMR (155.6 MHz, [D◦8]THF, 25 ◦C): d -0.8 (s).
7
Experimental section
11B NMR (128.4 MHz, [D8]THF, 25 C): d -33.6 (s). 13C NMR
(50.3 MHz, [D8]THF, 25 ◦C): d 5.12 (t, 1JC,P = 77.4 Hz, 1C, PCP),
15.7 (s, CH3 Et2O), 66.2 (s, CH2 Et2O), 127.2 (d, JC,P = 9.4 Hz, 8C,
CH Ph), 127.9 (s, 4C, p-CH Ph), 133.1 (d, JC,P = 9.2 Hz, 8C, CH
General considerations
All manipulations were carried out by using Schlenk tech-
niques under an atmosphere of argon. Prior to use, tetrahy-
drofuran, dimethoxyethane, and diethyl ether were dried over
potassium hydroxide and distilled over Na/benzophenone in an
argon atmosphere. Starting [LiCH(PPh2)2],23 [KCH(PPh2)2],27 and
1
Ph), 142.8 (d, JC,P = 56.7 Hz, 4C, i-C Ph). 31P NMR (81 MHz,
[D8]THF, 25 ◦C): d 16.3 (br). Recrystallization of 3 from 1,2-
dimethoxyethane yielded compound [(dme)3Li][CH(PPh2)2] (3¢)
which was used for elemental analysis: C37H57B2LiO6P2 (688.37),
calcd.: C 64.56, H 8.35%; found: C 64.26, H 8.24%.
30
H2C(PPh2BH3)2 were prepared according to literature proce-
dures using toluene instead of benzene. H NMR and 13C NMR
1
Synthesis of [(thf)Ca{HC(PPh2BH3)2}2] (4). Solid KOtBu
(0.18 g, 1.61 mmol) was added to a stirred solution of 3 in
35 ml of diethyl ether, prepared from H2C(PPh2BH3)2 (0.72 g,
1.75 mmol) and a solution of n-butyllithium (1.1 ml of 1.6M
hexane solution, 1.76 mmol). The resulting reaction mixture
was stirred for 2 h. Afterwards the formed pale yellow solid of
K{HC(PPh2BH3)2} (0.73 g) was isolated by filtration and dried in
vacuo. This pottassium salt was used without characterization or
further purifications. Solid K{HC(PPh2BH3)2} (0.60 g, 1.33 mmol)
was added to a stirred solution of (thf)4CaI2 (0.31 g, 0.53 mmol)
in 15 ml of THF, leading to the precipitation of colorless KI.
The reaction mixture was stirred for an additional hour and
reduced to dryness. The remaining colorless residue was dried
in vacuo for 5 min and afterwards suspended in 15 ml of toluene.
After 30 min the remaining solids were removed by filtration. The
colorless solution was concentrated in vacuo to 8 ml and stored
spectra were recorded at ambient temperature on a Bruker AC
200 or AC 400 MHz spectrometer. All spectra were referenced to
TMS or deuterated solvent as an internal standard.
[(tmeda)(thf)Li{CH(PPh2)2}] (1). Recrystallization of Li-
{CH(PPh2)2} from a mixture of THF and 1,2-bis(dimethylamino)-
ethane (tmeda) gave crystals of [(tmeda)(thf)Li{CH(PPh2)2}]·
THF (1), suitable for◦ X-ray diffraction studies. 1H NMR
(200 MHz, [D8]THF, 25 C): d 1.56 (t, 2JH,P = 8.6 Hz, 1H, PCHP),
2.12 (s, 12H, CH3 tmeda), 2.27 (s, 4H, CH2 tmeda), 6.85–7.1 (m,
12H, CH-Ph), 7.45–7.58 (m, 8H, CH Ph). 13C NMR (50.3 MHz,
◦
1
[D8]THF, 25 C): d 17.9 (t, JC,P = 19.4 Hz, 1C, PCP), 46.1 (s,
4C, CH3 tmeda), 58.8 (s, 2H, CH2 tmeda), 125.4 (s, 4C, p-CH Ph),
127.4 (br, 8C, CH Ph), 132.0 (t, 3JC,P = 7.8 Hz, 8C, CH Ph), 152.3
(t, 1JC,P = 4 Hz, 4C, i-C Ph). 31P NMR (81 MHz, [D8]THF, 25 ◦C):
d 2.9 (s).
◦
at -20 C for 2 days. The formed colorless crystals were isolated
Synthesis of [(thf)3Ca{CH(PPh2)2}2] (2). Solid KOtBu (0.17 g,
1.52 mmol) was added to a stirred solution of LiCH(PPh2)2 (0.70 g,
1.75 mmol) in diethyl ether (35 ml). The resulting yellow solution
was stored for 2 days at -20 ◦C. Afterwards the formed pale yellow
precipitate was isolated by filtration and dried in vacuo (yield:
0.41 g). This K{CH(PPh2)2} (0.25 g, 0.59 mmol) was added to a
stirred solution of (thf)4CaI2 (0.16 g, 0.275 mmol) in 5 ml of THF,
resulting in the precipitation of KI. The suspension was stirred
for 30 min and the solid was removed. The clear yellow solution
was stored for 3 days at -40 ◦C in order to precipitate crystalline
CaI2(thf)4 which was removed by decantation afterwards. The
solution was concentrated in vacuo until the remaining yellow
oil started to crystallize. Crystallization was complete after 1 day
at 0 ◦C and the obtained solid, consisting of 2 and traces of
H2C(PPh2)2, was dried in vacuum. 1H NMR (200 MHz, [D8]THF,
25 ◦C): d 2.02 2JH,P = 6.8 Hz, 2H, PCHP), 6.95–7.2 (m, 24H, CH-
Ph), 7.55–7.70 (m, 16H, CH Ph). 13C NMR (50.3 MHz, [D8]THF,
by filtration and dried in vacuo. Yield: 0.27 g (54%). Elemental
analysis (C54H62CaB4OP4, 934.307): calcd.: C 69.42, H 6.69%;
found: C 67.15, H 6.50%. 1H NMR (400 MHz, [D6]benzene,
◦
3
25 C): d 1.08 (t, JH,H = 6.4 Hz, 4H, thf), 1.2–2.2 (br, 12H,
BH3), 1.53 (t, 2JH,P = 14 Hz, 2H, PCHP), 3.76 (t, 3JH,H = 6.4 Hz,
4H, thf), 6.9–7.05 (m, 24H, Ph), 7.65–7,75 (m, 16H, Ph). 11B
◦
NMR (128.4 MHz, [D6]benzene, 25 C): d -31.5 (br). 13C NMR
◦
1
(100.6 MHz, [D6]benzene, 25 C): d 5.56 (t, JC,P = 51 Hz, 2C,
PCP), 25.0 (s, 2C, thf), 69.7 (s, 2C, thf), 128.1 (signal overlaps with
the solvent signal, 16C, CH Ph), 129.2 (s, 8C, p-CH Ph), 131.9 (d,
JC,P = 9.6 Hz, 8C, CH Ph), 138.0 (d, 1JC,P = 66.1 Hz, 4C, i-C Ph).
31P NMR (162 MHz, [D8]THF, 25 ◦C): d 11.1 (br).
Crystal structure determinations
The intensity data for the compounds 1, 2, 3 and 4 were
collected on a Nonius KappaCCD diffractometer using graphite-
monochromated Mo Ka radiation. Data were corrected for
Lorentz and polarization effects but not for absorption effects.47,48
The structures were solved by direct methods (SHELXS)49
◦
1
25 C): d 16.5 (t, JC,P = 31.1 Hz, 2C, PCP), 126.6 (s, 8C, p-CH
Ph), 127.8 (s, 16C, CH Ph), 131.9 (t, 3JC,P = 6.4 Hz, 16C, CH Ph),
149.1 (br, 8C, i-C Ph). 31P NMR (81 MHz, [D8]THF, 25 ◦C): d 1.0
(s).
2
and refined by full-matrix least squares techniques against Fo
Synthesis of [(Et2O)2Li{HC(PPh2BH3)2}] (3) and [(dme)3Li]-
[HC(PPh2BH3)2] (3¢). Solid H2C(PPh2BH3)2 (0.65 g, 1.58 mmol)
was suspended in 30 ml of diethyl ether and a solution of
n-butyllithium (1.0 ml of 1.6M hexane solution, 1.6 mmol) was
(SHELXL-97) (Table 2).50 The hydrogen atoms for all CH
fragments and for the borane of 3 and 4 were located by difference
Fourier synthesis and refined isotropically. All other hydrogen
atoms were included at calculated positions with fixed thermal
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Table 2 Crystal data and refinement details for the X-ray structure determinations of compounds 1 to 4
Compound
1
2
3
3¢
4
Formula
C35H45LiN2OP2, C4H7O
649.71
-90(2)
Monoclinic
P21/c
21.3975(6)
9.8321(2)
18.8821(6)
90.00
108.9380(10)
90.00
3757.43(18)
4
1.149
1.50
26018
6195
8610/0.0582
0.1564
0.0594
1.018
0.689/–0.485
712109
C62H66CaO3P4
1023.11
-90(2)
C33H47B2LiO2P2
566.21
[C25H27B2P2]- [C12H30LiO6]+
C54H62B4CaOP4
934.24
-90(2)
Monoclinic
P21/c
13.4163(4)
13.8646(4)
28.3332(6)
90.00
101.003(2)
90.00
5173.4(2)
4
1.199
2.82
31260
7944
11746/0.0644
0.1457
0.0562
1.022
0.467/–0.264
712113
Fw/g mol-1
688.33
-90(2)
T/◦C
-90(2)
Crystal system
Space group
Monoclinic
P21/c
Triclinic
Triclinic
¯
P1
¯
P1
˚
a/A
12.2090(4)
16.6792(5)
27.0731(6)
90.00
95.218(2)
90.00
5490.2(3)
4
1.238
2.76
34850
6779
12534/0.0900
0.1498
10.0747(8)
11.1578(7)
16.7869(13)
97.819(4)
104.841(3)
106.881(4)
1699.7(2)
2
1.106
1.54
11602
5238
7587/0.0555
0.2287
0.0834
1.067
0.665/–0.515
712111
11.2500(2)
12.3814(2)
29.6450(5)
86.239(1)
81.939(1)
82.513(1)
4048.91(12)
4
1.129
1.47
28533
11470
17957/0.0394
0.2805
0.0934
1.005
1.642/–0.807
712112
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
r/g cm-3
m/cm-1
Measured data
Data with I > 2s(I)
Unique data/Rint
wR2 (all data, on F2)a
R1 (I > 2s(I))a
0.0588
0.997
0.581/–0.295
712110
sb
-3
˚
Res. dens./e A
CCDC No.
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
2
2
a Definition of the R indices: R1 = ( ꢀFo| - |Fcꢀ)/ |Fo|, wR2 = { [w(Fo - Fc2)2]/ [w(Fo2)2]} with w-1 = s (Fo2) + (aP)2. b s = { [w(Fo
-
1/2
Fc2)2]/(No - Np)}
.
parameters. All non-disordered non-hydrogen atoms were refined
anisotropically.50 The cation [(dme)3Li]+ of compound 3¢ is heavily
disordered and therefore the structural discussions are concen-
trated on the non-disordered part. XP (SIEMENS Analytical
X-ray Instruments, Inc.) was used for structure representations.
14 F. Feil and S. Harder, Organometallics, 2000, 19, 5010–5015.
15 W. A. Herrmann and C. Ko¨cher, Angew. Chem., 1997, 109, 2256–2282,
(Angew. Chem., Int. Ed., 1997, 36, 2162–2187).
16 A. J. Arduengo, F. Davidson, R. Krafczyk, W. J. Marshall and M.
Tamm, Organometallics, 1998, 17, 3375–3382.
17 H. Schumann, J. Gottfriedsen, M. Glanz, S. Dechert and J. Demtschuk,
J. Organomet. Chem., 2001, 617–618, 588–600.
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MacDougall, M. F. Mahon and P. A. Procopiou, Organometallics,
2008, 27, 3939–3946.
Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG, Bonn-Bad Godesberg, Germany). We also acknowledge
the financial support by the Fonds der Chemischen Industrie
(Frankfurt/Main, Germany).
19 L. Orzechowski, G. Jansen and S. Harder, J. Am. Chem. Soc., 2006,
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20 (a) M. S. Hill and P. B. Hitchcock, Chem. Commun., 2003, 1758–1759;
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25, 394–402.
21 L. Orzechowski and S. Harder, Organometallics, 2007, 26, 2144–
2148.
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