Heavy group 15 element compounds of a sterically demanding bis(iminophosphorane)methanide and -methanediide

Article abstract of DOI:10.1021/om401059x

Complexes of the heavy pnictogen elements Sb and Bi of monoanionic (C,N-chelated: Sb, Bi) and dianionic (N,C,N-pincer type: Bi) bulky substituted bis(diphenyl(arylimino)phosphorano)methane H₂C(Ph₂PNR) ₂ (R = 2,6-diisopropylphenyl (dipp)) have been prepared via metathetical reactions, and tautomerism within the monoanionic ligand backbone has been observed. The complexes have been characterized by means of X-ray analysis and NMR studies. The dianionic complex was found to feature the rare structural motif of a formal carbon-bismuth(III) double bond. The molecular structure of the solvate-free potassium salt K[HC(Ph₂PNdipp) ₂] is reported.

Full text of DOI:10.1021/om401059x

Article
pubs.acs.org/Organometallics
Heavy Group 15 Element Compounds of a Sterically Demanding
Bis(iminophosphorane)methanide and -methanediide
Christian P. Sindlinger,† Andreas Stasch,‡ and Lars Wesemann*,†
†Institute of Inorganic Chemistry, University of Tubingen, Auf der Morgenstelle 18, 72076 Tubingen, Germany
̈
̈
‡School of Chemistry, Monash University, P.O. Box 23, Melbourne, Victoria 3800, Australia
S
* Supporting Information
ABSTRACT: Complexes of the heavy pnictogen elements Sb
and Bi of monoanionic (C,N-chelated: Sb, Bi) and dianionic
(N,C,N-pincer type: Bi) bulky substituted bis(diphenyl-
(arylimino)phosphorano)methane H2C(Ph2PNR)2 (R = 2,6-
diisopropylphenyl (dipp)) have been prepared via metathetical
reactions, and tautomerism within the monoanionic ligand
backbone has been observed. The complexes have been
characterized by means of X-ray analysis and NMR studies.
The dianionic complex was found to feature the rare structural motif of a formal carbon−bismuth(III) double bond. The
molecular structure of the solvate-free potassium salt K[HC(Ph2PNdipp)2] is reported.
forthcoming, as well as complexes of the structurally related
mono- and dianionic N-dipp-substituted diketiminates (nac-
nac) with bismuth chloride.3,6
We have investigated the coordination chemistry of bis-
(diphenyl(arylimino)phosphorane)methane systems toward
the heavy group 15 elements bismuth and antimony, applying
the bulky N-bonded dipp residue H2C(Ph2PNdipp)2 (1). Our
work has resulted in the synthesis of [EX2{C(Ph2PNdipp)-
(Ph2PNHdipp)}] (2, EX2 = BiCl2; 3, EX2 = SbI2) and
[BiCl{C(Ph2PNdipp)2}] (4), which we now report.
INTRODUCTION
■
In recent years, the coordination chemistry of neutral, mono-
and dianionic, sterically hindered bis(iminophosphorane)-
methane ligands with main-group elements, transition metals,
and f-block elements has been intensely studied.1 A broad range
of different coordination modes has been found, highlighting
the flexibility of the ligand system going back to the great
number of the systems’ mesomeric descriptions and the
delocalization of charge therein. The strong delocalization of
charge in the case of the dianionic ligand demanded intensive
discussions of adequate descriptions for the bonding situation,
especially in the case of main-group complexes.1c,f,g A variety of
sterically demanding N-bond residues enables a fine tuning of
the ligand systems’ bulkiness, which has a direct influence on
the oligomerization of the respective complexes.2 The majority
of the reported bis(iminophosphorane)methanide and -meth-
anediide compounds apply trimethylsilyl and mesityl residues
attached to the imino nitrogen atom, while the application of
the sterically more demanding 2,6-diisopropylphenyl moiety is
less common.1a,b,h,2d
Scheme 1 summarizes the ligand and its alkali-metal salts that
were used as precursors for this study. For the dilithio salt the
Scheme 1
Most importantly, through an internally stabilized dianionic
carbon moiety the dideprotonated bis(iminophosphorane)-
methane ligand class provides a formal precursor for carbon−
element double bonds, which are interesting structural motifs in
organometallic chemistry. Especially in the case of bismuth only
a few structurally characterized examples of R2CBiIII(X/R)
are known in the literature.3 Along with numerous examples of
alkali-metal and alkali-earth-metal compounds there are several
reported examples of group 13 and 14 complexes.2a,c,4 In the
course of the preparation of this paper, complexes of the
monoanionic N-trimethylsilyl system with [EI2]+ (E = As, Sb,
Bi) have been reported.5 Bi and Sb compounds of the related
dianionic bissulfido system bis(diphenylsulfidophosphorane)-
methane, [ECl{C(Ph2PS)2}] (E = Sb, Bi), have also been
depicted description with alternating positive and negative
charges was previously found to represent an important
canonical description for bis(iminophosphorane)methanediides
by means of computational methods.2a
RESULTS AND DISCUSSION
■
The known potassium salt 1c was shown to be a convenient
synthetic precursor for the formation of various bis-
(iminophosphorane)methanide complexes via salt metathesis
reactions.4b In the course of our studies we obtained an X-ray
Received: October 31, 2013
Published: December 9, 2013
© 2013 American Chemical Society
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structure from colorless crystals of the so far unknown solvent-
free potassium salt 1c from a hexane solution. X-ray analysis
revealed a polymeric structure in which the potassium cation is
coordinated by the ligand in a C,N-chelate type, further
supported by η6 coordination of the aromatic moiety of the
dipp group attached to the noncoordinating nitrogen. An
additional η2 interaction is given with the aromatic phenyl
moiety of an adjacent molecule. Figure 1 depicts the polymeric
paper.5 On consideration of the Lewis acidity of a coordinated
element halide fragment to cause a proton shift, it is interesting
that for smaller elements with potentially more Lewis acidic
fragments such as [AlCl2]+, [AlBr2]+, and [GaCl2]+, a N,N-
chelating coordination mode forming a six-membered ring is
adopted and no proton shift occurs.4d,7 A somehow comparable
shift has already been described for neutral bis-
(iminophosphorane)methane ligands coordinating to transition
metals (Rh, Ir, Pt).8 On protonation of bis-
(iminophosphorane)methanes H2C(Ph2PNR′′)2 (R″ = i-
Pr,Ph) a similar shift has been observed, forming a cation with
the constitution [HC(Ph2PN(H)R″)2]+.9 Additionally a
substantial increase of the acidity of a methanide proton in
metal complexes was described by Le Floch for the case of
neodymium methanide complexes, in which a further
deprotonation can be achieved by amine bases to yield a
methanediide complex.1i
Figure 2 shows the crystal structure of complex 2. Bright
yellow crystals grew from hexane extracts of the crude reaction
Figure 1. ORTEP plot of the molecular structure of 1c. Thermal
ellipsoids are shown at the 50% probability level. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å): K(1)−N(1)
2.737(3), K(1)−C(1) 3.146(3), K(1)−Cdipp range 3.173(3)−
3.244(4), K(1)−C(17) 3.304(5), K(1)−C(18) 3.111(4), P(1)−
N(1) 1.584(3), P(1)−C(1) 1.708(3), P(2)−C(1) 1.722(3), P(2)−
N(2) 1.580(3).
structure found for the solvent-free potassium salt 1c. In
comparison to the structural findings for the THF adduct, no
significant changes for the bond length of the NPCPN moiety
are observed. Nevertheless, polymeric 1c reveals shorter K1−
C1 (3.146(3)/3.501(6) Å) as well as K1−N1 bonds (2.668(5)/
2.737(3) Å). In the case of polymeric 1c, K1 is coordinated
more symmetrically to the dipp group, indicated by a smaller
K(1)−Cdipp range (3.173(3)−3.244(4)/3.106(6)−3.450(8) Å).
On reaction of the monolithiated ligand Li[HC-
(Ph2PNdipp)2]4c (1a) with 1 equiv of BiCl3 in a THF/toluene
mixture at −78 °C and workup, we obtained 2 as a bright
yellow compound (Scheme 2). Single-crystal diffraction of
Figure 2. ORTEP plot of the molecular structure of 2·0.5(n-hexane).
Thermal ellipsoids are shown at the 50% probability level. Hydrogen
atoms (except H55) and the solvent molecule as well as a potential
H55−Cl1 interaction have been omitted for clarity. Hydrogen atom
H55 was located in the Fourier map. Selected bond lengths (Å) and
angles (deg): C(1)−P(2) 1.708(3), C(1)−P(1) 1.727(3), P(1)−N(2)
1.630(3), P(2)−N(1) 1.672(3), C(1)−Bi(1) 2.217(3), N(2)−Bi(1)
2.354(2), P(1)−Bi(1) 2.9961(8), Bi(1)−Cl(2) 2.6121(10), Bi(1)−
Cl(1) 2.7040(8), Cl(1)−H(55) 2.621(30); P(1)−C(1)−P(2)
132.1(2), C(1)−Bi(1)−N(2) 67.5(1), C(1)−Bi(1)−Cl(2) 105.2(1),
C(1)−Bi(1)−Cl(1) 90.2(1), N(2)−Bi(1)−Cl(1) 157.2(1), Cl(1)−
Bi(1)−Cl(2) 92.9(1), N(2)−Bi(1)−Cl(2) 88.9(1).
Scheme 2. Synthetic Procedure for 2 and 3
product or from saturated ethereal solutions. The crystal system
was found to be monoclinic in the space group P21/c. In
comparison to the free neutral ligand, C−P bond lengths are
contracted and P−N bond lengths are elongated, indicating
mesomeric delocalization of charge. C(1) is shown to be almost
planar three-coordinate with a sum of bond angles of 358.4°.
The C,N-chelating coordination of a monoanionic CPN
moiety toward bismuth, forming a CPNBi four-membered
heterocycle, represents a rare structural motif. The absence of
significant pyramidalization at C(1) contradicts the assumption
of a carbon-localized, stereochemically active lone pair and a
formal residual negative charge (Scheme 3, C). Moreover, a
bonding situation as depicted in A and B with delocalized
double-bond character within the PCP system seems to be an
appropriate description. The N(2)−Cipso(dipp) bond is only
crystals from diethyl ether revealed 2 to be monomeric in the
solid state. The [BiCl2]+ fragment turns out not to be
incorporated into a six-membered ring by the ligand applying
a N,N-chelate coordination mode but rather a four-membered
BiCPN heterocycle is formed in which [BiCl2]+ is coordinated
in an unsymmetrical C,N-chelate mode. The PCP carbon atom
was unexpectedly found to be fully deprotonated. Most likely
coordination of the Lewis acidic Bi3+ causes a sufficient change
in acidity of the C−H to undergo an intramolecular 1,3-proton
shift to the alkaline noncoordinating second P-imino nitrogen.
Such a proton shift can be seen as a P analogue of the known
imine−enamine tautomerism and has been described by most
recent works published in the course of the preparation of this
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structure as observed for the bismuth chloride analogue 2 (see
the Supporting Information). Moreover, NMR spectroscopic
data are found to be essentially identical. The thermolability
above ambient temperature of 3 toward decomposition into the
free ligand was found to be even more distinctive than for 2.
In both cases no further coordination contacts with halides of
adjacent molecules were found. The coordination geometry
around bismuth in 2 as well as around antimony in 3 represents
a distorted seesaw analogous to the reported “cis”-type
complexes found for the trimethylsilyl-substituted derivatives,
in which the [EX2]+ fragment features a bent alignment.5 On
the basis of a sole X-ray structure Chivers and Vargas-Baca et al.
found a symmetrically N,C,N-chelating coordination type for an
almost linear [BiI2]+ fragment and applied quantum mechanical
calculations to provide an explanation for the absence of the
intramolecular 1,3-proton shift in the case of bismuth. In their
findings the generally energetically favored CH tautomer of the
ligand is overcompensated by a stabilizing interaction energy
between the ligand anion and the metal fragment (for which
only a linear arrangement was considered). The amount of the
stabilizing interaction decreases descending from As to Bi,
which is why [AsI2]+ and [SbI2]+ favor a coordination by the
NH tautomer over the CH tautomer found for [BiI2]+.5 The
fact that we found the NH tautomer [BiCl2]+ complex as the
sole product is interesting and may go back to differences in the
nature of the halides (iodide vs chloride), the arrangement of
the metal halide fragment (linear vs bent), and the basicity of
the imino nitrogens depending on the residues attached
(trimethylsilyl vs dipp). Nevertheless, it may be a good
indication that the energetic differences between the two
opponent coordination modes are small.
Scheme 3
slightly twisted out of the Bi(1)N(2)P(1)C(1) least-squares
plane by 15.3° (0° expected for pure sp2 hybridization at N(2),
54.7° for sp3), indicating that sp2-type hybridization is
considerably predominant (Scheme 3, B). The Bi1−N2
(2.354(2) Å) distance is essentially equal to those reported
for four-membered NCNBi cycles in amidinate complexes of
[BiCl2]+ (2.333(5), 2.359(4) Å)10 but much shorter than in a
comparable CCNBi four-membered cycle found in a dianionic
nacnac complex coordinating two [BiCl2]+ fragments
(2.500(13), 2.539(11) Å).6
1
Solution H NMR experiments for 2 revealed three sets of
isopropyl moieties. For the iPr methine protons two over-
lapping septets in the range 3.70−3.85 ppm are observed. For
the methyl protons two broad resonances at 1.34 and 0.56 ppm
and one sharp doublet at 1.21 ppm with a relative integration of
1:1:2 are observed. The broad methyl resonances are assigned
to the dipp group attached to N2, and their different chemical
shifts are deduced from their orientation toward the CPNBi
plane. The sharp doublet is assigned to the free dipp group
attached to N1. By means of an H−15N HSQC experiment a
1
proton resonance at 7.65 ppm was clearly identified as the N1-
bonded amine proton. The chemical shift of the N-bonded
proton is in accordance with iminophosphorane hydrochlorides
known in the literature.11 The 31P{1H} NMR spectrum shows a
very broad resonance at 45.3 ppm and a sharp doublet at 26.8
Reacting BiCl3 with the dilithium salt of the ligand
Li2[C(Ph2PNdipp)2] (1b) in a mixture of THF and toluene
at −35 °C or by treatment of 2 with 1 equiv of a non-
nucleophilic base such as lithium 2,2,5,5-tetramethylpiperidide
in THF resulted in the formation of another yellow compound
with a singlet resonance in the 31P{1H} NMR spectrum at 3.5
ppm (Scheme 4). Any attempts to generate the corresponding
ppm with a JPP coupling constant of 48.3 Hz. 1H−31P
2
experiments reveal cross-coupling between proton H55 and P2
and enable the assignment of the sharp doublet to P2. The
reason for the significant broadening of the phosphorus
incorporated in the CPNBi four-membered ring could not be
fully determined, though it results most likely from dynamic
effects. Coupling with the considerably strong quadrupole
nucleus of Bi with I = 9/2 and 100% natural abundance seemed
likely, but no comparable broadening was observed for
[BiCl{C(Ph2PNdipp)2}] (4) (vide infra). When a sample in
benzene-d6 was heated to 50 °C, the half-width decreased
significantly, but due to the thermolability of the compound
decomposition was observed, indicated by increasing signals of
the free ligand. However, this decomposition with formation of
1 was not accompanied by an observable formation of 4 (vide
infra).
Scheme 4. Synthetic Procedures for 4
Taking into account that there is a considerably short
H(55)−Cl(1) distance (2.62 Å) and a fitting spatial alignment
indicating a concrete interaction, compound 2 can be described
as a zwitterionic intramolecularly generated HCl adduct of the
twice deprotonated [BiCl{C(Ph2PNdipp)2}] (4) (Scheme 3).
Analogously, the related antimony complex [SbI2{C-
(Ph2PNdipp)(Ph2PNHdipp)}] (3) was obtained by treatment
of antimony(III) iodide with 1c in a mixture of THF and
toluene at −50 °C as a yellow solid that is highly sensitive
toward water and oxygen. From various experiments with
carefully dried solvents hydrolysis products such as 1·2HI or [1-
H]I3 crystallized. Plate-shaped crystals of 3 in the monoclinic
space group P21/c obtained by various approaches were
repeatedly of low quality but reveal the same molecular
homologous dianionic complex of Sb by an analogously
performed deprotonation of 3 did not lead to any successful
isolation but to a mixture of several products according to
31P{1H} NMR. For the reaction of the dilithiated N-
trimethylsilyl bis(iminophosphorane)methane derivative with
bismuth iodides an inseparable mixture of products was found
previously.5 While some examples for monoanionic N,C,N
pincer complexes of bismuth have been reported in the
literature,5,12 4 represents the first dianionic compound
featuring this structural motif.
Since the preparation of pure dilithium compound 1b can be
low-yielding, the two-step reaction with another 1 equiv of base
represents an easier, more reliable access to 4. Crystals of the
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symmetrically coordinated compound 4 can be obtained by
gas-phase diffusion of n-pentane into solutions of 4 in benzene.
X-ray analysis (Figure 3) revealed the monomeric methanediide
around C19 amounts to 351° with a large PCP angle of
150.93(12)° (143.0(4)° for the sulfido system).3 Unlike what
was stated in the respective literature in the NMR spectra, a 13
C
resonance for the doubly deprotonated PCP carbon of the
methanediide complex of Bi can be observed as a triplet at δ
64.1 ppm (1JPC = 134.49 Hz), demonstrating a stronger
downfield shift and an increased coupling constant in
comparison to those for a reported structurally related
sulfido-Sb compound (δ 32.7 ppm, JPC = 42.2 Hz).3
1
Nevertheless, the PCP 13C resonances for the stated
[{(Me3SiNPPh2)2C}(MCl2)] (M = Ti, Zr) emerge at
lower field (191.7, 101.0 ppm), indicating an increased carbene
character therein with consequences for the MC double
bond.13b Recently the PCP 13C resonance for [{(Me3SiN
PPh2)2C}(Ce(Odipp)2)] has been reported at δ 324.6 ppm as
an example of a methanediide complex featuring the typical
strong downfield shift known for carbene complexes.1f Taking
this into consideration and including the expectably weak
orbital overlap between carbon and bismuth, a significant
carbon−bismuth π interaction (and therefore a BiC bond)
can be neglected. Altogether, the bonding situation is
potentially best described by a partially ionic model with a
polar Bi−C single bond and two dative N−Bi bonds. Within
the NPCPN backbone an anionic charge is delocalized,
balancing a residual positive charge on the bismuth halide
fragment.
The 31P{1H} NMR spectrum confirms the symmetry within
the molecule in solution at room temperature. The symmetric
coordination mode is preserved in potentially coordinating
1
donor solvents such as THF-d8. At room temperature the H
Figure 3. ORTEP plot of the molecular structure of 4 from a frontal
perspective (top) and upon the CPNBi planes (bottom). Thermal
ellipsoids are shown at the 50% probability level. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): Bi1(1)−C(19) 2.1822(18), Bi1(1)−N(1) 2.3987(15), Bi(1)−
N(2) 2.4496(15), Bi(1)−Cl(1) 2.5430(5), P(1)−C(19) 1.7098(18),
P(2)−C(19) 1.7056(18), P(1)−N(1) 1.6310(17), P(2)−N(2)
1.6214(16); P(1)−C(19)−P(2) 150.9(1), N(1)−Bi(1)−N(2)
132.2(1), C(19)−Bi(1)−Cl(1) 105.6(1), N(1)−Bi(1)−Cl(1)
92.5(1), N(2)−Bi(1)−Cl(1) 90.1(1).
NMR reveals one broad resonance for the iPr methine protons
(δ 3.92 ppm) and two iPr methyl resonances (one broad at δ
1.17 ppm, one sharp at δ 1.03 ppm). When the sample is
cooled in toluene-d8, a splitting of this pattern is observed with
a coalescence near −20 °C. Upon further cooling down to −80
°C the methine resonances split into two resonances at δ 4.73
and 3.17 ppm. The methyl protons split into a set of four broad
singlet signals at δ 1.83, 0.98, 0.91, and 0.41 ppm. The 31P{1H}
NMR remains unchanged by variation of the temperature. The
spectra correspond to the structure determined by X-ray
diffraction. In the case of lower temperatures the two methine
signals represent an orientation of the iPr moiety above or
below the NBiCP planes, while the four methyl signals
discriminate between the orientation above or below the
respective plane and their orientation toward the front of the
molecule or the PPh2 groups within the backbone. A putative
mechanism to explain the changes on cooling includes the
assumption of restricted rotation around the N−Cipso(dipp)
bond. The suppression of free rotation at lower temperatures is
consistent with the changes observed in the spectra. Another
explanation including a rapid change of the chloride orientation
within the coordination sphere of bismuth in the room
temperature case can be ruled out, since two multiplet
resonances of higher order can be found in the 13C{1H}
spectra for Cipso of the phenyl groups attached to phosphorus
representing orientations “cis” and “trans” to the bismuth-
bonded chloride.
complex of the [BiCl]2+ fragment to be almost symmetric with
a short Bi−C bond length of 2.182(2) Å, comparable to the
bond length reported for the [(SPPh2)2C]2− complex
(2.160(7) Å).3 The bond lengths in the monoanionic complex
[BiI2{HC(Ph2PN(TMS))2}] recently reported are 2.392(6) Å
(Bi−C) and 2.412(5)/2.462(5) Å (Bi−N).5 Interestingly,
further deprotonation almost solely results in shortening of
the Bi−C bond by approximately 0.2 Å, while the Bi−N bonds
are only shortened by approxinately 0.02 Å. The P−C and P−
N bond lengths for [BiI2{HC(Ph2PN(TMS))2}] are 1.756(6)/
1.763(6) and 1.581(5)/1.596(5) Å, respectively.5 In compar-
ison to the findings for the dianionic complex 4, shortening of
the P−C bonds by approximately 0.05 to 1.71 Å and a very
small elongation of the P−N bonds are observed. These
comparisons are potentially influenced by electronic differences
caused by the N-bonded residue.
Unlike the pentacoordinated bismuth center in the dimerized
sulfido complex, 4 features a tetracoordinated Bi(III) ion.3 The
“open book”-type structure strongly resembles findings for the
N-trimethylsilyl-substituted bis(iminophosphorane)-
methanediide complexes of Ti and Zr halides.13 The two
least-squares planes CPNBi intersect along the Bi−C bond at a
small angle of approximately 12.6°, and the sum of angles
Preliminary insights into the formation processes of some
discussed species were drawn from a simple NMR-scale
experiment in which an excess of approximately 1.5 equiv of
the monolithiated ligand 1a was added to BiCl3. After a few
minutes the 31P{1H} NMR spectrum of the reaction mixture
revealed four singlet signals for the lithium salt 1a, the free
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Figure 4. 31P{1H} NMR of the reaction of BiCl3 with 1.5 equiv of 1a in C6D6/THF-d8 over time.
ligand 1, the methanediide complex 4, and another yet
unassigned singlet at 25.1 ppm (Figure 4). After a few hours
a sample drawn from the same reaction revealed only the
signals for 2, 4, and 1. The monolithiated compound 1a has
completely reacted, and the unassigned resonance at 25.1 ppm
is no longer observed. We conclude that the singlet at 25.1 ppm
represents a transiently formed symmetrical monoanionic
complex (2a) of the [BiCl2]+ fragment that undergoes quick
subsequent deprotonation by excess 1a to form 1 and 4.
Further tautomerism to the structurally characterized 2 is
potentially slower. A possible ligand disproportion reaction of 2
equiv of pure 2 into 1 and 4 has never been observed.
Moreover, NMR sample solutions in benzene-d6 or THF-d8 of
pure 2 and 3 stored at room temperature were stable even for
several weeks. In the synthesis of 2, attempts to isolate 2a by
quenching the reaction through solvent removal at an early
stage followed by extraction of the residue remained
unsuccessful and only 2 was obtained. It should be mentioned
that the formation of methanediide complexes by metathetical
reactions applying an excess of monolithiated bis-
(iminophosphorane)methane as additional base has been
described earlier in the case of the synthesis of group 14
vinylidene analogues.4e The N,C,N-pincer structure for 2a
depicted in Figure 4 is putative but is supported by Chivers’
findings and does not exclude the possibility of a N,N-chelate
type coordination as found for some nacnac systems.5,6
Nevertheless, the first coordination type may represent a
more reasonable intermediate, considering the obvious
subsequent tautomerism.
coordination type of this flexible ligand system. Moreover, an
unprecedented dianionic Bi N,C,N-pincer-type complex with
interesting structural features and a formal CBi double bond
has been prepared and characterized, augmenting the still small
number of structurally determined examples for such carbon−
bismuth interactions.3,14
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were carried out under an
argon atmosphere using standard Schlenk techniques or an MBraun
glovebox. THF, diethyl ether, and benzene were distilled from
sodium/benzophenone, toluene was distilled from sodium, and hexane
was distilled from potassium. Pentane was obtained from an MBraun
solvent purification system. Benzene-d6 was distilled from sodium and
stored over potassium; THF-d8 was distilled from LiAlD4 and stored
under exclusion of light.
An insoluble impurity of BiOCl (up to 15%) was removed from
BiCl3 (Aldrich, >98%) by extraction of BiCl3 with THF and removal of
the solvent under reduced pressure (0.001 mbar) for 2 days. 1 was
synthesized according to literature procedures.1e All other compounds
were purchased commercially (Aldrich) and used without further
purification.
Elemental analysis was performed by the Institut fur Anorganische
̈
Chemie, Universitat Tubingen, using a Vario MICRO EL analyzer.
̈
̈
[BiCl2{C(Ph2PNdipp)(Ph2PNHdipp)}] (2). To a solution of BiCl3
(0.223 g, 0.708 mmol, 1.05 equiv) in THF (5 mL) at −78 °C was
slowly added a solution of 1a (0.500 g, 0.675 mmol, 1 equiv) dropwise,
and the initially pale yellow solution was stirred overnight, during
which time the mixture was warmed to room temperature. The
solvents of the orange solution were completely removed under
reduced pressure, and the yellow residue was washed with warm
hexane (2 × 8 mL). The residue was then repeatedly extracted with
warm ether (15, 10, 5 mL), and the combined ethereal extracts were
reduced in volume to approximately 15−20 mL and stored at −28 °C
for a few days to obtain bright yellow crystals of 2·Et2O (0.200 g, 0.186
mmol, 28%, first crop). Further amounts of crystalline 2 could be
obtained by further concentration of the supernatant solution and
storage in the freezer. Crystals suitable for X-ray diffraction were
CONCLUSION
■
In summary, we have prepared bulky bis(iminophosphorane)-
methanide and -methanediide complexes of heavy group 15
elements. Tautomerism within the methanide complex was
observed, adding a further example of a recently reported new
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3
obtained from ethereal solutions as described above or (in very small
quantities) from the hexane wash phases. The crystals discussed in the
text 2·0.5(n-hexane) were obtained from the hexane solutions, though
molecular parameters such as bond lengths and angles do not differ
significantly from those of the Et2O cosolvate structure. For 2·Et2O,
Et2O does not show any coordinative interaction. Analytical data are as
follows. 1H (400.13 MHz, C6D6): δ 7.80−7.75 (m, 8H, o-CPhH), 7.65
(br s, 1H, PN(H)dipp), 7.18−7.16 (m, 2H, m-CdippH), 7.11−7.09 (m,
2H, m-CdippH), 7.03−6.98 (m, 4H, p-CdippH/p-CPhH), 6.92−6.88 (m,
Hdipp, JH−H = 7.56 Hz), 7.12−7.04 (m, 8H, overlapping signals of p-
Hdipp (2H), m-H(Ph2) (4H), p-H(Ph2) (2H)), 7.00−6.97 (m, 2H, p-
H(Ph1)), 6.95−6.90 (m, 4H, m-H(Ph1)), 3.92 (br, 4H, CHMe2), 1.17
3
(br, 12H, CHMe2(i-Pr1)), 1.03 (d, 12H, CHMe2(i-Pr2), JH−H = 7.00
Hz). 13C{1H}-UDEFT (125.76 MHz, C6D6): δ 147.4 (s, o-Cdipp),
1
3
140.0 (m, i-C(Ph1), JP−C + JP−C = 91.0 Hz), 139.7 (s, i-Cdipp), 136.6
(m, i-C(Ph2), 1JP−C + 3JP−C = 94.2 Hz), 132.0 (vtr, o-C(Ph1), JP−C = 5.7
Hz), 131.9 (vtr, o-C(Ph2), JP−C = 4.5 Hz), 130.7 (s, p-C(Ph2)), 129.8
(s, p-C(Ph1)), 128.1−127.9 (overlapping with strong solvent
resonances, m-C(Ph1), m-C(Ph2)), 124.3 (s, p-Cdipp), 123.3 (s, m-
3
10H, m-CPhH/p-CPhH), 3.79 (sept, 2H, CHMe2, JH−H = 6.75 Hz),
1
3
3.74 (sept, 2H, CHMe2, JH−H = 6.75 Hz), 3.38 (quart, 4H,
Cdipp), 63.4 (t, PCP, JP−C = 135.0 Hz), 28.3 (s, CHMe2), 26.2 (s,
CHMe2 (i-Pr2)), 24.1 (s, CHMe2 (i-Pr1)). 31P{1H} (202.5 MHz,
C6D6): δ 3.5 (s). Anal. Calcd for C49H54N2P2BiCl: C, 60.22; H, 5.57;
N, 2.87. Found: C, 60.25; H, 5.46; N, 3.08.
3
O(CH2Me)2, JH−H = 7.00 Hz), 1.34 (br s, 6H, CHMe2), 1.23 (t,
6H, O(CH2Me)2, 3JH−H = 7.00 Hz), 1.21 (d, 12H, CHMe2, 3JH−H = 6.5
Hz), 0.56 (br s, 6H, CHMe2). 13C{1H}-UDEFT (100.62 MHz, C6D6):
δ 148.2 (d, JP−C = 3.0 Hz, quat-Cdipp), 147.9 (d, JP−C = 5.5 Hz, quat-
Cdipp), 137.6 (s, i-CAryl), 136.7 (s, i-CAryl), 135.9 (vtr, JP−C = 6.1 Hz),
133.7 (d, JP−C = 10.8 Hz, o-CPh), 132.7 (d, 10.2 Hz, o-CPh), 131.6 (d,
JP−C = 2.1 Hz, m/p-CPh), 130.8 (d, JP−C = 2.6 Hz, m/p-CPh), 127.7 (s,
Method B. To a solution of 2·Et2O (45 mg, 0.041 mmol, 1 equiv) in
THF (0.5 mL) was added a solution of lithium 2,2,6,6-
tetramethylpiperidide (LiTMP; 6 mg, 0.041 mmol, 1 equiv) in THF
(0.8 mL) dropwise over a period of 5 min at room temperature. The
bright yellow solution was stirred for 30 min before the solvents were
removed under reduced pressure and the residue was redissolved in
benzene (1.5 mL). Gas-phase diffusion of pentane into the benzene
solution over 2 days afforded bright yellow crystals of 4 (32 mg, 0.033
mmol, 80%), which were isolated, washed with pentane (0.5 mL), and
dried under reduced pressure. Spectral data were in accord with those
reported for method A.
overlaid by strong solvent signals, p-Cdipp + m/p-CPh), 125.3 (d, JP−C
=
3.3 Hz, p-Cdipp), 123.5 (s, m-Cdipp), 123.3 (d, JP−C = 2.9 Hz, m-Cdipp),
1
69.1 (t, JP−C = 116.6 Hz, PCP), 65.7 (s, O(CH2Me)2), 29.9 (s,
CHMe2), 28.3 (s, CHMe2), 28.0 (br, CHMe2) 23.6 (s, CHMe2), 22.7
(br, CHMe2), 15.3 (s, O(CH2Me)2). 31P{1H} (169.97 MHz, C6D6): δ
2
45.3 (br, CPNBi-ring), 26.8 (d, JP−P = 48.3 Hz, P(Ph)2(NHdipp)).
Anal. Calcd for C53H65N2P2BiCl2O: C, 58.51; H, 6.02; N, 2.57. Found:
C, 58.87; H, 6.23; N, 2.52.
[SbI2{C(Ph2PNdipp)(Ph2PNHdipp)}] (3). To a solution of SbI3
(0.163 g, 0.324 mmol, 1 equiv) in THF (5 mL) at approximately −50
°C was added a solution of 1c (0.250 g, 0.323 mmol, 1 equiv) in
toluene/THF (5 mL/0.8 mL) dropwise. The resulting bright yellow
solution was stirred overnight and slowly warmed to room
temperature. Solvents were removed under reduced pressure, and
the bright yellow residue was washed with warm hexane (2 × 8 mL)
and extracted with toluene (3 × 5 mL). The solvent of the combined
toluene extracts was removed under reduced pressure to give 3 (0.240
g, 0.216 mmol, 67%) as a bright yellow solid. NMR spectral data and
elemental analysis indicate the presence of some residual solvated
toluene (approximately 0.3 molecules per 3). Plate-shaped crystals of
3·(toluene) of minor quality for X-ray diffraction were repeatedly
obtained from overlaying solutions in toluene (3−4 mL) with hexane
ASSOCIATED CONTENT
* Supporting Information
Text, figures, a table, and CIF files giving specifications on
NMR and X-ray instrumentation and data treatment, synthesis
of the literature-known ligand precursor salts 1a,4c 1b, and 1c,4b
X-ray structure of 3 along with selected bond lengths, tabulated
■
S
1
crystallographic data for 1c, 2·0.5C6H14, 3·C7H8, and 4, H,
13C{1H}, and 31P{1H} NMR spectra of 2−4 and the compiled
low-temperature spectra for 4 and crystallgraphic data for all
reported structures. This material is available free of charge via
the Internet at http://pubs.acs.org.
1
AUTHOR INFORMATION
Corresponding Author
*E-mail for L.W.: lars.wesemann@uni-tuebingen.de.
Notes
(20 mL). Analytical data are as follows. H (250.13 MHz, C6D6): δ
■
7.64 (br, 9H, H, o-CPhH overlapping with PN(H)dipp), 7.22−6.80 (br
m, 18H, CHAr), 3.85 (br, 2H, CHMe2), 3.70 (br, 2H, CHMe2), 1.38
(br d, 6H, CHMe2, 3JH−H = 6.5 Hz), 1.23 (br, 12H, CHMe2), 0.44 (br
d, 6H, CHMe2, 3JH−H = 6.6 Hz). 13C{1H} (62.90 MHz, C6D6): δ 148.3
(d, JP−C = 3.3 Hz, Car), 147.7 (d, JP−C = 5.2 Hz, Car), 137.6 (s, Car),
136.8 (vtr, JP−C = 5.8 Hz, Car), 133.6 (br d, JP−C = 7.1 Hz, Car), 132.9
(d, JP−C = 10.1 Hz, Car), 132.0 (br, Car), 130.9 (d, JP−C = 2.5 Hz, Car),
129.8 (s, Car), 127.6 (s, Car), 125.4 (s, Car), 125.1 (d, JP−C = 3.8 Hz,
Car), 124.2 (d, JP−C = 3.0 Hz, Car), 123.3 (d, JP−C = 2.0 Hz, Car), 29.9
(s, CHMe2), 28.4 (s, CHMe2), 27.5 (s, CHMe2), 23.2 (s, CHMe2).
31P{1H} (101.25 MHz, C6D6): δ 37.3 (br, CPNSb-ring), 28.9 (d,
2JP−P= 42.2 Hz, P(Ph)2(NHdipp)). Anal. Calcd for 3·0.3C7H8,
C51.1H57.4N2P2SbI2: C, 53.97; H, 5.09; N, 2.46. Found: C, 53.82; H,
5.29; N, 2.44. An X-ray structure of 3 is attached in the Supporting
Information.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support of the Studienstiftung des dt. Volkes, the
DAAD RISE program, and the Fonds der Chemischen
Industrie is gratefully acknowledged.
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