Synthesis and Coordination Ability of a Donor-Stabilised Bis-Phosphinidene

Article abstract of DOI:10.1002/chem.202004300

Chelating phosphines have long been a mainstay as efficient directing ligands in transition-metal catalysis. Low-valent derivatives, namely chelating phosphinidenes, are to date unknown, and could lead to chelating complexes containing more than one metal centre due to the intrisic capacity of phosphinidenes to bind two metal fragments at one P-centre. Here we describe the synthesis of the first such chelating bis-phosphinidene ligand, XantP₂ (2), generated by the reduction of a diphosphino xanthene derivative, Xant(PH₂)₂ (1) with ^iPrNHC (^iPrNHC=[:C{N(iPr)C(H)}₂]). Initial studies have shown that this novel chelating ligand can act as a bidentate ligand towards element dihalides (i.e. FeCl₂, ZnI₂, GeCl₂, SnBr₂), forming cationic complexes with the tetryl elements. In contrast, XantP₂ demonstrates an ability to bind multiple metal centres in the reaction with CuCl, leading to a cationic Cu₃P₃ ring complex, with Cu centres bridged by phosphinidene arms. Density Functional Theory calculations show that 2 indeed holds 4 lone pairs of electrons, shedding further light on the coordination capacity for this novel ligand class through observation of directionality and hybridisation of these electron pairs.

Full text of DOI:10.1002/chem.202004300

Accepted Article
Accepted Article
Title: Synthesis and coordination ability of a donor-stabilised bis-
phosphinidene
Authors: Terrance John Hadlington, Matthias Driess, and Arseni
Kostenko
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To be cited as: Chem. Eur. J. 10.1002/chem.202004300
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Synthesis and coordination ability of a donor-stabilised bis-
phosphinidene
Terrance J. Hadlington,*[a],[b] Arseni Kostenko,[a] and Matthias Driess*[a]
[a]
Dr. T. J. Hadlington, Dr. A. Kostenko, Prof. Dr. M. Driess
Department of Chemistry, Metalorganics and Inorganic Materials
Techniche Universität Berlin
Strasse des 17. Juni 135, Sekr. C2, 10623 Berlin, German
E-mail: terrance.hadlington@tum.de
matthias.driess@tu-berlin.de
[b]
Dr. T. J. Hadlington
Department of Chemistry
Technische Universität München
Lichtenbergstraße 4, D-85748 Garching, Germany
Supporting information for this article is given via a link at the end of the document.
Abstract: Chelating phosphines have long been a mainstay as
efficient directing ligands in transition-metal catalysis. Low-valent
derivatives, namely chelating phosphinidenes, are to date unknown,
and could lead to chelating complexes containing more than one
metal centre due to the intrisic capacity of phosphinidenes to bind
two metal fragments at one P-centre. Here we describe the
synthesis of the first such chelating bis-phosphinidene ligand,
XantP2 (2), generated by the reduction of a diphosphino xanthene
derivative, Xant(PH2)2 (1) with iPrNHC (iPrNHC = [:C{N(Pri)C(H)}2]).
Initial studies have shown that this novel chelating ligand can act as
a bidentate ligand towards element dihalides (i.e. FeCl2, ZnI2, GeCl2,
SnBr2), forming cationic complexes with the tetryl elements. In
contrast, XantP2 demonstrates an ability to bind multiple metal
centres in the reaction with CuCl, leading to a cationic Cu3P3 ring
complex, with Cu centres bridged by phosphinidene arms. Density
Functional Theory calculations show that 2 indeed holds 4 lone pairs
of electrons, shedding further light on the coordination capacity for
this novel ligand class through observation of directionality and
hybridisation of these electron pairs.
Figure 1. Combining the concepts of chelating bis-phosphines and
phosphinidenes, coming to the chelating bis-phosphinidenes.
the classical chelating ligand structure, we wished to design a
system which may accommodate multiple metal centres. In this
regard, few examples are known; recent work from Lu et al. has
employed tripodal phosphine-functionalised tris-amido ligands,
allowing for the systematic design of heterobimetallic
complexes.[9] Conversely, we chose to explore a chelating ligand
where the binding centres have more than one binding site, i.e.
more than one free pair of electrons. A key class of readily
accessible compounds satisfying this characteristic are the
NHC-stabilised phosphinidenes,[ 10 ] which can be seen as
inversely polarized phosphalkenes,[11] and formally hold two lone
pairs of electrons at P.[12] Indeed, such species have shown the
ability to bind two metals at one P-centre (Figure 1).[13] A wide
range of carbene-stabilised aryl-phosphinidenes are now known,
which are accessed in good yields from ArPH2 or ArPCl2
precursors utilizing NHCs or s-block metal reductants,
respectively.[14] More recently, a number of PI compounds have
been synthesised through the CO-liberation reaction of the
phosphaethynolate ([PCO]) fragment,[ 15 ] a notable example
being the recent isolation of a phosphino-phospinidene with a
monocoordinated terminal P-atom.[16] Combining the concepts of
classical chelating phosphines with multidentate phosphinidenes,
we envisaged that employing two phosphinidene centres in
close proximity may allow for the bidentate chelation of two
Introduction
The chelate effect describes the binding of a multi-dentate
ligand to a metal centre through more than one ligand ‘arm’.[1]
On entropic grounds, this leads to highly stabilised metal
complexes, a key factor in generating effective and long-lived
catalytically active complexes. Classic examples of neutral
chelating ligands are the diphosphino-ethane derivatives,[2] with
which over 7000 structurally authenticated transition-metal (TM)-
complexes have been reported.[3] Indeed, these ligands are still
broadly employed in catalysis today, as well as in the
stabilisation of highly reactive TM fragments.[2](b),[4] Nowadays, a
huge number of neutral chelating ligands are known utilizing a
number of different donor atoms. In our group, we have focused
on the synthesis and employment of chelating bis-silylene
ligands, which have proved to be powerful assets in TM
catalysed processes,[5] as well as in the stabilisation of reactive
complexes of BI,[6] Ge0,[7] and Si0.[8] However, moving beyond
1
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metal centres by a single ligand. We thus targeted the synthesis
of
a bis-phosphinidene via reduction of a bis-phosphine
precursor, and investigations regarding the coordination
behaviour of this novel ligand scaffold. Herein we discuss the
synthesis of the first isolable example of a chelating bis-
phosphinidene ligand, whereby each phosphinindene centre
formally holds two lone pairs of electrons. The utilisation of this
ligand in the formation of mono-metallic and multi-metallic
coordination systems has also been explored, and is discussed.
Figure 2. Molecular structures of 2A
and 2B, with probability ellipsoids at 30%, and protons removed for clarity.
Selected bond lengths (Å) and angles (°) for 2A: P1-C16 1.830(5); P2-C25
1.826(6); C16-N1 1.354(7); C16-N2 1.393(7); C25-N3 1.329(8); C25-N4
1.385(8); P1…P2 3.965(2); C2-P1-C16 99.65(3); C12-P2-C25 97.50(2). For
2B: P1-C16 1.790(5); P2-C25 1.821(3); C16-N1 1.364(5); C16-N2 1.356(5);
C25-N3 1.359(4); C25-N4 1.359(4); P1…P2 4.452(1); C16…P2 3.619(4); C2-
P1-C16 105.72(2); C12-P2-C25 97.60(1).
Results and Discussion
Numerous chelating phosphine systems have been
reported in the literature, which typically utilise a readily
available scaffold upon which to build the chelating ligand, such
as xanthene, ferrocene, and naphthalene.[17] Low-cost and easily
accessible ligands are desirable, giving the potential for broader
usage of these systems in industry and academia. These two
key points guided our initial design of a bis-phosphinidene ligand.
Scheme 1. The synthesis of bis-phosphinidene ligand 2. (i) nBuLi,
1:0.2/hexane:Et2O, 45 °C; (ii) (EtO)2PCl, -78 °C – RT; (iii) LiAlH4, Me3SiCl, -
78 °C – RT; (iv) NHC, toluene, 100 °C.
Figure 3. (a) 31P NMR spectrum of bis-phosphine 1, and (b) bis-
phosphinidene 2 in D8-THF.
As the backbone scaffold for our ligand we chose to develop a
xanthene-derived system, given the prominence of ‘XantPhos’ in
1H NMR spectrum, presenting as a doublet of multiplets (δ =
4.04 ppm, 1JPH = 202 Hz; Figure S2 in ESI), through coupling to
P as well as xanthene-Ar protons. Concordantly, the 31P NMR
spectrum presents a triplet of multiplets, due to Ar-CH couplings;
this signal collapses to a singlet in the 31P{1H} NMR spectrum (δ
= -140.6 ppm; Figure S3 in ESI).
As mentioned, Radius et al. have reported that the addition
of iPrNHC to PhPH2 followed by heating to just below reflux in D8-
toluene leads to the clean formation of iPrNHC→PPh.[14] We thus
hypothesised that a similar approach may be utilised in
generating bis-phosphinidene 2 from 1. Addition of an excess of
iPrNHC to an NMR sample of 1 in C6D6 leads initially to the
formation of a yellow precipitate, which dissolves upon heating
the reaction mixture to 65 °C. Continued heating for 2 days
leads to the formation of a bright orange solution containing a
single new P-containing species (δ = -77.2 ppm; Figure S7 in
ESI), shifted up-field relative to that for iPrNHC→PPh (δ = -59.9
ppm), but in keeping with the general resonances expected for
carbene-stabilised phosphinidenes.[10](b) Upon cooling of this
sample, bright orange crystals of compound 2 readily formed,
giving considerably more expedient access to X-ray diffraction
18
chemical catalysis.[ ] We also envisaged that the resulting P…P
distance would be great enough to disfavour attractive
interactions between the PI centres. Our synthetic route to the
xanthene-derived chelating bis-phosphinidene ligand, 2,
involved the formal reduction of Xant-(PH2)2 (1) with iPrNHC
(iPrNHC = [:C{N(Pri)C(H)}2]) in the formation iPrNHC·H2, which is
in close relation to the reduction of PhPH2 by the same N-
heterocyclic carbene (NHC), yielding iPrNHC→PPh, reported by
Radius et al..[14] The initial synthesis of 1 is relatively straight
forward, following modifications to the procedure reported by
19
Osborn et al. some years ago,[ ] following double-deprotonation
of 9,9-dimethylxanthene with two molar equivs. nBuLi in a
20
]
hexane:diethyl ether mixture.[
In our hands, bis-phosphine
derivative 1 could be isolated as a colourless oil through
extraction of the crude reaction mixture with Et2O following
aqueous work up, in 78% yields, and was of adequate purity for
subsequent chemistry. Spectroscopic data is lacking in the
original publication of this compound, and so is briefly discussed
here. The -PH2 fragments of this species are clearly visible in its
2
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Figure 4. Calculated relative energies for isomers of 2.
analysis of which confirmed the connectivity in this species
(polymorph 2A, vide infra). A preparative-scale reaction for the
formation of 2 conducted in toluene at 100 °C this compound,
with the reaction being complete after 12 h as ascertained
through NMR spectroscopic analysis. After completion of the
reaction, removing all volatiles from the crude mixture and
washing with copious amounts of diethyl ether and hexane
yielded essentially pure 2 in moderate yields.
Compound 2 is insoluble in hexane, only sparingly soluble
in diethyl ether, and rapidly reacts with CDCl3. Upon heating 2
becomes quite soluble in THF, and is readily soluble in
acetonitrile at ambient temperatures. Typically, in any solvent, 2
crystallises/precipitates upon modest cooling. We tentatively
assign this characteristic to the lattice structure of polymorph 2A
(Figure 2, left), where compound 2 appears to form 1D H-
bonded chains through the interaction of the NHC backbone-CH
moieties of one molecule of 2 with the phosphinidene centres of
another. As is perhaps expected, due to the high electron
density at the two P centres and their two-coordiante nature, no
P···P interaction is apparent in 2A (d(P···P) = 3.965(2) Å), with
both [CPC] arms sitting essentially coplanar with the xanthene
backbone. Notably, recrystallising 2 from dilute THF solutions
leads to a second polymorph, 2B (Figure 2, right), in which no
strong intermolecular interactions are observed, leading to a
monomeric structure. Here the P…P distance is slightly larger
than that in 2A (d(P···P) = 4.452(1) Å), and one interactions
between one P-centre and the NHC C-centre of the [CNHC-P-
CXant] arm is rotated by 136° relative to those in 2A. It is likely
that this conformer is favoured due to intramolecular second
[CNHC-P-CXant] arm, given the inversed polarization of such
NHC→P moieties leading a positively polarized carbon atom.[11]
Although the P…CNHC distance here (d(P···CNHC) = 3.619(4) Å) is
slightly larger than the sum of the van der Waals radii for these
two elements (3.5 Å), the overall geometrical parameters
perhaps hint towards such an electrostatic interaction.
Figure 5. Selected orbitals of 2B.
With bis-phosphinidene 2 in hand, we wished to explore its
use as a ligand towards TM fragments, and further towards to
the formation of multi-metallic systems. The addition of a THF
suspension of ZnI2 to a suspension of 2 in THF rapidly led to
complete loss of the bright orange colour of 2, and the formation
of a slightly pale-yellow solution (Scheme 2). A 1H NMR spectral
analysis of the crude reaction mixture indicated the formation of
Scheme 2. Synthesis of 1:1 TM complexes,
phosphinidene 2.
3 and 4, utilising bis-
To gain insight into the above phenomena, the molecular
structure of 2 was optimised using Density Functional Theory
(DFT), at the B3PW91 level of theory (details in the ESI). The
optimised structure of one molecule of 2 converges to the
isolated polymorph 2B. Furthermore, we were able to identify
two additional isomers of 2, having the Cs and C2 symmetries.
However, both Cs and C2 isomers are higher in energy than 2B,
both in gas phase and in solution, by between 3.7 and 4.9
kcalmol-1 (Figure 4). Selected orbitals of 2B are presented in
Figure 4, representing the lone electron pairs available for
binding in 2. The HOMO and HOMO-1 correspond to π-type
lone pairs at the phosphorous centres, whilst the HOMO-3 and
HOMO-4 correspond to σ-type lone pairs (Figure 5). The
corresponding NBOs are presented in Figure S25 (see the ESI).
Figure 6. Molecular structures of 3
(left) and 4 (right) with 30% probability ellipsoids, and H atoms removed for
clarity. Selected bond lengths (Å) and angles (°) for 3: P1-Zn1 2.433(4); P1-C1
1.827(4); C1-N1 1.362(5); C1-N2 1.366(6); P1-Zn1-P1’ 101.23(1); C1-P1-Zn1
111.19(5); Zn1-P1-C10 103.76(4). For 4: P1-Fe1 2.471(2); P2-Fe1 2.490(1);
P1-C1 1.828(5); P2-C10 1.832(5); P1-Fe1-P2 103.10(5); C1-P1-Fe1
109.87(2); C10-P2-Fe1 114.32(2); Fe1-P1-C20 105.46(2); Fe1-P2-C30
103.11(2).
3
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a single new product. Crystals isolated from a concentrated THF
extract of the reaction mixture were confirmed to be the 1:1
coordination product, 3, through an X-ray diffraction analysis
(Figure 6). Compound 3 contains a tetrahedral coordinated ZnII
centre, bound by two iodide ligands, and the two P centres of
the bis-phosphinidene ligand. The xanthene backbone in 3 is
planar, however, both P centres hold a trigonal-pyramidal
geometry indicative of stereoactive lone pairs of electrons. Both
Zn-P-CXant angles are equal due to a symmetry plane through
the centre of its molecular structure (103.76(4)°), and are
surprisingly acute, with both carbene donors sitting out-of-plane
relative to the xanthene backbone. This is further borne out by
the CXant-P···P-CNHC torsion angles, which deviate considerably
from linearity (44.13(8)°). This effectively forms an open binding
pocket on the open face of the bis-phosphinidene ligand.
Despite this apparent ‘open pocket’, addition of a further
equivalent of ZnI2 to 3 does not lead to formation of the desired
bis-adduct. In fact, addition of a second metal dihalide, namely
FeCl2, to THF solutions of 3 does not lead to a heterobimetallic
complex, but rather to ZnI2 displacement, and formation of
yellow solutions of XantPP∙FeCl2 (4, Scheme 2). This species is
orbitals depicted in Figure 7. The HOMO and the HOMO-1
correspond to the dative interactions between the two
phosphorus centres and Zn, with the HOMO-10 and HOMO-11
corresponding to the remaining pairs of electrons at the two
phosphorous centres, presenting as σ-type lone pairs. The NBO
diagram of the participating orbitals is presented in Figure S26
(ESI). These latter σ-type lone pairs lie perpendicular to the
xanthene plane, and thus parallel to eachother, therefore not
allowing for the chelation of a second metal. It is likely, however,
that either utilising a more flexible backbone, or a backbone
leading to reduced P…P distance, could circumvent this
situation.
also quantitatively formed upon addition of FeCl2, as
a
suspension in THF, to bis-phosphinidene 2. The 1H NMR
spectrum of 4 dissolved in D8-THF is extremely broadened due
to paramagnetism, whilst the 31P NMR spectrum is silent.
Compound 4 crystallises from concentrated THF or acetonitrile
solutions as yellow crystals, with a molecular structure similar to
that for 3 (Figure 6).§ That is, CXant-P-Fe angles are near-right-
angles (105.46(2) and 103.11(2)), and considerable torsion of
the NHC units away from the xanthene plane can be observed
(39.1(4)° and 54.6(4)°). Addition of further FeCl2 does not lead to
the complexation of a second equivalent of this metal halide.
A DFT analysis of 3 hints as to why the desired bis-
metallated species are geometrically inaccessible, with selected
Figure 8. Molecular structure of the cationic part of 5 with 30% probability
ellipsoids, and H atoms removed for clarity. Metrical parameters are excluded
due to low crystal quality.
Similar to the ZnI2 displacement observed upon addition of
FeCl2 to 3, we also observed that the addition of CuCl to either 3
or 4 in acetonitrile leads to Zn/Fe displacement, respectively,
and formation of the cluster [(XantP2)Cu3Cl2]+Cl- (5). Interestingly,
we found that the 1:1 addition of CuCl to XantP2 led to the same
cluster complex, as did the 2:1 addition, indicating
a
considerable relative stability of 5 over the 1:1 and 2:1
1
XantP2:CuCl complexes. The H NMR spectrum of 5 at ambient
temperature is highly complex, featuring a number of essentially
indistinguishable broad peaks, indicative of the unsymmetrical
nature of this species. In keeping with this, the 31P NMR
spectrum of 5 at ambient temperature also shows a number of
broad signals. Satisfyingly, however, heating this sample to
60 °C shows a clean coalescence of signals in the 1H NMR
spectrum, leading to assignable signals (Figure S14 in ESI).
Similarly, the 31P NMR spectrum also coalescence to a single
peak at this temperature (δ = -95.5 ppm; Figure S14 in ESI),
suggesting to some degree rapid ligand exchange processes
upon heating samples of 5 in solution. Cooling the sample
returns the highly complicated spectra observed prior to heating.
This 31P NMR signal for 5 is considerably shifter to higher field
than previously reported NHC-phosphindene complexes of a
CuCl,[13](d),[21] perhaps indicating a greater donor strength for the
phosphindene centres in 2 relative to previously reported
examples. Isolated crystals of compound
5
contained
Figure 7. Selected orbitals of 3.
considerable amounts of highly disordered solvent in the crystal
lattice, which led to the acquisition of data of below publishable
quality. This precludes a discussion of specific structural
4
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parameters in the molecular structure of 5, but does confirm its
connectivity (Figure 8).
complex 6·Cl (Figure 9). This contrasts with reported chelating
bis-phosphine complexes of GeCl2, which typically form neutral,
four-coordinate species,[ 25 ] indicating the strong coordination
ability of 2. Notably, the Cl- counterion in 6·Cl is readily
exchanged upon reaction of this complex with NaBPh4 in
acetonitrile, leading to 6·BPh4. In conjunction with this, the
consecutive addition of SnBr2 and NaBPh4 to a solution of 2 in
acetonitrile led to the analogous complex of BrSn+, namely
7·BPh4 (Figure 8). To the best of our knowledge, these
complexes represent the first examples of phosphinidene-
coordinated tetrylene species. Both BPh4 species could be
crystallised from acetonitrile, although due to considerable
disorder in the BPh4 anion, the crystallographic data for 7∙BPh4
are insufficient for discussion. Nevertheless, the collected data
confirm the connectivity in this species (Figure S1 in ESI). In the
solid state, the cationic part of 6 and 7 are essentially
isostructural, and all feature the central E-X fragment disordered
over two positions, with this bond sitting parallel above the
xanthene plane, or rotated by 180° in the plane of the xanthene
backbone. This backbone is considerably puckered in all three
species when compared with the described TM complexes 3
and 4, seemingly due to the near-acute P-E-P angles in the
tetrylene complexes (6·Cl: 98.13(3)°; 6·BPh4: 94.72(1)°),
Unlike compounds 3 and 4, the molecular structure of
compound 5 demonstrates the capacity of the bis-phosphinidene
ligand 2 to act as a tetra-dentate chelating ligand. Of the four P-
centres in 5, three are found bridging two Cu-centres, forming a
six-membered ring structure, which, given the above described
NMR spectra, is likely labile. All Cu centres are three-coordinate,
two being bound by two P centres and a chloride, and the third
by three P centres, resulting in the formation of a cationic Cu
centre and a free chloride counter ion. This structural motif is in
contrast to previously reported mono or bis-CuCl adducts of
NHC-phosphinidenes, which are monomeric, or show bridging
CuCl…CuCl interactions, in the solid state.[21] However, the
molecular structure of 5 is reminiscent of reported trimeric
Ph2PCu complexes, (i.e. [L→CuPPh2]3; L = DippNHC or 1,10-
phenanthroline; tBuNHC = [:C{N(tBu)C(H)}2]),[ 22 ] and perhaps
even more so to the CuCl complex of an inversely polarised
phosphalkene reported by Weber et al.,[23] all of which hold a six-
membered Cu3P3 core with alternating Cu and P atoms.
Following from the synthesis of TM systems utilising bis-
phosphinidene 2, we sought related chemistry involving low-
valent group 14 fragments (Figure 9). To this end,
GeCl2·dioxane was reacted with 2. Addition of THF to a rapidly
stirred mixture of this dihalide and 2 led initially to dissolution of
the solids, followed by precipitation of a pale yellow powder after
a few minutes. This was presumed to be due to the formation of
the salt separated ion pair, i.e. [2·GeCl]+Cl-, based on similar
results reported previously for the combination of strongly
donating bidentate ligands with group 14 element dihalides.[24]
Layering an acetonitrile solution of GeCl2·dioxane with a solution
of 2 in the same solvent led to the formation of large crystals
after 12 h at ambient temperature. The molecular structure
ascertained from these crystals confirmed our hypothesis
regarding the formation of separated ion pairs, leading to Ge
compared with the more open angles in 3 (angleP1-Zn1-P2
=
101.24(2)°) and 4 (angleP1-Fe1-P2 = 103.10(5)°). P-E distances are
in keeping with known dative P→E single bonds. As with
complexes 3 and 4, addition of further EX2 species (E = Ge, Sn;
X = halide) to 6 or 7 did not lead to complexation, again due to
the structure of these complexes ‘opening’ the binding angle of
the opposite face of the phosphinidene ligand to too great a
degree. Taken as a whole, however, these initial results are a
highly promising starting point to explore the further utility of this
novel bis-phosphinidene ligand scaffold.
Conclusion
In conclusion, we report the initial synthesis of the readily
accessible chelating bis-phosphinidene ligand 2, and have
probed its complexation reactivity in conjunction with Cu, Fe, Zn,
Ge, and Sn halides. In the former case, the ability for 2 to bind
multiple metal centres at each P centre has been demonstrated,
whilst complexes with GeII and SnII halides readily form ion
separated pairs. We are currently further exploring the unusual
coordination chemistry of this ligand class towards further metals,
and in the formation of easily accessible hetero-multimetallic
systems.
Experimental Section
Experimental procedures and characterization data for all new
compounds, full details of the computational studies, crystal data, and
details of data collections and refinements are available in the Supporting
Information. General experimental considerations and the synthesis of
compound 2 are outlined below.
Figure 9. Synthesis of cationic adduct complexes 6 and 7, and the molecular
structure of the cationic part of 6∙BPh4 with 30% probability ellipsoids, and H
atoms removed for clarity. Selected bond lengths (Å) and angles (°): P1-Ge1
2.507(3); P2-Ge1 2.488(4); C1-P1 1.842(8); P2-C10 1.831(6); P1-Ge1-P2
94.70(1); C1-P1-Ge1 98.49(2); C10-P2-Ge1 101.06(2); C20-P1-Ge1
101.18(2); C30-P2-Ge1 97.80(2).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.2012xxxxx
General considerations. All experiments and manipulations were
carried out under dry oxygen free dinitrogen using standard Schlenk
5
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Chemistry - A European Journal
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techniques or in an MBraun inert atmosphere glovebox containing an
atmosphere of high purity dinitrogen. Hexane, toluene, diethyl ether, THF,
and acetonitrile were dried by standard methods. C6D6, CD3CN, and D8-
THF were stirred over a sonicated potassium mirror for a period of 48 h
and recondensed into a Schlenk tube containing activated 4 Å mol sieves.
[7]
[8]
[9]
Y. Wang, M. Karni, S. Yao, Y. Apeloig, and M. Driess, J. Am. Chem.
Soc., 2019, 141, 1655 − 1664.
Y. Wang, M. Karni, S. Yao, A. Kaushansky, Y. Apeloig, and M. Driess,
J. Am. Chem. Soc., 2019, 141, 12916 − 12927.
NMR spectra were recorded on
a Bruker AV 200, 400, or 500
(a) P. A. Rudd, S. Liu, N. Planas, E. Bill, L. Gagliardi, and C. C. Lu,
Angew. Chem. Int. Ed., 2013, 52, 4449 – 4452; (b) R. C. Cammarota, L.
J. Clouston, and C. C. Lu, Coord. Chem. Rev., 2017, 334, 100 – 111.
1
Spectrometer. The H and 13C{1H} NMR spectra were referenced to the
residual solvent signals as internal standards. 11B NMR spectra were
externally calibrated with BF3·OEt2 (15% in CDCl3); 31P NMR spectra
were externally calibrated with H3PO4 (85% in H2O). The starting material
NHC (NHC = [:C{N(Pri)C(H)}2]) was synthesized according to the known
literature procedure.26 All other reagents were used as received.
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2
in either THF or
a
benzene/THF mixture, giving two different
1
3
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3
Hz, 24H, NHC-iPr-CH3), 1.53 (s, 6H, Xant-(CH3)2), 4.99 (sept, JHH = 6.8
Hz, 4H, NHC-iPr-CH), 6.54 (m, 2H, Xant-Ar-H), 6.84 (m, 4H, Xant-Ar-H),
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Acknowledgements
This work was funded by the DFG (German Research
Foundation) under Germany´s Excellence Strategy – EXC 2008
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This article is protected by copyright. All rights reserved.

10.1002/chem.202004300
Chemistry - A European Journal
FULL PAPER
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This article is protected by copyright. All rights reserved.

10.1002/chem.202004300
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
It’s a P-P-Party! A facile synthetic route to a new form of chelating phosphorous ligand, namely the chelating bis-phosphinidene
XantP2, has been developed, allowing for the gram-scale synthesis of this novel ligand scaffold. Computational investigations
corroborate that each P-centre holds two lone pairs of electrons, allowing for the binding of multiple metal centres. Initial efforts
towards the coordination chemistry of XantP2 are reported.
Institute and/or researcher Twitter usernames: @DrHadlington, TU Munich
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This article is protected by copyright. All rights reserved.