Synthesis and Reactivity of Nickel-Stabilised μ2:η2,η2-P2, As2 and PAs Units

Article abstract of DOI:10.1002/anie.201710582

The reactivity of two paramagnetic nickel(I) compounds, CpNi(NHC) (where Cp=cyclopentadienyl; NHC=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) or 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)), towards [Na(dioxane)_x][PnCO] (Pn=P, As) is described. These reactions afford symmetric bimetallic compounds (μ²:η²,η²-Pn₂){Ni(NHC)(CO)}₂. Several novel intermediates en route to such species are identified and characterised, including a compound containing the PCO^? anion in an unprecedented μ²:η²,η²-binding mode. Ultimately, on treatment of the (μ²:η²,η²-Pn₂){Ni(IMes)(CO)}₂ compounds with carbon monoxide, the Pn₂ units can be released, affording P₄ in the case of the phosphorus-containing species, and elemental arsenic in the case of (μ²:η²,η²-As₂){Ni(IMes)(CO)}₂.

Full text of DOI:10.1002/anie.201710582

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Accepted Article
Title: Synthesis and reactivity of nickel-stabilised µ2:η2,η2-P2, As2 and
PAs units.
Authors: Gabriele Hierlmeier, Alexander Hinz, Robert Wolf, and Jose
Manuel Goicoechea
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201710582
Angew. Chem. 10.1002/ange.201710582
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10.1002/anie.201710582
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Synthesis and reactivity of nickel-stabilised µ2:η2,η2-P2, As2 and
PAs units.
Gabriele Hierlmeier,[a] Alexander Hinz,[b] Robert Wolf,*[a] Jose M. Goicoechea*[b]
Abstract: The reactivity of two paramagnetic nickel(I) compounds,
element in question via the phosphorus atom (E–P=C=O).[13]
These species thermally and/or photolytically decarbonylate to
afford putative phosphinidene intermediates,[14] however such
species typically dimerise to compounds which largely fall into
one of two main categories: 1) diphosphacyclobutadiene
CpNi(NHC) (where Cp = cyclopentadienyl; NHC = 1,3-bis(2,4,6-
trimethylphenyl)-imidazol-2-ylidene
diisopropylphenyl)-imidazol-2-ylidene
(IMes)
or
(IPr)),
1,3-bis(2,6-
towards
[Na(dioxane)x][PnCO] (Pn = P, As) is described. These reactions
afford symmetric bimetallic compounds (µ2:η2,η2-Pn2){Ni(NHC)(CO)}2. analogues (A in Figure 1), or 2) diphosphene-bridged
Several novel intermediates en route to such species are identified
and characterised, including a compound containing the PCO– anion
in an unprecedented µ2:η2,η2-binding mode. Ultimately, on treatment
of the (µ2:η2,η2-Pn2){Ni(NHC)(CO)}2 compounds with carbon
monoxide the Pn2 units can be released, affording P4 in the case of
the phosphorus-containing species, and elemental arsenic in the
case of (µ2:η2,η2-As2){Ni(IMes)(CO)}2.
compounds (B, C and D in Figure 1). Diarsacyclobutadiene type
compounds analogous to A have also recently been reported
using AsCO– as a reagent.[15]
Over the last three years, the 2-phosphaethynolate anion, PCO–,
has emerged as a versatile reagent for the synthesis of a variety
of novel phosphorus compounds. This remarkable species was
first
isolated
as
[Li(DME)2][PCO]
(where
DME
=
dimethoxyethane), however due to difficulties associated with
the manipulation of this particular salt, the synthetic utility of
PCO– lay dormant for two decades.[1] In 2011 and 2012, novel
syntheses of sodium salts of the anion were published,[2,3]
followed by a further report on the synthesis of a [K(18-crown-
6)]+ salt a year later.[4] However it was not until 2014, that a
reliable and scalable synthesis of the anion was reported.[5] In
the ensuing years, the 2-phosphaethynolate anion has been
employed for the synthesis of novel phosphines and
organophosphorus compounds,[6,7] as a pseudo-halide in the
coordination sphere of main group, transition metal and actinide
compounds,[8–10] and in a number of processes where the anion
is shown to decarbonylate, acting as a formal source of a
monoanionic phosphide ion (P–).[11] The recently synthesised
arsenic-containing analogue, AsCO–, has also been shown to
readily lose carbon monoxide.[12] Arguably this latter reactivity
mode is the most interesting of those available to PnCO– (Pn =
P, As) and one that will form the focus of this report.
Figure 1. Selected examples of dimeric compounds resulting from the
decarbonylation of phosphaketenyl precursors. Ar = 2,6-diisopropylphenyl; R =
H, Me, tBu; Ar' = 2,6-dimethylphenyl; Ad = 1-admantyl; Tol = p-tolyl; Ph =
phenyl. P–P interatomic distances: A: 3.606
Å (mean value for two
crystallographically independent molecules); B: 2.021(1) Å; C: 2.045(1) Å; D:
2.1113(2) Å.
The further reactivity of the E2Pn2 cores of the resulting
molecules remains largely unexplored despite the fact that,
particularly in the diphosphene bridged compounds, they may be
of relevance for the synthesis of novel pnictogen-containing
molecules. Also, given that such species are formed through
dimerisations, it is also possible to envision the synthesis of
compounds with a phosphaarsene (PAs) core through the
dimerization of a phosphinidene with an arsinidene. In this report
we describe our attempts to explore such possibilities. We
investigate the reactivity of two nickel(I) compounds, CpNi(NHC)
Salt-metathesis reactions of [Na(dioxane)x][PCO] (where x =
1–5) with a variety of main group and transition metal halides
afford phosphaketenyl compounds where PCO– bonds to the
(where Cp
trimethylphenyl)-imidazol-2-ylidene (IMes) or 1,3-bis(2,6-
diisopropylphenyl)-imidazol-2-ylidene towards
(IPr)),[16]
[Na(dioxane)x][PnCO] (Pn = P, As) salts, which ultimately give
rise to compounds with butterfly-like cores (µ2:η2,η2-
Pn2){Ni(NHC)(CO)}2. While both of the aforementioned reagents
ultimately yield similar reaction products, we were able to isolate
different intermediates depending on the N-heterocyclic carbene
(NHC) associated with the nickel(I) centre.
=
cyclopentadienyl; NHC
=
1,3-bis(2,4,6-
[a]
[b]
G. Hierlmeier, Prof. Dr. R. Wolf*
Institute of Inorganic Chemistry
University of Regensburg
93040 Regensburg, Germany
E-mail: robert.wolf@ur.de
Dr. A. Hinz, Prof. Dr. J. M. Goicoechea*
Department of Chemistry
University of Oxford
Chemistry Research Laboratory, 12 Mansfield Road, Oxford, OX1
3TA, U.K.
E-mail: jose.goicoechea@chem.ox.ac.uk
Reactions of CpNi(NHC) with one equivalent of
[Na(dioxane)1.8][PCO] in THF afford the compounds (µ2:η2,η2-
Supporting information (including experimental and analytical data)
for this article is given via a link at the end of the document.
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P2){Ni(NHC)(CO)}2 (NHC = IMes (1a) and IPr (1b)), with NaCp
generated as a side product (Scheme 1).
respectively, comparable those recorded for metallo-
phosphaketene type compounds. In the case of CpNi(IMes), this
species is short-lived (approximately 20 minutes), but for
CpNi(IPr) this compound is sufficiently stable to be isolated and
characterised.
Scheme 1. Synthesis of 1a and 1b by reaction of CpNi(NHC) (NHC = IMes,
IPr) with one equivalent of [Na(dioxane)1.8][PCO].
The single crystal X-ray structure of 1a (Figure 2) reveals a
butterfly core that is unlike other E2P2 systems synthesised
through decarbonylation reactions involving PCO–, but closely
related to well established compounds typically accessed by
dehalosilylation of silylphosphanes or the activation of white
phosphorus.[17] Examples include a handful of isoelectronic and
isostructural group 10 compounds.[18] The P–P bond length in 1a
(2.076(2) Å) is close to the value expected for a P=P double
bond (2.04 Å),[19] and similar to the values reported for (µ2:η2,η2-
P2){Ni(depe)}2 (depe = bis(diethylphosphino)ethane; 2.121(6) Å)
and (µ2:η2,η2-P2){Ni(IiPr)2}2 (IiPr = 1,3-bis(isopropyl)-imidazol-2-
ylidene; 2.091(1) Å). The structure of 1b is very similar with that
of 1a (see Supporting Information).
Scheme 2. Synthesis of 2a/2b and 3a by reaction of CpNi(NHC) with 0.5
equivalents of [Na(dioxane)1.8][PCO].
Crystals of 2b·hexane grown from hexane at –30 °C reveal a
symmetrical
bimetallic
dimer
(µ2:η5,η5-Cp)[µ2:η2,η2-
PCO]{Ni(IPr)}2 (2b; Figure 3). The PCO– ion bridges the two
nickel(I) centres in an unprecedented µ2:η2,η2-binding mode. A
related chloride-bridged dimer (µ2:η5,η5-Cp)[µ2-Cl]{Ni(IPr)}2 was
reported by Nova, Hazari and co-workers.[16a] Due to positional
disorder of the 2-phosphaethynolate and cyclopentadienide
anion, the interpretation of bond metric data should be
performed with caution, nonetheless, there is no ambiguity
regarding the coordination mode of the PCO– ion. The
phosphorus and carbon atoms are equidistant from the two
nickel(I) centres. The side on coordination of a PCO– ion is rare,
and has only been reported for a copper complex with a cyclic
alkyl amino carbene.[13a]
Figure 2. Molecular structure of 1a·hexane. Anisotropic displacement
ellipsoids pictured at 50% probability. Hydrogen atoms and solvent of
crystallization omitted for clarity. Atoms of the Mes groups pictured as spheres
of arbitrary radius. Selected bond lengths (Å) and angles (°): Ni1–C1, 1.752(3);
Ni1–C2, 1.922(2); Ni1–P1, 2.241(1); Ni1–P1', 2.250(1); C1–O1, 1.140(4), P1–
P1', 2.076(2), Ni1···Ni1' 2.988(7). C1–Ni1–C2, 107.17(11); C1–Ni1–P1,
98.16(9); C1–Ni1–P1', 152.96(9); C2–Ni1–P1, 152.88(7); C2–Ni1–P1',
98.73(7); P1–Ni1–P1', 55.07(3). Symmetry operation ': –x, 1–y, z.
Figure 3. Molecular structure of 2b·hexane (minor positionally disordered
component omitted for clarity). Anisotropic displacement ellipsoids pictured at
50% probability. Hydrogen atoms and solvent of crystallization omitted for
clarity. Atoms of the Dipp groups pictured as spheres of arbitrary radius.
Selected bond lengths (Å) and angles (°): P1–C1, 1.80(2); C1–O1, 1.15(2);
Ni1–P1, 2.187(5); Ni1–C1, 2.087(18); Ni2–P1, 2.186(4); Ni2–C1, 2.095(17);
Ni1–C2, 1.9262(17), Ni1–Cpcent, 2.411(10); Ni1–Ni2, 2.3719(4); Ni2–C29,
1.9260(17) Ni2–Cpcent, 2.454(10); P1–C1–O1, 158.5(10); C2–Ni1–P1,
114.71(13); C2–Ni1–C1, 115.1(5); C2–Ni1–Ni2, 169.91(5); C29–Ni2–P1,
114.14(14); C29–Ni2–C1, 116.3(5); C29–Ni2–Ni1 170.26(5); Ni1–P1–Ni2,
65.70(13); Ni1–C1–Ni2, 69.1(5).
Singlet resonances are observed in the 31P NMR spectrum
at 120.0 and 130.3 ppm (in C6D6) for 1a and 1b, respectively.
The 1H, and 13C{1H} NMR data are consistent with the molecular
structures obtained by X-ray crystallography (see the Supporting
Information). Infrared spectra reveal bands at 1952 and 1967
cm–1, for 1a and 1b, respectively, arising from terminal CO
ligands.
With the aim of identifying reaction intermediates, we
reacted the CpNi(NHC) complexes (NHC = IMes and IPr) with
0.5 equivalents of [Na(dioxane)1.8][PCO]. 31P NMR spectra
reveal resonances at –293.1 (2a) and –288.9 ppm (2b),
The reaction of 0.5 equivalents of [Na(dioxane)1.8][PCO] with
CpNi(IMes) ultimately affords the carbene-phosphinidenyl-
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bridged dimer, (µ2-CO)[µ2-P(IMes)]Ni2(IMes)Cp (3a). The clean
formation of 3a is evidenced by a singlet resonance at –16.5
ppm in the 31P NMR spectrum, and the observation of two
magnetically inequivalent IMes substituents in the 1H NMR
spectrum.
longer than the P–P bond in 1a, in line with the increased
covalent radius of arsenic (rAs – rP = 0.12 Å).[19a] Related
compounds with a (µ2:η2,η2-As2)E2 core are relatively well
known,[21] however there is only one isoelectronic group 10
metal complex, (µ2:η2,η2-As2){Pt(PPh3)2}2 [As–As 2.274 (±0.001)
Å].[22] Compound 4b could be isolated using a similar procedure,
although extensive crystal twinning precluded a satisfactory
structure determination.
Single crystals of 3a·0.5toluene obtained from toluene reveal
a dimeric compound with a Ni–Ni bond length of 2.399(1) Å
consistent with a single bond (Figure 4).[19] One of the nickel
atoms retains a cyclopentadienyl ligand (and has a formal
valence electron count of 18), while the second is coordinated
by an IMes ligand (and has a valence electron count of 16). Both
centres are bridged in a µ2-fashion by a carbonyl (originating
from the PCO– reagent) and a formally anionic phosphinidenyl
ligand, [P(IMes)]–. Metal compounds with [P(NHC)]– type ligands
are rare and have only recently become synthetically
available.[20] The [P(IMes)]– ligand is largely equidistant from
both of the nickel centres (2.269(1) and 2.186(1) Å), with the
shortest distance being to the least electronically saturated
nickel centre. The same is also true of the Ni–CO distances:
1.909(3) and 1.793(3) Å.
Figure 5. Molecular structure of 4a·hexane. Anisotropic displacement
ellipsoids pictured at 50% probability. Hydrogen atoms and solvent of
crystallization omitted for clarity. Atoms of the Mes groups pictured as spheres
of arbitrary radius. Selected bond lengths (Å) and angles (°): Ni1–C1,
1.760(10); Ni1–C2, 1.934(7); Ni1–As1, 2.3405(13); Ni1–As1', 2.3450(16); C1–
O1, 1.127(12), As1–As1', 2.3006(18), Ni1···Ni1' 3.055(2). C1–Ni1–C2,
107.3(4); C1–Ni1–As1, 95.9(3); C1–Ni1–As1', 154.5(3); C2–Ni1–As1,
154.5(2); C2–Ni1–As1', 97.1(2); As1–Ni1–As1', 58.81(5). Symmetry operation
': 2–x, 1–y, z.
(µ2:η5,η5-Cp)[µ2:η2,η2-PCO]{Ni(IMes)}2 (2a) is likely an
intermediate in the formation of 3a (both compounds are
constitutional isomers). 3a would be formed by decarbonylation
and carbene migration from a nickel(I) centre to the resulting
phosphinidyne. We believe that the short-lived intermediate
observed at –293.1 ppm in the 31P NMR spectrum of crude
reaction mixtures which ultimately afford 3a is 2a. Compounds
2b and 3a both react further with one equivalent of
[Na(dioxane)1.8][PCO] to afford 1b and 1a, respectively.
1H NMR spectroscopy suggests that reactions of CpNi(IMes)
with 0.5 equivalents of [Na(dioxane)3.0][AsCO] proceed to the
carbene-arsinidenyl-bridged
dimer,
(µ2-CO)[µ2-
As(IMes)]Ni2(IMes)Cp (5a). Addition of a molar equivalent of
[Na(dioxane)3.0][AsCO] to 5a readily affords 4a. Single-crystal
XRD on 5a·0.5hexane grown from toluene/hexane revealed a
formally anionic arsinidenyl ligand [As(IMes)]– which bridges two
nickel(I) centres. To our knowledge, to date there are no
structurally authenticated NHC-arsinidenyl compounds reported.
In an attempt to access µ2:η2,η2-PAs bridged compounds, we
reacted the phosphaketenyl-bridged compound, 2b, and the
phosphinidenyl-bridged compound, 3a, with one equivalent of
[Na(dioxane)3.0][AsCO].
Equivalent
reactions
with
[Na(dioxane)1.8][PCO] readily give rise to the µ2:η2,η2-P2 bridged
compounds 1a and 1b. Similarly, the arsinidenyl-bridged dimer,
5a, was reacted with [Na(dioxane)1.8][PCO] in an attempt to form
(µ2:η2,η2-PAs){Ni(IMes)(CO)}2. Each of these reactions gave
novel compounds, including the targeted complexes (µ2:η2,η2-
PAs){Ni(IMes)(CO)}2 (6a; 31P NMR: 175.3 ppm) and (µ2:η2,η2-
PAs){Ni(IPr)(CO)}2 (6b; 31P NMR: 187.9 ppm), however these
species cannot be accessed quantitatively as the formation of
the µ2:η2,η2-P2 and µ2:η2,η2-As2 bridged compounds cannot be
avoided. Nonetheless, these preliminary findings, and
subsequent reactivity studies, strongly suggest that the
formation of novel compounds with a µ2:η2,η2-PAs bridge, may
be possible by modifying reaction conditions, and/or in the
coordination sphere of other metals.
Figure 4. Molecular structure of 3a·0.5toluene. Anisotropic displacement
ellipsoids pictured at 50% probability. Hydrogen atoms and solvent of
crystallization omitted for clarity. Atoms of the Mes groups pictured as spheres
of arbitrary radius. Selected bond lengths (Å) and angles (°): Ni1–Ni2,
2.399(1); Ni1–Cpcent, 1.779(4); Ni1–C1, 1.909(3); Ni1–P1, 2.269(1); C1–O1,
1.179(4), P1–C2, 1.797(3), C1–Ni2, 1.793(3), P1–Ni2, 2.186(1), Ni2–C23,
1.891(2). Ni1–C1–Ni2, 80.74(13); Ni1–P1–Ni2, 65.15(2); Ni1–Ni2–C23,
145.02(5); Ni1–P1–C2, 114.76(10); C1–Ni2–C23, 104.67(10); C2–P1–Ni2,
103.83(9); P1–Ni2–C23, 144.80(6).
Reactions of CpNi(NHC) and [Na(dioxane)3.0][AsCO] in a 1:1
ratio yielded (µ2:η2,η2-As2){Ni(NHC)(CO)}2 (NHC = IMes (4a) and
IPr (4b)). Crystals of 4a·hexane obtained from concentrated
hexane solutions are isomorphous with the phosphorus
analogue 1a·hexane. The As–As bond (2.301(2) Å) is 0.225 Å
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While trapping reactions using DMB cleanly afford TMDPDD
and Ni(IMes)(CO)3 as the sole reaction products, treatment of
the products under a dynamic vacuum and redissolution gives
rise to a number of species in the 31P NMR spectrum. We
believe that this is due to the decarbonylation of Ni(IMes)(CO)3
under a dynamic vacuum, which results in complexation of
TMDPDD by nickel(0). When treated with further CO, such
mixtures readily revert back to TMDPDD and Ni(IMes)(CO)3.
Through
decarbonylated mixtures, we have identified several compounds
crystallographically, including TMDPDD-bridged dimeric
compound, (µ2:η1,η1-TMDPDD){Ni(IMes)(CO)2}2 (7) and
fractional
crystallisation
from
the
partially
a
a
trimetallic compound bridged by three TMDPDD ligands and a
4,5-dimethyl-3,6-dihydro-1,2-diphosphinine species (8), a formal
cycloaddition product of P2 with one equivalent of DMB (see
Supporting Information for structures). The uncontrolled nature
of the synthesis of these compounds, coupled with the
concomitant low yields, precluded their full characterisation.
Figure 6. Molecular structure of 5a·0.5hexane. Anisotropic displacement
ellipsoids pictured at 50% probability. Hydrogen atoms and solvent of
crystallization omitted for clarity. Atoms of the Mes groups pictured as spheres
of arbitrary radius. Selected bond lengths (Å) and angles (°): Ni1–Ni2,
2.424(1); Ni1–Cpcent, 1.774(4); Ni1–C1, 1.898(3); Ni1–As1, 2.389(1); C1–O1,
1.188(4), As1–C2, 1.955(3), C1–Ni2, 1.782(4), As1–Ni2, 2.282(1), Ni2–C23,
1.877(3). Ni1–C1–Ni2, 82.33(13); Ni1–As1–Ni2, 62.467(19); Ni1–Ni2–C23,
146.43(10); Ni1–As1–C2, 112.15(8); C1–Ni2–C23, 105.95(14); C2–As1–Ni2,
102.66(8); As1–Ni2–C23, 144.29(9).
31P NMR spectroscopy evidenced the formation of P4 (–
521.3 ppm) and AsP3 (–485.2 ppm) when reaction mixtures
containing 1b and the heteroatomic bridged compound 6b were
treated with CO. AsP3 was first reported by Cummins and co-
workers, and has a characteristic singlet resonance in its 31P
NMR spectrum, which allows for its characterisation.[25] These
carbonylation reactions strongly suggest that (µ2:η2,η2-
PAs){Ni(IPr)(CO)}2 is present in the reaction mixture, and that
AsP3 results from the recombination of P2 and PAs or their
nickel-coordinated synthetic equivalents.
Treatment of solutions of 1a and 4a with carbon monoxide (2
bar) affords Ni(IMes)(CO)3 as corroborated by 1H and 13C{1H}
NMR, and infrared spectroscopy.[23] The 31P NMR spectrum of a
solution of 1a pressurised with CO reveals the formation of P4
after just seven hours (31P NMR = –521.1 ppm in C6D6).
Similarly, trapping reactions employing 2,3-dimethyl-1,3-
butadiene (DMB) yield the desired Diels–Alder cycloaddition
To conclude, we prepared compounds of the type (µ2:η2,η2-
Pn2){Ni(NHC)(CO)}2 (Pn = P, NHC = IMes (1a) or IPr (1b); Pn =
As, NHC = IMes (4a) or IPr (4b)) by salt metathesis of
[Na(dioxane)x][PnCO] (Pn = P, As) with N-heterocyclic carbene
cyclopentadienyl nickel(I) complexes. Several intermediates en
route to these novel compounds were identified and
characterised, including an unusual bimetallic compound in
which the PCO– ion bridges two metal centres in an
unprecedented µ2:η2,η2-binding mode (2b), and the first
structurally authenticated example of an arsinidenyl-bridged
compound (5a). Reactions of the novel butterfly compounds with
CO reveal that these species may be used as Pn2 sources.
Further reactivity studies in this field are currently on-going.
product
3,4,8,9-tetramethyl-1,6-diphosphabicyclo(4.4.0)deca-
3,8-diene (TMDPDD) (observed in the 31P NMR spectrum at –
54.2 ppm, Scheme 3). This strategy has been previously
employed by Cummins to trap transient P2 molecules.[24]
Reactions involving 4a and CO, by contrast, result in the
formation of grey arsenic as determined by EDX spectroscopy
(not As4). Trapping reactions with DMB show evidence for
formation of 3,4,8,9-tetramethyl-1,6-diarsabicyclo(4.4.0)deca-
3,8-diene (see Supporting Information).
1/2 P4
OC
IMes
CO
IMes
Acknowledgements
2 bar CO
IMes
Ni
Ni
:
] +
P
OC
:
P
[
Ni
P
CO
CO
We acknowledge financial support from the EPSRC
(EP/M027732/1) and the Bayer foundation (Otto Bayer
fellowship for G.H.). We also thank the University of Oxford for
access to Chemical Crystallography and Advanced Research
Computing facilities. Dr. Colin Johnston (Department of
Materials, Oxford) collected the EDX spectra and Dr. Michael
Bodensteiner (Regensburg) assisted with some of the single
crystal X-ray structures. Both are gratefully acknowledged.
P
P
P
Scheme 3. Reactivity of 1a towards CO both in the absence and presence of
3-dimethyl-1,3-butadiene.
Keywords: 2-phosphaethynolate • 2-arsaethynolate •
phosphorus • arsenic • nickel(I) compounds
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[2]
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10.1002/anie.201710582
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
Layout 2:
COMMUNICATION
Gabriele Hierlmeier, Alexander Hinz,
Robert Wolf, Jose M. Goicoechea*
Page No. – Page No.
Synthesis and reactivity of nickel-
stabilised µ2:η2,η2-P2, As2 and PAs
units
The reactivity of two paramagnetic nickel(I) compounds, CpNi(NHC) (where Cp =
cyclopentadienyl; NHC = N-heterocyclic carbene), towards [Na(dioxane)x][PnCO]
(Pn = P, As) is described.
This article is protected by copyright. All rights reserved.