The interaction of 2-arsa- and 2-stiba-1,3-dionato lithium complexes with Group 8-12 metal halides

Article abstract of DOI:10.1039/b105010a

The reactivity of a range of 2-arsa- and 2-stiba-dionato lithium complexes, [{(solv)Li{E[C(O)R]₂}}₂], E = As or Sb, R = alkyl or aryl, toward a variety of Group 8-12 transition metal complexes has been examined. The heterodionate ligands in the generated complexes have displayed a variety of coordination modes which in many cases have been confirmed by X-ray crystallographic studies. Modes that were encountered were η¹-As or Sb in [(C₅Me₅)Fe(CO)₂-{As[C(O)Ph]₂}], trans-[PtCl(PEt₃)₂{As[C(O)Ph]₂}] and trans-[PtCl(PEt₃)₂{Sb[C(O)(C₂H₂Me ₃-2,4,6)]₂}]; η²-O, O in [M{As[C(O)Bu^t]₂}₂(DME)] M = Fe or Co and [RuCl₂(PPh₃)₂{As[C(O)Bu^t]₂ }]; η¹- As: η¹-O: η² - CO in [RuCl(PPh₃)₂{As[C(O)Bu^t]₂}] and η¹-As: η²-O, O in [Zn{As[C(O)Bu^t]₂[LiCl(DME)]}₂]. The syntheses of a number of related complexes are reported, as is the preparation and structural characterisation of the tetraacyldiarsane, [As{C(O)Ph}₂]₂.

Full text of DOI:10.1039/b105010a

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The interaction of 2-arsa- and 2-stiba-1,3-dionato lithium
complexes with Group 8–12 metal halides
Cameron Jones,*a Peter C. Junk,b Jonathan W. Steed,c Ryan C. Thomasa and
Thomas C. Williamsa
a Department of Chemistry, University of Wales, Cardiff, P.O. Box 912, Park Place, Cardiff,
UK CF10 3TB
b Department of Chemistry, James Cook University, Townsville, Qld, 4811, Australia
c Department of Chemistry, King’s College London, Strand, London, UK WC2R 2LS
Received 6th June 2001, Accepted 16th August 2001
First published as an Advance Article on the web 15th October 2001
The reactivity of a range of 2-arsa- and 2-stiba-dionato lithium complexes, [{(solv)Li{E[C(O)R]2}}2], E = As or Sb,
R = alkyl or aryl, toward a variety of Group 8–12 transition metal complexes has been examined. The heterodionate
ligands in the generated complexes have displayed a variety of coordination modes which in many cases have been
confirmed by X-ray crystallographic studies. Modes that were encountered were η1-As or Sb in [(C5Me5)Fe(CO)2-
{As[C(O)Ph]2}], trans-[PtCl(PEt3)2{As[C(O)Ph]2}] and trans-[PtCl(PEt3)2{Sb[C(O)(C2H2Me3-2,4,6)]2}]; η2-O,O
in [M{As[C(O)But]2}2(DME)] M = Fe or Co and [RuCl2(PPh3)2{As[C(O)But]2}]; η1-As : η1-O : η2-CO in
[RuCl(PPh3)2{As[C(O)But]2}] and η1-As : η2-O,O in [Zn{As[C(O)But]2[LiCl(DME)]}2]. The syntheses
of a number of related complexes are reported, as is the preparation and structural characterisation
of the tetraacyldiarsane, [As{C(O)Ph}2]2.
Introduction
The extensive development of the field of low coordination
phosphorus chemistry over the last 20 years has led to the
realisation that there is a close analogy between P and the
valence isoelectronic CR fragment.1 In contrast, the poorer
thermal stabilities of corresponding low coordinate arsenic and
antimony compounds have hindered their evolution relative
to their phosphorus counterparts.2 In our laboratories we are
involved in the further development of such compounds,
especially with regard to their use as ligands in organometallic
synthesis. Our efforts in this area have revealed that there can
be remarkable differences in the coordination chemistries of
these materials that revolve around the nature of the Group 15
element involved.
One notable class of compounds we have been examining
are the 2-hetero-1,3-dionato lithium complexes, [{(solv)Li{E-
[C(O)R]2}}2], 1 E = As or Sb, R = alkyl or aryl.3 The hetero-
dionate ligands in these compounds are closely related to β-
diketonates, the complexes of which are among the most widely
studied systems in inorganic chemistry and have found a variety
of applications in areas ranging from organic synthesis to
chemical vapour deposition (CVD) processes.4 We wished to
explore the analogy between β-diketonate–transition metal
complexes and their heterodionate counterparts and saw the
lithium complexes, 1, as ideal transfer reagents for the form-
ation of the latter. Preliminary studies in this area have led to a
number of novel and often unexpected results which include the
preparation of 2–5 from the treatment of 1 with transition
metal halide complexes.5,6 It is noteworthy that several related
diacyl-arsenido and -stibanido complexes, 6, have been reported
though these were synthesised by routes not involving complexes
such as 1.7 0.
It was the aim of this study to systematically explore the
interaction of a variety of Group 8–12 transition metal halide
complexes with heterodionate complexes, the expectation being
that a number of interesting structural and chemical trends
would emerge depending upon the Group 15 element and tran-
sition metal involved. The results of these investigations are
reported herein.
Results and discussion
Group 8
The previously reported diacylarsenido–and diacylstibanido–
Group 8 complexes, 6, were prepared via the trimethylsilyl
DOI: 10.1039/b105010a
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elimination reactions of [(C5R5)M(CO)2E(SiMe3)2] R = H or Me,
M = Fe or Ru, E = As or Sb, with two equivalents of the appro-
priate acyl chloride.7 It seemed logical that similar complexes
could be prepared by salt elimination reactions of lithium
heterodionates with Group 8 halide complexes. Several reac-
tions of this type were carried out and these led to the expected
complexes, 7–9, in moderate to good yields (Scheme 1). The
Scheme 1 Reagents and conditions: i, [CpFe(CO)2I] or [Cp*Fe(CO)2-
(NCMe)][BF4], DME.
Fig. 1 Molecular structure of compound 8. Selected bond lengths (Å)
and angles (Њ): As(1)–C(1) 2.003(4), As(1)–C(2) 2.030(4), As(1)–Fe(1)
2.3974(7), Fe(1)–C(26) 1.746(5), Fe(1)–C(25) 1.764(5), C(1)–O(1)
1.203(5), C(2)–O(2) 1.205(5), C(25)–O(3) 1.140(5), O(4)–C(26)
1.156(5); C(1)–As(1)–C(2) 92.54(17), C(1)–As(1)–Fe(1) 109.84(11),
C(2)–As(1)–Fe(1) 104.00(13), O(1)–C(1)–As(1) 121.2(3), O(2)–C(2)–
As(1) 120.7(3).
spectroscopic data for these compounds are consistent with
their proposed structures and similar to those seen for 6. Most
notably their IR spectra all show metal carbonyl and acyl
carbonyl stretching bands in the expected regions. In addition,
the 13C NMR spectra of the compounds exhibit low field signals
for the carbon centres associated with these groups.
As no terminal diacylarsenido Group 8 complexes have been
structurally characterised an X-ray crystal structure analysis of
8 was carried out (Fig. 1). This showed it to be monomeric with
the diacylarsenide ligand η1-coordinated through a pyramidal
arsenic centre. Unlike in the arsadionate precursor there
appears to be no delocalisation over the ligand as both the As–
C distances are normal for single bonded interactions and both
C–O distances are consistent with double bonds. Although 8
contains the first structurally authenticated terminal η1-
diacylarsenide (cf. η1 : η2- in 2 and µ-η1 : η1- in 35) the closely
related diacyl-phosphide and -stibanide complexes, [Cp*Ru-
(CO)2P{C(O)But}2]8 and 6, E = Sb, M = Ru, R = Ph, RЈ = Me,7a
respectively, have been crystallographically characterised and
are structurally very similar to 8.
In order to investigate the possibility of forming the first
transition metal complex in which an arsadionate ligand
coordinates in an η2-O,O-fashion, FeCl2 was treated with two
equivalents of 10 in DME (Scheme 2). This led to a moderate
yield of the dark red octahedral complex, 11. By contrast, treat-
ing FeCl2 with the lithium stibadionate, 12, afforded only an
intractable mixture of products. Presumably in this reaction the
antimony analogue of 11 is formed but is not stable at room
temperature. In addition, all attempts to form an iron() com-
plex by reaction of FeCl3 with three equivalents of 10 met with
failure as an unidentifiable mixture of products was formed.
Compound 11 is paramagnetic with a µeff of 5.0 µB which
corresponds to the expected 4 unpaired electrons of a high spin
d6 complex. Because of this, NMR studies on the compound
gave no useful information but it was characterised by a number
of other techniques. For example, its mass spectrum displayed a
molecular ion peak and its infrared spectrum showed strong
overlapping absorptions in the region 1500–1550 cmϪ1 which
were assigned to CO stretches of the dionate ligand. In the
UV/visible spectrum of the compound a broad d–d transition
(ε = 19 dm3 molϪ1 cmϪ1) was observed at 758 nm and another
stronger feature (ε = 380 dm3 molϪ1 cmϪ1) was noted at 515 nm.
The origin of the latter peak is not known but it likely gives rise
to the red-orange colour of the compound and is of an intensity
normally seen for unsaturated organic ligand to metal charge
transfers.9 Cyclic voltammetric studies on 11 were not very
informative but did highlight two non-reversible reductions at
0.08 V and 0.42 V vs. SCE using ferrocene as an internal stand-
ard. These most likely correspond to decomposition processes.
The most illuminating data on 11 came from its X-ray crystal
structure analysis (Fig. 2). This proved the complex to be
monomeric with a distorted octahedral geometry about the iron
centre. Unlike in 8 both the arsadionate ligands coordinate the
metal centre in a chelating η2-O,O-fashion and are essentially
planar. In addition, they appear to be largely delocalised as
all the As–C bond lengths are similar (1.908 Å ave.) and
lie between values normally seen for As–C single (1.96 Å)10
and double bonds (e.g. 1.821(3)
Å in [CpFe(CO) As᎐
᎐
2
CBut(OSiMe3)]11). Similarly, all the C–O bond lengths suggest
delocalisation.
In an attempt to form the ruthenium analogue of 11
[RuCl2(PPh3)3] was treated with two equivalents of 10 in DME
(Scheme 2). This led to the unexpected formation of the novel
complex, 13, in which only one of the chloride ligands of the
ruthenium precursor could be substituted with an arsadionate
ligand, even when the reaction was carried out at elevated tem-
peratures. Therefore the reaction was repeated using a 1 : 1
stoichiometry and a high yield (73%) of 13 resulted. Substitu-
tion of the second chloride ligand presumably does not occur
due to steric hindrance about the metal centre in the complex.
Scheme
2
Reagents and conditions: i, MCl2, DME, ϪLiCl; ii,
[RuCl2(PPh3)3], DME, ϪPPh3, ϪLiCl; iii, CO, DME.
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Fig. 2 Molecular structure of compound 11. Selected bond lengths
(Å) and angles (Њ): Fe(1)–O(1) 2.025(3), Fe(1)–O(2) 2.025(3), Fe(1)–
O(4) 2.036(3), Fe(1)–O(3) 2.038(3), Fe(1)–O(5) 2.183(4), Fe(1)–O(6)
2.203(3), As(1)–C(2) 1.906(5), As(1)–C(1) 1.908(5), As(2)–C(11)
1.893(5), As(2)–C(12) 1.923(4), O(1)–C(1) 1.260(6), O(2)–C(2) 1.253(5),
O(3)–C(11) 1.268(5), O(4)–C(12) 1.240(5); O(1)–Fe(1)–O(2) 89.06(13),
O(3)–Fe(1)–O(4) 88.10(12), C(2)–As(1)–C(1) 100.2(2), C(11)–As(2)–
C(12) 101.2(2), O(1)–C(1)–As(1) 127.2(4), O(2)–C(2)–As(1) 127.9(3),
O(3)–C(11)–As(2) 127.7(3).
Fig. 4 Molecular structure of compound 15. Selected bond lengths
(Å) and angles (Њ): Ru(1)–O(2) 2.097(4), Ru(1)–O(1) 2.109(4), Ru(1)–
P(1) 2.3970(18), Ru(1)–Cl(1) 2.400(4), Ru(1)–P(2) 2.4080(19), Ru(1)–
Cl(2) 2.448(4), As(1)–C(2) 1.921(7), As(1)–C(1) 1.937(7), C(1)–O(1)
1.263(8), O(2)–C(2) 1.234(8); O(1)–Ru(1)–O(2) 90.94(17), Cl(1)–Ru(1)–
Cl(2) 94.97(10), C(2)–As(1)–C(1) 101.9(3), O(1)–C(1)–As(1) 128.9(5),
O(2)–C(2)–As(1) 128.2(5), C(1)–O(1)–Ru(1) 131.7(4), C(2)–O(2)–Ru(1)
133.9(4).
for localised double bonds. The ligand is not planar as would be
expected if it was delocalised and the arsenic centre can be
considered as having a heavily distorted pyramidal environment
which includes a long interaction [2.5992(9) Å] to the
ruthenium centre as part of its octahedral coordination (cf. the
mean value for all crystallographically determined As–Ru bond
lengths 2.44 Å12). The length of this bond and the distorted
nature of the geometry about As(1) indicates that the ligand is
strained and because it is largely localised it can be thought of
as a diacylarsenide. In addition, both oxygen centres take up
coordination sites at the ruthenium centre. The first of these,
O(1), presumably coordinates through a lone pair [C(1)–O(1)–
Ru(1) 106.7(3)Њ] whilst the carbonyl group containing the
other, O(2), seems to be η2-coordinated to Ru(1) [C(2)–O(2)–
Ru(1) 84.0(3)Њ, Ru(1)–C(2) 2.143(5) Å, Ru(1)–O(2) 2.203(4) Å].
Although the Ru(1)–C(2) distance is long it does lie within
the normal distance for carbonyl groups η2-coordinated to
ruthenium.12
Considering the weakness of the As–Ru bond in 13 it was
thought that if a 2-electron donor was added to this complex
the As centre might be displaced from the ruthenium centre and
a more symmetrical arsadionate complex could be formed. To
this end CO was passed through a red DME solution of 13
which effected a colour change to yellow and subsequent
precipitation of 14 as a microcrystalline solid (Scheme 2). A
preliminary X-ray structure of 14 suggested its gross molecular
framework but the data were too weak for a refinement of the
structure to be completed. Despite this, all the spectroscopic
evidence points toward the proposed structure. The 31P{1H}
NMR spectrum of 14 exhibits a singlet, there is a strong
absorption at 1950 cmϪ1 corresponding to the CO stretch of the
Fig. 3 Molecular structure of compound 13. Selected bond lengths
(Å) and angles (Њ): Ru(1)–O(1) 2.106(4), Ru(1)–O(2) 2.203(4), Ru(1)–
P(2) 2.2561(16), Ru(1)–P(1) 2.3376(16), Ru(1)–Cl(1) 2.4148(17), Ru(1)–
As(1) 2.5992(9), Ru(1)–C(2) 2.143(5), As(1)–C(1) 1.984(5), As(1)–C(2)
1.988(6), O(1)–C(1) 1.238(7), O(2)–C(2) 1.240(7); O(1)–Ru(1)–O(2)
76.51(15), O(1)–Ru(1)–As(1) 69.31(11), O(2)–Ru(1)–As(1) 72.20(10),
C(1)–As(1)–C(2) 90.2(2), C(1)–As(1)–Ru(1) 71.75(17), C(2)–As(1)–
Ru(1) 61.79(17), C(1)–O(1)–Ru(1) 106.7(3), C(2)–O(2)–Ru(1) 84.0(3),
O(1)–C(1)–As(1) 112.2(4), O(2)–C(2)–As(1) 122.1(4).
The spectroscopic data for the compound are consistent with
its formulation and suggest the molecule is unsymmetrical as
there are two resonances in its 31P{1H} NMR spectrum and an
inspection of its 1H and 13C NMR spectra confirm that the acyl
fragments are chemically inequivalent. In addition, the CO
stretching absorptions are at higher frequency than in delocal-
ised systems, e.g. 11, which implies that the arsadionate ligand is
not fully delocalised.
To confirm this an X-ray crystal structure analysis of 13 was
carried out (Fig. 3). This showed the molecule to be monomeric
with a distorted octahedral geometry about the ruthenium
centre. The two triphenylphosphine groups are cis to each other
and the arsadionate ligand is facially coordinated in an unusual
fashion. Firstly, the ligand does appear to be largely localised as
both As–C distances are in the normal single bond length
region and the C–O distances are close to those typically seen
1
carbon monoxide ligand and the H and 13C NMR spectra
highlight a chemical inequivalence between the two ButCO
fragments of the arsadionate ligand.
It should be noted that in the preparation of 14 several larger
orange crystals were formed in addition to the bulk yellow
microcrystalline material. There was not enough of this
material for a full spectroscopic characterisation so its crystal
structure was obtained (Fig. 4) which showed it to be the closely
related Ru() complex, 15 (Scheme 2). It is not known how
the compound was formed under the reducing conditions
employed in the reaction and its preparation was not repro-
ducible. Despite this its structure is included here for sake of
J. Chem. Soc., Dalton Trans., 2001, 3219–3226
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bond lengths are close to those in 11 and strongly suggest the
planar arsadionate ligands are largely delocalised. This con-
trasts to the situation in the rhodium complexes, 2 and 3, which
possess related localised ligands.
Group 10
In a preliminary study we have shown that the treatment of cis-
[PtCl2(PEt3)2] with 10 or 12 led to the Pt(0) distibene and the
Pt() diarsenide–dione complexes, 4 and 5, respectively, both
via loss of the α-diketone, {ButC(O)}2.6 By contrast, reaction of
12 with [MCl2(PEt3)2], M = Ni or Pd afforded the acyl metal
complexes, trans-[MCl{C(O)But}(PEt3)2] with a concomitant
deposition of an antimony mirror.6 Therefore it was apparent
that the heterodionate ligands in 10 and 12 are unstable toward
E–C, E = As or Sb, bond cleavage upon coordination to Group
10 metal fragments. As a result, the possibility of altering the
alkyl substituents on these ligands to form more stable com-
plexes was examined with mixed results.
Firstly, the reaction of the phenyl substituted lithium–
arsadionate, 17, with NiBr2ؒ2DME did not lead to the expected
arsadionate–nickel complex but instead to decomposition and
deposition of insoluble arsenic containing materials. More
success was had when cis-[PtCl2(PEt3)2] was treated with two
equivalents of either 17 or 18 which surprisingly gave the trans-
complexes, 19 and 20. These were found to be stable to chloride
substitution by the second equivalent of lithium heterodionate
which remained in solution (Scheme 3). These compounds pre-
sumably form via an associative mechanism involving five-
coordinate intermediates, [PtCl2(PEt3)2{η1-E[C(O)R]2}], which
undergo isomerisation upon displacement of one chloride
ligand. It is interesting that both 19 and 20 are stable to E–C
bond cleavage when 4 and 5 are formed by such a process in
very similar reactions. It can not be certain why changing
the heterodionate substituents has such a great effect in these
reactions but it is likely a combination of steric and electronic
factors.
Fig. 5 Molecular structure of compound 16. Selected bond lengths
(Å) and angles (Њ): As(1)–C(2) 1.879(11), As(1)–C(1) 1.906(10), As(2)–
C(12) 1.893(13), As(2)–C(11) 1.918(11), Co(1)–O(1) 2.025(7), Co(1)–
O(2) 2.031(7), Co(1)–O(3) 1.977(7), Co(1)–O(4) 2.015(8), Co(1)–O(5)
2.179(8), Co(1)–O(6) 2.141(8), C(1)–O(1) 1.266(12), C(2)–O(2)
1.265(11), C(11)–O(3) 1.249(12), C(12)–O(4) 1.277(15); C(2)–As(1)–
C(1) 100.8(4), C(12)–As(2)–C(11) 100.7(5), O(3)–Co(1)–O(4) 92.4(3),
O(1)–Co(1)–O(2) 91.0(3), O(1)–C(1)–As(1) 128.6(7), O(2)–C(2)–As(1)
129.6(7), O(3)–C(11)–As(2) 127.8(8), O(4)–C(12)–As(2) 128.9(9).
comparison with 13. It was originally thought that the structure
was of 14 with the Cl and CO ligands positionally disordered.
All attempts to model such a disorder met with failure and
indeed the IR spectrum of a single crystal of 15 showed no CO
stretch in the normal region for a coordinated carbon monoxide
ligand. The ruthenium centre in the compound has a slightly
distorted octahedral environment with trans-phosphine and cis-
chloride ligands. The bond lengths within the planar arsadion-
ate ligand suggest full delocalisation and unlike in 13 there is no
interaction of the As centre with Ru(1).
Group 9
The only known examples of stiba- or arsa-dionate complexes
of Group 9 metals are the novel rhodium complexes, 2 and 3,
recently reported by us.5 We wished to extend this work to the
formation of cobalt complexes, in particular those in which the
ligand bonds in an η2-O,O-mode as such simple complexes
could make suitable CVD precursors. Accordingly, CoCl2 was
treated with two equivalents of 10 in DME to afford a moderate
yield of the red-orange Co() complex, 16, (Scheme 2). As was
the case with the iron complex, 11, all attempts to form the
stibadionate analogue of 16 led to intractable mixtures of
products, presumably due to the thermal instability of that
complex. Compound 16 was revealed to be high spin (µeff 4.2
µB) and so solution NMR studies did not provide any useful
information. However, its APCI mass spectrum exhibited a
molecular ion peak. A peak was observed in its visible spectrum
at a similar position and of a similar intensity (510 nm, ε = 225
dm3 molϪ1 cmϪ1) to that seen for 11. Again, the origin of this
peak is not known but may arise from a LMCT process. A
weaker d–d transition would be expected in the general region
of this peak but is probably masked by the stronger absorption.
The other expected spin allowed d–d transition was not
observed as it most likely exists in the near-IR region as with
most octahedral Co() complexes. Cyclic voltammetric studies
were carried out on 16 under a range of conditions but gave no
useful information.
Scheme 3 Reagents and conditions: i, cis-[PtCl2(PEt3)2], DME, ϪLiCl.
The spectroscopic data for 19 and 20 are compatible with
their proposed structures in that both show single phosphine
resonances in their 31P{1H} NMR spectra. In addition, each
1
resonance possesses platinum satellites with large JPtP coup-
lings (19 3081, 20 3296 Hz), as would be expected for chemically
equivalent phosphines trans to each other in square planar
platinum complexes. The IR spectra of both complexes display
strong absorptions in the normal region for localised carbonyl
1
groups and their H NMR and mass spectra suggest only one
heterodionate ligand is present in each compound.
The molecular structures of 19 and 20 are depicted in Fig. 6
and 7 respectively. Both Pt() compounds are monomeric and
are structurally similar. Each platinum centre has a slightly
distorted square planar coordination environment with trans-
phosphine ligands and an η1-ligated heterodionate ligand trans
to a chloride. The E–C and C–O bond lengths in each non-
planar heterodionate ligand are normal for localised single and
double bonded interactions respectively. In addition, the
antimony and arsenic centres have distorted pyramidal geom-
etries and therefore each has a stereochemically active lone pair.
As a consequence of this, the ligands are best thought of as
diacyl pnictides (cf. 8) rather than heterodionates.
The X-ray crystal structure of 16 (Fig. 5) showed the com-
pound to be monomeric and isomorphous to its iron analogue,
11. As in that case the metal centre has a distorted octahedral
coordination environment which includes two chelating arsadi-
onate ligands and one DME molecule. The As–C and C–O
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Fig. 8 Molecular structure of compound 22. Selected bond lengths
(Å) and angles (Њ): Zn(1)–Cl(1) 2.2939(15), Zn(1)–Cl(2) 2.2957(13),
Zn(1)–As(1) 2.4933(10), Zn(1)–As(2) 2.5198(15), As(1)–C(6) 1.983(4),
As(1)–C(1) 1.988(4), As(2)–C(16) 1.970(4), As(2)–C(11) 1.984(4),
Cl(1)–Li(1) 2.471(7), Cl(2)–Li(2) 2.497(7), C(1)–O(1) 1.220(5), C(6)–
O(2) 1.225(5), C(11)–O(3) 1.213(5), C(16)–O(4) 1.227(5); Cl(1)–Zn(1)–
Cl(2) 105.54(5), Cl(1)–Zn(1)–As(1) 108.78(4), Cl(2)–Zn(1)–As(1)
109.62(4), Cl(1)–Zn(1)–As(2) 110.03(5), Cl(2)–Zn(1)–As(2) 107.98(5),
As(1)–Zn(1)–As(2) 114.51(4), C(6)–As(1)–C(1) 97.57(16), C(6)–As(1)–
Zn(1) 92.61(11), C(1)–As(1)–Zn(1) 91.27(11), C(16)–As(2)–C(11)
98.76(16), C(16)–As(2)–Zn(1) 91.50(12), C(11)–As(2)–Zn(1) 88.56(11),
Zn(1)–Cl(1)–Li(1) 98.45(16), Zn(1)–Cl(2)–Li(2) 100.83(16).
Fig. 6 Molecular structure of compound 19. Selected bond lengths
(Å) and angles (Њ): Cl(1)–Pt(1) 2.3989(13), As(1)–C(1) 2.006(5), As(1)–
C(8) 2.012(5), As(1)–Pt(1) 2.4032(6), Pt(1)–P(1) 2.3212(13), Pt(1)–P(2)
2.3228(13), C(1)–O(1) 1.220(6), C(8)–O(2) 1.210(6); C(1)–As(1)–C(8)
99.9(2), C(1)–As(1)–Pt(1) 110.08(15), C(8)–As(1)–Pt(1) 104.09(15),
Cl(1)–Pt(1)–As(1) 175.36(3), O(1)–C(1)–As(1) 120.0(4), O(2)–C(8)–
As(1) 118.8(4).
Fig. 7 Molecular structure of compound 20. Selected bond lengths
(Å) and angles (Њ): Pt(1)–P(1) 2.3330(14), Pt(1)–P(2) 2.3418(13),
Pt(1)–Cl(1) 2.4101(13), Pt(1)–Sb(1) 2.6042(4), Sb(1)–C(1) 2.257(5),
Sb(1)–C(2) 2.295(5), C(1)–O(1) 1.227(6), C(2)–O(2) 1.210(6); Cl(1)–
Pt(1)–Sb(1) 173.92(3), C(1)–Sb(1)–C(2) 96.46(18), C(1)–Sb(1)–Pt(1)
104.83(13), C(2)–Sb(1)–Pt(1) 109.99(14), O(1)–C(1)–Sb(1) 123.1(4),
O(2)–C(2)–Sb(1) 126.6(4).
Scheme 4 Reagents and conditions: i, CuCl or AgCl, ϪCu(s) or Ag(s);
ii, ZnCl2, DME; iii, [Hg{N(SiMe3)2}2], DME, ϪHN(SiMe3)2, ϪHg(l).
was proposed to yield a chelated arsadionate–zinc complex.
Despite this, stirring solutions of 22 for extended periods at
room temperature led to no further reaction and at elevated
temperatures decomposition occurred. A parallel can be drawn
between 22 and 2, the latter of which was found to be a trapped
intermediate in a salt elimination reaction that yielded 3.
The spectroscopic data for 22 are all consistent with its
proposed structure which was confirmed by an X-ray crystal
structure analysis. Its molecular structure (Fig. 8) can be best
described as containing a tetrahedrally coordinated zinc centre
which is η1-ligated by two largely localised diacylarsenide
ligands, each of which also chelates a LiCl(DME) fragment
through its oxygen lone pairs. These fragments themselves
coordinate the zinc centre through chloride lone pairs. The dis-
tance of these interactions is very close to the mean Zn–Cl bond
length, 2.270 Å.12 Each arsenic centre has a distorted pyramidal
geometry and both Zn–As distances represent the shortest yet
reported.
Groups 11 and 12
There had been no reports of arsa- or stiba-dionate complexes
of Group 11 or 12 metals prior to this study. We set about
to reverse this situation as related β-diketonate complexes,
especially of Group 11, have found application as volatile CVD
precursors.4 Consequently, it was thought that their hetero-
substituted analogues might be of a similar utility if they could
be prepared. Unfortunately, this did not prove to be the case as
the reaction of 10 with either Cu() or Ag() salts always led to
oxidative coupling reactions involving the deposition of the
metal involved and the formation of the known tetraacyldi-
arsane, 2113 (Scheme 4). Similarly, the reaction of cadmium and
mercury() halides with two equivalents of 10 gave intractable
mixtures of products.
This was not the case in the reaction of 10 with ZnCl2 which
unexpectedly afforded the novel complex, 22, in a moderate
yield (Scheme 4). This compound can be considered as an
intermediate in the intended salt elimination reaction which
Considering that reactions of 10 with Group 12 dihalides did
not give the expected arsadionate complexes another strategy
was employed. This involved the reaction of two equivalents of
J. Chem. Soc., Dalton Trans., 2001, 3219–3226
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were recorded on Bruker AMX360, WM250, DPX400 or JEOL
Eclipse 300 spectrometers in C6D6 and were referenced to the
1
residual H resonances of the solvent used (1H NMR) or to
external 85% H3PO4, 0.0 ppm (31P NMR). Mass spectra were
recorded using a VG Fisons Platform II instrument under EI or
APCI conditions. UV/visible spectra were recorded on a
Perkin-Elmer Lambda 20 machine. Magnetic susceptibilities
were determined using the Evans method.14 Electrochemical
studies were carried out on Autolab PGStat 12 instrument
using an 0.1 M dichloromethane solution of NBu4PF6 as a
supporting electrolyte and ferrocene as an internal standard.
Melting points were determined in sealed glass capillaries under
argon, and are uncorrected. Elemental analyses were carried
out at the Warwick Analytical Service. The starting mat-
erials 10,3 12,3 17,15 1815 and 2315 were prepared by literature
procedures. All other reagents were used as received.
Syntheses
Fig. 9 Molecular structure of compound 24. Selected bond lengths
(Å) and angles (Њ): As(1)–C(8) 2.017(3), As(1)–C(1) 2.051(3), As(1)–
As(1)Ј 2.4254(6), C(1)–O(1) 1.198(4), C(8)–O(2) 1.212(3); C(8)–As(1)–
C(1) 93.75(12), C(8)–As(1)–As(1)Ј 90.13(9), C(1)–As(1)–As(1)Ј
91.88(9), O(1)–C(1)–As(1) 119.4(2), O(2)–C(8)–As(1) 118.6(2).
[(C5H5)Fe(CO)2{As[C(Ph)O]2}] 7. A solution of 17 (0.390 g,
1.02 mmol) in DME (40 ml) was added dropwise to a solution
of [CpFe(CO)2I] (0.309 g, 1.02 mmol) in DME (30 ml) at Ϫ78
ЊC. The resulting dark red/brown solution was allowed to warm
to room temperature and stirred for 24 h. Volatiles were
removed in vacuo leaving a dark brown residue which was
extracted with diethyl ether (3 × 30 ml), filtered and the filtrate
placed at Ϫ30 ЊC yielding 7 as red crystals (yield 0.29 g, 63%),
mp 80 ЊC (decomp.); NMR: 1H (400 MHz, C6D6), δ 4.60 (5H, s,
C5H5), 7.32–7.91 (10H, m, ArH); 13C (100.6 MHz, C6D6), δ 85.2
(C5H5), 129.2 (m-Ar), 130.3 (o-Ar), 133.5 (p-Ar), 142.3 (quat.
Ar), 214.3 (FeCO), 225.6 (AsC); IR (Nujol, ν/cmϪ1) FeCO 1997
s, 1962 s, AsCO 1661 m, 1623 s; MS APCI: m/z 462 (Mϩ, 100%).
the 2-arsa-1,3-dione, 23, with Group 12 amide complexes,
[M{N(SiMe3)2}2], M = Zn, Cd or Hg. It was hoped that this
would lead to amine elimination and formation of arsadionate
complexes. However, when M = Zn or Cd a reaction occurred but
only a complex mixture of products resulted. By contrast, the
reaction with [Hg{N(SiMe3)2}2] was cleaner and the tetraacyldi-
arsane, 24, was isolated in moderate yield (Scheme 4). It is likely
that this compound arises from an initially formed intermediate,
[Hg{As[C(O)Ph]2}2], which is unstable at room temperature and
decomposes to give 24 via an oxidative coupling reaction involv-
ing a simultaneous elimination of elemental mercury.
The spectroscopic data for 24 are unexceptional and are
compatible with the structure depicted in Scheme 4. This was
verified by an X-ray crystal structure analysis which shows the
molecule (Fig. 9) to be dimeric with two pyramidal arsenic
centres generated by a crystallographic centre of inversion.
Both the As–As and As–C bond lengths are typical for single
bonds and all the C–O distances are in the double bond range.
The structure is similar to that of the only other crystal-
lographically characterised tetraacyldiarsane, 21.13
[(C5Me5)Fe(CO)2{As[C(Ph)O]2}] 8. A solution of 17 (0.366 g,
0.96 mmol) in DME (40 ml) was added dropwise to a solution
of [Cp*Fe(CO)2(NCMe)][BF4] (0.354 g, 0.96 mmol) in DME
(30 ml) at Ϫ78 ЊC. The resulting dark red/brown solution was
allowed to warm to room temperature and stirred for 24 h.
Volatiles were removed in vacuo leaving a dark brown residue
which was extracted with diethyl ether (3 × 30 ml), filtered and
the filtrate placed at Ϫ30 ЊC yielding 8 as red/orange crystals
(yield 0.23 g, 54%), mp 124 ЊC (decomp.); NMR: 1H (400 MHz,
C6D6), δ 1.56 (15H, s, C5Me5), 6.83–8.48 (10H, m, ArH); 13C
(100.6 MHz, C6D6), δ 11.0 (CH3), 97.1 (C5Me5) 130.1 (m-Ar),
132.2 (o-Ar), 134.1 (p-Ar), 144.2 (quat. Ar), 217.7 (FeCO),
225.9 (AsC); IR (Nujol, ν/cmϪ1) FeCO 1999 s, 1941 s, AsCO
1668 m, 1627 s; MS APCI: m/z 533 (MHϩ, 100%).
Conclusions
In summary, we have described the interaction of a range of
arsa- and stiba-dionatolithium complexes with a variety of
Group 8–12 halide complexes. This work builds upon prelimin-
ary results and highlights the versatile nature of the hetero-
dionate ligand system which has exhibited a diverse array
of coordination modes. Although these ligands can behave
similarly to their β-diketonate counterparts they normally do
not. It can be expected that they will form a similar array of
novel complexes with both early transition and main group
metals. We are currently investigating this area and will report
on it in a forthcoming series of publications. In addition we are
exploring the utility of complexes such as 11 and 16 as potential
CVD precursors to either the metal involved or binary metal–
pnictide materials. The results of this study will be reported in
due course.
[(C5H5)Fe(CO)2{Sb[C(But)O]2}] 9. A solution of 12 (0.433 g,
1.26 mmol) in DME (40 ml) was added dropwise to a solution
of [CpFe(CO)2I] (0.382 g, 1.26 mmol) in DME (30 ml) at Ϫ78
ЊC. The resulting deep red solution was allowed to warm to
room temperature and stirred for 24 h. Volatiles were removed
in vacuo leaving a dark red residue which was extracted with
diethyl ether (3 × 30ml), filtered and the filtrate placed at Ϫ30
ЊC yielding 9 as red needles (yield 0.18 g, 30%), mp 80 ЊC
1
(decomp.); NMR: H (400 MHz, C6D6), δ 1.10 (18H, s, But),
4.28 (5H, s, CpH); 13C (100.6 MHz, C6D6), δ 26.4 (C(CH3)),
33.5 (C(CH3)), 84.1 (C5H5), 214.0 (FeCO), 237.9 (SbC); IR
(Nujol, ν/cmϪ1) FeCO 1998 s, 1957 s, AsCO 1672 m, 1625 s;
MS APCI: m/z 412 (Mϩ Ϫ But, 100%); calc. for C17H23O4FeSb:
C 43.5, H 4.9; found: C 42.0, H 4.8%.
[Fe{As[C(But)O]2}2(DME)] 11. A solution of 10 (0.514 g,
1.73 mmol) in DME (40 ml) was added dropwise to a suspen-
sion of FeCl2 (0.11 g, 0.86 mmol) in DME (10 ml) at Ϫ78 ЊC.
The resulting red solution was allowed to warm to room
temperature and stirred for 24 h. Volatiles were removed
in vacuo leaving a dark red residue which was extracted with
hexane (3 × 30ml), filtered and the filtrate placed at Ϫ30 ЊC
yielding 11 as red blocks (yield 0.20 g, 35%), mp 115 ЊC
Experimental
General remarks
All manipulations were carried out using standard Schlenk and
glove box techniques under an atmosphere of high purity argon
or dinitrogen. The solvents diethyl ether, hexane, toluene and
DME were distilled over either potassium or Na/K alloy then
freeze/thaw degassed prior to use. 1H, 13C and 31P NMR spectra
3224
J. Chem. Soc., Dalton Trans., 2001, 3219–3226

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(decomp.); IR (Nujol, ν/cmϪ1) AsCO 1545 s, 1530 s; MS APCI:
m/z 245 (O2C2But2As, 45%), 169 (O2C2But2, 100%), 85 (COBut,
56%); µeff = 5.0 µB; UV/vis/nm (hexane) 758 (ε 19), 515 (ε 380
dm3 molϪ1 cmϪ1); calc. for C24H46O6As2Fe: C 45.3, H 7.24;
found: C 44.93, H 7.21%.
[Ru{As[C(O)But]2}Cl(PPh3)2] 13. A solution of 10 (0.423 g,
1.42 mmol) in DME (40 ml) was added dropwise to a solution
of [RuCl2(PPh3)3] (1.366 g, 1.42 mmol) in DME (30 ml) at
Ϫ78 ЊC. The resulting brown suspension was allowed to warm
to room temperature and stirred for 24 h after which it had
turned deep red. Volatiles were removed in vacuo leaving a dark
red residue which was washed with hexane (60 ml) and
extracted with diethyl ether (3 × 30 ml), filtered and the filtrate
placed at Ϫ30 ЊC yielding 13 as dark red needles (yield 0.94 g,
73%), mp 138 ЊC (decomp.); NMR: 1H (300 MHz, C6D6), δ 0.60
(9H, s, But), 1.61 (9H, s, But), 6.80–8.21 (30H, m, ArH); 13C
(100.6 MHz, C6D6), δ 23.8 (C(CH3)), 26.7 (C(CH3)), 48.2
(C(CH3)), 49.0 (C(CH3)), 126.1–137.2 (Ph), 250.0, 256.1 (AsC);
31P{1H} (36.3 MHz, C6D6) δ 62.5, 38.2 (br s, PPh3); IR (Nujol,
ν/cmϪ1) AsCO 1637 s, 1585 m; MS APCI: m/z 870 (Mϩ Ϫ Cl,
100%); calc. for C46H48O2P2AsRuCl: C 61.0, H 5.3; found:
C 61.30, H 5.95%.
[Ru{As[C(O)But]2}Cl(CO)(PPh3)2] 14. Compound 13 (0.62 g,
6.85 mmol) was dissolved in DME (30 ml) and dry CO gas
passed through the deep red solution for 30 min. During this
time the solution changed to a yellow colour and a yellow
microcrystalline material deposited from solution. This was
recrystallised from DME (20 ml) to give small yellow crystals
1
of 14 (yield 0.51 g, 79%), mp 175 ЊC (decomp.); NMR: H
(300 MHz, C6D6), δ 0.58 (9H, s, But), 0.92 (9H, s, But), 6.80–
8.19 (30H, m, ArH); 13C (100.6 MHz, C6D6), δ 24.9 (C(CH3)),
27.8 (C(CH3)), 49.0 (C(CH3)), 50.0 (C(CH3)), 126.1–136.4 (Ph),
257.0, 264.2 (AsC), RuCO not observed due to low solubility of
compound; 31P{1H} (36.3 MHz, C6D6) δ 32.0 (PPh3); IR (Nujol,
ν/cmϪ1) RuCO 1951 vs, AsCO 1521 s; MS APCI: m/z 898 (Mϩ
Ϫ Cl, 35%), 636 (Mϩ Ϫ Cl Ϫ PPh3, 100%).
[Co{As[C(But)O]2}2(DME)] 16. A solution of 10 (0.30 g, 1.01
mmol) in DME (20 ml) was added dropwise to a suspension of
CoCl2 (0.06 g, 0.51 mmol) in DME (10 ml) at Ϫ78 ЊC. The
resulting light green solution was allowed to warm to room
temperature and stirred for 24 h after which time it had turned
dark red. Volatiles were removed in vacuo leaving a dark red
residue which was extracted with hexane (3 × 30 ml), filtered
and the filtrate placed at Ϫ30 ЊC yielding 16 as red blocks (yield
0.13 g, 40%) mp 102 ЊC (decomp.); IR (Nujol, ν/cmϪ1) AsCO
1548 s, 1537 m; MS APCI: m/z 640 (MHϩ, 32%), 57 (Butϩ,
100%); µeff = 4.2 µB; UV/vis/nm (hexane) 510 (ε 225 dm3 molϪ1
cmϪ1); calc. for C24H46O6As2Co: C 45.1, H 7.2; found: C 44.18,
H 7.15%.
trans-[PtCl(PEt3)2{As[C(O)Ph]2}] 19. A solution of 17 (0.53
g, 1.42 mmol) in DME (10 ml) was added dropwise to a suspen-
sion of cis-[PtCl2(PEt3)2] (0.36 g, 0.7 mmol) in DME (10 ml) at
Ϫ78 ЊC. The resulting solution was allowed to warm to room
temperature and stirred for 18 h. Volatiles were removed in
vacuo leaving a red oily residue which was washed with hexane
(40 ml) and extracted with toluene (ca. 7 ml), filtered and the
filtrate placed at Ϫ30 ЊC yielding 19 as orange needles (yield
0.19 g, 36%) mp 138 ЊC (decomp.); NMR: 1H (250 MHz, C6D6),
δ 0.98 (dt, 18H, 3JPH 16, 3JHH 7.7, P(CH2CH3)3), 1.99 (dq, 12H,
3
2JPH 21, JHH 7.7 Hz, P(CH2CH3)3), 7.40–8.47 (br m, 10H,
2
3
ArH); 13C (100.6 MHz, C6D6), δ 8.38 (d, JPC 5.8, JPtC 33,
P(CH2CH3)3), 14.91 (d, 1JPC 24.8, 2JPtC 41.2 Hz, P(CH2CH3)3),
133.5, 131.8, 130.9 (ArCH), 172.1 (AsC); 31P{1H} (101.2 MHz,
C6D6) δ 10.8 (s, 1JPtP 3081 Hz, PEt3); IR (Nujol, ν/cmϪ1) AsCO
1650 s, 1606 s; MS APCI: m/z 716 (Mϩ Ϫ Cl, 23%), 105 (PhCO,
100%).
J. Chem. Soc., Dalton Trans., 2001, 3219–3226
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trans-[PtCl(PEt3)2{Sb[C(O)(C6H2Me3-2,4,6)]2}] 20. A solu-
tion of 18 (0.35 g, 0.74 mmol) in DME (10 ml) was added
dropwise to a suspension of cis-[PtCl2(PEt3)2] (0.19 g, 0.37
mmol) in DME (10 ml) at Ϫ78 ЊC. The resulting solution was
allowed to warm to room temperature and stirred for 18 h.
Volatiles were removed in vacuo leaving a red oily residue which
was washed with hexane (40 ml) and extracted with diethyl
ether (ca. 5 ml), filtered and the filtrate placed at Ϫ30 ЊC yield-
ing 20 as red needles (yield 0.08 g, 22%), mp 115 ЊC (decomp.);
measurements were made using an Enraf-Nonius CAD4 dif-
fractometer for all compounds except 20, the data for which
were collected on a Nonius Kappa CCD diffractometer. The
structures were solved by direct methods and refined on F 2 by
full matrix least squares (SHELX-97)16 using all unique data.
All non-hydrogen atoms are anisotropic with H-atoms included
in calculated positions (riding model). A molecule of diethyl
ether is included in the crystal lattice of 13 and a molecule of
toluene is included in the lattice of 19. The data for compound
16 are weak and as a result the structure did not refine as well as
is normally expected. However, the fact that it is isomorphous
with compound 11 leaves no doubt about its gross molecular
framework. Crystal data, details of data collections and refine-
ments are given in Table 1. The molecular structures of the
complexes are depicted in Fig. 1–9.
1
3
3
NMR: H (250 MHz, C6D6), δ 1.00 (dt, 18H, JPH 16, JHH
2
3
7.2, P(CH2CH3)3), 1.96 (dq, 12H, JPH 22, JHH 7.2 Hz,
P(CH2CH3)3), 2.06 (s, 6H, p-ArCH3), 2.50 (s, 12H, o-ArCH3),
6.60 (s, 4H ArH); 13C (100.6 MHz, C6D6), δ 7.24 (br s,
P(CH2CH3)3), 8.23 (br s, P(CH2CH3)3), 18.63, 19.62 (s,
ArCH3), 127.9, 128.2 (ArCH), 131.2, 136.7, 145.8 (quat. ArC),
1
229.7 (SbC); 31P{1H} (101.2 MHz, C6D6) δ 14.5 (s, JPtP 3269
CCDC reference numbers 165257–165265.
See http://www.rsc.org/suppdata/dt/b1/b105010a/ for crystal-
lographic data in CIF or other electronic format.
Hz, PEt3); IR (Nujol, ν/cmϪ1) SbCO 1664 s, 1603 s; MS APCI:
m/z 148 (CH2Me3ϩ, 48%), 118 (PEt3ϩ, 100%).
[Zn{As[C(O)But]2[LiCl(DME)]}2] 22. A solution of 10 (0.34
g, 1.14 mmol) in DME (20 ml) was added dropwise to a suspen-
sion of ZnCl2 (0.08 g, 0.57 mmol) in DME (10 ml) at Ϫ78 ЊC.
The resulting pale yellow solution was allowed to warm to
room temperature and stirred for 24 h. Volatiles were removed
in vacuo leaving a yellow oil which was washed with hexane
(30 ml), extracted with diethyl ether (50 ml), filtered and the
filtrate placed at Ϫ30 ЊC yielding 22 as pale yellow crystals
(yield 0.13 g, 28%), mp 85 ЊC (decomp.); NMR: 1H (400 MHz,
C6D6), δ 1.80 (s, 36H, But), 3.42 (s, 8H, OCH2), 3.65 (s, 12H,
OMe); 13C NMR (101.6 MHz, C6D6), δ 27.6 (C(CH3)3), 51.4
(CMe3), 59.6 (OMe), 71.0 (OCH2), 250.8 (AsC); IR (Nujol,
ν/cmϪ1) SbCO 1644 s, 1608 s; MS APCI: m/z 641 (Mϩ Ϫ 2
DME, 79%), 245 (As{C(O)But}2 100%); calc. for C28H56O8Cl2-
Li2As2Zn: C 40.9, H 6.8, found: C 39.69, H 6.79%.
Acknowledgements
We gratefully acknowledge financial support from EPSRC
(studentships for T. C. W and R. C. T).
References
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[As{C(O)Ph}2]2 24. A solution of 23 (0.42 g, 1.5 mmol) in
DME (20 ml) was added to a solution of [Hg{N(SiMe3)2}2] (0.3
g, 0.75 mmol) in DME (20 ml) at Ϫ50 ЊC. The resulting solution
was allowed to stir for 4 h whilst warming to room temperature
during which time deposition of mercury metal was observed.
Volatiles were removed in vacuo and the green residue was
extracted with hexane, filtered and concentrated to ca. 5 ml.
Slow cooling of this solution to Ϫ30 ЊC afforded 24 as thin
yellow plates (yield 0.12 g, 29%), mp 121 ЊC (decomp.); NMR:
1H (400 MHz, C6D6), δ 7.31–7.45 (br m, 20H, ArH); 13C NMR
(101.6 MHz, C6D6), δ 123.4, 128.9, 131.2 (ArCH), 147.4 (quat.
Ar), 181.0 (AsC); IR (Nujol, ν/cmϪ1) AsCO 1695 s, 1645 s; MS
EI: m/z 179 (AsC(O)Phϩ, 75%), 105 (C(O)Phϩ, 100%).
5 C. Jones, S. J. Black and J. W. Steed, Organometallics, 1998, 17, 5924.
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10 F. A. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen
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12 Value determined from a search of the Cambridge Structural
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Structure determinations
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Crystals of 8, 11, 13, 15, 16, 19, 20 and 22 suitable for X-ray
structure determination were mounted in silicone oil whilst a
crystal of 24 was mounted in epoxy resin. Crystallographic
3226
J. Chem. Soc., Dalton Trans., 2001, 3219–3226