Synthesis and structural characterization of novel rhodium-diacylarsenido complexes

Article abstract of DOI:10.1021/om9807607

The reaction of [Li{η²-OC(Mes′)AsC(Mes′)O} (OEt₂)], Mes′ = C₆H₂Prⁱ ₃-2,4,6, with [{RhCl(COD)}₂], COD = 1,5-C ₈H₁₂, in either a 1:1 or 2:1 stoichiometry yields the novel rhodium-diacylarsenido complexes, [{Rh(COD)}₂-μ-Cl-μ- {As[C(O)Mes′]₂}] and [Rh(COD){η¹- As[C(Mes′)O]₂Li(OEt₂)Cl}], respectively. The X-ray crystal structure of each is described and mechanisms for their formations proposed.

Full text of DOI:10.1021/om9807607

5924
Organometallics 1998, 17, 5924-5926
Syn th esis a n d Str u ctu r a l Ch a r a cter iza tion of Novel
Rh od iu m -Dia cyla r sen id o Com p lexes
Cameron J ones*
Department of Chemistry, University of Wales, Cardiff, P.O. Box 912, Park Place,
Cardiff CF1 3TB, United Kingdom
Steven J . Black
Department of Chemistry, University of Wales, Swansea, Singleton Park,
Swansea SA2 8PP, United Kingdom
J onathan W. Steed
Department of Chemistry, King’s College London,
Strand, London WC2R 2LS, United Kingdom
Received September 9, 1998
Summary: The reaction of [Li{η2-OC(Mes′)AsC(Mes′)O}-
Sch em e 1
(OEt2)], Mes′ ) C6H2Pri -2,4,6, with [{RhCl(COD)}2],
3
COD ) 1,5-C8H12, in either a 1:1 or 2:1 stoichiometry
yields the novel rhodium-diacylarsenido complexes,
[{Rh(COD)}2-µ-Cl-µ-{As[C(O)Mes′]2}] and [Rh(COD){η1-
As[C(Mes′)O]2Li(OEt2)Cl}], respectively. The X-ray crys-
tal structure of each is described and mechanisms for
their formations proposed.
In tr od u ction
â-Diketonates are one of the most versatile and
extensively studied ligand systems in inorganic chem-
istry.1 Their complexes with transition metals exhibit
a wide range of coordination modes but O,O-chelation
is by far the most common. Such complexes have numer-
ous applications in areas ranging from organic synthesis
to chemical vapor deposition processes.1,2 In our labora-
tory we are interested in investigating the analogy
between the heavier group 15 elements and the valence
isoelectronic CR (R ) alkyl, H) fragment. To this end
we have recently reported the first crystallographically
characterized 2-stiba- and 2-arsa-1,3-dionatolithium
complexes, [{[Li{η2-OC(But)EC(But)O}(DME)0.5]2}∞], E
) Sb or As, which are structurally similar to their
â-diketonato counterparts.3 Prior to this report several
main-group4 and transition-metal5 complexes of related
2-phospha-1,3-dionate ligands had been described in
which the ligand can coordinate the metal in either an
η2-O,O- or η1-P-fashion. In addition, several transition-
metal-diacylarsenido complexes have been reported6
though, to the best of our knowledge, none have been
structurally characterized. We have begun to examine
the use of 2-arsa-1,3-dionatolithium species, e.g. 1, as
transfer reagents in the synthesis of a similar range of
compounds which include the first structurally authen-
ticated transition-metal-diacylarsenido complexes re-
ported herein.
(1) Siedle, A. R. In Comprehensive Coordination Chemistry; Wilkin-
son, G., Ed.; Pergamon Press: New York, Vol. 2, 1987.
(2) (a) The Chemistry of Metal CVDl Kodas, T. T., Hampden-Smith,
M. J ., Eds.; VCH: New York, 1994. (b) Spencer, J . T. Prog. Inorg.
Chem. 1994, 145 and references therein.
(3) Durkin, J .; Hibbs, D. E.; Hitchcock, P. B.; Hursthouse, M. B.;
J ones, C.; J ones, J .; Malik, K. M. A.; Nixon, J . F.; Parry, G. J . Chem.
Soc., Dalton Trans. 1996, 3277.
(4) (a) Becker, G.; Becker, W.; Schmidt, M.; Schwartz, W.; Wester-
hausen, M. Z. Anorg. Allg. Chem. 1991, 605, 7. (b) Becker, G.;
Birkhahn, M.; Massa, W.; Uhl, W. Angew. Chem., Int. Ed. Engl. 1980,
19, 741. (c) Becker, G.; Beck, H. P. Z. Anorg. Allg. Chem. 1977, 430,
91.
Resu lts a n d Discu ssion
In an attempt to form the monomeric arsadionato-
rhodium complex, [Rh(COD){OC(Mes′)AsC(Mes′)O}], a
diethyl ether suspension of [{RhCl(COD)}2] was treated
with 2 equiv of 1. Remarkably, this led to an almost
quantitative yield of 2 (Scheme 1) which can be consid-
ered as an intermediate in the intended salt elimination
reaction. Compound 2 is not thermally stable in the solid
(5) (a) Weber, L.; Reizig, K.; Boese, R. Organometallics 1985, 4, 1890.
(b) Becker, G.; Ro¨ssler, M.; Uhl, G. Z. Anorg. Allg. Chem. 1982, 495,
73.
(6) Weber, L.; Meine, G.; Boese, R.; Bungardt, D. Z. Anorg. Allg.
Chem. 1987, 549, 73.
10.1021/om9807607 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 12/01/1998

Notes
Organometallics, Vol. 17, No. 26, 1998 5925
F igu r e 2. Molecular structure of 3. Selected bond lengths
(Å) and angles (deg): Rh(1)-Cl(1) 2.4220(8), Rh(1)-As(1)
2.4321(4), As(1)-C(9) 2.019(3), O(1)-C(9) 1.201(4), Cl(1)-
Rh(1)-As(1) 80.80(3), C(9)-As(1)-C(9)′ 97.9(2), C(9)-As-
(1)-Rh(1) 112.79(8), C(9)′-As(1)-Rh(1) 117.79(8), Rh(1)-
As(1)-Rh(1)′ 98.92(2), Rh(1)-Cl(1)-Rh(1)′ 99.48(4), O(1)-
C(9)-As(1) 119.9(2).
F igu r e 1. Molecular structure of 2 (isopropyl groups
omitted for sake of clarity). Selected bond lengths (Å) and
angles (deg): Rh(1)-As(1) 2.5206(7), As(1)-C(25) 1.991-
(5), As(1)-C(9) 1.991(5), Cl(1)-Li(1) 2.390(9), O(1)-C(25)
1.226(6), O(1)-Li(1) 1.922(10), O(2)-C(9) 1.221(6), O(2)-
Li(1) 1.965(10), O(3)-Li(1) 1.963(10), Cl(1)-Rh(1)-As(1)
93.30(4), C(25)-As(1)-C(9) 98.3(2), C(25)-As(1)-Rh(1)
104.70(14), C(9)-As(1)-Rh(1) 95.21(13), Rh(1)-Cl(1)-Li-
(1) 112.3(2), C(25)-O(1)-Li(1) 121.8(3), C(9)-O(2)-Li(1)
120.3(4), O(2)-C(9)-As(1) 127.1(4), O(1)-Li(1)-O(2) 95.4-
(4), O(1)-Li(1)-Cl(1) 103.0(4), O(2)-Li(1)-Cl(1) 100.1(4).
Ta ble 1. Cr ysta l Da ta for Com p ou n d s 2 a n d 3
2
3
chemical formula
fw
C
44H68O3LiClAsRh
C48H70O2ClAsRh2
995.23
865.20
cryst syst
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
orthorhombic
Pcab
17.3477(6)
19.1711(8)
26.3489(9)
90
monoclinic
C2/c
17.3253(9)
10.7319(4)
24.8474(11)
98.6310(10)
4567.6(4)
4
state and decomposes to intractable products over ca. 7
days at room temperature. By contrast, ethereal solu-
tions of 2 decompose over 12 h at 25 °C to yield lithium
chloride and the dinuclear rhodium complex, 3 (27%),
as the only identifiable products; presumably via some
form of redistribution reaction. A direct synthesis to this
compound was devised whereby [{RhCl(COD)}2] was
treated with only 1 equiv of 1 which afforded 3 in a 76%
yield after recrystallization from diethyl ether. In this
case the reaction was complete in less than 1 h and most
likely occurs via an initial formation of 2 from which
LiCl is rapidly displaced by the RhCl(COD) fragment.
The 1H and 13C NMR spectroscopic data for com-
pounds 2 and 3 support their proposed structures.
Additionally, the FAB mass spectrum of 3 displays a
cluster of peaks corresponding to its molecular ion. In
contrast, no molecular ion was seen in the mass
spectrum of 2, but a cluster with the correct isotopic
distribution pattern for the loss of the coordinated
diethyl ether from this molecule was observed.
The molecular structures of 2 and 3 are depicted in
Figures 1 and 2, respectively (see also Table 1). In both,
the Rh centers have slightly distorted square planar
coordination geometries. Their As-C distances all lie
close to the normal value for single bonds (1.96 Å),7
while their C-O bond lengths are in good agreement
with the typical double-bonded distance (1.19 Å).7
Therefore, in 2 and 3 the hetero-ligand can be viewed
as a localized diacylarsenide rather than a delocalized
arsadionate, as is the case in 1. In accordance with this
description is the distorted pyramidal geometry (Σ
angles ) 298.2°) for As(1) in 2 and a near tetrahedral
8763.0(6)
8
T (K)
100(2)
100(2)
λ (Å)
0.71070
1.312
12.36
0.71070
1.447
15.36
Fcalcd (g cm-1
)
µ (Mo KR) (cm-1
F (000)
)
3632
2056
reflns collected
62 680
17 833
no. unique reflns
cryst size (mm)
θ range (deg)
Ra (all data)
7600
4476
0.2 × 0.1 × 0.1
3.46-25.00
0.1003
0.0685
0.1550
0.5 × 0.5 × 0.5
3.48-26.00
0.0434
0.0367
0.1145
Ra (I > 2σ(I))
b
wR′ (all data)
b
wR′ (I > 2σ(I))
0.1044
0.0952
a
b
R ) ∑(∆F)/∑(Fo). wR′ ) [∑{w(∆F2)2}/∑{w(Fo2)2}]1/2. w )
1/[σ2(Fo2) + (aP)2] where P ) [max(Fo2) + 2(Fc2)]/3 and a ) 0.000
for 2 and 0.033 for 3.
geometry for the arsenic center in 3. This suggests that
the sp3-hybridized As(1) center in 2 has a stereochemi-
cally active lone pair and consequently that the molecule
is best described as a rhodium(I)-diacylarsenido com-
plex, [Rh(COD){η1-As[C(O)But]2}], that forms an adduct
with a solvated lithium chloride molecule via lone pair
donation from both O centers to the tetrahedral Li(1)
center, and a similar donation from Cl(1) to Rh(1). All
of the bond lengths incorporating these centers are in
the normal range. The six-membered chelate ring in 2
is nonplanar since the As and Li centers both lie
significantly above the least-squares plane defined by
O(1), O(2), C(9), and C(25), [As(1) 0.924(11) Å, Li(1)
0.314(7) Å]. In a fashion similar to 2, complex 3 can be
seen as an adduct of [Rh(COD){η1-As[C(O)But]2}] with
a RhCl(COD) fragment, though in this case a crystal-
lographic 2-fold axis prevents any distinction being
made between the two rhodium centers.
(7) Allen, F. A.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1987, S1.

5926 Organometallics, Vol. 17, No. 26, 1998
Notes
g, 0.62 mmol) in 20 mL of Et2O at -78 °C. The suspension
was slowly warmed to room temperature and stirred for 1 h.
Volatiles were removed in vacuo, and the residue was ex-
tracted with hexane (30 mL) and filtered. The hexane was
removed in vacuo, and the residue was recrystallized from
Et2O (5 mL) to yield orange blocks of 3 (0.475 g, 75.8%): mp
119-121 °C (dec); 1H NMR (400 MHz, C6D6, 298 K) δ 1.32 (d,
Con clu sion
In summary, we have described the synthesis and
structural characterization of two novel diacylarsenido-
rhodium complexes. Remarkably, one of these, 2, rep-
resents a trapped intermediate in the salt elimination
reaction that forms the other, 3. Work continues in our
laboratory on a comparison of the coordination chem-
istry of 2-arsa- and 2-stibadionates with that of their
â-diketonate counterparts.
3
12H, J HH ) 6.5 Hz, p-CH(CH3)2), 1.44 (br, 12H, o-CH(CH3)2),
1.62 (br, 8H, COD CH2), 1.74 (br, 8H, COD CH2), 1.83 (br, 12H,
o-CH(CH3)2), 2.24 (br, 4H, COD CH), 2.33 (br, 4H, COD CH),
3
2.89 (septet, 2H, J HH ) 6.5 Hz, p-CH(CH3)2), 3.78 (br, 4H,
o-CH(CH3)2, 7.23 (s, 4H, aromatic CH); 13C NMR (100.6 MHz,
C6D6, 298 K) δ 23.2 (p-CH(CH3)2), 24.2 (p-CH(CH3)2), 26.4 (o-
CH(CH3)2), 29.5 (br, COD CH2), 31.2 (o-CH(CH3)2), 33.2 (br,
COD CH2), 34.8 (o-CH(CH3)2), 71.3 (br, COD CH), 90.9 (br,
COD CH), 120.9 (aromatic CH), 142.3, 143.9, 148.9 (aromatic
quaternary), 223.9 (AsCO); FAB mass spectrum (NBA matrix)
m/z 994 (M+, 5%), 886 (M+ - COD, 40%), 778 (M+ - 2COD,
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were carried out
using standard Schlenk and glovebox techniques under an
atmosphere of high-purity argon or dinitrogen. The solvents
diethyl ether and hexane were distilled over Na/K alloy and
then freeze/thaw-degassed prior to use. 1H and 13C NMR
spectra were recorded on a Bruker AM 400 spectrometer in
C6D6 and were referenced to the residual 1H resonances of the
solvent (1H NMR) or the 13C resonance of the deuterated
solvent (13C NMR), respectively. Mass spectra were recorded
using a VG-autospec/Cs+ ions/25kV/NBA matrix (FAB) instru-
ment and conditions. The microanalysis of 3 was obtained from
the University of Wales, Cardiff Microanalytical Service. A
reproducible microanalysis of 2 could not be obtained because
of its thermal instability at room temperature. Melting points
were determined in sealed glass capillaries under argon and
are uncorrected. The starting materials, [Li{η2-OC(Mes′)AsC-
(Mes′)O}(OEt2)]3 and [{RhCl(COD)}2],8 were prepared by
published procedures.
10%), 763 (M+ - CO(2,4,6-Pri Ph), 100%); IR (Nujol, cm-1
)
3
1667(s), 1651(s). Calcd for C48H70O2AsClRh2: C, 57.92; H, 7.09.
Found: C, 58.22; H, 6.89.
X-r a y Str u ctu r e Deter m in a tion s of 2 a n d 3. Crystals of
both compounds were mounted on a glass fiber using silicone
grease and cooled on the diffractometer. All crystallographic
measurements were carried out with a Nonius KappaCCD
diffractometer equipped with graphite-monochromated Mo KR
radiation using φ rotations with 2° frames and a detector-to-
crystal distance of 25 mm. Integration was carried out by the
program DENZO-SMN.9 Data sets were corrected for Lorentz
and polarization effects and for the effects of absorption using
the program Scalepack.9 Structures were solved using the
direct methods option of SHELXS-9710 and developed using
conventional alternating cycles of least-squares refinement and
difference Fourier synthesis (SHELXL-97).10 In general, all
non-hydrogen atoms were refined anisotropically, while hy-
drogen atoms were fixed in idealized positions and allowed to
ride. Hydrogen atom thermal parameters were tied to those
of the atom to which they were attached. Some disorder was
noted for the COD ligand in 3 which was modeled in terms of
two positions each for C(4) and C(7), both of 50% occupancy.
All calculations were carried out on a Silicon Graphics Indy
workstation or an IBM-PC compatible personal computer.
Crystal data and details of the data collections and refinements
are given in Table 1.
Syn th esis of 2. A solution of 1 (0.27 g, 0.44 mmol) in 10
mL of Et2O was added to a suspension of [{RhCl(COD)}2] (0.11
g, 0.22 mmol) in 10 mL of Et2O at -78 °C. The suspension
was slowly warmed to 0 °C and stirred for 30 min to yield an
orange solution. This was concentrated in vacuo to ca. 3 mL
and slowly cooled to -30 °C to yield 2 as pale orange rods
(0.376 g, 98%): mp 88-90 °C (dec); 1H NMR (400 MHz, C6D6,
298 K) δ 1.09 (d, 24H, 3J HH ) 6.1 Hz, o-CH(CH3)2, 1.10 (d, 12H,
3J HH ) 7.1 Hz, p-CH(CH3)2), 1.05 (t, 6H, J HH ) 7.4 Hz,
3
OCH2CH3), 1.37 (br, 4H, COD CH2), 1.63 (br, 4H, COD CH2),
2.03 (septet, 4H, 3J HH ) 6.1 Hz, o-CH(CH3)2), 2.67 (septet, 2H,
3J HH ) 7.1 Hz, p-CH(CH3)2), 3.28 (br, 2H, COD CH), 3.60 (q,
3
4H, J HH ) 7.4 Hz, OCH2CH3), 3.78 (br, 2H, COD CH), 7.14
(s, 4H, aromatic CH); 13C NMR (100.6 MHz, C6D6, 298 K) δ
15.3 (OCH2CH3), 24.2 (o-CH(CH3)2), 24.3 (p-CH(CH3)2), 25.3
(o-CH(CH3)2), 29.5 (COD CH2), 30.8 (p-CH(CH3)2), 33.1 (COD
Ack n ow led gm en t. We thank the Leverhume Trust
for funding (for S.J .B.) and King’s College London and
the EPSRC for provision of the diffractometer system.
1
CH2), 66.0 (OCH2CH3), 70.9 (d, J RhC ) 14.02 Hz, COD CH),
90.3 (d, 1J RhC ) 10.2 Hz, COD CH), 121.3 (aromatic CH), 143.9,
145.1, 149.9 (aromatic quaternary), 239.6 (AsCO); FAB mass
spectrum (NBA matrix) m/z 791 (M+ - Et2O, 25%), 682 (M+
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and bond angles and
distances for 2 and 3 (23 pages). Ordering information is given
on any current masthead page.
- (Et2O + COD), 10%), 587 (M+ - (Et2O + 2,4,6-Pri Ph),
3
100%); IR (Nujol, cm-1) 1625(m), 1605(s).
OM9807607
Syn th esis of 3. A solution of 1 (0.39 g, 0.63 mmol) in 10
mL of Et2O was added to a suspension of [{RhCl(COD)}2] (0.31
(9) Otwinowski, Z.; Minor, W. in Methods in Enzymology; Carter,
C. W., Sweet, R. M., Eds.; Academic Press: New York, 1996.
(10) Sheldrick, G. M. SHELX-97, University of Go¨ttingen, 1997.
(8) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1990, 28, 88.