Guanidines as neutral monodentate ligands; syntheses and crystal structures of [Co{PhN=C(NHPh)2}2Cl2] and [Ag{PhN=C(NHPh)2}]-[SO3CF3]

Article abstract of DOI:10.1039/a704570k

Two complexes exhibiting monodentate metal co-ordination of a neutral guanidine have been synthesized and structurally characterised. Treatment of CoCl₂ with 1,2,3-triphenylguanidine in tetrahydrofuran solution produced the tetrahedral complex [Co{(PhN)C(NHPh)₂}₂Cl₂] 1 in which the guanidine ligands are co-ordinated through their imine nitrogen atoms alone. Similarly, treatment of the guanidine with Ag[SO₃CF₃] in toluene provided the linear complex [Ag{(PhN)C(NHPh)₂}₂][SO₃CF₃] 2 in which the triflate counter ion remains uncoordinated, but is hydrogen bonded to the guanidine hydrogen atoms. Both complexes have been characterised by X-ray crystallography.

Full text of DOI:10.1039/a704570k

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Guanidines as neutral monodentate ligands; syntheses and crystal
structures of [Co{PhN᎐C(NHPh) } Cl ] and [Ag{PhN᎐C(NHPh) }]-
᎐
᎐
2 2
2
2
[SO3CF3]
Philip J. Bailey,* Keith J. Grant, Stuart Pace, Simon Parsons and Lisa J. Stewart
Department of Chemistry, The University of Edinburgh, The King’s Buildings, West Mains Road,
Edinburgh, UK EH9 3JJ
Two complexes exhibiting monodentate metal co-ordination of a neutral guanidine have been synthesized and
structurally characterised. Treatment of CoCl2 with 1,2,3-triphenylguanidine in tetrahydrofuran solution
produced the tetrahedral complex [Co{(PhN)C(NHPh)2}2Cl2] 1 in which the guanidine ligands are co-ordinated
through their imine nitrogen atoms alone. Similarly, treatment of the guanidine with Ag[SO3CF3] in toluene
provided the linear complex [Ag{(PhN)C(NHPh)2}2][SO3CF3] 2 in which the triflate counter ion remains unco-
ordinated, but is hydrogen bonded to the guanidine hydrogen atoms. Both complexes have been characterised by
X-ray crystallography.
The nitrogen analogues of carboxylic acids, amidines
(RN᎐CR᎐NHR) and triazenes (RN᎐N᎐NHR), have been
R
R
R
R
᎐
᎐
R
R
N
O
H
O
N
H
N
N
H
N
shown to be excellent ligands for transition metals, in particular
as anionic chelating or bridging amidinates and triazenates.1
However, their behaviour as neutral monodentate ligands is
comparatively uncommon, although a number of such com-
plexes have been characterised.2–5 The increased basicity (donor
strength) of the nitrogen donors over oxygen, and the added
flexibility provided by manipulation of the electronic and steric
properties of the R groups, are features of these ligands which
have been exploited on many occasions. In particular, the
potential of complexes in which the sterically demanding bis-
(trimethylsilyl)benzamidinate ligand [PhC(NSiMe3)2]Ϫ replaces
a cyclopentadienyl ligand to provide new unsaturated com-
plexes has attracted considerable attention over recent years.6
Carboxylic acid
Amidine
Triazene
R
N
H
H
O
R
R
N
N
O
H
O
H
Guanidine
Carbonic acid
and di-anions.12 Here we report the syntheses and structural
characterisation of rare examples of complexes containing a
guanidine co-ordinated as a neutral monodentate ligand. To
our knowledge there are only two previous examples of com-
plexes containing monodentate guanidine ligands which have
been structurally characterised,13,14 and in both of these the
Guanidines [RN᎐C(NHR) ] bear the same relationship to car-
᎐
2
bonic acid as amidines and triazenes do to carboxylic acids, and
as such should be excellent ligands given the above consider-
ations. Furthermore, there exists the possibility of a second
deprotonation to provide a dianionic ligand [C(NR)3]2Ϫ, the
nitrogen analogue of carbonate,7 which is unavailable to the
carboxylic acid analogues. Carbonate is a highly versatile ligand
which has been structurally characterised in a multitude of
mono-, di- and tri-hapto co-ordination modes,8 and it is there-
fore surprising that the potential of guanidines as ligands with a
diverse co-ordination chemistry is only now beginning to be
appreciated.
Our initial interest in the potential of guanidines and their
anions as ligands was prompted by the prospect that the
[C(NR)3]2Ϫ dianion might exhibit an η3-co-ordination mode in
which all three nitrogen donors are bound to a single metal
ion.7 This is a co-ordination mode unknown for the carbonate
ligand, but its ubiquity for the trimethylenemethane ligand
[C(CH2)3]2Ϫ, the carbon analogue of this system,9 fuelled our
expectation that it might also be observed for the nitrogen
ligand. Although we have yet to demonstrate the existence of
such a co-ordination mode for the guanidine dianion, we have
now developed the co-ordination chemistry of guanidines to a
considerable extent. We have previously reported ruthenium
and rhodium complexes containing chelating guanidinate
ligands,10 and the redox pair [Mo2{µ-η2-(NPh)2CNHPh}4]0/ϩ
which gave the first indications of the flexible donor properties
of these ligands.11 In addition we have characterised a number
of main-group complexes containing both guanidine mono-
ligand is a 1,1,3,3-tetrasubstituted guanidine [(R N) C᎐NH].
The ligand reported here is, in contrast, a 1,2,3-trisubstituted
᎐
2
2
guanidine [(NHR) C᎐NR].
᎐
2
Results and Discussion
Our previous observations of the reactivity of 1,2,3-triphenyl-
guanidine with the metal halide complexes [{Rh(η-C5Me5)Cl2}2]
and [Ru(η-MeC6H4Pri-p)Cl2}2] had shown that, in addition to
cleaving the chloro-bridges, the guanidine also acts as a base to
provide a chelating guanidinate ligand with concomitant form-
ation of the guanidinium chloride.10 Indeed, treatment of these
dimers with 4 molar equivalents of the guanidine in toluene
solution rapidly leads to precipitation of the salt and formation
of the guanidinate complexes in good yield at room temper-
ature. Given the observation that amidines and triazenes can
act as neutral imine donors to provide tetrahedral complexes
with transition-metal dihalides,2,3 we were interested to investi-
gate the possibility that guanidines could behave in a similar
fashion.
[Co{(PhN)C(NHPh)2}2Cl2] 1
Treatment of CoCl2 with 2 molar equivalents of 1,2,3-
triphenylguanidine in tetrahydrofuran (thf) under reflux pro-
vides a bright blue solution of [Co{(PhN)C(NHPh)2}2Cl2] 1
J. Chem. Soc., Dalton Trans., 1997, Pages 4263–4266
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Table 1 Selected bond lengths (Å) and angles (Њ) for molecule 1 of
[Co{(PhN)C(NHPh)2}2Cl2] 1
Co(1)᎐N(11)
Co(1)᎐N(12)
Co(1)᎐Cl(11)
Co(1)᎐Cl(21)
C(11)᎐N(11)
2.014(6)
2.013(5)
2.280(2)
2.284(2)
1.312(8)
C(11)᎐N(21)
C(11)᎐N(31)
C(12)᎐N(12)
C(12)᎐N(22)
C(12)᎐N(32)
1.342(8)
1.384(8)
1.295(8)
1.375(8)
1.361(8)
N(11)᎐Co(1)᎐N(12) 113.2(2)
Cl(11)᎐Co(1)᎐Cl(21) 105.32(8)
N(11)᎐Co(1)᎐Cl(11) 109.3(2)
N(12)᎐Co(1)᎐Cl(11) 111.0(2)
N(12)᎐Co(1)᎐Cl(21) 109.3(2)
N(11)᎐Co(1)᎐Cl(21) 109.3(2)
N(11)᎐C(11)᎐N(21) 120.3(6)
N(11)᎐C(11)᎐N(31) 121.3(6)
N(21)᎐C(11)᎐N(31) 118.4(6)
N(12)᎐C(12)᎐N(22) 118.5(6)
N(12)᎐C(12)᎐N(32) 124.2(6)
N(22)᎐C(12)᎐N(32) 117.3(6)
Fig. 2 Thermal ellipsoid plot of [Ag{(PhN)C(NHPh)2}2][SO3CF3] 2
showing the atom numbering scheme. The silver ion is located at an
inversion centre which relates the two ligands. A second molecule in the
unit cell, which is not shown, has similar metrical parameters
the bond angles around the cobalt are however observed for the
guanidine and formamidine complexes; whilst the N᎐Co᎐N
angles for the two complexes are almost identical [113.2(2) and
113.0(2)Њ respectively], the Cl᎐Co᎐Cl angles differ markedly
[105.32(8) and 115.10(6)Њ respectively]. However, the chemical
significance of these observations is questionable since the
corresponding angles for the second molecule of 1 in the unit
cell differ significantly [N᎐Co(2)᎐N 108.1(2), Cl᎐Co(2)᎐Cl
107.35(8)Њ] thus indicating that the effects of crystal packing
may account for considerable distortions of geometry about the
cobalt ion in these tetrahedral CoCl2L2 complexes. The NH
hydrogens were located in Fourier-difference maps and their
attachment to the non-ligating nitrogens clearly indicates that it
is the imine nitrogen atoms of the guanidine ligands which are
co-ordinated to cobalt as suggested by the infrared evidence.
This is confirmed by the observation that the C᎐N bonds
between the central guanidine carbons and the ligating nitro-
gens [1.312(8) and 1.295(8) Å] are significantly shorter than the
remaining bonds to these carbons [range 1.342(8)–1.384(8) Å].
As far as we are aware 1 represents the first structurally charac-
terised example of a guanidine acting as a neutral monodentate
ligand towards a transition metal.
Following our characterisation of the M᎐M bonded dimers
[Mo2{µ-η2-(NPh)2CNHPh}4]0/ϩ, our intention in preparing
complex 1 was as a precursor to the corresponding cobalt
dimer. We have found that 1 does indeed react with methyl-
lithium, mimicking the preparation of the corresponding
iron formamidinate dimers [Fe2{µ-η2-(PhN)2CH}4]18 and
[Fe2{µ-η2-(PhN)2CH}3]19 from [Fe(PhNCHNHPh)2Cl2], but we
have as yet been unable to cleanly isolate any product from this
reaction. However, we are confident that it should be possible to
synthesize such a dimer since both the formamidinate-
and benzamidinate-bridged dimers [Co2{µ-η2-(PhN)2CR}4]20
(R = H or Ph) and their reduced analogues [Co2{µ-η2-
(PhN)2CR}3]21 have been synthesized by this route. The
triazenate-bridged complex [Co2{µ-η2-(p-MeC6H4N)2N}4] has
also been characterised.22 We are therefore continuing our work
in this area.
Fig. 1 Thermal ellipsoid plot of [Co{(PhN)C(NHPh)2}2Cl2] 1 show-
ing the atom numbering scheme. A second molecule in the unit cell,
which is not shown, has similar metrical parameters
which may be obtained as the crystalline bis(dichloromethane)
solvate in 77% yield by slow evaporation of a dichloromethane–
hexane solution. The infrared spectrum of this complex as a
Nujol mull shows the ν(C᎐N) mode of the co-ordinated guan-
᎐
idine at 1626 cmϪ1 which compares with a value of 1637 cmϪ1
for the free guanidine. Previous studies of transition-metal
guanidine complexes have shown a similar reduction in C᎐N
᎐
stretching frequency.14,15 Thus, a low-energy shift of between 60
and 67 cmϪ1 has been observed for the 1,1,3,3-tetramethyl-
guanidine (L) complexes [ML4][ClO4]2 (M = Co, Cu or Zn) and
this was interpreted as indicating co-ordination through the
imine rather than an amine nitrogen. The ν(N᎐H) modes of the
ligand appear as a rather broad unresolved band at 3351 cmϪ1
in the spectrum of 1 which contrasts with the sharp band at
3382 cmϪ1 observed in the spectrum of the free guanidine.
A crystal structure determination shows that complex 1 con-
tains two independent molecules per unit cell, solvated by two
molecules of CH2Cl2. In all cases, the differences in bond
lengths for the two molecules are not crystallographically sig-
nificant at the 3σ level and therefore only data for the molecule
containing Co(1) will be discussed; this is however not the case
for bond angles. The molecular structure of 1 is shown in Fig. 1,
and selected bond lengths and angles are provided in Table 1.
The Co᎐Cl bond lengths are only slightly (ca. 0.01 Å) longer
than in the analogous compound with N,NЈ-di(p-tolyl)form-
amidine ligands,2 but significantly longer than those found
in [CoCl2(NC5H4OMe-2)2]16 and [CoCl2(NC5H4Me-4)2]17 (ca.
0.06 and 0.21 Å respectively), however the Co᎐N bond lengths
[2.014(6) and 2.013(5) Å] do not differ significantly from those
for the formamidine complex. Significant differences between
[Ag{(PhN)C(NHPh)2}2][SO3CF3] 2
The reaction of silver triflate with 1,2,3-triphenylguanidine
proceeds at reflux in toluene to provide the toluene-soluble
complex [Ag{(PhN)C(NHPh)2}2][SO3CF3] 2 which may be
crystallised as well formed colourless blocks by layering with
hexane. The infrared spectrum of 2 shows the C᎐N stretching
᎐
band at 1618 cmϪ1 and the ν(N᎐H) modes as two sharp absorp-
tions at 3366 and 3304 cmϪ1. A crystal structure determination
shows the crystals of 2 to contain two independent molecules
per unit cell each consisting of a linear [AgL2]ϩ complex with an
associated triflate counter ion. Complex 2 is illustrated in Fig. 2
and selected bond lengths and angles are given in Table 2. Both
4264
J. Chem. Soc., Dalton Trans., 1997, Pages 4263–4266

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reflux with an excess of thionyl chloride for 30 min followed by
drying at 50 ЊC under dynamic vacuum for 1 h. The NMR
spectra were recorded on a Bruker AC 250 spectrometer and the
infrared spectra on a Perkin-Elmer Paragon 1000 spectrometer
from samples as Nujol mulls and mass spectra on a Kratos
MS50 TC instrument in positive-ion FAB mode using 3-nitro-
benzyl alcohol as matrix and CsI as calibrant. Elemental analy-
ses were conducted by the microanalytical service of this
department.
Table 2 Selected bond lengths (Å) and angles (Њ) for [Ag{(PhN)-
C(NHPh)2}2][SO3CF3] 2
Ag(1)᎐N(11)
C(11)᎐N(11)
C(11)᎐N(21)
C(11)᎐N(31)
2.135(8)
1.32(1)
1.36(1)
1.36(1)
Ag(2)᎐N(12)
C(12)᎐N(12)
C(12)᎐N(22)
C(12)᎐N(32)
2.146(8)
1.29(1)
1.35(1)
1.36(1)
Ag(1)᎐N(11)᎐C(11) 122.5(6)
N(11)᎐C(11)᎐N(21) 120.7(8)
N(11)᎐C(11)᎐N(31) 125.7(8)
N(21)᎐C(11)᎐N(31) 113.5(7)
Ag(2)᎐N(12)᎐C(12) 117.5(6)
N(12)᎐C(12)᎐N(22) 123.7(9)
N(12)᎐C(12)᎐N(32) 125.3(9)
N(22)᎐C(12)᎐N(32) 111.0(9)
Syntheses
[Co{(PhN)C(NHPh)2}2Cl2] 1. Anhydrous CoCl2 (1.854 g,
12.27 mmol) and 1,2,3-triphenylguanidine (8.199 g, 28.53
mmol) were heated together to reflux in thf (90 cm3) for 89 h.
The resulting bright blue solution was reduced to dryness and
the residue dissolved in CH2Cl2 (50 cm3) and the solution
filtered through a pad of Celite. Hexane was added until pre-
cipitation commenced and the precipitate was then dissolved by
adding CH2Cl2 dropwise. Crystallisation by slow evaporation
provided well formed needles of complex 1ؒ2CH2Cl2 (8.20 g,
77%) (Found: C, 63.61; H, 4.75; N, 11.82. C40H38Cl6CoN6
requires C, 54.92; H, 4.35; N, 9.61%). This is consistent with
solvent loss by the crystals of approximately 1.8 molecules of
CH2Cl2 per molecule of 1 (1ؒ0.2CH2Cl2 requires C, 63.58; H,
4.77; N, 11.65%). IR (Nujol mull): 3351 (N᎐H) and 1626 cmϪ1
complexes possess an inversion centre at silver which relates the
two ligands, and although the differences in some of the metri-
cal data for these two complexes is crystallographically signifi-
cant the essential features are the same for the two, and con-
sequently only the complex containing Ag(1) is discussed in
detail. The Ag᎐N distances in the two independent molecules
[2.135(8) and 2.146(8) Å] of 2 are intermediate between those
found for the bis(ammine) complex [Ag(NH3)2][ClO4] [2.112(6)
and 2.117(6) Å)]23 and the polymeric ethane-1,2-diamine com-
plex [{Ag(en)}n][ClO4]n [2.17(1) Å],24 both of which also
exhibit essentially linear co-ordination of the silver ion. As far
as the ligand is concerned, the most closely related, structurally
characterised complex is the recently reported three-co-
(C᎐N). Positive-ion FAB mass spectrum: m/z (%) 704 (0.1, Mϩ),
᎐
668 (1.1, M Ϫ Cl), 633 (0.4, M Ϫ 2Cl), 612 (3.3, M Ϫ NHPh)
and 288 (100, triphenylguanidine). UV/VIS (CH2Cl2): ν /
cmϪ1 = 40 000 (ε = 24 550) and 15 360 (ε = 345 dm3 molϪ1
cmϪ1).
ordinate silver formamidine complex [Ag(PhN᎐CH᎐NHPh) -
᎐
2
(O3SCF3)] in which the Ag᎐N distances were found to be
2.179(4) and 2.206(4) Å,4 significantly longer than those in 2.
Although in this complex, as in 2, the silver is co-ordinated by
two Ph᎐N᎐C imine nitrogen atoms, the difference in Ag᎐N dis-
᎐
[Ag{(PhN)C(NHPh)2}2][SO3CF3] 2. Silver triflate (427 mg,
1.66 mmol) and 1,2,3-triphenylguanidine (955 mg, 3.32 mmol)
were placed in a Schlenk tube under nitrogen and aluminium
foil was wrapped around the tube to exclude light. Toluene (40
cm3) was added and the mixture heated to reflux for 1 h. The
resulting mixture was filtered through a Celite pad to remove a
small amount of pale brown material and the resulting very
pale pink solution was reduced to ca. 10 cm3 under vacuum.
The solution was layered with hexane (20 cm3) and allowed to
stand overnight to yield a crop of colourless crystals suitable for
X-ray crystallography (720 mg, 52%) (Found: C, 57.67; H, 4.51;
N, 10.54. C39H34AgF3N6O3S requires C, 56.32; H, 4.12; N,
10.11%). IR (Nujol mull): 3366 (m, N᎐H), 3304 (m, N᎐H) and
1618 cmϪ1 (s, C᎐N). 1H NMR (250 MHz, CDCl ): δ 7.37 (br, 2
tances between the two may be attributed to the change in
geometry brought about by the weak co-ordination of triflate in
the formamidine complex (N᎐Ag᎐N 142Њ) rather than by any
difference between the nitrogen ligands. This is supported by
our observation that the Co᎐N distances in the two tetrahedral
complexes 1 and [CoCl {HC(᎐NR)NHR} ] (R = p-tolyl) do not
᎐
2
2
differ significantly (see above). The anticipated similarity of the
donor properties of the imine nitrogen atoms of the form-
amidine (PhN᎐CH᎐NHPh) and guanidine [PhN᎐C(NHPh) ]
᎐
᎐
2
ligands would suggest that the reason for the difference in co-
ordination environments for the silver ions in the two com-
plexes is steric rather than electronic in origin. Indeed, it is clear
from the structure of 2 that the silver is shielded from further
co-ordination by two flanking phenyl groups on unco-ordin-
ated nitrogens.
᎐
3
H, NH and 7.25–6.92 (m, 15 H, C6H5. 13C NMR (62.9 MHz,
CDCl3): δ 152.7 (CN3), 129.1, 124.6, 122.8 (C6H5). Positive-ion
FAB mass spectrum: m/z 684 (Mϩ), 394 (Mϩ Ϫ triphenyl-
guanidine), 288 (triphenylguanidine) and 194 (diphenyl-
carbodiimide).
Although the NH hydrogens in complex 2 were not directly
located in the crystallographic study, co-ordination of the imine
rather than an amine nitrogen to the silver is indicated by com-
parison of the central C᎐N bond distances within the ligands.
For molecule 1 these distances are 1.32(1) Å for the carbon to
co-ordinated nitrogen and 1.39(1) Å for the two bonds to the
unco-ordinated nitrogens. The corresponding distances for
molecule 2 are 1.29(1), 1.35(1) and 1.36(1) Å respectively. The
X-Ray crystallography
Crystals of complex 1 were grown from saturated dichloro-
methane–hexane solutions by slow evaporation at room tem-
perature, while those of 2 were obtained by slow diffusion of
hexane into a toluene solution.
[SO3CF3]Ϫ counter ion in 2 is hydrogen bonded via two S᎐O
᎐
oxygens to the NH hydrogens of the guanidine ligands. The
N᎐O distances in these N᎐H ؒ ؒ ؒ O systems range from
2.912(12) to 3.109(13) Å and the N᎐H᎐O angle from 128.5 to
145.3Њ.
Crystal data. For 1ؒ2CH2Cl2: C40H38Cl6CoN6, M = 874.40,
monoclinic, space group P21/n, a = 13.080(2), b = 29.624(3),
c = 21.925(3) Å, β = 91.467(12)Њ, U = 8492(2) Å3 (from 46
reflections, 15 < θ < 16Њ measured at ω, λ = 0.710 73 Å),
Z = 8, Dc = 1.368 g cmϪ3, F(000) = 3592, blue columnar block,
Experimental
General
0.58 × 0.29 × 0.29 mm, T = 220 K, µ(Mo-Kα) = 0.818 mmϪ1
.
For 2: C39H34AgF3N6O3S, M = 831.66, triclinic, space group
¯
All reactions were carried out under an atmosphere of dry,
oxygen-free nitrogen using standard Schlenk techniques and
solvents which were dried and distilled under nitrogen immedi-
ately prior to use. The 1,2,3-triphenylguanidine was prepared
by condensation of aniline with diphenylcarbodiimide in
toluene solution. The CoCl2 (Aldrich) was dried by heating to
P1, a = 9.802(5), b = 13.760(7), c = 15.464(7) Å, α = 66.81(2),
β = 81.65(2), γ = 75.39(3)Њ, U = 1852.73 Å3 (from 26 reflections,
12 < θ < 13Њ measured at ω, λ = 0.710 73 Å), Z = 2 (two
independent molecules lying on crystallographic inversion
centres), Dc = 1.49 g cmϪ3, F(000) = 846.24, colourless block,
0.33 × 0.23 × 0.19 mm, T = 220 K, µ(Mo-Kα) = 0.65 mmϪ1
.
J. Chem. Soc., Dalton Trans., 1997, Pages 4263–4266
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6 A. N. Chernaga, R. Gomez and M. L. H. Green, J. Chem. Soc.,
Data collection, solution and refinement. Data were collected
using Mo-Kα radiation in the range 5 р 2θ р 50Њ for complex 1
and 5 р 2θ р 45Њ for 2 on a Stoe Stadi4 diffractometer equipped
with an Oxford Cryosystems low-temperature device25 using
ω–θ scans. An absorption correction based on ψ scans was
applied for 1 (maximum and minimum transmission co-
efficients: 0.540 and 0.498), Rint = 0.1958 (based principally on
a weak high-angle data). Owing to rather low crystal quality,
characterised by poor peak shapes and high backgrounds, a
consistent set of ψ scans could not be obtained for 2, leaving
little option but to apply a correction during refinement
(DIFABS, correction applied to Fc maximum and minimum
corrections 1.347 and 0.683, respectively).26 Both structures
were solved by direct methods (SIR 92).27 Complex 1 was
refined against F2 (SHELXTL)28 with anisotropic displacement
parameters for all non-H atoms, and H atoms placed in calcu-
lated positions, although those attached to nitrogen were dis-
cernible in a difference map. The refinement converged to
R1 = 0.0759 [based on F and 7721 data with F > 4σ(F)] and
wR2 = 0.2013 (based on F2 and all 14 784 data) for 956 para-
meters). The final difference-synthesis maximum and minimum
were ϩ0.51 and Ϫ0.50 e ÅϪ3, respectively. Complex 2 was
refined against F using 2895 data with F > 4σ(F ) (out of a total
of 4264 unique data, CRYSTALS).29 Hydrogen atoms were
placed in calculated positions, and anisotropic displacement
parameters were refined for all other atoms, giving a final R of
0.0639, RЈ = 0.0704 for 481 parameters. The final difference-
Chem. Commun., 1993, 1415; R. Duchateau, C. T. van Wee,
A. Meetsma and J. H. Teuben, J. Am. Chem. Soc., 1993, 115, 493.
7 P. J. Bailey, A. J. Blake, M. Kryszczuk, S. Parsons and D. Reed,
J. Chem. Soc., Chem. Commun., 1995, 1647.
8 See, for example, G. Kolks, S. J. Lippard and J. V. Waszczak, J. Am.
Chem. Soc., 1980, 102, 4832; F. W. B. Einstein and A. C. Wills, Inorg.
Chem., 1981, 20, 609; A. Escuer, R. Vicente, E. Penalba, X. Solans
and M. Font-Bardia, Inorg. Chem., 1996, 35, 248.
9 M. D. Jones and R. D. W. Kemmitt, Adv. Organomet. Chem., 1987,
27, 279.
10 P. J. Bailey. L. A. Mitchell and S. Parsons, J. Chem. Soc., Dalton
Trans., 1996, 2839.
11 P. J. Bailey, S. F. Bone, L. A. Mitchell, S. Parsons, K. J. Taylor and
L. J. Yellowlees, Inorg. Chem., 1997, 36, 867.
12 P. J. Bailey, L. A. Mitchell, P. R. Raithby, M. A. Rennie,
K. Verhorevoort and D. S. Wright, Chem. Commun., 1996, 1359;
P. J. Bailey, R. O. Gould, C. N. Harmer, S. Pace, A. Steiner and
D. S. Wright. Chem. Commun., 1997, 1161.
13 N. de Vries, C. E. Costello, A. G. Jones and A. Davidson, Inorg.
Chem., 1990, 29, 1348.
14 W. P. Fehlhammer, R. Metzner and W. Sperber, Chem. Ber., 1994,
127, 829.
15 R. Longhi and R. S. Drago, Inorg. Chem., 1965, 4, 11.
16 J. R. Allan, C. R. Jones and L. Sawyer, J. Inorg. Nucl. Chem., 1981,
43, 2707.
17 M. Laing and G. Carr, Acta Crystallogr., Sect. B, 1975, 31, 2683.
18 F. A. Cotton, L. M. Daniels and C. A. Murillo, Inorg. Chim. Acta,
1994, 224, 5.
19 F. A. Cotton, L. M. Daniels, L. R. Falvello and C. A. Murillo, Inorg.
Chim. Acta, 1994, 219, 7.
20 L. P. He, C. L. Yao, M. Naris, J. D. Korp and L. J. Bear, Inorg.
Chem., 1992, 31, 620; F. A. Cotton, L. M. Daniels, X. Feng,
D. J. Maloney, J. H. Matonic and C. A. Murillo, Inorg. Chim. Acta,
1997, 256, 291.
map extrema were 0.81 and Ϫ1.32 e ÅϪ3
.
CCDC reference number 186/725.
21 F. A. Cotton, L. M. Daniels, D. J. Maloney, J. H. Matonic and
C. A. Murillo, Inorg. Chim. Acta, 1997, 256, 283.
Acknowledgements
22 F. A. Cotton and R. Poli, Inorg. Chem., 1987, 26, 3652.
23 H. M. Mauer and A. Weiss, Z. Kristallogr., 1977, 146, 247.
24 E. Bang, Acta Chem. Scand., 1978, 32, 555.
25 J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105.
26 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158.
27 A. Altomare, M. C. Burla, M. Camelli, G. Cascarano,
C. Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr.,
1994, 27, 435.
28 G. M. Sheldrick, SHELXTL, version 5, Siemens Analytical X-Ray
Instruments, Madison, WI, 1995.
29 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Betteridge,
CRYSTALS, version 10, Chemical Crystallography Laboratory,
University of Oxford, 1996.
We thank the Engineering and Physical Science Research
Council (EPSRC) for a studentship (to S. P.) and provision of
a four-circle diffractometer, and The Leverhulme Trust for a
fellowship (to K. J. G.).
References
1 K. Vrieze and G. van Koten in Comprehensive Coordination
Chemistry, Pergamon, Oxford, 1987, vol. 2, p. 195.
2 F. A. Cotton, L. M. Daniels, D. J. Maloney, J. H. Matonic and
C. A. Murillo, Polyhedron, 1994, 13, 815.
3 D. I. Arnold, F. A. Cotton, D. J. Maloney, J. H. Matonic and
C. A. Murillo, Polyhedron, 1997, 16, 133.
4 D. I. Arnold, F. A. Cotton, J. H. Matonic and C. A. Murillo,
Polyhedron, 1997, 16, 1837.
5 C. M. Knowles and G. W. Watt, J. Am. Chem. Soc., 1942, 64, 935.
Received 30th June 1997; Paper 7/04570K
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J. Chem. Soc., Dalton Trans., 1997, Pages 4263–4266