Tuning low-coordinate metal environments: High spin d5-d7 complexes supported by bis(phosphinimino)methyl ligation

Article abstract of DOI:10.1039/b210467a

Treatment of FeCl₂ with the lithium derivative of [CH₂(Ph₂P=NC₆H₂Me₃- 2.4.6)₂] in THF and crystallisation from Et₂O gave the 'ate' complex [{CH(Ph₂PNC₆H₂Me₃- 2.4.6)₂}Fe(μ-Cl)₂Li(THF)(OEt₂)] in which the iron is four-coordinate and the chlorides bridge to lithium. Treatment of [M{N(SiMe₃)}₂] (M = Mn, Fe, Co) with [CH₂ (Ph₂P=NC₆H₂Me₃-2.4.6)₂] in toluene afforded the complexes [{CH(Ph₂PNC₆ H₂Me₃-2.4.6)₂} MN(SiMe₃)₂] which all feature essentially planar N(1)-N(2) -N(3)-M coordination. The carbanionic character of the bis(phosphinimino)methyl ligand results in close C(1)-M contacts in both the Mn and Co complexes effectively raising the coordination number to four. The analogous iron compound is strictly three-coordinate as demonstrated by X-ray crystallography and ⁵⁷Fe Moessbauer. However protonolysis of this compound with Ph₃COH yields the iron alkoxide [{CH(Ph₂PNC₆ H₂Me₃-2.4.6)₂} FeOCPh₃] that features a close C(1)-Fe contact of 2.375 A. Although the iron centre in this complex is only marginally pyramidalised by this contact, its ⁵⁷Fe Moessbauer spectrum indicates a significant perturbation to the local electronic environment at the metal.

Full text of DOI:10.1039/b210467a

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Tuning low-coordinate metal environments: high spin d5–d7
complexes supported by bis(phosphinimino)methyl ligation
David J. Evans,a Michael S. Hill*b and Peter B. Hitchcockc
a Department of Biological Chemistry, John Innes Centre, Norwich Research Park, Colney,
Norwich, UK NR4 7UH
b Department of Chemistry, Imperial College of Science, Technology and Medicine,
Exhibition Road, South Kensington, London, UK SW7 2AY. E-mail: mike.hill@ic.ac.uk
c School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer,
Brighton, UK BN1 9QJ
Received 23rd October 2002, Accepted 6th December 2002
First published as an Advance Article on the web 17th January 2003
Treatment of FeCl with the lithium derivative of [CH (Ph P᎐NC H Me -2,4,6) ] in THF and crystallisation from
᎐
2
2
2
6
2
3
2
Et2O gave the ‘ate’ complex [{CH(Ph2PNC6H2Me3-2,4,6)2}Fe(µ-Cl)2Li(THF)(OEt2)] in which the iron is four-
coordinate and the chlorides bridge to lithium. Treatment of [M{N(SiMe )} ] (M = Mn, Fe, Co) with [CH (Ph P᎐
᎐
2
3
2
2
NC6H2Me3-2,4,6)2] in toluene afforded the complexes [{CH(Ph2PNC6H2Me3-2,4,6)2}MN(SiMe3)2] which all feature
essentially planar N(1)–N(2)–N(3)–M coordination. The carbanionic character of the bis(phosphinimino)methyl
ligand results in close C(1)–M contacts in both the Mn and Co complexes effectively raising the coordination number
to four. The analogous iron compound is strictly three-coordinate as demonstrated by X-ray crystallography and 57Fe
Mössbauer. However protonolysis of this compound with Ph3COH yields the iron alkoxide [{CH(Ph2PNC6H2Me3-
2,4,6)2}FeOCPh3] that features a close C(1)–Fe contact of 2.375 Å. Although the iron centre in this complex is only
marginally pyramidalised by this contact, its 57Fe Mössbauer spectrum indicates a significant perturbation to the
local electronic environment at the metal.
Introduction
The presence of a low-coordinate or coordinatively unsaturated
transition metal centre is fundamental to a great number of
industrial and biocatalytic processes.1 The desire to model and
better understand the fundamental chemistry of these systems
has prompted a general interest in the development of ligands
that are capable of supporting a range of low-coordinate metal
centres. For example, several recent reports describe the use of
bulky aryl-substituted β-diketiminate ligands such as I and II,
to support three coordinate iron() complexes.2 The primary
importance of these compounds derives from their ability to
promote reduction of dinitrogen in a stepwise manner and thus
their relationship to the iron centres of the iron–molybdenum
cofactor (FeMoco), III, of the nitrogenase enzyme.2b,c The
recognition that six of the seven iron sites of FeMoco possess
trigonal geometry was based upon X-ray crystallographic data
with a resolution greater than 1.55 Å.3 A recent higher reso-
lution (to 1.16 Å) crystallographic study has revealed that this
assignment of coordination geometry is erroneous and that a
light atom (most plausibly nitrogen, as depicted in III, although
refinement for carbon and oxygen also yielded acceptable tem-
perature factors) resides in a central location of the cofactor.4
This additional ligand interaction effectively raises the coordin-
ation number of these iron sites to four and indicates that future
model compounds must also include contacts to similar light
atom donors in order to accommodate the presence of this
previously undetected interstitial atom. The realisation of
this goal therefore dictates an increasingly refined supporting
ligand design and ever greater control over the resultant metal
coordination geometry.
the coordination geometry adopted in these compounds can be
determined by the both the metal and co-ligand identity.
Results and discussion
Reaction of the lithium derivative of [CH (Ph P᎐NC H Me -
᎐
2
2
6
2
3
2,4,6)2], [IV]Li, and FeCl2 in THF (Scheme 1), followed by crys-
tallisation from diethyl ether at Ϫ30 ЊC allowed the isolation of
an air-sensitive colourless crystalline compound. Although this
was only sparingly soluble in hydrocarbon solvents, its solubil-
ity in THF-d8 allowed the determination of a solution magnetic
moment (Evans’ method, 298 K) of 5.0 µB. This is typical for
tetrahedral d6 high spin iron()7a as are the 57Fe Mössbauer
With such considerations in mind, we have recently
embarked upon a program of study that aims to assemble a
suite of sterically demanding ligands that allow control of
both coordination geometry and compound symmetry in low-
coordinate systems.5 We now wish to report the synthesis of
divalent Mn, Fe and Co complexes supported by the mesityl-
substituted bis(phosphinimino)methyl ligand IV,6 and present
preliminary evidence that both the denticity of the ligand and
parameters in the solid state (isomer shift (i.s.) = 0.93 mm sϪ1
,
quadrupole splitting (q.s.) = 3.54 mm sϪ1).7a An X-ray diffrac-
tion study revealed this product to be the ‘ate’ complex,
[{CH(Ph2PNC6H2Me3-2,4,6)2}Fe(µ-Cl)2Li(THF)(OEt2)] 1 (Fig.
1). Details of the crystallographic analysis are given in Table 1
and selected bond lengths and angles are listed in Table 2. The
iron coordination sphere of 1 is similar that of the recently
reported β-diketiminate derivative [I]Fe(µ-Cl)2Li(THF)2,2a in
D a l t o n T r a n s . , 2 0 0 3 , 5 7 0 – 5 7 4
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
570

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Table 1 Selected crystallographic and data collection parameters for compounds 1–5
1
2
3
4
5
Chemical formula
Formula weight
C51H61N2P2Cl2O2FeLi
929.65
C49H61N3P2Si2Mn
865.07
C49H61N3P2Si2Fe
865.98
C49H61N3P2Si2Co
869.06
C62H58N2P2OFe
964.89
T /K)
173(2)
173(2)
173(2)
173(2)
173(2)
Crystal size/mm3)
0.2 × 0.15 × 0.05
Triclinic
0.30 × 0.30 × 0.25
Orthorhombic
Pna21 (no. 33)
23.9011(4)
15.5577(3)
12.6739(2)
90
90
90
4
0.15 × 0.15 × 0.05
Monoclinic
P21/n (no. 14)
11.9774(3)
18.4685(4)
21.5940(7)
90
94.420(1)
90
4
0.3 × 0.3 × 0.2
Monoclinic
P21/n (no. 14)
12.2503(6)
19.5120(9)
19.5346(10)
90
94.046(2)
90
4
0.4 × 0.4 × 0.2
Triclinic
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
γ/Њ
¯
¯
P1 (no. 2)
P1 (no. 2)
12.8140(12)
13.1172(7)
16.2526(16)
91.262(6)
101.066(4)
117.249(5)
2
2364.5(3)
1.31
0.54
10.4976(2)
12.7168(2)
19.7847(4)
92.801(1)
92.638(1)
107.006(1)
2
2517.63(8)
1.27
0.41
Z
V/Å3
4712.74(14)
1.22
0.44
4762.5
1.21
0.47
4657.7(4)
1.24
0.53
Dc/Mg mϪ3
µ/mmϪ1
θ range/Њ
3.70 to 21.95
0.048, 0.093
0.080, 0.105
12078/5716/0.065
4151
3.77 to 24.69
0.035, 0.065
0.046, 0.069
30367/7304/0.058
6402
3.72 to 23.04
0.049, 0.100
0.074, 0.112
24917/6580/0.078
5041
3.71 to 22.99
0.051, 0.116
0.080, 0.131
20510/6409/0.093
4662
3.77 to 27.50
0.052, 0.105
0.090, 0.119
24791/11383/0.056
7910
R1; wR2 [I > 2σ(I )]
R1; wR2 all data
Measured/indep. rflns./R(int)
Rflns. with I > 2σ(I )
I and IV ligands and the flattened twist boat conformation that
is enforced upon the bis(phosphinimino)methyl group by the
pseudo-tetrahedral P() centres. That the bidentate ligands I
and IV provide similar donation of charge however may be
gauged from the similarity of the Fe–N bond lengths that are
only marginally longer in 1 [2.025(3), 2.046(3) Å vs. 2.006(3),
2.021(4) Å].
Several three-coordinate Mn(), Fe() and Co() deriv-
atives have been synthesised by reaction of bulky β-diketimine
ligands and the appropriate metal silylamide [M{N(SiMe3)2}2]
(M = Mn, Fe and Co).8–10 In the same manner, reaction of
[CH (Ph P᎐NC H Me -2,4,6) ] and [M{N(SiMe ) } ] in toluene
᎐
2
2
6
2
3
2
3 2 2
afforded the formally 11-, 12- and 13-electron amido derivatives
[{CH(Ph2PNC6H2Me3-2,4,6)2}MN(SiMe3)2], compounds 2 (M
= Mn), 3 (M = Fe) and 4 (M = Co) (Scheme 1). The three
compounds were isolated as colourless (compounds 2 and 3)
and green (compound 4) crystalline solids from toluene
solutions. Their solution magnetic moments (Evans’ method,
298 K) were determined in C6D6 and afforded values consistent
with high spin d5 (2, µB = 5.80), d6 (3, µB = 5.25) and d7 (4, µB =
4.90) electron configurations with five, four and three unpaired
electrons, respectively. These values are similar to those
reported for the closely related β-diketiminate derivatives,
[IM]N(SiMe3)2.2e Recrystallisation from concentrated toluene
solution provided crystals of 2–4 suitable for single crystal
X-ray diffraction analysis. The molecular structures are illus-
trated in Figs. 2–4, while details of the X-ray analyses and
selected bond lengths and angles are listed in Tables 1 and 2,
respectively.
Scheme 1 Reagents and conditions for the synthesis of 1–5. 1:
(i) n-BuLi, THF; (ii) FeCl2. 2–4: (iii) [M{N(SiMe3)2}2], toluene; 2,
M = Mn; 3, M = Fe; 4, M = Co. 5: (iv) Ph3COH, toluene.
In all three compounds 2–4 the metal is bound to one
bis(phosphinimino)methyl and a single N(SiMe3)2 ligand. The
N(1)–N(2)–N(3)–M coordination planes reveal in each case a
very minor pyramidalisation of the metal centre (Σangles = 2:
356.16Њ; 3: 359.45Њ; 4: 358.93Њ). Compound 3 is unambiguously
three-coordinate. The lower coordination number of the iron
atom causes the Fe–N(1) and Fe–N(2) bond lengths in 3
[1.992(3), 1.997(3) Å] to decrease in comparison to 1. Although
there is a slight decrease of ligand bite angle in 3 [106.99(11)Њ]
compared to that of 1 this value, as are the N(1)–M–M(2) bond
angles in the analogous Mn and Co derivatives [2: 109.16(9)Њ; 4:
110.87(12)Њ], is some 10–15Њ wider than the corresponding
bite angles of three coordinate β-diketiminate derivatives con-
taining the same metal and coligand.2e The remaining inter-
ligand angles around the metal centres are, as a consequence,
more acute and show less overall variation. Although the
M–N(3) distances [2: 2.012(2); 3: 1.932(3); 4: 1.934(3) Å] are
within the range previously observed in three-coordinate
Fig. 1 Molecular structure of 1. Hydrogen atoms omitted for clarity,
thermal ellipsoids at 50% probability.
that coordination to the distorted tetrahedral iron centre is pro-
vided by two nitrogen atoms of the chelated ligand and two
chlorides which bridge to lithium. There is a significant widen-
ing of the N(1)–Fe–N(2) angle in 1 [110.11(13) vs. 93.21(14)Њ]
that results, most likely, from the differing steric demands of the
D a l t o n T r a n s . , 2 0 0 3 , 5 7 0 – 5 7 4
571

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Table 2 Selected bond lengths (Å) and angles (Њ) for compounds 1–5
1
2
3
4
5
M–N(1)
M–N(2)
M–Cl/N(3)/O
P(1)–N(1)
P(2)–N(2)
P(1)–C(1)
P(2)–C(1)
2.025(3)
2.046(3)
2.110(2)
2.124(2)
2.012(2)
1.618(2)
1.609(2)
1.735(3)
1.717(3)
1.992(3)
1.997(3)
1.932(3)
1.632(3)
1.620(3)
1.710(4)
1.706(4)
1.996(3)
1.997(3)
1.934(3)
1.616(3)
1.618(3)
1.729(4)
1.735(4)
2.083(2)
2.1096(19)
1.8558(16)
1.614(2)
1.603(2)
1.739(3)
1.737(2)
2.371(1)a 2.368(1)b
1.632(3)c
1.636(3)d
1.706(4)
1.722(4)
N(1)–M–N(3)
N(2)–M–N(3)
N(1)–M–N(2)
M–N(1)–P(1)
M–N(2)–P(2)
N(1)–P(1)–C(1)
N(2)–P(2)–C(1)
P(1)–C(1)–P(2)
119.23(10)e 108.05(10)f
110.41(10)g 112.69(10)h
110.11(13) 95.61(4)i
123.06(18)
108.66(16)
109.63(19)
120.27(9)
126.76(9)
109.16(9)
104.62(11)
104.99(11)
107.10(14)
106.12(14)
130.73(18)
125.37(12)
127.09(12)
106.99(11)
117.02(15)
117.54(15)
111.40(16)
109.46(16)
136.2(2)
126.00(13)
122.06(13)
110.87(12)
101.73(16)
102.97(16)
106.65(17)
105.34(18)
133.5(2)
132.17(8)j
123.32(8)k
103.25(8)
95.48(9)
96.57(9)
106.77(11)
103.90(11)
128.23(15)
117.72(19)
125.2(3)
a Fe–Cl(1). b Fe–Cl(2). c P(2)–N(1). d P(1)–N(2). e N(1)–Fe–Cl(1). f N(1)–Fe–Cl(2). g N(2)–Fe–Cl(1). h N(2)–Fe–Cl(2). i C(1)–Fe–Cl(2). j N(1)–Fe–O.
k N(2)–Fe–O.
Fig. 2 Molecular structure of 2. Hydrogen atoms omitted for clarity,
thermal ellipsoids at 25% probability.
Fig. 4 Molecular structure of 4. Hydrogen atoms omitted for clarity,
thermal ellipsoids at 25% probability.
divalent manganese, iron and cobalt derivatives that are ter-
minally bonded to the N(SiMe3)2 ligand,11–13 they do not show
the expected sequence Mn–N > Fe–N > Co–N that would
be consistent with the decreasing size of the M2ϩ ions.14 The
observation that the Co–N(3) bond length of 4 is effectively
identical to that of the Fe–N(3) bond length of 3 may be related
to the more pronounced boat conformation of the chelating
bis(phosphinimino)methyl ligand adopted in the cobalt com-
plex (Fig. 5). This results in a significantly closer approach of
the C(1) methanide carbon to the cobalt centre in 4 [2.570 Å] in
comparison to the C(1)–Fe distance [3.177 Å] observed in 3 and
effectively increases the cobalt coordination number to four.
That this occurs without significant pyramidalisation at the
cobalt centre is surprising and may be related to the crowded
environment provided by the bulky bis(phosphinimino)methyl
and hexamethyldisilazide ligands. A shortening of the C(1)–M
distance also occurs in the manganese analogue 2 [2.689 Å].
We have recently observed such ligand distortions in a series
of three-coordinate zinc compounds of IV,15 while Cavell
and coworkers have reported several structurally similar zinc
and aluminium derivatives of a bis(phosphinimino)methyl
Fig. 3 Molecular structure of 3. Hydrogen atoms omitted for clarity,
thermal ellipsoids at 25% probability.
ligand bearing trimethylsilyl substituents.16 At present we
D a l t o n T r a n s . , 2 0 0 3 , 5 7 0 – 5 7 4
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Fig. 6 The molecular structure of 5. Hydrogen atoms omitted for
clarity, thermal ellipsoids at 25% probability.
coordination plane in 5 (Σangles = 359.24Њ). It is accompanied
however by a lengthening of the Fe–N bonds [2.083(2), 2.191(2)
Å] from the corresponding distances in the three-coordinate
compound 3. A number of structurally characterised bis(phos-
phinimino)methyl complexes have been shown to contain direct
metal to methanide carbon bonds including the closely related
i
complex [NiBr{HC(Ph2PNC6H3 Pr2-2,6)2}].6 In this latter case,
the bromine atom is sufficiently small to allow the nickel
coordination geometry to adjust to square planar with a direct
Ni–C bond of 2.008(2) Å. In compound 5, the bulk of the
triphenylmethoxy substituent is apparently sufficient to prevent
such a dramatic structural distortion and the formation of an
iron to carbon bond that would be more typical of four-
coordinate iron() alkyls (<2.15 Å).19
Fig. 5 The N–P–C–P–N–M chelate cores of (a) 2, (b) 3 and (c) 4
emphasising the M–C(1) contact of compounds 2 and 4. For 2, 3 and 4
the respective angles defined by the P(1)–C(1)–P(2) and N(1)–M–N(2)
least square planes and the P(1)–N(1)–P(2)–N(2) plane are; 2: 61.25,
54.36Њ; 3: 24.01, 37.87Њ; 4: 51.47, 64.89Њ.
believe that this structural feature is most straightforwardly
rationalised as a consequence of the substantial carbanionic
character of the methanide centre C(1). The ligand frameworks
of 2, 3 and 4 nevertheless provide evidence for considerable
delocalisation of charge via the P–N linkages. The P–C(1)
(Table 2) bonds are shortened in comparison to typical P–C σ
bonds while the P–N bond (Table 2) distances are elongated
compared to the corresponding values of structurally charac-
Although the lack of any appreciable pyramidalisation at
iron in 5 mitigates against the formulation of this Fe–C(1)
contact as being directly coordinative, one of us (D. J. E.) has
demonstrated previously that longer range (<2.5 Å) inter-
actions in low-coordinate iron complexes are important in
assigning coordination number and geometry. Such long
range interactions can have a significant effect on the electron
density and electric field gradient experienced by the iron
nucleus and may be examined by 57Fe Mössbauer spectro-
scopy.20 The observed i.s. and q.s. parameters for compound 3
of 0.57 mm sϪ1 and 0.89 mm sϪ1 respectively fall within the
established range for truly three-coordinate iron (e.g. for
[Fe{N(SiMe3)2}2]2, i.s. = 0.58 mm sϪ1, q.s. = 1.02 mm sϪ1).19 On
the other hand the parameters for compound 5 (i.s. = 0.96 mm
terised bis(phosphinimino)methanes [e.g. for [H C(Ph P᎐
᎐
2
2
NSiMe3)2] P–C(1) = 1.825(1); P–N = 1.536(2) Å].17
We have previously observed that Zn() analogues of com-
pounds 2–4 may be reacted with sterically demanding phenols
and alcohols to form three-coordinate aryloxy- and alkoxy-zinc
derivatives supported by the bidentate ligand IV.15 Such com-
pounds are of interest as potential catalysts for the living ring
opening polymerisation of cyclic esters such as rac-lactide.18 As
catalysts based upon ferric alkoxides have also been reported to
mediate polymer formation in a controlled manner, we have
begun to explore whether a similar protolytic strategy will
enable the synthesis of comparable systems based on iron().
Consequently, reaction of 3 with triphenylmethanol in toluene
affected clean elimination of (Me3Si)2NH and the formation of
s
Ϫ1, q.s. = 2.02 mm sϪ1) are significantly larger, consistent with
an increased coordination number and asymmetry at the iron
nucleus.
In conclusion, we have demonstrated that the coordination
environment provided by IV is suitable for the support of low
coordinate d5–d7 first row transition metal centres. The ligand
framework allows considerable conformational adjustment
with variation of co-ligand identity and a transition from
bidentate to effectively tridentate coordination. Compound
5 includes a direct contact from iron to the methanide carbon
of the ligand, which results in significant perturbation to the
electronic environment of the iron centre without significant
pyramidalisation of the otherwise planar geometry.
The prospect of being able to fine tune the coordination
geometry of low coordinate centres in this manner offers great
potential for the subtle adjustment of the local metal
environment. We are continuing to study the chemistry of
these and related systems to determine whether these observ-
ations are essentially electronic or steric in origin and are
exploring the possibility of tuning the strength of the weak
[{CH(Ph2PNC6H2Me3-2,4,6)2}FeOCPh3], compound 5 (µeff
=
5.10 µB, 298 K, C6D6), in high yield. Crystallisation from tolu-
ene gave 5 as analytically pure yellow crystals suitable for an
X-ray analysis. The molecular structure is illustrated in Fig. 6,
while details of the X-ray analysis and selected bond lengths
and angles are listed in Tables 1 and 2, respectively.
The most notable feature of 5 is the pronounced boat con-
formation adopted by the bis(phosphinimino)methyl ligand,
which allows a close Fe–C(1) contact of 2.375 Å and the adop-
tion of an unusual trigonal pyramidal geometry. As was noted
for the manganese and cobalt derivatives, 2 and 4, this inter-
action causes little disruption to the planarity of the ON2M
D a l t o n T r a n s . , 2 0 0 3 , 5 7 0 – 5 7 4
573

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axial interaction provided by the methanide carbon centre of
bulky bis(phosphinimino)methyl ligands.
Crystal structure determinations
Data were collected at 173 K on a Nonius Kappa CCD dif-
fractometer, λ(Mo-Kα) = 0.71073 Å; details are given in Table
1. The structures were solved by direct methods (SHELXS-
97)22 and refined by full matrix least squares (SHELXL-97)23
with non-H atoms anisotropic and H atoms included in riding
mode.
CCDC reference numbers 191080–191082 and 198768–
198769.
See http://www.rsc.org/suppdata/dt/b2/b210467a/ for crystal-
lographic data in CIF or other electronic format.
Experimental
All reactions were conducted under an atmosphere of dry
argon and manipulated either on a double manifold vacuum
line or in a dinitrogen-filled drybox operating at less than 1 ppm
of O2. Toluene was purified by distillation from molten
sodium and diethyl ether from sodium/benzophenone ketyl.
[M{N(SiMe3)2}2] (M = Mn, Fe, Co),8–10 mesityl azide21 and IV6
were synthesised by literature procedures. Mass spectra were
obtained at 70 eV. Mössbauer spectra, recorded at 77 K, in zero
magnetic field, on an ES-Technology MS-105 spectrometer
with a 75 MBq 57Co source in a rhodium matrix at ambient
temperature, were referenced to a 25 µm iron foil at 298 K and
spectral parameters obtained by fitting of Lorentzian curves.
Solid samples were prepared by grinding with boron nitride
under an atmosphere of dinitrogen. Elemental analyses were
performed by SACS at the University of North London.
Acknowledgements
The Royal Society is thanked for the provision of a University
Research Fellowship (MSH) and the BBSRC are thanked for
funding (D. J. E).
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Chem. Soc., 2002, 124, 3012; (d ) T. J. J. Sciarone, A. Meetsma,
B. Hessen and J. H. Teuben, Chem. Commun., 2002, 1580;
(e) A. Panda, M. Stender, R. J. Wright, M. M. Olmstead, P. Klavins
and P. P. Power, Inorg. Chem., 2002, 41, 3909.
[{CH(Ph2PNC6H2Me3-2,4,6)2}Fe(ꢀ-Cl)2Li(OEt2)(THF)] 1
A solution of IVLi, prepared in THF (25 mL) from IV (0.75 g,
1.15 mmol) and n-BuLi (1.15 mmol), was added at Ϫ78 ЊC to
a stirred suspension of FeCl2 (0.15 g, 1.18 mmol) in THF
(25 mL). This was allowed to warm to room temperature to give
a light brown solution. Filtration to remove a small amount of
suspended solid, followed by removal of solvent and crystallis-
ation from Et2O (30 mL) at Ϫ30 ЊC produced 1 as large colour-
less crystals. (Yield 59%). Anal. Calc. for C51H61Cl2N2P2O2-
LiFe: C 65.83, H 6.56, N 3.01; Found: C 65.59, H 6.45, N
2.86%. MS (m/z): 740 [L3FeCl2ϩ]. 57Fe Mössbauer; i.s. = 0.93
3 M. K. Chan, J. Kim and D. C. Rees, Science, 1993, 260, 792.
4 O. Einsle, F. A. Tezcan, S. L. A. Andrade, B. Schmid, M. Yoshida,
J. B. Howard and D. C. Rees, Science, 2002, 297, 1696.
mm sϪ1, q.s. = 3.54 mm sϪ1, Γ = 0.12 mm sϪ1
.
½
5 See, for example: (a) M. S. Hill and P. B. Hitchcock, Angew. Chem.,
Int. Ed., 2001, 40, 4089; (b) M. S. Hill and P. B. Hitchcock,
Organometallics, 2002, 21, 220; (c) M. S. Hill and P. B. Hitchcock,
Organometallics, 2002, 21, 3258.
6 S. Al-Benna, M. J. Sarsfield, M. Thornton-Pett, D. L. Ormsby,
P. J. Maddox, P. Brès and M. Bochmann, J. Chem. Soc.,
Dalton Trans., 2000, 4247.
[{CH(Ph2PNC6H2Me3-2,4,6)2}MN(SiMe3)2] (M ؍ Mn 2, Fe 3,
Co 4)
These compounds were prepared by the same general method.
A solution of [CH (Ph P᎐NC H Me -2,4,6) ] (1.00 g, 1.54
᎐
2
2
6
2
3
2
mmol) in toluene (20 mL) was added at room temperature
to an equimolar solution of the appropriate silylamide,
[M{N(SiMe3)2}2] in toluene (20 mL). In the case of the iron
derivative this produced an immediate darkening of the
solution and a colour change from green to red/brown. The
solutions were stirred for 14 h at which point they were
concentrated to incipient crystallisation (ca. 5 mL). 2, 3 and 4
were crystallised by slow cooling of this solution from 60 ЊC
and isolated as large colourless (2, 3) or green (4) crystals in ca.
60–70% yields. 2: Anal. Calc. for C49H61N3P2Si2Mn: C 68.03, H
7.12, N 4.86; Found: C 68.02, H 7.23, N 4.71%. MS (m/z): 864
[Mϩ], 849, 793, 740, 703 [L3Mnϩ], 440. 3: Anal. Calc. for
C49H61N3P2Si2Fe: C 67.96, H 7.11, N 4.85; Found: C 68.06,
H 7.06, N 4.80%. MS (m/z): 865 [Mϩ], 704 [L3Feϩ]. 57Fe
7 See for example: (a) S. L. Stokes, W. M. Davies, A. L. Odom and
C. C. Cummins, Organometallics, 1996, 15, 4521; (b) C. D.
Burbridge and D. M. L. Goodgame, J. Chem. Soc. A, 1967, 694.
8 H. Bürger and U. Wannagat, Monatsh. Chem., 1963, 94, 1007.
9 H. Bürger and U. Wannagat, Monatsh. Chem., 1964, 95, 1099.
10 R. A. Andersen, K. Faegri, J. C. Green, A. Haarland, M. F. Lappert,
W.-P. Leung and K. Rypdal, Inorg, Chem., 1988, 27, 1782.
11 D. C. Bradley, M. B. Hursthouse, K. M. A. Malik and R. Moseler,
Transition Met. Chem., 1978, 3, 353.
12 (a) P. P. Power and B. D. Murray, Inorg. Chem., 1984, 23, 4584;
(b) U. Siemeling, U. Vorfeld, B. Neumann and H.-G. Stammler,
Inorg. Chem., 2000, 39, 5159 and references therein.
13 M. M. Olmstead, P. P. Power and S. C. Shoner, Inorg. Chem., 1991,
30, 2547.
14 R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751.
15 M. S. Hill and P. B. Hitchcock, J. Chem. Soc., Dalton Trans., 2002,
4694.
16 (a) A. Kasani, R. McDonald and R. G. Cavell, Organometallics,
1999, 18, 3775; (b) K. Aparna, R. McDonald, M. Ferguson and
R. G. Cavell, Organometallics, 1999, 18, 4241; for a general review of
iminophosphorane coordination chemistry, see; (c) A. Steiner,
S. Zacchini and P. I. Richards, Coord. Chem. Rev., 2002, 227, 193.
17 A. Müller, M. Möhlen, B. Neumüller, N. Faza, W. Massa and
K. Dehnicke, Z. Anorg. Allg. Chem., 1999, 625, 1748.
18 General review of catalyst types in lactide polymerisation:
B. J. O’Keefe, M. A. Hillmyer and W. B. Tolman, J. Chem. Soc.,
Dalton Trans., 2001, 2215.
19 See for example: H. K. Lee, B.-S. Luo, T. C. W. Mak and
W.-P. Leung, J. Organomet. Chem., 1995, 489, C71.
Mössbauer; i.s. = 0.57 mm sϪ1, q.s. = 0.89 mm sϪ1, Γ
=
½
0.12 mm sϪ1. 4: Anal. Calc. for C49H61N3P2Si2Fe: C 67.72,
H 7.09, N 4.84; Found: C 67.68, H 6.98, N 4.84. MS (m/z): 869
[Mϩ], 707 [L3Coϩ], 574, 522, 440.
[{CH(Ph2PNC6H2Me3-2,4,6)2}FeOCPh3] 5
A solution of Ph3COH (0.12 g, 0.46 mmol) in toluene (15 mL)
was added at room temperature to a stirred solution of 3 in
toluene (15 mL). This produced a colour change from colour-
less to pale yellow. After stirring had been continued for 13 h,
the solution was concentrated to incipient crystallisation and 3
was isolated as large pale yellow crystals by slow cooling from
60 ЊC. (Yield 75%). Anal. Calc. for C62H58N2P2OFe: C 77.17,
H 6.07, N 2.90; Found: C 76.88, H 5.94, N 2.86%. MS (m/z):
20 D. J. Evans, D. L. Hughes and J. Silver, Inorg. Chem., 1997, 36, 747.
21 I. Ugi, H. Perlinger and L. Behringer, Chem. Ber., 1958, 91, 2324.
22 G. M. Sheldrick, SHELXS-97, Program for the Solution of Crystal
Structures, Göttingen, 1997.
23 G. M. Sheldrick, SHELXL-97, Program for the Refinement of
Crystal Structures, Göttingen, 1997.
965 [Mϩ], 705 [L3Fe]. 57Fe Mössbauer; i.s. = 0.96 mm sϪ1
,
q.s. = 2.02 mm sϪ1, Γ = 0.12 mm sϪ1
.
½
D a l t o n T r a n s . , 2 0 0 3 , 5 7 0 – 5 7 4
574