Low coordinate lanthanide(II) complexes supported by bulky guanidinato and amidinato ligands

Article abstract of DOI:10.1039/b924367d

The preparation of a series of homoleptic, four-coordinate lanthanide(ii) complexes, [Ln(Priso)₂] (Ln = Sm, Eu or Yb) incorporating the bulky guanidinate ligand Priso^- ([(ArN)₂CNPrⁱ ₂]^-, Ar = 2,6-diisopropylphenyl) is described. X-ray crystallography shows the complexes to be isostructural and to exhibit coordination geometries midway between tetrahedral and planar. Comparisons between the geometries of the complexes and those of the bulkier systems, [Ln(Giso)₂] (Giso^- = [(ArN)₂CNCy ₂]^-, Cy = cyclohexyl) are discussed. Attempts to prepare the less hindered amidinate complexes, [Ln(Piso)₂] (Piso^- = [(ArN)₂CBu^t]^-), were not successful, but did give rise to the heteroleptic complex, [(κ¹-N, η⁶-Piso)Sm(THF)(μ-I)₂Sm(κ¹-N, η⁶-Piso)]. Whereas the amidinate ligands in this complex chelate the samarium centre in an κ¹-N,η⁶-Ar-fashion, in the closely related complex, [{(κ²-N,N′-Priso)Yb(THF) (μ-I)}₂], the ytterbium atoms are κ²-N,N′- chelated by the guanidinate ligand. The facility of the planar four-coordinate complex, [Sm(Giso)₂], to act as a one-electron reducing agent towards a variety of unsaturated substrates has also been explored. The complex has been shown to selectively reductively couple CS₂, via a C-S bond formation, to give the samarium(iii) dimer, [(Giso)₂Sm(μ- η²-:η²-S₂CSCS)Sm(Giso)₂]. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b924367d

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Low coordinate lanthanide(II) complexes supported by bulky guanidinato and
amidinato ligands†‡
Dennis Heitmann,a Cameron Jones,*b David P. Millsa,b and Andreas Staschb
Received 19th November 2009, Accepted 11th December 2009
First published as an Advance Article on the web 7th January 2010
DOI: 10.1039/b924367d
The preparation of a series of homoleptic, four-coordinate lanthanide(II) complexes, [Ln(Priso)2] (Ln =
Sm, Eu or Yb) incorporating the bulky guanidinate ligand Priso- ([(ArN)2CNPri2]-, Ar =
2,6-diisopropylphenyl) is described. X-ray crystallography shows the complexes to be isostructural and
to exhibit coordination geometries midway between tetrahedral and planar. Comparisons between the
geometries of the complexes and those of the bulkier systems, [Ln(Giso)2] (Giso- = [(ArN)2CNCy2]-,
Cy = cyclohexyl) are discussed. Attempts to prepare the less hindered amidinate complexes, [Ln(Piso)2]
(Piso- = [(ArN)2CBut]-), were not successful, but did give rise to the heteroleptic complex,
1
6
1
6
[(k -N,h -Piso)Sm(THF)(m-I)2Sm(k -N,h -Piso)]. Whereas the amidinate ligands in this complex
1
6
chelate the samarium centre in an k -N,h -Ar-fashion, in the closely related complex,
2
2
[{(k -N,N¢-Priso)Yb(THF)(m-I)}2], the ytterbium atoms are k -N,N¢-chelated by the guanidinate
ligand. The facility of the planar four-coordinate complex, [Sm(Giso)2], to act as a one-electron
reducing agent towards a variety of unsaturated substrates has also been explored. The complex has
been shown to selectively reductively couple CS2, via a C–S bond formation, to give the samarium(III)
2
2
dimer, [(Giso)2Sm(m-h -:h -S2CSCS)Sm(Giso)2].
chelated ytterbium complex, 4, was also detailed. Remarkably,
this was found to eliminate its coordinated THF molecule in the
solid state under reduced pressure to give complex 5 in which the
ytterbium centre is k -N,h -chelated. This process was found to be
reversible.
Introduction
The chemistry of amidinato and guanidinato complexes of the
lanthanide metals in the +3 oxidation state has rapidly developed
in recent decades.1,2 The interest in such compounds stems from
the many applications they have found in, for example, homo-
geneous catalysis and as materials precursors.1,2 In comparison,
lanthanide(II) amidinate and guanidinate complexes are rare,2,3
despite the significant potential they possess as one-electron
1
6
4
reducing agents in organic and inorganic syntheses (cf. SmI2
5
and SmCp*2 ). Rarer still are homoleptic four-coordinate exam-
ples of this compound class, the first structurally characterised
representatives of which, 1-3, were reported by us in a prelim-
inary communication in 2007.6 The coordinatively unsaturated
nature of these complexes is almost certainly derived from their
extremely bulky guanidinate ligands, Giso- ([(ArN)2CNCy2]-,
Ar = 2,6-diisopropylphenyl, Cy = cyclohexyl). Noteworthy is
the fact that 1 and 2 were the first examples of complexes to
exhibit planar four-coordinate lanthanide geometries,7 whereas
the distorted tetrahedral ytterbium geometry exhibited by 3,
had been previously described for related bulky b-diketiminate
(Nacnac) complexes, [Yb(Nacnac)2].8,9 In our initial report, the
While the origins of the differences between the coordination
geometry of 3 and those of 1 and 2 are unknown, the considerably
smaller Ln2+ ionic radius of Yb relative to those of the other
2+
two metals (values for six-coordinate Ln2+: Sm2+ 1.19 A, Eu
2
˚
preparation and characterisation of the heteroleptic k -N,N¢-
2+
10
˚
˚
1.17 A, Yb 1.02 A ) must play a part. In addition, the substantial
steric bulk of the Giso- ligand presumably has an influence. In
order to probe the level of this influence, it seemed appropriate
to prepare analogues of 1-3, but with marginally smaller ligand
backbone substituents. The guanidinate, Priso- ([(ArN)2CNPri2]-),
and the amidinate, Piso- ([(ArN)2CNBut]-), were chosen for this
purpose, as we have previously shown that the subtle decrease
in ligand bulk in the series Giso- > Priso- > Piso- can lead to
significant differences in the chemistry of low oxidation state s-,
p- and d-block metal complexes incorporating these ligands.11,12
aSchool of Chemistry, Main Building, Cardiff University, Cardiff, UK CF10
3AT
bSchool of Chemistry, PO Box 23, Monash University, VIC, 3800, Australia.
E-mail: cameron.jones@sci.monash.edu.au
† Dedicated to Professor David W. H. Rankin on the occasion of his
retirement.
‡ Electronic supplementary information (ESI) available: ORTEP diagrams
for 7 and 8. CCDC reference numbers 755335–755340 (6-11). For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b924367d
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◦
˚
The results of our efforts in this direction are reported here, as is
a demonstration of the use of 1 as a one-electron reducing agent.
Table 1 Selected bond lengths (A) and angles ( ) for 6-8 (Ln = Sm, Eu
or Yb)
6
7
8
Results and discussion
Ln-N
2.507(2)
2.515(3)
1.353(3)
1.332(3)
1.397(5)
1.403(5)
52.8(1)
53.8(1)
113.5(3)
114.3(4)
2.496(2)
2.503(2)
1.340(3)
1.350(3)
1.399(4)
1.400(4)
53.33(9)
53.96(9)
113.2(3)
114.5(3)
2.376(3)
2.390(3)
1.341(4)
1.348(4)
1.390(5)
1.397(5)
55.8(1)
55.8(1)
112.0(4)
114.2(4)
The 2 : 1 reactions of [K(Priso)] with THF solutions of LnI2 (Ln =
Sm, Eu or Yb) afforded low to moderate yields (ca. 30-50%) of the
deeply coloured homoleptic complexes, 6-8, after recrystallisation
from hexane (Scheme 1). As was the case with 1-3, there was
no evidence for the coordination of THF to the metal centres of
the isolated complexes, despite the reactions being carried out
in that solvent. This contrasts with the 2 : 1 reaction of SmI2
with the sodium salt of the smaller formamidinate ligand, Fiso-
([(ArN)2CH]-), which gave the octahedral samarium(II) complex,
[Sm(Fiso)2(THF)2].3c The reactions that gave 6-8 were not clean
and generated significant amounts of the guanidine, PrisoH, by an
unknown process. In addition, the reaction that gave 8 also led to a
very low yield of the heteroleptic complex, 9 (cf. 4). Less successful
were the 2 : 1 reactions of [K(Piso)] with LnI2 in THF, which in no
instance led to isolated complexes of the type [Ln(Piso)2]. However,
a few crystals of the heteroleptic complex, 10, were obtained from
the reaction with SmI2. A rational synthesis of 10, involving the
treatment of SmI2 with ca. one equivalent of [K(Piso)] in THF,
gave an increased, but still low yield (14%) of the complex.
C–N(Ar)
C–N(Pri)2
N-Ln-N
(Ar)N–C–N(Ar)
[Yb(Nacnac)2] complexes in the range d 2650 200 ppm,8b though
these are generally very broad and sometimes not observable.
Considering the difficulties with spectroscopically character-
ising 6-10, the X-ray crystal structures of all complexes were
determined. As compounds 6-8 are isostructural, only the molec-
ular structure of 6 is depicted in Fig. 1, while selected metrical
parameters for each complex are collected in Table 1. The dihedral
angles between the CN2Ln least squares planes in the complexes
(6 46.5◦, 7 47.2◦, 8 47.4◦) show them to have metal coordination
geometries almost mid-way between planar and tetrahedral. These
values differ to those of close to planar 1 (1.4◦) and 2 (1.7◦), and
heavily distorted tetrahedral 3 (58.2◦).6 Consequently, it is clear
that small changes in the steric profile of the backbone substituents
of the guanidinate ligand can have a substantial effect on the
geometry of homoleptic lanthanide(II) complexes. That said, the
effect of crystal packing forces may also be influential, given the
ionic nature of the N-Ln interactions in the complexes. There
appears to be delocalisation over the coordinated NCN fragments
of the complexes, and their N-Ln bond distances decrease in the
series Ln = Sm > Eu > Yb, as expected based on the Ln2+ ionic
radii of the metals.
Scheme 1 i) 2 [K(Priso)], THF, -2 KI; ii) Ln = Sm, [K(Piso)], THF, -KI.
Due to the paramagnetic nature of 6, 7 and 10, no useful
information could be obtained from their NMR spectra. The
1
1H and 13C{ H} NMR spectra of 8 and 9 all display very broad
resonances, as was the case for the spectra of 3 and 4. Attempts to
examine the origin of the signal broadening in both compounds
using variable temperature NMR studies were thwarted by their
low solubility in D8-toluene below ambient temperature. However,
examination of the solid state structure of 8 (vide infra) suggests
that in this case the broadening may be due to restricted rotation
of its interlocked bulky Ar groups and/or the aryl isopropyl
Fig. 1 Molecular structure of 6 (25% thermal ellipsoids are shown;
hydrogens omitted). Symmetry operation: ¢y, x, -z.
1
substituents. No signals were observed in the 171Yb{ H} NMR
The molecular structures of 9 and 10 are shown in Fig. 2
and 3 respectively. Complex 9 possesses heavily distorted trigonal
bipyramidal ytterbium centres that are symmetrically bridged by
spectra of saturated samples of either complex. In comparison,
signals have been reported in the spectra of closely related
1878 | Dalton Trans., 2010, 39, 1877–1882
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1
the bulk of the ligands involved, but it is worth noting that k -
6
N,h -chelation of ytterbium(II) centres has also been observed in
the THF free complex 5.6 The iodide ligands of 10 effectively
symmetrically bridge its two samarium centres, each of which has
1
6
an h -interaction with an amido centre, and an h -interaction with
an Ar-substituent of the Piso- ligand. Moreover, the Sm(1) centre
of the complex is additionally coordinated by a molecule of THF. It
is likely that coordination of the other samarium atom by THF
is disfavoured for steric reasons. The lengths of all interactions
to each samarium atom are in the normal ranges,13 while the CN2
fragments of the amidinate ligands appear to be significantly more
2
localised than those in any of the k -N,N¢-chelated complexes, 6-9.
It has been proposed that the planar four-coordinate geometries
of the samarium(II) compound 1 could lend it to use in one-
electron reductions of small unsaturated substrates that can access
the “vacant” sites above and below the coordination plane of
the complex.6,14 If this were the case, the possibility exists that
the unique steric profile of the complex might lead to reduction
product selectivities that differ compared to those previously
observed for other lanthanide(II) reducing agents, e.g. SmI2 and
SmCp*2.4,5 To test these possibilities, toluene solutions of 1 were
treated with a variety of substrates. No reactions occurred with
Fig.
2 Molecular structure of 9 (25% thermal ellipsoids are
˚
shown; hydrogens omitted). Selected bond lengths (A) and angles
(◦): Yb(1)-N(2) 2.364(10), Yb(1)-N(1) 2.425(9), Yb(1)-O(1) 2.427(10),
Yb(1)-I(1) 3.0946(14), Yb(1)-I(1)¢ 3.1347(16), N(1)-C(1) 1.332(17),
C(1)-N(2) 1.364(15), C(1)-N(3) 1.400(16); N(2)-Yb(1)-N(1) 55.4(3),
I(1)-Yb(1)-I(1)¢ 89.82(3), N(1)-Yb(1)-O(1) 145.0(4), N(2)-Yb(1)-O(1)
95.4(3), O(1)-Yb(1)-I(1) 90.3(3), O(1)-Yb(1)-I(1)¢ 90.1(3). Symmetry op-
eration: ¢ -x+1, -y+1, -z+1.
t
t
t
t
= =
=
≡
Bu CN, Bu CNS, Bu CNO, CyN C NCy, PhN NPh, Bu C P
t
=
or {(Bu )N C(H)}2, despite the fact that there are many reports
of SmII reductions of such substrates in the literature.4,5 While at
first glance this may seem surprising, it should be remembered that
the “vacant” Sm coordination sites of 1 are not occupied by THF,
despite this being the solvent used in its preparation. Therefore, it
seems logical that only substrates less sterically demanding than
THF will be able to coordinate the Sm centre of 1 prior to their
reduction.
One such substrate is carbon monoxide which has previously
been shown to be reductively coupled by the Cp*2Sm fragment.15
In contrast, toluene solutions of compound 1 were found not
react with CO at atmospheric pressure and temperatures up to
◦
80 C. Attention then turned to CO2 as a linear, and potentially
Fig.
3
Molecular structure of 10 (25% thermal ellipsoids are
˚
more reactive, substrate. Previous studies into its reactivity with
[Cp*2Sm(THF)2] revealed that it is reductively coupled to give
the oxalate complex, [(Cp*2Sm)2(m-h :h -O2CCO2)].16 Conversely,
shown; hydrogens omitted). Selected bond lengths (A) and an-
gles (◦): Sm(1)-N(1) 2.552(4), Sm(1)-O(1) 2.605(4), Sm(1)-I(2)
3.2945(8), Sm(1)-I(1) 3.3218(8), Sm(1)-Ar-centroid 2.697(4), I(1)-Sm(2)
3.1972(8), Sm(2)-N(3) 2.483(4), Sm(2)-I(2) 3.2207(8), Sm(2)-Ar-centroid
2.603(4), N(1)-C(1) 1.363(6), C(1)-N(2) 1.310(6), N(3)-C(34) 1.345(6),
N(4)-C(34) 1.316(6); O(1)-Sm(1)-Ar-centroid 175.0(1), N(1)-Sm(1)-I(1)
143.22(10), N(1)-Sm(1)-I(2) 129.68(10), I(2)-Sm(1)-I(1) 86.416(15),
N(3)-Sm(2)-I(1) 132.68(10), N(3)-Sm(2)-I(2) 127.50(10), I(1)-Sm(2)-I(2)
89.790(15), I(1)-Sm(2)-Ar-centroid 105.4(1), I(2)-Sm(2)-Ar-centroid
112.2(1), N(3)-I(1)-Sm(2)-Ar-centroid 87.7(1), N(2)-C(1)-N(1) 120.7(5),
N(4)-C(34)-N(3) 120.8(5).
2
2
the samarium(II) complex reacts with COS to yield a dispro-
portionation product, [Cp*2Sm(m-h :h -S2CO)SmCp*2(THF)].16
Moreover, other very hindered samarium(II) complexes have been
shown to react with CO2 via reductive disproportionation, yielding
carbonate complexes and CO.17 In the current study compound
1 was found to rapidly react with excesses of either CO2 or COS,
but these reactions were not clean and yielded GisoH as the only
isolable product by an unknown process. Similarly, the fate of the
samarium in these reactions is presently unknown.
2
1
two iodide atoms. The coordinating NCN fragments of the com-
pound are largely delocalised and the apical Yb(1)-N(1) distances
(2.425(9) A) are significantly longer than the equatorial Yb(1)-
The reaction of 1 with carbon disulfide, CS2, was found to be
more controllable and under several stoichiometries (ca. 1 : 1, 1 : 2
or 1 : 10) led to the reductive coupling of CS2 and the formation
of the deep green complex 11 in a moderate isolated yield (55%)
(Scheme 2). The reductive coupling proceeds via formation of an
S–C bond, giving rise to the [SCSCS2]2- fragment which bridges
the two SmIII centres in 11. Although reductive couplings of CS2
have been reported on several occasions, these normally proceed
via the formation of a C–C bond (yielding [S2CCS2]2-),18 though
a small number of C–S couplings have been observed in reactions
with d-block metal complexes.19 It is possible that in the reaction
˚
˚
N(2) separations (2.364(10) A). The compound is isostructural
with 4 and is closely related to the dimeric, heteroleptic yt-
terbium(II) complex, [{[(Me3Si)2NC(NCy)2]Yb(THF)2(m-I)}2].3b
However, the smaller guanidinate ligand in that system allows
coordination of two THF molecules at its metal centres, giving it
an octahedral geometry. In contrast to 9 in which the ytterbium
2
centres are k -N,N¢-chelated, the samarium centres of 10 are
1
6
k -N,h -chelated by the amidinate ligand. It is unknown if this
difference arises from the variations in the size of the metals, or
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Fig. 4 Molecular structure of 11 (25% thermal ellipsoids are shown;
˚
hydrogens and isopropyl groups omitted). Selected bond lengths (A)
Scheme 2 i) CS2, toluene.
and angles (◦): Sm(1)-N(4) 2.386(5), Sm(1)-N(2) 2.416(5), Sm(1)-N(5)
2.455(5), Sm(1)-N(1) 2.486(5), Sm(1)-S(1) 2.979(10), Sm(1)-S(2) 2.998(5),
N(1)-C(3) 1.356(9), N(2)-C(3) 1.360(9), N(4)-C(40) 1.365(8), N(5)-C(40)
1.363(8), Sm(2)-N(7) 2.403(5), Sm(2)-N(10) 2.416(6), Sm(2)-N(8)
2.448(6), Sm(2)-N(11) 2.473(6), Sm(2)-S(4) 2.813(8), Sm(2)-C(2)
2.444(14), N(7)-C(77) 1.369(9), N(8)-C(77) 1.355(8), N(10)-C(114)
1.360(9), N(11)-C(114) 1.364(8), S(1)-C(1) 1.710(12), C(1)-S(2)
1.682(11), C(1)-S(3) 1.778(12), C(2)-S(4) 1.605(13), C(2)-S(3) 1.720(14);
N(2)-Sm(1)-N(1) 54.82(18), N(4)-Sm(1)-N(5) 55.50(19), S(1)-Sm(1)-S(2)
59.85(19), N(7)-Sm(2)-N(8) 55.11(19), N(10)-Sm(2)-N(11) 55.03(19),
C(2)-Sm(2)-S(4) 34.7(3), S(2)-C(1)-S(1) 123.0(8), S(2)-C(1)-S(3) 125.0(7),
S(1)-C(1)-S(3) 111.9(7), C(2)-S(3)-C(1) 113.6(6), S(4)-C(2)-S(3) 130.9(9).
with 1, the heavily sterically hindered Sm centre of the complex
only allows end-on coordination of the linear CS2 substrate, which
in turn may disfavour a subsequent C–C coupling of this substrate.
As 11 is paramagnetic, no meaningful data could be obtained
1
1
from its H and 13C{ H} NMR spectra. Accordingly, the X-ray
crystal structure of 11 was determined and its molecular structure
is highlighted in Fig. 4. Both of its Sm centres display distorted
octahedral coordination environments. One, Sm(1), is chelated
2
1
by a CS2 fragment (cf. [Cp*2Sm(m-h :h -S2CO)SmCp*2(THF)]16),
giving rise to a SmS2C four-membered ring, while the other, Sm(2),
2
has an h -interaction with a CS moiety. Because the [SCSCS2]2-
amidinate, Piso-, were not successful. These results reveal that
small changes in ligand sterics can have a significant effect on the
outcome of, and the geometry of products derived from, reactions
between bulky guanidinate/amidinate salts and lanthanide(II)
iodides. This study has also demonstrated that while the planar
complex, [Sm(Giso)2], is generally unreactive towards unsaturated
substrates, it does selectively reductively couple CS2 via a C–S bond
formation. We continue to explore the utility of bulky guanidinates
for stabilising low oxidation state/low coordination number metal
complexes.
ligand of the complex is disordered over two sites, and a number of
crystallographic constraints were imposed during the modelling
of this disorder in the crystallographic refinement, the metrical
parameters of the fragment should not be considered as fully
reliable. Therefore, it is difficult to confidently discuss the degree of
double bond delocalisation over the fragment. This said, the gross
molecular framework of the complex is unambiguous. The Giso-
ligands are ordered and a meaningful discussion of their geometry
is possible. As was the case with 1, the bond lengths within their
NCN backbones suggest a significant degree of delocalisation.
˚
The Sm–N bond lengths in 11 (2.435 A mean) are well within the
known range, but all are considerably shorter than those in the
Experimental section
˚
starting material, [Sm(Giso)2] 1 (2.546 A mean). This is a direct
result of the increase in the oxidation state of the samarium centres
upon reaction.
General considerations
All manipulations were carried out using standard Schlenk and
glove box techniques under an atmosphere of high purity argon
or dinitrogen. THF, hexane and toluene were distilled over potas-
sium. Melting points were determined in sealed glass capillaries
under argon and are uncorrected. Mass spectra were recorded
at the EPSRC National Mass Spectrometric Service at Swansea
University. Reproducible microanalyses could not be obtained for
compounds 6-9 as all consistently co-crystallised with significant
amounts of PrisoH, and the complete manual separation of PrisoH
from the compounds was not possible. Similarly, compound 10 co-
crystallised with PisoH. IR spectra were recorded using a Nicolet
Conclusion
In summary, a sterically bulky guanidinate ligand, Priso-, has
been utilised in the preparation of a series of homoleptic, four-
coordinate lanthanide(II) complexes, [Ln(Priso)2] (Ln = Sm, Eu or
Yb). These are isostructural and exhibit coordination geometries
between those of planar [Ln(Giso)2] (Ln = Sm or Eu) and
distorted tetrahedral [Yb(Giso)2], all of which bear the slightly
bulkier guanidinate ligand, Giso-. The attempted preparations
of the related complexes, [Ln(Piso)2], incorporating the smaller
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Table 2 Crystal data for compounds 6–11
Compound
6·(hexane)
7·(hexane)
8·(hexane)
9
10·(hexane)0.5
11·(toluene)4
Empirical Formula
FW
T/K
C68H110N6Sm
1161.97
150(2)
C68H110N6Eu
1163.58
150(2)
C68H110N6Yb
1184.66
150(2)
C70H112I2N6O2Yb2
1669.54
150(2)
C65H101I2N4O
1509.00
150(2)
C178H256N12S4Sm2
2992.89
150(2)
Cryst Syst
Space Group
tetragonal
P41212
14.203(2)
14.203(2)
33.354(7)
90
tetragonal
P41212
14.193(2)
14.193(2)
33.380(7)
90
tetragonal
P43212
13.983(2)
13.983(2)
33.631(7)
90
Monoclinic
P21/c
15.374(3)
10.524(2)
23.481(5)
90
105.23(3)
90
3665.5(13)
2
1.513
3.422
1672
10431
6079 (0.1200)
R1 = 0.0872
Monoclinic
P21/n
16.840(3)
10.807(2)
37.239(7)
90
97.64(3)
90
6717(2)
4
1.492
1.492
3028
20771
11672 (0.0428)
R1 = 0.0433
Monoclinic
P21/c
21.416(4)
18.051(4)
44.847(9)
90
102.99(3)
90
16893(6)
4
1.177
0.790
6384
49987
29126 (0.0976)
R1 = 0.0786
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
90
90
90
90
90
90
3
˚
Vol/A
Z
6728.8(19)
4
1.147
0.914
2488
6724.0(19)
4
1.149
0.974
2492
6576.2(19)
4
1.197
1.464
2520
Density (calcd) (Mg m-3)
m(Mo-Ka)/mm-1
F(000)
No. of reflections collected
No. of independent reflns (Rint)
Final R1 (I > 2s(I)) and wR2
indices (all data)
11764
11408
14101
5909 (0.0317)
R1 = 0.0367
5891 (0.0202)
R1 = 0.0271
7150 (0.0234)
R1 = 0.0359
wR2 = 0.0771
wR2 = 0.0594
wR2 = 0.0939
wR2 = 0.1800
wR2 = 0.0750
wR2 = 0.1764
510 FT-IR spectrometer as Nujol mulls between NaCl plates. 1H
overnight afforded orange-yellow crystals of 9 (yield: 0.10 g,
6% based on [K(Giso)]). Further concentration to ca. 4 cm3
and placement at -30 ◦C overnight gave green crystals of 8
(yield: 0.40 g, 32% based on [K(Giso)]). 8: Mp: 223-225 ◦C
(decomp.); 1H NMR (400.13 MHz, 300 K, C6D6): d = 0.40
(br, 24 H, NCH(CH3)2), 0.66 (br, 12 H, CH(CH3)2), 0.79 (br,
12 H, CH(CH3)2), 1.20 (br, 12 H, CH(CH3)2), 1.55 (br, 12 H,
CH(CH3)2), 3.85 (br, 4 H, CH(CH3)2), 4.08 (br, 8 H, CH(CH3)2
1
and 13C{ H} NMR spectra were recorded on a Bruker DPX400
spectrometer and were referenced to the resonances of the solvent
used. THF solutions of LnI2 (Ln = Sm, Eu or Yb),20 [K(Priso)],21
K[(Piso)]12b and [Sm(Giso)2]6 were prepared using variations of
literature procedures. All other reagents were used as received.
Preparation of [Sm(Priso)2] 6
1
and NCH(CH3)2), 7.03-7.42 (br m, 12 H, ArH); 13C{ H} NMR
SmI2 (13 cm3 of a 0.1 M solution in THF, 1.30 mmol) was added
to a solution of [K(Priso)] (2.50 mmol) in THF (30 cm3) at
-80 ◦C. The mixture was slowly warmed to room temperature
overnight with stirring. All volatiles were removed under reduced
pressure. The residue was extracted with hexane (80 cm3), filtered,
(100.6 MHz, 300 K, C6D6): d = 20.5 (br, NCH(CH3)2), 21.3
(br, CH(CH3)2), 22.5 (br, CH(CH3)2), 23.2 (br, CH(CH3)2), 25.1
(br, CH(CH3)2), 25.5 (br, CH(CH3)2), 26.4 (br, CH(CH3)2), 46.5
(br, NCH(CH3)2), 120.9, 122.0, 134.4, 140.0 (br, ArC), 165.4 (br,
CN3); IR n/cm-1 (Nujol): 1611 (s), 1582 (m), 1260 (m), 1108 (s),
1044 (m), 931 (m), 797 (m), 755 (m); MS/EI m/z (%): 1098.5
(M+, 1), 464.5 (PrisoH+, 100); accurate mass (EI), m/z: calc. for
C62H96N6170Yb (1094.7039), found (1094.7031). 9: Mp: 183-186 ◦C
◦
and the filtrate concentrated to ca. 12 cm3. Placement at -30 C
overnight afforded deep violet crysta◦ls of 6 (yield: 0.77 g, 53%
based on [K(Giso)]). Mp: 210-212 C (decomp.); IR n/cm-1
(Nujol): 1612 (s), 1583 (m), 1258 (m), 1179 (m), 1109 (m), 1043
(m), 930 (m), 859 (m), 796 (m), 754 (s), 661 (m); MS/EI m/z (%):
464.5 (PrisoH+, 100).
1
(decomp.); H NMR (400.13 MHz, 300 K, C6D6): d = 0.83 (br,
24 H, NCH(CH3)2), 1.24 (br, 24 H, CH(CH3)2), 1.41 (br, 32 H,
THF-CH2 and CH(CH3)2), 3.65 (br, 8 H, CH(CH3)2), 3.77 (br, 12
1
H, OCH2 and NCH(CH3)2), 6.80-7.22 (br, 12 H, ArH); 13C{ H}
Preparation of [Eu(Priso)2] 7
NMR (100.6 MHz, 300 K, C6D6): d = 21.8 (br, NCH(CH3)2), 23.1
(br, CH(CH3)2), 23.7 (br, CH(CH3)2), 26.8 (br, THF-CH2), 27.9
(br, CH(CH3)2), 49.0 (br, NCH(CH3)2), 69.1 (br, OCH2), 121.8,
123.8, 142.0, 146.4 (br, ArC), 164.5 (br, CN3); IR n/cm-1 (Nujol):
1611 (s), 1582 (m), 1260 (m), 1110 (s), 1018 (m), 861 (m), 797 (m),
755 (m); MS/EI m/z (%): 464.5 (PrisoH+, 100).
A procedure similar to that used to prepare 6 was employed for the
synthesis of orange-red crystalline 7 (yield: 46%). Mp: 201-203 ◦C
(decomp.); IR n/cm-1 (Nujol): 1611 (s), 1582 (m), 1258 (m), 1154
(s), 1043 (m), 930 (m), 861 (m), 796 (s), 753 (s), 661 (m); MS/EI
m/z (%): 464.5 (PrisoH+, 100).
Preparation of [Yb(Priso)2] 8 and
Preparation of [(j1-N,g6-Piso)Sm(THF)(l-I)2Sm(j1-N,g6-Piso)]
10
[{(j2-N,N¢-Priso)Yb(THF)(l-I)}2] 9
YbI2 (80 cm3 of a 0.02 M solution in THF, 1.60 mmol) was
added to a solution of [K(Priso)] (2.10 mmol) in THF (20 cm3)
at -80 ◦C. The mixture was slowly warmed to room temperature
overnight with stirring. All volatiles were then removed under
reduced pressure. The residue was extracted with hexane (60 cm3)
[K(Piso)] (3.10 mmol) in THF (20 cm3) was added to SmI2
(35.5 cm3 of a 0.1 M solution in THF, 3.55 mmol) at -80 ◦C. The
mixture was warmed to room temperature overnight with stirring.
Volatiles were then removed under reduced pressure and the
residue extracted with hexane (80 cm3). Concentration of the
extract to ca. 40 cm3 and subsequent placement at -30 ◦C overnight
◦
and the extract concentrated to ca. 30 cm3. Placement at -30 C
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Dalton Trans., 2010, 39, 1877–1882 | 1881
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afforded deep violet crystals of 10 (yield: 0.33 g, 14%). Mp: 218-
Fedorova, G. G. Skvortsov, G. K. Fukin, Y. A. Kurskii and M. N.
Bochkarev, Izv. Akad. Nauk SSSR, Ser. Khim., 2006, 422; (c) M. L.
Cole and P. C. Junk, Chem. Commun., 2005, 2695; (d) M. Wedler, M.
Noltemeyer, U. Pieper, H.-G. Schmidt, D. Stalke and F. T. Edelmann,
Angew. Chem., Int. Ed. Engl., 1990, 29, 894.
◦
220 C (decomp.); IR n/cm-1 (Nujol): 1614 (m), 1585 (m), 1259
(m), 1155 (m), 1108 (m), 1027 (m), 926 (s), 767 (s); MS/EI m/z
(%): 421.4 (PisoH+, 100).
4 See, for example (a) K. C. Nicolaou, S. P. Ellery and J. S. Chen, Angew.
Chem., Int. Ed., 2009, 48, 7140; (b) G. A. Molander and C. R. Harris,
Chem. Rev., 1996, 96, 307, and references therein.
5 See, for example (a) W. J. Evans and B. L. Davis, Chem. Rev., 2002, 102,
2119; (b) W. J. Evans, Polyhedron, 1987, 6, 803; and references therein.
6 D. Heitmann, C. Jones, P. C. Junk, K.-A. Lippert and A. Stasch, Dalton
Trans., 2007, 187.
7 Other examples have recently been described. C. L. Pan, X. Li
and H. Zhang, Chem. Eur. J. advance article published online,
10.1002/chem.200901991.
8 See, for example (a) S. Harder, Angew. Chem., Int. Ed., 2004, 43, 2714;
(b) A. G. Avent, P. B. Hitchcock, A. V. Khostov, M. F. Lappert and
A. V. Protchenko, Dalton Trans., 2003, 1070.
9 A related homoleptic, four-coordinate ytterbium(II) amidopyridine
complex, [Yb{NC5H3(NAr)-2-(C6H3Me2-2,6)-6}2], has also been re-
ported. S. Qayyum, K. Haberland, C. M. Forsyth, P. C. Junk, G. B.
Deacon and R. Kempe, Eur. J. Inorg. Chem., 2008, 557.
10 R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor.
Gen. Crystallogr., 1976, 32, 751. N.B. The, value for Sm2+ was obtained
by extrapolation.
Preparation of [(Giso)2Sm(l-g2-:g2-S2CSCS)Sm(Giso)2] 11
0.5 cm3 of a 1.66 M solution of CS2 in toluene (0.81 mmol) was
added to a suspension of [Sm(Giso)2] (0.40 g, 0.32 mmol) in toluene
(10 cm3) at -78 ◦C to give a deep green solution. The reaction
mixture was warmed to 20 ◦C and stirred for three hours. The
solution was concentrated to ca. 4 cm3, filtered and the filtrate
stored at -30 ◦◦C to give deep green blocks of 11 (0.24 g, 55%).
Mp: 131-133 C (decomp.); IR n/cm-1 (Nujol): 1612 (s), 1583
(s), 1322 (m), 1240 (m), 1013 (m), 933 (m), 894 (m), 794 (m),
778 (m); MS/EI m/z (%): 545 (GisoH+, 100); anal. calc. for
C178H256N12S4Sm2 (11·(toluene)4): C 71.43, H 8.62, N 5.62%; found:
C 71.31, H 8.56, N 5.49%.
X-ray crystallography
11 C. Jones, Coord. Chem. Rev., advance article published online,
Crystals of 6-11 suitable for X-ray structural determination were
mounted in silicone oil. Crystallographic measurements were
made using a Nonius Kappa CCD diffractometer. The structures
were solved by direct methods and refined on F2 by full matrix
least squares (SHELX9722) using all unique data. Hydrogen
atoms have been included in calculated positions (riding model)
for all structures. A discussion of the crystallographic disorder
encountered for the structure of 11 can be found in its CIF file in
the ESI. The absolute structure parameters for 6-8 are 0.198(12),
0.009(9) and 0.182(12) respectively. Crystal data, details of data
collections and refinement are given in Table 2.
10.1016/j.ccr.2009.07.014.
12 See, for example (a) C. Jones, C. Schulten, R. P. Rose, A. Stasch, S.
Aldridge, W. D. Woodul, K. S. Murray, B. Moubaraki, M. Brynda,
G. La Macchia and L. Gagliardi, Angew. Chem., Int. Ed., 2009, 48,
7406; (b) R. P. Rose, C. Jones, C. Schulten, S. Aldridge and A. Stasch,
Chem.–Eur. J., 2008, 14, 8477; (c) S. P. Green, C. Jones and A. Stasch,
Science, 2007, 318, 1754; (d) S. P. Green, C. Jones, G. Jin and A. Stasch,
Inorg. Chem., 2007, 46, 8; (e) C. Jones, P. C. Junk, J. A. Platts and A.
Stasch, J. Am. Chem. Soc., 2006, 128, 2206; (f) S. P. Green, C. Jones,
P. C. Junk, K.-A. Lippert and A. Stasch, Chem. Commun., 2006, 3978.
13 As determined by a survey of the Cambridge Crystallographic
Database, November, 2009.
14 Samarium(II) compounds are more reducing than their europium and
ytterbium counterparts. The reduction potentials of the Ln3+/Ln2+
couples have been reported as Ln = Sm (-1.55 V), Eu (-1.15 V), Yb
(-0.35 V) (vs. NHE).L. R. Morss, Chem. Rev., 1976, 76, 827.
15 W. J. Evans, J. W. Grate, L. A. Hughes, H. Zhang and J. L. Atwood,
J. Am. Chem. Soc., 1985, 107, 3728.
Acknowledgements
We thank the Australian Research Council (fellowships for CJ and
AS) and the Engineering and Physical Sciences Research Council
(EPSRC), UK (partial studentship for DPM) for financial support.
The EPSRC Mass Spectrometry Service at Swansea University is
also thanked.
16 W. J. Evans, C. A. Seibel and J. W. Ziller, Inorg. Chem., 1998, 37,
770.
17 N. W. Davies, A. S. P. Frey, M. G. Gardiner and J. Wang, Chem.
Commun., 2006, 4853.
18 See, for example (a) N. L. Cromhout, A. R. Manning, C. J. McAdam,
A. J. Palmer, A. L. Rieger, P. H. Reiger, B. H. Robinson and J. Simpson,
Dalton Trans., 2003, 2224; (b) V. Christou, S. P. Wuller and J. Arnold,
J. Am. Chem. Soc., 1993, 115, 10545.
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20 P. L. Watson, T. H. Tulip and I. Williams, Organometallics, 1990, 9,
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21 G. Jin, C. Jones, P. C. Junk, K.-A. Lippert, R. P. Rose and A. Stasch,
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22 G. M. Sheldrick, SHELX-97, University of Go¨ttingen, 1997.
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1882 | Dalton Trans., 2010, 39, 1877–1882
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The Royal Society of Chemistry 2010
©