Crystalline di- or trianionic metal (Al, Sm) β-diketiminates

Article abstract of DOI:10.1039/c0dt00071j

The new [Al(L^Tol)Br₂] (1) and the known [Al(L ^Ph)Me₂] (2) were prepared as potential precursors to more novel aluminium compounds. In the event, only the latter was effective. Thus 2 and two equivalents of potassium was the source of [{Al(L^Ph)Me ₂K₂(OEt₂)}₂] (3). The complexes [{KSm(L^Ph)₂}₂] (4), [Sm₂(L ^Dph)₃] (5) and [Sm(L^Tol,Ad)(L ^Tol,Ad-H)] (6) were obtained from SmI₂ and two equivalents of the appropriate potassium β-diketiminate [L^Ph or L ^Tol or L^Dph = {N(SiMe₃)C(Ar)}₂CH, Ar = Ph or C₆H₄Me-4 or C₆H₄Ph-4; L^Tol,Ad = N(SiMe₃)C(C₆H₄Me-4)C(H) C(Ad)NSiMe₃, L^Tol,Ad-H = N(SiMe₃)C(C ₆H₄Me-4)C(H)C(Ad)NSiMe₂CH₂, Ad = 1-adamantyl]. Crystalline complexes 3-6 were isolated in very low (4, 5) or satisfactory (3, 6) yield and characterised by X-ray diffraction. From comparisons of the M-N, N-C, C-C and C-C_Ar bond lengths with suitable standards, complexes 3-5 are assigned as containing Al³⁺/(L ^Ph)^3- for 3, Sm³⁺/(L^Ph) ^-/(L^Ph)^3- for 4, and {Sm³⁺} ₂/(L^Dph)^-/(L^Dph)^2-/ (L^Dph)^3- for 5. Complex 6 is best formulated as a Sm ³⁺ compound with one "normal" (L^Tol,Ad) ^- and one deprotonated (L^Tol,Ad-H)^2- ligand. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0dt00071j

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www.rsc.org/dalton | Dalton Transactions
Crystalline di- or trianionic metal (Al, Sm) b-diketiminates†‡
Martyn P. Coles, Peter B. Hitchcock, Alexei V. Khvostov, Michael F. Lappert* and Andrey V. Protchenko
Received 4th March 2010, Accepted 25th May 2010
First published as an Advance Article on the web 21st June 2010
DOI: 10.1039/c0dt00071j
The new [Al(LTol )Br2] (1) and the known [Al(LPh)Me2] (2) were prepared as potential precursors to more
novel aluminium compounds. In the event, only the latter was effective. Thus 2 and two equivalents of
potassium was the source of [{Al(LPh)Me2K2(OEt2)}2] (3). The complexes [{KSm(LPh)2}2] (4),
[Sm2(LDph)3] (5) and [Sm(LTol,Ad)(LTol,Ad-H)] (6) were obtained from SmI2 and two equivalents of the
appropriate potassium b-diketiminate [LPh or LTol or LDph = {N(SiMe3)C(Ar)}2CH, Ar = Ph or
C6H4Me-4 or C6H4Ph-4; LTol,Ad = N(SiMe3)C(C6H4Me-4)C(H)C(Ad)NSiMe3, LTol,Ad-H =
N(SiMe3)C(C6H4Me-4)C(H)C(Ad)NSiMe2CH2, Ad = 1-adamantyl]. Crystalline complexes 3–6 were
isolated in very low (4, 5) or satisfactory (3, 6) yield and characterised by X-ray diffraction. From
comparisons of the M–N, N–C, C–C and C–CAr bond lengths with suitable standards, complexes 3–5
are assigned as containing Al3+/(LPh)3- for 3, Sm3+/(LPh)-/(LPh)3- for 4, and
3-
{Sm3+}2/(LDph)-/(LDph)2-/(LDph
)
for 5. Complex 6 is best formulated as a Sm3+ compound with one
“normal” (LTol,Ad)- and one deprotonated (LTol,Ad-H)2- ligand.
The first b-diketiminatosamarium complexes to be described
were [Sm({N(Pri)C(Me)}2CH)2Br],2 [Sm({N(Ph)C(Me)}2CH)3]
(obtained from SmI2 and the appropriate Li b-diketiminate),3
[Sm(LPh)2Cl]4 and [Sm(LPh)2(thf)2].4 More recent examples
were [Sm({N(C6H2Me3-2,4,6)C(Me)}2CH)Cl(thf)(m-Cl)2Li(thf)2]
and three derivatives,5 and [Sm(LNDipp)Cl(m-Cl)3Sm(LNDipp)(thf)]
and nine products [LNDipp = {N(C6H3Pri2-2,6)C(Me)}2CH].6 The
heteroleptic compound [SmCp’(LNTol)(BH4)] [Cp¢ = C5Me4Prn,
LNTol = {N(C6H4Me-4)C(Me)}2CH] was studied as a stere-
Introduction
b-Diketiminates, shown in their most generalised monoanionic p-
delocalised form in A, are important spectator ligands. They bind
strongly to a metal or bridge two metals and usually are N,N¢,
but rarely also N,C-centred. Their steric and electronic demands
can be varied widely, particularly by choice of the substituents
R1 and R5. Their substantial steric effects are well illustrated
by noting that very few tris(b-diketiminato)metal complexes are
known. Many such species are coordinatively unsaturated, which
is crucial to their frequent use as catalysts or pro-catalysts for
systems ranging from numerous olefinic transformations to ring-
opening polymerisation of lactide. In a 2002 review we noted that
ca. 180 publications, including 65 post-2000, dealt with complexes
of 43 metals.1 The significance of b-diketiminato ligands continues
apace.
3
ospecific isoprene polymerisation catalyst,7 while [Sm(LNDipp)(h -
C3H5)2]8 and [Sm(LNClPh)3]9 [LNClPh = {N(C6H4Cl-4)C(Me)}2CH]
were effective initiators for the ring-opening polymerisa-
tion of e-caprolactone and rac-lactide. The Sm(III) derivative
[Sm(LNPend)Br2] [LNPend = {N(CH2CH2NMe2)C(Me)}2CH] of a
ligand possessing two pendant arms has been described.10 About
sixty b-diketiminatoaluminium(III) complexes were cited in the
2002 review,1 as well as the first aluminium(I) b-diketiminate
[Al(LNDipp)];11 some of its oxidative adducts were later disclosed.12
The dicationic Al(III) salt [Al({N(C6F5)C(Me)}2CH)(tren)][OTf]2
is of interest.13
More than 500 b-diketiminatometal complexes have been
reported. Apart from three lithium and five ytterbium N,N¢bis-
(trimethylsilyl) compounds, all have been monoanionic. The Li
The four ligands, which feature as samarium and aluminium
complexes in the present study, are a sub-class A’ of A (R1 =
SiMe3 = R5):
compounds have been the dianionic [Li(tmeda)(m-LPh)Li(OEt2)]
and the [LPh,t-Bu
]
analogue [LPh,t-Bu
=
N(SiMe3)C(Ph)-
2-
C(H)C(But)NSiMe3] and the trianionic [{Li3({N(SiMe3)-
C(C6H4But-4)}2CH)(tmeda)}2];14 the precursors in each case
included the appropriate Li b-diketiminate and one or two
equivalents of the metal. The ytterbium complexes were [Yb{(m-
LPh)Li(thf)}2] (B) and the LDph analogue,14,15 [Yb3(LPh)3(thf)] (C)14,16
and [Yb3(LPh)2(dme)2];14 compounds B and C were prepared from
[Yb(LPh)2Cl] + 3Li and [Yb(C10H8)(thf)3] + [Yb(LPh)2], respectively.
A final Yb compound [Yb5(LPh)(L1)(L2)(L3)(thf)4], isolated in
very low yield from 2Yb + [Yb(LPh)2], contained (LPh)3- and
three, L1 to L3, polyanionic LPh fragments: [LPh minus H+]4-,
[NC(Ph)CHC(Ph)H]3- and [N(SiMe2CH2)]3-, respectively.14 Cyclic
Department of Chemistry and Biochemistry, University of Sussex, Brighton,
UK BN1 9QJ. E-mail: m.f.lappert@sussex.ac.uk; Fax: +44 1273 876687;
Tel: +44 1273 678316
† Dedicated to Professor David W. H. Rankin on the occasion of his
retirement.
‡ CCDC reference number 768769–768772. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00071j
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voltammetry showed that the primary reduction potential in thf
containing [NBu4][PF6] decreased in the sequence (i) Li(LPh) >
Li(LPh,t-Bu) ꢀ Li(LDipp) and (ii) [Yb(LPh)2] ꢀ [Yb(LDipp)2], consistent
with the notion that two (LPh) or one (LPh,t-Bu) C-phenyl sub-
stituents are available for p-electron delocalisation of the reduced
species, whereas the bulky N-aryl groups are sterically unable to
participate in such conjugation.17
a K mirror prepared from slightly more than two equivalents of
potassium; lustrous violet crystals of [{Al(LPh)Me2K2(OEt2)}2] (3)
precipitated at room temperature. The low solubility of 3 in Et2O
or hydrocarbons and its extremely high sensitivity to moisture and
air prevented preparation of an analytically pure sample. The 1H
NMR spectrum of 3 in thf-d8 showed low frequency shifted signals
for ortho- and para- protons of the Ph substituents, consistent with
the b-diketiminato ligand being doubly reduced.14
Results and discussion
The paper deals with the synthesis, structure and bonding of
selected aluminium and samarium b-diketiminates and their one-
or two-electron reduction products. These elements have two stable
oxidation states in some of their b-diketiminates, Al(I)/Al(III) and
Sm(II)/Sm(III), while certain C-aryl or C,C¢diaryl b-diketiminates
such as LPh are readily reduced. Hence the nature of the bonding
in some of their reduced b-diketiminates was the major objective
of the present study.
Experiments in aluminium chemistry
The b-diketiminatoaluminium(III) complex, originally chosen as a
prospective precursor to a reduced species, was the new, yellow
b-diketiminatoaluminium(III) dibromide 1, prepared as shown
in eqn. (1). Attempts to obtain characterisable products from 1
and metallic potassium were unsuccessful. Thus from 1 and an
equivalent portion of K, as a mirror in C6D6 or PhMe, there was a
rapid colour change from yellow to green and then to brown; the
green intermediate was too unstable to be characterised while only
non-crystalline material was isolated from the brown solution.
Scheme
1
Synthesis of [Al(LPh)Me2] (2) and its reduction to
[{Al(LPh)Me2K2(OEt2)}2] (3) (R = SiMe3)
The molecular structure of the crystalline centrosymmetric
dimeric compound 3 is shown as an ORTEP representation in
Fig. 1. Selected bond lengths and angles are listed in Table 1. The
6
two monomeric units are joined by short K ◊ ◊ ◊ h -C6H5 contacts
˚
(K1 ◊ ◊ ◊ M1¢ and M1 ◊ ◊ ◊ K1¢ of 2.901(3) A; M1 and M1¢ are the
We next turned to the known19 yellow complex [Al(LPh)Me2]
(2); it was prepared by a new method (step 1 of Scheme 1)
using [Pb(LPh)2]20 as the source of the LPh ligand. Treatment of
2 with an equivalent portion of potassium in diethyl ether resulted
in dissolution of potassium and formation of a green solution;
centroids of the transoid C6H5 groups of units containing K1 and
K1¢, respectively); thus, K1 is sandwiched between the NCCCN
backbone of an LPh ligand of one unit and a C6H5 group of the
second. The second potassium atom K2 is in a five-coordinate
environment, having short contacts to the oxygen atom of an Et2O
ligand, the b-carbon atom (C3) of the LPh ligand, the adjacent
ipso-carbon atom (C10) of the C6H5 group, and the AlMe2 methyl
carbon atoms C22 of the same and C23¢ of the neighbouring
molecule. The relative magnitude of the two Cipso–C(LPh) bond
◦
cooling at -27 C afforded dark green paramagnetic (1H NMR)
crystals (not of X-ray quality) believed to be of a 1 : 1-complex
(step 2 of Scheme 1). Finally, the stoichiometry was altered so
that (step 3 of Scheme 1) an Et2O solution of 2 was added to
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◦
Table 1 Selected bond distances (A) and angles (◦) for
Table 2 Selected bond distances (A) and angles ( ) for [{KSm(LPh)2}2]
˚
˚
[{Al(LPh)Me2K2(OEt2)}2] (3)
(4)
Sm–N1
Sm–N2
Sm ◊ ◊ ◊ C1
Sm ◊ ◊ ◊ C2
Sm ◊ ◊ ◊ C3
N1–C1
N2–C3
C1–C2
C2–C3
C1–C4
C3–C10
N1–Si1
N2–Si2
K ◊ ◊ ◊ C22
K ◊ ◊ ◊ C23
K ◊ ◊ ◊ C24
2.412(3)
2.391(3)
2.919(4)
2.940(4)
2.905(4)
1.335(5)
1.324(5)
1.423(6)
1.422(6)
1.501(6)
1.489(6)
1.740(4)
1.741(4)
2.940(4)
2.923(4)
2.987(4)
Sm–N3
Sm–N4
2.309(3)
2.308(3)
2.562(4)
2.611(4)
2.601(4)
1.422(5)
1.428(5)
1.418(6)
1.448(6)
1.484(6)
1.463(6)
1.703(3)
1.688(4)
2.812(3)
2.873(3)
2.928(5)
Al–N1
Al–N2
Al–C22
Al–C23
N1–C1
N2–C3
C1–C2
C2–C3
C1–C4
C3–C10
N1–Si1
N2–Si2
1.888(2)
1.902(2)
1.990(3)
1.992(3)
1.430(3)
1.459(3)
1.376(4)
1.438(3)
1.480(3)
1.425(4)
1.718(2)
1.720(2)
K1–M1¢
K1–N1
K1–N2
K1–C1
K1–C2
K1–C3
K2–O
K2–C10
K2–C3
K2–C22
K2–C23”
2.901(3)
2.934(2)
3.033(2)
3.054(2)
2.973(3)
2.959(3)
2.644(3)
2.839(2)
2.968(3)
3.021(4)
3.061(3)
Sm ◊ ◊ ◊ C22
Sm ◊ ◊ ◊ C23
Sm ◊ ◊ ◊ C24
N3–C22
N4–C24
C22–C23
C23–C24
C22–C25
C24–C31
N3–Si3
N4–Si4
K–N3
K–N4
K ◊ ◊ ◊ M’
N1–Al–N2
C22–Al–C23
Al–N1–C1
Al–N2–C3
N1–C1–C2
N2–C3–C2
C1–C2–C3
99.75(10)
104.03(17)
105.28(16)
110.95(15)
121.5(2)
117.8(2)
132.7(2)
N1–C1–C4
N2–C3–C10
C2–C3–C10
C2–C1–C4
N1–K1–M1¢
O–K2–C10
O–K2–C3
119.6(2)
122.4(2)
117.6(2)
117.7(2)
157.62(5)
112.93(9)
121.72(8)
N1–Sm–N2
Sm–N1–C1
Sm–N2–C3
N1–C1–C2
N2–C3–C2
C1–C2–C3
C2–C3–C10
C2–C1–C4
M’–K–N3
78.08(12)
98.2(2)
98.8(2)
123.9(4)
123.3(4)
128.7(4)
115.3(4)
115.7(4)
150.97(12)
N3–Sm–N4
83.07(11)
83.1(2)
84.8(2)
122.2(4)
120.0(3)
134.6(4)
116.4(4)
117.6(4)
140.79(12)
Sm–N3–C22
Sm–N4–C24
N3–C22–C23
N4–C24–C23
C22–C23–C24
C23–C22–C25
C23–C24–C31
M’–K–N4
M1¢ is centroid of the C10¢ to C15¢ ring. Symmetry transformations used
to generate equivalent atoms: ’ -x, -y, -z; “ -x - 12 , y + 21 , -z +
1
2
M’ is centroid of the C31¢ to C36¢ ring. Symmetry transformations used
to generate equivalent atoms: ’ -x,-y,-z
of the green (4, 5) or blue (6) filtrate, addition of pentane (4, 6)
or hexane (5), and cooling at -10 ◦C afforded (Scheme 2), in low
(4, 5) or significant (60% for 6) yield, X-ray quality crystals of the
dark brown (4, 5) or blue (6) samarium complexes [{KSm(LPh)2}2]
(4), [Sm2(LDph)3] (5) and [Sm(LTol,Ad)(LTol,Ad-H)] (6). The 1H NMR
spectra of each of the compounds 4 and 5 showed one set
of paramagnetically shifted (sharp and having the appropriate
multiplicity) signals characteristic for the appropriate ligand (LPh
and LDph) and another set of broad signals which could not be
integrated separately due to increased line-width. This fact is
indicative of the presence of two types (terminal and bridging)
1
of ligands in compounds 4 and 5. The H NMR spectrum of
complex 6 was unassignable.
Fig. 1 Molecular structure of crystalline 3 (50% ellipsoids).
The molecular structure of the crystalline centro-symmetric
dimeric compound 4 is shown in an ORTEP representation in
Fig. 2a and for a monomer fragment in greater detail in Fig. 2b;
selected bond lengths and angles are listed in Table 2. The two
lengths indicates that C3–C10, unlike C1–C4, is a double bond
(the formal single/double bond distribution is shown in Scheme 1).
The C–C distances in the backbone of the LPh ligand are unequal,
with C2–C3 > C1–C2, consistent with the notion that the latter is
a double bond; the N–C bonds are significantly longer than those
6
monomeric units are joined by the close K ◊ ◊ ◊ h -C6H5 contacts
˚
(K ◊ ◊ ◊ C31¢ to 36¢ at 3.24 0.10 A). The potassium atom also has
in 2 (av. 1.334 A).19 The LPh : Al : K 1 : 1 : 2 stoichiometry would be
˚
short contacts to the five backbone atoms of the bridging LPh lig-
appropriate either for an (LPh)3-/Al3+ or (LPh)-/Al+ assignment; the
former is preferred not only on the basis of the above discussion,
˚
˚
and N3C22C23C24N4 of 2.84 0.03 A (N3/N4) and 2.87 0.06 A
(C22/C23/C24); the K–N distances may be compared to those in
but also because the Al–N distances in 3 are significantly shorter
Ph
˚
19
[K(m-L )(thf)2]• (2.827(3) and 2.833(3) A).21 This virtually planar
˚
˚
than the 1.921(4) A in 2, and the Al–CH3 length (av. 1.991 A)
is longer than in 2 (apparently due to the presence of additional
K ◊ ◊ ◊ CH3 interactions in 3).
5
ligand is bound in an h -fashion to the Sm atom via very short Sm–
N and Sm–C interactions. Thus, the Sm–N3 and Sm–N4 distances
are shorter than similar distances in the Sm(III) b-diketiminates
[Sm(LNDipp)Cl(NR2)] and [Sm(LNDipp)(NR2)2] (2.344 0.010 and
Synthesis and structures of three crystalline
b-diketiminatosamarium compounds 4, 5 and 6
6
˚
2.465
0.038 A, respectively), but very close to the Sm(III)-
Namide distances in the above-mentioned compounds [2.276(3)
6
˚
Treatment of a suspension of SmI2 in diethyl ether (4, 6) or
tetrahydrofuran (5) with two equivalents of the appropriate
potassium b-diketiminate and successive filtration, concentration
and 2.311 0.013 A, respectively], and in the bulky triamides
22
23
˚
˚
[Sm(NCy2)3(thf)] (2.27 0.01 A) and [Sm(NR2)3] (2.284(3) A)
˚
(R = SiMe3). The Sm–C distances (C22/C23/C24, 2.59 0.03 A)
6428 | Dalton Trans., 2010, 39, 6426–6433
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Scheme 2 Synthesis of samarium complexes 4, 5 and 6 (R = SiMe3, Ar = C6H4Ph-4)
Fig. 2 Molecular structure of crystalline 4 (20% ellipsoids): (a) dimeric molecule (left); (b) monomeric unit (right).
are much shorter than the Sm–C(Cp*) distances in the bulky
The LPh : Sm : K 2 : 1 : 1 stoichiometry would be appropriate either
for an Sm2+/(LPh)-/(LPh)2- or Sm3+/(LPh)-/(LPh)3- assignment (as
the terminal ligand is certainly monoanionic); to assign the Sm
atom oxidation state the Sm–N bond lengths are compared with
those in Sm formamidinate complexes (in the absence of a well-
characterised Sm(II) b-diketiminate in the literature) for which
both Sm(II) and Sm(III) complexes have been prepared.26 Thus, the
6
Sm(III) compounds [Sm(LNDipp)(CH2R)(Cp*)] [2.746(5) A] or
˚
24
˚
[Sm(Cp*)2Me(thf)] [2.711(6) A] (Cp* = C5Me5), and similar
to the shortest Sm–C(allyl) distances in [Sm(LNDipp)(h -C3H5)2]
3
(2.606(4) and 2.612(4) A). The second, terminal, LPh ligand
8
˚
5
is attached to the Sm atom in an h -fashion with the Sm–N
distances being ca. 0.1 A longer and the Sm ◊ ◊ ◊ C contacts ca.
˚
Ph
˚
˚
0.3 A longer than those for the bridging L ligand. The Sm–
Sm–N bonds in [Sm(Form)2(thf)2] (2.58 0.05 A) are significantly
(LPh)terminal bonding situation is very similar to that in [Nd(LPh)2Cl],4
longer than those in [SmF(Form)2(thf)] (2.449 0.005 A) or in
˚
i
˚
where the appropriate Nd–N and Nd ◊ ◊ ◊ C distances are ca.
[Sm(Form)3] (2.46 0.01 A) [Form = {N(C6H3Pr 2-2,6)}2CH],
+3
0.03 A longer, consistent with the difference in the Sm and
which is in good agreement with the difference in Sm2+ and Sm3+
ionic radii.25 It is noteworthy that [Sm(Form)3] was obtained from
[Sm(Form)2(thf)2], [SmI2(thf)2] and NaI with no oxidant added
(formally [SmI2(thf)2] (a well-known reducing agent) was regarded
as the oxidant yielding a Sm0 co-product) as in the case of the
reactions of Scheme 2. None of the Sm complexes 4, 5 or 6 have
Sm–N bond lengths approaching the values found in the Sm(II)
˚
Nd+3 ionic radii.25 The backbone N–C and (to a lesser extent)
C–C bond lengths are longer in the bridging ligand, consistent
with its being reduced; the slightly shorter backbone-to-phenyl
C–C bonds in this ligand suggest some delocalisation of the
negative charge to the Ph rings, especially to the potassium-
bound ring, which is nearly coplanar with the ligand backbone.
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◦
Table 3 Selected bond distances (A) and angles ( ) for [Sm2(LDph)3] (5)
˚
Sm1–N1
Sm1–N2
Sm1 ◊ ◊ ◊ C1
Sm1 ◊ ◊ ◊ C2
Sm1 ◊ ◊ ◊ C3
N1–C1
N2–C3
C1–C2
C2–C3
C1–C10
C3–C22
N1–Si1
N2–Si2
N3–Si3
2.411(7)
2.380(8)
2.803(10)
2.772(10)
2.784(9)
1.328(12)
1.353(12)
1.430(13)
1.424(13)
1.521(14)
1.508(13)
1.758(8)
1.759(8)
1.728(7)
1.738(7)
Sm2–N5
Sm2–N6
Sm2 ◊ ◊ ◊ C67
Sm2 ◊ ◊ ◊ C68
Sm2 ◊ ◊ ◊ C69
N5–C67
2.320(7)
2.303(7)
2.694(9)
2.742(9)
2.763(9)
1.420(9)
1.390(9)
1.408(12)
1.431(12)
1.450(13)
1.484(13)
1.732(8)
1.720(8)
Sm1–N3
Sm1–N4
Sm2–N3
Sm2–N4
Sm1 ◊ ◊ ◊ C34
Sm1 ◊ ◊ ◊ C35
Sm1 ◊ ◊ ◊ C36
Sm2 ◊ ◊ ◊ C34
Sm2 ◊ ◊ ◊ C35
Sm2 ◊ ◊ ◊ C36
N3–C34
2.317(7)
2.464(7)
2.488(7)
2.407(7)
2.623(9)
2.644(9)
2.590(9)
2.697(9)
2.726(9)
2.730(8)
1.447(9)
1.417(9)
1.427(12)
1.421(12)
1.484(12)
1.497(13)
N6–C69
C67–C68
C68–C69
C67–C76
C69–C88
N5–Si5
N4–C36
N6–Si6
C34–C35
C35–C36
C34–C43
C36–C55
N4–Si4
N1–Sm1–N2
Sm1–N1–C1
Sm1–N2–C3
N1–C1–C2
N2–C3–C2
C1–C2–C3
C2–C3–C22
C2–C1–C10
N1–Sm1–N3
N1–Sm1–N4
N2–Sm1–N3
N2–Sm1–N4
79.1(3)
92.5(6)
92.3(6)
N5–Sm2–N6
Sm2–N5–C67
Sm2–N6–C69
N5–C67–C68
N6–C69–C68
C67–C68–C69
C68–C67–C76
C68–C69–C88
Sm2–N3–C34
Sm2–N4–C36
N3–Sm2–N5
N3–Sm2–N6
85.3(3)
88.8(4)
93.5(4)
121.6(8)
122.6(7)
135.3(9)
118.3(8)
115.6(8)
81.9(4)
87.1(3)
128.2(2)
129.9(2)
N3–Sm1–N4
Sm1–N3–C34
Sm1–N4–C36
N3–C34–C35
N4–C36–C35
C34–C35–C36
C35–C34–C43
C35–C36–C55
N4–Sm2–N5
N4–Sm2–N6
75.1(2)
85.0(3)
78.7(4)
118.8(7)
121.2(7)
132.1(8)
119.4(8)
117.1(8)
121.4(3)
124.7(3)
124.2(9)
124.6(9)
127.7(9)
115.6(8)
113.6(9)
116.6(2)
133.8(2)
121.4(3)
135.7(3)
formamidinate [Sm(Form)2(thf)2]26 or guanidinate [Sm(Giso)2]
27
[Giso = {N(C6H3Pri2-2,6)}2CN(C6H11)2; Sm–N 2.55 0.02 A].
˚
Hence, complex 4 is best formulated as Sm3+/(LPh)-/(LPh)3-.
An ORTEP representation of the structure of the crystalline
dinuclear complex 5 is presented in Fig. 3 and selected geometrical
parameters are shown in Table 3. Each samarium atom has a
terminal b-diketiminato ligand LDph, and the two Sm atoms are
each attached to the N3, C34, C35, C36 and N4 atoms of a bridging
L
Dph. The two terminal ligands differ significantly, most notably
˚
by the magnitude of the N–C bond lengths of ca. 1.34 0.013 A
˚
for N1–C1/N2–C3 and 1.405 0.015 A for N5–C67/N6–C69
5
and their distances to the h -coordinated Sm atoms of ca. 2.396
˚
˚
0.016 A for Sm1–N1/N2 and 2.78 0.02 A for Sm1–C1/C2/C3
˚
˚
and 2.312 0.009 A for Sm2–N5/N6 and 2.73 0.04 A for Sm2–
C67/C68/C69. The h :h -bridging LDph ligand has very short Sm–
C34/C35/C36 contacts to the Sm1 atom of ca. 2.62 0.03 A
5
5
˚
and slightly longer from C34, C35, C36 to the Sm2 of 2.72
˚
0.02 A, the former being similar to those in 4. The Sm–N(bridging)
˚
bond lengths vary widely from ca. 2.32 to 2.49 A increasing in the
sequence Sm1–N3 < Sm2–N4 < Sm1–N4 < Sm2–N3. Within the
three LDph ligands the N–C bond lengths decrease in the sequence
N3–C4 > N5–C67 ª N4–C36 > N6–C69 ꢀ N2–C3 > N1–C1,
while each of the six C–C distances fall in a narrow range centred
˚
on 1.420 0.012 A. The variation of the backbone-to-aryl C–C
bond lengths (C1–C10 > C3–C22 > C36–C55 > C34–C43 ª C69–
C88 ꢀ C67–C76) is somewhat greater and is centred on 1.485
Fig. 3 Molecular structure of crystalline 5 (20% ellipsoids).
˚
0.035 A.
Based on the comparison of Sm–N bond lengths (as in the case
For the complex 6, the first structure refinement was made
assuming that it was a Sm(II) compound with two monoanionic
LTol,Ad ligands, as its preparation was similar to that of the
of complex 4) and the notion that all three ligands in complex 5
are different, the formal charge distribution for 5 is formulated as
{Sm3+}2/(LDph)-/(LDph)2-/(LDph)3-.
6430 | Dalton Trans., 2010, 39, 6426–6433
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known ytterbium(II) compound [Yb(LTol,Ad)2].18 However, this
Table 4 Selected bond distances (A) and angles (◦) for
[Sm(LTol,Ad)(LTol,Ad-H)] (6) and the Yb complex [Yb(LTol,Ad)2].18
˚
˚
model had inexplicably short contacts Sm ◊ ◊ ◊ C(Me) of 2.643(6) A
˚
and Sm ◊ ◊ ◊ H of 1.81 A, which were considerably shorter than
6 (M = Sm)
[Yb(LTol,Ad)2] (M = Yb)
expected for an agostic interaction. Thus, the structure was re-
refined as [Sm(LTol,Ad)(LTol,Ad-H)] considering one ligand being
deprotonated and the Sm atom having a Sm–C s-bond (although
the difference map showed three peaks near the C52 atom, one was
of a lower intensity and deviated from the expected tetrahedral
geometry).
M–N1
M–N2
M–N3
M–N4
N1–C1
N2–C3
N3–C27
N4–C29
C1–C2
C2–C3
C27–C28
C28–C29
Sm–C52
2.420(4)
2.417(4)
2.350(4)
2.363(4)
1.322(6)
1.330(6)
1.355(6)
1.313(6)
1.424(6)
1.418(6)
1.411(6)
1.438(6)
2.627(6)
2.412(7) (Yb–N3)
2.364(7) (Yb–N4)
2.378(7) (Yb–N2)
2.371(7) (Yb–N1)
1.282(12) (N3–C27)
1.337(11) (N4–C29)
1.336(11) (N2–C3)
1.341(12) (N1–C1)
1.460(12) (C27–C28)
1.390(12) (C28–C29)
1.406(12) (C2–C3)
1.432(13) (C1–C2)
The molecular structure of the crystalline samarium b-
diketiminate 6 is illustrated in an ORTEP representation in Fig. 4,
and selected geometrical parameters are listed in Table 4 together
with those of the ytterbium compound [Yb(LTol,Ad)2].18 The Sm–
N bond lengths in 6 are very similar to the Yb–N bond lengths
in the Yb(II) complex having a similar coordination environment.
However, due to theca. 0.13 Adifference in the Sm+3 and Yb+2 ionic
˚
N1–M–N2
N3–M–N4
N1–C1–C2
N3–C27–C28
M–N1–C1
M–N3–C27
N4–Si4–C50
N4–Si4–C51
N4–Si4–C52
77.67(12)
78.96(13)
125.9(4)
123.8(4)
94.4(3)
81.7(2) (N3–Yb–N4)
82.4(2) (N1–Yb–N2)
127.0(8) (N3–C27–C28)
125.6(8) (N1–C1–C2)
99.8(5) (Yb–N3–C27)
96.3(5) (Yb–N2–C3)
radii,25 the Sm–N bonds are expected to be considerably longer,
as was found in [Sm({N(C6H3Pri2-2,6)}2CH)2(thf)2] with Sm–Nav.
26
˚
of 2.58
0.05 A, or the Sm(II) bis-guanidinate [Sm(Giso)2]
[Giso = {N(C6H3Pri2-2,6)}2CN(C6H11)2] with Sm–Nav. of 2.55
95.6(3)
27
106.4(3)
115.7(3)
100.4(2)
˚
0.02 A. On the other hand these distances are very close to the
Sm–N distances in most of the known Sm(III) b-diketiminates or
the Sm(III) formamidinate [Sm({N(Ar)}2CH)3] (Ar = C6H3Pri2-
2,6,26 C6H3Me2-2,6,28 C6H3Et2-2,6,28 C6H4Ph-228). The N–C and
C–C bond lengths of the ligand backbone are similar to those
in [Yb(LTol,Ad)2]18 and for the terminal ligand in 4, indicating that
the ligands in 6 are not reduced. The Sm–C52 distance is slightly
longer than such distances in Sm(III) alkyl complexes but is similar
Angle between N1–M–N2 and N3–M–N4 planes: 58◦ (M = Sm), 58◦ (M =
Yb). Angle between N1C1C3N2 and N3C27C29N4 planes: 10◦ (M = Sm),
15◦ (M = Yb). C2 out of N1C1C3N2 plane: 0.22 A (M = Sm), 0.21 A
˚
˚
˚
˚
(M = Yb). C28 out of N1C27C29N2 plane: 0.21 A (M = Sm), 0.24 A
(M = Yb).
3
to the Sm–C bond lengths in the allyl complex [Sm(LNDipp)(h -
route. Their novelty arises because a b-diketiminato ligand in each
is other than monoanionic, a situation without precedent except
in lithium and ytterbium chemistry. Noteworthy is the formation
of Sm(III) products from a Sm(II) precursor. The assignment
of charges [Al3+/(LPh)3- for 3, Sm3+/(LPh)-/(LPh)3- for 4, and
for 5] is based on analysis of
selected bond lengths and comparisons with those in known Al/N
8
˚
C3H5)2] (2.606(4) and 2.612(4) A). Involvement of the C52 atom
in bonding with the Sm atom has caused a significant change
in the geometry of the adjacent Si4 atom with the N4–Si4–C52
angle being considerably reduced compared to the N4–Si4–C50
and N4–Si4–C50 angles.
3-
{Sm3+}2/(LDph)-/(LDph)2-/(LDph
)
compounds for 3 and Sm/N compounds for 4, 5 and 6.
Experimental
General methods
The preparations of [Al(LTol )Br2] (1), [Al(LPh)Me2] (2),
[{Al(LPh)Me2K2(OEt2)}2] (3), [{KSm(LPh)2}2] (4), [Sm2(LDph)3]
(5) and [Sm(LTol,Ad)(LTol,Ad-H)] (6) were carried out under an
atmosphere of argon or in a vacuum, using Schlenk apparatus
and vacuum line techniques. The compounds K(LPh),14 K(LTol ),14
K(LDph),14 K(LTol,Ad),14 and [Pb(LPh)2]16 were prepared by published
procedures; AlBr3, AlMe3 in PhMe, K and SmI2 were commercial
samples (Aldrich). The solvents employed were dried and dis-
tilled over sodium-potassium alloy (pentane, hexane) or sodium-
benzophenone (Et2O, thf) and stored over a sodium mirror under
argon. The NMR spectra were recorded using the DPX 300 and
AMX 500 Bruker instruments and calibrated internally to residual
Fig. 4 Molecular structure of crystalline 6 (20% ellipsoids).
1
solvent resonances for 1H and 13C{ H}.
Conclusions
The unusual X-ray-characterised crystalline metal complexes
[{Al(LPh)Me2K2(OEt2)}2] (3), [{KSm(LPh)2}2] (4), [Sm2(LDph)3] (5)
and [Sm(LTol,Ad)(LTol,Ad-H)] (6) have been prepared via potassium
reduction (3) or a salt metathesis/disproportionation (4, 5, 6)
Synthesis of [Al(LTol )Br2] (1)
Potassium b-diketiminate, K(LTol ), (0.455 g, 1.05 mmol) was added
to a stirred suspension of AlBr3 (0.305 g, 1.14 mmol) in toluene
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Table 5 Crystal data and structure refinement for 3, 4, 5 and 6
Compound
3
4
5·C6H14
6
Empirical formula
Formula weight
Crystal system
Space group
C27H45AlK2N2OSi2
575.01
Monoclinic
P21/n (No. 14)
13.8525(7)
14.1721(8)
16.9078(7)
90
101.807(3)
90
3249.1(3)
4
1.18
0.41
C84H116K2N8Si8Sm2
1841.47
Monoclinic
P21/n (No. 14)
13.0232(5)
20.0158(5)
17.9052(7)
90
94.925(2)
90
4650.1(3)
2
1.32
1.49
C105H125N6Si6Sm2
1940.35
C52H81N4Si4Sm
1024.92
Monoclinic
P21/c (No. 14)
16.0256(6)
18.5440(9)
20.9627(7)
90
104.300(2)
90
6036.6(4)
4
1.13
1.09
Triclinic
¯
P1(No. 2)
˚
a/A
14.3495(6)
16.7924(9)
24.5587(14)
97.177(3)
95.469(3)
111.259(3)
5408.2(5)
2
1.19
1.19
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
U/A
Z
Dc/Mg m-3
m/mm-1
Independent reflections
Reflections with I > 2s(I)
Final R indices [I > 2s(I)]
R indices (all data)
6334 [R(int) = 0.049]
8199 [R(int) = 0.063]
12909 [R(int) = 0.074]
8331 [R(int) = 0.058]
4600
6183
9200
6791
R1 = 0.051, wR2 = 0.100
R1 = 0.081, wR2 = 0.112
R1 = 0.039, wR2 = 0.080
R1 = 0.064, wR2 = 0.089
R1 = 0.059, wR2 = 0.141
R1 = 0.094, wR2 = 0.158
R1 = 0.041, wR2 = 0.091
R1 = 0.057, wR2 = 0.101
(20 mL) at -30 ◦C. The mixture was slowly warmed up to
ambient temperature and stirred overnight. A white precipitate
was filtered off; the solvent was removed in vacuo from the filtrate
and the residue was washed with cold pentane (2 ¥ 10 mL). The
resulting yellow solid was dried in vacuo, yielding pure (by NMR)
was insufficient for an X-ray diffraction study; the crystals decom-
posed quickly after being removed from the mother solution.
(ii) A solution of [Al(LPh)Me2] (2) (0.173 g, 0.41 mmol) in
diethyl ether (10 mL) was added to a potassium mirror (0.040 g,
1.02 mmol) at ambient temperature. The solution first turned green
and then blue-violet with the formation of extremely air-sensitive,
dark violet with a bronze lustre, crystals of [Al(LPh)Me2K2(OEt2)]
(3) on the surface of the K metal (0.165 g, 70%). X-ray quality
crystals were obtained by storing the decanted solution at -10 ◦C
overnight. 1H-NMR (thf-d8): d 6.58 (d, 3JH–H = 7.5, 4H, o-CH of
Ph), 6.48 (t, 3JH–H = 7.0, 4H, m-CH of Ph), 5.79 (s, 1H, middle CH),
5.65 (t, 3JH–H = 6.3 Hz, 2H, p-CH of Ph), 3.39 (q, 4H, OCH2CH3),
1.12 (t, 6H, OCH2CH3), 0.01 (s, 18H, SiMe3), -1.07 ppm (s, 6H,
AlCH3).
1
[Al(LTol )Br2] (1) (0.425 g, 0.73 mmol, 70%). H-NMR (C6D6): d
7.03 (d, 4H, m-H of tolyl), 6.72 (d, 4H, o-H of tolyl), 5.51 (s, 1H,
middle CH), 1.96 (s, 6H, CH3 of tolyl), 0.29 ppm (s, 18H, SiMe3).
13C-NMR (C6D6): d 179.10 (s, NC(Tol)CH), 140.62 and 139.71
(two s, ipso-C and p-C of tolyl), 129.00 and 127.56 (two s, m- and
o-CH of tolyl), 110.79 (s, middle CH), 21.09 (s, CH3 of tolyl),
4.07 ppm (s, SiMe3).
Synthesis of [Al(LPh)Me2] (2)
Synthesis of [{KSm(LPh)2}2] (4)
Excess AlMe3 (1 mL of a 2 M solution in toluene, 2.0 mmol) was
added to a stirred solution of the lead b-diketiminate [Pb(LPh)2]
(0.618 g, 0.66 mmol) in toluene (10 mL) at ambient temperature.
The mixture was stirred for 1 h (a black powder started to
precipitate after 10 min) and then filtered. The volatiles were
removed from the filtrate in vacuo and the resulting yellow
crystalline solid was dried in vacuo at 60 ◦C, yielding pure (by
NMR) [Al(LPh)Me2] (2) (0.550 g, 1.30 mmol, 98% based on LPh).
1H-NMR (C6D6): d 7.16–7.21 (m, 4H, Ph), 6.91–6.98 (m, 6H, Ph),
5.39 (s, 1H, middle CH), 0.09 (s, 18H, SiMe3), -0.02 ppm (s, 6H,
AlCH3). 13C-NMR (C6D6): d 177.93 (s, NC(Ph)CH), 144.75 (s,
ipso-C of Ph), 129.08 (s, p-CH of Ph), 128.20 and 127.76 (two s, m-
and o-CH of Ph), 109.53 (s, middle CH), 3.29 (s, SiMe3), -4.86 ppm
(s, AlCH3).
Potassium b-diketiminate K(LPh) (0.83 g, 2.05 mmol) was added to
a stirred suspension of SmI2 (0.41 g, 1.01 mmol) in Et2O (80 mL)
at ambient temperature; stirring was continued overnight. A white
precipitate was filtered off; ca. three quarters of the solvent was
removed in vacuo from the ◦green filtrate, which was layered with
pentane and stored at -10 C resulting in the formation of dark
brown crystals of [{KSm(LPh)2}2] (4) (0.092 g, 10%), which gave
1
a purple solution in deuterated benzene. H-NMR (C6D6): d (i)
sharp signals: 23.13 (s, 1H, middle CH), 5.96 (t, 3JH–H = 7.3, 2H, p-
CH of Ph), 4.92 (t, 3JH–H = 7.6, 4H, m-CH of Ph), 2.33 (d, 3JH–H
=
7.3 Hz, 4H, o-CH of Ph), -7.47 ppm (s, 18H, SiMe3); (ii) broad
signals: 29.3, 7.1, 1.14, -0.7 ppm.
Synthesis of [Sm2(LDph)3] (5)
Reduction of 2
Potassium b-diketiminate K(LDph) (1.52 g, 2.73 mmol) was added
to a stirred solution of SmI2 (0.55 g, 1.36 mmol) in thf (80 mL)
at ambient temperature and stirred overnight. A white precipitate
was filtered off; the solvent was removed in vacuo from the dark
green filtrate; the residue was dissolved in hexane and stored
at -10 ◦C resulting in the formation of dark brown crystals of
[Sm2(LDph)3] (5) (0.264 g, 20%). 1H-NMR (C6D6): d (i) sharp
(i) A solution of [Al(LPh)Me2] (2) (0.195 g, 0.46 mmol) in
diethyl ether (10 mL) was added to a potassium mirror (0.019 g,
0.49 mmol) at ambient temperature. The solution immediately
turned green; after stirring for 2 h, the potassium had disap-
peared.◦ Upon storing the concentrated (to ca. 3 mL) mixture
at -27 C overnight, dark green crystals (tentatively assigned as
[K(OEt2)xAl(LPh)Me2]) precipitated. The quality of these crystals
3
signals: 26.64 (s, 1H, middle CH), 6.67 (t, JH–H = 7.3, 2H,
6432 | Dalton Trans., 2010, 39, 6426–6433
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p-CH of Ph), 6.57 (t, 3JH–H = 7.3, 4H, m-CH of Ph), 6.36 (d, 3JH–H
=
Notes and references
7.3, 4H, o-CH of Ph), 5.28 and 2.61 (two d, 3JH–H = 8.8 Hz, 4H +
4H, o- and m-CH of C6H4), -7.29 ppm (s, 18H, SiMe3); (ii) broad
signals: 33.2, 27.5, 11.1, 1.33 (~36H, SiMe3), -0.8, -4.5 ppm.
1 L. Bourget-Merle, M. F. Lappert and J. R. Severn, Chem. Rev., 2002,
102, 3031.
2 D. Drees and J. Magull, Z. Anorg. Allg. Chem., 1995, 621, 948.
3 D. Drees and J. Magull, Z. Anorg. Allg. Chem., 1994, 620, 814.
4 P. B. Hitchcock, M. F. Lappert and S. Tian, J. Chem. Soc., Dalton
Trans., 1997, 1945.
Synthesis of [Sm(LTol,Ad)(LTol,Ad-H)] (6)
5 Z.-Q. Zhang, Y.-M. Yao, Y. Zhang, Q. Shen and W.-T. Wong, Inorg.
Chim. Acta, 2004, 357, 3173.
6 C. Cui, A. Shafir, J. A. R. Schmidt, A. G. Oliver and J. Arnold, Dalton
Trans., 2005, 1387.
7 F. Bonnet, M. Visseaux, D. Barbier-Baudry, E. Vigier and M. M.
Kubicki, Chem.–Eur. J., 2004, 10, 2428.
8 L. F. Sa´nchez-Barba, D. L. Hughes, S. M. Humphrey and M.
Bochmann, Organometallics, 2005, 24, 3792.
Potassium b-diketiminate K(LTol,Ad) (0.30 g, 0.63 mmol) was added
to a stirred suspension of SmI2 (0.13 g, 0.32 mmol) in Et2O
(50 mL) at ambient temperature and stirred overnight. A white
precipitate was filtered off; the dark blue filtrate was evaporated in
vacuo; pentane was added to the oily residue, which only partially
dissolved. Storing the mixture at -10 ◦C resulted in the formation
of blue crystals of [Sm(LTol,Ad)(LTol,Ad-H)] (6) (0.197 g, 60%).
9 M. Xue, R. Jiao, Y. Zhang, Y. Yao and Q. Shen, Eur. J. Inorg. Chem.,
2009, 4110.
10 A. M. Neculai, D. Neculai, H. W. Roesky and J. Magull, Polyhedron,
X-ray crystallographic studies for 3, 4, 5 and 6
2004, 23, 183.
11 C. Cui, H. W. Roesky, H.-G. Schmidt, M. Noltemeyer, H. Hao and F.
Cimpoesu, Angew. Chem. Int. Ed., 2000, 39, 4274.
12 S. Nagendran and H. W. Roesky, Organometallics, 2008, 27, 457.
13 D. Vidovic, M. Findlater, G. Reeske and A. H. Cowley, J. Organomet.
Chem., 2007, 692, 5683.
14 A. G. Avent, P. B. Hitchcock, A. V. Khvostov, M. F. Lappert and A. V.
Protchenko, Dalton Trans., 2004, 2272.
15 A. G. Avent, A. V. Khvostov, P. B. Hitchcock and M. F. Lappert, Chem.
Commun., 2002, 1410.
16 O. Eisenstein, P. B. Hitchcock, A. V. Khvostov, M. F. Lappert, L.
Maron, L. Perrin and A. V. Protchenko, J. Am. Chem. Soc., 2003, 125,
10790.
17 S. K. Ibrahim, A. V. Khvostov, M. F. Lappert, L. Maron, L. Perrin,
C. J. Pickett and A. V. Protchenko, Dalton Trans., 2006, 2591.
18 A. G. Avent, P. B. Hitchcock, A. V. Khvostov, M. F. Lappert and A. V.
Protchenko, Dalton Trans., 2003, 1070.
19 F. Cosle´dan, P. B. Hitchcock and M. F. Lappert, Chem. Commun., 1999,
705.
Diffraction data were collected on a Nonius Kappa CCD diffrac-
˚
tometer using monochromated Mo-Ka radiation, l = 0.71073 A
at 173(2) K. Crystals were coated in oil and then directly mounted
on the diffractometer under a stream of cold nitrogen gas. The
structures were refined by a full-matrix least-squares procedure
based on F2, using SHELXL-97;29 absorption corrections were
applied using MULTISCAN. For 3 there are K ◊ ◊ ◊ Me contacts to
C22 and C23 and for both groups hydrogen atoms were refined;
all other H atoms were in riding mode. For 4 distance (SADI)
and DELU constraints were applied to the Si2Me3 group. In 5 the
hexane solvate molecule was poorly defined and only five carbon
atoms were included with isotropic displacement parameters. In
6 for C52 a difference map showed three regions of density,
initially suggesting a methyl group. However, a free refinement
of these three H atoms was unsuccessful and including them
with idealised geometry but with the torsion angle refined led
20 P. B. Hitchcock, M. F. Lappert and A. V. Protchenko, Chem. Commun.,
2005, 951.
21 P. B. Hitchcock, M. F. Lappert, D.-S. Liu and R. Sablong, Chem.
Commun., 2002, 1920.
22 R. K. Minhas, Y. Ma, J.-I. Song and S. Gambarotta, Inorg. Chem.,
1996, 35, 1866.
23 E. D. Brady, D. L. Clark, J. C. Gordon, P. J. Hay, D. W. Keogh, R. Poli,
B. L. Scott and J. G. Watkin, Inorg. Chem., 2003, 42, 6682.
24 W. J. Evans, L.R. Chamberlain, T. A. Ulibarry and J. W. Ziller, J. Am.
Chem. Soc., 1988, 110, 6423.
25 R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor.
Gen. Crystallogr., 1976, 32, 751.
26 M. L. Cole and P. C. Junk, Chem. Commun., 2005, 2695.
27 D. Heitmann, C. Jones, P. C. Junk, K.-A. Lippert and A. Stasch, Dalton
Trans., 2007, 187.
28 M. L. Cole, G. B. Deacon, C. M. Forsyth, P. C. Junk, K. Konstas and
J. Wang, Chem.–Eur. J., 2007, 13, 8092.
29 G. M. Sheldrick, SHELXL-97, University of Go¨ttingen, Go¨ttingen,
Germany.
˚
to an inexplicably short Sm ◊ ◊ ◊ H bond (1.81 A). The group
was therefore modelled as a methylene carbon with the two
hydrogen atoms in idealised positions. There are two regions of
poorly defined residual density, presumably due to uncharacterised
solvate molecules; this was modelled by including seven isotropic
carbon atoms in the refinement. Further details on the four
structures are in Table 5.
Acknowledgements
We are grateful for the support of EPSRC and the Leverhulme
Trust with fellowships for A.V.K. and A.V.P.
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6426–6433 | 6433
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