Bulky formamidinate-supported lanthanoid halides and alkyls, including a rare terminal La-Me species

Article abstract of DOI:10.1021/om301048b

The oxidation of [Sm(DippForm)₂(thf)₂] (1; DippFormH = N,N′-bis(2,6-diisopropylphenyl)formamidine) by tert-butyl chloride, 1,2-dibromoethane, and iodine, respectively, at ambient temperature led to the isolation of the light yellow crystalline samarium(III) halide complexes [Sm(DippForm)₂X(thf)] (2, X = Cl; 3, X = Br; 4, X = I) in good yield. The subsequent metathesis reaction of [Ln(DippForm)₂X(thf)] (2, Ln = Sm, X = Cl; Ln = La, X = F) with LiMe and LiCH₂SiMe₃ generated the samarium alkyl complexes [Sm(DippForm)₂R(thf)] (5, R = Me; 6, R = CH₂SiMe₃) and the rare terminal La-Me complex [La(DippForm)₂Me(thf)] (7). The attempted ligand exchange reaction of 7 with 1,2,3,4-tetraphenylcyclopentadiene gave, unexpectedly, the homoleptic tris(formamidinato)lanthanum complex [La(DippForm)₃] (8) in very low yield. The redox transmetalation/protolysis (RTP) reaction from samarium metal with bis(2-bromo-3,4,5,6-tetrafluorophenyl)mercury and DippFormH in thf yielded the mono(formamidinato)samarium(III) complex [Sm(DippForm)Br₂(thf) ₃] (9) as a coproduct with the bis(formamidinate) 3. Redox reaction of the divalent samarium complex [Sm(DippForm)₂(thf)₂] (1) with diphenylmercury resulted in the ethenolate complex [Sm(DippForm) ₂(OCH=CH₂)(thf)] (10) instead of the target Sm-Ph complex, the product resulting from the decomposition of Lewis base thf molecules.

Full text of DOI:10.1021/om301048b

Article
pubs.acs.org/Organometallics
Bulky Formamidinate-Supported Lanthanoid Halides and Alkyls,
Including a Rare Terminal La−Me Species
Marcus L. Cole,† Glen B. Deacon,* Peter C. Junk,*,‡ and Jun Wang
School of Chemistry, Monash University, Clayton, Victoria 3800, Australia
S
* Supporting Information
ABSTRACT: The oxidation of [Sm(DippForm)2(thf)2] (1; DippFormH = N,N′-
bis(2,6-diisopropylphenyl)formamidine) by tert-butyl chloride, 1,2-dibromoethane,
and iodine, respectively, at ambient temperature led to the isolation of the light
yellow crystalline samarium(III) halide complexes [Sm(DippForm)2X(thf)] (2, X =
Cl; 3, X = Br; 4, X = I) in good yield. The subsequent metathesis reaction of
[Ln(DippForm)2X(thf)] (2, Ln = Sm, X = Cl; Ln = La, X = F) with LiMe and
LiCH2SiMe3 generated the samarium alkyl complexes [Sm(DippForm)2R(thf)] (5, R
= Me; 6, R = CH2SiMe3) and the rare terminal La−Me complex [La-
(DippForm)2Me(thf)] (7). The attempted ligand exchange reaction of 7 with
1,2,3,4-tetraphenylcyclopentadiene gave, unexpectedly, the homoleptic tris-
(formamidinato)lanthanum complex [La(DippForm)3] (8) in very low yield. The
redox transmetalation/protolysis (RTP) reaction from samarium metal with bis(2-
bromo-3,4,5,6-tetrafluorophenyl)mercury and DippFormH in thf yielded the
mono(formamidinato)samarium(III) complex [Sm(DippForm)Br2(thf)3] (9) as a coproduct with the bis(formamidinate) 3.
Redox reaction of the divalent samarium complex [Sm(DippForm)2(thf)2] (1) with diphenylmercury resulted in the ethenolate
complex [Sm(DippForm)2(OCHCH2)(thf)] (10) instead of the target Sm−Ph complex, the product resulting from the
decomposition of Lewis base thf molecules.
and related ligand systems. The bonding mode (κ2(N,N′))
INTRODUCTION
■
encapsulates much of the coordination sphere of lanthanoid
Organolanthanoid halides LnRnX3−n are often target molecules
metals effectively and leaves the remaining coordination sphere
in synthetic organolanthanoid chemistry, since they are possible
accessible to a coligand such as halide/alkyl (overall formula
isolable products directly from metathesis reactions between
[Ln(RNC(R′)NR)2L′(S)n], L′ = halide, alkyl, etc., solv,
lanthanoid trihalides and alkali-metal salts of anionic organic
usually n = 0, 1). The catalytic studies of amidinato/
ligands.1 Such organolanthanoid halides are key starting
guanidinato rare-earth-metal complexes in various processes
materials for derivatization to give other organolanthanoids,
such as homogeneous polymerizations, though at an early stage,
including alkyl, hydride, organoamide, and alkoxide complexes
have proven to be promising.5
LnRnZ3−n (Z = R′, H, NR′2, OR′). Lanthanoid alkyl complexes,
Our research in rare-earth-metal amidinate coordinaton
e.g., LnCpnR3−n, are generally highly reactive, and both halides
chemistry focuses on formamidinate ([RNC(H)NR]−)
and alkyl derivative complexes have found applications as
complexes, where the proton on the backbone carbon of the
catalysts or cocatalysts in some catalytic processes.2 Over the
anionic heteroallyl group has minimal steric and electronic
course of organolanthanoid chemistry studies, cyclopentadienyl
and related ligand systems have been dominant in the synthesis
effects in comparison with other amidinates/guanidinates
([RNC(R′)NR]−, R′ = alkyl/amine).6−9 The backbone
of lanthanoid halide, alkyl, and other relevant heteroleptic
proton is also an advantage in monitoring the reaction
complexes.3 For non-cyclopentadienyl ligands,4 the syntheses
pathways or identifying the formation of new formamidinate
of relevant heteroleptic lanthanoid halide derivatives are usually
complexes by NMR spectroscopy due to the resonances often
prerequisites before conversion into alkyl, organoamide, and
appearing isolated from other protons of the molecule.
related reactive species to establish the systems as alternatives
Formamidines are readily prepared and can be tuned sterically
and electronically. Previously, we have reported the synthesis of
to their cyclopentadienyl analogues.
1,3-Diazaallyl related ligand systems ([RNC(R′)NR]−, R′
homoleptic tris(formamidinato) lanthanoid(III) complexes
= H, formamidinate; R′ = alkyl, amidinate; R′ = amine,
[Ln(RNC(H)NR)3(thf)n] (R = aryl, n = 0−2) and
guanidinate) have shown potential in stabilizing the coordina-
heteroleptic bis(formamidinato)complexes [Ln(RNC(H)-
Special Issue: Recent Advances in Organo-f-Element Chemistry
tion of lanthanoid metals.5 Two anionic 1,3-diazaallyl moieties
bicapping a large Lewis acidic rare-earth-metal center in a
mononuclear complex is a typical bonding mode for amidinate/
guanidinate ligand systems and is comparable to the ubiquitous
sandwiching bonding modes of two cyclopentadienyl groups
Received: November 2, 2012
Published: December 24, 2012
© 2012 American Chemical Society
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a
Scheme 1. Synthesis of Halogeno and Alkyl Bis(formamidinato)lanthanoid(III) Complexes 2−7
a
Dipp = 2,6-diisopropylphenyl. Legend: (i) Ln = Sm, R = tBu, X = Cl (2), R = BrC2H4 or 2-HC6F4, X = Br (3), X2 = I2 (4); (ii) Ln = Sm, X = Cl, R′
= Me (5), R′ = CH2SiMe3 (6), Ln = La, X = F, R′ = Me (7).
NR)2R′(thf)], (R = aryl, R′ = F, CCPh),6−8 by the redox
transmetalation/protolysis (RTP) method. We have also
synthesized the divalent samarium formamidinate complex
[Sm(DippForm)2(thf)2] (1) and explored its reactivity with
Hg(C6F5)2, Hg(CCPh)2, and carbodiimides, forming the
trivalent samarium formamidinate complexes [Sm-
(DippForm)2(L′)(thf)n] (L′ = F, CCPh, RNC(R′)NR (R
= aryl, R′ = H, CH2Ph); n = 0, 1).6,8,9 Now we report new
oxidation reactions of the samarium(II) complex to form new
key reagents: viz., the structurally characterized samarium(III)
halide complexes [Sm(DippForm)2X(thf)] (X = Cl, Br, I).
These are potential reagents for the formation of the
heteroleptic alkyl, aryl, hydride, organoamide, alkoxide, and
aryloxide derivatives [Sm(DippForm)2Z(solv)] (Z = R, Ar, H,
NR2, OR, etc.), as foreshadowed by their conversion and that of
[La(DippForm)2F(thf)]8 into alkyl derivatives, including a La
complex with a rare terminal La−Me bond. In addition,
[La(DippForm)3], [Sm(DippForm)Br2(thf)3], and [Sm-
(DippForm)2(OCHCH2)(thf)] have been structurally char-
acterized, even though they were not obtained in amounts
allowing further characterization.
resonances are observed with substantial paramagnetic shifting
for X = Cl, Br, I and increase according to the sequence F
(6.90−7.32 ppm)6 → Cl (12.16 ppm) → Br (12.35 ppm) → I
(13.07 ppm) (at 303 K).
The subsequent metathesis reactions of lanthanoid halides
[Ln(DippForm)2X(thf)] (Ln = Sm, La; X = Cl, F) with the
lithium reagents LiMe and LiCH2SiMe3 at ambient temperature
in toluene yielded crystalline [Ln(DippForm)2Me(thf)] (Ln =
Sm, 5, light yellow; Ln = La, 7, colorless) and light yellow
[Sm(DippForm)2(CH2SiMe3)(thf)] (6) in moderate yields
(Scheme 1(ii)). C, H, and N elemental analyses are consistent
with the proposed molecular formulas. Their identities have
been authenticated by their X-ray crystal structures (see below).
IR absorption bands from formamidinate and coordinating thf
ligands are evident at frequencies similar to those of the
relevant metal halides 2−4.
1
In the H NMR spectra, the typical sharp singlet resonances
of NC(H)N protons in alkyl complexes 5−7 vary over a wide
range, with paramagnetic 5 being at frequencies lower than
those of 2−4 and that of 6 being near the value of the iodide 4.
Diamagnetic 7 has the resonance shifted to higher frequency
from the parent fluoride7 (see the Experimental Section). Sm−
CH3 (or −CH2) proton resonances in 5 and 6 are observed as
broad singlets, presumably due to the strong paramagnetic
effect of the samarium atom in close proximity to the protons.10
In contrast, La−CH3 protons of the diamagnetic lanthanum
complex 7 show a sharp singlet at 0.22 ppm.
Alkyl complexes 5−7 are among the rare species of amidinate
complexes incorporating direct Ln−C bonding.5 The lantha-
num complex 7 is a rare case of a species with a terminal La−
Me bond in organolanthanum chemistry.11 The relatively high
decomposition temperatures (ca. 250 °C) for alkyllanthanoid
derivatives are attributable to the crowded structures (below).
However, the precursor halides have even higher thermal
stability, melting without decomposition at ca. 340 °C because
of fewer possible decomposition paths in comparison to those
for the alkyl derivatives.
Because of our current interest in lanthanoid complexes with
bulky polyarylcyclopentadienyl ligands,12 the ligand exchange
reaction of [La(DippForm)2Me(thf)] (7) with 1,2,3,4-
tetraphenylcyclopentadiene (H2C5Ph4) was attempted but
failed to generate the direct ligand exchange product [La-
(DippForm)2(HC5Ph4)] (Scheme 2(i)). Instead, colorless
crystalline [La(DippForm)3] (8) was formed in low yield
(Scheme 2(ii)). The formation of the congener of the
previously reported samarium complex [Sm(DippForm)3] is
surprising, and the mechanism of the formation is not fully
understandable at the current stage. A previous attempt from 3
equiv of the group 1 metal salt ([Na(DippForm)(thf)3]) and 1
equiv of LnCl3 failed to deliver the homoleptic complexes.6
RESULTS AND DISCUSSION
■
Syntheses, Reactivity, and Analytical/Spectroscopic
Characterization. The oxidation of the green divalent
samarium complex [Sm(DippForm)2(thf)2] (1) by tert-butyl
chloride, 1,2-dibromoethane, and iodine, respectively, in
toluene at ambient temperature led to isolation of the light
yellow crystalline samarium(III) halide complexes [Sm-
(DippForm)2X(thf)] (2, X = Cl; 3, X = Br; 4, X = I) in
good yields (Scheme 1(i)). The samarium(III) bromide 3 was
also isolated from a redox reaction of 1 with 1-bromo-2,3,4,5-
tetrafluorobenzene, but with a yield lower than that from the
reaction with 1,2-dibromoethane.
C, H, and N analyses for compounds [Sm(DippForm)2X-
(thf)] were consistent with the proposed composition, and
their molecular structures were further confirmed by single-
crystal X-ray crystallography (see below). Infrared spectra of
the samarium(III) halides 2−4 are similar, as expected from
their isomorphous structures, and some tentative assignments
are provided in the Experimental Section.
The NMR spectra show resonances assignable to relevant
protons of the molecules. Thus, the methyl protons of the
isopropyl groups of 2−4 display two separate broad resonances
(0.00−1.50 ppm) at 303 K, indicating steric hindrance
hampering free rotation of the aryl group about the N−
C(Ar) axis and/or the isopropyl group along C(iPr)−C(Ar)
axis. However, there is relatively free rotation at 333 K, as the
resonances coalesce, as shown for 3. The CH(iPr) resonances
are broad at 2.85−3.13 ppm. Typical NC(H)N proton
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Scheme 2. Formation of [La(DippForm)3] (8)
Scheme 3. Formation of [Sm(DippForm)2X(thf)] (3),
[Sm(DippForm)Br2(thf)3] (9), and
a
[Sm(DippForm)2(OCHCH2)(thf)] (10)
Likewise, the attempted alternative metathesis reaction between
[Ln(DippForm)2X(thf)] (Ln = Sm, X = Cl; Ln = La; X = F)
and [Li(DippForm)(thf)3] in C6D6 at 70 °C overnight did not
generate the homoleptic complexes, nor did the attempted
protolysis reactions between [Ln(DippForm)2Me(thf)] (Ln =
Sm, La) and DippFormH under the same conditions. The
unsuccessful transformation to [Ln(DippForm)3] obviously
results from the bulky characteristics of the DippForm ligand. A
similar situation was encountered previously in the reactions of
[Sm(DippForm)2(CCPh)(thf)] with carbodiimides, where the
reaction goes smoothly with less bulky carbodiimides, giving
[Sm(DippForm)2(RNC(CCPh)NR] (R = mesityl, cyclohexyl),
but no reaction occurs with the bulkier N,N′-bis(2,6-
diisopropylphenyl)carbodiimide.9 The molecular structures of
[Ln(DippForm)3] (Ln = Sm,6 La) impressively display a
sterically hindered coordination environment (see Molecular
Structures). The bulky nature of the formamidinate ligand
makes homoleptic [Ln(DippForm)3] free of Lewis base
molecule coordination. This is in contrast with the less bulky
formamidinate complexes, e.g., [La(XylForm)3(thf)], where a
Lewis base molecule coordinates.8
The redox transmetalation/protolysis (RTP) reaction of
samarium metal with bis(pentafluorophenyl)mercury and N,N′-
bis(2,6-diisopropylphenyl)formamidine in thf also did not yield
[Sm(DippForm)3] but led to the isolation of [Sm-
(DippForm)2F(thf)].6 The reaction is considered to proceed
through a pathway involving C−F activation, as shown in
Scheme 3((i) and (iii); Ar = C6F5; X = F). The corresponding
RTP reaction with bis(2-bromo-3,4,5,6-tetrafluorophenyl)mer-
cury has now been found to yield [Sm(DippForm)2Br(thf)]
(3) and the coproduct [Sm(DippForm)Br2(thf)3] (9), both
identified by single-crystal X-ray structural determinations from
a cocrystallized mixture. The reaction probably involves the
intermediate samarium 2-bromo-3,4,5,6-tetrafluorophenyl com-
plex [Sm(DippForm)2(2-BrC6F4)(thf)] (Scheme 3(i), Ar = 2-
BrC6F4), which undergoes C−Br activation to form [Sm-
(DippForm)2Br(thf)] (3) (Scheme 3(iii), X = Br). Tetra-
fluorobenzyne has previously been trapped as an N-function-
alized formamidine from analogous but high-yielding RTP
reactions.8 The isolation of the dibromo(formamidinato)-
samarium(III) complex coproduct 9 from the RTP reaction is
surprising, and it is considered to be formed by C−Br activation
of the intermediate [Sm(DippForm)(2-BrC6F4)2(thf)n] formed
in the RTP reaction (Scheme 3(i,ii), Ar = 2-BrC6F4). The
dibromo product 9 is inseparable (apart from hand-picked
a
Legend: (i) Ar = C6F5,6 2-BrC6F4, −Hg; (ii) Ar = 2-BrC6F4, X = Br,
−2“C6F4”; (iii) Ar = C6F5,6 2-BrC6F4; X = F,6 Br. −“C6F4”; (iv)
HgPh2, PhMe, 110 °C, Ar = Ph, −Hg; (v) HgPh2, PhMe, 110 °C,
−Hg, −PhH, −CH2CH2; (vi) thf, Ar = Ph, −PhH, −CH2CH2.
crystals) from 3 in the mixture, which prohibited more
characterization of 9.
As the redox reaction of [Sm(DippForm)2(thf)2] (1) with
the mercurial reagent Hg(CCPh)2 at ambient temperature
afforded the complex [Sm(DippForm)2(CCPh)(thf)] in good
yield (Scheme 3(iv), Ar = CCPh),8 the possible synthesis of the
analogous [Sm(DippForm)2Ph(thf)] was attempted (Scheme
3(iv), Ar = Ph). However, the reaction of 1 with HgPh2 under
similar conditions caused no color change from the green
samarium(II) complex. Further, NMR spectrum monitoring of
the reaction mixture confirmed that no reaction occurred.
However, after the reaction mixture was heated to 110 °C, a
gradual color change from green to light yellow occurred.
Subsequent crystallization gave a mixture of crystals, some of
them being identified by X-ray crystallography (see Molecular
Structures) as [Sm(DippForm)2(OCHCH2)(thf)] (10)
(Scheme 3(v)), in contrast to the isolation of [Sm(C5Me5)2Ph-
(thf)] from the reaction of [Sm(C5Me5)2(thf)2] with HgPh2.13
The mixture was inseparable, prohibiting further character-
ization. The ethenolate ligand in 10 is plausibly formed through
the formation of a reactive Sm−Ph intermediate (Scheme 3(iv),
Ar = Ph) which abstracts a proton from thf at 110 °C (Scheme
3(vi)). The formation of 10 is not surprising, since similar
decomposition processes of thf molecules by other M−C
species have been observed previously.14
Molecular Structures. N,N′-bis(2,6-diisopropylphenyl)-
formamidinate complexes [Ln(DippForm)2L′(thf)] (Ln =
Sm, L′ = Cl (2), Br (3), I (4), CH3 (5), CH2SiMe3 (6),
OCCH2 (10); Ln = La, L′ = CH3 (7)) are all mononuclear
species, and their molecular structures are shown in Figure 1
(for 3), Figure 2 (for 6), Figure 3 (for 7), and Figure 4 (for
10). The lanthanoid metals are six-coordinate in these
heteroleptic species. Both formamidinate ligands in each
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Figure 3. Molecular structure of 7 shown with 50% thermal ellipsoids.
Hydrogen atoms (excluding those on C51) are omitted for clarity.
Figure 1. (a) Molecular structure of 3 shown with 50% thermal
ellipsoids. Hydrogen atoms are omitted for clarity. (b) Depiction of
the coordination core of 3 drawn as sticks with the equatorial
Sm1C1C26 plane (marked by dashed lines) orthogonal to the page.
Figure 4. Molecular structure of 10 shown with 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
samarium/lanthanum methyl complexes 5 and 7 (see the
Experimental Section). This isomorphism, however, does not
extend to complexes with the larger anionic ligands
(trimethylsilyl)methyl (6) and ethenolate (10) and the smallest
halide in the fluoride complex [Sm(DippForm)2F(thf)] (space
group P21/n (No. 14), unit cell data a = 20.4714(2) Å, b =
12.1996(2) Å, c = 21.6593(3) Å, β = 110.0650(10) Å, V =
5080.93(12) Å3).6
The N-aryl groups are nearly orthogonal to the NCN plane
(e.g. torsion angles of the two planes for 3 range from 69.8(2)
to 84.6(2)°), values typical of a coordinating amidinate such as
DippForm.6−9 The negative charges of anionic formamidinates
are delocalized on the NCN cores, as the C−N bond lengths
are similar and intermediate between typical single bonds and
double bonds (e.g. ∼1.32 Å in 3). As a result, the two Ln−N
bond lengths from the same formamidinate ligand can be very
close (e.g., Sm1−N1 = 2.440(5) Å and Sm1−N2 = 2.460(4) Å
in 2). However, Ln1−N1 and/or Ln1−N3 bond lengths are
generally marginally shorter than values for Ln1−N2 and/or
Ln1−N4 bonds (Tables 1 and 2), suggesting that the negative
charge of each formamidinate may be slightly asymmetrically
distributed. The N1C1N2 and N3C26N4 planes are both more
or less perpendicular to the C1Sm1C26 plane according to the
individual specific coordination environment (e.g., 75.9(2) and
44.8(2)° in 3, Figure 1(b)). The mean Sm−N bond lengths are
Figure 2. Molecular structure of 6·PhMe shown with 50% thermal
ellipsoids. Lattice solvent molecules and hydrogen atoms (excluding
those on C51) are omitted for clarity.
molecule are κ2-bonded to the metal atom through two
nitrogen donor atoms. The coordination geometry of these
complexes can be described by a distorted tetrahedron if the
formamidinate ligand is considered to be a single-point donor
located on the backbone carbon (NCN carbon). These
complexes all crystallized in the P1 space group with a shared
̅
isomorphism among samarium halide complexes 2−4 and
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(2.455(4) Å).17 The La−C(methyl) bond length in 7 (2.508(3)
Å) is slightly longer than the Sm−C length in 5 (2.476(3) Å)
but less than that expected for the different metal size, implying
considerable steric strain in the Sm complex. However, there is
no closely relevant reported terminal La−C(methyl) bond
length for comparison.11 The bond length is similar to that of a
discrete cation in [LaMe(thf)6][B(C6H4F-4)4]2 (2.456(6) Å).21
The Sm−O(thf) bond lengths of all bis(formamidinate)
complexes are in the close range of 2.45−2.49 Å, and they
are, as expected, longer than the Sm-OCHCH2 (anionic)
bond in 10 (2.111(3) Å). The Sm−O bond length of the
anionic ethenolate is comparable with that in Yb−O-
(ethenolate) (2.069 Å) in the four-coordinate [Yb{N(SiMe3)-
Table 1. Selected Bond Lengths (Å) and Angles (deg) in 2−
4 and 10
10, L′ =
OCH
2, L′ = Cl
3, L′ = Br
4, L′ = I
CH2
Ln1−N1
Ln1−N2
Ln1−N3
Ln1−N4
Ln1−X1
Ln1−O(thf)
2.440(5)
2.460(4)
2.404(5)
2.456(4)
2.5977(16)
2.453(4)
84.79(10)
132.61(16)
2.394(3)
2.462(3)
2.436(4)
2.458(3)
2.7508(5)
2.454(3)
84.95(7)
133.17(11)
2.3784(15)
2.4751(15)
2.4238(16)
2.4529(15)
2.9851(1)
2.4535(13)
85.33(3)
2.462(2)
2.472(2)
2.418(2)
2.495(2)
2.109(2)
2.453(2)
85.46(10)
131.34(8)
a
a
O−Sm−X1
C1···Sm···C26
133.30(5)
C6H3 Pr2-2,6}2(OCHCH2)ClLi(thf)3]22 and Sc−O(ethenolate)
i
a
For 10, X1 = OCHCH2.
(1.90 Å) in the four-coordinate diketiminate [Sc-
{2,6-i Pr2 C6 H3 NC(Me)CHC(Me)N−C6 H3 Pr2 -2,6}-
i
Table 2. Selected Bond Lengths (Å) and Angles (deg) in 5−
7
23
i
(NHC6H3 Pr2-2,6)(OCHCH2)], after consideration of metal
size and coordination number differences.
5, L′ = Me
6·PhMe, L′ = CH2SiMe3
7, L′ = Me
The homoleptic tris(formamidinato)lanthanum complex
[La(DippForm)3] (8) crystallized in space group P21/n (Figure
5 and Table 3) and is isomorphous with its samarium congener
Ln1−N1
Ln1−N2
Ln1−N3
Ln1−N4
Ln1−C(51)
Ln1−O(thf)
O−Sm−C51
C1···Sm···C26
2.436(3)
2.477(3)
2.460(2)
2.478(3)
2.475(3)
2.467(2)
84.19(9)
135.06(9)
2.462(3)
2.502(3)
2.441(3)
2.536(3)
2.420(4)
2.490(2)
89.43(11)
129.76(10)
2.534(2)
2.564(2)
2.506(2)
2.555(2)
2.508(3)
2.553(2)
84.34(9)
134.33(7)
close in bis(formamidinato)samarium(III) complexes 2−5 (2,
2.44 Å; 3, 2.43 Å; 4, 2.43 Å; 5, 2.46 Å) and 10 (2.46 Å). They
are all slightly shorter than in 6 (2.48 Å), a result of the steric
effect of the relatively bulkier CH2SiMe3 group. These values
are comparable to the mean Sm−N bond length in [Sm-
(DippForm)2F(thf)] (2.45 Å).6 As expected, they are all
shorter than the mean La−N bond length (2.54 Å) in 7,
consistent approximately with the different size of the two
metals (six-coordinate La is 0.07 Å larger than Sm).15 The angle
between the two bulky amidinates in terms of the nonbonding
angle C1−Ln−C26 (e.g., 133.17° for 3) is much larger than the
bond angle of the other two less bulky unidentate ligands (e.g.,
O−Ln−Br = 84.95° for 3).
The Sm−X bond length (X = F, 2.093(2) Å;6 X = Cl,
2.5977(16) Å; X = Br, 2.7512(5) Å; X = I, 2.9851(1) Å) in
these bis(formamidinate) complexes increases according to the
size of each halide.15 The Sm−Cl bond length in 2 is in the
range of those closely relevant mononuclear six-coordinate
samarium complexes [Sm(Ap′)2Cl(thf)] (2.5681(6) Å, Ap′ =
(2,6-diisopropylphenyl)[6-(2,6-dimethylphenyl)pyridin-2-yl]-
aminate)1 6 and [Sm{2-(2,6-i Pr2 -C6 H3 NCH)-
5-tBuC4H2N}2Cl(thf)] (2.625(2) Å).17 The Sm−Br bond
length in 3 (2.7512(5) Å) is comparable with the reported
values for seven-coordinate [SmBr3(thf)4] (2.8083(4),
2.8314(4), 2.8582(4) Å)18 after allowing for coordination
number differences. The Sm−I bond length in 4 (2.9851(1) Å)
is shorter than that in the 1-azaallyl complex [Sm(Me3SiCH
C(tBu)NSiMe3)2I(thf)] (3.092(1) Å),19 attributable to either
different steric effects or trans influences of the respective
chelating ligands. The terminal Sm1−C51(methyl) bond in 5
(2.476(3) Å) is comparable with that of the eight-coordinate
[Sm(C5Me5)2Me(thf)] (2.484(14) Å),20 despite the coordina-
tion number difference, while the Sm1−C51(methylene) bond
distance in 6 (2.420(4) Å) is comparable with that of [Sm{2-
(2,6-iPr2-C6H3NCH)-5-tBuC4H2N}2(CH2SiMe3)(thf)]
Figure 5. (a) Molecular structure of 8·2C6D6·PhMe shown with 50%
thermal ellipsoids. Isopropyl groups on arene rings are drawn as sticks,
and hydrogen atoms and lattice solvent molecules are omitted for
clarity. (b) Depiction of coordination core of 8 as sticks with the
C1C26C51 plane in the plane of the page.
[Sm(DippForm)3].6 If the amidinate ligand is treated as a single
donor ligand located on the backbone carbon (NCN), the
geometry of the coordination of samarium can be described as
almost perfectly trigonal planar (∑(C−Sm−C angles) =
359.9°). As seen previously for the structure of [Sm-
(DippForm)3], the sterically hindered coordination environ-
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Organometallics
Article
that of the [LnCpBr2(thf)3] complexes,25 suggesting an analogy
between tridentate Cp and the bulky bidentate DippForm
ligand.
Table 3. Selected Bond Lengths (Å) and Angles (deg) in 8
and 9
[La(DippForm)3] (8)
[Sm(DippForm)Br2(thf)3] (9·PhMe)
CONCLUSION
■
Ln1−N1
2.538(2)
2.558(2)
2.541(2)
2.546(2)
2.544(2)
2.562(2)
Ln1−N1
Ln1−N2
Ln1−Br1
Ln1−Br2
Ln1−O1(thf)
Ln1−O2(thf)
Ln1−O3(thf)
Br1−Sm1−Br2
O1−Sm1−O3
O2−Sm1···C1
2.434(3)
Rare species of alkyl samarium/lanthanum amidinate com-
plexes with an uncommon terminal La−Me bond have been
synthesized in satisfactory yields. The very bulky anionic N,N′-
bis(2,6-diisopropylphenyl)formamidinate ligand has shown the
ability to stabilize bis(formamidinato)samarium/lanthanum
halide (2−4) and alkyl (5−7) complexes, where two amidinate
ligands are capping the metal atom each through κ2 bonding
from two nitrogen donors. The bonding modes act effectively
so that the remaining coordination sites of the lanthanoid metal
are occupied by either a halide or an alkyl ligand and an
additional Lewis base molecule (thf). A very low yield of the
homoleptic tris(formamidinato)lanthanum complex 8 was
isolated, and the molecule shows a sterically hindered
coordination environment. The synthesis of bulky 8 has proven
to be a challenge, as several alternative attempts (including
metathesis reactions) were unsuccessful. The mono-
(formamidinato)samarium dibromide complex 9 was identified
from an RTP reaction, and the complex incorporates a seven-
coordinate metal atom rather than the six-coordinate metals
seen in bis- or tris(formamidinate) complexes 2−8.
Ln1−N2
Ln1−N3
Ln1−N4
Ln1−N5
Ln1−N6
2.465(3)
2.8331(4)
2.8395(4)
2.449(2)
2.514(2)
2.476(2)
C1···La1···C26
C26···La1···C51
C1···La1···C51
119.00(7)
121.20(7)
119.79(7)
166.614(13)°
148.00(8)°
177.23(8)°
ment results in a dramatic deviation of the arene rings from
perpendicular to the metallacycle NCNLn, e.g. the torsion
angles of two planes for 8 range from 57.1(1) to 63.0(2)°, in
contrast with the bis(amidinate) complexes 2−7 and 10, where
the N-aryl rings are nearly orthogonal to the NCNLn plane.
The mean La−N bond length (2.54 Å) is similar to the mean
distances of [La(tBuNC(Me)NBut)3] (2.54 Å)24 and [La(2,6-
Et2C6H3NC(H)NC6H3-Et22,6)3] (2.52 Å)8 and the bis-
(amidinato)lanthanum complex 7 (2.54 Å).
The mono(formamidinate) samarium dibromide complex
[Sm(DippForm)Br2(thf)3] (9) crystallized in the Pbca space
group. The seven-coordinate samarium complex also adopts a
mononuclear form (Figure 6 and Table 3). As can be seen from
EXPERIMENTAL SECTION
■
General Considerations. The compounds described herein were
prepared and handled under dinitrogen with conventional techniques.
IR spectra were recorded as Nujol mulls between NaCl plates using
either a Perkin-Elmer 1600 Series FTIR instrument or a Perkin-Elmer
Spectrum RX I FTIR spectrometer within the range 4000−600 cm−1.
1H NMR spectra were recorded on a Bruker DPX 300 spectrometer,
1
and chemical shifts were referenced to the residual H resonances of
the deuterated solvents. Melting points were determined in sealed
glass capillaries under nitrogen and are uncalibrated. Microanalyses
were determined by the Campbell Microanalytical Service, University
of Otago (New Zealand). Toluene, hexane, and thf were predried over
sodium metal and distilled over sodium (for toluene) or sodium
benzophenone ketyl (hexane and thf) before being stored under an
atmosphere of nitrogen. C6D6 was dried over sodium and stored under
an atmosphere of nitrogen. tert-Butyl chloride, 1,2-dibromoethane,
MeLi (1.60 M in diethyl ether), LiCH2SiMe3 (1.0 M in pentane), and
HgPh2 were purchased from Aldrich, and iodine was obtained from
Merck; all were used as supplied. Lanthanoid metals were purchased
from Santoku (America Int.) or Tianjiao (Baotou, People's Republic of
China) as ingots, powders, or rods and stored under nitrogen in a
glovebox. [Sm(DippForm)2(thf)2] (1),9 [La(DippForm)2F(thf)],7
tetraphenylcyclopentadiene,26 [Li(DippForm)(thf)3],27 Dipp-
Figure 6. Molecular structure of 9 shown with 50% thermal ellipsoids.
Hydrogen atoms are omitted for clarity.
29
FormH,28 and Hg(2-BrC6F4)2 were prepared by literature methods.
Synthesis of [Sm(DippForm)2Cl(thf)] (2). A solution of tert-butyl
chloride (0.10 g, 1.1 mmol) in toluene (10 mL) was added with
stirring at ambient temperature to a green solution of [Sm-
(DippForm)2(thf)2] (1; 1.02 g, 1.0 mmol) in toluene (40 mL). The
solution turned light yellow in 5 min, and the mixture was stirred
the aforementioned bis(formamidinato)lanthanoid complexes,
the formamidinate in this complex is similarly κ2 bonded to the
metal atom through two nitrogen donor atoms. The mean Sm−
N bond length (2.45 Å) is close to that in the six-coordinate
monobromo samarium complex 3 (2.43 Å), but the mean Sm−
Br bond length (2.84 Å) is longer than in 3 (2.7512(5) Å), and
the former is in the range of Sm−Br bond lengths of
[SmBr3(thf)4] (2.8083(4), 2.8314(4), 2.8582(4) Å).18 If the
amidinate ligand is treated as a single donor ligand located on
the backbone carbon (NCN), the geometry of the coordination
of samarium can be described as distorted octahedral with two
bromides occupying two vertices in a near-trans array (Br1−
Sm1−Br2 = 166.614(13)°). The Br2(thf)3 array is similar to
1
continuously for /2 h. The solution was reduced in volume to 5 mL
under vacuum and stored at −30 °C for 2 days, during which time
light yellow crystalline 2 precipitated and was collected (yield: 0.83 g,
91%). Mp: 330−334 °C. Anal. Calcd for C54H78ClN4OSm (985.04):
C, 65.84; H, 7.98; N, 5.69. Found: C, 65.66; H, 7.84; N, 5.55. IR
(Nujol, cm−1): 1666 w (ν(CN)), 1592 w, 1520 w and 1506 w
(ν(CC)), 1316 m, 1278 m, 1192 w (β(CH)), 1109 w, 1098 w, 1056 w
(ν(C−O), thf), and 1016 m (β(CH)), 943 w, 862 w (ring mode, thf),
800 w, 775 w, 757 m (γ(CH)). 1H NMR (C6D6, 303 K, ppm): 0.50 (s,
broad, 24H, CH3), 1.39 (s, broad, 28H, CH3 + thf), 3.15 (m, broad,
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Table 4. Crystal Data and Structure Refinement Details for Complexes 2−10
[Sm(DippForm)2
Cl(thf)] (2)
[Sm(DippForm)2
Br(thf)] (3)
[Sm(DippForm)2
[Sm(DippForm)2
Me(thf)] (5)
[Sm(DippForm)2(CH2SiMe3)
I(thf)] (4)
(thf)]·PhMe (6·PhMe)
formula
Mr
C54H78ClN4OSm
985.00
C54H78BrN4OSm
1029.46
C54H78IN4OSm
1076.45
C55H81N4OSm
964.64
C65H97N4OSiSm
1128.91
space group
a (Å)
P1
P1
P1
P1
P1
̅
̅
̅
̅
̅
11.283(2)
14.597(3)
16.373(3)
84.14(3)
77.90(3)
80.80(3)
2596.1(9)
2
11.4129(2)
14.5854(3)
16.3356(3)
83.9810(10)
77.8760(10)
80.5180(10)
2615.31(9)
2
11.6940(2)
14.5418(2)
16.2892(3)
83.4130(10)
77.4830(10)
79.7300(10)
2652.49(8)
2
11.238(2)
14.685(3)
16.382(3)
83.97(3)
77.94(3)
80.91(3)
2603.4(9)
2
12.858(3)
13.488(3)
18.772(4)
108.51(3)
93.48(3)
95.08(3)
3061.4(11)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
μ (mm−1
)
1.222
1.926
1.727
1.167
1.021
ρcalcd (g cm−3
)
1.260
1.307
1.348
1.231
1.225
Nτ
24021
29084
40351
28121
46141
N (Rint)
9124 (0.1229)
0.0659/0.0825
11910 (0.0766)
0.0458/0.0958
12012 (0.0313)
0.0225/0.0466
11914 (0.0667)
0.0442/0.0839
14001 (0.0945)
0.0508/0.1078
R1/wR2 (I >
2σ(I))
R1/wR2 (all
data)
0.0971/0.1335
0.0766/0.1092
0.0280/0.0487
0.0666/0.0904
0.0806/0.1191
GOF
0.965
1.017
1.033
1.005
1.013
max/min Δe (e
0.967/−0.777
1.410/−1.825
0.426/−0.490
1.253/−0.953
0.127/−1.007
Å−3
)
[La(DippForm)2Me(thf)]
[La(DippForm)3]·2C6D6·PhMe
[Sm(DippForm)Br2(thf)3]·PhMe
(9·PhMe)
[Sm(DippForm)2(OCHCH2)
(thf)] (10)
(7)
(8·2C6D6·PhMe)
formula
Mr
C55H81N4OLa
953.15
C94H77D48N6La
1477.98
P21/n
C44H67Br2N2O3Sm
982.17
C56H81N4O2Sm
992.60
space group
a (Å)
P1
̅
Pbca
P1
̅
11.2278(2)
14.7760(3)
16.4311(3)
83.683(1)
77.954(1)
80.980(1)
2624.51(9)
2
13.033(3)
37.741(8)
16.757(3)
90
19.5632(3)
19.1357(3)
23.8446(4)
90
12.2755(3)
14.0703(3)
17.8816(5)
78.3150(10)
69.9430(10)
67.8920(10)
2678.30(11)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
μ (mm−1
ρcalcd (g cm−3
96.42(3)
90
90
90
8191(3)
4
8926.4(2)
8
)
0.853
0.570
3.144
1.138
)
1.206
1.208
1.462
1.231
Nτ
32704
89472
63397
62130
N (Rint)
12055 (0.0554)
0.0408/0.0720
18757 (0.0663)
0.0464/0.1058
10226 (0.0959)
0.0379/0.0822
12287 (0.0401)
0.0367/0.0780
R1/wR2 (I >
2σ(I))
R1/wR2 (all data)
GOF
0.0582/0.0764
1.014
0.0730/0.1130
1.019
0.0724/0.0936
0.978
0.0432/0.0825
1.068
max/min Δe (e
0.093/−0.693
0.086/−0.711
1.314/−0.979
1.314/−0.979
Å−3
)
1
8H, CH, Pri), 3.70 (s, 4H, thf), 7.20−7.48 (m, 12H, C6H3), 12.16 (s,
2H, NC(H)N).
C6H3), 12.35 (s, 2H, NC(H)N). H NMR (C6D6, 333 K, ppm):
0.68 (s, broad, 48H, CH3), 1.36 (s, 4H, thf), 2.85 (s, broad, 8H, CH,
Pri), 4.46 (s, 4H, thf), 7.04−7.50 (m, 12H, C6H3), 12.51 (s, 2H,
NC(H)N). The unit cell was determined and is similar to that of 3
Synthesis of [Sm(DippForm)2Br(thf)] (3). (a) A solution of 1,2-
dibromoethane (0.10 g, 0.50 mmol) in toluene (10 mL) was added
with stirring at ambient temperature to a green solution of
[Sm(DippForm)2(thf)2] (1; 1.02 g, 1.0 mmol) in toluene (40 mL).
The solution turned light yellow gradually, and the mixture was stirred
given in Table 4: space group P1, a = 11.4407 Å, b = 14.6045 Å, c =
̅
16.3514 Å, α = 83.876°, β = 77.848°, γ = 80.520°, V = 2627.04 Å3.
(b) A solution of 1-bromo-2,3,4,5-tetrafluorobenzene in thf (0.008
M, 45 mL, 0.36 mmol) was added dropwise with stirring to a dark
green solution of [Sm(DippForm)2(thf)2] (1; 0.37 g, 0.36 mmol) in
thf (30 mL), at ambient temperature. After 1 h, the resulting light
yellow solution was filtered, dried in vacuo, and extracted into the
minimum volume of toluene (ca. 2 mL). Light yellow blocks of 3
deposited after standing for several days (yield 0.16 g, 43%), and the
X-ray crystal structure was determined.
1
continuously for /2 h. The solution was reduced in volume to 3 mL
under vacuum and stored at ambient temperature for 2 days, during
which time light yellow crystalline 3 precipitated and was collected
(yield: 0.80 g, 78%). Mp: 336−340 °C. Anal. Calcd for
C54H78BrN4OSm (1029.46): C, 63.00; H, 7.64; N, 5.44. Found: C,
62.95; H, 7.75; N, 5.56. IR (Nujol, cm−1): 1667 w, 1592 w, 1518 m,
1316 m, 1276 m, 1191 w, 1108 w, 1055 w, 1043 w, 1014 m, 942 w,
1
860 w, 800 m, 757 s, 670 w. H NMR (C6D6, 303 K, ppm): 0.11 (s,
Synthesis of [Sm(DippForm)2I(thf)] (4). A solution of iodine
(0.13 g, 1.0 mmol) in toluene (10 mL) was added with stirring at
ambient temperature to a green solution of [Sm(DippForm)2(thf)2]
broad, 24H, CH3), 1.11 (s, broad, 24H, CH3), 1.34 (s, broad, 4H, thf),
2.91 (m, broad, 8H, CH, Pri), 3.86 (s, 4H, thf), 7.27−6.85 (m, 12H,
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(1; 1.02 g, 1.0 mmol) in toluene (40 mL). The solution turned light
yellow gradually, and the mixture was stirred continuously for /2 h.
mL) in a J. Young valve equipped NMR tube. The mixture was heated
to 70 °C and kept at this temperature overnight. The mixture was
stored for 1 week at ambient temperature, during which time colorless
rod-shaped crystals deposited that were sufficient for an X-ray crystal
structure determination.
1
The solution was reduced in volume to 10 mL under vacuum and
stored at −30 °C for 2 days, during which time light yellow crystalline
4 precipitated and was collected (yield: 0.87 g, 81%). Mp: 338−342
°C. Anal. Calcd for C54H78IN4OSm (1076.51): C, 60.25; H, 7.30; N,
5.20. Found: C, 60.20; H, 7.37; 5.22. IR (Nujol, cm−1): 1667 w, 1592
w, 1519 s, 1361 w, 1316 m, 1277 m, 1235 w, 1191 m, 1108 w, 1055 w,
1043 w, 1013 w, 943 w, 859 w, 800 m, 775 w, 757 m. 1H NMR (C6D6,
303 K, ppm): 0.16 (s, broad, 24H, CH3), 1.20 (s, broad, 24H, CH3),
1.80 (s, 4H, thf), 3.03 (m, broad, 8H, CH, Pri), 4.63 (s, 4H, thf), 7.14−
Attempted Reaction of [Sm(DippForm)2Cl(thf)] (2) or [La-
(DippForm)2F(thf)] with [Li(DippForm)(thf)3]. C6D6 (0.7 mL) was
added to a J. Young valve equipped NMR tube charged with
[Sm(DippForm)2Cl(thf)] (2) or [La(DippForm)2F(thf)] (0.030 g)
and [Li(DippForm)(thf)3] (0.030 g). The mixture was heated to 70
1
°C and kept at this temperature overnight. H NMR spectroscopy
1
7.50 (m, 12H, C6H3), 13.07 (s, 2H, NC(H)N). H NMR (C6D6,
showed only two starting compounds and no appreciable new species
formed.
333 K, ppm): 0.71 (s, broad, 48H, CH3), 1.73 (s, 4H, thf), 2.98 (s,
broad, 8H, CH, Pri), 4.46 (s, 4H, thf), 7.14−7.50 (m, 12H, C6H3),
13.15 (s, 2H, NC(H)N).
Attempted Reaction of [Sm(DippForm)2Me(thf)] (5) or
[La(DippForm)2Me(thf)] (7) with DippFormH. C6D6 (0.7 mL)
was added to a J. Young valve equipped NMR tube charged with
[Sm(DippForm)2Me(thf)] (5) or [La(DippForm)2Me(thf)] (7)
(0.030 g) and DippFormH (0.030 g). The mixture was heated to 70
Synthesis of [Sm(DippForm)2Me(thf)] (5). A solution of
methyllithium in diethyl ether (1.6 M, 0.80 mL, 1.3 mmol) was
added to a solution of [Sm(DippForm)2Cl(thf)] (2; 0.91 g, 1.0 mmol)
in toluene (20 mL) with stirring at ambient temperature. The mixture
1
°C and kept at this temperature overnight. H NMR spectroscopy
1
was stirred continuously for /2 h. The solvent was removed under
showed only the two starting compounds and no appreciable new
species formed.
vacuum and replaced by toluene (30 mL). The insoluble precipitate
was filtered off, and the volume of the solution was reduced to 5 mL
under vacuum. The solution was stored at −30 °C for 2 days, during
which time bright yellow crystalline 5 precipitated and was collected
(yield: 0.48 g, 50%). Dec pt: 258 °C. Anal. Calcd for C55H81N4OSm
(964.62): C, 68.48; H, 8.46; N, 5.81. Found: C, 68.21; H, 8.19; N,
5.66. IR (Nujol, cm−1): 1667 w, 1592 w, 1522 s, 1361 w, 1315 m, 1280
m, 1192 m, 1109 w, 1098 w, 1056 w, 1044 w, 1024 w, 942 w, 868 w,
Synthesis of [Sm(DippForm)Br2(thf)3] (9). Tetrahydrofuran (20
mL) was added to a Schlenk flask charged with freshly filed Sm metal
(0.09 g, 0.60 mmol), Hg(2-BrC6F4)2 (0.20 g, 0.30 mmol), and
DippFormH (0.22 g, 0.60 mmol). The resulting slurry was stirred
overnight to give a light burgundy reaction mixture. Filtration followed
by removal of reaction volatiles in vacuo afforded an oily brown solid
that was extracted into toluene (10 mL); the extract was concentrated
to the point of crystallization and left to stand at ambient temperature.
Light yellow prisms of 9·C7H8 and blocks of 3 codeposited after
standing for several days. The mixture is inseparable, which prohibited
the isolation of a bulk amount of 9 and its further characterization.
Synthesis of [Sm(DippForm)2(OCHCH2)(thf)] (10). A
Schlenk flask was charged with [Sm(DippForm)2(thf)2] (1; 0.50 g,
0.50 mmol), diphenylmercury (0.090 g, 0.25 mmol), and toluene (20
mL). The mixture was heated to 110 °C and kept at this temperature
overnight. The volume of the solution was reduced to 2 mL under
vacuum and stored for 1 week, during which time light yellow solid
products precipitated. The precipitate contains light yellow crystals of
10, which were identified by X-ray crystallography. However, 10 was
inseparable from the rest of the mixture, which prohibited other
characterization.
X-ray Crystal Structure Determinations. Crystals were
mounted in paraffin oil on glass fibres or cryoloops. Intensity data
were collected on an Enraf-Nonius Kappa CCD diffractometer (3, 5, 6,
and 9) or a Bruker X8 APEX II CCD diffractometer (2, 4, 7, and 10)
using Mo Kα radiation at 123 K (λ = 0.71073 Å). The data sets were
empirically corrected for absorption with SORTAV30 or SADABS.31
The data of compound 8 were collected on the Australian Synchrotron
MX1 beamline at 100 K with wavelength λ = 0.712 Å using the
BlueIce32 GUI and processed with the XDS33 software package. All
structures were solved by conventional methods and refined by full-
matrix least squares on all F2 data using SHELX97,34 in conjunction
with the X-Seed graphical user interface.35 Anisotropic thermal
parameters were refined for non-hydrogen atoms, and hydrogen
atoms on carbons were calculated and refined with a riding model.
Crystal data collection and refinement details are given in Table 4.
1
801 m, 774 w, 757 s, 728 w, 671 w. H NMR (C6D6, 303 K, ppm):
0.33 (s, 4H, thf), 1.03 (s, 48H, CH3, Pri), 1.91 (s, br, 3H, CH3), 2.16
(s, 4H, thf), 3.16 (s, 8H, CH, Pri), 6.95−7.32 (m, 12H, C6H3), 10.83
(s, 2H, NC(H)N).
Synthesis of [Sm(DippForm)2(CH2SiMe3)(thf)] (6). A solution
of ((trimethylsilyl)methyl)lithium in pentane (1.0 M, 1.2 mL, 1.2
mmol) was added to a solution of [Sm(DippForm)2Cl(thf)] (2; 0.91
g, 1.0 mmol) in toluene (30 mL) with stirring at ambient temperature.
1
The mixture was stirred continuously for /2 h. The precipitate was
filtered off, and the solution was reduced in volume to 5 mL under
vacuum. The solution was stored at −30 °C for 2 days, during which
time yellow crystals of 6·PhMe precipitated and were collected (yield:
0.60 g, 53%). Dec pt: 256 °C. Anal. Calcd for C65H97N4OSiSm
(1128.94): C, 69.15; H, 8.66; N, 4.96. Found: C, 69.04; H, 8.74; N,
5.33. IR (Nujol, cm−1): 1666 m (ν(CN)), 1593 w and 1526 s
(ν(CC)), 1362 w, 1317 m, 1286 s, 1251 w, 1238 m, 1187 m (β(CH)),
1108 w, 1054 w (ν(CO, thf)), 1044 w, and 1022 m (β(CH)), 940 m,
866 m (ring mode, thf), 800 m, 768 m, 755 m (γ(CH)), 728 m, 694 w,
673 w. 1H NMR (C6D6, 333 K, ppm): −0.01 (s, br, 2H, CH2Si), 0.11
(s, 9H, SiCH3), 0.68 (s, 48H, CH3, Pri), 1.04 (s, 4H, thf), 2.11 (s, 3H,
CH3, PhMe), 2.71 (s, 8H, CH, Pri), 3.29 (s, 4H, thf), 6.75−7.13 (m,
17H, C6H3 + C6H5), 12.92 (s, br, 2H, NC(H)N).
Synthesis of [La(DippForm)2Me(thf)] (7). A solution of
methyllithium in diethyl ether (1.6 M, 0.8 mL, 1.3 mmol) was
added to a solution of [La(DippForm)2F(thf)] (0.96 g, 1.0 mmol) in
toluene (20 mL) with stirring at ambient temperature. The mixture
1
was stirred continuously for /2 h. The solvent was removed under
vacuum and replaced by toluene (30 mL). The precipitate was filtered
off, and the solution was reduced in volume to 5 mL under vacuum.
The solution was stored at −30 °C for 2 days, during which time
colorless crystals of 7 precipitated and were collected (0.46 g, 48%).
Anal. Calcd for C55H81N4OLa (953.16): C, 69.30; H, 8.57; N, 5.88.
Found: C, 68.41; H, 8.61; N, 5.78. IR (Nujol, cm−1): 1667 w
(ν(CN)), 1592 w and 1518 s (ν(CC)), 1361 w, 1314 m, 1284 s, 1233
w, 1190 s (β(CH)), 1108 w, 1098 w, 1056 w (ν(CO), thf), 1043 w
and 1025 w (β(CH)), 1013 w, 940 m, 868 m (ring mode, thf), 822 w,
800 m, 774 m, 757 m (γ(CH)), 728 w, 669 w. 1H NMR (C6D6, 303 K,
ppm): 0.22 (s, 3H, CH3), 0.98 (m, br, 4H, thf), 1.24 (d, 48H, CH3,
Pri), 3.55 (m, 12H, CH(Pri) + CH2(thf)), 6.98−7.12 (m, 12H, C6H3),
8.21 (s, 2H, NC(H)N).
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystal data for 2−10. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
Synthesis of [La(DippForm)3] (8). [La(DippForm)2Me(thf)] (7;
0.030 g) was added to a solution of H2C5Ph4 (0.030 g) in C6D6 (0.7
*E-mail: glen.deacon@monash.edu (G.B.D.).
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dx.doi.org/10.1021/om301048b | Organometallics 2013, 32, 1370−1378

Organometallics
Article
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Present Addresses
†School of Chemistry, University of New South Wales, Sydney
2052, Australia.
‡School of Pharmacy and Molecular Sciences, James Cook
University, Townsville, Queensland 4811, Australia.
Notes
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(16) Qayyum, S.; Skvortsov, G. G.; Fukin, G. K.; Trifonov, A. A.;
The authors declare no competing financial interest.
Kretschmer, W. P.; Doring, C.; Kempe, R. Eur. J. Inorg. Chem. 2010,
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ACKNOWLEDGMENTS
■
248−257.
We thank the Australian Research Council for support. Aspects
of this research were undertaken on the MX1 beamline at the
Australian Synchrotron, Victoria, Australia.
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