Synthesis, structures and reactivity of lanthanoid(II) formamidinates of varying steric bulk

Article abstract of DOI:10.1002/chem.201202861

New reactive, divalent lanthanoid formamidinates [Yb(Form) ₂(thf)₂] (Form=[RNCHNR]; R=o-MeC₆H₄ (o-TolForm; 1), 2,6-Me₂C₆H₃ (XylForm; 2), 2,4,6-Me₃C₆H₂ (MesForm; 3), 2,6-Et ₂C₆H₃ (EtForm; 4), o-PhC₆H ₄ (o-PhPhForm; 5), 2,6-iPr₂C₆H₃ (DippForm; 6), o-HC₆F₄ (TFForm; 7)) and [Eu(DippForm) ₂(thf)₂] (8) have been prepared by redox transmetallation/protolysis reactions between an excess of a lanthanoid metal, Hg(C₆F₅)₂ and the corresponding formamidine (HForm). X-ray crystal structures of 2-6 and 8 show them to be monomeric with six-coordinate lanthanoid atoms, chelating N,N′-Form ligands and cis-thf donors. However, [Yb(TFForm)₂(thf)₂] (7) crystallizes from THF as [Yb(TFForm)₂(thf)₃] (7 a), in which ytterbium is seven coordinate and the thf ligands are pseudo-meridional . Representative complexes undergo C-X (X=F, Cl, Br) activation reactions with perfluorodecalin, hexachloroethane or 1,2-dichloroethane, and 1-bromo-2,3,4,5-tetrafluorobenzene, giving [Yb(EtForm)₂F]₂ (9), [Yb(o-PhPhForm)₂F]₂ (10), [Yb(o-PhPhForm) ₂Cl(thf)₂] (11), [Yb(DippForm)₂Cl(thf)] (12) and [Yb(DippForm)₂Br(thf)] (16). X-ray crystallography has shown 9 to be a six-coordinate, fluoride-bridged dimer, 12 and 16 to be six-coordinate monomers with the halide and thf ligands cis to each other, and 11 to have a seven-coordinate Yb atom with pseudo-meridional unidentate ligands and thf donors cis to each other. The analogous terbium compound [Tb(DippForm)₂Cl(thf)₂] (13), prepared by metathesis, has a similar structure to 11. C-Br activation also accompanies the redox transmetallation/protolysis reactions between La, Nd or Yb metals, Hg(2-BrC ₆F₄)₂, and HDippForm, yielding [Ln(DippForm)₂Br(thf)] complexes (Ln=La (14), Nd (15), Yb (16)). Copyright

Full text of DOI:10.1002/chem.201202861

DOI: 10.1002/chem.201202861
Synthesis, Structures and Reactivity of Lanthanoid(II) Formamidinates of
Varying Steric Bulk
Marcus L. Cole,[a, b] Glen B. Deacon,[a] Craig M. Forsyth,[a] Peter C. Junk,*[a, c]
Kristina Konstas,[a, d] Jun Wang,[a] Henry Bittig,[a] and Daniel Werner[a]
Dedicated to Professor Cameron Jones on the occasion of his 50th birthday
Abstract: New reactive, divalent lan-
thanoid formamidinates [Yb(Form)2-
(thf)2] (Form=[RNCHNR]; R=o-
MeC6H4 (o-TolForm; 1), 2,6-Me2C6H3
(XylForm; 2), 2,4,6-Me3C6H2 (Mes-
Form; 3), 2,6-Et2C6H3 (EtForm; 4), o-
PhC6H4 (o-PhPhForm; 5), 2,6-iPr2C6H3
(DippForm; 6), o-HC6F4 (TFForm; 7))
G
E
ordinate, fluoride-bridged dimer, 12
and 16 to be six-coordinate monomers
with the halide and thf ligands cis to
each other, and 11 to have a seven-co-
ordinate Yb atom with “pseudo-meri-
dional” unidentate ligands and thf
donors cis to each other. The analo-
G
ACHTUNGTRENNUNG
gous
terbium
compound
[Tb-
and [Eu
G
N
A
(thf)2] (13), prepared by
been prepared by redox transmetalla-
tion/protolysis reactions between an
metathesis, has a similar structure to
ꢀ
11. C Br activation also accompanies
excess of a lanthanoid metal, Hg
N
the redox transmetallation/protolysis
reactions between La, Nd or Yb
and the corresponding formamidine
(HForm). X-ray crystal structures of 2–
6 and 8 show them to be monomeric
with six-coordinate lanthanoid atoms,
chelating N,N’-Form ligands and cis-thf
metals, Hg
ACHTUNGTRENNUNG
Form, yielding [Ln
N
ACHTUNGTRENNUNG
complexes (Ln=La (14), Nd (15), Yb
(16)).
donors. However, [YbACHTNUTRGENNUG(TFForm)2ACHTUNGTERN(NUGN thf)2]
(7) crystallizes from THF as [Yb-
Introduction
ACHTUNGTRENNUNG
a
As part of our studies of N-donor alternatives to the cyclo-
pentadienyl family of ligands,[1] we have previously reported
([R1NCR2NR3]ꢀ). Formamidines (HForm) are readily syn-
thesised from aromatic amines and triethyl orthoformate,
permitting the tuning of their steric and electronic proper-
ties.[3] The availability of formamidines as neutral species
(unlike many other groups of amidinates) makes them suita-
ble for free-metal-based syntheses.[4] Accordingly, [Ln-
the first syntheses of
a
wide range of tris
ACHTUNGTRENNUNG
A
U
[a] Prof. Dr. M. L. Cole, Prof. Dr. G. B. Deacon, Dr. C. M. Forsyth,
Prof. Dr. P. C. Junk, Dr. K. Konstas, Dr. J. Wang, H. Bittig, D. Werner
School of Chemistry, Monash University
A
3ACHTUNGTRENUN(NG thf)n] complexes were prepared by a redox transme-
Victoria 3800 (Australia)
AHCTUNGTRENNUNG
[b] Prof. Dr. M. L. Cole
nyl)mercury and N,N’-diACTHNUGRTENUNG(aryl)formamidines [Eq. (1)] in tet-
Present address:
School of Chemistry, University of New South Wales
Sydney, NSW, 2052 (Australia)
rahydrofuran.[2,5] The steric bulk of the Form ligand affects
not only the number of tetrahydrofuran co-ligands in the re-
sulting complex, but, in the case of N,N-bis(2,6-diisopropyl-
phenyl)formamidine (DippFormH), the bulkiest N,N’-di-
[c] Prof. Dr. P. C. Junk
School of Pharmacy and Molecular Sciences, James Cook University
Townsville, Qld, 4811 (Australia)
E-mail: peter.junk@jcu.edu.au
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
[d] Dr. K. Konstas
coproduct. This coproduct incorporates a ring-opened THF
molecule and a trapped fluorobenzyne derivative as shown
Present address:
CSIRO Division of Material Science and Engineering
Clayton, VIC, 3168 (Australia)
in Equation (2)].[2,5] The outcome was attributed to C F ac-
ꢀ
tivation of a [Ln
A
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202861.
species formed by oxidation of a putative bis(formamidina-
1410
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 1410 – 1420

FULL PAPER
to)lanthanoid(II) species by Hg
[Eqs. (3) and (4)].
G
Results and Discussion
Synthesis and spectroscopic characterisation: Ytterbium(II)
complexes were synthesised by the treatment of freshly filed
Yb metal with two equivalents of the corresponding forma-
midine proACTHNUGRTENNUGliACHUTNGTRENNUGgand and one equivalent of either bis(penta-
fluorophenyl)mercury or diphenylmercury in THF
(Scheme 1). These one-pot reactions afforded seven new di-
2 Lnþ3 HgðC F Þ þ 6 FormH THF
ƒƒ!
6
5 2
ð1Þ
ð2Þ
ð3Þ
ð4Þ
2 ½LnðFormÞ3ðthfÞnꢁ þ 6 C6F5H þ 3 Hg; n ¼ 0 ꢀ 2
2 Lnþ3 Hgð2-XC F Þ þ 6 DippFormH THF
ƒƒ!
6
4 2
2 ½LnðDippFormÞ2FðthfÞꢁ þ 3 Hg þ 4 ð2-XC6F4HÞ
þ2 ð2-XHC6F3OðCH2Þ4ðDippFormÞÞ; X ¼ H or F
2 ½LnðDippFormÞ2ꢁ þ Hgð2-XC6F4Þ2 !
‘‘2 ½LnðDippFormÞ2ð2-XC6F4Þꢁ’’ þ Hg
‘‘½LnðDippFormÞ ð2-XC F Þꢁ’’ HDippForm
ƒƒƒƒƒ!
2
6
4
THF
½LnðDippFormÞ2FðthfÞꢁ
þ2-XC6F3OðCH2Þ4ðDippFormÞ; X ¼ H or F
Scheme 1. Synthesis of complexes 1–8. Ln=Yb for 1–7 and Ln=Eu for
8. Ar=2-MeC6H4 (o-TolForm) for 1, 2,6-Me2C6H3 (XylForm) for 2, 2,4,6-
Me3C6H2 (MesForm) for 3, 2,6-Et2C6H3 (EtForm) for 4, 2-PhC6H4 (o-
PhPhForm) for 5, 2,6-iPr2C6H3 (DippForm) for 6 and 8 and 2,3,4,5-F4C6H
(TFForm) for 7.
Support for this hypothesis was provided by the observed
formation of [Sm(DippForm)2(F)(thf)] on reaction of [Sm-
(DippForm)2A(thf)2] with Hg
(C6F5)2,[6] and by the isolation of
[Sm(DippForm)2A(CCPh)(thf)] from the reaction of the same
divalent precursor, [Sm(DippForm)2A(thf)2], with Hg-
(CCPh)2.[2] These observations serve to focus attention on
the divalent lanthanoid formamidinates, of which only [Sm-
(DippForm)2A
(thf)2] has been reported.[6] We have also re-
ported a range of reactions of this complex with carbodi-
imides as a source of bulky [Sm(DippForm)3] and bulky
G
ACHTUNGTRENNUNG
A
N
ACHTUNGTRENNUNG
A
N
ACHTUNGTRENNUNG
E
CHTUNGTRENNUNG
valent ytterbium–formamidinate complexes, that is, [Yb(o-
ACHTUNGTRENNUNG
TolForm)
(MesForm)
PhPhForm)
(6) and [Yb
tals of [Yb(TFForm)
from THF (for abbreviations see Scheme 1). The europium
analogue [Eu(DippForm)2A(thf)2]·2THF (8) was prepared
similarly by using Eu metal in place of Yb with HDippForm
as the proligand. Compound 1 could be synthesised with
either mercury reagent, compounds 2–4 and 6–8 were pre-
pared from [Hg(C6F5)2], and compound 5 was synthesised
with [HgPh2]. The corresponding [Yb(Form)3A(thf)n], (n=0,
2A
R
2ACHTUNGTREN(NUNG thf)2] (2), [Yb-
A
G
U
CHTUNGTRENNUNG
A
CHTUNGTRENNUNG
C
E
CHTUNGTRENNUNG
E
CHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
N
CHTUNGTRENNUNG
[SmACHTUNGTRENNUNG
(DippForm)2Form’] complexes.[7] Even in the broader
area of benzamidinate chemistry, LnII derivatives have been
neglected.[1g–k] However, divalent ytterbium benzamidinates,
A
CHTUNGTRENNUNG
[YbACHTUNGTRENNUNG{CArACHTUNGTRENNUNG(NSiMe3)2}2ACHTNUGNERTN(GUN thf)n] (Ar=Ph, 4-MeOC6H4, n=2;
A
A
Ar=4-PhC6H4, n=0), formed from metathesis reactions,
have been reported by Edelmann and co-workers.[8] More
recently, Lee and co-workers have reported syntheses, struc-
tures and reactions of LnII (Ln=Sm, Eu, Yb) complexes of
a novel unsymmetrical benzamidinate ligand,[9a] and related
guanidinates have been reported.[9b]
We now report the syntheses, structures and C X activa-
tion reactions (X=F, Cl or Br) of a range of bis(formamidi-
nato)ytterbium(II) complexes, the synthesis and structure of
AHCTUNGTRENNUNG
A
CHTUNGTRENNUNG
1) complexes have been previously prepared by a simliar
method.[2] However, for these syntheses of YbII compounds,
a larger Yb/Hg ratio was used. Compounds 1–5 and 7 are
deep red in colour, compound 6 is orange, consistent with
the divalent oxidation state of ytterbium,[10] and compound
8 is yellow. The colours of LnII species are usually more in-
tense because of Laporte-allowed 4f!5d transitions.[10]
Compounds 1–6, 7a and 8 were crystallised from THF and
all complexes were isolated in good to high yields (58–
81%). Evidently, both mercury reagents are suitable re-
agents to obtain the lanthanoid compounds in their divalent
state, although the poorer oxidant of the two, [HgPh2], is
often better suited for the synthesis of LnII species.[11,12] Al-
ꢀ
a
G
europium(II) analogue and the trivalent [Ln-
(DippForm)2(Br)(thf)] complexes (Ln=La, Nd and Yb).
Use of Hg(2-BrC6F4)2 with ytterbium metal provided access
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
to the bromoytterbiumACTHNUTRGENN(UG III) complex [YbACHTUGNTREN(NUGN DippForm)2(Br)-
ꢀ
G
was established by similar preparations of [Ln-
A
ACHTUNGTRENNUNG(thf)] (Ln=La, Nd). Complexes of this
though the divalent complexes [Ln
Eu, Yb) are freely accessible from lanthanoid metal, Hg-
(C6F5)2 and DippFormH, attempts to prepare the trivalent
[Ln(DippForm)3] (Ln=Eu, Yb) analogues by modification
of the stoichiometry, as is possible for less bulky formami-
dines,[2] failed. [Ln
(DippForm)2(F)(thf)] (Ln=Yb, Eu) de-
ACHUTGTNRNE(NGU DippForm)2ACHTUNGTRNEN(UGN thf)2] (Ln=
AHCTUNGTRENNUNG
U
ACHTUNGTRENNUNG
ꢀ
The C X activation reactions suggest the possibility of a
broad reaction chemistry for these divalent formamidinates.
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
rivatives were also unobtainable by such methods in contrast
to reactions with other lanthanoid elements (Ln=La, Ce,
Nd, Sm and Tm).[2]
Chem. Eur. J. 2013, 19, 1410 – 1420
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1411

P. C. Junk et al.
Control reactions were carried out to investigate the reac-
tion pathway. Firstly, the formamidine ligand was treated
with HgACHTUNGTRENNUNG(C6F5)2 in THF and ytterbium metal was treated
7a in C7D8 gave a lower chemical shift (d=501 ppm) that is
consistent with the increased coordination number (seven
instead of six) in related structures.[16,17,19]
with the formamidine ligand in THF. As was found for simi-
lar reactions of the alkaline earth metals,[13] IR spectra of
the material isolated from the control-reaction mixtures in-
ꢀ
The methine carbon (NCHN) resonances in the
13C{1H} NMR spectra of 1 and 2 are observed at 163 ppm
and 175 ppm, respectively. The observed chemical shifts are
found at significantly higher frequencies than those for the
neutral o-TolFormH and XylFormH ligands (147 ppm and
146 ppm, respectively). Similar changes in chemical shift for
the methine carbon resonances were observed in the
13C{1H} NMR spectra of 6, 7 and 8. The 19F NMR spectrum
of 7 suggests that the substituent chemical shift of the NCN
group is about 10 ppm for an ortho fluorine substituent.
dicated the presence of the n˜ACTHNUGRTNEUNG(N H) absorption of the for-
mamidine ligand (around 3350 cmꢀ1) and the characteristic
absorption bands of HgACTHNUTRGNEUNG
(C6F5)2.[14] These results indicate that
successful syntheses of LnII complexes require all three re-
agents.
Compounds 2–7a and 8 were authenticated by single-crys-
tal X-ray diffraction (see discussion below). In general, the
compositions of 1–8 were supported by microanalyses, Ln
1
analyses, and spectroscopic data. The H NMR spectra and/
Reactivity studies: Treatment of compounds 4 and 5 with
perfluorodecalin in THF at room temperature resulted in
the isolation of the trivalent ytterbium–fluoride complexes
[{YbACTHUGNNERTN(NUG EtForm)2ACHTUNRTGE(NGNUN m2-F)}2] (9) and [{Yb(o-PhPhForm)2ACHTUNGTRENNUNG(m2-F)}2]
(10; Scheme 2). Perfluorodecalin acts as the oxidant and has
or microanalyses of some compounds (5, 6 and 8) indicated
the loss of THF of solvation. Satisfactory carbon microanal-
ysis values for 6 and 8 could not be obtained even on re-
peated preparation, whereas the Ln analyses performed
promptly after preparation are more consistent with partial
loss of lattice THF. Compounds 1–8 showed complete de-
protonation of the formamidine reagents as indicated by the
ꢀ
absence of an n˜ACHTUNGTRENNUNG(N H) absorption in the infrared spectrum
1
ꢀ
and the lack of an N H resonance in the H NMR spectrum
of the dry, bulk crystalline material.
Because of the diamagnetic nature of divalent complexes
1
1–7 and their good solubility in C6D6, H and 13C{1H} NMR
data could be obtained but the paramagnetic compound 8
gave a broadened spectrum, which could not be satisfactori-
ly integrated. Only a single, symmetrical formamidinate en-
vironment is evident in the 1H NMR spectra of all com-
pounds, an observation which is indicative of either a sym-
metrically bound ligand or a rapidly exchanging system.[15]
The methine proton resonances (NCHN) in the 1H NMR
spectra of 1–8 are shifted to significantly higher frequencies
relative to the value for the neutral ligand. For example, the
methine proton resonance occurs at d=7.72, 7.05 and
6.88 ppm for o-TolFormH, XylFormH and MesFormH, re-
spectively, and at d=8.88, 8.44 and 8.33 ppm in 1–3, respec-
Scheme 2. Synthesis of complexes 9–12 and 16. For 9 Ar=2,6-Et2C6H3,
RX=C10F18, X=F, n=0, m=2; for 10 Ar=2-PhC6H4, RX=C10F18, X=
F, n=0, m=2; for 11 Ar=2-PhC6H4, RX=C2Cl6; X=Cl; n=2, m=1;
for 12 Ar=2,6-iPr2C6H3, RX=1,2-Cl2C2H4; X=Cl; n=1, m=1; for 16
Ar=2,6-iPr2C6H3; RX=o-HBrC6F4; X=Br; n=1, m=1.
been used in ytterbium(II) cyclopentadienyl and/or arylox-
ide chemistry to give [{YbCp2F
ACHTUNGERTN(NUNG thf)}2] (Cp=cyclopentadien-
yl) and [{Yb(OAr’)2F(thf)}2] (Ar’=C6H4tBu2-2,6-Y-4, Y=H,
A
ACHTUNGTRENNUNG
Me, tBu).[21,22] in the first examples of C-F activation of a sa-
turated fluorocarbon by a lanthanoid complex. Intermolecu-
lar abstraction of fluorine from perfluorocycloalkanes by di-
valent lanthanoids is driven by the negative reduction poten-
tial of the LnIII/LnII couple and the formation of very strong
lanthanoid–fluoride bonds.[23]
tively. In the case of 5 and 6 the methine resonances show
3
171Yb satellites with J
(1H,171Yb) couplings of 44 and 45 Hz,
respectively. 171Yb NMR spectra were obtained for 2–6
showing broad signals in the range of d=600–700 ppm. In
the case of 5 and 6, there were resolvable splittings giving a
triplet from coupling to the methine protons with 3J-
Compound 9 was isolated as yellow crystals from hexane
and compound 10 was isolated as a yellow powder from
THF. Elemental analyses (C, H, N, Yb) and infrared spectra
support the proposed formulae of both compounds (below).
Additionally, the structure of 9 was established by X-ray
crystallography. The infrared spectra (n˜ =4000–600 cmꢀ1) of
9 and 10 display similar features to those found for [Yb-
ACHTUNGTRENNUNG
(1H,171Yb)=48 and 44 Hz, respectively. The range of chemi-
cal shifts observed (d=600–700 ppm) corresponds closely to
those known for a number of four-coordinate [Yb(NR2)2-
(solv)2] (solv=thf, Et2O, etc.) complexes,[16–19] but the shifts
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
measured cannot be explained by loss of thf ligands in C6D6
(or C6D6/toluene), a known phenomenon, because the addi-
tion of an excess of THF to representative solutions of com-
plexes 2 and 4 had little effect on the spectra observed.
However, the chemical shifts are similar to those of some
AHCTUNGTRENNUNG
(Form)3] complexes.[2] During formation of 9, an insoluble
precipitate with no IR absorptions was also deposited,
which may be YbF3 possibly from the rearrangement of 9.
Reactions of 5 and 6 with hexachloroethane and 1,2-di-
chloroethane in THF or toluene at room temperature yield-
six-coordinate YbII complexes of bulky di(2-pyridyl)
ides,[20] which, like the complexes studied herein, have a con-
jugated NCN backbone. Examination of seven-coordinate
ACHTUNGERTNaNUNG m-
G
ed [Yb(o-PhPhForm)2Cl
ACHTUNGRTEN(NUNG thf)2]·2THF (11) and [Yb-
A
ACHTUNGTRENNUNG
1412
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 1410 – 1420

Lanthanoid(II) Formamidinates
FULL PAPER
idation was accompanied by a typical colour change from
red or orange to yellow. In the H NMR spectrum of 11, the
sorptions in the spectra of both 10 and 11 at n˜ =390 cmꢀ1
1
ꢀ
may be assigned to n˜
The syntheses of [Ln
G
chemical shift of the backbone RN(CH)NR proton shifts
from d=8.93 in 5 to 12.1 ppm as result of the oxidation.
Otherwise, the broadness of the spectrum precluded satis-
factory integration, and the compound was principally iden-
tified by its X-ray crystal structure (see discussion below). A
crystal structure of 12 was also obtained in which the bulkier
formamidine apparently leads to a lower coordination
number than in 11. However, to provide a further structural
comparison, a synthesis by metathesis from TbCl3 and Na-
G
ꢀ
achieved by two methods. In the first, C Br activation reac-
tions between excess Ln metal, Hg(2-BrC6F4)2, and HDipp-
AHCTUNGTRENNUNG
Form in THF at room temperature and subsequent crystalli-
sation from toluene (Ln=La, Nd) or diethyl ether (Ln=
Yb) yielded the complexes [LnACHTNUGRTENN(UG DippForm)2BrACHTUNGTRENN(UGN thf)]·solv
(Ln=La (14), Nd (15); solv=none; Ln=Yb (16), solv=
Et2O; Scheme 3). Although this method parallels the prepa-
[2,5,6]
ꢀ
rations of [Ln
(DippForm)2F
G
A
R
there is one notable difference in that neither further oxida-
ACHTUNGTRENNUNG
pound 13 was shown to be
seven coordinate by X-ray
crystallography. Although Tb3+
is somewhat (0.05 ꢁ) larger
[24]
than Yb3+
,
it may be that
the crystallisation solvent de-
termines the observed struc-
ture, because crystals of 12
were obtained from toluene
and those of 13 were obtained
Scheme 3. Formation of [Ln
Yb. Ar=2,6-iPr2C6H3 for 14–16.
ACHUTGTNRNE(UNG DippForm)2BrACHTUNTGREN(NUNG thf)] complexes. For 14 Ln=La, for 15 Ln=Nd and for 16 Ln=
ꢀ
from THF. The microanalyses of 12 and 13 are indicative of
the loss of lattice THF.
tion to [Yb
giving [Yb(DippForm)2F
tween Yb metal, Hg(C6F5)2 and HDippForm. Instead, diva-
U
2ACHTUNGTREN(UNG C6F5)ACHTUTGNREN(NUGN thf)n] nor C F activation
A
ACHTUNGTRENNUNG
Bands in the far-IR spectrum of 10 at n˜ =336 and
298 cmꢀ1 of medium to strong intensity were not observed
in the spectrum of the analogous chloro complex, 11, and
ꢀ
ACHTUNGTRENNUNG
lent compound 6 is obtained (Scheme 1). Ytterbium induced
ꢀ
C Br activation herein can be attributed to the reduced
can be assigned to the two expected[25] n˜
(Yb F) modes of a
bond strength of C Br than C F. In the second synthesis, a
ꢀ
ꢀ
ꢀ
[{Yb(o-PhPhForm)
N
C Br activation occurs between 6 and 1-bromo-2,3,4,5-tetra-
the crystallographically established fluoride-bridged dimer 9.
fluorobenzene, giving 16 (Scheme 2).
The frequencies are found in the expected range since nine-
THF seems to be readily lost from bulk 14 because it is
1
coordinate dimeric [{YbCp2F
(thf)}2] has bridging fluoride li-
not detected in either its H or 13C NMR spectra but the mi-
ꢀ1 [21]
ꢀ
gands with n˜
A
croanalysis suggests the presence of some THF, as observed
ꢀ1
ꢀ
a n˜
A
in single crystals. In the case of the Nd complex, 15, the
[{YbCp’2F}4] (Cp’=MeC5H4) has a band at 328 cmꢀ1.[22] Di-
presence of THF is evident from H NMR spectroscopy and
1
meric five-coordinate aryloxide complexes [{Yb
G
microanalysis. The structure of 16 as a diethyl ether solvate
was established by X-ray crystallography and the microanal-
ysis is consistent with the retention of both coordinated
THF and diethyl ether of crystallisation in the bulk sample.
(thf)}2][22] (Ar’ as above) have intense n˜
E
ꢀ
in the range of 390–375 and at 300 cmꢀ1. In three-coordinate
YbF3, which was isolated in a matrix, the terminal n˜
absorptions are predictably at much higher frequencies (n˜ =
The properties of these complexes closely resemble those of
569 and 546 cmꢀ1).[26]
known Ln F analogues.
[2,5,6]
ꢀ
In the far-IR spectrum of the chloro complex, 11, there
are medium to strong intensity bands at n˜ =261 and
248 cmꢀ1, which are not present with this intensity in the
spectrum of the fluoro analogue 10. One of these bands is
ꢀ
X-ray crystallographic studies: Compounds 1–6 and 8 con-
tain isostructural metal complexes with six-coordinate Ln
atoms surrounded by two chelating Form ligands and two
cis-thf donors. Complex 2, as shown in Figure 1, is a repre-
sentative example of this geometry. Compounds 3 and 4 are
isotypic, as are 6 and 8. It is also likely that 1 has a similar
presumably attributable to the n˜ACHTUNTRGNEUNG(Yb Cl) of the monomeric
ꢀ
complex. For terminal chloro ligands, n˜ACHTNUTRGNEUNG(Yb Cl) is expected
at 269–237 cmꢀ1 for monomeric six-coordinate [YbCl3-
ꢀ
ꢀ
A
E
structure. The average Yb N and Yb O bond lengths
(Table 1) are near the average values (2.45 and 2.42 ꢁ, re-
spectively) for six-coordinate YbII complexes found in the
Cambridge Crystallographic Data Centreꢂs structural data-
base.[31] In 6, which has the bulkiest formamidinate ligand
ꢀ
264 cmꢀ1 in eight-coordinate [YbCp2Cl(thf)].[28] In six-coor-
dinate [YbCl6]3ꢀ the absorption is in the range of 263–
253 cmꢀ1.[29] The values for bridging chloro ligands are 223
2ACTHNUTRGNEUNG
and 211 cmꢀ1 in [{YbCp2Cl} (thf)][28] and 222 and 206 cmꢀ1
in [YbCp2Cl]2.[30] Thus, either band observed in the spectrum
of 11, at 261 or 248 cmꢀ1, is consistent with a terminal
chloro ligand in a seven-coordinate environment. Strong ab-
(DippForm), the Yb OACTHNGUTERN(UNG thf) bond lengths are significantly
ꢀ
longer than in 2–5 but the Yb N bond lengths are not elon-
gated and those in 5 are, marginally, the longest found in
Chem. Eur. J. 2013, 19, 1410 – 1420
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1413

P. C. Junk et al.
Figure 2. Molecular structure of [YbACHTUNRGTENNUG(TFForm)2ACHTUNTGERN(NGUN thf)3]·2THF (7a). Hydro-
gen atoms are omitted for clarity and thermal ellipsoids are set to the
35% probability level.
Figure 1. Molecular structure of cis-[Yb
atoms are omitted for clarity and thermal ellipsoids are set to the 35%
probability level). [Yb(MesForm)2A(thf)2] (3), [Yb(EtForm)2A(thf)2] (4),
[Yb(o-PhPhForm)2A(thf)2]·2THF (5), [Yb(DippForm)2A(thf)2]·2THF (6)
and [Eu(DippForm)2A(thf)2]·2THF (8) are structurally similar.
ACHUTGTNRENN(GU XylForm)2ACHUTNGTREN(NUGN thf)2] (2; Hydrogen
G
E
A
CHTUNGTRENNUNG
G
A
CHTUNGTRENNUNG
N
CHTUNGTRENNUNG
than the amount expected for
the change in ionic radius with
Table 1. Selected bond lengths [ꢁ] for [Yb
(thf)2] (4), [Yb(o-PhPhForm)2A(thf)2]·2THF (5), [Yb
(thf)2]·2THF (8)[a]
G
R
(MesForm)
G
ACHTUNGTRNEN(UNG EtForm)2-
G
G
E
ꢀ
coordination number, the Yb
O bond lengths (Table 1) are
R
.
Complex
2
3
4
5
ꢀ
comparable to the shorter Yb
ꢀ
Yb(1) N(1)
2.466(3)
2.476(3)
2.484(3)
2.443(3)
2.429(3)
2.429(3)
2.455(4)
2.481(4)
2.429(4)
2.483(4)
2.441(4)
2.446(4)
2.480(7)
2.478(6)
2.483(7)
2.462(7)
2.409(6)
2.419(6)
2.473(6)
2.519(7)
2.487(7)
2.488(6)
2.425(6)
2.435(6)
O separations in 2–6, reflecting
the enhanced Lewis acidity of
Yb resulting from the fluori-
nated ligands. Complex 7a
readily loses a thf ligand, as
shown by the composition of
the bulk material obtained
ꢀ
Yb(1) N(2)
ꢀ
Yb(1) N(3)
ꢀ
Yb(1) N(4)
ꢀ
Yb(1) O(1)
ꢀ
Yb(1) O(2)
ꢀ
Yb(1) O(3)
[a] Symmetry operators used to generate equivalent atoms: #1=ꢀx, y, 3/2ꢀz.
from toluene, [Yb
(thf)2], as was observed in 1–6.
All Yb···F interatomic distan-
ACHTUNGTRNEN(UNG TFForm)2-
AHCTUNGTRENNUNG
this study (Table 1). The o-PhPhForm ligands in 5 do not
show any p-Ph···Yb interactions, because the shortest sepa-
ces (ꢂ3.91 ꢁ) are greater than the accepted distances for
appreciable bonding contact.
ration observed, 3.58 ꢁ, is significantly larger than the ac-
The X-ray structure of 9 shows a fluoride-bridged dimer
(Figure 3) in which the six-coordinate ytterbium atom is co-
ordinated by two chelating formamidinate ligands and two
bridging fluoride ligands. It is likely that 10, which could not
be obtained as single crystals, has a similar structure on the
ꢀ
II
ꢀ
cepted Ph(C) Yb p-bonding range of 2.76–3.18 ꢁ as estab-
lished in [Yb
2A
ꢀ
The differences in corresponding bond lengths (Ln N, O, D
0.10–0.13 ꢁ) between 6 and 8, are less than the difference in
metal-centre ionic radii (0.15 ꢁ),[24] indicating greater steric
basis of the n˜ACTHUNTGRNEUNG(Yb F) absorptions observed (see discussion
ꢀ
ꢀ
stress in 6. A surprising feature is the variation in the O
above). The Yb N bond lengths (Table 2) found for 9 are
shorter than those in 2–6 by approximately the expected dif-
ꢀ
Yb O angles (Table S1 in the Supporting Information),
which cannot be wholly related to Form-ligand bulk. Where-
ference (0.15 ꢁ) for a change from six-coordinate YbII to
III
ꢀ
ꢀ
ꢀ
ꢀ
as the smallest O Yb O angles are found in the structures
of 6 and 8, consistent with the bulk of the DippForm ligand,
Yb . With bite angles approaching 608 and F Yb F angles
of approximately 698 (see the Supporting Information), the
coordination geometry of Yb in 9 is distorted trigonal pris-
ꢀ
ꢀ
the next smallest O Yb O angle is that found for the least
ꢀ
ꢀ
bulky ligand, XylForm, in 2. Furthermore, the largest O
matic. The Yb F bond lengths are similar to those in a
ꢀ
Yb O angle is observed in 4, which has the second bulkiest
Form ligand (EtForm).
number of fluoride-bridged complexes. Examples of such
complexes include [{YbCp2F
(thf)}2],[22] [{Yb (thf)}2][22] (OAr=2,6-di-tert-butyl-4Y-
(OAr)2F
phenolate; Y=tBu or H), [{YbCp2F}3][22] and [{Yb-
(MeCp)2F}4],[22] in which, despite a variation of coordination
(thf)}2],[21] [{Yb
ACHUTGTNERNNUG AHCUTNGTREN(NUGN MeCp)2F-
In 7a the coordination number is seven with two chelating
TFForm ligands and three “pseudo-meridional” (that is, the
ligands are located similarly to mer-ligands of octahedral
complexes) thf donors (Figure 2). The higher coordination
number can be attributed to a combination of reduced steric
strain (o-F vs. o-Me), and the electron-withdrawing effect of
A
R
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ꢀ
numbers from 5 to 9, the Yb F bond lengths fall within a
narrow range (2.139(4)–2.143(9) ꢁ). It seems that bulky al-
ternatives to Cp ligands have much the same effect as Cp
ꢀ
ꢀ
the multiple fluorine substituents. Although the Yb N bond
lengths in 7a (Table 1) are longer than those of 2–6 by more
rings on bridging Ln F distances, regardless of formal coor-
ꢀ
dination numbers. As expected, the Yb F bond lengths in 9
1414
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ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 1410 – 1420

Lanthanoid(II) Formamidinates
FULL PAPER
Figure 4. Molecular structure of [Yb(o-PhPhForm)2Cl
Hydrogen atoms and lattice solvent have been omitted for clarity and
thermal ellipsoids are set at 35%. Complex [Tb(DippForm)2Cl-
(thf)2]·2.5THF (13) has a similar structure.
ACHTUNGRTEN(NGNU thf)2]·2THF (11).
AHCTUNGTRENNUNG
Figure 3. Molecular structure of [{YbACTHNUGTRENN(GU EtForm)2ACHTUNGTREN(NGUN m2-F)}2] (9). Hydrogen
atoms are omitted for clarity and thermal ellipsoids are set to the 35%
probability level.
AHCTUNGTRENNUNG
Table 2. Selected bond lengths [ꢁ] for [{Yb
Atoms Length Atoms Length
Yb(1) N(1) 2.309(3) Yb(2) N(5) 2.338(3) Yb(1) F(1) 2.177(2)
A
(m2-F)}2] (9).
Length
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Yb(1) N(2) 2.315(3) Yb(2) N(6) 2.305(3) Yb(1) F(2) 2.168(2)
ꢀ
ꢀ
ꢀ
Yb(1) N(3) 2.341(3) Yb(2) N(7) 2.334(3) Yb(2) F(1) 2.179(2)
ꢀ
ꢀ
ꢀ
Yb(1) N(4) 2.306(3) Yb(2) N(8) 2.302(3) Yb(2) F(2) 2.160(2)
ꢀ
are significantly longer than the terminal Yb F bond
lengths found in [Yb
N
U
six-coordinate [Tm
A
(thf)] (2.020(2) ꢁ;[2] Tm3+
ACHTUNGTRENNUNG
and Yb3+ have similar ionic radii[24]). Complex 9 appears to
be the first crystallographically established example of a
Figure 5. Molecular structure of [YbACTHNUGRTENN(UG DippForm)2ClACHTUNGTREN(NUNG thf)]·THF (12). Hy-
drogen atoms and lattice solvent are omitted for clarity and thermal ellip-
soids are set to the 35% probability level.
neutral ytterbium
plex.[1g–6] The related halogen-bridged YbIII amidinate com-
pound [Yb2A(Me3SiNC(Ph)N-
(CH2)3NC(Ph)NSiMe3) (m-Cl)2A(thf)] is the only
ACHTUNGTRENNUNG(III) fluoride-bridged amidinate com-
CTHUNGTRENNUNG
A
R
CHTUNGTRENNUNG
Table 3. Selected bond lengths [ꢁ] for [Yb(o-PhPhForm)2Cl
ACHTUNGRTEN(NUGN thf)2]·2THF (11), [Yb-
other known example of such a compound and has
two inequivalent ytterbium centres (six and seven
coordinate).[33]
A
E
N
ACHTUNGTRENNUNG
11 12
16
Atoms
Length
Atoms
Length
Atoms
Length
The X-ray structures of 11 and 13 show seven-
coordinate monomeric complexes with two chelat-
ing formamidinate ligands, a terminal chloride and
two thf donors. The three unidentate ligands have
a “pseudo-meridional” arrangement with the O
atoms cis and O(1) trans to Cl(1) (Figure 4 for 11).
By contrast, 12 has a six-coordinate ytterbium
atom with O(1) cis to Cl(1) (Figure 5). The change
in coordination number is perhaps most clearly ex-
ꢀ
ꢀ
ꢀ
Yb(1) O(1)
2.306(1)
2.323(1)
2.408(2)
2.338(2)
2.398(2)
2.389(2)
2.562(1)
Yb(1) O(1)
2.3291(17)
2.319(2)
2.357(2)
2.358(2)
2.310(2)
2.5062(6)
Yb(1) O(1)
2.343(2)
2.331(3)
2.361(3)
2.331(3)
2.366(3)
2.6659(7)
ꢀ
ꢀ
ꢀ
Yb(1) O(2)
Yb(1) N(1)
Yb(1) N(1)
ꢀ
ꢀ
ꢀ
Yb(1) N(1)
Yb(1) N(2)
Yb(1) N(2)
ꢀ
ꢀ
ꢀ
Yb(1) N(2)
Yb(1) N(3)
Yb(1) N(3)
ꢀ
ꢀ
ꢀ
Yb(1) N(3)
Yb(1) N(4)
Yb(1) N(4)
ꢀ
ꢀ
ꢀ
Yb(1) N(4)
Yb(1) Cl(1)
Yb(1) Br(1)
ꢀ
Yb(1) Cl(1)
plained as arising from differences in crystallisation solvent
same as in 12. The behaviour of 11 is associated with a mer-
ꢀ
(see discussion above). The Yb N bond lengths in 12
(Table 3) are similar to those in the six-coordinate fluoride-
array of unidentate ligands and mirrors the relationship be-
ꢀ
tween the Yb O bond lengths in seven-coordinate 7a,
ꢀ
ꢀ
bridged dimer 9. The Yb(1) N and Yb(1) Cl(1) bond
lengths in 12 are shorter than the corresponding separations
in seven-coordinate 11 by approximately 0.05 ꢁ, which is
similar to the difference in the appropriate ionic radii.[24]
which has mer-thf ligands, and those in the six-coordinate
species 2–6.
Isotypic 14, 15 and 16 (Figure 6) are isostructural with the
corresponding chloride, 12. There is some asymmetry in the
ꢀ
ꢀ
Surprisingly, the Yb O distances in 11 are virtually the
DippForm chelation, as in 12. As expected, the Yb N and
Chem. Eur. J. 2013, 19, 1410 – 1420
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1415

P. C. Junk et al.
analytical Laboratory, Chemistry Department, University of Otago, Dun-
edin, New Zealand. Metal analyses were carried out by EDTA titrations
with Xylenol Orange indicator following acid digestion and buffering
with hexamine. Melting points were determined in glass capillaries sealed
under nitrogen and are uncalibrated. o-TolFormH, XylFormH, Mes-
FormH, EtFormH, o-PhPhFormH and DippFormH were synthesised ac-
cording to the published procedures[34] and [Na
ACTHNUTRGENN(GU DippForm)ACHTUNGTRENNUNG(thf)3] was
prepared as reported.[3] Lanthanoid metals were purchased from Tianjiao
(Baotou, China) or Santoku as metal ingots, stored under purified nitro-
gen and freshly filed prior to use. Polyfluoroaromatic compounds were
obtained from Bristol Organics or Aldrich, perfluorodecalin from Avoca-
do Chemicals and diphenylmercury, hexachloroethane and 1,2-dibromo-
ethane from Aldrich. Bis(pentafluorophenyl)mercury[14] and bis(2-bromo-
3,4,5,6-tetrafluorophenyl)mercury[35] were prepared as reported. Caution!
Diarylmercury compounds should be handled in a well-ventilated fume
cupboard, protective gloves should be worn and residues should be in-
cluded in heavy-metal waste or recycled as mercury metal. Tetrahydrofur-
an (THF) was pre-dried over sodium wire and freshly distilled from
sodium benzophenone ketyl under nitrogen. Hexane and toluene were
pre-dried over sodium and distilled from sodium under nitrogen.
Figure 6. Molecular structure of [YbACHTUNRGTENNUG(DippForm)2BrACHTUNGTERN(NNGU thf)]·Et2O (16). Hy-
drogen atoms and lattice solvent are omitted for clarity and thermal ellip-
soids are set to the 35% probability level. Complexes [Ln-
ACHTUNGTRENNUNG(DippForm)2BrACHTUNGTRENNUNG(thf)] (Ln=La (14), Nd (15) have similar structures.
Synthesis
TFFormH: 2,3,4,5-Tetrafluoroaniline (5.0 g, 0.030 mol) and a slight excess
of triethyl orthoformate (2.78 g, 0.019 mol) were mixed in a flask charged
with acetic acid (6 drops) catalyst. The unstoppered mixture was slowly
stirred at 708C. The evaporated ethanol was replaced intermittently with
hexane. After 1 h, hexane was no longer added and the solution was pro-
gressively cooled. After 15 min, stirring was stopped and a white precipi-
tate settled. The pure white solid was collected and recrystallised from
acetone to produce white blocks of TFFormH (4.74 g; 93%). M.p. 131–
ꢀ
Yb O bond lengths in 12 and 16 are comparable (Table 3).
ꢀ
ꢀ
The Yb Br bond length exceeds the corresponding Yb Cl
value by the amount expected from the Brꢀ and Clꢀ ionic
radii.[24] In 14 and 15 the expected difference[24] in Ln N,O
ꢀ
ꢀ
and Ln Br bond lengths is observed.
1
1338C; H NMR (300.13 MHz, C6D6, 303.2 K): d=5.76 (brs, 1H; C-NH),
6.74 ppm (s, 1H; N-CH=N); 19F NMR (282.40 MHz, C6D6, 303.2 K):
ꢀ139.7 (brs, 2F; F5), ꢀ155.2 (brs, 2F; F3), ꢀ156.6 (brs, 2F; F2), d=
ꢀ163.38 ppm (brs, 2F; F4); IR (KBr): n˜ =3437 (w), 3160 (m), 2726 (s),
2345 (w), 2200 (w), 1654 (vs), ꢃ1520 (vs), 1292 (s), 1261 (s), 1196 (s),
1124 (w), 1079 (s), 1055 (s), 1003 (m), 944 (s), 846 (s), 753 (s), 721 (s),
670 (vw), 591 (vw), 561 cmꢀ1 (vw); HRMS: (ESI): m/z calcd for
C13H4N2F8 +H+: 341.032 [M+H]; found: 341.032.
Conclusion
A wide range of a rare class of divalent lanthanoid formami-
dinates, [LnACHTUNGTRENNUNG(Form)2ACHTUNGTREN(NUGN thf)2], has been prepared by redox
transmetallation/protolysis reactions. The complexes are
generally monomeric with six-coordinate metal centres and
[Yb(o-TolForm)2ACTHNUTRGNENUG(thf)2] (1): Method 1: Tetrahydrofuran (40 mL) was
added to a Schlenk flask charged with an excess of freshly filed Yb metal
(0.20 g, 1.15 mol), bis(pentafluorophenyl)mercury (0.54 g, 1.02 mmol) and
o-TolFormH (0.45 g, 2.00 mmol) under purified nitrogen. The slurry was
stirred at ambient temperature for 72 h before the red-coloured solution
was filtered from the elemental mercury deposited and the excess of Yb
metal. The solvent was removed in vacuo and the remaining material was
extracted into THF (approximately 10 mL). The solution was concentrat-
ed (to 2–3 mL) and after standing at ꢀ68C for several weeks no crystals
formed and a red-coloured powder was obtained when all of the solvent
was removed in vacuo to give 1 (0.58 g; 74%). M.p. 82–848C, decomp
2708C; 1H NMR (300.13 MHz, C6D6): d=1.53 (brs, 8H; CH2, thf), 2.32
(s, 12H; CH3), 4.22 (brs, 8H; OCH2, thf), 6.92 (brm, 16H; ArH), 8.88
(brs, 2H; NC(H)N); 13C{H} NMR (75.47 MHz, C6D6): d=19.3 (CH3),
26.6 (CH2, thf), 67.8 (OCH2, thf), 119.1 (Ar-CH), 121.7 (Ar-CH), 127.5
(Ar-CH), 130.5 (Ar-C), 131.0 (Ar-CH), 151.9 (Ar-CN), 163.5 (NC(H)N);
IR (Nujol): n˜ =1665 (s), 1595 (m–s), 1522 (s), 1302 (s), 1221 (s), 1183 (s),
1109 (s), 1031 (s), 980 (m), 934 (m), 877 (m), 837 (m), 775 (m), 751 (s),
719 (s), 613 cmꢀ1 (s); elemental analysis calcd (%) for C38H46N4O2Yb
(763.85): C 59.75, H 6.07, N 7.33, Yb 22.65; found: C 58.95, H 5.98, N
7.54, Yb 23.02.
cis-thf ligands. However, [YbACHTNUTRGENNUG(TFForm)2ACHTUNGTREN(NGUN thf)3] (7a) with
electron-withdrawing o-HC6F4 substituents on the formami-
dinate ligands, is seven-coordinate with mer-thf ligands. The
ꢀ
complexes are highly reactive in C X (X=F, Cl, Br) activa-
tion reactions and provide access to a range of LnIII forma-
midinate complexes such as [{Yb
(Form)2X(thf)n] (X=Cl or Br; n=1 or 2). In addition, C Br
activation occurs durring the redox transmetallation/protoly-
sis reactions between La, Nd or Yb, Hg(2-BrC6F4)2 and
HDippForm, yielding [Ln(DippForm)2Br(thf)] complexes.
ACHTUNGRTEN(UNGN Form)2F}2] and [Yb-
ꢀ
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Experimental Section
General: All manipulations were performed by conventional Schlenk
and glovebox techniques under an atmosphere of purified nitrogen. Infra-
red spectra (n˜ =4000–500 cmꢀ1) of Nujol mulls, unless indicated other-
wise, were recorded on a Perkin–Elmer 1600 Fourier transform infrared
spectrometer. Far-IR spectra (n˜ =500–100 cmꢀ1) of Vaseline mulls were
Method 2: Following the procedure used above, Yb metal (0.30 g,
1.74 mmol), HgPh2 (0.35 g, 1.04 mmol) and o-TolFormH (0.45 g,
2.08 mmol) gave red complex 1 (0.51 g; 67%). M.p. 84–868C, decomp
2708C; IR (Nujol): As for the product from method 1; elemental analysis
calcd (%) for C38H46N4O2Yb (763.85): Yb 22.65; found: Yb 22.89.
1
recorded on a Bruker 120HR spectrometer. H NMR spectra of solutions
in C6D6 were recorded at 300.13 MHz and 13C{1H} NMR spectra were re-
corded at 75.47 MHz on a Bruker AC 300 spectrometer at 303.2 K and at
400.13 MHz (1H) and 100.62 MHz (13C) on a Bruker AC 400 spectrome-
[Yb
ACHUTGTRENN(UG XylForm)2ACHTUNTGR(ENUNNG thf)2] (2): Following the procedure used for 1, Yb metal
1
ter at 303.2 K. Chemical shifts were referenced to the residual H and 13C
(0.20 g, 1.15 mol), HgAHCTUNGRT(ENUNNG C6F5)2 (0.49 g, 0.92 mmol) and XylFormH (0.46 g,
resonances of deuterobenzene. 19F NMR spectra were recorded on the
Bruker AC300 spectrometer at 282.40 MHz and were referenced to ex-
ternal CFCl3. All microanalyses were carried out by the Campbell Micro-
1.85 mmol) gave red rectangular crystals (0.42 g; 58%) of 2 from THF
(2 mL) at room temperature. M.p. 182–1868C; 1H NMR (300.13 MHz,
C6D6): d=1.30 (brs, 8H; CH2, thf) 2.16 (s, 24H; CH3), 3.58 (brs, 8H;
1416
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Chem. Eur. J. 2013, 19, 1410 – 1420

Lanthanoid(II) Formamidinates
FULL PAPER
OCH2, thf), 6.90 (t, 3J
7.34 Hz, 8H; H3,5),
N
E
DippFormH (0.50 g, 1.37 mmol) in THF (50 mL) were stirred at ambient
temperature for 24 h, yielding an orange solution after filtration. Evapo-
ration to the point of crystallisation and cooling to ꢀ208C for several
days gave 6 (0.59 g; 72%) as large orange crystals. M.p. 2328C (decomp),
solvent loss at 1088C; 1H NMR (300.1 MHz, C6D6, loss of THF of solva-
tion): d=1.16 (d, 3J
thf), 3.37 (brm, 8H; thf), 3.55 (m, 8H; CH
7.12 (m, 4H; p-ArH), 8.19 ppm (s, Yb171 satellites, 3J
combined 15% by integration, 2H; NC(H)N); 13C{1H} NMR (75.5 MHz,
C6D6): d=25.3 (CH(CH3)2), 28.4 (CH(CH3)2), 123.6 (Ar-CH), 123.8 (Ar-
CH), 143.3 (Ar-C), 149.0 (Ar-C), 168.2 ppm (NCN); IR (Nujol): n˜ =1922
(w), 1860 (w), 1793 (w), 1665 (m sh), 1592 (m), 1520 (s), 1439 (s), 1362
(msh), 1314 (m), 1293 (m), 1249 (m), 1233 (m), 1182 (msh), 1100 (m),
1090 (m), 1038 (m), 933 (m), 919 (m), 880 (m), 803 (msh), 758 cmꢀ1
(msh); elemental analysis calcd (%) for C66H102N4O4Yb (1188.58): C
66.69, H 8.65, N 4.71; calcd (%) for C58H86N4O2Yb (loss of THF of solva-
tion; 1044.37): C 66.70, H 8.30, N 5.36; found: C 65.02, H 8.28, N 5.07.
C
ACHTUGNTRENUN(GN CH3)2), 1.34 (brm, 8H;
1
303 K): d=668 ppm (brs (Dw = =136 Hz); after addition of THF
2
1
AHCTUNGTRENNUNG
(4 drops): d=665 ppm (Dw = =75 Hz); IR (Nujol): n˜ =1651 (m–s), 1594
2
AHCTUNGTRENNUNG
(m–s), 1536 (s), 1292 (s), 1232 (m), 1198 (s), 1092 (s), 1033 (s), 1004 (m),
934 (m), 918 (w–m), 879 (w–m), 760 (s), 699 cmꢀ1 (s); elemental analysis
calcd (%) for C42H54N4O2Yb (819.96): C 61.47, H 6.64, N 6.83, Yb 21.10;
found: C 61.10, H 6.34, N 6.41, Yb 20.70.
G
ACHTUNGTRENNUNG
[Yb
ACHTUNGTRENNUNG(MesForm)2ACHTUNGTRENNUNG
(thf)2] (3): Following the procedure used for 1, Yb metal
(C6F5)2 (0.21 g, 0.40 mmol) and MesFormH (0.22 g,
0.81 mmol) gave red rectangular crystals (0.43 g; 65%) of 3 from THF
(0.20 g, 1.15 mol), HgACHTUNGTRENNUNG
1
(5 mL) at ꢀ68C. M.p. 176–1788C, decomp 2808C; H NMR (300.13 MHz,
C6D6): d=1.52 (brs, 8H; CH2, thf), 1.90 (s, 12H; p-CH3), 2.17 (s, 24H; o-
CH3), 3.32 (brs, 8H; OCH3, thf), 6.76 (brs, 8H; m-ArH), 8.33 ppm (s,
2H; NC(H)N); 13C{H} NMR(75.47 MHz, C6D6): d=18.8 (CH3), 21.2
(CH3), 26.1 (CH2, thf), 68.3 (OCH2, thf), 130.5 (Ar-CH), 134.5 (Ar-C),
135.5 (Ar-C), 141.7 (Ar-CN), 165.1 ppm (NC(H)N); 171Yb NMR
In a repeated synthesis of compound 6, orange crystals (0.47 g; 65%)
identical to the above were obtained, the identity of which was confirmed
by unit cell comparison. Crystal system: monoclinic; a=23.85, b=15.41,
c=19.99 ꢁ; b=1158. M.p. 234–2368C; 1H and 13C NMR spectra were in
agreement with above; 171Yb NMR (52.55 MHz, C6D6/PhMe, 303 K): d=
1
1
(52.55 MHz, C6D6/PhMe 1:4, 303 K): d=678 ppm (brs, Dw = =313 Hz);
IR (Nujol): n˜ =1663 (m), 1531 (s), 1304 (m), 1287 (m), 1232 (m), 1213
(m), 1148 (w), 1073 (s), 1033 (s), 952 (w), 912 (w), 878 (w), 852 (m), 829
(w), 795 (w), 755 (m), 698 (s), 433 cmꢀ1 (w); elemental analysis calcd.
(%) for C46H62N4O2Yb (876.06): C 63.07, H 7.13, N 6.40, Yb 19.75;
found: C 62.41, H 7.07, N 6.61, Yb 19.66.
2
605 ppm (brt, Dw = =94 Hz, 3J
(
171Yb,1H)=44 Hz; NC(H)NYb); elemen-
2
tal analysis calcd (%) for C58H86N4O2Yb (no THF of solvation; 1044.37):
C 66.70, H 8.30, N 5.36, Yb 16.56; calcd for C62H94N4O3Yb (one THF of
solvation; 1116.48): C 66.70, H 8.49, N 5.02, Yb 15.50; found: C 64.77, H
8.34, N 5.31, Yb 15.84.
[Yb
ACHTUNGTRENNUNG(EtForm)2ACHTUNGTRENNUNG
(thf)2] (4): Following the procedure used for 1, Yb metal
[Yb
ACHUTGTRENN(UG TFForm)2ACHTUNTGR(ENUNNG thf)2] (7): Ytterbium metal (in large excess, 0.53 g,
(0.20 g, 1.15 mol), HgACHTUNGTRENNUNG(C6F5)2 (0.21 g, 0.40 mmol) and EtFormH (0.24 g,
3.06 mmol), HgACHTUNGTRENNUNG
(C6F5)2 (0.31 g, 0.57 mmol) and TFFormH (0.39 g,
0.80 mmol) gave red rectangular crystals (0.24 g; 65%) of 4 from THF
(3 mL) at room temperature. M.p. 168–1708C; 1H NMR (400.13 MHz,
1.15 mmol) in THF (20 mL) were sonicated for one day. Once the mix-
ture had settled, the solution was filtered to remove mercury and excess
lanthanoid. Solvent and pentafluorobenzene were removed in vacuo. The
resulting red powder was extracted into toluene and evaporated to dry-
C6D6): d=1.16 (t, 3J
thf), 2.75 (s, 3J
7.04 (t, 3J(1H,1H)=7.0 Hz, 8H; Ar-H), 7.13 (d, 3J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(1H,1H)=7.4 Hz, 24H; CH3), 1.23 (brs, 8H; CH2,
ACHTUNGTRENNUNG
T
1
Ar-H), 8.13 ppm (brs, 2H; NC(H)N); 13C{H} NMR 100.62 MHz, C6D6):
d=16.0 (CH3), 25.0 (CH2, thf), 25.6 (CH2), 69.0 (OCH2, thf), 122.9 (Ar-
CH), 126.4 (Ar-CH), 138.3 (Ar-C), 150.3 (Ar-CN), 167.5 ppm (NC(H)N);
171Yb NMR (52.55 MHz, C6D6/PhMe 1:4, 303 K) d=668 ppm (brs,
ness, giving red 7 (0.47 g; 82%). M.p. 160–1628C; H NMR (300.13 MHz,
C6D6, 303.2 K): d=2.13 (brs, 8H; thf), 3.51 (brs, 8H; thf), 6.56 (m, 4H;
Ar-H), 7.96 ppm (s, 2H; N(CH)N); 19F NMR (282.40 MHz, C6D6,
303.2 K): d=ꢀ136.0 (s, 4F; Ar-F5), ꢀ152.0 (s, 4F; Ar-F3), ꢀ153.0 (s, 4F;
Ar-F2), ꢀ162.9 ppm (s, 4F; Ar-F4); IR (Nujol): n˜ =1622 (w–m), 1559
(m–s), 1298 (s), 1261 (s), 1199 (m), 1154 (m), 1073 (m), 1054 (m), 1023
(m), 974 (w), 938 (m), 861 (vw), 799 cmꢀ1 (w); UV/Vis (THF): lmax (e)
=316 nm (13600 mꢀ1 cmꢀ1); elemental analysis calcd (%) for
C34H22F16N4O2Yb (995.58): C 41.02, H 2.23, N 5.63, Yb 17.37; found: C
40.52, H 2.21, N 5.37, Yb 16.76.
1
1
2
Dw = =95 Hz); after addition of THF (4 drops): d=657 ppm (brs, Dw =
=
2
90 Hz); IR (Nujol): n˜ =1666 (m), 1594 (m), 1525 (s), 1294 (s), 1256 (w),
1231 (s), 1192 (s), 1104 (m), 1073 (w), 1039 (m–s), 999 (w), 952 (w), 932
(w–m), 874 (w–m), 828 (w), 799 (w–m), 771 (m–s), 759 (s), 698 cmꢀ1 (s);
elemental analysis calcd (%) for C50H70N4O2Yb (932.17): C 64.42, H 7.57,
N 6.01, Yb 18.57; found: C 63.64, H 7.70, N 6.19, Yb 18.65.
Recrystallization of [YbACTHNUGRTEN(NUNG TFForm)2ACHTUNGTRENNUNG
(thf)2] from THF (5 mL) and cooling
[Yb(o-PhPhForm)2ACHTUNGTRENNUNG(thf)2]·2THF (5): Following the procedure used for 1,
Yb metal (0.20 g, 1.15 mol), diphenylmercury (0.14 g, 0.32 mmol) and o-
PhPhFormH (0.22 g, 0.63 mmol) gave red rectangular crystals (0.25 g,
to ꢀ308C, yielded red crystals of [Yb
A
CHTUNGTRENNUNG
ble for X-ray crystallography after three months of storage at ꢀ308C.
171Yb NMR: (52.55 MHz, C7D8, 303 K): d=501 ppm (brs).
81%) of
5
from THF (5 mL) at ꢀ68C. M.p. 120–1228C, decomp
>3008C; 1H NMR (400.13 MHz, C6D6; loss of one THF of solvation):
d=1.34 (brs, 12H; CH2, thf), 3.47 (brs, 12H; OCH2, thf), 6.81 (t, 3J-
[EuACHTUNRTGENN(UG DippForm)2ACHTUNGTREN(NGUN thf)2]·2THF (8): Following the procedure used for 6,
europium metal filings (0.10 g, 0.66 mmol), bis(pentafluorophenyl)mer-
cury (0.37 g, 0.69 mmol) and DippFormH (0.50 g, 1.37 mmol) in tetrahy-
drofuran (50 mL) were stirred at ambient temperature for 24 h and yield-
ed a light-yellow solution after filtration. Concentration under reduced
pressure until crystallisation and storage at ꢀ208C for several days gave
large yellow crystals (0.26 g; 34%). M.p. 2438C (decomp), solvent loss at
868C; IR (Nujol): n˜ =1858 (w), 1793 (w), 1666 (msh), 1593 (m), 1530 (s),
1439 (s), 1360 (msh), 1317 (m), 1295 (m), 1255 (m), 1231 (m), 1182
(msh), 1098 (m), 1071 (m), 1054 (m), 1037 (m), 934 (m), 878 (m), 801
(msh), 766 (msh), 753 cmꢀ1 (msh); elemental analyses calcd (%) for
ACHTUNGTRENNUNG ACHTUNGTRENNUGN
(1H,1H)=7.3 Hz, 4H; p-ArH), 6.88 (d, 3J(1H,1H)=8.0 Hz, 4H; m-ArH),
6.93 (td, 3J
(1H,1H)=7.5 Hz, 8H; m-ArH), 7.06 (d, 3J
7.14 (d, 3J(1H,1H)=7.1 Hz, 4H; o-ArH), 7.21 (td, 3J
(1H,1H)=1.6 Hz, 4H; m-ArH), 8.93 ppm (s, 171Yb satellites, 3J-
171Yb,1H)=44 Hz, 2H; NC(H)N); 13C{H} NMR (100.62 MHz, C6D6): d=
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(1H,1H)=7.4 Hz, 4J
G
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(
26.0 (CH2, thf), 68.4 (OCH2 thf), 118.4 (Ar-CH), 121.5 (Ar-CH), 127.1
(Ar-CH), 128.9 (Ar-CH), 129.2 (Ar-CH), 130.0 (Ar-CH), 131.3 (Ar-CH),
134.5 (Ar-C), 144.3 (Ar-C), 149.3 (Ar-CN), 162.5 ppm (NC(H)N);
171
3
1
Yb NMR (52.55 MHz, C6D6, 303 K) d=695 ppm (brt, Dw = =55 Hz, J-
C66H102EuN4O4 (1167.50):
C
67.90,
H 8.81, N 4.80; calcd for
2
ACHTUNGTRENNUNG(
171Yb,1H)=48 Hz; NC(H)NYb,); IR (Nujol): n˜ =1665 (m), 1597 (m),
C58H86EuN4O2 (loss of THF of solvation; 1023.29): C 68.08, H 8.47, N
5.48; found: C 65.01, H 8.20, N 5.81.
1520 (s), 1317 (s), 1265 (w), 1230 (s), 1159 (w), 1110 (w), 1073 (m), 1033
(m), 1008 (w), 947 (w), 921 (w-m), 874 (w), 829 (w-m), 776 (w), 760 (s),
746 (s), 699 (s), 612 (w), 434 cmꢀ1 (w); elemental analysis calcd (%) for
C66H70N4O4Yb (1156.35): C 68.55, H 6.10, N 4.85, Yb 14.96; calcd (%)
for C62H62N4O3Yb (loss of one THF of solvation; 1084.24): C 68.68, H
5.76, N 5.14, Yb 15.96; found: C 68.33, H 5.61, N 5.43, Yb 15.85.
In a repeated synthesis, compound 8 was similarly obtained (0.40 g, 60%)
and confirmed by unit cell comparison. Crystal system: monoclinic; a=
23.90, b=16.00, c=18.79 ꢁ; b=1148. M.p 218–2208C; 1H NMR
(300.13 MHz, C6D6; satisfactory integration was not possible because of
paramagnetic broadening): d=1.00 (brs, CH3), 1.30 (brm; thf), 3.10
[Yb
(DippForm)
E
(brm; thf), 3.40 (brm; CHACTHNGUTERNNU(G CH3)), 7.10 (brs; Ar-H), 10.01 ppm (brs;
0.69 mmol), bis(pentafluorophenyl)mercury (0.37 g, 0.69 mmol) and
NC(H)N); 13C NMR (75.47 MHz, C6D6, 300 K): d=23.8 (CH
ACHTUNGTRENNUNG(CH3)2),
Chem. Eur. J. 2013, 19, 1410 – 1420
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1417

P. C. Junk et al.
28.1 (CH
N
(50 mL). The resulting colourless solution was stirred at room tempera-
ture overnight, filtered and concentrated until crystallization (approxi-
assigned), 151.5 ppm (NC(H)N); elemental analysis calcd (%) for
C58H86EuN4O2: (loss of THF of solvation; 1023.29): C 68.08, H 8.47, N
5.48, Eu 14.85; calcd (%) for C62H94EuN4O3 (one THF of solvation;
1095.40): C 67.98, H 8.65, N 5.11, Eu 13.87; found: C 66.54, H 8.42, N
5.44, Eu 14.09.
mately 10 mL). Storage at 08C for 2 d yielded [Tb
ACHTUNGTREN(NUNG DippForm)2Cl-
AHCTUNGTRENNUNG
1988C; IR (Nujol): n˜ =1928 (w), 1867 (w), 1800 (w), 1667 (s), 1587 (m),
1520 (s), 1361 (m), 1279 (s), 1235 (s), 1189 (s), 1097 (m), 1039 (m), 1014
(m), 934 (m), 860 (w), 823 (w), 800 (m), 756 cmꢀ1 (m); elemental analysis
calcd (%) for C68H106ClN4O4.5Tb (1245.94): C 65.55, H 8.58, N 4.50; calcd
(%) for C58H86ClN4O2Tb (loss of lattice thf; 1065.71): C 65.37, H 8.13, N
5.26; found: C 65.29, H 8.21, N 5.37.
[{Yb
A
added to
(10 mL). The biphasic mixture was stirred for 24 h at room temperature.
The resulting yellow solution was filtered to remove a green/grey precipi-
tate and the solvent and other volatiles were removed under vacuum to
give a yellow powder. The powder could be crystallised from hexane
(3 mL) at room temperature to give yellow block-shaped crystals
(0.060 g; 40%); IR (Nujol): n˜ =1667 (s), 1588 (m), 1519 (s), 1277 (s),
1202 (m), 1187 (m), 1102 (brm), 1015 (brm), 950 (w), 864 (w), 807 (m),
762 (m), 722 (w), 668 (w), 518 (w), 413 (m), 402 cmꢀ1 (m); It was not pos-
[La
Schlenk flask charged with freshly filed La metal (0.07 g, 0.50 mmol), Hg-
AHCTUNTGRENNG(NU 2-BrC6F4)2 (0.45 g, 0.69 mmol) and DippFormH (0.50 g, 1.37 mmol). The
ACHUTGTNRNE(UNG DippForm)2BrACHTUNGTREN(NUNG thf)] (14): Tetrahydrofuran (20 mL) was added to a
colourless slurry was stirred at ambient temperature overnight to give a
pale-yellow reaction mixture. Filtration, to remove elemental mercury
and excess La metal, followed by removal of volatiles under vacuum
gave an off-white solid that crystallised from toluene (4–5 mL) as pure 14
upon standing at ambient temperature for several days (0.17 g; 37%).
M.p. 2738C (decomp); IR (Nujol): n˜ =1926 (w), 1860 (w), 1797 (w), 1667
(s), 1586 (s), 1381 (m), 1362 (m), 1334 (s), 1296 (s), 1235 (m), 1188 (s),
1107 (m), 1046 (w), 1013 (m), 934 (w), 824 (m), 800 (m), 756 (s), 728 (w),
674 (w), 608 cmꢀ1 (m); 1H NMR (300.13 MHz, C6D6, vacuum dried
sible to obtain H or 19F NMR spectra because of the paramagnetic prop-
erties of the compound; elemental analysis calcd (%) for C84F2H108N8Yb2
(1613.19): C 62.51, H 6.74, N 6.94; found: C 62.18, H 6.71, N 6.83. No in-
frared absorption peaks were observed for the grey precipitate between
n˜ =4000 and 600 cmꢀ1; m.p. >3608C.
[{Yb(o-PhPhForm)2ACHTUNGTRENNUNG(m-F)}2] (10): Perfluorodecalin (0.08 g, 0.18 mmol)
was added to a red-coloured solution of 5 (0.20 g, 0.18 mmol) in THF
(15 mL). The biphasic mixture was stirred for 24 h at room temperature.
The resulting yellow precipitate (0.12 g; 38%) was filtered from a red
solution and washed with THF (5 mL; the red solution was concentrated
and left to crystallise at ꢀ68C. No crystals were obtained). M.p. 166–
1708C, decomp 240–2428C; IR (Nujol): n˜ =1663 (m), 1595 (m–s), 1533
(s), 1302 (s), 1214 (s), 1178 (w), 1158 (m), 1110 (w–m), 1066 (s), 1051
(w), 1030 (m), 1008 (w–m), 992 (s), 944 (s), 913 (s), 876 (s), 830 (m), 770
(s), 727 (s), 718 (s), 702 (s), 611 cmꢀ1 (m); far-IR (vaseline): n˜ =565 (m),
547 (m), 512 (brm), 492 (w), 473 (m), 390 (s), 370 (sh w), 336 (sbr), 298
(m–s), 282 (shw), 259 (w), 204 (s), 164 cmꢀ1 (w); elemental analysis calcd
(%) for C100F2H76N8Yb2 (1774.49): C 67.71, H 4.32, N 6.32, Yb 19.51;
found: C 66.61, H 4.59, N 6.24, Yb 19.61.
ACTHNUTRGNEUNG
sample, THF lost): d=1.26 (d, 3J(1H,1H)=6.8 Hz, 48H; CH3, iPr), 3.61
(septet, 3JHH =6.8 Hz, 8H; CH, iPr), 7.17 (m, 12H; Ar-H), 8.28 ppm (s,
2H; NC(H)N); 13C{1H} NMR (vacuum dried sample): d=24.1 (CH3, iPr),
28.7ACTHNUTRGNE(NUG CH, iPr), 123.8 (Ar-CH), 125.4 (Ar-CH), 143.5 (Ar-C), 146.4 (Ar-C),
170.0 ppm (NC(H)N); elemental analysis calcd (%) for C54H78BrLaN4O
(1018.02): C 63.71, H 7.72, N 5.50; calcd for C50H70BrLaN4 (THF lost;
945.93): C 63.49, H 7.46, N 5.92; found: C 64.03, H 7.89, N 5.28. The
1H NMR spectrum of the crude product showed evidence of the presence
of o-HC6F4O
cell determination of hand picked single crystals.
[Nd(DippForm)2Br(thf)] (15): Following a similar procedure to that for
the synthesis of 14, Nd metal (0.08 g, 0.55 mmol), Hg(2-BrC6F4)2 (0.45 g,
(DippForm)[2,5] (Scheme 3), as confirmed by a unit
ACHTUGTNRENG(NU CH2)4ACHTUTGNRENNUGN
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
[Yb(o-PhPhForm)2ClACHTUNGTRENNUNG(thf)2]·2THF (11): THF (10 mL) was added to a
0.69 mmol) and DippFormH (0.51 g, 1.40 mmol) gave blue-green blocks
of 15 upon recrystallisation from toluene (approximately 4 mL) at 08C
(0.22 g; 47%). M.p. 2798C (decomp); IR (Nujol): n˜ =1936 (w), 1868 (w),
1797 (w), 1666 (s), 1592 (s), 1389 (s), 1366 (s), 1316 (m), 1278 (m), 1231
(s), 1192 (s), 1108 (m), 1044 (w), 1014 (m), 944 (m), 860 (w), 830 (w), 800
(m), 757 (s), 729 (w), 700 (s), 670 cmꢀ1 (w); 1H NMR (300.13 MHz,
C6D6): d=ꢀ3.28 (brs, 48H; CH3, iPr), 1.93 (m, 4H; CH2), 2.39 (brs, 8H;
CH, iPr), 3.89 (m, 4H; OCH2), 7.61 (m, 12H; Ar-H), 9.37 ppm (brs, 2H;
NC(H)N); elemental analysis calcd (%) for C54H78BrN4NdO (1023.35): C
63.38, H 7.68, N 5.47; found: C 63.25, H 7.37, N 5.54. The co-product o-
Schlenk flask charged with compound 5 (0.44 g, 0.44 mmol) and hexa-
chloroethane (51 mg, 0.22 mmol). The mixture turned yellow and it was
stirred at room temperature for 1 h. The solvent was removed under re-
duced pressure to give a yellow powder (0.45 g, 0.38 mmol, 86%). M.p.
132–1348C; IR (Nujol): n˜ =1661 (m), 1590 (shw), 1569 (shw), 1538 (s),
1298 (s), 1262 (sh w), 1205 (m), 1109 (m), 1070 (m), 1052 (shw), 1019
(m), 991 (w), 939 (m) 912 (m), 866 (m), 762 (m), 738 (s), 699 cmꢀ1 (s);
far-IR (vaseline): n˜ =614 (m), 562 (s), 550 (s), 537 (s), 519 (s), 506 (s),
479 (w), 452 (w), 390 (sbr), 371 (shw), 340 (w), 327 (w), 289 (w), 261 (m–
s), 248 (m–s), 217 (w), 200 (w), 187 (w), 160 (w), 148 (w), 125 cmꢀ1 (w);
1H NMR (300.13 MHz, C6D6): d=12.1 ppm (brs, NC(H)N), the rest of
HC6F4O
[Yb(DippForm)2Br
dure to that for the synthesis of 14, Yb metal (0.12 g, 0.69 mmol), HgACHTUNGTRENNUNG
ACHTUGTNRENG(NU CH2)4ACHTUGNTRENNNUG
(DippForm) was characterised as for 14.
(thf)]·Et2O (16): Method 1: Following a similar proce-
(2-
G
ACHTUNGTRENNUNG
the spectrum could not be integrated owing to para
precluding unequivocal assignments.
ACHTUNGTRENmNUNG agnetic broadening,
BrC6F4)2 (0.45 g, 0.69 mmol) and DippFormH (0.50 g, 1.37 mmol) gave a
dark yellow solution in THF (50 mL) that was stirred overnight. Filtra-
tion, and removal of volatiles under vacuum gave a light-yellow micro-
crystalline powder that was recrystallised as dark-yellow prismatic crys-
tals (0.43 g; 55%) from diethyl ether (50 mL) at ꢀ308C. M.p. 2708C
A second reaction solution of 11 was concentrated, left to crystallise and
small yellow needles formed at ꢀ48C after 5 days. After 10 weeks crys-
tals suitable for X-ray crystal structure analysis were obtained.
[YbACHTUNGTRENNUNG(DippForm)2ClACHTUNGTRENNUNG(thf)]·THF (12): A solution of 1,2-dichloroethane
(0.12 g, 1.2 mmol) in toluene (10 mL) was added, with stirring, at ambient
temperature, to an orange solution of 6 (1.04 g, 1.0 mmol) in toluene
(40 mL). The solution was heated to 708C and was kept, with stirring, at
this temperature for 2 h. The volume of solution was reduced to 10 mL
under vacuum and stored at ꢀ308C for 2 d, during which time bright-
yellow crystalline complex 12 precipitated and was collected (0.74 g,
68%). M.p. 280–2848C; IR (Nujol): n˜ =1592 (w), 1526 (s), 1461 (s), 1361
(w), 1319 (m), 1273 (s), 1236 (w), 1194 (m), 1179 (w), 1161 (w), 1109 (w),
1098 (w), 1055 (w), 1043 (w), 1015 (m), 947 (w), 934 (w), 861 (w), 800
(m), 773 (m), 756 (m), 670 cmꢀ1 (w); elemental analysis calcd (%) for
C54H78ClN4OYb (loss of lattice thf; 1007.72): C 64.36, H 7.80, N 5.56;
found C 64.38, H 8.02, N 5.51.
(decomp). The co-product o-HC6F4OACHTNUTRGENNUG(CH2)4ACHTUNGTRNEN(UGN DippForm) was detected as
for 14.
Method 2: 1-Bromo-2,3,4,5-tetrafluorobenzene (0.10 mL, 0.81 mmol) was
added dropwise by syringe to a stirred deep-orange solution of 6 (0.15 g,
0.13 mmol) in diethyl ether (50 mL). The resulting yellow solution was
stirred for 2 h, filtered and dried in vacuo for 2 h to yield 16 as a light-
yellow powder (0.12 g, 84%). M.p. 2688C (decomp); IR (Nujol): n˜ =1926
(w), 1860 (w), 1796 (w), 1666 (s), 1586 (s), 1381 (s), 1361 (s), 1334 (s),
1297 (s), 1254 (m), 1235 (s), 1188 (s), 1107 (m), 1096 (m), 1055 (m), 1013
(m), 957 (w), 934 (m), 884 (w), 825 (s), 800 (s), 757 (s), 674 (w), 608 cmꢀ1
(w); elemental analysis (vacuum dried sample) calcd (%) for
C54H78BrN4OYb (loss of Et2O of crystallisation; 1052.15): C 61.64, H
7.47, N 5.32; calcd (%) for C58H88BrN4O2Yb (retention of THF and
Et2O; 1126.27): C 61.85, H 7.88, N 4.97; found: C 62.25, H 7.55, N 5.04.
[Tb
(DippForm)
pale-yellow solution of anhydrous TbCl3 (0.15 g, 0.57 mmol) in THF
A
ACHTUNGTRENNUNG(thf)2]·2.5THF (13): A colourless solution of [Na-
A
ACHTUNGTRENNUNG
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Chem. Eur. J. 2013, 19, 1410 – 1420

Lanthanoid(II) Formamidinates
FULL PAPER
Control experiments:
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HgACHTUNGTRENNUNG(C6F5)2 and XylFormH: In a pre-weighed conical flask, HgCAHTUNGTRENN(UNG C6F5)2
(0.10 g, 0.18 mmol) and XylFormH (0.09 g, 0.37 mmol) were dissolved in
pre-dried THF (20 mL) and the conical flask was stoppered. The clear
solution was left to stir at room temperature in air for 48 h. The solvent
was removed by slow evaporation and the white material remaining
(0.19 g) was weighed and characterised by IR spectroscopy. IR (Nujol):
n˜ =1649 (s), 1637 (s), 1588 (s), 1578 (w), 1560 (w), 1556 (s), 1509 (s),
1473 (s), 1310 (s), 1277 (m), 1250 (s), 1201 (s), 1148 (s), 1091 (s), 1069
(vs), 1034 (m), 1018 (m), 1001 (w), 983 (w), 965 (vs), 924 (w), 820 (w),
807 (s), 758 (s), 719 (m), 668 (w), 661 (m), 620 cmꢀ1 (m; Underlined
values correspond to the absorption bands for Hg
respond to the absorption bands for XylFormH).
ACHTNUGTRNE(NNUG C6F5)2 and others cor-
Hg
ACHTUNGTRENNUNG
experiment 1, HgACHTUNGTRENNUNG
0.36 mmol) gave a white powder (0.22 g) which was identified by IR
spectroscopy as above as the starting materials.
Yb metal and XylFormH: Tetrahydrofuran (15 mL) was added to a flask
charged with excess Yb metal (0.05 g, 0.28 mmol) and XylFormH (0.05 g,
0.19 mmol) and left to stir at room temperature under purified N2. The
clear solution was filtered and the solvent was removed under vacuum to
give a white powder, which was identified as XylFormH by IR spectros-
ACHTUNGTRENNUNGcopy. IR (Nujol): n˜ =1649 (s), 1588 (s), 1556 (s), 1464 (s), 1367 (s), 1311
(s), 1250 (s), 1203 (s), 1148 (s), 1091 (s), 1034 (m), 1001 (w), 985 (w), 924
(w), 820 (w), 758 (s), 661 (m), 620 cmꢀ1 (m).
X-ray crystallography: Crystalline samples of compounds 2–9 and 11–16
were mounted on glass fibres in highly viscous silicone oil at 123(2) K. A
summary of the crystallographic data can be found in Table S5 in the
Supporting Information. Data were collected on an Enraf–Nonius Kappa
CCD or a Bruker X8 APEX CCD (compound 7a) diffractometer with
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with the graphical interface X-Seed.[38] Hydrogen atoms were refined as
described in the .cif files.
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Acknowledgements
The authors would like to thank the Australian Research Council (ARC
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Received: August 9, 2012
Published online: November 30, 2012
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Chem. Eur. J. 2013, 19, 1410 – 1420