Ti and Zr complexes of ferrocenyl amidinates

Article abstract of DOI:10.1039/c0dt00530d

Preparation of a N-ferrocenyl-amidinate complex was achieved by employing (TMEDA)Li[(CpFeC₅H₄)NC(Ph)NSiMe₃] (1) to prepare Cp*Zr[(CpFeC₅H₄)NC(Ph)NSiMe ₃]Cl₂ (2). Complex 2 exhibited poor polymerization activity and thus a series of C-ferrocenyl bis(amidinate) complexes of the type M(L)₂Cl₂ (M = Zr, 4; M = Ti, 5; L = (CyNC(CpFeC ₅H₄)NCy) were synthesized via reaction of ferrocenyl-amidine, H(L) and M(NMe₂)₂Cl₂ (M = Ti, Zr·2THF). Half sandwich mono(amidinate) complexes, Cp′ZrLCl₂ (Cp′ = Cp, 7; Cp′ = Cp*, 8), were prepared by the reaction of Cp′ZrCl₃ with Li(L) and subsequently alkylated to give M(L)₂Me₂ (M = Zr, 9; M = Ti, 11), CpZr(L)(CH₂Ph)₂ (12) and Cp*Zr(L)Me ₂ (10) with the appropriate alkylating agent. Abstraction of a methyl group from 7 with B(C₆F₅)₃ and [Ph ₃C][B(C₆F₅)₄] proceeded cleanly to give [{CyNC(CpFeC₅H₄)NCy}₂ZrMe][MeB(C ₆F₅)₃] 13 and [{CyNC(CpFeC₅H ₄)NCy}₂ZrMe][B(C₆F₅)₄] 14, respectively. Similarly, the analogous CpZr and Cp*Zr derivatives LZr{CyNC(CpFeC₅H₄)NCy}CH₂Ph] [PhCH ₂B(C₆F₅)₃] L = Cp 15, Cp* 17 and [LZr{CyNC(CpFeC₅H₄)NCy}CH₂Ph][B(C ₆F₅)₄] L = Cp 16, Cp* 18 were prepared. Cyclic voltammetry studies on the metal complexes containing ferrocenyl-amidinates reveal quasi reversible oxidation and reduction waves for the ferrocene/ferrocenium couple. The dichloride complexes (4-8) activated with MAO and dialkyl complexes (9,10) activated with B(C₆F ₅)₃ and [Ph₃C][B(C₆F ₅)₄] showed low ethylene polymerization activities. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00530d

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PAPER
www.rsc.org/dalton | Dalton Transactions
Ti and Zr complexes of ferrocenyl amidinates†
Kanwarpal Multani, Louisa J. E. Stanlake and Douglas W. Stephan*
Received 22nd May 2010, Accepted 6th July 2010
DOI: 10.1039/c0dt00530d
Preparation of a N-ferrocenyl-amidinate complex was achieved by employing
(TMEDA)Li[(CpFeC5H4)NC(Ph)NSiMe3] (1) to prepare Cp*Zr[(CpFeC5H4)NC(Ph)NSiMe3]Cl2 (2).
Complex 2 exhibited poor polymerization activity and thus a series of C-ferrocenyl bis(amidinate)
complexes of the type M(L)2Cl2 (M = Zr, 4; M = Ti, 5; L = (CyNC(CpFeC5H4)NCy) were synthesized
via reaction of ferrocenyl-amidine, H(L) and M(NMe2)2Cl2 (M = Ti, Zr·2THF). Half sandwich
mono(amidinate) complexes, Cp¢ZrLCl2 (Cp¢ = Cp, 7; Cp¢ = Cp*, 8), were prepared by the reaction of
Cp¢ZrCl3 with Li(L) and subsequently alkylated to give M(L)2Me2 (M = Zr, 9; M = Ti, 11),
CpZr(L)(CH2Ph)2 (12) and Cp*Zr(L)Me2 (10) with the appropriate alkylating agent. Abstraction of a
methyl group from 7 with B(C6F5)3 and [Ph3C][B(C6F5)4] proceeded cleanly to give
[{CyNC(CpFeC5H4)NCy}2ZrMe][MeB(C6F5)3] 13 and [{CyNC(CpFeC5H4)NCy}2ZrMe][B(C6F5)4] 14,
respectively. Similarly, the analogous CpZr and Cp*Zr derivatives LZr{CyNC(CpFeC5H4)-
NCy}CH2Ph] [PhCH2B(C6F5)3] L = Cp 15, Cp* 17 and [LZr{CyNC(CpFeC5H4)NCy}-
CH2Ph][B(C6F5)4] L = Cp 16, Cp* 18 were prepared. Cyclic voltammetry studies on the metal
complexes containing ferrocenyl-amidinates reveal quasi reversible oxidation and reduction waves for
the ferrocene/ferrocenium couple. The dichloride complexes (4–8) activated with MAO and dialkyl
complexes (9,10) activated with B(C6F5)3 and [Ph3C][B(C6F5)4] showed low ethylene polymerization
activities.
cyclopolymerization of 1,5-hexadiene using ferrocenyldimethylsi-
Introduction
lyl substituted zirconocene precatalysts (Scheme 1b) compared to
Cp2ZrCl2.4 Recently, we have incorporated ferrocenyl substituents
on phosphinimide ligands affording a series of highly active
catalysts (Scheme 1c).5
Derivatives of ferrocene have received an enormous amount of at-
tention as components of polymeric materials and biomolecules.1
In addition, its use as a substituent on a ligand is motivated
by its high stability, low cost, facile synthesis, rigid structure,
and well-behaved redox chemistry. Group 4 complexes containing
ferrocene based ligands are active olefin polymerization catalysts
(Scheme 1).2 For example, Arnold and coworkers have prepared
titanium and zirconium complexes with the bis(amino)ferrocenyl
ligand (Scheme 1a), and demonstrated high ethylene polymer-
ization activity for the zirconium complex upon activation with
[Ph3C][B(C6F5)4].2d,3 Mukaiyama and co-workers reported greater
ethylene polymerization activity and superior stereoselectivity in
The incorporation of ferrocene also offers the possibility of
redox tunable catalysts,6 in which changing the oxidation state of
iron could impact the catalyst activity, co-monomer incorporation
and stereoregularity of the resulting polymer. While the study of
redox tunable olefin polymerization catalysts has been limited, the
FeIII ferrocenium derivative of the bis(amino)ferrocenyl zirconium
complex (Scheme 1a) was isolated and shown to be an active
catalyst.7 Recently, Gibson and coworkers have reported very sim-
ilar ethylene polymerization activities by FeII and FeIII derivatives
based on ferrocenyl substituted bis(imino)pyridyl complexes.8
Group 4 complexes containing azaallyl9 and amidinates10 as an-
cillary ligands have been studied. For example bis(benzamidinate)
complexes and half sandwich mono(benzamidinate) complexes
have been reported to polymerize propylene, 1-hexene and styrene
with moderate activities.11 In this paper we explore species
that are derived from amidinate ligands that also incorporate
ferrocenyl substituents. The synthesis and characterization and
electrochemical properties of these systems are presented and these
complexes are evaluated in olefin polymerization.
Scheme 1 Active olefin polymerization catalyst precursors containing
ferrocene based ligands.
Department of Chemistry, University of Toronto, 80 St. George St. Toronto,
Ontario, Canada, M5S 3H6. E-mail: dstephan@chem.utoronto.ca; Tel: 416-
946-3294
† Electronic supplementary information (ESI) available: NMR spectra.
CCDC reference numbers 778595–778599. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c0dt00530d
Experimental section
All preparations were done under an atmosphere of dry, O2-
free, N2 employing both Schlenk-line techniques and Innovative
Technology or Vacuum Atmospheres inert atmosphere glove
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boxes. Solvents were purified employing a Grubbs-type column
for C25H39FeLiN4Si: C, 62.65; H, 7.89; N, 11.24. Found: C, 61.42;‡
H, 7.08; N, 10.01.
1
system manufactured by Innovative Technology. H, 13C, 31P,11B
and 19F NMR spectroscopy spectra were recorded on Varian 200,
1
300, 400 MHz and Bruker 400 MHz spectrometers. H and 13C
Synthesis of Cp*Zr[(CpFeC5H4)NC(Ph)NSiMe3]Cl2 (2)
NMR spectra are referenced to SiMe4 using the residual solvent
peak impurity of the given solvent. 31P, 11B and 19F NMR spectra
were referenced to 85% H3PO4, Et2O·BF3, and CFCl3, respectively.
Chemical shifts are reported in ppm and coupling constants in
Hz. C6D6, C6D5CD3, CDCl3, CD2Cl2 and BrC6D5 were used
as the NMR solvents after being dried over Na/benzophenone
(C6D6, C6D5CD3) or CaH2 (the others), vacuum-transferred into
Young bombs and freeze-pump-thaw degassed (three cycles).
Combustion analyses were performed in house employing a
Perkin Elmer 2400 Series II CHNS Analyzer. Cyclic voltammetry
experiments were performed in a BASi RDE-2 cell stand for
rotating disk electrochemical experiments, using a glassy carbon
working electrode with a disk diameter of 3.0 mm, an aqueous
Ag/AgCl reference electrode and a Pt wire auxiliary electrode. The
working electrode was polished with alumina (0.05 mm) and rinsed
with deionised water prior to use. [NBu4][PF6] was used as the
supporting electrolytes (0.1 M solutions). All the potentials were
referenced versus Cp2Fe+/0. All electrochemical data were acquired
with a computer controlled BASi Epsilon EC potentiostat, using
the Epsilon EC software.
MeLi (1.6 M in ether), MeMgBr (1.4 M in toluene–
THF 7 : 1), dicyclohexylcarbodiimide and methylaluminoxane
(10% w/w in toluene) were purchased from Aldrich Chemical
Company and used without further purification. [NBu4][PF6]
and [NBu4][BF4], purchased from Aldrich, was recrystallized
three times from absolute ethanol and ethyl acetate, re-
spectively and dried overnight at 100 ◦C in vacuo. Cp2Fe,
CpZrCl3 and Cp*ZrCl3 were purchased from Strem Chemi-
cals. CpFeC5H4NH2,12 CpFeC5H4NH(SiMe3),13 Ti(NMe2)2Cl2,14
Zr(NMe2)2Cl2(THF)2,15 CpFeC5H4Li16 and KCH2Ph17 were pre-
pared from literature methods.
Inside an inert atmosphere glovebox a 20 mL vial was charged with
Cp*ZrCl3 (37 mg, 0.11 mmol) and THF (5 mL). The solution was
cooled to -30 ◦C, where a solution of 1 (56 mg, 0.11 mmol) in THF
(5 mL) was added dropwise. The resultant orange solution was
warmed to room temperature and stirred for 2 h. The reaction was
concentrated and suspended in CH2Cl2 (5 mL) and filtered through
a pipette plug of Celite to remove the LiCl salt. The solution was
concentrated and washed 3 ¥ 5 mL pentane to obtain an orange
1
solid (55 mg, 75%). H NMR (C6D6): 7.32 (m, 2H, m-Ph), 7.04
(m, 2H, o-Ph), 6.97 (m, 1H, p-Ph), 4.70 (br s, 1H, H2–C5H4),
4.05 (s, 5H, Cp), 3.82 (br s, 1H, H5–C5H4), 3.53 (br s, 1H, H3-
C5H4), 2.73 (br s, 1H, H4–C5H4), 2.11 (s, 15H, C5Me5), 0.06 (s, 9H,
1
SiMe3). 13C{ H} (C6D6): 142.1(ipso-C), 129.8, 127.0, 126.3(Ph),
70.2 (Cp*, C5H5), 69.2 (ipso-C5H4), 66.8, 65.4, 64.6, 60.9 (C5H4),
12.9 (Cp*–Me), 3.4 (SiMe3). MS(EI): 672 [M+]. Anal. Calcd. for
C30H38Cl2FeN2SiZr: C, 53.56; H, 5.69; N, 4.16. Found: C, 55.12;
H, 5.82; N, 4.67.
Synthesis of [CyNC(CpFeC5H4)NCy]H (3)
A modified literature procedure18 was developed. A 50 mL
Schlenk flask was charged with monolithioferrocene (0.20 g,
1.04 mmol) and THF (10 mL). The flask was cooled to 0 ◦C
and a solution of dicyclohexyl carbodiimide (0.21 g, 1.04 mmol)
in THF (10 mL) was added dropwise. The reaction was warmed to
room temperature and stirred for 1 h before quenching with water
(5 mL). The aqueous portion was washed with hexanes (2 ¥ 5 mL),
and the combined organic layers were washed with water and dried
over MgSO4. The volatiles were removed in vacuo resulting in
yellow solid without requiring further purification (0.31 g, 85%).
The procedure can be scaled up or down without any noticeable
effect on yield. The NMR data is in agreement with the literature.18
1H NMR (C6D6): 4.64 (d, 3JH–H = 6.7 Hz, 1H, NH), 4.28 (t, 3JH–H
=
Synthesis of (TMEDA)Li[(CpFeC5H4)NC(Ph)NSiMe3] (1)
1.8 Hz, 2H, H2,5-C5H4), 4.26–4.13 (m, 1H, a-H Cy), 4.01 (s, 5H,
The following modified literature preparation was followed.23
A
3
Cp), 3.94 (t, JH–H = 1.8 Hz, 2H, H3,4-C5H4), 3.62–3.50 (m, 1H,
solution of nBuLi (0.48 mL, 0.76 mmol, 1.6 M in ether) and
tetramethylethylenediamine (TMEDA) (0.11 mL, 0.74 mmol) in
diethyl ether (5 mL) was added to a cooled (-30 ◦C) bright
orange solution of CpFeC5H4NH2SiMe3 (0.21 g, 0.76 mmol)
in diethylether (10 mL). The resulting suspension was warmed
to room temperature and stirred overnight. The solution was
concentrated to remove volatiles and then suspended in diethyl
ether (10 mL) and cooled to -30 ◦C. Benzonitrile (0.080 g,
0.77 mmol) was added dropwise to the cooled reaction mixture,
and the resultant red solution was warmed to room temperature
and stirred for 2 h. The solution was filtered through a pipette plug
of Celite and concentrated to an orange solid. The product was
recrystallized from cold pentane to obtain an orange crystalline
a-H Cy), 2.28–2.16 (m, 2H, Cy), 1.87–1.12 (m, 18H, Cy).
Synthesis of [CyNC(CpFeC5H4)NCy]2MCl2 M = Zr (4), Ti (5)
These compounds were prepared in a similar fashion and thus only
one preparation is detailed. A 100 mL Schlenk flask was charged
with Zr(NMe)2Cl2(THF)2 (0.50 g, 1.3 mmol) and slight excess of 2
equiv of 3 (1.05 g, 2.7 mmol). Toluene (50 mL) was added and the
orange solution was heated to reflux overnight. The volatiles were
removed under reduced pressure. The solid was washed with ether
(1 ¥ 5 mL) and hexanes (3 ¥ 10 mL) until the washings turned from
orange to pale yellow indicating the complete removal of excess
3. The orange powder was dried under vacuum (1.02 g, 85%).
Crystals suitable for X-ray diffraction analysis were grown from
slow evaporation of toluene solution at room temperature. (4): 1H
1
solid (0.326 g, 89%). H NMR (C6D6): 7.37 (m, 2H, m-Ph), 7.21
(m, 2H, o-Ph), 7.11 (t, 1H, p-Ph), 4.14 (s, 5H, Cp), 3.79 (t, 3JH–H
=
3
NMR (CD2Cl2): 4.54 (t, JH–H = 1.7 Hz, 4H, H2,5-C5H4), 4.37 (t,
3
2.0 Hz, 2H, H2,5-C5H4), 3.51 (t, JH–H = 2.0 Hz, 2H, H3,4-C5H4),
1
2.04 (s, 12H, NMe2), 1.83 (s, 4H, CH2), 0.10 (s, 9H, TMS). 13C{ H}
‡ In a number of cases repeated efforts to obtain elemental analysis resulted
in satisfactory N and H analyses with carbon values that are lower than
expected. This was attributed to the formation of metal carbides during
the combustion process.
(C6D6): 134.9(ipso-C), 128.1, 127.9, 127.4, 126.9 (Ph), 69.0 (ipso-
C5H4), 68.9 (C5H4), 63.5 (3,4-C5H4), 62.1 (2,5-C5H4), 56.5 (NMe2),
45.6 (CH2), 3.5 (SiMe3). MS(EI): 376 [M+-TMEDA]. Anal. Calcd.
8958 | Dalton Trans., 2010, 39, 8957–8966
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3JH–H = 1.8 Hz, 4H, H3,4–C5H4), 4.29 (s, 10H, Cp–Fe), 4.17–4.05
(m, 4H, a-H Cy), 2.09-1.92 (m, 8H, Cy), 1.90-1.80 (m, 8H, Cy),
1.80–1.70 (m, 8H, Cy), 1.69-1.61 (m, 4H, Cy), 1.38-1.18 (m, 12H,
N, 4.41. Found: C, 53.05; H, 5.83; N, 4.65. (8): 0.30 g, 34%.
Crystals suitable for X-ray diffraction analysis were grown from
1
hexanes solution at room temperature. H NMR (CD2Cl2): 4.50
1
3
3
Cy). 13C{ H} (CD2Cl2): 179.6 (Cipso(NCy)2), 71.2 (Cipso–C5H4), 70.7
(t, JH–H = 1.8 Hz, 2H, H2,5–C5H4), 4.35 (t, JH–H = 1.8 Hz, 2H,
3,4–C5H4), 4.28 (s, 5H, Cp–Fe), 4.14-4.24 (m, 2H, a-H Cy), 2.21
(C3,4-C5H4), 70.4 (Cp–Fe), 70.1 (C2,5–C5H4), 57.3 (a-C Cy), 35.8
(C2,6–Cy), 26.5 (C3,5–Cy), 26.2 (C4–Cy). E-Chem: E1/2 (CH2Cl2) =
439 mV, -455 mV, E1/2 (MeCN) = 391 mV, -400 mV. Anal. Calcd.
for C46H62Cl2Fe2N4Zr: C, 58.48; H, 6.61; N, 5.93. Found: C, 57.40;‡
H, 6.41; N, 5.90. (5): Yield: 0.84 g, 77%. Crystals suitable for X-
ray diffraction analysis were grown from slow diffusion of hexanes
into a saturated solution of 5 in CH2Cl2. 1H NMR (CD2Cl2): 4.56
H
(s, 5H, C5Me5-Zr), 1.94-1.43 (m, 12H, Cy), 1.37-0.95 (m, 8H, Cy).
1
13C{ H} NMR: 177.2 (Cipso(NCy)2), 126.4 (C5Me5), 73.8(C5H4),
70.8 (C5H4), 70.6(Cp–Fe), 69.6 (C5H4), 58.3 (a-C Cy), 36.1, 33.1,
26.7, 26.3, 13.6 (C5Me5). E-Chem: E1/2 (CH2Cl2) = 437 mV,
-557 mV, E1/2 (MeCN) = 402 mV, Epa = -399 mV. Anal. Calcd. for
C33H46Cl2FeN2Zr·CH2Cl2: C, 52.78; H, 6.25; N, 3.62. Found: C,
52.68;‡ H, 5.90; N, 3.58.
(br, 4H, H2,5–C5H4), 4.41 (m, 2H, a-H Cy), 4.35 (br, 4H, H3,4
–
C5H4), 4.29 (s, 10H, Cp–Fe), 3.99 (m, 2H, a-H Cy), 2.70-2.53 (m,
2H, Cy), 2.42-2.28 (m, 2H, Cy), 2.22-1.05 (m, 36H, Cy). 13C{ H}
1
Synthesis of [CyNC(CpFeC5H4)NCy]2ZrMe2 (9),
Cp*Zr[CyNC(CpFeC5H4)NCy]Me2 (10)
(CD2Cl2): 177.9 (Cipso(NCy)2), 72.0 (Cipso–C5H4), 70.5 (C5H4), 70.6
(C5H4), 70.4 (Cp–Fe), 70.0 (C5H4), 69.5 (C5H4), 61.3 (a-C Cy), 59.1
(a-C Cy), 35.5, 35.4, 35.0, 33.5, 26.9, 26.7, 26.3, 26.1. E-Chem:
E1/2 (CH2Cl2) = 351 mV, -487 mV, -1574 mV. Anal. Calcd. for
C46H62Cl2Fe2N4Ti: C, 61.29; H, 6.93; N, 6.22. Found: C, 59.22;‡
H, 7.31; N, 6.48.
These compounds were prepared in a similar fashion and thus only
one preparation is detailed. Methyllithium (0.40 mL, 0.64 mmol,
1.6 M in ether) was added dropwise to an orange suspension of
7 (0.30 g, 0.32 mmol) in toluene (18 mL) at -30 ◦C and stirred
for 6 h at room temperature. The solution was concentrated to
10 mL under reduced pressure and filtered through a plug of
Celite on a sintered glass frit. The volatiles were removed under
reduced pressure and the orange residue was washed with ether
(3 ¥ 1 mL) and dried in vacuo (0.22 g, 75%). Crystals suitable for
X-ray diffraction analysis were grown from slow evaporation of
Synthesis of Li[CyNC(CpFeC5H4)NCy] (6)
The following modified literature preparation was followed.19
A
bright orange solution of 3 (2.00 g, 5.1 mmol) in hexanes (50 mL)
was cooled to 0 ◦C and treated with MeLi (3.27 mL, 5.1 mol,
1.6 M in ether). The resulting suspension was warmed to room
temperature and stirred overnight. The solution was concentrated
to 30 mL and filtered to provide a yellow solid. The solid was
washed with hexanes and dried under vacuum (1.7 g, 84%). The
NMR data is consistent with the literature preparation. 1H NMR
(C6D6): 4.90-4.10 (overlapping broad m, 9H, Cp–Fe–C5H4), 2.6-
1.2 (m, 22H, Cy).
toluene solution at -30 ◦C. (9): 1H NMR (C6D6): 4.31 (t, 3JH–H
=
1.7 Hz, 4H, H2,5–C5H4), 4.28-4.19 (m, 4H, a-H Cy), 4.15 (s, 10H,
Cp–Fe), 4.07 (t, 3JH–H = 1.8 Hz, 4H, H3,4–C5H4), 2.19-2.05 (m, 8H,
Cy), 2.02-1.92 (m, 8H, Cy), 1.87-1.76 (m, 8H, Cy), 1.70-1.59 (m,
4H, Cy), 1.41-1.23 (m, 12H, Cy), 1.12 (s, 6H, Zr–Me2). 13C{ H}
1
(C6D6): 178.1 (Cipso(NCy)2), 73.5 (Cipso–C5H4), 70.2 (C3,4–C5H4),
70.0 (Cp-Fe), 69.1 (C2,5–C5H4), 56.7 (a-C Cy), 45.3(Zr–Me2), 36.3
(C2,6–Cy), 26.6 (C3,5–Cy), 26.3 (C4–Cy). E-Chem: E1/2 (CH2Cl2) =
447 mV, 108 mV, Anal. Calcd. for C48H68FeN2Zr: C, 63.77; H,
7.58; N, 6.20. Found: C, 62.18;‡ H, 7.34; N, 6.31. (10): 0.13 g, 32%.
Synthesis of LZr[CyNC(CpFeC5H4)NCy]Cl2 L = Cp (7), Cp* (8)
3
These compounds were prepared in a similar fashion and thus
only one preparation is detailed. A 100 mL Schlenk flask was
charged with 6 (1.0 g, 2.5 mmol) and THF (25 mL), and cooled
to -78 ◦C. The red solution of 6 was cannula transferred dropwise
into a second 100 mL Schlenk flask containing a solution of
CpZrCl3 (0.66 g, 2.5 mmol) in THF (40 mL) at -78 ◦C. The
1H NMR (CD2Cl2): 4.42 (t, JH–H = 1.8, 2H, H2,5–C5H4), 4.28 (t,
3JH–H = 1.8, 2H, H3,4–C5H4), 4.23 (s, 5H, Cp–Fe), 4.09-3.98 (m, 2H,
a-H Cy), 2.07 (s, 15H, C5Me5), 1.75-0.94 (m, 20H, Cy), -0.10 (s,
1
6H, Zr–Me2). 13C{ H} NMR (CD2Cl2): 176.7 (Cipso(NCy)2), 120.2
(C5Me5), 74.9 (Cipso–C5H4), 70.7 (C3,4–C5H4), 70.3 (Cp–Fe), 68.9
(C2,5–C5H4), 57.8 (a-C Cy), 46.9 (Zr–Me2), 35.9 (br, C2,6–Cy), 26.6
(C3,5–Cy), 26.2 (C4–Cy), 12.5 (C5Me5). E-Chem: E1/2 (CH2Cl2) =
334 mV, Epa = 170 mV. Anal. Calcd. for C35H52FeN2Zr·0.5CH2Cl2:
C, 61.76; H, 7.74; N, 4.06. Found: C, 61.08;‡ H, 7.72; N, 4.18.
◦
reaction mixture was stirred at -78 C for 2 h, warmed to room
temperature and stirred overnight. The solvent was removed under
reduced pressure and the solid was extracted with CH2Cl2. The
solution was filtered through a plug of Celite on a sintered glass
frit followed by removal of volatiles under reduced pressure. The
resulting orange residue was washed with hexanes (3 ¥ 10 mL)
and ether (2 ¥ 5 mL), and dried in vacuo (0.93 g, 61%). The solid
was recrystallized from CH2Cl2 solution layered with hexanes at
room temperature (0.59 g, 38%).(7): 1H NMR (CD2Cl2): 6.68
Synthesis of [CyNC(CpFeC5H4)NCy]2TiMe2 (11)
All glassware was covered with aluminium foil due to the light
sensitive nature of the product. A 100 mL Schlenk flask was
charged with 5 (0.3 g, 0.33 mmol) and toluene (50 mL). The flask
was cooled to -78 ◦C and methyl magnesium bromide (0.48 mL,
0.67 mmol, 1.4 M in toluene–tetrahydrofuran 7 : 1) was added to
the suspension dropwise over a 5 min period. A colour change
from pink to dark yellow was observed immediately. After stirring
for 5 min, the solution was concentrated to 25 mL under reduced
pressure. The solution was filtered through a plug of Celite on a
sintered glass frit and the volatiles were removed in vacuo. The
yellow solid was washed with hexanes (3 ¥ 4 mL) resulting in 90%
3
(s, 5H, Cp–Zr), 4.53 (t, JH–H = 1.9 Hz, 2H, H2,5–C5H4), 4.40
3
(t, JH–H = 1.9 Hz, 2H, H3,4–C5H4), 4.30 (s, 5H, Cp–Fe), 4.17–
4.25 (m, 2H, a-H Cy), 1.89-1.72 (m, 8H, Cy), 1.64-1.53 (m, 6H,
1
Cy), 1.33-1.07 (m, 6H, Cy). 13C{ H} NMR: 174.4 (Cipso(NCy)2),
116.0 (Cp–Zr), 71.0 (Cipso–C5H4), 70.8 (C3,4–C5H4), 70.6 (Cp–
Fe), 70.1 (C2,5–C5H4), 57.8 (a-C Cy), 35.2(C2,6–Cy), 26.4 (C3,5
–
Cy),25.9 (C4–Cy). E-Chem: E1/2 (CH2Cl2) = 430 mV, -483 mV.
Anal. Calcd. for C28H36Cl2FeN2Zr·0.2CH2Cl2: C, 53.29; H, 5.77;
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pure product (0.086 g, 30%). Dilute conditions and stirring time
(C6D5Br): -132.1 (br, 6F, o-C6F5), -161.5 (br, 3F, p-C6F5), -165.5
(br, 6F, m-C6F5) (m,p-F gap) = 4.0 ppm. 11B (C6D5Br): -16.1. (15):
1H (C6D5Br): 7.25-6.77 (overlapping m, 8H, m, p-ZrCH2C6H5 and
BCH2C6H5), 6.49 (d, 3JH–H = 6.9 Hz, 2H, o-ZrCH2C6H5), 5.90 (s,
5H, Cp–Zr), 4.42 (br, 2H, H2,5–C5H4–Fe), 4.32 (br, 2H, H3,4-C5H4–
Fe), 4.13 (br, 5H, Cp–Fe), 3.37 (s, 2H, BCH2), 2.90 (s, 2H, ZrCH2),
1.97-0.67 (m, 20H, Cy). 19F (C6D5Br): -129.9 (d, 3JF–F = 22 Hz, 6F,
o-C6F5), -163.4 (t, 3JF–F = 21 Hz, 3F, p-C6F5), -166.1 (t, 3JF–F = 21
Hz, 6F, m-C6F5) (m,p-F gap) = 2.8 ppm. 11B (C6D5Br): -12.2. (16):
1H (C6D5Br): 7.23-6.85 (overlapping m, 23H, PhCH2CPh3 and
1
are crucial to minimize the decomposition products. H NMR
(CD2Cl2): 4.47 (t, 3JH–H = 1.8 Hz, 4H, H2,5–C5H4), 4.36 (t, 3JH–H
=
1.8 Hz, 4H, H3,4–C5H4), 4.26 (s, 10H, Cp–Fe), 4.19-4.08 (m, 4H, a-
H Cy), 2.05-1.58 (m, 30H, Cy), 1.38-1.17 (m, 16H, Cy), 1.23 (s, 6H,
1
Ti–Me2). 13C{ H} (CD2Cl2, partial): 178.6 (s, Cipso(NCy)2), 69.2
(C5H4), 64.7 (Ti–Me2), 70.3 (Cp–Fe), 70.4 (C5H4), 35.7 (br, Cy),
26.7-26.4 (overlapping peaks, Cy). Sufficient elemental analysis
could not be obtained due to the thermal instability and the light
sensitive nature of the product.
3
m,p-ZrCH2C6H5), 6.49 (d, JH–H = 6.5 Hz, 2H, o-CH2C6H5-Zr),
5.91 (s, 5H, Cp–Zr), 4.42 (br, 2H, H2,5–C5H4–Fe), 4.33 (br, 2H,
Synthesis of CpZr[CyNC(CpFeC5H4)NCy](CH2Ph)2 (12)
H
3,4–C5H4–Fe), 4.13 (br, 5H, Cp–Fe), 3.84 (s, 2H, PhCH2CPh3),
A 50 mL Schlenk flask was charged with 7 (0.25 g, 0.40 mmol)
and KCH2Ph (0.11 g, 0.80 mmol), and cooled to -30 ◦C. Toluene
(20 mL), precooled to -30 ◦C, was added to the Schlenk flask and
the suspension was stirred for 1 h at -30 ◦C. Then, the suspension
was warmed to room temperature and stirred overnight. The red
suspension changed to a yellow solution over time. The solution
was filtered through a plug of Celite on a sintered glass frit and
the volatiles were removed under reduced pressure. The resulting
yellow solid was washed with hexanes (3 ¥ 2 mL) and ether (3 ¥
2 mL) and dried in vacuo (0.14 g, 47%). Crystals suitable for X-ray
diffraction analysis were grown from slow evaporation of hexanes
2.89 (s, 2H, ZrCH2), 1.89-0.77 (m, 20H, Cy). 19F (C6D5Br): -131.6
(d, 3JF–F = 10 Hz, 6F, o-C6F5), -161.7 (t, 3JF–F = 21 Hz, 3F, p-C6F5),
-165.7 (t, 3JF–F = 18 Hz, 6F, m-C6F5) (m,p-F gap) = 4.0 ppm. 11
B
(C6D5Br): -16.2. (17): 1H (C6D5Br): 4.40 (br, 2H, H2,5–C5H4–Fe),
4.28 (br, 2H, H3,4-C5H4–Fe), 4.21-4.07 (overlapping m, 7H, a-H
Cy and CpFe), 4.10 (s, 5H, Cp–Fe), 1.94 (br, 15H, C5Me5), 1.82-
0.70 (overlapping m, 23H, Cy and Zr–Me), 1.13 (br, 3H, Zr–Me),
0.64 (s, 3H, BMe). 19F (C6D5Br): -132.1 (d, 3JF–F = 24 Hz, 6F, o-
C6F5), -163.5 (t, 3JF–F = 21 Hz, 3F, p-C6F5), -166.0 (t, 3JF–F = 19 Hz,
6F, m-C6F5) (m,p-F gap) = 2.5 ppm. 11B (C6D5Br): -14.4. (18): 1H
(C6D5Br): 7.18-7.04 (m, 15H, Ph3CMe), 4.43 (br, 2H, H2,5–C5H4–
Fe), 4.32 (br, 2H, H3,4-C5H4–Fe), 4.20-4.06 (overlapping m, 7H,
a-H Cy and CpFe), 4.09 (s, 5H, Cp–Fe), 2.04 (br, 3H, Ph3CCH3),
1.90 (s, 15H, C5Me5), 1.79-0.93 (m, 20H, Cy), 0.61 (s, 3H, Zr–Me).
solution at room temperature. 1H NMR (CD2Cl2): 7.15 (t, 3JH–H
=
3
7.7 Hz, 4H, m-Ph), 6.89 (d, JH–H = 7.3 Hz, 4H, o-Ph), 6.81 (t,
3JH–H = 7.3 Hz, 2H, p-Ph), 6.01 (s, 5H, Cp-Zr), 4.52 (t, 3JH–H = 1.7
Hz, 2H, H2,5–C5H4), 4.40 (t, 3JH–H = 1.8 Hz, 2H, H3,4 –C5H4), 4.31
(s, 5H, Cp–Fe), 4.19-4.10 (m, 2H, a-H Cy), 2.35 (d, 3JH–H = 10.4
Hz, 2H, CH2Ph), 1.87 (d, 3JH–H = 10.6 Hz, 2H, CH2Ph), 1.81-1.48
19F (C6D5Br): -131.7 (d, 3JF–F = 9 Hz, 6F, o-C6F5), -161.9 (t, 3JF–F
=
3
21 Hz, 3F, p-C6F5), -165.7 (t, JF–F = 19 Hz, 6F, m-C6F5) (m,p-F
gap) = 3.8 ppm. 11B (C6D5Br): -16.2.
1
(m, 16H, Cy), 1.36-1.07 (m, 4H, Cy). 13C{ H} NMR (CD2Cl2):
176.6 (s, Cipso(NCy)2), 151.7 (Cipso-Ph), 128.6 (m-Ph), 125.9 (o-Ph),
121.0 (p-Ph), 114.4 (Cp-Zr), 73.3 (Cipso–C5H4), 71.9 (CH2Ph), 70.7
(C3,4–C5H4), 70.5 (Cp–Fe), 69.5 (C2,5 –C5H4), 58.3 (a-C Cy), 36.2
(C2,6–Cy), 26.6 (C3,5–Cy), 26.1 (C4–Cy). E-Chem.: E1/2 (CH2Cl2) =
4257 mV, 95 mV, Anal. Calcd. for C42H50FeN2Zr: C, 69.11; H,
6.90; N, 3.84. Found: C, 68.56;‡ H, 6.65; N, 3.67.
Polymerization protocol
In all cases, trials were done in duplicate and the average activity is
reported. Solutions of precatalyst and cocatalyst were prepared
inside a glovebox and stored at -30 ◦C freezer. A 250 mL
Schlenk flask was charged with toluene (50 mL) and MAO (1000
equivalents of precatalyst). The flask was connected to a Schlenk
line, briefly evacuated and refilled with dry ethylene gas (repeated
5 times) A solution of dichloride precatalyst (10 mmol) in toluene
(3 mL) was added to the stirring solution (500 rpm) in the Schlenk
flask. The pressure of ethylene used for these trials was 1 atm. The
mixture was stirred for 20 min. at room temperature and quenched
with 10% HCl (v/v) in methanol solution. The polymer was
filtered, washed with methanol and dried under vacuum overnight.
For dimethylated precatalysts, the Schlenk flask was charged
with toluene (50 mL). After placing it under ethylene atmosphere,
iBu3Al (10% w/w in toluene, 0.5 mL, 200 mmol) was added and the
solution was stirred for 5 min. The precatalyst (10 mmol in 1 mL
toluene) was added to the solution immediately followed by the
cocatalyst solution (10 mmol in 1 mL toluene). The mixture was
quenched after stirring for 20 min. and the polymer was collected
as described above.
Synthesis of [{CyNC(CpFeC5H4)NCy}2ZrMe][MeB(C6F5)3] (13),
[{CyNC(CpFeC5H4)NCy}2ZrMe][B(C6F5)4] (14),
[LZr{CyNC(CpFeC5H4)NCy}CH2Ph][PhCH2(C6F5)3] L = Cp
(15), Cp* (17), [LZr{CyNC(CpFeC5H4)NCy}CH2Ph] [B(C6F5)4]
L = Cp (16), Cp* (18)
These compounds were prepared in a similar fashion and thus
only one preparation is detailed. B(C6F5)3 (5.7 mg, 11 mmol)
was added to a solution of 9 (10 mg, 11 mmol) in C6D5Br at
-35 ◦C. The solution was transferred to Teflon sealed J-Young
NMR tube. NMR data support the quantitative formation of the
cationic metal monoalkyl species paired with borate anions. (13):
1H (C6D5Br): 4.55-3.70 (m, 22H, a-H Cy and CpFeC5H4), 4.39
(br, 4H, H2,5–C5H4–Fe), 4.33 (br, 4H, H3,4–C5H4–Fe), 4.13 (s, 10H,
Cp–Fe), 2.05-0.60 (m, 43H, Cy and Zr–Me), 0.75 (s, 3H, B–Me).
19F (C6D5Br): -132.6 (br, 6F, o-C6F5), -162.2 (br, 3F, p-C6F5),
-165.3 (br, 6F, m-C6F5) (m,p-F) = 3.07. 11B (C6D5Br): -14.4. (14):.
1H (C6D5Br): 7.18-7.04 (m, 15H, Ph3CMe), 4.53-3.97 (m, 22H,
a-H Cy and CpFeC5H4), 4.42 (br, 4H, H2,5–C5H4Fe), 4.33 (br,
4H, H3,4–C5H4Fe), 4.12 (s, 10H, CpFe), 2.04 (s, 3H, Ph3CMe),
1.94-1.02 (m, 43H, Cy and Zr–Me), 0.85 (br, 3H, Zr-Me). 19F
X-ray data collection and reduction
Crystals were manipulated and suspended in Paratone inside a
glovebox, mounted on a MiTegen Micromount, and placed under
a N2 stream, thus maintaining a dry, O2-free environment for
8960 | Dalton Trans., 2010, 39, 8957–8966
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each crystal. The data for crystals were collected on a Bruker
Apex II diffractometer with Mo-Ka radiation (l = 0.71069 A).
The frames were integrated with the Bruker SAINT software
package using a narrow-frame algorithm. Data were corrected
for absorption effects using the empirical multi-scan method
(SADABS). Subsequent solution and refinement were performed
using the SHELXTL solution package.
attempts were made to make a Zr complex by transmetallation
were performed with CpZrCl3. While spectroscopic data sug-
gested the formation of the desired product, it could not be
obtained in a pure form. Similar problems were encountered
in efforts to prepare the Ti analog. In contrast the species
Cp*Zr[(CpFeC5H4)NC(Ph)NSiMe3]Cl2 (2) was readily prepared
˚
1
and isolated as an orange solid in 75% yield. The H NMR and
1
13C{ H} were as expected. A preliminary test of the polymerization
activity, employing 1 and 1000 equiv of MAO led only to traces
of polyethylene. It was speculated that this poor performance was
attributed to ligand degradation via Cp–C–H bond activation by
the transient cationic Zr complex. While such C–H activation
has been demonstrated recently for the reactions of zirconocene
cations and ferrocene,22 effort to probe this in the present system
were plagued by problems with scale up of the ligand synthesis.
Adopting an alternative synthetic strategy, N,N¢-dicyclohexyl
ferrocenyl-amidine and the corresponding lithium amidinate salt
were synthesized by a modified literature procedure.18 Subse-
quently bis(amidinate) complexes were successfully prepared by
treatment of M(NMe2)2Cl2 (M = Zr·2THF, Ti; Scheme 3) with
2.05 equivalents of 3 after refluxing in toluene. The species
[CyNC(CpFeC5H4)NCy]2ZrCl2 4 was isolated as an orange solid
in high yields (85%) by trituration of the resulting reaction mixture
with hexanes followed by subsequent washings with hexanes and
ether. Hexane washings are required to completely remove the
unreacted amidine, 3. The titanium analog 5 was isolated in 77%
yield as a purple solid using the same workup procedure as for 4.
Structure solution and refinement
Non-hydrogen atomic scattering factors were taken from the
literature tabulations.20 The heavy atom positions were determined
using direct methods employing the SHELXTL direct methods
routine. The remaining non-hydrogen atoms were located from
successive difference Fourier map calculations. The refinements
were carried out by using full-matrix least squares techniques on F,
minimizing the function w (Fo - Fc)2 where the weight w is defined
2
2
as 4Fo /2s(Fo ) and Fo and Fc are the observed and calculated
structure factor amplitudes, respectively. In the final cycles of each
refinement, all non-hydrogen atoms were assigned anisotropic
temperature factors in the absence of disorder or insufficient data.
In the latter cases atoms were treated isotropically. C–H atom
positions were calculated and allowed to ride on the carbon to
˚
which they are bonded assuming a C–H bond length of 0.95 A. H-
atom temperature factors were fixed at 1.10 times the isotropic
temperature factor of the C-atom to which they are bonded.
The H-atom contributions were calculated, but not refined. The
locations of the largest peaks in the final difference Fourier map
calculation as well as the magnitude of the residual electron
densities in each case were of no chemical significance. Additional
details are provided in the supplementary data.
Results and discussion
Incorporation of ferrocenyl-fragments into amidinate ligands
was achieved employing a synthetic strategy similar to that
used to prepared dissymmetric amidinates (Scheme 2).21 The
12
species CpFeC5H4NH2 was prepared and subsequently con-
verted to CpFeC5H4NH(SiMe3).13 Lithiation and reaction with
benzonitrile afforded (TMEDA)Li[(CpFeC5H4)NC(Ph)NSiMe3]
(1). Spectroscopic data for 1 were consistent with this formulation
and this reagent was used without further purification. Initial
Scheme 3 Synthesis of 4–12.
1
The H NMR spectra are consistent with the formation of 4
and 5 and assignments were assisted by DEPT135 and HSQC
experiments. Sharp resonances for the unsubstituted Cp ring
of the ferrocene for both bis(amidinate) complexes are similar
at ca. 4.29 ppm. The resonances for the substituted Cp rings
and the alpha-proton of the cyclohexyl ring are observed in
the 4.6-4.0 ppm region while broad resonances are observed in
2.5-1.0 ppm region for the cyclohexyl protons. In the case of
5 the C2 symmetry of the bis(amidinate) complexes results in
inequivalent nitrogen atoms as evidenced by two multiplets at
4.41 ppm and 3.99 ppm attributed to the alpha-protons of the
cyclohexyl rings. Similarly, two resonances were observed in the
13C NMR spectra at 61 ppm and 59 ppm corresponding to the
alpha-carbon atoms. In contrast, the NMR spectra of 4 shows
single resonances arsing from the corresponding protons and
Scheme 2 Synthesis of 1,2.
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Table 1 Crystallographic data
4
5(CH5l2)
7
8(0.5C6H16)
9
Formula
C46H62Cl2Fe2N4Zr
944.82
Monoclinic
P21/n
11.0872(3)
18.5813(7)
21.3216(6)
C47H64Cl4Fe2N4Ti
986.42
Monoclinic
P21/n
10.7232(5)
22.1321(11)
19.1676(9)
C28H36Cl2FeN2Zr
618.56
Monoclinic
P21/c
19.1426(13)
18.5720(14)
7.4148(5)
C72H106Cl4Fe2Zr2
1463.55
Orthorhombic
Pna21
19.7051(12)
14.5964(10)
24.6497(16)
C48H68Fe2N4Zr
903.98
Orthorhombic
Pca21
18.6543(10)
11.9951(6)
19.4642(10)
Formula wt
Cryst. syst.
Space group
˚
a/A
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
95.434(2)
93.048(2)
96.285(4)
3
˚
V/A
Z
4372.8(2)
4
4542.6(4)
4
2620.2(3)
4
7089.8(8)
4
4355.3(4)
4
T/K
150(2)
1.435
0.0685
1.048
40303
10062
496
0.0413
0.0951
1.006
150(2)
1.442
0.0720
1.075
75328
10329
523
0.0408
0.0912
1.008
150(2)
1.568
0.0408
1.175
62648
8715
150(2)
1.371
0.0434
0.880
113245
12881
769
0.0341
0.0786
1.008
150(2)
1.379
0.0916
0.930
36674
9775
d
(calc)/g cm-3
R(int)
m/cm-1
Total data
Data >3s(Fo
Variables
R (>3s)
Rw
2
)
307
498
0.0269
0.0690
1.021
0.0533
0.1099
0.981
GOF
˚ ˚
center. The M–Cl bond distances in 4 (2.4311(7) A, 2.4413(9) A)
carbons atoms. This infers facile interchange of the dissimilar
cyclohexyl groups in 4 at room temperature. Upon cooling a
CD2Cl2 solution of 4 to 230 K, the 1H NMR signals for the
alpha-proton broadened and the signals for the substituted Cp-
protons split presumably a result of restricted rotation of the
ferrocene moiety. This was also observed for 5. Further cooling
to 200 K did not afford a limiting spectrum and thus the
kinetic parameters for the interconversion were not determined.
Xue and coworkers have previously described similar behavior
for the bis(amidinate) complexes M(NMe2)2(CyNC(Me)NCy)2
(M = Zr; Ti),23 where the smaller titanium center is static, and
the larger Zr species fluxional at room temperature. Richeson
and coworkers proposed that bulky substituents on the central
carbon also inhibits the fluxionality.24,25 The mechanism of the
fluxional process for 4 could involve a dissociative pathway or
an intramolecular twist mechanism. The latter twist mechanism
involving a trigonal prismatic intermediate has been proposed
for related group 4 metal bis(amidinate) and bis(ketenimine)
complexes.23,26–28
˚
˚
are longer than those in 5 (2.3069(8) A, 2.3204(7) A). The Cl–M–
Cl angles in both complexes are similar (93.92(3)◦ for 4; 93.84(3)◦
for 5) and smaller than that in Cp2ZrCl2 (97.1◦),30 This angle
in 4 is similar compared to that see in [CyNC(Me)NCy]2ZrCl2
(93.1(1)◦) and significantly smaller than the corresponding angle in
[Me3SiNC(Ph)NSiMe3]2ZrCl2 (103.71◦).29,10h In this description,
two of the vertices are defined as the vectors that bisect the amidi-
nate ligand at the central carbons and the other two vertices as the
Zr–Cl vectors.31 Using the Richeson description of bis(amidinate)
complexes as pseudotetrahedral complexes,29 the C–M–C angles
is in 4 and 5 are 115.46◦ and 115.85◦, respectively, significantly
smaller than the Cp–Zr–Cp angle of 134◦ in Cp2ZrCl2.
The zirconium mono(amidinate) half sandwich complexes
LZr[CyNC(CpFeC5H4)NCy]Cl2 L = Cp 7, Cp* 8 were synthesized
by salt metathesis using Cp¢ZrCl3 (Cp¢ = Cp; Cp*) and 1 equiv
of 6. These products were isolated in 60% and 55% yields,
respectively (Scheme 3). It is noteworthy that initial attempts using
Na[CyNC(CpFeC5H4)NCy], were unsuccessful. The 1H NMR
spectra of 7 and 8 show the resonances for the unsubstituted
Cp ring of ferrocene at ca. 4.30 ppm, which is shifted downfield
from the protonated amidine, 6. Only one resonance for the alpha-
proton of the cyclohexyl ring is observed due to the CS symmetry
of the complex. Furthermore, this resonance appears as a triplet
of triplets due to difference in coupling between the neighbouring
axial and equatorial protons on the cyclohexyl ring.
The molecular structures of 4 and 5 (Fig. 1, Table 1) illustrate
the pseudo octahedral environment of the metal centers comprised
of four N- and two Cl- atoms. The bidentate amidinate ligands are
positioned cis to each other. In complex 5, the Ti–N bond distance
differ for the NCy groups cis and trans to Cl. The former Ti–N
˚
˚
bonds (2.041(2) A, 2.037(2) A) are shorter than those trans to Cl
˚
˚
(2.079(2) A, 2.103(2) A), consistent with the trans effect. However,
interestingly this trend is not evident for Zr–N bond distances
in 4. The amidinate bite angles in 5 (63.94(8)◦, 63.76(8)◦) are
larger than those in 4 (60.02(8)◦, 59.86(8)◦). This phenomenon
has been previously observed.29 Charge delocalization and partial
double bond character in the amidinate NCN backbone is evident
from the C–N bond distances in 4 and 5 which range from
1.323(3) A to 1.350(4) A. The average M–N–Calpha angle in 4
is 139.4◦ and is smaller than the corresponding average angle
in [CyNC(Me)NCy]2ZrCl2 (142.4◦), suggesting the bulk of the
ferrocenyl group pressures the Cy-groups closer to the metal
The molecular structure of 7 and 8 (Fig. 2) display the
expected pseudotetrahedral geometry about Zr. The amidinate
binding in 7 is asymmetric with Zr–N distances of 2.224(1)
˚
˚
A and 2.110(1) A. In contrast, the Zr–N bond distances in 8
˚
˚
are indistinguishable (2.215(3) A, (2.217(3) A). Nonetheless, the
amidinate bite angles in 7 (59.99(4)◦) and 8 (60.18(9)◦) are very
similar. The ferrocenyl-Cp plane is tilted relative to the amidinate
NCN plane by 52.09(15)◦ for 7 and 52.39(11)◦ for 8, indicating
no p conjugation. The species [CyNC(CpFeC5H4)NCy]2ZrMe2
(9) and Cp*Zr[CyNC(CpFeC5H4)NCy]Me2 (10) were prepared
˚
˚
8962 | Dalton Trans., 2010, 39, 8957–8966
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Fig. 1 ORTEP drawing of 4; 50% thermal ellipsoids are shown.
˚
Hydrogen atoms are omitted for clarity. Selected bond distances (A)
and bond angles (◦) for 4: Zr–Cl(1) 2.4311(7), Zr–Cl(2) 2.4413(9),
Zr–N(1) 2.189(2), Zr–N(2) 2.209(2), Zr–N(3) 2.186(2), Zr–N(4) 2.238(3),
N(1)–C(1) 1.339(4), N(2)–C(1) 1.338(3), C(1)–C(15) 1.487(4), N(3)–C(2)
1.350(4), N(4)–C(2) 1.328(3), C(2)–C(37) 1.477(4), N(1)–Zr–N(2) 60.02(8),
N(3)–Zr–N(4) 59.86(8), Cl(1)–Zr–Cl(2) 93.92(3), N(1)–C(1)–N(2)
110.51(24), N(3)–C(1)–N(4) 111.04(25), The structure of 5 is analogous:
Ti–Cl(1) 2.3069(8), Ti–Cl(2) 2.3204(7), Ti–N(1) 2.079(2), Ti–N(2) 2.041(2),
Ti–N(3) 2.037(2), Ti–N(4) 2.103(2), N(1)–C(1) 1.329(3), N(2)–C(1)
1.347(3), C(1)–C(15) 1.484(4), N(3)–C(2) 1.363(3), N(4)–C(2) 1.323(3),
C(2)–C(37) 1.475(4), N(1)–Ti–N(2) 63.94(8), N(3)–Ti–N(4) 63.76(8),
Cl(1)–Ti–Cl(2) 93.84(3), N(1)–C(1)–N(2) 109.25(22), N(3)–C(1)–N(4)
109.03(22).
Fig. 2 ORTEP drawings of 7 and 8; 50% thermal ellipsoids are shown.
Hydrogen atoms are omitted for clarity. Selected bond distances (A) and
˚
bond angles (◦) for 7: Zr–Cl(1) 2.4404(4), Zr–Cl(2) 2.4375(4), Zr–N(1)
2.224(1), Zr–N(2) 2.110(1), N(1)–C(6) 1.341(2), N(2)–C(6) 1.341(2),
C(6)–C(19) 1.487(2), N(1)–Zr–N(2) 59.99(4), Cl(1)–Zr–Cl(2) 90.65(2),
N(1)–C(1)–N(2) 111.07(12), 8. Zr–Cl(1) 2.4426(9), Zr–Cl(2) 2.4245(9),
Zr–N(1) 2.215(3), Zr–N(2) 2.217(3), N(1)–C(6) 1.334(4), N(2)–C(6)
1.343(4), C(6)–C(19) 1.485(4), N(1)–Zr–N(2) 60.18(9), Cl(1)–Zr–Cl(2)
89.80(3), N(1)–C(1)–N(2) 112.18(27).
in 75% and 71% isolated yields, respectively, by treatment of a
toluene solution of 4 with MeLi. The 1H and 13C NMR spectra of
9 and 10 show the Zr–Me resonances at 1.12 ppm and 45 ppm, and
-0.21 ppm and 47 ppm, respectively. The molecular structure of
9 (Fig. 3) is structurally similar to 4 with Zr–C bond distances of
˚
˚
2.269(6) A and 2.277(6) A. The corresponding C–Zr–C¢ bond
angle in 9 is 88.22(21)◦, significantly smaller than the Cl–Zr–
Cl¢ angle in 4 and also smaller than the corresponding angles
in [CyNC(Me)NCy]2ZrMe2 (92.4(3)◦) and Cp2ZrMe2 (95.6◦).29,32
Similarly the amidinate bite angle in 9 (58.49(16)◦, 58.45(17)◦) is
smaller than the bite angle in 4.
at room temperature in the presence of light in d8-toluene showed
the liberation of methane, ferrocene and protonated ligand. This
thermal instability of 11 is not surprising as Cp2TiMe2 exhibits
similar characteristics.
Attempts to methylate 7 led to an unexpected ligand redistribu-
tion affording Cp2ZrMe2 and 9. Such reactivity has been observed
previously for other half sandwich zirconium mono(amidinate)
complexes.10f,33 Attempts to alkylate 7 with a benzyl Grignard
reagent led to CpZr[CyNC(CpFeC5H4)NCy](CH2Ph)2 12 in low
yields (< 10%). However, 12 was readily synthesized and isolated
in 60% yield via alkylation with KCH2Ph. The difference in yields
with the alkylating agent has been observed before in the alkylation
Alkylation of 5 was initially attempted using MeLi, even at
-78 ◦C in the dark resulted black mixtures after a few minutes.
However, reaction of 5 with MeMgBr in toluene at -78 ◦C afforded
[CyNC(CpFeC5H4)NCy]2TiMe2 (11) albeit in low yields (32%).
Complex 11 proved to be difficult to purify as it was both thermally
unstable and light sensitive. Although the mechanistic details of
1
decomposition were not investigated, H NMR data after 1 day
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Fig.
4
Cyclic voltammogram of 4. (10-3 in CH2Cl2, 10-1
M M
[nBu4N][PF6], scan rates: 50 mV s-1 (grey) and 250 mV s-1 (black).
in 4, 7 and 8 is similar at ca. 430 mV, while the E1/2 for 5 is 88 mV
lower and Ep is broader by 134 mV in comparison to 4. These
complexes exhibit Fe oxidations at higher potentials compared
to the protonated amidine, 3 (quasi-reversible, E1/2 of 310 mV).19
This is consistent with the withdrawal of electron density from the
amidinate by complexation. Complex 9 and 12 shows similar E1/2
as their corresponding dichloride complexes, whereas, 10 shows
lower E1/2 by 100 mV compared to 8. The quasi-reversible nature
of the FeII oxidations results in a cathodic to anodic peak ratio
that is significantly lower in amidinate complexes compared to the
ferrocene standard. This loss of current in the return wave suggests
that the oxidized FeIII species undergo a subsequent chemical
reaction before reduction. The lack of stability of the ferrocenium
species may be due to an attack by Lewis basic substituents, solvent
or supporting electrolyte.35 although use of MeCN as the solvent or
[nBu4N][BF4] as the electrolyte had minimal impact on the nature
of the observed wave.
Abstraction of
a methyl group from 9 with B(C6F5)3
and [Ph3C][B(C6F5)]4 in C6D5Br proceeded cleanly to form
[{CyNC(CpFeC5H4)NCy}2ZrMe][MeB(C6F5)3] 13 and [{CyNC-
(CpFeC5H4)NCy}2ZrMe][B(C6F5)4] 14, respectively (Scheme 4).
The 1H NMR spectra of 13 and 14 show broad overlapping
resonances in the 4.0–4.5 ppm and 2.0-0.6 ppm region arising form
the Cp and cyclohexyl substituents, respectively. For 13, the 11B
NMR signal at -14.4 ppm and the difference in the resonances
from meta and para-fluorines36 in the 19F NMR spectrum is
-
consistent with the formation of MeB(C6F5)3 . In contrast,
Fig. 3 ORTEP drawings of 9, 50% thermal ellipsoids are shown.
˚
Hydrogen atoms are omitted for clarity. Selected bond distances (A) and
bond angles (◦) for 9: Zr–C(47) 2.269(6), Zr–C(48) 2.277(6), Zr–N(1)
2.246(5), Zr–N(2) 2.273(4), Zr–N(3) 2.262(5), Zr–N(4) 2.235(5), N(1)–C(1)
1.338(6), N(2)–C(1) 1.330(6), C(1)–C(15) 1.488(8), N(3)–C(2) 1.335(7),
N(4)–C(2) 1.322(7), C(2)–C(37) 1.492(8), N(1)–Zr–N(2) 58.49(16),
N(3)–Zr–N(4) 58.45(17), C(47)–Zr–C(48) 88.22(21), N(1)–C(1)–N(2)
111.66(49), N(3)–C(2)–N(4) 111.43(50).
of iron amidinates by Hessen and coworkers.34 It was postulated
that Mg2+ cations may facilitate ligand redistribution.
The cyclic voltammograms of (4–8) show a quasi-reversible
oxidation of FeII in dichloromethane solution using [nBu4N][PF6]
as the electrolyte. The voltammograms also show a second redox
couple at E1/2 ranging from -400 mV to -487 mV (Fig. 4). Complex
5 shows an irreversible reduction at -1574 mV corresponding to
the reduction of titanium from TiIV to TiIII as commonly observed
with other titanium complexes. The E1/2 of FeII/FeIII redox couple
Scheme 4 Synthesis of 13–18.
8964 | Dalton Trans., 2010, 39, 8957–8966
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attempts to characterize the analogous titanium complexes were
unsuccessful as the generation of a mixture of products was
evident. However, the analogous CpZr and Cp*Zr derivatives
LZr{CyNC(CpFeC5H4)NCy}CH2Ph] [PhCH2B(C6F5)3] L = Cp
15, Cp* 17 and [LZr{CyNC(CpFeC5H4)NCy}CH2Ph] [B(C6F5)4]
L = Cp 16, Cp* 18 were cleanly generated by methyl and benzyl
group abstraction as evidenced by NMR data. In the case of the
benzyl cationic species 15 and 17, the upfield resonance of the
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1
ortho-proton of the benzyl group at 6.49 ppm in the H NMR
2
spectrum, suggested an h bonding to Zr.37 Decomposition of 15
and 16 was observed in solution after 24 h but other ion pairs were
stable for few days.
Catalysts derived from the activation of the complex 4, 5, 7 and
8 with MAO showed low polymerization activity of 66, 27, 36 and
8 g (mmol h atm)-1, respectively. These activities are significantly
lower than the Cp2ZrCl2 standard (627 g (mmol h atm)-1. The trend
for the higher activity of the Zr derivative 4 in comparison to the
Ti species 5 has been observed for benzamidinate complexes.29,10h
Similarly, polymerizations were conducted using 10 mmol of the
respective precatalyst (9,10), one equivalent of either B(C6F5)3 or
i
[Ph3C][B(C6F5)4] and twenty equivalents of Bu3Al as a solvent
scrubber in 50 mL of toluene. Again, only moderate activities at
best were observed. It is noted that the catalysts generated from
9 and 10 showed activities of 45 and 43 g (mmol h atm)-1 upon
activation with B(C6F5)3 and 87 and 57 g (mmol h atm)-1 upon
activation with [Ph3C][B(C6F5)4]. The activities derived from 11
and 12 were very low even at elevated temperatures and could not
be measured reproducibly.
Conclusions
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Herein we have shown that ferrocenyl-(amidinate) complexes of
Ti and Zr are readily prepared. Bis-ligand dichloride complexes
as well as cyclopentadienyl derivatives are reported. Subsequent
alkylation and alkyl group abstraction affords neutral dialkyl-
and monoalkyl cationic derivatives. Electrochemical studies re-
vealed quasi reversible oxidation and reduction waves for the
ferrocene/ferrocenium couple. These complexes are also shown
to be precursors for ethylene polymerization catalysts that show
low activities. Building on these observations we are now targeting
new ferrocenyl-based ligands for the development of more active
catalysts. The results of these studies will be reported in due course.
16 B. Bildstein, M. Malaun, H. Kopacka, K. Wurst, M. Mitterbock, K.-
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Acknowledgements
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The financial support of SABIC is gratefully acknowledged. DWS
is also grateful for the award of a Canada Research Chair and a
Killam Research Fellowship.
71–147.
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©