First examples of a new family of redox-functionalised chelate complexes based on a 1,1′-ferrocenediyl-bridged di(amido) ligand

Article abstract of DOI:10.1002/1099-0682(200104)2001:4<913::AID-EJIC913>3.0.CO;2-Z

Treatment of Fe[(C₅H₄)NHPh]₂ (1H₂) with M(NMe₂)₄ (3a: M = Ti, 3b: M = Zr) in benzene afforded the chelates (1)Ti(NMe₂)₂ (4) and (1)Zr(NMe₂)₂(HNMe₂) (5), respectively. Chelate 5 was cleanly oxidised by ferrocenium hexafluorophosphate in acetonitrile. Treatment of 5 with two equivalents of [Me₂NH₂]Cl (6) in benzene afforded (1)ZrCl₂(HNMe₂) (7). The chelates 5 and 7 were characterised by X-ray structure analyses. The new redox-active chelate complexes are precatalysts for the polymerisation of ethylene.

Full text of DOI:10.1002/1099-0682(200104)2001:4<913::AID-EJIC913>3.0.CO;2-Z

SHORT COMMUNICATION
First Examples of a New Family of Redox-Functionalised Chelate Complexes
Based on a 1,1Ј-Ferrocenediyl-Bridged Di(amido) Ligand
Ulrich Siemeling,*[a] Oliver Kuhnert,[b] Beate Neumann,[b] Anja Stammler,[b]
Hans-Georg Stammler,[b] Benno Bildstein,[c] Michael Malaun,[c] and Piero Zanello[d]
Keywords: Amides / Sandwich compounds / Polymerisation / Titanium / Zirconium
Treatment of Fe[(C5H4)NHPh]2 (1H2) with M(NMe2)4 (3a:
M = Ti, 3b: M = Zr) in benzene afforded the chelates
(1)Ti(NMe2)2 (4) and (1)Zr(NMe2)2(HNMe2) (5), respectively.
lents
of
[Me2NH2]Cl
(6)
in
benzene
afforded
(1)ZrCl2(HNMe2) (7). The chelates 5 and 7 were charac-
terised by X-ray structure analyses. The new redox-active
Chelate 5 was cleanly oxidised by ferrocenium hexafluoro- chelate complexes are precatalysts for the polymerisation of
phosphate in acetonitrile. Treatment of 5 with two equiva- ethylene.
The search for new generation nonmetallocene catalysts
for the polymerisation of α-olefins is of continuing inter-
est.[1] Complexes of the Group 4 metals containing chelat-
ing di(amido) ligands represent a very promising class of
(pre-)catalysts in this context. This has been demonstrated
in recent years by the groups of Bochmann,[2] Eisen,[3] Gib-
son,[4] McConville,[5] Schrock,[6] and others,[7] building on
earlier work by Bürger et al.[8] Ziegler and co-workers, using
quantum-chemical methods, have rationalised the factors
governing the ethylene polymerisation activity of such cata-
lysts.[9]
[13]
Metathesis of 1H2
with one equivalent of Ti(NMe2)4
We decided to utilise the novel 1,1Ј-ferrocenediyl-bridged
ligand system Fe[(C5H4)NPh]2 (1) in this context. This li-
gand is related to 2, recently reported by Kempe and co-
workers.[10] They found that, because of the high flexibility
of 2, complexes of the type 2TiXY (X ϭ Y ϭ NMe2; X ϭ
NMe2, Y ϭ Cl) are unstable. Not surprisingly, therefore,
catalytically active complexes of 2 are unknown. In con-
trast, 1 would be expected to provide a fairly rigid ligand
framework and should furthermore exhibit excellent π-
donor qualities (beneficial for olefin insertion),[9] since the
amido nitrogen atoms are directly connected to the elec-
tron-rich ferrocene moiety.[11]
We note that the electronic properties of our redox-active
ligand system can be changed quite dramatically by oxida-
tion. In fact, the development of redox-active ligands which
allow the electrochemical control of stoichiometric and
catalytic reactivities of transition metal centres is of great
current interest.[12]
(3a) afforded (1)Ti(NMe2)2 (4). Analogously, treatment of
1H2 with Zr(NMe2)4 (3b) gave (1)Zr(NMe2)2(HNMe2) (5),
and treatment of this with two equivalents of [Me2NH2]Cl
(6) furnished (1)ZrCl2(HNMe2) (7) (Scheme 1). Di(amido)-
zirconium(IV) complexes may be viewed as relatives of zir-
conocene derivatives[4] and hence ours are akin to the ferro-
cenediyl-bridged zirconocene dichloride {Fe[(C5H4)-
C5Me4]2}ZrCl2 reported by Brintzinger and co-workers.[14]
Cyclic voltammetric studies have shown that the ligand
precursor 1H2 undergoes a chemically reversible, one-elec-
tron oxidation at E°Ј ϭ Ϫ0.06 V (vs. SCE) in dichlorome-
thane solution. Such an easy oxidation matches well the
corresponding process exhibited by the related species
Fe[(C5H4)NMe2]2 and Fe[(C5H4)NPh2]2.[15,16] Com-
plexation of the metal-ligand fragment causes the ferrocene-
diyl-centred oxidation of the zirconaferrocenophane
(1)Zr(NMe2)2(HNMe2) (5) to become slightly more diffi-
cult, by about 40 mV (E°Ј ϭ Ϫ0.02 V), indicating that the
Zr(NMe2)2(HNMe2) fragment withdraws electron density
from the ferrocene subunit. Chemical oxidation of 5 was
cleanly achieved with one equivalent of ferrocenium hexa-
fluorophosphate in acetonitrile.
[a]
Fachbereich 18 (Physik) der Universität Gesamthochschule
Kassel,
Heinrich-Plett-Straße 40, 34132 Kassel, Germany
Fax: (internat.) ϩ49-561/804-4777
E-mail: siemeling@uni-kassel.de
[b]
Fakultät für Chemie der Universität Bielefeld,
Single crystal X-ray diffraction studies have been per-
formed for both new zirconium compounds. The zirconium
atom in 5 is coordinated by five nitrogen atoms in a dis-
torted trigonal bipyramidal arrangement (Figure 1). The
axial positions are occupied by the amino ligand and the
Universitätsstraße 25, 33615 Bielefeld, Germany
[c]
Institut für Allgemeine, Anorganische und Theoretische
Chemie der Universität Innsbruck,
Innrain 52a, 6020 Innsbruck, Austria
[d]
`
Dipartimento di Chimica, Universita di Siena,
Via Aldo Moro, 53100 Siena, Italy
Eur. J. Inorg. Chem. 2001, 913Ϫ916
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0404Ϫ0913 $ 17.50ϩ.50/0
913

U. Siemeling et al.
SHORT COMMUNICATION
Scheme 1. Synthesis of the chelate complexes 4, 5, 5[PF6], and 7
amido ligand trans to it, their ligating atoms forming an
angle of 171.4(3)° with the Zr atom. The N(1)ϪZr(1)ϪN(2)
bite angle of the chelating ligand 1 is 132.9(3)°. The amino
nitrogenϪzirconium distance is 243.8(8) pm — consistent
with a ZrϪN(sp3) single bond — while, thanks to their par-
tial
double-bond
character,
the
four
amido
nitrogenϪzirconium bonds are much shorter, ranging from
205.7(7) to 215.4(7) pm. These bond lengths are similar to
those found for the related compound [Ph2Si(N-
Ar)2]Zr(NMe2)2(HNMe2) (Ar ϭ 2,6-Me2C6H3).[4] The
cyclopentadienyl rings of the ferrocene unit are in an ec-
lipsed orientation. The parallel sandwich structure is
slightly distorted and opens up towards the zirconium
centre with a cyclopentadienyl ring tilt angle of 11.4°. The
FeϪZr distance of 333.9 pm precludes a significant bond-
ing interaction between the two metal atoms.
The core geometry of 7 is also best described as distorted
trigonal bipyramidal (Figure 2). Again, the amino ligand is
in an axial position, the second axial position being occu-
pied by a chloro ligand [N(3)ϪZr(1)ϪCl(1) 172.12(10)°]. In
related systems containing linked amido-cyclopentadienyl
ligands,[17] the amino ligand is positioned between the two
chloro ligands. The N(1)ϪZr(1)ϪN(2) bite angle is essen-
tially identical to that in 5, while the corresponding
zirconiumϪnitrogen bond lengths are slightly shorter, re-
sulting in a smaller cyclopentadienyl tilt angle of 9.4° and
a shorter FeϪZr distance of 331.0 pm. In both compounds,
Figure 1. Molecular structure of 5 in the crystal; selected bond
lengths (pm) and angles (°): Zr(1)ϪN(1) 212.8(7), Zr(1)ϪN(2)
215.3(7), Zr(1)ϪN(4) 215.4(7), Zr(1)ϪN(5) 205.7(7), N(1)ϪC(5)
142.3(11), N(1)ϪC(11) 139.5(10), N(2)ϪC(10) 141.3(10),
N(2)ϪC(22) 138.9(9); N(3)ϪZr(1)ϪN(5) 92.5(3), N(4)ϪZr(1)Ϫ
N(5) 96.0(3)
Preliminary investigations have shown that these new
all amido nitrogen atoms are trigonal planar and the phenyl compounds are precatalysts for the polymerisation of ethyl-
rings lie approximately in the plane defined by the zirco- ene.[18] The results of a detailed study, which also addresses
nium atom and the amido nitrogen atoms of the chelating the aspect of redox-tuning of catalyst activity, will be re-
ligand 1.
ported in due course.
914
Eur. J. Inorg. Chem. 2001, 913Ϫ916

Redox-Functionalised Chelate Complexes
SHORT COMMUNICATION
was reduced to dryness in vacuo, leaving the product as a brownish
yellow solid. Yield 0.90 g (76%). Ϫ 1H NMR (CDCl3): δ ϭ 3.24 (s,
12 H, NMe2), 3.63 (s, 4 H, C5H4), 4.54 (s, 4 H, C5H4), 6.71 (‘‘t’’,
apparent J ϭ 6.9 Hz, 2 H, Ph), 6.78 (‘‘d’’, apparent J ϭ 7.9 Hz, 4
H, Ph), 7.16 (‘‘t’’, apparent J ϭ 7.2 Hz, 4 H, Ph). Ϫ 13C{1H} NMR
(CDCl3): δ ϭ 45.1 (NMe2), 68.9, 71.0, 87.3 (C5H4), 115.4, 118.1,
128.9, 154.5 (Ph). Ϫ C26H30FeN4Ti (502.3): calcd. C 62.17, H 6.02,
N 11.15; found C 61.18, H 5.88, N 11.71.
Complex 5: Benzene (7 mL) was added to 1H2 (0.87 g, 2.35 mmol)
and 3b (0.60 g, 2.35 mmol), affording a light yellow precipitate. The
mixture was stirred for 1 h at room temperature. Crystallisation
from a minimal quantity of hot benzene afforded the product as
light yellow crystals. Yield 0.99 g (71%). Ϫ 1H NMR (CDCl3): δ ϭ
2.39 (br. s, 6 H, HNMe2), 3.05 (s, 12 H, NMe2), 3.70 (t, J ϭ 1.9 Hz,
4 H, C5H4), 4.62 (t, J ϭ 1.9 Hz, 4 H, C5H4), 6.66 (‘‘t’’, apparent
J ϭ 7.2 Hz, 2 H, Ph), 6.74 (‘‘d’’, apparent J ϭ 7.8 Hz, 4 H, Ph),
7.17 (‘‘t’’, apparent J ϭ 7.7 Hz, 4 H, Ph). Ϫ 13C{1H} NMR
(CDCl3): δ ϭ 39.1 (HNMe2), 43.2 (NMe2), 68.5, 70.5, 89.9 (C5H4),
115.3, 117.0, 129.1, 153.9 (Ph). Ϫ C28H37FeN5Zr (590.7): calcd. C
56.93, H 6.31, N 11.86; found C 56.69, H 6.11, N 11.20.
Figure 2. Molecular structure of 7 in the crystal; selected bond
lengths (pm) and angles (°): Zr(1)ϪN(1) 206.0(4), Zr(1)ϪN(2)
207.6(4),
Zr(1)ϪN(3)
238.3(4),
Zr(1)ϪCl(1)
245.95(16),
Zr(1)ϪCl(2) 241.76(14), N(1)ϪC(5) 141.6(6), N(1)ϪC(11) 141.4(6),
N(2)ϪC(10) 141.9(6), N(2)ϪC(17) 139.4(6); N(3)ϪZr(1)ϪCl(2)
81.56(10), Cl(1)ϪZr(1)ϪCl(2) 91.02(5)
Complex 5[PF6]: A solution of 5 (59 mg, 0.10 mmol) and ferrocen-
ium hexafluorophosphate (33 mg, 0.10 mmol) in acetonitrile
(5 mL) was stirred at room temperature for 5 h. The volatile com-
ponents (solvent and ferrocene) were then removed in vacuo, leav-
ing the product as
C28H37F6FeN5PZr (735.6): calcd. C 45.72, H 5.07, N 9.52; found
C 45.69, H 5.02, N 8.87.
a brown solid. Yield 73 mg (99%). Ϫ
Experimental Section
General: All manipulations were performed under an inert atmo-
sphere (purified argon or dinitrogen), using standard Schlenk and
cannula techniques or a conventional glovebox. Solvents and re-
agents were dried and purified by standard procedures. Ϫ NMR
spectra were recorded at 300 K with a Bruker DRX 500 spectro-
Complex 7: A solution of 5 (0.28 g, 0.47 mmol) and 6 (77 mg,
0.94 mmol) in benzene (10 mL) was stirred at room temperature
for 15 h. The resulting yellow precipitate was then filtered off. Crys-
tallisation from a minimal quantity of chloroform afforded the
product as yellow needles. Yield 59 mg (22%). Ϫ 13C{1H} NMR
(CDCl3): δ ϭ 39.1 (HNMe2), 43.2 (NMe2), 68.9, 71.0, 87.3 (C5H4),
115.4, 118.1, 128.9, 154.5 (Ph). Ϫ C24H25Cl2FeN3Zr·2CHCl3
(812.2): calcd. C 38.45, H 3.35, N 5.17; found C 39.04, H 3.23,
N 5.20.
1
meter operating at 500.13 MHz for H; TMS was used as external
reference. Ϫ The materials and apparatus used for the electrochem-
ical investigations have been described elsewhere.[19] Ϫ Elemental
analyses were performed by the Microanalytical Laboratory of
Universität Bielefeld.
Complex 4: A solution of 1H2 (0.87 g, 2.35 mmol) and 3a (0.53 g,
2.35 mmol) in benzene (1 mL) was kept at 70 °C for 2 h. The volat-
ile components were then removed in vacuo. The residue was ex-
tracted with n-hexane (20 mL) and the extract filtered. The filtrate
Crystal Structure Determinations of 5 and 7:[20] A yellow single crys-
tal of 5 (dimensions 0.5 ϫ 0.5 ϫ 0.25 mm) and 6 (dimensions 0.8
ϫ 0.4 ϫ 0.4 mm), respectively, was used for data collection at 173 K
on a Siemens P21 four-circle diffractometer with graphite-mono-
Table 1. X-ray structure analysis data of 5 and 7
Chem. formula
Mol. wt.
C28H37FeN5Zr
590.70
C24H25Cl2FeN3Zr·2 CHCl3
812.18
Space group
Monoclinic, P21/c
12.771(5)
12.605(5)
17.149(11)
98.03(4)
2734(2)
Orthorhombic, Pbcn
15.029(6)
˚
a [A]
˚
b [A]
17.751(6)
24.766(10)
˚
c [A]
β [°]
3
˚
V [A ]
6607(4)
8
1.633
1.424
3248
Z
4
ρ(calcd.) [g/cm3]
1.435
µ [mmϪ1
F(000)
]
0.937
1224
Index ranges
0 Յ h Յ 15, 0 Յ k Յ 14, Ϫ20 Յ l Յ 20
0 Յ h Յ 20, 0 Յ k Յ 23, 0 Յ l Յ 33
θ range [°]
1.6Ϫ25.0
5046
1.6Ϫ28.5
8388
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R1[a] [I Ͼ 2σ(I)]/wR2[b]
4814 [R(int.) ϭ 0.0701]
4814/0/322
1.052
8388
8388/0/360
1.013
0.0814/0.1911
1.041/Ϫ0.901
0.0609/0.1348
1.041/Ϫ1.182
3
˚
Larg. diff. peak/hole [e/A ]
[a]
[b]
2
2 2
2 2
R1 ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo|. Ϫ wR2 ϭ {Σ[w(Fo ϪFc ) ]/Σ[w(Fo ) ]}0.5
.
Eur. J. Inorg. Chem. 2001, 913Ϫ916
915

U. Siemeling et al.
SHORT COMMUNICATION
[8d]
˚
Wiegel, J. Organomet. Chem. 1977, 124, 279Ϫ292. Ϫ
D. J.
chromated Mo-Kα radiation (λ ϭ 0.71073 A). The structure was
Brauer, H. Bürger, K. Wiegel, J. Organomet. Chem. 1978, 150,
solved by direct methods. Programs used were Siemens SHELXTL
PLUS[21] and SHELXL-97.[22] Full-matrix, least-squares refine-
ment on F2 was carried out anisotropically for the non-hydrogen
atoms. Hydrogen atoms were included at calculated positions, using
a riding model. Further X-ray structure analysis data are given
in Table 1.
215Ϫ231. Ϫ [8e] H. Bürger, D. Beiersdorf, Z. Anorg. Allg. Chem.
[8f]
1979, 459, 111Ϫ118. Ϫ
H. Bürger, W. Geschwandtner, G.
R. Liewald, J. Organomet. Chem. 1983, 259, 145Ϫ156.
[9a] P. Margl, L. Deng, T. Ziegler, J. Am. Chem. Soc. 1998, 120,
[9]
[9b]
5517Ϫ5525. Ϫ
P. Margl, L. Deng, T. Ziegler, Organometal-
lics 1998, 17, 933Ϫ946.
[10]
[11]
[12]
A. Spannenberg, P. Arndt, M. Oberthur, R. Kempe, Z. Anorg.
Allg. Chem. 1997, 623, 389Ϫ393.
See, for example: H. Plenio, D. Burth, Organometallics 1996,
15, 4054Ϫ4062.
Acknowledgments
This work was generously supported by the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie. P. Z. grate-
fully acknowledges financial support by the University of Siena
(PAR 1999). Jens Vor der Brüggen and Giuliana Opromolla are
thanked for electrochemical measurements.
Review: A. M. Allgeier, C. A. Mirkin, Angew. Chem. 1998, 110,
936Ϫ952; Angew. Chem. Int. Ed. 1998, 37, 894Ϫ908.
B. Bildstein, M. Malaun, unpublished results.
P. Scott, U. Rief, J. Diebold, H. H. Brintzinger, Organometallics
1993, 12, 3094Ϫ3101.
[13]
[14]
[15]
[16]
[17]
K.-P. Stahl, G. Boche, W. Massa, J. Organomet. Chem. 1984,
277, 113Ϫ125.
[1]
Review: G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew.
W. E. Britton, R. Kashyap, M. El-Hashash, M. El-Kady, M.
Herberhold, Organometallics 1986, 5, 1029Ϫ1031.
See, for example: [17a]D. W. Carpenetti, L. Kloppenburg, J. T.
Kupec, J. L. Petersen, Organometallics 1996, 15, 1572Ϫ1581. Ϫ
[17b] A. K. Hughes, A. Meetsma, J. H. Teuben, Organometallics
1993, 12, 1936Ϫ1945.
Chem. 1999, 111, 448Ϫ468; Angew. Chem. Int. Ed. 1999, 38,
428Ϫ447.
[2]
N. A. H. Male, M. Thornton Pett, M. Bochmann, J. Chem.
Soc., Dalton Trans. 1997, 2487Ϫ2491.
[3]
H. Mack, M. S. Eisen, J. Organomet. Chem. 1996, 525, 81Ϫ87.
[18]
[19]
[20]
[4]
U. Siemeling, O. Kuhnert, M. O. Kristen, G. Hauck, unpub-
V. C. Gibson, B. S. Kimberley, A. J. P. White, D. J. Williams,
lished results.
P. Howard, Chem. Commun. 1998, 313Ϫ314.
[5]
A. Togni, M. Hobi, G. Rihs, G. Rist, A. Albinati, P. Zanello,
D. Zech, H. Keller, Organometallics 1994, 13, 1224Ϫ1234.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC-149674 (for 5) and CCDC-149675
(for 7). Copies of the data can be obtained free of charge
on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK [Fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
See, for example: J. D. Scollard, D. H. McConville, N. C.
Payne, J. J. Vidal, Macromolecules 1996, 29, 5241Ϫ5243.
[6]
See, for example: T. H. Warren, R. R. Schrock, W. M. Davis,
Organometallics 1998, 17, 308Ϫ321.
[7]
[7a]
See, for example:
Z. Ziniuk, I. Goldberg, M. Kol, Inorg.
[7b]
Chem. Commun. 1999, 2, 549Ϫ551. Ϫ
Y.-M. Jeon, S. J.
Park, J. Heo, K. Kim, Organometallics 1998, 17, 3161Ϫ3163.
Ϫ
[7c] F. Jäger, H. W. Roesky, H. Dorn, S. Shah, M. Noltemeyer,
[7d]
H.-G. Schmidt, Chem. Ber./Recl. 1997, 130, 399Ϫ403. Ϫ
S.
Tinkler, R. J. Deeth, D. J. Duncalf, A. McCamley, Chem. Com-
[21]
[22]
[7e]
G. M. Sheldrick, SHELXTL PLUS, Siemens Analytical Instru-
mun. 1996, 2623Ϫ2624. Ϫ
A. D. Horton, J. de With, A. J.
ments, Madison, WI, USA, 1990.
van der Linden, H. van de Weg, Organometallics 1996, 15,
2672Ϫ2674.
See, for example:
G. M. Sheldrick, SHELXL-97, University of Göttingen, Ger-
many, 1997.
[8]
[8a]
H. Bürger, K. Wiegel, Z. Anorg. Allg.
[8b]
Chem. 1976, 419, 157Ϫ162. Ϫ
Anorg. Allg. Chem. 1976, 426, 301Ϫ308. Ϫ
H. Bürger, K. Wiegel, Z.
Received September 25, 2000
[8c]
H. Bürger, K.
[I00366]
916
Eur. J. Inorg. Chem. 2001, 913Ϫ916