Synthesis of the sterically constrained ligand precursor cyclopentadienyl-2,6-diphenylbenzene and structure of [(2,6-Ph 2-C6H3-η5-C5H 4)Zr(NEt2)3]

Article abstract of DOI:10.1016/S1387-7003(03)00222-3

A Pd-catalysed Stille coupling of 2,6-diphenyliodobenzene with tributylcyclopentadienyltin gave the sterically constrained ligand precursor cyclopentadienyl-2,6-diphenylbenzene (1). Treatment of this precursor with tetrakis(diethylamido)zirconium(IV) gave the three-legged piano-stool complex [(2,6-Ph₂-C₆H₃-η⁵-C ₅H₄)Zr(NEt₂)₃] (2). Complex 2 was characterised by ¹H- and ¹³C{¹H}-NMR spectroscopy as well as by X-ray crystallography which showed significant distortions of the three-legged piano-stool geometry as a result of steric interactions with the bulky aryl substituent.

Full text of DOI:10.1016/S1387-7003(03)00222-3

Inorganic Chemistry Communications 6 (2003) 1201–1204
www.elsevier.com/locate/inoche
Synthesis of the sterically constrained ligand precursor
cyclopentadienyl-2,6-diphenylbenzene and structure of
[(2,6-Ph2–C6H3-g5-C5H4)Zr(NEt2)3]
*
€
Owen J. Curnow , Glen M. Fern, Dominik Woll
Department of Chemistry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Received 28 April 2003; accepted 2 July 2003
Published online: 26 July 2003
Abstract
A Pd-catalysed Stille coupling of 2,6-diphenyliodobenzene with tributylcyclopentadienyltin gave the sterically constrained ligand
precursor cyclopentadienyl-2,6-diphenylbenzene (1). Treatment of this precursor with tetrakis(diethylamido)zirconium(IV) gave the
three-legged piano-stool complex [(2,6-Ph2–C6H3-g5-C5H4)Zr(NEt2)3] (2). Complex 2 was characterised by 1H- and 13C{1H}-NMR
spectroscopy as well as by X-ray crystallography which showed significant distortions of the three-legged piano-stool geometry as a
result of steric interactions with the bulky aryl substituent.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Crystal structures; Zirconium complexes; Cyclopentadienyl ligands; Stille couplings
1. Introduction
bulky aryliodide to give a new sterically constrained
cyclopentadiene ligand precursor. We also report a
tris(diethylamido)zirconium complex with this ligand
that illustrates its steric effects.
The synthesis of unusual cyclopentadienyl ligands is
of prime importance in homogeneous catalysis since
variation of electronic and steric properties can have a
significant effect on a complexÕs structure and reactivity
[1]. Catalytic cyclopentadienyl–arene coupling reactions
as a route to new cyclopentadienyl ligands have only
recently been investigated and those that have been de-
scribed are of sterically undemanding systems: Wahren
and co-workers [2] first reported stoichiometric cyclo-
pentadienyl–arene coupling reactions using cyclopenta-
dienylcopper and aryliodide reagents and Rosenblum
and co-workers [3] reported a low-yielding reaction of
NaCp with phenyliodide; in 1993, Katz, Brintzinger and
co-workers [4] described a catalysed indenyltin–arylio-
dide Stille coupling reaction using Pd(PPh3)2Cl2. There
have been a number of catalysed coupling reactions
described since then [5].
2. Experimental
2.1. Synthesis of cyclopentadienyl-2,6-diphenylbenzene ð1Þ
Iodo-2,6-diphenylbenzene [6] (4.84 g, 13.6 mmol) and
tributylcyclopentadienyltin [7] (5 ml, 8.5 g, 24 mmol)
were dissolved in THF (150 ml). Pd(PhCN)2Cl2 (47 mg,
0.123 mmol), copper(I) iodide (239 mg, 1.25 mmol) and
triphenylarsine (117 mg, 0.38 mmol) were then added
and the solution was heated to reflux for 72 h to give a
dark-brown solution. It was poured onto water and
twice extracted with petroleum ether. The orange or-
ganic layer was washed with water, dried over MgSO4,
filtered, and the solvent pumped off to give an orange
residue, which was redissolved in warm petroleum ether
(50 ml). A non-soluble brown precipitate could not be
redissolved. Flash chromatography on a silica column
with petroleum ether and crystallisation from the
In this communication, we describe the Pd-catalysed
Stille coupling of a cyclopentadienyltin reagent with a
* Corresponding author. Tel.: +64-3-364-2819; fax: +64-3-364-2110.
E-mail address: owen.curnow@canterbury.ac.nz (O.J. Curnow).
1387-7003/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S1387-7003(03)00222-3

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O.J. Curnow et al. / Inorganic Chemistry Communications 6 (2003) 1201–1204
concentrated and cooled solution gave light-orange
crystals of 1 (3.07 g, 77% yield based on the iodide). Two
isomers of 1 were obtained in a 7:3 ratio for 1a and 1b,
respectively. Anal. Calcd. for C23H18: C, 93.82; H, 6.18.
Found: C, 92.68; H, 6.10. m.p.: 114 °C. 1H NMR
(CDCl3): d 7.42–7.20 (m, 13H + 13H, Ph of 1a and 1b),
6.23 (m, 1H, CH2CH @ CH of 1a) 6.14 (m, 1H,
CH2CH @ CH of 1a), 6.11 (m, 1H, CH2CH @ CH of
1b), 5.95 (m, 1H, CH2CH @ CH of 1b), 5.89 (m, 1H,
CH2CH @ CH–CH of 1a), 5.71 (m, 1H, CHCH2CH @
CH of 1b), 2.73 (m, 2H, CH2 of 1b), 2.50 (m, 2H, CH2 of
1a). 13C NMR (CDCl3): for isomer 1a: d 134.40 (s, Cp),
132.65 (s, Cp), 132.11 (s, Cp), 129.33 (s, 2C, p-Ph),
129.30 (s, 4C, o- or m-Ph), 127.73 (s, 4C, o- or m-Ph),
126.74 (s, 1C, 4-arene), 126.38 (s, 2C, 3,5-arene), 44.78
(s, CH2). Unassigned quaternary resonances were ob-
served at 144.90, 142.65 and 141.96 ppm. For isomer 1b:
d 136.25 (s, Cp), 133.20 (s, Cp), 131.49 (s, Cp), 129.60 (s,
4C, o- or m-Ph), 129.30 (s, 2C, p-Ph), 127.54 (s, 4C, o- or
m-Ph), 126.97 (s, 1C, 4-arene), 126.34 (s, 2C, 3,5-arene),
41.49 (s, CH2). Ipso-Ph resonances were observed at
142.27 and 141.75 ppm. EI-MS: 294.1 (100%, Mþ),
293.1 (52.9%, [M–H]þ), 279 (33.4%), 278.1 (22.62%),
265.1 (33.8%), 252.1 (20.1%), 215.1 (17.0%), 133.1
(18.6%), 51.0 (64.2%).
163(2) K. The h range for data collection was from 2.19°
to 26.41°. The completeness to h was 97.5%. An absorp-
tion correction was applied with the maximum and min-
imum transmission factors of 1.000 and 0.824,
respectively. Crystal data for C35H47N3Zr: MW ¼ 600:98,
triclinic, space group P ꢂ 1; Z ¼ 2; a ¼ 9:568ð2Þ;
ꢀ
b ¼ 10:806ð2Þ; c ¼ 15:754ð4Þ A, a ¼ 92:707ð3Þ; b ¼
3
ꢀ
93:670ð3Þ; c ¼ 103:174ð3Þ°, V ¼ 1579:5ð6Þ A , l ¼ 0:375
mmꢂ1, dCalcd: ¼ 1:264 Mg mꢂ3. The structure was solved
by direct methods using SHELXS [9] and refined on F 2 by
full-matrix least-squares procedures with SHELXL-97
[10]. All non-hydrogen atomic positions were located in
difference Fourier maps and refined anisotropically. Hy-
drogen atoms were placed in calculated positions and
refined isotropically. The Rint is 0.0189 based on 6308
independent reflections (from 19,688 collected reflections)
and R1 is 0.0232 (wR2 ¼ 0:0620) for 5991 reflections with
I > 2rðIÞ. Goodness-of-fit on F 2 ¼ 1:063, residual elec-
ꢀꢂ3
tron density: 0.760 and )0.345 e A
.
3. Results and discussion
Iodo-2,6-diphenylbenzene reacts with a twofold ex-
cess of tributyl(cyclopentadienyl)tin in the presence of
Pd(PhCN)2Cl2, Ph3As, and CuI (in a 1:3:10 ratio with a
Pd loading of 9% with respect to the iodide) in THF
solvent under refluxing conditions for 3 days to give the
cyclopentadienyl–aryl coupled product cyclopentadie-
nyl-2,6-diphenylbenzene (1) in 77% yield after isolation.
1H-NMR spectroscopy indicates the presence of ring
isomers 1a and 1b in a 7:3 ratio. The more sterically
congested allylic isomer has not been observed.
2.2. Synthesis of ð2,6-Ph2–C6H3-g5-C5H4ÞZrðNEt2Þ3 (2)
Cyclopentadiene 1 (625 mg, 2.13 mmol) was dissolved
in toluene (20 ml) and Zr(NEt2)4 [8] (0.79 ml, 807 mg, 2.13
mmol) was added. The solution was then heated with
stirring at 100 °C for 18 h. Solvent was then removed in
vacuo and the residue dissolved in a minimum volume of
diethyl ether. Cooling to )20 °C for 2 d gave colourless
crystals of 2 (0.32 g, 25%). The air-sensitivity of the
compound prevented attempts to obtain a good micro-
analytical result (the best result is most consistent with the
hydrolysis product (C6H3Ph2C5H4)Zr(OH)3 ꢀ 0.5H2O:
Anal. Calcd. for C23H21O3:5Zr: C, 62.83; H, 4.76. Found:
1
C, 62.04; H, 5.05). H NMR (CDCl3): d 7.33–7.05 (m,
13H, Ph), 5.71 (pseudo-t, J ¼ 3 Hz, 2H, C5H4), 5.44
(pseudo-t, J ¼ 3 Hz, 2H, C5H4), 2.92 (q, J ¼ 6:8 Hz, 12H,
CH2), 0.74 (t, J ¼ 6:8 Hz, 18H, CH3). 13C NMR (CDCl3):
d 144.53 (s, ipso-Ph), 142.36 (s, ipso-Ph), 131.30 (s, 2C, Ph
or 3,5-arene), 129.62 (s, 4C, o- or m-Ph), 128.15 (s, 4C, o-
or m-Ph), 126.48 (s, 2C, 3,5-arene or Ph), 125.07 (s, 1C, 4-
arene), 114.23 (s, C5H4), 107.26 (s, C5H4), 43.95 (s, CH2),
14.41 (s, CH3). The ipso-Cp and 1-arene quaternary car-
bons were not unambiguously identified.
Treatment of 1 with Zr(NEt2)4 at 100 °C for 18 h in
toluene gave the air-sensitive pale-yellow three-legged
piano-stool complex 2. Observation of a classical
AA0BB0 pattern for the cyclopentadienide resonances at
5.71 and 5.44 ppm indicates the formation of a sym-
metric piano-stool complex. The ethyl and phenyl
groups are also equivalent on the NMR timescale
by both 1H- and 13C-NMR spectroscopy at ambient
temperature. A closely related ligand, cyclopentadie-
nylpentaphenylbenzene, is present in the ferrocene
(C6Ph5-g5-C5H4)(g5-C5H5)Fe, however, this ligand has
not been prepared independently of the ferrocene [11].
2.3. Crystal structure determination of complex 2
A pale yellow crystal (0.84 ꢁ 0.80 ꢁ 0.20 mm3) was
mounted on a glass capillary. Data collection was carried
out on a Bruker P4 SMART diffractometer with a CCD
ꢀ
detector with Mo Ka radiation (k ¼ 0:71073 A) at

O.J. Curnow et al. / Inorganic Chemistry Communications 6 (2003) 1201–1204
1203
Zr atom. Another effect of the close non-bonding phe-
nyl–Zr interaction is that two of the amido groups have
been pushed away from the idealised three-legged piano-
stool geometry: N(5)–Zr–N(4) is 117.69(5)° compared to
less than 100° for the other N–Zr–N angles.
All of the N atoms are trigonal planar with the planes
of N(4) and N(5) exhibiting a perpendicular arrangement
with respect to the C5 ring. This not only minimises the
steric interaction with the encroaching phenyl ring but
also maximises the pp–dp bonding between these amides
and an empty d orbital on the Zr atom [14,15]. The plane
of the other amide is oriented parallel to the C5 ring, which
allows p donation into a different and perpendicular
empty d orbital. Since N(4) and N(5) are sharing the same
d orbital in their pp–dp bonding interaction, it is not
surprising that the Zr–N(4) and Zr–N(5) distances
The structure of 2 was confirmed by X-ray crystallog-
raphy. Fig. 1 shows a perspective view of the complex as
determined by the crystallographic analysis.
It is clear that the bulky aryl substituent has had a
significant effect on the structure of 2. One of the phenyl
groups on the benzene ring is oriented towards the Zr
atom with a closest Zr–C non-bonded distance of
ꢀ
4.0055(15) A to C(22). This has slipped the Zr(NEt2)3
moiety away from the benzene ring as evidenced by an
angle slip w of 5.1° between the normal of the C5 plane
and the Zr–CNT (CNT, centroid of the five-membered
ring) vector; the slip distortion D (the distance of the
centroid from the normal of the C5 plane to the metal) is
ꢀ
(2.0888(13) and 2.0866(13) A, respectively) are longer
ꢀ
than the Zr–N(6) distance( 2.0689(13) A). They are also at
the long end for terminal amido–zirconium complexes in
which the distances generally lie in the range 2.00 to 2.085
ꢀ
0.202 A; and the Zr–C distances range from 2.4898(15)
ꢀ
A [13,15–17]. Interestingly, the three CNT–Zr–N angles
ꢀ
for C(14) to 2.6765(15) A for C(11). The angle slip and
are within only a few degrees of each other: 112.96, 113.38
and 114.77° for N(4), N(5) and N(6), respectively. The
angles for N(4) and N(5) are what would be expected for a
compromise between maximising pp–dp bonding and
minimising steric interactions with the C5H4 ring and
compare closely with 110.3° for the perpendicular amide
ligand in [(g5-C2B9H11)Zr(NMe2)2(NHEt2)] (3) [16]. The
angle for N(6), however, is smaller than might be ex-
pected; for example, the parallel amide in 3 has an angle of
123.5° [16]. This smaller angle for N(6) is probably a result
of steric interactions with the other diethylamido ligands
that have been pushed towards it.
slip distortion parameters are in the ranges typical of
indenyl ligands rather than cyclopentadienyl ligands
ꢀ
[12]. The Zr–CNT distance of 2.276 A is long for
a Zr(IV)–CNT (for a Cp or Cp* ligand) distance,
ꢀ
which are normally less than 2.24 A [13], suggesting
that the ring has also been pulled away slightly from the
It is noteworthy that the Zr–phenyl interaction is
non-bonding: since the three amido groups are acting as
three-electron donor ligands, the Zr atom is already
electronically saturated with 18 electrons and so cannot
accommodate additional electrons from the phenyl
group.
4. Conclusions
We have described the synthesis of a new sterically
constrained cyclopentadienyl ligand by a Pd-catalysed
cyclopentadienyl–aryliodide coupling reaction and a
complex with Zr, which displays significant distortions
as a result of the bulky aryl substituent. Further chem-
istry of this new ligand, especially with electron-deficient
metal centres, is being explored.
Fig. 1. Perspective view of complex 2 showing the atomic-labelling
scheme. The atoms are shown as 40% probability ellipsoids. Selected
ꢀ
bond distances (A), angles (°) and torsion angles (°): Zr(1)–N(6)
2.0689(13), Zr(1)–CNT 2.2759, Zr(1)–N(5) 2.0866(13), Zr(1)–N(4)
2.0888(13), Zr(1)–C(13) 2.5417(15), Zr(1)–C(14) 2.4898(15), Zr(1)–
C(12) 2.6385(15), Zr(1)–C(15) 2.5362(14), Zr(1)–C(11) 2.6765(15),
N(6)–Zr(1)–N(5) 96.70(5), CNT–Zr(1)–N(4) 112.96, N(6)–Zr(1)–N(4)
99.41(5), CNT–Zr(1)–N(5) 113.38, N(5)–Zr(1)–N(4) 117.69(5), CNT–
Zr(1)–N(6) 114.77, C(43)–N(4)–C(41) 110.69(12), C(2)–C(1)–C(11)–
C(12) )32.1(2), CNT–Zr(1)–N(4)–C(41) 0.1, CNT–Zr(1)–N(5)–C(53)
12.1, CNT–Zr(1)–N(6)–C(61) )89.0.
Acknowledgements
The New Zealand Lotteries Science Grants Board is
thanked for a grant to purchase precious metals.

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[9] G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467.
References
€
[10] G.M. Sheldrick, SHELXL-97, University of Gottingen, Germany,
1997.
[1] B. Cornils, W.A. Herrmann (Eds.), Applied Homogeneous
Catalysis with Organometallic Compounds: A Comprehensive
Handbook, Wiley–VCH, Weinheim, Germany, 2000.
[11] H.K. Gupta, S. Brydges, M.J. McGlinchey, Organometallics 18
(1999) 115;
A. Siegel, M.D. Rausch, Synth. React. Inorg. Met.-Org. Chem. 8
(1978) 209.
€
[2] M. Nilsson, R. Wahren, O. Wennerstrom, Tetrahedron Lett.
(1970) 4583;
[12] J.W. Faller, R.H. Crabtree, H. Habib, Organometallics 4 (1985)
929.
R. Wahren, J. Organomet. Chem. 57 (1973) 415.
[3] M.-T. Lee, B.M. Foxman, M. Rosenblum, Organometallics 4
(1985) 539.
[13] W.-P. Leung, F.-Q. Song, Z.-Y. Zhou, F. Xue, T.C.W. Mak,
J. Organomet. Chem. 575 (1999) 232;
[4] T.J. Katz, A.M. Gilbert, M.E. Huttenloch, G. Min-Min, H.-H.
Brintzinger, Tetrahedron Lett. 34 (1993) 3551.
[5] For examples of catalysed cyclopentadienyl–aryl coupling reac-
D.C. Carpenetti, L. Kloppenburg, J.T. Kupec, J.L. Petersen,
Organometallics 15 (1996) 1572;
Y. Bai, H.W. Roesky, M. Noltemeyer, M. Witt, Chem. Ber. 125
(1992) 825.
€
tions, see R. Boese, G. Braunlich, J.-P. Gotteland, J.-T. Hwang, C.
Troll, K.P.C. Vollhardt, Angew. Chem. Int. Ed. Engl. 35 (1996)
995;
[14] J.W. Lauher, R. Hoffmann, J. Am. Chem. Soc. 98 (1976)
1729;
R.L. Halterman, A. Tretyakov, M.A. Khan, J. Organomet. Chem.
41 (1998) 568;
A.M. Martins, J.R. Ascenso, C.G. de Azevedo, M.J. Calhorda,
A.R. Dias, S.S. Rodrigues, L. Toupet, P. de Leonardis, L.F.
Veiros, J. Chem. Soc., Dalton Trans. (2000) 4332.
[15] J.N. Christopher, G.M. Diamond, R.F. Jordan, J.L. Petersen,
Organometallics 15 (1996) 4038.
M. Miura, S. Pivsa-Art, G. Dyker, J. Heiermann, T. Satoh,
M. Nomura, Chem. Commun. (1998) 1889;
R.W. Baker, B.J. Wallace, Chem. Commun. (1999) 1405;
G. Dyker, J. Heiermann, M. Miura, J.-I. Inoh, S. Pivsa-Art,
T. Satoh, M. Nomura, Chem. Eur. J. 6 (2000) 3426;
A.F. Littke, C. Dai, G.C. Fu, J. Am. Chem. Soc. 122 (2000)
4020.
[16] D.E. Bowen, R.F. Jordan, R.D. Rogers, Organometallics 14
(1995) 3630.
[17] K. Hagen, C.J. Holwill, D.A. Rice, J.D. Runnacles, Inorg. Chem.
27 (1988) 2032;
[6] A. Saednya, H. Hart, Synthesis (1996) 1455.
[7] H.P. Fritz, C.G. Kreiter, J. Organomet. Chem. 1 (1964) 323.
[8] D.C. Bradley, I.M. Thomas, J. Chem. Soc. 163 (1960) 3857.
Z. Ziniuk, I. Goldberg, M. Kol, J. Organomet. Chem. 545–546
(1997) 441.