Coordination modes of 2-(indenyl)phenoxide ligation at early d-block metal centers

Article abstract of DOI:10.1039/a906443e

Three distinct bonding modes for the ligand 2-(indenyl)4,6-di-tert- butylphenoxide at early d-block metal centers have been identified.

Full text of DOI:10.1039/a906443e

Coordination modes of 2-(indenyl)phenoxide ligation at early d-block metal
centers
Matthew G. Thorn,a Phillip E. Fanwick,a Robert W. Chesnut*b and Ian P. Rothwell*a
a 1393 Brown Building, Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393, USA.
E-mail: rothwell@purdue.edu
b Department of Chemistry, Eastern Illinois University, 600 Lincoln Avenue, IL 61920, USA
Received (in Bloomington, IN, USA) 6th August 1999, Accepted 22nd October 1999
Three distinct bonding modes for the ligand 2-(indenyl)-
4,6-di-tert-butylphenoxide at early d-block metal centers
have been identified
The use of constrained geometry cyclopentadienyl ligation has
had a considerable impact on early transition metal chemistry in
recent years.1 As part of our work on novel ortho-substituted
aryloxide ligation2 we have synthesized the compound
2-(inden-3-yl)-4,6-di-tert-butylphenol 1 (Scheme 1).3 Unlike
previously reported ligands of this type, chelation of 1 to a metal
center via deprotonation will generate an inherently chiral
environment. Here we report on our initial forays into the
chemistry of this ligand, which demonstrate three distinct
bonding modes to transition metal centers.
Scheme 2
both the 1H and 13C NMR spectra at ambient temperatures but
appear as two well resolved resonances at lower temperatures.
Variable temperature NMR studies of 2 and 3 in toluene-d8
allow the barrier to inden-3-yl rotation (enantiomer inter-
conversion) to be estimated at 13.9(5) kcal mol21 (at 20 °C) and
13.4(5) kcal mol21 (at 25 °C), respectively. These barriers are
significantly lower than that measured for corresponding
2-(1-naphthyl)phenoxides.2c
Addition of 1 to the zirconium precursor [Zr(NMe2)4]4 leads
to the complex [Zr{(OC6H3But2-4,6-(h -Ind)}2] 4. In solution 4
5
is shown by NMR to exist as a mixture of two isomers (Scheme
3). Recrystallization from benzene–pentane generates crystals
of 4a shown (Fig. 2) to contain a crystallographic C2 axis of
symmetry. It can be seen that in the solid state both indenyl rings
Scheme 1
5
are h -bound to the same zirconium metal center, Zr–O–C angle
Compound 1 is obtained in gram quantities via the synthetic
route shown in Scheme 1. When 1 is added to the compound
[CpTiCl3] in the presence of excess pyridine the simple
aryloxide [Cp2Ti(OC6H2But2-4,6-Ind-2)Cl2] 2 is obtained.†
The solid state structure of 2 (Fig. 1) shows the ortho-inden-3-yl
group to be unbound with a Ti–O–C angle of 158.7(1)°.‡
Surprisingly, addition of LiMe to 2 produces the corresponding
dimethyl derivative 3 (Scheme 2) with no deprotonation of the
inden-3-yl ligand being observed. At ambient temperatures the
potentially diastereotopic methylene protons in the ortho-inden-
= 128.4(2)°. In CDCl3 solution 4a undergoes slow (days at
room temperature) conversion to a 50+50 mixture of 4a+4b. In
both 4a and 4b the aryloxide groups are equivalent (NMR)
ruling out their formulation as the two alternative isomers 4c
and 4d that contain no symmetry elements (Scheme 3).
Treatment of the compound [Ta(NMe2)5]5 with 1 initially
produces the substitution compound 5 (Scheme 4) with
elimination of one equivalent of HNMe2. Upon theromolysis
1
3-yl groups of both 1 and 2 appear as broad singlets in the H
NMR spectra owing to inden-3-yl rotation on the NMR
timescale. At lower temperatures these signals broaden and
resolve into the AB pattern expected for the static structure.
Similarly both Ti–Me groups in 3 appear as one broad singlet in
Fig. 1 Molecular structure of 2 showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Ti–O(1) 1.785(2), Ti–
Cl(1) 2.2581(8), Ti–Cl(2) 2.2554(8); Cl–Ti–Cl 100.24(4), Cp–Ti–O(1)
118.1(1), Ti–O(1)–C(11) 158.7(1).
Scheme 3
Chem. Commun., 1999, 2543–2544
This journal is © The Royal Society of Chemistry 1999
2543

Notes and references
† Spectral data obtained in C6D6 at 30 °C unless otherwise stated. 1H NMR:
1: (CDCl3) d 7.27–7.67 (aromatics); 6.78 (t, 3J 2.1 Hz, CH); 5.68 (s, OH);
3.69 (d, 3J 1.6 Hz, CH2); 1.57 (s), 1.44 [s, C(CH3)3]. 2: d 7.13–7.61
(aromatics); 6.61 (t, CH); 5.81 (s, C5H5); 3.36 (br, CH2); 1.61 (s), 1.28 [s,
C(CH3)3]. (C7D8, 230 °C): d 6.72–7.58 (aromatics); 6.60 (br, CH); 5.67 (s,
C5H5); 3.48 (d), 3.12 (d, 2J 23.8 Hz, CH2); 1.58 (s), 1.25 [s, C(CH3)3]. 3: d
4
7.57 (d), 7.33 (d, J 2.4 Hz, mC6H2); 7.04-7.55 (other aromatics); 6.29 (t,
CH); 5.59 (s, C5H5); 3.05 (d, CH2); 1.60 (s), 1.28 [s, C(CH3)3]; 0.64 (br,
TiMe). (C7D8, 245 °C): d 6.97–7.61 (aromatics); 6.31 (d, CH); 5.50 (s,
C5H5); 2.99 (AB, CH2); 1.64 (s), 1.30 [s, C(CH3)3]; 0.76 (s), 0.65 (s, TiMe).
5
4: d 6.79-7.40 (aromatics); 6.18 (d), 6.12 (d), 5.19 (d, h -C5H2); 1.36 (s),
1.29 (s), 1.29 (s), 1.24 [s, C(CH3)3]. (CDCl3): d 6.89–7.48 (aromatics); 6.89
5
(d), 6.75 (d), 6.62 (d), 5.42 (d, h -C5H2); 1.31 (s), 1.30 (s), 1.19 (s), 1.05 [s,
C(CH3)3]. 5: d 7.17–7.73 (aromatics); 6.60 (t, CH); 3.48 (br, CH2); 3.15 (s,
NMe2); 1.70 (s), 1.37 [s, C(CH3)3]. 6: d 7.58 (d), 7.51 (d), 7.28 (t), 7.05 (t,
C6H4); 7.43 (d), 6.76 (d, m-H); 7.10 (d), 6.62 (d, C5H2); 2.76 (br, NMe2);
1.74 (s), 1.15 [s, C(CH3)3]. (C7D8, 40 °C): d 7.56 (d), 7.49 (d), 7.25 (t), 7.05
(t, C6H4); 7.39 (d), 6.69 [d, 4J 1.7 Hz, m-H); 7.09 (d), 6.64 (d, C5H2); 2.87
(s, NMe2); 1.73 (s), 1.21 [s, C(CH3)3]. (C7D8, 230 °C): d 6.59-7.63
(aromatics); 2.98 (br), 2.43 (br), 1.92 (br, NMe2); 1.79 (s), 1.18 [s,
C(CH3)3]. (C7D8, 255 °C): d 6.57–7.64 (aromatics); 3.00 (s, 6H), 2.86 (s,
6H), 2.36 (s, 3H), 1.88(s, 3H, NMe2); 1.81 (s), 1.17 [s, C(CH3)3]. Selected
13C NMR, 1: (CDCl3): d 149.3 (OC); 144.4, 144.2, 141.7, 141.5, 135.3,
132.7, 126.5, 125.5, 124.1, 123.9, 123.8, 121.2, 120.9 (unsaturated C); 38.7
(CH2); 35.1, 34.3 [C(CH3)3); 31.7, 29.7 [C(CH3)3]. 2: d 165.5 (TiOC);
121.0 (C5H5); 38.7 (CH2); 35.9, 34.7 [C(CH3)3]; 31.5, 30.6 [C(CH3)3]. 3: d
161.7 (TiOC); 114.3 (C5H5); 57.7 (br, TiMe); 38.4 (CH2); 35.7, 34.5
[C(CH3)3]; 31.7, 30.5 [C(CH3)3]. (C7D8, 245 °C): d 161.6 (TiOC); 114.3
(C5H5); 58.8, 56.8 (TiMe); 38.3 (CH2); 35.8, 34.6 [C(CH3)3]; 31.7, 30.3
Fig. 2 Molecular structure of 4a showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Zr–O(1) 2.015(2), Zr–
C(23) 2.487(3), Zr–C(22) 2.500(3), Zr–C(21) 2.532(3), Zr–C(24) 2.568(3),
Zr–C(29) 2.640(3), O(1)–Zr-O(1) 97.6(1), Zr–O(1)–C(1) 128.4(2).
Scheme 4
5
[C(CH3)3]. 4: d 172.2, 171.5 (ZrOC); 115.5, 97.0, 96.9 (h -C5H2); 35.1,
34.5, 34.4 [C(CH3)3]; 31.9, 29.6 [C(CH3)3]. (CDCl3, 30 °C): d 171.5, 170.9
(100 °C) in C6D6, a further equivalent of HNMe2 is lost from 5
with formation of 6 (Scheme 4). The solid state structure of 6
5
(ZrOC); 115.2, 99.9, 96.6, 96.4 (h -C5H2); 34.7, 34.3, 34.2, 34.1 [C(CH3)3];
31.8, 31.8, 30.2, 29.2 [C(CH3)3]. 5: d 157.2 (TaOC); 47.1 (NMe2); 39.1
(CH2); 35.8, 34.5 [C(CH3)3]; 31.8, 30.3 [C(CH3)3]. 6: d 163.0 (TaOC);
103.4 (TaC); 44.5 (NMe2); 35.1, 34.5 [C(CH3)3]; 32.0, 30.4 [C(CH3)3].
‡ Crystallographic data: for 2 at 203 K: TiOCl2C31H35, M = 542.43, space
group P21/n (no. 14), a = 12.2422(4), b = 12.6093(4), c = 18.9505(6) Å,
b = 102.517(2)°, V = 2855.8(3) Å3, Dc = 1.262 g cm23, Z = 4. Of the
5004 unique reflections collected (8.00 @ 2q @ 60.94°) with Mo-Ka (l
1
(Fig. 3) shows the ligand to be chelated to the metal via an h -
indenyl interaction, Ta–O–C angle = 122.7(6)°. The metal is
attached to the ipso carbon atom yielding a five-membered
metallacycle ring. The coordination environment about the Ta
metal center in 6 is best described as tbp, with an axial oxygen
1
atom. In the ambient temperature H NMR spectrum of 6 a
2
= 0.71073 Å), the 4070 with Fo > 2 s(Fo2) were used in the final least-
single broad resonance is observed for the Ta–NMe2 protons. At
lower temperatures this signal splits out into four singlets in the
ratio of 2+2+1+1. We interpret the two larger signals as being
due to the two, non-equivalent equatorial Ta–NMe2 groups
undergoing rapid rotation. The remaining signals are due to the
unique axial Ta–NMe2 group that is undergoing restricted
rotation on the NMR timescale. Presumably the higher barrier to
squares refinement to yield R(Fo) = 0.045 and Rw(Fo2) = 0.111; for 4a at
203 K: ZrO2C52H58, M
= 806.26, space group C2/c (No. 15), a =
14.3043(4), b = 10.7900(5), c = 28.522(1) Å, b = 97.875(3)°, V =
4360.7(5) Å3, Dc = 1.228 g cm23, Z = 4. Of the 4399 unique reflections
collected (8.00 @ 2q @ 52.73°) with Mo-Ka (l = 0.71073 Å), 3651 with
2
Fo > 2 s(Fo2) were used in the final least-squares refinement to yield R(Fo)
= 0.055 and Rw(Fo2) = 0.132; for 5 at 203 K: TaON3C29H44, M = 631.64,
¯
1
space group P1 (no. 2), a = 9.6679(5), b = 12.1261(6), c = 13.9575(4) Å,
rotation of the axial group is due to the presence of the h -
a = 86.118(3), b = 72.704(3), g = 67.257(2)°, V = 1438.8(2) Å3, Dc
=
indenyl ring (Fig. 3).
1.458 g cm23, Z = 2. Of the 5428 unique reflections collected (8.00 @ 2q
We thank the National Science Foundation (Grant CHE-
9700269) for financial support of this research.
2
@ 52.75°) with Mo-Ka (l = 0.71073 Å), 5011 with Fo > 2s (Fo2) were
used in the final least-squares refinement to yield R(Fo) = 0.061 and
2
Rw(Fo
) = 0.153. Atom C(32) was refined isotropically. CCDC
182/1465.
1 G. J. P.Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed.,
1999, 38, 428 and references therein; M.Bochmann, J. Chem. Soc.,
Dalton Trans., 1996, 255; H.-H. Brintzinger, D. Fischer, R. Mülhaupt, B.
Rieger and R. M. Waymouth, Angew. Chem., Int. Ed. Engl., 1995, 34,
1143; P. C. Möhring and N. J. Coville, J. Organomet. Chem., 1994, 479,
1; W. Kaminsky, K. Kulper and H. H. Brintzinger, Angew. Chem., Int.
Ed. Engl., 1985, 24, 507.
2 (a) J. S. Vilardo, M. A. Lockwood, L. G. Hanson, J. R. Clark, B. C.
Parkin, P. E. Fanwick and I. P. Rothwell, J. Chem. Soc., Dalton Trans.,
1997, 3353; (b) J. S. Vilardo, M. G. Thorn, , P. E. Fanwick and I. P.
Rothwell, Chem. Commun., 1998, 2425; (c) M. G. Thorn, J. S. Vilardo,
P. E. Fanwick and I. P. Rothwell, Chem. Commun., 1998, 2427.
3 For related ligands, see: (a) Y.-X. Chen, P.-F. Fu, C. L. Stern and T. J.
Marks, Organometallics, 1997, 16, 5958; (b) K. Kawai, T. Kitahara and
T. Fujita, (Mitsui Petrochemical Ind, Japan), Jpn. Kokai Tokkyo Koho
JP08,325,283, 1996 (Chem. Abstr. 1996, 126, 172048h).
Fig. 3 Molecular structure of 6 showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Ta–N(2) 1.95(1), Ta–
N(3) 1.95(1), Ta–N(4) 2.005(8), Ta–C(121) 2.285(9), Ta–O(1) 2.025(7);
O(1)–Ta–N(4) 169.9(3), O(1)–Ta–N(2) 90.8(3), O(1)–Ta–N(3) 93.8(4),
O(1)–Ta–C(121) 75.4(3), N(2)–Ta–N(3) 117.6(5), N(2)–Ta–N(4) 92.8(4),
N(3)–Ta–N(4) 92.9(4), C(121)–Ta–N(2) 123.6(4), C(121)–Ta–N(3)
117.7(4), C(121)–Ta–N(4) 94.7(3), Ta–O(1)–C(11) 122.7(6).
4 G. M. Diamond, R. F. Jordan and J. L. Petersen, J. Am. Chem. Soc., 1996,
118, 8024.
5 P. N. Riley, J. R. Parker, P. E. Fanwick and I. P. Rothwell,
Organometallics, 1999, 18, 3579.
Communication 9/06443E
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Chem. Commun., 1999, 2543–2544