Cyclopentadienyl titanium chlorides containing ortho-(1-naphthyl)phenoxide ligation

Article abstract of DOI:10.1039/a805034a

A series of mono-cyclopentadiene derivatives of titanium containing ortho-(1-naphthyl)phenoxide ligands have been studied; the Ti-Ti distance in the d¹-d¹ species [Cp(ArO)Ti(μ-Cl)₂Ti(OAr)Cp] is exactly intermediate between

Full text of DOI:10.1039/a805034a

Cyclopentadienyl titanium chlorides containing ortho-(1-naphthyl)phenoxide
ligation
Jonathan S. Vilardo, Matthew G. Thorn, Phillip E. Fanwick and Ian P. Rothwell*
Department of Chemistry, 1393 Brown Building, Purdue University, West Lafayette, IN 47907-1393, USA.
E-mail. rothwell@chem.purdue.edu
Received (in Bloomington, IN, USA) 30th June 1998, Accepted 2nd September 1998
A series of mono-cyclopentadiene derivatives of titanium
containing ortho-(1-naphthyl)phenoxide ligands have been
studied; the Ti–Ti distance in the d1–d1 species [Cp(Ar-
O)Ti(m-Cl)2Ti(OAr)Cp] is exactly intermediate between that
found in paramagnetic [Cp2Ti(m-Cl)2TiCp2] and diamag-
netic [(ArO)2Ti(m-Cl)2Ti(OAr)2].
oxide ligands. Straightforward synthetic strategies lead to the
non-symmetric 6 and symmetric 7 and 8 (Scheme 1, Np = 1-
naphthyl).† Both 7 and 8 are produced as a 50/50 mixture of
non-chiral meso and dl forms. In the case of 7 inter-conversion
of the two forms occurs on the NMR timescale with the barrier
for naphthyl rotation estimated as 18.0(5) kcal mol21 at 67 °C.
Presumably a similar barrier will be present for other o-
(1-naphthyl)phenols lacking meta substituents. In the case of
meta-phenyl blocked 8 it is possible to isolate the pure,
crystalline meso form from CH2Cl2–heptane and show that
inter-conversion in this case requires days at 100 °C.5 In
contrast an adaptation of the chemistry of the late Sir Derek
Barton6 leads to 9 (Scheme 1) which is produced as a single
isomer whose subsequent chemistry (below) shows it to be the
chiral form.
Ortho-phenyl phenoxide ligands, e.g. 1 (Scheme 1) and 2, are an
important subset of aryloxide ligation that have been used to
support inorganic/organometallic chemistry at p-block,1 d-
block2 and f-element3 metal centers. Following our successful
development of cyclometalation resistant, e.g. 3 and 4, and
immune, 5 (Scheme 1) aryloxide ligation4 we have begun to
study the chemistry of potentially chiral o-(1-naphthyl)phen-
Reaction of phenols 1, 4–6 and 9 in the presence of pyridine
(py) or the lithium salt of 5 with [CpTiCl3] yields the
compounds 10–12 as orange solids in high yield (Scheme 2).
The solid state structure of 12b (Fig. 1)‡ confirms the chiral
nature of the single isomer of phenol 9 generated by the
particular method of synthesis. The solution NMR spectro-
scopic properties of 10–12 are as expected with single C5H5
resonances and a single set of aryloxide signals in each cause.†
1
In the H NMR spectrum of 12b the C5H5 protons resonate at
significantly higher field, d 5.32 compared to the d 5.6–5.8
region found for the other derivatives. This indicates much
greater diamagnetic shielding of adjacent ligand protons and is
caused by the presence of the two ortho-(1-naphthyl) rings,
which are locked in place by the meta-tert-butyl groups.
Treatment of 10b with sodium amalgam (1 Na per Ti) leads
to a red solution of the dimeric species 13 (Scheme 2). The solid
state structure of 13 (Fig. 2)‡ shows a dinuclear compound with
a Ti(m-Cl)2Ti core and terminal aryloxide and Cp groups. The
Scheme 1
Scheme 2
Chem. Commun., 1998, 2425–2426
2425

Table 1 Structural parameters for [(X)(Y)TiCl2] and [(X)(Y)Ti(m-Cl)2Ti(X)(Y)]; X, Y = Cp or ArO (Np = 1-naphthyl)
Compound
X–Ti–Y/°
Cl–Ti–Cl/°
Ti–Cl/Å
Ti–Ti/Å
Ref.
Cp2TiCl2
131
118
109
133
125
144
94
102
113
79
115
102
2.36 (av.)
2.23 (av.)
2.206(1)
2.55 (av.)
2.40 (av.)
2.37 (av.)
—
—
—
3.95 (av.)
3.336(1)
2.9827(7)
7
CpTi(OC6HNp2-2,6-But2-3,5)2Cl2 12b
Ti(OC6H3Ph2-2,6)2Cl2
This work
8
9
This work
10
[Cp2Ti(m-Cl)]2
[CpTi(OC6H2Np-2-But2-4,6)(m-Cl)]2 13
[Ti(OC6H3Ph2-2,6)2(m-Cl)]2
We thank the National Science Foundation (Grant CHE-
9321906) for financial support of this research.
Notes and references
† Selected spectroscopic data: aromatic signals unless indicated: 1H NMR
(C6D6, unless otherwise stated, 30 °C): 6: (CDCl3) d 7.00–7.90; 4.82 (s,
OH); 1.44 (s), 1.32 [s, C(CH3)3]. 7: (CDCl3) d 6.80–8.20; 4.78 (s), 4.74 (s,
OH). 8: (CDCl3) d 7.00–8.10; 4.95 (s), 4.93 (s, OH). 9: d 7.9–7.23 (m); 4.15
(s, OH); 1.18 [s, C(CH3)3]. 10a: d 7.22–8.20; 5.60 (s, C5H5); 1.67 (s), 1.25
[s, C(CH3)3]. 10b: d 7.20–7.60; 5.70 (s, C5H5); 1.63 (s), 1.27 [s, C(CH3)3].
11: d 7.19–7.36; 6.79 (s, para-H); 5.78 (s, C5H5); 2.03 (s, meta-CH3). 12a:
d 7.72 (s, para-H); 7.30–7.16 (m); 5.91 (s, C5H5); 1.23 [s, C(CH3)3]. 12b:
d 7.87 (s, para-H); 7.71–7.13 (m); 5.32 (s, C5H5); 1.10 [s, C(CH3)3]. 13C
NMR (C6D6, unless otherwise stated, 30 °C): 6: (CDCl3) d 149.3 (O–C);
123.8–141.8; 35.1, 34.4 [C(CH3)3]; 31.7, 29.7 [C(CH3)3]. 7: (CDCl3) d
150.7, 150.6 (CO); 135.1, 135.0, 133.8, 131.95, 131.88, 127.0, 126.93;
131.3, 129.3, 128.4, 128.3, 128.0, 127.8, 126.3, 126.2, 126.0, 125.9, 125.6,
120.3, 120.2. 8: (CDCl3) d 151.43, 151.38 (CO); 124.0–141.0. 9: d 151.7
(O–C); 148.5, 136.2, 133.5, 129.5, 128.1, 128.0, 126.6, 126.1, 125.9, 125.3,
122.8, 118.0, 109.5; 37.2 [C(CH3)3]; 32.4 [C(CH3)3]. 10a: d 165.0 (Ti–O–
C); 120.6 (C5H5); 36.0, 34.7 [C(CH3)3]; 31.5, 30.7 [C(CH3)3]. 10b: d 164.6
(Ti–O–C); 121.1 (C5H5); 35.9, 34.7 [C(CH3)3]; 31.5, 30.6 [C(CH3)3]. 11: d
164.3 (Ti–O–C); 120.2 (C5H5); 20.7 (meta-CH3). 12a: d 165.8 (O–C);
147.9, 138.5, 132.9, 131.1, 128.5, 127.8, 121.4; 119.8 (C5H5); 37.5
[C(CH3)3]; 33.0 [C(CH3)3]. 12b: d 166.2 (O–C); 149.1, 136.6, 135.5, 134.2,
130.4, 128.8, 128.7, 128.3, 127.3, 126.3, 126.1, 125.3, 122.4; 119.6 (C5H5);
37.9 [C(CH3)3]; 32.8 [C(CH3)3].
Fig. 1 Molecular structure of 12b showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Ti–O(10) 1.774(3), Ti–
Cl(1) 2.230(2), Ti–Cl(2) 2.244(2); Cl–Ti–Cl 102.36(7), Cp–Ti–O(10)
118.6(2), Ti–O(10)–C(11) 164.1(3).
‡ Crystal data: for 12b at 296 K: TiCl2OC39H38, M = 641.54, space group
P1 (no. 2), a = 10.960(1), b = 11.644(3), c = 15.603(1) Å, a = 71.003(7),
b = 104.23(3), g = 63.402(5)°, V = 1673.5(3) Å3, Dc = 1.273 g cm23
,
Z = 2. Of the 6851 unique reflections collected (7.69 @ 2q @ 62.74°) with
2
Mo-Ka (l = 0.71073 Å), the 6851 with Fo > 2s(Fo2) were used in the
final least-squares refinement to yield R(Fo) = 0.076 and Rw(Fo2) = 0.190.
For 13 at 296 K: Ti2Cl2O2C58H64, M = 959.86, space group P21/n (no. 14),
a = 12.5923(5), b = 12.7390(6), c = 17.4609(8) Å, b = 109.814(2)°,
V = 2635.1(4) Å3, Dc = 1.210 g cm23, Z = 2. Of the 6836 unique
reflections collected (5.90 @ 2q @ 61.46°) with Mo-Ka (l = 0.71073 Å),
Fig. 2 Molecular structure of 13 showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Ti–Ti 3.336(1), Ti–O(10)
1.817(2), Ti–Cl(1) 2.400(1), 2.406(1); Cl(1)–Ti–Cl(1) 92.07(4), Cp–Ti–
O(10) 125.1(3), Ti–O(10)–C(11) 166.7(2).
2
the 6836 with Fo > 2s(Fo2) were used in the final least-squares refinement
to yield R(Fo) = 0.074 and Rw(Fo2) = 0.169.
1 S. Saito and H. Yamamoto, Chem. Commun., 1997, 1585.
2 I. P. Rothwell, Chem. Commun., 1997, 1331; Acc. Chem. Res., 1988, 21,
153.
3 D. L. Clark, G. B. Deacon, T. Feng, R. V. Hollis, B. L. Scott,
B. W. Skelton, J. G. Watkin and A. H. White, Chem. Commun., 1996,
1729 and references therein.
Cp ligands are arranged in a transoid fashion, with a
crystallographic inversion center being present. The molecular
structure of 13 is such that each dimeric unit contains two
naphthylphenoxides of opposite chirality.
Table 1 collects some structural parameters for selected
derivatives of Ti(iv/iii), focusing on the effects of replacing Cp
ligands by OAr groups. Some trends can be discerned. The Ti–
Cl distance decreases significantly in both series of compounds
as Cp is replaced by OAr, reflecting an increase in electro-
philicity of the metal center. In the tetrahedral Ti(iv) series the
Cl–Ti–Cl angle opens up as the corresponding X–Ti–Y angle
closes down upon replacement of Cp by OAr.7,8 The most
interesting parameter is the Ti–Ti distances in the d1–d1
dimers.9,10 The 3.95(av.) distance in the Cp2Ti compounds is
consistent with the complete lack of any metal–metal bonding.
In contrast the short distance in the diamagnetic bis(aryloxide)
is consistent with the presence of a Ti–Ti single bond.10 In the
case of the ‘hybrid’ paramagnetic species 13, the Ti–Ti distance
is exactly intermediate between the previous two molecules. In
this case there is clearly no metal–metal bond present and the
observed Ti–Ti distance possibly is purely a consequence of the
Ti–Cl distances within the Ti(m-Cl)2Ti unit.
4 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.
5 For related ortho-(2-alkylphenyl)phenols see S. Saito, T. Kano,
K. Hatanaka and H. Yamamoto, J. Org. Chem., 1997, 62, 5651.
6 D. H. R. Barton, D. M. X. Donnelly, P. J. Guiry and J. H. Reibenspies,
J. Chem. Soc., Chem. Commun., 1990, 1110; D. H. R. Barton,
N. Y. Bhatnagar, J.-C. Blazejewski, B. Charpiot, J.-P. Finet, D. J. Lester,
W. B. Motherwell, M. T. B. Papoula and S. P. Stanforth, J. Chem. Soc.,
Perkin Trans. 1, 1985, 2657.
7 A. Clearfield, D. K. Warner, C. H. Saldarriaga-Molina and R. Ropal,
Can. J. Chem., 1975, 53, 1622.
8 J. R. Dilworth, J. Hanich, M. Krestel, J. Beck and J. Strahle,
J. Organomet. Chem., 1986, 315, C9.
9 R. Jungst, D. Sekutowski, J. Davis, M. Luly and G. Stucky, Inorg.
Chem., 1977, 7, 1645.
10 J. E. Hill, P. E. Fenwick and I. P. Rothwell, Polyhedron, 1990, 9,
1617.
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Chem Commun., 1998, 2425–2426