Formation and reactivity of cationic alkyl derivatives of titanium containing ortho-(1-naphthyl)phenoxide ligation

Article abstract of DOI:10.1039/a805476b

A series of dimethyl compounds of Ti(IV) have been isolated containing both cyclopentadiene and ortho-arylphenoxide ligation; reaction with [B(C₆F₅)₃] generates corresponding cationic methyl species which eliminate methane and form [Cp(ArO)Ti{CH₂B(C₆F₅)₂}(C₆F₅)] derivatives.

Full text of DOI:10.1039/a805476b

Formation and reactivity of cationic alkyl derivatives of titanium containing
ortho-(1-naphthyl)phenoxide ligation
Matthew G. Thorn, Jonathan S. Vilardo, 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) 14th July 1998, Accepted 2nd September 1998
1
A series of dimethyl compounds of Ti(IV) have been isolated
containing both cyclopentadiene and ortho-arylphenoxide
ligation; reaction with [B(C6F5)3] generates corresponding
cationic methyl species which eliminate methane and form
[Cp(ArO)Ti{CH2B(C6F5)2}(C6F5)] derivatives.
species are highly informative. Low temperature H and 13C
NMR spectra of 7a and 8 show a single set of Cp and OAr
resonances along with resolved Ti-Me (sharp) and Ti-Me-B
(broad) resonances. Spectra obtained for 7a at ambient
temperature show broadening of these methyl signals, but the
thermal instability precludes obtaining limiting high tem-
perature spectra. We interpret this broadening as due to
exchange of the boron between methyl groups (boron exchange)
which is becoming fast on the NMR time scale. For 7b, two
broad methyl signals and a single, sharp Cp resonance are
present at room temperature. At 210 °C (toluene-d8) the Ti-Me
and Ti-Me-B signals sharpen up, but there is still only a single
Cp resonance. At 230 °C the Cp resonance splits into two
signals in the ratio of 80 : 20 representing the two, diaster-
eoisomeric forms. The methyl signals also split into two large,
equal intensity signals and one resolvable smaller peak
(presumably the second methyl signal is obscured by OAr
resonances). We interpret these changes as representing two
distinct dynamic processes. The faster process involves ex-
change between the two diastereoisomers (80 : 20 ratio) of 7b
(Scheme 2) without methyl exchange. This process involves
cation–anion dissociation and rearrangement and can only be
detected using the chiral o-(1-naphthyl)phenoxide. An alter-
native process for exchange of diastereoisomers would involve
naphthyl rotation. However, the variable temperature NMR
studies on 4b and data presented below show that this process is
too slow to account for the observed process. The slower
process in 7b, which is also detected for 7a and 8, involves Ti-
Me/Ti-Me-B exchange. In the case of 7b this process alone
cannot lead to exchange of methyl signals in the NMR spectra.
However, when coupled with the faster ion-pair dissociation, it
leads to methyl exchange (Scheme 2). Previous work by Marks
et al. has shown similar dynamics are present in [CpA2Zr(Me)-
{MeB(C6F5)3}] species.8 Based upon the spectra obtained for
7b we estimate the free energy of activation for ion-pair
dissociation to be 12.4(5) kcal mol21 at 225 °C (Cp
There is continued research interest in the chemistry of cationic
Group 4 metal alkyl compounds.1 We have recently isolated a
series of titanium chloride compounds containing both cyclo-
pentadiene and o-arylphenoxide ligation.2,3 We report here on
the structure, dynamics and reactivity of the corresponding
neutral and cationic methyl derivatives.4,5
Treatment of 1–3 with LiMe leads to the corresponding
dimethyl compounds 4–6 as yellow solids (Scheme 1, Np =
1-naphthyl).† The solid state structure of 4b is shown in Fig. 1.‡
The Ti–Me distances of 2.076(4) and 2.091(4) Å are inter-
mediate between those reported for [Cp2TiMe2],6 2.170(2) and
2.181(2) Å, and values of 2.052(2) and 2.069(2) Å found in
[Ti(OC6H3Ph2-2,6)2Me2].7 There is also a corresponding
opening up of the Me–Ti–Me angle upon replacing Cp by OAr;
c.f. 91.3(1)° for [Cp2TiMe2], 97.5(2)° in 4b and 103.9(1)° in
[Ti(OC6H3Ph2-2,6)2Me2]. In the solution NMR spectra of 4a, 5
and 6a, only one signal is present for the Ti–Me groups in the 1H
and 13C NMR spectra. This indicates in the case of 4a that
rotation about the Ti–O–Ar bonds is fast on the NMR time-
scale. In contrast two well-resolved Ti–Me resonances are
observed for the o-(1-naphthyl) derivatives 4b and 6b. In the
case of 6b this is consistent with the presence of the chiral, dl-
form of the ligand. Variable temperature NMR studies of 4b
show that the two methyl signals remain sharp even at 90 °C
(toluene-d8), indicating slow naphthyl rotation on the NMR
timescale at this temperature.
Addition of [B(C6F5)3]8 to 4,5 in benzene or toluene solvent
leads to the rapid (NMR) formation of the thermally unstable
(vide infra) cationic 7,8. Variable temperature spectra of these
Fig. 1 Molecular structure of 4b showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Ti–O(10) 1.815(2), Ti–
C(6) 2.076(4), Ti–C(7) 2.091(4), C(6)–Ti–C(7) 97.5(2), Cp–Ti–O(10)
123.7(2), Ti–O(10)–C(11) 158.8(2).
Scheme 1
Chem. Commun., 1998, 2427–2428
2427

C5H5); 1.52 (s, Ti-CH3); 1.32 (s), 1.16 [s, C(CH3)3]; 0.94 (br, B-CH3). 7b:
d 7.05–7.68; 5.36 (s, C5H5); 1.32 (s), 1.19 [s, C(CH3)3]; 0.91 (br, Ti-CH3);
0.81 (br, B-CH3). (C7D8, 210 °C): d 6.97–7.68; 5.27 (s, C5H5); 1.31 (s),
1.15 [s, C(CH3)3]; 0.96 (br, Ti-CH3); 0.77 (br, B-CH3). 1H NMR (C7D8,
230 °C): d 6.96–7.67; 5.23 (s, C5H5-major); 5.14 (s, C5H5-minor); 1.31 (s),
1.21 [s, C(CH3)3]; 0.95 (br, Ti-CH3-major); 0.76 (br, B-CH3-major); 0.54
(br, B-CH3-minor). 8: d 6.80–7.32; 6.74 (s, para-H); 5.44 (s, C5H5); 1.90 (s,
meta-CH3); 0.68 (br, Ti-CH3); 0.53 (br, B-CH3). (C7D8, 220 °C): d
6.63–7.14; 5.39 (s, C5H5); 1.87 (s, meta-CH3); 0.67 (s, Ti-CH3); 0.46 (br, B-
CH3). 9a: d 7.56 (d), 7.13 [d, 4J(1H–1H) = 2.5 Hz, meta-H]; 6.10 (s, C5H5);
4.21 (br), 3.23 (br, Ti-CH2-B); 1.62 (s), 1.26 [s, C(CH3)3]. 9b: d 6.72–7.86;
6.24 (s), 5.80 (s, C5H5); 4.16 (br), 4.14 (br), 3.00 (m, Ti-CH2-B); 1.60 (s),
1.57 (s), 1.19 (s), 1.15 [s, C(CH3)3]. 10: d 6.85–7.18; 6.68 (s, para-H); 5.65
(s, C5H5); 3.56 (br), 2.67 (br, Ti-CH2-B); 1.84 (s, meta-CH3). 13C NMR
(C6D6, 30 °C) 4a: d 160.8 (Ti-O-C); 114.4 (C5H5); 58.4, (Ti-CH3); 35.8,
34.5 [C(CH3)3]; 31.7, 30.5 [C(CH3)3]. 4b: d 161.6 (Ti-O-C); 114.1 (C5H5);
58.4, 57.8 (Ti-CH3); 35.8, 34.6 [C(CH3)3]; 31.7, 30.6 [C(CH3)3]. 5: d 161.1
(Ti-O-C); 113.7 (C5H5); 56.1, (Ti-CH3); 20.8 (meta-CH3). 6a: d 163.0 (O-
C); 147.5, 140.8, 132.6, 130.9, 128.3, 126.9, 118.7; 113.5 (C5H5); 56.9
(CH3); 37.4, [C(CH3)3]; 33.1 [C(CH3)3]. 6b: d 163.6 (O-C); 152.0, 148.7,
138.9, 135.1, 134.0, 129.7, 126.0, 125.3, 119.9; 113.3 (C5H5); 56.5, 56.1
(CH3); 37.7, [C(CH3)3]; 32.0 [C(CH3)3]. 7a: d 163.0 (Ti-O-C); 120.4
(C5H5); 113.0 (br, B-CH3); 77.7 (br, Ti-CH3); 35.1, 34.4 [C(CH3)3]; 30.8,
29.7 [C(CH3)3]. (C7D8, 210 °C): d 163.2 (Ti-O-C); 120.7 (C5H5); 112.9
(br, B-CH3); 77.4 (s, Ti-CH3); 35.4, 34.7 [C(CH3)3]; 31.1, 30.0 [C(CH3)3].
7b: d 163.3 (Ti-O-C); 119.9 (C5H5); 113.1 (br, B-CH3); 79.4 (br, Ti-CH3);
35.1, 34.4 [C(CH3)3]; 30.9, 30.0 [C(CH3)3]. 8: d 162.5 (Ti-O-C); 119.3
(C5H5); 113.0 (br, B-CH3); 77.8 (Ti-CH3); 19.9 (meta-CH3). 9a: d 163.7
(Ti-O-C); 119.4 (C5H5); 107.1 (br, Ti-CH2-B); 35.8, 34.7 [C(CH3)3]; 31.4,
30.6 [C(CH3)3]. 9b: d 164.4, 164.3 (Ti-O-C); 119.2, 119.0 (C5H5); 107.0,
105.5 (br, Ti-CH2-B); 35.9, 35.8, 34.7, 34.7 [C(CH3)3]; 31.4, 31.4, 30.7,
30.6 [C(CH3)3]. 10: d 162.3 (Ti-O-C); 118.1 (C5H5); 114.2 (br, Ti-CH2-B);
20.1 (meta-CH3).
Scheme 2
‡ Crystal data for 4b at 296 K: TiOC31H38, M = 474.55, space group P21/c
(no. 14), a
= 13.1917(8), b = 11.7251(6), c = 18.788(1) Å, b =
107.115(2)°, V = 2777.4(5) Å3, Dc = 1.135 g cm23, Z = 4. Of the 6750
unique reflections collected (4.54 @ 2q @ 61.36°) with Mo-Ka (l =
0.71073 Å), the 6750 with Fo > 2s(Fo2) were used in the final least-
squares refinement to yield R(Fo) = 0.064 and Rw(Fo2) = 0.166. For 10 at
203 K: TiF15OC44BH24, M
2
¯
= 912.37, space group P1 (no. 2), a =
12.2084(5), b = 12.3668(2), c = 13.7876(5) Å, a = 71.440(2), b =
84.811(1), g = 83.982(2)°, V = 1958.9(2) Å3, Dc = 1.547 g cm23, Z = 2.
Of the 9835 unique reflections collected (8.00 @ 2q @ 61.10°) with Mo-Ka
Fig. 2 Molecular structure of 10 showing the atomic numbering scheme.
Selected interatomic distances (Å) and angles (°): Ti–O(10) 1.770(2), Ti–
C(20) 2.115(2), Ti–C(41) 2.176(2), Cp–Ti–O(10) 126.9(1), C(20)–Ti–
C(41) 98.73(8), Ti–O(10)–C(11) 176.2(1).
2
(l = 0.71073 Å), the 9835 with Fo > 2s(Fo2) were used in the final least-
squares refinement to yield R(Fo) = 0.052 and Rw(Fo2) = 0.126. CCDC
182/996.
coalescence temperature at 300 MHz) while that for the methyl
exchange is 15.0(5) kcal mol21 at 235 °C.
1 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 J. S. Vilardo, M. G. Thorn, P. E. Fanwick and I. P. Rothwell, Chem.
Commun., 1998, 2425.
3 I. M. M. Fussing, D. Pletcher and R. J. Whitby, J. Organomet. Chem.,
1994, 470, 109; K. Nomura, N. Naga, M. Miki, K. Yanagi and A. Imai,
Organometallics, 1998, 17, 2152.
4 For related chemistry of perfluorophenoxide derivatives see S. W. Ewart,
M. J. Sarsfield, D. Jeremic, T. L. Tremblay, E. F. Williams and M. C.
Baird, Organometallics, 1998, 17, 1502; M. J. Sarsfield, S. W. Ewart,
T. L. Tremblay, A. W. Roszak and M. C. Baird, J. Chem. Soc., Dalton
Trans., 1997, 3097; T. L. Tremblay, S. W. Ewart, M. J. Sarsfield and
M. C. Baird, Chem. Commun., 1997, 831.
1
When monitored by H NMR, solutions of 7,8 at ambient
temperatures over hours eliminate methane and form the neutral
species 9,10 (Scheme 2). The solid state structure of 10 (Fig. 2)
confirms the molecular structure and shows that the boron atom
is trigonal planar with no interaction present with the adjacent
Ti-C6F5 unit.9 In the 1H NMR spectra of 9a and 10, a single set
of Cp and OAr resonances are present along with well-resolved
diastereotopic Ti-CH2-B protons. In the case of 9b containing
the chiral o-(1-naphthyl) ligand, two sets of sharp NMR signals
are present representing a 70 : 30 mixture of the two possible
diastereoisomers. The fact that exchange of these isomers is
slow on the NMR timescale at ambient temperature confirms
that naphthyl rotation cannot account for the observed flux-
ionality in 7b.
5 For linked Cp-phenoxide derivatives see Y.-X. Chen, P.-F. Fu, C. L.
Stern and T. J. Marks, Organometallics, 1997, 16, 5958.
6 U. Thewalt and T. Wohrle, J. Organomet. Chem., 1994, 464, C17.
7 P. E. Fanwick, personal communication.
Notes and references
† Selected spectroscopic data: aromatic signals unless indicated: 1H NMR
(C6D6, 30 °C, unless otherwise stated) 4a: d 6.70–7.60; 5.57 (s, C5H5); 1.68
(s), 1.32 [s, C(CH3)3]; 0.85 (s, CH3). 4b: d 7.10–8.00; 5.41 (s, C5H5); 1.64
(s), 1.26 [s, C(CH3)3]; 0.58 (s), 0.15 [s, CH3]. 5: d 7.07–7.29; 6.82 (s, para-
H); 5.63 (s, C5H5); 2.09 (s, meta-CH3); 0.26 (s, Ti-CH3). 6a: d 7.71 (s, para-
H); 7.31–7.02 (m); 5.75 (s, C5H5); 1.29 [s, C(CH3)3]; 0.10 (s, CH3). 6b: d
7.90 (s, para-H); 7.62–7.15 (m); 5.17 (s, C5H5); 1.21 [s, C(CH3)3]; 20.35,
20.81, (s, CH3). 7a: d 6.87–7.45; 5.44 (s, C5H5); 1.43 (br, Ti-CH3); 1.34 (s),
1.19 [s, C(CH3)3]; 0.90 (br, B-CH3). (C7D8, 210 °C): d 6.91–7.40; 5.37 (s,
8 X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1994, 116,
10015; J. A. Ewen and M. J. Elder, Chem. Abstr., 1991, 115, 136998g;
A. G. Massey and A. J. Park, J. Organomet. Chem., 1964, 2, 245.
9 J. D. Scollard, D. H. McConville and S. J. Rettig, Organometallics, 1997,
16, 1810; R. E. von H. Spence, D. J. Parks, W. E. Piers, M.-A.
MacDonald, M. J. Zaworotko and S. J. Rettig, Angew. Chem., Int. Ed.
Engl., 1995, 34, 1230.
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