Facile resolution of constrained geometry indenyl-phenoxide ligation

Article abstract of DOI:10.1039/b212724e

The 2-(inden-3-yl)phenoxide ligand can be resolved at both tetrahedral and octahedral Group 4 metal centers using chiral binaphthoxide ligands.

Full text of DOI:10.1039/b212724e

Facile resolution of constrained geometry indenyl-phenoxide ligation†
Luke E. Turner, Matthew G. Thorn, Phillip E. Fanwick and Ian P. Rothwell*
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2038, USA.
E-mail: rothwell@purdue.educ; Fax: 765-494-0239; Tel: 765-494-5473
Received (in Cambridge, UK) 2nd January 2003, Accepted 6th March 2003
First published as an Advance Article on the web 28th March 2003
The 2-(inden-3-yl)phenoxide ligand can be resolved at both
tetrahedral and octahedral Group 4 metal centers using
chiral binaphthoxide ligands.
The remaining dimethylamido ligands in 3–5 can undergo
protonolysis reactions with a variety of reagents. Reaction of the
Ti compounds 3 or 4 with (S)-3,3A-bis(trimethylsilyl)-1,1A-
binapthyl-2,2A-diol in aromatic solvents was found to initially
produce a mixture of two diasteroisomers (6 and 7, Scheme 1)
with well-resolved ligand signals within the NMR spectra.
However, although at low temperatures a 50/50 mixture of
isomers was observed for 6, at ambient temperature the
formation of a major isomer was found to take place. Isolated
crystals from this reaction mixture were found to contain only
one diastereoisomer, the thermodynamically more stable (p-
S,S) form of 6. The presence of the methyl substituents on the
indenyl ring of 7 does not appear to allow isomerization and a
50/50 mixture is maintained even at 100 °C for days.
Crystallization, however, did lead to the pure (p-S,S) form of 7
(Figure 2). In previous studies of pseudo-tetrahedral rac-
bis(indenyl) ligand systems it has been shown that (S)-
binapthoxide ligands lead to a preferential (p-S) coordination of
the indenyl rings.5 The change in chirality of the chelated
indenyl-phenoxide ligand cannot occur via simple phenoxide
dissociation. Instead “flipping” of the indenyl ring must occur.
We believe this occurs via a reversal of the process that leads to
3 and 4. Specifically it seems reasonable to propose reversible
protonation of the indenyl ring can occur by the dimethylamine
generated within the reaction. There is precedence for such a
process in the interconversion of mer- and rac-bis(indenyl)
systems.6 In the case of the 2,3-dimethyl-indenyl ligand,
however, this process cannot lead directly to ring-flipping as the
proton has to be abstracted from the same face to which it was
originally delivered.
The chemistry of ansa metallocenes and constrained geometry
ligands at Group 4 metal centers continues to be an important
area of transition metal chemistry.1 Of particular interest has
been the design and application of chiral ligands of this type.2
We have begun to study the coordination chemistry of
2-(indenyl)phenoxide ligands, which demonstrate a variety of
coordination modes.3 We wish to report here the resolution of
this ligand system at both tetrahedral and an unusual octahedral
Group 4 metal center.
Hydrocarbon solution of the ligands 1 and 2 (1 equiv.) react
with the substrates [M(NMe2)4] (M = Ti, Zr)4 to produce the
corresponding bis(amides) 3–5 via activation of both the
phenolic OH and indenyl CH bonds (Scheme).†‡ Structural
studies of 3–5,§ show the presence of both the (p-R) and (p-S)
enantiomers within the unit cell due to the planar chirality
generated via the indenyl coordination; Figure 1 shows (p-R)-
3.
The reaction of 5 with (R)-3,3A-bis(trimethylsilyl)-1,1A-
binaphthyl-2,2A-diol also gave an initial 50/50 mixture of
Scheme 1 Synthesis of compounds.
Fig. 1 Selected bond distances (Å) and angles (°) for 3; (p-R form shown)
Ti–O(1) 1.895(1), Ti–N(2) 1.905(2) ,Ti–N(3) 1.913(2), Ti–C(121)
2.366(2), Ti–C(122) 2.381(2), Ti–C(123) 2.380(2), Ti–C(124) 2.417(2),
Ti–C(129) 2.405(2), O(1)–Ti–N(2) 107.07(6), O(1)–Ti–N(3) 100.22(6),
N(2)–Ti–N(3) 102.02(6).
† Electronic supplementary information (ESI) available: synthesis of
compounds 1–8 and ORTEP views of4,5 and 6. See http://www.rsc.org/
suppdata/cc/b2/b212724e/
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5
6.85–7.59 (aromatics); 6.55, 6.19 (d, h -CH); 2.91, 2.31 (s, NMe2); 1.64,
5
1.44 (s, CMe3). 13C NMR (C6D6, 25 °C): d 171.0 (Zr–O–C); 95.5 (h -CH).
5
For 6(p-S,S): 1H NMR (C6D6, 25 °C): d 6.65–8.25 (aromatics); 5.44 (d, h -
CH); 1.35, 1.32 (s, CMe3); 0.42, 0.29 (s, SiMe3). 13C NMR (C6D6, 25 °C):
5
d 173.1, 165.6, 156.6 (Ti–O–C); 106.3 (h -CH). For 7(p-S,S): 1H NMR
(C6D6, 25 °C): d 6.49–8.16 (aromatics); 2.27, 1.62 (s, CH3); 1.35, 1.22 (s,
CMe3); 0.49, 0.28 (s, SiMe3). 13C NMR (C6D6, 25 °C): d 173.2, 163.8, 160.7
5
(Ti–O–C); 100.3 (h -CMe). (p-R, S): 1H NMR (C6D6, 25 °C): d 5.81–7.96
(aromatics); 2.24, 1.59 (s, CH3); 1.47, 1.33 (s, CMe3); 0.46, 0.16 (s, SiMe3).
5
13C NMR (C6D6, 25 °C): d 173.0, 168.7, 156.9 (Ti–O–C); 108.1 (h -CMe).
5
For 8(p-R,R): 1H NMR (C6D6, 25 °C): d 6.53–8.28, (aromatics); 5.59 (s, h -
CH); 3.57 (s, O–CH2–CH2); 1.39 (s, O–CH2–CH2); 1.35, 1.26 (s, CH3);
1.35 (s), 1.22 (s, CMe3); 0.49 (s), 0.36 (s, SiMe3). Selected 13C NMR (C6D6,
5
25 °C): d 171.9, 160.7 (Zr–O–C); 99.4 (h -CH).
§ Crystal data: For 3 at 150 K: C27H38N2OTi, M = 454.52, space group
P21/n (No. 14), a = 12.4594(3), b = 11.7575(3), c = 18.0226(4) Å, b =
108.1734(13)°, V = 2508.5(2) Å3, dcalc = 1.203 g cm23, Z = 4. Of the 5700
unique reflections collected (5 5 q 5 27°) with Mo–Ka (l = 0.71073 Å),
Fig. 2 Selected bond distances (Å) and angles (°) for (p-S,S)-7: Ti–O(1)
1.864(2), Ti–O(2) 1.862(2), Ti–O(3) 1.866(2), Ti–C(11) 2.310(3), Ti–C(12)
2.318(3), Ti–C(13) 2.361(3), Ti–C(14) 2.522(3), Ti–C(19) 2.472(3), O(1)–
Ti–O(2) 96.91(9), O(2)–Ti–O(3) 102.09(9), O(1)–Ti–O(3) 115.72(9).
2
the 5694 with Fo > 2.0 s (Fo2) were used in the final least-squares
refinement to yield R
= 0.041 and RW = 0.099. For 4 at 150 K:
C29H42N2OTi, M = 482.57, space group P21/c (No. 14), a = 10.0202(2),
b = 13.0802(3), c = 22.0926(4) Å, b = 102.3111(13)°, V = 2829.01(19)
Å3, dcalc = 1.133 g cm23, Z = 4. Of the 6044 unique reflection collected
2
(5 5 q 5 27°) with Mo–Ka (l = 0.71073 Å), the 6040 with Fo > 2.0 s
(Fo2) were used in the final least-squares refinement to yield R = 0.061 and
¯
RW = 0.160. For 5 at 150 K: C27H38N2OZr, M = 497.84, space group P1
(No. 2), a = 12.9534(3), b = 14.0719(4), c = 15.2631(4) Å, V = 2589.5(2)
Å3, dcalc = 1.277 g cm23, Z = 4. Of the 11660 unique reflections collected
2
(5 5 q 5 27°) with Mo–Ka (l = 0.71073 Å), the 9145 with Fo > 2.0 s
(Fo2) were used in the final least-squares refinement to yield R = 0.053 and
RW = 0.136. For 6 at 150 K: C49H54O3Si2Ti, M = 795.05, space group P21
(No. 4), a = 11.9436(10), b = 13.1268(10), c = 16.1538(12) Å, b =
102.861(4)°, V = 2469.1(6) Å3, dcalc = 1.069 g cm23, Z = 2. Of the 7600
unique reflections collected (5 5 q 5 25°) with Mo–Ka (l = 0.71073 Å),
2
the 7586 with Fo > 2.0 s (Fo2) were used in the final least-squares
refinement to yield R
= 0.087 and RW = 0.187. For 7 at 150 K:
C
49H54O3Si2Ti, M = 823.10, space group P21 (No. 4), a = 12.0012(4), b
= 13.6234(5), c = 16.3611(6) Å, b = 105.5417(14)°, V = 2577.2(3) Å3,
dcalc = 1.061 g cm23, Z = 2. Of the 10232 unique reflection collected (5
5 q 5 30°) with Mo–Ka (l = 0.71073 Å), the 10199 with Fo > 2.0 s (Fo
Fig. 3 Selected bond distances (Å) and angles (°) for (p-R,R)-8: Zr–O(1)
2.100(3), Zr–O(2) 2.017(3), Zr–O(3) 2.095(3), Zr–O(4) 2.387(3), Zr–O(5)
2.356(3), Zr–C(11) 2.531(4), Zr–C(12) 2.511(4), Zr–C(13) 2.564(4), Zr–
C(14) 2.723(4), Zr–C(19) 2.696(4), O(1)–Zr–O(2) 99.1(1), O(2)–Zr–O(3)
92.6(1), O(1)–Zr–O(3) 150.5(1), O(2)–Zr–O(5) 82.25(12), O(3)–Zr–O(5)
76.0(1), O(1)–Zr–O(5) 78.8(1), O(2)–Zr–O(4) 159.0(1), O(3)–Zr–O(4)
79.2(1), O(1)–Zr–O(4) 80.3(1), O(5)–Zr–O(4) 77.1(1).
2
2
)
were used in the final least-squares refinement to yield R = 0.053 and RW
= 0.148. For 8*C7H8*C4H8O at 150 K: C68H86O6Si2Zr, M = 1146.83,
space group P212121 (No. 19), a = 12.5231(3), b = 19.2231(4), c =
25.9127(6) Å, V = 2964.61(10) Å3, dcalc = 1.221 g cm23, Z = 4. Of the
12567 unique reflections collected (5 5 q 5 26°) with Mo–Ka (l =
2
0.71073 Å), the 12553 with Fo > 2.0 s (Fo2) were used in the final least-
squares refinement to yield R = 0.063 and RW = 0.136. Flack parameters:
compound 6, 0.04(5); compound 7, 20.01(2); compound 8, 0.03(4). CCDC
201167–201170, 201172, 201174. See http://www.rsc.org/suppdata/cc/b2/
b212724e/ for crystallographic data in .cif or other electronic format.
diastereoisomers. It has proven difficult to isolate crystalline
products from hydrocarbon solvents. However, use of THF was
found to lead to crystals of a new compound 8 shown to contain
a pseudo-octahedral zirconium metal center (Figure 3). Inter-
estingly 8 can be seen to contain a p-R chelated indenyl-
phenoxide and two, cis-coordinated THF molecules along with
the (R)-binol ligand. It is also important to note that the indenyl
1 R. Beckhaus, in Metallocenes, ed. A. Togni and R. L. Halterman, Wiley-
VHC, Weinheim, 1998, p. 153; E.-I. Negishi and J. Montchamp, in
Metallocenes, ed. A. Togni and R. L. Halterman, Wiley-VHC, Wein-
heim, 1998, p. 241.
2 A. L. McKnight and R. M. Waymouth, Chem. Rev., 1998, 98, 2587; R. L.
Halterman, Chem. Rev., 1992, 92, 965; J. Okuda, Topics Curr. Chem.,
1991, 160, 99; C. Janiak and H. Schumann, Adv. Organomet. Chem.,
1991, 33, 291.
3
ring is only h -bound in the solid state of 8, with significant
elongation of the Zr–C(aromatic) distances (Figure 3). A similar
bonding mode is also seen in 7 (Figure 2) whereas the indenyl
5
ring in 3 (Figure 1) more closely approaches h -coordination.
We thank the National Science Foundation (Grant CHE-
0078405) for financial support of this research.
3 M. G. Thorn, P. E. Fanwick, R. W. Chesnut and I. P. Rothwell, Chem.
Commun., 1999, 2543.
4 Zr(NMe2)4 was prepared using the procedure outlined by G. M. Diamond
and R. F. Jordan, Organometallics, 1995, 14, 5.
5 F. R. W. P. Wild, J. Zsolnai, G. Huttner and H. H. Brintzinger, J.
Organomet. Chem., 1982, 232, 233; B. Chin and S. L. Buchwald, J. Org.
Chem., 1996, 61, 5650.
6 G. M. Diamond, S. Rodewald and R. F. Jordan, Organometallics, 1995,
14, 5; G. M. Diamond and R. F. Jordan, Organometallics, 1996, 15, 4030;
G. M. Diamond, R. F. Jordan and J. L. Petersen, J. Am. Chem. Soc., 1996,
118, 8024.
Notes and references
‡
Selected spectroscopic data. For 3: 1H NMR (C6D6, 25 °C): d
5
6.75–7.61 (aromatics); 6.43, 6.33 (d, h -CH); 3.27, 2.49 (s, NMe2); 1.68,
1.44 (s, CMe3). 13C NMR (C6D6, 25 °C): d 172.5 (Ti–O–C); 101.3 (h -CH).
5
For 4: 1H NMR (C6D6, 25 °C): d 6.81–7.60 (aromatics); 3.11, 2.59 (s,
NMe2); 2.22, 1.99 (s, CH3); 1.65, 1.44 (s, CMe3). 13C NMR (C6D6, 25 °C):
5
d 172.2 (Ti–O–C); 108.1 (h -CMe). For 5: 1H NMR (C6D6, 25 °C): d
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