Chiral complexes of a new diazaallyl ligand: Group 4 aminooxazolinates

Article abstract of DOI:10.1021/om049518s

A new biaryl-bridged bis(iminooxazolidine) proligand H₂L is prepared in good yield from 2,2-diamino-6,6′-dimethylbiphenyl. The direct reaction of H₂L with [Ti(CH₂Ph)₄] leads via deprotonation of the ligand to the C₂-symmetric dibenzyl complex [LTi(CH₂Ph)₂] (85%) containing diazaallyl ligation. The analogous group 4 complexes [LZr(CH₂Ph)₂] (79%) and [LHf(CH₂Ph)₂] (91%) are similarly obtained. Molecular structures of these three compounds indicate C₂-symmetry in all cases and that the chirality of the backbone is well expressed in the coordination sphere. Reaction of H₂L with Ti(NMe₂)₄ gives the amide [LTi(NMe₂)₂] (90%), which on reaction with SiMe₃Cl gives the chloride [LTiCl₂] (78%). The dichloride [LZr-(NMe₂H)Cl₂] is prepared via treatment of H ₂L with Zr(NMe₂)₂Cl₂(THF) ₂ (86%). The direct reaction of H₂L with TiCl ₄(THF)₂ gives the adduct [(H₂L)TiCl ₄] (83%), which is shown by X-ray crystallography to contain intramolecular NH...C1 hydrogen bond contacts. The complexes were tested as precatalysts for the polymerization of ethene and 1-hexene using a range of cocatalysts and were found to display low activity. Correspondingly, NMR studies on a presumed active species [LZr(CH₂Ph)] [B(C₆F ₃)₃(CH₂Ph)] were consistent with tight ion pairing on the NMR chemical shift time scale.

Full text of DOI:10.1021/om049518s

5066
Organometallics 2004, 23, 5066-5074
Ch ir a l Com p lexes of a New Dia za a llyl Liga n d : Gr ou p 4
Am in ooxa zolin a tes
Ian Westmoreland, Ian J . Munslow, Adam J . Clarke, Guy Clarkson, and
Peter Scott*
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, U.K.
Received J uly 1, 2004
A new biaryl-bridged bis(iminooxazolidine) proligand H2L is prepared in good yield from
2,2-diamino-6,6′-dimethylbiphenyl. The direct reaction of H2L with [Ti(CH2Ph)4] leads via
deprotonation of the ligand to the C2-symmetric dibenzyl complex [LTi(CH2Ph)2] (85%)
containing diazaallyl ligation. The analogous group 4 complexes [LZr(CH2Ph)2] (79%) and
[LHf(CH2Ph)2] (91%) are similarly obtained. Molecular structures of these three compounds
indicate C2-symmetry in all cases and that the chirality of the backbone is well expressed in
the coordination sphere. Reaction of H2L with Ti(NMe2)4 gives the amide [LTi(NMe2)2] (90%),
which on reaction with SiMe3Cl gives the chloride [LTiCl2] (78%). The dichloride [LZr-
(NMe2H)Cl2] is prepared via treatment of H2L with Zr(NMe2)2Cl2(THF)2 (86%). The direct
reaction of H2L with TiCl4(THF)2 gives the adduct [(H2L)TiCl4] (83%), which is shown by
X-ray crystallography to contain intramolecular NH‚‚‚Cl hydrogen bond contacts. The
complexes were tested as precatalysts for the polymerization of ethene and 1-hexene using
a range of cocatalysts and were found to display low activity. Correspondingly, NMR studies
on a presumed active species [LZr(CH2Ph)][B(C6F5)3(CH2Ph)] were consistent with tight ion
pairing on the NMR chemical shift time scale.
In tr od u ction
(Cp) ligands,5,6 but apart from some notable exceptions5c,7
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* To whom correspondence should be addressed. Fax: 024 7657
2710. E-mail: peter.scott@warwick.ac.uk.
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10.1021/om049518s CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/16/2004

Group 4 Aminooxazolinates
Organometallics, Vol. 23, No. 21, 2004 5067
Sch em e 1. Syn th esis of th e C2-Sym m etr ic Oxa zolin e Liga n d H2La
a
Reagents and conditions: (i) 1,1′-thiocarbonyldi-2(1H)-pyridone, DCM (97%); (ii) 2-amino-2-methylpropanol, THF (94%); (iii)
p-toluenesulfonyl chloride, NaOH, THF (85%).
tives” to the metallocenes,9 the complexes may simply
not operate with usefully high turnover rate or number
in the target catalyses. For example, while the expres-
sion of chirality in early transition metal complexes of
II appears to be very good, little catalytic activity was
observed.10 In contrast, our related biaryl-bridged com-
F igu r e 1. Molecular structure of H2L dimer showing the
inter- and intramolecular hydrogen bonds.
extensive in L2-, thus improving the stability of the
spectator ligand sphere of its complexes in comparison
to aminopyridinates based on II. We also note that other
classes of oxazoline complexes of the early transition
metals and lanthanides have been used successfully in
catalysis.15,16
plexes with amide and alkoxide ligation have been
rather more successful in, for example, enantioselective
hydroamination.11 Encouraged by the success of amidi-
nate complexes in the arena of olefin polymerization,12,13
we have recently developed a new class of C2-symmetric
diazaallyl complexes H2L (Scheme 1), and this work is
reported here. As with the guanidinate anions,14 we
envisioned that the delocalization of charge would be
Resu lts a n d Discu ssion
The C2-symmetric iminooxazolidine proligand H2L
was synthesized in high yield from 117 via a three-step
procedure. The reaction of 1 with 1,1′-thiocarbonyldi-
2(1H)-pyridone gives the di(isothiocyanate) 2 in 97%
yield after passing a solution of the crude product
through silica to remove the 2-hydoxypyridine byprod-
uct.18 Using Kim’s synthesis of 2-phenylamino-2-oxazo-
lines19 we prepared the thiourea 3 via reaction of 2 with
2-amino-2-methylpropanol in 94% yield. Subsequent
ring closure of 3 by treatment with TsCl and NaOH is
straightforward, and the proligand H2L was obtained
in 85% yield. Crystals of racemic H2L suitable for X-ray
structural determination were grown from a concen-
trated solution in dichloromethane, and the molecular
structure is shown in Figure 1. The crystallographically
centrosymmetric dimer is assembled via two hydrogen
bonds [H(30)-N(23) 1.96(7) Å] in a manner reminiscent
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(17) The biaryl diamine 1 was prepared according to our procedure;
see: Gillespie, K. M.; Sanders, C. J .; O’Shaughnessy, P. N.; Westmo-
reland, I.; Thickitt, C. P.; Scott, P. J . Org. Chem. 2002, 67, 3450.
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57, 7137.

5068 Organometallics, Vol. 23, No. 21, 2004
Westmoreland et al.
Sch em e 2. Syn th esis a n d Rea ction s of [LMX2] (M
of 125.3(6)° and 129.8(7)° in the solid state structure of
the free ligand (Figure 1). The N-C bond lengths are
1.301(9) and 1.321(9) Å, compared to 1.253(7) and 1.364-
(8) Å in the proligand.
) Ti, Zr , Hf; X ) ch lor id e, a m id e, a lk yl)a
A range of methods were employed in an attempt to
convert [(H2L)TiCl4] to the corresponding dichloride;
treatments with KH, BuLi, TEA, and DBU under
various conditions were all unsuccessful. We have,
however, developed a convenient method for the syn-
thesis of [LTiCl2] via the corresponding amide (vide
infra).
The proligand H2L reacts very cleanly with Ti(NMe2)4
in diethyl ether at ambient temperature to give the
titanium amido complex [LTi(NMe2)2] as a bright
orange solid. The 1H and 13C NMR spectra of [LTi-
(NMe2)2] are as expected for a C2-symmetric complex
in solution.
a
Reagents and conditions: (i) Ti(CH2Ph)4, toluene (85%);
(ii) Hf(CH2Ph)4, toluene (91%); (iii) TiCl4(THF)2, DCM (83%);
(iv) Zr(CH2Ph)4, toluene (79%); (v) Ti(NMe2)4, Et2O (90%); (vi)
Ti(NMe2)4, Et2O, then TMSCl, toluene (89%); (vii) Zr(NMe2)2Cl2-
(THF)2, toluene (86%); (viii) TMSCl, toluene (78%).
Reaction of [LTi(NMe2)2] with an excess of chlorotri-
methylsilane in toluene at -78 °C gave the dichloride
[LTiCl2] as a brown microcrystalline solid (78%). It is
also possible, and somewhat more convenient, to pre-
pare the dichloride via reaction of chlorotrimethylsilane
with [LTi(NMe2)2] formed in-situ (see Experimental
Section).
As observed with the analogous titanium compound
(vide supra), the direct reaction of the proligand H2L
with tetrabenzylzirconium(IV) gave the complex [LZr-
(CH2Ph)2] as fine yellow microcrystals (Scheme 2). The
1H and 13C NMR spectra of this compound are consis-
tent with a C2-symmetric environment in solution. The
hafnium analogue [LHf(CH2Ph)2] was similarly ac-
cessed. Crystals of [LHf(CH2Ph)2] suitable for X-ray
structural determination were obtained from a concen-
trated solution in heptane, and the molecular structure
is shown in Figure 3.
The six-coordinate complex is C2-symmetric, and the
auxiliary benzyl groups occupy mutually cis positions,
at a C-Hf-C bond angle of 99.0(3)°. The Hf-Nbiaryl and
Hf-Noxazoline bond lengths, measured at 2.27 and 2.22
Å, respectively, are similar to those observed in two half-
sandwich Cp-amidinate complexes of hafnium20,21 and
Polomo’s aminopyridinato complex,22 all falling within
the range 2.18-2.28 Å. Zirconium amidinates have
similar bond lengths, but the M-Npyridyl bonds tend to
be slightly longer at 2.34-2.36 Å.12a,g,h,23,24 The N-Hf-N
bond angle of 60.24(18)° observed in [LHf(CH2Ph)2] is
typical of those measured for the amidinate compounds
of both Hf and Zr detailed above, which lie in the range
58.94(6)-64.17(9)°. The aminopyridinato compounds
have slightly smaller N-M-N angles; an aminopyridi-
nato N-Hf-N angle of 58.4° was found in tetrakis{2-
(phenylamido)pyridine}hafnium(IV).22 Deprotonation and
coordination have significantly reduced the N-C-N
bond angle from 129.8(7)° observed in the free ligand
to 116.5(6)° in [LHf(CH2Ph)2]. This angle is, however,
F igu r e 2. Molecular structure of [(H2L)TiCl4].
of carboxylic acids. A second pair of intra-monomer
hydrogen bonds is also present [H(8)-O(25) 2.54(6) Å].
The dibenzyl compound [LTi(CH2Ph)2] (Scheme 2)
was readily obtained as fine black crystals following
direct reaction of H2L with tetrabenzyltitanium(IV) in
toluene (85% yield). The 1H and 13C NMR spectra of this
compound are indicative of a C2-symmetric environment
in solution. The cis dialkyl structure of [LTi(CH2Ph)2]
was confirmed via X-ray diffraction studies, but the data
were unfortunately not of suitable quality for publica-
tion.
The reaction of H2L with TiCl4(THF)2 gave the adduct
[(H2L)TiCl4], rather than the desired dichloride product
[LTiCl2]. The 1H NMR spectrum of this compound in
d6-benzene solution contains a singlet resonance at 7.24
ppm, for which there is no corresponding cross-peak in
1
the H-13C correlation spectrum, and which we assign
to the oxazolidine N-H protons. Single crystals of [(H2L)-
TiCl4] were grown from a concentrated solution in
dichloromethane, and the molecular structure, deter-
mined by X-ray crystallography, shows that the coor-
dination sphere is essentially octahedral (Figure 2). The
two imino N atoms occupy mutually cis coordination
sites with N(1)-Ti(1) and N(3)-Ti(1) bond lengths of
2.137(6) and 2.153(5) Å, respectively. These distances
are almost identical to those observed in a previously
reported R-cis Schiff-base complex of titanium.8c The
complex [(H2L)TiCl4] exhibits a bond angle N(1)-Ti(1)-
N(3) of 85.3°, slightly greater than the 76.7° observed
in the biaryldiimine Schiff-base compound.
(20) Zhang, Y.; Kissounko, D. A.; Fettinger, J . C.; Sita, L. R.
Organometallics 2003, 22, 21.
(21) Chernega, A. N.; Gomez, R.; Green, M. L. H. J . Chem. Soc.,
Chem. Commun. 1993, 1415.
(22) Polamo, M.; Leskela, M. Acta Chem. Scand. 1997, 51, 69.
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1792. (b) Keaton, R. J .; Koterwas, L. A.; Fettinger, J . C.; Sita, L. R. J .
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(24) (a) Morton, C.; O’Shaughnessy, P.; Scott, P. Chem. Commun.
2000, 2099. (b) Khempe, R.; Brenner, S.; Arndt, P. Organometallics
1996, 15, 1071.
The N-C-N bond angles in [(H2L)TiCl4], observed
at 127.4(7)° and 128.7(6)°, are very similar to the values

Group 4 Aminooxazolinates
Organometallics, Vol. 23, No. 21, 2004 5069
dination of a dimethylamine ligand is unusual. Gibson26
and Passarelli27 have both reported zirconium com-
pounds containing this moiety, and Kempe has de-
scribed a related aminopyridinate titanium complex.28
The molecule [LZr(NMe2H)Cl2] is not C2-symmetric, and
1
at room temperature the H NMR spectrum is broad.
Cooling to 243 K gave a sharp spectrum corresponding
to a C1-symmetric structure, which contained four 6H
singlets for the oxazolinyl ring methyls between 1.16
and 1.79 ppm and a further two 6H singlets for the
backbone aromatic methyls at 1.96 and 2.14 ppm. Two
pairs of AB doublets (4H in total) centered at 3.56 and
3.36 ppm were observed for the ring methylene protons.
As the temperature was increased to 313 K, the peaks
began to coalesce, consistent with reversible loss of the
dimethylamine ligand. By 363 K the system is in rapid
exchange on the NMR chemical shift time scale, and a
spectrum corresponding to a C2-symmetric structure is
obtained.
Perhaps, given the structure of this compound, it is
unsurprising that we were unable to access [LZrCl2] via
the methods discussed above. It is also worth noting that
we were unable to synthesize the hafnium analogue via
reaction of either the sodium or potassium salt of H2L
with HfCl4.
Given the ability of amidinate12f,g,29 and half-sandwich
Cp-acetamidinate complexes13,20,23b to act as precata-
lysts for alkene polymerization, we were interested to
study how the aminooxazolinyl complexes would fare.
The results of attempts to polymerize ethylene and
1-hexene using a variety of catalyst activators are
summarized in Table 1.
First it is evident that none of the compounds are
efficient initiators for polymerization of these olefins.
(MAO is unsuccessful as a cocatalyst in this system.
This may be due to reaction of the activator at the oxazo-
line O atom.) Nevertheless, some useful observations
can be made. The protic borate activator [PhNMe2H]-
[B(C6F5)4] in the presence of the intended alkylating
agent and scavenger AliBu3 gave at least a trace of poly-
(ethylene) in most cases, but the presence of dimethyl-
aniline coproduct may be the cause of deactivation via
coordination to the metal center. Correspondingly, the
borane B(C6F5)3 in the presence of AliBu3 gives some
activity with the metal halides, even giving a small
amount of poly(hexene) with the zirconium compound.
The trityl borate activator [Ph3C][B(C6F5)4] in conjunc-
tion with AliBu3 gave significant amounts of poly-
(ethylene) with the titanium compounds but not the
zirconium or hafnium species, and a seemingly random
selection of “hits” with 1-hexene.
F igu r e 3. Views of the molecular structure of [LHf(CH2-
Ph)2].
slightly larger than those measured in comparable
group 4 compounds, which fall within the range 111.8-
(2)-115.0(5)°. The aminopyridinato compounds have
slightly smaller N-C-N bond angles of 108.4(3)° and
110.1(5)°.
The proligand H2L reacts cleanly with sodium hydride
in THF to give the doubly deprotonated species Na2L‚
n(THF). The amount of THF present in the complex was
established by integration of the THF resonances ob-
1
served in the H NMR spectrum obtained in deuterated
pyridine. The potassium salt K2L‚n(THF) was similarly
obtained and characterized. However, rather surpris-
ingly, we were unable to access [LMCl2] (M ) Zr, Hf)
via reaction of either of these salts with MCl4 or MCl4-
(THF)2.
We note that Sita’s half-sandwich acetamidinate
catalysts for 1-hexene polymerization were found to
operate most successfully in chlorobenzene solution.13
However, in our system this solvent gave results similar
to those obtained with toluene.
The reaction of H2L with ZrCl4 or ZrCl4(THF)2 in the
presence of TEA or DBU did not yield [LZrCl2]. When
H2L was treated with Zr(NMe2)4, a poorly defined and
possibly polymeric material was obtained. We have
experienced problems of this type with an aminopyri-
dine ligand related to L.10b Attempts to convert the
dibenzyl compound [LZr(CH2Ph)2] to [LZrCl2] via reac-
tion with TEA‚HCl failed.
To probe the formation of cationic species, we studied
the reactions between the group 4 dibenzyl compounds
(25) Brenner, S.; Kempe, R.; Arndt P. Z. Anorg. Allg. Chem. 1995,
621, 2021.
(26) Gibson, V. C.; Kimberley, B. S.; White, A. J . P.; Williams, D.
J .; Howard, P. Chem. Commun. 1998, 313.
(27) Passarelli, V.; Benetollo, F.; Zanella, P.; Carta, G.; Rossetto,
G. J . Chem. Soc., Dalton Trans. 2003, 1411.
(28) Fuhrmann, H.; Brenner, S.; Arndt, P.; Kempe, R. Inorg. Chem.
1996, 35, 6742.
The compound [LZr(NMe2H)Cl2] was obtained via the
reaction of H2L with Zr(NMe2)2Cl2(THF)2.25 The coor-

5070 Organometallics, Vol. 23, No. 21, 2004
Westmoreland et al.
Ta ble 1. Resu lts of P olym er iza tion Exp er im en ts: P r od u ctivity of P olym er /g-1 m m ol h ba r a
precatalyst
cocatalyst
[LTiBn2]
[LTiCl2]
[LZrBn2]
[LZr(NMe2H)Cl2]
[LHfBn2]
ethylene
[Me2NHPh][B(C6F5)4]/AliBu3
B(C6F5)3/AliBu3
trace
trace
14
trace
14
14
trace
trace
trace
6
9
0
0
0
[B(C6F5)4][Ph3C]/AliBu3
hexene
trace
[Me2NHPh][B(C6F5)4]/AliBu3
B(C6F5)3/AliBu3
0
0
0
7
0
6
7
0
0
0
0
8
9
0
0
0
10
[B(C6F5)4][Ph3C]/AliBu3
b
[B(C6F5)4][Ph3C]/AliBu3
a
45 min runs, see Experimental Section for conditions. bEmploying chlorobenzene as solvent.
Ta ble 2. Cr ysta llogr a p h ic Da ta , Collection P a r a m eter s, a n d Refin em en t P a r a m eter s for H2L, [(H2L)TiCl4],
a n d [LHf(CH2P h )2]
H2L
[(H2L)TiCl4]
[LHf(CH2Ph)2]
empirical formula
fw
C
24H30N4O2
C
25H32Cl6N4O2Ti
C38H42HfN4O2C1.5
765.25
0.21 × 0.18 × 0.17
monoclinic
P2(1)/n
16.8011
13.0020
17.0017
90.9210(10)
3713.5(2)
1.401
406.52
681.15
cryst size (mm3)
cryst syst
space group
a (Å)
0.32 × 0.12 × 0.08
monoclinic
P21/c
9.127(2)
12.697(3)
19.664(5)
92.187(4)
2277.2(9)
1.186
0.20 × 0.20 × 0.18
monoclinic
P2(1)/n
10.8613(2)
20.8319(3)
13.3001(3)
94.44
3000.29(10)
1.508
0.850
b (Å)
c (Å)
â (deg)
V (Å3)
Dcalcd (Mg/m3)
µ (mm-1
F000
)
0.077
872
2.846
1580
1400
total no. of reflns
no. of indep reflns
Rint
11 009
3990
0.1998
15 744
5266
0.1099
23 017
8964
0.0670
no. of data/restraints/ params
R1, [I > 2σ(I)]
wR2
3990/0/284
0.0823
0.1400
5277/0/350
0.0879
0.1704
8964/0/424
0.0498
0.1081
GoF on F2
0.924
1.212
0.928
Ta ble 3. Selected Bon d Len gth s a n d An gles for H2L, [(H2L)TiCl4], a n d [LHf(CH2P h )2]
H2L
[(H2L)TiCl4]
[LHf(CH2Ph)2]
O(1)-C(2) ) 1.350(7)
O(1)-C(7) ) 1.429(6)
C(2)-N(3) ) 1.253(7)
C(2)-N(8) ) 1.364(8)
N(3)-C(4) ) 1.476(7)
C(4)-C(7) ) 1.542(8)
N(8)-C(9) ) 1.408(7)
C(9)-C(10) ) 1.400(8)
C(22)-N(23) ) 1.426(7)
N(23)-C(24) ) 1.279(7)
C(24)-N(30) ) 1.356(7)
O(25)-C(26) ) 1.430(6)
C(27)-N(30) ) 1.475(7)
Ti(1)-N(1) ) 2.137(6)
Ti(1)-N(3) ) 2.153(5)
Ti(1)-Cl(2) ) 2.262(2)
Ti(1)-Cl(1) ) 2.288(2)
Ti(1)-Cl(4) ) 2.315(2)
Ti(1)-Cl(3) ) 2.328(2)
N(3)-C(20) ) 1.301(9)
N(4)-C(20) ) 1.323(9)
N(1)-C(15) ) 1.320(9)
N(2)-C(15) ) 1.321(9)
Hf(1)-N(4) ) 2.216(5)
Hf(1)-N(2) ) 2.218(5)
Hf(1)-C(100) ) 2.248(7)
Hf(1)-N(1) ) 2.263(5)
Hf(1)-C(200) ) 2.274(7)
Hf(1)-N(3) ) 2.279(5)
Hf(1)-C(20) ) 2.613(6)
Hf(1)-C(15) ) 2.617(6)
N(1)-C(15) ) 1.330(8)
N(1)-C(6) ) 1.414(7)
N(2)-C(15) ) 1.315(8)
N(2)-C(17) ) 1.487(8)
N(3)-C(20) ) 1.317(8)
N(3)-C(9) ) 1.412(8)
N(4)-C(20) ) 1.332(8)
N(1)-Ti(1)-N(3) ) 85.3(2)
N(1)-Ti(1)-Cl(2) ) 90.29(17)
N(3)-Ti(1)-Cl(2) ) 89.78(16)
N(1)-Ti(1)-Cl(1) ) 90.03(16)
N(3)-Ti(1)-Cl(1) ) 174.72(16)
Cl(2)-Ti(1)-Cl(1) ) 92.62(8)
N(1)-Ti(1)-Cl(4) ) 174.90(17)
N(3)-Ti(1)-Cl(4) ) 89.79(16)
Cl(2)-Ti(1)-Cl(4) ) 90.86(8)
Cl(1)-Ti(1)-Cl(4) ) 94.88(8)
N(1)-Ti(1)-Cl(3) ) 89.16(16)
N(3)-Ti(1)-Cl(3) ) 87.08(16)
Cl(2)-Ti(1)-Cl(3) ) 176.84(9)
Cl(1)-Ti(1)-Cl(3) ) 90.50(8)
Cl(4)-Ti(1)-Cl(3) ) 89.39(8)
N(1)-C(15)-N(2) ) 127.4(7)
N(4)-C(20)-N(3) ) 128.7(6)
N(4)-C(22) ) 1.484(8)
N(4)-Hf(1)-N(2) ) 147.14(19)
N(4)-Hf(1)-C(100) ) 114.6(2)
N(2)-Hf(1)-C(100) ) 86.5(2)
N(4)-Hf(1)-N(1) ) 95.77(18)
N(2)-Hf(1)-N(1) ) 60.24(18)
C(100)-Hf(1)-N(1) ) 146.7(2)
N(4)-Hf(1)-C(200) ) 88.9(2)
N(2)-Hf(1)-C(200) ) 113.5(2)
C(100)-Hf(1)-C(200) ) 99.0(3)
N(1)-Hf(1)-C(200) ) 94.7(2)
N(4)-Hf(1)-N(3) ) 60.13(19)
N(2)-Hf(1)-N(3) ) 91.89(18)
C(100)-Hf(1)-N(3) ) 102.6(3)
N(1)-Hf(1)-N(3) ) 80.25(18)
C(200)-Hf(1)-N(3) ) 147.6(2)
N(1)-C(15)-N(2) ) 116.5(6)
C(2)-O(1)-C(7) ) 105.8(5)
N(3)-C(2)-O(1) ) 119.4(6)
N(3)-C(2)-N(8) ) 129.8(7)
O(1)-C(2)-N(8) ) 110.9(7)
C(2)-N(8)-C(9) ) 128.4(6)
C(10)-C(9)-N(8) ) 121.0(6)
C(15)-C(9)-N(8) ) 117.4(6)
C(16)-C(22)-N(23) ) 124.3(6)
C(21)-C(22)-N(23) ) 116.3(6)
C(24)-N(23)-C(22) ) 117.6(5)
N(23)-C(24)-O(25) ) 124.4(6)
N(23)-C(24)-N(30) ) 125.3(6)
O(25)-C(24)-N(30) ) 110.3(6)
C(24)-O(25)-C(26) ) 109.3(5)
C(24)-N(30)-C(27) ) 111.3(6)
1
and various boron-based activators. The results were
varied, usually giving complex mixtures. However, the
reaction between [LZr(CH2Ph)2] and B(C6F5)3 was more
interesting, and the H NMR spectrum recorded at 253
K is shown in Figure 4. Four AB doublet resonances
for the chemically inequivalent methylene protons Ha-d

Group 4 Aminooxazolinates
Organometallics, Vol. 23, No. 21, 2004 5071
the drybox. Deuterated chloroform was dried in the bottle over
molecular sieves (4 Å).
NMR spectra were recorded on Bruker ACF-250,DPX-300,
DPX-400, AV-400, and DPX-500 spectrometers. 1H and 13C
spectra were referenced internally using residual protio solvent
resonances relative to tetramethylsilane (δ ) 0 ppm); EI and
CI mass spectra were obtained on a VG Autospec mass
spectrometer. Infrared spectra were obtained either as Nujol
mulls using a Perkin-Elmer Paragon 1000 FTIR spectrometer
or directly using an Avatar 320 FTIR instrument. Elemental
analyses were performed by Warwick Analytical Services. The
low carbon values obtained in the elemental analysis of two
of the titanium complexes, [LTi(Ch2Ph)2] and [LTi(NMe2)2],
are attributed to the partial formation of metal carbides in
the combustion process, as often observed with organometallic
complexes of this type.30 Flash chromatography was performed
either in standard glassware or with a FlashMaster Personal
chromatography system and a selection of prepacked dispos-
able columns. Thin-layer chromatography was performed using
Merck 0.25 mm silica layer foil-backed plates.
F igu r e 4. 1H NMR spectrum obtained from the reaction
between [LZr(CH2Ph)2] and B(C6F5)3 recorded in C6D5Br
at 253 K.
were detected. This indicates C1-symmetry for the
compound, and all other resonances are consistent with
this. One Zr-bound benzyl group He,f gives rise to a pair
of AB doublets. Two broad peaks, each of integral 1H,
appear also, and we attribute these to Hg,h of the boron-
bound benzyl group in the anionic component [B(C6F5)3-
(CH2Ph)]-. The inequivalence of these resonances is
evidence that the ion pair is tightly bound to the metal
center and is thus rendered diastereotopic. This is
perhaps the reason for the low activity of these systems
in olefin polymerization.
2,2′-Diisoth iocya n a to-6,6′-d im eth ylbip h en yl (2). Dichlo-
romethane (100 mL) was added to a round-bottom flask
charged with 117 (500 mg, 2.36 mmol), and the mixture was
stirred to dissolve the solids. 1,1′-Thiocarbonyldi-2(1H)-pyri-
done (1.16 g, 5.00 mmol) was added via powder funnel, and
the resulting orange solution was stirred at ambient temper-
ature. The progress of the reaction was monitored by TLC.
After 15 h the solution was washed with water (2 × 30 mL),
and the aqueous washings were back-extracted with dichlo-
romethane. The combined organic phases were washed with
brine (1 × 30 mL) and dried over MgSO4. Concentration of
the solution under reduced pressure gave an orange residue.
The crude material was purified by flash chromatography on
silica gel with a hexane/ethyl acetate (2:1) mobile phase
(essentially a filtration through a column of silica). The product
was obtained as a fine white microcrystalline solid. Yield: 680
mg, 97%. Anal. Calcd for C16H12N2S2: C, 64.83; H, 4.08; N,
Con clu d in g Rem a r k s
The atropisomerism of H2L strongly directs the he-
licity of the resulting complexes [LMX2], such that only
a single diastereomer (with respect to the chiral metal
center) is formed on reaction with homoleptic alkyls of
group 4 metals. These systems are potentially well
suited for application to enantioselective catalysis and/
or stereoselective polymerization, because they contain
two mutually cis coordination sites at which reactions
can be mediated under the potent influence of the well-
expressed chiral architecture.
1
9.34. Found: C, 64.86; H, 4.08; N, 9.34. H NMR (400 MHz,
3
298 K, CDCl3): δ 7.25 (2H, t, J HH ) 8 Hz, Ar-H), 7.18 (2H, d,
3J HH ) 2 Hz, Ar-H), 7.08 (2H, d, 3J HH ) 8 Hz, Ar-H), 1.97 (6H,
s, Me). 13C{1H} NMR (100.6 MHz, 298 K, CDCl3): δ 139.0,
137.4, 134.8, 131.6, 129.7, 129.6, 123.5, (Ar), 20.2 (Me). MS
(EI): m/z 296 [M+], 281 [40%, M+ - CH3]. IR (Golden Gate ν
cm-1): 2034, 1588, 1568, 1458, 1377, 1259, 1164, 1102, 1029,
970, 894, 828, 738, 673.
N′,N′-Bis(1-h yd r oxy-2-m et h ylp r op -2-yl)-2,2′-b is(t h io-
u r ea )-6,6′-d im eth ylbip h en yl (3). A solution of 2 (480 mg,
1.62 mmol) in THF (30 mL) was added dropwise over 5 min
to a solution of 2-amino-2-methylpropanol (302 mg, 3.40 mmol)
in THF (30 mL). The resulting colorless solution was stirred
for 15 h at ambient temperature. After this time the solvent
was removed in vacuo. The crude material was suspended in
diethyl ether and heated to 40 °C. After 1 h at this temperature
the mixture was filtered under suction and the solid was dried
under reduced pressure. The product was thus obtained as a
fine white microcrystalline solid. Yield: 720 mg, 94%. Anal.
Calcd for C24H34N4O2S2: C, 60.73; H, 7.22; N, 11.80. Found:
C, 60.58; H, 7.31; N, 11.50. 1H NMR (400 MHz, 298 K,
The complexes display low activity for the polymer-
ization of olefins, and this is perhaps a result of close
association between the presumed active species cation
and the counteranion, as indicated by NMR studies.
Exp er im en ta l Deta ils
Gen er a l Com m en ts. Where necessary, procedures were
carried out under an inert atmosphere of argon by using a
dual-manifold vacuum/argon line and standard Schlenk tech-
niques, or in an MBraun drybox. Solvents were dried by
refluxing for 3 days under dinitrogen over the appropriate
drying agents (sodium for toluene; potassium for THF, ben-
zene, and heptane; sodium-potassium alloy for diethyl ether,
petroleum ether, and pentane; calcium hydride for dichlo-
romethane, chlorobenzene, and 1-hexene) and were degassed
before use. Solvents were stored in glass ampules under argon.
All glassware and cannulae were stored in an oven (>373 K)
and flame dried immediately prior to use. Most chemicals and
reagents were purchased from either Aldrich Chemical Co. or
Acros Chemical Co. and used without further purification.
Deuterated solvents were freeze-thaw degassed and dried by
refluxing over potassium (or calcium hydride for d2-dichlo-
romethane) for 3 days before being vacuum distilled (trap-to-
trap) to a clean, dry Young’s tap ampule and being stored in
3
CDCl3): δ 9.53 (2H, s, NH), 7.84 (2H, d, J HH ) 8 Hz, Ar-H),
3
7.29 (2H, m, Ar-H), 7.15 (2H, d, J HH ) 7 Hz, Ar-H) 6.47 (2H,
3
s, NH) 4.18 (2H, s, OH), 3.51 (2H, d, J HH ) 6 Hz, CH2) 3.09
3
(2H, d, J HH ) 6 Hz, CH2) 1.95 (6H, s, Me), 1.35 (6H, s, Me),
1.12 (6H, s, Me). 13C{1H} NMR (100.6 MHz, 298 K, CDCl3): δ
181.8 (sulfonic Cq), 138.5, 138.3, 129.9, 127.8, 127.3, 124.9, (Ar),
70.4 (CH2), 58.8 (aliphatic Cq), 27.63, 22.1, 20.1 (Me). MS
(29) (a) Avebuj, C.; Eisen, M. S. J . Am. Chem. Soc. 1999, 121, 8755
(b) Volkis, V.; Nelkenbaum, E.; Lisovskii, A.; Hasson, G.; Semiat, R.;
Kapon, M.; Botoshansky, M.; Eishen, Y.; Eisen, M. S. J . Am. Chem.
Soc. 2003, 125, 2179.
(30) Carpenetti, D. W.; Kloppenburg, L.; Kupec, J . T.; Petersen, J .
L. Organometallics 1996, 15, 1572.

5072 Organometallics, Vol. 23, No. 21, 2004
Westmoreland et al.
(EI): m/z 474 [M+], 459 [M+ - CH3]. IR (Golden Gate ν cm-1):
1573, 1533, 1459, 1395, 1289, 1240, 1163, 1049, 969, 827, 780,
750.
mL) and filtered via cannula. Cooling of the concentrated
filtrate to -30 °C afforded the product as fine black prisms.
The material was collected by filtration and dried in vacuo.
Yield: 436 mg, 85%. Anal. Calcd for C38H42N4O2Ti: C, 71.92;
H2L. THF (30 mL) was added to a Schlenk vessel charged
with 3 (520 mg, 1.10 mmol), and the mixture was stirred to
dissolve the solid. A solution of sodium hydroxide (220 mg,
5.50 mmol) in water (5 mL) was added to a solution of
p-toluenesulfonyl chloride (460 mg, 2.41 mmol) in THF (5 mL).
This mixture was added dropwise via syringe to the solution
of 3. The resulting pale yellow solution was stirred for 15 h in
the absence of light. After this time the solution was washed
with water (2 × 20 mL) and the organic layer taken. The
aqueous washings were back-extracted with diethyl ether (2
× 20 mL). The combined organic phases were washed with
brine (1 × 30 mL) and dried over MgSO4. Concentration under
reduced pressure gave an off-white residue. The crude material
was heated to 120 °C for 2 h under vacuum. After this time
the product was obtained as a microcrystalline white solid.
Yield: 379 mg, 85%. Anal. Calcd for C24H30N4O2: C, 70.91; H,
7.44; N, 13.78. Found: C, 70.81; H, 7.48; N, 13.65. 1H NMR
(400 MHz, 298 K, CDCl3): δ 8.02 (2H, s, Ar-H), 7.21 (2H, t,
1
H, 6.67; N, 8.83. Found: C, 70.51; H, 6.70; N, 8.63. H NMR
3
(400 MHz, 298 K, CD2Cl2): δ 7.15 (4H, d, J HH ) 7 Hz, Ar-H),
7.06 (6H, m, Ar-H), 6.89 (2H, d, 3J HH ) 7 Hz, Ar-H), 6.85 (2H,
3
3
d, J HH ) 7 Hz, Ar-H), 6.79 (2H, t, J HH ) 7 Hz, Ar-H), 3.68
(2H, d, J ) 8 Hz, CH2), 2.95 (4H, s, CH2), 2.50 (2H, d, J ) 8
Hz, CH2), 1.86 (6H, s, Me), 0.97 (6H, s, Me), 0.67 (6H, s, Me).
13C{1H} NMR (100.6 MHz, 298 K, CD2Cl2): δ 167.6 (oxazoline
Cq), 148.3, 145.6, 140.4, 131.8, 129.3, 128.7, 128.4, 126.4, 125.2,
122.7 (Ar), 99.35, 82.1 (CH2), 65.8 (Cq), 28.6, 27.4, 20.5 (Me).
MS (EI): m/z 465 [M+ - CH2Ph, - Ph], 406 [H2L]. IR (Nujol
ν cm-1): 1556, 1260, 1204, 1064, 802.
[(H2L)TiCl4]. Dichloromethane (25 mL) was added at -78
°C to a Schlenk vessel charged with H2L (200 mg, 0.49 mmol)
and TiCl4‚2THF (129 mg, 0.49 mmol). The mixture was stirred
to dissolve the solids, and a dark red solution was obtained.
The cold bath was then removed, and the solution was allowed
to warm to ambient temperature. Stirring was continued for
15 h with the exclusion of light. After this time the solution
was concentrated to dryness and was washed with pentane.
The orange residue obtained was redissolved in dichlo-
romethane (10 mL), and pentane (5 mL) was added. Cooling
of the solution to -30 °C afforded the product as fine orange
prisms. The solid material was isolated by filtration and dried
in vacuo. Yield: 242 mg, 83%. Anal. Calcd for C24H30Cl4N4O2-
Ti: C, 48.75; H, 5.07; N, 9.30. Found: C, 48.79; H, 5.06; N,
3
3J HH ) 8 Hz, Ar-H), 6.87 (2H, d, J HH ) 8 Hz, Ar-H) 5.54 (2H,
s, NH) 3.76 (4H, s, CH2), 1.85 (6H, s, Me) 1.20 (12H, s, Me).
13C{1H} NMR (100.6 MHz, 298 K, CDCl3): δ 153.6, 137.8,
136.3, 127.8, 123.0, 115.6, (Ar), 83.2, (Cq), 76.8, (CH2) 66.9,
(Cq), 27.5, 18.8 (Me). MS (EI): m/z 406 [M+], 391 [M+ - CH3].
IR (Golden Gate ν cm-1): 3412, 2657, 2354, 2046, 1517, 1443,
1330, 1287, 746.
[Na 2L‚(THF )0.45]. To a Schlenk vessel charged with H2L
(200 mg, 0.49 mmol) and sodium hydride (60 mg, 2.46 mmol)
was added THF (20 mL). The resulting white suspension was
stirred for 15 h under reduced pressure. After this time the
stirring was ceased and unreacted NaH was allowed to settle.
The solution was filtered, and the colorless filtrate was
evaporated in vacuo to yield a microcrystalline off-white solid.
1
9.02. H NMR (400 MHz, 298 K, CD2Cl2): δ 7.24 (2H, s, NH),
3
3
7.13 (2H, t, J HH ) 8 Hz, Ar-H), 7.05 (2H, d, J HH ) 8 Hz, Ar-
3
H), 6.92 (2H, d, J HH ) 8 Hz, Ar-H), 3.98 (2H, d, J ) 9 Hz,
CH2), 3.84 (2H, d, J ) 9 Hz, CH2), 1.95 (6H, s, Me), 1.34 (6H,
s, Me), 1.00 (6H, s, Me). 13C{1H} NMR (100.6 MHz, 298 K, CD2-
Cl2): δ 162.1 (oxazoline Cq), 148.1, 137.0, 133.8, 128.7, 128.1,
125.4 (Ar), 80.1, (CH2), 60.8 (Cq), 27.3, 26.4, 19.6 (Me). MS
(EI): m/z 594 [M+]. IR (Nujol ν cm-1): 1611, 1202, 1052, 723.
[LTi(NMe2)2]. A Schlenk vessel was charged with tetrakis-
(dimethylamido)titanium (0.83 mL, 0.45 M in pentane, 0.37
mmol), and the bright yellow solution was stirred and cooled
to -78 °C. A solution of H2L (150 mg, 0.37 mmol) in diethyl
ether (15 mL) was added dropwise to the titanium amide
solution over 10 min. The addition was accompanied by a color
change to deep red. Light was excluded from the vessel, and
stirring was continued for 60 min at this temperature. After
this time the cold bath was removed and the reaction vessel
was allowed to warm to ambient temperature. Stirring was
continued for a further 15 h in the dark. The solvent was then
removed in vacuo to afford dark orange residue. Recrystalli-
zation from DCM/pentane at -30 °C gave the product as a
microcrystalline orange solid. The solid material was isolated
by filtration and dried under reduced pressure. Yield: 180 mg,
90%. Anal. Calcd for C28H40N6O2Ti: C, 62.22; H, 7.46; N, 15.55.
1
Analysis by H NMR spectroscopy in d5-pyridine showed the
composition of the product to be Na2L‚(THF)0.45. Yield: 222
1
mg, 94%. H NMR (400 MHz, 298 K, d5-pyridine): δ 8.77 (2H,
3
3
d, J HH ) 8 Hz, Ar-H), 7.18 (2H, t, J HH ) 8 Hz, Ar-H), 6.54
3
(2H, d, J HH ) 7 Hz, Ar-H), 3.63 (m, THF), 3.60 (2H, d, J ) 8
Hz, CH2), 3.34 (2H, d, J ) 8 Hz, CH2), 1.93 (6H, s, Me), 1.58
(m, THF), 1.31 (6H, s, Me), 1.22 (6H, s, Me). 13C{1H} NMR
(100.6 MHz, 298 K, d5-pyridine): δ 177.6 (oxazoline Cq), 138.2,
138.0, 137.24, 128.8, 122.0, 120.6 (Ar), 77.6 (CH2), 70.2 (Cq),
67.3 (THF), 32.8, 32.7 (Me), 28.2 (THF), 23.1 (Me).
[K2L‚(THF )0.33]. THF (20 mL) was added to a Schlenk
vessel charged with H2L (200 mg, 0.49 mmol) and potassium
hydride (100 mg, 2.46 mmol). The pale yellow suspension
obtained was stirred for 15 h under reduced pressure. After
this time the stirring was ceased and unreacted KH was
allowed to settle before filtering the solution. The filtrate was
evaporated in vacuo to yield a microcrystalline white solid.
1
Analysis by H NMR spectroscopy in d5-pyridine showed the
1
Found: C, 61.78; H, 7.19; N, 15.31. H NMR (400 MHz, 298
composition of the product to be K2L‚(THF)0.33. Yield: 218 mg,
3
88%. 1H NMR (400 MHz, 298 K, d5-pyridine): δ 8.67 (2H, d,
K, CD2Cl2): δ 7.30 (2H, t, J HH ) 8 Hz, Ar-H), 6.84 (2H, d,
3J HH ) 8 Hz, Ar-H), 6.79 (2H, d, 3J HH ) 7 Hz, Ar-H), 3.55 (2H,
d, J ) 8 Hz, CH2), 3.36 (12H, s, NMe2), 2.41 (2H, d, J ) 8 Hz,
CH2), 1.88 (6H, s, Me), 1.05 (6H, s, Me), 0.99 (6H, s, Me). 13C-
{1H} NMR (100.6 MHz, 298 K, CD2Cl2): δ 164.9 (oxazoline
Cq), 146.2, 139.8, 133.7, 127.6, 124.6, 124.5 (Ar), 80.3, (CH2),
64.2 (Cq), 48.4 (NMe2), 29.7, 28.0, 20.7 (Me) ppm. MS (CI): m/z
540 [M+], 510 [M+ - 2 × CH3]. IR (Nujol ν cm-1): 1601, 1579,
1067, 722.
3
3J HH ) 8 Hz, Ar-H), 7.09 (2H, t, J HH ) 8 Hz, Ar-H), 6.53 (2H,
3
d, J HH ) 7 Hz, Ar-H), 3.67 (m, THF), 3.65 (2H, d, J ) 7 Hz,
CH2), 3.47 (2H, d, J ) 7 Hz, CH2), 2.03 (6H, s, Me), 1.63 (m,
THF), 1.40 (6H, s, Me), 1.26 (6H, s, Me). 13C{1H} NMR (100.6
MHz, 298 K, d5-pyridine): δ 167.1 (oxazoline Cq), 156.2, 138.1,
137.9, 128.1, 122.2, 119.4 (Ar), 77.1 (CH2), 69.8 (THF), 66.4
(Cq), 32.6, 32.2 (Me), 27.8 (THF), 22.8 (Me).
[LTi(CH2P h )2]. To a Schlenk vessel charged with H2L (330
mg, 0.81 mmol) and titanium tetrabenzyl31 (334 mg, 0.81
mmol) was added toluene (20 mL). The dark purple solution
obtained was stirred for 15 h in the absence of light. After this
time the solvent was removed under reduced pressure to give
a dark red solid. This material was redissolved in heptane (30
[LTiCl2]. Meth od A. Toluene (15 mL) was added to a
Schlenk vessel charged with LTi(NMe2)2 (85 mg, 0.16 mmol).
The resulting orange solution was stirred and cooled to -78
°C. Chlorotrimethylsilane (0.1 mL, 88 mg, 0.80 mmol) was
added to the solution via cannula, and the mixture was stirred
for 15 min at this temperature in the absence of light. After
this time the cold bath was removed and the reaction vessel
was allowed to warm to ambient temperature. Stirring was
(31) Zucchini, Z.; Aibizatti, E.; Gianni, U. J . Organomet. Chem. 1971,
26, 357.

Group 4 Aminooxazolinates
Organometallics, Vol. 23, No. 21, 2004 5073
continued for a further 15 h in the dark. All volatiles were
then removed under reduced pressure to give a dark red
residue. This material was extracted with warm heptane (2
× 10 mL). Cooling of the combined extracts to 0 °C afforded
the product as fine brown prisms. The solid material was
isolated by filtration and dried under reduced pressure (yield
) 65 mg, 78%).
vacuo to leave a white microcrystalline solid. Yield: 343 mg,
86%. Anal. Calcd for C26H35Cl2N5O2Zr: C, 51.05; H, 5.77; N,
11.45. Found: C, 50.89; H, 5.83; N, 11.61. 1H NMR (500 MHz,
3
243 K, d8-toluene): δ 7.65 (1H, d, J HH ) 8 Hz, Ar-H), 7.27
3
3
(1H, t, J HH ) 8 Hz, Ar-H), 7.11 (1H, t, J HH ) 8 Hz, Ar-H),
3
3
6.95 (1H, d, J HH ) 8 Hz, Ar-H), 6.91 (1H, d, J HH ) 8 Hz,
3
2
Ar-H), 6.88 (1H, d, J HH ) 8 Hz, Ar-H), 3.68 (1H, d, J HH ) 8
2
2
Hz, CH2), 3.43 (1H, d, J HH ) 8 Hz, CH2), 3.41 (1H, d, J HH
)
Meth od B. A Schlenk vessel was charged with tetrakis-
(dimethylamido)titanium (138 mL, 0.45 M in pentane, 0.62
mmol), and the bright yellow solution was cooled to -78 °C
with stirring. A solution of H2L (250 mg, 0.62 mmol) in diethyl
ether (20 mL) was added dropwise to the titanium amide
solution over 10 min. The resulting deep red solution was
stirred for 2 h at this temperature in the absence of light. After
this time the cold bath was removed and the mixture was
allowed to warm to room temperature. Stirring was continued
for a further 15 h. All volatiles were then removed in vacuo to
yield a bright orange residue. The residue was redissolved in
toluene (20 mL) and cooled to 0 °C. Chlorotrimethylsilane (0.2
mL, 167 mg, 1.54 mmol) was added to the solution via cannula,
and a color change to dark brown was observed. The mixture
was stirred for 30 min following the addition and was then
allowed to warm to ambient temperature. Stirring in the
absence of light was continued for 15 h. All remaining volatiles
were then removed under reduced pressure to leave a dark
brown residue. This material was extracted with hot heptane
(3 × 15 mL), and the combined extracts were cooled to 0 °C.
The product was subsequently obtained as fine brown prisms.
Yield: 286 mg, 89%. Anal. Calcd for C24H28Cl2N4O2Ti: C,
55.09; H, 5.39; N, 10.71. Found: C, 55.14; H, 5.68; N, 10.88.
2
8 Hz, CH2), 3.31 (1H, d, J HH ) 8 Hz, CH2), 2.16 (1H, septet,
HNMe2), 2.14 (3H, s, Ar-Me), 1.96 (3H, s, Ar-Me), 1.81 (3H, d,
3J HH ) 6 Hz, HNMe2), 1.79 (3H, s, Ox-Me), 1.53 (3H, d, 3J HH
)
6 Hz, HNMe2), 1.41 (3H, s, Ox-Me), 1.18 (3H, s, Ox-Me), 1.16
(3H, s, Ox-Me). 1H NMR (500 MHz, 363 K, d8-toluene): δ 7.06
3
3
(2H, t, J HH ) 8 Hz, Ar-H), 7.00 (2H, d, J HH ) 7 Hz, Ar-H),
3
2
6.85 (2H, d, J HH ) 7 Hz, Ar-H), 3.78 (2H, d, J HH ) 8 Hz,
CH2), 3.65 (2H, d, 2J HH ) 8 Hz, CH2), 2.16 (1H, septet, HNMe2),
2.05 (6H, s, Ar-Me), 1.95 (6H, s, HNMe2), 1.59 (6H, s, Ox-Me),
1.24 (6H, s, Ox-Me). 13C{1H} NMR (100.6 MHz, 298 K,
d8-toluene): δ 169.3, 168.6 (oxazoline Cq), (144.5, 142.4, 138.2,
136.1, 133.7, 133.1, 127.8, 125.4, 124.6, 123.4, 119.0, 116.8 (Ar),
80.5, 80.2 (CH2), 63.1, 62.9 (Cq), 38.6, 38.0 (HNMe2), 27.0, 26.8,
26.6, 26.5, 19.0, 18.8 (Me). MS (EI): m/z 610 [M+], 566 [M+
-
HNMe2], 551 [M+ - Me, - HNMe2]. IR (Nujol ν cm-1): 2360,
1639, 1556, 1532, 1462, 1413, 1377, 1284, 1261, 1199.
[LHf(CH2P h )2]. Toluene (30 mL) was added at -78 °C to
a Schlenk vessel charged with H2L (240 mg, 0.59 mmol) and
tetrabenzyl hafnium32 (320 mg, 0.59 mmol). The mixture was
stirred to dissolve the solids, and a pale yellow solution was
obtained. The cold bath was removed after stirring for 10 min
at this temperature, and the reaction vessel was allowed to
warm to ambient temperature. Stirring was continued for a
further 15 h in the absence of light. The solution was then
concentrated in vacuo, and an off-white residue was obtained.
Recrystallization of this material from toluene/pentane at -30
°C gave the product as fine colorless prisms, which were
isolated by filtration, washed with pentane, and dried under
reduced pressure. Yield: 410 mg, 91%. Anal. Calcd for
3
1H NMR (400 MHz, 298 K, CD2Cl2): δ 7.16 (2H, t, J HH ) 8
3
3
Hz, Ar-H), 7.05 (2H, d, J HH ) 8 Hz, Ar-H), 7.02 (2H, d, J HH
) 8 Hz, Ar-H), 3.87 (2H, d, J ) 8 Hz, CH2), 2.67 (2H, d, J )
8 Hz, CH2), 1.93 (6H, s, Me), 1.31 (6H, s, Me), 1.29 (6H, s, Me).
13C{1H} NMR (100.6 MHz, 298 K, CD2Cl2): δ 170.1 (oxazoline
Cq), 144.4, 140.4, 131.7, 129.0, 128.4, 125.8 (Ar), 83.3, (CH2),
68.0 (Cq), 29.3, 27.2, 20.5 (Me). MS (EI): m/z 522 [M+], 487
[M+ - Cl]. IR (Nujol ν cm-1): 1560, 1262, 1078, 944, 802, 722.
[LZr (CH2P h )2]. A Schlenk vessel charged with H2L (315
mg, 0.77 mmol) and tetrabenzyl zirconium31 (353 mg, 0.77
mmol) was cooled to -78 °C. Toluene (30 mL) was added, and
the yellow mixture was stirred in the absence of light for 1 h.
After this time the cold bath was removed and the reaction
vessel was allowed to warm to ambient temperature. Stirring
was continued for a further 12 h in the dark. After this time
the solution was filtered. The bright yellow filtrate was
concentrated to dryness, and the residue obtained was washed
with pentane. The residue was redissolved in heptane (15 mL).
Cooling of the solution to 0 °C gave the product as bright yellow
needles. The solid material was collected by filtration and dried
in vacuo. Yield: 412 mg, 79%. Anal. Calcd for C38H42N4O2Zr:
C, 67.32; H, 6.24; N, 8.26. Found: C, 67.57; H, 6.48; N, 8.07.
C
38H42N4O2Hf: C, 59.64; H, 5.53; N, 7.32. Found: C, 59.84;
1
H, 5.79; N, 7.04. H NMR (400 MHz, 298 K, CD2Cl2): δ 7.05
(10H, m, Ar-H), 6.89 (4H, m, 3J HH ) 8 Hz, 4J HH ) 2 Hz, Ar-H),
6.71 (2H, m, Ar-H), 3.62 (2H, d, J ) 8 Hz, CH2), 2.55 (2H, d,
J ) 8 Hz, CH2), 1.90 (4H, s, CH2), 1.86 (6H, s, Me), 0.87 (6H,
s, Me), 0.63 (6H, s, Me). 13C{1H} NMR (100.6 MHz, 298 K, CD2-
Cl2): δ 167.4 (oxazoline Cq), 145.3, 143.5, 140.5, 132.8, 128.9,
128.4, 128.3, 126.5, 125.1 121.9 (Ar), 82.5, 76.0 (CH2), 64.0 (Cq),
28.8, 27.8, 20.5 (Me). MS (EI): m/z 675 [M+ - CH2Ph] 584
[M+ - 2 × CH2Ph]. IR (Nujol ν cm-1): 1562, 1284, 1200, 1072,
959, 790, 723, 694.
Eth ylen e P olym er iza tion s. Polymerizations were per-
formed at ca. 1 atm in a 500 mL round-bottom Schlenk flask.
The vessel was evacuated and filled with argon. Toluene (150
mL) and either triisobutylaluminum (2.0 mL, 0.086 M in
toluene, 0.17 mmol) or methylaluminoxane (10 wt % solution
in toluene, 1000 equiv relative to precatalyst) were added to
the flask, and the mixture was stirred. Approximately 20 mL
of this solution was transferred to a Schlenk vessel charged
with precatalyst (10 mg, ca. 15 µmol, 1 equiv) and, when
triisobutylaluminum was employed, catalyst activator (1 equiv).
A colored solution was obtained, which was then transferred
to the polymerization flask. The system was evacuated and
then reopened to a continuous supply of ethylene gas. The
mixture was stirred for 45 min before the gas flow was closed,
and the polymerization was stopped by the addition of
methanol (50 mL). Hydrochloric acid (50 mL, 2.0 M in
methanol) was then added, and the resulting mixture was
stirred for 10 min. After this time the flask was allowed to
stand for 30 min and the resulting polymer was separated by
filtration and dried at 90 °C to constant mass.
3
1H NMR (400 MHz, 298 K, CD2Cl2): δ 7.08 (4H, t, J HH ) 8
3
Hz, Ar-H), 7.01 (6H, m, Ar-H), 6.88 (2H d, J HH ) 8 Hz, Ar-
H), 6.80 (4H, m, Ar-H), 3.60 (2H, d, J ) 8 Hz, CH2), 2.53 (2H,
d, J ) 8 Hz, CH2), 2.38 (2H, d, J ) 8 Hz, CH2), 2.10 (2H, d, J
) 8 Hz, CH2), 1.85 (6H, s, Me), 0.87 (6H, s, Me), 0.77 (6H, s,
Me). 13C{1H} NMR (100.6 MHz, 298 K, CD2Cl2): δ 166.8
(oxazoline Cq), 144.8, 143.1, 140.4, 132.6, 130.0, 129.1, 128.3,
126.2, 124.8, 122.9 (Ar), 81.2, 71.0 (CH2), 64.3 (Cq), 29.3, 27.9,
20.5 (Me). MS (EI): m/z 585 [M+ - CH2Ph], 494 [M+ - 2 ×
CH2Ph]. IR (Nujol ν cm-1): 1560, 1262, 1202, 1066, 802, 722.
[LZr (NMe2H)Cl2]. A solution of Zr(NMe2)2Cl2(THF)225 (257
mg, 0.65 mmol) in toluene (15 mL) was cooled to -78 °C with
stirring. To this was added a solution of H2L in toluene (10
mL). The resulting colorless mixture was stirred for 20 min
at this temperature. The cold bath was then removed, and the
solution was allowed to warm to ambient temperature. Stirring
was continued for a further 15 h. After this time the volatiles
were removed under reduced pressure and a white residue was
obtained. The solid was washed with pentane and dried in
(32) Felten, J . J .; Anderson, W. P. J . Organomet. Chem. 1972, 36,
87.

5074 Organometallics, Vol. 23, No. 21, 2004
Westmoreland et al.
1-Hexen e P olym er iza tion s. Polymerizations were per-
formed in a standard Schlenk vessel. Toluene (15 mL) and
either triisobutylaluminum (2.0 mL, 0.086 M in toluene, 0.17
mmol) or methylaluminoxane (10 wt % solution in toluene, 500
equiv relative to precatalyst) were added to the vessel, and
the mixture was stirred. The solution was added to a Schlenk
vessel charged with precatalyst (10 mg, ca. 15 µmol, 1 equiv)
and, when triisobutylaluminum was employed, catalyst activa-
tor (1 equiv). To the colored solution thus obtained was added
1-hexene (40 mL), and the resulting mixture was stirred for
45 min. After this time the polymerization was stopped by the
addition of methanol (50 mL). Hydrochloric acid (50 mL, 2.0
M in methanol) was then added, and the resulting mixture
was stirred for 10 min. After this time the vessel was allowed
to stand for 30 min. All volatiles were removed in vacuo to
leave an off-white residue. This material was extracted with
toluene, and the combined extracts were precipitated into
acidic methanol. Polymer obtained in this way was dried under
reduced pressure.
reflections (SADABS). The structures were solved by direct
methods (SHELXS) with additional light atoms found by
Fourier methods. For H2L hydrogen atoms attached to N(30)
and N(8) were located from a difference map. They were given
isotropic displacement parameters equal to 1.5 times the
equivalent isotropic displacement parameter of the nitrogen
atom to which they are attached, and their positions were
allowed to refine. The crystal structure of [(H2L)TiCl4] contains
one molecule of the crystallization solvent, dichloromethane,
within the asymmetric unit of the unit cell. For [LHf(CH2Ph)2]
a region of diffuse electron density, probably due to the
presence of disordered solvent, was located. This was modeled
as three half-occupancy carbon atoms. All non-hydrogen atoms
were refined anisotropically. All H atoms were constrained
with a riding model; U(H) was set at 1.2 (1.5 for methyl and
amido hydrogen atoms as applicable) times Ueq for parent
atom. Programs used were Bruker AXS SMART (control),
SAINT (integration), and SHELXTL for structure solution,
refinement, and molecular graphics.
Cr ysta llogr a p h y. Crystals of H2L were obtained as fine
colorless prisms from a concentrated solution in dichloro-
methane, via slow evaporation of the solvent at ambient
temperature. Crystals of [(H2L)TiCl4] were obtained as fine
orange prisms by cooling a concentrated solution in dichlo-
romethane to -30 °C. Crystals of [LHf(CH2Ph)2] were similarly
obtained from a concentrated solution in heptane. Crystals
were coated in an inert oil prior to transfer to a cold nitrogen
gas stream on a Bruker-AXS SMART three-circle CCD area
detector diffractometer system equipped with Mo KR radiation
(λ ) 0.71073 Å). Data were collected using narrow (0.3° in ω)
frame exposures. Intensities were corrected semiempirically
for absorption, based on symmetry-equivalent and repeated
Ack n ow led gm en t. P.S. thanks EPSRC for support.
I.W. is a University of Warwick Postgraduate Research
Fellow and a Society of Chemical Industry Messel
Scholar.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, atomic coordinates, distances and angles, and hydrogen
coordinates. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM049518S