Titanium Lewis acids for asymmetric catalysis: Synthesis and structural characterization of dichloro[diolato(2-)-κO, κO′]bis(solvent)titanium ([TiCl2(diolato)(solvent)2]) complexes

Article abstract of DOI:10.1002/1522-2675(200206)85:6<1597::AID-HLCA1597>3.0.CO;2-N

The complexes [TiCl₂{(R,R)-TADDOLato}(DME)]·MeCN (3), and [TiCl₂{(R,R)-1-Nph-TADDOL-ato}(MeCN)₂] ·CH₂Cl₂ (4b) (DME = 1,2-dimethoxyethane; (R,R)-TADDOLato=(4R,5R)-2,2-dimethyl-α,α,α′, α′-tetraphenyl-1,3-dioxolane-4,5-dimethanolato(2-)-κO, κO′; (R,R)-1-Nph-TADDOLato = (4R,5R)-2,2-dimethyl-α,α,α′,α′-tetra (naphthalen-1-yl)-1,3-dioxolane-4,5-dimethanolato(2-)-κO,κO ′) were prepared and isolated in high yield as stable crystalline materials (Scheme 1). They constitute ideally suited and easy-to-handle catalyst precursors for a large number of Ti-catalyzed asymmetric reactions, for which they have been previously generated in situ. The X-ray crystal structures of 3 and 4b show a distorted octahedral geometry around Ti with the chloro ligands in mutual trans positions (Figs. 5 and 6). The new chiral diols α-(1S,3R)-3-hydroxy-2,2,3-trimethylcyclopentyl]-α- phenylbenzenemethanol (13a), derived from camphoric acid (5), and (M)-6,6′-dimethyl-α,α,α′,α′ -tetraphenyl[1,1′-biphenyl]-2,2′-dimethanol (15) were prepared (Schemes 3 and 4). These new ligands are able to form mononuclear complexes with the Ti^IVCl₂ fragment. The corresponding complex 14 derived from 13a was characterized by X-ray as a mixed THF/MeCN adduct.

Full text of DOI:10.1002/1522-2675(200206)85:6<1597::AID-HLCA1597>3.0.CO;2-N

Helvetica Chimica Acta Vol. 85 (2002)
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Titanium Lewis Acids for Asymmetric Catalysis: Synthesis and Structural
Characterization of Dichloro[diolato(2À)-kO,kO']bis(solvent)titanium
([TiCl2(diolato)(solvent)2]) Complexes
by Lukas Hintermann, Diego Broggini, and Antonio Togni*
Department of Chemistry, Swiss Federal Institute of Technology, ETH Hˆnggerberg, CH-8093 Z¸rich
(Tel: 016322236; e-mail: togni@inorg.chem.ethz.ch)
The complexes [TiCl2{(R,R)-TADDOLato}(DME)] ¥ MeCN (3), and [TiCl2{(R,R)-1-Nph-TADDOL-
ato}(MeCN)2] ¥ CH2Cl2 (4b) (DME ˆ 1,2-dimethoxyethane; (R,R)-TADDOLato ˆ (4R,5R)-2,2-dimethyl-
a,a,a',a'-tetraphenyl-1,3-dioxolane-4,5-dimethanolato(2À)-kO,kO';
(R,R)-1-Nph-TADDOLato ˆ (4R,5R)-
2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxolane-4,5-dimethanolato(2À)-kO,kO') were prepared
and isolated in high yield as stable crystalline materials (Scheme 1). They constitute ideally suited and easy-
to-handle catalyst precursors for a large number of Ti-catalyzed asymmetric reactions, for which they have been
previously generated in situ. The X-ray crystal structures of 3 and 4b show a distorted octahedral geometry
around Ti with the chloro ligands in mutual trans positions (Figs. 5 and 6). The new chiral diols a-(1S,3R)-3-
hydroxy-2,2,3-trimethylcyclopentyl]-a-phenylbenzenemethanol (13a), derived from camphoric acid (5), and
(M)-6,6'-dimethyl-a,a,a',a'-tetraphenyl[1,1'-biphenyl]-2,2'-dimethanol (15) were prepared (Schemes 3 and 4).
These new ligands are able to form mononuclear complexes with the TiIVCl2 fragment. The corresponding
complex 14 derived from 13a was characterized by X-ray as a mixed THF/MeCN adduct.
1. Introduction. Complexes of the general formula [TiCl2(OR)2] serve as Lewis
acid catalysts or mediators (i.e., in stoichiometric amounts) in allylation reactions of
aldehydes in the presence of allylstannanes, hetero-Diels-Alder reactions, ene reactions,
Michael additions, Mukaiyama silyl-aldol condensations, and other reactions (see review
[1]). Of particular interest are those complexes derived from an enantiomerically pure
chelating diol. Thus, [TiCl2(BINOLato)] complexes (BINOLato ˆ [1,1'-binaphtha-
lene]-2,2'-diolato(2À)-kO,kO') have found specific use in enantioselective Mukaiyama
aldol reactions [2], cyanosilylation of aldehydes [2], carbonyl-ene reactions [3],
carbonyl allylsilane or allylstannane additions [4 6], ene cyclizations [7], (hetero)-
Diels-Alder reactions [8], and others (for a review, see [9]). Complexes of the type
[TiCl2(TADDOLato)]1) serve as catalysts in enantioselective cyanosilylations [10],
(hetero)-Diels-Alder [11 15], [2 ‡ 2] cycloadditions [16 18], [2 ‡ 3] cycloadditions
[19], 1,3-dipolar cycloadditions [20], nitro-aldol reactions [21], fluorinations [22], and
others (for reviews, see [9][23]).
When inspecting the procedures for the generation of the titanium catalysts used in
the reactions mentioned above, one notes that they are prepared in situ according to
1
)
(R,R)-TADDOL 1 ˆ (4R,5R)-2,2-dimethyl-a,a,a',a'-tetraphenyl-1,3-dioxolane-4,5-dimethanol; (R,R)-1-
Nph-TADDOL 2 ˆ (4R,5R)-2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxolane-4,5-dimethanol;
(R,R)-TADDOLato ˆ (4R,5R)-2,2-dimethyl-a,a,a',a'-tetraphenyl-1,3-dioxolane-4,5-dimethanolato(2À)-
kO,kO'; (R,R)-1-Nph-TADDOLato ˆ (4R,5R)-2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxo-
lane-4,5-dimethanolato(2À)-kO,kO'.

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different protocols and sometimes in the presence of molecular sieves, the role and
mode of action of which remains unclear [11][21][23]. In connection with our recent
work on catalytic enantioselective fluorination [22], chlorination, and bromination
[24], we explored in some detail the synthesis and complex chemistry of [TiCl2(TAD-
DOLato)(solvent)] species. This led to the isolation and characterization of the
complexes [TiCl2(TADDOLato)(DME)] ¥ MeCN (3; DME ˆ 1,2-dimethoxyethane)
and [TiCl2(1-Nph-TADDOLato)(MeCN)] (4a) (Scheme 1)1). These materials proved
to be handy catalyst precursors for the enantioselective halogenation reactions. Our
interest in chiral dichloro(diolato)titanium Lewis acids with potential use in
asymmetric catalysis led us to study additional systems as well. Thus, two enantiomeri-
cally pure diols were prepared from (‡)-camphoric acid (5) and converted to the
corresponding TiCl2 complex derivatives. Furthermore, we explored for the first time
an enantiomerically pure a,a,a',a'-tetraphenyl[1,1'-biphenyl]-2,2'-dimethanol and its
unstable Ti complex.
Scheme 1
1-Nph ˆ naphthalen-1-yl, DME ˆ 1,2-dimethoxyethane
a) 1. [TiCl2(OiPr)2], MeCN. 2. Evaporation. 3.àMeCN, DME (for 3). Complex 3 crystallized with ca. 1 equiv.
of MeCN as solvent of crystallization.
2. Results and Discussion. 2.1. Preparation and Characterization of Complexes
Containing TADDOLato Ligands. For the synthesis of dichloro(diolato)titanium
complexes, the most popular in situ preparation method is the reversible ligand-
exchange reaction starting from [TiCl2(OiPr2)] and the diol ligand in, e.g., toluene [25].
This reaction is sometimes performed in the presence of powdered molecular sieves, or
with subsequent evaporation of the solution. The second method was thought to
azeotropically remove iPrOH from the equilibrium, whereas the role of the molecular
sieves is not clear [11][23][26]. However, when we prepared complex solutions starting
from the simple (R,R)-TADDOL1) (1) and [TiCl2(OiPr)2] in toluene, we found by
i
1H-NMR spectroscopy that PrOH was still present in materials obtained after
evaporation, probably as ligand completing the coordination sphere of Ti ([TiCl2-
(TADDOLato)(iPrOH)n]; n ꢀ 2). However, these materials were not crystalline and
still contained impurities. On the other hand, if the ligand-exchange reaction was
carried out in the coordinating solvent MeCN2), a single evaporation of the reaction
i
solution removed most of the PrOH and yielded a material of the composition
We note that TADDOL 1 is hardly soluble in MeCN, but slowly dissolves on addition of [TiCl2(OiPr)2] to a
2
)
suspension of the ligand in the same solvent, thus indicating that complex formation is relatively fast.

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[TiCl2(TADDOLato)(MeCN)n] (n ꢁ 2). This material was not easily purified due to its
high solubility in MeCN and loss of coordinated solvent on drying, but it could be
converted to the highly crystalline complex [TiCl2(TADDOLato)(DME)] ¥ MeCN (3)
by simple addition of a stoichiometric amount of DME (1,2-dimethoxyethane) to the in
situ prepared MeCN solution, whereupon 3 precipitated and could, thus, be isolated
analytically pure in a yield of up to 90%.
Complex 3 was characterized by X-ray, NMR, and elemental analysis (C, H, N, Cl).
It is a white crystalline material that can be handled for prolonged periods in air and
stored in closed vessels for months. It is soluble in CH2Cl2, CHCl3, and THF, but only
sparingly so in MeCN. The MeCN molecule (actually only ca. 0.8equiv. per complex
1
unit are present, as shown by X-ray and H-NMR) is not coordinated to the metal
center, but is solvent of crystallization. Under high vacuum at room temperature, some
MeCN, but no DME was lost. The stability of 3 is also reflected by its melting point of
1
2008 (with decomposition; browning from 1908). The H- and 13C-NMR spectra of 3
give the sets of signals expected for a C2-symmetric species (Fig. 1). The signal patterns
remain unchanged at low temperature (233 K in CDCl3), thus indicating that the
species actually observed is the most stable isomer containing the Cl ligands in mutual
trans-diaxial position, as observed for the solid-state structure (vide infra).
Fig. 1. 1H-NMR (300 MHz, CDCl3) of [TiCl2(TADDOLato)(DME)] ¥ MeCN (3)
Upon addition of 1-Nph-TADDOL1) (2) to [TiCl2(OiPr)2] in MeCN, rapid ligand
exchange occurred, as indicated by a color change from almost colorless to yellow. Slow
evaporation under high vacuum of such solutions led to the precipitation of a beige
powder of the composition [TiCl2(1-Nph-TADDOL)(MeCN)n] (n ꢁ 2) that is only
sparingly soluble in many solvents (CDCl3, CH2Cl2, MeCN, THF, C6H6)3). Although
3
)
Precipitation or crystallization may sometimes also occur spontaneously, without previously evaporating
solvents.

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this material was easily prepared and isolated in good yield, we were not able to obtain
a consistent elemental analysis, possibly due to loss of MeCN on drying under high
vacuum. Redissolution of this material in CH2Cl2/MeCN yielded, on evaporation of
CH2Cl2, a bright yellow powder of the composition [TiCl2(1-Nph-TADDOLato)-
(MeCN)] (4a). Under an inert atmosphere, this compound is stable for at least several
months, but it slowly deteriorates in air as shown by the darkening of samples stored in
vessels occasionally opened to air. However, even these samples performed in our
catalytic fluorination reaction [22] with reactivity and selectivity equal to fresh samples.
The substance 4a is only slightly soluble in CDCl3, CH2Cl2, MeCN, and THF, and its
exact structure is not known. Upon slow evaporation from MeCN/CH2Cl2 solutions, the
complex [TiCl2(1-Nph-TADDOLato)(MeCN)2] ¥ CH2Cl2 (4b) was obtained as trans-
parent yellow crystals suited for an X-ray-crystal-structure study (vide infra). It is thus
reasonable to assume that the species containing two coordinated MeCN molecules is
dominant in solution with excess MeCN, whereas, at lower MeCN concentration, the
monosolvated form precipitates.
Crystalline mixed solvates [TiCl2(1-Nph-TADDOLato)(THF)n(MeCN)2Àn] ¥
CH2Cl2 were obtained by slow evaporation from MeCN/CH2Cl2/THF solutions, but
the addition of DME or of the less volatile 1-(benzyloxy)-2-methoxyethane to 4a in
MeCN/CH2Cl2 did not afford the corresponding ether complexes. This is in contrast to
the case of 3, which is, apparently, a very stable complex with DME. We assume that
the increased steric demand of the naphthalenyl-substituted TADDOL is responsible
for the relative instability of the corresponding adducts with chelating diethers.
2.2. Synthesis of a Camphor-Derived Ligand and Formation of Titanium Complexes.
Several enantiomerically pure diol ligands can be derived in a few steps from (‡)-
camphoric acid (5). Camphoric anhydride (6) reacted with PhMgBr to yield a 1.6 :1
mixture of regioisomeric diphenylcampholides 7a and 7b, after cyclization of the
intermediate hydroxy acids [27] (Scheme 2)4).
It has been described in the older literature that the main isomer 7a is the only
product isolated from the reaction of dimethyl camphorate (8) with PhMgBr [27], and,
indeed, on repetition of this reaction under these conditions, we could not detect the
minor isomer 7b in the crude product, meaning that the regioselectivity in that case
must be in the range of 7a/7b ꢂ 50 :1. The difference in regioselectivity for the reaction
of 6 or 8 can be rationalized by comparing the different directions of attack, according
to the Felkin-Ahn model (Fig. 2). The energetically most-favored pathway of attack to
8 (case A) cannot be realized analogously for 6 (case B), as the carbonyl groups are
fixed in a ring system.
LiAlH4 Reduction of campholide 7a afforded the 1,5-diol 9 as a new potential
ligand. An in situ complex was generated upon reaction with [TiCl2(OiPr)2] in MeCN,
followed by evaporation. The 1H-NMR analysis gave clear evidence of the formation of
a single complex species 10. In particular, a single set of new signals, shifted with respect
to those of the free ligand 9, is observed (Fig. 3). Furthermore, a singlet at 2.03 ppm is
assigned to coordinated MeCN, and broadened signals due to one of the Ph groups
4
)
The regioisomer ratio was determined from a small-scale reaction with PhMgCl at 08, cyclization of the
hydroxy acids with Ac2O, and 1H-NMR analysis of the crude product. In the large-scale reaction, the
isomers were isolated, after purification, in a ratio 7a/7b of 3 :1.

Helvetica Chimica Acta Vol. 85 (2002)
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Scheme 2
a) PhMgCl or PhMgBr, THF. b) Ac2O, CH2Cl2, 508; 57% 7a ‡ 18% 7b. c) PhMgCl, THF, 83%. d) LiAlH4,
tBuOMe; 82%. e) [TiCl2(OiPr)2], MeCN; evaporation.
Fig. 2. Regioselectivityof the PhMgCl attack rationalized bythe Felkin-Ahn model: A from 8 and B from 6
indicate hindered rotation. This same phenomenon is observed in the diphenylcam-
pholide 7a, where the Ph2C fragment is part of a ring system. The hindered rotation of
one Ph group of 10 is, therefore, taken as an indication of chelate-ring formation.
We have used the in situ formed complex 10 for the catalytic fluorination reaction,
however, with only limited success [28]. In a first attempt to prepare a chiral diol with
increased steric requirements, the reaction of campholide 7a with an excess of MeMgCl
gave only the methyl ketone 11 (Scheme 3) in low yield, instead of the expected bis-
tertiary alcohol. Finally, an isomeric mixture of the diphenylmethanols 13a/13b could
be obtained from the corresponding mixture of campholytolactones 12a/12b (derived
form Pb(OAc)4 oxidation of (‡)-camphoric acid (5) [29 31]) upon reaction with
PhMgBr (Scheme 3). Compounds 13a/13b could easily be separated by chromatog-
raphy.
The diol 13a was submitted to in situ complex formation with [TiCl2(OiPr)2] in
MeCN, as usual. However, it is interesting to note that a crystalline compound 14 could
be obtained only from solvent mixtures of THFand MeCN. This material was shown by
X-ray analysis (vide infra) to be a MeCN/THF 1:1 solvate, [TiCl2 (13a-ato)(THF)-
(MeCN)] ¥ MeCN (14).
2.3. A Chiral Bis(trityl alcohol) (ˆa,a,a',a'-Tetraphenyl[1,1'-biphenyl]-2,2'-dime-
thanol) Ligand. When one considers the frequent occurrence of both the 1,1'-biaryl unit

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Fig. 3. 1H-NMR (300 MHz, CDCl3) Spectra of diol 9 and the in situ formed complex 10
and the diphenylmethanol moiety [23] in ligands for asymmetric catalysis, it is somewhat
surprising that these two structural elements have not yet been combined into one
ligand. We present here a new enantiomerically pure bis(trityl alcohol) derivative 15,
easily obtained in high yield from double addition of a [1,1'-biaryl]-2,2'-diyldilithium
(generated from the diiodo compound 16 and tBuLi) to benzophenone (Scheme 4)5).
On treating diol 15 with an equimolar amount of [TiCl2(OiPr)2] in MeCN and THF
(added to increase solubility), the resulting −catalyst× solution was inactive in a
fluorination reaction [22], and by TLC analysis, 15 could no longer be detected in the
reaction mixture, although it was used in slight excess. Most probably, 15 had cyclized to
the corresponding ether under the influence of traces of HCl, as previously described
by Wittig and Petri for a similar diol [32]. We, thus, repeated the in situ preparation of
the complex in the presence of the sterically hindered base 2,6-di(tert-butyl)pyridine
which is known to remove traces of protic acid without blocking Lewis acid metal
centers [34][35]. This time, the corresponding solution gave a single TLC spot for the
ligand 15, and it catalyzed a fluorination reaction, albeit with low activity and
stereoselectivity [28]. We are, thus, confident that a complex 17 had formed in solution,
and that such species may find future applications in Lewis acid catalyzed reactions.
2.4. Solid-State Structure of TADDOL Complexes 3 and 4b and of Complex 14. The
structure of some (TADDOLato)titanium complexes has been determined by X-ray
5
)
A similar substance has been prepared in a enantiomerically pure state by Wittig and Petri in 1933 [32]. A
series of related racemic substances have been reported in 1996 [33]. In both cases, the use of these
molecules as ligands for catalysis was not considered.

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Scheme 3
a) MeMgCl, THF, 908, 3 d; 34% (36% 7a re-isolated). b) [31]. c) PhMgBr, THF; 51% 13a ‡ 18% 13b.
d) [TiCl2(OiPr)2], MeCN; then THF, MeCN.
Scheme 4
a) 1. tBuLi, THF, À788. 2. Ph2CO; 94%. b) [TiCl2(OiPr)2], 2,6-di(tert-butyl)pyridine, MeCN, THF.
crystallography previously. Thus, known derivatives include the spirocyclic alkoxide
{3[Ti(TADDOLato)2]} ¥ 0.5 Et2O [36], the chloro-cyclopentadienyl complexes
[TiCl(h5-cp)(TADDOLato)] [37] and [{Ti(h5-cp)(TADDOLato)}2(m2-O)] [38], the
latter being a partial hydrolysis product of the former. Most important for our study are
the [TiCl2(TADDOLato)] derivatives [TiCl2(TADDOLato){(3-cinnamoyl)-1,3-oxa-
zolidin-2-one}] ¥ CH2Cl2 (18) [39], [TiCl2(TADDOLato)(diphos)] (19) [40a], and
[TiCl2(TADDOLato)(THF)2] (20) [40b] described more recently (Fig. 4). The
structure of compounds 3 and 4 has been reported in preliminary form from our
laboratories in conjunction with the first catalytic asymmetric fluorination [22]. We note

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Fig. 4. Three [TiCl2(TADDOLato)] complexes whose crystal structures have been reported previously: 18 [39],
19 [40a], and 20 [40b]
that 4 is the first reported structure of a [Ti(TADDOLato)] complex where the
TADDOL ligand is different from 1. The Table provides a summary of important bond
distances and angles for the three complexes 3, 4b, and 14. One notes that the bonding
parameters of the three compounds define a distorted octahedral geometry around the
Ti-center, with the two Cl ligands in mutual axial positions, with respect to the
equatorial plane containing the diol O-atoms and solvent donor atoms. The extent of
the distortion is very similar for 3, 4b, and 14. Therefore, the most-relevant geometrical
features will be pointed out explicitly for 3 only.
Complex 3 crystallizes in form of colorless transparent platelets of up to millimeter
size. The X-ray structural analysis was complicated by the presence of MeCN solvent of
crystallization forming layers, through which it can diffuse. As a result, there are solvent
positions with partial occupancy. This observation is in line with the 1H-NMR
quantification of MeCN, where less than 1 equiv. was found. Crystals belong to the
orthorhombic crystal system, space group P212121, and the unit cell contains one and a
half independent molecular units. In the fully asymmetric unique molecule, shown in
Fig. 5, the coordinated solvent DME assumes a pseudo-meso configuration, i.e., with
the two Me groups in mutual cis orientation. The axial Cl ligands and the Ti-atom span
an angle Cl(1)ÀTiÀCl(2) of 164.97(10)8. This deviation from an idealized 1808 for an
octahedral geometry is typical for all [TiCl2(OR)2(L)2] complexes so far structurally
characterized, as reflected also by the corresponding parameter of, e.g., 18 (164.48 [39])
and 19 (157.28 [40a]). The TiÀO(olato) bond lengths, as well as the angles around the
olato O-atom (each 147.0(4)8) are in line with partial multiple-bond character for the
TiÀO bonds. The relatively long bond distances to the DME O-atoms from Ti
(TiÀO(5) 222.5(5) pm; TiÀO(6) 216.4(6) pm) and the acute angle O(5)ÀTiÀO(6) of
73.7(2)8 constitute a geometric indication that the solvent molecule is only weakly
bound to Ti. It is also known that O-donors forming 5-membered chelate rings usually
do not afford very stable mononuclear complexes with TiIV [25]. The position of the Ph
groups can be defined as pseudo-axial and pseudo-equatorial, respectively, relative to
the plane of the dioxolane ring. However, relative to the main coordination plane of Ti
(TiO4), they show pseudo-mirror symmetry, and the coordination plane is bisecting the
angles C(12)ÀC(1)ÀC(18) and C(30)ÀC(4)ÀC(24). However, the relevant aspect
concerning the aryl substituents in complexes of TADDOLs being very important
when discussing chiral induction in catalytic reactions is their orientation with respect
to an axial coordination site, here occupied by a Cl ligand. Thus, one observes that the

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Table. Selected Bond Lengths [ä] and Bond Angles [8] for the Complexes 3, 4b, and 14
3
4b
14
Bond distances:
TiÀCl(1)
2.337(2)
2.342(3)
1.752(5)
1.765(5)
2.3343(13)
2.3610(16)
2.3772(16)
1.755(4)
TiÀCl(2)
2.3622(13)
1.780(3)
1.773(3)
TiÀO(1)
TiÀO(2)
1.764(3)
TiÀO(5)/TiÀO(6)
TiÀN(1)/TiÀN(2)
TiÀN(1)/TiÀO(6)
Bond angles:
Cl(1)ÀTiÀCl(2)
O(1)TiÀO(2)
O(5)ÀTiÀO(6)
N(1)ÀTiÀN(2)
N(1)ÀTiÀO(6)
TiÀO(1)ÀC
2.225(5)/2.164(6)
2.283(4)/2.264(4)
2.313(6)/2.222(4)
164.97(10)
98.6(2)
73.7(2)
162.11(5)
97.18(12)
156.32(7)
95.17(16)
83.25(14)
86.16(16)
147.6(3)
150.6(3)
147.0(4)
147.0(5)
145.8(2)
148.0(2)
TiÀO(2)ÀC
Fig. 5. ORTEP View (30% probability ellipsoids) of the unique independent complex molecule in
[TiCl2(TADDOLato)(DME)] ¥ MeCN (3). H-Atoms and solvent of crystallization are omitted. C-Atoms are
numbered without bearing atom symbols.
four aryl groups are pairwise characterized by an −edge-on and −face-on× orientation,
respectively, as previously noted also in the structure of free TADDOLs [23], as well as
for chiral chelating diphosphines.
As illustrated in Fig. 6, the same description applies to the bis(acetonitrile) solvate
[TiCl2(1-Nph-TADDOLato)(MeCN)2] ¥ CH2Cl2 (4b; obtained as orthorhombic crys-
tals, space group P212121) where the distinction between −edge-on× and −face-on×
naphthalenyl group is particularly pronounced. The −edge-on× naphthalenyl groups
point away from Ti and toward the dioxolane ring where they come in close proximity
to the Me groups. This is also reflected in the 1H-NMR spectrum of 4 in CDCl3 (with

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Fig. 6. ORTEP View (30% probability ellipsoids) of [TiCl2(1-Nph-TADDOLato)(MeCN)2] ¥ CH2Cl2 (4b). H-
Atoms and solvent of crystallization are omitted for clarity.
excess CD3CN for solubilization) by a shift to lower frequency of the signals for the Me
groups (d(H) ˆ À0.27). As we reported elsewhere [41], the −face-on× naphthalenyl
groups are a key factor in determining stereoselectivity in the catalytic fluorination
reaction of b-keto esters by virtue of their shielding of one enantioface of the
coordinated enolate.
The coordinating solvent molecules in 14 (monoclinic crystals, space group P21) occupy
the two different coordination sites in the equatorial plane of Ti according to their steric
requirements: the small linear MeCN lies cis to the sterically demanding Ph2CO unit,
whereas the THF molecule resides next to the primary alcoholato function (Fig. 7).
The bond lengths TiÀO(olato) are shorter than typical TiÀO single bonds (ca. 18 5 pm
Fig. 7. ORTEP View (30% probability ellipsoids) of [TiCl2(13a-ato)(THF)(MeCN)] ¥ MeCN (14)

Helvetica Chimica Acta Vol. 85 (2002)
1607
[42]), but consistent with data from the TADDOL complexes discussed above. This
applies also to all other features of the distorted octahedral geometry around the Ti-atom.
3. Conclusions. It has been pointed out by Duthaler and Hafner that, to obtain
stable complexes of the dichlorotitanium/chelating diolato type, the chelating diol
should be of the 1,3, 1,4, or 1,5 type [25]. Complexes with 1,2-diols tend to form
multinuclear species with alcoholato ligands bridging two metal centers, whereas diols
with rather distant coordinating groups tend to form polymeric complexes [25][43].
TADDOL-Type 1,4-diol ligands are well-pre-organized for complex formation with Ti-
centers, but complexes can also easily be obtained from other diols fulfilling the
requirements mentioned above. Although it is common practice to prepare such
species in situ, our experience is that they can often be isolated as crystalline materials,
when the choice of solvent and co-ligands (very often these are coordinating solvent) is
appropriate. We worked with MeCN as solvent, and it seems that this was a good choice
for preparing the titanium species in question. As a first beneficial consequence, the
displacement of iPrOH (which is liberated during the ligand-exchange reaction of diol
ligands with [TiCl2(OiPr)2]) was never a problem, whereas it is not possible to remove
iPrOH by azeotropic distillation or under high vacuum when toluene is used as solvent
for complex synthesis, because the alcohol remains strongly coordinated to the Ti-atom.
Second, the presence of excess sterically undemanding MeCN ligands assures
coordinative saturation and, thus, makes the dichlorotitanium entity less susceptible
towards hydrolysis. Still, the strength of coordination of MeCN is not too high to
prevent ligand exchanges, with substrates (and thus catalytic processes) to take place.
Third, the coordination of solvents may convert otherwise amorphous or polymeric
metal species into mononuclear, crystalline complexes of defined composition. These
may be useful as catalyst precursors that are easy to handle. Given the wide range of
solvents available, it should be possible to find one that favors the formation of a
crystalline product. However, sometimes a suitable combination of solvents is
necessary. This is exemplified by the highly crystalline complexes 3 (both MeCN and
DME necessary) or 14 (THFand MeCN). Obviously, a fine balance of co-ligands at the
central metal is necessary to obtain crystalline materials, and one approach to find the
suitable ones is to use a −multiple choice× approach in which the complex species is
exposed to a mixture of several coordinating solvents.
The complexes 3 and 4 are easily prepared catalyst precursors. They are stable
compounds that can be stored for prolonged times. Unlike many in situ prepared
catalysts, they need not be prepared each time just before a catalytic experiment. Our
own experience in catalytic enantioselective fluorination reactions has shown that the
results of catalytic experiments were of better reproducibility, and that the enantiomer
excess of the products was often a few % ee higher, when these crystalline complexes
were used in catalysis, as opposed to in situ prepared catalysts [22]. While there is no
definitive explanation for this, one may assume that the high purity (also the
enantiomer purity!) and uniformity of the crystalline catalyst precursors is responsible.
We propose that complexes 3 and 4 are applicable in all reactions published in the
literature, where in situ prepared [TiCl2(TADDOLato)] species have been used
previously [23].
L. H. thanks Solvias AG, Basel, for financial support.

1608
Helvetica Chimica Acta Vol. 85 (2002)
Experimental Part
General. TADDOL ligands 1 and ((4R,5R)-2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxolane-
4,5-dimethanol; 2) were obtained from Fluka and Aldrich resp.; other TADDOLs were prepared according to
Beck et al. [44]. [TiCl2(OiPr)2] was prepared according to [45] and used either as pure substance or as 1m soln. in
MeCN. Dimethyl camphorate (8) was obtained by dimethyl sulfate alkylation of (‡)-camphoric acid (Acros), as
described in [46]; camphoric anhydride (ˆ(1R,5S)-1,8,8-trimethyl-3-oxabicyclo[3.2.1]octane-2,4-dione; 6) was
obtained commercially or from (‡)-camphoric acid and Ac2O. PhMgCl was prepared according to [47], (M)-
2,2'-diiodo-6,6'-dimethyl-1,1'-biphenyl (16) was available from earlier work. Syntheses of metal complexes were
performed under an inert atmosphere and air-sensitive substances handled in a glove box. DME ˆ 1,2-
dimethoxyethane; Nph ˆ naphthyl; h.v. ˆ high vacuum (ꢀ0.01 mbar); NMR Spectra: at 300 (1H) and 75.5 MHz
1
(13C) in CDCl3, if not stated otherwise; d in ppm, referenced to SiMe4 (ˆ0 ppm; H) or solvent signal (13C; d
(CDCl3) 77.0), J in Hz.
Crystallographic data (excluding structure factors) for the structures reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as supplementary publications no. CCDC 145414
(3), CCDC 145415 (4b), and CCDC 172511 (14). Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (‡44) 1223336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Dichloro[1,2-di(methoxy-kO)ethane][(4R,5R)-2,2-dimethyl-a,a,a',a'-tetraphenyl-1,3-dioxolane-4,5-di-
methanolato(2À)-kO,kO']titanium-Acetonitrile ([TiCl2(TADDOLato)(DME)] ¥ MeCN; 3). To a suspension of
(R,R)-TADDOL (1; 2.59 g, 5.55 mmol) in MeCN (10 ml) 1m [TiCl2(OiPr)2] in MeCN (5.55 ml, 5.55 mmol) was
added and the mixture stirred for 1 d at r.t. After evaporation and drying of the remaining crust for 1 d under
h.v., the solid was redissolved in MeCN (40 ml) at 508 and the resulting soln. evaporated to almost dryness. Fresh
MeCN was added to reach a total volume of 20 ml. To this soln., DME (0.65 ml, 6.25 mmol) was added at r.t.
under vigorous stirring. As soon as a homogeneous soln. was obtained, the stirring was stopped and the soln. set
aside for crystallization (which started within seconds!). The mother liquor was removed with a filter stick at
À208, and the crystals were washed twice with MeCN (20 ml) at À208. The product was dried for 1 d under h.v.
(0.002 mbar), whereupon it lost some solvent of crystallization (MeCN): 3.507 g (89%) of 3 as [TiCl2(R,R-
TADDOLato)(DME)] ¥ 0.86 MeCN. M.p. 200 2028 (dec.; browning at 1908). IR (fluorolube, NaCl plates):
3053w, 2978w, 2939w, 2904w, 2250w, 1598w, 1495m, 1444s, 1383m, 1371s. 1H-NMR (400 MHz): 0.62 (s, 6 H,
2 Me); 1.97 (s, 2.58H, MeCN); 3.79 ( d, J ˆ 6.0, 2 H, CH2CH2); 3.78( s, 6 H, 2 MeO); 4.09 (d, J ˆ 6.0, 2 H,
CH2CH2); 5.50 (s, 2 H, 2 CH); 7.23 7.36 (m, 12 arom. H); 7.44 7.48( m, 4 arom. H); 7.60 7.64 (m, 4 arom. H).
13C-NMR (100.6 MHz): 1.8(Me, MeCN); 27.2 (Me); 63.5 (Me (DME)); 71.7 (CH2 (DME)); 80.0 (CH); 102.4
(C); 111.5 (C); 116.4 (br. s, MeCN); 127.0 (CH); 127.3 (CH); 127.6 (CH); 127.7 (CH); 127.9 (CH); 129.9 (CH);
142.7 (C); 143.6 (C). Anal. calc. for C35H38Cl2O6Ti ¥ 0.86 C2H3N (708.801): C 62.22, H 5.77, N 1.70, Cl 10.00;
found: C 62.50, H 5.91, N 1.70, Cl 9.77.
Crystals suitable for an X-ray determination were grown by diffusion of a complex soln. in a CH2Cl2/MeCN
mixture against heptane.
(Acetonitrile)dichloro[(4R,5R)-2,2-dimethyl-a,a,a',a'-tetra(naphthalen-1-yl)-1,3-dioxolane-4,5-dimeth-
anolato(2À)-kO,kO']titanium ([TiCl2(TADDOLato)(MeCN)]; 4a). In MeCN (15 ml), 1-Nph-TADDOL (2;
1.022 g, 1.533 mmol; Aldrich) and [TiCl2(OiPr)2] (1.6 mmol) were stirred for 1 d at r.t. The yellow soln. was
slowly (40 min) evaporated to ca. 4 ml (r.t./h.v.) under stirring whereupon precipitation of a bright beige powder
set in. The volume was further reduced until a thick suspension was obtained. To this, MeCN (5 ml) was added,
stirring was continued for 1 h at À108, and the yellow mother liquor was removed with a filter stick. The fine
powder was again suspended in MeCN (5 ml) and the (almost colorless) mother liquor removed. This material
corresponds most probably to the formula [TiCl2(TADDOLato)(MeCN)2], but a correct elemental analysis
was not obtained due to loss of coordinated solvent in the dry state. The powder was dried for 1 h under h.v. and
then further purified by recrystallization. Suspension in MeCN (5 ml), and adding a total of 25 ml of CH2Cl2
gave a soln. that was filtered and then slowly evaporated to 5 ml under h.v. under stirring. Bright yellow crystals
of 4b separated. Filtration and drying of the crystals for 12 h under h.v. yielded 923 mg (73%) of 4a as
C47H36Cl2O4Ti ‡ C2H3N (Mr 824.61). Dark yellow powder. 1H-NMR (CDCl3/CD3CN 4 :1): À0.27 (s, 6 H, 2 Me);
1.97 (s, 3 H, MeCN); 6.30 (s, 2 H, CH); 6.71 (ddd, J ˆ 8.9, 6.7, 1.5, 2 arom. H); 6.94 (ddd, J ˆ 8.7, 6.7, 1.3,
2 arom. H); 7.07 (ddd, J ˆ 8.0, 6.7, 1.0, 2 arom. H); 7.20 (ddd, J ˆ 8.1, 6.7, 1.0, 2 arom. H); 7.54 (d, J ˆ 9.0,
2 arom. H); 7.63 (dd, J ˆ 8.3, 1.1, 2 arom. H); 7.68 (−t×, J ˆ 7.7, 2 arom. H); 7.72 7.92 (m, 8arom. H); 8.13 ( d, J ˆ
8.7, 2 arom. H); 8.33 (d, J ˆ 7.3, 2 arom. H); 9.15 (dd, J ˆ 7.2, 1.5, 2 arom. H). 13C-NMR (CDCl3/CD3CN): 0.9
(Me, MeCN); 25.8(Me); 80.9 (CH); 100.8(C); 111.7 (C); 123.1 (CH); 123.4 (CH); 123.8(CH); 124.0 (CH);

Helvetica Chimica Acta Vol. 85 (2002)
1609
124.2 (CH), 124.3 (CH), 125.1 (CH); 126.6 (CH); 127.2 (CH); 127.3 (CH); 127.6 (CH); 127.8(CH); 128.5 (CH);
128.5 (CH); 130.9 (C); 132.1 (C); 133.5 (C); 134.0 (C); 139.1 (C); 139.5 (C). Anal. calc. for C49H39Cl2NO4Ti
(824.61); C 71.37, H 4.77, N 1.70; found: C 71.20, H 4.91, N 1.66 (sample sealed in glovebox).
(1R,5S)-1,8,8-Trimethyl-4,4-diphenyl-3-oxabicyclo[3.2.1]octan-2-one (7a) and (1S,5R)-5,8,8-Trimethyl-4,4-
diphenyl-3-oxabicyclo[3.2.1]octan-2-one (7b) from Camphoric Anhydride (6). To a suspension of 6 (2.00 g,
10.98mmol) in THF (10 ml) PhMgBr (30 mmol) in THF (12 ml) was added within 15 min at 0 8. On warming to
r.t., an exothermic reaction set in (caution! cooling advisable). After 2 h of stirring at r.t., the mixture was
heated for 30 min at 708, cooled to r.t., and quenched with 2m HCl (8ml). Workup with tBuOMe/H2O gave,
after drying and evaporation, 3.527 g of a white foam, consisting of isomeric hydroxy acids (TLC, NMR). To the
crude material Ac2O (3 ml) and CH2Cl2 (3 ml) were added, and the mixture was stirred overnight at 508. After
evaporation, the residue was separated by FC (tBuOMe/hexane 1:15): 7a (1.992 g, 57%), 7b (0.649 g, 18%), and
some mixed fractions (<100 mg).
Campholide 7a from Dimethyl Camphorate (8) [27]. To a soln. of 8 [46] (20.2 g, 88.5 mmol) in THF
(50 ml), a soln. of PhMgCl (350 mmol) in THF (120 ml) was added at 08 within 1.5 h. The mixture was stirred
and warmed to r.t. overnight and then carefully quenched by the addition of sat. NH4Cl soln. (20 ml) and 2m
H2SO4 (100 ml). After workup with tBuOMe and H2O, washing with H2O, drying (MgSO4) and evaporation, a
crude yield of 28.84 g of a slightly yellow solid was obtained. Crystallization from hot EtOH (40 ml) gave a solid
mass that was triturated with pentane (50 ml), filtered, and washed with additional pentane: 23.406 g (83%) of
7a. White powder.
Data of 7a: TLC (tBuOMe/hexane 1:10): Rf 0.28. M.p. 152 1538 ([58]: 154 1558). [a]D ˆ ‡149.3 (c ˆ
0.99, MeOH). IR (KBr): 3067w, 3053w, 2981m, 2969m, 2937m, 2873w, 1723s, 1448m, 1316m, 1217m, 1152s,
1083m, 742m, 702s, 653m. 1H-NMR: 0.61 (s, 1 Me); 1.04 (s, 1 Me); 1.17 (s, 1 Me); 1.43 1.55 (m, 1 H); 1.62 1.75
(m, 1 H); 1.84 2.03 (m, 2 H); 3.23 (d, J ˆ 6.7, 1 H); 7.08(br. s, 1 arom. H); 7.09 7.18( m, 2 arom. H); 7.20 7.32
(m, 4 arom. H); 7.51 (br. s, 1 arom. H); 7.72 (br. s, 2 arom. H). 13C-NMR: 14.3; 23.2; 24.3; 24.4; 33.9; 43.9; 49.9;
‡
53.2; 89.6; 123.5 (br.); 125.1 (br.); 126.4; 126.7; 128.5 (br.); 146.0; 146.1; 176.3. EI-MS (pos.): 320 (100, M ), 243
‡
(24, [M À C6H5] ), 193 (87), 183 (81), 138 (86), 105 (93), 95 (48). Anal. calc. for C22H24O2 (320.43): C 82.46,
H 7.55; found: C 82.37, H 7.53.
Data of 7b: TLC (tBuOMe/hexane 1 :10): Rf 0.19. M.p. 136 1398. [a]D ˆ À121.9 (c ˆ 0.99, MeOH). IR
(KBr): 3062w, 3050w, 3011w, 2980m, 2963m, 2921m, 2881m, 1741s, 1478m, 1444m, 1386w, 1313m, 1259s, 1083s,
755m, 702s, 460s. 1H-NMR: 0.80 (s, 1 Me); 0.96 (s, 1 Me); 1.55 (ddd, J ˆ 14.6, 12.1, 5.4, 1 H); 1.68( s, 1 Me); 1.80
(ddd, J ˆ 13.9, 9.9, 5.4, 1 H); 2.02 (dddd, J ˆ 13.9, 12.1, 6.9, 4.4, 1 H); 2.25 (ddd, J ˆ 14.6, 9.8, 4.5, 1 H); 2.60
(d, J ˆ 6.9, 1 H); 7.12 7.31 (m, 6 arom. H); 7.52 7.58( m, 2 arom. H); 7.74 7.79 (m, 2 arom. H). 13C-NMR:
20.0; 22.7; 25.1; 26.0; 35.6; 46.3; 51.1; 54.1; 93.8; 126.7; 126.7; 126.8; 127.2; 127.7; 127.8; 144.3; 145.3; 174.6. FAB-
‡
‡
‡
‡
MS: 1537 (50, [2M À Cl] ), 786 (27, M ), 750 (92, [M À Cl] ), 714 ([M À 2 Cl] , 100), 630 (74). Anal. calc. for
C22H24O2 (320.43): C 82.46, H 7.55; found: C 82.44, H 7.78.
(1S,3R)-2,2,3-Trimethyl-a,a-diphenylcyclopentane-1,3-dimethanol (9). A soln. of 7a (1.00 g, 3.12 mmol) in
t
tBuOMe (10 ml) was added dropwise to LiAlH4 (80 mg, 2.11 mmol) in BuOMe (5 ml). Additional LiAlH4
(120 mg, 3.16 mmol) was added in portions to the mixture (TLC control). After 1 h stirring at r.t., the excess
reagent was destroyed by dropwise addition of H2O, followed by workup with 2m KOH and tBuOMe. Drying of
t
the org. phase (Na2SO4) and evaporation gave 1.049 g of a colorless resin (quant.), containing some BuOMe
(1H-NMR). The material was dissolved in EtOH (2 ml) and slowly evaporated by standing in air. Large
colorless crystals separated that were collected and washed with tBuOMe. The remaining material was dissolved
t
in BuOMe (10 ml), the soln. filtered, evaporated to ca. 2 ml, and overlayered with pentane (4 ml). After
crystallization at À208 (in the presence of a trace of the crystalline material) the mother liquor was decanted,
and the colorless crystals were washed with pentane. Total yield: 829 mg (82%) of 9. TLC (tBuOMe/hexane
1:1): Rf 0.25. M.p. 120.0 120.68. [a]D ˆ À99.5 (c ˆ 0.92, MeOH). IR (KBr): 3577s, 3462s (br.), 3055w, 2996w,
2965s, 2872m, 1599w, 1493w, 1474w, 1447s, 1379m, 1344m, 1317m, 1266m, 1185m, 1158m, 1069m, 1049m, 1027m,
1
1004m, 98 0m, 916w, 8 90w, 8 68w, 757s, 748s, 707s, 698s. H-NMR: 0.57 (s, 1 Me); 0.89 (s, 1 Me); 0.94 (s, 1 Me);
1.36 1.48( m, 1 H); 1.57 1.81 (m, 3 H); 1.80 (br. s, CH2OH, exchange with D2O); 3.27 3.35 (m, 1 H); 3.33
(br. s, C(Ph)2OH, exchange with D2O); 3.43 (d, J ˆ 10.7, 1 H, CH2OH); 3.54 (d, J ˆ 10.7, 1 H, CH2OH); 7.07
7.15 (m, 2 arom. H); 7.20 7.29 (m, 4 arom. H); 7.53 7.59 (m, 4 arom. H); in fresh CDCl3, a coupling of OH (d
1.80, J ꢁ 5) to CH2(a') was observed. 13C-NMR: 25.1; 20.5; 25.1; 28.1; 33.5; 45.1; 49.3; 54.8; 69.5; 79.8; 125.3;
‡
125.7; 125.9; 126.1; 127.7; 128.1; 146.7; 149.6. EI-MS (pos.): 306 (11, [M À H2O] ), 288 (3), 273 (4), 247 (3), 219
(7), 183 (100), 167 (12), 105 (24). Anal. calc. for C22H28O2 (324.46): C 81.44, H 8.70; found: C 81.36, H 8.88.
1-[(1R,3S)-3-(Hydroxydiphenylmethyl)-1,2,2-trimethylcyclopentyl]ethanone (11). At 08, 3m MeMgCl in
THF (1.3 ml, 3.9 mmol) was added to a soln. of 7a (3.62 mmol) in THF (5 ml). After stirring overnight at r.t., no

1610
Helvetica Chimica Acta Vol. 85 (2002)
product was detected by TLC. After a new addition of MeMgCl (3.5 ml, 10.5 mmol) the mixture was refluxed
for 3 d at 908. Workup with sat. NH4Cl soln., H2O, and tBuOMe gave, after drying of the org. phase (MgSO4),
1.277 g of crude product that was separated by FC (tBuOMe/hexane 1 :10): 412 mg (36%) of 7a and 415 mg
(34%) of 11 as colorless crystals. For analysis, the sample 11 was crystallized from CH2Cl2/hexane by slow
evaporation. TLC (tBuOMe/hexane 1:5): Rf 0.25. M.p. 110.6 112.58. [a]D ˆ À99.5 Æ 1.3 (c ˆ 1.455, MeOH). IR
(KBr): 3496s, 3058w, 2968m, 1682s, 1598w, 1491w, 1446m, 1373m, 1354m, 1255m, 1167m, 1062w, 98 5w, 8 8 w3,
760m, 746m, 78 6s, 642w. 1H-NMR: 0.69 (s, 1 Me); 0.87 (s, 1 Me); 1.20 (s, 1 Me); 1.45 (ddd, J ˆ 14.7, 8.8, 5.9,
1 CH); 1.58 1.91 ( m, 2 CH); 2.11 (s, MeCO); 2.22 (ddd, J ˆ 13.2, 10.1, 6.4, 1 CH); 3.28( s, OH); 3.31 (t, J ˆ 9.5,
1 CH); 7.08 7.16 ( m, 2 arom. H); 7.20 7.30 (m, 4 arom. H); 7.54 7.59 (m, 4 arom. H). C-NMR: 20.5; 21.9;
25.0, 27.5; 29.3; 32.9; 46.8; 54.2; 61.9; 79.5; 125.3; 125.8; 126.0; 126.2; 127.7; 128.2; 146.4; 149.5; 214.9. EI-MS:
‡
‡
(pos.): 336 (0.4, M ), 318(17, [ M À H2O] ), 234 (17), 219 (16), 193 (27), 183 (100), 167 (37), 154 (16), 105 (39).
Anal. calc. for C23H28O2 (336.47): C 82.10, H 8.39; found: C 82.04, H 8.18.
a-[(1S,3R)-3-Hydroxy-2,2,3-trimethylcyclopentyl]-a-phenylbenzenemethanol (13a) and a-[(1R,3S)-3-Hy-
droxy-1,2,2-trimethylcyclopentyl]-a-phenylbenzenemethanol (13b). To a soln. of campholytolactones 12a/b
(2.640 g, 17.1 mmol) obtained in the ratio 81:19 by lead tetraacetate oxidation of (‡)-camphoric acid (5) as
reported [31] (cf. also [29][30]) in THF (20 ml) at r.t., 2.5m PhMgBr in THF (50 ml, 125 mmol) was added, and
the resulting soln. was refluxed for 40 h (required reaction time may be much shorter). After workup with
tBuOMe, sat. NH4Cl soln., and H2O, the org. phase was washed with sat. NH4Cl soln., sat. NaCl soln., dried
(Na2SO4), and evaporated leaving a few ml of a yellow oil. By FC (tBuOMe/hexane 1:10, 1:5, and 1:3),
impurities (biphenyl and phenol) were separated and the following 4 fractions were obtained. Fr. 1: 13a and
some PhOH (550 mg); Fr. 2: pure 13a (2.521 g); Fr. 3: mixture 13a/b (71 mg); Fr. 4: pure 13b. Fr. 1 and 2 were
t
crystallized separately from BuOMe/pentane at À208 to yield 0.478and 2.246 g, resp., of colorless crystals of
t
13a, total 2.724 g (51.3%). Fr. 4 was dissolved in BuOMe, the soln. concentrated to ca. 3 ml, overlayered with
pentane (7 ml), and left for 1 d for crystallization at À208. Decantation and washing with pentane yielded
0.973 g (18.3%) of 13b as white crystalline powder. The product alcohols retained traces of H2O and were thus
sublimed, 13a at 1208/0.002 mbar and 13b at 1008/0.003 mbar, for elemental analysis and Ti-complex syntheses.
Data of 13a: TLC (tBuOMe/hexane 1:5): Rf 0.24. M.p. 153.2 154.48 (before sublimation), 153.0 154.28
(after sublimation). [a]D ˆ ‡6.8 Æ 0.6 (c ˆ 1.14, MeOH). IR (KBr): 3562m, 3509w, 3333s (br.), 3062w, 3018w,
2969s, 1596w, 1489m, 1472m, 1449s, 1394m, 1370w, 1314w, 1170m, 1146m, 1086m, 1010m, 934w, 8 11w, 8 98w,
770m, 745s, 78 6s, 661w, 636w, 539w. 1H-NMR: 0.58( s, 1 Me); 1.01 (s, 1 Me); 1.16 (s, 1 Me); 1.49 1.85 (m, 4 H);
2.21 (br. s, 1 OH); 3.43 (t, J ˆ 7.8, 1 H); 5.66 (br. s, 1 OH); 7.01 7.13 (m, 2 arom. H); 7.17 7.29 (m, 4 arom. H);
7.54 7.68( m, 4 arom. H). 13C-NMR: 19.6 (Me); 21.4 (Me); 24.4 (CH2); 31.4 (Me); 37.5 (CH2); 47.8(C); 55.5
(CH); 78.9 (C); 84.0 (C); 125.4 (CH); 125.5 (CH); 125.5 (CH); 125.6 (CH); 127.8 (CH); 149.3 (C); 149.5 (C).
‡
‡
EI-MS (pos.): 310 (0.4, M ), 292 (3, [M À H2O] ), 274 (11), 259 (7), 219 (16), 183 (100), 167 (15), 105 (44).
Anal. calc. for C21H26O2 (310.44): C 81.25, H 8.44; found: C 81.14, H 8.58.
Data of 13b: TLC (tBuOMe/hexane 1:5): Rf 0.13. M.p. 163.6 163.98 (before sublimation), 163.0 164.38
(after sublimation). [a]D ˆ À70.9 Æ 1.0 (c ˆ 1.05, MeOH). IR (KBr): 3358s (br.), 3096w, 3057w, 2994m, 2970s,
1597w, 1493m, 1467m, 1444m, 1388m, 1366m, 1264w, 1194m, 1068s, 1035s, 8 92w, 8 40w, 759m, 730m, 698s, 578w.
1H-NMR: 0.73 (s, 1 Me); 0.86 (s, 1 Me); 1.18 1.26 ( m, 1 CH); 1.28( s, 1 Me); 1.59 (dddd, J ˆ 14.7, 9.2, 5.2, 4.1,
1 CH); 1.96 2.12 (m, 2 CH); 2.89 3.01 (m, CH); 3.77 (br. s, 2 OH); 7.12 7.34 (m, 6 arom. H); 7.51 7.57
(m, 2 arom. H); 7.71 7.77 (m, 2 arom. H). 13C-NMR: 21.0 (Me); 24.5 (Me); 25.5 (Me); 29.5 (CH2); 34.5 (CH2);
54.6 (C); 82.3 (CH); 83.1 (C); 126.4 (CH); 126.4 (CH); 127.1 (CH); 127.3 (CH); 128.3 (CH); 128.8 (CH); 146.8
‡
(C); 146.9 (C). EI-MS (pos.): 292 (3, [M À H2O] ), 274 (2), 259 (1), 220 (2), 205 (4), 191 (2), 183 (100), 105
(24). Anal. calc. for C21H26O2 (310.44): C 81.25, H 8.44; found: C 81.04, H 8.22 (sublimed sample).
(M)-6,6'-Dimethyl-a,a,a',a'-tetraphenyl[1,1'-biphenyl]-2,2'-dimethanol (15). To a soln. of (M)-2,2'-diiodo-
t
6,6'-dimethyl-1,1'-biphenyl (16; 2.049 g, 4.72 mmol) in 10 ml THF, 1.6m BuLi in pentane (12.2 ml, 19.5 mmol)
was added dropwise at À788, and the resulting yellow suspension was stirred for 30 min. Still at À788, a soln. of
benzophenone (2.00 g, 11.0 mmol) in THF (5 ml) was added dropwise to the mixture, resulting in a green
coloration. After 1 h stirring, the cooling bath was removed and the mixture stirred for an additional 3 h at r.t.
t
Quenching with 10 ml sat. NH4Cl soln. was followed by workup with H2O (100 ml), BuOMe (100 ml), and
CH2Cl2 (50 ml). The org. phase was washed with H2O, sat. NaHCO3 soln., and sat. NaCl soln., dried (Na2SO4),
and evaporated to yield a semi-crystalline mass that was triturated with pentane (2 Â 10 ml and 1 Â 5 ml),
yielding 2.417 g (94%) of 15. White powder. TLC (tBuOMe/hexane 1 :10): Rf 0.23. M.p. 270 2758. [a]D
ˆ
‡117.9 (c ˆ 0.615, CH2Cl2). IR (KBr): 3504m, 3428m, 3056m, 3023w, 2913w, 1942w, 1879w, 1810w, 1598w,
1492m, 1446s, 1322w, 1162m, 1042m, 1032m, 1007m, 78 6m, 764s, 757s, 750m, 733m, 698s, 649m, 638s. 1H-NMR
(250 MHz): 0.74 (s, 2 Me); 4.69 (s, 2 OH); 6.86 6.91 (m, 4 arom. H); 7.11 (dd, J ˆ 8.2, 7.2, 2 arom. H); 7.16

Helvetica Chimica Acta Vol. 85 (2002)
1611
7.31 (m, 20 arom. H). 13C-NMR (62.9 MHz): 18.4; 84.3; 126.2; 126.8; 127.3; 127.6; 127.7; 128.0; 128.7; 128.8;
‡
129.4; 138.2; 138.3; 143.3; 143.7; 148.9. EI-MS: 528 (41, [M À H2O] ), 451 (100), 435 (57), 374 (47), 346 (29),
331 (48), 105 (36). Anal. calc. for C40H34O2 (546.71): C 87.88, H 6.27; found: C 87.93, H 6.44.
In situ Preparation of Bis(acetonitrile)dichloro[(1S,3R)-2,2,3-trimethyl-a,a-diphenylcyclopentane-1,3-
dimethanolato(2À)-kO,kO']titanium (10) from Diol 9. To a soln. of 9 (330 mg, 1.02 mmol) in MeCN (20 ml;
dist. from P2O5), 3-ä molecular sieves (pulvis; 250 mg) and 1m [TiCl2(OiPr)2] in MeCN (0.98ml, 0.98mmol)
were added. The suspension was stirred overnight, heated to 708, and slowly evaporated under h.v. (1 h),
followed by drying for 5 h under h.v. A sample of the solid was dissolved in dry CDCl3 (in the glove box) and
analyzed spectroscopically. 1H-NMR: 0.47 (s, 1 Me); 0.71 (s, 1 Me); 0.95 (s, 1 Me); 1.44 1.62 (m, 2 H, CH2);
1.68 1.85 ( m, 2 H, CH2); 2.03 (s, 3 H, >1 MeCNÀTi); 2.92 (d, J ˆ 6.3, 1 H); 3.37 (d, J ˆ 10.9, 1 H, CH2OTi);
3.92 (dd, J ˆ 11.0, 1.2, 1 H, CH2OTi); 7.00 7.13 (m, 2 arom. H); 7.15 7.29 (m, 3 arom. H); 7.34 (br. s,
2 arom. H); 7.38(br. s, 2 arom. H); 7.62 (br. s, 2 arom. H); due to slow relaxation, the integral for coordinated
MeCN protons may be low.
In-situ Preparation of Ti-Complex from Diol 13a, and Crystallization of (Acetonitrile)dichloro{a-[(1S,3R)-
3-(oxylato-kO)-2,2,3-trimethylcyclopentyl]-a-phenylbenzenemethanolato(2À)-kO}(tetrahydrofuran)titanium-
Acetonitrile ([TiCl2 (13a-ato)(THF)(MeCN)] ¥ MeCN; 14). To a soln. of 13a (101 mg, 0.325 mmol) in MeCN
(5 ml), 1m [TiCl2(OiPr)2] in MeCN (0.31 ml, 0.31 mmol) was added dropwise. After stirring the faint beige soln.
for 30 h at r.t., it was evaporated and the remaining foam dried 3 h under h.v. The material was dissolved in THF
(5 ml) and the resulting soln. evaporated and dried under h.v. overnight. When the glassy solid was treated with
MeCN (5 ml), it dissolved to immediately crystallize in large pieces that only slowly dissolved in the total
volume of MeCN. On cooling to À208, colorless crystals formed reproducibly from the soln. One of the crystals
was used for an X-ray structure analysis.
In
situ
Preparation
of
Dichloro{(M)-6,6'-dimethyl-a,a,a',a'-tetraphenyl[1,1'-biphenyl]-2,2'-
dimethanolato(2À)-kO,kO']titanium (17) from Diol 15. To 15 (273 mg, 0.50 mmol) in THF (10 ml), 2,6-
di(tert-butyl)pyridine (23 ml) and 1m [TiCl2(OiPr)2] in MeCN (0.48ml, 0.48mmol) was added and the soln.
stirred 15 h at r.t.
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Received February5, 2002