New, axially chiral, bimetallic catalysts for asymmetric alkylation of aldehydes with diethylzinc

Article abstract of DOI:10.1002/(SICI)1522-2675(19990113)82:1<125::AID-HLCA125>3.0.CO;2-W

Axially chiral bis(salicylidene)ethylenediamine (H₂salen)-type ligands 3 (cf. Schemes 1 and 3) are efficient ligands for the enantioselective addition of diethylzinc to aldehydes. There is ample evidence that an active bimetallic catalyst forms an effective chiral pocket (see Fig. 2); of a series of first-row transition-metal complexes with these ligands, the most stereoselective were the Co(II) complexes (see Fig. 1). Best ee values as well as the fastest rates (see Tables 2 and 3) were obtained with these Co(II) complexes when an EtO substituent was present at C(3) of the salicylaldehyde residues of ligand 3 (R¹ = EtO), i.e., complex [Co(II)(3'h)] produce d up to 93% ee with aromatic aldehydes and 78% ee for aliphatic aldehydes (see Table 4).

Full text of DOI:10.1002/(SICI)1522-2675(19990113)82:1<125::AID-HLCA125>3.0.CO;2-W

Helvetica Chimica Acta ± Vol. 82 (1999)
125
New, Axially Chiral, Bimetallic Catalysts for Asymmetric Alkylation
of Aldehydes with Diethylzinc
1
by Felix Keller ) and Andreas Johannes Rippert*
Organisch-chemisches Institut der Universität Zürich, Winterthurerstr. 190, CH-8057 Zürich
Axially chiral bis(salicylidene)ethylenediamine (H2salen)-type ligands 3 (cf. Schemes 1 and 3) are efficient
ligands for the enantioselective addition of diethylzinc to aldehydes. There is ample evidence that an active
bimetallic catalyst forms an effective chiral pocket (see Fig. 2); of a series of first-row transition-metal
complexes with these ligands, the most stereoselective were the CoII complexes (see Fig. 1). Best ee values as
well as the fastest rates (see Tables 2 and 3) were obtained with these CoII complexes when an EtO substituent
was present at C(3) of the salicylaldehyde residues of ligand 3 (R1 ˆ EtO), i.e., complex [CoII(3'h)] produced
up to 93% ee with aromatic aldehydes and 78% ee for aliphatic aldehydes (see Table 4).
1. Introduction. ± Chiral N,N'-bis(salicylidene)ethylenediamine (H2salen) ligands
have attracted much interest in asymmetric catalysis. Their complexes with several
first-row transition metals have shown high levels of asymmetric induction with several
first-row transition metals in the following reactions: e.g., the epoxidation of
unfunctionalized olefins (MnIII) [1], the ring opening of meso-epoxides with Me3SiN3
(CrIII) [2] or carboxylates (CoII) [3], and the ring opening and kinetic resolution of
epoxides with water (CoII) [4] as well as hetero-Diels-Alder additions (CrIII) [5]. The
advantages of these H2salen ligands are their easy and high-yielding accessibility by a
condensation reaction between a diamine and salicylaldehydes (ˆ 2-hydroxybenzalde-
hydes) and, therefore, an easy tuning of the steric and electronic properties of the
ligand. Until now, the chiral diamines used in transition-metal catalysis possessed
central chirality. Recently Meunier et al. [6] used an axially chiral diamine, namely
[1,1'-binaphthalene]-2,2'-diamine, as the chiral backbone of H2salen-type ligands,
which showed, when coordinated to MnIII, low asymmetric induction in the catalyzed
epoxidation of unfunctionalized olefins (up to 15% ee). These results are in contrast
to those realized with axially chiral phosphine ligands, which are, like binap
(a binaphthalene-based diphosphine), the most successful ligands in asymmetric
catalysis [7].
Herein, we wish to report the synthesis of a new axially chiral diamine and the
corresponding H2salen-type ligands, as well as their use as ligands in bimetallic
asymmetric transition-metal catalysis. This is exemplified by the widely used C
C
bond formation reaction of aldehydes with diethylzinc (ZnEt2) (reviews: [8]) to
produce synthetically useful chiral secondary alcohols. The reaction is catalyzed since
only a slow reaction takes place between benzaldehyde and ZnEt2 at room temper-
ature. Similar catalyses have been observed with ligand classes such as amino alcohols
1
)
Part of the diploma thesis of F. K., University of Zurich 1997

126
Helvetica Chimica Acta ± Vol. 82 (1999)
[9], ferrocene-based amino alcohol [10], polymer-bound [1,1'-binaphtalene]-2,2'-diol
[11], or chiral taddol complexes with TiIV [12], disulfonamides [13], and dihydroxy-
disulfonamides [14].
2. Results and Discussion. ± The new, axially chiral diamine 1 was synthesized in a
straightforward manner in five steps, starting with 3-methylanthranilic acid, including
separation into the optical antipodes of (P)- or (M)-6,6'-dimethyl[1,1'-biphenyl]-2,2'-
dimethanamine ((P)- or (M)-1, resp.) with tartaric acid (see Scheme 1). Based on
preliminary results [15], we optimized the total yield of the sequence up to 30% for one
enantiomer with respect to the starting 3-methylanthranilic acid. The corresponding
axially chiral H2salen-type ligands 3 were formed by condensation of 1 with various
salicylaldehydes 2.
Scheme 1
Ligands of type 3 have already been successfully tested in the Mn-catalyzed
epoxidation of some unfunctionalized olefins with 3-chloroperbenzoic acid at low
temperature [15]. Cozzi et al. [16] showed that the addition of ZnEt2 to aromatic
aldehydes can be performed and accelerated by Schiff-base ligands of the Jacobsen
type, namely (S,S)-N,N-bis[3,5-di(tert-butyl)salicylidene]cyclohexane-1,2-diamine (ee
up to 77%). We screened the reaction of benzaldehydes and ZnEt2 with the new ligands
3, as outlined in Scheme 2. Our first results with these new, axially chiral ligands were
generally disappointing in terms of enantioselectivity (cf. Table 1).

Helvetica Chimica Acta ± Vol. 82 (1999)
127
Scheme 2
Table 1. Results of the Reductive Alkylation of Benzaldehyde with ZnEt2
Entry Ligand Configuration R1
R2
Solvent ee [%]a) Configuration of the
Yield [%]c)
of the ligand
secondary alcohol 4b)
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
3b
3b
(M)
(M)
(P)
H
MeO
MeO Br
H
H
t-Bu
MeO
MeO
H
H
toluene 15
toluene 25
toluene 19
(S)
(S)
(R)
(R)
(S)
(R)
(S)
(S)
74
82
76
78
71
68
79
72
(P)
MeO toluene
4
7
5
(M)
(M)
(M)
(M)
Br
t-Bu
H
toluene
toluene
CH2Cl2 24
THF 13
H
a) ee Values were determined by HPLC on a chiral column (Chiracel OD-H). b) The absolute configuration
of the formed major stereoisomer was established by comparison of the retention time by HPLC of optically
pure (R)-1-phenylpropan-1-ol. c) Yields were determined by integration of PhCHO (10.0 ppm) and
1
PhCH(OH)Et (4.55 ppm) in the H-NMR.
The best asymmetric induction and the highest yield were reached when we used
ligand 3b with a MeO group at C(3) of the salicylaldehyde residues (R1 ˆ MeO, R2 ˆ
H; see Scheme 1, and for the result Entry 2, Table 1). By adding an electron-
withdrawing group R2 at C(5) of the salicylaldehyde residues of the ligand 3, the ee
value and the yield decreased to 19% ee and 76%, respectively (Entry 3). That the
donating group at C(3) is necessary for coordination is obvious from the observation
that a MeO group at C(5) reduced the ee value to 4% (Entry 4). Sterically demanding
groups such as t-Bu at C(3) and C(5) showed low asymmetric induction and a low yield
(Entry 6). This is in contrast to results reported in [16]. However, the ee value was very
small, and the absolute configuration of the major alcohol stereoisomer, induced by this
ligand (M)-3f, was opposite to that observed with all the other ligands. Normally,
ligands with (M) axial chirality induced, as the major stereoisomer, (S)-configuration
in the formed alcohol. If the donating group at C(3) of the salicylaldehyde residues is
necessary, a solvent with good donating properties should influence the ee value.
Indeed, no effect was observed when we used a weakly coordinating solvent such as
CH2Cl2, but with the well coordinating solvent, THF, a remarkable decrease of the ee
value was observed (cf. Entries 7 and 8).
We regard this finding as evidence that donating groups are probably important for
asymmetric induction. In the case of a bimetallic catalyst, it would be possible to
optimize the asymmetric induction by changing the transition metal which is first bound
to the ligand of type 3b. The binding of transition metals to the central O N N O
à Ã
Ã
binding core of these H2salen-type ligands 3 will change the geometry and electronic

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Helvetica Chimica Acta ± Vol. 82 (1999)
properties of the complex. The results of this test are summarized in Fig. 1. In terms of
enantioselectivity, the best value was found with CoII (79% ee). All other tested
transition metals showed far lower ee values (4 ± 21% ee). AlIII exhibited a reasonable
ee value of 38%, but two other achiral products were formed, benzyl alcohol and
propiophenone. A possible explanation for this finding is the dehydrogenation of the
formed chiral alcohol, leading to propiophenone; the abstracted hydride then attacks
the benzaldehyde to form benzyl alcohol.
Fig. 1. Tests of various transition metals of the first-row and AlIII with ligand 3b in the reductive alkylation of
benzaldehyde with ZnEt2. Yellow bars: ee values; red bars: conversion of benzaldehyde after 18 h.
Next, we screened the influence of the donating substituents at C(3) of the
salicylaldehyde residues by varying the alkyl groups bound to the O-atom. These
differently substituted salicylaldehydes were synthesized from 3-hydroxysalicylalde-
hyde, as outlined in Scheme 3 [17]. The results of the reductive alkylation of
benzaldehyde with ZnEt2 in the presence of the corresponding CoII complexes are
summarized in Table 2. The CoII complex that showed the highest asymmetric
induction as well as the best reactivity was that obtained with ligand 3h which bears an
EtO group at C(3) (90% ee, 61% conversion after 1 h; Entry 5, Table 2). Sterically
more or less demanding groups at C(3) lower both the ee values and the reactivity
(Entries 3 and 6 ± 9). Also noteworthy is the result obtained with [CoII(3'a)]2) which
has no substituent at C(3) of the salicylaldehyde residues of the ligand. No asymmetric
induction took place, and the racemic secondary alcohol 4 was formed (Entry 1,
Table 2). This is in contrast to the result obtained with the in situ generated [ZnII(3'a)]
(15% ee; Entry 1, Table 1) and thus indicates that no metal exchange in [CoII(3'a)] took
place when an excess of ZnEt2 was added. There were other factors that lowered the
asymmetric induction in this catalytic reaction by the new [CoII(ligand 3')]2)
complexes: a more ionic donor group at C(3) of the salicylaldehyde residues of ligand
2
)
In the complexes, the ligands 3 are doubly deprotonated, this is symbolized by a primed key number,
i.e., 3'.

Helvetica Chimica Acta ± Vol. 82 (1999)
129
3, such as the OH groups in 3g, showed almost no asymmetric induction (Entry 2,
Table 2). An electron-withdrawing group at C(5) of the salicylaldehyde residues of
ligand 3c was also found to induce a lower asymmetric induction in the secondary
alcohol (4) as compared to the 5-unsubstituted ligand 3b (cf. Entries 4 and 3, Table 2).
Scheme 3
Evidence for a bimetallic catalysis was given by three facts: i) as discussed above, no
asymmetric induction was observed by the [CoII(3'a)] complex in contrast to the ZnII
analogue (cf. Entry 1 in Table 2 and Entry 1 in Table 1), ii) the ee value was
temperature-dependent in the CoII-complex-mediated reductive alkylation of benzal-
dehyde. The highest ee value could be reached when [CoII(3'b)] was first stirred with an
equimolar amount of ZnEt2 for 30 min at room temperature and then cooled to 08
before additional ZnEt2 and benzaldehyde were added (82% ee). When [CoII(3'b)]
and an equimolar amount of ZnEt2 were cooled to 08 or heated to 408 from the
beginning, the ee values were significantly lower (08, 67% ee; 408, 69% ee). Thus, an
initial complexation of an equimolar amount of ZnEt2 to the free binding sites of the
[CoII(3'b)] complex takes place and is crucial. iii) Binding studies, carried out by means
of a titration of ligand 3b with ZnEt2 monitored by 1H-NMR spectroscopy, showed that
coordination of ZnII took place initially at the central H salen-type O N N O core of
à Ã
Ã
2

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Helvetica Chimica Acta ± Vol. 82 (1999)
Table 2. Influence of the Alkoxy Substituents in the Reduction of Benzaldehyde with ZnEt2
Entry Complex
Configuration R1
of the ligand
R2 ee [%]a) Configuration of the
Conversion [%]c)
secondary alcohol 4b) after 1 h
1
2
3
4
5
6
7
8
9
[CoII(3'a)]
[CoII(3'g)]
[CoII(3'b)]
[CoII(3'c)]
[CoII(3'h)]
[CoII(3'i)]
[CoII(3'k)]
[CoII(3'l)]
(M)
(M)
(M)
(P)
(M)
(P)
H
HO
H
H
H
0
2
78
±
14
15
48
42
61
52
35
8
(S)
(S)
(R)
(S)
(R)
(S)
(R)
(S)
MeO
MeO
EtO
PrO
BzO
i-BuO
i-Pro
Br 69
H
H
H
H
H
90
75
55
7
(M)
(P)
[CoII(3'm)] (M)
14
15
a) ee Values were determined by GC on a chiral column (Cyclodex B). b) The absolute configuration of the
formed major stereoisomer was established by comparison of the retention time by HPLC or GC of optically
pure (R)-1-phenylpropanol. c) Conversion was established by GC, and quantified vs. mesitylene as an internal
standard.
ligand 3b. This was established by the disappearance of the 1H-NMR signal (300 MHz,
C6D6) of the OH group of 3b at 13.80 ppm and a d shift of the two H-atoms bound to
the C ˆ N group from 7.31 (ligand 3b) ! 6.84 ppm (complex [Zn(3'b)]; see Exper.
Part). Addition of a second equiv. of ZnEt2 could not be established because of the low
solubility of the formed complex in C6D6 which prevented the recording of suitable
1H-NMR spectra. Thus, we propose the presence of a bimetallic complex (see Fig. 2)
which acts as a catalyst.
Fig. 2. Proposed structure for the bimetallic catalyst
Bimetallic complexes of CoII/SnII and NiII/SnII with similar salen ligands, which have
propane-1,3-diamine as the backbone, were characterized by X-ray crystallographic
analyses [18]. In these complexes, the first-row transition metal was bound to the
central salen O N N O core and the SnII was coordinated to the O-atoms of the alkoxy
à à Ã
groups, as well as to the same O-atoms to which the first-row transition metal was
bound. Very recently, another bimetallic complex (MnIII/CuII) with a salen ligand has
been proposed for a catalyst [19] which showed high activities towards H2O2
decomposition.
To obtain more information about the rate and selectivity dependence of our
bimetallic system, we screened the CoII complexes under different reaction conditions.

Helvetica Chimica Acta ± Vol. 82 (1999)
131
The second-order rate law was determined by GC analysis for each set of conditions.
The resulting k2 values are summarized in Table 3. The catalyst concentration increased
the rate and, slightly, the enantioselectivity (Entries 1 ± 3, Table 3). Of the tested
solvents, toluene produced the highest rate and the best ee values (Entries 1 and 4 ± 6).
An alkoxy substituent in the salicylaldehyde residues resulted in lower rates as well as
lower ee values when a sterically less or more demanding group (see 3b and 3i, resp.)
than the EtO substituent (see 3b) was introduced (Entries 1, 7, and 8, Table 3; cf.
Table 2). The dialkylzinc reagents also influence the rate. When using ZnMe2, the
reaction with benzaldehyde was ca. 10 times slower compared with that obtained using
ZnEt2. However, ZnMe2 produced almost the same level of asymmetric induction in
the formed alcohol, namely 1-phenylethanol (Entries 1 and 9 in Table 3).
Table 3. Influence of Various Reaction Conditions on the Rate and Stereoselectivity of the Bimetallic Catalytic
System (CoII/ZnII)
b
ee a)
(k2 Æ s) ´ 10
)
6
Entry
Complex
Concentration of
catalyst [mol-%]
Solvent
R1
X of ZnX2
1
2
3
4
5
6
7
8
9
[CoII(3'h)]
[CoII(3'h)]
[CoII(3'h)]
[CoII(3'h)]
[CoII(3'h)]
[CoII(3'h)]
[CoII(3'b)]
[CoII(3'i)]
[CoII(3'h)]
10
5
toluene
toluene
toluene
hexane
benzene
PhCl
toluene
toluene
toluene
EtO
EtO
EtO
EtO
EtO
EtO
MeO
PrO
EtO
Et
Et
Et
Et
Et
Et
Et
Et
Me
90
87
91
87
87
87
78
75
88
6.40 Æ 0.34
1.58 Æ 0.06
18.6 Æ 0.9
20
10
10
10
10
10
10
6.00 Æ 0.06
2.29 Æ 0.13
2.26 Æ 0.05
3.60 Æ 0.11
1.26 Æ 0.03
0.50 Æ 0.01
a) ee Values were determined by GC on a chiral column (CyclodexB). b) Conversion was established by GC,
and quantified vs. mesitylene as an internal standard.
With the most selective and reactive complex [CoII(3'h)], several aldehydes were
tested and showed the trends summarized in Table 4. The best ee values were observed
with substituted benzaldehydes possessing electron-withdrawing groups (cf. Entries 1 ±
3, Table 4); donating groups showed lower asymmetric induction (Entries 4 and 6).
Also, ortho-substituents produced lower ee values, when compared with the same
substituents in the para-position (Entries 5 and 6). Naphthalene-1-carbaldehyde and
-2-carbaldehyde showed similar enantioselectivities to benzaldehyde (Entries 7 and 8).
Even aliphatic aldehydes could be reduced with reasonable asymmetric induction
(Entries 9 and 10), except for the sterically demanding pivalaldehyde (ˆ 2,2-dimethyl-
propanal) which showed a low ee as well as low conversions.
The stereochemical outcome of the reaction between aldehydes and both ZnEt2
and ZnMe2 in the presence of the new complexes [CoII(3')] can be explained by the
structure proposed in Fig. 2. Complexation of the aldehyde takes place at the CoII ion.
If we use a ligand with (M)-chirality, the aldehyde will be oriented by steric and
p-p interactions in such a way that the si-face is pointing towards the 3-substituent of
the salicylaldehyde residue, where the ZnEt2 can be complexed (cf. Fig. 3).
3. Conclusion. We could show that the new axially chiral O N N O ligands 3 of the
à Ã
Ã
H2salen type are potential ligands for asymmetric transition-metal catalysis. Good

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Helvetica Chimica Acta ± Vol. 82 (1999)
Table 4. Reductive Alkylation of Various Aldehydes with ZnEt2 and [CoII(3'h)] (10 mol-%) as the Catalyst
Entry Aldehydes
ee
Conversion
Entry Aldehydes
ee
Conversion
[%]a) [%]b) after 1 h
[%]a) [%]b) after 1 h
1
91
93
82
7
89
89
32
52
2
3
> 99
8
9
93
> 99
75
19
4
5
6
88
72
82
30
27
14
10
11
79
36
25
traces
a) ee Values were determined by GC on a chiral column (CyclodexB); in the case of aliphatic alcohols, their
corresponding acetyl derivatives were analyzed. b) Conversion was established by GC and quantified vs.
mesitylene as an internal standard.
levels of asymmetric induction were found in the reductive alkylation of aldehydes with
ZnEt2, when an alkoxy group is attached at C(3) of the salicylaldehyde residues of
ligand 3. There is evidence for an active bimetallic catalyst, with CoII in the central
Fig. 3. Orientation of aldehydes at the site of the bimetallic catalyst with (M)-chirality

Helvetica Chimica Acta ± Vol. 82 (1999)
133
salen-type O N N O core of the ligand, and in which the second transition metal ZnII is
à Ã
Ã
coordinated to the two additional donor groups of the alkoxy substituents at C(3) of the
salicylaldehyde residues of the ligand, as well as to the same two O-atoms of the central
salen-type core which are also bound to the CoII atom, these O-donors bridging the two
metal atoms (cf. Fig. 2). Therefore, the reaction of the aldehyde and ZnEt2 takes place
in a chiral pocket, comparably to many highly enantioselective enzymatic reactions that
occur in a deeply embedded active site.
Further studies are in progress to use this bimetallic system in other trans-
formations.
We thank Prof. M. Hesse and his coworkers for mass spectra, Mrs. J. Kessler for elemental analyses, Prof. W.
von Philipsborn and his coworkers for NMR support, cand. chem. H. Spillmann for the optimization of the
optical resolution of 1, and Prof. H.-J. Hansen for his enthusiastic interest. The financial support of this work by
the Swiss National Science Foundation is gratefully acknowledged.
Experimental Part
1. General. All catalytic reactions were performed under N2. All solvents were distilled under N2 prior to
their use. THF was purified over Al2O3 (basic, act. I). 3-Methyl-2-nitrobenzoic acid (Fluka, purum) was reduced
with H2 and Pd/C (Fluka) to the corresponding 2-amino-3-methylbenzoic acid. Benzaldehyde (Fluka, puriss.)
was distilled under N2. ZnEt2 (Fluka, purum; 1.1m in toluene), [Co(AcO)2]. 4 H2O (Fluka, purum p.a.),
[Mn(AcO)2] ´ 4 H2O (Fluka, purum p.a.), FeCl2 (Fluka, purum), [Ni(AcO)2]. 4 H2O (Fluka, purum p.a.),
[Cu(AcO)2] ´ H2O (Fluka, puriss p.a.), AlCl(Et)2 (Fluka, pract. 1m in hexane), and Ti(i-PrO)4 (Aldrich) were
used without further purification. GC: CE Instruments GC-8000Top apparatus equipped with a CyclodexB
column (30 m  0.25 mm, 0.25 mm; J & W Scientific) for the determination of the ee values and the conversion in
ꢀ
catalytic reactions. HPLC: LichroCart -(S,S)-Whelk-O-1 column (244 mm  4 mm, 5 mm; Merck, No. 1.50164)
with LiChrospher ꢀ 100 Diol as a precolumn (4 mm  4 mm, 5 mm; Merck, No. 1.50960) for determination of the
separation of (M)- and (P)-1; and Chiracel OD-H column (250 mm  4.6 mm, 5 mm) with Spherisorb Si
(50 mm  4.6 mm, 5 mm; Daicel) as a precolumn for the determination of the ee value of 4; UV photodiode-
array detector (Jasco, model MD-910) and Milton-Roy pump (model CM 4000). M.p.: Büchi 510 melting point
apparatus or apparatus constructed and assembled by K. Hochreutener, University of Zurich; not corrected.
1
Optical rotations: Perkin Elmer-MC-941 polarimeter. CD: Jasco-J-715 spectropolarimeter; l in nm (De). H-
and 13C-NMR: Bruker-AC-300, -ARX-300, and -AMX-600 spectrometers; d in ppm rel. to an internal standard
(d(SiMe4) ˆ 0 ppm).
1. (M)- or (P)-6,6'-Dimethyl[1,1'-biphenyl]-2,2'-dimethanamine ((M)- or (P)-1). 2-Amino-3-methylben-
zoic acid was diazotized with NaNO2 (Fluka), and the coupling to the biphenyl was achieved by a CuI salt
derived from CuSO4 (see [20] [21]) (yield after crystallization from acetone, 78%). Reduction of (MP)-6,6'-
dimethyl[1,1'-biphenyl]-2,2'-dicarbocylic acid with LiAlH4 (Fluka) in Et2O (yield after crystallization from
toluene, 95%) followed by bromination with PBr3 (Fluka) in toluene led to (MP)-2,2'-bis(bromomethyl)-6,6'-
dimethyl[1,1'-biphenyl] (yield after crystallization from EtOH, 93%). Subsequent exchange of the Br-atoms
with potassium phthalimide (Fluka) in DMF (yield, 93%) and Gabriel synthesis with hydrazine (Fluka) in
EtOH and acidic workup (conc. HCl soln.) gave (MP)-1 (yield of crude product, 86%). Separation of the
enantiomers was achieved by two crystallizations with the corresponding tartaric acid in EtOH/0.001m HCl:
57% (crystallization) of (P)-1 obtained with l-tartaric acid (Fluka) and 53% (crystallization) of (M)-1 obtained
with d-tartaric acid (Fluka). Overall yield: 31% of (P)-1 and 29% of (M)-1.
Data of (P)-1: M.p. 698 (EtOH). [a]D20
ˆ
21.0 (c ˆ 1.0, EtOH). CD (c ˆ 3.08 ´ 10 5 m, hexane): 193.2
(
17.30); 208.8 (5.76); 218.1 (4.52, sh); 242.6 ( 1.24). IR (KBr): 3354m (br.), 3019m, 2917m, 1578s, 1462s,
1377m, 1321m, 1166w, 1034w, 1002w, 935w, 886w, 821w, 761s, 598w. 1H-NMR (300 MHz, CDCl3): 7.31 (dd, 3J ˆ
7.7, 4J ˆ 1.8,
H
C(3,3')); 7.27 (t, 3J ˆ 7.6,
H
C(4,4')); 7.17 (dd, 3J ˆ 7.0, 4J ˆ 1.7,
H C(5,5')); 3.36,
3.29 (AB, JAB ˆ 14.3, 2 CH2NH2); 1.82 (s, 2 Me); 1.30 (br. s, 2 NH2). 13C-NMR (75 MHz, CDCl3): 140.5
(C(2,2')); 137.6(C(1,1')); 135.7(C(6,6')); 128.5(C(5,5')); 127.6(C(4,4')); 125.0(C(3,3')); 44.1(CH2NH2);
19.8(Me). 1H-NOE (300 MHz, CDCl3): 1.82(Me) ! 7.17 (s, H C(5,5')). 1H,13C-HETCOR (300 MHz,
CDCl3): 7.31! 125.0; 7.27! 127.6; 7.17 ! 128.5; 3.36 and 3.29! 44.1; 1.82 ! 19.8. H, 13C-COLOC (300 MHz,
1
CDCl3): 7.31 ! 137.6(w), 128.5(m); 7.27 ! 140.5(m), 135.7(w); 7.17 ! 137.6(m), 125.0 (m), 19.8(m); 3.36

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Helvetica Chimica Acta ± Vol. 82 (1999)
and 3.29 ! 140.5(m), 137.6(w), 125.0(m); 1.82 ! 137.6(m), 135.7(s), 128.5(m). Anal. calc. for C16H20N2 ´
C4H6O6 (390.44): C 61.53, H 6.71, N 7.17; found: C 61.23, H 6.68, N 7.05.
Data of (M)-1: M.p. 698 (EtOH). [a]2D0 ˆ‡ 21.1 (c ˆ 1.0, EtOH). CD (c ˆ 3.52 ´ 10 5 m, hexane): 193.1
(17.10 ); 208.8( 5.71); 218.4( 4.43, sh); 242.6(1.23).
2. Determination of the Optical Purity of the Enantiomers (P)- and (M)-1. To a clear soln. of (P)- or (M)-1
(50 mg, 0.21 mmol) in CH2Cl2 (10 ml) and a few drops of pyridine, pivaloyl chloride (2,2-dimethylpropanoyl
chloride; 0.05 ml, 0.43 mmol) was added ( ! white precipitation). The mixture was stirred at r.t. for 1 h and
then extracted with 1m HCl and sat. NaHCO3 soln. The org. phase was dried (Na2SO4) and evaporated. The
colorless residue of (P)- or (M)-N,N'-({6,6'-dimethyl[1,1'-biphenyl]-2,2'-diyl}bis(methylene))[2,2-dimethylpro-
panamide] was examined by HPLC ((S,S)-Whelk-O-1 column, hexane/EtOH 95:5, flow 1 ml): tR 16.4 (P) and
19.0 min (M); a ˆ 1.19.
3. Optically Pure H2Salen-Type Ligands: General Procedure. To the colorless soln. of (P)- or (M)-1
(1 mmol) in CH2Cl2 (10 ml) in the presence of 4-Š molecular sieves, the corresponding salicylaldehyde
(2 mmol-equiv.) was added (immediate color change to yellow). After 1 h stirring at r.t., the yellow soln. was
filtered over silica gel (1% Et3N) and evaporated. The residue was dried and crystallized (EtOH).
(M)-N,N'-Bis[(2-hydroxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanamine (3a): M.p.
898 (EtOH). CD (c ˆ 1.06 ´ 10 5 m, EtOH): 211(11.14), 228( 13.77), 262( 11.81), 280( 3.85, sh),
332( 0.35). IR (KBr): 3055m, 2924m, 2850m, 1625s, 1579m, 1494s, 1460s, 1442m, 1409m, 1384m, 1334m,
1280s, 1209m, 1150m, 1116m, 1039m, 991m, 888w, 817m, 797m, 785m, 757s, 655m, 570w, 528w, 474w, 458w.
1H-NMR (300 MHz, CDCl3): 13.32 (br. s, 2 OH); 7.62 (s, 2 NˆC H); 7.34 ± 7.23 (m, 8 arom. H); 7.00 (dd,
3J ˆ 7.6, 4J ˆ 1.7,
2
arom. H); 6.89 (dt, 3J ˆ 7.6, 4J ˆ 1.0,
2
arom. H); 4.33, 4.16 (AB, JAB ˆ 14.0,
2 CH2N); 1.89 (s, 2 Me). 13C-NMR (75 MHz, CDCl3): 167.5; 161.0; 138.0; 136.2; 135.3; 132.2; 131.5; 129.6;
127.7; 126.8; 118.6; 118.5; 116.9; 62.2 (CH2N); 19.8 (Me). Anal. calc. for C30H28N2O2 (448.57): C 80.33, H 6.29,
N 6.25; found: C 80.48, H 6.47, N 6.05.
(M)-N,N'-Bis[(2-hydroxy-3-methoxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanamine
(3b): M.p. 788 (EtOH). CD (c ˆ 9.67 ´ 10 6 m, EtOH): 213(1.72), 229( 4.62), 272( 8.45). IR (KBr): 3443w,
(br.), 3060w, 3000w, 2923m, 1629s, 1464s, 1381m, 1335m, 1254s, 1169w, 1080m, 1045m, 973m, 950w, 839m, 780m,
736s, 644w, 570w, 516w. 1H-NMR (300 MHz, CDCl3): 13.83 (br. s, 2 OH); 7.63 (s, 2 NˆC H); 7.30 ± 7.21 (m, 6
arom. H); 6.84 (dd, 3J ˆ 7.9, 4J ˆ 1.5, 2 arom. H); 6.71 (d, 3J ˆ 8.0, 2 arom. H); 6.63 (dd, 3J ˆ 7.9, 4J ˆ 1.5, 2 arom.
H); 4.33, 4.15 (AB, JAB ˆ 14.0, 2 CH2N); 3.87 (s, 2 MeO); 1.89 (s, 2 Me). 1H-NMR (300 MHz, C6D6): 13.80 (br.
s, 2 OH); 7.31 (s, 2 NˆC H); 7.17 (d, 3J ˆ 7.2, 2 arom. H); 7.09 (t, 3J ˆ 7.2, H C(4,4')); 7.01 (d, 3J ˆ 7.2, 2
arom. H); 6.68 ± 6.52 (m, 6 arom. H); 4.04, 3.93 (AB, JAB ˆ 14.2, 2 CH2N); 3.49 (s, 2 MeO); 1.75 (s, 2 Me).
13C-NMR (75 MHz, CDCl3): 165.7; 151.8; 148.3; 137.8; 136.2; 135.2; 129.6; 127.9; 126.7; 123.1; 118.4; 117.7;
113.9; 61.5 (CH2N); 56.0 (MeO); 19.8(Me). Anal. calc. for C32H32N2O4 (508.62): C 75.57, H 6.34, N 5.51; found:
C 75.42, H 6.31, N 5.47.
(P)-N,N'-Bis[(5-bromo-2-hydroxy-3-methoxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'dimethan-
amine (3c): M.p. 758 (EtOH). CD (c ˆ 1.01 ´ 10 5 m, EtOH): 211 ( 15.45), 225(12.30), 248( 8.64),
270( 7.13), 342(1.29). IR (KBr): 3443w(br.), 2933m, 2848m, 1631s, 1574m, 1472s, 1442s, 1395m, 1335m,
1272s, 1252s, 1099m, 1048m, 977m, 950w, 910w, 865m, 840m, 763m, 736m, 692w, 577w, 512w. 1H-NMR
(300 MHz, CDCl3): 13.87 (br. s, 2 OH); 7.54 (s, 2 NˆC H); 7.32 ± 7.24 (m, 6 arom. H); 6.90 (d, 4J ˆ 2.2, 2
arom. H); 6.73 (d, 4J ˆ 2.2, 2 arom. H); 4.35, 4.12 (AB, JAB ˆ 14.3, CH2N); 3.86 (s, 2 MeO); 1.90 (s, 2 Me).
13C-NMR (75 MHz, CDCl3): 164.5; 151.7; 149.4; 137.8; 136.3; 129.8; 128.1; 126.7; 124.8; 118.9; 116.9; 109.0; 61.2
(CH2N); 56.3(MeO); 19.8(Me).
(P)-N,N'-Bis[(2-hydroxy-5-methoxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'dimethanamine
(3d): M.p. 738 (EtOH). CD (c ˆ 1.03 ´ 10 5 m, EtOH): 219( 16.35), 240(22.75), 263(10.91), 359( 1.06). IR
(KBr): 3444w(br.), 2998m, 2922m, 1635s, 1590s, 1492s, 1463s, 1370m, 1332s, 1270s, 1225s, 1195m, 1158s, 1037s,
934w, 911w, 847m, 764s, 680w, 666w, 631w, 587w, 462w. 1H-NMR (300 MHz, CDCl3): 12.75 (br. s, 2 OH);
7.59 (s, 2 NˆC H); 7.32 ± 7.22 (m, 6 arom. H); 6.85 (m, 4 arom. H); 6.52 (d, 4J ˆ 2.5, 2 arom. H); 4.33,
4.15 (AB, JAB ˆ 14.0, 2 CH2N); 3.72 (s, 2 MeO); 1.89 (s, 2 Me). 13C-NMR (75 MHz, CDCl3): 165.3; 155.0; 151.8;
137.9; 136.2; 135.3; 129.5; 127.8; 126.7; 119.1; 118.3; 117.7; 115.0; 62.2 (CH2N); 55.8(MeO); 19.7(Me).
(M)-N,N'-Bis[(5-bromo-2-hydroxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanamine
(3e): M.p. 878 (EtOH). CD (c ˆ 1.06 ´ 10 5 m, EtOH): 216(26.31), 234( 26.81), 253( 10.10), 318( 0.80),
349(0.23). IR (KBr): 3443w(br.), 2919m, 1631s, 1570m, 1475s, 1441m, 1384m, 1362m, 1328w, 1279s, 1237w,
1203m, 1181m, 1129w, 1076m, 1046m, 985w, 956w, 891w, 880w, 820s, 795m, 764m, 688m, 625m, 553w, 464w.
1H-NMR (300 MHz, CDCl3): 13.26 (br. s, 2 OH); 7.56 (s, 2 NˆC H); 7.36 ± 7.23 (m, 8 arom. H); 7.10 (d, 4J ˆ
2.2, 2 arom. H); 6.80 (d, 3J ˆ 8.7, 2 arom. H); 4.33, 4.17 (AB, JAB ˆ 14.0, 2 CH2N); 1.89 (s, 2 Me). 13C-NMR

Helvetica Chimica Acta ± Vol. 82 (1999)
135
(75 MHz, CDCl3): 164.2; 159.9; 137.9; 136.3; 134.9; 134.8; 133.4; 129.7; 128.0; 126.8; 119.9; 118.9; 109.9; 62.1
(CH2N); 19.7 (Me). Anal. calc. for C30H26Br2N2O2 (606.36): C 59.43, H 4.32, N 4.62; found: C 59.30, H 4.34,
N 4.60.
(M)-N,N'-Bis{[3,5-di(tert-butyl)-2-hydroxyphenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
amine (3 f): M.p. 948 (EtOH). IR (KBr): 3418w, 2959s, 2868s, 1629s, 1596m, 1467s, 1441s, 1392m, 1361m, 1329m,
1273m, 1251s, 1234m, 1202m, 1173m, 1132w, 1042w, 947w, 879m, 828m, 801m, 772m, 761m, 731w, 712w, 644w,
518w. 1H-NMR (300 MHz, CDCl3): 13.70 (br. s, 2 OH); 7.60 (s, 2 NˆC H); 7.35 ± 7.21 (m, 8 arom. H);
6.84 (d, 4J ˆ 2.4, 2 arom. H); 4.32, 4.18 (AB, JAB ˆ 13.9, 2 CH2N); 1.89 (s, 2 Me); 1.42 (s, 4 t-Bu). 13C-NMR
(75 MHz, CDCl3): 166.6; 158.0; 139.9; 138.1; 136.5; 136.3; 135.7; 129.5; 127.7; 126.8; 126.2; 117.8; 62.2 (CH2N);
34.9; 34.2; 29.4(Me3C); 19.7(Me).
(M)-N,N'-Bis[(2,3-dihydroxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanamine (3g):
M.p. 958 (EtOH). CD (c ˆ 6.99 ´ 10 5 m, EtOH): 212(0.45, sh), 226( 1.36), 250(0.75), 277( 3.80), 306
(
0.74, sh), 333 (0.38). IR (KBr): 3375m, 3060m, 2919m, 1634s, 1546m, 1464s, 1381s, 1204s, 1164s, 1028m,
850m, 802w, 783m, 737s, 569w, 495w, 470w. 1H-NMR (300 MHz, CDCl3): 13.70 (br. s, 2 OH); 7.66 (s, 2
NˆC H); 7.37 ± 7.23 (m, 6 arom. H); 6.92 ± 6.89 (m, 2 arom. H), 6.59 ± 6.56 (m, 2 arom. H), 4.32,
4.27 (AB, JAB ˆ 14.3, 2 CH2N); 1.95 (s, 2 Me). 13C-NMR (75 MHz, CDCl3): 165.3; 156.1; 146.6; 137.5; 136.1;
134.4; 130.1; 128.3; 126.3; 122.1; 116.8; 115.8; 59.0 (CH2N); 19.6 (Me).
(M)-N,N'-Bis[(3-ethoxy-2-hydroxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanamine
(3h): M.p. 578 (EtOH). CD (c ˆ 6.26 ´ 10 5 m, EtOH): 198(11.11), 229( 5.17), 243( 0.91, sh), 250( 0.49),
273( 6.93), 330(0.37). IR (KBr): 3443w, 3060w, 2978m, 2881m, 1628s, 1582m, 1465s, 1382m, 1335m, 1272s,
1251s, 1175m, 1115m, 1079m, 1045m, 952w, 891m, 833m, 778s, 762m, 736s, 646w, 572w, 509w. 1H-NMR
(300 MHz, CDCl3): 13.83 (br. s, 2 OH); 7.64 (s, 2 NˆC H); 7.33 ± 7.21 (m, 6 arom. H); 6.86 (dd, 3J ˆ 7.7, 4J ˆ
1.7, 2 arom. H), 6.70 (t, 3J ˆ 7.7, 2 arom. H); 6.64 (dd, 3J ˆ 7.7, 4J ˆ 1.7, 2 arom. H), 4.31, 4.15 (AB, JAB ˆ 14.2, 2
CH2N); 4.07 (q, 3J ˆ 7.0, 2 MeCH2O); 1.88 (s, 2 Me); 1.46 (t, 3J ˆ 7.0, 2 MeCH2O). 13C-NMR (75 MHz, CDCl3):
165.6; 152.0; 147.6; 137.8; 136.2; 135.2; 129.6; 127.9; 126.8; 123.1; 118.6; 117.8; 115.5; 64.5; 61.5; 19.8(Me);
14.9(MeCH2O). Anal. calc. for C34H36N2O4 (536.68): C 76.09, H 6.76, N 5.22; found: C 75.82, H 6.68, N 5.15.
(P)-N,N'-Bis[(2-hydroxy-3-propoxyphenyl)methylidene]-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanamine
(3i): M.p. 558 (EtOH). CD (c ˆ 4.74 10 5 m, EtOH): 198 ( 11.35), 213 ( 0.45, sh), 230 (5.44), 245 (0.64, sh)
252 (0.15), 246( 0.15), 273(6.86), 302(1.21, sh), 334( 0.98). IR (KBr): 3424w, 3060w, 2963m, 2934m, 2876m,
1629s, 1582m, 1464s, 1381m, 1335m, 1253s, 1174w, 1080m, 1047m, 977w, 943m, 910w, 843m, 779m, 735s, 641w,
571w, 512w. 1H-NMR (300 MHz, CDCl3): 13.83 (br. s, 2 OH); 7.63 (s, 2 NˆC H); 7.31 ± 7.20 (m, 6 arom. H);
6.86 (dd, 3J ˆ 7.8, 4J ˆ 1.6, 2 arom. H); 6.70 (t, 3J ˆ 7.8, 2 arom. H); 6.63 (dd, 3J ˆ 7.8, 4J ˆ 1.7, 2 arom. H); 4.30,
4.14 (AB, JAB ˆ 14.2,
2
CH2N); 3.96 (t, 3J ˆ 6.7,
2
MeCH2CH2O); 1.88 (s, 2 Me); 1.86 (sext., 3J ˆ 7.1,
2
MeCH2CH2O); 1.04 (t, 3J ˆ 7.4, 2 MeCH2CH2O). 13C-NMR (75 MHz, CDCl3): 165.7; 152.1; 147.8; 137.8;
136.2; 135.3; 129.5; 127.9; 126.8; 123.2; 118.6; 117.7; 115.7; 70.6; 61.5; 22.6; 19.8(Me); 10.5.
(M)-N,N'-Bis{[2-hydroxy-3-(phenylmethoxy)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
amine (3k): M.p. 558 (EtOH). CD (c ˆ 4.66 ´ 10 5 m, EtOH): 213(4.99), 229(1.89), 241( 0.71), 246( 0.15),
252( 0.55), 274(5.18), 295(2.32, sh), 333( 1.35). IR (KBr): 3440m, 3060m, 3029m, 2877m, 1628s, 1497m,
1461s, 1376m, 1334m, 1252s, 1172m, 1083m, 1069m, 1044m, 975m, 910m, 845m, 778m, 736s, 696s, 649w, 576w,
508w, 469w. 1H-NMR (300 MHz, CDCl3): 13.83 (br. s, 2 OH); 7.63 (s, 2 NˆC H); 7.44 (d, 3J ˆ 7.1, 2 arom. H);
7.37 ± 7.20 (m, 12 arom. H); 6.90 ± 6.84 (m, 2 arom. H), 6.65 ± 6.63 (m, 4 arom. H); 5.13 (s, 2 PhCH2O), 4.32,
4.16 (AB, JAB ˆ 14.1, 2 CH2N); 1.89 (s, 2 Me). 13C-NMR (75 MHz, CDCl3): 165.7; 152.5; 147.3; 137.9; 137.3;
136.3; 135.2; 129.6; 128.5; 127.9; 127.8; 127.4; 126.8; 125.7; 123.9; 118.8; 117.7; 117.1; 71.1; 61.5; 19.7(Me).
(P)-N,N'-Bis{[(2-hydroxy-3-(2-methylpropoxy)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-di-
methanamine (3l): M.p. 428 (EtOH). CD (c ˆ 4.98 ´ 10 5 m, EtOH): 213( 2.07, sh), 230(2.96), 250( 0.08),
274(6.23), 302(1.09, sh), 335( 1.00). IR (KBr): 3417w (br.), 3061w, 2956m, 2871m, 1629s, 1583m, 1462s,
1392m, 1334m, 1251s, 1175m, 1077m, 1044m, 984m, 948w, 843m, 778m, 735s, 649w, 566w, 508w. 1H-NMR
(300 MHz, CDCl3): 13.73 (br. s, 2 OH); 7.59 (s, 2 NˆC H); 7.30 ± 7.19 (m, 6 arom. H); 6.85 (dd, 3J ˆ 7.8, 4J ˆ
1.5, 2 arom. H); 6.69 (t, 3J ˆ 7.8, 2 arom. H), 6.61 (dd, 3J ˆ 7.8, 4J ˆ 1.6, 2 arom. H); 4.31, 4.13 (AB, JAB ˆ 14.1, 2
CH2N); 3.75 (d, 3J ˆ 6.7, 2 Me2CHCH2O); 2.16 (sept., 3J ˆ 6.7, 2 Me2CHCH2O); 1.88 (s, 2 Me); 1.03 (d, 3J ˆ 6.7,
2 Me2CHCH2O). 13C-NMR (75 MHz, CDCl3): 165.7 (CHˆN); 152.1; 147.9; 137.8; 136.1; 135.2; 129.5; 127.8;
126.7; 123.1; 118.5; 117.6; 115.8; 75.6 (Me2CHCH2O); 61.6(CH2); 28.2(Me2CHCH2O); 19.7(Me); 19.3,
19.2(Me2CHCH2O).
(M)-N,N'-Bis{[2-hydroxy-3-(1-methylethoxy)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
amine (3m): M.p. 518 (EtOH). CD (c ˆ 4.74 ´ 10 5 m, EtOH): 196(11.16), 213(1.37, sh), 228( 3.34),
244( 0.85), 272( 6.43), 304( 0.83, sh), 335( 0.74). IR (KBr): 3406w, 3061w, 2974m, 2921m, 1629s, 1462s,

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Helvetica Chimica Acta ± Vol. 82 (1999)
1381s, 1333m, 1270s, 1251s, 1171m, 1138m, 1110s, 1034m, 923m, 857m, 825m, 781m, 762m, 737s, 647w, 571w,
510w. 1H-NMR (300 MHz, CDCl3): 13.81 (br. s, 2 OH); 7.62 (s, 2 NˆC H); 7.30 ± 7.19 (m, 6 arom. H);
6.89 (dd, 3J ˆ 7.7, 4J ˆ 1.8, 2 arom. H), 6.70 (t, 3J ˆ 7.6, 2 arom. H); 6.65 (dd, 3J ˆ 7.7, 4J ˆ 1.9, 2 arom. H);
4.54 (sept. 3J ˆ 6.1, 2 Me2CHO); 4.29, 4.15 (AB, JAB ˆ 14.0, 2 CH2N); 1.87 (s, 2 Me); 1.35, 1.34 (2d, 3J ˆ 6.1, 2
Me2CHO). 13C-NMR (75 MHz, CDCl3): 165.6 (CHˆN); 152.9; 146.2; 137.4; 136.1; 135.2; 129.5; 128.0; 127.8;
126.7; 123.7; 119.0; 117.7; 71.4(Me2CHO); 61.4(CH2N); 22.1, 22.0(Me2CHO); 19.7(Me).
4. CoII Complexes: General Procedure. The ligand 3 (1 mmol) in EtOH (30 ml) was deprotonated with 2m
KOH/MeOH (3 ml). To the yellow soln., [CoII(AcO)2] ´ 4 H2O (Fluka, 1 mmol equiv.) was added. The dark red
soln. was stirred under N2 at r.t. for 1 h, and then evaporated. The residue was extracted with CHCl3 (5 Â 50 ml),
the collected org. phase dried (Na2SO4) and evaporated, and the brown powder crystallized (toluene or CH2Cl2/
hexane): CoII complex[CoII(3')].
The elemental analysis of CoII complexes with alkoxy-substituted ligands indicated the presence of H2O.
Even after drying under high vacuum, followed immediately by analysis, H2O was present. A series of successive
analyses revealed the uptake of H2O, even when the samples were stored under N2.
{(M)-N,N'-Bis{[2-(hydroxy-kO)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethanaminato(2 )-
kN,kN'}cobalt ([CoII(3'a)]): M.p. 1758 (CH2Cl2/hexane). IR (KBr): 3017m, 2918m, 1609s, 1534s, 1465s, 1445s,
1397m, 1348s, 1319s, 1248w, 1190m, 1147s, 1128m, 1055m, 1030m, 970w, 908m, 849w, 798m, 752s, 679w, 612w,
588w, 512w, 465w. EI-MS: 505(100), 399(12), 372(19), 370(17), 191(58), 178(23). FAB-MS: 506 ([M ‡ 1]).
‡
HR-FAB-MS: 506.1399 (C30H27CoN2O2 ; calc. 506.1404). Anal. calc. for C30H26CoN2O2 (505.49): C 71.28,
H 5.18, N 5.54; found: C 71.05, H 5.11, N 5.49.
{(M)-N,N'-Bis{[2-(hydroxy-kO)-3-methoxyphenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
aminato(2-)-kN,kN'}cobalt ([CoII(3'b)]): M.p. 1658 (CH2Cl2/hexane). IR (KBr): 3441m, 3052m, 2922m, 2828m,
1603s, 1543s, 1467s, 1438s, 1400s, 1318s, 1244s, 1214s, 1168m, 1110m, 1082m, 1049m, 981m, 865m, 807w, 779m,
737s, 660w, 623w, 566w. ESI-MS: 565.2. Anal. calc. for C32H30CoN2O4 ´ (H2O)0.5 (570.04): C 67.43, H 5.39, N 4.91;
found: C 67.21, H 5.42, N 4.83.
{(P)-N,N'-Bis{[5-bromo-2-(hydroxy-kO)-3-methoxyphenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-
dimethanaminato(2-)-kN,kN'}cobalt ([CoII(3'c)]): M.p. 1978 (CH2Cl2/hexane). IR (KBr): 3447m, 2928m, 1621s,
1540s, 1464s, 1316s, 1238s, 1212s, 1100m, 1050s, 985w, 874m, 839m, 791m, 758s, 701m, 662w, 620w, 568m, 540w,
527w, 514w, 502w , 487w, 474w. ESI-MS: 723.1.
{(M)-N,N'-Bis{[2-(hydroxy-kO)-3-hydroxyphenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
aminato(2 )-kN,kN'}cobalt ([CoII(3'g)]): M.p. 1978 (CH2Cl2/hexane). IR (KBr): 3401w, 3059w, 2928m, 1618s,
1554m, 1447s, 1403m, 1317m, 1264s, 1235s, 1095m, 1035s, 858m, 778m, 734s, 668w, 472w. ESI-MS: 537.5.
{(M)-N,N'-Bis{[3-ethoxy-2-(hydroxy-kO)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
aminato(2 )-kN,kN'}cobalt ([CoII(3'h)]): M.p. 1728 (CH2Cl2/hexane). IR (KBr): 3446w, 2974m, 2923m, 1608s,
1541s, 1466s, 1438s, 1395s, 1316s, 1239s, 1212s, 1175m, 1093m, 1048m, 901m, 858m, 806w, 779m, 737s, 650w, 457w.
ESI-MS: 593.1. Anal. calc. for C34H34CoN2O4 ´ (H2O)0.5 (593.59): C 68.28, H 5.81, N 4.68; found: C 67.99,
H 5.90, N 4.54.
{(P)-N,N'-Bis{[2-(hydroxy-kO)-3-propoxyphenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
aminato(2 )-kN,kN'}cobalt ([CoII(3'i)]): M.p. 1788 (CH2Cl2/hexane). IR (KBr): 3452w, 2961m, 2870m, 1602s,
1544m, 1463s, 1439s, 1402m, 1317m, 1240m, 1211s, 1082w, 1055m, 958w, 861m, 778m, 736s, 649w, 509w. ESI-MS:
621.3.
{(M)-N,N'-Bis{[2-(hydroxy-kO)-3-(phenylmethoxy)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-
dimethanaminato(2-)-kN,kN'}cobalt ([CoII(3'k)]): M.p. 1928 (CH2Cl2/hexane). IR (KBr): 3445w, 3028w, 2892m,
1603s, 1542m, 1496w, 1438s, 1401m, 1316m, 1212s, 1171m, 1087w, 1049m, 980w, 861m, 807w, 778m, 736s, 696m,
668w, 649w, 618w, 507w. ESI-MS: 713.4.
{(P)-N,N'-Bis{[2-(hydroxy-kO)-3-(2-methylpropoxy)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-
dimethanaminato(2-)-kN,kN'}cobalt ([CoII(3'l)]): M.p. 1828 (CH2Cl2/hexane). IR (KBr): 3445w, 3053m, 2955m,
2870m, 1603s, 1543m, 1463s, 1437s, 1401m, 1318m, 1242s, 1211s, 1175m, 1080m, 1045m, 862m, 779m, 737s, 650w,
512w, 448w. ESI-MS: 649.3.
{(M)-N,N'-Bis{[2-(hydroxy-kO)-3-(1-methylethoxy)phenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-
dimethanaminato(2-)-kN,kN'}cobalt ([CoII(3'm)]): M.p. 1728 (CH2Cl2/hexane). IR (KBr): 3445w, 3055w,
2959m, 2875m, 1604s, 1545m, 1464s, 1440s, 1401m, 1317m, 1241s, 1211s, 1079m, 1052m, 863m, 779m, 737s, 648w,
510w. ESI-MS: 621.3.
Complexes [MnII(3'b)], [FeII(3'b)], [NiII(3'b)], and [CuII(3'b)] were synthesized similarly to the CoII
complexes.

Helvetica Chimica Acta ± Vol. 82 (1999)
137
{(P)-N,N'-Bis{[2-(hydroxy-kO)-3-methoxyphenyl]methylidene}-6,6'-dimethyl[1,1'-biphenyl]-2,2'-dimethan-
aminato(2 )-kN,kN'}zinc ([Zn(3'b)]) was synthesized by addition of ZnEt2 (0.2 mmol; previously evaporated
from 1.0m ZnEt2 soln. in hexane), in (D6)benzene to 3b (0.2 mmol) in (D6)benzene (2 ml). 1H-NMR (300 MHz,
C6D6): 6.90 ± 6.85 (m, 4 arom. H); 6.84 (s, 2 NˆC H); 6.63 (t, 3J ˆ 7.4); 6.58 (dd, 3J ˆ 7.4, 4J ˆ 1.4); 6.48 (t, 3J ˆ
7.8); 6.30 (dd, 3J ˆ 8.0, 4J ˆ 1.7); 4.04 (Ad, JAB ˆ 14.7, 4J ˆ 1.4, 2 H, 2 CH2N); 3.67 (s, 2 MeO); 3.53 (Bd, JAB
14.8, 2 H, 2 CH2N); 1.71 (s, 2 Me).
ˆ
5. Ethylation of Aldehydes with Various Transition-Metal Catalysts: General Procedure. 5.1. For AlClEt2,
Ti(i-PrO)4, and ZnEt2. Under N2 and r.t., the ligand 3a ± f (0.05 mmol) was dissolved in toluene (2 ml). To the
yellow soln., the basic Al, Ti, Zn complex (0.05 mmol) was added, and stirring was continued for 1 h. Then,
ZnEt2 (1 mmol) was added, followed, after 5 min, by benzaldehyde (0.5 mmol). The soln. was stirred for 18 h at
1
r.t. and then analyzed by HPLC and H-NMR. Results: see Fig. 1 and Table 1.
5.2. Complexes [CoII(3'a ± m)], [MnII(3'b)], [FeII(3'b)], [NiII(3'b)], or [CuII(3'b)]. The corresponding
complex (0.05 mmol) was dissolved in toluene (2 ml). ZnEt2 (1 mmol) was added in one portion to the colored
soln. After 5 min, the aldehyde was added as described in Exper. 5.1. The mixture was stirred at r.t., and then the
conversion (mesitylene as internal standard) and the stereochemical outcome were analyzed by HPLC and
1H-NMR or GC. Results: see Fig. 1 and Tables 2 ± 4.
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Received September 14, 1998