Symmetric and asymmetric samarium alkoxide derivatives of bridging sulfur biphenolate and binaphtholate ligands; synthetic, structural, and catalytic studies

Article abstract of DOI:10.1016/S0022-328X(01)01425-5

The new thio-binaphthol 2,2′thiobis(3,6-di-tert-butylnaphth-2-ol), and a phenolic analogue 2,2′thiobis(6-tert-butyl-4-methyl phen-2-ol) react with the Sm(III) aryloxide ancillary ligands, [Sm{1,1′-S(2-OC₁₀H₄Bu ^t₂-3,6)₂}(OC₆H₃Bu ^t₂-2,6)]₂ and [Sm{1,1′-S (2-OC₆H₂Bu^t-3-Me-5)₂} (OC₆H₃Bu^t₂-2,6)]₂. Symmetric and asymmetric derivatives of both ligands have been prepared by careful tuning of the preparative procedure, the asymmetric naphtholate derivative, and the ligand from which it derives have both been structurally characterised. The asymmetric derivatives are found to be highly selective catalyst for diol desymmetrisation.

Full text of DOI:10.1016/S0022-328X(01)01425-5

Journal of Organometallic Chemistry 647 (2002) 205–215
www.elsevier.com/locate/jorganchem
Symmetric and asymmetric samarium alkoxide derivatives of
bridging sulfur biphenolate and binaphtholate ligands; synthetic,
structural, and catalytic studies
Polly L. Arnold *, Louise S. Natrajan, Jonathan J. Hall, Stephan J. Bird,
Claire Wilson
School of Chemistry, Uni6ersity of Nottingham, Uni6ersity Park, Nottingham NG7 2RD, UK
Received 28 September 2001; accepted 8 November 2001
Abstract
The new thio-binaphthol 2,2%thiobis(3,6-di-tert-butylnaphth-2-ol), and a phenolic analogue 2,2%thiobis(6-tert-butyl-4-methyl
phen-2-ol) react with the Sm(III) aryloxide [Sm(OC6H3But2-2,6)3] to give the first f-element complexes supported by S-bridged
biphenolate or binaphtholate ancillary ligands, [Sm{1,1%-S(2-OC10H4But2-3,6)2}(OC6H3Bu2t -2,6)]2 and [Sm{1,1%-S(2-OC6H2But-3-
Me-5)2}(OC6H3But2-2,6)]2. Symmetric and asymmetric derivatives of both ligands have been prepared by careful tuning of the
preparative procedure, the asymmetric naphtholate derivative, and the ligand from which it derives have both been structurally
characterised. The asymmetric derivatives are found to be highly selective catalysts for diol desymmetrisation. © 2002 Elsevier
Science B.V. All rights reserved.
Keywords: Sulfur biphenolate; Sm(III) Lewis acid; Binaphtholate ancillary ligands; Aryloxide; Asymmetric monoacylation; Desymmetrisation
1. Introduction
mediating the reactivity of these electropositive cations,
mono-and bidentate alkoxides have become increas-
ingly popular [1].
The replacement of a cyclopentadienyl ligand with
the harder, isolobal, monodentate phenolate fragment,
The continuing development of alternatives to the
bis(Cp) ancillary ligand set in lanthanide chemistry
constantly reveals new catalysts and unusual small-
molecule activation reactivity. As robust, cheap, tune-
able, and even potentially recyclable ancillary sets for
for
example
to
form
complexes
such
as
[Cp*Y(OC6H3But2-2,6)H]2, [2] can be advantageous in
that the harder aryloxide ligand suppresses b-elimina-
tion in ethene polymerisation reactions. The incorpora-
tion of harder ligands also generates complexes such as
[(Me3SiH2C)2Y(OC6H3Bu2t -2,6)(thf)2] [3] that catalyse
o-caprolactone ring-opening polymerisation in addition
to ethene polymerisation chemistry. The use of a biden-
tate ligand to support such reactivities has the advan-
tage of avoiding destructive ligand redistribution
reactions, and allows the opportunity to design asym-
metry into the ligand set. For example, the lanthanide
alkyl o-tert-butylbiphenolate chelate [La{CH(SiMe3)2}-
{1,1%-(2-OC6H2But2-3,5)2}] has a very low energy barrier
for the twisting motion that eclipses the two phenol
planes and destroys the chirality of the complex,
whereas the analogous o-triphenylsilylbinaphtholate
derivative [La{CH(SiMe3)2}{1,1%-(2-OC10H5SiPh3-3)2}-
Fig. 1. 2,2%Thiobis(3,5-tert-butyl-2-naphthol), H2LSN
2,2%thiobis(6-tert-butyl-4-methylphenol), H2LS, 2.
,
1
and
* Corresponding author. Tel.: +44-115-9513437; fax: +44-115-
9513563.
E-mail address: polly.arnold@nott.ac.uk (P.L. Arnold).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01425-5

206
P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
(OEt2)] is a rigid C2-symmetric complex [4]. The latter
also undergoes insertion reactions of CO, but no cata-
lytic activity has been reported for these alkyl com-
plexes. Less sterically hindered binol derivatives have
more recently been used to access an interesting range
of homoleptic, symmetric and asymmetric Lewis acidic
catalysts for organic transformations [5].
To date, the potential of the sulfur-bridged bipheno-
late ligand 2,2%thiobis(6-tert-butyl-4-methyl phenol),
H2LS, Fig. 1, has not been studied as an ancillary
ligand set for f-element co-ordination chemistry. This
chelating biphenolate has an exemplary record as an
auxiliary ligand set in transition metal catalysis-serving
to stabilise highly active Ti(IV) polymerisation cata-
lysts, [6] and a copper system that behaves as a func-
tional model for Galactose Oxidase in its catalysis of
the aerial oxidation of both primary and secondary
alcohols [7].
small molecules and new types of Lewis acid catalysts
for certain organic transformations. We herein report
our synthesis of the first f-element derivative of this
type of sulfur-bridged-bisaryloxide ligand; a Sm(III)
derivative of the new thio-binaphtholate dianion
derived from 1, and a comparison of its catalytic reac-
tivity with the Sm(III) biphenolate analogue, to our
knowledge, the first use of 2 as a ligand in lanthanide
co-ordination chemistry.
2. Results and discussion
Surprisingly to date there have been no reported
lanthanide complexes containing heteroatom-bridged
biphenolate or binaphtholate ligands. Our aims in this
study were to gain an understanding of the ability of
the sulfur donor atom in the ancillary ligand set LS and
LSN to influence the reactivity of lanthanide derivatives,
the relative rigidity of these ligand sets, and the ability
of the lanthanide complexes to function as Lewis acid
catalysts. Structural studies show the chelated naphtho-
late ligand is capable of providing an asymmetric,
stereochemically rigid ligand framework for Sm(III).
Our preliminary data that show the new Sm complexes
catalyse the acylation-desymmetrisation of 1,2-diols.
The ligand H2LS has been described as a ‘breathing
ligand’ in early transition metal chemistry due to the
ability of the weakly co-ordinating sulfur to reversibly
bind to the metal centre during a reaction. Theoretical
studies based on DFT methods suggest that the labilis-
ing effect of the electron-rich sulfur atom of a Group 4
olefin polymerisation catalyst not only reduces the en-
ergy barrier for ethene binding in the trans position, but
also lowers the energy barrier for the alkene insertion
process [8]. These predictions were borne out when the
Group 4 complexes were later synthesised and struc-
turally characterised [6]. In addition, stereoregular poly-
mers were produced when sufficient steric bulk was
incorporated at the ortho positions of the ligand. This
non-innocent, reversible trans-labilisation of a substrate
in electropositive metal–LS complexes is anticipated to
lead to the activation/functionalisation of a range of
2.1. Ligand synthesis
The first employment of the ligand H2LS was in 1984
and involved the synthesis of new main-group heterocy-
cles with silicon, germanium and phosphorus [9]. It was
noted at this time that both sulfur-bridged biphenol
and binaphthols yielded the eight-membered ring con-
taining compounds, but alkylation of the ortho-aryl
positions to produce sterically encumbered diols was
pursued only for the biphenol.
The reagent 2-naphthol is alkylated by isobutene in
refluxing toluene to give 3,6-di-tert-butylnaphth-2-ol in
good yield, Scheme 1. Both sulfur-bridged derivatives
are easily synthesised in a one pot reaction, using a
ZnCl2 Lewis acid catalyst (Scheme 1); the desired prod-
ucts 1 and 2 may be recrystallised from hexanes.
The ligand H2LS has previously been structurally
characterised [10]. For comparison, a single crystal of
H2LSN suitable for a structural determination was
grown from a cooled diethyl ether solution, the molecu-
lar structure of which is shown in Fig. 2. Notably, the
two naphthol rings are eclipsed, with the planes twisted
with respect to each other by 88.73(2)°. The hydroxyl
protons were located in the Fourier map, each oriented
in the plane of, and pointing towards the sulfur atom.
The sulfurꢀCnaphthol distances, Table 1, are 1.780(2) and
,
1.785(2) A, consistent with non-alkylated structurally
characterised S-bridged binaphthol compounds [11];
other distances and angles are also as anticipated.
Scheme 1. Preparation of S-bridged binaphthol and biphenols, H2LSN
and H2LS.

P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
207
[Sm{1,1%-S(2-OC10H4But2-3,6)2}(OAr)]2 3, as an air and
moisture-sensitive sunflower-yellow solid, after work up
to remove eliminated di-tert-butylphenol (Eq. (1)).
Fig. 2. Ellipsoid plot of the molecular structure of 1.Et2O (30%
probability). Solvent and H atoms included.
Table 1
(1)
,
Selected distances (A) and angles (°) for 1
Crude 3 is characterised in solution as an asymmetric
dinuclear complex, although samples stubbornly retain
one molecule of eliminated phenol rather than thf; this
is removed by recrystallisation from hydrocarbon sol-
vents. This dinuclearity is retained in solution at ambi-
ent temperature as evidenced by 1H-NMR
spectroscopy. Heating a benzene solution of 3 to 350 K
in the NMR spectrometer results in a broadening and
slight convergence of related resonances of the ligands,
but due to partial decomposition in solution at this
temperature, the sample was not heated further, so no
exchange process can be accessed at low temperatures
that render the ‘wings’ of the naphthyl groups equiva-
lent. It is possible that the decomposition is occurring
subsequent to the cleavage of the dimer in the absence
of any other additional potential donor ligands.
Bond distances
S(1)ꢀC(21)
S(1)ꢀC(11)
O(1)ꢀC(12)
O(2)ꢀC(22)
C(11)ꢀC(12)
1.780(2)
1.785(2)
1.372(2)
1.376(2)
1.399(2)
Bond angles
C(21)ꢀS(1)ꢀC(11)
C(12)ꢀC(11)ꢀC(19)
C(12)ꢀC(11)ꢀS(1)
C(19)ꢀC(11)ꢀS(1)
106.89(9)
120.6(2)
116.11(14)
123.10(14)
2.2. Synthesis of Sm(III) deri6ati6es
The reaction of H2LSN with [Sm(OAr)3], where
OAr=OC6H3But2-2,6 in thf or toluene affords
Single crystals suitable for diffraction were obtained
by cooling a toluene solution of 3; in addition to
confirming the asymmetric dinuclearity of 3, the solid
state structure, shown in Fig. 3, has a number of
interesting features. Selected distances and angles are
reported in Table 2.
The first, rather unusual feature is that one of the
naphthyloxide rather than a phenoxide bridges the two
metal centres, in accordance with the asymmetry iden-
tified by NMR spectroscopy. The twist of 88.79(6)°
between the two naphtholate moieties places one ring
system between the two metal centres and gives rise to
SmꢀOnaphth distances in the asymmetric core of 2.392(3)
,
and 2.296(3) A, both at the short end of the range
observed to date. This affords an unusually short
,
SmꢀSm% distance of 3.6084(5) A. An agostic interaction
with the naphthyl ipso and ortho ring carbons, C11 and
C12, is also suggested by the structure. With the sulfur
atom co-ordinated to Sm, the LSN ligand presents a fac
conformation at Sm. In structurally characterised ex-
amples reported to date, the biphenol ligand H2LS has
consistently maintained a fac- conformation in co-ordi-
Fig. 3. Ellipsoid plot of the molecular structure of 3 (30% probabil-
ity). Methyl groups on naphthyl fragments and toluene molecules
have been omitted for clarity.

208
P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
Table 2
in vacuo at 70 °C for 8 h) releases co-ordinated thf as
well as residual phenol, to give an asymmetric complex
4, which is presumably the related thiophenolate-
bridged dimer, analogous to 3, Scheme 2. A range of
mass spectrometry and NMR spectroscopy experiments
also support this formulation.
We have been unable so far to grow single crystals
suitable for X-ray analysis, and without further struc-
tural information we cannot rule out the possibility of
an h6-arene interaction in 4, between each Sm ion and
the arene of LS, as is observed after desolvation of the
monomeric [Ln(C6H3-Ph2-2,6)3] and dimeric [Ln(C6H3-
Pri2-2,6)3]2 aryloxide complexes [16]. However, the
chemical shift differences between the two sets of aryl-
H resonances (which were originally identical) are
small, so the absence of such an electrostatic interaction
with one arene is not considered likely.
The stabilisation of Group 3 and lanthanide com-
plexes by forming bonding interactions with neutral
thioether groups has predominantly been studied for
thiophene and thioether-crown ligands. From the mea-
sured structural rigidity of the derivatives 3 and 4, we
infer that the bridging sulfur atom interaction in the LS
and LSN derivatives must provide a strong electrostatic
influence on stabilising the structures.
,
Selected distances (A) and angles (°) 3
Bond distances
Sm1ꢀO5
Sm1ꢀO2
Sm1ꢀO1
Sm1ꢀO1a
Sm1ꢀS4
Sm1ꢀC11
Sm1ꢀC12
Sm1ꢀSm1a
2.138(3)
2.157(3)
2.392(3)
2.296(3)
3.1172(11)
3.027(4)
2.801(5)
3.6084(5)
Bond angles
O5ꢀSm1ꢀO2
O5ꢀSm1ꢀO1
O2ꢀSm1ꢀO1
O5ꢀSm1ꢀO1a
O2ꢀSm1ꢀO1a
O1aꢀSm1ꢀO1
O5ꢀSm1ꢀS4
O2ꢀSm1ꢀS4
O1aꢀSm1ꢀS4
O1ꢀSm1ꢀS4
103.17(12)
125.08(11)
123.98(11)
125.66(11)
95.61(11)
79.38(11)
159.67(9)
65.18(8)
73.59(7)
59.89(7)
nating to Group 4, 5 and 6 derivatives [12], but adopts
a mer- conformation around the Cu(II) derivative
[Cu(LS)]2Cl2 [13]. The terminal phenoxide lies close to a
trans disposition to the S atom; the SmꢀO distance is
2.3. Dilithio biphenolate and binaphtholate precursors
for Sm(III) LSN and LS complexes
,
2.138(3) A. Subtraction of the Van der Waals radius for
four-co-ordinate Sm3+ gives 1.298 A, which at the long
,
end of the range of values obtained after subtraction of
the metal ion radius for structurally characterised Ln3+
aryloxide complexes [14]. The SmꢀS distance of
,
3.117(1) A is long compared with reported lan-
thanide(III) thioether-substituted cyclopentadienyl,
thiophene and crown ligand interactions [15].
(2)
The reaction of H2LS with [Sm(OAr)3] (OAr=OBut2-
2,6–C6H3), at −30 °C in thf affords the first reported
f-element LS derivative as a thf adduct; [Sm{1,1%-S(2-
OC6H2But-3-Me-5}(OAr)(thf)]2 4·thf, is an air and
moisture-sensitive bright yellow solid. Interestingly, at
ambient temperatures the LS adduct 4·thf is symmetri-
cal in solution, contrary to results observed for the LSN
adduct, 3. No exchange of solvating thf has been
observed in solution. However, purification to remove
traces of eliminated phenol from the product (heating
The elimination of phenolic byproducts from the
syntheses of 3 and 4 involves prolonged heating, so we
have sought an alternative metathetical route to the LS
and LSN derivatives. Okuda et al. have recently re-
ported the in situ preparation of Li2LS in hexane/thf
Scheme 2. Synthesis of Sm(LS) derivatives.

P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
209
Scheme 3. Preparation of symmetric and asymmetric binaphtholate and biphenolate derivatives.
solvent [17]. The analogous conversion of 1 to dilithio
salts is outlined in Eq. (2); treatment of 1 with n-butyl-
lithium in a thf/diethyl ether mixture affords the dilithio
salt Li2LSN.2thf, 5, cleanly and in good yield. For our
purposes, treatment of 2 with lithium bis(trimethylsi-
lyl)amide in diethyl ether affords unsolvated Li2LS, 6 in
high yield and purity after drying in vacuo for 8 h. The
1H-NMR spectral resonances of the dry product are
significantly broadened and no 13C-NMR spectrum
could be obtained for this complex. Solubility con-
straints prevent a thf-free synthesis of Li2LSN, which
retains two moles of co-ordinated thf.
complex [Sm{1,1%-S(2-OC10H4But2-3,6)2}(OAr)]2 7, un-
expectedly contains no co-ordinated thf, even though
the reaction solvent is thf and the lithiated reagent
incorporates thf. This shows an unexpected difference
between the biphenolate and binaphtholate ligands; the
syntheses of the derivatives is summarised in Scheme 3.
The reaction of base-free Li2LS, 6, with [Sm(OAr)3] also
proceeds very cleanly at 20 °C in toluene within a few
hours, to give 4 – the unsolvated, asymmetric dinuclear
LS complex which was originally isolated after pro-
longed heating in the absence of thf. We are unable to
isolate the thf solvated, samarium binaphtholate from
any of the reactions we have attempted so far. The
combination of biphenolate, aryloxide and thf ligands
is capable of stabilising the monomeric Sm(III) centre
(as 4.thf), but the analogous naphthyloxide combina-
tion is not (3 and 7 are identified instead). We do not
have structural data for 4 that would allow us to
identify a stabilising interaction of the S atom. So far
we have seen no evidence for any interconversion be-
tween 3 and 7, and so infer a significant rigidity of the
twisted binaphtholate conformation in the Sm
complexes.
2.4. Alternati6e syntheses of Sm(III) LSN and LS
complexes from metathetical routes
Of the factors that determine the bonding in elec-
tropositive metal-aryloxides, the most relevant in a
comparison between the LSN and the LS systems is
probably the p-interaction between the O(2p) orbitals
and the aryl ring (MO+Ph−) [18]. The relative ability of
the aryloxide and naphthyloxide to stabilise an anionic
charge on the O atom may explain the inability of
simply an additional thf molecule to stabilise a
monomeric naphthyloxide derivative.
(3)
Treatment of the thf-solvate 5 with [Sm(OAr)3] in
toluene results in the immediate precipitation of elimi-
nated [LiOAr] and the formation of yellow, toluene-sol-
uble complex 7 which is symmetrical, Eq. (3). The

210
P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
3. Reactivity of 3 and 4 as promoters for selective
acylation
in the catalytic cycle. In an NMR tube fitted with a ptfe
valve the binaphtholate 3 was treated with one equiva-
lent of meso-hydrobenzoin, in the absence of acylating
agent. Within 10 min resonances due to both 3 and the
diol have disappeared with only traces of unidentified
diamagnetic material remaining. The analogous reac-
tion with the monoacylated product also resulted in the
disappearance of any tractable adduct from the NMR
spectrum. However, the reaction of 3 with the propy-
lester derivative proceeds over 15 h to afford a stable
To identify whether these ligand sets can stabilise
new Sm-based Lewis Acid catalysts, we have studied
the ability of 3 and 4 to catalyse the acylation of
1,2-diols, Eq. (4).
The selective protection of chemically similar alcohol
groups is a key tool in organic synthetic methodology
[19]. While sterically or electronically different hydrox-
yls may be selectively modified with ease, methods for
the mono-functionalisation of similar hydroxyl groups
are decidedly fewer in number, although this is a partic-
ularly useful derivatisation in large-molecule synthesis.
Traditional methods for this are multi-step or time
consuming, requiring procedures such as continual ex-
traction methods, heterogeneous or solid supported
methods or the selective opening of cyclic ‘acetal-like’
systems [20]. It has recently been discovered that Lewis
acid lanthanide trihalides can promote the reaction
with greater efficiency and selectivity than the previ-
ously used methods, although to date, we have no
information about the mechanism of action, or whether
this selectivity can be broadened to encompass 1,3-diol
desymmetrisation reactions [21].
1
adduct identifiable by its H-NMR spectrum as a para-
magnetic Sm derivative 8, Eq. (5).
(5)
Both terminally co-ordinated phenolate ligands in the
dimer have been replaced by propionate, which show
strongly paramagnetically shifted H resonances. Al-
though the asymmetric naphtholate framework remains
virtually unperturbed, two equivalents of either the R-
or S- form of the ester bind to any one dimer, since two
sets of resonances for the ester are observed.
Under an atmosphere of dry dinitrogen, a thf solu-
tion of meso-hydrobenzoin was treated with an excess
(10 equivalents) of acetic anhydride and a Sm(III)
complex at 10 mol% at 25 °C (Eq. (4)), and the reac-
tion monitored over 24 h.
By the end of 24 h, using 3 as a promoter for the
reaction resulted in 34% monoesterification of the diol
(i.e. the ratio of diol:monoacylated:bisacylated product
was 2:1:0). So the complex is a slow but highly selective
catalyst for this acylation procedure. By the end of the
same time period, using 4 as a promoter resulted in
50% monoesterification of the diol (i.e. the ratio of
diol:monoacylated:bisacylated product was 1:1:0). The
reactions studied so far have only been allowed to
progress for 24 h at room temperature, but it is clear
that both are effective, and selective catalysts for the
desymmetrisation reaction. By way of comparison, re-
actions with standards SmCl3 (thionyl chloride/thf
4. Conclusions
The new thio-binaphthol 2,2%thiobis(3,6-di-tert-butyl-
naphth-2-ol), and its phenolic analogue 2,2%thiobis(6-
tert-butyl-4-methyl phen-2-ol) afford the first f-element
Sm(III) complexes supported by S-bridged biphenolate
or binaphtholate ancillary ligands, [Sm{1,1%-S(2-
OC10H4But2-3,6)2}(OC6H3Bu2t -2,6)]2 and [Sm{1,1%-S(2-
OC6H2But-3-Me-5)2}(OC6H3Bu2t -2,6)]2, which exhibit
weak interactions with the sulfur atom. The electronic
influence of the sulfur atom and the naphthol/phenol
groups has been found to influence the stability of the
symmetric or asymmetric derivatives of both ligands, as
does the preparative procedure. The binaphtholate lig-
and does not provide sufficient electrostatic stabilisa-
tion, in combination with aryloxide and thf ligands, to
stabilise a monuclear Sm(III) derivative. However, it
provides a highly structurally rigid ancillary ligand for
the metal, which can be coordinated in a pseudo-C26 or
pseudo-C2 symmetric fashion. Preliminary results indi-
cate that the asymmetric derivatives are highly found to
be highly selective Lewis acid catalysts for diol desym-
metrisation, and initial results concerning the interac-
dried), and [Sm(OAr)3], for 24
h the ratio of
diol:monoacylated:diacylated product was 0:2:3 and
3:1:0, respectively, i.e. either unselective diacylation or
very little conversion.
(4)
The fact that tractable LSN and LS complexes of a
paramagnetic metal can promote this reaction has
prompted an attempt to identify possible intermediates

P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
211
tion of the catalyst and substrate have been obtained
5.2.1. H2LSN (1)
for this reaction.
To an ethereal solution of 3,6 di-tert-butyl-2-naph-
thol (10 g, 390 mmol, 40 ml) at 0 °C was added 0.04 g
ZnCl2 (0.176 mmol). A solution of 1.55 ml (0.195
mmol) sulfur dichloride in 15 ml diethyl ether was
added dropwise over a period of 30-min. On comple-
tion of addition, the reaction was left stirring for a
further 30 min under a slow N2 sweep to remove
evolved HCl, by which time the product had precipi-
tated. The solid was washed at −30 °C with diethyl
ether (3×20 ml). Pure 2 was isolated as a white powder
in 70% yield (7.28 g). M.p. 234–237 °C.
5. Experimental
5.1. General details
All experimental procedures were performed under
an atmosphere of dinitrogen or argon, using standard
Schlenk techniques or in a glove box under dry nitro-
gen. Solvents were freshly distilled from the appropriate
drying reagent under dinitrogen, and were thoroughly
degassed prior to use, diethyl ether from sodium/ben-
zophenone, pentane and toluene from sodium, hexane
and benzene-d6 from potassium, and thf from potas-
sium/benzophenone. 1H-NMR spectra run at 298 K,
3
NMR/C6D6 lH 8.41 (d, 1H, 8-H, JHH 8.9 Hz), 7.58
4
(d, 1H, 5-H, JHH 1.89 Hz), 7.63 (s, 1H, 4-H) 7.47 (dd,
3
4
1H, 7-H, JHH 8.9 Hz, JHH 1.89 Hz), 1.51 (s, 9H,
3-But), 1.19 (s, 9H, 6-But). lC (CDCl3) 155.2 (2-C),
146.4 (1-C), 137.9 (8-C), 131.1 (5-C), 129.1 (4-C), 128.1
(7-C), 125.8 (3-C), 124.1 (10-C), 123.1 (9-C), 110.2
(6-C), 31.3 (3-But), 29.7 (6-But). IR (nujol mull)
w(cm−1): 3399 (w), 1170 (w), 1081 (w), 818 (w). EIMS:
m/z 540 (82%, [M+]-2H). Anal. Calc. for C36H46O2S
0.5Et2O: C, 78.71; H, 8.86. Found: C, 78.36; H, 8.52%.
Crystals suitable for X-ray diffraction were grown by
slow cooling of a diethyl ether solution of 1 to −
30 °C.
1
300 MHz (400 MHz for experiments in Section 5.3), H
and 13C referenced versus external TMS, 7Li versus
external LiCl at 0.0 ppm. All reagents were obtained
from Aldrich, except LiBun (Acros), and sulfur dichlo-
ride (Acros). 2,2%-Thiobis(6-tert-butyl-4-methylphenol)
was synthesised according to a literature procedure [22].
5.2.2. Sm[LSN](OC6H3-But2-2,6) (3)
5.2. 3,6-But2C10H5-2-OH
To a solution of 0.300g (3.9 mmol) Sm(OAr)3 in 15
ml thf at −30 °C was added dropwise a solution of
H2LSN 0.213 g (3.9 mmol) in 15 ml thf over a period of
60-min. The solution was allowed to warm to room
temperature (r.t.) with stirring. After 24 h, all volatiles
were removed under reduced pressure and residual
2,6-di-tert-butyl phenol sublimed onto a cold finger
yielding a yellow solid. The solid was recrystallised
from toluene, yielding pure 3 in 42% yield (147 mg).
According to a modification of a literature proce-
dure, [23] 2-naphthol (60 g, 0.42 mole), p-TSA (12 g,
0.063 mole), and toluene (200 ml), were added to a 500
ml 3-necked round bottom flask, equipped with stirrer
bar, thermometer and gas bubbler. The mixture was
heated to 110 °C, and isobutylene gas was bubbled
through the solution slowly (ꢀ120 bubbles per min).
The reaction was monitored by 1H-NMR. After 12
days, the reaction was quenched by adding ꢀ700 ml
water. Toluene was added (ꢀ200 ml) to dissolve the
precipitated material, and the layers were separated.
The toluene layer was isolated and dried over MgSO4.
Subsequent removal of toluene under reduced pressure
and recrystallisation from hexane resulted in pure
product. The product was isolated as white needles,
yield 18% (19.19 g), m.p. 135 °C.
3
NMR/C6D6 lH 10.87 (d, 1H, 8-H, JHH 8.52 Hz),
3
9.67 (d, 1H, 8-H, JHH 7.77 Hz), 9.05 (s,1H, 4-H), 8.75
3
(s, 1H, 4-H), 8.60 (d, 1H, 5-H, JHH 8.97 Hz), 8.14 (d,
3
3
1H, 5-H JHH 7.41 Hz), 7.44 (d, 1H, 7-H JHH 8.97 Hz),
3
6.03 (d, 1H, 7-H, JHH 8.40 Hz), 8.75 (m, 3H OAr),
3.59, 0.18 (s, 9H, 6-But), 1.73, 1.60 (s, 9H, But-OAr),
−1.49, −4.41 (s, 9H, 3-But). lC 4.0, −3.2 (6-But), 1.2,
0.8 (But-OAr), −5.9, −41.8 (3-But). Only the But
resonances were visible in the 13C-NMR spectrum.
EIMS m/z 1588 (100%, [{MꢀHOAr]+), 1012 (23%,
NMR/CDCl3 lH 1.41 (s, 9H, 6-But), 1.52 (s, 9H,
3-But), 5.00 (s, 1H, OH), 6.97 (s, 1H, 1-H), 7.50 (dd,
[{Mꢀ(C10H3But2)3ꢀCBut]+).
Anal.
Calc.
for
3
4
1H, 7-H, JHH 8.63 Hz, JHH 1.86 Hz), 7.57 (d, 1H,
C100H130O6S2Sm2: C, 67.01; H, 7.26. Found: C, 61.66;
H, 7.45%. Repeated determinations give the same re-
sults, suggesting metal carbide formation. Crystals suit-
able for X-ray diffraction were grown by slow cooling
of a toluene solution of 3 to −30 °C.
3
8-H, JHH 8.63 Hz). 7.70 (s, 2H, 4-H, 5-H). lC 153.6
(2-C), 145.6 (1-C), 138.4 (4-C), 131.1 (5-C), 128.4 (8-C),
125.6 (7-C), 124.8 (10-C), 124.4 (9-C), 122.6 (3-C),
110.0 (6-C), 31.2 (3-But), 29.7 (6-But). IR (nujol mull)
w(cm−1): 3517 (b), 2945(s), 1261(s), 1018 (m), 8619 (w),
805 (w), 722.18 (w). EIMS: m/z 256 (55% [M]+). Anal.
Calc. for C18H24O: C, 84.38; H, 9.38. Found: C, 84.76;
H, 9.81%.
5.2.3. Sm[LS](OC6H3-But2-2,6)(thf ) (4·thf)
A thf solution of H2LS (47 mg, 0.13 mmol, 10 ml)
was added dropwise to a stirring thf solution of

212
P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
Sm(OAr)3 (100 mg, 0.13 mmol, 10 ml) at −30 °C over
30 min. The solution was then heated to reflux. After
120 h, the solvent was removed under reduced pressure
yielding an oily yellow solid 4.thf in 66% yield (61 mg).
NMR/C6D6 lH 9.45 (s, 2H, aryl H), 8.28 (d, 2H,
m-OAr JHH=7.7 Hz), 7.67 (t, 1H, p-OAr JHH=7.7
Hz), 7.61 (s, 2H, aryl H), 2.69 (s, 6H, CH3), 2.61 (thf),
1.76 (s, 18H, But-OAr), 0.91 (thf), 0.26 (s, 18H, But-Ls).
Only the But and Me resonances were visible in the
13C-NMR spectrum. lC 36.4 (s, C(CH3)3-OAr), 35.4 (s,
C(CH3)3-Ls), 33.0 (s, C(CH3)3-OAr), 31.9 (s, C(CH3)3-
Ls), 22.6 (s, CH3).
solution of H2Ls in diethyl ether (2.0 g, 5.6 mmol, 10
ml), causing the formation of a precipitate. The suspen-
sion was allowed to warm to r.t. with stirring over 12 h.
The precipitated solid was recrystallised from diethyl
ether to yield 6 (x=2) as a white powder in 60% (1.2 g
non-optimised yield). Prolonged drying in vacuo re-
duces x to 0.09. Addition of one drop of distilled water
3
3
1
regenerated the H-NMR spectrum of H2LS.
NMR/C6D6 lH (thf adduct) 7.02 (d, J=6.8 Hz, 4H,
aryl H), 1.97 (s, 6H, methyl CH3), 1.47 (s, 18H,
C(CH3)3). lLi 2.40 (s). lH (diethyl ether adduct) 7.59 (s,
br, 4H, aryl H), 2.10 (s, br, 6H, methyl CH3), 1.28 (s,
br, 18H, C(CH3)3). lLi 1.82 (br s). lC 31.1 (s, C(CH3)3),
20.7 (s, CH3). Aryl H were broadened to baseline in
non-coordinating NMR solvents, precluding assign-
ment. ESMS (MeOH solution) 466 (18%, [M.3Me-
OH]+), 241 (9%, [MꢀBut2Me]+). Anal. Calc. for
C22H28O2SLi2: C, 71.34; H, 7.62. Found: C, 71.98; H,
8.10%.
Coordinated volatiles were removed by sublimation
under reduced pressure onto a cold finger, affording a
yellow solid 4 in 34% yield (32 mg).
NMR/C6D6 lH 9.77 (m, 1H, m-OAr), 8.78 (t, 1H,
p-OAr 3JHH=7.7 Hz), 8.61 (s, 1H, aryl H), 8.52 (s, 1H,
aryl H), 8.23 (m, 1H, m-OAr), 7.41 (s, 1H, aryl H),
6.88 (s, 1H, aryl H), 2.71 (s, 3H, CH3), 1.42 (s, 9H,
But-OAr), 0.22 (s, 9H, But-OAr), −1.24 (s, 3H, CH3),
−1.66 (s, 9H, But-Ls), −4.30 (s, 9H, But-Ls). lC 152.9,
138.9, 135.3, 134.7, 133.0, 129.8, 129.6, 128.4, 128.2,
127.9, 127.7, 127.5, 125.4, 125.2, 124.3, 123.9, 118.9,
115.8 (s, aryl C), 36.4, 35.6 (s, CMe3OAr), 30.9, 30.3 (s,
CMe3Ar), 33.0, 31.9 (s, CMe3OAr), 28.9, 22.5 (s,
CMe3Ar), 30.0, 20.2 (s, Me). FABMS m/z 1370 (100%,
[MꢀC3H3Me]+), 1196 (7%, [MꢀC3H3C6H3But2]+), 1158
(8%, [MꢀC6H2But2Me2SO]+). Anal. Calc. for
C36H44O3SSm: C, 60.71; H, 6.94. Found: C, 53.88; H,
7.78%.
5.2.6. Reaction of Li2LS and Sm(OAr)3 to gi6e
[Sm[LS](2,6-Bu2t -OC6H3)]2 (4)
A toluene solution of Li2LS (75 mg, 0.20 mmol, 10
ml) was added dropwise to a stirring toluene solution of
Sm(OAr)3 (155 mg, 0.20 mmol, 10 ml) at −30 °C over
30 min. The solution was allowed to warm to r.t. with
stirring. After 24 h, the solvent was removed under
reduced pressure and the resultant solid recrystallised
from a hexane–toluene mixture (4:1), affording a yel-
low solid 4 in 44% yield (64 mg).
5.2.4. 2,2%-Li2[LSN]·2thf (5)
5.2.7. Reaction of Li2LSN and Sm(OAr)3 to gi6e
symmetrical [Sm[LSN](2,6-Bu2t -OC6H3)]2 (7)
To a diethyl ether:thf (5:2) solution of H2LSN (2.0 g,
3.69 mmol, 35 ml), at −78 °C was added LinBu (4.60
ml, 1.6 M in hexane, 7.38 mmol) dropwise over 30 min.
The solution was allowed to warm to r.t. with stirring.
After 24 h, the product had precipitated from the
reaction mixture. The supernatant was decanted off,
and the solid washed with three aliquots of 10 ml cold
diethyl ether to yield a fine white powder of 5 in 51%
yield. M.p. 220 °C (dec.).
A toluene solution of Li2LSN (456 mg, 0.65 mmol, 15
ml) was added dropwise to a stirring toluene solution of
Sm(OAr)3 500 mg, 0.65 mmol, 15 ml) at −30 °C over
30 min. The solution was allowed to warm to r.t. with
stirring. After 24 h, the solvent was removed under
reduced pressure and the resultant solid recrystallised
from toluene, affording a yellow solid 7 in 20% yield
(230 mg).
3
3
NMR/C6D6 lH 9.3(d, 1H, 8-H J 8.10 Hz), 7.84(s,
NMR/C6D6 lH 9.57 (d, 1H, 8-H, JHH 9 Hz), 7.77
3
4
1H, 7-H), 7.76 (s, 1H, 5-H), 7.63(s, 1H 4-H), 1.43(s, 9H,
3-But), 1.31(s, 9H, 6-But), 3.05(br, 4H, thf), 0.91(br,
4H, thf), no measurable coupling constants. lC 142.4
(2-C), 135.6 (1-C), 124.4 (m, br, 3-C to 10-C), 67.9 (thf)
35.6 (thf), 31.4 (3-But), 30.4 (6-But). lLi 3 (br s). Addi-
tion of one drop of distilled water regenerated the
1H-NMR spectrum of H2LSN. ESMS 438 (100%,
[Mꢀ2ButH]+, 397 (5%, [MꢀC8H4But]+. Anal. Calc. for
C36H44O2SLi2·2thf: C, 74.98; H, 7.99. Found: C, 73.35;
H, 8.25%.
(dd, 7-H JHH 9Hz, JHH 1.9 Hz), 7.48 (d, 1H, 5-H,
4JHH 1.9 Hz), 7.27 (s, 1H, 4-H), 6.87, (m, 3H OAr), 1.35
(s, 9H, 6-But), 1.10 (s, 9H 3-But), 1.73 (s, 9H, But-OAr).
5.3. 1,2-Diol desymmetrisation catalysis
To a stirring solution of [catalyst] (20 mg, 10 mol%)
(where x=SmCl3, Sm(OAr)3, Sm[LSN](2,6-Bu2t -OC6H3)
3, Sm[LS](2,6-Bu2t -OC6H3) 4) and meso-hydrobenzoin
in thf (2.4 ml) was added acetic anhydride (ten equiva-
lents). The reaction was monitored by TLC (1:1 diethyl
ether:hexane). After 24 h, the reaction was diluted with
ethyl acetate (25 ml), and washed successively with
saturated NaHCO3 (2×20 ml) and brine (20 ml). The
5.2.5. 2,2%-Li2[LS]·xEt2O (x=0–2) (6)
A solution of LiN(SiMe3)2 in diethyl ether (2.33 g,
11.2 mmol, 10 ml) was added dropwise to a stirred

P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
213
organics were dried (MgSO4) and the solvent evapo-
rated to give the crude product, which was purified by
recrystallisation from ethyl acetate/hexane. The spec-
troscopic data for the products were identical to that
previously reported in the literature [24].
and meso-(2-acetoxy-1,2-biphenylethanol) (meso-hy-
drobenzoin) (1.0 mg, 3.36 mmol). The yellow solution
became pale brown over 15 min, and the 1H-NMR
spectrum showed no NMR-active species other than
trace diamagnetic impurities.
5.4. NMR tube reactions
5.4.3. Reaction of 3 with rac-hydrobenzoin-2-propanoyl
ester
5.4.1. Reaction of 3 with meso-hydrobenzoin
In a Youngs ptfe tap equipped NMR tube, two
equivalents of meso-hydrobenzoin-2-propanoyl ester
(1.0 mg, 3.36 mmol) in d6-benzene were added to a
d6-benzene solution of 3 (5.0 mg, 1.68 mmol). No colour
A Youngs ptfe tap equipped NMR tube was charged
with 5.0 mg (1.68 mmol) 3 in d6-benzene and one
equivalent of meso-hydrobenzoin in d6-benzene (1.68
mmol, 0.4 mg) resulted in an immediate colour change
from yellow to pale brown. The 1H-NMR spectrum
showed no NMR-active species other than trace dia-
magnetic impurities.
1
change from pale yellow was observed. The H-NMR
spectrum of the reaction mixture 15 h after addition
shows no residual starting materials, large free ArOH
peaks and no paramagnetically shifted OAr moieties.
3
NMR/C6D6 lH 8.96 (d, 1H, 8-H, JHH 10.56 Hz),
5.4.2. Reaction of 3 with
meso-(2-acetoxy-1,2-biphenylethanol)
A Young’s ptfe tap equipped NMR tube was charged
with a d6-benzene solution of 3 (5.0 mg, 1.68 mmol),
8.52 (d, 1H, 8-H, 3JHH 8.76 Hz), 8.37, 7.98 (s, 1H, 5-H),
3
8.34, 7.88 (s, 1H, 4-H), 7.53 (d, 1H, 7-H, JHH 6.9 Hz),
3
7.29 (d, 1H, 7-H, JHH 8.37 Hz), 6.97, 6.24 (m, 5H, Ph),
3.89, 3.66 (s, 3H, CH3), 1.55, 1.25 (s, 9H, 3-But), 1.22,
0.88 (s, 9-H, 6-But), 1.59, 0.68, −2.02, −4.57 (s, 1H,
CH), −2.83, −6.21 (s, 2H, CH2).
Table 3
Crystallographic data for [H2LSN] (1) and [Sm(LSN)(But2OC6H3)]2 (3)
[H2LSN
]
[Sm(LSN)-
(But2OC6H3)]2
5.5. Crystallographic data
Empirical formula
Formula weight
C40H56O3S
616.91
C71H89O3SSm
1172.83
X-ray data, see Table 3, were collected using Mo–Ka
,
radiation (u=0.71073 A) on a Bruker SMART1000
(g mol−1
)
CCD area detector diffractometer using ꢀ scans. Struc-
ture solution and refinement was carried out using the
SHELX suite of programs [25].
(
Crystal system, space
group
Unit cell dimensions
Triclinic, P1
Monoclinic,
P21/c
,
a (A)
11.542(2)
11.899(2)
13.571(2)
88.106(2)
87.369(2)
78.311(2)
1822.8(5)
2
18.2022(11)
12.7397(8)
27.862(2)
,
b (A)
,
c (A)
h (°)
i (°)
6. Supplementary material
100.8860(10)
90
6344.7(7)
4
1.003
k (°)
Full X-ray crystallographic data and atomic co-ordi-
nates for the ligand 1 and the Sm complex 3. Crystallo-
graphic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC no. 171416 for compound 1 and no.
171417 for compound 3. Copies of this information
may be obtained freeof charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
3
,
V (A )
Z
Absorption coefficient
0.123
−1
(mm
)
Crystal size (mm), colour 0.26×0.14×0.12,
0.13×0.10×0.08,
yellow
Hexagonal prism
14 957, 8584
[Rint=0.069]
8584
colourless
Block
15 799, 7977
[Rint=0.086]
4633
Habit
Reflections collected,
unique
Reflections observed
(\2|)
Absolute correlation,
Tmin, Tmax
Number of parameters
Completeness to
2q=55°/(%)
None
Multi-scan,
0.869, 0.928
592
399
95.3
98.7
Acknowledgements
Final R indices [I|2(I)]c R1=0.0501,
wR2=0.1055
R1=0.0500,
wR2=0.1071
R1=0.1062,
wR2=0.1211
1.228 and
The authors thank Dr Paul A. Clarke for help with
the catalysis testing and for useful discussions, Dr Ali
Abdul Sada for the EIMS data, and the EPSRC (fel-
lowship for P.L.A., studentship for L.S.N. and J.J.H.)
and the Royal Society for funding.
R indices (all data)
R1=0.0952,
wR2=0.1196
Residual extrema
0.354 and −0.240
−3
,
(e A
)
−0.653

214
P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
[12] (a) S. Fokken, T.P. Spaniol, H.C. Kang, W. Massa, J. Okuda,
References
Organometallics 15 (1996) 5069;
(b) L. Porri, A. Ripa, P. Colombo, E. Miano, S. Capelli, S.V.
Meille, J. Organomet. Chem. 514 (1996) 213;
(c) C.R. Cornman, K.M. Keiser-Bush, J.W. Kampf, Inorg.
Chem. 38 (1999) 4303;
(d) Y. Nakayama, H. Saito, N. Ueyama, A. Nakamura,
Organometallics 18 (1999) 3149.
[1] Reviews: (a) F.T. Edelmann, Angew. Chem. Int. Ed. Engl. 34
(1995) 2466;
(b) G.J.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem.
Int. Ed. Engl. 38 (1999) 428;
(c) W.J. Evans, New J. Chem. 19 (1995) 525;
(d) C.E. Daitch, P.D. Hampton, E.N. Duesler, T.M. Alam, Am.
Chem. Soc. J. 118 (1996) 7769;
(e) G.B. Deacon, P.E. Fanwick, A. Gitlits, I.P. Rothwell, B.W.
Skelton, A.H. White, Eur. J. Inorg. Chem. (2001) 1505;
(f) R. Duchateau, T. Tuinstra, E.A.C. Brussee, A. Meetsma, P.T.
Van Duijnen, J.H. Teuben, Organometallics 16 (1997) 3511;
(g) L. Lee, D.J. Berg, F.W. Einstein, R.J. Batchelor,
Organometallics 16 (1988) 1819;
(h) H.A. Stecher, A. Sen, A.L. Rheingold, Inorg. Chem. 27
(1988) 1130;
(i) D.L. Clark, J.C. Gordon, J.C. Huffman, J.G. Watkin, B.D.
Zwick, Organometallics 13 (1994) 4266;
(j) Z.M. Hou, Y.G. Zhang, T. Yoshimura, Y. Wakatsuki,
Organometallics 16 (1997) 2963;
(k) W.J. Evans, M.A. Greci, M.A. Johnston, J.W. Ziller, Chem.
Eur. J. 5 (1999) 3482;
(l) Z.M. Hou, Y.G. Zhang, H. Tezuka, P. Xie, O. Tardif, T.
Koizumi, H. Yamazaki, Y. Wakatsuki, Am. Chem. Soc. J. 122
(2000) 10533.
[13] P. Chaudhuri, M. Hess, U. Florke, K. Wieghardt, Angew.
Chem. Int. Ed. 37 (1998) 2217.
,
[14] Range calculated=1.24–1.31 A. (a) P.L. Arnold, A.J. Blake,
S.N. Hall, B.D. Ward, C. Wilson, J. Chem. Soc. Dalton Trans.
(2001) 488;
(b) G.B. Deacon, P.E. Fanwick, A. Gitlits, I.P. Rothwell, B.W.
Skelton, A.H. White, Eur. J. Inorg. Chem. (2001) 1505;
(c) D.R. Click, B.L. Scott, J.G. Watkin, Chem. Crystallogr. J. 29
(1999) 921;
(d) Y.M. Yao, Q. Shen, K.B. Yu, Acta Crystallogr. Sect. C,
Cryst. Struct. Commun. 56 (2000) 1330;
(e) M. Yousaf, Q.C. Liu, J.L. Huang, Y.L. Qian, A.S.C. Chan,
Inorg. Chem. Commun. 3 (2000) 105;
(f) R.J. Butcher, D.L. Clark, J.C. Gordon, J.G. Watkin,
Organomet. Chem. J. 577 (1999) 228;
(g) Z. Hou, Y. Zhang, T. Yoshimura, Y. Wakatsuki,
Organometallics 16 (1997) 2963;
(h) Z.M. Hou, A. Fujita, T. Yoshimura, A. Jesorka, Y.G.
Zhang, H. Yamazaki, Y. Wakatsuki, Inorg. Chem. 35 (1996)
7190;
(i) D.L. Clark, J.C. Gordon, J.G. Watkin, J.C. Huffman, B.D.
Zwick, Polyhedron 15 (1996) 2279;
(j) G.H. Qi, Y.G. Lin, J.Y. Hu, Q. Shen, Polyhedron 14 (1995)
413;
[2] (a) C.J. Schaverien, J.H.G. Frijns, H.J. Heeres, J.R. Van den
Hende, J.H. Teuben, A.L. Spek, Chem. Commun. (1991) 642;
(b) C.J. Schaverien, Chem. Commun. (1992) 11.
[3] W.J. Evans, R.N.R. Broomhall-Dillard, J.W. Ziller, J.
Organomet. Chem. 569 (1998) 89.
[4] C.J. Schaverien, N. Meijboom, A.G. Orpen, Chem. Commun.
(1992) 124.
[5] (a) N. Yoshikawa, J.M.A. Yamada, J. Das, H. Sasai, M.
Shibasaki, J. Am. Chem. Soc. 121 (1999) 4168;
(b) V.K. Aggarwal, A. Mereu, G.J. Tarver, R. McCague, J. Org.
Chem. 63 (1998) 7183;
(k) D.M. Barnhart, D.L. Clark, J.C. Gordon, J.C. Huffman,
R.L. Vincent, J.G. Watkin, B.D. Zwick, Inorg. Chem. 33 (1994)
3487;
(l) D.L. Clark, J.C. Gordon, J.C. Huffman, R.L. Vincenthollis,
J.G. Watkin, B.D. Zwick, Inorg. Chem. 33 (1994) 5903;
(m) P.B. Hitchcock, M.F. Lappert, A. Singh, Chem. Commun.
(1983) 1499;
(c) H.C. Aspinall, J.L.M. Dwyer, N. Greeves, A. Steiner,
Organometallics 18 (1999) 1366;
(n) P.B. Hitchcock, M.F. Lappert, R.G. Smith, Inorg. Chim.
Acta 139 (1987) 183;
(o) W.J. Evans, M.A. Johnston, M.A. Greci, J.W. Ziller, Polyhe-
dron 20 (2001) 277.
(d) H.C. Aspinall, J.F. Bickley, J.L.M. Dwyer, N. Greeves, R.V.
Kelly, A. Steiner, Organometallics 19 (2000) 5416;
(e) H. Ishitani, S. Kobayashi, Tetrahedron. Lett. 37 (1996) 7357;
(f) H. Kodama, J. Ito, K. Hori, T. Ohta, I. Furukawa, J.
Organomet. Chem. 603 (2000) 6.
[15] (a) M. Geissinger, J. Magull, Z. Anorg. Allg. Chem. 623 (1997)
755;
[6] (a) J. Okuda, E. Masoud, Macromol. Chem. Phys. 199 (1998)
543;
(b) H.J. Heeres, A. Meetsma, J.H. Teuben, J. Organomet. Chem.
414 (1991) 351;
(c) H. Schumann, K. Herrmann, J. Demtschuk, S.H. Muhle, Z.
Anorg. Allg. Chem. 625 (1999) 1107.
(b) A. Van der Linden, C.J. Schaverien, N. Meijboom, C.
Ganter, A.G. Orpen, J. Am. Chem. Soc. 117 (1995) 3008.
[7] (a) M. Hess, K. Wieghardt, P. Chaudhuri, US Patent 6153779;
(b) H.-J. Krueger, Angew. Chem. Int. Ed. 38 (1999) 627;
(c) P. Chaudhuri, M. Hess, J. Muller, K. Hildenbrand, E. Bill, T.
Weyhermuller, K. Wieghardt, J. Am. Chem. Soc. 121 (1999)
9599;
(d) P. Chaudhuri, M. Hess, T. Weyhermuller, K. Wieghardt,
Angew. Chem. Int. Ed. 38 (1999) 1095.
[8] R.D.J. Froese, D.G. Musaev, K. Morokuma, Organometallics
18 (1999) 373.
[16] (a) G.B. Deacon, S. Nickel, P. MacKinnon, E.R.T. Tiekink,
Austr. J. Chem. 43 (1990) 1245;
(b) D.M. Barnhart, D.L. Clark, J.C. Gordon, J.C. Huffman,
R.L. Vincent, J.D. Watkin, B.D. Zwick, Inorg. Chem. 33 (1994)
3487.
[17] F. Amor, S. Fokken, T. Kleinhenn, T.P. Spaniol, J. Okuda, J.
Organomet. Chem. 621 (2001) 3.
[18] W.A. Howard, T.M. Trnka, G. Parkin, Inorg. Chem. 34 (1995)
5900.
[19] (a) H. Fujioka, Y. Nagatomi, N. Kotoku, H. Kitagawa, Y. Kita,
Tetrahedron 56 (2000) 10141;
(b) N. Maezaki, M. Soejima, M. Takeda, A. Sakamoto, T.
Tanaka, C. Iwata, Chem. Commun. (1994) 1345;
(c) N. Maezaki, M. Murakami, M. Soejima, T. Tanaka, T.
Imanishi, C. Iwata, Chem. Pharm. Bull. 44 (1996) 1146.
[20] (a) J.H. Babler, M.J. Coghlan, Tetrahedron Lett. 20 (1979) 1971;
(b) T. Nishiguchi, H.J. Taya, Am. Chem. Soc. 111 (1989) 9102;
[9] S.D. Pastor, J.D. Spivack, L.P. Steinhenbel, J. Heterocycl.
Chem. 21 (1984) 1285.
[10] A. Chetkina, V.E. Zavodnik, V.K. Bel’skii, I.G. Arzamanova,
M.I. Naiman, Y.A. Gurvich, Zh. Strukt. Khim. 25 (1984) 114.
[11] (a) M. Krishnaiah, K.D. Berlin, Heteroat. Chem. 6 (1995) 485;
(b) O.N. Kataeva, I.A. Litvinov, V.A. Naumov, I.V. Anoni-
mova, J. Mol. Struct. 344 (1996) 95;
(c) R.M.L. Mercado, A. Chandrasekaran, R.O. Day, R.R.
Holmes, Organometallics 18 (1999) 906.

P.L. Arnold et al. / Journal of Organometallic Chemistry 647 (2002) 205–215
215
(j) H. Fujioka, Y. Nagatomi, N. Kotoku, H. Kitagawa, Y. Kita,
Tetrahedron 56 (2000) 10141.
(c) H. Ogawa, M. Amano, T. Chihara, Chem. Commun. (1998)
495;
[21] (a) R.A. Holton, Z. Zhang, P.A. Clarke, H. Nadizadeh, D.J.
Procter, Tetrahedron Lett. 39 (1998) 2993;
(b) P.A. Clarke, R.A. Holton, N.E. Kayaleh, Tetrahedron Lett.
41 (2000) 2687.
[22] S.D. Pastor, J.D. Spivack, L.P. Steinheubel, J. Heterocycl.
Chem. 49 (1984) 4302.
[23] D.W. Chasar, J. Org. Chem. 49 (1984) 4302.
[24] P.C. Zhu, J. Lin, C.U. Pittman, J. Org. Chem. 60 (1995) 5729.
[25] (a) Bruker, SHELXTL 5.10. Bruker AXS Inc., Madison, Wiscon-
sin, USA, 1997. G.M. Sheldrick Acta Crystallogr Sect. A 46
(1990) 467;
(d) M. Oikawa, A. Wada, F. Okazaki, S. Kusumoto, J. Org.
Chem. 61 (1996) 4469;
(e) P.C. Zhu, J. Lin, C.U. Pittman Jr., J. Org. Chem. 60 (1995)
5729;
(f) N. Maezaki, M. Soejima, M. Takeda, A. Sakamoto, T.
Tanaka, C. Iwata, Chem. Commun. (1994) 1345;
(g) G. Egri, E. BaitzGacs, L. Poppe, Tetrahedron: Asymmetry 7
(1996) 1437;
(h) K.F. Hsiao, F.L. Yang, S.H. Wu, K.T. Wang, Biotechnol.
Lett. 18 (1996) 1277;
(i) M. Kinugasa, T. Harada, A. Oku, Tetrahedron Lett. 39
(1998) 4529;
(b) G.M. Sheldrick, SHELXL97, University of Go¨ttingen, Ger-
many 1997.