Synthesis of Pd(II) and Pt(II) complexes possessing bicyclo[3.2.0]heptanyl phosphinite ligands: Identification of a novel Pd(II) precatalyst for 1,6-diene cycloisomerisation

Article abstract of DOI:10.1016/j.jorganchem.2005.01.037

The synthesis of monodentate and bidentate phosphinite ligands, possessing the unusual bicyclo[3.2.0]heptane framework, are reported. A convenient, tin-free synthesis of a key intermediate, namely 3-endo-6-endo- dihydroxybicyclo[3.2.0]heptane, is described. The air-sensitive phosphinite ligand 1 was either protected as the borane adduct, which is air-stable, or reacted directly with bis(acetonitrile)palladium(II)chloride to give the novel air and moisture stable palladium(II) complex 11. A platinum(II) relative 12 has also been synthesised by reaction of phosphinite 1 with bis(benzonitrile) platinum(II)chloride. Each complex has been thoroughly characterised and their molecular structures confirmed by X-ray diffraction studies. In catalytic applications, such as cross-coupling reactions of organometallic reagents with organohalides, an unexpectedly poor activity has been established for 11. For example, Suzuki-Miyaura cross-coupling of activated and deactivated aryl bromides with aryl boronic acids, in the presence of catalytic quantities of 11, proceed in low yield, accompanied by substantial homocoupling. Palladium agglomeration, to produce catalytically inactive Pd black, is rapid in these reactions, under both aqueous and non-aqueous conditions. The poor reactivity is proposed to arise through an unfavourable near tetrahedral '(PP′)Pd(0)' geometry, which slows the oxidative addition step in the catalytic cycle with either activated or deactivated aryl halides. The steric bulk of the ligand and the associated large P-M-P′ bite angle, particularly at the palladium zero oxidation state, is proposed to account for the poor reactivity. However, we have established that cationic derivatives of 11 promote the cycloisomerisation of diallylmalonate in a regioselective fashion.

Full text of DOI:10.1016/j.jorganchem.2005.01.037

Journal of Organometallic Chemistry 690 (2005) 4462–4477
www.elsevier.com/locate/jorganchem
Synthesis of Pd(II) and Pt(II) complexes possessing
bicyclo[3.2.0]heptanyl phosphinite ligands:
Identification of a novel Pd(II) precatalyst for 1,6-diene
cycloisomerisation q
a,
a
a
b
Ian J.S. Fairlamb *, Stephanie Grant , Adrian C. Whitwood , John Whitthall ,
c
Andrei S. Batsanov , Jonathan C. Collings
c
a
Department of Chemistry, University of York, Heslington, York YO10 5DD, UK
Stylacats Ltd., The Heath Technical and Business Park, Runcorn, Cheshire WA7 4QX, UK
b
c
Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Received 30 September 2004; received in revised form 11 January 2005; accepted 11 January 2005
Available online 19 March 2005
Abstract
The synthesis of monodentate and bidentate phosphinite ligands, possessing the unusual bicyclo[3.2.0]heptane framework, are
reported. A convenient, tin-free synthesis of a key intermediate, namely 3-endo-6-endo-dihydroxybicyclo[3.2.0]heptane, is described.
The air-sensitive phosphinite ligand 1 was either protected as the borane adduct, which is air-stable, or reacted directly with bis(ace-
tonitrile)palladium(II)chloride to give the novel air and moisture stable palladium(II) complex 11. A platinum(II) relative 12 has
also been synthesised by reaction of phosphinite 1 with bis(benzonitrile)platinum(II)chloride. Each complex has been thoroughly
characterised and their molecular structures confirmed by X-ray diffraction studies. In catalytic applications, such as cross-coupling
reactions of organometallic reagents with organohalides, an unexpectedly poor activity has been established for 11. For example,
Suzuki–Miyaura cross-coupling of activated and deactivated aryl bromides with aryl boronic acids, in the presence of catalytic
quantities of 11, proceed in low yield, accompanied by substantial homocoupling. Palladium agglomeration, to produce catalytically
inactive Pd black, is rapid in these reactions, under both aqueous and non-aqueous conditions. The poor reactivity is proposed to
arise through an unfavourable near tetrahedral ꢀ(PP0)Pd(0)ꢁ geometry, which slows the oxidative addition step in the catalytic cycle
with either activated or deactivated aryl halides. The steric bulk of the ligand and the associated large P–M–P0 bite angle, partic-
ularly at the palladium zero oxidation state, is proposed to account for the poor reactivity. However, we have established that cat-
ionic derivatives of 11 promote the cycloisomerisation of diallylmalonate in a regioselective fashion.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Palladium; Cross-coupling; Suzuki; Dienes; Atom economic 3
1. Introduction
Transition metal catalysed reactions are extremely
versatile methods for a variety of synthetic transforma-
tions, not least in the formation of carbon–carbon and
carbon–heteroatom bonds, through cross-coupling pro-
cesses [1]. A focus on the development of highly active
catalysts (that exhibit high TONs and TOFs) for Heck,
q
This paper was first accepted at the 14th International Conference
on Homogeneous Catalysis in Munich on July 9, 2004.
*
Corresponding author. Tel.: +44 1904 434091; fax: +44 1904
432516.
E-mail address: ijsf1@york.ac.uk (I.J.S. Fairlamb).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.037

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4463
Sonogashira, Stille and Suzuki reactions, is very appar-
ent. Significant advances have culminated to provide an
important step-change in this field [2]. As well as creat-
ing highly active catalysts for these reactions, selectivity,
particularly chemo-, regio-, stereo- and enantio-selectiv-
ity, is of the utmost importance. For cyclisation
approaches (non-metathesis type), a defined effort is still
required to improve these individual parts, more so if
these reactions are to be routinely employed in target-di-
rected synthesis. We have interests in selectivity [3] and
the employment of more demanding substrates in Sono-
gashira, Stille and Suzuki reactions [4]. Roberts and
co-workers [5] reported the synthesis of bidentate phos-
phinite ligands 1, based on the bicyclo[3.2.0]heptane ring
system, and their uses in Rh-catalysed asymmetric
hydrogenation reactions (Fig. 1). This ligand has great
potential in catalysis, as the donor phosphinite substitu-
ents are ideally positioned for bidentate coordination to
transition metals, offering potentially large bite angles
with interesting geometry (non-symmetric P,P-metal
coordination). There is also interest outside our own
group in utilisation of bicyclo[3.2.0]heptane chiral li-
gands for application in asymmetric reactions [6]. We
believe that bidentate ligand 1, and the related mono-
dentate ligands 2 and 3, could generally prove useful
in other transition metal-catalysed reactions, particu-
larly for palladium.
On a general note, phosphinite ligands [7], as well as
their variants such as aminophophinites [8], amidophos-
phinites [9], and phosphinite-oxazolines [10], have been
used in key reactions such as asymmetric allylic alkyl-
ation [11], hydroformylation [12], and in cross-coupling
processes [13]. Thus, ligands based on the bicy-
clo[3.2.0]heptane framework could find further applica-
tion in these areas of catalysis. The availability of both
enantiomeric forms of the bicyclo[3.2.0]heptane frame-
work, and the stereoselective functionalisation that is
possible, could promote use of these ligands, generally,
in asymmetric processes, as well as other types of transi-
tion metal mediated reactions, where the unusual bicy-
clo[3.2.0]heptane ring system could infer interesting
catalytic activity and selectivity.
and Pt(II) complexes, 11 and 12, respectively, contain-
ing phosphinite 1. The Pd(II) complex of 3, appears to
be complicated by a competing b-hydrogen elimina-
tion pathway. Pd(II) complex 11 has been screened
for catalytic activity (as a precatalyst) in Suzuki–
Miyaura cross-coupling reactions. Surprisingly, poor
catalytic activity is seen using 11, which we attribute
to an increase in the natural P–Pd–P0 bite angle, in
the ꢀ(PP0)Pd(0)ꢁ species, which appears to exacerbated
by conformational changes (endo- to exo-envelope ring
flip) in the bicyclo[3.2.0]heptane backbone. Monocat-
ionic derivatives of 11, generated in situ, are active
and regioselective catalysts for the cycloisomerisation
of diallylmalonate.
2. Synthesis of ligands from 3-endo-6-endo-
dihydroxybicyclo[3.2.0]heptane (8)
Commercially available bicyclo[3.2.0]hept-2-en-6-one
(5) was used as the starting point for the synthesis of 8
[14]. Regio- and stereo-selective bromohydration of 5
to give 6 can be achieved in greater than >92% yield
using either N-bromosuccinimde (NBS), N-bromoaceta-
mide (NBA) or N,N-dibromo-dimethylhydantoin in a
acetone/water mixture (Scheme 1).
This reaction is higher yielding with unpurified bro-
minating reagent, where it appears that trace quanti-
ties of bromine are beneficial for the reaction (note:
that significant amounts of succinimide sometimes
accompanies the product when performed on large scale,
>50 g). The hydrodebromination of 6 using n-tributyl-
tin hydride in the presence of catalytic AIBN in dry
toluene at 80 ꢁC gives 7 after 1 h. Alcohol 7 is volatile
and care should be taken on removal of toluene in
O
O
O
i
ii
(92%)
(30%)
Br
6
7
5
OH
iii
We herein describe details for the preparation of 1–
3; some limitations with the original synthetic route to
1 and improvements; the preparation of novel Pd(II)
OH
(80%) iii
HO
(80%)
HO
O
iv
H
H
H
H
O
H
H
(74%)
B
HO
Br
OPR2
OPR2
O
P
OPR2
O
OH
9
8
10
OH
R
Scheme 1. Reagents and conditions: (i) NBS, acetone/H2O (3/1, v/v);
(ii) n-Bu3SnH (1.1 equiv.), AIBN, toluene, reflux, 4 h; (iii) NaBH4,
MeOH, ꢀ78 ꢁC, 2 h; (iv) EPHP (10 equiv.), AIBN, toluene, reflux,
24 h.
1
2
3
Fig. 1. Phosphinite ligands based on the bicyclo[3.2.0]heptane ring
system 1–3.

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I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
vacuo (temperatures on removal of the solvent should
be <20 ꢁC at 12 mmHg, making toluene removal cum-
bersome). The inherent volatility of 7 contributes to
the low yield (30%). We also had problems removing
trace quantities of tin residues (n-Bu3SnBr). Indeed,
these were clearly visible in the 1H and 13C NMR
spectra of 7. Alternative work-up procedures were
investigated such as partitioning the crude product be-
tween acetonitrile and hexane; stirring the crude prod-
uct with aqueous KF for 1 h, followed by extraction
with ether; or a DBU/I2/Et2O procedure [15], without
success. Compound 7 was stereoselectively reduced
using sodium borohydride in methanol at ꢀ78 ꢁC to
give 8 in 80% yield. However, this material still con-
tained trace quantities of tin containing by-products.
In order to provide large quantities of 8 in pure form
and in high yield, the synthetic route was optimised.
We identified that a ꢀtin-freeꢁ hydrodebromination
reaction could be beneficial, but importantly we
wanted to avoid volatile alcohol 7. Bromohydrin 6
was reduced stereoselectively using NaBH4 in metha-
nol at ꢀ78 ꢁC to give diol 9 in 80% yield, in crystal-
line form. We identified a phosphoryl radical mediated
hydrodebromination reaction as a suitable ꢀtin-freeꢁ
procedure. Ethyl piperidine hypophosphate (EPHP)
was employed in presence of the radical initiator,
AIBN, in toluene at reflux to give 8 in 74% yield
[16]. Purification was easier than the tin-mediated hyd-
rodebromination procedure.
BH3
Ph2PO
Ph2PO
i
ii
8
(57%)
(91%)
1
1'
OPPh2
BH3
OPPh2
Scheme 2. Reagents and conditions: (i) Ph2PCl (2 equiv.), DABCO,
THF, 0–25 ꢁC; (ii) BH3 Æ THF (3 equiv.), THF, 0–25 ꢁC.
H
H
H
H
Ph
P
i
OPPh2
OPPh2
O
Ph
Cl
O
1
M
P
M = Pd, 11
M = Pt, 12
Cl
Ph
Ph
Scheme 3. Reagents and conditions: (i) (CH3CN)2PdCl2 (1 equiv.) or
(PhCN)2PtCl2 (1 equiv.), ligand 1 (1 equiv.), CH2Cl2, rt, 3 h.
production of substantial amounts of the borane ad-
duct, Et3N Æ BH3, that could not be separated, even by
careful chromatography, from the desired product 10
(the borane adduct of DABCO is observed which can
be separated from 10).
In a stoichiometric reaction, ligand 1 was reacted
with (CH3CN)2PdCl2 and (PhCN)2PtCl2 to give com-
plexes 11and 12 in quantitative yield, respectively. This
synthesis is relatively straightforward, when the ligands
are taken in semi-purified form in dry, degassed CH2Cl2
at 25 ꢁC (Scheme 3).
Complexes 11 and 12 are stable to air, moisture
and light (over several months), as expected for
16-electron late transition metal M(II) complexes.
The X-ray structure of 11 (Fig. 2) exhibits a distorted
cis-square coordination of the Pd atom, with a biden-
tate, P,P-chelating role of the diphosphinite ligand.
The chelation is slightly asymmetric, the Pd–P distances
Having established a tin-free route to diol 8, the
phosphinite ligand 1 was prepared. Treatment of 8 with
diphenylchlorophosphine, in the presence of triethyl-
amine (Et3N) or diazabicyclo[2.2.2]octane (DABCO)
in THF at 0 ꢁC and subsequent warming to room tem-
perature with stirring (for 3 h), gave ligand 1 in 91%
yield. The air sensitivity of the free phosphinite ligand
1 is a limitation. However, protection of 1 as the borane
adduct, stabilises it toward oxidation, indeed 10 is indef-
initely stable in air (Scheme 2).
Use of DABCO as a base in the borane protection
reaction is essential. Switching to Et3N results in the
(a)
(b)
Fig. 2. Two possible structures of 11 in crystal, due to the disorder of the bicyclo[3.2.0]heptane-O(1) moiety. Thermal ellipsoids are drawn at 50%
probability level, phenyl H atoms omitted.

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4465
Table 1
˚
Selected bond distances (A) and angles (ꢁ) in 11 (M = Pd) and 12
(M = Pt)
Complex
11
12
Bond
M–P(1)
M–P(2)
2.2568(6)
2.2345(7)
2.3501(7)
2.3503(6)
1.623(2)
1.600(2)
3.337(1)
2.215(2)
2.232(2)
2.368(2)
2.349(2)
1.605(4)
1.598(4)
3.274(2)
M–Cl(1)
M–Cl(2)
O(1)–P(1)
O(2)–P(2)
P(1)ꢁ ꢁ ꢁP(2)
Angle
P(1)–M–P(2)
P(1)–M–Cl(1)
P(1)–M–Cl(2)
P(2)–M–Cl(1)
P(2)–M–Cl(2)
Cl(1)–M–Cl(2)
M–O(1)–P(1)
M–O(2)–P(2)
95.99(2)
87.08(2)
178.32(2)
168.54(2)
85.56(2)
91.53(2)
123.28(7)
113.76(7)
94.84(6)
91.45(6)
176.70(7)
170.09(6)
85.45(6)
87.83(6)
120.8(2)
115.8(2)
Fig. 3. An asymmetric unit in the crystal structure of 12 Æ 2CH2Cl2.
ety; thus 12 (line 11) shows simultaneously a tetrahedral
and a pyramidal distortion of the square coordination of
the metal. Besides one molecule of 12, the asymmetric
unit contains two DCM molecules, all H atoms of which
form close contacts with the Cl(1) and Cl(2) atoms
˚
differing by ca. 0.02 A (see Table 1). Both Pd–P and
Pd–Cl distances are practically the same as in five pre-
viously reported cis-(ROPh2P)2PdCl2 complexes,
whether containing a chelating diphosphinite ligand
or two monophosphinite ones [17]. The metal coordi-
nation deviates substantially from planarity: while the
Pd, P(1), P(2) and Cl(2) atoms are coplanar, Cl(1) is
˚
(2.67–2.85 A, cf. the sum of van der Waals radii [18]
˚
of 2.86 A).
We were also interested in the incorporation of tert-
butyl phosphinite substituents into the bicyclo[3.2.0]hep-
tane framework. We expected that the stronger r-donor
properties of this ligand could be useful for cross-
coupling reactions, particularly with respect to use of
unactivated aryl chlorides. It was anticipated that this li-
gand could be air-sensitive, and as with ligand 1, it was
synthesised and then added directly to a CH2Cl2 solution
of (MeCN)2PdCl2 at 25 ꢁC (Scheme 4).
˚
tilted out of their mean plane by 0.47 A, away from
the bicyclo[3.2.0]heptane system. With respect to the
latter, the PdCl2 moiety adopts an exo-orientation. It
is noteworthy that the entire bicyclo[3.2.0]heptane
backbone, together with the O(1) atom, is disordered
in a 4:1 ratio between two positions, which correspond
to opposite enantiomeric configurations of the back-
bone. The crystal being centrosymmetric (racemic),
the molecules shown and their inversion equivalents
are present in equal amounts.
The coordination mode in CDCl3 solution of 11 is the
same as in the solid-state, exhibiting a pair of doublets
(P1 at d 100.49; P2 at d 106.69, DdPP = 6.20). A large
2JPP spin–spin coupling (51.1 Hz) was observed, derived
from cis-coordination of the ligand to Pd(II). In stark
contrast, the Pt(II) analog 12 shows a much smaller
2JPP coupling (7.7 Hz), although showing the expected
inequivalent phosphorus environments (P1 at d 74.05;
P2 at d 79.07, DdPP = 5.02). The expected spin–spin cou-
pling is seen between 135Pt and 31P (1JPtP2 = 2126;
1JPtP1 = 2140 Hz). The molecular structure of 12 is very
similar to that of the major component of 11, but exhib-
its no disorder (Fig. 3). The P–M–P bite angle in 12 is ca.
Compound 8 did react with (t-Bu)2PCl under the stan-
dard conditions (as ajudged by disappearance of 8 by rig-
orous TLC analysis of the reaction mixture and by the
formation of a stoichiometric quantity of Et3N Æ HCl)
to give 13. The complexation reaction to (MeCN)2PdCl2
also appeared to have worked (the colour of the solution
went from yellow to colourless). The volatiles were re-
moved in vacuo to provide a white solid. The 31P
NMR spectrum of this material in CDCl3 exhibited
two broad singlets, which we believe is attributable to
the non-equivalent phosphorus environments in 14 (P1
at d 143.71; P2 at d 151.12, DdP1P2 = 7.41). However,
1
the H NMR spectrum of 14 was very broad and it
was not possible to assign proton environments. The
(t-Bu)2PO
O
(t-Bu)2P
ii
i
8
˚
1ꢁ smaller and the M–P(1) bond is ca. 0.04 A shorter
than in 11 (although the M–P(2) distance is practically
Cl2Pd
˚
the same), cumulating in a 0.06 A shortening of the
(t-Bu)2P
O
(t-Bu)2PO
13
14
intramolecular Pꢁ ꢁ ꢁP distance (Table 1). The Cl(1) and
Cl(2) atoms deviate from the PtP2 plane by 0.31 and
˚
0.14 A, respectively, away from the bicycloheptane moi-
Scheme 4. Reagents and conditions: (i) (t-Bu)2PCl (2 equiv.), Et3N,
THF, 0–25 ꢁC; (ii) (MeCN)2PdCl2 (1 equiv.), CH2Cl2, 25 ꢁC.

4466
I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
material was slowly recrystallised from CH2Cl2/ether (1/
5, v/v, c = 0.1 M) over two months at ꢀ20 ꢁC, which pro-
duced colourless crystals. The 1H NMR spectrum of
these crystals showed only high field resonances (attrib-
utable to t-Bu and OH) and the curious absence of the
bicyclo[3.2.0]heptane unit. A single crystal X-ray diffrac-
tion study has shown the new material to be 15, possess-
ing a trans-square planar geometry around the Pd atom,
which occupies a crystallographic inversion centre (Fig.
4). Both the Pd–P and Pd–Cl distances (2.3450(3) and
rapid ring-opening/rearrangement. The filtrate from the
crystallisation of 15 contains alkene-containing side-
products, as shown by 1H NMR spectroscopy, thus a b-
hydrogen elimination pathway appears most plausible.
Interestingly, complex 15 (and the related dimeric
complexes) has recently been reported as a highly active
Pd-catalyst for cross-coupling of deactivated aryl halides
[20].
The elimination pathway represents a useful synthetic
approach to the exclusive formation of trans-15, which
is usually isolated as a mixture of cis- and trans-isomers
(in CDCl3 solution at 25 ꢁC their distribution does not
alter to any great extent, as shown by 31P NMR spec-
troscopy). The near exclusive formation of trans-15 is
intriguing, as it is to be expected that the bidendate li-
gand, being cis-chelating, should eliminate to release
cis-15 (isomerisation to trans-15) should be slow, vide
supra but at least a roughly equal mixture of cis- and
trans-isomers should be seen. We have considered that
this bulky bidendate ligand is trans-chelating, promoted
by conformational changes in the constrained bicy-
clo[3.2.0]heptane framework (Fig. 5).
Given the large steric congestion around the Pd(II)
centre in 14, a conformational change from the cis-
endo-envelope form I to a cis-exo-envelope II is expected
to be fast. The large natural bite angle (>100 ꢁ) in the
cis-exo-envelope II conformation should enable slow
isomerisation to the trans-exo-envelope III. Elimination
of H7-exo in III is expected to occur first to give trans-
exo-envelope IV, given that elimination at H4-exo and
H2-exo are positioned unfavourably. Once elimination
has occurred, however, a rapid ring-flip to give trans-
endo-envelope V facilitates elimination from either
H4-exo (as shown) or H2-exo to give 15.
˚
2.3132(3) A, respectively) are longer than in the only
one previously studied trans-bis-phosphinite-dichloro-
palladium(II) complex, PdCl2(PPh2OR)2, where R is a
bulky calixarene moiety (Pd–P 2.325(1), Pd–Cl 2.301(1)
˚
A) [19]. The differences in Pd–P distances can be attrib-
uted to weaker electron withdrawal by t-Bu compared
to Ph groups and hence higher basicity of the P atom
in 15, while the elongation of Pd–Cl is probably caused
by intramolecular hydrogen bonds O-Hꢁ ꢁ ꢁCl (Fig. 4).
The 31P NMR spectrum exhibited two sharp singlets at
d 123.35 and 124.63 in a ratio of ꢂ15:1, attributable to
the cis- and trans-forms of 15, the former being the major
isomer in solution (identical to an authentic sample con-
taining both isomers).
Molecular models of the cis- and trans-forms of 14
show severe steric constraints imposed on the bicy-
clo[3.2.0]heptane skeleton, which we believe promotes
b-hydrogen elimination to yield 15 and 1,4-diene 16
(Scheme 5), although we have been unable to fully charac-
terise 16 which is highly volatile and probably undergoes
3. Attempted synthesis of monodentate ligand 2
The synthesis of the novel monodentate phosphinite
ligand based on 2 was next attempted. Compound 8
was reacted with PhPCl2 in THF, in the presence of
DABCO or Et3N, to give 2a, under similar conditions
employed for the synthesis of 1 (see Scheme 6).
Complete disappearance of 8 was confirmed by TLC
analysis. Compound 2a was isolated as an oil and found
to be very air sensitive, oxidising rapidly in the presence
of trace quantities of air to give oxide 17a (<5 min). The
combined yield of the material produced from this reac-
tion was 24%; oligomerisation/oxidation account for
this inadequate yield [21]. The 31P NMR spectrum of
the material produced from the reaction carried out in
the presence of Et3N shows two singlets (d 176.88 and
178.12), expected for diastereoisomeric phosphinates
(2a0 and 2a00). A broad peak is observed between d 23
and 34, which is attributable to diastereoisomeric phos-
phonates (17a0 and 17a00), as well as polymerised,
Fig. 4. X-ray structure of 15, showing intramolecular hydrogen bonds.
Atoms generated by the inversion centre are primed, methyl H atoms
˚
are omitted; P–O distance 1.613(1) A, Cl–Pd–P angle 88.98(1)ꢁ.
OH
rapid elimination
P(t-Bu)2
Cl
cis/trans-14
Pd
+
Cl
(t-Bu)2P
OH
15
16 ?
Scheme 5. Rapid elimination of the bicyclo[3.2.0]heptane backbone to
give 15 and bicyclic diene 16.

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4467
Slow
isomerisation
Fast
O
P(t-Bu)2
O
O
Cl
Cl
P(t-Bu)2
O
O
Pd
O
(t-Bu)2P
(t-Bu)2P
Pd
Cl
(t-Bu)2P
Pd
P(t-Bu)2
Cl
Cl
14
Cl
cis-exo-envelope (II)
cis-endo-envelope (I)
trans-exo-envelope (III)
H7-exo
elimination
H4-exo
Fast
elimination
O
15
Cl
Cl
O
OH
Cl
O
O
OH
(t-Bu)2P
Pd
P(t-Bu)2
(t-Bu)2P
Pd
P(t-Bu)2
(t-Bu)2P
Pd
P(t-Bu)2
Cl
trans-exo-envelope (III)
Cl
trans-exo-envelope (IV)
Cl
trans-endo-envelope (V)
Fig. 5. Proposed conformational changes in the strained bicyclo[3.2.0]heptane backbone.
H
H
H
H
O
H
O
H
O
O
Ph
O
H
rapid oxidation
H
i
P
P
R
P
P
8
Ph
Ph
O
O
O
O
H
H
H
H
2a'
2a''
17a
R= Ph,2a (oligomerisation and oxidation).
t-BuP,2b (oligomerisation).
H
H
O
Scheme 6. Reagents and conditions: (i) ArPCl2 (1 equiv., Ar = Ph, 2a;
t-Bu, 2b), DABCO or Et3N (1.2 equiv.), THF, 0–25 ꢁC;
(ii) (CH3CN)2PdCl2 (1 equiv.), ligand 2a/2b (2 equiv.), CH2Cl2, rt, 3 h.
O
H
Ph
O
H
H
H
P
P
O
Ph
O
O
ring-opened phosphonates. Further evidence for oligo-
merisation is seen in an attempt to synthesise the tert-
butyl phosphinite derivative 2b. FAB-MS shows that
dimeric and trimeric species m/z (461 [2M + 1]), ESI
(483 [2M + Na]; 713 [3M + Na]) are produced in this
reaction. (see Fig. 6)
H
H
17a''
17a'
H
H
H
Ph
H
*
H
H
O
O
P
O
H
O
O
P
O
H
4. Synthesis of monodentate ligand 3 and its Pd(II)
complex 19
*
n
Ph
polymers
Fig. 6. Compounds 2a0/2a00 and other side-products.
A diphenylphosphinite monodentate ligand 3 was
synthesised from ketone 5. Stereoselective carbonyl
reduction using NaBH4 in MeOH at ꢀ78 ꢁC gave
endo-alcohol 18 in 62% yield (Scheme 7).
However, three phosphorus species are observed (Fig.
7). The signal at d 109.84 is spin–spin coupled with
2
0
the signal at d 98.4 ð JPP ¼ 25:97 HzÞ and this is
The phosphinite ligand 3 was produced by reaction
of 18 with Ph2PCl in the presence of Et3N in THF at
ꢀ78 ꢁC to give 3 in quantitative yield. The air sensitiv-
ity of 3 is again a problem (we have included selected
NMR spectroscopic data in Section 8), however, direct
complexation with (MeCN)2PdCl2 does afford trans-19
attributed to cis-19. The similar chemical shift of d
107.30, but absence of spin–spin coupling, is attributed
to trans-19. The preferred conformations of the bicy-
clo[3.2.0]heptane ring may account for the inequivalent
phosphorus environments seen in the more sterically
hindered cis-19.
1
in 89% yield. In CDCl3 solution, the H and 31P NMR
The signal at d 78.12 is attributed to the product de-
rived from decomposition of cis/trans–19 to 20 in CDCl3
solution (previously stored over activated molecular
sieves). X-ray crystallography provided the means to
spectra of trans-19 indicated the presence of the bicy-
clic ring and that it is bound to phosphorus (H6 is
characteristic at d 4.64), which is coordinated to Pd.

4468
I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
Scheme 7. Reagents and conditions: (i) NaBH4, MeOH, ꢀ78 ꢁC, 2 h; (ii) Ph2PCl, Et3N, THF, ꢀ78 ꢁC to rt; (iii) (MeCN)2PdCl2, CH2Cl2, 25 ꢁC. In
X-ray structure drawing for 20, a disordered CH2Cl2 is omitted.
OR
H
H
Ph
Ph
R =
Ph Ph
Cl
PPh2
Cl
O
P
P
O
Pd
Cl
Cl
Ph2P
H
Pd
Pd
H
OR
trans-19
O
P
P
O
Ph Ph
20
Ph Ph
OR
Cl
Cl
PPh2
Pd
PPh2
OR
cis-19
110.0
105.0
100.0
95.0
90.0
85.0
80.0
ppm (f1)
Fig. 7. 31P NMR (162 MHz) spectrum of a CDCl3 solution of material produced in the reaction of 3 with (MeCN)2PdCl2.
prove the identify of this as [l2-ClPd(PPh2-OH)
(PPh2O)]2 (20). The solid material produced from the
reaction was recrystallised by layering a relatively con-
centrated CH2Cl2 solution (ꢂ0.2 M) with hexane/ether
(1/1, v/v) at 25 ꢁC over two days. Only 20 crystallised
from solution. A literature survey reveals that 20 has
been produced from other phosphinite ligands, and that
HCl or trace quantities or water are responsible for elim-
ination [22].
5. Suzuki–Miyaura cross-coupling reactions
To evaluate whether 11 could be a useful precatalyst
for cross-coupling reactions, the Suzuki–Miyaura reac-
tion1 of organohalides with organoboronic acids, in
the presence of base, was investigated. This reaction
arguably represents one of the most applied reactions
in academia and industry and therefore we expected it
would be a useful test (Eq. (1)).

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4469
[Pd]Cat.
Base
seen using (Ph3P)2PdCl2 (5 mol%) in our hands. Precat-
alyst 11 is, albeit surprisingly, ineffective at promoting
the Suzuki–Miyaura cross-coupling reaction. In start
contrast, Suzuki–Miyaura cross-coupling reaction of
4-bromoacetophenone with phenyl boronic acid to give
4-acetobiphenyl in the presence of 19 (1 mol%) did pro-
ceed well (86% conversion, 2 h). However, on testing the
eliminated Pd dimer complex 20 (0.5 mol%), similar cat-
alytic activity was observed (evolution profile, as shown
by GC analysis, including reaction rate and % conver-
sion after 2 h, is near identical for 19 and 20). We believe
that 19 represents a steady source of 20, the latter com-
plex is known to exhibit catalytic activity for this
reaction.
We questioned why 11 was an ineffective for this reac-
tion. The electron deficient ligand might account for the
low level of catalytic reactivity, but the fact that other
phosphinites have been employed with great success in
these reactions, would count against this statement.
Conformational changes are expected within the bicy-
clo[3.2.0]heptane backbone of the ligand, as proposed
in Fig. 5; an endo–exo ring flip would increase the
ꢀP–Pd–Pꢁ natural bite angle (bn) dramatically, which is
96ꢁ in the endo-envelope 11, to >106ꢁ in the exo-enve-
lope (calculated by molecular mechanics using the mod-
els developed by Casey and Whiteker [29] and Dierkes
and van Leeuwen [30]). This change would be mani-
fested on reduction of Pd(II) to Pd(0). Van Leeuwen
and co-workers studied the effect of bn in chelating
diphosphines on the activity and selectivity in palla-
dium-catalysed cross-coupling reactions [31]. In the
coupling of sec-butylmagnesium chloride with bromo-
benzene the optimal bite angle was found to 102.7ꢁ.
Increasing bn to >105ꢁ resulted in lower yields of the
cross-coupled product and substantial amounts of
homocoupling. Homocoupling was a problematic side
reaction observed in reactions mediated by 11. Increas-
ing the natural bite angle of the ligand towards 109ꢁ
could lead to distortion toward a tetrahedral coordina-
tion mode, explaining the decrease rate of reaction with
aryl halides (Scheme 9).
ð1Þ
+
R R'
R
X
R ' B(OH)2
There are many highly active Pd-catalysts for this reac-
tion, particularly for aryl halides; [23] the differences be-
tween these, most commonly, arise through changes in
the coordinating ligand, e.g., use of electron rich alkyl
phosphines, such as (t-Bu)3P or biphenyl(t-Bu)2P (devel-
oped by Littke and Fu [2] and Buchwald and co-workers
[24], respectively), N-heterocyclic carbenes (Beller and
co-worker [25] and Nolan and co-workers [26]) or phos-
phinites (particularly those developed by Bedford et al.
[27]). An extensive screen of reactions mediated by 11,
under aqueous and non-aqueous conditions were per-
formed. However, the cross-coupled product was at best
produced in ꢂ20% yield, although substantial quantities
of homocoupled products, derived from oxidative dimer-
isation of the organoboronic acid, were detected by GC/
NMR (>25%) (Scheme 8). Under aqueous conditions,
Pd black was produced after ꢂ 10 min at 80 ꢁC. Under
non-aqueous conditions, the formation of Pd black was
not seen after 24 h at the same temperature (both reac-
tions were conducted employing identical reactant and
catalyst concentration; 0.12 M, 5 mol% [Pd]). To assess
whether Pd agglomeration [28] was a problem, lower
Pd loadings (0.1–0.01 mol% [Pd]) were employed, but
this was equally as ineffective. Our conditions were vali-
dated by use of Pd(OAc)2 (5 mol%) in the presence of
Ph3P (10 mol%), under either aqueous or non-aqueous
conditions, which showed that cross-coupling proceeds
effectively for the substrates shown in Scheme 9 (within
ꢂ3 h and isolated yields of 70–95%). Similar results are
B(OH)2
Br
Yields - 0-20%
R = H,4-COMe,4-Me,2-Me, 4-CO2Me,
2-CO2Me, 4-NO2, 4-OMe, 2-OMe
"Pd" (5 mol%)
R
R
aqueous or non-aqueous conditions
Scheme 8. Aqueous conditions: [Pd] cat. (5 mol%), 2 M aq. Na2CO3,
benzene/EtOH, 80 ꢁC; 1 M aq. Na2CO3, THF, 60–80 ꢁC. Non-aqueous
conditions: KF (3 equiv.), dioxane or THF, 25–80 ꢁC; CsF (3 equiv.),
dioxane or THF, 25–80 ꢁC.
The production of homocoupled product, from the
organoboronic acid, in these reactions may be explained
by reoxidation of Pd(0) back to Pd(II), possibly by
O
reduction
Fast
O
PPh2
Pd
PPh2
Pd(0)
O
PPh2
Pd(0)
S
S
S
S
Cl
O
O
Ph2P
Ph2P
Ph2P
O
Cl
11
cis-endo-envelope-
square planar (I)
cis-exo-envelope-
tetrahedral (II)
Scheme 9. Proposed conformational changes in the bicyclo[3.2.0]heptane backbone on reduction of Pd(II) to Pd(0).

4470
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Table 2
1,6-Diene cycloisomerisation selectivity using precatalyst 11 under
monocationic conditions
adventitious oxygen. A classic Pd(II) reduction to give
the homocoupled product is plausible. It is important
to note, however, that aryl bromide homocoupling is
not observed, excluding the involvement of a possible
trigonal-bipyramidal Pd(IV) complex [32] (known to
be stabilised by ligands with bite angles near 110ꢁ) which
explains homocoupling, from aryl halides, in the system
described by van Leeuwen and co-workers [31].
After determining the poor catalytic properties of the
phosphinite Pd(II) complexes in Suzuki–Miyaura cross-
coupling reactions, we considered their utilisation in
other reactions. Electrophilic, neutral and cationic, Pd
catalysts/precatalysts have been used to mediate the
cycloisomerisation of 1,6-dienes to give cyclopentenes
with varying functionality [33]. Investigations were thus
initially pursued employing 11 as the precatalyst.
E
E
E
E
E
E
E
E
i
+
+
+
E
E
22c
21
22a
22b
21'
Additive
Temperature (ꢁC)
Time (h)a
4
24
AgOTf
40
60
80
70/5/21/4
5/0/14/46b
28/0/21/51
39/0/49/12
8/0/5/57c
11/0/25/64
NaBAr04
AgSbF6
40
60
80
89/0/10/1
46/0/54/0
18/0/81/1
52/0/45/3
0/0/95/5
4/0/91/5
40
60
80
79/7/14/0
90/0/10/0
15/0/81/4
60/5/32/3
72/0/27/1
1/0/93/6
AgBF4
40
60
80
80/3/17/0
90/0/10/0
65/0/35/0
60/8/32/0
63/0/37/0
36/0/63/1
6. Cycloisomerisation of dimethyl diallylmalonate 22
mediated by Pd(II) complex 11
a
Ratio of 21/22a/22b/22c as determined by 1H NMR spectroscopy.
Isomerised starting material 210 (35%) was observed.
Isomerised starting material 210 (30%) was observed.
b
c
The benchmark substrate for 1,6-diene cycloisomeri-
sation is dimethyl diallylmalonate 21 [33]. There are sev-
eral palladium catalysts/precatalysts reported that
promote cycloisomerisation of this substrate [34]. Three
cycloisomerisation products (22a–c) are usually ob-
served with varying distribution (Scheme 10). In addi-
tion, the isomerised 1,5-diene 210 is often observed,
sometimes exclusively.
after 24 h, isomerised to either 22b or 22c, whereas
for SbF6 and BF4 anions, 22a still remains at this tem-
perature. At both 60 and 80 ꢁC, 22a is not detected for
any of the additives investigated. The highest selectivity
is seen for the BAr04 anion at 60 ꢁC, which after 24 h
gave predominately 22b (90% selective at 100% conver-
sion). Although SbF6 is selective for 22b (ꢂ96%),
percentage conversion to products (28%) is low.
Increasing the temperature to 80 ꢁC improves the
conversion to products (99%), but at the expense of
selectivity for 22b (86%). It appears that the non-coor-
dinating anion is essential for higher catalytic activity
but not selectivity. At 60 ꢁC, the more coordinating
BF4 anion produces 22b exclusively (100%), at the ex-
pense of higher conversion (37%). Only after 72 h is
the more thermodynamically stable symmetrical prod-
uct 22c observed (AgBF4, 60 ꢁC, 72 h; 21/22b/22c, 26/
73/1). Increasing the temperature to 80 ꢁC gives higher
conversions (64%), and reaction is still selective for 22b
(ꢂ98%).
In our first reaction, 5 mol% of 11 was added to a
1,2-dichloroethane solution of 21 under a nitrogen
atmosphere and the reaction heated to 60 ꢁC for 24
h. No products were formed under these conditions.
Heating to 80 ꢁC for several days showed no further
changes. However, the addition of one equivalent of sil-
ver(I) salt with respect to Pd, in this case AgOTf
(OTf = triflate), promoted cycloisomerisation at 60 ꢁC,
but this was accompanied by isomerisation (double
bond migration) of 21 ! 210 (Table 2). Trace quantities
of triflic acid (TfOH) presumably promote the isomeri-
sation side reaction. A variety of silver(I) salts and reac-
tion temperatures were studied to assess their affect on
the production and distribution of the cycloisomerised
products (22a–c), and isomerisation of 21 ! 210. Some
important observations come out of the results shown
in Table 2. At 40 ꢁC the formation of the kinetic exo-
cyclic product 22a is observed, an exception being
NaBAr04 (Ar0 = bis(3,5-trifluoromethyl)benzene). In the
presence of the OTf anion, this product disappears
The evolution of cycloisomerised products 22b and
22c, mediated by 11 (5 mol%) in the presence of
NaBAr04 (5 mol%) in DCE at 60 ꢁC, is shown in Fig.
8. Significantly, the kinetic profile exhibits an absence
of a period of induction under the reaction conditions.
E
E
E
E
E
E
E
E
E
E
i
+
+
+
22c
21
22a
22b
21'
Scheme 10. Reagents and conditions: (i) [Pd] (5 mol%), 1,2-dichloroethane (DCE), 25 ꢁC.

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4471
It is assumed, but not proven, that a ‘‘Pd–H’’ spe-
cies is involved in the catalytic cycle. The mechanism
is expected to be similar to that proposed by Widen-
hoefer and co-workers [35] for cationic palladium phe-
nanthroline complexes (Scheme 11). The catalytic cycle
is dependent on the generation of cationic palladium
hydride complex [36], (P,P0)PdH+ (II) from cationic
palladium complex, (P,P0)PdCl+ (I). The P,P0 ligand
is expected to undergo a series of associative/dissocia-
tive processes (bidentate ! monodentate) throughout
the catalytic cycle. Hydropalladation of an alkene in
21 would form palladium alkyl alkene intermediate
III. Intramolecular carbopalladation of III reveals pal-
ladium cyclopentylmethyl complex IV which then
undergoes b-hydride elimination to form palladium
methylenecyclopentane complex V. A second hydropal-
ladation event provides the tertiary palladium cyclo-
pentylmethyl complex VI, from which a regioselective
b-hydride elimination process from the secondary
hydrogen atom in VI forms the tri-substituted cyclo-
pentene 23b, with regeneration of the active cationic
palladium hydride species II.
100
90
80
70
60
50
40
30
20
10
0
0
4
8
12
Time / h
16
20
24
Fig. 8. Kinetic profile for the cycloisomerisation of dimethyl diallyl-
malonate 21 by 11 (5 mol%), NaBAr04 (5 mol%), DCE, 60 ꢁC
(monitored by 1H NMR spectroscopy; [21] at t0 = 0.245 M). Key:
h, 1,6-diene 22; j, endocyclic product 23b; s, tetrasubstituted
cyclopentene 23c.
It remains a remote possibility that the generated cat-
ion (P,P0)PdCl+ might react with the counterions BAr04,
SbF6 and BF4 at eleꢀvated temperatures in DCE, via an-
ion abstraction (Ar0 or Fꢀ), to release trace quantities
of the Lewis acids BAr03, SbF5 and BF3, and
(P,P0)PdClY (where Y = F or Ar0). However, to the best
of our knowledge there is no literature precedent for Le-
wis acid assisted 1,6-diene cycloisomerisation (note: en-
yne cycloisomerisation mediated by Lewis acids has
been reported) [37]. To assess this possibility, the sepa-
rate reactions of 21 mediated by SbF5 and BF3 Æ Et2O
Prolonged reaction to 72 h shows negligible isomerisa-
tion of 22b to 22c (remains at ꢂ95:5). The linear forma-
tion of the endocyclic product 22b is seen up to
ꢂ50% conversion (4 h). The rate of reaction then slows
and it is at this point that the formation of 22c is
observed.
We have also evaluated the ability of Pt(II) complex
12 to mediate dimethyl diallylmalonate cycloisomerisa-
tion, under both neutral and cationic (using NaBAr04;
12 : NaBAr04; 1 : 1) conditions in DCE at 60 ꢁC. Negli-
gible conversion to products (ꢂ10% after 48 h) is seen in
each case, but 22a was the only cycloisomerisation
product.
1
(5 mol%) in DCE at 60 ꢁC were conducted. H NMR
spectroscopic analysis of samples withdrawn from each
reaction at 2, 4 and 24 h intervals showed no detectable
cycloisomerisation products, derived from 21, under the
CH3
Pd
CH3
Pd
P
E
E
P
E
E
E
E
P
P
Intramolecular
carbopalladation
IV
III
21
Hydropalladation
NaBAr'4
P
P
P
P
β
-Hydride
?
elimination
Pd
H
11
Pd Cl
I
II
NaCl
β
-Hydride
CH3
CH3
P
CH3
elimination
E
E
Hydropalladation
E
H
H
CH3
E
E
E
P
=
Pd
Pd
P
H
OPPh2
OPPh2
P
CH3
P
P
VI
V
Major regio-isomer 23b
Scheme 11. Proposed mechanism for 1,6-diene cycloisomerisation by cationic palladium bisphosphinite complex 11.

4472
I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
Lewis acid promoted conditions. However, for each Le-
wis acid, extensive double bond isomerisation was ob-
served (21 ! 210, >75% in both cases).
31P NMR spectra at 109, 162 or 202 MHz. Chemical
shifts are reported in parts per million (d) downfield
from an internal tetramethylsilane reference. Coupling
constants (J values) are reported in hertz (Hz), and spin
multiplicities are indicated by the following symbols:
s (singlet), d (doublet), t (triplet), q (quartet), m (multi-
plet), br (broad). The characterisation data for com-
pounds 5–7 have previously been reported [5].
Compounds 21, 210 and 22a–c have previously been
characterised [34h].
7. Conclusion
In summary, we have described the synthesis of novel
Pd(II) and Pt(II) complexes possessing bicyclo[3.2.0]hep-
tane ligands based on 1. Alteration of phosphinite sub-
stituents from phenyl to tert-butyl resulted in rapid
elimination of the bicyclic backbone to give pure trans-
15. The attempted synthesis of ligands 2 and 3 was
complicated by rapid oxidation and ring-opening/poly-
merisation reactions. Although 3 was isolated and
reacted directly with (MeCN)2PdCl2 to give 20, a
b-hydrogen elimination pathway affords Pd(II) dimer
21. The catalytic activity of 11 in Suzuki–Miyaura
cross-coupling was surprisingly poor. However, the unu-
sual bicyclic framework was utilised in promoting di-
methyl diallylmalonate cycloisomerisation. Here, in situ
generated cationic Pd(II) species are essential and the
judicious choice of the anion led to the development of
a highly regioselective cationic catalytic system for the
endocyclic cycloisomerisation product 22b. Studies are
in progress to determine the most likely mechanism for
the cycloisomerisation reactions mediated by cationic
derivatives of 11, as well as other bidentate phosphinite
and phosphine complexes.
8.1. 2-exo-Bromo-3-endo-6-endo-dihydroxybicyclo
[3.2.0]heptane (9)
To a magnetically stirred solution of 6 (5.00 g, 24.5
mmol) in methanol (50 mL) was at ꢀ78 ꢁC was added
NaBH4 (1.38 g, 1.5 equiv.) in small portions. On com-
plete addition (ꢂ0.2 h) the reaction mixture was stirred
at ꢀ78 ꢁC for 3 h. The reaction was quenched with a 2
M hydrochloric acid solution (50 mL) and then concen-
trated in vacuo to half volume (until complete removal
of MeOH was accomplished) and then the aqueous
phase was extracted with Et2O (3 · 100 mL) (use of
EtOAc as the extraction solvent gives a product contain-
ing succinimide). The combined organic extracts were
washed with water (100 mL), brine (100 mL), dried
(MgSO4) and concentrated in vacuo to give a clear oil
(4.01 g, 79.5%). Rf = 0.17 (EtOAc/PE, 1/1, v/v); mmax
(CH2Cl2, cmꢀ1) 3306, 2941, 1430, 1276, 1167, 1147,
1106, 1021, 973, 944; dH (CDCl3, 400 MHz) 1.84 (1H,
2
m, H7-exo), 2.02 (1H, d, J = 14.9, H4-endo), 2.29 (1H,
8. Experimental
m, H4-exo), 2.57 (1H, m, H7-endo), 2.83 (1H, m, H1),
3.27 (1H, m, H5), 4.07 (1H, s, H2-endo), 4.21 (1H, m,
H3-exo), 4.49 (1H, d, J = 4.9, H6-exo), 4.57 (1H, OH/D),
5.33 (1H, OH/D); dC (CDCl3, 100 MHz) 31.35 (CH2
C4), 37.27 (CH2 C7), 42.81 (CH, C5), 45.44 (CH, C1),
60.30 (CH, C2), 63.76 (CH, C6), 81.79 (CH, C3); MS
(CI) m/z 224 (M+ + NH4, 99), 206 (M+, 6), 190 (54),
144 (100), 127 (51); HRMS (CI) calcd. for C7H15O2BrN:
224.02862. Found: 224.02824.
THF, toluene and benzene were dried over sodium-
benzophenone ketyl (distilled prior to use). Dry CH2Cl2,
Et3N and CH3CN were distilled over calcium hydride.
All reactions were conducted under an inert atmosphere
of Ar or N2 on a Schlenk line. (MeCN)2PdCl2 was either
purchased from Aldrich or prepared by refluxing PdCl2
with dry acetonitrile for 4 h. Melting points were re-
corded on an electrothermal IA9000 Digital Melting
Point Apparatus and are uncorrected. TLC analysis
was performed on Merck 5554 aluminium backed silica
gel plates and compounds visualised by ultraviolet light
(254 nm), 1% ninhydrin in EtOH or dilute KMnO4
aqueous solution (containing a drop of H2SO4). The rel-
ative proportion of solvents in mixed chromatography
solvents refers to the volume/volume ratio. Infrared
spectra were recorded on a ATI Mattson Genesis FT-
IR. Mass spectrometry was carried out using a Fisons
Analytical (VG) Autospec instrument. High-resolution
masses are within 5 ppm of theoretical values. 1H
NMR spectra were recorded at 270 MHz using a JEOL
EX270 spectrometer, at 400 MHz using a JEOL
ECX400 spectrometer or 500 MHz on a Bruker 500
spectrometer; 13C NMR spectra at 68 or 100 MHz;
8.2. 4,6-Dioxa-5-bora-tricyclo[5.2.1.03,9]decan-5-ol (10)
To a Schlenk flask containing 7 (3.57 g, 28 mmol) in
methanol (120 mL) at ꢀ78 ꢁC was added sodium boro-
hydride (1.38 g, 36.4 mmol, 1.3 equiv.) in portions and
the reaction stirred at this temperature for 2 h. The reac-
tion mixture was quenched at ꢀ78 ꢁC with saturated
aqueous ammonium chloride (15 mL) and was allowed
to stir for 1 h. The mixture was allowed to warm to
room temperature and extracted with EtOAc (100
mL · 3). The combined organic extracts were washed
with water (100 mL) and brine (100 mL). The solution
was dried (MgSO4) and concentrated in vacuo to give
a yellow oil (1.31 g, 30.8%). M.p. 108–109 ꢁC; mmax
(CH2Cl2, cmꢀ1) 3211, 1779, 1429, 1345, 1181, 1165; dH

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4473
(CDCl3, 270 MHz) 1.69 (1H, br), 1.74 (2H, m), 2.11
8.4. Synthesis of 1 and its borane adduct 10
(1H, br), 2.49 (1H, m), 2.64 (2H, m), 3.10 (1H, m),
4.26 (1H, m), 4.52 (1H, m); dC (CDCl3, 100 MHz)
32.71 (CH), 35.49 (CH2), 38.35 (CH2), 43.21 (CH2),
45.62 (CH), 65.29 (CH), 76.37 (CH); dB (CDCl3, 160
MHz) 18.19; MS (CI) m/z 172 (M+ + NH4, 52), 154
(M+, 100), 129 (58), 111 (35), 84 (40); HRMS (CI) calcd.
for C7H15O3BN: 172.11449. Found: 172.11395.
Under an atmosphere of argon a THF solution (2
mL) of 8 (73.0 mg, 0.6 mmol, 1 equiv.) was cooled to
0 ꢁC and then DABCO (78.5 mg, 0.7 mmol, 1.2 equiv.,
vacuum dried) in THF (2 mL) was added via cannula
and allowed to stir at this temperature for 0.5 h. Chloro-
diphenylphosphine (286.8 mg, 0.24 mL, 1.3 mmol, 2.2
equiv.) was added dropwise slowly at 0 ꢁC. DAB-
CO Æ HCl formed immediately (precipitate). The mixture
was allowed to warm to 25 ꢁC and stirring was contin-
ued for 16 h. After this time, the mixture was passed
through Celiteꢂ under nitrogen atmosphere (washed
through with THF (50 mL). The solvent was removed
in vacuo to give 1 as a viscous colourless oil (which
was reacted directly with the M(II) precursors or
BH3 Æ THF).
8.3. 3-endo-6-endo-Dihydroxybicyclo[3.2.0]heptane (8)
8.3.1. Synthesis of ethylpiperidine hypophosphite
A magnetically stirred solution of aqueous hypophos-
phorous acid (50%, w/w) was dried in vacuo at 50 ꢁC
(ꢂ7 mmHg). After complete removal of water, the acid
was placed under an inert atmosphere (N2) and cooled
to 0 ꢁC. 1-Ethylpiperidine (1 equiv.) was added to the
acid at 0 ꢁC, whilst stirring slowly to precipitate out a
white salt (hygroscopic). The reaction proceeds in quan-
titative yield. This salt was used without any further
purification as a reagent. EPHP is commercially avail-
able but it is relatively expensive given that it may be
prepared on large scale very easily (100 g). The acid
must be thoroughly dried, otherwise the product formed
is a viscous oil, which is extremely difficult to dry – this
was noticed on larger scale reactions, where trace quan-
tities of water could still be present. In our hands, the
salt does not form immediately. This seems to be depen-
dant on the scale of the preparation (ꢂ0.3 h). EPHP
must be stored at ꢀ20 ꢁC in a sealed flask, but can be
weighed out in air.
8.4.1. Borane adduct 10
As above, the reaction mixture was not filtered.
The reaction mixture was cooled to 0 ꢁC and then
BH3 Æ THF (1.8 mmol) was added dropwise. The mix-
ture was allowed to stir for 1 h at 0 ꢁC and then
warmed to 25 ꢁC and stirring continued for 3 h.
The reaction was quenched by the addition of water
(5 mL), and the mixture was extracted with CH2Cl2
(3 · 5 mL). The combined organic extracts were dried
(MgSO4) and concentrated in vacuo. Purification by
chromatography gave the product as viscous yellow
oil (0.18 g, 57%). mmax (CH2Cl2, cmꢀ1) 3400 (br),
1966, 1897, 1820, 1732, 1589, 1483, 1437, 1374,
1268, 1113, 1065, 1033, 1001, 980, 941, 919. dH
8.3.2. Hydrodebromination procedure
(CDCl3, 500 MHz) 1.75 (3H, m, H4endo & H4exo &
H7-exo), 2.20 (4H, m, H2-endo & H2-exo & H5 & H7-endo),
To a solution of 9 (0.206 g, 1 mmol, 1 equiv.) in dry
toluene (20 mL), was added EPHP (10 equiv.) and
AIBN (0.05 equiv.) in one portion under an inert atmo-
sphere (N2). The reaction mixture was heated to reflux
and monitored by TLC, until all starting material had
been consumed (16 h). The reaction was allowed to cool,
then quenched with water and extracted with ether (20
mL · 4). All the organic extracts were combined, dried
(MgSO4) and concentrated in vacuo. The product was
purified by column chromatography using EtOAc/PE
(1/1, v/v increased by gradient elution to 2/1, v/v) to give
the product as a white crystalline solid (0.095 g, 74%).
Rf = 0.10 (EtOAc/PE, 1/1, v/v); dH (CDCl3, 270 MHz)
1.67 (4H, m, H4-exo, H2-endo and H2-exo, H7-exo), 2.09
2.87 (1H, m, H ), 3.30–3.52 (6H, m, 2· BH3), 4.64
1
(1H, m, H3-exo), 4.83 (1H, m, H6exo), 7.17 (20H, m,
Aryl). dC (CDCl3, 100 MHz) 31.17 (CH), 34.34
(CH), 36.71 (CH2), 41.08 (CH2), 65.94 (CH), 68.62
(CH), 83.21 (CH), 128.59, 128.64, 128.70, 131.38,
131.80. dP (CDCl3, 202 MHz) 103.499 (P1, attached
to C6), 104.258 (P2, attached to C3). d11B (CDCl3,
160 MHz) ꢀ39.48 (B1, attached to C6), ꢀ39.87 (B2,
attached to C3). LRMS (CI) m/z 542 (M+ + NH4,
26), 509 (77), 420 (31), 242 (69), 203 (61), 186 (100),
108 (62). HRMS (CI) calcd. for C31H40B2NO2P2:
542.27204. Found: 542.27312.
2
(1H, d, J = 15.1, H4-endo), 2.48 (1H, m, H1), 2.62 (1H,
m, H7-endo), 3.10 (1H, m, H5), 3.53 (1H, m, H3) 4.28
8.5. [3-endo-6-endo-Bis(diphenylphosphinooxy)bicyclo-
[3.2.0]heptanyl]palladium(II)chloride (11)
3
(2H, OH/D), 4.51 (1H, d, J = 4.3, H6); dC (CDCl3, 68
MHz) 32.79 (CH, C1), 35.61 (CH2, C2), 38.16 (CH2,
C4), 42.98 (CH2, C7), 45.52 (CH, C5), 65.29 (CH, C3),
75.82 (C H, C6); LRMS (CI) m/z 146 (M+ + NH4, 77),
129 (M+ + H, 100), 111 (37), 93 (24), 67 (9); HRMS
(CI) calcd. for C7H16O2N: 146.11810. Found:
146.11798.
To a solution of 1 (1.06 g, 2.13 mmol, 1 equiv.) in
dry CH2Cl2 (3.0 mL) was added via cannula transfer
a
solution of bis(acetonitrile)palladium(II)chloride
(0.44 g, 2.13 mmol, 1 equiv.) in CH2Cl2 (5.0 mL).
The solution was allowed to stir overnight at 25 ꢁC.
The solvent was removed in vacuo to yield a yellow

4474
I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
solid (1.30 g, 91%). M.p. 147–149 ꢁC (decomp.); mmax
(CH2Cl2, cmꢀ1) 3063, 3046, 2949, 1435, 1275, 1103,
1082, 1046, 1032, 1007, 962, 778, 763, 738, 723, 707,
8.8. 5-Phenyl-cis-4,6-dioxa-5-phosphatricyclo[5.2.1.03,9]-
decane (2a)
696. dH (CDCl3, 500 MHz) 1.74 (3H, m, H2-endo
,
8.8.1. Attempted preparation
H2-exo and H4-exo), 1.93 (1H, d, 2J = 16.0 H4-endo),
2.19 (1H, m, H7-exo), 2.42 (2H, m, H1 and H5), 3.74
To a THF solution (15 mL) of 8 (0.537 g, 4.2 mmol,
1 equiv.) at 0 ꢁC was added Et3N (0.935 g, 9.2 mmol,
2.2 equiv.). Dichlorophenylphosphine (0.751 g, 4.2
mmol, 1 equiv.) was added dropwise at 0 ꢁC. Once
the addition was complete, the reaction was allowed
to warm to 25 ꢁC and allowed to stirred overnight.
The mixture was filtered through a pad of dried alu-
mina layered over dried Celiteꢂ, and was concentrated
on the schlenk line to yield a pale viscous yellow oil
(24.5%). See main text for selected dP NMR spectro-
scopic data. LRMS (CI) m/z 271 (M + HCl, 64%),
235 (M + H, 24%), 160 (100%); HRMS (CI) calcd.
for C13H16O2P: 235.08879. Found: 235.08914.
2
(1H, d, J = 15.5, H7-endo), 4.23 (1H, m, H3-exo), 4.43
(1H, dd, 3J = 4.0, 8.0, H6-exo), 7.16 (20H, m, Ar-H).
dP (CDCl3, 109 Hz) 100.48 (d, 2J=51.1), 106.69
(d,2J = 51.1). MS (FAB) m/z 637 (M+ ꢀ Cl, 62), 529
(72), 460 (53), 307 (28), 154 (100); HRMS (FAB) calcd.
for C31H30O2P2ClPd: 637.044. Found 637.045. Anal.
Calc. for C31H30O2P2Cl2Pd: C, 55.09; H, 4.77. Found:
C, 55.33; H, 4.76%.
8.6. [3-endo-6-endo-Bis(diphenylphosphinooxy)bicyclo-
[3.2.0]heptanyl]platinum(II)chloride (12)
To a solution of 1 (0.240 g, 0.48 mmol, 1 equiv.) in
dry DCM (5.0 mL) was added via cannula transfer a
solution of bis(benzonitrile)platinum(II)chloride (0.229
g, 0.48 mmol, 1 equiv.) in CH2Cl2 (25 mL). The solu-
tion was allowed to stir for 2 h at 25 ꢁC. A colour
change from pale green to a pale yellow was observed
on ligand complexation. The solvent was removed in
vacuo to yield a yellow solid (0.298 g, 81%). M.p.
65–66 ꢁC (decomp.). dH (CDCl3, 400 MHz) 1.74 (3H,
8.9. 6-endo-Hydroxybicyclo[3.2.0]hept-2-ene (18)
To a MeOH (30 mL) solution containing NaBH4
(0.62 g, 16.4 mmol, 1.2 equiv.) at ꢀ78 ꢁC was added
a MeOH (10 mL) solution of 5 (1.48 g, 13.7 mmol, 1
equiv.) dropwise over ꢂ0.5 h. The mixture was allowed
to stir at this temperature for 3 h, after which time
TLC analysis indicated the complete disappearance of
the starting material and the appearance of a new
product. The reaction was quenched with water (20
mL), followed by dilute hydrochloric acid (1 M, 20
mL). The aqueous mixture was extracted with ether
(3 · 30 mL), which were combined, washed with satu-
rated aqueous NaCl (1 · 30 mL), dried (MgSO4) and
concentrated in vacuo to yield a pale yellow oil. This
was purified by column chromatography using
EtOAc/PE (7/3, v/v) to give the title compound as a pale
yellow oil (0.94 g, 62%). mmax (neat, cmꢀ1) 3339 (br
OH), 3048, 2930, 2850, 1607 (C@C), 1432, 1350,
1324, 1210, 1167, 1108. dH (CDCl3, 400 MHz) 1.57
(1H, m, H4-endo), 2.35 (1H, m, H4-exo), 2.50 (1H, br s,
OH), 2.66 (2H, m, H7-endo and H5), 2.99 (1H, m,
H7-exo), 3.12 (1H, m, H1), 4.41 (1H, m, H6-exo), 5.84
(2H, m, H2 and H3). dC (CDCl3, 100 MHz) 31.51
(CH2 C4), 39.72 (CH2 C7), 40.47 (CH, C1), 42.32
(CH, C5), 66.89 (CH, C6), 132.53 (CH, C3), 135.45
(CH, C2). LRMS (CI) m/z 128 (M+ + NH4, 75), 110
(M+, 40), 93 (M+–OH, 100), 81 (28), 66 (84). HRMS
(CI) calcd. for C7H14NO: 128.1075. Found: 128.1073.
2
m, H2-endo, H2-exo and H4-exo), 1.92 (1H, d, J = 14.9,
H4-endo), 2.26 (1H, m, H7-exo), 2.46 (2H, m, H1 and
H5), 4.02 (1H, d, 2J = 15.2, H7-endo), 4.29 (1H, m,
H3-exo), 4.53 (1H, m, H6-exo), 7.15 (20H, m, Ar-H).
dC (CDCl3, 100 MHz, selected peaks) 81.88 (C6,
3
3JPtC6 = 7.7 Hz), 74.56 (C6, JPtC3 = 13.8 Hz), 45.45
4
(C1), 42.62 (C7, d, JPtC7 = 7.7 Hz), 35.96 (C2/4, d,
4
4JPtC2/4 = 3.8 Hz), 34.57 (C2/4, d, JPtC2/4 = 9.2 Hz),
32.87 (C5). dP (CDCl3, 162 MHz) 74.05 (P2, attached
to C3, dd, JPP = 7.7 Hz; JPtP2 = 2140 Hz) and 79.07
2
1
2
1
(P1 attached to C6, dd, JPP = 7.7 Hz; JPtP2 = 2126
Hz). MS (FAB) m/z 727 (M+ ꢀ Cl, 60), 598 (7), 529
(16), 307 (22), 219 (86), 154 (100); HRMS (FAB) calcd.
for C31H30O2P2ClPd: 727.051. Found: 727.106. We
have been unable to obtain accurate elemental analysis
for this complex. The 31P NMR solution spectrum
shows a phosphorus purity of >95% to the limits of
detection.
8.7. trans-Bis(di-tert-butylphosphinic acid)palladium(II)-
chloride (15)
8.10. 6-endo-(Diphenylphosphinite)bicyclo[3.2.0]-
hept-2-ene (3)
dH (CDCl3, 400 MHz) 1.30 (1H, s, OH), 1.33 (1H, s,
OH), 1.37 (38H, t, JHP = 7.64). dC (CDCl3, 68 MHz)
3
27.64 (CH3), 39.30 (C). dP (CDCl3, 162 MHz) 123.35
(s). MS(FAB) m/z 503 (M+, 80%), 468 (40), 411 (67),
389 (6), 375 (8), 285 (25), 215 (100), 181 (16). Anal. Calc.
for C16H38Cl2O2P2Pd: C, 38.30; H, 7.63. Found: C,
38.48; H, 7.81%.
mmax (neat, cmꢀ1) 3339 (br OH), 3048, 2930, 2850,
1607 (C@C), 1432, 1350, 1324, 1210, 1167, 1108. dH
(CDCl3, 270 MHz) 1.79 (1H, m), 2.30 (1H, m), 2.59
(1H, m), 2.86 (1H, m), 3.14 (1H, m), 4.56 (1H, m),
4.56 (1H, m), 5.77 (2H, m), 7.32 (10H, m). dP (CDCl3,

I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
4475
109 MHz) 107.15. LRMS (CI) m/z 294 (M+, 24), 262
(11), 245 (53), 201 (100), 108 (8), 92 (20), 66 (16).
8.12. X-ray crystallography
X-ray quality single crystals of 11 were grown by
slow evaporation of a CH2Cl2/hexane solution (5/1, v/v),
those of 12 from a solution of CH2Cl2 (ꢂ0.3 M) lay-
ered with ether/hexane (1/1, v/v), which gave the
12 Æ 2CH2Cl2 solvate. The X-ray diffraction experiment
(Durham) for 11 was carried out on a Bruker 3-circle
diffractometer with a SMART 6000 CCD area detec-
tor, using graphite-monochromated Mo Ka radiation
8.11. trans-Bis(6-endo-diphenylphosphinooxy)bicyclo-
[3.2.0]hept-2-enyl)palladium(II)chloride (trans-20)
To a CH2Cl2 solution (5 mL) of 18 (0.59 g, 2.0 mmol, 1
equiv.) under an atmosphere of nitrogen was added a
solution of bis(acetonitrile)palladium(II)chloride (0.26
g, 0.1 mmol, 0.5 equiv.) in CH2Cl2 (25 mL) via cannula.
A colour change from deep orange to bright yellow oc-
curred within minutes. The mixture was stirred for 3 h
at 25 ꢁC, and then the solvent was removed in vacuo to
give a pale yellow solid. The solid was purified by dissolu-
tion in fresh CH2Cl2, filtered through a cotton wool plug
to give a bright yellow filtrate which was concentrated in
vacuo to give a pale yellow solid (0.68 g, 89%). M.p. 92 ꢁC
(decomp.). dH (CDCl3, 400 MHz) 1.90 (4H, m, 2· H4endo
H4exo), 2.09 (2H, m, 2· H1), 2,37 (2H, m, 2· H5), 2.59 (2H,
m, 2· H7-endo), 2.94 (2H, m, 2· H7-exo), 4.64 (2H, m, 2·
H6exo), 5.65 (4H, m, 2· H2 and H3), 7.22 (20H, m, Ar-
H). dC (CDCl3, 100 MHz) 32.77 (CH2), 39.05 (CH2),
39.55 (CH), 43.32 (CH), 74.63 (CH), 128.20 (CH),
128.54 (CH), 132.33 (CH), 132.46 (CH), 132.58 (CH),
134.22 (CH). dP (CDCl3, 109 MHz) 107.30 (s). LRMS
(FAB, +ve mode) 764 (M+, 1), 729 (M+ ꢀ Cl, 40), 601
(M+-2·C7H9, 67), 509 (42), 279 (100), 219 (81), 154 (84).
HRMS (FAB, +ve mode) calcd. for C38H3802P2Cl2Pd:
764.076. Found: 764.077 (exhibits the correct isotopic dis-
tribution for this formula). Anal. Calc. for
ꢀ
˚
ðk ¼ 0:71073 AÞ. The X-ray diffraction experiments
(York) for 12, 15 and 20 were carried out on a Bruker
Smart Apex diffractometer with Mo Ka radiation
ꢀ
˚
ðk ¼ 0:71073 AÞ using a SMART CCD camera. Low
temperature of the crystals was maintained with a
Cryostream (Oxford Cryosystems) open-flow gas cryo-
stat. The reflection intensities were corrected for
absorption by a semi-empirical method based on the
intensities of Laue equivalents and multiple measure-
ments of identical reflections [38]. The structures were
solved by the Patterson and Fourier technique and re-
fined by full-matrix least-squares against F2 of all
reflections, using SHELXTL software [39]. All non-H
atoms were refined in anisotropic approximation, all
H atoms in 11 and 12 were treated in ꢀridingꢁ model.
In 15, methyl and hydroxyl groups were refined as rigid
bodies, rotating around the C–C and O–P axes. In 11,
the atoms O(1), C(1), C(2), C(3), C(4), C(7), H(1),
H(21), H(22), H(3), H(41), H(42), H(5), H(71) and
H(72) are disordered between positions A (80%) and
B (20%). Crystal data and other experimental details
are listed in Table 3.
1
C39H39Cl3O2P2Pd ðM þ CH2Cl2Þ: C, 57.51; H, 4.83.
2
Found: C, 57.84; H, 5.35%.
Table 3
Crystal data and X-ray experimental parameters
11
12
15
Empirical formula
Formula weight
T (K)
C
31H30Cl2O2P2Pd
C31H30Cl2O2P2Pt Æ 2CH2Cl2
C16H38Cl2O2P2Pd
501.70
115(2)
673.79
120(2)
932.33
115(2)
Triclinic
Crystal system
Space group
Monoclinic
P21/n (# 14)
10.859(1)
16.635(5)
16.145(2)
90
Monoclinic
P21/n (# 14)
8.3569(5)
14.5098(8)
9.2099(5)
90
ꢀ
P1 ð#2Þ
˚
a (A)
10.8684(14)
12.8477(17)
13.3514(17)
100.216(2)
92.062(3)
108.848(3)
1727.6(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
103.69(1)
90
96.070(1)
90
3
˚
V (A )
2833.6(10)
4
1.579
1110.0(1)
2
1.500
Z
Dcalc (Mg mꢀ3
)
1.792
4.65
Absorption coefficient (mmꢀ1
Crystal size (mm3)
)
0.99
1.23
0.46 · 0.46 · 0.29
50630
8269
0.19 · 0.09 · 0.03
10244
6691
0.17 · 0.13 · 0.12
7526
2556
Number of reflections collected
Number of independent reflections
Rint
0.044
6705
0.040
5275
0.016
2412
Refelections with I > 2r(I)
R [I > 2r(I)]
0.032
0.085
0.041
0.093
0.016
0.040
wR (F2), all data

4476
I.J.S. Fairlamb et al. / Journal of Organometallic Chemistry 690 (2005) 4462–4477
Manetto, E. Marotta, A. Mazzanti, P. Righi, N. Scardovi, G.
Rosini, J. Org. Chem. 69 (2004) 1353.
Acknowledgements
[7] T. Sell, S. Laschat, I. Dix, P.G. Jones, Eur. J. Org. Chem. (2000)
4119.
We are very grateful to Prof. Stanley M. Roberts (Uni-
versity of Liverpool/Stylacats) for informative discus-
sions and for his support of this research. Prof. Todd B.
Marder (University of Durham) is thanked for important
discussions and for use of his laboratories (I.J.S.F.) dur-
ing summer 2003. Mr. Anant R. Kapdi and Dr. Danielle
Schott (York) are thanked for assistance with some exper-
iments. Prof. Guy C. Lloyd-Jones is thanked for discus-
sion relating to cycloisomerisation. The EPSRC are
acknowledged for a CNA grant (converted to DTA) for
S.G., and I.J.S.F. is grateful to the University of York
for an Innovation and Research Priming Fund grant.
We thank the referees for their careful reading of the man-
uscript and insightful comments.
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Appendix A. Supplementary material
Crystallographic data (excluding structure factors)
for 11, 12 and 15 have been deposited at the Cambridge
Crystallographic Data Centre, CCDC Nos. 228634 (11),
250070 (12) and 250069 (15). Copies of this information
can be obtained from the Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax +44 1233
336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk). Supplementary data asso-
ciated with this article can be found, in the online
version at doi:10.1016/j.jorganchem.2005.01.037.
(c) F. Menges, A. Pfaltz, Adv. Synth. Catal. 344 (2002) 40;
(d) G. Jones, C.J. Richards, Tetrahedron Lett. 42 (2001) 5553;
(e) K. Yonehara, K. Mori, T. Hashizume, K.G. Chung, K. Ohe,
S. Uemura, J. Organomet. Chem. 603 (2000) 40;
(f) K. Yonehara, T. Hashizume, K. Mori, K. Ohe, S. Uemura, J.
Org. Chem. 64 (1999) 9374.
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Chem. Commun. (1999) 415.
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Spek, D. Vogt, Organometallics 23 (2004) 3177;
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4477
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