1,8-dimethylnaphthalene-bridged diphosphine ligands: Synthesis and structural comparison of their palladium complexes

Article abstract of DOI:10.1039/b600837b

The synthesis of a new series of ligands with a 1,8-dimethylnaphthalene backbone is reported, 1,8-(R₂PCH₂)₂C ₁₀H₆, where R = ^tBu 1 (dbpn), ⁱPr 2 (dippn), Cy 3 (dchpn) and Ph 4 (d

Full text of DOI:10.1039/b600837b

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
1,8-Dimethylnaphthalene-bridged diphosphine ligands: synthesis and
structural comparison of their palladium complexes
Ronan M. Bellabarba,*a Colin Hammond,†a Grant S. Forman,a Robert P. Toozea and Alexandra M. Z. Slawinb
Received 19th January 2006, Accepted 10th March 2006
First published as an Advance Article on the web 17th March 2006
DOI: 10.1039/b600837b
The synthesis of a new series of ligands with a 1,8-dimethylnaphthalene backbone is reported,
t
1,8-(R2PCH2)2C10H6, where R = Bu 1 (dbpn), iPr 2 (dippn), Cy 3 (dchpn) and Ph 4 (dphpn). The
ligand 1 is structurally characterised by X-ray crystallography. A comparative structural study of the
respective (diphosphine)Pd(dba) and (diphosphine)PdCl2 complexes is carried out, comparing the
X-ray crystal structures of complexes 6, 7, 8, 10, 11 and 12. It is shown that the geometry at the metal
is affected by not only ligand demands, but also by the palladium oxidation state and the electronic
properties of the ligands. Two qualitative stability series are also identified: 9 < 10 < 11 ≈ 12 is
observed, and P2Pd(dba) complexes are more stable than the corresponding P2PdCl2 complexes
towards opening of the chelate ring. It is also concluded that the bite angle is heavily influenced by
the electron donating properties of the ligand.
longer (e.g. transphos5) or it is a long aliphatic chain and thus
Introduction
tends to bridge two metals.10
The bite angle of chelating diphosphines is an important factor in
We wish to report the preparation of a closely related series of
many catalytic reactions. It has been shown, for instance, that the
1,8-dimethylnaphthalene-bridged bidentate phosphines. We have
bite angle can have a crucial influence on the stability of formal
oxidation states,1 on the rate of reductive elimination from Pd
also undertaken structural studies of some of their palladium
complexes. Within this family of ligands only the ligand 4 has been
complexes,2 on the alcoholysis of acyl–palladium bonds,3 and on
the structure of CO/ethylene polymers formed.4 This subject has
been reviewed by van Leeuwen.5 We have found that sterically
hindered wide bite angle diphosphines such as 1,2-bis(di-tert-
butylphosphino)methyl benzene can stabilise unusual trigonal-
planar palladium carbonyl complexes,6 and others have found
that it is possible to spectroscopically observe reactive palladium
hydrides withthesameligand.7 These observations may be relevant
to the understanding of catalytic properties of metal complexes.
A large range of bidentate ligands has been reported in the
literature and studied according to their structural parameters.
As part of our ongoing investigations on this topic we wanted to
carry out a comparative investigation of the structures of a series of
Pd(0) and Pd(II) complexes. In this study, the ligands considered
have a very rigid carbon backbone with methylene linkages to
the phosphorus donor, thereby giving some scope for changes
in P–P distances and ligand–metal structures. Van Leeuwen and
co-workers have reported a structural study on a series of wide
bite-angle ligands and their Pd(TCNE) complexes.8 It is difficult
to compare the type of structure reported below with any relevant
literature studies: either the bridge is smaller (1,2-bis(di-tert-
butylphosphino)methyl benzene),7 contains heteroatoms present
(e.g. Xantphos5), it is more flexible (e.g. BISBI9), the bridge is
previously reported,11,12 prepared by reductive cleavage of PPh3
and reaction with 1,8-di(bromomethyl)naphthalene, and used to
prepare its palladium dichloride adduct.12
Results and discussion
The synthesis of these ligands is achieved as shown in Scheme 1 by
double deprotonation14 of 1,8-dimethylnaphthalene and reaction
with the appropriate phosphorus halide to give ligands of the
t
general formula 1,8-(R2PCH2)2C10H6, where for R = Bu 1(dbpn),
iPr 2 (dippn), Cy 3 (dchpn) and Ph 4 (dphpn) (Scheme 1). The
new ligands 1, 2, and 3 were recrystallised from alcoholic solvent
and found to be pure by elemental analysis. The ligand 1 was also
characterised by single-crystal X-ray diffraction (Fig. 1).
Scheme 1 Synthetic route to bidentate ligands.
Treatment of Pd2(dba)3 with two equivalents of ligands 1, 2,
3 and 4 gave the complexes 5 (dbpn)Pd(dba), 6 (dippn)Pd(dba),
7 (dchpn)Pd(dba) and 8 (dphpn)Pd(dba), respectively, as shown
in Scheme 2. These complexes display broad 31P NMR resonance
data due to the fluxionality of the dba ligand at room temperature.
Low-temperature NMR studies of complexes 7 and 8 showed that
the complexes were still fluxional at −80 ◦C.
aSasol Technology (UK) Ltd, Purdie Building, North Haugh, St Andrews,
Fife, UK KY16 9ST. E-mail: ronan.bellabarba@uk.sasol.com; Fax: +44
(0)1334 460939; Tel: +44 (0)1334 460934
bSchool of Chemistry, Purdie Building, North Haugh, St Andrews, Fife,
UK KY16 9ST. E-mail: amzs@st-and.ac.uk; Fax: +44 (0)1334 463384;
Tel: +44 (0)1334 467280
The complexes 5, 6 and 7 can be converted to their respec-
tive dichloride complexes 9 (dbpn)PdCl2, 10 (dippn)PdCl2 and
† Current address: School of Chemistry, University of Bristol, Cantock’s
Close, Bristol, UK, BS8 1TS.
2444 | Dalton Trans., 2006, 2444–2449
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
Scheme 2 Preparation of the palladium complexes. *Not synthesised by this method, see ref. 12.
to obtain crystals suitable for diffraction. The complex 11 appears
to be stable in solution at room temperature.
The solid-state structures of complexes (dippn)Pd(dba) 6,
(dchpn)Pd(dba) 7, (dphpn)Pd(dba) 8, (dippn)Pd(Cl2) 10 and
(dchpn)PdCl2 11 have been determined by X-ray crystallography.
Unfortunately, despite several attempts, the crystallographic data
for 6 was not of as high quality as could be desired, although bond
distance and angle data could be determined. For comparison, we
also include a structure of the free ligand 1 (Fig. 1) and some data
from the previously known complex 12.12 The solid state structures
of 6, 7, 8, 10 and 11 are shown in Fig. 2–6 respectively, and selected
bond distances and angles are shown in Table 1. All 31P NMR and
1H data are given in Table 2 and crystallographic data in Table 3.
All these structures present a near-planar naphthalene back-
bone; however, the bridgehead CH2 groups appear to be slightly
forced apart in the metal complexes. For instance, the difference
between the C10–C2 and the C12–C1 distances in 8 (Fig. 4) is
Fig. 1 X-Ray crystal structure of the ligand 1.
◦
˚
Table 1 Selected average bond distances (A) and angles ( )
11 (dchpn)PdCl2 by treatment with two equivalents of HCl
(Scheme 2). The palladium dichloride complex 12, (dphpn)PdCl2,
is known and has been structurally characterised by Yamamoto
et al.12 Although we have no doubt that the complex 12 can be
obtained in the same fashion as 9–11, we have not carried out
the synthesis, but we include some structural data for comparison
purposes.
Pd–P
P–Pd–P
P–C–CAr
6, (dippn)Pd(dba)
7, (dchpn)Pd(dba)
8, (dphpn)Pd(dba)
10, (dippn)PdCl2
11, (dchpn)PdCl2
2.32
2.31
2.29
2.27
2.28
2.27
104.7
103.9
98.5
100.3
100.9
93.5
117.2
117.7
111.5
119.6
119.0
111.3
a
12, (dphpn)PdCl2
The dichloride complex 9 is not stable. When synthesised as
described in Scheme 2, it is isolated as a pale yellow powder which
is soluble in halogenated solvents such as methylene chloride.
However, upon standing in solution, it inevitably forms a gel-like
substance which dries to a powder and which is then extremely
insoluble in all common solvents. This deteri◦oration seems to
occur irrespective of the solvent and even at −20 C. The 31P NMR
shows a single, weak peak at d 72.1 ppm tentatively assigned to 9.
The 1H NMR spectrum was difficult to interpret meaningfully due
to the presence of extremely broad resonances. It seems reasonable
to conclude that what is occurring is initial formation of 9, which
would be soluble, followed by ring-opening of the eight-membered
chelate structure to form an insoluble polymeric material with pre-
sumably trans-phosphines and chlorides. Attempting the synthesis
from (COD)PdCl2 immediately and directly generates a similarly
insoluble and intractable product.
a Ref. 12.
This instability does not appear to occur in the case of the
Pd(dba) complex 5 which appears to be stable in solution. The 1H
NMR spectrum, like all the other Pd(dba) complexes, displays very
broad peaks, whilst the 31P NMR shows a singlet at d 77.5 ppm.
A similar if much less pronounced effect is observed with 10,
where a solution of this complex will very slowly generate a
precipitate upon standing. However, the complex is stable enough
Fig. 2 X-Ray crystal structure of 6.
Dalton Trans., 2006, 2444–2449 | 2445
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
Table 2 1H and 31P NMR data for all new compounds
d 31P (solvent)
35.9, s, C6D6
8.7, s, C6D6
d 1H
1
2
1.13, d (3JPH = 11 Hz), 36H, tBu; 3.97, br s, 4H, CH2; 7.33, dt (3JHH = 8 Hz, 4JHH = 3 Hz) 2H, ArCH; 7.59, br d (3JHH
=
8 Hz) ArCH; 8.37, m, 2H, ArCH.
1.01, dd (3JHH = 7.2 Hz, 3JPH = 11.8 Hz), 24H (CH3)2CH; 1.64, dh (3JHH = 7.2 Hz, 2JPH = 1.8 Hz), 4H (CH3)2CH; 3.94, d
(2JPH = 2.6 Hz), 4H, CH2; 7.27, dd (3JHH = 7.6 Hz), 2H, ArCH; 7.35, d (3JHH = 7.4 Hz), 2H, ArCH; 7.46, d (3JHH = 8.2),
2H, ArCH.
3
4
1.0, s, C6D6
1.1–2.0, br m, CyH, 44H; 4.0, br s, CH2, 4H; 7.30, t (3JHH = 7.5 Hz), 2H, ArH; 7.59, d (3JHH = 6.4 Hz), 2H, ArH; 7.68, d
(3JHH = 7.2 Hz), 2H, ArH.
−10.3, s, C6D6
4.37, d (2JPH = 4.4 Hz), 4H, CH2; 6.64, m, 2H, ArCH; 6.83–6.99, m, 18H, ArCH; 7.23, m, 4H, ArCH; 7.43, d (3JHH
=
7.6 Hz) 2H, ArCH.
Broad/fluxionala
Broad/fluxionala
Broad/fluxionala
Broad/fluxionala
Broad/fluxionala
5
6
7
8
9
77.5, s, C6D6
43.4, br, C6D6
36.0, 33.3, br, C6D6
21.9, br, C7H8
72.1, s, CDCl3
10 60.9, s, CD2Cl2
0.49, dd (3JHH = 7.2 Hz, 3JPH = 18.8 Hz), 6H (CH3)2CH; 1.33, virt. q (3JHH = 7.2 Hz, 3JPH = 18.8 Hz), 12H (CH3)2CH;
1.48, dd (3JHH = 7.2 Hz, 3JPH = 18.8 Hz), 6H (CH3)2CH; 2.30, dh (2JPH = 4.9 Hz, 3JPH = 7.2 Hz), 2H (CH3)2CH; 3.35, h
(3JPH = 7.2 Hz), 2H (CH3)2CH; 3.50, dt (2JHH = 15.2 Hz, 2JPH = 6.9 Hz), 2H, CH2; 3.92, dd (2JHH = 15.2 Hz, 2JPH
=
5.4 Hz), 2H, CH2; 7.39, m, ArCH, 4H; 7.82, m, ArCH, 2H.
11 54.26, s, CDCl3
0.3, br, 2H, CyCH2; 0.5, br, 2H, CyCH2; 1–2.3, br m, 36H, CyCH2; 2.7, br, 2H, CyCH; 3.1, br, 2H, CyCH; 3.58, dt (2JPH
6.4 Hz, 2JHH = 15.1 Hz), 2H, PCH2; 3.88, dd (2JPH = 5.0, 2JHH = 15.1 Hz), 2H, PCH2; 7.41, m, 4H; 7.80, m, 2H.
=
a See text.
Fig. 4 X-Ray crystal structure of 8.
Fig. 3 X-Ray crystal structure of 7.
˚
˚
approximately 0.55 A, compared to 0.43 A in the free ligand 1
(Fig. 1). Similar observations can be made for the other structures.
All of the metal complexes have unusually short intramolecular
H–H separations between H atoms at C1 and C12 in the ligand in
˚
all the complexes; the relevant separations are as short as 1.57 A.
As is apparent from Table 1, there is only a small change in Pd–
P distance with variation of the ligand or formal oxidation state
of the metal. Within the limits of this study, it would appear that
the metal-phosphorus bond length is not affected so much by the
donor ability of the ligand but by the oxidation state of the metal.
The Pd–P distance in the Pd(II) complexes is slightly shorter than
in the Pd(0) complexes; but this variation is very subtle and may
not be significant.
Fig. 5 X-Ray crystal structure of 10.
However, there is a significant difference between bite angle in
the alkyl diphosphine Pd(0) complexes (6, 7) and aryl diphosphine
Pd(0) (8), and especially upon changing the formal oxidation state
of the metal from Pd(0) to Pd(II) (6 and 10, 7 and 11, 8 and 12).
2446 | Dalton Trans., 2006, 2444–2449
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
Fig. 6 X-Ray crystal structure of 11.
Similar observations have been previously made on palladium
complexes of xylene-bridged diphosphine ligands.13
This series of structures can be considered in the light of what
Van Leeuwen and Dierkes assert5 on the subject of a “metal
preferred” bite angle and a “ligand preferred” bite angle.
The metal preferred bite angle is influenced by the formal
oxidation state. In this case, the same bidentate ligand leads to a
structure which is closer to the ideal square-planar conformation
(i.e. P–Pd–P closer to 90◦) when bound to Pd(II). We feel that,
sterically, the halide ligands in these cases have but a small part
to play, as the same diphosphine ligand-metal fragment in the
complex [(dphpn)Pd(CNAr)2]2+ prepared by Yamamoto and co◦-
workers12 exhibits a P–Pd–P angle of 93.1◦, very close to the 93.5
in 12.
The ligand preferred bite angle is determined by the constraints
imposed by the backbone and by steric interactions.5 In this
study we have tried to limit to the utmost the influence of any
other parameters that could affect the solid state structure of the
complexes, such as bite angle, nature of the metal, and ancillary
ligands. The only parameters that we tried to vary in complexes
6–11 were the nature of the phosphine, and the oxidation state of
the metal. Despite the attempted simplification, it is apparent that
there are significant effects on the bite angle. Thus, the P–Pd–P
angle for the Pd(0) complexes 6 and 7 is very similar (103.7, 103.9◦),
whilst the phenyl analogue 8 has a much more acute angle (98.5◦).
The same trend is observed in the Pd(II) complexes 10, 11 and 12.
It is also conceivable that these trends are due to crystal packing
interactions, and not ligand properties, but we feel that solid-state
interactions cannot account for these significant differences.
Another measurable parameter of this is the ‘fold angle’, i.e. the
angle between the P-donor, the CH2 carbon and the aryl carbon.
These angles follow similar trends and appear to correlate with
the bite angle at the metal, as shown in Table 1.
Conclusions
We found that in the series of complexes 5–12, the structure is
obviously influenced by the ligand’s requirements, but also affected
by the metal oxidation state and the donating ability of the P-
fragments. In the case of ligand 1, the balance between steric
demands of the ligand and the requirements of the metal leads to
complexes which are unstable when the metal fragment is Pd(II): in
qualitative terms, the favourable chelation is offset by the demands
of binding a very bulky ligand and of forming an eight-membered
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2444–2449 | 2447
©

View Article Online
ring. Thus the qualitative stability series 9 < 10 < 11 ≈ 12 is
observed, but also that P2Pd(dba) complexes are more stable than
the corresponding P2PdCl2 complexes towards ring-opening of the
chelate ring in this series. Similar behaviour has been previously
observed by Milstein.1a It is difficult to distinguish between steric
and electronic effects on the bite angle and more work would be
required to do so. However, we anticipate that this study should
provide useful extra data for any ongoing investigations.
Synthesis of Pd(dba) complexes: typical procedure
Pd2(dba)3 (100 mg, 0.11 mmol) and the ligand (2 equivalents)
were suspended in thf (25 ml), and the mixture was stirred at
room temperature for 1 h. The mixture was filtered to give
a clear orange solution which reduced to a solid foam under
vacuum. This material is a mixture of product and dba; washing
with cold diethyl ether to remove as much dba as possible
was, in our hands, the most successful method of purification
but accompanied by unacceptable losses of product. Attempts
at crystallisation invariably resulted in co-precipitation or co-
crystallisation of yellow dba and orange–red product. For this
reason, the product was often contaminated with dba, but pure
enough for our purposes. Yields are typically 70–90%. Single
crystals could be obtained from evaporation of a diethyl ether
solution or from pentane at −20 ◦C.
Experimental
All syntheses involving air-sensitive materials were carried
out using dried and degassed solvents under dinitrogen. 1,8-
Dimethylnaphthalene, tBu2PCl, iPr2PCl, Cy2PCl, Ph2PCl and
KOtBu (Aldrich or Strem) were used as supplied (unless clearly
degraded, in which case they were vacuum distilled trap-to-trap)
and stored in Young’s tap ampoules. BuLi was received from
suppliers, transferred to and stored in Young’s tap ampoules at
4 ◦C. With the exception of CDCl3, NMR solvents were degassed
Synthesis of PdCl2 complexes: typical procedure
The material obtained in the previous step was dissolved in diethyl
ether and treated with 2.1 equivalents of a solution of HCl in
diethyl ether with stirring. A yellow precipitate forms rapidly,
which can be isolated by filtration and exhaustively washed with
diethyl ether to yield the product in quantitative yield. X-Ray
diffraction quality crystals of the stable complexes 10 and 11 could
be obtained by layering a dichloromethane solution with diethyl
ether.
and stored in Young’s tap ampoules under dinitrogen. 1H and 31
P
NMR spectra were recorded using a Bruker AV300 spectrometer,
and referenced either internally (1H, 300.06 MHz, residual protio
solvent resonance relative to SiMe4 at d 0) or externally (31P,
121.47 MHz, externally to 85% H3PO4 at d 0). All chemical
shifts are quoted in d (ppm), using the high frequency positive
convention, and coupling constants in Hz. Elemental analyses
were carried out by Stephen Boyer at London Metropolitan
University.
Crystallography
Crystal data and refinement details are shown in Table 3. Data
(Mo radiation) were collected at −180 ◦C using a Rigaku MM007
high brilliance rotating anode/confocal optics with for 1, 6, 7, 10
and 11 a Mercury ccd detector and for 8 a Saturn ccd detector. In
all cases a full hemisphere was collected. Intensities were corrected
for Lorentz-polarisation and for absorption. The structures were
solved by direct methods. For 6 we collected full data sets on five
different crystals but always experienced difficulty with crystal
quality and solvent, only the Pd, P and O atoms are refined
anisotropically in this structure. For all of the other structures all
non-hydrogen atoms were refined anisotropically. The positions of
the hydrogen atoms were idealised and refined with riding thermal
parameters. Refinements were by full-matrix least squares based
on F2 using SHELXTL.15
Synthesis of diphosphine ligands: typical procedure
BuLi (2.5 M solution in hexanes, 1.6 mL, 4 mmol) and KOtBu
(450 mg, MW 112.2, 4 mmol)14 were suspended in petroleum ether
(bp 40–60 ◦C, 50 ml) and 1,8-dimethylnaphthalene (312 mg, MW
156.2, 2 mmol) was added. The mixture was stirred for at least
2 h, during which time the suspension changed colour to brown
and then to brick red. The liquid was filtered off, the red solid was
washed twice with petroleum ether (bp 40–60 ◦C, 20 ml) and dried
under vacuum.‡
The red solid was cooled to −78 ◦C, and cold diethyl ether
(50 ml) was added to it to yield a red suspension. The desired
halophosphine (4 mmol, 2 equivalents) was added slowly via
syringe at −78 ◦C, then the mixture was allowed to warm to room
temperature and stirred for at least 1 h, until all red coloration
was discharged to yield a white or pale yellow suspension. The
suspension was filtered and the residue extracted with diethyl ether
(3 × 50 mL), and the combined extracts dried under vacuum
to yield the crude product which could be recrystallised from
refluxing methanol (1,2), ethanol (3) or pentane (4) if required.
Unoptimised yields and elemental analysis: 1, 50%. Anal. (%).
Found (required): C, 75.57 (75.64); H, 10.59 (10.43); HRMS, m/z
found: 445.3141, required: 445.3153; 2, 40%. Anal. (%). Found
(required): C, 74.09 (74.20); H, 9.92 (9.86); 3, 56%. Anal. (%).
Found (required): C, 78.78 (78.79); H, 9.99 (9.92); 4,11,12 15%.
CCDC reference numbers 295570–295575.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b600837b
Acknowledgements
We would like to thank Dr Tomas Lebl for VT NMR experiments
and Ms Caroline Horsburgh for high-resolution MS.
References
1 (a) M. Portnoy and D. Milstein, Organometallics, 1993, 12, 1655–1664;
(b) M. Portnoy and D. Milstein, Organometallics, 1993, 12, 1665–1673.
2 J. M. Brown and P. J. Guiry, Inorg. Chim. Acta, 1994, 220, 249–259.
3 P. W. N. M. van Leeuwen, M. A. Zuideveld, B. H. G. Swennenhuis, Z.
Freixa, P. C. J. Kamer, K. Goubitz, J. Fraanje, M. Lutz and A. L. Spek,
J. Am. Chem. Soc., 2003, 125, 5523–5539.
‡ This red material is the dipotassium salt of 1,8-dimethylnaphthalene
(CAUTION: extremely pyrophoric) and best used as soon as possible,
although it can be stored under inert atmosphere for a few weeks.
2448 | Dalton Trans., 2006, 2444–2449
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
4 E. Drent, J. A. M. Broeckhoven and M. J. Doyle, J. Organomet. Chem.,
1991, 417, 235.
10 See, for instance: B. L. Shaw, J. Organomet. Chem., 1980, 200, 307–
318; N. A. Al-Salem, H. D. Empsall, R. Markham, B. L. Shaw and B.
Weeks, J. Chem. Soc., Dalton Trans., 1979, 1972; N. A. Al-Salem, W. S.
McDonald, R. Markham, M. C. Norton and B. L. Shaw, J. Chem. Soc.,
Dalton Trans., 1980, 59; C. Crocker, R. J. Errington, R. Markham, C. J.
Moulton and B. L. Shaw, J. Chem. Soc., Dalton Trans., 1982, 387.
11 R.-X. Li, N.-B. Wong, X.-J. Li, T. C. W. Mak, Q.-C. Yang and K.-C.
Tin, J. Organomet. Chem., 1998, 571, 223–229.
5 P. Dierkes and P. W. N. M. van Leeuwen, J. Chem. Soc., Dalton Trans.,
1999, 1519–1529.
6 R. M. Bellabarba, R. P. Tooze and A. M. Z. Slawin, Chem. Commun.,
2003, 1916–1917.
7 W. Clegg, G. R. Eastham, M. R. J. Elsegood, B. T. Heaton, J. A. Iggo,
R. P. Tooze, R. Whyman and S. Zacchini, J. Chem. Soc., Dalton Trans.,
2002, 3300–3308.
8 M. K. Kranenburg, J. G. P. Delis, P. C. J. Kamer, P. W. N. M.
van Leeuwen, K. Vrieze, N. Veldman, A. L. Spek, K. Goub-
itz and J. Fraanje, J. Chem. Soc., Dalton Trans., 1997, 1839–
1849.
9 H. Bahrmann, K. Bergrath, H.-J. Kleiner, P. Lappe, C. Naumann,
D. Peters and D. Regnat, J. Organomet. Chem., 1996, 520, 97–
100.
12 Y. Yamamoto, Y. Fukui, K. Matsubara, H. Takeshima, F. Miyauchi, T.
Tanase and G. Yamamoto, J. Chem. Soc., Dalton Trans., 2001, 1773–
1781.
13 W. Clegg, G. R. Eastham, M. R. J. Elsegood, R. P. Tooze, X. L. Wang
and K. H. Winston, Chem. Commun., 1999, 1877.
14 Encyclopaedia of Reagents for Organic Synthesis, ed. L. A. Paquette,
J. Wiley & Sons, Chichester, 1995, vol. 2, p. 923.
15 SHELXTL 6.01, G. M. Sheldrick, Bruker AXS, Madison, 2001.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 2444–2449 | 2449
©