A remarkable cis- and trans-spanning dibenzylidene acetone diphosphine chelating ligand (dbaphos)

Article abstract of DOI:10.1002/chem.201203691

A multidentate and flexible diolefin-diphosphine ligand, based on the dibenzylidene acetone core, namely dbaphos (1), is reported herein. The ligand adopts an array of different geometries at Pt, Pd and Rh. At Pt^II the dbaphos ligand forms cis- and trans-diphosphine complexes and can be defined as a wide-angle spanning ligand. ¹H NMR spectroscopic analysis shows that the β-hydrogen of one olefin moiety interacts with the Pt^II centre (an anagostic interaction), which is supported by DFT calculations. At Pd⁰ and Rh^I, the dbaphos ligand exhibits both olefin and phosphine interactions with the metal centres. The Pd⁰ complex of dbaphos is dinuclear, with bridging diphosphines. The complex exhibits the coordination of one olefin moiety, which is in dynamic exchange (intramolecular) with the other "free" olefin. The Pd⁰ complex of dbaphos reacts with iodobenzene to afford trans-[Pd^II(dbaphos)I(Ph)]. In the case of Rh^I, dbaphos coordinates to form a structure in which the phosphine and olefin moieties occupy both axial and equatorial sites, which stands in contrast to a related bidentate olefin, phosphine ligand ("Lei" ligand), in which the olefins occupy the equatorial sites and phosphines the axial sites, exclusively. Copyright

Full text of DOI:10.1002/chem.201203691

DOI: 10.1002/chem.201203691
A Remarkable cis- and trans-Spanning Dibenzylidene Acetone Diphosphine
Chelating Ligand (dbaphos)
Amanda G. Jarvis,[a] Petr E. Sehnal,[a] Somia E. Bajwa,[a] Adrian C. Whitwood,[a]
Xiangbiao Zhang,[b] Man Sing Cheung,[b] Zhenyang Lin,*[b] and Ian J. S. Fairlamb*[a]
Dedicated to Professor Piet W. N. M. van Leeuwen for his distinguished contributions to the design of wide-angle spanning
ligands
Abstract: A multidentate and flexible
diolefin–diphosphine ligand, based on
the dibenzylidene acetone core, namely
dbaphos (1), is reported herein. The
ligand adopts an array of different geo-
metries at Pt, Pd and Rh. At PtII the
dbaphos ligand forms cis- and trans-di-
phosphine complexes and can be de-
fined as a wide-angle spanning ligand.
1H NMR spectroscopic analysis shows
that the b-hydrogen of one olefin
moiety interacts with the PtII centre
(an anagostic interaction), which is sup-
ported by DFT calculations. At Pd0
and RhI, the dbaphos ligand exhibits
both olefin and phosphine interactions
with the metal centres. The Pd0 com-
plex of dbaphos is dinuclear, with
bridging diphosphines. The complex
exhibits the coordination of one olefin
moiety, which is in dynamic exchange
(intramolecular) with the other “free”
olefin. The Pd0 complex of dbaphos
reacts with iodobenzene to afford
trans-[PdII
ACTHNUTRGNE(NUG dbaphos)I(Ph)]. In the case
of RhI, dbaphos coordinates to form a
structure in which the phosphine and
olefin moieties occupy both axial and
equatorial sites, which stands in con-
trast to
a related bidentate olefin,
phosphine ligand (“Lei” ligand), in
which the olefins occupy the equatorial
sites and phosphines the axial sites, ex-
clusively.
Keywords: bite angle · coordina-
tion modes · density functional cal-
culations · ligands effects · structure
elucidation
Introduction
have been reported.[8] In these complexes, intramolecular
dba-H olefin–olefin exchange occurs readily at Pd0, through
C=O coordination, with several conformers being accessi-
ble.[9] Addition of ligands (L) such as phosphines (monoden-
tate or bidentate) or bipyridyls[10] give complexes of the type
Dibenzylidene acetone (dba-H) is an electron-deficient 1,4-
diene ligand that coordinates transition metals in a variety
of modes, through either the olefin as a 1,4-diene or bridg-
ing ligand, and/or carbonyl moieties, for example in [Rh
G
[Pd0
(h2-dba)(L)2]. The platinum variant, [Pt0
ACHUTNGTERNNUG 2ACHTUNGTREN(NGUN dba-H)3], is
C5Me5)(h2,h2-dba-H)][1] and [Fe(CO) (h4-{(CO)
3ACTHNUGTRENNUGN ACHTUNGTRENNNUG
also known.[11]
Ph)2})],[2] in addition to other complexes (Fe,[3] Ru,[4] U[5]
Recently, we reported a multidentate ligand based on the
dba core structure, namely dbathiophos (an olefin–phos-
phine sulfide hybrid ligand),[12] which has a high affinity for
cationic and neutral CuI ions (see Figure 1); the CuI com-
plexes are competent catalysts for olefin cyclopropanation.
Lei and co-workers reported that the chalcone-phosphino
ligand (“Lei ligand”) effectively promotes Pd-catalysed Ne-
gishi cross-couplings.[13] This, coupled with other known pos-
itive dba effects in catalysis,[14] has encouraged us to explore
new dba ligands containing a phosphine donor group(s).
Our efforts to synthesise a new phosphine ligand, dbaphos
(1), and the eclectic array of Pt, Pt and Rh complexes that
are accessible through complexation, are described herein.
We envisaged that 1 could act as both a wide-angle spanning
chelating and bridging ligand, indeed the ability of ligands
to access both cis- and trans-geometries is of considerable
interest.[15]
complexes; selected examples are given in Figure 1).[6] [Pd0 -
2
ACHTUNGTRENNUNG
(dba-H)3] is the best known transition-metal complex[7] bear-
ing a dba-H ligand, and is a widely used Pd0 precursor in
synthetic chemistry, catalysis and organometallic chemistry.
Related complexes, [Pd0 (dba-Z)3] and [Pd0
2ACHTNUTRGENNGU ACHTUGNTREN(NUGN dba-Z)2] (dba-
Z=dibenzylidene acetone with different Z-substituents),
[a] Dr. A. G. Jarvis, Dr. P. E. Sehnal, Dr. S. E. Bajwa,
Dr. A. C. Whitwood, Prof. Dr. I. J. S. Fairlamb
Department of Chemistry, University of York
York, YO10 5DD (UK)
Fax : (+44)1904-322516
E-mail: ian.fairlamb@york.ac.uk
[b] Dr. X. Zhang, M. S. Cheung, Prof. Dr. Z. Lin
Department of Chemistry, The Hong Kong University
of Science and Technology, Clear Water Bay, Kowloon
Hong Kong (P. R. China)
E-mail: chzlin@ust.hk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203691.
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FULL PAPER
Scheme 1. Synthesis of dbaphos (1).
backbone exists in an extended linear s-cis,s-cis conforma-
tion. Changes in conformation about the 1,4-dien-3-one
moiety, especially in solution, are expected (vide infra).
Ligand 1 has several potential coordination sites (i.e.,
phosphorus, olefin and carbonyl). Olefins are often consid-
ered as hemilabile moieties compared to phosphines, al-
though the extent of hemilability depends on the metal
centre.[17] In exploratory PtII complexation experiments sep-
arate equimolar reactions were carried out. Both cis-[PtCl2-
A
2ACTHUGNTREN(UNGN MeCN)2] reacted with 1 in CH2Cl2 to
A
CHTUNGTRENNUNG
material, which was most likely polymeric; on reducing the
reaction concentration to 0.066m a product soluble in
CH2Cl2 was formed. A single signal in the 31P NMR spec-
trum (d=4.72 ppm) indicated that the two phosphorus cen-
tres were in the same chemical environment, that is, the
Figure 1. Representative dba-metal complexes, the “Lei” ligand and
“dbaphos” ligand 1 (for the metal complexes the 1,4-dien-3-one confor-
mations are denoted in the figure).
Results and Discussion
Dbaphos 1 can in principle be prepared by Claisen–Schmidt
condensation, Horner–Wadsworth–Emmons (HWE), or
Wittig reactions. Having assessed all of these synthetic
methods, the HWE reaction was found most acquiescent.
For example, HWE reaction of
Scheme 2. Synthesis of cis-[PtIICl2(1)] and trans-[PtIICl2(1)].
bisphosphonate 2 (see the Sup-
porting Information for prepa-
rative details) with o-diphenyl-
phosphinobenzaldehyde (3) in
the presence of NaOH at reflux
for 2 h under inert atmosphere,
affords dbaphos (1) (Scheme 1)
in 84% yield (>96% purity, as
determined by 31P NMR spec-
troscopy).[16] Crystals of 1, suit-
ACHTUNGTRENNUNGable for X-ray diffraction analy-
sis, were obtained by crystallisa-
tion from MeCN at ꢀ208C
Figure 2. X-ray structure of dbaphos (1). Thermal ellipsoids shown at 50% probability; selected hydrogens
(Figure 2). The 1,4-dien-3-one omitted for clarity.
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Z. Lin, I.J. S. Fairlamb et al.
ligand acts as a symmetrical bidentate phosphine ligand. In
CD2Cl2, the JPt,P coupling constant of the product derived
rule out the formation of dinuclear species and note limited
product solubility in CH2Cl2 and DMSO.
1
from cis-[PtCl2ACHTUNGTRENNUNG(cod)] and 1 is 3562 Hz, indicating that the
phosphines are located cis to each other (at PtII).[18a] The X-
ray crystal structure of cis-[PtCl2(1)] supports the NMR
spectroscopic evidence (Figure 3).
On the interaction of the b-olefin hydrogen with PtII: Inter-
ꢀ
ꢀ
actions between N H and C H bonds and transition metals
are well recognised.[19] Two different types of interactions
have been clearly identified, namely agostic and anagostic
interactions.[20] Agostic interactions refer to 3-centre-2-elec-
tron interactions and are characterised by small M···H dis-
tances (ca. 1.8–2.3 ꢁ), small C-H-M angles (ca. 90–1408),
ꢀ
and an upfield shift in dH of the C H upon coordination,
along with low JC,H values. Agostic interactions require the
1
metal centre to be coordinately unsaturated, with an empty
ꢀ
orbital available for s-donation from the C H bond. The
term “anagostic” was used by Lippard and co-workers to de-
[21]
ꢀ
scribe any C H···M interactions that were not agostic.
Other terms such as “pregostic” have been used, and ana-
gostic interactions also cover those described by hydrogen
bonding. Anagostic interactions are characterised by larger
M···H distances (ca. 2.3–2.9 ꢁ), larger C-H-M angles (ca.
ꢀ
110–1708) and by a downfield shift in dH of the C H upon
coordination (a general feature of hydrogen bonds). Ana-
gostic interactions do not need an empty orbital and there-
fore can involve 18-electron metal centres. For d8 square-
Figure 3. X-ray crystal structure of cis-[PtCl2(1)]. Selected hydrogen
atoms removed for clarity. Thermal ellipsoids shown at 50%. Selected
angles (8) include: P(2)-Pt(1)-P(1)=105.89(5), P(2)-Pt(1)-Cl(2)=81.18
(5), P(1)-Pt(1)-Cl(2)=169.71 (4), P(2)-Pt(1)-Cl(1)=167.60(4),
P(1)-Pt(1)-Cl(1)=86.49 (5), Cl(2)-Pt(1)-Cl(1)=86.45 (5).
planar complexes either agostic or anagostic interactions are
8
ꢀ
able to occur. While the N H···M(d ) interactions can be
confidently described with a 3-centre-4-electron bond (hy-
8
ꢀ
drogen bond), the C H···M(d ) interactions are believed to
be much more complicated. It has been proposed that a
weak hydrogen bond is involved.[19a]
ꢀ
The X-ray diffraction data for cis-[PtCl2(1)] shows a Pt H
The P-Pt-P bite angle in cis-[PtCl2(1)] is 105.98, and is
similar in size to other wide-bite-angle ligands such as Xant-
PHOS and related ligands.[18b,c] A comparison of the bite
angles of Xantphos and dbaphos 1 shows that the latter has
the larger bite angle by 58 (at PtII). The X-ray crystal struc-
ture of cis-[PtCl2(1)] shows that the dbaphos ligand is not
symmetrical around the PtII centre as shown by the differ-
interaction of 2.642 ꢁ in the crystal structure, and a down-
1
field shift of the H(7) and H(11) protons in the H NMR
spectrum, suggesting an anagostic interaction of some type
is present. Using theoretical calculations we wished to gain
a greater understanding of this interesting interaction. It was
1
also clear from the H NMR spectrum that exchange of the
H(7) and H(11) protons (see Figure 3) was rapid, as the
spectrum was sharp, with only one signal observed for these
protons. DFT calculations were performed with no simplifi-
cation of cis-[PtCl2(1)], to gain an insight into the nature of
the short platinum-proton interaction and the exchange
process shown in Scheme 3 (H(7) and H(11) are denoted Ha
and Hb).
DFT calculations at the MPW1PW91 level were carried
out for complex optimisation (details given in the Support-
ing Information).[22] The structure of cis-[PtCl2(1)] was opti-
mised, with the calculated structural values agreeing with
ꢀ
ence of 0.0268(19) ꢁ in the two P Pt bond lengths.
ꢀ
The P Pt bonds are similar to related complexes with
ꢀ
long P Pt bonds (a search of the Cambridge structural data-
base reveals that the mean P Pt distance in cis complexes is
ꢀ
ꢀ
2.233 ꢁ). One of the olefins (C(7) C(8)) displays a short
Pt H contact, 2.642 ꢁ. 1H NMR spectroscopic analysis
ꢀ
shows that there is a Pt···H interaction; the most electron-
deficient olefin protons (H(7) and H(11) in the crystal struc-
ture) have shifted to d=9.82 ppm (+1.52 ppm) compared
with the free ligand 1. A rapid exchange process is occurring
in solution, as indicated by the sharp olefin-proton signals.
We have also evaluated the reactions of [PdCl2ACTHUNRTGNE(GNU cod)] with
1 (see Supporting Information). A trans-[PdCl2(1)] complex
appears to have been formed with a solid-state 31P NMR
spectrum showing a slightly distorted AB multiplet with a
2JP, P coupling of 540 Hz, indicative of trans-phosphines. Also,
the most deshielded olefin protons share a chemical shift
similar to the equivalent protons in trans-[PtCl2(1)], being
substantially different to cis-[PtCl2(1)]. However, we cannot
Scheme 3. Rapid exchange of Pt···Ha/b
.
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Diphosphine Chelating Ligand
FULL PAPER
Table 1. Comparison of experimental and calculated bond lengths [ꢁ] in
cis-[PtCl2(1)].
Bond
Experimental
Calculated
Difference
ꢀ
Pt Ha
ꢀ
Pt Ca
2.642
3.450
3.480
2.2802(13)
2.2534(14)
2.3592(13)
2.3395(12)
2.595
3.422
3.455
2.304
2.297
2.376
2.371
0.047
0.028
0.025
ꢀ0.0238
ꢀ0.0436
ꢀ0.0268
ꢀ0.0415
ꢀ
Figure 4. NBO results for a simplified model of cis-[PtCl2(1)].
Pt Cb
ꢀ
Pt P(1)
ꢀ
Pt P(2)
ꢀ
Pt Cl(1)
of the calculations, the deshielding effect in cis-[PtCl2(1)]
can be attributed to a weak hydrogen bond resulting from
ꢀ
Pt Cl(2)
the Pt
N
those obtained by experiment (Table 1). The largest devia-
tion was seen between the calculated and experimental
Interestingly, dissolution of cis-[PtCl2(1)] in [D6]DMSO
leads to isomerisation[26] to trans-[PtCl2(1)] with a JPt,P value
of 2565 Hz. Heating cis-[PtCl2(1)] to 608C for 4 h results in
complete isomerisation to trans-[PtCl2(1)]. The latter com-
ꢀ
C Ha···Pt distances. This could be expected as the hydrogen
atoms in the experimental structure were placed using a
“riding model”. As the calculated Ca···Pt and Cb···Pt distan-
ces were in good agreement with the experiment it is be-
plex can also be directly synthesised from trans-
ACHTUNGTRENNUNG[PtCl2-
AHCTUNGTRENNUNG
lieved that the calculated C H···Pt is more realistic than the
CD2Cl2 exhibits a 31P chemical shift of d=14.9 ppm and
1JPt,P coupling constant of 2577 Hz, indicating the phosphines
are trans-disposed. The 1H NMR spectrum of trans-
[PtCl2(1)] shows that the 1,4-dien-3-one is symmetrical and
most likely in a s-trans,s-trans conformation. An insoluble
precipitate (including reactions in [D6]DMSO) is observed
within hours, which we believe is a binuclear PtII complex or
higher order polymer containing 1. DFT calculations show
that the difference in energy between cis- and trans-
[PtCl2(1)] complexes (on the complete structures of cis- and
trans-[PtCl2(1)] complexes) is significantly different, with
the trans-geometry being more thermodynamically stable
(Pt, DG0 =ꢀ8.0 kcalmolꢀ1), which confirms its feasibility as
an isomeric product.
ꢀ
experimental value. The barrier for the exchange was calcu-
lated to be 1.04 kcalmolꢀ1 in electronic energy and 1.16 kcal
molꢀ1 in free energy, which is consistent with the experimen-
tal observation that the exchange is very rapid. It is also
consistent with a previously reported theoretical estimate of
II
ꢀ1 [23]
ꢀ
a C H···Pd interaction of 0.8 kcalmol .
ꢀ
In order to understand the nature of the C H···Pt interac-
tions, natural bond orbital (NBO) analyses[24] were carried
out on the basis of the electronic structures calculated for
cis-[PtCl2(1)]. No appreciable Wiberg bond index[25] (a
measure of bond strength) was seen for the close C H···Pt
contact. However, an appreciable second-order perturbation
energy related to the donor–acceptor interaction of Pt-
ꢀ
ꢀ
ACHTUNGTRENNUNG
Synthesis of Pd and Rh complexes containing dbaphos: We
next examined the synthesis of Pd0 and PdII complexes con-
taining ligand 1. Experiments involving reaction of [Pd0 -
2
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
ꢀ
of a weak hydrogen bond, the C H···Pt contact distances for
PhC3H4)], which has been described by Baird and co-work-
ers as a “stable precursor” for the preparation of Pd0 com-
plexes.[27] Upon addition of two equivalents of phosphine
the allyl and cyclopentadienyl (Cp) fragments undergo re-
the simplified model complexes shown in Figure 4 were cal-
culated and the relevant NBO analysis performed. The re-
sults indicate that the less electronegative X is (X=O, S and
Se), the longer the C H···Pt contacts are and a smaller
second-order energy lowering is observed. The changes
along the series of different X atoms are only marginal, sug-
ductive elimination to give the Pd0
ACHTUNGTRENNUNG
ꢀ
ganic byproducts). The reaction of 1 with [PdAHCTUNGTRENNUNG
PhC3H4)] gave a single complex as judged by 1H and
31P NMR spectroscopy (Scheme 4). Two phosphorus doublet
signals at d=31.2 and 13.2 ppm (2JP, P =20.5 Hz) suggest that
ꢀ
gesting that the C H···Pt interactions are weak.
The results from the NBO analysis are consistent with
both the small energies calculated from DFT for the ex-
change and with the experimental observations. A deshield-
ed proton resonance for Ha/Hb is seen in the H NMR spec-
trum of cis-[PtCl2(1)] with respect to the free ligand. In light
1
the ligand is coordinated unsymmetrically to Pd. H NMR
spectroscopic analysis reveals two broad coupled olefin pro-
tons shifted upfield at d=5.28 and 5.95 ppm (confirmed by
COSY), suggesting that an exchange process is occurring.
1
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6037

Z. Lin, I.J. S. Fairlamb et al.
molecular, with the barrier to exchange being explained by
enthalpic differences. The free energy of activation (DG°) at
298 K was determined to be (71.5ꢁ4.7) kJmolꢀ1.
X-ray crystallographic analysis on a single crystal of
[Pd0 (1)2] allowed the structural connectivity to be deter-
2
mined[31] (Figure 6). The olefin C=C bond lengths indicate
0
ꢀ
substantial back-bonding from Pd (C(7) C(8)=1.435(11) ꢁ
ꢀ
and C(48) C(49)=1.411(12) ꢁ; the C=C bond length in
ligand 1=1.324(2) ꢁ}. The bond lengths are similar to that
Scheme 4. Synthesis of [Pd0 (1)2].
2
Cooling the sample to 255 K sharpened the proton signals
and a more complex spin–spin coupling network was re-
vealed, namely a doublet of doublets (dd; d=5.3 ppm) and
doubled doublet of doublets (ddd; d=5.9 ppm). Thus the
olefin signal at d=5.9 ppm is coupling to two phosphorus
nuclei and that at d=5.3 ppm to one phosphorus nuclei.
Conclusive evidence confirming a Pd–olefin bonding inter-
action was provided by 13C NMR and HSQC spectra, which
showed the olefin carbons associated with these upfield
olefin protons had also shifted upfield to d=83 and 69 ppm,
respectively.
The UV/Vis spectrum supports the presence of a Pd–
olefin bonding interaction. A metal-to-ligand charge transfer
(MLCT) band at 454 nm, e=7088 molꢀ1 dm3 cmꢀ1 (CH2Cl2)
is observed. This value sits between those recorded for [Pd-
(h2-dba)
(dba)3] (530 nm, MeOH).[29]
31P–31P exchange spectroscopy (EXSY) experiments were
used to obtain rate constants for the exchange process by
varying the mixing time (d8) at different temperatures
(Figure 5).[30] The exchange processes are affected by tem-
perature to a greater extent than nOe processes, allowing
the exchange to be frozen out. At 268 K no nOe cross-peaks
ACHTUNGTRENNUNG
(PPh3)2] (396 nm, DMF, 405 nm MeOH)28 and [Pd2-
Figure 6. X-ray structure of [Pd0 (1)2].
2
found in the olefin–Pd interaction in [PdACTHNGUTRENNUG ACHTUNGTRENNUNG(dppe)]
(h2-dba)
(dppe=1,2-bis(diphenylphosphino)ethane),[32] which also
ꢀ
shares similar Pd P bond lengths.
The stoichiometric oxidative-addition reaction of iodoben-
zene and [Pd0 (1)2] in [D8]THF at 300 K was followed by
2
NMR spectroscopy, taking approximately 1 h to reach com-
pletion (quantitative). The 31P NMR spectrum of the prod-
uct showed one single 31P resonance (d=16.8 ppm) indicat-
ing that the ligand was acting as a trans-spanning ligand.
Four of the aromatic signals (from iodobenzene) in the
1H NMR spectrum appear significantly upfield, roughly be-
tween 5.9–6.4 ppm, which we interpret as being due to
shielding from the phenyl rings of the phosphine, for exam-
ple, sandwich-like p-stacking interactions,[33] leading us to
propose trans-[PdIII(Ph)(1)] as the only isomer formed.
Crystals suitable for X-ray diffraction were grown at 188C,
which confirmed the trans-chelating nature of the dbaphos
Figure 5. Dynamic exchange in [Pd0 (1)2].
2
ligand 1 (Figure 7). The P,P bite angle in this complex is
II
ꢀ
were observed on irradiating at d=31.2 ppm, allowing the
exchange processes to be observed exclusively. An Arrhe-
nius plot of 1/T against ln2k gave a straight line with slope
ꢀEa/R, allowing the activation energy to be estimated
(68.2 kJmolꢀ1). Using the Eyring equation, the enthalpy and
entropy of activation were calculated; DH° =(65.7ꢁ
3.4) kJmolꢀ1 and DS° =(ꢀ19.5ꢁ11.1) Jmolꢀ1 Kꢀ1. The small
value for DS° is in keeping with the exchange being intra-
172.37(3)8, and the C(7) H(7) bond points towards the Pd
centre, the distance between the metal and hydrogen atoms
is longer than in the cis-[PtCl2(1)], complex, 2.90 versus
2.64 ꢁ. The other ligand bond lengths (C=O, C=C and C P)
are within error of those in cis-[PtCl2(1)]. It is of particularly
note that the Morita–Bayliss–Hillman dimer diphosphine
derived from the Lei ligand forms a similar trans-PdII com-
plex.[34]
ꢀ
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Diphosphine Chelating Ligand
FULL PAPER
Figure 7. Single-crystal X-ray structure of trans-[PdIII(Ph)(1)]. Disordered
solvent molecules (THF) and selected hydrogen atoms removed for clari-
ty. Thermal ellipsoids shown at 50%. Selected bond lengths (ꢁ) and
Figure 8. NMR spectra of [RhCl(1)] in CD2Cl2. Top: 1H NMR spectra;
bottom: variable-temperature 31P NMR spectra.
ꢀ
ꢀ
ꢀ
bond angles (8): C(15) O(1)=1.226(5), C(16) C(17)=1.342(5), C(14)
ꢀ
ꢀ
ꢀ
C(13)=1.335(5), P(1) C(7)=1.827(4), P(2) C(23)=1.831(4), P(2) Pd=
ꢀ
ꢀ
ꢀ
2.3181(10), P(1) Pd=2.3459(10), Pd I=2.6810(5), Pd C(1)=2.028(4);
P(1)-Pd-P(2)=172.37(3).
COSY-correlated and their large upfield shifts from the free
ligand olefin protons (Dd=ꢀ4.7 and ꢀ4.2 ppm, respectively)
are evidence for strong olefin binding to RhI.
The two other olefin protons (olefin b) have shifted by
Dd=ꢀ2.7 and ꢀ1.2 ppm. The spin–spin coupling constants
have decreased in both cases from 16 Hz to 13.5 Hz (ole-
fin b) and roughly 7 Hz (olefin a)—a clear indication of Rh–
olefin binding and a five-coordinate structure. The 31P NMR
spectrum exhibits two sharp doublet of doublet phosphorus
Finally, we explored the reactivity of ligand 1 toward RhI.
The initial reaction of [{RhClACHTNUTRGNENG(U cod)}2] (cod=1,5-cycloocta-
1
diene) with 1 in CD2Cl2 was monitored by H and 31P NMR
spectroscopy (Scheme 5, showing the major product, 95%
conversion).
signals (at 255 K) for the major product at d=55.3 ppm
2
(1JRh,P =128 Hz, JP ,P =36 Hz) and 30.0 ppm (1JRh,P
=
a
a
b
b
2
144 Hz, JP ,P =36 Hz) (Figure 8, bottom spectrum). The
a
b
minor product exhibits a signal at d=38.3 ppm (1JRh,P
=
124 Hz), the structure of which cannot be determined from
the available data. Previous work with phosphino–olefin li-
gands and five-coordinate trigonal bipramidal RhI com-
plexes has demonstrated that olefins preferentially bind in
the equatorial plane.[35] From the 31Pa,31Pb spin–spin coupling
constant of 36 Hz it is clear that the phosphines are not
trans to one another, as much larger coupling constants are
observed (ca. 300 Hz).[36] As olefins prefer the equatorial
plane it would seem logical to place one phosphine group
and chloride ion in axial positions, with the remaining phos-
phine in the equatorial plane. However, the large difference
in the chemical shifts of the two coordinated olefins needs
to be factored in. Crucially, with the data in hand, it is not
possible to ascertain the two positions of the olefins (note:
attempts to crystallise [RhICl(1)] failed). There is also the
Scheme 5. Synthesis of [RhCl(1)], a RhI complex containing dbaphos (1).
Two products were formed in an approximate 95:5 ratio
(in quantitative conversion). A similar outcome was noted
in [D6]benzene (ca. 93:7). Leaving these reactions to run
overnight led to the formation of other minor products,
which we believe are due to interference of the cod ligand.
After two weeks an orange precipitate was formed, which
was filtered and shown to be a mixture of products in a
ratio 93:7. Running a reaction with [{RhACTHNUTRGNEUNG
(h2-C2H4)2Cl}2] in
toluene gave the same products (ca. 93:7). So, irrespective
of the Rh precursor the outcome is essentially the same.
The 1H and 31P NMR spectra are quite broad at 295 K
due to exchange processes (Berry psuedorotation; Figure 8).
Cooling the sample sharpened the proton signals and re-
vealed the spin–spin multiplicities of the olefin protons. The
two olefin protons at d=3.6 and 2.6 ppm (olefin a) are
possiblity of a dinuclear structure, although molecular
models, and comparison with the X-ray structure of
[Pd0 (1)2], indicate that it is unlikely.[37]
2
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6039

Z. Lin, I.J. S. Fairlamb et al.
Preliminary diffusion ordered spectroscopy (DOSY)
measurements (in CD2Cl2), comparing the major species of
ACTHNUTRGNEUNG
[RhICl(1)] and [RhICl(Lei)2] have proven inconclusive.[38]
Further structural data could be obtained through the syn-
thesis and characterisation of the RhI complex containing
the Lei ligand. Reaction of the Lei ligand (hereafter refered
to as “Lei”)[13e] with [{Rh
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
Scheme 6. Synthesis of [RhICl
ligands.
(Lei)2], a RhI complex containing two Lei
ACHTUNGTRENNUNG
Figure 10. X-ray structure of [RhICl
ACTHNUTRGNEN(UG Lei)2].
spectra (CDCl3) showed that two ligands were coordinated
to RhI through both the olefin and phosphine groups
(Figure 9). X-ray crystallography on a single crystal of
mately d=4.8–5.6 ppm (one overlapping signal and two par-
tially-resolved signals). 31P NMR spectroscopic analysis of
[RhICl
ACHTNUTRGNE(UNG Lei)2] shows two doublet of doublets signals (note:
ABX system). The spin–spin coupling-constant values for
the two doublets differ slightly, highlighting a small differ-
ence in the chemical environments of the two phosphorus
atoms. The chemical shift of Pa is d=24.3, with spin–spin
coupling constants of JP ,P =474 Hz and JRh,P =93 Hz. The
a
b
a
chemical shift of Pb is d=31.8 ppm, with spin–spin coupling
constant values of JP ,P =474 Hz and JRh,P =100 Hz. The
b
a
b
JRh,P coupling values correspond well with those reported for
axially-disposed phosphines in [RhClACHTNURTGNE(UNG PMe3)3] complexes
containing a p-bound diyne (ca. 97 Hz).[39] The origin of the
phosphorus inequivalence in solution is not clear. Also, to
the best of our knowledge, the JP ,P coupling is one of the
b
a
highest ever recorded for a RhI complex.
Thus, from the 31P NMR spectroscopic analysis of [RhCl-
AHCTUNGTRENNUNG
(Lei)2] we predict that Pa in [RhICl(1)] is located in the
equatorial position (higher chemical shift) and Pb in the
axial position (similar to the P atoms in [RhICl
AHCTUNGTRENNUNG
structural connectivity proposed in Scheme 5 for [RhCl(1)]
is most likely from the evidence available. DFT calculations
(B3LYP) provide further support the proposed structure.
Three conformations about the 1,4-dien-3-one moiety are
possible, with s-trans,s-trans and pseudo-s-cis,s-trans being
most feasible (Figure 11). The former conformer was found
to be 4 kcalmolꢀ1 lower in relative free energy than the
pseudo-s-cis,s-trans. Indeed a s-trans,s-trans ligated dba was
ACTHNUTRGNEUNG
Figure 9. NMR spectra of [RhICl(Lei)2] in CDCl3 (298 K): Top: 1H NMR
spectrum; bottom: 31P NMR spectrum (note: the peak at ca. d=31.4 ppm
found viable in [RhACTHNUTRGNEUNG
(h5-C5Me5)(h2,h2-dba-H)].[1] The coordi-
is trace phosphine oxide of the free ligand).
nated olefins show a significant increase in bond length for
the equatorially bound olefin (equatorial olefin C=C bond
length=1.466 ꢁ; axial olefin C=C bond length=1.402 ꢁ).
This difference adequately accounts for the substantially
shielded olefin a protons observed in NMR spectra of
[RhCl(1)]. The differences observed between the [RhCl(1)]
[RhICl
ACHTUNGTRENNUNG(Lei)2] revealed that the two phosphine groups are
positioned trans in axial positions, whereas the two olefins
and chloride ligands are found in the equatorial positions
(Figure 10). The 1H NMR spectrum further showed that
both olefins (non-identical in solution) are found at approxi-
and [RhClACHTUNGRTNENG(U Lei)2] complexes can be explained by the former
6040
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Chem. Eur. J. 2013, 19, 6034 – 6043

Diphosphine Chelating Ligand
FULL PAPER
AHCTUNGTRENNUNG
Figure 11. DFT-calculated structures of [RhICl(s-trans,s-trans-1)2] and
[RhICl(pseudo-s-cis,s-trans-1)2].
having cis-phosphines, whereas the latter has trans-phos-
phines, in addition to the olefins being s-trans and not s-cis.
Conclusion
In conclusion, dbaphos 1 is a flexible multidentate ligand
which is capable of forming both cis- and trans-metal com-
plexes.[15,40] It also serves as a bridging ligand, in which the
olefin interactions with Pd0 have been noted. In the case of
RhI, ligand 1 is able to coordinate through two phosphines
and two olefins, a quite remarkable finding, which highlights
the flexibility and diversity of coordination modes that are
accessible using the dbaphos ligand. Moreover, the “ex-
treme-back-bonding” for olefin a in [RhCl(1)] indicates that
the Rh centre is closer to a +III oxidation state, which
cis-[PtCl2(1)]: [PtCl2ACTHNUTRGNE(NUG cod)] (125 mg, 1 equiv, 0.33 mmol) was added to a
solution of dbaphos (1) (200 mg, 1 equiv, 0.33 mmol) in dry and degassed
CH2Cl2 (5 mL). The solution was stirred for 1 h under N2 at room tem-
perature. A pale yellow precipitate formed. Et2O (2 mL) was added and
the mixture filtered through a funnel with a sintered glass frit and
washed with Et2O (15 mL) to afford the product as a pale yellow powder
1
(224 mg, 78%). M.p. 1408C (decomp); H NMR (400 MHz, CD2Cl2): d=
9.82 (d, J=16.5 Hz, 2H; Hc), 7.88–7.81 (m, 4H; o-Ph), 7.78 (dd, J=8.0,
4.0 Hz, 2H; Ar), 7.61–7.55 (m, 2H; p-Ph), 7.52–7.43 (m, 8H; m-Ph and
Ar), 7.38–7.23 (m, 2H; Ar), 7.05–6.98 (m, 2H; p-Ph), 6.91–6.82 (m, 4H;
o-Ph), 6.74–6.65 ppm (m, 6H; Hb and m-Ph); 31P NMR (162 MHz,
CD2Cl2): d=4.72 ppm (s, 1JPt,P =3562 Hz); IR (KBr): n˜ =3680–3300 (w,
br, H2O), 3055 (m), 3020 (w), 1635 (s), 1616 (s), 1586 (w), 1481 (m), 1461
(m), 1434 (s), 1313 (w), 1293 (m), 1271 (m), 1199 (w), 1188 (w), 1121 (w),
1096 (s), 998 (w), 968 (m), 904 (w), 886 (w), 876 (w), 846 (w), 760 (s), 745
(s), 693 (s), 570 (m), 548 (s), 517 (s), 475 cmꢀ1 (w); HRMS (ESI): m/z
calcd for C41H33Cl2OP2Pt: 868.1026 [M<M+ >H]+; found: 868.1046; m/
z calcd for C41H32ClOP2Pt: 832.1259 [MꢀCl]+; found 833.1235; m/z calcd
for C41H31OP2Pt: 796.1492 [MꢀHCl2]+; found 796.1467; elemental analy-
sis calcd (%) for C41H32OP2PtCl2·H2O (868): C 55.54, H 3.87; found: C
stands in contrast with the [RhClACHTNUTRGNEUNG(Lei)2] complex (in which
less back-bonding was found to occur). We believe the coor-
dination chemistry detailed herein could be exploited in var-
ious transition-metal-catalysed processes.
Experimental Section
55.70,
H 3.62 (water is observed in the IR spectrum); solid-state
General details: See Supporting Information, which includes details of
the compound synthesis, characterisation (including known compounds)
and representative NMR spectra. Details for all novel compounds are
given below. See the Supporting Information for the NMR structural as-
signments. CCDC-905779 (1), 905778 (cis-[PtCl2(1)]), 914497 ([Pd2(1)2]),
CPMAS-NMR: 31P NMR (162 MHz): d=4.4 (1JPt,P =3590 Hz), 1.9 ppm
(1JPt,P =3590 Hz); 13C NMR (101 MHz): d=192.2, 145.2, 141.5, 139.3,
138.3, 135.8, 134.0, 132.9, 129.6, 125.6 ppm; In [D6]DMSO 31P NMR
(162 MHz, [D6]DMSO): d=15.33 (1JPt,P =2565 Hz, trans-
ACHTUNGTRENNUNG
4.68 ppm (1JPt,P =3554 Hz, cis-
only the trans-[PtCl2(1)] was observed: H NMR (400 MHz, [D6]DMSO):
ACHTUNGTRENNUNG
905781 (trans-[PdI(Ph)(1)]) and 905780 ([RhClACTHNURTGNENG(U Lei)2]) contain the sup-
1
plementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
ACHTUNGTRENNUNG
d=8.81 (d, J=16.5 Hz, 2H), 8.20 (d, J=8.0 Hz, 2H), 7.98–7.27 (m, 22H),
7.14–7.04 (m, 2H), 6.97 (d, J=16.5 Hz, 2H), 6.87–6.78 ppm (m, 2H);
Chem. Eur. J. 2013, 19, 6034 – 6043
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6041

Z. Lin, I.J. S. Fairlamb et al.
31P NMR (162 MHz, [D6]DMSO) d=15.33 ppm (1JPt,P =2565 Hz);
a
ing overnight a brown precipitate was collected by cannula filtration,
(37 mg, 30%). M.p. 222–2408C (decomp); 1H NMR (500 MHz, CD2Cl2,
255 K): major product (A)[40] d=7.86 (dd, J=11.0, 7.5 Hz, 2H; Ar), 7.56
(t, J=8.0 Hz, 2H; Ar), 7.45–7.28 (m, 10H; Ar), 7.24–6.94 (m, 13H; Ar),
6.86 (t, J=6.5 Hz, 2H; Ar), 6.75–6.65 (m, 3H; Ar), 5.57 (dd, J=13.5,
2.5 Hz, 1H; Hj), 5.52 (d, J=13.5 Hz, 1H; Hk), 3.56 (d, J=6.5 Hz, 1H;
Hg), 2.56 ppm (dd, J=8.5, 7.5 Hz, 1H; Hh); minor product (B) visible
peaks d=7.51–7.45 (m, 1H), 6.83–6.75 (m, 1H), 4.51 (dd, J=10.5, 3.0 Hz,
0.2H), 3.94 ppm (dd, J=10.0, 5.5 Hz, 0.2 Hz); 31P NMR (202 MHz,
CD2Cl2, 255 K): d=55.32 (dd, 1JRh,P =128.0, 2JP, P =35.5 Hz, 0.97P), 38.27
(d, 1JRh,P =124.0 Hz, 0.03P), 30.04 ppm (dd, 1JRh,P =143.5, 2JP, P =35.5 Hz,
0.97P); IR (KBr): n˜ =3051 (w), 1628 (w, br), 1554 (m), 1482 (m), 1454
(m), 1434 (s), 1419 (s), 1354 (w), 1291 (w), 1273 (w), 1246 (w), 1209 (m),
1187 (w), 1156 (w), 1120 (w), 1093 9 m), 1068 (w), 1028 (w), 999 (w), 980
(w), 877 (w), 868 (w), 829 (w), 753 (m), 740 (m), 705 (m), 694 (s), 657
(w), 626 (w0, 592 (w), 534 (m), 517 (m), 505 (s), 464 cmꢀ1 (w); HRMS
(ESI): m/z calcd for C41H32OP2Rh: 705.0978 [MꢀCl]+; found 705.0948.
minor product was also observed in the 31P NMR spectrum d=43.04 (d,
2
2JP, P =12 Hz), 20.32 ppm (d, JP, P =12 Hz), containing no Pt satellites.
trans-[PtCl2(1)]: A solution of dbaphos 1 (20 mg, 1 equiv, 0.033 mmol) in
dry and degassed CD2Cl2 (0.8 mL) was added to trans-[PtCl2ACHTNURGTNEUNG(MeCN)2]
(12 mg, 1 equiv, 0.033 mmol) in a glove-box. The reaction was monitored
by 1H and 31P NMR spectroscopy. A pale yellow precipitate formed.
After 3 h the precipitate was collected by filtration, washed with Et2O
(5 mL) and dried in vacuo to give a pale yellow solid (14 mg, 50%).
M.p.>2308C (decomp); 1H NMR (500 MHz, CD2Cl2): d=8.90 (d, J=
16.5 Hz, 2H; Hc), 7.98 (d, J=8.0 Hz, 2H; Ar), 7.71–7.62 (m, 8H; Ph),
7.51–7.46 (m, 6H; p-Ph and Ar), 7.43–7.36 (m, 8H; Ph), 7.30–7.23 (m,
2H; Ar), 6.93 (dtd, J=7.0, 5.5, 1.0 Hz, 2H; Ar), 6.78 ppm (d, J=16.5 Hz,
2H; Hb); 31P NMR (202 MHz, CD2Cl2): d=14.89 ppm (1JPt,P =2577 Hz);
IR (KBr): n˜ =3680–350 (w, br, H2O), 3053 (m), 1634 (s), 1560 (w), 1478
(w), 1462 (m), 1432 (s), 1301 (m), 1274 (w), 1202 (m), 1122 (w), 1095
(m), 970 (m), 770 (w), 750 (m), 740 (w), 705 (m), 692 (s), 570 (w), 514
(s), 485 cmꢀ1 (w); MS (LIFDI): m/z (%): 868.05 (28) [M]+, 832.02 (12)
[MꢀCl]+, 795.11 (100) [MꢀHCl2]+; HRMS (ESI): m/z calcd for
C41H32OP2Pt: 796.1496 [MꢀHCl2]+; found: 796.1470.
[RhICl (cod)}2] (0.037 g, 7.51ꢂ10ꢀ5 mol) and
AHCTUNTGRENUNNG AHCTUNRTGEG(NNNU Lei)2]: A solution of [{RhClACHTNGUTRENNGUN
“Lei” ligand (0.086 g, 0.22 mmol, ca. 1.5 equiv to Rh) in benzene (10 mL)
was stirred for 2 h at ambient temperature. The solvent was removed and
concentrated in vacuo to approximately 5 mL, which led to the precipita-
tion of a light yellow microcrystalline solid (0.098 g, 71%). Mp 221–
2238C; 1H NMR (400 MHz, CDCl3): d=8.64 (m, 2H), 8.23 (m, 2H),
7.58–7.74 (br m, 11H), 7.51 (dd, J=7.5, 4.0 Hz, 1H), 7.20–7.38 (br m,
7H), 7.14 (t, J=7.5 Hz, 1H), 7.00–7.09 (br m, 2H), 6.88–6.99 (br m, 5H),
6.78 (m, 4H), 6.53 (m, 3H), 5.52 (m, 2H), 5.32 (ddd, J=10.5, 7.5, 2.5 Hz,
1H), 4.83 ppm (m, 1H); 31P NMR (162 MHz, CDCl3): d=31.8 (dd,
[Pd0 (1)2]: Dry and degassed CH2Cl2 (3.5 mL) was added to a Schlenk
mixture was stirred at room temperature for 2 h. The solvent was then re-
moved in vacuo to give a red solid. Dry and degassed Et2O (8 mL) was
added and the mixture stirred to dissolve any remaining organics. Filtra-
tion by cannula, followed by drying the solid in vacuo gave the product
as a red/purple solid (79 mg, 66%). M.p. 1888C (decomp); 1H NMR
(500 MHz, CD2Cl2, 295 K): d=8.92 (dd, J=16.5, 4.5 Hz, 2H; Hk), 7.47–
6.67 (m, 56H; Ar), 5.95 (m with underlying d, J=16.5 Hz, 4H; Hj and
Hg), 5.28 ppm (dd, J=11.5, 8.0 Hz, 2H; Hh); 13C NMR (126 MHz,
CD2Cl2): d=185.7 (Ci), 134.6 (d, J=17 Hz), 133.9 (d, J=16 Hz), 133.1,
132.6 (d, J=13 Hz; Ck), 131.2 (Cj), 130.6, 129.9, 129.6, 129.3, 128.9 (d, J=
9 Hz), 128.7–128.5 (m), 128.2 (d, J=10 Hz), 127.7 (d, J=5 Hz), 82.9 (d,
J=21 Hz; Cg), 69.5–69.2 ppm (m; Ch); 31P NMR (202 MHz, CD2Cl2): d=
31.15 (d, J=20.5 Hz), 13.19 ppm (d, J=20.5 Hz); IR (KBr): n˜ =3050 (w),
1653 (m), 1588(m), 1478 (m), 1457 (m), 1433 (s), 1298 (m), 1209 (w),
1180 (w), 1118 (w), 1093 (m), 1026 (w), 998 (w), 968 (w), 830 (w), 742
(m), 693 (s), 574 (w), 505 cmꢀ1 (m); UV/Vis (CH2Cl2): lmax (e)=454
(7088), 284 nm (18951 molꢀ1 m3 cmꢀ1); HRMS (LIFIDI): m/z (monomer)
calcd for C41H32OP2Pd: 708.0963 [M]+; found: 708.0887; elemental analy-
sis calcd (%) for C41H32OP2Pd (708): C 69.45 H 4.55; found: C 69.32 H
J
Pb,Pa =474 Hz, JRh,Pb =100 Hz), 24.3 ppm (dd, JPa,Pb =474 Hz, JRh,Pa =
93 Hz); IR (KBr): n˜ =3054 (s), 2923 (s), 1695 (s), 1652 (s), 1635 (s), 1595
(s), 1482 (s), 1456 (s), 1433 (s), 1384 (s), 1325 (s), 1225 (s), 1189 (s), 1092
(s), 1044 (s), 1022 (s), 791 (s), 751 cmꢀ1 (s); (LIFDI): m/z calcd for Rh-
AHCTUNGTRENNUNG
(C27H21PO)2: 887.17 [M]+; found: 887.16.
Acknowledgements
We thank Professor Todd B. Marder (Institut fꢄr Anorganische Chemie,
Wꢄrzburg) for his insight into the geometry of RhI–phosphine complexes.
A.G.J. was funded by an EPSRC DTA PhD studentship. We thank Dr.
A. Wild for part-funding SEBꢃs PhD studentship (York Wild Fund).
I.J.S.F. thanks the Royal Society for support (University Research
Fellow). EPSRC grant EP/D078776/1, P.E.S., part-funded this work. We
are grateful to the referees for their constructive and critical reading of
our manuscript.
4.55. Crystals of [Pd0 (1)2] were obtained from CD2Cl2 layered with Et2O
2
(CD2Cl2/Et2O, 1:1, v/v).
trans-[PdI(Ph)(1)]: Iodobenzene (1.8 mL, measured as 1 equiv) was
added under a flow of Ar to a solution of [Pd0 (1)2] (11.6 mg, 1 equiv,
2
0.015 mmol) in [D8]THF (0.8 mL) in a Youngꢃs tap NMR tube. The reac-
tion was monitored by 1H and 31P NMR spectroscopy. After 1 h the oxi-
dative addition was complete (100% conversion by 31P NMR spectrosco-
py). 1H NMR (500 MHz, [D8]THF): d=8.88 (d, J=16.5 Hz, 2H; Hc),
8.02–7.91 (m, 6H; Ar), 7.41–7.30 (m, 8H; Ar), 7.24 (apparent t, J=
7.5 Hz, 2H; Ar), 7.17 (d, J=7.5 Hz, 1H; Ho), 7.09–7.04 (m, 6H; Ar),
7.01–6.95 (m, 4H; Ar), 6.93–6.84 (m, underlying d, J=16.5 Hz, 4H; Hb
and Ar), 6.42 (apparent t, J=7.5 Hz, 1H; Hn), 6.36 (apparent t, J=
7.5 Hz, 1H; Hm), 6.15 (apparent d, J=7.5 Hz, 1H; Hk), 5.95 ppm (appa-
rent t, J=7.5 Hz, 1H; Hl); 31P NMR (202 MHz, [D8]THF): d=16.83 ppm
(s); MS (LIFDI): m/z (%): 911.06 (8) [M]+ {isotope pattern 908.99 (24),
910.12 (47), 911.10 (86), 912.01 (40), 913.08 (100), 914.07 (25), 915.08
(21)}, 784.14 (100) [MꢀI]+ {isotope pattern: 782.14 (17), 783.15 (58),
784.14 (100), 786.13 (67), 788.14 (25), 789.45 (8)}, 706.09 (31), 679.26
(44); HRMS (LIFDI): m/z calcd for C47H36OP2Pd: 784.1276 [MꢀI]+;
found: 784.1377. Crystals of trans-[PdI(Ph)(1)], suitable for X-ray diffrac-
tion, were grown by cooling the reaction mixture to ꢀ188C ([D8]THF).
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ACHTUNGTRENNUNG 2ACHTUNGTRENNUNG(m-Cl)2ACHTUNGTRENNUNG(C2H4)4] (32 mg, 0.5 equiv, 0.083 mmol) was
[RhICl(1)]: [Rh
placed in a Schlenk flask, evacuated and refilled with N2 three times,
then dbaphos 1 (100 mg, 1 equiv, 0.166 mmol) was added (under a flow
of N2). Dry and degassed toluene (5 mL) was added and the reaction
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Diphosphine Chelating Ligand
FULL PAPER
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Received: October 10, 2012
Published online: March 11, 2013
Chem. Eur. J. 2013, 19, 6034 – 6043
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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