Special effects of ortho-isopropylphenyl groups. Diastereoisomerism in platinum(II) and palladium(II) complexes of helically chiral PAr3 ligands

Article abstract of DOI:10.1039/b416525j

The coordination chemistry of the four phosphines, P{C₆H ₃(o-CH₃)(p-Z)}₃ where Z = H (1a) or OMe (1b) and P{C₆H₃(o-CHMe₂)(p-Z)}₃ Z = H (1c) or OMe (1d) with platinum(II) and palladium(II) is reported. Mononuclear complexes trans-[PdCl₂L₂] (L = 1a,b) and trans-[PtCl ₂L₂] (L = 1a-c) have been prepared and the crystal structures of trans-[PdCl₂(1b)₂] and trans-[PtCl ₂(1c)₂] as their dichloromethane solvates have been determined. The structures show that in these complexes, the ligands adopt g⁺g⁺a conformations. Examination of the Cambridge Structural Database confirms this to be one of only two conformer types that tri-o-tolylphosphines adopt and the only viable conformer in 4 and 6 coordinate complexes. The binuclear complexes trans-[Pd₂Cl₄L ₂] (L = 1c,d) are formed even when an excess of the bulky 1c,d is used in the synthesis and the crystal structure of trans-[Pd₂Cl ₄(1c)₂] as its chloroform solvate is reported. Reaction of [PtCl₂(NCBu¹)₂] with 1b-d in refluxing toluene gave the cycloplatinated species [Pt₂Cl₂(L - H) ₂] where L - H is phosphine 1b-d deprotonated at one of the ortho-methyl carbon atoms. Variable temperature ³¹P and ¹H NMR spectroscopy reveals that all the complexes reported are fluxional. The processes are analysed in terms of restricted P-C and P-M rotations that give rise to diastereoisomeric rotamers because of the helically chiral orientations of the aryl substituants. For the complexes of the bulky ligands 1c,d, rotation about the P-C bond is slow on the NMR timescale even up to 75°C. The crystal structure of the cyclometallated complex [Pt₂Cl₂(1d - H)₂] has been determined. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b416525j

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F U L L P A P E R
Special effects of ortho-isopropylphenyl groups. Diastereoisomerism
in platinum(II) and palladium(II) complexes of helically chiral PAr3
ligands
R. Angharad Baber, A. Guy Orpen,* Paul G. Pringle,* Matthew J. Wilkinson and
Richard L. Wingad
School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK BS8 1TS
Received 28th October 2004, Accepted 3rd December 2004
First published as an Advance Article on the web 17th January 2005
The coordination chemistry of the four phosphines, P{C6H3(o-CH3)(p-Z)}3 where Z = H (1a) or OMe (1b) and
P{C6H3(o-CHMe2)(p-Z)}3 Z = H (1c) or OMe (1d) with platinum(II) and palladium(II) is reported. Mononuclear
complexes trans-[PdCl2L2] (L = 1a,b) and trans-[PtCl2L2] (L = 1a–c) have been prepared and the crystal structures of
trans-[PdCl2(1b)2] and trans-[PtCl2(1c)2] as their dichloromethane solvates have been determined. The structures show
that in these complexes, the ligands adopt g+g+a conformations. Examination of the Cambridge Structural Database
confirms this to be one of only two conformer types that tri-o-tolylphosphines adopt and the only viable conformer
in 4 and 6 coordinate complexes. The binuclear complexes trans-[Pd2Cl4L2] (L = 1c,d) are formed even when an
excess of the bulky 1c,d is used in the synthesis and the crystal structure of trans-[Pd2Cl4(1c)2] as its chloroform
solvate is reported. Reaction of [PtCl2(NCBut)2] with 1b–d in refluxing toluene gave the cycloplatinated species
[Pt2Cl2(L − H)2] where L − H is phosphine 1b–d deprotonated at one of the ortho-methyl carbon atoms. Variable
temperature 31P and 1H NMR spectroscopy reveals that all the complexes reported are fluxional. The processes are
analysed in terms of restricted P–C and P–M rotations that give rise to diastereoisomeric rotamers because of the
helically chiral orientations of the aryl substituents. For the complexes of the bulky ligands 1c,d, rotation about the
P–C bond is slow on the NMR timescale even up to 75 ◦C. The crystal structure of the cyclometallated complex
[Pt2Cl2(1d − H)2] has been determined.
Introduction
Arylphosphines are of immense importance in coordination
chemistry and catalysis and the stereoelectronic effects of
ortho-substituents (especially ortho-isopropyl) on an arylphos-
phine can profoundly influence the catalytic properties of its
complexes.1 One significant consequence of ortho-substituents is
an increase in the rigidity of the phosphine caused by restricted
P–C bond rotation. Howell2 and others3 have published a
series of studies on ortho-substituted triarylphosphines and their
stereodynamics. Here we report a study of the platinum(II)
and palladium(II) coordination chemistry of the bulky tri(o-
alkylphenyl)phosphines 1a–d and show that in these complexes,
chirality at the triarylphosphine is manifested as conformational
diastereoisomerism in bis(phosphine) species.
Scheme
1 Chiral C3-symmetric conformers in triarylphosphines
viewed along the M–P bond showing the helically chiral M and P
conformers (termed g+g+g+ and g−g−g− respectively in this paper and A
and Aꢀ by Howell et al.2).
can be defined by the M–P–Cipso –Cortho torsion angles xl 3 which
–
typically (see below) take values of about 50◦, i.e. gauche (de-
noted g+ or g−), or 180◦, i.e. anti (denoted a). The C3 symmetric
M conformation then becomes g+g+g+ (which is the same as
conformation A, one of the exo3 conformations described by
Howell et al.2) while the enantiomeric P conformation (= Aꢀ)
is denoted g−g−g−. We have previously used this terminology
to describe the conformations of trialkylphosphine and related
species.5
Results and discussion
The phosphines 1a–d were made by modifications of literature
methods (see Experimental section).
Mononuclear dichloroplatinum and dichloropalladium complexes
The conformations of triarylphosphines carrying three ortho-
substituted aryl rings may be described in a number of ways.
It is well known that triaryl rotor systems may exhibit helical
chirality in M and P conformations (see Scheme 1) which can
interconvert by a range of processes.4 The helical conformations
Phosphines 1a and 1b react with [PtCl2(NCBut)2] or
[PdCl2(NCPh)2] in toluene to give products for which ele-
mental analyses and FAB mass spectrometry correspond to
[MCl2(PAr3)2] and the IR spectra (in the 200–400 cm−1 region)
were consistent with the trans-isomers 2a,b and 3a,b (see
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7
6 5 9
©

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◦
˚
Experimental section). Complexes 2a and 3a have been pre-
viously reported6,7 and are only sparingly soluble. However the
p-methoxytolyl derivatives 2b and 3b were sufficiently soluble
for detailed NMR analysis (see below).
Table 2 Selected bond lengths (A) and angles ( ) for trans-[PtCl2(1c)2]
(2c)·2CH2Cl2
Pt(1)–Cl(1)
2.3039(10)
Pt(1)–P(1)
2.3436(11)
Crystals of 3b, as a dichloromethane solvate, suitable for
X-ray crystallography were obtained. Crystals of 2c, as a
dichloromethane solvate, were obtained as a by-product from
a cyclometallation reaction (see below) and its structure is
described now since it elucidates the discussion of the NMR
behaviour of all the complexes described here.
Cl(1A)–Pt(1)–Cl(1)
Cl(1)–Pt(1)–P(1A)
180
87.71(4)
Cl(1)–Pt(1)–P(1)
P(1A)–Pt(1)–P(1)
92.29(4)
180
Molecules of trans-[PdCl2(1b)2] (3b) have crystallographic Ci
symmetry (see Fig. 1 and Table 1 which lists selected bond
˚
lengths and angles). The average P–C bond length in 3b is 1.83 A,
with an average C–P–C bond angle of 106.4◦ and a mean Pd–
P–C bond angle of 112.1◦. Ligand 1b has a cone angle of 181◦
in this structure in which it adopts a conformation with Pd–P–
Cipso –Cortho(Me) torsion angles of −47.3, −69.9, and 170.9◦, i.e. a
Fig. 2 X-Ray crystal structure of trans-[PtCl2(1c)2] (2c). Hydrogen
−
−
˚
atoms are omitted for clarity.
g g a conformation. The shortest Pd · · · H contact is 2.91 A and
involves the ortho-hydrogen on the aryl group that adopts the
anti conformation. The shortest methyl hydrogen to Pd contacts
involve hydrogens on the gauche aryl rings and are at marginally
˚
P–C bond length in 2c is 1.84 A, with an average C–P–C bond
angle of 105.3◦ and a mean Pt–P–C bond angle of 113.4◦. Ligand
1c has a cone angle of 195◦ in this structure, in which it adopts
a conformation at P(1) with Pt–P–Cipso –Cortho torsion angles of
−66.0, −65.6, 177.5, i.e. a g−g−a conformation. The isopropyl
groups adopt an orientation that has the Me2CH hydrogen
eclipsed to the aromatic ring and towards the phosphorus
atom. All ortho-isopropylphenylphosphine fragments in the
Cambridge Structural Database (CSD)8 adopt this conforma-
˚
longer Pd · · · H distances (2.95 and 3.16 A).
Crystals of trans-[PtCl2(1c)2] (2c)·2CH2Cl2 were obtained
from CH2Cl2/toluene solution (see below). Complex 2c has
crystallographic Ci symmetry in the solid state. (See Fig. 2 and
Table 2 which lists selected bond lengths and angles). The average
˚
tion. The shortest Pt · · · H contact in 2c is 3.01 A and involves
the ortho-hydrogen on the aryl group that adopts the anti
conformation. The Me2CH hydrogens on the gauche aryl rings
˚
are at marginally longer Pt · · · H distances (3.07 and 3.32 A).
The influence of ortho-substituents in triarylphosphine com-
plexes was investigated by searching the CSD for tri-o-
alkylphenyl phosphine structures. The most numerous such
species are metal complexes of tri-o-tolylphosphine and for
the 66 fragments in 60 crystal structures, only two conformer
types are observed, corresponding to g+g+g+ and equivalent
conformations (49 examples) and g+g+a and equivalent con-
formations (17 examples). All square planar and octahedral or
pseudo-octahedral (piano-stool etc.) complexes are of the gga
conformer type as observed in 3b and 2c (and 4c below); this is
the conformation termed B (or Bꢀ) and exo2 by Howell et al.3 The
more sterically demanding umbrella-like g+g+g+ conformation
(see Scheme 1) is seen in lower coordination number (e.g. 2 or 3)
and tetrahedral metal complexes where its larger cone angle is
tenable. The complete absence of other conformations (e.g. g+aa
or g+g−a) implies that large volumes of the conformation space
of the three-rotor M–P(o-tolyl)3 system are empty, presumably
because the conformers in these regions are of unacceptably high
energy. Notably both the observed conformer types (g+g+g+ and
g+g+a) are chiral (see Schemes 1 and 2).
Fig. 1 X-Ray crystal structure of trans-[PdCl2(1b)2] (3b). Hydrogen
The complexes 2b and 3b showed broad NMR signals
indicating fluxionality. For example, the 31P signal for 2b at
+23 ◦C in CD2Cl2 was a very broad singlet (w1/2 90 Hz) at d 15.8
which, in C2D2Cl4, partially resolved into two broad singlets
(w1/2 80 Hz) at d 16.1 and 15.1. A variable temperature NMR
study was carried out (see Fig. 3).
atoms are omitted for clarity.
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for trans-[PdCl2(1b)2]
(3b)·4CH2Cl2
Pd(1)–Cl(1)
2.3076(14)
Pd(1)–P(1)
2.3589(11)
In C2D2Cl4, the 31P signals for 2b coalesced at ca. +50 ◦C and
Cl(1A)–Pd(1)–Cl(1)
Cl(1)–Pd(1)–P(1A)
180
86.79(5)
Cl(1)–Pd(1)–P(1)
P(1A)–Pd(1)–P(1)
93.21(5)
180
at +100 ◦C a sharp (w1/2 5 Hz) singlet at d 15.9 with J(PtP)
1
2582 Hz was observed. At 0 ◦C in CD2Cl2, two singlets at d
6 6 0
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7

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Scheme 2 Chiral gga conformers of o-substituted triarylphosphines, as
observed in 3b, 2c and 4c and in examples from the CSD.
Fig. 4 1H NMR spectrum of 2b at (a) −60; (b) +23; (c) +100 ◦C;
spectrum a was measured in CD2Cl2 and spectra b and c were measured
in C2D2Cl4. The inset is an expansion of the high frequency aromatic
region of spectrum a showing the two major and two minor signals.
Fig. 3 Variable temperature 31P NMR study of 2b; spectra a–d were
measured in C2D2Cl4 and spectra e–h were measured in CD2Cl2. The
inset is an expansion of the central region of spectrum h showing the
two major and two minor signals.
the o-tolyl groups equivalent on the NMR timescale. At low
temperatures, the 31P and 1H NMR spectra of 2b show the
presence of 2 major and 2 minor trans-PtCl2P2 species that we
associate with the presence of diastereomeric rotamers. Since
no P–P coupling was observed, the trans P atoms must be
equivalent in each of the species. From the database results noted
above, the g+g+g+ conformer has not previously been observed
in square planar species. Given this and that the equivalence of
the P atoms would require formation of ggg/ggg and gga/gga
rotamers exclusively (and none of the mixed ggg/gga rotamers),
we believe it more probable, and therefore assume henceforth,
that the ligands adopt only the enantiomeric g+g+a and g−g−a
conformations. The two major species at low temperatures are
therefore the Ci symmetric meso (g+g+a/g−g−a) rotamer and
the enantiomeric pair of C2 symmetric rac (g+g+a/g+g+a and
g−g−a/g−g−a) rotamers.
15.5 and 14.2 were resolved (intensities ca. 1 : 2), with very
1
similar J(PtP) values (2547, 2522 Hz), consistent with both
being trans mononuclear species. At −40 ◦C, an additional two
minor signals (ca. 0.2 × intensity of the major peaks) are resolved
at d 16.1 with 1J(PtP) 2562 Hz and 14.2 with 1J(PtP) obscured
but estimated to be ca. 2500 Hz. The intensities and chemical
shifts of the four signals changed considerably with temperature
(see Fig. 3); for the two maj◦or species, the ratio changes from 2 :
1 at 0 ◦C to 2 : 3 at −80 C. Variable temperature H NMR
1
spectroscopy further elucidated the fluxionality of 2b (see Fig. 4).
◦
1
At +23 C in C2D2Cl4, the H NMR signals for 2b were
all broad (w1/2 ca. 60 Hz): five resonances in the 1.5–3.2 ppm
range (integrating for 18 protons) were assigned to the tolyl-CH3
groups, a broad singlet at 3.75 ppm (integrating for 18 protons)
and assigned to the OMe groups, and finally the aromatic signals
which fell into two regions 7.1–7.8 (integrating for 16 p◦rotons)
and 8.7–9.1 ppm (integrating for 2 protons). By +100 C, the
signals are all sharp: the alkyl signals have coalesced to singlets
at 2.28 (CH3) and 3.88 ppm (OCH3) and the aromatic signals
have coalesced to two signals at 7.81 (6H) and 6.76 (12H) ppm.
At −60 ◦C, 6 major singlets and 6 minor singlets are observed
for the tolyl-CH3 groups and 2 major and 2 minor ‘quartets’
Some insight into the nature of the fluxionality may be gained
from examination of the crystal structures of 2c and 3b. The
structure of 2c in the crystal is redrawn in Scheme 3 viewed along
the P–M–P axis and the proposed process for interconversion of
the diastereoisomeric rotamers is shown.
The meso-rotamer is shown in a staggered (Ci) conformation
as is observed in the solid state structures of 2c as well as 3b and
in trans-[PtI2(1a)2]7 and trans-[PdBr2(1a)2].9 The P–C rotation
process (in which the back triarylphosphine goes from g+g+a
to g−g−a) shown in step i, yields the rac-rotamer but as drawn,
this has C1 symmetry making the P-atoms inequivalent. A 120◦
rotation around one M–P bond (step ii) would render the P
atoms equivalent, as shown in Scheme 3.
1
31
(which reduce to doublets in the H{ P} NMR spectrum) are
observed in the 8.5–9.5 ppm region. The variable temperature
1
1
31P{ H} and H NMR spectra for the palladium analogue 3b
were closely similar to those for 2b (see Experimental section).
In the light of the structural and database studies, the
fluxionality observed in the NMR spectra of 2b and 3b can
be interpreted in terms of restricted rotation about the P–C
and P–M bonds in a similar fashion to Howell’s treatment of
the fluxionality of [Cr(CO)5(1a)].2 At high temperatures, the
spectra are consistent with rapid rotation processes rendering
1
From the variable temperature H NMR spectra of 2b, a Tc
of 323 K was measured giving a calculated barrier† of ca. 65
† The barriers (DG‡) to rotation given in this paper were calculated from
the expression DG‡ = 0.0194Tc (9.972 + log{Tc/dm}) where Tc is the
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7
6 6 1

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Scheme 4 Proposed interconversion of meso and rac rotamers viewed
along the P–M–P axis (idealised structures).
slow in 2c since significant broadening of the 1H and 31P signals
◦
is observed only above +75 C. From a Tc of 373 K observed
1
in the H NMR spectra, the barrier to rotation is estimated to
1
be 80 ( 2) kJ mol−1. In contrast to 2b, the 31P and H NMR
◦
◦
spectra of 2c in CH2Cl2 were the same at +23 C and −80 C
and no signals for additional rotamers of the type meso/rac-A
and meso/rac-B (Scheme 4) were resolved. From consideration
of the greater steric bulk in 2c than 2b, it can be understood why
one rotamer (e.g. meso-A) would be preferred in solution.
Scheme 3 (a) The structure of 2c in the crystal viewed along the
P–M–P axis and its schematic representation used in (b), the proposed
interconversion of meso- and rac-rotamers (with the chloride ligands not
shown but lying in the plane across the page as in (a)).
( 2) kJ mol−1 for the g+g+a/g−g−a interconversion which is
considerably higher than the barrier for the related process in
[Cr(CO)5(1a)] (barrier ca. 40 kJ mol−1).2 From inspection of
molecular models, it is apparent that the high barrier to P–C
rotation observed in the square planar complexes reported here,
arises from the potential energy trough created by the bulky
ortho-substituents occupying the voids above and below the
square plane as well as the potential energy peaks associated
with the bulky ortho-substituents passing the cis M–Cl groups.
The four isomers observed at low temperatures in the 31P
NMR spectra of 2b and 3b (see above) may be due to arrested M–
P rotation. As shown in Scheme 4, the meso/rac-isomers, could
then form two rotamers (with the P atoms equivalent in each)
associated with their relative orientations across the P–M–P axis:
staggered (i.e. meso-A and rac-A) and eclipsed (i.e. meso-B and
rac-B). In the solid state, species of this type have been shown
to adopt meso-A (see above), rac-A and rac-B conformations.10
From the variable temperature 31P NMR spectra (Tc 263 K),
the energy barrier for these M–P bond rotation processes
is estimated to be ca. 55 ( 2) kJ mol−1. Restricted M–PR3
rotations are common for bulky phosphines and barriers of up
to 58 kJ mol−1 have been previously reported for square planar
complexes of the type trans-[RhCl(CO)(PR3)2].11
Binuclear chloroplatinum and chloropalladium complexes
Treatment of [PdCl2(NCPh)2] with 1 equivalent of 1b in refluxing
toluene gave a precipitate of the binuclear 4b (see Experimental
section for characterising data).
Phosphines 1c and 1d react with [PdCl2(NCPh)2] to give
binuclear complexes 4c and 4d regardless of the Pd : PR3
ratio. These products were characterised by a combination of
elemental analysis, FAB mass spectrometry, IR spectroscopy
(see Experimental section), 31P and 1H NMR spectroscopy.
The crystal structure of 4c has been determined as its
chloroform solvate. Molecules of trans-[Pd2Cl4(1c)2] (4c) have
crystallographic Ci symmetry (see Fig. 5 and Table 3 which lists
selected bond lengths and angles). The average P–C bond length
◦
˚
in 4c is 1.83 A, with an average C–P–C bond angle of 107.4 and
mean Pt–P–C bond angle 111.4◦. Ligand 1c has a cone angle of
The 31P NMR spectrum of 2c at room temperature showed
two singlets at d 26.4 and 24.7 (intensity ratio 3 : 1) which were
1
assigned to trans-PtP2Cl2 species on the basis of the J(PtP)
values of 2555 and 2603 Hz. The 1H NMR spectrum of 2c was
sharp and showed the signals for a 3 : 1 mixture of similar species.
There were 6 major and 6 minor doublets for the CH(CH3)2
groups along with 3 major and 3 minor multiplets for the
CH(CH3)2 groups showing the inequivalence of the isopropyl
groups. Two deshielded signals at 9.25 and 8.74 ppm (3 : 1) were
also evident. These data are consistent with the presence of rac
and meso rotamers analogous to the structures discussed above
for 2b but significantly, these are static on the NMR timescale
at room temperature. The P–C rotation process is remarkably
coalescence temperature of signals separated by dm in the 1H or 31P
NMR spectra. The error given in brackets allows for an error in Tc of up
to 10 ◦C (see J. Sandstro¨m, Chapter 7 in Dynamic NMR Spectroscopy,
Academic Press, 1982).
Fig. 5 X-Ray crystal structure of trans-[Pd2Cl4(1c)2] (4c). Hydrogen
atoms are omitted for clarity.
6 6 2
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7

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˚
Table 3 Selected bond lengths (A) and angles ( ) for trans-[Pd2Cl4(1c)2]
(4c)·4CHCl3
Pd(1)–Cl(1)
Pd(1)–Cl(2)
2.319(2)
2.300(2)
Pd(1)–Cl(1A)
Pd(1)–P(1)
2.403(2)
2.244(2)
Cl(1)–Pd(1)–P(1)
Cl(1A)–Pd(1)–P(1)
Cl(2)–Pd(1)–P(1)
94.53(8)
177.50(9)
89.83(8)
Cl(1A)–Pd(1)–Cl(1)
Cl(2)–Pd(1)–Cl(1A)
Cl(1)–Pd(1)–Cl(2)
85.22(7)
90.19(8)
172.95(8)
208◦ in this structure in which it adopts a conformation at P(1)
with Pd–P–Cipso –Cortho torsion angles of −54.5, −64.2, −178.69◦,
i.e. a g−g−a conformation. The shortest Pd · · · H contact is
˚
2.77 A and involves a CH(CH3)2 hydrogen on a gauche aryl
1
ring; the ortho-hydrogen on the aryl group that adopts the anti
conformation is at 2.81 A from the palladium. The (CH3)2C–
Particularly diagnostic are the very large J(PtP) values of
4993 and 5046 Hz and a broad 1H signal at 3.19 ppm for the Pt–
CH2 groups with a J(PtH) value of 108 Hz, as expected.16 The 1H
NMR spectrum (in CD2Cl2) shows broad signals for the tolyl-
CH3 (at 2.64 ppm, w1/2 60 Hz) and one of the aromatic protons
(at 6.95 ppm, w1/2 30 Hz). In C6D5CD3, the Pt–CH2 resonance
is shifted ca. 0.5 ppm to high frequency; at temperatures above
+50 ◦C, the Pt–CH2 signal is resolved into two singlets (1 : 2) at
3.74 (J(PtH) 114 Hz) and 3.67 ppm J(PtH) 108 Hz) and there
are two sharp singlets for the tolyl-CH3. This high temperature
behaviour shows that cis- and trans-5b do not interconvert on the
NMR timescale. At −60 ◦C in CD2Cl2, the 31P NMR spectrum
showed the presence of 4 singlets (in the ratio of ca. 1 : 1 : 1 :
2) and the 1H NMR spectrum showed 4 pairs of methyl singlets
and complex overlapping signals for the Pt–CH2 group. The low
temperature NMR spectra imply there are four species present
which we assign to rac- and meso-rotamers of cis- and trans-5b
(see below).
˚
H · · · Pd contacts involving the isopropyl groups on the gauche
aryl rings are at marginally longer Pd · · · H distances (2.96 and
˚
3.04 A). The structure, and in particular the conformation
of its triarylphosphine, is similar to those of complexes in
the CSD with refcodes ELENIS12 and POBVEH13 which are
both complexes of the form trans-[Pd2(l-Br)2(aryl)(1a)2] and
are meso-diastereoisomers having tri-o-tolylphosphine ligands
in g+g+a and g−g−a conformations.
Similar spectroscopic (IR and NMR) properties are observed
for 4c and 4d. The 31P NMR spectrum of 4d at +23 ◦C showed
two species are present in a ca. 1 : 1 ratio: a singlet at 28.2 and
two doublets at d 27.9 and 28.7 with a small J(PP) of 6 Hz.
This suggests that the two products are similar and in one of
them, the P atoms are inequivalent. The 31P NMR spectrum
of 4c similarly showed the presence of 2 species at +23 ◦C,
◦
1
the signals for which merged to a singlet at +75 C. The H
◦
NMR (COSY) spectrum of 4c at +23 C showed the presence
In the 2 : 1 reaction of 1b : Pt described earlier, the only
product observed was the mononuclear trans species 2b which
implies that cyclometallation to 5b is inhibited by the presence
of the phosphine.
As noted above, treatment of [PdCl2(NCPh)2] with 1b gave
the binuclear 4b under conditions similar to those which
produced the cycloplatinated complex 5b. This indicates that
cycloplatination occurs more readily than cyclopalladation
in these complexes; similar observations have been made by
others.16 However, in the toluene filtrate of the reaction mixture
of 6 major doublets and 12 minor doublets for the CH(CH3)2
groups; some of the doublet resonances were to low frequency
of TMS and therefore highly shielded. Three multiplets in the
region 9–9.5 ppm are present integrating for 1 : 2 : 1. At higher
temperatures, the H NMR signals broaden and by +100 ◦C
1
some of the signals have coalesced. In particular, the three high
frequency signals become a single broad resonance (w1/2 45 Hz)
at 9.3 ppm, the CH(CH3)2 signals become 2 signals at 3.8 and
2.5 ppm (intensity ratio 2 : 1), and the CH(CH3)2 signals become
4 broad signals at 2.2, 1.5, 1.1 and 0.0◦ppm (in intensity ratios 3 :
6 : 3 : 6). It is clear that even at 100 C, there is not rapid P–C
bond rotation on the NMR timescale. This behaviour is again
interpreted in terms of meso (Ci, as observed in the solid state)
and putative rac (C1) rotamers; the P atoms are equivalent in
meso-4c and inequivalent in rac-4c in agreement with the NMR
observations. The barrier to rotation in 4c was calculated (Tc
375 K) to be 74 ( 2) kJ mol−1 which is similar to that in 2d and
therefore supports the idea that the main impediment to P–C
rotation is the passage of the ortho-substituent past the adjacent
Pt–Cl groups.
1
to produce 4b, a minor species was observed which had H
signals consistent with a cyclopalladated analogue of 5b (see
Experimental section).
The 19 cyclometallated tri-o-tolylphosphine structures in the
CSD show conformations that are in a number of respects
similar to the non-cyclometallated species except that the torsion
angle x3 of the metallated aryl is perforce close to zero (typically
0–25◦) and the other two are g+g+ (typically x1 = 30–40◦ and
x2 = 60–80◦), as shown in Scheme 5. Only when the metal is 6-
coordinate is a g+a (ca. 80◦ and −160◦) conformation observed.
In any event, in such species there is helical chirality in
the cyclometallated species. Therefore rac and meso forms of
bis-cyclometallated species are to be expected. Indeed in the
crystal structure of [Pd2(l-I)2{1a − H}2] (where 1a − H is
cyclometallated 1a), the meso diastereoisomer is observed.15
No reaction was observed between [PtCl2(NCBut)2] and 1c
or 1d at room temperature but in refluxing toluene, a product
assigned the binuclear cyclometallated structure 6d is obtained.
The structure of 6d is assigned on the basis of IR (m(PtCl) 279,
248 cm−1) and the characteristic 31P NMR spectrum (C6D5CD3)
which showed two singlets (1 : 1) at d 14.0 and 13.9 with very large
1J(PtP) of ca. 5275 Hz. Structure 6d contains a cyclometallated
tertiary carbon atom which is rare (e.g. a few Pd17 and Rh18
metallocycles containing tertiary carbons have been reported).
The two species present may be the cis/trans isomers of 6d or
more likely, rac and meso isomers of trans-6d, which in this case
would each contain equivalent P atoms.
When crystals of meso-4c were dissolved in CDCl3, a mixture
of meso- and rac-4c was observed by 31P NMR spectroscopy.
This indicates that while rac–meso interconversion is not evident
on the NMR timescale at ambient temperatures, the isomers do
interconvert on the timescale of minutes to form equilibrium
mixtures.
Tri(o-tolylphosphine) (1a) forms cyclometallates with
palladium14,15 and platinum16 and this prompted us to attempt
cyclometallations with 1b–d. Treatment of [PtCl2(NCBut)2] with
1 equiv. of 1b in refluxing toluene for 4 h gave a mixture of
several products, one of which (d −4.5 and J(PtP) 4093 Hz)
was assigned to the binuclear [Pt2Cl4(1b)2]. After refluxing the
solution for a further 24 h, two products (ratio 2 : 1) were
observed by 31P NMR spectroscopy and were assigned to the
binuclear platinacycles trans-5b and cis-5b, principally by NMR
spectroscopy (see Experimental section).
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7
6 6 3

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◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for trans-[Pt2(l-
Cl)2(1d − H)2] (6d)
Pt(1)–C(11)
Pt(1)–Cl(1A)
2.115(18)
2.416(4)
Pt(1)–P(1)
2.177(3)
Cl(1A)–Pt(1)–P(1)
C(11)–Pt(1)–P(1)
Cl(1A)–Pt(1)–Cl(1)
173.32(14) C(11)–Pt(1)–Cl(1A)
82.5(4) Cl(1)–Pt(1)–C(11)
79.65(13) Pt(1)–Cl(1)–Pt(1)a
97.6(4)
167.3(4)
100.35(13)
Pt–P–C bond angle of 113.0◦. Cyclometallated ligand {1d − H}
has a cone angle of 233◦ in this structure in which it adopts
a conformation at P(1) with Pt–P–Cipso –Cortho torsion angles of
−18.8, −46.5, and −65.8◦, i.e. a g−g− conformation. The shortest
˚
Pt · · · H contact is 2.72 A and involves a CH(CH3)2 hydrogen on
a gauche aryl ring.
Some features of interest emerge when the structure of 6d
is compared with the related cyclometallated trimesitylphos-
phine species 7 (Ar = 2,4,6-trimethylphenyl, CSD refcode
VANHEB).19 The Pt–CMe2 distance (2.12(2) A) in 6d is slightly
˚
˚
longer than the corresponding Pt–CH2 distance (2.035(4) A) in
Scheme 5 Chiral g+g+, g−g−, g+a and g−a conformations of cyclomet-
allated tri-o-tolylphosphine ligands.
7 presumably as a consequence of the greater steric crowding in
6d. Despite this, the Pt–Cl (trans to C) distance in 6d of 2.480(4)
A is similar to the corresponding Pt–Cl distance of 2.474(1) A
in 7 which indicates that the tertiary alkyl in 6d has a similar
trans influence to the primary alkyl in 7. Furthermore the Pt–P
distances (2.177(3) A in 6d, 2.210(1) in 7) and Pt–Cl trans to
P distances (2.416(4) A in 6d, 2.386(1) in 7) indicate that the
˚
˚
˚
˚
phosphorus in 6d is more strongly bonded to platinum and has
a higher trans influence than the phosphorus in 7. This is also
consistent with the 1J(PtP) for 6d, being ca. 150 Hz larger than
for 7.19
The reaction of [PtCl2(NCBut)2] with 1c in refluxing toluene
gave an off-white precipitate which was so insoluble in common
organic solvents that characterisation by NMR was not possible;
the product is tentatively assigned the binuclear cyclometallate
structure 6c on the basis of elemental analysis, the FAB mass
spectrum and the IR spectrum (see Experimental section). The
31P NMR spectrum of the toluene filtrate, showed the presence
of the mononuclear species 2c; crystals of 2c were obtained from
this solution and its structure is discussed above.
Poor quality crystals of trans-6d were obtained and its crystal
structure determined (see Fig. 6 and Table 4 which lists selected
bond lengths and angles). The trans stereochemistry of 6d is
established and the trans influence of the CMe2 is markedly
greater than the phosphine (Pt–Cl trans to C 2.480(4), Pt–Cl
Attempts to cyclopalladate 1c or 1d under the conditions
used for cycloplatination, gave only the unmetallated binuclear
complexes 4c and 4d.
˚
trans to P 2.416(4) A). The average P–C bond length in 6d is
◦
˚
1.817 A, with an average C–P–C bond angle of 105.5 and mean
Conclusion
The coordination chemistry of bulky PAr3 ligands 1a–d was
investigated in the hope of shedding light on the catalytic
activating effect we have observed with ortho-substituted phenyl
phosphines, which is especially pronounced with ligands con-
taining o-isopropylphenyl groups.1 Not surprisingly, complexes
of the type [MCl2(1a–d)2] all have trans-geometry and for the
very bulky 1c,d, there is a tendency to form binuclear complexes
of the type trans-[M2Cl2(l-Cl)2(1c,d)2]. Steric congestion within
the coordination sphere leads to the highly restricted P–C
and P–M rotation apparent from the NMR studies. The P–C
rotation is so slow in complexes of the ligands containing o-
isopropylphenyl groups that diastereomeric rotamers associated
with the chiral conformations of the PAr3 groups are observed
even at elevated temperatures. To our knowledge, this is the first
time diastereoisomerism of this type has been observed at room
temperature and above. Although P–C rotation was observed in
these systems on the laboratory timescale (i.e. minutes), molec-
ular rigidity would prevail on a reaction timescale and therefore
may have consequences in catalysis. The crystal structure of
the cyclometallated species 6d revealed some unusual bonding
features which may also be significant in understanding the
special effect of o-isopropylphenyl groups.
Fig. 6 X-Ray crystal structure of trans-[Pt2Cl2(1d − H)2](6d). Hydrogen
atoms are omitted for clarity.
6 6 4
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7

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(w1/2 90 Hz, J(PtP) 2570); 31P{ H} NMR (CD2Cl2, −40 ◦C):
d = 16.08 (1J(PtP) 2562), 15.49 (1J(PtP) 2547), 14.24 (1J(PtP)
≈2500), 14.17 (1J(PtP) 2522); 1H NMR (CD2Cl2): d = 8.80 (br),
1
1
Experimental
Unless otherwise stated, all work was carried out under a
dry nitrogen atmosphere, using standard Schlenk line tech-
niques. Dry N2-saturated solvents were collected from a Grubbs
system20 in flame and vacuum dried glassware. 4-Bromo-
3-isopropylanisole,21 [PtCl2(NCBut)2]22 and [PdCl2(NCPh)2]23
were prepared by literature methods. Tri(o-tolyl)phosphine (1a)
was purchased from Strem and all other starting materials were
1
7.05 (br), 6.59 (br) 3.72 (br), 2.95 (br), 1.92 (br), 1.50 (br); H
◦
NMR (CD2Cl2, −60 C): d = 9.23 (q), 9.08 (q), 8.85 (q), 8.55
(q), 7.20–6.51 (m), 3.81 (s), 3.76 (s), 3.75 (s), 3.74 (s), 3.66 (s),
3.21 (s), 2.99 (s), 2.72 (s), 2.57 (s), 2.26 (s), 2.20 (s), 2.07 (s), 1.80
(s), 1.69 (s), 1.49 (s), 1.46 (s), 1.43 (s).
11
2c
purchased from Aldrich. Ligand 1c and complexes 2a and 3a
trans-[PtCl2(1c)2] (2c). Complex 2c was formed as a by-
product during the preparation of 6c (see below). IR: m(Pt–Cl)
have been previously reported. NMR spectra were measured on
a Jeol Eclipse 300, Jeol Eclipse 400 or Jeol GX 400 spectrometer.
Unless otherwise stated 1H, 13C and 31P NMR spectra were
recorded at 300, 100, and 121 MHz respectively at +23 ◦C. Mass
spectra were recorded on a Fisons MD800. Infrared spectra
were recorded on a Perkin Elmer Spectrum 1 spectrometer as
Nujol mulls between polythene plates. Elemental analyses were
carried out by the Microanalytical Laboratory of the School of
Chemistry, University of Bristol.
1
348, 337 cm−1; 31P{ H} NMR (CD2Cl2): d = 26.43 (1J(PtP)
1
2555), 24.72 (1J(PtP) 2603); H NMR (CD2Cl2): d = 9.25 (q),
8.74 (q), 7.7–6.9 (m), 4.20 (m), 4.0 (m), 3.8 (m), 3.32 (m), 2.92
(quintet), 2.61 (quintet), 1.72 (d), 1.56 (d), 1.43 (d), 1.25 (d),
1.20(d), 1.08 (d), 0.89 (d), 0.25 (d), 0.06 (d), −0.15 (d), −0.24
(d), −0.30 (d).
trans-[PdCl2(1a)2] (3a). Tri-o-tolylphosphine (1a) (0.718 g,
2.35 mmol) and [PdCl2(NCPh)2] (0.450 g, 1.18 mmol) were
mixed in toluene (70 cm3) and the suspension heated at reflux
for 21 h and then allowed to cool to room temperature to yield
a yellow precipitate. The solvent was removed and the resulting
solid triturated with cold toluene, filtered off, washed with cold
toluene (2 × 20 cm3) and then dried in vacuo to give 3a as a
yellow powder (0.61 g, 0.776 mmol, 66%). Elemental analysis
(calc): C, 64.30 (64.18); H, 5.25 (5.39%); MS (FAB) m/z =
788 (M+), 751 (M+ − Cl), 713 (M+ − 2 Cl); IR: m(Pd–Cl)
354 cm−1. The insolubility of 3a precluded characterization by
NMR spectroscopy.11
Syntheses
Tri(p-methoxy-o-tolyl)phosphine (1b). 4-Bromo-3-methyl-
anisole (16.02 g, 79 mmol) was added to Mg turnings (1.92 g,
79 mmol) in THF (15 cm3) over 5 min. The mixture was heated
at reflux for 2 h until the Mg turnings had disappeared. The grey
solution was then allowed to cool to room temperature before the
dropwise addition of PCl3 (3.62 g, 26 mmol) at 0 ◦C. The reaction
was stirred overnight and then 2 M NH4Cl solution (100 cm3)
was added and the mixture stirred for 30 min. The mixture was
then extracted with Et2O (3 × 30 cm3) and the ethereal extracts
combined and dried over MgSO4. The solution was filtered,
stirred with activated charcoal for 20 min and filtered through
Florisil. The solvents were removed in vacuo to yield an off white
solid, which was digested with ethanol (3 × 20 cm3) to leave a
white precipitate. The supernatant ethanol was then removed
with a cannula before the powder was washed with cold ethanol
(2 × 20 cm3) and the product 1b was dried in vacuo to leave a
fine white powder (6.00 g, 0.015 mol, 58%). Elemental analysis
(calc): C, 72.6 (73.1); H, 6.45 (6.90%); MS (CI) m/z: 394 (M+);
trans-[PdCl2(1b)2] (3b). Complex 3b as a yellow solid
(0.179 g, 0.19 mmol, 46%) was prepared in a similar fashion
to 3a from ligand 1b. Satisfactory elemental analyses were not
obtained (calc): C, 55.10 (59.67); H, 5.53 (5.63%); IR: m(Pd–
1
Cl) 349 cm−1; 31P{ H} NMR (CD2Cl2): d = 18.80 (w1/2 85 Hz);
31P{ H} NMR (CD2Cl2, −80 ◦C): d = 19.17, 18.46, 17.64,
1
17.18;1H NMR (CD2Cl2): d = 8.79 (br), 7.02 (br), 6.65 (br),
3.72 (br), 2.30 (br), 1.70 (br); 1H NMR (CD2Cl2, −80 ◦C): d =
9.12 (q), 9.00 (q), 8.77 (q), 8.49 (q), 7.20–6.52 (m), 3.83 (s), 3.76
(s), 3.67 (s), 3.64 (d), 3.62 (d), 3.59 (d), 3.21 (s), 3.09 (s), 2.68 (s),
2.56 (s), 2.27 (s), 2.25 (d), 2.16 (s), 2.14 (s), 2.04 (s), 1.74 (m),
1.65 (s), 1.44 (s), 1.40 (s).
1
1
31P{ H} (CDCl3): d = −34.8; H NMR (CDCl3): d = 6.70 (d,
1H), 6.52 (m, 2H,), 3.63 (s, 3H,), 2.25 (s, 3H); 13C NMR (CDCl3):
d = 160.2 (s), 144.3 (d), 134.3 (s), 126.3 (d), 115.8 (d), 111.5 (s),
55.1 (s), 21.2 (d).
[Pd2Cl4(1b)2] (4b). Tri(p-methoxy-o-tolyl)phosphine (1b)
(0.128 g, 0.32 mmol) and [PdCl2(NCPh)2] (0.124 g, 0.32 mmol)
were dissolved in toluene (10 cm3), heated at reflux for 18 h and
then cooled to room temperature to give an orange precipitate
and a yellow solution. The solution, containing a cyclopalladate
analogue of 5b (see below), was separated by filtration and the
precipitate was washed with toluene (2 × 1 cm3) and then dried in
vacuo to give 4b as an orange powder (110 mg, 0.096 mmol, 60%).
Elemental analysis (calc): C, 50.39 (50.42); H, 4.62 (4.76%); IR:
Tri-(o-isopropyl-p-methoxyphenyl)phosphine (1d). Complex
1d was prepared in a similar fashion to 1b from 4-bromo-3-
isopropylanisole to give a white powder (2.14 g, 4.47 mmol,
53%). Elemental analysis (calc): C, 74.90 (75.29); H, 8.60
(8.21%); MS (CI) m/z: 478 (M+); 31P{ H} (CDCl3): d = −42.6;
1
1H NMR (CDCl3): d = 6.81 (1H, dd), 6.56 (2H, dd), 3.72 (3H, s),
3.56 (1H, septet), 1.03 (6H, d); 13C NMR (CDCl3): d = 160.3 (s),
155.1 (d), 135.5 (s), 126.6 (s), 111.6 (s), 110.8 (s), 55.0 (s), 31.2
(s), 23.9 (s).
1
m(Pd–Cl) 346, 294, 263 cm−1; 31P{ H} NMR (CD2Cl2): d =
1
24.1 and 22.4; H NMR (CD2Cl2): d = 9.10 (br), 7.00 (br),
trans-[PtCl2(1a)2] (2a). Tri-o-tolylphosphine (1a) (0.301 g,
0.99 mmol) and [PtCl2(NCBut)2] (0.215 g, 0.494 mmol) were
dissolved in toluene (10 cm3), heated at 90 ◦C for 6 h and
then cooled to room temperature. The solvent was removed and
the remaining white solid was washed with cold toluene (2 ×
10 cm3) before drying in vacuo to give 2a as a white powder
(0.195 g, 0.22 mmol, 45%). Satisfactory elemental analyses were
not obtained and the insolubility of the product precluded
purifications by recrystallisation (calc): C, 56.51 (57.67); H, 4.87
(4.84%); IR: m(Pt–Cl) 341 cm−1 in agreement with literature
value.11
6.61 (br), 3.76 (br), 3.38 (br), 1.98 (br), 1.45 (br). The toluene
filtrate was reduced to dryness to give an oily yellow solid
(60 mg, 0.056 mmol, 35%) which was tentatively assigned to
the cyclopalladate analogue of 5b on the basis of the following
1
NMR data. 31P{ H} NMR (CD2Cl2): d = 34.87, 35.48. 1H NMR
(CD2Cl2): d = 7.55 (m), 7.40 (m), 7.11 (m), 6.89 (m), 6.65 (m),
3.71 (m), 3.33 (br), 2.60 (br, m), 2.32 (s), 2.25 (s).
[Pd2Cl4(1c)2] (4c). Tri-o-isopropylphenylphosphine (1c)
(0.051 g, 0.13 mmol) and [PdCl2(NCPh)2] (0.050 g, 0.13 mmol)
were dissolved in toluene (5 cm3) and stirred at room
temperature for 1 h to yield an orange precipitate. The product
was filtered off, washed with cold toluene (2 × 20 cm3) and
then dried in vacuo to give 4c as an orange powder (0.042 g,
0.04 mmol, 57%). The product can be recrystallised from
CHCl3. Elemental analysis (presence of solvent confirmed by
1H NMR) (calc 4c·4CHCl3): C, 43.59 (43.29); H, 4.65 (4.38%);
trans-[PtCl2(1b)2] (2b). Complex 2b as a yellow solid
(0.303 g, 0.29 mmol, 56%) was prepared in a similar fashion
to 2a from ligand 1b. Elemental analysis (calc): C, 54.73 (54.65);
H, 5.37 (5.16%); MS (FAB) m/z = 1018 (M+ − Cl), 983 (M+ − 2
Cl); IR: m(Pt–Cl) 342 cm−1; 31P{ H} NMR (CD2Cl2): d = 15.84
1
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7
6 6 5

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Table 5 Crystal and refinement data for 3b·4CH2Cl2, 2c·2CH2Cl2, 4c·4CHCl3 and 6d
Compound
3b·4CH2Cl2
2c·2CH2Cl2
4c·4CHCl3
6d
Colour, habit
Size/mm
Formula
Yellow block
0.2 × 0.2 × 0.2
C52H62Cl10P2O6Pd
1305.86
Yellow plate
0.25 × 0.25 × 0.05
C56H70Cl6P2Pt
1212.85
Orange block
0.05 × 0.05 × 0.05
C58H70Cl16P2Pd2
1609.08
Yellow plate
0.01 × 0.05 × 0.08
C60H76Cl2P2O6Pt2
1416.23
Formula weight
Crystal system
Space group (No.)
Triclinic
Triclinic
Triclinic
Triclinic
¯
¯
¯
¯
P1 (2)
P1 (2)
P1 (2)
P1 (2)
˚
a/A
11.035(2)
12.020(2)
12.441(3)
63.49(3)
77.64(3)
89.59(3)
1435.2(5)
1
9.6403(19)
11.055(2)
14.148(3)
97.94(3)
95.31(3)
113.82(3)
1564.7(7)
1
12.189(3)
12.331(3)
12.420(3)
90.563(4)
94.222(4)
111.771(4)
1727.5(7)
1
11.359(3)
11.719(3)
13.130(6)
101.28(3)
104.34(2)
112.02(3)
1486.5(9)
1
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
l/mm−1
0.891
2.996
1.221
4.891
Unique data
Rint
Final R1 [I > 2r(I)]
6547
0.0494
0.0582
6182
0.0387
0.0338
7821
0.1052
0.0709
6304
0.0677
0.0654
MS (FAB) m/z = 1098 (M+ − Cl), 1061 (M+ − 2 Cl), 1025
(s); 13C NMR (75 MHz, CDCl3): d = 162.3 (s), 161.5 (s), 160.6
(d), 160.3 (d), 144.5 (m), 134.8 (d), 131.9 (d), 131.7 (d), 127.8
(d), 126.9 (d), 117.8 (d), 113.0 (d), 112.6 (d), 111.0 (m), 55.4 (s),
55.3 (s), 23.6 (br), 17.0 (s, CH2), 15.8 (s, CH2).
1
(M+ − 3 Cl); IR: m(Pd–Cl) 354, 297, 264 cm−1; 31P{ H} NMR
(CDCl3): d = 33.04 (br), 32.39 (s), 32.13 (br), the broadness
1
is interpreted as due to◦the small (unresolved) J(PP); 31P{ H}
1
NMR (C2D2Cl4, +100 C): d = 32.17; H NMR (CDCl3): d =
[Pt2Cl2(1c − H)2] (6c). Tri-o-isopropylphenylphosphine (1c)
(0.178 g, 0.458 mmol) and [PtCl2(NCBut)2] (0.100 g, 0.231 mmol)
were dissolved in toluene (10 cm3), heated at reflux for 50 h and
then cooled to room temperature to give a white solid and a
pale yellow solution. The solution, containing 2c (see above),
was removed by filtration and the resulting solid was washed
with cold toluene (2 × 20 cm3) and then dried in vacuo to give
6c as a white powder (0.073 g, 0.059 mmol, 51%). Elemental
analysis (calc): C, 52.37 (52.47); H, 5.25 (5.22%); MS (FAB)
m/z = 1234 (M+), 1199 (M+ − Cl); IR: m(Pt–Cl) 277, 246 cm−1.
The lack of solubility of 6c precluded characterisation by NMR
spectroscopy.
9.34 (dd), 9.24 (dd), 9.16 (dd), 7.75 (m), 7.60 (m), 7.39 (m),
7.18 (m), 4.10 (br), 3.96 (br, m), 3.74 (br), 3.49 (br, m), 2.60
(d), 2.48 (br, m), 2.27 (d), 1.97 (d), 1.90 (br), 1.77 (br), 1.57
(m), 1.45 (d), 1.40 (d), 1.29 (d), 1.02 (d), −0.05 (d), −0.12 (d),
−0.15 (m); note that from the off-diagonal peaks in the1H
COSY NMR all 18 CH(CH3)2 signals (in the region 2.60 to
−0.15) and all 9 CH(CH3)2 signals (in the region 4.10 to 2.48)
were identified which were overlapping in the 1D spectrum. 1H
◦
NMR (C2D2Cl4, +100 C): d = 9.32 (br), 7.53 (br), 7.14 (br),
3.80 (br, d), 2.49 (br), 2.25 (br), 1.48 (br), 1.09 (br), 0.00 (br).
[Pd2Cl4(1d)2] (4d). Complex 4d was prepared in a similar
fashion to 4c from ligand 1d except that hexane was added
to induce precipitation from toluene to give the orange solid
product (0.08 g, 0.061 mmol, 62%). Elemental analysis (presence
[Pt2Cl2(1d − H)2] (6d). Tri-(o-isopropyl-p-methoxyphenyl)-
phosphine (1d) (0.051 g, 0.107 mmol) and [PtCl2(NCBut)2]
(0.023 g, 0.053 mmol) were dissolved in toluene (5 cm3), heated
at reflux for 28 h and then cooled to room temperature. Hexane
(20 cm3) was added and the solution was cooled in a freezer until
a white precipitate appeared. The solid was filtered off, washed
with cold hexane (2 × 2 cm3) and then dried in vacuo to give
1d as a white powder (0.026 g, 0.018 mmol, 69%). IR: m(Pt–Cl)
1
of solvent confirmed by H NMR) (calc 4d·0.5C6H5CH3): C,
56.75 (56.17); H, 6.06 (6.09%); MS (FAB) m/z = 1276 (M+
−
1
Cl), 1240 (M+ − 2 Cl); IR: m(Pd–Cl) 344, 285, 252 cm−1; 31P{ H}
4
NMR (CDCl3): d = 28.18 (s), 28.72 (d, J(PP) = 6 Hz), 27.95
(d, 4J(PP) = 6 Hz); 1H NMR (CDCl3): d = 9.17 (m), 7.23 (m),
7.19 (m), 6.95 (d), 6.67 (m), 3.86 (m), 3.74 (d), 3.51 (m), 2.55 (d),
2.48 (m), 2.25 (d), 1.95 (d), 1.53 (d), 1.40 (d), 1.29 (d), 1.01 (d),
0.05 (d), 0.00 (d), −0.06 (d).
1
279, 248 cm−1; 31P{ H} NMR (C6D5CD3): d = 14.03 (1J(PtP) ≈
5275 Hz), 13.90 (1J(PtP) ≈ 5275 Hz).
X-Ray crystal structure analyses of 3b·4CH2Cl2, 2c·2CH2Cl2,
4c·4CHCl3 and 6d
[Pt2Cl2(1b − H)2] (5b). Tri(p-methoxy-o-tolyl)phosphine
(1b) (0.347 g, 0.879 mmol) and [PtCl2(NCBut)2] (0.380 g,
0.879 mmol) were dissolved in toluene (15 cm3), heated at reflux
for 22 h and then cooled to room temperature. The dark brown
solution was filtered through a 2 cm thick plug of Florasil to give
a yellow solution. The solvent was then removed in vacuo to give
the product 5b as a pale yellow powder (0.500 g, 0.401 mmol,
91%). Satisfactory elemental analyses were not obtained despite
attempts to purify by recrystallisation (calc): C, 44.51 (46.20);
X-Ray diffraction experiments on 3b, 2c and 4c as their solvates
(at −100 ◦C) and 6d (at room temperature) were carried out
on Bruker CCD diffractometers using Mo-Ka X-radiation (k =
˚
0.71073 A). Crystal and refinement data are given in Table 5.
Absorption corrections were based on equivalent reflections
2
and structures refined against all Fo data with hydrogen atoms
riding in calculated positions. Final difference maps showed no
features of chemical significance with the largest features lying
close to solvent molecules exhibiting unresolved disorder and/or
the metal atoms.
CCDC reference numbers 254102–254105.
See http://www.rsc.org/suppdata/dt/b4/b416525j/ for crys-
tallographic data in CIF or other electronic format.
1
H, 4.68 (4.20%); IR: m(Pt–Cl) 278, 247 cm−1. 31P{ H} NMR
(CD2Cl2): d = 14.59 (s, 1J(PtP) = 4993 Hz), 14.82 (s, 1J(PtP) =
◦
1
5046 Hz);31P{ H} NMR (C6D5CD3, +50 C): d = 14.95, 14.77;
◦
31P{ H} NMR (CD2Cl2, −40 C): d = 14.60, 14.13, 13.95, 13.82
(approx 1 : 1 : 1 : 2 ratio); 1H NMR (CD2Cl2): d = 7.12 (m), 6.95
(br), 6.74 (m), 6.66 (m), 3.71 (s), 3.19 (br, s, 2J(HPt) = 108 Hz),
2.64 (br), 2.48 (br);1H NMR (C6D5CD3, +50 ◦C): d = 7.22 (m),
1
2
2
6.74 (m), 6.43 (m), 3.74 (s, J(HPt) 114 Hz), 3.67 (s, J(HPt)
108 Hz), 3.30 (m), 2.94 (s), 2.78 (s); 1H NMR (CD2Cl2, −40 ◦C):
d = 7.15 (m), 6.98 (m), 6.80 (m), 6.59 (m), 3.74 (m), 3.16 (m),
2.81 (s), 2.70 (s), 2.68 (s), 2.65 (s), 2.55 (s), 2.46 (s), 2.36 (s), 2.35
Acknowledgements
We would like to thank Martin Murray of University of Bristol
for helpful discussions of the NMR spectra, EPSRC for support,
6 6 6
D a l t o n T r a n s . , 2 0 0 5 , 6 5 9 – 6 6 7

View Article Online
Johnson Matthey for an Industrial CASE award (to M. J. W.) and
The Leverhulme Trust for a Research Fellowship (to P. G. P.).
9 J. Vicente, J. A. Abad, E. Martinez-Viviente and M. C. R. Arellano,
Private Communication to the Cambridge Structural Database,
1997.
10 We have recently determined the crystal structures of [PtCl2(1c)]
as a chloroform solvate and [PdCl2(AsAr3)2] (Ar = C6H3(o-Pri)(p-
OMe)) which have rac-A and rac-B conformations respectively (see
subsequent papers).
11 C. H. Bushweller, S. Hoogasian, A. D. English, J. S. Miller and M.
Lourandos, Inorg, Chem., 1981, 20, 3448 and refs. therein.
12 F. Paul, J. Patt and J. F. Hartwig, J. Am. Chem. Soc., 1994, 116,
5969.
References and notes
1 For example see: (a) S. J. Dossett, A. Gillon, A. G. Orpen, J. S.
Fleming, P. G. Pringle, D. F. Wass and M. Jones, Chem. Commun.,
2001, 699; (b) N. A. Cooley, S. M. Green, D. F. Wass, K. Heslop,
A. G. Orpen and P. G. Pringle, Organometallics, 2001, 20, 4769; (c) J.
Dennett, A. L. Gillon, K. Heslop, D. J. Hyett, J. S. Fleming, E. Lloyd-
Jones, A. G. Orpen, J. Scutt, R. H. Weatherhead, P. G. Pringle and
D. F. Wass, Organometallics, 2004, 23, 6077; (d) A. H. Roy and J. F.
Hartwig, Organometallics, 2004, 23, 1533 and refs. therein.
2 (a) J. A. S. Howell, M. G. Palin, P. C. Yates, P. McArdle, D. Cunning-
ham, Z. Goldschmidt, H. E. Gottlieb and D. Hezroni-Langerman,
J. Chem. Soc., Perkin Trans. 2, 1992, 1769; (b) J. A. S. Howell, M. G.
Palin, P. McArdle, D. Cunningham, Z. Goldschmidt, H. E. Gottlieb
and D. Hezroni-Langerman, Inorg. Chem., 1993, 32, 3493; (c) J. A. S.
Howell, P. C. Yates, M. G. Palin, P. McArdle, D. Cunningham, Z.
Goldschmidt, H. E. Gottlieb and D. Hezronilangerman, J. Chem.
Soc., Dalton Trans., 1993, 2775; (d) J. A. S. Howell, J. D. Lovatt,
P. McArdle, D. Cunningham, E. Maimone, H. E. Gottlieb and Z.
Goldschmidt, Inorg. Chem. Comm., 1998, 1, 118; (e) J. A. S. Howell,
N. Fey, J. D. Lovatt, P. C. Yates, P. McArdle, D. Cunningham, E.
Sadeh, H. E. Gottlieb, Z. Goldschmidt, M. B. Hursthouse and M. E.
Light, J. Chem. Soc., Dalton Trans., 1999, 3015.
3 (a) S. D. Chappell and D. J. Cole-Hamilton, J. Chem. Soc., Dalton
Trans., 1993, 533; (b) J. Fornies, A. Martin, R. Navarro, V. Sicilia and
P. Villarroya, Organometallics, 1996, 15, 1826; (c) M. R. Whitnall,
K. K. M. Hii, M. Thornton-Pett and T. P. Kee, J. Organomet. Chem.,
1997, 529, 35.
4 A. K. Colter, R. J. Kurland and I. I. Schuster, J. Am. Chem. Soc.,
1965, 87, 2279.
5 M. B. Smith, A. G. Orpen, P. G. Pringle and K. Worboys,
J. Organomet. Chem., 1998, 550, 255.
6 M. A. Bennett and P. A. Longstaff, J. Am. Chem. Soc., 1969, 91,
6266.
13 C. Bartolome, P. Espinet, J. M. Martin-Alvarez and F. Villafane,
Eur. J. Inorg. Chem., 2003, 3127.
¨
14 W. A. Herrmann, C. Brossmer, K. Ofele, C. P. Reisinger, T. Priermeier,
M. Beller and H. Fischer, Angew. Chem. Int. Ed., 1995, 34, 1844.
15 A. L. Rheingold and W. C. Fultz, Organometallics, 1984, 3, 1414.
16 (a) S. D. Chappell and D. J. Cole-Hamilton, J. Chem. Soc., Dalton
Trans., 1983, 1051; (b) J. Fornie´s, A. Mart´ın, V. Sicilia and P.
Villarroya, Organometallics, 1996, 15, 1826; (c) S. A. Dias and E. C.
Alyea, Transition Met. Chem., 1979, 4, 205.
17 (a) F. Balegroune, D. Grandjean, D. Lakkisb and D. Matt, J. Chem.
Soc., Chem. Commun., 1992, 1084; (b) P. Kocovsky, S. Vyskocil, I.
Cisarova, J. Sejbal, I. Tislerova, M. Smrcina, G. C. Lloyd-Jones, S. C.
Stephen, C. P. Butts, M. Murray and V. Langer, J. Am. Chem. Soc.,
1999, 121, 7714; (c) P. Dotta, P. G. A. Kumar and P. S. Pregosin,
Organometallics, 2003, 22, 5345.
18 (a) A. Vigalok, H.-B. Kraatz, L. Konstantinovsky and D. Milstein,
Chem. Eur. J., 1997, 4, 253; (b) A. Vigalok, B. Rybtchinski, L. J. W.
Shimon, Y. Ben-David and D. Milstein, Organometallics, 1999, 18,
895.
19 (a) E. C. Alyea, G. Fergusen, J. Malito and B. L. Ruhl,
Organometallics, 1989, 8, 1188; (b) E. C. Alyea and J. Malito,
J. Organomet. Chem., 1988, 340, 119.
20 A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen and
F. J. Timmers, Organometallics, 1996, 15, 1518.
21 (a) N. J. Hales, H. Heeney, J. H. Holinshead and S. V. Ley,
Tetrahedron, 1995, 51, 7741; (b) H. Konishi, K. Aritomi, T. Okano
and J. Kiji, Bull. Chem. Soc. Jpn., 1989, 62, 591.
22 D. Fraccarollo, R. Bertani, M. Mozzon, U. Belluco and R. Michelin,
Inorg. Chim. Acta, 1992, 201, 15.
7 E. C. Alyea, S. A. Dias, G. Ferguson and P. J. Roberts, J. Chem. Soc.,
Dalton Trans., 1979, 948.
8 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 1
and 31.
23 J. R. Doyle, P. E. Slade and H. B. Jonassen, Inorg. Synth., 1960, 6,
218.
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