Chelate ring-opening of Pd(II) triphos complexes: Ligand exchange, selective phosphine oxidation, and X-ray crystal structure of [Pd(Ph2P(CH2)2PPh(CH2) 2P(O)Ph2)2Br]Br

Article abstract of DOI:10.1016/S0277-5387(98)00307-6

³¹P NMR studies show that chelate ring-opening of [Pd(triphos)Cl]⁺ , 4, (triphos = Ph₂P(CH₂)₂PPh(CH₂) ₂PPh₂) can be achieved in solution by reaction with excess of triphos with the formation of [Pd(Ph₂P(CH₂)₂PPh(CH₂)2PPh ₂-P,P)₂]²⁺. In the X-ray crystal structure, [Pd(triphos)Br]Br, 1 has a distorted square-planar geometry, and the oxidation of 1 with H₂O₂ gives rise to [Pd(Ph₂P(CH₂)₂PPh(CH₂) ₂P(O)Ph₂-P,P)₂]²⁺, 2, which contains two bidentate ligands. The presence of two dangling arm phosphine oxide groups was confirmed by X-ray crystallography for the related complex [Pd(Ph₂P(CH₂)₂PPh(CH₂) ₂P(O)Ph₂-P,P)₂Br]Br, 3, which contained square-pyramidal five-coordinated Pd(II).

Full text of DOI:10.1016/S0277-5387(98)00307-6

\
Polyhedron 07 "0888# 272Ð278
PERGAMON
Chelate ring!opening of Pd"II# triphos complexes] Ligand
exchange\ selective phosphine oxidation\ and X!ray crystal
structure of ðPd"Ph1P"CH1#1PPh"CH1#1P"O#Ph1#1BrŁBr
Paloma Sevillanob\ Abraha Habtemariama\ Alfonso Castineirasb\ M[ Esther Garc(ab\
ꢀ
½
Peter J[ Sadlera\ ꢁ
a Department of Chemistry\ University of Edinburgh\ King|s Buildings\ West Mains Road\ EH8 2JJ Edinburgh\ U[K[
b Deparment of Inorganic Chemistry\ University of Santiago de Compostela\ E!04695 Santiago de Compostela\ Spain
Received 1 July 0887^ accepted 3 August 0887
Abstract
20P NMR studies show that chelate ring!opening of ðPd"triphos#ClŁ¦\ 3\ "triphosꢂPh1P"CH1#1PPh"CH1#1PPh1# can be achieved in
solution by reaction with excess of triphos with the formation of ðPd"Ph1P"CH1#1PPh"CH1#1PPh1!P\P#1Ł1¦[ In the X!ray crystal
structure\ ðPd"triphos#BrŁBr\ 0 has a distorted square!planar geometry\ and the oxidation of 0 with H1O1 gives rise to
ðPd"Ph1P"CH1#1PPh"CH1#1P"O#Ph1!P\P#1Ł1¦\ 1\ which contains two bidentate ligands[ The presence of two dangling arm phosphine
oxide groups was con_rmed by X!ray crystallography for the related complex ðPd"Ph1P"CH1#1PPh"CH1#1P"O#Ph1!P\P#1BrŁBr\ 2\
which contained square!pyramidal _ve!coordinated Pd"II#[ Þ 0888 Elsevier Science Ltd[ All rights reserved[
Keywords] Palladium"II# complexes^ Triphosphine ligand^ NMR spectroscopy^ Phosphine oxidation^ Chelate ring!opening^ X!ray crystallography
0[ Introduction
structures of ðPd"Ph1P"CH1#1PPh"CH1#1P"O#Ph1!P\P#1BrŁ
Br\ 2\ and ðPd"triphos#BrŁBr\ 0[ The latter complex under!
goes facile selective oxidation of coordinated triphos pro!
ducing dangling arm phosphine oxide groups[
There is much current interest in novel metal complexes
containing derived polydentate phosphine ligands on
account of their potential in catalytic and biomedical
activity ð0Ð5Ł[ Chelating phosphine ligands are useful for
stabilizing metal!metal bonds ð6Ð8Ł\ and can result in
unusual coordination numbers and geometries ð09Ł[ The
chelating nature of the ligands often prevents phosphine
dissociation\ in contrast to the behaviour of analogous
complexes of monophosphine ligands ð00Ł[
The way in which a given linear tridentate phosphine
ligand coordinates with transition metal centres depends
on the metal and the other ligands surrounding the metal
centre[ The substituent groups on the donor atoms may
in~uence the coordination mode[ Dangling arm donors
with ÐPPh1 groups are quite common and they are usually
highly reactive ð3Ł[ Thus\ we are interested in the study of
chelate ring!opening reactions of metal complexes
because they may provide activation mechanisms for
metal complexes in vivo and lead to useful bioactivity
ð01\02Ł[ In this paper we report chelate ring opening reac!
tions of Pd"II# triphos complexes and the X!ray crystal
1[ Experimental
1[0[ Rea`ents
High!purity bis!"1!diphenylphosphinoethyl#phenyl!
phosphine "86)#\ PdCl1 "88)# and PdBr1"88)# were
purchased from Strem Chemicals\ and used as received[
NaCl and NaBr were of G[R[ grade "Merck or Panreac#[
H1O1 "29) w:v# was purchased from Panreac[
1[1[ General procedures
Microanalysis was performed by the elemental mic!
roanalyzer of the University of Santiago de Compostela\
Fisons Instruments EA 0097 CHNS!O[ Melting points
were measured on an Electrothermal melting point
apparatus[ Mass spectra of complexes were obtained by
fast atomic bombardment "FAB# on a KRATOS MS 49
spectrometer using nitrobenzylic alcohol as the matrix[
Infrared spectra were recorded at ambient temperature
ꢁ Corresponding author[
9166!4276:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[
PII] S9166!4276"87#99296!5

273
P[ Sevillano et al[ : Polyhedron 07 "0888# 272Ð278
as KBr pellets "3999Ð499 cm−0# and Nujol mulls "499Ð
099 cm−0# on a Mattson Cygnus 099 spectrophotometer[
The bands are reported as vsꢂvery strong\ sꢂstrong\
mꢂmedium\ wꢂweak\ and shꢂshoulder[ Con!
ductivities were obtained at 14>C from 09−2 M solutions
in DMF on a WTW model LF!2 instrument[ 20P"0H#
NMR spectra were recorded on a Bruker AMX499
instrument at 191[35 MHz[ All NMR spectra were rec!
orded at ambient temperature "½19>C# in CDCl2[ Chemi!
cal shifts are reported in ppm relative to external 74)
H2PO3\ "dꢂchemical shift in ppm^ tꢂtriplet\ dꢂdoublet\
ddꢂdoublet of doublets\ Jꢂcoupling constant in Hz#
Absorption corrections were calculated using the pro!
gramme DIFFABS ð04Ł[ Non!hydrogen atoms were
re_ned anisotropically[ Hydrogen atoms were re_ned
using a riding model Sꢂ0[912 and 9[855 for 0 and 2\
respectively[ Calculations were performed on DEC199
Alpha Station using the programmes HELENA ð05Ł\
SHELXS75 ð06Ł\ SHELXS82 ð07Ł\ and ZORTEP ð08Ł[
Further details of the crystal structure determination
can be ordered from FACHINFORM!ATIONSZEN!
TRUM KARLSRUHE\ 65233 Eggen!stein!Leo!
poldshafen e!mail] crysdataÝFIZ!Karlsruhe[de under
the depository number CSD!397748 for complex 2 and
CSD!397759 for complex 0[
1[2[ X!ray diffraction structural study
1[3[ Preparation of ðPd"triphos#BrŁBr "0#
Table 0 summarises the crystal data\ data collection\
structural solution and re_nement parameters for com!
plexes 0 and 2[ The X!ray data were collected on an Enraf
Nonius MACH2 di}ractometer using the v scan model
ð03Ł[ The structures were solved by direct methods and
re_ned by a full!matrix least!squares analysis on F1[
The preparation was based on a published procedure
ð19Ł] a suspension of PdCl1 "9[0889 g\ 9[964 mmol# and
NaBr "9[0428 g\ 0[385 mmol# in water "19 ml# was stirred
on a heated water bath "89>C# until it became a clear
solution[ It was left to cool to room temperature and a
Table 0
Crystallographic data and data collection parameters for complexes 0 and 2
Complex
0
2
Formula
Colour
M
C23H22Br1P2Pd
Colourless
799[62
C57H55Br1O1P5Pd
Yellow
0256[14
Temperature "K#
Crystal system
Space group
181"1#
Monoclinic
P10:n
182"1#
Monoclinic
P10:n
Ä
l "A#
9[60962
9[60962
Ä
a "A#
09[1725"02#
19[338"1#
05[909"2#
89[99
85[176"02#
89[99
2235[3"7#
3
0[478
00[7745"6#
16[103"1#
11[473"1#
89[99
82[014"7#
89[99
6182[7"8#
3
0[134
Ä
b "A#
Ä
c "A#
a ">#
b ">#
g ">#
2
Ä
U "A #
Z
Dc "g:cm−2
#
m "mm−0
F"999#
#
2[097
0481
0[419 "MoÐKa#
1673
Crystal size "mm#
u Range ">#
Index ranges
9[24×9[29×9[09
1[12 to 15[29
9¾h¾01
9¾k¾14
−08¾l¾08
6064
9[24×9[14×9[09
1[01 to 11[66
−01¾h¾01
9¾k¾18
−13¾l¾9
09015
Re~ections collected
Independent re~ections "Rint
Absorption correction
Max[ and min[ transmission
Re_nement method
Data:restraints:parameters
Goodness of _t on F1
Final R ind[ðI×1s"I#Ł
R ind[ "all data#
#
5689 "9[9329#
C scans
8732 "9[0913#
C scans
9[866 and 9[553
0[999 and 9[393
Full!Matrix Least!Squares
5689:9:260
0[912
R0ꢂ9[9425\ wR1ꢂ9[0353
R0ꢂ9[0447\ wR1ꢂ9[0685
0[158 and −9[649
Full!Matrix Least!Squares
8732:9:602
9[855
R0ꢂ9[9742\ wR1ꢂ9[0619
R0ꢂ9[1549\ wR1ꢂ9[1013
9[343 and −9[441
−2
Ä
Largest di}[ peak and hole "e[A
#

P[ Sevillano et al[ : Polyhedron 07 "0888# 272Ð278
274
solution of triphos "9[3 g\ 9[64 mmol# in CH1Cl1 "49 ml#
was added dropwise[ The mixture was stirred for 13 h\
CH1Cl1 was removed in vacuo\ whereupon a yellow crys!
talline solid formed[ The solid was recrystallised from
CH1Cl1:n!hexane "1]0#[ Colourless prismatic crystals of 0
suitable for X!ray crystallography were obtained from a
solution of acetone:ether "1]0#[ Yield] 79)\ m[p[ 067>C[
Found] C\ 40[03^ H\ 3[14[ Calc[ For C23H22P2PdBr1] C\
"PdCl# 207 vs[ m:z 564 "M¦!Cl\ 099)#[ L "DMF#]
80[37 V−0 cm1 mol−0
[
1[7[ Titration of ðPd"triphos#ClŁCl with triphos
To a solution of 3 "9[9103 g\ 9[92 mmol# in CDCl2
"9[4 ml#\ aliquots of solutions containing 9[14 molar equi!
valents of triphos in CDCl2 "9[94 ml# were added stepwise
to give a total of 9[14\ 9[4\ 9[64\ 0 and 0[14 molar equi!
valents of triphos and their 20P!"0H# NMR spectra were
recorded[
2
49[80^ H\ 3[01)[ 20P"0H# NMR] d 34[9 ð1P\ d\ J"P!P#
2
ꢂ7[1 Hz\ !PPh1Ł\ 009[3 ð0P\ t\ J"P!P#ꢂ7[1 Hz\ ×PPhŁ[
nmax:cm−0] "Pd!Br# 196 s[ m:z 613 "M¦!Br\099)#[ L]
58[5 V−0 cm1 mol−0
[
2[ Results and discussion
1[4[ Preparation
of
ðPd"Ph1P"CH1#1PPh"CH1#1
P"O#Ph1P\P#1ŁðPdBr3Ł "1#
Complex ðPd"triphos#BrŁBr\ 0\ was prepared following
a literature method ð19Ł and crystals were obtained from
acetone:ether solutions[ The X!ray structure shown in
Fig[ 0 contains four!coordinate square!planar Pd"II# as
has been previously reported for the chloride analogue
To a solution of 0 "9[0 g\ 9[01 mmol# in acetone:ether
"1]0\ 09 ml#\ H1O1 "29)\ 0 ml# was added[ The solvent
was evaporated in air and a yellow crystalline solid
formed[ The solid was washed with ethanol\ and dried[
Yield] 69)\ m[p[ 179>C[ Found] C\ 38[74^ H\ 3[12[ Calc[
For C57H55P5O1Pd1Br3] C\ 38[85^ H\ 3[93)[ 20P"0H#
NMR] d 20[2 ð1P\ d\ 2J"!P"O#Ph1!×PPh#ꢂ48[3 Hz\
!P"O#Ph1Ł\ 53[3 ð1P\ d\ 2J"!PPh1!×PPh#ꢂ06[9 Hz\
!PPh1Ł\Ł\ 62[0 ð1P\ dd\ ×PPhŁ[ nmax:cm−0] "Pd!Br# 124m\
068 vs\ "Pd!P# 255 m\ 241 w\ "PꢂO# 0073 vs[ This com!
pound was also prepared by the addition of H1O1 "29)\
0 ml# to a solution of 0 "9[0 g\ 9[901 mmol#\ triphos
"9[956 g\ 9[901 mmol# in acetone:ether "1]0\ 09 ml#[ The
solvent was slowly evaporated in air\ and the resulting
solid was washed with ethanol and dried[
Ä
ð10Ł[ The distance PdÐBr"0#\ 1[343 A\ is in the expected
range\ and selected bond lengths and angles are shown
in Table 1[ The 20P NMR spectrum of 0 shows two signals\
a doublet at 34[9 ppm integrating for 1 P and a triplet
at 009[3 ppm integrating for 0 P with 20P!20P couplings
"central and terminal# of ca[ 7 Hz[
X!ray crystallographic studies of a crystal obtained
from one of the recrystallizations of 0 "from acetone:
ether in air# surprisingly showed the presence of a _ve!
coordinate
Pd"II#
complex\
ðPd"Ph1P"CH1#1PPh
"CH1#1P"O#Ph1!P\P#1BrŁBr\ 2\ where a curious oxidation
of one terminal phosphorus of the ligand had occurred\
perhaps due to the presence of peroxides in the solvent[
The structure is shown in Fig[ 1[ Selected bond lengths
and angles are given in Table 2[ In contrast to the dis!
torted square!planar geometry in ðPd"triphos#BrŁ¦\ com!
plex 2 exhibits an arrangement of metal bonds derivable
by small distortions from a square!pyramid\ having the
four phosphorus atoms at the base with palladium
1[5[ Preparation
of
ðPd"Ph1P"CH1#1PPh"CH1#1
P"O#Ph1P\P#1BrŁBr "2#
A solution of 0 "9[0 g\ 9[01 mmol# in acetone:ether "1]0\
4 ml# was slowly evaporated to dryness in air[ Yellow
crystals of 2 formed which were suitable for X!ray
di}raction[
Ä
9[025 A below the plane and bromine at the apex[ The
degree of distortion between tetragonal pyramidal and
bipyramidal geometries can be estimated from the struc!
tural parameter t introduced by Addison et al ð11Ł[
ðtꢂ"a−b#:59^ where a and b are the maximum basal
angles between opposite atomsŁ[ For the compound
under study\ P"01#!Pd!P"11#ꢂaꢂ060[69> and P"00#!Pd!
P"10#ꢂbꢂ063[76>\ giving tꢂ9[942\ which is consistent
with the ideal value "tꢂ9# for a tetragonal pyramid[ All
four angles between the apical bond and the basal bonds
are slightly greater than 89> again indicative of tetragonal
pyramidal stereochemistry[
1[6[ Preparation of ðPd"triphos#ClŁCl "3#
A suspension of PdCl1 "9[0070 g\ 9[554 mmol# and
NaCl "9[9667 g\ 0[22 mmol# in H1O "04 ml# was heated on
a water bath "79>C# until a clear solution was obtained[
This was cooled to ambient temperature and triphos
"9[3 g\ 9[637 mmol# in CH1Cl1 "29 ml# was added drop!
wise[ The resultant solution was stirred for 0 h at ambient
temperature[ CH1Cl1 was removed in vacuo to leave a
white solid[ The solid was _ltered o}\ washed with water\
dried in vacuo and recrystallized from CH1Cl1:n!hexane\
to give colourless prisms[ Yield 57)\ m[p[ ×149>C[
Found] C\ 46[90^ H\ 3[89[ Calc[ for C23H22P2PdCl1] C\
46[20\ H\ 4[05)[ 20P"0H# NMR "CDCl2#] d 33[11 ð1P\
d\ J"PP#ꢂ8[3\ !PPh1Ł^ 098[23 "0P\ t\ ×PPh#[ nmax:cm−0
Ä
The distance Pd"0#ÐBr"0#\ "1[787 A# is quite long com!
Ä
pared to the normal bond distance of 1[34 A ð12Ł found
in analogous four!coordinate complexes\ but below the
Ä
sum of the van der Waals radii\ 2[3Ð2[5 A ð13Ł[ A similar
Ä
distance of 1[8 A for PdÐBr has been reported for dis!

275
P[ Sevillano et al[ : Polyhedron 07 "0888# 272Ð278
Fig[ 0[ ORTEP view of 0[
Table 1
square!planar Ni"II# complexes[ In the complex PdðMe3
ð03ŁaneP3ŁBr1 ð18Ł\ where a square!planar geometry is
imposed by the macrocyclic ligand\ the bromide anions
are located above and below the Pd"II# ion\ with distances
comparable to the sum of the van der Waals radii
Ä
Selected bond lengths "A# and angles "># for complex ðPd"triphos#BrŁBr
0[
PdÐP"0#
PdÐP"1#
PdÐP"2#
PdÐBr"0#
1[223"1#
1[104"1#
1[213"1#
1[3425"00#
Ä
"2[365 A#[
The square!pyramidal arrangement in 2 is very similar
to that found in other Pd"II# complexes containing
macrocyclic tetradentate phosphine ligands ð15Ł where
the metal is forced somewhat out of the plane\ creating
a slightly activated _fth coordination site[ Other _ve!
coordinate palladium complexes with di}erent ligands
have been described as intermediate between square!pyr!
amidal and trigonal!bipyramidal ð29Ł or trigonal!bipyr!
amidal around the metal centre ð20Ł[ However\ with
monophosphines\ stereochemically non!rigid pen!
tacoordinate Ni"II# complexes with bipyramidal geo!
metries are obtained ð21Ł[ This geometry is also imposed
in Ni"II# complexes of tris"1!diphenylphosphino!
ethyl#phosphine "P2P?#\ ðNi"h3!P2P?#XŁ¦ "XꢂCl\ Br\ Y#
ð22Ł[
There appear to be only a few reports of the facile
oxidation of coordinated\ chelated\ tertiary phosphine
ligands to produce dangling arm phosphine oxide groups[
For example\ Bao et al[ ð23Ł noted that for complexes of
the type ðCpCo"P+P#IŁI\ chelate ring strain plays a role\
possibly together with other factors such as light which
were not well understood[ Although chelate ring!opening
P"1#ÐPdÐP"0#
P"1#ÐPdÐP"2#
P"2#ÐPdÐP"0#
P"0#ÐPdÐBr"0#
P"1#ÐPdÐBr"0#
P"2#ÐPdÐBr"0#
72[83"7#
73[93"7#
056[82"6#
87[91"5#
066[99"5#
83[92"5#
torted square!pyramidal _ve!coordinate palladium com!
plexes\ PdL2Br1 "Lꢂ4!Me!4H!dibenzophosphole#\ by
Chui and Powell ð14Ł[ The increase in coordination
number\ from four to _ve\ results in increases in the bond
lengths for all the atoms around the metal centre\ and
the axial bond is always found to be longer[ This has also
been observed for square!pyramidal complexes con!
taining PdÐCl axial bonds\ for which PdÐCl bond dis!
tances of 1[72 A ð15Ł and even 2[096 A ð16Ł have been
reported\ compared to the normal value of 1[215 A ð12Ł[
A similar behaviour has also been observed for Ni"II#
complexes ð17Ł where the NiÐBr distance of 1[558 A in
Ä
Ä
Ä
Ä
the _ve coordinate tetragonalÐpyramidal complex\ can
be compared to the expected value of 1[317 A ð15Ł for
Ä
and
oxidation
of
the
strained
diphenyl!

P[ Sevillano et al[ : Polyhedron 07 "0888# 272Ð278
276
Fig[ 1[ ORTEP view of 2 without hydrogen atoms[
Table 2
halogenated solvents gives products with bridged coor!
dinated phosphine oxide ligands ð26Ł[
Ä
Selected bond lengths "A# and angles "># for complex
ðPd"Ph1P"CH1#1PPh"CH1#1P"O#PPh1#1BrŁBr "2#
Controlled oxidation of complex 0 with H1O1 was car!
ried out in order to investigate the mechanism by which
2 was formed[ Thus to a solution of ðPd"triphos#BrŁBr in
acetone:ether\ H1O1 "29)# was added and the reaction
mixture left for 2 days[ The 20P "0H# NMR analysis of
the reaction mixture "Fig[ 2# showed that in addition to
two peaks belonging to 0"0a\ and 0b#\ two new peaks
were present] two doublets at 22 and 53 ppm assignable
to ÐP"O#Ph1 "1a# and ÐPPh1 "1b# groups\ respectively\
and a doublet of doublets at 62[0 ppm assignable to
×PPh "1c#[ The coupling constants 2JðP"O#Ph1!
PPhŁꢂ48[3 Hz and 1JðPPh1!PPhŁꢂ06[9 Hz are consistent
with this assignment[ Thus the product can be formulated
as the tetracoordinate Pd"II# complex ðPd"Ph1
P"CH1#1PPh"CH1#1P"O#Ph1!P\P#1ŁðPdBr3Ł\ 1[ After wash!
ing the above product with ethanol\ the peaks due to 0
disappeared to give complex 1 only[ This was con_rmed
by 20P "0H# NMR as well as elemental analysis[
PdÐP"00#
PdÐP"10#
PdÐP"01#
PdÐP"11#
PdÐBr"0#
1[296"3#
1[217"3#
1[222"3#
1[234"3#
1[787"1#
P"00#ÐPdÐP"10#
P"00#ÐPdÐP"01#
P"10#ÐPdÐP"01#
P"00#ÐPdÐP"11#
P"10#ÐPdÐP"11#
P"01#ÐPdÐP"11#
P"00#ÐPdÐBr"0#
P"10#ÐPdÐBr"0#
P"01#ÐPdÐBr"0#
P"11#ÐPdÐBr"0#
063[76"03#
72[23"03#
85[47"03#
84[52"03#
72[69"03#
060[69"03#
81[23"00#
81[67"09#
84[64"09#
81[41"00#
phosphinomethane "dppm# complexes ðNiX1"dppm#Ł has
been observed\ it occurs only at high temperature
"×114>C# ð24Ł[ In the reaction of Co"tripod#Cl1 "tri!
podꢂMeC"CH1PPh1#2# with O1 it was possible to detect
intermediates ð25Ł\ namely the complexes ðh1!"P\P#!tri!
pod!OŁCoCl1 with an uncoordinated phosphine oxide
group and ðh1!"P\O#!tripod!O1ŁCoCl1 with coordinated
and uncoordinated phosphine oxide[ In the case of
ðCu"dppe#ClŁ2 and Cu1"dppe#1"NO2#1\ air oxidation in
Complex 1 was also prepared by oxidation with H1O1
"29)# of ðPd"triphos#BrŁBr in the presence of one molar
equivalent of triphos[ The 20P "0H# NMR spectrum also
showed the presence of free triphos!O2 "×P"O#Ph triplet
2
at d 35[9 ppm with J"P!P#ꢂ42[1 Hz\ and\ a doublet for
the two P"O#Ph1 groups at d 24[4 ppm#[ The product was
washed with ethanol to leave complex 1 only[
Formation of complex 1 from 0 clearly involves inter!
molecular ligand transfer[ Intermolecular ligand transfer

277
P[ Sevillano et al[ : Polyhedron 07 "0888# 272Ð278
Fig[ 2[ 20P "0H# NMR spectrum for the reaction of ðPd"triphos#BrŁBr\ 0\ with H1O1 "29)#[ Assignments] 0a\ !PPh1 0b\ !PPh! of ðPd"triphos#BrŁBr^
1a "doublet#\ !P"O#PPh1\ 1b\ !PPh1 and 1c "doublet of doublets# !PPh! of ðPd"Ph1P"CH1#1PPh"CH1#1P"O#Ph1!P\P#1ŁðPdBr3Ł\ 1[
Fig[ 3[ 20P "0H# NMR spectrum of ðPd"triphos#ClŁCl\ 3\ in CDCl2 after addition of "A# 9[4 mol equiv\ and "B# 0 mol equiv of triphos[ Assignments]
3a\ !PPh1\ 3b\ !PPh! of ðPd"triphos#ClŁCl\ 3^ c\ d\ e ring!opened complex "peaks d and e broadened by exchange#\ f\ g free triphos[
has been described for palladium complexes by Salem
and Wild ð27Ł[ In order to investigate the mechanism in
the present case\ and to decide whether chelate ring!
opening is followed by oxidation of the terminal phos!
phorus ð28Ł\ or whether formation of a bridged complex
precedes oxidation of the terminal phosphorus ð23Ł\
titration of ðPd"triphos#ClŁCl\ 3\ with 9[14\ 9[4\ 9[64\ 0\
0[14 molar equivalents of triphos in CDCl2 was carried
out and followed by 20P!"0H# NMR spectroscopy ðFig[
3"A and B#Ł[ In the presence of 0 mol equiv of the tri!
phosphine ligand\ there was evidence of chelate ring!
opening\ as seen from the disappearance of the peaks for
3 "3a and 3b# and the appearance of three new peaks[
The sharp peak at 36[63 ppm "c#\ can be assigned to the
central phosphorus bound to the metal\ and the two
broad peaks at d 40[45 "d# and −02[87 "e# may be due to
the terminal phosphorus atoms in fast exchange "on the
NMR timescale# between chelate ring!opened and ring
closed forms[ Thus\ the addition of one mol of triphos
seems to result in chelate ring!opening of coordinated
triphos leading to a square!planar PdP3 complex with
uncoordinated terminal phosphorus available for
oxidation[ Furthermore\ since the free ligand is com!
pletely oxidized by H1O1 under similar conditions\ a
mechanism whereby chelate ring!opening precedes oxi!
dation is the most likely[
The oxidized terminal phosphorus atoms of two tri!
phos ligands are uncoordinated in the four! and _ve!
coordinate Pd"II# complexes\ 1 and 2 respectively\ and
this provides the potential for formation of new het!
erobimetallic compounds\ for example with hard metal
ions ð39\30Ł[ Such oxidations may also improve the aque!
ous solubility of this type of complex and may lead to
interesting biological activity[

P[ Sevillano et al[ : Polyhedron 07 "0888# 272Ð278
278
ð07Ł Sheldrick GM\ Program for Crystal Structure Re_nement\ Uni!
versity of Gottingen\ Germany "0882#[
Acknowledgements
ð08Ł Zsolnai L\ ZORTEP\ A Program for the Presentation of Thermal
Ellipsoids\ University of Heidelberg\ Germany "0883#[
ð19Ł de Assis EF\ Filgueiras CAL[ Trans Met Chem 0883^08]373[
ð10Ł Housecroft CE\ Shaykh BAM\ Rheingold AC\ Haggerty BS[ Acta
Cryst 0889^C35]0437[
We thank the Xunta de Galicia "project
XUGA19892A82#\ Predoctoral Grant for P[S[#\ BBSRC
and EPSRC for their support for this work[
ð11Ł Addison AW\ Rao TN\ Reedijk J\ van Rijn J\ Verschoor GC[ J
Chem Soc\ Dalton Trans 0873^0238[
ð12Ł Orpen AG\ Braummer L\ Allen FH\ Kennard O\ Watson DG\
Taylor R[ J Chem Soc\ Dalton Trans 0878^S58[
ð13Ł Huheey JE[ Inorganic Chemistry] Principles of Structure and Reac!
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ð14Ł Chui KM\ Powell HM[ J Chem Soc\ Dalton Trans 0863^0768[
ð15Ł Bartsch R\ Hietkamp S\ Morton S\ Peters H\ Stelzer O[ Inorg
Chem 0872^11]2513[
ð16Ł Brauer DJ\ Gol F\ Hietkamp S\ Peters H\ Sommer H\ Stelzer O\
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