Chelate ring-opening of Pd(II) triphos complexes:

Chelate ring-opening of Pd(II) triphos complexes:

\ PERGAMON Polyhedron 07 "0888# 272Ð278 Chelate ring!opening of Pd"II# triphos complexes] Ligand exchange\ selective phosphine oxidation\ and X!ray ...

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\ PERGAMON

Polyhedron 07 "0888# 272Ð278

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 Castin½eirasb\ M[ Esther Garc(ab\ Peter J[ Sadlera\  a b

Department of Chemistry\ University of Edinburgh\ King|s Buildings\ West Mains Road\ EH8 2JJ Edinburgh\ U[K[ Deparment of Inorganic Chemistry\ University of Santiago de Compostela\ E!04695 Santiago de Compostela\ Spain Received 1 July 0887^ accepted 3 August 0887

Abstract 20

P NMR studies show that chelate ring!opening of ðPd"triphos#ClŁ¦\ 3\ "triphosPh1P"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 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  Corresponding author[

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[ 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

9166!4276:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[ PII] S 9 1 6 6 ! 4 2 7 6 " 8 7 # 9 9 2 9 6 ! 5

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as KBr pellets "3999Ð499 cm−0# and Nujol mulls "499Ð 099 cm−0# on a Mattson Cygnus 099 spectrophotometer[ The bands are reported as vsvery strong\ sstrong\ mmedium\ wweak\ and shshoulder[ 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\ "dchemical shift in ppm^ ttriplet\ ddoublet\ dddoublet of doublets\ Jcoupling 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 S0[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 Temperature "K# Crystal system Space group # l "A # a "A # b "A # c "A a "># b "># g ">#  2# U "A Z Dc "g:cm−2# m "mm−0# F"999# Crystal size "mm# u Range "># Index ranges

C23H22Br1P2Pd Colourless 799[62 181"1# Monoclinic P10:n 9[60962 09[1725"02# 19[338"1# 05[909"2# 89[99 85[176"02# 89[99 2235[3"7# 3 0[478 2[097 0481 9[24×9[29×9[09 1[12 to 15[29 9¾h¾01 9¾k¾14 −08¾l¾08 6064 5689 "9[9329# C scans 9[866 and 9[553 Full!Matrix Least!Squares 5689:9:260 0[912 R09[9425\ wR19[0353 R09[0447\ wR19[0685 0[158 and −9[649

C57H55Br1O1P5Pd Yellow 0256[14 182"1# Monoclinic P10:n 9[60962 00[7745"6# 16[103"1# 11[473"1# 89[99 82[014"7# 89[99 6182[7"8# 3 0[134 0[419 "MoÐKa# 1673 9[24×9[14×9[09 1[01 to 11[66 −01¾h¾01 9¾k¾18 −13¾l¾9 09015 8732 "9[0913# C scans 0[999 and 9[393 Full!Matrix Least!Squares 8732:9:602 9[855 R09[9742\ wR19[0619 R09[1549\ wR19[1013 9[343 and −9[441

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#  −2# Largest di}[ peak and hole "e[A

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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\ 49[80^ H\ 3[01)[ 20P"0H# NMR] d 34[9 ð1P\ d\ 2J"P!P# 7[1 Hz\ !PPh1Ł\ 009[3 ð0P\ t\ 2J"P!P#7[1 Hz\ ×PPhŁ[ nmax:cm−0] "Pd!Br# 196 s[ m:z 613 "M¦!Br\099)#[ L] 58[5 V−0 cm1 mol−0[ 1[4[ Preparation of ðPd"Ph1P"CH1#1PPh"CH1#1 P"O#Ph1P\P#1ŁðPdBr3Ł "1# 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#48[3 Hz\ !P"O#Ph1Ł\ 53[3 ð1P\ d\ 2J"!PPh1!×PPh#06[9 Hz\ !PPh1Ł\Ł\ 62[0 ð1P\ dd\ ×PPhŁ[ nmax:cm−0] "Pd!Br# 124m\ 068 vs\ "Pd!P# 255 m\ 241 w\ "PO# 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[ 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[ 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#8[3\ !PPh1Ł^ 098[23 "0P\ t\ ×PPh#[ nmax:cm−0

274

"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[ Results and discussion 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  \ is in the expected ð10Ł[ The distance PdÐBr"0#\ 1[343 A 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  below the plane and bromine at the apex[ The 9[025 A degree of distortion between tetragonal pyramidal and bipyramidal geometries can be estimated from the struc! tural parameter t introduced by Addison et al ð11Ł[ ðt"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#a060[69> and P"00#!Pd! P"10#b063[76>\ giving t9[942\ which is consistent with the ideal value "t9# 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[  # is quite long com! The distance Pd"0#ÐBr"0#\ "1[787 A  ð12Ł found pared to the normal bond distance of 1[34 A in analogous four!coordinate complexes\ but below the  ð13Ł[ A similar sum of the van der Waals radii\ 2[3Ð2[5 A  distance of 1[8 A for PdÐBr has been reported for dis!

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Fig[ 0[ ORTEP view of 0[

Table 1  # and angles "># for complex ðPd"triphos#BrŁBr Selected bond lengths "A 0[ PdÐP"0# PdÐP"1# PdÐP"2# PdÐBr"0# P"1#ÐPdÐP"0# P"1#ÐPdÐP"2# P"2#ÐPdÐP"0# P"0#ÐPdÐBr"0# P"1#ÐPdÐBr"0# P"2#ÐPdÐBr"0#

1[223"1# 1[104"1# 1[213"1# 1[3425"00# 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 "L4!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!  ð15Ł and even 2[096 A  ð16Ł have been tances of 1[72 A  ð12Ł[ reported\ compared to the normal value of 1[215 A A similar behaviour has also been observed for Ni"II#  in complexes ð17Ł where the NiÐBr distance of 1[558 A the _ve coordinate tetragonalÐpyramidal complex\ can  ð15Ł for be compared to the expected value of 1[317 A

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  #[ "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¦ "XCl\ 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 and oxidation of the strained diphenyl!

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276

Fig[ 1[ ORTEP view of 2 without hydrogen atoms[

Table 2  # and angles Selected bond lengths "A ðPd"Ph1P"CH1#1PPh"CH1#1P"O#PPh1#1BrŁBr "2# 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#

">#

for

complex

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! podMeC"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

halogenated solvents gives products with bridged coor! dinated phosphine oxide ligands ð26Ł[ 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! PPhŁ48[3 Hz and 1JðPPh1!PPhŁ06[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[ 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 at d 35[9 ppm with 2J"P!P#42[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

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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[

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Acknowledgements We thank the Xunta de Galicia "project XUGA19892A82#\ Predoctoral Grant for P[S[#\ BBSRC and EPSRC for their support for this work[

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