Synthesis and structural characterization of platinum and palladium complexes containing O-donor C6X2O42− ligands

\ PERGAMON

Polyhedron 07 "0888# 392Ð301

Synthesis and structural characterization of platinum and palladium complexes containing O!donor C5X1O1− ligands 3 Jose Mar(a Casas\ Larry R[ Falvello\ Juan Fornies\ Gabriel Mansilla\ Antonio Mart(n Departamento de Qu(mica Inorganica\ Instituto de Ciencia de Materiales de Aragon[ Universidad de Zaragoza!C[S[I[C[ 49998\ Zaragoza\ Spain Received 11 June 0887^ accepted 5 August 0887

Abstract The reactions between "NBu3#1"C5X1O3# "XH\ dihydroxybenzoquinonate^ XCl\ chloranilate# and cis!ðPt"C5F4#1"THF#1Ł in 0]0 molar ratio render the mononuclear complexes ðNBu3Ł1ðPt"C5X1O3#"C5F4#1Ł "XH "0#\ Cl "1##[ If the reaction is carried out in 0]1 molar ratio the dinuclear complexes ðNBu3Ł1ðM1"m!C5X1O3#"C5F4#3Ł "MPt\ XH "2#^ MPt\ XCl "3#^ MPd\ XH "4#^ MPd\ XCl "5## are obtained[ Complexes 2Ð5 can also be prepared by reacting C5X1O1"OH#1 with the dinuclear complexes ðNBu3Ł1ðM1"m! C5F4#1"C5F4#3Ł in molar 0]0 ratio[ Cyclic voltammetry studies on 2 indicates that these complexes can be reversibly reduced[ Nevertheless\ the reduction products cannot be isolated[ The oxidation of the platinum complexes 2 and 3 with an excess of Cl1 leads to the synthesis of a mononuclear complex of Pt"IV#\ "OC!5!20#ðNBu3ŁðPtCl2"C5F4#1"H1O#Ł "6#[ The molecular structures of 2 and 6 have been determined by single!crystal X!ray di}raction[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ Keywords] Dinuclear^ Platinum^ Penta~uorphenyl^ Dihydroxybenzoquinonate^ Chloranilate

0[ Introduction Di! and polynuclear complexes of nickel\ palladium or platinum "II# with a suitable structural disposition between the metal atoms "proximity between them\ and suitable orbital orientation# and:or bridging systems cap! able of delocalizing electron density are able to reach formally higher\ lower or fractional oxidation states of the metal centres\ than are normally observed ð0\1Ł[ Several types of ligands can be used to force the proximity of the metal atoms in such a way that they can contact each other[ Our group has recently synthesised several di! and polynuclear complexes containing penta~uorophenyl and phosphide bridging ligands "C! and P! donor ligands# which react with oxidizing reagents to render mixed valence and high oxidation states complexes ð2Ð4Ł[ Benzoquinones are well known as versatile redox agents and are among the most pervasive natural prod! ucts on the earth|s surface ð5Ł[ As ligands in coordination complexes of transition metals they have the capacity to delocalize electron density undergoing intramolecular interligand ð6Ł or metal!ligand ð7Ł electron transfer reac! tions[ These features give benzoquinone complexes inter! esting redox ð8Ł and magnetic ð09Ł properties[  Corresponding author[ Tel[] 9923 865 650075^ fax] 9923 865 650076[

Dihydroxybenzoquinones have been used to prepare one! ð00Ł two! ð01Ł or three!dimensional ð02Ł coordination polymers[ These kind of compounds can be an important factor in creating not only systems with special optical\ electronic or magnetic properties\ but also an inter! calation system for ion! or molecule!exchange\ absorp! tion\ and catalytic properties[ Since dihydroxybenzoquinonates can be found in sev! eral resonant forms "see Scheme 0# several coordination modes are possible "Scheme 1#[ In the p!quinone form ðScheme 0aŁ dihydroxybenzoquinonate acts as a chelating ligand by using the 0\1! and 3\4!oxygen atoms\ and forms bridges between two metal centres ðScheme 1aŁ ð5Ł[ The o!quinone form ðScheme 0bŁ is less frequent and appears in some mononuclear complexes ðScheme 1bŁ ð02Ł"a#[ The bis"carbanion# form ðScheme 1cŁ has been found in com! plexes of metal ions with remarkable a.nity for spð2Ł! hybridised carbons\ such as Pd"II# or Pt"II# ðScheme 1cŁ ð03Ł[ Examples in which the metal centres are p!bonded to the benzoquinone ligands are also known ðScheme 1dŁ ð03Ł[ In some cases\ the dihydroxybenzoquinonate ligands can act as bridges between several metal centres dis! playing several coordination modes simultaneously "see Scheme 2# ð8Ł[ In this paper we describe the synthesis of mono! and dinuclear complexes of Pd and Pt containing dihy! droxybenzoquinonate and its derivative chloranilate "in

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 8 ! X

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Scheme 0[

1[ Experimental 1[0[ General procedures

Scheme 1[

C\ H and N analyses were performed with a PerkinÐ Elmer 139B microanalyzer[ Infrared spectra "3999Ð199 cm−0# were recorded from Nujol mulls between poly! ethylene sheets on a Perkin Elmer 722 spec! trophotometer[ NMR measurements were done either on a Varian XL199 or a Unity 299 spectrometer[ Cyclic voltammetric studies were performed using an EG+G model 162 potentiostat in conjunction with a three!elec! trode cell[ The three!electrode system consists of a plati! num disc working electrode\ a platinum wire auxiliary electrode and a saturated calomel reference electrode "SCE#[ The measurements were carried out in CH1Cl1 solutions 4×09−3 M in the test compounds and 9[0 M in ðNBu3ŁðPF5Ł as supporting electrolyte[ Under the con! ditions used\ the E> values for the couple ðFe"h4!C4H4#1Ł¦! ðFe"h4!C4H4#1Ł was 9[36 V[ Complexes cis! ðM"C5F4#1"THF#1Ł ð04Ł and ðNBu3Ł1ðM1"m!C5F4#1"C5F4#3Ł ð05Ł"c#ð06Ł "MPd\ Pt^ THFtetrahydrofuran# were prepared as described elsewhere[

Scheme 2[

1[1[ Syntheses of ðNBu3Ł1ðPt"C5X1O3#"C5F4#1Ł "XH "0#\ Cl "1##

which the hydrogen atoms have been replaced by chlor! ine# by using the complexes cis!ðM"C5F4#1"THF#1Ł and ðNBu3Ł1ðM1"m!C5F4#1"C5F4#3Ł "MPd\ Pt^ THFtetra! hydrofuran# as precursors[ The complexes cis! ðM"C5F4#1"THF#1Ł ð04Ł are excellent precursors for the preparation of complexes not accessible by other routes since the two THF groups are easily replaced by other ligands ð05Ł[ On the other hand\ the complexes ðNBu3Ł1ðM1"m!C5F4#1"C5F4#3Ł ð05Ł"c#ð06Ł have penta! ~uorophenyl groups acting as bridges between the two metal centres\ and the bridges can be replaced by ligands with acidic hydrogen atoms[ The complexes reported here have been characterized by IR and NMR spectroscopies\ and\ in two cases\ by single crystal X!ray di}raction[

To a solution of 9[19 g of C5X1O1"OH#1 "XH\ 0[32 mmol^ Cl\ 9[846 mmol# in CH1Cl1 "29 mL#\ NBu3"OH# "0M in MeOH\ XH\ 1[8 ml\ 1[75 mmol^ Cl\ 0[8 ml\ 0[80 mmol# was added\ changing the color from orange "XH# or yellow "XCl# to red[ The solution was stirred at room temperature for 4 min\ and then evaporated to dryness[ To the residue 2 ml of CH1Cl1 was added\ and then evaporated to dryness[ This operation was repeated three times\ and then 19 ml of CH1Cl1 was added[ On this solution of "NBu3#1"C5X1O3# prepared in situ cis!ðPt"C5F4#1"THF#1Ł "XH\ 9[851 g\ 0[32 mmol^ Cl\ 9[533 g\ 9[846 mmol# is added\ making the solution become darker[ After 0 h of stirring\ the solution was evaporated to dryness and the residue was treated with i PrOH rendering complexes 0 and 1 "yields] 80 and 64) respectively#[

J[M[ Casas et al[ : Polyhedron 07 "0888# 392Ð301

1[2[ Analytical and spectroscopic data 0] Anal[ found"calcd# C 40[75"41[01#\ H 5[78"5[36#\ N 1[85"1[32#[ IR data\ cm−0] C5F4 X!sensitive] ð07Ł 799"s#\ 700"s#\ C5F4 others] 845"s#\ 0959"s#\ 0387"s#^ C5H1O1− 3 ] n"CO# 0425"s#\ 0485"s#\ others] 407"m#\ 456"m#\ 630"m#\ 0133"s#\ 0247"s#\ 0271"s#\ 0393"s#^ NBu3¦773"m#[ 0H NMR data ðCDCl2\ room temperatureŁ\ ppm] C5H1O1− 3 ] 4[30 "s\ 1H#^ NBu¦ ] 9[85 "t\ 01H\ CH #\ 0[33 "m\ 7H\ a!CH 3 2 1#\ 0[51 "m\ 7H\ b!CH1#\ 2[05 "m\ 7H\ g!CH1#[ 08F NMR data ðCDCl2\ room temperatureŁ\ ppm] −019[1 "3F\ o!F\ J"Pt\F#407 Hz#\ −056[0 "3F\ m!F#\ −054[8 "1F\ p!F#[ 1] Anal[ found"calcd# C 37[71"38[07#\ H 4[24"4[83#\ N 1[27"1[18#[ IR data\ cm−0] C5F4 X!sensitive] ð07Ł 790"s#\ 701"s#\ C5F4 others] 847"s#\ 0951"s#\ 0384"s#^ C5Cl1O1− 3 ] n"CO# 0420"s#\ 0489"s#\ others] 458"m#\ 478"w#\ 592"w#\ 08 F NMR data 730"m#\ 0293"m#\ 0245"s#^ NBu¦ 3 770"m#[ ðCDCl2\ room temperatureŁ\ ppm] −007[1 "3F\ o!F\ J"Pt\F# 413 Hz#\ −056[7 "3F\ m!F#\ −056[0 "1F\ p!F#[ 1[3[ Syntheses of ðNBu3Ł1ðM1"m!C5X1O3#"C5F4#3Ł "MPt\ XH "2#^ MPt\ XCl "3#^ MPd\ XH "4#^ MPd\ XCl "5## A typical preparation "2# follows] To a solution of 9[199 g "9[095 mmol# of ðNBu3Ł1ðPt1"m!C5F4#1"C5F4#3Ł in CH1Cl1 "19 mL# 9[904 g "9[00 mmol# of C5X1O1"OH#1 was added\ changing the color of the solution from yellow to dark red[ The solution was stirred at room temperature for 0 h\ and then evaporated to dryness[ The residue was treated with iPrOH rendering complex 2 "yield] 89)#[ Analogous preparations for 3Ð5 lead to the following yields] 3\ 64)^ 4\ 65)^ 5\ 67)[ Complexes 2 and 3 have also been prepared as follows "2#] To a solution of 9[260 mmol of "NBu3#1"C5X1O3# in CH1Cl1 "19 mL#\ prepared in situ as described above\ 9[499 g "9[631 mmol# of cis!ðPt"C5F4#1"THF#1Ł was added\ changing the color of the solution from orange to dark red[ The solution was stirred at room temperature for 29 min\ and then evaporated to dryness[ The residue was treated with iPrOH giving complex 2 "yield] 80)#[ The analogous preparation for 3 yields 63)[ 2] Anal[ found"calcd# C 33[27"33[94#\ H 3[32"3[37#\ N 0[55"0[55#[ IR data\ cm−0] C5F4 X!sensitive] ð07Ł 795"s#\ 704"s#\ C5F4 others] 847"s#\ 0951"s#\ 0490"s#^ C5H1O31−] n"CO# 0425"s#\ others] 169"m#\ 498"w#\ 444"w#\ 0142"s#\ 0 0158"m#\ 0294"s#\ 0250"s#^ NBu¦ 3 771"m#[ H NMR data 1− ðCDCl2\ room temperatureŁ\ ppm] C5H1O3 ] 4[46 "s\ 1H#^ NBu¦ 3] 9[85 "t\ 01H\ CH2#\ 0[39 "m\ 7H\ a!CH1#\ 0[58 "m\ 7H\ b!CH1#\ 2[15 "m\ 7H\ g!CH1#[ 08F NMR data ðCDCl2\ room temperatureŁ\ ppm] −019[6 "7F\ o!F\ J"Pt\F# 494 Hz#\ −055[1 "7F\ m!F#\ −053[1 "3F\ p!F#[ 3] Anal[ found"calcd# C 30[73"31[63#\ H 3[30"3[04#\ N 0[59"0[59#[ IR data\ cm−0] C5F4 X!sensitive] ð07Ł 795"s#\ 705"s#\ C5F4 others] 859"s#\ 0952"s#\ 0499"s#^ C5Cl1O31−] n"CO# ¼0499"br#\ others] 146"w#\ 178"m#\ 457"m#\

394

08 591"m#\ 0142"s#\ 0250"s#^ NBu¦ F NMR data 3 779"m#[ ðCDCl2\ room temperatureŁ\ ppm] −010[0 "7F\ o!F\ J"Pt\F# 403 Hz#\ −057[8 "7F\ m!F#\ −056[0 "3F\ p!F#[ 4] Anal[ found"calcd# C 32[29"32[40#\ H 3[12"3[25#\ N 0[47"0[52#[ IR data] C5F4 X!sensitive] ð07Ł 689"s#\ 790"s#\ C5F4 others] 844"s#\ 0918"s#\ 0388"s#^ C5H1O31−] n"CO# 0418"s#\ others] 169"m#\ 176"m#\ 384"m#\ 437"w#\ 700"m#\ 0 0149"s#\ 0246"s#\ 0302"s#^ NBu¦ 3 773"m#[ H NMR data 1− ðCDCl2\ room temperatureŁ\ ppm] C5H1O3 ] 4[33 "s\ 1H#^ NBu¦ 3] 0[94 "t\ 01H\ CH2#\ 0[31 "m\ 7H\ a!CH1#\ 0[59 "m\ 7H\ b!CH1#\ 2[01 "m\ 7H\ g!CH1#[ 08F NMR data ðCDCl2\ room temperatureŁ\ ppm] −005[8 "7F\ o!F#\ −054[0 "7F\ m!F#\ −051[4 "3F\ p!F#[ 5] Anal[ found"calcd# C 33[62"33[00#\ H 3[94"3[39#\ N 0[59"0[50#[ IR data\ cm−0] C5F4 X!sensitive] ð07Ł 680"s#\ 791"s#\ C5F4 others] 846"s#\ 0948"s#\ 0388"s#^ C5Cl1O31−] n"CO# ¼0499"br#\ others] 178"m#\ 383"m#\ 461"m#\ 08 F NMR data 502"m#\ 741"s#\ 0248"s#^ NBu¦ 3 770"m#[ ðCDCl2\ room temperatureŁ\ ppm] −004[2 "7F\ o!F#\ −054[6 "7F\ m!F#\ −052[2 "3F\ p!F#[

1[4[ Synthesis of "OC!5!20#ðNBu3ŁðPtCl2"C5F4#1"H1O#Ł "6# To a solution of 9[199 g "9[003 mmol# of 3 in CH1Cl1\ "19 mL# 9[09 mL of a 1[0 N solution of Cl1 in CCl3 was added dropwise\ changing the color of the solution from dark brown to yellow[ The solution was stirred at room temperature for 04 min\ and then evaporated to dryness[ The residue is treated with iPrOH\ rendering complex 6 "yield] 59)#[ Complex 6 can also be prepared with a similar yield using 2 as starting material[ 6] Anal[ found"calcd# C 26[61"26[42#\ H 3[05"3[13#\ N 0[44"0[45#[ IR data\ cm−0] C5F4 X!sensitive] ð07Ł 685"s#\ 793"s#\ C5F4 others] 869"s#\ 0968"s#\ 0401"s#\ 0539"s#^ H1O] n"OH# 2193"br#^ n"Pt!Cl#] 189"m#\ 228"s#^ NBu¦ 3 789"m#[ 08 F NMR data ðCDCl2\ room temperatureŁ\ ppm] −009[7 "0F\ o!F\ J"Pt\Fo# 55 Hz#\ −004[5 "0F\ o!F\ J"Pt\Fo# 016 Hz#\ −007[2 "0F\ o!F\ J"Pt\F# 005 Hz#\ −019[1 "0F\ o!F\ J"Pt\Fo# 87 Hz#\ −053[8 "0F\ m!F#\ −054[1 "1F\ m!F#\ −055[0 "0F\ m!F#\ −050[1 "1F\ p!F#[ 1[5[ Preparation of crystals of 2 for X!ray structure deter! mination Suitable crystals for X!ray purposes were obtained by slow di}usion of n!hexane into a CHCl2 solution of 2 at 3>C[ 1[6[ Preparation of crystals of 6 = 0[4CH1Cl1 for X!ray structure determination Suitable crystals for X!ray purposes were obtained by slow di}usion of n!hexane into a CH1Cl1 solution of 6 at 3>C[

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1[7[ X!ray structure analysis of 2

1[8[ X!ray structure analysis of 6 = 0[4CH1Cl1

Crystal data and other details of the structure analysis are presented in Table 0[ A crystal of 2 was mounted at the end of a quartz _ber and glued in place with epoxy adhesive[ All di}raction measurements were made on an EnrafÐNonius CAD3 di}ractometer\ using graphite monochromated Mo!Ka X!radiation[ Unit cell dimen! sions were determined from 14 centered re~ections in the range 11[7³1u³20[7>[ Di}racted intensities were mea! sured in a unique quadrant of reciprocal space by v:u scans[ Three check re~ections remeasured after every 2 h[ showed ca[ 02) decomposition of the crystal over the period of data collection[ The structure was solved by direct methods and developed and re_ned in series of alternating di}erence Fourier maps and least squares analyses using all data\ with the program SHELXL!82 ð08Ł[ All non!hydrogen atoms were assigned anisotropic displacement parameters and re_ned without positional constraints[ The hydrogen atoms were constrained to idealised geometries and assigned isotropic displacement parameters of 0[1 times the Uiso value of their attached carbon "0[4 times for the methyl hydrogen atoms#[ Full! matrix least!squares re_nement of this model to F1 con! verged to _nal residual indices given in Table 0[ Final di}erence electron density maps showed three peaks  −2 "1[24\ 1[10 and 0[95^ Largest di}[ hole above 0 e A  of the platinum atoms[ −0[13# lying within 0[05 A

Crystal data and other details of the structure analysis are presented in Table 0[ A crystal of 6 = 0[4CH1Cl1 was mounted at the end of a glass _ber and held in place with a ~uorinated oil[ All di}raction measurements were made on a Siemens P3 four circle di}ractometer\ using graphite monochromated Mo!Ka X!radiation[ Unit cell dimen! sions were determined from 62 centered re~ections in the range 18[5³1u³29[9>[ Di}racted intensities were mea! sured in a unique quadrant of reciprocal space by v! scans[ Three check re~ections remeasured after every 186 ordinary re~ections showed no decay of the crystal over the period of data collection[ Lorentz and polarisation corrections were applied[ The structure was solved by direct methods and developed and re_ned in series of alternating di}erence Fourier maps and least squares analyses using all data\ with the program SHELXL!82 ð08Ł[ All non!hydrogen atoms were assigned anisotropic displacement parameters[ The hydrogen atoms were con! strained to idealised geometries and assigned isotropic displacement parameters of 0[1 times the Uiso value of their attached carbon "0[4 times for the methyl hydrogen atoms#[ One of the CH1Cl1 solvent molecules lies near a two!fold axis and is disordered over two positions with 49) occupancy each[ Full!matrix least!squares re_ne! ment of this model to F1 converged to _nal residual indi! ces given in Table 0[ Final di}erence electron density

Table 0 Crystal data and structure re_nement for complexes 2 and 6 = 0[4CH1Cl1 Complex Formula Formula weight Space group # a "A # b "A # c "A b ">#  2# V "A Z # wavelength "A temperature "K# Dcalc "Mg:m2# m "mm−0# Crystal size "mm# transmission factors absoprtion correction scan range index ranges re~ections collected independent re~ections data:restraints: parameters GOF on F1 _nal R indices ðI×1s"I#Ł R indices "all data#

2 C51H63F19N1O3Pt1 0570[30 P10:c 09[2188"6# 06[0865"01# 06[7256"09# 89[245"09# 2057[5"3# 1 9[60962 035"1# 0[651 3[406 9[39×9[29×9[14 9[157\ 9[112 C scans 3[5³1u³49> ¦h\ ¦k\ 2l 4809 4446 ðR"int# 9[9535Ł 4445:9:309 0[015 R09[9264\ wR19[9875 R09[9340\ wR19[0927

6 = 0[4CH1Cl1 C17H27Cl2F09NOPt[0[4CH1Cl1 0912[31 C1:c 16[1142"11# 03[7822"03# 12[9274"08# 012[078"4# 6706[5"01# 7 9[60962 062"1# 0[628 3[962 9[44×9[34×9[29 9[620\ 9[899 C scans 3[1³1u³49> ¦h\ ¦k\ 2l 6909 5745 ðR"int# 9[9180Ł 5744:4:341 0[931 R09[9282\ wR19[9896 R09[9455\ wR19[9884

R0S"=Fo=−=Fc=#:S=Fo=^ wR1 ðSw"Fo1−Fc1#1:Sw"Fo1#1Ł9[4^ GOF  ðSw"Fo1−Fc1#1:"nobs − nparam#Ł9[4

J[M[ Casas et al[ : Polyhedron 07 "0888# 392Ð301

 −2 "0[42 and 0[40^ largest maps showed 1 peaks above 0 e A di}[ hole −0[60# in the solvent area[ 2[ Results and discussion 2[0[ Synthesis of the mononuclear complexes ðNBu3Ł1ðPt"C5X1O3#"C5F4#1Ł "XH "0#\ Cl "1## The neutral dihydroxybenzoquinone "XH# or chro! ranilic acid "XCl# are deprotonated in situ[ To a solu! tion in CH1Cl1 of the ligand\ a methanolic solution of NBu3"OH# is added in 0]1 molar ratio[ The resulting solution turns immediately from yellow to red[ To elim! inate the H1O formed and the MeOH\ after 4 min[ of stirring\ the solvents are evaporated under vacuum[ Again\ CH1Cl1 is added to the oily residue\ thus obtaining a solution of "NBu3#1"C5X1O3# "XH\ dihy! droxybenzoquinonate^ XCl\ chloranilate#[ To this solu! tion\ cis!ðPt"C5F4#1"THF#1Ł is added in 0]0 molar ratio\ the solution turning instantaneously to dark brown[ After 4 min of stirring\ the solution is evaporated to dryness and the residue is treated with iPrOH\ rendering the dark brown solids which are identi_ed as ðNBu3Ł1ðPt"C5X1O3#"C5F4#1Ł "XH "0#\ Cl "1## "eq[0#[ The IR spectra of 0 and 1 shows intense absorptions corresponding to n"CO# at 0425 and 0485 cm−0 for 0 and 0420 and 0489 cm−0 for 1[ These values are smaller than those found for the protonated free ligands "0527\ 0510 cm−0 for dihydroxybenzoquinone and 0556\ 0520 cm−0 for the chloranilic acid# thus indicating a weakening of all the CÐO bonds of the ligand due to the coordination of the platinum centre through the oxygen atom[ The two bands found in the IR spectra of 0 and 1 in the C5F4 X!sensitive region ð07Ł indicate the mutually cis disposition of the penta~uorophenyl groups[ The 0H NMR spectrum of 0 shows\ besides the signals corresponding to the NBu3 cation\ a singlet cor! responding to the hydrogen atoms of the dihy! droxybenzoquinonate at d 3[30[ The 08F NMR spectra of 0 and 1 show only three signals\ integrating to 1]0]1\ corresponding to the ortho\ para and meta ~uorine atoms respectively\ and thus indicating the equivalence of the

396

two C5F4 groups\ and the existence of a mirror plane on the NMR time scale[ Despite the fact that the coordination mode rep! resented in Scheme 1c has been previously found in com! plexes of Pd and Pt ð03Ł\ the spectroscopic data of complexes 0 and 1 seem to indicate that their structure is the one depicted in eq[ 0[ 2[1[ Synthesis of the dinuclear complexes ðNBu3Ł1ðM1"m! C5X1O3#"C5F4#3Ł "MPt\ XH "2#^ MPt\ XCl "3#^ MPd\ XH "4#^ MPd\ XCl "5## The dinuclear complexes 2Ð5 can be prepared via two di}erent routes[ One is very similar to those used in the syntheses of complexes 0 and 1\ and involves the addition of cis!ðM"C5F4#1"THF#1Ł to a solution of "NBu3#1"C5X1O3# in CH1Cl1\ prepared in situ as described above\ in 1]0 molar ratio "eq[ 1#[ Evaporation to dryness and addition of iPrOH allow the isolation of complexes 2Ð5 as dark brown or dark purple solids[ The other way to prepare complexes 2Ð5 is through reaction of the C5X1O1"OH#1 ligands with the dinuclear complexes ðNBu3Ł1ðM1"m! C5F4#1"C5F4#3Ł in CH1Cl1\ in 0]0 molar ratio[ The intense yellow solutions of the Pt and Pd complexes become very dark upon addition of the ligand[ After some minutes\ the solvent is removed and iPrOH is added\ yielding com! plexes 2Ð5[ The deprotonation of the ligand occurs in situ and 1 equivalents of C5F4H are formed in the reaction process "eq[ 2#[ The IR spectra of complexes 2Ð5 show that the absorp! tions corresponding to the n"CO# have shifted down by ca[ 099 cm−0 with respect to the free "i[e[ not depro! tonated# ligands\ thus indicating coordination of the oxy! gen atoms to the metal centres[ In the X!sensitive region ð07Ł of the penta~uorophenyl groups two bands appear in all cases\ indicating the mutually cis disposition of these ligands[ The 0H NMR spectra of 2 and 4 show the signals corresponding to the NBu¦3 cation and one at ca[ d 4[4 corresponding to the hydrogen atoms of the dihy! droxybenzoquinonate ligand[ The 08F NMR spectra of complexes 2Ð5 are very similar\ each showing three sig! nals integrating 1]0]1\ corresponding to the ortho\ para

Equation 0

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J[M[ Casas et al[ : Polyhedron 07 "0888# 392Ð301

Equation 1[

Equation 2[

and meta ~uorine atoms respectively\ and thus indicating the equivalence of the four C5F4 groups which present AA?MM?X spin systems[ Again\ the spectroscopic data for complexes 2Ð5 indicate a planar\ symmetrical struc! ture as represented in eq[ 1 and eq[ 2[ This structure has been con_rmed in the solid state by a single crystal X!ray study of complex 2[ 2[2[ Crystal structure of ðNBu3Ł1ðPt1"m!C5H1O3#"C5F4#3Ł "2#

in agreement with the electronic structure presented in Scheme 0a "see Fig[ 1#[ There is electron de!localization through the bond sequence OÐCaÐCbÐCaÐO and\ as a consequence\ the value of the distances CaÐCb and CaÐ  \ CÐ O is intermediate between single "CÐO 0[321 A  \ C1C  # and double bonds "C1O 0[100 A C 0[425 A  # ð19Ł[ The distance CaÐCa clearly corresponds 0[215 A to a single CÐC bond\ and thus an aromatization of the ring can be discarded[ 2[3[ Electrochemical studies

The structure of the anion of complex 2 with the atom numbering scheme is shown in Fig[ 0[ Selected bond distances and angles are listed in Table 1[ The two halves of the complex are related by an inversion centre located in the centre of the six!membered ring of the dihy! droxybenzoquinonate ligand\ and thus the two platinum! atom environments are identical[ The dihy! droxybenzoquinonate ligand is planar and is coplanar with the square planar environment of the platinum atoms "dihedral angle 9[4"1#>#[ The penta~uorophenyl groups make angles of 51[9"1#> "C"0## and 42[8"1#> "C"6## with the central platinum!containing plane[ PtÐC and PtÐO distances are in the range commonly found for penta~uorophenyl complexes of platinum ð04\05Ł[ The CÐC and CÐO distances in the C5H1O3 ring are

Complex ðNBu3Ł1ðPt1"m!C5H1O3#"C5F4#3Ł "2#\ was stud! ied by cyclic voltammetry[ The experiments were carried out in CH1Cl1 employing ðNBu3ŁðPF5Ł as the supporting electrolyte\ a Pt disk electrode and a saturated calomel reference electrode "SCE#[ Complex 2 exhibits a reversible process at E0:1−9[69 V "ic:ia 0# and the value of DEp is 9[023 V\ which suggests a fast two!electron couple indi! cating the electrochemically reversible reduction[ With the available data\ it is not possible to state if the dinu! clear platinum"II# complex reduces to a structurally simi! lar dinuclear platinum"I# complex\ or if it is the ligand which reduces forming an aromatic C5X1O3− 3 entity with four phenolate oxygen atoms[ Analysis of this wave at 49\ 099 and 199 mVs−0 gives clear evidence of a di}usion!

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398

Fig[ 0[ Drawing of the crystal structure of the anion of ðNBu3Ł1ðPt1"m!C5H1O3#"C5F4#3Ł "2#\ showing the atom labelling scheme[ Non!hydrogen atoms are represented by their 49) probability ellipsoids[

Fig[ 1[ Schematic representation of the structure of the anion of ðNBu3Ł1ðPt1"m!C5H1O3#"C5F4#3Ł "2#\ showing the important interatomic distances[

controlled couple\ indicated by a constant current func! tion "ip\av−0:1#[ An additional irreversible oxidation peak at 0[34 V in the range −0[5 to 0[5 V is observed but not related reduction is seen[ The results of the cyclic voltammetry studies on 2 pro! mpted us to try the chemical reduction of complexes 2Ð 5[ We used ðNBu3ŁðBH3Ł as reducing agent[ The reaction did occur\ since we observed a fast color change in the solution when the reductor was added[ We did not how! ever succeed in isolating any of the products\ since they appeared to be very unstable\ even under inert atmo! sphere[ The reason is probably the high negative charge "−3# that these compounds would bear[ The oxidation of the platinum complexes 2 and 3 with an excess of a solution of Cl1 in CCl3 leads to the synthesis of a mononuclear complex of Pt"IV#\ "OC!5Ð20#ðNBu3Ł ðPtCl2"C5F4#1"H1O#Ł "6#[ Our attempts to determine the fate of the dihydroxybezoquinonate ligand in this reac! tion have failed\ since we could not identify any other compound from the mother liquors[ The molecule of water coordinated to the platinum centre in 6 has to come from imperfectly dried solvents used in its synthesis[ Similar oxidation attempts carried out on the palladium

complexes 4 and 5 lead to ðNBu3Ł1ðPd1"m!Cl#1Cl3Ł as the only isolable compound[ The 08F NMR spectrum of 6 shows that the two pen! ta~uorophenyl groups are inequivalent and within each group all the ~uorine atoms are di}erent[ As expected\ the magnitude of the 084PtÐF coupling constants are smal! ler than those usually found for Pt"II# complexes ð04Ł[ 2[4[ Crystal structure of the complex "OC!5Ð20# ðNBu3ŁðPtCl2"C5F4#1"H1O#Ł = 0[4CH1Cl1 "6 = 0[4CH1 Cl1# The structure of the anion of complex 6 with the atom numbering scheme is shown in Fig[ 2[ Selected bond distances and angles are listed in Table 2[ The complex anion has a slightly distorted octahedral structure\ with cis angles ranging between 75[64"5#> and 85[0"1#>[ The largest value corresponds to the angle C"0#ÐPtÐC"6#\ probably due to the steric requirements of the pen! ta~uorophenyl groups[ PtÐC ð04\ 05Ł and PtÐO ð10Ł dis! tances have the usual values for this kind of complex[ The  and 1[330"1# A ^ PtÐCl distances range between 1[206"1# A the longest distance corresponds to the chlorine trans to one of the penta~uorophenyl groups[

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Fig[ 2[ Drawing of the crystal structure of the anion of "OC!5!20#ðNBu3ŁðPtCl2"C5F4#1"H1O#Ł = 0[4CH1Cl1 "6 = 0[4CH1Cl1#\ showing the atom labelling scheme[ Non!hydrogen atoms are represented by their 49) probability ellipsoids[

Table 1  # and angles "># for ðNBu3Ł1ðPt1"m!C5H1O3#"C5F4#3Ł "2# Selected bond lengths "A Pt0C"0# Pt0O"0# O"0#0C"02# C"02#0C"04?# C"03#0C"04#

0[878"5# 1[097"3# 0[162"6# 0[268"8# 0[286"7#

C"6#0Pt0C"0# C"0#0Pt0O"1# C"0#0Pt0O"0# C"02#0O"0#0Pt O"0#0C"02#0C"04?# C"04?#0C"02#0C"03# O"1#0C"03#0C"02# C"02?#0C"04#0C"03#

89[2"1# 063[4"1# 85[4"1# 003[3"3# 013[9"4# 008[5"4# 005[9"4# 008[7"4#

Pt0C"6# Pt0O"1# O"1#0C"03# C"02#0C"03# C"04#0C"02?#

0[865"5# 1[984"3# 0[164"6# 0[410"7# 0[268"8#

C"6#0Pt0O"1# C"6#0Pt0O"0# O"1#0Pt0O"0# C"03#0O"1#0Pt O"0#0C"02#0C"03# O"1#0C"03#0C"04# C"04#0C"03#0C"02#

84[1"1# 062[1"1# 67[9"1# 004[9"3# 005[3"4# 012[4"4# 019[4"4#

Table 2  # and angles "># for "OC!5Ð20#ðNBu3ŁðPtCl2"C5F4#1"H1O#Ł = Selected bond lengths "A 0[4CH1Cl1 "6 = 0[4CH1Cl1# Pt0C"0# Pt0O Pt0Cl"1# Cl"1|# = = = H"1# C"6#0Pt0C"0# C"0#0Pt0O C"0#0Pt0Cl"0# C"6#0Pt0Cl"1# O0Pt0Cl"1# C"6#0Pt0Cl"2# O0Pt0Cl"2# Cl"1#0Pt0Cl"2# C"5#0C"0#0Pt C"01#0C"6#0Pt

1[930"5# 1[058"4# 1[224"1# 1[557 81[9"2# 89[3"1# 76[8"1# 77[5"1# 80[01"02# 80[6"1# 74[82"03# 75[64"5# 012[8"4# 011[3"4#

Pt0C"6# Pt0Cl"0# Pt0Cl"2# Cl"2|# = = = H"0# C"6#0Pt0O C"6#0Pt0Cl"0# O0Pt0Cl"0# C"0#0Pt0Cl"1# Cl"0#0Pt0Cl"1# C"0#0Pt0Cl"2# Cl"0#0Pt0Cl"2# C"1#0C"0#0Pt C"7#0C"6#0Pt

1[907"6# 1[206"1# 1[300"1# 1[073 066[6"1# 85[0"1# 73[01"02# 83[3"1# 063[64"5# 065[1"1# 89[69"5# 010[7"4# 012[0"4#

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Fig[ 3[ Drawing of the intermolecular hydrogen bonding present in the crystal structure of the anion of "OC!5Ð20#ðNBu3ŁðPtCl2"C5F4#1"H1O#Ł = 0[4CH1Cl1 "6 = 0[4CH1Cl1#[ Non!hydrogen atoms are represented by their 49) probability ellipsoids[

In the unit cell\ the anions of 6 form pairs linked by hydrogen bonds established by the hydrogen atoms of the water molecule bonded to the platinum\ and two of the chlorine atoms of the second molecule "see Fig[ 3#[  and 1[56"5# A  \ and The Cl = = = H distances are 1[07"5# A the shorter distance corresponds to a strong interaction ð11Ł[

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Acknowledgements ð00Ł

We thank the Direccion General de Ensen½anza Superior "Spain# for _nancial support "projects PB84! 9992!CO1!90 and PB84!9681#[ ð01Ł

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