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Inorganica Chimica Acta 300–302 (2000) 790–799

The reaction chemistry of 2- and 3-aminoalkanethiols with[PtMe3I]4: a new example of the structural diversity of metal

thiolates

Nuria Duran a, William Clegg b, Kelly A. Fraser b, Pilar Gonzalez-Duarte a,*a Departament de Quımica, Uni6ersitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona, Spain

b Department of Chemistry, Uni6ersity of Newcastle, Newcastle upon Tyne, NE1 7RU, UK

Received 2 November 1999; accepted 29 November 1999

Abstract

The reaction of substitution of iodine in [PtMe3I]4 by 2- and 3-aminoalkanethiols, at several metal to ligand ratios and variousreaction conditions in organic solvents, proceeds differently depending mainly on the aminoalkanethiol nature. The substitutionby 2-diethylaminoethanethiol has led to a partial replacement of iodine affording the complexes [(PtMe3)4(m-I){m-S(CH2)2NEt2}3]and [(PtMe3)3{m-I,m-S(CH2)2NHEt2}2]I. 1H NMR data in solution for the former complex and the X-ray structure of the lattershow that both are structurally related to the initial [PtMe3I]4 cubane. The replacement of iodine by 2-dimethylaminoethanethiolhas led to [Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2], as the only product. The X-ray structure of this complex can be described asconsisting of two Pt(IV)Me3(SCH2CH2NMe2)2 octahedra linked to a naked Pt(II) atom by means of the thiolate sulfur atoms.Consequently, a total substitution of iodine in [PtMe3I]4 together with the reduction of Pt(IV) to Pt(II) have taken place. Thereaction of [PtMe3I]4 with the cyclic 3-aminoalkanethiol HSCH(CH2CH2)2NMe and with the acyclic 3-aminoalkanethiol,HS(CH2)3NMe2, afforded the complexes Na[(PtMe3)2{m-SCH(CH2CH2)2NMe}3], [(PtMe3)2{m-SCH(CH2CH2)2NHMe}3]I2 and[(PtMe3)2{m-S(CH2)3NHMe2}3]X2 (X = I or BPh4). They all consist of face-shared bioctahedral diplatinum(IV) units of generalformula [Me3Pt(m-SR)3PtMe3]z, in which the 3-aminothiolates function as bridging ligands through their sulfur atoms. Overall, inthe case of 3-aminothiols there is a total replacement of iodine, which is accompanied by the disruption of the initial cubanestructure. © 2000 Elsevier Science S.A. All rights reserved.

Keywords: Crystal structures; Platinum complexes; Aminothiolato complexes; Thiolato complexes

1. Introduction

The renaissance of metal thiolate chemistry initiated3 decades ago [1] continues with increasing vitality. Theinterest in this family of complexes centres on two mainfeatures: the extremely rich structural diversity offeredby metal–thiolate complexes [2], and the involvementof metal–thiolate coordination in metalloproteins withboth redox and non-redox roles [3]. Although manyefforts have already been made, fundamental issues inthe inorganic and bioinorganic chemistry of metal–thi-olates are not yet totally known. Thus, common ques-

tions within well known families of compounds, such asthe stoichiometry and the structure of a new memberobtained under specific conditions, often find no defin-ite answer in the field of metal thiolates. The excep-tional versatility of thiolate–sulfur as ligand accountsfor most of the difficulties encountered when trying tomake a prediction. Remarkable examples can be foundamong thiolate complexes of transition metals, andvery particularly when they have a d10 electronicconfiguration [4–6]. In this case the lack of a strongelectronic preference for a particular coordination ge-ometry about the metal and secondary metal–sulfurinteractions increase even more the degree ofuncertainty.

Up to date, the structural characterization of metalthiolate complexes has been most successful for species

* Corresponding author. Tel.: +34-935-811 363; fax: +34-935-813 101.

E-mail address: pilar.gonzalez.duarte@uab.es (P. Gonzalez-Duarte)

0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.

PII: S 0 0 2 0 -1693 (00 )00014 -1

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of intermediate nuclearity, for which a substantial bodyof information has been obtained [2a,e]. The investiga-tion of low and very high nuclearity complexes, eithermolecular or polymeric, has proved to be more difficultbecause of the high solubility of the former and the wellknown insolubility of the latter in common solvents.Different approaches, such as the use of thiol ligandswith an additional functional group, have been fol-lowed in these cases.

Aminothiol ligands, or thiols containing an aminefunction, have offered important advantages comparedwith simple thiols. They behave as monofunctionalthiols when the amine group is protonated or quater-nized, but the solubility of their metal complexes isgenerally much greater than that of the correspondingsimple thiolate complexes. Thus, it has been possible toreport new structural types [5–8] and solution equi-libria studies [9–12] on a number of complexes withacyclic or cyclic 3-aminoalkanethiolate ligands.

Metal–thiolate complexes structurally characterizedto date include very few examples of platinum(IV)complexes. The cubane clusters [(PtMe3)4(m-SR)4], withR=Me [13] or Ph [14], are the only platinum(IV)thiolates which have been crystallographically charac-terized, apart from the mixed platinum(II)�plati-num(IV) species [(dppe)Pt(m-SMe)2PtClMe3] (dppe=Ph2PCH2CH2PPh2), which is representative of a familyof complexes with general formula [(dppe)M-(m-SMe)2PtXMe3] (M=Pd or Pt; X=Cl, Br or I) [15].In the preparation of both cubane clusters from[PtMe3]2SO4·4H2O by treatment with the correspondingthiol in basic aqueous medium a mixture of productswas observed.

As part of a continuing research programme involv-ing metal complexes of aminoalkanethiolate ligands weundertook a systematic study with Ni(II), Pd(II) andPt(II) [16–20]. As an extension of this work we carriedout a detailed study of the substitution (Eq. (1)) andaddition (Eq. (2)) reactions:

[PtMe3I]4+2- or 3-aminoalkanethiol (1)

[PtMe3I]4+ [Pt(II)(3-aminoalkanethiolate)2(dppe)] (2)

where 2-aminoalkanethiol denotes the acyclicHS(CH2)2NR2, R=Me or Et, and 3-aminoalkanethioldenotes the cyclic HSCH(CH2CH2)2NMe or the acyclicHS(CH2)3NMe2 compounds. Results corresponding tothe synthesis (Eq. (2)) and X-ray structure of[(dppe)Pt{m-SCH(CH2CH2)2NMe}2PtIMe3] togetherwith theoretical, structural and NMR studies of flux-ionality in thiolato-bridged Pt(IV)�Pt(II) complexeswere reported recently [21]. This paper reviews theresults of our studies on the substitution reaction,which proceeds very differently depending on theaminoalkanethiolate ligand, and includes new resultsobtained with 2-aminoalkanethiols. A previous report

on the substitution of iodide in [PtMe3I]4 by 3-aminoalkanethiols [22] and on the X-ray structure of[(PtMe3)3{m-I,m-S(CH2)2NHEt2}2]I [23], the first Pt(IV)thiolate complex with an incomplete cubane structure,has already been given.

When we started this work we considered that thesubstitution reaction (Eq. (1)) with 2- and 3-aminothiolligands under appropriate reaction conditions couldgive rise to [(PtMe3)4(SR)4] species structurally relatedto the initial [PtMe3I]4 complex. However, dependingon the nature of the aminothiol, other possibilitiesshould not be ignored. Thus, a partial substitution ofthe iodide triply bridging anion could lead to newcubane structures of general formula [(PtMe3)4(SR)xIy ],where x+y=4. In addition, the substitution reactioncould eventually cause the disruption of the initial[PtMe3I]4 cubane affording Pt(IV) thiolate species oflower nuclearity. These expectations of complexity havebeen realised and the reaction of [PtMe3I]4 with the 2-and 3-aminoalkanethiols indicated above gave rise tocomplexes which differ significantly in the stoichiome-try (Scheme 1) and in the structure (Scheme 2). In nocase has the substitution reaction afforded a cubanestructure with a total replacement of the iodine atomsby −SR ligands. Comparison of the complexes ob-tained provides a new example of the diversity ofmetal–thiolate chemistry and thus of the complexityinvolved when making predictions in this field ofchemistry.

2. Experimental

2.1. General remarks

The 2-aminoalkanethiol ligands as hydrochlorides:HS(CH2)2NR2·HCl, where R=Me or Et, and[PtMe3I]4 were obtained commercially. Treatment withKMeO or NaMeO in absolute methanol at the appro-priate molar ratio afforded the free aminothiol or thecorresponding thiolate salt. The synthesis of the cyclicHSCH(CH2CH2)2NMe or the linear HS(CH2)3NMe2

3-aminoalkanethiols has already been described [22].Conventionally dried and degassed solvents were usedand standard Schlenk techniques were employed. Mi-croanalyses were performed with a Carlo–Erba NA-1500 analyser. IR spectra in the range 4000–400 cm−1

were recorded from KBr discs on a Perkin–Elmer 1710spectrophotometer. Proton, 13C and 195Pt NMR spectrawere performed on a Bruker AM-400 or AC-400 spec-trometer with SiMe4 or H2PtCl6 as reference.

2.2. Synthesis of [(PtMe3)4{S(CH2)2NEt2}3I] and[(PtMe3)3{S(CH2)2NHEt2}2I2]I

[PtMe3I]4 (0.5 g, 0.34 mmol) was added to a filteredsolution containing initially HS(CH2)2NEt2·HCl (0.35

N. Duran et al. / Inorganica Chimica Acta 300–302 (2000) 790–799N. Duran et al. / Inorganica Chimica Acta 300–302 (2000) 790–799792

Scheme 1.

g, 2.04 mmol) in 15 ml of acetonitrile and NaMeO (2mmol) in 0.37 ml of absolute methanol. After three daysof stirring at room temperature (r.t.) the white solidformed was filtered off, washed with acetonitrile anddried under nitrogen atmosphere. Anal. Calc. forC30H78IN3Pt4S3: C, 24.27; N, 2.83; S, 6.47. Found: C,24.86; N, 2.85; S, 6.34%.

The mother liquor was evaporated to dryness and thesolid residue redissolved in isopropanol containing a fewdrops of acetonitrile. After some minutes a small amountof a white solid separated. Its IR spectrum was indicativeof either the hydroiodide of the ligand, [HS(CH2)2-NHEt2]I, or the corresponding disulfide, [S(CH2)2-NHEt2]2I2. The resulting yellow solution was slowlyevaporated under open atmosphere affording yellowcrystals suitable for X-ray diffraction. Anal. Calc. forC21H57I3N2Pt3S2·CH3CN: C, 19.60; H, 4.26; N, 2.98; S,4.55. Found: C, 19.53; H, 4.23; N, 2.14; S, 4.80%. Thesynthesis of the same complex was also achieved bystraightforward procedure as already described [23].

2.3. Synthesis of[Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2]

Solid [PtMe3I]4 (0.26 g, 0.18 mmol) was added to afiltered solution containing initially HS(CH2)2NMe2·

HCl (0.12 g, 0.82 mmol) in 15 ml of acetonitrile andKMeO (1.63 mmol) in absolute methanol. After threedays of stirring the initial yellow suspension became aclear yellow solution, which was filtered and evaporatedto dryness. The solid residue was extracted with acetoneand the remaining KI separated by filtration. Slowevaporation of the solution under nitrogen atmosphereafforded crystals suitable for X-ray diffraction. Both themother liquor and the crystalline solid are sensitive totraces of oxygen. Anal. Calc. for C22H58N4Pt3S4: C,23.00; H, 5.30; N, 4.86; S, 11.11. Found: C, 24.12; H,5.15; N, 4.84; S, 11.44%.

2.4. Crystal structure of[Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2]

Crystal data are in Table 1, together with otherinformation on the structure determination. Data weremeasured on a Stoe–Siemens four-circle diffractometer.Cell parameters were obtained by least-squares refine-ment based on 2u values of 31 reflections measured at9v ; intensities were measured with v/u scans andon-line profile fitting [24]. Semi-empirical absorptioncorrections were based on azimuthal scans of sets ofsymmetry-equivalent reflections [25]. The structure wasdetermined by direct methods and refined on all unique

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Scheme 2.

measured F2 values [25]. Anisotropic displacementparameters were refined for all non-hydrogen atoms,and isotropic H atoms were constrained with a ridingmodel; H atoms were not included on the metal-boundmethyl groups. Extinction effects were negligible.High displacement parameters for some atoms of theligand aminoalkyl chains indicate possible unresolveddisorder, and restraints were applied to the geometryand displacement parameters of the ligands. The lar-gest residual electron density peaks lie close to metalatoms.

Selected geometrical results are given in Table 2. Fullgeometry is available as Supplementary material (seeSection 5).

3. Results and discussion

3.1. Description of the crystal structure of[Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2]

The title compound consists of trinuclear moleculescontaining platinum atoms in two different oxidationstates, Pt(II) and Pt(IV), and with different coordina-tion environments, Fig. 1. The unit cell contains foureach of two chemically equivalent but crystallographi-cally independent molecules without significant addi-tional interactions. As depicted in Fig. 2, each moleculecan be regarded as formed by two crystallographicallyindependent octahedra, which are linked by a naked

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Table 1Crystallographic data for [Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2]

Empirical formula C22H58N4Pt3S4

1092.2Formula weightTemperature (K) 160

Mo Ka, 0.71073Radiation, wavelength (l)Crystal system monoclinic

P21/nSpace groupUnit cell dimensions

16.598(4)a (A, )8.751(2)b (A, )

c (A, ) 46.360(11)92.18(6)b (°)6729(3)V (A, 3)

Z 82.156Dcalc (g cm−3)12.709m (mm−1)0.44×0.31×0.25Crystal size (mm3)22.5; 17, 9, 49umax (°); max. indices hkl9735Reflections measured8728, 0.075Unique reflections, Rint

Transmission factors 0.07–0.16595, 790Refined parameters, restraints0.308Rw(F2) (all data)0.081R(F) (F2\2s)1.060Goodness-of-fit

Max., min. electron density (e A, −3) 3.10, −3.35

Table 2Selected bond lengths (A, ) and angles (°) for [Pt(II){Pt(IV)-Me3(SCH2CH2NMe2)2}2]

2.06(4)Pt(11)�C(117) Pt(11)�C(116) 2.06(4)Pt(11)�N(11) 2.28(3)Pt(11)�C(115) 2.08(4)Pt(11)�S(13)2.409(10) 2.483(9)Pt(11)�S(11)

2.08(4)Pt(12)�C(127) Pt(12)�C(125) 2.09(4)Pt(12)�N(12)Pt(12)�C(126) 2.31(3)2.10(4)Pt(12)�S(14)2.431(9) 2.476(9)Pt(12)�S(12)

2.319(9)Pt(13)�S(14) Pt(13)�S(13) 2.319(9)2.327(9)Pt(13)�S(12) Pt(13)�S(11) 2.335(10)

Pt(21)�C(216)2.00(5) 2.02(4)Pt(21)�C(217)2.08(4)Pt(21)�C(215) Pt(21)�N(21) 2.22(3)2.429(10)Pt(21)�S(21) Pt(21)�S(23) 2.470(9)

Pt(22)�C(225)2.08(5) 2.10(4)Pt(22)�C(227)2.11(4)Pt(22)�C(226) Pt(22)�N(22) 2.28(3)

Pt(22)�S(24)2.412(9) 2.498(10)Pt(22)�S(22)2.320(9)Pt(23)�S(21) Pt(23)�S(22) 2.320(9)2.322(10)Pt(23)�S(24) Pt(23)�S(23) 2.335(9)

C(117)�Pt(11)�C(115)C(117)�Pt(11)�C(116) 86.7(19)89(2)C(117)�Pt(11)�N(11)C(116)�Pt(11)�C(115) 174.4(15)88.8(17)C(115)�Pt(11)�N(11)95.1(16) 97.3(15)C(116)�Pt(11)�N(11)

90.8(14)C(117)�Pt(11)�S(11) C(116)�Pt(11)�S(11) 94.7(12)175.7(12)C(115)�Pt(11)�S(11) N(11)�Pt(11)�S(11) 84.9(8)

C(116)�Pt(11)�S(13)90.0(14) 174.5(12)C(117)�Pt(11)�S(13)C(115)�Pt(11)�S(13) N(11)�Pt(11)�S(13)96.5(11) 85.8(8)

C(127)�Pt(12)�C(125)80.0(3) 87.7(19)S(11)�Pt(11)�S(13)87.8(18)C(127)�Pt(12)�C(126) C(125)�Pt(12)�C(126) 86.3(17)

C(125)�Pt(12)�N(12)C(127)�Pt(12)�N(12) 95.4(16)175.9(14)C(127)�Pt(12)�S(12)95.0(16) 92.3(12)C(126)�Pt(12)�N(12)

177.9(13)C(125)�Pt(12)�S(12) C(126)�Pt(12)�S(12) 95.8(13)84.5(8)N(12)�Pt(12)�S(12) C(127)�Pt(12)�S(14) 91.5(12)

C(126)�Pt(12)�S(14)99.1(13) 174.6(12)C(125)�Pt(12)�S(14)85.4(8)N(12)�Pt(12)�S(14) S(12)�Pt(12)�S(14) 78.8(3)98.9(3)S(14)�Pt(13)�S(13) S(14)�Pt(13)�S(12) 84.2(3)

S(14)�Pt(13)�S(11)175.0(3) 173.5(4)S(13)�Pt(13)�S(12)85.0(3)S(13)�Pt(13)�S(11) S(12)�Pt(13)�S(11) 92.2(3)

Pt(13)�S(12)�Pt(12)95.0(3) 95.2(3)Pt(13)�S(11)�Pt(11)93.5(3)Pt(13)�S(13)�Pt(11) Pt(13)�S(14)�Pt(12) 94.2(3)87(2)C(217)�Pt(21)�C(216) C(217)�Pt(21)�C(215) 91(2)

C(217)�Pt(21)�N(21)88.1(16) 174.2(15)C(216)�Pt(21)�C(215)C(215)�Pt(21)�N(21)C(216)�Pt(21)�N(21) 94.0(16)95.6(19)C(216)�Pt(21)�S(21)90.2(15) 95.9(12)C(217)�Pt(21)�S(21)

175.9(11)C(215)�Pt(21)�S(21) N(21)�Pt(21)�S(21) 84.6(9)90.2(16)C(217)�Pt(21)�S(23) C(216)�Pt(21)�S(23) 174.8(14)

N(21)�Pt(21)�S(23)96.6(11) 86.4(10)C(215)�Pt(21)�S(23)S(21)�Pt(21)�S(23) C(227)�Pt(22)�C(225)79.5(3) 95(2)

C(225)�Pt(22)�C(226)87(2) 84.7(15)C(227)�Pt(22)�C(226)171.1(16)C(227)�Pt(22)�N(22) C(225)�Pt(22)�N(22) 94.0(16)94.0(16)C(226)�Pt(22)�N(22) C(227)�Pt(22)�S(22) 85.7(15)

C(226)�Pt(22)�S(22)178.1(11) 97.1(10)C(225)�Pt(22)�S(22)C(227)�Pt(22)�S(24)N(22)�Pt(22)�S(22) 91.5(15)85.4(8)C(226)�Pt(22)�S(24)98.6(11) 176.6(10)C(225)�Pt(22)�S(24)

86.6(9)N(22)�Pt(22)�S(24) S(22)�Pt(22)�S(24) 79.6(3)92.7(3)S(21)�Pt(23)�S(22) S(21)�Pt(23)�S(24) 177.9(3)

S(21)�Pt(23)�S(23)85.2(3) 84.6(3)S(22)�Pt(23)�S(24)S(24)�Pt(23)�S(23) 97.5(3)S(22)�Pt(23)�S(23) 177.3(3)Pt(23)�S(22)�Pt(22)95.5(3) 96.8(3)Pt(23)�S(21)�Pt(21)

Pt(23)�S(23)�Pt(21) Pt(23)�S(24)�Pt(22)94.0(3) 94.4(3)

Pt(II) atom. This has square planar coordination tofour sulfur atoms, each pair coming from two amino-thiolate ligands of a different octahedron. The twooctahedral units have the same coordination of Pt(IV).This consists of a fac-PtMe3 fragment and two−SCH2CH2NMe2 aminothiolate ligands in anionicform; one behaves as S-terminal and the other asS,N-chelating. Simultaneously, each sulfur atombridges to the Pt(II) atom and thus the octahedroncentred at Pt(IV) and the square plane centred at Pt(II)share a common edge.

The central core of the trinuclear molecule can beconsidered as formed by three planes, which describe azigzag chain as shown below:

Species of general formula [M3(SR)4], where M=Co(II) [26], Ni(II) [27], Pd(II) [28], and SR=2- or3-aminoalkanethiolate ligands in anionic form, show acomparable core. However, in these cases, unlike thetrinuclear Pt(IV)Pt(II)Pt(IV) complex, the three metalatoms have the same coordination geometry as a conse-quence of a common oxidation state, +2, and allligands show the same behaviour, as S,N-chelating andS-bridging.

An additional novelty of the present structure is thedifferent coordinative behaviour of the 2-dimethy-laminoethanethiolate ligand in the same complex. This

has already been observed with 3-aminoalkanethiols asin [Zn{S(CH2)3NMe2}2]8 [29], but not with 2-amino-alkanethiols. These show a great tendency to behave aschelates when the nitrogen atom of the amine

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Fig. 1. Structure of one of the two crystallographically independentcomplex molecules, with hydrogen atoms omitted for clarity. Theother molecule has an analogous atom numbering scheme.

Pt(IV)�nitrogen bond length is 2.27 A, . The octahedralcoordination of each Pt(IV) atom is distorted mainly bya small S�Pt�S angle within the Pt2S2 ring and by asmall S�Pt�N bite angle within the chelate ring, as is tobe expected.

The dihedral angles between pairs of consecutiveplanes shown in the diagram above, making up thezigzag chain of the central core of the molecules, are152.4, 152.3, 154.1, and 159.9° (these would be 180° fora completely planar Pt3S4C4 core).

3.2. Solution NMR studies of[(Pt(IV)Me3)4{S(CH2)2NEt2}3I]

Analysis of the 1H NMR spectrum of the title com-plex (Fig. 3) allows elucidation of its structure in solu-tion. The chemical shift of the different alkyl protons,the corresponding assignments, and the calculated cou-pling constants are given in Table 3.

Signals at 1.11, 1.27 and 1.48 ppm are due to themethyl groups of the PtMe3 fragment. Their relativeintensities, 1:2:1, can be explained by considering thatthe structure of the complex is the same as that of[PtMe3I]4 but with three of the iodine atoms of thecubane structure replaced by thiolate–sulfur. This isshown in Fig. 4, which also allows examination of thenature of the substituents in cis (c) and trans (t) posi-tion to each methyl group. Accordingly, there are threedifferent types of Me groups: Me(ItScSc), Me(StScIc)and Me(StScSc), with a relative intensity of 1:2:1. As aresult, the triplet signal at 1.27 ppm can be assigned toCH3�Pt(StScIc). Literature data [21,30] provide evi-dence for assigning the other two triplet signals of thesame intensity; that at 1.11 ppm to CH3�Pt(StScSc) andat 1.48 ppm to CH3�Pt(ItScSc), as Me groups having Iin trans position appear at lower fields than thosehaving S in trans position.

To obtain additional information on the structure ofthe [(Pt(IV)Me3)4{S(CH2)2NEt2}3I] complex, the signals

Fig. 2. Representation of the three units, two octahedra centred atPt(IV) linked by a naked Pt(II), which describe the structure of[Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2].

group is not either protonated or quaternized as foundin the complex cyclo-[{Pt(II)(m-SCH2CH2NMe2)Br}3],where the ligand is S-bridging and S,N-chelating [19].

Platinum(II)�sulfur distances average 2.325 A, overthe two crystallographically independent molecules, andagree well with those found in several Pt(II)–aminothi-olate complexes [18]. The Pt(II) atom in each moleculeshows distorted square-planar geometry, the S�Pt�Sangles within the Pt2S2 rings being reduced below 90°.The coordination planes, defined by the four S atoms ineach case, have root-mean-square (rms) deviations be-low 0.1 A, and the Pt(II) atoms lie no more than 0.013A, out of these planes.

Platinum(IV)–sulfur distances average 2.451 A, ; theyfall clearly into two ranges, averaging 2.420 A, for thebonds to chelating ligands and 2.482 A, for the bonds tonon-chelating ligands. These mean values and those forPt(IV)–methyl at 2.07 A, are close to the correspondingvalues found in the incomplete cubane [(PtMe3)3{m-I,m-S(CH2)2NHEt2}2]I [23] and in the cubane structures of[PtMe3(SR)]4, R=Me [13], Ph [14]. The mean

Table 3Proton chemical shift assignments and coupling constants involvingH and Pt for the complex [(PtMe3)3{m-S(CH2)2NEt2}3(m-I)]

d (ppm) a Assignment b J (Hz)

1.05(t) CH3�CH2�N 3JH�H=7.12CH3�Pt(StScSc)1.11(t) 2JPt�H=69.6CH3�Pt(StScIc)1.27(t) 2JPt�H=69.2CH3�Pt(ItScSc)1.48(t) 2JPt�H=78.7

3JH�H=7.15CH3�CH2�N2.56(q)3JH�H=7.12.73(m) N�CH2�CH2�S

N�CH2�CH2�S3.17(m) 3JPt�H=14.13JH�H=7.1

a t= triplet, q=quartet and m=multiplet.b c=cis and t= trans. See Fig. 4 for the different environment

about the platinum atoms.

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Fig. 3. 1H NMR spectrum of complex [(PtMe3)4{S(CH2)2NEt2}3I] at 300 K in CDCl3 solution. The signals at 2.17 and 1.62 ppm correspond toacetone and water, respectively.

at 2.74 and 3.165 ppm, corresponding to the protons ofthe Pt�S�CH2�CH2�N fragment, were further analysed.Thus, irradiation of the sample at 2.74 ppm shows amultiplet at 3.17 ppm, while irradiation at 3.17 ppmleads to a singlet at 2.74 ppm (Fig. 5). These data areclearly indicative that the signal at 3.17 corresponds toPt�S�CH2 protons and that at 2.74 to CH2�N.

Analysis of the multiplet signal centred at 3.17 ppm,Fig. 5(b), required calculation of the number of possibleisotopomers due to the partial magnetic activity ofplatinum nuclei. However, the ideal C3 axis in theproposed pseudo-cubane structure (Fig. 4) reduces to 4

the initial 16 isotopomers. Calculation of the relativeintensity of the signal of each isotopomer and consider-ation of the splitting caused by the magnetically activeplatinum nuclei (3JPt�H=14.1 Hz) leads to a septet ofrelative intensities 1:12:51:88:51:12:1. These featuresagree well with the multiplet at 3.17 ppm except for thetwo outermost peaks, which are unobserved (Fig. 5(b)).Consideration of the additional splitting caused by theadjacent CH2�N protons with 3JH�H=7.1 Hz wouldgive rise to a nonet signal with intensities1:14:127:204:380:204:127:14:1, which is also in goodagreement with the multiplet observed at 3.17 ppm inthe absence of irradiation at 2.74 (Fig. 5(a)).

3.3. The substitution reaction of iodine in [PtMe3I]4 by2-aminoalkanethiols

The substitution of iodine in [PtMe3I]4 by 2-aminoalkanethiol ligands, HSCH2CH2NR2 where R=Me or Et, has proceeded differently depending on thenature of the R substituents on the amine group(Scheme 1) even though the total substitution of iodineleading to [PtMe3(SR)]4 complexes has never beenachieved.

Thus, when R=Et, the complex [(PtMe3)4{S(CH2)2-NEt2}3I] was obtained for any SR to Pt(IV) molarratio greater than 1. The formula of this complex isindicative of a partial substitution of iodine in theinitial [PtMe3I]4 cubane. However, at a smaller molarratio (SR: Pt(IV)=1), the formula of the complexobtained, [(PtMe3)3{S(CH2)2NHEt2}2I2]I, was not

Fig. 4. The structure of complex [(PtMe3)4{S(CH2)2NEt2}3I] in solu-tion based on 1H NMR data. The three different types of Me groupsaccording to the nature (S or I) and disposition (cis or trans) of theother substituents bound to platinum are labeled as Me*(ItScSc),Me°(StScIc) and Me (StScSc). The alkyl carbon chains bound tosulfur atoms have been omitted for the sake of clarity.

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Fig. 5. Selected regions of the 1H NMR spectrum corresponding to the Pt�S�CH2�CH2�N fragment of the complex [(PtMe3)4{S(CH2)2NEt2}3I]:(a) signal assigned to the Pt�S�CH2 protons (Fig. 3); (b) the previous signal after irradiation of the sample at 2.74 ppm and (c) the signalcorresponding to the Pt�S�CH2�CH2�N protons recorded with irradiation at 3.17 ppm.

easily compatible with that of a cubane structure. Thislatter complex was obtained not only by direct synthe-sis but also from the mother liquor of the formercomplex after separation of part of the ligand, asdescribed in the experimental section (Section 2.2).Based on the NMR data previously described and inagreement with the stoichiometric formula it is reason-able to assume that the structure of [(PtMe3)4{S(CH2)2-NEt2}3I] is of cubane type, Scheme 2, with three sulfurand one iodine atoms occupying four alternate vertices,and the Pt(IV)Me3 groups at the other four vertices ofthe cube. The structure of the [(PtMe3)3{S(CH2)2-NHEt2}2I2]I complex has been solved by X-ray diffrac-tion [23]. The cation can be considered as a cubane typestructure, [(PtMe3)4(m-SR, m-I)2], but lacking one PtMe3

vertex and thus as an incomplete cubane. These struc-tural data show that the replacement of only two of theiodine atoms of the initial [PtMe3I]4 cubane, at a SR toPt(IV) molar ratio of 1, is concomitant with the partialfragmentation of the cubane structure.

Overall, the substitution of iodine in [PtMe3I]4 byHSCH2CH2NEt2 proceeds only partially, affordingcomplexes of formula [(PtMe3)4I(SR)3] and [(PtMe3)3-I2(SR)2], both structurally related to the initial [PtMe3I]4cubane. Our data indicate that the aminothiol to Pt(IV)molar ratio in the reaction medium determines thedegree of substitution of iodine in [PtMe3I]4 and alsothat the anionic or zwitterionic behaviour of the amino-thiol in the complexes [(PtMe3)4(m-I){m-S(CH2)2NEt2}3]

and [(PtMe3)3{m-I,m-S(CH2)2NHEt2}2]I, respectively,are both compatible with their cubane-type structure.

The results obtained in the substitution reaction (Eq.(1)) with HSCH2CH2NMe2 differ significantly fromthose with HSCH2CH2NEt2. Thus, the structure of thecomplex obtained at a SR to Pt(IV) molar ratio of1, [Pt(II){Pt(IV)Me3(m-SCH2CH2NMe2-S,N)(m-SCH2-CH2NMe2-S)}2], can be regarded as formed by twooctahedral Pt(IV)Me3S2N fragments linked to a Pt(II)atom by means of sulfur–thiolate bridges, Fig. 2. Thepresence of these Pt(IV) mononuclear units and theabsence of iodine in the final complex shows that itsreplacement in [PtMe3I]4 is accompanied by the totaldisruption of the cubane structure. Formation of Pt(II)must be due to a redox reaction between Pt(IV) and thethiolate function of the ligand, which leads to thecorresponding disulfide. Both the great tendency tobehave as chelate and the ease of oxidation even in thepresence of only traces of oxygen are main features ofthe HSCH2CH2NR2 ligands, particularly in the casewith R=Me. The high affinity of Pt(II) towards thio-late sulfur is also in good agreement with the frame-work of the central core of the trinuclearPt(IV)�Pt(II)�Pt(IV) species.

These results indicate that under our experimentalconditions the replacement of iodine in [PtMe3I]4 byHSCH2CH2NMe2 entails the complete substitutionof iodine and the total disruption of the cubane struc-ture.

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3.4. The substitution reaction of iodine in [PtMe3I]4by 3-aminoalkanethiols

The reaction of [PtMe3I]4 with the cyclicHSCH(CH2CH2)2NMe or the linear HS(CH2)3NMe2

3-aminothiols, or with the sodium salt of each of thesethiols, under various stoichiometries has given the com-plexes Na[(PtMe3)2{m-SCH(CH2CH2)2NMe}3], [(Pt-Me3)2{m-SCH(CH2CH2)2NHMe}3]I2, and [(PtMe3)2{m-S(CH2)3NHMe2}3]X2 (X=I or BPh4) [22], Scheme 1.The structures of Na[(PtMe3)2{m-SCH(CH2CH2)2-NMe}3] and [(PtMe3)2{m-S(CH2)3NHMe2}3](BPh4)2

have been established by X-ray diffraction. Both areclosely related and consist of face-shared bioctahedraldiplatinum(IV) complexes, in which the 3-aminothio-lates function as bridging ligands through their sulfuratoms, to give an octahedral coordination of Pt(IV)with a fac-PtMe3S3 configuration. Based on analyticaland multinuclear NMR data it is reasonable to assumethat the complexes [(PtMe3)2{m-SCH(CH2CH2)2-NHMe}3]I2, and [(PtMe3)2{m-S(CH2)3NHMe2}3]I2 arestructurally similar to those of known structure,Scheme 2.

The fact that various SR: Pt(IV) molar ratios anddifferent reaction conditions have always led to com-plexes of general formula [Me3Pt(m-SR)3PtMe3]z indi-cates that such dinuclear species are particularly stable.Moreover, the preference for this structural type is notaffected by the cyclic or linear nature of the carbonchain and it does not depend on whether the ligand isin anionic or zwitterionic form. However, platinum(IV)complexes consisting of confacial bioctahedra withbridging sulfur atoms were previously unreported. Incontrast, a significant number of dinuclear platinum(II)complexes with a central Pt2S2 ring have been struc-turally characterized [18].

Overall, the substitution reaction of iodine in[PtMe3I]4 by 3-aminoalkanethiolate ligands proceedscompletely, affording only one identified product ofgeneral formula [Me3Pt(m-SR)3PtMe3]z. Our structuraldata show that this replacement leads to fragmentationof the cubane structure of the starting material.

4. Conclusions

The study of the reaction of substitution of iodine in[PtMe3I]4 by 2- and 3-aminoalkanethiols at severalmetal to ligand ratios and different reaction conditionsin organic medium shows that: (i) the substitution by2-diethylaminoethanethiol, HSR, leads to a partial re-placement of iodine and affords complexes of formula[(PtMe3)4(SR)3I] or [(PtMe3)3(SR)2I2], both structurallyrelated to the initial cubane structure; (ii) the replace-ment of iodine by 2-dimethylaminoethanethiol proceedscompletely but it is concomitant with the reduction of

Pt(IV) to Pt(II); as a result the structure of the complexobtained, [Pt(II){Pt(IV)Me3(SCH2CH2NMe2)2}2], is notrelated to that of the starting material; (iii) the reactionwith 3-aminothiol ligands, 3-dimethylaminoprop-anethiol and 4-mercapto-1-methylpiperidine, affords al-ways only one species of general formula [Me3Pt(m-SR)3PtMe3]z, which indicates a total replacement ofiodine but a fragmentation of the initial cubane.

5. Supplementary material

Complete atomic coordinates, displacement parame-ters and bond lengths and angles have been depositedat the Cambridge Crystallographic Data Centre. Copiesof this information can be obtained free of charge fromThe Director, CCDC, 12 Union Road, Cambridge,CB2 1EZ, UK (fax: +44-1223-336 033; e-mail: deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

We thank the Spanish Ministerio de Educacion yCultura (Grant PB97-0216) and the UK Engineeringand Physical Sciences Research Council for financialsupport. We also thank the Servei de RessonanciaMagnetica Nuclear, Universitat Autonoma deBarcelona, for allocating instrument time to thisresearch.

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