Cowley, AR

Hogarth, G

Knight, ER

Wilton-Ely, J

Dalton Transactions

English

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Wilton-Ely, JDET

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CREATED USING THE RSC COMMUNICATION TEMPLATE (VER. 3.1) - SEE WWW.RSC.ORG/ELECTRONICFILES FOR DETAILS ARTICLE TYPE www.rsc.org/xxxxxx  |  XXXXXXXX This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00  |  1 Bifunctional dithiocarbamates: A bridge between coordination chemistry and nanoscale materials Edward R. Knight,a Andrew R. Cowley,a Graeme Hogarth,b and James D. E. T. Wilton-Elya* Received (in XXX, XXX) Xth XXXXXXXXX 200X, Accepted Xth XXXXXXXXX 200X First published on the web Xth XXXXXXXXX 200X 5 DOI: 10.1039/b000000x A dithiocarbamate-based methodology is employed to prepare linked heteromultimetallic complexes and then further exploited in the surface functionalisation of gold nanoparticles.  10 A vast range of transition metal dithiocarbamate complexes is known1 with examples finding use in applications as diverse as materials science, medicine and agriculture. Their ability to stabilise a wide range of oxidation states and their associated metal-centred electrochemistry2 have often proved key factors in these applications. 15  While polyfunctional variants of many ligands have been use to create multimetallic systems, this approach to dithiocarbamates has rarely been exploited. Recent work to harness their versatility in the field of supramolecular design has illustrated their utility in this regard.3 Our recent contributions in this area have centred on the use of a piperazine 20 dithiocarbamate that exists as a zwitterion, S2CNC4H8NH2.4 This species can be used to coordinate a first metal centre, while retaining the potential to bond to a second at the other end of the molecule on deprotonation and functionalisation with CS2. A general strategy for the synthesis of homo- and hetero-bimetallic complexes using a piperazine dithiocarbamate ligand 25 is shown in Scheme 1.  Scheme 1 General scheme for generation of bimetallic complexes.   The key aspect is the accessibility of heterobimetallic systems via this 30 route. Until now, the metal units linked by such bis(dithiocarbamate) ligands1 have all been identical, producing symmetrical compounds. Treatment of [Ru(S2CNC4H8NH2)(dppm)2](BF4)2 (1)4 with carbon disulfide under basic conditions followed by addition of [PdCl2(PPh3)2] led to the formation of the complex 35 [(dppm)2Ru(S2CNC4H8NCS2)Pd(PPh3)2](BF4)2 (2) in 94% yield. The overall composition for this and the complexes discussed below was supported by multinuclear NMR and IR spectroscopy, FAB mass spectrometry and microanalysis. Single crystals suitable for X-ray diffraction were obtained of complex 2 allowing the structure determination 40 shown in Figure 1. The distorted octahedral environment of the ruthenium centre contrasts with the near perfect square planar geometry of the palladium unit. The two metals are linked by a piperazine bis(dithiocarbamate) bridge in the chair conformation.5  45 Fig. 1 Structure of [(dppm)2Ru(S2CNC4H8NCS2)Pd(PPh3)2]2+ (2).   This result illustrated the utility of the above approach to prepare heterobimetallic species but it was clear that further metals could be introduced by judicious choice of ligands. Using 1,1'-50 bis(diphenyl)phosphinoferrocene as a convenient example, it was sought to combine all three first row transition metals of groups 8-10 within the same molecule. This was achieved as shown in Scheme 2 starting from [Co(η5-C5H5)I2(CO)]. Deprotonation and treatment of [Co(η5-C5H5)(S2CNC4H8NH2)(PPh3)](PF6)2 (3) with CS2 was followed by addition 55 of [NiCl2(dppf)] to yield the heterotrimetallic [(dppf)Ni(S2CNC4H8NCS2)Co(η5-C5H5)(PPh3)](PF6)2 (4). A literature search revealed that this complex is only the second example of a non-cluster compound containing just the three metals, Fe, Co and Ni. The first was the unusual trimetallic triple-decker metallacarborane compound 60 [(η5-C9H7)Fe(Et2C2B4H4)Ni(Et2MeC3B2Et2)Co(η5-C5H5)].6 N NH2CoSSN NSSNiPh2PFePPh2FeRhRuCo NiPtOs IrPdPh3PCoIIOCCoSSPh3P(i) S2CNC4H8NH2(i) NEt3, CS2,(ii) [NiCl2(dppf)]NH4PF6(ii) PPh3++++  Scheme 2 Constructing the FeCoNi trimetallic 4.  65  Encouraged by this success, an attempt was made to prepare a heterotrimetallic complex of the same groups, but diagonally across the periodic table, incorporating the metals Fe, Rh and Pt. We recently reported a synthesis of the thiocarbamoyl compound [Rh(η2-SCNMe2)Cl2(PPh3)2].7 This complex reacts with the zwitterion S2CNC4H8NH2 to yield [Rh(η2-70 LnM1SSN NH2LnM1SSN N M1LnSSHN NH H2N NSSLnM1SSN NSSLnM1SSN N M2LnSSM2LnCS2 M1LnNEt3, CS2NEt3, CS2M1Ln2 M1Ln+ +−− 2  |  Journal Name, [year], [vol], 00–00 This journal is © The Royal Society of Chemistry [year] SCNMe2)(S2CNC4H8NH2)(PPh3)2]+ (5) by displacement of the chloride ligands. The target complex [(dppf)Pt(S2CNC4H8NCS2)Rh(η2-SCNMe2)(PPh3)2](PF6)2 (6) is obtained on treatment of 5 with NEt3, CS2 and [PtCl2(dppf)] (Scheme 3). To the best of our knowledge, compound 6 appears to be the only molecular complex containing just the three metals, 5 Fe, Rh and Pt. SSN NH2RhClClN NSSPtPh2PFePPh2FeRhRuCo NiPtOs IrPdPPh3PPh3SMe2NRhPPh3PPh3SMe2NSSRhPPh3PPh3SMe2NS2CNC4H8NH2(i) NEt3, CS2(ii) [PtCl2(dppf)]NH4PF6+ ++ +  Scheme 3 Constructing the FeRhPt trimetallic 6.  10  The generation of a metalla-dithiocarbamate of the form [LnM(S2CNC4H8NCS2)] underpins the synthetic routes described above. The application of such species to the emerging field of functionalised gold nanoparticles was then explored.8 These materials have received much attention but very few reports exist in which the surface is modified to 15 incorporate transition metal units.9 Despite the widespread use of thiols to stabilise gold colloids, dithiocarbamates were only first used very recently in this manner.10 The first report of complexed metals being tethered to the surface through dithiocarbamates appeared shortly afterwards.11  Using a modification of the Brust-Schiffrin method,12 HAuCl4 was 20 reduced by sodium borohydride in the presence of a phase transfer agent (n-tetraoctylammonium bromide, TOAB) followed by addition of the zwitterionic complex [Ru(S2CNC4H8NCS2)(dppm)2] generated in situ (Scheme 4).  25  Scheme 4 Preparation of ruthenium-functionalised nanoparticles (NP1) using the Brust-Schiffrin method.   The black nanoparticles formed (NP1) were characterised by NMR (31P, 30 1H) spectroscopy in CDCl3 and this revealed broadened resonances at chemical shift values only slightly deviating from those observed for the molecular precursor. Transmission Electron Microscopy (TEM) showed that the particles displayed an average diameter of 3.4 (± 0.3) nm (Fig. 2). Material containing nanoparticles of larger diameter were obtained by 35 displacing the outer shell of citrate-stabilised gold colloids using [Ru(S2CNC4H8NCS2)(dppm)2]. TEM measurements of this blue material (NP2) gave a diameter of 14.4 (± 2.5) nm (Fig. 2). Before analysis, the nanoparticles were washed copiously with water and warm ethanol to remove salts (TOAB, citrate etc.) and excess compound 1, respectively. 40 Complex 1 is soluble in warm ethanol and washing was continued until no further free metalla-dithiocarbamate was present (NMR spectroscopy). Both types of nanoparticles gave rise to absorptions in the UV-Visible spectra with λmax = 265, 333 nm, attributable to LMCT bands, which are also observed in [Ru(S2CNC4H8NH2)(dppm)2](BF4)2.13 Broad, less intense bands 45 were observed at 574 and 683 nm for NP1 and NP2, respectively. These were attributed to a superimposition of ruthenium-based features and the Surface Plasmon Resonance band normally found at around 520 nm. The latter is sometimes observed to be shifted away from this value, particularly in chloroform solution.14 Other contributory factors may also include the 50 surface charge on the nanoparticles and interparticle interactions (TEM of NP2 in Fig. 2). Infrared absorptions attributable to the diphosphine ligands and a clearly identifiable νC-S band at 1000 cm-1 was observed for NP1 and NP2. The presence of the surface units was also supported by EDX data. In addition to gold, phosphorus, sulfur and ruthenium were clearly present. 55 Based on the TEM measurements, the approximate number of gold atoms in NP1 is around 1600 with 550 at the surface.15 This contrasts with the substantially greater surface area of NP2 (11000 surface atoms with 145000 core gold atoms). The surface area covered by the tethered species will play an important role when examining catalytic or sensing properties. In 60 preliminary work aimed at the latter application, we were pleased to discover that the nanoparticles displayed well-behaved, reversible electrochemistry with a Ru(II)/Ru(III) couple at 0.73 V (vs. Fc/Fc+). This is a similar potential to that found in the complex [Ru(S2CNC4H8NH2)(dppm)2](BF4)2,13 and bodes well for future work 65 addressing the electrochemical sensing of anions by ruthenium dithiocarbamate systems immobilised on gold nanoparticles.   Fig.2 TEM images of nanoparticles NP1 (3.2 ± 0.3 nm, left) and NP2 (14.4 70 ± 2.5 nm, right).   In conclusion, the versatility of the approach described here has been applied to the preparation of unsymmetrical bi- and trimetallic complexes, including triads of consecutive metals in the periodic table. Furthermore, its 75 utility for the introduction of transition metals onto the surface of gold nanoparticles has also been illustrated, paving the way for facile functionalisation of these materials for applications in catalysis and sensing. The accessibility of S2CNC4H8NH2 from inexpensive piperazine in multigram quantities13 and the ready preparation of the dithiocarbamate 80 complexes, make it possible to prepare nanoparticles with a wide range of transition metal surface units in a few hours without the need for specialised chelates with thiol tethers.   This journal is © The Royal Society of Chemistry [year] Journal Name, [year], [vol], 00–00  |  3 Notes and references a Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K. Fax: +44 1865 285002; Tel: +44 1865 276374; E-mail: james.wilton-ely@chem.ox.ac.uk b Department of Chemistry, University College London, 20 Gordon St., 5 London WC1H 0AJ, U.K.  † Electronic Supplementary Information (ESI) available: Experimental, spectral data and crystallographic details. See DOI: 10.1039/b000000x/ ‡ The authors thank Prof. D. J. Watkin and Dr. A. L. Thompson for 10 assistance with crystallography and Dr. K. B. Holt (UCL) for electrochemical measurements. Merton College, Oxford, is acknowledged for a Fitzjames Research Fellowship.  1 G. Hogarth, Prog. Inorg. Chem., 2005, 53, 71-561. 15 2 A. M. Bond and R. L. Martin, Coord. Chem. Rev., 1984, 54, 23-98. 3 J. Cookson and P. D. Beer, Dalton Trans., 2007, 1459-1472. 4 J. D. E. T. Wilton-Ely, D. Solanki and G. Hogarth, Eur. J. Inorg.  Chem., 2005, 4027-4030. 5 Crystals of 2.(OEt2)(CH2Cl2)3 were grown by slow diffusion of 20  diethylether into dichloromethane. Single crystal X-ray diffraction  data were collected using an Enraf-Nonius KappaCCD diffractometer  equipped with a Cryostream N2 open-flow cooling device.16 Cell  parameters and intensity data were processed using the DENZO-SMN  package.17 The structure was solved by direct methods using SIR9218 25  and refined on F using the CRYSTALS suite.19 Crystal data.  C99H98B2Cl6F8N2OPdRuS4, M = 2239.78, triclinic, a = 13.9532(2) Å,  b = 15.4074(2) Å, c = 25.2067(4) Å, α = 102.9433(6)º, β =  92.8485(6)º, γ = 106.8897(6)º, V = 5015.09(13) Å3, T = 150(2) K,  space group P-1, Z = 2, µ(Mo-Kα) = 0.732 mm-1, Dcalcd = 1.483 g/cm3, 30  75176 reflections collected, 22434 independent (Rint = 0.044), R1 =  0.0647, wR2 = 0.0650 [I>2σ(I)]. 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Bifunctional dithiocarbamates: a bridge between coordination chemistry and nanoscale materials

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