Synthetic methodologies for semiconductor quantum dots (QDs) have improved greatly in recent years, and for some materials, most notably CdSe, monodisperse samples of predetermined size can now be prepared with relative ease. 1 As a result, the unique electronic and luminescent properties of these particles have been studied extensively, 2 potentially paving the way for QDs to be employed in diverse technologies, such as light-emitting diodes 3 and nonradioactive biological labels. 4 However, many applications will require that the particles be arranged spatially on a surface or organized into three-dimensional materials. 5 Moreover, the ability to organize one or more types of nanoparticles into ordered structures 6 would allow for the construction of completely new types of hybrid materials with new and potentially interesting and useful properties. Unfortunately, precise control over extended structure, particularly for multicomponent materials, has remained elusive.DNA is the ideal synthon for programming the assembly of nanoscale building blocks into periodic two-and three-dimensional extended structures, and our group previously demonstrated that it can be utilized effectively to guide the construction of macroscopic network assemblies of Au nanoparticles. 7 These assemblies already have been utilized to develop an entirely new colorimetric detection scheme for DNA 7b and offer promise in other areas, including catalysis, 8 Raman spectroscopy, 9 and nanoscale electronics. 3 Importantly, the many attributes of DNA, which include ease of synthesis, extraordinary binding specificity, and virtually unlimited programmability by virtue of nucleotide sequence, can be exploited for the use of QD assembly. However, modification of QDs with DNA has proven to be much more difficult than for Au nanoparticles. Citrate-stabilized gold particles are ideally suited for direct surface substitution reactions, since the citrate-Au interaction is relatively weak. Indeed, alkylthiol functionalized DNA can be used to replace surface bound citrate to generate stable particles with surface bound oligonuleotides susceptible to hybridization with complementary oligonucleotides or particles. On the other hand, the common methods for preparing highly luminescent CdSe QDs yield materials that are coated with a mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP). As a result, these QDs are soluble only in nonpolar solvents, making them difficult to functionalize with highly charged DNA strands by direct reaction. We have overcome this difficulty and report in this communication the first successful modification of semiconductor nanoparticles with single stranded DNA, the generation of DNA-linked QD assemblies, and a preliminary account of the optical properties of these novel structures. It should be noted that others, in elegant studies, have looked at the interactions between QDs and duplex DNA, 10 but these studies do not make use of the sequence specific binding properties of DNA to direct the assembly of extended ...

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Various ruthenium silyl complexes of the type Cp*(Me3P)2RuSiR3 (Cp* = η5-C5Me5; SiR3 = SiCl3 (1), Si(NMe2)3 (2), Si(SEt)3 (3), Si(S-2-Naph)3 (4), (5), Si(SCy)2Cl (6), and Si(SMes)2Cl (7, Mes = 2,4,6-trimethylphenyl)) were prepared by the reaction of Cp*(Me3P)2RuCH2SiMe3 with the appropriate silane HSiR3. Compound 3 was converted to the triflate Cp*(Me3P)2RuSi(SEt)2OTf (8) by the reaction of 3 with Me3SiOTf. Similar reactions produced Cp*(Me3P)2RuSi(NMe2)2OTf (13), Cp*(Me3P)2RuSi(NMe2)(OTf)2 (14), Cp*(Me3P)2RuSi(SMes)2OTf (18), and Cp*(Me3P)2RuSi(SMes)(Cl)OTf (19). By NMR spectroscopy, compound 8 in dichloromethane solution appears to possess a labile triflate group. Reactions of the triflates 8 and Cp*(Me3P)2RuSi(S-p-Tol)2OTf (10) with NaBPh4 provided the silylene complexes [Cp*(Me3P)2RuSi(SR)2][BPh4] (20, R = Et; 21, R = p-Tol). Similarly, the reaction of 6 with NaBPh4 gave [Cp*(Me3P)2RuSi(SCy)2][BPh4] (22), and the reaction of 4 with B(C6F5)3 produced [Cp*(Me3P)2RuSi(S-2-Naph)2][MeB(C6F5)3] (23). Silylene complexes 20−23 display characteristic 29Si NMR shifts in the region of δ 250−270. The non-heteroatom-stabilized silylene complexes [Cp*(Me3P)2RuSiR2][B(C6F5)4] (24, R = Me; 25, R = Ph), obtained via reactions of (Et2O)LiB(C6F5)4 with Cp*(Me3P)2RuSiR2OTf (11, R = Me; 12, R = Ph) exhibit 29Si NMR shifts around δ 300. The crystal structure of 24 revealed a Ru−Si distance of 2.238(2) Å, and the Cp*(centroid)−Ru−Si−Me dihedral angle is 34°. Compound 24 reacts quantitatively with 1 equiv of PMe3 or PPh3 in dichloromethane-d 2 to form the base-stabilized silylene complexes [Cp*(Me3P)2RuSiMe2(PR3)][B(C6F5)4] (28, R = Me; 29, R = Ph), identified by 1H and 31P NMR spectroscopy. These complexes are thermally labile and decompose with elimination of the dimethylsilylene fragment to give [Cp*(Me3P)2RuPR3][B(C6F5)4] (R = Me, Ph). The ylide CH2PPh3 reacts with 24 to form [Cp*(Me3P)2RuSiMe2CH2PPh3][B(C6F5)4] (32a), and the characterization of [Cp*(Me3P)2RuSiMe2CH2PPh3][OTf] (32b) by X-ray crystallography suggests that the complex is best viewed as a ruthenium silyl derivative with the positive charge localized on the “ylide” phosphorus atom. Reactions of 20 and 24 with hydrogen proceed slowly and result in relatively complex product mixtures that contain various ruthenium hydride species. The reaction involving 20 also produced HSi(SEt)3, perhaps via redistribution of initially formed H2Si(SEt)2. For the reaction of 24 with hydrogen, no H2SiMe2 was detected in the product mixture. The reaction of 20 with H3SiSiPh3 gave [Cp*(Me3P)2Ru(H)(SiH2SiPh3)][BPh4] (35) and HSi(SEt)3, and the corresponding reaction of H3SiMes in dichloromethane gave [Cp*(Me3P)2RuHCl][BPh4] (34), BPh3, and H2SiMes(SEt), among other products. By NMR spectroscopy, the intermediate [Cp*(Me3P)2Ru(H)(SiH2Mes)][BPh4] (36) was observed for the latter process. Compound 36, generated independently by reaction of [Cp*(Me3P)2Ru(NCMe)][BPh4] with H3SiMes, was shown to react with HSi(SEt)3 to give H2SiMes(SEt).

The synthesis and characterization of neutral platinum silylene complexes (R 3 P) 2 Pt=SiMes 2 (R = i-Pr (1) or cyclohexyl (2), Mes = 2,4,6-trimethylphenyl) is reported. The dimesitylsilylene ligand in 2 is displaced by a number of ligands including phosphines, alkenes, alkynes, and O 2 . Complex 2 reacts with ROH substrates (R = H, Me, Et) to give (Cy 3 P) 2 Pt and Mes 2 Si(OR)(H) and with H 2 to give trans-(Cy 3 P) 2 Pt(H)SiHMes 2 (3). Reaction of H 2 SiMes 2 with (Cy 3 P) 2 Pt gave cis-(Cy 3 P) 2 Pt(H)SiHMes 2 (4). EXSY NMR experiments of 4 reveal that exchange of silicon and platinum hydrides occurs via reductive elimination -oxidative addition and not via a silylene intermediate.