Bifunctional Chalcogen Linkers for the Stepwise Generation of Multimetallic Assemblies and Functionalized Nanoparticles.

The disulfide ligand (SC6H4CO2H-4)2 acts as a simple but versatile linker for a range of group 8 transition metals through reaction of the oxygen donors. This leads to a range of homobimetallic ruthenium and osmium alkenyl compounds, [{M(CH═CHR)(CO)(PPh3)2(O2CC6H4S-4)}2] (M = Ru, Os; R = C6H4Me-4). Additional metal-based functionality can be added through the use of precursors incorporating rhenium bipyridine units (R = (bpy)ReCl(CO)3). The more robust diphosphine ligands in [{Ru(dppm)2(O2CC6H4S-4)}2]2+ (dppm = diphenylphosphinomethane) allow reduction of the disulfide bond with sodium borohydride to yield the thiol complex [Ru(O2CC6H4SH-4)(dppm)2]+. This complex reacts with [AuCl(PPh3)] to afford the bimetallic compound [Ru(dppm)2(O2CC6H4S-4)Au(PPh3)]+. However, an improved route to the same and related heterobimetallic compounds is provided by the reaction of cis-[RuCl2(dppm)2] with [Au(SC6H4CO2H-4)(L)] (L = PPh3, PCy3, PMe3, IDip) in the presence of base and NH4PF6 (IDip = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). The heterotrimetallic compound [Au(SC6H4CO2Ru(dppm)2)2]+ is accessible through the reaction of the homoleptic gold(I) dithiolate [Au(SC6H4CO2H-4)2]PPN (PPN = bis(triphenylphosphine)iminium) with cis-[RuCl2(dppm)2]. Without departure from the same methodology, greater complexity can be incorporated into the system to provide the penta- and heptametallic assemblies [(dppf){AuSC6H4CO2Ru(dppm)2}2]2+ and [(dppf){AuSC6H4CO2Os(CH═CH-bpyReCl(CO)3)(CO)(PPh3)2}2]. The same stepwise approach provides the dinuclear organometallic complexes [(L)Au(SC6H4CO2-4)M(CH═CHC6H4Me-4)(CO)(PPh3)2] (M = Ru, Os; L = PPh3, IDip). Complexes containing three metals from different groups of the periodic table [(L)Au(SC6H4CO2-4)M{CH═CH-bpyReCl(CO)3}(CO)(PPh3)2] (M = Ru, Os) can also be prepared, with one ruthenium example (L = PPh3) being structurally characterized. In order to illustrate the versatility of this approach, the synthesis and characterization (IR and NMR spectroscopy, TEM, EDS, and TGA) of the functionalized gold and palladium nanoparticles Au@[SC6H4CO2Ru(dppm)2]+ and Pd@[SC6H4CO2Ru(dppm)2]+ is reported.

Multimetallic complexes based on a diphosphine-dithiocarbamate "Janus" ligand.

The HCl salt of the aminodiphosphine ligand HN(CH2CH2PPh2)2 reacts with [M(CO)4(pip)2] (M = Mo, W; pip = piperidine) to yield [M{κ(2)-HN(CH2CH2PPh2)2}(CO)4]. The molybdenum analogue readily loses a carbonyl ligand to form [Mo{κ(3)-HN(CH2CH2PPh2)2}(CO)3], which was structurally characterized. The same ligand backbone is used to form the new bifunctional ligand, KS2CN(CH2CH2PPh2)2, which reacts with nickel and cobalt precursors to yield [Ni{S2CN(CH2CH2PPh2)2}2] and [Co{S2CN(CH2CH2PPh2)2}3]. Addition of [AuCl(tht)] (tht = tetrahydrothiophene) to [Ni{S2CN(CH2CH2PPh2)2}2] leads to formation of the pentametallic complex, [Ni{S2CN(CH2CH2PPh2AuCl)2}2]. In contrast, addition of [PdCl2(py)2] (py = pyridine) to [Ni{S2CN(CH2CH2PPh2)2}2] does not lead to a trimetallic complex but instead yields the transmetalated cyclic compound [Pd{S2CN(CH2CH2PPh2)2}]2, which was structurally characterized. The same product is obtained directly from [PdCl2(py)2] and KS2CN(CH2CH2PPh2)2. In contrast, the same reaction with [PtCl2(NCPh)2] yields the oligomer, [Pt{S2CN(CH2CH2PPh2)2}]n. Reaction of KS2CN(CH2CH2PPh2)2 with cis-[RuCl2(dppm)2] provides [Ru{S2CN(CH2CH2PPh2)2}(dppm)2](+), which reacts with [AuCl(tht)] to yield [Ru{S2CN(CH2CH2PPh2AuCl)2}(dppm)2](+). Addition of [M(CO)4(pip)2] (M = Mo, W) to the same precursor leads to formation of the bimetallic compounds [(dppm)2Ru{S2CN(CH2CH2PPh2)2}M(CO)4](+), while treatment with [ReCl(CO)5] yields [(dppm)2Ru{S2CN(CH2CH2PPh2)2}ReCl(CO)3](+). Reaction of KS2CN(CH2CH2PPh2)2 with [Os(CH═CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) provides [Os(CH═CHC6H4Me-4){S2CN(CH2CH2PPh2)2}(CO)(PPh3)2], but reaction with the analogous ruthenium precursor fails to yield a clean product.

Kinetico-mechanistic insights on the assembling dynamics of allyl-cornered metallacycles: the Pt-Npy bond is the keystone.

The square-like homo- and heterometallamacrocycles [{Pd(η(3) -2-Me-C3 H4 )(L(n) )2 }2 {M(dppp)}2 ](CF3 SO3 )6 (dppp=1,3-bis(diphenylphosphino)propane) and [{Pd(η(3) -2-Me-C3 H4 )(L(1) )2 }2 {M(PPh3 )2 }2 ](CF3 SO3 )6 [py=pyridine, M=Pd, Pt, L(n=) 4-PPh2 py (L(1) ), 4-C6 F4 PPh2 py (L(2) )] containing allyl corners were synthesised by antisymbiotic self-assembly of the different palladium and platinum metallic corners and the ambidentate N,P ligands. All the synthesised assemblies displayed a complex dynamic behaviour in solution, the rate of which is found to be dependent on the electronic and/or steric nature of the different building blocks. A kinetico-mechanistic study by NMR line shape analysis of the dynamics of some of these assemblies was undertaken in order to determine the corresponding thermal activation parameters. Both an enhanced thermodynamic stability and slower dynamics were observed for platinum-pyridine-containing species when compared with their palladium analogues. Time-dependent NMR spectroscopy in combination with ESI mass spectrometry was used to study the exchange between the assemblies and their building blocks, as well as that occurring between different metallamacrocycles. Preliminary studies were carried out on the activity of some of the metallamacrocyclic compounds as catalytic precursors in the allylic substitution reaction, and the results compared with that of the monometallic allylic corner [Pd(η(3) -2-Me-C3 H4 )(L(1) )2 ](+) .

Dinuclear pyridine-4-thiolate-bridged rhodium and iridium complexes as ditopic building blocks in molecular architecture.

A series of dinuclear pyridine-4-thiolate (4-Spy)-bridged rhodium and iridium compounds [M(µ-4-Spy)(diolef)]2 [diolef = 1,5-cyclooctadiene (cod), M = Rh (1), Ir (2); diolef = 2,5-norbornadiene (nbd), M = Rh (3)] were prepared by the reaction of Li(4-Spy) with the appropriate compound [M(µ-Cl)(diolef)]2 (M = Rh, Ir). The dinuclear compound [Rh(µ-4-Spy)(CO)(PPh3)]2 (4) was obtained by the reaction of [Rh(acac)(CO)(PPh3)] (acac = acetylacetonate) with 4-pySH. Compounds 1-4 were assessed as metalloligands in self-assembly reactions with the cis-blocked acceptors [M(cod)(NCCH3)2](BF4) [M = Rh (a), Ir (b)] and [M(H2O)2(dppp)](OTf)2 [M = Pd (c), Pt (d); dppp = 1,3-bis(diphenylphosphino)propane]. The homometallic hexanuclear metallomacrocycles [{M2(µ-4-Spy)2(cod)2}2{M(cod)}2](BF4)2 (M = Rh [(1a)2], Ir [(2b)2]) and the heterometallic hexanuclear metallomacrocycles [{Rh2(µ-4-Spy)2(cod)2}2{Ir(cod)}2](BF4)2 [(1b)2], [{Rh2(µ-4-Spy)2(cod)2}2{M'(dppp)}2](OTf)4 (M' = Pd [(1c)2], Pt [(1d)2]), and [{Ir2(µ-4-Spy)2(cod)2}2{M'(dppp)}2](OTf)4 (M' = Pd [(2c)2], Pt [(2d)2]) were obtained. NMR spectroscopy in combination with electrospray ionization mass spectrometry was used to elucidate the nature of the metalloligands and their respective supramolecular assemblies. Most of the synthesized species were found to be nonrigid in solution, and their fluxional behavior was studied by variable-temperature (1)H NMR spectroscopy. An X-ray diffraction study of the assemblies (1a)2 and (1d)2 revealed the formation of rectangular (9.6 Å × 6.6 Å) hexanuclear metallomacrocycles with alternating dinuclear (Rh2) and mononuclear (Rh or Pt) corners. The hexanuclear core is supported by four pyridine-4-thiolate linkers, which are bonded through the thiolate moieties to the dinuclear rhodium units, exhibiting a bent-anti arrangement, and through the peripheral pyridinic nitrogen atoms to the mononuclear corners.

A General Approach To Fabricate Fe3O4 Nanoparticles Decorated with Pd, Au, and Rh: Magnetically Recoverable and Reusable Catalysts for Suzuki C-C Cross-Coupling Reactions, Hydrogenation, and Sequential Reactions.

A facile strategy has been explored for loading noble metals onto the surface of ferrite nanoparticles with the assistance of phosphine-functionalized linkers. Palladium loading is shown to occur with participation of both the phosphine function and the surface hydroxyl groups. Hybrid nanoparticles containing simultaneously Pd and Au (or Rh) are obtained by successive loading of metals. Similarly, ferrite nanoparticles decorated with Pd, Au, and Rh have also been formed by using the same strategy. The catalytic properties of the new nanoparticles are evidenced in processes such as reduction of 4-nitrophenol or hydrogenation of styrene. Besides, the sequential process involving a cross-coupling reaction followed by reduction of 1-nitrobiphenyl has been successfully achieved by employing Pd/Au decorated nanoferrite particles.

New insights into the factors that govern the square/triangle equilibria of Pd(II) and Pt(II) supramolecules. Unexpected participation of a mononuclear species in the equilibrium.

The new rigid fluorinated ligand 4,4'-bis(4-pyridyl)octafluorobiphenyl (L1) has been synthesized by a nucleophilic substitution reaction between the organolithium derivative of the 4-bromopyridine and the compound decafluorobiphenyl. The use of L1 as building block of supramolecular species containing diphosphane or ethylenediamine Pd(II) and Pt(II) fragments has been explored, and the results have been compared with those previously reported for the smaller ligand 1,4-bis(4-pyridyl)tetrafluorobenzene (L2). The observed differences (particularly, square/triangle ratio) are discussed in terms of different parameters such as the nature of the ancillary ligands, solvent, or reaction temperature. The synthesis of water-soluble palladium metallamacrocycles derived from L1 has been attempted using ethylenediamine (en) or tetramethylethylenediamine (tmen) as ancillary ligand. Interestingly, in the latter case, the resulting solutions of the compounds showed, together with the square/triangle equilibrium, the unexpected presence of an additional lower nuclearity species, whose nature has been determined by means of bidimensional (1)H NMR experiments.

Synthesis of carbosilane dendrimers containing up to four metal layers.

Metallodendrimers are an important class of materials with valuable properties and applications in a large number of areas. Herein, we report a highly efficient route for the synthesis of carbosilane dendrimers containing multimetal layers. The procedure involves the use of heteroditopic and tritopic P,N ligands as connectors of the metal layers. The synthetic strategy is based on the ability of the latter ligands to react selectively with the metal complexes [AuCl(tht)] (tht: tetrahydrothiophene), [{RuCl(2)(p-cymene)}(2)] and [Pd(eta(3)-2-MeC(3)H(4))(cod)](OTf) (cod: 1,5-cyclooctadiene; OTf: triflate). In this way, metallodendrimers containing trimetallic Ru-Au-Pd or tetrametallic Ru-Au-Au'-Pd layers have been formed and characterized. The trimetallic dendrimer 9 can be selectively deconstructed by cleavage of the Ru-N or Au-N bonds by reaction with chloride or iodide salts, respectively.

DNA interaction and antiproliferative behavior of the water soluble platinum supramolecular squares [(en)Pt(N-N)]4(NO3)8 (en=ethylenediamine, N-N=4,4'-bipyridine or 1,4-bis(4-pyridyl)tetrafluorobenzene).

The interaction with DNA of two water soluble platinum supramolecular squares [(en)Pt(N-N)]4(NO3)8 (en=ethylenediamine, N-N=1,4-bis(4-pyridyl)tetrafluorobenzene, compound 1, N-N=4,4'-bipyridine, compound 2) has been studied by circular dichroism, electrophoretic mobility and atomic force microscopy. the two complexes drastically modify the second and tertiary structures of DNA, but compound 2 does it strongly due probably to its smaller size by comparison with compound 1 and its more suitable structural features for intercalation between base pairs. The two supramolecular squares were assayed against the HL-60 tumor cell line for 24 and 72 h. The IC50 values for 24 h are smaller than that of cisplatin for this time, however for 72 h the IC50 have higher values being the corresponding to compound 2 comparable to that of cisplatin. Apoptotic assays were also carried out for the compounds 1 and 2 against the tumor cell line.

Unprecedented eight-palladium(I) crown-cycle with metal-metal unsupported bonds.

Tri(N-pyrrolyl)phosphine reacted with the sigma/pi complex [Pd(mu-Cl)(COD-MeO)]2 to give the octa-cycle [Pd(mu-Cl)[P(pyrl)3]]8 containing four Pd(I)-Pd(I) unbridged bonds.

Synthetic strategies for the surface functionalisation of gold nanoparticles with metals and metal clusters.

The reaction of the new ditopic thiol-phosphine compound HS(CH(2))(11)OOCC(6)H(4)PPh(2) (L) with an excess of dodecanethiol-protected gold nanoparticles gave the asymmetric gold complex [CH(3)(CH(2))(11)SAuPPh(2)C(6)H(4)COO(CH(2))(11)SH] (4), but no phosphine-protected gold nanoparticles were formed. However, by blocking the phosphine function in L with metal fragments, we have been able to produce gold nanoparticles functionalised with AuCl- and cluster [Fe(2)(CO)(7)Au] units on the surface by the method of ligand-place exchange reaction.

Self-assembly reactions between the cis-protected metal corners (N-N)MII (N-N = ethylenediamine, 4,4'-substituted 2,2'-bipyridine; M = Pd, Pt) and the fluorinated edge 1,4-bis(4-pyridyl)tetrafluorobenzene.

The self-assembly reactions between the fluorinated ditopic ligand 1,4-bis(4-pyridyl)tetrafluorobenzene (A) and different nitrogen-protected palladium(II) and platinum(II) complexes have been investigated. While dynamic equilibria between molecular triangles and squares were observed when the diimine compounds 4,4'-R2bipy (bipy = 2,2'-bipyridine; R = H, Me, t-Bu) were employed as ancillary ligands, only square species were obtained from ethylenediamine (en) derivatives. Characterization of the obtained metallomacrocycles was accomplished by 1H and 19F NMR spectroscopy in combination with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR). Molecular dynamics simulations (UFF) have been performed to interpret the influence of the fluorinated ring on the square/triangle relative stability. Density functional calculations using the GIAO method have been employed for the interpretation of the chemical shift assignments. The study of the ability of these compounds to act as hosts of electron-rich aromatic guests has shown that the palladium ethylenediamine square is capable of establishing this type of intermolecular interaction exclusively in aqueous media. The host-guest stoichiometry and association constants have been determinated by 1H NMR spectroscopy.

Single and double metallic layer-containing ruthenium dendrimers. Synthesis and catalytic properties.

The reaction of a series of phosphanyl-terminated carbosilane dendrimers displaying only one phosphorus ligand per arm with [RuCl(2)(p-cymene)](2) resulted in the grafting of RuCl(p-cymene) moieties on the periphery of the dendrimer. In these species, the chloride ligand is easily displaced by the organic bases pyridine, 4-cyanopyridine and 4,4[prime or minute]-bipyridine to afford new cationic metallodendrimers. NMR studies have confirmed the chirality of the ruthenium centre. The species containing 4,4[prime or minute]-bipyridine reacts through the uncoordinated pyridyl nitrogen with a new equivalent of [RuCl(2)(p-cymene)](2) or [RhCl(CO)(2)](2) to lead to homo- or hetero-bimetallic layer-containing dendrimeric systems. The ruthenodendrimers were tested as catalysts in the transfer hydrogenation of cyclohexanone by propan-2-ol and their activity compared with that of some analogous mononuclear ruthenium(ii) complexes.

Equilibria between metallosupramolecular squares and triangles with the new rigid linker 1,4-bis(4-pyridyl)tetrafluorobenzene. Experimental and theoretical study of the structural dependence of NMR data.

The new fluorinated rigid ligand L, 1,4-bis(4-pyridyl)tetrafluorobenzene, was used in combination with different diphosphine Pd(II) and Pt(II) triflates to build metallosupramolecular assemblies. Complex equilibria between triangular and square entities were detected for all the cases. Characterization of the equilibria was accomplished by 1H, 31P(1H), 19F, and 195Pt(1H) NMR in combination with mass spectrometry. The square/triangle ratio was seen to depend on several factors, such as the nature of the metal corners, the concentration, and the solvent. The relative stability of the square and triangular complexes was explored by using force field methods. A GIAO-DFT study was carried out to analyze the changes of the 31P and 1H NMR data with the geometry of the complexes.