Irreversible Insertion of Benzonitrile into Platinum(II)−Nitrogen Bonds of Nucleobase Complexes. Synthesis and Structural Characterization of Stable Azametallacycle Compounds

Deprotonation of 1-methylcytosine (1-MeCy) and 9-methyladenine (9-MeAd) promoted by cis-[L2Pt(μ-OH)]2(NO3)2 (L = PPh3, PMePh2, 1/2dppe) in PhCN causes the irreversible insertion of a nitrile molecule into the Pt−N4 and Pt−N6 bonds of the cytosinate and adeninate ligands, respectively, to form the stable azametallacycle complexes cis-[L2PtNHC(Ph){1-MeCy(−2H)}]NO3 (L = PPh3, 1; PMePh2, 2; 1/2dppe, 3) and cis-[L2PtNHC(Ph){9-MeAd(−2H)}]NO3 (L = PPh3, 4; PMePh2, 5) containing the deprotonated form of the molecules (Z)-9-N-(1-methyl-2-oxo-2,3-dihydropyrimidin-4(1H)-ylidene)benzimidamide and (Z)-N-(9-methyl-1H-purin-6(9H)-ylidene)benzimidamide. Single-crystal X-ray analyses of 2 and 4 show the metal coordinated to the N3 cytosine site [Pt−N3 = 2.112(7) Å̊] and to the N1 site of adenine [Pt−N1 = 2.116(6) Å̊] and to the nitrogen atom of the inserted benzonitrile [Pt−N2 = 2.043(6) and 2.010(6) Å̊ in 2 and 4, respectively], with the exocyclic nucleobase amino nitrogen bound to the carbon atom of the CN group. Complex 2, in solution, undergoes a dynamic process related to a partially restricted rotation around Pt−P bonds, arising from a steric interaction of the oxygen atom of the cytosine with one ring of the phosphine ligands. The reaction of 4 with acetylacetone (Hacac) causes the quantitative protonation of the anionic ligand, affording the acetylacetonate complex cis-[(PPh3)2Pt(acac)]NO3 and the free benzimidamide NHC(Ph){9-MeAd(−H)}. In the same experimental conditions, complex 3 reacts with Hacac only partially

Heterobimetallic Indenyl Complexes. Kinetics and Mechanism of Substitution and Exchange Reactions of <i>trans</i>-[Cr(CO)₃-indenyl-Rh(CO)₂] with Olefins

The trans coordination of the benzene ring of the indenyl-Rh(CO)2 complex with tricarbonylchromium strongly enhances the rate of substitution of CO's with bidentate olefins, 1,5-cyclooctadiene (COD) and norbornadiene (NBD) (“extra-indenyl effect”). The activation parameters suggest an associative reaction pathway assumed to proceed via the intermediacy of a nonisolable low-hapticity species, η1-indenyl-Rh(CO)2(L2). In addition, the rate of exchange of the Cr(CO)3 group of the complexes trans-[Cr(CO)3-indenyl-Rh(CO)2], 3, and trans-[Cr(CO)3-indenyl-Rh(COD)], 3a, and suitable acceptors (hexamethylbenzene and cycloheptatriene) is markedly increased with respect to that measured for the same reaction in the monometallic complex η-naphthalene-Cr(CO)3 (“extra-naphthalene effect”). These mutual effects of the Cr(CO)3 and RhL2 units are transmitted through the 10 π electron indenyl framework, and the results obtained are in agreement with the existence of an haptomeric ground-state equilibrium between the two isomers trans-[Cr(CO)3-μ,η6:η3-indenyl-RhL2], I, and trans-[Cr(CO)3-μ,η4:η5-indenyl-RhL2], II

New Methacrylate-Functionalized Ba and Ba−Ti Oxoclusters as Potential Nanosized Building Blocks for Inorganic−Organic Hybrid Materials: Synthesis and Characterization

Two different methacrylate modified barium−titanium and barium-based oxoclusters, Ba2Ti10(μ3-O)8(μ2-OH)5(μ2-OMc)20(OiPrOMe)2 (1) and [Ba(OMc)2(McOH)3]n (2), were synthesized by reacting methacrylic acid with barium−titanium and barium−zirconium double alkoxides, respectively. The X-ray structure determination of oxocluster 1 shows a core consisting of a ring of 10 titania octahedra, sharing corners, that surround the two barium oxygen decaeders which are linked by common edges to the titania octahedra and the neighboring barium decaeder. The solid-state structure of 2 consists of zigzag chains of edge-sharing {BaO9} polyhedra linked through bridging bidentate metacrylate anions, displaying different coordination mode of carboxylate groups. The presence of methacrylate groups surrounding the two polynuclear compounds has been exploited for the embedding of the oxocluster in inorganic−organic hybrid materials, and some preliminary results are presented

Heterobimetallic Indenyl Complexes. Mechanism of Cyclotrimerization of Dimethyl Acetylenedicarboxylate (DMAD) Catalyzed by <i>trans</i>-[Cr(CO)₃(Heptamethylindenyl)Rh(CO)₂ ]^†

The complex trans-[Cr(CO)3(heptamethylindenyl)Rh(CO)2] (II) is a very efficient catalyst precursor in the cyclotrimerization reaction of dimethyl acetylenedicarboxylate (DMAD) to hexacarbomethoxybenzene. The formation of the “true” catalyst, likely to be the complex trans-[Cr(CO)3−Ind*−Rh(DMAD)2], is the slow step of the reaction and takes place during the induction period, the length of which is temperature dependent. After total consumption of the monomer two organometallic complexes were isolated from the inorganic residue, viz., the catalyst precursor II and the complex trans-[Cr(CO)3−Ind*−Rh(CO)(FADE)] (III; FADE = fumaric acid dimethyl ester), which turns out to be active in the trimerization reaction as II. The hydrogenation of DMAD to FADE is probably occurring via C−H bond activation of the solvent cyclohexane

Group 10 Metal Complexes with Chelating Macrocyclic Dicarbene Ligands Bearing a 2,6-Lutidinyl Bridge: Synthesis, Reactivity, and Catalytic Activity

Palladium­(II) and platinum­(II) complexes of the title ligands have been prepared; the two carbene moieties of the ligand coordinate to the metal in <i>cis</i> fashion, while the bridging pyridyl group remains outside the metal coordination sphere but close to the metal center. In this peculiar situation, the pyridyl group can assist the oxidation of the metal center to the +IV oxidation state upon coordination to the metal in the product. Furthermore, the pyridyl group is found to promote the catalytic role of the palladium­(II) complexes in copper- and amine-free Sonogashira reactions

Group 10 Metal Complexes with Chelating Macrocyclic Dicarbene Ligands Bearing a 2,6-Lutidinyl Bridge: Synthesis, Reactivity, and Catalytic Activity

Palladium­(II) and platinum­(II) complexes of the title ligands have been prepared; the two carbene moieties of the ligand coordinate to the metal in <i>cis</i> fashion, while the bridging pyridyl group remains outside the metal coordination sphere but close to the metal center. In this peculiar situation, the pyridyl group can assist the oxidation of the metal center to the +IV oxidation state upon coordination to the metal in the product. Furthermore, the pyridyl group is found to promote the catalytic role of the palladium­(II) complexes in copper- and amine-free Sonogashira reactions

New Methacrylate-Functionalized Ba and Ba−Ti Oxoclusters as Potential Nanosized Building Blocks for Inorganic−Organic Hybrid Materials: Synthesis and Characterization

Two different methacrylate modified barium−titanium and barium-based oxoclusters, Ba2Ti10(μ3-O)8(μ2-OH)5(μ2-OMc)20(OiPrOMe)2 (1) and [Ba(OMc)2(McOH)3]n (2), were synthesized by reacting methacrylic acid with barium−titanium and barium−zirconium double alkoxides, respectively. The X-ray structure determination of oxocluster 1 shows a core consisting of a ring of 10 titania octahedra, sharing corners, that surround the two barium oxygen decaeders which are linked by common edges to the titania octahedra and the neighboring barium decaeder. The solid-state structure of 2 consists of zigzag chains of edge-sharing {BaO9} polyhedra linked through bridging bidentate metacrylate anions, displaying different coordination mode of carboxylate groups. The presence of methacrylate groups surrounding the two polynuclear compounds has been exploited for the embedding of the oxocluster in inorganic−organic hybrid materials, and some preliminary results are presented

New Methacrylate-Functionalized Ba and Ba−Ti Oxoclusters as Potential Nanosized Building Blocks for Inorganic−Organic Hybrid Materials: Synthesis and Characterization

Two different methacrylate modified barium−titanium and barium-based oxoclusters, Ba2Ti10(μ3-O)8(μ2-OH)5(μ2-OMc)20(OiPrOMe)2 (1) and [Ba(OMc)2(McOH)3]n (2), were synthesized by reacting methacrylic acid with barium−titanium and barium−zirconium double alkoxides, respectively. The X-ray structure determination of oxocluster 1 shows a core consisting of a ring of 10 titania octahedra, sharing corners, that surround the two barium oxygen decaeders which are linked by common edges to the titania octahedra and the neighboring barium decaeder. The solid-state structure of 2 consists of zigzag chains of edge-sharing {BaO9} polyhedra linked through bridging bidentate metacrylate anions, displaying different coordination mode of carboxylate groups. The presence of methacrylate groups surrounding the two polynuclear compounds has been exploited for the embedding of the oxocluster in inorganic−organic hybrid materials, and some preliminary results are presented

New Methacrylate-Functionalized Ba and Ba−Ti Oxoclusters as Potential Nanosized Building Blocks for Inorganic−Organic Hybrid Materials: Synthesis and Characterization

Two different methacrylate modified barium−titanium and barium-based oxoclusters, Ba2Ti10(μ3-O)8(μ2-OH)5(μ2-OMc)20(OiPrOMe)2 (1) and [Ba(OMc)2(McOH)3]n (2), were synthesized by reacting methacrylic acid with barium−titanium and barium−zirconium double alkoxides, respectively. The X-ray structure determination of oxocluster 1 shows a core consisting of a ring of 10 titania octahedra, sharing corners, that surround the two barium oxygen decaeders which are linked by common edges to the titania octahedra and the neighboring barium decaeder. The solid-state structure of 2 consists of zigzag chains of edge-sharing {BaO9} polyhedra linked through bridging bidentate metacrylate anions, displaying different coordination mode of carboxylate groups. The presence of methacrylate groups surrounding the two polynuclear compounds has been exploited for the embedding of the oxocluster in inorganic−organic hybrid materials, and some preliminary results are presented

Gold Fusion: From Au₂₅(SR)₁₈ to Au₃₈(SR)₂₄, the Most Unexpected Transformation of a Very Stable Nanocluster

The study of the molecular cluster Au₂₅(SR)₁₈ has provided a wealth of fundamental insights into the properties of clusters protected by thiolated ligands (SR). This is also because this cluster has been particularly stable under a number of experimental conditions. Very unexpectedly, we found that paramagnetic Au₂₅(SR)₁₈⁰ undergoes a spontaneous bimolecular fusion to form another benchmark gold nanocluster, Au₃₈(SR)₂₄. We tested this reaction with a series of Au₂₅ clusters. The fusion was confirmed and characterized by UV–vis absorption spectroscopy, ESI mass spectrometry, ¹H and ¹³C NMR spectroscopy, and electrochemistry. NMR evidences the presence of four types of ligand and, for the same proton type, double signals caused by the diastereotopicity arising from the chirality of the capping shell. This effect propagates up to the third carbon atom along the ligand chain. Electrochemistry provides a particularly convenient way to study the evolution process and determine the fusion rate constant, which decreases as the ligand length increases. No reaction is observed for the anionic clusters, whereas the radical nature of Au₂₅(SR)₁₈⁰ appears to play an important role. This transformation of a stable cluster into a larger stable cluster without addition of any co-reagent also features the bottom-up assembly of the Au₁₃ building block in solution. This very unexpected result could modify our view of the relative stability of molecular gold nanoclusters