Metallaboranes from Metal Carbonyl Compounds and Their Utilization as Catalysts for Alkyne Cyclotrimerization

Time-resolved control of nanoparticle integration in titanium-organic frameworks for enhanced catalytic performance

Among the multiple applications of metal-organic frameworks (MOFs), their use as a porous platform for the support of metallic nanoparticles stands out for the possibility of integrating a good anchorage, that improves the stability of the catalyst, with the presence of a porous network that allows the diffusion of substrates and products. Here we introduce an alternative way to control the injection of Au nanoparticles at variable stages of nucleation of a titanium(iv) MOF crystal (MUV-10). This allows the analysis of the different modes of nanoparticle integration into the porous matrix as a function of the crystal formation stage and their correlation with the catalytic performance of the resulting composite. Our results reveal a direct effect of the stage at which the Au nanoparticles are integrated into MUV-10 crystals not only on their catalytic activity for the cyclotrimerization of propargyl esters and the hydrochlorination of alkynes, but also on the selectivity and recyclability of the final solid catalyst, which are far superior than those reported for the same reactions with TiO2 supports.

Diborane(6) and Its Analogues Stabilized by Mono-, Bi-, and Trinuclear Group 7 Templates: Combined Experimental and Theoretical Studies

Irradiation of [Re₂(CO)₁₀] in the presence of BH₃·thf resulted in the formation of several rhenium diborane(6) species, for example, [{(OC)₄Re}{Re(CO)₃}₂(μ₃-η²:η²:η²-B₂H₆)(μ-H)], 1; [{(OC)₄Re}₂{Re(CO)₃}(μ₃-η²:η²:η¹-B₂H₆)(μ-H)], 2; and [{(OC)₄Re}₂(μ-η²:η²-B₂H₆)], 3, comprising diverse coordination modes of the [B₂H₆]^2- ligand. Compound 1 contains a tris(bidentate) [B₂H₆]^2- unit, whereas 2 consists of an unsymmetrically bound [μ₃-η²:η²:η¹-B₂H₆]^2- ligand. In contrast, the irradiation of [Mn₂(CO)₁₀] with BH₃·thf yielded only the Mn analogue of 1, [{(OC)₄Mn}{Mn(CO)₃}₂(μ₃-η²:η²:η²-B₂H₆)(μ-H)], 1'. In an attempt to generate the bimetallic Mn-diborane(6), we have carried out the reaction of 1' with PCy₃ under photolytic conditions. The reaction led to the formation of two single base stabilized unsymmetrical diborane(5) species, [{Mn(CO)₃}{Mn(CO)₂PCy₃}(μ-η²:η²-B₂H₅·PCy₃)(μ-H)], 4, and [{Mn(CO)₂PCy₃}(η³-B₂H₅·PCy₃)], 5. As [B₂H₆]^2- and [B₂H₅·PCy₃]^- are isoelectronic, the bondings in 4 and 5 are analogous to that of diborane(6) species 1-3. All the new species have been characterized spectroscopically, and their structures were further confirmed by single-crystal X-ray diffraction studies. DFT-type quantum chemical calculations were carried out that provided insight into the bonding interaction of [B₂H₆]^2- and [B₂H₅·PCy₃]^- with the M(CO)_n fragments.

Five-Membered Ruthenacycles: Ligand-Assisted Alkyne Insertion into 1,3-N,S-Chelated Ruthenium Borate Species

Building upon previous work, the chemistry of [(η⁶ -p-cymene)Ru{P(OMe)₂ OR}Cl₂ ], (R=H or Me) has been extended with [H₂ B(mbz)₂ ]^- (mbz=2-mercaptobenzothiazolyl) using different Ru precursors and borate ligands. As a result, a series of 1,3-N,S-chelated ruthenium borate complexes, for example, [(κ² -N,S-L)PR₃ Ru{κ³ -H,S,S'-H₂ B(L)₂ }], (2 a-d and 2 a'-d'; R=Ph, Cy, OMe or OPh and L=C₅ H₄ NS or C₇ H₄ NS₂ ) and [Ru{κ³ -H,S,S'-H₂ B(L)₂ }₂ ], (3: L=C₅ H₄ NS, 3': L=C₇ H₄ NS₂ ) were isolated upon treatment of [(η⁶ -p-cymene)RuCl₂ PR₃ ], 1 a-d (R=Ph, Cy, OMe or OPh) with [H₂ B(mp)₂ ]^- or [H₂ B(mbz)₂ ]^- ligands (mp=2-mercaptopyridyl). All the Ru borate complexes, 2 a-d and 2 a'-d' are stabilized by phosphine/phosphite and hemilabile N,S-chelating ligands. Treatment of these Ru borate species, 2 a'-c' with various terminal alkynes yielded two different types of five-membered ruthenacycle species, namely [PR₃ {C₇ H₄ S₂ -(E)-N-C=CH(R')}Ru{κ³ -H,S,S'-H₂ B(L)₂ }], (4-4'; R=Ph and R'=CO₂ Me or C₆ H₄ NO₂ ; L=C₇ H₄ NS₂ ) and [PR₃ {C₇ H₄ NS-(E)-S-C=CH(R')}Ru{κ³ -H,S,S'-H₂ B(L)₂ }], (5-5', 6 and 7; R=Ph, Cy or OMe and R'=CO₂ Me or C₆ H₄ NO₂ ; L=C₇ H₄ NS₂ ). All these five-membered ruthenacycle species contain an exocyclic C=C moiety, presumably formed by the insertion of a terminal alkyne into the Ru-N and Ru-S bonds. The new species have been characterized spectroscopically and the structures were further confirmed by single-crystal X-ray diffraction analysis. Theoretical studies and chemical-bonding analyses established that charge transfer occurs from phosphorus to ruthenium center following the trend PCy₃ <PPh₃ <P(OPh)₃ <P(OMe)₃ .

In search for new bonding modes of the methylenedithiolato ligand: novel tri- and tetra-metallic clusters

Photolysis ofarachno-[(Cp*Ru)₂(B₃H₈)(CS₂H)] in the presence of [Re₂(CO)₁₀] produced [(Cp*Ru)₂B₃H₅(CH₂S₂){Re(CO)₄}₂], with a planar 8-membered ring containing heavier transition metals and a main group element.

Mixed-metal chalcogenide tetrahedral clusters with an exo-polyhedral metal fragment

The reaction of metal carbonyl compounds with group 6 and 8 metallaboranes led us to report the synthesis and structural characterization of several novel mixed-metal chalcogenide tetrahedral clusters. Thermolysis of arachno-[(Cp*RuCO)2B2H6], 1, and [Os3(CO)12] in the presence of 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Os3(CO)9}S], 3, and [Cp*Ru(μ-H){Os3(CO)11}], 4. In a similar fashion, the reaction of [(Cp*Mo)2B5H9], 2, with [Ru3(CO)12] and 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Ru3(CO)9}S], 5, and conjuncto-[(Cp*Mo)2B5H8(μ-H){Ru3(CO)9}S], 6. Both compounds 3 and 5 can be described as 50-cve (cluster valence electron) mixed-metal chalcogenide clusters, in which a sulfur atom replaces one of the vertices of the tetrahedral core. Compounds 3 and 5 possess a [M3S] tetrahedral core, in which the sulfur is attached to an exo-metal fragment, unique in the [M3S] metal chalcogenide tetrahedral arrangements. All the compounds have been characterized by mass spectrometry, IR, and (1)H, (11)B and (13)C NMR spectroscopy in solution, and the solid state structures were unequivocally established by crystallographic analysis of compounds 3, 5 and 6.

Synthesis, characterization and crystal structure analysis of cobaltaborane and cobaltaheteroborane clusters

A novel class of cobaltaborane and cobaltaheteroborane clusters, isocloso-[(Cp*Co)₃B₆H₇Co(CO)₂], closo-[(Cp*Co)₂B₂H₅Mo₂(CO)₆I], nido-[(Cp*Co)₂B₂H₂S₂], and closo-[(Cp*Co)₂B₄H₂Br₄] were investigated (see picture).