Donella Rovai

Reactivity of ruthenium carbonyl carboxylates under hydroformylation conditions

Abstract Ru(CO) 2 (MeCOO) 2 (PBU 3 ) 2 , Ru 2 (CO) 4 (MeCOO) 2 (PBu 3 ) 2 , Ru 4 (CO) 8 (MeCOO) 4 (PBu 3 ) 2 , and [Ru 2 (CO) 4 (MeCOO) 2 ] n react, in the presence of CO, with molecular hydrogen, losing the carboxylato ligand while the metal is reduced to Ru(O). Evidence is given of the involvement of ruthenium hydrides in this reaction. The role of the above precursors in the catalytic cycle of the hydroformylation of olefins is discussed.

Nanoscale Assembly of Paramagnetic Organic Radicals on Au(111) Single Crystals

The successful thin-film deposition of a pyrene-substituted nitronyl nitroxide radical under controlled conditions has been demonstrated. The electronic properties, chemical environment at the interface, and morphology of the thin films have been investigated by a multitechnique approach. Spectroscopic and morphological analyses indicate a Stranski-Krastanov growth mode and weak physisorption of molecules onto the metallic surface. Electron spin resonance (ESR) spectroscopy shows that evaporation processes and deposition do not affect the paramagnetic character of the molecules. Useful concepts for the engineering of new, purely organic-based magnets, which may open the way to fruitful exploitation of organic molecular-beam deposition for assembly on solid surfaces in view of future technological applications, are presented.

Molecular Order in Buried Layers of TbPc2 Single-Molecule Magnets Detected by Torque Magnetometry

Cantilever torque magnetometry is used to elucidate the orientation of magnetic molecules in thin films. The technique allows depth-resolved investigations by intercalating a layer of anisotropic magnetic molecules in a film of its isotropic analogues. The proof-of-concept is here demonstrated with the single-molecule magnet TbPc2 evidencing also an exceptional long-range templating effect on substrates coated by the organic molecule perylene-3,4,9,10-tetracarboxylic dianhydride.

Addition of RHg+ fragments to PP bonds of heteroatomic clusters

Abstract Treatment of a dichloromethane solution of [(triphos)MP3] [triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane; M = Co, Rh] with RHgCl (R = CH3

Low-Temperature Magnetic Force Microscopy on Single Molecule Magnet-Based Microarrays

The magnetic properties of some single molecule magnets (SMM) on surfaces can be strongly modified by the molecular packing in nanometric films/aggregates or by interactions with the substrate, which affect the molecular orientation and geometry. Detailed investigations of the magnetism of thin SMM films and nanostructures are necessary for the development of spin-based molecular devices, however this task is challenged by the limited sensitivity of laboratory-based magnetometric techniques and often requires access to synchrotron light sources to perform surface sensitive X-ray magnetic circular dichroism (XMCD) investigations. Here we show that low-temperature magnetic force microscopy is an alternative powerful laboratory tool able to extract the field dependence of the magnetization and to identify areas of in-plane and perpendicular magnetic anisotropy in microarrays of the SMM terbium(III) bis-phthalocyaninato (TbPc2) neutral complex grown as nanosized films on SiO2 and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and this is in agreement with data extracted from nonlocal XMCD measurements performed on homogeneous TbPc2/PTCDA films.

Specific heat and μ+SR measurements in Gd(hfac)3NITiPr molecular magnetic chains: Indications for a chiral phase without long-range helical order

Low-temperature specific heat C(T) and zero-field muon spin resonance (μ + SR) measurements were performed in Gd(hfac) 3 NITiPr, a quasi-one-dimensional molecular magnet with competing nearest-neighbor and next-nearest-neighbor intrachain exchange interactions. The specific heat data exhibit a λ peak at T 0 =2.08 ′0.01 K that disappears upon the application of a 5 T magnetic field. Conversely, the μ + SR data do not present any anomaly at T2 K, proving the lack of divergence of the two-spin correlation function as required for usual three-dimensional long-range helical order. Moreover, no muon spin precession can be evinced from the μ + SR asimmetry curves, thus excluding the presence of a long-range-ordered magnetic lattice. These results provide indications for a low-T phase where chiral order is established in absence of long-range helical order.

Synthesis of a rhodium methylthiolate and insertion of CS2 into the Rh—SCH3 bond. Structure of the thioxanthate [(pp3)RhSC(S)SCH3] [pp3 = tris(2-(diphenylphosphino)ethyl)phosphine]

The reaction between the (pp 3 )Rh I fragment [pp 3 = tris(2-diphenylphosphino)-ethyl)phosphine, P(CH 2 CH 2 PPh 2 ) 3 ] and NaSCH 3 readily yields the methylthiolate derivative [(pp 3 )RhSCH 3 ]. The sulphur atom of this compound is attached by the electrophile CF 3 SO 3 CH 3 to yield the stable dimethylsulphide complex [(pp 3 )RhS(CH 3 ) 2 ]CF 3 SO 3 . Furthermore, the rhodium methylthiolate undergoes CS 2 insertion to form the thioxanthate [(pp 3 )RhSC(S)SCH 3 ], which has been characterized by a complete X-ray crystallographic analysis.

Crystal structure and reactivity of [(pp3)Rh(H)(SeCH3)]BPh4. An organometallic complex from metal-assisted SeH activation

The crystal structure of the hydride methylselenide derivative [(pp3)Rh(H)(SeCH3)]BPh4 [pp3 = tris(2-(diphenylphosphino)ethyl) phosphine, P(CH2CH2PPh2)3] (obtained through an intramolecular oxidative addition following initial methylation of the hydroselenide complex [(pp3)RhSeH]) has been determined through an X-ray diffraction study. The Rh atom is in an approximately octahedral environment, formed by three P atoms of the phosphine ligand and the Se atom in equatorial positions and the other P atom and the hydride ligand in apical positions. (The hydride ligand was not located in the X-ray study but there is evidence for its presence in the coordination sphere.) The compound can be readily transformed to the stable methylselenide [(pp3)Rh(SeCH3)] and dimethylselenide [(pp3)Rh{Se(CH3)2}]BPh4 derivatives.

Post-synthetic isotopic labeling of an azamacrocyclic ligand

Abstract A simple post-synthetic method for the preparation of 1,4,7-triazacyclononane-d12 (90% atom D) is reported. The macrocycle is first converted into 1,4,7-trinitroso-1,4,7-triazacyclononane, whose solid-state and solution properties are herein described. In CD3OD/D2O solution, the trinitroso derivative undergoes fast base-catalyzed H/D exchange on the whole set of methylene hydrogens and can be subsequently denitrosated by reduction with Ni/Al alloy.

High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac)3NITEt and the magnetically frustrated Gd(hfac)3NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr8 closed ring and in Cr7Cd and Cr8Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.