Lorraine E. Aleandri

[Ti(MgCl)2· xTHF]q: a reagent for the McMurry reaction and a novel inorganic Grignard complex

Abstract The stepwise formation of two distinct bimetallic titanium/magnesium complexes during the reduction of TiCl 3 (or TiCl 4 ) by magnesium in tetrahydrofuran (THF) has been identified. [TiMgCl 2 · x THF] ( 1 ) is produced in a first stage, but reacts further with excess Mg to give [Ti(MgCl) 2 · x THF] ( 2 ). The reaction is reversible in the presence of excess TiCl 3 . X-ray absorption spectroscopy has been used to identify the local environment in 2 . The most striking feature is the existence of the shortest TiMg interatomic distance yet observed. The TiMg bond length, 2.72(1) A, is close to the sum of the Pauling single bond metallic radii (2.69 A) and the complex is termed an inorganic Grignard reagent by analogy with other complexes containing direct transition metalmagnesium bonds. Overall, a dimeric model is compatible with the EXAFS-derived structural parameters and solubility characteristics. The titanium atoms are linked through two bridging MgCl 2 Mg units and their coordination shells are completed by THF ligands. The structure of 2 , and the existence of intermediate 1 , can be used to rationalize the known catalytic activity of the TiCl 3 /Mg/THF system with respect to ether cleavage.

[HTiCl(THF)∼0.5]x : a highly reactive titanium hydride and an active species in the McMurry reaction

Abstract The complex [TiCl3(THF)3] reacts with catalytically-prepared solid magnesium hydride (MgH2★) or dissolved magnesium hydride (MgH2′) with evolution of hydrogen to give a highly reactive titanium hydride, [HTiCl(THF)∼0.5]x (1). The well-known low valent titanium species, obtained by reduction of TiCl3 with LiAlH4, utilized in the McMurry reaction, has been shown to be 1. An X-ray absorption spectroscopy study (EXAFS) of 1 reveals that the Ti absorber is surrounded by O (from THF) and Cl atoms plus two types of Ti neighbors. Possible structural models for 1 compatible with the EXAFS results are proposed. Complex 1 is an active reagent for the coupling reaction of benzophenone to give tetraphenylethene. During the reaction hydrogen is liberated and the inorganic side product has been shown to be titanium(III) oxychloride; thus the McMurry reaction employing 1 as the reagent can be described by Ph2CO+1THF or→toluen 0.5 PPh2CCPh2 + 0.5H2↑ + [TiOCl(THF)x]. On the basis of these results, a new interpretation of the mechanism for the McMurry reaction is presented. Complex 1 also undergoes a number of carbenoid type reactions, which may proceed via a “titanium carbenoid” intermediate 9a–c.

Structural investigation of bimetallic RH–Pt nanoparticles through X-ray absorption spectroscopy

The reduction, with tetraalkylammonium hydrotriorganoborates, of noble-metal salts suspended in tetrahydrofuran gives metal colloids which are protected against agglomeration by the surrounding tetraalkylammonium ions. The mean particle size of the isolated metal aggregates, as determined by TEM, is 3 nm and below. The use of two different metal halides simultaneously, allows coreduction to occur, giving an X-ray amorphous bimetallic product. In order to determine whether the resulting colloid is a mixture of the two individual metals or contains a bimetallic alloy, the environment of each metal in a Rh0.44Pt0.56 product was examined using EXAFS spectroscopy at LURE, France (Rh Kand Pt L3-edges). In each case, mixed-metal shells were observed, compatible with the formation of intermetallic aggregates. The environment around the Rh absorber consists of 3.5 Rh atoms at a distance of 2.72 A and 4.7 Pt atoms at 2.74 A(total 8.2 neighbours) and, around the Pt absorber, 3.6 Rh at 2.72 A and 8.3 Pt atoms at 2.75 A(total 11.9 neighbours). The average coordination number (CN) is lower than the expected CN of 12 for a face-centred cubic structure, which is consistent with the nanoparticulate nature of the bimetallic system. Furthermore, the CN of rhodium is less than that of platinum indicating that, on average, rhodium is segregated from the core to the surface of the alloy nanoparticles. The system is best described as a nanoparticulate Rh/Pt alloy, surface rich in rhodium. The implications of this finding in catalysis are discussed.

Ba3Cu3(InO3)4: A novel quarternary perovskite derivative

Abstract The novel compound, Ba 3 Cu 3 (InO 3 ) 4 , is prepared via the reaction between BaCO 3 , CuO and In 2 O 3 at 1200 K as a dark reddish brown powder. Diffuse reflectivity measurement showed an optical band gap of 1.5 eV while resistivity measurement on a pressed pellet confirmed semiconducting behaviour. Magnetic susceptibility measurements indicated the presence of Cu 2+ cations (measured magnetic moment of 1.90 μ B , a typical value expected for a Cu 2+ cation including spin-orbital coupling) which undergo antiferromagnetic ordering below 15 K. The crystal structure was determined from single-crystal X-ray data and refined to a residual of 0.046 for 513 unique reflections with 27 parameters. Ba 3 Cu 3 (InO 3 ) 4 crystallizes in an tetragonal cell (space group, I4 mcm (No. 140)) with four formula units per cell and the lattice constants a = 12.131(2) A and c = 8.509(2) A . The structure is an unusual derivative of the perovskite-type framework where the barium atoms in a quarter of the [BaInO 3 ] − units are replaced by copper atoms. The copper atoms are located in the square planar sites on four of the faces of the [InO 3 ] 3− unit, thereby yielding a defect NaCl-type oxocuprate indate substructure, 1 ∞ [ m Cu 2 InO 3 o ]. The CuO 4 square planar units are further interconnected to form unprecedented open-link chains which run parallel to the barium occupied channels of the parent perovskite framework.

Nanocrystalline Zintl Phases from Main‐Group Metal Chlorides and Magnesium Anthracene or Activated Magnesium

Ga, Tl, Sn, Pb, As, Sb, Bi, Cd, and Hg chlorides react with magnesium anthracene · 3 THF (MgA), anthracene-activated magnesium, or “active magnesium” (Mg*) in THF, generating the respective Mg intermetallics in a nanocrystalline or amorphous state (Eqs. 1–3). Mg intermetallics accessible through the wet-chemical route can be exploited by metathetical exchange reactions for the preparation of other, highly active intermetallics and alloys; EXAFS investigation of X-ray amorphous Cu–Sn and Pd–Pb solids thus prepared (Eqs. 13 and 14) shows that they are true bimetallic alloys (solid solutions).