From an Al4-Cluster to Al+ Complexes: Lessons on Metalloidal Clustering

Low-valent aluminium compounds are among the most reactive and widely researched main-group compounds. Since the isolation of [(AlCp*)4] in 1991 as the first stable, molecular AlI compound, a variety of highly reactive neutral or anionic low-valent aluminium complexes were developed. In particular, the strongly basic aluminyl anions allowed for nucleophilic activation of a large variety of small molecules and formation of elusive transition-metal complexes. By contrast, an accessible cationic, low-valent aluminium compound combining the nucleophilicity of low-valent compounds with the electrophilicity of aluminium is hitherto unknown. Here, we report the synthesis of [Al(AlCp*)3]+[Al(ORF)4]– (RF = C(CF3)3) via a simple metathesis route. Unexpectedly, the complex ion forms a dimer in the solid state and in concentrated solutions. Addition of Lewis bases results in monomerization and coordination to the unique formal Al+ atom giving [(L)xAl(AlCp*)3]+ salts with L = hexaphenylcarbodiphosporane (cdp; x = 1), tetramethylethylenediamine (tmeda; x = 1) and 4-dimethylamino-pyridine (dmap; x = 3). Depending on the donor strength of the ligand added, the Al+–AlCp* bonds in the [(L)xAl(AlCp*)3]+ cluster cations can be finely tuned between very strong (L = nothing) to very weak and approaching isolated [Al(L)3]+ ions (L = dmap). We anticipate our easily accessible low-valent aluminium cation salts to be the starting point for investigation and potential application of this unusual compound class. In particular, the ambiphilic reactivity of the cationic, low-valent compounds will be studied. Moreover, knowledge gained from the stabilization of the reported complex salts is expected to facilitate the isolation and application of novel cationic, low-valent Al complexes.

Thermo-Rheological and Shape Memory Properties of Block and Random Copolymers of Lactide and ε-Caprolactone

Biodegradable block and random copolymers have attracted numerous research interests in different areas, due to their capability to provide a broad range of properties. In this paper, an efficient strategy has been reported for preparing biodegradable PCL-PLA copolymers with improved thermal, mechanical and rheological properties. Two block-copolymers are synthesized by sequential addition of the cyclic esters lactide (L-LA or D,L-LA) and ε-caprolactone (CL) in presence of a dimethyl(salicylaldiminato)aluminium compound. The random copolymer of L-LA and CL was synthetized by using the same catalyst. Chain structure, molar mass, thermal, rheological and mechanical properties are characterized by NMR, SEC, TGA, DSC, Rheometry and DMTA. Experimental results show that by changing the stereochemistry and monomer distribution of the copolymers it is possible to obtain a variety of properties. Promising shape-memory properties are also observed in the di-block copolymers characterized by the co-crystallization of CL and L-LA segments. These materials show great potential to substitute oil-based polymers for packaging, electronics, and medicine applications.

Hydroalumination and hydrogallation of an aryl-chloro-dialkynylsilane: Si–Cl bond activation by intramolecular Al–Cl and Ga–Cl interactions

The chlorine functionalized dialkynylsilane (4-tBu-C6H4)(Cl)Si(C≡C-tBu)2 (3) reacted with equimolar quantities of H–AltBu2 or H–GatBu2 by hydrometallation of a C≡C triple bond and formation of mixed alkenyl-alkynylsilanes (4 and 5) in which the Si and Lewis acidic metal atoms adopt geminal positions at the α-C atoms of the alkenyl groups. Intramolecular M···Cl interactions (M=Al, Ga) afforded four-membered SiCMCl heterocycles which in comparison with 3 had significantly lengthened Si–Cl bonds. Dual hydrometallation of 3 was only observed for H–GatBu2. One Ga atom of the product (6) was coordinated by the silicon-bound Cl atom, while the second one showed an interaction with the aromatic ring of the tert-butyl-phenyl group. Treatment of the aluminium compound 4 with two equivalents of H–GatBu2 afforded a Si–H bond by Cl-H exchange and release of Cl–AltBu2. The resulting silane (7) has the Si atom and two Ga atoms bridged by the α-C atoms of two vinyl groups. The specific functionality of 4 caused a remarkable reactivity. Phenyl isocyanate reacted by the formal insertion into the Al–C(vinyl) and the activated Si–Cl bonds and resulted in the formation of a C–C bond. The product (8) has a SiC2N heterocycle with an Si–N bond and exocyclic C=C and C=O double bonds. The keto group is coordinated to a Cl–AltBu2 molecule, which was formed by the shift of the Cl atom from silicon to aluminium.

Feline vaccine-associated fibrosarcoma induced by aluminium compound in two cats: Short communication

Two cases of feline vaccine-associated fibrosarcoma (FVAF) are reported. The excised tumours were both characterised as well circumscribed, subcutaneous, firm and white with central necrosis. Histopathologically, they consisted of well-differentiated and variably sized and shaped anaplastic cells, characterised by marked nuclear and cellular pleomorphism including giant cells. The mitotic activity was low. Aluminium was demonstrated in the central necrosis and giant cells. Neoplastic cells were positive for vimentin and negative for desmin and cytokeratin. The presence of feline sarcoma virus and feline immunodeficiency virus could not be detected by PCR in either case.