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The synthesis of a new Costa-type ligand (H2mdo), in which the propylene bridge has been replaced by a methylenedioxy bridge has been accomplished: two molecules of butanedione monoxime are coupled via a CH2 group by reaction with CH2Cl2 and 50% aqueous NaOH in the presence of a phase-transfer reagent. Dihalidocobalt and alkyl(halido)cobalt complexes of the deprotonated ligand have been prepared and structurally characterized by NMR spectroscopy.

The paper considers a novel technique for manipulator motion in a constrained environment due to the presence of obstacles. The basic problem is that of avoiding collisions of the manipulator with the obstacles. The main idea is to cover the free space (i.e. the points of the configurations space in which no collisions are possible) by a connected family of polyhedral sets which are controlled-invariant. Each of these polyhedral regions includes some crossing points to the confining regions. The tracking control is hierarchically structured. A high-level controller establishes a connected chain of regions to be crossed to reach the one in which the reference is included. A low-level control solves the problem of tracking, within a region, the crossing point to the next confining region and, eventually, tracking the reference whenever it is included in the current one. The scheme assures that the reference is asymptotically tracked and that the transient trajectory is completely included in the admissible configuration space. A connection graph associated with the cluster of regions, and the high-level control is achieved by solving a minimum-path problem. As far as the low-level control is concerned, we consider both speed-control and torque-control. We propose two types of controllers. The first type is based on a linear stabilizing feedback which is suitably adapted to achieve a local tracking controller. Such a controller is computed by the plane representation of the sets which is more natural and useful then the vertex representation considered in previous work. The second is a speed-saturated type of controller which considerably improves the performance of linear-based control laws. Both these controllers have a speed-control and torque-control version. Experimental results on a laboratory Cartesian robot are provided.

A new cobaloxime-type model for coenzyme B12 has been synthesized. For this model strong steric repulsion between its dioxymethylene bridge and (one of) the axial ligands on cobalt presages enhanced rates of axial ligand exchange.

1H NMR data (300 and 500 MHz) are reported for methyl- and fluoro-substituted 6- and 7-ethoxy-1-methoxytricyclo[3.3.0.02,8]oct-3-enes, products of the meta photocycloaddition of methyl- and fluoro-anisoles to ethyl vinyl ether. COSY 45 (300 and 500 MHz) and COSY 90 (300 MHz) experiments were performed for the determination of the structures of these products.

Photoaddition of ethylvinylether to 3-methylanisole yields six derivatives of 1-methoxytricyclo[3.3.0.02,8]oct-3-ene. Four of the adducts have the ethoxy group in an endo position. Products in which the methyl group is at position 4 are favoured. Photoaddition of ethylvinylether to 3-fluoroanisole yields three isomeric adducts, to endo and one exo.

The meta photocycloaddition of anisole to 2,3- and 2,5-dihydrofuran, 1,3-dioxole and ethyl vinyl ether is described. The NMR data of the adducts are presented. The reaction yields mixtures of endo and exo adducts. The endo/exo ratio is strongly influenced by the presence of one or two oxygen atoms next to the double bond of the alkene. A mechanism is presented in which a zwitterionic intermediate is formed from the excited anisole and the alkene.

A new cobaloxime-type model for coenzyme B12 has been synthesized. For this model strong steric repulsion between its dioxymethylene bridge and (one of) the axial ligands on cobalt presages enhanced rates of axial ligand exchange.