Michael Ciesielski

A Novel and Effective Synthetic Approach to 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) Derivatives

DOPO and its derivatives generally exhibit an outstanding performance as flame retardants in various polymers. Starting from trivalent 10-alkoxy-10H-9-oxa-10-phosphaphenanthrenes, a broad range of DOPO derivatives was synthesized via transesterification with aliphatic alcohols and subsequent Michaelis-Arbuzov rearrangement using catalytic amounts of p-toluenesulfonic acid methylester. Due to the considerable differences in the nature of the alcohols employed, several procedures for processing them are presented.

Salicylaldimine Dizinc Complexes: Activation of Water Molecules and Fixation of CO2 in the Coordination Sphere of Zinc

Bi- and tetranuclear zinc complexes of the tridentate N,N,O ligand [{[2-(2-pyridyl)ethyl]imino}methyl]phenol (HL) and their enzyme-like reactions are described. The coordinated water molecules in a dizinc complex of this ligand can be deprotonated reversibly similar to those in the resting states of zinc enzymes. The resulting tetranuclear complex bearing bridging hydroxide ions allows the reversible uptake of CO2. Whereas the coordination of hydrogen carbonate has not been observed, a tetranuclear carbonate complex with a unique structure was isolated. Its carbonate ion is coordinated to all four zinc atoms. The X-ray structures of the reported complexes are discussed. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

New Phosphacyclic Molecules and Their Application aS Flame Retardants for Epoxy Resins

Abstract 9,10-Dihydro-9,10-oxa-10-phosphaphenanthrene-10-oxide (DOPO) has been commercialized as a gas phase active flame retardant. Its P‒H bond allows its reactive incorporation into epoxy resins and formation of new additives via Michael-like addition. To better understand of the role of radicals in the flame retardant mechanism, 9,10-dihydro-9-aza-10-phosphaphenanthrene-10-oxide (DAPO) and 9,10-dihydro-9,10-oxa-10-phosphaphenanthrene-10-sulfide (DOPS) were synthesized. DAPO was found to undergo unprecedented tautomerism for a P(V) cycle. The detailed synthetic approach and spectroscopic characterization of DAPO and the flame retardant behavior of DAPO and DOPS will be discussed.

Copper-mediated oxidative cyclization of heterocyclically substituted aldimines

Copper-mediated cascade reactions were performed with heterocyclically substituted aldimines. These oxidative heterocyclizations include sequences of oxidations and cycloadditions or nucleophilic additions which take place in the coordination sphere of copper ions. When two heterocyclically substituted aldimines were reacted in the presence of copper (II) salts under air, pyridine derivatives were produced. In one case a 1,4-diazatricyclo-[3.2.1.02.7]oct-3-ene was also formed. The basic structure of this new tetracyclic compound contains five new chirale carbon atoms. This cage-like structure has been revealed by X-ray crystallography. The synthesis of 2H-pyrroles by copper-assisted conversions of the aldimines with dimethylacetylene carboxylate or quinones was also described.

Synthesis and reactivity of 6-mercapto-6H-dibenzo[c,e][1,2]oxaphosphinine 6-sulfide

The synthesis route of the novel 6-mercapto-6H-dibenzo[c,e][1,2]oxaphosphinine 6-sulfide 4 from 6-chloro-6H-dibenzo[c,e][1,2]oxaphosphinine 1 and its spectroscopic investigation are presented. In addition, reaction of the thiol group with unsaturated functionalities such as acrylates demonstrated that the newly synthesized compound could undergo thiol-ene chemistry. Moreover, modification of the reaction condition led to the formation of the rearrangement product of a thiol-Michael reaction of compound 4 with benzoquinone.