M. Desamparados Velasco

Synthesis and electrochemical study of novel oxazolo-ferrocene derivatives displaying redox-switchable character

Abstract A synthetic procedure has been developed to prepare new oxazolo-ferrocene ligands. The method, which allows the formation of homobimetallics oxazole–ferrocenes 4 – 7 containing two oxazole rings in the conjugation chain, is based on the aza-Wittig reaction of α-azidoacetyl ferrocene 1 with diacyl chlorides and triphenylphosphine. This route has the characteristic of tuning the size and shape of the spacer which could have aliphatic, aromatic, and heteroaromatic nature. Likewise, the reaction of 1,1′-bis(α-azidoacetyl) ferrocene 3 with aroyl chlorides in the presence of triphenylphosphine affords ferrocene ligands 11 linked to two oxazole rings. The stable solids were thoroughly characterized by spectroscopic means and electrochemical methods. Ligands 4 – 7 showed chemically reversible oxidations with two one-electron processes, indicating that the iron centres do not electronically communicate with each other. Electrochemical investigations reveal the respective ferrocene–ferrocenium redox couples of the ligands 11 and 14 are perturbed to a more positive potentials upon protonation and co-ordination of Zn(II) guest cation.

AZA-WITTIG REACTIONS OF IMINOPHOSPHORANES DERIVED FROM FERROCENYLAZIDO KETONES : PREPARATION AND ELECTROCHEMICAL STUDY OF NOVEL FERROCENYL-SUBSTITUTED AZAHETEROCYCLES

Abstract α-Azidoacetylferrocene and 3-(o-azidophenyl)-1-ferrocenylpropenone have been prepared from acetylferrocene and they have proven to be useful building blocks for the synthesis of azaheterocycles. Thus, the three-component reaction of α-azidoacetylferrocene, isocyanates or acid chlorides and triphenylphosphine allows the direct formation of ferrocene-substituted oxazoles. Aza-Wittig reaction of the iminophosphorane derived from 3-(o-azidophenyl)-1-ferrocenylpropenone with isocyanates provides access to the corresponding carbodiimides which are cyclised either by the action of TBAF or amines to give ferrocenyl-substituted dihydroquinazoline derivatives. The bis(ferrocenyl)oxazole 13 showed in the cyclic voltammogram (†E 1 2 = 150 mV) moderate electronic coupling between the two ferrocenes through the oxazole ring.

Isolation, Reactivity and Intramolecular Trapping of Phosphazide Intermediates in the Staudinger Reaction of Tertiary Phosphines with Azides

Abstract The Staudinger reaction of the N -substituted o -azidobenzamide 1 with triphenylphosphine or diphenylmethylphosphine allows the isolation of the intermediate phosphazides as crystalline solids, which have been characterized by spectroscopic methods. These compounds react in aza Wittig type fashion with isocyanates to give unexpectedly the corresponding 1,2,3-benzotriazinone derivative. Trapping of a Z -phosphazide by intramolecular aza Wittig reaction is reported for the first time.

P,N-Heterodifunctional ligands by selective Staüdinger reaction of β-substituted vinylazides with (Z)-1,2-bis(diphenylphosphanyl)ethene and formation of cyclometalled complexes of palladium(II) of these ligands — crystal and molecular structure of a new chiral cyclometallaphosphoraniminophosphane of palladium(II)

Abstract Staudinger reactions of the β-aryl-, heteroaryl- and ferrocenylvinylazides ( 2 ) with ( Z )-1,2-bis(diphenylphosphanyl)ethene afford the P , N -ligands ( 3 ) in good yields. Reaction of 3 with dichlorobis(benzonitrile)palladium(II) leads to the Pd(II) metallacycle derivatives 5 . The molecular structure of 5e has been determined by X-ray crystallography. The electrochemical behavior of this compound is also reported.

Electrochemical ring-contraction of fused [1,3,4]thiadiazinium salts: preparation of fused pyrazole derivatives

Abstract The electroreduction of several fused [1,3,4]-thiadiazinium salts on mercury pool cathode in an aprotic medium has been studied. In preparative experiments using dimethylformamide 0.2 M in lithium perchlorate as the electrolyte, the [1,3,4]-thiadiazinium salts 1 - 3 formed a mixture of the corresponding fused pyrazoles and ketimines. On the basis of results of preparative electrolyses (products and reaction potentials) and cyclic voltammograms a posible mechanism is proposed.