| abstract |
in which M represents a metal atom, R <1>, R <2>, R <3> and R <4> represent, independently of one another, a hydrogen atom, or an alkyl or cycloalkyl group , aryl, alkoxy, aryloxy, alkylthio, cycloalkylthio, optionally substituted, R <5> represents an alkyl, cycloalkyl, aryl, alkoxy, aryloxy, alkylthio, cycloalkylthio, arylthio, optionally substituted group, R <6> represents a halogen atom or a substituted or unsubstituted alkylalkynyl, arylalkynyl, alkylthio or arylthio group. |