title: Versatile stereoselective cycloadditions between heterocumulenes and phosphagermaallene Tip(tBu)Ge=C=PMes*: experimental and theoretical investigations.
abstract: Phosphagermaallene Tip(tBu)Ge=C=PMes* 1 (Tip=2,4,6-triisopropylphenyl, Mes*=2,4,6-tri-tert-butylphenyl) reacts with phenyl isocyanate and tert-butyl isocyanate by a [2+2] cycloaddition that involves the Ge=C and C=O double bonds to afford 1-oxa-2-germacyclobutanes 2 and 3. With N,N'-dicyclohexylcarbodiimide, a [2+2] cycloaddition is observed between the Ge=C and C=N unsaturations to lead to 1-aza-2-germacyclobutane 6 with exocyclic P=C and C=N double bonds. In sharp contrast, 1 reacts with phenyl isothiocyanate, ethyl isothiocyanate, and carbon disulfide according to a [3+2] cycloaddition that involves the whole Ge=C=P unit and the C=S double bond to give transient phosphagermacarbenes (PGeHCs) 11, 12, and 13. These new PGeHCs undergo C-H insertions into one o-tBu group of Mes* (in the case of 11 and 12) or one o-iPr group of Tip (in the case of 13) with formation of tricyclic compounds 8, 9, and 10, respectively. The reaction mechanisms that involve 1 and the phenyl isocyanate and the phenyl isothiocyanate are described and their regioselectivity is explained by theoretical calculations.
authors.affiliation: Université de Toulouse, UPS, LHFA, Toulouse, France.
authors.forename: Dumitru
authors.initials: D
authors.lastname: Ghereg
authors.forename: Erwan
authors.initials: E
authors.lastname: André
authors.forename: Heinz
authors.initials: H
authors.lastname: Gornitzka
authors.forename: Jean
authors.initials: J
authors.lastname: Escudié
authors.forename: Fatima
authors.initials: F
authors.lastname: Ouhsaine
authors.forename: Nathalie
authors.initials: N
authors.lastname: Saffon
authors.forename: Karinne
authors.initials: K
authors.lastname: Miqueu
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Sotiropoulos