Versatile 1,2- and 1,3-Dipole Behavior of the 1-Arsa-3-Germaallene Tip(t-Bu)GeCAsMes*: Formation of a Heterocyclic Arsa(germa)carbene (AsGeHC)

The 1-arsa-3-germaallene Tip­(t-Bu)­GeCAsMes* (1; Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) reacts with selenium, fluorenone, N-tert-butylphenylnitrone, and 9,10-phenanthrenequinone as a 1,2-dipole by the GeC double bond, to give the corresponding three-, four-, five-, and six-membered-ring derivatives 2–5, respectively. Both [2 + 2] and [2 + 4] cycloadditions involving the GeC double bond are observed between 1 and benzil, leading to the four- and six-membered-ring derivatives 6 and 7. In great contrast, 1 reacts with diphenylketene as a 1,3-dipole by the whole GeCAs unit to afford the transient heterocyclic arsa­(germa)­carbene 12 according to a [3 + 2] cycloaddition. DFT calculations were carried out to understand this particular behavior. This first heavier analogue of an NHC with an arsenic atom rearranges to the tricyclic compound 11.