Insertion of CS2 into a Phosphorus–Arsenic Single Bond and Investigations on Phosphane Arsanyldithiocarboxylates

The synthesis and reactivity of sterically demanding phosphaarsanes TerR1P–AsR2 (3) is described. These species were selectively synthesized via metathesis reactions of Ter-stabilized [Ter = 2,6-bis­(2,4,6-trimethylphenyl)­phenyl] potassium phosphides TerR1PK (1) with the N-heterocyclic chloroarsane ClAs­{N­(tBu)­CH2}2 (2). Conversion of the n-butyl-substituted phosphaarsane 3c with the reactive heterocumulene CS2 leads to an insertion into the P–As bond, yielding the phosphane arsanyldithiocarboxylate TerR1P–C­(S)­S–AsR2 (4c) as a new structural motif. Because full conversion of 3c with CS2 requires long reaction times, an alternative synthetic route is reported herein, involving the conversion of 2 with phosphane dithiocarboxylates TerR1–C­(S)­SK (5), enabling synthetic access to a wider range of phosphane arsanyldithiocarboxylates. These interpnictogen dithiocarboxylates show an interesting bonding situation with a significantly elongated As–S bond due to negative hyperconjugation within the molecule. All products along the reaction path were fully characterized.