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.