Synthesis and Onwards Coordination of an AsI Centered Zwitterion

The bis(phosphino)borate ligand class is used as an anionic anchor to stabilize reactive, low coordinate arsenic centers. The neutral, zwitterionic As^I species, 2 , is formed very cleanly, and isolated in good yields using cyclohexene as a halogen scavenger. The uniqueness of this heterocyclic As^I compound is on display with the coordination to Group 6 metal centers, ( 2 M(CO)₅ ; M=Cr, Mo, W). The arsenic? metal bond lengths are longer than the related AsPh₃ complexes suggesting that compound 2 is a weak sigma donor. The metal complexes reveal a trigonal pyramidal arsenic atom, which provides the first experimental evidence for the presence of two “lone pairs” of electrons on the As^I center. When more flexible and more electron‐donating isopropyl substituents were used, an intermediate (compound 5 ) in the formation of low coordinate pnictogen compounds was crystallographically characterized. This structure, formally a base‐stabilized dichloroarsenium cation, provides an alternative mechanistic proposal to the one described in the literature.