Transition-metal-mediated activation of the heptaarsenide trianion: isolation of a diaryltetraarsenabutadienediide.

Reaction of an ethylenediamine solution of K(3)As(7) with the low-valent, low-coordinate cobalt(II) complex [Co(mes)(2)(PEt(2)Ph)(2)] yielded the novel dianionic species [Co(η(3)-As(3)){η(4)-As(4)(mes)(2)}](2-) (1). The [η(4)-As(4)(mes)(2)](2-) moiety present in 1 is a rare example of a group 15 analogue of a butadienediide.