Synthesis and structural characterization of base-stabilized oligomeric heterovinylidenes

Metalation of the (iminophosphoranyl)phosphine PPh₂CH ₂(PPh₂=NSiMe₃) (1) with an equimolar amount of n-BuLi afforded the monolithium salt [Li{CH(PPh₂)(PPh ₂=NSiMe₃)}(THF)₂] (2). The reaction of 2 with GeCl₂·1,4-dioxane has led to the formation of a germavinylene moiety, which trimerized to form a new heterocyclic cage compound, [{(PPh ₂=NSiMe₃)(PPh₂)C=Ge:}{(PPh₂= NSiMe₃)(PPh₂)C}₂Ge→Ge:] (3). A similar reaction of the lithium methanide complex 2 with SnCl₂ afforded the stannavinylidene moiety, which underwent a "head-to-tail" cycloaddition to form a stable 1,3-distannacyclobutane, 4. A trapping reaction of 4 with diiron nonacarbonyl gave the novel iron stannavinylidene complex 5. The solid-state structure analysis of 5 reveals that it contains two stannavinylidene moieties bonded in a Sn-P "head-to-tail" fashion, with one of the tin(II) centers coordinating to a Fe(CO)₄ moiety. The X-ray structures of 2-5 have been determined by X-ray crystallography. In addition, the dynamic behavior of 5 has been studied by means of variable-temperature ³¹P and ¹¹⁹Sn NMR spectroscopy.