Heavily π-Bond-Loaded Tungsten Phosphonio−Alkylidyne Complexes via a Domino Transylidation Cascade at (Organoimido)tungsten Tetrachlorides

Transylidation reactions of (arylimido)tungsten tetrachlorides [W(NR)Cl4] with 7 equiv of Ph3P−CH2 lead to the tetrahedral complexes [W(NR)(C−PPh3)(CH−PPh3)2] (R = Dip (1), Mes (2)), exhibiting one metal−nitrogen and three metal−carbon multiple bonds. The crystal structure analysis of 1 presents the first example of a terminal phosphonio−methylidyne functionality, [M⋮C−PR3] ↔ [MCPR3], formed via a transylidation reaction. Due to the high level of π-bond competition of four π-donor ligands, the MCP axis is considerably bent: 154.0(4)°.