Abstract: | Sigma‐ versus Pi‐Coordination in Bis‐indenyl‐ and Bis‐2‐methallyl Imido Complexes of Hexavalent Molybdenum and Tungsten: DF‐Calculations and Crystal Structure Analysis Bis‐indenyl and bis‐2‐methallyl imido complexes (C9H7)2M(NR)2] (M = Mo, W; R = tert‐butyl, mesityl) 1 — 4 and (H3C‐C3H4)2M(NtBu)2] (M = Mo, W) 6 , 7 have been prepared starting from Mo(NtBu)2Cl2] or M(NR)2Cl2L2] (M = W, R = tBu, L = py; M = Mo, W, R = Mes, L2 = dme) and indenyl lithium or 2‐methallyl magnesium bromide, respectively. According to spectroscopic data and the crystal structure of 4 there are two different coordination modes of the indenyl ligands, (η3‐C9H7)M(NR)2(η1‐C9H7)], in solution as well as in the solid state. These compounds show fluxional rearrangements in solution, namely σ, π‐exchange of η1‐ and η3‐coordinated ligands. Similar behavior has been observed for the 2‐methallyl complexes 6 and 7 in solution. In agreement with experimental observations, DF calculations on models of 6 strongly suggest a (σ+π)‐coordination mode of the η3‐coordinated ligand. |