Diimidokomplexe [M(NR) 2 (PMe 3 )2(L)] des vierwertigen Molybdäns und Wolframs: Struktur, Moleküldynamik und Aktivierung π‐acider Liganden

Highervalent Derivatives of the d‐Metal Acids, 14 [1] . — Diimido Complexes [M(NR) 2 (PMe 3 ) 2 (L)] of Tetravalent Molybedenum and Tungsten: Structure, Molecular Dynamics, and Activation of π‐Acidic Ligands [M(NMes) 2 Cl 2 (dme)] (M = Mo 1 , W 2 ; Mes = mesityl) or the trans ‐phosphane complexes [M(NMes) 2 (PMe 3 ) 2 Cl 2 ] ( 3, 4 ) are reduced by C 8 K in the presence of PMe 3 to give diamagnetic d 2 complexes [Mo(NMes) 2 (PMe 3 } 3 ] ( 5 ) and [W(NMes) 2 ‐(PMe 3 ) 3 ] ( 6 ). At least one PMe 3 ligand in 5 and 6 is readily substituted by more π‐acidic substrates such as ethene, ethyne, 2‐butyne, and P(OEt) 3 . The reaction with ethene leads to [Mo(NMes) 2 (η 2 ‐C 2 H 4 )(PMe 3 ) 2 ] ( 7 ) and [W(NMes) 2 ‐(η 2 ‐C 2 H 4 )(PMe 3 ) 2 ] ( 8 ). Furthermore, pentacoordinate complexes [Mo(NMes) 2 (η 2 ‐C 2 Me 2 )(PMe 3 ) 2 ] ( 9 ), [W(NMes) 2 (η 2 ‐C 2 H 2 )(PMe 3 ) 2 ] ( 10 ), and [W(NMes) 2 (PMe 3 ){P(OEt) 3 ) 2 ] ( 11 ) have been synthesized from 5 or 6 . The X‐ray structure analysis of 8 reveals a trigonal‐bipyramidal geometry about tungsten with both arylimido groups perfectly lying in the equatorial mirror plane. The ethene ligand is occupying the third equatorial position. The C 2 vector is oriented perpendicular to the WN 2 plane. Dynamic NMR studies are consistent with a tbp geometry being also present in solution at the low‐temperature limit. At higher temperatures a rapid exchange of the PMe 3 ligands with noncoordinated phosphane according to a dissociative mechanism is observed.