An Iminophosphonamido‐Chlorosilylene as a Strong σ‐Donating NHSi Ligand: Synthesis and Coordination Chemistry

The N ‐heterocyclic silylene (NHSi) [Ph 2 P( t BuN) 2 ]SiCl ( 1 ), supported by an iminophosphonamide ligand, was obtained from the dehydrochlorination of [Ph 2 P( t BuN) 2 ]SiHCl 2 ( 2 ) with LiN(SiMe 3 ) 2 . NHSi 1 contains an extremely high‐energy HOMO level and consequently displays unique coordination behavior toward Rh I complexes. When 1 was treated with 1/4 of an equivalent of [RhCl(cod)] 2 (cod=1,5‐cyclooctadiene), the 14‐electron Y‐shaped bis(chlorosilylene) Rh I complex 5 was obtained as dark purple crystals. The reaction of 1 with 1/6 of an equivalent of [RhCl(cod)] 2 yielded the cationic tris(silylene)‐Rh I complex [ 6 ] + ⋅Cl − as red crystals, wherein a two‐coordinated silylene ligand engages in a Si=Rh double bond. A structural analysis of 5 and [ 6 ] + ⋅Cl − revealed that the central rhodium atoms adopt trigonal and square‐planar coordination geometries, respectively, with considerably shortened Si‐Rh bonds [ 5 : 2.1605(5) Å; [ 6 ] + : 2.133(1) Å].