The Way into the Bridge: A New Bonding Mode of Tertiary Phosphanes, Arsanes, and Stibanes

Until recently, tertiary phosphanes, arsanes, and stibanes were considered to bind to transition‐metal centers only in a terminal coordination mode. Investigations on the reactivity of square‐planar trans ‐[RhCl(CRR′)(L) 2 ] compounds revealed that compounds in which L=Sb i Pr 3 can be converted upon heating into dinuclear complexes [Rh 2 Cl 2 (μ‐CRR′) 2 (μ‐Sb i Pr 3 )] with the carbene and stibane ligands in bridging positions. Although attempts to replace the stibane in these complexes with a tertiary arsane or phosphane failed, substitution of the chloro ligands for acetylacetonates followed by bridge–ligand exchange allowed the preparation of the phosphane‐ and arsane‐bridged compounds [Rh 2 (acac) 2 (μ‐CRR′) 2 (μ‐PR 3 )] and [Rh 2 (acac) 2 (μ‐CRR′) 2 (μ‐AsMe 3 )]. The acac ligands can be replaced by anionic Lewis bases to give either monomeric [Rh 2 X 2 (μ‐CRR′) 2 (μ‐ER 3 )] or dimeric chain‐like [XRh(μ‐CRR′) 2 (μ‐ER 3 )Rh(μ‐X) 2 Rh(μ‐CRR′) 2 (μ‐ER 3 )RhX] molecules.