The condensation of imidazole moieties with boranes leading to molecular units with N–BR2–N bridges was accomplished by attaching three imidazole units to a single phosphorus atom. In this way, boron bridged trisimidazolylphosphines 3–7 were synthesized in good yields. The chiral derivatives 5a, 5d, 6, and 7 are C3 symmetric, whereas 5b and 5c carry no symmetry element (C1). The steric bulk of the ligands can easily be tuned by introduction of different substituents at the three bridging boron atoms. All phosphines feature small CPC angles between 91–93° leading to a s‐type lone pair donor at the phosphorus atom combined with reasonable π‐accepting properties. Ni (8) and Au metal complexes (9, 10) with very short metal phosphorus bonds were synthesized. The short metal–phosphorus distance is a consequence of the pronounced s‐character of the phosphine lone pair.
The cover picture shows a new class of chiral phosphine ligands bearing three imidazole units bridged by boranes. The bowl shaped, C3 symmetric molecules are obtained by a simple condensation procedure. The steric bulk of these monodentate ligands can easily be adjusted over a large range by the use of different chiral or achiral boranes. The ligand character is determined by the almost pure s‐character of the phosphorous lone‐pair, leading to very short metal‐P distances. Details are discussed in the article by Markus Enders, Helene Schall, and Olaf Fritz, et al. on page http://onlinelibrary.wiley.com/doi/10.1002/zaac.201800016/abstract.
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