η~3-Vinylborane Complexes of Platinum and Nickel: Borataallyl- and Alkyl/Borataalkene-Like Coordination Modes

摘要

Complexes of carbon-based π ligands have occupied a central position in d- and f-block element organometallic chemistry since the remarkably early synthesis of Zeise's salt, KPtCl3-(C2H4)·H2O, in 1827. By contrast, π-ligand complexes containing boron and carbon have only been developed in the past 50 years. Formally monoanionic boratabenzene and dianionic borole ligands, which are isoelectronic with arefie and cyclopentadienyl ligands (Figure 1), respectively, are now prominent examples in this area. However, boron analogues of acyclic at ligands are rare. For example, mononuclear η~2- borataalkene complexes (Figure 1) are limited to the tantalum complexes reported by Piers and co-workers, Cp2TaL_x-{CH2B(C6F5)2} (L = CNtBu and CO; x = 0 or 1; III in Figure 2), and η-borataallyl complexes (Figure 1) are limited to the palladium and zirconium complexes, PdCl2{η~3-PhB(CHPPh3)2} and ZrCl4{η~3-PhB(CHPPh3)2) (I and II, Figure 2), that were reported by the Shapiro group. The PhB(CHPPh3)2 ligand may be viewed as a borane-bridged diylide or a zwitterionic 1,3-di-phosphonium-substituted 2-borataallyl ligand.