No abstract

The ambiphilic triphosphine-borane ligand 1 {TPB = [o-iPr2P-(C6H4)3B} readily coordinates to all group 10 and 11 metals to afford a complete series of metal boratranes (TPB)[M] 2-8 (2: M = Ni, 3: M = Pd, 4: M = Pt, 5: M = CuCl, 6: M = AgCl, 7: M = AuCl, 8: M = Au+). Spectroscopic and structural characterization unambiguously establishes the presence of M-B interactions in all of these complexes. The first evidence for borane coordination to copper and silver is provided, and the Au-->B interaction is shown to persist upon chloride abstraction. Experimental and theoretical considerations indicate that the M-->B interaction is strongest in the Pt and Au complexes. The influence of the oxidation state and charge of the metal is substantiated, and the consequences of relativistic effects are discussed. The coordination of the sigma-acceptor borane ligand is found to induce a significant bathochromic shift of the UV-vis spectra, the Ni, Pd, and Pt complex presenting strong absorptions in the visible range. In addition, all of the group 10 and 11 metal boratranes adopt C3 symmetry both in the solid state and in solution. The central M-->B interaction is found to moderately influence the degree of helicity and configurational stability of these three-bladed propellers, and DFT calculations support a dissociative pathway for the inversion process.

Since the mid 2000's, the incorporation of Lewis acid moieties in ligands for transition metals has been studied extensively. So-called ambiphilic ligands were shown to possess rich and unusual coordination properties and special focus was given to the coordination of Lewis acids as σ-acceptor ligands (concept of Z-type ligands). Recent studies have demonstrated that the presence of Lewis acids at or nearby transition metals can also strongly impact their reactivity. These results are surveyed in this review. The stoichiometric transformations and catalytic applications of complexes deriving from ambiphilic ligands are presented. The different roles the Lewis acid can play are discussed.