Utilizing the 8-Methoxycyclooct-4-en-1-ide Unit As a Hydrogen Atom Acceptor en Route to “Metal–Borane Pincers”

The synthesis and characterization of palladium and platinum complexes containing the neutral ligand HB(mp)2 (where mp = 2-mercaptopyridyl) are presented. Addition of 2 equiv of Na[H2B(mp)2] to [M(Cl)(COEOMe)]2 (where M = Pt, Pd; COEOMe = 8-methoxycyclooct-4-en-1-ide) in the presence of 2 equiv of PPh3 leads to the formation of the metal–borane pincer complexes [Pt{κ3SBS-HB(mp)2}(PPh3)] and [Pd{κ3SBS-HB(mp)2}(PPh3)]. In these reactions, a hydrogen migration reaction occurs from the borohydride ligand to the metal center, eventually leading to the elimination of the COEOMe unit from the metal center. X-ray crystallographic characterization of the two isostructural complexes reveals a rare mer-κ3S,B,S coordination mode with short platinum– and palladium–boron distances: 2.098(4) and 2.091(3) Å, respectively (the shorter distances of two independent complexes in the unit cells of both structures). The complexes [Pd{κ3S,B,S-HB(mp)2}(PPh3)] and [Pt{κ3S,B,S-HB(mp)2}(PPh3)] are the first examples of metal–borane complexes featuring a pincer-type coordination where one hydrogen substituent remains at the boron center.