Coordination Chemistry of a Tripodal S₂ON Ligand: Syntheses, Structures, and Reactivity of the Molybdenum(VI) and Nickel(II) Complexes of Bis(2-mercaptoethyl)-2-amino-4-methylphenol (H₃btap) and Comparison to V^VO(btap)

The tripodal tetradentate ligand H3btap coordinates to VV, MoVI, and NiII via three different bonding modes to yield three complexes with unique ligand-based oxidation chemistry. For VV and MoVI (1), all four of the heteroatom donors are coordinated to the metal ion forming a trigonal bipyramidal complex with the oxovanadium(V) ion, VVO3+, and an octahedral complex with the cis-dioxomolybdenum(VI) ion, [MoO2]2+. Only three of the heteroatom donors of H3btap are used to coordinate to NiII (2), two thiolate sulfurs and the amine nitrogen, yielding a dimeric structure in which each nickel(II) ion has NS3 coordination. The ability of VVO(btap) to form η2-sulfenates, while [MoO2(btap)]- does not form stable η2-sulfenates, has been ascribed to the electron-deficient, π-accepting nature of VVO3+ relative to [MoVIO2]2+. Crystal data for 1 (C11H16NO4S2KMo): space group Pbcn, a = 6.6596(9) Å, b = 13.7446(9) Å, c = 32.992(2) Å, α = β = γ = 90°, Z = 8. Crystal data for 2 (C24H38N2O4S4Ni): space group Pbcn, a = 12.0841(3) Å, b = 14.4948(4) Å, c = 16.7751(4) Å, α = β = γ = 90°, Z = 4.