Steric and electronic effects on arylthiolate coordination in the pseudotetrahedral complexes [(Tp Ph,Me )Ni–SAr] (Tp Ph,Me = hydrotris{3-phenyl-5-methyl-1-pyrazolyl}borate)

Synthesis and characterization of several new pseudotetrahedral arylthiolate complexes [(Tp Ph,Me )Ni–SAr] (Tp Ph,Me = hydrotris{3-phenyl-5-methyl-1-pyrazolyl}borate; Ar = Ph, 2,4,6- i Pr 3 C 6 H 2 , C 6 H 4 -4-Cl, C 6 H 4 -4-Me, C 6 H 4 -4-OMe) are reported, including X-ray crystal structures of the first two complexes. With prior results, two series of complexes are spanned, [(Tp Ph,Me )Ni–S–2,4,6-R′′3C 6 H 2 ] (R′′ = H, Me, i Pr) plus the xylyl analogue [(Tp Ph,Me )Ni–S–2,6-Me 2 C 6 H 3 ], as well as [(Tp Ph,Me )Ni–S–C 6 H 4 –4-Y] (Y = Cl, H, Me, OMe), intended to elucidate steric and/or electronic effects on arylthiolate coordination. In contrast to [(Tp Me,Me )Ni–SAr] analogues that adopt a sawhorse conformation, the ortho -disubstituted complexes show enhanced trigonal and Ni–S–Ar bending, reflecting the size of the 3-pyrazole substituents. Moreover, weakened scorpionate ligation is implied by spectroscopic data. Little spectroscopic effect is observed in the series of para -substituted complexes, suggesting the observed effects are primarily steric in origin. The relatively electron-rich and encumbered complex [(Tp Ph,Me )Ni–S–2,4,6- i Pr 3 C 6 H 2 ] behaves uniquely when dissolved in CH 3 CN, forming a square planar solvent adduct with a bidentate scorpionate ligand, [(κ 2 -Tp Ph,Me )Ni(NCMe)(S–2,4,6- i Pr 3 C 6 H 2 )]. This adduct was isolated and characterized by X-ray crystallography. Single-point DFT and TD-DFT calculations on a simplified [(κ 2 -Tp)Ni(NCMe)(SPh)] model were used to clarify the electronic spectrum of the adduct, and to elucidate differences between Ni–SAr bonding and spectroscopy between pseudotetrahedral and square planar geometries.