"Bidentate" and "tridentate" sulfonamide ligands for titanium complexes: Crystal structures and solution dynamics elucidating an η² or η³-coordination mode

Highly air- and moisture-sensitive complexes having sulfonamide ligands, (TsNR)₂Ti(NMe₂)₂ (Ts = p-MeC₆H₄SO₂), were prepared by treatment of two equivalents of TsNHR with Ti(NMe₂)₄ at room temperature. One of the compounds, where R = i-Pr (1), was studied in detail; the crystal structure of 1 revealed that both of the TsNi-Pr ligands were bound to the metal in an η²-coordination mode. Solution dynamics of 1 showed that an η¹/η² interconversion occurred above 60°C with an activation energy of 15.8 kcal mol^-1. Treatment of Ti(NMe₂)₄ with the sulfonamide TsHN(CH₂)₂O(CH₂)₂NHTs (3), led to the formation of [TsN(CH₂)₂O(CH₂)₂NTs]Ti(NMe ₂)₂ (2) in high yield, in which the sulfonamide moiety was coordinated to the titanium center in an η³ (NON) mode. No sign of η¹/η² interconversion of the sulfonamide ligands was seen in solution. Treatment of 2 with Me₃SiCl resulted in the formation of [{TsN(CH₂)₂O(CH₂)₂NTs}Ti(NMe ₂)Cl]₂ (4) and [{TsN(CH₂)₂O(CH₂)₂NTs}TiCl ₂]₂ (5). An X-ray structure determination of 4 revealed that sulfonyl oxygen bridging resulted in the formation of an eight membered ring.