Transition-Metal Complexes of Diphosphanes Containing the η7‑Cycloheptatrienyl‑η5‑Cyclopentadienyl Titanium (Troticene) Sandwich Moiety

Dilithiation of the sandwich complex η7-cycloheptatrienyl-η5-cyclopentadienyl titanium (troticene) with n-butyllithium in the presence of N,N′,N′,N″,N″-pentamethyldiethylenetriamine (pmdta) and subsequent reaction with chlorodialkylphosphanes (ClPR2) afforded the diphosphanes [(η7-C7H6PR2)­Ti­(η5-C5H4PR2)] (4R, R = iPr, Cy, tBu). The reactions of the cyclohexyl derivative 4Cy with transition-metal dichlorides furnished the complexes [(4Cy)­MCl2] (7M), which showed tetrahedral (M = Fe, Co Ni, Zn) and square-planar (M = Pd) coordination spheres. The corresponding platinum complexes trans- and cis-[(4Cy)­PtCl2] (trans-7Pt and cis-7Pt) were isolated from the reactions of 4Cy with either trans- or cis-[(SEt2)2PtCl2], and trans-7Pt slowly converted into the thermodynamically more stable cis-7Pt within ca. 17.5 h in dichloromethane solution at room temperature. Chloride abstraction from cis-7Pt with potassium tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate (KBArF24) gave the bimetallic chloro-bridged complex [(4Cy)­Pt­(μ-Cl)]2[BArF24]2 (8) or, in the presence of trimethylphosphane (PMe3), the cationic complex [(4Cy)­PtCl­(PMe3)]­[BArF24] (9); however, these species did not feature the anticiptated titanium–platinum interactions. An intramolecular redox reaction was observed upon the reaction of 4Cy with cis-[(MeCN)2PtCl2)], affording the titanium­(IV)–platinum(0) complex 10 with a bridging ketimide (MeCN). Density functional theory (DFT) calculations suggest that this complex might have formed via [{(η5-C5H4PCy2)­TiCl2(η1-C7H6PCy2)}­Pt] (11) with subsequent insertion of acetonitrile into the remaining Ti–C bond between titanium and the seven-membered ring.