Synthesis, Reactivity and Ring-Opening Polymerization of a Tin-Bridged ansa-Cycloheptatrienyl-Cyclopentadienyl Titanium Sandwich Complex

Graphical Abstract

The synthesis of a tBu₂Sn-bridged ansa-cycloheptatrienyl-cyclopentadienyl titanium sandwich complex is presented. As a result of its tilted structure, this strained stanna[1]troticenophane is easily converted into poly(troticenylstannanes) by ring-opening polymerization and undergoes regioselective insertion of platinum(0) into the ipso-C₇H₆–Sn bond upon reaction with [Pt(PEt₃)₃].

Abstract

The tBu₂Sn-bridged [1]troticenophane [(η⁷-C₇H₆)Ti(η⁵-C₅H₄)]SntBu₂ (2) has been synthesized by low-temperature salt elimination reaction between stoichiometric amounts of the dilithiated troticene [(η⁷-C₇H₆Li)Ti(η⁵-C₅H₄Li)]·pmdta (1; pmdta = N,N′,N′,N″,N″-pentamethyltriethylenetriamine) and tBu₂SnCl₂. Compound 2 was isolated as a blue-green crystalline solid in moderate yield and characterized by multinuclear ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, UV/Vis spectroscopy and elemental analysis. Compound 2 and the co-crystal 2·[(pmdta)LiCl] were characterized in the solid state by X-ray diffraction analyses. The dihedral angles between the planes of the C₅H₄ and C₇H₆ rings are 16.3(3) and 17.2(1)°, respectively, for 2 and its co-crystal. Compound 2 is the first monocrystalline structurally characterized heteroleptic stanna[1]troticenophane. The reaction of 2 with [Pt(PEt₃)₃] afforded the platinastanna[2]troticenophane 3, in which the Pt⁰ fragment was inserted by regioselective cleavage of the ipso-C₇H₆–Sn bond, as evidenced by ¹³C NMR spectroscopy and X-ray diffraction analysis. Compound 2 underwent thermal ring-opening polymerization in the solid state to form poly(troticenylstannane) 4. In solution and in the presence of nBuLi as initiator, 2 opens and reassembles to form the metallopolymer 5. The polymeric nature of both 4 and 5 was determined by gel permeation chromatography.