Pyridylalkenolato-Stabilized Heavier Tetrylenes: Air-Stability Studies and Preliminary Coordination Chemistry

The potential of 3,3,3-trifluoro-1-(2-pyridyl)prop-1-en-2-ol (tfppOH) as a precursor to synthesize air-stable heavier tetrylenes (HTs), either free or coordinated, was examined. Thus, the stability toward air and water of the homoleptic HTs E(tfppO)₂ (E = Ge (1_Ge), Sn (1_Sn)), which were previously reported by Mathur and coworkers and claimed to be highly air-stable, was evaluated together with that of the novel heteroleptic chloro-HTs E(tfppO)Cl (E = Ge (2_Ge), Sn (2_Sn)). These analyses have shown that all these compounds are susceptible to undergo hydrolysis at room temperature, albeit at very different rates for each HT. DFT calculations have been used to study the mechanism of these hydrolytic processes. Additionally, a preliminary study of the coordination chemistry of these HTs was conducted. The reactions of 0.5 equiv of [Ir₂Cl₂(μ-Cl)₂(η⁵-Cp*)₂] with 2_Ge cleanly afforded the Ge-Ir complex [IrCl₂(η⁵-Cp*){κ¹Ge-Ge(tfppO)Cl}] (3_Ge); however, the analogous stannylene 2_Sn led to a complex mixture, and the homoleptic derivatives 1_E resulted in ligand degradation (formation of the HT-free complex [IrCl(η⁵-Cp*){κ²N,O-(tfppO)}] (4)). The Ge-Au complexes [AuCl{κ¹Ge-Ge(tfppO)₂}] (5_Ge) and [AuCl{κ¹Ge-Ge(tfppO)₂}₂] (6_Ge) could be prepared by reacting 1_Ge with [AuCl(tht)] (tht = tetrahydrothiophene); however, only the precipitation of dark-purple solids was observed using 1_Sn. On the other hand, both 1_E were capable of rendering the diHT-Ag analogous compounds [Ag{κ¹E-E(tfppO)₂}₂]OTf (E = Ge (7_Ge), Sn (7_Sn)) in their reactions with AgOTf. The air-stability of all these complexes in solution was proven to be similar or lower (for 7_Sn) than that of the corresponding metal-free HTs.