σ or π? Bonding interactions in a series of rhenium metallotetrylenes

Abstract

Salt metathesis reactions between a low-valent rhenium(I) complex, Na[Re(η⁵-Cp)(BDI)] (BDI = N,N′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate), and a series of amidinate-supported tetrylenes of the form ECl[PhC(N^tBu)₂] (E = Si, Ge, Sn) led to rhenium metallotetrylenes Re(E[PhC(N^tBu)₂])(η⁵-Cp)(BDI) (E = Si (1a), Ge (2), Sn (4)) with varying extents of Re–E multiple bonding. Whereas the rhenium–stannylene 4 adopts a σ-metallotetrylene arrangement featuring a Re–E single bond, the rhenium–silylene (1a) and –germylene (2) both engage in π-interactions to form short Re–E multiple bonds. Temperature was found to play a crucial role in reactions between Na[Re(η⁵-Cp)(BDI)] and SiCl[PhC(N^tBu)₂], as manipulation of reaction conditions led to isolation of an unusual rhenium–silane, (BDI)Re(μ-η⁵:η¹-C₅H₄)(SiH[PhC(N^tBu)₂]) (1b) and a dinitrogen bridged rhenium–silylene, (η⁵-Cp)(BDI)Re(μ-N₂)Si[PhC(N^tBu)₂] (1c), in addition to 1a. Finally, the reaction of Na[Re(η⁵-Cp)(BDI)] with GeCl₂·dioxane led to a rare μ₂-tetrelido complex, μ₂-Ge[Re(η⁵-Cp)(BDI)]₂ (3). Bonding interactions within these complexes are discussed through the lens of various spectroscopic, structural, and computational investigations.