The path to an open-shell metallo-germylene: direct ligation, or reduction and metathesis?

Abstract

Reaction of chelating cationic germylene ligand [^PhiPDipGe]⁺ (1; ^PhiPDip = {[Ph₂PCH₂Si(ⁱPr)₂](Dip)N}; Dip = 2,6-ⁱPr₂C₆H₃) with the NHC-stabilised Co⁰ system [IPr·Co(η₂-vtms)₂] (IPr = [(H)CN(Dip)C:]; vtms = C₂H₃(SiMe₃) gives ready access to the first example of an open-shell metallo-germylene in high yields, in T-shaped Co complex 2. The Co centre in 2 is found to have a low-spin d⁷ electronic structure which bears a high-spin density of the single unpaired electron in this complex, corroborated by SQUID magnetometry, EPR spectroscopy, and quantum-chemical calculations. Detailed analysis of the electronic structure of 2 establishes the electron-sharing covalent nature of the germanium cobalt interaction. Still, the pathway to 2 is not trivial: at first glance, it seems as though complex 2 is formed via a simple insertion of Co⁰ into the P–Ge bond in 1. However, modifying reaction conditions leads to the isolation of fragments of complex 2 (viz. 3, 4, and 5), all of which are fully characterised. It is ultimately found that these arise from the initial formation of dimeric germanium(I) species 7, formed by reduction of 1 by Co⁰. Depending on stoichiometry, 7 reacts with intermediary Co^I species forming fragments 3–5, or the target cobalto-germylene 2. These results thus demonstrated that 2 is in fact formed via the homolytic metathesis of a Ge^I–Ge^I bond at Co^I, so opening an unprecedented route to such metallo-tetrylenes.