σ‐ or π‐Coordination? Complexes of Univalent Gallium Salts with Aromatic Nitrogen Bases

Abstract

Abstract To answer the question as to whether gallium in its oxidation state +1 favors a σ‐ or a π‐coordination of aromatic nitrogen bases, we reacted [Ga(C 6 H 5 F) 2 ] + [Al(OR F ) 4 ] – {R F = C(CF 3 )} with pyrazine and 2,6‐di‐ tert ‐butyl‐4‐methylpyridine (DTBMP). In doing so, we obtained the first tricoordinate, nonchelated, homoleptic N‐donor complex of gallium(I): [Ga(pyrazine) 3 ] + [Al(OR F ) 4 ] – , in which each gallium(I) cation is coordinated in a trigonal‐pyramidal fashion by three η 1 ‐donating pyrazine ligands. Hence, the gallium(I) cations favor σ‐ over π‐coordination. Depending on the reaction conditions, and due to the bifunctionality of pyrazine, 1D coordination polymers of {[Ga(μ‐pyrazine) 2 (η 1 ‐pyrazine)] + [Al(OR F ) 4 ] – } ∞ were also obtained. With the sterically demanding DTBMP, which is conventionally used as a proton scavenger, the mixed complex [Ga(C 6 H 5 F) 2 (DTBMP)] + [Al(OR F ) 4 ] – was isolated, thus proving incorrect the perception of DTBMP being “non‐nucleophilic”. The structural findings were confirmed by multinuclear NMR investigations and density functional performed at the RI‐BP86/SV(P) level.