Ligand effects in the syntheses and structures of novel heteroleptic and homoleptic bismuth(iii) formamidinate complexes

Abstract

Metathesis reactions of the alkali metal formamidinates M(RNC(H)NR), M = Li or K; R = C₆H₃-2,6-Prⁱ₂ (L¹), C₆H₃-2,6-Et₂ (L²); C₆H₂-2,4,6-Me₃ (L³), C₆H₃-2,6-Me₂ (L⁴) or C₆H₄-2-Ph (L⁵), with BiX₃ (X = Cl or Br) gave a range of bismuth(III) formamidinate complexes [Bi(L)Br(µ-Br)(thf)]₂ (L = L¹, L⁴), [{Bi(L¹)Cl₂(thf)}₂Bi(L¹)Cl₂], [Bi(L)₂X] (L = L², L⁵, X = Br; L = L¹, X = Cl), and [Bi(L)₃] (L = L², L³). An analogous organometallic complex Bi(L¹)₂Buⁿ was also isolated as a side product in one instance. Structural characterisation of the di-halide complexes show symmetrical dimers for X = Br, with two bromide bridges, and a coordinated thf molecule on each Bi atom, whereas for X = Cl a thf deficient species was crystallised, and has a weakly associated trinuclear array with two coordinated thf molecules per three Bi atoms. Complexes of the form Bi(L)₂X (X = Br, Cl, Buⁿ) and Bi(L)₃ all have monomeric structures but the Bi(L)₃ species show marked asymmetry of the formamidinate binding, suggesting that they have reached coordination saturation.