s- and p-Block Dinuclear Metal(loid) Complexes Bearing 1,4-Phenylene and 1,4-Cyclohexylene Bridged Bis(amidinate) Ligands

Treating two 2,6-diisopropylphenyl (Dip) substituted, 1,4-phenylene or 1,4-cyclohexylene bridged, bis(amidine)s, viz. C₆H_n{[Dip(H)N](DipN=)C}₂-1,4 (n = 4 (PhAmid₂H₂) or 10 (CyAmid₂H₂)), with groups 1 and 2 alkyl complexes, proceeded via alkane elimination and the formation of the lithium and magnesium bis(amidinate) complexes, [{(THF)₂Li}₂(µ-PhAmid₂)], [{(THF)₃K(µ-PhAmid₂)K}_∞], [(Et₂O)IMg(µ-PhAmid₂)MgI(OEt₂)₂], and [{(Et₂O)₂IMg}₂(µ-CyAmid₂)]. The crystal structures of the complexes reveal variable modes of coordination at the metal centre. Two lithium bis(amidinate) compounds have been utilized in salt elimination reactions with group 13 and 14 halides, yielding a series of bis(amidinato) aluminum(III), silicon(IV), germanium(II) and tin(II) halide complexes, viz. [(I₂Al)₂(µ-PhAmid₂)], [(X₃Si)₂(µ-PhAmid₂)] (X = Cl, Br or Cl/H), [(ClM)₂(µ-PhAmid₂)] (M = Ge or Sn), and [(ClGe)₂(µ-CyAmid₂)]. Attempts to reduce the bis(amidinato) metal(loid) halide complexes with a series of s-block metal reducing agents have been carried out, with the aim of obtaining dinuclear or polymeric bis(amidinato) metal(I) systems. However, these reductions typically led to intractable mixtures of products. In other attempted reductions, treating [(Cl₂HSi)₂(µ-PhAmid₂)] with two N-heterocyclic carbenes (NHCs), :C{(RNCMe)₂} (R = Me (TMC) or Prⁱ (IPrIMe)) led to single dehydrochlorination reactions, affording the cyclohexa-2,5-diene-1,4-diylidene bridged bis(diamide) silicon(IV) complexes, [{(NHC)Cl₂Si}{µ-(DipN)₂C=(C₆H₄)=C(NDip)₂}{SiHCl(NHC)}] (NHC = TMC or IPrIMe), in which the bis(amidinate) ligand has been transformed into a tetra(amide).