The first homoleptic lanthanide(II)-guanidinate complexes have been prepared and shown to have differing coordination geometries (including unprecedented examples of planar 4-coordination) that depend on the size of the lanthanide metal.

Cyclic diamino plumbylenes derived from saturated heterocycles are obtained from deprotonation of diamines and subsequent reaction with PbCl(2), or by reaction of a suitable diamine with Pb[N(SiMe(3))(2)](2). Single crystal X-ray studies have been used to probe the solid state structures of a range of these complexes and have shown the fine balance between monomer and dimer formation which is related to the bulk of the organic group attached to the nitrogen atoms. Dimerisation is also shown to effect structural changes within the core of the heterocyclic plumbylene.

The preparation of a series of homoleptic, four-coordinate lanthanide(ii) complexes, [Ln(Priso)(2)] (Ln = Sm, Eu or Yb) incorporating the bulky guanidinate ligand Priso(-) ([(ArN)(2)CNPr(i)(2)](-), Ar = 2,6-diisopropylphenyl) is described. X-ray crystallography shows the complexes to be isostructural and to exhibit coordination geometries midway between tetrahedral and planar. Comparisons between the geometries of the complexes and those of the bulkier systems, [Ln(Giso)(2)] (Giso(-) = [(ArN)(2)CNCy(2)](-), Cy = cyclohexyl) are discussed. Attempts to prepare the less hindered amidinate complexes, [Ln(Piso)(2)] (Piso(-) = [(ArN)(2)CBu(t)](-)), were not successful, but did give rise to the heteroleptic complex, [(kappa(1)-N,eta(6)-Piso)Sm(THF)(mu-I)(2)Sm(kappa(1)-N,eta(6)-Piso)]. Whereas the amidinate ligands in this complex chelate the samarium centre in an kappa(1)-N,eta(6)-Ar-fashion, in the closely related complex, [{(kappa(2)-N,N'-Priso)Yb(THF)(mu-I)}(2)], the ytterbium atoms are kappa(2)-N,N'-chelated by the guanidinate ligand. The facility of the planar four-coordinate complex, [Sm(Giso)(2)], to act as a one-electron reducing agent towards a variety of unsaturated substrates has also been explored. The complex has been shown to selectively reductively couple CS(2), via a C-S bond formation, to give the samarium(iii) dimer, [(Giso)(2)Sm(mu-eta(2)-:eta(2)-S(2)CSCS)Sm(Giso)(2)].

Reaction of the N,N'-diisobutyl-substituted benzannulated N-heterocyclic plumbylene (NHPb) 1 with [Pd(PPh(3))(4)] and [Pt(PPh(3))(4)] gave the complexes [M(NHPb)(PPh(3))(3)] (M = Pd [2], Pt [3]). X-ray diffraction studies of both complexes showed an angle of ~125° between the plumbylene plane and the transition-metal-Pb axis, indicating coordination of the transition metal to the empty π orbital of the plumbylene Pb atom. The experimentally determined metric parameters of complexes [2] and [3] are discussed on the basis of DFT calculations.

The reaction of N,NЈ-dialkyl-1,2-diaminobenzenes with bis[bis(trimethylsilyl)amido]lead(II) leads to the corresponding N-heterocyclic plumbylenes (R = Me: 1; R = Et: 2; R = isobutyl: 3; R = neopentyl: 4). The steric demand of the N,NЈ-dialkyl substituents determines the mode of aggregation of the plumbylenes. X-ray diffraction analyses show both 3