N-Heterocyclic carbenes (NHCs) possessing one or two 3,4-dimethylphosphaferrocenyl substituents and either methylene or ethylene alkyl bridges have been prepared. These carbenes turned out to be remarkably stable and were characterized by NMR methods and partly by mass spectrometry. Their molybdenum and ruthenium complexes were examined in order to determine the electronic properties and the coordination behaviour of these chiral PC- and PCP-chelate ligands, which combine a NHC unit as a strong sigma-donor with pi-accepting phosphaferrocene moieties. Crystal structures of one ligand precursor and of three complexes have been determined.

The synthesis of new planar chiral P,N-ligands based on 3,4-dimethylphosphaferrocene and either pyrazole or 1-methylimidazole is described. The coordination chemistry of the hemilabile pyrazole derivatives 3a and 3b (a features a methylene bridge between the heterocycles, b an ethylene bridge) was investigated and afforded complexes [Mo(3)(CO) 5 ], cis-[Mo(3) 2 (CO) 4 ], [Cp*RuCl(3)], [Cp*Ru-(3) 2 ]OTf, [Cp*RuCl(3)(PPh 3 )], and [Pd(η 3 -allyl)(3)]PF 6 . Reaction of the imidazole derivatives 4a and 4b with [Pd(η 3 -allyl)Cl] 2 and TlPF 6 yielded [Pd(η 3 -allyl)( 4)]PF 6 . The Pd complexes of 3 and 4 were tested in the catalytic asymmetric allylic alkylation reaction of 1,3-diphenylallyl acetate with sodium dimethylmalonate. X-ray structures of one Ru complex and one Pd complex of 3a were determined.

The influence of the length of the linking alkyl spacer and of the presence of either a proton or a methyl group, in four related terdentate N3 Schiff base ligands, on the structures and properties of the resulting iron(II) and cobalt(II) complexes has been investigated. The four ligands were prepared in situ by condensation of 2‐(2‐aminoethyl)pyridine or 2‐(aminomethyl)pyridine with 2‐acetylpyridine (L1 vs. L3) or 2‐formylpyridine (L2 vs. L4). Hence they comprised a mixture of a relatively rigid chelate with a 2‐iminopyridyl moiety, comparable to bipyridine coordination, and a more flexible chelate containing the –(CH2)n– spacer. Four iron(II) complexes, [Fe(L1)2](BF4)2 (1), [Fe(L2)2](BF4)2 (2), [Fe(L3)2](BF4)2 (3), [Fe(L4)2](BF4)2 (4), were obtained whereas only in the case of the two ethylene (i.e. not methylene) spaced ligands could pure cobalt(II) complexes, [Co(L1)2](BF4)2 (5), [Co(L2)2](BF4)2 (6), be obtained. The 1H NMR spectra confirmed that in MeCN 1–4 are diamagnetic whereas 5 and 6 are paramagnetic. X‐ray structure determinations of the ethylene‐linked complexes, 1, 5 and 6, revealed distorted octahedral geometries due to chelate ring restrictions. The M–N distances were typical for high‐spin cobalt(II) (5 and 6) and for low‐spin iron(II) (1). The magnetic data on 5 and 6 are typical of those expected for distorted octahedral high‐spin d7 species; fitting attempts have yielded zero‐field splitting and low symmetry ligand field parameters. A metal‐centred M2+/3+ redox wave and ligand‐based reduction processes were observed for 1–6 in MeCN. The metal‐centred redox potential (Fe: 1 0.59, 2 0.68, 3 0.58, 4 0.70 V; Co: 5 0.03, 6 0.09 V vs. Fc/Fc+) was influenced much more strongly by the presence of the proton vs. methyl group (Fe: shift of 0.09–0.12 V, Co: shift of 0.06 V) than by the bridging methylene vs. ethylene group (Fe: shift of 0.01–0.02 V).

A heteroleptic N(6) coordinated Ru(II) complex acts as a building block for a discrete tetranuclear mixed metal Ru(II)(2)Ag(I)(2) coordination compound; both complexes have been structurally characterised by X-ray crystallography.