A combination of phase-transfer and traditional alkylation strategies has been employed to synthesise sterically encumbered 1,3-di(cyclohexyl) and 1,3-di(tert-butyl) substituted indenes in multi-gram quantities. These indenyl ligands and sterically demanding alkyl cyclopentadienyl ligands have been used to prepare a series of [(η(7)-C(7)H(7))Zr(η(5)-L)] (L = Cp and Ind) complexes by straightforward salt metathesis between [(η(7)-C(7)H(7))ZrCl(tmeda)] and the corresponding sodium indenide or cyclopentadienide. All of these Zr complexes have been characterized by elemental analysis, NMR spectroscopy and single crystal X-ray diffraction. The structural information derived from these studies was employed to evaluate the steric demand of these ligands in a realistic manner.

The synthesis, structures, and magnetic properties of monomeric half-sandwich iron and cobalt imidazolin-2-iminato complexes have been comprehensively investigated. Salt metathesis reactions of [Cp'M(μ-I)] 2 (1-M, M = Fe, Co; Cp' = η 5 -1,2,4-tri-tertbutylcyclopentadienyl) with [Im Dipp NLi] 2 (Im Dipp N = 1,3-bis(2,6diisopropylphenyl)imidazolin-2-iminato) furnishes the terminal halfsandwich compounds [Cp'M(NIm Dipp )] (2-M, M = Fe, Co), which can be regarded as models for elusive half-sandwich iron and cobalt imido complexes. X-ray diffraction analysis confirmed the structure motif of a one-legged piano stool. Complex 2-Co can also be prepared by an acid−base reaction between [Cp'Co{N(SiMe 3 ) 2 }] (3-Co) and Im Dipp NH. The electronic and magnetic properties of 2-M and 3-Co were probed by 57 Fe Mossbauer spectroscopy (M = Fe), X-band EPR spectroscopy (M = Co), and solid-state magnetic susceptibility measurements. In particular, the central metal atom adopts a high-spin (S = 2) state in 2-Fe, while the cobalt complex 2-Co represents a rare example of a Co(II) species with a coordination number different from six displaying a low-spin to high-spin spin-crossover (SCO) behavior. The experimental observations are complemented by DFT calculations.

Adducts [Cp′FeI(NHC)] exhibit a highly anisotropic magnetic Ms = ±2 ground state resulting in unusual large spin–lattice (Orbach) relaxation barriers observed by zero-field 57Fe Mössbauer spectroscopy.

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Facile pseudohalide activation occurs in the reaction of SCN–, SeCN– and N3– with the iron half-sandwich [Cp′Fe(μ-I)]2.

Salt metathesis of [Cp′FeI]2 [1, Cp′ = η5‐1,2,4‐(Me3C)3C5H2] and NaBH4 (2 equiv.) in tetrahydrofuran yields the low‐spin iron complex [Cp′Fe(η3‐BH4)] (2), which is thermally unstable and degrades slowly to the trimeric complex [Cp′FeBH2]3 (3) and H2. Both molecules have been fully characterized by various spectroscopic techniques. An X‐ray structure analysis of 3 confirms its nature and reveals rather long B–B distances of 1.883(9) Å. DFT methods in combination with three complementary approaches [Wiberg bond indices (WBI), atoms in molecules (AIM) and compliance constants] have been used to explain the bonding in these iron(II) complexes. All methods predict a weak bonding interaction between the boron atoms in 3.

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