Square-Planar Iron(II) Silyl Complexes: Synthesis, Characterization, and Insertion Reactivity

Four- and three-coordinate planar iron(II) complexes supported by bulky organosilyl ligands

The ligand exchange reaction of (THF)2Fe[Si(SiMe3)3]2 with 2 equivalents of an N-heterocyclic carbene (NHC) led to the formation of a square-planar iron(II) complex with trans-oriented -Si(SiMe3)3 ligands. Conversely, the introduction of a cis-coordinate bidentate organosilyl ligand instead of -Si(SiMe3)3 resulted in the formation of a square planar iron(II) complex supported by a cis-coordinate bidentate organosilyl ligand. A three-coordinate planar iron(II) bis(silyl) complex was also synthesized using a cis-coordinate bidentate organosilyl ligand and a cyclic (alkyl)(amino)carbene auxiliary ligand. Investigation of the catalytic performance of these complexes in the hydrosilylation of acetophenone revealed that the square-planar iron(II) complex with trans-oriented -Si(SiMe3)3 ligands exhibits superior reactivity relative to its tetrahedral precursor.

Hydrosilylation of Aldehydes and Ketones Catalyzed by a 2-Iminopyrrolyl Alkyl-Manganese(II) Complex

A well-defined and very active single-component manganese(II) catalyst system for the hydrosilylation of aldehydes and ketones is presented. First, the reaction of 5-(2,4,6-iPr₃C₆H₂)-2-[N-(2,6-iPr₂C₆H₃)formimino]pyrrolyl potassium (KL) and [MnCl₂(Py)₂] afforded the binuclear 2-iminopyrrolyl manganese(II) pyridine chloride complex [Mn₂{κ²N,N'-5-(2,4,6-iPr₃C₆H₂)-NC₄H₂-2-C(H)═N(2,6-iPr₂C₆H₃)}₂(Py)₂(μ-Cl)₂] 1. Subsequently, the alkylation reaction of complex 1 with LiCH₂SiMe₃ afforded the respective (trimethylsilyl)methyl-Mn(II) complex [Mn{κ²N,N'-5-(2,4,6-iPr₃C₆H₂)-NC₄H₂-2-C(H)═N(2,6-iPr₂C₆H₃)}(Py)CH₂SiMe₃] 2 in a good yield. Complexes 1 and 2 were characterized by elemental analysis, ¹H NMR spectroscopy, Evans' method, FTIR spectroscopy, and single-crystal X-ray diffraction. While the crystal structure of complex 1 has been identified as a binuclear entity, in which the Mn(II) centers present pentacoordinate coordination spheres, that of complex 2 corresponds to a monomer with a distorted tetrahedral coordination geometry. Complex 2 proved to be a very active precatalyst for the atom-economic hydrosilylation of several aldehydes and ketones under very mild conditions, with a maximum turnover frequency of 95 min^-1, via a silyl-Mn(II) mechanistic route, as asserted by a combination of experimental and theoretical efforts, the respective silanes were cleanly converted to the respective alcoholic products in high yields.

Trapping of two mononuclear silyl platinum(ii)/palladium(ii) complexes and a unique dinuclear bis(μ2-disilene)(silyl)nickel(ii) complex

Two rare mononuclear bis(silyl)platinum(ii)/palladium(ii) intermediates and an unprecedented dinuclear bis(μ₂-disilene)(silyl)nickel(ii) complex have been trapped and prepared.

Manipulating metal spin states for biomimetic, catalytic and molecular materials chemistry

The relationship between ligand design and spin state in base metal compounds is surveyed. Implications and applications of these principles for light-harvesting dyes, catalysis and materials chemistry are summarised.