Olefin metathesis is one of the most important industrial processes for the production of alkenes. In contrast, silicon versions of metathesis are unknown given the lack of available silylene transition-metal complexes suitable for [2 + 2] cycloaddition with unsaturated substrates. Here, we report the synthesis of 18-electron titanium silylene complexes featuring different Lewis base ligands and classified on the basis of structural, computational, and reactivity studies as Schrock-type silylene complexes. Because of the presence of loosely bound Lewis base ligands, such silylene complexes readily undergo reaction with simple unsaturated hydrocarbons, such as alkynes, forming the corresponding [2 + 2] cycloaddition products.

Unprecedented base-free bicyclic silylene complexes of molybdenum and tungsten 3a,b (a, M = Mo; b, M = W) were prepared by the reaction of the calcium salt of 1,2,3,4-tetrakis(di-tert-butylmethylsilyl)tetrasilabicyclo[1.1.0]butane-2,4-diide 2(2-) x Ca(2+) with Cp(2)MCl(2) (M = Mo, W). The unusual structural features of 3b (long SiW double bond, short skeletal (sp(2)-Si)-(sp(3)-Si) bonds and extremely long Si-Si bridge) are indicative of a contribution from the zwitterionic resonance form W(delta-)-Si(delta+), in which the electrophilic silicon center is stabilized by the Si(3)-homoaromatic conjugation. This was supported by the theoretical calculations (NBO, NPA) revealing the presence of pi(WSi) and sigma(Si-Si bridge) interactions.

Kein Ferryl als Oxidans: Die Oxidation von Thiafettsäuren durch P450BM3 (CYP102A1) ist das Ergebnis der Oxidation durch eine Eisen(III)‐hydroperoxy‐Verbindung (Verb. 0) und nicht durch die erwartete Eisen(IV)‐Verbindung (Verb. 1). Das ist der erste Hinweis darauf, dass die Schwefeloxidation in einem P450‐Wildtyp über eine Hydroperoxystufe verläuft.