Experimental and theoretical charge density studies and molecular orbital analyses suggest that the complexes [Cp2Ti(PMe3)SiH2Ph2] (1) and [Cp2Ti(PMe3)SiHCl3] (2) display virtually the same electronic structures. No evidence for a significant interligand hypervalent interaction could be identified for 2. A bonding concept for transition-metal hydrosilane complexes aims to identify the true key parameters for a selective activation of the individual M-Si and Si-H bonds.

In general, it is assumed that the reaction between silanes and late transition metal fragments yields silyl hydride species as oxidative addition products. However, the silane complex Ni(iPr 2 Im) 2 (SiHMePh 2 ) (iPr 2 Im = 1,3-diisopropylimidazolin-2-ylidene) (3a), might represent one of the rare systems where a stable η 2 -(Si-H)Ni intermediate of the oxidative addition process has been isolated. Indeed, 3a is characterized by an acute ЄSi-Ni-H angle of * Prof. Dr. U. Radius,

We will outline that the sign and magnitude of J(Si,H) coupling constants provide a highly sensitive tool to measure the extent of Si-H bond activation in nonclassical silane complexes. Up to now, this structure-property relationship was obscured by erroneous J(Si,H) sign determinations in the literature. These new findings also help to identify the salient control parameters of the Si-H bond activation process in nonclassical silane complexes.

We outline in this combined experimental and theoretical NMR study that sign and magnitude of J(Si,H) coupling constants provide reliable indicators to evaluate the extent of the oxidative addition of Si-H bonds in hydrosilane complexes. In combination with experimental electron density studies and MO analyses a simple structure-property relationship emerges: positive J(Si,H) coupling constants are observed in cases where M → L π-back-donation (M = transition metal; L = hydrosilane ligand) dominates. The corresponding complexes are located close to the terminus of the respective oxidative addition trajectory. In contrast negative J(Si,H) values signal the predominance of significant covalent Si-H interactions and the according complexes reside at an earlier stage of the oxidative addition reaction pathway. Hence, in nonclassical hydrosilane complexes such as CpTi(PMe)(HSiMeCl) (with n = 1-3) the sign of J(Si,H) changes from minus to plus with increasing number of chloro substituents n and maps the rising degree of oxidative addition. Accordingly, the sign and magnitude of J(Si,H) coupling constants can be employed to identify and characterize nonclassical hydrosilane species also in solution. These NMR studies might therefore help to reveal the salient control parameters of the Si-H bond activation process in transition-metal hydrosilane complexes which represent key intermediates for numerous metal-catalyzed Si-H bond activation processes. Furthermore, experimental high-resolution and high-pressure X-ray diffraction studies were undertaken to explore the close relationship between the topology of the electron density displayed by the η(Si-H)M units and their respective J(Si,H) couplings.

Experimentelle und theoretische Ladungsdichtestudien in Verbindung mit Molekülorbital‐Analysen legen nahe, dass [Cp2Ti(PMe3)SiH2Ph2] (1) und [Cp2Ti(PMe3)SiHCl3] (2) nahezu identische elektronische Strukturen aufweisen. Folglich kann für 2 kein Beweis für signifikante hypervalente Wechselwirkungen zwischen den Liganden gefunden werden. Das vorgeschlagene Bindungskonzept für Übergangsmetall‐Hydrosilankomplexe soll dabei helfen, die entscheidenden Parameter für eine selektive M‐Si‐ und Si‐H‐Bindungsaktivierung zu identifizieren.