Molybdenocene trihydride complexes: influence of a [Me2Si] ansa bridge on classical versus nonclassical nature, stability with respect to elimination of dihydrogen, and acidity.

Experimental and computational studies on a series of cationic molybdenocene trihydride complexes, namely [Cp2MoH3]+, [(CpBut)2MoH3]+, [Cp*2MoH3]+, and {[Me2Si(C5Me4)2]MoH3}+, demonstrate that the most stable form for the ansa molybdenocene derivative is a nonclassical dihydrogen−hydride isomer, {[Me2Si(C5Me4)2]Mo(η2-H2)(H)}+, whereas the stable forms for the non-ansa complexes are classical trihydrides, [Cp2Mo(H)3]+, [(CpBut)2Mo(H)3]+, and [Cp*2Mo(H)3]+. In addition to altering the classical versus nonclassical nature of [Cp*2MoH3]+ and {[Me2Si(C5Me4)2]Mo(η2-H2)(H)}+, the [Me2Si] ansa bridge also markedly influences the stability of the complex with respect to elimination of H2 and dissociation of H+. Finally, computational studies on {[H2Si(C5H4)2]MoH2D}+ and {[H2Si(C5H4)2]MoHD2}+ establish that deuterium exhibits a greater preference than hydrogen to occupy dihydrogen versus hydride sites.