The reactivity patterns of a series of molybdenum silyl hydrido complexes, [MoH3{[Ph2PCH2CH2P(Ph)C6H4-o]2(R)Si-P,P,P,P,Si}] (2a, R = Ph; 2b, R = C6F5; 2c, R = 4-Me2NC6H4; 2d, R = cyclohexyl; 2e, R = n-C6H13), toward electrophilic materials, including dioxygen, carbon dioxide, carboxylic acids, and triflic acid, have been explored. The influence of substituents directly attached to the Si atom in the quintuply chelating diphosphine–silyl ligands during the course of the reactions has been studied in detail. Complexes 2a–c react readily with dioxygen at ambient temperature, yielding η2-O2 complexes 3a–c, in which the dioxygen ligand ligates at the site opposite to the Si atom. Single-crystal X-ray studies have established that the Mo–O distance of 3a, which contains a phenyl-substituted Si fragment, is significantly longer than that found in common η2-O2 complexes, in which the sizes of the central atoms are nearly equal to that of Mo as a consequence of the strong trans influence of the silyl ligand. In contrast, the replacement of the phenyl group on a Si fragment by an electron-withdrawing perfluoro phenyl group, as in 3b, gives rise to a dramatic decrease in the trans influence. Treatment of 2a–c with 2 equiv of carboxylic acids, such as formic acid, acetic acid, and benzoic acid, readily leads to the formation of carboxylato molybdenum complexes, in which the carboxylate ligand coordinates to the metal in a monodentate mode. The resulting formato complex 4a1 can also be derived from the insertion of CO2 into the Mo–H bond of 2a. In addition, complexes 2a,c,e mediate the catalytic carbon dioxide hydrogenation. The activity of the catalysts depends dramatically on the electronic effects of the substituents attached to the Si atom; electron-donating substituents lead to an increase in the catalytic activity. Reactions of complexes 2a,d with triflic acid yield highly labile triflato complexes, which can be further treated with aqueous NaOH to give hydroxo complexes 5a,d, respectively. The molecular structure of 5d has been determined by single-crystal X-ray diffraction. The reactivities of 2a–e are discussed in comparison with those of the parent complex [MoH4(dppe)2] (1; dppe = Ph2PCH2CH2PPh2).

A molybdenum trihydride complex containing a tridentate silyl-phosphine ligand reacts with isocyanides to give isocyanide complexes, in which the Si atom and the isocyanides are cis to each other; the preferred configuration in the resulting complexes is reasonably explicable provided the Si fragment is acting as a good π-acid ligand.

Treatment of η3-allyl compound [Cp2Mo(η3-C3H5)]+ (1; Cp = η5-C5H5) with MH (M = Li, Na) resulted in reduction of the allyl ligand to give propane. Deuterium-labeling studies were used to trace the origins and fates of the hydrogen atoms. The mechanism is discussed in light of the HSAB principle. The studies showed that the formation of propane can be explained by 1,2-hydrogen migration from the central to the terminal carbon of the allyl ligand, and the subsequent double nucleophilic addition of the hydride at the central carbon.

The reaction of Cp2MoH2 (Cp=η5-C5H5) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η3-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η3-crotyl complex.The reaction of Cp2MoH2 (Cp=η5-C5H5) with homoallyl alcohol in the presence of a protonic acid afforded a cationic η3-crotyl molybdenum complex and a cyclic α-methyl-γ-hydroxypropyl molybdenum complex. This reaction proceeds via the stepwise formation of the cyclic complex, followed by formation of the η3-crotyl complex.

A complex [MoH3{Si(Ph)[Ph2PCH2CH2P(Ph)C6H4-o]2}] (1) can act as single-component catalyst for dehydrogenative polymerization of ArSiH2R (Ar = Ph, p-tolyl, o-tolyl; R = H, Me) to (ArSiR)n: p- and o- tolylsilane produced the polymers of respectable molecular weights (Mw of 17300 and 6700 respectively) and polymerization of secondary silane, methylphenylsilane, gave a substantial molecular weight (Mw of 1750).

A molybdenum trihydride complex containing a tridentate silyl-phosphine ligand reacts with isocyanides to give isocyanide complexes, in which the Si atom and the isocyanides are cis to each other; the preferred configuration in the resulting complexes is reasonably explicable provided the Si fragment is acting as a good π-acid ligand.