Reactions of bls(imldo) compounds (RN)2Mo(PMe3) n {n = 2, R = tBu; n = 3, R =2,6-dlmethylphenyl (Ar′) and 2,6-dlisopropylphenyl (Ar)) and (RN)2W(PMe 3)3 (R = 2,6-dimethylphenyl and 2,6-dlisopropylphenyl) with sllanes afford four types of products: the β-agostic silylamldo compounds (RN)(η3-RN-SiR′2-H ⋯)MCl(PMe3)2 (M = Mo and W), mono(lmides) (RN)MCl2(PMe3)3 (M = Mo and W), silyl hydride bis(imido) derivative (ArN)2W(PMe3)(H)(SiMeCl 2), and Si - Cl⋯W bridged product (ArN)(η2-ArN- SiHMeCl-Cl ⋯)WCl(PMe3)2. Reactions of molybdenum compounds (RN)2Mo(PMe3)m (m=2 or 3) with mono- and dichlorosilanes HSiClnR′3-n (R′ = Me, Ph; n = 1,2) afford mainly the agostic compounds (RN)(η3-RN- SiR′2-H ⋯)MoCl(PMe3)2, accompanied by small amounts of mono(lmido) derivatives (RN) MoCl2(PMe 3)3. In contrast, the latter compounds are the only transition metal products in reactions with HSiCl3, the silicon co-product being the sllanlmine dlmer (RNSiHCl)2. The reaction of (ArN)2W(PMe3)3 with HSiCl2Me under continuous removal of PMe3 affords the silyl hydride species (ArN)2W(PMe3)(SiMeCl2)H, characterized by NMR and X-ray diffraction. This product is stable in the absence of phosphine, but addition of catalytic amounts of PMe3 causes a fast rearrangement into the Si-Cl⋯W bridged product (ArN)(η2-ArN-SiHMeCl-Cl⋯) WCl(PMe3)2. The mechanism of silane addition to complexes (RN)2Mo(PMe3)n has been elucidated by means of density functional theory calculations of model complexes (MeN) 2Mo(PMe3)n (n=1-3). Complex (MeN) 2Mo(PMe3)2 is found to be the most stable form. It undergoes facile silane-to-imldo addition reactions that afford sllylamido hydride complexes stabilized by additional Si ⋯ H interactions. The ease of this addition increases from HSiMe2Cl3 to HSiCl 3, consistent with experimental observations. The most stable final products of silane addition are the agostlc complexes (MeN)(η3- MeN-SiR2-H - ⋯) MoCl(PMe3)2 (R 2 = Me2, MeCl, Cl2) and Cl-brldged silylamldo complexes (MeN)(η-MeN-SiRH-Cl ⋯)MoCl(PMe3)2 (R = Me or Cl). In the case of HSiMeCl2 addition the former is the most stable, but for HSiCl3 addition the latter ls the preferred product. In all cases, the isomeric silyl hydride species (MeN)2Mo(PMe 3)(H)(SiClR2) are less stable by about 6 kcal mol -1. Silane additions to the imido ligand of the tris(phosphine) (MeN)2Mo(PMe3)3 afford octahedral sllylamido hydride derivatives. The different isomers of these addition products are destabilized relative to (MeN)2Mo(PMe3)3 only by 7-24 kcal mol-1 (for the HSiMe2Cl additions), but since the starting tris(phosphlne) ls 14.8 kcal mol-1 less stable than (MeN)2Mo(PMe3)2, silane addition to the latter ls a more preferred pathway. A double phosphine dissociation pathway via the species (MeN)2Mo(PMe3) was ruled out because this complex is by 24.7 kcal mol-1 less stable than (MeN)2Mo(PMe 3)2. © 2009 American Chemical Society.
