Sergei F. Vyboishchikov

Cp(Pri2MeP)FeH2SiR3 : Nonclassical Iron Silyl Dihydride

Reactions of a new borohydride complex 2 with hydrosilanes afford half-sandwich dihydride silyl complexes 3a-f. According to X-ray and DFT evidence complexes 3 have unprecedented double H...Si...H interligand interactions.

Facile activation of H-H and Si-H bonds by boranes.

The borane B(C(6)F(5))(3) is a precatalyst for H/Dexchange between H(2) and deuterium-labeled silanes (D(3)SiPh, D(2)SiMePh, DSiMe(2)Ph, DSiEt(3)). Experimental and DFT studies reveal that B(C(6)F(5))(3) itself cannot activate dihydrogen but converts to HB(C(6)F(5))(2) under the action of hydrosilane. The latter species easily activates H-H and Si-H bonds by a σ-bond metathesis mechanism, which was further confirmed by the reactions of BD(3)·THF with H(2).

NIOBOCENE SILYL HYDRIDE COMPLEXES WITH NONCLASSICAL INTERLIGAND HYPERVALENT INTERACTIONS

Niobocene mono- and bis(silyl) hydrides with dimethylhalosilyl groups exhibit a nonclassical interligand hypervalent interaction (IHI) between the hydride and silyl ligands. These interactions result in well-defined structural and reactivity trends and were found in two forms: three-centre, four-electron (A) and five-centre, six-electron (B), as shown schematically.

Oxidative Cleavage of C=S and P=S Bonds at an AlI Center: Preparation of Terminally Bound Aluminum Sulfides

The treatment of cyclic thioureas with the aluminum(I) compound NacNacAl (1; NacNac=[ArNC(Me)CHC(Me)NAr]- , Ar=2,6-Pri2 C6 H3 ) resulted in oxidative cleavage of the C=S bond and the formation of 3 and 5, the first monomeric aluminum complexes with an Al=S double bond stabilized by N-heterocyclic carbenes. Compound 1 also reacted with triphenylphosphine sulfide in a similar manner, which resulted in cleavage of the P=S bond and production of the adduct [NacNacAl=S(S=PPh3 )] (8). The Al=S double bond in 3 can react with phenyl isothiocyanate to furnish the cycloaddition product 9 and zwitterion 10 as a result of coupling between the liberated carbene and PhN=C=S. All novel complexes were characterized by multinuclear NMR spectroscopy, and the structures of 5, 9, and 10 were confirmed by X-ray diffraction analysis. The nature of the Al=S bond in 5 was also probed by DFT calculations.

Dynamics of Si-H-Si Bridges in Agostically Stabilized Silylium Ions

The silylium ion [C(6)(SiMe(2))(SiHMe(2))(5)](+) offers an amazing example of multiple Si...H interactions. It exhibits a symmetric Si(alpha)-H-Si(alpha) motif supported by two additional Si(beta)-H...Si(alpha) agostic interactions. This cation is highly fluctional in NMR spectra at room temperature due to shift of the hydride bridge. The DFT calculations show that the hydride shift is related to internal rotation of silyl groups. We performed NMR, static DFT, and dynamics studies of this process and found two possible mechanisms, associated with internal rotation of either beta- or gamma-silyls. The energy barrier is largely caused by the silyl internal rotation, whereas the hydride transfer itself is intrinsically quite easy. The gamma-silyl rotation is somewhat more favorable than the beta-silyl rotation. Vibrational dynamics of the cation is also discussed.

Unusual Reactions of NacNacAl with Urea and Phosphine Oxides

The reaction of cyclic urea 1,3-dimethyl-2-imidazolidinone with the aluminum(I) compound NacNacAl (1) gives an unexpected adduct of urea with the isomerized aluminum(III) hydride NacNacAlH(O═SIMe) (3). A related reaction of 1 with phosphine oxides results in cleavage of the P═O bond and formation of hydroxyl derivatives NacNacAl(OH)(O═PR3) [R = Ph (5) and Et (6)]. Density functional theory calculations revealed that these reactions proceed via a bimolecular mechanism in which either the basic aluminum(I) center or the transient Al═O species deprotonate the methyl group of the NacNac ligand.