(Me3N)Mo(CO)5-Catalyzed Reduction of DMF by Disiloxane and Disilane Moieties: Fate of the Silicon-Containing Fragments

The use of HSiMe 2 OSiMe 2 H ( 1 ) and various hydrodisilanes, R 3 SiSiMe 2 H ( 2; R = alkyl, aryl), as reductants for N,N -dimethylformamide (DMF) in the presence of (Me 3 N)Mo(CO) 5 as a catalyst led to the formation of a series of novel and structurally interesting siloxanes as well as trimethylamine. In the case of 1 the cyclic poly(dimethylsiloxanes) D 4 and D 6 are obtained, and for 2 the products are bis(disilyl) ethers, (R 3 SiSiMe 2 ) 2 O. Siloxymethylamine intermediates resulting from an initial hydrosilylation of DMF, (Me 2 NCH 2 OSiMe 2 ) 2 O ( 3 ) and R 3 SiSiMe 2 OCH 2 NMe 2 ( 4; R = Me, Ph), from the reactions of 1 and 2, respectively, can be observed and, in the case of 3, isolated and purified. In the presence of the respective starting silanes and the catalyst the intermediates readily react to form the appropriate siloxane materials and trimethylamine. Compound 3 was functionalized by reaction with R 3 ECl (E = Si, Ge, R = Me, Ph) to provide group 14 containing products (R 3 EOSiMe 2 ) 2 O (R = Me, E = Si ( 5a ), Ge ( 6a ); R = Ph, E = Si ( 5b ), Ge ( 6b )). Reactions of Me 3 SiSiMe 2 OCH 2 NMe 2 ( 4a ) with R 3 ECl produced Me 3 SiSiMe 2 OER 3 (R = Me, E = Si ( 7 ), R = Ph, E = Ge, 8 ). The crystal structure of (Ph 3 SiSiMe 2 ) 2 O ( 9c ) is reported and exhibits an Si–O–Si angle of 165° and the longest Si–Si bond length (2.376(2) Å) for such bis(disilyl) ethers. The new (Ph 3 EOSiMe 2 ) 2 O derivatives 5b and 6b have been structurally characterized and exhibit distinct conformations about the central SiOSi fragment. In the case of the Ph 3 Si compound 5b the dihedral angle between the two end groups is 180° with completely staggered SiMe groups on the central Si atoms, whereas for the Ge congener it is 55.7° and the structure exhibits eclipsed SiMe groups. The distinction seems to be due to both intra- and intermolecular phenyl group π stacking in 6b stabilizing this formally higher energy conformation.