Abstract:
This thesis describes the synthesis, structural studies, stoichiometric and catalytic
reactivity of novel Mo(IV) imido hydride complexes (Cp)(ArN)Mo(H)(PMe3) (1) and
(Tp )(ArN)Mo(H)(PMe3) (2). Both 1 and 2 catalyze hydrosilylation of a variety of
carbonyls. Detailed kinetic and DFT studies found that 1 reacts by an unexpected
associative mechanism, which does not involve Si-H addition either to the imido group or
the metal. Despite 1 being a d2 complex, its reaction with PhSiH3 proceeds via a a-bond
metathesis mechanism giving the silyl derivative (Cp )(ArN)Mo(SiH2Ph)(PMe3). In the
presence of BPh3 reaction of 1 with PhSiH3 results in formation of
(Cp)(ArN)Mo(SiH2Ph)(H)2 and (Cp)(ArN)Mo(SiH2Ph)2(H), the first examples ofMo(VI)
silyl hydrides.
AI: 1 : 1 reaction between 2, PhSiD3 and carbonyl substrate established that
hydrosilylation is not accompanied by deuterium incorporation into the hydride position
of the catalyst, thus ruling out the conventional mechanism based on carbonyl insertion
carbonyl. As 2 is nomeactive to both the silane and ketone, the only mechanistic
alternative we are left with is that the metal center activates the carbonyl as a Lewis acid.
The analogous nonhydride mechanism was observed for the catalysis by
(ArN)Mo(H)(CI)(PMe3), (Ph3P)2(I)(O)Re(H)(OSiMe2Ph) and (PPh3CuH)6.
Complex 2 also catalyzes hydroboration of carbonyls and nitriles. We report the first
case of metal-catalyzed hydroboration of nitriles as well as hydroboration of carbonyls at
very mild conditions. Conversion of carbonyl functions can be performed with high
selectivities in the presence of nitrile groups. This thesis also reports the first case of the HlH exchange between H2 and Si-H of
silanes mediated by Lewis acids such as Mo(IV) , Re(V) , Cu(I) , Zn(II) complexes,
B(C6Fs)3 and BPh3.
