A New Catalytic Route for the Activation of sp-Hybridized Carbon–Hydrogen Bonds

Inorganometallics (Transition Metal-Metalloid Complexes) and Catalysis

While the formation and breaking of transition metal (TM)-carbon bonds plays a pivotal role in the catalysis of organic compounds, the reactivity of inorganometallic species, that is, those involving the transition metal (TM)-metalloid (E) bond, is of key importance in most conversions of metalloid derivatives catalyzed by TM complexes. This Review presents the background of inorganometallic catalysis and its development over the last 15 years. The results of mechanistic studies presented in the Review are related to the occurrence of TM-E and TM-H compounds as reactive intermediates in the catalytic transformations of selected metalloids (E = B, Si, Ge, Sn, As, Sb, or Te). The Review illustrates the significance of inorganometallics in catalysis of the following processes: addition of metalloid-hydrogen and metalloid-metalloid bonds to unsaturated compounds; activation and functionalization of C-H bonds and C-X bonds with hydrometalloids and bismetalloids; activation and functionalization of C-H bonds with vinylmetalloids, metalloid halides, and sulfonates; and dehydrocoupling of hydrometalloids. This first Review on inorganometallic catalysis sums up the developments in the catalytic methods for the synthesis of organometalloid compounds and their applications in advanced organic synthesis as a part of tandem reactions.

Fluoride Ion-Initiated Decarboxylation of Silyl Alkynoates to Alkynylsilanes

This communication describes the development of a metal-free catalytic decarboxylation of silyl alkynoates to alkynylsilanes. Treatment of a silyl alkynoate with a catalytic amount of tetrabutylammonium difluorotriphenylsilicate (TBAT) in N,N-dimethylformamide at 150 °C resulted in decarboxylation to give the corresponding alkynylsilane in good to excellent yield (75 → 95%). The TBAT system was applicable to the decarboxylation of sterically demanding silyl alkynoates such as tert-butyldiphenylsilyl 3-phenylpropiolate. Mechanistic studies revealed that the tetrabutylammonium alkynoate derived from TBAT and the silyl alkynoate act as a catalyst for the decarboxylation.

Ruthenium-catalyzed dealkenative N-silylation of amines by substituted vinylsilanes

The [RuHCl(CO)(PCy₃)₂]-catalyzed N-silylation of primary and secondary amines with substituted vinylsilanes leads to the formation of a Si–N bond with the evolution of olefin.

α-Functionalization of non-activated aliphatic amines: ruthenium-catalyzed alkynylations and alkylations

Catalytic α-alkylations and -alkynylations of non-activated aliphatic amines with silylated alkynes proceed selectively in the presence of the Shvo catalyst.

Highly selective dehydrogenative silylation of alkenes catalyzed by rhenium complexes

Choosy chemicals: Rhenium(I) complexes of type [ReBr(2)(L)(NO)(PR(3))(2)] (L=H(2) (1), CH(3)CN (2), ethylene (3); R=iPr (a), cyclohexyl (b)) proved to be suitable catalyst precursors for the highly selective dehydrogenative silylation of alkenes. Two types of rhenium(I) hydride species, [ReBrH(NO)(PR(3))(2)] (4) and [ReBr(eta(2)-CH(2)=CHR(1))H(NO)(PR(3))(2)] (5), were found in the [ReBr(2)(L)(NO)(PR(3))(2)]-catalyzed dehydrogenative silylation of alkenes.Rhenium(I) complexes of type [ReBr(2)(L)(NO)(PR(3))(2)] (L=H(2) (1), CH(3)CN (2), and ethylene (3); R=iPr (a) and cyclohexyl (Cy; b)) catalyze dehydrogenative silylation of alkenes in a highly selective manner to yield silyl alkenes and the corresponding alkanes. Hydrosilylation products appear only rarely depending on the type of olefinic substituent, and if they do appear then it is in very minor amounts. Mechanistic studies showed that two rhenium(I) hydride species of type [ReBrH(NO)(PR(3))(2)] (R=iPr (4 a) and Cy (4 b)) and [ReBr(eta(2)-CH(2)=CHR(1))H(NO)(PR(3))(2)] (R(1)=p-CH(3)C(6)H(4), R=iPr (5 a), Cy (5 b); R(1)=H, R=iPr (5 a'), Cy (5 b')) are involved in the initiation pathway of the catalysis. The rate-determining steps of the catalytic cycle are the phosphine dissociation from complexes of type 5 and the reductive eliminations to form the alkane components. The catalytic cycle implies that the given rhenium systems have the ability to activate C-H and Si-H bonds through the aid of a facile redox interplay of Re(I) and Re(III) species. The molecular structures of 4 b and 5 a were established by means of X-ray diffraction studies.

Catalytic coupling of sp2- and sp-hybridized carbon-hydrogen bonds with vinylmetalloid compounds

In the Account given herein, it has been shown that silylative coupling of olefins, well-recognized as a new catalytic route for the activation of double bond C-H bond of olefins and double bond C-Si bond of vinylsilicon compounds with ethylene elimination, can be extended over both other vinylmetalloid derivatives (double bond C-E) (where E = Ge, B, and others) as well as the activation of triple bond C-H, double bond C aryl-H, and -O-H bond of alcohols and silanols. This general transformation is catalyzed by transition-metal complexes (mainly Ru and Rh) containing or initiating TM-H and/or TM-E bonds (inorganometallics). This new general catalytic route for the activation of double bond C-H and triple bond C-H as well as double bond C-E bonds called metallative coupling or trans-metalation (cross-coupling, ring-closing, and polycondensation) constitutes an efficient method (complementary to metathesis) for stereo- and regioselective synthesis of a variety of molecular and macromolecular compounds of vinyl-E (E = Si, B, and Ge) and ethynyl-E (E = Si and Ge) functionality, also potent organometallic reagents for efficient synthesis of highly pi-conjugated organic compounds. The mechanisms of the catalysis of this deethenative metalation have been supported by equimolar reactions of TM-H and/or TM-E with initial substances and reactions with deuterium-labeled reagents.