Silylated alkynes, borylation

In relation to the mechanistic proposal, an interesting reactivity of (boryl)(silyl)platinum(n) complex has been reported.223 The complex is prepared by the reaction of silylborane with Pt(cod)2 complex via oxidative addition (Scheme 46). The (boryl)(silyl)platinum complex undergoes insertion of alkynes at the B-Pt bond to give (/3-borylalkenyl)(silyl)platinum(n) complex in high yield. Importantly, the insertion takes place regioselectively, with Pt-G bond formation at the internal. -carbon atom. This result may indicate that the boron-transition metal bond is more prone to undergo insertion of unsaturated molecules. 

Addition of silylpinacolborane to alkenes has been achieved with platinum catalysts (Equation (83)).225 The reaction proceeds regioselectively to provide products in which the silyl groups are attached to the terminal carbon atoms contrary to the silaboration of alkynes. Although no regioisomers are detected, 1-boryl-l-silylalkenes are formed as major byproducts. 

The (boryl)(silyl)palladium intermediate 43, which is formed by oxidative addition of silylborane onto palladium, would play a aitical role for the reaction (Scheme i9).P0],[2i] The thioboration of alkynes with 9-(alkylthio)-9-borabicyclo[3.3.1]nonane also proceeds with high regio- and stereoselectivity in the presence of Pd(0) catalyst. Like other... 

In contrast to the rare occurrence of the oxidative addition of C-C bonds, the oxidative addition of the nonpolar bonds between two main group atoms, such as boron and silicon, can be facile. The oxidative addition of Si-Si bonds in disilanes and the B-B bond in diborane(4) reagents is likely to be a step in a variety of catalytic reactions, including the additions of disilanes, - diborane(4) reagents, and silaboranes - across olefins and alkynes, the silylation and borylation of arene C-H bonds, - - the borylation of alkane C-H bonds, and the conversion of aryl halides to arylsilanes and arylbo-ronate esters. " ... 

As mostly discussed earlier. Type III alkenyl derivatives, that is, ( )-R CH= CHM(or X), are widely and satisfactorily generated by (i) alkyne hydrometallation (M = B, Zr or, in some cases, Al, etc.) (Table 3.2, Scheme 3.6), (ii) polar halogenation reactions ofalkynes (Eqs. (1), (2), and (7), Scheme 3.15), and additionally, (iii) anti bromoboration of ethyne [53] followed by Negishi coupling (Eq. (1), Scheme 3.12). On the other hand. Type IV alkenyl derivatives may be prepared by (i) Normant alkylcupration of ethyne [67, 68] (Eqs. (5) and (6), Scheme 3.11), (ii) Zr-catalyzed alkylalumination of ethyne, (iii) syn hydroboration of 1-halo-l-alkynes followed by hydride-induced inversion of configuration [59] (Scheme 3.9), (iv) hydroboration of 1-alkynes followed by brominolysis (but not iodinolysis) with inversion [95], and (v) syn hydrozirconation or syn hydroalumination of 1-boryl- or 1-silyl-l-alkynes followed by protonolysis of the C-Al or C-Zr bond [96-98]. 

Silaborative C-C Bond Forming Reactions. In the presence of a nickel(O) catalyst generated in situ by the reaction of Ni(acac)2 with DIBAH, 1 reacts with 2 equiv of alkynes to give l-boryl-4-silyl-1,3-butadienes (eq 20). ... 

The same regioselectivity in favor of the branched isomer with imusual stereoselectivity was produced with borylated alkynes in place of silylated alkynes to lead to the synthesis of p,p-disubstituted vinyl boronates [63] [Eq. (25)]. 

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