Dimetallation, Hydrometallation, and Hydrogenation Reactions

Organometallic compounds which have main group metal-metal bonds, such as S—B, Si—Mg,- Si—Al, Si—Zn, Si—Sn, Si—Si, Sn—Al, and Sn—Sn bonds, undergo 1,2-dimetallation of alkynes. Pd complexes are good catalysts for the addition of these compounds to alkynes. The 1,2-dimetallation products still have reactive metal-carbon bonds and are used for further transformations. 

The cis thioboration of terminal alkynes with 9-(arylthio)-9-BBN is catalyzed by Pd(Pli3P)4 in the presence of styrene. The product 136 is converted into the vinyl sulfides 137 and 138 by the treatment with MeOH or by Pd-catalyzed cross-coupling with aryl or alkenyl halides using K3PO4 in DMF[68]. No thioboration takes place with internal alkynes. 

147 was converted into 148 by the Pd-catalyzed displacement of the stannyl group with acyl chloride[78]. The stannylzincation product was converted into the 2-stannylalkene I49[76]. 

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79], 

However, Bu3SnSiMe2H (154) reacts with terminal aikynes to give the 3,4-disubs tituted silacyclopenta-2,4-diene 156 at room temperature. The dimetliyl-silylene 155 is an intermediate[80]. (Me3Sn)2 undergoes facile addition to aikynes to give the 1,2-distannylalkene 157[8I-83], 

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