[reaction: see text] Upon attempted silaboration of acyclic 1- and 1,4-substituted 1,3-dienes, a new disproportionation reaction was discovered, yielding 1:1 mixtures of allylsilanes and dienylboranes. It was demonstrated that, as a key step in this new catalytic process, hydrogen is being transferred from one diene moiety to another.

Silaboration of 1,3-cyclohexadiene in the presence of Pt(acac) 2 , DIBALH, and a phosphoramidite prepared from (S)-1,1'-bi-2-naphthol and diisopropylamine led to (1R,4S)-1-(dimethylphenylsilyl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-cyclohexene with 70% ee. Chiral catalysts based on Ni gave no or essentially racemic product, whereas complexes containing Pd were inactive.

Silaborative carbocyclization of 1,6-enynes catalyzed by Pd-PEPPSI-IPr {PEPPSI = pyridine-enhanced precatalyst preparation stabilization and initiation; IPr = N,N-bisA C H T U N G T R E N N U N G [2,6-(diisopropyl)phenyl]imidazolium} employing either (dimethylphenylsilyl)pinacolborane or (chlorodimethylsilyl)pinacolborane provides access to densely functionalized five-membered rings as single diastereomers in excellent yields. The vinylboronate functions were employed in palladium-catalyzed Suzuki cross-coupling reactions with a range of aryl bromides, containing electron-withdrawing as well as electron-donating substituents, furnishing arylated exo-methylenecyclopentanes or exo-methylenepyrrolidines in good yields. Subsequent oxidation of the isopropoxydimethylsilyl function generated via addition of (chlorodimethylsilyl)-pinacolborane provided access to hydroxymethyl derivatives of the arylated compounds. Use of a chiral ester, bismenthyl (2-propenyl)(2-propynyl)malonate, afforded two diastereomeric products which could be separated, thereby giving access to the cyclized compounds as single isomers, with opposite absolute configurations at the newly formed stereocenter.

The chemical reduction of Pt(acac) 2 by DIBALH in the presence of phosphanes, which is used to generate active Pt 0 complexes in the Pt-catalyzed silaboration of cyclohexadiene by 2-(dimethylphenylsilyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (1) leading to the 1,4-silaborated product, was mimicked by the electrochemical reduction of Pt(acac) 2 in the presence of 2 equiv. of PR 3 (R = Ph, nBu). The electrochemical reduction generates free acac anions and neutral Pt 0 -(PR 3 ) 2 complexes. The kinetics of the oxidative addition of bromobenzene (used first as a model molecule) and silylborane 1 to the Pt 0 complexes was investigated and the rate constants determined. Pt 0 (PnBu 3 ) 2 is much more reactive than Pt 0 (PPh 3 ) 2 towards 1. From the electrochemical study, it emerges that the acac anions released in the reduction of Pt(acac) 2 do not coordinate to the Pt 0 (PR 3 ) 2 complexes. Consequently, the rate of the oxidative addition of 1 to Pt 0 (PR 3 ) 2 , generated either by the electrochemical reduction or by the

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