Intermolecular acceptorless dehydrogenative coupling of silanes with arene C-H bonds and intramolecular coupling of silanes with aryl and alkyl C-H bonds occur in good yield in the presence of 5 mol % of TpMe2PtMe2H (TpMe2 = hydridotris(3,5-dimethylpyrazolyl)borate) and related platinum(IV) complexes. The intermolecular reactions of arenes occurred with both trialkyl and dialkylaryl silanes. Intramolecular reactions of dialkylsilylalkylarenes occurred at aryl C-H bonds, and reactions of tributylsilane or dibutylphenylsilane occurred intramolecularly at the aliphatic, primary C-H bond. The reactions of arenes occurred preferentially at the least sterically hindered C-H bonds and preferentially with more electron-poor arenes. Crossover experiments and the lack of reactivity of the arylsilanes with H2 imply that the dehydrogenative silylation of arenes can be irreversible, even in a closed reaction vessel.
A novel binucleating ligand, N,N‘-bis[(2-diphenylphosphino)phenyl]formamidine (Hdpfam),
has been prepared and utilized for the synthesis of homo- and heterobimetallic palladium/platinum complexes M2R2(μ-X)(μ-dpfam) (M = Pd, Pt; R = Me, p-Tol, Cl; X = Cl, Br, I; dpfam
= N,N‘-bis[(2-diphenylphosphino)phenyl]formamidinate). Treatment of Hdpfam with 2 equiv
of MRX(tmeda) or MRX(cod) in the presence of tmeda produced the homobimetallic
complexes. The heterobimetallic complex PdPtMe2(μ-Cl)(μ-dpfam) was obtained by the
reaction of PdMeCl(cod) with PtMe(dpfam), which was produced from PtMe2(cod) and
Hdpfam. The crystal structures of Pd2Cl2(μ-Cl)(μ-dpfam) and Pt2Me2(μ-Cl)(μ-dpfam) have
been determined by X-ray analysis. The results indicate that both complexes have P−M−Cl−M−P A-frame structures, in which each metal center has a slightly distorted square-planar geometry and the nonbridging σ-donor ligands (Cl or Me) and μ-Cl are in a cis
orientation. Treatment of Pt2Me2(μ-Cl)(μ-dpfam) with NaBH4 gave the hydride-bridged
complex Pt2Me2(μ-H)(μ-dpfam).
Reactions of alkynes with arenes proceeded in the presence of dinuclear palladium complexes and trialkylboranes to yield alkyne hydroarylation products with high stereoselectivity. In the reactions of monosubstituted benzenes, meta and para products were formed in statistical ratios, while no ortho isomers were detected.
Dinuclear and mononuclear palladium complexes having N,N'-bis[2-(diphenylphosphino)phenyl]amidinate (DPFAM) as a ligand catalyzed the cross-addition of triisopropylsilylacetylene (TIPSA) to unactivated internal alkynes, giving enynes selectively. When palladium catalysts having PPh3, TDMPP, dppe, or dppf were used, dimers of TIPSA were obtained as major products. The reactions of TIPSA with several terminal alkynes also gave cross-adducts selectively, although the yields were moderate.
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