Novel regioselection in insertion of a 1,4-disubstituted-1,3-enyne into ruthenium–hydrogen bonds

Abstract

The reaction of a conjugated enyne, cis-(Me3Si)CH=CHC=CSiMe3, with [ R u C I ( C O ) H ( P P ~~) ~] gives a quantitative yield of a stable complex whose molecular structure is formally regarded as the result of either 1,2-addition of the H-Ru t o the double bond or 1,4-addition of the H-Ru t o the conjugated enyne; the former bonding scheme operates when the enyne is hydrogenated b y [Ru(CO)H2(PPh3)3] or [ R u H ~( P P ~~) ~] ,the sole product being Me3SiCH2CH2C-=CSiMe3.

Catalytic Enantioselective Carbonyl Propargylation Beyond Preformed Carbanions: Reductive Coupling and Hydrogen Auto‐Transfer

“…Furthermore, for the ruthenium‐catalyzed reactions, carbonyl addition could be conducted from the alcohol oxidation level of the reactant via hydrogen auto‐transfer. Mechanistic studies corroborate pathways involving enyne hydroruthenation to form nucleophilic allenylruthenium intermediates . These processes, which represent the first examples of transfer hydrogenative carbonyl propargylation, set the stage for the development of diverse diastereo‐ and enantioselective transformations of this type (Scheme )…”

Syntheses of Heterocycles via Alkyne Cycloadditions Catalyzed by Cyclopentadienylruthenium-Type Complexes

“…Since the pioneering studies of stoichiometric reactions of cobaltacyclopentadienes by Wakatsuki and Yamazaki, 8 the TM-catalyzed [2 + 2 + 2] cycloadditions of two molecules of alkynes with nitriles or heterocumulenes have emerged as powerful tools for the synthesis of six-membered heterocycles such as pyridines and pyridones. Later, various TM complexes have been investigated to identify efficient catalysts for these useful synthetic processes.…”

Complexes of Ruthenium and Osmium Containing η2–η6 Hydrocarbon Ligands: (i) Complexes not Containing Cyclobutadiene, Cyclopentadienyl or η-Arene Coligands

“…The orange, crystalline product* contains a coplanar RuC 3 unit and can be represented by the limiting structures (81a) and (81b); the bond lengths suggest that (81b) may make the more important contribution*. 180 Closely related complexes are formed in the dimerization of acetylides or terminal ethynes at ruthenium or osmium centres. The complex [Os(C 2 Ph) 2 (PMe 3 ) 4 ] is oxidized slowly by AgPF 6 37 ' 186 In these T| 3 -enynyl complexes the longest M-C bond is generally that to the terminal carbon atom that does not carry the vinylidene substituent; for example, the Os-C bond lengths in [(Me,P) 4 Os(Ti 3 -PhC~C~C=CHPh)] + (82) …”