New Mechanism for the Intermolecular Hydroamination of Alkynes:  Catalysis by Dinuclear Ruthenium Complexes with a Rigid Dicyclopentadienyl Ligand

Abstract

The dinuclear ruthenium complex {(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 3 (C 2 H 4 )H + BF 4 -(1) catalyzes the intermolecular hydroamination of arylalkynes (e.g., phenylacetylene) with arylamines (e.g., p-toluidine) to give imines (e.g., (Ph(Me)CdN(p-MeC 6 H 4 )). Although the catalyst has a limited lifetime (up to 6 turnovers), details of the reaction mechanism have been elucidated by isolation and characterization (X-ray and/or NMR) of six of the seven intermediates and reaction-terminating species. The mechanism is fundamentally different from all previously proposed mechanisms for alkyne hydroamination. The rigid doubly bridged bis((dimethylsilyl)cyclopentadienyl) ligand is an important feature of the catalyst that facilitates this new type of hydroamination mechanism.

The catalytic hydroamination of alkynes

“…A mechanism that is fundamentally different from all previously discussed mechanisms for alkyne hydroaminations is proposed for the Markovnikov-selective addition of arylamines to terminal arylalkynes catalyzed by a dinuclear ruthenium complex with a doubly bridged rigid dicyclopentadienyl ligand. 30 Although the in situ generated catalytically active complex {(g 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 3 {NH 2 (p-MeC 6 H 4 )} has a limited lifetime (up to 6 turnovers), most of the intermediates involved in the catalytic cycle are fully characterized (X-ray and/or NMR). Since the corresponding nonbridged Ru-dimer does not catalyze the hydroamination, the catalytic activity seems to be the result of the unique bridging nature of the (g 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 ligand.…”

Highly Selective Hydrogenation of Carbon–Carbon Multiple Bonds Catalyzed by the Cation [(C6Me6)2Ru2(PPh2)H2]+: Molecular Structure of [(C6Me6)2Ru2(PPh2)(CHCHPh)H]+, a Possible Intermediate in the Case of Phenylacetylene Hydrogenation

“…The RuRu distance [2.7923(6) Å] is in the range of a ruthenium–ruthenium single bond. However, it is slightly shorter than those observed in the analogous complexes [Ru 2 (CO) 4 (CHCHPh)(dppm) 2 ][BF 4 ] (dppm=bis(diphenylphosphino)methane)20a and [{(C 5 H 3 ) 2 (SiMe 2 ) 2 }Ru 2 (CO) 3 (CHCHPh)][BF 4 ] 20b. The presence of PPh 2 and styrene bridging ligands forces the arene moieties to adopt a tilted geometry.…”

Reactivity of Silyl-Substituted Iron–Platinum Hydride Complexes toward Unsaturated Molecules: 4. Insertion of Fluorinated Aromatic Alkynes into the Platinum–Hydride Bond. Synthesis and Reactivity of Heterobimetallic Dimetallacylopentenone, Dimetallacyclobutene, μ-Vinylidene, and μ2-σ-Alkenyl Complexes

“…However, the bond length of 2.6026(15) Å is somewhat longer than the mean distances of μ-vinylidenes 3 (2.5494(8) Å) and dimetallacyclopentenones 4 (2.5842(12) Å). An elongation of the metal–metal bond has also been noticed for the dimetallacyclobutene [{(η 5 -C 5 H 3 ) 2 (SiMe 2 ) 2 }­Ru 2 (CO) 2 (μ-CO)­{μ 2 -η 1 :η 1 -C­(Ph)C­(H)}] and its μ-vinylidene isomer . Note that dinuclear dimetallacyclobutenes bearing a symmetric M–C­(R)C­(R)–M moiety are now quite common, but it seems that complexes 5 represent the first examples of heterodinuclear complexes spanned by a terminal alkyne.…”