Tungsten(0) η²-Thiophene Complexes:  Dearomatization of Thiophene and Its Facile Oxidation, Protonation, and Hydrogenation

Abstract

Complexes of the form TpW(NO)(PMe 3 )(η 2 -thiophene) have been synthesized in 31-40% yield by reduction of TpW(NO)(PMe 3 )(Br) in the presence of the thiophene ligand. The dynamics of protonation and the subsequent deprotonation for the corresponding 2Hthiophenium complexes have been investigated. Hydrogenation of the uncoordinated double bond was accomplished, and sulfur-carbon, sulfur-oxygen, and carbon-carbon bond-forming reactions were explored with these complexes.

Experiments and Direct Dynamics Simulations That Probe η2-Arene/Aryl Hydride Equilibria of Tungsten Benzene Complexes

“…For the latter complexes (7−9), 1 H NMR spectra closely match those of the PMe 3 analogue, and characterization was not pursued further. 27,48,49 As has been noted by Jones and co-workers for the rhodiumbased systems RhCp(L) and RhCp*(L) (L = PMe 3 , P(OMe) 3 ), 5 the equilibrium between η 2 -arene and C−H activated adducts depends on the extent of disruption to the πsystem when dihaptocoordination occurs. Hence just as for RhCp*(PMe 3 ), the [(η 2 -R 2 CCHR)]/[(R 2 CCR)(H)] equilibrium ratio decreases as the ligand is adjusted from alkene to naphthalene to benzene.…”

“…In these cases, we presume that an increased thermodynamic stability relative to the aryl or vinyl hydride is the reason for the lack of a hydridic species. For the latter complexes ( 7 – 9 ), 1 H NMR spectra closely match those of the PMe 3 analogue, and characterization was not pursued further. ,, …”

Organocatalytic enantioselective dearomatization of thiophenes by 1,10-conjugate addition of indole imine methides

“…1a ) 6 , 14 . Consequently, a high energy barrier is typically encountered, resulting in often harsh conditions for this type of transformations and imposing formidable challenges in controlling regioselectivity and stereoselectivity 15 – 18 . Beyond that, the strong coordination ability of the generated sulfur-containing product may deactivate the metal catalyst or interfere with stereocontrol by competing for binding, thus representing another important issue to address.…”

η^2 bonded Nickel(0) thiophene π-complexes - identifying the missing link in catalyst transfer polymerization

“…[24][25][26][27] A direct analogy between arene and thiophene binding modes is therefore potentially problematic as has been noted previously 23,28 . Only two structurally-characterized complexes are known to adopt the proposed C,C-η 2 binding motif: the Harman group identified a saturated 18etungsten complex with a weakly bound C,C-η 2 thiophene ligand 29 and Agapie and coworkers isolated a unique palladium(I) dimer with a bridging cis-μ-η 2 :η 2 thiophene 30 . Although these two reports demonstrate the feasibility of C,C-η 2 binding for thiophene, they differ both structurally and electronically from the proposed CTP intermediates and thus cannot directly address whether such bonding may be achieved in a low valent d 10 system.…”