Retro-Vinylidene Rearrangements of P- and S-Substituted Ruthenium Vinylidene Complexes

Abstract

P- and S-substituted vinylidene complexes, [Ru{CC(R)(E)}(dppe)Cp]BArF 4 [E = PO(OMe)2, PO(OEt)2, POPh2, SPh, and SO2Ph], were found to be active for retro-vinylidene rearrangements to add new entries of reversible systems of vinylidene/alkyne isomerization. Isotope labeling experiments revealed that PO(OMe)2- and POPh2-substituted complexes underwent the retro-vinylidene rearrangement via selective 1,2-migration of the P-substituents. In contrast, in the case of a SPh-substituted complex, both the SPh and the R groups served as migrating groups during the reversible alkyne/vinylidene isomerization, though the migration of the SPh group was still the major reaction path. These findings would deepen the mechanistic understanding of alkyne/vinylidene rearrangements of heteroatom-substituted internal alkynes.

Inorganometallic allenes [(Mn(η5-C5H5)(CO)2)2(μ-E)] (E = Si–Pb): bis-allylic anionic delocalisation similar to organometallic allene but differential σ-donation and π-backdonation

“…16 We have reported a similar bis-allylic anionic-type conjugation for the lighter organometallic allene 2C. 12 The p > skeleton, unambiguously, is identified to be comprised of three orbitals viz. two occupied orbitals, namely the bonding combination HOMOÀ5, non-bonding combination HOMO and an unoccupied antibonding combination LUMO+1.…”

“…In our earlier analysis pertaining to the organometallic allene 2C, we identified two MOs present as a sp-hybrid resulting from the mixing of the in-plane bonding combination of the d xz -orbitals on the TM centres with the anti-bonding combination of the s-group orbitals on the TM centres. 12 The p x -and p z -orbitals on the central carbon centre also underwent similar mixing, resulting in hybrid, bent MOs. Here also, the sand p 8 -MOs corresponding to the Mn-Si-Mn skeleton can undergo mixing resulting in sp-hybrid MOs.…”

“…9h With an intention to study the inconspicuous relationship between the organic allene C(CH 2 ) 2 , and its organometallic counterpart, [(MnCp(CO) 2 ) 2 (m-C)], we carried out a detailed structure-property-reactivity analysis of these two contemporary carbon complexes. 12 The detailed bonding analysis of the organometallic allene indicates that the central carbon atom acts as a 4e À s-donor, and a 4e À p-acceptor with the TM fragments. The bonding analysis further indicated the presence of mutually orthogonal p-delocalised systems, which is found to be similar to the p-conjugation in an allylic anion.…”

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

“…3). As in the Ti case, 19 the ligand's bidentate chelation in 2 results in a seven-membered metallacycle with a 'twist-boat' geometry. The ring is less puckered in 2, likely due to the lower coordination number of Al (four vs. five in the Ti case).…”

“…The O,C bidentate and monoanionic NHC-aryloxide [ Ar O-CH 2 -NHC] − ligand class with a flexible -CH 2linker has so far been explored with metals like Y, 12 Yb, 13 Fe, 14 Ni,15 Mg, 15b Ag, 16 Ir, 17 Ru, 16 and Ga. 18 Introducing a new [ Ar O-CH 2 -NHC] − derivative of [O-4,6-Bu t 2 -C 6 H 2 -2-CH 2 {C(NCHvCHNDipp)}] − (L; Dipp = 2,6-Pr i 2 -C 6 H 3 ), we recently reported its Ti complex [Ti (L)(NMe 2 ) 2 Br] as the first NHC-bound Ti(IV) catalyst for the ROP of ε-caprolactone (CL). 19 The polymerization works without a cocatalyst and at room temperature through a bifunctional MLC-type (metal-ligand cooperation) mechanism, where the NHC itself acts as an internal nucleophile in the initiation step, conforming to the weakness of the C NHC -Ti bond (Fig. 2).…”