Mono- and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis-1,4-([3]Cumulene)-p-carboquinoid System.

An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs.

NH/PH isomerization and a Lewis pair for carbon dioxide capture.

Bis(di-i-propylphosphino)amine 1 reacts with B(C6F5)3 to form an adduct with concomitant N/P H-isomerization. This species reacts smoothly with carbon dioxide. An attempt to prepare an anionic derivative resulted in the formation of a novel heterocycle derived from the PNP ligand and B(C6F5)3.

Metal complexes (M = Zn, Sn, and Pb) of 2-phosphinobenzenethiolates: insights into ligand folding and hemilability.

The divalent metal complexes M(II){(SC6H4-2-PR2)-κ(2)S,P}2 (3-7, and 9-11) (M = Zn, Sn, or Pb; R = (i)Pr, (t)Bu, or Ph), the Sn(IV) complexes Sn{(SC6H4-2-PR2)-κ(2)-S,P}Ph2Cl (12 and 13) (R = (i)Pr and (t)Bu), and the ionic Sn(IV) complexes [Sn{(SC6H4-2-PR2)-κ(2)-S,P}Ph2][BPh4] (14 and 15) (R = (i)Pr and (t)Bu) have been prepared and characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction when suitable crystals were afforded. The Sn(II) and Pb(II) complexes with R = Ph, (i)Pr, or (t)Bu (5, 6, 9, and 10) demonstrated ligand "folding" hinging on the P,S vector-a behavior driven by the repulsions of the metal/phosphorus and metal/sulfur lone pairs and increased M-S sigma bonding strength. This phenomenon was examined by density functional theory (DFT) calculations for the compounds in both folded and unfolded states. The Sn(IV) compound 13 (R = (t)Bu) crystallized with the phosphine in an axial position of the pseudotrigonal bipyramidal complex and also exhibited hemilability in the Sn-P dative bond, while compound 12 (R = (i)Pr), interestingly, crystallized with phosphine in an equatorial position and did not show hemilability. Finally, the crystal structure of 15 (R = (t)Bu) revealed the presence of an uncommon, 4-coordinate, stable Sn(IV) cation.

Facilitated carbon dioxide reduction using a Zn(II) complex.

Two new Zn(II) complexes have been prepared and evaluated for their capacity to activate and reduce CO2. The electrochemical properties of dichlorobis[diphenyl-(2-pyridyl)phosphine-κ(1)-N]zinc(II) [corrected]. and dichloro[diphenyl-(2-pyridyl)phosphine-κ(1)-N]zinc(II) 2 are compared using cyclic voltammetry. Electrochemical results indicate that 2 leads to a facilitated CO2 reduction to evolve CO at a glassy carbon electrode.