Stable [Pb(ROH)_N]²⁺Complexes in the Gas Phase:  Softening the Base To Match the Lewis Acid

Abstract

Experiments have been performed in the gas phase to investigate the stability of complexes of the general form [Pb(ROH)(N)](2+). With water as a solvent, there is no evidence of [Pb(H(2)O)(N)](2+); instead [PbOH(H(2)O)(N-1)](+) is observed, where lead is considered to be held formally in a +2 oxidation state by the formation of a hydroxide core. As the polarizability of the solvating ligands is increased through the use of straight chain alcohols, ROH, solvation of Pb(2+) is observed without proton transfer when R >or= CH(3)CH(2)CH(2)-. The relative stabilities of [Pb(ROH)(4)](2+) complexes with respect to proton transfer are further investigated through the application of density functional theory to examples where R = H, methyl, ethyl, and 1-propyl. Of three trial structures examined for [Pb(ROH)(4)](2+) complexes, in all cases those with the lowest energy comprised of three solvent molecules were directly bound to the central cation, with the fourth molecule held in a secondary shell by hydrogen bonds. The implications of this arrangement as a favorable starting structure for proton transfer are discussed. Conditions for the stability of particular Pb(II)/ligand combinations are also discussed in terms of the hard-soft acid-base principle. Charge population densities calculated for the central lead cation and oxygen donor atoms across the ROH range are used to support the proposal that proton transfer occurs when a ligand is hard. Stability of the [Pb(ROH)(4)](2+) unit is commensurate with a decrease in the ionic character of the bond between Pb(2+) and a ligand; this in turn reflects a softening of the ligand as the alkyl chain increases in length. From the calculations, the most favorable protonated product is, in all cases, (ROH)(2)H(+). The trends observed with lead are compared with Cu(II), which is capable of forming stable gas-phase complexes with water and all of the alcohols considered here.

Elucidation of the collision induced dissociation pathways of water and alcohol coordinated complexes containing the uranyl cation

“…The preferred elimination of nitric acid at the MS 4 stage might instead suggest that the complex ion has the former composition, and that a proton is transferred from a coordinating alcohol molecule to the nitrate anion during the dissociation reaction. Such a proton transfer process is not without precedent, and has been recently reported for gas-phase alcohol complexes incorporating Pb 2ϩ [47]. The strong tendency to form alkoxide species, noted above, may be a driving force for the apparent proton transfer step and subsequent elimination of HNO 3 .…”

Chemical synthesis of lactic acid from cellulose catalysed by lead(II) ions in water

“…S19). Many studies have demonstrated the formation of Pb(II)-OH in an aqueous solution of Pb(II) (Supplementary Note S4) [31][32][33][34] . Our experimental studies using Fourier-transform ion cyclotron resonance mass spectrometry, which is a very powerful technique for the structural determination of new compounds with ultra-high mass resolution and accuracy 35,36 , provided further evidence for the existence of the Pb(II)-OH species in the Pb(II) aqueous solution ( Supplementary Fig.…”

“…This may allow Pb(II) to mediate the initial proton transfer more effectively in the above step. In addition, the lone electron pair (6s 2 ) of Pb (II) may promote the proton transfer 31,32 contributing to its outstanding catalytic performances. These features may explain why Pb(II) demonstrates better catalytic performances for the formation of lactic acid than many other metal ions (Fig.…”

Understanding Lead Chemistry from Topological Insights: The Transition between Holo‐ and Hemidirected Structures within the [Pb(CO)n]2+ Model Series

“…[20,21] The gas-phase chemistry of Pb 2 + is less known although a number of species have been experimentally detected. [6,[22][23][24] However, the spectroscopic and theoretical investigations of gas-phase complexes remain surprisingly rare despite available high-level theoretical data. [25] To the best of our knowledge, studies devoted to such species are limited to: PbA C H T U N G T R E N N U N G (H 2 O), PbA C H T U N G T R E N N U N G (HO 2 ), PbOH, PbH 2 , PbO, PbO 2 and PbO 3 .…”