Search

A series of ferrocenyl- and ruthenocenyl-containing β-diketonato (triphenylphosphine)gold(I) complexes of the type [(RCO)(R′CO)-HαC-AuPPh3] were synthesized via the reaction of appropriate β-diketones, RCOCαH2COR′, with [(Ph3PAu)3][OBF4]. Complexes with R = R′ = CH3(1), or R = Fc = FeII(η5-C5H4)(η5-C5H5), and R′ = CF3(2), CH3(3), Ph = C6H5(4), or Fc (5), as well as R = RuII(η5-C5H4)(η5-C5H5) and R′ = CF3(6), CH3(7), Ph (8), Rc (9), or Fc (10), were obtained. The Au–αC bonding mode between gold and β-diketonato ligands was spectroscopically (NMR, FTIR, and XPS) identified as the only bonding mode for all complexes lacking a CF3moiety, while a mixture of Au–αC- and Au–(κO,κO)-bonded isomers in equilibrium with each other was observed for CF3-containing complexes 2and 6. This experimental observation is supported by a theoretical study utilizing density functional theory. Cyclic and square wave voltammetric studies in CH2Cl2/[N(nBu)4][B(C6F5)4] displayed only the metallocene-based redox processes of 2–10as reversible, well-resolved ferrocenyl and irreversible ruthenocenyl one-electron transfer steps. XPS spectra for each element in the complexes were measured, and an uncommon indirect proportionality between Au 4f7/2binding energies and the sum of R group electronegativities, ΣχR, as well as between the Fe 2p3/2binding energies and formal ferrocenyl reduction potentials, E°′, was obtained.

Treatment of hydroxylated silica nanopowders S1and allyl-functionalized silica nanopowders S2with 3-(diphenylborano)- or 3-bis(pentafluorophenylborano)propyltrimethoxysilane or 2-(diphenylphosphino)- or 2-(dicyclohexylphosphino)ethyltriethoxysilane generates silica nanopowder supported Lewis acids S3and silica nanopowder supported Lewis bases S4. These surfaces were characterized by 13C, 11B, and 31P cross-polarization magic angle spinning nuclear magnetic resonance (CP MAS NMR), X-ray photoelectron spectroscopy (XPS), and attenuated total reflection Fourier transform infrared (ATR FTIR). When S3is combined with solution-phase Lewis bases PR3(R = C6F5, C6H5, mesityl), six associated silica nanopowder supported frustrated Lewis pairs (FLPs) are formed. In another set of six reactions, the interactions between the supported Lewis bases S4and solution-phase Lewis acids BR3with R = C6F5, C6H5, mesityl produced six more associated supported FLPs. The capture of CO2by these FLPs producing FLP-CO2Lewis pair adducts S5and S6were highlighted by ATR FTIR, and it was found that FLP S5ewith R = C6H5on both the supported Lewis acid and solution-phase Lewis base trapped the largest quantities of CO2on the silica nanopowder supports. Conversion of CO2to HCOOH was achieved by first activating H2to generate activated FLP-H2surfaces S7and S9. Addition of CO2then generated HCOOH via the silica nanopowder supported FLP-HCOOH adducts S8and S10. Qualitative identification of HCOOH generation was achieved by ATR FTIR measurements, and surface 10bwith R = C6H5proved to be the most successful silica nanopowder surface bound FLP in HCOOH generation. In some cases, diborano formates (−BO(CH)OB−) S11and S12were also identified as side products during HCOOH formation. Spectroscopic characterization of purposefully synthesized S11and S12included 11B and 31P CP MAS NMR.

In order to better understand intramolecular communication between molecular fragments, a series of ferrocene-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, 1, CH3, 2, Ph = C6H5, 3, and Fc = FeII(η5-C5H4)(η5-C5H5), 4, the mixed ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)], 5, as well as the acac complex [Mn(CH3COCHCOCH3)3], 6, were subjected to an electrochemical and X-ray photoelectron spectroscopy (XPS) study. The ferrocenyl (FeII) and MnIIIredox potentials, E°′, and photoelectron lines were sufficiently resolved in each complex to demonstrate a linear correlation between E°′ and group electronegativities of ligand R groups, χR, or ΣχR, as well as with binding energies of both the Fe 2p3/2and Mn 2p3/2photoelectron lines. These relationships are consistent with effective communication between molecular fragments of 1–5. From these relationships, prediction of Mn and Fe core electron binding energies in [Mn(R1COCHCOR2)3] complexes from known manganese and/or ferrocenyl redox potentials are, therefore, now possible. Ligand infrared carbonyl stretching frequencies were successfully related to binding energy as a measure of the energy required for inner-sphere reorganization. In particular it became possible to explain why, upon electrochemical oxidation or photoionization, the ferrocenyl FeIIinner-shell of 1–5needs more energy in complexes with ligands bearing electron-withdrawing (CF3) groups than in ligands bearing electron-donating groups such as ferrocenyl. The XPS determined entity Iratio(the ratio between the intensities of the satellite and main metal 2p3/2photoelectron lines) is an indication not only of the amount of charge transferred, but also of the degree of inner-sphere reorganization. Just as for binding energy, the quantity Iratiowas also found to be related to the energy requirements for the inner-sphere reorganization depicted by the vibrational frequency, vco.