In diesem Projekt ging es um die Eigen­schaf­ten innova­ti­ver Goldka­ta­ly­sa­to­ren. Das Ziel war es, neue Infor­ma­tio­nen über die Mecha­nis­men und Arten zu erhal­ten, die in Goldka­ta­lyse-Reaktio­nen invol­viert sind. Es handelte sich dabei um eine Koope­ra­tion der Hector Fellows A. Stephen K. Hashmi und Manfred Kappes sowie den HFA Postdoktorand*innen Dr. Sarah Bay (Ruprecht-Karls-Univer­si­tät Heidel­berg) und Dr. Jean-Francois Greisch (Karls­ru­her Insti­tut für Technologie).

Follo­wing the develo­p­ment of new highly active catalyst systems, it was shown that homoge­neous gold cataly­sis might be well-suited for indus­trial appli­ca­tion and econo­mic­ally effici­ent use. To achieve this goal a funda­men­tal under­stan­ding of highly reactive gold catalyst systems is necces­sary. Within this project, the resear­chers wanted to deter­mine the struc­tures and reaction pathways of selec­ted gold catalysts. Their studies aimed at charac­te­ri­zing reaction inter­me­dia­tes by combi­ning organic synthe­tic strate­gies with elabo­ra­ted mass spectro­me­tric methods.

The figure shows the workhorse, a dual activa­tion catalyst. Direct activity assess­ment inclu­ding the influence of bypro­ducts (e.g. small clusters of various charge states) as well as the identi­fi­ca­tion of reaction inter­me­dia­tes has been missing, which finally preven­ted effici­ent optimiza­tion. Since concen­tra­ti­ons of the new highly active gold catalysts are typically low and the active species are fragile, charac­te­riza­tion using analy­tic techni­ques is challenging.

Nevert­hel­ess, the combi­na­tion of high-resolu­tion mass spectro­me­try and mild ioniza­tion methods provi­ded a unique oppor­tu­nity to directly probe catalyst-substrate-inter­me­dia­tes using a broad range of spectro­sco­pic techniques.

Via ion mobility measu­re­ments, colli­sion cross-sections could be infer­red and struc­tu­ral infor­ma­tion on the isola­ted inter­me­dia­tes of reactions obtai­ned. Reaction of gas-phase species with vapors could provide unique infor­ma­tion on the reacti­vity, making it possi­ble to assess how diffe­rent isomers/conformers contri­bute to the reaction. Finally, optical spectro­sco­pic techni­ques could be used to probe the struc­ture and the electro­nic states as well as to isolate species for further inves­ti­ga­tion via hole-burning spectroscopy.

By analy­zing the reaction mixture and develo­ping new approa­ches to acces­sing transi­ent species, the project aimed at obtai­ning unpre­ce­den­ted infor­ma­tion on the mecha­nisms and species invol­ved in gold-cataly­zed reactions.