Open AccessBorylated Cymantrenes and Tromancenium Salts with Unusual Reactivity
Author(s) -
Reinhard Thaler,
Holger Kopacka,
Klaus Wurst,
Thomas Müller,
Dennis F. Dinu,
Klaus R. Liedl,
Florian R. Neururer,
Stephan Hohloch,
Benno Bildstein
Publication year - 2022
Publication title -
organometallics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.231
H-Index - 172
eISSN - 1520-6041
pISSN - 0276-7333
DOI - 10.1021/acs.organomet.2c00179
Subject(s) - chemistry , transmetalation , cyclopentadienyl complex , boron , reactivity (psychology) , inorganic chemistry , cationic polymerization , manganese , moiety , cyclic voltammetry , photochemistry , medicinal chemistry , polymer chemistry , organic chemistry , electrochemistry , medicine , alternative medicine , electrode , pathology , catalysis
In continuation of our study of the chemistry of cationic (cycloheptatrienyl)(cyclopentadienyl)manganese(I) sandwich complexes, so-called "tromancenium" salts, we report here on their boron-substituted derivatives focusing on useful boron-mediated synthetic applications. Transmetalation of lithiated tricarbonyl(cyclopentadienyl)manganese ("cymantrene") with boric or diboronic esters affords monoborylated cymantrenes that are converted by advanced high-power LED photosynthesis followed by oxidation with tritylium to their 8-boron-substituted tromancenium complexes. These new functionalized tromancenium salts are fully characterized by 1 H/ 11 B/ 13 C/ 19 F/ 55 Mn NMR, IR, UV-vis, HRMS spectroscopy, single-crystal structure analysis (XRD) and cyclic voltammetry (CV). IR spectra were thoroughly analyzed by density functional theory (DFT) on the harmonic approximation in qualitative agreement of calculated vibrations with experimental values. Uncommon chemical reactivity of these borylated tromancenium salts is observed, due to the strongly electron-withdrawing cationic tromancenium moiety. No Suzuki-type cross-coupling reactions proved so far achievable, but unusual copper-promoted amination with sodium azide under microwave irradiation is possible. Diazoniation of aminotromancenium affords an extremely reactive dicationic tromanceniumdiazonium salt, which is too labile for standard Sandmeyer reactions, in contrast to analogous chemistry of cobaltocenium salts. Overall, borylated tromancenium salts display unexpected and intriguing chemical properties with the potential for novel synthetic applications in future work.