Supporting information includes Table S1 on gas phase analysis and related details of the analytical protocol used.

No abstract

The capability to characterize lignin, lignocellulose, and their degradation products is essential for the development of new renewable feedstocks. Electrospray ionization high-resolution time-of-flight mass spectrometry (ESI-HR TOF-MS) method was developed expanding the lignomics toolkit while targeting the simultaneous detection of low and high molecular weight (MW) lignin species. The effect of a broad range of electrolytes and various ionization conditions on ion formation and ionization effectiveness was studied using a suite of mono-, di-, and triarene lignin model compounds as well as kraft alkali lignin. Contrary to the previous studies, the positive ionization mode was found to be more effective for methoxy-substituted arenes and polyphenols, i.e., species of a broadly varied MW structurally similar to the native lignin. For the first time, we report an effective formation of multiply charged species of lignin with the subsequent mass spectrum deconvolution in the presence of 100 mmol L formic acid in the positive ESI mode. The developed method enabled the detection of lignin species with an MW between 150 and 9000 Da or higher, depending on the mass analyzer. The obtained M and M values of 1500 and 2500 Da, respectively, were in good agreement with those determined by gel permeation chromatography. Furthermore, the deconvoluted ESI mass spectrum was similar to that obtained with matrix-assisted laser desorption/ionization (MALDI)-HR TOF-MS, yet featuring a higher signal-to-noise ratio. The formation of multiply charged species was confirmed with ion mobility ESI-HR Q-TOF-MS. Graphical Abstract ᅟ.

Direct cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazoline using palladium acetate in acetic acid or acetonitrile provided a mixture of two isomeric compounds, the endo μ-AcO dimeric complex with a C(sp3)−Pd bond and the corresponding exo derivative with a C(sp2)−Pd bond, with the former being the major product. The μ-AcO dimeric complexes were converted to the corresponding μ-Cl analogues 3 and 4 by treatment with LiCl in acetone; the latter compounds were transformed to the corresponding PPh3 adducts 5 and 6. The NMR data suggested the puckered structure of the endo palladacycle in complexes 3 and 5, the twisted λ(S) conformation of the oxazoline ring in 3, 4, and 6, and the δ(S) conformation of the heterocycle in complex 5. The X-ray crystal structure of 5 confirmed the δ(S) conformation of the oxazoline ring in the solid state and the twisted conformation of the palladacycle and revealed a P-propeller chiral configuration of the PPh3 ligand. A series of ab initio quantum chemical calculations were performed on two model compounds generated by replacing the PPh3 ligands with NH3 in complexes 5 and 6. The structures and energies of the two model exo and endo isomers were calculated at the RHF, BLYP, and MP2 levels of theory with a 6-31G* basis for the light atoms and LANL2DZ ECP for the palladium and were found to be comparable. Single point coupled cluster calculations, with single double excitations (CCSD), corroborated the results.