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Two novel BODIPY‐Ugi (boron dipyrromethene) adducts exhibit peculiar room temperature (T=20 °C) H‐1 NMR spectra in that several protons located at the aromatic aniline‐type ring are lost in the baseline. This observation revealed the existence of a dynamic conformational process where rotation around the C−N bond is hindered. Variable‐temperature H‐1 and C‐13 NMR spectroscopic analysis confirmed this conclusion; that is, low‐temperature spectra show distinct signals for all four aromatic protons below coalescence, whereas average signals are recorded above coalescence (T=+120 °C). Particularly interesting was the rather large difference in chemical shifts for the ortho protons below coalescence, Δδ=1.45 ppm, which was explained based on DFT computational analysis. Indeed, the calculated lowest‐energy gas‐phase conformation of the BODIPY Ugi adducts locates one half of the aniline‐type ring in the shielding anisotropic cone of the bridge phenyl ring in the BODIPY segment. This is in contrast to the solid‐state conformation established by X‐ray diffraction analysis that shows a nearly parallel arrangement of the aromatic rings, probably induced by crystal packing forces. [ABSTRACT FROM AUTHOR]

The trapping of a phosphinidene (R-P) in an NCN pincer is presented. Stabilized phosphinidene 1 was characterized by 31P{1H}, 1H, and 13C{1H} NMR spectroscopy, exhibiting an averaged C2 v symmetry in solution between −60 and 60 °C. In the solid state, the phosphinidene is coordinated by one adjacent N atom featuring a formal P−N bond (1.757(2) Å) to give a five-membered ring with some aromatic character, confirmed by DFT calculations (B3LYP-D3/6-311G**++) to be the ground-state structure. Equilibration of the two N ligands occurs rapidly in solution via a 'bell-clapper'-type process through an associative symmetric transition state calculated to lie 4.0 kcal mol−1 above the ground state. [ABSTRACT FROM AUTHOR]

New 6,6′-dibromo- and 6,6′-bis(dimethylamino)-substituted 2,2′-diphosphanylbiphenyl ligands 11- 14 were prepared starting from 2,2′-dibromo-4,4′-dimethyl-6,6′-dinitro-1,1′-biphenyl ( 4). Depending on the phosphane groups [diphenylphosphanyl ( 11, 13) or diisopropylphosphanyl ( 12, 14)] the palladium dichloride complexes show different coordination symmetry. Whereas the smaller diphenylphosphanyl groups lead to C2-symmetric complexes, the respective bis(diisopropyl)phosphanes 12 and 14 form C1-symmetric complexes that show fluxional behavior due to the restricted rotation of the isopropyl groups as well as the exchange of atom positions within the C1-symmetric conformer. All complexes have been tested as precatalysts in the Suzuki-Miyaura cross coupling reaction of 2-bromotoluene and phenylboronic acid. The activity of the catalytic system increases with the size of the diphosphanes and the donating ability of the ligand. In contrast to C2-symmetric palladium complex 15, platinum complex 19 was found to be C1-symmetric in the solid state despite the fact that both complexes have the small bis(diphenylphosphanyl)-substituted diphosphane ligand 11 in common. NiBr2 adduct 20 with a similar diphosphane 13 exists as a mixture of distorted square-planar and tetrahedral coordination sphere geometries in equilibrium with each other. [ABSTRACT FROM AUTHOR]