PPh₃ Propeller Diastereomers: Bonding Motif Ph_PPh3 Face-On π-Ar in Half-Sandwich Compounds [(π-Ar)LL′MPPh₃]

Abstract

Chiral-at-metal compounds ( R Ru , S C )/( S Ru , S C )-[CyRu(1O-2N)PPh 3 ]PF 6 and ( R Ru , S C )/( S Ru , S C )-[CyRu(2O-1N)PPh 3 ]PF 6 were prepared using anions 1O-2N – and 2O-1N – of the Schiff bases, derived from the hydroxynaphthaldehydes and ( S )-1-phenylethylamine. The pure ( R Ru , S C )-diastereomers were obtained by crystallization. In the unit cell of ( R Ru , S C )-[CyRu(1O-2N)PPh 3 ]PF 6 , there are three independent molecules, which differ in the propeller sense of the PPh 3 ligand. Molecules [1] and [2] have ( M PPh 3 )-configuration and molecule [3] has ( P PPh 3 )-PPh 3 configuration. PPh 3 diastereoisomerism is discussed including other pairs of compounds, differing only in the PPh 3 configuration. A conformational analysis reveals an internal stabilization inside the PPh 3 ligand by a system of attractive CH/π interactions and a new bonding motif Ph PPh 3 face-on π-Ar, both characteristic features of [(π-Ar)LL′MPPh 3 ] compounds. The propeller diastereomers interconvert via a low-energy pathway and a high-energy pathway, corroborated by density functional theory calculations.

The Chirality Chain in Valine: How the Configuration at the Cα Position through the OcisC′CαN Torsional System Leads to Distortion of the Planar Group CαC′(Ocis)Otrans to a Flat Tetrahedron

“…In Figure the reaction HURXEX(1) → ROKBOI02(4) is embedded in an energy profile with respect to rotation around the C′−C α bond in valine. The accumulation of sample points is interpreted as the energy minimum . Following the arrows towards the energy minimum, conformations of type HURXEX(1) rotate preferentially counter‐clockwise stretching the flat tetrahedron, whereas those of type ROKBOI02(4) rotate clockwise flattening the tetrahedron.…”

Trend‐Analysis of Solid‐State Structures: Low‐Energy Conformational ‘Reactions’ Involving Directed and Coupled Movements in Half‐Sandwich Compounds [CpFe(CO){C(=O)R}PPh3]

“…The molecular movements described here are below full rotations around the C i −P and P−Fe axes and even below the transition states, which interconvert the face/edge/ trans ‐phenyl rings of the PPh 3 ligand . By trend analysis of solid‐state structures, they are easily recognized.…”

“…In (π‐Ar)MPPh 3 complexes, a weak bonding stabilization is ascribed to the Ph PPh3 face‐on π‐Ar interaction . For the complexes [CpFe(CO){C(=O)R}PPh 3 ], this means a weak attraction of Cp and Ph face .…”

“…The coupled movements work hand in hand to strengthen the Ph PPh3 face‐on Cp stabilization. Eclipsing of Ph edge and Ph trans with the carbonyl and acyl substituents prevents a further decrease of the rotation angle of Ph face . In the back ‘reaction’ KEWSEK→VIVTEZ, the increase of the rotation angle ρ weakens the Ph PPh3 face‐on Cp interaction.…”

“…In (p-Ar)MPPh 3 complexes,aw eak bonding stabilization is ascribed to the Ph PPh3 face-on p-Ar interaction. [6] For the com- Figure 4s hows that the sample points of the three phenyl rings crowd within narrow ranges of their rotation angles, constraining the rotationa roundt he PÀFe axis to small degree intervals ( Table 1). Ac hange of the face/edge/ trans-character of the phenylr ings would afford passage over higher transition states.…”