The dibenzo[b,f ]azepinate (DBAP) complexes (DBAP)Li•(THF) 3 , (DBAP) 2 Mg•(THF) 2 , and (DBAP) 2 Ca•(THF) 3 could be isolated as highly air-sensitive compounds in yields of 93%, 72%, and 48%, respectively. Crystal structures of these THF adducts reveal monomeric complexes in which the degree of ring puckering depends on the nature of the metal. The most extreme deviation from planarity is found for the most covalent bound metal, Mg, but in all cases no interaction between the metal and the azepine CC bond is observed. The THF-free complex [(DBAP) 2 Mg] 2 , which could be obtained in 77% yield, crystallizes as an unusual dimer with three bridging and one terminal DBAP ligand. The bridging DBAP ligands are highly bent and span a cavity in which a Mg 2+ ion is bound through three alkene−Mg interactions with an average Mg•••C distance of 2.794(3) Å. Theoretical calculations support these contacts. A combination of AIM and NPA analyses shows polarization of the alkene π-electron density toward the metal (vertical polarization) but also demonstrates a polarization of electron density toward the C atom closest to Mg (horizontal polarization). Such metal−alkene interactions and implicit CC bond polarization are key features in main group metal catalyzed alkene conversions.

A stereodivergent synthesis using inexpensive reagents, i.e., dibenzazepine and glucose-derived t-Bu-sulfinate diastereomers (R S )-6 or (S S )-6, affords respective S(O)-alkene hybrid ligands (S)-7 and (R)-7 on gram scales and in excellent optical purity (ee > 99%). Phenyl substitution of the dibenzoazepine backbone generates planar chirality to give epimerizationresistant (pS,R S )-10 diastereoisomer in high isomeric purity. Furthermore, the crystal structure of widely used sulfinate (R S )-6 is disclosed for the first time since its discovery a quarter of a century ago. Ligands 7 and 10 coordinate Rh(I) in a bidentate fashion through the S atoms and the alkene functions as evidenced by the crystal structures of complexes (R)-11 and (S N ,S S )-12. (R)-11 catalyzes the conjugate addition of arylboronic acids to enones with enantioselectivities of up to 77% ee. The reaction proceeds smoothly also under base-free conditions at 40 °C. The planar chirality in ligand (pS,R S )-10 is shown to override and invert the sense of chiral induction predicted by the configuration of the sulfur donor atom.

10-Phenyl-5H-dibenz[b,f ]azepine ( 5) is synthesized by Suzuki cross coupling of the protected bromo alkene 4 with PhB(OH) 2 . 5 reacts with PCl 3 to afford the dichlorophosphanyl-azepine 6 in >90% yield. Alkylation of 6 with 1 equiv of t-BuMgBr leads, after recrystallization in Et 2 O, to the diastereomerically enriched (dr > 98:2) chloride rac-7, which the crystal structure reveals to be the (pS,R P )/ (pR,S P ) pair. The fact that rac-7 crystallizes in the Sohncke space group P2 1 2 1 2 1 opens up the possibility of a mechanical separation of the enantiomers. Methylation of rac-7 is perfectly stereoselective with inversion of configuration at the P atom to yield the new ligand rac-8 as the (R,R)/(S,S) pair. The corresponding BH 3protected diastereomer rac-9 (i.e., the (R,S)/(S,R) pair), is isolated after flash column chromatography in 73% yield. Compounds 5−9 are accessible in multigram quantities. X-ray crystal structures of Ru(II) complexes demonstrate the ambidentate nature of ligand rac-8: Complex 10 is exclusively P-coordinated, while in complex 11 two ligands bind Ru through their P donors and stabilize the 14-electron metal center with a double agostic interaction. In complex 12, the ligand coordinates in a κP,η 2 -alkene bidentate fashion.

Multigram quantities of the optically pure amino−bis-sulfoxide ligand (S,S)-bis(4-tert-butyl-2-(ptolylsulfinyl) phenyl)amine ((S,S)-3) are accessible by in situ lithiation of bis(2-bromo-4-tert-butylphenyl)amine (1) followed by a nucleophilic displacement reaction with Andersen's sulfinate 2. Deprotonation of (S,S)-3 with MgPh2 yields the magnesium amido−bis-sulfoxide salt (S,S)-4 quantitatively. AbstractMulti-gram quantities of the optically pure amino-bissulfoxide ligand (S,S)-bis(4-tert-butyl-2-(ptolylsulfinyl)phenyl)amine ((S,S)-3) are accessible by in situ lithiation of bis-(2-bromo-4-tertbutylphenyl)amine 1 followed by a nucleophilic displacement reaction with Andersen's sulfinate 2.

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