Chiral amide-containing bisdiazaphospholane (BDP) ligands developed in the Landis Group are state-of-the-art ligands for Asymmetric Hydroformylation (AHF). This ligand class shows high regio- and enantioselectivity towards a variety of alkene substrates. Regioselective control of allylic alcohols, however, remains difficult. This research focuses on the design of scaffolding phosphine ligands containing boronate substituents able to covalently and reversibly bind allylic alcohols with the potential to facilitate increased reactivity and selectivity in AHF. Both the ortho- and meta-phenyl boronic acid containing diazaphospholanes (B(OH)2-DiazaPhos) were synthesized successfully. Hydroformylation of allylic alcohols utilizing the novel B(OH)2-DiazaPhos ligands was found to not undergo directed AHF. Several hypotheses were tested to investigate this basis. First, preliminary exchange spectroscopy (EXSY) studies with PhB(OH)2 showed qualitatively that transesterification occurs faster than the herein performed AHF. Second, a boronate bisdiazaphospholane was synthesized. This chelating bisphosphine will allow for more well-defined catalyst species analysis compared to monophospholanes. Lastly, other boronate phosphines with varying P–B distance are targeted to investigate the ideal ligand conformation for a directing effect and further improve boronate phosphine ligand design for directed AHF. In addition, novel diazaphospholane frameworks with sp3-N backbone mimicking the highly selective class of (Bisphospholano)ethane (Ph-BPE) ligands were synthesized. The catalytic activity of these novel diazaphospholanes was evaluated, showing improved regioselectivity compared to the non-reduced parent Tetraphenyl BDP.

Novel diazaphospholane ligands for asymmetric hydroformylation

251st National Meeting (2016)

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