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Isoelectronic BN Substitution for C 2 in Phosphine Ligands

Isoelectronic BN Substitution for C 2 in Phosphine Ligands. Triphenylphosphine. DuPhos. Dppe. Jonathan Bailey. Why study P-B ligands?. ?. P-O. P-C. P-B. P-N. P-F. electronegativity. Pringle Angew . Chem. Int. Ed. 2012 , 51. Phosphinoboranes vs. boryl phosphines.

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Isoelectronic BN Substitution for C 2 in Phosphine Ligands

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  1. Isoelectronic BN Substitution for C2 in Phosphine Ligands Triphenylphosphine DuPhos Dppe Jonathan Bailey

  2. Why study P-B ligands? ? P-O P-C P-B P-N P-F electronegativity Pringle Angew. Chem. Int. Ed. 2012, 51 Phosphinoboranes vs. borylphosphines ‘Phosphinoborane’ ‘Boryl Phosphine’ Examples of P-B containing ligands Nöth, 1992 Weller, 2013 Bourissou, 2012 Buchwald, 2012

  3. B-N substituted aryl ligands Initial targets vs. vs. Liu,2009 7 steps, 10% yield Dewar, 1958 Piers, 2007 Need a milder source of phosphorus

  4. B-Cl + P-Si exchange B-Cl + P-Si → B-P + SiCl? Noeth,Chem. Berichte1965, 98, 352 ≡ Advantages: • Mild conditions • No work-up needed • NH - group tolerant

  5. Electronic Properties ν(CO) = 1942 cm-1 ν(CO) = 1940 cm-1

  6. Carbon analogues vs P P

  7. Diisopropyl ligands ν(CO) = 1940 cm-1 ν(CO) = 1953 cm-1 Electron donating Electron withdrawing 1939 cm-1 Buchwald 2015 cm-1 Pringle PPh3 PCy3 1940 cm-1 1943 cm-1 1979 cm-1

  8. Phobane ligands ν(CO) = 1942 cm-1 ν(CO) = 1951 cm-1 Substituting C-C for B-N renders the ligand much more electron donating > Why? σ-donation stronger for B-N

  9. DFT calculations ≈ 90° ≈ 180° 1.993 Å 1.941 Å Good overlap of lone pair with aromatic framework Little overlap of lone pair with aromatic framework BP86/6-31G*, LACV3P on TM atoms

  10. Scope of B-Cl + P-Si exchange B-Cl + P-Si → B-P + SiCl?

  11. NBN ligand ν(Rh-CO) = 1945 cm-1 (cf. 1942 for BN analogue) P-B: 1.93 Å

  12. Electron-Poor Groups on Boron Stephan JACS 2008,12632 versus B-Cl + P-Si → B-P + SiCl? Bourissou, JACS 2012, 6560 Lose ClSiMe3 to form P=B?

  13. ? Add a source of Cl- to catalyse the loss of ClSiMe3? Sequential adduct formation and loss of ClSiMe3 to give phosphinoborane

  14. Conclusions and future work • Exploit electron donating ability of phosphine in oxidative addition reactionsand catalysis. • Investigate the stability of ligands. Route to P-B under mild conditions Substituting C2 for BN dramatically increases electron donating ability of ligand Silyl exchange route to phosphinoboranes Extremely electron rich phosphine

  15. Acknowledgments • Prof. Paul Pringle • Dr.MairiHaddow - X-Ray • Dr. Natalie Fey - DFT • Dr. Didier Bourissou and Dr.AbderrahmaneAmgoune - Toulouse • Pringles

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