Bulky N-substituted 1,3-benzazaphospholes: access via Pd-catalyzed C-N and C-P cross coupling, lithiation, and conversion to novel P=C-PtBu2 hybrid ligands.
The syntheses of novel bulky N-substituted 1,3-benzazaphospholes are presented, together with their reactions with tert-butyllithium and coupling with tBu 2PCl to novel P, P'-hybrid ligands that combine the highly basic and bulky di- tert-butylphosphanyl group with pi-acidic low-coordinated phosphorus. The syntheses start with the preparation of new N-secondary 2-bromoanilines 1 by reduction of N-acyl 2-bromoanilides or more generally by Pd-catalyzed selective monoamination of o-dibromobenzene, followed by Pd-catalyzed C-P coupling with P(OEt) 3 to the respective 2-anilino-phosphonates 2. The next steps are reduction to 2-phosphanylanilines 3 and condensation with Me 2NCH(OMe) 2, which leads via phosphaalkenes 4 to the corresponding N-substituted benzazaphospholes 5. The reaction with tBuLi depends on the steric demand of the N substituent. Methyl, neopentyl-, and mesityl-derivatives were converted to P=C Li species 6 and coupled with tBu 2PCl to novel P=C-P tBu 2 ligands 7, whereas N-adamantyl and N-2,6-diisopropylphenyl-derivatives prefer addition of tBuLi at the PC bond to form dihydroderivatives. The chemical shifts of the low-coordinated phosphorus of 5 and 7 were found to reflect electronic and steric effects of the N substituents. The comparison of the crystal structures of N-neopentyl-1,3-benzazaphospholes 5 and 7 gives evidence of steric repulsion between the adjacent di- tert-butyl and neopentyl groups by the preferred anti orientation of the P- tert-butyl groups and moderate deviations of C2 and P3 of 7b from the ring plane.
Aluri
Bhaskar Reddy
BR
Institut für Biochemie - Anorganische Chemie Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Str. 4, D-17487 Greifswald, Germany.
Kindermann
Markus K
MK
Jones
Peter G
PG
Dix
Ina
I
Heinicke
Joachim
J
D000814:Aniline Compounds / Q000737:chemistry; D001372:Aza Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D002244:Carbon / Q000737:chemistry*; D002384:Catalysis; D008024:Ligands; D008094:Lithium / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*
D000814:Aniline Compounds; D001372:Aza Compounds; D008024:Ligands; D010758:Phosphorus; D010165:Palladium; D002244:Carbon; D008094:Lithium; D009584:Nitrogen