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

Abstract

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.

π‐Excess σ2P=C–N–Heterocycles: Catalytic P‐Arylation and Alkylation of N‐Alkyl‐1,3‐benzazaphospholes and Isolation of P,N‐Disubstituted Dihydrobenzaza­phosphole P‐Oxides

“…1,3-Benzazaphospholes 1, 4, [29] and 7 [30] and also their 2-phosphanylaniline precursors were prepared as previously reported. PdCl 2 , CsOAc, Cs 2 CO 3 , K 2 CO 3 , and K 3 PO 4 were stored over P 4 O 10 in a dry box.…”

π-Rich σ2P-Heterocycles: Bent η1-P- and μ2-P-Coordinated 1,3-Benzazaphosphole Copper(I) Halide Complexes

“…Removal of the solvent from the filtrate provided a pale yellow viscous substance (297 mg), δ 31 P(CDCl 3 ) = 65.4, which from a small amount of MeOH gave crystals of excess 1 (210 mg, 51%), identified by the known unit cell parameters. 11 Reaction of 1 with CuBr (Reactant Ratio 2:1). Filtration of the suspension formed from 1 (368 mg, 1.80 mmol) and CuBr (129 mg, 0.90 mmol) in THF after 4 days and evaporation of the solvent under vacuum gave 250 mg of 2b·0.9 THF (yield 97% rel.…”

Hydrosilylative Reduction of Tertiary Amides to Amines Catalyzed by N‐(Phosphinoaryl)anilido Complexes of Iron and Cobalt

“…Benzene‐ d 6 was degassed via three freeze‐pump‐thaw cycles and stored over 4 Å molecular sieves. N ‐(2‐Bromophenyl)‐2,6‐diisopropylaniline was prepared by use of previously reported methods . Amide substrates were prepared from the corresponding acyl chlorides by using previously reported conditions .…”