Sterically and polarity-controlled reactions of tBuLi with P=CH-NR heterocycles: novel heterocyclic P- and P,O-ligands and preliminary tests in transition-metal catalysis.
(1R)-1,3-Benzazaphospholes 1 a-c, P=CH-NR heterocycles of the indole type, react with tBuLi in two ways, depending on the steric demand of the N-substituent and the polarity of the medium. The presence of small N-alkyl groups induces CH-deprotonation in the 2-position to give hetaryllithium reagents 2 a and 2 b, whereas bulky N-substituents and nonpolar solvents change the reactivity towards addition at the P=C bond. The preferred regioselectivity is tert-butylation at phosphorus, occurring with excellent diastereoselectivity for trans-adducts 3 b and 3 c, but the inverse tert-butylation at C2 to 5 b was also observed. N-Neopentyl groups, with intermediate steric demand, give rise to formation of mixtures in ethers but allow switching either to selective CH lithiation in THF/KOtBu or to addition in pentane. Bulkier N-adamantyl groups always cause preferred addition. Protonation, silylation, and carboxylation were used to convert the P=CLi-NR, (E)-tBuP-CHLi-NR, and LiP-CH(tBu)-NR species into the corresponding sigma(2)-P or sigma(3)-P compounds 4 b and 6 a,b, 7 b,c, or 8 b-10 b with additional N and/or O donor sites. Slow diffusion-controlled air oxidation of 10 b led to the meso-diphosphine 11 b. Preferred eta(1)-P coordination was shown for an [Rh(cod)Cl] complex 12 b, and the potential of the new ligands 4 b and 7 b in catalysis was demonstrated by examples of Pd-catalyzed C-N coupling and Ni-catalyzed ethylene oligomerization (TON>6300). Crystal structures of 6 b, 11 b, and 12 b are presented.
Aluri
Bhaskar R
BR
Institut für Biochemie-Anorganische Chemie, Ernst-Moritz-Arndt-Universität Greifswald, Felix-Hausdorff-Str. 4, 17487 Greifswald, Germany.
Kindermann
Markus K
MK
Jones
Peter G
PG
Heinicke
Joachim
J
D001372:Aza Compounds / Q000737:chemistry; D002384:Catalysis; D018360:Crystallography, X-Ray; D006574:Heterocyclic Compounds, 2-Ring / Q000138:chemical synthesis / Q000737:chemistry*; D007211:Indoles / Q000138:chemical synthesis / Q000737:chemistry; D008024:Ligands; D009532:Nickel / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry; D013237:Stereoisomerism
D001372:Aza Compounds; D006574:Heterocyclic Compounds, 2-Ring; D007211:Indoles; D008024:Ligands; D009942:Organometallic Compounds; D009943:Organophosphorus Compounds; C434823:n-butyllithium; D010165:Palladium; D009532:Nickel