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

(IR)-1,3-Benzazaphospholes la-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 2a and 2b, whereas bulky N-substituents and nonpolar solvents change the reactivity towards addition at the P=C bond. The preferred regio-selectivity is tert-butylation at phosphorus, occurring with excellent diastereoselectivity for trans-adducts 3b and 3c, but the inverse tert-butylation at C2 to 5b 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 spe-cies into the corresponding sigma(2)-p or sigma(3)-P compounds 4b and 6a,b, 7b,c, or 8b-10b with additional N and/or O donor sites. Slow diffusion-controlled air oxidation of 10b led to the meso-diphosphine 11b. Preferred eta(1)-P coordination was shown for an [Rh(cod)Cl] complex 12b, and the potential of the new ligands 4b and 7b in catalysis was demonstrated by examples of Pd-catalyzed C-N coupling and Ni-catalyzed ethylene oligomerization (TON > 6300). Crystal structures of 6b, 11b, and 12b are presented.