π‐Excess Aromatic σ2P Ligands: Formation of a Heterocyclic 1,2‐Diphosphine by the Addition of tBuLi and Subsequent Inverse Addition of the Product at the P=C Bonds of Two Molecules of 1‐Neopentyl‐1,3‐benzazaphosphole

The reactivity of tBuLi (pentane) toward the N-neopentyl-substituted p-excess P=CH-N heterocycle 1 depends on the solvent (tetrahydrofuran, diethyl ether, hexane, and toluene) and reaction conditions. Trapping of the resulting organolithium compounds with CO2/ClSiMe3, ClSiMe3, or EtI led to various products indicating CH lithiation (1a, b), normal addition of tBuLi at the P=C bond (E/Z-2a, b), inverse addition of the primary addition product 2(Li) at the P=C bond of a second molecule 1, affording 3-tert-butyl-2,2'-bis(1,3-benzazaphospholines) 3, or inverse addition of tBuLi (4b, c). The formation of 3 demonstrates a novel route to asymmetric heterocyclic 1,2-diphosphine ligands. The structure elucidation of the new compounds is based on their P-31 and C-13 NMR data with conclusive chemical shifts and P-C coupling constants, that of the isolated PH-functionalized diphosphine 3 on crystal structure analysis. (C) 2015 Wiley Periodicals, Inc.