Metalated 1,3-azaphospholes: synthesis of lithium-1,3-benzazaphospholides and reactivity towards organoelement and organometal halides

Metalation of benzazaphospholes 1a–e with t-BuLi provided the ambident anions 1a–eLi in high selectivity. A crystal structure analysis of 1bLi·3THF reveals monomers and coordination of lithium at nitrogen. The tungsten pentacarbonyl complexes also react preferably at nitrogen as shown by the reaction of 2a and 2d with t-BuLi. Addition at the PC bond is a minor process in the case of 2a. Compounds 1a,cLi as well as 2dLi react with alkyl halides at phosphorus to give the 3-alkyl-1,3-benzazaphospholes 3a and 3d or the respective W(CO)5 complex 4d. Even acetyl and pivaloyl chloride attack 1eLi at phosphorus affording the P-acyl derivatives 5e and 6e. Silylation can occur at nitrogen or phosphorus to give 7 and/or 8 depending on steric and electronic effects exerted by the substituent in position 2. The different effect of 2-t-butyl groups on the steric hindrance at N and P is illustrated by the molecular geometry of 1d determined by crystal structure analysis. Soft organometallic halides such as Me3SnCl, CpFe(CO)2I and CpW(CO)3Cl react with 1Li preferably at phosphorus affording the stannyl or monomer organo-transition metal derivatives 9–11. The products are characterized by multinuclear NMR data of all new compounds.