Alkali Metal Complexes of Phosphine-Borane-Substituted Benzyl Ligands and Their Application in the Synthesis of B-H\ub7\ub7\ub7Sn Stabilized Dialkylstannylenes

\ua9 2024 The Authors. Published by American Chemical Society.The benzyl-substituted phosphine-boranes PhCH2P(BH3)R2 [R = iPr (1H), Ph (2H), Cy (3H)] are accessible through either the reaction between R2PCl and PhCH2MgBr, followed by treatment with BH3\ub7SMe2 or the reaction between R2P(BH)3Li and PhCH2Br. Treatment of 1H, 2H, or 3H with nBuLi, PhCH2Na, or PhCH2K gave the corresponding alkali metal complexes [{iPr2P(BH3)CHPh}Li(THF)]2 (1Li), [{Ph2P(BH3)CHPh}Li(OEt2)2] (2Li), [{Cy2P(BH3)CHPh}Li(TMEDA)] (3Li), [iPr2P(BH3)CHPh]Na (1Na), [{Ph2P(BH3)CHPh}Na(THF)2]2 (2Na), [Cy2P(BH3)CHPh]Na(THF)0.5 (3Na), [{iPr2P(BH3)CHPh}K]∞ (1K), [{Ph2P(BH3)CHPh}K(THF)]∞ (2K), and [{Cy2P(BH3)CHPh}K.0.5PhMe]∞ (3K). X-ray crystallography revealed that, while 2Li and 3Li crystallize as monomers, 1Li and 2Na crystallize as borane-bridged dimers. The potassium complexes 1K, 2K, and 3K all crystallize with polymeric structures, in which the monomer units are linked to each other through a range of both bridging BH3 groups and multihapto interactions between the potassium cations and the aromatic rings. The reactions between two equivalents of either 1Li or 3Li and Cp2Sn gave the corresponding dialkylstannylenes [{R2P(BH3)CHPh}2Sn] [R = iPr (1Sn), Cy (3Sn)]. These compounds were isolated as mixtures of the rac and meso diastereomers. X-ray crystallography reveals that rac-1Sn and rac-3Sn crystallize as discrete monomers each exhibiting two agostic-type B-H\ub7\ub7\ub7Sn contacts