Tris(borane) Adducts of Diphosphanylmethanides: The [H 3 BCH(PPh 2 BH 3 ) 2 ] – Anion and Its Alkali Metal Complexes

The reactivity of lithium complexes that contain the borane‐modified diphoshanylmethanide ligand [CH(PPh 2 BH 3 ) 2 ] – towards different Lewis base adducts of BH 3 was studied to gain further insight into the mechanism of the isomerization of this derivative, which formally proceeds through a shift of one BH 3 group from the phosphorus atom to the carbon atom. Whereas the use of BH 3 · THF in THF only resulted in the thf adduct of the starting material, [Li{CH(PPh 2 BH 3 ) 2 }(thf) 2 ] ( 1 ), the application of BH 3 · SMe 2 in toluene resulted in the formation of the novel compound [(Li{H 3 BCH(PPh 2 BH 3 ) 2 }) ∞ ] ( 2 ). The subsequent addition of ethereal ligands led to the isolation of [Li{H 3 BCH(PPh 2 BH 3 ) 2 }(Me 4 thf)] ( 3 ) and [Li{H 3 BCH(PPh 2 BH 3 ) 2 }(thf) 3 ] ( 4 ). Treatment of these complexes with stronger Lewis bases such as N , N , N′ , N′ ‐tetramethylethane‐1,2‐diamine (tmeda) results in the removal of one phosphorus‐bound BH 3 molecule and the formation of the [Ph 2 PCH(BH 3 )PPh 2 BH 3 ] – anion. These results indicate that the isomerization of [CH(PPh 2 BH 3 ) 2 ] – requires an additional BH 3 source and a rather strong Lewis base. Complexes 1 – 4 and the related derivatives [Li{CH(PPh 2 BH 3 ) 2 }(Me 4 THF)] ( 5 ) and [K{H 3 BCH(PPh 2 BH 3 ) 2 }(dme) 2 ] ( 6 ; dme = 1,2‐dimethoxyethane) were characterized by multinuclear NMR spectroscopy and by single‐crystal X‐ray diffraction analysis.