X-ray crystallographic and solution studies of the pentamethyldiethylenetriamine and tetramethylethylenediamine adducts of lithium diphenylphosphide

X-ray crystallographic studies on the lithium diphenylphosphide adducts (Me2NCH2CH2)2NMe2 · LiPPh2 ( 1) and Me2NCH2CH2NMe2 · LiPPh2 (2) are reported. 1 is monomeric, with a terminal PPh2 unit containing a pyramidally coordinated phosphorus atom attached to the four-coordinate metal atom by a Li-P bond of length 2.567(6) Å. 2 crystallizes as dimers, (Me2NCH2CH2NMe2 · LiPPh2)2, with bridging PPh2 units containing (distorted) tetrahedrally coordinated phosphorus atoms: their planar (LiP)2 rings are roughly square-shaped (mean PLiP angle 91°, mean LiP distance 2.61 Å). Discussion of features of these structures is facilitated by ab initio MO calculations on the model systems LiPH2 and (LiPH2)2. Cryoscopic molecular mass measurements and high-field 7Li/31P NMR spectroscopic studies on solutions of 1 and 2 indicate that both solid-state structures are retained in arene solution, though some dissociation of2 into monomers is apparent.