Aluminum Complexes Incorporating Bidentate Amido Phosphine Ligands

A series of aluminum complexes supported by o-phenylene-derived amido phosphine ligands, N-(2-diphenylphosphinophenyl)-2,6-dimethylanilide ([Me-NP]-) and N-(2-diphenylphosphinophenyl)-2,6-diisopropylanilide ([iPr-NP]-),
have been prepared. The reactions of trialkylaluminum with H[Me-NP] and H[iPr-NP], respectively, in refluxing
toluene produced the corresponding dialkyl complexes [Me-NP]AlR2 and [iPr-NP]AlR2 (R = Me, Et). Deprotonation
of H[Me-NP] with n-BuLi in THF at −35 °C followed by addition of AlCl3 in toluene at −35 °C afforded [Me-NP]AlCl2, which was subsequently reacted with 2 equiv of trimethylsilylmethyllithium in toluene to give [Me-NP]Al(CH2SiMe3)2. The aluminum complexes were all characterized by 1H, 13C, 31P, and 27Al NMR spectroscopy. The solid-state structures of monomeric, four-coordinate [Me-NP]AlEt2 and [iPr-NP]AlMe2 and five-coordinate [Me-NP]AlCl2(THF)
were determined by X-ray crystallography. The 1H NMR studies of [Me-NP]AlEt2, [Me-NP]Al(CH2SiMe3)2, and
[iPr-NP]AlEt2 indicate diastereotopic α-hydrogen atoms in these molecules. Heteronuclear COSY and NOE
experiments suggest that the phosphorus donor in [Me-NP]Al(CH2SiMe3)2 and [iPr-NP]AlEt2 is coupled to only one
of the diastereotopic α-hydrogen atoms that is virtually antiperiplanar with respect to the phosphorus atom.