Structure and bonding of the tris(diphenylmethyleneamino)aluminium dimer [Al(NCPh2)3]2: relative strengths of bridging and terminal Al–X bonds in systems X2Al(µ2-X)2AlX2
Abstract
The title compound, prepared by reaction of LiNCPh2 with AlC3 in 2:1 → 3:1 molar ratio, crystallises as the dimer (Ph2CN)2Al(µ2-NCPh2)2Al(NCPh2)2, with Al–N distances (terminal 1.78, bridging 1.93 Å) and CN-Al angles (terminal 148–175, bridging 130–133°) consistent with a bonding description in which each ligand functions as a source of three electrons, making the terminal Al-N bonds twice as strong as the bridging ones, an interpretation supported by molecular orbital bond index (MOBl) calculations which show this to be a general characteristic of species Al2X6, whether electron-precise (XCl, NR2, or NCR2) or electron-deficient (XMe or H).