N- versus P-coordination in bis(amino)cyclodiphosph(III)azane complexes of aluminum.

The reaction of the bis(amino)cyclodiphosph(III)azane, cis-{(tBuNH)(2)(PNtBu)(2)}, with AlMe(3), AlClMe(2), AlCl(2)Me, and AlCl(3) is reported. The less Lewis acidic compound AlMe(3) forms the adduct cis-[(tBuNH)(2)(PNtBu){P.(AlMe(3))NtBu}] (1), in which the aluminum atom is exclusively coordinated to one phosphorus atom. At elevated temperatures AlMe(3) undergoes migratory exchange between the two phosphorus atoms, but no methane elimination is observed. By using the more Lewis acidic compound AlClMe(2) the P-coordinated compound cis-[(tBuNH)(2)(PNtBu){P(AlClMe(2))NtBu}] (2) can be obtained at low temperatures. Compound 2 rearranges irreversibly to a product in which the AlClMe(2) group is coordinated by one exo-cyclic nitrogen atom. A concomitant 1,2-H shift from this nitrogen atom onto the phosphorus atom is observed. The N-coordinated rearrangement product slowly decomposes via a P-N bond cleavage in solution. Reaction of the even more Lewis acidic compounds AlCl(2)Me and AlCl(3) finally led to stable adducts, cis-[(tBuNH)(PNtBu)(tBuNAlCl(2)Me){P(H)NtBu}] (3), and cis-[(tBuNH)(PNtBu)(tBuNAlCl(3)){P(H)NtBu}] (4), in which the aluminum atoms are N-coordinated by a tBuN=PH unit.