Coordination chemistry and structural rearrangements of the Me2PCH2AlMe2 ambiphilic ligand

Reaction of 2 equivalents of (Me2PCH2AlMe2)2 with [{RhCl(cod)}2] (cod = 1,5-cyclooctadiene) afforded [{κ2P,P-(Me3Al)ClMeAl(CH2PMe2)2}Rh(cod)] (1), which features a κ2-coordinated bis(phosphino)aluminate anion. In compound 1, an Al–Cl substituent bridges to a molecule of AlMe3, which could be removed in vacuo to provide [{κ2P,P-ClMeAl(CH2PMe2)2}Rh(cod)] (2). By contrast, reaction of 1 equiv. of (Me2PCH2AlMe2)2 with [{RhCl(cod)}2] yielded [Rh(cod)(μ-Cl)(Me2PCH2AlMe2)] (3) as the major product, where the phosphine donor of an intact Me2PCH2AlMe2 ligand is coordinated to rhodium and a chloride ligand bridges between Rh and Al. [Rh(cod)(μ-Cl)(Me2PCH2AlClMe)] (3A) and 2 were also formed as minor products. The aforementioned reactions were carried out in benzene or toluene, whereas the 1 : 1 reaction of (Me2PCH2AlMe2)2 with [{RhCl(cod)}2] in THF afforded [{Rh(μ-CH2PMe2)(cod)}2] (4). Reactions of (Me2PCH2AlMe2)2 with iridium(i), gold(i) and platinum(ii) precursors were also explored. A 1 : 1 reaction of (Me2PCH2AlMe2)2 with [{IrCl(cod)}2] afforded [{κ2P,P-Cl2Al(CH2PMe2)2}Ir(cod)] (5) as one of two major phosphine-containing products; unlike 3, this compound features two chlorine substituents on aluminium. For comparison, the rhodium analogue of 5, [{κ2P,P-Cl2Al(CH2PMe2)2}Rh(cod)] (6), was also synthesized via the 1 : 1 reaction of {ClAl(CH2PMe2)2}2 with [{RhCl(cod)}2]. Reactions of (Me2PCH2AlMe2)2 with [AuCl(CO)] or [PtCl2(cod)] also resulted in chloride–methyl group exchange between the transition metal and aluminium. However, these reactions generated free (Me2PCH2AlClMe)2 accompanied by gold and ethane, or [PtMe2(cod)], respectively. Reaction of 1.5 equivalents of (Me2PCH2AlMe2)2 with [PtMe2(cod)] at 75 °C afforded zwitterionic [(PtMe{μ-κ1P:κ2P,P-MeAl(CH2PMe2)3})2] (7) which features two tris(phosphino)aluminate anions bridging between PtMe units. Compounds 1–2, 3/3A, 4–7 and (Me2PCH2AlClMe)2 were crystallographically characterized.