Coordination chemistry and structural rearrangements of the MePCHAlMe ambiphilic ligand.

Reaction of 2 equivalents of (MePCHAlMe) with [{RhCl(cod)}] (cod = 1,5-cyclooctadiene) afforded [{κ,-(MeAl)ClMeAl(CHPMe)}Rh(cod)] (1), which features a κ-coordinated bis(phosphino)aluminate anion. In compound 1, an Al-Cl substituent bridges to a molecule of AlMe, which could be removed to provide [{κ,-ClMeAl(CHPMe)}Rh(cod)] (2). By contrast, reaction of 1 equiv. of (MePCHAlMe) with [{RhCl(cod)}] yielded [Rh(cod)(μ-Cl)(MePCHAlMe)] (3) as the major product, where the phosphine donor of an intact MePCHAlMe ligand is coordinated to rhodium and a chloride ligand bridges between Rh and Al. [Rh(cod)(μ-Cl)(MePCHAlClMe)] (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 (MePCHAlMe) with [{RhCl(cod)}] in THF afforded [{Rh(μ-CHPMe)(cod)}] (4). Reactions of (MePCHAlMe) with iridium(I), gold(I) and platinum(II) precursors were also explored. A 1 : 1 reaction of (MePCHAlMe) with [{IrCl(cod)}] afforded [{κ,-ClAl(CHPMe)}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, [{κ,-ClAl(CHPMe)}Rh(cod)] (6), was also synthesized the 1 : 1 reaction of {ClAl(CHPMe)} with [{RhCl(cod)}]. Reactions of (MePCHAlMe) with [AuCl(CO)] or [PtCl(cod)] also resulted in chloride-methyl group exchange between the transition metal and aluminium. However, these reactions generated free (MePCHAlClMe) accompanied by gold and ethane, or [PtMe(cod)], respectively. Reaction of 1.5 equivalents of (MePCHAlMe) with [PtMe(cod)] at 75 °C afforded zwitterionic [(PtMe{μ-κ:κ,-MeAl(CHPMe)})] (7) which features two tris(phosphino)aluminate anions bridging between PtMe units. Compounds 1-2, 3/3A, 4-7 and (MePCHAlClMe) were crystallographically characterized.