Coordination chemistry and structural rearrangements of the Me2PCH2AlMe2 ambiphilic ligand

Abstract

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.