Formation of an Unsymmetrical Pt-Ir Tetraalkynyl Complex and Investigation into Subsequent Construction of Multimetallic Systems

Résumé

The reactions between [Pt(C≡CR)4]2- (R = Ph, t-Bu, SiMe3) and [Ir(μ-Cl)(COD)]2 have been studied, but the formation of an unsymmetrical heterobinuclear complex (NBu4)[(COD)Ir(μ-1κCα:η2- C≡CSiMe3) (μ-2κCα:η2-C≡CSiMe3)Pt (C≡CSiMe3)]2, (NBu4)[{Ir-Pt}(C≡CSiMe3)2], 1 was only observed with the homoleptic species [Pt(C≡CSiMe3)4]2-. Complex 1 exhibits in the solid state a bent σ,τ double-alkynyl bridging system, which is formed through a migration of one σ-alkynyl group from platinum to iridium. The stability of the remaining Pt-acetylide σ-bonds in 1 and its possible application in the assembly of multimetallic compounds containing the {Ir-Pt} "pincer" unit has been investigated. Treatment of (NBu4)[{Ir-Pt}(C≡CSiMe3)2] (1) with neutral [cis-M(C6F5)2(THF)2] (THF = tetrahydrofuran, M = Pt, Pd) or cationic [Rh(COD)(acetone)x]+ or [Pd(η3-C3H5)Sx]+ solvento species (the latter generated "in situ") leads to very unusual anionic (NBu4)[{Ir-Pt} (μ-2ΚCα:η2- C≡CSiMe3)2M(C6F5)2] (M = Pt, 2; Pd, 3) or neutral heterotrimetallic complexes [{Ir-Pt-}(μ-2ΚCα:η2-C≡ CSiMe3)2Rh+(COD)] (4) and [{Ir-Pt-}(μ-2ΚCα:η2-C≡ CSiMe3)2Pd+ (η3-C3H5)] (5), respectively. The molecular structure of 4 confirms the presence of a formally heterotrimetallic zwitterion [(COD)Ir(μ-1ΚCα:η2- C≡CSiMe3) (μ-2ΚCα:η2-C≡CSiMe3)Pt - (μ-2ΚCα:η2- C≡CSiMe3)2Rh+(COD)], formed by the binuclear anionic fragment [(COD)Ir(μ-1Κ Cα:η2-C≡CSiMe3) (μ-2ΚCα:η2-C≡CSiMe3)Pt (C≡CSiMe3)2]-, which in its turn acts as a chelating dimetallo bidentate ligand toward the cationic [Rh(COD)]+ unit. However, a similar neutralization reaction of 1 with 1 equiv of AgClO4 produces an unusual hexanuclear trimetallic complex [(η2-{Ir-Pt}-(C≡CSiMe3)2)2 Ag2] (6), in which the heterobimetallic diyne anionic substrate [{Ir-Pt}- (C≡CSiMe3)2]- acts as a μ-η2:η2 bridging ligand of two different silver(I) centers.