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

The reactions between [Pt(C⋮CR) 4 ] 2 - (R = Ph, t -Bu, SiMe 3 ) and [Ir(μ-Cl)(COD)] 2 have been studied, but the formation of an unsymmetrical heterobinuclear complex (NBu 4 )[(COD)Ir(μ-1κ C α:η 2 -C⋮CSiMe 3 )(μ-2κ C α:η 2 -C⋮CSiMe 3 )Pt(C≡CSiMe 3 ) 2 ], (NBu 4 )[{Ir−Pt}(C⋮CSiMe 3 ) 2 ], 1 was only observed with the homoleptic species [Pt(C⋮CSiMe 3 ) 4 ] 2 - . Complex 1 exhibits in the solid state a bent σ,π 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 (NBu 4 )[{Ir−Pt}(C⋮CSiMe 3 ) 2 ] ( 1 ) with neutral [ cis -M(C 6 F 5 ) 2 (THF) 2 ] (THF = tetrahydrofuran, M = Pt, Pd) or cationic [Rh(COD)(acetone) x ] + or [Pd(η 3 -C 3 H 5 )S x ] + solvento species (the latter generated “in situ”) leads to very unusual anionic (NBu 4 )[{Ir−Pt}(μ-2κ C α:η 2 -C⋮CSiMe 3 ) 2 M(C 6 F 5 ) 2 ] (M = Pt, 2; Pd, 3 ) or neutral heterotrimetallic complexes [{Ir−Pt - }(μ-2κ C α:η 2 -C⋮CSiMe 3 ) 2 Rh + (COD)] ( 4 ) and [{Ir−Pt - }(μ-2κ C α:η 2 -C⋮CSiMe 3 ) 2 Pd + (η 3 -C 3 H 5 )] ( 5 ), respectively. The molecular structure of 4 confirms the presence of a formally heterotrimetallic zwitterion [(COD)Ir(μ-1κ C α:η 2 -C⋮CSiMe 3 )(μ-2κ C α:η 2 -C⋮CSiMe 3 )Pt - (μ-2κ C α:η 2 -C⋮CSiMe 3 ) 2 Rh + (COD)], formed by the binuclear anionic fragment [(COD)Ir(μ-1κ C α:η 2 -C⋮CSiMe 3 )(μ-2κ C α:η 2 -C⋮CSiMe 3 )Pt(C⋮CSiMe 3 ) 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 AgClO 4 produces an unusual hexanuclear trimetallic complex [(η 2 -{Ir−Pt}(C⋮CSiMe 3 ) 2 ) 2 Ag 2 ] ( 6 ), in which the heterobimetallic diyne anionic substrate [{Ir−Pt}(C⋮CSiMe 3 ) 2 ] - acts as a μ-η 2:η 2 bridging ligand of two different silver(I) centers.