Bis-ortho-chelated diaminoaryl platinum compounds with σ-acetylene substituents. Investigations into their stability and subsequent construction of multimetallic systems. The crystal structure of [(μ2-[(η2-NCN)Pt(η 1-CO)C≡CSiMe3])Co2(CO)6] (NCN = 2,6-bis[(dimethylamino)methyl]phenyl)

Article abstract of DOI:10.1021/om000272a

A series of related platinum σ-acetylide complexes {Pt}C≡CR ({Pt} = [Pt(C₆H₃{Me₂NCH₂} ₂-2,6)]⁺) were prepared by reacting lithium acetylides with {Pt}Cl (1) in order to investigate the stability of the Pt-acetylide σ-bond and their possible application in the assembly of multimetallic compounds containing the {Pt} "pincer" unit. This may be achieved by η²-coordination of the acetylide or by incorporating a second ligating site in the acetylide anion. Both of these approaches are demonstrated herein. {Pt}C≡CSiMe₃ (2) was reacted with [M][BF₄] ([M] = [Cu(NCMe)₄], Ag) and different forms of Cu(I) halides. Only with the former was the formation of stable π-coordinated M(I) compounds observed. [(η²-[{Pt}C≡CSiMe₃]₂)-Cu][BF ₄] exhibits η²-coordination of both acetylenic units to a formal Cu(I) metal center, thus forming a heterotrimetallic compound. In the presence of halide ions, 2 undergoes cleavage of the Pt-C≡C σ-bond with concomitant formation of {Pt}X (X = Cl or I). The reaction of 2 with Co₂(CO)₈ leads via π-coordination to the formation of a trimetallic dicobaltatetrahedrane. The structure of [(μ²-[(η²-NCN)Pt(η ¹-CO)C≡CSiMe₃])Co₂(CO)₆] in the solid state shows that one ortho-CH₂NMe₂ substituent of the NCN ligand is no longer coordinated to the Pt metal center. Instead, a CO ligand coordinates trans to the Pt-N bond, yielding a metal center with four different ligand donor atoms. Attempts to obtain related Pt(IV) acetylides by reaction of 2 with CuCl₂ resulted in the formation of {Pt}Cl₃, [CuX]_n, and [CuC≡CSiMe₃]_n. The reaction with I₂ gave neither a Pt(IV) diiodide nor a Pt(II) η₁-I₂ complex, but instead led to Pt-C(acetylide) bond cleavage and formation of {Pt}I and IC≡CSiMe₃. The reaction of {Pt}C≡CC₆H₄CN-4 with [{Pt}H₂O][BF₄] and {Ru}N≡N{Ru} ({Ru} = [RuCl₂(C₅H₃N{CH₂NMe ₂}₂-2,6)]) gives air-stable well-defined bimetallic compounds. In contrast, the reaction of {Pt}C≡CC₆H₄CN-4 with [AuCl₃]₂ or Au(CO)Cl leads to the formation of a gold mirror, NCC₆H₄(C≡C)₂C₆H₄CN, and {Pt}Cl₃ or {Pt}Cl, respectively. Cyclic voltammetry studies with representative Pt-acetylides show irreversible oxidative processes which are shifted to a more negative potential upon substitution of Cl by acetylide.