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(η¹-CO)C⋮CSiMe₃])Co₂(CO)₆] (NCN = 2,6-Bis[(dimethylamino)methyl]phenyl)

A series of related platinum σ-acetylide complexes {Pt}C⋮CR ({Pt} = [Pt(C 6 H 3 {Me 2 NCH 2 } 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 η 2 -coordination of the acetylide or by incorporating a second ligating site in the acetylide anion. Both of these approaches are demonstrated herein. {Pt}C⋮CSiMe 3 ( 2 ) was reacted with [M][BF 4 ] ([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. [(η 2 -[{Pt}C⋮CSiMe 3 ] 2 )Cu][BF 4 ] exhibits η 2 -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 Co 2 (CO) 8 leads via π-coordination to the formation of a trimetallic dicobaltatetrahedrane. The structure of [(μ 2 -[(η 2 -NCN)Pt(η 1 -CO)C⋮CSiMe 3 ])Co 2 (CO) 6 ] in the solid state shows that one ortho -CH 2 NMe 2 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 CuCl 2 resulted in the formation of {Pt}Cl 3, [CuX] n, and [CuC⋮CSiMe 3 ] n . The reaction with I 2 gave neither a Pt(IV) diiodide nor a Pt(II) η 1 −Ι 2 complex, but instead led to Pt−C(acetylide) bond cleavage and formation of {Pt}I and IC⋮CSiMe 3 . The reaction of {Pt}C⋮CC 6 H 4 CN-4 with [{Pt}H 2 O][BF 4 ] and {Ru}N⋮N{Ru} ({Ru} = [RuCl 2 (C 5 H 3 N{CH 2 NMe 2 } 2 -2,6)]) gives air-stable well-defined bimetallic compounds. In contrast, the reaction of {Pt}C⋮CC 6 H 4 CN-4 with [AuCl 3 ] 2 or Au(CO)Cl leads to the formation of a gold mirror, NCC 6 H 4 (C⋮C) 2 C 6 H 4 CN, and {Pt}Cl 3 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.