LiC⋮CFc (2; Fc = (η5-C5H4)(η5-C5H5)Fe) reacts with [Ti]Cl2 (1a) ([Ti] = (η5-C5H4SiMe3)2Ti) in a 2:1 molar ratio to produce the C2-bridged titanocene−ferrocenyl complex [Ti](C⋮CFc)2 (3). While treatment of heterotrinuclear 3 with Ni(CO)4 (4) affords the heterotetranuclear tweezer complex {[Ti](C⋮CFc)2}Ni(CO) (5), reaction of 3 with NiCl2 (6) yields FcC⋮CC⋮CFc (7) along with [Ti]Cl2 (1a) and Ni0 in a redox reaction. 7 can also be synthesized in the chemical oxidation of 3 with 2 equiv of AgPF6. The electrochemical behavior of compounds 3 and 5 is discussed. The X-ray structure analysis of complex 3 is reported.

A series of related platinum σ-acetylide complexes {Pt}CtCR ({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 2coordination of the acetylide or by incorporating a second ligating site in the acetylide anion. Both of these approaches are demonstrated herein. {Pt}CtCSiMe 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}CtCSiMe 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-CtC 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)CtCSiMe 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 [CuCtCSiMe 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 ICtCSiMe 3 . The reaction of {Pt}CtCC 6 H 4 CN-4 with [{Pt}H 2 O][BF 4 ] and {Ru}NtN{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}CtCC 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 (CtC) 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.

The gold(I) acetylide (Ph3P)AuC⋮CC6H3(CH2NMe2)2-3,5 (3) is accessible by the reaction of (Ph3P)AuCl (1) with HC⋮CC6H3(CH2NMe2)2-3,5 (2) in a 1:1 molar ratio. Base-catalyzed desilylation of (Ph3P)AuC⋮CSiMe3 (4) produces the homobimetallic gold(I) species (Ph3P)AuC⋮CAu(PPh3) (5). However, the intermediate formation of (Ph3P)AuC⋮CH could not be evidenced, but is most likely. The coordination chemistry of 5 and (Ph3P)AuC⋮CFc (6) toward different copper(I) halides [CuX] n (7a, X = Cl; 7b, X = Br) is presented. While heterodinuclear 6 affords with equimolar amounts of 7a hexanuclear {[η2-(Ph3P)AuC⋮CFc]Cu(μ-Cl)}2 (8), homobinuclear 5 produces with 7b in a 1:1 molar ratio via ligand exchange polymeric [CuC⋮C] n (10) and mononuclear (Ph3P)AuBr (11). A feasible reaction mechanism for the formation of the latter species is presented. The solid-state structure of 8 is reported. It exhibits a linear array around the gold(I) center and a coplanar arrangement of the Cu2Cl2 and the gold(I) acetylide entities.