Trigonal-Planar-Coordinated Organogold(I) Complexes Stabilized by Organometallic 1,4-Diynes: Reaction Behavior, Structure, and Bonding

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Abstract

The reaction of the bis(alkynyl) titanocenes [Ti](C⋮CR1)(C⋮CR2) ([Ti] = (η5-C5H4SiMe3)2Ti; 1a R1 = R2 = SiMe3; 1b R1 = R2 = tBu; 1c R1 = SiMe3, R2 = tBu) with (C5H5N)AuCl3 (2), LAuCl (5a, L = PPh3; 5b, L = SMe2) as well as (Me2S)AuR3 (6b, R3 = C⋮CSiMe3; 6c, R3 = C⋮CtBu; 6d, R3 = C6H2(CF3)3-2,4,6; 6e, R3 = Me) is described. Treatment of [Ti](C⋮CSiMe3)2 (1a) with (C5H5N)AuCl3 (2) produces [Ti]Cl2 (3) and Me3SiC⋮C−C⋮CSiMe3 (4a) together with Au(0). However, the linear two-coordinated gold(I) chlorides LAuCl (5a,b) react with 1a to afford different products, depending on the Lewis bases applied. While in the reaction of the Ph3P donor-stabilized gold(I) chloride 5a, the titanocene dichloride (3) along with (Ph3P)AuC⋮CSiMe3 (6a) is obtained, with the appropriate Me2S donor-stabilized molecule 5b, the titanocene dichloride (3) along with the heterobimetallic tweezer molecule {[Ti](C⋮CSiMe3)2}AuC⋮CSiMe3 (7a) is formed. A possible mechanism for the different chemical behavior is discussed. Likewise, molecules of the latter type (compounds 7a−e) can be synthesized in much better yields by the reaction of [Ti](C⋮CR1)(C⋮CR2) (1a−c) with (Me2S)AuR3 (6b−e). In the heterobimetallic titanium−gold complexes {[Ti](C⋮CR1)(C⋮CR2)}AuR3 (7a, R1 = R2 = SiMe3, R3 = C⋮CSiMe3; 7b, R1 = R2 = tBu, R3 = C⋮CtBu; 7c, R1 = SiMe3, R2 = tBu, R3 = C⋮CSiMe3; 7d, R1 = R2 = SiMe3, R3 = C6H2(CF3)3-2,4,6; 7e, R1 = R2 = SiMe3, R3 = Me), a low-valent monomeric organogold(I) moiety in a trigonal-planar environment is present, which is stabilized by the chelating effect of the organometallic π-tweezer bis(alkynyl) titanocene. The thermolysis of selected organogold(I) complexes affords, on elimination of the bis(alkynyl) titanocene fragment, the coupling products R3−R3 (4) and gold films. The X-ray structure analyses of compounds 7a, 7b, and 7d are reported. It is found that in all compounds short titanium−gold bond lengths are present (7a, 3.007(2) Å; 7b, 2.975(1) Å; 7d, 2.995(1) Å). Calculations show that the complexation of the Au−R3 monomers with the organometallic π-tweezer bis(alkynyl) titanocene is described by a four-center two-electron bond. The monomeric organogold(I) moieties are stabilized by a synergetic in-plane donation and back-donation of electron density between the bis(alkynyl) titanocene and the Au−R3 species. A direct donor−acceptor Au−Ti interaction contributes to this stabilization.

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