Synthesis and structure of bimetallic complexes with σ,π-bridging thienyl and benzothienyl ligands

Abstract

The ligand properties of the organometallic fragment (η 5 -SC 4 H 3 )Cr(CO) 3 were studied in the new σ,π-bimetallic complexes [Cr{(η 5 -SC 4 H 3 )PtL 2 (SC 4 H 3 )}(CO) 3 ] with L = CO and PMe 3 1 or L 2 = dppe [1,2-bis(diphenylphosphino)ethane] 2, [Cr{(η 5 -SC 4 H 3 )Au(PPh 3 )}(CO) 3 ] 3 and [Cr(η 5 -SC 4 H 3 SnMe 3 )(CO) 3 ] 4. Whereas the intermediates [Cr{(η 5 -SC 4 H 3 )PtL 2 Cl}(CO) 3 ] (L = PMe 3 or dppe) and [Pt{(SC 4 H 3 )Cr(CO) 3 } 2 L 2 ] were too unstable to isolate and characterize, 4 slowly converted into [Cr{η 5 -SC 4 H 2 (SnMe 3 ) 2 }(CO) 3 ] 5. By contrast, the reaction of lithiated [Cr(η 6 -SC 8 H 6 )(CO) 3 ] with [Pt(dppe)Cl 2 ] afforded the stable trinuclear complex, [Pt{(η 6 -SC 8 H 5 )Cr(CO) 3 } 2 (dppe)] 6.Studies of the activation of organic substrates by more than one transition metal in dinuclear organometallic complexes are increasingly being reported. 2 The interest in such complexes stems not only from their intriguing structural diversities 2,3 but also from their potential catalytic activity, 4 their possible importance in materials with conducting properties 5 and their role in bioinorganic chemistry. 6 Furthermore, metal-ligand activation in dinuclear complexes has not yet been studied systematically and an improved understanding of the scope and extent of such activations is very relevant. Two metals in close proximity sharing a common unsaturated ligand can cooperatively activate and assist in novel reactions, unique transformations and can cause severe structural deformations. 7 Examples are carbon-carbon bond-cleavage and coupling reactions, 8 sterically and/or electronically controlled sites of activity, 9 stabilization of reactive intermediates via co-ordination 1,10 and migratory movements of ligands or metal fragments. 11In our laboratories studies relating to heterobimetallic complexes with σ,π-bridged phenyl and thienyl ligands are of particular interest. 12 Recently we discovered an interesting activation mechanism surrounding a shared thienyl ligand which was π bonded to Cr(CO) 3 and σ bonded to Mn(CO) 5 in the 2 position. The two metal fragments irreversibly, and according to an intramolecular mechanism, exchanged σ,π co-ordination sites. 13 This novel conversion was a direct result of the metals being in electronic contact through the bridging thienyl ligand. These results prompted us further to investigate the extent of activation by σ-bonded early and late transition-metal substituents and their influence on thienyl ligands which are π bonded to Cr(CO) 3 . In this paper we describe the synthesis and characterization of dinuclear complexes with σ-bonded platinum() and gold() fragments in the 2 position of a bridging π-coordinated thienyl ligand.The platinum group metals show very high hydrodesulfurization (HDS) activity 14 and Maitlis and co-workers 15 recorded an oxidative insertion of Pt 0 into the C᎐S bond of thiophenes. Unfortunately for HDS purposes the reverse reaction, regenerating thiophene, is favoured. Efforts to prepare platinum() complexes of 2-(2...

Ferrocenyl‐Functionalized η5‐Thiophene Cr(CO)3 Half‐Sandwich Compounds

“…The Cr(CO) 3 fragment exhibits a piano‐stool coordination environment, clarified by almost ideal carbonyl C–Cr–C angles of 86.9(4)–91.1(10) °. One carbonyl is directed antiperiplanar towards the sulfur atom by 172.8(10)–174.1(10) °, which is in accordance to literature reported solid‐state structures of Cr(CO) 3 complexed thiophenes . The cyclopentadienyls of one of each ferrocenyl substituent in 3a , b adopts an ecliptic conformation [1.6(10) to 8.9(7) °], whereas the other one reveals a rather staggered positioning [18.6(6)–31.6(12) °].…”

“…The synthesis of the η 5 ‐thiophene Cr(CO) 3 compounds 3a – g was performed by reacting the appropriate Fc‐substituted thiophenes 1a – g with [Cr(CO) 3 (CH 3 CN) 3 ] ( 2 ) (Scheme ). [10a] This approach is contrary to literature reported procedures, where a post‐functionalization of the η 5 ‐thiophene Cr(CO) 3 compounds is realized , ,. [10b], [10c], , Thiophenes 1a – g are accessible by cross‐coupling protocols that were recently reported by our group.…”

“…Within this family of compounds, η 5 ‐thiophene chromium tricarbonyl was first prepared by Fischer and Öfele as early as 1958 in a solvothermal metathesis reaction of thiophene and Cr(CO) 6 . Up to date, only a few Cr(CO) 3 complexes with η 5 ‐bonded thiophenes bearing additional organometallic fragments have been reported, including titanocene structures, Pt complexes, silyl groups, –M(CO) 5 (M = Mn/Cr,W). Although, basic knowledge of their reaction behavior and NMR properties were investigated, electrochemical studies are still pending.…”

Thiophenes in Organotransition Metal Chemistry: Patterns of Reactivity

“…On the other hand, neutral η 5 -thiophene complexes typically resist attack but undergo deprotonation (eq 26) with strong nucleophiles/bases. This latter reactivity is found in (η 5 -T)Cr(CO) 3 , which reacts with n -BuLi to give the lithiated product (OC) 3 Cr(η 5 -C 4 H 3 SLi), which has been used to form a series of thienyl-bridged complexes , in which the thienyl ligand is η 5 -coordinated to the Cr(CO) 3 unit and η 1 -bonded to another metal. One such complex, 39 , undergoes the remarkable interchange of metals and CO ligands shown in eq 27 …”

Steric and Electronic Effects of Metal-Containing Substituents in Fischer Carbene Complexes of Chromium

“…The deprotonation of the benzo[ b ]thienyl ring π-coordinated to Cr(CO) 3 is readily achieved at −40 °C with n -BuLi and [Cr(CO) 5 {C(OEt)((η 6 -2-BT)Cr(CO) 3 )}] ( 3 ) was obtained in a high yield after alkylation with the oxonium salt. Although the Cr(CO) 3 fragment is bonded to the benzene ring in [Cr(η 6 -2-BT)(CO) 3 ], deprotonation occurs at the 2-position of the thiophene ring . It was decided to employ benzo[ b ]thiophene (BTH) as carbene substituent after preliminary experiments with lithiated [Cr(η 5 -2-thiophene)(CO) 3 ], and subsequent metalation with titanocene dichloride did not generate the desired trimetallic carbene complexes.…”