Spontaneous Formation of an η⁴-Ethylene Bis(carbene) Ligand by Alkyne Coupling at Rhenium(III)

Abstract

The C/C coupling activity of the cationic Re­(III) species [(C5H5)­ReBr]+ with different heteroatom-substituted alkynes was investigated. By using the sulfide-substituted bis­(benzylsulfanyl)­acetylene an unprecedented rhenacyclopentatriene complex was obtained. An XRD structure determination of [(C5H5)­ReBr­(CSBn)4]+ uncovered the coordination of the remote ethylene moiety at Re leading to an η4-coordination mode of the C4(SBn)4 ligand and a folded five-membered metallacycle. In contrast, reaction of the monoalkyne complex [(C5H5)­ReBr­(CSBn)2]+ with diphenylacetylene as well as diiodoacetylene led to the mixed bis­(alkyne) complexes. The different behavior is attributed to kinetic reasons according to DFT calculations. XRD as well as IR studies with the cationic bis­(alkyne) complexes [(C5H5)­ReBr­(CSBn)2(C2Ph2)]+ and [(C5H5)­ReBr­(CSBn)2(C2I2)]+ revealed clear differences in the bond strengths of the coordinated alkynes at the same metal center. Further investigations on the coupling activity resulted in addition products with H2O and a trimerization of two diphenylacetylene molecules and one bis­(benzylsulfanyl)­acetylene, both as byproducts and involved in a sulfide bond cleavage.

Square Planar Coordination of Silver in a η4‐Cyclobutadiene‐(η5‐C5H5)ReBr2 Complex Framework

“…According to our published protocol purple rhenacyclo‐pentatriene complex 5 ‐BF 4 (Scheme ) was synthesized from the green alkyne complex [(η 5 ‐C 5 H 5 )Re{η 2 ‐C 2 (SBn) 2 }Br 2 ] by addition of AgBF 4 in the presence of bis(benzylsulfanyl)acetylene. Attempts to complement this specific coupling product with the iodido derivative starting with alkyne complex 2b failed.…”

“…Mass spectrometry by electrospray ionization (ESI) was obtained with an Agilent 6210 time‐of‐flight LC/MS. The starting materials [(η 5 ‐C 5 H 5 )Re(CO) 2 Br 2 ], [(η 5 ‐C 5 H 5 )Re(CO) 2 I 2 ] and bis(benzylsulfanyl)acetylene as well as 2a , 4a , and 5 ‐BF 4 were synthesized according to literature protocols.…”

“…Mechanistic conceptions almost always include the formation of intermediate metallacyclopentadienes . In this conjunction, the formation and interconvertion of alternatively connected products by combination of two alkynes and a central metal atom are of interest either as bypasses like η 4 ‐cyclobutadiene and η 3 ‐allenylcarbene, complexes or as potential intermediates like folded metallacyclopentatrienes , …”

“…In addition, the different coupling behavior of regular C‐ and specific S‐substituted alkynes were supported by bromide abstraction at ambient temperature. Addition of a Ag + salt to the side‐on alkyne complex [(η 5 ‐C 5 H 5 )Re{η 2 ‐C 2 (SBn) 2 }Br 2 ] ( 2a ) in the presence of an additional equivalent of alkyne provided the cationic rhenacyclopentatriene complex 5 + , which adopts a remarkable folded five‐membered ring structure to allow a remote donation of the distal double bond . The lack of a corresponding reactivity with C‐based alkynes pointed to a stronger C/C coupling tendency of S‐substituted alkynes.…”

Dual nucleophilic substitution at a W(ii) η2-coordinated diiodo acetylene leading to an amidinium carbyne complex

“…Most recently our group succeeded in isolating a bis(alkyne) rhenium complex with C 2 I 2 . 5 In fact, we seek for suitable starting materials for substitution reactions in the metal complex, because our work is focused on polynuclear complexes bearing heterodonor substituted alkynes as bridging ligands. 6 Based on the successful assembly of polynuclear complexes with bridging C 2 S 2 2À (acdt 2À ) moieties, we recently expanded this chemistry to mixed S,N donor alkyne complexes.…”