An investigation of C–S bond activation in transition metal crown thioether complexes using extended Hückel theory and electrospray mass spectrometry

Abstract

Complexes of Re and Tc with 1,4,7-trithiacyclononane (9S3) differ from their later transition metal analogues in that their d 6 form ([M(9S3) 2 ] ϩ ) undergoes instantaneous C-S bond cleavage yielding ethene and [M(9S3)L] ϩ (L = SCH 2 CH 2 SCH 2 CH 2 S), a stable metal() thiolate complex, cleanly in aqueous solution. This contrast is interpreted as signifying increased π-back donation by Re and Tc, compared to later metals, into ligand C-S σ* orbitals. In order to validate this hypothesis within an established theoretical framework, and to compare the predicted relative C-S bond lability with relative experimental lability in a series of d 6 analogues, extended Hückel theory (EHT) was used to investigate the bonding (M = Mo, Tc, Ru, Rh or Pd) while electrospray mass spectrometry (ES-MS) was used to compare ethene loss, in a series of analogous complexes (M = Tc, Re, Ru or Os). The C-S overlap populations were smaller for M = Tc II and Tc I than for later metal() analogues, and were smaller for Tc I than for Tc II . Fragment molecular orbitals corresponding to C-S σ* were more highly populated for M = Tc II and Tc I than for later analogues, and also more highly populated for Tc I than for Tc II . ES-MS showed that ethene loss from Tc/Re I and Tc/Re II complexes occurred at much lower energies than from the Ru/Os II analogues. EHT supports the hypothesis that C-S activation is caused by π-back donation into C-S σ* orbitals, and correctly predicts that ethene loss occurs more readily from rhenium and technetium d 5 and especially d 6 complexes than from later transition metal analogues.

Hybrid Car-Parrinello/Molecular Mechanics Modelling of Transition Metal Complexes: Structure, Dynamics and Reactivity

“…This observation has been explained in terms of the fact that Tc and Re exhibit a stronger p-back donation from metal d-orbitals into empty C À S s* ligand orbitals. Several experimental studies including solution experiments, crystallographic data and electro spray mass spectrometry show the same trend [29].…”

Recent developments in thio‐, seleno‐, and telluro‐ether ligand chemistry

“…The cyclic seleno-ethers [8] (Fig. 8) shows a 2-D sheet structure with SbBr 3 units coordinated weakly to two Se atoms from different selenoethers, giving distorted square pyramidal Sb(III).…”

“…The group 16 chalcogenoether ligands ER 2 (E = S, Se, or Te) are usually regarded as modest -donors to transition-metal centers, with little evidence for significant -effects, except in a small number of specific complexes [8]. However, as group 16 is descended the electronegativity of the chalcogen reduces, and this is manifested in increased E → M -donation.…”

C–S bond cleavage in pyridylmethylthioether systems promoted by oxorhenium(V) ion

“…But in hydrated alcoholic medium no C-S bond cleavage induced by ReO(V) ion occurred in any of the BPT systems rather the conversion of ReO(V) into perrhenate salt was observed; this reaction mixture, in turn on reaction with copper(II) nitrate trihydrate salt, produce [Cu(BPT)Cl]ReO 4 (2) type complexes. The solidstate structures of complexes 1a and 2a were established by X-ray crystallography.Ó 2009 Elsevier B.V. All rights reserved.The transition-metal-mediated cleavage of a C-S bond has been paid considerable attention due to its importance in synthetic chemistry, [1-3] petrochemical hydrodesulfurization, [4][5][6][7][8][9][10][11] biorganic and bioinorganic chemistry [12][13][14][15]. Several examples of C-S bond cleavage within organic molecules by different metal ions [16][17][18][19][20][21] were reported, considering the fundamental urgency of this aspect.…”

“…The transition-metal-mediated cleavage of a C-S bond has been paid considerable attention due to its importance in synthetic chemistry, [1][2][3] petrochemical hydrodesulfurization, [4][5][6][7][8][9][10][11] biorganic and bioinorganic chemistry [12][13][14][15]. Several examples of C-S bond cleavage within organic molecules by different metal ions [16][17][18][19][20][21] were reported, considering the fundamental urgency of this aspect.…”