Synthesis and Systematic Structural Analysis of Cationic Half‐Sandwich Ruthenium Chalcogenocarbonyl Complexes

Abstract

Although the chemistry of transition‐metal complexes with carbonyl (CO) and thiocarbonyl (CS) ligands has been well developed, their heavier analogues, namely selenocarbonyl (CSe) and tellurocarbonyl (CTe) complexes remain scarce. The limited availability of such CSe and CTe complexes has so far hampered our understanding of the differences between such chalcogenocarbonyl (CE: E=O, S, Se, Te) ligands. Herein, we report the synthesis and properties of a series of cationic half‐sandwich ruthenium CE complexes of the type [CpRu(CE)(H2IMes)(CNCH2Ts)][BArF4] (Cp=η5‐C5H5−; H2IMes=1,3‐dimesitylimidazolin‐2‐ylidene; ArF=3,5‐(CF3)2C6H3). A combination of X‐ray diffraction analyses, NMR spectroscopic analyses, and DFT calculations revealed an increasing π‐accepting ability of the CE ligands in the order O<S<Se<Te. A variable‐temperature NMR analysis of the thus obtained chiral‐at‐metal CE complexes indicated high stereochemical stability.

Advances in Transition Metal Seleno‐ and Tellurocarbonyl Chemistry

“…Accordingly, for transition metal chalcocarbonyl complexes, L n MCE, the MC bond becomes stronger and the CE bond weaker upon descending group 16 . In valence bond terms (Figure ) one may consider canonical forms ( ii ) and ( iii ) as providing only a minor contribution to the resonance description of CO complexes, but an increasingly substantial contribution to the overall bonding of CS, CSe and CTe complexes . This also results in an increasingly strong trans influence in the order CO<CS<CSe<CTe.…”

“…Similar conclusions emerged more recently from highly detailed systematic studies which examined three sets of ruthenium chalcocarbonyls; [RuCl 2 (CE)(H 2 IMes)(DMAP) 2 ] ( 2‐E ), [RuCl(CE)(H 2 IMes)(η 5 ‐C 5 H 5 )] ( 3‐E ) and [Ru(CE)(CNCH 2 Ts)(H 2 IMes)(η 5 ‐C 5 H 5 )][BAr F 4 ]( 4‐E ) (H 2 IMes=1,3‐dimesitylimidazolin‐2‐ylidene; DMAP=4‐(dimethylamino)pyridine; Ts= p ‐toluenesulfonyl; Ar F =C 6 H 3 (CF 3 ) 2 –3,5, Figure ). The experimental results from these studies confirmed that, upon descending group 16, trans ligand dissociation rates increased and the M–CE distances shorten as π‐acidity of the CE ligands increases.…”

“…These studies were also supported by computational analysis, which determined that the metal‐carbon bond order (quantified using Wiberg bond indices) increases down the group . This is congruent with the approximate contribution of each resonance form, evaluated using natural resonance theory, which indicated that, while canonical form ( i ) is the major contributor in all cases, it has progressively reduced influence for the heavier chalcocarbonyls as canonical forms ( ii ) and ( iii ) become progressively more important …”

“…A further example from Mutoh and Ishii involves the reactions of [RuCl 2 (C)(H 2 IMes)(PCy 3 )] ( 19 , H 2 IMes=1,3‐dimesitylimidazolin‐2‐ylidene) with Se or Te to give [RuCl 2 (CE)(H 2 IMes)(PCy 3 )] (E=Se 2‐Se ; E=Te 2‐Te ; Scheme ) . Such reactions are reliable and typically high‐yielding however terminal carbido ligands are exceedingly rare and this strategy has only led to a small number of reported examples …”

Thiolate-Thione Redox-Active Ligand with a Six-Membered Chelate Ring via Template Condensation and Its Pt(II) Complexes

“…Two mechanisms to make the π* orbitals the LUMOs have been demonstrated in extant examples: (i) substituents with extended π systems that can accommodate additional electrons ,,,,, or (ii) additional ligands that force a change in coordination number and drive metal orbital energies below those of ligand LUMOs and facilitate ligand reduction. , Herein, we report a third and potentially more general approach. When the donor atoms are S, and not O or N, the π* orbitals are lower in energy and sufficiently so as to accept electrons, as we have now observed in the {Pt­(cta) 2 } system.…”