Deprotonation ofC‐Alkyl Groups of Cationic Triruthenium Clusters Containing CyclometalatedC‐Alkylpyrazinium Ligands: Experimental and Computational Studies

Abstract

The C-alkyl groups of cationic triruthenium cluster complexes of the type [Ru3(μ-H)(μ-κ(2)N(1),C(2)-L)(CO)10](+) (HL represents a generic C-alkyl-N-methylpyrazium species) have been deprotonated to give kinetic products that contain unprecedented C-alkylidene derivatives and maintain the original edge-bridged decacarbonyl structure. When the starting complexes contain various C-alkyl groups, the selectivity of these deprotonation reactions is related to the atomic charges of the alkyl H atoms, as suggested by DFT/natural-bond orbital (NBO) calculations. Three additional electronic properties of the C-alkyl C-H bonds have also been found to correlate with the experimental regioselectivity because, in all cases, the deprotonated C-H bond has the smallest electron density at the bond critical point, the greatest Laplacian of the electron density at the bond critical point, and the greatest total energy density ratio at the bond critical point (computed by using the quantum theory of atoms in molecules, QTAIM). The kinetic decacarbonyl products evolve, under appropriate reaction conditions that depend upon the position of the C-alkylidene group in the heterocyclic ring, toward face-capped nonacarbonyl derivatives (thermodynamic products). The position of the C-alkylidene group in the heterocyclic ring determines the distribution of single and double bonds within the ligand ring, which strongly affects the stability of the neutral decacarbonyl complexes and the way these ligands coordinate to the metal atoms in the nonacarbonyl products. The mechanisms of these decacarbonylation processes have been investigated by DFT methods, which have rationalized the structures observed for the final products and have shed light on the different kinetic and thermodynamic stabilities of the reaction intermediates, thus explaining the reaction conditions experimentally required by each transformation.

Alternative Transformations of N-Heterocyclic Carbene Complexes of the Group 11 Metals in Transmetalation Reactions (A Review)

“…It should be noticed that the formation of the complexes with two identical Group 11 metal atoms bridged by a carbene ligand is well known [231][232][233][234][235][236][237][238][239][240][241][242][243][244]. At the same time, the examples of similar heterometallic systems have not been found, which can indirectly evidence their low stability.…”

Ein redoxaktives, heterobimetallisches N‐heterocyclisches Carben auf Basis eines Bis(imino)pyrazin‐Liganden

“…Nach bestem Wissen ist die Nutzung eines Pyrazinringes als Grundgerüst zur Erzeugung eines NHCs und die Synthese entsprechender Metallkomplexe nicht bekannt. [20] Die molekularen Strukturen von 7 und 8 konnten durch Einkristallrçntgenstrukturanalyse aufgeklärt werden (Abbildung 1). [21] Die Struktur von 7 zeigt, dass der Pyrazinring seine Aromatizitätb ehält [22] und eine planare Struktur aufweist.Der N-Ca-C Winkel ist dennoch verkleinert (]114.29-(14)8 8 in 7,v erglichen mit 119.03(18) in 1•[I] [8] ).…”

Pyridine-, Pyridazine-, Pyrimidine-, and Pyrazine-Derived Carbenes as Ligands for Transition-Metal Complexes: Perspectives from DFT Calculations

“…Chromium and tungsten complexes of pyrimidin-4-ylidenes were obtained from Fischer carbene complexes and N-phenylbenzamide (Figure c) . Cabeza et al reported the synthesis and reactivity of a series of pyrimidin-2-ylidene (Figure d), pyrimidin-4-ylidene, , and pyrazin-2-ylidene , carbene–ruthenium complexes obtained by the reaction of the corresponding heterocycles with triruthenium dodecacarbonyl [Ru 3 (CO) 12 ] followed by alkylation of the non-coordinated nitrogen atom. Rosca reported the generation of pyrazin-2-ylidene by deprotonation of pyrazinium salt at low temperature followed by the formation of a rhodium complex in which pyrazin-2-ylidene acts as a ditopic ligand (Figure e) .…”