Intramolecular Nitrene Transfer via the C≡N Bond Cleavage of Acetonitrile to a μ₃-Alkylidyne Ligand on a Cationic Triruthenium Plane

Abstract

The μ3-η2-iminoacyl-μ3-hexylidyne complex, [(Cp*Ru)3(μ3-CC5H11)­(μ3-η2-HNCMe)­(μ-H)] (2a) (Cp* = η5-C5Me5), was prepared by the reaction of the μ3-η2:η2(⊥)-hexyne complex, [{Cp*Ru­(μ-H)}3(μ3-η2:η2- n BuCCH)] (1a), with acetonitrile. Protonation of 2a yielded an equilibrated mixture of cationic μ3-η2-iminoacyl complexes, [(Cp*Ru)3(μ3-CC5H11)­(μ3-η2-HNCMe)­(μ-H)2]+ (3a and 3b), which are positional isomers with respect to the bridging hydrides. While the μ3-η2-iminoacyl ligand in 2a was rigid at the NMR time-scale, in 3b it exhibited mobility, owing to the reduced back-donation from the cationic Ru3 core. In contrast to robust 2a, 3b underwent skeletal rearrangement upon thermolysis because of the mobility of the μ3-η2-iminoacyl ligand. The equilibrated mixture of 3a and 3b was transformed into an equilibrated mixture of μ3-ethylidyne-μ3-η2-1-iminohexyl complexes, [(Cp*Ru)3(μ3-CCH3)­(μ3-η2-HNCC5H11)­(μ-H)2]+ (4a and 4b) at 140 °C, via the intramolecular nitrene transfer from the iminoacyl ligand to the μ3-hexylidyne carbon. Density functional theory (DFT) calculations suggest that the μ3-ethylidyne ligand in 4a, b leads to decreased steric repulsion with the surrounding Cp* groups, as compared with the μ3-hexylidyne ligand in 3a, b. The stabilization arising from the formation of the μ3-ethylidyne ligand is a possible driving force for the transformation.

C≡N and N≡O Bond Cleavages of Acetonitrile and Nitrosyl Ligands at a Dimolybdenum Center to Render Ethylidyne and Acetamidinate Ligands

“…While all of these processes are themselves unusual, we note that previous examples of cleavage of the C�N bond of nitriles by reactive metal complexes mostly led to nitride and/or carbyne derivatives. 9 However, examples of the generation of a vinylidene group from MeCN are restricted, to our knowledge, to the recently reported reaction of laser-ablated B atoms with MeCN on a solid neon matrix under full arc irradiation. 10 Compound 1 was prepared following the method previously developed for the ditungsten analogue [W 2 Cp 2 (μ-I)(μ-PPh 2 )-(NO) 2 ].…”

B(C6F5)3-Catalyzed Reductive Denitrogenation of Benzonitrile Derivatives

“…In turn, methods for converting a cyano into a methyl group by “direct” removal of the nitrogen atom are rather rare. To date, known methods that can completely break CN bonds are mostly dependent on the stoichiometric use of well-defined molybdenum-, tungsten-, and ruthenium-based complexes as well as catalytic heterogeneous hydrogenolysis under forced reaction conditions (Scheme , top). Given the current limitations, the development of milder protocols to defunctionalize nitriles is an important task.…”