Reactivity of Fe and Ru Complexes of Picolyl-Substituted N-Heterocyclic Carbene Ligand: Diverse Coordination Modes and Small Molecule Binding

Abstract

Complexes [MClCp*(HL)] (1[Fe]/1[Ru]) (where HL = 1-mesityl-3-(pyridin-2-ylmethyl)imidazol-2-ylidene) were synthesized from the reaction of in situ generated HL ligand and [FeClCp*(TMEDA)] (where TMEDA is N,N,N',N'-tetramethylethylenediamine) or [RuClCp*], respectively. The deprotonation of 1[Fe]/1[Ru] with 1 equiv of LiHMDS led to cyclometalation through the o-Me of the mesityl group, forming [MCp*(L-κC,κC',κN)] 2[Fe]/2[Ru]. The coordinatively unsaturated compounds [MCp*(HL)]BPh 3[Fe]/3[Ru] were prepared from 1[Fe]/1[Ru] and halide scavenger NaBPh. Complex 3[Ru] showed agostic interactions between the o-Me group of the mesityl moiety and the metal center in solution and the solid state. When the vacant coordination site of 3[Fe]/3[Ru] is occupied by CO, the resulting [MCp*(CO)(HL)]BPh 4[Fe]/4[Ru] can be deprotonated with 1 equiv of KHMDS at the pyridylic position to afford complexes [MCp*L'(CO)] 5[Fe]/5[Ru], where the L' ligand chelates to the metal center through the nitrogen donor atom of the dearomatized pyridine ring and the carbene carbon. Complex 2[Fe] reacted rapidly with CO to afford the simple ligand substitution product [FeCp*(L-κC,κC')(CO)] 6[Fe], where the L acts as a bidentate chelating ligand through the carbene carbon and benzylic carbon. Under the same condition, the reaction of 2[Ru] with CO forms [RuCp*L″(CO)] 7[Ru], where the L″ ligand (an isomer of L and L') chelates to the metal center through the carbene carbon and a pyridyl carbon. Complexes 3[Fe]/3[Ru] reversibly bind dinitrogen to form [MCp*(HL)(N)]BPh 8[Fe]/8[Ru]. 3[Ru] reversibly binds dihydrogen to give [MCp*(H)(HL)]BPh 9[Ru], while no reaction was observed between 3[Fe] and H. The reaction of 3[Ru] with dioxygen led to the isolation of a stable side-on O complex [RuCp*(HL)(O)]BPh 10[Ru], while the reaction of 3[Fe] with dioxygen led to an intractable mixture of products.

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

“…The 13 C{ 1 H} NMR chemical shifts of the CE ligands in 2-CE are in good agreement with those of known CE complexes ( Table 6). [1,2,21,22] The signals clearly shiftedd ownfield upon de-scendingG roup 16 from oxygen to tellurium due to the paramagnetic contribution, [20a, 23] which also reflects the increasing p-accepting character of the CE ligands in the order CO < CS < CSe < CTe. [20a] This trend for the increasingly p-acidic nature of the CE ligands is consistent with the results obtained from the [11] The chemical shifts of the CN (isocyanide)a nd Cp ligands were also within the expectedr ange.…”

Piano-Stool Iron Complexes as Precatalysts for gem-Specific Dimerization of Terminal Alkynes

“…N-heterocyclic carbenes (NHCs) are widely used ligands in coordination chemistry and homogeneous catalysis due to their strong σ-donating and weak π-accepting nature along with their easily accessible and tunable structures. − Our group has been interested in the chemistry of iron–NHC complexes toward organic transformations, especially when ligand-based reactivity is involved. ,,− We have developed a piano-stool iron catalyst featuring Cp* and picolyl–NHC ligands toward the geminal specific dimerization of terminal alkynes ( I in Chart ). Both aryl and aliphatic alkynes are compatible, and a broad range of functional groups can be tolerated, including NH and OH groups.…”

Synthesis, Characterization, and Structural Transformation of Picolyl-Functionalized Polynuclear Silver(I)– and Gold(I)–N-Heterocyclic Carbene Complexes

“…Multidentate NHC ligands featuring other donating atoms (N, P, O, and S) could combine the advantages of different donors and further offer opportunities for the construction of novel metallosupramolecular assemblies. − Especially, the design and synthesis of N-donor-functionalized NHCs with diverse electronic and steric properties have received continuous attention in recent years. − Motivated by the multidirectional coordination sites of N-donor-functionalized NHC ligands, we speculate that the application of such ligands may significantly improve the construction of metallosupramolecular architectures with diversified 3D structures and a variety of applications.…”