Reversible Modulation of the Electronic and Spatial Environment around Ni(0) Centers Bearing Multifunctional Carbene Ligands with Triarylaluminum

Designing and modulating the electronic and spatial environments surrounding metal centers is a crucial issue in a wide range of chemistry fields that use organometallic compounds. Herein, we demonstrate a Lewis-acid-mediated reversible expansion, contraction, and transformation of the spatial environment surrounding nickel(0) centers that bear N-phosphine oxide-substituted N-heterocyclic carbenes (henceforth referred to as (S)PoxIms). Reaction between tetrahedral (syn-κ-C,O-(S)PoxIm)Ni(CO)₂ and Al(C₆F₅)₃ smoothly afforded heterobimetallic Ni/Al species such as trigonal-planar {κ-C-Ni(CO)₂}(μ-anti-(S)PoxIm){κ-O-Al(C₆F₅)₃} via a complexation-induced rotation of the N-phosphine oxide moieties, while the addition of 4-dimethylaminopyridine resulted in the quantitative regeneration of the former Ni complexes. The corresponding interconversion also occurred between (SPoxIm)Ni(η²:η²-diphenyldivinylsilane) and {κ-C-Ni(η²:η²-diene)}(μ-anti-SPoxIm){κ-O-Al(C₆F₅)₃} via the coordination and dissociation of Al(C₆F₅)₃. The shape and size of the space around the Ni(0) center was drastically changed through this Lewis-acid-mediated interconversion. Moreover, the multinuclear NMR, IR, and XAS analyses of the aforementioned carbonyl complexes clarified the details of the changes in the electronic states on the Ni centers; i.e., the electron delocalization was effectively enhanced among the Ni atom and CO ligands in the heterobimetallic Ni/Al species. The results presented in this work thus provide a strategy for reversibly modulating both the electronic and spatial environment of organometallic complexes, in addition to the well-accepted Lewis-base-mediated ligand-substitution methods.

Late-stage ligand functionalization via the Staudinger reaction using phosphine-appended 2,2'-bipyridine

The ability of a phosphine-appended-2,2'-bipyridine ligand ((Ph2P)2bpy) to serve as a platform for late-stage ligand modifications was evaluated using tetrahedral (Ph2P)2bpyFeCl2. We employed a post-metalation Staudinger reaction to install a series of functionalized arenes, including those containing Brønsted and Lewis acidic groups. This reaction sequence represents a versatile strategy to both tune the ligand donor properties as well as directly incorporate appended functionality.

Exploitation of the Second Coordination Sphere to Promote Significant Increase of Room-Temperature Luminescence Lifetime and Anion Sensing in Ruthenium-Terpyridine Complexes

This paper deals with the synthesis, characterization, and photophysical behaviors of three Ru(II)-terpyridine complexes derived from a terpyridyl-imidazole ligand (tpy-HImzPh₃Me₂), wherein a terpyridine moiety has been coupled with a dimethylbenzil unit through a phenylimidazole spacer. The three complexes display strong emission at RT having excited-state lifetimes in the range of 2.3-43.7 ns, depending upon the co-ligand present and the solvents used. Temperature-dependent emission spectral measurements have demonstrated that the energy separation between emitting metal-to-ligand charge transfer state and non-emitting metal-centered state is increased relative to that of [Ru(tpy)₂]²⁺. In contrast to our previously studied Ru(II) complexes containing similar terpyridyl-imidazole motif but differing by peripheral methyl groups, significant enhancement of RT emission intensity and quantum yield and remarkable increase of emission lifetime occur for the present complexes upon protonation of the imidazole nitrogen(s) with perchloric acid. Additionally, by exploiting imidazole NH motif(s), we have examined their anion recognition behaviors in organic and aqueous media. Interestingly, the complexes are capable of visually recognizing cyanide ions in aqueous medium up to the concentration limit of 10^-8 M. Computational studies involving density functional theory (DFT) and time-dependent DFT methods have been carried out to obtain insights into their electronic structures and to help with the assignment of absorption and emission bands.