Electronic influences of bridging and chelating diimine ligand coordination in formamidinate-bridged Rh2(II,II) dimers

Abstract

Two new formamidinate-bridged Rh 2 II,II complexes, cis-[Rh 2 II,II (µ-DTolF) 2 (µ-np) 2 ] 2+ (3; DTolF = N,N′-dip -tolylformamidinate; np = 1,8-naphthyridine) and cis-[Rh 2 II,II (µ-DTolF) 2 (κ 2-dap) 2 ] 2+ (4; dap = 1,12-diazaperylene), were synthesized from [Rh 2 II,II (µ-DTolF) 2 (CH 3 CN) 6 ](BF 4) 2 (1), and their properties were compared to those of [Rh 2 II,II (µ-DTolF) 2 (phen) 2 ](BF 4) 2 (2). Density functional theory (DFT) and electrochemical analyses support the description of the highest occupied molecular orbitals (HOMOs) of 3 and 4 as possessing contributions from the metals and formamidinate bridging ligands, with Rh 2 /form character, and lowest unoccupied molecular orbitals (LUMOs) localized on the respective diimine ligand np and dap π* orbitals. Both 3 and 4 display strong, low energy Rh 2 /formdiimine(π*) metal/ligand-to-ligand charger transfer (1 ML-LCT) transitions with maxima at 566 nm (ε = 3,600 M −1 cm −1) for 3 and at 630 nm (ε = 2,900 M −1 cm −1) for 4 in CH 3 CN. Time dependent-DFT (TD-DFT) calculations support these assignments. The ability of both the bridging np and chelating dap diimine ligands to produce strong absorption of these Rh 2 II,II complexes throughout the visible region is potentially useful for the development of new photocatalysts for H 2 production and photochemotherapeutics.

Dirhodium Complexes as Panchromatic Sensitizers, Electrocatalysts, and Photocatalysts

“…[11k, 12] In the heteroleptic partial-paddlewheel complexes of the type cis-[Rh 2 (DTolF) 2 (L) 2 ] 2 + ,w here Li saneutral diimine ligand that is easily reduced, the L(p*) orbital is the lowest unoccupied molecular orbital (LUMO), resultingi nastrong low-energy metal/ ligand-to-ligand charget ransfer (ML-LCT) transition from the Rh 2 (d*)/DTolF(p*) HOMO to the L(p*) LUMO. [7,12,14] In cis-Rh 2 (DTolF) 2 (npCOO) 2 ,t he two axial positions of the dirhodium core are blocked by carboxylate coordination,a sd epicted in Figure7,astructuralf eature that leads to a5 0-foldl onger lifetime of the 3 ML-LCT excited, 25 ns, as compared to that of cis-[Rh 2 (DTolF) 2 (np) 2 ] 2 + (9,n p = 1,8-naphthiridine;F igure 7). [7b] The antisymmetric linear combination of ligand orbitals coordinating to the axil positions is of the correct symmetry to interact with the unoccupied Rh 2 (s*) orbital, thusr aising its energy.…”

“…[11] The modificationsi n the coordination sphere surrounding the bimetallic core result in electronic and structuralc hanges that provide control of the excited state and redox properties, along with steric hindrance at the axial and equatorial positions that can be used to tune the selectivity of the reactivity. [12] Although dirhodium complexes have long been shownt os erve as effective catalysts for organic transformations, including carbene and nitrene generation reactions, functionalization, and the synthesis of heterocycles, [13] this Minireview focuses on bimetallic complexes that serve as electro-and photocatalysts for carbon dioxide reduction and hydrogen evolution.…”

The crystal structure of 1,12-diazaperylene, C18H10N2

“…A dirhodium dap complex with bridging acetato groups was found to have the dual capability of intercalative and coordinative binding to DNA [13]. Formamidinat-bridged dirhodium complexes exhibit broad, strong absorption throughout the UV-visible range [14] well suited for photophysical applications. More recently, absorption and emission spectra of N-derivatives of perylene -including dap -were simulated using a timedependent approach based on correlation functions determinated by density functional theory.…”

Electrospray mass spectrometry and molecular modeling study of formation and stability of silver complexes with diazaperylene and bisisoquinoline

“…21,22 These ligands are intensely studied chelating ligands in the coordination chemistry of transition metal ions. [23][24][25] Complex formation and stability of the ligands 1 to 12 (Scheme 1A) with various types of transition metal ions in the gas phase has been studied by us using ESI-MS and collision-induced dissociation (CID) measurements. The homoleptic [1:1] and [1:2] silver (1) complexes of ligands 1 and 2 had been investigated earlier.…”

“…Recently, we described the synthesis of a wide range of diazaperylenes as large‐surface ligands with increased π‐delocalization and the corresponding flexible nonplanar bisisoquinolines . These ligands are intensely studied chelating ligands in the coordination chemistry of transition metal ions . Complex formation and stability of the ligands 1 to 12 (Scheme A) with various types of transition metal ions in the gas phase has been studied by us using ESI‐MS and collision‐induced dissociation (CID) measurements.…”