The Synthesis of Dimeric Re^I–Phenylenediimine Conjugates: Spectroscopic and Electrochemical Studies

Abstract

A series of dimeric ReI(CO)3 compounds have been prepared by means of a one‐pot reaction of [Re(CO)5X] (X = Cl, Br), pyridine‐2‐carboxyaldehyde, and o‐, m‐, or p‐phenylenediamine. For the m‐ and p‐substituted phenylenediamine reactions, phenyl‐bridged bis(pyridine‐2‐carbaldimine) compounds of the formula [Re(CO)3X]2(μ‐PPC) [3–7; X = Cl, Br; μ‐PPC = m‐ or p‐phenylene bis(pyridine‐2‐carbaldimine)] were produced, with m‐phenylenediamine forming a mixture of isomers. For reactions with o‐phenylenediamine, multiple products formed (compounds 8–11), which ranged from the desired o‐phenylene bis(pyridine‐2‐carbaldimine) adduct to 2‐pyridylbenzimidazole and bridging dipyridinylquinoxaline complexes. An example of each complex was structurally elucidated by single‐crystal X‐ray methods. The dimeric m‐ and p‐phenylene‐bridged Re(CO)3X compounds, including a sulfonate derivative designed to improve solubility, were investigated for possible photophysical applications through the use of UV/Vis spectroscopy and cyclic voltammetry; the study revealed coupling between the rhenium centers.

Using hydrazine to link ferrocene with Re(CO)3: A modular approach

“…All of the transitions occur between 400 and 500 nm, which is typical for this class of compounds. Compounds 7 and 8 exhibit a significant amount of bathochromic shifting; we observed similar trends in other dimeric Re(CO) 3 complexes [41,46]. All of the conjugates display diagnostic CO stretching frequencies in their IR spectra; these correspond to the a 1 and e type modes that result from the facial Re(CO) 3 unit.…”

“…The molar absorptivities of 4 and 5 were comparable to those observed in mono-rhenium tricarbonyl Schiffs base compounds with absorptivities around 3,000–4,000 M −1 cm −1 [44,45]. Complexes ( 6 and 7 ) show stronger absorbtivities in the range of 7,000–8,000 M −1 cm −1 , about twice as much as those of monomeric Re(CO) 3 Schiff’s base complexes, which is consistent with their dimeric structures [41,46]. All of the transitions occur between 400 and 500 nm, which is typical for this class of compounds.…”

“…Previously, we have used this approach to confirm the presence of mixed-valence systems in both ferrocene and Re(CO) 3 systems [41,46]. Figure 5 shows the oxidative and reductive spectroelectrochemistry of compound 4 and 5 , with the 1:1 ferrocene:rhenium ratio.…”

“…In conjugates with either two ferrocenes or two Re(CO) 3 diimine centers, we have previously observed coupling and the formation of mixed valence behavior [41,46]. We probed the precursor molecules 1 and 3 as well as the 1:1 conjugate compounds 4 and 5 using cyclic voltammetry.…”

Facile solid phase peptide synthesis with a Re-lysine conjugate generated via a one-pot procedure

“…19 We and others have used this reaction to generate covalent diimine adducts, often with a substituted phenyl ring attached to the imine nitrogen. 14,20-21 However, this chemistry can also be used to produce compounds where the imine group is substituted with a biologically relevant moiety, such as a peptide or a fluorescein. 14,17,19 We surmised that we could extend this chemistry to the Nε of a protected lysine that could subsequently be employed as a reagent for solid phase peptide synthesis (SPPS).…”