Spectroscopic and Electronic Properties of Molybdacarborane Complexes with Non‐innocently Acting Ligands

Abstract

The molybdacarboranes [3‐{L‐κ2N,N}‐3‐(CO)2‐closo‐3,1,2‐MoC2B9H11] (L=2,2′‐bipyridine (2,2′‐bpy, 1 a) or 1,10‐phenanthroline (1,10‐phen, 1 b)) incorporating well‐known potentially non‐innocent ligands (CO, 2,2′‐bpy, 1,10‐phen) and the “non‐spectator” nido‐carborane ([η5‐C2B9H11]2−) ligand were prepared and fully characterised. High‐resolution mass spectrometry, single‐crystal X‐ray diffraction methods, spectroscopy (IR, (resonance) Raman, NMR), cyclic voltammetry and spectroelectrochemistry (electrochemical properties) were supported by theoretical investigations of the electronic structure (DFT, CAS‐SCF, TD‐DFT).

2,2′‐Bipyridine‐Modified Tamoxifen: A Versatile Vector for Molybdacarboranes

“…The absorption spectra of the ternary systems (BSA‐site marker‐drug, Figure S16, SI) show the same overall trend concerning binding events as the fluorescence spectra. Notably, the UV‐Vis spectrum of 10 in PBS/DMSO mixture is essentially the same as for i ; therefore, similar electronic structures can be assumed . The absorption spectrum suggests that the solubility of 6 is improved on binding to BSA noMg , because the baseline shift, due to scattering, is suppressed.…”

“…Unlike the molybdacarboranes bearing a simple 2,2′‐bipyridine or 1,10‐phenanthroline ligand, complexes 8 – 10 could be purified by flash column chromatography on silica gel in low to moderate yields (18–35 %). These low yields are most likely related to a side reaction which was not observed for the simple N,N‐chelating ligands (e. g. 2,2′‐bipyridine or 1,10‐phenanthroline) . During the purification process, more than one violet band could be observed for every complexation reaction.…”

“…Exemplarily for 9 , the second violet fraction was collected in sufficient purity and identified by 1 H, 13 C{ 1 H}, 11 B{ 1 H} and 11 B NMR spectroscopy, HR‐ESI mass spectrometry and diffraction methods as a chlorine B(8)‐substituted derivative of 9 (see SI), where the respective position in the carborane ligand was activated for EINS‐type (electrophile induced nucleophilic substitution) reactions ( 9 b , Figure S2, SI) . This one‐pot two‐step reaction (proton‐mediated ligand exchange and EINS‐type reaction at the dicarbollide) was attempted before without success for complexes with the 2,2′‐bipyridine and 1,10‐phenanthroline ligand, [3‐(L‐κ 2 N , N ′)‐3‐(CO) 2 ‐ closo ‐3,1,2‐MoC 2 B 9 H 11 ], with L=2,2′‐bipyridine or 1,10‐phenanthroline, using different strong acids and solvents . Further studies for employing the chloride in carborane substitution chemistry are in progress.…”

“…The color of all the ligands ranges from colorless to pale yellow. On coordination to molybdenum(II), a color change to deep purple is observed for complexes 8 – 10 (for UV‐Vis spectra of 6 and 10 see Figure S16, SI) indicating metal‐to‐ligand (MLCT) and ligand‐to‐metal charge transfer (LMCT) (with L= 3 , 5 or 6 ) . In the infrared spectra, typical vibrations of all functional groups are observed, e. g. ν(BH) (2595–2480 cm −1 ) and ν(CO) (1955–1874 cm −1 ) vibrations, which are unique in biological systems and could, therefore, be used for label‐free imaging (first attempts have been reported for [3‐(2,2′‐bipyridine‐κ 2 N , N ′)‐3‐(CO) 2 ‐ closo ‐3,1,2‐MoC 2 B 9 H 11 ] .…”

“…On coordination to molybdenum(II), a color change to deep purple is observed for complexes 8-10 (for UV-Vis spectra of 6 and 10 see Figure S16, SI) indicating metal-to-ligand (MLCT) and ligand-to-metal charge transfer (LMCT) (with L = 3, 5 or 6). [28] In the infrared spectra, typical vibrations of all functional groups are observed, e. g. ν(BH) (2595-2480 cm À 1 ) and ν(CO) (1955-1874 cm À 1 ) vibrations, which are unique in biological systems and could, therefore, be used for label-free imaging (first attempts have been reported for [3-(2,2'-bipyridine-k 2 N,N')-3-(CO) 2 -closo-3,1,2-MoC 2 B 9 H 11 ]. [29] In the 1 H NMR spectra of the complexes 8, 9 and 10, there is a clear coordination shift observed compared to the chemical shifts of the ligands 3, 5 and 6 ( Figure S3-S5, SI).…”