Synthesis and Substituent Interactions of Tricarbonylchromium-complexed Arylalkynylbenzenes - Novel Organometallic Push-pull Chromophores

The tricarbonylchromium complexes chlorobenzene 1 reacts with terminal alkynes 2 through a palladium‐copper‐catalyzed coupling to give a variety of Cr(CO)3‐complexed phenylethynyl arenes, heteroarenes and ferrocene 3 in good to excellent yield. Due to the electron‐withdrawing nature of the Cr(CO)3 group these novel complexes can be regarded as organometallic push‐pull chromophores. Analogously, the corresponding free ligands 4 (phenylethynyl arenes, heteroarenes and ferrocene) were synthesized by coupling iodobenzene and 2. The crystal structure analysis of the singly Cr(CO)3‐complexed tolane 3e reveals a strong deviation from coplanarity of both phenyl rings by an angle of 50.9(2)° presumably due to crystal packing. Correlations are established between selected substituent parameters (σP, σI, σR, σP+ and Δπ) and the carbonyl carbon resonances in the 13C‐NMR spectra for the complexes 3. The overall electronic substituent effect is transmitted to the carbonyl groups by both mesomeric and inductive mechanisms. The push‐pull complexes 3 display relatively small negative solvochromicities of longest wavelength absorption band (MLCT band).