Cooperative Reactivity of Methylene‐Linked Bis‐Triazolylidene Ligands in Tungsten‐Catalyzed Alcohol Dehydrogenation

New tetracarbonyl chromium and tungsten bis(1,2,3‐triazolylidene) complexes were synthesized and evaluated as catalysts for the synthesis of 2‐phenylquinoline via acceptorless dehydrogenative coupling (ADC) of 2‐aminobenzyl alcohol and 1‐phenylethanol. The tungsten complex exhibited excellent activity, affording quantitative conversion in 7 h and clearly outperforming its molybdenum and chromium analogs. Mechanistic investigations combining experimental and DFT studies revealed an unprecedented base‐promoted deprotonation of the methylene bridge in the W(CO) 4 (bis‐triazolylidene) complex. A plausible mechanism for the acceptorless dehydrogenation coupling (ADC) of alcohols was calculated by DFT in which a related bridge deprotonated species W(CO) 3 (bis‐triazolylidene) was identified as the catalytically active intermediate. In our proposal the deprotonated bridge acts as an internal base to deprotonate the alcohol and is involved in the H 2 release step. This finding provides the first evidence of metal–ligand cooperativity in a bis‐triazolylidene complex operative in acceptorless dehydrogenative coupling, unveiling a new mode of ligand‐assisted reactivity.