Photoredox Catalysis Mediated by Tungsten(0) Arylisocyanides

W(CNAr) 6 (CNAr = arylisocyanide) photoreductants catalyze base-promoted homolytic aromatic substitution (BHAS) of 1-(2-iodobenzyl)-pyrrole in deuterated benzene. Moderate to high efficiencies correlate with W(CNAr) 6 excited-state reduction potentials upon one-photon 445 nm excitation, with 10 mol % loading of the most powerful photoreductants W(CNDipp) 6 (CNDipp = 2,6-diisopropylphenylisocyanide) and W(CNDippPh OMe3 ) 6 (CNDippPh OMe3 = 4-(3,4,5-trimethoxyphenyl)-2,6-diisopropylphenylisocyanide) affording nearly complete conversion. Stern–Volmer quenching experiments indicated that catalysis is triggered by substrate reductive dehalogenation. Taking advantage of the large two-photon absorption (TPA) cross sections of W(CNAr) 6 complexes, we found that photocatalysis can be driven with femtosecond-pulsed 810 nm excitation. For both one- and two-photon excitation, photocatalysis was terminated by the formation of seven-coordinate W II -diiodo [WI 2 (CNAr) 5 ] complexes. Notably, we discovered that W(CNDipp) 6 can be regenerated by chemical reduction of WI 2 (CNDipp) 5 with excess ligand present in solution.