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 [WI2(CNAr)(5)] complexes. Notably, we discovered that W(CNDipp)(6) can be regenerated by chemical reduction of WI2(CNDipp)(5) with excess ligand present in solution.