A 13C-NMR. Study of naphthalene chromium complexes. Correlation with reactivity: Nucleophilic aromatic substitution reactions

The ¹³C-NMR. spectra of the series of complexes η⁶-naphthalene · CrL₃ (L? CO ( 1 ), PF₃ ( 2 ), PF₂OMe ( 6 ), P(OMe)₃ ( 3 ), C₁₀H₈ (= 3 L) ( 4 ) and PMe₃ ( 5 )) are reported. Definite assignments of the ¹³C-NMR. resonances were made through the synthesis of 2, 3, 6, 7-²H₄]-naphthalene complexes. The coordinated ring ¹³C-resonance are found to undergo a smooth transition to higher field with increasing donor character of the coligands L. A correlation of the coordination shifts with the reactivity of the coordinated naphthalene is proposed. In complexes containing strong acceptor ligands the naphthalene is activated to attack by nucleophiles. Sequential treatment of complexes 1–4 , 6 and C₁₀H₈FeC₅H₅]⁺PF₆]^? ( 7 ) with stabilized carbanions and I₂ or Ce(IV)-salt yields α-substituted naphthalenes in the case of 1 , 2 , 6 and 7 but not in the case of 3 and 4 . Treatment of 3 with an excess of HBF₄ results not in the expected metal protonation but in a novel ligand transformation to yield 6 .