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

Abstract

Abstract The 13 C‐NMR. spectra of the series of complexes η 6 ‐naphthalene · CrL 3 (LCO ( 1 ), PF 3 ( 2 ), PF 2 OMe ( 6 ), P(OMe) 3 ( 3 ), C 10 H 8 (= 3 L) ( 4 ) and PMe 3 ( 5 )) are reported. Definite assignments of the 13 C‐NMR. resonances were made through the synthesis of [2, 3, 6, 7‐ 2 H 4 ]‐naphthalene complexes. The coordinated ring 13 C‐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 [C 10 H 8 FeC 5 H 5 ] + [PF 6 ] − ( 7 ) with stabilized carbanions and I 2 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 HBF 4 results not in the expected metal protonation but in a novel ligand transformation to yield 6 .