Ring Expansion of Spirocyclic Cyclobutenylidene Ligands in Pentacarbonylchromium Complexes to Tetrahydroindene Derivatives

Abstract

Pentacarbonyl(pentamethylenevinylidene)chromium, [(CO)5Cr[DOUBLE BOND]C[DOUBLE BOND]C(CH2)5] (1), reacts with 1-methylthio-1-propyne (2a) and N-(1-propynyl)phenothiazine (2b) by regio-specific addition of the C[DOUBLE BOND]C bond of the alkyne to the C[DOUBLE BOND]C bond of the vinylidene ligand of 1. Initially, complexes with a spirocyclic cyclobutenylidene ligand are formed, [(CO)5Cr[DOUBLE BOND]chemical structure image(CH2)5] (3) and [(CO)5-Cr[DOUBLE BOND]chemical structure image(CH2)5] (10). Subsequent thermally initiated ring expansion affords the 2-methyl-4,5,6,7-tetrahydroindenyl(methyl)thioether complex [(CO)5-Cr–S(Me)(Me-C9H10)] (4) and the N-(2-methyl-4,5,6,7-tetrahydroindenyl)phenothiazine complex [(CO)5Cr–S(C6H4)2-N–(Me-C9H10)] (11), respectively. In both complexes, 4 and 11 the ligand is coordinated to the metal via the sulfur atom. The constitutions were established by (H,H)-, (H,C)- and NOE-correlated NMR spectroscopy. In the reaction of 1 with 2a, in addition to 3 and 4, the methyl(propynyl)thioether complex [(CO)5Cr–S(Me)C[TRIPLE BOND]CMe] (5) was formed. An isolable 3-methylthio-substituted cyclobutenylidene complex, [(CO)5Cr[DOUBLE BOND]chemical structure imagePh2] (9) was obtained from [(CO)5Cr[DOUBLE BOND]C[DOUBLE BOND]CPh2] (8) and 2a. The 4,5,6,7-tetrahydroindenylthioether ligand of 11 was cleaved from the metal by exposure of 11 adsorbed on silica gel to air or by treatment of 11 with [NEt4]Br in dichloromethane.