Skeletal Modification of Benzothiophene Mediated by Iron Carbonyls: Insertion of Terminal Alkynes with Migration of Amino and Alkoxy Groups

Abstract

A thiolate-bridged diiron carbonyl complex derived from benzothiophene, [Fe2(μ-SC6H4CHCH)(CO)6], reacted with terminal alkynes HCCR (R = SiMe3, Ph, isobutyl) under photoirradiation conditions to afford diiron complexes with a 2,4-pentadienoyl moiety, [Fe2{μ-SC6H4(CH)3C(R)CO}(CO)5], via alkyne and CO insertion. In a similar reaction with N,N-dimethylpropargylamine, a diiron complex with a pentadienyl moiety, [Fe2{μ-SC6H4(CH)3C(NMe2)CH2}(CO)5], was obtained as an alkyne insertion product without CO insertion. This reaction involves 1,2-migration of a dimethylamino group. The corresponding reactions with alkyl propargyl ethers also produced diiron complexes containing pentadienyl moieties with an alkoxycarbonyl group via alkoxy migration with CO insertion. The migration process via C–N or C–O bond cleavage could be related to the coordination ability of N or O in the propargyl compounds.

The reaction of nonacarbonyldiiron with 8‐alkynyloxyquinolines: Alkynyl activation, cyclization via C‐N bond formation, and C‐H bond cleavage

“…As C13 coordinates to Fe1 as well, the electron density of the motif is diverted away by this bridging bonding. Therefore, the η 3 ‐bonding in complex 3 (Figure 5) is very much of the nature of an allene η 3 ‐bonding with a bent angle and similar bond distance as found in analogous systems 44,45 . The fact that the bond distances of both C12‐C13 and C13‐C14 are about 1.4 Å and the skeleton C12‐C13‐C14 is bent after forming η 3 ‐bonding with Fe2 firmly supports the above analysis.…”

“…The bond distance of C12-C13 in 2 is 1.421( 5) Å (Table 2 and Figure 4), falling in the range between a single bond and a double bond, which is consistent with bond elongation caused by η-bonding between a metal center and a C=C bond. [44][45][46][47] For example, in iron(0) tricarbonyl η 4 -1-azadiene complexes ([Fe 0 (CO) 3 (η 4 -N(R 1 ) = C-C=C(R 2 )]), the distance of C=C bond is ca. 1.41 Å.…”

“…Therefore, the η 3 -bonding in complex 3 (Figure 5) is very much of the nature of an allene η 3bonding with a bent angle and similar bond distance as found in analogous systems. 44,45 The fact that the bond distances of both C12-C13 and C13-C14 are about 1.4 Å and the skeleton C12-C13-C14 is bent after forming η 3 -S C H E M E 2 Synthetic routes for the iron carbonyl complexes (1a, 1b, 2, and 3).…”