Issue 9, 2005

Binuclear biscarbene complexes of furan

Abstract

Carbene complexes of chromium and tungsten with a bridging furan substituent were synthesized from lithiated furan precursors and metal hexacarbonyls. The binuclear biscarbene complexes [(CO)5M{C(OEt)–C4H2O–C(OEt)}M′(CO)5] (M = M′ = Cr (3), W (4)) were obtained as well as the corresponding monocarbene complexes [M{C(OEt)–C4H3O}(CO)5] (M = Cr (1), W (2)). A method of protecting the carbene moiety during the metal acylate stage was used to increase not only the yields of the binuclear Fischer biscarbene complexes 3 and 4 but to establish a method to synthesize analogous mixed heterobinuclear carbene complexes (M = W, M′ = Cr (5)) in high yields. The binuclear biscarbene complexes 3 and 5 were reacted with 3-hexyne and yielded the corresponding benzannulated monocarbene complexes [M{C(OEt)–C14H17O3}(CO)5] (M = Cr (6), W(7)). Complex 5 reacted regioselectively with the benzannulation reaction occurring at the chromium–carbene centre. The major products from refluxing 3 in the presence of [Pd(PPh3)4] were a monocarbene-ester complex [Cr{C(OEt)–C4H2O–C(O)OEt}(CO)5] (8), the 2,5-diester of furan (9) and a carbenecarbene coupled olefin EtOC(O)–C4H2O–C(OEt)[double bond, length as m-dash]C(OEt)–C4H2O–C(O)OEt (10). X-Ray structure analysis of 4 and 6 confirmed the molecular structures of the compounds in the solid state and aspects of electron conjugation between the transition metals and the furan substituents in the carbene ligands were investigated.

Graphical abstract: Binuclear biscarbene complexes of furan

Supplementary files

Article information

Article type
Paper
Submitted
21 Dec 2004
Accepted
03 Mar 2005
First published
04 Apr 2005

Dalton Trans., 2005, 1649-1657

Binuclear biscarbene complexes of furan

C. Crause, H. Görls and S. Lotz, Dalton Trans., 2005, 1649 DOI: 10.1039/B419148J

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