Cyclooctatetraene (COT)-Coordinated Diiron Carbene Complexes and Their Remarkable Thermolysis Reactions

Abstract

The reactions of the COT-coordinated diiron cationic bridging carbyne complexes [Fe 2 (μ-CAr)(CO) 4 (η 8 -C 8 H 8 )]BF 4 (1, Ar = C 6 H 5 ; 2, Ar = p-CH 3 C 6 H 4 ; 3, Ar = p-CF 3 C 6 H 4 ) with p-methylaniline gave the COT-coordinated diiron Fischer-type carbene complexes [Fe 2 {= C(Ar)NHC 6 H 4 CH 3 -p}(μ-CO)(CO) 3 (η 8 -C 8 H 8 )] (7, Ar = C 6 H 5 ; 8, Ar = p-CH 3 C 6 H 4 ; 9, Ar = p-CF 3 C 6 H 4 ). Heating the solution of diiron carbene complexes [Fe 2 {=C(Ar)NHC 6 H 5 }(μ-CO)-(CO) 3 (η 8 -C 8 H 8 )] (4, Ar = C 6 H 5 ; 5, Ar = p-CH 3 C 6 H 4 ; 6, Ar = p-CF 3 C 6 H 4 ) in benzene in a sealed tube at 85-90 °C for 72 h afforded the chelated diiron carbene complex [Fe 2 {=C(C 6 H 5 )-NC 6 H 5 }(η 2 :η 3 :η 2 -C 8 H 9 )(CO) 4 ] (4a), C 8 ring addition products [Fe 2 {N(C 6 H 5 )=C(Ar)(η 1 :η 3 :η 2 -C 8 H 9 )}(CO) 5 ] (10, Ar = C 6 H 5 ; 12, Ar = p-CH 3 C 6 H 4 ; 14, Ar = p-CF 3 C 6 H 4 ), and C 7 contraction ring products [Fe 2 {N(C 6 H 5 )=C(Ar)CH(η 2 :η 3 -C 7 H 8 )(CO) 4 }] (11, Ar = C 6 H 5 ; 13, Ar = p-CH 3 C 6 H 4 ; 15, Ar = p-CF 3 C 6 H 4 ), respectively. The similar thermolysis of complexes 7 and 8 afforded corresponding thermolysis products [Fe 2 {=C(C 6 H 5 )NC 6 H 4 CH 3 -p}(η 2 :η 3 :η 2 -C 8 H 9 )(CO) 4 ] (7a), [Fe 2 {N(C 6 H 4 CH 3 -p)=C(Ar)(η 1 :η 2 :η 3 -C 8 H 9 )}(CO) 5 ] (16, Ar = C 6 H 5 ; 18, Ar = p-CH 3 C 6 H 4 ), and [Fe 2 {N(C 6 H 4 CH 3 -p)=C(Ar)CH(η 2 :η 3 -C 7 H 8 )}(CO) 4 ] (17, Ar = C 6 H 5 ; 19, Ar = p-CH 3 C 6 H 4 ), respectively. Interestingly, products 4a and 7a were transformed into the eight-membered ring products 10 and 16 and seven-membered ring products 11 and 17, respectively, under similar conditions. Surprisingly, compounds 10, 16, and 18 can also be partially transformed into compounds 11, 17, and 19, respectively, by further thermolysis at higher temperature (100-105 °C). The structures of complexes 7, 10, 11, 18, and 19 have been established by X-ray diffraction studies.