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

Abstract

The reactions of the COT-coordinated diiron cationic bridging carbyne complexes [Fe2(μ-CAr)(CO)4(η8-C8H8)]BF4 (1, Ar = C6H5; 2, Ar = p-CH3C6H4; 3, Ar = p-CF3C6H4) with p-methylaniline gave the COT-coordinated diiron Fischer-type carbene complexes [Fe2{C(Ar)NHC6H4CH3-p}(μ-CO)(CO)3(η8-C8H8)] (7, Ar = C6H5; 8, Ar = p-CH3C6H4; 9, Ar = p-CF3C6H4). Heating the solution of diiron carbene complexes [Fe2{C(Ar)NHC6H5}(μ-CO)(CO)3(η8-C8H8)] (4, Ar = C6H5; 5, Ar = p-CH3C6H4; 6, Ar = p-CF3C6H4) in benzene in a sealed tube at 85−90 °C for 72 h afforded the chelated diiron carbene complex [Fe2{C(C6H5)NC6H5}(η2:η3:η2-C8H9)(CO)4] (4a), C8 ring addition products [Fe2{N(C6H5)C(Ar)(η1:η3:η2-C8H9)}(CO)5] (10, Ar = C6H5; 12, Ar = p-CH3C6H4; 14, Ar = p-CF3C6H4), and C7 contraction ring products [Fe2{N(C6H5)C(Ar)CH(η2:η3-C7H8)(CO)4}] (11, Ar = C6H5; 13, Ar = p-CH3C6H4; 15, Ar = p-CF3C6H4), respectively. The similar thermolysis of complexes 7 and 8 afforded corresponding thermolysis products [Fe2{C(C6H5)NC6H4CH3-p}(η2:η3:η2-C8H9)(CO)4] (7a), [Fe2{N(C6H4CH3-p)C(Ar)(η1:η2:η3-C8H9)}(CO)5] (16, Ar = C6H5; 18, Ar = p-CH3C6H4), and [Fe2{N(C6H4CH3-p)C(Ar)CH(η2:η3-C7H8)}(CO)4] (17, Ar = C6H5; 19, Ar = p-CH3C6H4), 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.

Thermolytic Products Derived from Thermolysis of Cycloolefin-Coordinated Diiron Bridging Carbene Complexes

“…It is well-known that the thermal decomposition of carbene complexes usually results in dimerization of the carbene ligand to produce alkene derivatives and that heating a Fischer-type carbene complex with an olefin generally results in addition of the double bond of the olefin to the carbene ligand to form cyclopropane products. , Recently, we have shown a number of thermolysis reactions of the olefin-coordinated monoiron alkoxycarbene complexes or their isomerized products and the COT-coordinated diiron Fischer-type carbene complexes, which produced a series of novel thermolytic products. , What happens when the cycloolefin-coordinated diiron bridging carbene complexes containing a bridging carbene ligand and a cycloolefin ligand are subjected to thermolysis? To explore thermolysis reactivity of such bridging carbene complexes and to compare their thermolysis reactivities with that of COT-coordinated diiron Fischer-type carbene complexes, we chose COT-coordinated diiron bridging alkoxycarbene complexes [Fe 2 {μ-C(OC 2 H 5 )Ar}(CO) 4 (η 8 -C 8 H 8 )] ( 1 , Ar = C 6 H 5 ; 2 , Ar = p -CH 3 C 6 H 4 ; 3 , Ar = p -CF 3 C 6 H 4 ), 7 H -indene-coordinated diiron bridging alkoxycarbene complex [Fe 2 {μ-C(OC 2 H 5 )C 6 H 5 }(CO) 4 (η 4 ,η 4 -C 9 H 8 )] ( 4 ), and analogous bridging arylthiocarbene complexes [Fe 2 {μ-C(Ar)SC 6 H 4 CH 3 - p }(CO) 4 (η 4 ,η 4 -C 9 H 8 )] ( 8 , Ar = C 6 H 5 ; 9 , Ar = p -C 6 H 5 C 6 H 4 ) as starting materials for the thermolysis reactions, which afforded a series of novel thermal decomposition products.…”