Triple-decker complexes XIV. Reactions of iron carbonyls with the triple-decker sandwich complexes (η 5-C 5H 5)Ni(μ,η 5-C 2B 2C)M(η 5-C 5H 5), (M = Co, Ni). Replacement of (η 5-C 5H 5)Ni by and insertion of the Fe(CO) 3 fragment into the (η 5-C 5H 5)Ni bond

Abstract

The reactions of Fe 2(CO) 9 with triple-decker sandwich complexes containing the 2-methyl-1,3,4,5-tetraethyl or the 4,5-diethyl-1,3-dimethyl derivatives of the 2,3-dihydro-1,3-diborole heterocycle C 2B 2C ( 4a,b) as a bridging ligand have been investigated. The paramagnetic triple-deckers, 32 valence electron (VE) [(η 5-C 5H 5)-Ni(μ,η 5-C 2B 2C)Co(η 5-C 5H 5)] ( 8a) and 33 VE [(η 5-C 5H 5)Ni(μ,η 5-C 2B 2C)Ni(η 5-C 5H 5)] ( 9b) react with Fe 2(CO) 9 to give products resulting either from replacement of a (η 5-C 5H 5)Ni fragment by Fe(CO) 3, or insertion of Fe(CO) 3 into the (η 5-C 5H 5)Ni bond. Thus, reaction of 8a with Fe 2(CO) 9 proceeds via Fe(CO) 3 insertion into the (η 5-C 5H 5)Ni bond to yield the trinuclear carbonyl-bridged complex [(η 5-C 5H 5)FeCO(μ-CO) 2Ni(μ,η 5-C 2B 2C)Co(η 5-C 5H 5)] ( 10a), and subsequently the tetranuclear [{(η 5-C 5H 5)Co(μ,η 5-C 2B 2C)Ni(μ-CO)} 2] ( 12a), and also via replacement of (η 5-C 5H 5)Ni to give the triple-decker [(η 5-C 5H 5)Co(μ,η 5-C 2B 2C)Fe(CO) 3] ( 13a). 33 VE 9b reacts with Fe 2(CO) 9 to give initially [(η 5-C 5H 5)Ni(μ,η 5-C 2B 2C)Fe(CO) 3] ( 14b); subsequent reactions lead to the carbonyl-bridged [(η 5-C 5H 5)Fe(CO)(μ-CO) 2Ni(μ,η 5-C 2B 2C)Fe(CO) 3] ( 15b), the tetra-decker [{(CO) 3Fe(μ,η 5-C 2B 2C)} 2Ni] ( 16b), and the triple-decker [(η 5-C 5H 5)Fe(μ,η 5-C 2B 2C)Fe(CO) 3] ( 17b). The unsymmetrical triple-decker complexes 14a and 14b have been made independently by stacking the Ni-sandwich complexes 20a and 20b with an Fe(CO) 3 fragment. A close chemical relationship between 32 VE 8a and 20 VE nickelocene has been established, and may be rationalised by consideration of electronic structures.