Crystal and molecular structure of the compound formed from tetracyanoethylene and tricarbonyl(cycloheptatriene)iron: a novel 2,3,4,9-tetrahapto-bonded system

Abstract

The compound formed from tricarbonyl(cycloheptatriene)iron and tetracyanoethylene contains a bicyclononane system. Crystals of this compound are triclinic, a= 12·18, b= 9·05, c= 7·38 Å, α= 107° 16′, β= 82° 19′, γ= 88° 20′, space group P, with two centrosymmetrically related molecules in the unit cell. The structure has been determined by conventional heavy-atom methods from diffractometer data and refined to R 0·081 for 885 independent reflections. The Fe(CO)₃ group is bonded to the seven-membered ring via a novel four-electron donor system: C-2, C-3, and C-4 comprise a π-allyl group, while atom C-9 is σ-bonded to the iron atom. The tetracyanoethylene links to the cycloheptatriene ring at C-1 and C-6 to form a new five-membered ring system of ‘envelope’ conformation exo to the Fe(CO)₃ group. The configuration around the iron atom is approximately octahedral, and the mean Fe–C and C–O distances for the three carbonyl groups are 1·75(3) and 1·19(2)Å.