The first [2,3-dialkyl-1,4-bis(1,3-dioxo-4,4,5,5-tetramethyl-2-borolanyl]-1,3-butadiene]Fe(CO)(3) complexes (2, alkyl = n-butyl; 3, alkyl = cyclopentyl; 4, 'alkyl' = phenyl; 5, alkyl = 3-chloropropyl) have been prepared from the reaction of bis(cis-cyclooctadiene)Fe(CO)(3) (1) with the borolanylbutadienes. The X-ray crystal structures of 2 and 3 are reported. The geometries of the coordinated ligands are compared with those of the free ligands. (C) 1999 Elsevier Science S.A. All rights reserved.