Comparing structures and reactivity in analogous Fe and Ru complexes.: (iPr-DAB)Fe(CO)2I2 and (iPr-DAB)FeI2:: a perfectly reversible CO-carrier system.: (R-DAB = N,N′-R2-1,4-diara-1,3-butadiene)

Fe(Pr-i-DAB)(CO)(3) (1a) oxidatively adds I-2 to give (Pr-i-DAB)Fe(CO)(2)-trans-I-2 (Za). Photochemically or thermally, 2a readily dissociates both carbonyl ligands to give tetrahedral Fe(Pr-i-DAB)I-2 (3a). Under an atmosphere of CO, complex 2a is quantitatively regenerated from 3a. The X-ray crystal structures of 2a and 3a have been determined. 2a: triclinic, space group P (1) over bar, a = 8.7624(3). b = 9.0550(4), c = 10.6512(6) Angstrom, alpha = 95,429(4) beta = 105.245(4), gamma = 95.209(3)degrees Z = 2, R = 0.0251. 3a: orthorhombic, space group Aba2, a = 11.2693(10), b = 15.933(2), c = 7.5958(10) A, Z = 4, R = 0.036. Contrasting the behaviour of 2a, the analogous ruthenium complexes (R-DAB)Ru(CO)(2)trans-I-2 (4) are very stable, and the carbonyl ligands cannot be dissociated thermally. In the dichloro complexes. of which both the kinetic trans- (5) and the thermodynamic cis-compounds (6) have been isolated, both isomers undergo a photochemical CO mono-substitution to give for example the isolable trans-dichloro methanol complex (7). (C) 1999 Elsevier Science S.A. All rights reserved.