PSEUDO-ALLYL COMPLEXES FROM MONOAZADIENES AND CO2(CO)8 BY ACTIVATION OF DIHYDROGEN UNDER MILD CONDITIONS

The reaction of monoazadienes (MAD, a-g) with Co2(CO)g under H-2 atmosphere, affording the new pseudo-(alpha-aminoallyl) complexes Co(CO)3{RC(H)C(H)C(H)NHR'} (1a-g), provides an example of activation of dihydrogen under mild conditions (293 K, 1.2 bar H-2). Complexes 1 have also been prepared by the reaction of HCo(CO)4 With MAD, by the reaction of Co2(CO)8 with MAD in the presence of small amounts of water, and by the reaction of CO4(CO)12 with MAD under H-2. The electron-donating properties of the alpha-amino substituent in 1, inducing an increase of electron density at Co and asymmetry in the allyl-bonding, has been studied by IR, H-1, C-13, and Co-59 NMR, and an X-ray crystal structure determination of 1a (R, R' = Me, p-Tol). Crystals of la are monoclinic, spacegroup P2(1)/c with cell constants a = 9.304 (1) angstrom, b = 20.585 (3) angstrom, c = 7.613 (1) angstrom, beta = 90.80 (2)-degrees, Z = 4. A total of 1091 reflections have been used in the refinement, resulting in a final R value of 0.068. Concerning the mechanism of H-2 activation, a radical pathway is proposed by which the observed quantitative yields of 1a/b (R' = aryl) and the moderate yields of 1c-g (R' = alkyl) can be explained. Also alpha,beta-unsaturated aldehydes appear to be suitable substrates in the H-2 activation reaction with Co2(CO)8, but the products are very unstable and could be characterized only partly.