75548-67-3Relevant academic research and scientific papers
Binuclear metal carbonyl DAB complexes. 6. Syntheses and spectroscopic properties of MCo(CO)5(μ2-CO)(DAB) (M = Mn, Re; DAB = 1,4-diazabutadiene). X-ray structure of [σ2-N,σ2-N′,η 2-C=N-[glyoxal bis(tert-butylimine)]]hexacarbonylcobaltmanganese
Staal,Keijsper,Van Koten,Vrieze,Cras,Bosman
, p. 555 - 562 (2008/10/08)
The reaction between Mn(CO)3Br(DAB) (DAB = 1,4-diazabutadiene) and [Co(CO)4]- yields complexes of the composition MnCo(CO)6(DAB). The analogous rhenium complexes could also be prepared. The single-crystal structure determination of [glyoxal bis(tert-butylimine)]hexacarbonylcobaltmanganese has been carried out on monoclinic crystals of space group P21/c. Cell constants are a = 9.024 (5) ?, b = 12.793 (3) ?, c = 17.324 (6) ?, β = 105.1 (1)°, Z = 4, d(calcd) = 1.540 g cm-3, and d(measd) = 1.55 g cm-3. A total of 1305 reflections have been used in the refinement, resulting in a final R value of 0.066, for 234 parameters varied. The DAB ligand acts as a six-electron donor system, donating two lone pairs on nitrogen and one pair of π electrons via a N=C unit. The Co-Mn distance of 2.639 (3) ? points to a Co-Mn single bond. The DAB ligand is η2-C=N coordinated to cobalt with Co-N(1) equal to 1.89 (1) ? and Co-C(3) equal to 2.07 (1) ?. The metal carbonyl skeleton of the complex contains a semibridging carbonyl group with Mn-C(63) equal to 2.33 (1) ? and Co-C(63) equal to 1.80 (1) ? and bond angles Mn-C(63)-O(63) of 127 (1)° and Co-C(63)-O(63) of 154 (1)°. MnCo(CO)7(DAB) complexes were observed as unstable intermediates in the reaction sequence, containing the DAB ligands in the σ,σ-N,N′ coordination mode. This indicates that the complexes are formed in a nucleophilic mechanism. All complexes have been characterized by 1H NMR, IR, and mass spectrometry. For MnCo(CO)6[biacetyl bis(cyclo-propylimine)] an exchange between the σ2-N and the σ2-N′,η2-C=N′ coordinated parts of the DAB ligand was observed with a coalescence temperature of -15°C. A mechanism for the exchange process has been proposed. It is shown that (CH3)C=N fragments have poor π-bonding abilitites as compared with (H)C=N fragments. A DAB ligand containing both fragments is found with the (CH3)C=N fragment on the σ-coordinated part of the molecule exclusively. A comparison is made with the reaction of [Mn(CO)5]- and Mn(CO)3Br(DAB), giving information about the role of the metal carbonyl fragment on the coordination of the DAB ligand.
