Synthesis and characterization of tetracarbonyl complexes of molybdenum and tungsten with functionalized imines. Crystal structure of cis-Mo(CO)42

Article abstract of DOI:10.1016/0022-328X(94)05278-J

A series of octahedral cis-iminetetracarbonyl molybdenum and tungsten complexes of the general formula , where L2 = R₁R₂C=N(CH2)CH(R₃)N=CR₁'R₂' have been prepared and characterized by IR, 1H and 13C NMR spectroscopies.These imine chelates complexes of molybdenum and tungsten have exocyclic double bonds.A consistent structural feature of these complexes appears to be the chelate bonding of the imine ligand with consequent rotation around the carbon-nitrogen bond.This phenomenon leads to isomeric compounds: 4 and 5; 8 and 9; 11 and 12.NMR data analysis established unambiguously the configuration of the following nine complexes: M(CO)4L2 1 = R'₂ = CH3, R'₁ = R₂ = C6H5, R₃ = H, M = Mo (4), M = W (8)>; 1 = R'₁ = C6H5, R₂ = R'₂ = CH3, R₃ = H, M = Mo (5), M = W (9)>; 1 = R'₁ = R₂ = R'₂ = C6H5, R₃ = H, M = Mo (6), M = W (10)>; 1 = R'₁ = R₂ = R'₂ = CH3, R₃ = H, M = Mo (7)>; 1 = R'₂ = C6H5, R'₁ = R₂ = CH3, R₃ = CH3, M = Mo (11)>; 1 = R'₁ = C6H5, R₂ = R'₂ = CH3, R₃ = CH3, M = Mo (12)>.Long-range coupling constants ⁵J(H-H) have confirmed the configuration and chemical shifts assignments for complexes 11 and 12.The 13C chemical shifts of the carbonyl groups are particularly useful in the characterization of the molybdenum compounds.Single-crystal X-ray diffraction studies of 4 confirm the formation of the nonsymmetric complex cis-tetracarbonylmolybdenum.The complex crystallizes in the space group P2₁/n with the unit cell parameters a = 11.112(1) Angstroem; b = 19.345(1) Angstroem; c = 11.680(1) Angstroem; β = 102.89(6) deg; V = 2447.5(3) Angstroem ³; Z = 4, D_x =1.39 g cm^-3.The structure was solved by direct methods and refined by full-matrix least-squares techniques to R and R_w values of 0.052 and 0.064, respectively, for 4706 observed reflections.The data obtained show that the structure has been solvated with half a molecule of benzene.Evidence of monocoordination of imine 1 to Mo(CO)4(NBD) has been obtained by 13C NMR spectroscopy and some insight into the mechanism of complex formation is provided.Keywords: Molybdenum; Tungsten; Carbonyls; Imines; Stereochemistry