Dimolybdenum(II) complexes linked by axial cyano bridges to organic and organometallic ligands: syntheses, structures, and characterization

Reaction of trans-[Mo-2(mu-OAc)(2)(dppma)(2)(NCCH3)(n)][BF4](2) (n=0-2, dpp ma=bis(diphenylphosphino)methylamine) with a variety of ligands containing a nitrile group leads to axially substituted complexes of formula trans-[Mo -2(mu-OAc)(2)(dppma)(2)(RCN)(2)][BF4](n) (n =0, 2), R can be both an organi c and an organometallic moiety. The obtained complexes are characterized by H-1-, C-13-, and P-31{H-1}-NMR, IR, Raman, and UV/Vis spectroscopy, elemen tal analyses and cyclic voltammetry. Four of these complexes are additional ly examined by single crystal X-ray analysis. The applied methods show that the axial ligands influence the spectroscopic and crystallographic data of the central moiety only slightly. However, while X-ray crystallography sho ws the MoMo quadruple bond length not to be significantly influenced by axi al ligands, Raman spectroscopy gives a more detailed insight: organic ligan ds of the type NCR (R=CH3, t-Bu, C6H5 etc.) in axial positions weaken the M oMo interaction less than organometallic ligands of the type [NC-M(CO)(5)]( -) (M=Cr, Mo, W) and NCFe(CO)(2)Cp. UV/Vis examination indicates charge tra nsfer from the organometallic axial ligands to the MoMo moiety.