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

摘要

Reaction of trains-[Mo_2(#mu#-OAc)_2(dppma)_2(NCCH_3)_n][BF_4]_2 (n = 0-2, dppma = 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][BF_4]_n (n = 0, 2), R can be both an organic and an organometallic moiety. The obtained complexes are characterized by ~1H-, ~(13)C-, and ~(31)P{~1H}-NMR, IR, Raman, and UV/Vis spectroscopy, elemental analyses and cyclic voltammetry. Four of these complexes are additionally 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 shows the MoMo quadruple bond length not to be significantly influenced by axial ligands, Raman spectroscopy gives a more detailed insight: organic ligands of the type NCR (R = CH_3, t-Bu, C_6H_5 etc.) in axial positions weaken the MoMo interaction less than organometallic ligands of the type [NC-M(CO)_5]~- (M = Cr, Mo, W) and NCFE(CO)_2Cp. UV/Vis examination indicates charge transfer from the organometallic axial ligands to the MoMo moiety.