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

Abstract

Reaction of trans-[Mo₂(µ-OAc)₂(dppma)₂(NCCH₃)_n][BF₄]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-[Mo₂(µ-OAc)₂(dppma)₂(RCN)₂][BF₄]_n (n = 0, 2), R can be both an organic and an organometallic moiety. The obtained complexes are characterized by ¹H-, ¹³C-, and ³¹P{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 = CH₃, t-Bu, C₆H₅etc.) 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.