Mixed alkyl isocyanide-1,4-diaza-1,3-butadiene complexes of molybdenum(II) and tungsten(II)

The reactions of M(CO)₄(R′-DAB) (M = Mo) or W; R′-DAB = R′-N=CHCH=NR′ (R′ = i-propyl, t-butyl, or cyclohexyl) with SnCl₄ in dichloromethane solution result in the formation, in high yield, of the orange, diamagnetic, seven-coordinate oxidative-addition products M(CO)₃(R′-DAB)(SnCl₃)Cl. The reactions of Mo(CO)₃(R′-DAB)(SnCl₃)Cl (R′ = i-Pr or Cy) with an excess of alkyl isocyanide RNC (R = CHMe₂, CMe₃, or C₆H₁₁) in the presence of KPF₆ lead to the formation of Mo(CNR)₄(R′-DAB)Cl]PF₆ or Mo(CNR)₅(R′-DAB)](PF₆)₂ depending upon the reaction stoichiometry and reaction conditions. The monocationic chloro species are converted to Mo(CNR)₅(R′-DAB)](PF₆)₂ upon reflux with the stoichiometric amount of RNC. Under similar reactions conditions M(CO)₃(t-Bu-DAB)(SnCl₃)Cl (M = Mo or W) derivatives react with alkyl isocyanides with the reductive-elimination of the elements of SnCl₄ and the formation of octahedral M(CO)₃(CNR)(t-Bu-DAB). The dark red compounds Mo(CNCMe₃)₅(R′-DAB)](PF₆)₂ (R′ = i-Pr or Cy) react readily with cyanide ions at ambient temperatures in methanol to yield Mo(CNCMe₃)₄(R′-DAB)(CN)]PF₆. Attempts to thermally dealkylate the parent complexes Mo(CNCMe₃)₅(R′-DAB)](PF₆)₂ (R′ = i-Pr or Cy) to these same cyano species were unsuccessful.