Bimetallic complexes III. Synthesis and reactions of c5h4pph2-bridged zirconium-molybdenum and zirconium-tungsten complexes

Article abstract of DOI:10.1016/S0022-328X(97)00324-0

The synthesis and reactions of bimetallic Zr-Mo and Zr-W complexes with bridging C₅H₄PPh₂ ligands (henceforth abbreviated as Cp′) are described. Reaction of Cp′₂ZrCl₂ (1) with organolithium or Grignard reagents gives Cp′₂ZrR₂ (R = Me (3), p-C₆H₄CH₃ (5), CH₂SiMe₃ (6)) while with A1Me₃ the mono-exchange product Cp′₂Zr(Cl)Me (2) is formed. Phenyllithium converts 2 into Cp′₂Zr(Me)Ph (4). From 1-3 the substitution products [(Cp′₂ZrMe)₂( μ-O)] (7), Cp′₂Zr(SR)₂ (R = Me (8a), Ph (8b), CH₂C₆H₄Cl (8c)), Cp′₂Zr(Me)OR (R = CH₂CF₃ (9a), t-Bu (9b)), and Cp′₂Zr(Cl)Ot-Bu (10) were obtained. Treatment of [Mo(CO)₄(norbornadiene)] with either 2, 4 or 9a gives the bis-Cp′ bridged binuclear tetracarbonyl complexes [Cp′₂Zr(Me)(X)Mo(CO)₄] (X = Cl (11), Ph (12), OCH₂CF₃ (13)). Binuclear complexes [Cp′₂Zr(X)( μ-Cl)M(CO)₃] (X = Me, M = Mo, W (14a,b), X = Ot-Bu, M = Mo (16)) which contain an additional bridging chloride ligand were obtained similarly from [M(CO)₃(cycloheptatriene)] and the appropriate zirconium compound. The chloride bridge is readily opened by addition of either PMe₃ or t-BuNC producing complexes [Cp′₂ZrCl₂M(CO)₃L] (L = PMe₃ (18a,b), t-BuNC (19a,b)) and [Cp′₂Zr(Cl)(Me)M(CO)₃PMe₃] (20a,b; M = Mo (a), W (b)). Exchange of zirconium-bound chloride for organic groups is achieved by treatment of 18a,b or 19a,b with LiR which gives [Cp′₂ZrMe₂M(CO)₃L] (L = PMe₃ (21a,b), t-BuNC (22a,b), M = Mo (a), W (b)) as well as [Cp′₂ZrR₂Mo(CO)₃PMe₃] (R = Ph (23), Tol (24)). C-C coupling of two nitrile ligands with a Zr-bound methyl group to give a bridging 1,3-diiminato ligand takes place upon reacting Cp′₂ZrMe₂ (3) with [W(CO)₃(NCR)₃]. The products [Cp′₂Zr( μ-HN-C(R)=CH-C(R)=N)W(CO)₃] (R = Ph (25), CH₂Ph (26)) were fully characterized by magnetic resonance including ¹³C-NMR of the doubly labelled derivative 26*. Protonation of 26 using [PhMe₂NH]BPh₄ gives the corresponding 1,3-diimine complex [Cp′₂Zr( μ-HN=C(R)-CH₂-C(R)=N)W(CO)₃]BPh₄ (R = CH₂Ph, 27).