A readily-prepared and efficient solid-supported scavenger for molybdenum alkoxides and a structurally characterized model complex

A very effective solid support for the removal of molybdenum-based metathesis catalysts can be prepared by placing a salicylimine on a polystyrene support. The resin is produced by treating Merrifield’s resin with H₂NBuⁿ, 4-chloromethylsalicylaldehyde, and p-toluidine in succession. The final resin had an identifiable CN stretch in the IR and a resonance assigned to the HCN hydrogen was found by MAS ¹H NMR of the swelled resin. Solutions of MoC(H)CMe₂Ph](NAr)(OBu^t_F6)₂ (Mo_F6) and MoC(H)CMe₂Ph](NAr)(OAd)₂ (Mo_Ad), where Ar = 2,6-diisopropylphenyl and Ad = 1-adamantyl, were treated with the scavenger, which reduced the remaining molybdenum concentration as examined by ICP-MS to 30-50 ppb. Catalyst was also scavenged from ring-closing metathesis of diethyl diallylmalonate by Mo_F6; the decrease in molybdenum concentration on addition of scavenger followed first order kinetics with initial and final concentrations of 54 000 and 15 ppb, respectively. We also prepared a model system where a soluble salicylimine (H-DIB) was reacted with MoC(H)CMe₂Ph](NAr)(OAd)₂ to produce MoC(H)CMe₂Ph](NAr)(DIB)₂, which was structurally characterized.