Variable coordination geometries via an amine-tethered-enamidophosphinimine ligand on cobalt

The synthesis of two new amine-tethered enamidophosphinimine donor sets is described and their coordination chemistry with cobalt(ii) detailed. Deprotonation of the enamine tautomers of each system generates the lithium derivatives that are used in metathesis reactions with either anhydrous CoCl₂ or CoCl₂(THF)_1.5 to generate tetrahedral κ³-(NNpN^R)CoCl (where R = DIPP, 2,6-diisopropylphenyl; R = TMS, trimethylsilyl) or tetrahedral κ²-(NNpN^TMS)₂Co, the latter likely due to the insolubility of the CoCl₂. For the R = DIPP derivative, replacement of the chloride proceeds smoothly by methathesis with LiCH₂SiMe₃ and KBEt₃H to generate the bulky alkyl derivative κ³-(NNpN^DIPP)CoCH₂SiMe₃, and the dihydride-bridged dimer [κ²-(NNpN^DIPP)Co]₂(μ-H)₂, respectively; interestingly, the hydride dimer has the diethylaminoethyl arms uncoordinated. Reduction of κ³-(NNpN^DIPP)CoCl with KC₈ under dinitrogen generates the π-arene complex, κ²:η⁶-(NNpN^DIPP)Co, and not the expected N₂ complex. In an attempt to generate a dinitrogen complex, we investigated the metathesis and reduction chemistry of the N-trimethylsilyl substituted phosphinimine cobalt derivative, κ³-(NNpN^TMS)CoCl. Although reaction with LiCH₂SiMe₃ produced the anticipated tetrahedral Co(ii) alkyl complex κ³-(NNpN^TMS)Co(CH₂SiMe₃), reaction with KBEt₃H and KC₈ did not give the analogous products to that of the DIPP derivative; instead, the reaction with hydride was complicated and the only product isolated was the bis(ligand) derivative, κ²-(NNpN^TMS)₂Co, while reaction with KC₈ under N₂ generated the C-H activated complex κ⁴-(NNpNSiMe₂CH₂)Co. Many of these complexes have been characterized by single-crystal X-ray analysis, elemental analysis and solution magnetic susceptibility measurements. In addition, a number of these derivatives were screened for their ability to act as catalyst precursors for the hydrosilylation of 1-hexene.