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

Abstract

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-(NNpNR)CoCl (where R = DIPP, 2,6-diisopropylphenyl; R = TMS, trimethylsilyl) or tetrahedral κ2-(NNpNTMS)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-(NNpNDIPP)CoCH2SiMe3, and the dihydride-bridged dimer [κ2-(NNpNDIPP)Co]2(μ-H)2, respectively; interestingly, the hydride dimer has the diethylaminoethyl arms uncoordinated. Reduction of κ3-(NNpNDIPP)CoCl with KC8 under dinitrogen generates the π-arene complex, κ2:η6-(NNpNDIPP)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-(NNpNTMS)CoCl. Although reaction with LiCH2SiMe3 produced the anticipated tetrahedral Co(ii) alkyl complex κ3-(NNpNTMS)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-(NNpNTMS)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.