Aminophobanes: hydrolytic stability, tautomerism and application in Cr-catalysed ethene oligomerisation

Abstract

9-Amino-9-phosphabicyclo[3.3.1]nonanes, (PhobPNHR′; R = Me or ⁱPr) are readily prepared by aminolysis of PhobPCl and are significantly less susceptible to hydrolysis than the acyclic analogues Cy₂PNHR′. Treatment of Cy₂PNHMe with Cy₂PCl readily gave Cy₂PNMePCy₂. By contrast, treatment of PhobPCl with PhobPNHMe in the presence of Et₃N does not afford PhobPNMePPhob but instead the salt [PhobP(NMeH)PPhob]Cl is formed which, upon addition of [PtCl₂(NC^tBu)₂] gives the zwitterionic complex [PtCl₃(PhobP(NMeH)PPhob)]. The neutral PhobP(NMe)PPhob is accessible from PhobNMeLi and is converted to the chelate [PdCl₂(PhobPNMePPhob)] by addition of [PdCl₂(cod)]. The anomalous preference of the PhobP group for the formation of PPN products is discussed. The unsymmetrical diphos ligands PhobPNMePAr₂ (Ar = Ph, o-Tol) are prepared, converted to [Cr(CO)₄(PhobPNMePAr₂)] and shown to form Cr-catalysts for ethene oligomerisation, producing a pattern of higher alkenes that corresponds to a Schulz-Flory distribution overlaid on selective tri/tetramerisation.