Abstract
9-Amino-9-phosphabicyclo[3.3.1]nonanes, (PhobPNHR'; R = Me or (i)Pr) 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(t)Bu)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.
Highlights
Significant differences between the donor properties of phosphacycles and their acyclic analogues are to be expected because of the effects that ring constraints can have on the frontier orbital energies and the steric properties of the P-donor.[1]
The bicyclic compounds PhobPNHR are significantly kinetically stabilised to hydrolysis with respect to the acyclic Cy2PNHR analogues
The resistance to hydrolysis of PhobPNHR is consonant with the phobyl moiety behaving as a bulky group.[12]
Summary
Significant differences between the donor properties of phosphacycles and their acyclic analogues are to be expected because of the effects that ring constraints can have on the frontier orbital energies and the steric properties of the P-donor.[1]. The PPN species L′3 smoothly converted over 30 min to PNP ligand L3 whose structure was confirmed by its conversion to the chelate complex 4 (Scheme 3), the crystal structure of which has been determined (Fig. 4).
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