Nucleophilic displacement reactions of cis-bis((2,2′-biphenylylene)phosphochloridite ester)tetracarbonylmolybdenum(0). The first example of an unusual hydrolysis reaction yielding unsymmetrically substituted products

Academic Article

Abstract

  • Ligands containing groups derived from bis(aryl)diols are widely used in asymmetric catalysis; however, few studies of the conformations of these ligands in transition-metal complexes have been reported. In this paper, the nucleophilic displacement reactions of cis-Mo(CO)4(2,2′-C12H8O2 PCl)2 (1) have been used to prepare a variety of complexes with [1,3,2]-dioxaphosphepin ligands, and the conformations of these ligands have been studied by NMR spectroscopy and X-ray crystallography. The nucleophilic substitution reactions yield both the expected disubstituted complexes cis-Mo(CO)4(2,2′-C12H8O2 PXR)2 (XR = NPrn (2), OMe (4), SC6H4 -4-Me (6)) and the unexpected hydrolysis products [R′3NH] [cis-Mo(CO)4(2,2′-C12H8O2PO)(2 ,2′-C12H8O2PXR)] (R′3 = PrnH2, XR = NPrn, 3; R′3 = Et3; XR = OMe, 5). NMR studies have demonstrated that the hydrolysis product is the major product when more than a minute amount of water is present, even in the presence of a large excess of the nucleophiles. This reaction is complete in approximately 90 min at 25°C. A very surprising feature of this reaction is that substitution of one chloride in 1 by the RX- nucleophile greatly enhances the rate of substitution of the second chloride either by water or by another RX- nucleophile. NMR studies of the [1,3,2]dioxaphosphepin complexes in chloroform-d solution suggest that the R* and S* enantiomers of the ligands interconvert via a low-energy pathway. Crystal structures of the complexes demonstrate that both the R*S* diastereomer (1) and racemic mixtures of the R*R* and S*S* diastereomers (2-4) are observed in the solid state. These results suggest that bulkier biaryl groups are needed to prevent the racemization of the [1,3,2]dioxaphosphepin ligands in solution.
  • Authors

    Published In

  • Organometallics  Journal
  • Digital Object Identifier (doi)

    Author List

  • Byrd H; Harden JD; Butler JM; Jablonsky MJ; Gray GM
  • Start Page

  • 4198
  • End Page

  • 4205
  • Volume

  • 22
  • Issue

  • 21