Jump to main content
Jump to site search

Issue 12, 1979
Previous Article Next Article

Formation of large chelate rings and cyclometallated products from diphosphines of type But2P(CH2)nPBut2(n= 5–8) and Ph2P(CH2)5PPh2 with palladium and platinum chlorides: factors affecting the stability and conformation of large chelate rings

Abstract

The new diphosphines But2P(CH2)nPBut2(n= 5–7) are described and the previously known Ph2P(CH2)5PPh2 characterized more fully. The compounds, But2P(CH2)nPBut2(n= 5–8) react with [PdCl2(NCPh)2] to give crystalline complexes of the type [{PdCl2[But2P(CH2)nPBut2]}x], where x= 2 for n= 5, 7, or 8 but unknown for n= 6. Also for n= 5 a volatile cyclometallated complex [[graphic omitted]But2)] is formed. With [PtCl2(NCPh)2] or [PtCl2(NCBut)2], But2P(CH2)5Pbut2 gives trans-[{PtCl2[But2P(CH2)5PBut2]}x](x is unknown) and a cyclometallated product [[graphic omitted]But2)](X = Cl) contaminated by a very similar species, possibly [[graphic omitted]But2)] from which it could not be separated. The complex [{PtCl2[But2P(CH2)5PBut2]}x] with CF3CO2H, however, gives pure [[graphic omitted]But2)](X = O2CCF3) in almost quantitative yield and other pure complexes of this type with X = Cl, Br, I, or H are readily prepared by metathesis. The compound But2P(CH2)6PBut2 with [PtCl2(NCPh)2] gives trans-[{PtCl2[But2P(CH2)6PBut2]}x](x is unknown) and the cyclometallated [[graphic omitted]But2)]. A remarkable difference in extent of deuteriation is observed on treating [[graphic omitted]But2)](X = Cl or Br) with CF3CO2D. The chloro-complex is not deuteriated but the bromo-complex is deuteriated in both t-butyl and methylene groups. Using 31P n.m.r. spectroscopy the large-chelate mixed compounds described in this and previous papers, containing PBut2 groups in ‘corner’ positions, are shown to be stable in solution relative to open-chain structures. The complexes trans-[Pd2Cl4{Ph2P(CH2)5PPh2}2] and cis-[Pt2Cl4{Ph2P(CH2)5PPh2}2] are described. The literature on large-chelate-ring compounds is surveyed. Factors affecting the stability and conformational homogeneity of carbocyclic and hetero-substituted rings, cyclic peptides, and depsipeptides, and cyclic monomer–polymer equilibria are discussed. Since the effects of sterically demanding substituents on the stability of purely organic rings (large and otherwise) has been explained purely in terms of bond lengths, angles, torsion angles, etc., sterically demanding substituents must have similar effects on chelate rings. Enthalpy and entropy factors affecting the stability of large chelate rings and their conformational homogeneity in solution are discussed from this point of view. Infrared, 1H, 13C, and 31P n.m.r., and mass spectral data are given and discussed.

Back to tab navigation
Please wait while Download options loads

Article type: Paper
DOI: 10.1039/DT9790001972
Citation: J. Chem. Soc., Dalton Trans., 1979, 1972-1982
  •   Request permissions

    Formation of large chelate rings and cyclometallated products from diphosphines of type But2P(CH2)nPBut2(n= 5–8) and Ph2P(CH2)5PPh2 with palladium and platinum chlorides: factors affecting the stability and conformation of large chelate rings

    N. A. Al-Salem, H. D. Empsall, R. Markham, B. L. Shaw and B. Weeks, J. Chem. Soc., Dalton Trans., 1979, 1972
    DOI: 10.1039/DT9790001972

Search articles by author