Nuclear magnetic resonance spectra of d4-complexes of rhenium(III) and osmium(IV) with phosphine and arsine ligands

Abstract

N.m.r. data are reported for paramagnetic complexes of rhenium(III) of the type ReX₃(PR₂Ph)₃(X = Cl, and R = Me Et, Prⁿ, or Buⁿ; X = Br, R = Me or Et) and for ReCl₃(AsMe₂Ph)₃. Results for osmium(IV) complexes, OsCl₄(PR₂Ph)₂(R = Me, Et, Prⁿ, or Buⁿ) are also reported. The data are interpreted in terms of meridional structures for rhenium(III) and trans-structures for osmium(IV). Temperature studies support a second-order Van Vleck mechanism for the paramagnetism, and an anisotropic susceptibility effect on the chemical shifts. A detailed discussion of conformation problems is given which supports the idea of concerted rotation of the methylene groups in the propyl and butyl compounds.