Preparation and carbon-13 nuclear magnetic resonance spectroscopic study of isonitrile substituted derivatives of [Os3(CO)12]

Abstract

The preparation of the complexes [Os₃(CO)_12–n(CNR)_n](n= 1 or 2 for R = Me, C₆H₄OMe, Buⁿ, or Bu^t; n= 3 or 4 for R = Buⁿ or Bu^t) is described. A variable-temperature ¹³C n.m.r. spectroscopic study of these complexes shows that, for n= 1, only the axial isomer is present in significant concentrations in solution at low temperatures, except for the most bulky ligand, CNBu^t, for which an equilibrium mixture of the axial and equatorial isomer is obtained at –60 °C. Above 0 °C these isomers interconvert rapidly on the n.m.r. time scale. For n= 2 only the trans-diaxially substituted isomers are present at low temperatures except in the case of CNBu^t for which a mixture of the trans-diaxial and a diequatorially substituted isomer is obtained. For the trisubstituted complex both CNBuⁿ and CNBu^t give a mixture of isomers at low temperature which again interconvert rapidly at higher temperatures. The same is true of the tetrasubstituted complex with CNBuⁿ as a ligand but with CNBu^t only an all-axially substituted isomer is found.