The Insertion of Carbon Dioxide in Combination with RNCS (R Is Et, Ph) or N,N′-Dihexylcarbodiimide into the Re–O(R) Bonds

Abstract

The heteromolecular insertion of carbon dioxide in combination with heterocumulenes, iso(thio)cyanates or N,N′-dicyclohexylcarbodiimide, into rhenium–alkoxy group bond was accomplished for the first time in relation to reactivity of rhenium oxoalkoxides. The ease of combined insertion of iso(thio)cyanate and carbon dioxide into Re–O(Me) bond is determined by the nature of the heterocumulene organic group. Indeed, if ethyl iso(thio)cyanate is used in the reaction, the insertion is reversible, whereas the reaction with PhNCS (unlike PhNCO) together with carbon dioxide leads to complete insertion into two Re–O(R) bonds to give the insertion product (OMe)₁₀O₆Re₄[OC(O){N(Ph)C(S)}₂-OMe]₂. In similar reactions carried out with N,N′-dicyclohexylcarbodiimide, a dependence of the number of bonds participating in the inner-sphere condensation of the inserted moieties on the duration of the experiment was found for the first time. An increase in the time of synthesis from 3 to 5 h results in insertion involving six rather than three bonds, the heteromolecular insertion products being (OMe),O₆Re₄{OC(O)[(Hex)N=C=N(Hex)]₂}₃ and (OMe)₆O₆Re₄{OC(O)[(Hex)N=C=N(Hex)]₂}₆, respectively.