Crown thioethers and the kinetic macrocyclic effect. Solvolysis of molybdenum(0) tricarbonyl complexes of cyclic and acyclic trithioethers

Abstract

Solvolysis of the macrocyclic trithioether complexes fac-[Mo(CO)3([9]aneS3)] ([9]aneS3 = 1,4,7-trithiacyclononane) and fac-[Mo(CO)3(ttob)] (ttob = 2,5,8-trithia[9]-o-benzenophane), and the acyclic trithioether complex fac-[Mo(CO)3(ttn)] (ttn = 2,5,8-trithiononane) in dimethylsulfoxide (DMSO) solution gives the free trithioether in each case. The kinetics of these reactions were studied by 1H-n.m.r. spectroscopy. In the absence of acid or base, the rate of solvolysis of [Mo(CO)3([9]aneS3)] is at least 4.6 × 105 slower than that of [Mo(CO)3(ttn)]; larger macrocycles give intermediate rates. [Mo(CO)3-([9]aneS3) and [Mo(CO)3(ttob)] undergo stoichiometric reactions with acid and base in DMSO which in all cases lead to more rapid loss of the intact macrocycle than in DMSO alone. The results are discussed in terms of the structure and bonding of likely intermediate complexes.