Abstract
Reactions of [MoReCp(μ-PMes*)(CO)(6)] with internal alkynes RC≡CR yielded the phosphapropenylidene-bridged complexes [MoReCp(μ-κ(2)(P,C):η(3)-PMes*CRCR)(CO)(5)] (Mes* = 2,4,6-C(6)H(2)(t)Bu(3); R = CO(2)Me, Ph). Terminal alkynes HC≡CR(1) gave mixtures of isomers [MoReCp(μ-κ(2)(P,C):η(3)-PMes*CHCR(1))(CO)(5)] and [MoReCp(μ-κ(2)(P,C):η(3)-PMes*CR(1)CH)(CO)(5)], with the first isomer being major (R(1) = CO(2)Me) or unique (R(1) = (t)Bu), indicating the relevance of steric repulsions during the [2 + 2] cycloaddition step between Mo=P and C≡C bonds in these reactions. Similar reactions were observed for [MoMnCp(μ-PMes*)(CO)(6)]. Addition of ligands to these complexes promoted rearrangement of the phosphapropenylidene ligand into the allyl-like μ-η(3):κ(1)(C) mode, as shown by the reaction of [MoReCp(μ-κ(2)(P,C):η(3)-PMes*CHC(CO(2)Me)}(CO)(5)] with CN(p-C(6)H(4)OMe) to give [MoReCp{μ-η(3):κ(1)(C)-PMes*CHC(CO(2)Me)}(CO)(5){CN(p-CH(4)OMe)}(2)]. The MoRe phosphinidene complex reacted with S=C=NPh to give as major products the phosphametallacyclic complex [MoReCp{μ-κ(2)(P,S):κ(2)(P,S)-PMes*C(NPh)S}(CO)(5)] and its thiophosphinidene-bridged isomer [MoReCp(μ-η(2):κ(1)(S)-SPMes*)(CO)(5)(CNPh)]. The first product follows from a [2 + 2] cycloaddition between Mo=P and C=S bonds, with specific formation of P-C bonds, whereas the second one would arise from the alternative cycloaddition involving the formation of P-S bonds, more favored on steric grounds. The prevalence of the μ-η(2):κ(1)(S) coordination mode of the SPMes* ligand over the μ-η(2):κ(1)(p) mode was investigated theoretically to conclude that steric congestion favors the first mode, while the kinetic barrier for interconversion between isomers is low in any case.