Macrocyclic complexes containing a platinacycle or palladacycle composed of an isocyanate dimer unit: Reactivity towards isocyanides and cyclotrimerization of isocyanates

Abstract

The reactions of [Pt(styrene)(PMe3)2] with 2equiv. of alkyl or aryl isocyanate affored five-membered platinacycles, cis-[Pt{–N(R)C(O)N(R)C(O)–}(PMe3)2] (R=CH2C6H5, p-ClC6H4, p-OMeC6H4). These complexes are the first examples of platinacycles containing an isocyanate dimer unit. When the five-membered bis(phosphine) platinacycles or palladacycles were treated with 2equiv. of elemental sulfur, 16-membered cyclic products as an assembly of four platinacycles or palladacycles, [M(PR3){–N(R)C(O)N(R)C(O)–}]4, were readily obtained. These cyclic tetramers were cleaved using tert-butyl isocyanide (CN–tbutyl, 4equiv.), affording the corresponding monomeric complexes, [M(PR3)(CN–tbutyl){–N(R)C(O)N(R)C(O)–}] (M=Pt, Pd). An unusual cyclotrimerization of organic isocyanates catalyzed by zerovalent Pt complexes or five-membered platinacycles was observed. In addition, the direct cyclotrimerization of alkyl or aryl isocyanates using dialkyl Pt(II) or Pd(II) complexes was investigated. The cross cyclotrimerization of an aryl isocyanate and its derivative using a zerovalent Pd complex was also investigated.