Use of Michael additions to (Ph2P)2CCH2 complexes to prepare thiophene- and pyrrole-functionalised metal–phosphine complexes

Abstract

The complex [Pd(O₂CMe)₂(vdpp)]1a[vdpp =(Ph₂P)₂CCH₂] undergoes nucleophilic addition at the double bond with primary alcohols to afford [Pd(O₂CMe)₂{(Ph₂P)₂CHCH₂OR}]2[R = Me, Et, CH₂CH₂C₄H₃S-3 or CH₂C₆H₃(OMe)₂-3,4]. These were not isolated pure, but metathesis with Nal gave the corresponding diiodides 3, which were isolated, and have been fully characterised by microanalysis and infrared and NMR (¹H and ³¹P-{¹H}) spectroscopies. By using 2-(3-thienyl)ethanol as the nucleophile, the complex, [Pdl₂{(Ph₂P)₂CHCH₂OCH₂CH₂C₄H₃S-3}]3c was obtained, and its electrochemistry examined. The reactivity of the double bond in 1a towards other potential weak nucleophiles has been examined. In particular, pyrrole underwent electrophilic addition with 1a to give, after work-up with Nal, [Pdl₂{(Ph₂P)₂CHCH₂C₄H₃NH}]4b. Proton NMR spectroscopy established that 4b was a mixture of 2- and 3-pyrrole isomers (ca. 3 : 1). The complexes [MCl₂(vdpp)](M = Pd 1c or Pt 1d) were less reactive, but underwent addition with alcohols in the presence of NEt₃ as catalyst to afford [MCl₂{(Ph₂P)₂CHCH₂OR}](M = Pd 5 or Pt 6, R = Et or CH₂CH₂C₄H₃S-3). The complex [Pt(vdpp)₂][PF₆]₂7 has been prepared from [PtCl₂(PhCN)₂], vdpp and AgPF₆ in dichloromethane–acetonitrile. Details of the reaction of 7 with 2-(3-thienyl)ethanol are given. The crystal structure of 3c has been determined.