Synthesis and characterisation by spectroscopy and X-ray structure determination of palladium complexes containing the 1–3-η-1,2-di-t-butyl-3-methyl-4-methylenecyclobutenyl ligand

Abstract

The (1,2-di-t-butyl-3,4-dimethylcyclobutadiene)palladium complex [Pd₂{C₄(Me)₂( Bu^t)₂}₂Cl₄] reacts with base with loss of HCl to give [Pd₂{C₄:CH₂(Me)(Bu^t)₂}₂Cl₂](2). An X-ray crystal structure determination on the acetylacetonato-derivative [Pd{C₄:CH₂(Me)(Bu^t)₂}(acac)](3) shows the acetylacetonatopalladium 1–3-η-bonded to a cyclobutenyl ligand bearing an unco-ordinated methylene substituent at C⁴, t-butyl groups at C¹ and C², and a methyl at C³. N.m.r. (¹H and ¹³C) spectroscopy showed that the ligand in (2) had the same structure. This was also true of the following derivatives that were synthesised: [Pd₂(A)₂X₂](X = Br, I, or SCN), [Pd(A)(L)Cl](L = Bu^tNC, p-ClC₆H₄NC, p-MeC₆H₄NH₂, PMe₂Ph, PMePh₂, PPh₃, or py), [Pd(A)L₂]⁺[L = SC(NH₂)₂, L₂= Ph₂PCH₂PPh₂, Ph₂PCH₂CH₂PPh₂, 2,2′-bipyridyl, 1,10-phenanthroline, or cyclo-octa-1,5-diene] and [Pd(A)(S₂CNR₂)](R = Et or Prⁱ)[A ={C₄:CH₂(Me)(Bu^t)₂}].