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

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The (1,2-di-t-butyl-3,4-dimethylcyclobutadiene)palladium complex [Pd2{C4(Me)2( But)2}2Cl4] reacts with base with loss of HCl to give [Pd2{C4:CH2(Me)(But)2}2Cl2](2). An X-ray crystal structure determination on the acetylacetonato-derivative [Pd{C4:CH2(Me)(But)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 = ButNC, 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)(But)2}].