HOMOLEPTIC CARBENE COMPLEXES .6. BIS(1,2'-METHYLENE-3,3'-DIALKYL-DIIMIDAZOLIN-2,2'-DIYLIDENE)PALLADIUM CHELATE COMPLEXES BY THE FREE CARBENE ROUTE

1,1'-Methylene-3,3'-dialkyldiimidazolium salts have been deprotonated with n-butyllithium in the presence of palladium(II) iodide to give the percarbene complexes 1 (alkyl = Me) and 2 (alkyl = Et), each containing two bidentate 1,1'-methylene-3,3'-dialkyldiimidazolin-2,2'-diylidene chelate ligands. The X-ray structure analysis of 1 reveals a stereochemistry in which the two spiro-linked six-membered metallacycles adopt boat-like conformations strongly bending out of the PdC4 coordination plane in opposite directions. The carbenoid imidazole rings, which are rotated by +42 and -43 degrees, respectively, relative to this plane, break down into two tightly bound pi-systems (N=4C=4N, (C=C) connected by long C-N bonds.