14-electron disilene palladium complex having strong pi-complex character

The first 14-electron disilene palladium complex eta2-tetrakis(tert-butyldimethylsilyl)disilene](tricyclohexylphosphine)palladium (4) was synthesized. In the solid state, complex 4 has one tricyclohexylphosphine ligand bound unsymmetrically to the palladium center in regard to the eta2-disilene moiety. The elongation of the Si-Si bond length from that of the corresponding free disilene (3.2%) and the bent back angles of the disilene moiety (4.41 degrees and 9.65 degrees ) for 4 were much smaller than those for the corresponding 16-electron eta2-disilene complex (Me3P)2Pdtetrakis(tert-butyldimethylsilyl)disilene] (4.6% and 27.2 degrees , respectively). Complex 4 is regarded as the complex having the strongest pi-complex character among the known disilene complexes. Highly symmetric NMR spectra were observed for 4; central Si1 and Si2 nuclei were equivalent and appeared as a doublet with 2J(29Si-31P) of 19 Hz, indicating facile flipping of the phosphine ligand in the Pd-Si-Si plane.