Cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane: Tedicyp, an Efficient Ligand in Palladium-Catalysed Reactions

Abstract

A tetraphosphine, the cis,cis,cis-1,2,3,4-tetrakis(diphen­ylphosphinomethyl)cyclopentane (Tedicyp), has been synthesised and used in Pd catalysis. This tetraphosphine in combination with [(η3-C3H5)PdCl]2 affords a catalyst precursor which is amongst the most active in allylic substitution, Heck, Suzuki or Sonogashira-type reactions. Turnover numbers up to 980,000 for allylic amination, 9,800,000 for allylic alkylation, 97,000,000 for Suzuki cross-coupling, 2,800,000 for Sonogashira alkynylation and 210,000,000 for Heck reaction have been obtained with this catalyst precursor. This complex seems to be very stable. This stability probably comes from the presence of the four diphenylphosphinoalkyl groups stereospecifically bound to the same face of the cyclopentane ring, which probably increases the coordination of the ligand to the metal and therefore, the catalyst longevity. Ligands are also often needed in order to modulate the rate of some of the catalytic steps like oxidative addition or reductive elimination. The ‘pressure to coordinate’ resulting of the presence of these four phosphines in a half space might also accelerate the reductive elimination step in the catalytic cycles. The complex formed by association of Tedicyp and [(η3-C3H5)PdCl]2 seems to possess a fine balance of steric and electronic properties, which allow fast catalytic processes with a very wide variety of substrates.