Novel diphenylphosphine derivatives of 2,2′-bithiophene, 2,2′:5′,2"-terthiophene, 2-(2′-thienyl)pyridine and 2,6-di-2′-thienylpyridine.: Crystal structures of 5,5′-bis(diphenylphosphino)-2,2′-bithiophene, diphenyl{5-[6′-(diphenylphosphino)-2′-pyridyl]-2-thienyl}phosphine and 2,6-bis[5′-(diphenylphosphino)-2′-thienyl]pyridine

We report the synthesis and characterisation of eight molecules that have in common a diphenylphosphino group bonded to an alpha -carbon atom of a thienyl or pyridyl ring: 5,5'-bis(diphenylphosphino)-2,2'-bithiophene 1; diphenyl(2,2'-bithienyl-5-yl) phosphine 2; 5,5"-bis(diphenylphosphino)-2,2': 5', 2"-terthiophene 3; diphenyl(2,2': 5', 2"-terthienyl-5-yl)phosphine 4; diphenyl[5-(2'-pyridyl)-2-thienyl]phosphine 5; diphenyl[6-(2'-thienyl)-2- pyridyl]phosphine 6; diphenyl{5-[6'-(diphenylphosphino)-2'-pyridyl]-2-thienyl}phosphine 7; and 2,6-bis[5'-(diphenylphosphino)-2'-thienyl]pyridine 8. Methods used for their synthesis range from lithiation of the parent heterocycle and subsequent reaction with PPh2Cl to the use of coupling reactions catalysed by metal complexes to assemble the molecule from its subunits. The crystal and molecular structures of 1, 7 and 8 have been determined and show that the 2,2'-bithienyl moiety in 1 adopts an s-trans-conformation, while the 2-(2'-thienyl) pyridyl moieties in 7 and 8 adopt s-cis-conformations in the solid state. These compounds represent a new series of ligands that are expected to bond to metals through the phosphorus and/or nitrogen atoms rather than a sulfur atom, in view of the poor donor ability of a thiophene sulfur towards metals.