Nickel"II#\ palladium"II#\ and platinum"II# complexes containing cis! or trans!0\1! bis"diphenylphosphino#ethene] isomorphous crystal structures in the cyanide case

Mono! and binuclear NiII\ PdII\ and PtII complexes of cis! or trans!0\1!bis"diphenylphosphino#ethene "cis! or trans!dppen# have been prepared and characterized by X!ray di}raction methods\ 084Pt 0H and 20P 0H NMR spectroscopy\ FAB mass spectrometry\ IR spectroscopy\ elemental analyses and melting points[ The X! ray structures of some rare examples of cis!dicyanide complexes of the type M"CN#1"cis!dppen# "M1Ni "0#\ M1Pd "1#\ M1Pt "2## are given for the _rst time[ All three crystal lattices are isomorphous and allow comparison of the radii of Ni\ Pd\ and Pt atoms[ In 02 the coordination is square planar[ In all cases the ethene bridges are nearly coplanar with the coordination planes\ which can be explained by p!bonding interactions[ Due to the isomorphous crystal lattices\ 02 show analogous shortest intermolecular repulsive CH===M contact approaches leading to small deviations from coplanarity[ The removal of one coordinated chloride in NiCl1"cis!dppen# by AgBF3 followed by subsequent treatment with bis"diphenylphosphino#amine\ NH"PPh1#1 "dppam#\ leads to the novel complex NiCl"cis!dppen# "dppam#"BF3# "3#[ However\ the analogous abstraction of both chlorides in MCl1"cis!dppen# "M1Pd\ Pt# and reaction with dppam produces M"cis!dppen#"dppam#"BF3#1 "M1Pd "4#\M1Pt "5##[ In the case of trans! dppen\ the reaction with Pd"CN#1 leads to another novel cis!dicyanide complex of the type Pd1"CN#3"m! trans!dppen#1 "6#[ Substitution of chloride in Pt1Cl3"m!trans!dppen#1 by cyanide leads to the analogous PtII compound Pt1"CN#3"m!trans!dppen#1 "7#[ It is believed\ that the unsaturated nature of cis! or trans!dppen leading to p!bonding interactions with the metal!ligand bonds\ is responsible for the unusual stability of cis! dicyanide complexes[ For dppam the presence of electronic delocalization is well!known[ These e}ects are discussed in view of the X!ray structures of 02 and related compounds[