The facile reaction of water with a bimetallic nickel tetrachloride tetraphosphine: A tale of two chelates

Abstract NMR studies demonstrate that rac - and meso -Ni 2 Cl 4 (P4), P4 = (Et 2 PCH 2 CH 2 )(Ph)PCH 2 P(Ph)(CH 2 CH 2 PEt 2 ), bimetallic complexes readily react with water in different organic solvents (acetone, acetonitrile, DMSO) to dissociate a chloride and most likely form a hydroxide-bridged bimetallic complex, [Ni 2 (μ-OH)Cl 2 (P4)] + . The meso bimetallic complex is very susceptible to dissociation of one of the external chelated phosphines, which leads to loss of one of the nickel atoms. The tetraphosphine ligand recoordinates to the remaining nickel center to form [NiCl(κ 3 - meso -P4)] + , which can, in turn, react with chloride to produce NiCl 2 (κ 2 - meso -P4). The meso diastereomers of these monometallic complexes then react with one another to form a double P4-coordinated bimetallic complex, [Ni 2 (μ-Cl)( meso -P4) 2 ] 3+ , which has been crystallographically characterized. Despite the presence of four bis-phosphino(ethane) chelates around two nickel centers, [Ni 2 (μ-Cl)( meso -P4) 2 ] 3+ readily fragments and can be converted back to the precursor mono- and bimetallic complexes by heating in the presence of chloride and NiCl 2 ·6H 2 O. The racemic dinickel diastereomer, Ni 2 Cl 4 ( rac -P4), also reacts with water to produce [Ni 2 (μ-OH)Cl 2 ( rac -P4)] + , but does not fragment further at room temperature unless oxygen is present. The rac- or meso- Ni 2 Cl 4 (P4-Ph) complexes based on the much stronger chelating tetraphosphine ligand with 1,2-phenylene chelate rings also react readily with water to form a hydroxide-bridged bimetallic complex, but further reaction and fragmentation chemistry is inhibited by the much stronger chelate effect present. [Ni 2 (μ-OH)Cl 2 ( meso -P4-Ph)] + has been crystallographically and spectroscopically characterized along with some intermediate monometallic rac - and meso -P4-Ph nickel complexes from cyanolysis attempts.