Pentacoordinate Nickel( II ) Complexes Double Bridged by Phosphate Ester or Phosphinate Ligands: Spectroscopic, Structural, Kinetic, and Magnetic Studies

The bis(phosphatediester)‐bridged complexes [{Ni([12]aneN 3 )(μ‐O 2 P(OR) 2 )} 2 ](PF 6 ) 2 {[12]aneN 3 =Me 3 [12]aneN 3 , 2,4,4‐trimethyl‐1,5,9‐triazacyclododec‐1‐ene; R=Me ( 1 ), Bu ( 2 ), Ph ( 3 ), Ph‐4‐NO 2 ( 4 ); [12]aneN 3 =Me 4 [12]aneN 3 , 2,4,4,9‐tetramethyl‐1,5,9‐triazacyclododec‐1‐ene; R=Me ( 5 ), Bu ( 6 ), Ph ( 7 ), Ph‐4‐NO 2 ( 8 )} were prepared by hydrolysis of the phosphate triester with the hydroxo complex [{Ni([12]aneN 3 )(μ‐OH)} 2 ](PF 6 ) 2 or by acid–base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid–base reaction was also used to synthesise the phosphinate‐bridged complexes [{Ni([12]aneN 3 )(μ‐O 2 PR 2 )} 2 ](PF 6 ) 2 {[12]aneN 3 =Me 3 [12]aneN 3 , R=Me ( 9 ), Ph ( 10 ); [12]aneN 3 =Me 4 [12]aneN 3 , R=Me ( 11 ), Ph ( 12 )}. The molecular structures of complexes 2 , 3 and 12 were established by single crystal X‐ray diffraction studies. The eight‐membered rings defined by the nickel atoms and the bridging ligands show distorted twist‐boat, chair and boat–boat conformations in 2 , 3 and 12 , respectively. The experimental susceptibility data for compounds 2 , 3 and 12 were fitted by least‐squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J =−0.11 cm −1 , D =−9.5 cm −1 and g =2.20 for 2 ; J =−0.97 cm −1 , D =−9.3 cm −1 and g =2.21 for 3 ; and J =−0.14 cm −1 , D =−11.9 cm −1 and g =2.195 for 12 . The magnetic‐exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the OPO bridges. The kinetics for the hydrolysis of TNP (tris(4‐nitrophenyl)phosphate) with the dinuclear nickel( II ) hydroxo complex [{Ni(Me 3 [12]aneN 3 )(μ‐OH)} 2 ](PF 6 ) 2 was studied by UV‐visible spectroscopy. The proposed mechanism for TNP‐promoted hydrolysis can be described as one‐substrate/two‐product, and can be fitted to a Michaelis–Menten equation.