Stabilization of Nickel Complexes with Ni0•••H-N Bonding Interactions Using Sterically Demanding Cyclic Diphosphine Ligands
The series of complexes Ni(P{sub 2}{sup tBu}N{sub 2}{sup R}), [Ni(P{sub 2}{sup tBu}N{sub 2}{sup R}){sub 2}]BF{sub 4}, [HNi(P{sub 2}{sup tBu}N{sub 2}{sup Ph}){sub 2}]BF{sub 4}, and [Co(P{sub 2}{sup tBu}N{sub 2}{sup Ph}){sub 2}]BF{sub 4} (P{sub 2}{sup tBu}N{sub 2}{sup R} = 1,5-dialkyl-3,7-tert-butyl-1,5-diaza-3,7-diphosphacyclooctane; alkyl (R) = phenyl, benzyl) have been synthesized and characterized. Spectroscopic, electrochemical, and X-Ray diffraction studies indicate these complexes are stable as a result of the tetrahedral arrangement of the two diphosphine ligands. Electrochemical oxidation of [HNi(P{sub 2}{sup tBu}N{sub 2}{sup Ph}){sub 2}]BF{sub 4} results in rapid proton transfer from nickel at a rate faster that can be observed on the CV timescale. Double protonation of Ni(P{sub 2}{sup tBu}N{sub 2}{sup BN}){sub 2} forms the endo-endo, endo exo, and exo-exo isomers of [Ni(P{sub 2}{sup tBu}N{sup BN}HN{sup BN}){sub 2}](BF{sub 4}){sub 2}, which were found to be more stable towards loss of H{sub 2} than previously observed for similar complexes. The presence of Ni{sup 0} {hor_ellipsis} HN bonds at the endo-protonation sites of [Ni(P{sub 2}{sup tBu}N{sup Bn}HN{sup BN}){sub 2}](BF{sub 4}){sub 2} results in significant differences in the Ni(I/0) oxidation potentials of each of the isomers. The differences in E{sub 1/2}(I/0) values correspond to bond free energies of 7.4 and 3.7 kcal/mol for the first and second Ni{sup 0} {hor_ellipsis} HN bonds of the endo-exo and endo-endo isomers, respectively. Computational studies of related model complexes reproduce these Ni{sup 0} {hor_ellipsis} HN bonds within 1-2 kcal/mol.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1033050
- Report Number(s):
- PNNL-SA-81603; KC0302010; KC0307010
- Journal Information:
- Organometallics, Journal Name: Organometallics Journal Issue: 1 Vol. 31; ISSN ORGND7; ISSN 0276-7333
- Country of Publication:
- United States
- Language:
- English
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