Dicationic Nickel(II) Carbonyl Complexes Containing Tetradentate Ligands

Abstract

This article describes the preparation and spectroscopic characterization of three dicationic Ni(II) carbonyl complexes containing tripodal tetradentate ligands. An X-ray diffraction study of [Ni(PP 3 E)(CO)](BF 4 ) 2 (where PP 3 E is tris(2-(diethylphosphino)ethyl)phosphine) has been completed and confirms a trigonal bipyramidal structure with an apical carbonyl ligand. The binding of CO is weak and reversible. The stability of these complexes is enhanced by the small chelate bite imposed by the tetradentate ligands. The electrochemical behavior of these complexes depends on the nature of the donor atom trans to CO. The [Ni(NP 3 E)-(CO)] 2+ (where NP 3 E is tris(2-(diethylphosphino)ethyl)amine) cation undergoes two reversible one-electron reductions, whereas the corresponding tetraphosphine cations undergo irreversible two-electron reductions.

Structural Examination of the Nickel Site inChromatium vinosumHydrogenase: Redox State Oscillations and Structural Changes Accompanying Reductive Activation and CO Binding

“…The Ni-C distance refined to 1.78(2) Å, and the Ni-O distance refined to 2.90(2) Å, leading to a C-O bond length of 1.12(4) Å. Although this is short for a C-O bond, it is not without precedent for Ni-CO complexes (57)(58)(59)(60) and indicates that the CO is approximately linear and a terminal ligand of the Ni center.…”

Selective Transformation of Nickel‐Bound Formate to CO or C−C Coupling Products Triggered by Deprotonation and Steered by Alkali‐Metal Ions

“…Bearing in mind that not many Ni II ‐CO complexes are known to date, [25, 28–39] due to the limited ability of Ni II to stabilize such entities via backbonding, we next tested whether a Ni II ‐CO complex with the L t Bu− ligand system would be stable at all and reacted the cationic complex [L t Bu Ni II (OH 2 )][B(Ar F ) 4 ] ( 2 , see S3) with CO gas. A change of color from green to purple could be observed, and evaporation of all volatiles left behind a purple solid.…”

“…Bearing in mind that not many Ni II -CO complexes are known to date, [25,[28][29][30][31][32][33][34][35][36][37][38][39] due to the limited ability of Ni II to stabilize such entities via backbonding,w en ext tested whether aN i II -CO complex with the L tBuÀ ligand system would be stable at all and reacted the cationic complex (Figure 2). Thestructure determination further revealed that one of the aryl rings of L tBu undergoes an h 2 coordination, thus completing as quare planar coordination sphere of the Ni center,w hich also reflects in ad iamagnetic 1 HNMR spectrum of as olution of 3 in CD 2 Cl 2 .…”

Synthesis of α‐Stereogenic Amides and Ketones by Enantioselective Conjugate Addition of 1,4‐Dicarbonyl But‐2‐enes

“…Most of these complexes are five‐coordinate, an observation that has been theoretically justified in terms of a more efficient π back‐donation from the Ni II center to the CO ligand 37. In fact, five‐coordinate nickel monocarbonyl derivatives containing the CO ligand in either axial or equatorial positions, show low‐frequency ν (CO) values as for instance in ( TBPY ‐5‐23)‐[NiI 2 (CO)(fdma)] (fdma=ferrocene‐1,1′‐bis(dimethylarsine); ν (CO)=2054 cm −1 ),38 ( TBPY ‐5‐22)‐[NiI 2 (CO)(PMe 3 ) 2 ] ( ν (CO)=2015 cm −1 )31 and ( TBPY ‐5‐13)‐[Ni(PP 3 E)(CO)] 2+ (PP 3 E=tris{2‐(diethylphosphino)ethyl}phosphine; ν (CO)=2050 cm −1 ) 39. Even in the tricarbonyl derivative ( TBPY ‐5‐11)‐[Ni(SiCl 3 ) 2 (CO) 3 ], the ν (CO) absorption appears at 2079 cm −1 33.…”