A T-Shaped Three-Coordinate Nickel(I) Carbonyl Complex and the Geometric Preferences of Three-Coordinate d⁹ Complexes

Abstract

A three-coordinate diketiminate-nickel(I) complex with a carbonyl ligand has been characterized using EPR and IR spectroscopies and X-ray crystallography. The T geometry (bending from the sterically favored C 2v structure) contrasts with that of isosteric d 9 copper(II) complexes. DFT calculations on a truncated model reproduce experimental geometries, implying that the geometric differences are electronic in nature. Analysis of the charge distribution in the complexes shows that the geometry of the threecoordinate d 9 complexes is affected by differential charge donation of the ligands to the metal center.Three-coordinate complexes of transition metals with partially filled d shells have received attention because of their unusual reactivity and electronic structure. 1 The predominant geometry in crystallographically characterized three-coordinate complexes is trigonal-planar, with the ligands symmetrically distributed to minimize steric effects. The main exception to this generalization is with low-spin d 8 systems, which clearly favor a T-shaped geometry. 2 In recent papers, we described the synthesis and electronic structure of a series of three-coordinate complexes with d 6 , d 7 , d 8 , and d 9 electronic configurations at the metal center. 3,4 A bulky -diketiminate ligand ("L") was used, and a sterically favored Y geometry was evident at the metal in each case. In the Y geometry, the nickel coordination environment is idealized C 2V , with the non-diketiminate ligand on both mirror planes. The d 9 example, L tBu Ni(THF) (Figure 1, left), is notable because there are few examples of isolable three-coordinate nickel(I) complexes, 5 one series of three-coordinate copper(II) complexes, 6 and no threecoordinate d 9 complexes of heavier metals. Understanding of three-coordinate nickel(I) complexes is also biologically relevant because three-coordination is potentially accessible in the low-coordinate "proximal" nickel site of acetylcoenzyme A synthase (where methylcobalamin, CO, and coenzyme A are transformed into acetyl-coenzyme A). 7 Below, we use synthetic, crystallographic, and theoretical studies to show that the first three-coordinate nickel(I) carbonyl complex prefers a T geometry. We compare it to relevant nickel(I) and copper(II) complexes to arrive at new * To whom correspondence should be addressed. E-mail: tomc@unt.edu (T.R.C.), holland@chem.rochester.edu (P.L.H. . Ellipsoids are at 50% probability, and hydrogen atoms are omitted for clarity.

Monovalent Nickel Complex Bearing a Bulky N-Heterocyclic Carbene Catalyzes Buchwald–Hartwig Amination of Aryl Halides under Mild Conditions

“…The T-or Y-shape of the threecoordinate nickel species has sometimes been discussed in reports, 15 probably due to not steric reasons but to some electronic influence arising from the ligands. 16 In our case, we discussed that difference of the electronic properties in NHC and PPh 3 ligands may also lead to such shape differences. Each bond distance between Ni(1) and Cl(1), P(1), or C(1) is in the range of normal single bond length, 2.179 (9) 2 previously, suggesting that most of the unpaired electron does not exist in the ligands but in the independent d orbital of nickel.…”

Glückszahl Sieben: Charakterisierung stabiler, T‐förmiger Kupfer(II)‐Komplexe von [32]Heptaphyrinen

“…Alle diese Komplexe sind diamagnetische 14-oder 16-Elektronen-Spezies, mit Ausnahme eines paramagnetischen d 9 -Nickel(I)-Carbonylkomplexes. [17] Der Paramagnetismus der Heptaphyrin-Komplexe, der für ihre Formulierung als Kupfer(II)-Systeme ausschlaggebend ist, wurde durch Messungen der magnetischen Suszeptibilität und EPR-Spektren der Festkörper nachgewiesen. Aus spektroskopischer Sicht am wertvollsten sind Spin-Hamilton-Daten, gewonnen aus dem EPR-Spektrum des "Originalsystems", d. h. aus dem Kupferkomplex des tetra-Nkondensierten Heptaphyrins.…”

Nacnac …︁ Are You Still There? The Evolution of β‐Diketiminate Complexes of Nickel

“…Specifically, distortion has been ascribed to both differential charge donation and Pauli repulsions of the third donor X. [7,8] Prior to b-diketiminates ligands taking the spotlight in stabilizing unusually low-coordination environments of mononuclear Ni I , examples of such systems were scant.…”