Preparation, Crystal Structures, and Spectroscopic and Redox Properties of Nickel(II) Complexes Containing Phosphane–(Amine or Quinoline)‐Type Hybrid Ligands and a Nickel(I) Complex Bearing 8‐(Diphenylphosphanyl)quinoline

Abstract

Nickel(II) complexes containing P–N‐type bidentate hybrid ligands of 2‐aminoethylphosphanes (RR′Pea; RR′ = Ph2 or MePh) or 8‐quinolylphosphanes (RR′Pqn), namely [Ni(P–N)2](BF4)2 [P–N = Ph2Pea (1), MePhPea (2), Ph2Pqn (3), or MePhPqn (4)] have been prepared, and their structural, spectroscopic, and electrochemical properties determined. The crystal structure analysis indicates that the 2‐aminoethylphosphane complexes (1 and 2) have a square‐planar coordination geometry around the NiII center with a cis(P,P) configuration, whereas the 8‐quinolylphosphane complexes (3 and 4) exhibit a severe tetrahedral distortion because of the steric repulsion between the ortho‐H atoms in the mutually cis‐positioned quinolyl rings. Complexes 1 and 2 maintain their diamagnetic square‐planar four‐coordinate structure on acetonitrile solution, whereas complexes 3 and 4 show paramagnetic behavior. Spectroscopic and electrochemical measurements suggest that the ligand‐field strengths of these four P–N‐type ligands increase in the order Ph2Pqn (3) < MePhPqn (4) < Ph2Pea (1) < MePhPea (2). The Ph2Pqn complex 3 is readily reduced by Zn powder to afford the corresponding nickel(I) complex [Ni(Ph2Pqn)2]BF4 (5). The crystal structure of complex 5 reveals that the NiI ion adopts a distorted tetrahedral coordination geometry with slightly longer (≈ 0.05 Å) Ni–P and Ni–N bond lengths than those in the corresponding NiII complex 3.

A Phosphine Functionalized β‐Diketimine Ligand for the Synthesis of Manifold Metal Complexes

“…In the Ni I compound 6 , the Ni‐P bond lengths are nearly identical and in the expected range (Ni−P1 2.2709(6), Ni−P2 2.2403(6) Å). A similar symmetric arrangement is seen for Ni−N bond lengths (Ni−N1 2.028(2), Ni−N2 2.042(2) Å) . The Ni I center is formally in a square planar coordination sphere, as indicated by the respective angles (N1‐Ni‐N2 86.95(7°); P1‐Ni‐P2 111.13(2)°), deviating slightly from an ideal 90°, which is a result of the rigid nature of the ligand.…”

“…P2‐Ni‐Cl 89.49(3)°, N2‐Ni‐Cl 93.90(8)°). The metal phosphorous (Ni−P1 2.1717(10), Ni−P2 2.1527(10) Å) and metal nitrogen bond lengths (Ni−N1 1.930(3), Ni−N2 1.933(3) Å) of 9 are both about 0.1 Å shorter than the Ni I complex 6 , which is most likely due to the higher oxidation state of the nickel center and a difference in ionic radii between Ni I and Ni II …”

“…As imilar symmetric arrangement is seen for NiÀN bond lengths( NiÀN1 2.028(2), NiÀN2 2.042(2) ). [65][66][67] The Ni I center is formally in as quare planar coordination sphere, as indicatedb yt he respective angles (N1-Ni-N2 86.95 (78); P1-Ni-P2 111.13(2)8), deviating slightly from an ideal 908,w hich is a result of the rigid nature of the ligand. Importantly,a si th as been reported for different b-diketiminate systems, the PNNP pocket of the PNac ligand stabilizes the nickel center in its uncommono xidation state of + 1.…”

“…3)o f9 are both about 0.1 shorter than the Ni I complex 6,w hich is most likely due to the higher oxidation state of the nickel center and ad ifference in ionic radii between Ni I and Ni II . [66] Compound 9 was also characterized by NMR and IR spectroscopy.I nc ontrastt o6,c omplex 9 allowed am eaningful characterization via NMR, confirming the presence of ad iamagnetic Ni II species. In the 31 P{ 1 H} NMR spectrum (CDCl 3 )a single resonance at d = 35.2 ppm, significantly downfield shifted compared to ligand 1 (d = À14.5 ppm), is detected, indicating as ymmetric phosphine nickel coordinationi ns olution.…”

Crystal structures of dichloridopalladium(II), -platinum(II) and -rhodium(III) complexes containing 8-(diphenylphosphanyl)quinoline

“…In addition, the steric requirement from the quinolyl moiety often has a strong influence on the properties of their metal complexes. For example, the nickel(II) and palladium(II) complexes containing two 8-(diphenylphosphanyl)quinoline (Ph 2 Pqn) molecules with a cis(P) configuration showed a severe distortion of the square-planar coordination geometry around Ni II and Pd II as a result of the steric hindrance between mutually cis-positioned quinolyl groups (Suzuki, 2004;Hashimoto et al, 2010). Several crystallographic studies have been performed for other Ph 2 Pqn complexes, as described in…”