Electrochemistry of the Nickel(II) Tris(2-diphenylphosphinoethyl)phosphine Halide Cations and an X-ray Crystallographic Structure of [Ni(.eta.4-P3P')Br][PF6].cntdot.1/2MeCN.cntdot.H2O
“…Similar behaviour has been previously observed for Ni complexes. [41][42][43][44][45] For [(HNP 2 )NiOTf]OTf, the CV shows oxidation processes above 1.0 V, similar to those observed for the corresponding bromide salt. These processes could not be assigned due to irreversibility and overlap.…”
A series of Co, Ni and Cu complexes with the ligand HN(CH(2)CH(2)P(i)Pr(2))(2) (HNP(2)) has been isolated and their electrochemical behaviour investigated by cyclic voltammetry. The nickel complexes [(HNP(2))NiOTf]OTf and [(HNP(2))NiNCCH(3)](BF(4))(2) display reversible reductions, as does the related amide derivative (NP(2))NiBr. The related copper(I) and cobalt(II) derivatives were also isolated and characterized. The addition of piperidine to [(HNP(2))NiNCCH(3)](BF(4))(2) led to the formation of the new species [(HNP(2))Ni(N(H)C(CH(3))NC(5)H(10))](BF(4))(2). The nucleophilic addition of piperidine to acetonitrile to produce HN=C(CH(3))NC(5)H(10) was found to be catalyzed by [(HNP(2))NiNCCH(3)](BF(4))(2).
“…Similar behaviour has been previously observed for Ni complexes. [41][42][43][44][45] For [(HNP 2 )NiOTf]OTf, the CV shows oxidation processes above 1.0 V, similar to those observed for the corresponding bromide salt. These processes could not be assigned due to irreversibility and overlap.…”
A series of Co, Ni and Cu complexes with the ligand HN(CH(2)CH(2)P(i)Pr(2))(2) (HNP(2)) has been isolated and their electrochemical behaviour investigated by cyclic voltammetry. The nickel complexes [(HNP(2))NiOTf]OTf and [(HNP(2))NiNCCH(3)](BF(4))(2) display reversible reductions, as does the related amide derivative (NP(2))NiBr. The related copper(I) and cobalt(II) derivatives were also isolated and characterized. The addition of piperidine to [(HNP(2))NiNCCH(3)](BF(4))(2) led to the formation of the new species [(HNP(2))Ni(N(H)C(CH(3))NC(5)H(10))](BF(4))(2). The nucleophilic addition of piperidine to acetonitrile to produce HN=C(CH(3))NC(5)H(10) was found to be catalyzed by [(HNP(2))NiNCCH(3)](BF(4))(2).
“…These angles are approximately 5° less than the ideal 90°, and the corresponding C(1)−Ni−P(eq) bond angles are 3−5° larger than the ideal 90°. This distortion is a result of the small chelate bite of the tetraphosphine ligand, and similar bond angles are observed for [Ni(PP 3 )(Br)](PF 6 ) 2 and [Ni(PP 3 )P(OMe) 3 ](AsF 6 ) 2 . , The Ni−C(1) distance of 1.780(11) Å is within the range observed for other Ni(II) carbonyl complexes (1.73−1.83 Å), and it is shorter than the Ni−C bond distances observed for the Ni(I) complexes [Ni(NS 3 t -Bu)(CO)] + (1.85(1) Å) and [Ni(NP 3 )(CO)] + (1.90(5) Å), respectively (where NS 3 t -Bu is N(CH 2 CH 2 S t -Bu) 3 and NP 3 is N(CH 2 CH 2 Ph 2 ) 3 ). , These results are consistent with a significant lengthening of the Ni−C bond upon reduction from Ni(II) to Ni(I), but more definitive evidence would be provided by structures of a single complex in both Ni(I) and Ni(II) oxidation states. 1 ORTEP showing the atom-numbering scheme for one of the [Ni(PP 3 E)(CO)] 2+ cations.…”
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.
“…The identical 31 P NMR spectra of Ni(Cl) L1 H BF 4 ( 1b ) and [Ni(Cl) L1 H ] 2 [NiCl 4 ] ( 1a ) show one doublet ( δ = 61.06 ppm) and one quartet ( δ = 25.91 ppm), indicating a C 3 ‐symmetrical trigonal bipyramidal geometry in solution (on the NMR time scale). C 3 ‐symmetrical diamagnetic complexes of tripodal tetradentate phosphines coordinated to nickel have been previously reported,, , and trigonal bipyramidal geometry was also reported for the d 8 [Ru(N 2 ) L1 H ] and the [Pd(Cl) L1 H ][Cl] complexes. Interestingly, whereas the coordination of nickel to L1 H results in the formation of the binary [Ni(Cl) L1 H ] 2 [NiCl 4 ] complex 2a , the palladium complex does not form the tetrachlorido palladate, but one of the chloride anions remains non‐coordinating .…”
Section: Resultsmentioning
confidence: 71%
“…Similar as for the cobalt analogue, the CV of 2b shows one reversible reduction‐oxidation peak at E 0 1/2 = –1.0 V vs. Fc/Fc + V. In addition, two non‐reversible reduction peaks were observed ( E = –2.0 V vs. Fc/Fc + and E = –2.5 V vs. Fc/Fc + ). CV measurements of [Ni(PP Ph 3 )(CH 3 CN)](BF 4 ) 2 showed only one reversible redox couple ( E 0 1/2 = –1.03 V vs. Fc/Fc + ; likely the Ni II /Ni I couple) and one non‐reversible reduction peak, ( E 0 1/2 = –1.28 V vs. Fc/Fc + ; likely the Ni I /Ni 0 couple) , . The chemical reduction of our [Ni L1 H ]BF 4 ( 2b ) complex with two equivalents of KC 8 resulted in formation of a yellow precipitate.…”
We report the coordination chemistry of indole based tripodal tetraphosphine ligands to iron(II), cobalt(II) and nickel(II). These complexes are formed by simple synthetic protocols and were characterized by a combination of spectroscopic techniques and single‐crystal X‐ray analysis. The molecular structures as determined by X‐ray diffraction show that the geometry of the nickel and cobalt complexes are distorted trigonal bipyramidal. The monocationic iron(II) complexes also have distorted trigonal bipyramidal geometries, but the dicationic analogue has an octahedral geometry. Two‐electron reduction of the cobalt(+II) and the nickel(+II) complexes in the presence of N2 did not lead to the coordination of N2. In contrast, two‐electron reduction of the iron(+II) complexes did lead to coordination of dinitrogen to the iron center. The Fe0N2
L1H complex has a trigonal bipyramidal geometry, and the N–N bond length of the coordinated dinitrogen ligand is longer than that of free dinitrogen, indicating that coordination to this iron(0) complex results in activation of the N≡N bond.
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