The synthesis and characterization of (tBuPBP)Ni(OAc) (
- Award ID(s):
- 1700982
- NSF-PAR ID:
- 10057944
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 9
- Issue:
- 5
- ISSN:
- 2041-6520
- Page Range / eLocation ID:
- 1144 to 1154
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 5 ) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1 ) is presented. An unexpected CO2cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2(6 ). Mechanistic investigation of this reaction indicates a reductive scission of CO2by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A ) that leads to a (tBuP2BO)−NiIcomplex (B ) via a likely radical pathway. The NiIspecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7 ). Additionally,13C and1H NMR spectroscopy analysis using13C‐enriched CO2provides information about the species involved in the CO2activation process. -
Abstract The synthesis and characterization of (tBuPBP)Ni(OAc) (
5 ) by insertion of carbon dioxide into the Ni−C bond of (tBuPBP)NiMe (1 ) is presented. An unexpected CO2cleavage process involving the formation of new B−O and Ni−CO bonds leads to the generation of a butterfly‐structured tetra‐nickel cluster (tBuPBOP)2Ni4(μ‐CO)2(6 ). Mechanistic investigation of this reaction indicates a reductive scission of CO2by O‐atom transfer to the boron atom via a cooperative nickel‐boron mechanism. The CO2activation reaction produces a three‐coordinate (tBuP2BO)Ni‐acyl intermediate (A ) that leads to a (tBuP2BO)−NiIcomplex (B ) via a likely radical pathway. The NiIspecies is trapped by treatment with the radical trap (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) to give (tBuP2BO)NiII(η2‐TEMPO) (7 ). Additionally,13C and1H NMR spectroscopy analysis using13C‐enriched CO2provides information about the species involved in the CO2activation process. -
Abstract Pincer‐type nickel–aluminum complexes were synthesized using two equivalents of the phosphinoamide, [PhNCH2PiPr2]−. The Ni0–AlIIIcomplexes, {(MesPAlP)Ni}2(μ‐N2) and {(MesPAlP)Ni}2(μ‐COD), whereMesPAlP is (Mes)Al(NPhCH2PiPr2)2, were structurally characterized. The (PAlP)Ni system exhibited cooperative bond cleavage mediated by the two‐site Ni–Al unit, including oxidative addition of aryl halides, H2activation, and ortho‐directed C−H bond activation of pyridine N‐oxide. One intriguing reaction is the reversible intramolecular transfer of the mesityl ring from the Al to the Ni site, which is evocative of the transmetalation step during cross‐coupling catalysis. The aryl‐transfer product,(THF)Al(NPhCH2PiPr2)2Ni(Mes), is the first example of a first‐row transition metal–aluminyl pincer complex. The addition of a judicious donor enables the Al metalloligand to convert reversibly between the alane and aluminyl forms via aryl group transfer to and from Ni, respectively. Theoretical calculations support a zwitterionic Niδ−–Alδ+electronic structure in the nickel–aluminyl complex.
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Abstract Pincer‐type nickel–aluminum complexes were synthesized using two equivalents of the phosphinoamide, [PhNCH2PiPr2]−. The Ni0–AlIIIcomplexes, {(MesPAlP)Ni}2(μ‐N2) and {(MesPAlP)Ni}2(μ‐COD), whereMesPAlP is (Mes)Al(NPhCH2PiPr2)2, were structurally characterized. The (PAlP)Ni system exhibited cooperative bond cleavage mediated by the two‐site Ni–Al unit, including oxidative addition of aryl halides, H2activation, and ortho‐directed C−H bond activation of pyridine N‐oxide. One intriguing reaction is the reversible intramolecular transfer of the mesityl ring from the Al to the Ni site, which is evocative of the transmetalation step during cross‐coupling catalysis. The aryl‐transfer product,(THF)Al(NPhCH2PiPr2)2Ni(Mes), is the first example of a first‐row transition metal–aluminyl pincer complex. The addition of a judicious donor enables the Al metalloligand to convert reversibly between the alane and aluminyl forms via aryl group transfer to and from Ni, respectively. Theoretical calculations support a zwitterionic Niδ−–Alδ+electronic structure in the nickel–aluminyl complex.
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Interest in O 2 -dependent aliphatic carbon–carbon (C–C) bond cleavage reactions of first row divalent metal diketonate complexes stems from the desire to further understand the reaction pathways of enzymes such as DKE1 and to extract information to develop applications in organic synthesis. A recent report of O 2 -dependent aliphatic C–C bond cleavage at ambient temperature in Ni( ii ) diketonate complexes supported by a tridentate nitrogen donor ligand [(MBBP)Ni(PhC(O)CHC(O)Ph)]Cl ( 7-Cl ; MBBP = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine) in the presence of NEt 3 spurred our interest in further examining the chemistry of such complexes. A series of new TERPY-ligated Ni( ii ) diketonate complexes of the general formula [(TERPY)Ni(R 2 -1,3-diketonate)]ClO 4 ( 1 : R = CH 3 ; 2 : R = C(CH 3 ) 3 ; 3 : R = Ph) was prepared under air and characterized using single crystal X-ray crystallography, elemental analysis, 1 H NMR, ESI-MS, FTIR, and UV-vis. Analysis of the reaction mixtures in which these complexes were generated using 1 H NMR and ESI-MS revealed the presence of both the desired diketonate complex and the bis-TERPY derivative [(TERPY) 2 Ni](ClO 4 ) 2 ( 4 ). Through selective crystallization 1–3 were isolated in analytically pure form. Analysis of reaction mixtures leading to the formation of the MBBP analogs [(MBBP)Ni(R 2 -1,3-diketonate)]X (X = ClO 4 : 5 : R = CH 3 ; 6 : R = C(CH 3 ) 3 ; 7-ClO4 : R = Ph; X = Cl: 7-Cl : R = Ph) using 1 H NMR and ESI-MS revealed the presence of [(MBBP) 2 Ni](ClO 4 ) 2 ( 8 ). Analysis of aerobic acetonitrile solutions of analytically pure 1–3 , 5 and 6 containing NEt 3 and in some cases H 2 O using 1 H NMR and UV-vis revealed evidence for the formation of additional bis-ligand complexes ( 4 and 8 ) but suggested no oxidative diketonate cleavage reactivity. Analysis of the organic products generated from 3 , 7-ClO4 and 7-Cl revealed unaltered dibenzoylmethane. Our results therefore indicate that N 3 -ligated Ni( ii ) complexes of unsubstituted diketonate ligands do not exhibit O 2 -dependent aliphatic C–C bond clevage at room temperature, including in the presence of NEt 3 and/or H 2 O.more » « less