Synthesis, Structure, and Reactivity of Co(II) and Ni(II) PCP Pincer Borohydride Complexes

Sathiyamoorthy Murugesan; Berthold Stöger; Matthias Weil; Luis F. Veiros; Karl Kirchner

doi:10.1021/acs.organomet.5b00075

Synthesis, Structure, and Reactivity of Co(II) and Ni(II) PCP Pincer Borohydride Complexes

Sathiyamoorthy Murugesan
, Berthold Stöger
, Matthias Weil
, Luis F. Veiros
, Karl Kirchner^*

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

59 Scopus citations

Abstract

The 15e square-planar complexes [Co(PCP^Me-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH₄ to afford complexes [Co(PCP^Me-iPr)(η²-BH₄)] (4a) and [Co(PCP-tBu)(η²-BH₄)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η²-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μ_B consistent with a d⁷ low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO₂ to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCP^Me-iPr)(η²-BH₄)] (5) via two different synthetic routes. One utilizes [Ni(PCP^Me-iPr)Cl] (3) and NaBH₄, the second one makes use of the hydride complex [Ni(PCP^Me-iPr)H] (6) and BH₃·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η²-mode. [Ni(PCP^Me-iPr)(η²-BH₄)] (5) loses readily BH₃ at elevated temperatures in the presence of NEt₃ to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of ¹H, ¹³C{¹H}, and ³¹P{¹H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO₂ to give the formate complex [Ni(PCP^Me-iPr)(OC(C=O)H] (7). The extrusion of BH₃ from [Co(PCP^Me-iPr)(η²-BH₄)] (4a) and [Ni(PCP^Me-iPr)(η²-BH₄)] (5) with the aid of NH₃ to yield the respective hydride complexes [Co(PCP^Me-iPr)H] and [Ni(PCP^Me-iPr)H] (6) and BH₃NH₃ was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCP^Me-iPr)(η²-BH₄)] (4a) and [Ni(PCP^Me-iPr)(η²-BH₄)] (5) were established by DFT computations. (Chemical Equation Presented).

Original language	English
Pages (from-to)	1364-1372
Number of pages	9
Journal	Organometallics
Volume	34
Issue number	7
DOIs	https://doi.org/10.1021/acs.organomet.5b00075
State	Published - 13 Apr 2015
Externally published	Yes

Bibliographical note

Publisher Copyright:
© 2015 American Chemical Society.

ASJC Scopus subject areas

Physical and Theoretical Chemistry
Organic Chemistry
Inorganic Chemistry

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10.1021/acs.organomet.5b00075

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@article{a31d1880cb02474d9d1f2dfcc17e0ba7,

title = "Synthesis, Structure, and Reactivity of Co(II) and Ni(II) PCP Pincer Borohydride Complexes",

abstract = "The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C\{1H\}, and 31P\{1H\} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C=O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations. (Chemical Equation Presented).",

author = "Sathiyamoorthy Murugesan and Berthold St{\"o}ger and Matthias Weil and Veiros, \{Luis F.\} and Karl Kirchner",

note = "Publisher Copyright: {\textcopyright} 2015 American Chemical Society.",

year = "2015",

month = apr,

day = "13",

doi = "10.1021/acs.organomet.5b00075",

language = "English",

volume = "34",

pages = "1364--1372",

journal = "Organometallics",

issn = "0276-7333",

number = "7",

}

TY - JOUR

T1 - Synthesis, Structure, and Reactivity of Co(II) and Ni(II) PCP Pincer Borohydride Complexes

AU - Murugesan, Sathiyamoorthy

AU - Stöger, Berthold

AU - Weil, Matthias

AU - Veiros, Luis F.

AU - Kirchner, Karl

PY - 2015/4/13

Y1 - 2015/4/13

N2 - The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C=O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations. (Chemical Equation Presented).

AB - The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C=O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations. (Chemical Equation Presented).

UR - https://www.scopus.com/pages/publications/84927922199

U2 - 10.1021/acs.organomet.5b00075

DO - 10.1021/acs.organomet.5b00075

M3 - Article

AN - SCOPUS:84927922199

SN - 0276-7333

VL - 34

SP - 1364

EP - 1372

JO - Organometallics

JF - Organometallics

IS - 7

ER -

Synthesis, Structure, and Reactivity of Co(II) and Ni(II) PCP Pincer Borohydride Complexes

Abstract

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