Open AccessSynthesis, Structure, and Reactivity of Co(II) and Ni(II) PCP Pincer Borohydride Complexes
Author(s) -
Sathiyamoorthy Murugesan,
Berthold Stöger,
Matthias Weil,
Luı́s F. Veiros,
Karl Kirchner
Publication year - 2015
Publication title -
organometallics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.231
H-Index - 172
eISSN - 1520-6041
pISSN - 0276-7333
DOI - 10.1021/acs.organomet.5b00075
Subject(s) - chemistry , reactivity (psychology) , borohydride , ligand (biochemistry) , sodium borohydride , pincer movement , electron paramagnetic resonance , medicinal chemistry , nickel , cobaltocene , unpaired electron , hydride , crystallography , nuclear magnetic resonance spectroscopy , paramagnetism , pincer ligand , stereochemistry , inorganic chemistry , molecule , electrochemistry , metal , organic chemistry , catalysis , ferrocene , nuclear magnetic resonance , alternative medicine , receptor , pathology , biochemistry , quantum mechanics , medicine , physics , electrode
The 15e square-planar complexes [Co(PCP Me - i Pr)Cl] ( 2a ) and [Co(PCP- t Bu)Cl] ( 2b ), respectively, react readily with NaBH 4 to afford complexes [Co(PCP Me - i Pr)(η 2 -BH 4 )] ( 4a ) and [Co(PCP- t Bu)(η 2 -BH 4 )] ( 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 η 2 -fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μ B consistent with a d 7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO 2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCP Me - i Pr)(η 2 -BH 4 )] ( 5 ) via two different synthetic routes. One utilizes [Ni(PCP Me - i Pr)Cl] ( 3 ) and NaBH 4 , the second one makes use of the hydride complex [Ni(PCP Me - i Pr)H] ( 6 ) and BH 3 ·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 η 2 -mode. [Ni(PCP Me - i Pr)(η 2 -BH 4 )] ( 5 ) loses readily BH 3 at elevated temperatures in the presence of NEt 3 to form 6 . Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO 2 to give the formate complex [Ni(PCP Me - i Pr)(OC(C=O)H] ( 7 ). The extrusion of BH 3 from [Co(PCP Me - i Pr)(η 2 -BH 4 )] ( 4a ) and [Ni(PCP Me - i Pr)(η 2 -BH 4 )] ( 5 ) with the aid of NH 3 to yield the respective hydride complexes [Co(PCP Me - i Pr)H] and [Ni(PCP Me - i Pr)H] ( 6 ) and BH 3 NH 3 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 - i Pr)(η 2 -BH 4 )] ( 4a ) and [Ni(PCP Me - i Pr)(η 2 -BH 4 )] ( 5 ) were established by DFT computations.