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Three-coordinate and four-coordinate cobalt hydride complexes that react with dinitrogen.

ABSTRACT: We report the formation and N(2) reactivity of novel cobalt hydride complexes supported by bulky beta-diketiminate ligands (L). Addition of KHBEt(3) to LCoCl gives [LCo(mu-H)](2) (1) or K(2)[LCoH](2) (2), depending on the amount of borohydride used. Compound 2 is the first example of a crystallographically characterized hydride complex in which a transition metal is three-coordinate. Both 1 and 2 react with N(2) at room temperature to give dinuclear N(2) complexes with loss of H(2).

SUBMITTER: Ding K

PROVIDER: S-EPMC2737074 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Three-coordinate and four-coordinate cobalt hydride complexes that react with dinitrogen.

Ding Keying K Brennessel William W WW Holland Patrick L PL

Journal of the American Chemical Society 20090801 31

We report the formation and N(2) reactivity of novel cobalt hydride complexes supported by bulky beta-diketiminate ligands (L). Addition of KHBEt(3) to LCoCl gives [LCo(mu-H)](2) (1) or K(2)[LCoH](2) (2), depending on the amount of borohydride used. Compound 2 is the first example of a crystallographically characterized hydride complex in which a transition metal is three-coordinate. Both 1 and 2 react with N(2) at room temperature to give dinuclear N(2) complexes with loss of H(2). ...[more]

PMID: 19621923

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Project description:The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ((iPr)PDI)FeN(2) and ((iPr)PDI)Fe(N(2))(2) ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N=CMe)(2)C(5)H(3)N), have been investigated by a combination of spectroscopic techniques (NMR, Mössbauer, X-ray Absorption and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ((iPr)RPDI)FeN(2) ((iPr)RPDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N=CR)(2)C(5)H(3)N; R = Et, (i)Pr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ((iPr)RPDI)FeN(2) compounds are intermediate spin ferrous derivatives (S(Fe) = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S(PDI) = 1). While this ground state description is identical to that previously reported for ((iPr)PDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally ?-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ((iPr)RPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ((iPr)RPDI)FeN(2) family, one of the iron SOMOs is essentially d(z2) in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ((iPr)RPDI)FeN(2) and ((iPr)PDI)Fe(DMAP) differ from ((iPr)PDI)Fe(N(2))(2), a highly covalent molecule with a redox non-innocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.

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Three-coordinate and four-coordinate cobalt hydride complexes that react with dinitrogen.

Publications

Three-coordinate and four-coordinate cobalt hydride complexes that react with dinitrogen.

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