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A square-planar Co4 amide cluster, Co4{N(SiMe3)2}4 ( 2), and an octahedral Co6 hydride cluster, Co6H8(P iPr3)6 ( 4), were obtained from metathesis-type amide to hydride exchange reactions of a CoII amide complex with pinacolborane (HBpin) in the absence/presence of P iPr3. The crystal structure of 4 revealed face-capping hydrides on each triangular [Co3] face, while the formal CoII2CoI4 oxidation state of 4 indicated a reduction of the cobalt centers during the assembly process. Cluster 4 catalyzes the hydrosilylation of 2-cyclohexen-1-one favoring the conjugate reduction. Generation of the catalytically reactive Co cluster species was indicated by a trapping experiment with a chiral chelating agent. [ABSTRACT FROM AUTHOR]

Multiple iron atoms bridged by hydrides is a common structural feature of the active species that have been postulated in the biological and industrial reduction of N 2 . In this study, the reactions of an Fe(II) amide complex with pinacolborane in the presence/absence of phosphines afforded a series of hydride-supported [Fe 4 ] and [Fe 6 ] clusters Fe 4 (μ-H) 4 (μ 3 -H) 2 {N(SiMe 3 ) 2 } 2 (PR 3 ) 4 (PR 3 = PMe 3 (2a), PMe 2 Ph (2b), PEt 3 (2c)), Fe 6 (μ-H) 10 (μ 3 -H) 2 (PMe 3 ) 10 (3), and (η 6 -C 7 H 8 )Fe 4 (μ-H) 2 {μ-N(SiMe 3 ) 2 } 2 {N(SiMe 3 ) 2 } 2 (4), which were characterized crystallographically and spectroscopically. Under ambient conditions, these clusters catalyzed the silylation of N 2 to furnish up to 160 ± 13 equiv of N(SiMe 3 ) 3 per 2c (40 equiv per Fe atom) and 183 ± 18 equiv per 3 (31 equiv per Fe atom). With regard to the generation of the reactive species, dissociation of phosphine and hydride ligands from the [Fe 4 ] and [Fe 6 ] clusters was indicated, based on the results of the mass spectrometric analysis on the [Fe 6 ] cluster, as well as the formation of a diphenylsilane adduct of the [Fe 4 ] cluster.

A square-planar Co 4 amide cluster, Co 4 {N(SiMe 3 ) 2 } 4 (2), and an octahedral Co 6 hydride cluster, Co 6 H 8 (P i Pr 3 ) 6 (4), were obtained from metathesis-type amide to hydride exchange reactions of a Co II amide complex with pinacolborane (HBpin) in the absence/presence of P i Pr 3 . The crystal structure of 4 revealed face-capping hydrides on each triangular [Co 3 ] face, while the formal Co II 2 Co I 4 oxidation state of 4 indicated a reduction of the cobalt centers during the assembly process. Cluster 4 catalyzes the hydrosilylation of 2-cyclohexen-1-one favoring the conjugate reduction. Generation of the catalytically reactive Co cluster species was indicated by a trapping experiment with a chiral chelating agent., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)