Ancillary ligand control of reactivity. Protonation at hydride vs. cyanide in trans-[FeH(CN)(R2PCH2CH2PR2)2](R = Et, Ph, p-tolyl) and X-ray crystal structure determination of trans-[FeH(CNH)(R2PCH2CH2PR2)2]BF4(R =p-tolyl)

Abstract

The ancillary ligands in trans-[FeH(CN)L2] control whether protonation occurs at hydride to produce a dihydrogen complex or at cyanide to produce a hydrogen isocyanide complex.

Reactions of a cyanosilane with an iron(II) centre. Synthesis and crystal structure of the isocyanotriphenylborate complex trans-[FeH(CNBPh3)(Ph2PCH2CH2PPh2)2] and anodic deprotonation of the hydrogen isocyanide (CNH) analogue

“…The conceivable involvement of the cyano complex trans-[FeH(CN)(dppe) 2 ] 3 as an intermediate in reaction (4) to give the isocyanide product 2 is corroborated by the alternative formation of the latter complex upon treatment of the former with HBF 4 (reaction 5, Scheme 1), a reaction already reported by others. 4 However, the single-pot route to 2 we have previously found 17 and now describe in detail (reaction 4) is a more direct one, and does not require the isolation of the cyano-complex 3.…”

“…The cyanosilane N᎐ ᎐ ᎐ CSiMe 3 was shown 1 to be a convenient source of the simplest isocyanide and aminocarbyne ligands, CNH x (x = 1 or 2, respectively), in reactions with the N 2binding electron-rich rhenium() centre trans-{ReCl(dppe) 2 } (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) to form trans-[ReCl(CNH)(dppe) 2 ] (in methanol) or trans-[ReCl(CNH 2 )(dppe) 2 ][BF 4 ] (in the presence of HBF 4 ). In view of the rarity of well defined complexes with such ligands and of the current interest 2 in the development of their organometallic chemistry, of particular significance in the field of nitrogen fixation, 3,4 we have attempted to explore further the above type of reactivity of N᎐ ᎐ ᎐ CSiMe 3 towards a phosphinic iron() centre which is also able to bind dinitrogen, and we now report the results we have obtained. They show that the cyanosilane behaves as a source not only of the cyano group in the formation of the isocyanide CNH (upon H ϩ addition) but also, unexpectedly, of isocyanotriphenylborate CNBPh 3 Ϫ (upon addition of BPh 3 generated from BPh 4…”

Asymmetric hydrogenation, transfer hydrogenation and hydrosilylation of ketones catalyzed by iron complexes

“…It is of interest that nature utilizes strong field carbonyl and cyanide ligands in the enzyme hydrogenase, possibly in order to stabilize hydride and dihydrogen intermediates on iron. [54][55][56] The more distorted structure of 3 with a wider P-Fe-P angle than 1 or 2 might explain the enhanced reactivity of 3 in catalysis.…”

Synthesis and properties of iron-group hydrido-cyano complexes trans-[MH(CN)(L)2], M = Fe, Ru or Os, L = diphosphine, and their hydrogen, trifluoroboron and triphenylboron isocyanide derivatives of the type trans-[MH(CNH)(L)2]O3SCF3, trans-[MH(CNBX3)(L)2], X = F or Ph, and trans-[M(H2)(CNBF3)(dppp)2]BF4 [dppp = Ph2P(CH2)3PPh2]

“…The ν(CN) stretching frequency also decreases as the diphosphine ligand is changed from dppm > dppe > depe > dppp. In this series, two factors contribute to the raising in energy of the metal d π orbitals that form π bonds with the cyanide ligand: (1) an increase in basicity of the diphosphine with constant bite angle (dppe < depe); (2) an increase in bite angle with fairly constant basicity (dppm < dppe < dppp). The resonance in the proton NMR spectra due to the hydride ligand of these complexes in CD 2 Cl 2 at 20 ЊC appears at high field as a quintet due to coupling to four equivalent 31 P nuclei.…”

“…The structure of 2*Fe5 has been described briefly. 2 The structures are oriented and labelled in a consistent fashion; for example Figs. 5); linearity is forced by crystal symmetry in the case of 2*Fe5.…”