154069-31-5Relevant academic research and scientific papers
Borole derivatives. 20. Three-center Fe-H-B bonding in (borole) (cyclopentadienyl)hydridoiron derivatives
Herberich, Gerhard E.,Carstensen, Tobias,K?ffer, Dieter P. J.,Klaff, Norbert,Boese, Roland,Hyla-Kryspin, Isabella,Gleiter, Rolf,Stephan, Martin,Meth, Helmut,Zenneck, Ulrich
, p. 619 - 630 (1994)
(Borole)tricarbonyliron complexes Fe(CO)3(3,4-R12C4H2BPh) (3a, R1 = H; 3b, R1 = Me) react with cyclopentadiene under irradiation to give the hydrides CpFeH(3,4-R12C4H2BPh) (1a,b). Deprotonation by NaH in THF produces the borataferrocene anions [CpFe(3,4-R12C4H2BPh)]-(5a -, 5b-). These can be alkylated in the 2-/5-position by alkyl iodides in the presence of NaH to give 2,5-dialkyl hydride derivatives: e.g. CpFeH(2,5-R22C4H2BPh) (1c, R2 = Me; 1g, R2 = CH2=CH(CH2)4; 1h, R2 = (CH2)2CHCH2). The structures of CpFeH(2,3,4,5-Me4C4BPh) (1d; Fe-B = 215.1(4) pm, Fe-H = 147(3) pm, B-H = 151(3) pm) and (C5H4Me)FeH(2,5-Me2C4H 2-BPh) (1f; Fe-B = 215.5(2) pm, Fe-H = 147.5(23) pm, B-H = 146.1(26) pm) as determined by low-temperature X-ray diffraction show the presence of an Fe-H-B three-center bond with a weak B-H interaction. In solution 1a establishes a mobile equilibrium between the ground state 1a-G with Fe-H-B three-center bonding and the agostic isomer 1a-A with Fe-H-C-2(C4H4B) three-center bonding with an estimated ΔG = 1.4 kcal/mol. The hydridic proton and the 2-/5-protons of the borole ring undergo fast intramolecular exchange (Tc = 333 K at 80 MHz and ΔG?333 = 17.0 ± 0.7 kcal/mol for 1a). A merry-go-round of the three H atoms involved with one hydrogen crossing the exo face of the borole ligand is proposed as an exchange mechanism. The bonding in CpFeH(C4H4BH) is analyzed by means of extended Hu?ckel calculations, which confirm the Fe-H-B three-center bonding. Exploratory extended Hu?ckel calculations also support the existence of agostic isomers as well as the proposed exchange mechanism. Cyclic voltammetry revealed the existence of the 17e complex CpFe(C4H4BPh) (5a), which is characterized by its EPR and paramagnetic 1H NMR spectra. 1a reacts with CNBut to give the boracyclopentenyl complex CpFe(CNBut)(C4H5BPh) (9a) and, probably via the intermediate Fe(CNBUt)(C4H4BPh)(C5H6) (10), the borole complex Fe(CNBUt)3(C4H4BPh) (11a) and 1 equiv of cyclopentadiene. Labeling experiments show that the shift of the hydridic hydrogen to the borole and Cp ligands, respectively, is an intramolecular process. 1c reacts analogously.
