| Abstract
| - A series of tetrahedral η1-hydrocarbyl complexes with hydrotrispyrazolylborato ligand (TpR‘), TpR‘−R (M = Fe, Co), is prepared and characterized by spectroscopy and crystallography. Despite the highly unsaturated electronic structures (14e (Fe), 15e (Co)) the hydrocarbyl complexes are stable under an inert atmosphere. In particular, the ethyl complexes containing β-hydrogen atoms survive heating above 70 °C.
- A series of hydrocarbyl complexes supported only by hydrotris(pyrazolyl)borato ligands(TpR‘ = 3,5-diisopropylpyrazolyl (TpiPr2) and 3,4,5-trimethylpyrazolyl derivatives (TpMe3)),TpR‘M−R (M/R/R‘ = Ni/η3-allyl/iPr2 (2iPr2Ni), Co/η3-allyl/iPr2 (2iPr2Co), Fe/η1-allyl/iPr2(2iPr2Fe), Ni/η3-prenyl/iPr2 (3iPr2Ni), Co/η1-p-methylbenzyl/iPr2 (4iPr2Co), Fe/η1-p-methylbenzyl/iPr2 (4iPr2Fe), Co/η1-p-methylbenzyl/Me3 (4Me3Co), Fe/η1-p-methylbenzyl/Me3 (4Me3Fe),Co/η1-α-naphthylmethyl/iPr2 (5iPr2Co), Co/η1-ethyl/iPr2 (6iPr2Co), Fe/η1-ethyl/iPr2 (6iPr2Fe))is prepared by reaction of the corresponding precursors, TpiPr2M−Cl (M = Fe (1iPr2Fe), Co(1iPr2Co), Ni (1iPr2Ni)) or TpMe3M(κ2-X) (M/X = Co/NO3 (1‘Me3Co), Fe/OAc (1‘Me3Fe)), withappropriate Grignard reagents. η1-Hydrocarbyl complexes are obtained when M = Fe, Co,and the thermally unstable η1-ethylnickel derivative 6iPr2Ni is characterized via conversionto the acyl derivative TpiPr2Ni(CO)C(O)Et (12). Characterization by a combination of variousspectroscopic methods (IR, NMR, UV, and ESR), magnetic susceptibility, X-ray crystallography, and chemical reactions reveals that the η1-hydrocarbyl complexes 2iPr2Fe and 4−6are tetrahedral, highly coordinatively unsaturated species with 14 (M = Fe) and 15 (M =Co) valence electrons. It is remarkable that the ethyl complexes 6 are thermally stable evenat higher temperatures (70 °C (Co); 110 °C (Fe)), although they contain β-hydrogen atoms.The presence of a metal−carbon bond in 4−6 has been confirmed by protonation andhydrogenolysis, giving alkane (R−H) and carbonylation leading to acyl−carbonyl species(TpR‘M(CO)nC(O)R: M/n = Fe/2 (7), Co/1 (8)). Despite the coordinative unsaturation atthe metal centers complexes 4−6 turn out to be sluggish toward unsaturated organiccompounds such as olefin, internal acetylene, ketone, and nitrile. Only phenylacetylenereacted with the ethyl complexes 6iPr2 to result in insertion of the C⋮C bond into theM−C bond (6iPr2Co) or protonolysis of the M−C bond to afford the acetylide complexTpiPr2FeC⋮CPh, which was characterized after carbonylation, giving TpiPr2Fe(CO)2C⋮CPh(12). The magnetic susceptibility of η1-hydrocarbyl complexes combined with the results ofEHMO calculations for the model complexes TpHM−CH3 (M = Fe, Co) reveals the high-spinconfiguration of d electrons, which leads to occupation of all five frontier orbitals by electronpairs or unpaired electrons. The lack of a vacant d orbital is concluded to be the origin ofthe thermal stability of the electron-deficient hydrocarbyl complexes.
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