The substitution of high-price noble metals such as Ir, Ru, Rh, Pd, and Pt by earth-abundant, inexpensive metals like Co is an attractive goal in (homogeneous) catalysis. Only two examples of Co catalysts, showing efficient C═O bond hydrogenation rates, are described. Here, we report on a novel, easy-to-synthesize Co catalyst family. Catalyst activation takes place via addition of 2 equiv of a metal base to the cobalt dichlorido precatalysts. Aldehydes and ketones of different types (dialkyl, aryl-alkyl, diaryl) are hydrogenated quantitatively under mild conditions partially with catalyst loadings as low as 0.25 mol%. A comparison of the most active Co catalyst with an Ir catalyst stabilized by the same ligand indicates the superiority of Co. Unique selectivity toward C═O bonds in the presence of C═C bonds has been observed. This selectivity is opposite to that of existing Co catalysts and surprising because of the directing influence of a hydroxyl group in C═C bond hydrogenation.
The synthesis of pyrroles via acceptorless dehydrogenative condensation of secondary alcohols and 1,2-amino alcohols mediated by a robust and reusable catalyst based on nanometer-sized iridium particles †
A series of guanidinato‐ligand‐stabilised titanium complexes has been synthesised and characterised. These compounds can be prepared by carbodiimide insertion into titanium–amide bonds. Reaction of carbodiimides N,N′‐bis(2,6‐diisopropylphenyl)carbodiimide, N,N′‐bis(2,6‐dimethylphenyl)carbodiimide and N‐tert‐butyl‐N′‐(2,6‐diisopropylphenyl)carbodiimide (2a–2c, respectively) with [(Et2N)TiCl3] led to mono(guanidinato)trichloridotitanium(IV) complexes (3a–3c). Subsequent conversion with methylmagnesium chloride gave the corresponding trimethyl complexes (4a and 4b). Single‐crystal X‐ray diffraction analyses were carried out for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of triethylaluminium and undergoes polymeryl chain transfer to aluminium. Irreversible coordinative chain‐transfer polymerisation and a unique combination of catalyst economy and high activity were observed. In the presence of 1000 equivalents of aluminium, a chain elongation of 83.3 % could be achieved with an activity of 9900 kgPE molcat–1 h–1 bar–1. The influence of the steric demand of the ligand on the polymerisation capability is significant and was investigated too.
Alkane elimination of the yttrium monoalkyl [Cp 2 Y(CH 2 Si-Me 3 )(thf)] (Cp = cyclopentadienyl, thf = tetrahydrofuran, Me = methyl) with the tungsten hydrido carbonyl complex [HW(CO) 3 Cp] in THF gave rise to the trinuclear complex [{CpW(CO) 2 (μ-CO)} 2 YCp(thf) 3 ] (1). In the course of the reaction, one Cp ligand per yttrium was redistributed, thus leading to the formation of [Cp 3 Y] as a side product. To avoid the observed ligand redistribution, other solvents were investigated. The reaction of [Cp 2 Y(CH 2 SiMe 3 )(thf)] with [HW(CO) 3 -Cp] in acetonitrile afforded the dinuclear complex [{CpW(CO) 2 (μ-CO)}YCp 2 (NCMe) 2 ] (2). The reaction of the yttrium dialkyl complex [Y(CH 2 SiMe 3 ) 2 (OC 6 H 3 tBu 2 -2,6)-(thf) 2 ] with [HW(CO) 3 Cp] in toluene gave the polymeric compound [{CpW(CO) 2 (μ-CO)} 2 Y(OC 6 H 3 tBu 2 -2,6)] n (3), whereas [a] Lehrstuhl
Diethylamidotitanium trichloride reacts with a variety of bulky amidines ArN(H)C(ArЈ)NAr [Ar = 2,6-diisopropylphenyl; ArЈ = Ph, p-Me 2 NC 6 H 4 , p-MeOC 6 H 4 , p-(2,5-dimethylpyrrole)C 6 H 4 ] to form ammonium titanates. These new titanium complexes undergo polyethylenyl chain transfer polymerization to aluminium alkyls after activation with [a]
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