[(NHC)CoR₂]: pre-catalysts for homogeneous olefin and alkyne hydrogenation

Abstract

[(ItBu)Co(CH2SiMe3)2] serves as an efficient, homogeneous olefin hydrogenation catalyst.

Reactivity of a Two-Coordinate Cobalt(0) Cyclic (Alkyl)(amino)carbene Complex

“…The two C alkyne atoms of the alkyne ligand are coplanar with the cobalt center and the two C carbene atoms. The distance of the C alkyne C alkyne bond (1.285(5) Å) is comparable to the C alkyne C alkyne distances in [(I t Bu)­Co­( η 2 -PhCCPh) 2 ] (1.282(2) Å, I t Bu = 1,3-di- tert -butylimidazolin-2-ylidene), [(IPr)­Fe­( η 2 -PhCCH) 2 ] (1.263(3) Å), and [(P i Pr 3 ) 2 Ni­(η 2 -EtCCEt)] (1.275(6) Å) and longer than the CC distance of free acetylenes (1.17 Å) . Along with the elongation of the C alkyne C alkyne bond, the C alkyne C alkyne C Et analogue in 9 is bent (139.3(1)°).…”

“…Structurally authenticated cobalt(0) complexes with coordination numbers of less than 4 are relatively scarce and were only known very recently (Chart ). − We reported that the combined ligand set of N -heterocyclic carbene with vinylsilanes is effective in stabilizing three-coordinate cobalt(0) complexes in the forms of (NHC) n Co­(CH 2 CHSiR 3 ) x ( n = 1, x = 2; n = 2, x = 1, Chart ). − These NHC–cobalt(0)–vinylsilane complexes show rich reactivity toward organic azides, − hydrosilanes, hydrophosphines, and nitrosoarenes, giving cobalt imido, silyl, phosphido, and nitrosyl complexes, respectively.…”

Ligand Exchange Reactions of [(tmeda)NiR2] (R = CH2CMe3, CH2SiMe3, CH2CMe2Ph) with N-Heterocyclic Carbenes and Bidentate Phosphines

“…19 In a recent study we have demonstrated that [(tmeda)CoR 2 ] complexes can be isolated in good yield and excellent purity when [(tmeda)Co(acac) 2 ] is treated with dialkylmagnesium reagents, MgR 2 . 20 Furthermore, the coordinated tmeda is readily displaced by bidentate phosphines or N-heterocyclic carbenes (NHC) 21 to form four-and three-coordinate complexes, respectively. 20 In this contribution we extend this general synthetic methodology to the preparation of compounds [(tmeda)NiR 2 ] (R = CH 2 SiMe 3 , CH 2 CMe 3 , CH 2 CMe 2 Ph).…”

“…20 Furthermore, the coordinated tmeda is readily displaced by bidentate phosphines or N-heterocyclic carbenes (NHC) 21 to form four-and three-coordinate complexes, respectively. 20 In this contribution we extend this general synthetic methodology to the preparation of compounds [(tmeda)NiR 2 ] (R = CH 2 SiMe 3 , CH 2 CMe 3 , CH 2 CMe 2 Ph). Moreover, their reactivity toward N-heterocyclic carbenes and a bidentate phosphine is described.…”

“…It is therefore unsurprising that the synthesis and reactivity of bis­(alkyl) Ni­(II) complexes of the type [L 2 NiR 2 ] have been extensively investigated, along with the intrinsic reactivity of the σ-Ni–C bond toward the insertion of small molecules. − Many important contributions can be traced back to the pioneering work of Carmona and co-workers. − In their original investigations of [L 2 NiR 2 ] (L = monodentate or bidentate ligands), [(py) 2 NiR 2 ] served as a useful starting material, being in turn prepared from [(py) 4 NiCl 2 ] and the corresponding Grignard reagents, RMgX. , Alternatively, [(tmeda)­NiMe 2 ] is accessible from the reaction of [(tmeda)­MgMe 2 ] and [(tmeda)­Ni­(acac) 2 ]. , The nickel precursor [(tmeda)­Ni­(acac) 2 ] combines many advantages; it can be prepared on a multigram scale, and it is readily purified by crystallization or sublimation . In a recent study we have demonstrated that [(tmeda)­CoR 2 ] complexes can be isolated in good yield and excellent purity when [(tmeda)­Co­(acac) 2 ] is treated with dialkylmagnesium reagents, MgR 2 . Furthermore, the coordinated tmeda is readily displaced by bidentate phosphines or N-heterocyclic carbenes (NHC) to form four- and three-coordinate complexes, respectively .…”