Steric and Electronic Properties of N-Heterocyclic Carbenes (NHC): A Detailed Study on Their Interaction with Ni(CO)4
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- 作者：Reto Dorta ; Edwin D. Stevens ; Natalie M. Scott ; Chiara Costabile ; Luigi Cavallo ; Carl D. Hoff ; and Steven P. Nolan
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：March 2, 2005
- 年：2005
- 卷：127
- 期：8
- 页码：2485 - 2495
- 全文大小：295K
- 年卷期：v.127,no.8(March 2, 2005)
- ISSN：1520-5126
文摘
N-heterocyclic carbene ligands IMes (1), SIMes (2), IPr (3), SIPr (4), and ICy (5) react withNi(CO)4 to give the saturated tricarbonyl complexes Ni(CO)3(IMes) (8), Ni(CO)3(SIMes) (9), Ni(CO)3(IPr)(10), Ni(CO)3(SIPr) (11), and Ni(CO)3(ICy) (12), respectively. The electronic properties of these complexeshave been compared to their phosphine analogues of general formula Ni(CO)3(PR3) by recording their 
COstretching frequencies. While all of these NHCs are better donors than tertiary phosphines, the differencesin donor properties between ligands 1-5 are surprisingly small. Novel, unsaturated Ni(CO)2(IAd) (13) andNi(CO)2(ItBu) (14) compounds are obtained from the reaction of Ni(CO)4 with IAd (6) and ItBu (7). Complexes13 and 14 are highly active toward substitution of the NHC as well as the carbonyl ligands. This has allowedthe determination of Ni-C(NHC) bond dissociation energies and the synthesis of various unsaturated Ni(0) and Ni(II) complexes. Computational studies on compounds 8-14 are in line with the experimentalfindings and show that IAd (6) and ItBu (7) are more bulky than IMes (1), SIMes (2), IPr (3), SIPr (4), andICy (5). Furthermore, a method based on %Vbur values has been developed for the direct comparison ofsteric requirements of NHCs and tertiary phosphines. Complexes 8-14, as well as NiCl(C3H5)(ItBu) (16)and NiBr(C3H5)(ItBu) (17), have been characterized by X-ray crystallography.
COstretching frequencies. While all of these NHCs are better donors than tertiary phosphines, the differencesin donor properties between ligands 1-5 are surprisingly small. Novel, unsaturated Ni(CO)2(IAd) (13) andNi(CO)2(ItBu) (14) compounds are obtained from the reaction of Ni(CO)4 with IAd (6) and ItBu (7). Complexes13 and 14 are highly active toward substitution of the NHC as well as the carbonyl ligands. This has allowedthe determination of Ni-C(NHC) bond dissociation energies and the synthesis of various unsaturated Ni(0) and Ni(II) complexes. Computational studies on compounds 8-14 are in line with the experimentalfindings and show that IAd (6) and ItBu (7) are more bulky than IMes (1), SIMes (2), IPr (3), SIPr (4), andICy (5). Furthermore, a method based on %Vbur values has been developed for the direct comparison ofsteric requirements of NHCs and tertiary phosphines. Complexes 8-14, as well as NiCl(C3H5)(ItBu) (16)and NiBr(C3H5)(ItBu) (17), have been characterized by X-ray crystallography.