Charge Effects in PCP Pincer Complexes of NiII bearing Phosphinite and Imidazol(i)ophosphine Coordinating Jaws: From Synthesis to Catalysis through Bonding Analysis |
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| Authors: | Dr. Boris Vabre Dr. Yves Canac Dr. Christine Lepetit Dr. Carine Duhayon Prof. Remi Chauvin Prof. Davit Zargarian |
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| Affiliation: | 1. Département de?chimie, Université de?Montréal, Montréal (Québec), H3C 3J7 (Canada);2. Laboratoire de?Chimie de?Coordination (LCC), CNRS, 205 Route de?Narbonne, 31077 Toulouse (France);3. Université de?Toulouse, UPS, INP, LCC, 31077 Toulouse (France) |
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| Abstract: | This contribution reports on a new family of NiII pincer complexes featuring phosphinite and functional imidazolyl arms. The proligands RPIMCHOPR′ react at room temperature with NiII precursors to give the corresponding complexes [(RPIMCOPR′)NiBr], where RPIMCOPR=κP,κC,κP‐{2‐(R′2PO),6‐(R2PC3H2N2)C6H3}, R=iPr, R′=iPr ( 3 b , 84 %) or Ph ( 3 c , 45 %). Selective N‐methylation of the imidazole imine moiety in 3 b by MeOTf (OTf=OSO2CF3) gave the corresponding imidazoliophosphine [(iPrPIMIOCOPiPr)NiBr][OTf], 4 b , in 89 % yield (iPrPIMIOCOPiPr=κP,κC,κP‐{2‐(iPr2PO),6‐(iPr2PC4H5N2)C6H3}). Treating 4 b with NaOEt led to the NHC derivative [(NHCCOPiPr)NiBr], 5 b , in 47 % yield (NHCCOPiPr=κP,κC,κC‐{2‐(iPr2PO),6‐(C4H5N2)C6H3)}). The bromo derivatives 3–5 were then treated with AgOTf in acetonitrile to give the corresponding cationic species [(RPIMCOPR)Ni(MeCN)][OTf] [R=Ph, 6 a (89 %) or iPr, 6 b (90 %)], [(RPIMIOCOPR)Ni(MeCN)][OTf]2 [R=Ph, 7 a (79 %) or iPr, 7 b (88 %)], and [(NHCCOPR)Ni(MeCN)][OTf] [R=Ph, 8 a (85 %) or iPr, 8 b (84 %)]. All new complexes have been characterized by NMR and IR spectroscopy, whereas 3 b , 3 c , 5 b , 6 b , and 8 a were also subjected to X‐ray diffraction studies. The acetonitrile adducts 6 – 8 were further studied by using various theoretical analysis tools. In the presence of excess nitrile and amine, the cationic acetonitrile adducts 6 – 8 catalyze hydroamination of nitriles to give unsymmetrical amidines with catalytic turnover numbers of up to 95. |
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| Keywords: | electron localization function Fukui indices hydroamination nickel pincer complexes |
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