The Preparation And Characterization Of Nickel Complexes Supported By ?-diimine And Ketones Ligands

The a-diimine Ni-Ni bond complex is the precursor in this article.We researched on the reaction of the precursor and 1,2-diketones,?,?-unsaturated ketones,and synthesised nine nickel metallorganic compounds.The former contains three potential redox active centers:nickel,?-diimine and 1,2-diketone.For the products of the latter,nickel coordinates with the C=C bond.These complexes were characterized by X-ray crystallography,NMR,EPR,magnetic susceptibility measurement,UV-vis-NIR absorption,and DFT computations.This paper is divided into three sections:1.Simply introduces some typical transition metal-metal bond compounds and the reaction of metallorganic compounds and unsaturated small molecules.2.Reaction of the a-diimine Ni-Ni-bonded compound[(Ni?L·-)2](1,L =[(2,6-iPr2C6H3)NC(Me)]2)with various 1,2-diketones afforded five heteroleptic complexes:[LNi(PhC(O)-C(O)Ph)](2),[LNi(PhC(O)-C(O)Me)](3),[LNi(3,5-tBu2C6H2O2](4),and[(LN i){?-?2,?2-(MeC(O)-C(O)Me)}(NiL)](5).Furthermore,the complex[Na(Et2O)][LNi{PhC(O)-C(O)Ph}](6)was generated by reduction of 2 with 2.0 equiv.of Na metal.It is shown that complexes 2-4 consist of neutral ?-diimine ligand L0,low spin nickel(?)ion(d8),and doubly reduced 1,2-diketone molecule[(BZ)2-,(PPD)2-,(TBQ)2-],while the dinuclear species 5 seemingly exhibits some valence tautomerism:[(L0)(L·-){Ni2}3+(DA)2-](5)or[(L0)(L·-){Ni2}2+(DA)·-](5A).Further reduction of 2 afforded the paramagnetic complex 6,which features an unpaired electron(S = 1/2)localized mainly on the ligand L.3.The Ni-Ni-bonded complex[{Ni?(?-L·-)}2](1)with bridging a-diimine ligands(L =[(2,6-iPr2C6H3)NC(CH3)]2)reacted with ketones through cleavage of the Ni-Ni bond to give the mononuclear product ?2-(C,O)coordinated complex[LNi{(?2-O=CC5H10}](7),and ?2-(C,C)coordinated complexes[LNi{?2-C=C-C=OC3H8}](8),LNi{?2-(C,C)Ph-CH=CH-C=OCH3}](9),[LNi{?2-(C,C)Ph-C=O-CH=CHCH3}](10).During the reaction process,electron transfer fom the monoanionic ligand(L·-)to nickel(?)occurred(Ni?L·-?Ni0L0),yielding the nickel(0)center that favors ?-coordination with the C=O or C=C bond.Furthermore,complex 8-10 exhibits regioselectivity between C=C and C=O bonds.