Nonsymmetrical nickel PCN pincer complexes [Ni­( iPrPCNX)­Cl] (X = NMe, CH2) are obtained by metalation of the benzene–pyridine-based pincer ligand iPrPCNX (X = NMe, CH2) with [Ni­(dme)­Cl2] (dme = 1,2-dimethoxyethane). These nickel species afforded the respective borohydride and ethyl complexes [Ni­( iPrPCNX)­L] (L = BH4, Et) upon treatment with NaBH4 and EtMgBr (or Et2Mg), respectively. Reacting [Ni­( iPrPCNX)­(κ2-BH4)] with CO2 gave the formate complexes [Ni­( iPrPCNX)­(OCHO)]. Treatment of [Ni­( iPrPCNX)­Cl] with the nitrosyl salt NOBF4 led to the formation of the unusual cationic square-pyramidal nickel nitrosyl pincer complexes [Ni­( iPrPCNX)­(NO)­Cl]+ featuring a strongly bent NO ligand (∠Ni–N–O 128.5°). These systems can be described as {NiNO}10 according to the Enemark–Feltham convention. Despite of the bent nature of the NO ligand the νNO is observed at 1849 cm–1 which is more typical for a linear Ni–N–O arrangement. The structure of these complexes is rationalized by means of DFT calculations. The molecular structures of representative complexes are presented.

The synthesis, characterization and reactivity of several new Cr(II) and Cr(III) complexes featuring an NCN pincer ligand with an arene backbone connected to amine donors NEt2 and NiPr2via CH2-linkers is described. Reacting the in situ lithiated ligand precursor N(C-Br)NCH2-Et (1) with [CrCl3(THF)3] resulted in the formation of the Cr(III) complex trans-[Cr(κ3NCN-NCNCH2-Et)(Cl)2(THF)] (3). Upon reaction of lithiated N(C-Br)NCH2-iPr (2) with a suspension of anhydrous CrCl2, the Cr(II) complex [Cr(κ2NC-NCNCH2-iPr)2] (4) is formed featuring two NCN ligands bound in κ2NC-fashion. In contrast, when lithiated 2 is reacted with a homogeneous solution of anhydrous CrX2 (X = Cl, Br), complexes [Cr(κ3NCN-NCNCH2-iPr)X] (5a,b) are obtained. Treatment of 5a with 1 equiv of PhCH2MgCl and LiCH2SiMe3 afforded the alkyl complexes [Cr(κ3NCN-NCNCH2-iPr)(CH2Ph)] (6) and [Cr(κ3NCN-NCNCH2-iPr)(CH2SiMe3)] (7). All Cr(II) complexes exhibit effective magnetic moments in the range of 4.7–4.9 µB which is indicative for d4 high spin systems. If a solution of lithiated 2 is treated with CrCl2, followed by addition of an excess of Na[HB(Et)3], the dimeric complex [Cr(κ2NC-NCNCH2-iPr)(µ2-H)]2 (8) is obtained bearing two bridging hydride ligands. [Cr(κ3NCN-NCNCH2-iPr)(CH2SiMe3)] (7) turned out to be catalytically active for the hydrosilylation of ketones at room temperature with a catalyst loading of 1 mol%. X-ray structures of all complexes are presented.

The synthesis and characterization of two Co(II) complexes stabilized by a tridentate SCS pincer ligand are described. Paramagnetic [Co(κ3-SCSCH2-Et)2] and [Co(κ3-SCSCH2-tBu)(κ2-SCSCH2-tBu)] were obtained via transmetalation protocol from CoBr2 and S(C-Br)SCH2-R (R = Et, tBu). Oxidation of the latter with [Cp2Fe]PF6 affords the diamagnetic 18 VE complex [Co(κ3-SCSCH2-tBu)2]PF6. X-ray structures and DFT calculations are presented. Graphical abstract