The synthesis of PNP-supported low-spin nitro manganese(I) carbonyl complexes

The coordination chemistry of Mn(CO)(5)Br was investigated with a series of PNP-pincer ligands. The ligands (PONOP)-P-iPr ((PONOP)-P-iPr = 2,6-bis(diisopropylphosphinito)pyridine) and (PNP)-P-iPr-P-H ((PNP)-P-iPr-P-H = HN (CH2CH2(PiPr(2))}(2)) gave the desired organometallic manganese complexes ((PONOP)-P-iPr)Mn(CO)(2)Br and ((PNP)-P-iPr-P-H)Mn(CO)(2)Br, respectively, upon chelation to Mn(CO)(5)Br. The reactivity of (PNNNP)-P-iPr ((PNNNP)-P-iPr = N,N'-bis(diisopropylphosphino)-2,6-diaminopyridine) with Mn(CO)(5)Br yielded a pair of products, [((PNNNP)-P-iPr)Mn(CO)(3)][Br] and ((PNNNCO)-P-iPr)Mn(CO)(3). The formation of the asymmetric chelate arises from a formal loss of iPr(2)PBr and C-N bond formation from a carbonyl ligand and NH, yielding a Mn(I) amide core. The nitration reactions of ((PONOP)-P-iPr)Mn(CO)(2)Br and ((PNHP)-P-iPr)Mn(CO)(2)Br were carried out using silver nitrite, yielding the nitro compounds ((PONOP)-P-iPr)Mn(CO)(2)(NO2) and ((PNP)-P-iPr-P-H)Mn (CO)(2)(NO2), respectively. The analogous iron complex ((PONOP)-P-iPr)Fe(CO)Cl-2 was nitrated under the same conditions to yield the salt pair [((PONOP)-P-iPr)Fe(CO)(2)][FeCl3NO]. This reactivity underlines the difference between iso-valent iron and manganese centers. The manganese complexes ((PONOP)-P-iPr)Mn(CO)(2)(NO2) and ((PNP)-P-iPr-P-H)Mn(CO)(2)(NO2) were ineffective as oxygen atom transfer reagents for a variety of substrates. (C) 2016 Elsevier Ltd. All rights reserved.