Iron and Chromium Complexes Containing Tridentate Chelates Based on Nacnac and Imino- and Methyl-Pyridine Components: Triggering CX Bond Formation

Nacnac-based tridentate ligands containing a pyridyl-methyl and a 2,6-dialkyl-phenylamine (i.e., (2,6-R2-C6H3NC(Me)CHC(Me)NH(CH2py); R = Et, {Et(nn)PM}H; R = i Pr, { i Pr(nn)PM}H) were synthesized by condensation routes. Treatment of M{N(TMS)2}THF n (M = Cr, n = 2; M = Fe, Co, n = 1; TMS = trimethylsilane; THF = tetrahydrofuran) with { i Pr(nn)PM}H) afforded { i Pr(nn)PM}MN(TMS)2 (1-M iPr; M = Cr, Fe); {Et(nn)PM}MN(TMS)2 (1-MEt; M = Fe, Co) was similarly obtained. {R(nn)PM}FeBr (R = i Pr, Et; 2-FeR) were prepared from FeBr2 and {R(nn)PM}Li, and alkylated to generate {R(nn)PM}FeneoPe (R = i Pr, Et; 3-FeR). Carbonylation of 3-FeR provided { i Pr(nn)PM}Fe(COneoPe)CO (4-Fe iPr), and carbonylations of 1-FeR (R = Et, i Pr) and 1-Cr iPr induced deamination to afford {R(nn)PI}Fe(CO)2 (R = i Pr, 5-Fe iPr; Et, 5-FeEt), where PI is pyridine-imine, and {κ2-N,N-pyrim-pyr}Cr(CO)4 (6-Cr iPr), in which the aryl-amide side of the nacnac attacked the incipient PI group. Carbon–carbon bonds were formed at the imine carbon of the {R(nn)PI} ligand. Addition of [{ i Pr(nn)PI}2–](K+(THF) x )2 to FeCl3 generated { i Pr(nn)CHpy}2Fe2Cl2 (7-Fe iPr), and TMSN3 induced the deamination of 1-FeEt, but with disproportionation to provide {[Et(nn)CHpy]2}Fe (8-FeEt). Ph2CN2 induced C–C bond formation with 1-Fe iPr via its thermal degradation to ultimately afford { i Pr(nn)CHpy}2(FeNCPh2)2 (9-Fe iPr). The compounds were examined by X-ray crystallography (1-M iPr, M = Cr, Fe; 1-CoEt; 2-Fe iPr; 4-Fe iPr; 5-Fe iPr; 6-Cr iPr; 7-Fe iPr; 8-FeEt; 9-Fe iPr), Mössbauer spectroscopy, and NMR spectroscopy. Structural parameters assessing redox noninnocence are discussed, as are structural and mechanistic consequences of the various electronic environments.