Attaching high charge density metal ions to surfaces and biomolecules. Reaction chemistry of hypodentate cobalt diamine complexes

Abstract

Hypodentate diamine cobalt(III) pentammine complexes [Co(NH₃)₅(NH₂(CH₂)_nNH₃)](ClO₄)₄ (8: a: n = 3; b: n = 4; c: n = 6; d: n = 8) have been synthesized via the reaction of [Co(NH₃)₅(OTf)](OTf)₂ (TfOH = CF₃SO₃H) with the corresponding diamines. The analogous t-boc protected diamine complexes [Co(NH₃)₅(NH₂(CH₂)_nNHt-boc)](ClO₄)₃ (7a–d) were prepared in 4–26% yield. Low yields for the formation of 7a–d are due to competing side reactions which also gave [Co(NH₃)₆]³⁺. Complexes 7a–d were deprotected using trifluoroacetic acid to give the corresponding hypodentate diamine complexes [Co(NH₃)₅(NH₂(CH₂)_nNH₃)](CF₃CO₂)_0.5(ClO₄)_3.5 (9a–d). HBTU coupling of 8c with N-(t-boc)-L-phenylalanine gave an amino acid functionalized cobalt pentammine complex [Co(NH₃)₅(NH₂(CH₂)₆NHt-boc)-L-phenylalanine)](ClO₄)₃ (10). All new complexes were characterized using UV-vis and ¹H NMR spectroscopy, and elemental analysis. Grafting of 8c onto 2.4 mm poly(ethylene-co-acrylic acid) (PEAA) beads was achieved via amide coupling. Complex 8c was coupled to thioctic acid via amide coupling and the resulting cobalt disulfide complex [Co(NH₃)₅(N-(6-aminohexyl)-5-(1,2-dithiolan-3-yl)pentanamide)](ClO₄)₃ (11) was attached to 10 nm Au nanoparticles. The amount of cobalt loading onto PEAA beads and Au nanoparticles was determined using ICP-MS and EDX.