Synthesis and Characterization of Structurally Diverse Alkaline-Earth Salen Compounds for Subterranean Fluid Flow Tracking

Abstract

A family of magnesium and calcium salen-derivatives was synthesized and characterized for use as subterranean fluid flow monitors. For the Mg complexes, di- n-butyl magnesium ([Mg(Bu ⁿ)₂]) was reacted with N, N'-ethylene bis(salicylideneimine) (H₂-salen), N, N'-bis(salicylidene)-1,2-phenylenediamine (H₂-saloPh), N, N'-bis(3,5-di- t-butylsalicylidene)-ethylenediamine (H₂-salo-Bu ^t), or N, N'-bis(3,5-di- t-butylsalicylidene)-1,2-phenylenediamine (H₂-saloPh-Bu ^t), and the products were identified by single-crystal X-ray diffraction as [(κ³-(O,N,N'),μ-(O')saloPh)(μ-(O),(κ²-(N,N'),μ-(O')saloPh)₂(μ-(O),κ³-(N,N',O')saloPh')Mg₄]·2tol (1·2tol; saloPh' = an alkyl-modified saloPh derivative generated in situ), [(κ⁴-(O,N,N',O')saloPh)Mg(py)₂]·py (2·py), [(κ⁴-(O,N,N',O')salo-Bu ^t)Mg(py)₂] (3), [(κ⁴-(O,N,N',O')saloPh-Bu ^t)Mg(py)₂]·tol (4·tol), and [(κ³-(O,N,N'),μ-(O')saloPh-Bu ^t)Mg]₂ (5), where tol = toluene; py = pyridine. For the Ca species, a calcium amide was independently reacted with H₂-salo-Bu ^t and H₂-saloPh-Bu ^t to generate the crystallographcially characterized compounds: [(κ⁴-(O,N,N',O')salo-Bu ^t)Ca(py)₃] (6), [(κ⁴-(O,N,N',O')saloPh-Bu ^t)Ca(py)₃]·py (7·py). The bulk powders of these compounds were further characterized by a number of analytical tools, where 2-7 were found to be distinguishable by Fourier transform infrared and resonance Raman spectroscopies. Structural properties obtained from quantum calculations of gas-phase analogues are in good agreement with the single-crystal results. The potential utility of these compounds as taggants for monitoring subterranean fluid flows was demonstrated through a series of experiments to evaluate their stability to high temperature and pressure, interaction with mineral surfaces, and elution behavior from a loaded proppant pack.