Mechanochemical P-derivatization of 1,3,5-Triaza-7-Phosphaadamantane (PTA) and Silver-Based Coordination Polymers Obtained from the Resulting Phosphabetaines

Abstract

We have described earlier that in aqueous solutions, the reaction of 1,3,5-triaza-7-phosphaadamantane (PTA) with maleic acid yielded a phosphonium-alkanoate zwitterion. The same reaction with 2-methylmaleic acid (citraconic acid) proceeded much slower. It is reported here, that in the case of glutaconic and itaconic acids (constitutional isomers of citraconic acid), formation of the corresponding phosphabetaines requires significantly shorter reaction times. The new phosphabetaines were isolated and characterized by elemental analysis, multinuclear NMR spectroscopy and ESI-MS spectrometry. Furthermore, their molecular structures in the solid state were determined by single crystal X-ray diffraction (SC-XRD). Synthesis of the phosphabetaines from PTA and unsaturated dicarboxylic acids was also carried out mechanochemically with the use of a planetary ball mill, and the characteristics of the syntheses in solvent and under solvent-free conditions were compared. In aqueous solutions, the reaction of the new phosphabetaines with Ag(CF₃SO₃) yielded Ag(I)-based coordination polymers. According to the SC-XRD results, in these polymers the Ag(I)-ion coordinates to the N and O donor atoms of the ligands; however, Ag(I)-Ag(I) interactions were also identified. The Ag(I)-based coordination polymer (CP1.2) formed with the glutaconyl derivative of PTA (1) showed considerable antimicrobial activity against both Gram-negative and Gram-positive bacteria and yeast strains.

Keywords: 1,3,5-Triaza-7-phosphaadamantane (PTA); antimicrobial activity; ball mill; coordination polymer; mechanochemistry; phosphonium salt; silver.

Figure 1

PTA and PTA-derived phosphonium salts.

Figure 2

Evolution in time of the ³¹P NMR spectra of aqueous reaction mixtures containing equivalent amounts of PTA and trans-glutaconic acid. Conditions: PTA (157 mg, 1.0 mmol), trans-glutaconic acid (130 mg, 1.0 mmol) in 2.5 mL water, T = 70 °C.

Figure 3

Synthesis of 1 and 2 in water or in a planetary ball mill (pbm).

Figure 4

Capped stick representation of 1 × H₂O (left) and 2 × 2H₂O (right) with partial atom numbering. Selected bond lengths and angles are shown in Table S2.

Figure 5

Typical view of 1 in its crystal structure. (Left): H-bonds between PTA units, (Right): H-bonds between PTA and H₂O molecules. (O42–H...O12⁽ⁱⁱ⁾ = 2.571(3) Å, O1W–H...O11 = 2.781(3) Å, O1W–H...N1⁽ⁱ⁾ = 2.889(3) Å [Symmetry codes: (i) x,y,−1 + z, (ii) 1 − x,−y,z]).

Figure 6

Partial packing view of 2. (Left): Hydrogen bonds between the PTA units. (Right): The connection between PTA units via H₂O molecules (Bond lengths (Å): O42–H...O12⁽ⁱⁱ⁾ = 2.515(7), O2W–H...O12⁽ⁱⁱⁱ⁾ = 2.806(8), O2W–H...O11⁽ⁱⁱ⁾ = 2.725(8), [Symmetry codes: (ii) 1 + x,y,–1 + z (iii) 2 − x,1 − y,1 − z]).

Scheme 1

Synthesis of the coordination polymers CP1.1 and CP1.2.

Figure 7

Partial packing view of CP1.1 Selected bond lengths (Å): Ag1–O11 = 2.294(3), Ag1–N2⁽ⁱ⁾ = 2.439(3), Ag1–N1⁽ⁱⁱ⁾ = 2.465(3), Ag1–O54 = 2.691(4), P1-O11 = 2.798(3), P1–C12 = 1.818(4), Ag1–O12 = 2.963(3), weak interactions: Ag1–O53⁽ⁱⁱⁱ⁾ = 3.248(6), Ag1–O52⁽ⁱⁱⁱ⁾ = 3.166(6) [Symmetry codes: (i) −x, 1 − y,1 − z, (ii) x,3/2 − y,1/2 + z (iii) x,3/2 − y,1/2 + z (iv) 1 − x,−1/2 + y,3/2 − z, (v) –x,2 − y,1 − z].

Figure 8

Partial packing view of CP1.2 with selected bond lengths (left). Geometry of Ag2…Ag2 junctions (right). Hydrogen atoms are omitted for the clarity. (Bond lengths (Å): Ag1–O12 = 2.282(3), Ag1–O3^(iv) = 2.641(6), Ag1–N2^(iv) = 2.445(3), Ag2–N1^(vi) = 2.420(3), Ag2–Ag2(ⁱⁱⁱ) = 2.8987(6), P1–C12 = 1.832(4), P1–O12 = 2.873(3), P1–O42 = 2.858(3), Ag2–O41 = 2.176(5), Ag2–O42⁽ⁱⁱⁱ⁾ = 2.217(3)Å). Ag2 – O11⁽ⁱ⁾ = 2.474(4), Ag2–O2⁽ⁱⁱⁱ⁾ = 2.781(5), [Symmetry code: (i) 1/2 – x,–1/2 + y,3/2 – z, (iii) –x,1 – y,1 – z, (iv) 1 – x,1 – y,1 – z, (vi) 1/2 + x,3/2 – y,1/2 + z]).

Scheme 2

Synthesis of the coordination polymers CP2.

Figure 9

Partial packing view of CP2. Selected bond lengths (Å): Ag1–O2W = 2.383(4), Ag1–O11 = 2.319(5), Ag1–Ag1⁽ⁱⁱⁱ⁾ = 2.8315(6), Ag1–O12⁽ⁱⁱⁱ⁾ = 2.253(5), Ag1–N2^(v) = 2.480(6), Ag2–O1W = 2.377(4), Ag2–O31 = 2.241(5), Ag2–O32 = 2.301(5), Ag2–N23⁽ⁱⁱ⁾ = 2.493(6), Ag2–Ag2^(iv) = 2.8310(6), Ag3–O1W = 2.357(6), Ag3–O32 = 2.668(4), Ag3–O33 = 2.342(6), Ag3–O81 = 2.584(3), Ag3–N1^(v) = 2.458(6), Ag3–O42 = 2.672(4), Ag4–O2W = 2.351(6), Ag4–O11 = 2.672(4), Ag4–O41 = 2.343(6), Ag4–O93 = 2.609(9), Ag4–N21 = 2.449(6), Ag1–Ag4 = 3.651, Ag2–Ag3 = 3.641, [Symmetry codes: (ii) 1 + x,y,z, (iii) –x,1 – y, – z, (iv) 1 – x,1 – y,–1-z (v) 1 – x,1 – y,–z ].