NMR spectroscopy and structural characterization of dithiophosphinate ligands relevant to minor actinideextraction processes

Abstract

Synthetic routes to alkyl and aryl substituted dithiophosphinate salts that contain non-coordinating PPh(4)(+) counter cations are reported. In general, these compounds can be prepared via a multi-step procedure that starts with reacting secondary phosphines, i.e. HPR(2), with two equivalents of elemental S. The synthetic transformation proceeds by oxidation of the phosphine followed by insertion of S into the H-P bond. This approach was used to synthesize a series of dithiophosphinic acids that were fully characterized, namely HS(2)P(p-CF(3)C(6)H(4))(2), HS(2)P(m-CF(3)C(6)H(4))(2), HS(2)P(o-MeC(6)H(4))(2) and HS(2)P(o-MeOC(6)H(4))(2). Although the insertion step was found to be much slower than the oxidation reaction, the formation of (NH(4))S(2)PR(2) from HPSR(2) occurred rapidly upon addition of NH(4)OH. Subsequent cation exchange reactions proceeded readily with PPh(4)Cl in water, under air and at ambient conditions to provide analytically pure samples of [PPh(4)][S(2)PR(2)] (R = p-CF(3)C(6)H(4), m-CF(3)C(6)H(4), o-CF(3)C(6)H(4), o-MeC(6)H(4), o-MeOC(6)H(4), Ph, and Me, 1b-7b, respectively), which were characterized by elemental analysis, multinuclear NMR, and IR spectroscopy. In addition, S(2)PPh(2)(-) and dithiophosphinates with ortho-substituted aryl groups (3b-6b) were characterized by X-ray crystallography. As opposed to the acids, which have short P=S double bonds and long P-SH single bonds, the metric parameters for the S atoms in S(2)PR(2)(-) are equivalent. In addition, the presence of large non-coordinating PPh(4)(+) cations guard against intermolecular P-S···X interactions and ensure that the P-S bond is isolated. These S(2)PR(2)(-) anions, which can be prepared in large quantities and isolated in crystalline form, are attractive for spectroscopic and theoretical studies because the P-S interaction can be probed independently in the absence of intermolecular interactions.

Unprecedented η3-Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)

“…The La1-S1 distance was found to be 2.950(2) Å and is slightly longer compared to a reported lanthanumsulfur single bond with the same supporting ligand (2.718(1) Å), [15] indicating a reduced negative charge on the sulfur atom and a potential partial conjugation of the CCAAC=C=P unit with the P-S bond. This would be in line with the P5-S1 bond length of 2.081(3) Å, which lies in between the values for a S=P double (≈1.95 Å) [28] and S-P single bond (≈2.12 Å). [29] Notably, a phosphaalkene thioether has recently been reported by Jones and Kollmann, [30] showing a S-P bond length (2.095(1) Å) comparable to the one determined in 5a.…”

N‐Heterocyclic Carbene Adducts of Phenyldioxophosphorane and Its Heavier Sulfur and Selenium Analogues

“…This is consistent with the trend established for the 31 P– 13 C coupling constants (Table ). The P–E bond lengths [ 3 : 1.9780(4) and 1.9688(4) Å; 4 : 2.1361(8) and 2.1299(8) Å] are longer than expected for P=E double bonds (P=S: 1.954 Å; P=Se: 2.093 Å) and lie in the range of comparable anionic R 2 PE 2 species …”

η3‐Coordination and Functionalization of the 2‐Phosphaethynthiolate Anion at Lanthanum(III)**

“…This would be in line with the P5−S1 bond length of 2.081(3) Å, which lies in between the values for a S=P double (ca. 1.95 Å) [28] and S−P single bond (ca. 2.12 Å) [29] .…”