Aminoalkyl‐1,1‐bis(phosphinic acids): Stability, Acid–Base, and Coordination Properties

Abstract

Four geminal bis(phosphinic acids), namely, aminomethylbis(H‐phosphinic acid) (H2L1) and 4‐aminobutyl‐1‐hydroxy‐1,1‐bis(R‐phosphinic acid) with R = H (H2L2), Me (H2L3) and CH2CH2COOH (H4L4), were studied. Their acid–base properties and coordination ability towards Cu2+, Ni2+ and Zn2+ ions were studied by potentiometry, UV/Vis spectroscopy and NMR spectroscopy. The amine group in H2L1 has a lower protonation constant (log Ka = 6.79) than those found for other studied bisphosphinates (log Ka = 10.75–11.05) with distant amine groups. The structure of [Ca(H2L2‐O,O′)(HL2‐O,O′)]Cl revealed an octahedral arrangement of the metal coordination sphere and a linear polymeric structure, which forms through eight‐membered Ca(–O–P–O–)2Ca rings. The structure of [Cu(HL3‐O,O′)2(H2O)]·5H2O shows two chelating bisphosphinate groups in an equatorial O4 environment. The structure of [Cu(H0.5L3‐O,O′)(NO3)0.5]·2.25H2O shows two different coordination environments, one is an elongated tetragonal pyramid, and the other is a trigonal bipyramid with a bidentate nitrate ion.

A convenient synthetic route towards H-bisphosphinates

“…These results are in contradiction with Kaboudin's values but in accordance with David's study. 20 Indeed, reported pka values for bis(methylphosphinic acid) are 1.95 and 3.63 corresponding to the two phosphinic acids and are in agreement with our experimental values for bis(H-phosphinic acid).…”

“…To complete our study, we investigated pka values of synthesised H-HMBPi derivatives, especially as only few contradictory data are available in the literature. [19][20] Surprisingly, Kaboudin et al reported two unexpected pka values between 8.1 and 8.7 and 9.3 and 11.9 respectively for aliphatic and aromatic HMBPi. 19 These surprising results encouraged us to determine pka values of some synthesised H-HMBPi derivatives 6.…”

“…The synthetic pathway started from substituted acid chlorides and readily available hypophosphorous acid in presence of N,O-bis(trimethylsilyl)acetamide (BSA) as silylating agent. This procedure provides easily purified H-HMBPi disodium salts in higher yields, shorter reaction times and a wide range of aliphatic and (hetero)aromatic substituents than previously reported [19][20][21]23,24 (Scheme 1).…”

“…In contrast to bisphosphonates, limited number of studies have focused on the synthesis and chemical properties of bisphosphinates. [19][20][21][22][23][24] David et al described only 3 examples of 1-hydroxymethylene-1,1-bis(H-phosphinic acids) to study their bone affinity and one aminoalkyl-1-hydroxymethylene-1,1-bis(H-phosphinic acid) in order to assess their stability, acid/base and coordination properties. 21 They proposed a procedure using a large excess of bis(trimethylsilyl)phosphonite (8 equivalents) to obtain total conversion of acid chloride (Scheme 1).…”

Mechanochemical Access to Elusive Metal Diphosphinate Coordination Polymer

“…In the last 10 years, we have extensively studied P,P -diphenylmethylene diphosphinic acid (H 2 pcp), P,P -diphenylethylene diphosphinic acid (H 2 pc 2 p) and P,P -diphenyl-p-xylylene diphosphinic acid (H 2 pxylp) [4,5] as shown in Scheme 1. Different diphosphinic acids were also reported [6,7].…”