Isomorphous rare-earth tris[bis(2,6-diisopropylphenyl) phosphate] complexes and their catalytic properties in 1,3-diene polymerization and in the inhibited oxidation of polydimethylsiloxane

Abstract

Crystals of mononuclear tris[bis(2,6-diisopropylphenyl) phosphato-κO]pentakis(methanol-κO)lanthanide methanol monosolvates of lanthanum, [La(CHOP)(CHOH)]·CHOH, (1), cerium, [Ce(CHOP)(CHOH)]·CHOH, (2), and neodymium, [Nd(CHOP)(CHOH)]·CHOH, (3), have been obtained by reactions between LnCl(HO) (n = 6 or 7) and lithium bis(2,6-diisopropylphenyl) phosphate in a 1:3 molar ratio in methanol media. Compounds (1)-(3) crystallize in the monoclinic P2/c space group and have isomorphous crystal structures. All three bis(2,6-diisopropylphenyl) phosphate ligands display a κO-monodentate coordination mode. The coordination number of the metal atom is 8. Each [Ln{OP(O-2,6-PrCH)}(CHOH)] molecular unit exhibits four intramolecular O-H...O hydrogen bonds, forming six-membered rings. The unit forms two intermolecular O-H...O hydrogen bonds with one noncoordinating methanol molecule. All six hydroxy H atoms are involved in hydrogen bonding within the [Ln{OP(O-2,6-PrCH)}(CHOH)]·CHOH unit. This, along with the high steric hindrance induced by the three bulky diaryl phosphate ligands, prevents the formation of a hydrogen-bond network. Complexes (1)-(3) exhibit disorder of two of the isopropyl groups of the phosphate ligands. The cerium compound (2) demonstrates an essential catalytic inhibition in the thermal decomposition of polydimethylsiloxane in air at 573 K. Catalytic systems based on the neodymium complex tris[bis(2,6-diisopropylphenyl) phosphato-κO]neodymium, (3'), which was obtained as a dry powder of (3) upon removal of methanol, display a high catalytic activity in isoprene and butadiene polymerization.

Dinuclear neodymium and lanthanum bis(2,6-diisopropylphenyl) phosphate complexes bearing a hydroxide ligand: catalytic activity of the Nd complex in 1,3-diene polymerization

“…complex (2) (this work), and not containing those, i.e. complex (3) (Nifant'ev et al, 2014;Minyaev et al, 2018a), with the same organophosphate ligand. This has allowed us to clarify the role of the neodymium salt composition on its catalytic activity.…”

“…The crystal structures of three isostructural tris(organophosphate) complexes [Ln{O 2 P-(O-2,6-i Pr 2 C 6 H 3 ) 2 } 3 (CH 3 OH) 5 ]ÁCH 3 OH (Ln = Nd, Ce and Lu), obtained using a 3:1 reagent molar ratio, have been established recently (Fig. 1, bottom left; Minyaev et al, 2018a). Syntheses of various Ln complexes with [(2,6-t Bu 2 -4-MeC 6 H 2 -O)(EtO)POO] À and [(2,6-i Pr 2 C 6 H 3 -O) 2 POO] À organophosphate ligands.…”

Crystal structure of tris[bis(2,6-diisopropylphenyl) phosphato-κO]pentakis(methanol-κO)europium methanol monosolvate

“…Meanwhile, a so-called 'antenna' ligand possessing a conjugated -electron system may increase the quantum yield of lanthanide complexes dramatically (Bü nzli & Piguet, 2005;Guillou et al, 2016). In order to examine the possibility of applying a disubstituted organophosphate anion as an 'antenna' ligand for luminescence sensitization, we have chosen the bis(2,6-diisopropylphenyl) phosphate anion, which allows single crystals of mono-and binuclear rare-earth complexes to be obtained (Minyaev et al, 2017(Minyaev et al, , 2018a, unlike most other di(alkyl/aryl) phosphate ligands that do not provide crystallizable lanthanide compounds. Mononuclear rare-earth complexes with this ligand form two isotructural series of bis-and tris(phosphate) complexes: {Ln[O 2 P(O-2,6-i Pr 2 C 6 H 3 ) 2 ] 2 Cl(CH 3 OH) 4 }Á2CH 3 OH (Ln = Nd, Y, Lu; Minyaev et al, 2017) and {Ln[O 2 P(O-2,6-i Pr 2 C 6 H 3 ) 2 ] 3 -(CH 3 OH) 5 }ÁCH 3 OH (Ln = La, Ce, Nd; Minyaev et al, 2018a).…”

[Bis(2,6-diisopropylphenyl) phosphato-κO]pentakis(methanol-κO)manganese bis(2,6-diisopropylphenyl) phosphate methanol trisolvate

“…Polydimethylsiloxane (PDMS) liquids are widely applied in many devices as shock-absorbing, hydraulic and damping liquids, as bases for greases and as heat-transfer agents for many industrial processes carried out at elevated temperatures. Various lipophilic derivatives of metals with variable valency, such as Mn, Fe, Ni, Ce, etc., are used for the inhibition of thermo-oxidative decomposition of polyorganosiloxane heat carriers (Swihart & Jones, 1985;Nielsen, 1961;Halm, 1980;Kobzova et al, 1966;Kishimoto et al, 1976;Rozanova et al, 1995;Minyaev et al, 2018a) in order to increase their operating time and temperature (usually up to ca 550 K). As manganese-based inhibitors, cymantrene and its derivatives have shown promising results (Sobolevskiy et al, 1970).…”

“…We tested the title Mn compound as a possible inhibitor for the thermal decomposition of the heat-transfer agent PDMS in air at a temperature of 573 K, and compared the obtained results with control experiments and with experiments, where the Ce complex [Ce{O 2 P(O-2,6-i Pr 2 C 6 H 3 ) 2 } 2 (CH 3 OH) 5 ]Á-CH 3 OH bearing the same ligand was used (Minyaev et al, 2018a). All experiments were carried out under the same conditions ( Table 1).…”