Polyanionic Ligand Platforms for Methyl- and Dimethylaluminum Arrays

Abstract

Trimethylaluminum finds widespread applications in chemical and materials synthesis, most prominently in its partially hydrolyzed form of methylalumoxane (MAO), which is used as a cocatalyst in the polymerization of olefins. This work investigates the sequential reactions of trimethylaluminum with hexaprotic phosphazenes (RNH)6P3N3 (=XH6) equipped with substituents R of varied steric bulk including tert-butyl (1H6), cyclohexyl (2H6), isopropyl (3H6), isobutyl (4H6), ethyl (5H6), propyl (6H6), methyl (7H6), and benzyl (8H6). Similar to MAO, the resulting complexes of polyanionic phosphazenates [XH n ] n−6 accommodate multinuclear arrays of [AlMe2]+ and [AlMe]2+. Reactions were monitored by 31P NMR spectroscopy, and structures were determined by single-crystal X-ray diffraction. They included 1H4(AlMe2)2, 1H3(AlMe2)3, 2H3(AlMe2)3, 3(AlMe2)4AlMe, 4H­(AlMe2)5, 4(AlMe2)6, {5H­(AlMe2)4}2AlMe, 5(AlMe2)6, 6(AlMe2)6, {7(AlMe2)4AlMe}2, and 8(AlMe2)6. The study shows that subtle variations of the steric properties of the R groups influence the reaction pathways, levels of aggregation, and fluxional behavior. While [AlMe2]+ is the primary product of the metalation, [AlMe]2+ is utilized to alleviate overcrowding or to aid aggregation. At the later stages of metalation, [AlMe2]+ groups start to scramble around congested sites. The ligands proved to be very robust and extremely flexible, offering a unique platform to study complex multinuclear metal arrangements.

(Amino)cyclophosphazenes as Multisite Ligands for the Synthesis of Antitumoral and Antibacterial Silver(I) Complexes

“…1.627(3) Å for 7 and 1.6270(15) Å for 9 ] than the P–N­(ring) bonds at the noncoordinating nitrogen center [av. 1.583(3) Å for 7 and 1.5861(15) Å for 9 ] and also the P–N­(ring) bond in the starting phosphazene phos-1 (1.598 Å). , Such an N–P bond length increase flanking the site of coordination (or protonation or alkylation) is known from studies on CPZs. ,,, This is consistent with the bonding model of Craig and Paddock . Accordingly, in such situations, the lone pair on the ring nitrogen atom of the cyclophosphazenes is not available for π-bonding interactions within the ring, causing an increase in the affected bond distance.…”

Gold(i) metallocyclophosphazenes with antibacterial potency and antitumor efficacy. Synergistic antibacterial action of a heterometallic gold and silver-cyclophosphazene

“…95,96 Such an N-P bond-length increase flanking the site of coordination (or protonation or alkylation) is known from studies on cyclotriphosphazenes. [97][98][99][100][101][102] This is consistent with the bonding model of Craig and Paddock. 103,104 Accordingly, in such situations the lone pair on the ring nitrogen atom of the cyclophosphazenes is not available for π-bonding interactions within the ring, causing an increase in the affected bond distance.…”

Effect of Cyclotriphosphazene-Based Curing Agents on the Flame Resistance of Epoxy Resins

“…After the filtration, HCACTP was vacuum-dried at 30 °C for 24 h. Finally, light white product (yield: 89.5%, purity: 99.5%) was prepared (seen in Figure 1). Richards et al [61] already described the procedure of the synthesis of HCACTP derivate that proceeded in toluene solution in the presence of trimethylamine. The yield of the prepared HCACTP according to [61] was only 72%.…”

“…Richards et al [61] already described the procedure of the synthesis of HCACTP derivate that proceeded in toluene solution in the presence of trimethylamine. The yield of the prepared HCACTP according to [61] was only 72%. To the contrary, in this work, an excess of cyclohexylamine instead of triethylamine was used and, moreover, tetrahydrofuran was used as the solvent.…”

“…In this work, two cyclotriphosphazene-based derivatives, namely hexacyclohexylamino-cyclotriphosphazene (HCACTP) [61,62] and novel diaminotetracyclohexylaminocyclotriphosphazene (DTCATP) have been successfully synthetized. These derivatives offer several advantages: halogen-free flame retarding epoxy materials can be produced with better chemical stability and increased flame resistance by introducing the flame retardant in the curing process.…”