Resorcinol Based Acyclic Dimeric and Cyclic Di- and Tetrameric Cyclodiphosphazanes: Synthesis, Structural Studies, and Transition Metal Complexes

Pre-arranged building block approach for the orthogonal synthesis of an unfolded tetrameric organic-inorganic phosphazane macrocycle

Inorganic macrocycles remain challenging synthetic targets due to the limited number of strategies reported for their syntheses. Among these species, large fully inorganic cyclodiphosphazane macrocycles have been experimentally and theoretically highlighted as promising candidates for supramolecular chemistry. In contrast, their hybrid organic-inorganic counterparts are lagging behind due to the lack of synthetic routes capable of controlling the size and topological arrangement (i.e., folded vs unfolded) of the target macrocycle, rendering the synthesis of differently sized macrocycles a tedious screening process. Herein, we report-as a proof-of-concept-the combination of pre-arranged building blocks and a two-step synthetic route to rationally enable access a large unfolded tetrameric macrocycle, which is not accessible via conventional synthetic strategies. The obtained macrocycle hybrid cyclodiphosphazane macrocycle, cis-[μ-P(μ-N^tBu)]₂(μ-p-OC₆H₄C(O)O)]₄[μ-P(μ-N^tBu)]₂ (4), displays an unfolded open-face cavity area of 110.1 Ų. Preliminary theoretical host-guest studies with the dication [MeNC₅H₄]₂²⁺ suggest compound 4 as a viable candidate for the synthesis of hybrid proto-rotaxanes species based on phosphazane building blocks.

Recent advances in organophosphorus-chalcogen and organophosphorus-pincer based macrocyclic compounds and their metal complexes

The design and development of phosphorus based macrocycles containing one or more other heteroatoms is of crucial importance for the enhancement of modern synthetic chemistry. In recent years focus on phosphorus based macromolecules has led to intriguing and innovative structures with a variety of applications, including photophysical and host-guest properties, and in organic synthesis. This article summarizes the recent advancements in the synthesis of macrocycles that consist of organophosphorus-chalcogen (P-E, P[double bond, length as m-dash]E; E = O, S, Se) and organophosphorus-pincer based macrocyclic ligands and their transition metal complexes with emphasis given to synthetic methodologies. The reactions involve the modification of simple macrocycles with phosphorus sources or phosphorus-based chalcogenating reagents. Transition metal complexes of phosphine-based macrocyclic pincer ligands and their reactivity are also included.

N-Bridged Acyclic Trimeric Poly-Cyclodiphosphazanes: Highly Tuneable Cyclodiphosphazane Building Blocks

We have synthesized a completely new family of acyclic trimeric cyclodiphosphazane compounds comprising NH, Nⁱ Pr, N^t Bu and NPh bridging groups. In addition, the first NH-bridged acyclic dimeric cyclophosphazane has been produced. The trimeric species display highly tuneable characteristics so that the distance between the terminal N(H)R moieties can be readily modulated by the steric bulk present in the bridging groups (ranging from ≈6 to ≈10 Å). Moreover, these species exhibit pronounced topological changes when a weak non-bonding NH⋅⋅⋅π aryl interaction is introduced. Finally, the NH-bridged chloride binding affinities have been calculated and benchmarked along with the existing experimental data available for monomeric cyclodiphosphazanes. Our results underscore these species as promising hydrogen bond donors for supramolecular host-guest applications.

Covalent and ionic bonding in bi- and tricyclic Group 15 amides: equidistant P-I and As-I bonds and fluxional cations

A series of trivalent Group 15 bis(tert-butylamido)cyclodiphosph(iii)azane element bi- and tricycles of the formulae {[(tBuNP)2(tBuN)2]ElX}, El = P, As, Sb, Bi, where X = Ph, OPh, OtBu, N3, hexamethyldisilylamide (HMDS), OTf, was synthesized from the corresponding chlorides via salt elimination. The ensuing compounds were studied spectroscopically and X-ray crystallographically with a particular focus on the length of the El-X bond. While the Group 15 element to phenyl and HMDS were of normal lengths and completely covalent, those to azide appeared to be partly ionic. The {[(tBuNP)2(tBuN)2]ElI} showed El-I bonds that were substantially longer than the typical element iodide bonds, suggesting a very high degree of polarity and bordering on ionic bonding. Finally, the triflate [(tBuNP)2(tBuN)2]P] + [SO3CF3]- proved to be an ion pair in the solid state. The antimony analog, however, showed a long covalent Sb-O bond in the solid state, although it appears to dissociate into ions in solution. The phosphonium triflate salt is fluxional and exhibits a previously unseen highly symmetrical structure in solution. The bonding trends from completely covalent to completely ionic are discussed in terms steric restrictions and the delocalization of charge in either the cation or the anion.

Catechol and 1,2,4,5-tetrahydroxybenzene functionalized cyclodiphosphazane ligands: synthesis, structural studies, and transition metal complexes

This paper describes the syntheses of two novel cyclodiphosphazane derivatives and their coordination chemistry with Cu^I, Ru^II, Rh^I, Pd^II and Au^I is also described.

Synthesis of tetra-pincer nickel(ii) and palladium(ii) complexes of resorcin[4]arene-octophosphinite [Res(OPR2)8] and rhodium-catalyzed regioselective hydroformylation reaction

This paper describes the synthesis of resorcin[4]arene based octaphosphinite ligands and their tetra-pincer Ni^II and Pd^II complexes and rhodium-octaphosphinite catalyzed hydroformylation of styrene and its derivatives.

The chameleonic reactivity of dilithio bis(alkylamido)cyclodiphosph(iii)azanes with chlorophosphines

Analogous reactions do not necessarily give analogous products.

First examples of tri- and tetraphosphametacyclophanes: synthesis and isolation of an unusual hexapalladium complex containing pincer units with Pd–P covalent bonds

First examples of tri- and tetraphosphametacyclophanes and a rare hexapalladium(ii) dipincer complex containing Pd–P covalent bonds are described.

Cyclodiphosphazanes: options are endless

This short review describes the transition metal chemistry of cyclodiphosphazanes.

Self-Assembled Cyclophane-Type Copper(I) Complexes of 2,4,6-Tris(diphenylphosphino)-1,3,5-triazine and Their Catalytic Application

The triazine-based trisphosphine, 2,4,6-tris(diphenylphosphino)-1,3,5-triazine (1) was prepared in improved yield by reacting cyanuric chloride with 3 equiv of trimethylsilyldiphenylphosphine. The solid-state structure of 1 showed short intermolecular P···P contacts of 3.362 Å, which is significantly shorter than the sum of the van der Waals radii of phosphorus atoms (3.6 Å). The reaction of 2,4,6-tris(diphenylphosphino)-1,3,5-triazine (1) with copper(I) salts in a 2:3 molar ratio yielded various cyclophane-type complexes in quantitative yield. The solid-state structures of these clusters have been found to depend on the size of the halide ions, the solvent employed, and the reaction conditions. Copper(I) chloride formed a monomeric metallocyclophane, whereas copper(I) bromide and copper(I) iodide derivatives preferred dimeric and 1D-polymeric structures, respectively. The tricationic complexes derived from Cu(I) ion and 2,4,6-tris(diphenylphosphino)-1,3,5-triazine also adopted monomeric metallocyclophane structures. These complexes have been employed in the A(3) coupling reaction under microwave irradiation. The copper(I) iodide derivative showed excellent catalytic efficiency.

A cyclodiphosphazane based pincer ligand, [2,6-{μ-((t)BuN)2P((t)BuHN)PO}2C6H3I]: Ni(II), Pd(II), Pt(II) and Cu(I) complexes and catalytic studies

Synthesis and late-transition metal complexes of pincer capable cyclodiphosphazane, 2,6-{μ-((t)BuN)2P((t)BuHN)PO}2C6H3I (1) are described. The condensation of 2-iodoresorcinol with cis-{ClP(μ-N(t)Bu)2PN(H)(t)Bu} produced a difunctional derivative 1 in good yield. The treatment of Ni(COD)2, Pd2(dba)3·CHCl3 or Pt(PPh3)4 with 1 afforded pincer complexes [2,6-{μ-((t)BuN)2P((t)BuHN)PO}2C6H3MI] (2 M = Ni; 3 M = Pd and 4 M = Pt). The reaction of complex 3 with copper halides resulted in the formation of heterobimetallic complexes bridged by rhombic {Cu(μ-X)}2 units, [{{Cu(μ-X)}2}{μ-((t)BuN)2P((t)BuHN)PO}2C6H3PdI] (5 X = I and 6 X = Br). The crystal structures of 1-3, and 6 were established by single X-ray diffraction studies. The palladium complex 3 was tested for catalytic P-arylation of diphenylphosphine oxide (Ph2P(O)H) under microwave irradiation. Moderate to good catalytic activity was observed with aryl bromides.

Steric C–N bond activation on the dimeric macrocycle [{P(μ-NR)}2(μ-NR)]2

The dimeric macrocyclophosphazane [{P(μ-N^tBu)}₂(μ-N^tBu)]₂ ( 1) was reacted with elemental selenium. An unexpected C–N cleavage reaction occurred producing P₄(μ-N^tBu)₃(μ-NH)₃Se₄ ( 2). The C–N bond cleavage is driven by the high steric ring strain present within the ring.

A phosphomide based PNP ligand, 2,6-{Ph2PC(O)}2(C5H3N), showing PP, PNP and PNO coordination modes

Coordination chemistry of a versatile phosphomide ligand, 2,6-{Ph₂PC(O)}₂(C₅H₃N), is described.

Dinuclear Cu(I) complexes of pyridyl-diazadiphosphetidines and aminobis(phosphonite) ligands: synthesis, structural studies and antiproliferative activity towards human cervical, colon carcinoma and breast cancer cells

The copper(i) complexes containing phosphorus donor ligands such as diazadiphosphetidine, cis-{(o-OCH2C5H4N)P(μ-N(t)Bu)}2 (1) and aminobis(phosphonite), C6H5N{P(OC6H3(OMe-o)(C3H5-p))2}2 (2, PNP), have been synthesized. Treatment of 1 with copper iodide afforded the 1D coordination polymer [{Cu(μ-I)}2{(o-OCH2C5H4N)P(μ-N(t)Bu)}2]n (3). Treatment of 3 with 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) produced mixed-ligand complexes [(L)2Cu2{(o-OCH2C5H4N)P(μ-N(t)Bu)}2][I]2 (4 L = bpy; 5 L = phen) in good yields. The reaction of 2 with copper iodide yielded a rare tetranuclear copper complex [(CuI)2C6H5N(PR2)2]2 (6), which on subsequent treatment with various pyridyl ligands produced binuclear complexes [{Cu(μ-I)(py)}2(μ-PNP)] (7), [Cu2(μ-I)(bpy)2(μ-PNP)]I (8), [Cu2(μ-I)I(bpy)(μ-PNP)] (9), [Cu2(phen)(bpy)(μ-PNP)](OTf)2 (10), [Cu2(μ-I)I(phen)(μ-PNP)] (11) and [Cu2(μ-I)(phen)2(μ-PNP)]I (12), in an almost quantitative yield. The new copper(i) complexes (4, 5 and 7-12) were tested for anti-cancer activity against three human tumor cell lines. Compounds 5, 10 and 12 showed in vitro antitumor activity 5-7 fold higher than cisplatin, the most used anticancer drug. These three most potent compounds (5, 10 and 12) were chosen for detailed study to understand their mechanism of action. The copper(i) compounds studied in the present investigation were found to inhibit tumor cell growth by arresting cells at the S-phase of the cell cycle. The characteristic nuclear morphology of treated cells showed signs of DNA damage. The experimental evidence clearly indicated that these compounds initiated apoptosis, which is mediated through the p53 pathway.

Quaternization and oxidation reactions of cyclodiphosphazane derivatives and their copper(I) and gold(I) complexes

The reactions of cyclodiphosphazane derivatives cis-{(t)BuN(H)P(μ-N(t)Bu)2PN(H)(t)Bu} (1), cis-{MeN(C4H8N)P(μ-N(t)Bu)2P(NC4H8Me)} (2) and {(Me2NCH2CH2O)P(μ-N(t)Bu)2P(OCH2CH2NMe2)} (3) with methyl iodide and methyl triflate and their subsequent reactions with elemental sulfur and selenium are reported. Interestingly, the reactions of 1-3 with an excess of methyl iodide resulted in quaternising only one phosphorus atom in cis-[{(t)BuNHP(μ-N(t)Bu)2P(CH3)NH(t)Bu}](I) (4), two exocyclic nitrogen atoms and one of the phosphorus atoms in cis-{(Me2NC4H8N)P(μ-N(t)Bu)2P(CH3)(NC4H8NMe2)}](I)3 (7) and only two exocyclic nitrogen atoms in cis-[{(Me3NCH2CH2O)P(μ-N(t)Bu)2P(OCH2CH2NMe3)}](I)2 (8). The reaction of 1 with one equiv. of methyl triflate produced cis-[{(t)BuN(H)P(μ-N(t)Bu)2P(CH3)N(H)(t)Bu}]OTf (5), whereas the same reaction in a 1 : 2 molar ratio afforded cis-{(t)BuN(H)P(CH3)(μ-N(t)Bu)2P(CH3)N(H)(t)Bu}(OTf)2 (6). Compounds 4 and 5 showed poor solubility in water, whereas 7 and 8 were high melting crystalline solids with moderate to good water solubility. Treatment of 4 with either elemental sulfur or selenium gave both cis- and trans-chalcogenide derivatives. Similar reactions of 7 and 8 produced both mono- and bischalcogenides. Reactions between 4 or 7 and CuI yielded dinuclear complexes, cis-[{Cu2(μ-I)3((t)BuN(H)P)(μ-N(t)Bu)2(P(CH3)N(H)(t)Bu)]2}(I)] (15) and cis-[{Cu2(μ-I)3[(Me2NC4H8N)P(μ-N(t)Bu)2P(CH3)(NC4H8NMe2)]2}(I)5] (16), while the reaction of 8 with CuI produced a coordination polymer [{Cu2(μ-I)3(μ-N(t)BuP)2(OCH2CH2NMe3)2}I]∞ (17), containing triiodo-bridged [Cu2(μ-I)3] linkers. The molecular structures of several of these compounds were confirmed by single crystal X-ray diffraction studies. The Cu(I)···Cu(I) distance of 2.55 Å in 15 is quite short and is the same as that found in copper metal and also in complexes containing [Cu2(μ-I)3] linkers. All the metal complexes exhibit strong intra-, inter- or both intra- and inter-molecular hydrogen bonding interactions.

Novel trisphosphine ligand containing 1,3,5-triazine core, [2,4,6-C3N3{C6H4PPh2-p}3]: synthesis and transition metal chemistry

The trisphosphine ligand with triazine core, 2,4,6-tris{4-(diphenylphosphino)phenyl}-1,3,5-triazine (2), was synthesized in moderate yield by reacting 2,4,6-tris(4-bromophenyl)-1,3,5-triazine with 3 equiv of KPPh2. The tris(phosphine) 2 undergoes facile oxidation to give trischalcogenides 2,4,6-C3N3{C6H4P(E)Ph2-p}3 (E = O, 3; S, 4; Se, 5) on treatment with aqueous H2O2, elemental sulfur, or selenium. The reaction between 2 and [AuCl(SMe2)] yielded a trinuclear complex, [(AuCl)3{2,4,6-C3N3(C6H4PPh2-p)3}] (6), which on further treatment with pyridyl ligands such as 2,2'-bipyridine (2,2'-bpy) and 1,10-phenanthroline (1,10-phen) produced the mixed-ligand complexes [{Au(2,2'-bpy)}3{2,4,6-C3N3(C6H4PPh2-p)3}](OTf)3 (7) and [{Au(1,10-phen)}3{2,4,6-C3N3(C6H4PPh2-p)3}](OTf)3 (8), where OTf indicates trifluoromethansulfonate. Several trimetallic complexes such as [{Ru(η(6)-cymene)Cl2}3{2,4,6-C3N3(C6H4PPh2-p)3}] (9), [{Pd(η(3)-C3H5)Cl}3{2,4,6-C3N3(C6H4PPh2-p)3}] (10), [{Rh(COD)Cl}3{2,4,6-C3N3(C6H4PPh2-p)3}] (11) and [{Ir(COD)Cl}3{2,4,6-C3N3(C6H4PPh2-p)3}] (12) have also been synthesized and characterized. The reactions of 2 with [M(COD)Cl2] and CuI afforded metallo-cyclophane type complexes, [(MCl2)3L2] (M = Pd; 13, Pt; 14) (L = 2,4,6-tris{4-(diphenylphosphino)phenyl}-1,3,5-triazine) and [(CuI)3L2] (15), in good yield.

Novel zeotype frameworks with soft cyclodiphosphazane linkers and soft Cu4X4 clusters as nodes

Two novel zeolitic phosphane cluster frameworks have been synthesized by using ferrocenyl cyclodiphosphazanes [Fe(η⁵-C₅H₄)₂{P(μ-N^tBu)}₂] as ditopic linkers and [Cu₄X₄] clusters as tetrahedral nodes.