Pendant Imine Research Articles

Direct Polymerization Approach to Synthesize Acid-Degradable Block Copolymers Bearing Imine Pendants for Tunable pH-Sensitivity and Enhanced Release.

The development of effective approaches to synthesize smart amphiphilic block copolymers (ABPs) exhibiting acid-responsive degradation through the cleavage of acid-labile imine bonds is extensively explored for controlled release of encapsulated biomolecules, particularly in drug delivery. Here, a new approach based on direct polymerization utilizing a controlled radical polymerization technique to synthesize acid-degradable ABPs bearing pendant imine linkages in hydrophobic block is reported. The approach centers on the synthesis of a novel methacrylate bearing benzoic imine group that can be polymerized to form the hydrophobic imine pendant block. The formed ABPs respond to mild acidic pHs equivalent to tumoral and endosomal/lysosomal acidic environments. This causes the dissociation of self-assembled nanoassemblies through change in their hydrophilic/hydrophobic balance upon the cleavage of pendant imine linkages to the corresponding aldehyde and primary amine, thus leading to the enhanced release of encapsulated drugs. The proof-of-concept results suggest that this robust approach is versatile to further design advanced nanoassemblies responding to dual/multiple stimuli, thus being more effective to intracellular drug delivery.

Synthesis of Hemilabile Cyclic (Alkyl)(amino)carbenes (CAACs) and Applications in Organometallic Chemistry.

A versatile methodology, involving readily available starting materials, allows for the synthesis of stable hemilabile bidentate cyclic (alkyl)(amino)carbenes (CAACs) featuring alkene, ether, amine, imine, and phosphine functionalities. The stability of the free carbenes has been exploited for the synthesis of copper(I) and gold(I) complexes. It is shown that the pendant imine moiety stabilizes the gold(III) oxidation state and enables the C-C bond oxidative addition of biphenylene to the corresponding cationic gold(I) complex. The latter and the corresponding copper(I) complex show high catalytic activity for the hydroarylation of α-methylstyrene with N,N-dimethylaniline, and the copper(I) complex promotes the anti-Markovnikov hydrohydrazination of phenyl acetylene with high selectivity.

Group 4 Metal Complexes of Chelating Cyclopentadienyl-ketimide Ligands

A pendant nitrile group attached to the lithium cyclopentadienide moiety in (C5H4CMe2CMe2CN)Li was alkylated using organyl lithium reagents (RLi, R = Ph, t-Bu, Me), giving rise to dianionic cyclopentadienyl-ketimides [C5H4CMe2CMe2C(R)═N]Li2, which were subsequently utilized as chelating ligands for the synthesis of group 4 bent metallocene or half-sandwich complexes (12 examples of the types [(η5-C5R′5){η5-C5H4CMe2CMe2C(R)═N-κN}MCl], R′ = H or Me, M = Ti, Zr, or Hf, and [{η5-C5H4CMe2CMe2C(R)═N-κN}TiX2], X = Cl or NMe2, respectively, were prepared and characterized). Consecutive protolysis of the intramolecularly bound ketimide moiety in bent metallocenes afforded pendant imine or cationic iminium moieties, respectively, attached to group 4 organometallic fragments. Selected compounds were used as precatalysts in a preliminary screening for ethylene polymerization activity.

Reaction of primary amines with N-ethynyl pendant arms attached to macrocyclic nickel(II) and copper(II) complexes: Formation of the complexes with pendant imine group(s)

The two N-CH2CCH pendant arms of [NiL1]2+ (L1=2,13-bis(N-propargyl)-3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosane) react readily with benzyl amine or n-propylamine to produce the trans-octahedral complexes, [NiL2]2+ and [NiL4]2+, bearing two N-CH2C(NCH2C6H5)CH3 or two N-CH2C(NCH2CH2CH3)CH3 pendant arms. [CuL1]2+, however, reacts with the primary amines to form a square-pyramidal complex [CuL3]2+ or [CuL5]2+ bearing one N-CH2C(NCH2C6H5)CH3 or N-CH2C(NCH2CH2CH3)CH3 pendant arm as well as one N-CH2CCH group under similar experimental conditions. The pendant imine group of the nickel(II) or copper(II) complexes of L2–L5 is involved in coordination and is inert against hydrolysis, even in aqueous 1.0M HClO4 or 1.0M NaOH solutions.

M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {Co(III), Ni(II), Cu(II) or Zn(II)} complexes bearing pendant Schiff base moieties: spectral characterization, fluorescence, cyclic voltammetric and TGA/DTA study

A series of neutral mononuclear complexes [M{κ2S,S-S2C-piperazine-C2H4N=C(R)}n] {R = Ph; M = Co(III) 1, Ni(II) 2, Cu(II) 3, Zn(II) 4; R = Naph; M = Co(III) 5, Ni(II) 6, Cu(II) 7, Zn(II) 8; n = 2 for 2–4, 6–8 and n = 3 for 1, 5} bearing pendant Schiff base moieties were synthesized through self-assembly involving N-[phenylmethylidene]-2-piperazin-1-ylethanamine (L1) or N-[naphthylmethylidene]-2-piperazin-1-ylethanamine (L2) with two equivalents each of CS2 and corresponding metal acetates. The complexes 1–8 were characterized by microanalysis, ESI-MS, IR, 1H, 13C NMR, DEPT 135, UV–visible absorption, and emission spectroscopy. Complexes 1, 3, and 8 exhibit fluorescence emissions at 342, 344, and 348 nm upon excitation at 273 (for 1 and 3) and 263 (for 8) with concomitant Stokes shifts of 69, 71, and 85 nm. The spectral and magnetic moment data support octahedral geometry around Co(III) and square planar/tetrahedral geometry around other metal centers. Thermal stabilities of 1–8 have been investigated by thermogravimteric analysis. The cyclic voltammograms clearly suggest that the complexes exhibit electroreduction principally associated with pendant imine moieties except Cu(II) complex 7 which displays quasi-reversible reduction corresponds to the Cu(II)/Cu(I) redox couples, in addition to reversible electroreduction of pendant imine groups associated with the coordinated ligands.

Early Transition Metal Complexes Bearing a C-Capped Tris(phenolate) Ligand Incorporating a Pendant Imine Arm: Synthesis, Structure, and Ethylene Polymerization Behavior

The ligand 3-[2,2'-methylenebis(4,6-di- tert-butylphenol)-5- tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L(1)H 3) was reacted with MCl 4 (M = Ti, Zr) or MCl 5 (M = Nb, Ta) to give complexes of the type [MCl 2(L(1)H 2) 2] (M = Ti (1); Zr (2)), [NbCl 3( L (1)H)] (3), or [TaCl 4(L(1)H 2)] (4), respectively. Single crystal X-ray diffraction of 1- 4 revealed common "iminium" species resulting in zwitterionic complexes. Reaction of [V(N p-tol)(O n-Pr) 3] with L (1)H3 afforded [{(VN p-tol)(L(1)H)} 2(mu-O n-Pr)2] (5), and a second complex [(VO) 2(mu-O)(L(3)H) 2] (6)(L(3)H being derived from 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene- p-tolylimine]). The condensation reaction between 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] (L(0)H 3) and o-phenylenediamine (1,2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} (L(5)H6), or the benzimidazolyl bearing ligand (L(6)H 3). The reaction of L (5)H6 or L(6)H 3 with [VO(O n-Pr) 3] under varying conditions produced the complexes [(VO)(L(5)H 4)] (7), [(VO) 2(L(5)H)] (8), or [VO(L(6)H 2) 2] (9). L (0)H 3 was reacted with a number of anilines to give the proligands {3-[2,2'-methylenebis(4,6-di- tert-butylphenol)-5-tert-butylsalicylidene-R-imine]}, where R = NC 6H 5 (L(2)H3), NC 6H 4-Me (L(3)H 3), and NC 6H 2-Me 3 (L(4)H 3). Reactions of these ligands with [VO(O n-Pr) 3] formed bischelating complexes of the form [(VO)(L(2-4)H 2)2] (10, 11, and 12, respectively). The reaction of L (1)H 3 with trimethylaluminum led to a bis-aluminum complex {(AlMe 2)[AlMe(NCMe)] L (1)} (13). The ability of complexes 1-12 to polymerize ethylene in the presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA), whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum cocatalysts. Using the combination of DMAC and ETA, complexes 5-12 were found to be highly active catalysts; in all cases, the polymer formed was of high molecular weight linear polyethylene.

Synthesis of poly condensation

in the present investigation new eight poly esrers as schiff bases wich containing pendant imine group were synthesized by treatment of poly acryloyl chlodire with ethanol amine group were synthesized by treatment of poly acryloyl chloride with ethanol

Stereochemically non-rigid transition metal complexes of 2,6-bis(phenyliminomethyl)pyridine and derivatives. Crystal structure of fac-[ReBr(CO) 3(PMTFA)] (PMTFA=2,6-pyridylene-bis-(methylene-2-trifluoromethylaniline)

The Schiff bases 2,6-bis(phenyliminomethyl)pyridine and its derivatives (L) form bidentate chelate complexes with transition metals Re I, Pt IV and Pd II of general formulation fac-[ReBr(CO) 3L], fac-[PtXMe 3L] (X=Cl, Br or I), and cis-[Pd( p-CF 3C 6F 4) 2L]. In solution these complexes are stereochemically non-rigid, undergoing 1,4-metallotropic shifts and restricted rotations of the substituted aromatic rings attached to the metal-coordinated imino nitrogen. Rates and activation energies of these internal motions were measured by one-dimensional NMR bandshape analysis and two-dimensional EXSY NMR experiments over a range of solution temperatures. Free energy values, Δ G ‡ (298.15 K), for the fluxional shifts were in the range 76–97 kJ mol −1 with the Pd II complexes having the lowest energies. An X-ray crystal structure of fac-[ReBr(CO) 3PMTFA] (PMTFA=2,6-pyridylene-bis(methylene-2-trifluoroaniline)) showed the pendant imine function to be in an E-conformation with its nitrogen trans to the pyridyl nitrogen.

New Zirconium Hydrocarbyl Bis(phosphoranimino) “Pincer” Carbene Complexes

Reaction of the bis(iminodi(phenyl)phosphorano)methanes CH2(Ph2PNR)2 (R = Ad 1, SiMe3 2) with Zr(CH2Ph)4 in toluene under mild conditions gave novel electronically unsaturated bis(hydrocarbyl) carbene complexes of the formula [Zr{C(Ph2PNR)2-κ3C,N,N‘}(CH2Ph)2] (R = Ad 3, SiMe3 4) in high yields. The 13C NMR resonances for the metal-bound carbon (82.8 (3), 84.7 (4) ppm) are shifted upfield relative to the previously known group 4 carbene complexes. The crystal structure of 3 shows a short metal carbon link which is common to two fused four-membered rings which are almost coplanar. The rings are formed by chelation of the two pendant imine centers of the ligand. These complexes represent the first examples of hydrocarbylmetal carbene complexes of a group 4 metal.

Stereochemically non-rigid transition metal complexes of 2,6-bis[1-(phenylimino)ethyl]pyridine (BIP). Part 3. Dynamic NMR studies of fac-[PtXMe 3(BIP)] (X=C1, Br, or I). Crystal structure of fac-[PtIMe 3(BIP)

The complexes fac-[PtXMe 3(BIP)] (X=Cl,Br or I;BIP=2,6-bis[1-(phenylimino)ethyl]pyridine) have been synthesised and characterised as involving BIP as a bidentate chelate ligand. In solution the metal-bound ligand exists in four conformational forms, namely distal and proximal E,E and E,Z-isomers. 2D-EXSY NMR has been used to measure 1,4-metallotropic shifts of the PtXMe 3 moiety between equivalent distal E,E forms, E,Z isomerisation of the pendant imine function and restricted CC rotation of the pendant arm of the BIP ligand. Activation energies, Δ G ≠ (298.15 K), for all these processes are in the range 67–96 kJ mol −1 and are essentially halogen independent. A crystal structure of fac-[PtIMe 3(BIP)] shows that the pendant imine function is in the E-conformation and is rotated at an angle of 80.1° to the plane of the pyridine.

Stereochemically non-rigid transition metal complexes of 2,6-bis[(1-phenylimino)ethyl]pyridine (BIP) Part 2. Dynamic NMR studies of fac-[ReX(CO)3(BIP)] (X = Cl, Br, or I). Crystal structure of fac-[ReBr(CO)3(BIP)

The complexes fac-[PtXMe3(BIP)] (X Cl,Br or I;BIP 2,6-bis[1-(phenylimino)ethyl]pyridine) have been synthesised andcharacterised as involving BIP as a bidentate chelate ligand. In solution the metal-bound ligand exists in four conformationalforms, namely distal and proximal E,E and E,Z-isomers. 2D-EXSY NMR has been used to measure 1,4-metallotropic shifts ofthe PtXMe3 moiety between equivalent distal E,E forms, E,Z isomerisation of the pendant imine function and restricted C Crotation of the pendant arm of the BIP ligand. Activation energies, DG (298.15 K), for all these processes are in the range 67–96kJ mol 1 and are essentially halogen independent. A crystal structure of fac-[PtIMe3(BIP)] shows that the pendant imine functionis in the E-conformation and is rotated at an angle of 80.1° to the plane of the pyridine.

Stereochemically non-rigid transition metal complexes of 2,6-bis[(1-phenylimino) ethyl]pyridine (BIP) part 1. Dynamic NMR studies of [M(C6F5) 2(BIP)] (M = PdII or PtII)

The complexes [M(C6F5)2(BIP)] (M = PdII or PtII, BIP = 2,6-bis[(1-phenylimino)ethyl]pyridine) have been synthesised and characterised as involving BIP as a bidentate chelate ligand. In solution they undergo 1,4 metallotropic shifts of the M(C6 F5)2 moiety, E,Z isomerisation of the pendant imine bond, and restricted C-C rotation of the pendant portion of the BIP ligand. 1H and 19F dynamic NMR studies yielded activation energies for these three types of fluxion. ΔG≠ (298 K) values for the three processes were 89.6, 86.6 and 47.4kJmol−1 respectively for the PtII complex. Values for the PdII complex were significantly lower in magnitude, namely 71.6, 70.4 and 41.8 kJ mol−1 respectively.