1,721,097 research outputs found
Complessi di oro con leganti imidazolici di interesse farmacologico
Full text linkL'imidazolo gioca un ruolo importante nella chimica biologica, difatti costituisce un componente laterale dell'istidina, amminoacido essenziale, e si trova anche in molte proteine.Nel nostro gruppo di ricerca da anni ci si occupa della sintesi di complessi con leganti eterociclici azotati, con metalli di transizione come oro, platino e palladio, sia con scopi catalitici che con scopi farmaceutici.Nello specifico il mio lavoro si e basato sulla sintesi di complessi di oro(I) e oro(III) con leganti contenenti anelli imidazolici
Reactivity of tertiary phosphines toward a cyclometallated platinum(II) complex: evaluation of steric and electronic contributions
No full textAn extended series of phosphines (L), having widely different steric and electronic properties, was used to study the kinetics of chloride substitution on the cyclometallated complex [Pt(N-N-C)Cl] (N-N-CH = 6-(1-methylbenzyl)-2,2'-bipyridine). The final cationic products [Pt(N-N-C)(L)](+) were fully characterised by H-1 and P-31{H-1} NMR spectroscopy in CDCl3 solution. The values of the (1)J(PtP) coupling constants for these complexes showed interesting dependencies upon the size and the sigma-donor ability of the ligands. The reaction, in dichloromethane as solvent at 298.2 K, takes place by way of a direct bimolecular attack of the ligand on the substrate, with no evidence of a significant solvent contribution. The order of reactivity is that expected on the Oasis of the nucleophilic reactivity constants (n(pt)(P), derived from previous studies. The values of the second-order rate constants (k(2), M-1 s(-1)) can be resolved quantitatively into steric, electronic and aryl contributions of the phosphine ligands, by use of a four-parameter equation log k(2) alpha + beta(pK(a)') + gamma(theta) + delta(E-ar), where pK(a)' measures the sigma-donor ability of the phosphines, theta (Tolman's cone angle) is a measure of the size of the P-donor ligand, and (ar) is related to the number of aryl groups attached to the ligand phosphorus atom. This is the first reported example of an aryl effect contributing to the nucleophilicity of phosphines as entering ligands on square-planar complexes. No steric threshold is observed. Steric and electronic profiles for the substitution process can be plotted showing the dependence of rates on the size and the sigma-donor ability of the phosphines. The sensitivity of the rates to pK(a)' is significant (beta = 0.20 +/- 0.04) and this is related to the structural properties of the substrate. (C) 1997 Elsevier Science S.A
Role of cyclometalation in controlling the rates of ligand substitution at platinum(II) complexes
No full textThe rates of chloride for triphenylphosphine substitution have been measured in dichloromethane for a series of cyclometalated [Pt(N-N-C)Cl] complexes containing a number of terdentate N-N-C. anionic ligands, derived from deprotonated alkyl-, phenyl-, and benzyl-6-substituted 2,2'-bipyridines. These rates have been compared with those of the corresponding [Pt(N-N)(C)Cl] (N-N = 2,2'-bipyridine; C = CH3 or C6H5) complexes having the same set of donor atoms but less constrained arrangements of the ligands. The reactions of the cyclometalated compounds occur as a single-stage conversion from the substrate to the ionic pair [Pt(N-N-C)(PPh3)]Cl products. There is no evidence by H-1 and P-31{H-1} NMR spectroscopy for the formation of other Pt(II) species or of concurrent ring-opening processes. In contrast, ih the monoalkyl- or monoaryl-2,2'-bipyridine complexes, chloride substitution is followed by subsequent slower processes which involve the detachment of one arm of the chelated 2,2'-bipyridine, fast cis to hans isomerization of the cis-[Pt(PPh3)(2)(eta (1)-bipy)(R)](+) transient intermediate, and, eventually, the release of free bipy, yielding trans-[Pt(PPh3)(2)(R)Cl] (R = Me or Ph). All reactions are first-order with respect to complex and phosphine concentration, obeying the simple rate law k(obsd) =: k(2)[PPh3]. The values of the second-order rate constant k(2) do not seem particularly sensitive to the nature of the bonded organic moiety (alkyl or aryl), to its structure (cyclometalated or not), to the size of the ring, or to the number of alkyl substituents on it. The effects are those foreseen on the basis of an associative mode of activation. The only exception to this pattern of behavior is constituted by the complex [Pt(bipy(phi)-H)Cl] (bipy(phi) = 6-phenyl-2,2(bipyridine), which features a significant rate enhancement with respect to the analogue [Pt(bipy)(Ph)Cl] complex. The results of this work, together with those of a previous paper, Suggest that there is not a specific role of cyclometalation in controlling the reactivity, unless an in-plane aryl ring becomes part of the pi -acceptor system of the chelated 2,2'-bipyridine, behaving as a cyclometalated analogue of the nitrogen terdentate 2,2':6',2 " -terpyridine
Regioselective C(sp2)-C(sp3) Coupling Mediated by Classical and Rollover Cyclometalation
No full textBy taking advantage of a sequence of oxidative addition/reductive elimination reactions, Pt(II) cyclometalated derivatives are able to promote a rare C(sp2)-C(sp3) bond coupling, resulting in the production of novel methyl-substituted pyridines and bipyridines. Starting from 6-phenyl-2,2′-bipyridine, the step-by-step full sequence of reactions has been followed, leading to the unprecedented 3-methyl-6-phenyl-2,2′-bipyridine, which was isolated and fully characterized. The synthesis involves the following steps: (1) rollover cyclometalation to give the starting complex [Pt(N^C)(DMSO)Me]; (2) the synthesis of a more electron-rich complex [Pt(N^C)(PPh3)Me] by the substitution of DMSO with triphenylphosphine; (3) oxidative addition with methyl iodide to give the Pt(IV) complex [Pt(N^C)(PPh3)(Me)2(I)]; (4) iodide abstraction with silver tetrafluoborate to give an unstable pentacoordinate intermediate, which rapidly evolves through a carbon–carbon reductive coupling, forming a new C(sp3)-C(sp2) bond; (5) finally, the extrusion and characterization of the newly formed 3-methyl-6-phenyl-2,2′-bipyridine. The reaction has been therefore extended to a well-known classical cyclometalating ligand, 2-phenylpyridine, demonstrating that the method is not restricted to rollover derivatives. Following the same step-by-step procedure, 2-phenylpyridine was converted to 2-o-tolyl-pyridine, displaying the potential application of the method to the larger family of classical cyclometalated complexes. The application of this protocol may be useful to convert an array of heterocyclic compounds to their methyl- or alkyl-substituted analogs
C(3) aurated 1,4-benzodiazepin-2-ones. Synthesis and characterization. Crystal structure of (L)Au[P(C6H4CH3-4)(3)] (HL = 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one, DIAZEPAM)
No full textThe synthesis of a series of gold(I) metallated derivatives of some 1,4-benzodiazepin-2-ones is described. They include mononuclear (L)Au(PR3) (R = C6H5, C6H4CH3-4 or C2H5) as well as dinuclear species (L)Au(Ph2P(CH2) PPh2)Au(L), n = 2, 3 (HL = 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one, DIAZEPAM or 7-chloro-1-(cyclopropylmethyl)-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin -2-one, PRAZEPAM). The deprotonated ligand is bonded to the AuPR3 moiety through the C(3) atom. Activation of the C(sp(3))-H bond is achieved by means of a strong base in the presence of the phosphinegold chloride intermediate. The structure of (L)Au[P(C6H5CH3-4)(3)] has been determined by X-ray diffraction. Some aspects of the reactivity of the metallated species is also reported. (C) 1998 Elsevier Science S.A.The synthesis of a series of goldI. metallated derivatives of some 1,4-benzodiazepin-2-ones is described. They include mononuclear
L.AuPR3. RsC6H5, C6H4CH3-4 or C2H5. aswell as dinuclear species L.AuPh2PCH2.nPPh2.AuL., ns2, 3 HLs7-chloro-
1,3-dihydro-1-methyl-5-phenyl-2H-1,4-benzodiazepin-2-one, DIAZEPAM or 7-chloro-1-cyclopropylmethyl.-1,3-dihydro-5-phenyl-2H-
1,4-benzodiazepin-2-one, PRAZEPAM.. The deprotonated ligand is bonded to the AuPR3 moiety through the C3. atom. Activation of
the Csp3.–H bond is achieved by means of a strong base in the presence of the phosphinegold chloride intermediate. The structure of
L.AuwPC6H5CH3-4.3x has been determined by X-ray diffraction. Some aspects of the reactivity of the metallated species is also
reported
Cu–iminopyridine complexes as catalysts for carbene and nitrene transfer reactions
No full textCopper complexes with chiral iminopyridine ligands were screened for their catalytic efficiency in carbene (cyclopropanation)
and nitrene transfer reactions (aziridination, C–H amidation). Both pre-formed and in situ formed complexes were considered.
The results highlighted the poor catalytic efficiency of these complexes in cyclopropanation reactions employing methyl
phenyldiazoacetate as the carbene source, whereas better results were obtained in nitrene transfer reactions, particularly in
the amidation of C–H bonds, albeit the enantioselectivity of the reactions was negligible in nearly all cases. Finally, copper complexes
were also found to promote an interesting oxidative functionalization of alkynes with PhI(OAc)2 at room temperature
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