Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 33
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Inorg Chem ; 51(5): 3186-93, 2012 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-22356560

RESUMO

Reported herein is the synthesis of the previously unknown [Ir(1,5-COD)(µ-H)](4) (where 1,5-COD = 1,5-cyclooctadiene), from commercially available [Ir(1,5-COD)Cl](2) and LiBEt(3)H in the presence of excess 1,5-COD in 78% initial, and 55% recrystallized, yield plus its unequivocal characterization via single-crystal X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, electrospray/atmospheric pressure chemical ionization mass spectrometry (ESI-MS), and UV-vis, IR, and nuclear magnetic resonance (NMR) spectroscopies. The resultant product parallels--but the successful synthesis is different from, vide infra--that of the known and valuable Rh congener precatalyst and synthon, [Rh(1,5-COD)(µ-H)](4). Extensive characterization reveals that a black crystal of [Ir(1,5-COD)(µ-H)](4) is composed of a distorted tetrahedral, D(2d) symmetry Ir(4) core with two long [2.90728(17) and 2.91138(17) Å] and four short Ir-Ir [2.78680 (12)-2.78798(12) Å] bond distances. One 1,5-COD and two edge-bridging hydrides are bound to each Ir atom; the Ir-H-Ir span the shorter Ir-Ir bond distances. XAFS provides excellent agreement with the XRD-obtained Ir(4)-core structure, results which provide both considerable confidence in the XAFS methodology and set the stage for future XAFS in applications employing this Ir(4)H(4) and related tetranuclear clusters. The [Ir(1,5-COD)(µ-H)](4) complex is of interest for at least five reasons, as detailed in the Conclusions section.

3.
Inorg Chem ; 48(10): 4411-20, 2009 May 18.
Artigo em Inglês | MEDLINE | ID: mdl-19351133

RESUMO

A 1997 Nature paper (Nature 1997, 388, 353-355) and subsequent 1998 J. Am. Chem. Soc. paper (J. Am. Chem. Soc. 1998, 120, 11969-11976) reported that a putative Ru(2)-substituted polyoxoanion, "[WZnRu(2)(III)(H(2)O)(OH)(ZnW(9)O(34))(2)](11-)", (1), is an all inorganic dioxygenase able to incorporate one O(2) into two adamantane CH bonds to yield 2 equiv of 1-adamantanol as the primary product. In a subsequent 2005 Inorg. Chem. publication (Inorg. Chem. 2005, 44, 4175-4188), strong evidence was provided that the putative dioxygenase chemistry is, instead, the result of classic autoxidation catalysis. That research raised the question of whether the reported Ru(2) precatalyst, 1, was pure or even if it contained two Ru atoms, since Ru is known to be difficult to substitute into polyoxoanion structures (Nomiya, K.; Torii, H.; Nomura, K.; Sato, Y. J. Chem. Soc. Dalton Trans. 2001, 1506-1521). After our research group had contact with three other groups who also had difficulties reproducing the reported synthesis and composition of 1, we decided to re-examine 1 in some detail. Herein we provide evidence that the claimed 1 actually appears to be the parent polyoxoanion [WZn(3)(H(2)O)(2)(ZnW(9)O(34))(2)](12-) with small amounts of Ru (

Assuntos
Dioxigenases/química , Rutênio/química , Compostos de Tungstênio/química , Catálise , Estrutura Molecular
4.
J Inorg Biochem ; 103(4): 575-84, 2009 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-19201030

RESUMO

Three vanadium complexes of chlorodipicolinic acid (4-chloro-2,6-dipicolinic acid) in oxidation states III, IV, and V were prepared and their properties characterized across the oxidation states. In addition, the series of hydroxylamido, methylhydroxylamido, dimethylhydroxylamido, and diethylhydroxylamido complexes were prepared from the chlorodipicolinato dioxovanadium(V) complex. The vanadium(V) compounds were characterized in solution by (51)V and (1)H NMR and in the solid-state by X-ray diffraction and (51)V NMR. Density Functional Theory (DFT) calculations were performed to evaluate the experimental parameters and further describes the electronic structure of the complex. The small structural changes that do occur in bond lengths and angles and partial charges on different atoms are minor compared to the charge features that are responsible for the majority of the electric field gradient tensor. The EPR parameters of the vanadium(IV) complex were characterized and compared to the corresponding dipicolinate complex. The chemical properties of the chlorodipicolinate compounds are discussed and correlated with their insulin-enhancing activity in streptozoticin (STZ) induced diabetic Wistar rats. The effect of the chloro-substitution on lowering diabetic hyperglycemia was evaluated and differences were found depending on the compounds oxidation state similar as was observed for the vanadium III, IV and V dipicolinate complexes (P. Buglyo, D.C. Crans, E.M. Nagy, R.L. Lindo, L. Yang, J.J. Smee, W. Jin, L.-H. Chi, M.E. Godzala III, G.R. Willsky, Inorg. Chem. 44 (2005) 5416-5427). However, a linear correlation of oxidation states with efficacy was not observed, which suggests that the differences in mode of action are not simply an issue of redox equivalents. Importantly, our results contrast the previous observation with the vanadium-picolinate complexes, where the halogen substituents increased the insulin-enhancing properties of the complex (T. Takino, H. Yasui, A. Yoshitake, Y. Hamajima, R. Matsushita, J. Takada, H. Sakurai, J. Biol. Inorg. Chem. 6 (2001) 133-142).


Assuntos
Hipoglicemiantes/química , Insulina/farmacologia , Ácidos Picolínicos/química , Compostos de Vanádio/química , Animais , Diabetes Mellitus Experimental/tratamento farmacológico , Espectroscopia de Ressonância de Spin Eletrônica , Hipoglicemiantes/farmacologia , Insulina/metabolismo , Espectroscopia de Ressonância Magnética , Oxirredução , Ácidos Picolínicos/farmacologia , Ratos , Ratos Wistar , Compostos de Vanádio/farmacologia
5.
J Am Chem Soc ; 130(40): 13471-89, 2008 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-18788799

RESUMO

Adding 1% of the metallic elements cerium, lanthanum, and yttrium to graphite rod electrodes resulted in different amounts of the hollow higher fullerenes (HHFs) C76-D2(1), C78-C2v(2), and C78-C2v(3) in carbon-arc fullerene-containing soots. The reaction of trifluoroiodomethane with these and other soluble HHFs at 520-550 degrees C produced 21 new C76,78,84,90(CF3)n derivatives (n = 6, 8, 10, 12, 14). The reaction with C76-D2(1) produced an abundant isomer of C2-(C76-D2(1))(CF3)10 plus smaller amounts of an isomer of C1-(C76-D2(1))(CF3)6, two isomers of C1-(C76-D2(1))(CF3)8, four isomers of C1-(C76-D2(1))(CF3)10, and one isomer of C2-(C76-D2(1))(CF3)12. The reaction with a mixture of C78-D3(1), C78-C2v(2), and C78-C2v(3) produced the previously reported isomer C1-(C78-C2v(3))(CF3)12 (characterized by X-ray crystallography in this work) and the following new compounds: C2-(C78-C2v(3))(CF3)8; C2-(C78-D3(1))(CF3)10 and C(s)-(C78-C2v(2))(CF3)10 (both characterized by X-ray crystallography in this work); C2-(C78-C2v(2))(CF3)10; and C1-C78(CF3)14 (cage isomer unknown). The reaction of a mixture of soluble higher fullerenes including C84 and C90 produced the new compounds C1-C84(CF3)10 (cage isomer unknown), C1-(C84-C2(11))(CF3)12 (X-ray structure reported recently), D2-(C84-D2(22))(CF3)12, C2-(C84-D2(22))(CF3)12, C1-C84(CF3)14 (cage isomer unknown), C1-(C90-C1(32))(CF3)12, and another isomer of C1-C90(CF3)12 (cage isomer unknown). All compounds were studied by mass spectrometry, (19)F NMR spectroscopy, and DFT calculations. An analysis of the addition patterns of these compounds and three other HHF(X) n compounds with bulky X groups has led to the discovery of the following addition-pattern principle for HHFs: In general, the most pyramidal cage C(sp(2)) atoms in the parent HHF, which form the most electron-rich and therefore the most reactive cage C-C bonds as far as 1,2-additions are concerned, are not the cage C atoms to which bulky substituents are added. Instead, ribbons of edge-sharing p-C6(X)2 hexagons, with X groups on less pyramidal cage C atoms, are formed, and the otherwise "most reactive" fullerene double bonds remain intact.

7.
Inorg Chem ; 46(23): 9827-40, 2007 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-17941629

RESUMO

A number of 4-substituted, dipicolinatodioxovanadium(V) complexes and their hydroxylamido derivatives were synthesized to characterize the solid state and solution properties of five- and seven-coordinate vanadium(V) complexes. The X-ray crystal structures of Na[VO2dipic-NH2].2H2O (2) and K[VO2dipic-NO2] (3) show the vanadium adopting a distorted, trigonal-bipyramidal coordination environment similar to the parent coordination complex, [VO2dipic]- (1), reported previously as the Cs+ salt. The observed differences in the chemical shifts of the complexes both in the 1H (ca. 0.7-1.4 ppm) and 51V (ca. 1-11 ppm) NMR spectra were consistent with the electron-donating or electron-withdrawing properties of the substituent groups, respectively. Stoichiometric addition of a series of hydroxylamine ligands (H2NOH, MeHNOH, Me2NOH, and Et2NOH) to complexes 1-3 led to the formation of seven-coordinate vanadium(V) complexes. The X-ray crystal structure of [VO(dipic)(Me2NO)(H2O)].0.5H2O (1c) was found to be similar to the previously characterized complexes [VO(dipic)(H2NO)(H2O)] (1a) and [VO(dipic)(OO-tBu)(H2O)]. While only slight differences in the 1H NMR spectra were observed upon addition of the hydroxylamido ligand, the signals in the 51V NMR spectra change by up to 100 ppm. The addition of the hydroxylamido ligand increased the complex stability of complexes 2 and 3. Evidence for a nonstoichiometric redox reaction was found for the monoalkyl hydroxylamine ligand. The reaction of an unsaturated five-coordinate species with a hydroxylamine to form a seven-coordinate vanadium complex will, in general, dramatically increase the amounts of the vanadium compound that remain intact at pH values near neutral.


Assuntos
Compostos de Vanádio/síntese química , Amidas/química , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Ácidos Picolínicos/química , Solubilidade , Compostos de Vanádio/química , Água/química
8.
Inorg Chem ; 46(21): 8505-7, 2007 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-17883269

RESUMO

The selective substitution of the antipodal F atom in 1-Me-CB(11)F(11)- with a SiPh(3) moiety led to the isolation and structure determination of the cesium(I) and silver(I) salts of the 1-Me-12-SiPh(3)-CB(11)F(10)- anion. The silver salt contains both a nearly trigonal-planar Ag(arene)(3)+ cation and the first example of a Ag(arene)(4)+ cation.

9.
Chem Commun (Camb) ; (16): 1650-2, 2007 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-17530089

RESUMO

The title compound, prepared from C(60) and CF(3)I at 500 degrees C, exhibits an unusual fullerene(X)12 addition pattern that is 40 kJ mol(-1) less stable than the previously reported C(60)(CF(3))12 isomer.

11.
Acta Crystallogr Sect E Struct Rep Online ; 64(Pt 1): o159, 2007 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-21200724

RESUMO

The title compound, C(72)F(36), is one of four isomers of C(60)(CF(3))(12) for which crystal structures have been obtained. The fullerene mol-ecule has an idealized I(h) C(60) core with the 12 CF(3) groups arranged in an asymmetric fashion on two ribbons of edge-sharing C(6)(CF(3))(2) hexa-gons, a para-meta-para-para-para-meta-para ribbon and a para-meta-para ribbon, giving an overall pmp(3)mp,pmp structure. There are no cage Csp(3)-Csp(3) bonds. The F atoms of two CF(3) groups are disordered over two positions; the site occupancy factors are 0.85/0.15 and 0.73/0.27. There are intra-molecular F⋯F contacts between pairs of CF(3) groups on the same hexa-gon that range from 2.521 (3) to 2.738 (4) Å.

12.
J Am Chem Soc ; 128(37): 12268-80, 2006 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-16967978

RESUMO

Reaction of C(60) with CF(3)I at 550 degrees C, which is known to produce a single isomer of C(60)(CF(3))(2,4,6) and multiple isomers of C(60)(CF(3))(8,10), has now been found to produce an isomer of C(60)(CF(3))(6) with the C(s)-C(60)X(6) skew-pentagonal-pyramid (SPP) addition pattern and an epoxide with the C(s)-C(60)X(4)O variation of the SPP addition pattern, C(s)-C(60)(CF(3))(4)O. The structurally similar epoxide C(s)-C(60)(C(2)F(5))(4)O is one of the products of the reaction of C(60) with C(2)F(5)I at 430 degrees C. The three compounds have been characterized by mass spectrometry, DFT quantum chemical calculations, Raman, visible, and (19)F NMR spectroscopy, and, in the case of the two epoxides, single-crystal X-ray diffraction. The compound C(s)-C(60)(CF(3))(6) is the first [60]fullerene derivative with adjacent R(f) groups that are sufficiently sterically hindered to cause the (DFT-predicted) lengthening of the cage (CF(3))C-C(CF(3)) bond to 1.60 A as well as to give rise to a rare, non-fast-exchange-limit (19)F NMR spectrum at 20 degrees C. The compounds C(s)-C(60)(CF(3))(4)O and C(s)-C(60)(C(2)F(5))(4)O are the first poly(perfluoroalkyl)fullerene derivatives with a non-fluorine-containing exohedral substituent and the first fullerene epoxides known to be stable at elevated temperatures. All three compounds demonstrate that the SPP addition pattern is at least kinetically stable, if not thermodynamically stable, at temperatures exceeding 400 degrees C. The high-temperature synthesis of the two epoxides also indicates that perfluoroalkyl substituents can enhance the thermal stability of fullerene derivatives with other substituents.

13.
Inorg Chem ; 45(15): 5804-11, 2006 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-16841985

RESUMO

The reactions of Cd2+ and Zn2+ with the pyridine-arm isoindoline ligand 4'-MeLH = 1,3-bis[2-(4-methylpyridyl)imino]isoindoline produced the series of octahedrally coordinated complexes M(4'-MeL)2, [M(4'-MeLH)2]2+, and [M(4'-MeL)(4'-MeLH)]+. The complexes M(4'-MeL)2 resulted from reactions of the respective metal perchlorates with deprotonated ligand, whereas the complexes [M(4'-MeLH)2](ClO4)2 resulted from reactions with ligand in the absence of added base. The mixed-ligand complexes [M(4'-MeL)(4'-MeLH)]+ were generated in solution by reactions of equimolar quantities of M(4'-MeL)2 and [M(4'-MeLH)2]2+. Whereas [Cd(4'-MeL)(4'-MeLH)]+ is stable in solution, [Zn(4'-MeL)(4'-MeLH)]+ converts to and establishes equilibrium with the tetrahedrally coordinated, trinuclear complex [Zn3(4'-MeL)4]2+. The complexes Cd(4'-MeL)2 (1), Zn(4'-MeL)2 (2), and [Cd(4'-MeL)(4'-MeLH)]ClO4 (5) were characterized by single-crystal X-ray diffraction, with the latter complex being shown to contain 4'-MeLH coordinated as a protonated iminium zwitterionic ligand. The [M(4'-MeLH)2]2+ and [M(4'-MeL)(4'-MeLH)]+ complexes are tautomeric in solution because of the shuttling of the iminium protons between imine N atoms. The rate of prototropic tautomerism in [Cd(4'-MeLH)2]+ was followed by 1H NMR spectroscopy. Over the temperature range 276-312 K, a linear Eyring plot with the activation parameters DeltaG++ = 16.0 +/- 0.1 kcal/mol, DeltaH++ = 2.9 +/- 0.1 kcal/mol, and DeltaS++ = -44.0 +/- 0.3 cal/mol.K was obtained.


Assuntos
Cádmio/química , Zinco/química , Cristalografia por Raios X , Entropia , Ligantes , Espectroscopia de Ressonância Magnética , Metais/química , Modelos Químicos , Modelos Moleculares , Conformação Molecular , Estrutura Molecular , Percloratos/química , Termodinâmica , Difração de Raios X
14.
Chem Commun (Camb) ; (3): 308-10, 2006 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-16391743

RESUMO

The high-temperature reaction of C60 and C2F5I produced poly(perfluoroethyl)fullerenes with unprecedented addition patterns.

15.
Inorg Chem ; 44(25): 9162-74, 2005 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-16323896

RESUMO

Cobalt(III) acetate and cyanide complexes of a series of 5,12-dioxocyclams capped across the 1,8-position by 4-substituted pyridines or pyrazine were synthesized and fully characterized. Both the spectroscopic and structural parameters for these complexes were remarkably insensitive to the electronic nature of the capping group, which ranged from the pi-accepting pyrazine group to the sigma-donating 4-[(dimethylamino)phenyl]pyridyl group. All of the complexes underwent an irreversible, one-electron reduction [Co(III)-->Co(II)] at potentials ranging from -0.95 V vs saturated calomel electrode (SCE) for the pyrazine-capped cobalt acetate complex to -1.36 V vs SCE for the pyridine-capped cobalt cyanide complexes. Pyridine-capped cobalt(III) cyanide complex underwent reaction with Rh2(OAc)4 and ruthenium(II) phthalocyanine[bis(benzonitrile)] to form tetrametallic and trimetallic complexes through coordination bridging by the cyanide nitrogen lone pair. These complexes represent two quite different structural types for cyanide-bridged polymetallics. Complex has a relatively long (2.192 A) cyanide N-to-Rh bond, and the CN-Rh bond angle (157.6 degrees) is strongly distorted from linear. In contrast, complex has a substantially shortened cyanide N-to-Ru bond (2.017 A) and an almost linear arrangement along the entire bridging axis of the molecule.


Assuntos
Cobalto/química , Compostos Heterocíclicos/química , Compostos Organometálicos/química , Compostos Organometálicos/síntese química , Piridinas/química , Cristalografia por Raios X , Espectroscopia de Ressonância Magnética/métodos , Espectroscopia de Ressonância Magnética/normas , Modelos Moleculares , Estrutura Molecular , Padrões de Referência , Sensibilidade e Especificidade , Espectrofotometria Infravermelho/métodos , Espectrofotometria Ultravioleta/métodos , Estereoisomerismo
17.
Inorg Chem ; 44(18): 6476-81, 2005 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-16124830

RESUMO

The sterically crowded isoindoline pincer ligand, 6'-MeLH, prepared by condensation of 4-methyl-2-aminopyridine and phthalonitrile, exhibits very different reaction chemistry with Cd2+, Zn2+, and Pd2+. Three different ligand coordination modes are reported, each dependent upon choice of metal ion. This isoindoline binds to Cd2+ as a charge-neutral, zwitterionic, bidentate ligand using imine and pyridine nitrogen atoms to form the eight-coordinate fluxional complex, Cd(6'-MeLH)2(NO3)2. In the presence of Zn2+, however, loss of a pyridine arm occurs through solvolysis and tetrahedrally coordinated complexes are formed with coordination of pyrrole and pyridine nitrogen atoms. Reaction with Pd2+ produces the highly distorted, square planar complex Pd(6'-MeL)Cl in which a deprotonated isoindoline anion coordinates as a tridentate pyridinium NNC pincer ligand.


Assuntos
Cádmio/química , Paládio/química , Zinco/química , Ligantes , Modelos Químicos , Modelos Moleculares , Estrutura Molecular
18.
J Am Chem Soc ; 127(23): 8362-75, 2005 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-15941270

RESUMO

A significant improvement in the selectivity of fullerene trifluoromethylation reactions was achieved. Reaction of trifluoroiodomethane with [60]fullerene at 460 degrees C and [70]fullerene at 470 degrees C in a flow reactor led to isolation of cold-zone-condensed mixtures of C60(CF3)n and C70(CF3)n compounds with narrow composition ranges: 6 < or = n < or = 12 for C(60)(CF3)n and 8 < or = n < or = 14 for C70(CF3)n. The predominant products in the C(60) reaction, an estimated 40+ mol % of the cold-zone condensate, were three isomers of C60(CF3)10. Two of these were purified by two-stage HPLC to 80+% isomeric purity. The third isomer was purified by three-stage HPLC to 95% isomeric purity. Thirteen milligrams of this orange-brown compound was isolated (5% overall yield based on C60, and its C1-symmetric structure was determined to be 1,3,7,10,14,17,23,28,31,40-C60(CF3)10 by X-ray crystallography. The CF3 groups are either meta or para to one another on a p-m-p-p-p-m-p-m-p ribbon of edge-sharing C6(CF3)2 hexagons (each pair of adjacent hexagons shares a common CF3 group). The selectivity of the C70 reaction was even higher. The predominant product was a single C70(CF3)10 isomer representing >40 mol % of the cold-zone condensate. Single-stage HPLC led to the isolation of 12 mg of this brown compound in 95% isomeric purity (27% overall yield based on converted C70. The new compounds were characterized by EI or S(8)-MALDI mass spectrometry and 2D-COSY 19F NMR spectroscopy. The NMR data demonstrate that through-space coupling via direct overlap of fluorine orbitals is the predominant contribution to J(FF) values in these and most other fullerene(CF3)n compounds.

19.
J Inorg Biochem ; 98(11): 1837-50, 2004 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-15522411

RESUMO

The effects of Mo-hydroxylamido complexes on cell growth were determined in Saccharomyces cerevisiae to investigate the biological effects of four different Mo complexes as a function of pH. Studies with yeast, an eukaryotic cell, are particularly suited to examine growth at different pH values because this organism grows well from pH 3 to 6.5. Studies can therefore be performed both in the presence of intact complexes and when the complexes have hydrolyzed to ligand and free metal ion. One of the complexes we examined was structurally characterized by X-ray crystallography. Yeast growth was inhibited in media solutions containing added Mo-dialkylhydroxylamido complexes at pH 3-7. When combining the yeast growth studies with a systematic study of the Mo-hydroxylamido complexes' stability as a function of pH and an examination of their speciation in yeast media, the effects of intact complexes can be distinguished from that of ligand and metal. This is possible because different effects are observed with complex present than when ligand or metal alone is present. At pH 3, the growth inhibition is attributed to the forms of molybdate ion that exist in solution because most of the complexes have hydrolyzed to oxomolybdate and ligand. The monoalkylhydroxylamine ligand inhibited yeast growth at pH 5, 6 and 7, while the dialkylhydroxylamine ligands had little effect on yeast growth. Growth inhibition of the Mo-dialkylhydroxylamido complexes is observed when a complex exists in the media. A complex that is inert to ligand exchange is not effective even at pH 3 where other Mo-hydroxylamido complexes show growth inhibition as molybdate. These results show that the formation of some Mo complexes can protect yeast from the growth inhibition observed when either the ligand or Mo salt alone are present.


Assuntos
Concentração de Íons de Hidrogênio , Hidroxilaminas/farmacologia , Molibdênio/farmacologia , Saccharomyces cerevisiae/efeitos dos fármacos , Cristalografia por Raios X , Meios de Cultura , Eletroquímica , Hidroxilaminas/química , Cinética , Modelos Moleculares , Conformação Molecular , Compostos Organometálicos/química , Compostos Organometálicos/farmacologia , Saccharomyces cerevisiae/crescimento & desenvolvimento
20.
J Am Chem Soc ; 126(17): 5502-14, 2004 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-15113222

RESUMO

A series of [Pd(diphosphine)(2)](BF(4))(2) and Pd(diphosphine)(2) complexes have been prepared for which the natural bite angle of the diphosphine ligand varies from 78 degrees to 111 degrees. Structural studies have been completed for 7 of the 10 new complexes described. These structural studies indicate that the dihedral angle between the two planes formed by the two phosphorus atoms of the diphosphine ligands and palladium increases by over 50 degrees as the natural bite angle increases for the [Pd(diphosphine)(2)](BF(4))(2) complexes. The dihedral angle for the Pd(diphosphine)(2) complexes varies less than 10 degrees for the same range of natural bite angles. Equilibrium reactions of the Pd(diphosphine)(2) complexes with protonated bases to form the corresponding [HPd(diphosphine)(2)](+) complexes were used to determine the pK(a) values of the corresponding hydrides. Cyclic voltammetry studies of the [Pd(diphosphine)(2)](BF(4))(2) complexes were used to determine the half-wave potentials of the Pd(II/I) and Pd(I/0) couples. Thermochemical cycles, half-wave potentials, and measured pK(a) values were used to determine both the homolytic ([HPd(diphosphine)(2)](+) --> [Pd(diphosphine)(2)](+) + H*) and the heterolytic ([HPd(diphosphine)(2)](+) --> [Pd(diphosphine)(2)](2+) + H(-)) bond-dissociation free energies, Delta G(H*)* and Delta G(H-)*, respectively. Linear free-energy relationships are observed between pK(a) and the Pd(I/0) couple and between Delta G(H-)* and the Pd(II/I) couple. The measured values for Delta G(H*)* were all 57 kcal/mol, whereas the values of Delta G(H-)* ranged from 43 kcal/mol for [HPd(depe)(2)](+) (where depe is bis(diethylphosphino)ethane) to 70 kcal/mol for [HPd(EtXantphos)(2)](+) (where EtXantphos is 9,9-dimethyl-4,5-bis(diethylphosphino)xanthene). It is estimated that the natural bite angle of the ligand contributes approximately 20 kcal/mol to the observed difference of 27 kcal/mol for Delta G(H-)*.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA