КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 10, с. 792-800
УДК 541.49
GOLD(I)-TRIPHENYLPHOSPHINE-ARYLAZOIMIDAZOLE: SYNTHESIS AND SPECTRAL (H, C, COSY, HMQC NMR)
CHARACTERIZATION
© 2007 P. Byabartta and M. Laguna
Departmento de Quimica Inorganica-Instituto de Ciencia deMateriales de Aragon, Universidad de Zaragoza-CSIC,
Zaragoza-50009, Spain Received May 2, 2006
The reaction of [Au(OSO2CF3)(PPh3)] with arylazoimidazole in dichloromethane followed by NH4PF6 leads to [Au(RAaiR')(PPh3)]PF6 (RAaiR' = p-R-N=N-C3H2-NN-1-R'), abbreviated as N,N'/-chelator, where N (imidazole) and N (azo) represent N and N', respectively; R = H (a), Me (b), Cl (c), and R' = Me (I), CH2CH3 (II), CH2Ph (III)]. IR spectra of the complexes show -C=N- and -N=N-stretchings at 1590 and 1370 and at 1100, 755, 695, 545, and 505 cm-1 due to the presence of the triphenylphosphine ring. The 1H NMR spectral measurements suggest that methylene (-CH2-) in (RAai)Et gives a complex of the AB type multiplet with a coupling constant of ~7.6 Hz while in RAaiCH2Ph it shows AB type quartets with coupling constant of av. 7.2 Hz. Considering the arylazoimidazole moity, there are different carbon atoms in the molecule giving different peaks in the 13C NMR spectrum of the complexes. In the 1H-1H COSY spectrum of the present complexes, the absence of any offdiagonal peaks extending from 5 = 14.12 and 9.55 ppm confirms their assignment of no proton on N(1) and N(3), respectively. Contour peaks in the 1H-13C HMQC spectrum in the present complexes, the absence of any contours at 5 = 157.12, 160.76, 155.67, and 157.68-160.2 ppm assign them to the C(2), C(6), C(12), and C(PPh3) carbon atoms, respectively. The solution structure and stereoretentive transformation in each step have been established from the *H NMR results.
Transition metal complexes of diimine and related ligands have attracted much attention [1-4]. Running years have witnessed a great deal of interest in the synthesis of the complexes of gold with a-diimine-type of ligands because of their photochemical and catalytic properties [5], energy conversion, and the ability to serve as building blocks in supramolecular arrays [6]. Researchers have engaged in modifying the properties of Au-pyridine complexes by replacing the ligands of other donor centers, altering the steric and electronic properties of the ligands, differently substituted poly-pyridine mixed donor heterocycles. The search for a suitable precursor to synthesize azoimine complexes is a challenging domain, and the compounds are found to be useful in this context [7]. The concept of "metallo-philic bonding" has added a new range of intermolecular interactions to the spectrum of chemical bonding in supramolecular aggregates [8]. A small number of scattered observations in the early structural chemistry of gold(I) complexes [1-4, 7, 9, 10] has grown into a wealth of reports on related phenomena in the last two decades, which finally provided a clear pattern of the conditions under which direct interactions between closed-shell gold(I) centers can contribute significantly to the stability of molecular and multidimensional structures [9-11]. The underlying "aurophilic" bonding has been analyzed in theoretical studies, which have confirmed the experimental results and gave an explanation for the finding that the "metallophilic" bonding is strongest and, therefore, most obvious for heavy met-
als in general and for gold complexes in particular [1-3]. Notwithstanding, there has also been growing evidence for weak metallophilic bonding between low-coordinate silver atoms [3] and, as a logical consequence, for gold-silver metallophilicity [5, 6, 8, 12-15].
In this article we present new and noteworthy examples taken from the important class of gold triphe-nylphosphines. Gold phosphine compounds have interesting photophysical properties [2] and are relevant to homogeneous gold catalysis [l] and gold/silver thin film technology [3]. Recently, we have developed the arylazoimidazole chemistry of ruthenium and have synthesized dichloro compounds [RuCl2(RAaiR')2] and diaquo species [Ru(OH2)2(RAaiR')2]2+ (RAaiR' = ^-R-C6H4-N=N-C3H2-NN-1-R', R = H, Me, Cl and R' = = Me, CH2CH3, CH2Ph abbreviated as N,N'-chelator, where N (imidazole) and N (azo) represent N and N', respectively). Syntheses of hetero-tris-chelates, [Ru(Bipy)„(RAaiR% - „KC^ (Bipy = 2,2'-bipyri-dine; n = 1, 2) from the solvento complexes [Ru(OH2)2(Bipy)J2+/[Ru(OH2)2 (RAAIR'')J2+ containing labile reaction centers are reported [4, 7, 9-11, 16, 17]. Syntheses of molybdenum-fe-chelates with carbonyl containing these ligand centers are reported from Ankermann's laboratory. A. Chakravorty has unfolded its rhenium chemistry on this ligand system. However the gold chemistry with 1D, 2D NMR spec-troscopy of this ligand system is totally unexplored. In this paper, we examined the reaction of RAaiR' with gold(I) triphenylphosphine deivatives, and the products
were isolated. The complexes are well characterized by IR, XH, 13C NMR, 1H-1H COSY NMR, 1H-13C HMQC, and ESI mass spectrometry.
EXPERIMENTAL
Published methods were used to prepare RAaiR/ [10, 11, 16], [AuCl(PPh3)] [5, 6, 8, 12-15]. All other chemicals and organic solvents used were of reagent grade (SRL, Sigma, Alhrich). The purification of MeCN used as solvent and other solvents were done following the literature method [6, 8, 11-13, 16, 17]. Microanalytical data (C, H, N) were collected using a Perkin Elmer 2400 CHN instrument. IR spectra were obtained using a Perkin Elmer spectrophotometer (using KBr disks, 4000-400 cm-1). The 1H NMR spectra in CDCl3 were obtained on a Bruker 400 MHz FT NMR spectrometer using SiMe4 as internal reference. Mass spectra were recorded on a VG Autospec ESI mass spectrometeter using 3-nitrobenzyl as matrix.
Synthesis of [{1-methyl-2-(p-tolylazo)imida-zole}(triphenylphosphine)aurate(I)]hexafluorophos-phate, [Au(MeAAIMe)(PPh3)]PF6 (Ib). A yellow dichloromethane solution of 1-methyl-2-(p-tolylazo)imi-dazole (0.039 g, 0.20 mmol) was slowly, dropwise, added to a dichloromethane colorless solution (15 ml) of [Au(OSO2CF3)(PPh3)] (0.941 g, 0.20 mmol) and the mixture was stirred at 343-353 K for 12 h. The red solution that resulted was concentrated (4 ml) and kept in a refrigerator overnight. The addition of hexane followed by ammonium hexafluorophosphate salt to the above red solution gives a precipitate, which was collected by filtration, washed thoroughly with hexane to remove excess ligand, and then dried in vacuo using a pump overnight. Analytically pure complex was obtained after chromatography on an alumina (neutral) column on eluting the red band with
toluene-acetonitrile (4 : 1, vol/vol) and evaporating slowly in air. The yield was 0.088 g (80%).
The complexes [Au(RAaiR/)(PPh3)]PF6, were prepared similarly for Ib, using as ligand RAaiR/(R' = Me, R = H (Ia), Cl (Ic); R' = Et, R = H (IIa), Me (IIb), Cl (IIc); R' = Bz, R=H (IIIa), Me (IIIb), Cl (IIIc). 31P{XH} NMR, ppm of Ia, 30.234; ESI mass, M (% abundance), 790 (90) [M+], 645 (34) [M - PF6], 721 (10) [Au(PPh3)2)]+; 31P{1H} NMR, ppm of Ib, 30.28; ESI mass, M (% abundance), 804 (70) [M+], 659 (31) [M -PF6], 721 (13) [Au(PPh3)2)]+; 31P{XH} NMR, ppm of Ic, 30.44; ESI mass, M (% abundance), 824.5 (45) [M+], 679.5 (34) [M - PF6], 721 (16) [Au(PPh3)2)]+; 31P{XH} NMR, ppm of IIa, 30.98; ESI mass, M (% abundance), 804 (70) [M+], 659 (31) [M - PF6], 721 (13) [Au(PPh3)2)]+; 31P{1H} NMR, ppm of IIb, 29.98; ESI mass, M (% abundance), 818 (70) [M+], 673 (31) [M - PF6], 721 (11) [Au(PPh3)2)]+; 31P{XH} NMR, ppm of IIc, 30.28; ESI mass, M (% abundance), 839.5 (70) [M+], 694.5 (31) [M - PF6], 721 (13) [Au(PPh3)2)]+; 31P{1H} NMR, ppm of IIIa, 31.02; ESI mass, M (% abundance), 866 (55) [M+], 721 (13) [M - PF6], 721 (6) [Au(PPh3)2)]+; 31P{1H} NMR, ppm of IIIb, 30.28; ESI mass, M (% abundance), 880 (67) [M+], 735 (31) [M - PF6], 721 (3) [Au(PPh3)2)]+; 31P{1H} NMR, ppm of IIIc, 31.01; ESI mass, M (% abundance), 901.5 (45) [M+], 756.5 (31) [M - PF6], 721 (10) [Au(PPh3)2)]+.
RESULTS AND DISCUSSION
The complexes [Au(RAaiR/)(PPh3)]PF6 (Ia-Ic, IIa-IIc, and IIa-IIIc), were prepared by removing OSO2CF3 from [Au(OSO2CF3)(PPh3)], with RAaiR under stirring at 343-353 K in dichloromethane solution in good yield (65-85%). The synthetic routes are shown below:
[AuCl(PPh3)] + [Ag(OSO2CF3)] + RAaiR'
R' = Me, R = H(Ia), Me(Ib), Cl(Ic) R' = Et, R = H(IIa), Me(IIb), Cl(IIc) R' = Bz, R = H(IIIa), Me(IIIb), Cl(IIIc)
CH2CI2
~-ol " +nh4pf6
Ph3^-Au-Ni 2 3N-R'
R
PF6
The composition of the complexes is supported by microanalytical results (Table 1). The red-orange complexes are soluble in common organic solvents, viz., acetone, acetonitrile, chloroform, and dichloromethane but are insoluble in H2O, methanol, and ethanol.
The population of gas phase ions generated by ESI often closely reflects that in solution. Hence, we used ESI-MS to verify the solution and gas-phase stability of
the complexes and to structurally characterize such iso-meric thermally labile complexes via ESI-MS. The ESI mass spectrum of a MeCN solution in the positive ion mode is structurally enlightening, since it displays a series of characteristic singly. The ESI-MS mass spectrum of one complex [Au(ClAaiBz)(PPh3)]PF6 (IIIc) was recorded in a MeCN medium. The maximum molecular peak of IIIc is observed at m/z 901.5 (50%),
Table 1. Data of elemental analysis and IR spectra of the complexes Ia-Ic, Ila-IIb, and Illa-IIIc
Contents (found/calcd), % IR
Compound C H N Cl P v(N=N), v(C=N), v(PPh3)
[Au(HAaiMe)(PPh3)]PF6, C28H25F6N4AuP2 (Ia) 42.59/42.58 3.18/3.08 7.18/7.2 7.80/7.90 1370, 1590 1100, 750, 690, 550, 505
[Au(MeAaiMe)(PPh3)]PF6 C29H27F6N4AUP2 (Ib) 43.39/43.58 3.38/3.28 6.97/6.99 7.71/7.80 1373, 1594 1106, 756, 695, 557, 515
[Au(ClAaiMe)(PPh3)]PF6 C28H24F6N4AuClP2 (Ic) 40.59/40.58 2.88/2.88 6.80/7.0 4.30/4.40 7.50/7.90 1370, 1590 1100, 750, 690, 550, 505
[Au(HAaiEt)(PPh3)]PF6 C29H27F6N4AUP2 (IIa) 43.39/43.58) 3.
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.