Syntheses and 31P NMR studies of transition metal complexes containing derivatives of dioxaphospholane and dioxaphosphorinane

Abstracts

The syntheses of various complexes of Pt(II), Pt(0) and Pd(II) with 2-chloro-1,3,2-dioxaphospholane, 2-fluoro-1,3,2-dioxaphospholane, 2-chloro-4,5-benzo-1,3,2-dioxaphospholane, 2-fluoro-4,5-benzo-1,3,2-dioxaphospholane, 2-chloro-1,3,2-dioxaphosphorinane, 2-fluoro-1,3,2-dioxaphosphorinane are reported. 31P{¹H} NMR studies of these complexes reveals some aspects still unexplored in terms of the magnitude of the coupling constants ¹J(PtP), which brings light to the soft and hard acid-base concept. This work also shows the 31P{¹H} nmr spectroscopic differences between cis and trans isomers.

31P NMR spectroscopy; acid-base hard and soft concept; dioxaphospholane and dioxaphosphorinane

A síntese de vários complexos de Pt(II), Pt(0) e Pd(II) com 2-cloro-1,3,2-dioxafosfolana, 2-fluoro-1,3,2-dioxafosfolana, 2-cloro-4,5-benzo-1,3,2-dioxafosfolana, 2-fluoro-4,5-benzo-1,3,2-dioxafosfolana, 2-cloro-1,3,2-dioxafosforinana e 2-fluoro-1,3,2-dioxafosforinana é descrita. Estudos de RMN de 31P{¹H} destes complexos revelam alguns aspectos inexplorados em relação às constantes de acoplamento ¹J(PtP), os quais chamam a atenção para o conceito de ácidos e bases duros e macios. Este trabalho mostra também as diferenças espectroscópicas de RMN de 31P{¹H} entre isômeros cis e trans.

Article

Syntheses and ³¹P NMR Studies of Transition Metal Complexes Containing Derivatives of Dioxaphospholane and Dioxaphosphorinane

Robson M. Matos^*, Ricardo F. F. da Costa, Vagner F. Knupp, João André D. Silva and Bernadette F. T. Passos

Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais,Av. Antônio Carlos, 6627, Pampulha, 31270-901, Belo Horizonte - MG, Brazil

A síntese de vários complexos de Pt(II), Pt(0) e Pd(II) com 2-cloro-1,3,2-dioxafosfolana, 2-fluoro-1,3,2-dioxafosfolana, 2-cloro-4,5-benzo-1,3,2-dioxafosfolana, 2-fluoro-4,5-benzo-1,3,2-dioxafosfolana, 2-cloro-1,3,2-dioxafosforinana e 2-fluoro-1,3,2-dioxafosforinana é descrita. Estudos de RMN de ³¹P{¹H} destes complexos revelam alguns aspectos inexplorados em relação às constantes de acoplamento ¹J(PtP), os quais chamam a atenção para o conceito de ácidos e bases duros e macios. Este trabalho mostra também as diferenças espectroscópicas de RMN de ³¹P{¹H} entre isômeros cis e trans.

The syntheses of various complexes of Pt(II), Pt(0) and Pd(II) with 2-chloro-1,3,2-dioxaphospholane, 2-fluoro-1,3,2-dioxaphospholane, 2-chloro-4,5-benzo-1,3,2-dioxaphospholane, 2-fluoro-4,5-benzo-1,3,2-dioxaphospholane, 2-chloro-1,3,2-dioxaphosphorinane, 2-fluoro-1,3,2-dioxaphosphorinane are reported. ³¹P{¹H} NMR studies of these complexes reveals some aspects still unexplored in terms of the magnitude of the coupling constants ¹J(PtP), which brings light to the soft and hard acid-base concept. This work also shows the ³¹P{¹H} nmr spectroscopic differences between cis and trans isomers.

Keywords: ³¹P NMR spectroscopy, acid-base hard and soft concept, dioxaphospholane and dioxaphosphorinane

Introduction

A variety of complexes containing phosphorus ligands have been reported over the past years and the interest on their chemistry is growing due to their possible catalytic activity. Our main interests have been to prepare new complexes containing unusual phosphorus ligands and investigate their chemical properties by the use of NMR spectroscopy.

The reactivity of dioxaphospholane and related compounds towards several organic compounds is well documented¹. As a result of those studies several applications for this class of compound have been found. Some examples are the use of dioxaphospholanes in the development of specific imunoassays for the detection of pesticides², polymerisation reactions^3,4, syntheses of naturally ocuring lipids⁵ and to analyse labile hydrogens functional on coal materials⁶. However few publications dealing with complexation of dioxaphospholanes have appeared in the literature. Recent reports of the new facile preparation methods of dioxaphospholane derivatives⁷ and their ruthenium (II) complexes⁸ prompted us to report some new platinum and palladium complexes.

The ligands C₂H₄O₂PCl 1, C₂H₄O₂PF 2, C₆H₄O₂PCl 3, C₆H₄O₂PF 4, C₃H₆O₂PCl 5 and C₃H₆O₂PF 6 used to prepare the platinum(0), platinum(II) and palladium(II) complexes, herein reported, are as follow.

Results and Discussion

Syntheses and characterisation of platinum(0) complexes

Complexes [Pt(PPh₃)₂(C₆H ₄O₂PCl)] 7, [Pt(PPh₃)₂ (C₃H₆O₂PCl)] 8 and [Pt(PPh₃)₂(C₃H ₆O₂PF)] 9 have been obtained by treatment of [Pt(PPh₃)₂(C₂H ₄)], in toluene, with ligands 3, 5 and 6 respectively, at 0^oC.

The ³¹P{¹H} NMR spectra of the three complexes show a similar pattern of lines, which consists of an AB₂X spin system (A,B = ³¹P, 100%; X = ¹⁹⁵Pt, 33.8%) for the two first compounds and of an AB₂XY spin system (A,B = ³¹P, 100%; X = ¹⁹⁵Pt, 33.8%; Y = ¹⁹F, 100%;) for the latter. Complexes 7 and 8 show a triplet with the platinum satellites at d 60 and d 38, respectively, relative to P_A whereas P_B is seen as a doublet with the platinum satellites at d 22 and d 27. A doublet of triplet at d 113 and a doublet of doublets at d 16 with the platinum satellites are observed in the ³¹P{¹H} NMR spectrum of 9. These results suggest a trigonal planar geometry around the platinum centre and due to the fact that both PPh₃ ligands are equivalent in the ³¹P{¹H} NMR spectra it can be said that either the chloro atom at the dioxaphospholane ligand lies on a perpendicular plane to the one containing the Pt atom and the two PPh₃ or there is a rapid rotation around the Pt-dioxaphospholane bond. Identical conclusion has been reached about a similar platinum(0) complex, [Pt(PPh₃)₂(R₂C=P-N(R)-PR)] ⁹. The ³¹P{¹H} NMR data are shown in Table 1.

It is interesting to compare the coupling constants ¹J(PtP_A)for complexes 8 and 9. As would be expected, the PtP_A coupling constant in 9 is larger than in 8, reflecting the increase of s character on the Pt-P bond, caused by the presence of the more electronegative fluorine, bonded through the P_A, in the first complex¹⁰. The ³¹P{¹H} NMR studies also suggest an increase in the magnitude of ¹J(PtP_A) on changing the group bonded to the oxygen atom in the phosphorus from -CH₂CH₂CH₂- to 1,2-benzo. A very small change is observed in the ¹JP_AF coupling constant of the ligand 6 (1304 Hz) upon coordination to platinum(0) to form complex 9 (vide Table 1). A long range ³J(P_BF) coupling constant is also observed in the ³¹P{¹H} NMR spectrum of 9.

Syntheses and characterisation of platinum(II) complexes

Treatment of [Pt₂Cl₄(PEt₃) ₂], in CH₂Cl₂ at room temperature, with the ligands 1 - 5 yields the square planar complexes [PtCl₂(PEt₃)(C₂H ₄O₂PCl)] 10, [PtCl₂(PEt₃)(C₂H ₄O₂PF)] 11, [PtCl₂(PEt₃)(C₆H ₄O₂PCl)] 12, [PtCl₂(PEt₃)(C₆H ₄O₂PF)] 13 and [PtCl₂(PEt₃)(C₃H ₆O₂PCl)] 14, respectively.

The ³¹P{¹H} NMR studies of complexes 10 - 14 showed that they posses a cis arrangement around the platinum centre since the values for the ²J(P_AP_B) coupling constants lie between 23 and 41 Hz and those for the ¹J(PtP) are typical for this kind of complexes¹⁰.

Some of these complexes - 10, 11 and 13 - have been obtained as a mixture of two conformers, a and b, as confirmed by the ³¹P{¹H} NMR spectra, which consist of two sub spectra with the pattern of lines corresponding to an ABX spin system (A, B = ³¹P, 100%; X = ¹⁹⁵Pt, 33,8%). In most of the spectra some lines, corresponding to one of the conformers, are superimposed to the ones of the other conformer. This is exemplified by the ³¹P{¹H} NMR spectrum of 10 in which the signal corresponding to P_A appears as a "false triplet" instead of two doublets. However, two doublets, in the P_B region of the spectrum, are easily assigned. As little difference is seen in the ³¹P{¹H} NMR data for both conformers a and b of 10, 11 and 12, their formation can be understood as a result of the coexistence of two conformers for the free ligands^11,12, as depicted in Scheme 1. In this case, the metal fragment [PtCl₂(PEt₃)] can be bonded through the phosphorus lone pair in an axial or equatorial position (Scheme 2).

The ³¹P{¹H} NMR spectra of complexes 11 and 13 show a decrease in the ¹J(PF)coupling constants (556 and 590 Hz, respectively) compared to those found for the free ligands (1302 and 1171 Hz, respectively). This large decrease in the ¹J(PF)coupling constants, upon complexation, suggests a fluxional behaviour involving a change between the fluorine bonded through the phosphorus atom with the chlorine bonded through the platinum atom. It is interesting to note that an additional long range ³J(PF)coupling constant has also been observed for both complexes and its value is ~26 Hz. Due to the small ²J(PP) coupling constants measured in the ³¹P{¹H} NMR spectra, a cis arrangement around the platinum centre can be suggested for both complexes. The ³¹P{¹H} NMR data for all the Pt(II) complexes, herein reported, have been compiled in Table 2.

Unlike for platinum(0) complexes, a change of chlorine for fluorine on the phosphorus of the dioxaphospholane does not produce an increase in the ¹J(PtP_A)coupling constant. The ¹J(PtP_A) observed for the chlorodioxaphospholane complexes 11 and 13 are in fact considerably larger than those found for their analogues with the fluorodioxaphospholanes 10 and 12 (vide Table 2). Similar results, though with smaller differences between the coupling constants, have been obtained by Nixon and co-workers¹³ for complexes of the type [RhCl(P_BPh₃)(h¹-XP_A=CR₂)], i.e. ¹J(RhP_A)= 264 Hz when X = Cl and 258 Hz when X = F. These results can be understood in terms of the hard and soft acid-base concept¹⁴. It seems that the fluoro ligands 2 and 4 are a lot softer than platinum(II). Then, complexes 11 and 13 can be regarded as a pair of hard acid-soft base, and in this case they will be less stable than their analogues with the chloro ligands, complexes 10 and 12. One would therefore expect the Pt-P_A bond length to be longer in complexes 11 and 13 than in the analogues 10 and 12. Longer bond lengths in a soft acid-hard base pair than in soft acid-not so hard base pair have been evidenced, very recently, by Durig and co-workers¹⁵. TheB-P bond length in the H₃BPF₃ pair is 1.836Å, whereas in H₃BPH₃ it is 1.943Å. So, if the bond lengths are longer, the ¹J(MP) must be smaller because of the smaller contact between the bonding orbitals of the metal and phosphorus nuclei, even if the s character in the phosphorus lone pair is increased. In fact, a less soft metal might simply not react with a ligand in which the s character of the phosphorus lone pair has been increased.

Syntheses and characterisation of palladium(II) complexes

Treatment of the dimeric complex [Pd₂Cl₄(PEt₃) ₂], in CH₂Cl₂ at room temperature, with ligands 1, 3 and 4 affords the square planar complexes [PdCl₂(PEt₃)(C₂H ₄O₂PCl)] 15, [PdCl₂(PEt₃)(C₆H ₄O₂PCl)] 16 and [PdCl₂(PEt₃)(C₆H ₄O₂PF)] 17, respectively, as depicted bellow.

Very simple ³¹P{¹H} NMRspectra have been obtained for complexes 15 - 17. Patterns of lines corresponding to AB or ABX spin systems (A, B = ³¹P, 100%; X = ¹⁹F, 100%) are observed for complexes derived from chloro ligands 15 and 16, and for that derived from the fluoro ligand, 17, respectively. Similarly to the platinum(II) complexes, palladium(II) complexes are also formed as a mixture of two conformers a and b (vide Table 3), with the exception to the fluoro derivative, which might be due to the small size of fluorine, compared to chlorine.

It is interesting that the chloro derivative ligands 1 and 3 yield trans complexes 15 and 16, as shown by the ²J(P_AP_B) coupling constants measured in the ³¹P{¹H} NMR spectra (Table 3), whereas ligand 4 affords complex 17 with cis configuration around the metallic centre¹⁰. Again, an explanation in terms of the combined sizes of palladium atom and the halogen bonded through the phosphorus can be given. Since platinum is bigger than palladium, it allows a cis configuration of the phosphorus ligand, showing a better trans influence of the chlorine ligand. In the palladium complexes 15 and 16 it seems that the major role is played by the steric hindrance of the chlorine in the dioxaphospholane. On the other hand, the trans influence of the chlorine is evidenced by the formation of a cis complex 17 because fluorine is smaller. The ²J(P_AP_B) coupling constants (Table 3) are in accordance with the data found in the literature^9,10.

Conclusions

The ³¹P{¹H} NMR results for the platinum(0) complexes show that changing the dioxaphospholane P bonded chlorine for fluorine leads to an increase in the s character of the phosphorus lone-pair and, as a consequence, to a increase in the Pt-P coupling constant. On the other hand, ¹J(PtP) coupling constants of platinum(II) complexes tend to decrease upon changing the chlorine for fluorine, thus revealing a relationship between the Pearson soft and hard acid-base concept and Pt-P coupling constants. Although a larger number of systems would need to be studied, the present work is a good starting point and dioxaphospholane and dioxaphosphorinane derivatives are good systems for the study of this relationship.

Experimental

All reactions were carried out either under dry dinitrogen in Schlenk tubes or by use of high-vacuum techniques. Glassware was flame-dried in vacuum and solvents were dried, freshly distilled under dinitrogen, and degassed prior to use. The NMR spectra were recorded on a Bruker DRX400 spectrometer at 400.13 MHz for ¹H and 161.98 MHz for ³¹P. All chemical shift data were recorded at 25^oC and are quoted in ppm, with positive values to high frequency of the indicated reference (external 85% H₃PO₄ for ³¹P and SiMe₄ for ¹H) and corrected with respect to the appropriate deuterium frequency. Coupling constants are quoted in Hertz.

2-chloro-1,3,2-dioxaphospholane 1, 2-chloro-4,5-benzo-1,3,2-dioxaphospholane 3 and 2-chloro-1,3,2-dioxaphosphorinane 5 have been prepared from the corresponding diol with PCl₃, following methods described in the literature⁷. The corresponding fluoro derivatives, 2-fluoro-1,3,2-dioxaphospholane 2, 2-fluoro-4,5-benzo-1,3,2-dioxaphospholane 4 and 2-fluoro-1,3,2-dioxaphosphorinane 6, have been prepared by treatment of 1, 3 and 5 with SbF₃, respectively¹⁶. The [Pt(PPh₃)₂(C₂H ₄)]; [Pt₂Cl₄(PEt₃) ₂] and [PdCl₄(PEt₃)₂] were prepared by the published methods^17,18.

Synthesis of (2-chloro-4,5-benzo-1,3,2-dioxaphospholane)bis (triphenylphosphane)platinum(0) 7

To a solution of 3 (0.15 g, 0.84 mmol), in dichloromethane (10 mL), a solution of [Pt(PPh₃)₂(C₂H ₄)] (0.63 g, 0.84 mmol), also in dichloromethane (20 mL), was added at room temperature. The mixture was keept under stirring for 24 h and the solvent was pumped till dry and the oil obtained was washed with toluene (8 x 10 mL) to yield a cream powder (0.27 g, 37%). Found: C, 56.00; H, 3.65. Calc. for C₄₂H₃₄P₃O₂ ClPt: C, 56.28; H, 3.80%.

Synthesis of (2-chloro-1,3,2-dioxaphosphorinane)bis(triphenyl-phosphane)platinum(0) 8

A solution of 5 (0.03 g, 0.20 mmol) in toluene (20 mL) was added dropwise, at ice temperature, to a solution of [Pt(C₂H₄)(PPh₃) ₂] (0.09 g, 0.20 mmol) in toluene (15 mL). After stirring for 24 h, the solvent was pumped off till dry to yield a yellow powder (0.07 g, 41%). Found: C, 55.31;H, 4.38. Calc. for C₃₉H₃₆P₃O₂ ClPt: C, 54.45; H, 4.20%.

Synthesis of (2-fluoro-1,3,2-dioxaphosphorinane)bis(triphenyl-phosphane)platinum(0) 9

To a solution of [Pt(PPh₃)₂(C₂H ₄)] (0.15 g, 0.35 mmol) in toluene (10 mL), at ice temperature, was added a solution of 6 (0.04 g, 0.35 mmol), also in toluene (10 mL). The mixture was kept under stirring, at ice temperature, for 2 h and for further 22 h at room temperature. After complete evaporation of the solvent, a green solid was obtained (0.12 g, 45%). Found: C, 56.00; H, 4.25. Calc. for C₃₉H₃₆P₃O₂ FPt: C, 56.18; H, 4.32%.

Synthesis of cis-dichloro(2-chloro-1,3,2-dioxaphospholane) platinum(II) 10

To a solution of 1 (0.07 g, 0.56 mmol) in dichloromethane (10 mL) a solution of [Pt₂Cl₄(PEt₃) ₂] (0.22 g, 0.28 mmol) in dichloromethane (20 mL), at ice temperature. The mixture was stirred for 2 h at ice temperature and for 46 h at room temperature. The oil obtained was washed with n-hexane (8 x 10 mL) to yield a yellow powder. (0.25 g, 89%). Found: C, 19.02; H, 3.90. Calc. for C₈H₁₉P₂O₂ Cl₃Pt: C, 18.80; H, 3.72%; ¹H nmr (CDCl₃): d 1.15- 1.19 (m, 9H; 3CH₃) d 2.16- 2.18 (m, 6H, 3CH₂) d 3.73 - 3.75 (m, 4H, 2CH₂).

Synthesis of cis-dichloro(2-fluoro-1,3,2-dioxaphospholane) platinum(II) 11

To a toluene solution of 2 (0.04 g, 0.35 mmol), [Pt₂Cl₄(PEt₃) ₂] (0.13 g, 0.17 mmol), in toluene (5 mL), was added and the mixture was stirred for 24 h to yield a yellow powder which was filtered and washed with n-hexane (8 x 10 mL). (0.09 g, 48%). Found: C, 19.35; H, 3.88. Calc. for C₈H₁₉P₂O₂ Cl₂FPt: C, 19.38; H, 3.92%.

Synthesis of cis-dichloro(2-chloro-4,5-benzo-1,3,2-dioxaphos-pholane)platinum(II) 12

To a solution of 3 (0.07 g, 0.42 mmol) in dichloromethane (10 mL) a solution of [Pt₂Cl₄(PEt₃) ₂] (0.16g, 0.21mmol), also in dichloromethane (20 mL), was added, at ice temperature. The mixture was kept under stirring for 2 h at ice temperature and for further 46 h at room temperature. After this time the solvent was pumped off till dryness and the oil obtained was washed with hexane (8 x 6 mL) to yield a yellow powder. (0.2 g, 91%). Found: C, 20.95; H, 2.80. Calc. for C₁₂H₁₉P₂O₂ Cl₃Pt: C, 21.65; H, 2.86%; ¹H nmr (CDCl₃): d 1.06 - 1.18 (m, 9H, 3CH₃) d 1.84 - 1.97 (m, 6H, 3CH₂) d 7.00 - 7.18 (m, 4H, 4CH).

Synthesis of cis-dichloro(2-fluoro-4,5-benzo-1,3,2-dioxaphos-pholane)platinum(II) 13

A solution of [Pt₂Cl₄(PEt₃) ₂] (0.33 g, 0.43 mmol) in toluene (40 mL) was added dropwise to a toluene solution of 4 (0.14 g, 0.86 mmol). The mixture was stirred for 24 h and the product was obtained as a yellow powder after filtration. (0.27 g, 57%). Found: C, 23.01; H, 2.78. Calc. for C₁₂H₁₉P₂O₂ Cl₂FPt: C, 22.55; H, 2.98%.

Synthesis of cis-dichloro(2-chloro-1,3,2-dioxaphosphorinane) platinum(II) 14

To a solution of [Pt₂Cl₄(PEt₃) ₂] (0.09 g, 0.12 mmol) in toluene (10 mL) was added to a solution of 5 ( 0.03 g, 0.24 mmol) in toluene (10 mL), at ice temperature. The mixture was stirred for 2 h at ice temperature and for further 48 h at room temperature. After this period the yellow solid obtained was filtered and washed with toluene. (0.05 g, 42%). Found: C, 20.31; H, 3.92. Calc. for C₉H₂₁P₂O₂ Cl₃Pt: C, 20.59; H, 4.00%.

Synthesis of trans-dichloro(2-chloro-1,3,2-dioxaphospholane) palladium(II) 15

To a solution of 1 (0.14 g, 1.12 mmol) in dichloromethane (10 mL) a solution of [Pd₂Cl₄(PEt₃) ₂] (0.33 g, 0.56 mmol), also in dichloromethane (20 mL), was added dropwise, at ice temperature. The mixture was stirred for 2h at ice temperature and for further 22 h at room temperature. Upon evaporation of the solvent, an oil was obtained and washed with hexane (8 x 6 mL) to yield a yellow solid. (0.30 g, 64%). Found: C, 22.00; H, 4.3. Calc. for C₈H₁₉P₂O₂ Cl₃Pd: C, 22.75; H, 4.5%.

Synthesis of trans-dichloro(2-chloro-4,5-benzo-1,3,2-dioxaphos-pholane)palladium(II) 16

To a solution of 3 (0.07 g, 0.42 mmol) in dichloromethane (10 mL) a solution of [Pd₂Cl₄(PEt₃) ₂] (0.12 g, 0.21 mmol), also in dichloromethane (20 mL), was added dropwise, at ice temperature. The mixture was stirred for 2 h at ice temperature and for further 22 h at room temperature. Upon evaporation of the solvent, an oil was obtained and washed with hexane (8x6mL) to yield a yellow solid. (0.16 g, 84%). Found: C, 27.98; H, 3.20. Calc. for C₁₂H₁₉P₂O₂ Cl₃Pd: C, 28.19; H, 3.46%.

Synthesis of cis-dichloro(2-fluoro-4,5-benzo-1,3,2-dioxaphos-pholane)palladium(II) 17

To a solution of 4 (0.06 g, 0.40 mmol) in dichloromethane (10 mL) a solution of [Pd₂Cl₄(PEt₃) ₂] (0.12 g, 0.20 mmol), also in dichloromethane (20 mL), was added dropwise, at ice temperature. The mixture was stirred for 2 h at ice temperature and for further 22 h at room temperature. Upon evaporation of the solvent, an oil was obtained and washed with hexane (8 x 6 mL) to yield a yellow solid. (0.10g, 60%). Found: C, 26.98; H, 3.02. Calc. for C₁₂H₁₉P₂O₂ Cl₃Pd: C, 27.51; H, 3.27%.

Acknowledgements

We thank Johnson Matthey plc for the loans of platinum and palladium salts and FAPEMIG, FINEP, PRPq-UFMG and CNPq-Brazil for the continuing support of this work.

Received: November 17, 1999

e-mail: [e-mail]

• 1. Corbridge, D. E. C. Phosphorus - An Outline of its Chemistry, Biochemistry and Technology, Amsterdam, 1990, p.643.
• 2. Tem Hoeve, W.; Wynberg, H.; Jones, W. T.; Harvey, D.; Ryan, G. B.; Reynolds, P. H. S. Bioconjugate Chem. 1997, 8, 257.
• 3. Kobayashi, S.; Okawa, M.; Saegusa, T. Macromolecules 1990, 23, 1873.
• 4. Kobayashi, S.; Kadokawa, J.; Vyama, H.; Shoda, S.; Lundmark, S. Macromolecules 1992, 25, 5861.
• 5. Martin, S. F.; Wagman, A. J. Org. Chem. 1993, 58, 5897. 
• 6. Verkade, J. G. Energy and Fuel 1990, 4, 190.
• 7. Matos, R. M.; da Costa, R. F. F.; Passos, B. F. T. Quím. Nova 1998, 21, 484.
• 8. Matos R. M.; da Costa, R. F. F.; Passos, B. F. T. J. Braz. Chem. Soc. 1999, 10, 21.
• 9. Hitchcock, P. B.; Matos, R. M.; Meidine, M. F.; Nixon, J. F.; Passos, B. F. T.; Barion, D.; Niecke, E. J. Organomet. Chem. 1993, 461, 61.
• 10. Nixon, J. F.; Pidcock, A. Ann. Rev. NMR Spect. 1969, 2, 459.
• 11. Gagnaire, D.; Robert, J. B.; Verrier, J.; Wolf, R. Bull. Soc. Chem. France 1966, 3719.
• 12. Mikolajczyk, M.; Grazy, K. P. P. In Phosphorus-31 NMR Spectral Properties in Compound Characterization and Structural Analysis; Quin, L. D.; Verkade, J. G., eds.; VCH; Weinheim, 1994, p.17.
• 13. Hitchcock, P. B.; Meidine, M. F.; Nixon, J. F.; Wang, H.; Gudat, D.; Niecke, E. J. Organomet. Chem. 1989, 368, C29.
• 14. Pearson, R. G. Coord. Chem. Rev. 1990, 100, 403.
• 15. Durig, J. R.; Shen, Z. Theochem. 1997, 397, 179.
• 16. Knupp, V. F., MSc. Dissertation; UFMG, Belo Horizonte - MG, Brazil 1998.
• 17. Hartley, F. R. Organomet. Chem. Rev. 1970, 6A, 119 and references therein.
• 18. McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc. 1976, 98, 652.

Publication Dates

• Publication in this collection
  06 Nov 2000
• Date of issue
  June 2000

History

• Received
  17 Nov 1999