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Synthesis and thermal stability of mixed-ligand lanthanide organometallics involving both cyclopentadienyl and o-nitrophenolato or α-nitroso-β-naphtholato ligands
Polyhedron Vol. 10, No. I, pp. 27-31, Printed in Great Britain
1991 0
0277-5387/91 $3.00+.00 1991 Pergamon press plc
SYNTHESIS AND THERMAL STABILITY OF MIXED-LIGAND LANTHANIDE ORGANOMETALLICS INVOLVING BOTH CYCLOPENTADIENYL AND o-NITROPHENOLATO OR a-NITROSO-/I-NAPHTHOLATO LIGANDS ZHONGZHI
WU* and ZHONGWEN
YE
Institute of Organic Chemistry, Anhui Normal University, Wuhu, Anhui 241000, P.R.C. (Received
18 January
1990 ; accepted 13 August 1990)
Abstract-By reaction of Cp,Nd or Cp,Yb (Cp = C5HS) with o-nitrophenol (HNP) or anitroso-Snaphthol (HNN), eight new mixed-ligand lanthanide organometallics of the general formula Cp,Ln(NP),_, and Cp,Ln(NN),_, (n = 1, 2; NP = o-nitrophenolato ligand ; NN = a-nitroso+naphtholato ligand ; Ln = Nd, Yb) have been synthesized. All the complexes were characterized by elemental analyses, and IR and MS spectra, showing that they are chelates with NP and NN as bidentate chelate ligands. Their thermal stability has been studied and discussed.
naphthol (HNN) in tetrahydrofuran room temperature. They are :
Many inorganic and organometallic complexes are extremely susceptible to heat, and some of them may disproportionate at low temperatures. I-3 Recently, we reported studies on the thermal stability of lanthanide complexes Cp,Sm(L) (L = 0COCH3, Cl, Br, I)4 and Cp,Ln(L)3_, (n = 1, 2 ; L = /?-diketonato, %quinolinolato, oaminophenolato, o-aldehydophenolato, furfuralcoholato ligand ; Ln = Nd, Yb)2*5-7and found that they are thermally unstable and tend to disproportionate at moderately high temperatures. In continuation of our previous studies, we have now carried out the synthesis and the study of the thermal stability of eight new mixed-ligand (Nd, Yb) organometallic complexes containing both cyclopentadienyl (Cp) and o-nitrophenolato (NP) or anitroso+naphtholato (NN) ligands, and the results are reported in this paper. RESULTS
1: 1
mole ratio of reactants
(THF)
at
1 : 2 mole ratio of reactants
Cp,Nd(NP) Cp,Nd(NN) CpzYb(NP)
(1) (2) (3)
CpNd(NP) z (5) CpNd(NN)2 (6) CPYb(NP) 2 (7)
Cp,YWN
(4)
CpWW2
(8)
All these complexes were characterized by elemental analyses (Table l), and IR (Table 2) and MS (Table 3) spectra. The elemental analyses for all the complexes are in compliance with the general formula Cp,Ln(L),_.. They are soluble in THF and insoluble in pentane, n-hexane and other alkane solvents, but sparingly soluble in benzene and toluene. None of the complexes have melting points ; decomposition is observed in a sealed capillary in the range 90-200°C. The IR spectra of all the complexes show absorptions at approx. 250, 780, 1010, 1440 and 3080 cm- I, characteristic of the v5-C!p group.’ All the complexes exhibit two bands in the IR spectra in the regions 1115 and 470 cm-‘. We attribute the first band to a Ln-O-C vibration mode and the second band to the v(Ln-0) stretching.g,’ ’ Complexes 1, 3, 5 and 7 exhibit two absorptions at ca 1325 and 1510 cm-‘, attributable to the symmetric
AND DISCUSSION
By adopting the very versatile method of liberating cyclopentadiene from a Cp,Ln moiety by the action of protonic acids stronger than CsH6, we have synthesized the mixed-ligand lanthanide organometallic complexes by reaction of Cp,Nd or Cp,Yb with o-nitrophenol (HNP) or a-nitroso-#?-
*Author to whom correspondence should be addressed. 27
ZHONGZHI
28
WU and ZHONGWEN
YE
Table 1. Analytical and physical data for complexes l-8
Complex
Formula
Yield
Decomposition temperature
Colour
(%)
(“C)
Ln
Yellow*range
72
120
34.6 (34.9) 32.6 (32.3) 38.9 (39.2) 37.0 (36.4) 29.6 (29.1) 26.5 (26.1) 33.6 (33.6) 29.7 (29.7)
Brown
80
140
Red-orange
72
170
Brown
33
200
Orange
91
90
Brown
82
120
Orange
74
150
Brown-black
86
180
and antisymmetric stretching vibrations of the NO* group, respectively. In the spectrum of the sodium salt of the ligand HNP, v(N0,) appears at 1334 and 1546 cm- ‘. Therefore, the shift of the stretching vibrations of the NO* group to lower frequencies in these complexes may indicate the coordination of the NO* group. lo The IR spectra of complexes 2, 4, 6 and 8 reveal that the @JO) in the sodium salt of the ligand HNN located at 1530 cm-’ is shifted to lower frequency on complexation to
Found(Calc.) (%) C
(2:)
53.1 (53.7) 42.9 (43.5) 50.6 (50.5) 42.0 (42.1) 53.7 (54.2) 39.1 (39.7) 51.4 (51.6)
H
N
3.0 (3.4)
:::,
(::&
(:4) 3.4
(;:;)
(3.2)
(3’::) 2.8
(::;) 5.9
(2.7) 3.3
(5.8) 5.2
(3.1)
(5.1) 5.6
(:::)
(5.4) (::B
approx. 1476 cm- ‘, suggesting coordination of the NO group. ’ ’ In addition, the strong band of the phenolic-OH stretching vibration for the free ligand HNP or HNN at ca 3000 cm-’ does not appear in the IR spectra of any of the complexes. This also proves the presence of the Ln-O-C bond in each complex. In the mass spectra of these complexes, the molecular ion peaks and main resulting fragments all appear. All the molecular ion intensities are low.
Table 2. IR spectral data for complexes l-8 (4000-200 cm- ‘) Main absorption peaks (cm- ‘)
Complex
CPWW’)
(1)
Q W(NN) (2) Cp,Yb(NF)
(3)
Cp,Yb(NN)
(4)
CpNd(NF),
0
CpNd(NN),
(6)
CpYb(NF),
(7)
CpYb(NN),
(8)
3082w, 3057w, 16OOm,1511m, 15OOs,1443m, 1324m, 1253m, 1115m, 1013m, 777m, 748m, 48Om, 255~ 3058w, 3025w, 1617s, 1596s, 1554s 1463m, 145Os, 1259m, 1113m, 1013s, 81Om, 767s, 722s, 475w, 252~ 3085w, 3035w, 16029, 151Os, 15Ols, 1442s, 1328s, 1256s 114Om, 1014m, 781s, 751s, 463m, 250~ 306Om, 302Ow, 1592m, 1465m, 1440m, 1260, 1259m, 1115m, IOlOm, 76Pm, 721m, 469w, 245~ 308Ow, 3052w, 1602m, 1512m, 15Ols, 1445s, 1325m, 1254m, 1114m, 102Om, 784m, 75Om, 47Om, 252~ 3065m, 303Ow, 1614s, 1595s, 1555s, 1465s, 1445s, 126Om, 1115m, 1015m, 785m, 766m, 721m, 471w, 248~ 3078w, 3032w, 16OOw, 1512m, 15Ols, 1438m, 1328m, 1253m, 1138m, 1018m, 77Pm, 749s, 470m, 248~ 3075w, 3025w, 1613s, 1597s, 1554s, 1435m, 1464m, 1262m, 1114m, lOOPm, 77Os, 722m, 466m, 250w
Synthesis and thermal stability of mixed-ligand lanthanide organometallics Table 3. MS data for complexes 14 at different evaporation
Complexes Cp,,Ln(L)J_, (Cp = CsHS) and molecular species 1 n = 2, L = CsH4(o-NO*)O, M = Cp,NdL, M’ = Cp,Nd
Temperature of evaporation (“C) 80-120 14&180
2 n = 2, L = CH : CHCH : CH&H2(o-NO)O, M = Cp,NdL, M’ = Cp,Nd
100-140
160-200
temperatures
Main ion peaks (m/z) 410(M), 380(M-NO), 345(M-Cp), 272(M - L), 207(M -Cp - L), 142(Nd) 337(M’), 272(M’-Cp), 207(M’-2Cp), 142(Nd) 444(M), 414(M-NO), 379(M-Cp), 314(M -2Cp), 272(M -L), 207(M -Cp-L), 142(Nd) 337(M’), 272(M’-Cp), 207(M’-2Cp), 142(Nd)
3 n = 2, L = CsH4(o-NOJO, M = Cp,YbL
180-300
442(M), 396(M -NOz), 377(M -Cp), 312(M-2Cp), 174(Yb)
4 n = 2, L = CH : CHCH : CHC,H2(o-NO)O, M = Cp,YbL
160-250
476(M), 446(M -NO), 41 l(M -Cp), 346(M - 2Cp), 174(Yb)
5 n = 1, L = C6H,(o-NO*)O, M = CpNdLz, M’ = Cp,NdL, M” = Cp,Nd
50-70 90-130 140-180
6 n = 1, L = CH : CHCH : CH&H&NO)O, M = CpNdL*, M’ = Cp,NdL, M” = Cp,Nd
60-100 120-140 160-200
7 n = 1, L = &H,(o-N02)0, M = CpYbLz, M’ = Cp,YnL
120-160 180-300
8 n = 1, L = CH : CHCH : CHC6H2(o-NO)O, M = CpYbLz, M’ = Cp,YbL
100-140 160-300
29
483(M), 437(M-NOz), 418(M-Cp), 345(M -L), 207(M -2L), 142(Nd) 483(M), 437(M-NO&, 418(M-Cp), 410(M’), 345(M’-Cp), 280(M’-2Cp), 142(Nd) 337(M”), 272(M” - Cp), 207(M” - 2Cp), 142(Nd) 551(M), 521(M-NO), 491(M-2NO), 486(M - Cp), 3 14(M - Cp- L), 142(Nd) 444(M’), 414(M’-NO), 379(M’-Cp), 3 14(M’ - 2Cp), 207(M’ - Cp - L), 142(Nd) 337(M”), 272(M” - Cp), 207(M” - 2Cp), 142(Nd) 515(M), 469(M - NOJ, 450(M - Cp), 312(M-Cp-L), 174(Yb) 515(M), 469(M-NO& 442(M’), 377(M’-Cp), 312(M’-2Cp), 174(Yb) 583(M), 553(M -NO), 518(M -Cp), 346(M - Cp - L), 142(Yb) 583(M), 553(M-NO), 518(M-Cp), 476(M’), 411(M’-Cp), 346(M’-2Cp), 174(Yb)
a MS data are given for the isotopes 14’Nd, ‘74Yb, 14N and 160, the peak patterns correspond to theoretical values based on the natural abundance of the isotopes.
are characterized by ready loss of the Cp group with the (M-Cp)+ ion as the base peak in the mass spectra. The ion peaks of (M-L)+ (L = NP, NN) formed by direct loss of the NP or NN ligand of the molecular ion are very low. This is consistent with the results that Cp groups form $-bonds with metals, whereas NP and NN ligands chelate with the metal atom to form a chelating ring. Thus, the Ln-Cp bond is weaker than the Ln-L bond, and the former breaks easily under electron impact. However, it was observed that in the mass spectra, the loss of NO* or NO fragments occurs during cleavage. This feature can be attributed to the existence of the electron-withdrawing
They
group NOz or NO weakening the C-NO1 or C-NO bond strength, thus leading to easy fragmentation of the molecular ion. From the above elemental and spectral analyses, it may be assumed that all the complexes are chelates with NP or NN as bidentate chelate ligands. This is in agreement with the fact that the greatest tendency to form chelate complexes is found with polyfunctional ligands whose donor atoms are separated by two or three carbon atoms, the chelating ring produced by chelate formation will be five- or six-membered. Therefore, the following structure for the eight new mixed-ligand complexes may be proposed (1,2).
30
ZHONGZHI
WU
and ZHONGWEN YE
(1)
In order to study the thermal stability of these complexes, their mass spectra were recorded at different evaporation temperatures. It is interesting to note that when the evaporation temperature of a sample of CpLnL-type complexes reaches a certain value, not only are the molecular ions CpLnL,+ observed in the spectra, but the peaks corresponding to Cp,LnL+ and their fragments are observed also. Furthermore, by increasing the evaporation temperature, the molecular ion peaks of CpLnL,+ gradually disappear and the peaks of Cp2LnL+ and its fragments are enhanced. In addition, we interestingly found that when the evaporation temperature reaches a moderately high value, the ion peaks of Cp,NdL+ completely disappear and the strong peaks corresponding to Cp,Nd+ and its fragments are observed instead. However, no Cp,Yb+ ion peak is observed in the mass spectra of complexes of CpYbLz or Cp,YbL. Thus, based on the above results, we predict that the complexes may undergo the following disproportionation reactions during the course of raising the temperature : 2CpLnL2 --i Cp,LnL+
LnL3
3Cp,LnL --t 2Cp,Ln+LnL,.
(1) (2)
This feature is consistent with the results reported in our previous studies. 6*7The ion peaks of disproportionation products LnL3 do not appear in the mass spectra. In view of the mass spectra, we also found that complexes of ytterbium, either of the Cp,LnL- or CpLnL,-type, are thermally more stable than the analogues of neodymium. Above 160°C the disproportionations of four neodymium complexes are apparently complete. But even at 3OO”C, the Cp,YbL-type complexes still remain unchanged. We assume that the greater thermal stability of the ytterbium complexes compared with their neodymium analogues is due to the lanthanide contraction. As the radius of Yb3+ is smaller than Nd3+, the attraction of the Yb-ligand bond formed by Yb3+ and an anionic ligand will be stronger than the Nd-ligand bond. Another reason for the superior thermal stability of ytterbium complexes
may be due to the greater steric saturation present around the smaller metal centre. ’ 2,I 3 Probably due to the large radii and coordinative unsaturation of light lanthanides, their organometallic complexes involving both Cp and Cl groups, such as unsolvated Cp,LnCl and CpLnCl, (Ln = La, Ce, Pr and Nd), have not yet been synthesized at room temperature.3*‘4 The reported facile preparation of the unsolvated and room-temperature stable complexes Cp,Nd(L),_, (n = 1, 2 ; L = NP, NN) is obviously due to stabilization of the species by the chelation effect. This also revealed that the steric bulky ligands are favourable for the stabilization of the Ln-C bond.
EXPERIMENTAL Materials
All operations were carried out in an atmosphere of dry oxygen-free argon using standard Schlenk techniques or in a glove box. All solvents were dried over sodium, refluxed over sodium benzophenone or finely divided LiA1H4, and distilled immediately before use. HNP and HNN were of chemically pure grade, and were dried in vacua before use. Cp,Nd and Cp,Yb were prepared and purified by the literature method. ’ ’ Physical measurements and elemental analyses
IR spectra were recorded on a Perkin-Elmer 9830 IR spectrophotometer as Nujol and Fluorolube mulls between CsI plates (2064000 cm- ‘). All the mass spectrometric measurements were performed on a MAT 3 12 mass spectrometer operating in the EI mode at a resolving power of 1000 (electron energy, 70 eV ; emission current, 1 mA ; ion acceleration, 3 kV). The samples were introduced by direct inlet techniques with a source temperature of 130°C and a sample evaporation temperature in the range 20-300°C. Metal analyses for lanthanides were accomplished using the literature method.16 Elemental analyses for carbon, hydrogen and nitrogen
Synthesis and thermal stability of mixed-ligand lanthanide organometallics
were carried out on a Yanaco MT2 CHN analyser. Decomposition
points
were determined
in a
31
ments of mass spectra. Thanks are also due to Dr Baohui Du and Jiping Hu for assistance.
sealed capillary filled with argon and are uncorrected.
REFERENCES Preparation
of
complexes
Cp,Ln(NP)
and
CpWNP) 2 A THF solution (20 cm’) of HNP (1.5 mmol or 3.0 mmol) was added dropwise to a THF solution 30 cm3) of Cp,Nd or Cp,Yb (1.5 mmol) at room temperature. After stirring for 24 h at room temperature, the resulting solution was concentrated via vacuum to ca 15 cm3. On the addition of 40 cm3 of n-hexane, a solid precipitated out, which was recrystallized twice from THF-n-hexane, washed with n-hexane and dried in vacua to afford the product. Yields and elemental analyses are given in Table 1. Preparation
of
complexes
Cp,Ln(NN)
and
QWNW
A THF solution (20 cm3) of HNN (1.5 or 3.0 mmol) was added dropwise to a THF solution (30 cm3) of Cp,Nd or Cp,Yb (1.5 mmol) at room temperature. The reaction solution was allowed to stir for 24 h at room temperature. A solid gradually precipitated, which was separated out by centrifugation, washed twice with n-hexane and dried in vacua to afford the product. Yields and elemental analyses are listed in Table 1. Acknowledgements--This research was financially supported by the National Science Foundation. The authors are grateful to the mass spectra group of Fujian Institute of Research on the Structure of Matter for the measure-
1. M. R. Litzow and T. R. Spalding, Mass Spectrometry of Inorganic and Organometallic Compounds. Elsevier, Amsterdam (1973). 2. Lanping Yang, Liang Dai, Huaizhu Ma and Zhongwen Ye, Organometallics 1989,8, 1129. 3. R. E. Maginn, S. Manastyskj and M. Dubeck, J. Am. Chem. Sot. 1963,85,672. 4. Zhongwen Ye, Huaizhu Ma and Yongfei Yu, J. LessCommon Metals 1986,125,405. 5. Huaizhu Ma and Zhongwen Ye, J. Organomet. Chem. 1987,326,369. 6. Zhongwen Ye and Zhongzhi Wu, Synth. React. Znorg. Met.-Org. Chem. 1989, 19, 157. 7. Zhongzhi Wu, Zhongwen Ye and Zhennan Zhou, Polyhedron 1989,8,2109. 8. C. Qian, C. Ye, H. Lu, Y. Li, J. Zhou, Y. Ge and M. Tsutsui, J. Organomet. Chem. 1983, 247, 161. 9. R. Lozano, J. Roman and F. D. Jesus, Polyhedron 1989,8,947. 10. K. Nakamoto, Infrared and Raman Spectra of Znorganic and Coordination Compounds, 3rd edn. WileyInterscience, New York (1978) (and refs cited therein). 11. Yulan Qi, Gaocong Peng, Xiaojing Li, Yuansheng Wu and Rudong Yang, Univer. J. Chem. (Chinese) 1988,9,844. 12. W. J. Evans, Polyhedron 1987,6, 803. 13. R. D. Fischer and Li Xing-Fu, J. Less-Common Metals 1985, 112, 303. 14. T. J. Marks, Prog. Znorg. Chem. 1978,24, 51. 15. G. Wilkinson and J. M. Birmingham, J. Am. Chem. Sot. 1956,78,42. 16. Changqin Ye and Yuqin Li, J. Org. Chem. (Chinese) 1981,210.
1991 0
0277-5387/91 $3.00+.00 1991 Pergamon press plc
SYNTHESIS AND THERMAL STABILITY OF MIXED-LIGAND LANTHANIDE ORGANOMETALLICS INVOLVING BOTH CYCLOPENTADIENYL AND o-NITROPHENOLATO OR a-NITROSO-/I-NAPHTHOLATO LIGANDS ZHONGZHI
WU* and ZHONGWEN
YE
Institute of Organic Chemistry, Anhui Normal University, Wuhu, Anhui 241000, P.R.C. (Received
18 January
1990 ; accepted 13 August 1990)
Abstract-By reaction of Cp,Nd or Cp,Yb (Cp = C5HS) with o-nitrophenol (HNP) or anitroso-Snaphthol (HNN), eight new mixed-ligand lanthanide organometallics of the general formula Cp,Ln(NP),_, and Cp,Ln(NN),_, (n = 1, 2; NP = o-nitrophenolato ligand ; NN = a-nitroso+naphtholato ligand ; Ln = Nd, Yb) have been synthesized. All the complexes were characterized by elemental analyses, and IR and MS spectra, showing that they are chelates with NP and NN as bidentate chelate ligands. Their thermal stability has been studied and discussed.
naphthol (HNN) in tetrahydrofuran room temperature. They are :
Many inorganic and organometallic complexes are extremely susceptible to heat, and some of them may disproportionate at low temperatures. I-3 Recently, we reported studies on the thermal stability of lanthanide complexes Cp,Sm(L) (L = 0COCH3, Cl, Br, I)4 and Cp,Ln(L)3_, (n = 1, 2 ; L = /?-diketonato, %quinolinolato, oaminophenolato, o-aldehydophenolato, furfuralcoholato ligand ; Ln = Nd, Yb)2*5-7and found that they are thermally unstable and tend to disproportionate at moderately high temperatures. In continuation of our previous studies, we have now carried out the synthesis and the study of the thermal stability of eight new mixed-ligand (Nd, Yb) organometallic complexes containing both cyclopentadienyl (Cp) and o-nitrophenolato (NP) or anitroso+naphtholato (NN) ligands, and the results are reported in this paper. RESULTS
1: 1
mole ratio of reactants
(THF)
at
1 : 2 mole ratio of reactants
Cp,Nd(NP) Cp,Nd(NN) CpzYb(NP)
(1) (2) (3)
CpNd(NP) z (5) CpNd(NN)2 (6) CPYb(NP) 2 (7)
Cp,YWN
(4)
CpWW2
(8)
All these complexes were characterized by elemental analyses (Table l), and IR (Table 2) and MS (Table 3) spectra. The elemental analyses for all the complexes are in compliance with the general formula Cp,Ln(L),_.. They are soluble in THF and insoluble in pentane, n-hexane and other alkane solvents, but sparingly soluble in benzene and toluene. None of the complexes have melting points ; decomposition is observed in a sealed capillary in the range 90-200°C. The IR spectra of all the complexes show absorptions at approx. 250, 780, 1010, 1440 and 3080 cm- I, characteristic of the v5-C!p group.’ All the complexes exhibit two bands in the IR spectra in the regions 1115 and 470 cm-‘. We attribute the first band to a Ln-O-C vibration mode and the second band to the v(Ln-0) stretching.g,’ ’ Complexes 1, 3, 5 and 7 exhibit two absorptions at ca 1325 and 1510 cm-‘, attributable to the symmetric
AND DISCUSSION
By adopting the very versatile method of liberating cyclopentadiene from a Cp,Ln moiety by the action of protonic acids stronger than CsH6, we have synthesized the mixed-ligand lanthanide organometallic complexes by reaction of Cp,Nd or Cp,Yb with o-nitrophenol (HNP) or a-nitroso-#?-
*Author to whom correspondence should be addressed. 27
ZHONGZHI
28
WU and ZHONGWEN
YE
Table 1. Analytical and physical data for complexes l-8
Complex
Formula
Yield
Decomposition temperature
Colour
(%)
(“C)
Ln
Yellow*range
72
120
34.6 (34.9) 32.6 (32.3) 38.9 (39.2) 37.0 (36.4) 29.6 (29.1) 26.5 (26.1) 33.6 (33.6) 29.7 (29.7)
Brown
80
140
Red-orange
72
170
Brown
33
200
Orange
91
90
Brown
82
120
Orange
74
150
Brown-black
86
180
and antisymmetric stretching vibrations of the NO* group, respectively. In the spectrum of the sodium salt of the ligand HNP, v(N0,) appears at 1334 and 1546 cm- ‘. Therefore, the shift of the stretching vibrations of the NO* group to lower frequencies in these complexes may indicate the coordination of the NO* group. lo The IR spectra of complexes 2, 4, 6 and 8 reveal that the @JO) in the sodium salt of the ligand HNN located at 1530 cm-’ is shifted to lower frequency on complexation to
Found(Calc.) (%) C
(2:)
53.1 (53.7) 42.9 (43.5) 50.6 (50.5) 42.0 (42.1) 53.7 (54.2) 39.1 (39.7) 51.4 (51.6)
H
N
3.0 (3.4)
:::,
(::&
(:4) 3.4
(;:;)
(3.2)
(3’::) 2.8
(::;) 5.9
(2.7) 3.3
(5.8) 5.2
(3.1)
(5.1) 5.6
(:::)
(5.4) (::B
approx. 1476 cm- ‘, suggesting coordination of the NO group. ’ ’ In addition, the strong band of the phenolic-OH stretching vibration for the free ligand HNP or HNN at ca 3000 cm-’ does not appear in the IR spectra of any of the complexes. This also proves the presence of the Ln-O-C bond in each complex. In the mass spectra of these complexes, the molecular ion peaks and main resulting fragments all appear. All the molecular ion intensities are low.
Table 2. IR spectral data for complexes l-8 (4000-200 cm- ‘) Main absorption peaks (cm- ‘)
Complex
CPWW’)
(1)
Q W(NN) (2) Cp,Yb(NF)
(3)
Cp,Yb(NN)
(4)
CpNd(NF),
0
CpNd(NN),
(6)
CpYb(NF),
(7)
CpYb(NN),
(8)
3082w, 3057w, 16OOm,1511m, 15OOs,1443m, 1324m, 1253m, 1115m, 1013m, 777m, 748m, 48Om, 255~ 3058w, 3025w, 1617s, 1596s, 1554s 1463m, 145Os, 1259m, 1113m, 1013s, 81Om, 767s, 722s, 475w, 252~ 3085w, 3035w, 16029, 151Os, 15Ols, 1442s, 1328s, 1256s 114Om, 1014m, 781s, 751s, 463m, 250~ 306Om, 302Ow, 1592m, 1465m, 1440m, 1260, 1259m, 1115m, IOlOm, 76Pm, 721m, 469w, 245~ 308Ow, 3052w, 1602m, 1512m, 15Ols, 1445s, 1325m, 1254m, 1114m, 102Om, 784m, 75Om, 47Om, 252~ 3065m, 303Ow, 1614s, 1595s, 1555s, 1465s, 1445s, 126Om, 1115m, 1015m, 785m, 766m, 721m, 471w, 248~ 3078w, 3032w, 16OOw, 1512m, 15Ols, 1438m, 1328m, 1253m, 1138m, 1018m, 77Pm, 749s, 470m, 248~ 3075w, 3025w, 1613s, 1597s, 1554s, 1435m, 1464m, 1262m, 1114m, lOOPm, 77Os, 722m, 466m, 250w
Synthesis and thermal stability of mixed-ligand lanthanide organometallics Table 3. MS data for complexes 14 at different evaporation
Complexes Cp,,Ln(L)J_, (Cp = CsHS) and molecular species 1 n = 2, L = CsH4(o-NO*)O, M = Cp,NdL, M’ = Cp,Nd
Temperature of evaporation (“C) 80-120 14&180
2 n = 2, L = CH : CHCH : CH&H2(o-NO)O, M = Cp,NdL, M’ = Cp,Nd
100-140
160-200
temperatures
Main ion peaks (m/z) 410(M), 380(M-NO), 345(M-Cp), 272(M - L), 207(M -Cp - L), 142(Nd) 337(M’), 272(M’-Cp), 207(M’-2Cp), 142(Nd) 444(M), 414(M-NO), 379(M-Cp), 314(M -2Cp), 272(M -L), 207(M -Cp-L), 142(Nd) 337(M’), 272(M’-Cp), 207(M’-2Cp), 142(Nd)
3 n = 2, L = CsH4(o-NOJO, M = Cp,YbL
180-300
442(M), 396(M -NOz), 377(M -Cp), 312(M-2Cp), 174(Yb)
4 n = 2, L = CH : CHCH : CHC,H2(o-NO)O, M = Cp,YbL
160-250
476(M), 446(M -NO), 41 l(M -Cp), 346(M - 2Cp), 174(Yb)
5 n = 1, L = C6H,(o-NO*)O, M = CpNdLz, M’ = Cp,NdL, M” = Cp,Nd
50-70 90-130 140-180
6 n = 1, L = CH : CHCH : CH&H&NO)O, M = CpNdL*, M’ = Cp,NdL, M” = Cp,Nd
60-100 120-140 160-200
7 n = 1, L = &H,(o-N02)0, M = CpYbLz, M’ = Cp,YnL
120-160 180-300
8 n = 1, L = CH : CHCH : CHC6H2(o-NO)O, M = CpYbLz, M’ = Cp,YbL
100-140 160-300
29
483(M), 437(M-NOz), 418(M-Cp), 345(M -L), 207(M -2L), 142(Nd) 483(M), 437(M-NO&, 418(M-Cp), 410(M’), 345(M’-Cp), 280(M’-2Cp), 142(Nd) 337(M”), 272(M” - Cp), 207(M” - 2Cp), 142(Nd) 551(M), 521(M-NO), 491(M-2NO), 486(M - Cp), 3 14(M - Cp- L), 142(Nd) 444(M’), 414(M’-NO), 379(M’-Cp), 3 14(M’ - 2Cp), 207(M’ - Cp - L), 142(Nd) 337(M”), 272(M” - Cp), 207(M” - 2Cp), 142(Nd) 515(M), 469(M - NOJ, 450(M - Cp), 312(M-Cp-L), 174(Yb) 515(M), 469(M-NO& 442(M’), 377(M’-Cp), 312(M’-2Cp), 174(Yb) 583(M), 553(M -NO), 518(M -Cp), 346(M - Cp - L), 142(Yb) 583(M), 553(M-NO), 518(M-Cp), 476(M’), 411(M’-Cp), 346(M’-2Cp), 174(Yb)
a MS data are given for the isotopes 14’Nd, ‘74Yb, 14N and 160, the peak patterns correspond to theoretical values based on the natural abundance of the isotopes.
are characterized by ready loss of the Cp group with the (M-Cp)+ ion as the base peak in the mass spectra. The ion peaks of (M-L)+ (L = NP, NN) formed by direct loss of the NP or NN ligand of the molecular ion are very low. This is consistent with the results that Cp groups form $-bonds with metals, whereas NP and NN ligands chelate with the metal atom to form a chelating ring. Thus, the Ln-Cp bond is weaker than the Ln-L bond, and the former breaks easily under electron impact. However, it was observed that in the mass spectra, the loss of NO* or NO fragments occurs during cleavage. This feature can be attributed to the existence of the electron-withdrawing
They
group NOz or NO weakening the C-NO1 or C-NO bond strength, thus leading to easy fragmentation of the molecular ion. From the above elemental and spectral analyses, it may be assumed that all the complexes are chelates with NP or NN as bidentate chelate ligands. This is in agreement with the fact that the greatest tendency to form chelate complexes is found with polyfunctional ligands whose donor atoms are separated by two or three carbon atoms, the chelating ring produced by chelate formation will be five- or six-membered. Therefore, the following structure for the eight new mixed-ligand complexes may be proposed (1,2).
30
ZHONGZHI
WU
and ZHONGWEN YE
(1)
In order to study the thermal stability of these complexes, their mass spectra were recorded at different evaporation temperatures. It is interesting to note that when the evaporation temperature of a sample of CpLnL-type complexes reaches a certain value, not only are the molecular ions CpLnL,+ observed in the spectra, but the peaks corresponding to Cp,LnL+ and their fragments are observed also. Furthermore, by increasing the evaporation temperature, the molecular ion peaks of CpLnL,+ gradually disappear and the peaks of Cp2LnL+ and its fragments are enhanced. In addition, we interestingly found that when the evaporation temperature reaches a moderately high value, the ion peaks of Cp,NdL+ completely disappear and the strong peaks corresponding to Cp,Nd+ and its fragments are observed instead. However, no Cp,Yb+ ion peak is observed in the mass spectra of complexes of CpYbLz or Cp,YbL. Thus, based on the above results, we predict that the complexes may undergo the following disproportionation reactions during the course of raising the temperature : 2CpLnL2 --i Cp,LnL+
LnL3
3Cp,LnL --t 2Cp,Ln+LnL,.
(1) (2)
This feature is consistent with the results reported in our previous studies. 6*7The ion peaks of disproportionation products LnL3 do not appear in the mass spectra. In view of the mass spectra, we also found that complexes of ytterbium, either of the Cp,LnL- or CpLnL,-type, are thermally more stable than the analogues of neodymium. Above 160°C the disproportionations of four neodymium complexes are apparently complete. But even at 3OO”C, the Cp,YbL-type complexes still remain unchanged. We assume that the greater thermal stability of the ytterbium complexes compared with their neodymium analogues is due to the lanthanide contraction. As the radius of Yb3+ is smaller than Nd3+, the attraction of the Yb-ligand bond formed by Yb3+ and an anionic ligand will be stronger than the Nd-ligand bond. Another reason for the superior thermal stability of ytterbium complexes
may be due to the greater steric saturation present around the smaller metal centre. ’ 2,I 3 Probably due to the large radii and coordinative unsaturation of light lanthanides, their organometallic complexes involving both Cp and Cl groups, such as unsolvated Cp,LnCl and CpLnCl, (Ln = La, Ce, Pr and Nd), have not yet been synthesized at room temperature.3*‘4 The reported facile preparation of the unsolvated and room-temperature stable complexes Cp,Nd(L),_, (n = 1, 2 ; L = NP, NN) is obviously due to stabilization of the species by the chelation effect. This also revealed that the steric bulky ligands are favourable for the stabilization of the Ln-C bond.
EXPERIMENTAL Materials
All operations were carried out in an atmosphere of dry oxygen-free argon using standard Schlenk techniques or in a glove box. All solvents were dried over sodium, refluxed over sodium benzophenone or finely divided LiA1H4, and distilled immediately before use. HNP and HNN were of chemically pure grade, and were dried in vacua before use. Cp,Nd and Cp,Yb were prepared and purified by the literature method. ’ ’ Physical measurements and elemental analyses
IR spectra were recorded on a Perkin-Elmer 9830 IR spectrophotometer as Nujol and Fluorolube mulls between CsI plates (2064000 cm- ‘). All the mass spectrometric measurements were performed on a MAT 3 12 mass spectrometer operating in the EI mode at a resolving power of 1000 (electron energy, 70 eV ; emission current, 1 mA ; ion acceleration, 3 kV). The samples were introduced by direct inlet techniques with a source temperature of 130°C and a sample evaporation temperature in the range 20-300°C. Metal analyses for lanthanides were accomplished using the literature method.16 Elemental analyses for carbon, hydrogen and nitrogen
Synthesis and thermal stability of mixed-ligand lanthanide organometallics
were carried out on a Yanaco MT2 CHN analyser. Decomposition
points
were determined
in a
31
ments of mass spectra. Thanks are also due to Dr Baohui Du and Jiping Hu for assistance.
sealed capillary filled with argon and are uncorrected.
REFERENCES Preparation
of
complexes
Cp,Ln(NP)
and
CpWNP) 2 A THF solution (20 cm’) of HNP (1.5 mmol or 3.0 mmol) was added dropwise to a THF solution 30 cm3) of Cp,Nd or Cp,Yb (1.5 mmol) at room temperature. After stirring for 24 h at room temperature, the resulting solution was concentrated via vacuum to ca 15 cm3. On the addition of 40 cm3 of n-hexane, a solid precipitated out, which was recrystallized twice from THF-n-hexane, washed with n-hexane and dried in vacua to afford the product. Yields and elemental analyses are given in Table 1. Preparation
of
complexes
Cp,Ln(NN)
and
QWNW
A THF solution (20 cm3) of HNN (1.5 or 3.0 mmol) was added dropwise to a THF solution (30 cm3) of Cp,Nd or Cp,Yb (1.5 mmol) at room temperature. The reaction solution was allowed to stir for 24 h at room temperature. A solid gradually precipitated, which was separated out by centrifugation, washed twice with n-hexane and dried in vacua to afford the product. Yields and elemental analyses are listed in Table 1. Acknowledgements--This research was financially supported by the National Science Foundation. The authors are grateful to the mass spectra group of Fujian Institute of Research on the Structure of Matter for the measure-
1. M. R. Litzow and T. R. Spalding, Mass Spectrometry of Inorganic and Organometallic Compounds. Elsevier, Amsterdam (1973). 2. Lanping Yang, Liang Dai, Huaizhu Ma and Zhongwen Ye, Organometallics 1989,8, 1129. 3. R. E. Maginn, S. Manastyskj and M. Dubeck, J. Am. Chem. Sot. 1963,85,672. 4. Zhongwen Ye, Huaizhu Ma and Yongfei Yu, J. LessCommon Metals 1986,125,405. 5. Huaizhu Ma and Zhongwen Ye, J. Organomet. Chem. 1987,326,369. 6. Zhongwen Ye and Zhongzhi Wu, Synth. React. Znorg. Met.-Org. Chem. 1989, 19, 157. 7. Zhongzhi Wu, Zhongwen Ye and Zhennan Zhou, Polyhedron 1989,8,2109. 8. C. Qian, C. Ye, H. Lu, Y. Li, J. Zhou, Y. Ge and M. Tsutsui, J. Organomet. Chem. 1983, 247, 161. 9. R. Lozano, J. Roman and F. D. Jesus, Polyhedron 1989,8,947. 10. K. Nakamoto, Infrared and Raman Spectra of Znorganic and Coordination Compounds, 3rd edn. WileyInterscience, New York (1978) (and refs cited therein). 11. Yulan Qi, Gaocong Peng, Xiaojing Li, Yuansheng Wu and Rudong Yang, Univer. J. Chem. (Chinese) 1988,9,844. 12. W. J. Evans, Polyhedron 1987,6, 803. 13. R. D. Fischer and Li Xing-Fu, J. Less-Common Metals 1985, 112, 303. 14. T. J. Marks, Prog. Znorg. Chem. 1978,24, 51. 15. G. Wilkinson and J. M. Birmingham, J. Am. Chem. Sot. 1956,78,42. 16. Changqin Ye and Yuqin Li, J. Org. Chem. (Chinese) 1981,210.