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Mössbauer study of a new organometallic tetradentate ligand trans, trans-Fe2[μ-(Ph2P)2Py-P,P]2(CO)6
Polyhedron Vol. 15, No. 15, pp. 2583-2585, 1996
~
Pergamon 0277-5387(95)00488-2
Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387/96 $15.00+0.00
MOSSBAUER STUDY OF A NEW ORGANOMETALLIC TETRADENTATE LIGAND tr ans, trans-F e2[lt-(Ph2P )2Py-P ,P] 2(C O ) 6 JING-KUN ZHANG,* ZE-MIN ZHANG, AO YU, SHU-LAN ZHAO and WEI-DONG ZHANG Test and Computation Center, Nankai University, Tianjin 300071, P.R. China
and ZHENG-ZHI ZHANG Elemento-Organic Chemistry Laboratory, Nankai University, Tianjin 300071, P.R. China
(Received 8 September 1995; accepted 11 October 1995) Abstract--A new route for the preparation of 2,6-bis(diphenylphosphino)pyridine [(Ph2P)2Py] is reported. Reaction of (PhzP)2Py with Fe(CO)5 in n-butanol gave the macrocyclodiiron complex, trans,trans-Fe2[#-(Ph2P)2Py-P,P]2(CO)6 (1). Treatment of 1 with HgCI2 gave the complex Fe2Hg[~t-(PhzP)2Py]2(CO)6C12- 2HgCI2 (2), with an F e - - H g - - F e linkage in which the central mercury atom resides within the cavity of the macrocycle and is coordinated to two nitrogen atoms and two iron atoms. Compounds 1 and 2 were characterized by elemental analyses, IR, 31p NMR, FD-MS and M6ssbauer spectra.
The compound 2,6-bis(diphenylphosphino) pyri- purified by distillation under nitrogen from standine [(PhzP)2Py] is an important tetradentate bridg- dard drying agents. ing ligand, which has been used in the preparations Preparation of 2,6-bis(diphenylphosphino)pyriof many novel bi- or polynuclear complexes.1 Using dine. A solution of 2,6-dichloropyridine (0.05 tool) this ligand, we have obtained a 12-membered bi- in T H F (40 cm 3) was added with stirring to a solumetallomacrocyclic complex, trans, trans-Fez[#- tion of Ph2PLi (0.1 tool) in T H F (80 cm 3) at 0°C. (Ph2P)2Py-P,P]2(CO)6 (1), The latter can act as a The reaction solution was stirred for 4 h at room neutral organometallic tetradentate ligand reacting temperature and then 15 cm 3 of methanol was with a Lewis acid metal centre to give a trimetal added. The methanol was removed and 100 cm 3 complex, Fe2Hg[#-(Ph2P)2Py] 2(CO)6C12 • 2HgC12 water was added to remove the lithium salt. The (2), with an F e - - H g - - F e donor-acceptor linkage. residue was extracted with CHzC12. After the In this paper, the structures of complexes I and 2 removal of CH2C12 and recrystallization from methare determined through M6ssbauer spectra. anol, a pale yellow solid product was obtained. It was proved to be 2,6-bis(diphenylphosphino) pyridine [(Ph2P)2Py] by IR, 31p N M R , FD-MS and EXPERIMENTAL m.p. determination. Syntheses Preparation of Fe2[#-(PheP)2Py-P,P]2(CO)6 (1). Fe(CO)5 (2.5 mmol) was injected into the solution All synthesis experiments were carried out under of sodium hydroxide dissolved in 30 cm 3 of n-butapurified nitrogen. The solvents were degassed and nol, and reaction solution was stirred for 30 rain under nitrogen. Then 3 mmol [(Ph2P)zPY] was * Author to whom correspondence should be addressed. added to the reaction solution, the mixture solution 2583
2584
JING-KUN ZHANG
(a)
et al.
as solvent. FD-MS was acquired with a Hitachi M-80 spectrometer.
IO0. O0
96. B8
R E S U L T S AND D I S C U S S I O N 93. 36 90. 04
-3
(b) ~ : ,
~"" lO0.
-1 0 1 2 Velocity (mm/s)
-2
.
3
°
°
" .~ v ' "
O0
"
:
~"
.~.
"
-
•
°°°
o
":..'.:'..'
V V -3
-2
1 2 Velocity (mm/s)
-I
0
3
Fig. 1. M6ssbauer spectra of compounds 1 (a) and 2 (b).
was refluxed for 2.5 h and then cooled to room temperature. A yellow precipitate was obtained, which was filtered, washed with methanol and recrystallized in CHzC12-CH3OH. The compound Fe2[/~-(Ph2P)2Py-P,P]2(CO)6 (1) was obtained. Preparation of Fe2Hg[kt-(PhzP)2PY]2(CO)6C12" 2HgC12 (2). At room temperature, 0.625 mmol HgC12 dissolved in 20 cm 3 1 : 2 butanone-2-benzene mixture was added with stirring to the solution containing 0.188 mmol Fe2(CO)6[(Ph2P)2PY]2 in the same solvent (30 cm 3) and the reaction solution was stirred for 30 min. A pale yellow precipitate was obtained. It was filtered off, washed with butanone2-benzene mixture and the product was obtained.
M6ssbauer measurements M6ssbauer effect spectra were obtained at 78 K on a constant-acceleration spectrometer (Model MS-500). The M6ssbauer source consisted of 57Co diffused in a palladium matrix. The M6ssbauer hyperfine parameters were obtained by a least-squares fitting using the Mosfun program. In our fitting procedure, each component of a quadrupole doublet was constrained to have the same linewidth. The IS values were determined relative to metallic iron foil.
Other spectral measurements IR spectra were recorded on a WFD-14 spectrometer as KBr discs. The 31p N M R spectra were recorded on a Jeol FX-90Q spectrometer at 36.19 MHz using H3PO4 as external standard and CDCI2
The M6ssbauer spectra of compounds 1 and 2 were obtained at 80 K. The compounds both gave one quadrupole doublet (Fig. 1). The MOssbauer parameters (IS = - 0 . 1 1 mm s -1, QS = 2.66 mm s-l) of complex 1 are much closer to those of the compound trans-Fe(CO)3(PPh3)2 (IS = - 0.10 mm s 1, Q S = 2 . 6 2 mm s-') and trans-Fe(CO)3 (PPh2Py)2 (IS= - 0 . 1 0 mm s -', QS = 2.59 mm s 1).2,3This indicated that the environments of the iron atoms in these complexes were identical. We suggest that complex 1 has the macrocyclic structure shown in Fig. 2. It is in agreement with IR and FD-MS findings. Two iron atoms and six carbonyls are presumably co-planar, and the plane is perpendicular to the cavity of the macrocycle. The distance between the two iron atoms is about 5.0/~. The IR spectrum exhibited only terminal carbonyl absorption, and did not show the low IR carbonyl absorption of F e - - - C - - O - - F e . Therefore, the carbonyl does not lie in the F e - - F e plane. The IS value for compound 2 is - 0 . 0 4 mm s-1, higher than that observed in complex 1. However, it is comparable to that for the compound Fe(CO)3 (PPh2Py)2 Hg(SCN)2 (IS = - 0 . 0 4 mm s -1) containing the Fe--Hg(SCN)2 bond? This indicated that both trans atoms were coordinated to the mercuric atoms to form F e - - H g bonds. The QS value for compound 2 is 1.12 mm s-~, lower than that for the complex Fe(CO)3(PPh2PY)2Hg(SCN)2 (QS= 1.54 mm s-l). This shows that the iron atoms in complex 2 had better symmetrical environment than that in Fe(CO)3(PPh2Py)2Hg(SCN)2, in which the iron atom is in a distorted octahedral coordination. From the above, we suggest that compound 2 has two possible structures, as shown in Fig. 3. If complex 2 had the structure I, though the region of the cavity is the forbidden region of carbonyls, it would not prevent the mercury atom from
(OC)~ i
~e(COb
Ph2P~,,,-PPh2
Fig. 2. Proposed structure of complex 1.
2585
A new organometallic tetradentate ligand
OC--Fe --~Hg"~-- .Fe--CO Ph2P~fPPh2
OC--Fe
OC- - Fe -4"-HgCI2
P h 2 ~ f
PPh2
1 II Fig. 3. Possible structures for compound 2.
entering. If the mercury atom is coordinated in the cavity, this would make the iron atoms have better symmetry than in structure II. Meanwhile, the two nitrogen atoms have coordinating ability and could stabilize the mercury atom with high oxidation states. Therefore, we suggest compound 2 has structure I rather than structure II. REFERENCES
1. (a) F. E. Wood, M. M. Olmstead and A. L. Balch, J.
Am. Chem. Soc. 1983, 105, 6332 ; (b) F. E. Wood, J. Hoosier, H. Hope and A. L. Balch. lnor9. Chem.
1984, 23, 4309; (c) G. R. Newkome, D. W. Evans and F. R. Fronczck, Inor9. Chem. 1987, 26, 3500; (d) A. L. Balch, H. Hope and F. E. Wood, J. Am. Chem. Soc. 1985, 107, 6936; (e) A. L. Balch, L. A. Fossetl and M. M. Olmstead, Inor9. Chem. 1986, 25, 4526; (f) F. E. Wood, J. Hooslef, H. Hope and A. L. Balch, J. Am. Chem. Soc. 1983, 105, 6986. 2. H. Mosbaek, Acta Chem. Scand. (A) 1975, 29, 957. 3. J. K. Zhang, Z. M. Zhang, N. Wang, Z. Z. Zhang and H. Cheng, Hyperfine Interactions 1994, 90, 509.
~
Pergamon 0277-5387(95)00488-2
Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277 5387/96 $15.00+0.00
MOSSBAUER STUDY OF A NEW ORGANOMETALLIC TETRADENTATE LIGAND tr ans, trans-F e2[lt-(Ph2P )2Py-P ,P] 2(C O ) 6 JING-KUN ZHANG,* ZE-MIN ZHANG, AO YU, SHU-LAN ZHAO and WEI-DONG ZHANG Test and Computation Center, Nankai University, Tianjin 300071, P.R. China
and ZHENG-ZHI ZHANG Elemento-Organic Chemistry Laboratory, Nankai University, Tianjin 300071, P.R. China
(Received 8 September 1995; accepted 11 October 1995) Abstract--A new route for the preparation of 2,6-bis(diphenylphosphino)pyridine [(Ph2P)2Py] is reported. Reaction of (PhzP)2Py with Fe(CO)5 in n-butanol gave the macrocyclodiiron complex, trans,trans-Fe2[#-(Ph2P)2Py-P,P]2(CO)6 (1). Treatment of 1 with HgCI2 gave the complex Fe2Hg[~t-(PhzP)2Py]2(CO)6C12- 2HgCI2 (2), with an F e - - H g - - F e linkage in which the central mercury atom resides within the cavity of the macrocycle and is coordinated to two nitrogen atoms and two iron atoms. Compounds 1 and 2 were characterized by elemental analyses, IR, 31p NMR, FD-MS and M6ssbauer spectra.
The compound 2,6-bis(diphenylphosphino) pyri- purified by distillation under nitrogen from standine [(PhzP)2Py] is an important tetradentate bridg- dard drying agents. ing ligand, which has been used in the preparations Preparation of 2,6-bis(diphenylphosphino)pyriof many novel bi- or polynuclear complexes.1 Using dine. A solution of 2,6-dichloropyridine (0.05 tool) this ligand, we have obtained a 12-membered bi- in T H F (40 cm 3) was added with stirring to a solumetallomacrocyclic complex, trans, trans-Fez[#- tion of Ph2PLi (0.1 tool) in T H F (80 cm 3) at 0°C. (Ph2P)2Py-P,P]2(CO)6 (1), The latter can act as a The reaction solution was stirred for 4 h at room neutral organometallic tetradentate ligand reacting temperature and then 15 cm 3 of methanol was with a Lewis acid metal centre to give a trimetal added. The methanol was removed and 100 cm 3 complex, Fe2Hg[#-(Ph2P)2Py] 2(CO)6C12 • 2HgC12 water was added to remove the lithium salt. The (2), with an F e - - H g - - F e donor-acceptor linkage. residue was extracted with CHzC12. After the In this paper, the structures of complexes I and 2 removal of CH2C12 and recrystallization from methare determined through M6ssbauer spectra. anol, a pale yellow solid product was obtained. It was proved to be 2,6-bis(diphenylphosphino) pyridine [(Ph2P)2Py] by IR, 31p N M R , FD-MS and EXPERIMENTAL m.p. determination. Syntheses Preparation of Fe2[#-(PheP)2Py-P,P]2(CO)6 (1). Fe(CO)5 (2.5 mmol) was injected into the solution All synthesis experiments were carried out under of sodium hydroxide dissolved in 30 cm 3 of n-butapurified nitrogen. The solvents were degassed and nol, and reaction solution was stirred for 30 rain under nitrogen. Then 3 mmol [(Ph2P)zPY] was * Author to whom correspondence should be addressed. added to the reaction solution, the mixture solution 2583
2584
JING-KUN ZHANG
(a)
et al.
as solvent. FD-MS was acquired with a Hitachi M-80 spectrometer.
IO0. O0
96. B8
R E S U L T S AND D I S C U S S I O N 93. 36 90. 04
-3
(b) ~ : ,
~"" lO0.
-1 0 1 2 Velocity (mm/s)
-2
.
3
°
°
" .~ v ' "
O0
"
:
~"
.~.
"
-
•
°°°
o
":..'.:'..'
V V -3
-2
1 2 Velocity (mm/s)
-I
0
3
Fig. 1. M6ssbauer spectra of compounds 1 (a) and 2 (b).
was refluxed for 2.5 h and then cooled to room temperature. A yellow precipitate was obtained, which was filtered, washed with methanol and recrystallized in CHzC12-CH3OH. The compound Fe2[/~-(Ph2P)2Py-P,P]2(CO)6 (1) was obtained. Preparation of Fe2Hg[kt-(PhzP)2PY]2(CO)6C12" 2HgC12 (2). At room temperature, 0.625 mmol HgC12 dissolved in 20 cm 3 1 : 2 butanone-2-benzene mixture was added with stirring to the solution containing 0.188 mmol Fe2(CO)6[(Ph2P)2PY]2 in the same solvent (30 cm 3) and the reaction solution was stirred for 30 min. A pale yellow precipitate was obtained. It was filtered off, washed with butanone2-benzene mixture and the product was obtained.
M6ssbauer measurements M6ssbauer effect spectra were obtained at 78 K on a constant-acceleration spectrometer (Model MS-500). The M6ssbauer source consisted of 57Co diffused in a palladium matrix. The M6ssbauer hyperfine parameters were obtained by a least-squares fitting using the Mosfun program. In our fitting procedure, each component of a quadrupole doublet was constrained to have the same linewidth. The IS values were determined relative to metallic iron foil.
Other spectral measurements IR spectra were recorded on a WFD-14 spectrometer as KBr discs. The 31p N M R spectra were recorded on a Jeol FX-90Q spectrometer at 36.19 MHz using H3PO4 as external standard and CDCI2
The M6ssbauer spectra of compounds 1 and 2 were obtained at 80 K. The compounds both gave one quadrupole doublet (Fig. 1). The MOssbauer parameters (IS = - 0 . 1 1 mm s -1, QS = 2.66 mm s-l) of complex 1 are much closer to those of the compound trans-Fe(CO)3(PPh3)2 (IS = - 0.10 mm s 1, Q S = 2 . 6 2 mm s-') and trans-Fe(CO)3 (PPh2Py)2 (IS= - 0 . 1 0 mm s -', QS = 2.59 mm s 1).2,3This indicated that the environments of the iron atoms in these complexes were identical. We suggest that complex 1 has the macrocyclic structure shown in Fig. 2. It is in agreement with IR and FD-MS findings. Two iron atoms and six carbonyls are presumably co-planar, and the plane is perpendicular to the cavity of the macrocycle. The distance between the two iron atoms is about 5.0/~. The IR spectrum exhibited only terminal carbonyl absorption, and did not show the low IR carbonyl absorption of F e - - - C - - O - - F e . Therefore, the carbonyl does not lie in the F e - - F e plane. The IS value for compound 2 is - 0 . 0 4 mm s-1, higher than that observed in complex 1. However, it is comparable to that for the compound Fe(CO)3 (PPh2Py)2 Hg(SCN)2 (IS = - 0 . 0 4 mm s -1) containing the Fe--Hg(SCN)2 bond? This indicated that both trans atoms were coordinated to the mercuric atoms to form F e - - H g bonds. The QS value for compound 2 is 1.12 mm s-~, lower than that for the complex Fe(CO)3(PPh2PY)2Hg(SCN)2 (QS= 1.54 mm s-l). This shows that the iron atoms in complex 2 had better symmetrical environment than that in Fe(CO)3(PPh2Py)2Hg(SCN)2, in which the iron atom is in a distorted octahedral coordination. From the above, we suggest that compound 2 has two possible structures, as shown in Fig. 3. If complex 2 had the structure I, though the region of the cavity is the forbidden region of carbonyls, it would not prevent the mercury atom from
(OC)~ i
~e(COb
Ph2P~,,,-PPh2
Fig. 2. Proposed structure of complex 1.
2585
A new organometallic tetradentate ligand
OC--Fe --~Hg"~-- .Fe--CO Ph2P~fPPh2
OC--Fe
OC- - Fe -4"-HgCI2
P h 2 ~ f
PPh2
1 II Fig. 3. Possible structures for compound 2.
entering. If the mercury atom is coordinated in the cavity, this would make the iron atoms have better symmetry than in structure II. Meanwhile, the two nitrogen atoms have coordinating ability and could stabilize the mercury atom with high oxidation states. Therefore, we suggest compound 2 has structure I rather than structure II. REFERENCES
1. (a) F. E. Wood, M. M. Olmstead and A. L. Balch, J.
Am. Chem. Soc. 1983, 105, 6332 ; (b) F. E. Wood, J. Hoosier, H. Hope and A. L. Balch. lnor9. Chem.
1984, 23, 4309; (c) G. R. Newkome, D. W. Evans and F. R. Fronczck, Inor9. Chem. 1987, 26, 3500; (d) A. L. Balch, H. Hope and F. E. Wood, J. Am. Chem. Soc. 1985, 107, 6936; (e) A. L. Balch, L. A. Fossetl and M. M. Olmstead, Inor9. Chem. 1986, 25, 4526; (f) F. E. Wood, J. Hooslef, H. Hope and A. L. Balch, J. Am. Chem. Soc. 1983, 105, 6986. 2. H. Mosbaek, Acta Chem. Scand. (A) 1975, 29, 957. 3. J. K. Zhang, Z. M. Zhang, N. Wang, Z. Z. Zhang and H. Cheng, Hyperfine Interactions 1994, 90, 509.