Synthesis and Characterization of the First Dinuclear Europium (II) Complex Supported by Carbon-Bridged Biphenolate Ligand

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MRJ E A R m JOURNAL OF RARE EARTHS 24 (2006) 264 - 267

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Synthesis and Characterization of the First Dinuclear Europium ( 1 ) Complex Supported by Carbon-Bridged Biphenolate Ligand Liu Bao (93 a ) ,Yao Yingming (#%g),Deng Mingyu (XkgF), Zhang Yong (% B ) , Shen Qi (k %)* (Key Laboratory of Organic Synthesis of Jiangsu Province , Department of Chemistry and Chemical Engineering, Suzhou University , Suzhou 215123 , China ) Received

21 October 2005; revised 14 December 2005

Abstract : Anhydrous EuC13 reacted with sodium carbon-bridged biphenolate LNa2[ L = 2,2'-methylene bis( 6-tert-butyl-4methyl-phenoxo] in a 1 : 1 molar ratio in THF in the presence of HMPA (HMPA = hexamethylphosphoric triamide) , then the product formed in situ was reduced by Na-K alloy to generate the divalent carbon-bridged biphenolate europium complex [ LEu(HMPA)2]2(THF)4( 1) in a good isolated yield. Complex 1 was fully characterized by elemental analysis, NMR and IR spectra, and X-ray structural determination. The crystal data of complex 1 are monoclinic, P 2 t / c space group, a = 1 . 6 5 2 1 ( 3 ) nm, 6=2.8274(3) nm, c=1.2074(2) nm, p=111.723(6)", V=5.2393(14) n m 3 , Z = 2 , D , = 1.2591ng.m-~,/ * = 1 . 3 0 4 m m - ' , F(000)=2092, R=0.0815, wR=0.1723. Complex 1 i s a d i m e r w i t h t w o E u - 0 bridges. The coordination geometry of each europium atom can be best described as a distorted trigonal bipyramid . Key words : inorganic chemistry ; carbon-bridged biphenolate lanthanide complex ; crystal structure ; rare earths CLC number : 0614.33 ; 0631 .5 Document code: A Article ID: 1002 - 0721 (2006)03 - 0264 - 04

Among possible alternatives to the traditional ancillary ligand bis ( cyclopentadienyl) set in rare earth metal chemistry, alkoxides (aryloxides) have received much attention and become increasingly popular since they are easily available, tunable and even potentially recyclable ancillary sets for mediating the reactivity of these electropositive cations"'21. The chelate biphenol and binaphthol have been found to be able to act as a dianionic ligand in the rare earth chemistry, which has the advantages of avoiding ligand redistribution reactions, and allowing the opportunity to design asymmetry into the ligand set. Furthermore, those complexes supported by the chelate biphenolate and binaphtholate ligands have a flexible coordination geometry, which allows the coordination of a wide range of substrates, and thus are applicable to potentially wide

range of reactions, For example, the lanthanide binol derivatives have been found to be a series of interesting homoleptic , symmetric and asymmetric Lewis acidic catalysts for organic transformationsr3]. Although a number of trivalent rare earth complexes supported by chelate biphenol have been reported in the literature, no lanthanide ( 1 ) complex with biphenolate ligand was reported, until very recently we reported the synthesis of the carbon-bridged biphenolate samarium (II ) and ytterbium ( II ) species by the proton-exchange reaction using Ln[ N ( SiMe3)I2(THF)*as starting rnaterial~'~].Herein we report the synthesis and characterization of the first divalent europium complex with carbon-bridged biphenolate ligand, 2,2'-methylene bis (6-tert-butyl-4-methyl-phenoxo)( L) .

* Corresponding author ( E-mail: qshen @suda.edu .cn) Foundation item: Project supported by the National Natural Science Foundation of China (20472063) Biography: Zhang Yong ( 1972 - 1, Male, Master; Majoring in organometallic chemistry

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Copyright 0 2 0 0 6 , by Editorial Committee of Journal of the Chinese Rare Earths Society. Published by Elsevier B V . All rights reserved.

Liu B et a1 . Synthesis and Characterization of First Dinuclear Europium ( I[ ) Complex

1 Experimental All manipulations were performed in a purified argon atmosphere using standard Schlenk techniques. The solvents were degassed and distilled from sodium benzophenone ketyl under argon prior to use. Deuterated benzene (C&) was purchased from Acros, and dried over sodium and vacuum transferred. 2 , 2’Methylene-bis ( 6-tert-butyl-4-methyl-phenol ) was purchased from Aldrich and degassed before use. Melting point was determined in sealed argon-filled capillaries and uncorrected. Europium analysis was carried out by complexometric titration. Carbon, hydrogen and nitrogen analyses were performed on a Carlo Erba l 110 spectrometer by direct combustion. The IR spectra (4000 400 cm- ) were recorded on a MAGNA-550 spectrometer as KBr pellets. ‘H NMR spectrum was obtained on an INOVA-400MHz apparatus, and referenced to benzene.

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1. 1

’

Synthesis of [ LEU ( HMPA > 2 1 2 (THF),(1)

A solution of LH2 ( 1 .80 g , 5 . 3 0 mmol) in THF (20 ml) was added dropwise to a NaH suspension ( 12.02 mmol) in THF at room temperature. The stirring was continued for 14 h , and the mixture was then filtered. The resulting pale yellow solution was added to a suspension of E d 3( 1 .37 g , 5.30 mmol) in THF (20 ml) and HMPA ( 1 . 9 0 ml, 1 0 . 9 0 mmol). The solution was stirred overnight at room temperature, and then the precipitation was separated from the reaction mixture by centrifugation. To the clear solution was added excess Na-K alloy, and the mixture was stirred at room temperature for another 3 d . The color of the solution gradually changed from pale blue to bright yellow. The precipitation was separated again by centrifugation, and the resulting solution was concentrated to about 15 ml. Complex 1 was isolated as bright yellow crystals in 1 d at - 15 “c ( 2 . 9 0 g , 64. 5 % ) . Mp, 231 232 “c (dec). Anal. Calcd. for CT0 H I ~ ~ E u ~ N I ~C,O ~ 52.02; P ~ : H , 8.27; N , 8.47; Eu, 15.31. Found: C, 52.34; H , 8.16; N , 8.29; Eu, 15.10. IR (KBr pellet, c m - I ) : 3 3 7 0 ( m ) , 2924 ( m ) , 2809(w), 1 6 3 6 ( w ) , 1 4 5 8 ( m ) , 1389 ( m ) , 1300(s), 1 1 9 6 ( s ) , 1 1 6 5 ( m ) , 9 8 8 ( s ) , 8 6 0 ( w ) , 7 5 2 ( ~ ) ‘H . NMR (C6D6, 8 ) : 6.91 - 7 . 3 8 ( m , 8 H , Ar), 4 . 6 1 ( s , 4 H , CH2); 3 . 4 2 ( s , 16H, THF-aCHI), 2 . 3 7 ( b r s , 84 H , CH3), 1 . 5 8 ( m , 16H, THF-P-CH2), 1.42 ( s , 36 H , C(CH3),).

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1. 2

265

X-ray structural determination of complex 1

Suitable single crystals of complex 1 were sealed in a thin-walled glass capillary to determine the singlecrystal structure. Intensity data were collected on a Rigaku Mercury CCD area detector in w scan mode using Mo Ka radiation ( A = 0.071070 nm) . The diffracted intensities were corrected for Lorentz polarization effects and empirical absorption corrections. Details of the intensity data collection and crystal data are given in Table 1 . The structure was solved by direct methods and refined by full-matrix least-squares procedures based on I F I . All of the non-hydrogen atoms were refined anisotropically . The hydrogen atoms in this complex were all generated geometrically, and were assigned appropriate isotropic thermal parameters, and were allowed to ride on their parent carbon atoms. All of the H atoms were held stationary and were included in the structure factor calculation in the final stage of fullmatrix least-squares refinement. The structure was solved and refined using SHELEXL-97 program.

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2 Results and Discussion Reaction of anhydrous EuC13 with sodium carbonbridged biphenolate LNa2 in a 1: 1 molar ratio in THF in the presence of HMPA, after removing the precipitate, to give a pale blue solution. Na-K alloy was added into the solution, and the color of the solution was changed gradually to bright yellow. After workup, complex 1 was isolated as bright yellow crystals from concentrated THF solution. The composition of complex 1 was established as [LEU(HMPA),]2(THF), by elemental analyses (C , H , N and Eu ) (Scheme 1 ) . The NMR spectrum of complex 1 shows very Table 1

Details of crystallographic data and refinements for complex 1

Empirical formula C ~ ~ H I M E W N I Z plmm-l ~~P~ Fw

1986.09

Crystal color

TIK 0 . 5 6 ~ 0 . 4 0 ~ 0 . 1 6T ,. Monoclinic T,,

Sizelmm

Crystal system

el(”)

Bright yellow

alnm

P211c ( # 14) 1.6521(3)

1.304

-

3.17 25.50 1!?3(2)

0.5288 0.8185

No. of coll. d n s

blnm

2.8274(3

48433 No. ofindep. retlns 9368 R l [ 1 > 2 . 0 ~ ( 1 ) ] !XXN

Clnm

1.24?74(2)

Variable

478

Pl(4

111.723(6)

R

0.0815

Space group

VInm’

5.2393(14)

WR

2

2

GOF

0. I r n 1.115

D,/(mg.m-’)

1.259

F(OM))

2092

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JOURNAL OF RARE EARTHS, Vol. 2 4 , No. 3 , Jun 2006

266

g

+2EuC1,+4 HMPA

Na-K alloy r.t. 72 h

+6NaCI

~

0

Complex I Scheme 1

slight paramagnetic shifting from the analogous diamagnetic Yb complexes'41. The IR data for complex l have a medium intensity band at 3370 3395 c m - ' , which is in the region expected for - OH group of the phenol. This may be attributed to partial hydrolysis of these complexes, because KBr pellets provide less adequate protection from hydrolysis than dry Nujol . Complex 1 is extremely sensitive to air and moisture, and has good solubility in THF, DME and toluene; but is insoluble in hexane. The molecular structure of complex 1 was determined by single crystal structure analysis. An ORTEP of complex 1 is depicted in Fig. 1 , and the selected bond distances and angles are listed in Table 2. Crystals of complex 1 that were suitable for an Xray structure determination were obtained from concentrated toluene solution at room temperature. Complex 1 has a dimeric structure; the two biphenolate europium moieties are connected by bridging of two phenolate units. This is the first example of the divalent europium species supported by the bridged biphenolate

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Fig. 1 Molecular structure of complex 1 (Three methyl groups of tert-butyl groups on the arene rings and hydrogen atoms are omitted for clarity)

Table 2 Selected bond distances (nm)and angles (") for complex 1 Bond distance

generate equivalent atoms: A:

- z + 1,

- y + 1,

-I +1

ligands. In complex 1, the central metal is bound to three oxygen atoms of the bisphenoxide ligands, and two oxygen atoms of HMPA. The europium atoms are five-coordinated in a distorted trigonal bipyramid , with one oxygeo atom from the bridging phenolate ligands (0( 2 A ) ) and one oxygen atom from the IMPA ( 0 ( 3 ) occupying axial positions and the terminal phenolate ( 0 ( 1 ) ) , the second bridging phenolate ( 0 ( 2 ) , and one HMPA molecule (O(4) ) in equatorial positions. The two bridging oxygen atoms and two lanthanide atoms are exactly coplanar as required by the crystallographic symmetry. As expected, the bridging europium-phenolate bond lengths in complex 1 of 0.2442 ( 6 ) and 0.25 16 ( 6 ) nm respectively are larger than that of the terminal one (0.2328 ( 6 ) nm 1, which are comparable with those reported in literature"'. The bridging mode of the phenolate ligands is slightly asymmetric in complex 1, in which the axial Eu-O(Ar) ( 0 . 2 4 4 2 ( 6 ) nm) bond is about 0.007 nm shorter than that of the equatorial one ( 0 . 2 5 1 6 ( 6 ) nm). These Eu-O(Ar) bond lengths are comparable with the corresponding Eu-0 (Ar) bond lengths of europium ( 1 ) aryloxide com-

Liu B et a1 . Synthesis and Characterization of First Dinuclear Europium ( I[ ) Complex

plexes with formal coordination number 3 5, such as [ Eu ( OC6H21Bu2-2, 6-Me-4 ) 2 ( THF ) 3 [ Eu2 ~. ( OC6H3-2, 6-Me2 ), ( N-methylimidazole ) 5 , [ Eu2 (OC6H3-2,6-Pri)4( CH3CN ) 3 I"], and [ Eu2 ( 0C6H32,6-Ph2 ), . Variations in the Eu-O-C angles are associated with the existence of agostic interaction in this complex. The Eu( 1 ) - 0 ( 2 ) - C ( 7 ) angle is 106.6 (4)", while Eu( 1)-0.( 1)-C( 1 ) angle is 154.2(6)". The bite angle 0 ( 1 ) - E u - 0 ( 2 ) in complex 1 of 101.9 (2)" is significantly larger than those found in [ Ln( 1 , 1'4 2-OC6H-Bu1-3-Me2-5, 6 ), ) { N ( SiHMe2 ) 2 1 (THF) I,( Ln = Y (88.79( 6 ) " ) , La ( 89.83 (7)") )['I, and [ L a { 1 , 1'-(2-OC6H2tBu2-3,5)2}{CH(SiMe3)2/ (THF),] (88.1 ( 3)0)r91; while the dihedral angle between the two arene rings of 75.9" compares well with t h e 7 2 . 9 ( 2 ) " f o u n d in [ L a { l ,1'-(2-OC&tBu2-3, 5),} { CH(SiMe3)2} (THF),lL9I, but it is apparently smaller than the 87.8(4)" in [La( 1 , lr-(2-OC6H-Bu'3-Me2-5,6)2) { N(SiHMe2)2 (THF) ]2['].

[4] Deng M Y, Yao Y M , Shen Q , et al. The novel lanthanide( II ) complexes supported by carbon-bridged biphenolate ligands : synthesis, structure and catalytic activity [J] . Dalton Trans. , 2004, (5): 944. [51 Deacon G B, Forsyth C M , Junk P C , et al. The strikine: influence of intramolecular lanthanoid-x-arene interactions on the structural architecture of the homoleptic aryloxolanthanoid( II ) complexes [Eu,(Odpp) (p-0dpp)3] and [Ybz ( Odpp )z ( p-Odpp )Z 1 and the Yb /Ybm trimetallic [Ybz(p-Odpp)j] + [ Y b ( O d ~ p ) ~(Odpp ]= 2,6-diphenylphenolate) [J]. Chem. Eur. J . , 1999, 5(5): 1452. [6] Van Den Hende J R , Hitchcock P B, Holmes S A, et al. Synthesis and characterization of lanthanide ( II ) aryloxides including the first structurally characterized europium ( ) compound [ E U ( O C ~ H ~ B ~ : - ~ , ~ - M ~ -[ J~] ) . ~(THF) J . Chem. Soc., Dalton Trans., 1995, ( 8 ) : 1427. [7] Evans W J , Greci M A , Ziller J W . The utility of Nmethylimidazole and acetonitrile as solvents for the direct reaction of europium with alcohols including the first example of acetonitrile as a p-?' : ?'-bridging ligand [ J ] . Chem. Commun. , 1998, ( 19) : 2367. [8] Gribkov D V, Hultzsch K C, Hampel F . Synthesis and characterization of new biphenolate and binaphtholate rareearth-metal amido complexes : catalysts for asymmetric olefin hydroaminatiodcyclization [ J ] . Chem . Eur . J . , 2003, 9(19): 4796. [9] Schaverien C J , Meijboom N , Orpen A G . A new ligand environment in organolanthanoid chemistry : sterically hindered, chelating diolato ligands and the X-ray structure of [La{CH(SiMe3)zI11, 1'-(2-OC,H,Bu:-3,5)zt (THF),] [ J ] . J . Chem. S o c . , Chem. Commun., 1992, ( 2 ) : 124. Y

n

References : [ 1 ] Mehrotra R C , Singh A, Tripathi U M . Recent advances in alkoxo and aryloxo chemistry of scandium, yttrium, and lanthanides [ J ] . Chem. Rev. , 1991, 91 ( 6 ) : 1287. [2] Evans W J . Beyond bis ( pentamethylcyclopentadienyl) coordination environments : An approach to alternative ancillary ligand sets in organometallic lanthanide chemistry [ J ] . NewJ. Chem., 1995, 1 9 ( 5 - 6 ) : 525. [3] Shibasaki M , Yoshikawa N . Lanthanide complexes in multifunctional asymmetrical catalysis [ J ] . Chem. Rev. , 2002, 102(6): 2187.

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High-Temperature Oxidation Behavior of 5Cr21Mn9Ni4N Steel Micro-Alloyed by Rare Earth Yu Shichang' , Wu Shenqing' * , Gong Youjun', Gong Yuansheng', Lian Mingsheng' , Ye Gang', Cheng Yijun'( 1 . Department of Material Science and Engineering, Southeast University, Nanjing 210096, China ; 2 . Jiangsu Shenyuan Special Steel Company, L t d . , Xinghua 225722, China ) Abstract: The oxidation resistance of 5Cr21Mn9Ni4N

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oxidation resistance of 5Cr21Mn9Ni4N steel at high temperature. The oxidation scale constitutes of refractory steel transfer from manganic oxide mostly to femc oxide mostly with the increase of temperature, which leads to descend of compactness and desquamation resistance of oxidation scale. The mass increase of femc oxide in the oxidation scale and the looseness of oxidation scale are the main reason to descend the oxidation resistance of refractory steel.

steel micro-alloying by RE at 700 900 "r: was investigated. The results indicate that oxidation exponent n and oxidation activation energy are increased, and oxidation velocity constant k, is decreased when 0. 2 % RE is added in 5Cr21Mn9Ni4N steel. The addition of RE elements does not alter phase constitution of oxidation scale, however it improves the configuration of oxidation scale, and increases thermal stability and adhesivity of oxidation scale, which results in the raise of Key words : 5Cr2 1Mn9Ni4N steel ; oxidation kinetics; oxidation scale ; oxidation resistance ; rare earths

(SeeJ. Chin. RE. Soc. ( i n c h i n . ) , 2006, 24(3): 333forfulltext)