Base-Free Lanthanoidocenes(II) Coordinated by Bulky

Article pubs.acs.org/Organometallics

Base-Free Lanthanoidocenes(II) Coordinated by Bulky Pentabenzylcyclopentadienyl Ligands Alexander N. Selikhov,† Tatyana V. Mahrova,† Anton V. Cherkasov,† Georgy K. Fukin,†,‡ Joulia Larionova,§ Jêrome Long,§ and Alexander A. Trifonov*,†,‡,∥ †

Institute of Organometallic Chemistry of Russian Academy of Scienes, Tropinina 49, GSP-445, 630950, Nizhny Novgorod, Russia Nizhny Novgorod State University, Gagarina 23, 603950, Nizhny Novgorod, Russia § Institut Charles Gerhardt Montpellier, UMR 5253 CNRS-UM2-ENSCM-UM1, Chimie Moléculaire et Organisation du Solide, Université Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 5, France ∥ Institute of Organoelement Compounds of Russian Academy of Scienes, Vavilova Street 28, 119334, Moscow, Russia ‡

S Supporting Information *

ABSTRACT: Metalation of CpBn5H with PhCH2K (1:1 molar ratio) and subsequent reactions with 0.5 equiv of LnI2(THF)n (Ln = Yb, Sm, Eu, n = 2, 3) (THF, 30 °C, 1 h) afforded new lanthanoidocenes (CpBn5)2Ln (Ln = Yb (1), Sm (2), Eu (3)), which were isolated in reasonable yields. The X-ray diffraction studies revealed that the obtained complexes adopt the structures of bent sandwiches (Cp Centr −Ln−CpCentr = 141.8−142.9°). Complexes 1−3 do not contain coordinated Lewis base molecules directly after recrystallization from toluene at ambient temperature; however they feature short contacts between Ln(II) ions and o-carbon atoms of two pendant Ph groups. The reaction of equimolar amounts of YbI2(THF)2 and CpBn5K in DME afforded monocyclopentadienyl Yb(II) complex [CpBn5Yb(DME)(μ-I)]2 (4). Complex 4 proved to be a centrosymmetric iodo-bridged dimer with trans-disposed cyclopentadienyl ligands, and no interactions of the Yb(II) ion with pendant Ph groups were detected. Complexes 1−3 were inert toward Lewis bases (THF, DME, PMe3, TMEDA), small molecules (H2, SiH4, N2, CO), and molecules containing multiple C−C bonds (CH2CH2, PhCHCH2, trans-PhCH CHPh, cis-PhCHCHPh, CH2CH−CHCH2, Ph−CHCH−CHCH−Ph, PhCCPh, Me3SiCCSiMe3). Among compounds 1−3 only the samarium derivative 1 reacts with bipy and phenazine, affording SmIII complexes CpBn52Sm(bipy−•) (5) and [(CpBn5)2Sm]2[μ-η3:η3-(C12H8N2)2−] (6). Complex 4 when illuminated with natural light undergoes redox reaction and in 72 h transforms into the mixed-valent compound {[CpBn5YbIIII2(μ-OMe)]2}2{YbII(DME)3} (7), being a separated ion pair.

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was unknown.7 Moreover, the very bulky pentasubstituted cyclopentadienyl ligands (C5iPr5, C5Ph5, C5(p-Ph-nBu)5) allowed to “straighten” the usually bent lanthanoidocene structures and to realize the first Ln(II) sandwich complexes having a parallel disposition of Cp rings.8 Unprecedented progress in organolanthanide chemistry was reached due to application of the Cp* ligand, which provided access to the previously unknown types of compounds containing nonconventional ligands for lanthanide chemistry (η2-complexes with olefin,9 internal acetylene,10 and dinitrogen11 ligands, etc.). The pentabenzylcyclopentadienyl ligand (CpBn5),12 featuring along with considerable steric demand a flexibility of the benzyl substituents, may be a suitable ligand system for coordination to large lanthanide ions and for the formation of low-coordinate lanthanoidocenes. Noteworthy is that variation of electrondonating/withdrawing properties of the substituents in cyclopentadienyl rings was shown to affect strong reactivity of the

INTRODUCTION Organolanthanides possess a unique set of properties that makes them an exciting object of research bringing plenty of surprises. Due to a combination of large ionic radii of lanthanides1 with Lewis acidity and the presence of unoccupied 5d and 6s orbitals, these compounds have a pronounced tendency to complex formation and exhibit high coordination numbers.2 Lanthanides are electropositive,3 and the metal− ligand interactions in their organic derivatives are predominantly ionic in character.4 That is why ligands capable of forming stable anions were traditionally applied in this field of chemistry, and until recently cyclopentadienyl complexes have prevailed among known organic derivatives of lanthanides.5 Large ionic sizes and electropositivity of lanthanides lead to considerable dependence of stability of their organic derivatives on the degree of coordination and steric saturation of the ion sphere and emphasize the role of design of ligand environment.6 The application of bulky polysubstituted cyclopentadienyl ligands enabled the synthesis of new Ln(II) compounds including the metals for which a stable divalent oxidation state © 2015 American Chemical Society

Received: March 21, 2015 Published: May 7, 2015 1991

DOI: 10.1021/acs.organomet.5b00243 Organometallics 2015, 34, 1991−1999

Article

Organometallics related lanthanoidocenes;13 thus a transition from the Cp* to CpBn5 ligand system can result in new types of structures and metal−ligand interactions. In addition an ability of lanthanide ions to coordinate aromatic ligands that act as weak Lewis bases14 can lead to the stabilization of low-coordinate Ln(II) centers. Herein we report on the synthesis, structures, and reactivity of the Ln(II) complexes (Ln = Sm, Eu, Yb) coordinated by CpBn5 ligands.

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RESULTS AND DISCUSSION Synthesis and Structures. The reactions of LnI2(THF)n (Ln = Yb, Sm, Eu, n = 2, 3)15 with two molar equivalents of CpBn5K obtained in situ from CpBn5H12 and PhCH2K16 were carried out in THF at 30 °C (1 h) (Scheme 1). Evaporation of Scheme 1. Synthesis of Complexes 1−3

Figure 1. Molecular structure of complexes 1−3. Thermal ellipsoids are drawn at the 30% probability level. Carbon atoms of Ph groups and hydrogen atoms are omitted for clarity.

Table 1. Selected Distances (Å) and Angles (deg) for Complexes 1−3 THF under vacuum, extraction of the solid residue with toluene, filtration of the toluene solution from the KI precipitate, concentration, and continuous cooling at −20 °C allowed for the isolation of complexes (CpBn5)2Ln (Ln = Yb (1), Sm (2), Eu (3)). Complexes 1−3 were isolated as green (1), purple (2), and bright orange (3) air- and moisturesensitive crystals in 50−66% yields. Complexes 1−3 are highly soluble in THF, DME, and aromatic hydrocarbons and poorly soluble in hexane. The moderate yields of complexes 1−3 can be explained by their high solubility in aromatic solvents. To evaluate the applicability of the CpBn5 ligand for stabilization of the divalent state of “nonclassical” Ln(II) metals, the reaction of TmI2(DME)3 with two equivalents of CpBn5K was carried out in DME at −20 °C. However, the attempts of isolation of the lanthanide-containing products failed. In the 1H and 13C NMR spectra of diamagnetic complex 1 the CpBn5 ligands give the expected set of signals. The 1H NMR spectra of 1 in C6D6 at ambient temperature display only one resonance for the benzyl protons at δ = 3.85 ppm. This reflects the absence of constraints of the free rotation of the pentabenzylcyclopentadienyl ligands around the metal−Cp ring and the Cp ring−CH2Ph bonds. Surprisingly despite high oxophilicity of the Yb(II) center and the use of THF as the reaction solvent, 1 does not contain coordinated THF molecules. The absence of coordinated THF molecules in 1− 3 was also evidenced by IR spectroscopy and microanalysis. The monocrystalline samples of complexes 1−3 were obtained by slow cooling of their concentrated toluene solutions from ambient temperature to −20 °C. The X-ray studies revealed that 1−3 are isostructural and crystallize in the monoclinic P2(1)/n space group. The molecular structures of 1−3 are depicted in Figure 1, and the crystal and structural refinement data are summarized in Table S1 (see the SI). The selected bond lengths and bond angles are compiled in Table 1. Complexes 1−3 were found to be base-free, featuring bent sandwich structures. It is known that molecules of donor

Ln(1)−C(1) Ln(1)−C(2) Ln(1)−C(3) Ln(1)−C(4) Ln(1)−C(5) Ln(1)−C(6) Ln(1)−C(7) Ln(1)−C(8) Ln(1)−C(9) Ln(1)−C(10) Ln(1)−Cpcenter Ln(1)−C(13) Ln(1)−C(52) Cpcenter−Ln(1)−Cpcenter

1

2

3

2.683(2) 2.713(2) 2.748(2) 2.745(2) 2.696(2) 2.685(2) 2.753(2) 2.796(2) 2.730(2) 2.649(2) 2.433(1) 2.441(1) 2.952(2) 3.197(2) 142.9

2.800(2) 2.814(2) 2.849(2) 2.853(2) 2.814(2) 2.799(2) 2.860(2) 2.904(2) 2.842(2) 2.764(2) 2.555(1) 2.565(1) 2.996(2) 3.161(2) 141.8

2.794(2) 2.816(2) 2.846(2) 2.847(2) 2.811(2) 2.792(2) 2.861(2) 2.903(2) 2.838(2) 2.758(2) 2.551(1) 2.561(1) 2.991(2) 3.163(2) 141.9

solvents coordinated to Ln(II) ions are difficult to remove from their coordination spheres17 while application of the bulky CpBn5 ligand allows for the facile synthesis of base-free lanthanoidocenes 1−3. The Ln(II) ions in 1−3 are coordinated by two η5-CpBn5 ligands, and their formal coordination numbers can be estimated as six; however saturation of the metal coordination spheres is reached due to interactions of Ln(II) with pendant Ph rings of the CpBn5 ligands. The arrangement of the benzyl groups relative to the Cp ring in 1−3 is noteworthy. In all obtained complexes three benzyl groups of one CpBn5 and four of the second one are directed away from the metal atom, while three others are turned toward the Ln(II) ions, thus resulting in short Ln−C distances. The Ln−C(Cp) bond lengths vary in rather large ranges: 2.649(2)−2.796(2) Å in 1, 2.764(2)− 2.904(2) Å in 2, 2.758(2)−2.903(2) Å in 3. The average Ln− C(Cp) bond lengths (1: 2.72 Å; 2: 2.83 Å; 3: 2.83 Å) and Ln− CpCentr distances (1: 2.433(1) and 2.441(1) Å; 2: 2.555(1) and 2.565(1) Å; 3: 2.551(1) and 2.561(1) Å) in 1−3 are noticeably longer compared to those of previously published base-free lanthanoidocenes(II) coordinated by bulkier ligands. [For 1992


Article

Organometallics comparison see the average Ln−C(Cp) bond lengths: (C5Ph5)2Yb, 2.664 Å,8d (CpBIG)2Yb, 2.673 Å,8a Cp*2Yb, 2.66 Å, [1,3-(Me3C)2C5H3]2Yb, 2.66 Å;18 [1,2,4-(Me3C)3C5H2]2Yb, 2.67 Å, [1,2,4-(Me 3 C) 3 C 5 H 2 ] 2 Sm, 2.79 Å, [1,2,4(Me3C)3C5H2]2Eu, 2.78 Å,19 (C5Pri5)2Eu, 2.826 Å,8c Cp*2Sm, 2.79 Å, Cp*2Eu, 2.79 Å.17] The nonvalent interactions of Ln(II) ions with the pendant Ph groups of the CpBn5 ligands result in short Ln−C(Ph) distances (1: 2.952(2), 3.197(2), and 3.318(2) Å; 2: 2.996(2), 3.161(2) Å; 3: 2.991(2), 3.163(2) Å), which fall into the range of values formerly reported for related compounds.20 The presence of short Ln−C(Ph) contacts does not affect the bond lenghts within the phenyl rings. On the other hand, the C(Cp)−C−C(Ph) angles in the benzyl groups coordinated to Ln(II) ions (1: 111.3(1)°, 114.5(2)°, 118.6(2)°; 2: 111.2(1)°, 113.7(1)°, 118.5(1)°; 3: 111.1(2)°, 113.8(2)°, 118.5(2)°) are narrower than in the benzyl groups directed away from the metal atoms (1: 115.0(1)−117.2(1)°; 2: 114.5(1)−117.1(1)°; 3: 114.7(2)−117.2(2)°). Unlike the C5Ph5-containing analogues,8d complexes 1−3 adopt bent sandwich structures. The CpCentr−Ln−CpCentr angles in 1−3 (142.9° (1), 141.8° (2), 141.9° (3)) are narrower than those in lanthanoidocenes with other bulky Cp ligands (for comparison the CpCentr−Ln−CpCentr angles: [1,3(Me 3 C) 2 C 5 H 3 ] 2 Yb, 147.0°; 18 [1,2,4-(Me 3 C) 3 C 5 H 3 ] 2 Yb, 166.0°19). Most likely this is due to the flexibility of benzyl groups. Surprisingly when comparing the CpBn5 and C5Me5 derivatives, this trend is not common. Thus, for Yb the CpCentr−Ln−CpCentr angle in 1 is narrower than in (C5Me5)2Yb (145.0−146.0°),18 while for Sm and Eu they are slightly larger ((C5Me5)2Sm: 140.1°, (C5Me5)2Eu: 140.3°).17 The reaction of equimolar amounts of YbI2(THF)2 and CpBn5K in DME afforded half-sandwich Yb(II) complex [CpBn5Yb(DME)(μ-I)]2 (4) (Scheme 2). The air- and

Figure 2. Molecular structure of complex 4. Thermal ellipsoids are drawn at the 30% probability level. Carbon atoms of DME molecules and Ph groups and hydrogen atoms are omitted for clarity. Selected distances (Å) and angles (deg): Yb(1)−C(1) 2.700(3), Yb(1)−C(2) 2.665(3), Yb(1)−C(3) 2.664(3), Yb(1)−C(4) 2.665(3), Yb(1)−C(5) 2.682(3), Yb(1)−Cpcenter 2.385(2), Yb(1)−I(1) 3.0940(3), Yb(1)− I(1A) 3.1615(3), Yb(1)−O(1S) 2.500(3), Yb(1)−O(2S) 2.462(3); I(1)−Yb(1)−I(1A) 85.707(8).

Yb(II)−Ph interactions were detected. The Yb−C distances are in the range 2.664(3)−2.700(3) Å. The values of the average Yb−C bond length (2.68 Å) and the Yb−CpCentr distance (2.385(2) Å) in 4 are similar to those previously observed for the related seven-coordinate Yb(II) complex [Cp*Yb(DME)(μ-I)]2 (Yb−CpCentr 2.38 Å).21 The Yb−O bond lengths (2.462(3) and 2.500(3) Å) fall into the range normally observed for derivatives of divalent ytterbium.22 Significant differences in the Yb−I bond lengths have been found for 4 (3.0940(3) and 3.1615(3) Å). The Yb−I distances are slightly shorter than the values previously observed for related dimeric complexes [Cp*Yb(DME)(μ-I)]2 (3.120(2) and 3.102(2) Å).21,23 The I−Yb−I bond angle (94.294(8)°) in 4 is significantly larger than that in the C 5 Me 5 analogue (88.28(5)°).21 Reactivity Studies. Due to the development of a synthetic approach to base-free low-coordinate lanthanoidocenes(II),17,18 fundamental progress has been made in organolanthanide chemistry, and new classes of compounds whose existence was previously difficult to believe were obtained.9−11 In order to investigate the influence of the steric and electronic properties of the supporting Cp ligands on the reactivity of the coordinatively unsaturated Ln(II) centers, a series of reactions of complexes 1−3 with different types of reagents were carried out. Another goal of this work was to estimate the strength of Ln(II)−Ph interactions and their resistance toward action of the Lewis bases and to elucidate the role of the electronic structure, oxidation state, and ion size of the metal center in this bonding. A number of small molecules (H2, SiH4, N2, CO) and molecules containing multiple C−C bonds (CH2CH2, PhCHCH 2 , trans-PhCHCHPh, cis-PhCHCHPh, CH 2 CH−CHCH 2 , Ph−CHCH−CHCH−Ph, PhCCPh, Me3SCiCSiMe3, hexyne-2) were attempted as prospective nonconventional ligands to coordinate to the unsaturated Ln(II) centers of 1−3. The reactions were carried out in toluene at ambient temperature. In the cases of gases their excess was used at a pressure of 1 bar, while the solid or liquid reagents were allowed to react with 1−3 in 1:1 molar ratio (reaction time 24 h). However, to our disappointment none of the reactions took place. Surprisingly even complex 2,

Scheme 2. Synthesis of Complex 4

moisture-sensitive orange-yellow crystals of 4 were isolated in 85% yield after recrystallization from DME. Complex 4 is well soluble in DME and THF, moderately soluble in toluene, and insoluble in hexane. Clear monocrystalline samples of 4 suitable for an X-ray diffraction study were obtained by slow concentration of its DME solution at ambient temperature. The molecular structure of 4 is shown in Figure 2. The crystal and structure refinement data are compiled in Table S1 (see the SI). The crystal structure determination revealed 4 to be a centrosymmetric iodo-bridged dimer with trans-disposed cyclopentadienyl ligands, similar to the structure adopted by its pentamethylcyclopentadienyl analogue [Cp*Yb(DME)(μI)]2.21 Each ytterbium center is coordinated by an η5cyclopentadienyl ring, two bridging iodides, and one DME ligand, thus resulting in the coordination number of seven. It is noteworthy that unlike complex 1 in 4 the Ph groups of the CpBn5 ligands are turned away from the metal ion and no 1993


Article

Organometallics

Cooling the concentrated reaction mixture causes precipitation of complex 5, which was isolated as a dark brown, crystalline solid in 76% yield. Complex 5 is highly air- and moisture-sensitive, moderately soluble in toluene, and poorly soluble in hexane. Crystals suitable for single-crystal X-ray diffraction studies were obtained by slow cooling of toluene solution of 5 to −20 °C. Complex 5 crystallizes as toluene solvate CpBn52Sm(bipy)·C7H8. The molecular structure of 5 is depicted in Figure 3; crystal and structural refinement data are listed in Table S1 (see the SI).

whose analogue Cp*2Sm proved to be highly reactive toward most of the tested reagents, remained inert in these reactions. Starting complexes 1−3 were recovered from the reaction mixtures in high yields. The NMR-scale reactions of diamagnetic complex 1 with H2, SiH4, CO, CH2CH2, and PhCCPh were carried out under control of 1H and 13C NMR spectroscopy. No evidence of Yb(II)−ligand interactions were detected. The second group involves the reactions of 1−3 with various Lewis bases (THF, DME, PMe3, TMEDA). Our intention was to evaluate the strength of the interactions of the Ph groups and the Ln(II) centers in 1−3 by breaking these presumably weak bonds due to Lewis base coordination. The reactions of 1−3 with THF, DME, PMe3, and TMEDA (1:10 molar ratio) were carried out in toluene at ambient temperature. To our great surprise complexes 1−3 were recovered from the reaction mixtures in high yields, and no coordination of the Lewis bases was detected. Unlike the previously reported complex (C5Ph5)2Yb,8c no dissociation of CpBn5−Ln(II) bonds after the treatment of 1−3 with THF was observed. Thereby one can conclude that the interactions between Ln(II) ions and the pendant Ph groups in 1−3 are rather strong. Bipyridyl (bipy) besides being a chelating donor ligand possesses a pronounced electron affinity and ability to oxidize electropositive metals. Complexation of lanthanoidocenes(II) with bipy has been extensively explored.13,24 Decamethylsamarocene Cp*2Sm(THF)2 is easily oxidized by bipy, affording Cp*2SmIII(bipy−•).24a In the reactions with ytterbocenes Cp′2Yb(Et2O) (Cp′ = Cp*, Me4C5H, 1,3-(Me3C)2C5H3, 1,3(Me3Si)2C5H3) bipy replaces monodentate ligands and forms Cp′2Yb(bipy) adducts, in which depending on the electronic properties of the cyclopentadienyl ligand the bipy ligand can be either neutral or radical-anionic.13 The reactions of complexes 1−3 with bipy in 1:1 molar ratio were carried out in toluene at ambient temperature. It was found that despite the absence of coordinated bases the derivatives of Yb(II) and Eu(II) do not react with bipy under these conditions. The reagents were recovered from the reaction mixtures quantitatively. However, in the case of the samarium complex 2 the reaction affords the corresponding adduct with bipy CpBn52Sm(bipy) (5) (Scheme 3).

Figure 3. Molecular structure of complex 5. Thermal ellipsoids are drawn at the 30% probability level. Carbon atoms of Ph groups and hydrogen atoms are omitted for clarity. Selected distances (Å) and angles (deg): Sm(1)−C(1) 2.773(3), Sm(1)−C(2) 2.756(3), Sm(1)− C(3) 2.777(2), Sm(1)−C(4) 2.771(2), Sm(1)−C(5) 2.749(2), Sm(1)−C(41) 2.765(3), Sm(1)−C(42) 2.771(3), Sm(1)−C(43) 2.759(2), Sm(1)−C(44) 2.763(2), Sm(1)−C(45) 2.755(3), Sm(1)− N(1) 2.437(2), Sm(1)−N(2) 2.439(2), Sm(1)−Cpcenter 2.484(3) and 2.481(2); Cpcenter−Sm(1)−Cpcenter 140.5.

The Sm−C(Cp) average distance in 5 (2.76 Å) is noticeably shorter than that in the starting complex 2 (2.83 Å) and is consistent with the three-valent state of the samarium center (compare to the Sm−C(Cp) average distance in Cp*2SmCl (2.72 Å),25a [(1,3-SiMe3)2C5H3)2SmCl]2 (2.71 Å),25b [CH2 CH(CH2)3C5Me4]2SmCl(THF) (2.73 Å)).25c The Sm−C(Cp) average bond length in 5 is close to the value reported for the related complex Cp*2Sm(bipy) (2.72 Å).24a The shortening of the Sm−C distances in 5 compared to those in the parent 2 indicates the oxidation of the SmII to SmIII. However, the magnitude of the shortening (0.07 Å) is considerably less than would be expected on the basis of the difference of the ionic radii of SmII and SmIII (0.19 Å).1 The Sm−N distances in 5 (2.437(2) and 2.439(2) Å) are in a good agreement with the analogous distances in Cp*2Sm(bipy) (2.427(2) and 3.436(2) Å);24a however they are longer than the typical covalent Sm(III)-NR2 (compare [η5-(CH2)2(C9H6)2]SmN(SiMe3)2, 2.264(6) Å;26a (C5Me5)2Sm(NHPh)(THF), 2.331(3) Å26b] but shorter than the coordination Sm(III)←NR3 bonds (compare: [Cp*2Sm(py)]2[μ-(NC5H5)2], 2.547(2) Å;27a [Cp*2Sm(NCPh2)(NH2CHPh2), 2.62(1) Å27b). The geometry of the bipy ligand in 5 strongly differs from that of free bipy,28 and the metric parameters indicate its reduced radical-anionic state. The most revealing feature is the short length (1.430(5) Å) of the C−C bond connecting two py fragments. In free bipy this bond length is 1.490(3) Å.28a The average C−N and C−C

Scheme 3. Synthesis of Complex 5

In complex 5 the samarium ion is η5-coordinated by the two cyclopentadienyl units and the two nitrogen atoms of the bipy ligand and adopts the geometry of a distorted tetrahedron. It is noteworthy that unlike parent complex 2 in 5 just one of the pendant Ph groups is oriented toward the Sm ion; however no more short Sm−C(Ph) contacts are retained (the shortest one is 4.071(2) Å). The values of Sm−C(Cp) bonds lie in the range 2.749(2)−2.777(2) Å. 1994


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Organometallics Scheme 4. Synthesis of Complex 6

Complexes 1−3 were treated with phenazine (1:1 molar ratio) in toluene at ambient temperature. As in the case of bipy only samarium complex 2 reacted with phenazine, affording 2:1 adduct [(CpBn5)2Sm]2[μ-η3:η3-(C12H8N2)] (6) (Scheme 4). Formerly it was reported that phenazine can be reduced by two equivalents of Cp*2Yb(Et2O), affording a binuclear complex containing a μ-bridging dianion;30 however a related complex (CpBn5)2Yb does not react under these conditions despite the absence of a coordinated Lewis base. For complex 3 also no product formation was observed, and the starting materials were recovered from the reaction mixture. Dark brown crystals of 6 were isolated in 80% yield. Crystals suitable for single-crystal X-ray diffraction studies were obtained by slow cooling of a toluene solution of 6 to −20 °C. Complex 6 crystallizes as the toluene solvate [(CpBn5)2Sm]2[μ-η3:η3(C12H8N2)]·8C7H8. The molecular structure of 6 is depicted in Figure 4, and crystal and structural refinement data are listed in

bond lengths in contrast are slightly longer compared to the free bipy molecule (1.344(2) and 1.387(2) Å).28a The torsion angle between the planes of the pyridine rings serves as an indicator of the electronic state of the bipy ligand in the complex. If this angle in the free bipy and complexes with the neutral bipy ligand is rather large (10−17°),28a,b the electron transfer to the LUMO of the bipy molecule leads to a change in its geometry, including its flattening due to partial double bonding between two C atoms at positions 2 and 2′13 (for comparison see also refs 13, 24). The CpCentr−Sm−CpCentr in 5 (140.5°) is slightly narrower compared to the parent complex 2 (141.8°). The magnetic properties of 5 were investigated using SQUID magnetometry in the temperature range 1.8−300 K with an applied magnetic strength of 1000 Oe. The magnetic moment of 5 at 300 K (2.52 μB, for details see SI Figure S4) is noticeably lower compared to the average values reported so far for organic derivatives of Sm(II) (3.5−3.8 μB)29 but higher than those of Sm(III) (1.34−2.10 μB).29 The Sm(III) ion has a 6 H5/2 ground state that is split into six levels with the spin− orbit coupling. However, due to a small energy difference, higher excited states such as 6H7/2 can be populated even at room temperature, which adds a temperature-independent contribution to the magnetic susceptibility. Consequently, the in-depth analysis of the magnetic properties of Sm(III) complexes remains difficult. However, the measured magnetic moment of 5 is slightly lower than the value of 3.23 μB expected for a Sm(III) ion (usual value of 1.50 μB)29 and a radical-anion of bipy (1.73 μB) without magnetic interaction. Upon cooling, a continuous decrease of the magnetic moment is observed. Below 50 K, a strong decrease of the magnetic moment occurs to reach a value of 0.40 μB at 1.8 K. This value is lower than the expected value of 0.84 μB for Sm(III) considering that only the ground state 6H5/2 is populated at this temperature. Thus, the steep decrease of the magnetic moment observed below 50 K may originate from the thermal depopulation of the first excited state and the occurrence of an antiferromagnetic interaction between the Sm(III) ion and the radical anion. The chemical shift of the resonances of the ring carbons (126.1 ppm) in the 13C{1H} NMR spectrum of 5 is characteristic of Sm(III) complexes rather than Sm(II).17 According to the trivalent oxidation state of the Sm ion, the IR and UV−vis spectra of 5 exhibit absorptions (IR: 943, 1494, 1542 cm−1, UV−vis: strong absorption bands in the regions 280−290 and 230−240 nm) typical of a reduced radical-anionic bipy ligand (see the SI).24a Thereby the structural, magnetochemical, and spectroscopic data of 5 are suggestive of the trivalent state of the Sm ion and radical-anionic form of the bipy ligand CpBn52SmIII(bipy−•).

Figure 4. Molecular structure of complex 6. Thermal ellipsoids are drawn at the 30% probability level. Carbon atoms of Ph groups and hydrogen atoms are omitted for clarity. Selected distances (Å) and angles (deg): Sm(1)−C(1) 2.743(2), Sm(1)−C(2) 2.743(3), Sm(1)− C(3) 2.762(2), Sm(1)−C(4) 2.762(2), Sm(1)−C(5) 2.755(2), Sm(1)−C(41) 2.758(3), Sm(1)−C(42) 2.756(3), Sm(1)−C(43) 2.735(2), Sm(1)−C(44) 2.724(2), Sm(1)−C(45) 2.743(3), Sm(1)− N(1) 2.398(2), Sm(1)−C(84) 2.869(2), Sm(1)−C(85) 2.901(2), Sm(1)−Cpcenter 2.472(2) and 2.461(2); Cpcenter−Sm(1)−Cpcenter 137.5.

Table S1 (see the SI). The X-ray study revealed that 6 is a binuclear centrosymmetric dimeric complex in which two (CpBn5)2Sm fragments are linked by a μ-bridging phenazine ligand. Complex 6 features a structure similar to that of compound [Cp*2La]2[μ-(C12H8N2)], which was obtained by the salt metathesis reaction of Cp*2La(μ-Cl)2K(DME)2 with the dianionic adduct of Na2[C12H8N2].31 The Sm−C12H8N2− 1995


Article

Organometallics Scheme 5. Synthesis of Complex 7

h). Quantitative precipitation of metallic copper indicated that the reactions were completed. However, all the attempts of isolation of the lanthanide-containing products failed. The volatiles’ removal under vacuum afforded viscous, oily products. To obtain mixed-ligand CpBn5 complexes, reactions of equimolar amounts of 4 and NaN(SiMe3)2 were carried out in THF. However, the reaction afforded a mixture of the disproportionation products: 1 and Yb[N(SiMe3)2]2(THF). The DME solution of complex 4 was found to be photosensitive. When it was left in daylight (20 °C) for 72 h, the solution color changed from orange-yellow to brown and the formation of pink crystals of complex {[CpBn5YbI2(μOMe)]2}{Yb(DME)3} (7) was observed (Scheme 5). The GC/MS analysis detected the presence of ethylene in the reaction mixture. Moreover 1 was isolated from the reaction mixture in 53% yield. In the dark this reaction does not take place. Obviously the formation of complex 7 is a result of cleavage of the C−O bond of DME and a ligand redistribution reaction. Complex 7 is air- and moisture-sensitive and poorly soluble in organic solvents. The X-ray study revealed that the complex crystallizes as solvate 7·DME. The molecular structure of 7 is depicted in Figure 5, and crystal and structural refinement data are listed in Table S1 (see the SI). Complex 7 is a mixed-valent separated ion pair. The anionic part {[CpBn5YbI2(μ-OMe)]2}2− presents a

Sm fragment is not planar, and the Sm ions are disposed above and below the plane of the phenazine ligand (Sm−plane distance is 1.66 Å). The (CpBn5)2Sm fragments are coordinated to the phenazine ligand via nitrogen atoms (2.398(2) Å), and short contacts (2.869(2), 2.901(2) Å) with two carbons of the neighboring six-membered ring are detected. It is noteworthy that in 6 the interaction of the Sm ion with one of the pendant phenyl rings remains intact, resulting in short Sm−C contacts (3.802(2) Å). The Sm−C(Cp) average bond length in 6 (2.75 Å) is close to that in 5 and considerably shorter than that in the parent complex 2 (2.83 Å). This bond length falls into the range characteristic for SmIII compounds.25 The shortening of the Sm−C distances in 6 compared to those in the parent 2 indicates the oxidation of the Sm(II) to Sm(III) in the course of the reaction. The Sm−Carene distances in 6 (2.869(2), 2.901(2) Å) are somewhat elongated compared to the related bond lengths in the dimeric Sm(III) complex with a μ-bridging anthracene ligand [Cp*2Sm]2[μη3:η3-(C14H10)] (2.595(4), 2.791(4), 2.840(4) Å) having a similar structure.32 The Sm−Carene distances in 6 can also be compared with the average Sm−C(ring) distances found in the η6-arene complexes Sm(η6-C6Me6)(AIC14)3 (2.88(2) and 2.90(4) Å)33a,b and Sm(η6-m-Me2-C6H4)(AlC14)3 (2.89(5) Å).33c,d It is noteworthy that the bonding situation within the [C12H8N2]2− fragment in 6 is very similar to that in the previously reported lanthanum analogue [Cp* 2 La] 2 [μ(C12H8N2)]31 but noticeably differs from neutral phenazine.34 Double reduction of phenazine and its coordination to two Sm ions result in shortening of long and elongation of short bonds compared to the parent C12H8N2 molecule. The value of the effective magnetic moment of 6 at 300 K (1.90 μB, for details see the SI, Figure S5) is indicative of the trivalent state of the samarium ions and falls into the interval characteristic for Sm(III) complexes (1.34−2.10 μB).29 In the 13 C NMR spectrum of 6 the signals related to the carbons of cyclopentadienyl rings appear at 113.5 ppm, giving further evidence for the trivalent oxidation state of samarium. Thus, complex 6 can be classified as a Sm(III) derivative in which two (CpBn5)2Sm(III) fragments are bridged by a diamagnetic dianionic [μ-η3:η3-(C12H8N2)] fragment. Interestingly unlike Sm(III) complex [Cp*2Sm]2[μ-η3:η3-(C14H10)],32 with a μbridging anthracene ligand, complex 6 is inert toward THF: no dissociation of the Sm−(C12H8N2) bond and formation of 2 took place when 6 was dissolved in THF. To find out the influence of the metal ion valence state (and consequently the ion size) on Ln(II)−Ph interactions, the reactions of 1 and 2 with one-electron oxidants were carried out. The reactions of 1 and 2 with equimolar amounts of CuX (X = Cl, I) were performed in THF at ambient temperature (72

Figure 5. Molecular structure of the anionic part of complex 7. Thermal ellipsoids are drawn at the 30% probability level. Carbon atoms of Ph groups and hydrogen atoms are omitted for clarity. Selected distances (Å) and angles (deg): Yb(1)−C(1) 2.643(4), Sm(1)−C(2) 2.628(4), Sm(1)−C(3) 2.625(4), Sm(1)−C(4) 2.616(4), Sm(1)−C(5) 2.622(4), Yb(1)−I(1) 3.0132(4), Yb(1)− I(2) 3.0174(3), Yb(1)−O(1) 2.200(3), Yb(1)−O(1A) 2.201(3), Yb(1)−Cpcenter 2.330(4), Yb(2)−O 2.480(6)−2.562(7); Cpcenter− Sm(1)−I(1) 114.2, Cpcenter−Sm(1)−I(2) 111.3, I(1)−Sm(1)−I(2) 84.47(1), O(1)−Sm(1)−O(1A) 70.4(1). 1996


Organometallics

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centrosymmetric MeO-bridged dimer consisting of an Yb(III) cation coordinated by a η5-CpBn5 ligand, two iodo ligands, and two μ-bridging methoxy groups, while the cationic part is composed of an Yb(II) cation coordinated by three DME molecules. The formal coordination number of Yb(III) is seven, while that of Yb(II) is six. Strangely despite the different oxidation states of the ytterbium ions in 4 and in the anionic part of 7, the value of the average YbIII−C(Cp) bond length in 7 (2.62 Å) is just slightly shorter than the YbII−C(Cp) in 4 (2.68 Å). Obviously this results from the negative charge delocalization on the anionic part. The Yb−I bond lengths in 7 (3.0132(4) and 3.0174(4) Å) are comparable to those in the eight-coordinate Yb III complex Cp* 2 Yb(μ-I) 2 Li(Et 2 O) 2 (3.027(1) Å).38 The average Yb−O bond length in the cationic part of 7, [YbII(DME)3]2+ (2.51 Å), is comparable to those in previously published analogues (2.51, 2.52 Å).36 The YbIII−OMe bonds of the anionic part (2.200(3), 2.201(3) Å) are somewhat longer than the distances in related seven-coordinate anionic YbIII complexes.37 At room temperature, the χT value of 5.87 cm3·K·mol−1 for 7 is slightly higher than the theoretical one of 5.14 cm3·K·mol−1 expected for a compound containing two Yb(III) ions (2F7/2, S = 1/2; L = 3, gJ = 8/7) and one Yb(II) being diamagnetic. Upon cooling, χT decreases to reach the value of 1.83 cm3·K· mol−1 at 1.8 K. Such a decrease reflects directly the presence of the thermal depopulation of the Stark sublevels. The field dependence of the magnetization performed at 1.8 K shows a value of 3.75 μB at 70 kOe without reaching the saturation. Conclusions. The bulky CpBn5 ligand bearing flexible benzyl groups proved to be suitable for coordination to large Ln(II) ions, providing access to both sandwich- and half-sandwichtype complexes. Application of the CpBn5 ligand allows for the synthesis of bent base-free lanthanoidocenes(II) (CpBn5)2Ln (Ln = Yb, Sm, Eu) featuring intramolecular interactions between Ln(II) ions and pendant phenyl rings. Despite the absence of Lewis bases in the coordination spheres of Ln(II) ions, new lanthanoidocenes were found to be inert not only toward small molecules (H2, SiH4, N2, CO) and organic molecules containing multiple C−C bonds (CH2CH2, PhCHCH 2 , trans-PhCHCHPh, cis-PhCHCHPh, CH 2 CH−CHCH 2 , Ph−CHCH−CHCH−Ph, PhCCPh, Me3SiCCSiMe3) but also toward Lewis bases (THF, DME, PMe 3 , TMEDA). Such an inertness of (CpBn5)2Ln toward Lewis bases may serve as indirect evidence for rather strong Ln(II)−Ph interactions. On the other hand a systematic comparison of the chemical properties of Cp*2Sm and (CpBn5)2Sm clearly demonstrated the affect of electrondonating ability of the ligands coordinated to Ln(II) ions on the reactivity of the related lanthanoidocenes. Surprisingly, complexes (CpBn5)2Ln (Ln = Yb, Eu) do not react with Ndonor bipy and phenazine ligands. These reactions turned out feasible only for the samarium derivative when they are associated with oxidation of the metal center. The oxidation reactions of (CpBn5)2Sm by bipy and phenazine afford Sm(III) complexes (CpBn5)2SmIII(bipy−•) and [(CpBn5)2SmIII]2[μ-η3:η3(C12H8N2)2−]. The half-sandwich complex [CpBn5Yb(DME)(μ-I)]2 when illuminated with natural light in DME undergoes a redox reaction and in 72 h transforms into the mixed-valent compound {[CpBn5YbIIII2(μ-OMe)]2}2-{YbII(DME)3}.

Article

EXPERIMENTAL SECTION

All experiments were performed in evacuated tubes by using standard Schlenk techniques, with rigorous exclusion of traces of moisture and air. After being dried over KOH, THF and DME were purified by distillation from sodium/benzophenone ketyl; hexane and toluene were dried by distillation from sodium/triglyme and benzophenone ketyl prior to use. C6D6 was dried with sodium and condensed in a vacuum into NMR tubes prior to use. 2,2′-Bipyridyl and phenazine were purchased from Aldrich and were used after recrystallization. SmI2(THF)3,15 YbI2(THF)2,15 EuI2(THF)2,15 benzylpotassium,16 and pentabenzylcyclopentadiene (CpBn5H)12 were prepared according to literature procedures. NMR spectra were recorded with Bruker DPX 200 and Bruker Avance DRX 400 spectrometers in CDCl3 and C6D6 at 25 °C, unless otherwise stated. Chemical shifts for 1H and 13C NMR spectra were referenced internally to the residual solvent resonances and are reported relative to TMS. IR spectra were recorded as Nujol mulls with a “Bruker-Vertex 70” instrument. Lanthanide metal analyses were carried out by complexometric titration.39 The C, H, and N elemental analyses were performed in the microanalytical laboratory of the G. A. Razuvaev Institute of Organometallic Chemistry. Synthesis of (CpBn5)2Yb (1). A solution of PhCH2K (0.10 g, 0.80 mmol) in THF (10 mL) was added to a solution of CpBn5H (0.40 g, 0.77 mmol) in 5 mL of THF at −78 °C. After 1 h at −78 the reaction mixture was slowly warmed to room temperature and stirred for 2 h. The resulting pale yellow solution of CpBn5K in THF was filtered and added to a solution of YbI2(THF)2 (0.22 g, 0.38 mmol) in THF (15 mL). The solution turned brown and KI precipitated. After 1 h at 30 °C THF was removed under vacuum, and toluene (20 mL) was added. The reaction mixture was filtered from KI, concentrated, and cooled to −20 °C. After 1 day at −20 °C 0.30 g (66%) of dark green crystals of compound 1 was isolated. 1H NMR (400 MHz, C6D6, 293 K): δ 3.85 (s, 20H, CH2), 6.87 (d, 20H, o-C6H5, 3JHH = 7.4 Hz), 6.97 (t, 10H, pC6H5, 3JHH = 7.28 Hz), 7.06 (t, 20H, m-C6H5, 3JHH = 7.44 Hz). 13 C{1H} NMR (100 MHz, C6D6, 293 K): δ 32.5 (CH2); 117.6 (Cp); 125.5 (p-C6H5); 127.9, 128.7 (o,m-C6H5); 141.8 (ipso-C6H5). IR (KBr): 1600 (s); 1490 (m); 1330 (m); 1291 (w); 1070 (m); 1027 (m); 874 (w); 820 (w); 745 (s); 708 (m); 694 (m); 616 (w); 597 (w); 579 (w); 565 (w); 518 (w); 478 (s); 460 (s) cm−1. Anal. Calcd for C80H70Yb: C, 79.77; H, 5.86; Yb, 14.37. Found: C, 79.39; H, 5.53; Yb, 14.69. Synthesis of (CpBn5)2Sm (2). A solution of PhCH2K (0.21 g, 1.6 mmol) in THF (10 mL) was added to a solution of CpBn5H (0.80 g, 1.55 mmol) in 8 mL of THF at −78 °C. After 1 h at −78 °C the reaction mixture was warmed slowly to room temperature and stirred for 2 h. The resulting pale yellow solution of CpBn5K in THF was filtered and added to a dark blue solution of SmI2(THF)3 (0.46 g, 0.75 mmol) in THF (5 mL). Immediately the solution turned brown and KI precipitated. After 1 h at 30 °C THF was removed under vacuum and toluene (40 mL) was added. The reaction mixture was filtered from KI and slowly concentrated. The purple crystals of 2 were separated from the mother liquor by decantation, washed with cold toluene, and dried for 40 min under vacuum. Compound 2 was isolated in 60% yield (0.53 g). 1H NMR (400 MHz, C6D6, 293 K): δ 4.19 (s, 20H, CH2), 6.52 (br s, 20H, o-C6H5), 6.60 (t, 10H, p-C6H5, 3 JHH = 7 Hz), 8.76 (br s, 20H, m-C6H5). 13C{1H} NMR (100 MHz, C6D6, 293 K): δ 110.0 (CH2); 122.1 (o-C6H5); 128.3 (Cp); 131.0 (mC6H5); 132.5 (p-C6H5); 154.4 (ipso-C6H5). IR (KBr): 1600 (s); 1491 (m); 1329 (m); 1291 (w); 1072 (m); 1028 (m); 1002 (w); 988 (w); 873 (w); 819 (w); 745 (s); 708 (m); 694 (m); 616 (w); 597 (w); 583 (w); 566 (w); 517 (w); 478 (s); 460 (s) cm−1. Anal. Calcd for C80H70Sm: C, 81.31; H, 5.97; Sm, 12.72. Found: C, 80.89; H, 5.67; Sm, 12.87. Synthesis of (CpBn5)2Eu (3). A solution of PhCH2K (0.19 g, 1.37 mmol) in THF (10 mL) was added to a solution of CpBn5H (0.70 g, 1.36 mmol) in 10 mL of THF at −78 °C. After 1 h at −78 the reaction mixture was warmed slowly to room temperature and stirred for 2 h. The resulting pale yellow solution of CpBn5K in THF was filtered and added to a solution of EuI2(THF)2 (0.37 g, 0.67 mmol) in THF (15 mL). Immediately the solution turned orange and KI precipitated. 1997


Article

Organometallics After 1 h at 30 °C THF was removed under vacuum and toluene (40 mL) was added. The reaction mixture was stirred in toluene for 1 h at 70 °C, filtered from KI, and slowly concentrated. The bright orange crystals of 3 were separated from the mother liquor by decantation, washed with cold toluene, and dried for 40 min in vacuum. Compound 3 was isolated in 50% yield (0.39 g). IR (KBr): 1596 (s); 1330 (w); 1182 (w); 1070 (m); 1028 (m); 901 (w); 871 (w); 746 (s); 708 (m); 695 (s); 617 (w); 597 (w); 583 (w); 566 (w); 517 (w); 478 (s); 460 (s) cm−1. Anal. Calcd for C80H70Eu: C, 81.20; H, 5.96; Eu, 12.84. Found: C, 80.88; H, 5.69; Eu, 13.00. Synthesis of [CpBn5Yb(DME)(μ-I)]2 (4). A solution of CpBn5H (0.79 g, 1.50 mmol) in THF (7 mL) was added at −78 °C to a solution of PhCH2K (0.21 g, 1.6 mmol) in THF (5 mL). After 3 h at −78 °C THF was removed under vacuum and DME (20 mL) was added. YbI2(THF)2 (0.873 g, 1.51 mmol) was slowly added to the reaction mixture at room temperature under vigorous stirring. The reaction mixture was stirred overnight. The brownish-yellow reaction mixture was filtered, DME was evaporated under vacuum, and an orange-yellow residue was recrystallized from DME by slow concentration. The mother liquor was decanted from orange-yellow crystals, which were dried under vacuum to afford 1.10 g (85%) of 4. 1 H NMR (400 MHz, C6D6, 293 K): δ 3.22 (s, 20H, CH2), 3.45 (s, 12H, OMe, DME), 4.03 (s, 8H, CH2CH2, DME), 6.91−7.15 (complex m, 50H, C6H5). 13C{1H} NMR (100 MHz, pyridine-d5, 293 K): δ 33.8 (CH2); 58.4 (CH3, DME); 71.8 (CH2, DME); 113.1 (Cp); 124.6 (pC6H5); 128.2 (o-C6H5); 128.7 (m-C6H5); 145.8 (ipso-C6H5). IR (KBr): 1599 (s); 1490 (s); 1333 (w); 1280 (w); 1241 (m); 1214 (w); 1190 (m); 1154 (w); 1105 (m); 1061 (s); 1027 (m); 1007 (w); 907 (w); 861 (s); 830 (m); 805 (w); 756 (m); 698 (s); 622 (m); 604 (m); 578 (w); 518 (w); 472 (m) cm−1. Anal. Calcd for C88H90I2O4Yb2: C, 58.34; H, 5.01; Yb, 19.11. Found: C, 57.91; H, 4.78; Yb, 19.25. Synthesis of (CpBn5)2Sm(bipy) (5). To a solution of 2 (0.70 g, 0.59 mmol) in toluene (30 mL) was added 2,2′-bipyridyl (0.09 g, 0.59 mmol). Immediately the solution turned dark yellow. Continuous cooling of the toluene solution at −20 °C afforded dark brown crystals of 5 in 76% yield (0.60 g). 1H NMR (400 MHz, C6D6, 293 K): δ 3.38 (s, 20H, CH2), 6.67 (m, 2H, 5,5′-bipy), 6.99 (complex m, 30H, m, pC6H5), 7.19 (m, 2H, 4,4′-bipy), 7.25 (d, 20H, o-C6H5, 3JHH = 7.3 Hz), 8.52 (d, 2H, 6,6′-bipy, 3JHH = 4.3 Hz), 8.73 (d, 2H, 3,3′-bipy, 3JHH = 8 Hz). 13C{1H} NMR (100 MHz, C6D6, 293 K): δ 29.8 (CH2); 120.9 (C3-bipy); 123.3 (C5-bipy); 126.0 (m-C6H5), 128.3 (p-C6H5); 131.6 (o-C6H5); 136.3 (C4-bipy); 140.0 (Cp); 143.2 (ipso-C6H5); 149.1 (C6-bipy); 156.4 (C1-bipy). IR (KBr): 1602 (s); 1542 (s); 1494 (s); 1290 (m); 1273 (m); 1260 (m); 1210 (w); 1147 (m); 1117 (m); 1077 (m); 1029 (m); 1014 (m); 1003 (w); 943 (s); 757 (m); 695 (s); 643 (m); 603 (w); 583 (w); 476 (m); 466 (m) cm−1. Anal. Calcd for C90H78N2Sm: C, 80.79; H, 5.88; N, 2.09; Sm, 11.24. Found: C, 80.30; H, 5.60; N, 2.11; Sm, 11.30. Synthesis of [(CpBn5)2Sm]2(C12H8N2) (6). To a solution of 2 (0.65 g, 0.50 mmol) in toluene (25 mL) was added phenazine (0.10 g, 0.57 mmol). The solution turned red-brown. Cooling of the toluene solution at −20 °C afforded dark brown crystals of 6 in 80% yield (0.56 g). 1H NMR (400 MHz, C6D6, 293 K): δ 3.44 (br s, 40H, CH2); 5.69 (m, 4H, C12H8N2); 6.22 (d, 40H, o-C6H5, 3JHH = 6.7 Hz); 6.45 (m,4H, C12H8N2); 6.57 (m, 60H, m,p-C6H5). 13C{1H} NMR (100 MHz, C6D6, 293 K): δ 40.0 (CH2); 112.1 (CH, C12H8N2); 121.0 (CH, C12H8N2); 123.6 (Cp); 125.0 (m-C6H5); 127.1 (o-C6H5); 127.6 (pC6H5); 136.8 (ipso-C6H5); 140.0 (C12H8N2). IR (KBr): 1602 (s); 1494 (s); 1313 (m); 1285 (m); 1205 (w); 1178 (w); 1117 (w); 1075 (m); 1029 (s); 1004 (w); 977 (w); 893 (s); 810 (w); 695 (s); 619 (w); 594 (w); 583 (w); 518 (w); 479 (m); 464 (m) cm−1. Anal. Calcd for C172H148N2Sm2: C, 81.21; H, 5.86; Sm, 11.82. Found: C, 80.83; H, 5.58; Sm, 12.00. Synthesis of [CpBn5YbI2(μ-OMe)]2[Yb(DME)3] (7). A solution of 6 (0.30 g, 0.33 mmol) in DME (15 mL) was left for 3 days in sunlight. The mother liquor was decanted from pink crystals, which were dried under vacuum for 15 min. A total of 0.17 g (85%) of 7 was isolated. Ethylene was detected in the mother liquor by GC/MS. Evaporation of DME in vacuum and recrystallization of the solid residue afforded 1 in 53% yield (0.053g). IR (KBr): 1600 (m); 1494 (m); 1338 (w);

1288 (w); 1248 (m); 1208 (w); 1187 (m); 1103 (m); 1075 (w); 1052 (s); 1033 (s); 983 (w); 914 (w); 858 (s); 828 (w); 765 (w), 698 (s); 623 (w); 611 (w); 593 (w); 583 (w); 521 (w); 479 (w); 471 (w). Anal. Calcd for C96H106I4O8Yb3: C, 47.45; H, 4.71; I, 20.46; Yb, 20.93. Found: C, 47.06; H, 4.35; Yb, 21.11. X-ray Crystallography. The X-ray data for 1−7 were collected on Bruker Smart Apex (1−3, 7) and Agilent Xcalibur E (4−6) diffractometers (graphite-monochromated, Mo Kα radiation, ω-scans techique, λ = 0.710 73 Å, T = 100(2) K). The structures were solved by direct methods and were refined on F2 using SHELXTL39 and CrysAlis Pro40 packages. All non-hydrogen atoms were found from Fourier syntheses of electron density and were refined anisotropically. All hydrogen atoms were placed in calculated positions and were refined in the rigid model. SADABS41 and ABSPACK39 were used to perform area-detector scaling and absorption corrections. CCDC1051041 (1), 1051042 (2), 1051043 (3), 1051044 (4), 1051045 (5), 1051046 (6), and 1051047 (7) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via ccdc.cam.ac.uk/ getstructures. Magnetic Measurements. Magnetic susceptibility data were collected with a Quantum Design MPMS-XL SQUID magnetometer working between 1.8 and 350 K with a magnetic field up to 7 T. The data were corrected for the sample holder, and the diamagnetic contributions calculated from the Pascal’s constants.42

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ASSOCIATED CONTENT

S Supporting Information *

Figures giving NMR and IR spectra, CIF files giving crystallographic data. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b00243.

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AUTHOR INFORMATION

Corresponding Author

*Fax: 007 831 4627497. Tel: 007 831 4623532. E-mail: trif@ iomc.ras.ru. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Russian Foundation for Basic Research (Grant No. 14-03-00527) and by the Ministry of Education and Science of the Russian Federation (the agreement of August 27, 2013, No. 02.B.49.21.0003, between the Ministry of Education and Science of the Russian Federation and Lobachevsky State University of Nizhny Novgorod). The autors (J.La., J.Lo.) thank the University of Montepllier, CNRS, for financial support. The authors thank also Corine Rebeil (PAC Balard) for magnetic measurements.

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REFERENCES

(1) Shannon, R. D. Acta Crystallogr. A 1976, 32, 751−767. (2) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, IVth ed.; Wiley: New York, 1980; p 23. (3) (a) Morss, L. R. Chem. Rev. 1976, 76, 827−841. (b) Mikheev, N. B. Inorg. Chim. Acta 1984, 94, 241−248. (4) (a) Krinsky, J. L.; Minasian, S. G.; Arnold. J. Inorg. Chem. 2011, 50, 345−357. (b) Minasian, S. G.; Krinsky, J. L.; Arnold. J. Chem. Eur. J. 2011, 17, 12234−12245. (c) Maron, L.; Eisenstein, O. J. Phys. Chem. A 2000, 104, 7140−7143. (d) Freedman, D.; Melman, J. H.; Emge, T. J.; Brennan, J. G. Inorg. Chem. 1998, 37, 4162−4163. (5) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem. Rev. 1995, 95, 865−986.

1998


Article

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1999


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