Chapter 4 Sm 4.1 4.2 4.3 4.4 4.5 4.6. 4.7 Organometallics The first compounds Alkyl derivatives Cyclopentadienyl derivatives Carbonyl and related complexes Arene complexes Cyclooctatetraene derivatives Divalent lanthanide chemistry U U Sm MSc: f-Elements, Prof. J.-C. Bünzli, 2008 1 Chapter 4 4.1 Organometallics The first compounds cyclopentadienyl Cpcyclooctatetraenyl Cot2- pentamethylcyclopentadienyl Cp* Ferrocene: [Fe(h5-C5H5)2] Fe 1952 h5 points to the binding of the 5 carbon atoms MSc: f-Elements, Prof. J.-C. Bünzli, 2008 2 Chapter 4 M 6L 2a1g 3t1u 2t1u 2t2g 1t1g Organometallics 1t2u d-Transition metals: 18-electron rule points to stable compounds. p s 2eg d 1t2g 1t1u 1eg What about f-elements? Much energy is needed to “transform” f-elements into d-elements: cf. the energies of the [Xe]4fN-15d16s2 configuration (Ch. 1) versus [Xe]4fN6s2. 1a1g MSc: f-Elements, Prof. J.-C. Bünzli, 2008 Slide 24 3 Chapter 4 Organometallics LnCl3(anh) + 3 NaCp [Ln(Cp)3] + 3 NaCl (in thf) J.M. Birmingham, G. Wilkinson, J. Am. Chem. Soc. 1954, 76, 6210 Ln Sm [U(h5-C U Cl 5H5)3Cl] dark red Ce, Sm: orange Pr: pale green Nd: pale blue L. T. Reynolds, G. Wilkinson, J. Inorg. Nucl. Chem. 1956, 2, 246 UCl4 + 3 NaCp [U(Cp)3Cl] + 3 NaCl MSc: f-Elements, Prof. J.-C. Bünzli, 2008 (in thf) 4 Chapter 4 U 1968 Organometallics UCl4 + 2 K2(Cot) [U(Cot)2] + 4 KCL (in thf) A. Streitwieser Jr. et al. J. Am. Chem. Soc. 1968, 90, 7368 d and f organometallic compounds are particularly sensitive to oxygen and water and this problem is more important for f-elements in view of their larger ionic radii and their lower propensity to form covalent bonds. For f-elements, relativistic effects (see Ch. 1) increase the complexity of theoretical models aiming at explaining the chemical bonds in organometallic compounds. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 5 Chapter 4 4.2 Organometallics Alkyl derivatives (-bonds) Most difficult to synthesize. Bulky ligands should be used. Two main paths: a) With the help of a bis(trimethylsilyl)methyl ligand Li[CH(SiMe3)2] + UL3 [U({CH(SiMe3)2}3] (in hexane) Me Me Me Si Me C Si Me H L = O- Me C3-symmetry U-C: 2.48 Å C-U-C: 107.7o MSc: f-Elements, Prof. J.-C. Bünzli, 2008 6 Chapter 4 Organometallics b) Smaller alkyl groups may also be used, often leading to negatively charged species LuCl3 + 4 Li(t-but) + Me2N-(CH2)2-NMe2 [Lu(t-but)4]-[Li(tmed)2]+ (in Et2O/pentane) H. Schumann et al., J. Organomet. Chem. 1986, 306, 215 CS symmetry Lu-C 2.32-2.43 Å C-Lu-C 107-109 o Allows alkylation reactions: HO O tBut O tBut MSc: f-Elements, Prof. J.-C. Bünzli, 2008 7 Chapter 4 Organometallics LuCl3 + 6 LiMe + 3 dme [Li(dme)]+3 [Lu(Me)6]3- + 3 LiCl The compounds are extremely air- and water-sensitive. They were obtained with several Ln. The structure of [Er(Me)6]3is also known, with [Li(Me2N(CH2)2NMe2]+ as counterion H. Schumann et al., J. Organomet. Chem. 1984, 263, 29. Lu-C C-Lu-C C-Lu-C eq MSc: f-Elements, Prof. J.-C. Bünzli, 2008 2.48-2.57 Å 86-96 o 176 o 8 Chapter 4 Organometallics Decomposition of alkyl complexes via b-elimination Ln H H R Ln LnH + R R f-elements do not form strong bonds with alkenes, so that decomposition proceeds easily Conditions for b-elimination: - the b-carbon must bear a H atom - the Ln-C-C-H fragment must be able to adopt a planar conformation - the metal ion must have an appropriate empty orbital for binding the H-atom MSc: f-Elements, Prof. J.-C. Bünzli, 2008 9 Chapter 4 Organometallics f-Elements have a large number of empty orbitals, so that they are extremely susceptible to b-elimination. The strategy for producing alkyl derivatives with low coordination numbers therefore involves bulky ligands for which b-elimination is not possible, such as CH(SiMe3)2. Agostic interaction H Me Me H C H Si Me3Si U L L U-H-C bridges are formed with H-atoms in g position with respect to U: this is called a g-agostic interaction. Therefore, the coordination number is larger than 3 in this compound and this is often the case for lowCN organometallic compounds MSc: f-Elements, Prof. J.-C. Bünzli, 2008 10 Chapter 4 4.3 Organometallics Cyclopentadienyl derivatives (-bonds) Cp and its derivatives are among the most popular ligands in organometallic chemistry of d- and f-transition metals. Cp forms both covalent and ionic complexes with 1-5 C-atoms coordinated. The h5-mode is usually considered to occupy 3 coordination sites (this is somewhat arbitrary). Simple LnCp3 cyclopentadienyls • LnCp3 features polar Ln-Cp bonds as shown by: 2 LnCp3 + 3 FeCl2 3 FeCp2 + 2 LnCl3 • Rapid exchange of Cp ligands occurs • LnClCp2 compounds can be isolated as dimers or as Lewis acid adducts MSc: f-Elements, Prof. J.-C. Bünzli, 2008 11 Chapter 4 Cl Ln Ln Cl Organometallics Most dimers feature Cl- as bridging ligands Cl Cl Ln O MSc: f-Elements, Prof. J.-C. Bünzli, 2008 Ln N 12 Chapter 4 Organometallics Structural changes along the series La-Pr “11-coordinate” [Ln(h5Cp)3(h2Cp)] (under the form of a coordination polymer) Ln Cp is counted as tridentate! Ln Ln Y, Sm-Yb “9-coordinate” [LnCp3] Sm-C 2.75 Å G.Laubereau & J.H. Burns Inorg.Chem. 1970, 9, 1091, MSc: f-Elements, Prof. J.-C. Bünzli, 2008 13 Chapter 4 Sc, Lu Organometallics “8-coordinate” [Lu(h5-Cp)2(h1-Cp)2 (coordination polymer) Ln Ln Ln Simple AnCpn cyclopentadienyls AnCp3 compounds behave similarly to LnCp3. Most of the Cp chemistry of Th, U, Pa and Np elements however involves +4 oxidation state: AnCl4 + n NaCp [AnCpnCl4-n] + n NaCl MSc: f-Elements, Prof. J.-C. Bünzli, 2008 14 Chapter 4 [An(Cp)4] are the only complexes with four h5-Cp coordinated in a tetrahedral arrangement. As a comparison, the ZrIV analogue is [Zr(h5-Cp)3(h1-Cp)] An Th-C Th-Cp U-Cp Organometallics 2.87 Å 2.61 Å 2.59 Å R. Maier e al., J. Alloys & Cmpnds 1993, 190, 269. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 15 Chapter 4 Organometallics [UCp3Cl] + FeCl2 ferrocene indicating a more covalent U-Cp bond than in the analogue Ln compounds. On the other hand, the Cl ligand in [AnCp3Cl] can easily be substituted, making these complexes important synthons in An organometallic chemistry. Substituted Cp’s are also used, as in this ThIV derivative: [Th(Me3SiCp)3Cl] R. C. Blake et al., J. Organomet. Chem. 1998, 551, 261. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 16 Chapter 4 Organometallics An AnCl4 TlCp NaOEt An LiMe An Cl OEt NaBH4 An CH3 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 BH4 17 Chapter 4 Organometallics Substituted cyclopentadienyls Cp Cp* Me Me Me Me Me Si Me Si Si Me Me Me Me Me Si Si Me Me Me Me Cp’’ The substitution gives more stable, more soluble compounds which are easier to crystallize. However, Ln(Cp*)3 and An(Cp*)3 are not very stable, because the ligand is too bulky. On the other hand, [Ln(Cp*)2Cl], [An(Cp*)2Cl] and [An(Cp*)2Cl2] are versatile and have an extensive chemistry. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 18 Chapter 4 Organometallics [Sm(Cp*)3] Trigonal co-ordination Sm-C 2.82 Å Cp*-Sm-Cp* 120o W. J. Evans et al., J. Am. Chem. Soc. 1991, 113, 7423 2 [Sm(Cp*)2] + Cot [Sm(Cp*)3] + [Sm(Cp*)(Cot)] MSc: f-Elements, Prof. J.-C. Bünzli, 2008 19 Chapter 4 Organometallics An active Th catalyst (A) for ethene polymerization: It also inserts CO: H Cl Th Th 2 Cl H 2 LiMe 2 CO Me 2 O Th Me H2 Th H Th H MSc: f-Elements, Prof. J.-C. Bünzli, 2008 A 20 Chapter 4 Organometallics 1,2-bis(dimethylphosphinoethane) Th H + 2 [Et3NH][BPh4] Th H … KCp*(18C6) Th-C Th-H dmpe [Th(Cp*)3H] 2.87 Å 2.33 Å W.J. Evans et al., Organometallics 2001, 20, 5489. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 21 Chapter 4 Organometallics tBut substituents are also commonly grafted onto Cp, yielding a wealth of interesting compounds [Yb{(tbut)2Cp}3] [{YbCl(tButCp)2}2] A.V. Khvostov et al. J. Organomet. Chem. 1998, 568, 113. J.S. Ren et al., Jiegou Huaxue 1997, 16, 380 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 22 Chapter 4 4.4 Organometallics Carbonyl and related complexes d-Transition metal chemistry: M C -donation O M C O -retrodonation 4f-Transition elements: the filled metal orbitals are not outside orbitals so that -overlap is not effective. Ln(g) + n CO (g) Ln(CO)n (g), n = 1-6, in Ar at <40 K Identified by IR spectra. Decompose upon increasing T. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 23 Chapter 4 Organometallics Laser-ablated Gd atoms and Gd2 dimers co-deposited with CO onto a CsI window (under Ar): Gd(CO)x Gd x = 1-3 Gd C O C O Gd C Activation of CO C O Gd Studied by vibrational spectroscopy with 12C/13C substitution + DFT calculations Gd Gd Cleavage of CO O Xi Jin et al. J. Phys. Chem. A 2006, 12585 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 24 Chapter 4 Organometallics 5f-Transition elements More covalent so that AnCp3CO complexes are known Me3Si SiMe3 U U CO CO SiMe3 n(CO) = 1976 cm-1 n(CO) = 1900 cm-1 Since n(CO) = 2146 cm-1 for free CO, these values point to a significant amount of back bonding. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 25 Chapter 4 Organometallics Dinitrogen, isocyanide, alkene, and alkyne compounds Dinitrogen is isoelectronic with CO, but less efficient for -bond formation. In the case of f-elements, is forms complexes only with the low oxidation states, e.g. SmII, YbII, UIII. R R N N R N U N N N U N R Isocyanides CN-R: N R N N R [LnCp3(CN-Et)] have n(CN) values higher than in free CN-R pointing to negligible backbonding Alkene and alkyne complexes are also very difficult to make and only occur with low oxidation states MSc: f-Elements, Prof. J.-C. Bünzli, 2008 26 Chapter 4 Organometallics 4.5 Arene complexes h6-arene ligands (such as benzene) are -acceptors and d-donors. Note ,,d,and frefer to the symmetry of the bonding interaction with respect to the metal-ligand axis: they correspond to 0, 1, 2, and 3 nodal planes. Arene ligands usually form complexes when the metal is in a low oxidation state. tBut Ln(g) + tBut3Ph tBut -196oC 0-valent compounds sublime in vacuo at 100 oC tBut Ln tBut tBut Ln = Pr, Nd, Gd, Tb, Dy, Ho, Er, Sc, Y tBut MSc: f-Elements, Prof. J.-C. Bünzli, 2008 27 Chapter 4 Organometallics The 0-valent compounds form only for Ln for which the promotion energy [Xe]4fN6s2 [Xe]4fN-15d16s2 is relatively small (cf. Ch. 1). Therefore, involvement of the 5d electron is holding the bis(arene) Ln0 compounds together. A SmIII compound is also known: SmCl3 + 3 AlCl3 + PhMe6 Cl Cl Al Cl Cl Sm Cl Cl Cl MSc: f-Elements, Prof. J.-C. Bünzli, 2008 Cl Al Cl Al Cl Cl Cl 28 Chapter 4 4.6 Organometallics Cyclooctatetraene complexes Cot2- is ideally suited for f-element organometallic chemistry because it has a high valency and is sterically bulky (as much as Cp*). Uranocene, D8h symmetry The two rings are eclipsed in conformation, therefore the D8h symmetry The major source of binding is the interaction between the ring e2g orbitals and the U(6d) orbitals (d-bonds). The second source of binding is between the ring e2u orbitals and the U(5f) orbitals (f-bonds).These are only available with f-elements. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 29 Chapter 4 Organometallics d-bonds (major contribution to binding) 6d Two vertical nodal planes, but no nodal plane between the rings, hence e2g MSc: f-Elements, Prof. J.-C. Bünzli, 2008 30 Chapter 4 Organometallics f-bonds Nodal plane between the rings, hence e2u MSc: f-Elements, Prof. J.-C. Bünzli, 2008 31 Chapter 4 Organometallics e2g e1g antibonding e2u+e2g 6d a1g e2u a2u e1u 5f e3u e1u+e1g d f a2u+a1g 20 e- U MSc: f-Elements, Prof. J.-C. Bünzli, 2008 UIV 2 e32 Chapter 4 Organometallics Lanthanide Cot2- complexes [Ce(h8-Cot)2] is known for a long time. Recent calculations tend to prove that it should however be formulated as [Ce3+(Cot2)3-]. It can be reduced by potassium: [Ce(h8-Cot)2] + K K[Ce(h8-Cot)2] Other Ln compounds are obtained as follows: LnCl3 + 2 K2Cot K[Ln(h8-Cot)2] + 3 KCl These compounds are essentially ionic. They react readily with UCl4 to give uranocene. MSc: f-Elements, Prof. J.-C. Bünzli, 2008 33 Chapter 4 Organometallics In sterically crowded complexes such as [Ln(Cp*)3], (Cp*)functions as one-electron reductive species. [Ln(Cp*)3] 1e- + ½ (Cp*)2 + [Ln(Cp*)2]+ Example: synthesis of the mixed species [Sm(Cp*)(Cot)] [Sm(Cp*)3] + Cot [SmCp*Cot] +(Cp*)2 W. J. Evans et al., Dalton Trans. 2000, 1609 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 34 Chapter 4 Organometallics 4.7 Divalent lanthanide chemistry Initial studies involved SmII, EuII, YbII SmI2 + 2 NaCp* [Sm(Cp*)2(thf)2] (in thf) [SmII(Cp*)2(thf)2] [SmII(Cp*)2] + 2 thf (upon heating) purple Sm-C: 2.79 Å 2.86 Å W. J. Evans et al., J. Am. Chem. Soc. 1981, 103, 6507 and 1984, 106, 4270 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 35 Chapter 4 Organometallics These species are highly reactive and generate interesting redox chemistry. For instance, they can add dinitrogen upon crystallization: 2 [Sm(Cp*)2] + N2 [Sm2(Cp*)4N2] First N22- complex of a Ln ion Sm-C 2.73 Å Sm-N 2.36 Å N-N 1.09 Å similar to N2 ? W. J. Evans et al., J. Am. Chem. Soc. 1988, 110, 6877 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 36 Chapter 4 Organometallics An O2- bridging ligand: [SmIII(Cp*)2-O-SmIII(Cp*)2 2 [SmII(Cp*)2(thf)2] + N2O [SmIII2(Cp*)4(m-O)] + N2 Sm-O Sm-C 2.09 Å 2.74 Å In fact, many O-containing substrates produce this compound (NO, thf, a.s.o) W. J. Evans et al., J. Am. Chem. Soc. 1985, 107, 405 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 37 Chapter 4 Organometallics Insertion of trans-azobenzene: [SmII2(Cp*)4N2Ph2] 2 [SmII(Cp*)2(thf)2] +N2Ph [SmIII2(Cp*)4(m-h1:h1-N2Ph2)] Magnetic data indicate the presence of SmIII (1.9 M.B.) blue Sm-C Sm-N N-N Sm-H distances (ortho position) are close to agostic interaction 2.74 Å 2.40 Å 1.25 Å, identical to neutral N2Ph2 expected distance: 1.44 Å W. J. Evans et al., J. Am. Chem. Soc. 1988, 110, 4983 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 38 Chapter 4 Organometallics Insertion of CO: [SmII2(Cp*)4Phe2N2] + 2 CO [SmII2(Cp*)4Phe2N2] (in thf) green C2h W. J. Evans et al., J. Am. Chem. Soc. 1988, 110, 4983 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 39 Chapter 4 Organometallics Chalcogenolate complexes: [SmII(Cp*)2(thf)2] + PhEEPh [SmIII2(Cp*)4(PhE)2] + 2 thf E = S, Se, Te orange [SmIII2(Cp*)4(PhS)2] Sm-S 2.76 Å W.J. Evans et al., Inorg. Chem. 2005, Published on the web, May 13 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 40 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 41