Ring-Opening of a Furyl Group Appended to the Cyclopentadienyl Ligand in Rare-Earth Metal Half-Sandwich Complexes

Abstract

A series of scandium, lutetium, and yttrium complexes containing a tetramethylcyclopentadienyl ligand with a pendant furyl group, [Ln{η5-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)2(THF)] (Ln = Sc, Lu, Y; R = H, Me), have been synthesized and structurally characterized. Single-crystal X-ray diffraction studies of the scandium complexes [Sc{η5-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)2(THF)] (R = H, Me) revealed a pseudo-four-coordinate metal center without additional coordination of the furyl group. The previously elusive lutetium complex [Lu{η5-C5Me4SiMe2(C4H2MeO-2)}(CH2SiMe3)2(THF)] could be isolated and exhibited structural features analogous to those of the scandium compound. Variable-temperature 1H NMR spectroscopic studies of the entire series confirmed the labile nature of both the THF ligands and furyl donor in solution. Rates for the ring-opening reaction, triggered by intramolecular C−H bond activation, were shown to depend primarily on the metal size. The ring-opening reaction resulted in the formation of the corresponding dinuclear yne−enolate complexes [Ln{η5:η1-C5Me4SiMe2(C⋮CCHCRO)}(CH2SiMe3)]2 (Ln = Sc, Lu, Y; R = H, Me). Substitution at the 5-furyl position did not markedly influence the rate of the ring-opening reaction but shifted the position of the monomer−dimer equilibrium toward the monomer. Only a large excess of THF allowed the observation of monomeric yne−enolate complexes such as [Y{η5:η1-C5Me4SiMe2(C⋮CCHCHO)}(CH2SiMe3)(THF)2], which was characterized by X-ray crystallography. Addition of THF increased the stability of the lutetium bis(alkyl) complexes and allowed the formation of the corresponding cationic compounds by treatment with [NEt3H][BPh4] to yield [Lu{η5:η1-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)(THF) n ][BPh4] (Ln = Lu; R = H, Me), which resisted ring- opening of the furyl group.

Homoleptic Rare-Earth Metal Complexes Containing Ln−C σ-Bonds

“…Mono(cyclopentadienyl) complexes 51 and 53 can undergo hydrogenolysis of both alkyl ligands, affording isolable hydrido clusters. ,,, The in situ generation of cationic mono(cyclopentadienyl) rare-earth metal complexes by alkyl abstraction using borate reagents [Ph 3 C][B(C 6 F 5 ) 4 ] and [PhNMe 2 H][B(C 6 F 5 ) 4 ], respectively, results in highly active polymerization catalysts (Table ). Scandium bis(alkyl) complex 51 Sc shows excellent activity for the syndiospecific styrene homopolymerization (activity, 1.36 × 10 4 (kg PS)/(mol Sc h); M w / M n = 1.37), and complexes 51 , 53 , and 54 proved suitable for the co- and terpolymerization of a series of monomers. ,,− …”

“…Scandium bis(alkyl) complex 51 Sc shows excellent activity for the syndiospecific styrene homopolymerization (activity, 1.36 × 10 4 (kg PS)/ (mol Sc h); M w /M n ) 1.37), and complexes 51, 53, and 54 proved suitable for the co-and terpolymerization of a series of monomers. 204,206,[210][211][212][213][214][215][216][217][218][219][220][221][222][223][224][225]…”

Ring-Opening Reactions of Aromatic N-Heterocycles by Scandium and Yttrium Alkyl Complexes

“…In some cases, metal complexes employing only σ bonds are able to ring-open oxygen or sulfur-containing heterocycles . However, to date, the most difficult case of ring opening, the cleavage of the C−N bonds in aromatic heterocycles, has been restricted to the involvement of metal−element multiple bonds.…”

Quinoline Ring C−H Bond Activation in Bis(3,5-di-tert-butylsalicylidene)-8-aminoquinoline Bis(trimethylsilyl)amido Lanthanide Complexes

“…Intra- and intermolecular C−H bond activations via σ-bond metathesis by lanthanide alkyls and hydrides have made great progress; an outstanding example of the activation of the normally inert C−H bond of methane by lanthanocene alkyl complex was reported by Watson . Various lanthanocene alkyl or hydride complexes, half-sandwich complexes, and non-cyclopentadienyl-supported analogues have been found to be able to attack the electron density of C−H bonds, thus forming agnostic interactions and activating these bonds. Moreover, the C−H bond activation and subsequent functionalization of hydrocarbon by lanthanocene alkyl complexes ,,,, and the counterparts bearing non-cyclopentadienyl ligands − ,− have recently been explored.…”