Tris(indenyl)lanthanoid(III) Sulfoxide Adducts (1:1) in the Solid State and in Solution: Ligand Chirality as a Powerful Diagnostic Tool for Rapid Intermolecular Sulfoxide Exchange and Indenylη5⇌η1 Fluxionality

Abstract

H NMR and f ± f circular dichroism (CD) spectroscopy indicate that a second chirogenic centre is generated that lies closer to the metal ion than the chiral sulphur atom of the MTSO ligand. In strict contrast, the congeners with Cp C 5 H 5 (Ln Pr, Nd, Yb) are practically CD-silent, although again the LnÀO distances are shorter by about 10 pm than in the corresponding THF adducts. Surprisingly, the NMR spectra of solutions of mixtures of [Ln(C 9 H 7 ) 3´M TSO] complexes with (R)-()-and (S)-(À)-MTSO, or/and with two different metals reveal rapid intermolecular sulphoxide exchange. On the other hand, mutual MTSO/THF exchange seems to be inhibited, which suggests that the facile sulphoxide exchange follows a special mechanistic pathway.

Tris(indenyl)lanthanoid Complexes (Ln = La, Pr, Nd) Containing either (S)-(−)-Nicotine or Two Simpler Pyridine Bases

“…Moreover, a chiral Lewis base L is also expected to control the chirality of the {Ln(Ind) 3 X} fragment [7] (X is the ligand atom that is bonded to the metal centre), provided that the chiral centre of the base resides only two bonds away from the metal centre, as in chiral sulfoxides [10] and 2-methyltetrahydrofuran. [11a] In the present study, our interest will be focused on whether a chiral centre located about twice as far from the metal centre than that in the recently investigated methyl tolyl sulfoxide (MTSO) adducts, [10] would still exert any detectable configuration controlling or electronic influence. While the chiral sulfur atom formational variations emerge from the crystal structure analyses.…”

“…This compares reasonably with corresponding results for [La(C 5 H 5 ) 3 ·THF] (δ ϭ Ϫ558, 450 Hz) and [La(C 5 H 5 ) 3 ·MTSO] (δ ϭ Ϫ563, 390 Hz). [8,10] In the 1 H NMR spectrum of 1, all the resonances for the nicotine protons were assigned in a similar manner to those in the 1 H NMR spectrum of a previously reported paramagnetic [PrCp 3 ·Nic] complex. [6] However, several lines in the 1 H NMR spectrum of 1 are overlapping.…”

“…The nicotine adducts appear to be thermally more stable (under N 2 ) than their corresponding MTSO congeners. [10] In the mass spectra of all three complexes, signals corresponding to the metal-containing fragments [Ind n Ln] ϩ with n ϭ 3, 2, 1, and 0 were found. Several weaker peaks assigned to purely organic fragments such as [Ind] 139 La NMR spectroscopic studies of 2 show that the signal is considerably broadened with decreasing temperature.…”

“…Ϫ450 2480 [10] Another interesting feature of the nicotine complexes 2Ϫ4 is that their melting points are quite low (2: 94Ϫ98; 3: 129Ϫ132; 4: 112Ϫ116°C). Only the melting point of 3 compares with those of the reported [Ln(Ind) 3 ·MTSO] systems.…”

“…[5,6] Our current interest in the structural details of diverse [(Ind) 3 Ln·Py*] systems results from more recent observations in which the three bulky benzo groups of the indenyl units may be oriented in various different ways [7Ϫ9] depending on the actual bulkiness of the metal-coordinated Lewis base. Moreover, a chiral Lewis base L is also expected to control the chirality of the {Ln(Ind) 3 X} fragment [7] (X is the ligand atom that is bonded to the metal centre), provided that the chiral centre of the base resides only two bonds away from the metal centre, as in chiral sulfoxides [10] and 2-methyltetrahydrofuran. [11a] In the present study, our interest will be focused on whether a chiral centre located about twice as far from the metal centre than that in the recently investigated methyl tolyl sulfoxide (MTSO) adducts, [10] would still exert any detectable configuration controlling or electronic influence.…”