Heteroleptic lanthanide(III) complexes: synthetic utility and versatility of the unsubstituted bis-scorpionate ligand framework

Abstract

The unsubstituted bis-hydrotris(1-pyrazolyl)borate) (Tp) ligand framework has been used to synthesise a range of heteroleptic Ln(III) coordination complexes [Ln(Tp)2(X)]. The precursor complexes [Ln(Tp)2(OTf)] 1-Ln (Ln = Y, Eu, Gd, Yb; OTf = triflate) were synthesised by reaction of Ln(OTf)3 with two equivalents of K(Tp). The 8-coordinate β-diketonate complexes [Ln(Tp)2(hfac)] 2-Ln (Ln = Y, Eu, Yb; hfac = hexafluoroacetylacetonate) were synthesised from Ln(OTf)3 by reacting 1-Ln generated in situ with an equivalent of K(hfac). The 7-coordinate amide complexes [Ln(Tp)2(N″)] 3-Ln (Ln = Y, Yb; N″ = bis(trimethylsilyl)amide) were synthesised from 1-Ln by reaction with K(N″). Reactivity of 3-Ln towards protonolysis was demonstrated by the isolation of the hydroxide dimer [{Y(Tp)2(μ-OH)}2] 4-Y from adventitious reaction with water and the aryloxide complex [Ln(Tp)2(OAr)] 5-Ln (Ln = Y, Yb; OAr = 2,6-tBu2-4-Me-phenoxide) from reaction with H(OAr). Full characterisation data are presented for all complexes, including solid-state molecular structure determination by single-crystal X-ray diffraction.

Reduction chemistry yields stable and soluble divalent lanthanide tris(pyrazolyl)borate complexes

“…All data are consistent with the lanthanide contraction 25 and the increase in ionic radius upon reduction from Ln( iii ) to Ln( ii ). 13 In the absence of coordinating solvents, complex 1-Eu (a) is an unusual example of a dimeric structure, whereas complex 1-Yb (b) is monomeric as expected. 6 a , c , d , f In 1-Eu (a) each Eu( ii ) is bound by a κ 3 -Tp ligand and an μ-κ 1 : η 5 Tp ligand.…”

“…The IR spectra of 1-Ln are near-identical, with weak absorptions between 2350–2560 cm −1 assigned to the ν BH of the Tp ligands. 6 d , f ,13 The IR data for 1-Ln(OPPh 3 ) 2 are consistent with 1-Ln but additionally display strong ν PO at 1117 cm −1 . The ν PO is shifted from 1184 cm −1 in free Ph 3 PO to lower wavenumbers upon coordination to the Ln( ii ).…”

“…We therefore explored the reduction chemistry of our Ln(III) (Ln = Eu, Yb) precursors with various reductants. Our previous work on the metathesis chemistry of [Ln(Tp) 2 (OTf)] 13 had shown that elimination of K(OTf) in noncoordinating solvents was most effective, and this is also the case for the reduction chemistry. Neither clean reduction nor K(OTf) elimination could be achieved in ethereal solvents (see Fig.…”

“…Moreover the THF-adduct complexes [Ln(Tp) 2 (THF) 2 ] were reported to be unstable in solution. 6 b ,12 Here we report the reduction chemistry of the heteroleptic Ln( iii ) precursors [Ln(Tp) 2 (OTf)], 13 to synthesise stable adduct-free homoleptic Ln( ii ) complexes [Ln(Tp) 2 ] 1-Ln (Ln = Eu, Yb), and Ph 3 PO adduct complexes 1-Ln(OPPh 3 ) 2 .…”

Lanthanide Amide Complexes Supported by the Bis‐tris(pyrazolyl)borate Ligand Environment

“…[14] The smaller unsubstituted hydrotris(1-pyrazolyl)borate (Tp) ligand can be utilised to overcome this steric limitation, and the Ln(III) complexes [Ln(Tp) 2 (N'')] (Ln = Y, Yb) were reported recently. [15] The primary lanthanide Ln(II) amide complexes with one Tp R ancillary ligand, [Ln(Tp tBu,Me )(NHR)(do) x ] (Ln = Sm, Eu, Yb; R = Dipp or C 6 H 3 i Pr 2 -2,6, Ar Me or C 6 H 3 Me 2 -2,6, Ar CF3 or C 6 H 3 (CF 3 ) 2 -3,5, SiPh 3 ; do = THF; x = 0, 1, or 2), [16] the Ln(III) complexes [Lu-(Tp tBu,Me )(NHR)(CH 3 )] (R = t Bu, adamantyl) [17] and [Y-(Tp*)(NHR)(CH 2 Ph)(THF)] (R = Ph, Dipp) [18] have been reported. In the case of the putative Tm(II) [Tm(Tp tBu,Me )(NHC 6 H 3 (2,5-t Bu 2 ))], dinitrogen activation was observed.…”