Lanthanoid Biphenolates as a Rich Source of Lanthanoid‐Main Group Heterobimetallic Complexes

Abstract

Several new trivalent dinuclear rare earth 2,2'methylenebis(6-tert-butyl-4-methylphenolate) (mbmp 2À ) complexes with the general form [Ln 2 (mbmp) 3 (thf) n ] (Ln = Sm 1, Tb 2 (n = 3), and Ho 3, Yb 4 (n = 2), and a tetravalent cerium complex [Ce(mbmp) 2 (thf) 2 ] (5) have been synthesised by RTP (redox transmetallation/protolysis) reactions from lanthanoid metals, Hg(C 6 F 5 ) 2 and the biphenol mbmpH 2 . These new complexes and some previously reported partially protonated rare earth biphenolate complexes [Ln(mbmp)(mbmpH)(thf) n ] react with lithium, aluminium, potassium and zinc organometallic reagents to form lanthanoid-main group heterobimetallic species. When reaction mixtures containing the Ln biphenolate complexes were treated with n-butyllithium, both molecular ([Li(thf) 2 Ln(mbmp) 2 (thf) n ] (Ln = La 6, Pr 7 (n = 2) and Er 8, Yb 9, and Lu 10 (n = 1)) and charge separated ([Li(thf) 4 ][Ln(mbmp) 2 (thf) 2 ] (Ln = Y 11, Sm 12, Dy 13, and Ho 14) complexes were isolated. Treatment with trimethylaluminium also led to isolation of molecular ([AlMe 2 Ln-(mbmp) 2 (thf) 2 ] (Ln = Pr 15, Sm 16, and Tb 17)) and ionic [La(mbmp)(thf) 5 ][AlMe 2 (mbmp)] ( 18) complexes. One gadolinium-potassium ([K(thf) 3 Gd(mbmp) 2 (thf) 2 ] ( 19)), and one ytterbium-zinc species ([ZnEtYb(mbmp) 2 (thf)] ( 20)) were isolated from treatment of reaction mixtures with potassium bis(trimethylsilyl)amide and diethylzinc respectively.

Carbon bridged biphenolate ligands in rare earth chemistry

“…When treating the [Ln(mbmp)(mbmpH)(thf) 3 ] (Ln = Y, Dy, Er and Lu) complexes with n -butyllithium as an organometallic base, they formed either a molecular complex [Li(thf) 2 Ln(mbmp) 2 (thf)] (Ln = Er and Lu) or an ionic complex [Li(thf) 4 ][Ln(mbmp) 2 (thf) 2 ] (Ln = Y and Dy) (Scheme 23). 38 Although the reactivities can be correlated with a change in size of the trivalent ion, a break between Y 3+ and Er 3+ is a surprise.…”

“…The gadolinium complex [Gd(mbmp)(mbmpH)(thf) 3 ] readily reacts with K{N(SiMe 3 ) 2 } to form the heterobimetallic [K(thf) 3 Gd(mbmp) 2 (thf) 2 ] (Scheme 24). 38…”

“…Using the same RTP approach and reaction conditions as those used for the synthesis of partially protonated [Ln(mbmp)(mbmpH)(thf) 3 ] complexes (Scheme 21), dinuclear complexes of the general form [Ln 2 (mbmp) 3 (thf) n ] (Ln = Sm, Tb ( n = 2), and Ho, Yb ( n = 3)) are synthesised (Scheme 25). 38 Importantly, these reaction conditions left one unreacted equivalent of mbmpH 2 in solution. Whilst it was previously thought that the nuclearity of the complex was dictated by the ionic radius of the metal centre, there appears to be no correlation with these newly described species.…”

“…When treated with n BuLi in the presence of one equivalent of mbmpH 2 , [Yb 2 (mbmp) 3 (thf) 2 ] underwent redistribution to form the heterobimetallic [Li(thf) 2 Yb(mbmp) 2 (thf)], whereas [Ln 2 (mbmp) 3 (thf) n +1 ] (Ln = Sm, n = 2, and Ln = Ho, n = 1) complexes gave the ionic heterobimetallic complexes [Li(thf) 4 ][Ln(mbmp) 2 (thf) 2 ] (Scheme 26). 38…”

“…Less common variations involve heterobimetallic species where the auxiliary metal coordinates to the bridging phenolate oxygens such as [Ln(mbmp) 2 M] 31 (Fig. 3 – I X ) and [Ln 2 (mbmp) 4 M] 37,38 (Fig. 3 – X ).…”