Carbon bridged biphenolate ligands in rare earth chemistry

Rare earth biphenolate species have become an increasingly studied series of complexes, owing to the diversity they offer over mononuclear aryloxide complexes, as well as their efficacy as catalysts and initiators in a range of organic transformations and polymerisation reactions. Compared to monodentate aryloxide ligands, biphenolate ligand systems are still in their infancy in rare earth coordination chemistry. In their limited use, the ligand 2,2 '-methylenebis(6-tert-butyl-4-methylphenol) (mbmpH(2)) has been a popular candidate. This review aims to highlight the chemistry that has been explored thus far with these carbon bridged lanthanoid biphenolate systems

Synthesis and characterisation of divalent di(1,3-bis(diphenylphosphano)cyclopentadienyl)lanthanoid and alkaline earth complexes as potential platforms for heterometallic complexes

New divalent lanthanoid and alkaline earth metal complexes bearing the 1,3-bis(diphenylphosphano)cyclopentadienyl ligand have been synthesised using the redox-transmetallation protolysis (RTP) approach. From the reaction of the corresponding metal, diphenylmercury and the proligand C5H4(PPh2)2, the compounds [M(η5-C5H3(PPh2)2-1,3)2(S)] (with M=Yb, S=(thf)2 or M=Yb, Eu, Ca, Sr, Ba, S=dme) were isolated and characterised by X-ray diffraction and multinuclear NMR spectroscopy. These compounds may provide a platform for early-late heterobimetallic complexes

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

Several new trivalent dinuclear rare earth 2,2’-methylenebis(6-tert-butyl-4-methylphenolate) (mbmp²¯) complexes with the general form [Ln₂(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(C₆F₅)₂ and the biphenol mbmpH₂. 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)₂Ln(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 ([AlMe₂Ln(mbmp)₂(thf)₂] (Ln=Pr 15, Sm 16, and Tb 17)) and ionic [La(mbmp)(thf)₅][AlMe₂(mbmp)] (18) complexes. One gadolinium-potassium ([K(thf)₃Gd(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

Selective carbon-phosphorus bond cleavage: expanding the toolbox for accessing bulky divalent lanthanoid sandwich complexes

The synthesis of two new tetra- and penta-phenycyclopentadienyldiphenylphosphine pro-ligands which readily undergo selective C–P bond cleavage has allowed for the facile synthesis of bulky divalent octa- and deca-phenylmetallocenes of europium, ytterbium and samarium

New lanthanoid biphenolate complexes, their further reactivity with trimethylaluminium and catalytic activity for the polymerisation of rac-lactide

A series of rare earth biphenolate complexes of the general form [Ln(mbmp)(mbmpH)(thf)3] (Ln = Y (1), Nd (2), Gd (3), Dy (4), Er (5), Tm (6) and Lu (7)) have been synthesised by redox transmetallation/protolysis (RTP) from the free rare earth metal, Hg(C6F5)2 and 2,2′-methylenebis(6-tert-butyl-4-methylphenol) (mbmpH2). The rare earth metal is six coordinate with one chelating biphenolate mbmp2- ligand and one unidentate monophenolate mbmpH- ligand. The yttrium complex, when crystallised from hot toluene or deuterated benzene, loses a coordinated thf and exhibits coordination through all three phenolate oxygen atoms, as well as the oxygen of the phenol, yielding two solvates [Y(mbmp)(mbmpH)(thf)2]·nsolv (solv = PhMe, n = 1 (8a) or C6D6, n = 2 (8b)). Of these rare earth complexes, the yttrium derivative (1) yielded the heterobimetallic complex [AlMe2Y(mbmp)2(thf)2] (9) when treated with trimethylaluminium, whereas all other complexes produced the transmetallation product [AlMe(mbmp)(thf)] (11). The dinuclear dysprosium complex [Dy2(mbmp)3(thf)3] (10) was isolated alongside 11 from the reaction of 4 with trimethylaluminium, suggesting trimethylaluminium instigates a redistribution reaction. The ROP activity of the mononuclear neodymium, dysprosium, lutetium, and aluminium complexes towards rac-lactide in toluene at 70 °C was found to be poor compared to rare earth complexes of monodentate aryloxides, but increased with increased rare earth ion size