Developing lanthanide single molecule magnets through methanediide-, nitrido- and boryloxy-based ligands

A family of bis-SCS (SCS = [C{P(Ph)2S}2]) lanthanide methanediide compounds with the general formula [Ln(SCS)2(M(seq)x)] (where M = alkali metal and seq = sequestering agent) was prepared following the deprotonation of a methanide-methanediide with a range of alkali metal benzyl reagents. Different sequestering agents were employed, which altered the coordination mode of the alkali metal along with the C=Ln=C bond angle. Extensive magnetic analysis was carried out on 24, 25-Dy, 26-Dy, which showed Ueff barriers of around 1000 K and TB around 12-15 K. Comparison of this system to an analogous imino-supported system revealed the first clear example of weakening the equatorial field on lanthanide SMM performance. The positive correlation of C=Dy=C bond angle to Ueff barrier within the bis-SCS system was the first to demonstrate the effect of linearity on SMM properties. [Y(BIPM)(DME)2][BPh4] (40) was prepared as a potential precursor to a lanthanide-BIPM-LUVN system through protonation of an yttrium-methanediide-benzyl species. Consequent attempts to coordinate [LUVN] to yttrium were unsuccessful due to the redox activity of uranium and the fragility of DME molecules within the system, resulting in [Y(BIPMH)(X)(µ-OMe)]2 (42) (where X is unknown), [K(DB15C5)2][BPh4] (41) and [LUVIN]. A bis-uranium bridging-nitride TrenTIPS yttrium-inserted system ([U2Y]) (48) was synthesised in the attempted preparation of a [Ln(LUVN)2(Me)] system due to one electron reduction of a uranium centre through reductive cleavage of a methyl group from the yttrium starting material. A borohydride-based lanthanide system was then used to avoid such a problem, which led to the synthesis of [LUVNLn(BH4)3][K(B15C5)2] (55). Magnetic analysis of this compound shows SMM behaviour, with slow relaxation up to 16 K. A new boryllithium reagent [(HCTrippN)2B(Li)(THF)2] was prepared and used with lanthanide starting materials in pursuit of [Ln((HCTrippN)2B)2(X)]. Following the expected transient formation of an unstable [Ln((HCTrippN)2B)2(X)], decomposition occurred to produce [(HCTrippN)2B(H)] as seen by 1H and 11B NMR. Subsequently, a boryloxy compound [(HCDippN)2BO]- was used to prepare [Y(BIPM)(BO)(THF)] (70) through a salt metathesis reaction as well as [Al(BO)2(Cl)(MeCN)] (71) following side reactivity with [Y(MeCN)9][AlCl4]3. Furthermore, the use of fluoride-containing WCAs in systems with [(HCDippN)2BO]- as a ligand resulted in the preparation of [(HCDippN)2BF] (72), highlighting the B-F bond strength. Using [Ln(BH4)3(THF)3], [Ln(BO)2(BH4)(THF)2] (74) was then prepared, with the BH4 group then abstracted to give [Ln(BO)2(THF)4][BPh4] (76). Analysis of the magnetometry of this compound showed slow relaxation up to around 100 K which corresponds to a Ueff barrier of around 894 K.