Rare-earth Metal Bis Research Articles

Rare-Earth Metal Complexes Supported by A Tridentate Amidinate Ligand: Synthesis, Characterization, and Catalytic Comparison in Isoprene Polymerization.

To systematically investigate the dependence of the initiating group and metal size on polymerization performance, a family of rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes supported by a monoanionic tridentate amidinate ligand [(2,6-iPr2C6H3)NC(Ph)N(C6H4-2-OMe]- (HL) were synthesized and well-characterized. Treatment of rare-earth metal tris(alkyl)/tris(benzyl)/tris(amide) complexes Y(CH2C6H4NMe2-o)3 or Y(CH2SiMe3)3(THF)2 or Ln[N(SiHMe2)2]3(THF)x (Ln = Sc, x = 1; Ln = Y, La, Sm, Lu, x = 2) with 1 equiv of HL gave the corresponding mono(amidinate) rare-earth metal bis(alkyl)/bis(benzyl)/bis(amide) complexes [(2,6-iPr2C6H4)NC(Ph)N(C6H4-2-OMe)]Y(CH2C6H4NMe2-o)2 (1), [(2,6-iPr2C6H4)NC(Ph)N(C6H4-2-OMe)]Y(CH2SiMe3)2(THF) (2), and [(2,6-iPr2C6H4)NC(Ph)N(C6H4-2-OMe)]Ln[N(SiHMe2)2]2(THF)n (Ln = Y, n = 1 (3); Ln = La, n = 1 (4); Ln = Sc, n = 0 (5); Ln = Lu, n = 0 (6); Ln = Sm, n = 0 (7)) in good isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction. In the presence of excess AlMe3 and on treatment with 1 equiv of [Ph3C][B(C6F5)4], these complexes could serve as precatalysts for cationic polymerization of isoprene, in which the dependence of the polymerization activity and regioselectivity on the initiating group and metal size was observed.

High cis-1,4-selectivity and activity coordination (co) polymerization of (polar) dienes by PNP-ligated rare-earth metal bis (aminobenzyl) complexes

The research on the synthesis of cis-1,4-selective poly (conjugated diene)s catalyzed by the transition metal complexes has been actively pursued in both industrial and academic laboratories until today. However, there has not been any reported rare-earth catalytic system that can achieve the cis-1,4-selective polymerization of multiple conjugated dienes. Polar and non-polar conjugated dienes, as well as copolymerization of different kinds of conjugated dienes affording novel copoly (diene)s, are included. Herein, the highly cis-1,4-selective homopolymerization of a series of (polar)dienes (such as IP, MY, OC, 2-MOPB, 2-FPB) was achieved by using PNP ligated rare-earth metal bis (aminobenzyl) complexes PNP-Ln (Ln = Ln = Sc, Lu, Y, Gd, Sm, 1-5)/[Ph3C][B(C6F5)4]/Al i Bu3 ternary catalyst systems. Moreover, the highly cis-1,4-selective copolymerization of (polar)dienes (such as 2-MOPB and IP, 2-FPB and IP, MEPB and IP, OC and IP as well as 2-FPB and MY) with a board range of comonomers contenting and random or block sequence distribution was also achieved.

Syndiospecific Copolymerization of Styrene with para-Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes.

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl3 with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH2PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH2SiMe3 in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH2Py)Ln(CH2SiMe3)2(THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y3+ in the η5/κ1 mode to form a constrained geometry configuration. In the presence of excess AliBu3, and on activation with 1 equiv of [Ph3C][B(C6F5)4] in toluene, complexes 1 and 2 became active for both styrene (St) and para-methoxystyrene (pMOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/AliBu3/[Ph3C][B(C6F5)4] was highly effective for the syndiospecific copolymerization of styrene with pMOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of pMOS in the copolymers could be easily tuned in a wide range (11-93 mol %) by simply changing the pMOS-to-St feed ratios.

Phosphine-functionalized amidinate ligated rare-earth metal complexes for highly 3,4-selective living polymerization of 1,3-conjugated dienes.

A series of rare-earth metal bis(alkyl) complexes have been prepared via protonolysis reactions of tris(aminobenzyl) complexes (Ln(CH2C6H4N(Me)2-o)3) with phosphine-functionalized amidinated ligands (DippNCN(CH2)nPPh2, n = 2 (L1-H) and n = 3 (L2-H)). The X-ray diffraction of P2-Sc (DippNCN(CH2)3PPh2Sc(CH2C6H4N(Me)2-o)2) showed the un-coordination of the diphenylphosphine group due to the inherent saturation of the central metal ion. In conjunction with [Ph3C][B(C6F5)4], all the rare-earth metal complexes showed a high catalytic activity for the polymerization of 1,3-conjugated dienes (isoprene, β-myrcene and β-farnesene), affording highly 3,4-regular polymers (up to 100% 3,4-) with high molecular weight and narrow molecular weight distribution. After the abstraction of the alkyl moiety -CH2C6H4N(Me)2-o of P1-Sc by [Ph3C][B(C6F5)4], the species with the coordination of the diphenylphosphine group to the central metal probably formed, as shown in the 31P NMR spectra and DFT calculation results, and it might serve as the true active species in the 3,4-selective polymerization of 1,3-conjugated dienes.

Synthesis, characterization and ε-caprolactone polymerization properties of ferrocenyl modified half-sandwich rare-earth metal complexes

Salt metathesis of RECl3 with FcC5Me4Li followed by the addition of LiCH2C6H4NMe2-o in THF gave the ferrocenyl functionalized half-sandwich rare-earth metal bis(o-dimethylaminobenzyl) complexes (FcC5Me4)RE(CH2C6H4NMe2-o)2 (RE = Sc, Y, Lu) in good isolated yields.

Two Rare-Earth Complexes (Sm, La) Based on a Carbon-Bridged Bis(phenolate): Synthesis and Crystal Structures

Two rare earth metal complexes based on the carbon-bridged bis(phenolate) ligand, 2,2'-methylene-bis(6-tert-butyl-4-methyl-phenoxo) (LH2), have been synthesized. Reaction of LH2 with (C5H5)3Sm(THF) in a 1.5 : 1 molar ratio in THF at 50°C produced rare earth metal bis(phenolate) complex (C5H5)Sm(L)(THF)2 (I) in almost quantitative yields. Complex I reacted with 0.5 molar ratio of LH2 in toluene at 80°C afforded (L)Sm(LH)(THF)2 (II) as the final product in good yield. Reaction of LNa2 with LaCl3 in a 2 : 1 molar ratio in THF at room temperature produced hetero-nuclear rare earth metal bis(phenolate) complex (L)La(LH)(THF)2Na(THF)2 (III). In addition, II and III were characterized by X-ray single-crystal diffraction analysis (CIF file CCDC nos. 1500917 (II) and 1826699 (III)) as well as characterizations including elemental analyses and IR spectra of both complexes. Furthermore, detail reasons of the difference of structures are presented. The ionic radii of the rare earth metal plays a significant role in the structure difference of two complexes.

Substituent Effects of Pyridyl-methylene Cyclopentadienyl Rare-earth Metal Complexes on Styrene Polymerization

Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl3 followed by the addition of two equivalents of LiCH2SiMe3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl) complexes (Cp′CH2- Py)Ln(CH2SiMe3)2(THF)n (Py = C5H4N, Cp′ = C5H4 (Cp), Ln = Sc, n = 0 (1); Cp′ = C9H6 (Ind), Ln = Sc, n = 0 (2); Cp′ = 3-Me3Si-C9H5 (3-Me3Si-Ind), Ln = Sc, n = 0 (3a), Ln = Lu (3b), Y (3c), n = 1; Cp′ = 2,7-(tBu)2C13H8 (2,7-(tBu)2-Flu), Ln = Sc (4a), n = 0, Ln = Lu (4b), Y (4c), n = 1) in moderate to good yields, which were characterized by NMR spectroscopy and single-crystal X-ray diffraction (for complex 3a). In the presence of [Ph3C][B(C6F5)4] and AliBu3, these complexes displayed different performances towards styrene polymerization. Rare-earth metal bis(alkyl) precursors bearing Cp, Ind, and 3-Me3Si-Ind segments exhibited very low catalytic activity to afford syndiotactic polystyrene. All electron-donating tBu substituted complexes 4a, 4b, and 4c showed very high activity and perfect syndiotactivity (rrrr > 99%), producing high molecular weight polystyrene (up to 54.1 × 104) with relatively narrow molecular distribution (PDI = 1.28−2.49).

Syndio-specific polymerization of styrene promoted by rare-earth metal bis(aminobenzyl) complexes bearing pyrrolyl-modified arylamide ligands

Acid-base reaction of the rare-earth metal tris(o-dimethylaminobenzyl) complexes Ln (CH2C6H4NMe2-o)3 with 1 equiv. of the pyrrolyl-modified arylamide ligands 2,5-Me2C4H2NSiMe2NHC6H4R (R = H, Cl-p, OMe-p) in toluene gave (2,5-Me2C4H2NSiMe2NC6H5)Ln (CH2C6H4NMe2-o)2 (Ln = Sc (1), Y (2), Lu (3)), (2,5-Me2C4H2NSiMe2NC6H4Cl-p)Y(CH2C6H4NMe2-o)2 (4), and (2,5-Me2C4H2NSiMe2NC6H4OMe-p)Y(CH2C6H4NMe2-o)2 (5) in good isolated yields. These complexes were well-characterized by elemental analysis and NMR spectroscopy. 1, 2 and 4 were structurally determined by single crystal X-ray diffraction. The catalyst systems of 1–5/AliBu3/[Ph3C][B(C6F5)4] were able to promote styrene polymerization to afford pure and highly syndio-tactic polystyrene (rrrr > 99%). Among these rare-earth metal complexes, the complexes with the central metal being the cheapest yttrium showed much higher activity than the expensive scandium analogues. The styrene polymerization catalyzed by 4/AliBu3/[Ph3C][B(C6F5)4] proceeded in a controlled fashion.

Synthesis, characterization and reactivity of rare-earth metal amide complexes supported by pyrrolyl-substituted cyclopentadienyl ligand

Absaact Amine elimination between rare-earth metal tris(amide) complexes Ln [N(SiHMe2)2]3 (THF)x and 1 equiv. of pyrrolyl-substituted cyclopentadienyl ligand C4H4NSiMe2C5Me4H was investigated. Reaction of C4H4NSiMe2C5Me4H and Ln [N(SiHMe2)2]3 (THF)x with small metals afforded the half-sandwich rare-earth metal bis(silylamide) complexes (C4H4NSiMe2C5Me4)Ln [N(SiHMe2)2]2 (Ln = Sc (1), Y (2)), while the same reaction using La [N(SiHMe2)2]3 (THF)2 isolated lanthanum mono-silylamide complex [C5Me4SiMe2N(SiHMe2)2]La [N(SiHMe2)2](C4H4N) (3). These complexes were characterized by elemental analysis and NMR spectroscopy. 1 and 3 were structurally authenticated by single crystal X-ray diffraction. The ternary catalyst systems of 1 or 2/AliBu3/[Ph3C][B(C6F5)4] showed activity towards styrene polymerization to give pure syndio-tactic polystyrenes (rrrr > 99%).

Rare-earth metal bis(aminobenzyl) complexes supported by pyrrolyl-functionalized arylamide ligands: synthesis, characterization and styrene polymerization performance.

An acid-base reaction between the rare-earth tris(o-dimethylaminobenzyl) complexes Ln(CH2C6H4NMe2-o)3 and the pyrrolyl-functionalized arylamide ligands 2,5-Me2C4H2NCH2SiMe2NHC6H4R (R = H, (HL1); R = Cl-p, (HL2)) was investigated. Treatment of HL1 and HL2 with 1 equiv. of Ln(CH2C6H4NMe2-o)3 in toluene at room temperature gave (2,5-Me2C4H2CH2NSiMe2NC6H5)Ln(CH2C6H4NMe2-o)2 (Ln = Sc (1), La (2), Lu (3)) and (2,5-Me2C4H2NCH2SiMe2NC6H4Cl-p)Ln(CH2C6H4NMe2-o)2 (Ln = Sc (4), La (5), Lu (6)) in good isolated yields. These complexes were characterized by elemental analysis and NMR spectroscopy. 2, 4 and 5 were structurally authenticated by single crystal X-ray diffraction. NMR and X-ray diffraction show that there are no interactions between the central metal and the pyrrolyl moiety in small sized metal complexes, while in large lanthanum complexes, besides the coordination of the arylamide moiety to La3+ in η1-bonding mode through a N atom, the pyrrolyl ring also has close contact with La3+ in 2 and 5. The binary systems of 1-6/[Ph3C][B(C6F5)4] were employed as catalysts for syndio-specific polymerization of styrene, and the pyrrolyl-ligated lanthanum complexes showed much higher activity than the complexes in which the pyrrolyl moiety had no coordination with the central metal.

Rare-earth metal bis(silylamide) complexes supported by ferrocene-substituted amidinate and their performance in cis-1,4 selective polymerization of isoprene

Amine elimination of rare-earth metal tris(silylamide) complexes Ln[N(SiHMe2)2]3(THF)n (Ln = Sc, n = 1; Ln = Y, Lu, n = 2) with 1 equiv. of the ferrocene-substituted amidine FcC(NCy)NHCy (Fc = ferrocenyl, Cy = cyclohexyl) afforded the mono(amidinate) rare-earth metal bis(silylamide) complexes [FcC(NCy)2]Ln[N(SiHMe2)2]2(THF) (Ln = Sc (1), Y(2), Lu (3)). Salt metathesis reaction of anhydrous LnCl3, [FcC(NCy)2]Li(THF) and LiN(SiMe3)2 in 1:1:2 M ratio gave [FcC(NCy)2]Ln[N(SiMe3)2]2 (Ln = Sc (4), Lu (5)) as neutral derivatives. All these complexes were well-characterized by elemental analysis, NMR spectroscopy, and FI-IR spectroscopy. Complexes 1 and 3 were structurally authenticated by single crystal X-ray diffraction. In the presence of excess AliBu3, and activated by one equivalent of [Ph3C][B(C6F5)4] in toluene, all these rare-earth metal bis(silylamide) complexes could serve as catalyst precursors for cis-1,4-selective polymerization of isoprene. The ternary catalyst system of 1/[Ph3C][B(C6F5)4]/AliBu3 promoted cis-1,4 selective polymerization of isoprene in a controlled fashion.

Sequence and Regularity Controlled Coordination Copolymerization of Butadiene and Styrene: Strategy and Mechanism

The stereoselective and sequence controlled coordination copolymerizations of butadiene (BD) and styrene (St) with diblock, tapered, gradient, and random sequence distributions were achieved for the first time through varying the central metals of the rare-earth metal bis(alkyl) catalyst precursors (Flu-CH2-Py)Ln(CH2SiMe3)2(THF)x (Flu = fluorenyl, Py = pyridyl, x = 1: Ln = Nd(1), Y(2), Tm(3); x = 0, Ln = Sc(4)). The thermal behavior, morphology, and the mechanical property of these copolymers were analyzed, and their relationships were established for the first time. The mechanism of central metal size tuning the sequence distribution was discussed based on DFT calculations.

Rare-earth metal dichloride and bis(alkyl) complexes containing amidinate-amidopyridinate ligands: synthesis, structure, and reactivity

A reaction of anhydrous yttrium chloride with an equimolar amount of lithium amidinateamidopyridinate obtained in situ by metallation of N,N’-bis(2,6-dimethylphenyl)-N-{6-[(2,6-dimethylphenyl)amino]pyridin-2-yl}acetimidamide ((2,6-Me2C6H3)NH(2,6-C6H3N)N(2,6-Me2C6H3)C(Me)=N(2,6-Me2C6H3), L1H) (1) with n-butyllithium in THF at–70 °C was used to synthesize the yttrium dichloride complex (L1)YCl2(THF)2 (2). The lutetium bis(alkyl) complex, namely, N’-(2,6-diisopropylphenyl)-N-(2,6-dimethylphenyl-N-{6-[(2,6-dimethylphenyl)amido]pyridin-2-yl}acetimidoamidinatebis(trimethylsilylmethyl)lutetium (4), was obtained by the reaction of N’-(2,6-diisopropylphenyl)-N-(2,6-dimethylphenyl)-N-(6-((2,6dimethylphenyl)amino)pyridin-2-yl)acetimidamide ((2,6-Me2C6H3)NH(2,6-C6H3N)N-(2,6-Me2C6H3)C(Me)=N(2,6-Pr 2 i C6H3), L2H (3)) with an equimolar amount of Lu(CH2SiMe3)3(THF)2. Complex 4 was found to be very stable and did not show indications of C—H-activation and other kinds of disintegration in benzene or toluene solution even upon prolonged heating at 60 °C. The reaction of complex 4 with an equimolar amount of 2,6-diisopropylaniline in toluene solution at room temperature led to the formation of the lutetium alkyl-anilide complex (L2)Lu(CH2SiMe3)(NH-2,6-Pr 2 i C6H3) (5). A three-component system 4—AlBu 3 i —[X][B(C6F5)4] ([X] = [Ph3C], [PhNHMe2], the molar ratio of 1: 10: 1) was found to catalyze polymerization of isoprene.

Synthesis, characterization and l-lactide polymerization behavior of rare-earth metal bis(silylamide) complexes supported by arylamido ligand

Salt metathesis of LnCl3, [2,6-iPr2C6H3N(SiMe3)]Li and LiN(SiHMe2)2 in 1:1:2 molar ratio in THF produced the mono-arylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-iPr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) (Ln = Y (1), Lu (2), La (3)) in good isolated yields. All these complexes were characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. 1 was further structurally authenticated by single crystal X-ray diffraction. These complexes alone could serve as highly active initiators for l-lactide polymerization in toluene at 50 °C. Employing 1 as the initiator, l-lactide polymerization proceeded in a controllable fashion via the coordination-insertion mechanism verified by end group analysis of the oligomer.

Rare-earth metal bis(silylamide) complexes supported by mono-dentate arylamido ligand: synthesis, reactivity, and catalyst precursors in living cis-1,4-selective polymerization of isoprene.

The salt metathesis reaction of LnCl3 with 1 equivalent of arylamido lithium [2,6-(i)Pr2C6H3N(SiMe3)]Li followed by addition of 2 equivalents of LiN(SiHMe2)2 in THF at room temperature obtained neutral mono-arylamido-ligated rare-earth metal bis(silylamide) complexes [2,6-(i)Pr2C6H3N(SiMe3)]Ln[N(SiHMe2)2]2(THF) (Ln = Y (), Lu (), La ()) in good isolated yields. Treatment of with excess AlMe3 produced the mono(arylamido) Ln/Al heterotrinuclear methyl complexes [2,6-(i)Pr2C6H3N(SiMe3)]Ln[(μ-Me)2AlMe2]2 (Ln = Y (), Lu (), La ()) via amide-alkyl exchange. All these complexes were well-characterized by elemental analysis, NMR spectroscopy and FT-IR spectroscopy. , and were further structurally authenticated by X-ray crystallography. In the presence of [Ph3C][B(C6F5)4] and Al(i)Bu3, were highly active for cis-1,4-selective polymerization of isoprene, whereas /[Ph3C][B(C6F5)4]/Al(i)Bu3 promoted the polymerization in a living fashion.

Rare-earth metal diisopropylamide-catalyzed intramolecular hydroamination.

Rare-earth metal diisopropylamide complexes LiLn(NiPr2)4(THF) (Ln = Sc, Y, La), [LiY(NiPr2)4]n, NaLn(NiPr2)4(THF) (Ln = Sc, Y), Sc(NiPr2)3(THF) and Ce(NiPr2)4 were screened as catalysts for the intramolecular hydroamination/cyclization (IHC) of 1-amino-2,2-dimethyl-4-pentene, 1-amino-2,2-diphenyl-4-pentene, and 1-amino-2,2-diphenyl-5-hexene at ambient and moderately increased temperature of 60 °C in C6D6. The lithium ate complexes displayed the most efficient precatalysts with high conversion rates at 60 °C for the phenyl-substituted substrates and Ln = Y and La, affording turnover frequencies Nt as high as 164 h-1. The catalytic activity could be increased by employing THF-free complex [LiY(NiPr2)4]n (Nt = 45.8 h-1 at 26 °C; 34.1 h-1 for LiY(NiPr2)4(THF)). In situ generation of putative LiY(NiPr2)4(THF) from YCl3(THF)3.3 and four equivalents of LiNiPr2 (LDA) in C6D6 generated a catalyst revealing Nt comparable to pre-isolated crystallized LiY(NiPr2)4(THF) but yielding even higher substrate conversion. The IHC reactions were also examined for rare-earth metal bis(trimethylsilyl)amide catalysts Ln[N(SiMe3)2]3 (Ln = Sc, Y, La) as well as for LDA using the same reaction conditions, revealing overall superior activity of the silylamide derivatives but poor performance of LDA compared to the rare-earth metal diisopropylamide complexes LiLn(NiPr2)4(THF). Cyclization of 1-amino-2,2-diphenyl-5-hexene to the 6-membered heterocycle 2-methyl-4,4-diphenylpiperidine by lanthanum derivative LiLa(NiPr2)4(THF) was accompanied by a competitive isomerization reaction affording max. 20% of 1-amino-2,2-diphenyl-4-hexene after 2 h at 60 °C. Crystalline tetravalent Ce(NiPr2)4 showed a better IHC performance than crystalline trivalent Sc(NiPr2)3(THF) as preliminary examined for 1-amino-2,2-diphenyl-4-pentene at 26 °C (Nt = 5.6 and 0.9 h-1, respectively), but cyclization came to a halt after 2 h, probably due to decomposition of the catalyst.

Rare-earth metal bis(alkyl) complexes bearing pyrrolidinyl-functionalized cyclopentadienyl, indenyl and fluorenyl ligands: synthesis, characterization and the ligand effect on isoprene polymerization

The ligand effect on isoprene polymerization was investigated using rare-earth metal bis(alkyl) complexes bearing pyrrolidinyl-functionalized cyclopentadienyl, indenyl and fluorenyl ligands.

Highly 3,4-selective living polymerization of 2-phenyl-1,3-butadiene with amidino N-heterocyclic carbene ligated rare-earth metal bis(alkyl) complexes

2-Phenyl-1,3-butadiene was polymerized using an amidino N-heterocyclic carbene lutetium bis(alkyl) precursor in high 3,4-selectivity (96.9%) and a living mode to afford a new plastic polydiene with a high Tg of 56.1 °C.

ChemInform Abstract: Synthesis of Guanidines from Amines and Carbodiimides Catalyzed by Mono‐Indenyl‐Ligated Rare Earth Metal Bis(silylamide) Complexes.

Nucleophilic addition of primary aromatic amines to carbodiimides in the presence of catalytic amount of the mono-indenyl-ligated rare earth metal bis(silylamide) complexes (C9H6CMe2CH2C5H4N-α)Ln[N(SiHMe2)2]2 at room temperature afforded efficiently a series of guanidines with a wide spectrum of substituents on the nitrogen atoms.

Synthesis of Guanidines from Amines and Carbodiimides Catalyzed by Mono‐Indenyl‐Ligated Rare Earth Metal Bis(silylamide) Complexes

AbstractNucleophilic addition of primary aromatic amines to carbodiimides in the presence of catalytic amount of the mono‐indenyl‐ligated rare earth metal bis(silylamide) complexes (C9H6CMe2CH2C5H4N‐α)Ln[N(SiHMe2)2]2 at room temperature afforded efficiently a series of guanidines with a wide spectrum of substituents on the nitrogen atoms.