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DOI: 10.1039/D4DT03060E (Paper) Dalton Trans., 2025, 54, 2320-2330

Phosphaguanidinate yttrium carbene, carbyne and carbide complexes: three distinct C1 functionalities†

Wen Jiang and Lixin Zhang *
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Jiangwan Campus, Fudan University, Shanghai 200438, China. E-mail: lixinzh@fudan.edu.cn

Received 1st November 2024 , Accepted 25th November 2024

First published on 2nd December 2024

Abstract

The phosphaguanidinate rare-earth-metal bis(aminobenzyl) complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(CH2C6H4 NMe2-o)2 (Ln = Y(1-Y) and Lu(1-Lu)) were synthesized by the protonolysis of (Ph2P)[C(NHR)(NR)] (R = 2,6-(iPr)2C6H3) with Ln(CH2C6H4NMe2-o)3 (Ln = Y and Lu). Interestingly, the ring-opening rearrangement product [o-Me2NC6H4CH2C(NC6H3iPr2-2,6)2]Lu(CH2C6H4NMe2-o)[O(CH2)4PPh2] (2) was obtained when the acid–base reaction was carried out in THF solution at 60 °C for 36 h. Additionally, the trinuclear homometallic yttrium multimethyl/methylidene complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Y(μ-Me)}3(μ3-Me)(μ3-CH2) (3) was synthesized by the treatment of 1-Y with AlMe3 (2 equiv.) in toluene at ambient temperature in a good yield. However, the binuclear lutetium methyl complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Lu(μ-Me)Me}2 (4) can be generated through the same synthetic method. Likewise, the heterobimetallic Ln-Al complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(Me)(AlMe4) (Ln = Y(6-Y) and Lu(6-Lu)) were afforded from the treatment of complex 1 with AlMe3 (3 equiv.) at ambient temperature for 6 h. Interestingly, upon extending the reaction time of the treatment of 1-Y with three equivalents of AlMe3, the phosphaguanidinate binuclear yttrium carbyne complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ4-CH)(μ-Me)(AlMe3)2 (7) and the yttrium carbide complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ5-C)(AlMe2)(μ-Me)(AlMe3)2 (8) were isolated via multiple C–H bond activation reactions. Furthermore, the heterobimetallic Y-Al complex [(Ph2P)C(NC6H3iPr2-2,6)2]Y(AlMe4)2 (9) was also obtained from the treatment of 1-Y with four equivalents of AlMe3.

Introduction

Since Lappert and co-workers discovered the first heterobimetallic Ln/Al alkyl species,1a heterobimetallic Ln/Al alkyl complexes have emerged as an area of intensive research.1b,c On the one hand, alkylaluminate ligands, acting as disguised alkyl ligands, can supplement more traditional rare-earth-metal alkyl complexes. On the other hand, these heterobimetallic Ln/Al alkyl complexes are highly likely to be potential precursors of rare-earth-metal alkylidene, alkylidyne, or carbide complexes. For instance, it has been confirmed that the methyl group can be transformed into CH22−, CH3−, and C4− moieties through C–H bond activation. Efforts in preparing rare-earth-metal methylidene complexes include simple methylene bridged species (A and B)2,3 and AlMe3-supported systems (C).4,5 Similarly, rare-earth-metal methylidyne complexes also exist in different bonding modes: simple methine bridged species (D)6 and AlMe3-supported mononuclear, binuclear, and cluster species (E–G).7–9 Despite these recent achievements, the chemistry of rare-earth-metal carbide complexes is still in its infancy, mainly manifested as multinuclear clusters. This is because the high charge densities of the hard carbon functionalities C4− drive the formation of clusters with relatively hard rare-earth-metal cations (M–Q).8,9b,10 For example, Anwander and his co-workers found that PMe3-induced alkylaluminate cleavage of La{Al(CH3)4}3 yields a cluster containing methylene, methine, and carbide moieties.9b Likewise, Mitzel et al. verified that the action of TMTAC (1,3,5-trimethyl-1,3,5-triazacyclohexane) on Ln{Al(CH3)4}3 (Ln = Y and Sm) leads to multiple methyl degradations, producing complex aggregates containing methylene, methine, and carbide units.10 Our laboratory has also isolated guanidinate binuclear yttrium carbide derivatives through C–H activation of the μ4-CH3− moiety.8 These results suggest that the use of appropriate ancillary ligands is equally crucial as they provide suitable steric protection and electronic support for the metal center, having a significant impact on the characterization of heterobimetallic Ln/Al complexes and their derivatives (Scheme 1).
image file: d4dt03060e-s1.tif
Scheme 1 Classes of rare-earth-metal methylidene, methylidyne and carbide complexes.

It is widely known that the development of rare-earth-metal complexes with non-Cp ligands (such as amidinate and guanidinate)11 is due to their unique reactivity compared with analogues having Cp ligands, as well as the characteristics of adjustable steric and electronic effects, which can control the stability and reactivity of the complexes.12 However, studies on phosphaguanidinate rare-earth-metal complexes are relatively scarce,13 although phosphaguanidines were originally reported in the 1980s by Schmidt and his co-workers.14 In this work, the monoanionic phosphaguanidinate ligand was used in the formation of Ln/Al alkyl complexes to expand our research. This paper provides a comprehensive description of the synthetic and structural chemistry of heterobimetallic Ln/Al complexes with the phosphaguanidinate ligand. The feasible reaction pathways for obtaining rare-earth-metal carbene, carbyne, and carbide complexes that contain highly reactive {Ln–(Me)x–Al} heterobimetallic linkages through C–H bond activation will be described.

Results and discussion

Synthesis and characterization of phosphaguanidinate rare-earth-metal bis(aminobenzyl) complexes

The process for preparing phosphaguanidinate rare-earth-metal bis(aminobenzyl) complexes is shown in Scheme 2. A convenient protonolysis method was used to synthesize the complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(CH2C6H4NMe2-o)2 (Ln = Y(1-Y, 83%) and Lu(1-Lu, 78%)) in solutions of THF or toluene. During this process, CH3C6H4NMe2-o was produced.
image file: d4dt03060e-s2.tif
Scheme 2 The syntheses of complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(CH2C6H4NMe2-o)2 (Ln = Y(1-Y) and Lu(1-Lu)) and [o-Me2NC6H4CH2C (NC6H3iPr2-2,6)2]Lu(o-CH2C6H4NMe2)[O(CH2)4PPh2] (2).

In the 1H NMR spectra (in C6D6) of complexes 1 at room temperature, the methylene protons of CH2C6H4NMe2-o that are bound to the metal ions show up as singlets at δ = 1.80 ppm for complex 1-Y and at 1.75 ppm for complex 1-Lu. The resonances of the NMe2 groups appear as broad singlets at δ = 2.29 ppm for 1-Y and at 2.27 ppm for complex 1-Lu, respectively. The methine protons display a multiplet signal at δ = 3.65 ppm for complex 1-Y and at 3.74 ppm for complex 1-Lu. The methyl protons of the isopropyl groups exhibit two groups of doublets at δ = 1.29 and 1.31 ppm (JH–H = 4 Hz) for 1-Y and at δ = 1.28 and 1.35 ppm (JH–H = 4 Hz) for complex 1-Lu. In the 13C{1H} NMR spectrum of complex 1-Y, the resonance of the methylene carbon in CH2C6H4NMe2-o results in a doublet at δ = 49.4 ppm (JY–C = 32 Hz). The signals at δ = 6.1 ppm (1-Y) and 7.3 ppm (1-Lu) in the 31P{1H} NMR spectra can be attributed to their corresponding phosphorus atoms in the phosphaguanidinate ligand.

Complexes 1 are stable under an inert atmosphere at room temperature and are slightly soluble in hexane. They dissolve easily in THF and aromatic solvents. Pale yellow single crystals of complexes 1 were obtained by growing them from concentrated toluene/n-hexane solutions at −35 °C. The solid-state molecular structures of complexes 1 were further determined through single-crystal X-ray diffraction analysis, confirming the distorted-octahedral geometry of those core structures as shown in Fig. 1. Selected bond distances and angles are presented in Table 1. The average bond lengths of Ln–Nligand (average for Y: 2.439(2) Å; average for Lu: 2.392(4) Å) are longer than those found in amidinate rare-earth-metal complexes [PhC(NC6H3iPr2-2,6)2]Ln(CH2C6H4NMe2-o)2 (average for Y: 2.373(3) Å; average for Lu: 2.349(5) Å), [o-Me2NC6H4CH2C(NC6H3iPr2-2,6)2]Ln(CH2C6H4NMe2-o)2 (average for Y: 2.369(5) Å; average for Lu: 2.325(4) Å)15 and guanidinate rare-earth-metal complexes [(PhCH2)2C(NC6H3iPr2-2,6)2]Ln(CH2C6H4NMe2-o)2 (average for Y: 2.358(3) Å; average for Lu: 2.318(3) Å).16 In contrast, the average distances of Ln–C bonds for 1-Y (2.438(3) Å) and 1-Lu (2.388(5) Å) are shorter than the corresponding bond lengths in amidinate and guanidinate complexes. Therefore, compared with amidinate and guanidinate, the interaction force between phosphaguanidinate and rare-earth metals is weaker due to the difference in steric and electronic effects.


image file: d4dt03060e-f1.tif
Fig. 1 Molecular structures of complexes 1-Y (left) and 1-Lu (right) with thermal ellipsoids at 30% probability. All hydrogen atoms are omitted for clarity.
Table 1 Selected bond lengths and angles of complexes 1
  1-Y 1-Lu
Bond lengths (Å)
Ln–N1 2.524(2) 2.487(4)
Ln–N2 2.607(2) 2.559(4)
Ln–N3 2.403(2) 2.358(4)
Ln–N4 2.475(2) 2.427(4)
Ln–C2 2.441(3) 2.381(5)
Ln–C11 2.436(3) 2.396(5)
Bond angles (°)
N1–Ln–C2 68.47(8) 68.39(15)
N1–Ln–N2 117.76(7) 119.28(14)
N1–Ln–C11 84.57(9) 81.93(16)
N2–Ln–C11 67.32(8) 69.21(17)
N2–Ln–C2 81.04(8) 85.23(17)
C2–Ln–C11 121.88(10) 124.08(19)

Surprisingly, when the reaction of Lu(o-CH2C6H4NMe2)3 with (Ph2P)[C(NR)(NHR)] (R = 2,6-(iPr)2C6H3) was carried out at 60 °C in THF for 36 hours through a tandem protonolysis-activation reaction, the unexpected ring-opening rearrangement product [o-Me2NC6H4CH2C(NC6H3iPr2-2,6)2]Lu(CH2C6H4NMe2-o)[O(CH2)4PPh2] (2) was obtained in an excellent yield (90%), accompanied by the generation of CH3C6H4NMe2-o, indicating that the C–P σ-bond of the ligand was cleaved. A few examples of cyclopentadienyl butoxide rare-earth-metal complexes have been obtained by the THF ring-opening insertion into Ln–P bonds,17 and only three non-Cp analogues have been reported to date.18 In the 1H NMR spectrum (in C6D6) of complex 2, four multiplet peaks at δ = 4.04, 2.31, 1.98, and 1.78 ppm are presumed to be the CH2 signals of the terminal O(CH2)4PPh2 ligand. The resonance of the Lu-bonded aminobenzyl shows two singlets at δ = 1.47 ppm for CH2 and 2.88 ppm for NMe2 (ESI Fig. S7†). The 31P{1H} NMR spectrum of 2 shows a singlet at δ = −16.9 ppm for the phosphaguanidinate ligand.

Complex 2 was also characterized by single-crystal X-ray diffraction analysis. This confirmed that complex 2 has a monometallic structure. The molecular structure profile of complex 2 is shown in Fig. 2. The bond distances of Lu–C (2.476(5) Å) and Lu–Naminobenzyl (2.535(4) Å) are longer than the corresponding values found in complex 1-Lu (Ln–C: 2.388(5) Å and Lu–N: 2.523(4) Å). This is because the latter has less steric hindrance and the oxygen atoms have a stronger electron-donating ability. The O(CH2)4PPh2 group coordinates to the lutetium atom in a terminal bonding mode. The bond length of Lu–O(2) (2.044(3) Å) is shorter than those found in {[(PhCH2)2NC(NC6H3iPr2-2,6)2]Lu(Me)[μ-O(CH2)4PPh2]}2 (2.194(5) and 2.191(5) Å).18c This may be due to the difference in coordination patterns of the O(CH2)4PPh2 group.


image file: d4dt03060e-f2.tif
Fig. 2 Molecular structure of complex 2 with thermal ellipsoids at 30% probability. All hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Lu(1)–N(1) 2.299(4), Lu(1)–N(2) 2.347(3), Lu(1)–N(4) 2.535(4), Lu(1)–O(2) 2.044(3), Lu(1)–O(1) 2.316(3), and Lu(1)–C(51) 2.476(5); N(1)–Lu(1)–O(2) 107.70(13), N(2)–Lu(1)–O(2) 101.95(13), N(1)–Lu(1)–C(51) 95.68(15), N(2)–Lu(1)–C(51) 95.07(15), N(1)–Lu(1)–O(1) 88.49(12), and N(2)–Lu(1)–O(1) 146.07(12).

Synthesis and structural characterization of the yttrium carbene, carbyne and carbide complexes with a phosphaguanidinate ligand

Based on the previous reaction results of amidinate rare-earth-metal bis-aminobenzyl complexes with AlMe3 in our group,3d we were able to obtain a series of rare-earth methyl complexes with unique structures and their derivatives by precisely controlling the quantity of methylaluminum. For example, the homometallic trinuclear methyl/methylidene complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Y(μ-Me)}3(μ3-Me)(μ3-CH2) (3) was obtained in a good yield when complex 1-Y was treated with two equivalents of AlMe3 in toluene at room temperature. Interestingly, when a similar synthetic method was used for the reaction of complex 1-Lu with AlMe3 (2 equiv.), the binuclear lutetium methyl complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Lu(μ-Me)Me}2 (4) was isolated instead of the carbene analogues (Scheme 3). This is mainly due to the smaller radius of Lu3+ than that of Y3+,19 which enables the phosphaguanidinate lutetium complex to stabilize in a bimetallic methylated state, whereas the Y analogue tends to transform further into the trinuclear carbene complex. Even when the reaction temperature was increased to 100 °C, the lutetium carbene complex was not detected by 13C DEPT-135 NMR spectroscopy. We only obtained the mixed amidinate/phosphaguanidinate lutetium methyl complex [(Ph2P)(NC6H3iPr2-2,6)2][(Me)C(NC6H3iPr2-2,6)2]Lu(Me) (5) through the C–P bond cleavage of the phosphaguanidinate ligand. Complexes 3 and 4 are slightly soluble in hexane but readily dissolve in THF and aromatic solvents.
image file: d4dt03060e-s3.tif
Scheme 3 The syntheses of the yttrium carbene complex {[(Ph2P)C(NC6H3iPr2-2,6)2]Y(μ-Me)}3(μ3-Me)(μ3-CH2) (3) and lutetium methyl complexes {[(Ph2P)C(NC6H3iPr2-2,6)2]Lu(μ-Me)Me}2 (4) and [(Ph2P)C(NC6H3iPr2-2,6)2][(Me)C(NC6H3iPr2-2,6)2]Lu(Me) (5).

In the 1H NMR spectrum of complex 3, μ3-Me and μ2-Me protons appear as two broad singlets at δ = 0.90 ppm and 1.05 ppm, respectively. The quartet signal at δ = 2.01 (J = 4 Hz), which corresponds to two protons according to integration, and a relatively downward doublet signal at δ = 109.8 (JY–C = 23 Hz) can clearly confirm the formation of a methylidene unit based on a comprehensive analysis of the 13C{1H}, 13C DEPT-135, and heteronuclear multiple quantum coherence (HMQC) NMR spectra (ESI Fig. S10–13†). The signals at δ = 47.5 ppm and 36.5 (JY–C = 22 Hz) ppm in the 13C{1H} NMR spectra can be attributed to the carbon atoms from the μ3-Me and μ2-Me moieties respectively, and the signal at δ = 1.4 ppm in the 31P{1H} NMR spectrum can be assigned.

In the 1H NMR spectrum of complex 4, we can only observe one singlet for the Lu–Me group at δ = 0.82 ppm due to the rapid exchange between μ2-Me and the terminal methyl in solvents at room temperature. Additionally, the singlet at δ = 43.2 ppm in the 13C{1H} NMR spectrum can be assigned to the carbon atoms of these moieties. The 31P{1H} NMR spectrum of complex 4 shows a singlet at δ = −1.3 ppm. The NMR spectra are consistent with the structure of complex 4, which is also verified by X-ray structure analysis (Fig. 3). The Lu atom is surrounded by two nitrogen atoms from the phosphaguanidinate ligand and three carbon atoms from methyl units, and the core of complex 4 adopts a distorted trigonal bipyramidal geometry. The bond length of the terminal Lu–Me (2.297(6) Å) is shorter than the bond lengths in (TptBu,Me)LuMe (CH2SiMe3) (2.343(2) Å)20 and (TptBu,Me)LuMe2 (2.369(3) Å).21 The average distance of the bridged Lu–Me (2.434(6) Å) is close to that of the complex [(η5-C5H4SiEt3)2YMe]2 (2.523(9) Å) after taking into consideration the difference between metal ionic radii.22


image file: d4dt03060e-f3.tif
Fig. 3 Molecular structure of complex 4 with thermal ellipsoids at 30% probability except for the 2,6-(iPr)2C6H3 groups and benzyl groups in the guanidinate ligand. All hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Lu(1)–Lu(1A) 3.3824(5), Lu(1)–N(1) 2.284(4), Lu(1)–N(2) 2.290(4), Lu(1)–C(1) 2.441(6), Lu(1)–C(1A) 2.428(6), and Lu(1)–C(2) 2.297(6); N(1)–Lu(1)–N(2) 58.58(14), N(1)–Lu(1)–C(1) 141.64(19), N(1)–Lu(1)–C(2) 109.12(19), N(2)–Lu(1)–C(1) 93.35(17), N(2)–Lu(1)–C(2) 111.70(18), C(1)–Lu(1)–C(2) 105.4(2), and C(1A)–Lu(1)–C(2) 110.7(2).

In the 1H NMR spectrum (in C6D6) of complex 5 at room temperature, the Lu-bonded methyl group shows a singlet at δ = 0.36 ppm, which clearly shifts to a higher field compared with complex 4. The 31P{1H} NMR spectrum of complex 5 shows a singlet at δ = 5.3 ppm. A single crystal of complex 5 could be obtained from concentrated toluene/n-hexane solutions, crystallizing in the monoclinic space group P21/c (Fig. 4). The Lu atom is surrounded by four nitrogen atoms from the phosphaguanidinate and amidinate ligands and one carbon atom from the methyl group, and the core of complex 5 has a distorted square pyramidal geometry. The Lu–Me bond length (2.308(4) Å) is slightly longer than that in complex 4 (2.297(6) Å), but it is significantly shorter than that in the complex [(PhCH2)2C(NC6H3iPr2-2,6)2]Lu(CH2C6H4NMe2-o)(Me)(THF) (2.369(4) Å).18c


image file: d4dt03060e-f4.tif
Fig. 4 Molecular structure of complex 5 with thermal ellipsoids at 30% probability. All hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Lu(1)–N(1) 2.305(3), Lu(1)–N(2) 2.316(3), Lu(1)–N(3) 2.244(3), Lu(1)–N(4) 2.308(3), Lu(1)–C(1) 2.308(4), C(39)–C(40) 1.501(5), and C(2)–P(1) 1.878(4); N(1)–Lu(1)–C(1) 93.43(15), N(2)–Lu(1)–C(1) 127.61(16), N(3)–Lu(1)–C(1) 107.38(16), N(4)–Lu(1)–C(1) 102.68(15), N(1)–Lu(1)–N(2) 57.84(11), and N(3)–Lu(1)–N(4) 59.17(11).

As we are aware, the degree of alkylation in the resulting heterobimetallic complexes is highly dependent on the amount of alkylaluminum reagent in the reaction mixture as well as the steric/electronic characteristics of the anionic ligands. As shown in Scheme 4, when three equivalents of AlMe3 were used to react with phosphaguanidinate rare-earth-metal bis(aminobenzyl) complexes, the heterobimetallic methyl/tetramethylaluminate complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(Me)(AlMe4) (Ln = Y(6-Y) and Lu(6-Lu)) were obtained in good yields. The 1H NMR spectrum of complex 6-Lu is consistent with its structure, in which two signals are observed for the metal-bound methyl protons, one broad singlet at δ = 0.16 ppm corresponding to twelve protons, and one singlet at δ = 0.29 ppm with an integral intensity of three protons. Only one signal is observed and is assigned to AlMe4, likely due to the rapid exchange between the bridged and terminal methyl groups in C6D6 at room temperature.4a In the 31P{1H} NMR spectrum of complex 6-Lu, a singlet appears at δ = −0.6 ppm. Unexpectedly, when the same reaction was carried out at room temperature for 24 h, the binuclear phosphaguanidinate yttrium carbyne complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ4-CH)(μ-Me)(AlMe3)2 (7) and the rare carbide complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ5-C)(AlMe2)(μ-Me)(AlMe3)2 (8) (31% yield) were obtained. Indeed, complex 6-Y could transform into complexes 7 and 8 in toluene solution for 24 h. However, such a reaction was not feasible for the smaller-sized lutetium center.8


image file: d4dt03060e-s4.tif
Scheme 4 The syntheses of the heterobimetallic Ln/Al methyl complexes [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(AlMe4)(Me) (6) and [(Ph2P)C(NC6H3iPr2-2,6)2]Ln(AlMe4)2 (9), the yttrium carbyne complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ4-CH)(μ-Me)(AlMe3)2 (7) and the yttrium carbide complex [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ5-C)(AlMe2)(μ-Me) (AlMe3)2 (8).

Single crystal X-ray diffraction analysis of complex 6-Lu was performed using a toluene/hexane mixture, which is a five-coordinate complex (Fig. 5). The bond length of the terminal Lu–Me (2.307(3) Å) is similar to that in complex 5 (2.308(4) Å). The single crystal X-ray diffraction analysis of complex 7 shows that two distorted octahedral yttrium centers are linked by μ4-CH and μ2-Me units to form a distorted square, and two AlMe3 groups act as bulky ligands to stabilize this binuclear carbyne complex (Fig. 6). It is notable that the Y–C1(μ4-CH) bond lengths of 2.390(2) Å and 2.414(2) Å are similar to those in [(PhCH2)2NC(NC6H3iPr2-2,6)2]2Y2(μ2-Me)(AlMe3)2 (μ4-CH) (2.398 (5) Å and 2.418(5) Å), but they are shorter than those in [{(C5Me5)Y(μ2-Me)2AlMe}2(μ2-Me)(μ4-CH)]2 (2.444(3)–2.464(3) Å)9a due to the steric effect. The average Y–C2(μ2-Me) bond length (2.523(3) Å) is shorter than that in [(PhCH2)2NC(NC6H3iPr2-2,6)2]2Y2(μ2-Me)(AlMe3)2(μ4-CH) (2.535(5) Å) due to the lower electron-donating ability of the phosphaguanidinate ligand. The opposite trend is observed for the Al–C2(μ4-CH) bond lengths (1.983(3) Å and 1.992(3) Å) compared with those (1.970(5) Å and 1.974(5) Å) for Al–C(μ4-CH).


image file: d4dt03060e-f5.tif
Fig. 5 Molecular structure of complex 6-Lu with thermal ellipsoids at 30% probability. All hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Lu(1)–C(1) 2.307(3), Lu(1)–C(2) 2.472(4), Lu(1)–C(3) 2.431(4), Al(1)–C(4) 1.959(3), Lu(1)–N(1) 2.276(2), and Lu(1)–N(2) 2.273(2); C(1)–Lu(1)–N(1) 112.43(11), C(1)–Lu(1)–N(2) 111.55(11), C(1)–Lu(1)–C(2) 102.93(13), and C(1)–Lu(1)–C(3) 105.83(14).

image file: d4dt03060e-f6.tif
Fig. 6 Molecular structure of complex 7 with thermal ellipsoids at 30% probability except for the 2,6-(iPr)2C6H3 groups and benzyl groups in the guanidinate ligand. All of the hydrogen atoms (except for H2) are omitted for clarity. Selected bond distances (Å) and angles (°): Y(1)–C(1) 2.538(3), Y(1)–C(2) 2.390(2), Y(2)–C(1) 2.508(3), Y(2)–C(2) 2.414(2), C(2)–Al(1) 1.992(3), C(2)–Al(2) 1.983(3), Y(1)–C(3) 2.593(3), Y(1)–C(6) 2.646(3), Y(2)–C(5) 2.601(3), and Y(2)–C(8) 2.609(3); C(1)–Y(1)–C(2) 85.28(9), C(1)–Y(2)–C(2) 85.42(9), Y(1)–C(1)–Y(2) 91.50(11), and Y(1)–C(2)–Y(2) 97.58(8).

The single crystal X-ray diffraction analysis of complex 8 shows that the stabilization of the carbide unit (C4−) is achieved by alkylaluminate ligands. The carbide carbon atom has a unique distorted trigonal bipyramidal geometry, where three Al atoms are located in the equatorial plane and two Y atoms occupy the axial positions (Fig. 7). The average Y–C2(μ2-Me) bond length (2.581(2) Å) is longer than that in [(PhCH2)2NC(NC6H3iPr2-2,6)2]2Y2(μ2-Me)(AlMe3)2(μ4-CH) (2.535(5) Å).8 It is notable that the average Y–C1(μ5-C) bond length of 2.425(3) Å is similar to that in [(PhCH2)2NC (NC6H3iPr2-2,6)2]2Y2(μ2-SMe)(AlMe3)2(μ5-C)(AlMe2) (average 2.434(3) Å), but it is shorter than the Y–C(μ6-C) bond in [(TMTAC)Y][Y2(μ2-Me)][{(μ6-C)[Al(μ2-Me)2(Me)]3}{(μ3-CH2)(μ2-Me)AlMe2}2] (average 2.696(6) Å),10 possibly due to the higher coordination numbers of the carbide atoms in the latter. A similar trend is observed for the Al–C(μ-Me) bond lengths (2.562(3)–2.620(3) Å) compared to 2.588(4)–2.687(5) Å for Al–C(μ-Me),8 probably due to the difference in the electron-donating ability of the surrounding ligand. The results suggest a bimolecular reaction in which the [CH]3− group is deprotonated by the methyl in the AlMe3 ligand to form a more stable carbide complex with the release of CH4. The 1H NMR spectrum of the coordinated AlMe3 in complex 8 shows that the terminal methyl and μ2-Me (Y–Me–Y) overlap with a singlet at δ = −0.12 ppm, and an integral value of 12 at δ = 0.77 ppm is attributed to μ2-Me (Y–Me–Al), which is mainly referenced to the methyl in the coordinated AlMe3 that does not undergo rapid exchange in C6D6 at room temperature. μ4-CAlMe2 has a singlet at δ = −0.73 ppm with an integral value of 6. In the 13C{1H} NMR spectrum, the peaks at δ = −0.3 ppm and 8.1 ppm are attributed to μ4-CAlMe2 and AlMe3, respectively. The carbon signal of μ2-Me exists in the form of a triple peak at δ = 32.0 (JY–C = 20 Hz) ppm due to the coupling cleavage of the bridged methyl carbon by Y3+. The 31P{1H} NMR spectrum of complex 8 shows a singlet at δ = 5.7 ppm (Table 2).


image file: d4dt03060e-f7.tif
Fig. 7 Molecular structure of complex 8 with thermal ellipsoids at 30% probability except for the 2,6-(iPr)2C6H3 groups and benzyl groups in the guanidinate ligand. All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Y(1)–Y(2) 3.6371(5), Y(1)–C(1) 2.429(3), Y(1)–C(2) 2.597(3), Y(1)–C(5) 2.574(3), Y(1)–C(8) 2.562(3), Y(2)–C(3) 2.620(3), Y(2)–C(6) 2.583(3), Y(2)–C(1) 2.421(3), Y(2)–C(2) 2.566(2), C(1)–Al(1) 1.939(3), C(1)–Al(2) 1.973(3), and C(1)–Al(3) 1.972(3); C(1)–Y(1)–C(2) 86.18(9), C(1)–Y(2)–C(2) 87.05(9), Y(1)–C(1)–Y(2) 97.17(9), Y(1)–C(2)–Y(2) 89.57(8), Al(1)–C(1)–Al(2) 93.82(12), Al(1)–C(1)–Al(3) 96.52(12), and Al(2)–C(1)–Al(3) 169.63(15).
Table 2 Structural and spectroscopic data for selected yttrium methylidene, methylidyne and carbide complexes
Formula Y–C distances (Å) CN 1 H (ppm) 13C (ppm) Solv. Ref.
{Y(C5Me5)(THF)}3(μ3-CH2)(μ-Cl)3(μ3-CI) 2.424(2)–2.450(2) 3 −0.39, −0.85 — THF-D8 3a
{Y(C5Me5)(THF)}3(μ3-CH2)(μ-Br)3(μ3-Br) 2.431(3)–2.532(3) 3 −0.33 — THF-D8 3g
{Y(C5Me4SiMe3)(THF)}3(μ3-CH2)(μ-Cl)3(μ3-CI) — 3 −0.42 — THF-D8 3g
{Y(C5Me4SiMe3)(THF)}3(μ3-CH2)(μ-Br)3(μ3-Br) — 3 −0.42 — THF-D8 3g
{Y(C5Me5)(THF)}3(μ2-Me)3(μ3-Me)(μ3-CH2) 2.283(4)–2.477(3) 3 −0.31 — C6D6 3g
{Y{N(Dipp)(SiMe3)}3(THF)}3(μ3-Me)3(μ3-Me)(μ3-CH2) 2.345(5)–2.424(4) 3 2.32 100.2 C6D6 3b
{Y[PhC(NC6H3iPr2-2,6)2]}3(μ-Me)3(μ3-Me)(μ3-CH2) 2.388(5)–2.408(5) 3 2.27 108.5 C6D6 23
[Al(TptBu,Me)Me]Y(AlMe4)[(μ3-CH2)(μ-Me)AlMe2]2(AlMe2) 2.344(8)–2.411(9) 3 0.35, 0.25 31.3, 31.0 C6D6 5a
[(TMTAC)Y][Y2(μ2-Me)]{(μ6-C)[Al(μ2-Me)2Me]3}[(μ3-CH2)(μ2-Me)AlMe2]2 2.367(5)–2.452(5) 3 — — — 10
{[Y(Ph2P)C(NC6H3iPr2-2,6)2](μ-Me)}3(μ3-Me)(μ3-CH2) — 3 2.01 109.9 C6D6 This work
{Y[PhC(NC6H3iPr2-2,6)2]}3(μ2-Me)3(μ3-CCSiMe3)(μ3-CH2) 2.382(7)–2.418(8) 3 2.33 113.8 C6D6 23
{Y[PhC(NC6H3iPr2-2,6)2]}3(μ2-Me)2(μ3-CH2)(μ3-η1:η2:η2–S2C = CH2) — 3 2.13 116.7 C6D6 23
[{Y(C5Me5)(μ-Me)2AIMe}2(μ-Me)(μ4-CH)]2 2.444(3)–2.464(3) 4 — — — 9a
{Y(PhCH2)2NC(NC6H3iPr2-2,6)2}2(μ-Me)(AIMe3)2(μ4-CH) 2.398(5)–2.418(5) 4 2.36 90.2 C6D6 8
{Y(Ph2P)C(NC6H3iPr2-2,6)2}2(μ-Me)(AIMe3)2(μ4-CH) 2.390(2)–2.414(2) 4 — — — This work
{Y(TMTAC)}{Y2[(μ-Me)2AIMe)]}(μ6-C)(μ3-CH2){(μ-Me)2AIMe}{(μ-Me)AlMe2}2 2.436(5)–2.696(6) 6 — — — 10
{(PhCH2)2NC(NC6H3iPr2-2,6)2}2Y2(μ2-SMe)(AlMe3)2(μ5-C)(AlMe2) 2.434(3) 5 — — — 8
{Y(Ph2P)C(NC6H3iPr2-2,6)2}2(μ-Me)(AIMe3)2(μ5-C)(AIMe2) 2.429(3)–2.566(2) 5 — — — This work

As depicted in Scheme 4, when four equivalents of AlMe3 were employed to react with complex 1-Y, the heterobimetallic bis(tetramethylaluminate) complex [(Ph2P)C(NC6H3iPr2-2,6)2]Y(AlMe4)2 (9) was isolated in a good yield. However, attempts to prepare the lutetium analogue through a similar synthetic process were unsuccessful. Due to the smaller-sized lutetium center, we only separated out complex 6-Lu as the major product. The 1H NMR spectrum of complex 9 is identical to its structure. Only one signal at δ = 0.07 ppm is assigned to [AlMe4]−, likely because of the rapid exchange between the bridged methyl and terminal methyl groups in C6D6 at ambient temperature.4a X-ray single crystals of complex 9-Y were obtained from a toluene/hexane mixture (Fig. 8), and the Y–Me bond length (2.552(6) Å) is close to that in [(PhCH2)2NC (NC6H3iPr2-2,6)2]Y(AlMe4)2 (2.556(7)–2.573(7) Å).8


image file: d4dt03060e-f8.tif
Fig. 8 Molecular structure of complex 9 with thermal ellipsoids at 30% probability. All hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (°): Y(1)–N(1) 2.326(4), Y(1)–N(2) 2.351(4), Y(1)–C(1) 2.528(4), Y(1)–C(2) 2.558(4), Y(1)–C(5) 2.541(4), and Y(1)–C(6) 2.570(4); C(1)–Y(1)–N(1) 103.90(11), C(1)–Y(1)–N(2) 97.65(11), C(2)–Y(1)–N(1) 94.93(12), C(2)–Y(1)–N(2) 150.89(13), C(5)–Y(1)–N(1) 96.19(11), C(5)–Y(1)–N(2) 99.99(12), C(6)–Y(1)–N(1) 151.81(13), C(6)–Y(1)–N(2) 95.77(12), C(1)–Y(1)–C(2) 79.89(13), and C(5)–Y(1)–C(6) 79.65(13).

Conclusions

In conclusion, phosphaguanidinate rare-earth-metal bis(aminobenzyl) complexes were synthesized through protonolysis reactions, and the THF ring-opening rearrangement product was isolated with an excellent yield as well. Moreover, a series of heterobimetallic Ln/Al complexes containing a phosphaguanidinate ligand were obtained in good yields. The degree of alkylation in the resulting heterobimetallic complexes is highly dependent on the amount of alkylaluminum reagent and the steric/electronic characteristics of the anionic ligands. We have successfully developed a synthesis method starting from heterobimetallic Y/Al complexes, which leads to the formation of yttrium carbene, carbyne, and carbide complexes via multiple C–H activation reactions. Additionally, studies on the reactivity of these complexes towards organic substrates are currently underway in our laboratory.

Experimental section

General procedures and materials

All manipulations were performed under the rigorous exclusion of air and moisture using standard Schlenk techniques and an MBRAUN glovebox (Unilab; <1 ppm O2, <1 ppm H2O). Solvents (toluene, hexane, and THF) were purified using Grubbs-type columns (MBRAUN SPS-800, solvent purification system) and dried over fresh Na chips in the glove box. Bis(2,6-diisopropylphenyl) carbodiimide was obtained from Tokyo Chemical Industry Co., Ltd and used without purification. CH3C6H4NMe2-o was purchased from Sigma-Aldrich and used without purification. Ph2PH, nBuLi (2.5 mol L−1 in hexane), diphenylphosphine and AlMe3 (1 mol L−1 in hexane) were purchased from J&K and used without purification. C6D6 was obtained from J&K and dried using sodium chips. The complexes Ln(CH2C6H4NMe2-o)3 were prepared according to the literature procedures.24 The 1H NMR, 13C{1H} NMR and 31P{1H} NMR spectra were recorded using a JEOL ECA-400 NMR spectrometer (FT, 400 MHz for 1H; 100 MHz for 13C{1H}; and 161.88 MHz for 31P{1H}) in C6D6 at room temperature. X-ray crystallographic data were obtained using a Bruker SMART APEX or Bruker SMART APEX II (at 173 K or 296 K) diffractometer with a CCD area detector using graphite-monochromated Mo/Ga Kα radiation (λ = 0.71073 Å/λ = 1.34138 Å). The structure was solved using the SHELXTL program. Refinement was performed using F2 anisotropically with the full-matrix least-squares method for all the non-hydrogen atoms. Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre. 2389279 (for 1-Y), 2389282 (for 1-Lu), 2389309 (for 2), 2389276 (for 4), 2389280 (for 5), 2389278 (for 6-Lu), 2389281 (for 7), 2389283 (for 8) and 2389277 (for 9)† contain the supplementary crystallographic data for this paper. The combustion method was used for the analysis of carbon, hydrogen and nitrogen using an Elementar Vario EL III analyzer at Fudan University (China).
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]Y(CH2C6H4NMe2-o)2 (1-Y). A THF solution (10 mL) of Y(o-CH2C6H4NMe2)3 (0.25 g, 0.5 mmol) was added into a stirred solution (20 mL) of (Ph2P)[C(NR)(NHR)] (R = 2,6-iPr2C6H3) (0.27 g, 0.5 mmol) in THF or toluene. The reaction solution was allowed to stir for 24 h at room temperature and all volatiles were removed under vacuum. The oily residue was washed with cold hexane and a yellow powder was obtained by filtration. The yellow powder was recrystallized in toluene at −35 °C for one day to give a pale yellow powder of 1-Y (0.38 g, 83%). 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 1.29 (d, 12H, 3JH–H = 4 Hz, CHMe2), 1.31 (d, 3JH–H = 4 Hz, 12H, CHMe2), 1.80 (s, 4H, CH2C6H4NMe2), 2.29 (s, 12H, CH2C6H4NMe2), 3.65 (m, 4H, CHMe2), 6.59–6.60 (m, 4H, Ar), 6.77–6.78 (m, 6H, Ar), 6.85–6.95 (m, 8H, Ar), 7.00–7.02 (m, 2H, Ar), 7.12–7.14 (m, 4H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 24.7 (d, J = 5 Hz, CHMe2), 25.7 (s, CHMe2), 29.4 (d, J = 1 Hz, CHMe2), 46.5 (s, CH2C6H4NMe2), 49.4 (d, JYC = 32 Hz, CH2C6H4NMe2), 118.4 (s, Ar), 120.7 (s, Ar), 124.1 (s, Ar), 125.3 (s, Ar), 126.7 (s, Ar), 127.6 (d, J = 5 Hz, Ar), 129.2 (s, Ar), 134.4 (d, J = 15 Hz, Ar), 135.8 (d, J = 23 Hz, Ar), 142.8 (s, Ar), 144.2 (d, J = 3 Hz, Ar), 145.1 (s, Ar), 145.9 (s, Ar), 178.1 (d, J = 78 Hz, NCN). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = 6.1 (q, J = 8.1 Hz, CPPh2). Anal. calcd for C55H68N4PY(%): C, 72.99; H, 7.57; N, 6.19. Found: C, 73.06; H, 7.21; N, 6.23.
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]Lu(CH2C6H4NMe2-o)2 (1-Lu). A toluene solution (10 mL) of Lu(o-CH2C6H4NMe2)3 (0.29 g, 0.5 mmol) was added into a stirred solution (20 mL) of (Ph2P)[C(NR) (NHR)] (R = 2,6-iPr2C6H3) (0.27 g, 0.5 mmol) in toluene. The reaction solution was allowed to stir for 24 h at 60 °C and all volatiles were removed under vacuum. The oily residue was washed with cold hexane and a yellow powder was obtained by filtration. The yellow powder was recrystallized in toluene at −35 °C for three days to give a yellow powder of 1-Lu (0.38 g 78%). 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 1.28 (d, 3JH–H = 4 Hz, 12H, CHMe2), 1.35 (d, 3JH–H = 4 Hz, 12H, CHMe2), 1.75 (s, 4H, CH2C6H4NMe2), 2.27 (s, 12H, CH2C6H4NMe2), 3.74 (m, 4H, CHMe2), 6.50–6.58 (m, 4H, Ar), 6.75 (m, 6H, Ar), 6.84 (m, 5H, Ar), 6.88–6.92 (m, 2H, Ar), 7.01–7.05(m, 2H, Ar), 7.10–7.13(m, 5H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 24.9 (d, J = 5 Hz, CHMe2), 25.8 (s, CHMe2), 29.2 (d, J = 5 Hz, CHMe2), 47.0 (s, CH2C6H4NMe2), 54.0 (s, CH2C6H4NMe2), 117.9 (s, Ar), 121.1 (s, Ar), 124.2 (s, Ar), 125.7 (s, Ar), 126.4 (s, Ar), 127.6 (d, J = 9 Hz, Ar), 129.8 (s, Ar), 134.2 (d, J = 15 Hz, Ar), 136.0 (d, J = 23 Hz, Ar), 143.2 (s, Ar), 144.2 (d, J = 4 Hz, Ar), 146.2 (d, J = 21 Hz, Ar), 178.5 (d, J = 79 Hz, NCN). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = 7.3 (s, CPPh2). Anal. calcd for C55H68N4PLu(%): C, 66.65; H, 6.92; N, 5.65. Found: C, 66.81; H, 6.88; N, 5.73.
Synthesis of [o-Me2NC6H4CH2C(NC6H3iPr2-2,6)2]Lu(CH2C6H4NMe2-o)[O(CH2)4PPh2] (2). A THF solution (10 mL) of Lu(o-CH2C6H4 NMe2)3 (0.29 g, 0.5 mmol) was added into a stirred solution (20 mL) of (Ph2P)[C(NR)(NHR)] (R = 2,6-iPr2C6H3) (0.27 g, 0.5 mmol) in THF. The reaction solution was allowed to stir for 36 h at 60 °C and all volatiles were removed under vacuum. The oily residue was washed with cold hexane and a yellow powder was obtained by filtration. The yellow powder was recrystallized in toluene at −35 °C for one day to give a pale yellow powder of 2 (0.51 g, 90%). 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 1.09 (br s, 4H, β-THF), 1.39 (d, 24H, 3JH–H = 4 Hz, CHMe2), 1.78 (m, 2H, O(CH2)2CH2CH2PPh2), 1.88 (s, 8H, CH2C6H4NMe2-o and CH2C6H4NMe2), 1.98 (m, 2H, OCH2CH2(CH2)2 PPh2), 2.31 (m, 2H, O(CH2)3CH2PPh2), 2.47 (s, 6H, CH2C6H4NMe2), 3.30 (br s, 4H, α-THF), 3.84 (br, 6H, CHMe2 and CH2C6H4NMe2), 4.04 (m, 2H, OCH2(CH2)3PPh2), 6.59–6.63 (m, 2H, Ar), 6.76 (d, 1H, 3JH–H = 4 Hz, Ar), 6.87 (t, 1H, 3JH–H = 8 Hz, Ar), 6.92 (t, 2H, 3JH–H = 8 Hz, Ar), 7.00–7.15 (m, 13H, Ar), 7.57 (m. 4H, Ar), 7.65 (d. 3JH–H = 4 Hz, 1H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 23.4 (d, J = 16 Hz, O(CH2)2CH2CH2PPh2), 24.7 (s, β-THF), 25.6 (s, CHMe2), 26.8 (s, CHMe2), 28.1 (br, CHMe2), 29.6 (d, J = 13 Hz, O(CH2)3CH2PPh2), 29.9 (s, CH2C6H4NMe2), 38.6 (d, J = 11 Hz, OCH2CH2(CH2)2PPh2), 44.5 (s, CH2C6H4NMe2), 44.7 (s, CH2C6H4NMe2), 46.4 (s, CH2C6H4NMe2), 69.3 (s, OCH2(CH2)3PPh2), 69.9 (s, α-THF), 116.8 (s, Ar), 118.6 (s, Ar), 120.2 (s, Ar), 123.9 (s, Ar), 124.6 (s, Ar), 124.7 (s, Ar), 127.0 (s, Ar), 128.7 (s, Ar), 128.8 (s, Ar), 129.3 (s, Ar), 132.1 (s, Ar), 133.1 (s, Ar), 133.3 (d, J = 18 Hz, Ar), 140.1 (d, J = 15 Hz, Ar), 140.7 (s, Ar), 143.1 (s, Ar), 143.9 (br, Ar), 147.6 (s, Ar), 152.7 (s, Ar), 176.6 (s, NCN). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = −16.9 (s, O(CH2)4PPh2). Anal. calcd for C63H84N4PO2Lu(%): C, 64.82; H, 7.25; N, 4.80. Found: C, 64.52; H, 7.20; N, 4.57.
Synthesis of {[(Ph2P)C(NC6H3iPr2-2,6)2]Y(μ-Me)}3(μ3-Me)(μ3-CH2) (3). A solution of AlMe3 (1.0 mL, 1 M in hexane, 1 mmol) in toluene (2 mL) was added slowly to a stirred solution of complex 1-Y (0.45 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 3 h. The toluene was removed under vacuum, and the oily yellow residue turned into a white powder after washing twice with hexane (2 mL), which was collected by filtration and dried. The white powder was crystallized in toluene and stored at −35 °C to yield complex 3 (0.30 g, 92%) as colorless crystals. 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 0.90 (s, 3H, μ3-Me), 1.05 (s, 9H, μ2-Me), 1.26 (d, 3JH–H = 4 Hz, 36H, CHMe2), 1.30 (d, 3JH–H = 8 Hz, 36H, CHMe2), 2.01 (s, 2H, μ3-CH2), 3.71 (br s, 12H, CHMe2), 6.83 (br s, 36H, Ar), 7.25 (br s, 12H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 23.7 (s, CHMe2), 27.8 (s, CHMe2), 29.0 (s, CHMe2), 36.5 (t, J = 24 Hz, μ2-Me), 47.6 (s, μ3-Me), 109.9 (d, JY–C = 23 Hz, μ3-CH2), 123.8 (s, Ar), 125.4 (s, Ar), 128.1 (s, Ar), 128.4 (s, Ar), 129.0 (s, Ar), 135.0 (d, J = 22 Hz, Ar), 136.3 (d, J = 16 Hz, Ar), 142.4 (s, Ar), 142.9 (s, Ar), 179.1 (d, J = 67 Hz, NCN). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = 1.4 (s, CPPh2). Anal. calcd for C116H146N6P3Y3(%): C, 70.22; H, 7.42; N, 4.24. Found: C, 70.01; H, 7.20; N, 4.04.
Synthesis of {[(Ph2P)C(NC6H3iPr2-2,6)2]Lu(μ-Me)Me}2 (4). A solution of AlMe3 (1.0 mL, 1 M in hexane, 1 mmol) in toluene (2 mL) was added slowly to a stirred solution of complex 1-Lu (0.49 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 3 h. The toluene was removed under vacuum, and the oily yellow residue turned into a white powder after washing twice with hexane (2 mL), which was collected by filtration and dried. The white powder was crystallized in toluene and stored at −35 °C to yield complex 4 (0.29 g, 78%) as colorless crystals. 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 0.82 (br, 12H, Lu–Me), 1.18 (d, 3JH–H = 4 Hz, 24H, CHMe2), 1.33 (d, 3JH–H = 8 Hz, 24H, CHMe2), 3.69 (m, 8H, CHMe2), 6.71–6.73 (m, 8H, Ar), 6.79–6.84 (m, 8H, Ar), 7.01–7.07 (m, 6H, Ar), 7.12–7.13 (m, 4H, Ar) 7.29–7.32 (m, 6H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 21.4 (s, CHMe2), 22.8 (s, CHMe2), 26.8 (s, CHMe2), 29.0 (s, CHMe2), 30.2 (s, CHMe2), 43.2 (s, Lu–Me), 123.5 (s, Ar), 125.7 (s, Ar), 128.2 (s, Ar), 128.6 (s, Ar), 129.1 (s, Ar), 129.3 (s, Ar), 134.5 (d, J = 13 Hz, Ar), 135.3 (d, J = 23 Hz, Ar), 137.9 (s, Ar), 141.5 (s, Ar), 142.3 (s, Ar). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = −1.3 (s, CPPh2). Anal. calcd for C78H100N4P2Lu2 (%): C, 62.23; H, 6.70; N, 3.72. Found: C, 62.02; H, 6.91; N, 4.02.
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2][(Me)C(NC6H3iPr2-2,6)2]Lu (Me) (5). 10 mL of a toluene solution of complex 4 (0.75 g, 0.5 mmol) was allowed to stir at 100 °C for 36 h. Then the toluene was removed under vacuum, and the oily yellow residue turned into a white powder after washing twice with hexane (2 mL), which was collected by filtration and dried. The white powder was crystallized in toluene and stored at −35 °C to yield complex 5 (0.21 g, 37%) as colorless crystals. 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 0.36 (s, 3H, Lu–Me), 1.01 (d, 3JH–H = 8 Hz, 12H, CHMe2), 1.06 (br, 12H, CHMe2), 1.13 (d, 3JH–H = 8 Hz, 12H, CHMe2), 1.22 (d, 3JH–H = 2 Hz, 6H, CHMe2), 1.39 (s, 3H, NC(Me)N), 1.43 (d, 3JH–H = 8 Hz, 6H, CHMe2), 3.30 (br, 4H, CHMe2), 3.56 (m, 2H, CHMe2), 3.84 (m, 2H, CHMe2), 6.72–6.80 (m, 10H, Ar), 7.04 (br s, 6H, Ar), 7.15–7.19 (m, 6H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 17.6 (s, NC(Me)N), 22.8 (s, CHMe2), 23.1 (d, J = 4 Hz, CHMe2), 24.6 (d, J = 5 Hz, CHMe2), 25.0 (s, CHMe2), 28.6 (d, J = 18 Hz, CHMe2), 28.9 (s, CHMe2), 29.3 (d, J = 4 Hz, CHMe2), 35.7 (s, Lu–Me), 123.2 (d, J = 22 Hz, Ar), 124.0 (s, Ar), 125.2 (d, J = 47 Hz, Ar), 127.9 (s, Ar), 128.2 (s, Ar), 128.4 (s, Ar), 134.5 (d, J = 13 Hz, Ar), 135.0 (d, J = 23 Hz, Ar), 141.7 (d, J = 5 Hz, Ar), 142.7 (s, Ar), 142.9 (s, Ar), 143.2 (s, Ar), 143.8 (s, Ar), 177.0 (s, NC(Me)N), 178.5 (d, J = 69 Hz, NC(P)N). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = 5.3 (s, CPPh2). Anal. calcd for C64H85N4PLu(%): C, 68.86; H, 7.68; N, 5.02. Found: C, 68.90; H, 7.39; N, 5.05.
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]Y(AlMe4)(Me) (6-Y). A solution of AlMe3 (1.5 mL, 1 M in hexane, 1.5 mmol) in toluene (2 mL) was added slowly to a stirred solution of 1-Y (0.45 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 2 h. Complex 6-Y is unstable in solution, and we could only detect the formation of 6-Y by 1H NMR of the reaction solution (about 95% NMR yield).81H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = −0.13 (s, 12H, AlMe4), 0.30 (s, 3H, Y–Me), 1.25 (br s, 24H, CHMe2), 3.58 (br s, 4H, CHMe2), 6.54–7.28 (m, Ar). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = −0.9 (s, CPPh2).
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]Lu(AlMe4)(Me) (6-Lu). A solution of AlMe3 (1.5 mL, 1 M in hexane, 1.5 mmol) in toluene (2 mL) was added slowly to a stirred solution of 1-Lu (0.49 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 3 h. The toluene was removed under vacuum, and the oily yellow residue turned into a white powder after washing twice with hexane (2 mL), which was collected by filtration and dried. The white powder was crystallized in toluene and stored at −35 °C to yield complex 6-Lu (0.30 g, 74%) as colorless crystals. 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 0.16 (s, 12H, AlMe4), 0.29 (s, 3H, Lu–Me), 0.97–1.26 (br s, 24H, CHMe2), 3.61 (br s, 4H, CHMe2), 6.73–6.85 (m, 12H, Ar), 7.25–7.29 (m, 4H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 6.4 (s, AlMe4), 22.6 (br s, CHMe2), 26.2 (br s, CHMe2), 27.7 (br s, CHMe2), 29.1 (s, CHMe2), 35.7 (s, CHMe2), 123.6 (s, Ar), 126.2 (s, Ar), 128.2 (s, Ar), 129.3 (s, Ar), 134.0 (d, J = 13 Hz, Ar), 135.0 (d, J = 23 Hz, Ar), 140.7 (d, J = 5 Hz, Ar), 142.4 (br s, Ar), 181.4 (d, J = 62 Hz, NCN). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = −0.6 (s, CPPh2). Anal. calcd for C42H59N2PLuAl (%): C, 61.16; H, 7.21; N, 3.40. Found: C, 60.92; H, 7.20; N, 3.18.
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ4-CH)(AlMe3)2(μ-Me) (7). A solution of AlMe3 (1.5 mL, 1 M in hexane, 1.5 mmol) in toluene (2 mL) was added slowly to a stirred solution of 1-Y (0.45 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 24 h. Due to the extremely low yield, sufficient quantities of complex 7 which can be used to data collections such as NMR (except for X-ray single crystal structures) were not obtained.
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]2Y2(μ5-C)(AlMe2)(AlMe3)2(μ-Me) (8). A solution of AlMe3 (1.5 mL, 1 M in hexane, 1.5 mmol) in toluene (2 mL) was added slowly to a stirred solution of 1-Y (0.45 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 24 h. The toluene was removed under vacuum, and the oily yellow residue turned into a white powder after washing twice with hexane (2 mL), which was collected by filtration and dried. The white powder was crystallized in toluene and stored at −35 °C to yield complex 8 (0.12 g, 31%) as colorless crystals. 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = −0.73 (br s, 6H, μ4-CAlMe2), −0.13 (br s, 9H, (μ2-Me)2AlMe and μ2-Me), 0.77 (br s, 12H, (μ2-Me)2AlMe), 1.25 (s, 24H, CHMe2), 1.30 (s, 24H, CHMe2), 3.62 (br s, 8H, CHMe2), 6.72 (br s, 24H, Ar), 7.12 (m, 8H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = −0.2 (s, μ4-CAlMe2), 8.24 (s, AlMe3), 23.4 (s, CHMe2), 28.9 (s, CHMe2), 29.1 (s, CHMe2), 32.0 (t, JY–C = 20 Hz, μ2-Me), 115.4 (s, Ar), 123.6 (s, Ar), 126.2 (s, Ar), 127.9 (s, Ar), 128.0 (s, Ar), 135.2 (d, J = 15 Hz, Ar), 135.9 (d, J = 24 Hz, Ar), 141.7 (d, J = 5 Hz, Ar), 143.1 (s, Ar), 180.8 (d, J = 69 Hz, NCN). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = 5.7 (s, CPPh2). Anal. calcd for C84H115N4P2Al3Y2(%): C, 67.20; H, 7.72; N, 3.73. Found: C, 67.01; H, 7.40; N, 4.11.
Synthesis of [(Ph2P)C(NC6H3iPr2-2,6)2]Y(AlMe4)2 (9). A solution of AlMe3 (2.0 mL, 1 M in hexane, 2 mmol) in toluene (2 mL) was added slowly to a stirred solution of 1-Y (0.452 g, 0.5 mmol) in toluene (10 mL) at ambient temperature. The reaction mixture was allowed to stir for 3 h. The toluene was removed under vacuum, and the oily yellow residue turned into a white powder after washing twice with hexane (2 mL), which was collected by filtration and dried. The white powder was crystallized in toluene and stored at −35 °C to yield complex 9 (0.34 g, 85%) as colorless crystals. 1H NMR (400 MHz, C6D6, 25 °C): δ (ppm) = 0.07 (s, 24H, AlMe4), 1.16 (d, 3JH–H = 4 Hz, 12H, CHMe2), 1.21 (d, 3JH–H = 8 Hz, 12H, CHMe2), 3.54 (m, 4H, CHMe2), 6.67–6.74 (m, 6H, Ar), 6.77–6.79 (m, 4H, Ar), 6.82–6.84 (m, 2H, Ar), 7.08–7.12 (m, 4H, Ar). 13C{1H} NMR (100 MHz, C6D6, 25 °C): δ (ppm) = 3.5 (s, AlMe4), 23.5 (d, J = 7 Hz, CHMe2), 28.2 (s, CHMe2), 29.1 (d, J = 2 Hz, CHMe2), 124.2 (s, Ar), 126.8 (s, Ar), 128.2 (s, Ar), 128.3 (s, Ar), 128.9 (s, Ar), 134.9 (s, Ar), 135.1 (d, J = 24 Hz, Ar), 140.8 (d, J = 5 Hz, Ar), 143.3 (s, Ar). 31P{1H} NMR (162 MHz, C6D6, 25 °C): δ (ppm) = 4.2 (s, CPPh2). Anal. calcd for C45H68N2PAl2Y (%): C, 66.65; H, 8.45; N, 3.46. Found: C, 67.01; H, 8.29; N, 3.35.

Data availability

The data that support the findings of this study are available in the ESI† of this article.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (grant no. 21871052). We thank Prof. Xigeng Zhou and Prof. Huadong Wang for their suggestions. We also thank Dr Yuejian Lin for the crystallographic structural analyses.

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Footnote

† Electronic supplementary information (ESI) available. CCDC 2389279 (for 1-Y), 2389282 (for 1-Lu), 2389309 (for 2), 2389276 (for 4), 2389280 (for 5), 2389278 (for 6-Lu), 2389281 (for 7), 2389283 (for 8) and 2389277 (for 9). For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d4dt03060e
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