Straightforward construction of a rare-earth diphosphanato complex from white phosphorus: synthesis and reactivity

Abstract

The direct construction of functionalized diphosphine ligands from P₄ is a highly valuable but challenging transformation. In this work, a simple method has been developed for the direct formation of an amido-functionalized diphosphanato ligand from a silyl-bridged amido/methylene yttrium complex and white phosphorus. The resulting amido-functionalized diphosphanato yttrium complex 2 has proved to be a useful intermediate for further diversification of the diphosphine ligand through the metal template procedure, for which no evident limitations are enforced by initially present substituents and ancillary ligands, and some unprecedented reactivity patterns of the RPPR unit are revealed. The results described here demonstrate that appending a strongly coordinative substituent to the alkyl ligand together with a coordination to rare earth ions is an efficient strategy for controlling the cleavage modes of P₄ during alkylation and the reactivity of the resulting diphosphanato complex.

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Introduction

Diphosphine-based ligands play an important role in catalysis, coordination and organometallic chemistry.^1–3 To tune their properties for potential applications and improve the overall synthetic efficiency, significant effort continues to be devoted to the development of new approaches for their synthesis and new diphosphine-based structures.^4–6 Among these approaches, the introduction of one or more heteroatoms (e.g. O, N, S, Se, Si, and F) into diphosphine backbones is especially attractive, as the presence of heteroatoms will have a much greater influence on the coordination modes and donor ability than the variation of organic substituents at the P atoms, and thus offers new opportunities for controlling the reactivity trends, catalytic behaviour and physical properties of metal complexes.^7–12 For example, the pendant amines on diphosphine ligands facilitate the binding and heterolytic cleavage of H₂ or serve as proton and hydride relays for metal-mediated hydrogen transfers.^9c,d

Traditionally, multifunctionalized diphosphine ligands are prefabricated by stepwise processes starting from PCl₃ or its equivalents before application in organic and organometallic syntheses. Alternatively, in a few cases they can be generated in situ by the reaction of a metal phosphinido or phosphinidene complex intermediate (Scheme 1A).¹³ Obviously, these synthetic approaches to metal complexes containing polyfunctional diphosphine ligands often require expensive and/or toxic reagents and generate a large amount of waste, further compounded by limitations of substituent scope due to difficulties in preparing related P-based reactant precursors. If white phosphorus (P₄) could be directly used in the construction of polyfunctional diphosphine ligands, it would provide a simpler, more environmentally benign and higher atom-economical process compared to the use of classical methods involving pollutants, such as PCl₃, as starting materials. Although a great deal of effort has been devoted to the activation of P₄ over the last four decades, reactions that can form diphosphine skeletons either as free species or as complexed ligands remain scarce.^6,14–17 In fact, there are currently no generally satisfactory routes to the formation of polyfunctional diphosphine moieties from P₄ without the formation of byproducts. The functionalization of P₄ using alkyl/aryl metal complexes is relatively uncontrollable and tends to form monophosphanes or partly P-alkylated (arylated) polyphosphorus species (Scheme 1B).^16,18,19 The difficulty of forming the diphosphanato or diphosphenyl complexes may reflect the challenge of controlling the cleavage pattern of P₄ during alkylation/arylation, requiring a larger energy input for the simultaneous cleavage of four P–P bonds compared with that for the relatively small number of P–P bonds in the formation of [P₄R_m]ⁿ⁻ (m = 1–3; n = 0–4; R = alkyl, aryl) moieties.

Scheme 1 Synthetic strategies to access functionalized diphosphanato and diphosphine metal complexes and main reactivity patterns of metal alkyl/aryl complexes toward P₄.

On the other hand, although metal-based reductive cleavage of P₄ to give a diphosphorus ligand is a well-established process, the exploration of the resulting P₂ fragment as a synthon for diphosphines remains limited.²⁰ Pioneering works reported by West, Bertrand, and Cummins et al. showed that the activation of P₄ by disilenes, carbenes or photochemical alkylation could lead to the formation of the corresponding silylene-, alkylidenyl- and alkyl-substituted diphosphanes, respectively, and these findings open new avenues for the generation of reactive intermediates in P₂ chemistry.^4a,e,5b,6

Metal diphosphanato complexes could be considered as attractive intermediates for the synthesis of a variety of neutral or anionic diphosphine ligands as evidenced by their participation in the formation of carbon–phosphorus and heteroatom–phosphorus bonds.^21,22 However, this class of compounds are still rare due to challenges in their synthesis.²³ Given the pronounced ability of rare earth metals to influence the reactivity of small molecule substrates and high activity of lanthanide–alkyl bonds,^24,25 we reasoned that the obstacles encountered in the direct conversion of P₄ to dialkyldiphosphanato complexes via reductive insertion processes might be overcome by appending the strong chelating coordination moiety to the alkyl ligand together with a coordination to lanthanide ions, because this not only offers a sterically forced preferred orientation of the nucleophilic attack at P₄ in an expected position for regioselective cleavage of P–P bonds, but also may inhibit the alkyl migration between P atoms (Scheme 1C). Here, we report a simple method for the direct and highly atom-economical construction and late-stage diversification of amido-functionalized diphosphanato ligands from white phosphorus enabled by rare earth metals, for which some unprecedented reactivity patterns of the RPPR moiety toward small molecule substrates are revealed.

Results and discussion

A new silyl-bridged amido/methylene yttrium complex 1 was prepared by the reaction of Tp^Me2YBn₂(THF) (Bn = CH₂Ph) with HN(SiMe₃)₂. Surprisingly, only a low yield of 1 was obtained when 1 equiv. of HN(SiMe₃)₂ was used, and complete transformation of Tp^Me2YBn₂(THF) into 1 would require the use of 2 equiv. of HN(SiMe₃)₂ (Scheme 2). These results indicate that 1 probably results from amine elimination of intermediate B rather than the toluene elimination of A, and steric crowding around the metal center might play a more important role than ligand basicity in driving the methyl deprotonation. Complex 1 has been characterized by elemental analysis, ¹H and ¹³C {¹H} NMR spectra, and its solid-state structure has also been determined by X-ray diffraction analysis (Fig. S26†).

Scheme 2 Synthesis of 1,2-dialkyldiphosphanato yttrium complex 2.

Treatment of 1 with 0.25 equiv. of P₄ in toluene at ambient temperature afforded the Y–C bond insertion/coupling product 2 in 60% isolated yield (Scheme 2), which represents the first example of the efficient formation of amido-functionalized diphosphanato metal complexes directly from P₄. Complex 2 is readily soluble in THF but sparingly soluble in toluene. The ³¹P NMR spectrum of 2 displayed a triplet peak at δ = 97.10 ppm (¹J_YP = 30 Hz), indicating that its binuclear structure is symmetric. Consistent with this, only one set of signals attributable to the Tp^Me2 ligand was observed in the ¹H and ¹³C {¹H} NMR spectra of 2. Crystallization of 2 in THF gave the THF adduct 2·THF. Significantly, the THF coordination triggers the difunctionalized diphosphanato ligand to isomerize from trans to cis (Fig. 1). Furthermore, in contrast to 2, 2·THF is insoluble in THF. The P–P distance in 2 (2.213(2) Å) is slightly longer than the values observed in Cp₂NbH(P₂Ph₂) (2.136(5) Å) and Cp₂TaH(P₂Cy₂) (2.131(3) Å).¹⁵

Fig. 1 Molecular structures of 2 (a) and 2·THF (b) with 30% thermal ellipsoids. All hydrogen atoms are omitted for clarity.

It should be noted that the chelating coordination of the pendant amido moiety might play a key role in determining the formation of 2. In our previous study,²⁶ we found that the rare-earth dialkyl complex Tp^Me2LnBn₂(THF) reacts with P₄ to yield novel rare-earth norbornane-BnP₇⁴⁻ and/or chain Bn₄P₆⁴⁻ complexes, accompanied by the formation of PBn₃,^26b and the rare-earth monoalkyl complex LYR(THF) (L = N,N′-2,6-diisopropylphenyl-1,4-diazabutadiene, R = CH₂C₆H₄NMe₂-2) reacts with P₄ to give a rare-earth organic cyclo-P₄ complex (LY·DMAP)₂[1,2-R₂-cyclo-P₄], which further transforms into other polyphosphorus species through alkyl migration.^26c These results demonstrate that appending a strongly coordinative amino substituent to the alkyl group, together with a coordination to Y³⁺ ions, surely offers a good stabilizing environment for 1,2-dialkyldiphosphanato dianion species.

CS₂ is a cheap and manageable feedstock for the synthesis of sulfur-containing molecules, and the development of new reactivity patterns of CS₂ and new methods for its activation under mild conditions is attracting scientific and industrial interest, including its use as a model for CO₂ and its implication in catalytic degradation of CS₂ pollutants.^27,28 Despite tremendous advances in fragmented coupling reactions involving CS₂, there is no report on the combined reorganization/cyclization of CS₂ with other organic functional groups.^28,29 Contrary to the metal complexes bearing other phosphorus-based ligands (e.g. phosphinidene and phosphinido),^13b,30 treatment of 2 with two equiv. of CS₂ in THF at room temperature led to the formation of the highly reorganized 2-sulfido-2,5-dihydro-1,2,5-thiadiphosphole-3,4-dithiolate dianion ligand that bridges the two yttrium atoms in a non-symmetric fashion (Scheme 3). Noticeably, the reaction works almost exclusively for the formation of 3. Our attempts to use 1 equiv. of CS₂ for the isolation of the reaction intermediates afforded 3 with the recovery of significant quantities of the starting material 2, which was also detected from ³¹P NMR spectra at the end of the reaction. The X-ray structure of 3 (Fig. 2) reveals that the resulting thiadiphosphole ring was coplanar. The C41–C42 distance (1.332(6) Å) is a normal C=C double bond length. The P1–S3 and P2–S3 distances (2.157(2) and 2.100(2) Å, respectively) exhibit typical P–S single bond characteristics, whereas the P2–S4 distance (1.999(2) Å) falls in the range of the P=S double bond lengths (1.949–2.09 Å).³¹ The Y2–S4 distance (2.805(2) Å) is longer than the Y2–S2 one (2.727(2) Å). The ³¹P NMR spectrum of 3 shows two characteristic signals at δ = 92.43 ppm (q, P1, ¹J_YP = 17.6 Hz) and 47.88 ppm (s, P2). The ¹³C {¹H} NMR spectrum of 3 displays two sets of peaks at δ = 152.68 ppm (dd, ¹J_PC = 3.21 Hz, ²J_YC = 1.56 Hz) and 152.21 ppm (d, ¹J_PC = 1.99 Hz), attributable to the resonances of the carbon atoms of the thiadiphosphole ring.

Scheme 3 Reaction of 1,2-dialkyldiphosphanato yttrium complex 2 with CS₂.

Fig. 2 Molecular structure of 3 with 30% thermal ellipsoids. All hydrogen atoms are omitted for clarity.

The great success of alkene metathesis has stimulated research activity aimed at mapping the analogous reactivity modes of unsaturated carbon–heteroatom functionalities.^32,33 However, CS₂ metathesis reactions remain little explored. In contrast to the classical metatheses, the formation of 3 is not accompanied by the loss of any fragments. This finding provides a new probe for designing convergent metatheses that allow the simultaneous cleavage of multiple different chemical bonds and sequential incorporation of all fragments into a single organic architecture, without any fragment dispersion. To obtain an insight into the driving force for the reaction, the reaction was further investigated by theoretical calculations at the DFT level. The reaction profile appears to be quite complex (Fig. S34, ESI†). The reaction begins by the sequential addition of two CS₂ molecules to the diphosphanato ligand. These electrophilic additions of CS₂ to the phosphorus are kinetically accessible and the height of the barrier is only associated with the binding of the incoming CS₂. This yields complex D, which is thermodynamically favorable (22.4 kcal mol⁻¹). From there, one CS₂ moiety can undergo a [2 + 2] addition to the P–P bond that is activated by the two electrophilic additions. This reaction is not assisted by the metal center, explaining that this is the rate determining step. After this migratory insertion, the C–S bond becomes strongly activated and can be easily cleaved to form a P–S–P bridge (complex F). The lack of stability of complex F allows further reaction. A kinetically accessible intramolecular cyclization transition state has been located, yielding a stable five-membered ring complex G (−30.1 kcal mol⁻¹). This complex undergoes a facile metal-assisted intramolecular C–S bond activation, affording the formation of the very stable complex 3 (−77.1 kcal mol⁻¹).

Diphosphorus ligands connected by a single atom have drawn considerable interest due to their complementary properties to wide bite-angle diphosphine ligands in homogeneous catalysis.³⁴ Interestingly, the reaction of 2 with excess CO (1 atm) at 50 °C afforded the P–P and Y–P bond insertion product 4 (Scheme 4). The resulting carbonyl-bridged diphosphorus anion ligand features an additional degree of electron-delocalization control over the binding sites. In the ¹H NMR spectra of 4, the two sets of signals for the methyl protons of Me₃Si substituents (δ −0.13 and −0.09 ppm) are consistent with the observation that the Y³⁺ ions have two different coordination environments. Moreover, different chemical shifts assigned to the two Tp^Me2 ligands were observed in its ¹H NMR spectrum. The ³¹P NMR spectrum shows two peaks at δ = 65.01 (d, ¹J_YP = 136.4 Hz) and −11.89 (d, ¹J_YP = 120.3 Hz) ppm. X-ray single crystal diffraction analyses of 4 (Fig. 3) clearly demonstrate the insertion of one CO molecule into the P–P bond to form a C–P single bond and a C=P double bond. Complex 4 has a distinctive Y–O(phosphaenolate) distance (2.153(2) Å).

Scheme 4 CO insertion into the P–P and Y–P bonds via an unusual Y–P addition and sequential phosphanyl migration pathway.

Fig. 3 Molecular structure of 4 with 30% thermal ellipsoids. All hydrogen atoms are omitted for clarity.

The catalytic carbonylation of organic substrates has become a powerful method in organic synthesis. Despite tremendous advances in this area, this process has mainly focused on late transition metals. Rare earth-mediated CO insertions have been largely unexplored. This is mainly due to the mismatch in the orbital energy between the hard rare earth ions and the soft carbon monoxide (or acyl) ligand, leading to an unstable acyl complex intermediate having a strong tendency toward dimerization or deoxygenative coupling.^13b,35,36 Therefore, the formation of 4 is somewhat surprising. To explain the unusual reactivity of 2 toward CO, a DFT investigation of a possible reaction mechanism was carried out (see Fig. S35†). It is found that CO insertion into a Y–P bond followed by the migration of another P atom to the resulting acyl carbon is a knetically facile (highest barrier of 13.8 kcal mol⁻¹) and thermodynamically favorable process (−33.9 kcal mol⁻¹). This is quite different from the conventional oxidative-addition followed by CO insertion and sequential reductive-elimination pathways for transition-metal-mediated CO insertion into a single bond of organic substrates.

To validate our proposal of the preferential addition of the Y–P bond over the P–P bond, we carried out the reaction of 2 with PhNCS (Scheme 5). The addition of 2 equiv. of PhNCS to a THF solution of 2 resulted in an immediate color change, yielding a colorless solution, and storing the solution at room temperature for 48 h gave the Y–P bond insertion product 5 as colorless crystals in 93% isolated yield. In contrast to CS₂ and CO, complex 5 did not undergo either isomerization or further reaction with excess PhNCS, even with prolonged heating at 70 °C. Regrettably, the low solubility of 5 precluded the acquisition of its NMR spectra. The same reactivity trend was observed when 2 reacted with 2 equiv. of PhNCO, giving the addition product 6. Recrystallization of 6 in THF/hexane led to the loss of one coordinated THF, giving compound 7, in which a different coordination situation of the diphosphine ligand was observed (Scheme 5). In contrast to 5, compounds 6 and 7 readily dissolve in THF. Notably, the transformation of 6 into 7 occurred slowly under vacuum conditions or exposure to nitrogen gas too. The ³¹P NMR spectrum of 7 shows two sets of signals at δ −39.64 (dd, J_PP = 374, 12.8 Hz) and −26.71 (dm, ¹J_PP = 374 Hz) ppm, which may be attributed to the free and coordinated P atoms, respectively.^20d The molecular structures of complexes 5–7 clearly indicate the formation of four-substituted diphosphine moieties (Fig. S28–S30†).

Scheme 5 Insertions of PhNCS, PhNCO and PhN=NPh into the Y–P bond of 2.

The ³¹P NMR monitoring data indicate that the reaction of 2 with azobenzene is much slower than those with CS₂ and PhNCO, which likely resulted from the larger steric hindrance and the non-polarity effect of azobenzene.^37,38 Compound 8 was sparingly soluble in THF-d₈, enabling the acquisition of ¹H NMR and ³¹P NMR data, but preventing characterization by ¹³C {¹H} NMR spectra. The ³¹P NMR spectrum displays only a singlet at δ = 50.66 ppm, revealing that 8 is a symmetric structure as confirmed by X-ray crystallography (Fig. S31 in the ESI†).

The reaction of 2 with 0.5 equiv. of S₈ in THF at room temperature gave the diphosphinodithioate complex 9 in 94% yield. Chalcogenylation is of great significance in adjusting the complexation ability and catalytic behaviour of diphosphines or in their potential utilization as synthetic intermediates.^39a,40 Despite a large number of structural variants, such a substitution pattern for diphosphorus-containing species is still unknown due to the absence of suitable synthetic methods. Although the chemistry of phosphine sulfide and selenide ligands has been extensively investigated, the complexes of diphosphoranes containing P–P bonds are primarily limited to diphosphane mono- and di-sulfides/selenides.^39b,40 The polychalcogenylations of either neutral or anionic P–P units with elemental sulfur (selenium) are typically accompanied by the P–P cleavage.²¹ To obtain a good insight into the formation process of 9, we firstly attempted the reaction of 2 with 0.25 equiv. of S₈, but it generated a mixture of 9 and several unidentified products. Furthermore, the reaction of 2 with Se, which is known to have relatively modest reactivity compared with S₈, was examined. 2 reacted with 3 equiv. of Se to yield the diphosphine triselenide complex 10 in 83% yield (Scheme 6). Despite several attempts, we were unable to gain the structural information of the product from a similar reaction of 2 with 4 equiv. of Se, owing to its low solubility even in polar organic solvents such as THF. The formation of 9 and 10 could be interpreted as a sulfur/selenium insertion into each Y–P bond of 2, followed by oxidative chalcogenylation of phosphorus. This further demonstrates that the reactivity of diphosphanato ligands toward small molecules may be adjusted by complexation of Y³⁺ ions. Complexes 9 and 10 were fully characterized; this information, including their single-crystal X-ray structures, can be found in the ESI (Fig. S32 and S33†).

Scheme 6 Oxidative chalcogenylation of 2 with S₈ and Se.

Experimental

General procedures

All manipulations involving air- and moisture-sensitive compounds were carried out with rigorous exclusion of air and water, using standard Schlenk techniques or a Vigor glovebox under an atmosphere of dinitrogen. THF, toluene and hexane were purified using an Mbraun SPS-800 solvent purification system, dried over fresh Na chips and stored in the glovebox. C₆D₆ and THF-d₈ were obtained from Cambridge Isotope and dried over Na/K alloy prior to use. (Tp^Me2)YBn₂(THF) was prepared according to the literature procedure.⁴¹ HN[Si(CH₃)₃]₂, CS₂, PhNCS and PhNCO were purchased from J&K and dried with 4 Å sieves. Other commercially available reagents were purchased and used without purification. P₄ was prepared by sublimation of red phosphorus at 450 °C in a quartz tube under vacuum conditions and stored in the refrigerator of the glovebox. Organometallic samples for NMR spectroscopic measurements were prepared in the glovebox using J. Young valve NMR tubes. ¹H NMR, ¹³C NMR and ³¹P NMR spectra were recorded using a Bruker Avance 400 MHz spectrometer (FT, 400 MHz for ¹H; 100 MHz for ¹³C; and 161 MHz for ³¹P) at room temperature. Chemical shifts for ¹H and ¹³C NMR were quoted in ppm referenced to the residual resonance of the deuterated solvents. H₃PO₄ (85%) sealed in a capillary was used as an external standard in ³¹P NMR analysis. Elemental analyses for C, H and N were carried out using a Vario EL III elemental analyzer. The resonances of the B–H bond in the Tp^Me2ligand are too broad to be observed in their¹H NMR spectra.Caution: P₄ is light-sensitive and highly flammable upon exposure to air. It should be handled carefully.

Synthesis of 1

A THF solution of HN[Si(CH₃)₃]₂ (3.22 g, 20.0 mmol) was added slowly to a stirred THF solution (50 mL) of Tp^Me2YBn₂(THF) (6.40 g, 10.0 mmol) at room temperature. After stirring for 8 hours, all volatiles were removed under vacuum. The residue was washed twice with n-hexane (10 mL × 2) and dried under vacuum to give 1 as a white powder (5.67 g, 92% yield). Recrystallization of the white powder in a mixed solvent of THF and n-hexane afforded colorless crystals of 1 suitable for X-ray diffraction analysis. ¹H NMR (400 MHz, C₆D₆, 25 °C): δ (ppm) 5.56 (s, 3H, 4-H-Tp^Me2), 3.56 (m, 4H, THF), 2.50 (s, 9H, 3-CH₃-Tp^Me2), 2.10 (s, 9H, 5-CH₃-Tp^Me2), 1.14 (m, 4H, THF), 0.79 (s, 6H, Si(CH₃)₂), 0.33 (s, 9H, Si(CH₃)₃), 0.13 (d, ²J_YH = 1.6 Hz, 2H, SiCH₂Y); ¹³C{¹H} NMR (100 MHz, C₆D₆, 25 °C): δ (ppm) 150.13 (Tp^Me2), 145.49 (Tp^Me2), 105.91 (4-C-Tp^Me2), 71.27 (THF), 26.90 (d, ¹J_YC = 30.81 Hz, SiCH₂Y), 25.29 (THF), 14.73 (CH₃-Tp^Me2), 13.07 (CH₃-Tp^Me2), 8.33 (s, Si(CH₃)₂), 8.32 (s, Si(CH₃)₂), 5.74 (Si(CH₃)₃). Elemental analysis: calcd (%) for C₂₅H₄₇N₇BOSi₂Y: C, 48.62; H, 7.67; N, 15.88. Found: C, 48.04; H, 7.74; N, 16.17.

Synthesis and characterization of the diphosphanato yttrium complex 2 and 2·THF

P₄ (31.0 mg, 0.25 mmol) was added to a stirred toluene solution (2 mL) of 1 (617 mg, 1.0 mmol) at ambient temperature. The color of the reaction mixture gradually changed from light yellow to reddish brown. After half an hour, a pale solid began to precipitate out. The mixture was continuously stirred overnight, and the precipitate was filtered under reduced pressure, washed with 2 mL of n-hexane and dried under vacuum to give 2 as a pale yellow powder (342 mg, 60% yield). Yellow crystals of 2 suitable for X-ray single crystal diffraction analysis were obtained by evaporation of the solvent from the solution of 2 in a 30 : 1 mixture of toluene and THF. ¹H NMR (400 MHz, THF-d₈, 25 °C): δ (ppm) 5.76 (s, 2H, 4-H-Tp^Me2), 5.74 (s, 2H, 4-H-Tp^Me2), 5.25 (s, 2H, 4-H-Tp^Me2), 2.67 (s, 6H, CH₃-Tp^Me2), 2.59 (s, 6H, CH₃-Tp^Me2), 2.38–2.33 (m, 24H, CH₃-Tp^Me2), 1.29 (s, 4H, SiCH₂P), 0.27 (s, 12H, Si(CH₃)₂), 0.15 (s, 18H, Si(CH₃)₃); ¹³C{¹H} NMR (100 MHz, THF-d₈, 25 °C): δ (ppm) 152.66 (Tp^Me2), 151.79 (Tp^Me2), 150.55 (Tp^Me2), 145.46 (Tp^Me2), 145.35 (Tp^Me2), 144.63 (Tp^Me2), 106.80 (4-C-Tp^Me2), 106.20 (4-C-Tp^Me2), 19.22 (CH₃-Tp^Me2), 15.65 (CH₃-Tp^Me2), 14.67 (m, SiCH₂P), 13.31 (CH₃-Tp^Me2), 13.18 (CH₃-Tp^Me2), 13.06 (CH₃-Tp^Me2), 8.43 (Si(CH₃)₂), 8.15 (Si(CH₃)₂), 6.15 (Si(CH₃)₃); ³¹P NMR (161 MHz, THF-d₈, 25 °C): δ (ppm) −97.10 (t, ¹J_YP = 30 Hz). Elemental analysis: calcd (%) for C₄₂H₇₈N₁₄B₂Si₄P₂Y₂: C, 43.76; H, 6.82; N, 17.00. Found: C, 42.86; H, 6.69; N, 17.33. It is noted that recrystallization of 2 in THF afforded 2·THF as yellow crystals. Elemental analysis: calcd (%) for C₅₀H₉₄N₁₄B₂O₂Si₄P₂Y₂: C, 46.30; H, 7.30; N, 15.12. Found: C, 45.66; H, 7.14; N, 15.37. However, the difficulty in redissolving the isolated crystals of 2·THF prevented its characterization by NMR spectroscopy.

Synthesis of 3

A cooled THF solution (5 mL) of CS₂ (30.3 mg, 0.40 mmol) was added slowly to a stirred THF solution (10 mL) of 2 (230 mg, 0.20 mmol) at ambient temperature. The color of the mixture gradually changed from yellow to reddish brown. After stirring for 1 hour, the solvent was removed under vacuum and the residue was washed twice with n-hexane (10 mL × 2) and dried under vacuum to give 3 as a yellow powder (260 mg, 94% yield). Crystals suitable for X-ray analysis were obtained by recrystallization of 3 in toluene. ¹H NMR (400 MHz, THF-d₈, 25 °C): δ (ppm) 5.82 (s, 1H, 4-H-Tp^Me2), 5.81 (s, 1H, 4-H-Tp^Me2), 5.79 (s, 1H, 4-H-Tp^Me2), 5.76 (s, 1H, 4-H-Tp^Me2), 5.68 (s, 1H, 4-H-Tp^Me2), 5.57 (s, 1H, 4-H-Tp^Me2), 3.62 (m, THF), 2.65 (s, 3H, CH₃-Tp^Me2), 2.51 (s, 3H, CH₃-Tp^Me2), 2.47 (s, 3H, CH₃-Tp^Me2), 2.41–2.40 (m, 18H, CH₃-Tp^Me2), 2.37 (s, 3H, CH₃-Tp^Me2), 2.28 (s, 3H, CH₃-Tp^Me2), 2.22 (s, 3H, CH₃-Tp^Me2), 1.94–1.81 (m, 4H, SiCH₂P), 1.77 (m, THF), 0.48 (s, 3H, Si(CH₃)₂), 0.45 (s, 3H, Si(CH₃)₂), 0.30 (s, 3H, Si(CH₃)₂), 0.24 (s, 3H, Si(CH₃)₂), 0.00 (s, 9H, Si(CH₃)₃), −0.50 (s, 9H, Si(CH₃)₃); ¹³C{¹H} NMR (100 MHz, THF-d₈, 25 °C): δ (ppm) 152.67 (q, ¹J_PC = 3.21 Hz, ²J_YC = 1.56 Hz, SCPS), 152.38 (Tp^Me2), 152.22 (d, ¹J_PC = 1.99 Hz, SCPS₂), 151.70 (Tp^Me2), 151.28 (Tp^Me2), 150.69 (Tp^Me2), 150.66 (Tp^Me2), 150.08 (Tp^Me2), 147.16 (Tp^Me2), 146.76 (Tp^Me2), 146.16 (Tp^Me2), 145.42 (Tp^Me2), 144.32 (Tp^Me2), 106.82 (4-C-Tp^Me2), 106.68 (4-C-Tp^Me2), 106.58 (4-C-Tp^Me2), 106.45 (4-C-Tp^Me2), 106.37 (4-C-Tp^Me2), 106.27 (4-C-Tp^Me2), 68.02 (THF), 41.11 (d, ¹J_PC = 44.71 Hz, SiCH₂P), 32.69 (d, ¹J_PC = 34.45 Hz, SiCH₂P), 26.17 (THF), 16.52 (CH₃-Tp^Me2), 16.15 (CH₃-Tp^Me2), 15.58 (CH₃-Tp^Me2), 15.50 (CH₃-Tp^Me2), 14.49 (CH₃-Tp^Me2), 14.36 (CH₃-Tp^Me2), 13.18 (CH₃-Tp^Me2), 13.09 (CH₃-Tp^Me2), 13.04 (CH₃-Tp^Me2), 12.93 (CH₃-Tp^Me2), 12.85 (CH₃-Tp^Me2), 12.77 (CH₃-Tp^Me2), 9.27 (d, ³J_PC = 7.28 Hz, Si(CH₃)₂), 8.66 (d, ³J_PC = 11.6 Hz, Si(CH₃)₂), 6.41 (Si(CH₃)₂), 6.38 (Si(CH₃)₃), 6.25 (Si(CH₃)₂), 4.76 (Si(CH₃)₃); ³¹P NMR (161 MHz, THF-d₈, 25 °C): δ (ppm) 92.43 (q, ¹J_YP = 17.6 Hz), 47.88 (s). Elemental analysis: calcd (%) for C₄₈H₈₆N₁₄B₂OSi₄P₂S₄Y₂: C, 41.86; H, 6.29; N, 14.24. Found: C, 41.14; H, 6.16; N, 14.45.

Synthesis of 4

A THF solution (10 mL) of 2 (230 mg, 0.20 mmol) was degassed using freeze–pump–thaw cycles and then exposed to an excess of 1.0 atm of CO. The color of the reaction mixture gradually changed from yellow to orange. After stirring at 50 °C for two days, the solvent was removed under vacuum to give an orange solid. The residue was washed twice with hexane (5 mL × 2) and dried under vacuum, giving 4 as an orange powder (185 mg, 74% yield). The orange single crystals of 4 for X-ray diffraction analysis were obtained by solvent evaporation from a concentrated toluene solution (ca. 2 mL) of 4. ¹H NMR (400 MHz, toluene-d₈, 25 °C): δ (ppm) 5.61 (s, 2H, 4-H-Tp^Me2), 5.57 (s, 1H, 4-H-Tp^Me2), 5.50 (s, 2H, 4-H-Tp^Me2), 5.46 (s, 1H, 4-H-Tp^Me2), 3.67 (s, 4H, THF), 3.01 (s, 3H, CH₃-Tp^Me2), 2.93 (s, 3H, CH₃-Tp^Me2), 2.75 (s, 3H, CH₃-Tp^Me2), 2.64 (s, 3H, CH₃-Tp^Me2), 2.51 (s, 3H, CH₃-Tp^Me2), 2.43 (s, 3H, CH₃-Tp^Me2), 2.15–2.21 (m, 15H, CH₃-Tp^Me2), 2.06 (s, 3H, CH₃-Tp^Me2), 1.29–1.37 (m, 2H, SiCH₂P), 1.33 (s, 4H, THF), 1.08–1.22 (m, 4H, SiCH₂P), 0.66 (s, 3H, Si(CH₃)₂), 0.49 (s, 3H, Si(CH₃)₂), 0.41 (s, 6H, Si(CH₃)₂), −0.18 (s, 9H, Si(CH₃)₃), −0.22 (s, 9H, Si(CH₃)₃); ³¹P NMR (161 MHz, toluene-d₈, 25 °C): δ (ppm) 65.01 (d, ¹J_YP = 136.4 Hz), −11.89 (d, ¹J_YP = 120.3 Hz). ¹H NMR (400 MHz, C₆D₆, 25 °C): δ (ppm) 5.64 (s, 3H, 4-H-Tp^Me2), 5.53 (s, 2H, 4-H-Tp^Me2), 5.46 (s, 1H, 4-H-Tp^Me2), 3.78 (m, 4H, THF), 3.15 (s, 3H, CH₃-Tp^Me2), 2.96 (s, 3H, CH₃-Tp^Me2), 2.81 (s, 3H, CH₃-Tp^Me2), 2.67 (s, 3H, CH₃-Tp^Me2), 2.56 (s, 3H, CH₃-Tp^Me2), 2.49 (s, 3H, CH₃-Tp^Me2), 2.11–2.21 (m, 15H, CH₃-Tp^Me2), 2.05 (s, 3H, CH₃-Tp^Me2), 1.29–1.37 (m, 2H, SiCH₂P), 1.17 (m, 2 + 4H, SiCH₂P + THF), 0.74 (s, 3H, Si(CH₃)₂), 0.57 (s, 3H, Si(CH₃)₂), 0.45 (s, 6H, Si(CH₃)₂), −0.09 (s, 9H, Si(CH₃)₃), −0.13 (s, 9H, Si(CH₃)₃); ¹³C NMR (100 MHz, C₆D₆, 25 °C): δ (ppm) 151.55 (CO), 151.42 (Tp^Me2), 150.31 (Tp^Me2), 150.22 (Tp^Me2), 150.10 (Tp^Me2), 149.65 (Tp^Me2), 146.79 (Tp^Me2), 146.24 (Tp^Me2), 145.79 (Tp^Me2), 144.71 (Tp^Me2), 144.54 (Tp^Me2), 106.64 (4-C-Tp^Me2), 106.40 (4-C-Tp^Me2), 106.09 (4-C-Tp^Me2), 105.86 (4-C-Tp^Me2), 72.51 (THF), 25.14 (THF), 19.72 (d, ¹J_PC = 49.66 Hz, SiCH₂P), 15.84 (d, ¹J_PC = 12.42 Hz, SiCH₂P), 15.47 (CH₃-Tp^Me2), 15.33 (CH₃-Tp^Me2), 15.25 (CH₃-Tp^Me2), 15.07 (CH₃-Tp^Me2), 14.84 (CH₃-Tp^Me2), 14.71 (CH₃-Tp^Me2), 14.62 (CH₃-Tp^Me2), 13.21 (CH₃-Tp^Me2), 13.04 (CH₃-Tp^Me2), 12.98 (CH₃-Tp^Me2), 9.00 (Si(CH₃)₂), 8.44 (s, Si(CH₃)₂), 8.24 (s, Si(CH₃)₂), 5.81 (Si(CH₃)₃), 4.80 (Si(CH₃)₃), 1.43 (Si(CH₃)₂); ³¹P NMR (161 MHz, C₆D₆, 25 °C): δ (ppm) 66.56 (br s), −11.81 (br s). Elemental analysis: calcd (%) for C₄₇H₈₆N₁₄B₂O₂Si₄P₂Y₂: C, 45.05; H, 6.92; N, 15.65. Found: C, 44.33; H, 6.77; N, 15.75.

Synthesis of 5

A cooled THF solution (3 mL) of PhNCS (27.5 mg, 0.20 mmol) was added slowly to a stirred THF solution (10 mL) of 2 (115.2 mg, 0.10 mmol) at ambient temperature. After stirring for 5 min, the reaction solution was left at room temperature for 2 days to give 5 as colorless crystals (145 mg, 93% yield). Regrettably, the low solubility of 5 precluded the acquisition of its NMR spectra. Elemental analysis: calcd (%) for C₆₄H₁₀₂N₁₆B₂O₂Si₄P₂S₂Y₂: C, 49.10; H, 6.57; N, 14.32. Found: C, 49.74; H, 6.52; N, 14.59.

Synthesis of 6 and 7

A cooled THF solution (5 mL) of PhNCO (47.6 mg, 0.40 mmol) was added slowly to a stirred THF solution (10 mL) of 2 (230 mg, 0.20 mmol) at ambient temperature. The color of the reaction solution gradually changed from yellow to colorless. After stirring at ambient temperature for 12 h, the solution was concentrated to ca. 3 mL under reduced pressure. After allowing to stand at room temperature for several days, colorless crystals of complex 6 were obtained (169 mg, 55% yield). However, if the reaction mixture was directly evaporated to dryness under vacuum, washing the residue with hexane three times (10 mL × 3) followed by crystallization in THF/hexane would lead to the loss of one coordinated THF, affording 7 as a crystalline solid (267 mg, 87% yield). Crystals suitable for X-ray diffraction analysis were obtained by gas phase diffusion of hexane into the THF solution of 7. Notably, retransformation of 7 into 6 is quite difficult to perform in THF at room temperature, whereas transformation of 6 into 7 occurred slowly under vacuum conditions or exposure to nitrogen gas too. For example, the ³¹P NMR monitoring data indicate the formation of a small amount of 7 after storing the solution of 6 in THF-d₈ at room temperature for 1 week (Fig. S14†). Therefore, compound 6 is not characterized by EA and NMR spectra. For 7: ¹H NMR (400 MHz, THF-d₈, 25 °C): δ (ppm) 7.32 (d, 2H, ³J_HH = 7.72 Hz, Ph), 7.03 (t, 2H, ³J_HH = 7.32 Hz, Ph), 6.73 (t, 1H, ³J_HH = 7.2 Hz, Ph), 6.27 (t, 1H, ³J_HH = 7.08 Hz, Ph), 5.91 (m, 2H, Ph), 5.89 (s, 1H, 4-H-Tp^Me2), 5.82 (s, 1H, 4-H-Tp^Me2), 5.74 (s, 1H, 4-H-Tp^Me2), 5.59 (m, 2H, Ph), 5.54 (s, 1H, 4-H-Tp^Me2), 5.27 (s, 1H, 4-H-Tp^Me2), 5.27 (s, 1H, 4-H-Tp^Me2), 3.62 (m, 4H, THF), 2.57 (s, 6H, CH₃-Tp^Me2), 2.49 (s, 3H, CH₃-Tp^Me2), 2.45 (s, 3H, CH₃-Tp^Me2), 2.35 (s, 12H, CH₃-Tp^Me2), 2.31 (s, 3H, CH₃-Tp^Me2), 2.24 (s, 3H, CH₃-Tp^Me2), 2.04 (s, 3H, CH₃-Tp^Me2), 1.89–1.86 (m, 2H, SiCH₂P), 1.77 (m, 4H, THF), 1.61–1.54 (m, 2H, SiCH₂P), 1.47 (s, 3H, CH₃-Tp^Me2), 0.46 (s, 3H, Si(CH₃)₂), 0.44 (s, 3H, Si(CH₃)₂), 0.36 (s, 3H, Si(CH₃)₂), 0.21 (s, 3H, Si(CH₃)₂), −0.45 (s, 9H, Si(CH₃)₃), −0.67 (s, 9H, Si(CH₃)₃); ¹³C{¹H} NMR (100 MHz, THF-d₈, 25 °C): δ (ppm) 181.61 (t, ¹J_PC = 5.0 Hz, PC=O), 165.83 (q, ¹J_PC = 3.0 Hz, PC=N), 151.38 (Tp^Me2), 150.44 (Tp^Me2), 150.42 (Tp^Me2), 149.96 (Tp^Me2), 149.69 (Tp^Me2), 149.54 (Tp^Me2), 146.34 (Tp^Me2), 146.04 (Tp^Me2), 144.88 (Tp^Me2), 144.49 (Tp^Me2), 128.11 (Ph), 127.44 (Ph), 126.72 (Ph), 125.34 (Ph), 124.84 (Ph), 123.61 (Ph), 122.27 (Ph), 121.01 (Ph), 106.71 (4-C-Tp^Me2), 106.48 (4-C-Tp^Me2), 106.24 (4-C-Tp^Me2), 105.82 (4-C-Tp^Me2), 105.20 (4-C-Tp^Me2), 104.74 (4-C-Tp^Me2), 68.02 (THF), 26.16 (THF), 15.43 (CH₃-Tp^Me2), 15.39 (CH₃-Tp^Me2), 15.06 (CH₃-Tp^Me2), 14.96 (CH₃-Tp^Me2), 14.33 (CH₃-Tp^Me2), 14.13 (CH₃-Tp^Me2), 14.06 (d, ¹J_PC = 27.45 Hz, SiCH₂P), 13.06 (d, ¹J_PC = 4.23 Hz, SiCH₂P), 12.93 (CH₃-Tp^Me2), 12.91 (CH₃-Tp^Me2), 12.87 (CH₃-Tp^Me2), 12.69 (CH₃-Tp^Me2), 9.64 (d, ³J_PC = 5.09 Hz, Si(CH₃)₂), 7.59 (d, ³J_PC = 10.91 Hz, Si(CH₃)₂), 6.31 (Si(CH₃)₃), 6.17 (Si(CH₃)₂), 4.68 (Si(CH₃)₃), 3.81 (d, ³J_PC = 4.28 Hz, Si(CH₃)₂); ³¹P NMR (161 MHz, THF-d₈, 25 °C): δ (ppm) −26.71 (dm, ¹J_PP = 374 Hz, PY), −39.64 (dd, J_PP = 374, 12.8 Hz, free P). Elemental analysis: calcd (%) for C₆₀H₉₄N₁₆B₂O₃Si₄P₂Y₂: C, 49.32; H, 6.48; N, 15.34. Found: C, 49.59; H, 6.34; N, 15.57.

Synthesis of 8

A THF solution (5 mL) of PhNNPh (39.6 mg, 0.20 mmol) was added slowly to a stirred THF solution (10 mL) of 2 (115 mg, 0.10 mmol) at ambient temperature. The colour of the reaction mixture gradually changed from yellow to greenish black. After stirring for 2 days, the solvent was removed under vacuum and the solid residue was washed twice with n-hexane (5 mL × 2) and dried under vacuum to give a yellow powder of 8 (141 mg, 85% yield). Yellow crystals suitable for X-ray diffraction analysis were obtained by solvent evaporation from a concentrated THF solution (ca. 2 mL) of 8. No satisfied ¹³C NMR data of 8 were obtained due to its poor solubility. ¹H NMR (400 MHz, THF-d₈, 25 °C): δ (ppm) 7.31 (d, 4H, ³J_HH = 7.92 Hz, –C₆H₅), 6.97 (t, ³J_HH = 7.88 Hz, 6H, –C₆H₅), 6.70 (br, 2H, –C₆H₅), 6.63 (t, ³J_HH = 7.12 Hz, 2H, –C₆H₅), 6.30 (br, 2H, –C₆H₅), 6.13 (t, ³J_HH = 6.4 Hz, 4H, –C₆H₅), 5.87 (s, 2H, 4-H-Tp^Me2), 5.82 (s, 2H, 4-H-Tp^Me2), 5.60 (s, 2H, 4-H-Tp^Me2), 3.60 (m, 4H, THF), 2.64 (s, 6H, CH₃-Tp^Me2), 2.52 (s, 6H, CH₃-Tp^Me2), 2.48 (s, 6H, CH₃-Tp^Me2), 2.46 (s, 6H, CH₃-Tp^Me2), 2.45 (s, 6H, CH₃-Tp^Me2), 2.39–2.41 (m, 4H, SiCH₂P), 2.11 (s, 6H, CH₃-Tp^Me2), 1.77 (m, 4H, THF), 0.14 (s, 6H, Si(CH₃)₂), −0.38 (s, 18H, Si(CH₃)₃), −0.56 (s, 6H, Si(CH₃)₂); ³¹P NMR (161 MHz, THF-d₈, 25 °C): δ (ppm) 50.66 (s). Elemental analysis: calcd (%) for C₇₄H₁₁₂N₁₈B₂O₂Si₄P₂Y₂: C, 53.56; H, 6.80; N, 15.19. Found: C, 53.27; H, 6.73; N, 15.27.

Synthesis of 9

A THF solution (5 mL) of S₈ (12.8 mg, 0.050 mmol) was added slowly to a stirred THF solution (10 mL) of 2 (115 mg, 0.10 mmol) at ambient temperature. After stirring for 5 min, the reaction solution was allowed to stand at room temperature for three days to give 9 as colorless crystals (120 mg, 94% yield). No satisfied NMR data of 9 were obtained due to its poor solubility even in heating THF-d₈. Elemental analysis: calcd (%) for C₄₂H₇₈N₁₄B₂S₄Si₄P₂Y₂: C, 39.37; H, 6.14; N, 15.31. Found: C, 38.53; H, 6.03; N, 15.26.

Synthesis of 10

Se powder (23.7 mg, 0.30 mmol) was added to a stirred THF solution (10 mL) of 2 (230 mg, 0.20 mmol) at ambient temperature. The color of the mixture gradually changed from greenish black to colorless. After stirring overnight and removing the solvent, a colorless solid was obtained, which was washed twice with hexane (10 mL × 2) and dried under vacuum to give 10 as a colorless powder (243 mg, 83% yield). Colorless crystals suitable for X-ray diffraction analysis were obtained by gas-phase diffusion of hexane into a concentrated THF solution (ca. 2 mL) of 10. ¹H NMR (400 MHz, THF-d₈, 25 °C): δ (ppm) 5.86 (s, 1H, 4-H-Tp^Me2), 5.83 (s, 3H, 4-H-Tp^Me2), 5.71 (s, 1H, 4-H-Tp^Me2), 5.60 (s, 1H, 4-H-Tp^Me2), 3.61 (m, 4H, THF), 2.75 (s, 3H, CH₃-Tp^Me2), 2.63 (s, 6H, CH₃-Tp^Me2), 2.60 (s, 3H, CH₃-Tp^Me2), 2.50 (s, 3H, CH₃-Tp^Me2), 2.44 (s, 12H, CH₃-Tp^Me2), 2.42 (s, 3H, CH₃-Tp^Me2), 2.34 (s, 3H, CH₃-Tp^Me2), 2.30 (s, 3H, CH₃-Tp^Me2), 2.12–2.27 (m, 4H, SiCH₂P), 1.77 (m, 4H, THF), 1.47 (s, 3H, CH₃-Tp^Me2), 0.42 (s, 3H, Si(CH₃)₂), 0.32 (s, 3H, Si(CH₃)₂), 0.30 (s, 6H, Si(CH₃)₂), −0.40 (s, 9H, Si(CH₃)₃), −0.50 (s, 9H, Si(CH₃)₃); ¹³C NMR (100 MHz, THF-d₈, 25 °C): δ (ppm) 151.65 (Tp^Me2), 151.50 (Tp^Me2), 151.35 (Tp^Me2), 151.05 (Tp^Me2), 150.95 (Tp^Me2), 150.14 (Tp^Me2), 147.03 (Tp^Me2), 146.97 (Tp^Me2), 146.95 (Tp^Me2), 146.47 (Tp^Me2), 145.60 (Tp^Me2), 144.60 (Tp^Me2), 106.90 (4-C-Tp^Me2), 106.84 (4-C-Tp^Me2), 106.73 (4-C-Tp^Me2), 106.66 (4-C-Tp^Me2), 106.17 (4-C-Tp^Me2), 68.02 (THF), 34.68 (d, ¹J_PC = 5.34 Hz, SiCH₂P), 34.49 (d, ¹J_PC = 5.87 Hz, SiCH₂P), 26.16 (THF), 17.51 (CH₃-Tp^Me2), 17.28 (CH₃-Tp^Me2), 16.76 (CH₃-Tp^Me2), 15.59 (CH₃-Tp^Me2), 15.48 (CH₃-Tp^Me2), 14.77 (CH₃-Tp^Me2), 12.97 (CH₃-Tp^Me2), 12.89 (CH₃-Tp^Me2), 12.86 (CH₃-Tp^Me2), 7.54 (d, ³J_PC = 3.81 Hz, Si(CH₃)₂), 7.46 (overlap d, Si(CH₃)₂), 7.42 (d, ³J_PC = 3.65 Hz, Si(CH₃)₂), 6.80 (d, ³J_PC = 5.19 Hz, Si(CH₃)₂), 5.53 (Si(CH₃)₃), 4.98 (s, Si(CH₃)₃); ³¹P NMR (161 MHz, THF-d₈, 25 °C): δ (ppm) 29.97 (d, ¹J_PP = 390 Hz), 23.68 (d, ¹J_PP = 390 Hz). Elemental analysis: calcd (%) for C₄₆H₈₆N₁₄B₂OSe₃Si₄P₂Y₂: C, 37.79; H, 5.93; N, 13.41. Found: C, 37.53; H, 5.81; N, 13.29.

X-ray crystallographic analysis method

Suitable crystals were wrapped in mineral oil and then were frozen at 173 or 223 K. Data collections were performed on a Bruker SMART APEX (at 293 K) or Bruker SMART APEX (II) (at 173 or 293 K) diffractometer with a CCD area detector using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Diffraction data were collected over the full sphere and corrected for absorption. Structure solutions were found with the SHELXS⁴² package using direct methods and were refined with the SHELXTL program⁴³ against F² using first isotropic and late anisotropic thermal parameters for all non-hydrogen atoms. Hydrogen atoms were placed at calculated positions and included in the structure calculation without further refinement of the parameters. The residual electron densities were of no chemical significance. Details of SQUEEZE are given in the cif files. Unfortunately, the precision of compounds 5 and 6 was limited by the poor quality of their crystals.

Conclusions

In summary, we have developed a simple and effective method for the direct preparation of an amido-functionalized diphosphanato metal complex from P₄ and the corresponding silyl-bridged amido/methylene yttrium complex. Moreover, it is found that the resulting diphosphanato yttrium complex displays some distinctive reactivities unprecedented in diphosphine chemistry, such as redox metathesis/cyclization of the P₂ unit with CS₂, and multichalcogenylations of the P₂ unit with S₈ and Se without the P–P bond cleavage, which provide access to previously unattainable but potentially useful classes of new polyfunctional diphosphine-based ligands in a convenient metal-coordinated form. The results presented here not only demonstrate that appending a strongly coordinative substituent to the alkyl ligand together with a coordination to rare earth ions is an efficient strategy for controlling the alkylated cleavage modes of P₄, but also highlight the potential of the diphosphanato yttrium complex as a versatile P₂ synthon in the development of new polyfunctional diphosphine ligands, achieved by the controllable Y–P and P–P bond insertions, P-based oxidation or their combination with other types of reactions. This valuable discovery opens up new pathways for the construction of cyclic and acyclic polyfunctional diphosphorus-containing organic ligands from white phosphorus and inexpensive, relatively simple and readily available small molecule substrates with perfect atom economy. This valuable discovery makes a previously unattainable class of dppm-like ligands, with varied substituents on the phosphorus donors, readily available, even those thought to be inaccessible due to the instability of the free diphosphinothioether. More research is currently underway to explore the chemistry of this underutilized class of polyfunctional diphosphine-based ligands.

Author contributions

All authors have given approval to the final version of the manuscript. F. Z. and K. H. synthesized and analyzed all new compounds. J. Z. conceived the idea and supervised the work. J. Z. and X. Z. interpreted the results. I. R. and L. M. conducted DFT calculations. All authors contributed to the preparation of the manuscript.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (grant no. 21871058, 22271051, and 22371049) and the 973 program (2015CB856600). LM is a member of the Institut Universitaire de France. Fudan University and the Chinese Academy of Science are acknowledged for financial support through visiting grants (LM). The authors also acknowledge the HPCs CALcul en Midi-Pyrénées (CALMIP-EOS grant 1415). We also greatly acknowledge Dr Yuejian Lin for single crystal X-ray diffraction analysis.

References

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Footnote

† Electronic supplementary information (ESI) available. CCDC 1879573 (1), 1879574 (2), 1879577 (2·THF), 1879583 (3), 1879582 (4), 1879576 (5), 1879581 (6), 1879575 (7·0.5C₆H₁₄), 1879580 (8), 1879579 (9), and 1879578 (10). For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d3qi02680a

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