Forging a Cage into a Chain: Stepwise Transformation of P ₄ by Silylenes to a Si ₃ P ₄ Motif

Open AccessCCS ChemistryCOMMUNICATION6 Jun 2022Forging a Cage into Chain: Stepwise Transformation of P4 by Silylenes to Si3P4 Motif Xiaofei Sun, Alexander Hinz and Peter W. Roesky Sun Institute Inorganic Chemistry, Karlsruhe Technology (KIT), 76131 Google Scholar More articles this author , *Corresponding author: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.022.202101709 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail We have discovered route access the longest low-valent molecular silaphospha-chain, seven-membered chain structure that incorporates three silicon four phosphorus atoms stepwise activation white (P4) using two different silylene precursors. The species was formed via highly reactive polyphosphide intermediate. isolation stable analogue reaction intermediate achieved with mono bis(silylenes). Due rigidity ferrocenediyl framework bis(silylene), isomerization process hampered. Theoretical studies such as natural bond orbital in molecules analyses indicated some degree delocalization double system. Download figure PowerPoint Introduction industrial production organophosphorus compounds relies on oxidation chlorine gas, yielding PCl3 or PCl5 versatile intermediates.1,2 Considering sustainability aspects, it is desirable construct phosphorus-containing an efficient controlled way directly from phosphorus. A well-established alternative utilizes transition metals coordinate functionalize P4, which commonly involves reduction moiety.3–7 In main group chemistry, synthetic monophosphines, intermediarily utilizing Bu3SnH for reported recently.8 more conventional approach employs tetrylenes initial step.9–23 were found be agents form unusual exotic silicon-functionalized polyphosphides reactions P4. common pathways activations, unit could retained broken down P1 P2 building blocks (Figure 1). Figure 1 | (a–c) Activation products mono- bis(silylenes) (Dipp = 2,6-iPr-C6H3, R (NtBu2)SiMe2, R? SiMe3).16–23 For instance, tetramesityldisilene shown activate butterfly-like Si2P2 bicyclobutane core.16 can react through insertion Si(II) center one ?-P–P bonds give strained SiP4 Si2P4 cage ( A– E, 1).17–19,22 monochloro(silylene) LPhSiCl (LPh PhC(NtBu)2) interconnected Si(I) LPhSiSiLPh forming compound F comprising four-membered planar ring.20 degradation zero-valent complex G most recently xanthene-bridged bis(silylene). From these examples, apparent typical processes are heterocycles cages, while chain-type structures rare. fact, best our knowledge, specific example disilatetraphospha-hexatriene H).21 general, constituting elements phosphazenes do not only play essential role polymer chemistry but also inorganic materials.24–26 Recently, P6 obtained reported.27 Intrigued possibility generating longer third row periodic table, we attempted assemble silaphospha-chain silylenes. Results Discussion experiment, synthesized [LSi(?2-P4)]17 A, L CH{C(Me)N(Dipp)}{C(CH2)-N(Dipp)}, Dipp 2,6-iPr-C6H3) study its amido-substituted monosilylene [LPhSi{N(SiMe3)2}],28 no transformation occurred, even when mixture heated at 80 °C 3 days. This rather surprising, [LPhSi{N(SiMe3)2}] had previously been six-membered H. To reduce steric strain enhance polarization effects, considered another where amido(pyridyl)-functionalized [LPhSi{N(2-py)Me}]29 employed [LSi(?2-P4)] (Scheme NMR-scale C6D6, sets 31P NMR patterns, assignable 2 (ca. 1:2 ratio) observed [see Supporting Information S11, minor component ? ?49.6, ?101.7, ?171.5, ?199.0; major component: 647.5, 424.7, 23.7, ?261.0] after 10 min time. solution, signals decreased rapidly within hour, quantitative formation inferred. pattern suggested both contained chemically inequivalent nuclei, large differences their chemical shifts strikingly distinct nature. set resonances span high-field region between ?50 ?200 ppm J(PP) coupling constants, expected range 1J indicating presence structural motif. contrast, appear very low fields (? 647.5 424.7 ppm), characteristic diphosphenes.9,30 Furthermore, resonance ?261.4 showed P atom isolated moiety. Scheme Formation diphosphene (see S1 proposed mechanism Table data). Several attempts identify made, difficulties arose short lifetime species. Only instances small amount benzene added [LPhSi{(NMe)(2-py)}] (1?2) did tiny orange needles occur. these, X-ray diffraction (XRD) analysis allowed identification incorporated pyridylaminosilylenes 2a), despite quality data. None recrystallize successful due isomeric 2. Nevertheless, data used starting point density functional theory (DFT) optimization. geometry remained essentially unchanged, parameters predicted model excellent agreement spectroscopically obs. ?50, ?102, ?172, ?199; calc. ?65, ?105, ?171, ?220 ppm, see S4). Molecular (a) (b) solid state. H non-coordinating solvent omitted clarity. Structural features summarized Information. crystallographic parameters, SiP3 heterocycle (Si2-P2-P3-P4) phosphasilene moiety coordinated ring. addition, pyridylaminosilylene connected P3 distance 2.198 Å (Si3–P3). All P–P Si–P distances ranged single bonds,31,32 electrons delocalized over all atoms. view supported DFT S6). Apparently, proceeded nucleophilic attack cleavage bonds, resulted opening [LSi(?2-P4)], giving unstable As established, identity still elucidated. isolate final product 2, solution [LPhSi{(NMe)(2-py)}]. turned purple few minutes. When left undisturbed 20 week, led red block-shaped crystals 32% yield. unambiguously determined XRD analysis, revealing non-symmetrically substituted (E)-diphosphene isomer [LPhSi{(NMe)(2-py)}P(LSi)] [(P)LPhSi{(NMe)(2-py)}] 2b). central motif consisted SiPSiP3Si chain; thus, so far. fragment 2.0577(4) (P2–P3) 2.1204(4) (P3–P4), respectively, whereas latter bonds.31,32 relatively bonds,21,31 supporting diphosphene. Si1–P1 length 2.1157(4) marginally than Si=P (2.06–2.09 Å).31,33,34 Si2–P2 (2.2517(4) Å) compared well classical (2.24–2.27 Å).21,35 Si2–P1 (2.1940(4) Si3–P4 (2.1628(4) fell average length, calculations (NBO) (AIM) Tables S7–S9). Within NBO formalism, ?-bond occupations significantly lower e, ?*-occupation found. Wiberg indices (WBI) along 0.96 1.24 1.30 1.57 bonds. magnitude WBI hinted strong covalent interactions; however, clear distinction significant electrostatic contribution. charges Si +1.40 1.74 adjacent bore ?0.40 ?0.87 e. These values comparable S7). Comparisons systems revealed S9) effect induced N-containing substituents Topological electron critical points ellipticity (0.09–0.32) corroborating delocalization. likely {LSi} P1–P2 bond. Related [3+1] fragmentations other functionalized derivatives,36,37 direct mesoionic carbenes P4.14 31P{1H} spectrum reveals AMRZ spin system assignment atoms). Simulations iterative fitting multiplets Figures S4 S15). Si1 Si2 ?261.0 doublet (2J(PMPZ) 23.8 Hz) satellites (J(PSi) 70 Hz, 154 Hz). Accordingly, 29Si spectrum, 6.8 ?6.9 ppm. signal detected 2.5 1J(SiP) 146 Hz assigned Si3. computed 648, 425, 24, ?261; 666, 432, 42, ?254 Since impractically featured pyridylamino-monosilylene moieties, sought prevent introducing geometric constraints employing bis(silylene) [LSi(?2-P4)]. Our choice ferrocenediyl-bridged [LPhSiFcSiLPh],38 bridging ferrocene rigid centers (4.048 Å).39 equimolar [LPhSiFcSiLPh] instantly afforded dark solution. AXYZ 6:5 ratio 3, 3a: ?60.4, ?126.3, ?159.0, ?191.8; 3b: ?57.3, ?119.4, ?173.9, ?178.3 ppm; isomers 3a 3b similar reminiscent 1. hypothesis corroborated single-crystal (SCXRD) 4). Si-polyphosphide analogous elucidated being responsible computations, calculated agree (calc. ?72, ?117, ?160, ?194; ?60, ?126, ?159, ?192 S5). Other establish nature fit ?62, ?138, ?179; ?57, ?119, ?174, ?178 ppm). cis 3a) trans 3b) respect relative orientation PZ methyl ?-diketiminate backbone slight energy difference 22 kJ/mol 2). (162.04 MHz) 3b. Experimental (top) simulated (bottom) spectrum. SiP4-cage open-caged 2.1258(8) (Si1–P1) 2.1973(8) (Si3–P3), lengths. newly ring folded about Si2?P3 axis 32.1°, “butterfly-shaped” structure. (Si2–P2 2.2813(7) shorter (Si2–P4 2.1658(7) dicoordinated atom. 3b, broad 35.5, 33.0, ?9.0, dynamic constraint made possible stabilize 3; therefore, pathway further hindered. 4 Synthesis S2 Conclusion tetraphosphasilatricyclopentane cleaved silylenes afford polyphosphides. case, amino-silylene show any reactivity, amido-pyridyl mono(silylene) [LPhSi{(NMe)(2-py)}], trisilatetraphospha-heptatriene bearing backbone, results showcase introduction sites control obtained. available includes: (1) synthesis characterization compounds, (2) spectra, (3) details simulation (4) IR (5) SXRD data, (6) quantum calculations. Conflict Interest There conflict interest. Funding work Deutsche Forschungsgemeinschaft (DFG) [project no. 470309834 (Ro2008/21-1 HI 2063/1-1)]. Acknowledgments thank Prof. D. 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