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Throughconjugation of Two Phosphaalkyne ('CP') Moieties

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Throughconjugation of Two Phosphaalkyne ('CP') Moieties Through-conjugation of two phosphaalkyne (`CP') moieties mediated by a bimetallic scaffold² Article (Published Version) Leech, Matthew C and Crossley, Ian R (2018) Through-conjugation of two phosphaalkyne (‘CP’) moieties mediated by a bimetallic scaffold†. Dalton Transactions, 47. pp. 4428-4432. ISSN 1477- 9226 This version is available from Sussex Research Online: http://sro.sussex.ac.uk/id/eprint/74320/ This document is made available in accordance with publisher policies and may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher’s version. Please see the URL above for details on accessing the published version. Copyright and reuse: Sussex Research Online is a digital repository of the research output of the University. Copyright and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable, the material made available in SRO has been checked for eligibility before being made available. Copies of full text items generally can be reproduced, displayed or performed and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. http://sro.sussex.ac.uk Dalton Transactions View Article Online COMMUNICATION View Journal | View Issue Through-conjugation of two phosphaalkyne (‘CuP’) moieties mediated by a bimetallic Cite this: Dalton Trans., 2018, 47, 4428 scaffold † Received 10th January 2018, Accepted 6th February 2018 Matthew. C. Leech and Ian R. Crossley * DOI: 10.1039/c8dt00110c rsc.li/dalton Through-conjugation of two phosphaalkyne moieties within an isolable molecule is demonstrated for the first time with the syn- thesis of [{Ru(dppe)2}2{μ-(CuC)2C6H4-p}(CuP)2], via base-induced 1 2+ desilylation of [{Ru(dppe)2}2{μ-(CuC)2C6H4-p}(η -PuCSiMe3)2] . The nature of the cyaphide ligands and their influence upon the bimetallic core are studied electrochemically. Creative Commons Attribution 3.0 Unported Licence. Phosphaalkynes (RCuP)1 are archetypal models of the phos- phorus–carbon analogy,2 being both isolobal and isoelectronic Chart 1 Known bis-phosphaalkynes.12,13 with alkynes. Though dichotomous in nature – by virtue of the polarity and lone-pair imparted by phosphorus – their chemi- cal analogy to alkynes is well-established, with a prevalence of viz. [M(L) (PuCtBu) ] (M = Mo, L = dppe, depe, R PC H PR , cycloaddition/oligomerisation reactions, while both η2-CP (cf. 2 2 2 2 4 2 u η1 R = Tol, ClC6H4); (M = W, L = dppe), [Mo(depe)2(P CAd)2] and alkynes) and -P (cf. nitriles, alkynyls) complexes with tran- 15 3 [Mo(dppe)2(PuCSiMe3)2], even the concept of metal- This article is licensed under a sition metals are known. Notwithstanding, an enduring omis- mediated conjugation (cf. bis-alkynyl complexes) was un- sion lies with the incorporation of the discrete ‘CuP’ moiety explored prior to our recent report of the unprecedented cya- into architectures featuring extended conjugation (cf. the – u u – phide alkynyl complexes trans-[Ru(dppe)2(C CR)(C P)] (R = prevalence of polyacetylides), a desirable target particularly 16 Open Access Article. Published on 28 February 2018. Downloaded 28/03/2018 16:18:20. CO Me, p-An). Herein, we extend this conceptual framework from an organometallic standpoint4 – given extensive interest 2 to consider, for the first time, extended conjugation between in acetylenic and phosphorus-containing moieties in the – multiple ‘CuP’ moieties, mediated by a bimetallic, redox- context of developing molecular electronic components.5 7 active, core; we also elucidate the electronic and redox nature Indeed, the conjugation of phosphaalkyne (‘CuP’) moieties of these complexes. with other π-systems is limited to the small range of aromatic 8 t 9 The sequential treatment of the bisethynylbenzene-bridged phosphaalkynes: PhCuP, 2,6-R-C6H3CuP (R = Mes, Bu), bimetallic complex [{Ru(dppe) } {μ-(CuC) C H -p}Cl ](1) with 2,6-R-4-R′-C H CuP(R=tBu, R′ = OMe, NMe ;9b R=R′ = tBu,10 2 2 2 6 4 2 6 2 2 u 11 u – u 12a,b 12c–e two equivalents of AgOTf and P CSiMe3 facilitates installation CMe2Et ) and the putative P C C E (E = CH, N, P ), 2+ of two terminal phosphaalkyne moieties to afford 2 which were generated (transiently) and observed in the gas 2+ (Scheme 1). Formation of 2 is evident from characteristic phase. The latter (PuC–CuP) is also among a very limited spectroscopic signatures indicative of a coordinated phos- range of compounds to feature two ‘CuP’ moieties (Chart 1),13 phaalkyne (δ 111.4, J 34 Hz) in proximity to the dppe and is the sole precedent example for which their mutual con- P PP ff δ sca old ( P 42.2 (1 : 4 ratio)), while the carbon-rich bridge jugation might reasonably be invoked (albeit unstudied). 13 1 remains apparent from C{ H} NMR and infrared (νCuC Though a small number of transition metal complexes fea- − 2054 cm 1) spectroscopic data. Retention of the silyl moieties turing trans-disposed η1-phosphaalkynes has been reported,14 follows from heteronuclear (1H–29Si) correlation, while the tri- flate counter-ion is observed in the 19F-NMR spectrum Department of Chemistry, University of Sussex, Brighton, UK. (δF −78.9); bulk composition is affirmed by microanalysis. 2+ E-mail: [email protected]; Fax: +44 (0)1273876678; Tel: +44 (0)1273 877302 The connectivity of 2 is further supported by X-ray diffrac- †Electronic supplementary information (ESI) available: Synthetic procedures, tion data (Fig. 1).17 The internal geometry is largely unremark- characterising data and spectra, computational and electrochemical details, orbital plots, X-ray diffraction data. CCDC 1811689. For ESI and crystallographic able, exhibiting only slight deviations from linearity about the data in CIF or other electronic format see DOI: 10.1039/c8dt00110c metal centres (∠ P–Ru–C 173.4(2), 175.3(2)°) and in the bridge 4428 | Dalton Trans.,2018,47, 4428–4432 This journal is © The Royal Society of Chemistry 2018 View Article Online Dalton Transactions Communication Table 1 Comparative experimental and calculated NMR spectroscopic dataa δ Δδ b δ Δδ b P(CP) P(CP) C(CP) C(CP) 2+ 2 111.4 — 189.8 — 3 159.7 48.3 281.8 92.0 u + — — [{Ru}(C2R)(P CSiMe3)] 108.4 192.6 u [{Ru}(C2R)(C P)] (R = CO2Me) 168.5 60.0 279.1 86.5 + [{Ru}(C2R)(PuCSiMe3)] 112.8 — 188.2 — [{Ru}(C2R)(CuP)] (R = p-An) 159.5 46.7 281.9 93.7 u +20a c — — [{Ru}H(P CSiPh3)] 143.8 175.1 20a Scheme 1 Reagents and conditions: (i) CH2Cl2, 2 AgOTf, (ii) 2 [{Ru}H(CuP)] 165.0 21.3 287.1 112.0 u t 2+ d P CSiMe3 in toluene, 1 h.; (iii) thf, 2 KO Bu, 1 h. [Ru] = Ru(dppe)2. 2 (calc) 118.4 — 188.8 — 3 (calc)d 166.4 48.0 271.4 82.6 a b Δδ η1 u {Ru} = Ru(dppe)2. on conversion from -P CR to terminal cya- c δ d phide. Increase in P due to SiPh3 vs. SiMe3. GIAO method with the PBE functional (lanl2dz for Ru; 6-31G** for all other atoms); referenced to H3PO4 or Me4Si at the same level of theory. acquisition of X-ray diffraction data. Nonetheless, the identity of 3 is readily established from the characteristic spectroscopic features and changes that accompany the desilylative 1 16,20a rearrangement of η -PuCSiMe3 to cyaphide; viz. (i) u Δν ∼ Creative Commons Attribution 3.0 Unported Licence. reduction in frequency of the C P stretch ( CuP − − −12 cm 1); (ii) loss of NMR resonances for silyl and OTf moi- eties; (iii) increase in frequency (ΔδP 48) for the phosphaalky- – nic P-centres, with reduced magnitude of the PCP Pdppe coup- ling (precluding its resolution); (iv) increased frequency (Δδc 92) for the cyaphidic carbon resonance, consistent with for- mation of an organometallic linkage (cf M–CO, M–CN). These data compare well with those we have noted previously16 and those for Grutzmacher’s seminal complex [RuH This article is licensed under a u 20a 3 (dppe)2(C P)]; they also concur with data calculated for using the PBE functional (Table 1). 2+ The optimized gas-phase geometries of 2 and 3 (see 22 Open Access Article. Published on 28 February 2018. Downloaded 28/03/2018 16:18:20. ESI†) both exhibit slightly greater linearity about the metal 2+ centres and bridge when compared with the solid-state struc- Fig. 1 Molecular structure of 2 ; 50% thermal ellipsoids, hydrogen 22+ u atoms omitted, and phenyl rings reduced for clarity. Selected bond dis- ture of , alongside marginally longer C P linkages tances (Å) and angles (°): Ru1–P1 2.264(1), Ru1–C2 2.035(4), Ru2–P6 (∼1.58 Å). These features are consistent with a prevalence of 2.269(1), Ru1–C11 2.022(4), P1–C1 1.526(5), C2–C3 1.203(6), C3–C4 packing effects in the solid state, as noted previously for 1.443(6)m P6–C12 1.526(5), C10–C11 1.214(6), C10–C7 1.441(6); P1– several η1-PuCR complexes,20,23 and for our precedent cya- – – – – – – Ru1 C2 175.23(13), P6 Ru2 C11 173.38(12), C1 P1 Ru1 179.3(2), C12 phide–alkynyls.16 The calculated CuP stretching mode for 3 P6–Ru2 177.3(2), Ru1–C2–C3 174.2(4), Ru2–C11–C10 174.5(4), C2–C3– ν −1 C4 171.7(5), C11–C10–C7 174.8(5).
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