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Throughconjugation of Two Phosphaalkyne ('CP') Moieties Through-conjugation of two phosphaalkyne (`CP') moieties mediated by a bimetallic scaffold² Article (Accepted 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 Please do not adjust margins Journal Name COMMUNICATION Through-conjugation of Two Phosphaalkyne (‘C ≡≡≡P’) Moieties Mediated by a Bimetallic Scaffold† Received 00th January 20xx, Accepted 00th January 20xx Matthew. C. Leech and Ian R. Crossley* DOI: 10.1039/x0xx00000x www.rsc.org/ Through-conjugation of two phosphaalkyne moieties within an isolable molecule is demonstrated for the first time with the synthesis of [{Ru(dppe) 2}2{µµµ-(C ≡≡≡C) 2C6H4-p}(C ≡≡≡P) 2], via base- induced desilylation of [{Ru(dppe) 2}2{µµµ-(C ≡≡≡C) 2C6H4-p}Cl 2]. The nature of the cyaphide ligands and their influence upon the bimetallic core are studied electrochemically. Phosphaalkynes (RC ≡P) 1 are archetypal models of the Chart 1: Known bis-phosphaalkynes 12,13 phosphorus-carbon analogy, 2 being both isolobal and isoelectronic with alkynes. Though dichotomous in nature – by virtue of the 16 polarity and lone-pair imparted by phosphorus – their chemical trans-[Ru(dppe) 2(C ≡CR)(C ≡P)] (R = CO 2Me, p-An). Herein, we analogy to alkynes is well-established, with a prevalence of extend this conceptual framework to consider, for the first time, cycloaddition / oligomerisation reactions, while both η2-CP (cf . extended conjugation between multiple ‘C ≡P’ moieties, mediated by alkynes) and η1-P (cf. nitriles , alkynyl) complexes with transition a bimetallic, redox-active, core; we also elucidate the electronic and metals are known. 3 Notwithstanding, an enduring omission lies redox nature of these complexes. with the incorporation of the discrete ‘C ≡P’ moiety into architectures The sequential treatment of the bisethynylbenzene-bridged featuring extended conjugation ( cf . the prevalence of bimetallic complex [{Ru(dppe) 2}2{µ-(C ≡C) 2C6H4-p}Cl 2] ( 1) with polyacetylides), a desirable target – particularly from an two equivalents of AgOTf and P ≡CSiMe 3 facilitates installation of 4 organometallic standpoint – given extensive interest in acetylenic two terminal phosphaalkyne moieties to afford 22+ (Scheme 1). and phosphorus-containing moieties in the context of developing Formation of 22+ is evident from characteristic spectroscopic 5-7 molecular electronic components. Indeed, the conjugation of signatures indicative of a coordinated phosphaalkyne ( δP 111.4, J PP phosphaalkyne (‘C ≡P’) moieties with other π-systems is limited to 34 Hz) in proximity to the dppe scaffold ( δP 42.2 (1:4 ratio)), while 8 the small range of aromatic phosphaalkynes: PhC ≡P, 2,6-R- the carbon-rich bridge remains apparent from 13 C{ 1H} NMR and t 9 -1 C6H3C≡P (R = Mes, Bu), 2,6-R-4-R’-C6H3C≡P (R = tBu, R’ = infrared (νC≡C 2054 cm ) spectroscopic data. Retention of the silyl 9b t 10 11 1 29 OMe, NMe 2; R=R’ = Bu, CMe2Et ) and the putative P ≡C−C≡E moieties follows from heteronuclear ( H- Si) correlation, while the 12a,b 12c-e 19 (E = CH, N, P ), which were generated (transiently) and triflate counter-ion is observed in the F-NMR spectrum ( δF −78.9); observed in the gas phase. The latter (P ≡C-C≡P) is also among a bulk composition is affirmed by microanalysis. very limited range of compounds to feature two ‘C ≡P’ moieties (Chart 1), 13 and is the sole precedent example for which their mutual conjugation might reasonably be invoked (albeit unstudied). Though a small number of transition metal complexes featuring trans-disposed η1-phosphaalkynes has been reported, 14 viz. t [M(L) 2(P ≡C Bu) 2] (M = Mo, L = dppe, depe, R 2PC 2H4PR 2, R = Tol, ClC 6H4); M = W, L = dppe), [Mo(depe) 2(P ≡CAd) 2] and 15 [Mo(dppe) 2(P ≡CSiMe 3)2], even the concept of metal-mediated conjugation ( cf. bis-alkynyl complexes) was unexplored prior to our recent report of the unprecedented cyaphide-alkynyl complexes a. Department of Chemistry, University of Sussex, Brighton, UK Email: [email protected] ; Fax: +44 (0)1273 876678; Tel: +44 (0) 1273 877302 Scheme 1: Reagents and conditions: i) CH 2Cl 2, 2 AgOTf, ii) 2 P≡CSiMe 3 in toluene, 1h.; iii) † Electronic Supplementary Information (ESI) available: Synthetic procedures, t characterising data and spectra, computational and electrochemical details, orbital thf, 2 KO Bu, 1h. [Ru] = Ru(dppe) 2. plots, x-ray diffraction data. See DOI: 10.1039/x0xx00000x This journal is © The Royal Society of Chemistry 20xx J. Name ., 2013, 00 , 1-3 | 1 Please do not adjust margins Please do not adjust margins COMMUNICATION Journal Name 2+ The connectivity of 2 is further supported by x-ray diffraction Table 1: Comparative Experimental and Calculated NMR Spectroscopic Data. a data (Figure 1). 17 The internal geometry is largely unremarkable, b b exhibiting only slight deviations from linearity about the metal δδδP(CP) ∆∆∆δ∆δδδP(CP) δδδC(CP) ∆∆∆δ∆δδδC(CP) centres (∠ P−Ru −C 173.4(2), 175.3(2) °) and in the bridge ( ∠ 22+ 111.4 - 189.8 - Ru −C≡C 174.5(4), 174.2(4); ∠ C≡C−C 174.5(5), 172.7(5) °) 3 159.7 48.3 281.8 92.0 18 + characteristic, respectively, of other bis-alkynyls and the limited [{Ru}(C 2R)(P ≡≡≡CSiMe 3)] 108.4 - 192.6 - range of structurally characterized complexes comprising the [{Ru}(C 2R)(C ≡≡≡P)] (R=CO 2Me) 168.5 60.0 279.1 86.5 19 + ‘Ru 2{µ-(C ≡C) 2C6H4-p}’ and related cores. The coordinated [{Ru}(C 2R)(P ≡≡≡CSiMe 3)] 112.8 - 188.2 - phosphaalkyne moieties are similarly consistent with related [{Ru}(C 2R)(C ≡≡≡P)] (R= p-An) 159.5 46.7 281.9 93.7 14-16,20 +20a c analogues. [{Ru}H(P ≡≡≡CSiPh 3)] 143.8 - 175.1 - 1 [{Ru}H(C P)] 20a 165.0 21.3 287.1 112.0 Conversion of the η -P≡CSiMe 3 moieties to terminal cyaphide ≡≡≡ 2+ d ligands (‘ −C≡P’) proceeds upon treating 22+ with 2 equiv. 21 KO tBu, 2 (calc) 118.4 - 188.8 - affording 3 in moderate yield (Scheme 1). While single crystals of 3 3 (calc) d 166.4 48.0 271.4 82.6 can be grown, their rapid desolvation during mounting (even at low a b 1 {Ru} = Ru(dppe) 2. ∆δ on conversion from η -P≡CR to terminal cyaphide. temperature) has precluded the acquisition of x-ray diffraction data. c d increase in δ due to SiPh vs SiMe . GIAO method with the PBE functional Nonetheless, the identity of 3 is readily established from the P 3 3 (lanl2dz for Ru; 6-31G** for all other atoms); referenced to H 3PO 4 or Me 4Si at the characteristic spectroscopic features and changes that accompany the same level of theory. 1 16,20a desilylative rearrangement of η -P≡CSiMe 3 to cyaphide; viz. i) ν -1 reduction in frequency of the C ≡P stretch ( ∆ C≡P ~ −12 cm ); ii) loss noted previously for several η1-P≡CR complexes, 20,23 and for our − of NMR resonances for silyl and OTf moieties; iii) increase in precedent cyaphide-alkynyls. 16 The calculated C ≡P stretching mode frequency ( ∆δ 48) for the phosphaalkynic P-centres, with reduced -1 P for 3 (asym. νC≡P 1224 cm ) also compares well with experiment magnitude of the P −P coupling (precluding its resolution); iv) -1 CP dppe (νC≡P 1247 cm ). Notably, the experimentally observed frequency increased frequency ( ∆δc 92) for the cyaphidic carbon resonance, reflects a slightly stronger C ≡P linkage for 3 than in consistent with formation of an organometallic linkage ( cf M−CO, -1 20a [RuH(dppe) 2(C ≡P)] ( νC≡P 1239 cm ), attributable to competition M−CN). These data compare well with those we have noted trans 16 with the -alkynyl for Ru →π* donation. Indeed, we noted this previously and those for Grutzmacher’s seminal complex ν 20a previously for cyaphide-alkynyls, though to a greater extent ( C≡P [RuH(dppe) 2(C ≡P)]; they also concur with data calculated for 3 1255, 1260 cm -1), 16 suggesting a reduced competition within the using the PBE functional (Table 1). bimetallic scaffold. 2+ 22 The optimized gas-phase geometries of 2 and 3 (see SI) both The frontier orbitals of 22+ and 3 (Figure 2) show similarities, the exhibit slightly greater linearity about the metal centres and bridge 2+ HOMO in each case being dominated by the bridging π-system (76 when compared with the solid-state structure of 2 , alongside %, 22+ ; 54 % 3) with a modest contribution from the metals (14 % marginally longer C ≡P linkages (~ 1.58 Å).
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