Chemical Science View Article Online EDGE ARTICLE View Journal | View Issue Uranium and thorium complexes of the phosphaethynolate ion† Cite this: Chem. Sci.,2015,6,6379 a a b c Clement´ Camp, Nicholas Settineri, Julia Lef`evre, Andrew R. Jupp, c b a Jose´ M. Goicoechea, Laurent Maron* and John Arnold* New tris-amidinate actinide (Th, U) complexes containing a rare O-bound terminal phosphaethynolate (OCPÀ) ligand were synthesized and fully characterized. The cyanate (OCNÀ) and thiocyanate (SCNÀ) Received 14th June 2015 analogs were prepared for comparison and feature a preferential N-coordination to the actinide metals. Accepted 17th July 2015 The Th(amid)3(OCP) complex reacts with Ni(COD)2 to yield the heterobimetallic adduct (amid)3Th(m- DOI: 10.1039/c5sc02150b h1(O):h2(C,P)-OCP)Ni(COD) featuring an unprecedented reduced (OCPÀ) bent fragment bridging the two www.rsc.org/chemicalscience metals. À Efficient synthetic routes to the phosphaethynolate ion (OCP ) – counterparts, as well as determining the reactivity prole of the Creative Commons Attribution 3.0 Unported Licence. the phosphorus analog of the cyanate anion – only appeared M-bound phosphaethynolate species. 1,2 2 recently. Since then, reports by the Grutzmacher¨ and Goi- We therefore targeted the use of Na(OCP)(dioxane)n as a À À coechea groups have shown that OCP exhibits a rich cycloaddi- source of the OCP ligand in order to explore its coordination tion and redox chemistry which allowed the synthesis of a variety properties with actinides. We reasoned that these oxophilic À of phosphorus-containing organic derivatives.1,3–8 Particular metals were suitable candidates to polarize the OCP moiety. À interest arises from two recent studies which showed that OCP Interaction of heteroallenes with actinide species has attracted could act as a P-transfer reagent when treated with imidazolium substantial interest over the past few years notably due to the salts9 or cyclotrisilene,10 suggesting that phosphaethynolate could propensity of low-valent actinides to activate small molecules 15–22 20,23–26 27–33 This article is licensed under a be used as a convenient phosphide source. Recent computational (CO2, CS2, azides ). Original uranium-mediated studies also predicted the possibility to generate transition metal formations of cyanate involving reductive co-coupling of CO phosphides from M-PCO precursors through carbonyl loss.11 and NO34,35 and carbonylation of terminal nitrido36 or silyli- However the high reactivity of this anion can be difficult to control mido37 uranium derivatives have also been described. Here we Open Access Article. Published on 20 July 2015. Downloaded 6/19/2018 11:46:25 AM. and generally yields diverse, unwanted decomposition products.12 report a series of uranium and thorium tris-amidinate À À À This likely explains why thus far only a single example of a complexes featuring linear OCP , OCN and SCN ligands as phosphaethynolate transition metal complex has been docu- well as preliminary reactivity studies involving the actinide- mented, Re(P]C]O)(CO)2(triphos) (triphos ¼ MeC(CH3- bound phosphaethynolate moiety with Ni(0). 12 À PPh2)3), featuring a terminal (OCP ) ligand which is P-bound to Salt-metathesis reactions between the tris-amidinate chloride 38 0 Re(I) and strongly bent around the pnictogen center (Fig. 1). While precursors MCl(amid)3 (1 M ¼ U ; 2 M ¼ Th; amid ¼ N,N -bis- À recent work by Grutzmacher¨ and coworkers has shown that OCP (trimethylsilyl)benzamidinate) and Na(OCP)(dioxane)2.9 affords 13 possesses an ambident nucleophilicity, several questions the desired phosphaethynolate complexes M(OCP)(amid)3 (3 M ¼ remain to be answered concerning its interaction with metal U; 4 M ¼ Th) as block-shaped crystals in 76% and 63% isolated centers and how this compares with its cyanate and thiocyanate yields, respectively (Scheme 1). Both compounds exhibit 1HNMR resonance patterns in agreement with C3-symmetric solution 31 species. The P NMR resonance for the OCP moiety in 4 (C6D6, 293 K) is signicantly shied downeld (d ¼334 ppm) compared aHeavy Element Chemistry Group, Chemical Sciences Division, Lawrence Berkeley 12 to that reported for Re(P]C]O)(CO)2(triphos) (d ¼398 ppm) National Laboratory and Department of Chemistry, University of California, Berkeley, California 94720, USA. E-mail: [email protected] bLPCNO, Universit´e de Toulouse, INSA Toulouse, 135 Avenue de Rangueil, 31077 Toulouse, France. E-mail: [email protected] cDepartment of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK. E-mail: [email protected] † Electronic supplementary information (ESI) available: Experimental details, NMR and IR spectra, crystallographic details and les in CIF format, Fig. 1 Left: structure of Re(PCO)(CO)2(triphos) (triphos ¼ MeC(CH3- – 14 À computational data. CCDC 1406759 1406765. For ESI and crystallographic data PPh2)3). Right: resonance structures for the OCP anion. in CIF or other electronic format see DOI: 10.1039/c5sc02150b This journal is © The Royal Society of Chemistry 2015 Chem. Sci.,2015,6,6379–6384 | 6379 View Article Online Chemical Science Edge Article Creative Commons Attribution 3.0 Unported Licence. Scheme 1 Synthesis of complexes M(OCP)(amid)3 (3 M ¼ U; 4 M ¼ Th), M(OCN)(amid)3 (5 M ¼ U; 6 M ¼ Th), and M(SCN)(amid)3 (7 M ¼ U; 8 M ¼ Th). TMS ¼ SiMe3. and alkali and alkaline earth phosphaethynolate salts (d(31P) range: À362 to À397 ppm).1,2,39 Due to the paramagnetism of the This article is licensed under a 31 U(IV)center,the PNMRsignalfor3 is observed at even higher frequency (d ¼285 ppm). Compounds 3 and 4 feature strong IR À absorption bands at almost identical wavenumbers (1685 cm 1 for Fig. 2 Solid-state molecular structures of compounds 3 (top), 5 Open Access Article. Published on 20 July 2015. Downloaded 6/19/2018 11:46:25 AM. À ff 3; 1683 cm 1 for 4) corresponding to the C–O stretching vibra- (middle) and 7 (bottom) determined by single-crystal X-ray di raction. À Ellipsoids are represented with 50% probability. Metrical parameters tional mode of the OCP ligand.Thisfeatureappearsatlower are reported in ESI.† ] ] À1 energy than that found in Re(P C O)(CO)2(triphos) (1860 cm ) À À1 and alkali OCP salts (1730 to 1780 cm ), which indicates – position. The O–C–P (179.1(4) in 3; 179.7(4) in 4) and An–O–C weakeningoftheCO bond order. As evidenced both by the 31 (170.9(3) in 3; 176.4(3) in 4) angles are close to linearity. The low wavenumber IR absorption of nC–O and the downeld P À ^ ˚ 3 ˚ 4 – ˚ 3 NMR chemical shi,theOCP moiety in 3 and 4 is best C P (1.576(5) Ain ; 1.561(4) Ain ) and C O (1.219(6) Ain ; ˚ 4 described as a phosphaalkyne-type limiting resonance structure 1.246(4) Ain ) bond lengths are in the expected range (for ^ ¼ ˚ – ˚ (see Fig. 1) in contrast with the P-bound phosphaketene-type comparison C P 1.579(3) A; C O 1.212(4) A in [K([18]crown- 1 ^ Re(P]C]O)(CO) (triphos)12 species. Altogether, these spectro- 6)][PCO]), with a strengthening of the C P triple bond and a 2 – scopic data suggest substantial strengthening of the C^Pbond weakening of the C O bond when compared with the metrical À ^ ¼ ˚ – upon coordination to the oxophilic actinide centers. parameters computed for the OCP anion (C P 1.625 A; C O À ˚ 12 – ˚ The O-coordination of the OCP fragment is conrmed by 1.203 A). The U O (2.297(3) A) bond length is slightly shorter – ˚ X-ray crystallography (Fig. 2-top). Complex 4 crystallized as two than that for Th O (2.318(2) A), which is consistent with the 40 independent molecules in the asymmetric unit, one of which larger ionic radius of Th(IV). Both distances are in the usual À featured an OCP group disordered over two positions with the range and fall in between those found in actinide complexes of – C^P motif pointing to two different directions in a 45 : 55 ratio. strongly donating aryloxide or siloxide ligands and An O dative 41–46 – – 4 interactions. The U Namid and Th Namid bond distances The discussion of metrical parameters for is, therefore, per- ˚ ˚ formed on the non-disordered molecule only. The thorium and average respectively 2.44(3) A and 2.49(3) A and compare well 38,47–49 uranium analogs adopt C -symmetry, with the three bidentate with related compounds. 3 5–8 amidinate ligands wrapping around the actinide in a propeller- The cyanate and thiocyanate counterparts (Scheme 1) À like geometry, and the OCP ligand pointing in the axial were prepared similarly, allowing a direct comparison of 6380 | Chem. Sci.,2015,6,6379–6384 This journal is © The Royal Society of Chemistry 2015 View Article Online Edge Article Chemical Science structurally analogous compounds. The 1H NMR patterns for NBO analysis of 4 indicates that the O-bound complex is these species are like those of compounds 1–4, in agreement preferred over the P-bound analog because of the donation from with An(IV) symmetric species in solution. The IR C–N stretches the lone pairs of the oxygen atom to the empty hybrid d/f orbital À À À for compounds 5–8 (2199 cm 1 in 5, 2200 cm 1 in 6, 2021 cm 1 of the metal (Wiberg index of 0.42). It is worthy to note that À in 7 and 2018 cm 1 in 8) are of high intensities and fall in the there is no interaction between the C–P and the C–O bonds; the À range of previously reported N-bound cyanate36,37,50 and thiocy- molecular orbitals within the OCP unit are localized onto À anate51,52 actinide compounds.