DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 2273–2274 2273 The first symmetrical tetrarheniumcyclodiyne type cluster containing phosphine ligands: Re4(Ï-O)4Cl4[P(C6H4OMe-p)3]4 Sophia S. Lau, Phillip E. Fanwick and Richard A. Walton * Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393, USA. E-mail: walton@chem.purdue.edu Received 28th April 1999, Accepted 27th May 1999 The reactions of methanol solutions of cis-Re2(Ï-O2- CCH3)2Cl4(H2O)2 with PAr3 (Ar = Ph, C6H4Me-p, C6H4Mem or C6H4Cl-p) afford the quadruply bonded dirhenium(IV,II) complexes Cl2(MeO)2ReReCl2(PAr3)2, whereas P(C6H4OMe-p)3 gives the complex Re4(Ï-O)4- Cl4[P(C6H4OMe-p)3]4, which X-ray crystallography has shown is the first symmetrical, neutral, tetrarheniumcyclodiyne type cluster containing phosphine ligands.The reactions of the dirhenium(III) carboxylate complex cis- Re2(m-O2CCH3)2Cl4(H2O)2 (1) with triphenylphosphine in primary alcohol solvents are unusual in that they aVord the unsymmetrical, quadruply bonded, alkoxide complexes Re2Cl4(OR)2(PAr3)2 (2), Ar = Ph [eqn.(1)], which are formally cis-Re2(O2CCH3)2Cl4(H2O)2 1 2PAr3 1 2ROH æÆ Re2Cl4(OR)2(PAr3)2 1 2CH3CO2H 1 2H2O (1) Re(IV)–Re(II) species that are derived from the Re(III)–Re(III) core by an intramolecular disproportionation.1 Subsequently, Chisholm and co-workers 2 discovered the remarkable compound Mo2(OPri)4(dmpe)2 (dmpe = Me2PCH2CH2PMe2) which is formally a Mo(IV)–Mo(0) complex, i.e.(PriO)4Mo- Mo(dmpe)2, and retains a metal–metal multiple bond.3,4 Our interest in probing the factors which favor the stability of unsymmetrical structures such as 2, coupled with attempts to design synthetic strategies to the symmetrical isomer 3,† have led us to study the reactions of the synthon cis-Re2(m-O2- CCH3)2Cl4(H2O)2 5 with triarylphosphines which vary in basicity and cone angle. We report in the present communication our findings concerning the reaction of 1 with P(C6H4OMe-p)3 in methanol which aVords a route to the prototype of a new class of neutral, symmetrical, tetrarheniumcyclodiyne type of cluster, viz., Re4(m-O)4Cl4[P(C6H4OMe-p)3]4 (4).Although methanol solutions of 1 react with PAr3 (Ar = Ph, C6H4Me-p, C6H4Me-m or C6H4Cl-p) to yield methoxide complexes of type 2, reactions with P(C6H4OMe-p)3 aVord the red complex 4 under these same conditions.‡ This compound could be isolated reproducibly in yields of ca. 35%.The use of refluxing ethanol as the reaction solvent produced only very small quantities of 4; the major product was the dirhenium(III,II) complex Re2(m-O2CCH3)Cl4[P(C6H4OMe-p)3]2,6§ along with small amounts of Re2Cl6[P(C6H4OMe-p)3]2 and Re2Cl4(OEt)2- O Re O Cl Cl PAr3 Re PAr3 Cl R R 2 Ar3P Re Cl Cl O Cl Re PAr3 O Cl 3 R R Cl Re Re O O Re Re OO Cl P Cl P Cl Cl P P 4 [P(C6H4OMe-p)3]2. The substitution of the pyridine analogue cis-Re2(m-O2CCH3)2Cl4(py)2 for 1 in the reaction with P(C6H4- OMe-p)3 in refluxing methanol aVorded 4 in low yield (<10%). While the reaction temperature may be important in the formation of 4, the origin of the oxygen in the {Re4(m-O)4} core of 4 is probably the alcohol solvent and not coordinated or adventitious water since the addition of varying amounts of water did not increase the yield of this product.The diamagnetic complex 4 was shown by X-ray crystallography to contain a rectangular cluster of metal atoms with two Re]] ] Re bonds and two Re–Re bonds.¶ Formally, this unit arises from the [2 1 2] cycloaddition of two Re]] ]] Re units (derived from two molecules of 1) by loss of their d components.An ORTEP representation of the structure of 4 is shown in Fig. 1. This centrosymmetric cluster possesses Re–Re Fig. 1 ORTEP13 representation of the structure of the tetranuclear cluster Re4(m-O)4Cl4[P(C6H4OMe-p)3]4 in crystals of 4?2MeOH. Thermal ellipsoids are drawn at the 50% probability level except for the phenyl group atoms of the P(C6H4OMe-p)3 ligands which are circles of arbitrary radius.Unlabeled atoms are related to the labeled atoms by an inversion center. Selected bond distances (Å) and bond angles (8): Re(1)–Re(2) 2.2726(5), Re(1)–Re(2)9 2.5388(5), Re(1)–Cl(1) 2.350(2), Re(2)–Cl(2) 2.359(2), Re(1)–P(1) 2.521(2), Re(2)–P(2) 2.524(2), Re(1)– O(1) 1.943(5), Re(1)–O(2) 1.995(5), Re(2)–O(1) 1.960(5), Re(2)–O(2) 1.988(5); Re(1)–Re(2)–Re(1)9 90.099(16), Re(2)9–Re(1)–Re(2) 89.901(16), Cl(1)–Re(1)–P(1) 84.16(7), Cl(2)–Re(2)–P(2) 84.41(7), O(1)–Re(1)–O(2) 96.0(2), O(1)–Re(2)–O(2) 95.7(2), Re(1)–O(1)–Re(2) 81.15(19), Re(2)–O(2)–Re(1) 79.19(19). The four Re atoms shown are those of the primary form of a disorder in which a secondary form (atoms Re(3) and Re(4)), appearing to share the same ligand atoms, is in a plane approximately orthogonal to the primary form.The distances Re(3)–Re(4) and Re(3)–Re(4)9 are 2.275(8) Å and 2.528(8) Å, respectively.2274 J.Chem. Soc., Dalton Trans., 1999, 2273–2274 bond distances of 2.273(1) Å and 2.539(1) Å, the longer distance being associated with the [Re(m-O)2Re] units. These Re]] ] Re and Re–Re bond distances are similar to those encountered in the [Bu4 nN]1 salts of the [Re4(m-O)2(m-OMe)2Cl8]22, [Re4(m-O)2(m- OMe)(m-Cl)Cl8]22 and [Re4(m-O)2(m-Cl)2Cl8]22 anions that have been structurally characterized by Cotton and co-workers.7,8 Unlike the latter species, compound 4 is neutral, contains phosphine ligands, and is the first tetrarheniumcyclodiyne type cluster with a [Re4(m-O)4]41 core.This compound represents one extreme in the chemistry of molecular rectangles (cyclic quartets) which range from those which contain four separate ligand-bridged metal centers 9 to those with pairs of ligandbridged multiply bonded dimetal units which may or may not be linked by metal–metal bonds within the rectangular cluster.10 While this type of dimerization of quadruply bonded dimetal complexes were first encountered by McCarley and co-workers many years ago,11 and has subsequently been developed quite extensively in Mo and W chemistry,12 it is rare in Re chemistry. 7,8 Our work expands this field and provides an interesting and potentially useful synthon for further reactivity studies. While 4 does not possess any readily accessible reversible redox chemistry, the P(C6H4OMe-p)3 ligands are substitutionally labile as shown by the conversion of 4 to Re4(m-O)4Cl4- (PMe2Ph)4 upon its reaction with PMe2Ph.Further studies are underway to develop the reaction chemistry of this new cluster and ones like it. Notes and references † Other isomers, based upon a (Ar3P)(RO)Cl2ReReCl2(OR)(PAr3) arrangement of ligands, are of course possible. ‡ Synthesis of 4: a sample of P(C6H4OMe-p)3 (184 mg, 0.522 mmol) was heated in methanol (20 mL) until it had completely dissolved, whereupon a quantity of 1 (113 mg, 0.169 mmol) was added via an addition sidearm. The resulting reaction mixture was then refluxed for 3 days, and the crop of red crystalline 4 was filtered oV, washed with methanol and diethyl ether; yield 67 mg (33%).Calc. for C86H92Cl4- O18P4Re4 (i.e. 4?2MeOH): C, 42.61; H, 3.83; Cl, 5.85. Found: C, 41.38; H, 3.63; Cl, 6.35%. A suitable single crystal of composition 4?2MeOH was selected from this batch for an X-ray structure analysis. Far IR spectrum (Nujol mull): n(Re–Cl) 326ms and 276m cm21. 1H NMR spectrum (CD2Cl2): d C6H4 of C6H4OMe-p 18.15m, 17.58m, 16.90m, 16.80m, 16.33m, 16.22m; OMe of C6H4OMe-p 13.87s, 13.84s; 13.58s; MeOH 13.42s. 31P-{1H} NMR spectrum (CD2Cl2): d 113.6s. Cyclic voltammogram (0.1 M Bu4 nNPF6 CH2Cl2, Pt-bead electrode, scan rate 200 mV s21, potential range 11.5 to 21.5 V, potentials vs. Ag– AgCl): Ep,a = 10.98 V. § This product has properties very similar to those of the structurally characterized complex Re2(m-O2CCH3)Cl4(PPh3)2.6 ¶ Crystal data: 4?2MeOH (C86H92Cl4O18P4Re4, M = 2424.19) at 296 K: space group P21/c with a = 13.9995(7), b = 23.5126(7), c = 14.3633(7) Å, b = 114.1998(16)8, U = 4312.4(6) Å3, Z = 2, Dc = 1.867 g cm23, m(Mo- Ka) = 5.937 mm21.Data collection performed on a Nonius Kappa- CCD and the structure solved by direct methods using SIR97 13 and refined through the use of SHELX-97:13 35082 reflections measured, 10854 unique (Rint = 0.101). Hydrogen atoms included but constrained to ride on the atom to which they are bonded.A cut-oV Fo 2 > 2s(Fo 2) used for R-factor calculations to give R(Fo) = 0.062, Rw(Fo 2) = 0.104, and GOF = 1.138. Disorder involving the four Re atoms of the rectangular cluster such that there are two incompletely occupied, approximately orthogonal sets, which to a first approximation share the same set of ligand atoms. The multiplicities of the primary and secondary forms are 0.949 and 0.051, respectively. CCDC reference number 186/1485.See http://www.rsc.org/suppdata/dt/1999/2273/ for crystallographic files in .cif format. 1 (a) A. R. Chakravarty, F. A. Cotton, A. R. Cutler, S. M. Tetrick and R. A. Walton, J. Am. Chem. Soc., 1985, 107, 4795; (b) A. R. Chakravarty, F. A. Cotton, A. R. Cutler and R. A. Walton, Inorg. Chem., 1986, 25, 3619. 2 M. H. Chisholm, J. C. HuVman and W. G. Van Der Sluys, J. Am. Chem. Soc., 1987, 109, 2514. 3 B. E. Bursten and W. F. Schneider, Inorg. Chem., 1989, 28, 3292. 4 R. Wiest, A.Strich and M. Bénard, New J. Chem., 1991, 15, 801. 5 R. A. Walton, J. Cluster Sci., 1994, 5, 173. 6 A. R. Cutler, P. E. Fanwick and R. A. Walton, Inorg. Chem., 1987, 26, 3811. 7 J. D. Chen and F. A. Cotton, J. Am. Chem. Soc, 1991, 113, 5857. 8 F. A. Cotton and E. V. Dikarev, J. Cluster Sci., 1995, 6, 411. 9 See for example: (a) J. A. Whiteford, C. V. Lu and P. J. Stang, J. Am. Chem. Soc., 1997, 119, 2524; (b) K. D. Benkstein, J. T. Hupp and C. L. Stern, J. Am. Chem. Soc., 1998, 120, 12982; (c) K. D. Benkstein, J. T. Hupp and C. L. Stern, Inorg. Chem., 1998, 37, 5404; (d ) S. M. Woessner, J. B. Helms, Y. Shen and B. P. Sullivan, Inorg. Chem., 1998, 37, 5406. 10 F. A. Cotton, L. M. Daniels, I. Guimet, R. W. Henning, G. T. Jordon, IV, C. Lin, C. A. Murillo and A. J. Schultz, J. Am. Chem. Soc., 1998, 120, 12531. 11 R. N. McGinnis, T. R. Ryan and R. E. McCarley, J. Am. Chem. Soc., 1978, 100, 7900. 12 F. A. Cotton and R. A. Walton, Multiple Bonds Between Metal Atoms, Oxford University Press, Oxford, 2nd edn., 1993, pp. 554–558. 13 A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacorazzo, A. Guagliardi, A. Moliterni, G. Polidori and R. Spagna, SIR97, J. Appl. Crystallogr., 1999, 32, 115; G. M. Sheldrick, SHELX-97, University of Göttingen, 1997; C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Communication 9/03367J