DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1061–1066 1061 Adducts of the Lewis acid [B(C6F5)3] with transition metal oxo compounds Georgina Barrado,a Linda Doerrer,b Malcolm L. H. Green a and Michael A. Leech b a Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR b Chemical Crystallography Laboratory, 9 Parks Road, Oxford, UK OX1 3PD Received 7th December 1998, Accepted 16th February 1999 The oxo anions [WO4]22 and [ReO4]2 react with the Lewis acid molecule [B(C6F5)3] to give the tris-adduct [WO{OB(C6F5)3}3]22 or the mono adduct [ReO3{OB(C6F5)3}]2 respectively.The crystal structure of the salt [nPr4N]2[WO{OB(C6F5)3}3] has been determined. The h-cyclopentadienyl-oxo compounds [Re(h-C5R5)O3] (where R = H or Me) react with [B(C6F5)3] giving the mono adducts [(h-C5R5)ReO2{OB(C6F5)3}] and the crystal structure of the compound where R = H has been determined. The triazacyclononane compounds [LMO3] (where L = N,N9,N0-trimethyl-1,4,7-triazacyclononane and M = Mo or W) with [B(C6F5)3] give the mono adducts [LMO2{OB(C6F5)3}] and the crystal structure of the tungsten compound is reported.The compound [Re{HB(pz)3}O3] [where {HB(pz)3} = hydridotris(1-pyrazolyl) borate] and [B(C6F5)3] gives the mono adduct [HB(pz)3ReO2{OB(C6F5)3}]. The Lewis acid [B(C6F5)3] is readily available as thermally stable volatile white crystals which are soluble in toluene. The solutions react only slowly with water and oxygen. Therefore, compared with the very volatile BF3 (bp 299.9 8C), which rapidly hydrolyses giving HF, the Lewis acid [B(C6F5)3] is much more convenient for the exploration of the Lewis base properties of transition metal compounds.Adducts formed between [B(C6F5)3] and metal-alkyl 1,2,3 metal-hydrido 4 and metal-oxo compounds5–8 are now well established. In this work we describe further the Lewis base properties of some neutral and anionic transition metal-oxo compounds. Results and discussion Treatment of the oxo compound [nPr4N]2[WO4] in CH2Cl2 solution with three equivalents of [B(C6F5)3] gave the compound [nPr4N]2[WO{OB(C6F5)3}3] 1 as white, microcrystalline, air-stable crystals in good yield.The compound 1 is very soluble in CH2Cl2, slightly soluble in toluene and insoluble in light petroleum ether and pentane. It has been characterised by IR and NMR (11B, 1H, 13C, 19F) spectroscopies, elemental analysis and X-ray diVraction. The analytical and selected spectroscopic data are given in Table 1 for compound 1 and the other new compounds 2–10.Crystals of 1 suitable for X-ray diVraction studies were grown from CH2Cl2/light petroleum ether (bp 30–40 8C). Selected distances and angles are given in Table 2 and the structure of the anion is shown in Fig. 1. The oxygen atoms attached to the tungsten have a slightly distorted tetrahedral geometry. The W–O–B units adopt a nearly linear disposition with angles 174.5(2), 174.4(1) and 170.1(1)8.The four W–O distances are within the range found for W–O bonds in the compound [tBuNH3][WO4] (1.60(6)–1.81(2) Å),9 but the three W–O distances of the atoms bonded to boron (1.781(2), 1.785(1), and 1.786(1) Å) are 0.07 Å longer than the distance to the uncoordinated oxygen atom (1.714(2) Å). The lengthening of the M–O bond in the W–O–B systems is of the same order as those reported for the M–O–B systems in the compounds [Ti{OB(C6F5)3}(acac)2], [V{OB(C6F5)3}(acac)2], [MoO{OB- (C6F5)3}(acac)2],6 [V(OBPh3)(C22H22N4)] 10 and [(C9H21N3)- WO2(OBPh3)].11 The O–B distances in 1 are 1.491(3), 1.508(3) and 1.494(3) Å and they lie in the range of O–B distances for other M–O–B adducts (from 1.460(6) in [(Me5Cp)2ZrOB- (C6F5)3] 5 to 1.59(3) Å in [(C9H21N3)WO2(OBPh3)] 11,12).The 11B NMR spectrum of 1 shows a very broad peak at d = 1, well within the range of a tetra-coordinated boron species and in the region of the other known M–O–B adducts.5,6,13 It was not possible to identify the W]] O absorption band in the IR spectrum because [B(C6F5)3] absorbs strongly in the same region as M]] O bonds.When [Pr4N]2[WO4] was reacted with one, two or four equivalents of [B(C6F5)3] the 11B NMR spectra of these solutions show the broad peak around 1 ppm indicating that a metal-oxo Lewis acid adduct has formed. The reaction of [nPr4N]2[WO4] with one equivalent of the Lewis acid led to the formation of a colourless oil that could not be fully characterised, but the reaction with 2–4 equivalents of [B(C6F5)3] yields only [nPr4N]2[WO{OB(C6F5)3}3] 1, as white crystals.Fig. 1 Crystal structure of 1, [nPr4N]2[WO{OB(C6F5)3}3], with a view along the W]] O bond and fluorine atoms removed for clarity.1062 J. Chem. Soc., Dalton Trans., 1999, 1061–1066 Table 1 Analytical and spectrscopic data Compound and analysis a [nPr4N]2[WO{OB(C6F5)3}3]?0.5CH2Cl2 1 White C (42.9) 42.9 H (2.6) 2.4 N (1.3) 1.3 B (1.5) 1.4 W (8.4) 8.2 NMR data b (ppm) 1H: 0.96 [t (7), 24H, NCH2CH2CH3], 1.63 [m, 16H, NCH2CH2CH3], 2.99 [m, 16H, NCH2CH2CH3] 13C: 148.0 [d (240), C6F5], 139.3 [d (246), C6F5], 136.8 [d (246), C6F5], 121.7 [s, C6F5], 60.8 [s, NCH2- CH2CH3], 15.5 [s, NCH2CH2CH3], 10.1 [s, NCH2CH2CH3] 19F: 2140.5 [d (19), C6F5], 2167.7 [t (19), C6F5], 2172.9 [dd (19, 19), C6F5] 11B: 1.0 very broad [nBu4N]2[WO{OB(C6F5)3}3] 2 Colorless oil C (45.5) 45.5 H (3.2) 3.35 N (1.2) 1.2 B (1.4) 1.4 W (8.1) 9.8 1H: 0.96 [t (7), 24H, NCH2CH2CH2CH3], 1.35 [m, 16H, NCH2CH2CH2CH3], 1.58 [m, 16H, NCH2- CH2CH2CH3], 2.99 [m, 16H, NCH2CH2CH2CH3] 13C: 146.6 [d (251), C6F5], 139.0 [d (254), C6F5], 136.4 [d (250), C6F5], 58.7 [s, NCH2CH2CH2CH3], 23.5 [s, NCH2CH2CH2CH3], 19.3 [s, NCH2CH2CH2CH3], 12.6 [s, NCH2CH2CH2CH3] 11B: 0.4 broad [nPr4N][ReO3{OB(C6F5)3}] 3 White C (38.0) 37.4 H (3.0) 3.7 N (1.5) 1.65 B (1.1) 0.9 Re (19.6) 20.5 1H: 1.04 [t (7), 12H, NCH2CH2CH3], 1.70 [m, 8H, NCH2CH2CH3], 3.09 [m, 8H, NCH2CH2CH3] 13C: 147.7 [d (234), C6F5], 140.0 [d (204), C6F5], 137.1 [d (234), C6F5], 60.5 [s, NCH2CH2CH3], 15.5 [s, NCH2CH2CH3], 10.1 [s, NCH2CH2CH3] 19F: 2137.8 [dd (24, 9) C6F5], 2162.9 [t (21), C6F5], 2168.7 [ddd (24, 21, 7), C6F5 11B: 3.1 [PhCH2Ph3P][ReO3{OB(C6F5)3}] 4 White C (46.3) 46.8 H (2.0) 1.73 B (0.97) 0.8 Re (16.7) 18.5 1H: 7.84–6.48 [m, 20H, Ph], 4.47 [d (14), 2H, CH2] 13C: 148.0 [d (242), C6F5], 138.9 [d (189), C6F5], 136.8 [d (261), C6F5], 135.8–116.4 [m, Ph], 31.8 [d (45), PhCH2P] 19F: 2134.5 [dd (24, 9), C6F5], 2159.8 [t (20), C6F5], 2165.4 [ddd (24, 20, 8), C6F5] 11B: 3.0 s 31P: 19.1 s [Ph4P][ReO3{OB(C6F5)3}] 5 White C (45.8) 45.9 H (1.8) 1.4 B (1.0) 0.8 Re (16.9) 19.0 1H: 7.91–6.58 [m, 20H, Ph] 13C: 148.0 [d (242), C6F5], 139.7 [d (246), C6F5], 137.3 [d (219), C6F5], 135.8–117.3 [m, Ph] 19F: 2.7 s 31P: 20.5 s 11B: 3.3 s [Re(h-C5H5)O2{OB(C6F5)3}] 6 Yellow C (34.05) 34.2 H (0.6) 0.4 B (1.3) 1.0 Re (22.95) 22.9 1H: 7.12 [s, 5H, C5H5] 13C: 149.2 [s, C6F5], 141.8 [s, C6F5], 138.7 [s, C6F5], 117.6 [s, C6F5], 116.1 [s, C5H5] 19F: 2145.7 [s, C6F5], 2157.8 [s, C6F5], 2164.9 [s, C6F5] 11B: 5.2 s [Re(h-C5Me5)O2{OB(C6F5)3}] 7 Orange C (38.2) 38.3 H (1.7) 2.0 B (1.2) 1.0 Re (21.1) 21.0 1H: 2.21 [s, 15H, C5Me5] 13C: 148.0 [d (234), C6F5], 139.2 [d (364), C6F5], 136.2 [d (85), C6F5], 122.9 [s, C5Me5], 119.7 [s, C6F5], 10.3 [s, C5Me5] 19F: 2133.6 [s, C6F5], 2156.5 [s, C6F5], 2165.1 [s, C6F5] 11B: 22.0 s [LMoO2{OB(C6F5)3}]?0.5CH2Cl2 8 White C (38.0) 37.4 H (2.55) 2.8 B (1.2) 1.4 Mo (11.0) 11.55 N (4.8) 4.1 1H: 3.15 [s, 9H, CH3], 2.91 [s, 12H, CH2] 19F: 2135.1 [d (25), C6F5], 2164.2 [t (19), C6F5], 2169.3 [dd (25, 19),C6F5] 11B: 1.1 s [LWO2{OB(C6F5)3}]?0.5CH2Cl2 9 White C (34.5) 34.4 H (2.3) 2.3 N (4.4) 4.7 B (1.1) 1.2 W (17.7) 23.0 1H: 3.27 [m, 9H, CH3], 2.99 [m, 12H, CH2] 13C: 148.2 [s, C6F5], 139.4 [s, C6F5], 137.1 [s, C6F5] 19F: 2131.6 [d (23), C6F5], 2161.0 [t (21), C6F5], 2166.1 [dd (23, 21), C6F5] 11B: 0.3 s [{HB(pz)3}ReO2{OB(C6F5)3}] 10 Yellow C (33.8) 33.9 H (1.05) 1.6 N (8.8) 8.2 B (2.25) 1.9 Re (19.4) 19.2 1H: 8.17 [s, 1H, CH], 7.79 [s, 1H, CH], 6.35 [s, 1H, CH] 19F: 2134.9 [s, C6F5], 2156.6 [s, C6F5], 2164.0 [s, C6F5] 11B: 24.9 s a Given as (found) calc.%. b All NMR spectra were measured in CD2Cl2. The treatment of [nBu4N]2[WO4] with one, two, three, or four equivalents of [B(C6F5)3] gives oils. After many attempts a few crystals were obtained and the elemental analysis was consistent with the formula [nBu4N]2[WO{O3B(C6F5)3}3] 2. The 11B NMR spectrum of 2 shows a broad peak at d 0.4 which is consistent with the formation of a tris-adduct.The salts of the perrhenate anion C1[ReO4]2, where C = nPr4N, (PhCH2)Ph3P or Ph4P, react with [B(C6F5)3] to give the mono adducts [C][ReO3{OB(C6F5)3}], where C = nPr4N 3, (PhCH2)Ph3P 4 or Ph4P 5, as white air-stable crystalline solids. These salts are very soluble in CH2Cl2, but insoluble in light petroleum ether, pentane or toluene.Despite many attemptsJ. Chem. Soc., Dalton Trans., 1999, 1061–1066 1063 it was not possible to grow crystals of 3–5 suitable for single-crystal X-ray diVraction. The NMR and IR spectra and elemental analyses of 3–5 support the proposed formulation of the products as the mono adducts. The 11B chemical shifts (3.1, 3.0 and 3.3 ppm respectively) are in the region expected for tetra-coordinated boron and inside the range for M–O–B adducts.5,6,13 The presence of the [B(C6F5)3] group is confirmed by 19F and 13C NMR spectra and by an IR spectrum.Treatment of the mono anion [ReO4]2 with an excess of [B(C6F5)3] gives only the mono adduct. Treatment of the oxo-complexes [Re(h-C5R5)O3] (where R = H or Me) with [B(C6F5)3] gives the mono adducts [(h-C5R5)- ReO2{OB(C6F5)3}] (where R = H 6 or R = Me 7) as air stable yellow and orange crystalline solids respectively. Both 6 and 7 are very soluble in CH2Cl2; 6 is insoluble in light petroleum ether, but 7 is slightly soluble.The compounds [Re(h-C5R5)O3] with an excess of [B(C6F5)3] give only the mono adducts. The spectroscopic data and elemental analysis support the proposed formulation and the crystal structure of 6 has been determined. The structure of 6 is shown in Fig. 2 and selected distances and angles are given in Table 3. The Re]] O distances of the terminal Re]] O groups are 1.708(4) and 1.705(3) Å and these are similar to the values for the Re]] O bonds in the starting compound 14 and also the related compounds [Re(h-C5H4Me)O3] 15 and [Re(h-C5Me4Et)O3].16 The Re–O distance in the Re–O–B system is 0.07 Å longer, as expected.The O–B distance is in the range for other known M–O–B adducts. 5,6,9,11,13 The W–O–B units in 1 show a linear disposition (174.5(2), 174.4(1) and 170.1(1)8), but in [(h-C5R5)- ReO2{OB(C6F5)3}] the unit has a bent arrangement (149.4(2)8). The M–O–B groups in the related compounds are also linear 6,12,17 or bent.5,10,11 Treatment of the triazacyclononane compounds [LMO3] (where L = N,N9,N0-trimethyl-1,4,7-triazacyclononane and M = Mo or W) with [B(C6F5)3] gives the mono adducts [LMO2- {OB(C6F5)3}], (where M = Mo 8, W 9) in good yields as white crystalline, air-stable solids.The compounds 8 and 9 are slightly Fig. 2 Crystal structure of 6, [Re(h-C5H5)O2{OB(C6F5)3}], with fluorine atoms removed for clarity. Table 2 Selected distances (Å) and angles (8) for the compound [nPr4N]2[WO{OB(C6F5)3}3], 1 W(1)–O(1) W(1)–O(101) W(1)–O(201) W(1)–O(301) O(101)–B(101) O(201)–B(201) O(301)–B(301) 1.714(2) 1.786(1) 1.785(1) 1.781(2) 1.491(3) 1.508(3) 1.494(3) O(1)–W(1)–O(10) O(101)–W(1)–O(201) O(1)–W(1)–O(201) O(101)–W(1)–O(301) O(1)–W(1)–O(301) O(201)–W(1)–O(301) W(1)–O(101)–B(101) W(1)–O(201)–B(201) W(1)–O(301)–B(301) 110.06(8) 111.16(7) 108.12(8) 109.29(7) 108.90(7) 109.28(7) 170.1(1) 174.4(1) 174.5(2) soluble in CH2Cl2, or hot toluene and insoluble in light petroleum ether or pentane.Reactions with an excess of [B(C6F5)3] yield only the mono adducts. The compounds 8 and 9 have been characterised by NMR and IR spectroscopy and elemental analysis. Due to their low solubility it was not possible to obtain satisfactory 13C NMR spectra. The 11B NMR spectra show resonances in the region expected for tetra-coordinated boron at 1.1 ppm for 8 and at 0.25 ppm for 9. The crystal structure of 9 has been determined.There are two molecules in the asymmetric unit, but the distances and angles of each are nearly identical. The structure of one molecule is shown in Fig. 3 and selected distances and angles are given in Table 4. The W–O distances of the uncoordinated oxygen atoms (average 1.721 Å) are 0.12 Å longer than the W–O distance of the coordinated oxygen (average 1.852 Å), in agreement with the expected lengthening of a metal oxygen bond upon coordination of the oxygen to the boron.6,10,11 The B–O distance (average 1.506 Å) lies in the range of the other known M–O–B moieties5,11 and the M–O–B unit adopts a bent disposition (average 141.18).The closely related compound [LWO2(OBPh3)] 11 also has a bent disposition (154.2(10)8). The W–O distance of the coordinated oxygen is slightly longer (0.07 Å) in 9 than in [LWO2(OBPh3)] and the O–B distance is slightly shorter (0.08 Å). This can be attributed to [B(C6F5)3] being a stronger Lewis acid than BPh3.Fig. 3 Crystal structure of one molecule of 9, [LWO2{OB(C6F5)3}], from the asymmetric unit, with fluorine atoms removed for clarity. Table 3 Selected distances (Å) and angles (8) for [Re(h-C5H5)O2- {OB(C6F5)3}], 6 Re(1)–O(1) Re(1)–O(2) Re(1)–O(3) O(3)–B(4) 1.708(4) 1.705(3) 1.775(3) 1.568(5) O(1)–Re(1)–O(2) O(2)–Re(1)–O(3) O(1)–Re(1)–O(3) Re(1)–O(3)–B(4) 104.9(2) 105.4(2) 104.4(2) 149.4(2) Table 4 Selected distances (Å) and angles (8) for the compound [LWO2{OB(C6F5)3}], 9 Molecule 1 in asymmetric unit Molecule 2 in asymmetric unit W(1)–O(2) W(1)–O(37) W(1)–O(38) W(1)–N(97) W(1)–N(101) W(1)–N(104) O(2)–B(3) O(2)–W(1)–O(37) O(2)–W(1)–O(38) O(37)–W(1)–O(38) W(1)–O(2)–B(3) 1.850(3) 1.708(3) 1.719(3) 2.357(4) 2.334(4) 2.384(4) 1.499(5) 107.6(1) 104.6(1) 106.7(2) 140.6(3) W(39)–O(40) W(39)–O(75) W(39)–O(76) W(39)–N(83) W(39)–N(87) W(39)–N(90) O(40)–B(41) O(40)–W(39)–O(76) O(75)–W(39)–O(76) O(40)–W(39)–O(75) W(39)–O(40)–B(41) 1.853(3) 1.720(3) 1.770(3) 2.298(4) 2.329(4) 2.290(3) 1.513(5) 104.3(1) 103.9(2) 103.9(1) 141.5(3)1064 J.Chem. Soc., Dalton Trans., 1999, 1061–1066 When the colourless compounds [Re{HB(pz)3}O3] (where {HB(pz)3} = hydridotris(1-pyrazolyl)borate) and [B(C6F5)3] are mixed in CH2Cl2 the solution immediately becomes yellow and the compound [HB(pz)3ReO2{OB(C6F5)3}], 10, can be isolated as yellow crystals. It has been characterised by NMR studies and elemental analysis. Instead of the two expected peaks, one for the pyrazolylborate ligand and the other for the Lewis acid, the 11B NMR spectrum shows a single broad peak at 24.9 ppm due to both ligands.The peak is rather broad so it seems that the two signals overlap, since the presence of the {HB(pz)3} ligand is confirmed by the 1H NMR spectrum which shows three singlets at 8.17, 7.79 and 6.35 ppm. The 19F NMR spectrum clearly shows the three resonances with chemical shifts of 2134.9, 2156.6 and 2164.0 ppm typical of [B(C6F5)3] adducts.In addition the elemental analysis supports the proposed formula. Due to the low stability of the compound it was not possible to record the 13C NMR spectrum or grow crystals of good quality for X-ray diVraction. In about 2 hours the solutions of 10 became colourless even when kept at 220 8C. In the solid state under nitrogen, it decomposed in a week. In conclusion, the synthesis and the structures proposed for the new compounds are shown in Scheme 1. The greater basicity of the dianion [WO4]22 compared to the mono anion [ReO4]2 is manifested by formation of the tris-adduct by the tungstate anion compared to the mono-adduct formed with the perrhenate anion.The formation of these adducts with the metal-oxo anions suggests there can be an extensive chemistry of related oxo-anion adducts. Experimental All manipulations were carried out under an N2 atmosphere by using standard Schlenk or dry-box techniques. Light petroleum ether (bp 40–60 8C), pentane, toluene, and dichloromethane were dried over suitable reagents and distilled under N2.The compounds [nBu4N]2[WO4], [Re(h-C5H5)O3], [Re(h- C5Me5)O3], [LWO3] (where L = N,N9,N0-trimethyl-1,4,7-triazacyclononane, M = Mo, W), [Re{HB(pz)3}O3] [{HB(pz)3} = hydridotris(1-pyrazolyl)borate] and [B(C6F5)3] were prepared as described.14,18–22 NMR spectra were recorded using a Bruker WM 300 spectrometer for 1H, 13C, 11B and 31P at 300, 75.5, 96 and 121.5 MHz respectively or a Varian AM 500 for 1H, 13C, 11B and 19F at 500, 125.7, 160 and 470 MHz respectively.The 1H and 13C chemical shifts are reported with respect to SiMe4, 11B to BF3?OEt3, 19F to CHF3 and 31P to trimethyl phosphate in D2O. Chemical shifts are given in ppm, a positive sign indicates a down field shift relative to the standard, and coupling constants in Hz. Infrared spectra were recorded as KBr discs in a Perkin-Elmer FT 1710 spectrometer, mass spectra by the EPSRC National Mass Spectrometry Service Centre.Elemental analyses were obtained by the analytical department of this laboratory. Syntheses [nPr4N]2[WO{OB(C6F5)3}3] 1. The compound [nPr4N]2[WO4] was prepared as described for [nBu4N]2[WO4] 18 using nPr4NOH instead of nBu4NOH. A mixture of [nPr4N]2[WO4] (200 mg, 0.32 mmol) and [B(C6F5)3] (495 mg, 0.97 mmol) was stirred in CH2Cl2 (20 ml) for 1 h. The colourless solution was filtered and the filtrate was concentrated to ca. 10 ml and then layered with light petroleum ether (10 ml) and cooled to 220 8C.Small colourless crystals were obtained after 48 h. Yield: 503 mg, 72%. [nBu4N]2[WO{OB(C6F5)3}3] 2. A mixture of [nBu4N]2[WO4] 18 (200 mg, 0.27 mmol) and [B(C6F5)3] (420 mg, 0.82 mmol) was stirred in CH2Cl2 (20 ml) for 1 h. The solution was filtered and the solvent removed in vacuum to give a colourless oil. [C][ReO4] (C 5nPr4N, (PhCH2)Ph3P, Ph4P). The compounds [C][ReO4] (C = nPr4N, (PhCH2)Ph3P, Ph4P) were prepared by addition of a solution of nPr4NOH, PhCH2Ph3PCl or Ph4PCl in water to a solution of NH4ReO4 in water.In each case there was an immediate formation of a white precipitate. These precipitates were collected by filtration, washed with water and dried in vacuum. These products were used without further purification or characterisation. Scheme 1 (i) In CH2Cl2 at room temperature for 1 h. (ii) In CH2Cl2 at room temperature for 1.5 h for 8 and reflux in CH2Cl2 for 4 h for 9. (iii) In CH2Cl2 at room temperature for 15 min.J.Chem. Soc., Dalton Trans., 1999, 1061–1066 1065 Table 5 Crystallographic collection and processing parameters for compounds 1, 6 and 9 Molecular formula Formula weight Crystal system Space group a/Å b/Å c/Å b/8 Unit-cell volume/Å3 Formula units per cell, Z rcalc/g cm23 m(Mo-Ka)/mm21 T/K Crystal size/mm qmax/8 No. of reflections: total unique in refinement [I > 3s(I)] No. of variables Residual electron density minimum maximum RR w [nPr4N]2[WO{OB(C6F5)3}3] 1 C78H56WO4B3F45N2 2156.51 Monoclinic P21/c 16.157(1) 21.204(1) 23.912(1) 92.731(2) 8182.78 4 1.75 1.59 100 0.21 × 0.23 × 0.32 26.69 58107 16848 14377 1198 20.42 0.98 0.0303 0.0301 [(h-C5H5)ReO2{OB(C6F5)3}] 6 C23H5ReO3BF15 811.27 Monoclinic P21/n 11.300(1) 9.585(1) 20.596(1) 90.648(2) 2230.62 4 2.42 5.67 100 0.25 × 0.15 × 0.05 26.72 14286 4469 3989 388 21.80 1.80 0.0346 0.0362 [LWO2{OB(C6F5)3}] 9 C56H46W2O6B2F30Cl4N6 2000.10 Monoclinic P21 13.289(1) 14.028(1) 18.270(1) 110.256(3) 3195.22 2 2.08 3.98 100 0.20 × 0.15 × 0.10 26.69 22644 6588 6496 956 20.92 0.73 0.0189 0.0220 [nPr4N][ReO3{OB(C6F5)3}] 3.A mixture of [nPr4N][ReO4] (200 mg, 0.2 mmol) and [B(C6F5)3] (234 mg, 0.4 mmol) was stirred in CH2Cl2 (20 ml) for 1 h. The colourless solution was filtered, the solvent removed in vacuum giving a white solid which was washed with light petroleum ether (2 × 10 ml) to yield a white solid. Yield: 365 mg, 81%. [(PhCH2)Ph3P][ReO3{OB(C6F5)3}] 4.A mixture of [(PhCH2)- Ph3P][ReO4] (300 mg, 0.5 mmol) and [B(C6F5)3] (254 mg, 0.5 mmol) was stirred in CH2Cl2 (25 ml) for 1 h. The solution was filtered and the solvent removed from the filtrate under reduced pressure. The white residue was washed with pentane (2 × 10 ml) to yield a white solid. Yield: 402 mg, 73%. [Ph4P][ReO3{OB(C6F5)3}] 5. [Ph4P][ReO3{OB(C6F5)3}] was prepared as a white solid as described for 4 from [Ph4P][ReO4] (200 mg, 0.39 mmol) and [B(C6F5)3] (174 mg, 0.34 mmol).Yield: 287 mg, 78%. [(Á-C5H5)ReO2{OB(C6F5)3}] 6. A solution of [B(C6F5)3] (171 mg, 0.33 mmol) in CH2Cl2 (5 ml) was added with stirring to a solution of [Re(h-C5H5)O3] (50 mg, 0.17 mmol) in CH2Cl2 (10 ml). The reaction mixture was stirred for 1 h. The resulting yellow-orange solution was filtered and concentrated to ca. 5 ml, then the solution was layered with light petroleum ether (5 ml) and stored at 220 8C overnight giving yellow crystals. Yield: 102 mg, 76%.[(Á-C5Me5)ReO2{OB(C6F5)3}] 7. The compound was prepared as described for [(h-C5H5)ReO2{OB(C6F5)3}] 6 using [Re(h-C5Me5)O3] (50 mg, 0.14 mmol) and [B(C6F5)3] (138 mg, 0.28 mmol), after three days at 220 8C red-orange crystals were obtained. Concentration of the mother liquor aVorded another crop. Yield: 87 mg, 73%. [LMoO2{OB(C6F5)3}] 8. A solution of [B(C6F5)3] (244 mg, 0.48 mmol) in CH2Cl2 (10 ml) was added with stirring to a suspension of [LMoO3] (150 mg, 0.48 mmol) in CH2Cl2 (10 ml).The reaction mixture was stirred for 1.5 h at room temperature. The resulting colourless solution was filtered and the solvent was removed under reduced pressure giving an oily solid. This was washed with light petroleum ether (2 × 5 ml) to give a white solid. Yield: 290 mg, 74%. [LWO2{OB(C6F5)3}]?0.5CH2Cl2 9. A solution of [B(C6F5)3] (190 mg, 0.37 mmol) in CH2Cl2 (5 ml) was added with stirring to a suspension of [LWO3] (150 mg, 0.37 mmol) in CH2Cl2 (10 ml) at room temperature.The reaction mixture was then refluxed for 4 h. The resulting colourless solution was filtered and the solvent was removed using reduced pressure giving an oily solid. The residue was washed with light petroleum ether (2 × 5 ml) giving a white solid. Yield: 220 mg, 65%. [{HB(pz)3}ReO2{OB(C6F5)3}] 10. A mixture of [{HB(pz)3}- ReO3] (50 mg, 0.11 mmol) and [B(C6F5)3] (115 mg, 0.22 mmol) was dissolved in CH2Cl2 (15 ml) and stirred for 15 min, then the yellow solution was filtered and concentrated to half volume, light petroleum ether (10 ml) was added and the solution was concentrated under reduced pressure until a crystalline yellow solid was formed.The solid was filtered, washed with light petroleum ether (2 × 5ml) and dried in vacuum. Yield: 77 mg, 72%. Crystal structure determination Crystals of the compounds [nPr4N]2[WO{OB(C6F5)3}3], 1, [(h-C5H5)ReO2{OB(C6F5)3}], 6, and [LWO2{OB(C6F5)3}], 9, were grown by slow diVusion of light petroleum ether into saturated solutions of the complexes in CH2Cl2 at 220 8C.The selected crystals were mounted on a nylon fibre using a drop of perfluoropolyether oil. They were rapidly cooled to 100 K in a flow of cold nitrogen using an Oxford Cryosystems CRYOSTREAM cooling system. The crystal data are given in Table 5. The data were collected on an Enraf–Nonius DIP2020 imageplate diVractometer using graphite monochromated Mo-Ka radiation (l = 0.7107 Å). The images were processed using the DENZO and SCALEPACK suite of programs.23 Data were corrected for Lorentz and polarisation eVects and a partial absorption correction applied by multi-frame scaling of the image-plate data using equivalent reflections. Structures were solved by direct methods, SIR92,24 giving all non-hydrogen atom positions, and refined using full-matrix least-squares procedures with anisotropic thermal parameters for all non-hydrogen atoms.The hydrogen atoms were placed in calculated positions during the final cycles of refinement.A three parameter Chebychev weighting scheme 25 and corrections for anomalous dispersion were applied to all data. All1066 J. Chem. Soc., Dalton Trans., 1999, 1061–1066 crystallographic calculations were carried out using CRYSTALS26 on a PC/AT computer. Neutral atom scattering factors were taken from reference 27. CCDC reference number 186/1355. See http://www.rsc.org/suppdata/dt/1999/1061/ for crystallographic files in .cif format.Acknowledgements We thank the Spanish Government for financial support (to G. B.) and St. John’s College, University of Oxford, for a Junior Research Fellowship (L. D.). G. B. thanks the European Commission for a Marie Curie Fellowship (contract no. 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