DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1387–1391 1387 Compounds in which the Mo2 41 unit is embraced by one, two or three formamidinate ligands together with acetonitrile ligands Malcolm H. Chisholm,*a F. Albert Cotton,*b Lee M. Daniels,b Kirsten Folting,a John C. HuVman,a Suri S. Iyer,a Chun Lin,b Ann M. Macintosh a and Carlos A. Murillo *b a Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, IN 47405, USA b Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University, PO Box 30012, College Station, TX 77842-3012, USA Received 13th January 1999, Accepted 1st March 1999 The cationic complexes [Mo2(DPhF)(MeCN)6]31[BF4 2]3?MeCN 1a [throughout this paper the formamidinate anions, RNC(H)NR2, will be abbreviated as DRF2, with specific aryl groups represented by Ph for phenyl, and Ani for p-anisyl], [Mo2(DAniF)(MeCN)6]31[BF4 2]3?1.59MeCN 1b, cis-[Mo2(DPhF)2(MeCN)4]21[BF4 2]2?MeCN 2a, cis- [Mo2(DAniF)2(MeCN)4]21[BF4 2]2?2MeCN 2b, and [Mo2(DPhF)3(MeCN)2]1[BF4 2] 3, have been prepared from the reactions between Mo2(DArF)4 and HBF4?Et2O or (Me3O)BF4 in an appropriate stoichiometry in acetonitrile or CH2Cl2–MeCN mixtures.A better procedure for the preparation of 3 involves the reaction between 2a and Li1(DPhF2) in acetonitrile. Compound 2a undergoes a reaction in pyridine to give the compound trans-[Mo2(DPhF)2- (py)4]21[BF4 2]2 4. The new compounds 1a, 1b, 2a, 2b and 4 have been structurally characterized and shown to contain Mo–Mo quadruple bonds.Introduction In previous work1 attempts have been made to link M–M multiply bonded complexes, bridged by carboxylates, together to form parallel or perpendicular polymers of the type shown below in I and II, respectively. Unfortunately for such oligomers of molybdenum and tungsten supported by carboxylate ligands, ligand scrambling occurred and rendered the polymers and smaller oligomers kinetically labile.Indeed, even a linked dimer of “dimers” was susceptible to disproportionation of the type shown in eqn. (1). [M2(O2CR)3]2(bridge) M2(O2CR)4 1 1/n[M2(O2CR)2(bridge)]n (1) Reactions of type (1) arise because the M2 41 centers, where M = Mo and W, are kinetically labile to substitution reactions. Carboxylate scrambling can be catalyzed by adventitious carboxylate anions or acid present in solution.2 In order to minimize such facile ligand scrambling we reasoned that the use of ligands lacking the active lone pairs of carboxylates might lead to more kinetically persistent linked di- and poly-nuclear species. As the first part of the continuing project in developing such systems, we report here the synthesis and characterization of cationic formamidinate bridged dimolybdenum complexes which, unlike their Mo2–carboxylate counterparts, are much less labile to ligand scrambling.A few examples of how they might be linked have been reported,3 but many more will be described in the near future.4 Results and discussion Synthesis This investigation was carried out independently by the groups at Indiana University and at Texas A&M University; one worked with the ligand DPhF [PhNC(H)NPh2], while the other worked with the anisyl (Ani) analogue, DAniF [AniNC(H)- NAni2].Though the synthetic procedures employed by both groups are fairly similar, there are important diVerences which make some comparison worthwhile.The general synthetic strategy for the formation of phenyl derivatives of Mo2- (DPhF)4 2 n n1 cationic complexes is shown in eqn. (2). Mo2(DPhF)4 1 2nHBF4?Et2O 25 8C MeCN [Mo2(DPhF)4 2 n(MeCN)2n]n1[BF4 2]n 1 n[H2DPhF]1[BF4 2]n (2) Reaction (2) is complicated by the fact that Mo2(DPhF)4 is very sparingly soluble in MeCN as a solvent. Thus, the reaction proceeds by the addition of HBF4?Et2O to a slurry of Mo2(DPhF)4. The resultant cationic Mo2 species are more soluble and thus go into solution.As a consequence the addition of HBF4?Et2O must proceed slowly if any control of product is desired beyond formation of the Mo2(MeCN)8 41 and Mo2- (DPhF)(MeCN)6 31 salts. To this end it is desirable to dilute the HBF4?Et2O in MeCN solution and to add the acid slowly. All the species have somewhat diVerent solubilities and colors. The Mo2(MeCN)8 41 cation is blue; Mo2(DPhF)- (MeCN)6 31 1a is purple; Mo2(DPhF)2(MeCN)4 21, 2a is red and Mo2(DPhF)3(MeCN)2 1 3 is pumpkin orange while Mo2- (DPhF)4 is yellow.The most diYcult compound in the series to obtain is [Mo2(DPhF)3(MeCN)2]1[BF4 2] 3, which in our hands was best prepared by the reaction shown in eqn. (3). [Mo2(DPhF)2(MeCN)4]21[BF4 2]2 1 LiDPhF 25 8C MeCN [Mo2(DPhF)3(MeCN)2]1[BF4 2] 1 Li1BF4 2 (3)1388 J. Chem. Soc., Dalton Trans., 1999, 1387–1391 Dissolving [Mo2(DPhF)2(MeCN)4]21[BF4 2]2 in pyridine leads to a facile replacement of the MeCN ligands by pyridine and a slow isomerization to give trans-[Mo2(DPhF)2(py)4]21[BF4 2]2 4.The anisyl analogues were prepared by slightly modified procedures which oVered more control over the reaction, especially for the preparation of 2b. Compound 1b was prepared in a 1 : 4 mixture of acetonitrile and dichloromethane. Mo2(DAniF)4 1 HBF4?Et2O(excess) 25 8C MeCN–CH2Cl2 [Mo2(DAniF)(MeCN)6][BF4 2]3 1 3 [H2DAniF][BF4] (4) Under these conditions it is not necessary to control the rate of addition of HBF4?Et2O. Furthermore, Mo2(DAniF)4 and [H2DAniF][BF4] are soluble in this mixture, and therefore the only species that precipitates is the purplish 1b.For the preparation of 2b we found that the use of wet (Me3O)BF4 is more advantageous than neat HBF4?Et2O. Mo2(DAniF)4 1 (Me3O)BF4(excess) 1 4H2O 25 8C MeCN [Mo2(DAniF)2(MeCN)4][BF4 2]2 1 2 [H2DAniF][BF4] 1 Me2O 1 4 MeOH (5) An acetonitrile slurry of (Me3O)BF4 and Mo2(DAniF)4 does not react but addition of a small amount of deoxygenated water slowly dissolves all of the Mo2(DAniF)4 producing a clear red solution.After removal of the solvent, the solid is washed with Et2O, then recrystallized from a mixture of CH2Cl2– MeCN which is layered with Et2O to produce an essentially quantitative yield of 2b. Structural characterizations [Mo2(DPhF)(MeCN)6]31[BF4 2]3?MeCN 1a. In the unit cell of space group P21/n there are two [Mo2(DPhF)(MeCN)6]31 cations and six BF4 2 anions. The Mo–Mo distances, 2.15(1) Å, are essentially identical for both molecules and the gross structural features are very similar.The Mo–N (formamidinate) distances 2.08(1) Å (average) are shorter by 0.05 to 0.10 Å than the Mo–N distances to the acetonitrile ligands. Each Mo atom is coordinated to four N atoms that lie roughly in a plane and the central Mo2N8 skeleton is virtually eclipsed as expected for Mo–Mo quadruply bonded complexes. In addition, there is a weak, 2.58 Å, interaction between Mo(1) and an axial MeCN.Selected bond distances are given in Table 1. [Mo2(DAniF)(MeCN)6]31[BF4 2]3?1.59MeCN 1b. Compound 1b crystallizes in space group P1� with the three BF4 2 groups and the weakly-interacting axial MeCN groups all disordered to some extent. One axial position is fully occupied although the MeCN group has two orientations in the approximate ratio of 53 :47. The MeCN group at the other axial position has a refined occupancy of 59%. Two of the BF4 2 sites were modeled as two interpenetrating tetrahedra. The third anion did not Table 1 Selected bond distances (Å) for [Mo2(DPhF)(MeCN)6]31- [BF4 2]3?MeCN 1a Mo(1)–Mo(2) Mo(1)–N(9) Mo(1)–N(18) Mo(1)–N(21) Mo(1)–N(24) Mo(1)–N(27) Mo(2)–N(11) Mo(2)–N(30) Mo(2)–N(33) Mo(2)–N(36) 2.149(1) 2.086(8) 2.58(1) 2.150(9) 2.19(1) 2.124(9) 2.078(8) 2.14(1) 2.168(9) 2.11(1) Mo(39)–Mo(40) Mo(39)–N(47) Mo(39)–N(56) Mo(39)–N(59) Mo(39)–N(62) Mo(39)–N(65) Mo(40)–N(49) Mo(40)–N(68) Mo(40)–N(71) Mo(40)–N(74) 2.151(1) 2.098(8) 2.567(9) 2.129(9) 2.165(9) 2.15(1) 2.076(8) 2.139(9) 2.173(9) 2.13(1) behave as well and the ensemble of electron density was simply modeled as a group of 8 F atoms of variable occupancy, with the total occupancy constrained to equal 4.Again, the Mo2N8 core is eentially eclipsed (torsion angles all less than 28) as expected. The axial interactions are very weak, with Mo–N distances of 2.70 and 2.82 Å. A view of the molecule is given in Fig. 1. Selected bond distances are given in Table 2.cis-[Mo2(DPhF)2(MeCN)4]21[BF4 2]2?MeCN 2a. Compound 2a crystallizes in the space group P1� with two formula units in the unit cell. One MeCN molecule is weakly ligated in an axial position to one of the Mo atoms, namely Mo(2) via a long, 2.595(3) Å, interaction. Selected bond distances are given in Table 3. The two m-formamidinate ligands are mutually cis and the shortest Mo–N distances involve formamidinate nitrogen atoms that are bound to Mo(1) which has only two attendant MeCN ligands.The Mo–Mo distance of 2.1457(7) Å is comparable to that in 1 and only somewhat longer than that in Mo2(DPhF)4, 2.0944(8) Å.5 cis-[Mo2(DAniF)2(MeCN)4]21[BF4 2]2?2MeCN 2b. Compound 2b also crystallizes in the space group P1� ; the structure is very similar to that of its phenyl analogue. The Mo–Mo distance of 2.1439(6) Å is equivalent to that of 2a. A view of the dication, shown in Fig. 2, reveals that a coordinated acetonitrile molecule is located at a distance of 2.590(4) Å from Mo(1).All other chemically equivalent dimensions are comparable for 2a and 2b. Selected bond distances are given in Table 4. Fig. 1 A view of the [Mo2(DAniF)(MeCN)6]31 cation in 1b, with ellipsoids drawn at the 40% probability level. Table 2 Selected bond distances (Å) for [Mo2(DAniF)(MeCN)6]31- [BF4 2]3?1.59MeCN 1b Mo(1)–Mo(2) Mo(1)–N(1) Mo(1)–N(3) Mo(1)–N(5) Mo(1)–N(7) 2.152(1) 2.09(1) 2.14(1) 2.17(1) 2.13(1) Mo(2)–N(2) Mo(2)–N(4) Mo(2)–N(6) Mo(2)–N(8) 2.09(1) 2.15(1) 2.14(1) 2.13(1) Table 3 Selected bond distances (Å) for cis-[Mo2(DPhF)2- (MeCN)4]21[BF4 2]2?MeCN 2a Mo(1)–Mo(2) Mo(1)–N(3) Mo(1)–N(18) Mo(1)–N(33) Mo(1)–N(36) 2.1457(7) 2.086(3) 2.100(3) 2.181(3) 2.183(3) Mo(2)–N(5) Mo(2)–N(20) Mo(2)–N(39) Mo(2)–N(42) Mo(2)–N(45) 2.118(3) 2.105(3) 2.180(3) 2.185(3) 2.595(3)J.Chem. Soc., Dalton Trans., 1999, 1387–1391 1389 Fig. 2 A drawing of the cation cis-[Mo2(DAniF)2(MeCN)4]21 in 2b, with ellipsoids drawn at the 40% probability level.[Mo2(DPhF)2(py)4]21[BF4 2]2?4py 4. The asymmetric unit contained one half of the dinuclear unit together with one BF4 2 anion and two molecules of interstitial pyridine. One of the solvent molecules C(40)–C(51) was severely disordered. However, the remainder of the structure was well behaved. A drawing of the centrosymmetric dication is given in Fig. 3 which shows the trans arrangement of the formamidinate ligands. Also in Fig. 3 we show a view looking down the Mo–Mo bond which reveals the eclipsed geometry of the ligands and the favorable p–p stacking of the pyridine ligands.Selected bond distances and angles are given in Table 5. Of note is the fact that the Mo–N distances are longer by ca 0.1 Å to the pyridine nitrogen atoms than those to the formamidinate nitrogen atoms. Also the Mo–Mo–N angles to the pyridine ligands are larger to accommodate a more favorable p–p stacking. Electronic spectra The color of the various anisyl derivatives changes from blue in the unsubstituted Mo2(MeCN)8 41 cation, to purple for Mo2- (DAniF)(MeCN)6 31 1b, to red for Mo2(DAniF)2(MeCN)4 21 2b, and to yellow for Mo2(DAniF)4.Their lowest transition ener- Table 4 Selected bond distances (Å) for cis-[Mo2(DAniF)2- (MeCN)4]21[BF4 2]2?2MeCN 2b Mo(1)–Mo(2) Mo(1)–N(1) Mo(1)–N(3) Mo(1)–N(7) Mo(1)–N(5) 2.1439(6) 2.115(3) 2.117(3) 2.185(3) 2.188(3) Mo(2)–N(2) Mo(2)–N(4) Mo(2)–N(6) Mo(2)–N(8) 2.085(3) 2.087(3) 2.172(3) 2.180(3) Table 5 Selected bond distances (Å) and angles (8) for trans-[Mo2- (DPhF)2(py)4]21[BF4 2]2 4 Mo(1)–Mo(19) Mo(1)–N(2) Mo(1)–N(4) Mo(19)–Mo(1)–N(2) Mo(19)–Mo(1)–N(17) 2.107(2) 2.151(6) 2.132(6) 92.6(2) 99.6(2) Mo(1)–N(17) Mo(1)–N(23) Mo(19)–Mo(1)–N(4) Mo(19)–Mo(1)–N(23) 2.226(6) 2.243(5) 92.3(2) 103.8(2) gies, which were assigned to dÆd* transitions, are 597, 570, 516 and 430 nm, respectively.This spectroscopic blue shift supports the idea that by increasing the number of the formamidinate ligands, the Mo–Mo bond strength increases.This correlates with the decrease of their Mo–Mo bond distances, which are 2.180,6 2.152, 2.144 and 2.096 Å,5 respectively. Reactivity studies of the phenyl substituted formamidinates In CD3CN as solvent the cationic complexes 1a and 2a exhibit facile CH3CN for CD3CN exchange. Similarly, for 4 exchange of coordinated py ligands with py-d5 is rapid. However, our key observations involve the lack of exchange of the formamidinate ligands.Thus, compound 2a and Mo2(DPhF)4 failed to yield the compound [Mo2(DPhF)3(MeCN)2]1[BF4 2] as judged by NMR spectroscopy in acetonitrile solvent. In part, this could have been attributed to the insolubility of Mo2(DPhF)4. However, a reaction between compound 2a and Li(DPhF) in MeCN did yield 3 in conjunction with some formation of Mo2(DPhF)4 (which could be removed by filtration). Because the solubilities of complex 2a and complex 3 are very similar, the optimum preparation of 3 involves the reaction between 2a and Li- (DPhF) (1.5 equivalents) in MeCN which results in 90% of 3 and 10% of 2a after filtration to remove Mo2(DPhF)4. We also attempted to study the comproportionation of the dicationic complex 2a with [Mo2(MeCN)10]41[BF4 2]4 7 in CD3CN.Here both species are fully dissolved. However, we observed no ligand exchange leading to the formation of the tricationic complex 1 as judged by the 1H NMR spectroscopy.Thus, in contrast to carboxylate ligands, we find the formamidinate ligands to be relatively inert to ligand scrambling. The reaction between compound 3 and the oxalate dianion was studied as shown in eqn. (6). 2[Mo2(DPhF)3(MeCN)2]1[BF4 2] 1 [Bun 4N1]2C2O4 25 8C MeCN [Mo2(DPhF)2]2(m-O2CCO2) 1 2[Bun 4N1][BF4 2] (6) The product of the reaction was a red-orange powder essentially insoluble in CD3CN, CD2Cl2 and py-d5. Given the recent1390 J. Chem. Soc., Dalton Trans., 1999, 1387–1391 report by some of us,3 we presume that reaction 6 provides an alternate synthesis of the m-oxalate type complex.Concluding remarks In this work we have prepared dimolybdenum cationic complexes supported by one, two and three formamidinate ligands. These have been shown to be notably less labile to ligand scrambling than their related carboxylate counterparts. The success in the preparation of the m-oxalate linked dimer of “dimers” in reaction (6) suggests that formamidinate ligands may lead to kinetically more persistent quartets (dimers of “dimers”) and higher oligomers.Experimental All manipulations were carried out under an inert atmosphere Fig. 3 An ORTEP10 drawing of [Mo2(DPhF)2(py)4][BF4]2 4, front-on view (top) and looking down the metal–metal bond axis (bottom), with the hydrogen atoms and the BF4 counter anions omitted for clarity. Thermal ellipsoids are drawn at the 50% probability level. by using standard Schlenk and glove-box techniques.All solvents were dried and degassed by standard methods and distilled prior to use. 1H NMR spectra were recorded on Varian Gemini-2000 and Varian XL-200E NMR spectrometers and referenced to residual protio impurities in the deuteriated solvent. Infrared spectra were obtained as KBr pellets on Nicolet 510 P FT-IR or Perkin-Elmer 16PC FTIR spectrometers. Elemental analyses were performed by Atlantic Microlabs, Norcross, GA or Canadian Microanalytical Service, Delta, BC.Tetrafluoroboric acid (54 wt.% or 85 wt.% in diethyl ether), N,N9-diphenylformamidine and n-butyllithium (1.6 M in hexanes) were purchased from Aldrich Chemical Company and used as received. Mo2(DPhF)4 was prepared according to the method described previously for Mo2[(p-tol)- NCHN(p-tol)]4 (p-tol = p-tolyl);8 the anisyl analogue Mo2- (DAniF)4 prepared by following a published procedure.5 Li(DPhF) was obtained by neutralizing a THF solution of N,N9-diphenylformamidine with 1 equivalent of n-butyllithium at 278 8C.After warming to room temperature, the volatile components were removed under vacuum and the resulting oV- white solid was washed with hexane. Syntheses [Mo2(DPhF)(MeCN)6][BF4]3?MeCN 1a. A solution of 0.84 mL (6.4 mmol) of HBF4?Et2O in 25 mL of MeCN was added dropwise over a 45 min period to a slurry containing 1.0 g (1.02 mmol) of Mo2(DPhF)4 in 25 mL of acetonitrile. Over this time, the color of the solution changed from pale yellow to plum.The solution was stirred for an additional 2 h to ensure completion and then filtered to remove unreacted Mo2(DPhF)4. The reaction mixture was concentrated to 10 mL after which 25 mL of diethyl ether was added resulting in the formation of a purple precipitate. The solid was isolated by filtration through a medium frit and dried under vacuum to yield 0.73 g (76%). Deep red crystals suitable for X-ray analysis were obtained by cooling a concentrated solution of 1, in MeCN, to 215 8C for several days. 1H NMR (CD3CN): d 9.05 (s, 1H), 7.3 (m, 4H), 7.2 (m, 6H), 1.95 (s, 11H). IR (cm21): 1599w, 1520m, 1450m, 1322m, 1217m, 1063vs (br), 761s, 699m, 692m, 520w, 461m. [Mo2(DAniF)(MeCN)6][BF4]3?1.59MeCN 1b. To a stirred solution of Mo2(DAniF)4 (150 mg, 0.124 mmol) in 20 mL of CH2Cl2 and 5 mL of MeCN, was added 0.3 mL of HBF4?Et2O (85% in Et2O). The yellow color quickly changed to red then purple. The reaction mixture was stirred at room temperature for 30 min.Diethyl ether (20 mL) was added. Then the solvent was decanted oV and the solid residue was extracted into MeCN (3 mL) and then filtered. The crystalline product was obtained by addition of CH2Cl2 (30 mL) to the filtrate. Yield, 100 mg (85%). Purple single crystals suitable for X-ray analysis were grown by diVusion of Et2O into a MeCN solution. 1H NMR (CD3CN): d 8.97 (s, 1H, NCHN), 7.15 (d, 4H, aromatic, 3J = 9.0), 6.88 (d, 4H, aromatic, 3J = 9.0 Hz), 3.75 (s, 6H, OCH3).IR (KBr, cm21): 2374w, 2338w, 2283w, 2050w, 1654w, 1637w, 1608m, 1528m, 1505s, 1461m, 1442m, 1401m, 1298m, 1246s, 1214s, 1175s, 1082s, 1035s, 832m, 805w, 767w, 593w, 533w, 522w, 464w. UV-vis, lmax/nm (e/M21 cm21): 570 (3130), 460 (2470), 290 (sh). [Mo2(DPhF)2(MeCN)4][BF4]2?MeCN 2a. To a slurry of Mo2(DPhF)4 (0.51 g, 0.51 mmol) in 25 mL of MeCN, a solution of HBF4?Et2O (0.28 mL, 2.1 mmol dissolved in 25 mL of MeCN) was added dropwise over a period of several hours.The addition of HBF4 resulted in a color change from pale yellow to deep red. The mixture was then stirred for an additional 2 h, filtered to remove any unreacted Mo2(DPhF)4, concentrated and cooled to 215 8C. Over a period of 2 days a red precipitate formed and was isolated by filtration through a medium frit and dried under vacuum to yield 0.343 g (72%). Deep red crystals ofJ. Chem. Soc., Dalton Trans., 1999, 1387–1391 1391 Table 6 Summary of crystal data Empirical formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 ZT /K Dc/g cm23 Crystal size/mm m(Mo-Ka)/cm21 2q range/8 No.unique data R(F) a or R(F 2, all data) b Rw(F) a or Rw(F 2, all data) b Goodness of fit 1a C27H32Mo2B3N9F12 934.90 Monoclinic P21/n 23.831(3) 12.218(1) 26.018(3) 94.13(0) 7555.76 8 104 1.644 0.25 × 0.25 × 0.40 7.377 6–45 9840 0.0539 a 0.0473 a 1.123 1b C30.18H37.77B3F12Mo2N9.59O2 1019.20 Monoclinic P1� 11.017(8) 11.065(8) 18.77(2) 87.28(3) 85.49(3) 82.67(5) 2260(4) 2 273 1.498 0.10 × 0.20 × 0.30 6.43 4.4–45 5562 0.114 b 0.255 b 1.256 2a C36H37B2F8Mo2N9 961.24 Triclinic P1� 12.027(3) 17.335(5) 10.341(3) 91.76(1) 109.71(2) 80.43(1) 2000.52 2 103 1.596 0.10 × 0.17 × 0.20 7.027 6–50 7101 0.0360 a 0.0352 a 0.955 2b C42H48B2F8Mo2N10O4 1122.40 Triclinic P1� 12.323(3) 13.155(2) 16.817(4) 94.04(1) 94.78(1) 111.90(1) 2505.4(9) 2 213 1.488 0.25 × 0.25 × 0.20 5.800 4–46 6490 0.058 b 0.134 b 1.071 4 C66H62B2F8Mo2N12 1388.79 Monoclinic C2/c 27.753(6) 12.462(2) 18.715(4) 106.51(1) 6205.83 4 98 1.486 0.15 × 0.15 × 0.30 4.800 6–45 4080 0.0632 a 0.0575 a 1,359 a R(F) = S Fo| 2 |Fc /S|Fo|, Rw(F) = [Sw(|Fo| 2 |Fc|)2/SwFo 2]� �� .b R(F 2) = [Sw(Fo 2 Fc)2/SwFo 2]� �� , Rw(F 2) = {S[w(Fo 2 2 Fc 2)2]/Sw(Fo 2)2}� �� . 2 suitable for X-ray analysis were obtained by slow evaporation of an acetonitrile solution. 1H NMR (CD3CN): d 8.8 (s, 1H), 7.1 (m, 6H), 6.7 (d, 4H, J = 8.7 Hz), 1.95 (s, 9H). IR (cm21): 2849w, 2775vw, 2363w, 1577s, 1491s, 1233m, 1094s (br), 841w, 776m.(Calc. for Mo2C34H34N8B2F8: C, 44.38; H, 3.73; N, 12.18. Found: C, 44.48; H, 3.88; N, 11.85%). [Mo2(DAniF)2(MeCN)4][BF4]2?2MeCN 2b. A 100 mL, threenecked, round-bottomed flask was charged with 242 mg (0.20 mmol) of Mo2(DAniF)4, 178 mg (1.20 mmol) of (Me3O)BF4, and 60 mL of MeCN. To the stirred suspension was added a small amount of deoxygenated H2O (ca. 2–3 drops). The resulting mixture was stirred at room temperature for ca. 5 h, after which time all of the yellow starting material had reacted to give a clear red solution. After the removal of solvent, the red residue was washed with Et2O (2 × 10 mL), then extracted with CH2Cl2–MeCN (19: 1, 2 × 5 mL). Diethyl ether (75 mL) was then carefully added to the extract, and the solution was stored for 24 h at room temperature. Large orange-red block-shaped crystals formed; they were collected by filtration and dried for 4 h in vacuo. The yield was essentially quantitative.Single crystals suitable for X-ray analysis were grown by diVusion of Et2O into an MeCN solution. 1H NMR (CD3CN): d 8.68 (s, 2H, NCHN), 6.69 (m, 16H, aromatic), 3.69 (s, 12H, OCH3). IR (KBr, cm21): 2373w, 2314w, 2283w, 2045w, 1695m, 1610m, 1532s, 1506s, 1464m, 1443m, 1342w, 1291m, 1249s, 1215s, 1178m, 1083s, 1030s, 830m, 766w, 723w, 592w, 526w. UV-vis, lmax/nm, (e/M21 cm21): 516 (2320), 410 (3430), 287 (sh). (Calc. for C38H42B2F8Mo2N8O4: C, 43.87; H, 4.07; N, 10.77.Found: C, 43.23; H, 4.07; N, 10.10%). [Mo2(DPhF)3(MeCN)2][BF4] 3. A 100 mL Schlenk flask was charged with 0.30 g (0.33 mmol) of 2 and 0.096 g (0.49 mmol) of Li(DPhF). To this mixture was added 35 mL of MeCN. The reaction was stirred at room temperature for 12 h, after which time the solution was filtered to remove the Mo2(DPhF)4, which formed as a result of 3 undergoing additional reaction with Li(PhNCHPh). Removal of the volatile components under dynamic vacuum yielded a pumpkin colored powder that contained 90% of [Mo2(DPhF)3(MeCN)2][BF4] and 10% of [Mo2(DPhF)2(NCMe)4][BF4]2 by 1H NMR. 1H NMR (CD3CN): d 9.1 (s, 2H), 8.4 (s, 1H), 7.1 (m, 8H), 7.0 (m, 4H), 6.8 (m, 6H), 6.7 (d, 8H), 6.2 (d, 4H), 1.95 (s, 5H). IR (cm21): 2197vw, 1696m, 1595m, 1534vs, 1489vs, 1319s, 1215s, 1063s (br), 758s, 696m, 517w, 434w. [Mo2(DPhF)2(py)4][BF4]2 4. To a flask containing 0.2 g (0.19 mmol) of 2 was added 25 mL of pyridine. The reaction was stirred at room temperature for 1 h.After 15 min the color of the solution changed from red to orange. The reaction mixture was filtered through a fine frit, concentrated and left undisturbed at ambient temperature. Hexagonal crystals of 4 suitable for X-ray analysis were obtained after 1 week. The yield is essentially quantitative. 1H NMR (pyridine-d5): d 9.9 (s, 1H), 7.6 (d, 4H), 7.5 (m, 6H), 7.2 (m, 25H), 6.7 (d, 4H). IR (cm21): 2900w, 1600s, 1520s, 1310s, 1094 vs (br), 841w, 776m (Calc. for Mo2C66H62N12B2F8: C, 57.08; H, 4.50; N, 12.10. Found: C, 57.10; H, 4.58; N, 12.11%). Crystallographic study General operating procedures and listings of programs have been described.4,9 A summary of crystal data is given in Table 6. CCDC reference number 186/1368. See http://www.rsc.org/suppdata/dt/1999/1387/ for crystallographic files in .cif format. Acknowledgements We thank the National Science Foundation for support. References 1 R. H. Cayton, M. H. Chisholm, J. C. HuVman and E. B. Lobkovsky, J. Am. Chem. Soc., 1991, 113, 8709. 2 M. H. Chisholm and A. M. Macintosh, J. Chem. Soc., Dalton Trans., 1999, 1205. 3 F. A. Cotton, C. Lin and Coc., Dalton Trans., 1998, 3151. 4 F. A. Cotton, L. M. Daniels, C. Lin and C. A. Murillo, J. Am. Chem. Soc., in press. 5 C. Lin, J. D. Protasiewicz, E. T. Smith and T. Ren, Inorg. Chem., 1996, 35, 6422. 6 F. A. Cotton, L. M. Daniels, C. A. Murillo and X. Wang, Polyhedron, 1998, 2781. 7 F. A. Cotton and K. J. Wiesinger, Inorg. Synth., 1992, 29, 134. 8 F. A. Cotton, X. Feng and M. Matusz, Inorg. Chem., 1989, 28, 594. 9 M. H. Chisholm, K. Folting, J. C. HuVman and C. C. Kirkpatrick, Inorg. Chem., 1984, 23, 1021. 10 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Paper 9/00389D