Organometallics 1982, I, 336-343
336
Redox Chemistry of Hexakis(phenyl isocyanide) Complexes of Molybdenum and Tungsten: The Synthesis of the Seven-Coordinate Cations [M(CNPh),12+ and Their Electrochemistry and Substitution Reactions Douglas D. Klendworth, Warren W. Welters, 111, and Richard A. Walton' Department of Chemistv, Purdue University, West Lafayette, Indiana 47907 Received August 3, 1981
The reactions of the quadruply bonded tungsten complexes Wz(mhp), and Wz(dmhp), (mhp and dmhp are the anions of 2-hydroxy-6-methylpyidine and 2,4-dimethyl-6-hydroxypyimidine, respectively) with excess phenyl isocyanidelead to reductive cleavage of the metal-metal bond and the formation of W(CNPh)& Oxidation of M(CNPh), (M = Mo or W) with Ag+ in the presence of free phenyl isocyanide yields the first examples of seven-coordinate, homoleptic aryl isocyanide complexes of molybdenum(I1) and tungsen(II), [M(CNPh)7](PF6)2.Oxidation of M(CNPh)6is also observed with Iz and NOPF,, reactions which yield [M(CNPh)61]+and [M(NO)(CNPh),]PF,, respectively. The reactions of [M(CNPh)7]2+(M = Mo or W) with a variety of mono- or bidentate phosphines generate seven-coordinate mixed-ligand cations of the types [M(CNPh)6(PR3)12',[M(CNPh)5(PR3)212+, [M(CNPh)&dppm)12+, and [M(CNPh),(dppe)lZ+,where dppm = bis(dipheny1phosphino)methane and dppe = 1,2-bis(diphenylphosphino)ethane. The cyclic voltammograms of these seven coordinate complexes are characterized by a single one-electron oxidation between +0.9 and +1.5 V and an irreversible two-electron reduction close to -1.0 V. Reduction of [M(CNPh)7]2+with magnesium regenerates the six-coordinate homoleptic complexes M(CNPh)& Spectroscopic characterization of these complexes have included measurement of their 'H NMR, IR, and electronic absorption spectra.
Introduction The fission of metal-metal multiple bonds by Ir-acceptor ligands such as CO and NO and alkyl and aryl isocyanides is well documented.l-1° One of the interesting features within this class of ligand induced cleavage reactions is the difference which exists between alkyl and aryl isocyanides in their reactions toward quadruply bonded dinuclear MO~(O~CCH~ and ),,~ complexes such as Cr2(02CCH3)4,5 W2(mhp), (mhp is the anion of 2-hydroxy-6-methyl~ y r i d i n e ) .In ~ the case of alkyl isocyanides, nonreductive cleavage yields the seven-coordinate cations [M(CNR),] 2+ (where M = Mo or W; R = CH,, CMe3, or C6Hll),whereas for aryl isocyanide, reductive cleavage has been found to produce the six-coordinate complexes M(CNAr), (where M = Cr or Mo). The formation of Cr(CNPh), and Mo(CNPh), by this latter procedure constitutes the most convenient synthetic route to these complexes. In spite of the strong tendency for reductive cleavage to occur in the presence of ArNC ligands, it seemed to us that this should not preclude the formation of salts containing the seven-coordinate phenyl isocyanide cations [M(CNPh)7]2+.Following our discovery of a convenient (1) Hertzer, C. A.; Myers, R. E.; Brant, P.; Walton, R. A. Inorg. Chem. 1978,17, 2383. (2) Nimry, T.; Urbancic, M. A.; Walton, R. A. Inorg. Chem. 1979,18,
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(3) Brant, P.; Cotton, F. A.; Sekutowski, J. C.; Wood, T. E.; Walton,
R. A. J . Am. Chem. SOC.1979, 101,6588. (4) Wood, T. E.; Deaton, J. C.; Corning, J.; Wild, R. E.; Walton, R. A.
Inorg. Chem. 1980,19, 2614. (5) Malatesta, L.; Sacco, A.; Ghielmi, S. Gazz. Chim.Ztal. 1952,82,516. (6) Mann, K. R.; Cimolino, M.; Geoffroy, G. L.; Hammond, G. S.; Orio, A. A.; Albertin, G.; Gray, H. B. Inorg. Chim. Acta 1976, 16, 97. (7) Mialki, W. S.;Wild, R. E.; Walton, R. A. Inorg. Chem. 1981, 20,
preparation of W(CNPh), we have now devised routes to [Mo(CNPh),](PF,), and [W(CNPh)7](PF6)2through the oxidation of M(CNPh), in the presence of excess phenyl isocyanide. In the present report we describe these results along with details of the spectroscopic and electrochemical properties of these new compounds and their substitution chemistry. Preliminary details of certain of these results have been reported previously.8
Experimental Section Starting Materials. The following compounds were prepared
by standard literature procedures: Mo(CNPh)6,BWz(mhp),," Wz(dmhp),,12and PhNC.13 All monodentate and bidentate phosphines, 2-hydroxy-6-methylpyridine(Hmhp), 2,4-dimethyl-6-hydroxypyrimidine(Hdmhp), and other reagents and solvents were obtained from commercial sources. Solvents were of the highest purity commerciallyavailable and were used without further purification with the exception of acetone, which was dried over CaSO,, and tetrahydrofuran,which was distilled from d u m benzophenone. Potassium hexafluorophosphate was recrystaUized from aqueous solution. Tetra-n-butylammonium hexafluorophosphate (TBAH) was obtained by reacting tetra-n-butylammonium iodide with KPF6 in hot water. The product was recrystallized from aqueous ethanol and dried in vacuo. Reaction Procedures. All reactions were carried out in a nitrogen atmosphere, and all solvents were deoxygenated prior to use by purging with N2gas. A. Preparation of W(CNPh)6from Quadruply Bonded Tungsten(I1) Complexes. (i) W,(dmhp), (dmhp Is the Anion of 2,4-Dimethyl-6-hydroxypyrimidine).A quantity of W2(dmhp), (0.60 g, 0.70 mmol) was added with stirring to 25 mL of methanol which was cooled to -20 "C in a dry ice bath. To this was added an excess (101)of phenyl isocyanide. The resulting reaction mixture was stirred for 1h and filtered and the resulting red solid washed sparingly with ethanol. The product was then dissolved in benzene and the solution passed through an alumina
1380.
(8)Klendworth, D. D.; Welters, W. W., III; Walton, R. A. J. Organomet. Chem. 1981, 213, C13. (9) Girolami, G. S.; Anderson, R. A. J. Organomet. Chem. 1979,182, c43. (10) Cotton, F. A.; Darensbourg, D. J.; Kolthammer, B. W. S. J. Organomet. Chem. 1981,217, C14.
(11) Cotton, F. A.; Fanwick, P. E.; Niswander, R. H.; Sekutowski, J. C. J. Am. Chem. SOC.1978,100,4725. (12) Cotton, F. A,; Niswander, R. H.; Sekutowski, J. C. Inorg. Chem. 1979,18, 1152. (13) Weber, W. P.; Gokel, G. W. Tetrahedron Lett. 1972, 1637.
0276-7333182/2301-0336$01.25/0 0 1982 American Chemical Society
Molybdenum and Tungsten Phenyl Isocyanide Complexes
Organometallics, Vol. 1, No. 2, 1982 337
column using benzene as the eluant. This procedure was carried out in the dark to avoid photodecomposition. The solvent was removed under a stream of Nz, and red crystals of the complex were isolated; yield 0.30 g (27%). Anal. Calcd for C4,HmN6W: C, 62.85; H, 3.76. Found: C, 63.09; H, 3.80. (ii) Wz(mhp), (mhp Is the Anion of 2-Hydroxy-6methylpyridine). A quantity of Wz(mhp)4 (0.421g, 0.52 mmol) was reacted by using a procedure analogous to that described in A(i);yield 0.24 g (29%). The resulting red crystals had the same spectroscopic properties as those of the sample of W(CNPh)6 prepared in A(i). B. Oxidation Reactions of Mo(CNPh),. (i) [Mo(NO)(CNPh)5]PF6.A quantity of Mo(Cwh), (0.2 g, 0.28 mmol) was dissolved in 30 mL of freshly distilled tetrahydrofuran. Slightly more than a stoichiometricamount of NOPF, (0.06g, 0.34 mmol) was added to the stirred solution via a side arm addition tube. The color of the solution changed immediately from bright red to dark purple. A small volume (10 mL) of deoxygenated hexane was then added to the reaction vesaeL The dark purple solid which formed was collected,washed well with diethyl ether, and dried in vacuo; yield 0.20 g(90%). Anal. Calcd for C96H&6MoN60P C, 53.44; H, 3.21; N, 10.69. Found: C, 53.11; H, 3.45; N, 10.78. After removal of the dark purple product by filtration, the filtrate w a taken ~ to dryness. Recrystallizationof the residue from acetone-diethyl ether yielded a small quantity of [Mo(Cwh),](PF6), as fine yellow needles;yield 0.029 g (9%). Anal. Calcd for C49HssF,zMoN7Pz:C, 53.12; H, 3.19; N, 8.85. Found: C, 53.32; H, 3.41; N, 8.59. A higher yield synthesis of this complex is described in B(iv). (ii) [Mo(CNPh)d]PF,. A dichloromethane solution of iodine (0.180 g, 0.71 mmol) was added dropwise to a stirred dichloromethane solution of Mo(CNPh), (0.5 g, 0.70 mmol). The color of the solution changed gradually from bright red to orange during this addition. Potassium heduorophosphate (0.25g, 1.36 mmol) dissolved in_acetonewas then added to the reaction vessel. The solvent was removed under a stream of Nz,and the resulting solid residue was dissolved in benzene. Upon the addition of petroleum ether bright orange crystals separated. The product was washed well with water, 2-propanol, and diethyl ether and dried in vacuo; yield 52%. Anal. Calcd for C42H&61MoN6P: c, 51.13;H,3.07; N, 8.52. Found C, 50.89; H, 3.31; N, 8.34. (iii) [Mo(CNPh),I]BPhl. This complex was prepared in a manner similar to that of ita analogous PF6-salt, except that an acetone solution of NaBPh, (0.4g, 1.17 mmol) was added following the iodine oxidation. The addition of an excess of diethyl ether induced precipitation of the desired product. The orange solid was recrystallized from acetone-diethyl ether, washed well with ethanol and diethyl ether, and dried in vacuo; yield 79%. Anal. Calcd for CBBH&IMoN6:C, 68.28; H, 4.35; N, 7.24. Found: C, 68.38; H, 4.35; N, 7.26. (iv) [ M O ( C N P ~ ) ~ ] ( P F ,A) ~mixture . of Mo(CNPh), (0.30 g, 0.42 mmol), AgN03 (0.17 g, 1.0 mmol), and KPF, (0.17 g, 0.92 mmol) was added to a 100-mL round-bottom flask followed by 25 mL of acetone and immediately thereafter 0.5 mL of phenyl isocyanide. The contents of the reaction flaak were stirred at room temperature for 3 h in the dark. The reaction mixture was then filtered and diethyl ether added to the filtrate until precipitation of a yellow crystalline solid occurred. This was filtered off and washed successively with water, 2-propanol, and diethyl ether. Recrystallization was carried out by dissolving the product in acetone followed by the careful addition of diethyl ether; yield 0.33 g (71%). Anal. Calcd for C49H35F12MoN7Pz: C, 53.12; H, 3.19; N, 8.85. Found C, 53.32; H, 3.32; N, 8.78. Workup of the reaction filtrate afforded a small quantity of the nitrosyl derivative [Mo(NO)(CNP~)~]PF, (yield less than 10%). Proof of its identity as the same complex as that prepared in B(i) was established by ita spectroscopic and electrochemical properties. C. Oxidation Reactions of W(CNPh)@ (i) [W(NO)(CNPh)5]PFB.A quantity of W(Cwh), (0.2 g, 0.249 mmol) was dissolved in 30 mL of acetone and a solution of NOPF6 (0.044 g, 0.25 mmol) in acetone or dichloromethane (15 mL) added dropwise. This mixture was stirred for 45 min and diethyl ether than added to precipitate the purple product; yield 0.161 g (74%). Anal. Calcd for CS5HZ5F6N6OPW: C,48.07; H, 2.88; N, 9.61. Found C, 47.92; H, 2.87; N, 9.50.
(ii) [W(CNPh)J]BPh4. A quantity of W(CNPh)6 (0.20 g, 0.249 mmol) was dissolved in dichloromethane (30 mL). To this
stirred solution was added dropwise a dichloromethane solution containing iodine (0.063g, 0.248 mmol). A similar procedure was followed to that described in B(iii); yield 0.217 g (70%). Anal. Calcd for C&&IN6W: C, 63.47; H,4.04. Found: C, 63.67; H, 4.21. (iii) [w(CNPh),](PF,),. A mixture of W(CNPh)6 (0.700 g, 0.87 mmol), powdered AgNO3 (0.30 g, 1.77 mmol), KPF6 (0.33 g, 1.79 mmol), and phenyl isocyanide (-0.3 mL) was reacted in 30
mL of acetone in an analogous procedure to that described in C, B(iv); yield 0.72 g (69%). Anal. Calcd for C49H35F12N7P2W 49.24; H, 2.92; N, 8.20. Found: C, 49.06; H, 3.04; N, 7.95. Workup of the reaction filtrate in a manner similar to B(iv) afforded a small crop of purple [W(NO)(CNPh),]PF, (yield
