Inorg. Chem. 1983, 22, 3275-3281 Registry No. 1, 86992-66-7; 2, 86943-70-6; 3, 86943-72-8; 4, 86943-73-9; 5, 86943-74-0; 6, 86943-76-2; [Rh(nbd)(PNP)1PF6, 86953-28-8; [Ir(cod)(PNP)]BF4, 86953-30-2; [Ir(cod)C112, 1211267-3. Supplementary Material Available: Tables of general temperature
3275
factor expressions, calculated hydrogen atom positional parameters, and calculated and observed structure factor amplitudes for 1 and 2, figures of N M R spectra for compounds 2, 3, 4, and 6,and stereoviews of 1 and 2 (62 pages). Ordering information is given on any current masthead page.
Contribution from the W. R. Kenan, Jr. Laboratory, Department of Chemistry, The University of North Carolina, Chapel Hill, North Carolina 27514
Chemical, Spectral, and Structural Features of MO(RC=CR)~(S~CNC~H~)~ Complexes Containing the Electronically Unique Pyrrole-N-carbodithioate Ligand RICHARD S. HERRICK, SHARON J. NIETER BURGMAYER, and JOSEPH L. TEMPLETON*
Received December 21, 1982 Syntheses of a series of bis(alkyne)bis(pyrrole-N-carbodithioato)molybdenum(II) complexes, including the unsubstituted acetylene derivative M o ( H C ~ H ) ~ ( S ~ C N C ~are H ~reported. )~, The molecular structure of the 2-butyne adduct, Mo(MeC2Me)2(S2CNC4H4)2, has been determined by a single-crystal X-ray diffraction study. The crystals were found to be monoclinic of space group P2,/n with a = 12.372 (4) A, b = 12.145 (3) A, c = 14.184 (3) A, and 0 = 101.50 ( 2 ) ' . The unit cell contains one independent molecule per asymmetric unit; the structure was refined to R = 0.056 and R , = 0.041 with use of 1470 reflections with I > 3 4 I ) . The molecular geometry can be described as a distorted octahedron with two cis-parallel alkynes and two bidentate carbodithioates in the coordination sphere. The pyrrole-N-carbodithioate ligands are essentially planar with a C-N distance of 1.37 A (average) in the S2C-NC4H4unit. The ring distances within the NC4H4 moiety are compared to those of free pyrrole and cyclopentadiene to address the question of aromaticity in this fragment. Dynamic NMR studies revealed two independent fluxional processes in Mo( MeC2Me)2(S2CNC4H4)2.The lower energy process (AC* = 10.7 kcal/mol) is believed to reflect rotation around the C-N bond of the chelating ligands while the higher energy molecular rearrangement (13.7 kcal/mol) is believed to correspond to rotation of the alkyne ligands around the molybdenum-alkyne bond axis. Both the crystallographic and DNMR results reflect the pyrrole nitrogen's reluctance to provide *-electron density to the CS2 fragment. The decreased electron donor ability of the pyrrole-Ncarbodithioate ligand relative to that of alkyl analogues is chemically evident in the lability of the carbonyl ligand in M O ( C O ) ( R C ~ R ) ( S ~ C N C ~which H ~ ) ~greatly , enhances the rate of formation of the bis(a1kyne) products. The chemical, spectroscopic, and structural properties of these complexes can be rationalized in terms of accepted valence bond descriptions of carbodithioate ligands.
Introduction The chemistry of low-oxidation-state, formally electrondeficient d4 transition-metal monomers containing both a-acid a n d r - b a s e ligands has m a t u r e d substantially.' A useful model of the electronic structure of these compounds2has been distilled from the s p e c t r o s ~ o p i c ,s ~t r~~ c t u r a l , ~ +t h~e. *~ r e t i c a l , ~ electrochemicallcJO and mechanistic" results accumulated for these complexes. (1) (a) Chisholm, M. H.; Huffman, J. C.; Kelly, R. L. J . Am. Chem. Soc. 1979, 101, 7615. (b) Churchill, M. R.; Wasserman, H. J. Holmes, S. J.; Schrock, R. R. Organometallics 1982, 1, 766. (c) Winston, P. B.; Nieter-Burgmayer, S. J.; Templeton, J. L. Ibid. 1983, 2, 167. (d) DeCian, A.; Cobin, J.; Schappacher, M.; Ricard, L.; Weiss, R. J. Am. Chem. Soc. 1981, 103, 1850. (e) Faller, J. W.; Murray, H. H. J. Organomet. Chem. 1979, 172, 171. (f) Davidson, J. L.; Green, M.; Stone, F. G. A.; Welch, A. J. J. Chem. SOC.,Dalton Trans. 1976,738. (g) Watson, P. L.; Bergman, R. G. J . Am. Chem. SOC.1980,102,2698. (2) Templeton, J. L.; Winston, P. B.;Ward, B. C. J. Am. Chem. SOC.1981, 103, 7713. (3) McDonald, J. W.; Newton, W. E.; Creedy, C. T. C.; Corbin, J. L. J . Organomet. Chem. 1975, 92, C25. (4) Templeton, J. L.; Ward, B. C.; Chen, G. J.-J.; McDonald, J. W.; Newton, W. E. Inorg. Chem. 1981, 20, 1248. (5) Templeton, J. L.; Ward, B. C. J . Am. Chem. SOC.1980, 102, 3288. (6) Herrick, R. S.; Templeton, J. L. Organometallics 1982, 1, 842. (7) Ricard, L.; Weiss, R.; Newton, W. E.; Chen, G. J.-J.; McDonald, J. W. J. Am. Chem. SOC.1978, 100, 1318. (8) Newton, W. E.; McDonald, J. W.; Corbin, J. L.; Ricard, L.; Weiss, R. Inorg. Chem. 1980, 19, 1997. (9) Kubibk, P.;Hoffmann, R. J . Am. Chem. SOC.1981, 103, 4320. (10) Templeton, J. L.; Herrick, R. S.; Morrow, J. R. Organometallics, in press. (1 1) Herrick, R. S.; Leazer, D. M.; Templeton, J. L. Organometallics 1983, 2. 834. 0020-1669/83/1322-3275$01.50/0
A significant subclass of six-coordinate d 4 monomers is the set of bis(dithiocarbamat0) derivatives of t h e type M(X)( Y ) ( S 2 C N R 2 ) 2(M = Mo, W; X = Y = C 0 ; l 2 X = CO, Y = R1C2R2;7>13 X = 0,y = R1C2R2;4A14 X = y = RIC2R2A6), T h e dithiocarbamate ligands serve to anchor these complexes by providing a variable degree of ?r-electron donation as evident in t h e chemistry12 and ~ t r u c t u r e 'of ~ Mo(CO)~(S~CNR~)~. Contributions from t h e three resonance forms (1-111) which
I
II
m
dominate metal-dithiocarbamate valence bond descriptions a r e relatively insensitive to minor variations of alkyl and aryl substituents on t h e nitrogen atom.16 T h e pyrrole-N-carbodithioate ligand (pdtc) prepared by Kellner et al.17 exhibits unusual bonding properties in homoleptic dithiocarbamate complexes. Bereman and his co-workers have substantiated the hypothesis that resonance form I11 is unfavorable for pdtc (12) (a) Colton, R.; Scollary, G. R.; Tomkins, I. B. Aust. J . Chem. 1968.21, 15. (b) Templeton, J. L. Adu. Chem. Ser. 1979, No. 173, 263. (c) Browmhead, J. A.; Young, C. G. Aust. J . Chem. 1982, 35, 277. (13) Ward, B. C.; Templeton, J. L. J . Am. Chem. SOC.1980, 102, 1532. (14) (a) Maatta, E. A.; Wentworth, R. A. D.; Newton, W. E.; McDonald, J. W.; Watt, G. D. J. Am. Chem. SOC.1978, 100, 1320. (b) Maatta, E. A.; Wentworth, R. A. D. Inorg. Chem. 1979, 18, 524. (15) Templeton, J. L.; Ward, B. C. J . Am. Chem. SOC.1980, 102, 6568. (16) Coucouvanis, D. Prog. Inorg. Chem. 1979, 26, 301. (17) (a) Kellner, R.; Prokopowski, P.; Malissa, H. Anal. Chim. Acta 1974, 68, 401. (b) El A'mma, A. G.; Drago, R. S. Inorg. Chem. 1977, 16, 2975. 0 1983 American Chemical Society
Herrick, Burgmayer, and Templeton
3276 Inorganic Chemistry, Vol. 22, No.22, 1983
transferred into a tared Schlenk tube, was added by connecting the neck joints of the two Schlenk flasks and inverting to drop the ligand into the solution. The solution immediately turned dark red, and gas evolved. After the mixture was stirred for 15 min, dimethylacetylene (0.23 mL, 0.16 g, 0.304 mmol) was added. The solution began to turn brown and displayed a strong C O stretch at 1953 cm-' in the IR spectrum. After 4 h solvent was removed in vacuo. The product was chromatographed and recrystallized as described above to yield large orange crystals (53% yield). M O ( P ~ C ~ P ~ ) ~ ( S ~ C N'HCN~ M H R~ )(CDC13) ~: 6 7.59 (m, 4 H, a-H), 7.36 (m, 20 H, C,H5), 6.29 (m, 4 H, P-H). M o ( P ~ C , H ) ~ ( S ~ C N C ~ H'H, ) ~N:M R (CDCl,) 6 10.66 (s, 2 H, H - G ) , 7.62 (m, 4 H, a-H), 7.39 (m, 10 H, C6H,), 6.30 (m, 4 H, P-H). M O ( P ~ C ~ M ~ ) ~ ( S ~ C N'HC N ~H M ~R )(CDC1,) ~: 6 7.67 (m, 4 H, a-H), 7.45 (m,10 H, C6H5), 6.32 (m, 4 H, 0-H), 3.1 1 (s, 6 H, CHI). M O ( M ~ C ~ M ~ ) ~ ( S ~ C N'HC N~ M HR ~ )(CDCl,) ~: 6 7.64 (m, 4 H, a-H), 6.25 (m, 4 H, P-H), 2.65 (s, 12 H, CH,); 13C N M R (C,D,) 6 215.94 (s, S2C), 179.53 and 178.76 (s, =C), 118.09 (d, a-C), 114.24 ( 4 P-C). Experimental Section Mo(E~C~E~)~(S$NCJ&),: 'H N M R (CDCl,) 7.67 (m, 4 H, a-H), Materials and Methods. Standard Schlenk techniques with a dry 6.28 (m, 4 H, P-H), 2.79-3.47 (poor q, 8 H, CH2), 1.16 (t, 12 H, deoxygenated nitrogen atmosphere were used for all manipulations. CH,); IR (KBr) v(C=C) 1787 (w) cm-'. Solvents were degassed prior to use. Molybdenum hexacarbonyl, Mo(/I-BuC~H)~(S~CNC~H~)~: 'H N M R (CDC13) 6 9.94 (s, 2 H, pyrrole, carbon disulfide, iodine, chlorine gas, tetraethylammonium H - G ) , 7.69 (m, 4 H, a-H), 6.36 (m, 4 H, P-H), 3.16 (m, 4 H, iodide, and alkynes were obtained from commerical sources. Acetone =C-CH2), 1.03-1.81 (m, 8 H, =C-CH2-CH2-CH2), 0.88 (m, was removed from acetylene gas by bubbling the gas through a 6 H, CH,). IR (KBr) v(C=C) 1715 (w) cm-I. saturated sodium metabisulfite/water solution followed by passing M o ( H C ~ H ) ~ ( S ~ C N CM ~H O (~C) ~O ) ~ ( S ~ C N C , H(1.52 ~ ) ~g, 3.27 through a calcium chloride drying tube. M o ( C O ) , ( S ~ C N C ~ H ~ ) ~ , ' ~mmol) was dissolved in 50 mL of CH2C12. Acetylene gas, purified M O ( C O ) ~ C IKS2CNC4H4:'/2THF,18 ~,~ and [(C2H5)4N][Mo(CO)51]2' as described above, was bubbled through the methylene chloride were prepared according to literature procedures. Proton N M R (100 solution. An infrared spectrum of the brown solution showed a strong MHz) spectra were recorded on a Varian XL-100 spectrometer. carbonyl stretch a t 1962 cm-l after 10 min. After 1.5 h this band Carbon-13 N M R (62.89 MHz) spectra were recorded on a Bruker had disappeared. The acetylene gas flow was stopped, and solvent W M 250 spectrometer. Chemical shifts are reported as parts per was removed on a rotary evaporator. The product was chromatomillion downfield of Me4Si. N M R sample temperatures were meagraphed on an alumina column with methylene chloride as eluent. sured with a thermocouple located in the probe. A Beckman IR 4250 A brown-orange band was eluted with mast of the material remaining spectrometer was used to record infrared spectra, which were calibrated as decomposition product on the column. Solvent was removed in with a polystyrene standard. vacuo to yield an oily solid. The bis(acety1ene) product was obtained Syntheses. Mo(R'C2R2) (SzCNC4H4)2. (a) From Mo( CO) (S2in 10%yield by this method but contained minor impurities, which CNC4H4)2(R' = R2 = Ph; R' = Ph,R2 = H,R' = Ph, R2 = Me; we were unable to separate from the product. 'H N M R (CDCI,) R' = R2 = Me; R 1 = R2 = Et; R' = n-Bu, R2 = H). The following 6 10.28 (s, 4 H, H-C=), 7.69 (m, 4 H, a-H), 6.30 (m, 4 H, P-H). preparative procedure is general for the synthesis of the alkyne Collection of Diffraction Data. Orange crystals of Mocomplexes listed above. MO(CO)~(S~CNC~H,), (1.08 g, 2.33 mmol) (MeC2Me)2(S2CNC4H4)2 were grown from a cooled solution of was dissolved in ether (30 mL), producing a purple solution (submethylene chloride and methanol. A roughly rectangular prism having stitution of tetrahydrofuran for ether also leads to a purple solution approximate dimensions 0.22 X 0.27 X 0.30 mm was selected, mounted while methylene chloride produces an orange solution; all are suitable on a glass wand, and coated with epoxy cement. Diffraction data solvents for the reaction). PhC2Ph (0.822 g, 4.61 mmol) was added were collected on an Enraf-Nonius CAD-4 automated diffractometer?2 to the solution while it was stirring. The solution immediately turned A monoclinic cell was indicated from 25 centered reflections found brown, and gas evolved. The solution IR shows a strong carbonyl in the region 30° < 20 < 34O and refined by least-squares calculations. band a t 1955 cm-' at this point which disappears with time. After The cell parameters are listed in Table I. 4 h solvent was removed in vacuo. The oily brown product was Diffraction data were collected in the quadrant +h,+k,*l under chromatographed on an alumina column with a methylene chlothe conditions specified in Table I. Three standard reflections were ride/toluene solvent mixture. The optimum solvent ratio varies demonitored for decay every 5 h, and the crystal was recentered as pending on the alkyne substituents with more soluble alkylalkynes necessary every 300 reflections. A total of 4056 data were processed requiring more toluene. An orange band was eluted, and decomposition and corrected for Lorentz-polarization effects. No correction was products remained on the column. The solution volume was reduced, made for absorption. A total of 1470 data having I > 3 4 0 were methanol was added, and the flask was placed in a refrigerator. The used in the refinement of the structure. solid that precipitated was filtered, washed with methanol, and dried Solution and Refmement of the Structure. The structure solution in vacuo to yield moderately air-stable orange crystals in 3040% yield. was straightforward from application of the heavy-atom method. The Isolation of M O ( ~ - B U C ~ H ) ~ ( S ~ C varied N C ~ Hfrom ~ ) ~this scheme space group P 2 J n deduced from systematic absences (hOl ( h + 1 = because it produced an oil despite recrystallization attempts with 2n 1) and OkO ( k = 2n + 1)) was verified by successful structure various solvents. determination. The single molybdenum atom was located in a (b) From [(C2H5)4NIMo(CO)51] (R' = R2 = Ph; R' = Ph, R2 = three-dimensional Patterson function. The positions of the remaining H R' = Ph, R2 = Me; R' = RZ= Me; R' = R2 = Et). The following non-hydrogen atoms were obtained from subsequent Fourier and preparative procedure is general for the synthesis of the alkyne difference Fourier calculations. Anisotropic full-matrix least-squares complexes listed above. [(C2H5)4N][Mo(CO),I] (0.75 g, 1.52 mmol) refinement of these 25 atoms produced residuals R = 0.066 and R, was dissolved in tetrahydrofuran (25 mL), forming a yellow solution. = 0.056.23 A difference electron density map showed no peak greater Iodine (0.386 g, 1.52 mmol) was added, immediately producing an orange-red solution. After 15 min the iodine had been completely (22) All programs utilized during data collection and structure solution and consumed. The hygroscopic pyrrole-N-carbodithioate ligand, Krefinement were provided by Enraf-Nonius as part of the Structure [S2CNC4H4].'/2THF(0.660 g, 3.04 mmol), which had been previously DeterminationPackage (SDP, 3rd ed., Aug 1978; revised June 1979). (23) The function minimized was ~ ~ ( 1 IFcl)*, ~ ~ 1where - w = [2F,/u(F:)l2 and u(F2) = [u2(r)+ p2P]' with p assigned a value of 0.01. Expressions for the residuals are R = xllFol - ~ F c ~ [ /and ~ ~RF, o= ~ (18) Bereman, R. D.; Nalewajek, D. Inarg. Chem. 1977, 16, 2687. (19) Herrick, R. S.; Templeton, J. L.,manuscript in preparation. [xw(lyol-,Fc1)2/x~(Fo)2]'/2. Although R, < R is somewhat unusual, our weighting scheme with p = 0.01 produces a lower R , than when p (20) Colton, R.; Tomkins, I. B. Aust. J . Chem. 1966, 19, 1143. = 0 is utilized, which leaves R , > R. (21) Abel, E. W.; Butler, I. S.; Reid, J. G. J . Chem. Sac. 1963, 2068.
ligands due to loss of pyrrole aromaticity upon delocalization of the nitrogen lone pair into the CS2 unit.'* We initiated a study of bis(alkyne)bis(pyrrole-N-carbodithioato)molybdenum(II) monomers in an effort to systematically modify the molecular properties of these complexes relative to those of the previously reported M o ( R ' C ~ R ~ ) ~ (S2CNR2),(R = Me, Et) complexes. We report here (1) the remarkably facile synthesis and the spectroscopiccharacterization of M ~ ( R ' c ~ R ~ ) ~ ( p dcomplexes tc)~ (pdtc = -S2CNC4H4;R' = R2 = Ph; R' = Ph, R2 = H, R' = Ph, R2 = Me, R' = R2 = Me, R' = R2 = Et; R' = n-Bu, R2 = H; R' = R2 = H), (2) the successful synthesis of the parent bis(acety1ene) complex, (3) the solid-state molecular structure of M ~ ( M e C ~ M e ) ~ ( p dillustrating tc)~ the cis-parallel alkyne orientation, and (4) DNMR studies reflecting a decreased S2C=N ?r-interaction in the pyrrole-N-carbodithioateligand compared to that in dialkyldithiocarbamate analogues.
+
Inorganic Chemistry, VoZ,22, No.22, 1983 3277
Mo(RC=CR),(S2CNC4H4), Complexes Table I Crystallographic Data for Mo(MeWMe),(pdtc), molecular formula MoS,N,C,,HzCl fw 488.57 space group P2, In cell parameters 12.327 (4) a, A 12.145 (3) b, a 14.184 (3) c, A 101.50 (2) A deg A3 2088 (2) p(calcd),g/cm3 1.554 4 Z
v,
Collection and Refinement Parameters Mo Ka (0.710 73) radiation (wavelength, A) linear abs. coeff, cm-' 10.04 scan type ~11.670 1.1 + 0.35 tan e scan width, deg bkgd 25% of full scan width on both sides e limits, deg i
