Journal of the American Chemical Society
5268
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101:18
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August 29, 1979
Stereochemically Rigid Seven-Coordinate Complexes. Synthesis, Structure, and Dynamic Stereochemistry of Chlorotris( N,N-dialkylmonothiocarbamato)titanium(IV) Complexes Stephen L. Hawthorne and Robert C. Fay* Contribution from the Department of Chemistry, Cornell University, Ithaca. New York 14853. Received March 5, 1979
Abstract: Seven-coordinate N,N-dialkylmonothiocarbamatecomplexes of the type [Ti(Rzmtc)3CI] (Rzmtc = SOCNR2; R = Me, Et, i-Pr, or i-Bu) have been prepared by reaction of titanium(1V) chloride with stoichiometric amounts of Na(R2mtc) in dichloromethane or benzene. The complexes have been characterized by conductance measurements, N M R spectra, and infrared spectra. The crystal and molecular structure of [Ti(Et2mtc)3CI] has been determined by X-ray diffraction and has been refined anisotropically by least-squares methods to R1 = 0.062 and R2 = 0.066 using 4862 independent diffractometer data having 2 0 5 56.75" ~ ~ lFoI ~ 1 1 . 5 8 ~The and ~ . compound crystallizes in the monoclinic space group C2/c with eight molecules in a cell having dimensions a = 27.888 (5) A, b = 9.786 ( I ) A, c = 17.819 (2) A, 6 = 97.674 (9)" (Pobsd = 1.328, P&d = 1.323 g crn-'). The crystal contains discrete seven-coordinate molecules which have pentagonal bipyramidal geometry and approximate symmetry Cs-m. The chlorine atom occupies an axial position (Ti-CI = 2.330 (1) A), and the monothiocarbamate ligands are oriented so as to cluster the three sulfur atoms in all-cis positions on one triangular face of the pentagonal bipyramid (Ti-S = 2.477-2.489 A; T i - 0 = 2.076-2.089 A). Low-temperature ' H N M R spectra of [Ti(Mezmtc)&l] favor the same structure in solution. At higher temperatures, N M R line-shape changes indicate the existence of two distinct kinetic processes: ( I ) a low-temperature intramolecular metal-centered rearrangement process that exchanges the spanning and the equatorial Mezmtc ligands (AG* (-58.2 "C) = 10.8 f 0.1 kcal/mol, AH* = 11.2 & 0.3 kcal/mol, AS* = 2.0 f 1.6 eu) and (2) a high-temperature process that involves rotation about the C"N bond in the Mezmtc ligands (AG* (1 I O "C) = 20 kcal/ mol). A polytopal rearrangement mechanism involving a monocapped octahedral transition state that maintains the all-cis arrangement of sulfur atoms is suggested for the metal-centered rearrangement.
Introduction Previous papers from this laboratory have described the preparation, characterization, and structure of eight-coordinate tetrakis(N,N-dialkylmonothiocarbamate)complexes of titanium(1V) and zirconium(IV), [M(Rzmtc)4], l.1-3 These M [>c-N/R] R'
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complexes exist in the solid state and in solution as dodecahedral stereoisomers which have an mmmm ligand wrapping pattern and a C2" arrangement of sulfur and oxygen donor atoms. Two of the sulfur atoms occupy dodecahedral A sites and two occupy B sites so as to give an all-cis arrangement with the four sulfur atoms on one side of the coordination polyhedron and the four oxygen atoms on the other side. These complexes are of special interest as rare examples of eightcoordinate tetrakis chelates that are stereochemically rigid on the N M R time scale a t readily accessible temperature^.^-^ The present paper reports the preparation and characterization of the seven-coordinate Ti(1V) analogues, [Ti(R2mtc)3Cl] (R = Me, Et, i-Pr, or i-Bu), the crystal and molecular structure of [Ti(Et2mtc)3C1I1 and a variable-temperature N M R study of [Ti(Me2mtc)3Cl]. The seven-coordinate complexes adopt a pentagonal bipyramidal structure that maintains the clustering of sulfur atoms in all-cis positions. [Ti(Mezmtc)3Cl] becomes rigid on the N M R time scale a t temperatures below -58 OC, and to our knowledge this compound is only the second example of a stereochemically rigid seven-coordinate halotris(che1ate) ~ o m p l e x . ~
Experimental Section Reagents and General Techniques. Sodium N,N-dimethylmonothiocarbamate, Na(Mezmtc), and sodium N,N-diethylmonothiocarbamate, Na(EtZmtc), were prepared as previously described.2
0002-7863/79/1501-5268$01 .OO/O
Titanium(1V) chloride (Matheson Coleman and Bell) and carbonyl sulfide (Matheson Gas Products) were used as purchased without further purification. Amines were distilled from sodium immediately before use. Solvents were dried by refluxing over calcium hydflde for at least 24 h and were distilled immediately before use. All syntheses and subsequent handling of the compounds were conducted under anhydrous conditions in a dry nitrogen atmosphere. Sodium N,N-Diisopropylmonothiocarbamate,Na(i-Przmtc). With stirring at 0 "C, carbonyl sulfide was bubbled very slowly for 24 h through a mixture of diisopropylamine (66.2 mL, 469 mmol) and sodium hydride (4.94 g, 206 mmol) in acetonitrile (280 mL). The pale yellow solution was filtered, and solvent was pumped off until the volume was -90 mL. Addition of benzene (400 mL) afforded a white precipitate which was filtered, washed with three 50-mL portions of benzene, and dried in vacuo for 20 h, yield 20.17 g (53%), mp 228-231 "C dec. Anal. Calcd for Na(C7H14NOS): C, 45.88; H, 7.70; N, 7.64; Na, 12.55. Found: C, 45.68; H, 8.06; N , 7.49; Na, 12.23. Sodium N,N-Diisobutylmonothiocarbamate,Na(i-Buzmtc). With stirring at 0 O C , carbonyl sulfide was bubbled slowly for 2.5 h through a mixture of diisobutylamine (75 mL, 410 mmol) and sodium hydride (3.47 g, 145 mmol) in benzene (250 mL). The mixture was stirred at room temperature for 18 h and then warmed gradually until it refluxed; since the reaction rate increased dramatically with the rise in temperature, the warming process was accomplished over a period of 5 days to avoid excessive foaming. After the solution had refluxed for 2 days, the insoluble white product was filtered, washed with two 50-mL portions of benzene, and dried in vacuo for 27 h, yield 25.23 g (83%), mp 210-212 "C. Anal. Calcd for Na(C9HlgNOS):C, 51.16; H, 8.59; N , 6.63; Na, 10.88. Found: C, 50.89; H, 8.66; N, 6.57; Na, 10.70. Chlorotris(N,N-dimethylmonothiocarbamato)titanium(IV), [Ti(Me2mtc)~CI].Titanium(1V) chloride (1.18 mL, 10.7 mmol) was added with rapid stirring to a suspension of Na(Me2mtc) (4.10 g, 32.2 mmol) in dichloromethane ( 1 50 mL), and the mixture was allowed to reflux for 5 h. The mixture was then filtered and the sodium chloride precipitate washed with three 15-mL portions of dichloromethane. Reduction of the combined filtrate and washings to -70 mL followed by addition of -1 50 mL of hexane afforded an orange powder, which was dried in vacuo at 100 "C for 24 h to remove dichloromethane of crystallization, yield 3.35 g (79%), mp 188-200 O C dec. Anal. Calcd
0 1979 American Chemical Society
Hawthorne, Fay / Chlorotris (N,N-dialky1monothiocarbamato)titanium ( I V ) Complexes for Ti(C3H6NOS)3CI: C, 27.31; H, 4.58; C1,8.96; N, 10.62; Ti, 12.10. Found: C, 27.10; H, 4.68; CI, 9.07; N , 10.55; Ti, 12.24.
Chlorotris(N,N-diethylmonothiocarbamato)titanium(IV), [Ti(Et2mtc)3CI].This complex was prepared from titanium(1V) chloride (3.15 mL, 28.7 mmol) and Na(Et2mtc) (13.40 g, 86.3 mmol) in dichloromethane (125 mL) using a procedure similar to that employed for preparation of [Ti( Mezrntc)3Cl]. The yield of large, red crystals was 11.14 g (81%), mp 129-149 "C dec. Anal. Calcd for Ti(C5HloNOS)3C1: C, 37.54; H, 6.30; CI, 7.39; N, 8.75; S, 20.04; Ti, 9.98. Found: C, 37.48; H, 6.27; CI, 7.60; N, 8.71; S, 19.90; Ti, 10.02. Chlorotris(N,N-diisopropylmonothiocarbamato)titanium(IV), [Ti(i-Pr2mtc)3CI].This complex was prepared in 72% yield by reaction of titanium(1V) chloride (0.40 mL, 3.6 mmol) with N a ( i - P r p t c ) (2.00 g, 10.9 mmol) in dichloromethane (125 mL). The resulting orange powder was dried in vacuo at 100 "C for 13.5 h to remove dichloromethane of crystallization, mp 153-156 "C. Anal. Calcd for Ti(C,HldNOS)3CI: C, 44.71; H, 7.50; CI, 6.28; N , 7.45; Ti, 8.49. Found: C, 44.86; H, 7.63; CI, 6.57; N, 7.32; Ti, 8.70. Chlorotris(N,N-diisobutylmonothiocarbamato)titanium(IV), [Ti(i-Bu~mtc)3CI].This complex was prepared from titanium(1V) chloride (1.30 mL, 11.8 mmol) and Na(i-Buzmtc) (7.73 g, 36.6 mmol) in benzene ( I 70 mL). The resulting bright yellow powder was dried in vacuo at 100 "C over 18 h to remove benzene of crystallization, yield 5.60 g (73%), mp 168-171 "C. Anal. Calcd for Ti(C9Hl8NOS)3CI: C,50.02;H,8.40;CI,5.47;N,6.48;Ti,7.39. Found:C,50.13;H,8.52; CI, 5.61; N, 6.55; Ti, 7.27. Bromotris(N,N-dimethylmonothiocarbamato)titanium(IV), [Ti(Metmtc)3Br]. This complex was prepared in 55% yield by reaction of Na(Mezmtc) (2.28 g, 15.9 mmol) with titanium(1V) bromide (2.20 g, 5.99 mmol) in refluxing dichloromethane (125 mL). Crystallization of the crude product from dichloromethane-hexane (1.2 v/v) afforded large, red crystals which were dried in vacuo at 60 " C for 12 h to remove dichloromethane of crystallization, mp 158-175 "C dec. Anal. Calcd for Ti(C3H6NOS)3Br: C, 24.55; H, 4.12; Br, 18.15; N , 9.54; Ti, 10.88. Found: C, 24.30; H, 4.37; Br, 18.30; N, 9.72; Ti, 11.07. Conductance Measurements. Conductance measurements were made in dichloromethane at 25.00 f 0.05 " C with an Industrial Instruments Model R C 16B2 conductivity bridge and a Freas-type solution cell with bright platinum electrodes. The bridge frequency was 60 Hz, and the cell constant was 0.113 cm-l. The specific conductance f 2 - l cm-l. of the purified solvent was less than 4.5 X Infrared Spectra. Infrared spectra were recorded in the region 4000-250 cm-l with a Perkin-Elmer 521 grating spectrophotometer. The complexes were studied as mineral oil mulls supported between cesium iodide plates. The estimated uncertainty in reported frequencies is 1 4 cm-I. Nuclear Magnetic Resonance Spectra. Proton chemical shifts and coupling constants were measured at ambient probe temperature (-34 "C) with a Varian EM-390 90-MHz spectrometer. Reported values are the averages of those obtained from at least three sweeps of each spectrum; the sweep width was calibrated with a sample of chloroform and tetramethylsilane. Variable-temperature pulsed Fourier-transform ' H N M R spectra of a 0.0590 M solution of [Ti(Mezmtc)3CI] in dichloromethane-dz were recorded in the temperature range -86.2 to 49.0 "C with a Bruker HX-90 spectrometer which was locked on the solvent deuterium resonance. Temperatures, determined with a copper-constantan thermocouple immersed in acetone, are estimated to be accurate to f 0 . 5 "C. Variable-temperature continuous-wave IH N M R spectra of a 0.0441 M solution of [Ti(Me2mtc)3CI] in diphenylmethane were recorded in triplicate in the temperature range 39.2-1 35.0 "C with a Varian EM-390 spectrometer locked on the methylene proton resonance of the solvent. Temperatures, estimated to be accurate to &0.5 "C, were determined from the temperature-dependent chemical shift between the nonequivalent protons of 1,2-ethanedi01.~~ I n the recording of both sets of variable-temperature spectra, care was taken to minimize the common sources of error in N M R line-broadening studies,2' as previously described.2z Spectra were analyzed using the line-shape program PZDMFX obtained from P. Meakin of E. I. du Pont de Nemours, Inc. Calculated spectra were evaluated by qualitative comparison with observed spectra, overlaying one on the other, and, in some cases, by comparison of measured parameters (peak separations, relative heights of maxima and minima, and peak widths at one-fourth, one-half, and threefourths maximum amplitude). The temperature-dependent transverse relaxation times, T2, used to generate calculated spectra were deter-
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mined from variable-temperature spectra of S-methyl-N,N-dimethylmonothiocarbamate, which evidences line broadening due to increasing solvent viscosity, but no line broadening due to kinetic exchange; CEN bond rotation in MezNC(0)SMe is fast on the N M R time scale,23even at -90 0C.24 Crystallography.Several air-sensitive red crystals of [Ti( Etzmtc)3CI], obtained by recrystallization from dichloromethane-hexane (-l:4 v/v), were sealed under dry nitrogen in 0.3-mm Lindemann capillaries. The lattice symmetry and the systematic extinctions (hkl for h k # 2n and h01 for I # 2n) observed in precession photographs indicated that the crystals were monoclinic with probable space group C2/c (C2h6, No. 15).25 The choice of the centric space group was confirmed by the distribution of reflection intensities26 and the successful refinement of the structure in that group. The lattice constantsofa = 2 7 . 8 8 8 ( 5 ) A , b = 9 . 7 8 6 ( 1 ) & ~ = 17.819(2)A,andP = 97.674 (9)" were determined by least-squares refinement of the diffraction geometry for 35 high-angle reflections (28 > 30") centered on a computer-controlled, four-circle Picker FACS-I diffractometer using Zr-filtered Mo KZ radiation (A = 0.710 69 A). The density calculated on the basis of eight molecules of [Ti(SOCN(C2H5)2)3CI] per unit cell is 1.323 g cm-3, which compares favorably with the obdetermined by flotation in carbon tetserved value of 1.328 g rachloride-hexane. An irregularly shaped crystal of approximate dimensions 0.25 X 0.35 X 0.60 mm was chosen for collection of intensity data. The data were collected at ambient temperature on the Picker diffractometer employing Zr-filtered Mo KZ radiation and a takeoff angle of -3". Intensities were measured using the 8-28 scan technique at a scan rate of 1O/min with a scan angle of 2" plus an allowance for dispersion of Mo K q and Mo K a z radiation. Background counts of 40-s duration were taken at each end of the scan. Reflections having counting rates greater than I O 000 counts/s were automatically attenuated by insertion of copper foil into the path of the diffracted beam until the intensity was reduced to less than that value. The intensities of three standard reflections, monitored at 50-reflection intervals, showed no trend with time. A total of 5686 independent reflections having 28 5 56.75" was collected; these data were corrected for background, use of attenuators, and Lorentz and polarization factors. Since the linear absorption coefficient for Mo KE radiation is 7.46 cm-l and the estimated maximum error resulting from neglect of absorption corrections is
