Organometallics 1993,12, 4161-4166
4161
Reactions of Carbon Monoxide with Phosphine Adducts of Nb(2,4-C7H&: Spontaneous Reduction to Niobium(1) Complexes Thomas E. Waldman,l Beth Waltermire,2Arnold L. Richard D. E r n s t * J
Rheingold,*92
and
Departments of Chemistry, University of Utah, Salt Lake City, Utah 84112, and University of Delaware, Newark, Delaware 19716 Received March 30, 1993
The reactions of 17 electron Nb(2,4-C7H&(L) species (L = PEt3, PMezCsH5) with CO lead to the loss of one pentadienyl ligand and formation of the 18 electron Nb(1) complexes Nb(2,4C7Hll)(L)(CO)3 in high yield. One carbonyl ligand may be thermally replaced by a second equivalent of phosphine, yielding "trans"-Nb(2,4-C7Hn)(PMe2Ph)2(CO)z, which adopts something close to a piano-stool geometry with the phosphines located by the open dienyl edge and the central dienyl carbon atom. The Nb(2,4-C7Hll)(L)(CO)3complexes are also susceptible to reduction by alkali metals, presumably leading to Nb(2,4-C7Hll)(C0)32-. Oxidation of these species under CO leads to Nb(2,4-C7Hll)(C0)4. Structural determinations have been carried out for Nb(2,4-C7Hll)(PMeaPh)(CO)3 and N~(~,~-C~HII)(PM~~P~)Z(CO)Z. For the former the space group is Pi with a = 7.911(5) A, b = 10.490(6)A, c = 12.829(6)A, (Y = 105.61(4)', /3 = 95.88(4)O, y = 107.59(4)O,and V = 957.5(8) A3 for 2 = 2. The structure has been refined to discrepancy indices of R = 0.031 and R, = 0.034. For the latter the space group is P21/c with a = 11.778(2) A, b = 13.966(2) A, c = 15.930(3) A, /3 = 96.33(1)' for 2 = 4. The structure was refined to discrepancy indices of R = 0.037 and R, = 0.039. Titanocene'and vanadocene are known as 18-electron dicarbonyP and 17-electronmonocarbony14complexes. In contrast, various electron deficient open titanocene and open vanadocene complexes react readily with CO only to yield monocarbonyl complexes, possessing 16- and 17electron counts, re~pectively.~ The inability of the open titanocene to incorporate a second carbonyl ligand may be traced to the much greater steric demand of pentadienyl ligands relative to C5H5 and even C5Me5. One might then expect that the steric demands of the dienyl ligands could be offset by the larger metals in the second or third transition series, and indeed, the 18-electron complex Zr(2,4-C,H11)&0)2 may be isolated from Zr(2,4-C7H&(PEt3), although it readily reverts to a monocarbonyl as It was therefore of interest to investigate related In reactions for phosphine adducts of Nb(2,4-C~H11)2.~ fact, again some unique behavior is observed, as one pentadienylligand is spontaneously lost under CO, leading to the 18-electron Nb(1) complexes Nb(dienyl)(C0)3(L) (L = PEt3, PMezPh). These and related results are described herein.
Experimental Section The compounds described exhibit varying degrees of air sensitivity and were therefore prepared, handled, and stored under nitrogen atmospheres. Hydrocarbon and ethereal solvents were predried and distilled under nitrogen from Nalbenzo(1) University of Utah. (2) University of Delaware. (3) Murray, J. G. J . Am. Chem. SOC.1961,83, 1287. (4) Calderazzo, F.; Fachinetti, G.; Floriani, C. J.Am. Chem. SOC.1974, 96,3695. (5) Ernst, R. D.; Liu, J.-Z.; Wilson, D. R. J. Organomet. Chem. 1983, 250, 257. (6) Waldman, T. E.; Stahl, L.; Wilson, D. R.; Arif, A. M.; Hutchinson, J. P.; Ernst, R. D. Organometallics 1993, 12, 1543. (7) Stahl, L.; Hutchinson, J. P.; Wilson, D. R.; Ernst, R. D. J. Am. Chem. SOC.1986, 107, 5016.
phenone prior to use. Magnetic and spectroscopic data were obtained as previously describedes The starting diene? dienyl anion,10 NbC4(THF)2,I1and phosphines12were either prepared by reported procedures or purchased. Nb(2,4-C7HI1)2(PMe2Ph). A 250-mL three-neck flask equipped with a magnetic stirring bar, nitrogen inlet, and dropping funnel was charged with 2.00 g (5.28 mmol) of NbC&(THF)2and 100 mL of THF. Dimethylphenylphosphine (0.75mL, 5.3 mmol) was added via syringe to the stirred yellow suspension, resulting in immediate reaction to yield a dark green solution. After the solution was cooled to -78 "C, 2.91 g (21.6 mmol) of potassium 2,4-dimethylpentadienidein 50 mL of THF was added dropwiseto the green solution. Addition was complete in ca. 10 min, during which time the solution had assumed a deep maroon color. The reaction mixture was then warmed to ambient temperature and stirred at this temperature for 1 h. At the end of this time the solution was dark green-brown and the solvent was removed in vacuo, resulting in a green-brown solid. Extraction of the solids with five 50-mL portions of diethyl ether and filtration through a Celite pad on a coarse frit gave a dark green filtrate. The dark green filtrate was concentrated in vacuo to ca. 100 mL and then cooled at -20 "C for 12 h, during which time deep green crystals of the product formed. The supernatant was transferred to a clean flask, and the crystals (1.07 g, mp 138-140 "C dec) were dried in vacuo. Further concentration of the supernatant and cooling at -20 "C for 2 days resulted in an additional 0.44 g of product, for an overall yield of 68%. IR (Nujolmull): 2970 (vs, br), 1455 (s), 1430(shoulder), 1372 (8, ah), 1365 (shoulder), 1325 (vw), 1275 (w, ah), 1158 (w), 1021 (m, sh), 998 (m), 928 (m, vsh), 911 (m, sh), 900 (a, sh), 861 (w), 848 (w), 833 (m),819 (m, sh), 788 (m), 745 (ms, sh), 739 (ms, sh), 720 (m), 697 (ms, sh) cm-1. Mass spectrum (EI, 17 eV; m/z (relative (8) Newbound, T. D.; Stahl, L.; Ziegler, M. L.; Emst, R. D. Organometallics 1990, 9, 2962. (9) Jitkow, 0. N.; Bogert, M. T. J. Am. Chem. SOC.1941,63,1979. (10) Wilson, D. R.; Stahl, L.; Ernst, R. D. Organomet. Synth. 1986,3, 136. (11) Manzer. L. E. Inom. Chem. 1977.16.525. (12) Wolfsberger, W.; Sdmidbaur, H. kynth. React. Znorg. Met.-Org. Chem. 1974,4, 149.
0276-733319312312-4161$04.00/0 0 1993 American Chemical Society
Waldman et al.
4162 Organometallics, Vol. 12, No. 10, 1993 intensity)): 421 (0.6), 283 (14), 138 (loo), 123 (64), 121 (21), 91 (13). Anal. Calcd for C22HaNbP: C, 62.71; H, 7.89. Found: C, 62.47; H, 8.10. ESR (toluene): a = 120.6 G. N~(~,~-C~HII)(CO)~(PM~~P~). A 250-mL two-neck flask equipped with a magnetic stirring bar and gas inlet was charged with 0.44 g (1.0 mmol) of Nb(2,4-C7H&(PMezPh) and 50 mL of THF. The resulting deep green solution was saturated with carbon monoxideand then stirred vigorously under an atmosphere of carbon monoxide. After being stirred for ca. 72 h the solution had become a deep blood red and the solvent was removed in vacuo; the resulting red oil was extracted with four 50-mL portions of hexane and filtered through a Celite and silica pad. The bright red hexane filtrate was concentrated in vacuo to ca. 15 mL and cooled to -20 "C, and after several hours blood red, needlelike crystals began to form. After it was cooled for an additional 12 h, the supernatant was removed by syringe and the product dried in vacuo, yielding 0.32 g (0.77 mmol, 74% yield) of moderately mp air-sensitive red needles of Nb(2,4-C,Hll)(C0)3(PMe2Ph), 118-120 "C dec. IH NMR (benzene-& ambient): 6 7.23-7.01 (m, 5H, Ph), 5.17 (9, lH, H-3), 2.90 (5,2H, H1,ssxo),1.80 (5,6H, CH3Pdl), 1.44 (d, 6H, J = 5.9 Hz, PCH3), 0.56 (d, 2H, J = 7.3 Hz, Hvando).l3C NMR (benzene-&, ambient): 6 260.5 (s, 2C, CO), 249.2 (s, lC, CO), 129.8-127.5 (m, 6C, PPh), 122.4 (s,2C, C-2,4), 88.7 (d, lC, J = 158.9 Hz, C-3), 68.1 (t,2C, J = 154.8 Hz, C-1,5), 29.4 (q,2C, J = 126.5 Hz, CH3-Pdl), 17.3 (q of d, 2C, J = 129.8, 23 Hz, P(CH3)).31PNMR (benzene-&, ambient): 6 28.65. IR (Nujol mull): 2930 (vs, br), 1961 (vs, sh), 1870 (vs, br), 1522 (vw), 1460 (s, br), 1370 (m, sh), 1155 (w, sh), 1098 (vw,br), 1027 (m, sh), 1008 (w, sh), 941 (8, sh), 912 (m, shoulder), 901 (s, sh), 885 (m),860 (w,sh),839 (m, sh),828 (m),738 (8, sh),732 (m,shoulder), 703 (m, sh), 690 (s), 671 (m, br) cm-l. Mass spectrum (EI, 17 eV; m/z (relative intensity)): 410 (3), 326 (1001, 283 (14), 139 (12), 138 (64), 123 (44), 121 (16), 91 (17), 79 (10). Anal. Calcd for CleH22Nb03P: C, 52.70; H, 5.40. Found: C, 52.84; H, 5.46. N~(~,~-C~HI~)(CO)~(PE~~). This compound was prepared from (triethylphosphine)bis(2,4-dimethylpentadienyl)niobium7 in a manner exactly analogous to that for the dimethylphenylphosphine adduct. Thus,0.60g (1.5mmol) of Nb(2,4-C,H& (PEts)in 50 mL of THF was stirred under a CO atmosphere for 3 days, and following an analogous workup, 0.40 g (69% yield, mp 126-128 "C dec) of bright red needles was obtained. lH NMR (benzene-de,ambient): 6 5.23 (8, lH, H-3),3.05 (s,2H, H1,sero), 0.84 1.89 (e, 6H, CH3-Pdl), 1.42 (qn, 6H, J = 7 Hz, PCH~CHS), (d o f t , 9H, J = 7, 15 Hz, PCHzCHa), 0.77 (d, 2H, J = 3.0 Hz, H1Pe,do). l3C NMR (benzene-&, ambient): 6 262.1 (8, 2c, c o ) , 249.4 (8, lC, CO), 122.2 (s,2C, C-2,4),89.0 (d, lC, J = 161.6 Hz, C-3), 65.5 (t, 2C, J = 156.0 Hz, C-1,5), 29.2 (q of m, 2C, J = 127.8 Hz, 6.2 Hz, CH3-Pdl), 20.9 (d of t, 3C, J = 127.9, 18.0 Hz, PCH~CHS), 7.6 (d of 9, 3C, J = 128.0, 4.0 Hz, PCH2CH3). 31P NMR (benzene-de, ambient): 6 18.44. IR (Nujol mull): 2920 (vs, br), 1959 (vs, sh), 1863 (vs, br), 1460 (m, br), 1362 (m), 1030 (w, sh), 1010 (vw,sh), 765 (vw,sh), 720 (vw,br) cm-l. Anal. Calcd for Cl&I26NbOsP: C, 49.24; H, 6.72. Found c , 49.43; H, 6.80. Nb(2,4-C7H11)(CO)~(PMezPh)z. A 100-mLthree-neck flask equipped with a water-cooled reflux condenser, nitrogen inlet, and magnetic stirring bar was charged with 0.50 g of Nb(2,4C,Hll)(CO)s(PMe2Ph) (1.2 mmol) and 50 mL of THF. Dimethylphenylphosphine (0.33 mL, 2.4 mmol) was added via syringe, and the reaction mixture was brought to reflux. Heating was continued for 3 days, during which time the color steadily darkened to brown-red and the IR spectrum indicated no peaks due to the starting material. The THF was removed in vacuo, and the oily residue was extracted with 50 mL of pentane and the extract filtered through a Celite pad under nitrogen. Concentration of the red-brown filtrate to ca. 10 mL and subsequent cooling at -80 "C for 2 days resulted in the formation of a red powder (0.22 g, 36% yield, mp 98-100 "C)that was isolated and dried in vacuo. The powder so isolated was sufficiently pure for elemental analysis and NMR studies; however, single crystals were obtained by the following procedure. The powder was redissolved in 5 mL of pentane and the flask insulated to prevent rapid cooling of the solution. The insulated flask was placed in a-80 "C freezer for 4 days, resulting in several
(a) Crystal Parameters CisH22Nb03P C2sH33Nb02P2 410.3 520.4 triclinic monoclinic Pi P2dC 7.911(5) 11.778(2) a, A 10.490(6) 13.966(2) b, 8, 12.829(6) 15.930(3) c, A 105.61 (4) a,deg 95.88(4) 96.33(1) 0. deg 107.59(4) 957.5(8) 2604.5(8) 2 4 Z 0.20 X 0.20 X 0.35 0.25 X 0.30 X 0.32 cryst dimens, mm dark red dark red cryst color 1.42 1.33 D(calcd), g cm-3 p(Mo Ka), cm-1 7.1 5.9 temp, K 298 298 1.087 1.045 T(max)/ T(min) (b) Data Collection diffractometer Nicolet R3m monochromator graphite Mo K a (A = 0.710 73 A) radiation 4-55 4-52 28 scan range, deg f 1 1 , f 1 4 , + 17 f15,+18,+20 data collected (hkC) 4670 5643 no. of rflns collected 4589 5321 no. of indpt rflns 3731 3477 no. of indpt obsd rflns, F, 2 5a(F0) 3 stdl197 rflns std rflns 3 stdl197 rflns 25.3
