Organometallics 1993,12, 2131-2139
2131
Acyl, Carbene, Vinyl, and Azavinylidene Ligands in Tungsten(11) Hydridotris( 3,5-dimethylpyrazolyl)borate Alkyne Complexes S. G. Feng, P. S. White, and J. L. Templeton’ W. R. Kenan, Jr., Laboratories, Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290 Received November 30, 1992
Reaction of [Tp’(CO)2W(PhCzMe)] [BF41with LiCuR2 (R = Ph, Me) generates neutral +acyl complexes Tp’(CO)(PhC2Me)W(+C(O)R) in which the alkyne ligand remains as a four-electron donor. Deprotonation of the alkyne methyl in Tp’(CO)(PhC2Me)W(q1-C(0)Me) produces a nucleophilic propargyl synthon which reacts with Me1 to yield an ethyl alkyne complex. Protonation or methylation of the neutral +acyl complexes a t the acyl oxygen results in the formation of Fischer-type hydroxy- or methoxycarbene cations, [Tp’(CO)(PhC2Me)W=C(OE)Rl+ (E = H, Me; R = Me, Ph, n-CdHs). Crystals of the methoxybutylcarbene complex belong to the orthorhombic space group P212121,Z = 4, with unit cell dimensions of a = 15.090(6), b = 16.562(4), and c = 14.624(4) A. Refinement of 273 variables over 2187 reflections led to an R value of 6.4% with R , = 6.7%. The alkyne ligand aligns itself parallel to the cis metal-carbonyl axis and perpendicular to the plane of the carbene ligand. Reaction of [Tp’(CO)(PhC2Me)W=C(OMe)Me] [CF3S031 with NaOH in MeOH generates a neutral a-vinyl complex,Tp’(CO)(PhCzMe) W(.r11-C(OMe)=CH2),via deprotonation of the carbene methyl group. Reaction of [Tp’(CO)(PhC2Me)W=C(OMe)Phl [CF3S03] with 2 equiv of KCN in MeOH yields a neutral azavinylidene complex, Tp’(CO)(PhC2Me)WN=C(CN)CH(OMe)Ph, in which the lone pair of electrons on the nitrogen of the azavinylidene ligand competes with the alkyne ?rl donor orbital for donation to the lone vacant metal d?r orbital.
Introduction Nucleophilic and electrophilic additions constitute two fundamental classes of ligand transformations. Nucleophiles often add to a ligand a-position,l*as illustrated by the conversion of carbenes (E) to alkyls (F),2carbynes (C) to carbenes (E) (Scheme I),3 carbonyls to acyls (eq 1):
M-CO
Nuc
0
li
M-C-Nuc
(1)
and recently nitrenes to amidos (eq Addition of an electrophileto a ligand often occurs at the @-position,lb as (1)(a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. F’rinciples and Applications of Organotramition Metal Chemistry; University ScienceBooks: Mill Valley, CA, 1987;Chapter 7. (b) Chapter 8. (2)(a) Casey, C.P.; Miles, W. H. J. Organomet. Chem. 1983,254,333. (b) Kreisel, F. R.; Fischer, E. 0.; Kreiter, C. G.;Fischer, H. Chem. Ber. 1973,106,1262. ( 3 ) (a) Bruce, A. E.; Gamble, A. S.;Tonker, T. L.;Templeton, J. L. Organometallics 1987,6,1350.(b) Jamison, G.M.; Bruce, A. E.; White, P. S.; Templeton, J. L.J. Am. Chem. SOC. 1991,113,5057.(c) Fischer, E.0.;Richter, K. Angew. Chem., Int. Ed. Engl. 1975,14,345. (4)(a) Semmelhack, M. F.; Tamura, R. J. Am. Chem. SOC.1983,105, 4099. (b) Fiecher, E. 0.;Maaabol, A. Chem. Ber. 1967,100,2445. (5)Luan,L.;White, P. S.;Brookhart, M.; Templeton, J. L. J. Am. Chem. Soc. 1990,112,8190. (6)Luan,L.;Brookhart, M.; Templeton, J. L.Organometallics 1992, 11,1433.
illustrated by the conversion of acetylides (A) to vinylidenes (B),7vinylidenes (B) to carbynes (C),7h*8vinyls (D)to carbenes (El9 (Scheme I), and acyls to carbeneslO (eq 3). Nucleophilic addition to the @-positionof nitrile and imine ligands has formed azavinylidene and amido ligands which react with electrophiles at the nitrogen (asite) to generate imine and amine ligands.” Nucleophilic addition to an alkyne ligand in tungsten monomers can form either +vinyl12 or + 7 i n y P ligands, and addition of electrophiles to these distinct vinyl ligands can then generate carbenes or 8-agostic carbenes, respectively12J4 (Scheme 11). (7)(a) Bruce, M. I.; Swincer, A. G.Ado. Organomet. Chem. l983,22, 59-128. (b) Bruce, M. I. Acre Appl. Chem. 1986,58,553. (c) Nickiaa, P.N.; Selegue, J. P.; Young, B. A. Organometallics 1988,7, 2248. (d) Birdwhistell, K. R.; Templeton, J. L.Organometallics 1986,4,2062.(e) Kostic, N. M.; Fenske, R. F. Organometallics 1982,1,974.(0Lomprey, J. R.; Selegue, J. P. J. Am. Chem. SOC.1992,114,5518. (B) Kelley, C.; Lugan, N.; Terry, M. R.; Geoffroy, G.L.;Haggerty, B. S.; Rheingold, A. L.J. Am. Chem. SOC.1992,114,6735.(h) B N ~ M. , I. Chem. Rev. 1991, 91,197. (8)(a) Mayr, A.; Schaefer,K. C.; Huang, E. Y. J. Am. Chem. Soc. 1984, 106,1517. (b) Beevor, R. G.;Green, M.; Orpen, A. G.;Williams,I. D. J. Chem. Soc., Chem. Commun. 1983, 673. (c) Birdwhistell, K. R.; Burgmayer, S.J. N.; Templeton, J. L.J.Am. Chem. SOC. 1983,105,7789. (9)(a) Cutler, A. R.; Hanna, P. K.; Vita, J. C. Chem. Rev. 1988,88, 1363. (b) Davieon, A.; Selegue, J. P. J. Am. Chem. SOC.1980,102,2456. (c) Bodner, G. S.;Smith, D. E.; Hatton, W.G.;Heah, P. C.; Georgiou, S.; Rheingold, A. L.;Geib, S. J.; Hutchineon, J. P.; Gladysz, J. A. J. Am. Chem. SOC.1987,109,7888.(d) Kremer, K. A. M.; Kuo, G. H.; O’Connor, E. J.; Helquist, P.; Kerber, R. C. J. Am. Chem. SOC.1982,104,6119.(e) Casey, C. P.; Miles, W. H.; Tukada, H.; OConnor, J. M. J. Am. Chem. Soc. 1982,104,3761. (10)Fischer, E.0.Adv. Organomet. Chem. 1976,14,1. (11)(a) Feng, S.G.;Templeton, J. L. J. Am. Chem. SOC.1989,111, 6477. (b) Feng, S.G.;Templeton, J. L.Organometallics 1992,11,1295. (12)Feng, S. G.;White, P. S.;Templeton, J. L. J. Am. Chem. SOC. 1992,114,2951. (13)Feng, 5.G.;Templeton, J. L. Organometallics 1992,11,2168. (14)Few, S. G.;White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1990,112,8192.
0276-7333/93/2312-2131$04.0Q/00 1993 American Chemical Society
Feng et al.
2132 Organometallics, Vol. 12, No. 6, 1993
Scheme I
-
.. ..
E
M-CEC-R
A /E
MZC-C-R C
* *
M=C=C
B
Y
/R
\E
v M-C
C ‘R -
’*
E‘
/Nu
D
I
E
Scheme I1
ill-vinyl
l+
l+
Ph
P-agostic carbene
4e donor
H
I
We now report Fischer carbene complexes in this series that complementthe alkyne carbene monomers described previously. Specifically we report: (1)formation of acyl complexesby addition of nucleophilesto a carbonyl ligand; (2) formation of cationic Fischer carbenes of the type [Tp’(CO)(PhC--=CMe)W-C(OE)R]+ from electrophilic addition to the #-acyl complexes (Tp’ = hydridotris(3,5dimethylpyrazolyl)borate, see Scheme 11); (3) a single crystal x-ray structure of the methoxy butyl carbene complex; (4) formation of an +vinyl ligand from deprotonation of the methoxymethylcarbeneligand; and (5) formation of an azavinylidene complex, Tp’(C0)(PhC2Me)W(N-C(CN)CH(OMe)Ph), from the reaction of cyanidewiththecarbene unit in [Tp’(CO)(PhMMe)W=C(OMe)Phl+ in methanol solution. Experimental Section Materials and Methods. Manipulations involving airsensitive reagents were performed under an atmosphere of pure dinitrogen using Schlenk techniques. Solvents were purified as follows: CHZClzwas distilled from P206. EbO, THF, and hexanes
were distilled from potassium benzophenone ketyl. Other solvents were purged with nitrogen prior to use. Literature methods were employed in the synthesis of [Tp’W(C0)2( P h W M e ) ][BF4Pand T ~ ’ ( C O ) ( P ~ ~ M ~ ) W ( ? ~ - C ( O ) B U “ ) . ’ ~ Methyl iodide was purified by passage through alumina. All other reagents were purchased from commercial sources and used as received. Infrared spectra were recorded on a Mattson Polaris FT-IR spectrometer. 1Hand 13CNMRspectra were recorded on a Varian XL-400(400MHz) spectrometer. Microanalyses were performed by Oneida Research Services, Whitesboro, NY. Syntheses. Tp’(C0)(PhCzMe)W [+C( 0)Me] (1). In a representative synthesis, a stoichiometric amount of LiCuMez, freshly prepared from reaction of CUI (0.40g, 2.1 mmol) and MeLi (1.4M in EkO, 3.0mL,.4.2mmol) at 0 OC in 20 mL of THF, was cannulated into a cold THF (-78 “C) solution of [Tp‘W(C0)2(PhCzMe)][BF4] (1.55g, 2.1 mmol) resulting in an immediate color change from green to red-brown. The solution was warmed to room temperature and stirred for an additional 20 min. The solvent was removed and the solid residue was chromatographed on alumina with CH2C12/MeOHas the eluent. A band was collected, and the solvents were removed. The solid which remained was recrystallized from CH2C12/hexanesto yield red-wine crystals (0.92g, 65%): IR (KBr, cm-l) YBH = 2546,YCO = 1900,Y C = ~1578; lH NMR (CD2C12,6) 7.29,6.88(m, C & J , 5.91,5.87,5.67 (Tp’CH), 3.61 (3H, PhCzCHs), 2.56, 2.49,2.45, 2.38, 1.36 (3:3:3:3:6,18H, Tp’CCH3), 1.76 (3H, c(o)cH3);I3C NMR (CDzC12,6) 291.8 (‘Jwc = 123 Hz, C(O)CH3), 236.7 (‘JWC = 136 Hz, CO), 213.6 (VWC = 53 Hz, MeCCPh), 208.6 (‘Jwc = 14 Hz, PhCCMe), 154.0, 153.7, 149.3, 145.4, 145.2, 144.7 (Tp’CCHs), 137.9, 129.2, 129.1, 128.9 (Ph), 108.1,107.9, 106.8 (Tp’CH), 55.5 (C(O)Me), 21.8 (PhCzCH31, 16.6,15.8,15.5,13.2, 13.0,12.5(Tp’CCH3). Anal. Calcdfor W C Z ~ H ~ ~ N ~C, O48.53; ZB: H, 4.94;N, 12.58. Found C, 48.29; H, 4.58; N, 12.58. Tp’(CO)(PhCzMe)W[+C( O)Ph] (2). This compound was prepared according to the procedure described above for 1 by using LiCuPh2 in place of LiCuMez. The product was isolated as red-purple crystals (75% ): IR (KBr, cm-9 VBH = 2543,vco = 1896,YC-O = 1543;‘H NMR (CDC13,6) 7.22,6.88(m, 10H,C a s ) , 5.91, 5.83, 5.62 (Tp’CH), 3.26 (3H, PhCzCH3), 2.58,2.54,2.44, 2.40,1.44,1.38 (3Heach, Tp’CCH3); I3C NMR (CDCl3, 6) 293.8 (‘Jwc = 120 Hz, C(O)Ph), 235.5 (‘Jwc = 137Hz, CO), 212.0 (‘Jwc = 50Hz,MeCCPh),208.3(lJwc = 15Hz,PhCCMe),160.5,153.4, 153.1,149.0,144.6, 144.1,143.9,137.7(Tp’CCH3and2Ciw),128.5, 128.4,128.3,127.9,127.4,124.6 (Ph), 108.0,107.9,106.6(Tp’CH), 21.4 (PhCZCHs), 16.5,16.2, 15.6, 13.0, 12.4 (Tp’CCH3). Anal. Calcd for Tp’(C0)(PhC2Me)W(q1-C(O)Ph)(CH2C12), WC33H37NsOzBC12: C, 48.61;H, 4.54;N, 10.31. Found: C, 48.65; H, 4.42;N, 10.48. Tp’(CO)(PhCzEt)W[+C(O)Me] (3). A stoichiometric amount of butyllithium (2.5M in hexanes, 0.3 mL) was added to a cold THF (-78 OC) solution of Tp’(CO)(PhC2Me)W(-C(O)Me) (0.5 g, 0.75 mmol), and the solution became yellow-brown. After 5 min, excess Me1 (1.0mL) was added through a layer of alumina, and the solution color returned to purple-brown. The solution was warmed to room temperature and stirred for an additional 20 min. The solvent was removed and the solid residue was chromatographed on alumina with THF as the eluent. A band was collected and the solvent was removed. The oily residue which remained was recrystallized from MeOH to yield red-wine crystals (0.41g, 80%): IR (KBr, cm-l) VBH = 2548,YCO = 1900, Y C = ~1572;lH NMR (CDCI3,6) 7.19,6.70(m, C a s ) , 5.85,5.72, 5.62 (Tp’CH), 4.10,3.82 (each 1 H, PhC&HHCH3), 2.50, 2.47, 2.42,2.32,1.42,1.31 (3Heach, Tp‘CCH& 1.85 (3H, c(O)c&), 1.68(t, 3 J = 7.6 ~ Hz, ~ CHZCH,); W N M R (CDCl3,6) 294.7 (c(0)CH3), 235.5 (‘Jwc = 136 Hz, CO), 214.0 (EtCCPh), 211.1 (PhCCEt), 153.5, 153.2, 148.6,144.5, 144.4, 143.7 (Tp’CCHd, 138.2,128.6,128.1,128.0 (Ph),107.9,107.8,106.5(Tp’CH), 55.6 (15) Feng,S. G.; Philipp, C. C.; Gamble, A. S.; White,P. S.; Templeton, 1991, 10, 3504.
J. L. Organometallics
W(Z0 Acyl, Carbene, Vinyl, and Azavinylidene Complexes
Organometallics, Vol. 12, No.6, 1993 2133
(C(O)Me),30.9 (CHZCH~), 14.2 (P~CZCHZCH~), 16.5,15.8,15.2, IR (KBr, cm-l) YBH = 2563, uco = 1973, YSO = 1270; ‘H NMR 13.0,12.8,12.4 (Tp’CCH3). Anal. Calcd for Tp‘(CO)(PhC2CH2(CD2C12, 6) 7.45, 7.37, 6.89 (m, C & J , 6.09, 6.01, 5.73 (Tp’CH), Me)W(q1-C(0)CH3).’/2CH~Cl~, W C Z ~ ~ ~ N ~ OC,Z47.23; B C ~H,: 3.92, 3.86 (OMe and PhC2CH3),2.62, 2.49, 2.47, 2.45, 1.27, 1.26 4.97; N, 11.60. Found C, 47.99; H, 5.35; N, 11.59. (3H each, Tp’CCH3), 2.87,2.00 (each a m, each 1H, CHHCH2CHZCH~), 1.55 (m, 4H, CHZCHZCHZCH~), 1.06 (t,VHH = 7 Hz, [Tp’(CO)(PhCzMe) W=C(OH)Me][BF4] (4). A purple3H, CHZCH~CHZCH~); 13CNMR (CDzC12, 6) 333.5 (VWC 133 brown solution of Tp’(CO)(PhC2Me)W(q1-C(0)CH3) (0.50g, 0.75 Hz,=C(OMe)CH&H&H&H3), 220.7 (VWC = 126Hz,CO), 218.9 mmol) in 30 mL of CH2C12/Et20(15) was cooled to 0 “C. A (‘Jwc = 49 Hz, MeCCPh), 213.9 (q, ‘JWC= 14 Hz, ‘JHC= 7 Hz, purple precipitate formed when a stoichiometric amount of PhCCMe), 154.2, 153.6, 150.1, 147.8, 146.9, 146.5 (Tp’CCHs), HBF4.Me20 was added dropwise. The flask was put in the freezer 135.7,132.0,130.1, 129.6 (Ph), 109.2,109.1, 108.0, (Tp’CH),62.9 (-40 “C) after 20 mL of Et20 had been added. The powder which (OMe), 55.1 (CH&H2CH&H3), 30.6 (CH2CH&H2CH3), 23.4 formed was isolated by filtration, washed with EbO (2 X 10 mL), (PhCzCHs), 23.3 (CHZCH~CH~CH~), 16.7, 15.7, 15.4, 13.8, 13.0, and dried in vacuo (0.45 g, 80%). Recrystallization from CH2Anal. Calcd far [Tp’(CO)12.6 (Tp’CCH3 and CHZCH~CH~CH~). CldEt20 produced purple crystals, IR (KBr, cm-’1 YBH = 2560, ( P h C z M e ) W ( = C ( O M e ) C H 2 C H 2 C H 3 ) 3 [CF3S03], YCO = 1966, YBF = 1069. Two isomers are observed by lH NMR in a ratio of 9:l: lH NMR (CD2C12, major isomer only, 6) 7.46, WC32H42N60aSF3: C, 43.95; H, 4.81; N, 9.61. Found C, 43.66; H, 4.79; N, 9.52. 7.37, 6.95 (m, C a b ) , 6.12, 6.00, 5.74 (Tp’CH), 3.86 (4.00 for the other isomer, 3H,PhC2CH3),2.88,2.61,2.54,2.48,2.45,1.33,1.26 Tp’(C0) (PhCzMe)W (+C(OMe)=CHZ) (8). One equivalent (3H each, Tp’CCH3 and =C(OH)Me); the hydroxy proton was of NaOH (0.034 g, 0.84 mmol) in 5 mL of MeOH was added to not located; 13CNMR (CD2C12, major isomer only, 6) 329.8 (VWC a cold MeOH (0 “C, 5 mL) solution of [Tp’(CO)(PhCzMe)W131Hz,=C(OH)CH3), 220.3 (‘Jwc = 130 Hz, CO), 218.5 (‘Jwc (=C(OMe)CH3)][CF3S03] (0.70 g, 0.84 mmol), resulting in a = 48Hz,MeCCPh),214.2(lJwc = 14Hz,PhCCMe),155.3,154.4, color change from purple to green as a blue powder precipitated. 150.0, 148.5, 146.9, 146.7 (Tp’CCHs), 135.7, 132.0, 130.4, 129.6 The crystalline solid was isolated by filtration after putting the (Ph), 109.8, 109.2, 107.9 (Tp’CH), 44.7 (=C(OH)CH3), 23.3 solution in a freezer (-40 “C) for 10 h. The product was (PhC2CH3),16.6, 15.5, 15.4, 13.2, 13.0, 12.6 (Tp’CCH3). Anal. recrystallized from CHZC12/MeOH to yield blue crystals (0.43 g, Calcd for [Tp’(CO)(PhC2Me)W=C(OH)CH31 [BF41, 75%): IR (KBr, cm-l) YBH = 2542, YCO 1890; ‘H NMR (CDC13, WC2gH34N602B2F4:C, 42.89; H, 4.50; N, 11.12. Found C, 42.15; 6) 7.18,6.69 (m, Ca5), 5.79,5.77,5.62 (Tp’CH), 4.49 (broad, lH, H, 4.37; N, 10.91. C(OMe)=CHH), 3.43 (4H, PhC2CH3 and C(OMe)=CHH), 3.15 [Tp’(CO)(PhCzMe)W(=C(OMe)CH3)][CF3503] (5). A (OMe),2.69,2.56,2.46,2.35, 1.41 (33:33:6, 18H, Tp’CCH3); 13C purple-brown solution of Tp’(CO)(PhC2Me)W(q1-C(0)CH3) (0.50 NMR (CDC13, 6) 239.3 (‘Jwc = 141 Hz, CO), 214.1, 206.8 g, 0.75 mmol) in 5 mL of CHzCl2 was cooled to 0 “C. Methyl (MeCECPh),208.3 (VWC = 50Hz, C(OMe)=CHH),153.8,153.7, triflate, [CH3][CF3SO3], (0.10 mL, 0.88 mmol) was added 148.9, 143.9, 142.9 (Tp’CCH,), 135.3 (ClW),128.5, 128.1, 127.5 dropwise. The flask was put in the freezer (-40 “C) after 20 mL (Ph), 107.3, 107.0, 106.3 (Tp’CH), 91.0 (d of d, ‘JHC = 157 Hz, of Et20had been added. The powder which formed was isolated ~JHC = 146 Hz, C(OMe)=CHH), 54.2 (OMe),20.8 (PhCzCHS), by filtration, washed with Et20 (2 X 10 mL), and dried in vacuo 15.9,15.1,12.9,12.5 (Tp’CCH3). Anal. CalcdforTp’(CO)(PhC2(0.53 g, 85 % ). Recrystallizationfrom CH2CldEbO yields purple Me)W(q1-C(0Me)=CH2).’/2CH2Ch, WC~.&I&J&BCI: C, 47.23; crystals: IR (KBr, cm-l) YBH = 2563, YCO = 1966, us0 = 1267. Two H, 4.97; N, 11.60. Found C, 47.87; H, 5.37; N, 11.59. isomers are observed (85%:15%): lH NMR (CDCl3, 6), major Tp’(CO)(PhCzMe)WN=C(CN)CH(OMe)Ph(9). KCN (0.11 isomer 7.30,6.81 (m, Cab), 5.99,5.89,5.65 (Tp’CH), 4.03,3.82, g, 1.68 mmol) was added to a cold MeOH solution (0 OC, 20 mL) 2.99 (PhC2CH3 and 2.5a(n (q1-C(0)CH2CH2CH2Me)*3 as the metal reagent (purple, 89%):
Feng et al.
2134 Organometallics, Vol. 12, No.6,1993 Table I. Crystallographic Data Collection Parameters for molecular formula fw crystal dimens, mm space group cell params a, A
b, A C, A
vol, A3
Z density (calcd), g/cm3
Scheme 111
WC~~H~~N~OSBF~ 814.43 0.20 X 0.20 X 0.30 p212121 15.090(6) 16.562(4) 14.624(4) 3655(2) 4 1.589
Collection and Refinement Parameters Mo Ka (0.709 30) radiation (wavelength, A) monochromator graphite linear abs coeff, cm-I 33.4 scan type e12e 28 limit, deg 50 octant collected +h,+k,+l total no. of rflns 3591 data with I L 2.5u(Z) 2187 R, % 6.4 R,, % 6.7 GOF 2.25 no. of params 213 largest param shift 0.189
were used in structure solutionand refinement.16 The data were corrected for Lorentz-polarizationeffects during the final stages of data reduction. Solution and Refinement of the Structure. Space group P212121 was confirmed and the position of the tungsten was deduced from the three-dimensional Patterson function. The positions of the remaining non-hydrogenatoms were determined through subsequent Fourier and differenceFourier calculations. The CF3S03 anion is not well defined, and it has been input as a rigid group with idealized geometry. The phenyl group was refined as a rigid body. Only the tungsten atom was refined anisotropicallydue to the relatively small number of observed data. Hydrogen atom positions were calculated by using a C-H distance of 0.96 A and an isotropic thermal parameter calculated from the anisotropic values for the atoms to which they were connected. The final residuals17 for 273 variables refined against 2187 data with Z > 2.5u(I) were R = 6.4% and R, = 6.7%.18 The final difference Fourier map had no peak greater than 1.60 e/A3.19
Results and Discussion An +Acyl Alkyne Complex. Use of cuprate reagents, LiCuRz (R= Me, Ph), results in nucleophilic addition to one of the carbonylligandsin [Tp’(CO)2W(PhCWMe)l+ to produce neutral +acyl alkyne complexes (1,2) as stable crystals in good yields (eq 4). Hence nucleophiles are not restricted to attack at the alkyne ligand even though formation of $-vinyl ligands dominated earlier reports of related rea~ti0ns.l~ That the carbonyls are susceptible to nucleophilic attack is not surprising given the high vco stretching frequencies for this dicarbonyl cation (2060, 1970cm-l). Addition of nucleophilesto the alkyne ligands in this dicarbonyl system has previously generated not (16) Programs used during solution and refinement were from the NRCVAX structure determination package. Gabe, E. J.; Le Page, Y.; Charland, J. P.; Lee, F. L.; White, P. S. J. Appl. Chem. 1989,22, 384. (17) The function minimized waa Ew(p
