Organometallics 1995, 14, 2102-2105
2102
Notes Synthesis and Structural Characterization of a Diiridium p-Acyl Complex Joseph M. O'Connor*J and Richard Merwin Departments of Chemistry, University of California, S a n Diego, La Jolla, California 92093-0358, and University of Nevada, Reno, Nevada 89557
Arnold L. Rheingold" and Melanie L. Adams Department of Chemistry, University of Delaware, Newark, Delaware 19716
-
Received December 16, 1994@
Summary: The metallacyclopentadiene chloride complex
Ir(CR=CRCR=CR)(AsPh3)zCl (3, R = CO2CH3) undergoes reaction with 3-butyn-1-01at room temperature to give the metallacycle-carbene complex
Scheme 1 PPh, I
PPh,
m
I~(CR=CRCR=CR)[=C(CH~~O](ASP~&C~ (1-AsPh3, R = COzCH3). Thermolysis of 1-AsPh3 at 75 "C leads to a 73% isolated yield of the diiridium pu-r/2-(C,0)-
acyl complex {[Ir(CR=CRCR=CR)(AsPh3)](p-C1),& C(=O)(CHd3(AsPhJ][Ir(CR=CRCR=CR)(As Ph3)](p-C1)2[ p - C(= 0 )( C H z ) 1
AS P h d I [ I r ( C R =C R C R =C R )I
(=C(CHd30)]} (4, R = COzCH3).
We previously reported the quantitative conversion iridacyclopentadiene-carbene complex the m Ir(CR=CRCR=CR)[=C(CH2)3O](PPh3)2Cl(l-PPh3, R = C02CH3) t o iridacyclobutene 2 upon thermolysis of 1-PPh3 at 72 "C in chloroform solution (Scheme 1).2On the basis of phosphine inhibition studies, we proposed a n initial loss of PPh3 from 1-PPh3. Subsequent steps would then include insertion of the carbene ligand into the iridium-carbon bond of the metallacycle and ring contraction of the metallacyclohexadiene intermediate (I). In the hope of facilitating this unprecedented insertion reaction we prepared the triphenylarsine analogue of 1-PPh3 and report herein that thermolysis of the arsine derivative leads not t o a metallacyclobutene but rather t o the first homodinuclear p q 2 (C,O)-acyl complex of the cobalt triad metals. of
Results and Discussion The bis(triphenylarsine1 complex h-(CR=CRCR=bR)(AsPh&Cl (3,R = C02CH3) was prepared from Ir( A S P ~ ~ ) ~ C Ofuroyl ) C ~ azide, ,~ and dimethyl acetylenedicarboxylate by a modification of Collman's procedure @Abstractpublished in Advance ACS Abstracts, March 15, 1995. (1)Address correspondence to this author a t the University of California. (2) OConnor, J. M.; Pu, L.; Woolard, S.; Chadha, R. K. J.Am. Chem. SOC.1990, 112, 6731. (3)Kubota, M.; Kiefer, G . W.; Ishikawa, R. M.; Bencala, K. E. Inorg. Chim. Acta 1973,7, 195.
0276-7333/95/2314-2102$09.00/0
L
I
for the synthesis of the triphenylphosphine a n a l ~ g u e . ~ In the solid state, brick red 3 rapidly and reversibly turned yellow upon exposure to air. At room temperature 3 underwent reaction with 3-butyn-1-01to give the
-
r
metallacycle-carbene complex Ir(CR=CRCR=CR)[=CI
(CH2)301(AsPh3)2Cl (l-AsPhs, R = C02CH3) in 82% isolated yield. The physical and spectroscopic properties of 1-AsPhs are similar to those of the triphenylphosphine analogue 1-PPh3. Both complexes are faint yellow, air-stable solids which exhibit similar melting point behavior (162-164 "C for 1-AsPh3, 168-170 "C for 1-PPh3). In the 13C{lH} NMR spectra both complexes exhibit a signal a t 286.2 ppm, assigned to the carbene carbon. When a methylene chloride solution of 1-AsPh3 (0.36 mmol, 36 mM) was heated a t 75 "C for 18 h the color darkened to a yellow-orange. Reduction of the solution volume and addition of diethyl ether led to precipitation of 4 as a n air-stable, yellow-orange, analytically pure powder in 73% yield (Scheme 2). The 'H NMR spectrum (CDCl3) of 4 exhibits four singlets integrating for 6 H s each a t 6 3.52, 3.50, 3.48, and 3.46, which are assigned to the methyl groups of the methoxycarbonyl metallacycle substituents. These signals are consistent with ~~
(4)Collman, J. P.; Kang, J. W.; Little, W. F.; Sullivan, M. F. Znog. Chem. 1968, 7 , 1298.
0 1995 American Chemical Society
Notes
Organometallics, Vol. 14, No. 4, 1995 2103 Scheme 2 AsPh,
P
P
h
+,
I
=-oH
I
AsPh, l-ASPh,
two equivalent 1,4-butadiendiyl ligands, each with four methoxycarbonyl environments, or two nonequivalent 1,4-butadiendiyl ligands, each with two methoxycarbonyl environments. Six two-proton multiplets are also observed in the lH NMR spectrum a t 6 4.60 (t, JHH = 7.2 Hz), 3.33 (m), 2.73 (t,JHH= 5.1 Hz), 2.10 (t,JHH = 7.8 Hz), 1.70 (m), and 1.59 (t,JHH = 7.8 Hz), consistent with two unique -CHzCHzCHz- fragments. For comparison, the methylene hydrogens in the oxacyclopentylidene ligand of l-AsPh3 are observed in the lH NMR spectrum (CDC13) at 6 4.28 (t, JHH = 7.95 Hz), 2.75 (t, JHH = 7.95 Hz),and 0.93 (m). Thus, on the basis of the lH NMR spectroscopic data only one oxacyclopentylidene ligand remains intact in 4. In the 13C(lH}NMR spectrum (CDCl3) of 4, two downfield singlets are observed at 256.2 and 253.4 ppm. These resonances are a t somewhat high field for carbene carbons but downfield of where an Vl-acyl carbon is typically observed. Ultimately we resorted to a single-crystal X-ray diffraction study to determine the structure of 4 (Tables 1 and 2). An orange crystal of 4 was obtained by recrystallization from THFhexanes. Refinement gave the structure shown in Figure 1. Bond distances and bond angles are summarized in Table 2. The structure consists of two iridium atoms bridged by two chloride ligands and a p-+(C,O)-acyl ligand. The iridiumiridium distance of 3.44 A is well beyond the upper limit of 3.2 8, for an iridium-iridium single bond.5 The average iridium-chloride bond distance is 0.032 longer to iridium(1) than to iridium(2). For comparison, the iridium-chloride bond distances in the symmetric dimer [1rCl~Me(C0)~1~ are 2.52 and 2.38 In solution, rapid rotation about the Ir(2)-C(25) double bond would account for the plane of symmetry required by the lH NMR data. In addition to the p-acyl ligand, two unusual structural features of 4 are the presence of 1,4-butadiendiyl ligands which do not bridge the metals and the facial arrangement of the carbene and butadiendiyl ligands on iridium(2). The only other stable metallacycle-carbene complexes reported to data have a meridional arrangement of these ligand^.^ The formation of the acyl ligand in 4 is the result of triphenylarsine-induced ring opening of the oxacyclo-
A
(5)Arif, A. M.; Heaton, D. E.; Jones, R. A.; Kidd, K. B.; Wright, T. C.; Whittlesey, B. R.; Atwood, J . L.; Hunter, W. E.; Zhang, H. Inorg. Chem. 1987,26, 4065. (6)Bailey, N. A.; Jones, C. J.; Shaw, B. L.; Singleton, E. J. Chem. SOC.,Chem. Commun. 1967, 1051. (7) OConnor, J . M.; Pu,L.;Rheingold, A. L. J . A m . Chem. SOC.1990, 112,6232.
Table 1. CrystallographicData for C,&&s2C12IrzOls formula fw cryst system space group a. A
h. 8, c,
A
(4)
(a) Crystal Parameters CbaHds2Cl~Ir~Ol" 1777.4 monoclinic P2dn 15.614(3) 13.722(4) 31.564(8)
a,deg P3
deg
Y deg
94.15(2)
9
v,A3
2
cryst dimens, mm cryst color D(calc), g cm' p(Mo Ka),cm-l temp, K T(max)/T(min)
6745(2) 4 0.07 x 0.22 x 0.36 orange 1.750 50.65 298 N/A
(b) Data Collection diffractometer Siemens P4 monochromator graphite radiation Mo K a (A = 0.7 10 73 A) 20 scan range, deg 4-45 data collcd (h,k,l) f 16,+ 14,+33 rflns collcd 9447 8812 indpt rflns R(merg), % 10.61 indpt obsvd fflns with, 531 I F, 1 nu(F,,) (n = 4) std fflns 3 std/197 rflns R(F), % R(w0, % Nu(max) NQ,e A-3 NdNv
GOF
(c) Refinement 7.86 9.34 0.0I5 3.12 9.5 1.22
pentylidene ligand. We previously observed this type of a transformation in the reaction of cationic metallacycle-carbene 5 with pyridine and PPh3 to give the mononuclear acyls 6-L.7 For v2-acyl 4 the carbene Ir(2)-C(25) double bond distance of 1.79 A is 0.22 A shorter than the acyl Ir(l)-C(29) distance of 2.01 A and the C(29)-0(18) distance is 1.305(26)A. For comparison, the +acyl ligand in 6-pyr has Ir-C and C-0 bond distances of 2.136(4) and 1.212(5)A,respectively. These structural comparisons indicate that the bridging acyl ligand of 4 is appropriately described by resonance structures I1 and 111,with I1 as the major contributor to the ground state structure. A search of the Cambridge Crystallographic Data Base failed to locate a structurally characterized ex-
2104 Organometallics, Vol. 14,No. 4,1995
Notes
Table 2. Selected Bond Distances (A) and Angles (deg) for 4 2.495(6) 2.561(3) 1.984(27) 2.464(6) 2.177(16) 2.001(21)
lr( I )-Cl( 1) Ir( I)-As(2) Ir( 1)-C(4) Ir(2)-C1( I ) Ir(2)-0( 18) Ir(2)-C(16) C1( 1)-Ir( I)-C1(2) C1(2)-Ir( 1)-As(2) C1(2)-Ir( I)+( I ) CI(1)-Ir( 1)-C(4) As(2)-Ir( 1)-C(4) CI(l)-lr( I)-C(29) As(2)-Ir( I)-C(29) C(4)-Ir( 1 )-C(29) Cl( l)-Ir(2)-Cl(2) CI(l)-Ir(2)-0( 18) C1( I)-Ir(2)-C( 13) C1( l)-Ir(2)-C( 16) O( 18)-1r(2)-C( 16) C1( I)-Ir(2)-C(25) C( 13)-Ir(2)-C(25)
8 I .8(2) 95.3(2) 171.0(6) 177.6(8) 92.6(8) 86.6(6) 174.6(6) 92.6( 10) 83.1(1) 82.7(4) 96.2(7) 173.3(6) 90.8(7) 95.6(8) 91.5(10)
Ir( 1)-C1(2) Ir( I)-C( 1) lr( I)-C(29) Ir(2)-C1(2) Ir(2)-C( 13) Ir(2)-C(25) CI(1)-Ir( I)-As(2) C1( 1)-lr( I)-C( I ) As(2)-Ir( 1 )-C( 1 ) C1(2)-Ir( 1)-C(4) C( 1)-lr( 1)-C(4) C1(2)-Ir( I)-C(29) C( 1) -Ir( 1) -C(29) C( 13)-1r(2)-C( 16) O(18)-1r(2)-C( 13) C1(2)-1r(2)-0( 18) Cl(2)-Ir(2)-C( 13) Cl(2)-Ir(2)-C( 16) O( 18)-Ir(2)-C(25) C1(2)-Ir(2)-C(25) C( 16)-Ir(2)-C(25)
2.492(6) 2.044(22) 2.010(20) 2.46 I(6) 2.020(22) I .786(34)
L, A PPh,
L
= pyr or PPh3
5, R = COzCH3
88.2(2) 103.7(6) 92.0(6) 95.8(8) 78.6( 10) 85.3(6) 87.9(9) 82.6(9) 94.6( 8) 8 1.4(5) 176.0(7) 97.6(6) I73.8(9) 92.5(8) 9 1.0( IO)
PPh,
-
6 - p y r , L pyridine 6-PPh3, L PPh3
R.
ample of a homodinuclear p-acyl complex within the cobalt triad. Kaesz et al. have structurally characterized the heterodinuclear @-acyl)iridium(III) complex 7 which exhibits iridium-carbon bond distances of 1.983(10) and 2.008(9)A for the benzoyl and acetyl ligands,
1
Ph, ,Ph
respectively.839
The mechanism for conversion of 1-AsPh3 to 4 is clearly a complicated one which involves dissociation of three triphenylarsine ligands, isomerization of a meridional metallacycle-carbene to a facial geometry, oxacyclopentylidene ligand ring opening, and the formation of three bridging ligands. We believe that the remarkable contrast in the thermal behavior of 1-PPh3 and 1-AsPh3is primarily related to the greater lability of triphenylarsine as compared to triphenylphosphine. Wovkulich and Atwood have measured the rate of h P h 3 dissociation from Cr(C015L to be 120 times faster than for L = PPh3.1° Manzer and Tolman have also established that the displacement energy for group 15 ligands from Pt(I1) complexes decreases in the order PPh3 > AsPhs > SbPh3.11 Thus, the open coordination sites necessary for establishment of ligand bridges are more readily generated in the case of l-AsPh3 than for 1-PPh3.
Experimental Section General Information. Commercially available reagents were used as received. Solvents were distilled and dried by standard procedures. All reactions were carried out under a (8)Blickensderfer, J.R.;Knobler, C. B.; Kaesz, H. D. J . Am. Chem. SOC.1976,97,2681. (9)Examples of structurally characterized homodinuclear p-acyl complexes: (a) Pyshnograeva, N. I.; Setkina, V. N.; Andrianov, V. G.; Struchkov, Yu. T.; Kursanov, D. N. J . Organomet. Chem. 1981,206, 169. (b) Mott, G.N.; Granby, R.; MacLaughIin, S. A,; Taylor, N. J.; Carty, A.J. Organometallics 1983,2,189. (c) Lindley, P.F.; Mills, 0. S. J . Chem. SOC.A 1969,1279. (d) Henrick, K.; McPartlin, M.; Iggo, J. A.; Kemball, A. C.; Mays, M. J.;Raithby, P. R. J . Chem. SOC.,Dalton Trans. 1987,2669. (e) Henrick, K.; Iggo, J. A.; Mays, M. J.; Raithby, P. R. J . Chem. SOC.,Chem. Commun. 1984,209. (0 Kampe, C. E.; Boag, N. M.; Kaesz, H. D. J . Mol. Catal. 1983,21,297.(g)Kreiter, C. G.; Franzreb, K. H.; Sheldrick, W. S. J . Organomet. Chem. 1984,270, 71. (h) Hoke, J. B.; Dewan, J. C.; Seyferth, D. Organometallics 1987, 6 , 1816. (i) Boag, N. M.; Sieber, W. J.; Kampe, C. E.; Knobler, C. B.; Kaesz, H. D. J . Organomet. Chem. 1988,355,385. (i)Chisholm, M. H.; Ho, D.; Huffman, J. C.; Marchant, N. S. Organometallics 1989,8, 1626. (k) Schweiger, M.J.;Nagel, U.; Beck, W. J . Organomet. Chem. 1988,355,289.(1) Flissler, Th.; Huttner, G. J . Organomet. Chem. 1989, 376,367. (10)Wovkulich, M. J.; Atwood, J. D. J . Organomet. Chem. 1979, 184, 77. (11)Manzer, L. E.;Tolman, C. A. J.Am. Chem. SF. 1976,97,1955.
Ph
7 dry nitrogen atmosphere. Melting points were determined on an Electrothermal melting point apparatus and are uncorrected. Elemental analyses were performed by Galbraith Laboratories, Knoxville, TN. Infrared spectra were obtained on a Perkin-Elmer 599 spectrometer. 'H and l3C{lH) NMR spectra were recorded at 300 and 75 MHz, respectively, on a GE GN-300 spectrometer. Proton and carbon chemical shifts are relative to the residual protio solvent resonance and solvent carbon resonance, respectively.
-
Ir(CR-CRCR=CR)(AsPh&Cl (3,R = CO&&). To a stirred methylene chloride solution (25 mL) of Ir(AsPh&(CO)Cl(1.27 g, 1.4 mmol) at room temperature was added an excess of dimethyl acetylenedicarboxylate (0.523 g, 3.68 mmol) by syringe. The mixture was degassed by N2-purge and stirred until homogenous, after which time a 25 mL methylene chloride solution of furoyl azide (0.282 g, 2.0 mmol) was added by cannula. The solution was stirred overnight at room temperature, and the volatiles were removed under vacuum. The residue was washed with methanol and recrystallized from methylene chloride/methanol to give 3 as a red solid in 78% yield (1.29 g): mp (sealed cap) 241-243 "C;'H NMR (CDC13) 6 7.6-7.5 (m, 12H) 7.4-7.3 (m, 18H), 3.44 (s, 6H), 3.25 (s,6H); l3C(lH} NMR (CDC13) 6 169.4,164.7, 150.7, 140.9, 135.1, 134.1, 130.0, 129.6, 128.4, 128.1, 51.2, 51.0; TR (Nujol) 1705 (vs), 1721 (vs), 1260 (s), 1220 (vs), 1170 (s) cm-l. Anal. Calcd for C ~ ~ H ~ ~ A S ~ C C,~ 51.27; I ~ O S H, : 3.76; C1, 3.15. Found: C, 51.16; H, 3.70; C1, 3.21.
-
I
I~(CR--CRCR-CR)[=C(CH~)SOI(A~P~~)~C~ (l-AsPh,R = C02CHs). To a stirred methylene chloride solution of 3 (0.5 g, 0.44 mmol) at -78 "C was added a slight excess of 3-butyn1-01 (0.034 g, 0.48 mmol) by syringe. The mixture was degassed by N2-purge and allowed to warm to room temperature. The reaction was stirred for 1.5 h, the solution volume reduced under vacuum, and diethyl ether added to give 1-AsPhs as a faint yellow powder (0.437 g) in 82% yield: mp (sealed cap) 241-243 "C; lH NMR (CDC13)d 7.6 (m, 12H) 7.3
Notes
Organometallics, Vol.14,No. 4,1995 2105
Figure 1. Molecular structure and numbering scheme for 4 with thermal ellipsoids drawn at t h e 35% level. X-ray Structure of 4. Crystallographic data for 4 are collected in Table 1. Cell constants and orientation matrices were determined by the least squares refinement of 25 high149.2,149.7,145.7,134.8,132.0,129.4,127.6,87.1,57.4,50.5, angle reflections. No absorption correction was required; the madmin transmission ratio was less than 1.1. The crystal 50.3,50.0,19.0;IR (Nujol) 1710 (s), 1380 (m), 1330 (w), 1205 (s) 1160(m)cm-'. Anal. Calcd for C ~ Z H ~ ~ A S ~C, C 52.29; ~ I ~ Q ~ : diffracted weakly and broadly leading to a decrease in the overall quality of the structural characterization. The strucH,4.34;C1, 2.97.Found: C, 52.37;H, 4.20;C1, 3.17. ture was solved by direct methods. All non-hydrogen atoms { [Ir(rl2-C4R4)(AsPh3)1((r-Cl)2[I1-C(=O)(CH~)~(AsPh3)1 drwere anisotropically refined, and the phenyl rings were fixed m as rigid hexagons. All computer programs used for data (q2-C&)[=C(CH2)sO)l} (4, R = COZCHS). A methylene collection and structure refinement are from the P4 and chloride solution of 1-AsPh3 (0.44g, 0.36mmol) was heated SHELXTL (G.Sheldrick, Siemens, Madison, WI) program in a sealed tube under a nitrogen atmosphere for 18 h. The libraries. solution volume was reduced under vacuum and diethyl ether added to give 4 as a faint yellow-orange powder (0.236g) in 73% yield: mp 214-216 "C; 'HNMR (CDC13) 6 7.6(m, 20H) Acknowledgment. Partial support by the National 7.3(m, lOH),4.60 (t, J = 7.2Hz, 2H), 3.52(s,6H), 3.50(s, Science Foundation is gratefully acknowledged. We are 6H),3.48(s, 6H),3.46(s, 6H),3.33 (m, 2H),2.73(t, J = 5.1 grateful to Johnson Matthey for a generous loan of Hz,2H),2.10(t,J=7.8Hz,2H),1.70(m,2H),1.59(t,J=7.8 precious metals. Hz, 2H);13C{lH} NMR (CDC13) 6 256.2,253.4,174.5,174.4, 165.6,164.7,154.6,154.0,143.4,148.1,134.6,133.8,133.1, Supplementary Material Available: Tables of bond 132.6,130.8,128.6,127.5,121.4,83.1,55.2,50.9,50.5, 50.2, lengths, bond angles, anisotropic thermal parameters, and 48.2,23.6,21.4, 18.5;IR (Nujol) 1730 (vs), 1705 (vs), 1550 (w), atomic coordinates and thermal parameters (8pages). Order1380 (m), 1330 (m), 1205 (vs) 1070 (m) cm-'. Anal. Calcd for ing information is given on any current masthead page. C68H~&SzClzIrz018: c, 45.97;H, 3.74;c1, 3.99. Found: c, OM940962C 46.00;H, 3.75;C1, 4.09.
(m, 18H),4.28(t, J = 7.95Hz, 2H),3.90(s,3H),3.63(s,3H), 3.46(s,3H),3.24(s, 3H),2.75(t, J = 7.95Hz,2H),0.93(m, 2H);13C{lH}NMR (CDC13)6 287.0,176.4,166.1,164.1,153.6,
