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The reaction between the tetrahedrane cluster PhCCo3(CO)9 (1) and the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione ...
Structural Chemistry, Vol. 12, Nos. 3/4, 2001

CO Substitution in PhCCo3 (CO)9 by 4,5-Bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Ligand Fluxionality, Kinetics, and X-Ray Structures of PhCCo3 (CO)7 (bpcd) and Co3 (CO)6 [m 2 -h 2 , h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) Simon G. Bott2, Huafeng Shen3, and Michael G. Richmond3,4 Received January 28, 2000; revised May 15, 2000; accepted June 11, 2000

The reaction between the tetrahedrane cluster PhCCo3 (CO)9 (1) and the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) leads to the replacement of two CO groups and formation of PhCCo3 (CO)7 (bpcd) (2). Cluster 2 is thermally unstable and readily transforms into the new cluster Co3 (CO)6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3). Both clusters 2 and 3 have been isolated and fully characterized in solution by IR and NMR (31 P and 13 C) spectroscopy. VT 31 P NMR data indicate that the bpcd ligand in PhCCo3 (CO)7 (bpcd) is fluxional in solution, with two chelating and one bridging isomer being observed at 176 K in THF. The kinetics for the conversion of 2 to 3 followed first-order kinetics in 1,2-dichloroethane (DCE). These data, coupled with the reaction rates being retarded in the presence of added CO, and the activation parameters (DH ‡ c 27.1 ± 0.3 kcal/ mol and DS‡ c 9 ± 1 eu) support a scheme involving a dissociative CO loss as the rate-limiting step. Clusters 2 and 3 have been structurally characterized by X-ray diffraction analyses. PhCCo3 (CO)7 (bpcd) crystallizes in the monoclinic ˚ , b c 21.743(3) A ˚ , c c 17.143(1) A ˚ , b c 97.522(8)8 , V c space group P21/ n: a c 10.731(2) A ˚ 3 , Z c 4, d calc c 1.552 g . cm − 3 ; R c 0.0598, Rw c 0.0671 for 1428 observed reflections 3965.4(8) A with l > 3j (l ). Co3 (CO)6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) crystallizes in ˚ , b c 11.702(1) A ˚ , c c 15.227(1) A ˚ , a c 106.716(6)8 , b the triclinic space group P1 a c 11.572(1) A ˚ 3 , Z c 2, d calc c 1.560 g . cm − 3 ; R c 0.0545, Rw c c 90.419(6)8 , g c 103.676(7)8 , V c 1912.4(3) A 0.0632 for 3149 observed reflections with l > 3j (l ). The chemistry exhibited by clusters 2 and 3 is compared with related clusters containing the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma). KEY WORDS: Clusters; Co substitution; P-C bond activation.

INTRODUCTION 1 Dedicated

to our friend and colleague Professor William H. Watson on the occasion of his 70th birthday. 2 Department of Chemistry, University of Houston, Houston, Texas 77204. 3 Department of Chemistry, University of North Texas, Denton, Texas 76203. 4 To whom all correspondence should be addressed.

Our groups have been interested in the substitution chemistry of metal cluster compounds with polydentate phosphine ligands as a means to prevent or retard cluster fragmentation in catalytic cycles and electron transfer rections [1–6]. Moreover, the introduction

225 1040-0400/ 01/ 0800-0225$19.50/ 0  2001 Plenum Publishing Corporation

Bott, Shen, and Richmond

226

of redox-active ligands into the coordination sphere of the metal cluster offers the possibility of producing new organometallic compounds that may exhibit long-range electronic communication due to an intervalence transition(s) that may be triggered by light absorption and/ or a controlled change in the oxidation state of one of the redox-active sites by electrochemical activation [7, 8]. While still in the infancy stage, such solid–state materials have the potential to serve as devices of technological interest because of their electrical and magnetic properties [9]. Several years ago in an attempt to synthesize cluster–ligand systems capable of exhibiting of mixedvalence behavior, we examined the substitution chemistry of the tricobalt cluster PhCCo3 (CO)9 with the redox-active phosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) [10]. The particular ligand was chosen, in part, because it possesses a relatively low-lying p∗ LUMO that may function as an electron reservoir in electron transfer reactions, coupled with the fact that no reaction chemistry of this diphosphine ligand with polynuclear metal clusters existed prior to our initial report. While we were not successful in producing a mixed-valence compound of the . form PhCCo3 (CO)7 (bma) − , we did observe the heretofore unknown reductive coupling of the bma ligand with the capping benzylidyne group, which afforded the new benzylidene-capped cluster Co3 (CO)6 [m 2 -h 2 : h 1 C(Ph)C — C(PPh2 )C(O)OC(O)](m 2 -PPh2 ) [10]. This particular reaction is illustrated in Eq 1.

the thermally unstable cluster PhCCo3 (CO)7 (bpcd) (2) and its conversion to Co3 (CO)6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3). Both clusters 2 and 3 have been fully characterized in solution and in the solid state by X-ray diffraction analysis. EXPERIMENTAL General Procedures Co2 (CO)8 was purchased from Strem Chemicals and was used as received. The 4,5-dichloro-4cyclopenten-1,3-dione used in the synthesis of bpcd was prepared according to published procedures [14]. PhCCo3 (CO)9 (1) was prepared from HCCo3 (CO)9 [15] and phenylmercuric chloride according to the procedure of Seyferth [16]. All reactions were conducted under argon using standard Schlenk techniques [17]. THF, toluene, and all alkane solvents were distilled from sodium/ benzophenone ketyl, while all halogenated solvents used were distilled from P2 O5 . All distilled solvents were stored under argon in Schlenk storage vessels that were equipped with Teflon stopcocks. The 13 CO (>99%) used in the preparation of 13 CO-enriched PhCCo3 (CO)9 was purchased from Isotec. The C and H micoanalyses were performed by Atlantic Microlab, Norcross, GA. All infrared spectra were recorded on a Nicolet 20SXB FT-IR spectrometer, using PC control and OMNIC software in 0.1-mm NaCl cells. The 13 C and 31 P NMR spectra were recorded on a Varian 300-VXR spectrometer, operating at 75 and 121 MHz, respectively. All 31 P chemical shifts are referenced relative to external H3 PO4 (85%), taken to have d c 0. Positive chemical shifts represent resonances that are low field to the external standard. Synthesis of PhCCo3 (CO)7 (bpcd) Using Me3 NO

Wishing to further examine the generality of this transformation depicted in Eq. (1), we have studied the reaction between the tricobalt cluster PhCCo3 (CO)9 (1) and the related diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). The bpcd ligand is structurally similar to the bma ligand. These ligands have been thoroughly studied by Fenske [11] and Tyler [12, 13] in a number of reactions involving simple mononuclear compounds. Herein we report our results on the synthesis and substitution lability of

To 0.20 g (0.39 mmol) of PhCCo3 (CO)9 and 0.18 g (0.39 mmol) of bpcd in 50 ml of THF at 08 C was added 60.8 mg (0.81 mmol) of Me3 NO under argon flush. The reaction solution was stirred for 1.5 hour at 08 C, after which the solution was removed under vacuum. The crude green colored product was purified by low-temperature column chromatography over silica gel using CH2 Cl2 as the eluent. The analytical sample and single crystals of PhCCo3 (CO)7 (bpcd) suitable for X-ray diffraction analysis were obtained from a CH2 Cl2 solu-

CO Substitution in PhCCo3 (CO)9 by bpcd tion of 2 that had been layered with pentane. Yield: 0.23 g (64%). IR (CH2 Cl2 ): n(CO) 2063 (s), 2012 (vs), 1860 (w), 1826 (w), 1749 (w, asym bpcd C — O), 1718 (m, sym bpcd C — O) cm − 1 . 31 P{1 H} NMR (THF, 176 K): d 56.4 and 49.3 (chelating isomer, 70%); 60.9 (chelating isomer, 13%); 33.3 (bridging isomer, 17%). 13 C{1 H} NMR (THF, 176 K): d 202.0 and 231.6 (major isomer); 204.8 and 205.5 (minor isomers). Anal. Calcd (found) for C43 H27 Co3 O9 P2 : C, 55.75 (55.51); H, 2.94 (2.94). Synthesis of Co3 (CO)6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) To 0.10 g (0.19 mmol) of PhCCo3 (CO)9 and 90.0 mg (0.19 mmol) of bpcd in a small Schlenk tube was added 20 ml of toluene. After the vessel was sealed, the vessel was heated overnight at 70–808 C. The solution was allowed to cool and then examined by IR and TLC analyses, which revealed the consumption of the starting materials and the presence of the desired product. Cluster 3 was isolated by chromatography over silica gel using CH2 Cl2 as the eluting solvent. The crude product was recrystallized from a 1 : 1 mixture of CH2 Cl2 / pentane to give 95.0 mg (55.7% yield) of black Co3 (CO)6 [m 2 h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ). IR (CH2 Cl2 ): n(CO) 2055 (s), 2032 (vs), 2017 (w), 1931 (w), 1719 (w, asym bpcd C — O), 1686 (m, sym bpcd C — O) cm − 1 . 31 P{1 H} NMR (THF, 176 K): d 200.5 (m 2 -phosphido), 18.6 (phosphine). 13 C{1 H} NMR (THF, 176 K): d 211.5 (1C, J P-C c 12.3 Hz), 204.1 (1C, J P-C c 8.2 Hz), 203.2 (1C), 201.9 (1C), 197.4 (1C), 196.6 (1C). Anal. Calcd (found) for C42 H27 Co3 O8 P2 : C, 56.15 (55.56); H, 3.03 (3.52). X-Ray Diffraction Data PhCCo3 (CO)7 (bpcd) A single crystal suitable for X-ray diffraction analysis was selected and sealed inside a Lindemann capillary, followed by mounting on the goniometer of an Enraf-Nonius CAD-4 diffractrometer. Data were col˚ ) radiation and a lected by using MoKa (l c 0.71073 A graphite monochromator. Standard procedures employed have already been described [18]. Pertinent details are given later in Table 2. Cell constants were obtained from a least-squares refinement of 25 reflections with 2v > 218 . Intensity data in the range of 2 < 2v < 408 were collected at room temperature (295 ± 2 K) using the q-

227

scan technique and variable scan speeds, and were corrected for Lorentz and polarization effects and absorption (DIFABS). The structure was solved by direct methods (SIR [19]) and the model refined by using fullmatrix least-squares techniques. With the exception of the cobalt atoms, all nonhydrogen atoms were treated with isotropic thermal parameters. Hydrogen atoms were located in difference maps, and then included in the model in idealized positions [U(H) c 1.3 Beq (C)]. Refinement converged at R c 0.0598 and Rw c 0.0671 for 1428 unique reflections with l > 3j (l ). All computations other than those specified were performed using Mo1EN [20]. Scattering factors were taken from the usual sources [21]. Co3 (CO)6 [m 2 -h 2 : h 1-C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) A single crystal of 3, which was grown from a benezene solution of 3 that had been layered with pentane, suitable for X-ray diffraction analysis was selected and sealed inside a Lindemann capillary, followed by mounting on the goniometer of an Enraf-Nonius CAD4 diffractrometer. Data were collected by using MoKa ˚ ) radiation and a graphite monochro(l c 0.71073 A mator. Pertinent details are given later in Table II. Cell constants were obtained from a least-squares refinement of 25 reflections with 2v > 368 . Intensity data in the range of 2 < 2v < 448 were collected at room temperature (295 ± 2 K) using the v / 2v scan technique and variable scan speeds and were corrected for Lorentz and polarization effects and absorption (DIFABS). The structure was solved by direct methods (SIR) and the model refined by using full-matrix least-squares techniques. All non-hydrogen atoms were refined anisotropically, except the carbon atoms of the phenyl groups, which were treated with isotropic thermal parameters. Hydrogen atoms were located in difference maps and then included in the model in idealized positions [U(H) c 1.3 Beq (C)]. Refinement converged at R c 0.0545 and Rw c 0.0632 for 3143 unique reflections with l > 3j (l ). Kinetic Measurements All kinetic reactions were conducted in Schlenk vessels under argon and monitored for a minimum of three half-lives by following the IR absorbance changes of the 1747 cm − 1 carbonyl band of 2. Plots of ln At versus time were found to be linear and the slopes of these plots afforded the first-order rate constants quoted

228

in Table I (see later). The activation parameters were determined by using the Eyring equation. RESULTS AND DISCUSSION Synthesis and Spectral Characterization The thermal reaction between PhCCo3 (CO)9 (1) and added bpcd proceeds readily at temperatures above 708 C in toluene to give PhCCo3 (CO)7 (bpcd) (2) and Co3 (CO)6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3). Monitoring these reactions by TLC and IR spectroscopy shows that compound 2 forms first and is slowly converted into 3. These data are consistent with our earlier work on the reaction between PhCCo3 (CO)9 and bma [10], where the intermediate cluster PhCCo3 (CO)7 (bma) was shown to be the precursor to corresponding P-C bond-cleavage product of Co3 (CO) 6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)OC(O)](m 2 -PPh2 ). Due to the difficulty in preparing pure 2 by the thermolysis route, we examined the reaction between PhCCo3 (CO)9 an bpcd in the presence of the oxidativedecarbonylation reagent Me3 NO. It is known that this particular reagent offers the possibility of affording thermally sensitive organometallic compounds under mild conditions [22]. Treatment of PhCCo3 (CO)9 and bpcd (1 : 1 ratio) with a slight excess of Me3 NO in THF at ice temperature led to the clean production of PhCCo3 (CO)7 (bpcd) without any sign of cluster 3. PhCCo3 (CO)7 (bpcd) was isolated by column chromatography over silica gel at 08 C using CH2 Cl2 . The IR spectrum of 2 in CH2 Cl2 reveals terminal carbonyl stretching bands at 2063 (s), 2012 (vs) cm − 1 , in addition to two weak n(CO) bands at 1860 and 1826 cm − 1 that may be assigned to bridging carbonyl groups (vide infra). The ancillary bpcd ligand exhibits n(CO) bands belonging to the dione moiety at 1749 and 1718 cm − 1 typical of a cluster coordinated bpcd ligand [23]. The 31 P{1 H} NMR spectrum of PhCCo3 (CO)7 (bpcd) in THF at room temperature exhibits a single, broad resonance at ca. d 49, whose relative location is strongly suggestive of a chelating bpcd ligand. Given that the related cluster PhCCo3 (CO)7 (bma) exhibited temperature-dependent 31 P spectra due to equilibrating chelating and bridging bma isomers [10], we investigated the VT 31 P NMR behavior of 2. Cooling a sample of PhCCo3 (CO)7 (bpcd) down to 176 K leads to the appearance of four distinct 31 P resonances at d 60.9,

Bott, Shen, and Richmond 56.4, 49.3, and 33.3. Samples of PhCCo3 (CO)7 (bpcd) that were cycled over the temperature range 176–273 K afforded unchanged spectra data, suggesting that the observed VT behavior was the result of a bpcd ligand equilibration about the cluster polyhedron. On the basis of the bpcd chemical shift and symmetry considerations, we are able to assign the 31 P NMR data to three specific bpcd isomers of 2, as shown below.

The high-field resonance at d 33.3 is readily assigned to the bridging isomer of PhCCo3 (CO)7 (bpcd) since bridging diphosphine ligands are known to experience a greater nuclear shielding relative to the same ligand in a chelating mode [24]. Moreover, the single resonance associated with this isomer indicates that the bpcd ligand resides in the equatorial plane defined by the cobalt atoms, as is commonly observed with this genre of cluster. This bridged isomer contributes 13% to the isomer composition at 176 K. The remaining two species present in solution are assigned to chelating bpcd isomers based on their higher field chemical shifts. As a rule of thumb, chelating ligands of this nature typically appear from d 50–75. The major isomer (70% contribution) exhibits two, inequivalent 31 P resonances at d 56.4 and 49.3 and is consistent with the X-ray structure of PhCCo3 (CO)7 (bpcd), which possesses carbonyl bridges along with apical and basal PPh2 groups (vide infra). Finally, the remaining isomer (17%) is theorized to have a chelating bpcd ligand that resides in the equatorial plane. The single resonance at d 60.9 indicates that both PPh2 groups are in a symmetric environment. The facile interconversion between the isomeric PhCCo3 (CO)7 (bpcd) compounds was demonstrated by a 31 P EXSY study at 176 K. The 31 P EXSY data revealed off-diagonal correlations between all three isomers with

CO Substitution in PhCCo3 (CO)9 by bpcd DG⬆ values of ca. 9–10 kcal/ mol for the intramolecular exchange [25]. The 13 C{1 H} NMR spectrum of PhCCo3 (CO)7 (bpcd) was also examined as a function of temperature in an effort to gain information about the fluxional nature of the ancillary CO ligands. A broad 13 C signal at ca. d 209 was found for PhCCo3 (CO)7 (bpcd) at 273 K, indicating the presence of rapidly exchanging CO groups. Recording the spectrum at 176 K leads to a slowing of the scrambling COs but did not produce a limiting 13 C NMR spectrum. Two prominent 13 CO resonances at d 202.0 and 231.6 and two minor 13 CO resonances at d 209.8 and 211.2 were observed at 176 K. The two major resonances may be assigned to an isomer of 2 that contains terminal and bridging CO groups that are still undergoing dynamic exchange about the cluster polyhedron [26]. This CO scrambling prevents us from making an unequivocal identification of each of these isomers, a situation that was also observed by us in our earlier NMR study on PhCCo3 (CO)7 (bpcd) [10]. The major difference between PhCCo3 (CO)7 (bma) and PhCCo3 (CO)7 (bpcd) deals with the coordination mode preferred by the diphosphine ligand. In the case of the bma derivative, the bridged isomer was found to be more stable in solution, whereas the bpcd ligand favors the chelation to a single cobalt center in PhCCo3 (CO)7 (bpcd). Heating cluster 2 at temperatures in excess of 508 C leads to CO loss and the formation of cluster 3. This reaction is depicted in Eq. (2) and establishes the relationship between PhCCo3 (CO)7 (bpcd) and Co3 (CO)6 [m 2 -h 2 ,h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ).

Cluster 3 could be isolated in moderate yields by column chromatography over silica gel using CH2 Cl2 . The IR spectrum of 3 exhibits thermal carbonyl stretching bands at 2055 (s), 2032 (vs), 2017 (w), 1931 (w) cm − 1 , in addition to two bpcd carbonyl bands at 1719 (w) and 1686 (m) cm − 1 , that have been assigned to the asymmetric and symmetric n(CO) modes of the dione moiety [27]. The 31 P{1 H} NMR spectrum of 3 in THF at

229 176 K revealed the presence of two resonances at d 200.5 (phosphido) and 18.6 (phosphine), in full agreement with the structure of 3. The low-temperature 13 C{1 H} NMR spectrum of cluster 3, prepared from a sample of 13 CO enriched PhCCo3 (CO)9 , exhibited six distinct resonances of d 211.5, 204.1, 203.2, 201.9, 197.4, and 196.6, each of which represents one Co-CO group. Warming the sample to room temperature led to the gradual broadening of these resonances as quadrupolar coupling between the Co and CO nuclei becomes more important, but at no time was any CO fluxionality about the cluster polyhedron observed, a fact that supports the existence of a static environment for the ancillary carbonyl groups in 3. The relative chemical shifts found in the 31 P and 13 C NMR spectra of 3 are virtually identical to those data reported for the related clusters Co3 (CO)6 [m 2 -h 2 , h 1 -C(Ph)C — C(PPh2 )C(O)OC(O)](m 2 -PPh2 ) [10] and

Co3 (CO)6 [m 2 -h 2 , h 1 -C(Fc)C — C(PPh2 )C(O)OC(O)](m 2 PPh2 ) [28]. As in our earlier study on PhCCo3 (CO)7 (bma), we studied the conversion of 2 to 3 by carrying out a sealed-tube 31 P NMR experiment, because we wished to confirm (1) the fact that cluster 2 affords 3 without any by-products and (2) the existence of the dynamic equilibration of the bpcd ligand in PhCCo3 (CO)7 (bpcd). Here we prepared ca. 0.05 M THF solution of PhCCo3 (CO)7 (bpcd) and recorded the 31 P NMR spectrum at 176 K before thermolysis. The 31 P NMR spectrum of 2 revealed the presence of the three bpcd-substituted isomers, discussed earlier. We next heated this sample at 348 K for a period of time sufficient to effect partial conversion to cluster 3, after which time the sample was quenched in a Dry Ice/ acetone bath. The composition of the sample was determined by 31 P NMR spectroscopy at 176 K. The presence of the phosphido cluster 3 was observed (ca. 20%) along with unreacted 2, whose isomeric composition exactly matched previously recorded samples of 2 at 176 K. The fact that the ratio of the three bpcd isomers of PhCCo3 (CO)7 (bpcd) (two chelating and one bridging) remained unchanged relative to the initial 31 P NMR spectrum clearly supports the facile equilibrium of the ancillary diphosphine ligand about the tricobalt frame.

Kinetic Data for the Conversion of 2 to 3 The kinetics for the conversion of PhCCo3 (CO)7 (bpcd) to

Bott, Shen, and Richmond

230 Table I. Experimental Rate Constants for the Transformation of PhCCo3 (CO)7 (bpcd) (2) to Co3 (CO)6 [m 2 − h 2 : h 1 -(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 –PPh2 ) (3)a Entry no.

T (K)

Solvent

105 kobsd , s − 1

1 2 3 4 5 6 7

308 316 316 316 323 330 338

DCE DCE DCE DCE DCE DCE DCE

3.1 ± 0.1 19.5 ± 0.5 17.0 ± 0.2b 0.63 ± 0.04c 59 ± 2 115 ± 4 263 ± 8

ca. 7.7 × 10 − 3 M PhCCo3 (CO)7 (bpcd) in DCE solvent by following the disappearance of the n(CO) band at 1747 cm − 1 . All of the quoted kinetic data represent the average of two measurements. b Reaction using ca. 3.3 × 10 − 3 M PhCCo (CO) (bpcd). 3 7 c In the presence of 1 atm of CO. a From

Co3 (CO)6 [m 2 -h 2 ,h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) were examined by IR spectroscopy in DCE over the temperature range 308–338 K. The reactions followed firstorder kinetics for a period of least three half-lives, and plots of ln At as a function of time gave the first-order rate constants, reported in Table I. The presence of CO (entry 4) leads to a retardation in the reaction rate by a factor of ca. 27, suggesting a rate-limiting step involving CO loss from PhCCo3 (CO)7 (bpcd). The observed unimolecular reaction, CO inhibition, and the activation parameters DH ‡ c 27.1 ± 0.3 kcal/ mol and DS‡ c 9 ± 1 eu support the intervention of the unsaturated cluster PhCCo3 (CO)6 (bpcd) prior to P — C bond cleavage and reductive coupling with the benzylidyne ligand. The observed rate law followed is rate c

k 1 k 2 [PhCCo3 (CO)7 (bpcd)] k − 1 [CO] + k 2

which, in the absence of added CO (k 2 > k − 1 [CO]), reduces to the commonly observed first-order rate c k 1 [PhCCo3 (CO)7 (bpcd) [29]. The kinetic data recorded for PhCCo3 (CO)7 (bpcd) are in good agreement with those data found by us for the conversion of PhCCo3 (CO)7 (bma) to Co3 (CO)6 [m 2 -h 2 ,h 1 -C(Ph)C — C(PPh2 )C(O)OC(O)](m 2 -PPh2 )

X-Ray Diffraction Structures of PhCCo3 (CO)7 bpcd) and Co3 (CO)6 [m 2 -h 2 ,h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) Single crystals of 2 and 3 were grown and the molecular structure of each cluster was crystallographically determined. Both 2 and 3 exist as discrete molecules in the unit cell with no unusually short interor intramolecular contacts. The X-ray data collection and processing parameters for both clusters are found in Table II, while the final fractional coordinates and selected bond distances and angles are given in Tables III and IV, respectively. The ORTEP diagrams, shown in Fig. 1, establish the molecular structure of each cluster. The important features seen in PhCCo3 (CO)7 (bpcd) include the presence of a chelating bpcd ligand and three bridging CO groups, while in the case of cluster 3 the six-electron m 2 -h 2 : h 1 -benzylidene(diphenylphosphino)4-cyclopenten-1,3-dione ligand and the ancillary m 2 PPh2 moiety are confirmed.

Table II. X-Ray Crystallographic Data and Processing Parameters for PhCCo3 (CO)7 (bpcd) (2) and Co3 (CO)6 [m 2 –h 2 : h 1 -(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 –PPh2 ) (3) 2

Space group ˚) a (A ˚) b (A ˚) c (A a (deg) b (deg) g (deg) ˚ 3) V (A Mol formula fw Formula units per cell (Z) r (g . cm − 3 ) Abs. coeff. (m), cm − 1 ˚) l (MoKa ) (A Collection range (deg) Total no. of data collected No. of indep. data [l > 3j (l)] GOF R Rw Weights

P21 / n, monoclinic 10.731(1) 21.743(3) 17.143(1)

3

3965.4(8) C43 H27 Co3 O9 P2 926.44

P1, ticlinic 11.572(1) 11.702(1) 15.227(1) 106.716(6) 90.419(6) 103.676(7) 1912.4(3) C42 H27 Co3 O8 P2 898.43

4 1.552

2 1.560

13.72 0.71073

14.18 0.71073

2.0 ≤ 2v ≤ 40.0

2.0 ≤ 2v ≤ 44.0

3831

4660

1428 0.76 0.0598 0.0671 [0.04F2 + (j F )2 ] − 1

3143 1.20 0.0545 0.0632 [0.04F2 + (j F )2 ] − 1

97.522(9)

CO Substitution in PhCCo3 (CO)9 by bpcd

231

Table III. Positional Parameters for the Non-Hydrogen Atoms in PhCCo3 (CO)7 (bpcd) (2) and Co3 (CO)6 [m 2 –h 2 : h 1 -(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3)a,b Atom

x

y

z

˚ 2) B (A

Atom

PhCCo3 (CO)7 (bpcd) (2) Co(1) Co(2) Co(3) P(1) P(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(12) O(14) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(111) C(112) C(113) C(114) C(115) C(116) C(117) C(118) C(119) C(120) C(121) C(122) C(211) C(212) C(213) C(214) C(215) C(216) C(217) C(218) C(219) C(220) C(221) C(222) a Estimated

0.2308(3) 0.1685(3) 0.3086(3) 0.1014(5) 0.2650(5) − 0.015(1) − 0.067(2) 0.165(2) 0.269(2) 0.186(2) 0.560(2) 0.398(1) − 0.089(1) 0.118(1) 0.085(2) 0.029(2) 0.171(2) 0.261(2) 0.236(2) 0.454(2) 0.327(2) 0.059(2) − 0.032(2) − 0.029(2) 0.079(2) 0.126(2) 0.330(2) 0.445(2) 0.468(2) 0.585(2) 0.682(2) 0.659(2) 0.546(2) 0.168(2) 0.153(2) 0.208(2) 0.274(2) 0.290(2) 0.239(2) − 0.041(2) − 0.131(2) − 0.231(2) − 0.241(2) − 0.156(2) − 0.055(2) 0.266(2) 0.376(2) 0.375(2) 0.266(2) 0.156(2) 0.152(2) 0.389(2) 0.475(2) 0.577(2) 0.589(2) 0.505(2) 0.399(2)

0.1332(1) 0.0278(1) 0.0360(2) 0.1995(3) 0.2016(3) 0.1228(7) − 0.0296(9) − 0.0053(8) − 0.0896(9) 0.026(1) 0.0018(9) 0.1604(7) 0.3253(8) 0.3110(7) 0.107(1) − 0.004(1) 0.007(1) − 0.033(1) 0.026(1) 0.020(1) 0.138(1) 0.2528(9) 0.306(1) 0.332(1) 0.300(1) 0.2539(9) 0.067(1) 0.0662(9) 0.023(1) 0.022(1) 0.059(1) 0.099(1) 0.101(1) 0.250(1) 0.237(1) 0.274(1) 0.322(1) 0.337(1) 0.300(1) 0.1724(9) 0.211(1) 0.188(1) 0.127(1) 0.086(1) 0.111(1) 0.1740(9) 0.1619(9) 0.138(1) 0.126(1) 0.136(1) 0.162(1) 0.2564(9) 0.258(1) 0.299(1) 0.339(1) 0.341(1) 0.298(1)

0.2554(2) 0.2024(2) 0.3243(2) 0.3043(3) 0.1660(3) 0.1588(8) 0.228(1) 0.040(1) 0.279(1) 0.465(1) 0.381(1) 0.3965(8) 0.2620(9) 0.0418(9) 0.188(1) 0.219(1) 0.108(1) 0.279(1) 0.409(1) 0.360(2) 0.339(1) 0.222(1) 0.212(1) 0.132(1) 0.104(1) 0.161(1) 0.223(1) 0.191(1) 0.130(1) 0.102(1) 0.129(1) 0.186(1) 0.214(1) 0.384(1) 0.459(1) 0.521(1) 0.502(1) 0.425(1) 0.365(1) 0.337(1) 0.360(1) 0.394(1) 0.405(1) 0.386(1) 0.350(1) 0.068(1) 0.036(1) − 0.039(1) − 0.085(1) − 0.057(1) 0.019(1) 0.174(1) 0.239(1) 0.244(1) 0.186(1) 0.125(1) 0.113(1)

3.13(6) 3.83(7) 4.24(7) 3.0(1)* 2.8(1)* 4.2(3)* 7.8(5)* 7.3(5)* 7.8(5)* 11.2(6)* 8.7(5)* 5.0(4)* 6.3(4)* 5.9(4)* 4.5(5)* 5.2(6)* 5.8(6)* 6.3(6)* 6.0(6)* 6.9(7)* 3.4(5)* 2.5(4)* 4.5(5)* 4.1(5)* 4.1(5)* 2.4(4)* 4.3(5)* 3.1(5)* 6.0(6)* 6.2(6)* 4.9(6)* 4.2(5)* 3.7(5)* 4.2(5)* 5.0(6)* 6.5(7)* 5.9(6)* 6.5(7)* 4.7(5)* 2.6(4)* 3.8(5)* 4.2(5)* 4.3(5)* 5.0(6)* 3.8(5)* 3.0(4)* 2.8(4)* 4.1(5)* 4.4(5)* 5.1(6)* 3.6(5)* 3.4(5)* 3.9(5)* 5.8(6)* 5.1(6)* 5.3(6)* 4.2(5)*

x

y

z

˚ 2) B (A

Co3 (CO)6 [m 2 -h 2 : h 1 -(Ph)C — C(PPh2 )C(O)CH2 C(O)] (m 2 -PPh-2) (3) Co(1) Co(2) Co(3) P(1) P(2) O(1) O(2) O(3) O(4) O(5) O(6) O(12) O(14) C(1) C(2) C(3) C(4) C(5) C(6) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(111) C(112) C(113) C(114) C(115) C(116) C(117) C(118) C(119) C(120) C(121) C(122) C(211) C(212) C(213) C(214) C(215) C(216) C(217) C(218) C(219) C(220) C(221) C(222)

0.6410(1) 0.8259(1) 0.7485(1) 0.7995(2) 0.7977(2) 0.4257(7) 0.6499(8) 1.0777(6) 0.8710(7) 0.6364(8) 0.9656(7) 0.8582(6) 0.5236(6) 0.5156(9) 0.6580(9) 0.9808(9) 0.8517(8) 0.6784(9) 0.8817(9) 0.7652(7) 0.7805(8) 0.6785(9) 0.6086(8) 0.6619(7) 0.6069(7) 0.4892(8) 0.4216(9) 0.314(1) 0.278(1) 0.340(1) 0.4471(9) 0.9169(8) 1.038(1) 1.126(1) 1.096(1) 0.980(1) 0.890(1) 0.7802(8) 0.6878(9) 0.661(1) 0.733(1) 0.825(1) 0.8529(9) 0.7050(9) 0.672(1) 0.599(1) 0.564(1) 0.597(1) 0.669(1) 0.9488(8) 1.004(1) 1.121(1) 1.174(1) 1.120(1) 1.004(1)

0.1577(1) 0.3307(1) 0.3032(1) 0.1235(2) 0.5037(2) 0.0198(7) 0.0094(7) 0.4116(7) 0.3569(7) 0.2447(9) 0.2373(8) 0.6568(6) 0.3204(6) 0.0783(9) 0.0802(9) 0.3793(8) 0.3469(8) 0.2877(9) 0.2640(9) 0.4845(7) 0.5628(8) 0.5105(9) 0.3908(8) 0.3817(7) 0.3070(8) 0.3204(8) 0.2333(9) 0.249(1) 0.351(1) 0.438(1) 0.4210(9) 0.0645(8) 0.116(1) 0.069(1) − 0.025(1) − 0.080(1) − 0.035(1) 0.0586(8) 0.0740(9) 0.019(1) − 0.058(1) − 0.072(1) − 0.0154(9) 0.6019(9) 0.685(1) 0.759(1) 0.745(1) 0.666(1) 0.591(1) 0.5939(8) 0.693(1) 0.758(1) 0.724(1) 0.628(1) 0.560(1)

0.23998(9) 0.33672(8) 0.16402(8) 0.3027(2) 0.2328(2) 0.2817(6) 0.0521(5) 0.3065(5) 0.5321(5) − 0.0163(5) 0.0894(5) 0.4748(5) 0.4397(5) 0.2707(7) 0.1256(7) 0.3156(6) 0.4556(7) 0.0533(7) 0.1191(6) 0.3446(6) 0.4397(6) 0.4897(7) 0.4228(6) 0.3329(6) 0.2415(6) 0.2088(6) 0.1330(7) 0.1026(7) 0.1479(8) 0.2233(8) 0.2554(7) 0.2439(6) 0.2766(7) 0.2258(9) 0.150(1) 0.117(1) 0.1662(9) 0.3995(6) 0.4521(7) 0.5222(8) 0.5334(8) 0.4837(8) 0.4158(7) 0.2132(7) 0.2834(7) 0.2678(8) 0.1768(8) 0.1072(9) 0.1229(8) 0.2287(6) 0.3003(8) 0.2898(9) 0.2137(9) 0.142(1) 0.1497(8)

2.65(3) 2.37(3) 2.62(3) 2.79(6) 2.78(6) 6.2(2) 6.3(2) 4.7(2) 5.7(2) 7.1(3) 6.0(2) 4.1(2) 4.4(2) 3.8(2) 4.0(3) 3.3(2) 3.3(2) 4.0(3) 3.7(3) 2.4(2) 2.9(2) 3.8(2) 2.9(2) 2.5(2) 2.4(2) 2.6(2)* 3.4(2)* 4.3(2)* 4.7(3)* 4.6(2)* 3.6(2)* 3.0(2)* 4.3(2)* 5.8(3)* 7.4(4)* 8.2(4)* 5.6(3)* 3.1(2)* 3.7(2)* 4.7(3)* 4.7(3)* 4.5(2)* 3.8(2)* 3.3(2)* 4.3(2)* 5.3(3)* 5.2(3)* 5.7(3)* 4.8(3)* 3.2(2)* 5.0(3)* 6.4(3)* 6.4(3)* 7.2(4)* 5.6(3)*

standard deviations in parentheses. indicate atoms that were refined isotropically. Anisotropically refined atoms are given in the form of the isotropic equivalent displacement parameter defined as: (4/ 3)*[a2 *B(1,1) + b2 *B(2,2) + c2 *B(3,3) + ab(cos g )*B(1,2) + ac(cos b)*B(1,3) + bc(cos a)*B(2,3)].

b Asterisks

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˚ ) and Angles (deg) in PhCCo3 (CO)7 (bpcd) (2) and Table IV. Selected Bond Distances (A 2 1 — Co3 (CO)6 [m 2 -h : h -(Ph)C C(PPh2 )C(O)CH2 C(O)](m 2 -PPh − 2) (3)a PhCCo3 (CO)7 (bpcd) (2) Bond distances Co(1) — Co(2) Co(1) — P(1) Co(1) — C(1) Co(1) — C(16) Co(2) — C(1) Co(2) — C(3) Co(2) — C(16) Co(3) — C(5) Co(3) — C(7) O(7) — C(7) O(14) — C(14) C(11) — C(15) C(13) — C(14)

2.522(4) 2.239(6) 1.91(2) 1.92(2) 1.94(2) 1.69(2) 1.92(2) 1.74(3) 2.25(2) 1.26(2) 1.21(3) 1.33(3) 1.50(3)

Co(1) — Co(3) Co(1) — P(2) Co(1) — C(7) Co(2) — Co(3) Co(2) — C(2) Co(2) — C(4) Co(3) — C(4) Co(3) — C(6) Co(3) — C(16) O(12) — C(12) C(11) — C(12) C(12) — C(13) C(14) — C(15)

2.511(4) 2.200(6) 1.66(2) 2.415(4) 1.70(2) 2.03(2) 1.74(3) 1.64(3) 1.91(2) 1.19(3) 1.50(3) 1.50(3) 1.45(3)

Bond angles Co(2) — Co(1) — Co(3) Co(2) — Co(1) — P(2) Co(3) — Co(1) — P(2) P(1) — Co(1) — C(1) P(1) — Co(1) — C(16) C(1) — Co(1) — C(7) C(1) — Co(2) — C(4) Co(1) — Co(3) — Co(2) C(4) — Co(3) — C(16) Co(1) — P(2) — C(15) Co(1) — C(1) — O(1) Co(2) — C(4) — Co(3) Co(3) — C(4) — O(4) Co(1) — C(7) — O(7)

57.4(1) 115.1(2) 145.2(2) 85.3(7) 171.1(7) 156(1) 147(1) 61.6(1) 88(1) 103.6(6) 143(2) 79(1) 148(2) 161(2)

Co(2) — Co(1) — P(1) Co(3) — Co(1) — P(1) P(1) — Co(1) — P(2) P(1) — Co(1) — C(7) P(2) — Co(1) — C(16) Co(1) — Co(2) — Co(3) C(1) — Co(2) — C(16) C(4) — Co(3) — C(7) Co(1) — P(1) — C(11) Co(1) — C(1) — Co(2) Co(2) — C(1) — O(1) Co(2) — C(4) — O(4) Co(1) — C(7) — Co(3) Co(3) — C(7) — O(7)

124.9(2) 123.4(2) 89.6(2) 88.8(7) 98.9(7) 61.1(1) 91.4(9) 157.6(9) 102.7(6) 82.0(8) 134.(2) 133.(2) 78.4(8) 120.(1)

Co3 (CO)6 [m 2 -h 2 : h 1 -(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3) Bond distances Co(1) — Co(2) Co(1) — P(1) Co(2) — Co(3) Co(2) — C(11) Co(3) — P(2) O(12) — C(12) C(11) — C(12) C(12) — C(13) C(14) — C(15)

2.582(1) 2.131(3) 2.677(2) 2.05(1) 2.207(3) 1.221(9) 1.46(1) 1.51(1) 1.49(1)

Co(1) — Co(3) Co(1) — C(16) Co(2) — P(2) Co(2) — C(15) Co(3) — C(16) O(14) — C(14) C(11) — C(15) C(13) — C(14) C(15) — C(16)

2.399(2) 1.93(1) 2.272(3) 2.125(9) 2.027(9) 1.21(1) 1.45(1) 1.51(1) 1.46(1)

Bond angles Co(2) — Co(1) — Co(3) P(1) — Co(1) — C(2) Co(1) — Co(2) — Co(3) C(11) — Co(2) — C(15) P(2) — Co(3) — C(16) Co(2) — C(15) — C(16) a Numbers

64.89(5) 101.2(4) 54.25(5) 40.5(3) 83.5(2) 102.5(6)

P(1) — Co(1) — C(1) P(1) — Co(1) — C(16) Co(3) — Co(2) — P(1) Co(1) — Co(3) — Co(2) Co(1) — P(1) — Co(2)

in parentheses are estimated standard deviations in the least significant digits.

110.8(4) 132.7(2) 90.11(8) 60.86(5) 71.7(1)

CO Substitution in PhCCo3 (CO)9 by bpcd

233

Fig. 1. ORTEP diagram of the non-hydrogen atoms of (A) PhCCo3 (CO)7 (bpcd) (2) and (B) Co3 (CO)6 [m 2 -h 2 : h 1 -(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3) showing the thermal ellipsoids at the 50% probability level. The phenyl groups associated with the phosphorus atoms have been omitted for clarity.

The internal polyhedron of PhCCo3 (CO)7 (bpcd) consists of a triangular array of cobalt atoms that is capped by a m 3 -benzylidyne ligand. The Co — Co bond lengths in PhCCo3 (CO)7 (bpcd) are clearly asymmetric in length, ranging in distance from 2.415(4) to 2.522(1) ˚ . The two longer, pairwise equivalent (assuming idealA ized symmetry) Co(1) — Co(2) and Co(1) — Co(3) bond ˚ , respectively, are the lengths of 2.522(4) and 2.511(4) A result of bpcd-induced perturbations within the metal core of PhCCo3 (CO)7 (bpcd). The unique Co(2) — Co(3) ˚ is ca. 0.1 A ˚ shorter than bond distance of 2.415(4) A the connecting Co — Co bonds bearing the bpcd ligands. The replacement of a CO ligand(s) by a larger phosphine ligand(s) promotes metal core deformations in a variety of polynuclear metal compounds. The mean distance ˚ , well within the for these metal–metal bonds is 2.483 A range expected of the Co — Co single-bond designation, and in good agreement with the X-ray data reported for PhCCo3 (CO)7 (bma) [10]. Cluster 2 exhibits three equatorially bound bridging CO groups, which is in agreement with the observation of m 2 -CO groups in the IR and 13 C NMR spectrum of PhCCo3 (CO)7 (bpcd). The cobalt-

carbon bond distances for the three bridging CO groups ˚ , with the mean distance range from 1.66(2) to 2.25(2) A ˚ . The dispersal of the increased electron density of 1.92 A at Co(1) due to the coordinated bpcd ligand is facilitated by presence of these m 2 -CO groups, a phenomenon that is common in phosphine-substituted tetrahedrane clusters [30]. The Co — Co and Co — m 2 — C bond lengths in PhCCo3 (CO)7 (bpcd) are summarized below.

Bott, Shen, and Richmond

234

The Co(1) — P(1) and Co(1) — P(2) bond distances ˚ , respectively, are within of 2.239(6) and 2.200(6) A acceptable distances for a Co-PR3 bond [31]. The observed bond angle of 89.2(2)8 for the P(2) — Co(1) — P(1) linkage agrees well the 90.5(1)8 bond angle found for the same atoms in the cluster PhCCo3 (CO)7 (bma) that possesses a chelating bma ligand in the solid state [10]. The bpcd ligand is unexceptional, showing a nor˚ for the mal carbon–carbon double bond of 1.33(3) A — C(11) C(15) atoms [32]. The remaining bond distances and bond angles associated with the diphosphine ligand fall within in standard distances and angles and do not require any comment. The ORTEP diagram of Co3 (CO)6 [m 2 -h 2 ,h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) confirms the presence of the phosphido ligand and the coupling of the benzylidyne and 4-cyclopenten-1,3-dione moiety in the product. The Co — Co bond distances in 3 range from ˚ [Co(2) — Co(3)], 2.399(2) [Co(1) — Co(3)] to 2.677(2) A and are comparable with cobalt–cobalt single bonds found in other polynuclear cobalt clusters [33]. The 2.131(3) ˚ bond lengths found for m 2 -P-Co(1) and and 2.272(3) A m 2 -P-Co(2), respectively, along with the 71.7(1)8 bond angle formed by the atoms Co(1) — P(1) — Co(2), are in good agreement with the values found in other phosphidobridged cobalt complexes [34]. The Co(3) — P(2) bond ˚ in 3 closely matches the cobalt– distance of 2.207(3) A phosphorus bond lengths reported in cluster 2 (vide supra) and other phosphine-substituted cobalt clusters [31]. The two cobalt-benzylidene bond lengths [Co(1) — C(16) and ˚ and Co(3) — C(16)] exhibit a mean distance of 1.99 A the newly formed C(16) — C(15) bond shows a distance ˚ , consistent with its single-bond nature. of 1.46(1) A Coordination of the bpcd p bond to Co(2) leads to a slight increase in the C(11) — C(15) bond distance relative to the uncoordinated bpcd p bond in cluster 2. The ˚ in cluster 3, C(11) — C(15) bond length of 1.45(3) A ˚ longer than that in 2 or the free bpcd which is ca. 0.12 A ligand, is not atypical of for this class of compounds. The acute angle of 40.5(3)8 formed by C(15) — Co(2) — C(11) falls within an acceptable value exhibited by many compounds having a coordinated p bond or metallacyclopropane moieties [35]. All other bond distances and angles are unexceptional, requiring no comment.

CONCLUSIONS The ligand substitution reaction of PhCCo3 (CO)9 with the redox-active diphosphine ligand bpcd yields

the new clusters PhCCo3 (CO)7 (bpcd) and Co3 (CO)6[m 2 h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ). The former cluster is a precursor to the latter cluster, as demonstrated by kinetic studies. The molecular structure of each of these clusters are established by X-ray crystallography. The isolation and characterization of Co3 (CO)6 [m 2 -h 2 ,h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) confirms the ease by which the coordinated bpcd ligand in PhCCo3 (CO)7 (bpcd) undergoes facile degradation by P — C cleavage and reductive coupling with the cobalt-benzylidyne ligand. This reactivity observed here is similar to the behavior of the related ligand bma, which has been previously reported us. ACKNOWLEDGMENT We are grateful the Robert A. Welch Foundation (B1039-MGR) for continued financial support. Textual presentations of the crystallographic experimental details and listings of crystallographic data, bond distances, bond angles, and hydrogen positional and thermal parameters for clusters PhCCo3 (CO)7 (bpcd) (2) to Co3 (CO)6 [m 2 -h 2 : h 1 -C(Ph)C — C(PPh2 )C(O)CH2 C(O)](m 2 -PPh2 ) (3). REFERENCES 1. Watson, W. H.; Nagl, A.; Hwang, S.; Richmond, M. G. J. Organomet. Chem. 1993, 445, 163. 2. Yang, K.; Bott, S. G.; Richmond, M. G. J. Organomet. Chem. 1993, 454, 273. 3. Don, M.-J.; Richmond, M. G.; Watson, W. H.; Krawiec, M.; Kashyap, R. P. J. Organomet. Chem. 1991, 418, 231. 4. Yang, K.; Chien, H.-S.; Richmond, M. G. J. Mol. Catal. 1994, 88, 159. 5. Schulman, C. L.; Richmond, M. G.; Watson, W. H.; Nagl, J. Organomet. Chem. 1989, 368, 367. 6. Richmond, M. G.; Kochi, J. K. Inorg. Chem. 1987, 26, 541. 7. Osella, D.; Milone, L.; Nervi, C.; Ravera, M. J. Organomet. Chem. 1995, 488, 1. 8. (a) Colbran, S.; Robinson, B. H.; Simpson, J. J. Chem. Soc. Chem. Commun. 1982, 1361; (b) Colbran, S.; Robinson, B. H.; Simpson, J. Organometallics 1983, 2, 952; (c) Colbran, S.; Hanton, L. R.; Robinson, B. H.; Robinson, W. T.; Simpson, J. J. Organomet. Chem. 1987, 330, 415; (d) Worth, G. H.; Robinson, B. H.; Simpson, J. J. Organomet. Chem. 1990, 387, 337; (e) Worth, G. H.; Robinson, B. H.; Simpson, J. Organometallics 1992, 11, 501, 3863. 9. McAdam, C. J.; Duffy, N. W.; Robinson, B. H.; Simpson, J. Organometallics 1996, 15, 3935 and references therein. 10. (a) Yang, K.; Smith, J. M.; Bott, S. G.; Richmond, M. G. Inorg. Chim. Acta 1993, 212, 1; (b) Yang, K.; Smith, J. M.; Bott, S. G.; Richmond, M. G. Organometallics 1993, 12, 4779. 11. (a) Fenske, D.; Becher, H. J. Chem. Ber. 1974, 107, 117; (b) Fenske, D.; Becher, H. J. Chem. Ber. 1975, 108, 2115; (c) Becher,

CO Substitution in PhCCo3 (CO)9 by bpcd

12.

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