Diyne and phosphorus-carbon bond reactivity in the reaction between [Co2(CO)6]2(PhC4Ph) and 2,3-Bis(diphenylphosphino)maleic anhydride (bma). Syntheses, molecular orbital properties, and x-ray diffraction structures of Co2(CO)4[μ-η2:η 2:η1:η1

Article abstract of DOI:10.1021/om950988j

Thermolysis (>80°C) of the diyne complex [Co₂(CO)₆]₂(PhC₄Ph) (1) with 2,3-bis(diphenylphosphino)maleic anhydride (bma) affords the new compounds Co₂(CO)₄[μ-η²:η ²:η¹:η¹-(Z)-Ph ₂P(Ph)C=C(PhC₂)C=C(Ph₂P)C(O)OC(O)] (3), Co₂(CO)₂(bma)₂ (4), and Co₂(CO)₂(bma)[μ-C=C(Ph ₂P)C(O)OC(O)](μ₂-Ph₂P) (5) in low yields, while [Co₂(CO)₆]₂(PhC₄Ph) reacts with added bma in either refluxing CH₂Cl₂ or in the presence of Me₃NO to give the thermally sensitive complex [Co₂(CO)₄(bma)(PhC₄Ph)Co₂(CO) ₆] (2). Independent experiments reveal that 3 arises from 2 by loss of the Co₂(CO)₆ group, coupled with P-C bond cleavage and diyne functionalization by the transient phosphido and maleic anhydride moieties, and the reaction between 2 and excess bma leads to both 4 and 5, with 5 originating from 4. The kinetics for the reaction of 4 to 5 have been measured by UV-vis spectroscopy, and on the basis of the first-order rate constants and the activation parameters (ΔH^? = 27.0 ± 0.6 kcal mol^-1 and ΔS? = 1.0 ± 0.3 eu), a mechanism involving dissociative CO loss as the rate-determining step is presented. Binuclear 4 is extremely photosensitive and is converted cleanly to 5 by 366 nm light with a quantum efficiency of 0.0043. Compounds 2-5 have been isolated and characterized in solution by IR and ³¹P NMR spectroscopy. The solid-state structures of 3-5 have been established by X-ray crystallography. The X-ray structure of 4 reveals the presence of two bma ligands that are attached to the Co₂(CO)₂ unit in a head-to-tail fashion via the PPh₂ groups and maleic anhydride π bond, and the X-ray structure of 5 supports the existence of a μ₂-PPh₂ moiety and a noncomplexed maleic anhydride π bond, the result of P-C(maleic anhydride) bond activation. The redox properties of 2-5 were explored by cyclic voltammetry in CH₂Cl₂, and the oxidation/reduction behavior is discussed with respect to redox stabilization that each complex experiences, as modulated by the bma ligand(s). The orbital composition of the HOMO and LUMO levels in 3-5 has been studied by extended Hu?ckel calculations, and the data are discussed relative to the observed electrochemistry. A plausible mechanism for the activation of Co₂(CO)₂(bma)₂ and the formation of Co₂(CO)₂(bma)[μ-C=C(Ph ₂P)C(O)OC(O)](μ₂-Ph₂P) is presented.

Full text of DOI:10.1021/om950988j

Organometallics 1996, 15, 2227-2236
2227
Diyn e a n d P h osp h or u s-Ca r bon Bon d Rea ctivity in th e
Rea ction betw een [Co2(CO)6]2(P h C4P h ) a n d
2,3-Bis(d ip h en ylp h osp h in o)m a leic An h yd r id e (bm a ).
Syn th eses, Molecu la r Or bita l P r op er ties, a n d X-r a y
Diffr a ction Str u ctu r es of
Co2(CO)4[µ-η2:η2:η1:η1-(Z)-P h 2P (P h )CdC(P h C2)-
CdC(P h 2P )C(O)OC(O)], Co2(CO)2(bm a )2‚CH2Cl2, a n d
Co2(CO)2(bm a )[µ-CdC(P h 2P )C(O)OC(O)](µ2-P h 2P )‚C6H14
Kaiyuan Yang, J effery A. Martin, Simon G. Bott,* and Michael G. Richmond*
Center for Organometallic Research and Education, Department of Chemistry,
University of North Texas, Denton, Texas 76203
Received December 27, 1995X
Thermolysis (>80 °C) of the diyne complex [Co2(CO)6]2(PhC4Ph) (1) with 2,3-bis(diphe-
nylphosphino)maleic anhydride (bma) affords the new compounds Co2(CO)4[µ-η2:η2:η1:η1-
(Z)-Ph2P(Ph)CdC(PhC2)CdC(Ph2P)C(O)OC(O)] (3), Co2(CO)2(bma)2 (4), and Co2(CO)2(bma)[µ-
CdC(Ph2P)C(O)OC(O)](µ2-Ph2P) (5) in low yields, while [Co2(CO)6]2(PhC4Ph) reacts with
added bma in either refluxing CH2Cl2 or in the presence of Me3NO to give the thermally
sensitive complex [Co2(CO)4(bma)(PhC4Ph)Co2(CO)6] (2). Independent experiments reveal
that 3 arises from 2 by loss of the Co2(CO)6 group, coupled with PsC bond cleavage and
diyne functionalization by the transient phosphido and maleic anhydride moieties, and the
reaction between 2 and excess bma leads to both 4 and 5, with 5 originating from 4. The
kinetics for the reaction of 4 to 5 have been measured by UV-vis spectroscopy, and on the
basis of the first-order rate constants and the activation parameters (∆Hq ) 27.0 ( 0.6 kcal
mol-1 and ∆Sq ) 1.0 ( 0.3 eu), a mechanism involving dissociative CO loss as the rate-
determining step is presented. Binuclear 4 is extremely photosensitive and is converted
cleanly to 5 by 366 nm light with a quantum efficiency of 0.0043. Compounds 2-5 have
been isolated and characterized in solution by IR and 31P NMR spectroscopy. The solid-
state structures of 3-5 have been established by X-ray crystallography. The X-ray structure
of 4 reveals the presence of two bma ligands that are attached to the Co2(CO)2 unit in a
head-to-tail fashion via the PPh2 groups and maleic anhydride π bond, and the X-ray
structure of 5 supports the existence of a µ2-PPh2 moiety and a noncomplexed maleic
anhydride π bond, the result of PsC(maleic anhydride) bond activation. The redox properties
of 2-5 were explored by cyclic voltammetry in CH2Cl2, and the oxidation/reduction behavior
is discussed with respect to redox stabilization that each complex experiences, as modulated
by the bma ligand(s). The orbital composition of the HOMO and LUMO levels in 3-5 has
been studied by extended Hu¨ckel calculations, and the data are discussed relative to the
observed electrochemistry. A plausible mechanism for the activation of Co2(CO)2(bma)2 and
the formation of Co2(CO)2(bma)[µ-CdC(Ph2P)C(O)OC(O)](µ2-Ph2P) is presented.
In tr od u ction
Co2(alkyne) core have found considerable utility in the
construction of complex carbocyclic ring systems and the
stereocontrolled formation of carbon-carbon bonds via
the Pauson-Khand and Nicholas reactions, respec-
tively.2,3
The coordination and functionalization of alkynes by
mononuclear transition-metal complexes have been
thoroughly examined over the last several years. Ex-
amples of natural product syntheses from elaborate
alkyne cyclooligomerization sequences and alkyne cou-
pling with CO2 and isocyanate feedstocks to give com-
modity chemicals represent just two of the many
reactions that proceed from a bona fide metal-alkyne
intermediate.1 Of the broad range of binuclear M2-
(alkyne) complexes that have been prepared and whose
reactivities have been explored, compounds based on the
(1) (a) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry,
University Science Books: Mill Valley, CA, 1987. (b) Harrington, P.
J . Transition Metals in Total Synthesis; Wiley: New York, 1990. (c)
Lukehart, C. M. Fundamental Transition Metal Organometallic Chem-
istry; Brooks/Cole: Monterey, CA, 1985. (d) Adams, R. D. Chem. Soc.
Rev. 1994, 335.
(2) (a) Pauson, P. L. Tetrahedron 1985, 41, 5855. (b) Krafft, M.; Scott,
I. L.; Romero, R. H.; Feibelmann, S.; Van Pelt, C. E. J . Am. Chem.
Soc. 1993, 115, 7199. (c) J amison, T. F.; Shambayati, S.; Crowe, W.
E.; Schreiber, S. L. J . Am. Chem. Soc. 1994, 116, 5505.
X Abstract published in Advance ACS Abstracts, April 1, 1996.
S0276-7333(95)00988-5 CCC: $12.00 © 1996 American Chemical Society

2228 Organometallics, Vol. 15, No. 9, 1996
Yang et al.
Recently, we reported our results on the alkyne com-
pounds Co2(CO)4(bma)(µ-RC2R′)4 and Co2(CO)4(bmf)(µ-
PhC2H)5 (where bmf ) 3,4-bis(diphenylphosphino)-5-
methoxy-2(5H)-furanone; R ) Ph, R′ ) Ph, H), where
we have observed both alkyne-bma ligand coupling and
attack on the alkyne moiety by the diphosphine ligand
(eqs 1-3).6
Herein it is shown that only one bma ligand may be
substituted on 1 to give the thermally sensitive bi-
nuclear compound [Co2(CO)4(bma)(PhC4Ph)Co2(CO)6]
(2). Evidence demonstrating that 2 is a key intermedi-
ate leading to 3 and 4 is presented, along with the
mechanistic results dealing with the formation of the
bridging phosphido compound 5 from 4.
Resu lts a n d Discu ssion
I. Syn th esis a n d Sp ectr oscop ic Da ta for Com -
p ou n d s 2-5. The diyne compound 1 reacts with an
equimolar amount of bma in refluxing CH2Cl2 to yield
the monosubstituted compound [Co2(CO)4(bma)(PhC4-
Ph)Co2(CO)6] (2), as the sole product isolated by column
chromatography. Maximum yields on the order of 40-
50% (isolated) could be achieved when the reaction was
monitored by IR spectroscopy. The reaction must be
terminated before the decomposition of 2 becomes too
extensive. Diyne activation using Me3NO11 also af-
forded the same product as that from the thermolysis
reaction, and in no case was any evidence obtained for
the introduction of a second bma ligand in 2. Attempts
to force a second bma ligand on 2 thermally led to
decomposition and the formation of compounds 3-5
(vide infra). The loss of the diyne ligand during the
introduction of multiple phosphine ligands is consistent
with the observations recently found by Robinson and
co-workers.10 Equation 4 shows the reaction leading to
2.
As an extension of our work on the reactivity of the
alkyne and bma ligands in Co2(CO)4(bma)(alkyne) com-
plexes we next sought to explore the substitution
chemistry and reactivity of the related diyne complex
[Co2(CO)6]2(PhC4Ph) (1) with diphosphine ligands. Cur-
rent interest in diyne compounds stems from (1) the
possibility of producing novel redox materials as a result
of cooperative electronic interactions between different
metal centers that can be tethered to the diyne moiety,7
(2) the use of such compounds as precursors for the
synthesis of metal-containing polymeric materials,8 and
(3) studies dealing with carbon-carbon bond reactivity
at polynuclear clusters.9 Accordingly, we report our
data on the reaction of [Co2(CO)6]2(PhC4Ph) with added
bma, which to our knowledge is the first report on the
substitution chemistry of this genre of compound.10
(3) (a) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207. (b) Caffyn, A.
J . M.; Nicholas, K. M. J . Am. Chem. Soc. 1993, 115, 6438. (c) Schreiber,
S. L.; Sammakia, T.; Crowe, W. E. J . Am. Chem. Soc. 1986, 108, 3128.
(d) Schreiber, S. L.; Klimas, M. T.; Sammakia, T. J . Am. Chem. Soc.
1987, 109, 5749.
(4) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1994,
13, 376, 3788.
Compound 2 was isolated by column chromatography
over silica (-78 °C), although with considerable decom-
position on the chromatographic support. The use of
alumina or Florisil did little to improve the situation.
The decomposition observed here presumably arises
(5) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1995,
14, 4977.
(6) The bmf compound depicted in eq 3 exists as a racemic mixture,
with one enantiomer shown for clarity. See ref 5 for details.
(7) (a) Worth, G. H.; Robinson, B. R.; Simpson, J . Organometallics
1992, 11, 501. (b) Osella, D.; Gambino, O.; Nervi, C.; Ravera, M.; Russo,
M. V.; Infante, G. Gazz. Chim. Ital. 1993, 123, 579. (c) Deeming, A. J .;
Felix, M. S. B.; Nuel, D. Inorg. Chim. Acta 1993, 213, 3. (d) Arnold, D.
P.; Heath, G. A. J . Am. Chem. Soc. 1993, 115, 12197. (e) See also:
Worth, G. H.; Robinson, B. R.; Simpson, J . J . Organomet. Chem. 1990,
387, 337.
(8) (a) Magnus, P.; Becker, D. P. J . Chem. Soc., Chem. Commun.
1985, 640. (b) J ohnson, B. F. G.; Lewis, J .; Raithby, P. R.; Wilkinson,
D. A. J . Organomet. Chem. 1991, 408, C9. (c) Housecroft, C. E.;
J ohnson, B. F. G.; Khan, M. S.; Lewis, J .; Raithby, P. R.; Robson, M.
E.; Wilkinson, D. A. J . Chem. Soc., Dalton Trans. 1992, 3171.
(9) (a) Corrigan, J . F.; Doherty, S.; Taylor, N. J .; Carty, A. J .
Organometallics 1992, 11, 3160; 1993, 12, 1365. (b) Corrigan, J . F.;
Taylor, N. J .; Carty, A. J . Organometallics 1994, 13, 3778. (c) Adams,
C. J .; Bruce, M. I.; Horn, E.; Tiekink, E. R. T. J . Chem. Soc., Dalton
Trans. 1992, 1157. (d) Adams, C. J .; Bruce, M. I.; Horn, E.; Skelton,
B. W.; Tiekink, E. R. T.; White, A. H. J . Chem. Soc., Dalton Trans.
1993, 3299, 3313.
(10) The reaction of monodentate phosphine ligands with [Co2-
(CO)6]2(diyne) compounds and the redox chemistry of the resulting
products have recently been examined. In this particular work only
one of the two Co2(CO)6 units could be substituted by phosphines before
decomposition was observed: Robinson, B. Private communication.
(11) (a) Koelle, U. J . Organomet. Chem. 1977, 133, 53. (b) Albers,
M. O.; Coville, N. Coord. Chem. Rev. 1984, 53, 227.

Diyne and Phosphorus-Carbon Bond Reactivity
Organometallics, Vol. 15, No. 9, 1996 2229
Ta ble 1. IR a n d 31P NMR Sp ectr oscop ic Da ta for
pseudoequatorial sites at the Co2(CO)4(bma) unit.15,16
A chelating bma ligand is expected to exhibit two,
inequivalent 31P resonances over the range of δ 50-70,
as found in the related chelating isomers of Co2(CO)4-
(bma)(RC2R′) (where R * R′).4,17
2-5
a
compd
IR (cm-1
)
31P NMR (δ)b
24.49 (2P)
2
2088 (s)
2054 (vs)
2029 (s)
2020 (s)
1983 (m)
Thermolysis of 1 with bma (2.0 mol equiv) in either
1,2-dichloroethane or toluene for 1.5 h afforded a
substantial amount of decomposition material and at
least five new products, as judged by TLC analysis.
Column chromatography of these materials allowed for
the isolation of the new dinuclear compounds 3-5. It
should be noted that the presence of compound 2 was
not observed by TLC analysis at any point during this
reaction. Moreover, substituting 2 in place of 1 and
repeating the same reaction gave a TLC plate identical
with that obtained using 1 as a starting material,
underscoring the extreme thermal sensitivity of 2.
Equation 5 depicts the reaction leading to compounds
3-5.
1819 (w, asym bma CdO)
1767 (m, sym bma CdO)
2050 (s)
3
22.68 (1P)
35.47 (1P)
2032 (vs)
2015 (s)
1980 (sh)
1812 (m, asym bma CdO)
1747 (s, sym bma CdO)
1989 (vs)
4
24.56 (2P)
1808 (sh, asym bma CdO)
1783 (m, asym bma CdO)
1740 (s, sym bma CdO)
2006 (s)
5c
34.50 (dd, broad, 1P,
J P-P ) 92, J P-P ) 30)
1985 (vs)
1810 (sh, asym bma CdO) 39.93 (quartet, broad, 1P,
J P-P ≈ 30)
1780 (m, asym bma CdO)
1743 (vs, sym bma CdO)
60.60 (s, 1P)
165.53 (d, µ2-PPh2,
J P-P ) 92)
a
b
All IR spectra were recorded in CH2Cl2. All 31P NMR spectra
were recorded at room temperature in CH2Cl2, unless otherwise
stated, with coupling constants expressed in Hz. c 31P NMR
spectrum recorded at -90 °C.
from the support-induced opening of the anhydride ring
of 2.12 To our surprise 2 is much more thermally
sensitive than its corresponding diphenylacetylene ana-
logue Co2(CO)4(bma)(PhC2Ph) (bridging isomer),4 with
noticeable decomposition observed over the course of
several days at room temperature. J ohnson, Lewis, and
co-workers have also reported that related [Co2(CO)6]2-
(diyne) compounds slowly decompose in solution to
uncharacterized materials.8b,c Such behavior may be
attributed to the steric hindrance that results from the
internal distortion inherent in the Co2C2 cores of this
genre of compound.8
2 was characterized by IR and 31P NMR spectroscopy,
with the spectral data shown in Table 1. Proof for the
fact that only one bma ligand is present in 2 derives
from the IR spectrum, where the observed high-
frequency ν(CO) bands at 2088 (s) and 2054 (vs) cm-1
may be assigned to the Co2(CO)6 unit, on the basis of
the spectral similarity to other Co2(CO)6(alkyne) com-
pounds.8,13 Unequivocal assignment of the terminal CO
groups associated with the Co2(CO)4(bma) moiety cannot
be made at this point, due to overlap with the Co2(CO)6
moiety; however, we note that the ν(CO) bands at 2029
(s) and 1983 (m) cm-1 are consistent with the frequen-
cies reported for other bridged Co2(CO)4(P-P)(alkyne)
compounds.4,14 The most revealing proof for the orien-
tation of the bma ligand in 2 comes from the single,
high-field 31P resonance at δ 24.49, which is congruent
only with a bridging bma ligand situated about the
The identities of 3-5 have been ascertained by
spectroscopic analysis (Table 1) and X-ray crystal-
lography (vide infra). Compound 3 is unremarkable in
comparison to the diphenylacetylene analogue Co2(CO)4-
[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC(Ph)C)C(Ph2P)C(O)OC-
(O)] that we have recently characterized.4 The pendant
PhCtC moiety that exists in 3 derives from the formal
loss of the Co2(CO)6 fragment that was present in 2. 4
is of interest, as it is best viewed as a Co2(CO)2 unit
(12) Yang, K.; Smith, J . M.; Bott, S. G.; Richmond, M. G. Organo-
metallics 1993, 12, 4779.
(13) (a) Happ, B.; Bartik, T.; Zucchi, C.; Rossi, M. C.; Ghelfi, F.; Pa´lyi,
G.; Va´radi, G.; Szalontai, G.; Horva´th, I. T.; Chiesi-Villa, A.; Guastini,
C. Organometallics 1995, 14, 809. (b) Bor, G.; Kettle, S. F. A.;
Stanghellini, P. L. Inorg. Chim. Acta 1976, 18, L18.
(14) (a) Sappa, E.; Predieri, G.; Marko, L. Inorg. Chim. Acta 1995,
228, 147. (b) Crow, J . P.; Cullen, W. R. Inorg. Chem. 1971, 10, 2165.
(c) Chia, L. S.; Cullen, W. R.; Franklin, M.; Manning, A. R. Inorg. Chem.
1975, 14, 2521.
(15) (a) Garrou, P. E. Chem. Rev. 1981, 81, 229. (b) Richmond, M.
G.; Kochi, J . K. Organometallics 1987, 6, 254. (c) Churchill, M. R.;
Lashewycz, R. A.; Shapley, J . R.; Richter, S. I. Inorg. Chem. 1980, 19,
1277.
(16) Cunninghame, R. G.; Hanton, L. R.; J ensen, S. D.; Robinson,
B. H.; Simpson, J . Organometallics 1987, 6, 1470.
(17) Yang, K.; Bott, S. G.; Richmond, M. G. J . Organomet. Chem.,
in press.

2230 Organometallics, Vol. 15, No. 9, 1996
Yang et al.
Ta ble 2. Exp er im en ta l Ra te Con sta n ts for th e
that possesses a head-to-tail ligation of two bma ligands.
Consistent with the idealized C2v symmetry in 4 is the
presence of one intense ν(CO) band for the two terminal
carbonyl groups, in addition to the single 31P NMR
resonance at δ 24.56. A chelating bma ligand would not
be expected to display such a high-field 31P resonance
in 4 in the absence of any other effects. However, as
found in related systems,18 the coordination of the
maleic anhydride π bond to the dimetal fragment leads
to a greater shielding of the 31P nuclei and the observed
upfield shift. The identity of the phosphido-bridged
compound 5 is readily confirmed by the 31P NMR
spectrum, on the basis of four 31P resonances, with the
µ2-PPh2 group confidently assigned to the chemical shift
appearing at δ 165.53.15a,19 Unequivocal assignment of
the three remaining 31P resonances is problematic, as
the two resonances at δ 34.50 and 39.93, which exhibit
phosphorus-phosphorus coupling, and the µ2-PPh2
group that comprise the ABX spin system (ignoring the
remaining phosphine group) afford a “deceptively simple”
NMR spectrum.20 Accordingly, no specific assignments
are presented here.
Rea ction of Co2(CO)2(bm a )2 (4) To Give
Co2(CO)2(bm a )[µ-CdC(P h 2P )C(O)OC(O)](µ2-P h 2P )
(5)a
entry no.
T, °C
104kobsd, s-1
1
2
3
4
5
6
7
77.2
82.2
82.2
82.2
87.4
92.7
97.0
1.84 ( 0.05
3.28 ( 0.14
1.98 ( 0.06b
3.20 ( 0.16c
5.83 ( 0.23
9.80 ( 0.39
14.45 ( 0.53
From 1.08 × 10-4 M Co2(CO)2(bma)2 in chlorobenzene solvent
a
by following the disappearance of the near-UV band at 326 nm.
All kinetic data quoted represent the average of two measure-
b
ments. In the presence of 1 atm of CO. c In toluene solvent.
CO inhibition, and the activation parameters ∆Hq
)
27.0 ( 0.6 kcal mol-1 and ∆Sq ) 1.0 ( 0.3 eu support
the intervention of the unsaturated intermediate Co2-
(CO)(bma)2 and the rate law12,21
rate ) k1k2[Co2(CO)2(bma)2]k-1[CO] + k2
The precursor(s) leading to complexes 3-5 was ex-
plored by using isolated samples of 2 and studying the
effect of added bma on the resulting product distribu-
tion. Thermolysis of 2 in 1,2-C2H4Cl2 in the absence of
added bma gave six products by TLC analysis, from
which compound 3 could be isolated. While the identity
of the remaining materials could not be determined due
to their low yields and decomposition upon chromato-
graphic workup, it was established that compounds 4
and 5 were not present. Treatment of 2 with excess bma
(3.0 mol equiv) at 80 °C yielded 4 and 5, along with a
small amount of decomposition. The isolated yield of
each of these compounds was ca. 15% each, and more
importantly there was no evidence for the formation of
3, underscoring the crucial role played by the added bma
in determining the product distribution starting from
2. No attempt was made to determine the fate of the
lost diyne ligand in the reactions leading to 4 and 5.
Finally, the thermolyses of pure samples of 4 were
shown to give 5 directly in good yields with only minimal
decomposition.
which, in the absence of added CO (k2 > k-1[CO]),
reduces to the commonly observed first-order expression
rate ) k1[Co2(CO)2(bma)2].
Routine reactivity studies employing 4 at room tem-
perature indicated that 5 was formed in ca. 50% yield
(isolated) when samples of 4 were stirred under fluo-
rescent room lights over a 2-day period. The possibility
of a thermally induced CO loss scenario from 4, followed
by generation of 5, is inconsistent with the kinetic data
just discussed because the extrapolated rate constant
for CO loss at room temperature is on the order of 26
days. This signals the intervention of a photochemically
promoted pathway involving 4. The importance of a
photochemically promoted pathway to 5 starting from
4 was verified by irradiating compound 4 with 366 nm
light. Here a rapid and clean conversion to 5 was
observed, with φdis ) 0.0043 being calculated. Photoly-
sis reactions conducted under CO (1 atm) were retarded
slightly, as evidenced by values of φdis ) 0.0013. Unlike
the recently reported example of near-UV-induced P-C
bond cleavage in Ru2(CO)6(bpcd) (where bpcd ) 4,5-bis-
(diphenylphosphino)-4-cyclopentene-1,3-dione), which
has been suggested to arise by homolysis of the Ru-Ru
bond, followed by P-C bond activation,18a the CO
inhibition data found here strongly suggest that CO loss
is a prerequisite for the formation of 5. Low-tempera-
ture matrix studies are presently underway with the
expectation of resolving the course of this reaction.
Scheme 1 shows the likely sequence of events for the
formation of the phosphido complex 5 from the thermal
and photochemical activation of Co2(CO)2(bma)2. Here
CO loss from 4 affords the unsaturated intermediate
Co2(CO)(bma)2, which is ideally setup for the ensuing
oxidative addition of the PsC bond. Capture of the
II. Th er m a l a n d P h otoch em ica l Da ta for th e
Con ver sion of 4 to 5. Definitive proof for the conver-
sion of 4 to 5 was obtained by measuring the rates of
the reaction in chlorobenzene via UV-vis spectroscopy
by following the decrease in the absorbance of the 326
nm near-UV band belonging to 4. The reaction exhib-
ited first-order kinetics for at least 4 half-lives over the
temperature range of 77-97 °C, and plots of ln(A∞
-
At) vs time afforded the first-order rate constants
reported in Table 2. The nature of the solvent does not
appear to be very important, as the reaction conducted
in toluene (entry 4) afforded rates that are the same,
within experimental error, as the rates obtained in
chlorobenzene. Moreover, the rate of the reaction is
slowed down by a factor of 1.7 in the presence of 1 atm
of CO (entry 3), suggesting a rate-limiting step involving
CO loss from 4. The observed unimolecular reaction,
liberated CO by Co2(CO)(bma)[µ-CdC(Ph2P)C(O)OC(O)]-
(µ2-Ph2P) then gives the phosphido complex 5.
III. X-r a y Diffr a ction Resu lts. The molecular
structures of 3-5 were determined by X-ray crystal-
lography, and all three compounds were shown to exist
as discrete molecules in the unit cell with no unusually
(18) (a) Shen, H.; Bott, S. G.; Richmond, M. G. Organometallics 1995,
14, 4625. (b) Yang, K.; Bott, S. G.; Richmond, M. G. Unpublished
results.
(19) Carty, A. J .; MacLaughlin, S. A.; Nucciarone, D. In Phosphorus-
31 NMR Spectroscopy in Stereochemical Analysis; Verkade, J . G., Quin,
L. D., Eds.; VCH: Deerfield Beach, FL, 1987; Chapter 16.
(20) Bovey, F. A. Nuclear Magnetic Resonance Spectroscopy; Aca-
demic Press: New York, 1969.
(21) (a) Atwood, J . D. Inorganic and Organometallic Reaction
Mechanisms; Brooks/Cole: Monterey, CA, 1985. (b) Darensbourg, D.
J . Adv. Organomet. Chem. 1982, 21, 113.

Diyne and Phosphorus-Carbon Bond Reactivity
Organometallics, Vol. 15, No. 9, 1996 2231
Ta ble 3. X-r a y Cr ysta llogr a p h ic a n d Da ta P r ocessin g P a r a m eter s for
Co2(CO)4[µ-η2:η2:η1:η1-(Z)-P h 2P (P h )CdC(P h C2)CdC(P h 2P )C(O)OC(O)] (3), Co2(CO)2(bm a )2‚CH2Cl2 (4), a n d
Co2(CO)2(bm a )[µ-CdC(P h 2P )C(O)OC(O)](µ2-P h 2P )‚C6H14 (5)a
3
4
5
space group
cell const
triclinic P1h
monoclinic P21/c
monoclinic P21/n
a Å
b, Å
c, Å
8.995(2)
12.068(4)
20.143(3)
81.07(2)
80.28(1)
71.81(2)
2035.2(9)
12.166(1)
22.565(2)
19.175(1)
15.297(2)
23.552(3)
15.633(2)
R, deg
â, deg
92.006(7)
107.211(9)
γ, deg
V, Å3
5260.8(8)
5380(1)
mol formula
fw
C
48H30Co2O7P2
C59H42Cl2Co2O8P4
1191.66
C64H54Co2O8P4
1192.90
898.58
formula units/cell (Z)
2
4
4
F, g cm-3
1.466
1.504
1.473
cryst size, mm3
abs coeff (µ), cm-1
λ (radiatn), Å
data collcn method
collcn range, deg
tot. no. of data collcd
no. of indep. data, I > 3σ(I)
tot. no. of variables
GOF
0.08 × 0.10 × 0.12
0.11 × 0.18 × 0.42
0.08 × 0.24 × 0.28
9.42
9.06
7.89
0.710 73
ω
2.0 e 2θ e 44.0
4983
2654
337
1.71
0.710 73
ω
2.0 e 2θ e 44.0
6972
3227
371
1.12
0.710 73
ω
2.0 e 2θ e 40.0
5402
2570
351
0.84
R
0.1020
0.0721
0.0661
Rw
weights
0.1265
0.0889
0.0753
[0.04F2 + (σF)2]-1
[0.04F2 + (σF)2]-1
[0.04F2 + (σF)2]-1
Sch em e 1
consistent with distances reported for related alkenyne
compounds.9a,b
The X-ray structure of 4 (Figure 2) confirms the head-
to-tail orientation of the two bma ligands that are
attached to the central Co2(CO)2 moiety. Each bma
ligand is coordinated to the adjacent cobalt centers via
the two PPh2 groups and the π bond of the maleic
anhydride ring, making each bma ligand a six-electron
donor. The C(11)-C(15) and C(31)-C(35) bond dis-
tances of 1.44(2) and 1.46(2) Å, respectively, are close
to the value found in other complexes containing a
coordinated maleic anhydride moiety prepared by us.4,12,24
The formation of 5 from 4 is accompanied by the
decoordination of the bma ligand that undergoes P-C
bond cleavage, as verified by the X-ray structure of 5
(Figure 3). The intact bma ligand in 5 is unremarkable
in comparison to 4. The two Co-(µ2-P) distances of
2.200(4) Å (Co(1)-P(4)) and 2.209(5) Å (Co(2)-P(4)) and
the Co(1)-P(4)-Co(2) bond angle of 70.1(1)° are in good
agreement with the corresponding values reported for
other µ2-phosphido compounds.25 The remaining bond
distances and angles require no further comment.
short inter- or intramolecular contacts. Table 3 lists the
X-ray data collection and processing parameters, and
Table 4 gives selected bond distances and angles,
respectively. Figures 1-3 shows the ORTEP diagrams
for 3-5.
(22) The crystal selection for 3 was hampered by the fact that the
sample consisted in the main of aggregates of very small crystals.
Attempts to separate these crystals generally led to complete frag-
mentation. Finally,
a crystal was selected for which a rotation
photograph contained two sets of reflections of relative intensity ca.
10:1. The initial search routine contained several pairs of “equivalent”
reflections, and the weaker one of each pair was not used in determin-
ing the unit cell. As would be expected from this situation, the data
were not of high quality. Moreover, it also proved impossible to measure
either the crystal faces or to obtain good ψ-scan absorption data.
However, the connectivity of compound 3 is without question.
(23) (a) Mirza, H. A.; Vittal, J . J .; Puddephatt, R. J .; Frampton, C.
S.; Manojlovic-Muir, L.; Xia, W.; Hill, R. H. Organometallics 1993, 12,
2767. (b) Cotton, F. A.; J amerson, J . D.; Stults, B. R. J . Am. Chem.
Soc. 1976, 98, 1774. (c) Bianchini, C.; Dapporto, P.; Meli, A. J .
Organomet. Chem. 1979, 174, 205. (d) Caffyn, A. J . M.; Mays, M. J .;
Solan, G. A.; Braga, D.; Sabatino, P.; Tiripicchio, A.; Tiripicchio-
Camellini, M. Organometallics 1993, 12, 1876. (e) Caffyn, A. J . M.;
Mart´ın, A.; Mays, M. J .; Raithby, P. R.; Solan, G. A. J . Chem. Soc.,
Dalton Trans. 1994, 609.
The molecular structure of 3 (Figure 1) is similar to
that of Co2(CO)4[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC(Ph)-
C)C(Ph2P)C(O)OC(O)], which was recently reported by
us,4 and serves to confirm the PsC bond activation and
diyne functionalization that are required for the forma-
tion of 3.22 The 2.618(4) Å CosCo bond distance found
for 3 is similar to the CosCo bond length found in other
structurally characterized dinuclear Co2 complexes.4,5,23
The C(18)-C(19) and C(16)-C(17) distances of 1.16(2)
and 1.54(2) Å, respectively, associated with the 2-[(Z)-
1,4-diphenyl-1-(diphenylphosphino)-1-buten-3-ynyl]-3-
(diphenylphosphino)maleic anhydride ligand system are
(24) Yang, K.; Bott, S. G.; Richmond, M. G. Organometallics 1995,
14, 919, 2718.

2232 Organometallics, Vol. 15, No. 9, 1996
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles (d eg) in
Yang et al.
Co2(CO)4[µ-η2:η2:η1:η1-(Z)-P h 2P (P h )CdC(P h C2)CdC(P h 2P )C(O)OC(O)] (3), Co2(CO)2(bm a )2‚CH2Cl2 (4), a n d
Co2(CO)2(bm a )[µ-CdC(P h 2P )C(O)OC(O)](µ2-P h 2P )‚C6H14 (5)a
Co2(CO)4[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC(PhC2)CdC(Ph2P)C(O)OC(O)] (3)
Bond Distances
Co(1)-Co(2)
Co(1)-C(1)
Co(1)-C(16)
Co(2)-P(2)
Co(2)-C(4)
Co(2)-C(15)
O(2)-C(2)
2.618(4)
1.81(2)
2.11(2)
2.185(6)
1.79(2)
2.00(2)
1.19(3)
Co(1)-P(1)
Co(2)-C(2)
Co(1)-C(17)
Co(2)-C(3)
Co(2)-C(11)
O(1)-C(1)
O(3)-C(3)
2.213(6)
1.72(2)
2.04(2)
1.81(2)
2.06(2)
1.13(2)
1.14(3)
O(4)-C(4)
1.13(3)
1.42(3)
1.21(3)
1.50(3)
1.41(2)
1.36(3)
O(12)-C(12)
O(13)-C(14)
C(11)-C(12)
C(14)-C(15)
C(16)-C(17)
C(18)-C(19)
1.16(3)
1.38(3)
1.38(3)
1.58(3)
1.54(2)
1.16(2)
O(13)-C(12)
O(14)-C(14)
C(11)-C(15)
C(15)-C(16)
C(17)-C(18)
Bond Angles
Co(2)-Co(1)-P(1)
Co(2)-Co(1)-C(2)
Co(2)-Co(1)-C(17)
Co(1)-Co(2)-C(3)
71.9(2)
165.9(5)
78.9(7)
96.5(8)
Co(2)-Co(1)-C(1)
Co(2)-Co(1)-C(16)
Co(1)-Co(2)-P(2)
Co(1)-Co(2)-C(4)
97.1(8)
72.8(5)
72.2(2)
165.4(7)
Co(1)-Co(2)-C(11)
C(11)-Co(2)-C(15)
Co(2)-P(2)-C(17)
Co(1)-C(17)-P(2)
76.9(7)
43.3(8)
95.8(7)
95(1)
Co(1)-Co(2)-C(15)
Co(1)-P(1)-C(11)
Co(2)-C(11)-C(15)
C(16)-C(17)-C(18)
67.0(6)
92.4(6)
66(1)
124(2)
Co2(CO)2(bma)2‚CH2Cl2 (4)
Bond Distances
Co(1)-Co(2)
Co(1)-P(2)
Co(1)-C(31)
Co(2)-P(3)
Co(2)-C(2)
Co(2)-C(15)
O(2)-C(2)
2.527(3)
2.217(4)
2.06(1)
2.209(4)
1.79(2)
2.07(1)
1.12(2)
Co(1)-P(1)
Co(1)-C(1)
Co(1)-C(35)
Co(2)-P(4)
Co(2)-C(11)
O(1)-C(1)
2.317(4)
1.78(1)
2.02(1)
2.317(4)
2.04(1)
1.14(2)
1.23(2)
O(13)-C(12)
1.42(2)
1.23(2)
1.39(2)
1.18(2)
1.44(2)
1.44(2)
1.49(2)
O(13)-C(14)
O(32)-C(32)
O(33)-C(34)
C(11)-C(12)
C(14)-C(15)
C(31)-C(35)
1.37(2)
1.19(2)
1.43(2)
1.46(2)
1.45(2)
1.46(2)
O(14)-C(14)
O(33)-C(32)
O(34)-C(34)
C(11)-C(15)
C(31)-C(32)
C(34)-C(35)
O(12)-C(12)
Bond Angles
Co(2)-Co(1)-P(1)
Co(2)-Co(1)-C(1)
Co(2)-Co(1)-C(35)
P(1)-Co(1)-C(31)
P(2)-Co(1)-C(31)
69.8(1)
175.7(5)
80.7(4)
145.2(4)
103.4(4)
Co(2)-Co(1)-P(2)
Co(2)-Co(1)-C(31)
P(1)-Co(1)-P(2)
P(1)-Co(1)-C(35)
P(2)-Co(1)-C(35)
79.5(1)
78.6(4)
85.1(2)
116.3(4)
143.2(4)
C(31)-Co(1)-C(35)
Co(1)-Co(2)-P(4)
Co(1)-Co(2)-C(11)
P(3)-Co(2)-P(4)
42.0(6)
69.9(1)
80.8(4)
85.7(2)
Co(1)-Co(2)-P(3)
Co(1)-Co(2)-C(2)
Co(1)-Co(2)-C(15)
C(11)-Co(2)-C(15)
79.0(1)
174.6(5)
78.1(4)
41.0(6)
Co2(CO)2(bma)[µ-CdC(Ph2P)C(O)OC(O)](µ2-Ph2P)‚C6H14 (5)
Bond Distances
Co(1)-Co(2)
Co(1)-P(4)
Co(1)-C(11)
Co(2)-P(1)
Co(2)-P(4)
Co(2)-C(35)
O(2)-C(2)
2.531(2)
2.200(4)
2.01(2)
2.261(5)
2.209(5)
1.94(2)
Co(1)-P(3)
Co(1)-C(1)
Co(1)-C(15)
Co(2)-P(2)
Co(2)-C(2)
O(1)-C(1)
2.233(5)
1.69(2)
2.06(1)
2.253(4)
1.76(1)
1.19(2)
1.22(2)
O(13)-C(12)
O(14)-C(14)
O(33)-C(32)
O(34)-C(34)
C(11)-C(15)
C(31)-C(32)
C(34)-C(35)
1.35(2)
1.20(2)
1.38(2)
1.17(2)
1.47(2)
1.51(2)
1.52(2)
O(13)-C(14)
O(32)-C(32)
O(33)-C(34)
C(11)-C(12)
C(14)-C(15)
C(31)-C(35)
1.39(2)
1.22(2)
1.37(2)
1.47(2)
1.47(2)
1.32(2)
1.15(2)
O(12)-C(12)
Bond Angles
Co(2)-Co(1)-P(3)
Co(2)-Co(1)-C(1)
Co(1)-Co(2)-C(2)
P(1)-Co(2)-P(2)
96.0(1)
161.2(6)
166.3(6)
83.1(2)
Co(2)-Co(1)-P(4)
P(3)-Co(1)-P(4)
Co(1)-Co(2)-C(35)
P(1)-Co(2)-P(4)
55.1(1)
94.1(2)
88.5(4)
89.5(2)
P(1)-Co(2)-C(35)
Co(1)-P(4)-Co(2)
Co(2)-C(2)-O(2)
164.4(4)
70.1(1)
173(2)
P(2)-Co(2)-P(4)
Co(1)-C(1)-O(1)
P(3)-C(31)-C(35)
130.5(2)
175(1)
123(1)
a
Numbers in parentheses are estimated standard deviations in the least significant digits.
IV. Cyclic Volta m m etr y Stu d ies. Cyclic voltam-
metry data on compounds 1-5 were collected at a
platinum electrode in CH2Cl2 containing 0.2 M tetra-
n-butylammonium perchlorate (TBAP) as the support-
ing electrolyte. Table 5 gives the pertinent electro-
chemical data. Compound 1 exhibits two diffusion-
controlled, irreversible responses assigned to the 0/1+
(multielectron) and 0/1- (2e in nature) redox couples
of the two noninteracting Co2(CO)6(alkyne) units. Simi-
lar reductive electrochemical data for the diyne com-
pound [Co2(CO)6]2[HC2C6H4C2H] have been observed by
Osella and co-workers.7b,26 The CV of 2 (Figure 4)
clearly shows the presence of two reversible reduction
waves at E1/2 ) -0.51 and -0.63 V attributed to
reductions (1e each) associated with the π* system of
the bma ligand4,17 and an irreversible reduction exhibit-
c
ing Ep ) -1.32 V.27 This latter redox response un-
doubtedly derives from the reduction of the Co2(CO)6
moiety, which remains insulated, in a redox sense, from
the bma-substituted Co2(CO)4(bma) moiety. The CV
data for compound 3 is identical with the published CV
data for Co2(CO)4[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC(Ph)-
CdC(Ph2P)C(O)OC(O)].4 The quasi-reversible nature of
the 0/1- redox couple is validated on the basis of the
observed ∆Ep value of 0.17 V, which is larger than the
(25) (a) Walther, B.; Hartung, H.; Reinhold, J .; J ones, P. G.; Mealli,
C.; Bo¨ttcher, H.-C.; Baumeister, U.; Krug, A.; Mo¨ckel, A. Organome-
tallics 1992, 11, 1542. (b) J ones, R. A.; Stuart, A. L.; Atwood, J . L.;
Hunter, W. E.; Rogers, R. D. Organometallics 1982, 1, 1721. (c)
Albright, T. A.; Kang, S.-K.; Arif, A. M.; Bard, A. J .; J ones, R. A.;
Leland, J . K.; Schwab, S. T. Inorg. Chem. 1988, 27, 1246. (d) Braga,
D. B.; Caffyn, A. J . M.; J ennings, M. C.; Mays, M. J .; Manojlovic-Muir,
L.; Raithby, P. R.; Sabatino, P.; Woulfe, K. W. J . Chem. Soc., Chem.
Commun. 1989, 1401. (e) Breen, M. J .; Geoffroy, G. L. Organometallics
1982, 1, 1437.
(26) For reports of the redox chemistry in Co2(CO)6(alkyne) com-
plexes, see: (a) Dickson, R. S.; Peake, B. M.; Rieger, P. H.; Robinson,
B. H.; Simpson, J . J . Organomet. Chem. 1979, 172, C63. (b) Casa-
grande, L. V.; Chen, T.; Rieger, P. H.; Robinson, B. H.; Simpson, J .;
Visco, S. J . Inorg. Chem. 1984, 23, 2019. (c) Arewgoda, M.; Rieger, P.
H.; Robinson, B. H.; Simpson, J .; Visco, S. J . J . Am. Chem. Soc. 1982,
104, 5633. (d) Arewgoda, M.; Robinson, B. H.; Simpson, J . J . Am. Chem.
Soc. 1983, 105, 1893.

Diyne and Phosphorus-Carbon Bond Reactivity
Organometallics, Vol. 15, No. 9, 1996 2233
F igu r e 1. ORTEP diagram of the non-hydrogen atoms of
Co2(CO)4[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC(PhC2)CdC(Ph2P)C-
(O)OC(O)], showing the thermal ellipsoids at the 50%
probability level.
F igu r e 3. ORTEP diagram of the non-hydrogen atoms of
Co2(CO)2(bma)[µ-CdC(Ph2P)C(O)OC(O)[(µ2-Ph2P)‚C6H14
,
showing the thermal ellipsoids at the 50% probability level.
Ta ble 5. Cyclic Volta m m etr y Da ta for Com p ou n d s
1-5a
redox coupleb
0/1+
0/1-
a
c
a
c
a
c
compd Ep
Ep Ipc/Ip ∆Ep E1/2 Ep
Ep
Ipa/Ip ∆Ep E1/2
1
1.07
0.72 0.60 0.53 0.12 0.66 -0.54 -0.48 1.00 0.06 -0.51
-1.11
2c
3
0.93
1.13
1.14
-0.95 -0.78 0.91 0.17 -0.87
-1.14 -1.02 0.94 0.12 -1.08
-1.13 -1.01 0.89 0.12 -1.07
4
5
a
In ca. 10-3 M CH2Cl2 solutions containing 0.2 M TBAP at room
temperature and a scan rate of 0.1 V s-1. Potentials are in volts
relative to a silver-wire quasi-reference electrode, calibrated
b
a
c
against either Cp2Fe or Cp*2Fe. Ep and Ep refer to the anodic
and cathodic peak potentials of the CV waves. The half-wave
potential E1/2, which represents the chemically reversible redox
couple, is defined as (Ep + Epc)/2. c CV recorded at 0 °C.
a
F igu r e 2. ORTEP diagram of the non-hydrogen atoms of
Co(CO)2(bma)2‚CH2Cl2, showing the thermal ellipsoids at
the 50% probability level.
theoretically expected value of ca. 0.06 V.27 Adding
Cp*2Fe to a solution of 3 gave a ∆Ep value of ca. 0.09 V
for the Cp*2Fe/Cp*2Fe+ redox couple, suggesting the
importance of a slow electron-transfer step (khet low) as
opposed to uncompensated solution resistance being the
major contributor to the large ∆Ep.27
F igu r e 4. Cathodic scan cyclic voltammogram of
[Co2(CO)4(bma)(PhC4Ph)Co2(CO)6] (2) (ca. 10-3 M) recorded
at 0 °C in CH2Cl2 containing 0.2 M TBAP at 0.1 V/s.
The CV data obtained for 4 and 5 are remarkably
similar. Here each of these compounds exhibits a quasi-
reversible one-electron reduction at ca. -1.1 V, occurring
primarily at the bma ligand, and an irreversible oxida-
(27) The usual criteria for determining the diffusion-controlled
nature (current function plots) and redox-couple reversibilty (∆Ep,
current ratios, and current calibration against Cp*2Fe) in 1-5 have
been applied. See: (a) Bard, A. J .; Faulkner, L. R. Electrochemical
Methods; Wiley: New York, 1980. (b) Rieger, P. H. “Electrochemistry;
Chapman & Hall: New York, 1994.
a
tion wave at Ep ≈ 1.1 V, which is multielectron in
nature.

2234 Organometallics, Vol. 15, No. 9, 1996
Yang et al.
With the exception of 1, the bma-substituted com-
pounds 2-5 all display a low-potential (<-1.2 V) redox
couple(s) that is characteristic of the redox stabilization
afforded these binuclear systems through the participa-
tion of a low-lying π* orbital that is localized on the bma
ligand(s). This is significant because simple, phosphine-
substituted derivatives based on Co2(CO)6(alkyne) typi-
cally display irreversible reduction processes; the elec-
trochemical irreversibility in such compounds arises
from Co2-core fragmentation reactions and ligand loss
pathways due to the population of an antibonding Co-
Co orbital and formation of a formal 37-electron com-
pound.26 Extrapolation of the 18 + δ concept originally
formulated for mononuclear compounds, as exemplified
by the work of Brown28 and Tyler,29 suggests that
compounds 2•--5•- are best viewed as 36 + δ species
rather than 37-electron compounds.
overlap of the bma π* system with the dxz orbitals
associated with the Co2(CO)2 frame. The dxz orbital on
each cobalt atom has been further shaped by added px
character for maximum bma interaction, affording an
orbital picture that is reminiscent of the M2L2 complexes
examined by Hoffmann et al.31 The HOMO is predomi-
nantly formed from the overlap (bonding) of the bma
π* system of one of two bma ligands (36%) with the dxz
orbital of a single Co atom. The dxz orbital of the other
cobalt atom bonds to the central carbon-carbon double
bond belonging to the bma π* system (4%) of the other
bma ligand. The LUMO here derives from the anti-
bonding overlap of a bma ligand (π*) with the dxz orbital
of one of the Co centers. As with the HOMO, the major
contribution to the LUMO (58%) comes from the π*
system of one of the bma ligands.
The phosphido complex Co2(CO)2(H4-bma)[µ-CdC-
V. Exten d ed Hu1 ck el Ca lcu la tion s. The model
compounds Co2(CO)4[µ-η2:η2:η1:η1-(Z)-H2P(H)CdC(HC2)-
(H2P)C(O)OC(O)](µ2-H2P) shows the same basic MO
features as reported for the bcpd-based complex Ru2-
CdC(H2P)C(O)OC(O)], Co2(CO)2(H4-bma)2, and Co2(C-
(CO)6[µ-CdC(H2P)C(O)CH2C(O)](µ2-H2P).18a Here the
HOMO (-11.96 eV) originates basically from the overlap
O)2(H4-bma)[µ-CdC(H2P)C(O)OC(O)](µ2-H2P) were ex-
amined by extended Hu¨ckel molecular orbital calcula-
tions in order to gain information on the HOMO and
LUMO in compounds 3-5. The bma-substituted com-
plex 2 was not explored here, since the closely related
derivatives Co2(CO)4(bma)(PhCtCPh) (chelating and
bridging isomers) have already been studied, and the
MO calculations on 2 are expected to mimic those data
obtained for Co2(CO)4(bma)(PhCtCPh).4 Figure 5 shows
the three-dimensional CACAO drawings of the impor-
tant HOMO and LUMO orbitals for these model Co2
compounds.30
2
2
of hybridized dx -y orbitals (40%), along with contribu-
tions from the intact bma ligand (24%) and Ru/CO
groups (8%). The LUMO (-10.19 eV) is concentrated
on the maleic anhydride ring of the bma ligand that had
undergone PsC bond activation (85%) and whose nodal
pattern is similar to that of ψ4 of other six-π-electron
systems.32
The MO data presented here for the model compounds
Co2(CO)4[µ-η2:η2:η1:η1-(Z)-H2P(H)CdC(HC2)CdC(H2P)C-
(O)OC(O)], Co2(CO)2(H4-bma)2, and Co2(CO)2(H4-bma)-
The HOMO of Co2(CO)4[µ-η2:η2:η1:η1-(Z)-H2P(H)CdC-
[µ-CdC(H2P)C(O)OC(O)](µ2-H2P) are valuable because
the contention concerning the role played by the π*
system of the bma ligand(s) in helping modulate the
potential of the 0/1- redox couple is clearly demon-
strated. Trends in the observed reduction potential of
these and related binuclear compounds possessing easily
reduced ligand(s) will continue to be studied in our labs,
with the goal of being able to predict a priori the redox
properties of this genre of compound as a function of
the coordination mode adopted by the ancillary redox-
active diphosphine ligand(s).
(HC2)CdC(H2P)C(O)OC(O)] is found at -11.54 eV and
is composed of major contributions from the two cobalt
centers (36%), the enyne ligand (12%), and the maleic
anhydride ring (12%). The σ-bonding interaction be-
tween the cobalt atoms is derived from the overlap of
2
2
dx -y orbitals, each of which have been hybridized by
2
added dz and px character. Also visible is the bonding
interaction between one of the cobalt centers (nonmaleic
anhydride substituted center) and the π bond (alkene)
of the enyne moiety. The LUMO, which is primarily a
Co2-based orbital (39%), has an energy of -9.89 eV and
is best described as an antibonding Co-Co orbital (σ*),
whose parentage is similar to that of the just mentioned
Co-Co σ bond. Complexation of the CdC bond of the
maleic anhydride moiety via the π* system to the one
cobalt center accounts for the second most significant
contribution (16%) to the LUMO. A similar orbital
pattern has recently been observed in the LUMO of the
related hydrocarbyl complex Co2(CO)4[µ-η2:η2:η1:η1-
Exp er im en ta l Section
Gen er a l P r oced u r es. The bma33 and 1,4-diphenylbuta-
1,3-diyne34 used in this work were synthesized by using
published procedures. Co2(CO)8 was purchased from Strem
Chemical Co. and stored under CO. The diyne compound
[Co2(CO)6]2(PhC4Ph) was prepared from Co2(CO)8 and 1,4-
diphenylbuta-1,3-diyne using the general procedure of Wender
et al.35 THF was distilled from Na/benzophenone, while CH2-
Cl2 and 1,2-C2H4Cl2 were distilled from P2O5. All purified
solvents were transferred to storage vessels equipped with
Teflon stopcocks using Schlenk techniques.36 The TBAP
HCdC(H)PH2CdC(H2P)C(O)OC(O)].17
The HOMO (-11.58 eV) and LUMO (-9.99 eV) levels
of the model complex Co2(CO)2(H4-bma)2 may be viewed
as being derived from the bonding and antibonding
(28) Brown, T. L. In Organometallic Radical Processes; Trogler, W.
C., Ed.; Elsevier: New York, 1990; Chapter 3.
(31) (a) Thorn, D. L.; Hoffmann, R. Inorg. Chem. 1978, 17, 126. (b)
Hoffman, D. M.; Hoffmann, R.; Fisel, C. R. J . Am. Chem. Soc. 1982,
104, 3858.
(32) (a) Hayakawa, K.; Mibu, N.; Osawa, E.; Kanematsu, K. J . Am.
Chem. Soc. 1982, 104, 7136. (b) Albright, T. A.; Burdett, J . K.;
Whangbo, M. H. Orbital Interactions in Chemistry; Wiley: New York,
1985.
(29) (a) Tyler, D. R.; Mao, F. Coord. Chem. Rev. 1990, 97, 119. (b)
Tyler, D. R. Acc. Chem. Res. 1991, 24, 325. (c) Mao, F.; Tyler, D. R.;
Bruce, M. R. M.; Bruce, A. E.; Rieger, A. L.; Rieger, P. H. J . Am. Chem.
Soc. 1992, 114, 6418. (d) Mao, F.; Tyler, D. R.; Rieger, A. L.; Rieger, P.
H. J . Chem. Soc., Faraday Trans. 1991, 87, 3113. (e) Schut, D. M.;
Keana, K. J .; Tyler, D. R.; Rieger, P. H. J . Am. Chem. Soc. 1995, 117,
8939.
(33) Mao, F.; Philbin, C. E.; Weakley, T. J . R.; Tyler, D. R.
Organometallics 1990, 9, 1510.
(30) Mealli, C.; Proserpio, D. M. J . Chem. Educ. 1990, 67, 399.
(34) Campbell, I. D.; Eglinton, G. Org. Synth. 1965, 45, 39.

Diyne and Phosphorus-Carbon Bond Reactivity
Organometallics, Vol. 15, No. 9, 1996 2235
F igu r e 5. CACAO drawings of the HOMO (left) and the LUMO (right) for (A) Co2(CO)4[µ-η2:η2:η1:η1-(Z)-H2P(H)CdC-
(HC2)CdC(H2P)C(O)OC(O)], (B) Co2(CO)2(H4-bma)2, and (C) Co2(CO)2(H4-bma)[µ-CdC(H2P)C(O)OC(O)](µ2-H2P).
(Caution: strong oxidant) was purchased from J ohnson Mat-
they Electronics and recrystallized from ethyl acetate/petro-
leum ether, after which it was dried under vacuum for at least
48 h. Microanalyses were performed by Atlantic Microlab,
Norcross, GA.
All infrared spectra were recorded on a Nicolet 20SXB FT-
IR in 0.1-mm NaCl cells, and the 31P NMR spectra were
recorded on a Varian 300-VXR spectrometer at 121 MHz. The
31P NMR data quoted within were referenced to external H3-
PO4 (85%), taken to have δ 0. Positive chemical shifts
represent resonances that are to low field of the external
standard.
The 366 nm photolysis experiments were conducted at room
temperature using two Sylvania Blacklight bulbs, mounted in
a parallel arrangement. The light intensity was determined
by ferrioxalate actinometry, which gave an intensity on the
order of ca. 1 × 10-7 einstein/min.37 All reported quantum
yields represent the average value for two separate determina-
tions.
Syn th esis of Com p ou n d 2. (a ) Me3NO Rea ction . To a
Schlenk tube containing 0.30 g (0.39 mmol) of [Co2(CO)6]2(PhC4-
Ph) and 0.18 g (0.39 mmol) of bma was added 30 mL of THF
by syringe, after which the solution was cooled to 0 °C using
an ice bath and treated with 0.061 g (0.82 mmol) of Me3NO.
The color of the solution changed from brown to black-brown
(35) Greenfield, H.; Sternberg, H. W.; Friedel, R. A.; Wotiz, J . H.;
Markby, R.; Wender, I. J . Am. Chem. Soc. 1956, 78, 120.
(36) Shriver, D. F. The Manipulation of Air-Sensitive Compounds;
McGraw-Hill: New York, 1969.
(37) Calvert, J . G.; Pitts, J . N. Photochemistry; Wiley: New York,
1966.

2236 Organometallics, Vol. 15, No. 9, 1996
Yang et al.
gradually. The reaction was found to be essentially complete
after 1 h by IR and TLC analysis, at which time the solvent
was removed under vacuum at 0 °C, followed by chromato-
graphic purification over silica gel at -78 °C. The unreacted
[Co2(CO)6]2(PhC4Ph) was first removed by elution with petro-
leum ether, with the desired compound [Co2(CO)4(bma)(PhC4-
Ph)Co2(CO)6] (2) being isolated as a black solid using a mixture
of CH2Cl2/petroleum ether (3:1) as the eluant. Yield: 0.17 g
(42%).
employed a platinum disk as the working and auxiliary
electrode. The reference electrode employed in all experiments
consisted of a silver-wire quasi-reference electrode, with all
potential data reported relative to the formal potential of the
Cp2Fe/Cp2Fe+ or Cp*2Fe/Cp*2Fe+ (internally added) redox
couples, taken to have E1/2 ) 0.307 V27a and E1/2 ) -0.20 V,42
respectively.
Kin etic Mea su r em en ts. All kinetic studies were con-
ducted in Schlenk vessels under argon and under red light
conditions. Each reaction was monitored spectrophotometri-
cally by using a Hewlett-Packard 8452A UV-vis spectrometer
equipped with a variable-temperature cell. The progress of
the reaction was followed by observing the absorbances
changes in the 326 nm band of 4 for at least 4 half-lives. A
VWR refrigerated constant temperature circulator was used
to maintain the temperature, to within (0.2 °C. Plots of ln-
(A∞ - At) vs time were found to be linear, and the slopes of
these plots gave the first-order rate constants (kobsd) displayed
in Table 2, with the activation parameters determined by using
the Eyring equation.43
(b) Th er m olysis Rea ction . To a Schlenk tube containing
0.30 g (0.39 mmol) of [Co2(CO)6]2(PhC4Ph) and 0.18 g (0.39
mmol) of bma was added 30 mL of CH2Cl2 via syringe. The
solution was heated to reflux and cooled after 3 h, due to the
substantial decomposition of 2 that was observed by IR and
TLC analysis. The solvent was next removed, and [Co2-
(CO)4(bma)(PhC4Ph)Co2(CO)6] (2) was isolated by chromatog-
raphy exactly as described above. Yield: 0.13 g (35%). The
thermal sensitivity of [Co2(CO)4(bma)(PhC4Ph)Co2(CO)6] pre-
cluded an accurate combustion analysis.
Syn th esis of Com p ou n d s 3-5. To 0.30 g (0.39 mmol) of
[Co2(CO)6]2(PhC4Ph) and 0.55 g (1.18 mmol) of bma in a
Schlenk vessel was added 35 mL of 1,2-C2H4Cl2, followed by
heating at 83 °C for 1.5 h. The reaction solution was then
cooled, and the solvent was removed under vacuum. Column
chromatography over silica gel using an initial solvent system
composed of CH2Cl2/petroleum ether (1:1) afforded 35.0 mg
(yield 10%) of green Co2(CO)4[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC-
MO Ca lcu la tion s. The extended Hu¨ckel calculations on
the model compounds Co2(CO)4[µ-η2:η2:η1:η1-(Z)-H2P(H)CdC-
(HC2)CdC(H2P)C(O)OC(O)], Co2(CO)2(H4-bma)2, and Co2(CO)2-
(H4-bma)[µ-CdC(H2P)C(O)OC(O)](µ2-H2P) were carried out
with the original program developed by Hoffmann,44 as modi-
fied by Mealli and Proserpio,30 with weighted Hij’s.45 The input
(PhC2)CdC(Ph2P)C(O)OC(O)] (3), 25.0 mg (yield 7%) of orange
Co2(CO)2(bma)2 (4) when a solvent mixture of CH2Cl2 and
petroleum ether (4:1) was employed, and 35.0 mg (yield 8%)
Z matrix for Co2(CO)4[µ-η2:η2:η1:η1-(Z)-H2P(H)CdC(HC2)CdC-
(H2P)C(O)OC(O)] was constructed by using the X-ray data of
3, followed by the replacement of all phenyl groups by
hydrogen atoms using the PC modeling program MOBY. A
C(sp2)-H distance of 1.07 Å and a C(sp)-H distance of 1.05 Å
were used in the calculations with Co2(CO)4[µ-η2:η2:η1:η1-(Z)-
of brown Co2(CO)2(bma)[µ-CdC(Ph2P)C(O)OC(O)](µ2-Ph2P) (5)
when CH2Cl2 was used as the eluant. Single crystals suitable
for X-ray diffraction analysis and samples for combustion
analysis of 3-5 were grown from the slow evaporation of CH2-
Cl2 from samples of 3-5 that had been dissolved in a 4:1
mixture of CH2Cl2/hexane. The isolated crystals used for
combustion analysis were dried under vacuum for 1 week.
Anal. Calcd (found) for Co2(CO)4[µ-η2:η2:η1:η1-(Z)-Ph2P(Ph)CdC-
H2P(H)CdC(HC2)CdC(H2P)C(O)OC(O)]. The input Z matrices
for Co2(CO)2(H4-bma)2 and Co2(CO)2(H4-bma)[µ-CdC(H2P)C-
(O)OC(O)](µ2-H2P) were constructed by using bma ligands
(intact) that were symmetrically bound about a linear Co2-
(CO)2. All PsH bonds were set to a distance of 1.42 Å,46 while
the remaining distances and angles were taken from the X-ray
data for 3-5.
(PhC2)CdC(Ph2P)C(O)OC(O)], C48H30Co2O7P2: C, 64.16 (63.92);
H, 3.37 (3.50). Anal. Calcd (found) for Co2(CO)2(bma)2‚CH2-
Cl2, C59H42Cl2Co2O8P4: C, 59.41 (59.60); H, 3.52 (3.66). Anal.
Calcd (found) for Co2(CO)2(bma)[µ-CdC(Ph2P)C(O)OC(O)](µ2-
Ph2P), C58H40Co2O8P4: C, 62.95 (62.44); H, 3.64 (3.73).
Ack n ow led gm en t. We thank Prof. Carlo Mealli for
providing us with a copy of his CACAO drawing
program. Financial support from the Robert A. Welch
Foundation (Grant Nos. B-1202-SGB and B-1039-MGR)
and the UNT Faculty Research Program is appreciated.
X-r a y Cr ysta llogr a p h y. All data were collected on an
Enraf-Nonius CAD-4 diffractometer using the ω-scan tech-
nique, Mo KR radiation (λ ) 0.710 73 Å), and a graphite
monochromator. The data collection procedures utilized have
been described.38 Pertinent details are given in Table 3. All
data were corrected for Lorentz and polarization effects, in
addition to absorption (DIFABS).39 The structures for com-
pounds 3-5 were solved by direct methods using SHELXS-
86, and each model was refined by using full-matrix least-
squares techniques. The treatment of the thermal parameters
was based on the number of observed data, with anisotropic
parameters incorporated for 3 (the Co and P atoms and all
non-phenyl carbons except for C16), 4 (all Co, P, and O atoms),
and 5 (all Co and P atoms). Hydrogen atoms were located in
difference maps, followed by inclusion in the model in idealized
positions (U(H) ) 1.3Beq(C)). All computations other than
those specified were performed by using MolEN,40 and scat-
tering factors were taken from the usual source.41
Su p p or tin g In for m a tion Ava ila ble: Textual presenta-
tions of the crystallographic experimental details, listings of
crystallographic data, bond distances, bond angles, and posi-
tional and thermal parameters, and figures showing the unit
cells of compounds 3-5 (58 pages). Ordering information is
given on any current masthead page.
OM950988J
(40) MolEN, An Interactive Structure Solution Program; Enraf-
Nonius: Delft, The Netherlands, 1990.
(41) Cromer, D. T.; Waber, J . T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV;
Table 2.
(42) Ryan, M. F.; Richardson, D. E.; Lichtenberger, D. L.; Gruhn,
N. E. Organometallics 1994, 13, 1190.
(43) Carpenter, B. K. Determination of Organic Reaction Mecha-
nisms; Wiley-Interscience: New York, 1984.
(44) (a) Hoffmann, R.; Lipscomb, W. N. J . Chem. Phys. 1962, 36,
2179. (b) Hoffmann, R. J . Chem. Phys. 1963, 39, 1397.
(45) Ammeter, J . H.; Bu¨rgi, H.-B.; Thibeault, J . C.; Hoffmann, R.
J . Am. Chem. Soc. 1978, 100, 3686.
(46) Weast, R. C., Ed. Handbook of Chemistry and Physics, 56th
ed.; CRC Press: Cleveland, OH, 1975.
Electr och em ica l Stu d ies. All cyclic voltammograms were
obtained with a PAR Model 273 potentiostat/galvanostat,
equipped with positive feedback circuitry to compensate for
iR drop. The airtight cyclic voltammetry cell was based on a
three-electrode design, and the electrochemical experiments
(38) Mason, M. R.; Smith, J . M.; Bott, S. G.; Barron, A. R. J . Am.
Chem. Soc. 1993, 115, 4971.
(39) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 159.