Carbon-carbon bond activation in biphenylene. Effect of η6-coordination to manganese tricarbonyl

Article abstract of DOI:10.1021/om990634i

Cleavage of a strained C-C bond in the four-membered ring in biphenylene (BP) is enormously facilitated by coordination of the electrophilic fragment Mn(CO)₃⁺ to one of the aromatic rings. Thus, the weak nucleophile Pt(PPh₃)₂(C₂H₄) is inert toward free BP, but reacts within seconds with [(η⁶-BP)Mn(CO)₃]⁺ to insert Pt(PPH₃)₂ into a C-C bond.

Full text of DOI:10.1021/om990634i

Organometallics 1999, 18, 4887-4888
4887
Ca r bon -Ca r bon Bon d Activa tion in Bip h en ylen e. Effect
of η6-Coor d in a tion to Ma n ga n ese Tr ica r bon yl
Xiao Zhang, Gene B. Carpenter, and Dwight A. Sweigart*
Department of Chemistry, Brown University, Providence, Rhode Island 02912
Received August 6, 1999
Summary: Cleavage of a strained C-C bond in the four-
membered ring in biphenylene (BP) is enormously
facilitated by coordination of the electrophilic fragment
(PPh3)2(C2H4). Both were found to show no detectable
reaction with free BP at room temperature after 24 h
in a CH2Cl2 solution. This result was anticipated in light
of a recent report6 that the much stronger nucleophile
Pt(PEt3)3 requires 10 days at 80 °C to react according
to eq 1 to afford (biphenyl)Pt(PEt3)2.
The reactivity of BP was found to change dramatically
upon coordination. Thus, 1 reacted with either Pt(PPh3)3
or Pt(PPh3)2(C2H4) to give the insertion product 2
according to eq 2. Both nucleophiles reacted so rapidly
+
Mn(CO)3 to one of the aromatic rings. Thus, the weak
nucleophile Pt(PPh3)2(C2H4) is inert toward free BP, but
reacts within seconds with [(η6-BP)Mn(CO)3]+ to insert
Pt(PPh3)2 into a C-C bond.
In tr od u ction
For both kinetic and thermodynamic reasons, the
activation of C-C bonds with transition metal com-
plexes is generally more difficult than is the activation
of C-H bonds. For these reasons, oxidative addition or
metal insertion into C-C bonds has most often been
demonstrated with systems that are predisposed to
react because the C-C bond cleavage results in relief
of strain or results in a product with increased aromatic
character. The activation of unstrained C-C bonds has
been achieved intramolecularly by precoordination of
the metal in such a way that the C-C bond in question
is forced into close proximity.1
at room temperature that the reaction was complete
before an IR spectrum could be recorded. This means
that the reaction half-life must be less than 30 s. Hence,
Metal insertion into the strained C-C bond of biphe-
nylene (BP) according to eq 1 has been reported with a
+
it may be concluded that the Mn(CO)3 moiety in eq 2
decreases the reaction half-life by many orders of
magnitude. In an analogous manner, coordination of
+
Mn(CO)3 to the carbocyclic ring in the stable hetero-
cycles benzothiophene and benzofuran has been shown
to greatly accelerate metal insertion into the C-S and
C-O bonds, respectively.8-10
number of nucleophilic metal reagents.2-7 These include
systems based on Ni(0), Pd(0), Pt(0), Co(I), Rh(I), and
Ir(I). The results suggest that the reaction is facilitated
by increasing the electron density on the metal nucleo-
phile. We became interested in examining how the ease
of metal insertion into BP would be influenced by
precoordination of one of the aromatic rings to an
electrophilic metal fragment. Herein it is shown that
C-C bond fission in (η6-BP)Mn(CO)3+ (1) is enormously
accelerated in comparison to that found with free BP.
Spectroscopic and elemental analysis data (see Ex-
perimental Section) provide convincing evidence for the
structural formulation of 2 shown in eq 2. In particular,
IR and 31P NMR data are precisely what would be
expected for structure 2. Attempts to crystallize 2 by
diffusing diethyl ether into a dichloromethane solution
produced only microcrystals unsuitable for X-ray dif-
fraction studies. After a period of weeks, however, small
clear yellow crystals formed that gave a single νCO band
in the IR (2068 cm-1 in CH2Cl2). X-ray diffraction
showed this product to have structure 3, indicating that
Resu lts a n d Discu ssion
To compare the reactivity of free and coordinated BP,
we choose the mild nucleophiles Pt(PPh3)3 and Pt-
(1) Rybtchinski, B.; Milstein, D. Angew. Chem., Int. Ed. Engl. 1999,
38, 870.
(2) Eisch, J . J .; Piotrowski, A. M.; Han, K. I.; Kru¨ger, C.; Tsay, Y.
H. Organometallics 1985, 4, 224.
(3) Perthuisot, C.; J ones, W. D. J . Am. Chem. Soc. 1994, 116, 3647.
(4) Lu, Z.; J un, C.-H.; de Gala, S. R.; Sigalas, M. P.; Eisenstein, O.;
Crabtree, R. H. Organometallics 1995, 14, 1168.
(5) Perthuisot, C.; Edelbach, B. L.; Zubris, D. L.; J ones, W. D.
Organometallics 1997, 16, 2016.
(6) Edelbach, B. L.; Lachicotte, R. J .; J ones, W. D. J . Am. Chem.
Soc. 1998, 120, 2843.
complex 2 had slowly lost a PPh3 ligand and scavenged
a CO from the manganese. It is tempting to suggest that
(8) (a) Dullaghan, C. A.; Sun, S.; Carpenter, G. B.; Weldon, B.;
Sweigart, D. A. Angew. Chem., Int. Ed. Engl. 1996, 35, 212. (b) Zhang,
X.; Dullaghan, C. A.; Watson, E. J .; Carpenter, G. B.; Sweigart, D. A.
Organometallics 1998, 17, 2067.
(7) Edelbach, B. L.; Vicic, D. A.; Lachicotte, R. J .; J ones, W. D.
Organometallics 1998, 17, 4784.
10.1021/om990634i CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/21/1999

4888 Organometallics, Vol. 18, No. 23, 1999
Notes
Ta ble 1. Cr ysta llogr a p h ic Da ta for
(Bip h en yl)P t(CO)(P P h 3) (3)
formula
fw
C31H23OPPt
637.55
temperature, K
wavelength, Å
crystal system
space group
a, Å
298
0.71073
monoclinic
P21/c
9.5309(4)
13.2397(5)
20.0843(7)
102.878(1)
2470.61(16)
4
b, Å
c, Å
â, deg
V, Å3
Z
d
calcd, g cm-3
1.714
5.766
1240
µ, mm-1
F(000)
crystal dimens, mm
θ range, deg
no. of reflns collected
no. of indept reflections
no. of data/restraints/params
GOF on F2
0.34 × 0.28 × 0.21
1.86-28.34
38583
6038 (Rint ) 0.0834)
6038/0/307
1.081
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
largest diff peak, hole
0.0287, 0.0672
0.0370, 0.0733
F igu r e 1. ORTEP drawing of (biphenyl)Pt(CO)(PPh3) (3)
with the ellipsoids shown at the 50% probability level.
Selected bond lengths (Å) and angles (deg) are as follows:
Pt(1)-C(13) 1.917(4), Pt(1)-P(1) 2.3514(9), Pt(1)-C(9)
2.068(4), Pt(1)-C(12) 2.076(4), C(13)-O(1) 1.128(5), C(9)-
C(10) 1.416(6), C(10)-C(11) 1.475(5), C(11)-C(12) 1.407-
(5), Pt(1)-C(13)-O(1) 176.5(4), P(1)-Pt(1)-C(13) 93.13-
(13), P(1)-Pt(1)-C(12) 94.85(10), C(9)-Pt-C(13) 91.72(17),
C(9)-Pt(1)-C(12) 80.58(16), Pt(1)-C(9)-C(10) 114.4(3), Pt-
(1)-C(12)-C(11) 114.2(3), C(10)-C(11)-C(12) 115.5(3),
C(9)-C(10)-C(11) 115.0(3).
0.944 and -1.259 e Å-3
version 5 software. Data reduction was carried out by SAINT
version 5 software and by SADABS and included profile
analysis and an empirical absorption correction. The structure
of 3 was determined by direct methods and refined on F2 using
the SHELXTL PC version 5 package. Twenty-one of the 23
hydrogen atoms appeared in a difference map. Each hydrogen
was introduced in an ideal position, riding on the atom to
which it is bonded; each was refined with an isotropic tem-
perature factor 20% greater than that of the ridden atom. All
other atoms were refined with anisotropic thermal parameters.
Crystallographic data are provided in Table 1.
this transformation is driven by the relief of steric
congestion around the platinum in 2.
[(Bip h en yl)P t(P P h 3)2‚Mn (CO)3]BF 4 (2). Pt(PPh3)2(C2H4)
(82 mg, 0.11 mmol) was added to a suspension of [(η6-BP)Mn-
(CO)3]BF4 (40 mg, 0.11 mmol) in CH2Cl2 (20 mL) at room
temperature under nitrogen. An immediate color change from
yellow to orange occurred, and an IR spectrum indicated that
the conversion of 1 to 2 was complete in less than 1 min. The
solution was then concentrated, and [2]BF4 precipitated as a
yellow powder by the addition of diethyl ether. Yield: 98% (114
mg). IR (CH2Cl2): νCO 2058 (s), 2002 (s, br) cm-1. 1H NMR (CD2-
Cl2): δ 7.7-7.0 (34H, Ph), 6.66 (br, 1H), 6.58 (br, 1H), 6.25
The structure of the air-stable 3 is shown in Figure
1. The biphenyl carbons C(1)-C(12) are nearly planar
(mean deviation ) 0.039 Å), with a C(9)-C(10)-C(11)-
C(12) torsion angle of 1.8(4)°. The platinum is in an
approximately planar environment consisting of C(9),
C(12), Pt, P, and C(13) (mean deviation 0.072 Å).
The conclusion from the results described above is
that metal coordination to an adjacent π-network can
be a viable way to electrophilically activate C-C bonds,
which can then be cleaved by metal nucleophiles.
(br, 1H), 5.76 (br, 1H). 31P NMR (CD2Cl2): δ 26.6 (dd, J P-P
15 Hz, J P-Pt ) 2487 Hz), 18.9 (dd, J P-P ) 15 Hz, J P-Pt ) 1940
Hz). Anal. Calcd for C51H38O3P2MnPtBF4: C, 55.78; H, 3.49.
Found: C, 56.00; H, 3.56.
)
Exp er im en ta l Section
As described above, attempts to grow crystals of [2]BF4 from
CH2Cl2/Et2O led to the isolation of small crystals of 3.
Spectroscopic data for 3 are as follows. IR (CH2Cl2): νCO 2068
Ma ter ia ls. Standard reagents were purchased from com-
mercial sources and used without further purification. Litera-
ture procedures were used to synthesize [(η6-biphenylene)Mn-
(CO)3]BF411 ([1]BF4) and Pt(PPh3)2(C2H4).12 31P NMR chemical
shifts are relative to 85% phosphoric acid external reference.
Cr ysta l Str u ctu r e of (Bip h en yl)P t(CO)(P P h 3) (3). A
single crystal of 3 was mounted on a glass fiber. X-ray data
collection was carried out using a Siemens P4 diffractometer
equipped with a CCD area detector and controlled by SMART
1
(s) cm-1. H NMR (CD2Cl2): δ 7.73-7.68 (m, 5H, Ph), 7.65 (d,
J ) 7 Hz, H4), 7.53-7.45 (m, 9H, Ph), 7.40 (d, J ) 7 Hz, H1),
7.35 (d, J ) 8 Hz, H5), 7.09 (t, J ) 7 Hz, H3), 6.93 (t, J ) 7
Hz, H2), 6.87 (t, J ) 7 Hz, H6), 6.85 (d, J ) 7 Hz, H8), 6.37 (t,
J ) 7 Hz, H7). 31P NMR (CD2Cl2): δ 25.9 (J P-Pt ) 1811 Hz).
Ack n ow led gm en t. This work was supported by
CHE-9705121 from the National Science Foundation.
(9) Dullaghan, C. A.; Zhang, X.; Greene, D. L.; Carpenter, G. B.;
Sweigart, D. A.; Camiletti, C.; Rajaseelan, E. Organometallics 1998,
17, 3316.
(10) Zhang, X.; Watson, E. J .; Dullaghan, C. A.; Gorun, S. M.;
Sweigart, D. A. Angew. Chem., Int. Ed. 1999, 38, 2206.
(11) Dullaghan, C. A.; Carpenter, G. B.; Sweigart, D. A. Chem. Eur.
J . 1997, 3, 75.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond lengths and angles, anisotropic displacement
parameters, and hydrogen coordinates for 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
(12) Nagel, U. Chem. Ber. 1982, 115, 1998.
OM990634I