5614 Organometallics, Vol. 16, No. 26, 1997
Communications
Sch em e 1
F igu r e 2. ORTEP drawing (40% probability level) of
[(DPPE){(C6H5)(C6H4)PCH2CH2P(C6H5)2}Ru]+ (cation of 6).
Parameters: Ru-P(1) ) 2.340(1), Ru-P(2) ) 2.349(1), Ru-
P(3) ) 2.319(1), Ru-P(4) ) 2.332(1), Ru-C(4) ) 2.12(5)
Å; P(1)-Ru-C(4) ) 68.3(1)°, P(2)-Ru-C(4) ) 100.2(1)°,
P(3)-Ru-C(4) ) 88.2(1)°, P(4)-Ru-C(4) ) 98.0(1)°.
carbon in an apical position (Figure 2). The Ru-C(sp2)
distance is 2.05 Å, which is shorter than the analogous
bond in 3.
the four-membered metallacycle are typical of those
reported in the literature;11 compound 3, for example,
has a P-Ru-C angle of 67.7°.
The structural relationship between the phenyl groups
and the chloride atoms in 1 and 3 prohibits direct
thermal elimination of HCl from 1 as the mechanism
for generating 3. Similarly, direct thermal elimination
of CH4 from 2 is untenable (see Scheme 1). The
generation of 3 might proceed via dissociation of one of
the DPPE phosphines in 1 followed by the oxidative
addition of an aryl C-H bond with consequent reductive
elimination of CH4 and reattachment of the phosphine.
Heating compound 1 in refluxing benzene or toluene in
the absence of AlMe3, however, fails to generate 3
(Scheme 1). Consequently, phosphine dissociation, if it
were to occur, would appear to require the assistance
of AlMe3. Since, however, the enthalpy of formation of
arylphosphine-AlX3 adducts is only weakly favorable,18
and the abstraction of chlorine from metal complexes
by alkylaluminum compounds is well-documented,19 the
role of AlMe3 is probably to abstract a chlorine (rather
than a phosphine) from 1. These factors suggest a
mechanism alternative to phosphine dissociation for the
generation of 3.
In experiments at room temperature, exposure of 3
in C6D6 to HCl generated cis- and trans-(DPPE)2RuCl2.12
Exposure of 3 in CD2Cl2 to H2 generated trans-(DPPE)2-
RuHCl.13 Complex 3 did not, however, appear to react
in CD2Cl2 with 1 atm of either CO or CH2dCH2.
Examples of the ortho-metalation of aryl phosphine
ligands during the alkylation of ruthenium are well-
known.10,11,14 The exact mechanism of the ortho-meta-
lation reaction, however, has not been firmly estab-
lished. We undertook several studies in an effort to
probe the mechanistic details of our system (Scheme 1).
The three cationic compounds [(DPPE)2RuCl]+[PF6]-
(4),15 [(DPPE)2RuCH3]+[PF6]- (5),16 and [(DPPE){(C6-
H5)(C6H4)PCH2CH2P(C6H5)2}Ru]+[PF6]- (6)17 were clean-
ly obtained by the reaction of 1-3, respectively, with
AgPF6 in CH2Cl2. Analysis by single-crystal X-ray
diffraction shows that the cation of 6 exists as a
distorted square pyramid with the orthometalated
(10) Advasio, V.; Diversi, P.; Ingrosso, G.; Lucherini A.; Marchetti,
F.; Nardelli, M. J . Chem. Soc., Dalton Trans. 1992, 3385. Diversi, P.;
Ingrosso, G.; Lucherini, A.; Marchetti F.; Adovasio, V.; Nardelli, M. J .
Chem. Soc. Dalton Trans. 1990, 1779.
(11) Cole-Hamilton, D. J .; Wilkinson, G. J . Chem. Soc., Dalton
Trans. 1977, 797. Chappell, S. D.; Engelhardt, L. M.; White, A. H. J .
Organomet. Chem. 1993, 462, 295. Fryzuk, M. D.; Montgomery, C. D.;
Rettig, S. J . Organometallics 1991, 10, 467.
There remain at least four plausible mechanisms by
which 3 might be produced during the attempted
synthesis of cis-(DPPE)2RuCH3Cl from 1. The first
involves isomerization of 1 to cis-(DPPE)2RuCl2 followed
(17) Prepared by reacting 0.100 g of 3 (1.07 × 10-4 mol) with 0.028
g of AgPF6 (1.1 × 10-4 mol) in 20 mL of CH2Cl2 at room temperature
for 30 min. The solvent was removed under vacuum, and the residue
was washed with hexane and then recrystallized from CH2Cl2/Et2O.
Yield: 90% of red crystals. Crystal data: C52H47F6P5Ru, Mr ) 1041.5;
monoclinic; P21/c; a ) 13.379(3) Å, b ) 26.742(6) Å, c ) 14.685(3) Å; V
) 5003 Å3; Z ) 4; D ) 1.50 g/cm3. 1H NMR (CD2Cl2; 300 MHz; 293 K):
δ 2.5-3.2 (m, 8 H, Ph2PCH2CH2PPh2), 5.8-7.7 (m, 39 H, Ph2PCH2-
CH2PPh2). 13C NMR (CD2Cl2; 75.5 MHz; 293 K): δ 22.5 (dd), 24.3 (dd),
28.5 (m), 122.5-134.4. 31P{1H} NMR (CD2Cl2; 121 MHz; 293 K): ABCD
pattern, δ 5.7 (dd), 7.7 (dd), 51.2 (dd), 53.2 (dd), 63.5 (dd), 65.4 (dd),
66.1 (dd), 68.1 (dd). A satisfactory analysis could not be obtained. Anal.
Calcd for C52H47F6P5Ru: C, 59.97, H, 4.51. Found: C, 59.23; H, 4.46.
(18) Levason, W.: McAuliffe, C. A. Coord. Chem. Rev. 1976, 19, 173.
(19) Eisch, J . J .; Piotrowski, A. M.; Brownstein, S. K.; Gabe, E. J .
J . Am. Chem. Soc. 1985, 107, 7219. Tebbe, F. N.; Parshall, S. W.;
Reddy, G. S. J . Am. Chem. Soc. 1978, 100, 3611.
(12) Mason, R.; Meek, D. W.; Scollary, G. R. Inorg. Chim. Acta 1976,
16, L11.
(13) J ames, B. R.; Wang, D. K. W. Inorg. Chim. Acta 1976, 19, L17.
(14) Diversi, P.; Ingrosso, G.; Lucherini, A.; Marchetti, F.; Adovasio,
V.; Nardelli, M. J . Chem. Soc., Dalton Trans. 1991, 203.
(15) Chin, A.; Lough, A. J .; Morris, R. H.; Schweitzer, C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278.
(16) Prepared by reacting 0.050 g of 2 (5.3 × 10-5 mol) with 0.013
g of AgPF6 (5.3 × 10-5 mol) in 15 mL of CH2Cl2 at room temperature
for 1 min. 1H NMR (CD2Cl2; 300 MHz; 293 K): δ -0.9 (quint, 3 H,
Ru-CH3, J PH ) 6 Hz), 2.4-2.7 (m, 8 H, Ph2PCH2CH2PPh2), 6.8-7.4
(m, 40 H, Ph2PCH2CH2PPh2). 31P{1H} NMR (CD2Cl2; 121 MHz; 293
K): δ 56.4 (s). These data strongly support
a square-pyramidal
structure for 5. Theoretical studies also support this geometry: Rachidi,
I. E.; Eisenstein, O.; J ean, Y. New J . Chem. 1990, 14, 671. Reihl, J .
F.; Eisenstein, O.; Pellissier, M. Organometallics 1992, 11, 729.