Selective C(α)-C(β) bond cleavage by water in allenylidene and alkenylvinylidene ruthenium complexes

Article abstract of DOI:10.1039/a900011i

The Ru(II) complex mer,trans-[(PNP)RuCl₂(PPh₃)] [PNP = MeCH₂CH₂N(CH₂CH₂PPh₂)₂] reacts in refluxing THF with propargyl alcohols HC≡CCRR'OH (R = R' = Me, Ph; R = Me, R' = Ph) yielding either the allenylidene complex fac,cis-[(PNP)RuCl₂{C=C=CPh₂}] or the alkenylvinylidene derivatives fac,cis-[(PNP)RuCl₂{C=C(H)C(R)=CH₂}] (R = Me, Ph); treatment of all these complexes in CH₂Cl₂ or THF with water results in the formation of the ruthenium carbonyl fac,cis-[(PNP)RuCl₂(CO)] and free alkenes H₂C=CRR' (R = R' = Me, Ph; R = Me, R' = Ph) via regioselective C(α)-C(β) bond cleavage.

Full text of DOI:10.1039/a900011i

Selective Ca–Cb bond cleavage by water in allenylidene and alkenylvinylidene
ruthenium complexes
Claudio Bianchini,* Maurizio Peruzzini,* Fabrizio Zanobini, Carlos Lopez, Isaac de los Rios and Antonio
Romerosa
Istituto per lo Studio della Stereochimica ed Energetica dei Composti di Coordinazione, ISSECC, CNR, Via J. Nardi,
39 - 50132 Firenze, Italy. E-mail: bianchin@fi.cnr.it; peruz@fi.cnr.it
Received (in Basel, Switzerland) 4th January 1999, Accepted 27th January 1999
Ph
C C OH
Ph
The Ru(ii) complex mer,trans-[(PNP)RuCl2(PPh3)] [PNP =
H C
H2O
PPh3
MeCH2CH2N(CH2CH2PPh2)2] reacts in refluxing THF with
propargyl alcohols HC·CCRRAOH (R = RA = Me, Ph; R =
Me, RA = Ph) yielding either the allenylidene complex
fac,cis-[(PNP)RuCl2{CNCNCPh2}] or the alkenylvinylidene
derivatives fac,cis-[(PNP)RuCl2{CNC(H)C(R)NCH2}] (R =
Me, Ph); treatment of all these complexes in CH2Cl2 or THF
with water results in the formation of the ruthenium
carbonyl fac,cis-[(PNP)RuCl2(CO)] and free alkenes
H2CNCRRA (R = RA = Me, Ph; R = Me, RA = Ph) via
regioselective Ca–Cb bond cleavage.
P
P
Cl
Cl
C
Ph
Ru PPh3
P
N
Ru
C
C
N
THF, reflux
Cl
Ph
Cl
P
Me
C
R
1
2
H2O
H
C
C
OH
THF, reflux
THF or CH2Cl2
H
Ph
Ph
H2O
PPh3
H
P
P
Cl
C
H
C
Cl
Understanding and rationalizing the reactivity of transition
Ru
Cl
N
Ru CO
Cl
N
H
H
THF or CH2Cl2
metal
complexes
containing
allenylidene
ligands,
C
C
R
MNCNCNCR2, is a topic of much current interest in organome-
tallic chemistry.1–3 Sound motivations arise from the increasing
applications of allenylidene complexes, especially of ruthenium
derivatives, to various catalytic reactions involving C–C bond
formation.4
P
P
H
H
R
H2O
5
R = Me, 3; Ph, 4
Me
Scheme 1
As a general trend, nucleophiles may attack either the Ca or
Cg carbon atom in allenylidene ligands affording Fischer-type
carbenes or alkynyl compounds, respectively.5 The addition of
water has been found to take place selectively at Ca to give
unsaturated hydroxycarbenes.6 At least in one case, however,
there was the suspicion that water might be able to cleave a C–C
bond in an allenylidene ligand but no experimental evidence
was reported supporting this hypothesis.7 The question regard-
ing the hydrolytic C–C bond cleavage in allenylidenes and
homologous ligands is not of trivial importance given the wide
use of their metal complexes as catalyst precursors in a variety
of homogeneous processes, especially in reactions where new
C–C bonds are formed.4,8 For this reason, we decided to
investigate the reactions of both allenylidene and alkenylvinyli-
dene complexes with water. Ruthenium was the metal of choice
as it is known to effectively stabilize cumulene complexes and
it also constitutes the essential ingredient in many C–C bond
forming reactions.4,8
otherwise they may tautomerize to alkenylvinylidenes (E).
Alternatively, the alkenylvinylidene ligand may form via direct
elimination of water from the hydroxyvinylidene intermediate
(D).13
Within this mechanistic picture, it was not surprising to find
that 1 reacts with either 1,1-dimethyl- or 1-methyl,1-phenyl-
propyn-1-ol yielding the alkenylvinylidenes fac,cis-
[(PNP)RuCl2{CNC(H)C(R)NCH2}] (R = Me, 3; Ph, 4).11‡ It
was surprising instead to discover that both the allenylidene
Following the well known Selegue’s synthetic protocol,9 the
neutral
allenylidene
complex
fac,cis-[(PNP)RuCl2-
{CNCNCPh2}] 2 was obtained in 78% yield by refluxing
mer,trans-[(PNP)Ru(Cl)2(PPh3)] 110 and 1,1-diphenylprop-
2-yn-1-ol in THF (Scheme 1).†
Complex 211 was authenticated by means of standard
spectroscopic techniques as well as a single-crystal X-ray
analysis (Fig. 1).‡ The crystallographic study confirmed the fac
stereochemistry of the PNP ligand and the trans disposition of
the diphenylallenylidene ligand and the nitrogen donor
atom.12
While p-alkyne coordination (A) and alkyne to vinylidene
tautomerization (B) are common steps to any propargyl alcohol
activation, the eventual dehydration process of the hydroxy-
vinylidene intermediate may occur with different regioselectiv-
ity (Scheme 2). Either allenylidene (C) or alkenylvinylidene
derivatives may indeed form depending on the presence of
hydrogens on the carbon atom proximal to the OH group. If
there are no hydrogens, the allenylidene products are stable,
Fig. 1 ORTEP drawing of complex 2.18 For sake of clarity only the ipso
carbon atoms of the phenyl substituents in the PNP ligand are reported.
Selected distances (Å) and angles (°): P(1)–Ru(1) 2.314(2), P(2)–Ru(1)
2.289(2), N(1)–Ru(1) 2.335(5), Ru(1)–Cl(1) 2.449(2), Ru(1)–Cl(2)
2.461(2), Ru(1)–C(8) 1.858(7), C(8)–C(9) 1.221(9), C(9)–C(10) 1.376(10),
N(1)–Ru(1)–P(1) 82.69(14), N(1)–Ru(1)–P(2) 83.11(15), N(1)–Ru(1)–
Cl(1) 90.15(14), N(1)–Ru(1)–Cl(2) 87.96(15), N(1)–Ru(1)–C(8) 173.4(2),
P(1)–Ru(1)–P(2) 100.17(8), P(1)–Ru(1)–Cl(1) 171.95(6), P(1)–Ru(1)–
Cl(2) 88.49(8), P(1)–Ru(1)–C(8) 90.66(19), P(2)–Ru(1)–Cl(1) 82.52(7),
P(2)–Ru(1)–Cl(2) 166.62(6), P(2)–Ru(1)–C(8) 98.35(19), Cl(1)–Ru(1)–
Cl(2) 87.59(8), Cl(1)–Ru(1)–C(8) 96.5(2), Cl(2)–Ru(1)–C(8) 91.67(19),
Ru(1)–C(8)–C(9) 175.8(6), C(8)–C(9)–C(10) 171.1(7).
Chem. Commun., 1999, 443–444
443

H
R
R
(A)
(B)
H
(C)
[M]
•
[M]
•
•
[M]
H
[M]
OH
R'
+
R'
-H2O
R'
R'
OH
R
OH
R
R' = CHR''2
-H2O
R' = CHR''2
(D)
(E)
H
[M]
•
R''
R''
R
Scheme 2
parameters (non-hydrogen atoms anisotropic, hydrogen atoms in idealised
positions, C–H = 0.96 Å). CCDC 182/1164.
complex 2 and the alkenylvinylidenes 3 and 4 are transformed
by water (5 equiv.) into the known carbonyl derivative fac,cis-
[(PNP)RuCl2(CO)] (5)14 and the corresponding free alkene
H2CNCRRA (R = RA = Ph; R = Me or Ph, RA = Me). The
quantitative formation of 1 equiv. of alkene was shown by GC–
MS analysis and NMR spectroscopy (1H, 13C) on both reaction
mixtures and samples isolated by TLC. The hydrolysis reactions
are quite fast at reflux temperature in either THF or CH2Cl2 but
take place also at room temperature. When D2O was employed
in the place of H2O, the alkene was found to regioselectively
incorporate two gem deuterium atoms (D2CNCRRA) indicating
that both terminal hydrogens come from water. Finally, the
selective incorporation of 18O in the carbonyl complex 5-18O,
n(C18O) 1899 cm21, was observed when the hydrolysis
reactions were carried out with H218O confirming that the Ca–
Cb bond scission in either allenylidene or alkenylvinylidene
ligand was brought about by water and not by adventitious
oxygen.15
In conclusion, for the first time it has been shown that both
allenylidene and alkenylvinylidene ruthenium complexes, dis-
solved in organic solvents, may react with water producing CO
ligands and free alkene via regioselective cleavage of the Ca–Cb
bond. The hydrolysis of metal vinylidenes has recently been
reported to give carbonyl species and the saturated hydrocarbon
derived from the homologation of the vinylidene substituent.15
From allenylidene and alkenylvinylidene complexes, unsat-
urated hydrocarbons are selectively formed, which may open
the door to the alternative synthesis of high-added value alkenes
or alkenes selectively deuterated at the unsubstituted end.
This work was supported by the bilateral program «Azione
Integrata» between the University of Florence (Italy) and
Almeria (Spain) and by the EC contracts INTAS 96-1176 and
INCO ERBIC15CT960746.
1 E. O. Fischer, H.-J. Halder, A. Franck, F. H. Ko¨hler and G. Huttner,
Angew. Chem., Int. Ed. Engl., 1976, 15, 623; H. Berke, Angew. Chem.,
Int. Ed. Engl., 1976, 15, 624.
2 For the general reactivity of allenylidenes, see: (a) M. A. Esteruelas,
A. V. Go´mez, A. M. Lo´pez, E. On˜ate and N. Ruiz, Organometallics,
1998, 17, 4959 and references therein; (b) R. Wiedemann, P. Steinert, O.
Gevert and H. Werner, J. Am. Chem. Soc., 1996, 118, 2495; (c) H.
Fischer, G. Roth, D. Reindl and C. Troll, J. Organomet. Chem., 1993,
454, 133; (d) V. N. Kalinin, V. V. Deunov, M. A. Lusenkova, P. V.
Petrovsky and N. E. Kolobova, J. Organomet. Chem., 1989, 379, 303;
(e) D. Touchard and P. H. Dixneuf, Coord. Chem. Rev., 1998, 178–180,
409; (f) M. I. Bruce, Chem. Rev., 1998, 98, 2797.
3 For theoretical studies, see: (a) M. A. Esteruelas, V. Go´mez, A. M.
Lo´pez, J. Modrego and E. On˜ate, Organometallics, 1997, 16, 5826; (b)
B. E. R. Schilling, R. Hoffmann and D. L. Lichtenberger, J. Am. Chem.
Soc., 1979, 101, 585.
4 A. Fu¨rstner, M. Picquet, C. Bruneau and P. H. Dixneuf, Chem.
Commun., 1998, 1315; B. M. Trost and J. A. Flygare, J. Am. Chem. Soc.,
1992, 114, 5476.
5 (a) V. Cadierno, M. P. Gamasa, J. Gimeno, M. C. Lo´pez-Gonzalez, J.
Borge and S. Garcia-Granda, Organometallics, 1997, 16, 4453; (b) C.
Bohanna, B. Callejas, A. J. Edwards, M. A. Esteruelas, F. J. Lahoz,
L. A. Oro, N. Ruiz and C. Valero, Organometallics, 1998, 17, 373; (c)
D. Touchard, P. Haquette, A. Daridor, A. Romero and P. H. Dixneuf,
Organometallics, 1998, 17, 3844; (d) D. Pilette, K. Ouzzine, H. Le
Bozec, P. H. Dixneuf, C. E. F. Rickard, and W. R. Roper, Organo-
metallics, 1992, 11, 809.
6 M. A. Esteruelas, A. V. Go´mez, F. J. Lahoz, A. M. Lo´pez, E. On˜ate and
L. A. Oro, Organometallics, 1996, 15, 3423.
1
7 The iridium ethenyl complex Ir(CRNCRCRNCR)(PPh3)2(CO)(h -
CHNCH2) (R
=
CO2Me) was indeed obtained by reacting
Ir(CRNCRCRNCR)(PPh3)2(CO)Cl (R = CO2Me) with HC·CCH2OH.
The hydrolysis of an undetected allenylidene intermediate was hypothe-
sized: J. M. O’Connor and K. Hilbner, Chem. Commun., 1995, 1209.
8 C. Bruneau and P. H. Dixneuf, Acc. Chem. Res., 1999, in press.
9 J. P. Selegue, Organometallics, 1982, 1, 217.
Notes and references
10 C. Bianchini, P. Innocenti, D. Masi, M. Peruzzini and F. Zanobini, Gazz.
Chim. Ital., 1992, 122, 461.
† Satisfactory elemental analyses were obtained for 2 (red purple crystals),
3 (pink crystals), and 4 (pink red crystals). Selected spectroscopic data for
11 Complexes 2–4 exhibit a rich chemistry which will be detailed in due
course; C. Bianchini and M. Peruzzini, manuscript in preparation.
12 X-Ray authenticated Ru(ii)-diphenylallenylidenes include: [CpRu(P-
2: IR (nCNCNC) 1916m cm21 31P{1H} NMR (CD2Cl2, 85% H3PO4, 294 K),
.
d 49.12 (s). 13C{1H} NMR (CD2Cl2, TMS, 294 K), d 304.3 (t, 2JCP 19.2 Hz,
5
Ca), 233.8 (s, Cb), 150.8 (s, Cg). For 3: IR (nCNC) 1610s cm21
.
1H NMR
Me3)2{CNCNCPh2}], ref. 9; [(h -C9H7)Ru(PPh3)2{CNCNCPh2}], ref.
5(b); [RuCl(Pri2CH2CH2OMe)2{CNCNCPh2}](OTf), M. Martin, O.
Gevert and H. Werner, J. Chem. Soc., Dalton Trans., 1996, 2275;
4
(CDCl3, TMS, 294 K), d 5.16 (t, JHP 3.3 Hz, 1H, CH), 4.63 and 4.15 (d,
2JHH 1.8 Hz, 1H each, CH2), 2.28 [s, 3H, CH3(alkenylvinylidene)]. 31P{1H}
NMR (CDCl3, 85% H3PO4, 294 K), 47.81 (s). 13C{1H} NMR (CDCl3,
TMS, 294 K), d 313.5 (t, 2JCP 18.0 Hz, Ca), 126.6 (s, Cd), 114.2 (s, Cb), 18.5
[s, CH3(alkenylvinylidene)], confirmed by a DEPT-135 experiment, Cg, not
assigned. For 4: IR (nCNC) 1617s cm21. 1H NMR (CD2Cl2, TMS, 294 K),
5.73 and 5.25 (d, 2JHH 1.6 Hz, 1H each CH2), 5.10 (t, 4JHP 8.2 Hz, 1H, CH).
31P{1H} NMR (CD2Cl2, 85% H3PO4, 294 K), d 49.20 (s). 13C{1H} NMR
(CD2Cl2, TMS reference, 294 K), 350.3 (t, 2JCP 17.5 Hz, Ca), 150.2 (s, Cg),
122.6 (s, Cd), 113.5 (s, Cb), confirmed by a DEPT-135 experiment.
‡ Crystal data: C46H45Cl2NP2Ru, Mw = 845.79, monoclinic, space group
P21/c, a = 11.881(9), b = 13.446(2), c = 25.264(5) Å, b = 98.00(5)°, V
= 3997(3) Å3, Z = 4, Dc = 1.406 g cm23, T = 293(2) K, m(Mo-Ka) =
0.640 mm21; red crystal, crystal size 0.23 3 0.35 3 0.29 mm, Enraf Nonius
CAD4 diffractometer, 5545 independent reflections. The structure was
solved by direct methods (SIR92)16 and refined (F02) using the program
SHELX-93.17 An empiric absorption correction was applied via y scan
(0.97–1.00). The final R, Rw indices [I > 2s(I)] were 0.0644, 0.1544 for 220
2
1
[RuCl2(h -Pri2CH2CH2OMe)(h -P-Pri2CH2CH2OMe){CNCNCPh2}],
H. Werner, A. Stark, P. Steinert, C. Gru¨nwald and J. Wolf.
13 (a) J. P. Selegue, B. A. Young and S. L. Logan, Oragnometallics, 1991,
10, 1972; (b) V. Cadierno, M. P. Gamasa, J. Gimeno, J. Borge and S.
Garcia-Granda, Organometallics, 1997, 16, 3187.
14 C. Bianchini, P. Innocenti, M. Peruzzini, A. Romerosa and F. Zanobini,
Organometallics, 1996, 15, 272.
15 The hydrolysis of related vinylidene species has been studied in detail,
see: C. Bianchini, J. A. Casares. M. Peruzzini, A. Romerosa and F.
Zanobini, J. Am. Chem. Soc., 1996, 118, 4585.
16 A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, C. Burla, G.
Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27, 435.
17 G. M. Sheldrick, SHELX-93, University of Göttingen, 1993.
18 C. K. Johnson, ORTEP, Oak Ridge, TN, 1976.
Communication 9/00011I
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Chem. Commun., 1999, 443–444