Novel three-component coupling using aluminum tris(2,6-diphenylphenoxide) (ATPH): The same synthetic strategy leads to trans- and cis-jasmonates

Article abstract of DOI:10.1002/1521-3773(20011001)40:19<3613::AID-ANIE3613>3.0.CO;2-3

A one-pot three-component coupling involving organolithium reagents, ATPH·cyclopentenone complex, and dihydrofuran·BCl₃ complex (see scheme) gives moderate to good yields of the products with selective formation of either the 2,3-cis or 2,3-trans isomer, depending on the nature of the lithium reagent.

Full text of DOI:10.1002/1521-3773(20011001)40:19<3613::AID-ANIE3613>3.0.CO;2-3

COMMUNICATIONS
coupling product 4, which was isolated in a yield of 71% (2,3-
trans-4/2,3-cis-4 ˆ 3.5:1; 2'E/2'Z ˆ 1:99). The formation of 4
was not observed before treatment with BCl3.[5] The addition
of a mixture of DHF and BCl3 gave a yield and selectivity
comparable to those achieved by sequential addition. Other
alkenyl- and alkynyllithiums, as well as lithium enolates, are
well suited to this process and give the corresponding
products in moderate to high yields with complete retention
of the original Z configuration (Table 1). The even more labile
cyclopentenone 3b was also compatible with these basic
conditions (entries 3 and 6), but scant 2,3-cis/trans selectivity
was observed with 2-alkylethenyllithiums (entries 2 and 3).
The 2,3-cis selectivity increases in the order isopropenyl- <
crotyl- < alkynyllithium, that is, with decreasing size of the
organolithium reagents (each prepared in DME) (entries 1, 2,
and 5).[6]
Novel Three-Component Coupling Using
Aluminum Tris(2,6-diphenylphenoxide)
(ATPH): The Same Synthetic Strategy Leads to
trans- and cis-Jasmonates
Susumu Saito, Satoko Yamazaki, and
Hisashi Yamamoto*
One-pot three-component coupling[1] is an important
procedure in organic synthesis and provides a powerful and
rapid means for construction of the prostaglandin[2] and
jasmonate[3] families. Here we report on a novel strategy for
three-component coupling (Scheme 1), which involves the
OH
O
O
C5H11
CO2tBu
TBSO
5
6
Tetrahydrofuran was also used as an alkylating agent in
place of DHF (Table 2), but in some cases the stereoselectiv-
ity was different from that with DHF. For instance, in the case
of isopropenyllithium, the 2,3-cis product predominated with
THF (Table 2, entries 2 ± 4),[6, 7] while the 2,3-trans product
was formed selectively with DHF (Table 1, entries 4 ± 6).
However, both DHF and THF gave the 2,3-cis product almost
exclusively with 1-hexynyllithium (Table 1, entry 1; Table 2,
entry 1).[6, 7] The TBSOTf ´ THF complex gives better 2,3-cis
selectivity than BCl3 ´ THF (Table 2, entries 2 ± 4). Both THF
and DHF showed a general trend to give high 2,3-trans
selectivity with lithium enolates (Table 1, entries 8 and 9;
Table 2, entries 5 ± 7).[8]
Scheme 1. Three-component coupling using ATPH. TBS ˆ tert-butyldi-
methylsilyl.
combined use of: 1) an organolithium reagent (RLi); 2)
aluminum tris(2,6-diphenylphenoxide) (ATPH;[4] see space-
filling model) cyclopentenone complexes 1a and 1b; and 3)
2,5-dihydrofuran (DHF) ´ BCl3 complex (2). This approach
leads efficiently to both trans- and cis-jasmonate derivatives.
With this new method in hand, various trans- and cis-
jasmonate derivatives can be obtained in a few steps by
assembling commercially available compounds. For example,
stereo- and regioselective methylation of diphenylphosphate
8 (Scheme 2), readily obtained from trans-7, was effected by
using trimethylzincate and a catalytic amount of FeIII
(Me2Zn ‡ MeMgBr (2 ‡ 2 equiv); [Fe(acac)3]: 1 mol%)[9] at
788C to give tert-butyl jasmonate 9 (2,3-trans/cis > 20:1)
together with small amounts of stereo- (2'Z/2'E ˆ 97:3; 10,
2%) and regioisomers (SN2/SN2' ˆ 87:13; 11, 11%); the total
yield of isomers was 87%, and the isomeric purity of 9 was
85%).[10] The ketone and ester groups remained intact under
these conditions. Subsequent displacement of a tert-butyl
group (HCO2H, RT) led to quantitative formation of trans-
jasmonic acid.
Precomplexation of a solution of ATPH (1.05 equiv) in
toluene with 2-cyclopenten-1-one (3a; 1.0 equiv) at 788C
was followed by treatment with a solution of isopropenyl-
lithium (1.1 equiv) in DME. After 1 h, sequential addition of
DHF (5.0 equiv) and BCl3 (2 equiv) gave three-component
Likewise, methyl cis-jasmonate was easily accessible from
three-component coupling product 12 (2,3-cis/trans ˆ 7.5 :1
and 71% yield from 3a). After separation of the diaster-
eomers (to 2,3-cis/trans ˆ 99:1), a similar phosphorylation ±
methylation[9] sequence (Scheme 3) caused only slight epime-
rization at C2 and gave 13 (2,3-cis/trans ˆ 31:1) in a reason-
able overall yield together with moderate amounts of stereo-
[*] Prof. Dr. H. Yamamoto, Dr. S. Saito, S. Yamazaki
Graduate School of Engineering, Nagoya University, SORST
Japan Science and Technology Corporation (JST), Chikusa
Nagoya 464-8603 (Japan)
Fax : (‡81)52-789-3222
E-mail: yamamoto@cc.nagoya-u.ac.jp
Angew. Chem. Int. Ed. 2001, 40, No. 19
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
1433-7851/01/4019-3613 $ 17.50+.50/0
3613

COMMUNICATIONS
Table 1. Three-component coupling of RLi, 1a (or 1b), and DHF ´ BCl3 complex.[a]
O
O
OH
ATPH
1) DHF
2) BCl3
RLi
toluene
X
R
X
3a : X = H
: X = OTBS
3b
Entry
1
RLi [equiv][b]
Ketone
Conditions [8C, h][c, d]
Products
Yield [%] (2,3-trans/2,3-cis)[e]
OH
OH
+
O
O
Li
ꢀ1:1†
3a
78, 2.5; 40, 2
44 (1:11)
OH
OH
+
O
O
Li
ꢀ1:1†
2
3
3a
3b
78, 5; 40, 0.5
57 (1.2:1)
46 (1:1)[f]
OH
+
O
OH
O
Li
C5H11
ꢀ1:2†
78, 20; 40, 10
TBSO
TBSO
TBSO
C5H11
C5H11
TBSO
TBSO
Li
ꢀ1:1†
OH
4
5
6
3a
3a
3b
78, 17.5; 40, 3
78, 1.5; 40, 3
78, 168
OH
+
59 (4.4:1)
O
O
2
cis-4
trans-4
3
Li
Li
ꢀ1:1†
ꢀ1:1†
71 (3.5:1)
OH
O
66 (79:11:10)[g]
TBSO
O
OH
OH
O
OLi
69 (>20:1)[h]
+
ꢀ2:0†
7
8
3a
3a
78, 18; 40, 2
OtBu
CO2tBu
cis-7
CO2tBu
trans-7
OH
OH
O
O
O
OLi
OMe
+
ꢀ2:0†
78, 19
47 (>20:1)
CO2Me
CO2Me
OH
OH
O
OLi
+
O
O
ꢀ2:0†
9
3a
78, 19; 40, 3
32 (>20:1)
[a] Unless otherwise specified, the reaction was performed with a solution of ATPH (1.05 equiv) in toluene, cyclopentenone (1.0 equiv), organolithium
(RLi), BCl3 or tert-butyldimethylsilyl triflate (TBSOTf), and DHF. [b] Each was prepared from the corresponding alkyne, bromide, or tin reagent with BuLi
(entries 1 ± 6) or from carbonyl compounds and lithium diisopropylamide (LDA; entries 7 ± 9) in DME (entries 1 ± 3 and 5) or diethyl ether (entries 4 and 6 ±
9). [c] The following conditions were used: BCl3 (2.0 equiv) ‡ DHF (5.0 equiv). [d] The indicated reaction temperatures and times are for the three-
1
component coupling process. [e] Yields of isolated, purified product. The diastereoselectivity was determined by H and 13C NMR spectroscopy. See also
ref. [7]. [f] Elimination product 5 (7%) was also obtained. [g] 2,3-trans,3,4-trans/2,3-cis,3,4-trans/2,3-trans,3,4-cis. [h] Protonated product 6 (27%) was
obtained.
3614
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
1433-7851/01/4019-3614 $ 17.50+.50/0
Angew. Chem. Int. Ed. 2001, 40, No. 19

COMMUNICATIONS
Table 2. Three-component coupling of RLi, ATPH ´ 3a (1a), and THF ´ Lewis acid.[a]
O
O
OY
ATPH
1) THF
RLi
toluene
2) BCl3 or TBSOTf
R
3a
X
Entry
1
RLi [equiv][b]
Alkylating agent[c]
Conditions [8C, h][d]
Products
Yield [%] (2,3-trans/2,3-cis)[e]
OH
OH
O
O
Li
+
ꢀ1:1†
A
78, 2.5; 40, 2
44 (1: > 20)
Li
OH
ꢀ1:1†
OH
+
2
3
A[f]
A
78, 7.5
78, 2
77 (1:2.7)
O
O
O
O
Li
ꢀ1:1†
85 (1:3.2)
OTBS
OTBS
+
Li
ꢀ1:1†
4
5
6
B
78, 2; 40,2.5
74 (1:4.0)
OH
OH
+
O
O
O
OLi
ꢀ2:0†
A
A
78, 15
43 (>20:1)
OtBu
CO2tBu
OH
CO2tBu
OH
O
OLi
+
ꢀ2:0†
78, 15
54 (>20:1)
57 (>20:1)
OMe
CO2Me
CO2Me
OH
OH
O
O
OLi
+
O
O
ꢀ2:0†
7
A
78, 15
[a] Unless otherwise specified, the reaction was performed with a solution of ATPH (1.05 equiv) in toluene, cyclopentenone (1.0 equiv), organolithium (RLi,
THF solution), and BCl3 or TBSOTf. [b] Each was prepared from the corresponding alkyne, bromide, or tin reagent with BuLi (entries 1 ± 4). Enolates were
prepared by using LDA (entries 5 ± 7). [c] The following conditions were used: A) BCl3 (2.0 equiv) ‡ THF (123 equiv); B) TBSOTf (7.0 equiv) ‡ THF
(123 equiv). Organolithiums or enolates were prepared in THF. [d] The indicated reaction temperatures and times are for the three-component coupling
process. [e] Yields of isolated, purified products. The diastereoselectivity was determined by 1H and 13C NMR spectroscopy. See also ref. [7]. [f] BCl3
(1.1 equiv) was used.
O
O
(2'Z/2'E ˆ 90:10; 14, 7%) and regioisomers (SN2/
SN2' ˆ 84:16; 15, 14%); the total yield of isomers
was 86%, and the isomeric purity of 13 was
73%.[10] Reduction of the ketone carbonyl group
was followed by hydroboration of the trimethyl-
silylacetylene[11] and subsequent oxidation. The
resulting crude carboxylic acid was selectively
methylated, and reoxidation of the remaining
hydroxy group would lead to methyl cis(epi)-
jasmonate[12] by the method previously de-
scribed.[13]
OPO(OPh)2
b
O
a
c
7
CO2tBu
CO2H
trans-jasmonic acid
CO2tBu
8
9
O
O
CO2tBu
CO2tBu
10
11
Scheme 2. Synthesis of trans-jasmonic acid. Reagents and conditions: a) Et3N,
ClPO(OPh)2, DMAP, CH2Cl2, 208C, 90%; b) Me3ZnMgBr, [Fe(acac)3] (1 mol%),
In summary, the present coupling was success-
ful under strongly basic conditions, which is
THF,
788C, <87%; c) HCO2H, RT, >99%. DMAP ˆ 4-(dimethylamino)pyridine,
acac ˆ acetyl acetone.
Angew. Chem. Int. Ed. 2001, 40, No. 19
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
1433-7851/01/4019-3615 $ 17.50+.50/0
3615

COMMUNICATIONS
1993, 93, 1533; c) B. H. Lipshutz, M. R. Wood, J. Am. Chem. Soc. 1994,
116, 11689; for reviews on domino reactions and multicomponent
coupling, see d) L. F. Tietze, U. Beifuss, Angew. Chem. 1993, 105, 137;
Angew. Chem. Int. Ed. 1993, 32, 131; e) A. Dömling, I. Ugi, Angew.
Chem. 2000, 112, 3300; Angew. Chem. Int. Ed. 2000, 39, 3168.
[2] a) M. Suzuki, A. Yanagisawa, R. Noyori, J. Am. Chem. Soc. 1985, 107,
3348; b) M. Suzuki, Y. Morita, H. Koyano, M. Koga, R. Noyori,
Tetrahedron 1990, 46, 4809; c) S. Chen, K. D. Janda, J. Am. Chem. Soc.
1997, 119, 8724; d) A. Fürstner, K. Grela, C. Mathes, C. W. Lehmann,
J. Am. Chem. Soc. 2000, 122, 11799; e) L. A. Arnold, R. Naasz, A. J.
Minnaard, B. L. Feringa, J. Am. Chem. Soc. 2001, 123, 5841. For a
4-oxa-prostaglandin derivative (ZK118182), see: f) S. Okamoto, S.
Katayama, N. Ono, F. Sato, Tetrahedron: Asymmetry 1992, 3, 1525.
[3] a) T. K. Sarker, B. K. Ghorai, J. Indian Chem. Soc. 1999, 76, 693, and
references therein; b) F.-T. Luo, E. Negishi, Tetrahedron Lett. 1985,
26, 2177; c) W. Oppolzer, M. Guo, K. Baettig, Helv. Chim. Acta 1983,
66, 2140; d) H. Gerlach, P. Kunzler, Helv. Chim. Acta 1978, 61, 2503;
two industrial syntheses: e) H. Kataoka, T. Yamada, K. Goto, J. Tsuji,
Tetrahedron 1987, 43, 4107; f) F. Näf, R. Decorzant, Helv. Chim. Acta
1978, 61, 2524.
[4] For review, see: a) S. Saito, H. Yamamoto, Chem. Commun. 1997,
1585; b) S. Saito, H. Yamamoto, Chem. Eur. J. 1999, 5, 1959; c) S.
Saito, M. Shiozawa, T. Nagahara, M. Nakadai, H. Yamamoto, J. Am.
Chem. Soc. 2000, 122, 7847; d) S. Saito, T. Sone, M. Murase, H.
Yamamoto, J. Am. Chem. Soc. 2000, 122, 10216; for Michael addition
to a,b-unsaturated carbonyl compounds, see: e) K. Maruoka, H.
Imoto, S. Saito, H. Yamamoto, J. Am. Chem. Soc. 1994, 116, 4131; for
novel reactivity and selectivity in the formation and reaction of ATPH
enolate complexes, see: f) S. Saito, S. Yamazaki, M. Shiozawa, H.
Yamamoto, Synlett 1999, 581; g) S. Saito, M. Shiozawa, H. Yamamoto,
Angew. Chem. 1999, 111, 1884; Angew. Chem. Int. Ed. 1999, 38, 1769;
h) S. Saito, M. Shiozawa, M. Ito, J. Am. Chem. Soc. 1998, 120, 813; i) S.
Saito, M. Ito, H. Yamamoto, J. Am. Chem. Soc. 1997, 119, 611; j) S.
Saito, M. Ito, K. Maruoka, H. Yamamoto, Synlett 1997, 357; k) K.
Maruoka, I. Shimada, H. Imoto, H. Yamamoto, Synlett 1994, 519.
[5] This means that neither LiI nor AlIII is the activating agent for DHF.
[6] At present, we do not have a reasonable explanation for these
unprecedented 2,3-cis selectivities, which might be ascribed to steric
influence of ATPH.
O
O
O
OH
OPO(OPh)2
a
b
12
13
TMS
TMS
TMS
c
O
OH
OH
e
d
CO2Me
methyl-cis-jasmonate
CO2Me
TMS
O
O
15
14
TMS
TMS
Scheme 3. Synthesis of methyl epi(cis)-jasmonate. Reagents and condi-
tions: a) Et3N, ClPO(OPh)2, 208C, 84%; b) Me3ZnMgBr, [Fe(acac)3]
(5 mol%), THF, 788C, <86%; c) NaBH4, MeOH, 08C, 91% (1,2-cis;2,3-
cis/1,2-trans;2,3-cis ˆ 3.2:1); d) (C6H11)2BH, THF, 08C; H2O2, NaOH,
MeOH/benzene, 08C; TMSCHN2, MeOH, 08C, 48%; e) see ref. [12].
TMS ˆ trimethylsilyl.
otherwise difficult to achieve. The synthetic potential of
ATPH may originate from: 1) The effective Michael addition
of organolithium reagents due to both steric (prevention of
1,2-addition and a- and/or g-deprotonation) and electronic
(activation of the b-position) influence of ATPH;[4e] and 2) the
novel reactivity of the resulting ATPH enolates, which
undergo either 2,3-cis- or -trans-selective alkylation by the
DHF/Lewis acid complexes. This eventually accommodated
the Z geometry of the new double bond in the a chain.
Experimental Section
[7] The diastereoselectivity (2,3-cis:2,3-trans) of three-component cou-
1
pling products was determined by H and 13C NMR spectroscopy, as
Representative procedure for the reaction of ATPH ´ 3a, isopropenyllithi-
um, and BCl3 ´ DHF: 3a (42 mL, 0.5 mmol) was added to a solution of
well as several cis and trans equilibration experiments (HCl, MeOH,
RT). We found that 13C NMR spectroscopy could be a powerful tool
for establishing the relative stereochemistry at the 2,3-vicinal carbon
atoms of 2,3-disubstituted-1-cyclopentanones. In general, 13C NMR
chemical shifts of C1' and C1'' of the cis adducts appear upfield due to
the greater shielding effects compared to those in the trans products.
For example, cis- and trans-2,3-dimethylcyclopentanones show d ˆ 9.5
(2-Me (C1')) and 14.8 (3-Me (C1'')), and d ˆ (2-Me (C1')) and 19.1 (3-
Me (C1'')), respectively (J. B. Stothers, C. T. Tan, Can. J. Chem. 1974,
52, 308); mthyl epi-jasmonate, cis: d ˆ 23.0 (2-CH2 (C1')), 33.7 (3-CH2
(C1'')); trans: d ˆ 25.6 (2-CH2 (C1')), 37.7 (3-CH2 (C1'')) (L. Crombie,
K. M. Mistry, J. Chem. Soc. Perkin Trans. 1 1991, 1981). We also found
that the equilibrium reached an inherent static point depending on the
size of the 3-substituent. Thus, the equilibrium lies on the trans side in
the order of bulkiness: isopropenyl (cis:trans ˆ 1:25) > crotyl
(cis:trans ˆ 1:11) > 1-hexynyl (cis:trans ˆ 1:1.6).
ATPH (0.53 mmol) in toluene (5.0 mL) at
788C under an argon
atmosphere. After 20 min, isopropenyllithium [generated by treatment of
a solution of isopropenyltributyltin (194 mg, 0.59 mmol) in DME (5.0 mL)
with a solution of nBuLi (1.66m, 0.33 mL, 0.55 mmol) in hexane at 788C
followed by stirring at 08C for 12 min and cooling to
788C] was
transferred by cannula to the solution of ATPH ´ 3a at 788C. The reaction
mixture was stirred at this temperature for 45 min. To this mixture were
then added DHF (0.189 mL, 2.5 mmol) and a solution of BCl3 (1.0m,
1.0 mL, 1.0 mmol) in hexane. After 1.5 h, the reaction mixture was warmed
to 408C, stirred for 3 h, quenched with aqueous NaHCO3, filtered
through a Celite pad, and extracted with Et2O. The organic layer was dried
over Na2SO4, and concentrated. The residue was purified by column
chromatography on silica gel to give 4 (69.4 mg, 71%) as a pale yellow oil.
1
trans-4: IR (neat): nÄ ˆ 3434, 2950, 1734, 1456, 1377, 1148, 1015, 895 cm
;
1H NMR (CDCl3, 300 MHz): d ˆ 5.74 ± 5.63 (m, 1H), 5.58 ± 5.41 (m, 1H),
4.87 (dt, 2H, J ˆ 12.3, 1.2 Hz), 4.16 (dd, 2H, J ˆ 6.6, 2.1 Hz), 2.57 ± 2.03 (m,
8H), 1.76 (s, 3H), 1.78 ± 1.63 (m, 1H); 13C NMR (CDCl3, 75 MHz): d ˆ
219.8, 144.9, 130.5, 128.6, 112.0, 58.0, 52.1, 48.8, 37.8, 26.4, 24.5, 19.0;
elemental analysis (%) calcd for C12H18O2: C, 74.19; H, 9.34; found: C,
74.09; H, 9.64. cis-4: 1H NMR (CDCl3, 300 MHz) d ˆ 4.90 (s, 1H), 4.72 (s,
1H), 4.18 ± 4.04 (m, 2H), 2.97 ± 2.90 (m, 1H), 1.70 (s, 3H); 13C NMR
(CDCl3, 75 MHz) d ˆ 219.8, 144.2, 130.1, 129.8, 112.4, 58.1, 51.7, 46.4, 36.4,
24.5, 23.4, 22.4.
[8] In general, the concomitant formation of Michael addition products
such as 6 through enolate protonation was a major side reaction.
Considerable formation of this type of product (ca. 30%) was
observed in several cases (Table 1, entries 8, and 9; Table 2, entries 1,
and 5 ± 7). It is highly unlikely that the trans selectivity is due to the
work-up procedure, since the same conditions were used throughout
the work (see Experimental Section).
[9] The details of this new stereo- and regioselective method for the
alkylation of allylic phosphates by the combined use of trialkyl- or
tetraalkylzincates and FeIII or FeII catalysts will be reported elsewhere.
[10] These selectivities (SN2 vs SN2'; 2'E vs 2'Z; 2,3-cis vs 2,3-trans) were
Received: June 7, 2001 [Z17236]
1
determined by H and 13C NMR spectroscopy and GC-MS.
[11] J. A. Miller, G. Zweifel, Synthesis 1981, 288.
[12] Perhaps the most efficient asymmetric synthesis of methyl cis-
jasmonate reported so far was reported by C. Fehr, J. Galindo,
[1] a) R. Noyori, M. Suzuki, Angew. Chem. 1984, 96, 854; Angew. Chem.
Int. Ed. Engl. 1984, 23, 847; b) P. W. Collins, S. W. Djuric, Chem. Rev.
3616
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
1433-7851/01/4019-3616 $ 17.50+.50/0
Angew. Chem. Int. Ed. 2001, 40, No. 19

COMMUNICATIONS
Angew. Chem. 2000, 112, 581; Angew. Chem. Int. Ed. 2000, 39, 569.
Other approaches to methyl cis-jasmonate are cited therein. See also
ref. [3a].
[13] a) T. K. Sarkar, B. Mukherjee, S. K. Ghosh, Tetrahedron 1998, 54,
3243; b) H. Stadtmüller, P. Knochel, Synlett 1995, 463; c) L. Crombie,
K. M. Mistry, J. Chem. Soc. Perkin Trans. 1 1991, 1981.
The First Platinum Formyl, a Member of a
Series of Hexanuclear Clusters Exhibiting a
Rare Structure**
Piero Leoni,* Fabio Marchetti, Lorella Marchetti,
Marco Pasquali, and Silvia Quaglierini
A large number of platinum clusters have been reported in
the past decades.[1] Nevertheless, only two hexanuclear
structures have been authenticated by X-ray crystallography:
[2a]
the trigonal-prismatic [Pt6(m-CO)6(CO)6]2
and the octa-
Scheme 1. Synthesis and further reactions of 2.
hedral [Pt6(CO)6(m-dppm)3]2‡ (dppm ˆ bis(diphenylphos-
phanyl)methane).[2b]
In
addition,
the
decanuclear
[Fe4Pt6(CO)22]2 ,[3] arising from the orthogonal dimerization
of two [Pt3(CO)3{m2-Fe(CO)4}2] triangles, contains a tetrahe-
dral Pt core, two opposite edges of which are each bridged by
another platinum atom. We have discovered a facile route to
platinum clusters having this unusual structure.[4] The pre-
cursor [Pt6(CO)6(m-PtBu2)4](CF3SO3)2 (2) was prepared by
treating the trinuclear hydrido cluster [Pt3(H)(CO)2(m-
PtBu2)3] (1)[5] with an excess of triflic acid under a CO
atmosphere (Scheme 1).
Figure 1 shows an ORTEP view of the cation 22‡, which
exhibits overall D2d symmetry.[7] Complex 2 is air-stable,
thermally robust (decomp 2288C), and remains unchanged,
even under forcing conditions, in the presence of CO (1008C,
100 atm, 12 h) or H2 (808C, 90 atm, 6 h). Interestingly, 2 reacts
with 13CO to give [Pt6(CO)4(13CO)2(m-PtBu2)4](CF3SO3)2 (2*),
the product of selective substitution of the carbonyl ligands
attached to the two ªapicalº atoms Pt2 and Pt5. A similar
remarkable regioselectivity was also observed in the reactions
of 2 with PMe3 or NaBH4 to give [Pt6(CO)4(PMe3)2(m-
PtBu2)4](CF3SO3)2 (3), and [Pt6(CO)4(CHO)2(m-PtBu2)4] (4),
respectively. The structures of 2*, 3, and 4 can be clearly
assigned on the basis of elemental analyses and IR and NMR
spectra. For example, the four bridging P nuclei are still
Figure 1. Molecular structure of 22‡ [7]
Methyl groups are omitted for
.
clarity (thermal ellipsoids at 30% probability; symmetry code: ' ˆ x, y, z).
Selected bond lengths [Š] and angles [8]: Pt1-Pt2 2.758(1), Pt1-Pt3 2.667(1),
Pt1-Pt4 2.841(1), Pt2-Pt3 2.762(1), Pt3-Pt4 2.841(1), Pt4-Pt4' 2.666(1), Pt4-
Pt5 2.756(1); Pt3-Pt1-Pt2 61.17(3), Pt1-Pt2-Pt3 57.79(3), Pt1-Pt3-Pt2
61.04(3), Pt3-Pt1-Pt4 62.00 (3), Pt1-Pt3-Pt4 62.00(3), Pt1-Pt4-Pt3 56.00(3),
Pt1-Pt4-Pt4' 62.01(2), Pt3-Pt4-Pt4' 62.01(2), Pt4'-Pt4-Pt5 61.071(15), Pt4-
Pt5-Pt4' 57.86(3).
isochronous and in the 31P{1H} NMR spectrum they give rise
2
to a central singlet (doublet in 3, J(Pm,Pterm ˆ 13 Hz) flanked
by a complex set of 195Pt satellites, very similar to those
observed for 2. Strong similarities were also observed in the
main features of the 195Pt{1H} NMR spectra, which still show
only two signals and hence rule out all other possible isomers.
Complex 4 is of particular interest, being the first platinum
formyl, and its structure was unequivocally confirmed by
comparison of its spectra with those of the labeled
[Pt6(CO)4(13CHO)2(m-PtBu2)4] (4*). In particular, the triplet
for the formyl group at d ˆ 18.9 (3J(H,P) ˆ 14 Hz) in the
1H NMR spectrum of 4 splits as expected in 4* (brdt,
1J(C,H) ˆ 152 Hz) for coupling with the adjacent 13C nucleus
(Figure 2a, b). The same coupling is exhibited by a doublet at
d ˆ 244.6 for the formyl C atom in the proton-coupled
13C NMR spectrum of 4* (Figure 2c, d).[6a] Furthermore, a
[*] Prof. P. Leoni, Dr. L. Marchetti, Prof. M. Pasquali, Dr. S. Quaglierini
Dipartimento di Chimica e Chimica Industriale
Via Risorgimento 35, 56126 Pisa (Italy)
Fax : (‡390)50-20237
E-mail: leoni@dcci.unipi.it
Prof. F. Marchetti
Dipartimento di Ingegneria Chimica dei Materiali
delle Materie Prime e Metallurgia
Via del Castro Laurenziano 7, 00161 Roma (Italy)
Á
[**] We thank the Ministero dellꢁUniversita e della Ricerca Scientifica e
Tecnologica (MURST), Programmi di Interesse Nazionale, 2000 ±
2001, for financial support.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
Angew. Chem. Int. Ed. 2001, 40, No. 19
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
1433-7851/01/4019-3617 $ 17.50+.50/0
3617