Photoinitiated Hydrosilations in Presence of Tetrahedral Heterometallic Clusters: Catalysis by Intact Clusters

Abstract

1969, 37 I I ; b) G. V. Ponomarev, R. P. Evstigneeva, N. A. Preobrazhenskii, J. Org. Chem. USSR 7(1971) 167. [5] Procedure (all operations carried out under argon): A mixture of 20 mL methanol (p.a.) and 0.5 mL acetic acid (p.a.) was evaporated down to 10 mL and cooled to room temperature, treated with 0.7 mL 35% formaldehyde-H,O solution and finally 147 mg (1.55 mmol) 3, and stored in the dark at room temperature. The fine crystals filtered off after 3 h were washed with methanol and dried over PaOlo at 50 "C in a vacuum. Yield 157 mg (94%) 4, colorless needles, thin-layer chromatographically and 'H-NMR spectroscopically pure (recrystallization from CHC13/CH,0H on exposure to air leads to decomposition): m.p. 234-235°C (dec.); Rr=0.53 (silica gel-TLC; CHdYbenzene I :0.5); IR (KBr): 3444.7 (N-H), 3429 (N-H), 3395 (assoc. N-H), 3368 c m -' (assoc. N-H); MS (inlet system temperature ca. 140°C); m/z=428 ( M + ; l0Oo/o); 'H-NMR (CDCII): 6 = 1.95 ( s ; 24H), 3.69 (5; SH), 6.91 ( s ; 4H). Angew. Chem. Int. Ed. Engl. 21 (1982) No. 10 1, L, = ,LloCp(CO), 3 , L m = Co(C0)2P(OCH3)3 2, L, = S1Cp 4 , L, = K i C p 5 , X = C H , L, = WCp(CO)2, M = C O 6 , X = S, L m = M O C~( C O )~, M = F e 7, X = P P h , L, = Fe(CO),, :M = C o (cob Angew. Chem. inf. Ed. Engl. 21 (1982) No. I0

Studies of metal exchange reactions: the synthesis and structures of heteronuclear metal clusters containing the indenyl ligand (μ3-CR)Co2M(CO)8(η5- Ind)(R=H,CH3,C6H5,COOC2H5; M=Mo,W)

“…Applications of cluster complexes in catalysis has stimulated great interest in the preparation and properties of heteronuclear clusters [1][2][3][4][5]. We are interested in cluster complexes containing a chiral tetrahedral skeleton because evidence for asymmetric induction by cluster-catalyzed reactions would provide definitively the proof that the clusters do not fragment during catalysis [4].…”

“…Following the pioneering methods of Vahrenkamp [6] and Stone [7], the metal exchange reaction is now the relatively straightforward method for preparing chiral clusters containing a tetrahedral skeleton. The alkylidyne clusters Co 2 M(l 3 -CR) (M ¼ Cr,Mo,W) synthesized by metal exchange reactions with (l 3 -CR) Co 3 (CO) 9 by using various neutral or anionic exchange reagents such as, Me 2 AsM (CO) 3 Cp [8][9][10][11][12], [M(CO) 3 Cp] 2 [13], ClM(CO) 3 Cp [14,15] and NaCpM(CO) 3 [6][7][8][9][10][11][12][13][14][15][16][17][18] M ¼ Cr,Mo,W) are excellent precursors for chiral tetrahedral-type cluster complexes. However, complexes containing the indenyl ligand (Ind), in place of the cyclopentadienyl (Cp) ligand, have rarely been introduced into the tetrahedral skeleton by the metal exchange reaction to date [19].…”

Direct resolution of novel tetrahedral metal clusters on a cellulose tris‐(3,5‐dimethylphenylcarbamate) chiral stationary phase by high‐performance liquid chromatography

“…Chiral tetrahedral clusters are a kind of organometallic compound of rapidly growing interest because of their potential application as catalysts for asymmetric reactions [10]. Use of a framework chirality cluster as the catalyst would not only mean a basic conceptual breakthrough in asymmetric catalysis, in which the greatest asymmetric induction originates from the central or planar chirality of the P or N ligand, but would also extend the methodology in the design of new chiral catalysts.…”

Diastereomeric control of enantioselectivity: evidence for metal cluster catalysis

“…This concept has been probed in the silylation of acetophenone using chiral tetrahedrane clusters, but cluster racemization was found to occur 30 faster than productive catalysis. 5 The generation of a chiral cluster framework through the coordination of a suitable chiral ligand allows the above criterion to be modified such that if asymmetric induction in a catalytic system is observed, and if the enantioselectivity of the catalytic reaction is reversed by using 35 another diastereomer of the cluster, where the chirality of the ligand remains the same but the chirality of the cluster framework has been changed, then this would constitute prima facie evidence for cluster-promoted asymmetric induction. Here we wish to present such a catalytic system that is based on two 40 diastereomeric cluster complexes, where an unprecedented reversal of the enantioselectivity of a catalytic asymmetric reaction occurs upon reversal of the chirality of the cluster 45 framework.…”

“…ESI †) and mass spectrometry showed no signs of changes in the clusters after catalytic runs. The catalysis results are summarized in Table 1 (7), Ru1-Ru3 2.9023(6), Ru2-Ru3 2.7536(6), Ru1-P1 2.359(2), Ru2-P2 2.333(1), Ru1-S1 2.368(2), Ru2-S1 2.375(2), Ru3-S1 2.346(2), Ru1-H1 1.75(5), Ru1-H2 1.69(5), Ru2-H2 1.76(4), Ru3-H1 1.76 (5). weakness in the chiral induction effected by clusters -the substrate is likely to bind at a metal site with minimum steric 40 hindrance (vide infra) and the chiral induction effected by bulky chiral ligands is thus diminished.…”