Functionalized Carbosilane Dendritic Species as Soluble Support in Organic Synthesis

A new methodology, which is compatible with the use of reactive organometallic reagents, has been developed for the use of carbosilane dendrimers as soluble supports in organic synthesis. Hydroxy-functionalized dendritic carbosilanes Si[CH2CH2CH2SiMe2(C6H4CH(R)OH)]4 (G0-OH, R = H or (S)-Me) and Si[CH2CH2CH2Si[CH2CH2CH2SiMe2(C6H4CH(R)OH)]3]4 (G1-OH, R = H or (S)-Me) were prepared and subsequently converted into the esters Si[CH2CH2CH2SiMe2(C6H4CH(R)OC(O)CH2Ph)]4 (R = H or (S)-Me) and Si[CH2CH2CH2Si[CH2CH2CH2SiMe2(C6H4CH(R)OC(O)CH2C6H4R')]3]4 (R = H and R' = H or R = (S)-Me and R' = H or R = H and R' = Br). As an example the latter compound was functionalized under Suzuki conditions. The functionalized carboxylic acid was obtained in high yield after cleavage from the dendritic support. Moreover, the ester functionalized dendrimers were converted to the corresponding zinc enolates followed by a condensation reaction with an imine to a -lactam in excellent yield and purity. Furthermore, it was demonstrated that a small combinatorial library of -lactams could be prepared starting from a carbosilane dendrimer functionalized with different ester moieties. These results show that carbosilane dendrimers can be applied as soluble substrate carriers for the generation of low molecular weight organic molecules. In combination with nanofiltration techniques, separation and recycling of the dendrimers can be realized

Multiple Use of Soluble Metallo-Dendritic Materials as Catalysts and Dyes

Different sizes of core-functionalized metallodendritic wedges were prepared by anchoring sensor-active arylplatinum(ii) sites at the focal point of Fréchet-type polyether dendritic wedges of various generations. The strong color of these metallodendrimers in the presence of SO2 was used to assess the permeability of nanofiltration membranes (molecular weight cut-off of 400 dalton) at ambient pressure. A primary result of these studies is that dendrimers do not have to be exceptionally large for successful retention. Hence, nanofiltration, membrane-capped, immersion vials were developed, which operate as sensor devices when loaded with metallodendrimers with good retention properties. Appropriate substitution of the dye site at the focal point of these metallodendritic wedges by a catalytically active group afforded dendritic catalysts that exhibit essentially the same physical properties (shape, retention) as the corresponding dye-functionalized dendritic wedges. When this homogeneous catalyst is compartmentalized in membrane-capped vials, a unique and convenient method for its retrieval from product solutions is available. Moreover, such immobilized metallodendritic catalysts can be regenerated and stored for months without losing their activity; this provides access for the development of novel sustainable homogeneous catalysts

Phosphino carboxylic acid ester functionalized carbosilane dendrimers: Nanoscale ligands for the Pd-catalyzed hydrovinylation reaction in a membrane reactor

Phosphino carboxylic acid ester terminated G0compounds Si{(CH2)3SiMe2(C6H4CH2OC(O)(CH2)nCH2PPh2}4(9a and 9b; n = 1, 2) and the carbosilane dendrimers Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2OC(O)(CH2)nCH2PPh2)3}4(10a and 19b; n = 1, 2) have been prepared as hemilabile nanoscale ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was carried out in a continuously operated nanofiltration membrane reactor. Under continuous conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II) precursor

Selective hydrovinylation in a membrane reactor: use of carbosilane dendrimers with hemilabile P,O-ligands

Phosphino carboxylic acid ester terminated G0 compounds Si{(CH2)3SiMe2(C6H4CH2OC(O)(CH2)nCH2PPh2}4 (9a and 9b; n = 1, 2) and the carbosilane dendrimers Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2OC(O)(CH2)nCH2PPh2)3}4 (10a and 10b; n = 1, 2) have been prepared as hemilabile nanoscale ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was carried out in a continuously operated nanofiltration membrane reactor. Under continuous conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II) precursor

(2,2'-Bipyridyl-N,N')dibromopalladium(II)

The title comlex, PdCl2(bipy), the 2,2'-bipyridine complex of palladium dichloride, has square-planar geometry for palladium with Pd-N 2.047(5) and Pd-Br 2.4102(9) Angstroms. The mean planes of the coordinated pyridine groups form a dihedral angle of 1.7(3) degrees with the coordination square plane; the parallel complexes stack with an interplanar spacing of 3.41(1) A and a Pd··Pd separation of 5.246(1) A to form a chain structure as reported for isomorphous PtI2(bipy) (where bipy is 2,2'-bipyridyl, C10H8N2). The structure differs from those found for related chain structures in the 'red' form of PtCl2(bipy) and in PdCl2(bipy) which is isomorphous with the 'yellow' form of PtCl2(bipy)

Application of S,N-chelating chiral zinc bis(aminoranethiolates) as new precursor catalysts in the enantioselective addition of dialkylzincs to aldehydes,

A new enantiomerically pure S,N-chelated zinc bis(aminoarenethiolate), (R,R)-Zn(SC6H4C(Me)HNMe2-2)2 ((R,R)-3b), has been synthesized by the reaction of the (R)-trimethylsilyl aminoarenethiolate species (R)-2b with ZnCl2 in a 2:1 molar ratio. (R,R)-3b is an efficient catalyst for the addition of dialkylzinc compounds to aliphatic and aromatic aldehydes to give the corresponding secondary alcohols in nearly quantitative yields with optical purities of 69-99% ee under mild reaction conditions. Although excellent selectivities were obtained with this simple ligand containing only one stereogenic (carbon) center, further modifications of the amino substituents were studied. Cyclic N(CH2)4 or N(CH2)5 amino-substituted aminoarenethiolate ligands considerably enhanced the reaction rates, resulting in shorter reaction times and higher ee's. The mechanism of these 1,2-addition reactions has the general characteristics as reported by Noyori et al. This conclusion is based on the synthesis, isolation, and characterization (X-ray, 1H and 13C NMR) of the enantiopure zinc bis(aminoarenethiolate) and organozinc aminoarenethiolate intermediates and on monitoring of the reaction process. We present evidence for an interpretation of the binding in the product-forming key intermediate complex in terms of an organozinc cation/anion pair. The possibility that the very efficient transfer of chiral information in this compact complex may be due to a combination of the shortness of the Zn-N coordinate bonds with concomitant 2 bonding of the aldehyde substrate is discussed. The solid-state structure of the zinc bis(aminoarenethiolate) (R,R)-Zn(SC6H4C(Me)HNMe2-2)2 is reported

Periphery-palladated carbosilane dendrimers : Synthesis and reactivity of model organopalladium(II) and (IV) complexes : Crystal structure of [PdMe(C6H4(OCH2Ph)-4)(bpy)] (bpy=2,2'-bipyridine

A carbosilane dendrimer with 12 peripheral iodoarene groups, [Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2OC6H4I-4))3}4] (G1-ArI, 9), and the corresponding G0 model compound [Si{(CH2)3SiMe2(C6H4CH2OC6H4I-4)}4] (G0-ArI, 8) have been prepared from [Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2Br))3}4] (G1-Br, 7) and the corresponding G0 model compound [Si{(CH2)3SiMe2(C6H4CH2Br)}4] (G0-Br, 6). These dendritic species react with [Pd2(dba)3·dba/tmeda] (dba = dibenzylideneacetone, tmeda = N,N,N',N'-tetramethylethylenediamine) to yield the periphery-palladated complexes [Si{(CH2)3SiMe2(C6H4CH2O(C6H4-4)PdI(tmeda))}4] (G0-ArPdI(tmeda), 10) and [Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2O(C6H4-4)PdI(tmeda))3}4] (G1-ArPdI(tmeda), 11). Complexes 10 and 11 react with LiMe and 2,2'-bipyridine (bpy) to yield the air-stable [Si{(CH2)3SiMe2(C6H4CH2OC6H4PdMe(bpy))}4] (G0-PdMe(bpy), 12) and [Si{(CH2)3Si((CH2)3SiMe2(C6H4CH2OC6H4PdMe(bpy)))3}4] (G1-ArPdMe(bpy), 13). Complexes 12 and 13 undergo oxidative addition with benzyl bromide to form species containing Pd(IV) centers. These complexes can undergo subsequent reductive elimination at ambient temperature involving both Me-Ar and Me-CH2Ph coupling on decomposition. Iodoarenes that model the arms of carbosilane-based dendrimers have been synthesized, and procedures have been developed for maximizing yields of organopalladium(II) and -(IV) derivatives of the iodoarenes as part of a program directed toward the isolation and study of organopalladium functionalized dendrimers. The iodoarenes RC6H4(CH2OC6H4I-4')-4 (R = H (1a), SiMe3 (1b)) were obtained and found to undergo facile oxidative addition to [Pd2(dba)3·dba/tmeda] to form [PdI(Ar)(tmeda)] (2a,b), which react with LiMe to form [PdMe(Ar)(tmeda)] (3a,b). Bpy displaces tmeda to form [PdMe(Ar)(bpy)] (4a,b), and the latter complexes undergo oxidative addition with benzyl bromide to form the complexes [PdBrMeAr(CH2Ph)(bpy)] (5a,b). The palladium(IV) complex 5a undergoes facile and clean reductive elimination at ambient temperature in CDCl3 to form the coupling products Me-C6H4(OCH2Ph)-4 (89%), PhCH2-C6H4(OCH2Ph)-4 (9%), and Me-CH2Ph (2%). However, 5b undergoes more complex behavior to form Me-C6H4(OCH2C6H4(SiMe3)-4')-4 (87%), Me-CH2Ph (6%), and PhCH2-CH2Ph (7%) together with [PdBr2(bpy)]. The complex [PdMe(C6H4(OCH2Ph)-4)(bpy)] (4a) has been characterized by X-ray diffraction. The asymmetric unit contains two similar but crystallographically independent molecules. Each molecule has square-planar geometry for palladium with the aryl ring tilted by 76.2(4) and 67.1(3) to the coordination plane, respectively. The crystal examined by X-ray diffraction exhibits significant substitutional disorder at one site: [PdX(C6H4(OCH2Ph)-4)(bpy)] (X = Me (71%), Cl (29%))

Organopalladium functionalised dendrimers: insertion of Pd(O) into peripheral carbon-iodine bonds of carbosilane dendrimers derived from polyols. Crystal structure of Si{(CH2)3OC(O)C6H4I-4)}4

A carbosilane dendrimer with 12 peripheral iodoarene groups, Si{(CH2)3{Si(CH2)3O2C(C6H4I-4)}3}4 (G1-ArI, 5), and the corresponding G0 model compound, Si{(CH2)3O2CC6H4I-4}4 (G0-ArI, 4) have been prepared from polyol precursors. These compounds react with Pd(dba)2/tmeda (dba = dibenzylideneacetone, tmeda = N,N,N',N'-tetramethylethylenediamine) to yield periphery-palladated complexes, Si{(CH2)3O2C(C6H4-4)PdI(tmeda)}4 (G0-ArPdI(tmeda), 6) and Si{(CH2)3{Si(CH2)3O2C(C6H4-4)PdI(tmeda)}3}4 (G1-ArPdI(tmeda), 7). Dendrimer 7 represents the first example of an exclusively -bonded completely periphery-palladated dendrimer. Reactions of the model palladium(II) complexes PdI(EtO2C(C6H4)-4)(tmeda) (2) and PdI(EtO2C(C6H4)-4)(bpy) (3) (bpy = 2,2'-bipyridyl) with the transmetalation reagents LiMe and SnMe4 were not successful, while no reaction occurred with the related reagent Sn(C~N)Me3 [C~N = 8-(dimethylamino)-1-naphthyl]. The molecular structure of G0-ArI (5) has been determined by X-ray crystallography and has C2v symmetry in the solid state

Organopalladium functionalised dendrimers: insertion of Pd(O) into peripheral carbon-iodine bonds of carbosilane dendrimers derived from polyols. Crystal structure of Si{(CH2)3OC(O)C6H4I-4)}4

A carbosilane dendrimer with 12 peripheral iodoarene groups, Si{(CH2)3{Si(CH2)3O2C(C6H4I-4)}3}4 (G1-ArI, 5), and the corresponding G0 model compound, Si{(CH2)3O2CC6H4I-4}4 (G0-ArI, 4) have been prepared from polyol precursors. These compounds react with Pd(dba)2/tmeda (dba = dibenzylideneacetone, tmeda = N,N,N',N'-tetramethylethylenediamine) to yield periphery-palladated complexes, Si{(CH2)3O2C(C6H4-4)PdI(tmeda)}4 (G0-ArPdI(tmeda), 6) and Si{(CH2)3{Si(CH2)3O2C(C6H4-4)PdI(tmeda)}3}4 (G1-ArPdI(tmeda), 7). Dendrimer 7 represents the first example of an exclusively -bonded completely periphery-palladated dendrimer. Reactions of the model palladium(II) complexes PdI(EtO2C(C6H4)-4)(tmeda) (2) and PdI(EtO2C(C6H4)-4)(bpy) (3) (bpy = 2,2'-bipyridyl) with the transmetalation reagents LiMe and SnMe4 were not successful, while no reaction occurred with the related reagent Sn(C~N)Me3 [C~N = 8-(dimethylamino)-1-naphthyl]. The molecular structure of G0-ArI (5) has been determined by X-ray crystallography and has C2v symmetry in the solid state