Michael Knorr

Reactivity of the metal-silicon bond in organometallic chemistry☆

Abstract The reactivity of molecules containing a metal-silicon bond is currently attracting considerable attention owing to its relevance to a number of important stoichiometric and catalytic transformations. The focus of this review concerns those stoichiometric reactions involving the metal-silicon bond which result in isolable Si-containing metal complex(es). Catalytic reactions are therefore only considered when strong evidence for MSi intermediate complexes is provided. Reactions in which the silicon atom leaves the metal complex are not examined. For convenience, the reactions will be classified into insertion and migration reactions, although this terminology does not necessarily have a mechanistic implication and is somewhat arbitrary since many reaction products could belong to one or the other section.

Reactivity of CuI and CuBr toward Et2S: a reinvestigation on the self-assembly of luminescent copper(I) coordination polymers.

CuI reacts with SEt(2) in hexane to afford the known strongly luminescent 1D coordination polymer [(Et(2)S)(3){Cu(4)(mu(3)-I)(4)}](n) (1). Its X-ray structure has been redetermined at 115, 235, and 275 K in order to address the behavior of the cluster-centered emission and is built upon Cu(4)(mu(3)-I)(4) cubane-like clusters as secondary building units (SBUs), which are interconnected via bridging SEt(2) ligands. However, we could not reproduce the preparation of a coordination polymer with composition [(Et(2)S)(3){Cu(4)(mu(3)-Br)(4)}](n) as reported in Inorg. Chem. 1975, 14, 1667. In contrast, the autoassembly reaction of SEt(2) with CuBr results in the formation of a novel 1D coordination polymer of composition [(Cu(3)Br(3))(SEt(2))(3)](n) (2). The crystal structure of 2 has been solved at 115, 173, 195, and 235 K. The framework of the luminescent compound 2 consists of a corrugated array with alternating Cu(mu(2)-Br)(2)Cu rhomboids, which are connected through two bridging SEt(2) ligands to a tetranuclear open-cubane Cu(4)Br(4) SBU, ligated on two external Cu atoms with one terminal SEt(2). The solid-state luminescence spectra of 1 and 2 exhibit intense halide-to-metal charge-transfer emissions centered at 565 and 550 nm, respectively, at 298 K. A correlation was also noted between the change in the full width at half-maximum of the emission band between 298 and 77 K and the relative flexibility of the bridging ligand. The emission properties of these materials are also rationalized by means of density functional theory (DFT) and time-dependent DFT calculations performed on 1.

Bimetallic silicon chemistry: New opportunities in coordination and organometallic chemistry

Abstract Bimetallic complexes containing silyl or siloxy ligands may display unique structures and reactivity patterns that are directly related to a subtle interplay between the metals and the ligands. Access to this class of compounds will be discussed. The recently discovered hemilabile behaviour of the bridging –Si(OR)3 ligand in heterobimetallic complexes has led to a number of developments in our group and others that are reviewed here. This will include the chemistry of Ph2PCH2PPh2 (dppm)-stabilized Fe–Pd and Fe–Pt alkyl complexes which allow, under mild conditions, controlled insertion reactions of isonitriles, alkynes or CO/olefins into the metal–carbon bond. In some cases, silicon migration reactions leading to new μ-siloxycarbene complexes have been observed. Other reactions that will be presented are the alkyne insertion into metal–hydride bonds, fluorination of the Si(OR)3 ligand and the catalytic dehydrogenative coupling of stannanes HSnR3. By altering the nature of the assembling ligand (μ-PR2 vs. μ-dppm) but keeping the metals and the silyl ligand unchanged, the first examples of intramolecular silyl migration from one metal to another were discovered. Finally, the use of aminosilyl in place of alkoxysilyl ligands led to the formation of new silylene complexes, to unprecedented examples of metal-mediated substituent exchange reactions between phosphorus and silicon, and to the characterization of the first complexes containing a bridging aminosilyl ligand. Many of these reactions involve steps that are directly relevant to the mechanisms of currently investigated catalytic systems.

A strategic approach to the synthesis of functionalized spirooxindole pyrrolidine derivatives: in vitro antibacterial, antifungal, antimalarial and antitubercular studies

A series of spiro[pyrrolidin-2,3′-oxindoles] has been synthesized by exo-selective 1,3-dipolar cycloaddition reaction of a stabilized azomethine ylide, generated in situ by thermal [1,5]-prototropy, across various (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones. The stereochemistry of these N-heterocycles has been confirmed using an X-ray diffraction study. To rationalize the observed regio- and stereoselectivity, DFT calculations at the B3LYP/6-31G(d,p) level were employed. It was found that this reaction preferentially affords the kinetic product. The compounds have been screened for their in vitro antibacterial, antifungal, antimalarial and antitubercular activities. Several compounds exhibited good activities comparable to those of established standard drugs.

Adsorption of Ni(II) ions on colloidal hybrid organic-inorganic silica composites.

Two new silica-based composites were prepared as adsorbents for the capture of Ni(II) ions. The first strategy consists in coating chitosan on colloidal fumed silica after acidic treatment yielding the composite SiO(2)+CS. The second route involves in a first step surface condensation of triethoxysilylbutyronitrile, followed by acidic hydrolysis of the surface-bound nitrile groups affording silica particles covered by carboxylic group. In a third step, chitosan has been grafted on the surface-bound C(=O)OH groups yielding the composite SiO(2)(CO(2)H)+CS. The novel hybrid materials were characterized by IR spectroscopy, scanning electron and AFM microscopy, and zeta potential measurements. Batch experiments were conducted to study the sorption performance of these composites for Ni(II) removal from aqueous NiCl(2) solution at different pH. Both Langmuir, Freundlich, and Temkin isotherm models provide good fits with the experimental data. It was shown that these low-cost materials present a promising capacity to adsorb Ni(II) ions. At pH 7, the maximum adsorption capacity q(max)of Ni(II) on the adsorbent, is found to be 182 mg g(-1) for SiO(2)+CS, and 210 mg g(-1) for SiO(2)(CO(2)H)+CS.

Synthesis and reactivity of phosphine-substituted hydrido silyl complexes mer-[FeH(SiR3)(CO)3{Ph2P(CH2)nPPh2}](n= 1 or 4), mer-[FeH{Si(OMe)3}(CO)3(PPh2H)] and mer-[FeH{Si(OMe)3}(CO)3{Ph2PCH2C(O)Ph}]. Synthesis of bimetallic complexes and crystal structure of mer-[(Ph3P)Cu(µ-dppm)Fe{Si(OMe)3}(CO)3]

Phosphine-substituted hydrido silyl complexes [FeH(SiR3)(CO)3L](L = phosphine) have been prepared by carbonyl substitution in cis-[FeH(SiR3)(CO)4]. The reaction of cis-[FeH{Si(OMe)3}(CO)4]1a with Ph2PCH2PPh2(dppm) in a 1 : 1 ratio afforded mer-[FeH{Si(OMe)3}(CO)3(dppm-P)]2a; mer-[FeH{Si(OEt)3}(CO)3(dppm-P)]2b was obtained similarly. The reaction of [FeH(SiPh3)(CO)4] with Ph2P(CH2)4PPh2(dppb) afforded mer-[FeH(SiPh3)(CO)3(dppb-P)]3a and that of 1a with vinylidenebis(diphenylphosphine)(vdpp) afforded under analogous conditions the chelated complex cis-[FeH{Si(OMe)3}(CO)2(vdpp-PP′)]3c. Reaction of 1a with the functional phosphine Ph2PCH2C(O)Ph yielded mer-[FeH{Si(OMe)3}(CO)3{Ph2PCH2C(O)Ph}]4 and with PPh2H, mer-[FeH{Si(OMe)3}(CO)3(PPh2H)]5 was obtained. The anionic complexes K[Fe(SiR3)(CO)3(PPh2X)]6a(R = OMe, X = CH2PPh2), 6b(R = OEt, X = CH2PPh2), 6c[R = Ph, X =(CH2)4PPh2] and 6d[R = OMe, X = CH2C(O)Ph] were generated from the corresponding hydrido complexes by deprotonation with excess of KH in tetrahydrofuran (thf). They were used to prepare metal–metal bonded heterobinuclear complexes mer-[LM(µ-dppm)Fe{Si(OMe)3}(CO)3]7b(M = Cu, L = PPh3), 7c(M = Cu, L = MeCN), 8a(M = Ag, L = AsPh3), 8b(M = Ag, L = PPh3) and 10(M = Au, L = PPh3). Complex 8a dissociates AsPh3 in solution with formation of mer-[[graphic omitted])Si(OMe)2}(CO)3]9, which contains an unusual alkoxysilyl bridge resulting in a AgFeSiO four-membered ring. This very labile complex was also obtained from the reaction of 6a with [Ag(MeCN)2]NO3. For comparative purposes, we also prepared mer-[(Ph3P)AuFe{Si(OMe)3}(CO)3(PPh3)]11. All complexes were characterized by elemental analysis and spectroscopic (IR and 1H and 31P-{1H} NMR) methods. The crystal structure of compound 7b has been determined by X-ray diffraction: monoclinic, space group P21/c, with a= 11.542(5), b= 18.567(7), c= 21.830(7)A, β= 94.67(2)° and Z= 4. The copper atom is trigonally co-ordinated by two phosphorus atoms from the dppm and PPh3 ligands and by the Fe atom [Fe–Cu = 2.540(2)A]. The Fe atom is in an octahedral arrangement determined by three carbon atoms from carbonyl groups, a phosphorus atom of the bridging dppm ligand and by the Si atom of the Si(OMe)3 group.

Regio- and Stereoselective Synthesis of Spiropyrrolizidines and Piperazines through Azomethine Ylide Cycloaddition Reaction

A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused piperazines through a stepwise [3 + 3] cycloaddition pathway is observed. The stereochemistry of these N-heterocycles has been confirmed by several X-ray diffraction studies. Some of these compounds exhibit extensive hydrogen bonding in the crystalline state. To enlighten the observed regio- and stereoselectivity of the [3 + 2] cycloaddition, calculations using the DFT approach at the B3LYP/6-31G(d,p) level were carried out. It was found that this reaction is under kinetic control.

(Phenylthiomethyl)silanes and (butyltelluromethyl)silanes as novel bifunctional ligands for the construction of dithioether-, ditelluroether- and transition metal /silicon complexes

Abstract The functionalized silanes (PhSCH2)2SiPh2 (1a), (PhSCH2)2Si(vinyl)Me (1b), (PhSCH2)2Si(H)Me (1c) and (PhSCH2)3SiH (1d) have been prepared and co-ordinated as chelating dithioether ligands or via a covalent MSi bond to various transition metal centers. Thus, reaction of 1a with [PtCl2(PhCN)2] affords the dithioether complex cis-[PtCl2{(PhSCH2)2SiPh2}] (3), which exist in solution as mixtures of dl - and meso-invertomers. Treatment of [Re(μ-Br)(CO)3THF]2 with 1a–c yielded the stereochemically rigid chelate complexes fac-[ReBr(CO)3{(PhSCH2)2SiR1R2}] (R1, R2=Ph (4a)), (R1=vinyl, R2=Me (4b)), (R1=H, R2=Me (4c)). Due to the presence of two different substituents R1 and R2 on Si, 4b and 4c are isolated as 50:50 mixtures of diastereomers. The presence of a SiH function in 1c,d can be exploited for SiH activation reactions. Thus, oxidative addition on [Pt(PPh3)2(CH2CH2)] yields the fluxional hydrido silyl complex [Pt(H)(PPh3)2{Si(CH2SPh)2Me}] (5a) and the rigid derivative [Pt(H)(PPh3)2{Si(CH2SPh)3}] (5b). The ditelluroether complexes cis-[PtCl2{(RTeCH2)2SiMe2)] (6a, R=Ph), (6b, R=n-Bu) are obtained by treatment of [PtCl2(PhCN)2] with (PhTeCH2)2SiMe2 (2a) and (n-BuTeCH2)2SiMe2 (2b), respectively. The complex fac-[ReBr(CO)3{(n-BuTeCH2)2SiMe2}] (7) results from the reaction of [Re(μ-Br)(CO)3THF]2 with (2b). The new compounds have been studied by multinuclear NMR techniques, the crystal structures of 3, 4a, 5 and 6b have been determined by X-ray diffraction studies.

Novel Metal‐to‐Metal Silyl‐Migration Reactions in Heterometallic Complexes

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 >> mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.

Formation of an unprecedented (CuBr)5 cluster and a zeolite-type 2D-coordination polymer: a surprising halide effect

A unique pentanuclear cluster within a zeolite-type polymer ([Cu5(μ4-Br)(μ3-Br)2(μ2-Br)2](μ2-MeSPr)3)n (1; void space >81%) and a luminescent 1D ([Cu(μ3-I)]4(MeSPr)3)n polymer, 2, are formed when MeSPr reacts with CuBr and CuI.