Bond properties of metal-ligand bonds

An empirical relation has been developed to compute the bond order of ionic systems. The computed values have been compared with those calculated by using the experimental values of bond polarizability derivatives and are found to be in fair agreement. This shows that the proposed empirical relation for computing bond orders is quite suitable for ions.

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Bindungseigenschaften von Metall-Ligand-Bindungen

Zusammenfassung Es wurde eine empirische Beziehung entwickelt, die die Berechnung von Bindungsordnungen für ionische Systeme erlaubt. Ein Vergleich der berechneten Werte mit solchen, die aus experimentellen Daten für Differentiale von Bindungspolarisierbarkeiten erhalten wurden, zeigte die Brauchbarkeit der Methode für Ionen.

     

Insertion of a stable dialkylsilylene into silicon-chlorine bonds

The reactions of a stable dialkylsilylene with chlorosilanes such as tetrachlorosilane, dimethyldichlorosilane, and dichlorosilane occurred smoothly at room temperature in hydrocarbon solvents to give the corresponding Si-Cl bond insertion products. In the reaction of the silylene with dichlorosilane, only the Si-Cl bond insertion product was obtained, while a similar reaction with dimethylchlorosilane gave only the Si-H insertion product, emphasizing the remarkable difference in the steric requirements between these two insertion reactions. No reaction took place during the treatment of the silylene with trimethylchlorosilane. The Si-Cl insertion reactions are expected to be applied in the synthesis of new organosilicon frameworks that cannot be obtained by conventional methods.     

Insertion of acetylene into osmium-hydrogen bonds incluster complexes

Complex H₂ Os₃ (CO)₁₀ reacts with acetylene or methyl-substituted acetylenes to give complexes of type HOs₃ (CH=CHR)(CO)₁₀ (R = H or Me) and Os₃ (R₁ C₂ R₂)(CO)₁₀ (R₁ and R₂ are H or Me) which convert to nonacarbonyl complexes with hydrogen transfer from ligand to metal.     

Organothorium complexes containing terminal metal-ligand multiple bonds

Organoactinide complexes containing terminal metal-ligand multiple bonds have received widespread attention over the past three decades. In the last few years, significant progress has been made in the synthesis and characterization of the imido, oxo, sulfido, and carbene-containing complexes of thorium. Such thorium complexes are of interest because of their unique structural properties, their potential application in novel group transfer reactions and catalysis, as well as their ability to engage the 5f orbitals in metal-ligand bonding. This short review summarizes the synthesis and reactivity of these thorium complexes.     

Transition metal promoted reactions of unsaturated hydrocarbons : III. Insertion of 1,2-dienes into allylic palladium bonds

Addition of strained olefins, based on norbornene, norbornadiene,benzonorbornadiene or bicyclo [2.2.2] octene skeletons to π-allylic(hexafluoroacetylacetonato) palladium(II) complexes [(π-All)Pd(Hfacac)], gives “enyl” products derived from “insertion” of the olefin into the least substituted terminal allylicpalladium bond. The reaction involves an initial rapid and reversible formation of (gs-allyl)(π-olefin)Pd(Hfacac). The rate-determining step involves migration of a σ-allylic carbon atom from Pd to the coordinated olefin in a concerted cis—exo addition of Pd---C across the double bond. Remote electronegative substituents on the olefin do not affect the coordinative ability of the olefin towards Pd. They do however inhibit the migration of the σ-allylic ligand to the coordinated olefin. This observation is interpreted in terms of a small degree of polarization of the π-olefin—Pd bond in the transition state for the σ-allyl migration.     

Inner-sphere activation barrier in reactions of electron transfer complex ions with asymmetric deformation of metal-ligand bonds

Summary An analysis has been made of the effects on the magnitude of the activation barrier from distortion of the configuration of a regular octahedron of the ligand skeleton in reactions of electron transfer between octahedral complexes of metals. The results obtained in numerical estimates of the magnitude of the barrier have been compared with the values calculated within the framework of the symmetric deformation model.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2441–2446, November, 1981.The author wishes to thank A. M. Kuznetsov for discussion of this work and for valuable comments.     

Insertion reactions of SO2 into Pd-OR bonds: preparation of alkyl sulfito complexes of palladium(II)

Mononuclear palladium-hydroxo complexes of the type [Pd(N-N)(C6F5)(OH)][(N-N = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine (Me2bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) react with SO2(1 atm) at room temperature in alcohol (methanol, ethanol, propanol or isopropanol) to yield alkyl sulfito palladium complexes [Pd(N-N)(C6F5)(SO2OR)](R = Me, Et, Pr or iPr). Similar alkyl sulfito complexes [Pd(N-N)(C6F5)(SO2OR)](N-N = bis(3,5-dimethylpyrazol-1-yl)methane); R = Me or Et) are obtained when [Pd(N-N)(C6F5)Cl] is treated with KOH in the corresponding alcohol ROH and SO2 is bubbled through the solution. The reaction of [Pd(bipy)(C6F5)(OH)] with SO2 in tetrahydrofuran gives [Pd(N-N)(C6F5)(SO2OH)]. The X-ray diffraction study of [Pd(tmeda)(C6F5)(SO2OPr)] has established the sulfur coordination of the propyl sulfito ligand.     

Insertion reactions of carbon dioxide into Zn-N bonds: syntheses and structures of tetrameric and dimeric alkylzinc carbamato complexes

The formal insertions of carbon dioxide into a series of methylzinc dialkylamide complexes (MeZnNR(2)) initially form solvent-free, tetrameric zinc carbamato complexes [Me(4)Zn(4)(O(2)CNR(2))(4)] (NR(2) = N(i-Pr)(2) (1), N(i-Bu)(2) (2), and piperidinyl (3)). These compounds have been characterized by traditional techniques as well as by single-crystal X-ray diffraction analyses. The tetrameric backbones seen in the solid state for 1-3 were structurally similar to each other. Addition of excess pyridine (py) to 1-3 breaks apart the tetramers and converts them into solvated dimeric species [Me(2)Zn(2)(O(2)CNR(2))(2)(py)(2)] (NR(2) = N(i-Pr)(2) (4), N(i-Bu)(2) (5), and piperidinyl (6)). X-ray crystallographic analyses of 4 and 5 confirmed the dimeric structure in the solid state. This study significantly increases the number of well-characterized zinc carbamates prepared via CO(2) insertion into zinc amides.     

Transition metal promoted reactions of unsaturated hydrocarbons : II. Insertion of bicyclic olefins into allylic-palladium and -platinum bonds

Addition of strained olefins, based on norbornene, norbornadiene,benzonorbornadiene or bicyclo [2.2.2] octene skeletons to π-allylic(hexafluoroacetylacetonato) palladium(II) complexes [(π-All)Pd(Hfacac)], gives “enyl” products derived from “insertion” of the olefin into the least substituted terminal allylicpalladium bond. The reaction involves an initial rapid and reversible formation of (gs-allyl)(π-olefin)Pd(Hfacac). The rate-determining step involves migration of a σ-allylic carbon atom from Pd to the coordinated olefin in a concerted cis—exo addition of PdC across the double bond. Remote electronegative substituents on the olefin do not affect the coordinative ability of the olefin towards Pd. They do however inhibit the migration of the σ-allylic ligand to the coordinated olefin. This observation is interpreted in terms of a small degree of polarization of the π-olefin—Pd bond in the transition state for the σ-allyl migration.     

Insertion reactions of phenyl isocyanate into hafnium nitrogen bonds: synthesis and reactivity of hafnium complexes bearing substituted pyrrolyl ligands

A bis(diethylamido)hafnium compound [C₄H₃N(CH₂NMe₂)-2]₂Hf(NEt₂)₂ (1) has been prepared in 79% yield by reacting Hf(NEt₂)₄ with 2 equiv. of [C₄H₃NH(CH₂NMe₂)-2] in heptane via deamination. Reacting compound 1 with 2 equiv. of phenyl isocyanate at room temperature in diethyl ether results in the PhNCO being inserted seletively into hafnium-NEt₂ bonds to generate [C₄H₃N(CH₂NMe₂)-2]₂Hf[PhNC(NEt₂)O]₂ (2) in 56% yield. Similarly, while reacting 1 with 2 equiv. of phenyl isocyanate for a week in toluene produces a mixture of 2 and [C₄H₃N(CH₂NMe₂)-2]Hf[PhNC(NEt₂)O]₃ (3). For comparison, reacting Hf(NEt₂)₄ with 4 equiv. of PhNCO in a toluene solution at room temperature results in the PhNCO inserted into Hf-N bonds, and forms a tetrakis-ureato hafnium compound Hf[PhNC(NEt₂)O]₄ (4) in 88% yield. A theoretical calculation found that the unpaired electrons of the ureato fragments of 2 are resonance delocalized between the C-O, C-NPh, and C-NEt₂ bonds, which are all partially doubly bonded.     

Insertion of group ivb metal dihalides into iron—carbon sigma bonds

The insertion reaction of GeCl₂, SnCl₂ and SnBr₂ into the iron—carbon sigma bond in the compounds Cp(CO)₂FeR (R = methyl, ethyl, n-propyl, p-methoxybenzyl, benzyl and p-trifluoromethyl- benzyl), to yield complexes with the Group IV metal bound to iron, is a radical chain process. A small substituent effect is observed in all cases for the benzyl series, the reaction being favoured by increasing electron donating ability of the para substituent. No clear reactivity trend is noted for the other alkyl complexes.     

Alkyne-functionalized ruthenium nanoparticles: ruthenium-vinylidene bonds at the metal-ligand interface

Stable ruthenium nanoparticles were prepared by the self-assembly of 1-dodecyne onto the "bare" Ru colloid surface. The formation of a Ru-vinylidene (Ru═C═CH-R) interfacial bonding linkage was confirmed by the specific reactivity of the nanoparticles with imine derivatives to form a heterocyclic complex at the metal-ligand interface, as manifested in (1)H and (13)C NMR, photoluminescence, and electrochemical measurements in which a ferrocenyl imine was used as the labeling probe. Notably, the resulting nanoparticles could also undergo olefin metathesis reactions with vinyl-terminated molecules, as exemplified by the functionalization of the nanoparticles with 1-vinylpyrene. In sharp contrast, no reactvity was observed with 1-dodecynide-stabilized ruthenium nanoparticles with either imine or vinyl derivatives, indicating that these (deprotonated) nanoparticles were stabilized instead by the formation of a Ru-C≡ dπ bond at the metal-ligand interface.     

Interaction of polyesters with epoxy polymers: Insertion of oxirane rings into ester bonds

Epoxy oligomers readily interact (hardening) with polyesters of different structures (heterochain, carbochain, aliphatic, aromatic), as indicated by the change of properties and infrared spectra of an epoxy polymer–polyester composition on heating. The curing is caused by the reaction of the oxirane ring with ester groups and proceeds by the mechanism of “insertion” of the fragment of the oxirane cycle into the ester bond without scission of the molecular chain of polyesters. This mechanism of interaction is confirmed by study of a model reaction of phenyl benzoate with phenylglycide ether to lead to the formation of 1,3-diphenyl ether of 2-benzoyl glycerine. The latter was also produced by another way. The reaction of polyarylate with phenylglycide ether confirmed also that interaction of the ester group with the oxirane ring proceeds by the mechanism of “insertion.” This interaction proceeds with a high conversion and without rupture of the macromolecules (molecular weight does not decrease). The reaction of the oxirane ring with the ester group is accelerated in the presence of sodium salts of carboxylic acids, carbonic acid, and sodium phenolates.     

Insertion reactions of silylenoid Ph2SiLi(OBu-t) into X-H bonds (X = F, OH, and NH2)

The insertion reactions of silylenoid [(tert-butoxy)diphenylsilyl]lithium Ph(2)SiLi(OBu-t) into HF, H(2)O, and NH(3) molecules have been studied by using density functional theory at the B3LYP/6-31G(d) level. To better understand the reactivity of silylenoid Ph(2)SiLi(OBu-t), its two most stable isomers, the p-complex (1) and the three-membered ring (2), were selected for reactants. Natural bond orbital (NBO) analysis has been performed to study the effects of charge transfer and to understand the nature of different interactions between atoms or groups. The results indicate that (i) the insertion of Ph(2)SiLi(OBu-t) into X-H bond proceeds in a concerted manner via a three-membered-ring transition state to form substituted silane Ph(2)SiHX with dissociation of LiOBu-t; (ii) the activation barrier increases in the order of HF < H(2)O < NH(3), and the barrier heights of the 1 insertions are higher than those of the 2 insertions, respectively; (iii) both 1 and 2 display ambiphilic character in their insertion reactions.     

Insertion reactions of thermally generated stannylenes R2Sn into Sn-X (X = Cl,Br, SPh) and Sn-Sn bonds

Thermally generated stannylenes R₂Sn insert efficiently into Sn-X bonds (X  Cl, 3r, SPh) as well as into electron deficient SnSn bonds e.g. in Me₂(Hal)SnSn(Hal)Me₂, but not into hexaalkyldistannanes R₆Sn₂ under the same conditions; stannylenes R₂Sn always behave as nucleophiles here.     

Insertion of unsaturated organic electrophiles into molybdenumbond-alkoxide and rheniumbond-alkoxide bonds of neutral,stable carbonyl complexes

Alkoxo complexes [Re(OR)(CO)(3)(N-N)] (R=Me, Et, tBu; N-N=2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'bipyridine (bipy'), 1,10-phenanthroline (phen)) and [M(OMe)(eta(3)-allyl)(CO)(2)(phen)] (M=Mo, W) have been synthesized in good yields and using mild conditions by the reaction of sodium alkoxides with [Re(OTf)(CO)(3)(N-N)] and [MCl(eta(3)-allyl)(CO)(2)(phen)] precursors. These have been characterized by IR and NMR spectroscopy as well as by X-ray diffraction for [W(OMe)(eta(3)-allyl)(CO)(2)(phen)] (10). The reactions of the molybdenum and rhenium alkoxo complexes with isocyanates, R'NCO, yield [L(n)M[N(R')C(O)OR]] complexes; the carbamate ligand, which results from an R'NCO insertion into the Mbond;OR bond, is monodentate through the nitrogen atom. The solid-state structures of Mo and Re examples have been determined by X-ray diffraction. The geometry around the carbamate nitrogen of these compounds is planar, and the distances indicate delocalization of the nitrogen lone pair involving mainly the carbonyl groups. Experiments carried out with the Re complexes showed that aryl isocyanates are more reactive than their alkyl counterparts, and that bulky R' groups led to slow rates of insertion. Insertion reactions were also observed with isothiocyanates, although here it is the Sbond;C bond that inserts into the Mbond;OR bond, and the resulting ligand is bound to the metal by sulfur. Competition experiments with the Re compounds indicate that isocyanates are more reactive than isothiocyanates towards the Rebond;OR bonds. Tetracyanoethylene inserts into the Rebond;OMe bond of [Re(OMe)(CO)(3)(bipy')], forming a complex with a 2-methoxytetracyanoethyl ligand; the structure of which was determined by X-ray diffraction. The formation of the xanthato complex [Re(SC(S)OtBu)(CO)(3)(bipy)] (20) by reaction of [Re(OTf)(CO)(3)(bipy)] with CS(2) and NaOtBu, but not by the reaction of CS(2) and [Re(OtBu)(CO)(3)(bipy)] (5 a), suggests that the insertion reactions do not take place by ionization of the alkoxo complexes to give the free alkoxide ion.     

Insertion of acrylonitrile into palladium methyl bonds in neutral and anionic Pd(II) complexes

The reactions of a series of Pd(II) methyl compounds of general formula LPd(NCCH(3))CH(3), where L is a bulky phenoxydiazene or phenoxyaldimine ligand with the polar olefin acrylonitrile (AN), are reported. The compounds react with an excess of AN to give the products of 2,1 insertion into the Pd-Me bond, yielding dimers and/or trimers which feature bridging alpha-cyano groups. The reactions were studied by low temperature (1)H NMR spectroscopy, revealing an initial formation of compounds featuring N-bound AN, which isomerized to an (unobserved) pi-bound species that rapidly underwent 2,1 insertion into the Pd-Me bond. Intermediate oligomeric complexes retaining a Pd-Me function were observed at low [AN] in these reactions. Under pseudo first-order conditions, k(obs) values of 8.5 x 10(-5) to 2.68 x 10(-3) M(-1) (-22 degrees C to 10 degrees C, 100 equiv of AN) and activation parameters of DeltaH++ = 14.4(5) kcal mol(-1) and DeltaS++ = -19(5) eu were obtained in one case. Comparison of the overall rates of insertion between two LPd(NCCH(3))CH(3), differing in the overall charge on the supporting ligand L, showed that the complex bearing a negatively charged ligand reacts with AN twice as fast as one with no anionic charge. The rates of insertion in both of these complexes are significantly faster than reported rates for analogous reactions in cationic Pd(II) derivatives, indicating that increasing the negative charge on the complex enhances the rate of AN insertion. These results provide fundamental mechanistic insights into a crucial reaction for incorporation of polar comonomers into alpha olefins via a coordination polymerization mechanism.     

Insertion of N-sulfinylsulfonamides and bis(methylsulfonyl)sulfur diimide into ironcarbon σ bonds

The N-sulfinylsulfonamides R′S(O)₂NSO (R′ = CH₃, p-CH₃C₆H₄) insert into the FeR bonds of η⁵-C₅H₅Fe(CO)₂R (R = CH₃, CH₂C₆H₅) to afford η⁵-C₅H₅Fe(CO)₂N[S(O)₂R′][S(O)R]. These products undergo oxidation by m-ClC₆H₄C(O)-OOH to η⁵-C₅H₅Fe(CO)₂N[S(O)₂R′][S(O)₂R] and rearrange on storage to η⁵-C₅H₅Fe(CO)₂S(O)[NS(O)₂R′]R. Reaction between the η⁵-C₅H₅Fe(CO)₂R and CH₃S(O)₂NSNS(O)₂CH₃ leads to the insertion products η⁵-C₅H₅Fe(CO)₂N-[S(O)₂CH₃][S(R)NS(O)₂CH₃].