Reactivity of terminal transition metal borylene complexes

The chemistry of terminal transition metal borylene complexes is reviewed, with particular attention to recent developments concerning the reactivity of these species. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:238–238, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20247     

Reactivity of terminal transition metal borylene complexes

The chemistry of terminal transition metal borylene complexes is reviewed, with particular attention to recent developments concerning the reactivity of these species. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:566–571, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20143     

Reactivity of cationic decamethylmetallocene complexes towards ketones

Reaction of decamethylmetallocene cations [Cp∗₂M]⁺ (M = Sc, Ti, V) with acetone and benzophenone resulted in the formation of the corresponding acetone adducts [Cp∗₂M(OCMe₂)_n]⁺ (M = Sc, n = 2; M = Ti, n = 1; M = V, n = 1) and benzophenone adducts [Cp∗₂M(OCPh)]⁺. The stoichiometry of these adducts is determined by both the electronic configuration of the metal center as well as steric pressure imparted by the large Cp∗-ligands. In addition, the M-O-C angle is controlled by the number of free valence orbitals of the Cp∗₂M unit.     

Reactivity of hexafluoride complexes of group IV-a elements

By means of the SCF MO LCAO method in the MNDO approximation, electronic and spatial structures have been calculated for complexes EF ₆ ^2– (E = Si, Ge, Sn) and also certain aqua derivatives of these complexes. It has been shown that an associative substitution mechanism may be realized for SnF ₆ ^2– , a conclusion that is supported by data on the kinetics of hydrolysis.Dnepropetrovsk Institute of Rail Transport Engineers. Translated from Teoreticheskaya i Éksperimental'naya khimiya, Vol. 27, No. 4, pp. 491–493, July–August, 1991. Original article submitted October 12, 1990.     

Reactivity of cyclometallated platinum complexes with chiral ligands

The reaction of [Pt₂Me₄(μ-SMe₂)₂] with 3-substituted iminic thiophenes and 2-phenylpyridine gives platinum (II) [C,N] cyclometallated complexes which contain a labile ligand (SMe₂ or CH₃CN). Several platinum (II) complexes have been synthesized by substitution reactions with phosphine or sulfoxide ligands to introduce, in most cases, a second chiral center. The new complexes’ reactions with methyl iodide were subsequently studied and showed results that are dependent on the steric and electronic effects of both the cyclometallated ligand and the ancillary phosphine or sulfoxide ligand. The structure of [PtMe((R)-C₁₀H₇CHMeNCHC₄H₂S)(CH₃CN)], a synthetic precursor, is also reported.     

Reactivity of copper(II)-alkylperoxo complexes

Copper(II) complexes 1a and 1b, supported by tridentate ligand bpa [bis(2-pyridylmethyl)amine] and tetradentate ligand tpa [tris(2-pyridylmethyl)amine], respectively, react with cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH(3)CN to provide the corresponding copper(II) cumylperoxo complexes 2a and 2b, the formation of which has been confirmed by resonance Raman and ESI-MS analyses using (18)O-labeled CmOOH. UV-vis and ESR spectra as well as DFT calculations indicate that 2a has a 5-coordinate square-pyramidal structure involving CmOO(-) at an equatorial position and one solvent molecule at an axial position at low temperature (-90 °C), whereas a 4-coordinate square-planar structure that has lost the axial solvent ligand is predominant at higher temperatures (above 0 °C). Complex 2b, on the other hand, has a typical trigonal bipyramidal structure with the tripodal tetradentate tpa ligand, where the cumylperoxo ligand occupies an axial position. Both cumylperoxo copper(II) complexes 2a and 2b are fairly stable at ambient temperature, but decompose at a higher temperature (60 °C) in CH(3)CN. Detailed product analyses and DFT studies indicate that the self-decomposition involves O-O bond homolytic cleavage of the peroxo moiety; concomitant hydrogen-atom abstraction from the solvent is partially involved. In the presence of 1,4-cyclohexadiene (CHD), the cumylperoxo complexes react smoothly at 30 °C to give benzene as one product. Detailed product analyses and DFT studies indicate that reaction with CHD involves concerted O-O bond homolytic cleavage and hydrogen-atom abstraction from the substrate, with the oxygen atom directly bonded to the copper(II) ion (proximal oxygen) involved in the C-H bond activation step.     

Reactivity of electrophilic terminal phosphinidene complexes toward phosphorus ylides

Stabilised phosphorus ylides react with transient terminal phosphinidene complexes [RP---W(CO)₅] (R=Ph, Me) to give products resulting from a formal insertion of P into a C---H bond via an initial nucleophilic attack of the ylidic carbon.     

Reactivity of carbon monoxide towards high valent molybdenum complexes

Reaction of carbon monoxide (3 atm) with Mo(O)₂(mes)₂ (mes = MESITYL = C₆H₂Me₃-2,4,6) in pyridine at room temperature affords dimesityl ketone 1 (5%) and 1,1′-bis(mesitoyl)-1,1′,4,4′-tetrahydro-4,4′-bipyridine 2 (25%), the molecular structure of which has been determined by an X-ray diffraction study. The formation of 2 represents the first example of N-acylation of a pyridine by CO mediated by a transition metal complex. It has been shown that the relative ratio of 1 and 2 is dependent on the reaction conditions and that the presence of pyridine is essential for the formation of 1. Reactions of CO with the isoelectronic complex Mo(N^tBu)₂mes₂ contrast sharply with Mo(O)₂mes₂ and, under the same conditions, no dihydropyridine is formed, the sole identified products being 1 (60%) and mesityltertiobutyl amide HN(^tBu)COmes (40%). In light of the experimental results and of extended Hückel calculations on dioxo and diimido d⁰ molybdenum complexes, a tentative mechanism for the formation of 2 is proposed which involves oxycarbene-like intermediates in the case of the more electrophilic dioxo molybdenum species.     

Reactivity of scandium terminal imido complexes towards metal halides

Reactions of scandium terminal imido complexes with CuI and [M(COD)Cl](2) (M = Rh, Ir) show two interesting reaction patterns, and the formed heterobimetallic complexes have intriguing structural features and show promising catalytic properties.     

Reactivity of carbyne and carbene complexes of molybdenum and tungsten

Summary The interconversion of carbyne, carbyne and hydride complexes derived from protonations oftrans-[M(CNMe)₂(dppe)₂](M = Mo or W) has been studied. The initial site of protonation is shown to be the isonitrile nitrogen and all protonations proceed through the common carbyne intermediatetrans-[M(CNHMe)(CNMe)(dppe)2]⁺. The CNHMe group in traps-[M(CNHMe)₂(dppe)₂]²⁺ is shown to be susceptible to electrophilic attack at N and nucleophilic attack at ligating C, the new complexestrans-[W(CNH2Me)(CNHMe)(dppe)₂](BF₄)₃ andtrans-[Mo(CHNHMe)(CNHMe)(dppe)2]BF4 being formed, respectively.     

Reactivity of molybdenum and rhenium hydroxo-carbonyl complexes toward organic electrophiles

The hydroxo compounds [Re(OH)(CO)(3)(N-N)] (N-N=bipy, 2 a; Me(2)-bipy, 2 b) were prepared in a biphasic H(2)O/CH(2)Cl(2) medium by reaction of [Re(OTf)(CO)(3)(N-N)] with KOH. In contrast, when anhydrous CH(2)Cl(2) was used, the binuclear hydroxo-bridged compound [[Re(CO)(3)(bipy)](2)(mu-OH)]OTf (3-OTf) was obtained. Compound [Re(OH)(CO)(3)(Me(2)-bipy)] (2 b) reacted with phenyl acetate or vinyl acetate to afford [Re(OAc)(CO)(3)(Me(2)-bipy)] (4) and phenol or acetaldehyde, respectively. The reactions of [Mo(OH)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1), 2 a, and 2 b toward several unsaturated organic electrophiles were studied. The reaction of 1 with (p-tolyl)isocyanate afforded an adduct of N,N'-di(p-tolyl)urea and the carbonato-bridged compound [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(mu-eta(1)(O),eta(1)(O)-CO(3))] (5). In contrast, the reaction of 2 a with phenylisocyanate afforded [Re(OC(O)NHPh)(CO)(3)(bipy)] (6); this results from formal PhNCO insertion into the O-H bond. On the other hand, compounds [Mo[SC(O)NH(p-tolyl)](eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (7), [Re[SC(O)NH(p-tolyl)](CO)(3)(Me(2)-bipy)] (8 a), and [Re[SC(O)NHEt](CO)(3)(Me(2)-bipy)] (8 b) were obtained by reaction of 1 or 2 b with the corresponding alkyl or aryl isothiocyanates. In those cases, RNCS was inserted into the M-O bond. The reactions of 1, 2 a, and 2 b with dimethylacetylenedicarboxylate (DMAD) gave the complexes [Mo[C(OH)-C(CO(2)Me)C(CO(2)Me)-O](eta(3)-C(3)H(4)-Me-2)(CO)(phen)] (9) and [Re[C(OH)C(CO(2)Me)C(CO(2)Me)O](CO)(2)(N-N)] (N-N=bipy, 10 a; Me(2)-bipy, 10 b). The molecules of these compounds contain five-membered metallacycles that are the result of coupling between the hydroxo ligand, DMAD, and one of the CO ligands. The new compounds were characterized by a combination of IR and NMR spectroscopy, and for [[Re(CO)(3)(bipy)(2)(mu-OH)]BF(4) (3-BF(4)), 4, 5, 6, 7, 8 b, 9, and 10 b, also by means of single-crystal X-ray diffraction.     

Reactivity of Al(III) complexes with substituted phthalocyanines

The results of a study of reactivity of Al(III) complexes with acido ligands (Cl^?, OH^?) and substituted phthalocyanine, containing 4 and 8 substituents (Cl, Br, NO₂ or COOH) in different positions of annelated benzene residues, are reviewed. Reactivity of coordinated phthalocyanines is studied by quantum-chemical and spectrophotometric methods for acid-base reactions and reactivity of coordination core is estimated by chemical kinetics methods using reactions of dissociation at the Al-N bonds. The Hammett-Taft correlation equations are derived for mono-and diprotonated tetrasubstituted phthalocyanines of Al(III) with positive ρ values of 10.2 and 59.8, respectively     

Reactivity of Schiff base rhenium(V) complexes with dimethylphenylphosphine

Summary The ReOX₂L(PPh₃) complexes (X = Cl or Br and L =N-methylsalicylideneiminate,N-phenylsalicylideneiminate, halfN,N-ethylenebis(salicylideneiminate) or 8-hydroxyquinolinate) react with dimethylphenylphosphine (PMe₂Ph) to give ReOX₂L(PMe₂Ph) initially by displacement of the phosphine ligand and then the ReX₂L(PMe₂Ph)₂ complexes with reduction of rhenium(V) to rhenium(III). The complexes were characterized by elemental analysis, magnetic susceptibility measurements and i.r. and¹H n.m.r. spectra.     

Reactivity of some “ladder” type complexes under conditions of metallation

The behavior of binuclear “ladder” type complexes FpL, where Fp=Cp(CO)₂Fe, L=p-MeC₆H₄Cr(CO)₃ (4), CH₂C₆H₅Cr(CO)₃ (5), andp-FpC₆H₄Cr(CO)₃ (6), under conditions of metallation was studied. Unlike compounds5 and6, the σ-bound ligand L in compound4 migrates from the iron atom to the cyclopentadienyl ring to give complexes Me(CO)₂FeC₅H₄−C₆H₄(p-Me)Cr(CO)₃. The electrochemical reduction potentials of the complexes4–6 and the rearrangement products were measured. The migration activity of L is determined by the ease of reductive cleavage of the Fe−L bond and the susceptibility of the system to undergo intramolecular electron transfer from the Cp ligand to the aromatic ring. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1832–1835, September, 1998.     

Reactivity of allylphosphines with iridium complexes: Diallylphosphines as new bidentate ligands

Addition of four equivalents of t-butyldiallylphosphine 1a to a solution of one equivalent of [(COE)₂IrCl]₂ in CHCl₃ at low temperature produced two isomers of thecomplex [t-Bu(C₃H₅)PCH₂CH=CH)]IrHCl(COE)-[PtBu(C₃H₅)₂] ( 2a ), which evolve at 40°C to [t-Bu(C₃H₅)PCH₂CH=CH)]IrCl(C₈H₁₅)[PtBu(C₃H₅)₂] ( 3a ), by a hydride transfer from iridium to the cyclooctene (COE) ligand. It is reasonable that the unsaturation at the iridium center is fulfilled by interactions with the allyl moieties of the phosphine that are not metalated. This has been demonstrated by bubbling CO into a solution of 3a in CHCl₃ at room temperature to obtain the carbonyl complex [t-Bu(C₃H₅)-PCH₂CH=CH)]Ir(CO)Cl(C₈H₁₅)[PtBu(C₃H₅)₂] ( 4a ). Under the same conditions, the reaction of diisopropylamindiallylphosphine 1b and anisyldiallylphosphine 1c afforded a mixture of isomers 3b and 3c , respectively. These results show that diallylphosphines can be considered to be a new family of bidentate ligands. Finally, the reaction of these phosphines with [(COD)IrCl]₂ (COD = 1,5 cyclooctadiene) shows the formation of tetracoordinated iridium (I) complexes IrCl(COD)(PR3), which are thermally stable. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:253–259, 1998     

Reactivity of allyl (o-halophenyl) ethers with organonickel (0) complexes

The reactivity of allyl (o-halophenyl) ethers with zerovalent nickel complexes, with triphenylphosphine and pyridine as ligands, leading to benzo[b]furan derivatives has been checked. Cyclization products were not isolated, but deallylation, substitution, reduction and rearrangement products were obtained in low to moderate yields. Mechanisms are proposed to explain the formation of these side products.

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Reactivity of palladium(II) complexes supported on carbon toward molecular hydrogen

The reactivity of Pd(II) complexes supported on carbon toward H₂ was studied. For the carboxylate complexes Pd(RCOO)₂ (R = Me, Me₃C, F₃C), it decreases upon decrease in the basicity of the acid RCO₂H. The reactivity of Pd(II) η³-allyl complexes increases with increase in the Mulliken charges on the C atom of the allyl ligand connected to the substituent R. The results are in line with the heterocyclic mechanism of H-H bond activation in the hydrogen molecule and can be used for optimization of the composition of the initial compounds for the preparation of palladium catalysts.