Formation and reactions of metal-metal bonded heterobimetallic (C5H4PR2)-bridged (Zr-Ir) and (Zr-Rh) complexes: evidence for the participation of metal hydride intermediates

Treatment of the complexes [(C(5)H(4)PR(2))(2)Zr(CH(3))(2)](b: R = isopropyl; c: R = cyclohexyl) with the reagent HIr(CO)(PPh(3))(3) (2b) yield the heterobimetallic complexes [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Ir(CO)(PPh(3)))] (4b, 4c) with evolution of methane. The reaction of the -PPh(2) substituted analogue with initially yields an intermediate [(H(3)C)(2)Zr(mu-C(5)H(4)PPh(2))(2)Ir(H)(CO)(PPh(3))] 5a, that still contains both methyl groups at zirconium and does not contain a metal-metal bond. At room temperature, the intermediate reacts further with methane formation to eventually yield the (Zr-Ir) complex 4a. The corresponding [mu-C(5)H(4)PR(2))(2)(H(3)C-Zr-Rh(CO)(PPh(3)))] complexes 3a (R = Ph) and 3b (R = isopropyl) react cleanly with isopropyl alcohol to liberate methane and yield the corresponding [mu-C(5)H(4)PR(2))(2)(Me(2)CHO-Zr-Rh(CO)(PPh(3)))] products (7a, 7b). Carefully monitoring the reaction of with Me(2)CHOH by NMR revealed that the Zr-Rh functionality is attacked first to give the intermediate [Me(Me(2)CHO)Zr([micro sign]-C(5)H(4)PR(2))(2)Rh(H)(CO)(PPh(3))] (6b). This intermediate then reacts further to cleave off methane and re-form the (Zr-Rh) metal-metal bond to yield the product 7b. The tetrametallic mu-oxo-(Zr-Rh) metallocene derivate 11a was obtained starting from the (Zr-Rh) complex 3a and it was characterized by X-ray diffraction. It may be that this reaction is also initiated by H-OH addition to the [Zr-Rh] metal-metal bond.     

Developing soluble polymers for high-throughput synthetic chemistry

Soluble polymers have emerged as viable alternatives to resin supports across the broad spectrum of high-throughput organic chemistry. As the application of these supports become more widespread, issues such as broad-spectrum solubility and loading are becoming limiting factors and therefore new polymers are required to overcome such limitations. This article details the approach made within our group to new soluble polymer supports and specifically focuses on parallel libraries of block copolymers, de novo poly(styrene-co-chloromethylstyrene), PEG- stealth stars, and substituted poly(norbornylene)s.     

Silver-catalyzed imination of sulfoxides and sulfides

[reaction: see text] Silver salts in the presence of a chelating ligand efficiently catalyze the stereospecific imination of sulfoxides and sulfides with sulfonylamides and PhI(OAc)(2) to afford sulfoximines and sulfilimines, respectively, in good yields.     

Reactivity of silyl-substituted heterobimetallic iron-platinum hydride complexes towards unsaturated molecules: Part II. Insertion of trifluoropropyne and hexafluorobutyne into the platinum-hydride bond

Insertion of hexafluorobutyne into the Pt-H bond of the heterobimetallic complexes [(OC)₃Fe{Si(OMe)₃}(μ-Ph₂PXPPh₂)Pt(H)(PPh₃)] (1a X = CH₂; 1b X = NH) yields the σ-alkenyl complexes [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-Ph₂PXPPh₂)Pt{C(CF₃)C(H)CF₃}] (3a X = CH₂; 3b X = NH). This insertion reaction is accompanied by dissociation of the platinum bound PPh₃ ligand and saturation of the vacant coordination site by a dative μ−η²-Si-O → Pt interaction. Addition of the Pt-H bond of 1a across the triple bond of 3,3,3-trifluoropropyne affords in a regiospecific manner [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-dppm)Pt{C(CF₃)CH₂}] (2) having the trifluoromethyl substituent on the α-carbon. Addition of RNC to 3 affords the isocyanide adducts [(OC)₃Fe{Si(OMe)₃}(μ-Ph₂PXPPh₂)Pt(CNR){C(CF₃)C(H)CF₃}] (4a R = t-Bu, X = CH₂; 4b R = 2,6-xylyl, X = CH₂; 4c R = 2,6-xylyl, X = NH). In dichloromethane solution 3a is gradually transformed into the C₄F₆-bridged compound [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt(CO)] 5. The Pt-bound carbonyl ligand of 5 is displaced by xylylisocyanide or trimethylphosphite affording the derivatives [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt(CNxylyl)] 6 and [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt{P(OMe)₃}] 7. The molecular structures of 4a, 5 and 6 have been determined by X-ray diffraction studies.     

Synthesis and use of alpha-silyl-substituted alpha-hydroxyacetic acids

[reaction: see text] Rhodium-catalyzed oxygen transfer was used to generate benzyl 2-silyl-2-oxoacetates in good yields. The hydrogenation of these compounds led to chiral alpha-silyl-substituted alpha-hydroxyacetic acids. Resolution by means of HPLC using a chiral stationary phase afforded an enantiomerically pure representative of this class of compounds, which was successfully applied as a chiral ligand in an asymmetric aldol-type reaction.     

Synthesis,spectral, thermal and structural characterization of {[Cu(H2O)3][Cu(MAL)2] · 2H2O}∞ and [Cu(MAL)(TEA)] · H2O (MAL = malonate and TEA = triethanolamine)

A polymeric malonato-bridged copper(II) complex, {[Cu(H₂O)₃][Cu(MAL)₂]· 2H₂O}, and a mononuclear malonato-copper(II) complex with triethanolamine, [Cu(MAL)(TEA)]·H₂O, have been prepared and characterized by elemental analyses, i.r., u.v.–vis, magnetic measurements and single crystal X-ray diffraction. The polymeric complex consists of one-dimensional chains containing the MAL bridged [Cu(H₂O)₃]²⁺ and [Cu(MAL)₂]^2– ions and each MAL ligand simultaneously exhibits chelating bidentate (at one copper atom) and bridging (at the adjacent copper atom) coordination modes. The intrachain Cu1...Cu2 separation is 4.963 Å and the polymeric complex exhibits antiferromagnetic behaviour. In the mononuclear complex, the copper(II) ion is octahedrally coordinated by one bidentate MAL and one tetradentate neutral TEA ligands. The i.r. spectra and thermal decompositions of both complexes are described.