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  • Author: Michael Hagel x
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A synthetic route to 6,6′-dimesityl-2,2′-bipyridine is presented that involves a Suzuki coupling of 6,6′-dibromo-2,2′-bipyridine with mesityl boronic acid. The new sterically crowded ligand is investigated by X-ray analysis and its coordination behavior in the presence of copper(I) is examined.

A three-step preparation of the benzofluorene core is presented. The last step involves thermal cyclization of 3 -ene-1,6 -diyne (7) leading to the formation of four benzofluorene derivatives, one of which has been investigated by X-ray analysis. The harsh thermal conditions indicate that the cyclization of 7 might not proceed via a biradical intermediate as would be anticipated by a mechanistic proposal from Ueda.

Abstract Allyl thioether complexes [CpRu(P-P)(SRR′)]PF6 (P-P = Ph2PCH2PPh2 (dppm), Ph2PC2H4PP2 (dppe), R = Me, Et, Ph, R′ = 3-propenyl, 3-cyclohexenyl, 2-methyl-2-buten-4-yl) and [CpRu(chir)(SRR′)]PF6 (chir = (S,S)-Ph2PCHMeCHMePPh2, R = Me, CH2Ph, R′ = 2-methyl-2-buten-4-yl) are obtained from the corresponding thiolate complexes by reaction with the appropriate allyl bromide. Careful oxidation with dimethyldioxirane (DMD) gave the allyl sulfoxide complexes [CpRu(P-P)(MeS(O)CH2CH=CH2)]PF6 (P-P = dppm, dppe). Double oxidation to the corresponding sulfinylmethyl epoxide complexes can be readily achieved with an excess of DMD. Oxidation of the chir complexes proceeds with only moderate diastereoselectivity. The structure of the (R, R/S, S) diastereomer of [CpRu(dppm)(MeS(O)CH2CHCH2O)]PF6 was determined: monoclinic space group P21/c (No. 14), a = 11.21(2), b = 16.762(9), c = 18.45(4) Å, β = 94.4(1)°, Z = 4. For a representative example, the decomplexation of the sulfoxide-epoxide ligand by sodium iodide in acetone was demonstrated.

Abstract

Reaction of the complex [CpRe(NO)(CO)2]BF4 with triisopropylphosphine gives the chiral CO substitution product [CpRe(NO){P(i-Pr)3}(CO)]BF4. The corresponding triphenylphosphite complex [CpRe(NO){P(OPh)3}(CO)]BF4 may be obtained by oxidative CO removal. Reduction of the remaining CO ligand with NaBH4 furnishes the corresponding methyl com­plexes [CpRe(NO)(L)(CH3)]. The structure of [CpRe(NO){P(i-Pr)3}(CH3)] was determined: triclinic space group P1̄ (No. 2), a = 8.442(4), b = 9.582(5), c -11.820(8) Å, α= 81.81 (4), β = 87.18(4), γ = 63.87(5)°, Z = 2. Reaction of the methyl complexes with HBF4 in the presence of thiols gives, after chromatographic workup, the thiolate derivatives [CpRe(NO)(L)(SR)] (L = CO, P(OPh)3, P(i-Pr)3, R = CH2Ph, CH2(4-C6H4Cl), CH2(4-C6H4OMe), CH3, C2H5). The structure of [CpRe(NO){P(i-Pr)3}(SCH3)] was determined: monoclinic space group P21 (No. 3), a = 7.0515(7), b = 17.3469(10), c = 7.9727(7) Å, β = 114.021(7)°, Z = 2. In both structures, a significant opening of the angle N-Re-X (X = C, S) suggests that antibonding interactions between orbitals of the ligand X and the second-highest MO of the [CpRe(NO)(L)] complex fragment are avoided.

Halfsandwich ruthenium thiolate complexes bearing electron-withdrawing phosphite or phosphonite ligands were prepared from [CpRu(PPh3)2(SR)] (R = Ph, CH2Ph, Me) and triphenylphosphite or (S,S)-bis(binaphthylphosphonito)ethane (bbpe), respectively. Reaction with 1-bromo-3-methyl-2-butene in the presence of NH4PF6 gave the corresponding allylthioether complexes [CpRu(PR'3)2(S(R)CH2CH=CMe2)]PF6. Treatment with an excess of dimethyldioxirane (DMD) transformed the triphenylphosphite derivatives into diastereomeric (oxiranylmethyl) sulfoxide complexes with 18 - 80% de. NMR monitoring of the reaction revealed that the oxidant attacks the sulfur atom and the C=C double bond with comparable rates. Similar oxidation of the bbpe complexes gave mixtures of four diastereoisomers with ratios of (64 : 15 : 13 : 8 ) and (51 : 24 : 15 : 10), respectively.

Four novel stable enols (one characterized by X-ray crystal structure analysis) were synthesized and investigated under oxidative conditions to yield benzofurans. Depending on the donor qualities of the heteroaryl substituent the reaction following the one-electron oxidation could be stopped on the stage of the cyclohexadienyl cation whose lifetime was measured. Oxidation potentials were determined for the enols, the enolates and the α-carbonyl radicals. Oxidation of benzofurans yielded dimeric species or intramolecular cyclization products.