William C. Pearl

Tetrarhena-heterocycle from the Palladium-Catalyzed Dimerization of Re2(CO)8(μ-SbPh2)(μ-H) Exhibits an Unusual Host–Guest Behavior

The six-membered heavy atom heterocycles [Re(2)(CO)(8)(μ-SbPh(2))(μ-H)](2), 5, and Pd[Re(2)(CO)(8)(μ-SbPh(2))(μ-H)](2), 7, have been prepared by the palladium-catalyzed ring-opening cyclo-dimerization of the three-membered heterocycle Re(2)(CO)(8)(μ-SbPh(2))(μ-H), 3. The palladium atom that lies in the center of the heterocycle 7 was removed to yield 5. The palladium removal was found to be partially reversible leading to an unusual example of host-guest behavior. A related dipalladium complex Pd(2)Re(4)(CO)(16)(μ(4)-SbPh)(μ(3)-SbPh(2))(μ-Ph)(μ-H)(2), 6, was also formed in these reactions of palladium with 3.

New catalytic liquid-phase ammoxidation approach to the preparation of niacin (vitamin B3).

New highly dispersed bimetallic nanoscale catalysts based on rhenium combined with antimony or bismuth have been shown to be highly effective for the ammoxidation of 3-picoline to nicotinonitrile (precursor for vitamin B3) under mild conditions in the liquid phase.

Rhenium-bismuth carbonyl cluster compounds.

The reaction of Re(2)(CO)(8)[mu-eta(2)-C(H)=C(H)Bu(n)](mu-H) with BiPh(3) in heptane solvent at reflux yielded three new compounds Re(2)(CO)(8)(mu-BiPh(2))(2), 1 (14% yield), [Re(CO)(4)(mu-BiPh(2))](3), 2 (5% yield), and Re(2)(eta(6)-C(6)H(5)Ph)(CO)(7), 3, 4.7 mg (7% yield). Compound 1 contains two Re(CO)(4) groups joined by two bridging BiPh(2) ligands in a four-membered ring. There is no Re-Re bond in 1, Re...Re = 4.483(1) A. Compound 2 contains a six-membered Re(3)Bi(3) ring in a twist-boat conformation. When heated to 110 degrees C in toluene, compound 1 was transformed into the heterocycle 2 (8% yield), the known compound Re(CO)(5)Ph, 4 (25% yield), and the new compound Re(2)(CO)(8)(mu-BiPh)(2), 5 (4% yield). Compound 5 contains two Re(CO)(4) groups joined by two bridging BiPh ligands and a Re-Re bond, Re-Re = 3.1006(18) A. When compound 2 was heated to reflux in an octane solution, it was converted to two new compounds: cis-Re(4)(CO)(16)(mu-BiPh(2))(2)(mu(4)-BiPhBiPh), cis-6 and trans-Re(4)(CO)(16)(mu-BiPh(2))(2)(mu(4)-BiPhBiPh), trans-7 and a small amount of 1 (3% yield). cis-6 and trans-7 are isomers. Both compounds contain two fused Re(2)Bi(3) rings that share a quadruply bridging BiPhBiPh ligand that contains a Bi-Bi bond; Bi-Bi = 3.0237(7) A in cis-6 and Bi-Bi = 2.9765(3) A in trans-7. The phenyl groups on the bridging BiPhBiPh ligand in cis-6 have a cis-orientation and in trans-7 they have a trans-orientation. In the presence of visible light, cis-6 and trans-7 are transformed into yet another isomer Re(4)(CO)(16)(mu-BiPh(2))(2)(mu-BiBiPh(2)), 8, by a shift of one of the phenyl ligands on the bridging BiPhBiPh ligand to the neighboring bismuth atom. Compound 8 contains two fused rings, one five-membered Re(2)Bi(3) ring, and one four-membered Re(2)Bi(2) ring.

Osmium−Bismuth Complexes from the Reaction of Os3(CO)11(NCMe) with BiPh3

Five new compounds were obtained from the reaction of Os(3)(CO)(11)(NCMe), 1, with BiPh(3) in hexane solution at reflux. These have been identified as Os(2)(CO)(8)(mu-BiPh), 2, Os(CO)(4)Ph(2), 3, Os(4)(CO)(14)(mu-eta(3)-O=CC(6)H(5))(mu(4)-Bi), 4, Os(4)(CO)(15)Ph(mu(4)-Bi), 5, and Os(5)(CO)(19)Ph(mu(4)-Bi), 6. Cleavage of the phenyl groups from the BiPh(3) was the dominant reaction pathway. Fragmentation of the original triosmium cluster was accompanied by reaggregation processes that were facilitated by the naked bismuth to yield the higher nuclearity osmium cluster complexes containing spiro-bridging bismuth ligands. Compound 6 was photo-decarbonylated to yield the compound HOs(5)(CO)(18)(mu-eta(2)-C(6)H(4))(mu(4)-Bi), 7, formed by ortho-CH activation of the sigma-bonded phenyl ring in 6 to form a bridging eta(2)-benzyne ligand. Compounds 2- 7 were each characterized structurally by a single-crystal X-ray diffraction analysis.

Synergistic Behavior of Bimetallic Rhenium Cluster Catalysts: Spectroscopic Investigation into the Nature of the Active Site

Single-site Re nanoparticles were produced by anchoring dirhenium organometallic clusters on to the inner walls of mesoporous silica. The presence of oxophilic atoms (Sb or Bi) is essential to obtain well dispersed Re(0) centers. The interaction between the organometallic cluster and the silica support is critical for the generation of well-defined and isolated Re(0) single sites. FTIR spectroscopy was used to track the decomposition of the organometallic precursors and the adsorption of probe molecules such as CO on the metal sites sheds valuable information on the catalytic potential of this new class of bimetallic nanocatalysts.

Transformations and reactions of Re2(CO)8(mu-SbPh2)(mu-H) induced by the addition of a platinum(tri-t-butylphosphine) group.

Three products Re(2)[Pt(PBu(t)(3))](mu-SbPh(2))(CO)(8)(mu-H), 2, Re(2)[Pt(CO)(PBu(t)(3))]Ph(CO)(8)(mu(3)-SbPh)(mu-H), 3, and Re(2)[Pt(PBu(t)(3))](2)(CO)(8)(mu(4)-Sb(2)Ph(2))(mu-H)(2), 4, were obtained from the reaction of Re(2)(CO)(8)(mu-SbPh(2))(mu-H), 1, with Pt(PBu(t)(3))(2). Compound 3 was also obtained from 2 by further reaction with Pt(PBu(t)(3))(2). Compound 2 is a Pt(PBu(t)(3)) adduct of 1 formed by the insertion of the platinum atom into one of the Re-Sb bonds of 1 with formation of two Pt-Re bonds. Compound 3 contains an open Re(2)Pt cluster and was also obtained in a low yield by the addition of CO to 2. The addition of SbPh(3) to 2 yielded the compound Re(2)Pt(PBu(t)(3))(Ph)(CO)(8)(SbPh(3))(mu(3)-SbPh)(mu-H), 5, a SbPh(3) derivative of 3. Compound 4 can be viewed as a dimer of the fragment Re[Pt(PBu(t)(3))](CO)(4)(SbPh)(mu-H). The two halves of the molecule are held together by Pt-Sb bonds and a significant interaction directly between the Sb atoms, Sb-Sb distance, 2.9834(7) A. The Sb-Sb bonding in 4 was explained by density functional calculations. Compound 4 adds 2 equiv of CO at 1 atm/25 degrees C, one to each platinum atom, to yield the compound [Re(CO)(4)Pt(H)(CO)(PBu(t)(3))(mu(3)-SbPh)](2) which exists as a mixture of two noninterconverting isomers, cis-6 and trans-6. Both isomers of 6 were isolated and structurally characterized. Each isomer of 6 consists of a central planar Re(2)Sb(2) core composed of two Re(CO)(4) groups with two bridging SbPh ligands. There is a Pt(H)(CO)(PBu(t)(3)) group coordinated to each antimony atom of 6. In the cis-isomer both Pt(H)(CO)(PBu(t)(3)) groups lie on the same side of the Re(2)Sb(2) plane. In the trans-isomer the Pt(H)(CO)(PBu(t)(3)) groups lie on opposite sides of the Re(2)Sb(2) plane.

Reactions of the platinum (tri-tert-butylphosphine) group with bridging SbPh2 ligands in rhenium-antimony carbonyl complexes.

The reaction of [Re(CO)(4)(mu-SbPh(2))](2) (1) with Pt[P(t-Bu)(3)](2) in n-octane solvent at reflux (125 degrees C) has yielded two platinum-rhenium-antimony compounds, Re(2)(CO)(8)[(mu(3)-SbCH(2)CMe(2))Pt(H)P(t-Bu)(2)]P(t-Bu)(3)(mu-SbPh(2)) (2), and Re(2)(CO)(8)[Pt(CO)(CH(2)CMe(2))P(t-Bu)(2)](mu(3)-SbPh)(mu-SbPh(2)) (3), in low yields. Both products were formed by the cleavage of phenyl group(s) from one of the bridging SbPh(2) ligands in 1 and the addition of a PtP(t-Bu)(3) or Pt[P(t-Bu)(3)](2) group to the antimony atom. In both products, one of the tert-butyl groups was metalated on one of its methyl groups. In 2, metalation occurred on the antimony atom, while in 3, it occurred on the platinum atom. When the same reaction was performed under an atmosphere of hydrogen (1 atm), two additional new platinum-rhenium-antimony compounds, PtRe(2)(CO)(8)P(t-Bu)(3)(mu(3)-SbPh)(mu-SbPh(2))(mu-H) (4) and Re(2)(CO)(8)[PtH(CO){P(t-Bu)(3)}](mu(3)-SbPh)(mu-SbPh(2)) (5), were formed. In both products, a phenyl group was cleaved from one of the bridging SbPh(2) ligands in 1 and the addition of a PtP(t-Bu)(3) group to the antimony atom, but there was no metalation of the tert-butyl groups in these products. Instead, a hydride ligand was added to the complex. Compound 5 was also obtained from 4 by the addition of CO. Compound 4 also reacts with SbPh(3) to form the new compound PtRe(2)(CO)(7)P(t-Bu)(3)(mu(3)-SbPh)(mu-SbPh(2))(2) (6; 42% yield), which contains an additional bridging SbPh(2) ligand across the Pt-Re bond. The reaction of 6 with Pt[P(t-Bu)(3)](2) in a hydrogen atmosphere yielded the new compound Pt(2)Re(2)(CO)(7)[P(t-Bu)(3)](2)(mu(3)-SbPh)(3) (7) by the cleavage of one phenyl ring from each of the two SbPh(2) ligands in 6 and the addition of a PtP(t-Bu)(3) group to the resultant SbPh ligands. Compound 7 contains three triply bridging SbPh ligands. Compounds 2-7 were each characterized by a combination of IR, NMR, and mass spectrometry spectra and single-crystal X-ray diffraction analyses.

Host–Guest Behavior of a Heavy-Atom Heterocycle Re4(CO)16(μ-SbPh2)2(μ-H)2 Obtained from a Palladium-Assisted Ring Opening Dimerization of Re2(CO)8(μ-SbPh2)(μ-H)

The heavy-atom heterocycle Pd[Re2(CO)8(μ-SbPh2)(μ-H)]2 (5) has been synthesized by the palladium-catalyzed ring-opening cyclodimerization of the three-membered heterocycle Re2(CO)8(μ-SbPh2)(μ-H) (3). The Pd atom occupies the center of the ring. The Pd atom in 5 can be removed reversibly to yield the palladium-free heterocycle [Re2(CO)8((μ-SbPh2)(μ-H)]2 (6).