- Addition of boranes to (E)-(η5-C5H 5)2Zr(CH=CHPh)Cl
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In this study, the addition of boranes to (E)-(η5-C 5H5)2Zr(CH=CHPh)Cl (3) has been examined in order to investigate the regioselectivity of these 'hydroboration' reactions. We have found that these additions proceed with remarkable selectivity to give exclusive formation of a saturated organic molecule where one carbon atom has both the boron and the zirconium fragments. These reactions do not proceed via a conventional hydroboration reaction, but instead go through an initial transmetalation step to generate (E)-(η5-C5H 5)2Zr(H)Cl (1) and the corresponding alkenyl boron intermediate, whereupon subsequent hydrozirconation of this latter species gives the geminal products. An x-ray diffraction study has been conducted on gem-(η5-C5H5)2Zr(CH(Bpin)CH 2Ph)Cl (pin = 1, 2-O2C2Me4) (2). Crystals of 2 were orthorhombic with a = 18.545(3) A, b = 15.713(3) A, c = 16.157(3) A in the space group Pccn. An x-ray diffraction study has also been conducted on the trinuclear zirconium oxide species (η5-C5H5)2ZrO 2[ZrCl(η5-C5H5) 2]2 (4). Crystals of 4 were orthorhombic with a = 13.6000(8) A, b = 14.2252(8) A, c = 17.6500(10) A in the space group P2(1)2(1)2(1). [Figure not available: see fulltext.]
- Ferland, Patrick,Prosser, Kathleen E.,Bourque, Jeremy L.,Edwards, Ian C.,Hamilton, Nathan S.,Joyce, Lori E.,Finniss, Mathew C.,Yorke, Scott R.,Vogels, Christopher M.,Fontaine, Frederic-Georges,Decken, Andreas,Westcott, Stephen A.
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p. 811 - 816
(2013/08/25)
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- Practical synthesis of pinacolborane for one-pot synthesis of unsymmetrical biaryls via aromatic C-H borylation-cross-coupling sequence
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A method for practical preparation of pinacolborane from borane-diethylaniline and pinacol was newly developed. Aromatic C-H borylation of arenes with pinacolborane or bis(pinacolato)diboron catalyzed by 1/2[Ir(OMe)(COD)]2-(4,4′-di-tert-butyl-2,2′-bipyridine) at 25 °C in hexane to give arylboronic esters was directly followed by cross-coupling with aromatic bromides at 60 °C in the presence of PdCl2(dppf) (3.0 mol %) and K3PO4 in DMF. This one-pot, two-step procedure provided a variety of unsymmetrical biaryls in high yields.
- Kikuchi, Takao,Nobuta, Yusuke,Umeda, Junko,Yamamoto, Yasunori,Ishiyama, Tatsuo,Miyaura, Norio
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p. 4967 - 4971
(2008/09/21)
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- Rhodium silyl boryl hydride complexes: Comparison of bonding and the rates of elimination of borane, silane, and dihydrogen
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Spoilt for choice: a silane, dihydrogen, borane, or hydridoborate complex? The silyl boryl hydride complex [Cp*Rh(H2) (Et 3Si)(Bpin)] (Bpin = (pinacolato) boryl) could adopt any of these structures, but it appears to contain stronger B-H bonding than Si-H or H-H bonding and undergoes elimination of pinacolborane faster than of silane or hydrogen (see scheme). The bonding situation is studied by experimental and theoretical methods.
- Cook, Kevin S.,Incarvito, Christopher D.,Webster, Charles Edwin,Fan, Yubo,Hall, Michael B.,Hartwig, John F.
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p. 5474 - 5477
(2007/10/03)
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- Synthesis and characterization of platinum(II)-Bis(boryl) catalyst precursors for diboration of alkynes and diynes: Molecular structures of cis-[(PPh3)2Pt(B-4-Butcat)2], cis-[(PPh3)2Pt(Bcat)2], cis-[(dppe)Pt(Bcat)2], cis-[(dppb)Pt(Bcat)2]
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The reactions of the B-B-bonded compounds B2(cat)2 (cat = 1,2-O2C6H4) (1a), B2(4-But-cat)2 (1b), and B2(OCMe2CMe2O)2 (1c) with the Pt(0)-bis(phosphine) complex [(PPh3)2Pt(η-C2H4)] (4) via oxidative addition of the B-B bond yield cis-bis(boryl) Pt(II) complexes. The molecular structures of cis-[(PPh3)2Pt(Bcat)2]·C 6D6 (3a) and cis-[(PPh3)2Pt(B-4-Butcat)2] (3b) were determined by single-crystal X-ray diffraction. Reaction of 3a with 1 equiv of the bidentate phosphine dppe (Ph2PCH2CH2PPh2) or dppb (Ph2P(CH2)4PPh2) proceeds smoothly in toluene to give cis-[(dppe)Pt(Bcat)2] (5a) and cis-[(dppb)Pt(Bcat)2] (5b), respectively, which have also been characterized by X-ray diffraction. Compounds 3a,b and 4 are highly active catalyst precursors for the diboration of alkynes and 1,3-diynes. X-ray crystal structures of (E)-(4-MeOC6H4)C(Bcat)=CH(Bcat) (10c), (Z)-(C6H5)C(Bcat)=C(C6H5)(Bcat) (10e), and (Z,Z)-(4-MeOC6H4)C(Bcat)=C(Bcat)C(Bcat)=C(4-MeOC 6H4)(Bcat) (14a) confirm the cis stereochemistry of the boron substituents in three representative cases, namely, products of the catalyzed diboration of the terminal alkyne 4-MeOC6H4C=CH, the internal alkyne PhC=CPh, and the tetraboration of the diyne 4,4′-MeOC6H4C=CC=CC6H4OMe. The presence of the C=CSiMe3 moiety in catalytic reactions gives rise to additional products other than those derived from the diboration of the alkyne group. Metathetical reactions involving the diboron reagent and products derived from C-Si bond cleavage give rise to novel tris(boronate esters) as a result of the subsequent diboration of the C=CB(OR2) moieties formed by this competing process. The absence of catalytic activity using compound 5a, the extremely low activity of 5b, and the strong decrease in activity of 3b in the presence of added PPh3 suggests that phosphine dissociation is a critical step in the catalytic pathway.
- Lesley, Gerry,Nguyen, Paul,Taylor, Nicholas J.,Marder, Todd B.,Scott, Andrew J.,Clegg, William,Norman, Nicholas C.
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p. 5137 - 5154
(2008/10/08)
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