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Rhodium complexes containing arylspiroborates derived from 3,5-di-tert-butylcatechol and their use in catalyzed hydroborations

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  • Michael J. Geier
  • Stephen J. Geier
  • Nathan R. Halcovitch
  • Christopher M. Vogels
  • Andreas Decken
  • Stephen A. Westcott
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<mark>Journal publication date</mark>22/03/2013
<mark>Journal</mark>Polyhedron
Volume52
Number of pages9
Pages (from-to)1181-1189
Publication StatusPublished
Early online date4/07/12
<mark>Original language</mark>English

Abstract

Tl(acac) reacts quantitatively with B2butcat3 (butcat = 3,5-di-tert-butylcatecholato) to give butcatB(acac) and Tl(Bbutcat 2) (1), the latter of which is soluble in common organic solvents such as THF and dichloromethane. Addition of 1 to a mixture of [RhCl(coe) 2]2 (coe = cis-cyclooctene) and diphosphine in THF gave the thallium bridged dinuclear complexes [(P2)Rh(μ-Cl) 2(μ-Tl)Rh(P2)][Bbutcat2] (2-5, P2 is dppm = 1,1′-bis(diphenylphosphino)methane, dppe = 1,2- bis(diphenylphosphino)ethane, dppp = 1,3-bis(diphenylphosphino)propane and dppb = 1,4-bis(diphenylphosphino)butane) as the only new rhodium containing species. Unsymmetrical binding of the thallium atom is observed in some cases owing to a secondary interaction with the phenyl rings of the phosphine ligands. Mononuclear cationic species of the type [(P2)Rh(NCCH 3)2][Bbutcat2] (6-9) were formed when reactions were carried out in acetonitrile, where preferential binding of the solvent was observed over the bulky arylspiroborate ligand. The zwitterionic species Rh(η6-butcatBbutcat)(P2), 11 and 12, could be generated via a different route, by addition of B2butcat3 to Rh(acac)(P2), but only for the sterically-constrained diphosphines dppm and dppe, respectively. While all new complexes effectively catalyzed the addition of catecholborane to 4-vinylanisole and α-methylstyrene, product distributions suffered from a competing dehydrogenative borylation pathway.