Cooperativity in bimetallic dihydroalkoxylation catalysts built on aromatic scaffolds

Significant rate enhancements with a rigid anthracene scaffold

Joanne H H Ho, Sandra W S Choy, Stuart A. MacGregor, Barbara A. Messerle*

*Corresponding author for this work

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

This work describes investigations into metal-catalyzed sequential reactions using a series of single metal and bimetallic Rh(I) and/or Ir(I) pyrazolyl complexes. Monometallic complexes with bis(1-pyrazolyl)methane (bpm) ligands [M(CO) 2(bpm)]BAr F 4 (1), bimetallic complexes [M 2(CO) 2(L scaffold)][BAr F 4] 2 (2-4) where M = Rh(I) or Ir(I) bearing bitopic ligands L scaffold = bis(1-pyrazolyl)methane-derived ligands, p-C 6H 4[CH(pz) 2] 2 (L p), m-C 6H 4[CH(pz) 2] 2 (L m), and anthracene-bridged 1,8-C 14H 8[CH(pz) 2] 2 (L Ant), [M 2(CO) 4(L p)]-[BAr F 4] 2 (2), [M 2(CO) 4(L m)][BAr F 4] 2 (3), and [M 2(CO) 4(L Ant)][BAr F 4] 2 (4) were used as catalysts. The efficiency of the complexes as catalysts was tested for the dihydroalkoxylation of a series of alkyne diol substrates, 2-(6-hydroxyhex-1-ynyl)benzyl alcohol (5), 1-methyl-3-heptyne-1,7-diol (6), 2-(5-hydroxypent-1-ynyl)benzyl alcohol (7), and 2-(4-hydroxybut-1-ynyl)benzyl alcohol (8), forming spiroketals. All complexes tested were highly effective catalysts for the intramolecular dihydroalkoxylation reaction. The homobimetallic complexes 2-4 showed significant enhancement in activity and selectivity relative to the single metal catalysts (1). The order of catalytic activity of the bimetallic complexes was found to be [M 2(CO) 4(L Ant)][BAr F 4] 2 > [M 2(CO) 4(L m)][BAr F 4] 2 > [M 2(CO) 4(L p)][BAr F 4] 2 for all substrates, and the bimetallic cooperativity index was established for each reaction.

Original languageEnglish
Pages (from-to)5978-5984
Number of pages7
JournalOrganometallics
Volume30
Issue number21
DOIs
Publication statusPublished - 14 Nov 2011
Externally publishedYes

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