Synthesis of Cobaltaborane Clusters from [Cp*CoCl]2 and Monoboranes. New Structures and Mechanistic Implications

Yasushi Nishihara, Kathryn J. Deck, Maoyu Shang, Thomas P. Fehlner, Brian S. Haggerty, Arnold L. Rheingold

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59 Citations (Scopus)

Abstract

The reaction of [Cp*CoCl]2, Cp* = η5-C5Me5, with BH3·THF leads to the formation of nido-1-(η5-C5Me5)Co-2-(η4-C5Me5H)CoB3H8, 1 (60%, monoclinic P21/n, a = 8.076(1), b = 20.359(2), c = 13.880(2) Å, β = 91.23(1)°, V = 2281.7(6) Å3, d(calcd) = 1.251g/cm3, Z = 4), and arachno-(η5-C5Me5)CoB4H10, 2 (2–10%, monoclinic P21/c, a = 13.954(3), b = 14.185(4), c = 29.383(7) Å, β = 100.61(2)°, V= 5717(2) Å3, d(calcd) = 1.150 g/cm3, Z = 16) via the metastable paramagnetic intermediate [{(η5-C5Me5)Co}(BH3Cl)]2, 9, with the coproduct BH2Cl. Heating 1 leads to nido-2,4-{(η5-C5Me5)Co}2B3H7, 3 (80%, tetragonal P42/n, a = b = 23.440(4), c = 8.317(2) Å, V = 4570(1) Å3, d(calcd) = 1.244 g cm-3, Z = 8). The reaction of [Cp*CoCl]2 with LiBH4 leads to the formation of closo-2,3,4-{(η5-C5Me5)Co}3B2H4, 4 (20%, rhombohedral, R3, a = 17.994 (1) Å, c = 15.986 (1) Å, V = 4477.3 Å3, d(calcd) = 1.347 g cm−3, Z = 6) and lesser amounts of closo-1,2,3-{(η5-C5Me5)Co}3B3H5, 5 (triclinic, P1, a = 8.461 (2) Å, b = 10.718 (2) Å, c = 17.591 (4) Å, V = 1511.0 (8) Å3, d(calcd) = 1.363 g cm−3, Z = 2), and closo-1,2,3,6-{(η5-C5Me5)Co}4B2H4, 6, via the sequential formation of the metastable intermediates [{(η5-C5Me5)Co}(BH4)]n, 7 (paramagnetic), and {(η5-C5Me5)Co}2B2H6, 8 (diamagnetic). These results demonstrate that a labile metal precursor permits control of the number of metal atoms in the metallaborane and the characterization of unusual and metastable cobaltaboranes. A kinetic study of the conversion of 1 to 3, which involves the intramolecular dehydrogenation of a η4-C5Me5H ligand and skeletal rearrangement, is reported and the mechanistic implications for the origin of 1 are discussed.

Original languageEnglish
Pages (from-to)4510-4522
Number of pages13
JournalOrganometallics
Volume13
Issue number11
DOIs
Publication statusPublished - Nov 1 1994
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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