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Group 2 Promoted Hydrogen Release from NMe 2 H⋅BH 3 : Intermediates and Catalysis
Author(s) -
Liptrot David J.,
Hill Michael S.,
Mahon Mary F.,
MacDougall Dugald J.
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201000127
Subject(s) - chemistry , reactivity (psychology) , magnesium , catalysis , hydride , medicinal chemistry , amide , alkyl , decomposition , thermal decomposition , hydrogen , elimination reaction , reductive elimination , stereochemistry , inorganic chemistry , organic chemistry , medicine , alternative medicine , pathology
Both homo‐ and heteroleptic alkyl and amide complexes of the Group 2 elements Mg and Ca are shown to be active for the catalytic dehydrocoupling of Me 2 NH ⋅ BH 3 . Reactions of either magnesium dialkyls or the β‐diketiminate complex [HC{(Me)CN(Dipp)} 2 Mg n Bu] with four or two equivalents of Me 2 NHBH 3 , respectively, produce compounds containing the [H 3 BNMe 2 BH 2 Me 2 N] − ion, which coordinates to the magnesium centers through MgN and Mg ⋅⋅⋅ HB interactions in both the solution and solid states. Thermolysis of these compounds at 60 °C produces the cyclic product [(H 2 BNMe 2 ) 2 ] and, it is proposed, magnesium hydrido species by an unprecedented δ‐hydride elimination process. Calcium‐based species, although less reactive than their magnesium‐based counterparts, are found to engage in similar dehydrocoupling reactivity and to produce a similar distribution of products under thermally promoted catalytic conditions. A mechanism for these observations is presented that involves initial production and insertion of H 2 BNMe 2 into polarized MN bonds as the major BN bond‐forming step. The efficacy of this insertion and subsequent β‐ or δ‐hydride elimination steps is proposed to be dependent upon the charge density and polarizing capability of the participating Group 2 center, providing a rationale for the observed differences in reactivity between magnesium and calcium.