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Calcium–Amidoborane–Ammine Complexes: Thermal Decomposition of Model Systems
Author(s) -
Harder Sjoerd,
Spielmann Jan,
Tobey Briac
Publication year - 2012
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.201102029
Subject(s) - protonation , chemistry , medicinal chemistry , crystal structure , calcium , inorganic chemistry , ion , crystallography , organic chemistry
Hydrocarbon‐soluble model systems for the calcium–amidoborane–ammine complex Ca(NH 2 BH 3 ) 2 ⋅ (NH 3 ) 2 were prepared and structurally characterized. The following complexes were obtained by the reaction of RNH 2 BH 3 (R=H, Me, i Pr, DIPP; DIPP=2,6‐diisopropylphenyl) with Ca(DIPP‐nacnac)(NH 2 ) ⋅ (NH 3 ) 2 (DIPP‐nacnac=DIPPNC(Me)CHC(Me)NDIPP): Ca(DIPP‐nacnac)(NH 2 BH 3 ) ⋅ (NH 3 ) 2 , Ca(DIPP‐nacnac)(NH 2 BH 3 ) ⋅ (NH 3 ) 3 , Ca(DIPP‐nacnac)[NH(Me)BH 3 ] ⋅ (NH 3 ) 2 , Ca(DIPP‐nacnac)[NH( i Pr)BH 3 ] ⋅ (NH 3 ) 2 , and Ca(DIPP‐nacnac)[NH(DIPP)BH 3 ] ⋅ NH 3 . The crystal structure of Ca(DIPP‐nacnac)(NH 2 BH 3 ) ⋅ (NH 3 ) 3 showed a NH 2 BH 3 − unit that was fully embedded in a network of BH⋅⋅⋅HN interactions (range: 1.97(4)–2.39(4) Å) that were mainly found between NH 3 ligands and BH 3 groups. In addition, there were NH⋅⋅⋅C interactions between NH 3 ligands and the central carbon atom in the ligand. Solutions of these calcium–amidoborane–ammine complexes in benzene were heated stepwise to 60 °C and thermally decomposed. The following main conclusions can be drawn: 1) Competing protonation of the DIPP‐nacnac anion by NH 3 was observed; 2) The NH 3 ligands were bound loosely to the Ca 2+ ions and were partially eliminated upon heating. Crystal structures of [Ca(DIPP‐nacnac)(NH 2 BH 3 ) ⋅ (NH 3 )] ∞ , Ca(DIPP‐nacnac)(NH 2 BH 3 ) ⋅ (NH 3 ) ⋅ (THF), and [Ca(DIPP‐nacnac){NH( i Pr)BH 3 }] 2 were obtained. 3) Independent of the nature of the substituent R in NH(R)BH 3 , the formation of H 2 was observed at around 50 °C. 4) In all cases, the complex [Ca(DIPP‐nacnac)(NH 2 )] 2 was formed as a major product of thermal decomposition, and its dimeric nature was confirmed by single‐crystal analysis. We proposed that thermal decomposition of calcium–amidoborane–ammine complexes goes through an intermediate calcium–hydride–ammine complex which eliminates hydrogen and [Ca(DIPP‐nacnac)(NH 2 )] 2 . It is likely that the formation of metal amides is also an important reaction pathway for the decomposition of metal–amidoborane–ammine complexes in the solid state.