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Jaska CA, Lough AJ, Manners I: Linear hybrid aminoborane/phosphinoborane chains: synthesis, proton-hydride interactions, and thermolysis behavior. Inorg Chem. 2004 Feb 9;43(3):1090-9.
The reaction of the lithiated phosphine-borane adducts Li [PPhR.BH (3)] or Li [CH (2)-PR (2).BH (3)] with Me (2) NH.BH (2) Cl afforded the hybrid linear species Me (2) NH-BH (2)-PPhR-BH (3) (1, R = Ph; 2, R = H) or Me (2) NH-BH (2)-CH (2)-PR (2)-BH (3) (3, R = Ph; 4, R = Me). Single-crystal X-ray diffraction studies on 1 and 3, the first for linear hybrid aminoborane/phosphinoborane adducts, confirmed the expected four-coordinate N-B-P-B and N-B-C-P-B frameworks. In addition, interactions between the protic N-H and hydridic B-H hydrogen atoms resulted in short intermolecular H...H contacts for 1, whereas 3 was found to possess an exceptionally short intramolecular H...H distance of 1.95 A. Solution and solid state infrared studies on 3 and 4 also suggest that these dihydrogen interactions were maintained even in dilute solution. Hydrogen bond strengths in the range of 7.9 to 10.9 kJ mol (-1) indicate the presence of a relatively weak interaction. The thermal and catalytic dehydrocoupling reactivities of 1-4 were also investigated. Chain cleavage reactions were observed for 1 and 2 upon thermolysis at 130 degrees C to afford species such as Me (2) NH.BH (3), [Me (2) N-BH (2)](2), PhPRH.BH (3) (R = Ph, H), PhPRH (R = Ph, H), Ph (2) PH-BH (2)-PPh (2)-BH (3), and also the low molecular weight polyphosphinoborane [PhPH-BH (2)](n) (M (w) approximately 5000). Similar products were observed for the attempted catalytic dehydrocoupling reactions but under milder reaction conditions (50 degrees C). Thermolysis of 3 at 130 degrees C yielded the six-membered ring [BH (2)-CH (2)-PPh (2)](2) (5), which presumably results from the dissociation of Me (2) NH.BH (3) from 3. Thermolysis of 4 at 90 degrees C afforded Me (2) NH.BH (3) and Me (3) P.BH (3), in addition to a product tentatively assigned as [BH (2)-CH (2)-PMe (2)](2) (6). |
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