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Dramatic Structural Effects of a Single Hydrogen Atom in HNPBut3

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journal contribution
posted on 06.09.2004, 00:00 by Sarah L. Hinchley, Mairi F. Haddow, David W. H. Rankin
The molecular structure of tri-tert-butylphosphine imide has been re-determined using the recently developed DYNAMITE method, which allows all assumptions about local symmetry to be removed without increasing the number of refining structural parameters excessively. The imide hydrogen causes the NPBut3 group to deviate hugely from local C3 symmetry, with N−P−C angles returned as 99.2(9), 110.9(7), and 111.5(11)°, while the C−P−C angles also deviate from symmetry, being 109.8(8), 110.5(9), and 113.9(9)°, so that the NPC3 fragment is close to Cs rather than C3 symmetry. The application of the DYNAMITE method to HNPBut3 also allows the methyl groups to be asymmetric, which has been shown to be important by ab initio methods. The re-determination of this structure using these more sophisticated methods has also resulted in a much shorter P−N bond than was previously determined, and is consistent with the molecule being regarded as HNPBut3, rather than HN-P+But3.