Pastor SD, Shum SP, DeBellis AD, Burke LP, Rodebaugh RK, Clarke FH, Rihs G. Atomic Proximity Due to Molecular Congestion: Rational Design of Bis(phosphite) Ligands by Restriction of Molecular Motion(1).
Inorg Chem 1996;
35:949-958. [PMID:
11666269 DOI:
10.1021/ic9509286]
[Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The synthesis and conformational analysis of the sterically congested bis(phosphite) ligand {2-{1-{3,5-(t)Bu(2)-2-[2,2'-CHCH(3)(4,6-(t)Bu(2)C(6)H(2)O)(2)PO]C(6)H(2)}Et}-4,6-(t)Bu(2)C(6)H(2)O}(PhO)(2)P (5) are reported. X-ray crystallographic, dynamic (31)P{(1)H} NMR, NOE, DNOE, CP-MAS (31)P NMR, and calculational studies of 5 as well as the structurally related bis(phosphites) 1 and 6 suggest that the conformational freedom of the molecule is severely restricted because of geometric restraints due to steric congestion. A through-space mechanism of coupling is suggested to explain the observed eight-bond P-P J coupling of 27.5 Hz in the (31)P{(1)H} NMR spectrum of 5, which is a result of the proximity of the two phosphorus atoms in 5. The results of this study support the contention that the restriction of molecular motion by steric congestion can be used to rationally design a ligand favoring a particular disposition of phosphorus atoms.
Collapse