Unexpectedly high barriers to M–P rotation in tertiary phobane complexes : PhobPR behavior that is commensurate with tBu2PR

The four isomers of 9-butylphosphabicyclo[3.3.1]nonane, s-PhobPBu, where Bu = n-butyl, sec-butyl, isobutyl, tert-butyl, have been prepared. Seven isomers of 9-butylphosphabicyclo[4.2.1]nonane (a5-PhobPBu, where Bu = n-butyl, sec-butyl, isobutyl, tert-butyl; a7-PhobPBu, where Bu = n-butyl, isobutyl, tert-butyl) have been identified in solution; isomerically pure a5-PhobPBu and a7-PhobPBu, where Bu = n-butyl, isobutyl, have been isolated. The σ-donor properties of the PhobPBu ligands have been compared using the JPSe values for the PhobP(═Se)Bu derivatives. The following complexes have been prepared: trans-[PtCl2(s-PhobPR)2] (R = nBu (1a), iBu (1b), sBu (1c), tBu (1d)); trans-[PtCl2(a5-PhobPR)2] (R = nBu (2a), iBu (2b)); trans-[PtCl2(a7-PhobPR)2] (R = nBu (3a), iBu (3b)); trans-[PdCl2(s-PhobPR)2] (R = nBu (4a), iBu (4b)); trans-[PdCl2(a5-PhobPR)2] (R = nBu (5a), iBu (5b)); trans-[PdCl2(a7-PhobPR)2] (R = nBu (6a), iBu (6b)). The crystal structures of 1a–4a and 1b–6b have been determined, and of the ten structures, eight show an anti conformation with respect to the position of the ligand R groups and two show a syn conformation. Solution variable-temperature 31P NMR studies reveal that all of the Pt and Pd complexes are fluxional on the NMR time scale. In each case, two species are present (assigned to be the syn and anti conformers) which interconvert with kinetic barriers in the range 9 to >19 kcal mol–1. The observed trend is that, the greater the bulk, the higher the barrier. The magnitudes of the barriers to M–P bond rotation for the PhobPR complexes are of the same order as those previously reported for tBu2PR complexes. Rotational profiles have been calculated for the model anionic complexes [PhobPR-PdCl3]− using DFT, and these faithfully reproduce the trends seen in the NMR studies of trans-[MCl2(PhobPR)2]. Rotational profiles have also been calculated for [tBu2PR-PdCl3]−, and these show that the greater the bulk of the R group, the lower the rotational barrier: i.e., the opposite of the trend for [PhobPR-PdCl3]−. Calculated structures for the species at the maxima and minima in the M–P rotation energy curves indicate the origin of the restricted rotation. In the case of the PhobPR complexes, it is the rigidity of the bicycle that enforces unfavorable H···Cl clashes involving the Pd–Cl groups with H atoms on the α- or β-carbon in the R substituent and H atoms in 1,3-axial sites within the phosphabicycle

Stereospecific Suzuki, Sonogashira, and Negishi Coupling Reactions of <i>N</i>‑Alkoxyimidoyl Iodides and Bromides

A high-yielding stereospecific route to the synthesis of single geometric isomers of diaryl oxime ethers through Suzuki coupling of <i>N</i>-alkoxyimidoyl iodides is described. This reaction occurs with complete retention of the imidoyl halide geometry to give single <i>E</i>- or <i>Z</i>-isomers of diaryl oxime ethers. The Sonogashira coupling of <i>N</i>-alkoxyimidoyl iodides and bromides with a wide variety of terminal alkynes to afford single geometric isomers of aryl alkynyl oxime ethers has also been developed. Several of these reactions proceed through copper-free conditions. The Negishi coupling of <i>N</i>-alkoxyimidoyl halides is introduced. The <i>E</i> and <i>Z</i> configurations of nine Suzuki-coupling products and two Sonogashira-coupling products were confirmed by X-ray crystallography

Stereospecific Suzuki, Sonogashira, and Negishi Coupling Reactions of <i>N</i>‑Alkoxyimidoyl Iodides and Bromides

A high-yielding stereospecific route to the synthesis of single geometric isomers of diaryl oxime ethers through Suzuki coupling of <i>N</i>-alkoxyimidoyl iodides is described. This reaction occurs with complete retention of the imidoyl halide geometry to give single <i>E</i>- or <i>Z</i>-isomers of diaryl oxime ethers. The Sonogashira coupling of <i>N</i>-alkoxyimidoyl iodides and bromides with a wide variety of terminal alkynes to afford single geometric isomers of aryl alkynyl oxime ethers has also been developed. Several of these reactions proceed through copper-free conditions. The Negishi coupling of <i>N</i>-alkoxyimidoyl halides is introduced. The <i>E</i> and <i>Z</i> configurations of nine Suzuki-coupling products and two Sonogashira-coupling products were confirmed by X-ray crystallography