Conformational Rigidity in Complexes [MCl(tBu₂PH)₃] (M = Rh, Ir)

Abstract

Reactions of [{M(μ‐Cl)(coe)2}2] (M = Rh, Ir; coe = cis‐cyclooctene) with the secondary phosphane tBu2PH under various molar ratios were investigated. Probably, for kinetic reasons, the reaction behavior of the rhodium species differed from that of the iridium analogue in some instances. During these studies complexes [MCl(tBu2PH)3] [M = Rh (1), Ir (2)] were isolated, and solution variable‐temperature 31P{1H} NMR studies revealed that these complexes show a conformational rigidity on the NMR time scale. Spectra recorded in the temperature range from 173 to 373 K indicated in each case only one rotamer containing three chemically nonequivalent phosphanes due to the restricted rotation of these ligands about the M–P bonds and the tert‐butyl substituents around the P–C(tBu) bonds, respectively. Compound 1 showed in solution already at room temperature in several solvents a dissociation of a phosphane ligand affording the known complex [{Rh(μ‐Cl)(tBu2PH)2}2] beside the free phosphane. In contrast to these findings, the iridium analogue 2 remained completely unchanged under similar conditions and exhibited, therefore, some kinetic inertness. For a better understanding of the NMR spectroscopic investigations, the molecular structure of 1 in the solid state was confirmed by X‐ray crystallography.

Interplay of Electronic and Steric Effects of R2PH (R = tBu, o‐tolyl) in Reactions with Triruthenium Dodecacarbonyl

“…Searching for an explanation for this observation, we assumed a temperature‐dependent stereodynamic behavior caused by restricted rotation about P–C bonds (and presumably about M –P bonds), due to the high steric demand of the o ‐tolyl substituents. We (and others) reported similar observations for t Bu groups in steric demanding phosphanes coordinated towards metal complexes . Even for complexes, bearing phosphane ligands with bulky o ‐tolyl groups, related stereodynamics were described.…”

An Entry to Double Phosphanyl‐Bridged Dinuclear Rhodium(II) Complexes

“…Recently we described the synthesis and crystal structure of the olefinic complex [RhCp(coe)(P t Bu 2 H)] (coe = cis ‐cyclooctene) which was obtained by reacting [RhCp(coe) 2 ] ( 1 ) with the corresponding secondary phosphine in refluxing toluene . In the past we showed that rhodium complexes containing labile coe ligands are suitable precursors to introduce secondary phosphine ligands . Herein we report a synthetic pathway to further complexes of the formula [RhCp(coe)(PR 2 H)] (R = Ph, 2a ; R = o ‐tolyl, 2b ), which were identified by 31 P{ 1 H} NMR spectroscopy.…”