The Influence of Steric Pressure on the Structure of Homodimetallic Rhodium(I) and Iridium(I) Complexes Containing a Bis(bidentate) Phosphane Ligand

Abstract

P{ 1 H}), mass spectrometry, IR spectroscopy, elemental analyses and melting points. Furthermore, the solid-state structures of seven of these new compounds were fully determined by single-crystal X-ray diffraction analyses to study the influence of steric pressure. The precursor complex [Rh 2 (η 4 -cod) 2 (dppcb)]X 2 (1), X -= BF 4 -, PF 6 -, SbF 6 -, completely characterized by its X-ray structure, smoothly reacts with mono-or bidentate ligands containing phosphorus or nitrogen donor atoms. Thus, monophosphanes and monophosphites produce compounds of the structure type [Rh 2 L 4 (dppcb)](SbF 6 ) 2 [L = PMe 2 Ph, 2; PMePh 2 , 3; P(OMe) 3 , 5; P(OPh) 3 , 6]. The X-ray structures of 3 and 6 show that PMePh 2 and P(OPh) 3 are capable of compensating steric interactions. The treatment of 1 with diphosphanes leads to the structure type [Rh 2 L 2 (dppcb)](SbF 6 ) 2 [L = bis(diphosphanyl)-methane, dppm, 7; bis(diphenylphosphanyl)amine, dppam, 8; 1,2-bis(diphenylphosphanyl)ethane, dppe, 9; cis-1,2-

TroposLigands in Asymmetric Rhodium(I)-Catalyzed Addition of Arylboronic Acids to Enones: How a Tunable Coordination Gives Different Reaction Products

“…As reported in the caption of Figure , the Rh−Cl bond distances show a significant dispersion with respect to the estimated standard deviations; their mean value, 2.426 Å, however, is in keeping with the values found for chlorines bridging between Rh(I) species . The Rh−P bond lengths are less dispersed, and their mean value, 2.149 Å, is the shortest Rh−P distance found in tetracoordinated Rh(I) phosphite complexes, which range between 2.22 and 2.27 Å . It compares well, however, with Rh−P bond distances found in dinuclear dichloro phosphoramidites of Rh(I) …”

Switching on the photochemical reactivity in heterodimetallic OsII–RuII bipyridyl complexes containing a bis(bidentate) phosphine

“…This clearly demonstrates that independent of crystal packing effects and diastereoisomeric forms large ''steric pressures'' are present in 1-4. Therefore, these ''steric pressures'' also occur in the solution structures of 1-4, as has already been shown for comparable compounds [13]. However, steric crowding reduces the non-radiative decay in 1-4 [4a] and hence a long-lived excited state of 273(1) ns becomes possible at ambient temperature also in the case of 3/4, where the d-d states are populated.…”

“…The analogous contacts between the phenyl rings along a trans axis of the cyclobutane rings are 3.022 Å in 1 and 3.024 Å in 3. These contact approaches are indicative of high ''steric pressure'' [4,13]. Interestingly, neither a different diastereoisomeric form nor different polymorphs essentially change this ''steric pressure''.…”

Regio- and chemoselective oxidation of the bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane via cobalt(II) mediated dioxygen activation

“…This folding parameter of 5 is typical of the onset of "steric pressure" in homodimetallic complexes of dppcb. 14,33 The apical Co(1)-I(1) bond length of 2.7614(8) A ˚is significantly larger than the corresponding parameter of 2.5746(8) A ˚for Co(1)-I( 2) belonging to the basal plane. This clearly indicates that square-pyramidal structures like 5 contain weakly bound ligands.…”

“…It is wellknown that an asymmetric conformation like 7c efficiently releases this "steric pressure". 33 The sequence of X-ray structures of 2a, 2b, 7a, 7b, and 7c clearly reveals that iodides induce "steric pressure". As a matter of fact, in this work, chlorides and bromides are only responsible for regioselectivity during dioxygen activation, whereas iodides induce chemoselectivity.…”