Dynamic stereochemical rearrangements in chiral organometallic complexes

Abstract

Organometallic complexes have long been known to display a wide variety of dynamic stereochemical processes. Classic examples of such processes include the exchange of axial and equatorial environments in trigonal bipyramidal complexes, such as Fe(CO)(5), and the migration of the metal moiety round the periphery of the cyclopentadiene ring in eta(1)-bound Cp complexes. The systematic study of fluxional processes is of interest because it can not only help provide a detailed, quantitative 'picture' of the bonding between the metals and ligands involved, but it can also help to rationalise chemical reactivity patterns. The introduction of chirality into organometallic complexes, usually in the form of a non-racemic chiral ligand, has led to an explosion in the importance such species, particularly with regard to their applications in organic functional group transformations. The presence of a chiral centre can also provide an excellent spectroscopic handle on the complex in question, enabling both novel fluxional processes to be observed and new light to be shed on old (unresolved) problems. In this critical review (101 references) the literature on metal-centred fluxional rearrangements in chiral transition and main group organometallic complexes is reviewed, complementing the recent review by Faller (see reference 8).

Adaptive Coordination Behavior of Bisphosphanylphosphanido‐Ligands Toward Group 2, 11 and 12 Metal Ions

“…The 31 P NMR spectra of compound 2‐Zn in C 6 D 6 confirms the trends found for the alkaline earth metal phosphanides: While the resonance of the formal phosphanide atom is barely influenced, the signals of the terminal P‐atoms are shifted towards lower field and the value of the 1 J PP coupling constant even exceeds that of 2‐Mg (see Table 1). By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before [43,44] . The 31 P NMR data are summarized in Table 1.…”

“…By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before. [ 43 , 44 ] The 31 P NMR data are summarized in Table 1 . Notably, 2‐Mg stands out of the other alkaline earth phosphanides featuring values very close to 2‐Zn , thus underlining the above‐mentioned similarity between the two types of ions.…”

Adaptive Coordination Behavior of Bisphosphanylphosphanido‐Ligands Toward Group 2, 11 and 12 Metal Ions

“…The 31 P NMR spectra of compound 2‐Zn in C 6 D 6 confirms the trends found for the alkaline earth metal phosphanides: While the resonance of the formal phosphanide atom is barely influenced, the signals of the terminal P‐atoms are shifted towards lower field and the value of the 1 J PP coupling constant even exceeds that of 2‐Mg (see Table 1). By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before [43,44] . The 31 P NMR data are summarized in Table 1.…”

“…By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before. [ 43 , 44 ] The 31 P NMR data are summarized in Table 1 . Notably, 2‐Mg stands out of the other alkaline earth phosphanides featuring values very close to 2‐Zn , thus underlining the above‐mentioned similarity between the two types of ions.…”

Ruthenium(II) Complexes Containing Lutidine‐Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of CN bonds

“…In addition, the dynamic behavior is rather independent of the solvent. Hence, this exchange may be accompanied by previous chloride or MeCN ligand dissociation facilitated by the large trans influence of the hydrido ligand 23. Moreover, unlike it was observed with PdCNC complexes, the calculated barriers are consistently higher for species with xilyl‐substituted CNC ligands than for derivatives containing the more encumbered pincer with mesityl groups, reflecting a likely case of “steric assistance” 24…”

Coordination Chemistry and Reactivity of Zinc Complexes Supported by a Phosphido Pincer Ligand

“…The fluxionality of k 2 species has been studied in depth for complexes of hemilabile ligands with redundant donor atoms. [48] Moreover, k 2 coordination of the related PNP ligand was recently observed for uranium halide complexes [40,49] and, in the case of phosphido pincer zinc complexes, it is supported by DFT calculations.…”

Adaptive Coordination Behavior of Bisphosphanylphosphanido‐Ligands Toward Group 2, 11 and 12 Metal Ions

“…The 31 P NMR spectra of compound 2‐Zn in C 6 D 6 confirms the trends found for the alkaline earth metal phosphanides: While the resonance of the formal phosphanide atom is barely influenced, the signals of the terminal P‐atoms are shifted towards lower field and the value of the 1 J PP coupling constant even exceeds that of 2‐Mg (see Table 1). By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before [43,44] . The 31 P NMR data are summarized in Table 1.…”

“…By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before. [ 43 , 44 ] The 31 P NMR data are summarized in Table 1 . Notably, 2‐Mg stands out of the other alkaline earth phosphanides featuring values very close to 2‐Zn , thus underlining the above‐mentioned similarity between the two types of ions.…”

Ruthenium(II) Complexes Containing Lutidine‐Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of CN bonds

“…In addition, the dynamic behavior is rather independent of the solvent. Hence, this exchange may be accompanied by previous chloride or MeCN ligand dissociation facilitated by the large trans influence of the hydrido ligand 23. Moreover, unlike it was observed with PdCNC complexes, the calculated barriers are consistently higher for species with xilyl‐substituted CNC ligands than for derivatives containing the more encumbered pincer with mesityl groups, reflecting a likely case of “steric assistance” 24…”

Coordination Chemistry and Reactivity of Zinc Complexes Supported by a Phosphido Pincer Ligand

“…The fluxionality of k 2 species has been studied in depth for complexes of hemilabile ligands with redundant donor atoms. [48] Moreover, k 2 coordination of the related PNP ligand was recently observed for uranium halide complexes [40,49] and, in the case of phosphido pincer zinc complexes, it is supported by DFT calculations.…”

Adaptive Coordination Behavior of Bisphosphanylphosphanido‐Ligands Toward Group 2, 11 and 12 Metal Ions

“…The 31 P NMR spectra of compound 2‐Zn in C 6 D 6 confirms the trends found for the alkaline earth metal phosphanides: While the resonance of the formal phosphanide atom is barely influenced, the signals of the terminal P‐atoms are shifted towards lower field and the value of the 1 J PP coupling constant even exceeds that of 2‐Mg (see Table 1). By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before [43,44] . The 31 P NMR data are summarized in Table 1.…”

“…By contrast to the previously discussed systems, the doublet is broadened, which can be attributed to a fast reversible dechelatation of one phosphine ligand in solution that has been proposed for similar systems before. [ 43 , 44 ] The 31 P NMR data are summarized in Table 1 . Notably, 2‐Mg stands out of the other alkaline earth phosphanides featuring values very close to 2‐Zn , thus underlining the above‐mentioned similarity between the two types of ions.…”

Ruthenium(II) Complexes Containing Lutidine‐Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of CN bonds

“…In addition, the dynamic behavior is rather independent of the solvent. Hence, this exchange may be accompanied by previous chloride or MeCN ligand dissociation facilitated by the large trans influence of the hydrido ligand 23. Moreover, unlike it was observed with PdCNC complexes, the calculated barriers are consistently higher for species with xilyl‐substituted CNC ligands than for derivatives containing the more encumbered pincer with mesityl groups, reflecting a likely case of “steric assistance” 24…”

Coordination Chemistry and Reactivity of Zinc Complexes Supported by a Phosphido Pincer Ligand

“…The fluxionality of k 2 species has been studied in depth for complexes of hemilabile ligands with redundant donor atoms. [48] Moreover, k 2 coordination of the related PNP ligand was recently observed for uranium halide complexes [40,49] and, in the case of phosphido pincer zinc complexes, it is supported by DFT calculations.…”