Synthesis and Application of the Transition Metal Complexes of α-Pyridinyl Alcohols, α-Bipyridinyl Alcohols, α,α'-Pyridinyl Diols and α,α'-Bipyridinyl Diols in Homogeneous Catalysis

Abstract

The paper presents a comprehensive survey on the synthetic procedures of transition metal complexes of α-pyridinyl alcoholato, α-bipyridinyl alcoholato, α,α'-pyridinyl dialcoholato and α,α'-bipyridinyl dialcoholato ligands and their coordination chemistry. Greater emphasis is, however, given to the catalytic activity of the complexes in homogeneous and asymmetric chemical reactions. The multidentate character of the pyridinyl alcohols and/or bipyridinyl diols is of great importance in the complexation with a large number and type of transition metals. The transition metal complexes of pyridinyl alcoholato or bipyridinyl dialcoholato ligands in most cases, and a few pyridinyl alcohols alone, were used as catalysts in homogeneous and chemical asymmetric reactions. In most of the homogeneously catalysed enantioselective chemical reactions, limited numbers and types of pyridinyl alcohols and or bipyridinyl diols were used in the preparation of chiral catalysts that led to a few investigations on the catalytic importance of the pyridinyl alcohols.

Keywords: bipyridinyl diol; catalyst; enantioselective; pyridinyl alcohol; synthesis; transition metal complex.

Scheme 1

Olefin metathesis reactions.

Figure 1

N,N- and N,O-bidentate metathesis catalysts.

Scheme 2

Synthetic procedures of complexes 2 and 3.

Figure 2

Tungsten(VI) phenylimido complexes.

Figure 3

Dendritic pyridinyl alcohols and Ru complexes.

Figure 4

Pyridinyl alcoholato ruthenium carbene complexes.

Figure 5

NHC pyridinyl alcoholato ruthenium carbene complexes.

Scheme 3

Synthesis of pyridinyl alcoholato ligands from Gr1 and Gr2 ruthenium carbenes.

Figure 6

Ligands and complexes used in polymerization reactions.

Figure 7

Neutral and cationic pyridinyl dialcoholato complexes of Zr.

Scheme 4

Synthesis of (imino)pyridinyl alcoholato complexes of Ni.

Figure 8

Structural differences between (imino)pyridinyl alcoholato Ni and Pd complexes.

Scheme 5

Synthesis of (imino)pyridinyl alcoholato complexes of Co and Ni.

Scheme 6

Synthesis of (amino)pyridinyl alcoholato complexes of Co and Ni.

Scheme 7

Synthesis of benzimidazolyl-pyridinyl alcoholato complexes of Co.

Figure 9

Ligands, complexes and epoxide products.

Figure 10

Multidentate catalysts for regioselective epoxidation.

Figure 11

Chiral pyridinyl alcoholato ligands and Mo complexes.

Figure 12

Mo complexes with chiral N,O-ligands.

Figure 13

Chiral Mo and achiral V complexes.

Figure 14

Pyridinyl alcoholato complexes of Re.

Figure 15

Ligands and typical Cu complex used for cyclopropanation.

Scheme 8

Nickel-catalysed conjugate addition of Et₂Zn to chalcones.

Figure 16

Pyridinyl alcoholato ligands used for asymmetric additions to chalcones.

Scheme 9

Mechanism of Ni-catalysed conjugate addition of Et₂Zn to chalcones.

Figure 17

Intermediates proposed for the Ni-catalyzed addition reactions [74,75].

Figure 18

Pyridinyl alcohol compounds used as ligands in enantioselective additions.

Figure 19

Intermediates proposed for the Zn-catalyzed addition reactions.

Figure 20

Substituted pyridinyl complexes used as ligands for addition reactions.

Figure 21

Dendrimeric pyridinyl alcohol compounds.

Figure 22

Cr complex and pyridinyl diols used in addition reactions of aldehydes.

Figure 23

Pyridinyl alcohols used as ligands in the addition of diethylzinc to benzaldehyde.

Scheme 10

The mechanism of benzaldehyde alkylation into the (S)-alcohol by Et₂Zn.

Figure 24

C₂-symmetric chiral bipyridinyl diol ligands.

Figure 25

Bipyridyl and polymer-supported pyridyl alcohol ligand precursors.

Figure 26

Chiral pyridinyl alcohols (α), diols (α,α’) and alkoxy-hydroxyls (α,α’) used as ligands.

Figure 27

Complex pyridinyl alcohols used in the diethylzinc addition reaction.

Scheme 11

Mechanism of Et₂Zn addition to benzaldehyde using pyridinyl alcohols 137 and 138.

Figure 28

Sterically strained pyridinyl alcohols used in the diethylzinc addition reaction.

Figure 29

Pyridinyl alcohol compounds substituted on the pyridinyl group.

Scheme 12

Pyridine ring chelation and re-face attack of benzaldehyde by Et₂Zn.

Scheme 13

Copper(I)-catalysed allylic oxidation of cyclohexene.

Scheme 14

Model transition states for the copper complex of 120 in the allylic oxidation of cyclohexene.

Scheme 15

Model transition states for the copper complex of 124 in the allylic oxidation of cyclohexene.

Scheme 16

A generalised ring-opening reaction of meso-epoxides by alcohols.

Figure 30

Pyridinyl alcohols with a di- and tripyridine backbone.

Figure 31

Tridentate coordination of an α,α’-bipyridinyl diol with Cu.

Scheme 17

A generalised aldol reaction catalysed by the lanthanide triflates.

Figure 32

Pyridino-crown-ether synthesized from 2,6-pyridine dimethanol.

Scheme 18

A model transition state for the aldol reaction of silyl enol ether in Pr³⁺-154 complex.

Figure 33

Chiral pyridinyl N-oxide ethers as catalysts in enantioselective aldol additions.

Scheme 19

Catalytic asymmetric allylic alkylation of aldehydes.

Figure 34

Unsupported and polymer-supported chiral pyridinooxazoline ligands.

Figure 35

Pyridine-phosphinite ligands.

Figure 36

Chiral pyridinooxazoline ligands.

Scheme 20

Nucleophilic allylic attack in Pd-catalysed allylic alkylation in the presence of pyridinooxazoline ligands.

Figure 37

Pyrrolidinopyridines with alkoxy substituents at the 6-position of the pyridine ring.

Figure 38

Chiral Zn-bipyridinyl complex.

Figure 39

α-Bipyridinyl alcohols with alkoxy groups at the α’-positions of the pyridine ring.

Scheme 21

Catalytic role of DMAP alcohol in chiral acyl transfer reaction.

Figure 40

Pyridinyl methanolato complexes of Mn.

Scheme 22

Transition metal free direct arylation of unactivated arenes.

Scheme 23

Carbonylative hydroesterification of cyclohexene.

Scheme 24

Synthesis of complex 176.

Scheme 25

Synthesis of complexes 177 and 178.