Multidentate 2-pyridyl-phosphine ligands – towards ligand tuning and chirality

Abstract

In the current work a range of multidentate pyridyl-phosphine ligands are synthesised with tuneable electronic and steric character, through the incorporation of a variety of alcohols into (amino)pyridyl-phosphine frameworks. The stoichiometric reactions of compounds of the type (RN)P(2-py) (2-py = 2-pyridyl) with alkyl as well as aryl alcohols result in the formation of (alkoxy)pyridyl-phosphines (RO)P(2-py) (R = Me, 2-Bu, Ph). This synthetic procedure also allows the introduction of enantiomerically pure alcohols, like (R)-(-)-2-BuOH and (S)-(+)-2-BuOH, and as such provides a very convenient two-step route to chiral multidentate pyridyl-phosphine ligand sets. Using the bis-amino-phosphine (EtN)P(2-py), the stepwise introduction of alcohols enables the synthesis of racemic alkoxy-amino-phosphines (RN)(RO)P(2-py), as well as alkoxy-phosphines (RO)P(2-py) and therefore offers easy access to a library of different pyridyl-phosphine ligands. Coordination studies of the (amino)pyridyl-phosphines and (alkoxy)pyridyl-phosphines with copper(i) reveal that ligands with two N donor atoms form dimeric arrangements, while (PhO)P(2-py), in-corporating only one N donor atom, shows completely different coordination behaviour.

How Changing the Bridgehead Can Affect the Properties of Tripodal Ligands

“…Our initial interest in 1 – 3 focused on the potential structural/functional effects of the increasing Lewis acidity of the bridgehead as Group 15 is descended. At the top of the group (N and P) the higher electronegativity, combined with the presence of compact lone pairs, is known to lead to ambidentate character in which both the N‐atoms of the 2‐py groups and the Group 15 atom (E) can donate to metal ions (Figure b) . However, the onset of electropositive character and relativistic stabilisation of the lone pair at Bi are anticipated to lead to increasing acceptor character for the bridgehead as the group is descended (Figure b) .…”

Tris(2-pyridyl) Bismuthines: Coordination Chemistry, Reactivity, and Anion-Triggered Pyridyl Coupling

“…[29][30][31] This behavior has led to new applications as thermally stable pyridyltransfer reagents as well as reagents for the rapid NMR spectroscopic determination of the enantiomeric excess (ee) of chiral alcohols. [32][33][34] Although the coordination chemistry of tris(2-pyridyl) ligands E(2-py)3 of the lighter Group 15 elements (E = N, P, As) has been extensively studied, [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] it was only very recently that heavier counterparts containing Sb and Bi have been introduced. Most relevant to the current study, we showed that 6-methyl substitution at the pyridine rings allows the synthesis of the stable ligand [Bi(6-Me-2-py)3] (1) (Fig 1d), which is to date the only example of a tris(2-pyridyl) bismuthine reported.…”

An experimental and theoretical study of the coordination and donor properties of tris-2-pyridyl-phosphine ligands

“…The 2-pyridyl-phosphine ligands were synthesised according to literature procedures. 35,36 13 C NMR spectra were referenced to TMS, whereas all other heteronuclei were referenced to TMS via the Ξ scale. 59 Unambiguous assignments of the NMR resonances were made on the basis of 2D NMR experiments ( 1 H-1 H COSY and 1 H- 13 C HMBC experiments).…”

“…The investigated ligand sets are summarised in Figure 2 and their reactivity and coordination chemistry were recently explored within our group. 35,36 The reaction of tris-2-pyridyl-phosphine P(2-py) 3 (1) with [W(CO) 5 (MeCN)] in a 1 : 1 stoichiometric reaction resulted in the formation of a brown solution. After six days at room temperature 31 P{ 1 H} NMR spectroscopy in CD 3 CN at room temperature revealed full consumption of the free ligand and the presence of various phosphorus-containing tungsten complexes, probably resulting from the various possible coordination modes of the ligand (e.g.…”