Tripodal ligand systems

There are a number of mixed-donor tripodal ligand systems which have been characterized with... 

The geometries of tripodal ligand systems are determined by the type of pendant arm and the number of atoms in the linker to the anchor (Fig. 2, Types A and B). 

The isolation of phosphazides has also been reported for Staudinger reactions of R3P (R = Me, Et, Ph) with azido-p-benzoquinonedibenzenesulfonimines. Enantioseparations have been carried by application of the Staudinger protocol. An interesting tripodal ligand system (5) has been prepared by the reaction of bis-2,6-diphenylphosphanyl pyridine with azides. Complexation of equimolar amounts of [MCl2(thf)2] (M = Co, Fe) with (5b) in thf leads to the formation of the complex (6) and (7), respectively. 

The non-innocent behaviour of the fcis(phosphinimino)methanide ligand [CH P(R2)=NR 2] provides an interesting way by which new and facile approach to new tripodal ligand systems. A novel example of this characteristic was recently illustrated by the reactions of [CH P(Ph2)=NSi-Mc3 2ZnR] [R=N(SiMe3)2 (29a), Ph (29b)] with BH3 thf. In the case of 29b... 

The exchange of the anionic Si bridge-head in the tripodal ligand systems by a neutral boron atom was evaluated in a next step. Moret and Peters introduced the neutral TPB ligand scaffold (where TPB=tris-(o-diisopropylphosphinophenyl)borane= B(o-C6H4P Pr2)3 ), which leads to a remarkable reactivity (Scheme 56). The TPB ligand is elec-... 

The zinc complex of a tripodal N2S20 pentadentate ligand undergoes amide alcoholysis of a coordinated amide group.893 Examples of amide hydrolysis are known for other ligand systems.894... 

A related procedure to that discussed for the tris-dmgH system has been employed to cap one end of Fe(n), Co(n), Ni(n) and Zn(n) complexes of the tripod ligand, tris(2-aldoxime-6-pyridyl)phosphine... 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Prior to our work, only two tripodal NHC ligand systems were known. The mesitylene-anchored tris(carbene) ligand (Fig. 4, 1) was unique... 

One purpose of our work is to mimic the chiral environment of the enzymes. Therefore, we thought it a reasonable goal to supply chiral models for the active sites of metalloenzymes. This was achieved before by Alsfasser et al. 113) or Vahrenkamp et al. 114) via amino acids that have been incorporated into the ligand systems. Modification of Tp ligands by chiral pyrazoles derived from the chiral pool is another way to chiral W,W,iV tripod ligands and has been achieved before by W. B. Tolman and coworkers (115). Thus, first we focused on the synthesis of a racemic mixture of a chiral NJtl,0 scorpionate... 

Linear systems with an NO3 donor set are exemplified by simple saturated molecules, which show preferences toward lighter, higher charged metal ions, such as linear (90). Branched systems include tripodal ligands having different central atoms and 0-donors terminating the chains, for example, (91) and (92). Their coordination chemistry is partly directed by their shape, which tends to support trigonal... 

---