Cyclophosphazenes as ligands

Another way of using cyclophosphazenes as ligands is to incorporate coordinating units on phosphorus. For example, the reaction of N3P3CI6 with the 3,5-dimethyl pyrazole affords N3P3(3,5-Mc2Pz)6, which is a very versatile multi-site coordination ligand (see Eq. 3.29). 

A third feature which stimulates interest in cyclophosphazenes is their behaviour as ligands towards transition metals [7,8]. Several types of coordination pattern involving either the skeletal ring nitrogen atoms and/or suitable exocyclic substituent donor atoms have been documented (Fig. 2). This area of research has been receiving widespread attention in recent years [7],... 

Cyclophosphazenes as scaffolds for the construction of multi-site coordination ligands 01CSR193. 

Other cyclophosphazenes have been used as ligands in coordination chemistry. Thus the complexes (178) (already known), (179) and (180), were prepared by... 

Alkyne- and butadiyne-derived fluorinated cyclophosphazenes have been used as ligands in reactions with diiron and dimolybdenum ear-bonyls (Scheme 15). Thus, the reaction of N3P3F5(C=C-Ph) with Fe2(CO)g afforded five compounds (105a-105b), (106) and (107a-107b). ... 

The diazaphosphane or aminoiminophosphane ligands with a NPN framework are another subclass of cyclophosphazenes. These compounds with both phosphorus in oxidation state (111) [104-110] and (V) [111-112] have been employed in the synthesis of four membered heterocycles and coordination chemistry with group 13 derivatives. Several complexes of trivalent phosphorus derivatives with both aluminum halide and alkyls are known as illustrated for 48 in Scheme 21 [113-119]. The structure determination of 48 confirms the formation of a four membered metallacycle [116, 117],... 

The comparison of the two sets of %ILS values allows us to conclude that MYKOMET 63 appears to be actually as active as MYKO 63, but not more active. In other words, the graft of methylated aziridinyl ligands on a six-membered cyclophosphazene ring does not significantly improve the antitumoral activity with respect to the non-methylated isologues. However, because MYKOMET 63 possesses only a slight toxicity compared to MYKO 63, the new drug reported here may be of interest for eventual clinical use, no matter what difficulties are encountered in its synthesis. 

In this case, in fact, the nucleophilicity sequence is reversed on switching from the complexes of crown ether 5 to the corresponding cryptates. Interestingly, the same trend of crown ether 5 is found with the corresponding complexes of cyclophosphazenic polypodand 2c. As shown in Table 3. cyclophosphazenic polypodands like 2c have a reactivity only slightly lower (three to four times) than that of the corresponding crown ethers and, hence, can be considered a valid alternative to the more sophisticated cyclic ligands. 

Linear one-dimensional polymers have been obtained by polymerisation of various acrylic monomers inside the cavities of (7.345a). Cyclophosphazenes can be used as scaffolds for the construction of muti-site ligands [22]. 

Synthetic approaches such as those shown above can be very useful for assembling a library of coordination ligands using the cyclophosphazene ring as a means for supporting such hgand architectures [17],... 

A new cyclophosphazene carrying phosphine ligands (166) has been prepared from bis(2,2 -dioxy-l,P-biphenyl)dichlorocyclotriphosphazene and ort/io-diphenylphosphine-phenol, and has been used to form the Au(i) and Pt(ii) complexes (167-169) as shown by X-ray crystallography. The sequential reaction of the potentially polydentate ligand hexakis(2-pyridyloxy)cyclotriphos-phazene (OPy) with the anhydrous dichlorides M Cl2 and M Cl2 (M = Cu or Co, M = Co or Zn) gave the heteropolynuclear complexes (170-172),... 

An important part of metallocene chemistry remains the use of the metallocene group as a ligand. Thus both ruthenocene and ferrocene cyclophosphazene complexes have been reported. Direct tungsten-carbon bonds can also be generated to give... 

---