Mixed Ligand Heteroleptic Complexes

A considerable number of adduct and heteroleptic silylamide complexes has been reported (Table 6) [124-137], In the following they are summarized with respect to their ligand combination. 

Adducts Ln(btsa)s(A). The availability of additional coordination sites was shown in Ln(btsa)3 complexes by isolation of their mono adducts OC(PPh3) [124] and OCPh2 [125], respectively, and their bis adducts of benzonitril [108], The stabilizing Ln - Si contacts in the homoleptic Ln(btsa)3 systems are obviously replaced by a stronger hard Ln - donor atom coordination. Other adduct complexes include the donating molecules THF [84], NCtBu and CNtBu [109b]. 

LnibtsahiSR). Complex [Gd(btsa)2(/i-StBu)]2 has been the first structurally characterized lanthanide thiolate complex (Gd-S, 2.760(5), 2.823(5) A) and was 

Ln(btsa)2(PR2). The diphenylphosphido complex La(btsa)2(PPh2)(OPPh3)2 (La-P, 3.165(6) A) was prepared according to the silylamide route [130b]. 

Ln(btsa)(COT). Reaction of [(COT)Sm(ji-ClXTHF)]2 with Na(btsa) did not yield the simple metathesis product (COT)Ln(btsa)(THF) as in the Y-, Gd-, Er-and Lu-case [136]. Amazingly, an inverse sandwich complex was obtained in the form of [(btsa SmMM -COT)] with elongated Sm-C(COT) bond lengths (av 2.688(5) A) and close Sm-C(btsa) contacts (2.970(2), 3.105(2) A) (Fig. 11). 

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It should be mentioned that in many cases it turns out to be impossible to isolate the bimetallic mixed-ligand complex. The isolable reaction products appear to be homometallic heteroleptic species. The composition of the reaction products is often dependent on the polarity and donor properties of the solvent as the molecules of the latter compete with the bridging alkoxo-, car-boxylato-, or p-diketonatoligands for the place in the coordination sphere of metal atoms. Thus if the reaction of Pb(OAc)2 with Sn(OBu )4 mentioned above is carried out in pyridine, it gives Sn(OBu )3(OAc)Py and Pb(OAc)(OBu ) as the major products and not the bimetallic complex [298]. Sn(OBu )3(OAc)Py turns also to be the major product of the reaction of Sn(OBu )4with Me3SiOAc... 

For a molecule with such a low basicity (only protonated in super-acidic media), CO is a surprisingly versatile ligand. The homoleptic (or binary) carbonyls (i.e. in which CO is the only ligand) already span oxidation states from -IV to +III, and higher oxidation states are known for heteroleptic complexes (mixed ligand sets) which have good 71-donor co-ligands, e.g. RuIV(CO)(SR)4. 

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