DIVALENT TIN AND LEAD COMPOUNDS EX2 ACTING AS BRIDGING LIGANDS IN [((CO)(5)M)(2)EX2](2-) (E=SN, PB M=CR, MO, W) - PREPARATION AND PROPERTIES

The reaction of Na-2[M-2(CO)10] (M = Cr, Mo, W) with SnHal(2) (Hal = C l, Br) is a well established procedure for the synthesis of anions of type A, [{(CO)(5)M}SnHal(3)](-). Conditions are described which, for t he same type of procedure, result in the additional formation of diani ons of type B, [{(CO)(5)M}(2)SnHal(2)](2-). Procedures for separating these two types of anions in the form of their stable [Ph4P](+) or [nB u(4)N](+) salts by appropriate salt metathesis are presented. The stru ctures of these species have been characterized by X-ray analysis of t hree salts containing type A anions and two salts containing type B an ions. The reactivity of the type B salts containing the bulky cations [Ph4P](+) or [nBu(4)N](+), respectively, is remarkably low; the salts are, however, transformed into highly reactive sodium salts by further metathesis with Na[BPh4]. In such salts the halide substituents are e asily exchanged as shown by the synthesis of [{(CO)(5)Cr}(2)Sn(oxinato )](-) (4)(-), from [Na-(THF)(x)](2)[{(CO)(5)Cr}(2)SnCl2] and sodium 8- oxoquinolate, Na[C9H6NO], The structure of the anion, 4, is compared t o the structure of [{(CO)(5)Cr}Sn(oxinato)(2)] (5), which is obtained from [{(CO)(5)Cr}SnCl2 . THF] and sodium 8-oxochinolate. The preparati on of the dinuclear anions [{(CO)(5)Cr}(2)E(OOCCH3)(2)](2-) (E = Sn, 2 g; E = Pb, 3) is accomplished by the reaction of [Ph4P](2)[Cr-2(CO)(10 )] with the corresponding acetates E(OOCCH3)(2). While 2g and 3 are fo rmal analogues of the type-B anions, their structures reveal an asymme trical eta(2)-coordination of the two acetato Ligands, in each case en ding up in a 4 + 2 coordination for the main group centres, instead of the four-coordination observed for [{(CO)(5)M}(2)SnHal(2)](2-). All c ompounds have been characterized by usual spectroscopic and analytical techniques. X-ray analyses have been performed for selected examples. Sn-119-NMR data are presented for all of the compounds which contain tin-centred ligands.