2 EXTREMES IN TIN CHEMISTRY - A NONBONDIN G SN-SN DISTANCE OF 285-PM AND A SN-119-NMR SHIFT DELTA=3301 IN ORGANOMETALLIC DERIVATIVES OF SN(0)

The reaction of Na[{Cp'(CO)(2)Mn}H-2] with SnCl2, which produces the i nidene compound [Cp'(CO)(2)Mn - Sn(Cl)- Mn-(CO)(2)Cp'](-) under standa rd workup procedures, results in the formation of O)(2)MnSn}(2){mu(2)- Mn(CO)(2)Cp'}(2){mu(2)-Cl}](-) (1) when quenched with unpolar solvents . While, formally, 1 contains tin in its oxidation state zero, it may be conceived as composed of an Sn-2(2-) entity, which is linearly end- on coordinated to two Cp'(CO)(2)Mn 16-electron species; in addition th e tin centers are bridged by two mu(2)-Mn(CO)2Cp' moieties and a mu(2) -Cl function. The resulting connectivity Sn-2{mu(2)-Mn(CO)(2)Cp'}(2){m u(2)-Cl} thus corresponds to a [1.1.1]propellane scaffolding. While th ere is no obvious need for a tin-tin bond in this propellane-type cage , a short Sn-Sn contact of only 285 pm is observed. While the Sn-119-N MR signal of 1 could not be recorded, the peculiar bonding in this typ e of compounds is generally mirrored in their unconventional Sn-119-NM R shift whereever signals can be observed: it is found that [{Cp(CO)( 2)Mn}(3)(mu(3)-Sn)], which contains trigonally planar-coordinated mu(3 )-Sn as a naked ligand atom, has its Sn-119-NMR resonance at delta = 3 301 well beyond the known range of Sn-119-NMR shifts. This finding is interpreted in terms of a relatively week Sn-p pi-Mn-d pi pi bonding w hich leads to low-energy unoccupied molecular orbitals as the prerequi sit for a large paramagnetic contribution to the NMR shift.