MECHANISTIC DETAILS FOR METATHETICAL EXCHANGE BETWEEN XCO (X = O AND RN) AND THE TIN(II) DIMER, (SN[N(SIME3)(2)](MU-OBUT))(2)

Metathetical exchange between carbon dioxide and the tin(II) dimer, {S n[N(SiMe3)(2)](mu-OBut)}(2) (3) has been observed to cleanly produce t he two new heteroleptic tin(II) dimers,Sn[N(SiMe3)(2)](mu-OBut)(2)Sn(O SiMe3) (6) and [Sn(OSiMe3)(mu-OBut)](2) (7). In addition, reaction of 3 with 1 equiv. of tert-butylisocyanate (8), at 25 degrees C, quantita tively provides 6, and with 2 equiv., quantitatively provides 7. Likew ise 6 reacts with 1 equiv. of 8 to quantitatively provide 7, The mecha nism for these latter processes has been investigated by low temperatu re H-1 NMR spectroscopy which reveals that metathetical exchange does not involve the tri-coordinate tin(ll) centers of the dimeric structur es, but rather, it occurs, in each case, via the transient monomeric t in(II) species, Sn[N(SiMe3)(2)](mu-OBut) (4), that undergoes metathesi s to produce, initially, the open dimer intermediate, Sn(OCNBut)(OSiMe 3)(mu-OBut)Sn(OBut)(OSiMe3) (12), that is observed at -10 degrees C. S ubsequent redistribution reactions then generate the final products th at are observed. Together, these mechanistic details provide additiona l support for the 'monomeric tin(II)' hypothesis proposed earlier for metathetical exchange between XCO and Sn[N(SiMe3)(2)](2) (1). (C) 1998 Elsevier Science S.A.