THE 1,3-SN2O2-HETEROCYCLE AS A LIGAND IN ORGANOMETALLIC COMPOUNDS - DIMERIZATION OF THE INIDENE SPECIES [((CO)(5)M)(2)SNOR](-) (M = CR, W)

Dimerized inidene complexes [(CO)(5)M - Sn(OR)- M(CO)(5)](2)(2-) (M = Cr, W; R = Et, iPr), 1, are obtained from [{(CO)(5)M}(2)SnCl2](2-) by different routes. Dimerization occurs via alkoxy-donor tin-acceptor bo nding by which a planar Sn2O2 ring is formed. The Sn-(M(CO)(5)) bonds are made in a plane vertical to this ring such that, with the R-O grou ps being almost coplanar with the Sn2O2 ring, the overall geometry of the compounds shows idealized D-2h symmetry. - The Sn-119-NMR resonanc es of 1 are found at rather low fields (M = Cr: delta approximate to 1 400; M = W: delta approximate to 1170) indicating a low-lying tin-cent ered orbital in the LUMO range. Correspondingly EHT analyses show that the 3-center-4 pi system, which characterizes monomeric inidene speci es [LnM - E(X) - MLn](n), is still prevalent in the dimeric species 1. The low-lying pi-type LUMOs of 1 are the rationale for the observed Sn-119-NMR low-field shifts compounds 1 react with 2,4-pentanedione to form chelate compounds of the same type as those characteristically o btained from monomeric inidene complexes: [{(CO)(5)Cr}(2SnOEt)-Sn-.](2 )(2-) (1a) reacts to give [{(CO)(5)Cr}(2)Sn(acac)](-) (2). The experim ental results are verified by X-ray analyses in addition to the usual spectroscopic and analytical investigations.