The 1,3-Sn2O2-heterocycle as a ligand in organometallic compounds -: Dimerization of the inidene species [{(CO)5M}2SnOR]- (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 bonding 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 groups being almost coplanar with the Sn2O2 ring, the overall geometry of the compounds shows idealized D-2h symmetry. - The Sn-119-NMR resonances of 1 are found at rather low fields (M = Cr: delta approximate to 1400; M = W: delta approximate to 1170) indicating a low-lying tin-centered orbital in the LUMO range. Correspondingly EHT analyses show that the 3-center-4 pi system, which characterizes monomeric inidene species [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 obtained from monomeric inidene complexes: [{(CO)(5)Cr}(2SnOEt)-Sn-.](2)(2-) (1a) reacts to give [{(CO)(5)Cr}(2)Sn(acac)](-) (2). The experimental results are verified by X-ray analyses in addition to the usual spectroscopic and analytical investigations.